glycogen and Insulin-Resistance

Hepatalin is a hormone secreted by the liver in response to pulses of insulin after a mixed nutrient meal, but only if the liver receives two permissive synergistic feeding signals from the stomach. Hepatalin stimulates glucose uptake and storage as glycogen in skeletal muscle, heart, and kidney but not liver, intestines, or adipocytes. Insulin acts primarily on liver and fat. Reduced hepatalin action results in postprandial hyperglycemia, compensatory elevation of insulin secretion, and a resultant shift in partitioning of nutrient energy storage from glycogen in muscle, to fat. Chronic hepatalin suppression leads to a predictable chronology of dysfunctions, first diagnosable as Absence of Meal-induced Insulin Sensitization (AMIS) which progresses to prediabetes, adiposity, and type 2 diabetes. The focus on nutrient partitioning and the role of hepatalin allows AMIS to be diagnosed, prevented, and treated, including through the use of lifestyle interventions.

Topics: Blood Glucose; Diabetes Mellitus, Type 2; Glycogen; Humans; Insulin; Insulin Resistance; Muscle, Skeletal; Obesity; Prediabetic State

The incidence of obesity, insulin resistance, and type II diabetes (T2DM) continues to rise worldwide. The liver is a central insulin-responsive metabolic organ that governs whole-body metabolic homeostasis. Therefore, defining the mechanisms underlying insulin action in the liver is essential to our understanding of the pathogenesis of insulin resistance. During periods of fasting, the liver catabolizes fatty acids and stored glycogen to meet the metabolic demands of the body. In postprandial conditions, insulin signals to the liver to store excess nutrients into triglycerides, cholesterol, and glycogen. In insulin-resistant states, such as T2DM, hepatic insulin signaling continues to promote lipid synthesis but fails to suppress glucose production, leading to hypertriglyceridemia and hyperglycemia. Insulin resistance is associated with the development of metabolic disorders such as cardiovascular and kidney disease, atherosclerosis, stroke, and cancer. Of note, nonalcoholic fatty liver disease (NAFLD), a spectrum of diseases encompassing fatty liver, inflammation, fibrosis, and cirrhosis, is linked to abnormalities in insulin-mediated lipid metabolism. Therefore, understanding the role of insulin signaling under normal and pathologic states may provide insights into preventative and therapeutic opportunities for the treatment of metabolic diseases. Here, we provide a review of the field of hepatic insulin signaling and lipid regulation, including providing historical context, detailed molecular mechanisms, and address gaps in our understanding of hepatic lipid regulation and the derangements under insulin-resistant conditions. © 2023 American Physiological Society. Compr Physiol 13:4785-4809, 2023.

Topics: Diabetes Mellitus, Type 2; Glycogen; Homeostasis; Humans; Insulin; Insulin Resistance; Lipid Metabolism; Liver; Non-alcoholic Fatty Liver Disease; Triglycerides

Exercise profoundly influences glycemic control by enhancing muscle insulin sensitivity, thus promoting glucometabolic health. While prior glycogen breakdown so far has been deemed integral for muscle insulin sensitivity to be potentiated by exercise, the mechanisms underlying this phenomenon remain enigmatic. We have combined original data from 13 of our studies that investigated insulin action in skeletal muscle either under rested conditions or following a bout of one-legged knee extensor exercise in healthy young male individuals (n = 106). Insulin-stimulated glucose uptake was potentiated and occurred substantially faster in the prior contracted muscles. In this otherwise homogenous group of individuals, a remarkable biological diversity in the glucometabolic responses to insulin is apparent both in skeletal muscle and at the whole-body level. In contrast to the prevailing concept, our analyses reveal that insulin-stimulated muscle glucose uptake and the potentiation thereof by exercise are not associated with muscle glycogen synthase activity, muscle glycogen content, or degree of glycogen utilization during the preceding exercise bout. Our data further suggest that the phenomenon of improved insulin sensitivity in prior contracted muscle is not regulated in a homeostatic feedback manner from glycogen. Instead, we put forward the idea that this phenomenon is regulated by cellular allostatic mechanisms that elevate the muscle glycogen storage set point and enhance insulin sensitivity to promote the uptake of glucose toward faster glycogen resynthesis without development of glucose overload/toxicity or feedback inhibition.

Topics: Glucose; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Resistance; Insulin, Regular, Human; Isophane Insulin, Human; Male; Muscle, Skeletal

Glycogen phosphorylase (PG) is a key enzyme taking part in the first step of glycogenolysis. Muscle glycogen phosphorylase (PYGM) differs from other PG isoforms in expression pattern and biochemical properties. The main role of PYGM is providing sufficient energy for muscle contraction. However, it is expressed in tissues other than muscle, such as the brain, lymphoid tissues, and blood. PYGM is important not only in glycogen metabolism, but also in such diverse processes as the insulin and glucagon signaling pathway, insulin resistance, necroptosis, immune response, and phototransduction. PYGM is implicated in several pathological states, such as muscle glycogen phosphorylase deficiency (McArdle disease), schizophrenia, and cancer. Here we attempt to analyze the available data regarding the protein partners of PYGM to shed light on its possible interactions and functions. We also underline the potential for zebrafish to become a convenient and applicable model to study PYGM functions, especially because of its unique features that can complement data obtained from other approaches.

Topics: Animals; Disease Models, Animal; Gene Expression Regulation; Glycogen; Glycogen Phosphorylase; Glycogen Storage Disease Type V; Humans; Insulin Resistance; Light Signal Transduction; Muscle Contraction; Muscle, Skeletal; Necroptosis; Neoplasms; Protein Interaction Mapping; Retinal Pigment Epithelium; Schizophrenia; Zebrafish

Non-alcoholic fatty liver disease (NAFLD) has emerged as the most prevalent liver disease in industrialized countries. It is regarded as the hepatic manifestation of the metabolic syndrome (MetS) resulting from insulin resistance. Moreover, insulin resistance impairs glycogen synthesis, postprandially diverting a substantial amount of carbohydrates to the liver and storing them there as fat. NAFLD has far-reaching metabolic consequences involving glucose and lipoprotein metabolism disorders and risk of cardiovascular disease, the leading cause of death worldwide. No pharmaceutical options are currently approved for the treatment of NAFLD. Exercise training and dietary interventions remain the cornerstone of NAFLD treatment. Current international guidelines state that the primary goal of nutritional therapy is to reduce energy intake to achieve a 7%-10% reduction in body weight. Meal replacement therapy (formula diets) results in more pronounced weight loss compared to conventional calorie-restricted diets. However, studies have shown that body mass index (BMI) or weight reduction is not obligatory for decreasing hepatic fat content or to restore normal liver function. Recent studies have achieved significant reductions in liver fat with eucaloric diets and without weight loss through macronutrient modifications. Based on this evidence, an integrative nutritional therapeutic concept was formulated that combines the most effective nutrition approaches termed "liver-fasting." It involves the temporary use of a low calorie diet (total meal replacement with a specific high-protein, high-soluble fiber, lower-carbohydrate formula), followed by stepwise food reintroduction that implements a Mediterranean style low-carb diet as basic nutrition.

Topics: Caloric Restriction; Diet, Carbohydrate-Restricted; Diet, Mediterranean; Exercise; Glycogen; Heart Disease Risk Factors; Humans; Insulin Resistance; Lipid Metabolism; Liver; Non-alcoholic Fatty Liver Disease; Nutrition Therapy; Nutritional Physiological Phenomena; Weight Loss

Aging is associated with insulin resistance and the development of type 2 diabetes. While this process is multifaceted, age-related changes to skeletal muscle are expected to contribute to impaired glucose metabolism. Some of these changes include sarcopenia, impaired insulin signaling, and imbalances in glucose utilization. Endurance and resistance exercise training have been endorsed as interventions to improve glucose tolerance and whole-body insulin sensitivity in the elderly. While both types of exercise generally increase insulin sensitivity in older adults, the metabolic pathways through which this occurs can differ and can be dependent on preexisting conditions including obesity and type 2 diabetes. In this review, we will first highlight age-related changes to skeletal muscle which can contribute to insulin resistance, followed by a comparison of endurance and resistance training adaptations to insulin-stimulated glucose metabolism in older adults.

Topics: Adult; Age Factors; Aged; Aged, 80 and over; Endurance Training; Exercise; Glucose; Glycogen; Humans; Insulin Resistance; Middle Aged; Muscle, Skeletal; Resistance Training

Both insulin deficiency and insulin resistance due to glucagon secretion cause fasting and postprandial hyperglycemia in patients with diabetes.. Metformin enhances insulin sensitivity, being used to prevent and treat diabetes, although its mechanism of action remains elusive.. Patients with diabetes fail to store glucose as hepatic glycogen via the direct pathway (glycogen synthesis from dietary glucose during the post-prandial period) and via the indirect pathway (glycogen synthesis from "de novo" synthesized glucose) owing to insulin deficiency and glucagoninduced insulin resistance. Depletion of the hepatic glycogen deposit activates gluconeogenesis to replenish the storage via the indirect pathway. Unlike healthy subjects, patients with diabetes experience glycogen cycling due to enhanced gluconeogenesis and failure to store glucose as glycogen. These defects raise hepatic glucose output causing both fasting and post-prandial hyperglycemia. Metformin reduces post-prandial plasma glucose, suggesting that the drug facilitates glucose storage as hepatic glycogen after meals. Replenishment of glycogen store attenuates the accelerated rate of gluconeogenesis and reduces both glycogen cycling and hepatic glucose output. Metformin also reduces fasting hyperglycemia due to declining hepatic glucose production. In addition, metformin reduces plasma insulin concentration in subjects with impaired glucose tolerance and diabetes and decreases the amount of insulin required for metabolic control in patients with diabetes, reflecting improvement of insulin activity. Accordingly, metformin preserves β-cell function in patients with type 2 diabetes.. Several mechanisms have been proposed to explain the metabolic effects of metformin, but evidence is not conclusive and the molecular basis of metformin action remains unknown.

Topics: Diabetes Mellitus, Type 2; Gluconeogenesis; Glucose; Glycogen; Humans; Hypoglycemic Agents; Insulin Resistance; Liver; Metformin

The prevalence of cardiometabolic disease has reached an exponential rate of rise over the last decades owing to high fat/high caloric diet intake and satiety life style. Although the presence of dyslipidemia, insulin resistance, hypertension and obesity mainly contributes to the increased incidence of cardiometabolic diseases, population-based, clinical and genetic studies have revealed a rather important role for inherited myopathies and endocrine disorders in the ever-rising metabolic anomalies. Inherited metabolic and endocrine diseases such as glycogen storage and lysosomal disorders have greatly contributed to the overall prevalence of cardiometabolic diseases. Recent evidence has demonstrated an essential role for proteotoxicity due to autophagy failure and/or dysregulation in the onset of inherited metabolic and endocrine disorders. Given the key role for autophagy in the degradation and removal of long-lived or injured proteins and organelles for the maintenance of cellular and organismal homeostasis, this mini-review will discuss the potential contribution of autophagy dysregulation in the pathogenesis of inherited myopathies and endocrine disorders, which greatly contribute to an overall rise in prevalence of cardiometabolic disorders. Molecular, clinical, and epidemiological aspects will be covered as well as the potential link between autophagy and metabolic anomalies thus target therapy may be engaged for these comorbidities.

Topics: Autophagy; Cardiovascular Diseases; Endocrine System Diseases; Glycogen; Homeostasis; Humans; Insulin Resistance; Lysosomes; Metabolic Syndrome; Metabolism, Inborn Errors; Muscular Diseases; Obesity

The present paper reviews the physiological responses of human liver carbohydrate metabolism to physical activity and ingestion of dietary sugars. The liver represents a central link in human carbohydrate metabolism and a mechanistic crux point for the effects of dietary sugars on athletic performance and metabolic health. As a corollary, knowledge regarding physiological responses to sugar ingestion has potential application to either improve endurance performance in athletes, or target metabolic diseases in people who are overweight, obese and/or sedentary. For example, exercise increases whole-body glycogen utilisation, and the breakdown of liver glycogen to maintain blood glucose concentrations becomes increasingly important as exercise intensity increases. Accordingly, prolonged exercise at moderate-to-high exercise intensity results in depletion of liver glycogen stores unless carbohydrate is ingested during exercise. The exercise-induced glycogen deficit can increase insulin sensitivity and blood glucose control, and may result in less hepatic lipid synthesis. Therefore, the induction and maintenance of a glycogen deficit with exercise could be a specific target to improve metabolic health and could be achieved by carbohydrate (sugar) restriction before, during and/or after exercise. Conversely, for athletes, maintaining and restoring these glycogen stores is a priority when competing in events requiring repeated exertion with limited recovery. With this in mind, evidence consistently demonstrates that fructose-containing sugars accelerate post-exercise liver glycogen repletion and could reduce recovery time by as much as half that seen with ingestion of glucose (polymers)-only. Therefore, athletes aiming for rapid recovery in multi-stage events should consider ingesting fructose-containing sugars to accelerate recovery.

Topics: Athletic Performance; Blood Glucose; Carbohydrate Metabolism; Dietary Sugars; Exercise; Fructose; Glycogen; Humans; Insulin Resistance; Liver; Muscle, Skeletal

The molecular and metabolic mechanisms underlying the increase in insulin sensitivity (i.e. increased insulin-stimulated skeletal muscle glucose uptake, phosphorylation and storage as glycogen) observed from 12 to 48 h following a single bout of exercise in humans remain unresolved. Moreover, whether these mechanisms differ with age is unclear. It is well established that a single bout of exercise increases the translocation of the glucose transporter, GLUT4, to the plasma membrane. Previous research using unilateral limb muscle contraction models in combination with hyperinsulinaemia has demonstrated that the increase in insulin sensitivity and glycogen synthesis 24 h after exercise is also associated with an increase in hexokinase II (HKII) mRNA and protein content, suggesting an increase in the capacity of the muscle to phosphorylate glucose and divert it towards glycogen synthesis. Interestingly, this response is altered in older individuals for up to 48 h post exercise and is associated with molecular changes in skeletal muscle tissue that are indicative of reduced lipid oxidation, increased lipogenesis, increased inflammation and a relative inflexibility of changes in intramyocellular lipid (IMCL) content. Reduced insulin sensitivity (insulin resistance) is generally related to IMCL content, particularly in the subsarcolemmal (SSL) region, and both are associated with increasing age. Recent research has demonstrated that ageing

Topics: Age Factors; Aging; Exercise; Glucose; Glycogen; Hexokinase; Humans; Insulin; Insulin Resistance; Lipid Metabolism; Muscle, Skeletal; Oxidation-Reduction; RNA, Messenger; Signal Transduction; Transcription, Genetic

Topics: Acetyl-CoA Carboxylase; AMP-Activated Protein Kinases; Animals; Coffee; Exercise; Glycogen; Humans; Insulin Resistance; Insulin-Secreting Cells; Muscle Cells; Muscle, Skeletal; Phosphorylation; Rats

Over the past decades, hypomagnesemia (serum Mg(2+) <0.7 mmol/L) has been strongly associated with type 2 diabetes mellitus (T2DM). Patients with hypomagnesemia show a more rapid disease progression and have an increased risk for diabetes complications. Clinical studies demonstrate that T2DM patients with hypomagnesemia have reduced pancreatic β-cell activity and are more insulin resistant. Moreover, dietary Mg(2+) supplementation for patients with T2DM improves glucose metabolism and insulin sensitivity. Intracellular Mg(2+) regulates glucokinase, KATP channels, and L-type Ca(2+) channels in pancreatic β-cells, preceding insulin secretion. Moreover, insulin receptor autophosphorylation is dependent on intracellular Mg(2+) concentrations, making Mg(2+) a direct factor in the development of insulin resistance. Conversely, insulin is an important regulator of Mg(2+) homeostasis. In the kidney, insulin activates the renal Mg(2+) channel transient receptor potential melastatin type 6 that determines the final urinary Mg(2+) excretion. Consequently, patients with T2DM and hypomagnesemia enter a vicious circle in which hypomagnesemia causes insulin resistance and insulin resistance reduces serum Mg(2+) concentrations. This Perspective provides a systematic overview of the molecular mechanisms underlying the effects of Mg(2+) on insulin secretion and insulin signaling. In addition to providing a review of current knowledge, we provide novel directions for future research and identify previously neglected contributors to hypomagnesemia in T2DM.

Topics: Blood Glucose; Calcium Channels, L-Type; Diabetes Mellitus, Type 2; Dietary Supplements; Disease Progression; Glucokinase; Glycogen; Glycolysis; Humans; Inflammation; Insulin; Insulin Resistance; Insulin Secretion; Insulin-Secreting Cells; KATP Channels; Liver; Magnesium; Magnesium Deficiency; Obesity; Potassium Channels, Inwardly Rectifying; Sodium Chloride Symporters; Sodium-Potassium-Exchanging ATPase; Water-Electrolyte Imbalance

While it has long been recognized that bile acids are essential for solubilizing lipophilic nutrients in the small intestine, the discovery in 1999 that bile acids serve as ligands for the nuclear receptor farnesoid X receptor (FXR) opened the floodgates in terms of characterizing their actions as selective signaling molecules. Bile acids act on FXR in ileal enterocytes to induce the expression of fibroblast growth factor (FGF)15/19, an atypical FGF that functions as a hormone. FGF15/19 subsequently acts on a cell surface receptor complex in hepatocytes to repress bile acid synthesis and gluconeogenesis, and to stimulate glycogen and protein synthesis. FGF15/19 also stimulates gallbladder filling. Thus, the bile acid-FXR-FGF15/19 signaling pathway regulates diverse aspects of the postprandial enterohepatic response. Pharmacologically, this endocrine pathway provides exciting new opportunities for treating metabolic disease and bile acid-related disorders such as primary biliary cirrhosis and bile acid diarrhea. Both FXR agonists and FGF19 analogs are currently in clinical trials.

Topics: Animals; Bile Acids and Salts; Cholesterol 7-alpha-Hydroxylase; Enterocytes; Fibroblast Growth Factors; Gene Expression Regulation; Gluconeogenesis; Glycogen; Homeostasis; Humans; Insulin Resistance; Lipid Metabolism; Mice; Receptors, Cytoplasmic and Nuclear; Signal Transduction

Type 2 diabetes mellitus (T2D) is characterized by insulin resistance, impaired glycogen synthesis, lipid accumulation, and impaired mitochondrial function. Exercise training has received increasing recognition as a cornerstone in the prevention and treatment of T2D. Emerging research suggests that resistance training (RT) has the power to combat metabolic dysfunction in patients with T2D and seems to be an effective measure to improve overall metabolic health and reduce metabolic risk factors in diabetic patients. However, there is limited mechanistic insight into how these adaptations occur. This review provides an overview of the intervention data on the impact of RT on glucose metabolism. In addition, the molecular mechanisms that lead to adaptation in skeletal muscle in response to RT and that are associated with possible beneficial metabolic responses are discussed. Some of the beneficial adaptations exerted by RT include increased GLUT4 translocation in skeletal muscle, increased insulin sensitivity and hence restored metabolic flexibility. Increased energy expenditure and excess postexercise oxygen consumption in response to RT may be other beneficial effects. RT is increasingly establishing itself as an effective measure to improve overall metabolic health and reduce metabolic risk factors in diabetic patients.

Topics: Diabetes Mellitus, Type 2; Exercise; Glucose; Glucose Transporter Type 4; Glycogen; Humans; Insulin Resistance; Muscles; Oxygen; Resistance Training

The energy/fuel sensor 5'-AMP-activated protein kinase (AMPK) is viewed as a master regulator of cellular energy balance due to its many roles in glucose, lipid, and protein metabolism. In this review we focus on the regulation of AMPK activity in skeletal muscle and its involvement in glucose metabolism, including glucose transport and glycogen synthesis. In addition, we discuss the plausible interplay between AMPK and insulin signaling regulating these processes.

Topics: Aminoimidazole Carboxamide; AMP-Activated Protein Kinases; Biological Transport; Energy Metabolism; Exercise; Glucose; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Muscle, Skeletal; Oxidation-Reduction; Ribonucleotides; Signal Transduction

While it has long been known that zinc (Zn) is crucial for the proper growth and maintenance of normal biological functions, Zn has also been shown to exert insulin-mimetic and anti-diabetic effects. These insulin-like properties have been demonstrated in isolated cells, tissues, and different animal models of type 1 and type 2 diabetes. Zn treatment has been found to improve carbohydrate and lipid metabolism in rodent models of diabetes. In isolated cells, it enhances glucose transport, glycogen and lipid synthesis, and inhibits gluconeogenesis and lipolysis. The molecular mechanism responsible for the insulin-like effects of Zn compounds involves the activation of several key components of the insulin signaling pathways, which include the extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3-K)/protein kinase B/Akt (PKB/Akt) pathways. However, the precise molecular mechanisms by which Zn triggers the activation of these pathways remain to be clarified. In this review, we provide a brief history of zinc, and an overview of its insulin-mimetic and anti-diabetic effects, as well as the potential mechanisms by which zinc exerts these effects.

Topics: Animals; Diabetes Mellitus; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Disease Models, Animal; ErbB Receptors; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Lipogenesis; Receptor, IGF Type 1; Signal Transduction; Zinc; Zinc Compounds

Fibroblast growth factor 19 (FGF19) is a postprandial hormone released from the small intestine. FGF19 improves glucose tolerance when overexpressed in mice with impaired glucose tolerance or diabetes. This review summarizes the recent advances in our understanding of the biology of FGF19 and its role in glucose homeostasis, with emphasis on publications from 2010 to 2012.. Protein engineering was used to generate FGF19 protein variants that allowed the separation of its mitogenic and metabolic functions. Its cognate receptor in the liver (FGFR4) mediated the effects of FGF19 on proliferation and bile salt synthesis, while this receptor was dispensable for its effects on glucose homeostasis. New metabolic activities of FGF19 were uncovered. FGF19 signaling was shown to stimulate glycogen and protein synthesis, and inhibit gluconeogenesis. FGF19 employed signaling routes distinct from those used by insulin to regulate these pathways. Mice with genetic disruption of Fgf15 (the mouse FGF19 ortholog) were glucose intolerant but had normal insulin levels and normal insulin sensitivity. Reduced hepatic glycogen stores and elevated hepatic gluconeogenesis were observed in the knock-out mice under the conditions in which insulin signaling was active.. FGF19 signaling regulates glucose homeostasis in mice. The (patho)physiological role of FGF19 in glucose homeostasis in humans remains to be determined. Its novel insulin-mimetic actions, combined with the elimination of its mitogenic activity by protein engineering, make FGF19 an attractive candidate for the treatment of type 2 diabetes.

Topics: Animals; Bile Acids and Salts; Blood Glucose; Diabetes Mellitus; Fibroblast Growth Factors; Gastrointestinal Hormones; Gluconeogenesis; Glucose Intolerance; Glycogen; Homeostasis; Humans; Insulin; Insulin Resistance; Liver; Protein Biosynthesis

This review deals with the role of glycogen storage in skeletal muscle for the development of insulin resistance and type 2 diabetes. Specifically, the role of the enzyme glycogen synthase, which seems to be locked in its hyperphosphorylated and inactivated state, is discussed. This defect seems to be secondary to ectopic lipid disposition in the muscle cells. These molecular defects are discussed in the context of the overall pathophysiology of hyperglycemia in type 2 diabetic subjects.

Topics: Diabetes Mellitus, Type 2; Glucose; Glycated Hemoglobin; Glycogen; Glycogen Synthase; Humans; Hyperglycemia; Insulin; Insulin Resistance; Lipid Metabolism; Muscle, Skeletal; Phosphorylation

Topics: Animals; Glycogen; Insulin Resistance; Mice; Muscle, Skeletal

In mammals, excess carbohydrate is stored as glycogen and glycogen synthase is the enzyme that incorporates glucose units into the glycogen particle. Glycogen synthase activity is regulated by phosphorylation and allosterically activated by glucose 6-phosphate. Phosphorylation of nine serines by different kinases regulates glycogen synthase affinity for glucose 6-phosphate and its substrate UDP-glucose. Glucose 6-phosphate increases both enzyme activity and substrate affinity. Insulin and exercise increase glycogen synthase affinity for glucose 6-phosphate and activity whereas high glycogen content and adrenaline decrease affinity for glucose 6-phosphate and activity. However, insulin, exercise and adrenaline also regulate intracellular concentration of glucose 6-phosphate which will influence in vivo glycogen synthase activity. Importantly, type 2 diabetes is associated with reduced insulin-stimulated glycogen synthase activation. The nine phosphorylation sites theoretically allow 512 combinations of phosphorylation configurations of glycogen synthase with different kinetic properties. However, due to hierarchal phosphorylation, the number of configurations in vivo is most likely much lower. Unfortunately, many studies only report data on glycogen synthase activity measured with high concentration of UDP-glucose which holds back information about changes in substrate affinity. In this paper we discuss the physiological regulation of glycogen synthase phosphorylation and how the phosphorylation pattern regulates glycogen synthase kinetic properties.

Topics: Allosteric Regulation; Animals; Diabetes Mellitus, Type 2; Epinephrine; Exercise; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Resistance; Muscle, Skeletal; Phosphorylation; Uridine Diphosphate Glucose

The daily oral ingestion of supplementary creatine monohydrate can substantially elevate the creatine content of human skeletal muscle. This chapter aims to summarize the current knowledge regarding the impact muscle creatine loading can have on exercise performance and rehabilitation. The major part of the elevation of muscle creatine content is already obtained after one week of supplementation, and the response can be further enhanced by a concomitant exercise or insulin stimulus. The elevated muscle creatine content moderately improves contractile performance in sports with repeated high-intensity exercise bouts. More chronic ergogenic effects of creatine are to be expected when combined with several weeks of training. A more pronounced muscle hypertrophy and a faster recovery from atrophy have been demonstrated in humans involved in resistance training. The mechanism behind this anabolic effect of creatine may relate to satellite cell proliferation, myogenic transcription factors and insulin-like growth factor-1 signalling. An additional effect of creatine supplementation, mostly when combined with training, is enhanced muscle glycogen accumulation and glucose transporter (GLUT4) expression. Thus, creatine may also be beneficial in sport competition and training characterized by daily glycogen depletion, as well as provide therapeutic value in the insulin-resistant state.

Topics: Administration, Oral; Anabolic Agents; Athletic Performance; Creatine; Exercise; Gene Expression Regulation; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Muscle Contraction; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy

Increased plasma levels of free fatty acids (FFA) occur in states of insulin resistance such as type 2 diabetes mellitus, obesity, and metabolic syndrome. These high levels of plasma FFA seem to play an important role for the development of insulin resistance but the mechanisms involved are not known. We demonstrated that acute exposure to FFA (1 h) in rat incubated skeletal muscle leads to an increase in the insulin-stimulated glycogen synthesis and glucose oxidation. In conditions of prolonged exposure to FFA, however, the insulin-stimulated glucose uptake and metabolism is impaired in skeletal muscle. In this review, we discuss the differences between the effects of acute and prolonged exposure to FFA on skeletal muscle glucose metabolism and the possible mechanisms involved in the FFA-induced insulin resistance.

Topics: Animals; Fatty Acids, Nonesterified; Glucose; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Mitochondria, Muscle; Muscle, Skeletal; Oxidative Phosphorylation; Palmitic Acid; Rats; Signal Transduction; Time Factors; Uncoupling Agents

Exercise-induced muscle damage (EIMD) is commonly experienced following either a bout of unaccustomed physical activity or following physical activity of greater than normal duration or intensity. The mechanistic factor responsible for the initiation of EIMD is not known; however, it is hypothesised to be either mechanical or metabolic in nature. The mechanical stress hypothesis states that EIMD is the result of physical stress upon the muscle fibre. In contrast, the metabolic stress model predicts that EIMD is the result of metabolic deficiencies, possibly through the decreased action of Ca(2+)-adenosine triphosphatase. Irrespective of the cause of the damage, EIMD has a number of profound metabolic effects. The most notable metabolic effects of EIMD are decreased insulin sensitivity, prolonged glycogen depletion and an increase in metabolic rate both at rest and during exercise. Based on current knowledge regarding the effects that various types of damaging exercise have on muscle metabolism, a new model for the initiation of EIMD is proposed. This model states that damage initiation may be either metabolic or mechanical, or a combination of both, depending on the mode, intensity and duration of exercise and the training status of the individual.

Topics: Adaptation, Physiological; Exercise; Glucose; Glycogen; Humans; Insulin Resistance; Muscle Fibers, Skeletal; Muscle Proteins; Muscle, Skeletal; Stress, Mechanical

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase, originally identified as a protein kinase by its ability to phosphorylate and inactivate glycogen synthase. It was found that the overexpression of GSK-3 is associated with some diseases, such as diabetes, Alzheimer disease and other neurodegenerative diseases. Some pharmacological inhibitors of GSK-3 have been demonstrated to mimic insulin signaling, adjust glycogen synthesis and glucose metabolism, and improve insulin resistance. So GSK-3 inhibitors are realized as a new approach of treating diabetes. This review summarizes current advances in research of GSK-3 inhibitors as a new therapeutic approach for diabetes.

Topics: Alzheimer Disease; Animals; Blood Glucose; Diabetes Mellitus; Enzyme Inhibitors; Glycogen; Glycogen Synthase Kinase 3; Humans; Insulin; Insulin Resistance; Signal Transduction

Recently, diets low in carbohydrate content have become a matter of international attention because of the WHO recommendations to reduce the overall consumption of sugars and rapidly digestible starches. One of the common metabolic changes assumed to take place when a person follows a low-carbohydrate diet is ketosis. Low-carbohydrate intakes result in a reduction of the circulating insulin level, which promotes high level of circulating fatty acids, used for oxidation and production of ketone bodies. It is assumed that when carbohydrate availability is reduced in short term to a significant amount, the body will be stimulated to maximize fat oxidation for energy needs. The currently available scientific literature shows that low-carbohydrate diets acutely induce a number of favourable effects, such as a rapid weight loss, decrease of fasting glucose and insulin levels, reduction of circulating triglyceride levels and improvement of blood pressure. On the other hand some less desirable immediate effects such as enhanced lean body mass loss, increased urinary calcium loss, increased plasma homocysteine levels, increased low-density lipoprotein-cholesterol have been reported. The long-term effect of the combination of these changes is at present not known. The role of prolonged elevated fat consumption along with low-carbohydrate diets should be addressed. However, these undesirable effects may be counteracted with consumption of a low-carbohydrate, high-protein, low-fat diet, because this type of diet has been shown to induce favourable effects on feelings of satiety and hunger, help preserve lean body mass, effectively reduce fat mass and beneficially impact on insulin sensitivity and on blood lipid status while supplying sufficient calcium for bone mass maintenance. The latter findings support the need to do more research on this type of hypocaloric low-carbohydrate diet.

Topics: Animals; Blood Glucose; Blood Pressure; Body Weight; Cardiovascular Diseases; Diet, Carbohydrate-Restricted; Diet, Reducing; Dietary Carbohydrates; Energy Metabolism; Glycogen; Humans; Insulin; Insulin Resistance; Insulin Secretion; Lipids; Neoplasms; Osteoporosis, Postmenopausal; Risk Factors

As a result of a marked decline in dry matter intake (DMI) prior to parturition and a slow rate of increase in DMI relative to milk production after parturition, dairy cattle experience a negative energy balance. Changes in nutritional and metabolic status during the periparturient period predispose dairy cattle to develop hepatic lipidosis and ketosis. The metabolic profile during early lactation includes low concentrations of serum insulin, plasma glucose, and liver glycogen and high concentrations of serum glucagon, adrenaline, growth hormone, plasma beta-hydroxybutyrate and non-esterified fatty acids, and liver triglyceride. Moreover, during late gestation and early lactation, flow of nutrients to fetus and mammary tissues are accorded a high degree of metabolic priority. This priority coincides with lowered responsiveness and sensitivity of extrahepatic tissues to insulin, which presumably plays a key role in development of hepatic lipidosis and ketosis. Hepatic lipidosis and ketosis compromise production, immune function, and fertility. Cows with hepatic lipidosis and ketosis have low tissue responsiveness to insulin owing to ketoacidosis. Insulin has numerous roles in metabolism of carbohydrates, lipids and proteins. Insulin is an anabolic hormone and acts to preserve nutrients as well as being a potent feed intake regulator. In addition to the major replacement therapy to alleviate severity of negative energy balance, administration of insulin with concomitant delivery of dextrose increases efficiency of treatment for hepatic lipidosis and ketosis. However, data on use of insulin to prevent these lipid-related metabolic disorders are limited and it should be investigated.

Topics: Animal Nutritional Physiological Phenomena; Animals; Blood Glucose; Cattle; Cattle Diseases; Energy Metabolism; Female; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Insulin Secretion; Ketosis; Lactation; Lipid Metabolism; Liver; Parturition; Postpartum Period; Pregnancy; Puerperal Disorders; Signal Transduction; Triglycerides

Insulin resistance is a feature of a number of clinical disorders, including type 2 diabetes/glucose intolerance, obesity, dyslipidaemia and hypertension clustering in the so-called metabolic syndrome. Insulin resistance in skeletal muscle manifests itself primarily as a reduction in insulin-stimulated glycogen synthesis due to reduced glucose transport. Ectopic lipid accumulation plays an important role in inducing insulin resistance. Multiple defects in insulin signalling are responsible for impaired glucose metabolism in target tissues of subjects with features of insulin resistance. Inflammatory molecules and lipid metabolites inhibit insulin signalling by stimulating a number of different serine kinases which are responsible for serine phosphorylation of Insulin Receptor Substrate-1 (IRS-1).

Topics: Cytokines; Fatty Acids; Glucose; Glucose Transporter Type 4; Glycogen; Humans; Insulin; Insulin Resistance; Muscles; Phosphatidylinositol 3-Kinases; Phosphoric Diester Hydrolases; Protein Kinase C; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Protein Tyrosine Phosphatases; Proto-Oncogene Proteins c-akt; Pyrophosphatases; Receptor, Insulin; Signal Transduction; Somatomedins

Compounds of the trace element vanadium exert various insulin-like effects in in vitro and in vivo systems. These include their ability to improve glucose homeostasis and insulin resistance in animal models of Type 1 and Type 2 diabetes mellitus. In addition to animal studies, several reports have documented improvements in liver and muscle insulin sensitivity in a limited number of patients with Type 2 diabetes. These effects are, however, not as dramatic as those observed in animal experiments, probably because lower doses of vanadium were used and the duration of therapy was short in human studies as compared with animal work. The ability of these compounds to stimulate glucose uptake, glycogen and lipid synthesis in muscle, adipose and hepatic tissues and to inhibit gluconeogenesis, and the activities of the gluconeogenic enzymes: phosphoenol pyruvate carboxykinase and glucose-6-phosphatase in the liver and kidney as well as lipolysis in fat cells contributes as potential mechanisms to their anti-diabetic insulin-like effects. At the cellular level, vanadium activates several key elements of the insulin signal transduction pathway, such as the tyrosine phosphorylation of insulin receptor substrate-1, and extracellular signal-regulated kinase 1 and 2, phosphatidylinositol 3-kinase and protein kinase B activation. These pathways are believed to mediate the metabolic actions of insulin. Because protein tyrosine phosphatases (PTPases) are considered to be negative regulators of the insulin-signalling pathway, it is suggested that vanadium can enhance insulin signalling and action by virtue of its capacity to inhibit PTPase activity and increase tyrosine phosphorylation of substrate proteins. There are some concerns about the potential toxicity of available inorganic vanadium salts at higher doses and during long-term therapy. Therefore, new organo-vanadium compounds with higher potency and less toxicity need to be evaluated for their efficacy as potential treatment of human diabetes.

Topics: Animals; Biological Transport; Blood Glucose; Diabetes Mellitus; Glycogen; Humans; Hypoglycemic Agents; Insulin Resistance; Lipid Metabolism; Models, Biological; Rats; Vanadium Compounds

Topics: Glucose; Glucose Intolerance; Glucose Tolerance Test; Glycogen; Humans; Insulin Resistance; Liver; Liver Cirrhosis; Liver Neoplasms; Muscle, Skeletal; Nutrition Therapy

Topics: Acarbose; Cyclohexanes; Diabetes Mellitus, Type 2; Diet Therapy; Enzyme Inhibitors; Exercise Therapy; Glucose; Glucose Intolerance; Glycogen; Glycoside Hydrolase Inhibitors; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Insulin Secretion; Metformin; Nateglinide; Phenylalanine; Sulfonylurea Compounds; Thiazolidinediones

Topics: Biomarkers; Diabetes Mellitus; Diagnostic Techniques, Endocrine; Glycogen; Humans; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Insulin-Secreting Cells; Lipid Metabolism; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphorylation; Polymorphism, Genetic; RNA; Signal Transduction; Specimen Handling

Topics: Diabetes Mellitus, Type 2; Fasting; Fatty Acids, Nonesterified; Gluconeogenesis; Glycogen; Humans; Insulin; Insulin Resistance

Interleukin-6 (IL-6) is produced locally in working skeletal muscle and can account for the exercise-induced increase in plasma IL-6. The transcription rate for IL-6 in muscle nuclei isolated from muscle biopsies during exercise is very high and is enhanced further when muscle glycogen content is low. Furthermore, cultured human primary muscle cells can increase IL-6 mRNA when incubated with the calcium ionophore ionomycin and it is likely that myocytes produce IL-6 in response to muscle contraction. The biological roles of muscle-derived IL-6 have been investigated in studies in which human recombinant IL-6 was infused in healthy volunteers to mimic closely the IL-6 concentrations observed during prolonged exercise. Using stable isotopes, we have demonstrated that physiological concentrations of IL-6 induce lipolysis. Although we have yet to determine the precise biological action of muscle-derived IL-6, our data support the hypothesis that the role of IL-6 released from contracting muscle during exercise is to act in a hormone-like manner to mobilize extracellular substrates and/or augment substrate delivery during exercise. In addition, IL-6 inhibits low-level TNF-alpha production, and IL-6 produced during exercise probably inhibits TNF-alpha-induced insulin resistance in peripheral tissues. Hence, IL-6 produced by skeletal muscle during contraction may play an important role in the beneficial health effects of exercise

Topics: Animals; Anti-Inflammatory Agents; Exercise; Glucose; Glycogen; Humans; Insulin Resistance; Interleukin-6; Lipolysis; Muscle Contraction; Muscle, Skeletal; Signal Transduction; Tumor Necrosis Factor-alpha

It has recently been demonstrated that the marked increase in the systemic concentration of cytokine interleukin-6 (IL-6) seen with exercise originates from the contracting limb and that skeletal muscle cells per se are the likely source of the production. This review summarizes the possible mechanisms for activation and biological consequences of muscle-derived IL-6. It appears that intramuscular IL-6 is stimulated by complex signaling cascades initiated by both calcium (Ca2+) -dependent and -independent stimuli. It also seems likely that skeletal muscle produces IL-6 to aid in maintaining metabolic homeostasis during periods of altered metabolic demand such as muscular exercise or insulin stimulation. It may do so via local and/or systemic effects. This review also explores the efficacy that IL-6 may be used as a therapeutic drug in treating metabolic disorders such as obesity, type 2 diabetes, and atherosclerosis.

Topics: Animals; Anti-Inflammatory Agents; Diabetes Mellitus, Type 2; Exercise; Glucose; Glycogen; Humans; Insulin Resistance; Interleukin-6; Lipid Metabolism; Models, Biological; Monocytes; Muscle, Skeletal; Signal Transduction

Insulin resistance is a principal feature of type 2 diabetes and precedes the clinical development of the disease by 10 to 20 years. Insulin resistance is caused by the decreased ability of peripheral target tissues (especially muscle) to respond properly to normal circulating concentrations of insulin. Defects in muscle glycogen synthesis play a significant role in insulin resistance, and 3 potentially rate-controlling steps in muscle glucose metabolism have been implicated in its pathogenesis: glycogen synthase, hexokinase, and GLUT4 (the major insulin-stimulated glucose transporter). Results from recent studies using nuclear magnetic resonance (NMR) spectroscopy implicate intracellular defects in glucose transport as the rate-controlling step for insulin-mediated glucose uptake in muscle. These alterations in glucose transport activity are likely the result of dysregulation of intramyocellular fatty acid metabolism, whereby fatty acids cause insulin resistance by activation of a serine kinase cascade, leading to decreased insulin-stimulated insulin receptor substrate (IRS)-1 tyrosine phosphorylation and decreased IRS-1-associated phosphatidylinositol 3-kinase activity, a required step in insulin-stimulated glucose transport into muscle. The thiazolidinedione class of antidiabetic agents directly targets insulin resistance in skeletal muscle by improving glucose transport activity and insulin-stimulated muscle glycogen synthesis. Although the precise mechanism of action is not known, recent NMR studies support the hypothesis that these agents improve insulin action in skeletal muscle and liver by promoting a redistribution of fat out of these tissues and into peripheral adipocytes.

Topics: Diabetes Mellitus, Type 2; Fatty Acids; Glucose; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Magnetic Resonance Spectroscopy; Muscle, Skeletal; Signal Transduction; Thiazoles

Topics: Adipose Tissue; Adrenocortical Hyperfunction; Diabetes Mellitus; Glucocorticoids; Gluconeogenesis; Glycogen; Glycolysis; Humans; Insulin Resistance; Liver; Muscles

Topics: Animals; Diabetes Mellitus, Type 2; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Resistance; Muscle, Skeletal; Phosphoprotein Phosphatases; Phosphorylation; Protein Kinases

Topics: Adipose Tissue; Diabetes Mellitus, Type 2; Energy Metabolism; Exercise; Exercise Therapy; Fatty Acids, Nonesterified; Glucose Transporter Type 4; Glycogen; Humans; Insulin; Insulin Resistance; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Receptor, Insulin

Topics: Adipocytes; Animals; Glucose; Glucose-6-Phosphatase; Glycogen; Humans; Hyperthyroidism; Insulin; Insulin Resistance; Insulin Secretion; Lipid Metabolism; Liver; Monosaccharide Transport Proteins; Muscle, Skeletal; Nuclear Proteins; Oligonucleotide Array Sequence Analysis; Protein Serine-Threonine Kinases; Proteins; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Receptors, Adrenergic, beta-2; Thyroid Hormones; Transcription Factors

Skeletal muscle contains the majority of the body's glycogen stores and a similar amount of readily accessible energy as intramyocellular triglyceride (imTG). While a number of factors have been considered to contribute to the pathogenesis of insulin resistance (IR) in obesity and type 2 diabetes mellitus (DM), this review will focus on the potential role of skeletal muscle triglyceride content. In obesity and type 2 DM, there is an increased content of lipid within and around muscle fibers. Changes in muscle in fuel partitioning of lipid, between oxidation and storage of fat calories, almost certainly contribute to accumulation of imTG and to the pathogenesis of both obesity and type 2 DM. In metabolic health, skeletal muscle physiology is characterized by the capacity to utilize either lipid or carbohydrate fuels, and to effectively transition between these fuels. We will review recent findings that indicate that in type 2 DM and obesity, skeletal muscle manifests inflexibility in the transition between lipid and carbohydrate fuels. This inflexibility in fuel selection by skeletal muscle appears to be related to the accumulation of imTG and is an important aspect of IR of skeletal muscle in obesity and type 2 DM.

Topics: Adipose Tissue; Diabetes Mellitus, Type 2; Glycogen; Humans; Insulin Resistance; Leptin; Muscle, Skeletal; Obesity; Triglycerides

Insulin resistance of skeletal muscle in humans, animals, and cells is often strongly correlated with increased lipid availability. The elevation of certain intracellular lipid species can lead to the activation of signal transduction pathways that inhibit normal insulin action. Thus, increased diacylglycerol levels in muscle are associated with the activation of one or more isoforms of the protein kinase C family, which is known to attenuate insulin signaling, especially at the level of IRS-1. In addition, de novo synthesis of ceramide can inhibit more distal sites by the activation of protein phosphatase 2A and hence promote the dephosphorylation and inactivation of protein kinase B. Such mechanisms may account at least in part for the reduced insulin sensitivity occurring in obesity and type 2 diabetes where lipid oversupply is a major factor.

Topics: Animals; Diglycerides; Enzyme Activation; Fatty Acids, Nonesterified; Glycogen; Humans; Insulin Resistance; Lipid Metabolism; Muscle, Skeletal; Protein Kinase C

Insulin is the most-potent physiological anabolic agent known, promoting the synthesis and storage of carbohydrates and lipids and inhibiting their degradation and release into the circulation. This action of the hormone is due in part to the acute regulation of metabolic enzymes through changes in their phosphorylation state. In fat, liver, and muscle, insulin stimulates the dephosphorylation of a number of enzymes involved in glycogen and lipid metabolism via activation of protein phosphatases. Numerous studies have indicated that protein phosphatase-1 (PP1) is the primary phosphatase involved in insulin action. Although PP1 is a cytosolic protein, the phosphatase is compartmentalized in cells by discrete targeting subunits. These proteins confer substrate specificity to PP1 and mediate the specific regulation of intracellular pools of PP1 by a variety of extracellular signals. Four proteins have been described that target the phosphatase to the glycogen particle. G(M) and GL are expressed exclusively in striated muscle and liver, while protein targeting to glycogen (PTG) and R6 are more widely expressed. Despite a common targeting function, these four proteins are not highly conserved, suggesting profound differences in the mechanisms by which they contribute to the hormonal regulation of PP1 activity. Overexpression studies in cell lines or animals have revealed major differences among these proteins regarding basal glycogen levels and hormonal responsiveness. Furthermore, alterations in the expression or function of PP1 glycogen-targeting subunits may contribute to the onset of insulin resistance and type 2 diabetes.

Topics: Amino Acid Sequence; Animals; Aprotinin; Cell Line; Diabetes Mellitus, Type 2; Glycogen; Humans; Insulin; Insulin Resistance; Liver; Mice; Mice, Knockout; Models, Biological; Molecular Sequence Data; Muscle, Skeletal; Phosphoprotein Phosphatases; Phosphorylation; Protein Binding; Protein Phosphatase 1; Recombinant Proteins; Sequence Homology, Amino Acid; Structure-Activity Relationship

Topics: Animals; Blood Glucose; Diabetes Mellitus, Type 2; Glycogen; Humans; Insulin; Insulin Resistance; Islets of Langerhans; Models, Biological; Obesity; Protein-Tyrosine Kinases; Receptor, Insulin; Receptors, Cytoplasmic and Nuclear; Signal Transduction; Transcription Factors

The serine/threonine kinase protein kinase B (PKB/Akt) has been shown to play a crucial role in the control of diverse and important cellular functions such as cell survival and glycogen metabolism. There is also convincing evidence that PKB plays a role in the insulin-mediated regulation of glucose transport. Furthermore, states of cellular insulin resistance have been shown to involve impaired PKB activation, and this usually coincides with a loss of glucose transport activation. However, evidence to the contrary is also available, and the role of PKB in the control of glucose transport remains controversial. Here we provide an overview of recent findings, discuss the potential importance of PKB in the regulation of glucose transport and metabolism, and comment on future directions.

Topics: Actins; Animals; Biological Transport; Ceramides; Enzyme Activation; Glucose; Glycogen; Humans; Insulin Resistance; Osmotic Pressure; Oxidants; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Signal Transduction

Insulin resistance is defined as a clinical state in which a normal or elevated insulin level produces an attenuated biologic response. Specifically, the biologic response most studied is insulin-stimulated glucose disposal, yet the precise cellular mechanism responsible is not yet known. However, the presence of insulin resistance is observed many years before the onset of clinical hyperglycemia and the diagnosis of Type 2 diabetes. Insulin resistance at this stage appears to be significantly associated with a clustering of cardiovascular risk factors predisposing the individual to accelerated cardiovascular disease. An overview of insulin resistance and the associated clinical insulin resistant state will be discussed.

Topics: Animals; Biological Transport; Cardiovascular Diseases; Diabetes Mellitus, Type 2; Glucose; Glycogen; Humans; Hyperglycemia; Insulin; Insulin Resistance; Models, Chemical; Signal Transduction; Syndrome

Nuclear magnetic resonance spectroscopy provides non-invasive and real-time assessment of the metabolic fluxes in skeletal muscle during exercise, recovery from exercise and stimulation by insulin. Carbon-13 nuclear magnetic resonance spectroscopy has proved that reduced glycogen synthesis is a consistent feature of insulin-resistant type 2 diabetic patients, their offspring, and obesity. Low intracellular glucose and glucose-6-phosphate concentrations indicate that decreased glucose transport is mainly responsible for common insulin resistance. An elevation of plasma free fatty acids causes similar alterations of muscle glucose metabolism, and could play a central role in the development of impaired muscle glucose transport associated with insulin resistance.

Topics: Carbon Isotopes; Diabetes Mellitus, Type 2; Exercise; Fatty Acids, Nonesterified; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Magnetic Resonance Spectroscopy; Muscle, Skeletal; Obesity

The liver plays an important role in glucose homeostasis. In the postabsorptive state, plasma glucose is regulated by both hepatic glucose output(HGO) and peripheral glucose utilization(PGU). Insulin and glucagon regulate both HGO and PGU. Increased HGO and decreased PGU, suggesting insulin resistances bring increased fasting blood glucose. While glucose homeostasis after glucose ingestion is regulated by several factors. The regulation of hepatic glucose uptake(HGU) occurs by way of the hormonal milieu(insulin and glucagon), the glucose level, and the rote of glucose delivery. The presence of coordinated changes in insulin, glucagon and the glucose level in combination with the portal signal ensures adequate HGU in response to liver. Hepatic insulin resistance(increased HGO and decreased HGU) and peripheral insulin resistance(decreased PGU) are the characters of glucose intolerance.

Topics: Animals; Diabetes Mellitus; Glucagon; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Liver

Topics: Diabetes Mellitus; Fatty Acids; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Models, Biological; Muscles

Prior to the advent of nuclear magnetic resonance (NMR) spectroscopy, human glucose metabolism was studied through tracer and tissue biopsy methodology. NMR spectroscopy now provides a noninvasive means to monitor metabolic flux and intracellular metabolite concentrations continuously. 13C NMR spectroscopy has shown that muscle glycogen synthesis accounts for the majority of insulin-stimulated muscle glucose uptake in normal volunteers and that defects in this process are chiefly responsible for insulin resistance in type 1 and type 2 diabetes mellitus, as well as in other insulin resistant states (obesity, insulin-resistant offspring of type 2 diabetic parents, elevation of plasma FFA concentrations). Furthermore, using 31P NMR spectroscopy to measure intracellular glucose-6-phosphate, it has been shown that defects in insulin-stimulated glucose transport/phosphorylation activity are primarily responsible for the insulin resistance in these states.

Topics: Carbon Isotopes; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Fatty Acids, Nonesterified; Glucose; Glucose-6-Phosphate; Glycogen; Humans; Insulin; Insulin Resistance; Magnetic Resonance Spectroscopy; Muscle, Skeletal; Obesity; Phosphorus Isotopes; Phosphorylation

This review considers the acute and chronic effects of different levels of carbohydrate (CHO) intakes. The type of CHO consumed, especially glucose vs fructose, affects the glycaemic, insulinaemic and thermogenic responses. In addition, other aspects of food (type of starch, method of processing or cooking, presence of other nutrients) affects the glycaemic response (glycaemic index). In general, the greatest benefit to health is derived from consuming foods with a low glycaemic index and a high non-starch polysaccharide (fibre) content. Healthy, moderately active adults require at least 200g CHO per day to sustain normal brain metabolism and muscle function. Moreover, the CHO content should represent at least 50% of energy intake. Higher intakes of CHO can have deleterious effects on blood lipids (especially plasma triacylglycerol) in middle-aged and elderly subjects, and are really only appropriate for subjects with a high level of physical activity who need to maintain muscle glycogen content. Meals with a high carbohydrate content can lead to problems of postprandial hypotension in the elderly, and impaired exercise capacity in patients with angina.

Topics: Adult; Age Factors; Aged; Brain Chemistry; Diet Surveys; Dietary Carbohydrates; Energy Intake; Energy Metabolism; Exercise; Global Health; Glycogen; Humans; Insulin Resistance; Muscles; Nutritional Requirements; Oxidation-Reduction

Carbon nuclear magnetic resonance (13C NMR) spectroscopy and phosphorus (31p) NMR spectroscopy have been used to help define the contribution of insulin-stimulated muscle glycogen synthesis to whole-body insulin-stimulated glucose metabolism in normal individuals and the extent to which this process is defective in patients with type 2 (non-insulin-dependent) diabetes. Assessments of the response to hyperglycemic-hyperinsulinemic clamping have shown that abnormalities of muscle glycogen synthesis, apparently mediated by a defect in GLUT-4 transport and/or hexokinase activity, play a major role in causing insulin resistance in type 2 diabetes. Studies of the mechanisms by which free fatty acids (FFA) cause insulin resistance in humans indicate that increased FFA levels inhibit glucose transport, which may be a consequence of decreased insulin receptor substrate (IRS-1)-associated phosphatidylinositol 3-kinase activity. 13C NMR spectroscopy studies have documented that liver glycogen concentrations are reduced and the rate of hepatic gluconeogenesis is increased in subjects with type 2 diabetes; thus, the higher rate of glucose production in type 2 diabetes can be attributed entirely to increased rates of hepatic gluconeogenesis. These cellular mechanisms of insulin resistance can be addressed through combination therapy with agents that reverse the principal pathophysiologic defects of type 2 diabetes. The biguanide metformin appears to lower glucose by suppressing hepatic glucose production, whereas the thiazolidinedione troglitazone appears to increase glucose clearance by peripheral tissues. The two agents together have been shown to provide better glucose control than either drug alone, without stimulating insulin secretion.

Topics: Diabetes Mellitus, Type 2; Glucose; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Magnetic Resonance Spectroscopy; Muscles

Topics: Glycogen; Humans; Insulin; Insulin Resistance; Monosaccharide Transport Proteins; Protein Kinases; Receptor, Insulin; Signal Transduction; Substrate Specificity

Natural-abundance 13C NMR spectroscopy is a non-invasive technique that enables in vivo assessments of muscle and/or liver glycogen concentrations. Over the last several years, 13C NMR has been developed and used to obtain information about human glycogen metabolism with diet and exercise. Since NMR is non-invasive, more data points are available over a specified time course, dramatically improving the time resolution. This improved time resolution has enabled the documentation of subtleties of muscle glycogen re-synthesis following severe glycogen depletion that were not previously observed. Muscle and liver glycogen concentrations have been tracked in several different human populations under conditions that include: (1) muscle glycogen recovery from intense localized exercise with normal insulin and with insulin suppressed; (2) muscle glycogen recovery in an insulin-resistant population; (3) muscle glycogen depletion during prolonged low-intensity exercise; (4) effect of a mixed meal on postprandial muscle and liver glycogen synthesis. The present review focuses on basic 13C NMR and gives results from selected studies.

Topics: Exercise; Food; Glycogen; Humans; Insulin; Insulin Resistance; Liver; Magnetic Resonance Spectroscopy; Muscle, Skeletal

Pyruvate and dihydroxyacetone are three carbon compounds that when infused directly into the blood or taken orally produce strong metabolic effects. When chronically fed to animals as part of their diet, pyruvate plus dihydroxyacetone reduce the rate of weight gain and body fat content during growth. These alterations in growth pattern appear to be the result of an increased loss of calories as heat at the expense of storage of lipid. Pyruvate-dihydroxyacetone supplementation has also been found to improve the insulin sensitivity of insulin resistant rats and reduce plasma cholesterol levels induced by a high cholesterol diet as well as lower blood pressure and heart rate in obese individuals. When infused in rats during prolonged treadmill running, pyruvate reduced run time to exhaustion by approximately 67%. However, when provided as an oral supplement for several days, it has enhanced aerobic endurance capacity. The mechanism of action is unclear, but available data suggest that the increase in performance following pyruvate-dihydroxyacetone supplementation may be a result of an increased reliance on blood glucose, thus sparing muscle glycogen. In summary, chronic supplementation of pyruvate-dihydroxyacetone may be beneficial from a preventive medicine prospective as well as for certain athletic endeavors.

Topics: Animals; Cholesterol; Dihydroxyacetone; Exercise; Glycogen; Humans; Insulin Resistance; Muscle, Skeletal; Physical Conditioning, Animal; Physical Endurance; Preventive Medicine; Pyruvic Acid; Rats

Skeletal muscle glucose uptake and metabolism are major determinants of whole body glucose metabolism in response to exercise and insulin stimulation. An understanding of the mechanisms responsible for increased muscle glucose uptake under these conditions is crucial for identifying strategies that enhance insulin action and exercise performance. Regular exercise, by favourably influencing the intramuscular determinants of glucose uptake, enhances insulin action. For this reason, it is recommended in the prevention and management of disease states that are characterised by insulin resistance ("metabolic syndrome"). Increased skeletal muscle glucose uptake, as a consequence of carbohydrate ingestion, maintains carbohydrate supply to contracting muscle, at a time when glycogen levels are reduced, and is associated with enhanced performance. Thus, both health and exercise performance are influenced by the metabolism of glucose within skeletal muscle.

Topics: Dietary Carbohydrates; Exercise; Exercise Therapy; Glucose; Glycogen; Health; Humans; Insulin; Insulin Resistance; Muscle Contraction; Muscle, Skeletal; Physical Exertion

Insulin-mediated non-oxidative glucose metabolism is more or less identical to glycogen synthesis in skeletal muscle and that is why this pathway is specifically discussed in this paper. All three major steps in non-oxidative glucose processing--glucose transport, phosphorylation and glycogen synthesis--are found to be reduced in response to insulin in insulin-resistant type 2 diabetic subjects compared with controls. The insulin-signalling cascade from the insulin receptor to PI-3-K was also found to be abnormal, resulting in a severely reduced phosphorylation degree of the IRS-1 (IRS-2?)-PI-3-K complex, which can explain both reduced glucose transport and glycogen synthesis. The most pronounced finding in our studies is reduced glycogen synthase activation by insulin which is found in prediabetic subjects with normal glucose tolerance as well as in type 2 diabetics, but more severely. This defect was not reversible after treatment (normalization of blood glucose) and is therefore a candidate for the primary defect which is likely to be of genetic origin, but also could be caused by genetic imprinting, intrauterine malnutrition and social inheritance (obesity). Most of the abnormalities in non-oxidative glucose metabolism may be of secondary origin due to hyperglycemia itself or obesity. Both events may stimulate production of glucosamine, malonyl CoA and intramuscular triglyceride accumulation. These metabolites can theoretically induce most of the defects in glucose processing and furthermore impair insulin signalling. Whether the primary defect in activation of glycogen synthase is due to an abnormality in the enzyme complex itself or in the insulin signalling cascade still has to be investigated.

Topics: Diabetes Mellitus, Type 2; Enzyme Activation; Fatty Acids, Nonesterified; Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase; Glycolysis; Hexokinase; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Phosphorylation; Signal Transduction; Twins

Topics: Blood Glucose; Diabetes Mellitus, Type 2; Glucose; Glucose Clamp Technique; Glycogen; Humans; Insulin Resistance; Muscle, Skeletal

Topics: Glucocorticoids; Gluconeogenesis; Glycogen; Glycolysis; Humans; Insulin Resistance

Topics: Animals; Diabetes Mellitus; Disease Models, Animal; Glycogen; Glycolysis; Hypoglycemic Agents; Insulin Resistance; Liver; Pioglitazone; Thiazoles; Thiazolidinediones

An increased supply of FFAs for oxidation leads to a reduced rate of glucose oxidation and interferes with the inhibitory action of insulin on hepatic glucose production. Available evidence indicates that in humans skeletal muscle is a site for such substrate competition, which involves both pyruvate oxidation and glycogen synthesis. The insulin resistance of obesity is thought to be mostly of metabolic origin, and fully reversible. A reduction in FFA supply by weight reduction can, however, reverse this defect. The insulin resistance associated with NIDDM is thought to be primary, with a strong genetic basis, and partially irreversible. Patients with NIDDM are unable to increase their glucose oxidation normally in response to insulin to meet the energy demands of the body. Increased oxidation of lipids represents a compensatory phenomenon to meet these demands. Therapeutic use of the glucose-FFA cycle to lower blood glucose levels has yielded conflicting results. Studies are in progress to develop agents that inhibit gluconeogenesis by interfering with FFA oxidation. Nicotinic acid derivatives seem to enhance glycogen synthesis acutely by activating glycogen synthetase. Whether these or similar agents can be used to restore impaired glycogen synthesis, the most characteristic genetic defect in NIDDM, cannot be answered until the effect has been proven in chronic studies. The existence of substrate competition between amino acids and glucose, and an intrinsic hypoaminoacidaemic property of amino acids, makes it possible to expand the Randel cycle into a glucose-FFA-amino acid cycle, which integrates control of substrate disposition at the whole body level.

Topics: Animals; Binding, Competitive; Diabetes Mellitus, Type 2; Fatty Acids, Nonesterified; Gluconeogenesis; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Lipid Metabolism; Liver; Muscles; Niacin; Obesity; Oxidation-Reduction; Rats

A metabolic hypothesis is presented for insulin resistance in obesity, in the presence or absence of Type 2 (non-insulin-dependent) diabetes mellitus. It is based on physiological mechanisms including a series of negative feed-back mechanisms, with the inhibition of the function of the glycogen cycle in skeletal muscle as a consequence of decreased glucose utilization resulting from increased lipid oxidation in the obese. It considers the inhibition of glycogen synthase activity together with inhibition of glucose storage and impaired glucose tolerance. The prolonged duration of increased lipid oxidation, considered as the initial cause, may lead to Type 2 diabetes. This hypothesis is compatible with others based on the inhibition of insulin receptor kinase and of glucose transporter activities.

Topics: Diabetes Mellitus; Diabetes Mellitus, Type 2; Glucose; Glycogen; Homeostasis; Humans; Insulin Resistance; Models, Biological; Muscles; Obesity

Topics: Animals; Blood Glucose; Dietary Fats; Glucose Transporter Type 4; Glycogen; Insulin Resistance; Membrane Lipids; Monosaccharide Transport Proteins; Muscle Proteins; Rats; Triglycerides

Topics: Diabetes Mellitus; Diabetes Mellitus, Type 2; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Insulin Secretion; Lipid Metabolism; Obesity; Oxidation-Reduction; Risk Factors

Topics: Adult; Blood Glucose; Diabetes Mellitus, Type 1; Diabetic Nephropathies; Female; Glucose; Glycogen; Homeostasis; Humans; Hypoglycemia; Insulin Resistance; Kidney; Kidney Failure, Chronic; Lactates; Lactic Acid; Male

By the term "insulin resistance" we understand the attenuation of insulin-stimulated glucose uptake, which is mainly due to attenuated glycogen synthesis in skeletal muscle and is partially compensated with regard to plasma glucose homeostasis by hyperinsulinemia. Other mechanisms of insulin are either not attenuated or are less so and may contribute via hyperinsulinemia to the prevalence of hypertension, obesity, dyslipoproteinemia and type-II diabetes. At the level of insulin receptors, resistance can be due to muscle-specific, preferential expression of the low-affinity B-isoform of the insulin receptors. In rare cases of extreme resistance, it can also be due to several mutations at the insulin receptor gene or due to insulin-receptor autoantibodies. At the postreceptor level, the translocation and or expression of the insulin-responsive glucose carrier GluT-4 can be down-regulated via the hexosamine pathway by hyperglycemia plus hyperinsulinemia. Furthermore, Glut-4 can be inhibited and/or down-regulated by sustained insulin deficiency, partially via c-AMP-dependent pathways. Additionally, the insulin-induced glycogen synthesis in skeletal muscle can be attenuated by the endogenous peptides amylin and calcitonin-gene-related peptide, and by modulations of endothelial function, perfusion and capillary recruitment in the microcirculation of skeletal muscle. Epidemiological data indicate a genetic predisposition for insulin resistance. However, among the many mechanisms potentially contributing to the complex syndrome of insulin resistance, no specific localization of that predisposition can be proposed at present.

Topics: Amyloid; beta-N-Acetylhexosaminidases; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Glycogen; Humans; Hyperglycemia; Hyperinsulinism; Insulin Resistance; Islet Amyloid Polypeptide; Monosaccharide Transport Proteins; Receptor, Insulin

In conclusion, a large body of available evidence indicates that the degree of physical conditioning is an important determinant of insulin sensitivity and overall glucose tolerance. Both acute exercise and chronic physical training are associated with enhanced disposal of a glucose load. Conversely, physical inactivity leads to a deterioration in glucose tolerance. The primary tissue responsible for accelerated glucose disposal following exercise is muscle. After an acute bout of exercise, enhanced glucose transport and augmented glycogen synthesis are largely responsible for the improvement in glucose tolerance. The beneficial effects of chronic physical training on glucose metabolism appear to be explained by multiple factors, including increased muscle mass, augmented muscle blood flow and capillary area, enhanced mitochondrial oxidative enzyme capacity, and activation of the glucose transport system. Despite these well-documented effects of training on glucose metabolism, the precise role of exercise in the treatment of diabetic patients remains to be established. In insulin-dependent (type I) diabetic individuals, acute exercise has been shown to be a helpful adjunct in establishing good glycemic control. However, the role of acute exercise in helping to smooth out glycemic control in non-insulin-dependent (type II) diabetic patients has received little attention. The role of chronic physical training in the treatment of both insulin-dependent (type I) and non-insulin-dependent (type II) diabetic individuals remains to be established.

Topics: Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Exercise Therapy; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Obesity; Physical Education and Training

Topics: Adipose Tissue; Animals; Blood Glucose; Diabetes Mellitus, Type 2; Epinephrine; Exercise Therapy; Glucose; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Lipolysis; Liver; Male; Metabolic Clearance Rate; Muscles; Obesity; Physical Conditioning, Animal; Physical Exertion

Topics: Adipose Tissue; Aerobiosis; Basal Metabolism; Body Composition; Body Temperature Regulation; Energy Metabolism; Female; Food; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Kinetics; Liver; Male; Muscles; Obesity; Oxygen Consumption; Physical Exertion; Rest; Sympathetic Nervous System

Topics: Adipose Tissue; Animals; Blood Glucose; Diabetes Mellitus; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Dietary Carbohydrates; Energy Metabolism; Exercise Therapy; Fatty Acids, Nonesterified; Food; Glucose; Glucose Tolerance Test; Glycogen; Homeostasis; Humans; Insulin; Insulin Resistance; Lipids; Liver; Muscles; Physical Exertion; Quality of Life

The degree of fasting hyperglycemia in patients with non-insulin-dependent diabetes mellitus is dependent on the rate of hepatic glucose production. The basal rate of hepatic glucose production is increased in patients with non-insulin-dependent diabetes mellitus, and there is a positive correlation between hepatic glucose production and fasting glucose levels. Diminished secretion of insulin, impaired hepatic sensitivity to insulin's effects, or a combination of these factors could contribute to the elevated hepatic glucose production in patients with non-insulin-dependent diabetes mellitus. The relationship between insulin secretion and hepatic glucose production is regulated by a closed feedback loop operating between glucose levels and pancreatic beta cells. Although fasting insulin levels are usually comparable between patients with non-insulin-dependent diabetes mellitus and normal subjects, insulin secretion is markedly impaired in non-insulin-dependent diabetes mellitus in relation to the degree of hyperglycemia present. In fact, the degree of fasting hyperglycemia in a given patient with non-insulin-dependent diabetes mellitus is closely related to the degree of impaired pancreatic beta-cell responsiveness to glucose. Such findings suggest that impaired insulin secretion leads to increased hepatic glucose production, which raises the plasma glucose level. The resulting hyperglycemia helps to maintain relatively normal basal insulin output. Chronic sulfonylurea drug therapy of patients with non-insulin-dependent diabetes mellitus enhances pancreatic islet sensitivity to glucose, leading to increased insulin secretion, suppression of hepatic glucose production, and a decline in the steady-state fasting glucose level.

Topics: Arginine; Blood Glucose; Diabetes Mellitus, Type 2; Fasting; Fatty Acids, Nonesterified; Feedback; Glucagon; Gluconeogenesis; Glucose; Glycogen; Homeostasis; Humans; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Liver; Somatostatin; Sulfonylurea Compounds

Topics: Adrenergic beta-Antagonists; Blood Glucose; Diabetes Mellitus, Type 1; Epinephrine; Fatty Acids; Gluconeogenesis; Glycogen; Growth Hormone; Homeostasis; Humans; Hydrocortisone; Hypoglycemia; Insulin; Insulin Resistance; Insulin, Regular, Pork; Kinetics; Lipolysis; Liver; Norepinephrine; Phentolamine; Propranolol; Receptors, Adrenergic, alpha; Receptors, Adrenergic, beta

Topics: Adipose Tissue; Autoantibodies; Blood Glucose; Cell Membrane; Diabetes Mellitus; Diet, Reducing; Fatty Acids; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Obesity; Receptor, Insulin; Triglycerides

Several types of experimental obesities are characterized by the occurrence of an early hypersecretion of insulin that produces an increase in both triglyceride secretion by the liver and fat deposition in adipose tissue. This hypersecretion of insulin, together with other ill-defined factors, is subsequently responsible for a state of insulin resistance. The early oversecretion of insulin in hypothalamic and genetic (e.g. fa/fa rats) obesities can be experimentally demonstrated. Thus, within 20 min of acute lesion of the ventromedial hypothalamus (VMH), glucose-induced insulin secretion is greater in lesioned than in non-lesioned control rats; this increase can be blocked by superimposed, acute vagotomy. Moreover, an infusion of glucose to 17-day-old, pre-weaned control and genetically pre-obese rats (i.e. animals genetically-determined to become obese but with a normal body weight at this age) elicits much greater insulinaemia in the pre-obese than in the controls, despite similar basal, pre-infusion values in both. This increased insulin secretion in the pre-obese rats can be restored to normal by pre-treating them acutely with the cholinergic inhibitor, atropine. Thus, in these two types of obesity, an increased vagal tone appears to be of importance for the early occurrence of insulin over-secretion. Hyperinsulinaemia produced by increased tone of the vagus nerve appears to be reinforced by the decreased activity of the sympathetic system observed in obese rodents. In many obese rodents, plasma growth hormone levels are abnormally low. The inadequate secretion of this hyperglycaemic hormone may explain why, in some types of obesity syndrome, hyperglycaemia is not necessarily present, despite insulin resistance. Insulin resistance in experimental obesities has been shown to occur at the level of the adipose tissue, the muscles and more recently, the liver. The latter has been demonstrated using the in vivo euglycaemic clamp technique; thus, glycogenolysis of genetically obese (fa/fa) rats could not be shut off, as in controls, by either basal or increased plasma insulin levels. This particular pathway is therefore insulin resistant. The precise etiology of the early over-secretion of insulin in VMH-lesioned rats is, however, unknown: with VMH lesions, the origin is clearly the central nervous system (CNS), but the pathways actually interrupted by the lesions and those responsible for the hyperactivity of the vagus, remain to be determined.(ABSTRACT TR

Topics: Adipose Tissue; Animals; Energy Metabolism; Glucose; Glycogen; Hyperinsulinism; Hypothalamus, Middle; Insulin; Insulin Resistance; Insulin Secretion; Liver; Models, Biological; Muscles; Obesity; Rats; Vagus Nerve

Topics: Adrenal Glands; Animals; Blood Glucose; Carbohydrate Metabolism; Carbon Isotopes; Gluconeogenesis; Glucose; Glucose Tolerance Test; Glycogen; Humans; Hyperglycemia; Insulin; Insulin Resistance; Insulin Secretion; Liver; Myocardium; Wounds and Injuries

Topics: Acidosis; Adipose Tissue; Animals; Animals, Laboratory; Blood Glucose; Diabetes Mellitus; Disease Models, Animal; Feeding Behavior; Glycogen; Guinea Pigs; Haplorhini; Hyperglycemia; Hyperinsulinism; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Ketone Bodies; Mice; Muscles; Obesity; Pancreas; Prediabetic State; Rats

A single bout of exercise is capable of increasing insulin sensitivity in human skeletal muscle. Whether this ability is affected by training status is not clear. Studies in mice suggest that the AMPK-TBC1D4 signalling axis is important for the increased insulin-stimulated glucose uptake after a single bout of exercise. The present study is the first longitudinal intervention study to show that, although exercise training increases insulin-stimulated glucose uptake in skeletal muscle at rest, it diminishes the ability of a single bout of exercise to enhance muscle insulin-stimulated glucose uptake. The present study provides novel data indicating that AMPK in human skeletal muscle is important for the insulin-sensitizing effect of a single bout of exercise.. Not only chronic exercise training, but also a single bout of exercise, increases insulin-stimulated glucose uptake in skeletal muscle. However, it is not well described how adaptations to exercise training affect the ability of a single bout of exercise to increase insulin sensitivity. Rodent studies suggest that the insulin-sensitizing effect of a single bout of exercise is AMPK-dependent (presumably via the α

Topics: Adult; AMP-Activated Protein Kinases; Bicycling; Blood Glucose; Exercise; Glucose; Glycogen; Glycogen Synthase; Humans; Insulin Resistance; Male; Muscle, Skeletal; Protein Subunits; Young Adult

Low testosterone levels in aging men are associated with insulin resistance. Mitochondrial dysfunction, changes in glycogen metabolism, and lipid accumulation are linked to insulin resistance in skeletal muscle. In this randomized, double-blinded, placebo-controlled study, we investigated the effects of six-month testosterone replacement therapy (TRT) and strength training (ST) on mitochondrial, glycogen, and lipid droplet (LD) content in skeletal muscle of aging men with subnormal bioavailable testosterone (BioT) levels. Mitochondrial, glycogen, and LD volume fractions in muscle biopsies were estimated by transmission electron microscopy. Insulin sensitivity (insulin-stimulated Rd) and body composition were assessed by euglycemic-hyperinsulinemic clamp and dual X-ray absorptiometry, respectively. TRT significantly increased total testosterone levels, BioT, and lean body mass (LBM) (p < 0.05), whereas percent body fat decreased (p < 0.05), and insulin sensitivity was unchanged. Baseline mitochondrial volume fraction correlated inversely with percent body fat (ρ = -0.43; p = 0.003). Δ-mitochondrial fraction correlated positively with Δ-total testosterone (ρ = 0.70; p = 0.02), and Δ-glycogen fraction correlated inversely with Δ-LBM (ρ = -0.83; p = 0.002) during six-month TRT, but no significant changes were observed in mitochondrial, glycogen, and LD volume fractions during TRT and ST. In conclusion, in this exploratory small-scale study, the beneficial effects of six-month TRT on total testosterone, LBM, and percent body fat were not followed by significant changes in fractions of mitochondria, glycogen, or lipid in skeletal muscle of aging men with lowered testosterone levels. Six-month ST or combined three-month ST+TRT did not change intramyocellular mitochondria, glycogen, and LD fractions compared to placebo. However, further studies with a larger sample size are needed.

Topics: Aged; Aging; Body Composition; Double-Blind Method; Glycogen; Hormone Replacement Therapy; Humans; Insulin Resistance; Lipid Droplets; Male; Middle Aged; Mitochondria; Muscle, Skeletal; Resistance Training; Testosterone

This study investigated which exercise mode (continuous or sprint interval) is more effective for improving insulin sensitivity. Ten young, healthy men underwent a non-exercise trial (CON) and 3 exercise trials in a cross-over, randomized design that included 1 sprint interval exercise trial (SIE; 4 all-out 30-s sprints) and 2 continuous exercise trials at 46% VO2peak (CELOW) and 77% VO2peak (CEHIGH). Insulin sensitivity was assessed using intravenous glucose tolerance test (IVGTT) 30 min, 24 h and 48 h post-exercise. Energy expenditure was measured during exercise. Glycogen in vastus lateralis was measured once in a resting condition (CON) and immediately post-exercise in all trials. Plasma lipids were measured before each IVGTT. Only after CEHIGH did muscle glycogen concentration fall below CON (P<0.01). All exercise treatments improved insulin sensitivity compared with CON, and this effect persisted for 48-h. However, 30-min post-exercise, insulin sensitivity was higher in SIE than in CELOW and CEHIGH (11.5±4.6, 8.6±5.4, and 8.1±2.9 respectively; P<0.05). Insulin sensitivity did not correlate with energy expenditure, glycogen content, or plasma fatty acids concentration (P>0.05). After a single exercise bout, SIE acutely improves insulin sensitivity above continuous exercise. The higher post-exercise hyperinsulinemia and the inhibition of lipolysis could be behind the marked insulin sensitivity improvement after SIE.

Topics: Adult; Bicycling; Blood Glucose; Cross-Over Studies; Energy Metabolism; Exercise; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Lipids; Male; Muscle, Skeletal; Oxygen Consumption; Young Adult

In health, food carbohydrate is stored as glycogen in muscle and liver, preventing a deleterious rise in osmotically active plasma glucose after eating. Glycogen concentrations increase sequentially after each meal to peak in the evening, and fall to fasting levels thereafter. Skeletal muscle accounts for the larger part of this diurnal buffering capacity with liver also contributing. The effectiveness of this diurnal mechanism has not been previously studied in Type 2 diabetes. We have quantified the changes in muscle and liver glycogen concentration with 13C magnetic resonance spectroscopy at 3.0 T before and after three meals consumed at 4 h intervals. We studied 40 (25 males; 15 females) well-controlled Type 2 diabetes subjects on metformin only (HbA1c (glycated haemoglobin) 6.4±0.07% or 47±0.8 mmol/mol) and 14 (8 males; 6 females) glucose-tolerant controls matched for age, weight and body mass index (BMI). Muscle glycogen concentration increased by 17% after day-long eating in the control group (68.1±4.8 to 79.7±4.2 mmol/l; P=0.006), and this change inversely correlated with homoeostatic model assessment of insulin resistance [HOMA-IR] (r=-0.56; P=0.02). There was no change in muscle glycogen in the Type 2 diabetes group after day-long eating (68.3±2.6 to 67.1±2.0 mmol/mol; P=0.62). Liver glycogen rose similarly in normal control (325.9±25.0 to 388.1±30.3 mmol/l; P=0.005) and Type 2 diabetes groups (296.1±16.0 to 350.5±6.7 mmol/l; P<0.0001). In early Type 2 diabetes, the major physiological mechanism for skeletal muscle postprandial glycogen storage is completely inactive. This is directly related to insulin resistance, although liver glycogen storage is normal.

Topics: Carbon Isotopes; Circadian Rhythm; Diabetes Mellitus, Type 2; Female; Glycogen; Humans; Insulin Resistance; Liver; Magnetic Resonance Spectroscopy; Male; Metformin; Middle Aged; Muscle, Skeletal; Osmolar Concentration; Plasma; Postprandial Period; Statistics, Nonparametric; Triglycerides

Within 2-3 days of starvation, pronounced insulin resistance develops, possibly mediated by increased lipid load. Here, we show that one exercise bout increases mitochondrial fatty acid (FA) oxidation and reverses starvation-induced insulin resistance. Nine healthy subjects underwent 75-h starvation on two occasions: with no exercise (NE) or with one exercise session at the end of the starvation period (EX). Muscle biopsies were analyzed for mitochondrial function, contents of glycogen, and phosphorylation of regulatory proteins. Glucose tolerance and insulin sensitivity, measured with an intravenous glucose tolerance test (IVGTT), were impaired after starvation, but in EX the response was attenuated or abolished. Glycogen stores were reduced, and plasma FA was increased in both conditions, with a more pronounced effect in EX. After starvation, mitochondrial respiration decreased with complex I substrate (NE and EX), but in EX there was an increased respiration with complex I + II substrate. EX altered regulatory proteins associated with increases in glucose disposal (decreased phosphorylation of glycogen synthase), glucose transport (increased phosphorylation of Akt substrate of 160 kDa), and FA oxidation (increased phosphorylation of acetyl-CoA carboxylase). In conclusion, exercise reversed starvation-induced insulin resistance and was accompanied by reduced glycogen stores, increased lipid oxidation capacity, and activation of signaling proteins involved in glucose transport and FA metabolism.

Topics: Adult; Biopsy, Needle; Caloric Restriction; Cross-Over Studies; Electron Transport Complex I; Fatty Acids; Female; Glycogen; Humans; Insulin Resistance; Male; Mitochondria, Muscle; Motor Activity; Oxidation-Reduction; Oxidative Phosphorylation; Oxygen Consumption; Quadriceps Muscle; Reactive Oxygen Species; Young Adult

Glycogen stored in skeletal muscle is the main fuel for endurance exercise. The present study examined the effects of oral hydroxycitrate (HCA) supplementation on post-meal glycogen synthesis in exercised human skeletal muscle. Eight healthy male volunteers (aged 22·0 (se 0·3) years) completed a 60-min cycling exercise at 70-75 % VO₂max and received HCA or placebo in a crossover design repeated after a 7 d washout period. They consumed 500 mg HCA or placebo with a high-carbohydrate meal (2 g carbohydrate/kg body weight, 80 % carbohydrate, 8 % fat, 12 % protein) for a 3-h post-exercise recovery. Muscle biopsy samples were obtained from vastus lateralis immediately and 3 h after the exercise. We found that HCA supplementation significantly lowered post-meal insulin response with similar glucose level compared to placebo. The rate of glycogen synthesis with the HCA meal was approximately onefold higher than that with the placebo meal. In contrast, GLUT4 protein level after HCA supplementation was significantly decreased below the placebo level, whereas expression of fatty acid translocase (FAT)/CD36 mRNA was significantly increased above the placebo level. Furthermore, HCA supplementation significantly increased energy reliance on fat oxidation, estimated by the gaseous exchange method. However, no differences were found in circulating NEFA and glycerol levels with the HCA meal compared with the placebo meal. The present study reports the first evidence that HCA supplementation enhanced glycogen synthesis rate in exercised human skeletal muscle and improved post-meal insulin sensitivity.

Topics: Base Sequence; Bicycling; CD36 Antigens; Citrates; Cross-Over Studies; Dietary Supplements; Exercise; Garcinia cambogia; Glucose; Glucose Transporter Type 4; Glycogen; Humans; Insulin Resistance; Male; Medicine, East Asian Traditional; Muscle, Skeletal; Postprandial Period; RNA, Messenger; Young Adult

During fasting, human skeletal muscle depends on lipid oxidation for its energy substrate metabolism. This is associated with the development of insulin resistance and a subsequent reduction of insulin-stimulated glucose uptake. The underlying mechanisms controlling insulin action on skeletal muscle under these conditions are unresolved. In a randomized design, we investigated eight healthy subjects after a 72-h fast compared with a 10-h overnight fast. Insulin action on skeletal muscle was assessed by a hyperinsulinemic euglycemic clamp and by determining insulin signaling to glucose transport. In addition, substrate oxidation, skeletal muscle lipid content, regulation of glycogen synthesis, and AMPK signaling were assessed. Skeletal muscle insulin sensitivity was reduced profoundly in response to a 72-h fast and substrate oxidation shifted to predominantly lipid oxidation. This was associated with accumulation of both lipid and glycogen in skeletal muscle. Intracellular insulin signaling to glucose transport was impaired by regulation of phosphorylation at specific sites on AS160 but not TBC1D1, both key regulators of glucose uptake. In contrast, fasting did not impact phosphorylation of AMPK or insulin regulation of Akt, both of which are established upstream kinases of AS160. These findings show that insulin resistance in muscles from healthy individuals is associated with suppression of site-specific phosphorylation of AS160, without Akt or AMPK being affected. This impairment of AS160 phosphorylation, in combination with glycogen accumulation and increased intramuscular lipid content, may provide the underlying mechanisms for resistance to insulin in skeletal muscle after a prolonged fast.

Topics: Adenylate Kinase; Adult; Cross-Over Studies; Fasting; Glucose; Glucose Clamp Technique; Glycogen; GTPase-Activating Proteins; Humans; Insulin; Insulin Resistance; Lipid Metabolism; Male; Muscle, Skeletal; Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction

The content of meals consumed after exercise can impact metabolic responses for hours and even days after the exercise session. The purpose of this study was to compare the effect of low dietary carbohydrate (CHO) vs. low energy intake in meals after exercise on insulin sensitivity and lipid metabolism the next day. Nine healthy men participated in four randomized trials. During the control trial (CON) subjects remained sedentary. During the other three trials, subjects exercised [65% peak oxygen consumption (Vo(2 peak)); cycle ergometer and treadmill exercise] until they expended approximately 800 kcal. Dietary intake during CON and one exercise trial (BAL) was designed to provide sufficient energy and carbohydrate to maintain nutrient balance. In contrast, the diets after the other two exercise trials were low in either CHO (LOW-CHO) or energy (LOW-EN). The morning after exercise we obtained a muscle biopsy, assessed insulin sensitivity (S(i); intravenous glucose tolerance test) and measured lipid kinetics (isotope tracers). Although subjects were in energy balance during both LOW-CHO and CON, the lower muscle glycogen concentration during LOW-CHO vs. CON (402 +/- 29 vs. 540 +/- 33 mmol/kg dry wt, P < 0.01) coincided with a significant increase in S(i) [5.2 +/- 0.7 vs. 3.8 +/- 0.7 (mU/l)(-1) x min(-1); P < 0.05]. Conversely, despite ingesting several hundred fewer kilocalories after exercise during LOW-EN compared with BAL, this energy deficit did not affect S(i) the next day [4.9 +/- 0.9, and 5.0 +/- 0.8 (mU/l)(-1) x min(-1)]. Maintaining an energy deficit after exercise had the most potent effect on lipid metabolism, as measured by a higher plasma triacylglycerol concentration, and increased plasma fatty acid mobilization and oxidation compared with when in nutrient balance. Carbohydrate deficit after exercise, but not energy deficit, contributed to the insulin-sensitizing effects of acute aerobic exercise, whereas maintaining an energy deficit after exercise augmented lipid mobilization.

Topics: Adaptation, Physiological; Adult; Biopsy; Blood Glucose; Diet, Carbohydrate-Restricted; Energy Intake; Energy Metabolism; Exercise; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Kinetics; Lipid Metabolism; Male; Muscle, Skeletal; Oxidation-Reduction; Palmitic Acid; Triglycerides

A fat-rich energy-dense diet is an important cause of insulin resistance. Stimulation of fat turnover in muscle cells during dietary fat challenge may contribute to maintenance of insulin sensitivity. Exercise in the fasted state markedly stimulates energy provision via fat oxidation. Therefore, we investigated whether exercise training in the fasted state is more potent than exercise in the fed state to rescue whole-body glucose tolerance and insulin sensitivity during a period of hyper-caloric fat-rich diet. Healthy male volunteers (18-25 y) received a hyper-caloric (∼+30% kcal day(-1)) fat-rich (50% of kcal) diet for 6 weeks. Some of the subjects performed endurance exercise training (4 days per week) in the fasted state (F; n = 10), whilst the others ingested carbohydrates before and during the training sessions (CHO; n = 10). The control group did not train (CON; n = 7). Body weight increased in CON (+3.0 ± 0.8 kg) and CHO (+1.4 ± 0.4 kg) (P < 0.01), but not in F (+0.7 ± 0.4 kg, P = 0.13). Compared with CON, F but not CHO enhanced whole-body glucose tolerance and the Matsuda insulin sensitivity index (P < 0.05). Muscle GLUT4 protein content was increased in F (+28%) compared with both CHO (P = 0.05) and CON (P < 0.05). Furthermore, only training in F elevated AMP-activated protein kinase α phosphorylation (+25%) as well as up-regulated fatty acid translocase/CD36 and carnitine palmitoyltransferase 1 mRNA levels compared with CON (∼+30%). High-fat diet increased intramyocellular lipid but not diacylglycerol and ceramide contents, either in the absence or presence of training. This study for the first time shows that fasted training is more potent than fed training to facilitate adaptations in muscle and to improve whole-body glucose tolerance and insulin sensitivity during hyper-caloric fat-rich diet.

Topics: Body Composition; Dietary Fats; Exercise; Fasting; Fatty Acids, Nonesterified; Glucose; Glycogen; Humans; Insulin Resistance; Lipid Metabolism; Male; Muscle, Skeletal; Physical Endurance; Young Adult

The purpose of this study was to determine whether exercise prescriptions differing in volume or intensity also differ in their ability to retain insulin sensitivity during an ensuing period of training cessation. Sedentary, overweight/obese subjects were assigned to one of three 8-mo exercise programs: 1) low volume/moderate intensity [equivalent of approximately 12 miles/wk, 1,200 kcal/wk at 40-55% peak O(2) consumption (Vo(2peak)), 200 min exercise/wk], 2) low volume/vigorous intensity ( approximately 12 miles/wk, 1,200 kcal/wk at 65-80% Vo(2peak), 125 min/wk), and 3) high volume/vigorous intensity ( approximately 20 miles/wk, 2,000 kcal/wk at 65-80% Vo(2peak), 200 min/wk). Insulin sensitivity (intravenous glucose tolerance test, S(I)) was measured when subjects were sedentary and at 16-24 h and 15 days after the final training bout. S(I) increased with training compared with the sedentary condition (P < or = 0.05) at 16-24 h with all of the exercise prescriptions. S(I) decreased to sedentary, pretraining values after 15 days of training cessation in the low-volume/vigorous-intensity group. In contrast, at 15 days S(I) was significantly elevated compared with sedentary (P < or = 0.05) in the prescriptions utilizing 200 min/wk (low volume/moderate intensity, high volume/vigorous intensity). In the high-volume/vigorous-intensity group, indexes of muscle mitochondrial density followed a pattern paralleling insulin action by being elevated at 15 days compared with pretraining; this trend was not evident in the low-volume/moderate-intensity group. These findings suggest that in overweight/obese subjects a relatively chronic persistence of enhanced insulin action may be obtained with endurance-oriented exercise training; this persistence, however, is dependent on the characteristics of the exercise training performed.

Topics: Anaerobic Threshold; Body Mass Index; Body Weight; Dyslipidemias; Exercise; Female; Glucose Tolerance Test; Glycogen; Homeostasis; Humans; Insulin; Insulin Resistance; Male; Middle Aged; Mitochondria, Muscle; Muscle, Skeletal; Obesity; Oxygen Consumption; Physical Fitness

Insulin resistance is a major risk factor for type 2 diabetes in women with polycystic ovary syndrome (PCOS). The molecular mechanisms underlying reduced insulin-mediated glycogen synthesis in skeletal muscle of patients with PCOS have not been established.. We investigated protein content, activity, and phosphorylation of glycogen synthase (GS) and its major upstream inhibitor, GS kinase (GSK)-3 in skeletal muscle biopsies from 24 PCOS patients (before treatment) and 14 matched control subjects and 10 PCOS patients after 16 wk treatment with pioglitazone. All were metabolically characterized by euglycemic-hyperinsulinemic clamps and indirect calorimetry.. Reduced insulin-mediated glucose disposal (P < 0.05) was associated with a lower insulin-stimulated GS activity in PCOS patients (P < 0.05), compared with controls. This was, in part, explained by absent insulin-mediated dephosphorylation of GS at the NH2-terminal sites 2+2a, whereas dephosphorylation at the COOH-terminal sites 3a+3b was intact in PCOS subjects (P < 0.05). Consistently, multiple linear regression analysis showed that insulin activation of GS was dependent on dephosphorylation of sites 3a+3b in women with PCOS. No significant abnormalities in GSK-3alpha or -3beta were found in PCOS subjects. Pioglitazone treatment improved insulin-stimulated glucose metabolism and GS activity in PCOS (all P < 0.05) and restored the ability of insulin to dephosphorylate GS at sites 2 and 2a.. Impaired insulin activation of GS including absent dephosphorylation at sites 2+2a contributes to insulin resistance in skeletal muscle in PCOS. The ability of pioglitazone to enhance insulin sensitivity, in part, involves improved insulin action on GS activity and dephosphorylation at NH2-terminal sites.

Topics: Adult; Biopsy; Double-Blind Method; Female; Glucose; Glycogen; Glycogen Synthase; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Muscle, Skeletal; Phosphorylation; Pioglitazone; Placebos; Polycystic Ovary Syndrome; Thiazolidinediones

In obese subjects, chronically elevated plasma concentrations of non-esterified fatty acids (NEFAs) exert a marked risk to contract insulin resistance and subsequently type 2 diabetes. When NEFA is acutely increased due to i.v. infusion of lipid, glucose disposal during a hyperinsulinemic-euglycemic clamp is reduced. This effect has been explained by a NEFA-induced decrease in skeletal muscle insulin sensitivity caused by accumulation of the lipid intermediates such as ceramide and diacylglycerol in the myocytes. However, neither the lipid-induced reduction of glucose disposal nor the intramyocellular lipid deposition has been compared directly in obese females and males.. We studied eight obese females and eight obese males (body mass index (BMI): 32.6+/-1.4 and 32.8+/-0.8 respectively, non significant (NS)) matched for cardiorespiratory fitness relative to lean body mass (43.7+/-1.6 and 47.6+/-1.3 ml/kg min respectively, NS).. Each subject underwent two hyperinsulinemic-euglycemic clamps with infusion of lipid or saline respectively. Furthermore, the subjects exercised during the last half an hour of each clamp.. The lipid-induced reduction in glucose disposal during the clamp was similar in females and males (46+/-10 and 60+/-4% respectively, NS). However, whole-body insulin sensitivity as well as non-oxidative glucose disposal was higher in obese females compared with obese males both during lipid and saline infusion (P<0.001 and P=0.01 respectively). Muscle ceramide, triacylglycerol (TAG), diacylglycerol (DAG), and glycogen content were similar between sexes and remained unchanged during the clamp and when exercise was superimposed.. The lipid-induced inhibition of glucose disposal is similar in obese females and males. However, obese females are more insulin sensitive compared with obese males (both during saline and lipid infusion), which is not due to differences in the concentration of the muscle lipid intermediates such as ceramide and DAG.

Topics: Absorptiometry, Photon; Adult; Analysis of Variance; Blood Glucose; Ceramides; Diglycerides; Enzyme-Linked Immunosorbent Assay; Exercise; Fatty Acids, Nonesterified; Female; Glucose Clamp Technique; Glycogen; Heparin; Humans; Infusions, Intravenous; Insulin; Insulin Resistance; Lipid Metabolism; Lipids; Male; Middle Aged; Muscles; Obesity; Oxidation-Reduction; Sex Factors; Triglycerides

To determine the effects of dexamethasone treatment on selected components of insulin signaling and glucose metabolism in skeletal muscle obtained from horses before and after administration of a euglycemic-hyperinsulinemic clamp (EHC).. 6 adult Standardbreds.. In a balanced crossover study, horses received either dexamethasone (0.08 mg/kg, IV, q 48 h) or an equivalent volume of saline (0.9% NaCl) solution, IV, for 21 days. A 2-hour EHC was administered for measurement of insulin sensitivity 1 day after treatment. Muscle biopsy specimens obtained before and after the EHC were analyzed for glucose transporter 4, protein kinase B (PKB), glycogen synthase kinase (GSK)-3alpha/beta protein abundance and phosphorylation state (PKB Ser(473) and GSK-3alpha/beta Ser(21/9)), glycogen synthase and hexokinase enzyme activities, and muscle glycogen concentration.. Dexamethasone treatment resulted in resting hyperinsulinemia and a significant decrease (70%) in glucose infusion rate during the EHC. In the dexamethasone group, increased hexokinase activity, abrogation of the insulin-stimulated increase in glycogen synthase fractional velocity, and decreased phosphorylation of GSK-3alpha Ser(21) and GSK-3B Ser(9) were detected, but there was no effect of dexamethasone treatment on glucose transporter 4 content and glycogen concentration or on PKB abundance and phosphorylation state.. In horses, 21 days of dexamethasone treatment resulted in substantial insulin resistance and impaired GSK-3 phosphorylation in skeletal muscle, which may have contributed to the decreased glycogen synthase activity seen after insulin stimulation.

Topics: Animals; Cross-Over Studies; Dexamethasone; Female; Glucose; Glycogen; Horses; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Signal Transduction

High plasma fatty acid availability and a positive energy balance in sedentary individuals reduce insulin sensitivity. This study's purpose was to determine whether high plasma fatty acid availability and systemic caloric excess after exercise also impair insulin sensitivity. On two separate occasions, seven nonobese women performed 90 min of exercise at approximately 65% peak oxygen uptake. In one trial, a lipid + heparin emulsion (Lipid) was infused overnight to increase plasma fatty acid availability. In the other trial, saline was infused as control. The next morning, a muscle biopsy was taken to measure muscle glycogen and intramuscular triglyceride (IMTG) concentrations. Three hours after the overnight infusion was stopped, insulin sensitivity was assessed with an intravenous glucose tolerance test, using minimal model analysis (Si). During the overnight infusions, plasma fatty acid concentration was approximately fourfold higher [means (SD): 0.84 (0.36) vs. 0.22 (0.09) mmol/l; P = 0.003], and the next morning IMTG concentration was approximately 30% greater [49.2 (6.6) vs. 38.3 (7.7) mmol/kg dry wt; P = 0.036] in Lipid compared with saline. However, muscle glycogen concentration was not different between trials (P = 0.82). Lipid caused a 24-h surplus of approximately 1100 kcal above energy balance (P = 0.00001), whereas energy balance was maintained in saline. Despite these differences in fatty acid and energy availability, Si the morning after exercise was not different between trials (P = 0.72). Thus insulin sensitivity the morning after a single exercise session was not reduced despite overnight exposure to a fourfold increase in plasma fatty acid concentration, elevated IMTG concentration, and systemic delivery of approximately 1,100-kcal excess.

Topics: Adolescent; Adult; Basal Metabolism; Blood Glucose; Energy Intake; Energy Metabolism; Exercise; Exercise Test; Fatty Acids; Female; Glucose Tolerance Test; Glycogen; Humans; Infusions, Intravenous; Insulin; Insulin Resistance; Lipids; Muscle, Skeletal; Triglycerides

This study investigates the consequences of inhibition of adipose tissue lipolysis on skeletal muscle substrate use. Ten subjects were studied at rest and during exercise and subsequent recovery under normal, fasting conditions (control trial, CON) and following administration of a nicotinic acid analog (low plasma free fatty acid trial, LFA). Continuous [U-13C]palmitate and [6,6-2H2]glucose infusions were applied to quantify plasma free fatty acid (FFA) and glucose oxidation rates and to estimate intramuscular triacylglycerol (IMTG) and glycogen use. Muscle biopsies were collected to measure 1) fiber type-specific IMTG content; 2) allosteric regulators of hormone-sensitive lipase (HSL), glycogen phosphorylase, and pyruvate dehydrogenase; and 3) the phosphorylation status of HSL at Ser563 and Ser565. Administration of a nicotinic acid analog (acipimox) substantially reduced plasma FFA rate of appearance and subsequent plasma FFA concentrations (P < 0.0001). At rest, this substantially reduced plasma FFA oxidation rates, which was compensated by an increase in the estimated IMTG use (P < 0.05). During exercise, the progressive increase in FFA rate of appearance, uptake, and oxidation was prevented in the LFA trial and matched by greater IMTG and glycogen use. Differential phosphorylation of HSL or relief of its allosteric inhibition by long-chain fatty acyl-CoA could not explain the increase in muscle TG use, but there was evidence to support the contention that regulation may reside at the level of the glucose-fatty acid cycle. This study confirms the hypothesis that plasma FFA availability regulates both intramuscular lipid and glycogen use in vivo in humans.

Topics: Adipose Tissue; Adult; Blood Glucose; Carbon Isotopes; Deuterium; Fatty Acids, Nonesterified; Glucose; Glycogen; Humans; Insulin Resistance; Lactic Acid; Lipolysis; Male; Muscle, Skeletal; Oxidation-Reduction; Palmitates; Physical Exertion; Rest; Triglycerides

A single session of exercise increases insulin sensitivity for hours and even days, and dietary carbohydrate ingested after exercise alters the magnitude and duration of this effect. Although increasing systemic fatty acid availability is associated with insulin resistance, it is uncertain whether increasing dietary fat availability after exercise alters the exercise-induced increase in insulin sensitivity. The purpose of this study was to determine whether adding fat calories to meals after exercise alters glucose tolerance the next day. Seven healthy men cycled 90 min at 66 +/- 2% peak oxygen uptake followed by a maximum of five high-intensity intervals. During the hours after exercise, subjects ingested three meals containing either low-fat (5% energy from fat) or high-fat (45% energy from fat) foods (Low-Fat and High-Fat groups, respectively). Each diet contained the same amount of carbohydrate and protein. An oral glucose tolerance test was performed the next morning. Muscle glycogen and intramuscular triglyceride (IMTG) concentrations were measured in muscle biopsy samples obtained immediately before exercise and the next morning. The day after exercise, muscle glycogen concentration was identical in High-Fat and Low-Fat (393 +/- 70 and 379 +/- 38 mmol/kg dry wt). At the same time, IMTG concentration was approximately 20% greater during High-Fat compared with Low-Fat (42.5 +/- 3.4 and 36.3 +/- 3.3 mmol/kg dry wt; P < 0.05). Despite the addition of approximately 165 g of fat to meals after exercise ( approximately 1,500 kcal) and a resultant elevation in IMTG concentration, glucose tolerance was identical in High-Fat and Low-Fat (composite index: 8.7 +/- 1.0 and 8.4 +/- 1.0). In summary, as long as meals ingested in the hours after exercise contain the same carbohydrate content, the addition of approximately 1500 kcal from fat to these meals did not alter muscle glycogen resynthesis or glucose tolerance the next day.

Topics: Adult; Area Under Curve; Blood Glucose; Body Composition; Diet; Dietary Fats; Energy Intake; Energy Metabolism; Exercise; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Oxygen Consumption

During exercise, obese individuals oxidize less glycogen and more fat than their lean counterparts, but the shift in substrate use may be mediated by insulin resistance rather than body fat per se. In addition, individuals with Type 2 diabetes are not resistant to contraction-mediated glucose uptake during exercise, but in vivo studies uncomplicated by hyperglycemia are lacking. The purpose of this study was to compare blood glucose uptake and the balance between carbohydrate and fat utilization during exercise in insulin-resistant (IR) and insulin-sensitive (IS) women of equivalent body fatness and maximal oxygen consumption (VO2 max). Twelve overweight sedentary women were divided into two groups with similar body mass index (IR = 28.5 +/- 1.6, IS = 27.5 +/- 1.9), lean mass (IR = 42.4 +/- 1.8 kg, IS = 41.5 +/- 1.9 kg), and VO2 max (IR = 29.7 +/- 3.5 ml.kg(-1).min(-1), IS = 30.7 +/- 3.9 ml.kg(-1).min(-1)) but a markedly different composite insulin sensitivity index (IR = 3.0 +/- 0.7, IS = 7.7 +/- 0.9). Blood glucose kinetics and substrate oxidation were assessed by stable isotope dilution and indirect calorimetry during 50 min of treadmill walking at 45% VO2 max. Total carbohydrate oxidation and estimated muscle glycogen use were significantly lower in the IR group. Blood glucose uptake was the same in the IR and IS groups. These data suggest that insulin resistance, independent of body fat, spares muscle glycogen and shifts substrate oxidation toward less carbohydrate use during exercise. Insulin-resistant individuals with normoglycemia appear to have no defect in blood glucose uptake during exercise.

Topics: Adult; Blood Glucose; Carbohydrate Metabolism; Energy Metabolism; Exercise; Female; Glycogen; Humans; Insulin; Insulin Resistance; Muscle, Skeletal; Obesity

Muscle contains the largest reservoir of glycogen (Glyc), a depot that is closely regulated and with influence on insulin sensitivity. The current study examines muscle Glyc in type 2 diabetes mellitus (T2DM) and obesity and with respect to muscle fiber type, intramyocellular lipid content (IMCL), and mitochondrial function (oxidative enzyme activity; OX-Enz). There is increasing interest in the relation of IMCL and mitochondrial dysfunction with insulin resistance (IR), yet the association with muscle Glyc has not been examined with regard to these parameters. Using a quantitative histological approach specific to muscle fiber types, we assessed muscle Glyc, IMCL, and OX-Enz in vastus lateralis obtained by percutaneous biopsy in lean nondiabetic (L; n = 16), obese nondiabetic (Ob; n = 15), and T2DM volunteers (n = 14). Insulin sensitivity was estimated using homeostasis model assessment (HOMA)-IR. Muscle Glyc was reduced in T2DM, a deficit evident for type IIa fibers, yet minor in types I and IIb fibers. Low Glyc in T2DM correlated with fasting hyperglycemia. Also, in T2DM and Ob, there was significantly higher IMCL and lower OX-Enz in all fiber types. The IMCL-to-OX-Enz ratio, especially for type I fibers, correlated strongly with IR. Similarly, a Glyc-to-OX-Enz ratio correlated with IR, particularly for type IIb fibers. This ratio tended to be higher in Ob and T2DM. In summary, there is decreased muscle Glyc in T2DM yet a disproportional Glyc-to-OX-Enz relationship that is related to IR, although not as robustly as the IMCL-to-OX-Enz ratio.

Topics: Diabetes Mellitus, Type 2; Fasting; Female; Glycogen; Homeostasis; Humans; Hyperglycemia; Insulin Resistance; Lipid Metabolism; Male; Middle Aged; Mitochondria, Muscle; Muscle Fibers, Skeletal; Muscle, Skeletal; Obesity; Reference Values

Myotube cultures from patients with type 2 diabetes mellitus (T2DM) represent an experimental in vitro model of T2DM that offers a possibility to perform gene expression studies under standardized conditions. During a time-course of insulin stimulation (1 microM) at 5.5 mM glucose for 0 (no insulin), 0.5, 1, 2, 4, 8, and 24 h, mRNA contents were analyzed in human myotubes for each time point using Affymetrix DNA chip technology. Insulin treatment induced an inflammatory and pro-angiogenic response in the myotubes, with expression of early response factors followed by inflammatory chemokines, metabolic enzymes, and finally cell cycle regulating genes. One-hundred-forty-four genes were differentially expressed in myotubes from donors with type 2 diabetes compared with control subjects, including HSP70, apolipoprotein D/E, tropomyosin, myosin, and actin previously reported from in vivo studies of diabetic skeletal muscle. We conclude, (i) that insulin induces a time-dependent inflammatory and pro-angiogenic transcriptional response in cultured human myotubes, (ii) that myotubes in vitro retain a gene expression pattern specific for type 2 diabetes and sharing five genes with that of type 2 diabetic skeletal muscle in vivo, and (iii) that insulin, despite similar metabolic effects of glucose uptake and glycogen synthesis, regulates different pools of genes in skeletal muscle during in vivo and in vitro conditions.

Topics: Adult; Cells, Cultured; Cytokines; Diabetes Mellitus, Type 2; Dose-Response Relationship, Drug; Gene Expression Profiling; Gene Expression Regulation; Glycogen; Humans; Inflammation; Insulin; Insulin Resistance; Kinetics; Male; Middle Aged; Muscle Fibers, Skeletal; Muscle, Skeletal; Neovascularization, Pathologic; Oligonucleotide Array Sequence Analysis; Signal Transduction

Therapy with some HIV protease inhibitors (PI) contributes to insulin resistance and type 2 diabetes mellitus, by inhibition of insulin-sensitive glucose transporters. Atazanavir (ATV) is a new PI with substantially less in vitro effect on glucose transport than observed with other PI, including lopinavir (LPV) or ritonavir (RTV).. Randomized, double-blind, crossover study of the effect of 5 days of administering ATV, lopinavir/ritonavir (LPV/r) or placebo on insulin-stimulated glucose disposal in 30 healthy HIV-negative subjects. Each subject was studied on two of three possible treatments with a wash-out period between treatments.. The mean insulin-stimulated glucose disposal (mg/min per kg body weight) per unit insulin (microU/ml) (M/I) was 9.88, 9.80 and 7.52 for placebo, ATV and LPV/r, respectively (SEM, 0.84 for all). There was no significant difference between ATV and placebo. The M/I for LPV/r was 23% lower than that for ATV (P = 0.010) and 24% lower than that for placebo (P = 0.008). The mean glycogen storage rates were 3.85, 4.00 and 2.54 mg/min per kg for placebo, ATV and LPV/r, respectively (SEM, 0.39 for all). There was no significant difference between ATV and placebo. The glycogen storage rate for LPV/r was 36% lower than ATV (P = 0.003) and 34% lower than placebo (P = 0.006).. ATV given to healthy subjects for 5 days did not affect insulin sensitivity, while LPV/r induced insulin resistance. This observation is consistent with differential in vitro effects of these PI on glucose transport. Further data are needed to assess clinical implications for body composition.

Topics: Adult; Analysis of Variance; Atazanavir Sulfate; Cross-Over Studies; Double-Blind Method; Energy Metabolism; Fatty Acids, Nonesterified; Glycogen; HIV Protease Inhibitors; HIV Seronegativity; Humans; Insulin Resistance; Lipids; Lipodystrophy; Lopinavir; Oligopeptides; Pyridines; Pyrimidinones

The information that insulin sensitivity and glycogen synthesis are reduced in hypertension arises primarily from studies using insulin infusions. Whether glycogen metabolism is actually altered in a physiological condition, such as during and after prolonged exercise, is currently unknown.. To examine this issue, 9 hypertensive and 11 normotensive subjects were evaluated on a rest day and after intense and prolonged exercise on a separate day. Insulin sensitivity and hemodynamic variables were measured on both days. On the exercise day, whole-body substrate utilization was assessed and muscle biopsies were taken in the leg at baseline, immediately after exercise, and 2.5 and 4 hours after exercise. Insulin sensitivity at rest was lower in hypertensive than normotensive subjects (P<0.05) and increased after exercise in normotensive (P<0.01) but not in hypertensive (P=NS) subjects. Leg blood flow increased after exercise in both groups but to a lesser extent in hypertensive than normotensive subjects. Baseline glycogen content and maximal glycogen synthase activity were higher in hypertensive than normotensive subjects (P<0.001). Glycogen concentration decreased relatively less (-35 versus -66%) and returned to baseline levels faster in hypertensive subjects after exercise. Hypertensive subjects used approximately 40% less carbohydrates during exercise (P<0.001) at the expense of greater free fatty acid oxidation.. It is concluded that increased intramuscular glycogen storage and resynthesis in hypertension are independent of blood flow and may represent compensatory mechanisms for the reduced insulin sensitivity and carbohydrate metabolism in this condition.

Topics: Adult; Biopsy; Blood Pressure; Glucose Tolerance Test; Glycogen; Glycogen Synthase; Hemodynamics; Humans; Hypertension; Insulin Resistance; Leg; Male; Muscle, Skeletal; Oxygen Consumption; Physical Exertion; Reference Values; Regional Blood Flow

Plasma concentrations of amino acids are frequently elevated in insulin-resistant states, and a protein-enriched diet can impair glucose metabolism. This study examined effects of short-term plasma amino acid (AA) elevation on whole-body glucose disposal and cellular insulin action in skeletal muscle. Seven healthy men were studied for 5.5 h during euglycemic (5.5 mmol/l), hyperinsulinemic (430 pmol/l), fasting glucagon (65 ng/l), and growth hormone (0.4 microg/l) somatostatin clamp tests in the presence of low (approximately 1.6 mmol/l) and increased (approximately 4.6 mmol/l) plasma AA concentrations. Glucose turnover was measured with D-[6,6-(2)H(2)]glucose. Intramuscular concentrations of glycogen and glucose-6-phosphate (G6P) were monitored using (13)C and (31)P nuclear magnetic resonance spectroscopy, respectively. A approximately 2.1-fold elevation of plasma AAs reduced whole-body glucose disposal by 25% (P < 0.01). Rates of muscle glycogen synthesis decreased by 64% (180--315 min, 24 plus minus 3; control, 67 plus minus 10 micromol center dot l(-1) center dot min(-1); P < 0.01), which was accompanied by a reduction in G6P starting at 130 min (DeltaG6P(260--300 min), 18 plus minus 19; control, 103 plus minus 33 micromol/l; P < 0.05). In conclusion, plasma amino acid elevation induces skeletal muscle insulin resistance in humans by inhibition of glucose transport/phosphorylation, resulting in marked reduction of glycogen synthesis.

Topics: Adenosine Diphosphate; Adult; Amino Acids; Blood Glucose; Deuterium; Epinephrine; Fasting; Glucagon; Glucose Clamp Technique; Glucose-6-Phosphate; Glycogen; Human Growth Hormone; Humans; Hydrocortisone; Hydrogen-Ion Concentration; Insulin; Insulin Resistance; Kinetics; Magnetic Resonance Spectroscopy; Male; Muscle, Skeletal; Phosphates; Phosphocreatine; Phosphorylation; Somatostatin

Free fatty acids (FFA) have been shown to inhibit insulin suppression of endogenous glucose production (EGP). To determine whether this is the result of stimulation by FFA of gluconeogenesis (GNG) or glycogenolysis (GL) or a combination of both, we have determined rates of GNG and GL (with (2)H(2)O) and EGP in 16 healthy nondiabetic volunteers (11 males, 5 females) during euglycemic-hyperinsulinemic (~450 pM) clamping performed either with or without simultaneous intravenous infusion of lipid plus heparin. During insulin infusion, FFA decreased from 571 to 30 micromol/l (P < 0.001), EGP from 15.7 to 2.0 micromol x kg(-1) x min(-1) (P < 0.01), GNG from 8.2 to 3.7 micromol x kg(-1). min(-1) (P < 0.05), and GL from 7.4 to -1.7 micromol x kg(-1). min(-1) (P < 0.02). During insulin plus lipid/heparin infusion, FFA increased from 499 to 1,247 micromol/l (P < 0.001). EGP decreased 64% less than during insulin alone (-5.1 +/- 0.7 vs. -13.7 +/- 3.4 micromol x kg(-1). min(-1)). The decrease in GNG was not significantly different from the decrease of GNG during insulin alone (-2.6 vs. -4.5 micromol x kg(-1). min(-1), not significant). In contrast, GL decreased 66% less than during insulin alone (-3.1 vs. -9.2 micromol x kg(-1). min(-1), P < 0.05). We conclude that insulin suppressed EGP by inhibiting GL more than GNG and that elevated plasma FFA levels attenuated the suppression of EGP by interfering with insulin suppression of GL.

Topics: Adult; Blood Glucose; Fatty Acids, Nonesterified; Female; Glucagon; Gluconeogenesis; Glucose; Glucose Clamp Technique; Glycogen; Humans; Hydrocortisone; Infusions, Intravenous; Insulin; Insulin Resistance; Liver; Male; Reference Values; Somatostatin

Topics: Cross-Over Studies; Diabetes Mellitus, Type 2; Energy Metabolism; Fatty Acids, Nonesterified; Food Deprivation; Gluconeogenesis; Glucose; Glycogen; Humans; Hypolipidemic Agents; Insulin Resistance; Liver; Male; Pyrazines

The hypotheses that postexercise replenishment of intramyocellular lipids (IMCL) is enhanced by endurance training and that it depends on fat intake were tested. Trained and untrained subjects exercised on a treadmill for 2 h at 50% peak oxygen consumption, reducing IMCL by 26-22%. During recovery, they were fed 55% (high fat) or 15% (low fat) lipid energy diets. Muscle substrate stores were estimated by (1)H (IMCL)- and (13)C (glycogen)-magnetic resonance spectroscopy in tibialis anterior muscle before and after exercise. Resting IMCL content was 71% higher in trained than untrained subjects and correlated significantly with glycogen content. Both correlated positively with indexes of insulin sensitivity. After 30 h on the high-fat diet, IMCL concentration was 30-45% higher than preexercise, whereas it remained 5-17% lower on the low-fat diet. Training status had no significant influence on IMCL replenishment. Glycogen was restored within a day with both diets. We conclude that fat intake postexercise strongly promotes IMCL repletion independently of training status. Furthermore, replenishment of IMCL can be completed within a day when fat intake is sufficient.

Topics: Adult; Body Composition; Body Weight; Carbon Isotopes; Dietary Fats; Exercise Test; Glycogen; Humans; Insulin Resistance; Lactic Acid; Lipid Metabolism; Lipids; Magnetic Resonance Spectroscopy; Male; Muscle, Skeletal; Oxygen Consumption; Physical Exertion; Physical Fitness; Time Factors

Carbohydrate metabolism was assessed in 20 glucose-intolerant subjects before and after 12 wk on a high-carbohydrate diet (HC) or the diet combined with exercise training (HC-EX). The diet provided 60% of energy as carbohydrate and 20% as fat. Neither treatment altered fasting glucose or insulin concentrations or their response to a meal. During a glucose clamp (216 pmol insulin/L) glucose disposal increased from 13.2 +/- 0.83 to 14.6 +/- 0.83 mumol.kg fat-free mass-1.min-1 (P < 0.05) in both groups. During more pronounced hyperinsulinemia (654 pmol/L) glucose disposal did not change significantly (49.9 +/- 3.8 to 50.7 +/- 3.8 mumol.kg fat-free mass-1.min-1). Muscle glycogen increased in the HC-EX group (78.5 +/- 8.1 to 161.1 +/- 15.7 mmol glucose/kg muscle), with no changes in the HC group. These results do not support the recommendation to increase the dietary carbohydrate content for improving postprandial glucose metabolism or insulin action in glucose-intolerant adults unless combined with exercise training, which promotes muscle glycogen storage.

Topics: Aged; Aging; Blood Glucose; Body Composition; Dietary Carbohydrates; Dose-Response Relationship, Drug; Energy Metabolism; Exercise; Female; Glucose Clamp Technique; Glucose Tolerance Test; Glycogen; Humans; Hyperinsulinism; Insulin; Insulin Resistance; Male; Middle Aged; Muscle, Skeletal; Time Factors

We have previously reported increased blood glucose concentrations and skeletal muscle glycogen depletion in severe COPD patients with chronic respiratory failure. In order to see if insulin resistance exists in severe COPD, we investigated nine patients with advanced COPD with chronic hypoxaemia and seven healthy control subjects of similar age, using the euglycaemic hyperinsulinaemic glucose clamp technique. We could not demonstrate a subnormal intravenous glucose requirement in response to insulin when maintaining euglycaemia in the COPD patients with chronic hypoxaemia. This indicates that the net metabolism of glucose in COPD patients with chronic hypoxaemia is not resistant to insulin.

Topics: Blood Gas Analysis; Blood Glucose; Female; Glucose Clamp Technique; Glycogen; Humans; Insulin; Insulin Resistance; Lung Diseases, Obstructive; Male; Middle Aged; Muscle, Skeletal; Respiratory Function Tests

Two study protocols to examine the effects of chronic (72-96 h) physiologic euglycaemic hyperinsulinaemia (+ 72 pmol/l) and chronic hyperglycaemic (+ 1.4 mmol/l) hyperinsulinaemia (+ 78 pmol/l) on insulin sensitivity and insulin secretion were performed in 15 healthy young subjects. Subjects received a three-step euglycaemic insulin (insulin infusion rates = 1.5, 3, and 6 nmol.kg-1.min-1) clamp and a hyperglycaemia (6.9 mmol/l) clamp before and after chronic insulin or glucose infusion. Following 4 days of sustained euglycaemic hyperinsulinaemia whole body glucose disposal decreased by 20-40%. During each insulin clamp step, the defect in insulin action was accounted for by impaired non-oxidative glucose disposal (p < 0.01). Chronic euglycaemic hyperinsulinaemia did not alter insulin-mediated suppression of hepatic glucose production. Following insulin infusion the ability of hyperglycaemia to stimulate insulin secretion was significantly diminished. Following 72 h of chronic glucose infusion (combined hyperglycaemic hyperinsulinaemia), there was no change in whole body glucose disposal. However, glucose oxidation during each insulin clamp step was significantly increased and there was a reciprocal decline in non-oxidative glucose disposal by 25-39% (p < 0.01); suppression of hepatic glucose production by insulin was unaltered by chronic hyperglycaemic hyperinsulinaemia. Chronic glucose infusion increased the plasma insulin response to acute hyperglycaemia more than twofold. These results demonstrate that chronic, physiologic hyperinsulinaemia, whether created by exogenous insulin infusion or by stimulation of endogenous insulin secretion, leads to the development of insulin resistance, which is characterized by a specific defect in the non-oxidative (glycogen synthetic) pathway. These findings indicate that hyperinsulinaemia should be considered, not only as a compensatory response to insulin resistance, but also as a self-perpetuating cause of the defect in insulin action.

Topics: Adult; Blood Glucose; Cholesterol; Female; Glucose; Glucose Clamp Technique; Glycogen; Humans; Hyperglycemia; Hyperinsulinism; Insulin; Insulin Resistance; Insulin Secretion; Liver; Male; Triglycerides

Finnish-specific gene variant p.P50T/AKT2 (minor allele frequency (MAF) = 1.1%) is associated with insulin resistance and increased predisposition to type 2 diabetes. Here, we have investigated in vitro the impact of the gene variant on glucose metabolism and intracellular signalling in human primary skeletal muscle cells, which were established from 14 male p.P50T/AKT2 variant carriers and 14 controls. Insulin-stimulated glucose uptake and glucose incorporation into glycogen were detected with 2-[1,2-3H]-deoxy-D-glucose and D-[14C]-glucose, respectively, and the rate of glycolysis was measured with a Seahorse XFe96 analyzer. Insulin signalling was investigated with Western blotting. The binding of variant and control AKT2-PH domains to phosphatidylinositol (3,4,5)-trisphosphate (PI(3,4,5)P3) was assayed using PIP StripsTM Membranes. Protein tyrosine kinase and serine-threonine kinase assays were performed using the PamGene® kinome profiling system. Insulin-stimulated glucose uptake and glycogen synthesis in myotubes in vitro were not significantly affected by the genotype. However, the insulin-stimulated glycolytic rate was impaired in variant myotubes. Western blot analysis showed that insulin-stimulated phosphorylation of AKT-Thr308, AS160-Thr642 and GSK3β-Ser9 was reduced in variant myotubes compared to controls. The binding of variant AKT2-PH domain to PI(3,4,5)P3 was reduced as compared to the control protein. PamGene® kinome profiling revealed multiple differentially phosphorylated kinase substrates, e.g. calmodulin, between the genotypes. Further in silico upstream kinase analysis predicted a large-scale impairment in activities of kinases participating, for example, in intracellular signal transduction, protein translation and cell cycle events. In conclusion, myotubes from p.P50T/AKT2 variant carriers show multiple signalling alterations which may contribute to predisposition to insulin resistance and T2D in the carriers of this signalling variant.

Topics: Diabetes Mellitus, Type 2; Finland; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Male; Muscle Fibers, Skeletal; Muscle, Skeletal; Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction

Topics: Eucommiaceae; Glucose; Glycogen; Glycogen Synthase Kinase 3 beta; Hep G2 Cells; Humans; Insulin; Insulin Resistance; Molecular Docking Simulation; Phosphatidylinositol 3-Kinase; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Quercetin; Serine

Type 2 Diabetes Mellitus (T2DM) is characterized by hepatic insulin resistance, which results in increased glucose production and reduced glycogen storage in the liver. There is no previous study in the literature that has explored the role of Xanthosine in hepatic insulin resistance. Moreover, mechanistic explanation for the beneficial effects of Xanthosine in lowering glucose production in diabetes is yet to be determined. This study for the first time investigated the beneficial effects of Tribulus terrestris (TT) and its active constituent, Xanthosine on gluconeogenesis and glycogenesis in Free Fatty Acid (FFA)-induced CC1 hepatocytes and streptozotocin (STZ)-induced Wistar rats. Xanthosine enhanced glucose uptake and decreased glucose production through phosphorylation of AMP-activated protein kinase (AMPK) and forkhead box transcription factor O1 (FoxO1), and downregulation of two rate limiting enzymes of gluconeogenesis, phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) expression in FFA-induced CC1 cells. Xanthosine also prevented FFA-induced decreases in the phosphorylation of AKT/Protein kinase B, glycogen synthase kinase-3β (GSK3β), and increased glycogen synthase (GS) phosphorylation to increase the glycogen content in the hepatocytes. Moreover, in STZ-induced diabetic rats, oral administration of TT n-butanol fraction (TTBF) enriched with compound Xanthosine (10, 50 & 100 mg/kg body weight) improved insulin sensitivity, reduced fasting blood glucose levels, improved glucose homeostasis by reducing gluconeogenesis via AMPK/FoxO1-mediated PEPCK and G6Pase down-regulation and increasing glycogenesis via AKT/GSK3β-mediated GS activation. Overall, Xanthosine may be developed further for treating insulin resistance and hyperglycemia in T2DM.

Topics: AMP-Activated Protein Kinases; Animals; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Gluconeogenesis; Glucose; Glycogen; Glycogen Synthase Kinase 3 beta; Glycosides; Homeostasis; Insulin Resistance; Liver; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; Xanthines

Sanhuang Xiexin Decoction (SHXXD) is a classic prescription for the treatment of diabetes. Excessive hepatic glucose production (HGP) is a major determinant of the occurrence and development of diabetes. Inhibition of HGP can significantly improve type 2 diabetes mellitus (T2DM).. To investigate the mechanism by which SHXXD inhibits HGP.. First, a mouse model of T2DM was established through high-fat diet (HFD) feeding combined with streptozotocin (STZ) injection to determine the pharmacodynamic effect of SHXXD in T2DM mice. Then, the possible pathways induced by SHXXD in the treatment of T2DM were predicted by network pharmacology combined with transcriptomics (including target prediction, network analysis and enrichment analysis). Finally, the specific mechanism of SHXXD was elucidated by in vitro experiments.. In vivo experiments showed that SHXXD reduced fasting blood glucose and alleviated weight loss in T2DM mice. Improved glucose clearance rates and insulin sensitivity improve dyslipidemia, liver tissue structural abnormalities and inflammatory cell infiltration as well as increase glycogen storage in T2DM mice. The results of network pharmacology and transcriptome analysis showed that SHXXD contained 378 compounds and 2625 targets. In total, 292 intersection targets were identified between the differentially expressed genes (DEGs) of the liver tissue insulin resistance (IR) related dataset GSE23343. KEGG enrichment analysis showed that the insulin/PI3K-Akt/FoxO signaling pathway may be related to SHXXD-mediated improvements in T2DM. In vitro experimental results showed that SHXXD increased glucose consumption by HepG2-IR cells and improved their insulin sensitivity. RT‒qPCR and Western blotting results showed that SHXXD inhibited hepatic gluconeogenesis through the insulin/PI3K-Akt/FoxO signaling pathway by promoting IGFIR, PIK3R1 and AKT2 expression and subsequently inhibiting PEPCK and FBP1 expression via phosphorylation of Foxo1. In addition, PI3K/Akt deactivated p-GSK3β through phosphorylation, thereby promoting GS expression and increasing glycogen synthesis.. SHXXD can target the liver to cooperate with the insulin/PI3K-Akt/FoxO signaling pathway to inhibit HGP to alleviate T2DM.

Topics: Animals; Diabetes Mellitus, Type 2; Glucose; Glycogen; Insulin; Insulin Resistance; Liver; Mice; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Signal Transduction

Triphenyl phosphate (TPHP) is a widely used flame retardant and plasticizer and has been detected extensively in environmental media, wildlife and human bodies. Several epidemiological and animal studies have revealed that TPHP exposure is positively associated with glucose homeostasis disruption and diabetes. However, the effects of TPHP on hepatic glucose homeostasis and the underlying mechanisms remain unclear. The present work aimed to investigate the cytotoxicity and glucose metabolism disruption of TPHP and its metabolite diphenyl phosphate (DPHP) within hepatocytes. The cell viability assay undertaken on human normal liver (L02) cells showed that TPHP exhibited more potent hepatotoxicity than DPHP. RNA sequencing (RNA-seq) data showed that TPHP and DPHP presented different modes of toxic action. Insulin resistance is one of the predominant toxicities for TPHP, but not for DPHP. The insulin-stimulated glucose uptake and glycogen synthesis were impaired by TPHP, while DPHP exhibited no significant impairment on these factors. TPHP exposure induced endoplasmic reticulum (ER) stress, and the ER stress antagonist 4-PBA restored the impairment of insulin-stimulated glucose uptake and glycogen synthesis induced by TPHP. TPHP could also induce liver ER stress and insulin resistance in mice. Taken together, the results suggested that TPHP induces more potent insulin resistance through ER stress than its metabolite DPHP.

Topics: Animals; Endoplasmic Reticulum Stress; Flame Retardants; Glucose; Glycogen; Humans; Insulin Resistance; Insulins; Liver; Mice; Organophosphates; Phosphates

Treatment with tyrosine kinase inhibitors (TKIs), especially nilotinib, often results in hyperglycemia, which may further increase cardiovascular disease risk in patients with chronic myeloid leukemia (CML). The mechanism underlying the TKI-induced glucose dysregulation is not clear. TKIs are suggested to affect insulin secretion but also insulin sensitivity of peripheral tissue has been proposed to play a role in the pathogenesis of TKI-induced hyperglycemia. Here, we aimed to assess whether skeletal muscle glucose uptake and insulin responses are altered in nondiabetic patients with CML receiving TKI treatment. After a glycogen-depleted exercise bout, an intravenous glucose bolus (0.3 g/kg body weight) was administered to monitor 2-h glucose tolerance and insulin response in 14 patients with CML receiving nilotinib, 14 patients with CML receiving imatinib, and 14 non-CML age- and gender-matched controls. A dynamic [

Topics: Blood Glucose; Cardiovascular Diseases; Fluorodeoxyglucose F18; Glucose; Glycogen; Humans; Hyperglycemia; Imatinib Mesylate; Insulin; Insulin Resistance; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Male; Pyrimidines; Tyrosine Kinase Inhibitors

Impaired glucose regulation is one of the most important risk factors for type 2 diabetes mellitus (T2DM) and cardiovascular diseases, which have become a major public health issue worldwide. Dysregulation of carbohydrate metabolism in liver has been shown to play a critical role in the development of glucose intolerance but the molecular mechanism has not yet been fully understood. In this study, we investigated the role of hepatic LCMT1 in the regulation of glucose homeostasis using a liver-specific LCMT1 knockout mouse model. The hepatocyte-specific deletion of LCMT1 significantly upregulated the hepatic glycogen synthesis and glycogen accumulation in liver. We found that the liver-specific knockout of LCMT1 improved high fat diet-induced glucose intolerance and insulin resistance. Consistently, the high fat diet-induced downregulation of glucokinase (GCK) and other important glycogen synthesis genes were reversed in LCMT1 knockout liver. In addition, the expression of GCK was significantly upregulated in MIHA cells treated with siRNA targeting LCMT1 and improved glycogen synthesis. In this study, we provided evidences to support the role of hepatic LCMT1 in the development of glucose intolerance induced by high fat diet and demonstrated that inhibiting LCMT1 could be a novel therapeutic strategy for the treatment of glucose metabolism disorders.

Topics: Animals; Diabetes Mellitus, Type 2; Diet, High-Fat; Glucose; Glucose Intolerance; Glycogen; Insulin Resistance; Leucine; Liver; Methyltransferases; Mice; Protein O-Methyltransferase

As a multifaceted metabolic disorder, insulin resistance is accompanied by the preceding onset of type 2 diabetes mellitus, hyperinsulinemia, metabolic dysfunction-associated fatty liver disease (MAFLD) and other metabolic syndromes. Currently, the number of existing drugs and mechanism-based strategies is limited to alleviate insulin resistance in clinics. As a natural polyphenol product derivative, 1,3,6,7-tetrapropylene acyloxy-ketone (TPX) showed a significant hypoglycemic effect in our previous studies. However, whether TPX could improve hepatic insulin sensitivity was unknown.. To explore whether insulin sensitivity can be improved by the treatment with TPX and further investigate its mechanism(s) of activity.. To mimic hyperglycemia and insulin resistance in vitro, human HepG2 and HL-7702 hepatocytes were exposed to high glucose. Cellular glucose uptake, glucose consumption, glycogen synthesis, and glucose production were quantified after TPX treatment. The effects of TPX on AMP-activated protein kinase (AMPK) phosphorylation, glucose metabolism, and insulin signal transduction were evaluated by western blotting and network pharmacology analysis. The eGFP-membrane of glucose transporter type 4 (GLUT4) lentivirus transfected cells were constructed to investigate the effects of TPX on GLUT4 mobilization. Reactive oxygen species activity in high glucose-induced insulin-resistant cells was measured by DCFH-DA to show oxidative stress.. Treatment with TPX improved glycogen synthesis and inhibited gluconeogenesis by regulating GSK3β, G6Pase, and PEPCK. Furthermore, high glucose-induced inhibition of glucose consumption, glucose uptake, and GLUT4-mediated membrane translocation were reverted by TPX. Accordingly, mechanistic investigations revealed that TPX interacted with AMPK protein and activated the phosphorylation of AKT, thereby improving energy homeostasis and further ameliorating hepatic insulin resistance. Network pharmacology analysis and molecular docking further confirmed AMPK as an active target of TPX. Concordantly, the pharmacological activity of TPX was reversed by the AMPK inhibitor compound C when hepatocytes were exposed to high glucose stimulation.. In summary, our study confirmed TPX contributions to insulin resistance improvements by targeting AMPK and PI3K/AKT to restore the insulin signaling pathway, which may be an important potential treatment strategy for insulin-resistance-related diseases, including MAFLD and diabetes.

Topics: AMP-Activated Protein Kinases; Diabetes Mellitus, Type 2; Glucose; Glycogen; Hepatocytes; Humans; Insulin; Insulin Resistance; Molecular Docking Simulation; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Signal Transduction

Diabetes Mellitus is a metabolic disorder characterized by insulin dysfunction or failure of the pancreatic β-cells to produce insulin resulting in hyperglycemia. Adverse effects of hyperglycemic conditions continue to be common, reducing treatment adherence. Intensified therapies are required for the constant loss of endogenous islet reserve.. This study aimed to evaluate the effect of Nimbin semi-natural analogs (N2, N5, N7, and N8) from A. indica on high glucose-induced ROS and apoptosis with insulin resistance in L6 myotubes evaluated along with Wortmannin and Genistein inhibitors and the expression of key genes in the insulin signalling pathway.. The analogs were screened for anti-oxidant and anti-diabetic activity using cell-free assays; The ability of analogs to suppress ROS and prevent apoptosis induced by High glucose and uptake glucose and glycogen storage in L6 myotubes was evaluated using DCFH-DA, AO-PI and 2NBDG staining. Further, the glucose uptake was performed in the presence of Insulin Receptor Tyrosine Kinase (IRTK) inhibitors, and the expression of key genes PI3K, Glut-4, GS and IRTK in the insulin signalling pathway were evaluated.. The Nimbin analogs were not toxic to the L6 cells, and the analogs could scavenge ROS and suppress cellular damage induced due to high glucose. Enhanced glucose uptake was observed in N2, N5 and N7 compared to N8. The maximum activity of optimum concentration was found to be 100 μM. The N2, N5 and N7 showed an increase in IRTK, which is equivalent to insulin at a concentration of 100 µM. The IRTK inhibitor with Genistein (50 µM) confirmed the presence of IRTK-dependent glucose transport activation; it also supports the expression of key genes PI3K, Glut-4, GS and IRTK. As a result of PI3K activation, N2, N5, and N7 exhibited the insulin-mimetic effect by enhancing glucose uptake and glycogen conversion regulating glucose metabolism.. N2, N5 and N7 could therapeutically benefit against insulin resistance by glucose metabolism modulation, insulin secretion, β-cell stimulation, inhibition of gluconeogenic enzymes and ROS protection.

Topics: Genistein; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Muscle Fibers, Skeletal; Phosphatidylinositol 3-Kinases; Reactive Oxygen Species

Interleukin 6 (IL6) is an multifunctional cytokine that modulates several biological responses, including glucose metabolism. However, its acute effects on hepatic glucose release are still uncertain. The main purpose of this study was to investigate the effects of IL6 on gluconeogenesis from several glucose precursors (alanine, pyruvate and glutamine) and on the suppressive action of insulin on cAMP-stimulated glycogen catabolism in rat liver. IL6 effect on insulin peripheral sensitivity was also evaluated. IL6 was injected intravenously into rats and, 1 h later, gluconeogenesis and glycogenolysis were assessed in liver perfusion and peripheral insulin sensitivity by insulin tolerance test (ITT). IL6 intravenous injection increased hepatic glucose production from alanine, without changing pyruvate, lactate and urea production. IL6 injection also increased hepatic glucose production from pyruvate and glutamine. In addition, IL6 decreased the suppressive effect of insulin on cAMP-stimulated glucose and lactate production and glycogenolysis, without affecting pyruvate production. Furthermore, IL6 reduced the plasma glucose disappearance constant (kITT), an indicator of insulin resistance. In conclusion, IL6 acutely increased hepatic glucose release (gluconeogenesis and glycogenolysis) by a mechanism that likely involved the induction of insulin resistance in the liver, as evidenced by the reduced suppressive effect of insulin on cAMP-stimulated glycogen catabolism. In consistency, IL6 acutely induced peripheral insulin resistance.

Topics: Alanine; Animals; Blood Glucose; Gluconeogenesis; Glucose; Glutamine; Glycogen; Glycogenolysis; Insulin; Insulin Resistance; Interleukin-6; Lactic Acid; Liver; Pyruvates; Rats

Objectives: manganese (Mn) is closely related to type 2 diabetes mellitus and insulin resistance (IR), but the exact mechanism is unclear. This study aimed to explore the regulatory effects and mechanism of Mn on IR using hepatocyte IR model induced by high palmitate (PA), high glucose (HG) or insulin. Methods: HepG2 cells were exposed to PA (200 μM), HG (25 mM) or insulin (100 nM) respectively, alone or with 5 μM Mn for 24 hours. The expression of key proteins in insulin signaling pathway, intracellular glycogen content and glucose accumulation, reactive oxygen species (ROS) level and Mn superoxide dismutase (MnSOD) activity were detected. Results: compared with control group, the expression of phosphorylated protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β) and forkhead box O1 (FOXO1) in the three IR groups was declined, and this decrease was reversed by Mn. The reduction of intracellular glycogen content and increase in glucose accumulation in IR groups were also inhibited by Mn. Additionally, the production of ROS was increased in IR models, compared with normal control group, while Mn reduced the excessive production of ROS induced by PA, HG or insulin. However, Mn did not alter the activity of MnSOD in the three IR models. Conclusion: this study demonstrated that Mn treatment can improve IR in hepatocytes. The mechanism is probably by reducing the level of intracellular oxidative stress, enhancing the activity of Akt/GSK-3β/FOXO1 signal pathway, promoting glycogen synthesis, and inhibiting gluconeogenesis.. Objetivos: el manganeso (Mn) está estrechamente relacionado con la diabetes mellitus tipo 2 y la resistencia a la insulina (RI), pero el mecanismo exacto aún no está claro. Este estudio tuvo como objetivo explorar los efectos reguladores y el mecanismo del Mn sobre la RI utilizando un modelo de RI en hepatocitos inducido por palmitato alto (PA), glucosa alta (HG) o insulina. Métodos: las células HepG2 se expusieron a PA (200 μM), HG (25 mM) o insulina (100 nM), solas o junto con 5 μM de Mn durante 24 horas. Se evaluó la expresión de proteínas clave en la vía de señalización de la insulina, el contenido intracelular de glucógeno y la acumulación de glucosa, el nivel de especies reactivas de oxígeno (ROS) y la actividad superóxido dismutasa del manganeso (MnSOD). Resultados: en comparación con el grupo de control, la expresión de proteína quinasa B fosforilada (Akt), la glucógeno sintasa quinasa-3β (GSK-3β) y la proteína forkhead box O1 (FOXO1) en los tres grupos de RI se redujo, y esta disminución fue revertida por el Mn. La reducción del contenido de glucógeno intracelular y el aumento de la acumulación de glucosa en los grupos de RI también fueron inhibidos por el Mn. Además, la producción de ROS aumentó en los modelos de RI en comparación con el grupo de control normal. Mientras que el Mn redujo la producción excesiva de ROS inducida por PA, HG o insulina. Sin embargo, el Mn no alteró la actividad de la MnSOD en los tres modelos de RI. Conclusión: este estudio demostró que el tratamiento con Mn puede mejorar la RI en hepatocitos. El mecanismo probablemente sea mediante la reducción del nivel de estrés oxidativo intracelular, mejorando la actividad de la vía de señalización Akt/GSK-3β/FOXO1, promoviendo la síntesis de glucógeno e inhibiendo la gluconeogénesis.

Topics: Diabetes Mellitus, Type 2; Glucose; Glycogen; Glycogen Synthase Kinase 3 beta; Hepatocytes; Humans; Insulin; Insulin Resistance; Manganese; Proto-Oncogene Proteins c-akt; Reactive Oxygen Species

Diabetes is one of the major global public health problems. Our previous results found that oat β-D-glucan exhibited ameliorative effects on diabetic mice, but the underlying mechanism is unclear. The present study indicates that oat β-D-glucan increased glycogen content, decreased glycogen synthase (GS) phosphorylation and increased hepatic glycogen synthase kinase 3β (GSK3β) phosphorylation for glycogen synthesis via PI3K/AKT/GSK3-mediated GS activation. Moreover, oat β-D-glucan inhibited gluconeogenesis through the PI3K/AKT/Foxo1-mediated phosphoenolpyruvate carboxykinase (PEPCK) decrease. In addition, oat β-D-glucan enhanced glucose catabolism through elevated protein levels of COQ9, UQCRC2, COXIV and ATP5F complexes involved in oxidative phosphorylation, as well as that of TFAM, a key regulator of mitochondrial gene expression. Importantly, our results showed that oat β-D-glucan maintained hepatic glucose balance via TLR4-mediated intracellular signal. After TLR4 blocking with anti-TLR4 antibody, oat β-D-glucan had almost no effect on high glucose-induced HepG2 cells. These data revealed that oat β-D-glucan maintains glucose balance by regulating the TLR4/PI3K/AKT signal pathway.

Topics: Animals; Avena; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Glucans; Glucose; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Insulin Resistance; Mice; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Toll-Like Receptor 4

Gestational diabetes mellitus (GDM) increases the risks of maternal, placental, and neonatal complications. Previously, we found that a diet enriched in extra virgin olive oil (EVOO) prevents increased maternal triglyceridemia and placental proinflammatory markers in a cohort of GDM patients. The aim of this work was to evaluate maternal circulating markers of insulin resistance, placental collagen, glycogen and lipid levels, and placental levels of proteins, mRNAs, and a microRNA involved in the endocytic pathway in the same cohort of control women and women with GDM who received or did not receive a diet enriched in EVOO (36 g/day) from weeks 24 to 28 of pregnancy until term.. At term, the TG/HDL cholesterol ratio, fatty acid binding protein 4 circulating levels, and maternal BMI were increased in the GDM patients, alterations prevented by the maternal diet enriched in EVOO. Although there were no changes in placental lipid levels and lipid profile, GDM placentas were thicker than controls and showed increased glycogen and collagen content, alterations prevented by the EVOO enriched diet. GDM placentas showed increases in megalin levels, in the expression of several genes involved in the endocytic pathway, and in miR-199, which targets these genes, alterations prevented by the maternal diet enriched in EVOO.. We identified novel beneficial effects of an EVOO-enriched diet in GDM women, a diet capable of regulating maternal insulin resistance, the structure and metabolism of the placenta, and the placental endocytic pathway, suggesting effects that may be beneficial for fetal development.

Topics: Diabetes, Gestational; Diet; Dietary Fats, Unsaturated; Female; Glycogen; Humans; Infant, Newborn; Insulin Resistance; Olea; Olive Oil; Placenta; Pregnancy

Obesity is linked to reduced fertility in various species, from Drosophila to humans. Considering that obesity is often induced by changes in diet or eating behavior, it remains unclear whether obesity, diet, or both reduce fertility. Here, we show that Drosophila females on a high-sugar diet become rapidly obese and less fertile as a result of increased death of early germline cysts and vitellogenic egg chambers (or follicles). They also have high glycogen, glucose and trehalose levels and develop insulin resistance in their fat bodies (but not ovaries). By contrast, females with adipocyte-specific knockdown of the anti-obesity genes brummer or adipose are obese but have normal fertility. Remarkably, females on a high-sugar diet supplemented with a separate source of water have mostly normal fertility and glucose levels, despite persistent obesity, high glycogen and trehalose levels, and fat body insulin resistance. These findings demonstrate that a high-sugar diet affects specific processes in oogenesis independently of insulin resistance, that high glucose levels correlate with reduced fertility on a high-sugar diet, and that obesity alone does not impair fertility.

Topics: Animals; Diet; Drosophila; Drosophila melanogaster; Female; Fertility; Glucose; Glycogen; Humans; Insulin Resistance; Obesity; Trehalose

Evidence has demonstrated that oxidative stress plays a crucial role in regulating cellular glucose metabolism. In previous studies, wheat germ peptide (WGP) was found to effectively mitigate oxidative stress induced by high glucose. Based on the information provided, we hypothesized that WGP could exhibit antihyperglycemic and anti-insulin-resistant effects in cells. The insulin-resistant cell model was established by insulin stimulation. The glucose consumption, glycogen content, and the activities of hexokinase and pyruvate kinase following WGP treatment were measured. The protein expression of SOCS3, phosphorylated insulin receptor substrate-1 (p-IRS1), IRS1, phosphorylated protein kinase B (p-Akt), Akt, glucose transporter 2 (GLUT2), phosphorylated GSK 3β, GSK 3β, FOXO1, G6P, and phosphoenolpyruvate carboxykinase were assessed by western blot analysis. Our results demonstrated that WGP treatment increased cellular glucose consumption and glycogen synthesis and enhanced hexokinase and pyruvate kinase activities. Additionally, WGP treatment was observed to cause a significant reduction in the expression of SOCS3, FOXO1, G6P, and phosphoenolpyruvate carboxykinase, as well as in the ratio of p-IRS1/IRS1. Conversely, the expression of GLUT2 and the ratios of p-Akt/Akt and p-GSK3β/GSK3β were upregulated by WGP. These findings suggested that WGP can activate the SOCS3/IRS1/Akt signaling pathway, thus promoting the phosphorylation of GSK-3β and increasing the expression of FOXO1 and GLUT2, which contribute to enhancing glycogen synthesis, inhibiting gluconeogenesis, and promoting glucose transport in insulin-resistant HepG2 cells.

Topics: Glucose; Glycogen; Glycogen Synthase Kinase 3 beta; Hepatocytes; Hexokinase; Humans; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Phosphoenolpyruvate; Proto-Oncogene Proteins c-akt; Pyruvate Kinase; Suppressor of Cytokine Signaling 3 Protein; Triticum

Cadmium is a nonessential transition metal considered one of the more hazardous environmental contaminants. The population is chronically exposed to this metal at low concentrations, designated as the LOAEL (lowest observable adverse effect level) dose. We aimed to investigate whether oral subacute exposure to cadmium LOAEL disrupts hormonal and metabolic effects of the liver-adipose axis in Wistar rats. Fifty male Wistar rats were separated into two groups: control (standard normocalorie diet + water free of cadmium) and cadmium (standard normocalorie diet + drinking water with 32.5 ppm CdCl

Topics: Adipose Tissue; Animals; Cadmium; Glycogen; Inflammation; Insulin; Insulin Resistance; Liver; Male; Rats; Rats, Wistar; Sterol Regulatory Element Binding Protein 1; Triglycerides

In this study, a novel peptide GPPGPA was screened from the collagen hydrolysates of Chinese giant salamander (

Topics: alpha-Glucosidases; Animals; Collagen; Diabetes Mellitus, Type 2; Glucose; Glycogen; Glycoside Hydrolase Inhibitors; Hep G2 Cells; Humans; Hypoglycemic Agents; Insulin Resistance; Kinetics; Malondialdehyde; Molecular Docking Simulation; Network Pharmacology; Oxidative Stress; Peptide Fragments; Protein Hydrolysates; Skin; Superoxide Dismutase; Urodela

Interleukin-6 (IL-6) influences both inflammatory response and anti-inflammatory processes. This cytokine can be released by exercising skeletal muscle, which characterizes it as a myokine. Unlike what is observed in inflammation, IL-6 produced by skeletal muscle is not preceded by the release of other pro-inflammatory cytokines, but it seems to be dependent on the lactate produced during exercise, thus causing different effects from those seen in inflammatory state. After binding to its receptor, myokine IL-6 activates the PI3K-Akt pathway. One consequence of this upregulation is the potentiation of insulin signaling, which enhances insulin sensitivity. IL-6 increases GLUT-4 vesicle mobilization to the muscle cell periphery, increasing the glucose transport into the cell, and also glycogen synthesis. Muscle glycogen provides energy for ATP resynthesis, and regulates Ca2+ release by the sarcoplasmic reticulum, influencing muscle contraction, and, hence, muscle function by multiple pathways. Another implication for the upregulation of the PI3K-Akt pathway is the activation of mTORC1, which regulates mRNA translational efficiency by regulating translation machinery, and translational capacity by inducing ribosomal biogenesis. Thus, IL-6 may contribute to skeletal muscle hypertrophy and function by increasing contractile protein synthesis.

Topics: Adenosine Triphosphate; Anti-Inflammatory Agents; Calcium; Contractile Proteins; Cytokines; Glucose; Glucose Transporter Type 4; Glycogen; Humans; Hypertrophy; Insulin; Insulin Resistance; Interleukin-6; Lactates; Mechanistic Target of Rapamycin Complex 1; Muscle, Skeletal; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; RNA, Messenger

Conventional in vitro study often involves the destruction of the cells followed by purification and dilution steps before applying enzymatic assay or metabolomic analysis. It is a costly and laborious process, and it cannot monitor changes as a function of time. Recently, we have developed a new label-free live-cell FTIR approach that can directly measure biochemical compositional changes within living cells in situ and the spectral changes are shown to be highly specific to the drug applied. In this work, we have demonstrated for the first time the effect of two anti-diabetic drugs, metformin and Resveratrol, on insulin-resistant liver cells (HepG2). Using live-cell FTIR with principal component analysis, we have shown the differences in the biochemical profiles between normal and insulin-resistant cells (p < 0.05), the lack of response/difference from the insulin-resistant cell to insulin (p > 0.05) and the restoration of the biochemical profile and sensitivity to insulin from the insulin-resistant cells after the drug treatment (p < 0.05). Particularly, a rise in the glycogen level, marked by three distinctive peaks at 1150, 1080 and 1020 cm

Topics: Biosensing Techniques; Glycogen; Humans; Insulin; Insulin Resistance; Metformin; Resveratrol; Spectroscopy, Fourier Transform Infrared

Starch binding domain-containing protein 1 (STBD1) is an endoplasmic reticulum (ER)-resident, glycogen-binding protein. In addition to glycogen, STBD1 has been shown to interact with several proteins implicated in glycogen synthesis and degradation, yet its function in glycogen metabolism remains largely unknown. In addition to the bulk of the ER, STBD1 has been reported to localize at regions of physical contact between mitochondria and the ER, known as Mitochondria-ER Contact sites (MERCs). Given the emerging correlation between distortions in the integrity of hepatic MERCs and insulin resistance, our study aimed to delineate the role of STBD1 in vivo by addressing potential abnormalities in glucose metabolism and ER-mitochondria communication associated with insulin resistance in mice with targeted inactivation of Stbd1 (Stbd1KO). We show that Stbd1KO mice at the age of 24 weeks displayed reduced hepatic glycogen content and aberrant control of glucose homeostasis, compatible with insulin resistance. In line with the above, Stbd1-deficient mice presented with increased fasting blood glucose and insulin levels, attenuated activation of insulin signaling in the liver and skeletal muscle and elevated liver sphingomyelin content, in the absence of hepatic steatosis. Furthermore, Stbd1KO mice were found to exhibit enhanced ER-mitochondria association and increased mitochondrial fragmentation in the liver. Nevertheless, the enzymatic activity of hepatic respiratory chain complexes and ER stress levels in the liver were not altered. Our findings identify a novel important role for STBD1 in the control of glucose metabolism, associated with the integrity of hepatic MERCs.

Topics: Animals; Endoplasmic Reticulum; Endoplasmic Reticulum Stress; Glucose; Glycogen; Insulin; Insulin Resistance; Liver; Mice; Mitochondria

This study aims to investigate the metabolic phenotype and mechanism of 40% calorie restriction (CR) in mice.. CR mice exhibit super-stable blood glucose, as evidenced by increased fasting blood glucose (FBG), decreased postprandial blood glucose, and reduced glucose fluctuations. Additionally, both fasting plasma insulin and the homeostasis model assessment of insulin resistance increase significantly in CR mice. Compared with control, the phosphorylation of insulin receptor substrates-1 and serine/threonine kinase decreases in liver and fat but increases in muscle of CR mice after insulin administration, indicating hepatic and adipose insulin resistance, and muscle insulin sensitization. CR reduces visceral fat much more than subcutaneous fat. The elevated FBG is negatively correlated with low-level fasting β-hydroxybutyrate, which may result from insufficient free fatty acids and diminishes ketogenic ability in CR mice. Furthermore, liver glycogen increases dramatically in CR mice. Analysis of glycogen metabolism related proteins indicates active glycogen synthesis and decomposition. Additionally, CR elevates plasma corticosterone and hypothalamic orexigenic gene expression.. CR induces lipid insufficiency and stress, resulting in global physiological insulin resistance except muscle and enhances glycogen metabolism, culminating in the stability of blood glucose manifests in increased FBG, which compensates for insufficient blood ketones.

Topics: 3-Hydroxybutyric Acid; Animals; Blood Glucose; Caloric Restriction; Corticosterone; Fatty Acids, Nonesterified; Glycogen; Insulin; Insulin Resistance; Lipid Metabolism; Liver; Liver Glycogen; Mice; Protein Serine-Threonine Kinases; Receptor, Insulin; Serine

Recurrent hypoglycemia (RH) impairs secretion of counterregulatory hormones. Whether and how RH affects responses within metabolically important peripheral organs to counterregulatory hormones are poorly understood.. To study the effects of RH on metabolic pathways associated with glucose counterregulation within liver, white adipose tissue and skeletal muscle.. Using a widely adopted rodent model of 3-day recurrent hypoglycemia, we first checked expression of counterregulatory hormone G-protein coupled receptors (GPCRs), their inhibitory regulators and downstream enzymes catalyzing glycogen metabolism, gluconeogenesis and lipolysis by qPCR and western blot. Then, we examined epinephrine-induced phosphorylation of PKA substrates to validate adrenergic sensitivity in each organ. Next, we measured hepatic and skeletal glycogen content, degree of breakdown by epinephrine and abundance of phosphorylated glycogen phosphorylase under hypoglycemia and that of phosphorylated glycogen synthase during recovery to evaluate glycogen turnover. Further, we performed pyruvate and lactate tolerance tests to assess gluconeogenesis. Additionally, we measured circulating FFA and glycerol to check lipolysis. The abovementioned studies were repeated in streptozotocin-induced diabetic rat model. Finally, we conducted epinephrine tolerance test to investigate systemic glycemic excursions to counterregulatory hormones. Saline-injected rats served as controls.. RH increased counterregulatory hormone GPCR signaling in liver and epidydimal white adipose tissue (eWAT), but not in skeletal muscle. For glycogen metabolism, RH did not affect total content or epinephrine-stimulated breakdown in liver and skeletal muscle. Although RH decreased expression of phosphorylated glycogen synthase 2, it did not affect hepatic glycogen biosynthesis during recovery from hypoglycemia or after fasting-refeeding. For gluconeogenesis, RH upregulated fructose 1,6-bisphosphatase 1 and monocarboxylic acid transporter 1 that imports lactate as precursor, resulting in a lower blood lactate profile during hypoglycemia. In agreement, RH elevated fasting blood glucose and caused higher glycemic excursions during pyruvate tolerance test. For lipolysis, RH did not affect circulating levels of FFA and glycerol after overnight fasting or upon epinephrine stimulation. Interestingly, RH upregulated the trophic fatty acid transporter FATP1 and glucose transporter GLUT4 to increase lipogenesis in eWAT. These aforementioned changes of gluconeogenesis, lipolysis and lipogenesis were validated in streptozotocin-diabetic rats. Finally, RH increased insulin sensitivity to accelerate glucose disposal, which was attributable to upregulated visceral adipose GLUT4.. RH caused metabolic adaptations related to counterregulation within peripheral organs. Specifically, adrenergic signaling was enhanced in liver and visceral fat, but not in skeletal muscle. Glycogen metabolism remained unchanged. Hepatic gluconeogenesis was augmented. Systemic lipolysis was unaffected, but visceral lipogenesis was enhanced. Insulin sensitivity was increased. These findings provided insights into mechanisms underlying clinical problems associated with intensive insulin therapy, such as high gluconeogenic flux and body weight gain.

Topics: Adrenergic Agents; Animals; Blood Glucose; Diabetes Mellitus, Experimental; Epinephrine; Fatty Acids; Fructose; Gluconeogenesis; Glucose; Glucose Transport Proteins, Facilitative; Glycerol; Glycogen; Glycogen Synthase; Hypoglycemia; Insulin; Insulin Resistance; Lactates; Lipolysis; Liver; Liver Glycogen; Monocarboxylic Acid Transporters; Pyruvates; Rats; Streptozocin

Topics: Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase Kinase 3; Humans; I-kappa B Kinase; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Isoflavones; JNK Mitogen-Activated Protein Kinases; Muscle Fibers, Skeletal; Muscle, Skeletal; Palmitates; Phosphatidylinositol 3-Kinase; Phosphatidylinositol 3-Kinases; Phosphorylation; Portulaca; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Proto-Oncogene Proteins c-akt; Serine; Tyrosine

Obesity causes progressive lipid accumulation and insulin resistance within muscle cells and affects skeletal muscle fibres and muscle mass that demonstrates atrophy and dysfunction. This study investigated the effects of naringin on the metabolic processes of skeletal muscle in obese rats. Male Sprague Dawley rats were divided into five groups: the control group with normal diet and the obese groups, which were induced with a high-fat diet (HFD) for the first 4 weeks and then treated with 40 mg/kg of simvastatin and 50 and 100 mg/kg of naringin from week 4 to 8. The naringin-treated group showed reduced body weight, biochemical parameters, and the mRNA expressions of protein degradation. Moreover, increased levels of antioxidant enzymes, glycogen, glucose uptake, the expression of the insulin receptor substrate 1 (IRS-1), the glucose transporter type 4 (GLUT4), and the mRNA expressions of protein synthesis led to improved muscle mass in the naringin-treated groups. The in vitro part showed the inhibitory effects of naringin on digestive enzymes related to lipid and glucose homeostasis. This study demonstrates the potential benefits of naringin as a supplement for treating muscle abnormalities in obese rats by modulating the antioxidative status, regulating protein metabolism, and improved insulin resistance in skeletal muscle of HFD-induced insulin resistance in obese rats.

Topics: Animals; Antioxidants; Diet, High-Fat; Flavanones; Glucose; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Male; Muscle, Skeletal; Muscular Atrophy; Obesity; Rats; Rats, Sprague-Dawley; RNA, Messenger; Simvastatin

Topics: alpha-Glucosidases; Antioxidants; Arabinose; Cellulase; Fucose; Galactose; Glucose; Glucuronic Acid; Glycogen; Hep G2 Cells; Humans; Hypoglycemic Agents; Insulin Resistance; Insulins; Mannose; Moringa oleifera; Polysaccharides; Powders; Reactive Oxygen Species; Rhamnose; Superoxide Dismutase; Superoxides; Ultrasonics; Xylose

This study investigated whether (E)-5-hydroxy-7-methoxy-3-(2'-hydroxybenzyl)-4-chromanone (HM-chromanone) could counteract the high glucose level-induced blockade of insulin signaling in human HepG2 cells. Cells were pre-incubated with glucose (5.5 or 33 mM) and then incubated with a medium containing various concentrations of HM-chromanone. Assays for glucose uptake, glycogen synthesis, and glucose production were performed. Western blotting helped elucidate the underlying molecular mechanisms. High glucose concentration (33 mM) significantly increased p-IRS-1

Topics: AMP-Activated Protein Kinases; Glucose; Glycogen; Hep G2 Cells; Humans; Insulin; Insulin Resistance; Phosphorylation; Proto-Oncogene Proteins c-akt; RNA, Small Interfering

Type 2 diabetes mellitus (T2DM) is a systemic metabolic disorder characterized by insulin deficiency and insulin resistance. Recently, it has become a significant threat to public health.

Topics: Animals; Blood Glucose; Cholesterol; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Glycogen; Glycogen Synthase Kinase 3 beta; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Mice; Polygonatum

During the first weeks of postnatal heart development, cardiomyocytes undergo a major adaptive metabolic shift from glycolytic energy production to fatty acid oxidation. This metabolic change is contemporaneous to the up-regulation and activation of the p38γ and p38δ stress-activated protein kinases in the heart. We demonstrate that p38γ/δ contribute to the early postnatal cardiac metabolic switch through inhibitory phosphorylation of glycogen synthase 1 (GYS1) and glycogen metabolism inactivation. Premature induction of p38γ/δ activation in cardiomyocytes of newborn mice results in an early GYS1 phosphorylation and inhibition of cardiac glycogen production, triggering an early metabolic shift that induces a deficit in cardiomyocyte fuel supply, leading to whole-body metabolic deregulation and maladaptive cardiac pathogenesis. Notably, the adverse effects of forced premature cardiac p38γ/δ activation in neonate mice are prevented by maternal diet supplementation of fatty acids during pregnancy and lactation. These results suggest that diet interventions have a potential for treating human cardiac genetic diseases that affect heart metabolism.

Topics: Animals; Animals, Newborn; Cardiomegaly; Diet, High-Fat; Enzyme Activation; Feeding Behavior; Female; Gene Deletion; Glucose Intolerance; Glycogen; Glycogen Synthase; Glycogen Synthase Kinase 3; Insulin Resistance; Lipid Metabolism; MAP Kinase Signaling System; Mice, Inbred C57BL; Mitogen-Activated Protein Kinase 12; Mitogen-Activated Protein Kinase 13; Myocardium; Myocytes, Cardiac; Organ Specificity; Phosphorylation

This study investigated the role of GABA in attenuating liver insulin resistance (IR) in type 2 diabetes parents and reducing its risk in their descendants' liver. Both sexes' rats were divided into four groups of non-diabetic control, diabetic control (DC), GABA-treated (GABA), and insulin-treated (Ins). The study duration lasted for six months and the young animals followed for four months. Consequently, hyperinsulinemic-euglycemic clamp was performed for all animals. Apart from insulin tolerance test (ITT), serum and liver lipid profile were measured in all groups. Glycogen levels, expression of Foxo1, Irs2, Akt2, and Pepck genes in the liver were assessed for all groups. Overall, GABA improved ITT, increased liver glycogen levels and decreased lipid profile, blood glucose level, and HbA1c in parents and their offspring in compared to the DC group. GIR also increased in both parents and their offspring by GABA. Moreover, the expression of Foxo1, Irs2, Akt2, and Pepck genes improved in GABA-treated parents and their descendants in compared to DC group. Results indicated that GABA reduced liver IR in both parents and their offspring via affecting their liver insulin signaling and gluconeogenesis pathways.

Topics: Animals; Blood Glucose; Body Weight; Diabetes Mellitus, Experimental; Endocrinology; Female; gamma-Aminobutyric Acid; Gluconeogenesis; Glucose; Glucose Clamp Technique; Glucose Tolerance Test; Glycogen; Hyperinsulinism; Insulin; Insulin Resistance; Liver; Male; Rats; Rats, Wistar; Signal Transduction

Topics: Angiotensin II; Apoptosis; bcl-2-Associated X Protein; Calreticulin; Cell Survival; Enzyme-Linked Immunosorbent Assay; Gene Silencing; Glucose; Glycogen; Human Umbilical Vein Endothelial Cells; Humans; Insulin; Insulin Resistance; Proto-Oncogene Proteins c-bcl-2

Environmental exposure to arsenic can cause a variety of health problems. Epidemiological and experimental studies have established a diabetogenic role for arsenic, but the mechanisms responsible for arsenic-induced impairment of insulin action are unclear. MicroRNAs (miRNAs) are involved in various metabolic disorders, particularly in the development of insulin resistance. The present study investigated whether arsenite, an active form of arsenic, induces hepatic insulin resistance and the mechanisms underlying it. After male C57BL/6J mice were exposed to arsenite (0 or 20 ppm) in drinking water for 12 months, intraperitoneal glucose tolerance tests (IPGTTs) and insulin tolerance tests (ITTs) revealed an arsenite-induced glucose metabolism disorder. Hepatic glycogen levels were lower in arsenite-exposed mice. Further, for livers of mice exposed to arsenite, miR-191 levels were higher, and protein levels of insulin receptor substrate 1 (IRS1), p-IRS1, and phospho-protein kinase B (p-AKT) were lower. Further, glucose transporter 4 (GLUT4) had lower levels on the plasma membrane. For insulin-treated L-02 cells, arsenite decreased glucose consumption and glycogen levels, increased miR-191 levels, and inhibited the IRS1/AKT pathway and the translocation of GLUT4 from the cytoplasm to the plasma membrane. For insulin-treated L-02 cells, the decreases of glucose consumption, glycogen levels, GLUT4 on the plasma membrane, and p-AKT levels induced by arsenite were reversed by SC79 (agonist of AKT) and an miR-191 inhibitor; these effects caused by miR-191 inhibitor were restored by IRS1 siRNA. In insulin-treated L-02 cells, miR-191, via IRS1, was involved in the arsenite-induced decreases of glucose consumption and glycogen levels and in inhibition of the translocation of GLUT4. Thus, miR-191 blocking the translocation of GLUT4 was involved in arsenite-induced hepatic insulin resistance through inhibiting the IRS1/AKT pathway. Our study reveals a mechanism for arsenite-induced hepatic insulin resistance, which provides clues for discovering biomarkers for the development of type 2 diabetes and for prevention and treatment of arsenic poisoning.

Topics: Animals; Arsenites; Diabetes Mellitus, Type 2; Glucose; Glucose Transporter Type 4; Glycogen; Insulin Receptor Substrate Proteins; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; MicroRNAs; Proto-Oncogene Proteins c-akt; Signal Transduction

A fucosylated chondroitin sulfate was isolated from the body wall of sea cucumber Stichopus japonicus (FCSsj), whose structure was characterized by NMR spectroscopy and HILIC-FTMS. At the ratio of 1.00:0.26:0.65, three fucosyl residues were found: 2,4-disulfated-fucose (Fuc2,4S), 4-sulfated-fucose (Fuc4S) and 3,4-disulfated-fucose (Fuc3,4S), which were only linked to the O-3 of glucuronic acid residues (GlcA). Besides mono-fucosyl moieties, di-fucosyl branches, namely Fuc2,4Sα(1→3)Fuc4S, were also found to be attached to the O-3 of GlcA. The antidiabetic activity of FCSsj was evaluated using glucosamine induced insulin resistant (IR) Hep G2 cells in vitro. It was found that FCSsj significantly promoted the glucose uptake and glucose consumption of IR-Hep G2 cells in a dose-dependent manner, and could alleviate the cell damage. Furthermore, FCSsj could promote the glycogen synthesis in the glucosamine-induced IR-Hep G2 cells. These results provided a supplement for studying the antidiabetic activity of FCSsj.

Topics: Animals; Chondroitin Sulfates; Fucose; Glucose; Glucuronic Acid; Glycogen; Hep G2 Cells; Humans; Hypoglycemic Agents; Insulin Resistance; Magnetic Resonance Spectroscopy; Sea Cucumbers; Stichopus

Plant-derived phytochemicals such as flavonoids have been explored to be powerful antioxidants that protect against oxidative stress-related diseases. In the present study, Morin, a flavonoid compound was studied for its antioxidant and antidiabetic properties in relation to oxidative stress in insulin resistant models conducted in rat skeletal muscle L6 cell line model.. Evaluation of antioxidant property of morin was assayed using in vitro methods such as cell viability by MTT assay, estimation of SOD and CAT activity and NO scavenging activity. The anti-oxidative nature of morin on L6 cell line was conducted by the DCF-DA fluorescent activity. Glucose uptake in morin treated L6 myotubes are accessed by 2-NBDG assay in the presence or absence of IRTK and PI3K inhibitors. Further glycogen content estimation due to the morin treatment in L6 myotubes was performed. Antioxidant and insulin signaling pathway gene expression was examined over RT-PCR analysis.. Morin has a negligible cytotoxic effect at doses of 20, 40, 60, 80, and 100 µM concentration according to cell viability assay. Morin revealed that the levels of the antioxidant enzymes SOD and CAT in L6 myotubes had increased. When the cells were subjected to the nitro blue tetrazolium assay, morin lowered reactive oxygen species (ROS) formation at 60 µM concentration displaying 39% ROS generation in oxidative stress condition. Lesser NO activity and a drop in green fluorescence emission in the DCFDA assay, demonstrating its anti-oxidative nature by reducing ROS formation in vitro. Glucose uptake by the L6 myotube cells using 2-NBDG, and with IRTK and PI3K inhibitors (genistein and wortmannin) showed a significant increase in glucose uptake by the cells which shows the up regulated GLUT-4 movement from intracellular pool to the plasma membrane. Morin (60 µM) significantly enhanced the expression of antioxidant genes GPx, GST and GCS as well as insulin signalling genes IRTK, IRS-1, PI3K, GLUT-4, GSK-3β and GS in L6 myotubes treated cells.. Morin has the ability to act as an anti-oxidant by lowering ROS levels and demonstrating insulin mimetic activity by reversing insulin resistance associated with oxidative stress.

Topics: Animals; Antioxidants; Cell Line; Cell Survival; Flavonoids; Glucose; Glycogen; Glycogen Synthase Kinase 3 beta; Hypoglycemic Agents; Insulin; Insulin Resistance; Muscle Fibers, Skeletal; Muscle, Skeletal; Myoblasts; Oxidative Stress; Phosphatidylinositol 3-Kinases; Rats; Reactive Oxygen Species; Signal Transduction

Spexin (SPX) is a 14 aa peptide discovered in 2007 using bioinformatics methods. SPX inhibits food intake and regulates lipid, and carbohydrate metabolism. Here, we evaluate the ability of SPX at improving metabolic control and liver function in obese and type 2 diabetic animals. The effects of 30 days SPX treatment of mice with experimentally induced obesity (DIO) or type 2 diabetes (T2DM) on serum glucose and lipid levels, insulin sensitivity and hormonal profile (insulin, glucagon, adiponectin, leptin, TNF alpha, IL-6 and IL-1β) are characterized. In addition, alterations of hepatic lipid and glycogen contents are evaluated. We report that SPX decreases body weight in healthy and DIO mice, and reduces lipid content in all three animal groups. SPX improves insulin sensitivity in DIO and T2DM animals. In addition, SPX modulates hormonal and metabolic profile by regulating the concentration of adiponectin (concentration increase) and leptin (concentration decrease) in the serum blood of DIO and T2DM mice. Lastly, SPX decreases lipid content as well as IL-6 and TNF-α protein levels in liver of DIO and T2DM mice, and reduces IL-6 and TNF-alpha concentrations in the serum derived from T2DM mice. Based on our results, we conclude that SPX could be involved in the development of obesity and type 2 diabetes mellitus and it can be further evaluated as a potential target for therapy of DIO and T2DM.

Topics: Animals; Blood Glucose; Body Weight; Diabetes Mellitus, Type 2; Diet, High-Fat; Disease Models, Animal; Female; Glycogen; Insulin Resistance; Lipid Metabolism; Lipids; Liver Function Tests; Mice; Obesity; Peptide Hormones

There are endocrine and immunological changes that occur during onset and progression of the overweight and obese states. The inhibitor of nuclear factor-κB kinase-ε (IKKε) was originally described as an inducible protein kinase; whole body gene deletion or systemic pharmaceutical targeting of this kinase improved insulin sensitivity and glucose tolerance in mice. To investigate the primary sites of action associated with IKKε during weight gain, we describe the first mouse line with conditional elimination of IKKε in the liver (IKKε

Topics: Animals; Blood Glucose; Diet, Fat-Restricted; Diet, High-Fat; Glucose Tolerance Test; Glycerides; Glycogen; I-kappa B Kinase; Insulin Resistance; Lipid Metabolism; Liver; Mice; Mice, Knockout; Obesity; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction

Pandemic vitamin D deficiency is associated with insulin resistance and type 2 diabetes. Vitamin D supplementation has been reported to have improved glucose homeostasis. However, its mechanism to improve insulin sensitivity remains unclear.. Male C57BL/6J mice are fed with/without vitamin D control (CD) or Western (WD) diets for 15 weeks. The vitamin-D-deficient lean (CDVDD) and obese (WDVDD) mice are further subdivided into two groups. One group is re-supplemented with vitamin D for 6 weeks and hepatic insulin signaling is examined. Both CD and WD mice with vitamin D deficiency developed insulin resistance. Vitamin D supplementation in CDVDD mice significantly improved insulin sensitivity, hepatic inflammation, and antioxidative capacity. The hepatic insulin signals like pAKT, pFOXO1, and pGSK3β are increased and the downstream Pepck, G6pase, and Pgc1α are reduced. Furthermore, the lipogenic genes Srebp1c, Acc, and Fasn are decreased, indicating that hepatic lipid accumulation is inhibited.. The results demonstrate that vitamin D deficiency induces insulin resistance. Its supplementation has significant beneficial effects on pathophysiological mechanisms in type 2 diabetes but only in lean and not in the obese phenotype. The increased subacute inflammation and insulin resistance in obesity cannot be significantly alleviated by vitamin D supplementation. This needs to be taken into consideration in the design of new clinical trials.

Topics: Animals; Body Weight; Diet, High-Fat; Forkhead Box Protein O1; Gluconeogenesis; Glucose; Glycogen; Hepatitis; Insulin Resistance; Liver; Male; Mice, Inbred C57BL; Non-alcoholic Fatty Liver Disease; Obesity; Oxidative Stress; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Vitamin D; Vitamin D Deficiency

Gut-liver cross talk is an important determinant of human health with profound effects on energy homeostasis. While gut microbes produce a huge range of metabolites, specific compounds such as short-chain fatty acids (SCFAs) can enter the portal circulation and reach the liver (Brandl K, Schnabl B.

Topics: Biomarkers; Cytokines; Gastrointestinal Microbiome; Gastrointestinal Tract; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Inflammation; Insulin Resistance; Liver; Propionates

Glycogen shortage during fasting coincides with dramatic changes in hepatic adenine nucleotide levels. The aim of this work was to study the relevance of liver glycogen in the regulation of the hepatic energy state during food deprivation. To this end, we examined the response of mice with sustained increased liver glycogen content to prolonged fasting. In order to increase hepatic glycogen content, we generated mice that overexpress protein targeting to glycogen (PTG) in the liver (PTG

Topics: Adipose Tissue; Animals; Body Weight; Energy Metabolism; Fasting; Food Deprivation; Gluconeogenesis; Glycogen; Insulin; Insulin Resistance; Ketones; Lipid Metabolism; Liver; Mice; Muscle, Skeletal; Organ Size

In this study, we investigated the effect of goat milk casein hydrolysates on glucose consumption rate, intracellular glycogen concentration, and mRNA expression of gluconeogenesis-related genes, including phosphoenolpyruvate carboxykinase 1 (PCK1) and glucose-6-phosphatase catalytic subunit (G6PC), in insulin-resistant HepG2 cells. From the obtained hydrolysates, we also purified and characterized novel peptides that ameliorated high-glucose-induced insulin resistance in HepG2 cells. The 3-h hydrolysate caused the highest glucose consumption rate in insulin-resistant HepG2 cells. It also showed positive effects on promoting intracellular glycogenesis and reducing mRNA expression of PCK1 and G6PC. We separated the obtained hydrolysates into 3 fractions (F1, F2, and F3) by gel filtration chromatography; we further purified F1 using reversed-phase HPLC and identified peptides using liquid chromatography-tandem mass spectrometry. The bioactive peptides identified were SDIPNPIGSE (α

Topics: Animals; Caseins; Chromatography, High Pressure Liquid; Chromatography, Liquid; Gluconeogenesis; Glucose; Glycogen; Goats; Hep G2 Cells; Humans; Insulin Resistance; Milk; Peptides

Insulin resistance (IR) contributes to diabetes and aging. Ultraconserved elements (UCEs) are a class of long noncoding RNAs (lncRNAs) that are 100% conserved in humans, mice, and rats. We identified the lncRNA uc.333 using an lncRNA microarray and then used quantitative real-time polymerase chain reaction to analyze its expression in the livers of nonalcoholic fatty liver disease (NAFLD) patients, db/db mice, high-fat diet-fed mice, IL-6-treated mice, and TNF-α-treated mice. The underlying mechanisms of uc.333 in IR were investigated using fluorescence in situ hybridization, Western blot, and miRNA microarray analyses. The results revealed that uc.333 expression was decreased in liver tissues from NAFLD patients and treated mice. Furthermore, overexpression of uc.333 decreased IR, whereas knocking down uc.333 increased IR. We also confirmed that uc.333 binds to miR-223 and that the levels of miR-223 were increased in the livers of patients and treated mice. These findings showed that uc.333 improves IR by binding to miR-223; thus, uc.333 may be a useful target for the treatment and prevention of IR.

Topics: Adipose Tissue; Animals; Base Sequence; Conserved Sequence; Dietary Fats; Forkhead Box Protein O1; Glucose; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Insulin Resistance; Interleukin-6; Liver; Male; Mice; MicroRNAs; Non-alcoholic Fatty Liver Disease; Oligonucleotide Array Sequence Analysis; Phosphorylation; Proto-Oncogene Proteins c-akt; RNA, Long Noncoding; RNA, Small Interfering; Tumor Necrosis Factor-alpha

Skeletal muscle glucose uptake and glucose metabolism are impaired in insulin resistance. Mechanical overload stimulates glucose uptake into insulin-resistant muscle; yet the mechanisms underlying this beneficial effect remain poorly understood. This study examined whether a differential partitioning of glucose metabolism is part of the mechanosensitive mechanism underlying overload-stimulated glucose uptake in insulin-resistant muscle. Mice were fed a high-fat diet to induce insulin resistance. Plantaris muscle overload was induced by unilateral synergist ablation. After 5 days, muscles were excised for the following measurements: (1) [

Topics: Animals; Blood Glucose; Carbohydrate Metabolism; Disease Models, Animal; Glucose; Glycogen; Glycolysis; Hexosamines; Insulin; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal

Most studies routinely use overnight or 6 h of fasting before testing metabolic glucose homeostasis in mice. Other studies used empirically shorter fasting times (<6 h). We attempted to determine the shortest fasting time required for optimal insulin responsiveness while minimizing metabolic stress.. A course of fasting for up to 24 h (0, 2, 4, 6, 12, and 24 h) was conducted in C57Bl/6J male mice. Body weight, metabolic parameters, and insulin tolerance were measured in each experimental group. The organs were collected at the same time on separate occasions and glycogen and metabolic gene expression were measured in the liver and skeletal muscle.. Our data show that blood glucose levels do not significantly change during a 6 h fast, while plasma insulin levels decrease to similar levels between 2 h and 6 h of fasting. During overnight (12 h) and 24 h fasts, a robust decrease in blood glucose and plasma insulin was observed along with a profound depletion in liver glycogen content. Insulin tolerance was comparable between baseline and 6 h fasts while 4 h and 6 h fasts were associated with a greater depletion of liver glycogen than 2 h fasts, impacting the glucose counter-regulatory response. Fasting induced progressive weight loss that was attenuated at thermoneutrality. Fasting longer than 4 h induced major body weight loss (>5%) and significant changes in catabolic gene expression in the liver and skeletal muscle.. Collectively, these data suggest that 2 h of fasting appears optimal for the assessment of insulin tolerance in mice as this duration minimizes major metabolic stress and weight loss.

Topics: Animals; Blood Glucose; Body Weight; Fasting; Glucose; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal

Understanding the mechanism by which the exogenous biomolecule modulates the GLUT-4 signalling cascade along with the information on glucose metabolism is essential for finding solutions to increasing cases of diabetes and metabolic disease. This study aimed at investigating the effect of hamamelitannin on glycogen synthesis in an insulin resistance model using L6 myotubes. Glucose uptake was determined using 2-deoxy-D-[1-

Topics: Animals; Biological Transport; Carbohydrate Metabolism; Cell Survival; Diabetes Mellitus, Type 2; Gallic Acid; Genistein; Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase Kinase 3 beta; Hexoses; Insulin; Insulin Antagonists; Insulin Resistance; Muscle Fibers, Skeletal; Myoblasts; Phosphatidylinositol 3-Kinases; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Rats; Signal Transduction; Wortmannin

Topics: Animals; Blood Glucose; Cannabidiol; Ceramides; Diet, High-Fat; Disease Models, Animal; Endocannabinoids; Glycogen; Insulin; Insulin Resistance; Male; Metabolic Networks and Pathways; Muscle, Skeletal; Obesity; Rats; Rats, Wistar; Signal Transduction; Sphingolipids

Sea cucumbers are widely consumed in traditional medicine and food. Sea cucumbers-derived sulfated sterol exhibits a sulfate group at C-3 position, which is different from phytosterol with a hydroxyl group. However, the effect of sterol sulfate on metabolic syndrome remains unknown. The purpose of the present study is to investigate the alleviation of sterol sulfate on high-fat-high-fructose diet (HFFD)-induced insulin resistance and inflammation. After 2 weeks feeding with HFFD, male C57BL/6J mice were continuously fed with HFFD plus 0.4 % (w/w) sterol sulfate or phytosterol for 6 weeks. The OGTT was carried out at 7 weeks. At the end of the experimental period, the changes of glycogen, circulating glucose, insulin, pro-inflammatory cytokine and adiponectin were measured. H&E staining was used to observe the morphological changes in adipose tissue. Furthermore, the underlying molecular mechanisms were investigated. Dietary sterol sulfate was superior to phytosterol in reducing body weight gain, adipocyte hypertrophy, and levels of circulating glucose and insulin, as well as increasing the glycogen content of tissues. Furthermore, sterol sulfate ameliorated insulin resistance mainly due to the inhibition of gluconeogenesis, the promotion of glycogen synthesis and GLUT4 translocation by activating PI3K/Akt signaling pathway. Additionally, sterol sulfate effectively attenuated inflammation by increasing serum adiponectin and reducing pro-inflammatory cytokine release. Sterol sulfate exhibited a more significant effect than phytosterol in alleviating HFFD -induced insulin resistance and inflammation, which might be closely related to the sulfate group. The results might provide insights into the prevention and alleviation of metabolic syndrome.

Topics: Adiponectin; Adipose Tissue; Animals; Anti-Inflammatory Agents; Blood Glucose; Cytokines; Diet, High-Fat; Fructose; Glucose Tolerance Test; Glycogen; Inflammation; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Obesity; Sea Cucumbers; Signal Transduction; Sterols

Branched-chain amino acids (BCAAs) are essential for critical metabolic processes; however, recent studies have associated elevated plasma BCAA levels with increased risk of insulin resistance. Using skeletal muscle cells, we aimed to determine whether continued exposure of high extracellular BCAA would result in impaired insulin signaling and whether the compound sodium phenylbutyrate (PB), which induces BCAA metabolism, would lower extracellular BCAA, thereby alleviating their potentially inhibitory effects on insulin-mediated signaling. Prolonged exposure of elevated BCAA to cells resulted in impaired insulin receptor substrate 1/AKT signaling and insulin-stimulated glycogen synthesis. PB significantly reduced media BCAA and branched-chain keto acid concentrations and increased phosphorylation of AKT [+2.0 ± 0.1-fold;

Topics: Amino Acids, Branched-Chain; Animals; Cell Line; Glycogen; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Mice; Muscle Cells; Muscle, Skeletal; Phenylbutyrates; Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction

Impairment of glucose (Glu) uptake and storage by skeletal muscle is a prime risk factor for the development of metabolic diseases. Heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) is a highly abundant RNA-binding protein that has been implicated in diverse cellular functions. The aim of this study was to investigate the function of hnRNP A1 on muscle tissue insulin sensitivity and systemic Glu homeostasis. Our results showed that conditional deletion of hnRNP A1 in the muscle gave rise to a severe insulin resistance phenotype in mice fed a high-fat diet (HFD). Conditional knockout mice fed a HFD showed exacerbated obesity, insulin resistance, and hepatic steatosis. In vitro interference of hnRNP A1 in C2C12 myotubes impaired insulin signal transduction and inhibited Glu uptake, whereas hnRNP A1 overexpression in C2C12 myotubes protected against insulin resistance induced by supraphysiological concentrations of insulin. The expression and stability of glycogen synthase (gys1) mRNA were also decreased in the absence of hnRNP A1. Mechanistically, hnRNP A1 interacted with gys1 and stabilized its mRNA, thereby promoting glycogen synthesis and maintaining the insulin sensitivity in muscle tissue. Taken together, our findings are the first to show that reduced expression of hnRNP A1 in skeletal muscle affects the metabolic properties and systemic insulin sensitivity by inhibiting glycogen synthesis.

Topics: Animals; Cell Line; Diabetes Mellitus, Experimental; Diet, High-Fat; Fatty Liver; Glycogen; Glycogen Synthase; Heterogeneous Nuclear Ribonucleoprotein A1; Insulin Resistance; Male; Mice, Knockout; Models, Biological; Muscle Fibers, Skeletal; Muscle, Skeletal; RNA Stability; Severity of Illness Index

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease. The literature suggests that the aryl hydrocarbon receptor (AHR) may be a key player in the pathogenesis of NAFLD, and it can modulate the synthesis of cytochrome P450 1A1 (CYP1A1) and tumor necrosis factor-α (TNF-α). Previous studies have shown that CYP1A1 is a key enzyme of oxidative stress, TNF-α is involved in the formation of insulin resistance (IR), oxidative stress and insulin resistance are the key factors for the formation of NAFLD. Therefore, it can be said that AHR may participate in contributing to NAFLD by regulating CYP1A1 and TNF-α. Alpha-naphthoflavone (ANF) is an effective AHR inhibitor. The present study was designed to explore the hepatoprotective effect of ANF in high fat diet (HFD)-induced NAFLD mice and oleic acid (OA)-treated HepG2 hepatocytes. Mice were fed HFD to induce NAFLD, HepG2 cells were exposed to OA to induce hepatocyte injury, and ANF significantly reduced mouse and cellular liver damage compared to the HFD-induced NAFLD and OA-treated HepG2 hepatocytes. ANF treatment reduces liver damage by reducing ROS and IR, the data show that ANF inhibits the expression of AHR, CYP1A1 and TNF-α in NAFLD. Taken together, these findings show that ANF alleviate NAFLD via regulation of AHR/CYP1A1 and AHR/TNF-α pathways, which may have potential for further development as novel therapeutic agents for NAFLD.

Topics: Animals; Benzoflavones; Catalase; Cell Proliferation; Diet, High-Fat; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Insulin Resistance; Lipid Droplets; Lipid Metabolism; Liver; Male; Malondialdehyde; Mice, Inbred C57BL; Non-alcoholic Fatty Liver Disease; Oleic Acid; Oxidative Stress; Superoxide Dismutase

Troxerutin (TRX) has a beneficial effect on blood viscosity and platelet aggregation, and is currently used for the treatment of chronic varicosity. Recently, TRX can improve lipid abnormalities, glucose intolerance and oxidative stress in high-fat diet-induced metabolic disorders. In this study, we tested the effect of TRX on metabolic syndrome-associated disorders using a non-obese model of metabolic syndrome-the Hereditary Hypertriglyceridaemic rats (HHTg).. Adult male HHTg rats were fed standard diet without or with TRX (150 mg/kg bwt/day for 4 weeks).. Compared to untreated rats, TRX supplementation in HHTg rats decreased serum glucose (p<0.05) and insulin (p<0.05). Although blood lipids were not affected, TRX decreased hepatic cholesterol concentrations (p<0.01) and reduced gene expression of HMGCR, SREBP2 and SCD1 (p<0.01), involved in cholesterol synthesis and lipid homeostasis. TRX-treated rats exhibited decreased lipoperoxidation and increased activity of antioxidant enzymes SOD and GPx (p<0.05) in the liver. In addition, TRX supplementation increased insulin sensitivity in muscles and epididymal adipose tissue (p<0.05). Elevated serum adiponectin (p<0.05) and decreased muscle triglyceride (p<0.05) helped improve insulin sensitivity. Among the beneficial effects of TRX were changes to cytochrome P450 family enzymes. Hepatic gene expression of CYP4A1, CYP4A3 and CYP5A1 (p<0.01) decreased, while there was a marked elevation in gene expression of CYP1A1 (p<0.01).. Our results indicate that TRX improves hepatic lipid metabolism and insulin sensitivity in peripheral tissues. As well as ameliorating oxidative stress, TRX can reduce ectopic lipid deposition, affect genes involved in lipid metabolism, and influence the activity of CYP family enzymes.

Topics: Animals; Disease Models, Animal; Glucose; Glycogen; Hydroxyethylrutoside; Hypolipidemic Agents; Insulin Resistance; Lipid Metabolism; Male; Metabolic Syndrome; Muscle, Skeletal; Oxidative Stress; Rats; Rats, Inbred Strains; Real-Time Polymerase Chain Reaction; Transcriptome

Insulin resistance is an independent negative predictor of outcome after elective surgery and increases mortality among surgical patients in intensive care. The incretin hormone glucagon-like peptide-1 (GLP-1) potentiates glucose-induced insulin release from the pancreas but may also increase insulin sensitivity in skeletal muscle and directly suppress hepatic glucose release. Here, we investigated whether a perioperative infusion of GLP-1 could counteract the development of insulin resistance after surgery. Pigs were randomly assigned to three groups; surgery/control, surgery/GLP-1, and sham/GLP-1. Both surgery groups underwent major abdominal surgery. Whole-body glucose disposal (WGD) and endogenous glucose release (EGR) were assessed preoperatively and postoperatively using D-[6,6-2H2]-glucose infusion in combination with hyperinsulinemic euglycemic step-clamping. In the surgery/control group, peripheral insulin sensitivity (i.e., WGD) was reduced by 44% relative to preoperative conditions, whereas the corresponding decline was only 9% for surgery/GLP-1 (P < 0.05). Hepatic insulin sensitivity (i.e., EGR) remained unchanged in the surgery/control group but was enhanced after GLP-1 infusion in both surgery and sham animals (40% and 104%, respectively, both P < 0.05). Intraoperative plasma glucose increased in surgery/control (∼20%) but remained unchanged in both groups receiving GLP-1 (P < 0.05). GLP-1 diminished an increase in postoperative glucagon levels but did not affect skeletal muscle glycogen or insulin signaling proteins after surgery. We show that GLP-1 improves intraoperative glycemic control, diminishes peripheral insulin resistance after surgery, and suppresses EGR. This study supports the use of GLP-1 to prevent development of postoperative insulin resistance.

Topics: Animals; Blood Glucose; Drug Evaluation, Preclinical; Female; Glucagon-Like Peptide 1; Glucose Clamp Technique; Glycogen; Incretins; Infusions, Intravenous; Insulin; Insulin Resistance; Liver; Muscle, Skeletal; Perioperative Care; Perioperative Period; Random Allocation; Surgical Procedures, Operative; Swine

The present investigation aimed to study the possible antidiabetic and related antioxidant potentials of tannic acid and melatonin in streptozotocin (STZ) induced diabetes in rats. Four groups of rats received intraperitoneal one dose of 50mg/kg body weight STZ for the induction of diabetes. The first group served as diabetic control group and received the vehicle. Four days after induction of diabetes, the remaining three groups received glibenclamide (6mg/kg/day), tannic acid (1 g/kg/day) and melatonin (10 mg/kg/day) for two weeks. A fifth group served as vehicle control group. At the end of the experimental period, blood samples and liver samples were collected for the determination of diabetes correlated biomarkers. Treatment of diabetic rats with tannic acid or melatonin attenuated most of the changes associated with STZ induced diabetes. The present results evidenced the beneficial effects of tannic acid and melatonin in diabetes management.

Topics: Animals; Antioxidants; Blood Glucose; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Insulin-Secreting Cells; Kidney Function Tests; Lipid Metabolism; Liver; Male; Melatonin; Rats, Wistar; Tannins

Type 2 diabetes (T2D) has become a major health problem worldwide. Skeletal muscle (SKM) is the key tissue for whole-body glucose disposal and utilization. New drugs aimed at improving insulin sensitivity of SKM would greatly expand available therapeutic options. β-arrestin-1 and -2 (Barr1 and Barr2, respectively) are two intracellular proteins best known for their ability to mediate the desensitization and internalization of G protein-coupled receptors (GPCRs). Recent studies suggest that Barr1 and Barr2 regulate several important metabolic functions including insulin release and hepatic glucose production. Since SKM expresses many GPCRs, including the metabolically important β2-adrenergic receptor, the goal of this study was to examine the potential roles of Barr1 and Barr2 in regulating SKM and whole-body glucose metabolism. Using SKM-specific knockout (KO) mouse lines, we showed that the loss of SKM Barr2, but not of SKM Barr1, resulted in mild improvements in glucose tolerance in diet-induced obese mice. SKM-specific Barr1- and Barr2-KO mice did not show any significant differences in exercise performance. However, lack of SKM Barr2 led to increased glycogen breakdown following a treadmill exercise challenge. Interestingly, mice that lacked both Barr1 and Barr2 in SKM showed no significant metabolic phenotypes. Thus, somewhat surprisingly, our data indicate that SKM β-arrestins play only rather subtle roles (SKM Barr2) in regulating whole-body glucose homeostasis and SKM insulin sensitivity.

Topics: Animals; beta-Arrestin 1; beta-Arrestin 2; Diabetes Mellitus, Type 2; Diet, High-Fat; Disease Models, Animal; Glucose; Glucose Clamp Technique; Glycogen; Humans; Insulin; Insulin Resistance; Male; Mice; Mice, Knockout; Muscle, Skeletal; Obesity; Signal Transduction

BACKGROUNDInsulin resistance results from impaired skeletal muscle glucose transport/phosphorylation, linked to augmented lipid availability. Despite greater intramuscular lipids, athletes are highly insulin sensitive, which could result from higher rates of insulin-stimulated glycogen synthesis or glucose transport/phosphorylation and oxidation. Thus, we examined the time course of muscle glycogen and glucose-6-phosphate concentrations during low and high systemic lipid availability.METHODSEight endurance-trained and 9 sedentary humans (VO2 peak: 56 ± 2 vs. 33 ± 2 mL/kg/min, P < 0.05) underwent 6-hour hyperinsulinemic-isoglycemic clamp tests with infusions of triglycerides or saline in a randomized crossover design. Glycogen and glucose-6-phosphate concentrations were monitored in vastus lateralis muscles using 13C/31P magnetic resonance spectroscopy.RESULTSAthletes displayed a 25% greater (P < 0.05) insulin-stimulated glucose disposal rate (Rd) than sedentary participants. During Intralipid infusion, insulin sensitivity remained higher in the athletes (ΔRd: 25 ± 3 vs. 17 ± 3 μmol/kg/min, P < 0.05), supported by higher glucose transporter type 4 protein expression than in sedentary humans. Compared to saline infusion, AUC of glucose-6-phosphate remained unchanged during Intralipid infusion in athletes (1.6 ± 0.2 mmol/L vs. 1.4 ± 0.2 [mmol/L] × h, P = n.s.) but tended to decrease by 36% in sedentary humans (1.7 ± 0.4 vs. 1.1 ± 0.1 [mmol/L] × h, P < 0.059). This drop was accompanied by a 72% higher rate of net glycogen synthesis in the athletes upon Intralipid infusion (47 ± 9 vs. 13 ± 3 μmol/kg/min, P < 0.05).CONCLUSIONAthletes feature higher skeletal muscle glucose disposal and glycogen synthesis during increased lipid availability, which primarily results from maintained insulin-stimulated glucose transport with increased myocellular glucose-6-phosphate levels for subsequent glycogen synthesis.TRIAL REGISTRATIONClinicalTrials.gov NCT01229059.FUNDINGGerman Federal Ministry of Health (BMG).

Topics: Adult; Biological Transport; Female; Glucose; Glucose Clamp Technique; Glycogen; Humans; Insulin Resistance; Lipids; Male; Muscle, Skeletal; Phosphorylation; Sports; Young Adult

Insulin resistance (IR) is the impaired insulin response that causes decreased glucose tolerance. Electrical stimulation (ES) can improve insulin sensitivity in the skeletal muscle. However, the underlying molecular mechanisms remain to be elucidated. In the present study, the effect of ES and diet therapy on IR and the role of the mammalian target of rapamycin (mTOR) pathway in the improvement of IR by ES were investigated. A total of 70 Sprague‑Dawley male rats were divided into five groups: Normal (n=10), IR control (n=15), diet (n=15), ES (n=15) and ES + diet (n=15) groups. An IR rat model was established by high‑fat and high‑carbohydrate diet for 5 weeks and confirmed by measurement of fasting plasma glucose (FPG), insulin, insulin sensitivity index (ISI) and IR index. ES on the Zusanli (ST36), Sanyinjiao (SP 6) and Weiwanxiashu (EX‑B3) acupoints and the low‑fat and low‑carbohydrate diet demonstrated protective effects. The body weight, concentrations of FPG, insulin, triglycerides (TG), free fatty acids (FFA) and total cholesterol (TC) of the rats were detected. Pathologic changes in the liver and pancreatic tissues were assessed. Western blotting and immunohistochemistry were performed to determine the role of PI3K/Akt/mTOR signaling. Results demonstrated that ES and diet therapy significantly increased ISI and reduced FPG, IR index, FFA, TG, TC and weight. Inflammatory cell infiltration in the liver and pancreatic tissues was ameliorated and lipid droplets and cavitation in hepatocyte were decreased after ES and diet therapy. The administration of ES and diet therapy also enhanced glucose transport by the upregulation of glucose transporter 4 and accelerated glycogen synthesis through the suppression of glycogen synthase kinase 3α/β via PI3K/Akt/mTOR signaling. Hence, the present results demonstrated that ES combined with diet therapy improved IR through PI3K/Akt/mTOR signaling. The proposed therapy was superior to the method of diet alone.

Topics: Animals; Body Weight; Diet Therapy; Diet, Carbohydrate-Restricted; Diet, Fat-Restricted; Electric Stimulation; Glycogen; Insulin; Insulin Resistance; Islets of Langerhans; Liver; Male; Muscles; Phosphatidylinositol 3-Kinases; Rats; Rats, Sprague-Dawley; Signal Transduction; TOR Serine-Threonine Kinases; Triglycerides

Sesamin (SES) has the ameliorating effect on L02 hepatocyte model of insulin resistance induced by high glucose and high insulin, based on insulin receptor signaling pathway IRS/PI3K/Akt. Treatment with SES (200, 100μg/ml) increased glucose consumption, glucose uptake and the intracellular glycogen synthesis of L02 hepatocyte model of insulin resistance significantly. Moreover, treatment with SES promoted the gene and protein expression levels of insulin receptor (InsR) and the post-receptor associated proteins, such as insulin receptor substrate 1 (IRS1), insulin receptor substrate 2 (IRS2), PI3K (phosphatidylinositol 3-kinase), GLUT4 (glucose transporter 4) significantly, which were determined by RT-PCR and immunoblot analysis. In conclusion, SES has the ameliorating effect on L02 hepatocyte model of insulin resistance induced by high glucose/high insulin, which might be related to its effect on promoting expression of insulin receptor and its associated proteins of IRS-PI3K-Akt passway, and thus promoting insulin sensitivity.

Topics: Antigens, CD; Cell Line; Chromatography, High Pressure Liquid; Dioxoles; Glucose; Glucose Transporter Type 4; Glycogen; Hepatocytes; Humans; Immunoblotting; Insulin Receptor Substrate Proteins; Insulin Resistance; Lignans; Receptor, Insulin; Reverse Transcriptase Polymerase Chain Reaction

The probiotic Lactobacillus gasseri SBT2055 (LG2055) has a protective effect against metabolic syndrome in rats and humans. Metabolic syndrome increases the risk of type 2 diabetes mellitus. In this study, Goto-Kakizaki rats were used as a diabetic model and fed diets containing LG2055-fermented or nonfermented skim milk for 4 wk. Indices of diabetes such as blood glucose levels, serum glucagon levels, plasma levels of insulin, C-peptide, and glucagon-like peptide-1, tissue glycogen contents, and pancreatic mRNA levels were measured. The plasma C-peptide levels and pancreatic mRNA levels of insulin genes (Ins1 and Ins2) and Pdx1 (a transcriptional factor of insulin genes) were increased in LG2055 diet-fed rats. The increase in insulin secretion corresponded to an improvement in serum and pancreatic inflammatory status, associated with decreases in serum levels of serum amyloid P and pancreatic levels of granulocyte colony-stimulating factor. Insulin resistance in Goto-Kakizaki rats was ameliorated by increased glycogen storage in the liver and quadriceps femoris muscles and decreased serum free fatty acid levels. This improvement may be related to the increased cecal production of short-chain fatty acids. In conclusion, dietary LG2055 improved insulin secretion in diabetic rats by improving the inflammatory status in the pancreas and serum.

Topics: Animals; Blood Glucose; Cecum; Diabetes Mellitus, Type 2; Diet; Fatty Acids, Volatile; Glucagon-Like Peptide 1; Glycogen; Humans; Insulin; Insulin Resistance; Insulin Secretion; Lactobacillus gasseri; Liver; Male; Muscle, Skeletal; Probiotics; Rats

Bscl2

Topics: Animals; Disease Models, Animal; Female; Gene Knockout Techniques; Glucose; Glycogen; GTP-Binding Protein gamma Subunits; Heterotrimeric GTP-Binding Proteins; Insulin Resistance; Lipid Metabolism; Lipodystrophy, Congenital Generalized; Male; Mice; Muscle, Skeletal; Organ Specificity; Oxidation-Reduction; Triglycerides

What is the central question of this study? What are the temporal responses of mitochondrial respiration and mitochondrial responsivity to insulin in soleus muscle fibres from mice during the development of obesity and insulin resistance? What is the main finding and its importance? Short- and long-term feeding with a high-fat diet markedly reduced soleus mitochondrial respiration and mitochondrial responsivity to insulin before any change in glycogen synthesis. Muscle glycogen synthesis and whole-body insulin resistance were present after 14 and 28 days, respectively. Our findings highlight the plasticity of mitochondria during the development of obesity and insulin resistance.. Recently, significant attention has been given to the role of muscle mitochondrial function in the development of insulin resistance associated with obesity. Our aim was to investigate temporal alterations in mitochondrial respiration, H

Topics: Animals; Blood Glucose; Cell Respiration; Diet, High-Fat; Dietary Fats; Glucose; Glycogen; Insulin; Insulin Resistance; Male; Mice; Mitochondria; Mitochondria, Muscle; Muscle, Skeletal; Obesity; Oxidative Phosphorylation; Rest

The miR-181 family plays an important role in the regulation of various cellular functions. However, whether miR-181b-5p mediates hepatic insulin resistance remains unknown. In this study, we investigated the effect of miR-181b-5p on the regulation of hepatic glycogen synthesis.. The miR-181b-5p levels in the livers of diabetic mice were detected by real-time PCR. The glycogen levels and AKT/GSK pathway activation were examined in human hepatic L02 cells and HepG2 cells transfected with miR-181b-5p mimic or inhibitor. The potential target genes of miR-181b-5p were evaluated using a luciferase reporter assay and Western blot analysis. EGR1-specific siRNA and pCMV-EGR1 were used to further determine the role of miR-181b-5p in hepatic glycogen synthesis in vitro. Hepatic inhibition of miR-181b-5p in mice was performed using adeno-associated virus 8 (AAV8) vectors by tail intravenous injection.. The miR-181b-5p levels were significantly decreased in the serum and livers of diabetic mice as well as the serum of type 2 diabetes patients. Importantly, inhibition of miR-181b-5p expression impaired the AKT/GSK pathway and reduced glycogenesis in hepatocytes. Moreover, upregulation of miR-181b-5p reversed high-glucose-induced suppression of glycogenesis. Further analysis revealed that early growth response 1 (EGR1) was a downstream target of miR-181b-5p. Silencing of EGR1 expression rescued miR-181b-5p inhibition-reduced AKT/GSK pathway activation and glycogenesis in hepatocytes. Hepatic inhibition of miR-181b-5p led to insulin resistance in C57BL/6 J mice.. We demonstrated that miR-181b-5p contributes to glycogen synthesis by targeting EGR1, thereby regulating PTEN expression to mediate hepatic insulin resistance.

Topics: Adult; Animals; Diabetes Mellitus, Type 2; Disease Models, Animal; Early Growth Response Protein 1; Female; Glycogen; Hep G2 Cells; Humans; Insulin Resistance; Liver; Male; Mice, Inbred C57BL; MicroRNAs; Middle Aged; PTEN Phosphohydrolase; Signal Transduction

Non-alcoholic fatty liver disease (NAFLD) is currently evolving as the most common liver disease worldwide. Dyslipidemia, pathoglycemia and insulin resistance are the major risk factors for the development of NAFLD. To date, no effective drug therapies for this condition have been approved.. The present study was to investigate the protective effects of yangonin, a kavalactone isolated from Kava, against NAFLD and further elucidate the mechanisms in vivo and in vitro.. A high-fat diet (HFD) induced mouse NAFLD model was used with or without yangonin treatment.. The body weight, relative liver weight and serum biochemical indicators were measured. H&E and Oil Red O staining were used to identify the amelioration of the liver histopathological changes. Serum and hepatic triglyceride, free fatty acids and total cholesterol were analyzed. siRNA, quantitative real-time PCR and Western blot assay were used to clarify the mechanisms underlying yangonin protection.. Yangonin had obvious protective effects against NAFLD via farnesoid X receptor (FXR) activation. Through FXR activation, yangonin attenuated lipid accumulation in the liver via inhibition of hepatic lipogenesis-related protein including sterol regulatory element-binding protein 1c (SREBP-1c), fatty acid synthetase (FAS), acetyl-CoA carboxylase 1 (ACC1) and stearoyl-CoA desaturase 1 (SCD1). Besides, yangonin promoted lipid metabolism through an induction in genes required for lipoprotein lipolysis and fatty acid β-oxidation. Furthermore, yangonin modulated blood glucose homeostasis through regulation of gluconeogenesis-related gene phosphoenol pyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), and glycogen synthesis-related gene glycogen synthase kinase 3β (GSK3β) and pyruvate dehydrogenase (PDase). Also, yangonin increased insulin sensitivity through upregulating phosphorylation of insulin responsive substrate 1, 2 (IRS-1 and IRS-2). Then, in vivo and in vitro evidence further demonstrated the involvement of FXR activation in yangonin hepatoprotection.. Yangonin protects against NAFLD due to its activation of FXR signalling to inhibit hepatic lipogenesis and gluconeogenesis, and to promote lipid metabolism and glycogen synthesis, as well as insulin sensitivity.

Topics: Animals; Diet, High-Fat; Gluconeogenesis; Glucose; Glycogen; Insulin; Insulin Resistance; Lipid Metabolism; Lipogenesis; Liver; Male; Mice, Inbred C57BL; Non-alcoholic Fatty Liver Disease; Protective Agents; Pyrones; Receptors, Cytoplasmic and Nuclear; Triglycerides

Lycium barbarum polysaccharide (LBP), as one bioactive macromolecular abstracted from goji berry, has shown an abundance of potential function. The present study aimed to evaluate the metabolic effects of LBP on the urine and liver metabolomics on a high-fat diet and streptozotocin-induced diabetic rat model. After 8 weeks of high-fat diet and streptozotocin induction of diabetes, 24 diabetic rats were randomly allocated to the diabetic control (DC) group, LBP low, moderate, and high dosage (LBP-L, LBP-M, LBP-H) groups and 6 non-diabetic rats were established as the non-diabetic control (NDC) group for 30 days' intervention. Metabolomics was performed on liver and urine. LBP positively regulated fasting blood glucose, hemoglobin-A1c, homeostasis model assessment for insulin resistance, liver glycogen and SOD levels significantly, as compared to the DC group. Liver metabolomics showed higher levels of myo-inositol and lower levels of L-malic acid, fumaric acid, D-arabitol, L-allothreonine 1, xylitol, O-phosphorylethanolamine, ribitol, 5-methoxytryptamine 2 and digitoxose 2 in the LBP-H group vs. the DC group, which indicates that LBP may regulate the citrate cycle, alanine, aspartate and glutamate metabolism, glyoxylate and dicarboxylate metabolism. Urine metabolomics showed increased levels of creatinine, D-galacturonic acid 2, 2,3-dihydroxybutyric acid and citric acid, and decreased levels of methylmalonic acid, benzoic acid and xylitol between the LBP-H and DC groups. The present study exhibited the effects of LBP on the urine and liver metabolomics in a high-fat diet and streptozotocin-induced rat model, which not only provides a better understanding of the anti-diabetic effects of LBP but also supplies a useful database for further specific mechanism study.

Topics: Animals; Antioxidants; Blood Glucose; Creatinine; Diabetes Mellitus, Experimental; Diet, High-Fat; Drugs, Chinese Herbal; Gas Chromatography-Mass Spectrometry; Glycated Hemoglobin; Glycogen; Insulin; Insulin Resistance; Liver; Lycium; Male; Metabolomics; Rats; Rats, Sprague-Dawley; Streptozocin; Urinalysis

Topics: Animals; Diet, High-Fat; Glucose; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Lipid Droplets; Male; Muscle Fibers, Fast-Twitch; Muscle Fibers, Skeletal; Muscle Fibers, Slow-Twitch; Muscle, Skeletal; Physical Conditioning, Animal; Rats; Rats, Wistar; Sedentary Behavior

Growth hormone (GH) has an important function as an insulin antagonist with elevated insulin sensitivity evident in humans and mice lacking a functional GH receptor (GHR). We sought the molecular basis for this sensitivity by utilizing a panel of mice possessing specific deletions of GHR signaling pathways. Metabolic clamps and glucose homeostasis tests were undertaken in these obese adult C57BL/6 male mice, which indicated impaired hepatic gluconeogenesis. Insulin sensitivity and glucose disappearance rate were enhanced in muscle and adipose of mice lacking the ability to activate the signal transducer and activator of transcription (STAT)5

Topics: Animals; Carrier Proteins; Fatty Liver; Glucose; Glycogen; Insulin Receptor Substrate Proteins; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Liver; Male; Mice; Mice, Knockout; Obesity; Phosphoenolpyruvate Carboxykinase (GTP); Receptor, Insulin; Signal Transduction; STAT5 Transcription Factor

Protein tyrosine phosphatase 1B (PTP1B) is a widely confirmed target of the type 2 diabetes mellitus (T2DM) treatment. Herein, we reported a highly specific PTP1B inhibitor 2,2',3,3'-tetrabromo-4,4',5,5'-tetrahydroxydiphenylmethane (compound 1), which showed promising hypoglycemic activity in diabetic BKS db mice. With the IC

Topics: Administration, Oral; Animals; Benzhydryl Compounds; Catalytic Domain; Cell Line; Diabetes Mellitus, Type 2; Glycogen; Hydrogen Bonding; Hypoglycemic Agents; Inhibitory Concentration 50; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Inbred NOD; Molecular Docking Simulation; Myoblasts; Plant Extracts; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Rhodophyta; Signal Transduction

The short-chain fatty acid propionate is a potent inhibitor of molds that is widely used as a food preservative and endogenously produced by gut microbiota. Although generally recognized as safe by the U.S. Food and Drug Administration, the metabolic effects of propionate consumption in humans are unclear. Here, we report that propionate stimulates glycogenolysis and hyperglycemia in mice by increasing plasma concentrations of glucagon and fatty acid-binding protein 4 (FABP4).

Topics: Animals; Fatty Acid-Binding Proteins; Female; Glucagon; Glycogen; Humans; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Propionates; Weight Gain

Sulforaphane (SFA), a naturally active isothiocyanate compound from cruciferous vegetables used in clinical trials for cancer treatment, was found to possess potency to alleviate insulin resistance. But its underlying molecular mechanisms are still incompletely understood. In this study, we assessed whether SFA could improve insulin sensitivity and glucose homeostasis both in vitro and in vivo by regulating ceramide production. The effects of SFA on glucose metabolism and expression levels of key proteins in the hepatic insulin signaling pathway were evaluated in insulin-resistant human hepatic carcinoma HepG2 cells. The results showed that SFA dose-dependently increased glucose uptake and intracellular glycogen content by regulating the insulin receptor substrate 1 (IRS-1)/protein kinase B (Akt) signaling pathway in insulin-resistant HepG2 cells. SFA also reduced ceramide contents and downregulated transcription of ceramide-related genes. In addition, knockdown of serine palmitoyltransferase 3 (SPTLC3) in HepG2 cells prevented ceramide accumulation and alleviated insulin resistance. Moreover, SFA treatment improved glucose tolerance and insulin sensitivity, inhibited SPTLC3 expression and hepatic ceramide production and reduced hepatic triglyceride content in vivo. We conclude that SFA recovers glucose homeostasis and improves insulin sensitivity by blocking ceramide biosynthesis through modulating SPTLC3, indicating that SFA may be a potential candidate for prevention and amelioration of hepatic insulin resistance via a ceramide-dependent mechanism.

Topics: Animals; Ceramides; Enzyme Inhibitors; Glucose; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Isothiocyanates; Liver; Male; Mice, Inbred C57BL; Palmitic Acid; Proto-Oncogene Proteins c-akt; Serine C-Palmitoyltransferase; Signal Transduction; Sulfoxides; Triglycerides

Agriophyllum squarrosum (L.) Moq. is a traditional Mongol medicine commonly used in the treatment of diabetes.. To examine the effects of Agriophyllum squarrosum extract (ASE) on glucose metabolism in type 2 diabetic KKAy mice, and to investigate the mechanisms underlying these effects.. KKAy mice were divided into a model control group (MCG), a low-dose Agriophyllum squarrosum extract group (LASEG), a medium-dose Agriophyllum squarrosum extract group (MASEG), a high-dose Agriophyllum squarrosum extract group (HASEG), and a metformin group (MEG). Syngeneic C57BL/6 mice were used as a normal control group (NCG). Drugs were administered to all mice by gavage for 8 weeks. Random blood glucose levels were measured in the mice at baseline and after 2, 4, and 8 weeks of treatment. Glucose tolerance was measured after 6 weeks of drug administration. After 8 weeks, glycated serum proteins (GSP) and advanced glycation end-products (AGEs) in the serum of all mice were measured. Sections of mouse liver tissues were used for periodic acid-Schiff staining (PAS) and the content of hepatic glycogen was determined. Immunohistochemistry was used to determine the effects of ASE on liver phospho-insulin receptor substrate 2 (P-IRS2) protein expression. Western blotting was used to quantify the protein expression levels of phosphatidylinositol 3-kinase (PI3K), AKT, phospho-AKT (S473) (P-AKT), glycogen synthase kinase 3β (GSK3β), and glucose transporters 4 (GLUT4), while PCR was used to quantify the mRNA expression levels of insulin receptor substrate 2 (IRS2), PI3K, AKT, GSK3β, and GLUT4.. ASE treatment decreased random blood glucose levels in type 2 diabetic KKAy mice; increased glucose tolerance; decreased serum GSP and AGEs content; increased glycogen synthesis in liver tissues; upregulated the protein expression levels of PI3K, AKT, GLUT4, and P-IRS2; downregulated the protein expression level of GSK3β in liver tissues; upregulated the mRNA expression levels of IRS2, PI3K, AKT, and GLUT4; and downregulated the mRNA expression level of GSK3β in liver tissues.. ASE treatment may increase glucose metabolism in KKAy mice and improve glucose tolerance. The underlying mechanisms of the beneficial effects of ASE may be associated with the increase of glycogen synthesis, the inhibition of AGEs production, the upregulation of IRS2, PI3K, AKT, and GLUT4 protein and mRNA expression, and the downregulation of GSK3β protein and mRNA expression.

Topics: Animals; Blood Proteins; Chenopodiaceae; Diabetes Mellitus, Experimental; Disease Models, Animal; Female; Glucose; Glycation End Products, Advanced; Glycogen; Glycogen Synthase Kinase 3 beta; Insulin Receptor Substrate Proteins; Insulin Resistance; Liver; Male; Mice, Inbred C57BL; Obesity; Phosphatidylinositol 3-Kinases; Plant Extracts; Proto-Oncogene Proteins c-akt

Muscle insulin sensitivity for stimulating glucose uptake is enhanced in the period after a single bout of exercise. We recently demonstrated that AMPK is necessary for AICAR, contraction, and exercise to enhance muscle and whole-body insulin sensitivity in mice. Correlative observations from both human and rodent skeletal muscle suggest that regulation of the phosphorylation status of TBC1D4 may relay this insulin sensitization. However, the necessity of TBC1D4 for this phenomenon has not been proven. Thus, the purpose of this study was to determine whether TBC1D4 is necessary for enhancing muscle insulin sensitivity in response to AICAR and contraction. We found that immediately after contraction and AICAR stimulation, phosphorylation of AMPKα-Thr172 and downstream targets were increased similarly in glycolytic skeletal muscle from wild-type and TBC1D4-deficient mice. In contrast, 3 h after contraction or 6 h after AICAR stimulation, enhanced insulin-stimulated glucose uptake was evident in muscle from wild-type mice only. The enhanced insulin sensitivity in muscle from wild-type mice was associated with improved insulin-stimulated phosphorylation of TBC1D4 (Thr649 and Ser711) but not of TBC1D1. These results provide genetic evidence linking signaling through TBC1D4 to enhanced muscle insulin sensitivity after activation of the cellular energy sensor AMPK.

Topics: Aminoimidazole Carboxamide; AMP-Activated Protein Kinases; Animals; Glucose; Glycogen; GTPase-Activating Proteins; Insulin; Insulin Resistance; Mice; Mice, Knockout; Muscle Contraction; Muscle, Skeletal; Phosphorylation; Ribonucleotides; Signal Transduction

Women with polycystic ovary syndrome (PCOS) commonly suffer from miscarriage, but the underlying mechanisms remain unknown. Herein, pregnant rats chronically treated with 5α-dihydrotestosterone (DHT) and insulin exhibited hyperandrogenism and insulin resistance, as well as increased fetal loss, and these features are strikingly similar to those observed in pregnant PCOS patients. Fetal loss in our DHT+insulin-treated pregnant rats was associated with mitochondrial dysfunction, disturbed superoxide dismutase 1 and Keap1/Nrf2 antioxidant responses, over-production of reactive oxygen species (ROS) and impaired formation of the placenta. Chronic treatment of pregnant rats with DHT or insulin alone indicated that DHT triggered many of the molecular pathways leading to placental abnormalities and fetal loss, whereas insulin often exerted distinct effects on placental gene expression compared to co-treatment with DHT and insulin. Treatment of DHT+insulin-treated pregnant rats with the antioxidant N-acetylcysteine improved fetal survival but was deleterious in normal pregnant rats. Our results provide insight into the fetal loss associated with hyperandrogenism and insulin resistance in women and suggest that physiological levels of ROS are required for normal placental formation and fetal survival during pregnancy.. Women with polycystic ovary syndrome (PCOS) commonly suffer from miscarriage, but the underlying mechanism of PCOS-induced fetal loss during pregnancy remains obscure and specific therapies are lacking. We used pregnant rats treated with 5α-dihydrotestosterone (DHT) and insulin to investigate the impact of hyperandrogenism and insulin resistance on fetal survival and to determine the molecular link between PCOS conditions and placental dysfunction during pregnancy. Our study shows that pregnant rats chronically treated with a combination of DHT and insulin exhibited endocrine aberrations such as hyperandrogenism and insulin resistance that are strikingly similar to those in pregnant PCOS patients. Of pathophysiological significance, DHT+insulin-treated pregnant rats had greater fetal loss and subsequently decreased litter sizes compared to normal pregnant rats. This negative effect was accompanied by impaired trophoblast differentiation, increased glycogen accumulation, and decreased angiogenesis in the placenta. Mechanistically, we report that over-production of reactive oxygen species (ROS) in the placenta, mitochondrial dysfunction, and disturbed superoxide dismutase 1 (SOD1) and Keap1/Nrf2 antioxidant responses constitute important contributors to fetal loss in DHT+insulin-treated pregnant rats. Many of the molecular pathways leading to placental abnormalities and fetal loss in DHT+insulin treatment were also seen in pregnant rats treated with DHT alone, whereas pregnant rats treated with insulin alone often exerted distinct effects on placental gene expression compared to insulin treatment in combination with DHT. We also found that treatment with the antioxidant N-acetylcysteine (NAC) improved fetal survival in DHT+insulin-treated pregnant rats, an effect related to changes in Keap1/Nrf2 and nuclear factor-κB signalling. However, NAC administration resulted in fetal loss in normal pregnant rats, most likely due to PCOS-like endocrine abnormality induced by the treatment. Our results suggest that the deleterious effects of hyperandrogenism and insulin resistance on fetal survival are related to a constellation of mitochondria-ROS-SOD1/Nrf2 changes in the placenta. Our findings also suggest that physiological levels of ROS are required for normal placental formation and fetal survival during pregnancy.

Topics: Abortion, Spontaneous; Animals; Dihydrotestosterone; Female; Glycogen; Hyperandrogenism; Insulin Resistance; Kelch-Like ECH-Associated Protein 1; Mitochondria; NF-E2-Related Factor 2; Polycystic Ovary Syndrome; Pregnancy; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Superoxide Dismutase-1; Trophoblasts

Korean pine nut protein (PNP) has a variety of biological activities, which are good for human health, but its ability to preventing diabetes has not been reported. This study evaluated the effects of water-soluble proteins of Korean pine nut obtained from a dilute alkali extract on carbohydrate metabolism of type 2 diabetic mice on a model of diabetes induced using a high fat diet combined with streptozotocin. The results showed that the hypoglycemic effect of PNP at a middle dose was the most significant, which was 38.7% lower than that of control. The extract significantly improved the oral glucose tolerance and liver indexes, increased the activity of the carbohydrate metabolism enzymes, and regulated the expression of the function of key genes for carbohydrate metabolism. It had a positive effect on both insulin resistance and glycolytic/gluconeogenesis signaling. In conclusion, PNP can regulate fasting blood glucose, improve insulin resistance, correct the glucose metabolism disorder in diabetic mice, and have a positive regulatory role. As the functional food, it has the potential to be beneficial in the treatment of type 2 diabetes mellitus as a new hypoglycemic functional food.

Topics: Administration, Oral; Amino Acids; Animals; Blood Glucose; Body Weight; Carbohydrate Metabolism; Diabetes Mellitus, Type 2; Diet; Drinking Behavior; Fasting; Feeding Behavior; Gene Expression Regulation; Glucose Tolerance Test; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Male; Mice; Muscles; Nut Proteins; Pinus; Solubility; Water

Obesity-related insulin resistance is associated with intramyocellular lipid accumulation in skeletal muscle. We hypothesized that in contrast to current dogma, this linkage is related to an upstream mechanism that coordinately regulates both processes. We demonstrate that the muscle-enriched transcription factor MondoA is glucose/fructose responsive in human skeletal myotubes and directs the transcription of genes in cellular metabolic pathways involved in diversion of energy substrate from a catabolic fate into nutrient storage pathways including fatty acid desaturation and elongation, triacylglyeride (TAG) biosynthesis, glycogen storage, and hexosamine biosynthesis. MondoA also reduces myocyte glucose uptake by suppressing insulin signaling. Mice with muscle-specific MondoA deficiency were partially protected from insulin resistance and muscle TAG accumulation in the context of diet-induced obesity. These results identify MondoA as a nutrient-regulated transcription factor that under normal physiological conditions serves a dynamic checkpoint function to prevent excess energy substrate flux into muscle catabolic pathways when myocyte nutrient balance is positive. However, in conditions of chronic caloric excess, this mechanism becomes persistently activated leading to progressive myocyte lipid storage and insulin resistance.

Topics: Animals; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Cell Line; Disease Models, Animal; Female; Fructose; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Lipid Metabolism; Lipids; Male; Metabolic Networks and Pathways; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscle Fibers, Skeletal; Muscle, Skeletal; Obesity; Signal Transduction; Transcription Factors; Transcriptome; Triglycerides

During the development of type 2 diabetes mellitus (T2DM), hyperinsulinemia is the earliest symptom. It is believed that long-term high insulin stimulation might facilitate insulin resistance in the liver, but the underlying mechanism remains unknown. Herein, we report that hyperinsulinemia could induce persistent early growth response gene-1 (Egr-1) activation in hepatocytes, which provides negative feedback inhibition of insulin sensitivity by inducing the expression of protein tyrosine phosphatase-1B (PTP1B). Deletion of Egr-1 in the liver remarkably decreases glucose production, thus improving systemic glucose tolerance and insulin sensitivity. Mechanistic analysis indicates that Egr-1 inhibits insulin receptor phosphorylation by directly activating PTP1B transcription in the liver. Our results reveal the molecular mechanism by which hyperinsulinemia accelerates insulin resistance in hepatocytes during the progression of T2DM.

Topics: Animals; Cells, Cultured; Diabetes Mellitus, Type 2; Disease Models, Animal; Early Growth Response Protein 1; Gene Knockout Techniques; Glucose; Glycogen; Hyperinsulinism; Insulin; Insulin Resistance; Liver; Male; Mice; Phosphorylation; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Receptor, Insulin; Transcriptional Activation

The present study investigated the effects of oral ethinylestradiol-levonorgestrel (EEL) on hepatic lipid and glycogen contents during high fructose (HF) intake, and determined whether pyruvate dehydrogenase kinase-4 (PDK-4) and glucose-6-phosphate dehydrogenase (G6PD) activity were involved in HF and (or) EEL-induced hepatic dysmetabolism. Female Wistar rats weighing 140-160 g were divided into groups. The control, EEL, HF, and EEL+HF groups received water (vehicle, p.o.), 1.0 μg ethinylestradiol plus 5.0 μg levonorgestrel (p.o.), fructose (10%

Topics: Administration, Oral; Animals; Antioxidants; Blood Glucose; Dose-Response Relationship, Drug; Drug Combinations; Ethinyl Estradiol; Female; Fructose; Glucosephosphate Dehydrogenase; Glycogen; Hyperinsulinism; Insulin Resistance; Levonorgestrel; Lipid Metabolism; Lipid Peroxidation; Liver; Protein Kinases; Rats; Rats, Wistar; Uric Acid

Cigarette smoke causes insulin resistance, which is associated with type 2 diabetes mellitus (T2DM). However, the mechanism by which this occurs remains poorly understood. Because the involvement of microRNAs (miRNAs) in the development of insulin resistance is largely unknown, we investigated, in hepatocytes, the roles of miR-191 in cigarette smoke extract (CSE)-induced insulin resistance. In L-02 cells, CSE not only decreased glucose uptake and glycogen levels but also reduced levels of insulin receptor substrate-1 (IRS-1) and Akt activation, effects that were blocked by SC79, an activator of Akt. CSE also increased miR-191 levels in L-02 cells. Furthermore, the inhibition of miR-191 blocked the decreases of IRS-1 and p-Akt levels, which antagonized the decreases of glucose uptake and glycogen levels in L-02 cells induced by CSE. These results reveal a mechanism by which miR-191 is involved in CSE-induced hepatic insulin resistance via the IRS-1/Akt signaling pathway, which helps to elucidate the mechanism for cigarette smoke-induced T2DM.

Topics: Cell Line; Cigarette Smoking; Diabetes Mellitus, Type 2; Glycogen; Hepatocytes; Humans; Insulin Receptor Substrate Proteins; Insulin Resistance; MicroRNAs; Proto-Oncogene Proteins c-akt; Signal Transduction

Insulin resistance (IR) plays a central role in the development of several metabolic diseases, which leads to increased morbidity and mortality rates, in addition to soaring health-care costs. Deep sea water (DSW) and fucoidans (FPS) have drawn much attention in recent years because of their potential medical and pharmaceutical applications. This study investigated the effects and mechanisms of combination treatment of DSW and FPS in improving IR in HepG2 hepatocytes induced by a high glucose concentration. The results elucidated that co-treatment with DSW and FPS could synergistically repress hepatic glucose production and increase the glycogen level in IR-HepG2 cells. In addition, they stimulated the phosphorylation levels of the components of the insulin signaling pathway, including tyrosine phosphorylation of IRS-1, and serine phosphorylation of Akt and GSK-3β. Furthermore, they increased the phosphorylation of AMPK and ACC, which in turn decreased the intracellular triglyceride level. Taken together, these results suggested that co-treatment with DSW and FPS had a greater improving effect than DSW or FPS alone on IR. They might attenuate IR by targeting Akt/GSK-3β and AMPK pathways. These results may have some implications in the treatment of metabolic diseases.

Topics: Cell Survival; Glucose; Glycogen; Hep G2 Cells; Humans; Insulin Resistance; Liver; Oncogene Protein v-akt; Phosphorylation; Polysaccharides; Seawater; Serine; Signal Transduction; Triglycerides

Momordica charantia (M. charantia) has antidiabetic effects, and cucurbitane-type triterpenoid is one of the compounds of M. charantia. This study aims to investigate whether the new cucurbitane-type triterpenoids affect insulin sensitivity both in vitro and in vivo, and the underlying mechanisms.. Four compounds (C1-C4) isolated from the ethanol extract of M. charantia enhance glucose uptake in C2C12 myotubes via insulin receptor substrate-1 (IRS-1) rather than via adenosine monophosphate-activated protein kinase. The most potent, compound 2 (C2), significantly increases the activation of IRS-1 and downstream signaling pathways, resulting in glucose transporter 4 translocation. Furthermore, these C2-induced in vitro effects are blocked by specific signal inhibitors. We further evaluate the antidiabetic effect of C2 using a streptozotocin (STZ)-induced diabetic mouse model. Consistent with in vitro data, treatment with C2 (1.68 mg kg. Our findings demonstrate that the new cucurbitane-type triterpenoids have potential for prevention and management of diabetes by improving insulin sensitivity and glucose homeostasis.

Topics: Absorption, Physiological; Animals; Cell Line; Diabetes Mellitus, Experimental; Drug Discovery; Ethnopharmacology; Fruit; Glucose; Glycogen; Hyperglycemia; Hypoglycemic Agents; Insulin Resistance; Male; Mice; Mice, Inbred ICR; Molecular Structure; Momordica charantia; Muscle Fibers, Skeletal; Muscle, Skeletal; Organ Specificity; Republic of Korea; Streptozocin; Triterpenes

Topics: Animals; Diet, High-Fat; Fructose-Bisphosphatase; Fructosephosphates; Gene Expression Regulation, Enzymologic; Gluconeogenesis; Glucose; Glycogen; Insulin Resistance; Isoenzymes; Muscle, Skeletal; Rats; Rats, Transgenic; Rats, Wistar; Up-Regulation

C-Phycocyanin (C-PC), a kind of blue protein isolated from Spirulina platensis, can ameliorate hyperglycemia, but its effects on gluconeogenesis and glycogenesis are unknown. In the present study, we investigated the effects and underlying mechanisms of C-PC on gluconeogenesis and glycogenesis in insulin resistant hepatocytes. Insulin resistance was induced by high glucose (HG) in human hepatocellular carcinoma (HepG2) cells. C-PC ameliorated glucose production and phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) expression in HG-induced insulin resistant HepG2 cells. It also increased glucose uptake, glycogen content and glycogen synthase (GS) activation in HG-induced insulin resistant HepG2 cells. The data revealed the mechanism of C-PC in improving glucose homoeostasis via activating the IRS/PI3 K/Akt and SIRT1/LKB1/AMPK signaling pathway in insulin resistant hepatocytes. C-PC could be a promising leading compound for the development of a hypoglycemic agent.

Topics: AMP-Activated Protein Kinases; Down-Regulation; Gluconeogenesis; Glucose; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Insulin; Insulin Resistance; Liver; Phycocyanin; Plant Extracts; Proto-Oncogene Proteins c-akt; Spirulina

We aimed to evaluate the effects of a single (acute) and repeated (chronic) exposure to forced-swimming stressor on glucose tolerance, insulin sensitivity, lipid profile and glycogen content in male rats.. Thirty adult male Sprague-Dawley rats (12 weeks old) were divided randomly into five groups: control group, single exposure (SE) to forced-swim stressor, repeated exposure to forced-swim stressor for 7 days (RE7), 14 days (RE14) and 28 days (RE28). Glucose tolerance test and Homeostatic Model Assessment-Insulin Resistance (HOMA-IR) were undertaken on fasting rats to obtain glucose and insulin profiles. ELISA was performed to assess plasma insulin and corticosterone levels. Total cholesterol, triglyceride, high- and low-density lipoproteins, hepatic and skeletal glycogen content were also determined.. Repeated exposure to stressor induced glucose intolerance and insulin resistance in the experimental rats. Results showed that all RE groups exhibited a significantly higher area under the curve compared with others (p=0.0001); similarly, HOMA-IR increased (p=0.0001) in all RE groups compared with control. Prolonged exposure to stressor significantly increased the plasma insulin and corticosterone levels but decreased the glycogen content in the liver and skeletal muscle when compared with the control group. Additionally, chronic stressor significantly increased the total cholesterol and triglyceride levels, however, acute stressor produced significantly elevated high-density lipoproteins level.. In conclusion, repeated exposure to forced-swimming stressor induced glucose intolerance and insulin resistance in rats by disrupting the insulin sensitivity as well as heightening the glycogenolysis in the liver and skeletal muscle. Acute stressor was unable to cause glucose intolerance and insulin resistance but it appears that may have a positive effect on the lipid metabolism.

Topics: Animals; Cholesterol; Corticosterone; Glucose; Glycogen; Insulin; Insulin Resistance; Lipoproteins, HDL; Lipoproteins, LDL; Male; Random Allocation; Rats; Rats, Sprague-Dawley; Stress, Psychological; Swimming; Triglycerides

Metabolic flexibility to lipid (MetFlex-lip) is the capacity to adapt lipid oxidation to lipid availability. Hypothetically, impaired MetFlex-lip in skeletal muscle induces accumulation of lipid metabolites that interfere with insulin signaling. Our aim was to compare MetFlex-lip during exercise in subjects with low (Low_IS) vs. high (High_IS) insulin sensitivity. Twenty healthy men were designated as Low_IS or High_IS on the basis of the median of the homeostatic model assessment of insulin resistance index. Groups had similar age, body mass index, and maximum oxygen uptake (V̇o

Topics: Adolescent; Adult; Exercise; Glycogen; Healthy Volunteers; Humans; Insulin Resistance; Lipid Metabolism; Male; Muscle Fibers, Skeletal; Muscle, Skeletal; Oxygen Consumption; Palmitic Acid; Real-Time Polymerase Chain Reaction; Young Adult

The operations involved in preimplantation genetic testing (PGT) occur during the key stages of gametogenesis and early embryonic development, and the health of progeny following PGT (PGT-born) is worthy of attention. In order to fully assess the potential risk of abnormal glucose metabolism in adult PGT-born offspring and to evaluate possible mechanisms, we compared a mouse model of PGT (in vitro cultured embryos with biopsy, hereafter "PTG-born mice"), an in vitro embryo manipulation mouse model (in vitro cultured embryos without biopsy), and normal mice. PGT-born mice displayed increased fasting glucose, and decreased glycogen synthesis and glucose oxidative utilization in the liver. Moreover, PGT-born mice also displayed reduced expression of insulin receptor, AKT, and insulin-stimulated Akt phosphorylation (pAkt) in the liver. These results suggest a potential risk of insulin resistance in adult PGT-born mice. By analyzing the DNA methylation profiles of 7.5 days postconception (dpc) embryos, we identified differentially methylated genes associated with liver development between PGT-born and control groups; some of these genes are associated with glucose homeostasis and insulin response. These results suggest that abnormal methylation in embryos that develop after PGT may be a potential mechanism occurring during embryonic development that can influence the risk of liver-derived insulin resistance in adulthood.

Topics: Animals; DNA Methylation; Embryo, Mammalian; Embryonic Development; Female; Gene Expression Regulation, Developmental; Genetic Testing; Glucose; Glycogen; Glycogen Synthase; Humans; Insulin Resistance; Liver; Mice, Inbred ICR; Pregnancy; Preimplantation Diagnosis; Receptor, Insulin; Risk Factors

AMPK activated protein kinase (AMPK), a master regulator of energy homeostasis, is activated in response to an energy shortage imposed by physical activity and caloric restriction. We here report on the identification of PAN-AMPK activator O304, which - in diet-induced obese mice - increased glucose uptake in skeletal muscle, reduced β cell stress, and promoted β cell rest. Accordingly, O304 reduced fasting plasma glucose levels and homeostasis model assessment of insulin resistance (HOMA-IR) in a proof-of-concept phase IIa clinical trial in type 2 diabetes (T2D) patients on Metformin. T2D is associated with devastating micro- and macrovascular complications, and O304 improved peripheral microvascular perfusion and reduced blood pressure both in animals and T2D patients. Moreover, like exercise, O304 activated AMPK in the heart, increased cardiac glucose uptake, reduced cardiac glycogen levels, and improved left ventricular stroke volume in mice, but it did not increase heart weight in mice or rats. Thus, O304 exhibits a great potential as a novel drug to treat T2D and associated cardiovascular complications.

Topics: AMP-Activated Protein Kinases; Animals; Blood Glucose; Blood Pressure; Cardiomegaly; Cardiovascular Diseases; Diabetes Mellitus, Type 2; Glucose; Glycogen; Heart; Heterocyclic Compounds; Holoprosencephaly; Homeostasis; Humans; Insulin Resistance; Insulin-Secreting Cells; Jaw Abnormalities; Metformin; Mice; Mice, Obese; Muscle, Skeletal; Rats; Stroke Volume

The kidney is an insulin-sensitive organ involved in glucose homeostasis. One major effect of insulin is to induce glycogen storage in the liver and muscle. However, no significant glycogen stores are detected in normal kidneys, but diabetic subjects present a characteristic renal histopathological feature resulting from extensive glycogen deposition mostly in nonproximal tubules. The mechanism of renal glycogen accumulation is yet poorly understood. Here, we studied in situ glycogen accumulation in the kidney from diabetic IRS2-knockout mice and the effect of the insulin-mimetic agent sodium tungstate (NaW). IRS2-knockout mice displayed hyperglycemia and hyperinsulinemia. NaW only normalized glycemia. There was no evident morphological difference between kidneys from untreated wild-type (WT), NaW-treated WT, and untreated IRS2-knockout mice. However, NaW-treated IRS2-knockout mice showed tubular alterations resembling clear cells in the cortex, but not in the outer medulla, that were correlated with glycogen accumulation. Immunohistochemical detection of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase, mostly expressed by renal proximal tubules, showed that altered tubules were of proximal origin. Our preliminary study suggests that IRS2 differentially regulates glycogen accumulation in renal tubules and that NaW treatment in the context of IRS2 ablation induces abnormal glycogen accumulation in cortical proximal tubules.

Topics: Animals; Diabetes Mellitus, Experimental; Diabetic Nephropathies; Glycogen; Hypoglycemic Agents; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Kidney; Kidney Tubules, Proximal; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Phosphoenolpyruvate Carboxykinase (ATP); Signal Transduction; Tungsten Compounds

Polysaccharides derived from mushrooms have potential to control blood sugar, reduce insulin resistance and prevent diabetic complications. The intracellular polysaccharopeptides of Trametes versicolor (TV) have been used as immunologic and oncologic adjuvants. The aim of this study was to investigate the potential activities and mechanisms of extracellular polysaccharopeptides (ePSP) obtained from TV strain LH-1 on regulating glucose homeostasis. Human hepatoma HepG2 cells incubated with normal glucose (5.5 mM, NG model), high glucose (33 mM, HG model), or high glucose (33 mM) plus high insulin (10-7 M, HGI model) concentrations were administered with TV LH-1 ePSP (50, 100, and 1000 μg/ml) for 24 hr. Glucose uptake of HepG2 cells, determined by flow cytometry, was significantly decreased in the HG and HGI models with insulin stimulation, suggesting insulin resistance of these cells; however, ePSP reversed this decrease in a dose-dependent manner (one-way ANOVA, p<0.05). In the HG and HGI models, ePSP significantly increased glycogen content, insulin receptor substrate-2 protein and phosphorylated AMP-activated protein kinase (AMPK), as determined by western blot analysis. In addition, ePSP significantly increased glucokinase in the NG and HG models, increased membrane glucose transporter-1 and decreased glycogen synthase kinase-3β in the HGI model, and increased glucose-6-phosphatase in the NG and HGI models (one-way ANOVA, p<0.05). In summary, TV LH-1 ePSP may elevate cellular glucose uptake to regulate glucose homeostasis via the activation of AMPK and glycogen synthesis in an insulin-independent manner. These results suggest that TV LH-1 ePSP may be a nutraceutical with anti-hyperglycemic activity.

Topics: Cell Survival; Dose-Response Relationship, Drug; Extracellular Space; Fermentation; Gene Expression Regulation; Glucose; Glycogen; Hep G2 Cells; Humans; Hypoglycemic Agents; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Phytotherapy; Proteoglycans; Trametes

Topics: AMP-Activated Protein Kinase Kinases; AMP-Activated Protein Kinases; Animals; Biomarkers; Blood Glucose; Disease Models, Animal; Enzyme Activation; Fructose; Glucosides; Glycogen; Insulin; Insulin Resistance; Lipids; Lipogenesis; Liver; Male; Monoterpenes; Non-alcoholic Fatty Liver Disease; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Rats, Sprague-Dawley; Signal Transduction

Annexin A6 (AnxA6) controls cholesterol and membrane transport in endo- and exocytosis, and modulates triglyceride accumulation and storage. In addition, AnxA6 acts as a scaffolding protein for negative regulators of growth factor receptors and their effector pathways in many different cell types. Here we investigated the role of AnxA6 in the regulation of whole body lipid metabolism and insulin-regulated glucose homeostasis. Therefore, wildtype (WT) and AnxA6-knockout (KO) mice were fed a high-fat diet (HFD) for 17 weeks. During the course of HFD feeding, AnxA6-KO mice gained less weight compared to controls, which correlated with reduced adiposity. Systemic triglyceride and cholesterol levels of HFD-fed control and AnxA6-KO mice were comparable, with slightly elevated high density lipoprotein (HDL) and reduced triglyceride-rich lipoprotein (TRL) levels in AnxA6-KO mice. AnxA6-KO mice displayed a trend towards improved insulin sensitivity in oral glucose and insulin tolerance tests (OGTT, ITT), which correlated with increased insulin-inducible phosphorylation of protein kinase B (Akt) and ribosomal protein S6 kinase (S6) in liver extracts. However, HFD-fed AnxA6-KO mice failed to downregulate hepatic gluconeogenesis, despite similar insulin levels and insulin signaling activity, as well as expression profiles of insulin-sensitive transcription factors to controls. In addition, increased glycogen storage in livers of HFD- and chow-fed AnxA6-KO animals was observed. Together with an inability to reduce glucose production upon insulin exposure in AnxA6-depleted HuH7 hepatocytes, this implicates AnxA6 contributing to the fine-tuning of hepatic glucose metabolism with potential consequences for the systemic control of glucose in health and disease.

Topics: Adiposity; Animals; Annexin A6; Dietary Fats; Gluconeogenesis; Glucose; Glycogen; Insulin Resistance; Lipids; Liver; Male; Mice; Mice, Knockout; Proto-Oncogene Proteins c-akt; Ribosomal Protein S6 Kinases

Insulin resistance in skeletal muscle is a major risk factor for the development of type 2 diabetes in women with polycystic ovary syndrome (PCOS). Despite this, the mechanisms underlying insulin resistance in PCOS are largely unknown.. To investigate the genome-wide DNA methylation and gene expression patterns in skeletal muscle from women with PCOS and controls and relate them to phenotypic variations.. In a case-control study, skeletal muscle biopsies from women with PCOS (n = 17) and age-, weight-, and body mass index‒matched controls (n = 14) were analyzed by array-based DNA methylation and mRNA expression profiling.. Eighty-five unique transcripts were differentially expressed in muscle from women with PCOS vs controls, including DYRK1A, SYNPO2, SCP2, and NAMPT. Furthermore, women with PCOS had reduced expression of genes involved in immune system pathways. Two CpG sites showed differential DNA methylation after correction for multiple testing. However, an mRNA expression of ∼30% of the differentially expressed genes correlated with DNA methylation levels of CpG sites in or near the gene. Functional follow-up studies demonstrated that KLF10 is under transcriptional control of insulin, where insulin promotes glycogen accumulation in myotubes of human muscle cells. Testosterone downregulates the expression levels of COL1A1 and MAP2K6.. PCOS is associated with aberrant skeletal muscle gene expression with dysregulated pathways. Furthermore, we identified specific changes in muscle DNA methylation that may affect gene expression. This study showed that women with PCOS have epigenetic and transcriptional changes in skeletal muscle that, in part, can explain the metabolic abnormalities seen in these women.

Topics: Adult; Biopsy; Case-Control Studies; Cells, Cultured; Collagen Type I; Collagen Type I, alpha 1 Chain; CpG Islands; DNA Methylation; Down-Regulation; Early Growth Response Transcription Factors; Epigenesis, Genetic; Female; Follow-Up Studies; Gene Expression Profiling; Glycogen; Humans; Insulin; Insulin Resistance; Kruppel-Like Transcription Factors; MAP Kinase Kinase 6; Muscle Fibers, Skeletal; Muscle, Skeletal; Polycystic Ovary Syndrome; Primary Cell Culture; Testosterone

Insulin resistance (IR) is considered as a major factor of type 2 diabetes (T2D), which is seriously detrimental to human health. In our present study, we found that the expression of miR-138-5p was increased in the insulin-resistant HepG2 cells induced by TNF-α. Therefore, we hypothesized that miR-138-5p might play a regulatory role in the IR. To examine this hypothesis, HepG2 cells were transfected with miR-138-5p inhibitor. Silencing of miR-138-5p increased glucose uptake and glycogen synthesis of TNF-α-stimulated HepG2 cells and decreased glucose concentration in medium, suggesting that downregulation of miR-138-5p suppressed IR in HepG2 cells. Besides that, we found that sirtuin 1 (SIRT1) was the target gene of the miR-138-5p. Moreover, co-transfection with SIRT1-siRNA and miR-138-5p inhibitor suppressed glucose uptake and glycogen synthesis of HepG2 cells compared with miR-138-5p inhibitor-transfected group, indicating that downregulation of SIRT1 weakened the inhibitory effect of miR-138-5p inhibitor on IR. In addition, overexpressed SIRT1 increased Beclin1, LC3 II/I level, and the number of GFP-LC3 dots and decreased p62 level, whereas downregulation of SIRT1 had the opposite effects. Our results demonstrated that overexpressed SIRT1 activated autophagy in HepG2 cells. Moreover, we observed that 3-methyladenine (an inhibitor of autophagy) treatment decreased the high glucose uptake and glycogen synthesis of miR-138-5p inhibitor-transfected HepG2 cells, suggesting that the inhibition of autophagy abolished the inhibitory effect of miR-138-5p inhibitor on IR in HepG2 cells. Taken together, this study suggested that miR-138-5p contributed to the TNF-α-induced IR, possibly through inducing autophagy in HepG2 cells by regulating SIRT1. MiR-138-5p might be a potential and promising target for the treatment of IR.

Topics: Adenine; Autophagy; Diabetes Mellitus, Type 2; Disease Progression; Down-Regulation; Glucose; Glycogen; Hep G2 Cells; Humans; Insulin; Insulin Resistance; MicroRNAs; Sirtuin 1; Tumor Necrosis Factor-alpha

Premature baboons exhibit peripheral insulin resistance and impaired insulin signaling. 5' AMP-activated protein kinase (AMPK) activation improves insulin sensitivity by enhancing glucose uptake (via increased glucose transporter type 4 [GLUT4] translocation and activation of the extracellular signal-regulated kinase [ERK]/ atypical protein kinase C [aPKC] pathway), and increasing fatty acid oxidation (via inhibition of acetyl-CoA carboxylase 1 [ACC]), while downregulating gluconeogenesis (via induction of small heterodimer partner [SHP] and subsequent downregulation of the gluconeogenic enzymes: phosphoenolpyruvate carboxykinase [PEPCK], glucose 6-phosphatase [G6PASE], fructose- 1,6-bisphosphatase 1 [FBP1], and forkhead box protein 1 [FOXO1]). The purpose of this study was to investigate whether pharmacologic activation of AMPK with AICAR (5-aminoimidazole-4-carboximide riboside) administration improves peripheral insulin sensitivity in preterm baboons. 11 baboons were delivered prematurely at 125±2 days (67%) gestation. 5 animals were randomized to receive 5 days of continuous AICAR infusion at a dose of 0.5 mg·g-1·day-1. 6 animals were in the placebo group. Euglycemic hyperinsulinemic clamps were performed at 5±2 and 14±2 days of life. Key molecules potentially altered by AICAR (AMPK, GLUT4, ACC, PEPCK, G6PASE, FBP1, and FOXO1), and the insulin signaling molecules: insulin receptor (INSR), insulin receptor substrate 1 (IRS-1), protein kinase B (AKT), and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) were measured using RT-PCR and western blotting. AICAR infusion did not improve whole body insulin-stimulated glucose disposal in preterm baboons (12.8±2.4 vs 12.4±2.0 mg/(kg·min), p = 0.8, placebo vs AICAR). One animal developed complications during treatment. In skeletal muscle, AICAR infusion did not increase phosphorylation of ACC, AKT, or AMPK whereas it increased mRNA expression of ACACA (ACC), AKT, and PPARGC1A (PGC1α). In the liver, INSR, IRS1, G6PC3, AKT, PCK1, FOXO1, and FBP1 were unchanged, whereas PPARGC1A mRNA expression increased after AICAR infusion. This study provides evidence that AICAR does not improve insulin sensitivity in premature euglycemic baboons, and may have adverse effects.

Topics: Administration, Intravenous; Aminoimidazole Carboxamide; Animals; Animals, Newborn; Fatty Acids, Nonesterified; Female; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Male; Muscle, Skeletal; Papio; Random Allocation; Ribonucleotides; RNA, Messenger

Topics: AMP-Activated Protein Kinases; Animals; Anti-Inflammatory Agents; Arachidonic Acids; Calcium-Calmodulin-Dependent Protein Kinase Kinase; Cell Differentiation; Diabetes Mellitus, Experimental; Embryonic Stem Cells; Endocannabinoids; Glucose; Glucose Transporter Type 4; Glycerides; Glycogen; Humans; Inflammation; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Myocytes, Cardiac; Rats; Rats, Inbred Lew; Receptor, Cannabinoid, CB1; RNA, Messenger; Signal Transduction; Tumor Necrosis Factor-alpha

Hyperglycemia is a typical pathogenic factor in a series of complications among patients with type II diabetes. Epigallocatechin-3-gallate (EGCG) is the major polyphenol extracted from green tea and is reported to be an antioxidant. The aim of the present study was to examine the effect of EGCG on insulin resistance in human HepG2 cells pretreated with high concentrations of glucose. The protein kinase B (AKT)/glycogen synthase kinase (GSK) pathways were analyzed using western blot analysis in HepG2 cells and primary mouse hepatocytes treated with high glucose and/or EGCG. Cellular glycogen content was determined using a glycogen assay kit. Reactive oxygen species (ROS) production was determined using dihydroethidium staining and flow cytometry. c‑JUN N‑terminal kinase (JNK)/insulin receptor substrate 1 (IRS1)/AKT/GSK signaling was explored using western blot analysis in HepG2 cells treated with high glucose and/or EGCG or N-acetyl-cysteine. High glucose significantly decreased the levels of phosphorylated AKT and GSK in HepG2 cells and mouse primary hepatocytes. Pretreatment with EGCG significantly restored the activation of AKT and GSK in HepG2 cells and primary hepatocytes exposed to high glucose. In HepG2 cells and primary hepatocytes, glycogen synthesis was improved by EGCG treatment in a dose‑dependent manner. High glucose significantly stimulated the production of ROS while EGCG protected high glucose‑induced ROS production. ROS is known to serve a major role in high glucose induced‑insulin resistance by increasing JNK and IRS1 serine phosphorylation. In the present study, EGCG was observed to enhance the insulin‑signaling pathway. EGCG ameliorated high glucose‑induced insulin resistance in the hepatocytes by potentially decreasing ROS‑induced JNK/IRS1/AKT/GSK signaling.

Topics: Animals; Catechin; Cell Line, Tumor; Glucose; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Insulin; Insulin Resistance; Male; Mice; Proto-Oncogene Proteins c-akt; Reactive Oxygen Species; Signal Transduction

Non-alcoholic fatty liver disease (NAFLD) has become a predictive factor of death from many diseases. The purpose of the present study is to investigate the protective effect of glycyrrhizic acid (GA), a natural triterpene glycoside, on NAFLD induced by a high-fat diet (HFD) in mice, and further to elucidate the mechanisms underlying GA protection. GA treatment significantly reduced the relative liver weight, serum ALT, AST activities, levels of serum lipid, blood glucose and insulin. GA suppressed lipid accumulation in liver. Further mechanism investigation indicated that GA reduced hepatic lipogenesis via downregulating SREBP-1c, FAS and SCD1 expression, increased fatty acids β-oxidation via an increase in PPARα, CPT1α and ACADS, and promoted triglyceride metabolism through inducing LPL activity. Furthermore, GA reduced gluconeogenesis through repressing PEPCK and G6Pase, and increased glycogen synthesis through an induction in gene expression of PDase and GSK3β. In addition, GA increased insulin sensitivity through upregulating phosphorylation of IRS-1 and IRS-2. In conclusion, GA produces protective effect against NAFLD, due to regulation of genes involved in lipid, glucose homeostasis and insulin sensitivity.

Topics: Animals; Body Weight; Cytoprotection; Diet, High-Fat; Fatty Acids; Gene Expression Regulation; Gluconeogenesis; Glucose Tolerance Test; Glycogen; Glycyrrhizic Acid; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Non-alcoholic Fatty Liver Disease; Organ Size; Receptors, Cytoplasmic and Nuclear; Triglycerides

Disruption of the

Topics: Acetyl-CoA Carboxylase; Active Transport, Cell Nucleus; Animals; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Cell Nucleus; Fatty Liver; Forkhead Box Protein O1; Glycogen; Glycogen Synthase Kinase 3; Hepatocytes; Insulin Receptor Substrate Proteins; Insulin Resistance; Mice; Mice, Knockout; Nuclear Proteins; Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction; Sterol Regulatory Element Binding Protein 1; Transcription Factors

Insulin resistance is central to the development of type 2 diabetes and related metabolic disorders. Because skeletal muscle is responsible for the majority of whole body insulin-stimulated glucose uptake, regulation of glucose metabolism in this tissue is of particular importance. Although Rho GTPases and many of their affecters influence skeletal muscle metabolism, there is a paucity of information on the protein kinase N (PKN) family of serine/threonine protein kinases. We investigated the impact of PKN2 on insulin signaling and glucose metabolism in primary human skeletal muscle cells in vitro and mouse tibialis anterior muscle in vivo. PKN2 knockdown in vitro decreased insulin-stimulated glucose uptake, incorporation into glycogen, and oxidation. PKN2 siRNA increased 5'-adenosine monophosphate-activated protein kinase (AMPK) signaling while stimulating fatty acid oxidation and incorporation into triglycerides and decreasing protein synthesis. At the transcriptional level, PKN2 knockdown increased expression of PGC-1α and SREBP-1c and their target genes. In mature skeletal muscle, in vivo PKN2 knockdown decreased glucose uptake and increased AMPK phosphorylation. Thus, PKN2 alters key signaling pathways and transcriptional networks to regulate glucose and lipid metabolism. Identification of PKN2 as a novel regulator of insulin and AMPK signaling may provide an avenue for manipulation of skeletal muscle metabolism.

Topics: Adenylate Kinase; Animals; Fatty Acids; Gene Knockdown Techniques; Glucose; Glycogen; Humans; In Vitro Techniques; Insulin Resistance; Lipid Metabolism; Male; Mice; Mice, Inbred C57BL; Muscle Fibers, Skeletal; Muscle, Skeletal; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Phosphorylation; Protein Biosynthesis; Protein Kinase C; Quadriceps Muscle; Signal Transduction; Sterol Regulatory Element Binding Protein 1; Triglycerides

To evaluate the incidence of insulin resistance and metabolic syndrome (MetS) in patients with glycogenic acanthosis (GA).. Thirty patients with GA, detected upon endoscopy, and 30 age- and sex-matched control patients without GA were included in this case-control study. Patients with GA were considered group 1 and control group was considered group 2. Anthropometric measurements [height, weight, and waist circumference (WC)], biochemical parameters [fasting plasma glucose (FPG), triglyceride, high-density lipoprotein (HDL), and low-density lipoprotein (LDL)], and serum fasting insulin levels were evaluated. Insulin resistance (IR) was estimated by the homeostatic model assessment of IR. MetS was diagnosed using the criteria of the National Cholesterol Education Program Adult Treatment Panel III. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated to evaluate associations with GA.. There were no differences in terms of FPG, triglyceride, HDL, and LDL between groups (p-values 0.118, 0.114, 0.192, 0.086, respectively). WC was significantly higher in group 1 than in group 2 (103.77 vs 97.03, p=0.032). The number of patients with IR and MetS were significantly higher in group 1 than in group 2 (53.3% vs 13.3%, p=0.003 and 53.3% vs 23.3%, p=0.034). ORs [95% CI] of WC, IR, and MetS for GA were 0.68 [0.17-2.62], 7.12 [1.89-26.72], and 4.11 [1.04-16.21], respectively.. These findings showed that IR and MetS were significantly associated with the presence of GA.

Topics: Adult; Case-Control Studies; Esophageal Diseases; Female; Glycogen; Humans; Incidence; Insulin; Insulin Resistance; Male; Metabolic Syndrome; Middle Aged; Risk Factors; Waist Circumference

Topics: Animal Feed; Animals; Animals, Newborn; Birth Weight; Blood Glucose; Diabetes Mellitus, Type 2; Diet; Female; Fetal Growth Retardation; Glucose-6-Phosphatase; Glycogen; Hyperglycemia; Insulin Resistance; Liver; Male; Methionine; Muscles; Phosphoenolpyruvate Carboxykinase (GTP); Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction; Swine; Weaning

Pregnancy is known to be a diabetogenic state. With sedentary lifestyle and wrong dietary choices, gestational diabetes mellitus is on the rise. This raises a concern as placenta is becoming an acceptable choice, as a source of Mesenchymal Stromal Cells (MSCs). In our current study we questioned whether there exists a difference between MSCs isolated from normal and diabetic (Gd-P-MSCs) placenta, as the health of the cells used in therapy is of prime importance. We isolated and verified the Gd-P-MSCs based on their surface markers and differentiation potential. We looked at viability and proliferation and did not see a difference between the two. We analysed the glucose uptake potential of these cells by assessing the remnant glucose in the media, glucose within the cells by 2-NBDG and by glycogen storage. Despite only a slight downregulation of mRNA expression levels of glucose transporters, Gd-P-MSCs exhibited decreased glucose uptake even upon insulin stimulation and decreased glycogen storage, indicative of an insulin resistant state. We then assessed the colony forming ability of the cells and found a decreased clonogenicity in Gd-P-MSCs. We also examined the angiogenic potential of the cells by tube formation. Gd-P-MSCs showed decreased angiogenic potential when compared to normal cells. Thus we show for the first time, the effect of gestational diabetes on cells isolated from the chorionic villi of term placenta. Gd-P-MSCs are indeed insulin resistant, exhibit decreased clonogenicity and angiogenic potential. The present investigation is of relevance to the choice of sample for MSC isolation for therapeutic purposes.

Topics: Case-Control Studies; Colony-Forming Units Assay; Diabetes, Gestational; Female; Glucose; Glycogen; Humans; Insulin Resistance; Mesenchymal Stem Cells; Neovascularization, Physiologic; Placenta; Pregnancy; Primary Cell Culture

Previous studies have shown that the short-term intake of a high-fat diet (HFD) impairs glucose metabolism. In this study, we investigated the influences of pre-exercise HFD intake for 3 d on post-exercise glycogen repletion in skeletal muscle in ICR mice. Mice received either an HFD (57% kcal from fat, 23% kcal from carbohydrate; HFD group) or standard laboratory chow (13% kcal from fat, 60% kcal from carbohydrate; Con group) for 3 d before exercise. Mice performed treadmill running at 25 m/min for 60 min and were orally administered a glucose (2 mg/g body weight) solution immediately after and at 60 min after exercise. A negative main effect of pre-exercise HFD intake was observed for skeletal muscle glycogen concentration from the pre-exercise phase to 120 min of post-exercise recovery (p<0.01). Blood glucose concentration in the HFD group was significantly higher than in the Con group at 120 min after exercise (p<0.01). No significant difference was observed in plasma insulin concentration. There were no significant between-group differences in the phosphorylation state of Akt Thr308, AMPK Thr172, AS160 Thr642, or glycogen synthase Ser641 or in glucose transporter 4 protein levels during post-exercise recovery. Our results suggest that the intake of a pre-exercise HFD for 3 d affects post-exercise glycogen repletion in skeletal muscle without impairing the insulin signaling cascade.

Topics: AMP-Activated Protein Kinases; Animals; Blood Glucose; Diet, Carbohydrate-Restricted; Diet, High-Fat; Dietary Carbohydrates; Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Liver; Liver Glycogen; Male; MAP Kinase Signaling System; Mice, Inbred ICR; Muscle, Skeletal; Phosphorylation; Physical Conditioning, Animal; Protein Processing, Post-Translational; Time Factors

4-vinilcyclohexene diepoxide (4-VCD) causes premature ovarian failure and may result in estrogen deficiency, characterizing the transition to estropause in rodents (equivalent to menopause in women). Estropause/menopause is associated with metabolic derangements such as glucose intolerance and insulin resistance. Glucocorticoids (GCs) are known to exert diabetogenic effects. Thus, we aimed to investigate whether rats with premature ovarian failure are more prone to the diabetogenic effects of GC. For this, immature female rats received daily injections of 4-VCD [160mg/kg body weight (b.w.), intraperitoneally (i.p.)] for 15 consecutive days, whereas control rats received vehicle. After 168days of the completion of 4-VCD administration, rats were divided into 4 groups: CTL-received daily injections of saline (1mL/kg, b.w., i.p.) for 5days; DEX-received daily injections of dexamethasone (1mg/kg, b.w., i.p.) for 5days; VCD-treated as CTL group; VCD+DEX-treated as DEX group. Experiments and euthanasia occurred one day after the last dexamethasone injection. 4-VCD-treated rats exhibited ovary hypotrophy and reduced number of preantral follicles (p<0.05). Premature ovarian failure had no impact on the body weight gain or food intake, but both were reduced by the effects of dexamethasone. The increase in blood glucose, plasma insulin and triacylglycerol levels as well as the reduction in insulin sensitivity caused by dexamethasone treatment was not exacerbated in the VCD+DEX group of rats. Premature ovarian failure did change neither the hepatic content of glycogen and triacylglycerol nor the glycerol release from perigonadal adipose tissue. Glucose intolerance was observed in the VCD group after an ipGTT (p<0.05), but not after an oral glucose challenge. Glucose intolerance and compensatory pancreatic β-cell mass caused by GC were not modified by ovarian failure in the VCD+DEX group. We conclude that reduced ovarian function has no major implications on the diabetogenic effects promoted by GC treatment, indicating that other factors related to aging may make rats more vulnerable to GC side effects on glucose metabolism.

Topics: Adipose Tissue; Aging; Animals; Blood Glucose; Cellular Senescence; Cyclohexenes; Dexamethasone; Drug Interactions; Female; Glucocorticoids; Glucose; Glucose Tolerance Test; Glycogen; Homeostasis; Humans; Insulin; Insulin Resistance; Insulin Secretion; Insulin-Secreting Cells; Liver; Ovarian Follicle; Ovary; Primary Ovarian Insufficiency; Rats; Rats, Wistar; Steroids; Vinyl Compounds

Topics: AMP-Activated Protein Kinases; Animals; Blotting, Western; Electrophoresis, Polyacrylamide Gel; Female; Glucose; Glycogen; Glycogen Synthase; GTPase-Activating Proteins; In Vitro Techniques; Insulin Resistance; Mice; Mice, Knockout; Muscle Contraction; Muscle, Skeletal; Phosphorylation; Physical Conditioning, Animal; Signal Transduction

Glycogen and triglyceride are two major forms of energy storage in the body and provide the fuel during different phases of food deprivation. However, how glycogen metabolism is linked to fat deposition in adipose tissue has not been clearly characterized. We generated a mouse model with whole-body deletion of PPP1R3G, a glycogen-targeting subunit of protein phosphatase-1 required for glycogen synthesis. Upon feeding with high-fat diet, the body weight and fat composition are significantly reduced in the PPP1R3G

Topics: 3T3-L1 Cells; Adipocytes; Animals; Basal Metabolism; Blood Glucose; Diet, High-Fat; Fatty Liver; Gene Deletion; Glycogen; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Obesity; Postprandial Period; Protein Phosphatase 1; Triglycerides

Dysregulation of glucose metabolism is a primary hallmark of metabolic disease (i.e., diabetes, obesity, etc.). Complementary nonpharmaceutical strategies are needed to prevent and/or ameliorate dysregulation of glucose metabolism and prevent progression from normoglycemia to prediabetes and type 2 diabetes across the lifespan. Cocoa compounds, particularly the procyanidins, have shown promise for improving insulin sensitivity and blood glucose homeostasis. However, the molecular mechanisms by which cocoa procyanidins exert these functions remain poorly understood. Furthermore, cocoa procyanidins exhibit size diversity, and evidence suggests that procyanidin bioactivity and size may be related. Here, we show that a procyanidin-rich cocoa extract elicits an antidiabetic effect by stimulating glycogen synthesis and glucose uptake, independent of insulin. Cocoa procyanidins did not appear to act via stimulation of AMPK or CaMKII activities. Additionally, in the presence of insulin, glycogen synthesis and AKT phosphorylation were affected. These mechanisms of action are most pronounced in response to oligomeric and polymeric procyanidins. These results demonstrate (1) specific mechanisms by which cocoa procyanidins improve glucose utilization in skeletal muscle and (2) that larger procyanidins appear to possess enhanced activities. These mechanistic insights suggest specific strategies and biological contexts that may be exploited to maximize the antidiabetic benefits of cocoa procyanidins.

Topics: Body Mass Index; Cacao; Cells, Cultured; Glucose; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Male; Molecular Weight; Muscle Fibers, Skeletal; Plant Extracts; Proanthocyanidins

Intermittent fasting (IMF) is a relatively new dietary approach to weight management, although the efficacy and adverse effects have not been full elucidated and the optimal diets for IMF are unknown. We tested the hypothesis that a one-meal-per-day intermittent fasting with high fat (HF) or protein (HP) diets can modify energy, lipid, and glucose metabolism in normal young male Sprague-Dawley rats with diet-induced obesity or overweight. Male rats aged 5 weeks received either HF (40% fat) or HP (26% protein) diets ad libitum (AL) or for 3 h at the beginning of the dark cycle (IMF) for 5 weeks. Epidydimal fat pads and fat deposits in the leg and abdomen were lower with HP and IMF. Energy expenditure at the beginning of the dark cycle, especially from fat oxidation, was higher with IMF than AL, possibly due to greater activity levels. Brown fat content was higher with IMF. Serum ghrelin levels were higher in HP-IMF than other groups, and accordingly, cumulative food intake was also higher in HP-IMF than HF-IMF. HF-IMF exhibited higher area under the curve (AUC) of serum glucose at the first part (0-40 min) during oral glucose tolerance test, whereas AUC of serum insulin levels in both parts were higher in IMF and HF. During intraperitoneal insulin tolerance test, serum glucose levels were higher with IMF than AL. Consistently, hepatic insulin signaling (GLUT2, pAkt) was attenuated and PEPCK expression was higher with IMF and HF than other groups, and HOMA-IR revealed significantly impaired attenuated insulin sensitivity in the IMF groups. However, surprisingly, hepatic and skeletal muscle glycogen storage was higher in IMF groups than AL. The higher glycogen storage in the IMF groups was associated with the lower expression of glycogen phosphorylase than the AL groups. In conclusion, IMF especially with HF increased insulin resistance, possibly by attenuating hepatic insulin signaling, and lowered glycogen phosphorylase expression despite decreased fat mass in young male rats. These results suggest that caution may be warranted when recommending intermittent fasting, especially one-meal-per-day fasting, for people with compromised glucose metabolism.

Topics: Adipose Tissue; Animals; Body Composition; Body Weight; Diet, High-Fat; Diet, High-Protein; Energy Metabolism; Fasting; Glucose; Glucose Tolerance Test; Glycogen; Insulin Resistance; Lipid Metabolism; Lipids; Liver; Male; Rats, Sprague-Dawley

Three new meroterpenoids, ganoleucin A-C (1-3), together with five known meroterpenoids (4-8), were isolated from the fruiting bodies of Ganoderma leucocontextum. The structures of the new compounds were elucidated by extensive spectroscopic analysis, circular dichroism (CD) spectroscopy, and chemical transformation. The inhibitory effects of 1-8 on HMG-CoA reductase and α-glucosidase were tested in vitro. Ganomycin I (4), 5, and 8 showed stronger inhibitory activity against HMG-CoA reductase than the positive control atorvastatin. Compounds 1, and 3-8 presented potent noncompetitive inhibitory activity against α-glucosidase from both yeast and rat small intestinal mucosa. Ganomycin I (4), the most potent inhibitor against both α-glucosidase and HMG-CoA reductase, was synthesized and evaluated for its in vivo bioactivity. Pharmacological results showed that ganomycin I (4) exerted potent and efficacious hypoglycemic, hypolipidemic, and insulin-sensitizing effects in KK-A

Topics: Adipose Tissue; Alanine Transaminase; alpha-Glucosidases; Animals; Aspartate Aminotransferases; Blood Glucose; Body Weight; Female; Ganoderma; Glycogen; Glycoside Hydrolase Inhibitors; Hydroquinones; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Hypoglycemic Agents; Insulin Resistance; Kinetics; Liver; Male; Mice; Molecular Docking Simulation; Protein Conformation

Steroid-induced diabetes is the most common form of drug-induced hyperglycemia. Therefore, metabolic and immunological alterations associated with chronic oral corticosterone were investigated using male nonobese diabetic mice. Three weeks after corticosterone delivery, there was reduced sensitivity to insulin action measured by insulin tolerance test. Body composition measurements revealed increased fat mass and decreased lean mass. Overt hyperglycemia (>250 mg/dL) manifested 6 weeks after the start of glucocorticoid administration, whereas 100% of the mice receiving the vehicle control remained normoglycemic. This phenotype was fully reversed during the washout phase and readily reproducible across institutions. Relative to the vehicle control group, mice receiving corticosterone had a significant enhancement in pancreatic insulin-positive area, but a marked decrease in CD3

Topics: Administration, Oral; Animals; Body Composition; CD3 Complex; Citrate (si)-Synthase; Corticosterone; Gene Expression Regulation, Enzymologic; Glycogen; Glycogen Synthase; Hyperglycemia; Insulin; Insulin Resistance; Islets of Langerhans; Male; Mice, Inbred NOD; Models, Biological; Phenotype; Rats; Thinness

Topics: Adrenal Medulla; Animals; Blood Glucose; Diabetes Mellitus, Type 2; Disease Models, Animal; Fasting; Glucose; Glucose Tolerance Test; Glycogen; Hypoxia; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Oxygen; Oxyhemoglobins; Sleep Apnea, Obstructive

The decoctions of Ficus carica Linn. (Moraceae) leaves are used in the folklore treatment of diabetes.. To evaluate the effect of F. carica on glucose and lipids levels, carbohydrate metabolism enzymes and β-cells protective effects in type 2 diabetes.. Diabetes was induced in 15 days high-fat diet (HFD)-fed Wistar rats by intraperitoneal injection of streptozotocin (STZ) (40 mg/kg). The ethyl acetate extract (250 and 500 mg/kg) of F. carica leaves was administered for 28 days. Oral glucose tolerance (OGTT) and intraperitoneal insulin tolerance tests (ITT) were evaluated on 15th and 25th days, respectively.. The ethyl acetate extract (250 and 500 mg/kg) of n F. carica leaves showed significant effect (p < 0.005) in the levels of blood glucose, total cholesterol (TC), triglycerides (TG), body weight and hepatic glycogen. In OGTT, F. carica (250 and 500 mg/kg) significantly (p < 0.005) detained the increase in blood glucose levels at 60 and 120 min and in ITT, F. carica enhanced the glucose utilization significantly (p < 0.005) over 30 and 60 min compared to diabetic control. Further, the altered activities of key carbohydrate metabolizing enzymes such as glucose-6-phosphatase, fructose-1,6-bisphosphatase and hexokinase in the liver tissue of diabetic rats were significantly (p < 0.005) reverted to near normal levels upon treatment with F. carica. Immumohistochemical studies of islets substantiated the cytoprotective effect on pancreatic β-cells.. F. carica leaves exerted significant effect on carbohydrate metabolism enzymes with promising hypoglycemic and hypolipidemic activities in type 2 diabetic rats.

Topics: Acetates; Animals; Biomarkers; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Diet, High-Fat; Dose-Response Relationship, Drug; Ficus; Glucose Tolerance Test; Glyburide; Glycogen; Hypoglycemic Agents; Hypolipidemic Agents; Insulin; Insulin Resistance; Insulin-Secreting Cells; Lipids; Liver; Male; Phytotherapy; Plant Extracts; Plant Leaves; Plants, Medicinal; Rats, Wistar; Solvents; Streptozocin; Time Factors

Dipeptidyl-peptidase 4 [DPP-4) has evolved into an important target in diabetes therapy due to its role in incretin hormone metabolism. In contrast to its systemic effects, cellular functions of membranous DPP-4 are less clear. Here we studied the role of DPP-4 in hepatic energy metabolism. In order to distinguish systemic from cellular effects we established a cell culture model of DPP-4 knockdown in human hepatoma cell line HepG2. DPP-4 suppression was associated with increased basal glycogen content due to enhanced insulin signaling as shown by increased phosphorylation of insulin-receptor substrate 1 (IRS-1), protein kinase B/Akt and mitogen-activated protein kinases (MAPK)/ERK, respectively. Additionally, glucose-6-phosphatase cDNA expression was significantly decreased in DPP-4 deficiency. Reduced triglyceride content in DPP-4 knockdown cells was paralleled by enhanced expressions of peroxisome proliferator-activated receptor alpha (PPARα) and carnitine palmitoyltransferase -1 (CPT-1) while sterol regulatory element-binding protein 1c (SREBP-1c) expression was significantly decreased. Our data suggest that hepatic DPP-4 induces a selective pathway of insulin resistance with reduced glycogen storage, enhanced glucose output and increased lipid accumulation in the liver. Hepatic DPP-4 might be a novel target in fatty liver disease in patients with glucose intolerance.

Topics: Blotting, Western; Carnitine O-Palmitoyltransferase; Dipeptidyl Peptidase 4; Gene Expression Regulation, Neoplastic; Glucose; Glucose-6-Phosphatase; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Insulin Resistance; Lipid Metabolism; Mitogen-Activated Protein Kinases; Phosphorylation; PPAR alpha; Proto-Oncogene Proteins c-akt; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; Sterol Regulatory Element Binding Protein 1; Triglycerides

Because of the paucity of information regarding metabolic effects of advanced glycation end products (AGEs) on liver, we evaluated effects of AGEs chronic administration in (1) insulin sensitivity; (2) hepatic expression of genes involved in AGEs, glucose and fat metabolism, oxidative stress and inflammation and; (3) hepatic morphology and glycogen content. Rats received intraperitoneally albumin modified (AlbAGE) or not by advanced glycation for 12 weeks. AlbAGE induced whole-body insulin resistance concomitantly with increased hepatic insulin sensitivity, evidenced by activation of AKT, inactivation of GSK3, increased hepatic glycogen content, and decreased expression of gluconeogenesis genes. Additionally there was reduction in hepatic fat content, in expression of lipogenic, pro-inflamatory and pro-oxidative genes and increase in reactive oxygen species and in nuclear expression of NRF2, a transcription factor essential to cytoprotective response. Although considered toxic, AGEs become protective when administered chronically, stimulating AKT signaling, which is involved in cellular defense and insulin sensitivity.

Topics: Albumins; Animals; Cell Nucleus; Gene Expression Regulation; Gluconeogenesis; Glycation End Products, Advanced; Glycogen; Glycogen Synthase Kinase 3 beta; HMGB1 Protein; Hormesis; Inflammation Mediators; Injections, Intraperitoneal; Insulin Resistance; Lipogenesis; Liver; Male; Models, Biological; NF-E2-Related Factor 2; Oxidation-Reduction; Proto-Oncogene Proteins c-akt; Rats, Wistar; Reactive Oxygen Species; Sterol Regulatory Element Binding Protein 1

Receptors of the T1R family are molecular sensors for sweet taste stimuli. They are expressed not only in the oral cavity, but in most of endocrine cells controlling homeostasis of glucose as well as in adipocytes. Earlier, we have demonstrated that deletion of the Taslr3 gene, which encodes the T1R3 protein, reduces glucose tolerance, elevates insulin resistance and cause a decrease of blood glucose level after food deprivation. The goal of the study was to elucidate an involvement of T1R3 in control of endogenous glucose synthesis and lipid metabolism. Experiments were performed with an inbred mouse strain C57BL/6ByJ and the Taslr3-gene knockout strain C57BL/6J-Tas1r3tm1Rfm maintained at the normocaloric diet. It was shown in vivo that the presence of intact T1R3 stimulates gluconeogenesis and lipid utilization during starvation and likely promotes glycogen synthesis. Additionally, T1R3 potentiates utilization of triglycerides and glycerol (in fed state) and restricts secretion of glucagon during fasting but does not affect insulin output. Thus, T1R3-mediated visceral reception of metabolites is involved in control of carbohydrate and lipid metabolism.

Topics: Animals; Gene Deletion; Gluconeogenesis; Glycogen; Insulin Resistance; Lipid Metabolism; Mice; Mice, Knockout; Receptors, G-Protein-Coupled

Angiopoietin-like protein 8 (ANGPTL8)/betatrophin, a newly identified protein, is primarily expressed in the liver and regulates the glucose metabolic transition during fasting and re-feeding in mice with or without insulin resistance. These findings strongly suggest that ANGPTL8/betatrophin could be a novel glucose-lowering candidate medicine for type 2 diabetes. However, the molecular mechanisms by which ANGPTL8/betatrophin regulates glucose metabolism are poorly understood in human. Two sub-clones of HepG2 cells, ANGPTL8/betatrophin knockouts and ANGPTL8/betatrophin over-expressors, were established using TALENs (transcription activator-like effector nucleases) and through stable transfection, respectively. Over-expression of ANGPTL8/betatrophin enhanced the insulin-stimulated activation of the Akt-GSK3β or Akt-FoxO1 pathway, no matter whether the cells were present with insulin resistance or not. In contrast, knockout of ANGPTL8/betatrophin did not affect the Akt-GSK3β or Akt-FoxO1 pathway unless the HepG2 cells were preset with insulin resistance. Our results suggest that ANGPTL8/betatrophin might play an important role in glucose metabolism in the context of insulin resistance.

Topics: Angiopoietin-Like Protein 8; Angiopoietin-like Proteins; Animals; Base Sequence; Forkhead Box Protein O1; Gene Knockout Techniques; Gluconeogenesis; Glucose; Glycogen; Glycogen Synthase Kinase 3 beta; Hep G2 Cells; Humans; Insulin; Insulin Resistance; Liver; Male; Mice, Inbred BALB C; Models, Biological; Peptide Hormones; Phosphorylation; Proto-Oncogene Proteins c-akt; RNA, Messenger; Signal Transduction; Transcription Activator-Like Effector Nucleases; Transfection; Up-Regulation

Insulin resistance is a serious health condition worldwide; however, its exact mechanisms are still unclear. This study investigates agmatine (AGM; an endogenous metabolite of L-arginine) effects on insulin resistance induced by high fructose diet (HFD) in rats and the possible involved mechanisms. Sprague Dawley rats were fed 60% HFD for 12 weeks, and AGM (10 mg/kg/day, orally) was given from week 9 to 12. AGM significantly reduced HFD-induced elevation in fasting insulin level, homeostasis model assessment of insulin resistance (HOMA-IR) index and liver glycogen content from 3.44-, 3.62- and 2.07- to 2.59-, 2.78- and 1.3-fold, respectively, compared to the control group, while it increased HFD-induced reduction in glucose tolerance. Additionally, AGM significantly decreased HFD-induced elevation in serum triglycerides, low density lipoprotein cholesterol and very low density lipoprotein cholesterol levels from 3.18-, 2.97- and 4.75- to 1.25-, 1.25- and 1.07-fold, respectively, compared to control group. Conversely, AGM had no significant effect on HFD-induced changes in fasting glucose, glycosylated hemoglobin, insulin tolerance and high density lipoprotein cholesterol. Furthermore, AGM significantly reduced HFD-induced elevation in mRNA expression of glucose transporter type-2 (GLUT-2), mammalian target of rapamycin (mTOR) and sterol regulatory element-binding protein-1c (SREBP-1c) without affecting that of peroxisome proliferator-activated receptor-alpha (PPAR-α) in the liver. Additionally, AGM enhanced ACh-induced aortic relaxation and attenuated liver steatosis induced by HFD. In conclusion, AGM may have a therapeutic potential in insulin resistance through suppressing SREBP-1c, mTOR and GLUT-2 in liver.

Topics: Agmatine; Animals; Aorta, Thoracic; Blood Glucose; Diet; Fructose; Glucose Tolerance Test; Glucose Transporter Type 2; Glycated Hemoglobin; Glycogen; In Vitro Techniques; Insulin; Insulin Resistance; Lipids; Liver; Male; PPAR alpha; Rats, Sprague-Dawley; RNA, Messenger; Sterol Regulatory Element Binding Protein 1; TOR Serine-Threonine Kinases

The goal of this study was to explore the effect of lifelong aerobic exercise (i.e., chronic training) on skeletal muscle substrate stores (intramyocellular triglyceride [IMTG] and glycogen), skeletal muscle phenotypes, and oxidative capacity (ox), in older endurance-trained master athletes (OA) compared with noncompetitive recreational younger (YA) athletes matched by frequency and mode of training.. Thirteen OA (64.8 ± 4.9 yr) exercising 5 times per week or more were compared with 14 YA (27.8 ± 4.9 yr) males and females. IMTG, glycogen, fiber types, succinate dehydrogenase, and capillarization were measured by immunohistochemistry in vastus lateralis biopsies. Fat-ox and carbohydrate (CHO)-ox were measured by indirect calorimetry before and after an insulin clamp and during a cycle ergometer graded maximal test.. V˙O2peak was lower in OA than YA. The OA had greater IMTG in all fiber types and lower glycogen stores than YA. This was reflected in greater proportion of type I and less type II fibers in OA. Type I fibers were similar in size, whereas type II fibers were smaller in OA compared with YA. Both groups had similar succinate dehydrogenase content. Numbers of capillaries per fiber were reduced in OA but with a higher number of capillaries per area. Metabolic flexibility and insulin sensitivity were similar in both groups. Exercise metabolic efficiency was higher in OA. At moderate exercise intensities, carbohydrate-ox was lower in OA but with similar Fat-ox.. Lifelong exercise is associated with higher IMTG content in all muscle fibers and higher metabolic efficiency during exercise that are not explained by differences in muscle fibers types and other muscle characteristics when comparing older with younger athletes matched by exercise mode and frequency.

Topics: Adolescent; Adult; Age Factors; Aged; Athletes; Carbohydrate Metabolism; Cross-Sectional Studies; Exercise; Female; Glycogen; Humans; Insulin Resistance; Lipid Metabolism; Male; Middle Aged; Muscle Fibers, Fast-Twitch; Muscle Fibers, Slow-Twitch; Muscle, Skeletal; Oxygen Consumption; Physical Endurance; Triglycerides; Young Adult

The impact of diet-induced weight loss and weight loss due to RYGB in patients with (T2DM, N = 16) and without (OB, N = 27) type 2 diabetes was studied.. At inclusion (A), after diet-induced weight loss (B), 4 months post-surgery (C) and 18 months post-surgery (D) body composition, hepatic glucose production (HGP), insulin-mediated glucose uptake (GIR), respiratory exchange ratio, hepatic insulin sensitivity and clearance were determined. GLUT4, intramuscular triglycerides (IMTG) and glycogen content were measured in skeletal muscle.. Weight loss was 35-40 kg, and approximately one-third of the total improvement in GIR in T2DM was observed after the diet-induced weight loss of only ~6 kg (B). Insulin clearance, visceral fat and fasting plasma insulin also improved significantly after the diet (P < 0.05). Throughout the study, HGP, GLUT4 and glycogen content did not change significantly, but IMTG decreased significantly consistent with significant increases in GIR. Metabolic flexibility and hepatic insulin sensitivity improved after RYGB.. Metabolic improvements of RYGB are present already after the diet-induced weight loss prior to surgery. GLUT4 content in skeletal muscle cannot and IMTG content can only partly explain increases in GIR after RYGB.

Topics: Adult; Blood Glucose; Diabetes Mellitus, Type 2; Diet, Reducing; Female; Gastric Bypass; Glycogen; Humans; Insulin; Insulin Resistance; Male; Obesity; Triglycerides; Weight Loss

This work investigated the underlying mechanism of high-fructose/sucrose and high-fat diets, which rapidly induce metabolic syndrome in vivo, via a new cell model.. Glucose and/or fructose were used to induce the human hepatoma cell (HepG2) in the presence of palmitic acid, oleic acid, or combined fatty acids (CFA) for 24 h. The alterations in lipid and uric acid production, glucose metabolism, oxidative status, and related genes and proteins were monitored. The cell model that featured metabolic disorders was established by treatment of 10 mM glucose and 15 mM fructose plus 1 mM CFA. Results showed that palmitic acid mainly induced insulin resistance, oxidative stress, and triglyceride (TG) secretion, whereas oleic acid mainly contributed to intracellular TG. Fructose was mainly responsible for uric acid and cholesterol production. In addition, fructose synergistically elevated the intra- and extracellular TG and extracellular malonaldehyde with glucose and CFA. Regulations of genes and proteins associated with carbohydrate metabolism and lipogenesis partially explained the action of fructose in inducing the metabolic disorders in cell.. The combination of glucose, fructose, and CFA could successfully induce metabolic disorders in HepG2 cells, including dyslipidemia, insulin resistance, hyperuricemia, and oxidative stress.

Topics: Cell Cycle; Cholesterol; Diet, High-Fat; Fatty Acids, Nonesterified; Fructokinases; Fructose; Glucose; Glycogen; Hep G2 Cells; Humans; Insulin Resistance; Lipid Metabolism; Malondialdehyde; Metabolic Syndrome; Oxidative Stress; Triglycerides; Uric Acid

Increasing studies have shown protective effects of intermittent hypoxia on brain injury and heart ischemia. However, the effect of intermittent hypoxia on blood glucose metabolism, especially in diabetic conditions, is rarely observed. The aim of this study was to investigate whether intermittent hypoxia influences blood glucose metabolism in type 1 diabetic rats. Streptozotocin-induced diabetic adult rats and age-matched control rats were treated with intermittent hypoxia (at an altitude of 3 km, 4 h per day for 3 weeks) or normoxia as control. Fasting blood glucose, body weight, plasma fructosamine, plasma insulin, homeostasis model assessment of insulin resistance (HOMA-IR), pancreas β-cell mass, and hepatic and soleus glycogen were measured. Compared with diabetic rats before treatment, the level of fasting blood glucose in diabetic rats after normoxic treatment was increased (19.88 ± 5.69 mmol/L vs. 14.79 ± 5.84 mmol/L, p < 0.05), while it was not different in diabetic rats after hypoxic treatment (13.14 ± 5.77 mmol/L vs. 14.79 ± 5.84 mmol/L, p > 0.05). Meanwhile, fasting blood glucose in diabetic rats after hypoxic treatment was also lower than that in diabetic rats after normoxic treatment (13.14 ± 5.77 mmol/L vs. 19.88 ± 5.69 mmol/L, p<0.05). Plasma fructosamine in diabetic rats receiving intermittent hypoxia was significantly lower than that in diabetic rats receiving normoxia (1.28 ± 0.11 vs. 1.39 ± 0.11, p < 0.05), while there were no significant changes in body weight, plasma insulin and β-cell mass. HOMA-IR in diabetic rats after hypoxic treatment was also lower compared with diabetic rats after normoxic treatment (3.48 ± 0.48 vs. 3.86 ± 0.42, p < 0.05). Moreover, intermittent hypoxia showed effect on the increase of soleus glycogen but not hepatic glycogen. We conclude that intermittent hypoxia maintains glycemia in streptozotocin-induced diabetic rats and its regulation on muscular glycogenesis may play a role in the underlying mechanism.

Topics: Animals; Blood Glucose; Body Weight; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Fructosamine; Glycogen; Humans; Hypoxia; Insulin; Insulin Resistance; Insulin-Secreting Cells; Liver; Male; Muscle, Skeletal; Rats

The leaf extract of Urtica dioica L. (UT) has been reported to improve glucose homeostasis in vivo, but definitive studies on efficacy and mechanism of action are lacking. We investigated the effects of UT on obesity- induced insulin resistance in skeletal muscle. Male C57BL/6J mice were divided into three groups: low-fat diet (LFD), high-fat diet (HFD) and HFD supplemented with UT. Body weight, body composition, plasma glucose and plasma insulin were monitored. Skeletal muscle (gastrocnemius) was analyzed for insulin sensitivity, ceramide accumulation and the post translational modification and activity of protein phosphatase 2A (PP2A). PP2A is activated by ceramides and dephosphorylates Akt. C2C12 myotubes exposed to excess free fatty acids with or without UT were also evaluated for insulin signaling and modulation of PP2A. The HFD induced insulin resistance, increased fasting plasma glucose, enhanced ceramide accumulation and PP2A activity in skeletal muscle. Supplementation with UT improved plasma glucose homeostasis and enhanced skeletal muscle insulin sensitivity without affecting body weight and body composition. In myotubes, UT attenuated the ability of FFAs to induce insulin resistance and PP2A hyperactivity without affecting ceramide accumulation and PP2A expression. UT decreased PP2A activity through posttranslational modification that was accompanied by a reduction in Akt dephosphorylation.

Topics: Animals; Body Composition; Body Weight; Cell Line; Diet, High-Fat; Glucose; Glycogen; Insulin; Insulin Resistance; Male; Mice; Muscle, Skeletal; Obesity; Plant Extracts; Protein Phosphatase 2; Signal Transduction; Urtica dioica

Among the 22 fibroblast growth factors (FGFs), FGF21 has now emerged as a key metabolic regulator. However, the mechanism whereby FGF21 mediates its metabolic actions per se remains largely unknown. Here, we show that FGF21 represses mammalian target of rapamycin complex 1 (mTORC1) and improves insulin sensitivity and glycogen storage in a hepatocyte-autonomous manner. Administration of FGF21 in mice inhibits mTORC1 in the liver, whereas FGF21-deficient mice display pronounced insulin-stimulated mTORC1 activation and exacerbated hepatic insulin resistance (IR). FGF21 inhibits insulin- or nutrient-stimulated activation of mTORC1 to enhance phosphorylation of Akt in HepG2 cells at both normal and IR condition. TSC1 deficiency abrogates FGF21-mediated inhibition of mTORC1 and augmentation of insulin signaling and glycogen synthesis. Strikingly, hepatic βKlotho knockdown or hepatic hyperactivation of mTORC1/ribosomal protein S6 kinase 1 abrogates hepatic insulin-sensitizing and glycemic-control effects of FGF21 in diet-induced insulin-resistant mice. Moreover, FGF21 improves methionine- and choline-deficient diet-induced steatohepatitis.. FGF21 acts as an inhibitor of mTORC1 to control hepatic insulin action and maintain glucose homeostasis, and mTORC1 inhibition by FGF21 has the therapeutic potential for treating IR and type 2 diabetes. (Hepatology 2016;64:425-438).

Topics: Animals; Diet, High-Fat; Fibroblast Growth Factors; Glycogen; Insulin; Insulin Resistance; Klotho Proteins; Liver; Male; Mechanistic Target of Rapamycin Complex 1; Membrane Proteins; Mice, Inbred C57BL; Mice, Knockout; Multiprotein Complexes; Non-alcoholic Fatty Liver Disease; Sucrose; TOR Serine-Threonine Kinases

The objective of this study was to evaluate the effects of dietary chromium (Cr), as chromium propionate, on measures of insulin sensitivity. Liver and muscle glycogen, and plasma glucose and non-esterified fatty acid (NEFA) concentrations were used as indicators of insulin sensitivity. In total, 288 newly hatched male Ross broilers were divided into 4 dietary treatments consisting of 0 (control diet analyzed 0.43 to 0.45 mg Cr/kg), 0.2, 0.4, or 0.6 mg supplemental Cr/kg diet, resulting in 4 treatments with 9 replicate pens per treatment containing eight birds per pen. At d 21, 2 birds per cage were removed based on the greatest deviation from pen mean BW, resulting in each pen containing 6 birds for the final analyses. Final BW were taken on d 40, and on d 42 two birds from each pen were sampled for plasma NEFA, glucose, and muscle and liver glycogen determination at the initiation and termination of a 22 h fast. The remaining 2 fasted birds were sampled after a 30 min refeeding period. No differences were observed in feed intake, BW gain, or feed efficiency on d 21 or d 40. Liver glycogen tended (P=0.10) to be greater in Cr-supplemented chicks in the fed state, and muscle glycogen concentrations tended (P=0.07) to be greater in Cr-supplemented chicks compared with controls following fasting and refeeding. Plasma glucose concentrations were not affected by dietary Cr in the fed, fasted, or refed state. Plasma NEFA levels were not affected by treatment in fed or fasted birds. However, plasma NEFA concentrations were lower (P<0.01) in chicks supplemented with Cr than in controls following fasting and refeeding, suggesting that Cr increased insulin sensitivity. No differences were detected among birds supplemented with 0.2 or 0.4 mg Cr/kg, and among those receiving 0.4 or 0.6 mg Cr/kg. Results of this study indicate that Cr propionate supplementation of a control diet containing 0.43 to 0.45 mg Cr/kg enhanced insulin sensitivity.

Topics: Animals; Blood Glucose; Chickens; Fatty Acids, Nonesterified; Glycogen; Insulin Resistance; Liver; Male; Muscle, Skeletal; Propionates

While age-related insulin resistance and hyperinsulinemia are usually considered to be secondary to changes in muscle, the liver also plays a key role in whole-body insulin handling and its role in age-related changes in insulin homeostasis is largely unknown. Here, we show that patent pores called 'fenestrations' are essential for insulin transfer across the liver sinusoidal endothelium and that age-related loss of fenestrations causes an impaired insulin clearance and hyperinsulinemia, induces hepatic insulin resistance, impairs hepatic insulin signaling, and deranges glucose homeostasis. To further define the role of fenestrations in hepatic insulin signaling without any of the long-term adaptive responses that occur with aging, we induced acute defenestration using poloxamer 407 (P407), and this replicated many of the age-related changes in hepatic glucose and insulin handling. Loss of fenestrations in the liver sinusoidal endothelium is a hallmark of aging that has previously been shown to cause deficits in hepatic drug and lipoprotein metabolism and now insulin. Liver defenestration thus provides a new mechanism that potentially contributes to age-related insulin resistance.

Topics: Aging; Animals; Disease Models, Animal; Endothelial Cells; Glucose; Glycogen; Insulin; Insulin Resistance; Liver; Male; Mice, Inbred C57BL; Microcirculation; Poloxamer; Porosity; Rats, Inbred F344; Staining and Labeling

Severe caloric restriction (CR), in a setting of regular physical exercise, may be a stress that sets the stage for adiposity rebound and insulin resistance when the food restriction and exercise stop. In this study, we examined the effect of mifepristone, a glucocorticoid (GC) receptor antagonist, on limiting adipose tissue mass gain and preserving whole body insulin sensitivity following the cessation of daily running and CR. We calorically restricted male Sprague-Dawley rats and provided access to voluntary running wheels for 3 wk followed by locking of the wheels and reintroduction to ad libitum feeding with or without mifepristone (80 mg·kg(-1)·day(-1)) for 1 wk. Cessation of daily running and CR increased HOMA-IR and visceral adipose mass as well as glucose and insulin area under the curve during an oral glucose tolerance test vs. pre-wheel lock exercised rats and sedentary rats (all P < 0.05). Insulin sensitivity and glucose tolerance were preserved and adipose tissue mass gain was attenuated by daily mifepristone treatment during the post-wheel lock period. These findings suggest that following regular exercise and CR there are GC-induced mechanisms that promote adipose tissue mass gain and impaired metabolic control in healthy organisms and that this phenomenon can be inhibited by the GC receptor antagonist mifepristone.

Topics: 11-beta-Hydroxysteroid Dehydrogenase Type 1; Adiposity; Animals; Blood Glucose; Blotting, Western; Body Weight; Caloric Restriction; Gluconeogenesis; Glucose Intolerance; Glucose Tolerance Test; Glycogen; Glycogenolysis; Hormone Antagonists; Insulin; Insulin Resistance; Intra-Abdominal Fat; Lipolysis; Liver; Male; Mifepristone; Physical Conditioning, Animal; Rats; Rats, Sprague-Dawley; Receptors, Glucocorticoid

The regulation of microRNAs (miRNAs) at different stages of the progression of type 2 diabetes mellitus (T2DM) and their role in glucose homeostasis was investigated.. Microarrays were used to assess miRNA expression in skeletal muscle biopsies taken from healthy individuals and patients with pre-diabetes or T2DM, and insulin resistant offspring of rat dams fed a high fat diet during pregnancy.. Twenty-three miRNAs were differentially expressed in patients with T2DM, and 7 in the insulin resistant rat offspring compared to their controls. Among these, only one miRNA was similarly regulated: miR-194 expression was significantly reduced by 25 to 50% in both the rat model and in human with pre-diabetes and established diabetes. Knockdown of miR-194 in L6 skeletal muscle cells induced an increase in basal and insulin-stimulated glucose uptake and glycogen synthesis. This occurred in conjunction with an increased glycolysis, indicated by elevated lactate production. Moreover, oxidative capacity was also increased as we found an enhanced glucose oxidation in presence of the mitochondrial uncoupler FCCP. When miR-194 was down-regulated in vitro, western blot analysis showed an increased phosphorylation of AKT and GSK3β in response to insulin, and an increase in expression of proteins controlling mitochondrial oxidative phosphorylation.. Type 2 diabetes mellitus is associated with regulation of several miRNAs in skeletal muscle. Interestingly, miR-194 was a unique miRNA that appeared regulated across different stages of the disease progression, from the early stages of insulin resistance to the development of T2DM. We have shown miR-194 is involved in multiple aspects of skeletal muscle glucose metabolism from uptake, through to glycolysis, glycogenesis and glucose oxidation, potentially via mechanisms involving AKT, GSK3 and oxidative phosphorylation. MiR-194 could be down-regulated in patients with early features of diabetes as an adaptive response to facilitate tissue glucose uptake and metabolism in the face of insulin resistance.

Topics: Animals; Cell Line; Diabetes Mellitus, Type 2; Diet, High-Fat; Disease Models, Animal; Female; Gene Expression Regulation; Glucose; Glycogen; Glycogen Synthase Kinase 3; Humans; Insulin; Insulin Resistance; Male; Mice, Inbred C57BL; MicroRNAs; Mitochondria; Muscle, Skeletal; Myoblasts; Oxidative Phosphorylation; Prediabetic State; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Signal Transduction

Resistance to the action of insulin affects fatty acid delivery to the liver, fatty acid synthesis and oxidation within the liver, and triglyceride export from the liver. To understand the metabolic consequences of hepatic fatty acid synthesis, partitioning, oxidation, and net liver fat content in the fasted and postprandial states, we used stable-isotope tracer methodologies to study healthy men and women with varying degrees of insulin resistance before and after consumption of a mixed meal. Subjects were classified as being normoinsulinemic (NI) (fasting plasma insulin <11.2 mU/L, n = 18) or hyperinsulinemic (HI) (fasting plasma insulin >11.2 mU/L, n = 19). Liver fat content was similar between HI and NI individuals, despite HI subjects having marginally more visceral fat. However, de novo lipogenesis was higher and fatty acid oxidation was lower in HI individuals compared with NI subjects. These data suggest that metabolic pathways promoting fat accumulation are enhanced in HI but, paradoxically, without any significant effect on liver fat content when observed in healthy people. This is likely to be explained by increased triglyceride secretion as observed by hypertriglyceridemia.

Topics: Adipose Tissue; Adult; Blood Glucose; Body Composition; Fasting; Fatty Acids; Fatty Liver; Female; Glycogen; Humans; Insulin; Insulin Resistance; Lipid Metabolism; Liver; Male; Middle Aged

Friend of GATA 2 (FOG2) is a transcriptional cofactor involved mostly in cardiac function. The aim of this study was to investigate the role of hepatic FOG2 in insulin sensitivity and lipid accumulation. FOG2 overexpression by adenovirus-expressing FOG2 (Ad-FOG2) significantly attenuates insulin signaling in hepatocytes in vitro. Opposite effects were observed when FOG2 was knocked down through adenovirus-expressing small hairpin RNA for FOG2 (Ad-shFOG2). Furthermore, FOG2 knockdown by Ad-shFOG2 ameliorated insulin resistance in leptin receptor-mutated (db/db) mice, and FOG2 overexpression by Ad-FOG2 attenuated insulin sensitivity in C57BL/6J wild-type (WT) mice. In addition, Ad-FOG2 reduced, whereas Ad-shFOG2 promoted, hepatic triglyceride (TG) accumulation in WT mice under fed or fasted conditions, which was associated with increased or decreased hepatic peroxisome proliferator-activated receptor α (PPARα) expression, respectively. Moreover, the improved insulin sensitivity and increased hepatic TG accumulation by Ad-shFOG2 were largely reversed by adenovirus-expressing PPARα (Ad-PPARα) in WT mice. Finally, we generated FOG2 liver-specific knockout mice and found that they exhibit enhanced insulin sensitivity and elevated hepatic TG accumulation, which were also reversed by Ad-PPARα. Taken together, the results demonstrate a novel function of hepatic FOG2 in insulin sensitivity and lipid metabolism through PPARα.

Topics: Animals; Blood Glucose; Cholesterol; DNA-Binding Proteins; Fatty Acids, Nonesterified; Female; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Lipid Metabolism; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; PPAR alpha; Receptors, Leptin; Signal Transduction; Transcription Factors; Triglycerides

A low carbohydrate diet (LCHD) as well as sodium glucose cotransporter 2 inhibitors (SGLT2i) may reduce glucose utilization and improve metabolic disorders. However, it is not clear how different or similar the effects of LCHD and SGLT2i are on metabolic parameters such as insulin sensitivity, fat accumulation, and especially gluconeogenesis in the kidney and the liver. We conducted an 8-week study using non-diabetic mice, which were fed ad-libitum with LCHD or a normal carbohydrate diet (NCHD) and treated with/without the SGLT-2 inhibitor, ipragliflozin. We compared metabolic parameters, gene expression for transcripts related to glucose and fat metabolism, and glycogen content in the kidney and the liver among the groups. SGLT2i but not LCHD improved glucose excursion after an oral glucose load compared to NCHD, although all groups presented comparable non-fasted glycemia. Both the LCHD and SGLT2i treatments increased calorie-intake, whereas only the LCHD increased body weight compared to the NCHD, epididimal fat mass and developed insulin resistance. Gene expression of certain gluconeogenic enzymes was simultaneously upregulated in the kidney of SGLT2i treated group, as well as in the liver of the LCHD treated group. The SGLT2i treated groups showed markedly lower glycogen content in the liver, but induced glycogen accumulation in the kidney. We conclude that LCHD induces deleterious metabolic changes in the non-diabetic mice. Our results suggest that SGLT2i induced gluconeogenesis mainly in the kidney, whereas for LCHD it was predominantly in the liver.

Topics: Animals; Body Weight; Cyclic AMP Response Element-Binding Protein; Diabetes Mellitus, Experimental; Diet, Carbohydrate-Restricted; Energy Intake; Fatty Acid Synthases; Forkhead Box Protein O1; Gluconeogenesis; Glucose Tolerance Test; Glucosides; Glycogen; Hyperglycemia; Insulin Resistance; Kidney; Lipid Metabolism; Liver; Male; Mice, Inbred C57BL; Obesity; RNA, Messenger; Sodium-Glucose Transporter 2; Sodium-Glucose Transporter 2 Inhibitors; Thiophenes; Triglycerides; Up-Regulation

Dysregulated mitochondrial metabolism during hepatic insulin resistance may contribute to pathophysiologies ranging from elevated glucose production to hepatocellular oxidative stress and inflammation. Given that obesity impairs insulin action but paradoxically activates mTORC1, we tested whether insulin action and mammalian target of rapamycin complex 1 (mTORC1) contribute to altered in vivo hepatic mitochondrial metabolism. Loss of hepatic insulin action for 2 weeks caused increased gluconeogenesis, mitochondrial anaplerosis, tricarboxylic acid (TCA) cycle oxidation, and ketogenesis. However, activation of mTORC1, induced by the loss of hepatic Tsc1, suppressed these fluxes. Only glycogen synthesis was impaired by both loss of insulin receptor and mTORC1 activation. Mice with a double knockout of the insulin receptor and Tsc1 had larger livers, hyperglycemia, severely impaired glycogen storage, and suppressed ketogenesis, as compared to those with loss of the liver insulin receptor alone. Thus, activation of hepatic mTORC1 opposes the catabolic effects of impaired insulin action under some nutritional states.

Topics: Animals; Citric Acid Cycle; Diet, High-Fat; Enzyme Activation; Gluconeogenesis; Glycogen; Insulin Resistance; Liver; Male; Mechanistic Target of Rapamycin Complex 1; Mice, Inbred C57BL; Mice, Transgenic; Mitochondria, Liver; Obesity; Oxidation-Reduction; Receptor, Insulin; Tuberous Sclerosis Complex 1 Protein; Tumor Suppressor Proteins

This study was initiated to investigate the mechanism by which oat β-d-glucan (OBG) can control blood sugar levels and improve hepatogenic glycometabolism in streptozotocin-nicotinamide induced mice. After administration of different concentrations and molecular weights of β-d-glucan by oral gavage for 28 days, the body weight, fasting blood glucose, serum insulin, hepatic glycogen, glucose kinase and glucose-6-phosphatase activity of the diabetic mice were measured. In comparison with a negative control group (saline), β-d-glucan, especially medium or high doses of high-molecular-weight β-d-glucan, had a strong hypoglycaemic effect in streptozotocin-nicotinamide-induced mice. The mechanism of this effect may be associated with the high viscosity of the solution, an increase in insulin secretion, a decline in insulin resistance, and especially an improvement in hepatogenic glycometabolism. Moreover, β-d-glucan also markedly repaired and improved the integrity of pancreatic islet β-cell and tissue structures.

Topics: Animals; beta-Glucans; Blood Glucose; Body Weight; Diabetes Mellitus, Experimental; Drinking; Fasting; Glucose Tolerance Test; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Liver Glycogen; Male; Mice; Molecular Weight; Niacinamide; Pancreas

To investigated the effects of urotensin II (UII) on hepatic insulin resistance in HepG2 cells and the potential mechanisms involved.. Human hepatoma HepG2 cells were cultured with or without exogenous UII for 24 h, in the presence or absence of 100 nmol/L insulin for the last 30 min. Glucose levels were detected by the glucose-oxidase method and glycogen synthesis was analyzed by glycogen colorimetric/fluorometric assay. Reactive oxygen species (ROS) levels were detected with a multimode reader using a 2',7'-dichlorofluorescein diacetate probe. The protein expression and phosphorylation levels of c-Jun N-terminal kinase (JNK), insulin signal essential molecules such as insulin receptor substrate -1 (IRS-1), protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β), and glucose transporter-2 (Glut 2), and NADPH oxidase subunits such as gp91(phox), p67(phox), p47(phox), p40(phox), and p22(phox) were evaluated by Western blot.. Exposure to 100 nmol/L UII reduced the insulin-induced glucose consumption (P < 0.05) and glycogen content (P < 0.01) in HepG2 cells compared with cells without UII. UII also abolished insulin-stimulated protein expression (P < 0.01) and phosphorylation of IRS-1 (P < 0.05), associated with down-regulation of Akt (P < 0.05) and GSK-3β (P < 0.05) phosphorylation levels, and the expression of Glut 2 (P < 0.001), indicating an insulin-resistance state in HepG2 cells. Furthermore, UII enhanced the phosphorylation of JNK (P < 0.05), while the activity of JNK, insulin signaling, such as total protein of IRS-1 (P < 0.001), phosphorylation of IRS-1 (P < 0.001) and GSK-3β (P < 0.05), and glycogen synthesis (P < 0.001) could be reversed by pretreatment with the JNK inhibitor SP600125. Besides, UII markedly improved ROS generation (P < 0.05) and NADPH oxidase subunit expression (P < 0.05). However, the antioxidant/NADPH oxidase inhibitor apocynin could decrease UII-induced ROS production (P < 0.05), JNK phosphorylation (P < 0.05), and insulin resistance (P < 0.05) in HepG2 cells.. UII induces insulin resistance, and this can be reversed by JNK inhibitor SP600125 and antioxidant/NADPH oxidase inhibitor apocynin targeting the insulin signaling pathway in HepG2 cells.

Topics: Acetophenones; Blotting, Western; Down-Regulation; Enzyme Inhibitors; Glucose; Glucose Transporter Type 2; Glycogen; Glycogen Synthase Kinase 3 beta; Hep G2 Cells; Humans; Hypoglycemic Agents; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; MAP Kinase Kinase 4; NADPH Oxidases; Phosphorylation; Proto-Oncogene Proteins c-akt; Reactive Oxygen Species; Urotensins

Increasing evidence has shown that pseudogenes can widely regulate gene expression. However, little is known about the specific role of PTENP1 and miR-499-5p in insulin resistance. The relative transcription level of PTENP1 was examined in db/db mice and high fat diet (HFD)-fed mice by real-time PCR. To explore the effect of PTENP1 on insulin resistance, adenovirus overexpressing or inhibiting vectors were injected through the tail vein. Bioinformatics predictions and a luciferase reporter assay were used to explore the interaction between PTENP1 and miR-499-5p. The relative transcription level of PTENP1 was largely enhanced in db/db mice and HFD-fed mice. Furthermore, the overexpression of PTENP1 resulted in impaired Akt/GSK activation as well as glycogen synthesis, while PTENP1 inhibition led to the improved activation of Akt/GSK and enhanced glycogen contents. More importantly, PTENP1 could directly bind miR-499-5p, thereby becoming a sink for miR-499-5p. PTENP1 overexpression results in the impairment of the insulin-signaling pathway and may function as a competing endogenous RNA for miR-499-5p, thereby contributing to insulin resistance.

Topics: 3' Untranslated Regions; Animals; Base Sequence; Binding Sites; Blotting, Western; Cell Line; Diet, High-Fat; Genes, Reporter; Glycogen; Glycogen Synthase Kinases; Insulin; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Mice, Obese; MicroRNAs; Oligonucleotides, Antisense; Proto-Oncogene Proteins c-akt; Pseudogenes; PTEN Phosphohydrolase; Real-Time Polymerase Chain Reaction; RNA Interference; RNA, Small Interfering; Sequence Alignment

The common complications in obesity and type 2 diabetes include hepatic steatosis and disruption of glucose-glycogen homeostasis, leading to hyperglycemia. Fatty acid translocase (FAT/CD36), whose expression is inducible in obesity, is known for its function in fatty acid uptake. Previous work by us and others suggested that CD36 plays an important role in hepatic lipid homeostasis, but the results have been conflicting and the mechanisms were not well understood. In this study, by using CD36-overexpressing transgenic (CD36Tg) mice, we uncovered a surprising function of CD36 in regulating glycogen homeostasis. Overexpression of CD36 promoted glycogen synthesis, and as a result, CD36Tg mice were protected from fasting hypoglycemia. When challenged with a high-fat diet (HFD), CD36Tg mice showed unexpected attenuation of hepatic steatosis, increased very low-density lipoprotein (VLDL) secretion, and improved glucose tolerance and insulin sensitivity. The HFD-fed CD36Tg mice also showed decreased levels of proinflammatory hepatic prostaglandins and 20-hydroxyeicosatetraenoic acid (20-HETE), a potent vasoconstrictive and proinflammatory arachidonic acid metabolite. We propose that CD36 functions as a protective metabolic sensor in the liver under lipid overload and metabolic stress. CD36 may be explored as a valuable therapeutic target for the management of metabolic syndrome.

Topics: Animals; Arachidonic Acid; CD36 Antigens; Diet, High-Fat; Fasting; Fatty Liver; Glycogen; Homeostasis; Hydroxyeicosatetraenoic Acids; Hypoglycemia; Insulin Resistance; Liver; Mice, Transgenic; Oxygen Consumption; Prostaglandins

In humans, low levels of growth hormone (GH) and its mediator, IGF-1, associate with hepatic lipid accumulation. In mice, congenital liver-specific ablation of the GH receptor (GHR) results in reductions in circulating IGF-1 and hepatic steatosis, associated with systemic insulin resistance. Due to the intricate relationship between GH and IGF-1, the relative contribution of each hormone to the development of hepatic steatosis is unclear. Our goal was to dissect the mechanisms by which hepatic GH resistance leads to steatosis and overall insulin resistance, independent of IGF-1. We have generated a combined mouse model with liver-specific ablation of GHR in which we restored liver IGF-1 expression via the hepatic IGF-1 transgene. We found that liver GHR ablation leads to increases in lipid uptake, de novo lipogenesis, hyperinsulinemia, and hyperglycemia accompanied with severe insulin resistance and increased body adiposity and serum lipids. Restoration of IGF-1 improved overall insulin sensitivity and lipid profile in serum and reduced body adiposity, but was insufficient to protect against steatosis-induced hepatic inflammation or oxidative stress. We conclude that the impaired metabolism in states of GH resistance results from direct actions of GH on lipid uptake and de novo lipogenesis, whereas its actions on extrahepatic tissues are mediated by IGF-1.

Topics: Animals; Blotting, Western; Fatty Acids; Fatty Acids, Nonesterified; Fatty Liver; Glycogen; Growth Hormone; Hyperinsulinism; Insulin Resistance; Insulin-Like Growth Factor I; Lipid Metabolism; Lipid Peroxidation; Liver; Male; Mice; Mice, Knockout; Oxidative Stress; Receptors, Somatotropin

Agrimonia pilosa Ledeb (AP) has already been applied in practice for the treatment of different disorders and is available to access without the provision of a medical prescription. The present study aims at investigating the effect of bioactive compounds isolated from AP on the improvement of insulin resistance, figuring out the mechanism in insulin-responsive cell lines. Five compounds were isolated from AP using column chromatography, including agrimonolide (K1), desmethylagrimonolide (K2), tormentic acid (K3), ursolic acid (K4), and quercetin (K5). Glucose metabolism was evaluated in insulin-resistant HepG2 cells. Ursolic acid had the strongest activity among all isolated compounds with the lowering value of 71.5% (1.24 mM glucose in DMEM) and 71.7% (1.23 mM) when compared to the control. K1 consisting of K2 effectively increased the insulin-mediated glycogen level in hepatocytes. At a concentration level of 20 μM, K2 significantly elevated the hepatic glucokinase (GK) activity (3.2 U min

Topics: Agrimonia; Biological Transport; Glucose; Glycogen; Hep G2 Cells; Humans; Insulin Resistance; Phenols; Plant Extracts

Simvastatin is a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor widely used for the treatment of hypercholesterolemia. Recent data indicates that simvastatin increases the risk of new-onset diabetes by impairing both insulin secretion and insulin sensitivity. However, systematic evaluation of mechanistic pathways is lacking. We aimed to explore the effects of simvastatin on glucose uptake and underlying mechanisms using L6 skeletal muscle myotubes. We performed our experiments at basal and insulin-stimulated conditions, at normal (5.5 mM) and high (16.7 mM) glucose. We showed that simvastatin inhibited glucose uptake at all conditions. We also found out that pravastatin, another widely used statin with different physicochemical properties, did not inhibit glucose uptake. The effect of simvastatin was reversed with geranylgeranyl pyrophosphate but not with farnesyl pyrophosphate, implying that reduced protein geranylgeranylation has a role in simvastatin-induced insulin resistance. Simvastatin also decreased phosphorylation of insulin receptor (IR), insulin receptor substrate 1 (IRS-1), AKT and glycogen synthase kinase 3β (GSK-3β), and downregulated GLUT4. In conclusion, our data indicate that simvastatin decreased both basal and insulin-stimulated glucose uptake through inhibiting the critical steps in IR/IRS-1/AKT signaling cascade, and by hindering GLUT4 function and normal regulation of glycogen synthesis, contributing to insulin resistance.

Topics: Animals; Cell Line; Cholesterol; Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase Kinase 3 beta; Insulin; Insulin Resistance; Muscle Fibers, Skeletal; Phosphorylation; Pravastatin; Proto-Oncogene Proteins c-akt; Rats; Signal Transduction; Simvastatin

Nonalcoholic fatty liver disease (NAFLD) is a risk factor for type 2 diabetes (T2D), but whether NAFLD plays a causal role in the pathogenesis of T2D is uncertain. One proposed mechanism linking NAFLD to hepatic insulin resistance involves diacylglycerol-mediated (DAG-mediated) activation of protein kinase C-ε (PKCε) and the consequent inhibition of insulin receptor (INSR) kinase activity. However, the molecular mechanism underlying PKCε inhibition of INSR kinase activity is unknown. Here, we used mass spectrometry to identify the phosphorylation site Thr1160 as a PKCε substrate in the functionally critical INSR kinase activation loop. We hypothesized that Thr1160 phosphorylation impairs INSR kinase activity by destabilizing the active configuration of the INSR kinase, and our results confirmed this prediction by demonstrating severely impaired INSR kinase activity in phosphomimetic T1160E mutants. Conversely, the INSR T1160A mutant was not inhibited by PKCε in vitro. Furthermore, mice with a threonine-to-alanine mutation at the homologous residue Thr1150 (InsrT1150A mice) were protected from high fat diet-induced hepatic insulin resistance. InsrT1150A mice also displayed increased insulin signaling, suppression of hepatic glucose production, and increased hepatic glycogen synthesis compared with WT controls during hyperinsulinemic clamp studies. These data reveal a critical pathophysiological role for INSR Thr1160 phosphorylation and provide further mechanistic links between PKCε and INSR in mediating NAFLD-induced hepatic insulin resistance.

Topics: Amino Acid Substitution; Animals; Diabetes Mellitus, Type 2; Dietary Fats; Glycogen; Insulin Resistance; Liver; Mice; Mice, Mutant Strains; Mutation, Missense; Non-alcoholic Fatty Liver Disease; Phosphorylation; Protein Kinase C-epsilon; Receptor, Insulin; Signal Transduction

Sang-Tong-Jian (STJ), a novel formula composed of flavonoids and alkaloids derived from mulberry leaf, has been found to reduce blood glucose levels in rats with type 2 diabetes mellitus (T2DM) in our previous studies. However, the precise mechanisms remain unknown. Insulin resistance is the main characteristic of T2DM, which may be due to impairment of the PI3K/AKT signaling pathway. In this study, we investigated the effects of STJ on glycometabolism and insulin resistance in KKAy mice.. A total of 50 KKAy male mice were randomly divided into five groups: model, metformin at 260mg/kg, and STJ at 105, 210 and 420mg/kg. C57BL/6J mice were used as the control group. Random blood glucose levels in KKAy mice were determined every 10days after treatments. At the 10th and 13th week, oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) were conducted after a 12h overnight fast, respectively. After 13-week treatments, glycosylated hemoglobin (GHb) and serum insulin were measured using a colorimetric method and ELISA kits. Liver glycogen and muscle glycogen levels were analyzed using a colorimetric method. The morphology of pancreas, liver, skeletal muscle and epididymal fat were visualized by haematoxylin and eosin staining. The gene level of GLUT2 (liver) and GLUT4 (skeletal muscle, epididymal fat) were detected by real-time PCR. The proteins of GLUT2, GLUT4, IRS1, PI3K, AKT and their phosphorylation were assayed by Western blot analyses.. STJ significantly decreased the random blood glucose and GHb levels, and increased liver and muscle glycogen levels. The results of OGTT and ITT and measurement of serum insulin indicated that STJ ameliorated insulin resistance in KKAy mice. STJ treatments also ameliorated the histopathological alterations in pancreas, liver, skeletal muscle and epididymal fat in KKAy mice. Furthermore, STJ upregulated the gene and protein expression of GLUT2 (liver) and GLUT4 (skeletal muscle, epididymal fat). Meanwhile, GLUT4 translocation and phosphorylation of IRS1, p85-PI3K and AKT were significantly increased by STJ treatments.. Our results indicated that STJ ameliorated glycometabolism and insulin resistance in KKAy mice, which might be due to activation of PI3K/AKT pathway.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Drugs, Chinese Herbal; Gene Expression Regulation; Glucose; Glucose Tolerance Test; Glucose Transporter Type 2; Glucose Transporter Type 4; Glycated Hemoglobin; Glycogen; Insulin; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Organ Specificity; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; RNA, Messenger; Signal Transduction

Preoperative oral carbohydrate (CHO) treatment is known to reduce postoperative insulin resistance, but the necessity of a preoperative evening dose is uncertain. We investigated the effect of single-dose CHO treatment two hours before surgery on postoperative insulin sensitivity.. Thirty two pigs (∼ 30 kg) were randomized to 4 groups (n = 8) followed by D-[6,6-(2)H2] glucose infusion and hyperinsulinemic-euglycemic step clamping. Two groups received a morning drink of 25 g carbohydrate (CHO/surgery and CHO/control). Animals in the other two groups were fasted overnight (fasting/surgery and fasting/control). Counter-regulatory hormones, free fatty acids (FFA) and liver and muscle glycogen content were measured serially.. Glucose infusion rates needed to maintain euglycemia were higher after CHO/surgery than fasting/surgery during low (8.54 ± 0.82 vs. 6.15 ± 0.27 mg/kg/min, P < 0.05), medium (17.26 ± 1.08 vs. 14.02 ± 0.56 mg/kg/min, P < 0.02) and high insulin clamping (19.83 ± 0.95 vs. 17.16 ± 0.58 mg/kg/min, P < 0.05). The control groups exhibited identical insulin sensitivity. Compared to their respective controls, insulin-stimulated whole-body glucose disposal was significantly reduced after fasting/surgery (-41%, P < 0.001), but not after CHO/surgery (-16%, P = 0.180). CHO reduced FFA perioperatively (P < 0.05) and during the clamp procedures (P < 0.02), but did not affect hepatic insulin sensitivity, liver and muscle glycogen content or counter-regulatory hormone profiles. A strong negative correlation between peripheral insulin sensitivity and mean cortisol levels was seen in fasted (R = -0.692, P = 0.003), but not in CHO loaded pigs.. Single-dose preoperative CHO treatment is sufficient to reduce postoperative insulin resistance, possibly due to the antilipolytic effects and antagonist properties of preoperative hyperinsulinemia on the suppressant actions of cortisol on carbohydrate oxidation.

Topics: Animals; Blood Glucose; Deuterium; Dietary Carbohydrates; Fasting; Fatty Acids, Nonesterified; Glucose; Glucose Clamp Technique; Glycogen; Insulin; Insulin Resistance; Liver; Muscles; Postoperative Complications; Preoperative Period; Swine

The present study analyzes the effect of the replacement of dietary casein by soy protein on the mechanisms underlying dyslipidemia, liver steatosis and altered glucose and lipid metabolism in the skeletal muscle which developed in rats fed long-term a sucrose-rich diet (SRD).. Wistar rats were fed a SRD for 4 months. From months 4 to 8, half the animals continued with the SRD, and the other half were fed a SRD in which the source of protein casein was replaced by soy. The control group received a diet with cornstarch as source of carbohydrate.. Compared to SRD-fed animals, the rats fed soy showed: A--in the liver: reduction of triglyceride and cholesterol storage and decreased steatosis; normalization of mature forms of the protein mass levels of SREBP-1 and the activities of lipogenic enzymes, while the protein mass level of PPAR-α and fatty acid oxidase activity increased. B-in the gastrocnemius muscle: normalization of the enhanced lipid storage and the altered glucose oxidation, improving glucose phosphorylation; decreasing protein mass level of nPKCθ in the membrane fraction; reversion of the impaired insulin-stimulated glucose transporter Glut-4, and glucose-6-phosphate and glycogen concentrations. Besides, dyslipidemia and glucose homeostasis returned to control values.. This study provides new information concerning some key mechanisms related to the effect of dietary soy on hepatic lipid metabolism and insulin action in the skeletal muscle in the presence of pre-existing dyslipidemia and insulin resistance induced by a SRD.

Topics: Animals; Blood Glucose; Cholesterol; Dietary Sucrose; Dyslipidemias; Fatty Acids, Nonesterified; Fatty Liver; Glucose Transporter Type 4; Glucose-6-Phosphate; Glycogen; Insulin; Insulin Resistance; Lipid Metabolism; Liver; Male; Muscle, Skeletal; PPAR alpha; Rats; Rats, Wistar; Soybean Proteins; Sterol Regulatory Element Binding Protein 1; Triglycerides; Weight Gain

Peripheral insulin resistance (IR) is one of the main side effects caused by glucocorticoid (GC)-based therapies, and the molecular mechanisms of GC-induced IR are not yet fully elucidated. Thus, we aimed to investigate the effects of dexamethasone treatment on the main components of insulin and inflammatory signaling in the adipose tissue of rats.. Male Wistar rats received daily injections of dexamethasone (1mg/kg body weight (b.w.), intraperitoneally (i.p.)) for 5 days (DEX), whereas control rats received saline (CTL). The metabolic status was investigated, and the epididymal fat fragments were collected for lipolysis and western blot analyses.. The DEX rats became hyperglycemic, hyperinsulinemic, insulin resistant and glucose intolerant, compared with the CTL rats (P<0.05). The basal glycerol release in the fat fragments was 1.5-fold higher in the DEX rats (P<0.05). The phosphorylation of protein kinase B (PKB) at ser(473) decreased by 44%, whereas, the phosphorylation of insulin receptor substrate (IRS)-1 at ser(307) increased by 93% in the adipose tissue of the DEX rats after an oral bolus of glucose (P<0.05). The basal phosphorylation of c-jun-N-terminal kinase (JNK) and inhibitor of nuclear factor kappa-B (IKKβ) proteins was reduced by 46% and 58%, respectively, in the adipose tissue of the DEX rats (P<0.05). This was paralleled with a significant reduction (47%) in the glucocorticoid receptor (GR) protein content in the adipose tissue of the DEX rats (P<0.05).. The insulin-resistant status of rats induced by dexamethasone administration have PKB and IRS-1 activity attenuated in epididymal fat without increases in the phosphorylation of the proinflammatory signals JNK and IKKβ.

Topics: Adipose Tissue; Animals; Body Weight; Cytokines; Dexamethasone; Epididymis; Glucocorticoids; Glycogen; I-kappa B Kinase; Inflammation; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Male; MAP Kinase Kinase 4; Phosphorylation; Proto-Oncogene Proteins c-akt; Pyruvic Acid; Rats; Rats, Wistar; Signal Transduction; Toll-Like Receptor 4

The IV anesthetic, propofol, when administered as fat emulsion-based formulation (Diprivan) promotes insulin resistance, but the direct effects of propofol and its solvent, Intralipid, on cardiac insulin resistance are unknown.. Hearts of healthy and type-2 diabetic rats (generated by fructose feeding) were aerobically perfused for 60 minutes with 10 μM propofol in the formulation of Diprivan or an equivalent concentration of its solvent Intralipid (25 μM) ± insulin (100 mU•L). Glucose uptake, glycolysis, and glycogen metabolism were measured using [H]glucose. Activation of Akt, GSK3β, AMPK, ERK1/2, p38MAPK, S6K1, JNK, protein kinase Cθ (PKCθ), and protein kinase CCβII (PKCβII) was determined using immunoblotting. GLUT4 trafficking and phosphorylations of insulin receptor substrate-1 (IRS-1) at Ser307(h312), Ser1100(h1101), and Tyr608(hTyr612) were measured. Mass spectrometry was used to determine acylcarnitines, phospholipids, and sphingolipids.. Diprivan and Intralipid reduced insulin-induced glucose uptake and redirected glucose to glycogen stores in diabetic hearts. Reduced glucose uptake was accompanied by lower GLUT4 trafficking to the sarcolemma. Diprivan and Intralipid inactivated GSK3β but activated AMPK and ERK1/2 in diabetic hearts. Only Diprivan increased phosphorylation of Akt(Ser473/Thr308) and translocated PKCθ and PKCβII to the sarcolemma in healthy hearts, whereas it activated S6K1 and p38MAPK and translocated PKCβII in diabetic hearts. Furthermore, only Diprivan phosphorylated IRS-1 at Ser1100(h1101) in healthy and diabetic hearts. JNK expression, phosphorylation of Ser307(h312) of IRS-1, and PKCθ expression and translocation were increased, whereas GLUT4 expression was reduced in insulin-treated diabetic hearts. Phosphatidylglycerol, phosphatidylethanolamine, and C18-sphingolipids accumulated in Diprivan-perfused and Intralipid-perfused diabetic hearts.. Propofol and Intralipid promote insulin resistance predominantly in type-2 diabetic hearts.

Topics: Anesthetics, Intravenous; Animals; Citrate (si)-Synthase; Diabetes Mellitus, Type 2; Emulsions; Fat Emulsions, Intravenous; Fructose; Glucose; Glucose Transporter Type 4; Glycogen; Glycolysis; Heart; Insulin Resistance; Male; Phospholipids; Propofol; Rats; Rats, Sprague-Dawley; Soybean Oil

Nymphaea stellata (Willd.) has been used in traditional medicine for centuries to treat several illnesses, including diabetes. However, scientific evidence supporting its mechanism of action is lacking. Here, we showed that an N. stellata flower chloroform extract (NSFCExt) has significant plasma glucose lowering ability. Furthermore, an active compound was identified and purified by column chromatography, and the structure of this compound, nymphayol, was determined by X-ray crystallographic analysis. Nymphayol was tested for its effects on insulin secretion by RIN-5F cells cultured in low or high glucose medium; we found that nymphayol treatment improved glucose-stimulated insulin secretion in vitro. Additionally, insulin sensitization and glucose uptake were increased in L6 myotubes. Nymphayol was administered to type 2 diabetic male Wistar rats at several doses (5, 10 or 20 mg/kg/day) for 45 days. After nymphayol administration, the plasma glucose concentration was significantly (p⩽0.05) lower (60.33%) than in control diabetic rats, and the plasma insulin level increased in a dose-dependent manner. In addition, the cellular insulin response was analyzed in type 2 diabetic rats; oral administration of nymphayol increased IRS1 phosphorylation and GLUT4 protein expression in liver and muscle. Nymphayol significantly (p⩽0.05) restored the levels of HbA1c, hepatic glycogen and hepatic glucose-metabolizing enzyme (hexokinase, glucose-6-phosphate dehydrogenase, glucose-6-phosphatase, fructose-1, 6-bisphosphatase, glycogen synthase and glycogen phosphorylase) activity in diabetic rats. The administration of glibenclamide, a reference drug (600 μg/kg), also produced a significant (p⩽0.05) reduction in blood glucose in STZ-nicotinamide induced diabetic rats. The results suggest that nymphayol may be a useful therapy for diabetes because it stimulates insulin secretion and promotes glucose absorption.

Topics: Animals; Biological Transport; Blood Glucose; Body Weight; Cell Line; Cell Proliferation; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Drinking; Gene Expression Regulation; Glucose; Glucose Transporter Type 4; Glycated Hemoglobin; Glycogen; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Insulin Secretion; Insulin-Secreting Cells; Liver; Male; Muscle Fibers, Skeletal; Phytosterols; Rats; Rats, Wistar; Reactive Oxygen Species

TNF-α is an inflammatory cytokine that plays an important role in insulin resistance observed in obesity and chronic inflammation. Many cellular components involved in insulin signaling cascade are known to be inhibited by TNF-α. Insulin receptor substrate (IRS)-1 is one of the major targets in TNF-α-induced insulin resistance. The serine phosphorylation of IRS-1 enables the inhibition of insulin signaling. Until now, many studies have been conducted to investigate the mechanism of TNF-α-induced insulin resistance based on Western blot. Intracellular protein kinase crosstalk is commonly encountered in inflammation-associated insulin resistance. The crosstalk among the signaling molecules obscures the precise role of kinases in insulin resistance. We have developed a cell lysis-free quantum dots (QDots) multicolor cellular imaging to identify the biochemical role of multiple kinases (p38, JNK, IKKβ, IRS1ser, IRS1tyr, GSK3β, and FOXO1) in inflammation-associated insulin resistance pathway with a single assay in one run. QDot-antibody conjugates were used as nanoprobes to simultaneously monitor the activation/deactivation of the above seven intracellular kinases in HepG2 cells. The effect of the test compounds on the suppression of TNF-α-induced insulin resistance was validated through kinase monitoring. Aspirin, indomethacin, cinnamic acid, and amygdalin were tested.. Through the measurement of the glycogen level in HepG2 cell treated with TNF-α, it was found that aspirin and indomethacin increased glycogen levels by almost two-fold compared to amygdalin and cinnamic acid. The glucose production assay proved that cinnamic acid was much more efficient in suppressing glucose production, compared with MAP kinase inhibitors and non-steroidal anti-inflammatory drugs. QDot multicolor cellular imaging demonstrated that amygdalin and cinnamic acid selectively acted via the JNK1-dependent pathway to suppress the inflammation-induced insulin resistance and improve insulin sensitivity.. The regulatory function of multiple kinases could be monitored concurrently at the cellular level. The developed cellular imaging assay provides a unique platform for the understanding of inflammation and insulin resistance signaling pathways in type II diabetes mellitus and how they regulate each other. The results showed that amygdalin and cinnamic acid inhibit serine phosphorylation of IRS-1 through targeting JNK serine kinase and enhance insulin sensitivity.

Topics: Anti-Inflammatory Agents, Non-Steroidal; Antibodies; Aspirin; Cinnamates; Forkhead Box Protein O1; Forkhead Transcription Factors; Glucose; Glycogen; Hep G2 Cells; Humans; Indomethacin; Inflammation; Insulin Receptor Substrate Proteins; Insulin Resistance; Molecular Imaging; Molecular Targeted Therapy; Protein Kinases; Quantum Dots; Reproducibility of Results; Serine; Tumor Necrosis Factor-alpha

The present study was designed to evaluate the potential hypoglycemic and hypolipidemic effects of Angelica sinensis polysaccharide (ASP), purified from the fresh roots of Angelica sinensis (AS), in prediabetic and streptozotocin (STZ)-induced diabetic BALB/c mice. It was observed that fasting blood glucose (FBG) levels in both models were reduced after a 4-week oral administration of ASP or metformin, and abnormal fasting serum insulin (FINS) concentrations were ameliorated as well. Moreover, the homeostasis model assessment-insulin resistance (HOMA-IR) index was decreased strikingly and body weight (BW) was reduced significantly in prediabetic mice after treatment with ASP. In addition, ASP also contributed to improving the dyslipidemia conditions. Elevated serum total cholesterol (TC) or triglyceride (TG) concentrations were reduced after treatment with ASP in prediabetic mice or STZ-induced diabetic mice. Meanwhile, hepatic glycogen (HG) and muscle glycogen (MG) concentrations were increased while insulin resistance (IR)-related inflammatory factors IL-6 and TNF-α in serum were reduced in STZ-induced diabetic mice. Histopathological examination indicated that the impaired pancreatic/hepatic tissues or adipose tissues were effectively restored in STZ-induced diabetic mice or prediabetic mice after the ASP treatment. Taken together, these results revealed that ASP efficiently exerted hypoglycemic and hypolipidemic benefits, and its potential effect was associated with the amelioration of IR. ASP can be applied in the prevention and treatment of diabetes.

Topics: Adipose Tissue, White; Angelica sinensis; Animals; Anti-Inflammatory Agents, Non-Steroidal; Diabetes Mellitus, Type 2; Glycogen; Hyperglycemia; Hyperinsulinism; Hyperlipidemias; Hypoglycemic Agents; Hypolipidemic Agents; Insulin Resistance; Lipid Metabolism Disorders; Liver; Male; Mice, Inbred BALB C; Muscle, Skeletal; Pancreas; Plant Roots; Polysaccharides; Prediabetic State; Random Allocation

Sphingolipids play an important role in the development of insulin resistance. Ceramides are the most potent inhibitors of insulin signal transduction. Ceramides are generated in response to stress stimuli and in old age. In this work, we studied the possible contribution of different pathways of sphingolipid metabolism in age-dependent insulin resistance development in liver cells. Inhibition of key enzymes of sphingolipid synthesis (serine palmitoyl transferase, ceramide synthase) and degradation (neutral and acidic SMases) by means of specific inhibitors (myriocin, fumonisin B1, imipramine, and GW4869) was followed with the reduction of ceramide level and partly improved insulin regulation of glucose metabolism in "old" hepatocytes. Imipramine and GW4869 decreased significantly the acidic and neutral SMase activities, respectively. Treatment of "old" cells with myriocin or fumonisin B1 reduced the elevated in old age ceramide and SM synthesis. Ceramide and SM levels and glucose metabolism regulation by insulin could be improved with concerted action of all tested inhibitors of sphingolipid turnover on hepatocytes. The data demonstrate that not only newly synthesized ceramide and SM but also neutral and acidic SMase-dependent ceramide accumulation plays an important role in development of age-dependent insulin resistance.

Topics: Aging; Aniline Compounds; Animals; Benzylidene Compounds; Ceramides; Fatty Acids, Monounsaturated; Fumonisins; Glucose; Glycogen; Hepatocytes; Imipramine; Insulin; Insulin Resistance; Male; Oxidoreductases; Rats; Serine C-Palmitoyltransferase; Sphingolipids; Sphingomyelin Phosphodiesterase

The ApcMin/+ mouse exhibits an intestinal tumor associated loss of muscle and fat that is accompanied by chronic inflammation, insulin resistance and hyperlipidemia. Since the liver governs systemic energy demands through regulation of glucose and lipid metabolism, it is likely that the liver is a pathological target of cachexia progression in the ApcMin/+ mouse. The purpose of this study was to determine if cancer and the progression of cachexia affected liver endoplasmic reticulum (ER)-stress, inflammation, metabolism, and protein synthesis signaling. The effect of cancer (without cachexia) was examined in wild-type and weight-stable ApcMin/+ mice. Cachexia progression was examined in weight-stable, pre-cachectic, and severely-cachectic ApcMin/+ mice. Livers were analyzed for morphology, glycogen content, ER-stress, inflammation, and metabolic changes. Cancer induced hepatic expression of ER-stress markers BiP (binding immunoglobulin protein), IRE-1α (endoplasmic reticulum to nucleus signaling 1), and inflammatory intermediate STAT-3 (signal transducer and activator of transcription 3). While gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) mRNA expression was suppressed by cancer, glycogen content or protein synthesis signaling remained unaffected. Cachexia progression depleted liver glycogen content and increased mRNA expression of glycolytic enzyme PFK (phosphofrucktokinase) and gluconeogenic enzyme PEPCK. Cachexia progression further increased pSTAT-3 but suppressed p-65 and JNK (c-Jun NH2-terminal kinase) activation. Interestingly, progression of cachexia suppressed upstream ER-stress markers BiP and IRE-1α, while inducing its downstream target CHOP (DNA-damage inducible transcript 3). Cachectic mice exhibited a dysregulation of protein synthesis signaling, with an induction of p-mTOR (mechanistic target of rapamycin), despite a suppression of Akt (thymoma viral proto-oncogene 1) and S6 (ribosomal protein S6) phosphorylation. Thus, cancer induced ER-stress markers in the liver, however cachexia progression further deteriorated liver ER-stress, disrupted protein synthesis regulation and caused a differential inflammatory response related to STAT-3 and NF-κB (Nuclear factor-κB) signaling.

Topics: Animals; Cachexia; Endoplasmic Reticulum Stress; Genes, APC; Glycogen; Hyperlipidemias; Inflammation; Insulin Resistance; Lipid Metabolism; Liver; Mice; NF-kappa B; Protein Biosynthesis; Signal Transduction; STAT3 Transcription Factor

Circulating redox state changes, determined by the ratio of reduced/oxidized pairs of different metabolites, have been associated with metabolic diseases. However, the pathogenic contribution of these changes and whether they modulate normal tissue function is unclear. As alterations in hepatic gluconeogenesis and glycogen metabolism are hallmarks that characterize insulin resistance and type 2 diabetes, we tested whether imposed changes in the extracellular redox state could modulate these processes. Thus, primary hepatocytes were treated with different ratios of the following physiological extracellular redox couples: β-hydroxybutyrate (βOHB)/acetoacetate (Acoc), reduced glutathione (GSH)/oxidized glutathione (GSSG), and cysteine/cystine. Exposure to a more oxidized ratio via extracellular βOHB/Acoc, GSH/GSSG, and cysteine/cystine in hepatocytes from fed mice increased intracellular hydrogen peroxide without causing oxidative damage. On the other hand, addition of more reduced ratios of extracellular βOHB/Acoc led to increased NAD(P)H and maximal mitochondrial respiratory capacity in hepatocytes. Greater βOHB/Acoc ratios were also associated with decreased β-oxidation, as expected with enhanced lipogenesis. In hepatocytes from fasted mice, a more extracellular reduced state of βOHB/Acoc led to increased alanine-stimulated gluconeogenesis and enhanced glycogen synthesis capacity from added glucose. Thus, we demonstrated for the first time that the extracellular redox state regulates the major metabolic functions of the liver and involves changes in intracellular NADH, hydrogen peroxide, and mitochondrial respiration. Because redox state in the blood can be communicated to all metabolically sensitive tissues, this work confirms the hypothesis that circulating redox state may be an important regulator of whole body metabolism and contribute to alterations associated with metabolic diseases.

Topics: 3-Hydroxybutyric Acid; Acetoacetates; Animals; Cysteine; Cystine; Diabetes Mellitus, Type 2; Gluconeogenesis; Glutathione; Glutathione Disulfide; Glycogen; Hepatocytes; Humans; Hydrogen Peroxide; Insulin Resistance; Mice; Mitochondria; NAD; Oxidation-Reduction; Respiration

Glucose homeostasis is distorted by defects of the PI3K/AKT and AMPK pathways in insulin-sensitive tissues, allowing the accumulation of glucose in the blood. The purpose of this study was to assess the effects and mechanisms by which ethanol extract of Caulerpa lentillifera (CLE) regulates glucose metabolism in C57BL/KsJ-db/db (db/db) mice.. Mice were administered CLE (250 or 500 mg/kg BW) or rosiglitazone (RSG, 10 mg/kg BW) for 6 weeks. Then, oral glucose tolerance test (OGTT) and intraperitoneal insulin tolerance test (IPITT) were performed, and blood glucose was measured in db/db mice. Levels of insulin and insulin resistance factors in plasma, glycogen content in the liver, and IRS, PI3K, AKT, and GLUT4 expressions in skeletal muscles were measured in db/db mice. Glucose uptake and insulin signaling molecules were measured in L6 myocytes, using fluorometry and Western blotting.. CLE significantly decreased fasting blood glucose, glucose level in OGTT and IPITT, plasma insulin, homeostatic model assessment-insulin resistant (HOMA-IR), TNF-α, IL-6, FFA, TG and TC levels, and hepatic glycogen content in db/db mice. CLE significantly increased the activation of IRS, AKT, PI3K, and GLUT4, which are the key effector molecules of the PI3K/AKT pathway in L6 myocytes and the skeletal muscles of db/db mice. The enhanced glucose uptake by CLE was abolished by treatment with a PI3K inhibitor (LY294002), but not by an AMPK inhibitor (compound C) in L6 myocytes. CLE regulated glucose uptake and homeostasis via the PI3K/AKT pathway in myocytes and db/db mice, respectively.. Our results suggest that CLE could be a potential candidate for the prevention of diabetes.

Topics: Adenylate Kinase; Adipose Tissue; Animals; Blood Glucose; Body Weight; Caulerpa; Cell Line; Diet; Epididymis; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Liver; Male; Mice, Inbred C57BL; Muscle Cells; Muscles; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Rats; RNA, Messenger; Signal Transduction

In previous studies, we demonstrated that down-regulation of lipoprotein lipase in L6 muscle cells increased insulin-stimulated glucose uptake. In the current study, we used RNA interference technology to silence the LPL gene in L6 cells and generate a LPL-knock-down (LPL-KD) cell line. ShRNA transfected cells showed a 88% reduction in the level of LPL expression. The metabolic response to insulin was compared in wild-type (WT) and LPL-KD cells. Insulin-stimulated glycogen synthesis and glucose oxidation were respectively, 2.4-fold and 2.6-fold greater in LPL-KD cells compared to WT cells. Oxidation of oleic acid was reduced by 50% in LPL-KD cells compared to WT cells even in the absence of insulin. The contribution of LPL in regulating fuel metabolism was confirmed by adding back purified LPL to the culture media of LPL-KD cells. The presence of 10 μg/mL LPL resulted in LPL-KD cells reverting back to lower glycogen synthesis and glucose oxidation and increased fatty acid oxidation. Thus, LPL depletion appeared to mimic the action of insulin. These finding suggests an inverse correlation between muscle LPL levels and insulin-stimulated fuel homeostasis.

Topics: Actins; Animals; Cell Line; Gene Expression; Glucose; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Lipoprotein Lipase; Muscle Fibers, Skeletal; Oleic Acid; Oxidation-Reduction; Rats; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; RNA, Small Interfering

The major role of liver glycogen is to supply glucose to the circulation maintaining the normal blood glucose level. In muscle and liver the accumulation and breakdown of glycogen are regulated by the reciprocal activities of glycogen phosphorylase and glycogen synthase. Glycogen phosphorylase catalyses the key step of glycogen degradation and its activity can be inhibited by glucose and its analogues. Obviously, any readily accessible inhibitor of glycogen phosphorylase can be used as a potential therapy of non-insulin-dependent or type 2 diabetes. Hepatic glycogen phosphorylase has been identified as a new target for drugs that control blood glucose concentration. In our experiments glucopyranosylidene-spirothiohydantoin (TH) was tested on the insulin sensitivity and blood glucose level of control and streptozotocin-treated rats. The streptozotocin-treated rats failed to gain weight and exhibited stable hyperglycemia (4.7 ± 0.5 mmol/L glucose in control vs. 7.8 ± 0.5 mmol/L) and low plasma insulin levels (9.6 ± 1.9 µIU/mL in control vs. 3.2 ± 2.2 µIU/mL). When insulin supplementation with slow-release implants (2 IU/day) was started 8 weeks after streptozotocin injection, blood glucose concentration remained suppressed, plasma insulin level dramatically increased and the insulin sensitivity restored. TH administration significantly reduced the high blood glucose concentration and restored the insulin sensitivity of STZtreated rats.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Experimental; Glycogen; Glycogen Phosphorylase; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Male; Monosaccharides; Rats, Wistar; Spiro Compounds; Streptozocin

In the liver, insulin-mediated activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway is at the core of metabolic control. Multiple PI3K and Akt isoenzymes are found in hepatocytes and whether isoform-selective interplays exist is currently unclear. Here we report that insulin signalling triggers the association of the liver-specific class II PI3K isoform γ (PI3K-C2γ) with Rab5-GTP, and its recruitment to Rab5-positive early endosomes. In these vesicles, PI3K-C2γ produces a phosphatidylinositol-3,4-bisphosphate pool specifically required for delayed and sustained endosomal Akt2 stimulation. Accordingly, loss of PI3K-C2γ does not affect insulin-dependent Akt1 activation as well as S6K and FoxO1-3 phosphorylation, but selectively reduces Akt2 activation, which specifically inhibits glycogen synthase activity. As a consequence, PI3K-C2γ-deficient mice display severely reduced liver accumulation of glycogen and develop hyperlipidemia, adiposity as well as insulin resistance with age or after consumption of a high-fat diet. Our data indicate PI3K-C2γ supports an isoenzyme-specific forking of insulin-mediated signal transduction to an endosomal pool of Akt2, required for glucose homeostasis.

Topics: Adiposity; Aging; Animals; Diet, High-Fat; Endosomes; Forkhead Transcription Factors; Glucose; Glycogen; Glycogen Synthase; Hepatocytes; Homeostasis; Hyperlipidemias; Insulin; Insulin Resistance; Liver; Mice; Mice, Inbred C57BL; Mice, Knockout; Phosphatidylinositol 3-Kinases; Phosphatidylinositol Phosphates; Proto-Oncogene Proteins c-akt; rab5 GTP-Binding Proteins; Ribosomal Protein S6 Kinases; Signal Transduction

Increased glucose production and reduced hepatic glycogen storage contribute to metabolic abnormalities in diabetes. Irisin, a newly identified myokine, induces the browning of white adipose tissue, but its effects on gluconeogenesis and glycogenesis are unknown. In the present study, we investigated the effects and underlying mechanisms of irisin on gluconeogenesis and glycogenesis in hepatocytes with insulin resistance, and its therapeutic role in type 2 diabetic mice. Insulin resistance was induced by glucosamine (GlcN) or palmitate in human hepatocellular carcinoma (HepG2) cells and mouse primary hepatocytes. Type 2 diabetes was induced by streptozotocin/high-fat diet (STZ/HFD) in mice. In HepG2 cells, irisin ameliorated the GlcN-induced increases in glucose production, phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) expression, and glycogen synthase (GS) phosphorylation; it prevented GlcN-induced decreases in glycogen content and the phosphoinositide 3-kinase (PI3K) p110α subunit level, and the phosphorylation of Akt/protein kinase B, forkhead box transcription factor O1 (FOXO1) and glycogen synthase kinase-3 (GSK3). These effects of irisin were abolished by the inhibition of PI3K or Akt. The effects of irisin were confirmed in mouse primary hepatocytes with GlcN-induced insulin resistance and in human HepG2 cells with palmitate-induced insulin resistance. In diabetic mice, persistent subcutaneous perfusion of irisin improved the insulin sensitivity, reduced fasting blood glucose, increased GSK3 and Akt phosphorylation, glycogen content and irisin level, and suppressed GS phosphorylation and PEPCK and G6Pase expression in the liver. Irisin improves glucose homoeostasis by reducing gluconeogenesis via PI3K/Akt/FOXO1-mediated PEPCK and G6Pase down-regulation and increasing glycogenesis via PI3K/Akt/GSK3-mediated GS activation. Irisin may be regarded as a novel therapeutic strategy for insulin resistance and type 2 diabetes.

Topics: Animals; Blotting, Western; Cells, Cultured; Chromones; Class I Phosphatidylinositol 3-Kinases; Diabetes Mellitus, Type 2; Fibronectins; Gluconeogenesis; Glucose; Glucose-6-Phosphatase; Glycogen; Glycogen Synthase; Hep G2 Cells; Hepatocytes; Heterocyclic Compounds, 3-Ring; Humans; Insulin Resistance; Liver; Male; Mice, Inbred C57BL; Morpholines; Phosphatidylinositol 3-Kinases; Phosphoenolpyruvate Carboxykinase (ATP); Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Proto-Oncogene Proteins c-akt; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction

Fibroblast growth factor 21 (FGF21) is an important regulator of hepatic glucose and lipid metabolism and represents a potential pharmacological agent for the treatment of type 2 diabetes and obesity. Mice fed a ketogenic diet (KD) develop hepatic insulin resistance in association with high levels of FGF21, suggesting a state of FGF21 resistance. To address the role of FGF21 in hepatic insulin resistance, we assessed insulin action in FGF21 whole-body knock-out (FGF21 KO) male mice and their littermate WT controls fed a KD. Here, we report that FGF21 KO mice have hepatic insulin resistance and increased hepatic glucose production associated with an increase in plasma glucagon levels. FGF21 KO mice are also hypometabolic and display increased fat mass compared with their WT littermates. Taken together, these findings support a major role of FGF21 in regulating energy expenditure and hepatic glucose and lipid metabolism, and its potential role as a candidate in the treatment of diseases associated with insulin resistance.

Topics: Animals; Blood Glucose; Energy Metabolism; Fibroblast Growth Factors; Glucagon; Gluconeogenesis; Glucose; Glycogen; Insulin Resistance; Lipids; Liver; Male; Mice; Mice, Knockout

Recently, there has been a growing interest in alternative therapies and in the therapeutic use of natural products for the treatment of diabetes. Therefore, in this study, we investigated the hypoglycemic and hypolipidemic effects of brown algae, Padina arborescens, in an animal model of type 2 diabetes. For 6 weeks, male C57BL/KsJ-db/db mice were administrated either control diet with no treatment or were treated with rosiglitazone (RG; 0.005%, w/w) or P. arborescens extract (PAE; 0.5%, w/w). At the end of the experimental period, the blood glucose levels, glycosylated hemoglobin levels, and plasma insulin levels were significantly lower in the RG and PAE groups compared with the control group. In addition, glucose tolerance was significantly improved in the RG and PAE groups. The homeostatic index of insulin resistance was lower in the RG and PAE groups than the diabetic control group. Also, the total cholesterol, LDL-cholesterol, triglyceride, and free fatty acid levels were lower in the PAE group than in the control group, whereas the HDL-C level was higher in the PAE group. Supplementation with PAE significantly lowered hepatic glucose-6-phosphatase and phosphoenolpyruvate carboxykinase activities, and increased glucokinase activity in the liver. Consequently, these results suggest that PAE may be beneficial in improving insulin resistance, hyperglycemia, and dyslipidemia in type 2 diabetics.

Topics: Adiponectin; Animals; Blood Glucose; Diabetes Mellitus, Type 2; Diet; Disease Models, Animal; Dyslipidemias; Fasting; Glucose Tolerance Test; Glycated Hemoglobin; Glycogen; Hyperglycemia; Hypoglycemic Agents; Insulin; Insulin Resistance; Lipids; Male; Mice; Mice, Inbred C57BL; Phaeophyceae; Rosiglitazone; Thiazolidinediones

Insulin regulates glycaemia, lipogenesis and increases mRNA translation. Cells with reduced eukaryotic initiation factor 6 (eIF6) do not increase translation in response to insulin. The role of insulin-regulated translation is unknown. Here we show that reduction of insulin-regulated translation in mice heterozygous for eIF6 results in normal glycaemia, but less blood cholesterol and triglycerides. eIF6 controls fatty acid synthesis and glycolysis in a cell autonomous fashion. eIF6 acts by exerting translational control of adipogenic transcription factors like C/EBPβ, C/EBPδ and ATF4 that have G/C rich or uORF sequences in their 5' UTR. The outcome of the translational activation by eIF6 is a reshaping of gene expression with increased levels of lipogenic and glycolytic enzymes. Finally, eIF6 levels modulate histone acetylation and amounts of rate-limiting fatty acid synthase (Fasn) mRNA. Since obesity, type 2 diabetes, and cancer require a Fasn-driven lipogenic state, we propose that eIF6 could be a therapeutic target for these diseases.

Topics: 3T3 Cells; Acetylation; Activating Transcription Factor 4; Adipocytes; Adipogenesis; Animals; Blotting, Western; CCAAT-Enhancer-Binding Protein-beta; CCAAT-Enhancer-Binding Protein-delta; Electrophoresis, Polyacrylamide Gel; Fatty Acid Synthases; Fatty Acids; Gene Expression Regulation; Gene Knockdown Techniques; Glucose; Glucose Tolerance Test; Glycogen; Glycolysis; HEK293 Cells; Hepatocytes; Histone Code; Humans; Insulin Resistance; Lactic Acid; Lipid Metabolism; Lipogenesis; Liver; Mesenchymal Stem Cells; Mice; Oxidation-Reduction; Peptide Initiation Factors; Protein Biosynthesis; Radiography; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Transcription, Genetic

Di(2-ethyl hexyl)-phthalate (DEHP) is an endocrine disrupter and is the most abundantly used phthalate derivative, which is suspected to be an inevitable environmental exposure contributing to the increasing incidence of type-2 diabetes in humans. Therefore, the present study was designed to address the dose-dependent effects of DEHP on insulin signaling molecules in L6 myotubes. L6 myotubes were exposed to different concentrations (25, 50, and 100 μM) of DEHP for 24 h. At the end of exposure, cells were utilized for assessing various parameters. Insulin receptor and glucose transporter4 (GLUT4) gene expression, insulin receptor protein concentration, glucose uptake and oxidation, and enzymatic and nonenzymatic antioxidants were significantly reduced, but glutamine fructose-6-phosphate amidotransferase, nitric oxide, lipid peroxidation, and reactive oxygen species levels were elevated in a dose-dependent manner in L6 myotubes exposed to DEHP. The present study in turn shows the direct adverse effect of DEHP on the expression of insulin receptor and GLUT4 gene, glucose uptake, and oxidation in L6 myotubes suggesting that DEHP exposure may have a negative influence on insulin signaling.

Topics: Animals; Antioxidants; Cell Line; Cell Survival; Diethylhexyl Phthalate; Dose-Response Relationship, Drug; Endocrine Disruptors; Glucose; Glucose Transporter Type 4; Glycogen; Insulin Resistance; Lipid Peroxidation; Muscle Fibers, Skeletal; Oxidation-Reduction; Oxidative Stress; Rats; Reactive Oxygen Species; Receptor, Insulin; Signal Transduction; Time Factors

The association between caffeine intake and the risk for chronic diseases, namely type 2 diabetes, has not been consistent, and may be influenced by the timing of caffeine ingestion. The aim of this study was to investigate the acute effect of caffeine administered in different scenarios of meal ingestion on postprandial glycemic and lipidemic status, concomitant with changes in body glycogen stores.. Forty overnight-fasted rats were randomly divided into five groups (meal-ingested, caffeine-administered, post-caffeine meal-ingested, co-caffeine meal-ingested, post-meal caffeine-administered), and tube-fed the appropriate intervention, then sacrificed 2 h later. Livers and gastrocnemius muscles were analyzed for glycogen content; blood samples were analyzed for glucose, insulin, triglycerides, and non-esterified fatty acid concentrations.. Postprandial plasma glucose concentrations were similar between groups, while significantly higher levels of insulin were witnessed following caffeine administration, irrespective of the timing of meal ingestion. Triglyceride concentrations were significantly lower in the caffeine-administered groups. Regarding glycogen status, although caffeine administration before meal ingestion reduced hepatic glycogen content, co- and post-meal caffeine administration failed to produce such an effect. Muscle glycogen content was not significantly affected by caffeine administration.. Caffeine administration seems to decrease insulin sensitivity as indicated by the sustenance of glucose status despite the presence of high insulin levels. The lower triglyceride levels in the presence of caffeine support the theory of retarded postprandial triglyceride absorption. Caffeine seems to play a biphasic role in glucose metabolism, as indicated by its ability to variably influence hepatic glycogen status.

Topics: Animals; Blood Glucose; Caffeine; Carbohydrate Metabolism; Glycogen; Insulin; Insulin Resistance; Male; Meals; Muscle, Skeletal; Postprandial Period; Rats; Rats, Sprague-Dawley; Time Factors; Triglycerides

To elucidate the complex impact of hypoxia on adipose tissue, resulting in biased metabolism, insulin resistance and finally diabetes we used mature adipocytes derived from a Simpson-Golabi-Behmel syndrome patient for microarray analysis. We found a significantly increased transcription rate of genes involved in glycolysis and a striking association between the pattern of upregulated genes and disease biomarkers for diabetes mellitus and insulin resistance. Although their upregulation turned out to be HIF-1α-dependent, we identified further transcription factors mainly AP-1 components to play also an important role in hypoxia response. Analyzing the regulatory network of mentioned transcription factors and glycolysis targets we revealed a clear hint for directing glycolysis to glutathione and glycogen synthesis. This metabolic switch in adipocytes enables the cell to prevent oxidative damage in the short term but might induce lipogenesis and establish systemic metabolic disorders in the long run.

Topics: Adipocytes; Adipogenesis; Arrhythmias, Cardiac; Biomarkers; Cell Hypoxia; Gene Expression Profiling; Gene Expression Regulation; Genetic Diseases, X-Linked; Gigantism; Glutathione; Glycogen; Glycolysis; Heart Defects, Congenital; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Insulin Resistance; Intellectual Disability; Oligonucleotide Array Sequence Analysis; Protein Interaction Mapping; Signal Transduction; Transcription Factor AP-1; Transcription, Genetic

Leptin is essential for energy homeostasis and regulation of food intake. Patients with congenital generalized lipodystrophy (CGL) due to mutations in 1-acylglycerol-3-phosphate-O-acyltransferase 2 (AGPAT2) and the CGL murine model (Agpat2(-/-) mice) both have severe insulin resistance, diabetes mellitus, hepatic steatosis, and low plasma leptin levels. In this study, we show that continuous leptin treatment of Agpat2(-/-) mice for 28 days reduced plasma insulin and glucose levels and normalized hepatic steatosis and hypertriglyceridemia. Leptin also partially, but significantly, reversed the low plasma thyroxine and high corticosterone levels found in Agpat2(-/-) mice. Levels of carbohydrate response element binding protein (ChREBP) were reduced, whereas lipogenic gene expression were increased in the livers of Agpat2(-/-) mice, suggesting that deregulated ChREBP contributed to the development of fatty livers in these mice and that this transcription factor is a target of leptin's beneficial metabolic action. Leptin administration did not change hepatic fatty acid oxidation enzymes mRNA levels in Agpat2(-/-) mice. The selective deletion of leptin receptors only in hepatocytes did not prevent the positive metabolic actions of leptin in Agpat2(-/-) mice, supporting the notion that the majority of metabolic actions of leptin are dependent on its action in nonhepatocyte cells and/or the central nervous system.

Topics: 1-Acylglycerol-3-Phosphate O-Acyltransferase; Animals; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Corticosterone; Fatty Acids; Fatty Liver; Gene Deletion; Gene Expression Regulation; Glucose; Glycogen; Hepatocytes; Insulin Resistance; Leptin; Lipodystrophy; Lipogenesis; Liver; Male; Mice; Nuclear Proteins; Oxidation-Reduction; Phosphorylation; Proto-Oncogene Proteins c-akt; Receptors, Leptin; Thyroxine; Transcription Factors; Transcription, Genetic; Triglycerides

AMP-activated protein kinase is a master regulator of cell metabolism and an attractive drug target for cancer and metabolic and cardiovascular diseases. Point mutations in the regulatory γ2-subunit of AMP-activated protein kinase (encoded by Prkag2 gene) caused a unique form of human cardiomyopathy characterized by cardiac hypertrophy, ventricular preexcitation, and glycogen storage. Understanding the disease mechanisms of Prkag2 cardiomyopathy is not only beneficial for the patients but also critical to the use of AMP-activated protein kinase as a drug target.. We sought to identify the pro-growth-signaling pathway(s) triggered by Prkag2 mutation and to distinguish it from the secondary response to glycogen storage.. In a mouse model of N488I mutation of the Prkag2 gene (R2M), we rescued the glycogen storage phenotype by genetic inhibition of glucose-6-phosphate-stimulated glycogen synthase activity. Ablation of glycogen storage eliminated the ventricular preexcitation but did not affect the excessive cardiac growth in R2M mice. The progrowth effect in R2M hearts was mediated via increased insulin sensitivity and hyperactivity of Akt, resulting in activation of mammalian target of rapamycin and inactivation of forkhead box O transcription factor-signaling pathways. Consequently, cardiac myocyte proliferation during the postnatal period was enhanced in R2M hearts followed by hypertrophic growth in adult hearts. Inhibition of mammalian target of rapamycin activity by rapamycin or restoration of forkhead box O transcription factor activity by overexpressing forkhead box O transcription factor 1 rescued the abnormal cardiac growth.. Our study reveals a novel mechanism for Prkag2 cardiomyopathy, independent of glycogen storage. The role of γ2-AMP-activated protein kinase in cell growth also has broad implications in cardiac development, growth, and regeneration.

Topics: AMP-Activated Protein Kinases; Animals; Cardiomyopathy, Hypertrophic, Familial; Cell Division; Cell Enlargement; Disease Models, Animal; Forkhead Box Protein O1; Forkhead Transcription Factors; Gene Knock-In Techniques; Genetic Complementation Test; Glucose-6-Phosphate; Glycogen; Glycogen Storage Disease; Glycogen Synthase; Insulin Resistance; Mice; Myocardium; Myocytes, Cardiac; Pre-Excitation Syndromes; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Earlier research on rats with normal insulin sensitivity demonstrated that acute exercise increased insulin-stimulated glucose uptake (GU) concomitant with greater phosphorylation of Akt substrate of 160 kDa (pAS160). Because mechanisms for exercise effects on GU in insulin-resistant muscle are unknown, our primary objective was to assess insulin-stimulated GU, proximal insulin signaling (insulin receptor [IR] tyrosine phosphorylation, IR substrate 1-phosphatidylinositol-3-kinase, and Akt phosphorylation and activity), and pAS160 in muscles from acutely exercised (one session) and sedentary rats fed either chow (low-fat diet [LFD]; normal insulin sensitivity) or a high-fat diet (HFD; for 2 weeks, insulin-resistant). At 3 h postexercise (3hPEX), isolated epitrochlearis muscles were used for insulin-stimulated GU and insulin signaling measurements. Although exercise did not enhance proximal signaling in either group, insulin-stimulated GU at 3hPEX exceeded respective sedentary control subjects (Sedentary) in both diet groups. Furthermore, insulin-stimulated GU for LFD-3hPEX was greater than HFD-3hPEX values. For HFD-3hPEX muscles, pAS160 exceeded HFD-Sedentary, but in muscle from LFD-3hPEX rats, pAS160 was greater still than HFD-3hPEX values. These results implicated pAS160 as a potential determinant of the exercise-induced elevation in insulin-stimulated GU for each diet group and also revealed pAS160 as a possible mediator of greater postexercise GU of insulin-stimulated muscles from the insulin-sensitive versus insulin-resistant group.

Topics: Animals; Cells, Cultured; Glucose; Glycogen; GTPase-Activating Proteins; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Phosphorylation; Physical Conditioning, Animal; Rats; Rats, Wistar

Acylcarnitine accumulation in skeletal muscle and plasma has been observed in numerous models of mitochondrial lipid overload and insulin resistance. Fish oil n3PUFA (omega-3 polyunsaturated fatty acids) are thought to protect against lipid-induced insulin resistance. The present study tested the hypothesis that the addition of n3PUFA to an intravenous lipid emulsion would limit muscle acylcarnitine accumulation and reduce the inhibitory effect of lipid overload on insulin action. On three occasions, six healthy young men underwent a 6-h euglycaemic-hyperinsulinaemic clamp accompanied by intravenous infusion of saline (Control), 10% Intralipid® [n6PUFA (omega-6 polyunsaturated fatty acids)] or 10% Intralipid®+10% Omegaven® (2:1; n3PUFA). The decline in insulin-stimulated whole-body glucose infusion rate, muscle PDCa (pyruvate dehydrogenase complex activation) and glycogen storage associated with n6PUFA compared with Control was prevented with n3PUFA. Muscle acetyl-CoA accumulation was greater following n6PUFA compared with Control and n3PUFA, suggesting that mitochondrial lipid overload was responsible for the lower insulin action observed. Despite these favourable metabolic effects of n3PUFA, accumulation of total muscle acylcarnitine was not attenuated when compared with n6PUFA. These findings demonstrate that n3PUFA exert beneficial effects on insulin-stimulated skeletal muscle glucose storage and oxidation independently of total acylcarnitine accumulation, which does not always reflect mitochondrial lipid overload.

Topics: Adult; Carnitine; Fatty Acids, Omega-3; Fish Oils; Glycogen; Humans; Insulin; Insulin Resistance; Lipids; Male; Muscle, Skeletal; Triglycerides

Treatment of diabetic subjects with cinnamon demonstrated an improvement in blood glucose concentrations and insulin sensitivity but the underlying mechanisms remained unclear. This work intends to elucidate the impact of cinnamon effects on the brain by using isolated astrocytes, and an obese and diabetic mouse model.. Cinnamon components (eugenol, cinnamaldehyde) were added to astrocytes and liver cells to measure insulin signaling and glycogen synthesis. Ob/ob mice were supplemented with extract from cinnamomum zeylanicum for 6 weeks and cortical brain activity, locomotion and energy expenditure were evaluated. Insulin action was determined in brain and liver tissues.. Treatment of primary astrocytes with eugenol promoted glycogen synthesis, whereas the effect of cinnamaldehyde was attenuated. In terms of brain function in vivo, cinnamon extract improved insulin sensitivity and brain activity in ob/ob mice, and the insulin-stimulated locomotor activity was improved. In addition, fasting blood glucose levels and glucose tolerance were greatly improved in ob/ob mice due to cinnamon extracts, while insulin secretion was unaltered. This corresponded with lower triglyceride and increased liver glycogen content and improved insulin action in liver tissues. In vitro, Fao cells exposed to cinnamon exhibited no change in insulin action.. Together, cinnamon extract improved insulin action in the brain as well as brain activity and locomotion. This specific effect may represent an important central feature of cinnamon in improving insulin action in the brain, and mediates metabolic alterations in the periphery to decrease liver fat and improve glucose homeostasis.

Topics: Acrolein; Adiposity; Animals; Astrocytes; Brain; Cell Line; Cinnamomum zeylanicum; Energy Intake; Eugenol; Glycogen; Humans; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Obese; Motor Activity; Obesity; Plant Extracts

The aim of this study was to investigate the mechanisms underlying the involvement of gut microbes in body weight gain of high-fat diet-fed obesity-prone (obese) and obesity-resistant (lean) mice. C57BL/6 mice were grouped into an obese group, a lean group and a normal control group. Both obese and lean mice were fed a high-fat diet while normal control mice were fed a normal diet; they were observed for six weeks. The results showed that lean mice had lower serum lipid levels, body fat and weight gain than obese mice. The ATPase, succinate dehydrogenase and malate dehydrogenase activities in liver as well as oxygen expenditure and rectal temperature of lean mice were significantly lower than in obese mice. As compared with obese mice, the absorption of intestinal carbohydrates but not of fats or proteins was significantly attenuated in lean mice. Furthermore, 16S rRNA abundances of faecal Firmicutes and Bacteroidetes were significantly reduced in lean mice. In addition, faecal β-D-galactosidase activity and short chain fatty acid levels were significantly decreased in lean mice. Expressions of peroxisome proliferator-activated receptor gamma 2 and CCAAT/enhancer binding protein-β in visceral adipose tissues were significantly downregulated in lean mice as compared with obese mice. Resistance to dyslipidaemia and high-fat diet-induced obesity was mediated by ineffective absorption of intestinal carbohydrates but not of fats or proteins, probably through reducing gut Bacteroidetes and Firmicutes contents and lowering of gut carbohydrate metabolism. The regulation of intestinal carbohydrates instead of fat absorption by gut microbes might be a potential treatment strategy for high-fat diet-induced obesity.

Topics: Adenosine Triphosphatases; Adipose Tissue; Animals; Bacteroidetes; beta-Galactosidase; Body Weight; Carbohydrate Metabolism; CCAAT-Enhancer-Binding Protein-beta; Diet, High-Fat; Dyslipidemias; Fatty Acids, Volatile; Feces; Glucose Tolerance Test; Glycogen; Insulin Resistance; Intestinal Mucosa; Intestines; Lipid Metabolism; Lipids; Liver; Malate Dehydrogenase; Male; Mice; Mice, Inbred C57BL; Mice, Obese; Obesity; Oxygen Consumption; PPAR gamma; Random Allocation; RNA, Ribosomal, 16S; Succinate Dehydrogenase; Weight Gain

Glycogen and lipids are major storage forms of energy that are tightly regulated by hormones and metabolic signals. We demonstrate that feeding mice a high-fat diet (HFD) increases hepatic glycogen due to increased expression of the glycogenic scaffolding protein PTG/R5. PTG promoter activity was increased and glycogen levels were augmented in mice and cells after activation of the mechanistic target of rapamycin complex 1 (mTORC1) and its downstream target SREBP1. Deletion of the PTG gene in mice prevented HFD-induced hepatic glycogen accumulation. Of note, PTG deletion also blocked hepatic steatosis in HFD-fed mice and reduced the expression of numerous lipogenic genes. Additionally, PTG deletion reduced fasting glucose and insulin levels in obese mice while improving insulin sensitivity, a result of reduced hepatic glucose output. This metabolic crosstalk was due to decreased mTORC1 and SREBP activity in PTG knockout mice or knockdown cells, suggesting a positive feedback loop in which once accumulated, glycogen stimulates the mTORC1/SREBP1 pathway to shift energy storage to lipogenesis. Together, these data reveal a previously unappreciated broad role for glycogen in the control of energy homeostasis.

Topics: Animals; Diet, High-Fat; Energy Metabolism; Feedback; Glycogen; HEK293 Cells; Humans; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Lipid Metabolism; Lipogenesis; Liver Glycogen; Male; Mechanistic Target of Rapamycin Complex 1; Mice; Mice, Knockout; Multiprotein Complexes; Obesity; Sterol Regulatory Element Binding Proteins; TOR Serine-Threonine Kinases

The aim of this study was to evaluate the effects of Bifidobacterium lactis HY8101 on insulin resistance induced using tumour necrosis factor-α (TNF-α) in rat L6 skeletal muscle cells and on the KK-A(Y) mouse noninsulin-dependent diabetes mellitus (NIDDM) model.. The treatment using HY8101 improved the insulin-stimulated glucose uptake and translocation of GLUT4 via the insulin signalling pathways AKT and IRS-1(Tyr) in TNF-α-treated L6 cells. HY8101 increased the mRNA levels of GLUT4 and several insulin sensitivity-related genes (PPAR-γ) in TNF-α-treated L6 cells. In KK-A(Y) mice, HY8101 decreased fasting insulin and blood glucose and significantly improved insulin tolerance. HY8101 improved diabetes-induced plasma total cholesterol and triglyceride (TG) levels and increased the muscle glycogen content. We observed concurrent transcriptional changes in the skeletal muscle tissue and the liver. In the skeletal muscle tissue, the glycogen synthesis-related gene pp-1 and GLUT4 were up-regulated in mice receiving HY8101 treatment. In the liver, the hepatic gluconeogenesis-regulated genes (PCK1 and G6PC) were down-regulated in mice receiving HY8101 treatment.. Bifidobacterium lactis HY8101 can be used to moderate glucose metabolism, lipid metabolism and insulin sensitivity in mice and in cells.. Bifidobacterium lactis HY8101 might have potential as a probiotic candidate for alleviating metabolic syndromes such as diabetes.

Topics: Animals; Bifidobacterium; Blood Glucose; Cell Line; Diabetes Mellitus, Type 2; Glucose; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Probiotics; Rats; Signal Transduction; Tumor Necrosis Factor-alpha

Two-dimensional difference gel electrophoresis (2-D DIGE)-based proteome analysis has revealed intrinsic insulin resistance in myotubes derived from type 2 diabetic patients. Using 2-D DIGE-based proteome analysis, we identified a subset of insulin-resistant proteins involved in protein turnover in skeletal muscle of type 2 diabetic patients, suggesting aberrant regulation of the protein homeostasis maintenance system underlying metabolic disease. We then validated the role of the ubiquitin-proteasome system (UPS) in myotubes to investigate whether impaired proteasome function may lead to metabolic arrest or insulin resistance. Myotubes derived from muscle biopsies obtained from people with normal glucose tolerance (NGT) or type 2 diabetes were exposed to the proteasome inhibitor bortezomib (BZ; Velcade) without or with insulin. BZ exposure increased protein carbonylation and lactate production yet impaired protein synthesis and UPS function in myotubes from type 2 diabetic patients, marking the existence of an insulin-resistant signature that was retained in cultured myotubes. In conclusion, BZ treatment further exacerbates insulin resistance and unmasks intrinsic features of metabolic disease in myotubes derived from type 2 diabetic patients. Our results highlight the existence of a confounding inherent abnormality in cellular protein dynamics in metabolic disease, which is uncovered through concurrent inhibition of the proteasome system.

Topics: Boronic Acids; Bortezomib; Cells, Cultured; Diabetes Mellitus, Type 2; Enzyme Inhibitors; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Lipid Metabolism; Male; Muscle, Skeletal; Oxidative Stress; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Protein Carbonylation; Proteome; Pyrazines; RNA Interference; Signal Transduction

To investigate whether alpha-lipoic acid (ALA) could attenuate the insulin resistance and metabolic disorders in high fat diet-fed mice.. Male mice were fed a high fat diet (HFD) plus ALA (100 and 200 mg·kg(-1)·d(-1)) or HFD plus a positive control drug metformin (300 mg·kg(-1)·d(-1)) for 24 weeks. During the treatments, the relevant physiological and metabolic parameters of the mice were measured. After the mice were euthanized, blood samples and livers were collected. The expression of proteins and genes related to glucose metabolism in livers were analyzed by immunoblotting and real time-PCR.. HFD induced non-alcoholic fatty liver disease (NAFLD) and abnormal physiological and metabolic parameters in the mice, which were dose-dependently attenuated by ALA. ALA also significantly reduced HFD-induced hyperglycemia and insulin resistance in HFD-fed mice. Furthermore, ALA significantly upregulated the glycolytic enzymes GCK, HK-1 and PK, and the glycogen synthesis enzyme GS, and downregulated the gluconeogenic enzymes PEPCK and G6Pase, thus decreased glucose production, and promoted glycogen synthesis and glucose utilization in livers. Moreover, ALA markedly increased PKB/Akt and GSK3β phosphorylation, and nuclear carbohydrate response element binding protein (ChREBP) expression in livers. Metformin produced similar effects as ALA in HFD-fed mice.. ALA is able to sustain glucose homeostasis and prevent the development of NAFLD in HFD-fed mice.

Topics: Animals; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Diet, High-Fat; Down-Regulation; Gluconeogenesis; Glucose; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Glycolysis; Hyperglycemia; Insulin Resistance; Liver; Male; Metabolic Diseases; Mice; Mice, Inbred C57BL; Non-alcoholic Fatty Liver Disease; Nuclear Proteins; Proto-Oncogene Proteins c-akt; Thioctic Acid; Transcription Factors; Up-Regulation

MicroRNAs (miRNAs) play an important role in insulin signaling and insulin secretion, but the role of miRNAs in the association between obesity and hepatic insulin resistance is largely unknown. This study reports that saturated fatty acid (SFA) and high fat diet (HFD) significantly induce miR-195 expression in hepatocytes, and that the insulin receptor (INSR), not insulin receptor substrate-1 (IRS-1), is a direct target of miR-195. Furthermore, the ectopic expression of miR-195 suppresses the expression of INSR, thereby impairing the insulin signaling cascade and glycogen synthesis in HepG2 cells. These findings suggest that the dysregulation of miR-195 by SFA is a detrimental factor for hepatic insulin sensitivity.

Topics: 3' Untranslated Regions; Animals; Binding Sites; Diet, High-Fat; Fatty Acids; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Insulin; Insulin Resistance; Mice; MicroRNAs; Obesity; Receptor, Insulin; Signal Transduction; Up-Regulation

The pyruvate dehydrogenase complex (PDH) has been hypothesized to link lipid exposure to skeletal muscle insulin resistance through a glucose-fatty acid cycle in which increased fatty acid oxidation increases acetyl-CoA concentrations, thereby inactivating PDH and decreasing glucose oxidation. However, whether fatty acids induce insulin resistance by decreasing PDH flux remains unknown. To genetically examine this hypothesis we assessed relative rates of pyruvate dehydrogenase flux/mitochondrial oxidative flux and insulin-stimulated rates of muscle glucose metabolism in awake mice lacking pyruvate dehydrogenase kinase 2 and 4 [double knockout (DKO)], which results in constitutively activated PDH. Surprisingly, increased glucose oxidation in DKO muscle was accompanied by reduced insulin-stimulated muscle glucose uptake. Preferential myocellular glucose utilization in DKO mice decreased fatty acid oxidation, resulting in increased reesterification of acyl-CoAs into diacylglycerol and triacylglycerol, with subsequent activation of PKC-θ and inhibition of insulin signaling in muscle. In contrast, other putative mediators of muscle insulin resistance, including muscle acylcarnitines, ceramides, reactive oxygen species production, and oxidative stress markers, were not increased. These findings demonstrate that modulation of oxidative substrate selection to increase muscle glucose utilization surprisingly results in muscle insulin resistance, offering genetic evidence against the glucose-fatty acid cycle hypothesis of muscle insulin resistance.

Topics: Animals; Carnitine; Citric Acid Cycle; Dietary Fats; Enzyme Activation; Fatty Acids; Glucose; Glycogen; Hyperinsulinism; Insulin Resistance; Isoenzymes; Mice; Mice, Inbred C57BL; Mice, Knockout; Models, Biological; Muscle, Skeletal; Nuclear Magnetic Resonance, Biomolecular; Oxidation-Reduction; Oxidative Stress; Phosphorylation; Protein Kinase C; Protein Kinase C-theta; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; Pyruvate Dehydrogenase Acetyl-Transferring Kinase; Pyruvate Dehydrogenase Complex; Reactive Oxygen Species; RNA, Messenger; Substrate Specificity

Physical exercise improves glucose metabolism and insulin sensitivity. Brain-derived neurotrophic factor (BDNF) enhances insulin activity in diabetic rodents. Because physical exercise modifies BDNF production, this study aimed to investigate the effects of chronic exercise on plasma BDNF levels and the possible effects on insulin tolerance modification in healthy rats.. Wistar rats were divided into five groups: control (sedentary, C); moderate- intensity training (MIT); MIT plus K252A TrkB blocker (MITK); high-intensity training (HIT); and HIT plus K252a (HITK). Training comprised 8 weeks of treadmill running. Plasma BDNF levels (ELISA assay), glucose tolerance, insulin tolerance, and immunohistochemistry for insulin and the pancreatic islet area were evaluated in all groups. In addition, Bdnf mRNA expression in the skeletal muscle was measured.. Chronic treadmill exercise significantly increased plasma BDNF levels and insulin tolerance, and both effects were attenuated by TrkB blocking. In the MIT and HIT groups, a significant TrkB-dependent pancreatic islet enlargement was observed. MIT rats exhibited increased liver glycogen levels following insulin administration in a TrkB-independent manner.. Chronic physical exercise exerted remarkable effects on insulin regulation by inducing significant increases in the pancreatic islet size and insulin sensitivity in a TrkB-dependent manner. A threshold for the induction of BNDF in response to physical exercise exists in certain muscle groups. To the best of our knowledge, these are the first results to reveal a role for TrkB in the chronic exercise-mediated insulin regulation in healthy rats.

Topics: Animals; Area Under Curve; Brain-Derived Neurotrophic Factor; Glucose Tolerance Test; Glycogen; Immunohistochemistry; Insulin; Insulin Resistance; Islets of Langerhans; Liver; Male; Muscle, Skeletal; Organ Size; Physical Conditioning, Animal; Rats; Rats, Wistar; Receptor, trkB; RNA, Messenger; ROC Curve

Benzopyrones are proven antidiabetic drug candidate in diabetic drug discovery. In this view novel synthetic benzopyrone analogues were selected for testing in experimental diabetes. Type 2 diabetes (T2D) was induced in Wistar rats by streptozotocin (60 mg/kg, i.p.) followed by nicotinamide (120 mg/kg i.p.). Rats having fasting blood glucose (FBG)>200 mg/dL, 7 days after T2D-induction, are selected for the study. Test compounds and standard treatment were continued for 15 days. FBG, oral glucose tolerance test (OGTT), and insulin tolerance test (ITT) were determined on 21st day after induction of T2D. Plasma lipids and serum insulin were estimated. Homeostatic model assessment (HOMA-IR) was then calculated from serum insulin. Rats were sacrificed and pancreas was isolated for histopathological observations. Oxidative stress markers were estimated in liver homogenate. Quercetin, a natural product with benzopyrone ring, showed significant hypoglycemic activity comparable to glibenclamide. Treatment with test compounds lowered the FBG and insulin resistance was significant alleviated as determined by OGTT, HOMA-IR, and ITT. There was significant normalisation of liver antioxidant enzymes compared to diabetic rats indicating that all the synthesised benzopyrone analogues are beneficial in reducing oxidative stress and are on par with the standard quercetin and glibenclamide in experimental T2D.

Topics: Animals; Biomarkers; Blood Glucose; Coumarins; Creatinine; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Fasting; Glucose Tolerance Test; Glycation End Products, Advanced; Glycogen; Hyperglycemia; Hypoglycemic Agents; Insulin; Insulin Resistance; Lipids; Liver; Male; Niacinamide; Oxidative Stress; Pancreas; Rats, Wistar; Streptozocin

Apelin, a novel adipokine, is the specific endogenous ligand of G protein-coupled receptor APJ. Consistent with its putative role as an adipokine, apelin has been linked to states of insulin resistance. However, the function of apelin in hepatic insulin resistance, a vital part of insulin resistance, and its underlying mechanisms still remains unclear. Here we define the impacts of apelin on TNF-α-induced reduction of glycogen synthesis in the hepatocytes. Our studies indicate that apelin reversed TNF-α-induced reduction of glycogen synthesis in HepG2 cells, mouse primary hepatocytes and liver tissues of C57BL/6J mice by improving JNK-IRS1-AKT-GSK pathway. Moreover, Western blot revealed that APJ, but not apelin, expressed in the hepatocytes and liver tissues of mice. We found that F13A, a competitive antagonist for G protein-coupled receptor APJ, suppressed the effects of apelin on TNF-α-induced reduction of glycogen synthesis in the hepatocytes, suggesting APJ is involved in the function of apelin. In conclusion, we show novel evidence suggesting that apelin ameliorates TNF-α-induced reduction of glycogen synthesis in the hepatocytes through G protein-coupled receptor APJ. Apelin appears as a beneficial adipokine with anti-insulin resistance properties, and thus as a promising therapeutic target in metabolic disorders.

Topics: Adipokines; Animals; Apelin; Apelin Receptors; Gene Expression Regulation; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Insulin Resistance; Intercellular Signaling Peptides and Proteins; Liver; Mice; Mice, Inbred C57BL; Primary Cell Culture; Receptors, G-Protein-Coupled; Signal Transduction; Tumor Necrosis Factor-alpha

Normal glucose regulation is achieved by having adequate insulin secretion and effective glucose uptake/disposal. Excess lipids in peripheral tissues - skeletal muscle, liver and adipose tissue - may attenuate insulin signaling through the protein kinase B (AKt) pathway and up-regulate protein tyrosine phosphatase 1B (PTP1B), a negative regulator of insulin signaling. We studied accumulation of lipid metabolites [triglycerides (TAGs), diglycerides (DAGs)] and ceramides in relation to insulin signaling and expression and phosphorylation of PTP1B by preincubating rat skeletal muscle cells (L6 myotubes) with three saturated and three unsaturated free fatty acids (FFAs) (200 μM). Cells were also evaluated in the presence of wortmannin, an inhibitor of phosphatidylinositol 3-kinases and thus AKt (0-100 nM). Unsaturated FFAs increased DAGs, TAGs and PTP1B expression significantly, but cells remained insulin sensitive as assessed by robust AKt and PTP1B phosphorylation at serine (Ser) 50, Ser 398 and tyrosine 152. Saturated palmitic and stearic acids increased ceramides, up-regulated PTP1B, and had AKt and PTP1B phosphorylation at Ser 50 impaired. We show a significant correlation between phosphorylation levels of AKt and of PTP1B at Ser 50 (R(2)=0.84, P<.05). The same was observed with increasing wortmannin dose (R(2)=0.73, P<.05). Only FFAs that increased ceramides caused impairment of AKt and PTP1B phosphorylation at Ser 50. PTP1B overexpression in the presence of excess lipids may not directly cause insulin resistance unless it is accompanied by decreased PTP1B phosphorylation. A clear relationship between PTP1B phosphorylation levels at Ser 50 and its negative effect on insulin signaling is shown.

Topics: Animals; Cells, Cultured; Ceramides; Diglycerides; Fatty Acids, Nonesterified; Glycogen; Insulin Resistance; Muscle Fibers, Skeletal; Muscle, Skeletal; Myoblasts; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Proto-Oncogene Proteins c-akt; Rats; Serine; Signal Transduction; Triglycerides

Plasma glucose levels are maintained within a narrow range in normal individuals. Both insulin-dependent and insulin-independent processes contribute to fasting and postprandial plasma glucose regulation. The brain and nervous system are insulin independent. Muscle and adipose tissue are responsive to insulin and can use either glucose or ketones and free fatty acids as their primary metabolic fuel. The essential components of metabolic syndrome are obesity, glucose intolerance, insulin resistance, lipid disturbances, and hypertension. The risk of type 2 diabetes increases exponentially as body mass index increases above about 25 kg/m2. The links between obesity and type 2 diabetes include proinflammatory cytokines, insulin resistance, deranged fatty acid metabolism, and cellular processes. Modest weight reduction can improve glycaemic control and reduce diabetes risk. Obesity also leads to hyperinsulinaemia and insulin resistance, with a progressive decrease in insulin secretory function. Ageing is another important risk factor for metabolic disorders, including obesity, impaired glucose tolerance, and type 2 diabetes.

Topics: Aging; Body Mass Index; Diabetes Mellitus, Type 2; Glucagon; Glucose; Glucose Intolerance; Glucose Transport Proteins, Facilitative; Glycogen; Homeostasis; Humans; Inflammation Mediators; Insulin; Insulin Resistance; Metabolic Syndrome; Obesity; Obesity, Abdominal; Sodium-Glucose Transport Proteins

The mammalian target of rapamycin is crucial in the regulation of cell growth and metabolism. Recent studies suggest that the mammalian target of rapamycin and its downstream 70-kDa ribosomal S6 kinase 1 negatively modulate the insulin-signaling pathway, which is considered the main cause of insulin resistance. The aim of this study is to investigate the effects of cardamonin, a potential inhibitor of the mammalian target of the rapamycin, on insulin-resistant vascular smooth muscle cells and the molecular mechanisms involved. Vascular smooth muscle cells were cultured with high glucose and high insulin to induce insulin resistance. The mammalian target of rapamycin was overstimulated in cells that were incubated with high glucose and high insulin, as reflected by the excessive activation of S6 kinase 1. Insulin-resistant vascular smooth muscle cells displayed hyperphosphorylation of insulin receptor substrate-1 at Ser residues 636/639, which decreased the activity of insulin receptor substrate-1. Also, the activation of protein kinase B and phosphorylation of glycogen synthesis kinase-3β were inhibited. Cardamonin increased the 2-deoxyglucose uptake and glycogen concentration, which was reduced by insulin resistance. As with rapamycin, cardamonin inhibited the activity of the mammalian target of rapamycin and S6 kinase 1, decreased the Ser 636/639 phosphorylation of insulin receptor substrate-1 and increased the activation of protein kinase B. Both of them increased the Ser9 phosphorylation of glycogen synthesis kinase-3β and decreased the expression of glycogen synthesis kinase-3β. However, neither cardamonin nor rapamycin increased the expression of glucose transport 4 which decreased in insulin-resistant vascular smooth muscle cells. This study suggests that cardamonin inhibited the activity of the mammalian target of rapamycin and eliminated the negative feedback of the mammalian target of rapamycin and S6 kinase 1 on the insulin-signaling pathway.

Topics: Animals; Blood Glucose; Cells, Cultured; Chalcones; Deoxyglucose; Glycogen; Insulin; Insulin Resistance; Mammals; Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Impaired glucose tolerance (IGT) is characterized by decreased oxidative capacity and reduced carbohydrate utilization during exercise. However, it is unclear if the presence of impaired fasting glucose (IFG) affects fuel utilization during exercise in adults with IGT. We tested the hypothesis that the presence of IFG in adults with IGT decreases reliance on carbohydrate during exercise. Middle-aged, obese, sedentary individuals (n = 6, IGT and n = 6, IFG+IGT) were compared during exercise at 60% peak O2 consumption for 45 min on a cycle ergometer. Glucose rates of appearance and disposal and muscle glycogen were assessed by stable isotope dilution methods, and fat utilization was estimated via indirect calorimetry. A 75-g oral glucose tolerance test was used to determine fasting and 2-h glucose concentrations. A glucose intolerance severity z-score was calculated from the oral glucose tolerance test. Glucose flux (i.e., rates of appearance and disposal) was not different between groups. However, individuals with IFG+IGT had lower muscle glycogen use (P < 0.05) and elevated fat oxidation (P < 0.01) during exercise compared with those with isolated IGT. Plasma nonesterified fatty acids and glucose were significantly higher during exercise in subjects with IFG+IGT vs. IGT alone (P < 0.05). Fat utilization during exercise correlated with fasting glucose (r = 0.57, P = 0.05), glucose intolerance severity z-score (r = 0.66, P = 0.01), and nonesterified fatty acids (trend; r = 0.55, P = 0.08). The presence of IFG shifts fuel selection toward increased fat oxidation and decreased muscle glycogen utilization during exercise in adults with IGT. Whether these differences in substrate use contribute to, or are the result of, movement along the continuum from prediabetes to type 2 diabetes awaits further work.

Topics: Adult; Anaerobic Threshold; Anthropometry; Blood Chemical Analysis; Blood Glucose; Calorimetry, Indirect; Exercise; Fasting; Fatty Acids, Nonesterified; Female; Glucose; Glucose Intolerance; Glucose Tolerance Test; Glycogen; Humans; Hyperglycemia; Insulin; Insulin Resistance; Lipid Metabolism; Male; Middle Aged; Oxygen Consumption

Low aerobic exercise capacity is a risk factor for diabetes and a strong predictor of mortality, yet some individuals are "exercise-resistant" and unable to improve exercise capacity through exercise training. To test the hypothesis that resistance to aerobic exercise training underlies metabolic disease risk, we used selective breeding for 15 generations to develop rat models of low and high aerobic response to training. Before exercise training, rats selected as low and high responders had similar exercise capacities. However, after 8 weeks of treadmill training, low responders failed to improve their exercise capacity, whereas high responders improved by 54%. Remarkably, low responders to aerobic training exhibited pronounced metabolic dysfunction characterized by insulin resistance and increased adiposity, demonstrating that the exercise-resistant phenotype segregates with disease risk. Low responders had impaired exercise-induced angiogenesis in muscle; however, mitochondrial capacity was intact and increased normally with exercise training, demonstrating that mitochondria are not limiting for aerobic adaptation or responsible for metabolic dysfunction in low responders. Low responders had increased stress/inflammatory signaling and altered transforming growth factor-β signaling, characterized by hyperphosphorylation of a novel exercise-regulated phosphorylation site on SMAD2. Using this powerful biological model system, we have discovered key pathways for low exercise training response that may represent novel targets for the treatment of metabolic disease.

Topics: Adaptation, Physiological; Animals; Energy Metabolism; Exercise Tolerance; Female; Glycogen; Insulin Resistance; Liver; Mitochondria; Muscle, Skeletal; Oxygen Consumption; Physical Conditioning, Animal; Physical Fitness; Rats; Signal Transduction; Triglycerides

To analyze Paraoxonase1 (PON1) impact on GLUT4 expression, glucose metabolism, and the insulin signaling pathway in skeletal muscle cells.. We analyzed the effect of PON1 in high-fat-diet-induced insulin resistance in C57BL/6J and in PON1KO mice. Mice were fed normal diet (ND) or high Fat Diet (HFD) for 8 weeks. PON1 deficiency caused enhanced insulin resistance in both ND and HFD mice. PON1 deficiency was associated with increased oxidative stress (OS), increased p38MAPK activity and attenuated insulin-mediated tyrosine phosphorylation of muscle insulin receptor substrate-1 (IRS-1), with a corresponding increase in serine phosphorylation. These effects resulted in decreased glucose uptake in whole-body level, as reflected by glucose tolerance test (GTT), by insulin tolerance test (ITT) and by cellular glycogen accumulation in the liver and in the muscles. PON1 addition to cultured C2 muscle cells enhanced GLUT4 mRNA expression, in a time and concentration dependent manner, increased GLUT4 protein and cellular glycogen accumulation. These effects were mediated via inhibition of p38MAPK activity, resulting in reduced IRS-1 serine phosphorylation and in enhanced IRS-1 tyrosine phosphorylation. The ability of PON1 to increase myocytes GLUT4 expression was partially inhibited upon blocking PON1 SH group, and completely abolished upon PON1 mutation in HIS115 of its catalytic site.. PON1 plays a beneficial role in glucose regulation and metabolism and may serve as an important tool in diabetes control.

Topics: Animals; Aryldialkylphosphatase; Diet, High-Fat; Dietary Fats; Glucose Intolerance; Glucose Transporter Type 4; Glycogen; Insulin Receptor Substrate Proteins; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscle Fibers, Skeletal; Muscle, Skeletal; Proto-Oncogene Proteins c-akt; Signal Transduction; Weight Gain

Insulin resistance represents a mechanism underlying defect metabolism of carbohydrate and lipid linked to inflammatory reactions in diabetic liver. We hypothesized that the changes may be secondary to endoplasmic reticulum (ER) stress, which could be alleviated by either argirein or valsartan.. Hepatosteatosis in diabetic liver was induced in rats fed with a high-fat diet (HFD) for 12 weeks combined with a single low dose of streptozotocin (STZ 35 mg/kg, ip). Interventions (mg/kg/d, po)with either argirein (50, 100 and 200) or valsartan (12) were conducted in the last 4 weeks.. In diabetic liver fat was significantly accumulated in association with elevated hepatic glucose, serum insulin and homeostasis model assessment of insulin resistance value. Downregulated glucose transporter 4, insulin receptor substrate-1 and leptin receptor (P < 0.01) were found relative to normal, where DNA ladder, downregulated B cell lymphoma/leukemia-2, upregulated B cell lymphoma/leukemia-2 Associated X protein and upregulated ER stress chaperones such as Bip/GRP78 (also known as Binding Protein, BiP), PKR-like ER kinase (PERK), p-PERK/PERK and C/EBP homologous protein were significant. These abnormalities were significantly ameliorated by argirein and valsartan.. Hepatosteatosis induced by HFD/low STZ manifests insulin resistance and apoptosis, linked to an entity of low-grade inflammation due to activated ER stress sensors. With anti-inflammatory activity either argirein or valsartan blunts hepatosteatosis through normalizing ER stress and apoptosis in the diabetic liver.

Topics: Animals; Anthraquinones; Anti-Inflammatory Agents; Apoptosis; Arginine; Diabetes Mellitus, Experimental; Diet, High-Fat; Drug Combinations; eIF-2 Kinase; Endoplasmic Reticulum Stress; Glucose; Glucose Transporter Type 4; Glutathione Peroxidase; Glycogen; Heat-Shock Proteins; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Liver; Male; PPAR alpha; PPAR gamma; Rats; Rats, Sprague-Dawley; Receptors, Leptin; Tetrazoles; Transcription Factor CHOP; Valine; Valsartan

The glucokinase activators improve the fasting as well as postprandial glucose control and are important investigational drugs for the treatment of diabetes. However, recent studies have implicated that continuous activation of glucokinase with a small molecule activator can increase hepatic triglycerides and the long term glucose control is not achieved. In this study, we investigated the effect of combination of glucokinase activator (GKA, Piragliatin) with GLP-1 receptor agonist exendin-4 (Ex-4) in male db/db mice. Twelve weeks combination treatment in the db/db mice resulted in a significant decrease in body weight gain, food consumption, random glucose and %HbA1c. The decrease in serum glucose and %HbA1c in combination group was more profound and significantly different than that of individual treatment (GKA or Ex-4) group. GKA treatment increased hepatic triglycerides, whereas combination of Ex-4 with GKA attenuated hepatic steatosis. The combination of GKA with Ex-4 reduced the hepatic lipid accumulation, improved the insulin sensitivity, and reduced hepatic glucose production in db/db mice. Overall, our data indicate that combination of GKA and GLP-1 receptor agonist Ex-4 improves glucose homeostasis, shows antiobesity activity, without causing harmful side effects like fatty liver.

Topics: Animals; Benzeneacetamides; Body Weight; Drug Synergism; Eating; Enzyme Activation; Exenatide; Fatty Liver; Glucokinase; Glucose; Glycogen; Homeostasis; Hyperglycemia; Hypoglycemic Agents; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Liver; Male; Mice; Mice, Inbred C57BL; Peptides; Venoms

CCR2 inhibition has produced promising experimental and clinical anti-hyperglycemic effects. These results support the thesis that insulin resistance and Type 2 diabetes (T2D) are associated with chronic unresolved inflammation. The aim of this study was to provide a broad analysis of the various physiological changes occurring in mouse models of T2D in connection with pharmacological CCR2 inhibition.. A mouse-active chemical analogue of the clinical candidate CCX140-B was tested in diet-induced obese (DIO) mice and db/db mice. Measurements included: adipose tissue inflammatory macrophage counts; peripheral blood glucose levels at steady-state and after glucose and insulin challenges; peripheral blood insulin and adiponectin levels; 24-h urine output and urinary glucose levels; pancreatic islet number and size; hepatic triglyceride and glycogen content; and hepatic glucose-6-phosphatase levels.. In DIO mice, the CCR2 antagonist completely blocked the recruitment of inflammatory macrophages to visceral adipose tissue. The mice exhibited reduced hyperglycemia and insulinemia, improved insulin sensitivity, increased circulating adiponectin levels, decreased pancreatic islet size and increased islet number. It also reduced urine output, glucose excretion, hepatic glycogen and triglyceride content and glucose 6-phosphatase levels. Similar effects were observed in the db/db diabetic mice.. These data indicate that pharmacological inhibition of CCR2 in models of T2D can reduce inflammation in adipose tissue, alter hepatic metabolism and ameliorate multiple diabetic parameters. These mechanisms may contribute to the promising anti-diabetic effects seen in humans with at least one CCR2 antagonist.

Topics: Adiponectin; Adipose Tissue; Animals; Biomarkers; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Diet, High-Fat; Dose-Response Relationship, Drug; Glucose-6-Phosphatase; Glycogen; Glycosuria; Hypoglycemic Agents; Inflammation; Insulin; Insulin Resistance; Insulin-Secreting Cells; Liver; Macrophages; Male; Mice; Mice, Inbred C57BL; Obesity; Receptors, CCR2; Triglycerides

An accumulation of ceramides has been implicated in the generation of insulin resistance in skeletal muscle upon an oversupply of fatty acid. Different ceramide species are generated through the actions of ceramide synthases (CerSs), which incorporate specific acyl side chains. We tested whether particular CerS isoforms promoted insulin resistance through the generation of more inhibitory ceramide species, thus representing potential targets for intervention.. CerS isoforms CerS1, CerS2, CerS4, CerS5 and CerS6 were overexpressed in L6 myotubes using adenovirus, and cells were treated with palmitate and stimulated with insulin. Alternatively, CerS isoforms were knocked down using siRNAs. Sphingolipids were examined by mass spectrometry and tracer incorporation. Phosphorylation of IRS1 and Akt was measured by immunoblotting, while glucose disposal was assessed by measuring GLUT4 translocation and the incorporation of [(14)C]glucose into glycogen.. Palmitate treatment increased the levels of several ceramides but reduced the levels of sphingomyelins, while insulin had no effect. The fatty acid also inhibited insulin-stimulated Akt phosphorylation and glycogen synthesis. Overexpression of CerS isoforms increased specific ceramides. Unexpectedly, the overexpression of CerS1 and CerS6 promoted insulin action, while no isoform had inhibitory effects. CerS6 knockdown had effects reciprocal to those of CerS6 overexpression.. Palmitate may increase intracellular ceramide levels through sphingomyelin hydrolysis as well as de novo synthesis, but no particular species were implicated in the generation of insulin resistance. The modulation of ceramides through an alteration of CerS expression does not affect the action of insulin in the same way as ceramide generation by palmitate treatment. Conversely, certain isoforms promote insulin action, indicating the importance of ceramides in cell function.

Topics: Ceramides; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Mass Spectrometry; Membrane Proteins; Muscle Fibers, Skeletal; Muscle, Skeletal; Oxidoreductases; Palmitates; Phosphorylation; Protein Isoforms; Sphingolipids

The dried succulent stem of Cistanche tubulosa (Schenk) R. Wight is one component of traditional Chinese medicine prescriptions for diabetes. However, there have been no modern scientific reports to confirm this traditional claim for the Cistanche species until now. Thus, we investigated the effects of Cistanche tubulosa on glucose homeostasis and serum lipids in male BKS.Cg-Dock7(m) +/+ Lepr(db)/J (db/db) mice, a model of type 2 diabetes.. The verbascoside and echinacoside contents of Cistanche tubulosa powder were evaluated using HPLC. The total phenolic content, polysaccharide content and antioxidant activity of Cistanche tubulosa powder were also evaluated. Then, different doses of Cistanche tubulosa (equivalent to 120.9, 72.6 or 24.2mg verbascoside/kg) were administered orally once daily for 45 days to male db/db mice. Age matched db/+ mice were used as normal controls. Body weight, fasting blood glucose, postprandial blood glucose and insulin tolerance test were measured during the experiment. At the time of sacrifice, blood was collected for measurement of insulin level, the homeostatic model assessment of insulin resistance (HOMA-IR), and total cholesterol, triglyceride, HDL-c, LDL-c and VLDL-c levels; liver and muscle were harvested for measurement of glycogen levels.. Cistanche tubulosa significantly suppressed the elevated fasting blood glucose and postprandial blood glucose levels, improved insulin resistance and dyslipidemia, and suppressed body weight loss in db/db mice. However, Cistanche tubulosa did not significantly affect serum insulin levels or hepatic and muscle glycogen levels.. This study provides scientific evidence for the traditional use of Cistanche tubulosa to treat diabetes, suggesting that Cistanche tubulosa has the potential for development into a functional food ingredient or drug to prevent hyperglycemia and treat hyperlipidemia.

Topics: Animals; Blood Glucose; Cistanche; Diabetes Mellitus, Type 2; Glycogen; Hypoglycemic Agents; Hypolipidemic Agents; Insulin Resistance; Lipids; Liver; Male; Mice; Mice, Mutant Strains; Muscle, Skeletal; Phytotherapy; Plant Extracts; Plant Stems

Glycogen synthesis is a major component of the insulin response, and defective glycogen synthesis is a major portion of insulin resistance. Insulin regulates glycogen synthase (GS) through incompletely defined pathways that activate the enzyme through dephosphorylation and, more potently, allosteric activation. We identify Epm2aip1 as a GS-associated protein. We show that the absence of Epm2aip1 in mice impairs allosteric activation of GS by glucose 6-phosphate, decreases hepatic glycogen synthesis, increases liver fat, causes hepatic insulin resistance, and protects against age-related obesity. Our work identifies a novel GS-associated GS activity-modulating component of insulin resistance.

Topics: Aging; Animals; Dual-Specificity Phosphatases; Glucose-6-Phosphate; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Resistance; Liver; Mice; Obesity; Phosphorylation; Protein Tyrosine Phosphatases, Non-Receptor

In the liver, insulin suppresses hepatic gluconeogenesis by activating Akt, which inactivates the key gluconeogenic transcription factor FoxO1 (Forkhead Box O1). Recent studies have implicated hyperactivity of the Akt phosphatase Protein Phosphatase 2A (PP2A) and impaired Akt signaling as a molecular defect underlying insulin resistance. We therefore hypothesized that PP2A inhibition would enhance insulin-stimulated Akt activity and decrease glucose production. PP2A inhibitors increased hepatic Akt phosphorylation and inhibited FoxO1in vitro and in vivo, and suppressed gluconeogenesis in hepatocytes. Paradoxically, PP2A inhibition exacerbated insulin resistance in vivo. This was explained by phosphorylation of both hepatic glycogen synthase (GS) (inactivation) and phosphorylase (activation) resulting in impairment of glycogen storage. Our findings underline the significance of GS and Phosphorylase as hepatic PP2A substrates and importance of glycogen metabolism in acute plasma glucose regulation.

Topics: Animals; Enzyme Activation; Forkhead Transcription Factors; Gluconeogenesis; Glycogen; Insulin Resistance; Liver; Male; Nerve Tissue Proteins; Protein Phosphatase 2; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley

This study investigated the effects of a combination of fucosylated chondroitin sulfate (CHS) and rosiglitazone (RSG) on glucose metabolism in the liver of insulin-resistant C57BL/6J mice fed a high-fat high-sucrose diet for 19 weeks. The results showed that the combination (CHS/RSG) synergistically improved body weight gain, liver weight, fasting blood glucose levels, glucose tolerance on an oral glucose tolerance test, serum insulin levels, homeostasis model assessment indexes, and hepatic glycogen content. In liver tissue, CHS/RSG significantly normalized the activities of hexokinase, pyruvate kinase, and glucose-6-phosphatase. In additionally, it increased the mRNA expression of insulin receptors, insulin receptor substrate 2, phosphatidylinositol 3 kinase (PI3K), protein kinase B (PKB), and glycogen synthase, and inhibited glycogen synthase kinase 3β(GSK-3β) mRNA expression in the liver. This suggests that CHS/RSG treatment improves glucose metabolism by modulating metabolic enzymes and strengthening the PI3K/PKB/GSK-3β signal pathway mediated by insulin at the transcriptional level.

Topics: Animals; Blood Glucose; Body Weight; Chondroitin Sulfates; Diet, High-Fat; Drug Synergism; Drug Therapy, Combination; Gene Expression Regulation; Glucose Tolerance Test; Glucose-6-Phosphatase; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Hexokinase; Hyperglycemia; Hypoglycemic Agents; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Organ Size; Phosphatidylinositol 3-Kinase; Proto-Oncogene Proteins c-akt; Pyruvate Kinase; Receptor, Insulin; Rosiglitazone; Sea Cucumbers; Signal Transduction; Thiazolidinediones

Dysfunctional zinc signaling is implicated in disease processes including cardiovascular disease, Alzheimer's disease and diabetes. Of the twenty-four mammalian zinc transporters, ZIP7 has been identified as an important mediator of the 'zinc wave' and in cellular signaling. Utilizing siRNA targeting Zip7 mRNA we have identified that Zip7 regulates glucose metabolism in skeletal muscle cells. An siRNA targeting Zip7 mRNA down regulated Zip7 mRNA 4.6-fold (p = 0.0006) when compared to a scramble control. This was concomitant with a reduction in the expression of genes involved in glucose metabolism including Agl, Dlst, Galm, Gbe1, Idh3g, Pck2, Pgam2, Pgm2, Phkb, Pygm, Tpi1, Gusb and Glut4. Glut4 protein expression was also reduced and insulin-stimulated glycogen synthesis was decreased. This was associated with a reduction in the mRNA expression of Insr, Irs1 and Irs2, and the phosphorylation of Akt. These studies provide a novel role for Zip7 in glucose metabolism in skeletal muscle and highlight the importance of this transporter in contributing to glycaemic control in this tissue.

Topics: Animals; Cation Transport Proteins; Cell Line; Gene Expression Regulation; Gene Knockdown Techniques; Glucose; Glycogen; Insulin Resistance; Mice; Muscle, Skeletal; Phosphorylation; Quadriceps Muscle; RNA, Messenger; RNA, Small Interfering

The objective of this study is to fully investigate the therapeutic effect and mechanisms of action of Gegen Qinlian decoction (GD) on type 2 diabetes mellitus (type 2 DM). A rat model of type 2 DM was established with the combination of high-fat diet and multiple low doses of streptozotocin (STZ). Biochemical indicators related to glucose metabolism disorders, insulin resistance, oxidative stress were observed. The type 2 DM rats were administrated with GD for 80 days, the above-mentioned indexes were detected. The results indicated that the hepatic glycogen synthesis level was promoted, fasting blood glucose level and fasting blood insulin level were significantly reduced, insulin sensitivity index was significantly improved; the level of superoxide dismutase (SOD) was increased and the level of malondialdehyde (MDA) was reduced; pathologic morphology of pancreas and kidney was ameliorated in the GD group. It was indicated that the therapeutic mechanisms of action of GD on type 2 DM might be related to its effect of ameliorating glucose metabolism disorders, relieving insulin resistance, increasing the tissues' sensitivity to insulin, improving the antioxidative ability of living system, GD has therapeutic effect on type 2 DM and protective effects against damaged pancreatic function.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Type 2; Drugs, Chinese Herbal; Female; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Kidney; Liver; Male; Malondialdehyde; Pancreas; Phytotherapy; Plants, Medicinal; Random Allocation; Rats; Rats, Sprague-Dawley; Streptozocin; Superoxide Dismutase

Air pollution is a global challenge to public health. Epidemiological studies have linked exposure to ambient particulate matter with aerodynamic diameters<2.5 μm (PM(2.5)) to the development of metabolic diseases. In this study, we investigated the effect of PM(2.5) exposure on liver pathogenesis and the mechanism by which ambient PM(2.5) modulates hepatic pathways and glucose homeostasis.. Using "Ohio's Air Pollution Exposure System for the Interrogation of Systemic Effects (OASIS)-1", we performed whole-body exposure of mice to concentrated ambient PM(2.5) for 3 or 10 weeks. Histological analyses, metabolic studies, as well as gene expression and molecular signal transduction analyses were performed to determine the effects and mechanisms by which PM(2.5) exposure promotes liver pathogenesis.. Mice exposed to PM(2.5) for 10 weeks developed a non-alcoholic steatohepatitis (NASH)-like phenotype, characterized by hepatic steatosis, inflammation, and fibrosis. After PM(2.5) exposure, mice displayed impaired hepatic glycogen storage, glucose intolerance, and insulin resistance. Further investigation revealed that exposure to PM(2.5) led to activation of inflammatory response pathways mediated through c-Jun N-terminal kinase (JNK), nuclear factor kappa B (NF-κB), and Toll-like receptor 4 (TLR4), but suppression of the insulin receptor substrate 1 (IRS1)-mediated signaling. Moreover, PM(2.5) exposure repressed expression of the peroxisome proliferator-activated receptor (PPAR)γ and PPARα in the liver.. Our study suggests that PM(2.5) exposure represents a significant "hit" that triggers a NASH-like phenotype and impairs hepatic glucose metabolism. The information from this work has important implications in our understanding of air pollution-associated metabolic disorders.

Topics: Animals; Disease Models, Animal; Fatty Liver; Glucose; Glucose Intolerance; Glycogen; Hepatitis; Homeostasis; Inhalation Exposure; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; JNK Mitogen-Activated Protein Kinases; Liver; Liver Cirrhosis; Male; Mice; Mice, Inbred C57BL; NF-kappa B; Non-alcoholic Fatty Liver Disease; Particulate Matter; Phenotype; PPAR alpha; PPAR gamma; Signal Transduction; Toll-Like Receptor 4

Recent ecological evidence has showed a lag-correlation between the prevalence of diabetes and consumption of niacin (nicotinamide and nicotinic acid) in the US. Nicotinamide has been demonstrated to induce insulin resistance due to excess reactive oxygen species and methyl depletion, whereas the effect of nicotinic acid is poorly understood.. To examine the mechanism of the effect of nicotinic acid on glucose metabolism.. Rats were injected with different cumulative doses of nicotinic acid (0.5, 2, 4 g/kg) and nicotinamide (2 g/kg). A glucose tolerance test was given 2 h after the final injection. The role of methyl consumption and reactive oxygen species generation were evaluated by measuring N(1)-methylnicotinamide and hydrogen peroxide.. Cumulative doses of nicotinic acid produced a dose-dependent increase in the plasma levels of N(1)-methylnicotinamide and hydrogen peroxide, which was associated with a decrease in liver and skeletal muscle glycogen levels. At the same dosage (2 g/kg), in comparison with nicotinamide, nicotinic acid was weaker in raising plasma N(1)-methylnicotinamide levels (0.7 ± 0.11 µg/mL vs. 4.69 ± 0.24 µg/mL, P < 0.001), but stronger in increasing plasma hydrogen peroxide levels (1.88 ± 0.07 µmol/L vs. 1.55 ± 0.05 µmol/L, P < 0.001). Moreover, nicotinamide, unlike nicotinic acid, did not reduce liver glycogen levels.. This study suggested that excessive nicotinic acid, like nicotinamide, might induce methyl consumption, oxidative stress and insulin resistance. Long-term consumption high niacin may increase the risk of type 2 diabetes.

Topics: Animals; Dose-Response Relationship, Drug; Glucose; Glucose Tolerance Test; Glycogen; Hydrogen Peroxide; Insulin Resistance; Liver; Male; Muscle, Skeletal; Niacin; Niacinamide; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species

Muscle contractile activity functions as a potent stimulus for acute interleukin (IL)-6 expression in working skeletal muscles. Recently, we established an "in vitro contraction model" using highly-developed contractile C2C12 myotubes by applying electric pulse stimulation (EPS). Herein, we characterize the effects of EPS-evoked contraction on IL-6 expression in contractile C2C12 myotubes. Both secretion and mRNA expression of IL-6 were significantly up-regulated by EPS in a frequency-dependent manner in contracting myotubes during a 24-h period, and the response was blunted by cyclosporine A, a calcineurin inhibitor. Longer time (~12h) was required for the induction of IL-6 after the initiation of EPS as compared to that of other contraction-inducible CXC chemokines such as CXCL1/KC, which were induced in less than 3 hours. Furthermore, these acute inducible CXC chemokines exhibited no autocrine effect on IL-6 expression. Importantly, contraction-dependent IL-6 up-regulation was markedly suppressed in the presence of high levels of glucose along with increased glycogen accumulations. Experimental manipulation of intracellular glycogen contents by modulating available glucose or pyruvate during a certain EPS period further established the suppressive effect of glycogen accumulations on contraction-induced IL-6 up-regulation, which appeared to be independent of calcineurin activity. We also document that EPS-evoked contractile activity improved insulin-responsiveness in terms of intracellular glycogen accumulations. Taken together, these data provide important insights into the regulation of IL-6 expression in response to contractile activity of muscle cells, which is difficult to examine using in vivo experimental techniques. Our present results thus expand the usefulness of our "in vitro contraction model".

Topics: Animals; Calcineurin; Calcineurin Inhibitors; Calcium Signaling; Cell Line; Chemokines, CXC; Electric Stimulation; Glucose; Glycogen; Hyperglycemia; Hypoglycemic Agents; Immunosuppressive Agents; Insulin; Insulin Resistance; Interleukin-6; Kinetics; Mice; Muscle Contraction; Muscle Fibers, Skeletal; RNA, Messenger; Up-Regulation

Interleukin-6 (IL-6) has a dual role in modulating insulin sensitivity, with evidence for this cytokine as both an enhancer and inhibitor of insulin action. We determined the effect of IL-6 exposure on glucose and lipid metabolism in cultured myotubes established from people with normal glucose tolerance or type 2 diabetes. Acute IL-6 exposure increased glycogen synthesis, glucose uptake, and signal transducer and activator of transcription 3 (STAT3) phosphorylation in cultured myotubes from normal glucose tolerant subjects. However, in type 2 diabetic patients, IL-6 was without effect on glucose metabolism and STAT3 signaling, concomitant with increased suppressor of cytokine signaling 3 (SOCS3) expression. IL-6 increased fatty acid oxidation in myotubes from type 2 diabetic and normal glucose tolerant subjects. Expression of IL-6, IL-6 receptor (IL-6R), or glycoprotein 130, as well as IL-6 secretion, was unaltered between cultured myotubes from normal glucose tolerant or type 2 diabetic subjects. Circulating serum IL-6 concentration was unaltered between normal glucose tolerant and type 2 diabetic subjects. In summary, skeletal muscle cells from type 2 diabetic patients display selective IL-6 resistance for glucose rather than lipid metabolism. In conclusion, IL-6 appears to play a differential role in regulating metabolism in type 2 diabetic patients compared with normal glucose tolerant subjects.

Topics: Animals; Cells, Cultured; Diabetes Mellitus, Type 2; Fatty Acids; Female; Glucose; Glycogen; Glycoproteins; Humans; Insulin Resistance; Interleukin-6; Male; Mice; Mice, Inbred C57BL; Middle Aged; Muscle Fibers, Skeletal; Muscle, Skeletal; Phosphorylation; Receptors, Interleukin-6; STAT3 Transcription Factor; Suppressor of Cytokine Signaling 3 Protein; Suppressor of Cytokine Signaling Proteins

Lower quantity and quality of high density lipoprotein (HDL) are important characteristics of type 2 diabetes mellitus. Acute HDL infusion results in a greater fall of plasma glucose in diabetes patients. Here, we aim to investigate the influence of long-term HDL infusion on metabolic phenotypes of diabetic db/db mice.. High density lipoprotein was introduced to db/db mice twice a week for 4 weeks. The phenotypes of the mice were monitored by analyzing metabolic parameters. Glycogen analysis was performed with amyloglucosidase. The corresponding signaling molecules were detected by western blot.. Long-term introduction of HDL decreased plasma glucose levels of db/db mice. Glycogen deposition was enhanced in gastrocnemius muscle, paralleling the elevated glycogen synthase kinase-3 phosphorylation. Meanwhile, increased Akt-Ser473 and adenosine monophosphate-activated protein kinase phosphorylations were detected in the muscle. Moreover, HDL reduced blood glucose and free fatty acids and improved pancreatic islet structure and function with increased C-peptide. Furthermore, decreased interleukin-6, C-reactive protein, monocyte chemoattractant protein-1, resistin, and malondialdehyde, as well as enhanced leptin levels were detected in HDL-treated mice.. Results of the present study suggest that long-term HDL infusion has positive therapeutic effects on the metabolic disturbances of db/db diabetic mice.

Topics: Adipose Tissue; Animals; Blood Glucose; Diabetes Mellitus, Type 2; Glycogen; Insulin Resistance; Islets of Langerhans; Lipid Metabolism; Lipid Peroxidation; Lipoproteins, HDL; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Phenotype

We determined whether: (1) an acute lipid infusion impairs skeletal muscle AMP-activated protein kinase (AMPK)α2 activity, increases inducible nitric oxide synthase (iNOS) and causes peripheral insulin resistance in conscious, unstressed, lean mice; and (2) restoration of AMPKα2 activity during the lipid infusion attenuates the increase in iNOS and reverses the defect in insulin sensitivity in vivo.. Chow-fed, 18-week-old C57BL/6J male mice were surgically catheterised. After 5 days they received: (1) a 5 h infusion of 5 ml kg(-1) h(-1) Intralipid + 6 U/h heparin (Lipid treatment) or saline (Control); (2) Lipid treatment or Control, followed by a 2 h hyperinsulinaemic-euglycaemic clamp (insulin clamp; 4 mU kg(-1) min(-1)); and (3) infusion of the AMPK activator, 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR) (1 mg kg(-1) min(-1)), or saline during Lipid treatment, followed by a 2 h insulin clamp. In a separate protocol, mice producing a muscle-specific kinase-dead AMPKα2 subunit (α2-KD) underwent an insulin clamp to determine the role of AMPKα2 in insulin-mediated muscle glucose metabolism.. Lipid treatment decreased AMPKα2 activity, increased iNOS abundance/activation and reduced whole-body insulin sensitivity in vivo. AICAR increased AMPKα2 activity twofold; this did not suppress iNOS or improve whole-body or tissue-specific rates of glucose uptake during Lipid treatment. AICAR caused a marked increase in insulin-mediated glycogen synthesis in skeletal muscle. Consistent with this latter result, lean α2-KD mice exhibited impaired insulin-stimulated glycogen synthesis even though muscle glucose uptake was not affected.. Acute induction of insulin resistance via lipid infusion in healthy mice impairs AMPKα2, increases iNOS and causes insulin resistance in vivo. However, these changes do not appear to be interrelated. Rather, a functionally active AMPKα2 subunit is required for insulin-stimulated muscle glycogen synthesis.

Topics: AMP-Activated Protein Kinases; Animals; Glucose; Glycogen; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Nitric Oxide Synthase Type II

Phycocyanin (PC) has been proven to have many therapeutic properties, but its effects on diabetes have not been investigated.. Antidiabetic activity of PC isolated from Spirulina platensis was evaluated in this study.. Oral administration of PC (100 mg/kg, once per day for 3 weeks) on KKAy mice were investigated by monitoring the changes in body weight, food intake, fasting plasma glucose level, 24 h random blood glucose levels, oral glucose tolerance tests (OGTTs), glycosylated serum protein (GSP), fasting serum insulin (FINS), glycogen, triglyceride (TG), total cholesterol (TC), total antioxidative capability (T-AOC) and malondialdehyde (MDA). Histopathological changes in the pancreas were also examined with hematoxylin-eosin staining.. Administration of PC significantly decreased the body weight, fasting plasma glucose, 24 h random blood glucose levels, FINS and GSP levels, TG and TC content in serum and livers, MDA content in livers (p < 0.05 or p < 0.01). On the other hand, glucose tolerance to glucose administration, T-AOC, and the content of glycogen in liver and muscle were enhanced following PC treatment (p < 0.05 or p < 0.01). Histopathological results showed that PC administration suppressed the abnormal enlargement of islets observed in the pancreas of KKAy mice.. The antidiabetic effect of PC on KKAy mice is most likely due to its ability to enhance insulin sensitivity, amelioration of insulin resistance of peripheral target tissues and regulation of glucolipide metabolism. Therefore, PC may have a potential clinical utility in combating type-2 diabetes.

Topics: Administration, Oral; Animals; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Female; Glucose Tolerance Test; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Islets of Langerhans; Liver; Mice; Phycocyanin; Spirulina

FL83B mouse hepatocytes were treated with tumor necrosis factor-α (TNF-α) to induce insulin resistance to investigate the effect of a wax apple aqueous extract (WAE) in insulin-resistant mouse hepatocytes. The uptake of 2-[N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)amino]-2-deoxyglucose (2 NBDG), a fluorescent D-glucose derivative, was performed, and the metabolism of carbohydrates was evaluated by examining the expression of glycogenesis or glycolysis-related proteins in insulin-resistant hepatocytes. The results show that WAE significantly improves the uptake of glucose and enhances glycogen content in insulin-resistant FL83B mouse hepatocytes. The results from Western blot analysis also reveal that WAE increases the expression of glycogen synthase (GS), hexokinase (HXK), glucose-6-phosphate dehydrogenase (G6PD), phosphofructokinase (PFK) and aldolase in TNF-α treated cells, indicating that WAE may ameliorate glucose metabolism by promoting glycogen synthesis and the glycolysis pathways in insulin-resistant FL83B mouse hepatocytes.

Topics: Animals; Cell Line; Fruit; Glycogen; Glycogen Synthase; Glycolysis; Hepatocytes; Insulin Resistance; Mice; Plant Extracts; Syzygium; Tumor Necrosis Factor-alpha

Diabetes mellitus is one of the three most common modem diseases. A number of animal models is used in investigations of the mechanisms of development of the disease. Most of these models replicate the symptoms of type 1 diabetes mellitus. The development of type 2 diabetes is caused by the insulin resistance, hyperglycemia, structural and functional disorders of the pancreatic cells. Investigation of pathogenesis of type 2 diabetes is complicated by the lack of adequate models of this disease. In this work, based on existing hyperglycemia model, we propose the model of metabolic syndrome as a precursor of type 2 diabetes. The development of metabolic syndrome symptoms was caused by 28 days long intramuscular injection of protamine sulfate to guinea pigs at a dose of 15 mg/kg along with keeping of animals on a high glucose diet. Increased blood glucose and cholesterol levels, reduction of glycogen in liver, the structural and functional damage and reduce in the number of functionally active beta-cells in the pancreas of the experimental animals were observed. The results confirm the development of the metabolic syndrome symptoms in experimental animals, which makes it possible to use such methodical approach in creation of promising type 2 diabetes model.

Topics: Animals; Diabetes Mellitus, Type 2; Diet; Disease Models, Animal; Glucose; Glycogen; Guinea Pigs; Hyperglycemia; Injections, Intramuscular; Insulin Resistance; Insulin-Secreting Cells; Liver; Male; Metabolic Syndrome; Protamines

Recent experiments in liver and adipocyte cell lines indicate that palmitate can induce endoplasmic reticulum (ER) stress. Since it has been shown that ER stress can interfere with insulin signalling, our hypothesis was that the deleterious action of palmitate on the insulin signalling pathway in muscle cells could also involve ER stress.. We used C2C12 and human myotubes that were treated either with palmitate or tunicamycin. Total lysates and RNA were prepared for western blotting or quantitative RT-PCR respectively. Glycogen synthesis was assessed by [¹⁴C]glucose incorporation.. Incubation of myotubes with palmitate or tunicamycin inhibited insulin-stimulated protein kinase B (PKB)/ v-akt murine thymoma viral oncogene homologue 1 (Akt). In parallel, an increase in ER stress markers was observed. Pre-incubation with chemical chaperones that reduce ER stress only prevented tunicamycin but not palmitate-induced insulin resistance. We hypothesised that ER stress activation levels induced by palmitate may not be high enough to induce insulin resistance, in contrast with tunicamycin-induced ER stress. Indeed, tunicamycin induced a robust activation of the inositol-requiring enzyme 1 (IRE-1)/c-JUN NH₂-terminal kinase (JNK) pathway, leading to serine phosphorylation of insulin receptor substrate 1 (IRS-1) and a decrease in IRS-1 tyrosine phosphorylation. In contrast, palmitate only induced a very weak activation of the IRE1/JNK pathway, with no IRS1 serine phosphorylation.. These data show that insulin resistance induced by palmitate is not related to ER stress in muscle cells.

Topics: Animals; Biomarkers; Cell Line; Cells, Cultured; Endoplasmic Reticulum Stress; Endoribonucleases; Glycogen; Glycosylation; Humans; Insulin Resistance; Mice; Muscle Cells; Muscle Fibers, Skeletal; Myoblasts; Palmitic Acid; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Signal Transduction; Tunicamycin

Upon exposure, TiO(2) nanoparticles (NPs) have been recovered in internal organs such as the liver, and are proposed to cause cellular/organ dysfunction, particularly in the liver and lungs. We hypothesized that despite being considered "inert" as bulk material, TiO(2) NPs may impair insulin responses in liver-derived cells, either indirectly by inflammatory activation of macrophages, and/or by directly interfering with insulin signaling. Using qRT-PCR and conditioned medium (CM) approaches, we show that exposure to TiO(2) NPs activates macrophages' expression of TNF-α, IL-6, IL-8, IL-1α and IL-1β and the resulting CM induces insulin resistance in Fao cells. Furthermore, direct exposure of Fao cells to TiO(2) results in activation of the stress kinases JNK and p38MAP kinase, and in induction of insulin resistance at the signaling and metabolic levels. Collectively, our findings provide a proof-of-concept for the ability of man-made NPs to induce insulin resistance in liver-derived cells, an endocrine abnormality underlying some of the most common human diseases.

Topics: Animals; Blotting, Western; Cell Line, Tumor; Culture Media, Conditioned; Glycogen; Insulin; Insulin Resistance; Liver; Macrophage Activation; Metal Nanoparticles; Rats; Real-Time Polymerase Chain Reaction; Signal Transduction; Titanium

The tissue-specific role of mitochondrial respiratory capacity in the development of insulin resistance and type 2 diabetes is unclear. We determined mitochondrial function in glycolytic and oxidative skeletal muscle and liver from lean (+/?) and obese diabetic (db/db) mice. In lean mice, the mitochondrial respiration pattern differed between tissues. Tissue-specific mitochondrial profiles were then compared between lean and db/db mice. In liver, mitochondrial respiratory capacity and protein expression, including peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), was decreased in db/db mice, consistent with increased mitochondrial fission. In glycolytic muscle, mitochondrial respiration, as well as protein and mRNA expression of mitochondrial markers, was increased in db/db mice, suggesting increased mitochondrial content and fatty acid oxidation capacity. In oxidative muscle, mitochondrial complex I function and PGC-1α and mitochondrial transcription factor A (TFAM) protein levels were decreased in db/db mice, along with increased level of proteins related to mitochondrial dynamics. In conclusion, mitochondrial respiratory performance is under the control of tissue-specific mechanisms and is not uniformly altered in response to obesity. Furthermore, insulin resistance in glycolytic skeletal muscle can be maintained by a mechanism independent of mitochondrial dysfunction. Conversely, insulin resistance in liver and oxidative skeletal muscle from db/db mice is coincident with mitochondrial dysfunction.

Topics: Animal Nutritional Physiological Phenomena; Animals; Blood Glucose; Blotting, Western; Cell Lineage; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; DNA-Binding Proteins; Glycogen; Glycolysis; High Mobility Group Proteins; Insulin Resistance; Mice; Mice, Inbred C57BL; Mice, Inbred NOD; Mice, Obese; Mitochondria; Mitochondria, Liver; Mitochondria, Muscle; Obesity; Oxygen Consumption; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Real-Time Polymerase Chain Reaction; Trans-Activators; Transcription Factors; Triglycerides

Insulin resistance and obesity are components of the metabolic syndrome that includes development of cardiovascular disease and diabetes with advancing age. The thrifty phenotype hypothesis suggests that offspring of poorly nourished mothers are predisposed to the various components of the metabolic syndrome due to adaptations made during fetal development. We assessed the effects of maternal nutrient restriction in early gestation on feeding behavior, insulin and glucose dynamics, body composition, and liver function in aged female offspring of ewes fed either a nutrient-restricted [NR 50% National Research Council (NRC) recommendations] or control (C: 100% NRC) diet from 28 to 78 days of gestation, after which both groups were fed at 100% of NRC from day 79 to lambing and through lactation. Female lambs born to NR and C dams were reared as a single group from weaning, and thereafter, they were fed 100% NRC recommendations until assigned to this study at 6 yr of age. These female offspring were evaluated by a frequently sampled intravenous glucose tolerance test, followed by dual-energy X-ray absorptiometry for body composition analysis prior to and after ad libitum feeding of a highly palatable pelleted diet for 11 wk with automated monitoring of feed intake (GrowSafe Systems). Aged female offspring born to NR ewes demonstrated greater and more rapid feed intake, greater body weight gain, and efficiency of gain, lower insulin sensitivity, higher insulin secretion, and greater hepatic lipid and glycogen content than offspring from C ewes. These data confirm an increased metabolic "thriftiness" of offspring born to NR mothers, which continues into advanced age, possibly predisposing these offspring to metabolic disease.

Topics: Aging; Animals; Body Composition; Eating; Female; Glucose; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Insulin Secretion; Lipids; Liver; Malnutrition; Maternal Nutritional Physiological Phenomena; Obesity; Sheep

To elucidate the molecular mechanisms behind physical inactivity-induced insulin resistance in skeletal muscle, 12 young, healthy male subjects completed 7 days of bed rest with vastus lateralis muscle biopsies obtained before and after. In six of the subjects, muscle biopsies were taken from both legs before and after a 3-h hyperinsulinemic euglycemic clamp performed 3 h after a 45-min, one-legged exercise. Blood samples were obtained from one femoral artery and both femoral veins before and during the clamp. Glucose infusion rate and leg glucose extraction during the clamp were lower after than before bed rest. This bed rest-induced insulin resistance occurred together with reduced muscle GLUT4, hexokinase II, protein kinase B/Akt1, and Akt2 protein level, and a tendency for reduced 3-hydroxyacyl-CoA dehydrogenase activity. The ability of insulin to phosphorylate Akt and activate glycogen synthase (GS) was reduced with normal GS site 3 but abnormal GS site 2+2a phosphorylation after bed rest. Exercise enhanced insulin-stimulated leg glucose extraction both before and after bed rest, which was accompanied by higher GS activity in the prior-exercised leg than the rested leg. The present findings demonstrate that physical inactivity-induced insulin resistance in muscle is associated with lower content/activity of key proteins in glucose transport/phosphorylation and storage.

Topics: Bed Rest; Benzodiazepinones; Blood Glucose; Gene Expression Regulation; Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase; GTPase-Activating Proteins; Humans; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Palmitates; Phosphorylation; Proto-Oncogene Proteins c-akt

The effect of dietary feeding of hydroxyethyl methylcellulose (HEMC) and hydroxypropyl methylcellulose (HPMC) on the glucose metabolism and antioxidative status in mice under high fat diet conditions was investigated. The mice were randomly divided and given experimental diets for six weeks: normal control (NC group), high fat (HF group), and high fat supplemented with either HEMC (HF+HEMC group) or HPMC (HF+HPMC group). At the end of the experimental period, the HF group exhibited markedly higher blood glucose and insulin levels as well as a higher erythrocyte lipid peroxidation rate relative to the control group. However, diet supplementation of HEMC and HPMC was found to counteract the high fat-induced hyperglycemia and oxidative stress via regulation of antioxidant and hepatic glucose-regulating enzyme activities. These findings illustrate that HEMC and HPMC were similarly effective in improving the glucose metabolism and antioxidant defense system in high fat-fed mice and they may be beneficial as functional biomaterials in the development of therapeutic agents against high fat dietinduced hyperglycemia and oxidative stress.

Topics: Animals; Antioxidants; Blood Glucose; Diet, High-Fat; Dietary Supplements; Glucose; Glycogen; Hypoglycemic Agents; Hypromellose Derivatives; Insulin; Insulin Resistance; Lipid Metabolism; Lipid Peroxidation; Liver; Male; Methylcellulose; Mice; Mice, Inbred C57BL; Oxidative Stress; Weight Gain

Chronic intake of high-carbohydrate or high-lipid diets is a well-known insulin resistance inducer. This study investigates the immediate effect (1-6 h) of a carbohydrate- or lipid-enriched meal on insulin sensitivity. Fasted rats were refed with standard, carbohydrate-enriched (C), or lipid-enriched (L) meal. Plasma insulin, glucose, and non-esterified fatty acids (NEFA) were measured at 1, 2, 4, and 6 h of refeeding. The glucose-insulin index showed that either carbohydrates or lipids decreased insulin sensitivity at 2 h of refeeding. At this time point, insulin tolerance tests (ITTs) and glucose tolerance tests (GTTs) detected insulin resistance in C rats, while GTT confirmed it in L rats. Reduced glycogen and phosphorylated AKT and GSK3 content revealed hepatic insulin resistance in C rats. Reduced glucose uptake in skeletal muscle subjected to the fatty acid concentration that mimics the high NEFA level of L rats suggests insulin resistance in these animals is mainly in muscle. In conclusion, carbohydrate- or lipid-enriched meals acutely disrupt glycemic homeostasis, inducing a transient insulin resistance, which seems to involve liver and skeletal muscle, respectively. Thus, the insulin resistance observed when those types of diets are chronically consumed may be an evolution of repeated episodes of this transient insulin resistance.

Topics: Animals; Blood Glucose; Deoxyglucose; Diet, High-Fat; Dietary Carbohydrates; Dietary Fats; DNA-Binding Proteins; Fasting; Fatty Acids, Nonesterified; Glucose Tolerance Test; Glycemic Index; Glycogen; Glycogen Synthase Kinase 3; Homeostasis; Insulin; Insulin Resistance; Liver; Male; Muscle, Skeletal; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; Transcription Factors

Insulin stimulates glycogen synthase (GS) through dephosphorylation of serine residues, and this effect is impaired in skeletal muscle from insulin-resistant [obese and type 2 diabetic (T2DM)] subjects. Exercise also increases GS activity, yet it is not known whether the ability of exercise to affect GS is impaired in insulin-resistant subjects. The objective of this study was to examine the effect of acute exercise on GS phosphorylation and enzyme kinetic properties in muscle from insulin-resistant individuals. Lean normal glucose-tolerant (NGT), obese NGT, and obese T2DM subjects performed 40 min of moderate-intensity cycle exercise (70% of Vo(2max)). GS kinetic properties and phosphorylation were measured in vastus lateralis muscle before exercise, immediately after exercise, and 3.5 h postexercise. In lean subjects, GS fractional activity increased twofold after 40 min of exercise, and it remained elevated after the 3.5-h rest period. Importantly, exercise also decreased GS K(m) for UDP-glucose from ≈0.5 to ≈0.2 mM. In lean subjects, exercise caused significant dephosphorylation of GS by 50-70% (Ser(641), Ser(645), and Ser(645,649,653,657)), and phosphorylation of these sites remained decreased after 3.5 h; Ser⁷ phosphorylation was not regulated by exercise. In obese NGT and T2DM subjects, exercise increased GS fractional activity, decreased K(m) for UDP-glucose, and decreased GS phosphorylation as effectively as in lean NGT subjects. We conclude that the molecular regulatory process by which exercise promotes glycogen synthesis in muscle is preserved in insulin-resistant subjects.

Topics: Adult; Bicycling; Biopsy; Body Mass Index; Diabetes Mellitus, Type 2; Female; Glycogen; Glycogen Synthase; Humans; Insulin Resistance; Kinetics; Male; Middle Aged; Motor Activity; Obesity; Oxygen Consumption; Phosphorylation; Protein Processing, Post-Translational; Quadriceps Muscle; Uridine Diphosphate Glucose

Diabetes mellitus (DM) often leads to disability from vascular complications and neurological complications. Tinospora crispa has been widely used in Asia and Africa as a remedy for diabetes and other diseases. In this study, we investigated the hypoglycemic actions of borapetoside C isolated from T. crispa, and the mechanisms underlying its actions. Acute treatment with borapetoside C (5mg/kg, i.p.) attenuated the elevated plasma glucose induced by oral glucose in normal and type 2 DM (T2DM) mice. Compared to the effect of injected insulin (0.5 IU/kg), borapetoside C caused a more prominent increase of glycogen content in skeletal muscle of T2DM mice, but a less increase in type 1 DM (T1DM) mice. Combined treatment of a low dose borapetoside C (0.1mg/kg, i.p.) plus insulin enhanced insulin-induced lowering of the plasma glucose level and insulin-induced increase of muscle glycogen content. Continuous treatment with 5mg/kg borapetoside C (twice daily) for 7 days increased phosphorylation of insulin receptor (IR) and protein kinase B (Akt) as well as the expression of glucose transporter-2 (GLUT2) in T1DM mice. Combined treatment of a low dose borapetoside C (0.1mg/kg, twice daily) plus insulin for 7 days enhanced insulin-induced IR and Akt phosphorylation and GLUT2 expression in the liver of T1DM mice. This study proved that borapetoside C can increase glucose utilization, delayed the development of insulin resistance and enhanced insulin sensitivity. The activation of IR-Akt-GLUT2 expression and the enhancement of insulin sensitivity may contribute to the hypoglycemic action of borapetoside C in diabetic mice.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Type 2; Diterpenes; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Drug Therapy, Combination; Glucose Tolerance Test; Glucose Transporter Type 2; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred ICR; Muscle, Skeletal; Phosphorylation; Plants, Medicinal; Proto-Oncogene Proteins c-akt; Receptor, Insulin; Signal Transduction; Tinospora

Exendin-4 is a stable peptide agonist of GLP-1 receptor that exhibits insulinotropic actions. Some in vivo studies indicated insulin-independent glucoregulatory actions of exendin-4. That finding prompted us to evaluate effects of exendin-4 on liver glucose metabolism. Acute and chronic treatment of exendin-4 resulted in increased hepatic glucokinase activity in db/db mice but not in lean C57 mice. The stimulatory effect of exendin-4 on glucokinase activity was abrogated by exendin 9-39, a GLP-1 antagonist. Exposure of hepatocytes isolated from db/db mice to exendin-4 elicited a rapid increase in cAMP, which was synergized by IBMX, an inhibitor of cAMP degradation. The GLP-1 antagonist, exendin 9-39, has abolished the cAMP generating effects of exendin-4 as well. Furthermore, chronic treatment of exendin-4 in streptozotocin-treated C57 mice resulted in restoration of hepatic glycogen, an indicator of improved glucose metabolism, without apparent changes in serum insulin levels. In conclusion, exendin-4 increased glucokinase enzyme protein and activity in liver via a mechanism parallel to and independent of insulin. Exendin-4-induced increase in hepatic glucokinase activity is more pronounced in the presence of hepatic insulin resistance. This beneficial effect of exendin-4 on liver glucokinase activity may be mediated by GLP-1 receptor.

Topics: Animals; Cyclic AMP; Diabetes Mellitus, Experimental; Exenatide; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucokinase; Glucose; Glycogen; Hepatocytes; Hyperglycemia; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Obese; Peptides; Receptors, Glucagon; Venoms

Hepatitis C virus (HCV) infection may cause liver diseases of various severities ranging from primary acute infection to life-threatening diseases, such as cirrhosis or hepatocellular carcinoma with poor prognosis. According to clinical findings, HCV infection may also lead to some extra-hepatic symptoms, including type 2 diabetes mellitus (DM). Since insulin resistance is the major etiology for type 2 DM and numerous evidences showed that HCV infection associated with insulin resistance, the involvement of E2 in the pathogenesis of type 2 DM and underlying mechanisms were investigated in this study.. Reverse transcription and real-time PCR, Western blot assay, Immunoprecipitation, Glucose uptake assay and analysis of cellular glycogen content.. Results showed that E2 influenced on protein levels of insulin receptor substrate-1 (IRS-1) and impaired insulin-induced Ser308 phosphorylation of Akt/PKB and Ser9 phosphorylation of GSK3β in Huh7 cells, leading to an inhibition of glucose uptake and glycogen synthesis, respectively, and eventually insulin resistance.. Therefore, HCV E2 protein indeed involved in the pathogenesis of type 2 DM by inducing insulin resistance.

Topics: Cell Line; Diabetes Mellitus, Type 2; Glucose; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Hepacivirus; Hepatocytes; Humans; Insulin Receptor Substrate Proteins; Insulin Resistance; Phosphorylation; Proto-Oncogene Proteins c-akt; Serine; Signal Transduction; Transfection; Viral Envelope Proteins

Aging is closely associated with muscle insulin resistance, hyperlipidemia, nonalcoholic fatty liver disease (NAFLD), and type 2 diabetes. We examined the hypothesis that muscle insulin resistance in healthy aging promotes increased hepatic de novo lipogenesis (DNL) and hyperlipidemia by altering the distribution pattern of postprandial energy storage. Healthy, normal weight, sedentary elderly subjects pair-matched to young subjects were given two high-carbohydrate meals followed by ¹³C/¹H magnetic resonance spectroscopy measurements of postprandial changes in muscle and liver glycogen and lipid content, and assessment of DNL using ²H₂O. Net muscle glycogen synthesis was reduced by 45% (P < 0.007) in the elderly subjects compared with the young, reflecting severe muscle insulin resistance. Net liver glycogen synthesis was similar between groups (elderly, 143 ± 23 mmol/L vs. young, 138 ± 13 mmol/L; P = NS). Hepatic DNL was more than twofold higher in the elderly than in the young subjects (elderly, 14.5 ± 1.4% vs. young, 6.9 ± 0.7%; P = 0.00015) and was associated with approximately threefold higher postprandial hepatic triglyceride (TG) content (P < 0.005) and increased fasting plasma TGs (elderly, 1.19 ± 0.18 mmol/L vs. young, 0.74 ± 0.11 mmol/L; P = 0.02). These results strongly support the hypothesis that muscle insulin resistance in aging promotes hyperlipidemia and NAFLD by altering the pattern of postprandial carbohydrate storage away from muscle glycogen and into hepatic DNL.

Topics: Adult; Aged; Aging; Dietary Carbohydrates; Fatty Liver; Female; Glycogen; Humans; Hyperlipidemias; Insulin Resistance; Lipogenesis; Liver; Male; Metabolic Syndrome; Muscle, Skeletal; Non-alcoholic Fatty Liver Disease; Postprandial Period; Triglycerides; Young Adult

A tracer technique referred to as "pancreatic-blood glucose clamp" allows assessment in response to a change in blood glucose, insulin, and/or glucagon of whole body glucose disposal, endogenous glucose production, specific tissue/organ glucose uptake and storage, and insulin secretion. This technique is currently considered the optimal method for measurement of insulin sensitivity and glucose effectiveness. We describe here, for use in conscious-unrestrained mice and rats, the pancreatic-blood glucose clamp technique and its associated methods; which include catheterization of blood vessels; a clamp of plasma insulin, glucagon, and glucose; analyses of metabolites and tracers; and calculations.

Topics: Animals; Blood Glucose; Catheterization; Catheters, Indwelling; Equipment Design; Glucagon; Glucose; Glucose Clamp Technique; Glycogen; Homeostasis; Insulin; Insulin Resistance; Mice; Pancreas; Rats; Vascular Surgical Procedures

Recent studies have suggested resveratrol (RSV) as a new natural therapeutic agent to treat type 2 diabetes and lipid-induced insulin resistance. Here, we investigated whether RSV could reverse palmitate-induced insulin resistance in human primary muscle cells.. Myotubes obtained from six healthy men (54 ± 3 years (mean ± SE), BMI 25.0 ± 1.7 kg/m(2), fasting plasma glucose concentration (fP-glucose) 5.47 ± 0.09 mmol/l) were treated for 4 h with 100 μmol/l RSV and/or 0.2 mmol/l palmitate, and stimulated with or without 100 nmol/l insulin. Assays of glucose uptake, glycogen synthesis, palmitate oxidation, intracellular signalling and AMP-activated protein kinase (AMPK) activity were performed.. RSV did not reverse palmitate-induced impairment of glucose metabolism. Surprisingly, RSV decreased glucose uptake and glycogen synthesis in human skeletal muscle cells. Palmitate oxidation and phosphorylation of AMPK and its downstream target acetyl-CoA carboxylase β (ACCβ) were inhibited by RSV, and RSV completely blocked the activity of AMPK isoform complexes α1/β2/γ1 and α2/β2/γ1 in in-vitro kinase activity assays. Endoplasmic reticulum (ER) stress was increased in response to RSV, as indicated by increased phosphorylation of eukaryotic initiation factor 2α (eIF2α) and increased expression of CCAAT/enhancer binding protein homologous protein (CHOP).. Acute exposure to RSV inhibits AMPK activity, fatty-acid oxidation and glucose metabolism in human myotubes.

Topics: AMP-Activated Protein Kinases; Cell Differentiation; Diabetes Mellitus, Type 2; Drug Interactions; Enzyme Inhibitors; Glucose; Glycogen; Humans; Insulin Resistance; Male; Middle Aged; Muscle Fibers, Skeletal; Palmitates; Phosphorylation; Primary Cell Culture; Resveratrol; Signal Transduction; Stilbenes

The skin, the body's largest organ, plays an important role in the biotransformation/detoxification and elimination of xenobiotics and endogenous toxic substances, but its role in oxidative stress and insulin resistance is unclear. We investigated the relationship between skin detoxification and oxidative stress/insulin resistance by examining burn-induced changes in nicotinamide degradation. Rats were divided into four groups: sham-operated, sham-nicotinamide, burn, and burn-nicotinamide. Rats received an intraperitoneal glucose injection (2 g/kg) with (sham-nicotinamide and burn-nicotinamide groups) or without (sham-operated and burn groups) coadministration of nicotinamide (100 mg/kg). The results showed that the mRNA of all detoxification-related enzymes tested was detected in sham-operated skin but not in burned skin. The clearance of nicotinamide and N(1)-methylnicotinamide in burned rats was significantly decreased compared with that in sham-operated rats. After glucose loading, burn group showed significantly higher plasma insulin levels with a lower muscle glycogen level than that of sham-operated and sham-nicotinamide groups, although there were no significant differences in blood glucose levels over time between groups. More profound changes in plasma H(2)O(2) and insulin levels were observed in burn-nicotinamide group. It may be concluded that decreased skin detoxification may increase the risk for oxidative stress and insulin resistance.

Topics: Animals; Antioxidants; Blood Glucose; Burns; Glycogen; Hydrogen Peroxide; Insulin; Insulin Resistance; Male; Niacinamide; Oxidative Stress; Rats; Rats, Sprague-Dawley; Skin; Xenobiotics

Atypical antipsychotic drugs such as Olanzapine induce weight gain and metabolic changes associated with the development of type 2 diabetes. The mechanisms underlying the metabolic side-effects of these centrally acting drugs are still unknown to a large extent. We compared the effects of peripheral (intragastric; 3 mg/kg/h) versus central (intracerebroventricular; 30 µg/kg/h) administration of Olanzapine on glucose metabolism using the stable isotope dilution technique (Experiment 1) in combination with low and high hyperinsulinemic-euglycemic clamps (Experiments 2 and 3), in order to evaluate hepatic and extra-hepatic insulin sensitivity, in adult male Wistar rats. Blood glucose, plasma corticosterone and insulin levels were measured alongside endogenous glucose production and glucose disappearance. Livers were harvested to determine glycogen content. Under basal conditions peripheral administration of Olanzapine induced pronounced hyperglycemia without a significant increase in hepatic glucose production (Experiment 1). The clamp experiments revealed a clear insulin resistance both at hepatic (Experiment 2) and extra-hepatic levels (Experiment 3). The induction of insulin resistance in Experiments 2 and 3 was supported by decreased hepatic glycogen stores in Olanzapine-treated rats. Central administration of Olanzapine, however, did not result in any significant changes in blood glucose, plasma insulin or corticosterone concentrations nor in glucose production. In conclusion, acute intragastric administration of Olanzapine leads to hyperglycemia and insulin resistance in male rats. The metabolic side-effects of Olanzapine appear to be mediated primarily via a peripheral mechanism, and not to have a central origin.

Topics: Animals; Antipsychotic Agents; Benzodiazepines; Blood Glucose; Glucose; Glucose Clamp Technique; Glycogen; Hyperglycemia; Insulin; Insulin Resistance; Liver; Male; Olanzapine; Rats; Rats, Wistar

A major problem in the insulin therapy of patients with diabetes type 2 (T2DM) is the increased occurrence of hypoglycemic events which, if left untreated, may cause confusion or fainting and in severe cases seizures, coma, and even death. To elucidate the potential contribution of the liver to hypoglycemia in T2DM we applied a detailed kinetic model of human hepatic glucose metabolism to simulate changes in glycolysis, gluconeogenesis, and glycogen metabolism induced by deviations of the hormones insulin, glucagon, and epinephrine from their normal plasma profiles. Our simulations reveal in line with experimental and clinical data from a multitude of studies in T2DM, (i) significant changes in the relative contribution of glycolysis, gluconeogenesis, and glycogen metabolism to hepatic glucose production and hepatic glucose utilization; (ii) decreased postprandial glycogen storage as well as increased glycogen depletion in overnight fasting and short term fasting; and (iii) a shift of the set point defining the switch between hepatic glucose production and hepatic glucose utilization to elevated plasma glucose levels, respectively, in T2DM relative to normal, healthy subjects. Intriguingly, our model simulations predict a restricted gluconeogenic response of the liver under impaired hormonal signals observed in T2DM, resulting in an increased risk of hypoglycemia. The inability of hepatic glucose metabolism to effectively counterbalance a decline of the blood glucose level becomes even more pronounced in case of tightly controlled insulin treatment. Given this Janus face mode of action of insulin, our model simulations underline the great potential that normalization of the plasma glucagon profile may have for the treatment of T2DM.

Topics: Algorithms; Blood Glucose; Carbohydrate Metabolism; Computer Simulation; Diabetes Mellitus, Type 2; Epinephrine; Glucagon; Glucose; Glycogen; Hepatocytes; Humans; Hypoglycemia; Hypoglycemic Agents; Insulin; Insulin Resistance; Kinetics; Liver; Models, Biological; Phosphorylation; Postprandial Period; Protein Processing, Post-Translational

There is a strong inverse relationship between a females own birth weight and her subsequent risk for gestational diabetes with increased risk of developing diabetes later in life. We have shown that growth restricted females develop loss of glucose tolerance during late pregnancy with normal pancreatic function. The aim of this study was to determine whether growth restricted females develop long-term impairment of metabolic control after an adverse pregnancy adaptation. Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham surgery (Control) in late pregnancy (E18) in F0 female rats. F1 Control and Restricted female offspring were mated with normal males and allowed to deliver (termed Ex-Pregnant). Age-matched Control and Restricted Virgins were also studied and glucose tolerance and insulin secretion were determined. Pancreatic morphology and hepatic glycogen and triacylglycerol content were quantified respectively. Restricted females were born lighter than Control and remained lighter at all time points studied (p<0.05). Glucose tolerance, first phase insulin secretion and liver glycogen and triacylglycerol content were not different across groups, with no changes in β-cell mass. Second phase insulin secretion was reduced in Restricted Virgins (-34%, p<0.05) compared to Control Virgins, suggestive of enhanced peripheral insulin sensitivity but this was lost after pregnancy. Growth restriction was associated with enhanced basal hepatic insulin sensitivity, which may provide compensatory benefits to prevent adverse metabolic outcomes often associated with being born small. A prior pregnancy was associated with reduced hepatic insulin sensitivity with effects more pronounced in Controls than Restricted. Our data suggests that pregnancy ameliorates the enhanced peripheral insulin sensitivity in growth restricted females and has deleterious effects for hepatic insulin sensitivity, regardless of maternal birth weight.

Topics: Adult; Animals; Animals, Newborn; Blood Glucose; Body Weight; Diabetes, Gestational; Female; Glucose Tolerance Test; Glycogen; Humans; Infant, Low Birth Weight; Infant, Newborn; Insulin; Insulin Resistance; Insulin-Secreting Cells; Liver; Male; Models, Biological; Placental Insufficiency; Pregnancy; Pregnancy, Animal; Rats; Risk; Triglycerides

Persimmon Leaf (PL), commonly consumed as herbal tea and traditional medicines, contains a variety of compounds that exert antioxidant, α-amylase and α-glucosidase inhibitory activity. However, little is known about the in vivo effects and underlying mechanisms of PL on hyperglycemia, hyperlipidemia and hepatic steatosis in type 2 diabetes. Powered PL (5%, w/w) was supplemented with a normal diet to C57BL/KsJ-db/db mice for 5 weeks. PL decreased blood glucose, HOMA-IR, plasma triglyceride and total cholesterol levels, as well as liver weight, hepatic lipid droplets, triglycerides and cholesterol contents, while increasing plasma HDL-cholesterol and adiponectin levels. The anti-hyperglycemic effect was linked to decreased activity of gluconeogenic enzymes as well as increased glycogen content, glucokinase activity and its mRNA level in the liver. PL also led to a decrease in lipogenic transcriptional factor PPARγ as well as gene expression and activity of enzymes involved in lipogenesis, with a simultaneous increase in fecal lipids, which are seemingly attributable to the improved hyperlipidemia and hepatic steatosis and decreased hepatic fatty acid oxidation. Furthermore, PL ameliorated plasma and hepatic oxidative stress. Supplementation with PL may be an effective dietary strategy to improve type 2 diabetes accompanied by dyslipidemia and hepatic steatosis by partly modulating the activity or gene expression of enzymes related to antioxidant, glucose and lipid homeostasis.

Topics: Adiponectin; Animals; Antioxidants; Blood Glucose; Cholesterol; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Dietary Supplements; Diospyros; Dyslipidemias; Fatty Liver; Gene Expression; Glucokinase; Glycogen; Hyperglycemia; Hypoglycemic Agents; Insulin Resistance; Lipid Metabolism; Lipogenesis; Liver; Male; Mice; Mice, Inbred C57BL; Oxidative Stress; Phytotherapy; Plant Leaves; Plant Preparations; PPAR gamma; RNA, Messenger; Triglycerides

Obesity has been shown to create stress in the endoplasmic reticulum (ER), and that initiates the activation of the unfolded protein response (UPR). This has been reported to cause insulin resistance in selective tissues through activation of the inositol-requiring enzyme 1α (IRE1α)-c-Jun NH(2)-terminal kinase (JNK) pathway, which results in the phosphorylation of the insulin receptor substrate-1 (IRS-1) at an inhibitory site and blocks insulin receptor signaling. In this study, we report that the Src homology domain-containing adaptor protein Nck1, previously shown to modulate the UPR, is of functional importance in obesity-induced ER stress signaling and inhibition of insulin actions. We have examined obese Nck1(-/-) and Nck1(+/+) mice for glucose tolerance, insulin sensitivity, and signaling as well as for ER stress markers and IRS-1 phosphorylation at Ser(307). Our findings show that obese Nck1-deficient mice display improved glucose disposal accompanied by enhanced insulin signaling in liver. This correlates with attenuated IRE1α and JNK activation and IRS-1 phosphorylation at Ser(307) compared with obese wild-type mice. Consistent with our in vivo data, we report that downregulation of Nck1 using siRNA in HepG2 cells results in decreased thapsigargin-induced IRE1α activation and signaling and IRS-1 phosphorylation at Ser(307), whereas it markedly enhances insulin signaling. Overall, in liver and in cultured cells, we show that depletion of Nck1 attenuates the UPR signal and its inhibitory action on insulin signaling. Taken all together, our findings implicate Nck1 in regulating the UPR, which secondary to obesity impairs glucose homeostasis and insulin actions.

Topics: Adaptor Proteins, Signal Transducing; Animals; Blood Glucose; Blotting, Western; Endoplasmic Reticulum; Glucose Intolerance; Glycogen; HEK293 Cells; Homeostasis; Humans; Insulin; Insulin Resistance; JNK Mitogen-Activated Protein Kinases; Liver; Membrane Proteins; Mice; Mice, Knockout; Mice, Obese; Oncogene Proteins; Phosphorylation; Protein Serine-Threonine Kinases; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Unfolded Protein Response

Symplocos cochinchinensis (Lour.) S. Moore. is used in Indian system of traditional medicine to treat diabetes mellitus. The present study aims to investigate the antidiabetic efficacy of the hexane extract of Symplocos cochinchinensis leaves in high fat diet-low streptozotocin (STZ) induced type 2 diabetic rats.. The doses for the study were fixed based on Irwin test. The hypoglycemic effect of the hexane extract of Symplocos cochinchinensis leaves were studied in normal rats. Oral glucose and insulin tolerance tests were carried out. The antihyperglycemic effect of the hexane extract at 250 and 500 mg/kg was studied in high fat diet-low STZ induced type 2 diabetic rats for 28 days.. The extracts showed no adverse effects up to 5 g/kg concentration. In hypoglycemic study, after treatment with hexane extract at 250 and 500 mg/kg the blood glucose was mildly reduced. In oral glucose tolerance test, the treatment with the hexane extract at 250 and 500 mg/kg showed a highly significant reduction of 12.07% and 23.58% in plasma glucose levels, respectively 30 min after glucose load. The insulin tolerance test also showed improved insulin sensitivity after 60 min of insulin treatment. In high fat diet-low STZ induced type 2 diabetic rats, after 28 days treatment with the hexane extract at 250 and 500 mg/kg reduced the plasma glucose level by 17.04% and 42.10%, respectively. A significant reduction in plasma insulin, plasma and hepatic total cholesterol (TC), triglycerides (TG) and free fatty acids (FFA) and a significant increase in liver glycogen were observed in treated diabetic rats.. This study demonstrated the potential antidiabetic property of hexane extract of Symplocos cochinchinensis leaves on type 2 diabetes mellitus, thus justifying its traditional usage.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Type 2; Dietary Fats; Glucose Tolerance Test; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Lipids; Liver; Male; Phytotherapy; Plant Extracts; Plant Leaves; Rats; Rats, Wistar; Streptozocin

Modified Si-Miao-San (mSMS) has showed anti-inflammatory potency and has been used in the clinic to treat metabolic disorders such as obesity and diabetes, but whether its anti-inflammatory activity contributes to improving insulin resistance remains to be determined. This study aims to investigate the mechanistic relationship between its anti-inflammatory activity and modulation of insulin sensitivity in free fatty acid-stimulated HepG2 cells.. HepG2 cells were stimulated with palmitate (PA) and the effect of mSMS on insulin mediated-glycogen synthesis and triglyceride secretion was observed. The inhibition of mSMS on gene expression of proinflammatory cytokine tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and inhibitor of NF-κB kinase-β (IKKβ) activation was investigated. In addition, the effects of mSMS on insulin signaling transduction along insulin receptor substrates-1 (IRS-1)/Akt pathway were also evaluated. Furthermore, the effect of mSMS on glucose intolerance induced by conditioned-medium derived from activated macrophages was also assessed in normoglycemic mice.. Treatment of hepatocytes with PA reduced insulin sensitivity and mSMS effectively increased insulin-mediated glycogen synthesis and restored insulin inhibition of triglyceride secretion. mSMS suppressed IKKβ activation and down-regulated TNF-α and IL-6 gene over-expression, demonstrating its anti-inflammatory activity in hepatocytes. PA-evoked inflammation impaired insulin signaling cascades and mSMS improved insulin signaling transduction by modification of Ser/Thr phosphorylation of IRS-1 and downstream Akt (T308), thereby improved insulin sensitivity in hepatocytes. mSMS also improved glucose intolerance induced by inflammatory cytokines in normoglycemic mice, which further demonstrated its modulation toward insulin sensitivity in vivo.. The results suggest that mSMS inhibited inflammatory response and improved insulin sensitivity in hepatocytes via an IKKβ/IRS-1/Akt-dependent pathway.

Topics: Animals; Anti-Inflammatory Agents; Atractylodes; Coix; Coptis; Down-Regulation; Drugs, Chinese Herbal; Glycogen; Hep G2 Cells; Hepatocytes; Humans; I-kappa B Kinase; Inflammation; Inflammation Mediators; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Interleukin-6; Male; Mice; Mice, Inbred ICR; Phytotherapy; Plants, Medicinal; Proto-Oncogene Proteins c-akt; Signal Transduction; Triglycerides; Tumor Necrosis Factor-alpha

Angelica acutiloba root (Japanese Dong Quai), used for treatment of gynecological disorders, is currently cultivated in Taiwan. The present study evaluated the preventative effect of Angelica acutiloba root (Japanese Dong Quai) on the induction of insulin resistance. Insulin resistance was induced in rats by feeding a high fructose diet for 6 weeks. Thereafter, the rats were maintained on the same diet and treated with oral A. acutiloba root extract or pioglitazone once daily for 8 weeks. At the end of treatment, the degree of basal insulin resistance was measured by homeostasis model assessment (HOMA-IR). Insulin sensitivity was calculated using the composite whole body insulin sensitivity index (ISIcomp). Protein expression was evaluated by immunoblotting. A. acutiloba (300 mg/kg/day) displayed similar characteristics to pioglitazone (20 mg/kg/day) in reducing HOMA-IR and elevating ISIcomp. Elevated glycosylated hemoglobin levels and hyperinsulinemia were ameliorated by A. acutiloba treatment without hepatotoxic or nephrotoxic effects. A. acutiloba treatment improved dyslipidemia, induced lipoprotein lipase activity and enhanced hepatic glycogen accumulation. Further, A. acutiloba treatment enhanced the action of insulin on muscle glucose transporter subtype 4 translocation and attenuated hepatic phosphoenolpyruvate carboxykinase expression. The findings suggest that A. acutiloba may be an effective ethnomedicine for improving insulin sensitivity.

Topics: Angelica; Animals; Body Weight; Fructose; Glucose Tolerance Test; Glucose Transporter Type 4; Glycogen; Homeostasis; Hypoglycemic Agents; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Lipids; Liver; Male; Phosphoenolpyruvate Carboxykinase (GTP); Pioglitazone; Plant Extracts; Plant Roots; Rats, Wistar; Thiazolidinediones

Recently, epidemiological and experimental studies have linked hyperhomocysteinemia (HHcy) to insulin resistance. However, whether HHcy impairs glucose homeostasis by affecting glycogenesis in the liver is not clear. In the present study, we investigated the effect of HHcy on hepatic glycogen synthesis. Hyperhomocysteinemia was induced in mice by drinking water containing two percent methionine. Mice with HHcy showed an increase in the phosphorylation of glycogen synthase and a significant decrease in hepatic glycogen content and the rate of glycogen synthesis. The expression of TRB3 (tribbles-related protein 3) was up-regulated in the liver of mice with HHcy, concomitantly with the dephosphorylation of glycogen synthase kinase-3β and Akt. The knockdown of TRB3 by short hairpin RNA suppressed the dephosphorylation of these two kinases. Homocysteine induced an increase in the levels of hepatic cAMP and cAMP response element-binding protein phosphorylation, which in turn up-regulated the expression of peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α and TRB3. The inhibition of PPAR-α by its inhibitor, MK886, or knockdown of PPAR-α by small interfering RNA significantly inhibited the expression of TRB3 induced by homocysteine. The current study demonstrates that HHcy impairs hepatic glycogen synthesis by inducing the expression of TRB3. These results provide a novel explanation for the development and progression of insulin resistance in HHcy.

Topics: Animals; Cell Cycle Proteins; Disease Progression; Glycogen; Homocysteine; Humans; Hyperhomocysteinemia; Indoles; Insulin Resistance; Liver Glycogen; Methionine; Mice; Phosphorylation; PPAR gamma; Protein Serine-Threonine Kinases; Repressor Proteins; Reverse Transcriptase Polymerase Chain Reaction; RNA, Small Interfering

We investigated the effect of Ishige okamurae extract on blood glucose level and insulin resistance in C57BL/-KsJ-db/db mice. We administered a standard AIN-93G diet with or without IOE to the animals for 6 weeks. After 6 weeks, blood glucose level was improved and blood glycosylated hemoglobin levels were lowered in sample group mice as compared to those in the diabetic control group mice. Hyperinsulinemia was reduced in the I. okamurae extract group mice with type 2 diabetes. With regard to hepatic glucose metabolic enzyme activities, glucokinase activity was enhanced in the IOE group mice, while glucose-6-phosphatase and phosphoenolpyruvate carboxykinase activities in the IOE group mice were significantly lowered than those in the diabetic control group mice. In addition, the hepatic glycogen content was elevated in the IOE group as compared to that in the diabetic control group. The homeostatic index of insulin resistance was lower in the I. okamurae extract group mice than in the diabetic control group mice. These results suggest that a dietary supplement of I. okamurae extract lowers the blood glucose level by altering the hepatic glucose metabolic enzyme activities and improves insulin resistance.

Topics: Animals; Blood Glucose; Body Weight; Eating; Glucose Tolerance Test; Glycated Hemoglobin; Glycogen; Hyperglycemia; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Liver Function Tests; Male; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Phaeophyceae; Plant Extracts

APPL1 is an adaptor protein that binds to both AKT and adiponectin receptors and is hypothesised to mediate the effects of adiponectin in activating downstream effectors such as AMP-activated protein kinase (AMPK). We aimed to establish whether APPL1 plays a physiological role in mediating glycogen accumulation and insulin sensitivity in muscle and the signalling pathways involved. In vivo electrotransfer of cDNA- and shRNA-expressing constructs was used to over-express or silence APPL1 for 1 week in single tibialis cranialis muscles of rats. Resulting changes in glucose and lipid metabolism and signalling pathway activation were investigated under basal conditions and in high-fat diet (HFD)- or chow-fed rats under hyperinsulinaemic-euglycaemic clamp conditions. APPL1 over-expression (OE) caused an increase in glycogen storage and insulin-stimulated glycogen synthesis in muscle, accompanied by a modest increase in glucose uptake. Glycogen synthesis during the clamp was reduced by HFD but normalised by APPL1 OE. These effects are likely explained by APPL1 OE-induced increase in basal and insulin-stimulated phosphorylation of IRS1, AKT, GSK3β and TBC1D4. On the contrary, APPL1 OE, such as HFD, reduced AMPK and acetyl-CoA carboxylase phosphorylation and PPARγ coactivator-1α and uncoupling protein 3 expression. Furthermore, APPL1 silencing caused complementary changes in glycogen storage and phosphorylation of AMPK and PI3-kinase pathway intermediates. Thus, APPL1 may provide a means for crosstalk between adiponectin and insulin signalling pathways, mediating the insulin-sensitising effects of adiponectin on muscle glucose disposal. These effects do not appear to require AMPK. Activation of signalling mediated via APPL1 may be beneficial in overcoming muscle insulin resistance.

Topics: Adaptor Proteins, Signal Transducing; Animals; Carrier Proteins; Dietary Fats; Gene Silencing; Glucose Clamp Technique; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; GTPase-Activating Proteins; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Male; Muscle, Skeletal; Nerve Tissue Proteins; Phosphatidylinositol 3-Kinase; Phosphorylation; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; RNA, Small Interfering; Signal Transduction

Adrenomedullin (ADM) has been recognized as a multipotent multifunctional peptide. To explore the pathophysiological roles of ADM in insulin resistance (IR), we studied the changes in ADM mRNA level in the myocardium and vessels and the effect of ADM supplementation on rats with IR induced by fructose feeding. Rats were fed 4% fructose in drinking water for 8 weeks, and ADM was administered subcutaneously in pure water through an Alzet Mini-osmotic Pump at 300 ng/kg/h for the last 4 weeks. Compared with controls, rats with IR showed increased levels of fasting blood sugar and serum insulin, by 95% and 67%, respectively (all P<0.01), and glycogen synthesis and glucose transport activity of the soleus decreased by 54% and 55% (all P<0.01). mRNA level and content of brain natriuretic peptide (BNP) in myocardial were all increased significantly. Fructose-fed rats showed increased immunoreactive-ADM content in plasma by 110% and in myocardia by 55% and increased mRNA level in myocardia and vessels (all P<0.01). ADM administration ameliorated the induced IR and myocardial hypertrophy. The glycogen synthesis and glucose transport activity of the soleus muscle increased by 41% (P<0.01) and 32% (P<0.05). ADM therapy attenuated myocardial and soleus lipid peroxidation injury and enhanced the antioxidant ability. Our results showed upregulation of endogenous ADM during fructose-induced IR and the protective effect of ADM on fructose-induced IR and concomitant cardiovascular hypertrophy probably by its antioxidant effect, which suggests that ADM could be an endogenous protective factor in IR.

Topics: Adrenomedullin; Animals; Blood Glucose; Cardiomegaly; Cardiotonic Agents; Fructose; Glycogen; Infusion Pumps; Infusions, Subcutaneous; Insulin; Insulin Resistance; Lipid Peroxidation; Male; Malondialdehyde; Muscle, Skeletal; Myocardium; Natriuretic Peptide, Brain; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

To test the hypothesis that physical inactivity impairs the exercise-induced modulation of pyruvate dehydrogenase (PDH), six healthy normally physically active male subjects completed 7 days of bed rest. Before and immediately after the bed rest, the subjects completed an oral glucose tolerance test (OGTT) and a one-legged knee extensor exercise bout [45 min at 60% maximal load (W(max))] with muscle biopsies obtained from vastus lateralis before, immediately after exercise, and at 3 h of recovery. Blood samples were taken from the femoral vein and artery before and after 40 min of exercise. Glucose intake elicited a larger (P ≤ 0.05) insulin response after bed rest than before, indicating glucose intolerance. There were no differences in lactate release/uptake across the exercising muscle before and after bed rest, but glucose uptake after 40 min of exercise was larger (P ≤ 0.05) before bed rest than after. Muscle glycogen content tended to be higher (0.05< P ≤ 0.10) after bed rest than before, but muscle glycogen breakdown in response to exercise was similar before and after bed rest. PDH-E1α protein content did not change in response to bed rest or in response to the exercise intervention. Exercise increased (P ≤ 0.05) the activity of PDH in the active form (PDHa) and induced (P ≤ 0.05) dephosphorylation of PDH-E1α on Ser²⁹³, Ser²⁹⁵ and Ser³⁰⁰, with no difference before and after bed rest. In conclusion, although 7 days of bed rest induced whole body glucose intolerance, exercise-induced PDH regulation in skeletal muscle was not changed. This suggests that exercise-induced PDH regulation in skeletal muscle is maintained in glucose-intolerant (e.g., insulin resistant) individuals.

Topics: Adult; Bed Rest; Biopsy; Blood Glucose; Enzyme Activation; Exercise; Exercise Test; Gene Expression Regulation, Enzymologic; Glucose Intolerance; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Lactic Acid; Male; Muscle Contraction; Oxygen Consumption; Phosphorylation; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; Pyruvate Dehydrogenase (Lipoamide); Pyruvate Dehydrogenase (Lipoamide)-Phosphatase; Pyruvate Dehydrogenase Acetyl-Transferring Kinase; Quadriceps Muscle; RNA, Messenger; Serine; Time Factors; Young Adult

Non-alcoholic fatty liver disease (NAFLD) is associated with hepatic insulin resistance with the molecular basis of this association being not well understood. Here we studied the effect of hepatic triglyceride accumulation induced by postprandial triglyceride-rich lipoproteins (TGRL) on hepatic insulin sensitivity in HepG2 cells. Incubation of HepG2 cells with purified TGRL particles induced hepatocellular triglyceride accumulation paralleled by diminished insulin-stimulated glycogen content and glycogen synthase activity. Accordingly, insulin-induced inhibition of glycogen synthase phosphorylation as well as insulin-induced GSK-3 and AKT phosphorylation were reduced by TGRL. The effects of TGRL were dependent on the presence of apolipoproteins and more pronounced for denser TGRL. Moreover, TGRL effects required the presence of heparan sulfate-proteoglycans on the cell membrane and lipase activity but were independent of the cellular uptake of TGRL particles by receptors of the LDL receptor family. We suggest postprandial lipemia to be an important factor in the pathogenesis of NAFLD.

Topics: Adult; Fatty Liver; Glycogen; Glycogen Synthase; Glycogen Synthase Kinase 3; Hep G2 Cells; Humans; Hypertriglyceridemia; Insulin Resistance; Lipoproteins; Liver; Male; Non-alcoholic Fatty Liver Disease; Postprandial Period; Proto-Oncogene Proteins c-akt; Receptors, LDL; Triglycerides

To evaluate the efficacy and safety of 2 analogs of L-carnitine on rats made insulin resistant by a high-fructose diet.. Using rats made insulin resistant by a high-fructose diet, we investigated the impact of 2 analogs of L-carnitine (25 mg/kg) and L-carnitine (250 mg/kg) on glucose, triglycerides and cholesterol blood levels, and liver glycogen. We also evaluated the safety of both analogs by the assessment of some biochemical and hematological parameters, a histological analysis and a study of embryotoxicity.. Both analogs reduced the levels of triglycerides in the liver and plasma, but only analog 2 reduced the cholesterol levels in insulin-resistant rats. No changes were observed in glycogen content. Safety evaluations revealed alterations in blood lymphocytes and embryotoxicity data.. This study demonstrated that the 2 analogs maintain the pharmacological properties of L-carnitine but have a different efficacy, potency and toxicity.

Topics: Animals; Blood Glucose; Body Weight; Carnitine; Chick Embryo; Cholesterol; Diet; Disease Models, Animal; Drug Evaluation, Preclinical; Embryo, Nonmammalian; Fructose; Glycogen; Insulin; Insulin Resistance; Liver; Male; Rats; Rats, Wistar; Sweetening Agents; Teratogens; Triglycerides; Vitamin B Complex

Recent evidence strongly supports the contention that grape seed extract (GSE) improves hyperglycaemia and hyperinsulinaemia in high-fructose-fed rats. To explore the underlying molecular mechanisms of action, we examined the effects of GSE on the expression of muscle proteins related to the insulin signalling pathway and of mRNA for genes involved in the adiponectin signalling pathway. Compared with rats fed on a normal diet, high-fructose-fed rats developed pathological changes, including insulin resistance, hyperinsulinaemia, hypertriacylglycerolaemia, a low level of plasma adiponectin and a high level of plasma fructosamine. These disorders were effectively attenuated in high-fructose-fed rats supplemented with GSE. A high-fructose diet causes insulin resistance by significantly reducing the protein expression of insulin receptor, insulin receptor substrate-1, Akt and GLUT4, and the mRNA expression of adiponectin, adiponectin receptor R1 (AdipoR1) and AMP-activated protein kinase (AMPK)-α in the skeletal muscle. Supplementation of GSE enhanced the expression of insulin signalling pathway-related proteins, including Akt and GLUT4. GSE also increased the mRNA expression of adiponectin, AdipoR1 and AMPK-α. In addition, GSE increased the mRNA levels of glycogen synthase and suppressed the mRNA expression of glycogen synthase kinase-3-α, causing an increase in glycogen accumulation in the skeletal muscle. These results suggest that GSE ameliorates the defective insulin and adiponectin signalling pathways in the skeletal muscle, resulting in improved insulin resistance in fructose-fed rats.

Topics: Adiponectin; AMP-Activated Protein Kinases; Animals; Base Sequence; Dietary Carbohydrates; Dietary Supplements; DNA Primers; Fructose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase Kinase 3; Grape Seed Extract; Hypoglycemic Agents; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; Receptors, Adiponectin; RNA, Messenger; Signal Transduction

Insulin replacement is the only effective therapy to manage hyperglycemia in type 1 diabetes mellitus (T1DM). Nevertheless, intensive insulin therapy has inadvertently led to insulin resistance. This study investigates mechanisms involved in the insulin resistance induced by hyperinsulinization. Wistar rats were rendered diabetic by alloxan injection, and 2 weeks later received saline or different doses of neutral protamine Hagedorn insulin (1.5, 3, 6, and 9 U/day) over 7 days. Insulinopenic-untreated rats and 6U- and 9U-treated rats developed insulin resistance, whereas 3U-treated rats revealed the highest grade of insulin sensitivity, but did not achieve good glycemic control as 6U- and 9U-treated rats did. This insulin sensitivity profile was in agreement with glucose transporter 4 expression and translocation in skeletal muscle, and insulin signaling, phosphoenolpyruvate carboxykinase/glucose-6-phosphatase expression and glycogen storage in the liver. Under the expectation that insulin resistance develops in hyperinsulinized diabetic patients, we believe insulin sensitizer approaches should be considered in treating T1DM.

Topics: Alloxan; Animals; Diabetes Mellitus, Experimental; Disease Models, Animal; Dose-Response Relationship, Drug; Forkhead Transcription Factors; Glucose; Glucose Transporter Type 4; Glucose-6-Phosphatase; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Male; Muscle, Skeletal; Nerve Tissue Proteins; Protein Serine-Threonine Kinases; Rats; Rats, Wistar

Amylin is co-secreted with insulin, responds to the same stimuli, is anorectic, lowers body weight by reducing fat mass, and is proposed for diabetes treatment. We examined the effect of a 3-day constant infusion of close to physiological doses of amylin in Wistar rats, on glucotransporter expression, glycogen content (G), glycogen synthase a activity (GSa) and glucose transport (GT), in liver, muscle and fat from insulin resistant (IR) and type 2 diabetic (T2D) models, compared to normal (N) animals; plasma glucose and insulin were measured. Plasma insulin in IR was higher than in N or T2D, and amylin normalized the value. In both, IR and T2D, liver G was lower than normal, accompanied by GLUT-2, mRNA and protein, higher and lower, respectively, than in N; amylin normalized G in both groups, without changes in GLUT-2, except for an mRNA increase in T2D. In IR and T2D, muscle GSa was reduced, together with respective over- and under-GLUT-4 expression; amylin induced only a trend toward GSa normalization in both groups. In isolated adipocytes, GT and GLUT-4 in IR and T2D were lower and higher, respectively, than in N; after amylin, not only GT was normalized in both groups but also the response to insulin was much more pronounced, including that in N, without major changes in GLUT-4. This suggests that the beneficial effect of amylin in states running with altered glucose homeostasis could occur by partially acting on the hexose metabolism of the liver and mainly on that of the adipose tissue.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Glucose Transporter Type 2; Glucose Transporter Type 4; Glycogen; Glycogen Synthase; Homeostasis; Humans; Insulin; Insulin Resistance; Islet Amyloid Polypeptide; Male; Rats; Rats, Wistar

We examined whether deletion of inducible nitric oxide synthase (iNOS) could prevent lipid infusion-induced insulin resistance in iNOS-knockout and wild-type mice with the in vivo euglycemic-hyperinsulinemic clamp technique. Plasma NO metabolites were increased in lipid-infused wild-type mice, while they were not increased in iNOS-knockout mice. Plasma tumor necrosis factor-α levels were increased in both wild-type and iNOS-knockout by lipid-infusion. Lipid infusion reduced glucose infusion rate (GIR) and whole body glucose uptake in wild-type mice, whereas iNOS-knockout mice displayed comparable GIR and whole body glucose uptake compared with the control. In the gastrocnemius, lipid infusion decreased glucose uptake and glycolysis that were accompanied with increased phosphorylation of c-Jun N-terminal kinase and reduced phosphorylation of phosphoinositide 3-kinases and serine/threonine kinase Akt. However, lipid infusion did not affect glucose uptake or phosphorylation of these proteins in iNOS-knockout mice. The mRNA levels of inflammatory cytokines were also increased in the gastrocnemis of wild-type and iNOS-knockout mice by lipid infusion. Nitrotyrosine level in the gastrocnemius was increased in lipid-infused wild-type mice but it was not increased in iNOS-knockout mice. These results suggest that lack of iNOS prevents lipid infusion-induced skeletal muscle insulin resistance without attenuating cytokine levels.

Topics: Animals; Emulsions; Fat Emulsions, Intravenous; Glucose; Glycogen; Insulin Resistance; Interleukin-1beta; Interleukin-6; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscle, Skeletal; Nitric Oxide Synthase Type II; Phospholipids; Soybean Oil; Tumor Necrosis Factor-alpha

We investigated if alterations in the insulin-signaling pathway could contribute to reduced hepatic glycogen levels in adult rats subjected to a protein deficiency during intrauterine life and lactation and reared through to recovery on a soybean diet.. Rats from mothers fed with 17% or 6% protein (casein) during pregnancy and lactation were maintained with a 17% casein diet (offspring born to and suckled by mothers fed a control diet and subsequently fed the same diet after weaning [CC group] and offspring born to and suckled by mothers fed a control diet and subsequently fed a soybean flour diet with 17% protein after weaning [CS group]), a soybean diet (offspring of mothers fed a low-protein diet and a control diet after weaning [LC group] and offspring of mothers fed a low-protein diet and fed a soybean flour diet containing 17% protein after weaning [LS group]), or a 6% casein diet (offspring of mothers fed a low-protein diet and subsequently fed the same diet after weaning [LL group]) from weaning until 90 d of life.. A soybean diet did not modify basal serum glucose and glucagon concentrations, but raised basal serum insulin and consequently increased the serum insulin/glucose ratio. Insulin receptor and insulin receptor substrate-1 levels were lower in rats fed a soybean diet compared with those maintained with a casein diet. In the LS group, the p85 levels were higher than in the LC group, whereas in CS rats its expression was lower than in CC rats. The expression of p110 was lower in the CS group compared with the CC group and similar in the LS and LC groups. Insulin receptor substrate-1 phosphorylation was similar in the LS, LC, and CS groups and lower compared with the CC group. The insulin receptor substrate-1-p85/phosphatidylinositol 3-kinase association was lower in LS than in LC rats and in CS than in CC rats. Akt phosphorylation was lower in the CS and LS groups than in the CC and LC groups.. Adult rats maintained with a soybean diet exhibited insulin resistance due, at least in part, to alterations in the early steps of the insulin signal transduction pathway.

Topics: Analysis of Variance; Animal Nutritional Physiological Phenomena; Animals; Blood Glucose; Blotting, Western; Body Weight; Caseins; Diet; Disease Models, Animal; Female; Glycine max; Glycogen; Insulin; Insulin Resistance; Lactation; Liver; Male; Pregnancy; Prenatal Nutritional Physiological Phenomena; Protein-Energy Malnutrition; Rats; Rats, Wistar

Caveolin, a member of the membrane-anchoring protein family, accumulates various growth receptors in caveolae and inhibits their function. Upregulation of caveolin attenuates cellular proliferation and growth. However, the role of caveolin in regulating insulin signals remains controversial. Here, we demonstrate that caveolin potently enhances insulin receptor (IR) signaling when overexpressed in the liver in vivo. Adenovirus-mediated gene transfer was used to overexpress caveolin specifically in the liver of diabetic obese mice, which were generated with a high-fat diet. Expression of molecules involved in IR signaling, such as IR or Akt, remained unchanged after gene transfer. However, hepatic glycogen synthesis was markedly increased with a decrease in phosphoenolpyruvate carboxykinase protein expression. Insulin sensitivity was increased after caveolin gene transfer as determined by decreased blood glucose levels in response to insulin injection and fasting blood glucose levels. Glucose tolerant test performance was also improved. Similar improvements were obtained in KKA(y) genetically diabetic mice. Adenovirus-mediated overexpression of caveolin-3 in hepatic cells also enhanced IR signaling, as shown by increased phosphorylation of IR in response to insulin stimulation and higher glycogen synthesis at baseline. These effects were attributed mostly to increased insulin receptor activity and caveolin-mediated, direct inhibition of protein tyrosine phosphatase 1B, which was increased in obese mouse livers. In conclusion, our results suggest that caveolin is an important regulator of glucose metabolism that can enhance insulin signals.

Topics: Adenoviridae; Age Factors; Aging; Animals; Blood Glucose; Caveolin 3; Diabetes Mellitus, Type 2; Dietary Fats; Disease Models, Animal; Gene Transfer Techniques; Genetic Vectors; Glucose Tolerance Test; Glycogen; Hep G2 Cells; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Mice; Obesity; Phosphoenolpyruvate Carboxykinase (GTP); Phosphorylation; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Rats; Receptor, Insulin; Signal Transduction

It has been suggested that thiazolidinediones (TZDs) ameliorate insulin resistance in muscle tissue by suppressing muscle lipid storage and the activity of novel protein kinase C (nPKC) isoforms. To test this hypothesis, we analyzed long-term metabolic effects of pioglitazone and the activation of nPKC-epsilon and -theta isoforms in an animal model of the metabolic syndrome, the spontaneously hypertensive rat (a congenic SHR strain with wild type Cd36 gene) fed a diet with 60 % sucrose from the age of 4 to 8 months. Compared to untreated controls, pioglitazone treatment was associated with significantly increased basal (809+/-36 vs 527+/-47 nmol glucose/g/2h, P<0.005) and insulin-stimulated glycogenesis (1321+/-62 vs 749+/-60 nmol glucose/g/2h, P<0.0001) in isolated gastrocnemius muscles despite increased concentrations of muscle triglycerides (3.83+/-0.33 vs 2.25+/-0.12 micromol/g, P<0.005). Pioglitazone-treated rats exhibited significantly increased membrane/total (cytosolic plus membrane) ratio of both PKC-epsilon and PKC-theta isoforms compared to untreated controls. These results suggest that amelioration of insulin resistance after long-term pioglitazone treatment is associated with increased activation of PKC-epsilon and -theta isoforms in spite of increased lipid concentration in skeletal muscles.

Topics: Animals; Animals, Congenic; Blood Glucose; CD36 Antigens; Dietary Sucrose; Disease Models, Animal; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Isoenzymes; Male; Metabolic Syndrome; Muscle, Skeletal; Pioglitazone; Protein Kinase C; Protein Kinase C-epsilon; Protein Kinase C-theta; Protein Transport; Rats; Rats, Inbred SHR; Thiazolidinediones; Time Factors; Triglycerides

In this study, we continued to investigate the hypoglycemic activity of Swertia punicea Helmsl., the hypoglycemic and hypolipidemic effects of methylswertianin and bellidifolin from the active ethyl acetate (EtOAc) fraction, and the potential mechanism(s) underlying the improvement of insulin resistance. Streptozotocin (STZ)-induced type 2 diabetic male BABL/c mice treated with methylswertianin and bellidifolin at different doses (orally, 200 and 100mg/kg body wt./day) for 4 weeks were analyzed in comparison to untreated mice. The results proved that methylswertianin and bellidifolin significantly reduced fasting blood glucose (FBG). The administration of both compounds also improved the oral glucose tolerance and lowered fasting serum insulin (FINS). Moreover, post-administration evaluation revealed lower serum total cholesterol (TC), low density lipoprotein cholesterol (LDL) and triglyceride (TG) levels and increased relative high density lipoprotein cholesterol (HDL) concentrations (HDL/TC). Methylswertianin and bellidifolin appeared to improve insulin resistance by enhancing insulin signaling. The expression levels of insulin-receptor alpha subunit (InsR-alpha), insulin-receptor substrate-1 (IRS-1), and phosphatidylinositol 3-kinase (PI3K) were also increased after administration. Meanwhile, methylswertianin and bellidifolin increased hepatic glycogen content, decreased glucokinase (GK) activities and increased glucose-6-phosphatase (G6Pase) activities. In conclusion, these result indicated that methylswertianin and bellidifolin could be useful for treating type-2 diabetes, likely via the improvement of insulin resistance (IR).

Topics: Animals; Blood Glucose; Cholesterol; Diabetes Mellitus, Experimental; Glucokinase; Glucose Intolerance; Glucose-6-Phosphatase; Glycogen; Hypoglycemic Agents; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Liver; Male; Mice; Mice, Inbred BALB C; Phosphatidylinositol 3-Kinases; Phytotherapy; Plant Extracts; Receptor, Insulin; Signal Transduction; Swertia; Triglycerides; Xanthones

This study investigated whether exercise training could prevent the negative side effects of dexamethasone. Rats underwent a training period and were either submitted to a running protocol (60% physical capacity, 5 days/week for 8 weeks) or kept sedentary. After this training period, the animals underwent dexamethasone treatment (1 mg/kg per day, i.p., 10 days). Glycemia, insulinemia, muscular weight and muscular glycogen were measured from blood and skeletal muscle. Vascular endothelial growth factor (VEGF) protein was analyzed in skeletal muscles. Dexamethasone treatment evoked body weight loss (-24%), followed by muscular atrophy in the tibialis anterior (-25%) and the extensor digitorum longus (EDL, -15%). Dexamethasone also increased serum insulin levels by 5.7-fold and glucose levels by 2.5-fold compared to control. The exercise protocol prevented atrophy of the EDL and insulin resistance. Also, dexamethasone-treated rats showed decreased muscular glycogen (-41%), which was further attenuated by the exercise protocol. The VEGF protein expression decreased in the skeletal muscles of dexamethasone-treated rats and was unaltered by the exercise protocol. These data suggest that exercise attenuates hyperglycemia and may also prevent insulin resistance, muscular glycogen loss and muscular atrophy, thus suggesting that exercise may have some benefits during glucocorticoid treatment.

Topics: Animals; Blood Glucose; Body Weight; Dexamethasone; Exercise Test; Glucocorticoids; Glycogen; Hyperinsulinism; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Muscular Atrophy; Physical Conditioning, Animal; Rats; Rats, Wistar; Time Factors

The present study focuses on identifying and developing an anti-diabetic molecule from plant sources that would effectively combat insulin resistance through proper channeling of glucose metabolism involving glucose transport and storage.. Insulin-stimulated glucose uptake formed the basis for isolation of a bioactive molecule through column chromatography followed by its characterization using NMR and mass spectroscopic analysis. Mechanism of glucose transport and storage was evaluated based on the expression profiling of signaling molecules involved in the process.. The study reports (i) the isolation of a bioactive compound 3beta-taraxerol from the ethyl acetate extract (EAE) of the leaves of Mangifera indica (ii) the bioactive compound exhibited insulin-stimulated glucose uptake through translocation and activation of the glucose transporter (GLUT4) in an IRTK and PI3K dependent fashion. (iii) the fate of glucose following insulin-stimulated glucose uptake was ascertained through glycogen synthesis assay that involved the activation of PKB and suppression of GSK3beta.. This study demonstrates the dual activity of 3beta-taraxerol and the ethyl acetate extract of Mangifera indica as a glucose transport activator and stimulator of glycogen synthesis. 3beta-taraxerol can be validated as a potent candidate for managing the hyperglycemic state.

Topics: 3T3 Cells; Adipocytes; Animals; Blood Glucose; Cell Survival; Deoxyglucose; Diabetes Mellitus, Type 2; Enzyme Activation; Glucose; Glycogen; Humans; Insulin Resistance; Mangifera; Mice; Oleanolic Acid; Phosphatidylinositol 3-Kinases; Plant Extracts

Topics: Adenoviridae; Animals; Blood Glucose; Caveolin 3; Diabetes Mellitus, Type 2; Gene Transfer Techniques; Genetic Vectors; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Mice; Phosphoenolpyruvate Carboxykinase (GTP); Phosphorylation; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Receptor, Insulin; Signal Transduction

Although germ-line deletion of c-Jun NH(2)-terminal kinase (JNK) improves overall insulin sensitivity in mice, those studies could not reveal the underlying molecular mechanism and the tissue site(s) in which reduced JNK activity elicits the observed phenotype. Given its importance in nonesterified fatty acids (NEFA) and glucose utilization, we hypothesized that the insulin-sensitive phenotype associated with Jnk deletion originates from loss of JNK function in skeletal muscle. Short hairpin RNA (shRNA)-mediated gene silencing was used to identify the functions of JNK subtypes in regulating energy metabolism and metabolic responses to elevated concentrations of NEFA in C2C12 myotubes, a cellular model of skeletal muscle. We show for the first time that cellular JNK2- and JNK1/JNK2-deficiency divert glucose from oxidation to glycogenesis due to increased glycogen synthase (GS) activity and induction of Pdk4. We further show that JNK2- and JNK1/JNK2-deficiency profoundly increase cellular NEFA oxidation, and their conversion to phospholipids and triglyceride. The increased NEFA utilization was coupled to increased expressions of selective NEFA handling genes including Cd36, Acsl4, and Chka, and enhanced palmitic acid (PA)-dependent suppression of acetyl-CoA carboxylase (Acc). In JNK-intact cells, PA inhibited insulin signaling and glycogenesis. Although silencing Jnk1 and/or Jnk2 prevented PA-induced inhibition of insulin signaling, it did not completely block decreased insulin-mediated glycogenesis, thus indicating JNK-independent pathways in the suppression of glycogenesis by PA. Muscle-specific inhibition of JNK2 (or total JNK) improves the capacity of NEFA utilization and glycogenesis, and is a potential therapeutic target for improving systemic insulin sensitivity in type 2 diabetes (T2D).

Topics: Acetyl-CoA Carboxylase; Animals; Blood Glucose; Fatty Acids, Nonesterified; Gene Silencing; Genes; Glycogen; Glycogen Synthase; Insulin Resistance; JNK Mitogen-Activated Protein Kinases; Lipid Metabolism; Lipid Peroxidation; Mice; Muscle Fibers, Skeletal; Oxidation-Reduction; Palmitic Acid; Phospholipids; Protein Serine-Threonine Kinases; Pyruvate Dehydrogenase Acetyl-Transferring Kinase; RNA, Small Interfering; Sequence Deletion; Signal Transduction; Triglycerides

TNF-alpha-induced insulin resistance is associated with generation of reactive oxygen species (ROS). This study aims at defining the link between ROS production and hepatic insulin resistance. Treatment with TNF-alpha increased ROS generation through activating NADPH oxidase 3 (NOX3) in HepG2 hepatocytes. Down-regulation of NOX3 using siRNA prevented TNF-alpha-induced decrease of cellular glycogen. In the cells treated with TNF-alpha, there were NOX3-dependent activation of JNK, inhibition of IRS1 and phosphorylation of AKT/PKB and GSK. In conclusion, the effects of TNF-alpha on hepatic insulin resistance appear to be, at least in part, mediated by NOX3-derived ROS through a JNK pathway.

Topics: Blotting, Western; Cell Line, Tumor; Fluorescent Antibody Technique; Glycogen; Hepatocytes; Humans; Immunohistochemistry; Insulin Resistance; JNK Mitogen-Activated Protein Kinases; Membrane Proteins; NADPH Oxidases; Reactive Oxygen Species; Reverse Transcriptase Polymerase Chain Reaction; RNA, Small Interfering; Signal Transduction; Tumor Necrosis Factor-alpha

Type 2 familial partial lipodystrophy (FPLD) is an autosomal-dominant lamin A/C-related disease associated with exercise intolerance, muscular pain, and insulin resistance. The symptoms may all be explained by defective metabolism; however, metabolism at the tissue level has not been investigated.. We hypothesized that in FPLD, insulin resistance and impaired aerobic exercise capacity are explained by a common underlying mechanism, presumably a muscular metabolic defect.. Carbohydrate and lipid metabolism was studied on 10 FPLD patients, one patient with limb-girdle muscular dystrophy (LGMD1B, a different lamin A/C disease), and 10 healthy control subjects before and during an oral glucose tolerance test by indirect calorimetry and im microdialysis. Muscle biopsies were taken for in vitro studies.. We observed marked increased skeletal muscle fatty acid beta-oxidation rate in vitro and in vivo, even after glucose ingestion in FPLD patients. However, fatty acid oxidation was largely incomplete and accompanied by increased ketogenesis. The lipid oxidation abnormality was associated with impaired glucose disposition through reduction in glucose oxidation, rather than decreased cellular glucose uptake. A microarray showed down-regulation of complex I respiratory chain, glycolysis, and nuclear transport genes. Although not overtly insulin resistant, the LGMD1B patient showed similar metabolic derangements as the FPLD patients.. Our study suggests imbalance between lipid oxidation and oxidative glucose metabolism in FPLD and LGMD1B patients. The observation suggests an intrinsic defect in skeletal muscle metabolism due to lamin A/C dysfunction. The metabolic FPLD phenotype likely results from this intrinsic defect combined with lipodystrophic "lipid pressure" due to decreased adipose tissue lipid storage capacity.

Topics: Adult; Blood Glucose; Carnitine; Cells, Cultured; Energy Metabolism; Female; Glycogen; Humans; Insulin; Insulin Resistance; Lamin Type A; Lipid Metabolism; Lipodystrophy, Familial Partial; Male; Middle Aged; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Dystrophies, Limb-Girdle; Mutation; Oligonucleotide Array Sequence Analysis; Oxidation-Reduction; Phenotype

Insulin stimulates glucose uptake and promotes the translocation of glucose transporter 4 (Glut 4) to the plasma membrane on L6 myotubes. The aim of this study is to investigate affect of Scoparia dulcis Linn water extracts on glucose uptake activity and the Glut 4 translocation components (i.e., IRS-1, PI 3-kinase, PKB/Akt2, PKC and TC 10) in L6 myotubes compared to insulin.. Extract from TLC fraction-7 (SDF7) was used in this study. The L6 myotubes were treated by various concentrations of SDF7 (1 to 50 microg/ml) and insulin (1 to 100 nM). The glucose uptake activities of L6 myotubes were evaluated using 2-Deoxy-D-glucose uptake assay in with or without fatty acid-induced medium. The Glut 4 translocation components in SDF7-treated L6 myotubes were detected using immunoblotting and quantified by densitometry compared to insulin. Plasma membrane lawn assay and glycogen colorimetry assay were carried out in SDF7- and insulin-treated L6 myotubes in this study.. Here, our data clearly shows that SDF7 possesses glucose uptake properties on L6 myotubes that are dose-dependent, time-dependent and plasma membrane Glut 4 expression-dependent. SDF7 successfully stimulates glucose uptake activity as potent as insulin at a maximum concentration of 50 microg/ml at 480 min on L6 myotubes. Furthermore, SDF7 stimulates increased Glut 4 expression and translocation to plasma membranes at equivalent times. Even in the insulin resistance stage (free fatty acids-induced), SDF7-treated L6 myotubes were found to be more capable at glucose transport than insulin treatment.. Thus, we suggested that Scoparia dulcis has the potential to be categorized as a hypoglycemic medicinal plant based on its good glucose transport properties.

Topics: Animals; Biological Transport; Cell Line; Cell Membrane; Dose-Response Relationship, Drug; Fatty Acids; Glucose; Glucose Transporter Type 4; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Muscle Fibers, Skeletal; Plant Components, Aerial; Plant Extracts; Rats; Scoparia

Protein hepatocyte nuclear factor 4alpha (HNF-4alpha) is atypically activated in the liver of diabetic rodents and contributes to hepatic glucose production. HNF-4alpha and Foxo1 can physically interact with each other and represent an important signal transduction pathway that regulates the synthesis of glucose in the liver. Foxo1 and HNF-4alpha interact with their own binding sites in the phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) promoters, and this binding is required for their effects on those promoters. However, the effect of physical activity on the HNF-4alpha/Foxo1 pathway is currently unknown. Here, we investigate the protein levels of HNF-4alpha and the HNF-4alpha/Foxo1 pathway in the liver of leptin-deficient (ob/ob) and diet-induced obese Swiss (DIO) mice after acute exercise. The ob/ob and DIO mice swam for four 30 min periods, with 5 min rest intervals for a total swimming time of 2h. Eight hours after the acute exercise protocol, the mice were submitted to an insulin tolerance test (ITT) and determination of biochemical and molecular parameters. Acute exercise improved insulin signalling, increasing insulin-stimulated Akt and Foxo1 phosphorylation and decreasing HNF-4alpha protein levels in the liver of DIO and ob/ob mice under fasting conditions. These phenomena were accompanied by a reduction in the expression of gluconeogenesis genes, such as PEPCK and G6Pase. Importantly, the PI3K inhibitor LY292004 reversed the acute effect of exercise on fasting hyperglycaemia, confirming the involvement of the PI3K pathway. The present study shows that exercise acutely improves the action of insulin in the liver of animal models of obesity and diabetes, resulting in increased phosphorylation and nuclear exclusion of Foxo1, and a reduction in the Foxo1/HNF-4alpha pathway. Since nuclear localization and the association of these proteins is involved in the activation of PEPCK and G6Pase, we believe that the regulation of Foxo1 and HNF-4alpha activities are important mechanisms involved in exercise-induced improvement of glucose homeostasis in insulin resistant states.

Topics: Active Transport, Cell Nucleus; Animals; Diabetes Mellitus; Disease Models, Animal; Down-Regulation; Forkhead Box Protein O1; Forkhead Transcription Factors; Glucose; Glucose Clamp Technique; Glucose-6-Phosphatase; Glycogen; Hepatocyte Nuclear Factor 4; Insulin; Insulin Resistance; Liver; Male; Mice; Obesity; Phosphatidylinositol 3-Kinases; Phosphoenolpyruvate Carboxykinase (GTP); Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Physical Exertion; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-akt; Signal Transduction; Swimming

Maternal nicotine (NIC) exposure during lactation leads to overweight, hyperleptinemia, and hypothyroidism in adult rat offspring. In this model, we analyzed adipocyte morphology, glucose homeostasis (serum insulin and adiponectin; liver and muscle glycogen), serum lipid, and the leptin signaling pathway. After birth, osmotic minipumps were implanted in lactating rats, which were divided into the groups NIC (6 mg/kg per day s.c. for 14 days) and control (C, saline). NIC and C offspring were killed at the age of 180 days. Adult NIC rats showed higher total body fat (+10%, P<0.05), visceral fat mass (+12%, P<0.05), and cross-sectional area of adipocytes (epididymal: +12% and inguinal: +43%, P<0.05). Serum lipid profile showed no alteration except for apolipoprotein AI, which was lower. We detected a lower adiponectin:fat mass ratio (-24%, P<0.05) and higher insulinemia (+56%, P<0.05), insulin resistance index (+43%, P<0.05), leptinemia (+113%, P<0.05), and leptin:adiponectin ratio (+98%, P<0.05) in the adult NIC group. These rats presented lower hypothalamic contents of the proteins of the leptin signaling pathway (leptin receptor (OB-R): -61%, janus tyrosine kinase 2: -41%, and p-signal transducer and activator of transcription 3: -56%, P<0.05), but higher suppressor of cytokine signaling 3 (+81%, P<0.05). Therefore, NIC exposure only during lactation programs rats for adipocyte hypertrophy in adult life, as well as for leptin and insulin resistance. Through the effects of NIC, perinatal maternal cigarette smoking may be responsible for the future development of some components of the metabolic syndrome in the offspring.

Topics: Adipocytes; Adiponectin; Animals; Animals, Newborn; Blood Glucose; Cotinine; Drug Resistance; Female; Glycogen; Homeostasis; Hypertrophy; Hypothalamus; Insulin; Insulin Resistance; Lactation; Leptin; Lipids; Liver; Male; Milk; Muscle, Skeletal; Nicotine; Rats; Signal Transduction

Excess energy intake via a palatable low-fat diet (cafeteria diet) is known to induce obesity and glucose intolerance in rats. However, the molecular mechanisms behind this adaptation are not known, and it is also not known whether exercise training can reverse it. Male Wistar rats were assigned to 12-wk intervention groups: chow-fed controls (CON), cafeteria diet (CAF), and cafeteria diet plus swimming exercise during the last 4 wk (CAF(TR)). CAF feeding led to increased body weight (16%, P < 0.01) and increased plasma glucose (P < 0.05) and insulin levels (P < 0.01) during an IVGTT, which was counteracted by training. In the perfused hindlimb, insulin-stimulated glucose transport in red gastrocnemius muscle was completely abolished in CAF and rescued by exercise training. Apart from a tendency toward an approximately 20% reduction in both basal and insulin-stimulated Akt Ser(473) phosphorylation (P = 0.051) in the CAF group, there were no differences in insulin signaling (IR Tyr(1150/1151), PI 3-kinase activity, Akt Thr(308), TBC1D4 Thr(642), GSK3-alpha/beta Ser(21/9)) or changes in AMPKalpha1 or -alpha2, GLUT4, Munc18c, or syntaxin 4 protein expression or in phosphorylation of AMPK Thr(172) among the groups. In conclusion, surplus energy intake of a palatable but low-fat cafeteria diet resulted in obesity and insulin resistance that was rescued by exercise training. Interestingly, insulin resistance was not accompanied by major defects in the insulin-signaling cascade or in altered AMPK expression or phosphorylation. Thus, compared with previous studies of high-fat feeding, where insulin signaling is significantly impaired, the mechanism by which CAF diet induces insulin resistance seems different.

Topics: Animals; Biological Transport, Active; Cyclic AMP-Dependent Protein Kinases; Diet; Energy Intake; Glucose; Glucose Tolerance Test; Glucose Transport Proteins, Facilitative; Glycogen; Hindlimb; Immunoblotting; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Male; Muscle, Skeletal; Oncogene Protein v-akt; Phosphatidylinositol 3-Kinases; Physical Conditioning, Animal; Rats; Rats, Wistar; Regional Blood Flow; Signal Transduction

The present study discusses the efficacy of Aloe emodin-8-O-glycoside (AEG), a plant derived anthroquinone, on alleviating insulin resistance and augmenting glycogen synthesis in L6 myotubes and 3T3L1 adipocytes. Dose-dependent increase in glucose uptake activity (GUA) was observed in both cell lines. Immunoblot analysis revealed an insulin-like glucose transporting mechanism of AEG by activating key markers involved in the insulin signaling cascade such as insulin receptor beta IRbeta, insulin receptor substrate1, 85 phosphatidyl inositol 3' kinase (PI3K) and PKB. Glucose transporter 4 translocation was confirmed by determining the uptake of glucose in the presence of insulin receptor tyrosine kinase and PI3K inhibitors. AEG was found to enhance glycogen synthesis through the inhibition of glycogen synthase kinase 3beta. In conclusion, AEG enhances glucose transport by modulating the proximal and distal markers involved in glucose uptake and its transformation into glycogen.

Topics: Adipocytes; Animals; Biological Transport; Carbohydrate Metabolism; Cell Differentiation; Glucose; Glycogen; Glycogen Synthase Kinases; Glycosides; Insulin; Insulin Resistance; Mice; Muscle Fibers, Skeletal; Phosphatidylinositol 3-Kinases; Receptor, Insulin

Visfatin is a newly characterized protein that is highly expressed in visceral adipose tissue and may play a role in insulin resistance. We investigated the effects of repeated short bouts of high-intensity exercise on plasma visfatin and related metabolic responses.. Six young, physically fit men (22.8 +/- 2.3 years; 78.5 +/- 2.3 kg; and body mass index 22.1 +/- 1.2) performed a single session of a running-based anaerobic sprint exercise (7 sets of 6 x 35 m every 10 s, with 1 min rest between sets). Venous blood samples were collected before, immediately after, and 45 and 90 min after exercise to assess plasma visfatin, insulin, glucose, lactate and glutathione responses.. After adjustment for postexercise changes in plasma volume, the data indicate a significant increase in plasma visfatin (12.5 +/- 2.0 vs. 26.6 +/- 3.9 ng/ml, p < 0.02), insulin (p < 0.05), and glucose (p < 0.002) concentrations, and homeostasis model assessment of insulin resistance (p < 0.02), immediately after the exercise session. At 45 min of recovery, all metabolic measures, with the exception of lactate, had returned to baseline levels.. The elevation in plasma visfatin, together with increased plasma glucose and insulin concentrations immediately after high-intensity exercise, may sensitize tissues for postexercise glucose uptake and glycogen restoration. Our results also support a temporary and early postexercise anorexigenic metabolic state.

Topics: Adult; Blood Glucose; Body Mass Index; Exercise; Exercise Test; Glycogen; Humans; Insulin; Insulin Resistance; Insulin Secretion; Intra-Abdominal Fat; Male; Nicotinamide Phosphoribosyltransferase

Elevated plasma free fatty acid (FFA) levels in obesity may play a pathogenic role in the development of insulin resistance. However, molecular mechanisms linking FFA to insulin resistance remain poorly understood. Oxidative stress acts as a link between FFA and hepatic insulin resistance. NADPH oxidase 3 (NOX3)-derived reactive oxygen species (ROS) may mediate the effect of TNF-α on hepatocytes, in particular the drop in cellular glycogen content. In the present study, we define the critical role of NOX3-derived ROS in insulin resistance in db/db mice and HepG2 cells treated with palmitate. The db/db mice displayed increased serum FFA levels, excess generation of ROS, and up-regulation of NOX3 expression, accompanied by increased lipid accumulation and impaired glycogen content in the liver. Similar results were obtained from palmitate-treated HepG2 cells. The exposure of palmitate elevated ROS production and NOX3 expression and, in turn, increased gluconeogenesis and reduced glycogen content in HepG2 cells. We found that palmitate induced hepatic insulin resistance through JNK and p38(MAPK) pathways, which are rescued by siRNA-mediated NOX3 reduction. In conclusion, our data demonstrate a critical role of NOX3-derived ROS in palmitate-induced insulin resistance in hepatocytes, indicating that NOX3 is the predominant source of palmitate-induced ROS generation and that NOX3-derived ROS may drive palmitate-induced hepatic insulin resistance through JNK and p38(MAPK) pathways.

Topics: Animals; Gene Expression Regulation, Enzymologic; Glycogen; Hep G2 Cells; Hepatocytes; Humans; Insulin Resistance; Liver; MAP Kinase Kinase 4; MAP Kinase Signaling System; Membrane Proteins; Mice; NADPH Oxidases; Obesity; Oxidative Stress; p38 Mitogen-Activated Protein Kinases; Palmitic Acid; Reactive Oxygen Species; Tumor Necrosis Factor-alpha

Topics: Active Transport, Cell Nucleus; Animals; Diabetes Mellitus; Disease Models, Animal; Down-Regulation; Forkhead Box Protein O1; Forkhead Transcription Factors; Glucose; Glucose Clamp Technique; Glucose-6-Phosphatase; Glycogen; Hepatocyte Nuclear Factor 4; Insulin; Insulin Resistance; Liver; Male; Mice; Obesity; Phosphatidylinositol 3-Kinases; Phosphoenolpyruvate Carboxykinase (GTP); Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Physical Exertion; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-akt; Signal Transduction; Swimming

In Drosophila melanogaster (D. melanogaster), neurosecretory insulin-like peptide-producing cells (IPCs), analogous to mammalian pancreatic beta cells are involved in glucose homeostasis. Extending those findings, we have developed in the adult fly an oral glucose tolerance test and demonstrated that IPCs indeed are responsible for executing an acute glucose clearance response. To further develop D. melanogaster as a relevant system for studying age-associated metabolic disorders, we set out to determine the impact of adult-specific partial ablation of IPCs (IPC knockdown) on insulin-like peptide (ILP) action, metabolic outcomes and longevity. Interestingly, while IPC knockdown flies are hyperglycemic and glucose intolerant, these flies remain insulin sensitive as measured by peripheral glucose disposal upon insulin injection and serine phosphorylation of a key insulin-signaling molecule, Akt. Significant increases in stored glycogen and triglyceride levels as well as an elevated level of circulating lipid measured in adult IPC knockdown flies suggest profound modulation in energy metabolism. Additional physiological outcomes measured in those flies include increased resistance to starvation and impaired female fecundity. Finally, increased life span and decreased mortality rates measured in IPC knockdown flies demonstrate that it is possible to modulate ILP action in adult flies to achieve life span extension without insulin resistance. Taken together, we have established and validated an invertebrate genetic system to further investigate insulin action, metabolic homeostasis and regulation of aging regulated by adult IPCs.

Topics: Aging; Animals; Cattle; Drosophila melanogaster; Energy Metabolism; Female; Fertility; Glucose; Glucose Tolerance Test; Glycogen; Homeostasis; Insulin; Insulin Resistance; Lipid Metabolism; Longevity; Neurons; Stress, Physiological

Recent studies showed that germ-free (GF) mice are resistant to obesity when consuming a high-fat, high-carbohydrate Western diet. However, it remains unclear what mechanisms are involved in the antiobesity phenotype and whether GF mice develop insulin resistance and dyslipidemia with high-fat (HF) feeding. In the present study, we compared the metabolic consequences of HF feeding on GF and conventional (conv) C57BL/6J mice. GF mice consumed fewer calories, excreted more fecal lipids, and weighed significantly less than conv mice. GF/HF animals also showed enhanced insulin sensitivity with improved glucose tolerance, reduced fasting and nonfasting insulinemia, and increased phospho-Akt((Ser-473)) in adipose tissue. In association with enhanced insulin sensitivity, GF/HF mice had reduced plasma TNF-α and total serum amyloid A concentrations. Reduced hypercholesterolemia, a moderate accretion of hepatic cholesterol, and an increase in fecal cholesterol excretion suggest an altered cholesterol metabolism in GF/HF mice. Pronounced nucleus SREBP2 proteins and up-regulation of cholesterol biosynthesis genes indicate that enhanced cholesterol biosynthesis contributed to the cholesterol homeostasis in GF/HF mice. Our results demonstrate that fewer calorie consumption and increased lipid excretion contributed to the obesity-resistant phenotype of GF/HF mice and reveal that insulin sensitivity and cholesterol metabolism are metabolic targets influenced by the gut microbiota.

Topics: Animals; Blotting, Western; Body Weight; Cholesterol; Dietary Fats; Germ-Free Life; Glucose Tolerance Test; Glycogen; Insulin Resistance; Lipids; Liver; Male; Mice; Mice, Inbred C57BL; Obesity; Oligonucleotide Array Sequence Analysis; Polymerase Chain Reaction

In view of multi-dimensional activity of plant drugs beneficial to complex disorders like diabetes, the present study has been undertaken to evaluate the effect of aqueous extract of C. peltata roots on serum glucose, lipid profile, insulin, inflammatory marker namely tumour necrosis factor (TNF)-alpha and muscle glycogen in type 2 diabetic rats. Aqueous extract of C. peltata at 40 and 60 mg/kg dose significantly decreased both the fasting and postprandial blood glucose of type 2 diabetic rats; 60 mg/kg dose having more pronounced effect on hyperglycemia. An enhanced insulin levels by the aqueous extract is primary for its glucose and lipid lowering activity. The extract significantly decreased the elevated TNF-alpha in type 2 diabetic rats. The extract at 40 and 60 mg/kg dose increased the glycogen levels in skeletal muscle by 58 and 60% respectively. Improved glycogen in peripheral tissue such as skeletal muscle indicates the ability of plant drug to combat insulin resistance of type 2 diabetes.

Topics: Animals; Blood Glucose; Cyclea; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Drug Evaluation, Preclinical; Female; Glyburide; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Lipids; Male; Medicine, Ayurvedic; Metformin; Mice; Muscle, Skeletal; Phytotherapy; Plant Extracts; Plant Roots; Plants, Medicinal; Random Allocation; Rats; Rats, Wistar; Solvents; Tumor Necrosis Factor-alpha; Water

The contribution of interleukin (IL)-6 signaling in obesity-induced inflammation remains controversial. To specifically define the role of hepatic IL-6 signaling in insulin action and resistance, we have generated mice with hepatocyte-specific IL-6 receptor (IL-6R) alpha deficiency (IL-6Ralpha(L-KO) mice). These animals showed no alterations in body weight and fat content but exhibited a reduction in insulin sensitivity and glucose tolerance. Impaired glucose metabolism originated from attenuated insulin-stimulated glucose transport in skeletal muscle and fat. Surprisingly, hepatic IL-6Ralpha-disruption caused an exaggerated inflammatory response during euglycemic hyperinsulinemic clamp analysis, as revealed by increased expression of IL-6, TNF-alpha, and IL-10, as well as enhanced activation of inflammatory signaling such as phosphorylation of IkappaBalpha. Neutralization of TNF-alpha or ablation of Kupffer cells restored glucose tolerance in IL-6Ralpha(L-KO) mice. Thus, our results reveal an unexpected role for hepatic IL-6 signaling to limit hepatic inflammation and to protect from local and systemic insulin resistance.

Topics: Adiposity; Animals; Energy Metabolism; Glucose; Glycogen; Homeostasis; Humans; Inflammation; Insulin; Insulin Resistance; Interleukin-10; Interleukin-6; Kupffer Cells; Liver; Mice; Mice, Knockout; Receptors, Interleukin-6; Signal Transduction; Tumor Necrosis Factor-alpha

Resistin has been considered to link obesity with type 2 diabetes. Liver glycogen metabolism plays an essential role in maintaining glucose homeostasis, we investigated the effect of resistin on liver glycogen metabolism and attempted to identify its role in initiating insulin resistance and type 2 diabetes. Primary culture of rat hepatocytes was treated by resistin and insulin. Glycogen content was determined by the anthrone-reagent method. Real-time PCR, Western blot and enzymatic activity assay were used to detect key enzymes and genes involved in glucose metabolism. Hepatocytes exposed to resistin, but only in the presence of insulin, show a decrease in insulin-stimulated glycogen content. Decreased insulin receptor expression and GS activity and elevated GP activity was observed after the treatment of hepatocytes with resistin. No significant changes in the expression of the genes for these proteins were observed. These results strongly suggest that resistin effects glycogen metabolism at the protein level, and resistin is highly associated with insulin resistance and type 2 diabetes and is a candidate for the prevention and treatment of type 2 diabetes. Our results should lead to the development of novel strategies for the treatment of type 2 diabetes.

Topics: Animals; Cells, Cultured; Glycogen; Hepatocytes; Insulin Resistance; Rats; Rats, Sprague-Dawley; Recombinant Proteins; Resistin

We evaluated the effects of stress as mimicked by corticosterone (CORT) administration on the uptake of glucose by skeletal muscles (M. fibularis longus) in broiler chickens (Gallus gallus domesticus). The results showed that both chronic (7 d) and short-term (3 h) CORT administration resulted in hyperglycemia and hyperinsulinemia. Plasma level of nitric oxide (NO) and the activity of NO synthase (NOS) were both suppressed by either chronic or acute stress. In vivo CORT treatment could stimulate the in vitro uptake of 2-deoxy-D-[1,2-3H]-glucose (2-DG). Sodium nitroprusside (SNP) administration improved the in vitro uptake of 2-DG in both CORT and control groups. In CORT treatment, however, the stimulating effect of NO on 2-DG uptake was relatively lower compared to control group, whereas it was restored by insulin. Insulin stimulated muscle in vitro 2-DG uptake in either control or CORT group, with the improvement being significantly higher in control chickens. The results indicated that the reduced circulating and muscle level of NO level via the suppression of NOS by corticosterone treatment was involved in the stress-induced insulin resistance. It appears that CORT could suppress the insulin stimulated glucose uptake in skeletal muscle, inducing insulin resistance in broiler chickens. We conclude that NO could stimulate glucose transport in chicken skeletal muscle and that the reduced circulating and muscle level of NO is involved in the insulin resistance induced by corticosterone treatment.

Topics: Animals; Biological Transport; Blood Glucose; Chickens; Corticosterone; Deoxyglucose; Diet; Enzyme Inhibitors; Glycogen; Hyperglycemia; Hyperinsulinism; Insulin; Insulin Resistance; Male; Muscle, Skeletal; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroprusside; Time Factors

Integrin receptor plays key roles in mediating both inside-out and outside-in signaling between cells and the extracellular matrix. We have observed that the tissue-specific loss of the integrin beta1 subunit in striated muscle results in a near complete loss of integrin beta1 subunit protein expression concomitant with a loss of talin and to a lesser extent, a reduction in F-actin content. Muscle-specific integrin beta1-deficient mice had no significant difference in food intake, weight gain, fasting glucose, and insulin levels with their littermate controls. However, dynamic analysis of glucose homeostasis using euglycemichyperinsulinemic clamps demonstrated a 44 and 48% reduction of insulin-stimulated glucose infusion rate and glucose clearance, respectively. The whole body insulin resistance resulted from a specific inhibition of skeletal muscle glucose uptake and glycogen synthesis without any significant effect on the insulin suppression of hepatic glucose output or insulin-stimulated glucose uptake in adipose tissue. The reduction in skeletal muscle insulin responsiveness occurred without any change in GLUT4 protein expression levels but was associated with an impairment of the insulin-stimulated protein kinase B/Akt serine 473 phosphorylation but not threonine 308. The inhibition of insulin-stimulated serine 473 phosphorylation occurred concomitantly with a decrease in integrin-linked kinase expression but with no change in the mTOR.Rictor.LST8 complex (mTORC2). These data demonstrate an in vivo crucial role of integrin beta1 signaling events in mediating cross-talk to that of insulin action.

Topics: Actins; Adipose Tissue; Animals; Body Weight; Carrier Proteins; Eating; Fasting; Glucose; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Integrin beta1; Liver; Mice; Mice, Knockout; Muscle, Striated; Organ Specificity; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor); Proto-Oncogene Proteins c-akt; Rapamycin-Insensitive Companion of mTOR Protein; Signal Transduction; Talin; TOR Serine-Threonine Kinases

Acute exercise, undertaken on the day before an oral fat tolerance test (OFTT), typically reduces postprandial triglycerides (TG) and increases high-density lipoprotein-cholesterol (HDL-C). However, the benefits of acute exercise may be overstated when studies do not account for compensatory changes in dietary intake. The objective of this study was to determine the influence of acute exercise, with and without carbohydrate (CHO) replacement, on postprandial lipid metabolism. Eight recreationally active young men underwent an OFTT on the morning after three experimental conditions: no exercise [control (Con)], prolonged exercise without CHO replacement (Ex-Def) and prolonged exercise with CHO replacement to restore CHO and energy balance (Ex-Bal). The exercise session in Ex-Def and Ex-Bal consisted of 90 min cycle ergometry at 70% peak oxygen uptake (Vo(2peak)) followed by 10 maximal 1-min sprints. CHO replacement was achieved using glucose solutions consumed at 0, 2, and 4 h postexercise. Muscle glycogen was 40 +/- 4% (P < 0.05) and 94 +/- 3% (P = 0.24) of Con values on the morning of the Ex-Def and Ex-Bal OFTT, respectively. Postprandial TG were 40 +/- 14% lower and postprandial HDL-C, free fatty acids, and 3-hydroxybutyrate were higher in Ex-Def compared with Con (P < 0.05). Most importantly, these exercise effects were not evident in Ex-Bal. Postprandial insulin and glucose and the homeostatic model assessment of insulin resistance (HOMA(IR)) were not significantly different across trials. There was no relation between the changes in postprandial TG and muscle glycogen across trials. In conclusion, the influence of acute exhaustive exercise on postprandial lipid metabolism is largely dependent on the associated CHO and energy deficit.

Topics: Administration, Oral; Dietary Carbohydrates; Energy Metabolism; Exercise; Exercise Test; Food Deprivation; Glucose Tolerance Test; Glycogen; Hemodynamics; Humans; Hypertriglyceridemia; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Oxygen Consumption; Postprandial Period; Pulmonary Gas Exchange; Triglycerides

In order to observe the effect of increased serum resistin on glucose metabolism, insulin sensitivity, and hepatic insulin resistance (IR), mice were intravenously injected with recombinant adenovirus carrying the resistin gene (Adv-resistin-EGFP). Changes in hepatic glucose metabolism were observed using the Periodic Acid-Schiff method. Hepatic AMP-activated protein kinase (AMPK) activation was assessed by Western blot analysis, and glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) mRNA expression was determined using real-time RT-PCR. Although no effect on fasting blood glucose was detected, increased fasting insulin levels, decreased glucose tolerance and insulin sensitivity, and reduced hepatic glycogen levels and AMPK activation were seen in the Adv-resistin-EGFP mice. Finally, elevated G6Pase and PEPCK mRNA expression levels were detected upon overexpression of resistin. Resistin may inhibit hepatic AMPK activity, which results in elevated expression of gluconeogenic enzymes thereby affecting glucose metabolism and leading to decreased glycogen storage that contributes to the development of hepatic IR.

Topics: Adenoviridae; AMP-Activated Protein Kinases; Animals; Blood Glucose; Blotting, Western; Enzyme Activation; Fasting; Gene Expression; Genetic Vectors; Glucose; Glucose Intolerance; Glucose-6-Phosphatase; Glycogen; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Phosphoenolpyruvate Carboxykinase (GTP); Recombinant Proteins; Resistin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

Type 2 diabetes is characterized by hyperlipidemia, hyperinsulinemia, and insulin resistance. The aim of this study was to investigate whether acute hyperlipidemia-induced insulin resistance in the presence of hyperinsulinemia was due to defective insulin signaling. Hyperinsulinemia (approximately 300 mU/l) with hyperlipidemia or glycerol (control) was produced in cannulated male Wistar rats for 0.5, 1 h, 3 h, or 5 h. The glucose infusion rate required to maintain euglycemia was significantly reduced by 3 h with lipid infusion and was further reduced after 5 h of infusion, with no difference in plasma insulin levels, indicating development of insulin resistance. Consistent with this finding, in vivo skeletal muscle glucose uptake (31%, P < 0.05) and glycogen synthesis rate (38%, P < 0.02) were significantly reduced after 5 h compared with 3 h of lipid infusion. Despite the development of insulin resistance, there was no difference in the phosphorylation state of multiple insulin-signaling intermediates or muscle diacylglyceride and ceramide content over the same time course. However, there was an increase in cumulative exposure to long-chain acyl-CoA (70%) with lipid infusion. Interestingly, although muscle pyruvate dehydrogenase kinase 4 protein content was decreased in hyperinsulinemic glycerol-infused rats, this decrease was blunted in muscle from hyperinsulinemic lipid-infused rats. Decreased pyruvate dehydrogenase complex activity was also observed in lipid- and insulin-infused animals (43%). Overall, these results suggest that acute reductions in muscle glucose metabolism in rats with hyperlipidemia and hyperinsulinemia are more likely a result of substrate competition than a significant early defect in insulin action or signaling.

Topics: Animals; Blood Glucose; Feedback, Physiological; Glycogen; GTPase-Activating Proteins; Infusions, Intravenous; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Lipids; Male; Metabolic Networks and Pathways; Muscle, Skeletal; Oncogene Protein v-akt; Phosphorylation; Rats; Rats, Wistar

A single exercise bout can increase insulin-independent glucose transport immediately postexercise and insulin-dependent glucose transport (GT) for several hours postexercise. Akt substrate of 160 kDa (AS160) and TBC1D1 are paralog Rab GTPase-activating proteins that have been proposed to contribute to these exercise effects. Previous research demonstrated greater AS160 and Akt threonine phosphorylation in rat skeletal muscle at 3-4 h postexercise concomitant with enhanced insulin-stimulated GT. To further probe whether these signaling events or TBC1D1 phosphorylation were important for the enhanced postexercise insulin-stimulated GT, male Wistar rats were studied using four experimental protocols (2-h swim exercise, differing with regard to timing of muscle sampling and whether food was provided postexercise) that were known to vary in their influence of insulin-independent and insulin-dependent GT postexercise. The results indicated that, in isolated rat epitrochlearis muscle, 1) elevated phosphorylation of AS160 (measured using anti-phospho-Akt substrate, PAS-AS160, and phosphospecific anti-Thr(642)-AS160, pThr(642)-AS160) consistently tracked with elevated insulin-stimulated GT; 2) PAS-TBC1D1 was not different from sedentary values at 3 or 27 h postexercise, when insulin sensitivity was increased; 3) insulin-stimulated Akt activity was not increased postexercise in muscles with increased insulin sensitivity; 4) PAS-TBC1D1 was increased immediately postexercise, when insulin-independent GT was elevated, and reversed at 3 and 27 h postexercise, when insulin-independent GT was also reversed; and 5) there was no significant effect of exercise or insulin on total abundance of AS160, TBC1D1, Akt, or GLUT4 protein with any of the protocols. The results are consistent with increased AS160 phosphorylation (PAS-AS160 or pThr(642)-AS160) but not increased PAS-TBC1D1 or Akt activity, which is important for increased postexercise insulin-stimulated GT in rat skeletal muscle. They also support the idea that increased TBC1D1 phosphorylation may play a role in the insulin-independent increase in GT postexercise.

Topics: Animals; Biological Transport; Glucose; Glycogen; GTPase-Activating Proteins; Insulin Resistance; Male; Muscle, Skeletal; Oncogene Protein v-akt; Phosphorylation; Physical Conditioning, Animal; Protein Kinases; Proteins; Rats; Rats, Wistar; Threonine; Up-Regulation

Resistin is a 12.5-KDa cysteine-rich peptide that has been implicated in the impairment of glucose homeostasis via the AMP-activated protein kinase (AMPK) pathway in a rodent model. However, the role resistin plays in humans is controversial. This study investigated the effect of resistin on glucose metabolism and insulin signaling using human recombinant resistin and small interfering RNA (siRNA) against AMPKalpha2 to treat the human liver HepG2 cells. The mRNA of key genes involved in glucose metabolism and the insulin-signaling pathway were detected by real-time RT-PCR. Phosphorylation levels of Akt and AMPK were measured by western blot. The incorporation of D-[U-(14)C] glucose into glycogen was quantitated by liquid scintillation counting. The results demonstrate that resistin stimulated expressions of glucose-6-phosphatase (G6Pase), phosphoenolypyruvate carboxykinase (PEPCK), and suppressor of cytokine signaling 3 (SOCS-3), repressed the expressions of insulin receptor substrate 2(IRS-2) and glucose transporter 2(GLUT2). In addition, resistin inhibited the insulin-induced phosphorylation of Akt independent of AMPK. In conclusion, our findings suggest that resistin induces insulin resistance in HepG2 cells at least partly via induction of SOCS-3 expression and reduction of Akt phosphorylation through an AMPK-independent mechanism. Resistin also increases glucose production via AMPK-mediated upregulated expression of the genes encoding hepatic gluconeogenic enzymes, G6Pase, and PEPCK.

Topics: AMP-Activated Protein Kinases; Carcinoma, Hepatocellular; Cell Line, Tumor; Gene Expression; Glucaric Acid; Glucose Transporter Type 2; Glucose-6-Phosphatase; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Liver Neoplasms; Phosphoenolpyruvate Carboxykinase (GTP); Phosphorylation; Proto-Oncogene Proteins c-akt; Resistin; RNA, Small Interfering; Signal Transduction; Suppressor of Cytokine Signaling 3 Protein; Suppressor of Cytokine Signaling Proteins

Reduced oxidative capacity of skeletal muscle has been proposed to lead to accumulation of intramyocellular triglyceride (IMTG) and insulin resistance. We have measured mitochondrial respiration before and after a 10% low-calorie-induced weight loss in young obese women to examine the relationship between mitochondrial function, IMTG, and insulin resistance. Nine obese women (age, 32.3 years [SD, 3.0]; body mass index, 33.4 kg/m(2) [SD, 2.6]) completed a 53-day (SE, 3.8) very low calorie diet (VLCD) of 500 to 600 kcal/d without altering physical activity. The target of the intervention was a 10% weight loss; and measurements of mitochondrial respiration, IMTG, respiratory exchange ratio, citrate synthase activity, mitochondrial DNA copy number, plasma insulin, 2-hour oral glucose tolerance test, and free fatty acids were performed before and after weight loss. Mitochondrial respiration was measured in permeabilized muscle fibers using high-resolution respirometry. Average weight loss was 11.5% (P < .05), but the levels of IMTG remained unchanged. Fasting plasma glucose, plasma insulin homeostasis model assessment of insulin resistance, and insulin sensitivity index (composite) obtained during 2-hour oral glucose tolerance test improved significantly. Mitochondrial respiration per milligram tissue decreased by approximately 25% (P < .05), but citrate synthase activity and mitochondrial DNA copy number remained unchanged. Respiratory exchange ratio decreased from 0.87 (SE, 0.01) to 0.79 (SE, 0.02) (P < .05) as a sign of increased whole-body fat oxidation. Markers of insulin sensitivity improved after the very low calorie diet; but mitochondrial function decreased, and IMTG remained unchanged. Our results do not support a direct relationship between mitochondrial function and insulin resistance in young obese women and do not support a direct relationship between IMTG and insulin sensitivity in young obese women during weight loss.

Topics: Adult; Biomarkers; Blood Glucose; Caloric Restriction; Cell Respiration; Citrate (si)-Synthase; DNA, Mitochondrial; Fatty Acids, Nonesterified; Female; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Ion Channels; Mitochondria, Muscle; Mitochondrial Proteins; Muscle, Skeletal; Obesity; Triglycerides; Uncoupling Protein 3; Weight Loss

TRB3 (a mammalian homolog of Drosophila) is emerging as an important player in the regulation of insulin signaling. TRB3 can directly bind to Ser/Thr protein kinase Akt, the major downstream kinase of insulin signaling. Conversely, physical exercise has been linked to improved glucose homeostasis and enhanced insulin sensitivity; however, the molecular mechanisms by which exercise improves glucose homeostasis, particularly in the hepatic tissue, are only partially known. Here, we demonstrate that acute exercise reduces fasting glucose in two models diabetic mice. Western blot analysis showed that 8 h after a swimming protocol, TRB3 expression was reduced in the hepatic tissue from diet-induced obesity (Swiss) and leptin-deficient (ob/ob) mice, when compared with respective control groups at rest. In parallel, there was an increase in insulin responsiveness in the canonical insulin-signaling pathway in hepatic tissue from DIO and ob/ob mice after exercise. In addition, the PEPCK expression was reduced in the liver after the exercise protocol, suggesting that acute exercise diminished hepatic glucose production through insulin-signaling restoration. Thus, these results provide new insights into the mechanism by which physical activity improves glucose homeostasis in type 2 diabetes.

Topics: Animals; Cell Cycle Proteins; Diabetes Mellitus, Experimental; Diet; Fasting; Glucose; Glycogen; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Obese; Phosphoenolpyruvate Carboxykinase (ATP); Physical Conditioning, Animal; Proto-Oncogene Proteins c-akt; Signal Transduction

Free fatty acids (FFA) have been implicated as an important causative link between obesity, insulin resistance, and Type 2 diabetes. However, the underlying mechanisms especially for FFA-mediated hepatic insulin resistance are not fully elucidated. Here, we investigated the impaired sites in insulin signaling pathways and mechanisms of insulin resistance induced by elevated FFA in L02 hepatocytes. L02 cells were cultured in Dulbecco's modified eagle medium containing various concentrations of palmitic acid (PA) for 24 h followed by 10(-7) mol/l insulin stimulation. In some experiments, cells were pre-treated with enzymatic inhibitor Wortmannin (10(-6) mol/l). Glucose levels in medium, cytosolic glycogen contents, and phosphoenolpyruvate carboxykinase (PEPCK) activity were measured. Protein level of insulin receptor substrate (IRS)-2 and phosphorylated Akt were detected by Western blot analysis. L02 cells treated with high levels of PA exhibited increased glucose levels, whereas hepatic glycogen contents were decreased in a dose-dependent manner as compared to the control cells. There was a significant attenuation of IRS- 2 protein expression in the cells cultured with PA, and Wortmannin intervention exhibited different IRS-2 protein level with or without PA treatment. In accordance with the reduced IRS-2 level, the insulin-stimulated phosphorylation of Akt was diminished in the PA-treated cells. Basal PEPCK activity and insulin- regulated PEPCK activity were overstimulated in the cells incubated with PA. These data indicate high levels of FFA can disrupt glucose homeostasis, inflict some defects in insulin signaling, and induce insulin resistance in L02 cells.

Topics: Cell Line; Dose-Response Relationship, Drug; Fatty Acids, Nonesterified; Glucose; Glycogen; Hepatocytes; Homeostasis; Humans; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Oncogene Protein v-akt; Palmitic Acid; Phosphorylation; Protein Serine-Threonine Kinases; Time Factors; Up-Regulation

Women have been shown to have higher muscle triacylglycerol (IMTG) levels than men and could therefore be expected to have lower insulin sensitivity than men, since previous studies have linked high IMTG to decreased insulin sensitivity. Therefore, insulin sensitivity of whole body and leg glucose uptake was studied in 9 women in the follicular phase and 8 men on a controlled diet and matched for maximal oxygen uptake per kilogram of lean body mass and habitual activity level. A 47% higher (P < 0.05) IMTG level was found in women than in men, and, at the same time, women also displayed 22% higher whole body insulin sensitivity (P < 0.05) and 29% higher insulin-stimulated leg glucose uptake (P = 0.05) during an euglycemic-hyperinsulinemic (approximately 70 microU/ml) clamp compared with matched male subjects. The higher insulin sensitivity in women could not be explained by higher expression of muscle glucose transporter GLUT4, insulin receptor, or Akt expression or by the ability of insulin to stimulate Akt Thr(308) or Akt Ser(473) phosphorylation. However, a 30% higher (P < 0.05) capillary density and 31% more type 1 muscle fiber expressed per area in the vastus lateralis muscle were noted in women than in matched men. It is concluded that despite 47% higher IMTG levels in women in the follicular phase, whole body as well as leg insulin sensitivity are higher than in matched men. This was not explained by sex differences in proximal insulin signaling in women. In women, it seems that a high capillary density and type 1 muscle fiber expression may be important for insulin action.

Topics: Adenosine Triphosphatases; Adult; Anaerobic Threshold; Blotting, Western; Carbon Dioxide; Citrate (si)-Synthase; Diet; Female; Glucose; Glucose Clamp Technique; Glycogen; Hormones; Humans; Insulin; Insulin Resistance; Leg; Male; Muscle Fibers, Skeletal; Muscle Proteins; Muscle, Skeletal; Oxygen; Regional Blood Flow; Signal Transduction; Spirometry; Triglycerides; Young Adult

Dietary trans-fatty acids are associated with increased risk of cardiovascular disease and have been implicated in the incidence of obesity and type 2 diabetes mellitus (T2DM). It is established that high-fat saturated diets, relative to low-fat diets, induce adiposity and whole-body insulin resistance. Here, we test the hypothesis that markers of an obese, prediabetic state (fatty liver, visceral fat accumulation, insulin resistance) are also worsened with provision of a low-fat diet containing elaidic acid (18:1t), the predominant trans-fatty acid isomer found in the human food supply. Male 8-week-old Sprague-Dawley rats were fed a 10% trans-fatty acid enriched (LF-trans) diet for 8 weeks. At baseline, 3 and 6 weeks, in vivo magnetic resonance spectroscopy (1H-MR) assessed intramyocellular lipid (IMCL) and intrahepatic lipid (IHL) content. Euglycemic-hyperinsulinemic clamps (week 8) determined whole-body and tissue-specific insulin sensitivity followed by high-resolution ex vivo 1H-NMR to assess tissue biochemistry. Rats fed the LF-trans diet were in positive energy balance, largely explained by increased energy intake, and showed significantly increased visceral fat and liver lipid accumulation relative to the low-fat control diet. Net glycogen synthesis was also increased in the LF-trans group. A reduction in glucose disposal, independent of IMCL accumulation was observed in rats fed the LF-trans diet, whereas in rats fed a 45% saturated fat (HF-sat) diet, impaired glucose disposal corresponded to increased IMCLTA. Neither diet induced an increase in IMCLsoleus. These findings imply that trans-fatty acids may alter nutrient handling in liver, adipose tissue, and skeletal muscle and that the mechanism by which trans-fatty acids induce insulin resistance differs from diets enriched with saturated fats.

Topics: Adiposity; Animals; Blood Glucose; Diet, Fat-Restricted; Energy Intake; Energy Metabolism; Glucose Clamp Technique; Glycogen; Hyperphagia; Insulin; Insulin Resistance; Intra-Abdominal Fat; Liver; Magnetic Resonance Spectroscopy; Male; Metabolic Syndrome; Muscle, Skeletal; Obesity; Oleic Acid; Oleic Acids; Prediabetic State; Rats; Rats, Sprague-Dawley; Time Factors; Trans Fatty Acids

Moutan Cortex is a well-known herb in traditional Korean, Chinese, and Japanese anti-diabetic formulae. In the current study, we investigated the metabolic effects of isolated triterpenes (1-7) in HepG2 cells under high glucose conditions. These compounds remakably stimulated AMP-activated protein kinase (AMPK), GSK-3beta, and ACC phosphorylation. The compounds also increased glucose uptake and enhanced glycogen synthesis. Among these, compound 1 displayed the greatest potential anti-diabetic activity though the AMPK activation pathway. Compound 1 significantly increased the levels of phospho-AMPK, phospho-ACC, and phospho-GSK-3beta and stimulated glucose uptake and glycogen synthesis in a dose-dependent manner. In conclusion, our results suggest that these compounds, especially compound 1, may have beneficial roles in glucose metabolism via the AMPK pathway.

Topics: AMP-Activated Protein Kinases; Cell Line, Tumor; Diabetes Mellitus, Type 2; Drugs, Chinese Herbal; Glucose; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Hypoglycemic Agents; Insulin Resistance; Paeonia; Phosphorylation; Terpenes; Triterpenes

Many studies have demonstrated that DNA damage may be associated with type 2 diabetes mellitus (T2DM) and its complications. The goal of this study was to evaluate the effects of the potential relationship between fat (thermolyzed) intake, glucose dyshomeostasis and DNA injury in rats. Biochemical parameters related to glucose metabolism (i.e., blood glucose levels, insulin tolerance tests, glucose tolerance tests and fat cell glucose oxidation) and general health parameters (i.e., body weight, retroperitoneal and epididymal adipose tissue) were evaluated in rats after a 12-month treatment with either a high fat or a high thermolyzed fat diet. The high fat diet (HFD) and high fat thermolyzed diet (HFTD) showed increased body weight and impaired insulin sensitivity at the studied time-points in insulin tolerance test (ITT) and glucose tolerance test (GTT). Interestingly, only animals subjected to the HFTD diet showed decreased epididymal fat cell glucose oxidation. We show which high fat diets have the capacity to reduce glycogen synthesis by direct and indirect pathways. HFTD promoted an increase in lipid peroxidation in the liver, demonstrating significant damage in lipids in relation to other groups. Blood and hippocampus DNA damage was significantly higher in animals subjected to HFDs, and the highest damage was observed in animals from the HFTD group. Striatum DNA damage was significantly higher in animals subjected to HFDs, compared with the control group. These results show a positive correlation between high fat diet, glucose dyshomeostasis, oxidative stress and DNA damage.

Topics: Adipose Tissue; Animals; Dietary Fats; DNA Damage; Glucose; Glucose Tolerance Test; Glycogen; Hippocampus; Insulin Resistance; Lipid Peroxidation; Liver; Male; Neostriatum; Oxidation-Reduction; Protein Carbonylation; Rats; Rats, Wistar; Temperature

Nutrition during pregnancy and lactation can program an offspring's metabolism with regard to glucose and lipid homeostasis. A suboptimal environment during fetal, neonatal and infant development is associated with impaired glucose tolerance, type 2 diabetes and insulin resistance in later adult life. However, studies on the effects of a low protein diet imposed from the beginning of gestation until adulthood are scarce. This study's objective was to investigate the effects of a low protein diet imposed from the gestational period until 4 months of age on the parameters of glucose tolerance and insulin responsiveness in Wistar rats. The rats were divided into a low protein diet group and a control group and received a diet with either 7% or 25% protein, respectively. After birth, the rats received the same diet as their mothers, until 4 months of age. In the low protein diet group it was observed that: (i) the hepatic glycogen concentration and hepatic glycogen synthesis from glycerol were significantly greater than in the control group; (ii) the disposal of 2-deoxyglucose in soleum skeletal muscle slices was 29.8% higher than in the control group; (iii) there was both a higher glucose tolerance in the glucose tolerance test; and (iv) a higher insulin responsiveness in than in the control group. The results suggest that the low protein diet animals show higher glucose tolerance and insulin responsiveness relative to normally nourished rats. These findings were supported by the higher hepatic glycogen synthesis and the higher disposal of 2-deoxyglucose in soleum skeletal muscle found in the low protein diet rats.

Topics: Aging; Animals; Deoxyglucose; Dietary Proteins; Female; Gestational Age; Glucose Tolerance Test; Glycerol; Glycogen; Insulin Resistance; Lactation; Liver; Male; Muscle, Skeletal; Pregnancy; Pregnancy Complications; Protein Deficiency; Rats; Rats, Wistar

In humans, antidiabetics thiazolidinediones (TZDs) upregulate stearoyl-CoA desaturase 1 (SCD1) gene in adipose tissue and increase plasma levels of SCD1 product palmitoleate, known to enhance muscle insulin sensitivity. Involvement of other tissues in the beneficial effects of TZDs on plasma lipid profile is unclear. In our previous study in mice, in which lipogenesis was suppressed by corn oil-based high-fat (cHF) diet, TZD rosiglitazone induced hepatic Scd1 expression, while liver triacylglycerol content increased, VLDL-triacylglycerol production decreased and plasma lipid profile and whole-body glycemic control improved. Aim of this study was to characterise contribution of liver to changes of plasma lipid profile in response to a 8-week-treatment by rosiglitazone in the cHF diet-fed mice. Rosiglitazone (10 mg/kg diet) upregulated expression of Scd1 in various tissues, with a stronger effect in liver as compared with adipose tissue or skeletal muscle. Rosiglitazone increased content of monounsaturated fatty acids in liver, adipose tissue and plasma, with palmitoleate being the most up-regulated fatty acid. In the liver, enhancement of SCD1 activity and specific enrichment of cholesteryl esters and phosphatidyl cholines with palmitoleate and vaccenate was found, while strong correlations between changes of various liver lipid fractions and total plasma lipids were observed (r=0.74-0.88). Insulin-stimulated glycogen synthesis was increased by rosiglitazone, with a stronger effect in muscle than in liver.. changes in plasma lipid profile favouring monounsaturated fatty acids, mainly palmitoleate, due to the upregulation of Scd1 and enhancement of SCD1 activity in the liver, could be involved in the insulin-sensitizing effects of TZDs.

Topics: Adipose Tissue, White; Animals; Corn Oil; Dietary Fats; Fatty Acids; Fatty Acids, Monounsaturated; Glucose Clamp Technique; Glycogen; Hypoglycemic Agents; Insulin Resistance; Lipids; Liver; Mice; Muscle, Skeletal; Oleic Acids; Organ Specificity; Random Allocation; Rosiglitazone; Stearoyl-CoA Desaturase; Thiazolidinediones; Up-Regulation

Type 2 diabetes is preceded by the presence of skeletal muscle insulin resistance, and drugs that increase insulin sensitivity in skeletal muscle prevent the disease. S15511 is an original compound with demonstrated effects on insulin sensitivity in animal models of insulin resistance. However, the mechanisms behind the insulin-sensitizing effect of S15511 are unknown. The aim of our study was to explore whether S15511 improves insulin sensitivity in skeletal muscles. Insulin sensitivity was assessed in skeletal muscles from S15511-treated rats by measuring intracellular insulin-signaling activity and insulin-stimulated glucose transport in isolated muscles. In addition, GLUT4 expression and glycogen levels were assessed after treatment. S15511 treatment was associated with an increase in insulin-stimulated glucose transport in type IIb fibers, while type I fibers were unaffected. The enhanced glucose transport was mirrored by a fiber type-specific increase in GLUT4 expression, while no improvement in insulin-signaling activity was observed. S15511 is a novel insulin sensitizer that is capable of improving glucose homeostasis in nondiabetic rats. The compound enhances skeletal muscle insulin sensitivity and specifically targets type IIb muscle fibers by increasing GLUT4 expression. Together these data show S15511 to be a potentially promising new drug in the treatment and prevention of type 2 diabetes.

Topics: 3-O-Methylglucose; Adaptor Proteins, Signal Transducing; Adipose Tissue; Animals; Biological Transport, Active; Body Weight; Fluorenes; Glucose; Glucose Transporter Type 4; Glycogen; Hypoglycemic Agents; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Male; Muscle, Skeletal; Phosphatidylinositol 3-Kinases; Phosphorylation; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; Signal Transduction

The present study was undertaken to determine the effect of Yi-Qi-Yang-Yin-Ye (Y-Q-Y-Y-Y), a compound of Traditional Chinese Herbal Medicine, on insulin resistance (IR) in the diet-induced obese rat model induced by intravenous injection with a low dose of streptozotocin and fed a high fat and high caloric diet. Y-Q-Y-Y-Y (2, 4, 8 g/kg) was administered via gavage daily for 4 weeks. The results showed that Y-Q-Y-Y-Y treatment decreased the levels of body weight, total cholesterol (TC), triglycerides (TG), low density lipoprotein-cholesterol (LDL-C), free fatty acid (FFA), insulin (INS) and fast blood glucose (FBG) and increased the level of high density lipoprotein-cholesterol (HDL-C) in the diet-induced obese rats. Glucose tolerance was improved in the diet-induced obese rats treated with Y-Q-Y-Y-Y as well as GIR (glucose infusion rate) in the hyperinsulinemic euglycemic clamp experiment compared to the model control rats (p < 0.01). Moreover, treatment with Y-Q-Y-Y-Y up-regulated glycogen contents in both liver and skeletal muscle and increased insulin receptor amounts on the erythrocytes surface as assessed by using (125)I-labeled auto-antibodies against insulin receptors. Taken together, our data suggested that Yi-Qi-Yang-Yin-Ye ameliorates insulin resistance in the diet-induced obese rats.

Topics: Animals; Blood Glucose; Body Weight; Disease Models, Animal; Drugs, Chinese Herbal; Energy Intake; Glycogen; Insulin; Insulin Resistance; Lipid Metabolism; Liver; Medicine, Chinese Traditional; Muscle, Skeletal; Obesity; Rats; Rats, Wistar; Receptor, Insulin

We determined whether muscle AMP-activated protein kinase (AMPK) has a role in the development of insulin resistance.. Muscle-specific transgenic mice expressing an inactive form of the AMPK alpha2 catalytic subunit (alpha2i TG) and their wild-type littermates were fed either a high-fat (60% kcal fat) or a control (10% kcal fat) diet for 30 weeks.. Compared with wild-type mice, glucose tolerance in alpha2i TG mice was slightly impaired on the control diet and significantly impaired on the high-fat diet. To determine whether the whole-body glucose intolerance was associated with impaired insulin sensitivity in skeletal muscle, glucose transport in response to submaximal insulin (450 microU/ml) was measured in isolated soleus muscles. On the control diet, insulin-stimulated glucose transport was reduced by approximately 50% in alpha2i TG mice compared with wild-type mice. High-fat feeding partially decreased insulin-stimulated glucose transport in wild-type mice, while high-fat feeding resulted in a full blunting of insulin-stimulated glucose transport in the alpha2i TG mice. High-fat feeding in alpha2i TG mice was accompanied by decreased expression of insulin signaling proteins in gastrocnemius muscle.. The lack of skeletal muscle AMPK alpha2 activity exacerbates the development of glucose intolerance and insulin resistance caused by high-fat feeding and supports the thesis that AMPK alpha2 is an important target for the prevention/amelioration of skeletal muscle insulin resistance through lifestyle (exercise) and pharmacologic (e.g., metformin) treatments.

Topics: AMP-Activated Protein Kinases; Animals; Blood Glucose; Body Weight; Dietary Fats; Fatty Acids, Nonesterified; Glucose; Glucose Tolerance Test; Glycogen; Immunoblotting; Insulin; Insulin Resistance; Mice; Mice, Transgenic; Muscles; Triglycerides

Glycogen is an immediate source of glucose for cardiac tissue to maintain its metabolic homeostasis. However, its excess brings about cardiac structural and physiological impairments. Previously, we have demonstrated that in hearts from dexamethasone (Dex)-treated animals, glycogen accumulation was enhanced. We examined the influence of 5'-AMP-activated protein kinase (AMPK) on glucose entry and glycogen synthase as a means of regulating the accumulation of this stored polysaccharide. After Dex, cardiac tissue had a limited contribution toward the development of whole body insulin resistance. Measurement of glucose transporter 4 (GLUT4) at the plasma membrane revealed an excess presence of this transporter protein at this location. Interestingly, this was accompanied by an increase in GLUT4 in the intracellular membrane fraction, an effect that was well correlated with increased GLUT4 mRNA. Both total and phosphorylated AMPK increased after Dex. Immunoprecipitation of Akt substrate of 160 kDa (AS160) followed by Western blot analysis demonstrated no change in Akt phosphorylation at Ser(473) and Thr(308) in Dex-treated hearts. However, there was a significant increase in AMPK phosphorylation at Thr(172), which correlated well with AS160 phosphorylation. In Dex-treated hearts, there was a considerable reduction in the phosphorylation of glycogen synthase, whereas glycogen synthase kinase-3-beta phosphorylation was augmented. Our data suggest that AMPK-mediated glucose entry combined with the activation of glycogen synthase and a reduction in glucose oxidation (Qi et al., Diabetes 53: 1790-1797, 2004) act together to promote glycogen storage. Should these effects persist chronically in the heart, they may explain the increased morbidity and mortality observed with long-term excesses in endogenous or exogenous glucocorticoids.

Topics: AMP-Activated Protein Kinases; Animals; Carbohydrate Metabolism; Dexamethasone; Glucose Transporter Type 4; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Insulin Resistance; Male; Myocardium; Phosphorylation; Protein Transport; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; RNA, Messenger; Time Factors

Advanced glycation end products (AGEs) could be implicated in insulin resistance. However, the molecular mechanisms underlying this are not fully understood. Since pigment epithelium-derived factor (PEDF) blocks the AGE-signaling pathways, we examined here whether and how PEDF improves insulin resistance in AGE-exposed hepatoma cells, Hep3B cells. Proteins were extracted from Hep3B cells, immunoprecipitated with or without insulin receptor substrate-1 (IRS-1) antibodies, and subjected to Western blot analysis. Glycogen synthesis was measured using [ (14)C]-d-glucose. AGE induced Rac-1 activation and increased phosphorylation of IRS-1 at serine-307 residues, JNK, c-JUN, and IkappaB kinase in association with decreased IkappaB levels in Hep3B cells. PEDF or overexpression of dominant negative Rac-1 blocked these effects of AGE on Hep3B cells. Further, AGEs decreased tyrosine phosphorylation of IRS-1, and subsequently reduced the association of p85 subunit of phosphatidylinositol 3-kinase with IRS-1 and glycogen synthesis in insulin-exposed Hep3B cells, all of which were inhibited by PEDF. Our present study suggests that PEDF could improve the AGE-elicited insulin resistance in Hep3B cells by inhibiting JNK- and IkappaB kinase-dependent serine phosphorylation of IRS-1 via suppression of Rac-1 activation. PEDF may play a protective role against hepatic insulin resistance in diabetes.

Topics: Adaptor Proteins, Signal Transducing; Cell Line, Tumor; Enzyme Activation; Eye Proteins; Genes, Dominant; Glycation End Products, Advanced; Glycogen; Hepatocytes; Humans; I-kappa B Kinase; I-kappa B Proteins; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; JNK Mitogen-Activated Protein Kinases; Models, Biological; Nerve Growth Factors; NF-KappaB Inhibitor alpha; Phosphoproteins; Phosphotyrosine; rac1 GTP-Binding Protein; Serpins; Signal Transduction

We have demonstrated previously in insulin-sensitive skeletal muscle that lithium, an alkali metal and non-selective inhibitor of glycogen synthase kinase-3 (GSK-3), activates glucose transport by engaging the stress-activated p38 mitogen-activated protein kinase (p38 MAPK). However, it is presently unknown whether this same mechanism underlies lithium action on the glucose transport system in insulin-resistant skeletal muscle. We therefore assessed the effects of lithium on basal and insulin-stimulated glucose transport, glycogen synthesis, insulin signalling (insulin receptor (IR), Akt, and GSK-3), and p38 MAPK in soleus muscle from female obese Zucker rats. Lithium (10 mM LiCl) increased basal glucose transport by 49% (p < 0.05) and net glycogen synthesis by 2.4-fold (p < 0.05). In the absence of insulin, lithium did not induce IR tyrosine phosphorylation, but did enhance (p < 0.05) Akt ser(473) phosphorylation (40%) and GSK-3beta ser(9) phosphorylation (88%). Lithium potentiated (p < 0.05) the stimulatory effects of insulin on glucose transport (74%), glycogen synthesis (2.4-fold), Akt ser(473) phosphorylation (39%), and GSK-3beta ser(9) phosphorylation (36%), and elicited robust increases (p < 0.05) in p38 MAPK phosphorylation both in the absence (100%) or presence (88%) of insulin. The selective p38 MAPK inhibitor A304000 (10 muM) completely blocked basal activation of glucose transport by lithium, and significantly reduced (42%, p < 0.05) the lithium-induced enhancement of insulin-stimulated glucose transport in insulin-resistant muscle. These results indicate that lithium enhances both basal and insulin-stimulated glucose transport and glycogen synthesis in insulin-resistant skeletal muscle of female obese Zucker rats, and that these lithium-dependent effects are associated with enhanced Akt and GSK-3beta serine phosphorylation. As in insulin-sensitive muscle, the lithium-induced activation of glucose transport in insulin-resistant skeletal muscle is dependent on the engagement of p38 MAPK.

Topics: Animals; Cattle; Enzyme Activation; Female; Glucose; Glycogen; Insulin; Insulin Resistance; Lithium; Male; Muscle, Skeletal; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Rats; Rats, Zucker; Signal Transduction

Oxidative stress can contribute to the multifactorial etiology of whole body and skeletal muscle insulin resistance. No investigation has directly assessed the effect of an in vitro oxidant stress on insulin action in intact mammalian skeletal muscle. Therefore, the purpose of the present study was to characterize the molecular actions of a low-grade oxidant stress (H(2)O(2)) on insulin signaling and glucose transport in isolated skeletal muscle of lean Zucker rats. Soleus strips were incubated in 8 mM glucose for 2 h in the absence or presence of 100 mU/ml glucose oxidase, which produces H(2)O(2) at approximately 90 microM. By itself, H(2)O(2) significantly (P < 0.05) activated basal glucose transport activity, net glycogen synthesis, and glycogen synthase activity and increased phosphorylation of insulin receptor (Tyr), Akt (Ser(473)), and GSK-3beta (Ser(9)). In contrast, this oxidant stress significantly inhibited the expected insulin-mediated enhancements in glucose transport, glycogen synthesis, and these signaling factors and allowed GSK-3beta to retain a more active form. In the presence of CT-98014, a selective GSK-3 inhibitor, the ability of insulin to stimulate glucose transport and glycogen synthesis during exposure to this oxidant stress was enhanced by 20% and 39% (P < 0.05), respectively, and insulin stimulation of the phosphorylation of insulin receptor, Akt, and GSK-3 was significantly increased by 36-58% (P < 0.05). These results indicate that an oxidant stress can directly and rapidly induce substantial insulin resistance of skeletal muscle insulin signaling, glucose transport, and glycogen synthesis. Moreover, a small, but significant, portion of this oxidative stress-induced insulin resistance is associated with a reduced insulin-mediated suppression of the active form of GSK-3beta.

Topics: Animals; Biological Transport; Female; Glucose; Glycogen; Glycogen Synthase; Glycogen Synthase Kinase 3; Hydrogen Peroxide; Insulin; Insulin Resistance; Muscle, Skeletal; Oxidative Stress; Phosphorylation; Rats; Rats, Zucker; Receptor, Insulin

The aim of the present study was to observe the effects of resistin on insulin sensitivity and glucose output in rat-derived hepatocytes.. The rat hepatoma cell line H4IIE was cultured and stimulated with resistin; supernant glucose and glycogen content were detected. The insulin receptor substrate (IRS)-1 and IRS-2, protein kinase B/Akt, glycogen synthase kinase-3beta(GSK-3 beta), the suppressor of cytokine signaling 3 (SOCS-3) protein content, as well as the phosphorylation status were assessed by Western blotting. Specific antisense oligodeoxynucleotides directed against SOCS-3 were used to knockdown SOCS-3.. Resistin induced insulin resistance, but did not affect glucose output in rat hepatoma cell line H4IIE. Resistin attenuated multiple effects of insulin, including insulin-stimulated glycogen synthesis and phosphorylation of IRS, protein kinase B/Akt, as well as GSK-3beta. Resistin treatment markedly induced the gene and protein expression of SOCS-3, a known inhibitor of insulin signaling. Furthermore, a specific antisense oligodeoxynucleotide directed against SOCS-3 treatment prevented resistin from antagonizing insulin action.. The major function of resistin on liver is to induce insulin resistance. SOCS-3 induction may contribute to the resistin-mediated inhibition of insulin signaling in H4IIE hepatocytes.

Topics: Animals; Cell Line; Glucose; Glycogen; Hepatocytes; Insulin Antagonists; Insulin Receptor Substrate Proteins; Insulin Resistance; Oligoribonucleotides, Antisense; Rats; Resistin; RNA; Suppressor of Cytokine Signaling 3 Protein; Suppressor of Cytokine Signaling Proteins

Topics: Animals; Cardiomyopathies; Codon, Nonsense; Diabetes Mellitus, Type 2; Exercise; Frameshift Mutation; Gene Frequency; Glycogen; Glycogen Phosphorylase; Glycogen Synthase; Heart; Humans; Infant, Newborn; Insulin; Insulin Resistance; Mice; Muscle, Skeletal; Myocardium; Organ Specificity; Phosphoprotein Phosphatases; United Kingdom; White People

The induction of peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), a key regulator of mitochondriogenesis, is well-established under multiple physical exercise regimens, including, endurance, resistance, and sprint training. We wanted to determine if increased expression of PGC-1alpha in muscle is sufficient to improve performance during exercise in vivo. We demonstrate that muscle-specific expression of PGC-1alpha improves the performance during voluntary as well as forced exercise challenges. Additionally, PGC-1alpha transgenic mice exhibit an enhanced performance during a peak oxygen uptake exercise test, demonstrating an increased peak oxidative capacity, or whole body oxygen uptake. This increased ability to perform in multiple exercise paradigms is supported by enhanced mitochondrial function as suggested by increased mitochondrial gene expression, mitochondrial DNA, and mitochondrial enzyme activity. Thus this study demonstrates that upregulation of PGC-1alpha in muscle in vivo is sufficient to greatly improve exercise performance under various exercise paradigms as well as increase peak oxygen uptake.

Topics: Anaerobic Threshold; Animals; Citrate (si)-Synthase; DNA, Mitochondrial; Glucose Intolerance; Glycogen; Insulin Resistance; Male; Mice; Muscle, Skeletal; Oxygen Consumption; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Physical Conditioning, Animal; PPAR gamma; Pulmonary Gas Exchange; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Running; Trans-Activators; Transcription Factors

Previous studies suggest that nitric oxide (NO) may modulate insulin-induced uptake of glucose in insulin-sensitive tissues. Asymmetrical dimethylarginine (ADMA) is an endogenous inhibitor of NO synthase (NOS). We hypothesized that a reduction in endogenous ADMA would increase NO synthesis and thereby enhance insulin sensitivity.. To test this hypothesis we used a transgenic mouse in which we overexpressed human dimethylarginine dimethylaminohydrolase (DDAH-I). The DDAH-I mice had lower plasma ADMA at all ages (22 to 70 wk) by comparison to wild-type (WT) littermates. With a glucose challenge, WT mice showed a prompt increase in ADMA, whereas DDAH-I mice had a blunted response. Furthermore, DDAH-I mice had a blunted increase in plasma insulin and glucose levels after glucose challenge, with a 50% reduction in the insulin resistance index, consistent with enhanced sensitivity to insulin. In liver, we observed an increased Akt phosphorylation in the DDAH-I mice after i.p. glucose challenge. Incubation of skeletal muscle from WT mice ex vivo with ADMA (2 mumol/L) markedly suppressed insulin-induced glycogen synthesis in fast-twitch but not slow-twitch muscle.. These findings suggest that the endogenous NOS inhibitor ADMA reduces insulin sensitivity, consistent with previous observations that NO plays a role in insulin sensitivity.

Topics: Amidohydrolases; Animals; Arginine; Female; Gene Expression; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Muscle, Skeletal; Nitric Oxide; Recombinant Proteins

Uteroplacental insufficiency has been shown to impair insulin action and glucose homeostasis in adult offspring and may act in part via altered mitochondrial biogenesis and lipid balance in skeletal muscle. Bilateral uterine vessel ligation to induce uteroplacental insufficiency in offspring (Restricted) or sham surgery was performed on day 18 of gestation in rats. To match the litter size of Restricted offspring, a separate cohort of sham litters had litter size reduced to five at birth (Reduced Litter), which also restricted postnatal growth. Remaining litters from sham mothers were unaltered (Control). Offspring were studied at 6 mo of age. In males, both Restricted and Reduced Litter offspring had reduced gastrocnemius PPARgamma coactivator-1alpha (PGC-1alpha) mRNA and protein, and mitochondrial transcription factor A (mtTFA) and cytochrome oxidase (COX) III mRNA (P < 0.05), whereas only Restricted had reduced skeletal muscle COX IV mRNA and protein and glycogen (P < 0.05), despite unaltered glucose tolerance, homeostasis model assessment (HOMA) and intramuscular triglycerides. In females, only gastrocnemius mtTFA mRNA was lower in Reduced Litter offspring (P < 0.05). Furthermore, glucose tolerance was not altered in any female offspring, although HOMA and intramuscular triglycerides increased in Restricted offspring (P < 0.05). It is concluded that restriction of growth due to uteroplacental insufficiency alters skeletal muscle mitochondrial biogenesis and metabolic characteristics, such as glycogen and lipid levels, in a sex-specific manner in the adult rat in the absence of impaired glucose tolerance. Furthermore, an adverse postnatal environment induced by reducing litter size also restricts growth and alters skeletal muscle mitochondrial biogenesis and metabolic characteristics in the adult rat.

Topics: Animals; Blood Glucose; Blotting, Western; DNA-Binding Proteins; Electron Transport Complex IV; Fatty Acids, Nonesterified; Female; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Litter Size; Male; Mitochondria, Muscle; Mitochondrial Proteins; Muscle, Skeletal; Organ Size; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Placental Insufficiency; Pregnancy; Rats; Rats, Inbred WKY; RNA; RNA-Binding Proteins; Sex Characteristics; Transcription Factors; Triglycerides

Thiazolidinediones are increasingly used drugs for the treatment of Type 2 diabetes. The individual response to thiazolidinedione therapy, ranging from the variable degree of metabolic improvement to harmful side-effects, is empirical, yet the underlying mechanisms remain elusive. In order to assess the pharmacogenomic component of thiazolidinediones' metabolic action, we compared the effect of rosiglitazone in two genetically defined models of metabolic syndrome, polydactylous (PD) and BN.SHR4 inbred rat strains, with their insulin-sensitive, normolipidemic counterpart, the Brown Norway (BN) rat.. 5-month-old male rats were fed a high-fat diet for 4 weeks, and the experimental groups received rosiglitazone (0.4 mg/100 g body weight) during the last 2 weeks of high-fat diet feeding. We assessed metabolic and morphometric profiles, oxidative stress parameters and gene expression in white adipose tissue.. In many followed parameters, we observed genetic background-specific effects of rosiglitazone administration. The mass and the sensitivity of visceral adipose tissue to insulin-stimulated lipogenesis increased with rosiglitazone treatment only in PD, correlating with a PD-specific significant increase in expression of prostaglandin D2 synthase. The glucose tolerance was enhanced in all strains, although fasting plasma glucose was increased by rosiglitazone in BN and BN.SHR4. Among the markers of lipid peroxidation, we observed the rosiglitazone-driven increase of plasma-conjugated dienes only in BN.SHR4. The genes with genotype-specific expression change included ADAM metallopeptidase domain 7, aquaporin 9, carnitine palmitoyltransferase 1B, caveolin 1, catechol-O-methyl transferase, leptin and prostaglandin D2 synthase 2.. Rosiglitazone's effects on lipid deposition and insulin sensitivity of peripheral tissues are largely dependent on the genetic background it acts upon.

Topics: Adipose Tissue; Adipose Tissue, White; Animals; Cholesterol, Dietary; Diet; Dietary Carbohydrates; Fatty Acids; Gene Expression; Glucose; Glucose Tolerance Test; Glycogen; Hypoglycemic Agents; Insulin Resistance; Lipids; Liver; Metabolic Syndrome; Microarray Analysis; Oxidation-Reduction; Oxidative Stress; Rats; Rats, Inbred BN; Rats, Inbred Strains; RNA; Rosiglitazone; Sucrose; Thiazolidinediones

Recent studies have identified the involvement of inhibitor IkappaB kinase (IKK) in the pathogenesis of insulin resistance. To investigate the mechanism involved, we examined the role of nuclear factor kappaB (NF-kappaB), the distal target of IKK, in hepatic glucose metabolism.. To inhibit NF-kappaB activity, db/db mice were infected with adenovirus expressing the IkappaBalpha super-repressor.. The IkappaBalpha super-repressor adenovirus infection caused a moderate reduction of NF-kappaB activity in liver. The treatment was associated with improved glucose tolerance, reduction in the serum insulin level, and increased hepatic triacylglycerol and glycogen contents, but had no effect on insulin-stimulated phosphorylation of Akt. On the other hand, quantification of mRNA in the liver revealed marked reduction of expression of gluconeogenic genes, such as those encoding phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase, concurrent with reduced expression of gene encoding peroxisome proliferator-activated receptor gamma coactivator-1alpha (PPARGC1A, also known as PGC-1alpha). Furthermore, the production of super-repressor IkappaBalpha suppressed the increase in blood glucose level after pyruvate injection.. Our results indicate that moderate inhibition of NF-kappaB improved glucose tolerance through decreased gluconeogenesis associated with reduced PGC-1alpha gene expression in db/db mice, and suggest that inhibition of NF-kappaB activity in liver is a potentially suitable strategy for the normalisation of blood glucose concentration in type 2 diabetes.

Topics: Adenoviridae; AMP-Activated Protein Kinases; Animals; Cyclic AMP Response Element-Binding Protein; Diabetes Mellitus; Disease Models, Animal; Female; Glucose; Glycogen; I-kappa B Proteins; Insulin Resistance; Liver; Mice; Mice, Inbred C57BL; Multienzyme Complexes; NF-kappa B; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Protein Serine-Threonine Kinases; STAT3 Transcription Factor; Trans-Activators; Transcription Factors; Triglycerides

We have used primary human muscle cell cultures to investigate the role of glycogen loading in cellular insulin resistance. Insulin pre-treatment for 2 h markedly impaired insulin signaling, as assessed by protein kinase B (PKB) phosphorylation. In contrast, insulin-dependent glycogen synthesis, glycogen synthase (GS) activation, and GS sites 3 de-phosphorylation were impaired only after 5 h of insulin pre-treatment, whereas 2-deoxyglucose transport was only decreased after 18 h pre-treatment. Insulin-resistant glycogen synthesis was associated closely with maximal glycogen loading. Both glucose limitation and 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR) treatment during insulin pre-treatment curtailed glycogen accumulation, and concomitantly restored insulin-sensitive glycogen synthesis and GS activation, although GS de-phosphorylation and PKB phosphorylation remained impaired. Conversely, glycogen super-compensation diminished insulin-sensitive glycogen synthesis and GS activity. Insulin acutely promoted GS translocation to particulate subcellular fractions; this was abolished by insulin pre-treatment, as was GS dephosphorylation therein. Limiting glycogen accumulation during insulin pre-treatment re-instated GS dephosphorylation in particulate fractions, whereas glycogen super-compensation prevented insulin-stimulated GS translocation and dephosphorylation. Our data suggest that diminished insulin signaling alone is insufficient to impair glucose disposal, and indicate a role for glycogen accumulation in inducing insulin resistance in human muscle cells.

Topics: Aminoimidazole Carboxamide; AMP-Activated Protein Kinase Kinases; Cells, Cultured; Deoxyglucose; Dose-Response Relationship, Drug; Enzyme Activation; Glucose; Glycogen; Glycogen Synthase; Glycogen Synthase Kinase 3; Humans; Insulin; Insulin Resistance; Myoblasts, Skeletal; Phosphorylation; Protein Kinases; Protein Transport; Proto-Oncogene Proteins c-akt; Ribonucleotides; Signal Transduction; Time Factors

This study displayed the physiological effects the tricyclic antidepressants amitriptyline or trimipramine have on glucose homoeostasis in male Wistar rats. An insulin secreting cell line (INS-1) was also used to determine effects tricyclic antidepressants have on insulin secretion and insulin displacement. Thirty rats each received a 1 mg kg-1 dose of amitriptyline or trimipramine for a period of 14 weeks; another 14 rats served as the control group. Blood glucose, serum insulin and muscle and liver glycogen levels were determined. Kidney, liver and muscle insulin degradation was measured and compared with insulin degrading enzyme concentrations in the latter two tissues. INS-1 cells were used to determine the effect 1 microM amitriptyline has on insulin secretion. Displacement studies for [3H]glibenclamide by amitriptyline or trimipramine were undertaken on INS-1 cells. A significant increase in blood glucose (P<0.01) was found for both test groups after 6 and 14 weeks of receiving the medication, which may be related to a significant decrease in liver and muscle glycogen levels (P<0.001). Serum insulin levels remained unchanged, although a significant increase in insulin degradation was observed in the muscle, liver and kidney, which may be related to a significant increase in insulin degrading enzyme (P<0.001) that was found. A significant increase in insulin secretion was observed for the INS-1 cells treated with amitriptyline, although no significant displacement for the [3H]glibenclamide was evident for amitriptyline or trimipramine. The significant alterations in glucose homoeostasis observed, as well as the significant changes associated with insulin secretion and degradation associated with amitriptyline or trimipramine treatment, imply that prolonged use of these medicines may lead to insulin resistance and full blown diabetes.

Topics: Amitriptyline; Animals; Antidepressive Agents, Tricyclic; Blood Glucose; Cell Line; Glucose; Glyburide; Glycogen; Hindlimb; Homeostasis; Hypoglycemic Agents; Insulin; Insulin Resistance; Insulysin; Kidney; Liver; Male; Muscle, Skeletal; Rats; Rats, Wistar; Trimipramine

Obesity and type 2 diabetes are worldwide health issues. The present paper investigates prenatal and postnatal pathways to obesity, identifying different metabolic outcomes with different effects on insulin sensitivity and different underlying mechanisms involving key components of insulin receptor signaling pathways. Pregnant Wistar rats either were fed chow ad libitum or were undernourished throughout pregnancy, generating either control or intrauterine growth restricted (IUGR) offspring. Male offspring were fed either standard chow or a high-fat diet from weaning. At 260 d of age, whole-body insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp, and other metabolic parameters were measured. As expected, high-fat feeding caused diet-induced obesity (DIO) and insulin resistance. Importantly, the insulin sensitivity of IUGR offspring was similar to that of control offspring, despite fasting insulin hypersecretion and increased adiposity, irrespective of postnatal nutrition. Real-time PCR and Western blot analyses of key markers of insulin sensitivity and metabolic regulation showed that IUGR offspring had increased hepatic levels of atypical protein kinase C zeta (PKC zeta) and increased expression of fatty acid synthase mRNA. In contrast, DIO led to decreased expression of fatty acid synthase mRNA and hepatic steatosis. The decrease in hepatic PKC zeta with DIO may explain, at least in part, the insulin resistance. Our data suggest that the mechanisms of obesity induced by prenatal events are fundamentally different from those of obesity induced by postnatal high-fat nutrition. The origin of insulin hypersecretion in IUGR offspring may be independent of the mechanistic events that trigger the insulin resistance commonly observed in DIO.

Topics: Animal Feed; Animals; Blood Glucose; C-Peptide; Caloric Restriction; Diabetes, Gestational; Dietary Fats; Female; Fetal Growth Retardation; Fetal Nutrition Disorders; Glucose Clamp Technique; Glycogen; Hyperinsulinism; Insulin; Insulin Resistance; Insulin Secretion; Lipid Metabolism; Liver; Male; Muscle, Skeletal; Obesity; Phosphoenolpyruvate Carboxykinase (GTP); Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Wistar

High-fat diets and oxidative damage may contribute to the development of type 2 diabetes. Hypolipidaemic drugs and antioxidants were supposed to prevent the development of the disease. In this study, we investigated preventive effects of fenofibrate (200 mg kg(-1)), vitamin C (30 mg kg(-1)), combination of both in mice induced by streptozotocin (35 mg kg(-1)) and soluble lard (15 ml kg(-1)). The results showed the mice demonstrated hyperglycaemia and hypercholesterolaemia, visceral fat accumulation, and a slight increase in liver glycogen/triglyceride and oxidative stress within 60 days of treatment. Fenofibrate enhanced insulin sensitivity, improved glycaemic control, lowered serum triglycerides, reduced body and visceral fat weights, and decreased liver glycogen/lipid levels but showed hepatotoxicity in the mice. Vitamin C neither itself prevented nor enhanced preventive effects of fenofibrate on glucose and lipid metabolism but partly attenuated the hepatotoxicity of fenofibrate. These results suggest that fenofibrate inhibit development of type 2 diabetes induced by high-fat diets and oxidative stress. However, here, vitamin C just can serve as an adjunct to fenofibrate therapy against its hepatotoxicity. In the future study, we should investigate if higher dosage of vitamin C or other antioxidants would enhance preventive effects of fenofibrate in type 2 diabetes.

Topics: Animals; Antioxidants; Ascorbic Acid; Blood Glucose; Chemical and Drug Induced Liver Injury; Cholesterol; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Dietary Fats; Drug Therapy, Combination; Fenofibrate; Glycogen; Hypercholesterolemia; Hyperglycemia; Hypoglycemic Agents; Hypolipidemic Agents; Insulin Resistance; Intra-Abdominal Fat; Liver; Liver Diseases; Male; Matrix Metalloproteinase 9; Mice; Oxidative Stress; Streptozocin; Triglycerides

Elevated non-esterified fatty acids, triglyceride, diacylglycerol, and ceramide have all been associated with insulin resistance in muscle. We set out to investigate the role of intramyocellular lipid metabolites in the induction of insulin resistance in human primary myoblast cultures. Muscle cells were subjected to adenovirus-mediated expression of perilipin or incubated with fatty acids for 18 h, prior to insulin stimulation and measurement of lipid metabolites and rates of glycogen synthesis. Adenovirus-driven perilipin expression lead to significant accumulation of triacylglycerol in myoblasts, without any detectable effect on insulin sensitivity, as judged by the ability of insulin to stimulate glycogen synthesis. Similarly, incubation of cells with the monounsaturated fatty acid oleate resulted in triacylglycerol accumulation without inhibiting insulin action. By contrast, the saturated fatty acid palmitate induced insulin resistance. Palmitate treatment caused less accumulation of triacylglycerol than did oleate but also induced significant accumulation of both diacylglycerol and ceramide. Insulin resistance was also caused by cell-permeable analogues of ceramide, and palmitate-induced resistance was blocked in the presence of inhibitors of de novo ceramide synthesis. Oleate co-incubation completely prevented the insulin resistance induced by palmitate. Our data are consistent with ceramide being the agent responsible for insulin resistance caused by palmitate exposure. Furthermore, the triacylglycerol derived from oleate was able to exert a protective role in sequestering palmitate, thus preventing its conversion to ceramide.

Topics: Carrier Proteins; Cells, Cultured; Ceramides; Diglycerides; Glycogen; Humans; Insulin Resistance; Myoblasts, Skeletal; Palmitates; Perilipin-1; Phosphoproteins; Time Factors; Triglycerides

Fatty liver is commonly associated with insulin resistance and type 2 diabetes, but it is unclear whether triacylglycerol accumulation or an excess flux of lipid intermediates in the pathway of triacyglycerol synthesis are sufficient to cause insulin resistance in the absence of genetic or diet-induced obesity. To determine whether increased glycerolipid flux can, by itself, cause hepatic insulin resistance, we used an adenoviral construct to overexpress glycerol-sn-3-phosphate acyltransferase-1 (Ad-GPAT1), the committed step in de novo triacylglycerol synthesis. After 5-7 days, food intake, body weight, and fat pad weight did not differ between Ad-GPAT1 and Ad-enhanced green fluorescent protein control rats, but the chow-fed Ad-GPAT1 rats developed fatty liver, hyperlipidemia, and insulin resistance. Liver was the predominant site of insulin resistance; Ad-GPAT1 rats had 2.5-fold higher hepatic glucose output than controls during a hyperinsulinemic-euglycemic clamp. Hepatic diacylglycerol and lysophosphatidate were elevated in Ad-GPAT1 rats, suggesting a role for these lipid metabolites in the development of hepatic insulin resistance, and hepatic protein kinase Cepsilon was activated, providing a potential mechanism for insulin resistance. Ad-GPAT1-treated rats had 50% lower hepatic NF-kappaB activity and no difference in expression of tumor necrosis factor-alpha and interleukin-beta, consistent with hepatic insulin resistance in the absence of increased hepatic inflammation. Glycogen synthesis and uptake of 2-deoxyglucose were reduced in skeletal muscle, suggesting mild peripheral insulin resistance associated with a higher content of skeletal muscle triacylglycerol. These results indicate that increased flux through the pathway of hepatic de novo triacylglycerol synthesis can cause hepatic and systemic insulin resistance in the absence of obesity or a lipogenic diet.

Topics: Adenoviridae; Animals; Deoxyglucose; Fatty Liver; Gene Expression; Glycerol-3-Phosphate O-Acyltransferase; Glycogen; Hyperlipidemias; Insulin Resistance; Interleukin-1beta; Lipid Metabolism; Liver; Male; Muscle, Skeletal; NF-kappa B; Protein Kinase C-epsilon; Rats; Rats, Wistar; Transduction, Genetic; Triglycerides; Tumor Necrosis Factor-alpha

Selective resistance to the effects of insulin on glucose metabolism in skeletal muscle and adipose tissue is a key feature of polycystic ovary syndrome (PCOS). The pathogenesis of insulin resistance in skeletal muscle in PCOS involves interaction of in vivo environmental factors with intrinsic defects in insulin signaling. We aimed to determine whether (1) intrinsic defects in insulin action/signaling and cytokine secretion were present in adipose cells in PCOS and (2) insulin resistance can be induced in control adipose cells by culture in medium conditioned by insulin-resistant PCOS fibroblasts. Subcutaneous abdominal preadipocytes from obese women with PCOS (n = 7) and age- and body mass index-matched controls (n = 5) were cultured for several generations in vitro. Basal and insulin-stimulated glycogen synthesis and basal glucose transport did not differ in the preadipocytes from women with PCOS and controls. Abundance of insulin receptor (IR) beta subunit, insulin receptor substrate (IRS) 1 and 2, p85 subunit of phosphatidylinositol 3-kinase, and extracellular signal-regulated kinase (ERK)1/2 activation did not differ. Secretion of tumor necrosis factor alpha and interleukin 6 did not differ. Insulin action on glycogen synthesis in control preadipocytes was not altered by coculture with or growth in media conditioned by PCOS skin fibroblasts with constitutive serine phosphorylation of IRbeta subunit (IR ser+), indicating that IR ser+ cells do not secrete an insulin resistance-inducing factor. We conclude that in contrast to skeletal muscle and skin fibroblasts, there is no evidence for intrinsic defects in insulin signaling in the PCOS adipose cell lineage, indicating that insulin resistance in these cells is likely due to factors in the in vivo environment.

Topics: Adipocytes; Adult; Cell Lineage; Extracellular Signal-Regulated MAP Kinases; Female; Glucose Transport Proteins, Facilitative; Glycogen; Humans; Insulin Receptor Substrate Proteins; Insulin Resistance; Interleukin-6; Intracellular Signaling Peptides and Proteins; Phosphatidylinositol 3-Kinases; Phosphoproteins; Polycystic Ovary Syndrome; Receptor, Insulin; Signal Transduction; Tumor Necrosis Factor-alpha

The aim of this study was to investigate the effect of insulin resistance on glycogen concentration and glycogen synthase activity in the red and white gastrocnemius muscles and to determine whether the inverse relationship existing between glycogen concentration and enzyme activity is maintained in insulin resistant state. These questions were addressed using 3 models that induce various degrees of insulin resistance: sucrose feeding, dexamethasone administration, and a combination of both treatments (dex+sucrose). Sucrose feeding raised triglyceride levels without affecting plasma glucose or insulin concentrations whereas dexamethasone and dex+sucrose provoked severe hyperinsulinemia, hyperglycemia and hypertriglyceridemia. Sucrose feeding did not alter muscle glycogen concentration but provoked a small reduction in the glycogen synthase activity ratio (-/+ glucose-6-phosphate) in red but not in white gastrocnemius. Dexamethasone administration augmented glycogen concentration and reduced glycogen synthase activity ratio in both muscle fiber types. In contrast, dex+sucrose animals showed decreased muscle glycogen concentration compared to dexamethasone group, leading to levels similar to those of control animals. This was associated with lower glycogen synthase activity compared to control animals leading to levels comparable to those of dexamethasone-treated animals. Thus, in dex+sucrose animals, the inverse relationship observed between glycogen levels and glycogen synthase activity was not maintained, suggesting that factors other than the glycogen concentration modulate the enzyme's activity. In conclusion, while insulin resistance was associated with a reduced glycogen synthase activity ratio, we found no correlation between muscle glycogen concentration and insulin resistance. Furthermore, our results suggest that sucrose treatment may modulate dexamethasone action in skeletal muscle.

Topics: Animals; Body Weight; Dexamethasone; Gene Expression Regulation; Glucose; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Male; Models, Biological; Muscle, Skeletal; Rats; Rats, Sprague-Dawley

We examined the hypothesis that insulin resistance in skeletal muscle promotes the development of atherogenic dyslipidemia, associated with the metabolic syndrome, by altering the distribution pattern of postprandial energy storage. Following ingestion of two high carbohydrate mixed meals, net muscle glycogen synthesis was reduced by approximately 60% in young, lean, insulin-resistant subjects compared with a similar cohort of age-weight-body mass index-activity-matched, insulin-sensitive, control subjects. In contrast, hepatic de novo lipogenesis and hepatic triglyceride synthesis were both increased by >2-fold in the insulin-resistant subjects. These changes were associated with a 60% increase in plasma triglyceride concentrations and an approximately 20% reduction in plasma high-density lipoprotein concentrations but no differences in plasma concentrations of TNF-alpha, IL-6, adiponectin, resistin, retinol binding protein-4, or intraabdominal fat volume. These data demonstrate that insulin resistance in skeletal muscle, due to decreased muscle glycogen synthesis, can promote atherogenic dyslipidemia by changing the pattern of ingested carbohydrate away from skeletal muscle glycogen synthesis into hepatic de novo lipogenesis, resulting in an increase in plasma triglyceride concentrations and a reduction in plasma high-density lipoprotein concentrations. Furthermore, insulin resistance in these subjects was independent of changes in the plasma concentrations of TNF-alpha, IL-6, high-molecular-weight adiponectin, resistin, retinol binding protein-4, or intraabdominal obesity, suggesting that these factors do not play a primary role in causing insulin resistance in the early stages of the metabolic syndrome.

Topics: Cytokines; Fasting; Glycogen; Hormones; Humans; Insulin Resistance; Magnetic Resonance Imaging; Metabolic Syndrome; Muscle, Skeletal

Hyperglycemia is a defining feature of Type 1 and 2 diabetes. Hyperglycemia also causes insulin resistance, and our group (Kraegen EW, Saha AK, Preston E, Wilks D, Hoy AJ, Cooney GJ, Ruderman NB. Am J Physiol Endocrinol Metab Endocrinol Metab 290: E471-E479, 2006) has recently demonstrated that hyperglycemia generated by glucose infusion results in insulin resistance after 5 h but not after 3 h. The aim of this study was to investigate possible mechanism(s) by which glucose infusion causes insulin resistance in skeletal muscle and in particular to examine whether this was associated with changes in insulin signaling. Hyperglycemia (~10 mM) was produced in cannulated male Wistar rats for up to 5 h. The glucose infusion rate required to maintain this hyperglycemia progressively lessened over 5 h (by 25%, P < 0.0001 at 5 h) without any alteration in plasma insulin levels consistent with the development of insulin resistance. Muscle glucose uptake in vivo (44%; P < 0.05) and glycogen synthesis rate (52%; P < 0.001) were reduced after 5 h compared with after 3 h of infusion. Despite these changes, there was no decrease in the phosphorylation state of multiple insulin signaling intermediates [insulin receptor, Akt, AS160 (Akt substrate of 160 kDa), glycogen synthase kinase-3beta] over the same time course. In isolated soleus strips taken from control or 1- or 5-h glucose-infused animals, insulin-stimulated 2-deoxyglucose transport was similar, but glycogen synthesis was significantly reduced in the 5-h muscle sample (68% vs. 1-h sample; P < 0.001). These results suggest that the reduced muscle glucose uptake in rats after 5 h of acute hyperglycemia is due more to the metabolic effects of excess glycogen storage than to a defect in insulin signaling or glucose transport.

Topics: Animals; Blood Glucose; Glucose; Glycogen; GTPase-Activating Proteins; Hyperglycemia; In Vitro Techniques; Infusions, Intravenous; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Oncogene Protein v-akt; Phosphorylation; Random Allocation; Rats; Rats, Wistar; Signal Transduction

In the present study, the polyherbal preparation diabegon, containing 18 plant extracts with hypoglycemic activity, was evaluated for its preventive effect during progression of type 2 diabetes in high-fructose-diet-fed rats. Oral administration of diabegon (100 mg/kg body weight) delayed development of glucose intolerance for 4 weeks in comparison with the diabetic control group, and the effect of diabegon was compared to that of the standard insulin sensitizer drug rosiglitazone. Diabegon treatment also ameliorated the elevation of glycosylated haemoglobin, liver glycogen content, plasma insulin, homeostasis model assessment, free fatty acids, triglycerides, total cholesterol, LDL-cholesterol, and VLDL-cholesterol, whereas it increased HDL-cholesterol after 56 days of treatment (P<0.05). The mechanism of action by which diabegon attenuates insulin resistance and dyslipidemia may be through induction of peroxisome proliferator-activated receptor-gamma and lipoprotein lipase activity in peripheral tissues (muscles). Moreover, diabegon administration for 56 days also produced no alteration in liver and kidney function tests, which seems to indicate its non-toxicity during treatment. Our present results suggest that diabegon may be included in diabetes mellitus treatment regimens, as a drug with good antidiabetic actions but no toxic manifestations.

Topics: Administration, Oral; Animals; Blood Glucose; Diabetes Mellitus, Experimental; Fructose; Glucose Tolerance Test; Glycated Hemoglobin; Glycogen; Homeostasis; Hyperglycemia; Hypoglycemic Agents; Insulin; Insulin Resistance; Kidney; Lipids; Lipoprotein Lipase; Liver; Male; Plant Extracts; PPAR gamma; Rats; Rats, Wistar

In this study we determined body weight-specific fetal (umbilical) glucose uptake (UGU), utilization (GUR), and production rates (GPR) and insulin action in intrauterine growth-restricted (IUGR) fetal sheep. During basal conditions, UGU from the placenta was 33% lower in IUGR fetuses, but GUR was not different between IUGR and control fetuses. The difference between glucose utilization and UGU rates in the IUGR fetuses demonstrated the presence and rate of fetal GPR (41% of GUR). The mRNA concentrations of the gluconeogenic enzymes glucose-6-phophatase and PEPCK were higher in the livers of IUGR fetuses, perhaps in response to CREB activation, as phosphorylated CREB/total CREB was increased 4.2-fold. A hyperglycemic clamp resulted in similar rates of glucose uptake and utilization in IUGR and control fetuses. The nearly identical GURs in IUGR and control fetuses at both basal and high glucose concentrations occurred at mean plasma insulin concentrations in the IUGR fetuses that were approximately 70% lower than controls, indicating increased insulin sensitivity. Furthermore, under basal conditions, hepatic glycogen content was similar, skeletal muscle glycogen was increased 2.2-fold, the fraction of fetal GUR that was oxidized was 32% lower, and GLUT1 and GLUT4 concentrations in liver and skeletal muscle were the same in IUGR fetuses compared with controls. These results indicate that insulin-responsive fetal tissues (liver and skeletal muscle) adapt to the hypoglycemic-hypoinsulinemic IUGR environment with mechanisms that promote glucose utilization, particularly for glucose storage, including increased insulin action, glucose production, shunting of glucose utilization to glycogen production, and maintenance of glucose transporter concentrations.

Topics: Animals; Blood Glucose; Cyclic AMP Response Element-Binding Protein; Female; Fetal Growth Retardation; Gene Expression; Glucose; Glucose Transport Proteins, Facilitative; Glucose-6-Phosphatase; Glycogen; Hyperglycemia; Insulin; Insulin Resistance; Lactic Acid; Liver; Male; Oxygen; Phosphoenolpyruvate Carboxykinase (GTP); Placental Insufficiency; Pregnancy; Pregnancy Complications; Regional Blood Flow; RNA, Messenger; Sheep, Domestic; Umbilical Cord

The present study was conducted to explore the effects of myricetin on insulin resistance in rats fed for 6 weeks with a diet containing 60% fructose. Repeated intravenous (i.v.) injection of myricetin (1 mg/kg per injection, 3 times daily) for 14 days was found to significantly decrease the high glucose and triglyceride levels in plasma of fructose chow-fed rats. Also, the higher degree of insulin resistance in fructose chow-fed rats as measured by homeostasis model assessment of basal insulin resistance was significantly decreased by myricetin treatment. Myricetin increased the whole-body insulin sensitivity in fructose chow-fed rats, as evidenced by the marked elevation of composite whole-body insulin sensitivity index during the oral glucose tolerance test. Myricetin was found to reverse the defect in expression of insulin receptor substrate-1 (IRS-1) and the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase) in soleus muscle of fructose chow-fed rats under the basal state, despite the protein expression of insulin receptor (IR). Increased basal phosphorylation of IR and IRS-1 as well as Akt was observed in parallel. The reduced level of insulin action on phosphorylation of IR, IRS-1 and Akt in soleus muscle of fructose chow-fed rats was reversed by myricetin treatment. Furthermore, myricetin treatment improved the defective insulin action on the translocation of glucose transporter subtype 4 (GLUT 4) in insulin-resistant soleus muscle. These findings indicate that myricetin improves insulin sensitivity through the enhancement of insulin action on IRS-1-associated PI 3-kinase and GLUT 4 activity in soleus muscles of animals exhibiting insulin resistance.

Topics: Animals; Blood Glucose; Blotting, Western; Cholesterol; Diet; Electrophoresis, Polyacrylamide Gel; Flavonoids; Flavonols; Fructose; Glucose Transporter Type 4; Glycogen; Hepatocytes; Hypoglycemic Agents; Immunoprecipitation; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Phosphatidylinositol 3-Kinases; Phosphorylation; Rats; Rats, Wistar; Receptor, Insulin; Rosiglitazone; Thiazolidinediones; Triglycerides

A single bout of exercise increases the rate of muscle glucose transport (GT) by both insulin-independent and insulin-dependent mechanisms. The purpose of this study was to determine whether high-fat diet (HFD) feeding interferes with the metabolic activation induced by moderate-intensity endurance exercise. Rats were fed an HFD or control diet (CD) for 4 weeks and then exercised on a treadmill for 1 hour (19 m/min, 15% incline). Insulin-independent GT was markedly higher in soleus muscle dissected immediately after exercise than in muscle dissected from sedentary rats in both dietary groups, but insulin-independent GT was 25% lower in HFD-fed than in CD-fed rats. Insulin-dependent GT in the presence of submaximally effective concentration of insulin (0.9 nmol/L) was also higher in both dietary groups in muscle dissected 2 hours after exercise, but was 25% lower in HFD-fed than in CD-fed rats. Exercise-induced activation of 5'adenosine monophosphate-activated protein kinase, a signaling intermediary leading to insulin-independent GT and regulating insulin sensitivity, was correspondingly blunted in the HFD group. High-fat diet did not affect glucose transporter 4 content or insulin-stimulated Akt phosphorylation. Our findings provide evidence that an HFD impairs the effects of short-term endurance exercise on glucose metabolism and that exercise does not fully compensate for HFD-induced insulin resistance in skeletal muscle. Although the underlying mechanism is unclear, reduced 5'adenosine monophosphate-activated protein kinase activation during exercise may play a role.

Topics: Adenylate Kinase; Animals; Blotting, Western; Dietary Fats; Enzyme Activation; Glucose; Glucose Transporter Type 4; Glycogen; Insulin Resistance; Male; Muscle Fibers, Skeletal; Muscle, Skeletal; Oncogene Protein v-akt; Phosphorylation; Physical Conditioning, Animal; Rats; Rats, Wistar; Triglycerides

AMPK is a key regulator of fat and carbohydrate metabolism. It has been postulated that defects in AMPK signaling could be responsible for some of the metabolic abnormalities of type 2 diabetes. In this study, we examined whether insulin-resistant obese Zucker rats have abnormalities in the AMPK pathway. We compared AMPK and ACC phosphorylation and the protein content of the upstream AMPK kinase LKB1 and the AMPK-regulated transcriptional coactivator PPARgamma coactivator-1 (PGC-1) in gastrocnemius of sedentary obese Zucker rats and sedentary lean Zucker rats. We also examined whether 7 wk of exercise training on a treadmill reversed abnormalities in the AMPK pathway in obese Zucker rats. In the obese rats, AMPK phosphorylation was reduced by 45% compared with lean rats. Protein expression of the AMPK kinase LKB1 was also reduced in the muscle from obese rats by 43%. In obese rats, phosphorylation of ACC and protein expression of PGC-1alpha, two AMPK-regulated proteins, tended to be reduced by 50 (P = 0.07) and 35% (P = 0.1), respectively. There were no differences in AMPKalpha1, -alpha2, -beta1, -beta2, and -gamma3 protein content between lean and obese rats. Training caused a 1.5-fold increase in AMPKalpha1 protein content in the obese rats, although there was no effect of training on AMPK phosphorylation and the other AMPK isoforms. Furthermore, training also significantly increased LKB1 and PGC-1alpha protein content 2.8- and 2.5-fold, respectively, in the obese rats. LKB1 protein strongly correlated with hexokinase II activity (r = 0.75, P = 0.001), citrate synthase activity (r = 0.54, P = 0.02), and PGC-1alpha protein content (r = 0.81, P < 0.001). In summary, obese insulin-resistant rodents have abnormalities in the LKB1-AMPK-PGC-1 pathway in muscle, and these abnormalities can be restored by training.

Topics: Acetyl-CoA Carboxylase; AMP-Activated Protein Kinase Kinases; AMP-Activated Protein Kinases; Animals; Body Weight; Glucose; Glycogen; Hexokinase; Insulin; Insulin Resistance; Lipids; Models, Biological; Multienzyme Complexes; Muscle, Skeletal; Obesity; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Phosphorylation; Physical Conditioning, Animal; Protein Kinases; Protein Serine-Threonine Kinases; Rats; Rats, Zucker; RNA-Binding Proteins; Signal Transduction; Transcription Factors

Increased lipid availability is associated with diminished insulin-stimulated glucose uptake and glycogen synthesis in muscle, but it is not clear whether alterations in glycogen synthase activity itself play a direct role. Because intracellular localization of this enzyme is involved in its regulation, we investigated whether fat oversupply causes an inhibitory redistribution. We examined the recovery of glycogen synthase in subcellular fractions from muscle of insulin-resistant, fat-fed rats and chow-fed controls, either maintained in the basal state or after a euglycaemic-hyperinsulinaemic clamp. Although glycogen synthase protein and activity were mostly recovered in an insoluble fraction, insulin caused translocation of activity from the smaller soluble pool to the insoluble fraction. Fat-feeding, which led to a reduction in glycogen synthesis during the clamp, was associated with a depletion in the soluble pool, consistent with an important role for this component. A similar depletion was also observed in cytosolic fractions of muscles from obese db/db mice, another model of lipid-induced insulin resistance. To investigate this in more detail, we employed lipid-pretreated L6 myotubes, which exhibited a reduction in insulin-stimulated glycogen synthesis independently of alterations in glucose flux or insulin signalling through protein kinase B. In control cells, insulin caused redistribution of a minor cytosolic pool of glycogen synthase to an insoluble fraction, which was again forestalled by lipid pretreatment. Glycogen synthase recovered in the insoluble fraction from pre-treated cells exhibited a low fractional velocity that was not increased in response to insulin. Our results suggest that the initial localization of glycogen synthase in a soluble pool plays an important role in glycogen synthesis, and that its sequestration in an insulin-resistant insoluble pool may explain in part the reduced glycogen synthesis caused by lipid oversupply.

Topics: Animals; Biological Transport; Cell Line; Cell Membrane; Cells, Cultured; Cytosol; Dietary Fats; Glucose; Glucose Clamp Technique; Glycogen; Glycogen Phosphorylase; Glycogen Synthase; Immunoblotting; Insulin; Insulin Resistance; Linoleic Acid; Mice; Mice, Obese; Muscle Fibers, Skeletal; Neptune; Rats; Rats, Wistar

Farnesoid X receptor (FXR) plays an important role in maintaining bile acid and cholesterol homeostasis. Here we demonstrate that FXR also regulates glucose metabolism. Activation of FXR by the synthetic agonist GW4064 or hepatic overexpression of constitutively active FXR by adenovirus-mediated gene transfer significantly lowered blood glucose levels in both diabetic db/db and wild-type mice. Consistent with these data, FXR null mice exhibited glucose intolerance and insulin insensitivity. We further demonstrate that activation of FXR in db/db mice repressed hepatic gluconeogenic genes and increased hepatic glycogen synthesis and glycogen content by a mechanism that involves enhanced insulin sensitivity. In view of its central roles in coordinating regulation of both glucose and lipid metabolism, we propose that FXR agonists are promising therapeutic agents for treatment of diabetes mellitus.

Topics: 3-Hydroxybutyric Acid; Adenoviridae; Animals; Blood Glucose; Blotting, Northern; Blotting, Western; Cholesterol; Diabetes Mellitus, Experimental; DNA-Binding Proteins; Etoposide; Gluconeogenesis; Glucose; Glycogen; Hepatocytes; Hyperglycemia; Hyperlipidemias; Insulin; Insulin Resistance; Isoxazoles; Lipids; Liver; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Models, Statistical; Receptors, Cytoplasmic and Nuclear; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Time Factors; Transcription Factors; Triglycerides

Many patients with heart failure have whole-body insulin resistance and reduced cardiac fluorodeoxyglucose uptake, but whether these metabolic changes have detrimental effects on the heart is unknown. Here, we tested whether there is a link between insulin resistance and ischemic damage in the chronically infarcted Wistar rat heart, postulating that the heart would have decreased insulin sensitivity, with lower GLUT4 glucose transporter protein levels due to high circulating free fatty acid (FFA) concentrations. A decreased capacity for glucose uptake would lower glycolytic adenosine triphosphate (ATP) production and thereby increase ischemic injury in the infarcted heart.. In vivo left ventricular ejection fractions, measured using echocardiography, were 40% lower in rats 10 weeks after coronary artery ligation than in sham-operated control rats. Insulin-stimulated D[2-3H]glucose uptake was 42% lower in isolated, perfused, infarcted hearts. Myocardial GLUT4 glucose transporter protein levels were 28% lower in the infarcted hearts and correlated negatively with ejection fractions and with fasting plasma FFA concentrations. Compared with controls, chronically infarcted hearts had 46% lower total glucose uptake and three-fold faster ATP hydrolysis rates, measured using phosphorus-31 nuclear magnetic resonance spectroscopy, during 32-min ischemia at 0.4 ml/min/gww. During reperfusion, recovery of left ventricular developed pressure in infarcted hearts was 42% lower than in control hearts.. Glucose uptake, in response to insulin or ischemia, was lower in the chronically infarcted rat heart and associated with increased circulating FFA concentrations and decreased GLUT4 levels. Thus, infarcted hearts had greater ATP depletion, and consequently incurred greater damage, during ischemia.

Topics: Adenosine Triphosphate; Animals; Echocardiography; Energy Metabolism; Fatty Acids, Nonesterified; Glucose; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Magnetic Resonance Spectroscopy; Male; Models, Animal; Myocardial Infarction; Myocardial Reperfusion Injury; Myocardium; Perfusion; Rats; Rats, Wistar; Time Factors; Ventricular Dysfunction, Left

Mice with liver-specific overexpression of dominant negative phosphorylation-defective S503A-CEACAM1 mutant (L-SACC1) developed chronic hyperinsulinemia resulting from blunted hepatic clearance of insulin, visceral obesity, and glucose intolerance. To determine the underlying mechanism of altered glucose homeostasis, a 2-h hyperinsulinemic euglycemic clamp was performed, and tissue-specific glucose and lipid metabolism was assessed in awake L-SACC1 and wild-type mice. Inactivation of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) caused insulin resistance in liver that was mostly due to increased expression of fatty acid synthase and lipid metabolism, resulting in elevated intrahepatic levels of triglyceride and long-chain acyl-CoAs. Whole body insulin resistance in the L-SACC1 mice was further attributed to defects in insulin-stimulated glucose uptake in skeletal muscle and adipose tissue. Insulin resistance in peripheral tissues was associated with significantly elevated intramuscular fat contents that may be secondary to increased whole body adiposity (assessed by (1)H-MRS) in the L-SACC1 mice. Overall, these results demonstrate that L-SACC1 is a mouse model in which chronic hyperinsulinemia acts as a cause, and not a consequence, of insulin resistance. Our findings further indicate the important role of CEACAM1 and hepatic insulin clearance in the pathogenesis of obesity and insulin resistance.

Topics: Acyl Coenzyme A; Animals; Blood Glucose; Carcinoembryonic Antigen; Disease Models, Animal; Fatty Acid Synthases; Fatty Acid Transport Proteins; Glucose; Glucose Clamp Technique; Glucose Intolerance; Glucose-6-Phosphate; Glycogen; Hyperinsulinism; Insulin; Insulin Resistance; Lipoprotein Lipase; Liver; Mice; Mice, Knockout; Muscle, Skeletal; Triglycerides

Hepatic insulin resistance in the leptin-receptor defective Zucker fa/fa rat is associated with impaired glycogen synthesis and increased activity of phosphorylase-a. We investigated the coupling between phosphorylase-a and glycogen synthesis in hepatocytes from fa/fa rats by modulating the concentration of phosphorylase-a. Treatment of hepatocytes from fa/fa rats and Fa/? controls with a selective phosphorylase inhibitor caused depletion of phosphorylase-a, activation of glycogen synthase and stimulation of glycogen synthesis. The flux-control coefficient of phosphorylase on glycogen synthesis was glucose dependent and at 10 mm glucose was higher in fa/fa than Fa/? hepatocytes. There was an inverse correlation between the activities of glycogen synthase and phosphorylase-a in both fa/fa and Fa/? hepatocytes. However, fa/fa hepatocytes had a higher activity of phosphorylase-a, for a corresponding activity of glycogen synthase. This defect was, in part, normalized by expression of the glycogen-targeting protein, PTG. Hepatocytes from fa/fa rats had normal expression of the glycogen-targeting proteins G(L) and PTG but markedly reduced expression of R6. Expression of R6 protein was increased in hepatocytes from Wistar rats after incubation with leptin and insulin. Diminished hepatic R6 expression in the leptin-receptor defective fa/fa rat may be a contributing factor to the elevated phosphorylase activity and/or its high control strength on glycogen synthesis.

Topics: Animals; Carrier Proteins; Cells, Cultured; Diabetes Mellitus, Type 2; Disease Models, Animal; Female; Glycogen; Hepatocytes; Insulin; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Leptin; Male; Obesity; Phosphoprotein Phosphatases; Phosphorylase a; Protein Subunits; Rats; Rats, Wistar; Rats, Zucker; Receptors, Cell Surface; Receptors, Leptin

Ethanolic extracts of Ananas comosus L. leaves (AC) enriched with phenols have hypoglycemic activity in diabetic rats. Here, we investigated the effect of AC on insulin sensitivity in rats and HepG2. In high-fat diet-fed and low-dose streptozotozin-treated diabetic Wistar rats subjected to challenge with exogenous human insulin, AC treatment at an oral dose of 0.40 g/kg could significantly improve sensitivity to exogenous insulin. After a sub-acute treatment, AC also could inhibit the development of insulin resistance in high-fat diet-fed and low-dose streptozotozin-treated diabetic rats following the test of loss of tolbutamide-induced blood glucose lowering action. For intravenous insulin/glucose infusion test, high-fat diet-fed and low-dose alloxan-treated Wistar rats were associated with insulin resistance, which was improved after AC or fenofibrate treatment. AC application inhibited the development of insulin resistance in HepG2 cells. The above animal models were well developed to simulate type 2 diabetes. Taken together, our results suggest that AC may improve insulin sensitivity in type 2 diabetes and could be developed into a new potential natural product for handling of insulin resistance in diabetic patients.

Topics: Ananas; Animals; Blood Glucose; Cell Line, Tumor; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Ethanol; Glucose; Glycogen; Humans; Insulin Resistance; Male; Phytotherapy; Plant Extracts; Plant Leaves; Rats; Rats, Wistar

An increase in circulating levels of specific NEFAs (non-esterified fatty acids) has been implicated in the pathogenesis of insulin resistance and impaired glucose disposal in skeletal muscle. In particular, elevation of SFAs (saturated fatty acids), such as palmitate, has been correlated with reduced insulin sensitivity, whereas an increase in certain MUFAs and PUFAs (mono- and poly-unsaturated fatty acids respectively) has been suggested to improve glycaemic control, although the underlying mechanisms remain unclear. In the present study, we compare the effects of palmitoleate (a MUFA) and palmitate (a SFA) on insulin action and glucose utilization in rat L6 skeletal muscle cells. Basal glucose uptake was enhanced approx. 2-fold following treatment of cells with palmitoleate. The MUFA-induced increase in glucose transport led to an associated rise in glucose oxidation and glycogen synthesis, which could not be attributed to activation of signalling proteins normally modulated by stimuli such as insulin, nutrients or cell stress. Moreover, although the MUFA-induced increase in glucose uptake was slow in onset, it was not dependent upon protein synthesis, but did, nevertheless, involve an increase in the plasma membrane abundance of GLUT1 and GLUT4. In contrast, palmitate caused a substantial reduction in insulin signalling and insulin-stimulated glucose transport, but was unable to antagonize the increase in transport elicited by palmitoleate. Our findings indicate that SFAs and MUFAs exert distinct effects upon insulin signalling and glucose uptake in L6 muscle cells and suggest that a diet enriched with MUFAs may facilitate uptake and utilization of glucose in normal and insulin-resistant skeletal muscle.

Topics: Amino Acid Transport System A; Amino Acid Transport Systems; Amino Acids; Aminoisobutyric Acids; Animals; Biological Transport; Cell Membrane; Cells, Cultured; Culture Media, Serum-Free; Cycloheximide; Enzyme Inhibitors; Fatty Acids, Monounsaturated; Glucose; Glucose Transporter Type 1; Glucose Transporter Type 4; Glycogen; Glycogen Synthase Kinase 3; Insulin; Insulin Resistance; Models, Biological; Muscle Cells; Muscle Proteins; Oleic Acid; Oxidation-Reduction; Palmitic Acid; Phosphorylation; Protein Synthesis Inhibitors; Protein Transport; Proto-Oncogene Proteins c-akt; Rats; Ribosomal Protein S6 Kinases, 70-kDa

Obesity is a metabolic disorder often associated with type 2 diabetes, insulin resistance, and hepatic steatosis. Leptin-deficient (ob/ob) mice are a well-characterized mouse model of obesity in which increased hepatic lipogenesis is thought to be responsible for the phenotype of insulin resistance. We have recently demonstrated that carbohydrate responsive element-binding protein (ChREBP) plays a key role in the control of lipogenesis through the transcriptional regulation of lipogenic genes, including acetyl-CoA carboxylase and fatty acid synthase. The present study reveals that ChREBP gene expression and ChREBP nuclear protein content are significantly increased in liver of ob/ob mice. To explore the involvement of ChREBP in the physiopathology of hepatic steatosis and insulin resistance, we have developed an adenovirus-mediated RNA interference technique in which short hairpin RNAs (shRNAs) were used to inhibit ChREBP expression in vivo. Liver-specific inhibition of ChREBP in ob/ob mice markedly improved hepatic steatosis by specifically decreasing lipogenic rates. Correction of hepatic steatosis also led to decreased levels of plasma triglycerides and nonesterified fatty acids. As a consequence, insulin signaling was improved in liver, skeletal muscles, and white adipose tissue, and overall glucose tolerance and insulin sensitivity were restored in ob/ob mice after a 7-day treatment with the recombinant adenovirus expressing shRNA against ChREBP. Taken together, our results demonstrate that ChREBP is central for the regulation of lipogenesis in vivo and plays a determinant role in the development of the hepatic steatosis and of insulin resistance in ob/ob mice.

Topics: Adipose Tissue; Animals; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Blood Glucose; Dietary Carbohydrates; Down-Regulation; Fatty Acids, Nonesterified; Fatty Liver; Glucose; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Leptin; Lipids; Liver; Male; Mice; Mice, Obese; Muscle, Skeletal; Nuclear Proteins; Obesity; RNA, Messenger; RNA, Small Interfering; Signal Transduction; Transcription Factors; Transfection; Triglycerides

Chronic excess of GH is known to cause hyperinsulinemia and insulin resistance. We developed human GH transgenic (TG) rats, which were characterized by high plasma levels of human GH and IGF-I. These TG rats showed higher levels of plasma insulin, compared with control littermates, whereas plasma glucose concentrations were normal. Insulin-dependent glucose uptake into adipocytes and muscle was impaired, suggesting that these rats developed insulin resistance. In contrast, insulin-independent glucose uptake into hepatocytes from TG rats was significantly increased, and glycogen and lipid levels in livers of TG rats were remarkably high. Because the role of liver in GH-induced insulin resistance is poorly understood, we studied insulin signaling at early stages and insulin action in liver and primary cultures of hepatocytes prepared from TG rats. There was no difference in insulin receptor kinase activity induced by insulin between TG and control rats; however, insulin-dependent insulin receptor substrate-2 tyrosine phosphorylation, glycogen synthase activation, and expression of enzymes that induce lipid synthesis were potentiated in hepatocytes of TG rats. These results suggest that impairment of insulin-dependent glucose uptake by GH excess in adipose tissue and muscle is compensated by up-regulation of glucose uptake in liver and that potentiation of insulin signaling through insulin receptor substrate-2 in liver experiencing GH excess causes an increase in glycogen and lipid synthesis from incorporated glucose, resulting in accumulation of glycogen and lipids in liver. This novel mechanism explains normalization of plasma glucose levels at least in part in a GH excess model.

Topics: Adipose Tissue; Animals; Animals, Genetically Modified; Female; Glucose; Glycogen; Glycogen Synthase; Hepatocytes; Human Growth Hormone; Insulin Receptor Substrate Proteins; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Lipid Metabolism; Liver; Male; Muscle, Skeletal; Phosphatidylinositol 3-Kinases; Phosphoproteins; Rats; Receptor, Insulin; RNA, Messenger; Tyrosine

Disturbance in glucose metabolism is a common feature in liver diseases and this is associated with skeletal muscle insulin resistance. However, the underlying molecular mechanisms are unclear. To characterize skeletal muscle insulin resistance associated with liver disease, we examined muscles from animals after an acute, 5 weeks perturbation of the common bile duct. Clinical findings, elevated plasma levels of liver enzymes and histological examinations confirmed cirrhosis.. : Cirrhotic animals were insulin resistant and this was associated with reduced glucose transport into muscles. Interestingly, activity in the proximal part of the insulin signaling cascade was not decreased, as evinced by increased activity of key enzymes in the signal to glucose transport. Expression of the glucose transporter, GLUT4, was normal. So together these results indicate that signaling downstream of PKB/Akt and/or the translocation of GLUT4 is impaired in skeletal muscle from cirrhotic animals.. In conclusion, in an animal model of liver cirrhosis whole body insulin resistance is associated with insulin resistance in skeletal muscles. Unlike other common forms of insulin resistance, muscles from cirrhotic animals have increased activity in the proximal insulin signaling cascade. This emphasizes the fact that skeletal muscle insulin resistance associated with liver cirrhosis is a unique entity.

Topics: Animals; Biological Transport, Active; Blotting, Western; Disease Models, Animal; Disease Progression; Follow-Up Studies; Glucose; Glucose Tolerance Test; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Liver Cirrhosis, Experimental; Male; Muscle, Skeletal; Rats; Rats, Wistar

Caveolin-3 (Cav-3) is expressed predominantly in skeletal muscle fibers, where it drives caveolae formation at the muscle cell's plasma membrane. In vitro studies have suggested that Cav-3 may play a positive role in insulin signaling and energy metabolism. We directly address the in vivo metabolic consequences of genetic ablation of Cav-3 in mice as it relates to insulin action, glucose metabolism, and lipid homeostasis. At age 2 mo, Cav-3 null mice are significantly larger than wild-type mice, and display significant postprandial hyperinsulinemia, whole body insulin resistance, and whole body glucose intolerance. Studies using hyperinsulinemic-euglycemic clamps revealed that Cav-3 null mice exhibited 20% and 40% decreases in insulin-stimulated whole body glucose uptake and whole body glycogen synthesis, respectively. Whole body insulin resistance was mostly attributed to 20% and 40% decreases in insulin-stimulated glucose uptake and glucose metabolic flux in the skeletal muscle of Cav-3 null mice. In addition, insulin-mediated suppression of hepatic glucose production was significantly reduced in Cav-3 null mice, indicating hepatic insulin resistance. Insulin-stimulated glucose uptake in white adipose tissue, which does not express Cav-3, was decreased by approximately 70% in Cav-3 null mice, suggestive of an insulin-resistant state for this tissue. During fasting, Cav-3 null mice possess normal insulin receptor protein levels in their skeletal muscle. However, after 15 min of acute insulin stimulation, Cav-3 null mice show dramatically reduced levels of the insulin receptor protein, compared with wild-type mice treated identically. These results suggest that Cav-3 normally functions to increase the stability of the insulin receptor at the plasma membrane, preventing its rapid degradation, i.e., by blocking or slowing ligand-induced receptor downregulation. Thus our results demonstrate the importance of Cav-3 in regulating whole body glucose homeostasis in vivo and its possible role in the development of insulin resistance. These findings may have clinical implications for the early diagnosis and treatment of caveolinopathies.

Topics: Adipose Tissue; Animals; Blood Glucose; Body Composition; Caveolin 3; Caveolins; Gene Expression; Glycogen; Insulin; Insulin Resistance; Islets of Langerhans; Liver; Mice; Mice, Knockout; Muscle, Skeletal; Receptor, Insulin; Signal Transduction

Insulin resistance with aging may be responsible for impaired glycogen synthesis in the skeletal muscle of aged rats and contribute to the well-known decreased ability to respond to stress with aging. For this reason, to assess the ability of the skeletal muscle to utilize glucose for glycogen synthesis during aging, the time course of glycogen synthesis was continuously monitored by 13C nuclear magnetic resonance for 2 h in isolated [13C] glucose-perfused gastrocnemius-plantaris muscles of 5-day food-deprived adult (6-8 months; n=10) or 5-day food-deprived aged (22 months; n=8) rats. [13C] glucose (10 mmol/L) perfusion was carried out in the presence or absence of an excess of insulin (1 micromol/L). Food deprivation only decreased glycogen level in adult rats (8.9+/-2.4 micromol/g in adults vs. 35.6+/-2.4 micromol/g in aged rats; P<.05). In the presence of an excess of insulin, muscle glycogen synthesis was stimulated in both adult and aged muscles, but the onset was delayed with aging (40 min later). In conclusion, this study highlights the important role of glycogen depletion in stimulating glycogen synthesis in muscles. Consequently, the absence of glycogen depletion in response to starvation in aged rats may be the origin of the delay in insulin-stimulated glycogen synthesis in the skeletal muscle. Glycogen synthesis clearly was not impaired with aging.

Topics: Aging; Animals; Carbon Isotopes; Food Deprivation; Glycogen; Insulin; Insulin Resistance; Kinetics; Magnetic Resonance Spectroscopy; Male; Muscle, Skeletal; Rats; Rats, Wistar

Glucocorticoids cause insulin resistance in skeletal muscle. The aims of the present study were to investigate the effects of contraction on glucose uptake, insulin signaling, and regulation of glycogen synthesis in skeletal muscles from rats treated with the glucocorticoid analog dexamethasone (1 mg x kg(-1) x day(-1) ip for 12 days). Insulin resistance in dexamethasone-treated rats was confirmed by reduced insulin-stimulated glucose uptake (approximately 35%), glycogen synthesis (approximately 70%), glycogen synthase activation (approximately 80%), and PKB Ser(473) phosphorylation (approximately 40%). Chronic dexamethasone treatment did not impair glucose uptake during contraction in soleus or epitrochlearis muscles. In epitrochlearis (but not in soleus), the presence of insulin during contraction enhanced glucose uptake to similar levels in control and dexamethasone-treated rats. Contraction also increased glycogen synthase fractional activity and dephosphorylated glycogen synthase at Ser(645), Ser(649), Ser(653), and Ser(657) normally in muscles from dexamethasone-treated rats. After contraction, insulin-stimulated glycogen synthesis was completely restored in epitrochlearis and improved in soleus from dexamethasone-treated rats. Contraction did not increase insulin-stimulated PKB Ser(473) or glycogen synthase kinase-3 (GSK-3) phosphorylation. Instead, contraction increased GSK-3beta Ser(9) phosphorylation in epitrochlearis (but not in soleus) in muscles from control and dexamethasone-treated rats. In conclusion, contraction stimulates glucose uptake normally in dexamethasone-induced insulin resistant muscles. After contraction, insulin's ability to stimulate glycogen synthesis was completely restored in epitrochlearis and improved in soleus from dexamethasone-treated rats.

Topics: Analysis of Variance; Animals; Blood Glucose; Dexamethasone; Glucocorticoids; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Male; Muscle Contraction; Muscle, Skeletal; Physical Conditioning, Animal; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; Signal Transduction; Statistics, Nonparametric

Insulin modulates glucose homeostasis, but the role of insulin-responsive transcription factors in such actions is not well understood. Recently, we have identified the insulin-response element-binding protein-1 (IRE-BP1) as a transcription factor that appears to mediate insulin action on multiple target genes. To examine the possibility that IRE-BP1 is an insulin-responsive glucoregulatory factor involved in the metabolic actions of insulin, we investigated the effect of adenoviral overexpression of hepatic IRE-BP1 on the glycemic control of insulin-resistant diabetic rats. Adenoviral IRE-BP1 lowered both fasting and postprandial glucose levels, and microarray of hepatic RNA revealed modulation of the expression of genes involved in gluconeogenesis, lipogenesis, and fatty acid oxidation. The insulin mimetic effects of IRE-BP1 were also confirmed in L6 myocytes; stable constitutive expressions of IRE-BP1 enhanced glucose transporter expression, glucose uptake, and glycogen accumulation in these cells. These findings showed physiologic sufficiency of IRE-BP1 as the transcriptional mediator of the metabolic action of insulin. Understanding IRE-BP1 action should constitute a useful probe into the mechanisms of metabolic regulation and an important target to develop therapeutic agents that mimic or enhance insulin action.

Topics: Animals; Base Sequence; Blood Glucose; Cell Line; Diabetes Mellitus, Experimental; DNA, Complementary; Gene Expression Profiling; Glucose; Glycogen; Hyperglycemia; Insulin Resistance; Iron Regulatory Protein 1; Liver; Male; Models, Biological; Monosaccharide Transport Proteins; Rats; Rats, Sprague-Dawley; Rats, Zucker; Transfection

Insulin covalently and allosterically regulates glycogen synthase (GS) and may also cause the translocation of GS from glycogen-poor to glycogen-rich locations. We examined the possible role of subcellular localization of GS and glycogen in insulin activation of GS in skeletal muscle of six obese monkeys and determined whether 1) insulin stimulation during a hyperinsulinemic euglycemic clamp and/or peroxisome proliferator-activated receptor (PPAR)-alpha agonist treatment (K-111, 3 mg.kg(-1).day(-1); Kowa) induced translocation of GS and 2) translocation of GS was associated with insulin activation of GS. GS and glycogen were present in all fractions obtained by differential centrifugation, except for the cytosolic fraction, under both basal and insulin-stimulated conditions. We found no evidence for translocation of GS by insulin. GS total (GST) activity was strongly associated with glycogen content (r = 0.70, P < 0.001). Six weeks of treatment with K-111 increased GST activity in all fractions, except the cytosolic fraction, and mean GST activity, GS independent activity, and glycogen content were significantly higher in the insulin-stimulated samples compared with basal samples, effects not seen with vehicle. The increase in GST activity was strongly related to the increase in glycogen content during the hyperinsulinemic euglycemic clamp after K-111 administration (r = 0.74, P < 0.001). Neither GS protein expression nor GS gene expression was affected by insulin or by K-111 treatment. We conclude that 1) in vivo insulin does not cause translocation of GS from a glycogen-poor to a glycogen-rich location in primate skeletal muscle and 2) the mechanism of action of K-111 to improve insulin sensitivity includes an increase in GST activity without an increase in GS gene or protein expression.

Topics: Adipose Tissue; Amino Acid Sequence; Animals; Cloning, Molecular; DNA, Complementary; Glucose Clamp Technique; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Lauric Acids; Macaca mulatta; Male; Molecular Sequence Data; Muscle, Skeletal; Obesity; PPAR alpha; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Subcellular Fractions

Variation in the calpain 10 gene has been reported to increase susceptibility to type 2 diabetes. Part of this susceptibility appears to be mediated by a decrease in whole body insulin sensitivity. As skeletal muscle is the primary tissue site of the peripheral insulin resistance in type 2 diabetes, the aim of this study was to use a human skeletal muscle cell culture system to explore the effects of calpain inhibition on insulin action. Calpain 10 mRNA and protein expression was examined in cultured myoblasts, myotubes, and whole skeletal muscle from non-diabetic subjects using RT-PCR and Western blotting. Changes in insulin-stimulated glucose uptake and glycogen synthesis in response to the calpain inhibitors ALLN and ALLM were measured. Calpain 10 expression was confirmed in cultured human myoblasts, myotubes, and native skeletal muscle. Insulin-stimulated glucose uptake was significantly decreased following preincubation with ALLN [404+/-40 vs 505+/-55 (mean+/-SEM)pmol/mg/min; with vs without ALLN: p = 0.04] and ALLM [455+/-38 vs 550+/-50 pmol/mg/min; with vs without ALLM: p = 0.025] in day 7 fused myotubes, but not in myoblasts. Neither ALLN nor ALLM affected insulin-stimulated glycogen synthesis in myoblasts or myotubes. These studies confirm calpain 10 expression in cultured human muscle cells and support a role for calpains in insulin-stimulated glucose uptake in human skeletal muscle cells that may be relevant to the pathogenesis of the peripheral insulin resistance in type 2 diabetes.

Topics: Base Sequence; Biological Transport; Calpain; Cell Culture Techniques; Cells, Cultured; Diabetes Mellitus, Type 2; DNA Primers; Gene Expression Regulation, Enzymologic; Genetic Predisposition to Disease; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Muscle, Skeletal; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Transcription, Genetic

Liver slices have been reported to retain histological integrity and metabolic capacity for over 24 hours in flask culture systems, and they have been used for pharmacological and toxicological studies before. However, whether this method is suitable to measure hepatic glucose output is unknown.. Precision-cut liver slices were prepared from fresh male rat liver. After high-glucose pre-incubation (11.2 mmol/l), medium was changed to low-glucose conditions (0.5 mmol/l). Glucose and lactate levels as well as aspartate aminotransferase activity were monitored for 50 minutes with or without addition of insulin (600 pmol/l) and/or epinephrine (0.5 micromol/l). Slice potassium content and histology were examined to prove liver viability.. We observed a stable glucose production from the liver slices of 0.3-0.4 micromol/g liver/min. Epinephrine increased (by 82+/-30%) and insulin decreased (by 80+/-8%) liver slice glucose output. Significant signs of ischemia were not detected.. Hepatic glucose release can be reliably measured in a liver slice culture system, and it is regulated by major hormone systems. This method may be helpful for further characterization of direct insulin action and resistance in a complex tissue as the liver; however, pharmacological applications such as the analysis of drug effects on hepatic glucose metabolism can also be envisioned.

Topics: Animals; Epinephrine; Glucose; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Male; Organ Culture Techniques; Rats; Rats, Wistar; Sympathomimetics

Moderate amounts of alcohol intake have been reported to have a protective effect on the cardiovascular system and this may involve enhanced insulin sensitivity. We established an animal model of increased insulin sensitivity by low ethanol consumption and here we investigated metabolic parameters and molecular mechanisms potentially involved in this phenomenon. For that, Wistar rats have received drinking water either without (control) or with 3% ethanol for four weeks. The effect of ethanol intake on insulin sensitivity was analyzed by insulin resistance index (HOMA-IR), intravenous insulin tolerance test (IVITT) and lipid profile. The role of liver was investigated by the analysis of insulin signaling pathway, GLUT2 gene expression and tissue glycogen content. Rats consuming 3% ethanol showed lower values of HOMA-IR and plasma free fatty acids (FFA) levels and higher hepatic glycogen content and glucose disappearance constant during the IVITT. Neither the phosphorylation of insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), nor its association with phosphatidylinositol-3-kinase (PI3-kinase), was affected by ethanol. However, ethanol consumption enhanced liver IRS-2 and protein kinase B (Akt) phosphorylation (3 times, P<0.05), which can be involved in the 2-fold increased (P<0.05) hepatic glycogen content. The GLUT2 protein content was unchanged. Our findings point out that liver plays a role in enhanced insulin sensitivity induced by low ethanol consumption.

Topics: Alcohol Drinking; Animals; Blotting, Northern; Blotting, Western; Body Weight; Cholesterol; Eating; Ethanol; Fatty Acids, Nonesterified; Gene Expression; Glucose Transporter Type 2; Glycogen; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Lipoproteins; Liver; Male; Monosaccharide Transport Proteins; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; Receptor, Insulin; Triglycerides

We investigated the effects of garlic oil and diallyl trisulfide on glycemic control in rats with streptozotocin-induced diabetes. Diabetic rats received by gavage garlic oil (100 mg/kg body weight), diallyl trisulfide (40 mg/kg body weight), or corn oil every other day for 3 weeks. Control rats received corn oil only. Both garlic compounds significantly raised the basal insulin concentration. The insulin resistance index as assessed by homeostasis model assessment and the first-order rate constant for glucose disappearance were significantly improved by both garlic compounds (P<0.05). Oral glucose tolerance was also improved by both garlic compounds and was accompanied by a significantly increased rate of insulin secretion (P<0.05). Glycogen formation (but not that of lactate or carbon dioxide) from glucose by the soleus muscle in the presence of 10 or 100 microU/ml of insulin was significantly better after treatment with both garlic compounds. Both garlic oil and diallyl trisulfide improve glycemic control in diabetic rats through increased insulin secretion and increased insulin sensitivity.

Topics: Allyl Compounds; Animals; Blood Glucose; Diabetes Mellitus, Experimental; Garlic; Glucose; Glucose Tolerance Test; Glycogen; Hypoglycemic Agents; In Vitro Techniques; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Plant Oils; Rats; Rats, Wistar; Sulfides; Time Factors; Weaning

Protein tyrosine phosphatase 1B (PTP1B) acts as a physiological negative regulator of insulin signaling by dephosphorylating the activated insulin receptor (IR). Here we examine the role of PTP1B in the insulin-sensitizing action of rosiglitazone (RSG) in skeletal muscle and liver. Fat-fed, streptozotocin-treated rats (10-week-old), an animal model of type II diabetes, and age-matched, nondiabetic controls were treated with RSG (10 micromol kg(-1) day(-1)) for 2 weeks. After RSG treatment, the diabetic rats showed a significant decrease in blood glucose and improved insulin sensitivity. Diabetic rats showed significantly increased levels and activities of PTP1B in the skeletal muscle (1.6- and 2-fold, respectively) and liver (1.7- and 1.8-fold, respectively), thus diminishing insulin signaling in the target tissues. We found that the decreases in insulin-stimulated glucose uptake (55%), tyrosine phosphorylation of IRbeta-subunits (48%), and IR substrate-1 (IRS-1) (39%) in muscles of diabetic rats were normalized after RSG treatment. These effects were associated with 34 and 30% decreases in increased PTP1B levels and activities, respectively, in skeletal muscles of diabetic rats. In contrast, RSG did not affect the increased PTP1B levels and activities or the already reduced insulin-stimulated glycogen synthesis and tyrosine phosphorylation of IRbeta-subunits and IRS-2 in livers of diabetic rats. RSG treatment in normal rats did not significantly change PTP1B activities and levels or protein levels of IRbeta, IRS-1, and -2 in diabetic rats. These data suggest that RSG enhances insulin activity in skeletal muscle of diabetic rats possibly by ameliorating abnormal levels and activities of PTP1B.

Topics: Animals; Blotting, Western; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Dietary Fats; Glucose; Glucose Tolerance Test; Glycogen; Hepatocytes; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Liver Glycogen; Male; Muscle, Skeletal; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Protein Tyrosine Phosphatases; Rats; Rats, Sprague-Dawley; Rosiglitazone; Signal Transduction; Thiazolidinediones

Pre-diabetic subjects with high insulin secretory capacity have double risk of cardiovascular disease compared with subjects who do not develop insulin-resistance. It is well established that the ability of the myocardium to increase its glycolytic ATP production plays a crucial role in determining cell survival under conditions of ischemia. Up to now, whether the pre-diabetic state reduces the tolerance of the heart to ischemia by affecting its ability to increase its energy production through glycolysis remains unknown. The aim of the present study was to assess whether insulin resistance affects the ability of the myocardium to increase glycolysis under ischemic conditions. Male Wistar rats were fed for 8 weeks a fructose-enriched (33%) diet to induce a pre-diabetic state. Hearts were isolated and subjected to ex-vivo low-flow (2%) ischemia for 30 min. The fructose diet increased sarcolemmal GLUT4 localisation in myocardial cells under basal conditions compared with controls. This effect was not accompanied by increased glucose utilisation. Ischemia induced the translocation of GLUT4 to the plasma membrane in controls but did not significantly modify the distribution of these transporters in pre-diabetic hearts. Glycolytic flux under ischemic conditions was significantly lower in fructose-fed rat hearts compared with controls. The reduction of glycolytic flux during ischemia in fructose-fed rat hearts was not due to metabolic inhibition downstream hexokinase II since no cardiac accumulation of glucose-6-phosphate was detected. In conclusion, our results suggest that the pre-diabetic state reduces the tolerance of the myocardium to ischemia by decreasing glycolytic flux adaptation.

Topics: Adaptation, Physiological; Animals; Diabetes Mellitus, Experimental; Fructose; Glucose; Glucose Transporter Type 4; Glycogen; Glycolysis; Hexosephosphates; In Vitro Techniques; Insulin Resistance; Lactic Acid; Male; Monosaccharide Transport Proteins; Muscle Proteins; Myocardial Ischemia; Myocardium; Myocytes, Cardiac; Prediabetic State; Protein Transport; Rats; Rats, Wistar; Sarcolemma

O-linked N-acetylglucosamine (O-GlcNAc) is an evolutionarily conserved modification of nuclear pore proteins, signaling kinases, and transcription factors. The O-GlcNAc transferase (OGT) catalyzing O-GlcNAc addition is essential in mammals and mediates the last step in a nutrient-sensing "hexosamine-signaling pathway." This pathway may be deregulated in diabetes and neurodegenerative disease. To examine the function of O-GlcNAc in a genetically amenable organism, we describe a putative null allele of OGT in Caenorhabditis elegans that is viable and fertile. We demonstrate that, whereas nuclear pore proteins of the homozygous deletion strain are devoid of O-GlcNAc, nuclear transport of transcription factors appears normal. However, the OGT mutant exhibits striking metabolic changes manifested in a approximately 3-fold elevation in trehalose levels and glycogen stores with a concomitant approximately 3-fold decrease in triglycerides levels. In nematodes, a highly conserved insulin-like signaling cascade regulates macronutrient storage, longevity, and dauer formation. The OGT knockout suppresses dauer larvae formation induced by a temperature-sensitive allele of the insulin-like receptor gene daf-2. Our findings demonstrate that OGT modulates macronutrient storage and dauer formation in C. elegans, providing a unique genetic model for examining the role of O-GlcNAc in cellular signaling and insulin resistance.

Topics: Animals; Caenorhabditis elegans; Carmine; Disease Models, Animal; DNA Primers; Fluorescent Antibody Technique; Glycogen; Immunoblotting; Insulin Resistance; Larva; Mutation; N-Acetylglucosaminyltransferases; Oxazines; Polymerase Chain Reaction; Signal Transduction; Trehalose; Triglycerides

Treatment with glucocorticoids, especially at high doses, induces insulin resistance. The aims of the present study were to identify the potential defects in insulin signalling that contribute to dexamethasone-induced insulin resistance in skeletal muscles, and to investigate whether the glycogen synthase-3 (GSK-3) inhibitor CHIR-637 could restore insulin-stimulated glucose metabolism.. Skeletal muscles were made insulin-resistant by treating male Wistar rats with dexamethasone, a glucocorticoid analogue, for 12 days. Insulin-stimulated glucose uptake, glycogen synthesis and insulin signalling were studied in skeletal muscles in vitro.. Dexamethasone treatment decreased the ability of insulin to stimulate glucose uptake, glycogen synthesis and glycogen synthase fractional activity. In addition, the dephosphorylation of glycogen synthase by insulin was blocked. These defects were paralleled by reduced insulin-stimulated protein kinase B (PKB) and GSK-3 phosphorylation. While expression of PKB, GSK-3 and glycogen synthase was not reduced by dexamethasone treatment, expression of the p85alpha subunit of phosphatidylinositol 3-kinase (PI 3-kinase) was increased. Inhibition of GSK-3 by CHIR-637 increased glycogen synthase fractional activity in soleus muscle from normal and dexamethasone-treated rats, although the effect was more pronounced in control rats. CHIR-637 did not improve insulin-stimulated glucose uptake in muscles from dexamethasone-treated rats.. We demonstrated that chronic dexamethasone treatment impairs insulin-stimulated PKB and GSK-3 phosphorylation, which may contribute to insulin resistance in skeletal muscles. Acute pharmacological inhibition of GSK-3 activated glycogen synthase in muscles from dexamethasone-treated rats, but GSK-3 inhibition did not restore insulin-stimulated glucose uptake.

Topics: Animals; Antibodies; Blood Glucose; Blotting, Western; Body Weight; Enzyme Inhibitors; Glucocorticoids; Glucose; Glycogen; Glycogen Synthase Kinase 3; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Phosphorylation; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar; Signal Transduction

Second-generation antipsychotic agents (SGAs) are increasingly replacing first-generation antipsychotic agents due to their superior activity against the negative symptoms of schizophrenia, decreased extrapyramidal symptoms and better tolerability. However, some SGAs are associated with adverse metabolic effects as significant weight gain, lipid disorders and diabetes mellitus. The pathogenesis of SGA-induced disturbances of glucose homeostasis is unclear. In vivo studies suggest a direct influence of SGAs on peripheral insulin resistance. To this end, we analyzed whether olanzapine might alter glycogen synthesis and the insulin-signaling cascade in L6 myotubes. Glycogen content was diminished in a dose- and time-dependent manner. Within the insulin-signaling cascade IRS-1 tyrosine phosphorylation was induced several fold by insulin and was diminished by preincubation with olanzapine. IRS-1-associated PI3K activity was stimulated by insulin three-fold in L6 myotubes. Olanzapine inhibited insulin-stimulated IRS-1-associated PI3K activity in a dose-dependent manner. Protein mass of AKT, GSK-3 and GS was unaltered, whereas phosphorylation of AKT and GSK-3 was diminished, and pGS was increased. Finally, we compared olanzapine with amisulpride, an SGA clinically not associated with the induction of diabetes mellitus. Glycogen content was diminished in olanzapine-preincubated L6 cells, whereas this effect was not observed under the amisulpride conditions. We conclude that olanzapine impairs glycogen synthesis via inhibition of the classical insulin-signaling cascade and that this inhibitory effect may lead to the induction of insulin resistance in olanzapine-treated patients.

Topics: Animals; Antipsychotic Agents; Benzodiazepines; Cell Line; Dose-Response Relationship, Drug; Glucose Metabolism Disorders; Glycogen; Insulin; Insulin Resistance; Muscle Fibers, Skeletal; Muscle, Skeletal; Olanzapine; Rats; Signal Transduction

Insulin activates several processes potentially dangerous for the arterial wall and hyperinsulinemia might be atherogenic. However, other insulin effects are protective for the vessel wall and thus anti-atherogenic. Aim of this study was to investigate whether insulin effects on potentially pro-atherogenic and anti-atherogenic processes were differently affected in cells from insulin-resistant individuals.. We determined insulin effect on nitric oxide (NO) production and plasminogen activator inhibitor (PAI)-1 synthesis in 12 fibroblast strains obtained from skin biopsy samples of 6 insulin-sensitive (IS) (clamp M >7 mg/kg body weight per minute) and 6 insulin-resistant (IR) (clamp M <5 mg/kg body weight per minute) healthy volunteers. Insulin effects on NO release and Akt phosphorylation were significantly impaired in fibroblasts from IR as compared with IS individuals. Conversely, there was not any difference between IR and IS strains in insulin ability to increase PAI-1 antigen levels and, after 24-hour insulin incubation, PAI-1 mRNA increase in IR strains was only slightly less than in IS strains. Insulin ability to induce MAPK activation was also comparable in IR and IS cells.. We conclude that in cells from IR individuals, insulin action on anti-atherogenic processes, such as NO release, is impaired, whereas the hormone ability to stimulate atherogenic processes, such as PAI-1 release, is preserved.

Topics: Adult; Atherosclerosis; Cells, Cultured; Culture Media; Female; Fibroblasts; Glucose; Glycogen; Humans; Hyperinsulinism; Insulin; Insulin Resistance; Male; MAP Kinase Signaling System; Nitric Oxide; Nitric Oxide Synthase Type III; Phosphorylation; Plasminogen Activator Inhibitor 1; Proto-Oncogene Proteins c-akt; RNA, Messenger; Serine

We have compared the insulin-like activity of bis(acetylacetonato)oxovanadium(IV) [VO(acac)2], bis(maltolato)oxovanadium(IV) [VO(malto)2], and bis(1-N-oxide-pyridine-2-thiolato)oxovanadium(IV) [VO(OPT)2] in differentiated 3T3-L1 adipocytes. The insulin-like influence of VO(malto)2 and VO(OPT)2 was decreased compared with that of VO(acac)2. Also, serum albumin enhanced the insulin-like activity of all three chelates more than serum transferrin. Each of the three VO2+ chelates increased the tyrosine phosphorylation of proteins in response to insulin, including the beta-subunit of the insulin receptor (IRbeta) and the insulin receptor substrate-1 (IRS1). However, VO(acac)2 exhibited the greatest synergism with insulin and was therefore further investigated. Treatment of 3T3-L1 adipocytes with 0.25 mM VO(acac)2 in the presence of 0.25 mM serum albumin synergistically increased glycogen accumulation stimulated by 0.1 and 1 nM insulin, and increased the phosphorylation of IRbeta, IRS1, protein kinase B, and glycogen synthase kinase-3beta. Wortmannin suppressed all of these classical insulin-signaling activities exerted by VO(acac)2 or insulin, except for tyrosine phosphorylation of IRbeta and IRS1. Additionally, VO(acac)2 enhanced insulin signaling and metabolic action in insulin-resistant 3T3-L1 adipocytes. Cumulatively, these results provide evidence that VO(acac)2 exerts its insulin-enhancing properties by directly potentiating the tyrosine phosphorylation of the insulin receptor, resulting in the initiation of insulin metabolic signaling cascades in 3T3-L1 adipocytes.

Topics: 3T3-L1 Cells; Adipocytes; Animals; Chelating Agents; Enzyme Activation; Glycogen; Glycogen Synthase; Hypoglycemic Agents; Insulin Resistance; Mice; Molecular Structure; Organometallic Compounds; Phosphorylation; Pyrones; Receptor, Insulin; Solutions; Tyrosine; Vanadates

In obesity, skeletal muscle accumulates triglyceride. Recent work from Hulver and colleagues (2005) in the October issue of Cell Metabolism implicates stearoyl-CoA desaturase as part of the underlying molecular mechanism.

Topics: Carnitine O-Palmitoyltransferase; Diabetes Mellitus, Type 2; Fatty Acids; Glycogen; Humans; Insulin Resistance; Malonyl Coenzyme A; Muscle Fibers, Skeletal; Muscle, Skeletal; Obesity; Oxidation-Reduction; Stearoyl-CoA Desaturase; Triglycerides

To determine effects of dexamethasone on insulin sensitivity, serum creatine kinase (CK) activity 4 hours after exercise, and muscle glycogen concentration in Quarter Horses with polysaccharide storage myopathy (PSSM).. 4 adult Quarter Horses with PSSM.. A 2 x 2 crossover design was used with dexamethasone (0.08 mg/kg) or saline (0.9% NaCl) solution administered IV every 48 hours. Horses were exercised on a treadmill daily for 3 wk/treatment with a 2-week washout period between treatments. Serum CK activity was measured daily 4 hours after exercise. At the end of each treatment period, serum cortisol concentrations were measured, a hyperinsulinemic euglycemic clamp (HEC) technique was performed, and muscle glycogen content was determined.. Mean +/- SEM serum cortisol concentration was significantly lower after 48 hours for the dexamethasone treatment (0.38 +/- 0.08 mg/dL), compared with the saline treatment (4.15 +/- 0.40 mg/dL). Dexamethasone significantly decreased the rate of glucose infusion necessary to maintain euglycemia during the HEC technique, compared with the saline treatment. Muscle glycogen concentrations and mean CK activity after exercise were not altered by dexamethasone treatment, compared with the saline treatment.. Dexamethasone significantly reduced whole-body insulin-stimulated glucose uptake in Quarter Horses with PSSM after a 3-week period but did not diminish serum CK response to exercise or muscle glycogen concentrations in these 4 horses. Therefore, a decrease in glucose uptake for 3 weeks did not appear to alleviate exertional rhabdomyolysis in these horses. It is possible that long-term treatment may yield other results.

Topics: Analysis of Variance; Animals; Creatine Kinase; Cross-Over Studies; Dexamethasone; Glucose; Glycogen; Glycogen Storage Disease; Horse Diseases; Horses; Insulin Resistance; Muscle, Skeletal; Physical Exertion

To elucidate the role of muscle glycogen storage on regulation of GLUT4 protein expression and whole-body glucose tolerance, muscle glycogen level was manipulated by exercise and insulin administration. Sixty Sprague-Dawley rats were evenly separated into three groups: control (CON), immediately after exercise (EX0), and 16 h after exercise (EX16). Rats from each group were further divided into two groups: saline- and insulin-injected. The 2-day exercise protocol consisted of 2 bouts of 3-h swimming with 45-min rest for each day, which effectively depleted glycogen in both red gastrocnemius (RG) and plantaris muscles. EX0 rats were sacrificed immediately after the last bout of exercise on second day. CON and EX16 rats were intubated with 1 g/kg glucose solution following exercise and recovery for 16 h before muscle tissue collection. Insulin (0.5 microU/kg) or saline was injected daily at the time when glucose was intubated. Insulin injection elevated muscle glycogen levels substantially in both muscles above saline-injected group at CON and EX16. With previous day insulin injection, EX0 preserved greater amount of postexercise glycogen above their saline-injected control. In the saline-injected rats, EX16 significantly increased GLUT4 protein level above CON, concurrent with muscle glycogen supercompensation. Insulin injection for EX16 rats significantly enhanced muscle glycogen level above their saline-injected control, but the increases in muscle GLUT4 protein and whole-body glucose tolerance were attenuated. In conclusion, the new finding of the study was that glycogen overload by postexercise insulin administration significantly abolished the exercise-induced increases in GLUT4 protein and glucose tolerance.

Topics: Animals; Blood Glucose; Glucose; Glucose Tolerance Test; Glucose Transport Proteins, Facilitative; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Male; Models, Biological; Models, Statistical; Monosaccharide Transport Proteins; Muscle, Skeletal; Muscles; Physical Conditioning, Animal; Rats; Rats, Sprague-Dawley; Temperature; Time Factors

Intestinal glucagon-like peptide-1 (GLP-1) is a hormone released into the hepatoportal circulation that stimulates pancreatic insulin secretion. GLP-1 also acts as a neuropeptide to control food intake and cardiovascular functions, but its neural role in glucose homeostasis is unknown. We show that brain GLP-1 controlled whole-body glucose fate during hyperglycemic conditions. In mice undergoing a hyperglycemic hyperinsulinemic clamp, icv administration of the specific GLP-1 receptor antagonist exendin 9-39 (Ex9) increased muscle glucose utilization and glycogen content. This effect did not require muscle insulin action, as it also occurred in muscle insulin receptor KO mice. Conversely, icv infusion of the GLP-1 receptor agonist exendin 4 (Ex4) reduced insulin-stimulated muscle glucose utilization. In hyperglycemia achieved by i.v. infusion of glucose, icv Ex4, but not Ex9, caused a 4-fold increase in insulin secretion and enhanced liver glycogen storage. However, when glucose was infused intragastrically, icv Ex9 infusion lowered insulin secretion and hepatic glycogen levels, whereas no effects of icv Ex4 were observed. In diabetic mice fed a high-fat diet, a 1-month chronic i.p. Ex9 treatment improved glucose tolerance and fasting glycemia. Our data show that during hyperglycemia, brain GLP-1 inhibited muscle glucose utilization and increased insulin secretion to favor hepatic glycogen stores, preparing efficiently for the next fasting state.

Topics: Adipose Tissue; Animals; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Blood Glucose; Brain; Dose-Response Relationship, Drug; Glucagon-Like Peptide 1; Glucose; Glucose Clamp Technique; Glucose Tolerance Test; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Hyperglycemia; Hyperinsulinism; Insulin; Insulin Resistance; Insulin Secretion; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscles; Nuclear Proteins; Osmosis; Peptide Fragments; Phosphatidylinositol 3-Kinases; Phosphorylation; Receptor, Insulin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Time Factors; Transcription Factors

Physical exercises have been recommended in the prevention of non-insulin dependent diabetes mellitus (NIDDM), but the mechanisms involved in this intervention are not yet fully understood. Experimental models offer the opportunity for the study of this matter. The present study was designed to analyze the diabetes evolution in rats submitted to neonatal treatment with alloxan with the objective of verifying the suitability of the model to future studies with exercises. For this, newly born rats (6 days old) received intraperitoneal alloxan (A=200 mg/kg of body weight). Rats injected with vehicle (citrate buffer) were used as controls (C). The fasting blood glucose level (mg/dL) was higher in the alloxan group at the day 28 (C=47.25 +/- 5.08; A=54.51 +/- 7.03) but not at the 60 day of age (C=69.18 +/- 8.31; A=66.81 +/- 6.08). The alloxan group presented higher blood glucose level during glucose tolerance test (GTT) (mg/dL. 120 min) in relation to the control group both at day 28 (C=16908.9 +/- 1078.8; A=21737.7 +/- 1106.4) and at day 60 (C=11463.45 +/- 655.30; A=15282.21 +/- 1221.84). Insulinaemia during GTT (ng/mL. 120 min) was lower at day 28 (C=158.67 +/- 33.34; A=123.90 +/- 19.80), but presented no difference at day 60 (C=118.83 +/- 26.02; A=97.88 +/- 10.88). At day 60, the glycogen concentration in the soleus muscle (mg/100 mg) was lower in the alloxan group (0.3 +/- 0.13) in relation to the control group (0.5 +/- 0.07). No difference was observed between groups in relation to (micromol/g.h): Glucose Uptake (C=5.8 +/- 0.63; A=5.2 +/- 0.73); Glucose Oxidation (C=4.3 +/- 1.13; A=3.9 +/- 0.44); Glycogen Synthesis (C=0.8 +/- 0.18; A=0.7 +/- 0.18) and Lactate Production (C=3.8 +/- 0.8; A=3.8 +/- 0.7) by the isolated soleus muscle. The glucose-stimulated insulin secretion (16.7mM) by the isolated islets (ng/5 islets. h) of the alloxan group was lower (14.3 +/- 4.7) than the control group (32.0 +/- 7.9). Thus, we may conclude that this neonatal diabetes induction model gathers interesting characteristics and may be useful for further studies on the role of the exercise in the diabetes mellitus appearance.

Topics: Animals; Animals, Newborn; Diabetes Mellitus, Experimental; Disease Progression; Female; Glucose; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Islets of Langerhans; Male; Muscle, Skeletal; Rats; Rats, Wistar; Weight Gain

To assess the role of the alpha1b-adrenergic receptor (AR) in glucose homeostasis, we investigated glucose metabolism in knockout mice deficient of this receptor subtype (alpha1b-AR-/-). Mutant mice had normal blood glucose and insulin levels, but elevated leptin concentrations in the fed state. During the transition to fasting, glucose and insulin blood concentrations remained markedly elevated for at least 6 h and returned to control levels after 24 h whereas leptin levels remained high at all times. Hyperinsulinemia in the post-absorptive phase was normalized by atropine or methylatropine indicating an elevated parasympathetic activity on the pancreatic beta cells, which was associated with increased levels of hypothalamic NPY mRNA. Euglycemic clamps at both low and high insulin infusion rates revealed whole body insulin resistance with reduced muscle glycogen synthesis and impaired suppression of endogenous glucose production at the low insulin infusion rate. The liver glycogen stores were 2-fold higher in the fed state in the alpha1b-AR-/- compared with control mice, but were mobilized at the same rate during the fed to fast transition or following glucagon injections. Finally, high fat feeding for one month increased glucose intolerance and body weight in the alpha1b-AR-/-, but not in control mice. Altogether, our results indicate that in the absence of the alpha1b-AR the expression of hypotalamic NPY and the parasympathetic nervous activity are both increased resulting in hyperinsulinemia and insulin resistance as well as favoring obesity and glucose intolerance development during high fat feeding.

Topics: Animals; Blood Glucose; Body Weight; Glucagon; Glucose; Glycogen; Homeostasis; Hyperinsulinism; Insulin Resistance; Leptin; Liver; Male; Mice; Mice, Mutant Strains; Mice, Obese; Receptors, Adrenergic; Receptors, Adrenergic, alpha-1; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Time Factors

In the liver, insulin controls both lipid and glucose metabolism through its cell surface receptor and intracellular mediators such as phosphatidylinositol 3-kinase and serine-threonine kinase AKT. The insulin signaling pathway is further modulated by protein tyrosine phosphatase or lipid phosphatase. Here, we investigated the function of phosphatase and tension homologue deleted on chromosome 10 (PTEN), a negative regulator of the phosphatidylinositol 3-kinase/AKT pathway, by targeted deletion of Pten in murine liver. Deletion of Pten in the liver resulted in increased fatty acid synthesis, accompanied by hepatomegaly and fatty liver phenotype. Interestingly, Pten liver-specific deletion causes enhanced liver insulin action with improved systemic glucose tolerance. Thus, deletion of Pten in the liver may provide a valuable model that permits the study of the metabolic actions of insulin signaling in the liver, and PTEN may be a promising target for therapeutic intervention for type 2 diabetes.

Topics: Adipose Tissue; Animals; Blood Glucose; Fasting; Fatty Acids; Fatty Liver; Gene Deletion; Gluconeogenesis; Glucose Tolerance Test; Glycogen; Hepatocytes; Hepatomegaly; Insulin; Insulin Resistance; Liver; Mice; Organ Specificity; RNA, Messenger

Insulin receptor substrate 2 (IRS-2) is the main mediator of insulin signalling in the liver, controlling insulin sensitivity. Sterol regulatory element binding proteins (SREBPs) have been established as transcriptional regulators of lipid synthesis. Here, we show that SREBPs directly repress transcription of IRS-2 and inhibit hepatic insulin signalling. The IRS-2 promoter is activated by forkhead proteins through an insulin response element (IRE). Nuclear SREBPs effectively replace and interfere in the binding of these transactivators, resulting in inhibition of the downstream PI(3)K/Akt pathway, followed by decreased glycogen synthesis. These data suggest a molecular mechanism for the physiological switching from glycogen synthesis to lipogenesis and hepatic insulin resistance that is associated with hepatosteatosis.

Topics: Animals; CCAAT-Enhancer-Binding Proteins; Cells, Cultured; DNA-Binding Proteins; Feedback, Physiological; Forkhead Transcription Factors; Glycogen; Hepatocytes; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Lipid Metabolism; Liver; Male; Mice; Mice, Inbred C57BL; Nuclear Proteins; Phosphatidylinositol 3-Kinases; Phosphoproteins; Promoter Regions, Genetic; Rats; Rats, Sprague-Dawley; Repressor Proteins; Response Elements; Signal Transduction; Sterol Regulatory Element Binding Protein 1; Transcription Factors; Transcriptional Activation

Skeletal muscle insulin resistance may be aggravated by intramyocellular accumulation of fatty acid-derived metabolites that inhibit insulin signaling. We tested the hypothesis that enhanced fatty acid oxidation in myocytes should protect against fatty acid-induced insulin resistance by limiting lipid accumulation. L6 myotubes were transduced with adenoviruses encoding carnitine palmitoyltransferase I (CPT I) isoforms or beta-galactosidase (control). Two to 3-fold overexpression of L-CPT I, the endogenous isoform in L6 cells, proportionally increased oxidation of the long-chain fatty acids palmitate and oleate and increased insulin stimulation of [(14)C]glucose incorporation into glycogen by 60% while enhancing insulin-stimulated phosphorylation of p38MAPK. Incubation of control cells with 0.2 mm palmitate for 18 h caused accumulation of triacylglycerol, diacylglycerol, and ceramide (but not long-chain acyl-CoA) and decreased insulin-stimulated [(14)C]glucose incorporation into glycogen (60%), [(3)H]deoxyglucose uptake (60%), and protein kinase B phosphorylation (20%). In the context of L-CPT I overexpression, palmitate preincubation produced a relative decrease in insulin-stimulated incorporation of [(14)C]glucose into glycogen (60%) and [(3)H]deoxyglucose uptake (40%) but did not inhibit phosphorylation of protein kinase B. Due to the enhancement of insulin-stimulated glucose metabolism induced by L-CPT I overexpression itself, net insulin-stimulated incorporation of [(14)C]glucose into glycogen and [(3)H]deoxyglucose uptake in L-CPT I-transduced, palmitate-treated cells were significantly greater than in palmitate-treated control cells (71 and 75% greater, respectively). However, L-CPT I overexpression failed to decrease intracellular triacylglycerol, diacylglycerol, ceramide, or long-chain acyl-CoA. We propose that accelerated beta-oxidation in muscle cells exerts an insulin-sensitizing effect independently of changes in intracellular lipid content.

Topics: Adenoviridae; Animals; Carnitine O-Palmitoyltransferase; Cells, Cultured; Deoxyglucose; Fatty Acids; Glucose; Glycogen; Insulin; Insulin Resistance; Isoenzymes; Lipid Metabolism; Muscle Fibers, Skeletal; Oxidation-Reduction; Palmitates; Rats; RNA, Messenger; Signal Transduction; Transduction, Genetic

Topics: Biological Transport; Erythrocyte Membrane; Glucose; Glycogen; Humans; Hyperinsulinism; Hypertension; Insulin; Insulin Resistance; Membrane Fluidity; Muscle, Skeletal

Short term high fat feeding in rats results specifically in hepatic fat accumulation and provides a model of non-alcoholic fatty liver disease in which to study the mechanism of hepatic insulin resistance. Short term fat feeding (FF) caused a approximately 3-fold increase in liver triglyceride and total fatty acyl-CoA content without any significant increase in visceral or skeletal muscle fat content. Suppression of endogenous glucose production (EGP) by insulin was diminished in the FF group, despite normal basal EGP and insulin-stimulated peripheral glucose disposal. Hepatic insulin resistance could be attributed to impaired insulin-stimulated IRS-1 and IRS-2 tyrosine phosphorylation. These changes were associated with activation of PKC-epsilon and JNK1. Ultimately, hepatic fat accumulation decreased insulin activation of glycogen synthase and increased gluconeogenesis. Treatment of the FF group with low dose 2,4-dinitrophenol to increase energy expenditure abrogated the development of fatty liver, hepatic insulin resistance, activation of PKC-epsilon and JNK1, and defects in insulin signaling. In conclusion, these data support the hypothesis hepatic steatosis leads to hepatic insulin resistance by stimulating gluconeogenesis and activating PKC-epsilon and JNK1, which may interfere with tyrosine phosphorylation of IRS-1 and IRS-2 and impair the ability of insulin to activate glycogen synthase.

Topics: Animals; Blotting, Western; Cell Membrane; Cytosol; Deoxyglucose; Enzyme Activation; Fatty Acids; Fatty Liver; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Lipid Metabolism; Liver; Male; Mitogen-Activated Protein Kinase 8; Mitogen-Activated Protein Kinases; Phosphorylation; Precipitin Tests; Protein Isoforms; Protein Kinase C; Protein Kinase C-epsilon; Protein Transport; Rats; Rats, Sprague-Dawley; RNA, Messenger; Signal Transduction; Time Factors; Tyrosine

We previously reported that the Goto-Kakizaki (GK) rat, an animal model of type 2 diabetes, has hepatic insulin resistance using a perfused rat liver model. Pioglitazone, eicosapentaenoic acid (EPA), and fenofibrate are antihyperlipidemic agents and improve glucose tolerance. There have been few studies showing that these agents directly improve hepatic insulin sensitivity in type 2 diabetes mellitus. The aim of this study was to explore the effects of these agents on hepatic insulin sensitivity directly using a perfused GK rat liver model.. GK rats were treated with oral pioglitazone (6 or 10 mg/kg body weight), EPA (1 or 2 g/kg body weight), or fenofibrate (30 mg/kg body weight) for 2 weeks. Livers were perfused in situ with glucagon or with glucagon and insulin, and hepatic glucose outputs were measured.. In the pioglitazone-treated GK rats, blood glucose levels were significantly decreased. In the pioglitazone- and EPA-treated GK rats, insulin infusion significantly attenuated hepatic glucose output stimulated by glucagon. In the fenofibrate-treated GK rats, fat deposits in the hepatocytes were decreased, and glucose output elicited by glucagon was significantly decreased compared with that in the untreated GK rats, whereas insulin infusion did not affect glucose output by glucagon.. These findings suggest that pioglitazone and EPA may improve glucose tolerance by directly increasing hepatic insulin sensitivity, while fenofibrate may improve glucose tolerance by improving hepatic glycogen metabolism in the GK rats. We previously reported that the Goto-Kakizaki (GK) rat, an animal model of type 2 diabetes, has hepatic insulin resistance using a perfused rat liver model. Pioglitazone, eicosapentaenoic acid (EPA), and fenofibrate are antihyperlipidemic agents and improve glucose tolerance. There have been few studies showing that these agents directly improve hepatic insulin sensitivity in type 2 diabetes mellitus. The aim of this study was to explore the effects of these agents on hepatic insulin sensitivity directly using a perfused GK rat liver model.

Topics: Animals; Diabetes Mellitus, Type 2; Eicosapentaenoic Acid; Fenofibrate; Glycogen; Hypoglycemic Agents; Hypolipidemic Agents; Insulin Resistance; Liver; Male; Models, Animal; Perfusion; Pioglitazone; Rats; Thiazolidinediones

Insulin resistance is one of the primary characteristics of type 2 diabetes. Mice overexpressing a dominant-negative IGF-I receptor specifically in muscle (MKR mice) demonstrate severe insulin resistance with high levels of serum and tissue lipids and eventually develop type 2 diabetes at 5-6 wk of age. To determine whether lipotoxicity plays a role in the progression of the disease, we crossed MKR mice with mice overexpressing a fatty acid translocase, CD36, in skeletal muscle. The double-transgenic MKR/CD36 mice showed normalization of the hyperglycemia and the hyperinsulinemia as well as a marked improvement in liver insulin sensitivity. The MKR/CD36 mice also exhibited normal rates of fatty acid oxidation in skeletal muscle when compared with the decreased rate of fatty acid oxidation in MKR. With the reduction in insulin resistance, beta-cell function returned to normal. These and other results suggest that the insulin resistance in the MKR mice is associated with increased muscle triglycerides levels and that whole-body insulin resistance can be, at least partially, reversed in association with a reduction in muscle triglycerides levels, although the mechanisms are yet to be determined.

Topics: Animals; CD36 Antigens; Diabetes Mellitus, Type 2; Fatty Acids; Glucose; Glucose Clamp Technique; Glycogen; Hyperglycemia; Hyperinsulinism; In Vitro Techniques; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Liver; Male; Mice; Mice, Transgenic; Muscle, Skeletal; Oxidation-Reduction; Triglycerides

Impaired insulin action is a characteristic feature of type 2 diabetes. The study aims were to investigate whether after prolonged culture skeletal muscle cultures from insulin-resistant, type 2 diabetic patients (taking >100 U insulin/d) displayed impaired insulin signaling effects compared with cultures from nondiabetic controls and to determine whether retained abnormalities were limited to insulin action by studying an alternative pathway of stimulated glucose uptake. Studies were performed on myotubes differentiated for 7 d between passages 4 and 6. Insulin-stimulated glucose uptake (100 nm; P < 0.05) and insulin-stimulated glycogen synthesis (1 nm; P < 0.01) were significantly impaired in the diabetic vs. control cultures. Protein kinase B (PKB) expression and phosphorylated PKB levels in response to insulin stimulation (20 nm) were comparable in the diabetic and control cultures. 5-Amino-4-imidazolecarboxamide riboside (AICAR) mimics the effect of exercise on glucose uptake by activating AMP-activated protein kinase. There was no difference in AICAR (2 mm)-stimulated glucose uptake between diabetic vs. control myotube cultures (P = not significant). In conclusion, diabetic muscle cultures retain signaling defects after prolonged culture that appear specific to the insulin signaling pathway, but not involving PKB. This supports an intrinsic abnormality of the diabetic muscle cells that is most likely to have a genetic basis.

Topics: Aged; Aminocaproic Acid; Cells, Cultured; Diabetes Mellitus, Type 2; Female; Glucose; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Resistance; Male; Middle Aged; Muscle Fibers, Skeletal; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Time Factors

We hypothesized that levodopa with carbidopa, a common therapy for patients with Parkinson's disease, might contribute to the high prevalence of insulin resistance reported in patients with Parkinson's disease. We examined the effects of levodopa-carbidopa on glycogen concentration, glycogen synthase activity, and insulin-stimulated glucose transport in skeletal muscle, the predominant insulin-responsive tissue. In isolated muscle, levodopa-carbidopa completely prevented insulin-stimulated glycogen accumulation and glucose transport. The levodopa-carbidopa effects were blocked by propranolol, a beta-adrenergic antagonist. Levodopa-carbidopa also inhibited the insulin-stimulated increase in glycogen synthase activity, whereas propranolol attenuated this effect. Insulin-stimulated tyrosine phosphorylation of insulin receptor substrate (IRS)-1 was reduced by levodopa-carbidopa, although Akt phosphorylation was unaffected by levodopa-carbidopa. A single in vivo dose of levodopa-carbidopa increased skeletal muscle cAMP concentrations, diminished glycogen synthase activity, and reduced tyrosine phosphorylation of IRS-1. A separate set of rats was treated intragastrically twice daily for 4 wk with levodopa-carbidopa. After 4 wk of treatment, oral glucose tolerance was reduced in rats treated with drugs compared with control animals. Muscles from drug-treated rats contained at least 15% less glycogen and approximately 50% lower glycogen synthase activity compared with muscles from control rats. The data demonstrate beta-adrenergic-dependent inhibition of insulin action by levodopa-carbidopa and suggest that unrecognized insulin resistance may exist in chronically treated patients with Parkinson's disease.

Topics: Animals; Carbidopa; Dopamine Agents; Drug Synergism; Glucose; Glucose Tolerance Test; Glycogen; Glycogen Synthase; Hypoglycemic Agents; Insulin; Insulin Resistance; Levodopa; Male; Muscle, Skeletal; Rats; Rats, Wistar

To assess the effect of taurine supplementation on respiratory gas exchange, which might reflect the improved metabolism of glucose and/or lipid in the type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats.. Male OLETF rats (16 weeks of age) were randomly divided into two groups: unsupplemented group and taurine-supplemented (3% in drinking water) group. After 9 weeks of treatment, indirect calorimetry and insulin tolerance tests were conducted. The amounts of visceral fat pads, tissue glycogen, the blood concentrations of glucose, triacylglycerol, taurine, and electrolytes, and the level of hematocrit were compared between groups. A nondiabetic rat strain (Long-Evans Tokushima Otsuka) was used as the age-matched normal control.. The indirect calorimetry showed that the treatment of OLETF rats with taurine could reduce a part of postprandial glucose oxidation possibly responsible for the increase of triacylglycerol synthesis in the body. Taurine supplementation also improved hyperglycemia and insulin resistance and increased muscle glycogen content in the OLETF rats. Supplementation with taurine increased the blood concentration of taurine and electrolyte and fluid volume, all of which were considered to be related to the improvement of metabolic disturbance in OLETF rats.. Taurine supplementation may be an effective treatment for glucose intolerance and fat/lipid accumulation observed in type 2 diabetes associated with obesity. These metabolic changes might be ascribed, in part, to the alteration of circulating blood profiles, where the improved hyperglycemia and/or the blood accumulation of taurine itself would play roles.

Topics: Animal Nutritional Physiological Phenomena; Animals; Blood; Blood Glucose; Blood Pressure; Body Weight; Calorimetry, Indirect; Diabetes Mellitus, Type 2; Dietary Supplements; Drinking; Eating; Electrolytes; Food; Glycogen; Hematocrit; Insulin; Insulin Resistance; Male; Osmolar Concentration; Pulmonary Gas Exchange; Rats; Rats, Inbred OLETF; Taurine

To determine the impact of insulin resistance and obesity on muscle triacylglycerol (IMTG) and glycogen metabolism during and after prolonged exercise.. Female lean (fa/?; N = 40, ZL) and obese insulin-resistant (fa/fa; N = 40, ZO) Zucker rats performed an acute bout of swimming exercise (8 times for 30 minutes) followed by 6 hours of carbohydrate supplementation (CHO) or fasting (FAST). IMTG and glycogen were measured in the extensor digitorum longus (EDL) and red vastus lateralis (RVL) muscles.. Despite resting IMTG content being 4-fold higher in ZO compared with ZL rats, IMTG levels were unchanged in either EDL or RVL muscles immediately after exercise. Resting glycogen concentration in EDL and RVL muscles was similar between genotypes, with exercise resulting in glycogen use in both muscles from ZL rats (approximately 85%, p < 0.05). However, in ZO rats, there was a much smaller decrease in postexercise glycogen content in both EDL and RVL muscles (approximately 30%). During postexercise recovery, there was a decrease in EDL muscle levels of IMTG in ZL rats supplemented with CHO after 30 and 360 minutes (p < 0.05). In contrast, IMTG content was increased above resting levels in RVL muscles of ZO rats fasted for 360 minutes. Six hours of CHO refeeding restored glycogen content to resting levels in both muscles in ZL rats. However, after 6 hours of FAST in ZO animals, RVL muscle glycogen content was still lower than resting levels (p < 0.05). At this time, IMTG levels were elevated above basal (p < 0.05).. In both healthy and insulin-resistant skeletal muscle, there was negligible net IMTG degradation after a single bout of prolonged exercise. However, during postexercise recovery, there was differential metabolism of IMTG between phenotypes.

Topics: Animals; Blood Glucose; Dietary Carbohydrates; Eating; Fatty Acids, Nonesterified; Female; Glycogen; Insulin; Insulin Resistance; Kinetics; Lactic Acid; Muscle, Skeletal; Obesity; Physical Exertion; Rats; Rats, Zucker; Triglycerides

Recent research has reported that high sugar diets increase insulin resistance, without abdominal obesity, in male, but not female Wistar rats. Whether a high sucrose (SU) diet increased insulin resistance in ovariectomized (OVX) rats was determined.. Female Sprague Dawley rats, weighing 273 +/- 20 g, had either an ovariectomy or a sham operation (sham). OVX and sham rats were divided into two groups: one group had a 68 En% SU diet and the other a 68 En% starch (ST) diet for 8 weeks.. The body weight was higher in the OVX than the sham rats, regardless of dietary carbohydrate subtype. The fasting serum glucose levels did not differ according to diet and ovariectomy. However, the fasting serum insulin levels were higher in the OVX than the sham rats, and in the OVX rats, a high SU diet increased the serum insulin levels more than a high ST diet. The whole body glucose disposal rates, which referred to the state of insulin sensitivity, were lower in the OVX rats fed both the high SU and ST diets, compared to sham rats. Glycogen deposits in the soleus and quadriceps muscles were lower in the OVX rats fed high SU and ST diets than in sham rats. The glucose transporter 4 content and fraction velocity of glycogen synthase in muscles showed similar glucose disposal rates. However, the triacylglycerol content in the muscles were higher in the OVX rats with a high SU diet than those with a high ST diet.. These results suggested that an OVX increased the weight gain due to higher food intakes, regardless of dietary carbohydrate subtypes. OVX-induced obesity may be involved in the induction of insulin resistance from an increased triacylglycerol content, decreased glucose uptake and glycogen synthesis in skeletal muscles, regardless of dietary carbohydrate subtypes.

Topics: Animals; Blood Glucose; Body Weight; Dietary Carbohydrates; Energy Intake; Estradiol; Female; Glucose Clamp Technique; Glucose Transporter Type 4; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Leptin; Models, Animal; Muscle, Skeletal; Ovariectomy; Rats; Rats, Sprague-Dawley; Time Factors; Triglycerides

Glycogen synthase kinase-3 (GSK-3) protein levels and activity are elevated in skeletal muscle in type 2 diabetes, and inversely correlated with both glycogen synthase activity and insulin-stimulated glucose disposal. To explore this relationship, we have produced transgenic mice that overexpress human GSK-3beta in skeletal muscle. GSK-3beta transgenic mice were heavier, by up to 20% (P < .001), than their age-matched controls due to an increase in fat mass. The male GSK-3beta transgenic mice had significantly raised plasma insulin levels and by 24 weeks of age became glucose-intolerant as determined by a 50% increase in the area under their oral glucose tolerance curve (P < .001). They were also hyperlipidemic with significantly raised serum cholesterol (+90%), nonesterified fatty acids (NEFAs) (+55%), and triglycerides (+170%). At 29 weeks of age, GSK-3beta protein levels were 5-fold higher, and glycogen synthase activation (-27%), glycogen levels (-58%) and insulin receptor substrate-1 (IRS-1) protein levels (-67%) were significantly reduced in skeletal muscle. Hepatic glycogen levels were significantly increased 4-fold. Female GSK-3beta transgenic mice did not develop glucose intolerance despite 7-fold overexpression of GSK-3beta protein and a 20% reduction in glycogen synthase activation in skeletal muscle. However, plasma NEFAs and muscle IRS-1 protein levels were unchanged in females. We conclude that overexpression of human GSK-3beta in skeletal muscle of male mice resulted in impaired glucose tolerance despite raised insulin levels, consistent with the possibility that elevated levels of GSK-3 in type 2 diabetes are partly responsible for insulin resistance.

Topics: Animals; Blotting, Western; Body Composition; Body Weight; DNA Primers; DNA, Complementary; Female; Glucose Intolerance; Glucose Tolerance Test; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Insulin Receptor Substrate Proteins; Insulin Resistance; Lipids; Liver; Male; Mice; Mice, Transgenic; Muscle, Skeletal; Phenotype; Phosphoproteins; Promoter Regions, Genetic; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

We previously demonstrated that transgenic mice overexpressing mouse apolipoprotein A-II (apoA-II) exhibit several traits associated with the insulin resistance (IR) syndrome, including increased atherosclerosis, hypertriglyceridemia, obesity, and IR. The skeletal muscle appeared to be the insulin-resistant tissue in the apoA-II transgenic mice. We now demonstrate a decrease in FA oxidation in skeletal muscle of apoA-II transgenic mice, consistent with reports that decreased skeletal muscle FA oxidation is associated with increased skeletal muscle triglyceride accumulation, skeletal muscle IR, and obesity. The decrease in FA oxidation is not due to decreased carnitine palmitoyltransferase 1 activity, because oxidation of palmitate and octanoate were similarly decreased. Quantitative RT-PCR analysis of gene expression demonstrated that the decrease in FA oxidation may be explained by a decrease in medium chain acyl-CoA dehydrogenase. We previously demonstrated that HDLs from apoA-II transgenic mice exhibit reduced binding to CD36, a scavenger receptor involved in FA metabolism. However, studies of combined apoA-II transgenic and CD36 knockout mice suggest that the major effects of apoA-II are independent of CD36. Rosiglitazone treatment significantly ameliorated IR in the apoA-II transgenic mice, suggesting that the underlying mechanisms of IR in this animal model may share common features with certain types of human IR.

Topics: Animals; Apolipoprotein A-II; Female; Gene Dosage; Glycogen; Heterozygote; Homozygote; Insulin Resistance; Liver; Male; Mice; Mice, Transgenic; Muscle, Skeletal

Amylin can evoke insulin resistance by antagonizing insulin in a non-competitive manner. Here, we investigated the glycogenolytic effect of amylin in isolated skeletal muscle and compared it to the effects of a calcitonin gene-related peptide (CGRP). Amylin alone had no statistically significant effect on glucose transport. However, amylin decreased insulin-stimulated glucose transport by about 30%. The involvement of cAMP could not be detected at the concentrations shown to promote glycogenolysis. Previously, it has been shown that increased glycogen synthase kinase 3 (GSK3) activity plays a role in insulin resistance. Here, the ratio of GSK3 alpha:beta isoforms in rat soleus was found to be 1.2:1. We found that amylin increased GSK3alpha activity, which in turn led to increased phosphorylation of glycogen synthase and decreased glycogen synthesis de novo.

Topics: Amyloid; Animals; Calcitonin Gene-Related Peptide; Cyclic AMP; Deoxyglucose; Glycogen; Glycogen Synthase Kinase 3; In Vitro Techniques; Insulin Resistance; Islet Amyloid Polypeptide; Muscle, Skeletal; Rats

To explore the molecular defects of insulin signalling in polycystic ovary and in vitro effects of troglitazone, one of the insulin sensitizers-thiazolidinediones on polycystic ovary syndrome (PCOS).. The metabolic and mitogenic effects of insulin and insulin-like growth factor 1 (IGF-1) were examined in cultured human ovarian luteinizing granulosa cells from PCOS (n = 11) and normally ovulatory (as control, n = 33) women with vehicle or troglitazone (1 microg/ml).. Basal rates were similar, but there were significant decreases in insulin-stimulated glucose incorporation into glycogen in PCOS cells, a metabolic action of insulin. However, IGF-1 response was found to be about twice greater in PCOS cells at all experimental concentrations with respect to thymidine incorporation compared to control cells, a mitogenic action. Troglitazone increased 2-3 fold the insulin-induced glycogen synthesis, but reduced the IGF-1 augmented responses of DNA synthesis in PCOS cells to within the range of control granulosa cells. As compared with control, PCOS granulosa cells had higher insulin receptor substrate 1 (IRS -1) expression, but lower IRS-2 expression. IRS-2 protein levels were increased and IRS-1 levels were reduced by troglitazone treatment, with a greater extent in the former.. There is a selective defect in insulin actions in PCOS granulosa cells, suggesting ovarian insulin resistance and this metabolic phenotype is associated with an enhanced IGF-1 mitogenic potential. Troglitazone could divergently alter signal protein expressions and thus insulin actions, as an ovarian insulin sensitizer and mitogen/steroidogenic inhibitor in PCOS.

Topics: Adult; Cells, Cultured; Female; Glycogen; Humans; Insulin; Insulin Resistance; Insulin-Like Growth Factor I; Ovary; Polycystic Ovary Syndrome; Signal Transduction; Thiazoles

To understand the day-to-day pathophysiology of impaired muscle glycogen storage in type 2 diabetes, glycogen concentrations were measured before and after the consumption of sequential mixed meals (breakfast: 190.5 g carbohydrate, 41.0 g fat, 28.8 g protein, 1253 kcal; lunch: 203.3 g carbohydrate, 48.1 g fat, 44.0 g protein, 1497.5 kcal) by use of natural abundance (13)C magnetic resonance spectroscopy. Subjects with diet-controlled type 2 diabetes (n = 9) and age- and body mass index-matched nondiabetic controls (n = 9) were studied. Mean fasting gastrocnemius glycogen concentration was significantly lower in the diabetic group (57.1 +/- 3.6 vs. 68.9 +/- 4.1 mmol/l; P < 0.05). After the first meal, mean glycogen concentration in the control group rose significantly from basal (97.1 +/- 7.0 mmol/l at 240 min; P = 0.005). After the second meal, the high level of muscle glycogen concentration in the control group was maintained, with a further rise to 108.0 +/- 11.6 mmol/l by 480 min. In the diabetic group, the postprandial rise was markedly lower than that of the control group (65.9 +/- 5.2 mmol/l at 240 min, P < 0.005, and 70.8 +/- 6.7 mmol/l at 480 min, P = 0.01) despite considerably greater serum insulin levels (752.0 +/- 109.0 vs. 372.3 +/- 78.2 pmol/l at 300 min, P = 0.013). This was associated with a significantly greater postprandial hyperglycemia (10.8 +/- 1.3 vs. 5.3 +/- 0.2 mmol/l at 240 min, P < 0.005). Basal muscle glycogen concentration correlated inversely with fasting blood glucose (r = -0.55, P < 0.02) and fasting serum insulin (r = -0.57, P < 0.02). The increment in muscle glycogen correlated with initial increment in serum insulin only in the control group (r = 0.87, P < 0.002). This study quantitates for the first time the subnormal basal muscle glycogen concentration and the inadequate glycogen storage after meals in type 2 diabetes.

Topics: Blood Glucose; C-Peptide; Diabetes Mellitus, Type 2; Fatty Acids, Nonesterified; Female; Glycogen; Humans; Insulin; Insulin Resistance; Lactic Acid; Magnetic Resonance Spectroscopy; Male; Middle Aged; Muscle, Skeletal; Postprandial Period; Triglycerides

Improvement of insulin sensitivity and lipid and glucose metabolism by coactivation of both nuclear peroxisome proliferator-activated receptor (PPAR)gamma and PPARalpha potentially provides beneficial effects over existing PPARgamma and alpha preferential drugs, respectively, in treatment of type 2 diabetes. We examined the effects of the dual PPARalpha/gamma agonist ragaglitazar on hyperglycemia and whole body insulin sensitivity in early and late diabetes stages in Zucker diabetic fatty (ZDF) rats and compared them with treatment with the PPARgamma preferential agonist rosiglitazone. Despite normalization of hyperglycemia and Hb A(1c) and reduction of plasma triglycerides by both compounds in both prevention and early intervention studies, ragaglitazar treatment resulted in overall reduced circulating insulin and improved insulin sensitivity to a greater extent than after treatment with rosiglitazone. In late-intervention therapy, ragaglitazar reduced Hb A(1c) by 2.3% compared with 1.1% by rosiglitazone. Improvement of insulin sensitivity caused by the dual PPARalpha/gamma agonist ragaglitazar seemed to have beneficial impact over that of the PPARgamma-preferential activator rosiglitazone on glycemic control in frankly diabetic ZDF rats.

Topics: Animals; Body Composition; Body Weight; Diabetes Mellitus, Type 2; Dose-Response Relationship, Drug; Eating; Fatty Acids, Nonesterified; Glucose Clamp Technique; Glycated Hemoglobin; Glycogen; Hypoglycemic Agents; Insulin Resistance; Islets of Langerhans; Liver; Male; Oxazines; Phenylpropionates; Rats; Rats, Zucker; Receptors, Cytoplasmic and Nuclear; Rosiglitazone; Thiazoles; Thiazolidinediones; Transcription Factors

This study aimed to investigate the effect of long-term oral nicotine administration on insulin resistance in an animal model of obesity. Eight-week-old male Zucker fatty rats (ZFRs) were administered nicotine tartrate dihydrate (4.6 mg/kg/day) in the drinking water. The control group was pair-fed. The body weights and food intake over 8 weeks were similar in both groups. Plasma glucose levels at 3, 6, 9, 12, and 15 min after insulin administration (0.5 U/kg) in the nicotine group were significantly lower than those in the control group. The calculated K(ITT) value for the nicotine group was significantly higher than that for the control group. Wet weight of the liver in the nicotine group was significantly lower than that in the control group. Transaminases and histological examination of the liver revealed no alteration by nicotine administration. Glycogen, glycogen synthetase activity and gluconeogenesis in the liver in the nicotine group were significantly lower than those in the control group. Phosphorylase-a activity of the liver in the nicotine group was significantly higher than that in the control group. Glycogen, glycogen synthetase, and phosphorylase-a activity of skeletal muscle were similar in both groups. These results suggest that long-term oral nicotine administration may reduce insulin resistance in obese diabetic rats through a reduced hepatic glucose release and, in part, contribute to lowering blood glucose levels.

Topics: Administration, Oral; Animals; Blood Glucose; Body Weight; Eating; Ganglionic Stimulants; Gluconeogenesis; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Liver; Male; Muscle, Skeletal; Nicotine; Obesity; Organ Size; Phosphorylase a; Rats; Rats, Zucker; Time Factors

In utero overexposure to glucocorticoids may explain the association between low birth weight and subsequent development of the metabolic syndrome. We previously showed that prenatal dexamethasone (dex) exposure in the rat lowers birth weight and programs adult fasting and postprandial hyperglycemia, associated with increased hepatic gluconeogenesis driven by elevated liver glucocorticoid receptor (GR) expression. This study aimed to determine whether prenatal dex (100 microg/kg per day from embryonic d 15 to embryonic d 21) programs adult GR expression in skeletal muscle and/or adipose tissue and whether this contributes to altered peripheral glucose uptake or metabolism. In utero dex-exposed rats remained lighter until 6 months of age, despite some early catch-up growth. Adults had smaller epididymal fat pads, with a relative increase in muscle size. Although glycogen storage was reduced in quadriceps, 2-deoxyglucose uptake into extensor digitorum longus muscle was increased by 32% (P < 0.05), whereas uptake in other muscles and adipose beds was unaffected by prenatal dex. GR mRNA was not different in most muscles but selectively reduced in soleus (by 23%, P < 0.05). However, GR mRNA was markedly increased specifically in retroperitoneal fat (by 50%, P < 0.02). This was accompanied by a shift from peroxisomal proliferator-activated receptor gamma 1 to gamma 2 expression and a reduction in lipoprotein lipase mRNA (by 28%, P < 0.02). Adipose leptin, uncoupling protein-3 and resistin mRNAs, muscle GLUT-4, and circulating lipids were not affected by prenatal dex. These data suggest that hyperglycemia in 6-month-old rats exposed to dexamethasone in utero is not due to attenuated peripheral glucose disposal. However, increased GR and attenuated fatty acid uptake specifically in visceral adipose are consistent with insulin resistance in this crucial metabolic depot and could indirectly contribute to increased hepatic glucose output.

Topics: Adipose Tissue; Animals; Birth Weight; Blood Glucose; Body Weight; Deoxyglucose; Dexamethasone; Epididymis; Fatty Acids; Female; Glucocorticoids; Glucose Transporter Type 4; Glycogen; Hyperglycemia; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Organ Size; Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Wistar; Receptors, Cytoplasmic and Nuclear; Receptors, Glucocorticoid; RNA, Messenger; Transcription Factors

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophins, has been reported to ameliorate hyperglycemia in obese diabetic animal models. To elucidate the mechanism of BDNF on glucose metabolism, we determined the glucose turnover under basal and euglycemic hyperinsulinemic (insulin infusion rate, 54 pmol. kg(-1). min(-1)) clamp conditions in obese insulin-resistant rats, male Zucker fatty rats, which had been acutely administered a subcutaneous injection of BDNF (20 mg/kg) (n = 9, BDNF) or vehicle (n = 8, vehicle). Under the basal condition, acute administration of BDNF did not affect the blood glucose level, plasma insulin level, rate of glucose disappearance (Rd), and endogenous glucose production (EGP). Under the clamp condition, the glucose infusion rate (GIR) was significantly higher in BDNF than in vehicle (mean +/- SD, 61.4 +/- 19.1 v 41.4 +/- 4.9 micromol. kg(-1). min(-1), P <.05). There was no significant difference in Rd and EGP between the 2 groups under the clamp condition, but the insulin-mediated suppression ratio of endogenous glucose production in BDNF was significantly greater than in vehicle (48.9 +/- 22.2 v 22.4% +/- 20.6%, P <.05). In BDNF, mRNA expressions of hepatic phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) were comparable to those of vehicle, while hepatic glucokinase (GK) mRNA expression was significantly higher (1.57 +/- 0.33 v 1.03 +/- 0.17, P <.05). We conclude that BDNF mainly improves hepatic insulin resistance in obese insulin-resistant rats, probably by affecting the hepatic GK flux.

Topics: Animals; Blood Glucose; Brain-Derived Neurotrophic Factor; Carboxy-Lyases; Glucokinase; Glucose-6-Phosphatase; Glycogen; Insulin; Insulin Resistance; Liver; Male; Obesity; Rats; Rats, Zucker; RNA, Messenger

Disruption of the PPP1R3A gene encoding the glycogen targeting subunit (G(M)/R(GL)) of protein phosphatase 1 (PP1) causes substantial lowering of the glycogen synthase activity and a 10-fold decrease in the glycogen levels in skeletal muscle. Homozygous G(M)(-/-) mice show increased weight gain after 3 months of age and become obese, weighing approximately 20% more than their wild-type (WT) littermates after 12 months of age. Glucose tolerance is impaired in 11-month-old G(M)(-/-) mice, and their skeletal muscle is insulin-resistant at > or =12 months of age. The massive abdominal and other fat depositions observed at this age are likely to be a consequence of impaired blood glucose utilization in skeletal muscle. PP1-G(M) activity, assayed after specific immunoadsorption, was absent from G(M)(-/-) mice and stimulated in the hind limb muscles of WT mice by intravenous infusion of insulin. PP1-R5/PTG, another glycogen targeted form of PP1, was not significantly stimulated by insulin in the skeletal muscle of WT mice but showed compensatory stimulation by insulin in G(M)(-/-) mice. Our results suggest that dysfunction of PP1-G(M) may contribute to the pathophysiology of human type 2 diabetes.

Topics: Adipose Tissue; Animals; Blood Glucose; Body Composition; Carrier Proteins; Glucose Intolerance; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Mice; Mice, Knockout; Muscle, Skeletal; Obesity; Phosphoprotein Phosphatases; Protein Phosphatase 1; Weight Gain

1. Exposure of isolated skeletal muscle to troglitazone has resulted in inconsistent findings ranging from inhibition to stimulation of fuel oxidation and the glycogenic pathway. To better understand such variation in outcome, the present study used isolated rat soleus muscle strips to examine the interdependent influences of prolonged maintenance in vitro and of troglitazone exposure. 2. If freshly isolated muscle strips were exposed to troglitazone (1 micro mol l(-1)) for 24 h, glucose oxidation was markedly reduced (-26+/-1%, P<0.0001), whereas glycogen synthesis remained unaffected (+9+/-7%, n.s.). 3. In contrast, extended exposure to troglitazone for 72 h increased both glucose oxidation (+65+/-28%, P<0.05) and glycogen synthesis (+46+/-11%, P<0.005), and a similar stimulatory effect was also observed in muscles exposed to troglitazone only during the last 24 h of their 72 h preincubation period (glucose oxidation: +61+/-15%, P<0.001; glycogen synthesis: +43+/-15%, P<0.01). 4. Troglitazone thus stimulated glucose utilization in long-term incubated muscle independent of the duration of exposure (24 or 72 h), whereas it inhibited glucose utilization in freshly isolated muscle. 5. The observed differences in troglitazone action on freshly isolated vs long-term incubated muscle suggest that findings on muscle tissue subject to prolonged maintenance in vitro cannot be extrapolated to native muscle in vivo.

Topics: Animals; Cells, Cultured; Chromans; Glucose; Glycogen; In Vitro Techniques; Incubators; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Mutation; Rats; Rats, Sprague-Dawley; Rats, Zucker; Thiazolidinediones; Time Factors; Troglitazone

Topics: Animals; Carrier Proteins; Glucose Intolerance; Glycogen; Humans; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Lipid Metabolism; Phosphoprotein Phosphatases

Protein targeting to glycogen (PTG) is a scaffolding protein that targets protein phosphatase 1alpha (PP1alpha) to glycogen, and links it to enzymes involved in glycogen synthesis and degradation. We generated mice that possess a heterozygous deletion of the PTG gene. These mice have reduced glycogen stores in adipose tissue, liver, heart, and skeletal muscle, corresponding with decreased glycogen synthase activity and glycogen synthesis rate. Although young PTG heterozygous mice initially demonstrate normal glucose tolerance, progressive glucose intolerance, hyperinsulinemia, and insulin resistance develop with aging. Insulin resistance in older PTG heterozygous mice correlates with a significant increase in muscle triglyceride content, with a corresponding attenuation of insulin receptor signaling. These data suggest that PTG plays a critical role in glycogen synthesis and is necessary to maintain the appropriate metabolic balance for the partitioning of fuel substrates between glycogen and lipid.

Topics: Aging; Animals; Carrier Proteins; Female; Gene Deletion; Glucagon; Glucose; Glycogen; Glycogen Synthase; Homeostasis; Humans; Insulin; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Liver; Male; Mice; Mice, Inbred Strains; Mice, Knockout; Phosphoprotein Phosphatases; Signal Transduction; Triglycerides

To determine if prior exercise enhances insulin-stimulated extraction of glucose by the liver, chronically catheterized dogs were submitted to 150 min of treadmill exercise or rest. After exercise or rest, dogs received portal glucose (18 micro mol x kg(-1) x min(-1)), peripheral somatostatin, and basal portal glucagon infusions from t = 0 to 150 min. A peripheral glucose infusion was used to clamp arterial blood glucose at 8.3 mmol/l. Insulin was infused into the portal vein to create either basal levels or mild hyperinsulinemia. Prior exercise did not increase whole-body glucose disposal in the presence of basal insulin (25.5 +/- 1.5 vs. 20.3 +/- 1.7 micro mol x kg(-1) x min(-1)), but resulted in a marked enhancement in the presence of elevated insulin (97.2 +/- 15.1 vs. 64.4 +/- 7.4 micro mol x kg(-1) x min(-1)). Prior exercise also increased net hepatic glucose uptake in the presence of both basal insulin (7.5 +/- 1.2 vs. 2.9 +/- 2.4 micro mol x kg(-1) x min(-1)) and elevated insulin (22.0 +/- 3.5 vs. 11.5 +/- 1.8 micro mol x kg(-1) x min(-1)). Likewise, net hepatic glucose fractional extraction was increased by prior exercise with both basal insulin (0.04 +/- 0.01 vs. 0.01 +/- 0.01 micro mol x kg(-1) x min(-1)) and elevated insulin (0.10 +/- 0.01 vs. 0.05 +/- 0.01). Hepatic glycogen synthesis was increased by elevated insulin, but was not enhanced by prior exercise. Although the increase in glucose extraction after exercise could be ascribed to increased insulin action, the increase in hepatic glycogen synthesis was independent of it.

Topics: Alanine; Animals; Blood Glucose; Dogs; Fatty Acids, Nonesterified; Female; Fructosephosphates; Glucose; Glucose-6-Phosphate; Glycerol; Glycogen; Glycogen Phosphorylase; Glycogen Synthase; Hypoglycemic Agents; Insulin; Insulin Resistance; Lactic Acid; Liver; Male; Physical Exertion

To study the secondary consequences of impaired suppression of endogenous glucose production (EGP) we have created a transgenic rat overexpressing the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) in the kidney. The aim of this study was to determine whether peripheral insulin resistance develops in these transgenic rats.. Whole body rate of glucose disappearance (R(d)) and endogenous glucose production were measured basally and during a euglycaemic/hyperinsulinaemic clamp in phosphoenolpyruvate carboxykinase transgenic and control rats using [6-(3)H]-glucose. Glucose uptake into individual tissues was measured in vivo using 2-[1-(14)C]-deoxyglucose.. Phosphoenolpyruvate carboxykinase transgenic rats were heavier and had increased gonadal and infrarenal fat pad weights. Under basal conditions, endogenous glucose production was similar in phosphoenolpyruvate carboxykinase transgenic and control rats (37.4+/-1.1 vs 34.6+/-2.6 micromol/kg/min). Moderate hyperinsulinaemia (810 pmol/l) completely suppressed EGP in control rats (-0.6+/-5.5 micromol/kg/min, p<0.05) while there was no suppression in phosphoenolpyruvate carboxykinase rats (45.2+/-7.9 micromol/kg/min). Basal R(d) was comparable between PEPCK transgenic and control rats (37.4+/-1.1 vs 34.6+/-2.6 micromol/kg/min) but under insulin-stimulated conditions the increase in R(d) was greater in control compared to phosphoenolpyruvate carboxykinase transgenic rats indicative of insulin resistance (73.4+/-11.2 vs 112.0+/-8.0 micromol/kg/min, p<0.05). Basal glucose uptake was reduced in white and brown adipose tissue, heart and soleus while insulin-stimulated transport was reduced in white and brown adipose tissue, white quadriceps, white gastrocnemius and soleus in phosphoenolpyruvate carboxykinase transgenic compared to control rats. The impairment in both white and brown adipose tissue glucose uptake in phosphoenolpyruvate carboxykinase transgenic rats was associated with a decrease in GLUT4 protein content. In contrast, muscle GLUT4 protein, triglyceride and long-chain acylCoA levels were comparable between PEPCK transgenic and control rats.. A primary defect in suppression of EGP caused adipose tissue and muscle insulin resistance.

Topics: Animals; Animals, Genetically Modified; Deoxyglucose; Glucose; Glucose Transporter Type 4; Glycogen; Insulin Resistance; Kidney; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Phosphoenolpyruvate Carboxykinase (GTP); Rats; RNA, Messenger; Triglycerides

In healthy individuals, peripheral insulin resistance evoked by dietary saturated lipid can be accompanied by increased insulin secretion such that glucose tolerance is maintained. Substitution of long-chain omega-3 fatty acids for a small percentage of dietary saturated fat prevents insulin resistance in response to high-saturated fat feeding. We substituted a small amount (7%) of dietary lipid with long-chain omega-3 fatty acids during 4 wk of high-saturated fat feeding to investigate the relationship between amelioration of insulin resistance and glucose-stimulated insulin secretion (GSIS). We demonstrate that, despite dietary delivery of saturated fat throughout, this manipulation prevents high-saturated fat feeding-induced insulin resistance with respect to peripheral glucose disposal and reverses insulin hypersecretion in response to glucose in vivo. Effects of long-chain omega-3 fatty acid enrichment to lower GSIS were also observed in perifused islets suggesting a direct effect on islet function. However, long-chain omega-3 fatty acid enrichment led to hepatic insulin resistance with respect to suppression of glucose output and impaired glucose tolerance in vivo. Our data demonstrate that the insulin response to glucose is suppressed to a greater extent than whole-body insulin sensitivity is enhanced by enrichment of a high-saturated fat diet with long-chain omega-3 fatty acids. Additionally, reduced GSIS despite glucose intolerance suggests that either long-chain omega-3 fatty acids directly impair the beta-cell response to saturated fat such that insulin secretion cannot be augmented to normalize glucose tolerance or beta-cell compensatory hypersecretion represents a response to insulin resistance at the level of peripheral glucose disposal but not endogenous glucose production.

Topics: Animals; Dietary Fats; Fatty Acids, Omega-3; Female; Fish Oils; Glucose; Glucose Clamp Technique; Glucose Intolerance; Glycogen; Hyperinsulinism; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Leptin; Liver; Phenotype; Rats; Rats, Wistar; Triglycerides

In type 2 diabetes, glucose phosphorylation, a regulatory step in glucose utilization by skeletal muscle, is impaired. Since glucokinase expression in skeletal muscle of transgenic mice increases glucose phosphorylation, we examined whether such mice counteract the obesity and insulin resistance induced by 12 wk of a high-fat diet. When fed this diet, control mice became obese, whereas transgenic mice remained lean. Furthermore, high-fat fed control mice developed hyperglycemia and hyperinsulinemia (a 3-fold increase), indicating that they were insulin resistant. In contrast, transgenic mice were normoglycemic and showed only a mild increase in insulinemia (1.5-fold). They also showed improved whole body glucose tolerance and insulin sensitivity and increased intramuscular concentrations of glucose 6-phosphate and glycogen. A parallel increase in uncoupling protein 3 mRNA levels in skeletal muscle of glucokinase-expressing transgenic mice was also observed. These results suggest that the rise in glucose phosphorylation by glucokinase expression in skeletal muscle leads to increased glucose utilization and energy expenditure that counteracts weight gain and maintains insulin sensitivity.

Topics: Animals; Carrier Proteins; Gene Expression; Glucokinase; Glucose Tolerance Test; Glucose-6-Phosphate; Glycogen; Insulin Resistance; Ion Channels; Mice; Mice, Transgenic; Mitochondrial Proteins; Models, Biological; Muscle, Skeletal; Obesity; Uncoupling Protein 3

A diet high in sucrose or fructose progressively impairs glucose and lipid metabolism, which leads to insulin resistance. As mitochondria are the sites of the oxidation and utilization of these substrates, we hypothesized that a high sucrose diet would alter mitochondrial respiration. Male Wistar rats were fed high-sucrose (SU) or control (CTL) diet for one week; mitochondrial respiration was investigated in mitochondria isolated from liver and both glycolytic and oxidative muscles, with pyruvate and palmitate as substrates. To test for metabolic disturbances, we measured not only glycogen content in muscles and liver, but also lactate, glucose and triglyceride blood concentrations. After one week of high-sucrose intake, we found no change in blood concentration of these variables, but glycogen content was significantly increased in liver (17.28 +/- 2.98 mg/g tissue SU vs 6.47 +/- 1.67 mg/g tissue CTL), oxidative muscle (1.59 +/- 0.21 mg/g tissue SU vs 0.70 +/- 0.24 mg/g tissue CTL) though not in glycolytic muscle (1.72 +/- 0.44 mg/g tissue SU vs 1.52 +/- 0.20 mg/g tissue CTL). State 3 mitochondrial respiration was significantly decreased in SU rats compared with CTL (p < 0.05) with pyruvate, while no change was observed with palmitate. This study shows that 1-week of high-sucrose diet altered mitochondrial pyruvate oxidation in rats and suggests that, in the context of a high-sucrose diet, impaired mitochondrial respiration could contributed to the development of insulin resistance.

Topics: Animals; Blood Glucose; Cell Respiration; Dietary Carbohydrates; Glycogen; Insulin Resistance; Lactic Acid; Male; Mitochondria, Liver; Mitochondria, Muscle; Rats; Rats, Wistar; Sucrose; Triglycerides

A strong correlation between intramyocellular lipid concentrations and the severity of insulin resistance has fueled speculation that lipid oversupply to skeletal muscle, fat, or liver may desensitize these tissues to the anabolic effects of insulin. To identify free fatty acids (FFAs) capable of inhibiting insulin action, we treated 3T3-L1 adipocytes or C2C12 myotubes with either the saturated FFA palmitate (C16:0) or the monounsaturated FFA oleate (C18:1), which were shown previously to be the most prevalent FFAs in rat soleus and gastrocnemius muscles. In C2C12 myotubes, palmitate, but not oleate, inhibited insulin-stimulation of glycogen synthesis, as well as its activation of Akt/Protein Kinase B (PKB), an obligate intermediate in the regulation of anabolic metabolism. Palmitate also induced the accrual of ceramide and diacylglycerol (DAG), two lipid metabolites that have been shown to inhibit insulin signaling in cultured cells and to accumulate in insulin resistant tissues. Interestingly, in 3T3-L1 adipocytes, neither palmitate nor oleate inhibited glycogen synthesis or Akt/PKB activation, nor did they induce ceramide or DAG synthesis. Using myotubes, we also tested whether other saturated fatty acids blocked insulin signaling while promoting ceramide and DAG accumulation. The long-chain fatty acids stearate (18:0), arachidate (20:0), and lignocerate (24:0) reproduced palmitate's effects on these events, while saturated fatty acids with shorter hydrocarbon chains [i.e., laurate (12:0) and myristate (14:0)] failed to induce ceramide accumulation or inhibit Akt/PKB activation. Collectively these findings implicate excess delivery of long-chain fatty acids in the development of insulin resistance resulting from lipid oversupply to skeletal muscle.

Topics: 3T3 Cells; Adipocytes; Animals; Ceramides; Diglycerides; Fatty Acids; Glycogen; Insulin Resistance; Mice; Muscle Fibers, Skeletal; Muscle, Skeletal; Myoblasts; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Signal Transduction

We recently demonstrated that in vivo insulin resistance is not retained in cultured skeletal muscle cells. In the present study, we tested the hypothesis that treating cultured skeletal muscle cells with fatty acids has an effect on insulin action which differs between insulin-sensitive and insulin-resistant subjects. Insulin effects were examined in myotubes from 8 normoglycemic non-obese insulin-resistant and 8 carefully matched insulin-sensitive subjects after preincubation with or without palmitate, linoleate, and 2-bromo-palmitate. Insulin-stimulated glycogen synthesis decreased by 27 +/- 5 % after palmitate treatment in myotubes from insulin-resistant, but not from insulin-sensitive subjects (1.50 +/- 0.08-fold over basal vs. 1.81 +/- 0.09-fold, p = 0.042). Despite this observation, we did not find any impairment in the PI 3-kinase/PKB/GSK-3 pathway. Furthermore, insulin action was not affected by linoleate and 2-bromo-palmitate. In conclusion, our data provide preliminary evidence that insulin resistance of skeletal muscle does not necessarily involve primary defects in insulin action, but could represent susceptibility to the desensitizing effect of fatty acids and possibly other environmental or adipose tissue-derived factors.

Topics: Adult; Cells, Cultured; Deoxyglucose; Female; Glycogen; Glycogen Synthase Kinase 3; Humans; Insulin; Insulin Resistance; Male; Muscle Fibers, Skeletal; Muscle, Skeletal; Palmitic Acid; Phosphatidylinositol 3-Kinases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt

To investigate the effect of prolonged adaptation to training and fat- or carbohydrate-rich diet on body composition and insulin resistance.. Longitudinal study. Of three groups two consumed a fat-rich diet, of which one performed regular training (FAT-Train, n=17) and the other maintained normal habitual activity (Fat-Control, n=8). The third group trained and consumed a carbohydrate-rich diet (CHO-Train, n=16).. Forty-one untrained, healthy male subjects.. Before and after 7 weeks body composition was estimated from skinfold measurements. At rest the respiratory exchange ratio (RER) was determined by the Douglas bag technique. Glycogen was determined in m vastus lateralis and concentrations of insulin and triacylglycerol in serum and glucose, fatty acid and beta-hydroxy-butyrate in plasma was measured. The insulin resistance index was calculated from fasting plasma insulin and glucose values.. Across the 7 weeks body weight was reduced (1.3+/-0.3%) in all three groups, however body fat mass was decreased only in the CHO-Train (13%) and maintained in the two FAT-groups. RER at rest was similarly decreased (5%) in the three groups. Plasma insulin tended to decrease (16%) in CHO-Train (P=0.065) and remained unchanged in the two FAT-groups. In contrast plasma glucose (4.6+/-0.1 mmol/l) and plasma FA (453+/-27 micromol/l) remained unchanged across the 7 weeks. The calculated insulin resistance index HOMA-R(mod) was significantly decreased by 19% in CHO-train but remained unchanged in both of the FAT-groups, whereas the calculated insulin secretion index HOMA-beta(mod) was unchanged in all three groups.. In the present study we demonstrate that despite of a mild energy deficit body fat mass was maintained after prolonged adaptation to fat-rich diet both when normal physical activity was maintained and when training was performed. In contrast a significant decrease in fat mass was observed when carbohydrate-rich diet and training was combined. Furthermore we observed that the insulin resistance index was significantly decreased only when training was combined with a carbohydrate-rich diet.

Topics: 3-Hydroxybutyric Acid; Adaptation, Physiological; Adipose Tissue; Adult; Anthropometry; Blood Glucose; Body Composition; Diet; Dietary Carbohydrates; Dietary Fats; Exercise; Fatty Acids; Glycogen; Humans; Insulin; Insulin Resistance; Longitudinal Studies; Male; Reference Values; Respiratory Function Tests; Triglycerides

The glycogen-associated protein phosphatase (PP1G/ R(GL))may play a central role in the hormonal control of glycogen metabolism in the skeletal muscle. Here, we investigated the in vivo epinephrine effect of glycogen metabolism in the skeletal muscle of the wild-type and R(GL) knockout mice. The administration of epinephrine increased blood glucose levels from 200 +/- +/- 20 to 325 +/- 20 mg/dl in both wild-type and knockout mice. Epinephrine decreased the glycogen synthase -/+ G6P ratio from 0.24 +/- 0.04 to 0.10 +/- 0.02 in the wild-type, and from 0.17 +/- 0.02 to 0.06 +/- 0.01 in the knockout mice. Conversely, the glycogen phosphorylase activity ratio increased from 0.21 +/- 0.04 to 0.65 +/- 0.07 and from 0.30 +/- 0.04 to 0.81 +/- 0.06 in the epinephrine treated wild-type and knockout mice respectively. The glycogen content of the knockout mice was substantially lower (27 percent) than that of both wild-type mice; and epinephrine decreased glycogen content in the wild-type and knockout mice. Also, in Western blot analysis there was no compensation of the other glycogen targeting components PTG/R5 and R6 in the knockout mice compared with the wild-type. Therefore, R(GL) is not required for the epinephrine stimulation of glycogen metabolism, and rather another phosphatase and/or regulatory subunit appears to be involved.

Topics: Animals; Blood Glucose; Blotting, Western; Carrier Proteins; Epinephrine; Glycogen; Glycogen Phosphorylase; Glycogen Synthase; Injections, Intraperitoneal; Insulin; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Mice; Mice, Knockout; Muscle, Skeletal; Phosphoprotein Phosphatases; Phosphorylase a; Phosphorylation; Protein Phosphatase 1

In the present study, we examined how the arterial insulin level alters the alpha-cell response to a fall in plasma glucose in the conscious overnight fasted dog. Each study consisted of an equilibration (-140 to -40 min), a control (-40 to 0 min), and a test period (0 to 180 min), during which BAY R 3401 (10 mg/kg), a glycogen phosphorylase inhibitor, was administered orally to decrease glucose output in each of four groups (n = 5). In group 1, saline was infused. In group 2, insulin was infused peripherally (3.6 pmol. kg(- 1). min(-1)), and the arterial plasma glucose level was clamped to the level seen in group 1. In group 3, saline was infused, and euglycemia was maintained. In group 4, insulin (3.6 pmol. kg(-1). min(-1)) was given, and euglycemia was maintained by glucose infusion. In group 1, drug administration decreased the arterial plasma glucose level (mmol/l) from 5.8 +/- 0.2 (basal) to 5.2 +/- 0.3 and 4.4 +/- 0.3 by 30 and 90 min, respectively (P < 0.01). Arterial plasma insulin levels (pmol/l) and the hepatic portal-arterial difference in plasma insulin (pmol/l) decreased (P < 0.01) from 78 +/- 18 and 90 +/- 24 to 24 +/- 6 and 12 +/- 6 over the first 30 min of the test period. The arterial glucagon levels (ng/l) and the hepatic portal-arterial difference in plasma glucagon (ng/l) rose from 43 +/- 5 and 5 +/- 2 to 51 +/- 5 and 10 +/- 5 by 30 min (P < 0.05) and to 79 +/- 16 and 31 +/- 15 (P < 0.05) by 90 min, respectively. In group 2, in response to insulin infusion, arterial insulin (pmol/l) was elevated from 48 +/- 6 to 132 +/- 6 to an average of 156 +/- 6. The hepatic portal-arterial difference in plasma insulin was eliminated, indicating a complete inhibition of endogenous insulin release. The arterial glucagon level (ng/l) and the hepatic portal-arterial difference in plasma glucagon (ng/l) did not rise significantly (40 +/- 5 and 7 +/- 4 at basal, 44 +/- 4 and 9 +/- 4 at 90 min, and 44 +/- 8 and 15 +/- 7 at 180 min). In group 3, when euglycemia was maintained, the insulin and glucagon levels and the hepatic portal-arterial difference remained constant. In group 4, the arterial plasma glucose level remained basal (5.9 +/- 1.1 mmol/l) throughout, whereas insulin infusion increased the arterial insulin level to an average of 138 +/- 6 pmol/l. The hepatic portal-arterial difference in plasma insulin was again eliminated. Arterial glucagon level (ng/l) and the hepatic portal-arterial difference in plasma glucagon (ng/l) did not change signific

Topics: Alanine; Animals; Blood Glucose; Consciousness; Dihydropyridines; Dogs; Fasting; Fatty Acids, Nonesterified; Female; Furans; Glucagon; Gluconeogenesis; Glycerol; Glycogen; Hypoglycemia; Insulin; Insulin Resistance; Islets of Langerhans; Ketones; Lactic Acid; Liver; Liver Circulation; Male

In a family with agenesis of the dorsal pancreas only the mother presents with insulin-dependent diabetes mellitus, whereas her sons are glucose tolerant. We examined whether metabolic defects can be detected early in this disease. Plasma glucose profiles were obtained from patients with dorsal pancreas agenesis and from matched healthy subjects. Hepatic glycogen synthesis and breakdown were determined from the time course of glycogen concentrations using noninvasive (13)C nuclear magnetic resonance spectroscopy. Gluconeogenesis was calculated from the difference between glucose production (measured with D-[6,6-(2)H(2)]glucose) and glycogen breakdown. Frequently sampled iv glucose tolerance tests were performed to assess insulin secretion and sensitivity. The mean plasma glucose level was higher (12.9 +/- 0.4 vs. 5.9 +/- 0.1 mmol/liter), whereas the peak plasma insulin level was lower (236 vs. 397 +/- 23 pmol/liter) in the diabetic mother than in her nondiabetic sons and healthy subjects. In all patients, however, glycogen synthesis and breakdown were reduced by approximately 55% (P < 0.05) and 40% (P < 0.02), respectively. Gluconeogenesis (6.8 +/- 0.8 vs. 4.2 +/- 0.3 micro mol/kg.min; P < 0.05) and hepatic insulin clearance (6.8 +/- 1.3 vs. 2.8 +/- 1.0 ml/kg.min) were increased in all patients. In conclusion, patients with complete agenesis of the dorsal pancreas exhibit marked defects in hepatic glycogen metabolism, which are present even in the nondiabetic offspring.

Topics: Blood Glucose; C-Peptide; Diabetes Mellitus, Type 1; Fatty Acids, Nonesterified; Female; Glucagon; Gluconeogenesis; Glucose Tolerance Test; Glycogen; Human Growth Hormone; Humans; Hydrocortisone; Insulin; Insulin Resistance; Insulin Secretion; Kinetics; Leptin; Liver; Magnetic Resonance Spectroscopy; Male; Middle Aged; Norepinephrine; Pancreas

We examined whether acute activation of 5'-AMP-activated protein kinase (AMPK) by 5'-aminoimidazole-4-carboxamide-1-beta-D-ribonucleoside (AICAR) ameliorates insulin resistance in isolated rat skeletal muscle. Insulin resistance was induced in extensor digitorum longus (EDL) muscles by prolonged exposure to 1.6 mM palmitate, which inhibited insulin-stimulated glycogen synthesis to 51% of control after 5 h of incubation. Insulin-stimulated glucose transport was less affected (22% of control). The decrease in glycogen synthesis was accompanied by decreased glycogen synthase (GS) activity and increased GS phosphorylation. When including 2 mM AICAR in the last hour of the 5-h incubation with palmitate, the inhibitory effect of palmitate on insulin-stimulated glycogen synthesis and glucose transport was eliminated. This effect of AICAR was accompanied by activation of AMPK. Importantly, AMPK inhibition was able to prevent this effect. Neither treatment affected total glycogen content. However, glucose 6-phosphate was increased after inclusion of AICAR, indicating increased influx of glucose. No effect of AICAR on the inhibited insulin-stimulated GS activity or increased GS phosphorylation by palmitate could be detected. Thus the mechanism by which AMPK activation ameliorates the lipid-induced insulin resistance probably involves induction of compensatory mechanisms overriding the insulin resistance. Our results emphasize AMPK as a promising molecular target for treatment of insulin resistance.

Topics: Adenylate Kinase; Amino Acid Sequence; Aminoimidazole Carboxamide; Animals; Enzyme Activation; Fatty Acids, Nonesterified; Glycogen; Hypoglycemic Agents; Insulin Resistance; Male; Molecular Sequence Data; Muscle, Skeletal; Palmitates; Rats; Rats, Wistar; Ribonucleotides

RSG is a member of the TZD group of drugs widely used in treatment of type 2 diabetes. The underlying mechanism of TZD action in insulin-sensitive tissues is not fully understood. In this study we show that 14-day RSG administration in a new rodent model of metabolic syndrome X, polydactylous rat strain (PD/Cub), substantially improves its lipid profile (serum TGs 4.20 +/- 0.23 vs 2.34 +/- 0.14 mmol/l, P < 0.0001; FFA 0.46 +/- 0.05 vs 0.33 +/- 0.02 mmol/l, P = 0.017), diminishes the liver TG depots (15.76 +/- 0.60 vs 8.44 +/- 0.55 micromol/g, P < 0.0001), serum insulin concentrations (1.10 +/- 0.08 vs 0.63 +/- 0.02 nmol/l, P < 0.0001) and promotes visceral adiposity (adiposity index 1.28 +/- 0.03 vs 1.85 +/- 0.07, P < 0.0001). No changes were observed in serum or liver concentrations of cholesterol. Concomitantly, both basal and insulin-stimulated glycogen synthesis in red-fibre type muscle (m. soleus) was enhanced, as well as glucose uptake into adipose tissue. However, glucose oxidation in soleus (basal and insulin-stimulated) remained unchanged. In consent with previously published data we suggest the current pharmacogenetic study as a further proof of substantial influence of genetic background on the physiological outcome of TZD therapy.

Topics: Adipose Tissue; Animals; Disease Models, Animal; Glucose; Glucose Tolerance Test; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Lipids; Male; Metabolic Syndrome; Rats; Rats, Inbred Strains; Rosiglitazone; Thiazoles; Thiazolidinediones

Glycogen-targeting subunits of protein phosphatase-1 facilitate interaction of the phosphatase with enzymes of glycogen metabolism. Expression of one family member, PTG, in the liver of normal rats improves glucose tolerance without affecting other plasma variables but leaves animals unable to reduce hepatic glycogen stores in response to fasting. In the current study, we have tested whether expression of other targeting subunit isoforms, such as the liver isoform G(L), the muscle isoform G(M)/R(Gl), or a truncated version of G(M)/R(Gl) termed G(M)DeltaC in liver ameliorates glucose intolerance in rats fed on a high fat diet (HF). HF animals overexpressing G(M)DeltaC, but not G(L) or G(M)/R(Gl), exhibited a decline in blood glucose of 35-44 mg/dl relative to control HF animals during an oral glucose tolerance test (OGTT) such that levels were indistinguishable from those of normal rats fed on standard chow at all but one time point. Hepatic glycogen levels were 2.1-2.4-fold greater in G(L)- and G(M)DeltaC-overexpressing HF rats compared with control HF animals following OGTT. In a second set of studies on fed and 20-h fasted HF animals, G(M)DeltaC-overexpressing rats lowered their liver glycogen levels by 57% (from 402 +/- 54 to 173 +/- 27 microg of glycogen/mg of protein) in the fasted versus fed states compared with only 44% in G(L)-overexpressing animals (from 740 +/- 35 to 413 +/- 141 microg of glycogen/mg of protein). Since the OGTT studies were performed on 20-h fasted rats, this meant that G(M)DeltaC-overexpressing rats synthesized much more glycogen than G(L)-overexpressing HF rats during the OGTT (419 versus 117 microg of glycogen/mg of protein, respectively), helping to explain why G(M)DeltaC preferentially enhanced glucose clearance. We conclude that G(M)DeltaC has a unique combination of glycogenic potency and responsiveness to glycogenolytic signals that allows it to be used to lower blood glucose levels in diabetes.

Topics: Adenoviridae; Animals; Dietary Fats; Fasting; Glucose; Glucose Intolerance; Glucose Tolerance Test; Glycogen; Humans; Insulin Resistance; Isoenzymes; Liver; Male; Muscle, Skeletal; Phosphoprotein Phosphatases; Protein Phosphatase 1; Protein Subunits; Rats; Rats, Wistar; Transgenes

Evidence has accumulated that activation of AMP kinase (AMPK) mediates the acute increase in glucose transport induced by exercise. As the exercise-induced, insulin-independent increase in glucose transport wears off, it is followed by an increase in muscle insulin sensitivity. The major purpose of this study was to determine whether hypoxia and 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), which also activate AMPK and stimulate glucose transport, also induce an increase in insulin sensitivity. We found that the increase in glucose transport in response to 30 microU/ml insulin was about twofold greater in rat epitrochlearis muscles that had been made hypoxic or treated with AICAR 3.5 h previously than in untreated control muscles. This increase in insulin sensitivity was similar to that induced by a 2-h bout of swimming or 10 min of in vitro electrically stimulated contractions. Neither phosphatidylinositol 3-kinase activity nor protein kinase B (PKB) phosphorylation in response to 30 microU/ml insulin was enhanced by prior exercise or AICAR treatment that increased insulin sensitivity of glucose transport. Inhibition of protein synthesis by inclusion of cycloheximide in the incubation medium for 3.5 h after exercise did not prevent the increase in insulin sensitivity. Contractions, hypoxia, and treatment with AICAR all caused a two- to three-fold increase in AMPK activity over the resting level. These results provide evidence that the increase in insulin sensitivity of muscle glucose transport that follows exercise is mediated by activation of AMPK and involves a step beyond PKB in the pathway by which insulin stimulates glucose transport.

Topics: Acetylcarnitine; Adenylate Kinase; Animals; Biological Transport; Cycloheximide; Enzyme Activation; Glucose; Glycogen; Hypoxia; Insulin; Insulin Resistance; Male; Muscle Contraction; Muscle, Skeletal; Protein Synthesis Inhibitors; Rats; Rats, Wistar; Signal Transduction

Hepatic glucose production is increased as a metabolic consequence of insulin resistance in type 2 diabetes. Because fructose 2,6-bisphosphate is an important regulator of hepatic glucose production, we used adenovirus-mediated enzyme overexpression to increase hepatic fructose 2,6-bisphosphate to determine if the hyperglycemia in KK mice, polygenic models of type 2 diabetes, could be ameliorated by reduction of hepatic glucose production. Seven days after treatment with virus encoding a mutant 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase designed to increase fructose 2,6-bisphosphate levels, plasma glucose, lipids, and insulin were significantly reduced in KK/H1J and KK.Cg-A(y)/J mice. Moreover, high fructose 2,6-bisphosphate levels downregulated glucose-6-phosphatase and upregulated glucokinase gene expression, thereby reversing the insulin-resistant pattern of hepatic gene expression of these two key glucose-metabolic enzymes. The increased hepatic fructose 2,6-bisphosphate also reduced adiposity in both KK mice. These results clearly indicate that increasing hepatic fructose 2,6-bisphosphate overcomes the impairment of insulin in suppressing hepatic glucose production, and it provides a potential therapy for type 2 diabetes.

Topics: Adipose Tissue; Animals; Blood; Body Weight; Diabetes Mellitus, Type 2; Epididymis; Female; Fructosediphosphates; Glucokinase; Glucose-6-Phosphatase; Glycogen; Insulin; Insulin Resistance; Liver; Male; Mice; Mice, Inbred Strains; Phosphofructokinase-2

This study evaluates the effect of fluoxetine (FXTN) on insulin resistance and glucose uptake by various tissues in 90% pancreatectomized (Px) and sham-operated (Sham) rats. Both the Px and Sham rats were divided into 2 groups: 1 group was given FXTN (5 mg/kg) for 8 weeks, and the other group was given a placebo. Whole body glucose disposal rates were measured using euglycemic hyperinsulinemic (EH) clamps while the rats were in an awake, unstressed, and fasting state. On the following day, all rats were intravenously injected with [1-(14)C]2-deoxyglucose solution and killed 45 minutes later. The body weight of the FXTN group was lower than that of the placebo group in the Sham and Px rats during the first 2 weeks (P <.05), but there was no difference in body weight between these groups after the third week. Evidently, FXTN did not alter serum glucose levels in the Sham and Px rats. Basal serum insulin levels at EH clamp were significantly lower in the FXTN group than the placebo group in Sham rats. Whole body glucose disposal rates increased with FXTN administration in Sham rats (44.8 +/- 3.4 v 36.4 +/- 2.9 mg/kg/min) and in Px rats (33.9 +/- 3.6 v 25.5 +/- 4.1 mg/kg/min) compared with placebo administration. The glycogen content of the soleus muscle tissue was higher in the FXTN group than in the placebo group of Sham and Px rats. The dose percentage of [1-(14)C]2-deoxyglucose uptake by soleus muscle tissue was higher in the FXTN group than in the placebo group of Sham and Px rats. In conclusion, (1) FXTN improves insulin sensitivity beyond the effect mediated through weight loss and (2) the effect of FXTN on insulin sensitivity may be achieved by increased glucose uptake and glycogen synthesis in the soleus muscle tissue.

Topics: Animals; Deoxyglucose; Fluoxetine; Glucose; Glycogen; Insulin; Insulin Resistance; Liver; Male; Muscle, Skeletal; Pancreas; Pancreatectomy; Rats; Rats, Sprague-Dawley; Selective Serotonin Reuptake Inhibitors

The 5'AMP-activated protein kinase is an important mediator of muscle contraction-induced glucose transport and a target for pharmacological treatment of Type II (non-insulin-dependent) diabetes mellitus. The 5'AMP-activated protein kinase can be activated by 5-aminoimidazole-4-carboxamide ribonucleoside. We hypothesised that 5-aminoimidazole-4-carboxamide ribonucleoside treatment could restore glucose homeostasis in ob/ob mice.. Lean and ob/ob mice were given 5-aminoimidazole-4-carboxamide ribonucleoside (1 mg.g body wt(-1).day(-1) s.c) or 0.9 % NaCl (vehicle) for 1-7 days.. Short-term 5-aminoimidazole-4-carboxamide ribonucleoside treatment normalised glucose concentrations in ob/ob mice within 1 h, with effects persisting over 4 h. After 1 week of daily injections, 5-aminoimidazole-4-carboxamide ribonucleoside treatment corrected hyperglycaemia, improved glucose tolerance, and increased GLUT4 and hexokinase II protein expression in skeletal muscle, but had deleterious effects on plasma non-esterified fatty acids and triglycerides. Treatment with 5-aminoimidazole-4-carboxamide ribonucleoside increased liver glycogen in fasted and fed ob/ob mice and muscle glycogen in fasted, but not fed ob/ob and lean mice. Defects in insulin-stimulated phosphatidylinositol 3-kinase and glucose transport in skeletal muscle from ob/ob mice were not corrected by 5-aminoimidazole-4-carboxamide ribonucleoside treatment. While ex vivo insulin-stimulated glucose transport was reduced in isolated muscle from ob/ob mice, the 5-aminoimidazole-4-carboxamide ribonucleoside stimulated response was normal.. The 5-aminoimidazole-4-carboxamide ribonucleoside mediated improvements in glucose homeostasis in ob/ob mice can be explained by effects in skeletal muscle and liver. Due to the apparently deleterious effects of 5-aminoimidazole-4-carboxamide ribonucleoside on the blood lipid profile, strategies to develop tissue-specific and pathway-specific activators of 5'AMP-activated protein kinase should be considered in order to improve glucose homeostasis.

Topics: Aminoimidazole Carboxamide; Animals; Biological Transport; Blood Glucose; Diabetes Mellitus; Diabetes Mellitus, Type 2; Glucose; Glucose Tolerance Test; Glycogen; Homeostasis; Hypoglycemic Agents; Injections, Subcutaneous; Insulin; Insulin Resistance; Liver; Liver Glycogen; Mice; Mice, Inbred C57BL; Mice, Obese; Muscle, Skeletal; Obesity; Ribonucleotides

To clarify the mechanism by which insulin resistance develops in obesity, Zucker fatty rats (ZFR) and lean litter mates (ZLR) were temporally subjected to oral glucose tolerance tests (OGTT) at 6 and 15 weeks of age.. As candidates for causative factors of insulin resistance, plasma leptin, free fatty acids (FFA) and tumor necrosis factor (TNF)-alpha levels were evaluated.. There was no difference in the body weight between the two groups at 6 weeks of age, but ZFR were significantly heavier than ZLR at 15 weeks of age. At 6 weeks of age, blood glucose levels and area under the curve of glucose (AUCg) during OGTT were not significantly different between the two groups, while plasma insulin levels and area under the curve of insulin (AUCi) in the ZFR group were significantly higher than those in the ZLR group. At 15 weeks of age, the blood glucose levels and AUCg as well as plasma insulin levels and AUCi in the ZFR group during OGTT were significantly higher than those in the ZLR group. The ratio of fasting insulin to glucose in the ZFR group was significantly higher than that in the ZLR group at 6 and 15 weeks of age. Peripheral and portal plasma leptin and FFA levels were significantly higher in ZFR than ZLR both at 6 weeks and 15 weeks of age. Meanwhile, at 6 weeks, plasma TNF-alpha levels and expression of TNF-alpha protein in subcutaneous and visceral fat tissues were similar in both groups; however at 15 weeks, these were significantly higher in the ZFR group than the ZLR group.. These results suggest that FFA rather than TNF-alpha may play an important role in early events involved in the development of insulin resistance and TNF-alpha accelerates insulin resistance together with FFA in the later stage.

Topics: Adipose Tissue; Animals; Blood Glucose; Blotting, Western; Body Weight; Eating; Fasting; Fatty Acids, Nonesterified; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Leptin; Liver; Male; Obesity; Organ Size; Rats; Rats, Zucker; Tumor Necrosis Factor-alpha

Topics: Acetyl-CoA Carboxylase; Diabetes Mellitus, Type 2; Glycogen; Humans; Insulin Resistance; Multienzyme Complexes; Muscle, Skeletal; Peroxisome Proliferators; Transcription Factors

We determined the interaction of exercise and diet on glucose transporter (GLUT-4) protein and mRNA expression in type I (soleus) and type II [extensor digitorum longus (EDL)] skeletal muscle. Forty-eight Sprague Dawley rats were randomly assigned to one of two dietary conditions: high-fat (FAT, n=24) or high-carbohydrate (CHO, n=24). Animals in each dietary condition were allocated to one of two groups: control (NT, n=8) or a group that performed 8 weeks of treadmill running (4 sessions week-1 of 1000 m @ 28 m min-1, RUN, n=16). Eight trained rats were killed after their final exercise bout for determination of GLUT-4 protein and mRNA expression: the remainder were killed 48 h after their last session for measurement of muscle glycogen and triacylglycerol concentration. GLUT-4 protein expression in NT rats was similar in both muscles after 8 weeks of either diet. However, there was a main effect of training such that GLUT-4 protein was increased in the soleus of rats fed with either diet (P < 0.05) and in the EDL in animals fed with CHO (P < 0.05). There was a significant diet-training interaction on GLUT-4 mRNA, such that expression was increased in both the soleus (100% upward arrowP < 0.05) and EDL (142% upward arrowP < 0.01) in CHO-fed animals. Trained rats fed with FAT decreased mRNA expression in the EDL ( downward arrow 45%, P < 0.05) but not the soleus ( downward arrow 14%, NS). We conclude that exercise training in CHO-fed rats increased both GLUT-4 protein and mRNA expression in type I and type II skeletal muscle. Despite lower GLUT-4 mRNA in muscles from fat-fed animals, exercise-induced increases in GLUT-4 protein were largely preserved, suggesting that control of GLUT-4 protein and gene expression are modified independently by exercise and diet.

Topics: Animals; Body Weight; Diet; Dietary Carbohydrates; Dietary Fats; Female; Gene Expression; Glucose; Glucose Transporter Type 4; Glycogen; Insulin Resistance; Monosaccharide Transport Proteins; Muscle Fibers, Fast-Twitch; Muscle Fibers, Slow-Twitch; Muscle Proteins; Muscle, Skeletal; Physical Conditioning, Animal; Rats; Rats, Sprague-Dawley; RNA, Messenger; Triglycerides

Although lipid excess can impair beta-cell function in vitro, short-term high-fat feeding in normal rats produces insulin resistance but not hyperglycemia. This study examines the effect of long-term (10-mo) high polyunsaturated fat feeding on glucose tolerance in Wistar rats. The high fat-fed compared with the chow-fed group was 30% heavier and 60% fatter, with approximately doubled fasting hyperinsulinemia (P < 0.001) but only marginal fasting hyperglycemia (7.5 +/- 0.1 vs. 7.2 +/- 0.1 mmol/l, P < 0.01). Insulin sensitivity was approximately 67% lower in the high-fat group (P < 0.01). The acute insulin response to intravenous arginine was approximately double in the insulin-resistant high-fat group (P < 0.001), but that to intravenous glucose was similar in the two groups. After the intravenous glucose bolus, plasma glucose decline was slower in the high fat-fed group, confirming mild glucose intolerance. Therefore, despite severe insulin resistance, there was only a mildly elevated fasting glucose level and a relative deficiency in glucose-stimulated insulin secretion; this suggests that a genetic or congenital susceptibility to beta-cell impairment is required for overt hyperglycemia to develop in the presence of severe insulin resistance.

Topics: Acyl Coenzyme A; Aging; Animals; Arginine; Blood Glucose; Body Composition; Diabetes Mellitus; Dietary Fats; Fasting; Genetic Predisposition to Disease; Glucose Clamp Technique; Glucose Intolerance; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Liver; Male; Muscle, Skeletal; Rats; Rats, Wistar; Time Factors; Triglycerides; Weight Gain

Insulin action is decreased by high muscle glycogen concentrations in skeletal muscle. Patients with McArdle's disease have chronic high muscle glycogen levels and might therefore be at risk of developing insulin resistance. In this study, six patients with McArdle's disease and six matched control subjects were subjected to an oral glucose tolerance test and a euglycemic-hyperinsulinemic clamp. The muscle glycogen concentration was 103 +/- 45% higher in McArdle patients than in controls. Four of six McArdle patients, but none of the controls, had impaired glucose tolerance. The insulin-stimulated glucose utilization and the insulin-stimulated increase in glycogen synthase activity during the clamp were significantly lower in the patients than in controls (51.3 +/- 6.0 vs. 72.6 +/- 13.1 micromol x min(-1) x kg lean body mass(-1), P < 0.05, and 53 +/- 15 vs. 79 +/- 9%, P < 0.05, n = 6, respectively). The difference in insulin-stimulated glycogen synthase activity between the pairs was significantly correlated (r = 0.96, P < 0.002) with the difference in muscle glycogen level. The insulin-stimulated increase in Akt phosphorylation was smaller in the McArdle patients than in controls (45 +/- 13 vs. 76 +/- 13%, P < 0.05, respectively), whereas basal and insulin-stimulated glycogen synthase kinase 3alpha and protein phosphatase-1 activities were similar in the two groups. Furthermore, the ability of insulin to decrease and increase fat and carbohydrate oxidation, respectively, was blunted in the patients. In conclusion, these data show that patients with McArdle's glycogen storage disease are insulin resistant in terms of glucose uptake, glycogen synthase activation, and alterations in fuel oxidation. The data further suggest that skeletal muscle glycogen levels play an important role in the regulation of insulin-stimulated glycogen synthase activity.

Topics: Adult; Blood Glucose; Calcium-Calmodulin-Dependent Protein Kinases; Fatty Acids, Nonesterified; Female; Glucose; Glucose Clamp Technique; Glucose Tolerance Test; Glycogen; Glycogen Phosphorylase; Glycogen Storage Disease Type V; Glycogen Synthase; Glycogen Synthase Kinase 3; Glycogen Synthase Kinases; Humans; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Oxidation-Reduction; Phosphoprotein Phosphatases; Phosphorylation; Protein Phosphatase 1; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt

Insulin resistance results in accumulation of triglyceride content and reduction of glycogen content in skeletal muscle. However, very few studies have measured lipid content and glycogen content in liver associated with insulin resistance. We studied the relationship between liver lipid content, liver glycogen, and insulin resistance in high-fat-fed rats, which are animal models of insulin resistance. High-fat-fed rats were hyperlipidemic, hyperglycemic, and hyperinsulinemic. Furthermore, the glucose infusion rates (GIR) were lower (normal rats, 10.35 +/- 1.66; high-fat-fed rats, 4.86 +/- 0.93 mg/kg/min; P <.01) and the triglyceride and cholesterol contents in liver were higher in the high-fat-fed rats than in normal rats. On the other hand, the glycogen content in liver was lower than in normal rats. There was an inverse relationship between liver triglyceride content and liver glycogen content. When the lipoprotein lipase (LPL) activator NO-1886 was administered to the high-fat-fed rats at a daily dose of 50 mg/kg body weight for 10 weeks, GIR (9.87 +/- 3.76 mg/kg/min, P <.05 v high-fat-fed control group) improved, causing an improvement of the hyperlipidemia, hyperglycemia, and hyperinsulinemia. Furthermore, NO-1886 decreased triglyceride and cholesterol concentrations and increased glycogen content in liver of the high-fat-fed rats. In this study, we found that insulin resistance caused fatty liver and reduced glycogen content in liver. Administration of the LPL activator NO-1886 improved the insulin resistance, resulting in an improvement in the relationship between triglyceride and glycogen content in liver of high-fat-fed rats.

Topics: Animals; Benzamides; Blood Glucose; Body Weight; Cholesterol; Dietary Fats; Enzyme Activation; Glucose Clamp Technique; Glycogen; Hypolipidemic Agents; Insulin; Insulin Resistance; Lipid Metabolism; Lipids; Lipoprotein Lipase; Liver; Male; Organophosphorus Compounds; Rats; Rats, Sprague-Dawley; Triglycerides

Cross talk between adrenergic and insulin signaling systems may represent a fundamental molecular basis of insulin resistance. We have characterized a newly established beta(3)-adrenoceptor-deficient (beta(3)-KO) brown adipocyte cell line and have used it to selectively investigate the potential role of novel-state and typical beta-adrenoceptors (beta-AR) on insulin signaling and action. The novel-state beta(1)-AR agonist CGP-12177 strongly induced uncoupling protein-1 in beta(3)-KO brown adipocytes as opposed to the beta(3)-selective agonist CL-316,243. Furthermore, CGP-12177 potently reduced insulin-induced glucose uptake and glycogen synthesis. Neither the selective beta(1)- and beta(2)-antagonists metoprolol and ICI-118,551 nor the nonselective antagonist propranolol blocked these effects. The classical beta(1)-AR agonist dobutamine and the beta(2)-AR agonist clenbuterol also considerably diminished insulin-induced glucose uptake. In contrast to CGP-12177 treatment, these negative effects were completely abrogated by metoprolol and ICI-118,551. Stimulation with CGP-12177 did not impair insulin receptor kinase activity but decreased insulin receptor substrate-1 binding to phosphatidylinositol (PI) 3-kinase and activation of protein kinase B. Thus the present study characterizes a novel cell system to selectively analyze molecular and functional interactions between novel and classical beta-adrenoceptor types with insulin action. Furthermore, it indicates insulin receptor-independent, but PI 3-kinase-dependent, potent negative effects of the novel beta(1)-adrenoceptor state on diverse biological end points of insulin action.

Topics: Adipocytes; Adipose Tissue, Brown; Adrenergic beta-1 Receptor Agonists; Adrenergic beta-1 Receptor Antagonists; Adrenergic beta-2 Receptor Agonists; Adrenergic beta-2 Receptor Antagonists; Adrenergic beta-Agonists; Adrenergic beta-Antagonists; Animals; Carrier Proteins; Cell Line; Enzyme Activation; Glucose; Glycogen; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Ion Channels; Membrane Proteins; Mice; Mice, Knockout; Mitochondrial Proteins; Phosphatidylinositol 3-Kinases; Phosphoproteins; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Receptor Cross-Talk; Receptor, Insulin; Receptors, Adrenergic, beta-1; Receptors, Adrenergic, beta-2; Receptors, Adrenergic, beta-3; Signal Transduction; Uncoupling Protein 1

In addition to suppressing appetite, leptin may also modulate insulin secretion and action. Leptin was administered here to insulin-resistant rats to determine its effects on secretagogue-stimulated insulin release, whole body glucose disposal, and insulin-stimulated skeletal muscle glucose uptake and transport. Male Wistar rats were fed either a normal (Con) or a high-fat (HF) diet for 3 or 6 mo. HF rats were then treated with either vehicle (HF), leptin (HF-Lep, 10 mg. kg(-1). day(-1) sc), or food restriction (HF-FR) for 12-15 days. Glucose tolerance and skeletal muscle glucose uptake and transport were significantly impaired in HF compared with Con. Whole body glucose tolerance and rates of insulin-stimulated skeletal muscle glucose uptake and transport in HF-Lep were similar to those of Con and greater than those of HF and HF-FR. The insulin secretory response to either glucose or tolbutamide (a pancreatic beta-cell secretagogue) was not significantly diminished in HF-Lep. Total and plasma membrane skeletal muscle GLUT-4 protein concentrations were similar in Con and HF-Lep and greater than those in HF and HF-FR. The findings suggest that chronic leptin administration reversed a high-fat diet-induced insulin-resistant state, without compromising insulin secretion.

Topics: 3-O-Methylglucose; Animals; Blood Glucose; Body Mass Index; Diet; Dietary Fats; Energy Intake; Glucose Clamp Technique; Glucose Tolerance Test; Glucose Transporter Type 4; Glycogen; Hyperinsulinism; Hypoglycemic Agents; Insulin; Insulin Resistance; Leptin; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Rats; Rats, Wistar; Tolbutamide

Insulin signaling is regulated by tyrosine phosphorylation of the signaling molecules, such as the insulin receptor and insulin receptor substrates (IRSs). Therefore, the balance between protein-tyrosine kinases and protein-tyrosine phosphatase activities is thought to be important in the modulation of insulin signaling in insulin-resistant states. We thus employed the adenovirus-mediated gene transfer technique, and we analyzed the effect of overexpression of a wild-type protein-tyrosine phosphatase-1B (PTP1B) on insulin signaling in both L6 myocytes and Fao cells. In both cells, PTP1B overexpression blocked insulin-stimulated tyrosine phosphorylation of the insulin receptor and IRS-1 by more than 70% and resulted in a significant inhibition of the association between IRS-1 and the p85 subunit of phosphatidylinositol 3-kinase and Akt phosphorylation as well as mitogen-activated protein kinase phosphorylation. Moreover, insulin-stimulated glycogen synthesis was also inhibited by PTP1B overexpression in both cells. These effects were specific for insulin signaling, because platelet-derived growth factor (PDGF)-stimulated PDGF receptor tyrosine phosphorylation and Akt phosphorylation were not inhibited by PTP1B overexpression. The present findings demonstrate that PTP1B negatively regulates insulin signaling in L6 and Fao cells, suggesting that PTP1B plays an important role in insulin resistance in muscle and liver.

Topics: Adenoviridae; Blotting, Western; Carcinoma, Hepatocellular; Cell Line; Gene Transfer Techniques; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Liver; Liver Neoplasms; Muscles; Myocardium; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphorylation; Platelet-Derived Growth Factor; Protein Serine-Threonine Kinases; Protein Tyrosine Phosphatases; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Signal Transduction; Tumor Cells, Cultured

To determine the immediate effect of thiazolidinediones on human skeletal muscle, differentiated human myotubes were acutely (1 day) and myoblasts chronically (during the differentiation process) treated with troglitazone (TGZ). Chronic TGZ treatment resulted in loss of the typical multinucleated phenotype. The increase of muscle markers typically observed during differentiation was suppressed, while adipocyte markers increased markedly. Chronic TGZ treatment increased insulin-stimulated phosphatidylinositol (PI) 3-kinase activity and membranous protein kinase B/Akt (PKB/Akt) Ser-473 phosphorylation more than 4-fold. Phosphorylation of p42/44 mitogen-activated protein kinase (42/44 MAPK/ERK) was unaltered. Basal glucose uptake as well as both basal and insulin-stimulated glycogen synthesis increased approximately 1.6- and approximately 2.5-fold after chronic TGZ treatment, respectively. A 2-fold stimulation of PI 3-kinase but no other significant TGZ effect was found after acute TGZ treatment. In conclusion, chronic TGZ treatment inhibited myogenic differentiation of that human muscle while inducing adipocyte-specific gene expression. The effects of chronic TGZ treatment on basal glucose transport may in part be secondary to this transdifferentiation. The enhancing effect on PI 3-kinase and PKB/Akt involved in both differentiation and glycogen synthesis appears to be pivotal in the cellular action of TGZ.

Topics: Adipocytes; Base Sequence; Biomarkers; Cell Differentiation; Cells, Cultured; Chromans; Diabetes Mellitus, Type 2; DNA Primers; Gene Expression; Glucose; Glucose Transporter Type 1; Glucose Transporter Type 4; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Phosphatidylinositol 3-Kinases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Receptors, Cytoplasmic and Nuclear; RNA, Messenger; Signal Transduction; Thiazoles; Thiazolidinediones; Transcription Factors; Troglitazone

Chronic calorie restriction in primates has been shown to have profound and unexpected effects on basal and on in vivo insulin action on skeletal muscle glycogen synthase (GS) activity. The decreased ability of insulin to activate skeletal muscle GS is a hallmark of insulin resistance and type 2 diabetes. The mechanism and role of in vivo insulin regulation of skeletal muscle GS are not fully understood. Two pathways for the activation of GS by insulin have been described by Larner and others: 1) insulin activates glucose transport that results in an increase in glucose-6-phosphate (G6P), thereby activating protein phosphatase-1, which in turn dephosphorylates and activates GS, therefore, pushing substrate into glycogen; and 2) insulin activates GS (perhaps by forming low-molecular-weight mediators which may activate protein phosphatase-1 and 2C) and activated GS subsequently pulls intermediates (e.g., G6P and uridine 5'-diphosphoglucose) into glycogen. To determine whether in vivo insulin regulates glycogen synthesis primarily via a push or pull mechanism and how this mechanism might be affected by long-term calorie restriction, skeletal muscle samples were obtained before and during a euglycemic hyperinsulinemic clamp from 41 rhesus monkeys. The monkeys varied widely in their degree of insulin sensitivity and age and included chronically calorie-restricted (CR) monkeys and ad libitum-fed monkeys. The ad libitum-fed monkeys included spontaneously type 2 diabetic, prediabetic and clinically normal animals. The apparent affinity of GS for the allosteric activator G6P (G6P Ka of GS) was measured and compared with G6P content in the muscle samples. Basal G6P Ka of GS was lower in the CR monkeys compared with the 3 ad libitum-fed groups (P: < or = 0.05). Only the normal ad libitum-fed monkeys had a decrease in the G6P Ka of GS with insulin (P: < 0.005). The insulin effect (insulin-stimulated minus basal) on the G6P Ka of GS was strongly positively related to the insulin effect on G6P content (r = 0.80, P: < 0.0001) across the entire group of monkeys. This finding supports the hypothesis that activation/dephosphorylation of GS by insulin is related to a decrease in G6P content and that paradoxical inactivation/phosphorylation of GS by insulin is related to an increase in G6P content (as demonstrated in 4 of 6 CR monkeys). Therefore, during a euglycemic hyperinsulinemic clamp, insulin regulates skeletal muscle glycogen synthesis primarily via a pull mechanism i

Topics: Animals; Basal Metabolism; Blood Glucose; Diabetes Mellitus, Type 2; Food Deprivation; Glucose Clamp Technique; Glucose-6-Phosphate; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Kinetics; Macaca mulatta; Muscle, Skeletal; Phosphoprotein Phosphatases; Phosphorylation; Protein Phosphatase 1

The present study was conducted to determine the effect of chronic administration of the long-acting beta(2)-adrenergic agonist clenbuterol on rats that are genetically prone to insulin resistance and impaired glucose tolerance. Obese Zucker rats (fa/fa) were given 1 mg/kg of clenbuterol by oral intubation daily for 5 wk. Controls received an equivalent volume of water according to the same schedule. At the end of the treatment, rats were catheterized for euglycemic-hyperinsulinemic (15 mU insulin. kg(-1). min(-1)) clamping. Clenbuterol did not change body weight compared with the control group but caused a redistribution of body weight: leg muscle weights increased, and abdominal fat weight decreased. The glucose infusion rate needed to maintain euglycemia and the rate of glucose disappearance were greater in the clenbuterol-treated rats. Furthermore, plasma insulin levels were decreased, and the rate of glucose uptake into hindlimb muscles and abdominal fat was increased in the clenbuterol-treated rats. This increased rate of glucose uptake was accompanied by a parallel increase in the rate of glycogen synthesis. The increase in muscle glucose uptake could not be ascribed to an increase in the glucose transport protein GLUT-4 in clenbuterol-treated rats. We conclude that chronic clenbuterol treatment reduces the insulin resistance of the obese Zucker rat by increasing insulin-stimulated muscle and adipose tissue glucose uptake. The improvements noted may be related to the repartitioning of body weight between tissues.

Topics: Adrenergic beta-Agonists; Animals; Blood Glucose; Body Weight; Clenbuterol; Female; Glucose; Glycogen; Insulin; Insulin Resistance; Muscle, Skeletal; Obesity; Organ Size; Rats; Rats, Zucker; Triglycerides

The regulatory-targeting subunit (RGL), also called GM) of the muscle-specific glycogen-associated protein phosphatase PP1G targets the enzyme to glycogen where it modulates the activity of glycogen-metabolizing enzymes. PP1G/RGL has been postulated to play a central role in epinephrine and insulin control of glycogen metabolism via phosphorylation of RGL. To investigate the function of the phosphatase, RGL knockout mice were generated. Animals lacking RGL show no obvious defects. The RGL protein is absent from the skeletal and cardiac muscle of null mutants and present at approximately 50% of the wild-type level in heterozygotes. Both the level and activity of C1 protein are also decreased by approximately 50% in the RGL-deficient mice. In skeletal muscle, the glycogen synthase (GS) activity ratio in the absence and presence of glucose-6-phosphate is reduced from 0.3 in the wild type to 0.1 in the null mutant RGL mice, whereas the phosphorylase activity ratio in the absence and presence of AMP is increased from 0.4 to 0.7. Glycogen accumulation is decreased by approximately 90%. Despite impaired glycogen accumulation in muscle, the animals remain normoglycemic. Glucose tolerance and insulin responsiveness are identical in wild-type and knockout mice, as are basal and insulin-stimulated glucose uptakes in skeletal muscle. Most importantly, insulin activated GS in both wild-type and RGL null mutant mice and stimulated a GS-specific protein phosphatase in both groups. These results demonstrate that RGL is genetically linked to glycogen metabolism, since its loss decreases PP1 and basal GS activities and glycogen accumulation. However, PP1G/RGL is not required for insulin activation of GS in skeletal muscle, and rather another GS-specific phosphatase appears to be involved.

Topics: Animals; Base Sequence; DNA Primers; Enzyme Activation; Female; Glucose; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscle, Skeletal; Phosphoprotein Phosphatases; Protein Subunits

The aim of this study was to ascertain whether the presence of hypertension conveys a more severe degree of insulin resistance in type 2 diabetes mellitus and, if so, which biochemical pathways are involved. We quantitated the rates of total glucose disposal, glycogen synthesis (GS), glycolysis, glucose oxidation, endogenous glucose production, and LOX in the basal state and during a 4-h euglycemic ( approximately 5 mM) hyperinsulinemic ( approximately 300 pM) clamp carried out in combination with a dual-tracer infusion ([(3)H]-3- and [(14)C]-U-D-glucose) and indirect calorimetry in 42 nonobese noninsulin-treated type 2 diabetic subjects (22 hypertensive and 20 normotensive) and 23 nonobese nondiabetic subjects (9 without and 14 with essential hypertension). Compared with normotensive controls, both groups of diabetic subjects were markedly insulin resistant. In the basal state, all glucose fluxes were similar in diabetic subjects with or without hypertension. During insulin infusion, total glucose disposal was significantly reduced in hypertensive diabetic subjects, compared with their normotensive counterparts (18.7 +/- 1.0 vs. 28.6 +/- 3.0 micromol/min.kg lean body mass; P < 0.01). This difference was almost entirely explained by a marked reduction in GS (4.5 +/- 2.0 vs. 12.5 +/- 3.3 micromol/min.kg lean body mass; P < 0.01). Endogenous glucose production was not different in the two diabetic groups during insulin infusion and was significantly higher than in normotensive controls. Lipid oxidation was less suppressed by hyperinsulinemia in hypertensive than in normotensive diabetic subjects (1.46 +/- 0.1 vs. 0.91 +/- 0.1 micromol/min.kg lean body mass; P < 0.01). Glucose fluxes were not significantly different in nondiabetic subjects with essential hypertension and in normotensive diabetic individuals. These results indicate that hypertension markedly aggravates insulin resistance featuring type 2 diabetes mellitus. The molecular defects underlying this phenomenon involve primarily GS.

Topics: Aged; Blood Glucose; Diabetes Mellitus, Type 2; Female; Glycogen; Humans; Hypertension; Insulin Resistance; Lipid Metabolism; Male; Middle Aged; Oxidation-Reduction

To investigate the physiological function of syntaxin 4 in the regulation of GLUT4 vesicle trafficking, we used homologous recombination to generate syntaxin 4-knockout mice. Homozygotic disruption of the syntaxin 4 gene results in early embryonic lethality, whereas heterozygous knockout mice, Syn4(+/-), had normal viability with no significant impairment in growth, development, or reproduction. However, the Syn4(+/-) mice manifested impaired glucose tolerance with a 50% reduction in whole-body glucose uptake. This defect was attributed to a 50% reduction in skeletal muscle glucose transport determined by 2-deoxyglucose uptake during hyperinsulinemic-euglycemic clamp procedures. In parallel, insulin-stimulated GLUT4 translocation in skeletal muscle was also significantly reduced in these mice. In contrast, Syn4(+/-) mice displayed normal insulin-stimulated glucose uptake and metabolism in adipose tissue and liver. Together, these data demonstrate that syntaxin 4 plays a critical physiological role in insulin-stimulated glucose uptake in skeletal muscle. Furthermore, reduction in syntaxin 4 protein levels in this tissue can account for the impairment in whole-body insulin-stimulated glucose metabolism in this animal model.

Topics: Adipocytes; Adipose Tissue, Brown; Animals; Biological Transport; Glucose; Glucose Clamp Technique; Glucose Tolerance Test; Glucose Transporter Type 4; Glycogen; Glycolysis; Heterozygote; Insulin Resistance; Liver; Membrane Proteins; Mice; Mice, Knockout; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Qa-SNARE Proteins

A subgroup of patients with type 2 diabetes shows a clustering of abnormalities such as peripheral insulin resistance, hypertension, and microalbuminuria. To evaluate whether these traits reflect intrinsic disorders of cell function rather than in vivo environmental effects, we studied a group of 7 nondiabetic hypertensive subjects with an altered albumin excretion rate (AER) (HyMA+) and 3 groups of patients with type 2 diabetes: 7 with normal blood pressure and normal AER (DH-MA-), 7 with high blood pressure and normal AER (DH+MA-), and 7 with both high blood pressure and altered AER (DH+MA+). Glucose disposal was measured during an hyperinsulinemic clamp (40 mU. m(2)(-1). min(-1)) with primed deuterated [6.6 (2)H(2)] glucose infusion. In the same subjects, a skin biopsy was performed and the following parameters were investigated: glucose transport (as determined by [(3)H]2-deoxyglucose uptake); glycogen synthase activity (as determined by [(14)C] glucose incorporation from UDP-[U-(14)C] glucose into glycogen); glycogen phosphorylase activity (as measured by the incorporation of [U-(14)C]glucose 1-phosphate into glycogen); and total glycogen content. In vivo glucose disposal was significantly reduced in DH+MA- and DH+MA+, with respect to DH-MA-, HyMA+, and controls. Insulin-stimulated glucose transport was similar in the 3 groups of patients with diabetes. A significant reduction of intracellular glycogen content was observed in DH+MA- and DH+MA+ compared with DH-MA- in both basal and insulin-stimulated conditions, probably because of a major impairment of glycogen synthase activity. Glycogen phosphorylase activity did not show differences between the groups. These results suggest that (1) the combination of type 2 diabetes with hypertension and altered AER is associated with impaired insulin sensitivity, and (2) intrinsic, possibly genetic, factors may account for increased peripheral insulin resistance in hypertensive microalbuminuric patients with type 2 diabetes, pointing to the reduction of glycogen synthase activity as a shared common defect.

Topics: Albuminuria; Cells, Cultured; Deoxyglucose; Diabetes Mellitus, Type 2; Female; Fibroblasts; Glucose; Glucose Clamp Technique; Glycogen; Glycogen Synthase; Humans; Hypertension; Insulin; Insulin Resistance; Liver; Male; Middle Aged

It is well known that troglitazone and voluntary running have the capacity to improve insulin resistance. The purpose of this study was to evaluate the combination effect of troglitazone and voluntary running on insulin action. Female rats aged 7 weeks were divided into high-fat diet (HF), high-fat diet + troglitazone (0.3% in diet; Tg), high-fat diet + voluntary running (for 3 wks; Tr), high-fat diet + troglitazone + voluntary running (Tg-Tr), and control (C) groups. A sequential euglycemic clamp experiment with two different insulin infusion rates of 3.0 (L-clamp) and 30.0 mU/kg BW/min (H-clamp) was performed on these rats after an overnight fast. Blood glucose concentrations were kept at fasting levels by periodic adjustment of the intravenous glucose infusion rate during the clamp experiment. Glucose infusion rates (GIRs) calculated from 60 to 90, 150 to 180 min were regarded as an index of whole body insulin action. After the clamp experiment, we determined the amount of glycogen content in the gastrocnemius muscle. Fat feeding markedly reduced GIRs in both L- and H- clamp experiments compared with C. Troglitazone treatment did not improve high-fat induced insulin resistance. In both L- and H-clamp experiments, GIRs were increased by voluntary running compared with HF, and reached the same levels as in C. GIRs of Tg-Tr were not greater than those of Tr. Glycogen content in gastrocnemius muscle showed the same trend as the results for GIRs. Therefore, the combination effect of troglitazone and voluntary running on insulin action was not found, but the effect of voluntary running was shown in fat-induced insulin resistance.

Topics: Animals; Blood Glucose; Body Weight; Chromans; Dietary Fats; Female; Glucose; Glucose Clamp Technique; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Muscle, Skeletal; Rats; Rats, Wistar; Running; Thiazoles; Thiazolidinediones; Troglitazone

Insulin resistance of skeletal muscle has been associated with increased lipid availability. This study aimed to estimate volume fractions of intramyocellular triglyceride droplets and glycogen granules in skeletal muscle using electron microscopy and furthermore, relate these findings to insulin sensitivity and the level of circulating lipids.. We compared 11 obese patients with Type II (non-insulin-dependent) diabetes mellitus and 11 obese normoglycaemic subjects matched for age and sex. Glucose metabolism was determined using the euglycaemic hyperinsulinaemic clamp technique (40 mU.m(-2).min(-1)) coupled with indirect calorimetry and tritiated glucose. On the second day, using an automatic procedure, a fasting muscle biopsy was carried out and processed for electron microscopy. Volume fractions of intramyocellular structures were estimated by pointcounting on photographic pictures in a blinded manner.. Insulin-stimulated total glucose disposal rate was lower in the Type II diabetic subjects compared with the obese normoglycaemic subjects (4.96 +/- 049 vs 10.35 +/- 0.89 mg.min(-1).kg ffm(-1), p < 0.001) as was glucose storage (2.03 +/- 0.50 vs 6.59 +/- 0.83, p < 0.001). The electron microscopy study revealed that the diabetic subjects had higher intramyocellular amounts of triglyceride (1.43 +/- 0.21 vs 0.39 +/- 0.07%, p < 0.001) and lower amounts of glycogen (3.53 +/- 0.33 vs 6.94 +/- 0.54%, p < 0.001). Mitochondrial volume was identical indicating equal aerobic capacity. The fractional intramyocellular lipid volume was found to be positively associated with fasting NEFA (r = 0.63, p = < 0.05 and r = 0.79, p = < 0.05) and triglyceride (r = 0.74, p = 0.01 and r = 0.62, p < 0.05) in the obese diabetic and normoglycaemic cohorts respectively. Intramyocellular lipid content was negatively correlated to insulin sensitivity (r = -0.71, p < 0.02) in the obese diabetic group whereas no significant association was found in the obese normoglycaemic group.. This study shows that fat accumulates intramyocellulary while glycogen stores are simultaneously reduced in obese subjects with Type II (non-insulin-dependent) diabetes mellitus. Quantitatively, a major component of the excessive lipid accumulation could be secondary in origin, related to the diabetic state in itself, although a contribution from the altered insulin action cascade of obesity and diabetes cannot be excluded. In both groups significant positive relations were found between circulating and intramyocellular lipid.

Topics: Adipocytes; Blood Glucose; Calorimetry, Indirect; Cholesterol; Cholesterol, HDL; Diabetes Mellitus; Fatty Acids, Nonesterified; Glucose Clamp Technique; Glucose Tolerance Test; Glycogen; Humans; Hyperinsulinism; Insulin Resistance; Lipid Metabolism; Middle Aged; Muscle, Skeletal; Obesity; Triglycerides; White People

Type 2 diabetes is characterized by peripheral tissue insulin resistance. The present study was carried out to determine the insulin sensitizing action of vanadium using dexamethasone-treated 3T3 adipocytes as an in-vitro model of insulin resistance.. Fully differentiated 3T3 adipocytes were incubated with or without 100 nM dexamethasone in the presence or absence of 200 nM insulin for 6 days. Sodium orthovanadate (0-1000 microM) was added on day 2 and was present during the last 4 days. At the end, insulin (100 nM) stimulated glycogen synthesis was determined.. Vanadate treatment for 4 days, caused 2-3-fold increase in glycogen synthesis in dexamethasone treated adipocytes. At 100 microM, vanadate completely reversed dexamethasone-induced insulin resistance (by increasing the levels from 9.65 +/- 0.80 to 28.4 +/- 4.9 nmol/h). In cells treated with dexamethasone and insulin, vanadium was partially active and it caused only 30% increase in glycogen synthesis. Exposure of dexamethasone treated cells for 24 h with vanadium did not affect glycogen synthesis. Under identical condition, vanadium had no significant effect in the normal insulin sensitive adipocytes. Vanadium at 100 microM had no effect on 125I-insulin binding to insulin-resistant adipocytes. Glycogen synthesis in the normal and insulin-resistant adipocytes was stimulated by lithium, an inhibitor of glycogen synthase kinase 3 beta, suggesting the involvement of phosphorylation events in dexamethasone-induced insulin resistance.. Since vanadium was active only in the insulin-resistant adipocytes it is likely that vanadium acts by relieving dexamethasone actions rather than having independent effects. These results provide evidence for the novel insulin sensitizing action of vanadium which might be of future clinical relevance.

Topics: 3T3 Cells; Adipocytes; Animals; Carbon Radioisotopes; Cell Differentiation; Dexamethasone; Diabetes Mellitus, Type 2; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Kinetics; Lithium; Mice; Vanadates

We assessed the effects of combined metformin treatment and exercise training on body composition, on insulin concentration following glucose loading, on insulin-stimulated glucose transport in skeletal muscle, and on muscle glycogen content. Male Sprague-Dawley rats were treated for 35 days with or without metformin (320 mg/kg/day) and/or treadmill exercise training (20 min at 20 m/min, 5 days/wk). Because metformin reduces food intake, pair-fed controls were included. Metformin, training, and pair-feeding all decreased food intake, body weight, and insulin concentration following glucose loading. Metformin and training reduced intra-abdominal fat, but pair feeding did not. In isolated strips derived from soleus, epitrochlearis and extensor carpi ulnaris muscles, metformin increased insulin-stimulated transport of [3H]-2-deoxyglucose by 90%, 89% and 125%, respectively (P < 0.02) and training increased [3H]-2-deoxyglucose transport in the extensor carpi ulnaris muscle only (66%, P < 0.05). Pair-feeding did not alter [3H]-2-deoxyglucose transport. Training increased gastrocnemius muscle glycogen by 100% (P < 0.001). Metformin and pair-feeding did not alter muscle glycogen. We conclude that metformin reverses the maturation-induced impairment of insulin responsiveness in Sprague-Dawley rats by increasing insulin-stimulated glucose transport in skeletal muscle and that this effect is not secondary to reduced food intake. We also conclude that metformin and exercise training may increase insulin sensitivity by different mechanisms, with training causing increased glucose transport only in some muscles and also causing increased muscle glycogen storage.

Topics: Aging; Animals; Body Composition; Drinking; Eating; Glucose; Glucose Tolerance Test; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Male; Metformin; Muscle, Skeletal; Physical Conditioning, Animal; Rats; Rats, Sprague-Dawley

It has been observed that opposite changes in cardiac workload result in similar changes in cardiac gene expression. In the current study, the hypothesis that altered gene expression in vivo results in altered substrate fluxes in vitro was tested. Hearts were perfused for 60 minutes with Krebs-Henseleit buffer containing glucose (5 mmol/L) and oleate (0.4 mmol/L). At 30 minutes, either insulin (1 mU/mL) or epinephrine (1 micromol/L) was added. Hearts weighed 35% less after unloading and 25% more after aortic banding. Contractile function in vitro was decreased in transplanted and unchanged in banded hearts. Epinephrine, but not insulin, increased cardiac power. Basal glucose oxidation was initially decreased and then increased by aortic banding. The stimulatory effects of insulin or epinephrine on glucose oxidation were reduced or abolished by unloading, and transiently reduced by banding. Oleate oxidation correlated with cardiac power both before and after stimulation with epinephrine, whereas glucose oxidation correlated only after stimulation. Malonyl-coenzyme A levels did not correlate with rates of fatty acid oxidation. Pyruvate dehydrogenase was not affected by banding or unloading. It was concluded that atrophy and hypertrophy both decrease insulin responsiveness and shift myocardial substrate preference to glucose, consistent with a shift to a fetal pattern of energy consumption; and that the isoform-specific changes that develop in vivo do not change the regulation of key metabolic enzymes when assayed in vitro.

Topics: Animals; Atrophy; Body Weight; Cardiomegaly; Enzyme Activation; Epinephrine; Fatty Acids; Glucose; Glycogen; Heart; Heart Transplantation; In Vitro Techniques; Insulin; Insulin Resistance; Male; Malonyl Coenzyme A; Myocardial Contraction; Myocardium; Oleic Acid; Organ Size; Oxidation-Reduction; Perfusion; Pyruvate Dehydrogenase Complex; Rats; Rats, Inbred WF

We determined the effect of an acute bout of swimming (8 x 30 min) followed by either carbohydrate administration (0.5 mg/g glucose ip and ad libitum access to chow; CHO) or fasting (Fast) on postexercise glycogen resynthesis in soleus muscle and liver from female lean (ZL) and obese insulin-resistant (ZO) Zucker rats. Resting soleus muscle glycogen concentration ([glycogen]) was similar between genotypes and was reduced by 73 (ZL) and 63% (ZO) after exercise (P < 0.05). Liver [glycogen] at rest was greater in ZO than ZL (334 +/- 31 vs. 247 +/- 16 micromol/g wet wt; P < 0.01) and fell by 44 and 94% after exercise (P < 0.05). The fractional activity of glycogen synthase (active/total) increased immediately after exercise (from 0.22 +/- 0.05 and 0.32 +/- 0.04 to 0.63 +/- 0.08 vs. 0.57 +/- 0.05; P < 0.01 for ZL and ZO rats, respectively) and remained elevated above resting values after 30 min of recovery. During this time, muscle [glycogen] in ZO increased 68% with CHO (P < 0.05) but did not change in Fast. Muscle [glycogen] was unchanged in ZL from postexercise values after both treatments. After 6 h recovery, GLUT-4 protein concentration was increased above resting levels by a similar extent for both genotypes in both fasted (approximately 45%) and CHO-supplemented (approximately 115%) rats. Accordingly, during this time CHO refeeding resulted in supercompensation in both genotypes (68% vs. 44% for ZL and ZO). With CHO, liver [glycogen] was restored to resting levels in ZL but remained at postexercise values for ZO after both treatments. We conclude that the increased glucose availability with carbohydrate refeeding after glycogen-depleting exercise resulted in glycogen supercompensation, even in the face of muscle insulin-resistance.

Topics: Animals; Dietary Carbohydrates; Eating; Fatty Acids, Nonesterified; Female; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Liver Glycogen; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Obesity; Physical Exertion; Rats; Rats, Zucker

High-fat and high-sucrose diets increase the contribution of gluconeogenesis to glucose appearance (glc R(a)) under basal conditions. They also reduce insulin suppression of glc R(a) and insulin-stimulated muscle glycogen synthesis under euglycemic, hyperinsulinemic conditions. The purpose of the present study was to determine whether these impairments influence liver and muscle glycogen synthesis under hyperglycemic, hyperinsulinemic conditions. Male rats were fed a high-sucrose, high-fat, or low-fat, starch control diet for either 1 (n = 5-7/group) or 5 wk (n = 5-6/group). Studies involved two 90-min periods. During the first, a basal period (BP), [6-3H]glucose was infused. In the second, a hyperglycemic period (HP), [6-3H]glucose, [6-14C]glucose, and unlabeled glucose were infused. Plasma glucose (BP: 111.2 +/- 1.5 mg/dl; HP: 172.3 +/- 1.5 mg/dl), insulin (BP: 2.5 +/- 0.2 ng/ml; HP: 4.9 +/- 0.3 ng/ml), and glucagon (BP: 81.8 +/- 1.6 ng/l; HP: 74.0 +/- 1.3 ng/l) concentrations were not significantly different among diet groups or with respect to time on diet. There were no significant differences among groups in the glucose infusion rate (mg x kg(-1) x min(-1)) necessary to maintain arterial glucose concentrations at approximately 170 mg/dl (pooled average: 6.4 +/- 0.8 at 1 wk; 6.4 +/- 0.7 at 5 wk), percent suppression of glc R(a) (44.4 +/- 7.8% at 1 wk; 63.2 +/- 4.3% at 5 wk), tracer-estimated net liver glycogen synthesis (7.8 +/- 1.3 microg x g liver(-1) x min(-1) at 1 wk; 10.5 +/- 2.2 microg x g liver(-1) x min(-1) at 5 wk), indirect pathway glycogen synthesis (3.7 +/- 0.9 microg x g liver(-1) x min(-1) at 1 wk; 3.4 +/- 0.9 microg x g liver(-1) x min(-1) at 5 wk), or tracer-estimated net muscle glycogenesis (1.0 +/- 0.3 microg x g muscle(-1) x min(-1) at 1 wk; 1.6 +/- 0.3 microg x g muscle(-1) x min(-1) at 5 wk). These data suggest that hyperglycemia compensates for diet-induced insulin resistance in both liver and skeletal muscle.

Topics: Analysis of Variance; Animals; Body Weight; Diet; Dietary Fats; Dietary Sucrose; Glucagon; Glucose; Glucose Clamp Technique; Glycogen; Hyperglycemia; Insulin; Insulin Resistance; Liver; Male; Muscle, Skeletal; Rats; Rats, Sprague-Dawley; Starch

There is no consensus regarding the results from in vivo and in vitro studies on the impact of chronic high insulin and/or high glucose exposure on acute insulin stimulation of glycogen synthase (GS) kinetic parameters in human skeletal muscle. The aim of this study was to evaluate the kinetic parameters of glycogen synthase activity in human myotube cultures at conditions of chronic high insulin combined or not with high glucose exposure, before and after a subsequent acute insulin stimulation. Acute insulin stimulation significantly increased the fractional activity (FV(0.1)) of GS, increased the sensitivity of GS to the allosteric activator glucose 6-phosphate (A(0.5)) and increased the sensitivity of GS to its substrate UDPG (K(m(0.1))) when myotubes were precultured at low insulin with/without high glucose conditions. However, this effect of acute insulin stimulation was abolished in myotubes precultured at high insulin with or without high glucose. Furthermore, we found significant correlations between the fractional velocities FV(0.1) of GS and K(m(0.1)) (rho=-0.72, P<0.0001), between FV(0.1) and A(0.5) (rho=-0.82, P<0.0001) and between K(m(0.1)) and A(0.5) values (rho=0.71, P<0.0001). Our results show that chronic exposure of human myotubes to high insulin with or without high glucose did not affect the basal kinetic parameters but abolished the reactivity of GS to acute insulin stimulation. We suggest that insulin induced insulin resistance of GS is caused by a failure of acute insulin stimulation to decrease A(0.5) and K(m(0.1)) in human skeletal muscle.

Topics: Biopsy; Cells, Cultured; Glucose; Glycogen; Glycogen Synthase; Humans; Immunohistochemistry; Insulin; Insulin Resistance; Kinetics; Muscle Fibers, Skeletal; Myosins

Obesity is often accompanied by a decreased ability of insulin to stimulate glucose uptake and glycogenesis in skeletal muscle. The aim of this study was to investigate the rate of glycogen formation and of muscular glucose content in relation to insulin sensitivity under euglycemic conditions.. We applied a hyperinsulinemic (430 pmol m-2 min-1) euglycemic clamp with infusion of 20% glucose (30% enriched with 13C-1-glucose) to 8 subjects with a wide range of insulin sensitivities. Glycogen and glucose levels were monitored simultaneously by in vivo 13C MRS of the calf muscle on a clinical MR system at 1.5T field strength.. Glycogen synthesis rate showed a strong correlation with whole body glucose uptake during the clamp (r = 0.93, P < 0.01). With the use of 13C MRS, total muscular glucose content could be determined in vivo, and showed a positive, linear correlation with glycogen synthesis rate (r = 0.85, P < 0.01). 13C MRS provides important information regarding in vivo insulin action. Preliminary results indicate that the glycogen synthesis rate improves after treatment with troglitazone.

Topics: Adult; Carbon Isotopes; Chromans; Glucose; Glucose Clamp Technique; Glycogen; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Magnetic Resonance Spectroscopy; Male; Middle Aged; Muscle, Skeletal; Obesity; Thiazoles; Thiazolidinediones; Troglitazone

Troglitazone lowers blood glucose levels in Type II diabetic patients. To evaluate the insulin sensitizing action of troglitazone on glycogen synthesis we have used dexamethasone-treated 3T3 adipocytes as an in vitro model. Differentiated 3T3 adipocytes were incubated with 100 nM dexamethasone for 6 days. Troglitazone (1.0 microM) or metformin (1.0 mM) with or without 200 nM insulin was added during the last 4 days. At the end, insulin (100 nM) stimulated glycogen synthesis was determined using (14)C-glucose. Dexamethasone caused a 50% reduction in glycogen synthesis. Troglitazone caused an approximately 3 fold increase in glycogen synthesis from 43.9+/-3.4 to 120+/-16.2 nmols h(-1). Under identical conditions metformin had no significant effect. When cells were incubated with troglitazone and dexamethasone simultaneously for 6 days, troglitazone but not metformin completely prevented dexamethasone-induced insulin resistance. RU 486 (1.0 microM) also completely prevented the insulin resistance. Chronic incubation with dexamethasone and insulin resulted in a 73% reduction in glycogen synthesis. In these adipocytes, troglitazone was partially active with glycogen synthesis rising from 23.1+/-3.0 to 44.4+/-4.5 nmol h(-1), P<0.01 while metformin was inactive. Troglitazone stimulated 2-deoxyglucose uptake by 2 - 3 fold in dexamethasone-treated adipocytes. Metformin also increased glucose uptake significantly. Troglitazone did not affect insulin binding while a 2 fold increase was observed in normal adipocytes where it exhibited a modest effect. Since the effect of troglitazone was greater in dexamethasone-treated adipocytes, troglitazone is likely to act by preventing dexamethasone-induced alterations which may include (i) binding to glucocorticoid receptor and (ii) effect on glucose uptake. These data demonstrate the direct insulin sensitizing action of troglitazone on glycogen synthesis and suggest a pharmacological profile different from metformin.

Topics: 3T3 Cells; Abortifacient Agents, Steroidal; Adipocytes; Animals; Binding Sites; Chromans; Dexamethasone; Dose-Response Relationship, Drug; Drug Interactions; Glucocorticoids; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Iodine Radioisotopes; Mice; Mifepristone; Thiazoles; Thiazolidinediones; Troglitazone

Obesity and insulin resistance in skeletal muscle are two major factors in the pathogenesis of type 2 diabetes. Mice with muscle-specific inactivation of the insulin receptor gene (MIRKO) are normoglycemic but have increased fat mass. To identify the potential mechanism for this important association, we examined insulin action in specific tissues of MIRKO and control mice under hyperinsulinemic-euglycemic conditions. We found that insulin-stimulated muscle glucose transport and glycogen synthesis were decreased by about 80% in MIRKO mice, whereas insulin-stimulated fat glucose transport was increased threefold in MIRKO mice. These data demonstrate that selective insulin resistance in muscle promotes redistribution of substrates to adipose tissue thereby contributing to increased adiposity and development of the prediabetic syndrome.

Topics: Adipose Tissue; Animals; Blood Glucose; Glucose; Glucose Clamp Technique; Glycogen; Glycolysis; Hyperinsulinism; Insulin; Insulin Resistance; Male; Mice; Mice, Knockout; Muscle, Skeletal; Obesity; Receptor, Insulin; Reference Values

The aim of these studies was to investigate whether insulin resistance is primary to skeletal muscle. Myoblasts were isolated from muscle biopsies of 8 lean insulin-resistant and 8 carefully matched insulin-sensitive subjects (metabolic clearance rates as determined by euglycemic-hyperinsulinemic clamp: 5.8 +/- 0.5 vs. 12.3 +/- 1.7 ml x kg(-1) x min(-1), respectively; P < or = 0.05) and differentiated to myotubes. In these cells, insulin stimulation of glucose uptake, glycogen synthesis, insulin receptor (IR) kinase activity, and insulin receptor substrate 1-associated phosphatidylinositol 3-kinase (PI 3-kinase) activity were measured. Furthermore, insulin activation of protein kinase B (PKB) was compared with immunoblotting of serine residues at position 473. Basal glucose uptake (1.05 +/- 0.07 vs. 0.95 +/- 0.07 relative units, respectively; P = 0.49) and basal glycogen synthesis (1.02 +/- 0.11 vs. 0.98 +/- 0.11 relative units, respectively; P = 0.89) were not different in myotubes from insulin-resistant and insulin-sensitive subjects. Maximal insulin responsiveness of glucose uptake (1.35 +/- 0.03-fold vs. 1.41 +/- 0.05-fold over basal for insulin-resistant and insulin-sensitive subjects, respectively; P = 0.43) and glycogen synthesis (2.00 +/- 0.13-fold vs. 2.10 +/- 0.16-fold over basal for insulin-resistant and insulin-sensitive subjects, respectively; P = 0.66) were also not different. Insulin stimulation (1 nmol/l) of IR kinase and PI 3-kinase were maximal within 5 min (approximately 8- and 5-fold over basal, respectively), and insulin activation of PKB was maximal within 15 min (approximately 3.5-fold over basal). These time kinetics were not significantly different between groups. In summary, our data show that insulin action and signaling in cultured skeletal muscle cells from normoglycemic lean insulin-resistant subjects is not different from that in cells from insulin-sensitive subjects. This suggests an important role of environmental factors in the development of insulin resistance in skeletal muscle.

Topics: Adult; Cells, Cultured; Dose-Response Relationship, Drug; Female; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Kinetics; Male; Muscle, Skeletal; Osmolar Concentration; Reference Values; Signal Transduction; Time Factors

Muscle glucose uptake, glycogen synthase activity, and insulin signaling were investigated in response to a physiological hyperinsulinemic (600 pmol/l)-euglycemic clamp in young healthy subjects. Four hours before the clamp, the subjects performed one-legged exercise for 1 h. In the exercised leg, insulin more rapidly activated glucose uptake (half activation time [t1/2] = 11 vs. 34 min) and glycogen synthase activity (t1/2 = 8 vs. 17 min), and the magnitude of increase was two- to fourfold higher compared with the rested leg. However, prior exercise did not result in a greater or more rapid increase in insulin-induced receptor tyrosine kinase (IRTK) activity (t1/2 = 50 min), serine phosphorylation of Akt (t1/2 = 1-2 min), or serine phosphorylation of glycogen synthase kinase-3 (GSK-3) (t1/2 = 1-2 min) or in a larger or more rapid decrease in GSK-3 activity (t1/2 = 3-8 min). Thirty minutes after cessation of insulin infusion, glucose uptake, glycogen synthase activity, and signaling events were partially reversed in both the rested and the exercised leg. We conclude the following: 1) physiological hyperinsulinemia induces sustained activation of insulin-signaling molecules in human skeletal muscle; 2) the more distal insulin-signaling components (Akt, GSK-3) are activated much more rapidly than the proximal signaling molecules (IRTK as well as insulin receptor substrate 1 and phosphatidylinositol 3-kinase [Wojtaszewski et al., Diabetes 46:1775-1781, 1997]); and 3) prior exercise increases insulin stimulation of both glucose uptake and glycogen synthase activity in the absence of an upregulation of signaling events in human skeletal muscle.

Topics: Adult; Amino Acid Sequence; Calcium-Calmodulin-Dependent Protein Kinases; Exercise; Glucose; Glucose Clamp Technique; Glycogen; Glycogen Synthase Kinase 3; Glycogen Synthase Kinases; Humans; Insulin; Insulin Resistance; Leg; Male; Muscle, Skeletal; Phosphorylation; Protein Serine-Threonine Kinases; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Signal Transduction

To investigate the contribution of inherited biochemical defects to the peripheral insulin resistance of type 2 diabetes, we studied cultured skeletal muscle from 10 insulin-resistant nondiabetic first-degree relatives of type 2 diabetic families and 6 control subjects. Insulin stimulation of glucose uptake and glycogen synthesis was maximal in myoblasts. Insulin-stimulated glucose uptake (fold-stimulation over basal uptake) was decreased in relative compared with control myoblasts at 0.001 micromol/l (0.93 +/- 0.05 [mean +/- SE] vs. 1.15 +/- 0.06, P < 0.05) and 0.1 micromol/l (1.38 +/- 0.10 vs. 1.69 +/- 0.08, P = 0.025) insulin. Insulin responsiveness was markedly impaired in 5 of the relative myoblast cultures, and in 4 of these, there was an associated increase in basal glucose uptake (76.7 +/- 7.0 vs. 47.4 +/- 5.5 pmol x min(-1) x mg(-1) protein, relative vs. control; P < 0.02). Expression of insulin receptor substrate 1, phosphatidylinositol 3-kinase, protein kinase B, and glycogen synthase was normal in the relative cultures with impaired insulin responsiveness. Glycogen synthesis was also normal in the relative cultures. We conclude that the persistence of impaired insulin responsiveness in some of the relative cultures supports the role of inherited factors in the insulin resistance of type 2 diabetes and that the association with increased basal glucose uptake suggests that the 2 abnormalities may be linked.

Topics: Adult; Biological Transport; Blood Glucose; Cells, Cultured; Diabetes Mellitus, Type 2; Europe; Female; Glucose; Glucose Transporter Type 1; Glucose Transporter Type 4; Glycogen; Humans; Insulin; Insulin Resistance; Male; Middle Aged; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Reference Values; Tritium

Soleus muscle strips from Wistar rats were preincubated with palmitate in vitro before the determination of insulin-mediated glucose metabolism in fatty acid-free medium. Palmitate decreased insulin-stimulated glycogen synthesis to 51% of control in a time- (0-6 h) and concentration-dependent (0-2 mM) manner. Basal and insulin-stimulated glucose transport/phosphorylation also decreased with time, but the decrease occurred after the effect on glycogen synthesis. Preincubation with 1 mM palmitate, oleate, linoleate, or linolenate for 4 h impaired glycogen synthesis stimulated with a submaximal physiological insulin concentration (300 microU/ml) to 50-60% of the control response, and this reduction was associated with impaired insulin-stimulated phosphorylation of protein kinase B (PKB). Preincubation with different fatty acids (all 1 mM for 4 h) had varying effects on insulin-stimulated glucose transport/phosphorylation, which was decreased by oleate and linoleate, whereas palmitate and linolenate had little effect. Across groups, the rates of glucose transport/phosphorylation correlated with the intramuscular long-chain acyl-CoA content. The similar effects of individual fatty acids on glycogen synthesis but different effects on insulin-stimulated glucose transport/phosphorylation provide evidence that lipids may interact with these two pathways via different mechanisms.

Topics: Acyl Coenzyme A; Adenosine Triphosphate; Animals; Dietary Fats; Fatty Acids; Glucose; Glucose-6-Phosphate; Glycogen; In Vitro Techniques; Insulin; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle, Skeletal; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Rats; Rats, Wistar

Glycogen synthase (GS) is the rate-limiting enzyme controlling nonoxidative glucose disposal in skeletal muscle. A reduction in GS activity and an impaired insulin responsiveness are characteristic features of skeletal muscle in type 2 diabetes. These properties also exist in human skeletal muscle cell cultures from type 2 diabetic subjects. To determine the effect of an isolated reduction in GS on skeletal muscle insulin action, cultures from nondiabetic subjects were treated with antisense oligonucleotides (ODNs) to GS to interfere with expression of the gene. Treatment with antisense ODNs reduced GS protein expression by 70% compared with control (scrambled) ODNs (P < .01). GS activity measured at 0.01 mmol/L glucose-6-phosphate (G-6-P) was reduced by antisense ODN treatment. The insulin responsiveness of GS was impaired. Insulin also failed to stimulate glucose incorporation into glycogen after antisense ODN treatment. The cellular glycogen content was lower in antisense ODN-treated cells compared with control ODN. The insulin responsiveness of glucose uptake was abolished by antisense ODN treatment. Thus, reductions in GS expression in human skeletal muscle cells lead to impairments in insulin responsiveness and may play an important role in insulin-resistant states.

Topics: Adult; Amino Acid Transport System X-AG; ATP-Binding Cassette Transporters; Culture Techniques; Down-Regulation; Gene Expression Regulation, Enzymologic; Gene Silencing; Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Resistance; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Oligoribonucleotides, Antisense; Phosphatidylethanolamines; RNA, Messenger

Type 2 diabetes is a polygenic disease characterized by defects in both insulin secretion and insulin action. We have previously reported that isolated insulin resistance in muscle by a tissue-specific insulin receptor knockout (MIRKO mouse) is not sufficient to alter glucose homeostasis, whereas beta-cell-specific insulin receptor knockout (betaIRKO) mice manifest severe progressive glucose intolerance due to loss of glucose-stimulated acute-phase insulin release. To explore the interaction between insulin resistance in muscle and altered insulin secretion, we created a double tissue-specific insulin receptor knockout in these tissues. Surprisingly, betaIRKO-MIRKO mice show an improvement rather than a deterioration of glucose tolerance when compared to betaIRKO mice. This is due to improved glucose-stimulated acute insulin release and redistribution of substrates with increased glucose uptake in adipose tissue and liver in vivo, without a significant decrease in muscle glucose uptake. Thus, insulin resistance in muscle leads to improved glucose-stimulated first-phase insulin secretion from beta-cells and shunting of substrates to nonmuscle tissues, collectively leading to improved glucose tolerance. These data suggest that muscle, either via changes in substrate availability or by acting as an endocrine tissue, communicates with and regulates insulin sensitivity in other tissues.

Topics: Acute-Phase Reaction; Animals; Blood Glucose; Deoxyglucose; Diabetes Mellitus, Type 2; Fasting; Glucose; Glucose Tolerance Test; Glycogen; Injections, Intraperitoneal; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Lipid Metabolism; Mice; Mice, Knockout; Muscle, Skeletal; Receptor, Insulin; Reference Values

Present animal models used to emulate type 2 diabetes may not accurately reflect the metabolic changes that occur in humans.. The purpose of this research was to evaluate diets reported to induce insulin resistance and impaired glucose metabolism in rats as a potentially useful model for studying type 2 diabetes.. Three groups of male Sprague Dawley rats (n=7) were fed either a control diet, based on AIN recommendations (53% cornstarch, 10% sucrose and 7% soybean oil), a high fat diet (25% soybean oil, 35% cornstarch) or a high fructose diet (53% fructose, 10% sucrose) for a 3 month period. Glucose tolerance tests were carried out in week 3 and week 9 of the experiment. At the termination of the experiment, serum insulin, glucose, cholesterol and triacylglycerols were measured. Glucose incorporation into glycogen and glycogen synthase activity were measured in soleus muscles.. Similar weight gain was observed for all three groups of rats. Glucose tolerance curves and fasting glucose levels were not significantly different at any time point in the experiment. Insulin levels were unchanged for the controls (171+/-21 pM), high fructose (164+/-16 pM) and high fat (181+/-30 pM) diets. Fasting serum triacylglycerols and cholesterol levels were not significantly elevated by dietary treatment. In soleus muscles, rats on all three diets had a significant increase in glycogen synthesis in response to insulin, but synthesis was similar in all three groups. Glycogen synthase activity was also not significantly affected by long-term dietary intervention.. In this study, healthy Sprague Dawley rats fed high fat or high fructose diets for 3 months adapted to the nutritional intervention without developing classical signs of insulin resistance and impaired glucose tolerance.

Topics: Adaptation, Biological; Animals; Cholesterol; Diabetes Mellitus, Type 2; Dietary Carbohydrates; Dietary Fats; Disease Models, Animal; Fructose; Glucose; Glucose Tolerance Test; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Male; Muscles; Rats; Rats, Sprague-Dawley; Time Factors; Triglycerides

Topics: Animals; Coronary Disease; Energy Metabolism; Glucose; Glycogen; Humans; In Vitro Techniques; Insulin Resistance; Magnetic Resonance Spectroscopy; Models, Cardiovascular; Myocardium; Rats

To examine the mechanism by which free fatty acids (FFA) induce insulin resistance in human skeletal muscle, glycogen, glucose-6-phosphate, and intracellular glucose concentrations were measured using carbon-13 and phosphorous-31 nuclear magnetic resonance spectroscopy in seven healthy subjects before and after a hyperinsulinemic-euglycemic clamp following a five-hour infusion of either lipid/heparin or glycerol/heparin. IRS-1-associated phosphatidylinositol 3-kinase (PI 3-kinase) activity was also measured in muscle biopsy samples obtained from seven additional subjects before and after an identical protocol. Rates of insulin stimulated whole-body glucose uptake. Glucose oxidation and muscle glycogen synthesis were 50%-60% lower following the lipid infusion compared with the glycerol infusion and were associated with a approximately 90% decrease in the increment in intramuscular glucose-6-phosphate concentration, implying diminished glucose transport or phosphorylation activity. To distinguish between these two possibilities, intracellular glucose concentration was measured and found to be significantly lower in the lipid infusion studies, implying that glucose transport is the rate-controlling step. Insulin stimulation, during the glycerol infusion, resulted in a fourfold increase in PI 3-kinase activity over basal that was abolished during the lipid infusion. Taken together, these data suggest that increased concentrations of plasma FFA induce insulin resistance in humans through inhibition of glucose transport activity; this may be a consequence of decreased IRS-1-associated PI 3-kinase activity.

Topics: Adolescent; Adult; Fatty Acids, Nonesterified; Female; Glucose; Glucose Clamp Technique; Glucose-6-Phosphate; Glycerol; Glycogen; Humans; Hyperinsulinism; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Lipid Metabolism; Magnetic Resonance Spectroscopy; Male; Muscle, Skeletal; Phosphatidylinositol 3-Kinases; Phosphoproteins

Type 2 diabetes mellitus and obesity are characterized by fasting hyperinsulinemia, insulin resistance with respect to glucose metabolism, elevated plasma free fatty acid (FFA) levels, hypertriglyceridemia, and decreased high-density lipoprotein (HDL) cholesterol. An association between hyperinsulinemia and dyslipidemia has been suggested, but the causality of the relationship remains uncertain. Therefore, we infused eight 12-week-old male catheterized conscious normal rats with insulin (1 mU/min) for 7 days while maintaining euglycemia using a modification of the glucose clamp technique. Control rats (n = 8) received vehicle infusion. Baseline FFAs were 1.07+/-0.13 mmol/L, decreased to 0.57+/-0.10 (P < .05) upon initiation of the insulin infusion, and gradually increased to 0.95+/-0.12 by day 7 (P = NS vbaseline). On day 7 after a 6-hour fast, plasma insulin, glucose, and FFA levels in control and chronically hyperinsulinemic rats were 32+/-5 versus 116+/-21 mU/L (P < .005), 122+/-4 versus 129+/-8 mg/dL (P = NS), and 1.13+/-0.18 versus 0.95+/-0.12 mmol/L (P = NS); total plasma triglyceride and cholesterol levels were 78+/-7 versus 66+/-9 mg/dL (P = NS) and 50+/-3 versus 47+/-2 mg/dL (P = NS), respectively. Very-low-density lipoprotein (VLDL) + intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and HDL2 and HDL3 subfractions of plasma triglyceride and cholesterol were similar in control and hyperinsulinemic rats. Plasma FFA correlated positively with total (r = .61, P < .005) triglycerides. On day 7 after an 8-hour fast, hyperinsulinemic-euglycemic clamps with 3-3H-glucose infusion were performed in all rats. Chronically hyperinsulinemic rats showed peripheral insulin resistance (glucose uptake, 15.8+/-0.8 v 19.3+/-1.4 mg/kg x min, P < .02) but normal suppression of hepatic glucose production (HGP) compared with control rats (4.3+/-1.0 v 5.6+/-1.4 mg/kg x min, P = NS). De novo tissue lipogenesis (3-3H-glucose incorporation into lipids) was increased in chronically hyperinsulinemic versus control rats (0.90+/-0.10 v 0.44+/-0.08 mg/kg x min, P < .005). In conclusion, chronic physiologic hyperinsulinemia (1) causes insulin resistance with regard to the suppression of plasma FFA levels and increases lipogenesis; (2) induces peripheral but not hepatic insulin resistance with respect to glucose metabolism; and (3) does not cause an elevation in VLDL-triglyceride or a reduction in HDL-cholesterol.

Topics: Animals; Blood Glucose; Chronic Disease; Energy Metabolism; Fatty Acids, Nonesterified; Glucose Clamp Technique; Glycogen; Glycolysis; Hyperinsulinism; Hyperlipidemias; Hypoglycemic Agents; Insulin; Insulin Resistance; Lipids; Lipoproteins; Liver; Male; Rats; Rats, Sprague-Dawley; Triglycerides

Insulin resistance, a major predictor of type 2 diabetes mellitus, is genetically inherited in Pima Indians, a population with a high prevalence of the metabolically complex disease. Protein targeting to glycogen/PPP1R5 has recently been identified as a potential regulator of glycogen synthase, the rate-limiting enzyme of the insulin-induced glycogenesis. The gene is located on chromosome 10q23-24, where there is a suggestive linkage to insulin action in this population, establishing it as a functional and positional candidate gene. In this study, we discovered 2 novel polymorphisms upstream of the 5'UTR of the gene, with only one found in Pima Indians, but no polymorphism in the coding sequence. The genotype frequencies of the polymorphism and transcript levels of the gene in skeletal muscle do not correlate with insulin action in the subjects. These results exclude any significant role of protein targeting to glycogen/PPP1R5 in insulin resistance in Pima Indians.

Topics: 5' Untranslated Regions; Base Sequence; Carrier Proteins; DNA Primers; DNA, Complementary; Glycogen; Humans; Indians, North American; Insulin; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Introns; Phosphoprotein Phosphatases; Polymorphism, Genetic; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

Glucosamine infusion induces insulin resistance in vivo, but the effect of glucosamine on intracellular metabolites of the hexosamine pathway, especially glucosamine-6-phosphate (GlcN6P) is unknown. Because of the structural similarity of glucose-6-phosphate (G-6-P) and GlcN6P, we hypothesized that accumulation of this metabolite might alter the activities of enzymes such as glycogen synthase and hexokinase. We infused glucosamine (30 micromol x kg(-1) x min(-1)) to induce insulin resistance in rats during a euglycemic-hyperinsulinemic clamp. Glucosamine induced whole-body insulin resistance, which was apparent after 90 min and continued progressively for 360 min. Despite inducing severe whole-body insulin resistance and decrease in glycogen synthase fractional activity in rectus abdominis muscle (69+/-3 vs. 83+/-1%, P<0.01) and heart (7+/-1 vs. 32+/-4%, P<0.001), glucosamine did not change the glycogen content in rectus and even increased it in the heart (209+/-13 vs. 117+/-9 mmol/kg dry wt, P<0.001). Glucosamine increased tissue concentrations of UDP-GlcNAc 4.4- and 4.6-fold in rectus abdominis and heart, respectively. However, GlcN6P concentrations increased 500- and 700-fold in glucosamine-infused animals in rectus abdominis (590+/-80 vs. 1.2+/-0.1 micromol/kg wet wt, P<0.001) and heart (7,703+/-993 vs. 11.2+/-2.3 micromol/kg wet wt, P<0.001). To assess the possible significance of GlcN6P accumulation, we measured the effect of GlcN6P on glycogen synthase and hexokinase activity in vitro. At the GlcN6P concentrations measured in rectus abdominis and heart in vivo, glycogen synthase was activated by 21 and 542%, while similar concentrations inhibited hexokinase activity by 5 and 46%, respectively. This study demonstrates that infusion of glucosamine during a euglycemic-hyperinsulinemic clamp results in marked accumulation of intracellular GlcN6P. The GlcN6P concentrations in the heart and rectus abdominis muscle reach levels sufficient to cause allosteric activation of glycogen synthase and inhibition of hexokinase.

Topics: Allosteric Regulation; Animals; Blood Glucose; Enzyme Activation; Enzyme Inhibitors; Glucosamine; Glucose Clamp Technique; Glucose-6-Phosphate; Glycogen; Glycogen Synthase; Glycolysis; Heart; Hexokinase; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Myocardium; Rats; Rats, Wistar

In healthy individuals, glycogen recovery after a strong depletion is known to be rapid and insulin independent during the initial phase, and subsequently, slow and insulin dependent. Free fatty acids (FFAs) as a putative source of insulin resistance (IR) could thus impair glycogen recovery during the second period. Using in vivo 13C nuclear magnetic resonance (NMR), we studied the effect of long-chain triglyceride emulsion on gastrocnemius glycogen resynthesis during a 3-h recovery period after 90 min of moderate exercise consisting of plantar flexion on overnight-fasted healthy men (n = 8). In separate experiments, each subject was infused with 10% Ivelip (0.015 ml x kg(-1) x min(-1)) or 10% glycerol (0.13 mg x kg(-1) x min(-1)). NMR spectra were acquired before and at the end of the exercise and during the recovery period. Whole-body glucose and lipid oxidation rates (indirect calorimetry), plasma insulin, C-peptide, glucose, lactate, beta-hydroxybutyrate, triglycerides, and FFAs were determined. Glycogen consumption was 47.6 +/- 4.5% (glycerol) and 49.7 +/- 4.8% (Ivelip) of the initial glycogen. An acquired IR in the Ivelip group was significant at the onset of the recovery period by homeostasis model assessment (P = 0.002). Glycogen resynthesis in the glycerol group appeared faster during the 1st h than during the subsequent 2nd h of the postexercise period. The glycogen resynthesis level was significantly lower in the Ivelip group than in the glycerol group during the recovery period (P = 0.04 during the 1st h and P = 0.001 during the next 2 h). During the recovery, plasma lactate and whole-body oxidation rates were similar in the two groups, whereas glycemia was significantly higher in the Ivelip group. A decreased cellular uptake of glucose as a substrate for glycogenosynthesis, rather than a competition between oxidation of carbohydrate and FFA, is discussed.

Topics: Adult; Carbon Isotopes; Emulsions; Exercise; Fatty Acids, Nonesterified; Glycerol; Glycogen; Humans; Infusions, Intravenous; Insulin Resistance; Lipid Metabolism; Magnetic Resonance Spectroscopy; Male; Muscle, Skeletal; Oxidation-Reduction; Reference Values; Triglycerides

Elevated serum and tissue lipid stores are associated with skeletal muscle insulin resistance and diminished glucose-stimulated insulin secretion, the hallmarks of type 2 diabetes. We studied the effects of 6-wk treatment with the insulin sensitizer troglitazone on substrate storage and utilization in lean control and Zucker diabetic fatty (ZDF) rats. Troglitazone prevented development of diabetes and lowered serum triglycerides (TG) in ZDF rats. Soleus muscle glycogen and TG content were elevated twofold in untreated ZDF rats, and both were normalized by troglitazone to lean control levels (P < 0.05). Troglitazone also normalized insulin-stimulated glucose uptake as well as basal and insulin-stimulated glycogen synthesis, implying increased skeletal muscle glycogen turnover. The proportion of active pyruvate dehydrogenase (PDH) in soleus muscle was reduced in ZDF relative to lean control rat muscle (16 +/- 2 vs. 21 +/- 2%) but was restored by troglitazone treatment (30 +/- 3%). Increased PDH activation was associated with a 70% increase in glucose oxidation. Muscle lipoprotein lipase activity was decreased by 35% in ZDF compared with lean control rats and was increased twofold by troglitazone. Palmitate oxidation and incorporation into TG were higher in ZDF relative to lean control rats but were unaffected by troglitazone treatment. Troglitazone decreased the incorporation of glucose into the acyl group of TG by 60% in ZDF rats. In summary, ZDF rats demonstrate increased skeletal muscle glycogen and TG stores, both of which were reduced by troglitazone treatment. Troglitazone appears to increase both glycogen and TG turnover in skeletal muscle. Normalization of PDH activity and decreased glucose incorporation into acyl TG may underlie the improvements in intracellular substrate utilization and energy stores, which lead to decreased serum TG and glucose.

Topics: Animals; Body Weight; Chromans; Eating; Glucose; Glycogen; In Vitro Techniques; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Lipoprotein Lipase; Muscle, Skeletal; Palmitates; Pyruvate Dehydrogenase Complex; Rats; Rats, Zucker; Thiazoles; Thiazolidinediones; Triglycerides; Troglitazone

BRL 26830A, a beta adrenoceptor agonist, has been shown to have antiobesity and antidiabetic properties in rodents. The aim of this study was to study the effects of chronic BRL 26830A treatment (20 mg/kg/day for 9 weeks) on weight gain and the development of insulin resistance in gold-thioglucose-injected mice (GTG). BRL 26830A slowed the rate of weight gain in GTG such that mice weighed significantly less between 2 w and 7 w of treatment. However, at the time of sacrifice (9 w), there was no difference in body weight between treated and untreated GTG. The obesity-induced reduction in lipogenesis in brown adipose tissue (BAT) was increased 9 fold to greater than CON levels. However, weight and fatty acid (FA) content of BAT were reduced, suggesting increased lipid turnover and thermogenesis. Lipogenesis, FA content and fat pad weight were unchanged in white adipose tissue (WAT) and decreased in liver of GTG. Glucose tolerance was improved in both CON and GTG. Hyperglycemia, hyperinsulinemia and changes in cardiac and hepatic glucose oxidation as indicated by PDHC activity were normalized. Serum triglycerides and non-esterified fatty acids were reduced. Thus, chronic BRL 26830A treatment prevented the development of insulin resistance and attenuated weight gain, but did not prevent the development of obesity in this model.

Topics: Adipose Tissue; Adipose Tissue, Brown; Adrenergic beta-Agonists; Animals; Aurothioglucose; Blood Glucose; Body Composition; Ethanolamines; Fatty Acids; Glycogen; Insulin; Insulin Resistance; Lipid Metabolism; Lipids; Male; Mice; Mice, Inbred CBA; Obesity; Pyruvate Dehydrogenase Complex; Weight Gain

We investigated the relation between glucose transport/phosphorylation and glycogen synthase activation in individual rat skeletal muscles in response to moderate hyperinsulinaemia in the absence or presence of hyperglycaemia during pregnancy.. Rats were studied on day 20 of pregnancy after 24-h starvation, with unmated rats as controls. Insulin and glucose were infused into conscious rats through an indwelling cannula as specified. Glucose transport/phosphorylation was assessed in vivo using 2-deoxy-[1-3H]glucose. Glycogen synthase activity was measured in muscle extracts < or = 10 mmol/l glucose-6-phosphate.. In unmated rats, stimulation of glucose transport/phosphorylation occurred in response to euglycaemic-hyperinsulinaemia in all muscles studied but activation of glycogen synthase was not observed. Muscle glucose transport/phosphorylation rates during euglycaemic-hyperinsulinaemia after 24-h starvation were lower in pregnant compared with unmated rats, whereas glycogen synthase activation by insulin occurred in two of three fast-twitch muscles of pregnant rats. When insulin and glucose concentrations were matched between the 24-h starved unmated and pregnant groups through variable glucose infusion (15 min), glycogen synthase activities in fast-twitch muscles did not differ between unmated and pregnant groups. The response of glycogen synthase to hyperglycaemia in slow-twitch muscle was, however, greater in the pregnant group.. Glycogen synthase activation in slow-twitch muscle in response to hyperinsulinaemia after 24-h starvation is enhanced in late pregnancy but the response is critically dependent on glycaemia. Pregnancy is, nevertheless, associated with reduced muscle glucose transport/phosphorylation. This disassociation ensures that available glucose is directed towards the fetus rather than the mother under conditions of moderate hyperinsulinaemia, for example during refeeding after starvation.

Topics: Animals; Biological Transport; Fasting; Fatty Acids, Nonesterified; Female; Food; Glucose; Glucose Clamp Technique; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Ketone Bodies; Lactic Acid; Muscle, Skeletal; Phosphorylation; Pregnancy; Rats; Rats, Wistar; Triglycerides

Growth hormone (GH) deficiency in adults is characterized by central obesity, dyslipidemia, coagulopathy and glucose intolerance, all features of the "metabolic syndrome", explaining the increased cardiovascular morbidity and mortality associated with GH deficiency in adults. Employing the 2-step euglycemic-hyperinsulinemic clamp, we have demonstrated severe insulin resistance in GH-deficient adults, with a reduction in insulin-mediated glucose utilization of -50%. Basal glucose turnover and partitioning of whole body glucose utilization into glycolytic flux (GF) and glycogen synthesis/glucose storage (GS) pathways are normal, but insulin activation of these 2 pathways is reduced, predominantly in the GS pathway. Activation of muscle glycogen synthase by insulin is markedly decreased, as is glycogen content of muscle. Insulin-induced muscle hexokinase activity appears also to be attenuated in GH-deficient adults with raised intramuscular cellular glucose and normal-reduced concentrations of glucose-6-phosphate. Beta-cell function is not excessive in GH-deficient adults and is inappropriately low for the insulin resistance. Following treatment of GH-deficient adults with recombinant GH (rhGH), the insulin resistance is either unchanged or more pronounced by 3, 6 or 24 months of treatment, despite the significant reduction in general and central obesity. The GF and GS pathways and muscle glycogen synthase and hexokinase activities remain severely impaired. Abnormalities in free fatty acid (FFA) metabolism are present in rhGH-treated GH-deficient adults and correlate significantly with the degree of insulin resistance as do the concentrations of rhGH-induced insulin-like growth factor (IGF)-I, the post-basal insulinemia and the duration of the GHD, but is independent of obesity. In conclusion, long-term rhGH treatment in GH-deficient adults results in persistent insulin resistance and abnormalities in the GF and GS pathways due to reduced glycogen synthase and hexokinase activities, in the presence of an ongoing reduction of central obesity. We postulate that the insulin resistance is due to chronic rhGH-induced alterations in FFA metabolism, non-physiological levels of IGF-I and chronic basal hyperinsulinemia.

Topics: Adult; Case-Control Studies; Glucose Clamp Technique; Glycogen; Glycolysis; Hormone Replacement Therapy; Human Growth Hormone; Humans; Insulin Resistance; Liver; Liver Glycogen; Muscles

We have employed C2C12 myotubes to investigate lipid inhibition of insulin-stimulated signal transduction and glucose metabolism. Cells were preincubated for 18 h in the absence or presence of free fatty acids (FFAs) and stimulated with insulin, and the effects on glycogen synthesis and signaling intermediates were determined. While the unsaturated FFAs oleate and linoleate inhibited both basal and insulin-stimulated glycogen synthesis, the saturated FFA palmitate reduced only insulin-stimulated glycogen synthesis, and was found to inhibit insulin-stimulated phosphorylation of glycogen synthase kinase-3 and protein kinase B (PKB). However, no effect of palmitate was observed on tyrosine phosphorylation, p85 association, or phosphatidylinositol 3-kinase activity in IRS-1 immunoprecipitates. In contrast, palmitate promoted phosphorylation of mitogen-activated protein MAP) kinases. Ceramide, a derivative of palmitate, has recently been associated with similar inhibition of PKB, and here, ceramide levels were found to be elevated 2-fold in palmitate-treated C2C12 cells. Incubation of C2C12 cells with ceramide closely reproduced the effects of palmitate, leading to inhibition of glycogen synthesis and PKB and to stimulation of MAP kinase. We conclude that palmitate-induced insulin resistance occurs by a mechanism distinct from that of unsaturated FFAs, and involves elevation of ceramide by de novo synthesis, leading to PKB inhibition without affecting IRS-1 function.

Topics: Animals; Calcium-Calmodulin-Dependent Protein Kinases; Cells, Cultured; Ceramides; Glycogen; Glycogen Synthase Kinases; Insulin; Insulin Resistance; Mice; Muscle, Skeletal; Palmitic Acid; Phosphatidylinositol 3-Kinases; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Response Elements

Young first-degree relatives of type 2 diabetic patients are insulin-resistant, with the insulin resistance mainly located in skeletal muscle due to decreased insulin-induced nonoxidative glucose metabolism and muscle glycogen synthase activation. We investigated whether the mechanism differs for dexamethasone (dex)-induced insulin resistance in first-degree relatives of type 2 diabetics versus healthy control subjects by quantifying intracellular glucose processing in muscle biopsies taken before and after 5 days of dex treatment (4 mg/d) in 20 normal glucose-tolerant relatives of type 2 diabetic patients and 20 matched controls (age, 29.4 +/- 1.7 v 29.4 +/- 1.6 years; body mass index, 25.1 +/- 1.0 v 25.1 +/- 0.9 kg/m2). In addition, an intravenous glucose tolerance test (IVGTT) combined with continuous indirect calorimetry was performed. Following 5 days of dex treatment, glucose tolerance deteriorated in both the relatives and the control subjects. Fasting dry-weight muscle glucose and fasting intracellular muscle glucose concentrations increased in response to dex only in the relatives (2.43 +/- 0.21 v 2.97 +/- 0.26 mmol/kg dry weight, P < .05; 0.28 +/- 0.07 v 0.45 +/- 0.08 mmol/L intracellular water, P < .05); no increases were observed in the control subjects. Fasting dry-weight muscle lactate also increased post-dex only in the relatives (7.37 +/- 0.40 v 10.77 +/- 1.22 mmol/kg dry weight, P < .001). Both basal muscle glucose and lactate concentrations from the IVGTT study correlated with the 2-hour post-dex glucose value obtained during the OGTT study in the relatives (R = .76 and R = .74, respectively, both P < .0001) but not in the control subjects. Basal intramuscular glycogen synthase activity decreased approximately 25% in both the relatives and control subjects post-dex; the decrement was significant (P < .01) only in control subjects. Indirect calorimetry during the post-dex IVGTT demonstrated increased glucose oxidation (P < .03) and reduced lipid oxidation (P < .03) in the relatives only. We postulate that the insulin resistance induced by dex in first-degree relatives of type 2 diabetic patients is associated with a preferential channeling of glucose into the glycolytic pathway (increased glucose oxidation and lactate production), probably associated with a preexisting downregulation of the glycosen synthase pathway.

Topics: Adult; Body Mass Index; Case-Control Studies; Dexamethasone; Diabetes Mellitus, Type 2; Female; Glucose; Glucose Tolerance Test; Glucose Transporter Type 4; Glucose-6-Phosphate; Glycogen; Glycogen Synthase; Humans; Insulin Resistance; Lactic Acid; Lipids; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Pedigree

Polycystic ovary syndrome (PCOS) is characterized by hyperandrogenemia that is amplified by insulin in the presence of resistance to insulin's action to stimulate glucose uptake in muscle and fat. To explore the mechanisms for this paradox, we examined the metabolic and mitogenic actions of insulin and insulin-like growth factor I (IGF-I) in cultured skin fibroblasts from PCOS (n = 16) and control (n = 11) women. There were no significant decreases in the number or affinity of insulin- or IGF-I-binding sites in PCOS compared to control fibroblasts. Basal rates were similar, but there were significant decreases in insulin-stimulated (control, 51.8 +/- 7.0; PCOS, 29.5 +/- 2.9 nmol/10(6) cells x 2 h at 1,000,000 pmol/L; P < 0.005) and IGF-I-stimulated (control, 48.9 +/- 6.7; PCOS, 33.0 +/- 3.2 PCOS nmol/10(6) cells x 2 h at 100,000 pmol/L IGF-I; P < 0.05) glucose incorporation into glycogen in PCOS fibroblasts, a metabolic action of insulin. Stimulation of thymidine incorporation, a mitogenic action of insulin, was similar in PCOS and control fibroblasts in response to both insulin and IGF-I. There were also no significant differences in insulin- or IGF-I-stimulated insulin receptor substrate-1-associated phosphatidylinositol-3-kinase activity in PCOS compared to control fibroblast cells. We conclude that 1) there is a selective defect in insulin action in PCOS fibroblasts that affects metabolic, but not mitogenic, signaling pathways; 2) there is a similar defect in IGF-I action, suggesting that insulin and IGF-I stimulate glycogen synthesis by the same postreceptor pathways; and 3) insulin receptor substrate-1-associated phosphatidylinositol 3-kinase activation by insulin and IGF-I is similar to the control value, suggesting that the metabolic signaling defect is in another pathway or downstream of this signaling step in PCOS fibroblasts.

Topics: Adolescent; Adult; Cells, Cultured; DNA; Female; Fibroblasts; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Insulin-Like Growth Factor I; Phosphatidylinositol 3-Kinases; Polycystic Ovary Syndrome; Signal Transduction

We report here that antiinsulin receptor (anti-IR) autoantibodies (AIRs) from a newly diagnosed patient with type B syndrome of insulin resistance induced cellular resistance not only to insulin but also to insulin-like growth factor I (IGF-I) for the stimulation of phosphatidylinositol 3-kinase and mitogen-activated protein kinase activities and of glycogen and DNA syntheses. The molecular mechanisms of this dual resistance were investigated. Patient AIRs bound the IR at the insulin-binding site and caused insulin resistance at the IR level by inducing a 50% decrease in cell surface IRs and a severe defect in the tyrosine kinase activity of the residual IRs, manifested by a loss of insulin-stimulated IR autophosphorylation and IR substrate-1 (IRS-1)/IRS-2 phosphorylation. In contrast, cell resistance to IGF-I occurred at a step distal to IGF-I receptors (IGF-IRs), as AIRs altered neither IGF-I binding nor IGF-I-induced IGF-IR autophosphorylation, but inhibited the ability of IGF-IRs to mediate tyrosine phosphorylation of IRS-1 and IRS-2 in response to IGF-I. Coimmunoprecipitation assays showed that in AIR-treated cells, IRs, but not IGF-IRs, were constitutively associated with IRS-1 and IRS-2, strongly suggesting that AIR-desensitized IRs impeded IGF-I action by sequestering IRS-1 and IRS-2. Accordingly, AIRs had no effect on the stimulation of mitogen-activated protein kinase activity or DNA synthesis by vanadyl sulfate, FCS, epidermal growth factor, or platelet-derived growth factor, all of which activate signaling pathways independent of IRS-1/IRS-2. Thus, AIRs induced cell resistance to both insulin and IGF-I through a novel mechanism involving a constitutive and stable association of IRS-1 and IRS-2 with the IR.

Topics: Aged; Animals; Autoantibodies; Calcium-Calmodulin-Dependent Protein Kinases; CHO Cells; Cricetinae; DNA; Female; Glycogen; Humans; Immunoglobulin G; Insulin Receptor Substrate Proteins; Insulin Resistance; Insulin-Like Growth Factor I; Intracellular Signaling Peptides and Proteins; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphorylation; Receptor, Insulin; Vanadium Compounds

To examine whether growth hormone (GH) induces peripheral insulin resistance by altering plasma free fatty acid (FFA) or insulin levels, the effects of GH infusion on insulin-stimulated glucose fluxes were studied in conscious rats under two protocols. In study 1, either saline (n = 7) or human recombinant GH (21 microg. kg(-1). h(-1); n = 8) was infused for 300 min, and insulin-stimulated glucose fluxes were estimated during the final 150-min period of hyperinsulinemic euglycemic clamps. In study 2, hyperinsulinemic euglycemic clamps were first conducted for 150 min (to raise plasma insulin and suppress FFA levels), and saline or GH (n = 7 for each) was subsequently infused for the following 300-min clamp period. In study 1, GH infusion in the basal state did not significantly alter plasma FFA or insulin levels. In contrast, GH infusion decreased insulin-stimulated glucose uptake, glycolysis, and glycogen synthesis by 32, 27, and 40%, respectively (P < 0.05). In study 2, GH infusion during hyperinsulinemic euglycemic clamps did not alter plasma FFA or insulin levels (P > 0.05). GH infusion had no effect on insulin-stimulated glucose uptake during the initial 150 min but eventually decreased insulin-stimulated glucose uptake by 37% (P < 0. 05), similar to the results in study 1. These data indicate that GH induces peripheral insulin resistance independent of plasma FFA and insulin levels. The induction of insulin resistance was preceded by suppression of glycogen synthesis, consistent with the hypothesis that metabolic impairment precedes and causes development of peripheral insulin resistance.

Topics: Animals; Fatty Acids, Nonesterified; Glucose; Glucose Clamp Technique; Glycogen; Glycolysis; Growth Hormone; Humans; Insulin; Insulin Resistance; Male; Rats; Rats, Wistar; Recombinant Proteins; Time Factors

Nitric oxide activates guanylate cyclase to form cGMP, comprising a signalling system that is believed to be a distinct mechanism for increasing glucose transport and metabolism in skeletal muscle. The effects of a selective cGMP phosphodiesterase inhibitor, zaprinast, on basal glucose utilization was investigated in incubated rat soleus muscle preparations isolated from both insulin-sensitive (lean Zucker; Fa/?) and insulin-resistant (obese Zucker; fa/fa) rats. Zaprinast at 27 microM significantly increased cGMP levels in incubated soleus muscle isolated from lean, but not obese, Zucker rats. Muscles were incubated with 14C-labelled glucose and various concentrations of zaprinast (3, 27 and 243 microM). Zaprinast (at 27 and 243 microM) significantly increased rates of net and 14C-labelled lactate release and of glycogen synthesis in lean Zucker rat soleus muscle; glucose oxidation was also increased by 27 microM zaprinast. In addition, regardless of concentration, the phosphodiesterase inhibitor failed to increase any aspect of 14C-labelled glucose utilization in soleus muscles isolated from obese Zucker rats. The maximal activity of nitric oxide synthase (NOS) was significantly decreased in insulin-resistant obese Zucker muscles. Thus the lack of effect of zaprinast in insulin-resistant skeletal muscle is consistent with decreased NOS activity. To test whether there is a defect in insulin-resistant skeletal muscle for endogenous activation of guanylate cyclase, soleus muscles were isolated from both insulin-sensitive and insulin-resistant Zucker rats and incubated with various concentrations of the NO donor sodium nitroprusside (SNP; 0.1, 1, 5 and 15 mM). SNP significantly increased rates of net and 14C-labelled lactate release, as well as glucose oxidation in muscles isolated from both insulin-sensitive and insulin-resistant rats. A decreased response to SNP was observed in the dose-dependent generation of cGMP within isolated soleus muscles from insulin-resistant rats. A possible link between impaired NO/cGMP signalling and abnormal glucose utilization by skeletal muscle is discussed.

Topics: Animals; Cell Fractionation; Cyclic GMP; Female; Glucose; Glycogen; Insulin; Insulin Resistance; Lactic Acid; Muscle, Skeletal; Nitric Oxide; Nitric Oxide Synthase; Nitroprusside; Obesity; Phosphodiesterase Inhibitors; Purinones; Rats; Rats, Zucker; Signal Transduction

Some patients with severe insulin resistance develop pathological tissue growth reminiscent of acromegaly. Previous studies of such patients have suggested the presence of a selective postreceptor defect of insulin signaling, resulting in the impairment of metabolic but preservation of mitogenic signaling. As the activation of phosphoinositide 3-kinase (PI 3-kinase) is considered essential for insulin's metabolic signaling, we have examined insulin-stimulated PI 3-kinase activity in anti-insulin receptor substrate (IRS)-1 immunoprecipitates from cultured dermal fibroblasts obtained from pseudoacromegalic (PA) patients and controls. At a concentration of insulin (1 nM) similar to that seen in vivo in PA patients, the activation of IRS-1-associated PI 3-kinase was reduced markedly in fibroblasts from the PA patients (32+/-7% of the activity of normal controls, P < 0.01). Genetic and biochemical studies indicated that this impairment was not secondary to a defect in the structure, expression, or activation of the insulin receptor, IRS-1, or p85alpha. Insulin stimulation of mitogenesis in PA fibroblasts, as determined by thymidine incorporation, was indistinguishable from controls, as was mitogen-activated protein kinase phosphorylation, confirming the integrity of insulin's mitogenic signaling pathways in this condition. These findings support the existence of an intrinsic defect of postreceptor insulin signaling in the PA subtype of insulin resistance, which involves impairment of the activation of PI 3-kinase. The PA tissue growth seen in such patients is likely to result from severe in vivo hyperinsulinemia activating intact mitogenic signaling pathways emanating from the insulin receptor.

Topics: Acromegaly; Adolescent; Adult; Calcium-Calmodulin-Dependent Protein Kinases; Cells, Cultured; Female; Fibroblasts; Gene Expression; Glycogen; Humans; Hypoglycemic Agents; Infant, Newborn; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Lymphocytes; Male; Mitogens; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphorylation; Polymorphism, Single-Stranded Conformational; Signal Transduction; Thymidine; Tumor Cells, Cultured

The mechanism of insulin resistance in obesity was examined in ten obese (BMI 33 +/- 1 kg/m2) and nine lean (BMI 22 +/- 1 kg/m2) Caucasian women during a hyperglycemic-hyperinsulinemic clamp using 13C and 31P nuclear magnetic resonance (NMR) spectroscopy to measure rates of muscle glycogen synthesis and intramuscular glucose-6-phosphate (G-6-P) concentrations. Under similar steady-state plasma concentrations of glucose (approximately 11 mmol/l) and insulin (approximately 340 pmol/l), rates of muscle glycogen synthesis were reduced approximately 70% in the obese subjects (52 +/- 8 micromol/[l muscle-min]) as compared with the rates in the lean subjects (176 +/- 22 micromol/[l muscle-min]; P < 0.0001). Basal concentrations of intramuscular G-6-P were similar in the obese and lean subjects; but during the clamp, G-6-P failed to increase in the obese group (deltaG-6-P obese 0.044 +/- 0.011 vs. lean 0.117 +/- 0.011 mmol/l muscle; P < 0.001), reflecting decreased muscle glucose transport and/or phosphorylation activity. We conclude that insulin resistance in obesity can be mostly attributed to impairment of insulin-stimulated muscle glycogen synthesis due to a defect in glucose transport and/or phosphorylation activity.

Topics: Adult; Cohort Studies; Female; Glucose; Glucose Clamp Technique; Glycogen; Humans; Insulin Resistance; Magnetic Resonance Spectroscopy; Obesity; White People

Insulin resistance and increased fat mass (FM) are common in human aging. We aimed to investigate the relationship between the age-dependent increase in FM and insulin resistance (by euglycemic hyperinsulinemic clamp technique), in a homogenous rodent model. The decline in insulin responsiveness was linear until late adulthood when body weight, FM, and epididymal fat reached a critical amount (r > .750, for all). Above this critical point, there was no further decline in insulin responsiveness with aging and with increased BW (p < .00001 for all spline curve analyses). This decline in insulin-mediated glucose uptake was accounted for by a decrease in whole body glycolytic rate with no change in the rate of glycogen synthesis. Thus, in this homogenous model, an early increase in FM is associated with impairment in insulin action until a critical FM is achieved, after which there is no additional insulin resistance with aging. We suggest that decreasing insulin responsiveness, in a heterogeneous group such as humans, will only occur within a specific accretion of visceral or total FM.

Topics: Adipose Tissue; Aging; Animals; Body Composition; Body Weight; Epididymis; Glucose; Glucose Clamp Technique; Glycogen; Glycolysis; Insulin; Insulin Resistance; Male; Rats; Rats, Sprague-Dawley

Membrane glycoprotein PC-1 inhibits insulin receptor (IR) tyrosine kinase activity and subsequent cellular signaling. PC-1 content is elevated in muscle and adipose tissue from insulin-resistant subjects, and its elevation correlates with in vivo insulin resistance. To determine whether elevated PC-1 content is a primary cause of insulin resistance, we have now measured PC-1 content in cultured skin fibroblasts from nonobese nondiabetic insulin-resistant subjects and found that 1) PC-1 content was significantly higher in these cells when compared with cells from insulin-sensitive subjects (6.7 +/- 0.9 vs. 3.1 +/- 0.6 ng/0.1 mg protein, mean +/- SE, P < 0.01); 2) PC-1 content in fibroblasts was highly correlated with PC-1 content in muscle tissue (r = 0.95, P = 0.01); 3) PC-1 content in fibroblasts negatively correlated with both decreased in vivo insulin sensitivity and decreased in vitro IR autophosphorylation; and 4) in cells from insulin-resistant subjects, insulin stimulation of glycogen synthetase was decreased. These studies indicate, therefore, that the elevation of PC-1 content may be a primary factor in the cause of insulin resistance.

Topics: Adult; Cells, Cultured; Cholesterol; Fasting; Female; Fibroblasts; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Male; Membrane Glycoproteins; Middle Aged; Muscles; Phosphatidylinositol 3-Kinases; Phosphoric Diester Hydrolases; Pyrophosphatases; Receptor, Insulin; Signal Transduction; Skin

Insulin-mediated muscle glycogen synthesis is impaired after several weeks of high-fat feeding in rats, but not by short-term (2-hour) nonesterified fatty acids (NEFA) elevation induced by intravenous triglyceride/heparin infusion (TG/H). We examined whether a longer TG/H infusion induces defective glycogen synthesis. Five-hour hyperinsulinemic (700 pmol/L) euglycemic clamps with either TG/H or saline infusion were performed. TG/H-infused rats developed insulin resistance, but only after 2 to 3 hours. Red gastrocnemius glycogen synthesis rate decreased by 50% (P < .01 v saline) associated with decreased glycogen synthase activity (GSa; assessed at several glucose-6-phosphate [G-6-P] levels; two-way ANOVA, P=.02) and increased muscle TG and total long-chain acyl coenzyme A (LCAC) content (twofold; P < .05 v saline). Thus a 3- to 5-hour NEFA elevation in the rat produced significant impairment of insulin-stimulated muscle glycogen synthesis, associated with muscle lipid accumulation. These effects were similar to those observed after several weeks of fat feeding. The 5-hour TG/H-infused rat is a useful model for studying lipid-induced muscle insulin resistance.

Topics: Animals; Fatty Acids, Nonesterified; Glucose; Glycogen; Insulin Resistance; Lipid Metabolism; Male; Muscle, Skeletal; Rats; Rats, Wistar; Time Factors

Epidemiological studies suggest that alcohol consumption is an independent risk factor for the development of non-insulin-dependent diabetes mellitus (NIDDM). Alcoholism is known to be associated with increased plasma levels of two novel diols, 2,3-butanediol and 1,2-propanediol, metabolites known to impair insulin action in isolated adipocytes. This study examines whether 2,3-butanediol and 1,2-propanediol have the capacity to impair insulin action acutely in vivo in the rat. Using the euglycemic-hyperinsulinemic clamp, it is shown that the two diols reduce whole-body glucose utilization (by approximately 30%), with the onset of insulin resistance in vivo occurring at plasma concentrations of 2,3-butanediol (33 micromol/L) at least one order of magnitude (P < .001) lower than 1,2-propanediol (432 micromol/L). Tracer methodologies using [U-14C]glucose and 2-deoxy[1-(3)H]glucose indicate that the reduction in whole-body glucose utilization is accompanied by a reduction in glucose uptake and glycogen synthesis in the skeletal muscle and heart. The association between elevated plasma diol levels and insulin resistance demonstrated in this report raises the question of whether there is a link between the high plasma diol levels in alcohol abusers and their increased susceptibility to NIDDM.

Topics: Alcoholism; Animals; Blood Glucose; Butylene Glycols; Diabetes Mellitus, Type 2; Glycogen; Insulin; Insulin Resistance; Male; Propylene Glycol; Rats; Rats, Wistar

Acute physical exercise usually enhances insulin sensitivity. We examined the effect of a competitive 42 km marathon run on glucose uptake and lipid oxidation in 7 runners with insulin-dependent diabetes mellitus (IDDM), aged 36 +/- 3 yr, BMI 23.9 +/- 0.5 kg m-2, VO2max 46 +/- 1 ml kg-1 min-1, HbA1c 7.7 +/- 0.3%, duration of diabetes 16 +/- 5 yr, runtime 3 h 47 +/- 8 min. On the marathon day, they reduced pre-race insulin doses by 26 +/- 8%, and ingested 130 +/- 33 g carbohydrate before, 91 +/- 26 g during, and 115 +/- 20 g after the race. During the run, blood glucose concentration fell from 14.4 +/- 2.0 to 7.4 +/- 3.0 mmol l-1 (p < 0.05) and serum insulin from 51 +/- 8 to 33 +/- 8 pmol l-1 (p < 0.05). Serum NEFA increased by 4-fold (p < 0.05), but fell to the normal level by next morning. Muscle glycogen content was 56% lower (p < 0.05) and glycogen synthase fractional activity 40% greater (p < 0.05) in the morning after the marathon as compared to the resting control day. In spite of glycogen depletion, whole body glucose disposal (euglycaemic insulin clamp) was unchanged, while glucose oxidation (indirect calorimetry) was decreased by 49% (p < 0.05) and lipid oxidation increased by 41% (p < 0.01). There was an inverse correlation between the rates of lipid oxidation and glucose uptake after the marathon (r = -0.75; p < 0.05).. after successfully managed marathon running in patients with IDDM, insulin sensitivity was not increased in spite of low glycogen content and enhanced glycogen synthase activity after marathon, probably because of increased lipid oxidation.

Topics: Adult; Arteries; Blood Glucose; Creatine Kinase; Diabetes Mellitus, Type 1; Energy Metabolism; Fatty Acids, Nonesterified; Female; Forearm; Glucagon; Glucose Clamp Technique; Glycogen; Glycogen Synthase; Growth Hormone; Humans; Hydrocortisone; Insulin; Insulin Resistance; Lipid Metabolism; Male; Muscles; Myoglobin; Oxidation-Reduction; Running

To determine whether an impairment of intracellular glucose metabolism causes insulin resistance, we examined the effects of suppression of glycolysis or glycogen synthesis on whole body and skeletal muscle insulin-stimulated glucose uptake during 450-min hyperinsulinemic euglycemic clamps in conscious rats. After the initial 150 min to attain steady-state insulin action, animals received an additional infusion of saline, Intralipid and heparin (to suppress glycolysis), or amylin (to suppress glycogen synthesis) for up to 300 min. Insulin-stimulated whole body glucose fluxes were constant with saline infusion (n = 7). In contrast, Intralipid infusion (n = 7) suppressed glycolysis by approximately 32%, and amylin infusion (n = 7) suppressed glycogen synthesis by approximately 45% within 30 min after the start of the infusions (P < 0.05). The suppression of metabolic fluxes increased muscle glucose 6-phosphate levels (P < 0.05), but this did not immediately affect insulin-stimulated glucose uptake due to compensatory increases in other metabolic fluxes. Insulin-stimulated whole body glucose uptake started to decrease at approximately 60 min and was significantly decreased by approximately 30% at the end of clamps (P < 0.05). Similar patterns of changes in insulin-stimulated glucose fluxes were observed in individual skeletal muscles. Thus the suppression of intracellular glucose metabolism caused decreases in insulin-stimulated glucose uptake through a cellular adaptive mechanism in response to a prolonged elevation of glucose 6-phosphate rather than the classic mechanism involving glucose 6-phosphate inhibition of hexokinase.

Topics: Amyloid; Animals; Fat Emulsions, Intravenous; Glucose; Glucose Clamp Technique; Glucose-6-Phosphate; Glycogen; Glycolysis; Heparin; Insulin; Insulin Resistance; Islet Amyloid Polypeptide; Male; Muscle, Skeletal; Rats; Rats, Wistar; Time Factors

To examine whether the hexosamine biosynthetic pathway might play a role in fat-induced insulin resistance, we monitored the effects of prolonged elevations in FFA availability both on skeletal muscle levels of UDP-N-acetyl-hexosamines and on peripheral glucose disposal during 7-h euglycemic-hyperinsulinemic (approximately 500 microU/ml) clamp studies. When the insulin-induced decrease in the plasma FFA levels (to approximately 0.3 mM) was prevented by infusion of a lipid emulsion in 15 conscious rats (plasma FFA approximately 1.4 mM), glucose uptake (5-7 h = 32.5+/-1.7 vs 0-2 h = 45.2+/-2.8 mg/kg per min; P < 0.01) and glycogen synthesis (P < 0.01) were markedly decreased. During lipid infusion, muscle UDP-N-acetyl-glucosamine (UDP-GlcNAc) increased by twofold (to 53.4+/-1.1 at 3 h and to 55.5+/-1.1 nmol/gram at 7 h vs 20.4+/-1.7 at 0 h, P < 0.01) while glucose-6-phosphate (Glc-6-P) levels were increased at 3 h (475+/-49 nmol/gram) and decreased at 7 h (133+/-7 vs 337+/-28 nmol/gram at 0 h, P < 0.01). To discern whether such an increase in the skeletal muscle UDP-GlcNAc concentration could account for the development of insulin resistance, we generated similar increases in muscle UDP-GlcNAc using three alternate experimental approaches. Euglycemic clamps were performed after prolonged hyperglycemia (18 mM, n = 10), or increased availability of either glucosamine (3 micromol/kg per min; n = 10) or uridine (30 micromol/kg per min; n = 4). These conditions all resulted in very similar increases in the skeletal muscle UDP-GlcNAc (to approximately 55 nmol/gram) and markedly impaired glucose uptake and glycogen synthesis. Thus, fat-induced insulin resistance is associated with: (a) decreased skeletal muscle Glc-6-P levels indicating defective transport/phosphorylation of glucose; (b) marked accumulation of the endproducts of the hexosamine biosynthetic pathway preceding the onset of insulin resistance. Most important, the same degree of insulin resistance can be reproduced in the absence of increased FFA availability by a similar increase in skeletal muscle UDP-N-acetyl-hexosamines. In conclusion, our results support the hypothesis that increased FFA availability induces skeletal muscle insulin resistance by increasing the flux of fructose-6-phosphate into the hexosamine pathway.

Topics: Animals; Diabetes Mellitus, Type 2; Fatty Acids; Fructosephosphates; Glucosamine; Glucose; Glucose-6-Phosphate; Glycogen; Glycolysis; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Phosphorylation; Rats; Rats, Sprague-Dawley; Uridine

We determined the effect of infusion of glucosamine (GlcN), which bypasses the rate limiting reaction in the hexosamine pathway, on insulin-stimulated rates of glucose uptake and glycogen synthesis in vivo in rat tissues varying with respect to their glutamine:fructose-6-phosphate amidotransferase (GFA) activity. Three groups of conscious fasted rats received 6-h infusions of either saline (BAS), insulin (18 mU/kg x min) and saline (INS), or insulin and GlcN (30 micromol/ kg x min, GLCN). [3-(3)H]glucose was infused to trace whole body glucose kinetics and glycogen synthesis, and rates of tissue glucose uptake were determined using a bolus injection of [1-(14)C]2-deoxyglucose at 315 min. GlcN decreased insulin-stimulated glucose uptake (315-360 min) by 49% (P < 0.001) at the level of the whole body, and by 31-53% (P < 0.05 or less) in the heart, epididymal fat, submandibular gland and in soleus, abdominis and gastrocnemius muscles. GlcN completely abolished glycogen synthesis in the liver. GlcN decreased insulin-stimulated glucose uptake similarly in the submandibular gland (1.3 +/- 0.2 vs. 2.0 +/- 0.3 nmol/mg protein x min, GLCN vs. INS, P < 0.05) and gastrocnemius muscle (1.4 +/- 0.3 vs. 3.1 +/- 0.5 nmol/mg protein x min), although the activity of the hexosamine pathway, as judged from basal GFA activity, was 10-fold higher in the submandibular gland (286 +/- 35 pmol/mg protein x min) than in gastrocnemius muscle (27 +/- 3 pmol/mg protein x min, P < 0.001). These data raise the possibility that overactivity of the hexosamine pathway may contribute to glucose toxicity not only in skeletal muscle but also in other insulin sensitive tissues. They also imply that the magnitude of insulin resistance induced between tissues is determined by factors other than GFA.

Topics: Adipose Tissue; Animals; Blood Glucose; Deoxyglucose; Glucosamine; Glucose; Glucose Clamp Technique; Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); Glycogen; Hexosamines; Hyperinsulinism; Infusions, Intravenous; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Myocardium; Rats; Rats, Wistar; Submandibular Gland

In male rats, 2 wk of high-sucrose feeding results in insulin resistance and hypertriglyceridemia [Pagliassotti, M.J., P.A. Prach, T.A. Koppenhafer, and D.A. Pan. Am. J. Physiol. 271 (Regulatory Integrative Comp. Physiol. 40): R1319-R1326, 1996]. The present study aimed to determine if female rats also become insulin resistant and hypertriglyceridemic in response to high-sucrose feeding. Female Wistar rats (7 wk old) were fed either a high-sucrose diet (68% energy) (SU) or a high-starch diet (68% energy) (ST) for 3, 5, or 8 wk. In each animal, glucose kinetics were measured using [3-(3)H]glucose under basal and hyperinsulinemic conditions (insulin infusion 4.0 mU.kg-1.min-1). Body weight and basal glucose kinetics were not different between diet groups at 3, 5, or 8 wk. Glucose infusion rate (mg.kg-1.min-1) was not different between groups (3 wk: 17.7 +/- 1.6 ST, 16.6 +/- 0.9 SU; 5 wk: 16.1 +/- 0.9 ST, 15.1 +/- 2.0 SU; 8 wk: 18.3 +/- 1.9 ST, 16.1 +/- 1.5 SU). Clamp rate of glucose appearance (mg.kg-1.min-1) was also not different between diet groups (3 wk: 4.0 +/- 1.6 ST, 3.6 +/- 1.4 SU; 5 wk: 2.6 +/- 1.0 ST, 2.3 +/- 1.14 SU; 8 wk: 5.9 +/- 1.8 ST, 7.7 +/- 1.2 SU). No difference was observed in plasma and tissue triglycerides or tissue glycogen between sucrose- and starch-fed animals. We therefore conclude that female rats, in contrast to males, do not develop sucrose-induced insulin resistance and hypertriglyceridemia.

Topics: Adipose Tissue; Animals; Blood Glucose; Body Weight; Dietary Sucrose; Energy Intake; Female; Glycogen; Insulin; Insulin Resistance; Liver; Muscles; Organ Size; Rats; Rats, Wistar; Sex Factors; Triglycerides

The racemic mixture of the antioxidant alpha-lipoic acid (ALA) enhances insulin-stimulated glucose metabolism in insulin-resistant humans and animals. We determined the individual effects of the pure R-(+) and S-(-) enantiomers of ALA on glucose metabolism in skeletal muscle of an animal model of insulin resistance, hyperinsulinemia, and dyslipidemia: the obese Zucker (fa/fa) rat. Obese rats were treated intraperitoneally acutely (100 mg/kg body wt for 1 h) or chronically [10 days with 30 mg/kg of R-(+)-ALA or 50 mg/kg of S-(-)-ALA]. Glucose transport [2-deoxyglucose (2-DG) uptake], glycogen synthesis, and glucose oxidation were determined in the epitrochlearis muscles in the absence or presence of insulin (13.3 nM). Acutely, R-(+)-ALA increased insulin-mediated 2-DG-uptake by 64% (P < 0.05), whereas S-(-)-ALA had no significant effect. Although chronic R-(+)-ALA treatment significantly reduced plasma insulin (17%) and free fatty acids (FFA; 35%) relative to vehicle-treated obese animals, S-(-)-ALA treatment further increased insulin (15%) and had no effect on FFA. Insulin-stimulated 2-DG uptake was increased by 65% by chronic R-(+)-ALA treatment, whereas S-(-)-ALA administration resulted in only a 29% improvement. Chronic R-(+)-ALA treatment elicited a 26% increase in insulin-stimulated glycogen synthesis and a 33% enhancement of insulin-stimulated glucose oxidation. No significant increase in these parameters was observed after S-(-)-ALA treatment. Glucose transporter (GLUT-4) protein was unchanged after chronic R-(+)-ALA treatment but was reduced to 81 +/- 6% of obese control with S-(-)-ALA treatment. Therefore, chronic parenteral treatment with the antioxidant ALA enhances insulin-stimulated glucose transport and non-oxidative and oxidative glucose metabolism in insulin-resistant rat skeletal muscle, with the R-(+) enantiomer being much more effective than the S-(-) enantiomer.

Topics: Animals; Antioxidants; Biological Transport; Blood Glucose; Deoxyglucose; Fatty Acids, Nonesterified; Female; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Muscle, Skeletal; Obesity; Rats; Rats, Zucker; Reference Values; Stereoisomerism; Thioctic Acid

Hearts from hyperinsulinemic, insulin-resistant JCR:LA-cp rats do not properly regulate intracellular Ca2+ concentration. We hypothesized, therefore, that these hearts may be unusually sensitive to ischemic insults in which Ca2+ overload would be expected. We investigated the response to global ischemia of hearts from JCR: LA-cp animals at three different ages. At 3 mo of age, isolated hearts from insulin-resistant cp rats were mildly resistant to both mild and severe ischemic insults in comparison to the lean control rat hearts. However, at 6 and 9 mo of age, the cp rats demonstrated a poorer recovery of developed tension after ischemia and/or a higher level of resting tension during reperfusion than the lean controls. Postischemic glycogen and ATP contents were significantly lower and lactate content was higher in hearts from 6-mo-old cp rats compared with controls. The results demonstrate that an insulin-resistant animal model exhibits an increased sensitivity to ischemic myocardial injury that develops with advancing age. The mechanism responsible for the enhanced sensitivity may involve augmented glycolytic metabolism. The data also emphasize the importance of the type of diabetes when cardiac dysfunction is examined.

Topics: Adenosine Triphosphate; Aging; Animals; Glycogen; Heart; In Vitro Techniques; Insulin Resistance; Lactates; Myocardial Contraction; Myocardial Ischemia; Myocardial Reperfusion; Myocardium; Rats; Rats, Mutant Strains; Reference Values; Triglycerides

Elevated serum-free fatty acid (FFA) levels induce insulin resistance in whole animals and humans. To understand the direct mechanism by which FFAs impact insulin-responsive tissue, we have used our previously developed in vitro model of long-chain saturated fatty acids (LCSFA)-induced insulin resistance in adipocytes. In addition to explanted rat adipocytes, we now demonstrate that overnight exposure of 3T3-L1 adipocytes to 1 mM individually of the LCSFA palmitate, myristate, and stearate, leads to an approximately 50% inhibition of insulin-induced glucose transport. Insulin resistance can be accomplished at 0.3 mM palmitate, which is within the range ofpalmitate found in diabetic and obese individuals. This inhibition was noted within 4 h of exposure to FFA, which is comparable to in vivo lipid infusion studies. Initial LCSFA-induced resistance is specific to glucose transport and does not affect insulin stimulation of glucose incorporation into glycogen. In 3T3-L1 adipocytes overexpressing the EGF receptor, LCSFA exposure also specifically inhibited EGF-induced GLUT4-mediated glucose transport, but not EGF-induced glycogen synthesis. We find that LCSFA treatment did not impair insulin stimulation of GLUT4 translocation or exofacial presentation on the cell surface as determined by trypsin accessibility. Our results suggest that the initial direct effect of elevated LCSFA is to impair activation of GLUT4 transporter activity and that this effect is specific for glucose transport.

Topics: Adipocytes; Animals; Cells, Cultured; Deoxyglucose; Epidermal Growth Factor; Fatty Acids; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle Proteins; Myristates; Palmitates; Phosphorylation; Rats; Rats, Sprague-Dawley; Receptor, Insulin; Stearates

To elucidate cellular mechanisms of insulin resistance induced by excess dietary fat, we studied conscious chronically high-fat-fed (HFF) and control chow diet-fed rats during euglycemic-hyperinsulinemic (560 pmol/l plasma insulin) clamps. Compared with chow diet feeding, fat feeding significantly impaired insulin action (reduced whole body glucose disposal rate, reduced skeletal muscle glucose metabolism, and decreased insulin suppressibility of hepatic glucose production [HGP]). In HFF rats, hyperinsulinemia significantly suppressed circulating free fatty acids but not the intracellular availability of fatty acid in skeletal muscle (long chain fatty acyl-CoA esters remained at 230% above control levels). In HFF animals, acute blockade of beta-oxidation using etomoxir increased insulin-stimulated muscle glucose uptake, via a selective increase in the component directed to glycolysis, but did not reverse the defect in net glycogen synthesis or glycogen synthase. In clamp HFF animals, etomoxir did not significantly alter the reduced ability of insulin to suppress HGP, but induced substantial depletion of hepatic glycogen content. This implied that gluconeogenesis was reduced by inhibition of hepatic fatty acid oxidation and that an alternative mechanism was involved in the elevated HGP in HFF rats. Evidence was then obtained suggesting that this involves a reduction in hepatic glucokinase (GK) activity and an inability of insulin to acutely lower glucose-6-phosphatase (G-6-Pase) activity. Overall, a 76% increase in the activity ratio G-6-Pase/GK was observed, which would favor net hepatic glucose release and elevated HGP in HFF rats. Thus in the insulin-resistant HFF rat 1) acute hyperinsulinemia fails to quench elevated muscle and liver lipid availability, 2) elevated lipid oxidation opposes insulin stimulation of muscle glucose oxidation (perhaps via the glucose-fatty acid cycle) and suppression of hepatic gluconeogenesis, and 3) mechanisms of impaired insulin-stimulated glucose storage and HGP suppressibility are not dependent on concomitant lipid oxidation; in the case of HGP we provide evidence for pivotal involvement of G-6-Pase and GK in the regulation of HGP by insulin, independent of the glucose source.

Topics: Acyl Coenzyme A; Animals; Blood Glucose; Dietary Fats; Glucokinase; Gluconeogenesis; Glucose Clamp Technique; Glucose-6-Phosphatase; Glycogen; Glycogen Synthase; Hyperinsulinism; Insulin; Insulin Resistance; Kinetics; Liver; Liver Glycogen; Muscle, Skeletal; Pyruvate Dehydrogenase Complex; Rats; Rats, Wistar; Reference Values; Triglycerides

The spontaneously hypertensive rat (SHR) has been reported to be insulin-resistant compared to the Wistar-Kyoto (WKY) parent strain. Because insulin resistance usually reflects a defect in insulin action at the muscle, we compared the ability of muscle (gastrocnemius) to store glycogen in response to a standard oral glucose challenge in SHR to that in WKY. As a control, we examined the glycogen response in liver in these two rat strains. However, in vivo insulin action reflects both tissue responsiveness as well as substrate and hormone availability at the tissue level. To evaluate tissue responsiveness in vitro, we examined two parameters of insulin action: 1) muscle glycogen synthesis using 3H-glucose and 2) muscle glucose transport using 3H-2-deoxy-glucose (3H-2-DG). Thirteen-week-old male rats were studied after overnight fasting. Liver glycogen increased similarly (mean +/- SD shown) in response to glucose gavage feeding in both groups [WKY: 15.2 +/- 6.9 to 50.6 +/- 17.9 micromol/g wet wt (P < .05); SHR: 30 +/- 18 to 63.5 +/- 33.3 micromol/g wet wt (P < .01)]. On the other hand, muscle glycogen increased in WKY [13.7 +/- 2 to 17.8 +/- 1.1 micromol/g wet wt (P < .05)], whereas in SHR there was no significant change [14.6 +/- 2.1 to 15.3 +/- 2.99 micromol/g wet wt P = NS)]. Results of in vitro studies demonstrated that glycogen synthesis increased from 377 +/- 120 to 439 +/- 175 disintegrations per minute (dpm) 3H-glucose/mg extensor digitorum longus (EDL) in WKY when insulin increased from 0 to 1000 microU/mL (P < .05), whereas SHR the increase was from 289 +/- 89 to 565 +/- 187 (P < .05). Glucose transport increased from 483 +/- 74 to 785 +/- 369 dpm 3H-2-DG/mg EDL in WKY when insulin was increased from 0 to 500 microU/mL (P < .03), whereas in SHR the increase was 516 +/- 61 to 997 +/- 347 (P < .001). In summary, liver glycogen increased in response to feeding in a similar manner in both WKY and SHR, whereas muscle glycogen increased only in WKY. We conclude that in vivo muscle glycogen accumulation may represent an index of insulin resistance in SHR. In contrast, in vitro data suggest that both muscle glucose transport and glycogen synthesis were stimulated to a comparable degree by insulin in EDL strips from WKY and SHR; there were no significant differences between WKY and SHR. Further studies are needed to clarify these differences.

Topics: Animals; Biological Transport; Glucose; Glycogen; Hypertension; In Vitro Techniques; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Rats; Rats, Inbred SHR; Rats, Inbred WKY

Topics: Animals; Biological Transport; Glucose; Glycogen; Glycolysis; Insulin Resistance; Lactates; Muscle, Skeletal; Phosphodiesterase Inhibitors; Purinones; Rats; Rats, Inbred SHR

We have investigated the antidiabetic action of troglitazone in aP2/DTA mice, whose white and brown fat was virtually eliminated by fat-specific expression of diphtheria toxin A chain. aP2/DTA mice had markedly suppressed serum leptin levels and were hyperphagic, but did not gain excess weight. aP2/DTA mice fed a control diet were hyperlipidemic, hyperglycemic, and had hyperinsulinemia indicative of insulin-resistant diabetes. Treatment with troglitazone alleviated the hyperglycemia, normalized the tolerance to intraperitoneally injected glucose, and significantly decreased elevated insulin levels. Troglitazone also markedly decreased the serum levels of cholesterol, triglycerides, and free fatty acids both in wild-type and aP2/DTA mice. The decrease in serum triglycerides in aP2/DTA mice was due to a marked reduction in VLDL- and LDL-associated triglyceride. In skeletal muscle, triglyceride levels were decreased in aP2/DTA mice compared with controls, but glycogen levels were increased. Troglitazone treatment decreased skeletal muscle, but not hepatic triglyceride and increased hepatic and muscle glycogen content in wild-type mice. Troglitazone decreased muscle glycogen content in aP2/DTA mice without affecting muscle triglyceride levels. The levels of peroxisomal proliferator-activated receptor gamma mRNA in liver increased slightly in aP2/DTA mice and were not changed by troglitazone treatment. The results demonstrate that insulin resistance and diabetes can occur in animals without significant adipose deposits. Furthermore, troglitazone can alter glucose and lipid metabolism independent of its effects on adipose tissue.

Topics: Adipose Tissue; Animals; Blood Glucose; Body Weight; Cholesterol; Chromans; Diabetes Mellitus, Type 2; Eating; Fatty Acids; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Insulin Secretion; Leptin; Lipoproteins, LDL; Lipoproteins, VLDL; Mice; Mice, Transgenic; Organ Size; Proteins; Receptors, Cytoplasmic and Nuclear; Thiazoles; Thiazolidinediones; Transcription Factors; Triglycerides; Troglitazone

Chronic high-fat feeding in rats induces profound whole-body insulin resistance, mainly due to effects in oxidative skeletal muscle. The mechanisms of this reaction remain unclear, but local lipid availability has been implicated. The aim of this study was to examine the influence of three short-term physiological manipulations intended to lower muscle lipid availability on insulin sensitivity in high-fat-fed rats. Adult male Wistar rats fed a high-fat diet for 3 weeks were divided into four groups the day before the study: one group was fed the normal daily high-fat meal (FM); another group was fed an isocaloric low-fat high-glucose meal (GM); a third group was fasted overnight (NM); and a fourth group underwent a single bout of exercise (2-h swim), then were fed the normal high-fat meal (EX). In vivo insulin action was assessed using the hyperinsulinemic glucose clamp (plasma insulin 745 pmol/l, glucose 7.2 mmol/l). Prior exercise, a single low-fat meal, or fasting all significantly increased insulin-stimulated glucose utilization, estimated at either the whole-body level (P < 0.01 vs. FM) or in red quadriceps muscle (EX 18.2, GM 28.1, and NM 19.3 vs. FM 12.6 +/- 1.1 micromol x 100 g(-1) x min(-1); P < 0.05), as well as increased insulin suppressibility of muscle total long-chain fatty acyl-CoA (LC-CoA), the metabolically available form of fatty acid (EX 24.0, GM 15.5, and NM 30.6 vs. FM 45.4 nmol/g; P < 0.05). There was a strong inverse correlation between glucose uptake and LC-CoA in red quadriceps during the clamp (r = -0.7, P = 0.001). Muscle triglyceride was significantly reduced by short-term dietary lipid withdrawal (GM -22 and NM -24% vs. FM; P < 0.01), but not prior exercise. We concluded that muscle insulin resistance induced by high-fat feeding is readily ameliorated by three independent, short-term physiological manipulations. The data suggest that insulin resistance is an important factor in the elevated muscle lipid availability induced by chronic high-fat feeding.

Topics: Acyl Coenzyme A; Animals; Blood Glucose; Dietary Carbohydrates; Dietary Fats; Energy Intake; Fasting; Glucose; Glucose Clamp Technique; Glycogen; Insulin; Insulin Resistance; Male; Malonyl Coenzyme A; Muscle, Skeletal; Physical Exertion; Rats; Rats, Wistar; Triglycerides

Glycogen synthesis is impaired in first degree relatives of subjects with non-insulin-dependent diabetes mellitus and genes relevant to this metabolic pathway are considered reasonable candidates in the pathogenesis of the disease. In skeletal muscle the de novo synthesis of glycogen in primed by an enzyme named glycogenin. We have cloned the glycogenin cDNA from human skeletal muscle mRNA: human glucogenin is a 333 amino acid protein exhibiting 93% identity with rabbit glycogenin. A single transcript of about 2.4 kb, prominent in skeletal muscle, was detected by Northern blot analysis. In situ hybridization unequivocally located the human glycogenin gene to chromosome 3q25.1. Furthermore, we mapped two intronless glycogenin-related sequences to human chromosomes 12 and 13.

Topics: Amino Acid Sequence; Animals; Base Sequence; Chromosome Mapping; Chromosomes, Human, Pair 12; Chromosomes, Human, Pair 13; Chromosomes, Human, Pair 3; Cloning, Molecular; Diabetes Mellitus, Type 2; DNA Primers; DNA, Complementary; Glucosyltransferases; Glycogen; Glycoproteins; Humans; In Situ Hybridization, Fluorescence; Insulin Resistance; Molecular Sequence Data; Muscle Proteins; Muscle, Skeletal; Open Reading Frames; Rabbits; Tissue Distribution

The role of increased lipid availability in the generation of insulin resistance by growth hormone has not been established. We investigated this in rats infused with saline (controls) or human growth hormone (hGH) (500 micrograms x kg-1 x 24 h-1) for 5 h or 3 days. hGH infusion increased basal plasma insulin at 5 h (335 +/- 33 vs. 197 +/- 15 [controls]; P < 0.005) and at 3 days (396 +/- 34 vs. 218 +/- 14 pmol/l; P < 0.0001). Plasma nonesterified fatty acid (0.26 +/- 0.01 vs. 0.21 +/- 0.01 [controls] g/l) and liver long-chain acyl-CoA (21.2 +/- 1.9 vs. 14.1 +/- 1.1 [controls] nmol/g wet wt) were elevated at 5 h (P < 0.01 for both) but were below control levels after 3 days of hGH infusion (P < 0.01 for both); indirect calorimetry after 3 days demonstrated decreased lipid oxidation. Clamp studies showed similar degrees of peripheral insulin resistance at 5-h and 3-day hGH infusion (glucose disposal reduced by 25% versus controls). Insulin-stimulated glucose metabolic index (Rg') in red gastrocnemius muscle (red muscle) was reduced (P < 0.05 and P < 0.01) at 5 h and 3 days of hGH infusion, respectively (e.g., 5 h, 10.0 +/- 1.8 vs. 24.1 +/- 4.4 [controls] micromol x 100 g-1 x min-1), whereas insulin-mediated muscle glycogen synthesis was reduced (P < 0.03) only in rats infused with hGH for 3 days. We conclude that in the rat, hGH rapidly induces persistent peripheral insulin resistance and basal hyperinsulinemia. However, the transient nature of increased lipid mobilization suggests that it is not an important factor in the manifestation of muscle insulin resistance during prolonged hGH elevation. The persistent insulin resistance is not associated with increased lipid oxidation but is associated with hyperinsulinemia and reduced insulin-mediated muscle glycogen synthesis.

Topics: Adipose Tissue; Animals; Blood Glucose; Body Weight; Epididymis; Fatty Acids, Nonesterified; Glycogen; Growth Hormone; Humans; Hyperinsulinism; Infusions, Intravenous; Insulin; Insulin Resistance; Kinetics; Male; Muscle, Skeletal; Myocardium; Patch-Clamp Techniques; Rats; Rats, Wistar; Reference Values; Triglycerides

To examine whether impairment of intracellular glucose metabolism precedes insulin resistance, we determined the time courses of changes in insulin-stimulated glucose uptake, glycolysis, and glycogen synthesis during high-fat feeding in rats. Animals were fed with a high-fat (66.5%) diet ad libitum for 0, 2, 4, 7, or 14 days (n = 10-11 in each group) after 5 days of a low-fat (12.5%) diet. Submaximal and maximal insulin-stimulated glucose fluxes were estimated in whole body and individual skeletal muscles using the glucose clamp technique combined with D-[3-3H]glucose infusion and 2-[1-14C]deoxyglucose injection. Both submaximal and maximal insulin-stimulated glucose uptake in whole body decreased gradually with high-fat feeding. However, the decreases were minimal and not statistically significant during the initial few days (i.e., 2 and 4 days) of high-fat feeding (P > 0.05). In contrast, insulin-stimulated whole-body glycolysis (both maximal and submaximal) significantly decreased by approximately 30% with 2 days of high-fat feeding and remained suppressed thereafter (P < 0.05). Similar patterns of changes in insulin-stimulated glucose uptake and glycolysis were also observed in skeletal muscle. Insulin-stimulated glycogen synthesis and glucose-6-phosphate (G-6-P) concentrations in skeletal muscle increased significantly during the initial few days of high-fat feeding and gradually returned to control levels by day 14, suggesting that increased G-6-P concentrations were responsible for increased glycogen synthesis. Thus, suppression of insulin-stimulated glycolysis and a compensatory increase in glycogen synthesis (presumably arising from the glucose-fatty acid cycle) preceded decreases in insulin-stimulated glucose uptake in skeletal muscle during high-fat feeding. These findings suggest that the insulin resistance may develop as a secondary response to impaired intracellular glucose metabolism.

Topics: Animals; Blood Glucose; Deoxyglucose; Diet, Fat-Restricted; Dietary Fats; Fatty Acids, Nonesterified; Glucose; Glucose Clamp Technique; Glycogen; Glycolysis; Insulin; Insulin Resistance; Kinetics; Male; Muscle, Skeletal; Rats; Rats, Wistar; Time Factors; Tritium

To examine the impact of insulin resistance on the insulin-dependent and insulin-independent portions of muscle glycogen synthesis during recovery from exercise, we studied eight young, lean, normoglycemic insulin-resistant (IR) offspring of individuals with non-insulin-dependent diabetes mellitus and eight age-weight matched control (CON) subjects after plantar flexion exercise that lowered muscle glycogen to approximately 25% of resting concentration. After approximately 20 min of exercise, intramuscular glucose 6-phosphate and glycogen were simultaneously monitored with 31P and 13C NMR spectroscopies. The postexercise rate of glycogen resynthesis was nonlinear. Glycogen synthesis rates during the initial insulin independent portion (0-1 hr of recovery) were similar in the two groups (IR, 15.5 +/- 1.3 mM/hr and CON, 15.8 +/- 1.7 mM/hr); however, over the next 4 hr, insulin-dependent glycogen synthesis was significantly reduced in the IR group [IR, 0.1 +/- 0.5 mM/hr and CON, 2.9 +/- 0.2 mM/hr; (P < or = 0.001)]. After exercise there was an initial rise in glucose 6-phosphate concentrations that returned to baseline after the first hour of recovery in both groups. In summary, we found that following muscle glycogen-depleting exercise, IR offspring of parents with non-insulin-dependent diabetes mellitus had (i) normal rates of muscle glycogen synthesis during the insulin-independent phase of recovery from exercise and (ii) severely diminished rates of muscle glycogen synthesis during the subsequent recovery period (2-5 hr), which has previously been shown to be insulin-dependent in normal CON subjects. These data provide evidence that exercise and insulin stimulate muscle glycogen synthesis in humans by different mechanisms and that in the IR subjects the early response to stimulation by exercise is normal.

Topics: Adult; Analysis of Variance; Blood Glucose; Diabetes Mellitus, Type 2; Epinephrine; Female; Glucagon; Glucose; Glucose-6-Phosphate; Glucosephosphates; Glycogen; Humans; Hydrogen-Ion Concentration; Infusions, Intravenous; Insulin; Insulin Resistance; Lactates; Magnetic Resonance Spectroscopy; Male; Muscle Contraction; Muscle, Skeletal; Nuclear Family; Phosphates; Phosphocreatine; Physical Exertion; Reference Values

The effect of insulin to increase the activity of glycogen synthase (GS) in muscle has been well documented, however, the effect of in vivo insulin to inactivate glycogen phosphorylase (GP) has not been previously shown. To determine the effects of insulin on glycogenolysis in rhesus monkeys, GP and glycogen were determined in muscle samples obtained under basal fasting and insulin-stimulated conditions during a euglycemic hyperinsulinemic clamp in a group of 27 monkeys ranging from normal to overtly diabetic (NIDDM) and compared to GS activity previously examined. The diabetic monkeys had lower basal and insulin-stimulated glycogen concentrations compared to the normal and hyperinsulinemic monkeys (p < 0.05). The response of GP activity ratio (AR) to insulin (delta) was inversely correlated to delta GS fractional velocity (fv) (r = -0.57, p < 0.002) in all of the monkeys. The AR of GP was inversely correlated to the fv of GS measured under insulin-stimulated conditions (r = -0.60, p < 0.05) in the 11 normal monkeys. In the normal group, the range in response of GS to insulin (delta GSfv) was previously shown to be 3-22%, with n = 6 < 11% ('low normals') and n = 5 > 11% ('high normals'). In the present study, the low normals were shown to have (1) higher delta GP independent activity and delta GP total activity compared to the high normals and hyperinsulinemic monkeys (p less than or equal to 0.05), (2) higher insulin-stimulated GP independent activity and GP total activity compared to the other three groups (p < 0.05), (3) higher insulin-stimulated GP activity ratio compared to the high normals and hyperinsulinemic monkeys (p < 0.05), (4) and lower whole-body insulin-mediated glucose disposal rates compared to the high normals (p < 0.05). We conclude that NIDDM is accompanied by low glycogen content in the muscle, and that some clinically normal monkeys have an alteration in insulin action on muscle GS, GP, and whole-body glucose disposal rates that may precede the development of hyperinsulinemia.

Topics: Animals; Diabetes Mellitus, Type 2; Glucose Clamp Technique; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Macaca mulatta; Muscle, Skeletal; Phosphorylases

A mutant insulin receptor, Ser323Leu, has been reported in two severely insulin-resistant patients with Rabson-Mendenhall syndrome. In both cases, extreme hyperglycaemia could not be controlled by conventional antidiabetic therapy. The SER323Leu mutant insulin receptor is inserted normally in the plasma membrane but has very low binding affinity for insulin. A monoclonal antibody directed against the extracellular domain of the insulin receptor (83.14) can mimic the natural ligand as far as the first step after ligand binding--autophosphorylation of the intracellular domain of the receptor. We have investigated whether antibody binding can imitate autophosphorylation of the Ser323Leu mutant receptor and lead to metabolic events within the cell.. The effects of insulin and the insulin-receptor monoclonal antibody on receptor autophosphorylation and glycogen synthesis were compared in Chinese hamster ovary cells expressing the wild-type human insulin receptor, mock-transfected cells, cells expressing an insulin-receptor mutant without autophosphorylation capacity, and cells expressing the Ser323Leu mutant receptor.. Cells expressing the SER323Leu mutant receptor had very low specific insulin binding and, unlike cells expressing wild-type insulin receptors, did not show autophosphorylation or stimulation of glycogen synthesis in response to insulin. However, exposure of cells expressing the Ser323Leu mutant receptor to monoclonal antibody 83.14 resulted in autophosphorylation and stimulation of glycogen synthesis similar to that seen in cells expressing wild-type insulin receptors.. Although insulin does not bind to cells expressing the Ser323Leu mutation, insulin signalling can be mimicked by exposure of the cells to an antibody to the extracellular domain of the insulin receptor. Activation by monoclonal antibodies of mutant transmembrane receptors that show normal cell-surface expression but defective ligand binding may provide an approach to the therapy of some subtypes of inherited hormone resistance for which little effective treatment is available.

Topics: Adult; Animals; Antibodies, Monoclonal; CHO Cells; Cricetinae; Glycogen; Humans; Insulin; Insulin Resistance; Male; Mutation; Phosphorylation; Receptor, Insulin; Syndrome

To examine the mechanism by which lipids cause insulin resistance in humans, skeletal muscle glycogen and glucose-6-phosphate concentrations were measured every 15 min by simultaneous 13C and 31P nuclear magnetic resonance spectroscopy in nine healthy subjects in the presence of low (0.18 +/- 0.02 mM [mean +/- SEM]; control) or high (1.93 +/- 0.04 mM; lipid infusion) plasma free fatty acid levels under euglycemic (approximately 5.2 mM) hyperinsulinemic (approximately 400 pM) clamp conditions for 6 h. During the initial 3.5 h of the clamp the rate of whole-body glucose uptake was not affected by lipid infusion, but it then decreased continuously to be approximately 46% of control values after 6 h (P < 0.00001). Augmented lipid oxidation was accompanied by a approximately 40% reduction of oxidative glucose metabolism starting during the third hour of lipid infusion (P < 0.05). Rates of muscle glycogen synthesis were similar during the first 3 h of lipid and control infusion, but thereafter decreased to approximately 50% of control values (4.0 +/- 1.0 vs. 9.3 +/- 1.6 mumol/[kg.min], P < 0.05). Reduction of muscle glycogen synthesis by elevated plasma free fatty acids was preceded by a fall of muscle glucose-6-phosphate concentrations starting at approximately 1.5 h (195 +/- 25 vs. control: 237 +/- 26 mM; P < 0.01). Therefore in contrast to the originally postulated mechanism in which free fatty acids were thought to inhibit insulin-stimulated glucose uptake in muscle through initial inhibition of pyruvate dehydrogenase these results demonstrate that free fatty acids induce insulin resistance in humans by initial inhibition of glucose transport/phosphorylation which is then followed by an approximately 50% reduction in both the rate of muscle glycogen synthesis and glucose oxidation.

Topics: Adult; Fatty Acids, Nonesterified; Female; Glucose; Glycogen; Humans; Insulin Resistance; Male; Middle Aged; Muscle, Skeletal

Insulin resistance of muscle glucose metabolism is a hallmark of NIDDM. The obese Zucker (fa/fa) rat--an animal model of muscle insulin resistance--was used to test whether acute (100 mg/kg body wt for 1 h) and chronic (5-100 mg/kg for 10 days) parenteral treatments with a racemic mixture of the antioxidant alpha-lipoic acid (ALA) could improve glucose metabolism in insulin-resistant skeletal muscle. Glucose transport activity (assessed by net 2-deoxyglucose [2-DG] uptake), net glycogen synthesis, and glucose oxidation were determined in the isolated epitrochlearis muscles in the absence or presence of insulin (13.3 nmol/l). Severe insulin resistance of 2-DG uptake, glycogen synthesis, and glucose oxidation was observed in muscle from the vehicle-treated obese rats compared with muscle from vehicle-treated lean (Fa/-) rats. Acute and chronic treatments (30 mg.kg-1.day-1, a maximally effective dose) with ALA significantly (P < 0.05) improved insulin-mediated 2-DG uptake in epitrochlearis muscles from the obese rats by 62 and 64%, respectively. Chronic ALA treatment increased both insulin-stimulated glucose oxidation (33%) and glycogen synthesis (38%) and was associated with a significantly greater (21%) in vivo muscle glycogen concentration. These adaptive responses after chronic ALA administration were also associated with significantly lower (15-17%) plasma levels of insulin and free fatty acids. No significant effects on glucose transporter (GLUT4) protein level or on the activities of hexokinase and citrate synthase were observed. Collectively, these findings indicate that parenteral administration of the antioxidant ALA significantly enhances the capacity of the insulin-stimulatable glucose transport system and of both oxidative and nonoxidative pathways of glucose metabolism in insulin-resistant rat skeletal muscle.

Topics: Animals; Antioxidants; Biological Transport; Body Weight; Female; Glucose; Glycogen; Insulin; Insulin Resistance; Muscles; Organ Size; Rats; Rats, Mutant Strains; Thioctic Acid

Topics: Adipocytes; Animals; Cells, Cultured; Glucose; Glycogen; Hypertension; Insulin; Insulin Resistance; Lipids; Muscle, Skeletal; Organ Specificity; Rats; Rats, Inbred SHR; Rats, Inbred WKY

The effect of omega-3 fatty acids derived from fish and marine mammals on subjects with normal glucose tolerance is still unclear. The aim of the present study was to test whether the hypolipidemia that follows the chronic administration of cod liver oil, rich in polyunsaturated fatty acids (omega-3), to normal rats is accompanied by changes in glucose metabolism, insulin secretion and sensitivity, and pancreatic insulin content. To achieve this goal, male Wistar rats were fed with a semisynthetic diet (w/w): 62.5% cornstarch, 7% cod liver oil plus 1% corn oil, and 17% protein (CD + CLO). Control rats were fed with the same semisynthetic diet with the only exception that the source of fat was 8% (w/w) corn oil (CD). Both diets were administered ad libitum for 1 month. At the end of the experimental period, the results obtained were as follows (mean +/- SEM): serum triacylglycerol (mM): CD + CLO 0.21 +/- 0.04 vs. CD 0.58 +/- 0.05 (p < 0.05); free fatty acids (microM): CD + CLO 257 +/- 20 vs. CD 288 +/- 22 (p = NS); total cholesterol (mM): CD + CLO 1.13 +/- 0.09 vs. CD 1.82 +/- 0.06 (p < 0.05); high-density lipoprotein cholesterol (mM): CD + CLO 0.58 +/- 0.08 vs. CD 1.07 +/- 0.04 (p < 0.05); plasma glucose (mM): CD + CLO 6.30 +/- 0.29 vs. CD 6.28 +/- 0.10 (p = NS); liver triacylglycerol (mumol/liver): CD + CLO 104.1 +/- 11.4 vs. CD 136.8 +/- 4.3 (p < 0.05); glycogen (mumol/g wet weight): CD + CLO 298.3 +/- 21.0 vs. CD 297.0 +/- 19.0 (p = NS); glucose-6-phosphate dehydrogenase (U/liver): CD + CLO 37.9 +/- 2.2 vs. CD 58.8 +/- 5.0 (p < 0.05); triacylglycerol secretion (nmol/min/100 g body weight): CD + CLO 101.0 +/- 2.0 vs. CD 166.0 +/- 9.7 (p < 0.01); removal of fat emulsion (K2% min-1): CD + CLO 15.0 x 10(-2) +/- 0.8 x 10(-2) vs. CD 8.2 x 10(-2) +/- 0.2 x 10(-2) (p < 0.01); intravenous glucose tolerance (kg 10(-2): CD + CLO 2.68 +/- 0.37 vs. CD 2.70 +/- 0.14 (p = NS); immunoreactive insulin (microU/ml/ min): with the area under the curve between 0 and 30 min CD + CLO 544 +/- 60 vs. CD 1,050 +/- 38 (p < 0.05), with the area under the curve between 0 and 60 min CD + CLO 1,188 +/- 150 vs. CD 2,160 +/- 137 (p < 0.05), and pancreas insulin content (microU/mg pancreas): CD + CLO 1.85 +/- 0.29 vs. CD 2.04 +/- 0.12 (p = NS). In conclusion, the present study shows that the strong hypolipidemic effect produced by the administration of low doses of fish oil to normal rats is accompanied by a significant reduction of plasma insulin levels without changes in glucose tole

Topics: Animals; Area Under Curve; Blood Glucose; Cholesterol; Cholesterol, HDL; Corn Oil; Dose-Response Relationship, Drug; Eating; Fatty Acids, Omega-3; Fish Oils; Glucose; Glucose Tolerance Test; Glucosephosphate Dehydrogenase; Glycogen; Insulin; Insulin Resistance; Insulin Secretion; Lipids; Liver; Male; Pancreas; Rats; Rats, Wistar; Triglycerides; Weight Gain

Acute physical exercise enhances insulin sensitivity in healthy subjects. We examined the effect of a 42-km marathon run on insulin sensitivity and lipid oxidation in 19 male runners. In the morning after the marathon run, basal serum free fatty acid concentration was 2.2-fold higher, muscle glycogen content 37% lower (P < 0.01), glycogen synthase fractional activity 56% greater (P < 0.01), and glucose oxidation reduced by 43% (P < 0.01), whereas lipid oxidation was increased by 55% (P < 0.02) compared with the control study. During euglycemic-hyperinsulinemic clamp, whole body glucose disposal was decreased by 12% (P < 0.01) because of a 36% lower glucose oxidation rate (P < 0.05), whereas the rate of lipid oxidation was 10-fold greater (P < 0.02) than in the control study. After the marathon, muscle glycogen content correlated positively with lipid oxidation (r = 0.60, P < 0.05) and maximal aerobic power (Vo2peak; r = 0.61, P < 0.05). Vo2peak correlated positively with basal lipid oxidation (r = 0.57, P < 0.05). In conclusion, 1) after the marathon run, probably because of increased lipid oxidation, the insulin-stimulated glucose disposal is decreased despite muscle glycogen depletion and the activation of glycogen synthase; 2) the contribution of lipid oxidation in energy expenditure is increased in proportion to physical fitness; 3) these adaptations of fuel homeostasis may contribute to the maintenance of physical performance after prolonged exercise.

Topics: Adult; Blood; Energy Metabolism; Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase; Humans; Insulin Resistance; Lipid Metabolism; Magnetic Resonance Imaging; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscles; Oxidation-Reduction; Physical Endurance; RNA, Messenger; Running

We examined the possibility that protein kinase C (PKC) is chronically activated and may contribute to impaired glycogen synthesis and insulin resistance in soleus muscles of hyperinsulinemic type II diabetic Goto-Kakizaki (GK) rats. Relative to nondiabetic controls, PKC enzyme activity and levels of immunoreactive PKC-alpha, beta, epsilon, and delta were increased in membrane fractions and decreased cytosolic fractions of GK soleus muscles. In addition, PKC-theta levels were decreased in both membrane and cytosol fractios, whereas PKC-zeta levels were not changed in either fraction in GK soleus muscles. These increases in membrane PKC (alpha, beta, epsilon, and delta) could not be accounted for by alterations in PKC mRNA or total PKC levels but were associated with increases in membrane diacylglycerol (DAG) and therefore appeared to reflect translocative activation of PKC. In evaluation of potential causes for persistent PKC activation, membrane PKC levels were decreased in soleus muscles of hyperglycemic streptozotocin (STZ)-induced diabetic rats; thus, a role for simple hyperglycemia as a cause of PKC activation in GK rats was not evident in the STZ model. In support of the possibility that hyperinsulinemia contributed to PKC activation in GK soleus muscles, we found that DAG levels were increased, and PKC was translocated, in soleus muscles of both (1) normoglycemic hyperinsulinemic obese/aged rats and (2) mildly hyperglycemic hyperinsulinemic obese/Zucker rats. In keeping with the possibility that PKC activation may contribute to impaired glycogen synthase activation in GK muscles, phorbol esters inhibited, and a PKC inhibitor, RO 31-8220, increased insulin effects on glycogen synthesis in soleus muscles incubated in vitro. Our findings suggested that: (1) hyperinsulinemia, as observed in type II diabetic GK rats and certain genetic and nongenetic forms of obesity in rats, is associated with persistent translocation and activation of PKC in soleus muscles, and (2) this persistent PKC activation may contribute to impaired glycogen synthesis and insulin resistance.

Topics: Adipocytes; Aging; Animals; Cell Membrane; Cytosol; Diabetes Mellitus, Type 2; Enzyme Activation; Glycogen; Insulin Resistance; Isoenzymes; Liver; Male; Muscle, Skeletal; Obesity; Protein Kinase C; Protein Kinase C beta; Protein Kinase C-alpha; Protein Kinase C-delta; Protein Kinase C-epsilon; Rats; Rats, Mutant Strains; Rats, Wistar; Rats, Zucker; Reference Values; RNA, Messenger; Transcription, Genetic

Insulin resistance in the offspring of parents with non-insulin-dependent diabetes mellitus (NIDDM) is the best predictor of development of the disease and probably plays an important part in its pathogenesis. We studied the mechanism and degree to which exercise training improves insulin sensitivity in these subjects.. Ten adult children of parents with NIDDM and eight normal subjects were studied before starting an aerobic exercise-training program, after one session of exercise, and after six weeks of exercise. Insulin sensitivity was measured by the hyperglycemic-hyperinsulinemic clamp technique combined with indirect calorimetry, and the rate of glycogen synthesis in muscle and the intramuscular glucose-6-phosphate concentration were measured by carbon-13 and phosphorus-31 nuclear magnetic resonance spectroscopy, respectively.. During the base-line study, the mean (+/-SE) rate of muscle glycogen synthesis was 63 +/- 9 percent lower in the offspring of diabetic parents than in the normal subjects (P < 0.001). The mean value increased 69 +/- 10 percent (P = 0.04) and 62 +/- 11 percent (P = 0.04) after the first exercise session and 102 +/- 11 percent (P = 0.02) and 97 +/- 9 percent (P = 0.008) after six weeks of exercise training in the offspring and the normal subjects, respectively. The increment in glucose-6-phosphate during hyperglycemic-hyperinsulinemic clamping was lower in the offspring than in the normal subjects (0.039 +/- 0.013 vs. 0.089 +/- 0.009 mmol per liter, P = 0.005), reflecting reduced glucose transport-phosphorylation, but this increment was normal in the offspring after the first exercise session and after exercise training. Basal and stimulated insulin secretion was higher in the offspring than the normal subjects and was not altered by the exercise training program.. Exercise increases insulin sensitivity in both normal subjects and the insulin-resistant offspring of diabetic parents because of a twofold increase in insulin-stimulated glycogen synthesis in muscle, due to an increase in insulin-stimulated glucose transport-phosphorylation.

Topics: Adult; Biological Transport, Active; Diabetes Mellitus, Type 2; Exercise; Female; Glucose; Glucose Clamp Technique; Glucose-6-Phosphate; Glycogen; Humans; Insulin; Insulin Resistance; Insulin Secretion; Male; Muscle, Skeletal; Phosphorylation; Physical Fitness

The effects of a similar exercise training stimulus on maximal insulin-stimulated (MIS) plasma membrane glucose transporter number and glucose transport were determined in lean and obese SHHF/Mcc-facp rats. Six-week-old lean and obese male rats were randomly divided into four groups: lean sedentary (LSed), obese sedentary (OSed), lean exercise (LEx), and obese exercise (OEx). An 8- to 12-wk treadmill running program equalized daily muscular work for LEx and OEx. Plasma membranes were isolated from control and MIS muscles of mixed fiber types. MIS significantly increased glucose transport (3.4- and 2.8-fold) in LSed and OSed, respectively. MIS significantly increased glucose transporter number (2.5-fold) in LSed, but there was no increase in glucose transporter number in OSed. Peak oxygen uptake and citrate synthase activity were increased a similar amount for LEx and OEx groups, demonstrating a similar training stimulus. MIS significantly and similarly increased glucose transport in LEx and OEx (4.4- and 5.1-fold, respectively). The effects of MIS on plasma membrane glucose transporter number in the exercise-trained rats were similar to the responses observed in the sedentary lean and obese groups. MIS significantly increased glucose transporter number (2.6-fold) in LEx, whereas there was no increase in glucose transporter number in OEx. The reduction in MIS glucose transport in OSed appears to be related to a defect in the processes associated with the translocation of glucose transporters to the plasma membrane. Exercise training of the obese rats apparently did not alter this defect. Similar increases in peak oxygen uptake, citrate synthase, and MIS glucose transport in LEx and OEx groups suggest that insulin resistance does not limit the ability of the glucose transport system to adapt to exercise training in the obese male SHHF/Mcc-facp rats.

Topics: 4-Nitrophenylphosphatase; Animals; Blood Glucose; Cell Membrane; Citrate (si)-Synthase; Cytochalasin B; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Obesity; Organ Size; Oxygen Consumption; Physical Conditioning, Animal; Rats; Rats, Inbred Strains

Prolonged glucosamine (GlcN) infusion increases the skeletal muscle hexosamine concentration and induces peripheral insulin resistance in conscious rats. IGF-1 and insulin share common steps in signal transduction, and the action of IGF-1 on carbohydrate metabolism is preserved in certain insulin-resistant states. In our study, we attempted to delineate whether increased GlcN availability also impairs the effects of IGF-1 on glucose uptake (Rd), glycolysis, and glycogen synthesis. We performed euglycemic IGF-1 (5 and 15 microg x kg(-1) x min(-1)) and insulin (3 and 18 mU mg x kg(-1) x min(-1)) clamp studies at 0-2 h and 5-7 h in conscious rats (n = 44) during saline or GlcN infusions. GlcN infusion raised plasma GlcN levels to approximately 2.0 mmol/l and skeletal muscle uridinediphospho-n-acetylglucosamine to 80-150 nmol/g (approximately three- to fivefold over basal). During physiological hyperinsulinemia (3 mU x kg(-1) x min(-1), plasma insulin approximately 50 microU/ml), GlcN infusion caused comparable decreases in Rd (15.7 +/- 1.0 [5-7 h] vs. 21.7 +/- 2.3 [0-2 h] mg x kg(-1) x min(-1); P < 0.01) and glycogen synthesis (5.4 +/- 0.5 [5-7 h] vs. 10.4 +/- 1.9 [0-2 h] mg x kg(-1) x min(-1); P < 0.005). Furthermore, GlcN markedly decreased Rd by 7.8 +/- 1.2 mg x kg(-1) x min(-1) (18.7 +/- 0.7 [5-7 h] vs. 26.5 +/- 1.3 [0-2 h] mg x kg(-1) x min(-1); P < 0.001 vs. control) during IGF-1 (5 microg x kg(-1) x min(-1)) clamp studies. This decline was associated with a 26% decrease in the steady-state concentration of skeletal muscle Glc-6-P (286 +/- 45 vs. 386 +/- 36 nmol/g; P < 0.01) and was primarily caused by impaired glycogen synthesis (6.7 +/- 0.5 [5-7 h] vs. 13.9 +/- 0.9 [0-2 h] mg x kg(-1) x min(-1); P < 0.005). The effects of GlcN infusion on glucose disposal (percentage decrease in Rd) were correlated (r2 = 0.803; P < 0.01) with the skeletal muscle concentration of UDP-GlcNAc. To investigate whether IGF-1 can overcome GlcN-induced insulin resistance, GlcN and insulin (18 mU x kg(-1) x min(-1)) were infused for 7 h during euglycemic clamps, and IGF-1 (15 microg x kg(-1) x min(-1)) was superimposed during the final 2 h. GlcN infusion induced severe impairment of insulin action on Rd (39.4 +/- 3.2 [4-5 h] vs. 49.8 +/- 3.6 [1-2 h] mg x kg(-1) x min(-1); P < 0.05), which the addition of IGF-1 failed to improve (35.9 +/- 2.3 [6-7 h] vs. 39.4 +/- 3.2 [4-5 h] mg x kg(-1) x min(-1); P > 0.1). In summary, GlcN induced severe resistance to the actions of both insu

Topics: Animals; Blood Glucose; Body Weight; Glucosamine; Glucose; Glucose Clamp Technique; Glycogen; Glycogen Synthase; Hexosamines; Insulin; Insulin Resistance; Insulin-Like Growth Factor I; Kinetics; Liver; Male; Muscle, Skeletal; Rats; Rats, Sprague-Dawley; Uridine Diphosphate N-Acetylglucosamine

To investigate the mechanism by which free fatty acids (FFA) affect glucose uptake, we studied the effect of chronic elevation (24 h) of plasma FFA in rats on whole body glucose disposal and glucose utilization index (GUI) in the basal state and under a euglycemic hyperinsulinemic clamp in relation to the amount of insulin-responsive glucose transporter (IRGT, i.e., GLUTU) protein in different muscles (oxidative and glycolytic) and adipose tissue. Infusion of intralipid in the basal state led to a approximately 40% increase in whole body glucose uptake and a approximately 250% increase in GUI in adipose tissue as compared to control rats. There was no change in the amount of IRGT protein in any of the muscle types whereas in fat depots it was either unchanged or decreased. Under moderate of supraphysiological hyperinsulinemia, increment of whole body glucose disposal was significantly lower in intralipid perfused rats when compared to controls (approximately 110 microU/mL: 0.7 +/- 0.1 vs. 1.3 +/- 0.1 mg/min, P < 0.02; approximately 1000 microU/mL: 3.0 +/- 0.2 vs. 3.9 +/- 0.4 mg/min, P < 0.02). Under moderate hyperinsulinemia stimulation, GUI was significantly reduced in different muscles and adipose tissue as compared to controls. We conclude that peripheral insulin resistance which occurs after elevation of plasma FFA levels does not seem to be explained by changes in the amount of IRGT protein in either oxidative or glycolytic skeletal muscle. Thus fatty acid infusion appears to be associated with a defect in IRGT translocation to the plasma membrane, fusion with the membrane, or intrinsic activity.

Topics: Adipose Tissue; Animals; Biological Transport, Active; Blood Glucose; Fat Emulsions, Intravenous; Fatty Acids, Nonesterified; Female; Glucose; Glucose Transporter Type 4; Glycogen; Glycolysis; Hyperlipidemias; Infusions, Intravenous; Insulin; Insulin Resistance; Kinetics; Liver Glycogen; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Rats; Rats, Wistar

We have recently shown that eccentric contractions (Ecc) of rat calf muscles cause muscle damage and decreased glycogen and glucose transporter GLUT-4 protein content in the white (WG) and red gastrocnemius (RG) but not in the soleus (S) (S. Asp, S. Kristiansen, and E. A. Richter. J. Appl. Physiol. 79: 1338-1345, 1995). To study whether these changes affect insulin action, hindlimbs were perfused at three different insulin concentrations (0, 200, and 20,000 microU/ml) 2 days after one-legged eccentric contractions of the calf muscles. Compared with control, basal glucose transport was slightly higher (P < 0.05) in Ecc-WG and -RG, whereas it was lower (P < 0.05) at both submaximal and maximal insulin concentrations in the Ecc-WG and at maximal concentrations in the Ecc-RG. In the Ecc-S, the glucose transport was unchanged in hindquarters perfused in the absence or presence of a submaximal stimulating concentration of insulin, whereas it was slightly (P < 0.05) higher during maximal insulin stimulation compared with control S. At the end of perfusion the glycogen concentrations were lower in both Ecc-gastrocnemius muscles compared with control muscles at all insulin concentrations. Fractional velocity of glycogen synthase increased similarly with increasing insulin concentrations in Ecc- and control WG and RG. We conclude that insulin action on glucose transport but not glycogen synthase activity is impaired in perfused muscle exposed to prior eccentric contractions.

Topics: Animals; Body Water; Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase; Hindlimb; Insulin Resistance; Leg; Male; Mannitol; Monosaccharide Transport Proteins; Muscle Contraction; Muscle Proteins; Muscle, Skeletal; Rats; Rats, Wistar; Regional Blood Flow

Insulin resistance is a predictor of the development of noninsulin-dependent diabetes mellitus (NIDDM) in humans. It is unclear whether insulin resistance is a primary defect leading to NIDDM or the result of hyperinsulinemia and hyperglycemia. To determine if insulin resistance is the result of extrinsic factors such as hyperinsulinemia primary skeletal muscle cell cultures were established from muscle biopsies from Pima Indians with differing in vivo insulin sensitivities. These cell cultures expressed a variety of muscle-specific phenotypes including the proteins alpha-actinin and myosin, muscle-specific creatine kinase activity, and RNA encoding GLUT4, MYF5, MYOD1, and MYOGENIN. Labeled glucose was used to measure the insulin-stimulated conversion of glucose to glycogen in these cultures. The in vivo rates of insulin-stimulated glycogen production (insulin resistance) were correlated with in vitro measures of glycogen production (P = 0.007, r = 0.58). This defect in insulin action is stable in a uniform culture environment and is retained over time. The retention of insulin resistance in myoblast derived cell cultures is consistent with the expression of an underlying biochemical defect in insulin resistant skeletal muscle.

Topics: Actinin; Adult; Blotting, Northern; Creatine Kinase; Diabetes Mellitus, Type 2; DNA-Binding Proteins; Dose-Response Relationship, Drug; Fluorescent Antibody Technique, Direct; Glucose; Glucose Transporter Type 4; Glycogen; Humans; Hypoglycemic Agents; Indians, North American; Insulin; Insulin Resistance; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; MyoD Protein; Myogenic Regulatory Factor 5; Myogenin; Myosins; RNA, Messenger; Trans-Activators

In the present study, the time course of change in sucrose-induced insulin resistance, triglyceride (TG) concentration, and liver fatty acid composition was examined. Male rats (n = 8-10/group per time point) was fed a high-starch (ST) diet for 2 wk and were then equicalorically fed ST or a high-sucrose (SU) diet for 1, 2, 5, or 8 wk. Body weight and percent body fat were similar between ST and SU diets at all time points. Glucose infusion rate (GIR) was significantly (P < 0.05) lower in the SU diet (9.2 +/- 0.9, 7.4 +/- 0.5, 6.2 +/- 1.0, and 6.0 +/- 0.9 mg.kg-1.min-1) vs. the ST diet (15.1 +/- 1.7, 15.7 +/- 0.7, 14.7 +/- 1.9, and 14.2 +/- 0.9 mg.kg-1.min-1) at 1, 2, 5, and 8 wk, respectively. Reduced suppression of glucose appearance accounted for 85, 50, 45, and 40% of the reduction in GIR at these same time points. Muscle glycogen synthesis was reduced (P < 0.05 vs. ST diet) in the SU diet at 2, 5, and 8 wk. Fasting plasma TG concentration was inversely related (r = -0.79, P < 0.001) to muscle glycogen synthesis, and liver TG concentration was positively related (r = 0.59, P < 0.01) to glucose appearance. Liver fatty acid composition was similar between diet groups. In summary, the SU diet produced insulin resistance in liver before muscle. TG concentration appears to be related to sucrose-induced insulin resistance in liver and muscle.

Topics: Animals; Blood Glucose; Dietary Sucrose; Fatty Acids; Glucose; Glycogen; Glycolysis; Insulin; Insulin Resistance; Liver; Male; Muscles; Rats; Rats, Wistar; Triglycerides

We studied the biological properties of insulin receptors (IRs) and insulin-like growth factor-I (IGF-I) receptors in cultured fibroblasts from a patient with leprechaunism (leprechaun Par-1). Patient cells displayed normal insulin binding capacity and affinity. Basal in vivo autophosphorylation and in vitro exogenous kinase activity of patient IRs were elevated twofold to threefold compared with control receptors, and insulin had no further effect on these processes. Moreover, patient IRs were unable to promote the stimulation of metabolic and mitogenic pathways. IR substrate-1 (IRS-1) and mitogen-activated protein (MAP) kinase tyrosine phosphorylation and glycogen and DNA synthesis were not increased in the basal state in patient fibroblasts and were also insensitive to the stimulatory effect of insulin. As for IGF-I, although binding and receptor kinase activity were normal, the ability to stimulate glycogen and DNA synthesis was altered in patient cells. Two mutant alleles of the IR gene were detected by denaturing gradient gel electrophoresis (DGGE) and direct sequencing. The maternal allele contained a point mutation in exon 18 encoding the tryptophan-for-arginine substitution at position 1092, and the paternal allele had a point mutation in exon 20 substituting lysine for glutamic acid at codon 1179. Thereby, leprechaun Par-1 was a compound heterozygote for two missense mutations located in the IR beta-subunit. The present investigation provides the first evidence that leprechaunism can be causally related to structural alterations in the tyrosine kinase domain of the IR. These alterations result in severe impairment of insulin and IGF-I action.

Topics: Animals; Cells, Cultured; DNA Replication; Electrophoresis, Polyacrylamide Gel; Female; Glycogen; Growth Disorders; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Insulin-Like Growth Factor I; Male; Pedigree; Phosphoproteins; Phosphorylation; Protein Binding; Protein Kinases; Rats; Receptor, Insulin; Signal Transduction

1. To examine metabolic correlates of insulin resistance in skeletal muscle, we used 31P magnetic resonance spectroscopy to study glycogenolytic and oxidative ATP synthesis in leg muscle of lean and obese Zucker rats in vivo during 6 min sciatic nerve stimulation at 2 Hz. 2. The water content of resting muscle was reduced by 21 +/- 7% in obese (insulin-resistant) animals compared with lean animals, whereas the lipid content was increased by 140 +/- 70%. These results suggest that intracellular water content was reduced by 17% in obese animals. 3. During exercise, although twitch tensions were not significantly different in the two groups, rates of total ATP synthesis (expressed per litre of intracellular water) were 48 +/- 20% higher in obese animals, suggesting a 50 +/- 8% reduction in intrinsic "metabolic efficiency'. Changes in phosphocreatine and ADP concentration were significantly greater in obese animals than in lean animals, whereas changes in intracellular pH did not differ. 4. These results imply that oxidative ATP synthesis during exercise is activated earlier in obese animals than in lean animals. This difference was not fully accounted for by the greater increase in the concentration of the mitochondrial activating signal ADP. Neither the post-exercise recovery kinetics of phosphocreatine nor the muscle content of the mitochondrial marker enzyme citrate synthase was significantly different in the two groups. The increased oxidative ATP synthesis in exercise must therefore be due to altered kinetics of mitochondrial activation by signals other than ADP. 5. Thus, the insulin-resistant muscle of obese animals may compensate for its decreased efficiency (and consequent increased need for ATP) by increased reliance on oxidative ATP synthesis.

Topics: Adenosine Triphosphate; Animals; Energy Metabolism; Female; Glycogen; Insulin Resistance; Magnetic Resonance Spectroscopy; Models, Biological; Muscle, Skeletal; Obesity; Oxidation-Reduction; Physical Exertion; Rats; Rats, Zucker

To explore the relationship between insulin resistance and hypertension, we examined whether acute induction of hypertension can engender insulin resistance. For this purpose we measured rates of insulin-mediated glucose uptake in awake unstressed rats with the euglycemic hyperinsulinemic (12 microns.kg-1.min-1) clamp technique during infusions of saline alone or after induction of hypertension by bolus administration of NG-monomethyl-L-arginine (L-NMMA, 30 and 15 mg/kg), a competitive inhibitor of nitric oxide synthase. Arterial pressure was approximately 20% greater with L-NMMA bolus than with saline alone. Isotopically determined steady-state rates of glucose uptake were 36 +/- 1 mg.kg-1.min-1 during saline alone and 26 +/- 2 and 19 +/- 1 mg.kg-1.min-1 with low- and high-dose L-NMMA (P < 0.001 vs. saline), respectively. To rule out that insulin resistance induced by L-NMMA was adrenergically mediated, clamp studies were repeated with alpha- and beta-blockade. Rates of glucose uptake remained approximately 20% below those observed with saline alone (P < 0.001). A significant inverse correlation was observed between the height of the blood pressure and the rate of glucose uptake (r = 0.32, P = 0.04). In conclusion, acute induction of hypertension with L-NMMA can cause marked insulin resistance. We postulate that reduced skeletal muscle perfusion and/or sympathetic nervous system activation may contribute to insulin resistance induced by L-NMMA.

Topics: Animals; Arginine; Blood Glucose; Glucose; Glycogen; Hypertension; Insulin; Insulin Resistance; Liver; Male; Muscle, Skeletal; Nitric Oxide Synthase; omega-N-Methylarginine; Osmolar Concentration; Rats; Rats, Sprague-Dawley

Insulin resistance is a common clinical feature of obesity and non-insulin-dependent diabetes mellitus, and is characterized by elevated serum levels of glucose, insulin, and lipids. The mechanism by which insulin resistance is acquired is unknown. We have previously demonstrated that upon chronic treatment of fibroblasts with insulin, conditions that mimic the hyperinsulinemia associated with insulin resistance, the membrane-associated insulin receptor beta subunit is proteolytically cleaved, resulting in the generation of a cytosolic fragment of the beta subunit, beta', and that the generation of beta' is inhibited by the thiol protease inhibitor E64 (Knutson, V. P. (1991) J. Biol. Chem. 266, 15656-15662). In this report, we demonstrate that in 3T3-L1 adipocytes: 1) cytosolic beta' is generated by chronic insulin administration to the cells, and that E64 inhibits the production of beta'; 2) chronic administration of insulin to the adipocytes leads to an insulin-resistant state, as measured by lipogenesis and glycogen synthesis, and E64 totally prevents the generation of this insulin-induced cellular insulin resistance; 3) E64 has no effect on the insulin-induced down-regulation of insulin receptor substrate-1, and therefore insulin resistance is not mediated by the down-regulation of insulin receptor substrate-1; 4) under in vitro conditions, partially purified beta' stoichiometrically inhibits the insulin-induced autophosphorylation of the insulin receptor beta subunit; and 5) administration of E64 to obese Zucker fatty rats improves the insulin resistance of the rats compared to saline-treated animals. These data indicate that beta' is a mediator of insulin resistance, and the mechanism of action of beta' is the inhibition of the insulin-induced autophosphorylation of the beta subunit of the insulin receptor.

Topics: 3T3 Cells; Adipocytes; Animals; Female; Glycogen; Insulin; Insulin Resistance; Leucine; Mice; Obesity; Peptide Fragments; Phosphorylation; Rats; Rats, Zucker; Receptor, Insulin; Triglycerides

To determine the effects of the amount of sucrose in the diet on insulin-stimulated glucose metabolism, euglycemic hyperinsulinemic clamps were performed on male Wistar rats after one of the following dietary treatments (n = 6-8/treatment): 1) high-starch diet (68% of total energy) for 8 wk (ST8), 16 wk (ST16), or 30 wk (ST30); 2) high-sucrose diet (68% of total energy) for 8 wk (SU8), 16 wk (SU16), or 30 wk (SU30); or 3) low-sucrose diet (18% of total energy) for 8 wk (SUL8), 16 wk (SUL16), or 30 wk (SUL30). Body weights were similar in starch- and sucrose-fed rats at 8 wk (502 +/- 9 g), 16 wk (563 +/- 10 g), and 30 wk (607 +/- 26 g). The glucose infusion rate (mumol.g-1.min-1) required to maintain similar glycemia during clamps was 73.1 +/- 8.8 in ST8, 29.7 +/- 4.9 in SU8 (P < 0.05 vs. ST8 and SUL8), and 76.4 +/- 8.2 in SUL8; 69.9 +/- 8.1 in ST16, 35.1 +/- 5.1 in SU16 (P < 0.05 vs. ST16 and SUL16), and 63.2 +/- 6.5 in SUL16; and 65.4 +/- 7.7 in ST30, 26.0 +/- 5.3 (P < 0.05 vs. ST30), and 36.3 +/- 6.0 in SUL30 (P < 0.05 vs. ST30). Impaired suppression of hepatic glucose production accounted for 43, 39, and 34% of the decrease in the glucose infusion rate in SU8 compared with ST8, SU16 compared with ST16, and SU30 compared with ST30, respectively, but 78% in SUL30 compared with ST30. These results suggest that both high- and low-sucrose diets can produce insulin resistance in young rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Glucose; Carbohydrates; Diet; Dose-Response Relationship, Drug; Glucose; Glycogen; Insulin; Insulin Resistance; Liver; Male; Muscles; Phosphoenolpyruvate Carboxykinase (GTP); Rats; Rats, Wistar; Sucrose; Time Factors; Triglycerides

The regulatory G-subunit of the glycogen-associated form of protein phosphatase 1 (PP1) plays a crucial part in muscle tissue glycogen synthesis and breakdown. As impaired insulin stimulated glycogen synthesis in peripheral tissues is considered to be a pathogenic factor in subsets of non-insulin-dependent diabetes mellitus (NIDDM) and obesity, the G-subunit of PP1 should be viewed as a candidate gene for inherited insulin resistance. When applying heteroduplex formation analysis and nucleotide sequencing of PP1G-subunit cDNA from 30 insulin resistant white NIDDM patients two cases were identified as heterozygous carriers of an Asp905 --> Tyr substitution. The carrier prevalence of the PP1G-subunit variant was 18% in 150 healthy subjects and 13% in 313 NIDDM subjects (chi 2 = 1.94, p = 0.16). Twenty-seven healthy subjects volunteered for a 4 h euglycaemic, hyperinsulinaemic clamp in combination with indirect calorimetry in order to elucidate the potential impact of the Tyr905 substitution on the whole body glucose metabolism. Interestingly, the Tyr905 variant was associated with altered routing of glucose: a decreased insulin stimulated non-oxidative glucose metabolism of peripheral tissues (glycogen synthesis) (p < 0.04) and an increased basal glucose oxidation rate (p < 0.04) when compared with wild type carriers. A population-based sample of 380 unrelated young healthy Caucasians was examined during a combined intravenous glucose and tolbutamide test to address whether the Asp905/Tyr905 polymorphism was associated with alterations in insulin secretion which might be secondary to the insulin resistance of skeletal muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Base Sequence; Case-Control Studies; Diabetes Mellitus, Type 2; DNA; DNA Primers; Female; Gene Frequency; Genetic Variation; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Insulin Secretion; Male; Middle Aged; Molecular Sequence Data; Nucleic Acid Heteroduplexes; Phosphoprotein Phosphatases; Polymorphism, Genetic; Protein Phosphatase 1

To test the hypothesis that increased flux through the hexosamine biosynthetic pathway can induce insulin resistance in skeletal muscle in vivo, we monitored glucose uptake, glycolysis, and glycogen synthesis during insulin clamp studies in 6-h fasted conscious rats in the presence of a sustained (7-h) increase in glucosamine (GlcN) availability. Euglycemic (approximately 7 mM) insulin (approximately 2,500 pM) clamps with saline or GlcN infusions were performed in control (CON; plasma glucose [PG] = 7.4 +/- 0.2 mM), diabetic (D; PG = 19.7 +/- 1.1), and phlorizin-treated (3-wk) diabetic rats (D + PHL; PG = 7.6 +/- 0.9). 7-h euglycemic hyperinsulinemia with saline did not significantly decrease Rd (360-420 min = 39.2 +/- 3.6 vs. 60-120 min = 42.2 +/- 3.7 mg/kg.min; P = NS). GlcN infusion raised plasma GlcN concentrations to approximately 1.2 mM and increased muscle and liver UDP-GlcNAc levels by 4-5-fold in all groups. GlcN markedly decreased Rd in CON (360-420 min = 30.4 +/- 1.3 vs. 60-120 min = 44.1 +/- 3.5 mg/kg.min; P < 0.01) and D + PHL (360-420 min = 29.4 +/- 2.5 vs. 60-120 min = 43.8 +/- 2.9 mg/kg.min; P < 0.01), but not in D (5-7 h = 21.5 +/- 0.8 vs. 0-2 h = 24.3 +/- 1.1 mg/kg.min; P = NS). Thus, increased GlcN availability induces severe skeletal muscle insulin resistance in normoglycemic but not in chronically hyperglycemic rats. The lack of additive effects of GlcN and chronic hyperglycemia (experimental diabetes) provides support for the hypothesis that increased flux through the GlcN pathway in skeletal muscle may play an important role in glucose-induced insulin resistance in vivo.

Topics: Animals; Blood Glucose; Glucosamine; Glucose; Glycogen; Glycolysis; Hexokinase; Hyperglycemia; Insulin Resistance; Male; Muscles; Rats; Rats, Sprague-Dawley

Glucose production and utilization and activities of key enzymes involved in liver and muscle glucose metabolism were studied in post-absorptive streptozotocin-diabetic rats after 12 h of severe hyperglycaemia (17.5 +/- 0.5 mmol/l) and insulinopenia (5 +/- 1 microU/ml). Basal glucose production was increased: 36.6 +/- 3.0 mg.kg.min-1, vs 24.4 +/- 2.5 in controls (p < 0.05); liver glycogen concentration was decreased by 40% (p < 0.05); liver phosphoenolpyruvate carboxykinase and glucose-6-phosphatase activities were increased by 375 and 156%, respectively (p < 0.001 and < 0.01). During a euglycaemic clamp at a plasma insulin level of 200 microU/ml, glucose production was totally suppressed in controls, but persisted at 20% of basal in diabetic rats. In these rats, glucose production was suppressed at a plasma insulin level of 2500 microU/ml. Basal whole body glucose utilization rate, 2-deoxy-1-[3H]-D-glucose ([3H]-2DG) uptake by muscles and muscle glycogen concentrations were similar in both groups, as well as total and active forms of pyruvate dehydrogenase and glycogen synthase activities. During the euglycaemic clamp, the total body glucose utilization rates and [3H]-2DG uptake by muscles were similar in control and diabetic rats at a plasma insulin level of 200 microU/ml, but lower in diabetic rats at a plasma insulin level of 2500 microU/ml. We conclude 1) in recent-onset severely insulinopenic rats, an excessive glucose production via gluconeogenesis prevailed, mainly accounting for the concomitant hyperglycaemia. This excess glucose output cannot be attributed to liver insulin resistance: the gluconeogenic pathway is physiologically less sensitive than glycogenolysis to the inhibition by insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adipose Tissue; Adipose Tissue, Brown; Animals; Blood Glucose; Deoxyglucose; Diabetes Mellitus, Experimental; Fatty Acids, Nonesterified; Glucagon; Glucose; Glucose Clamp Technique; Glycogen; Glycolysis; Hyperglycemia; Insulin; Insulin Resistance; Liver; Liver Glycogen; Male; Muscle, Skeletal; Myocardium; Organ Specificity; Rats; Rats, Wistar; Reference Values

To examine whether tissue sensitivity to insulin is dependent upon the prevailing plasma insulin concentration, the ability of acute hyperinsulinemia to stimulate glucose disposal was investigated in six normal subjects before and after prolonged reduction of the plasma insulin concentration. Glucose turnover ([6,6-2H2]glucose), whole body glucose oxidation and nonoxidative glucose disposal (indirect calorimetry), and glycogen synthase activity in muscle were determined in the postabsorptive and in the insulin-stimulated states (euglycemic hyperinsulinemic clamp: 3 mU.kg-1.min-1) before and after a 4-day subcutaneous infusion of the somatostatin analogue octreotide (200 micrograms/24 h). Constant octreotide infusion 1) decreased postabsorptive and meal-stimulated plasma insulin levels by approximately 30-40% but did not significantly alter overall glucose tolerance, free fatty acid, growth hormone, and glucagon levels and 2) was associated with significant increases in insulin-mediated whole body glucose disposal (pre-drug: 10.29 +/- 0.49 vs. postdrug: 11.42 +/- 0.72 mg.kg-1.min-1, P < 0.04), nonoxidative glucose disposal (6.82 +/- 0.57 vs. 7.68 +/- 0.62, P < 0.03), and fractional glycogen synthase activity (0.14 +/- 0.03 vs. 0.20 +/- 0.04 mU/mg protein, P < 0.02). In contrast, infusion of saline instead of octreotide for 4 days to control subjects did not alter any of the metabolic parameters. We conclude that lowering the plasma insulin concentration over a prolonged period of time increases insulin sensitivity. The effects of insulin to stimulate whole body glucose utilization, nonoxidative glucose disposal, and glycogen synthase activity in muscle are therefore functions of the preexisting plasma insulin concentration.

Topics: Female; Glucose; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Resistance; Lipid Metabolism; Male; Muscles; Octreotide; Osmolar Concentration; Oxidation-Reduction; Proteins; Sodium Chloride

The role of glucagon in glucose homeostasis during chronic malnutrition was studied in weanling-littermate rats either fed ad libitum or restricted to 60% of ad libitum intake for 8 weeks. Fasting glucose and insulin levels were lower in malnourished rats, and their response to glucagon (0.02 mg/kg intravenous [IV]) after a 16-hour fast was significantly less than in control littermates for both glucose (P = .039) and insulin (P = .008). During euglycemic glucose clamp studies at identical plasma glucose (PG) levels, insulin suppression of hepatic glucose production (HGP) was impaired in malnourished rats, indicating insulin resistance (mean +/- SE HGP: 48 +/- 5 v 32 +/- 10 mumol.kg-1.min-1 for controls, P = .028). Glucose disposal was not significantly different in the two groups. However, after IV glucagon, the increase in HGP was markedly impaired in malnourished rats (P = .0004), with the total amount of glucose produced by the liver over 15 minutes being 1,397 +/- 114 mumol/kg as compared with 2,031 +/- 118 in controls (P = .0047). The impaired response was not due to defective glycogenolysis, because the release of glucose from prelabeled glycogen in response to glucagon injection contributed only 6% to 8% of the overall increase in glucose output from the liver, and was not different in the two groups. Furthermore, liver glycogen stores were virtually exhausted after the 16-hour fast, without glucagon injection. Glucagon receptor affinity and number were not affected by malnutrition. It is concluded that (1) chronic malnutrition is associated with hepatic resistance to both insulin and glucagon, (2) the glucagon resistance is not due to impaired glycogenolysis, and (3) it is mediated by a postreceptor defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adaptation, Physiological; Animals; Blood Glucose; Drug Resistance; Food Deprivation; Glucagon; Glucose Clamp Technique; Glycogen; Homeostasis; Insulin; Insulin Resistance; Liver; Male; Rats; Rats, Sprague-Dawley; Receptors, Glucagon; Time Factors; Weight Gain

The effect of rat pancreastatin on glycogen synthesis and glycolysis rate was studied in insulin-stimulated rat hepatocytes. We have determined the incorporation of [U-14C]glucose into glycogen as a measurement of the rate of glycogen synthesis; and the production of lactate as a measurement of the rate of glycolysis. Rat pancreastatin by itself did not affect either the rate of glycogen synthesis or glycolysis in rat hepatocytes from 6 h fasted rats. However, pancreastatin inhibited about 45% the insulin-stimulated glycogen synthesis whereas it enhanced the rate of glycolysis of insulin-stimulated hepatocytes about 25%. These effects were found to be dependent on pancreastatin concentration from 10(-11) M to 10(-7) M. Maximal effect was achieved at 10(-8) M and the half-maximal effect was observed at 0.3 nM. Pancreastatin decreased the rate of glycogen synthesis in a wide range of insulin concentrations (10(-12) - 10(-8) M). However, the effect on insulin-stimulated glycolysis was only observed at high concentrations of pancreastatin and insulin. These results suggest a role of pancreastatin in the possible mechanisms involved in insulin resistance.

Topics: Animals; Chromogranin A; Dose-Response Relationship, Drug; Glycogen; Glycolysis; Insulin; Insulin Resistance; Liver; Male; Pancreatic Hormones; Rats; Rats, Wistar

We investigated stable cirrhotic patients for muscle glycogen content. Muscle biopsy samples were taken of 14 patients after overnight fasting. Electron microscopy showed normal intracellular distribution of glycogen (n = 8). Muscle glycogen concentration was 16.5 +/- 7.1 gm/kg wet muscle weight (normal range, 10 to 20 gm/kg). Basal, early postabsorptive, exercise-induced and insulin-induced respiratory quotients as well as insulin sensitivity (euglycemic clamp technique, 7.2 pmol insulin/kg body weight/min) and glucose tolerance were assessed. The glucose disposal rate was 23.0 +/- 10.1 mumol/kg/min (mean +/- S.D.), indicating moderate insulin resistance in these patients. We found no association between basal muscle glycogen content and basal or postprandial respiratory quotient, insulin sensitivity, nutritional status or glucose tolerance. However, there was a positive correlation between muscle glycogen content and exercise, as well as insulin-induced respiratory quotient (r = 0.651, p < 0.03 and r = 0.587, p < 0.03, respectively). We conclude that postabsorptive muscle glycogen stores, which are effectively maintained in patients with cirrhosis, are one determinant of exercise-induced and insulin-induced whole body fuel metabolism in these patients.

Topics: Adult; Aged; Basal Metabolism; Calorimetry, Indirect; Carbohydrate Metabolism; Exercise Test; Factor Analysis, Statistical; Female; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Liver Cirrhosis; Male; Middle Aged; Muscles; Nutritional Status; Respiration

Cystic fibrosis (CF) patients demonstrate a spectrum of pancreatic beta-cell abnormalities. Those with no exocrine insufficiency (NEXO) have normal insulin secretion. Exocrine-insufficient CF patients with overt diabetes (EXO-IT) have impaired insulin secretion and fasting hyperglycemia. Exocrine-insufficient patients without diabetes (EXO) have impaired insulin secretion but maintain normoglycemia. We postulated that EXO individuals compensate for insulin deficiency by increasing insulin sensitivity and investigated glucose utilization in CF. To examine hepatic and peripheral insulin sensitivity, euglycemic-hyperinsulinemic clamp studies were performed by using the hot GINF isotope dilution technique. Insulin was sequentially infused at 0.25, 1.0, and 10.0 mU.kg-1.min-1. Glucose-mediated glucose uptake (GMGU) was assessed on another day with hyperglycemic clamp studies, during which insulin and somatostatin were infused to hold insulin-mediated glucose uptake constant between the two clamp studies. Skeletal muscle GLUT4 levels were assessed in EXO and control patients with Western blotting. Three patterns of peripheral and hepatic insulin sensitivity were seen that were related to the degree of pancreatic beta-cell dysfunction. NEXO individuals had normal peripheral and hepatic insulin sensitivity. EXO individuals had enhanced peripheral insulin sensitivity that was not associated with a change in skeletal muscle glucose transporter abundance compared with control patients; paradoxically, EXO subjects demonstrated hepatic insulin resistance. EXO-IT had peripheral and hepatic insulin resistance. GMGU was diminished in both EXO and EXO-IT subjects. The unique combination of increased hepatic glucose production and increased peripheral glucose utilization seen in EXO may be a metabolic adaptation to increased peripheral energy needs.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Blood Glucose; Blotting, Western; Cystic Fibrosis; Female; Glucose; Glucose Clamp Technique; Glucose Transporter Type 4; Glycogen; Humans; Insulin; Insulin Resistance; Islets of Langerhans; Liver; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscles

In rabbit muscle, analyzed by Western blot, the glycogen-bound protein phosphatase-1 (PP-1G) is composed of a 37-kilodalton (kDa) catalytic subunit complexed to a 160-kDa glycogen-binding subunit (G-subunit) responsible for the interaction of PP-1G with glycogen. PP-1G has not been characterized in humans. In the present study, G-subunit was identified in human muscle extracts by Western blot using an antibody raised against a sequence (the phosphoregulatory domain) of the rabbit muscle G-subunit. The human G-subunit was also a 160-kDa protein by Western blot. When the G-subunit content of skeletal muscle was quantitated in 17 Pima Indians with a wide range of insulin sensitivities determined during euglycemic clamps, there was a significant negative correlation (r = -0.55; P = 0.02) between the G-subunit content and in vivo insulin-mediated glucose disposal rates. The results suggest that insulin resistance is associated with an increased content and/or immunoreactivity of G-subunit in human muscle.

Topics: Adult; Animals; Binding Sites; Blood Glucose; Blotting, Western; Female; Glycogen; Humans; Indians, North American; Insulin; Insulin Resistance; Male; Muscles; Phosphoprotein Phosphatases; Protein Phosphatase 1; Rabbits

In different types of mammalian cells, insulin has been shown to promote the release of an inositol phosphate glycan (InsP-glycan) through the hydrolysis of a glycosyl-phosphatidylinositol (glycosyl-PtdIns). This InsP-glycan, which has been demonstrated to be taken up by intact cells, may mediate some of the biological effects of insulin. We have investigated how the insulin resistance expressed in genetically obese (fa/fa) rats affects the glycosyl-PtdIns signaling system in isolated hepatocytes compared to what occurs in hepatocytes isolated from lean (Fa/-) rats. The hepatocyte content of glycosyl-PtdIns was reduced by about 30% in obese rats, with respect to that measured in lean rats (2553 +/- 138 vs. 3334 +/- 115 dpm/mg protein; P < 0.01; n = 5). This reduction was accompanied by a marked blockade of the insulin-mediated glycosyl-PtdIns hydrolysis as well as a decrease (approximately 30%) in the rate of InsP-glycan uptake by the isolated liver cells. Obese Zucker rat hepatocytes also showed a significant decrease in the effects of both insulin and InsP-glycan on the stimulation of glycogen synthesis and the activation of glycogen synthase compared to hepatocytes isolated from lean rats. Our results demonstrate that genetic obesity in Zucker (fa/fa) rats is associated with an impairment of the glycosyl-PtdIns-dependent insulin signaling system.

Topics: Animals; Glycogen; Glycogen Synthase; Glycosylphosphatidylinositols; In Vitro Techniques; Insulin Resistance; Liver; Male; Obesity; Rats

We characterized the mechanisms underlying acute endotoxin-induced alterations in glucose metabolism and determined the extent to which catecholamines mediate these changes. Acute endotoxemia was induced in chronically catheterized awake rats by a bolus injection of lipopolysaccharide (LPS; 1 mg/kg; LD10). Basal glucose turnover (Rt; infusion of [5-3H]glucose), in vivo insulin action on overall glucose utilization (euglycemic clamp), glycolysis, and glycogen synthesis were determined in four groups of rats. These groups received 1) LPS (LPS rats; n = 6), 2) saline (control rats; n = 6), 3) LPS and alpha beta-blockade (alpha beta-blockade and LPS rats; n = 9), or 4) saline and alpha beta-blockade (alpha beta-blockade control rats; n = 9). In the basal state, LPS induced hypotension and transient hyperglycemia. These changes were associated with glycogen depletion in both skeletal muscle and liver, and increased Rt. During hyperinsulinemia, whole body glucose disposal was 37% decreased (105 vs. 166 mumol/kg.min; P < 0.01). This whole body insulin resistance was characterized by decreased glycogen synthesis and glycogen synthase activity, but not by altered whole body glycolysis. alpha beta-Blockade abolished transient hyperglycemia, increased Rt, and accelerated basal liver glycogen depletion (45 vs. 105 mmol/kg dry, LPS and alpha beta-blockade rats vs. LPS rats; P < 0.05), but inhibited muscle glycogenolysis. alpha beta-Blockade did not reverse the insulin resistance induced by endotoxin. These data suggest that catecholamines counteract the LPS-induced increase in basal glucose turnover and stimulate muscle glycogenolysis during acute endotoxemia. These effects might explain the better preservation of hepatic glycogen in the absence than in the presence of alpha beta-blockade and serve as a defense mechanism against hypoglycemia. Catecholamines do not seem to be the immediate causes of insulin resistance during acute endotoxemia.

Topics: Animals; Blood Glucose; Blood Pressure; Catecholamines; Endotoxins; Glycogen; Glycolysis; Insulin Resistance; Lipopolysaccharides; Male; Muscles; Phentolamine; Propranolol; Rats; Rats, Wistar; Salmonella typhimurium

Reduced type 1 protein phosphatase (PP-1) activity in human muscle extracts may contribute to the reduced insulin-stimulated glycogen synthase activity associated with insulin resistance for glucose disposal in humans. Because inactive forms of PP-1 can be activated with trypsin plus Mn2+, these reagents were used to compare the PP-1 activities in skeletal muscle extracts before and after separation into cytosolic and glycogen microsomal (GM) fractions. PP-1 activities were reduced in the GM fraction from insulin-resistant subjects (54 +/- 2 vs. 61 +/- 1, P < 0.01) but, in contrast to our previously published results, were elevated in the extract (33 +/- 6 vs. 18 +/- 3, P < 0.05). Recombination of the cytosol and GM fractions (reconstituted extract) demonstrated that the low extract PP-1 activities could only be regenerated when the GM fraction from insulin-sensitive subjects was recombined with cytosol from either group. The results indicate that the elevated PP-1 activity observed in extracts of insulin-resistant compared with insulin-sensitive subjects is caused by an inhibitor of extract PP-1 activity that sediments with the GM pellet and is more active in the insulin-sensitive subjects.

Topics: Adult; Cytosol; Dithiothreitol; Drug Resistance; Female; Glycogen; Humans; Insulin Resistance; Male; Manganese; Microsomes; Muscles; Osmolar Concentration; Phosphoprotein Phosphatases; Trypsin

The ability of dietary sucrose to induce insulin resistance independent of changes in body weight is controversial. In the present study male rats were fed a high-starch (ST) diet (starch 68% of total kcal) ad libitum for 2 wk and then were fed equicalorically either the ST diet or a high-sucrose (SU) diet (sucrose 68% of total kcal) for 8 wk. Euglycemic, hyperinsulinemic (0, 1.2, 4.1, 8, 15 mU.kg-1.min-1, n = 6-8/group per dose) clamps were then used to establish dose-response relationships for glucose kinetics and metabolism. Body weight (513 +/- 3 g) and composition were similar between groups after the 8-wk dietary period. Glucose infusion rates (GIR; mg.kg-1.min-1) were significantly less in SU (0.9 +/- 5.8 +/- 0.6, 14.8 +/- 1.3, and 18 +/- 1.1) than in ST rats (4.1 +/- 0.9, 12.3 +/- 1.2, 22.6 +/- 1.5, and 25.9 +/- 1.8) at 1.2, 4.1, 8, and 15 mU.kg-1.min-1, respectively. Impaired suppression of endogenous glucose production accounted for 46, 43, 23, and 0% of the reduction in GIR in SU rats at 1.2, 4.1, 8, and 15 mU.kg-1.min-1, respectively. Despite basal hyperinsulinemia (38 +/- 2 microU/ml in SU vs. 26 +/- 2 microU/ml in ST rats), liver phosphoenolpyruvate carboxykinase (PEPCK) activity was 50% higher in SU than in ST rats and remained elevated in SU rats (by 30-40%) at the two lower insulin doses. No skeletal muscle glycogen accumulation occurred in SU rats at any of the insulin doses, and glycogen synthase I activity was significantly lower in SU rats at the two highest insulin doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adipose Tissue; Animals; Blood Glucose; Body Weight; Dietary Carbohydrates; Dose-Response Relationship, Drug; Glucose Clamp Technique; Glycogen; Infusions, Intravenous; Insulin; Insulin Resistance; Liver; Liver Glycogen; Male; Muscles; Organ Size; Rats; Rats, Wistar; Sucrose

Female obese Zucker rats aged 5 wk were randomly assigned to a control diet or one of two experimental diets. Experimental diets contained 6% of energy as pyruvate in the form of calcium-pyruvate (Ca-pyr) or 6% pyruvylglycine (pyr-gly). Diets were pair-fed according to the experimental group with the lowest food consumption. During the 3 wk of dietary treatment, Ca-pyr- and pyr-gly-fed rats gained significantly less weight, had a lower food-conversion efficiency, and maintained a higher resting oxygen consumption (mL.min-1 x kg-0.67) than control rats. Ca-pyr and pyr-gly also lowered the respiratory exchange ratio of the rats resulting in a 90% increase in their lipid oxidation and a 50% decrease in their carbohydrate oxidation. Glucose tolerance, assessed by an oral glucose load, was not different among treatments, but the insulin response of the pyr-gly-fed rats was significantly less than that of the control rats despite elevated plasma triglyceride concentrations in the pyr-gly-fed rats (control, 1.43 +/- 0.16 vs pyr-gly, 3.76 +/- 0.87 mmol/L). These results suggest that pyr-gly, like Ca-pyr, favorably alters the metabolism of obese Zucker rats. In addition, pyr-gly appeared to reduce the insulin resistance that develops spontaneously in obese rats.

Topics: Analysis of Variance; Animals; Blood Glucose; Body Weight; Cholesterol; Energy Metabolism; Female; Glucose Tolerance Test; Glycine; Glycogen; Insulin; Insulin Resistance; Lipids; Obesity; Oxygen Consumption; Pyruvates; Pyruvic Acid; Random Allocation; Rats; Rats, Zucker; Time Factors; Triglycerides

Skeletal muscle is insulin resistant in the obese Zucker rat. Endurance training reduces muscle insulin resistance, but the effects of a single acute exercise session on muscle insulin resistance in the obese Zucker rat are unknown. Therefore, insulin responsiveness of muscle glucose uptake was measured in 15-week-old obese rats either 1, 48, or 72 hours after two hours of intermittent exercise (30:30 min; work:rest). Hindlimbs of sedentary lean (LS) and obese (OS) rats and exercised obese (OE) rats were perfused after a 10-hour fast under both basal (0 mU x ml(-1)) and maximal (20 mU x ml(-1)) insulin concentrations to measure net glucose uptake. Insulin responsiveness of net glucose uptake was significantly reduced in OS compared to LS (8.5 +/- 1.6 vs 15.3 +/- 2.0 micromol x g(-1) x h(-1), respectively). Compared to OS, insulin responsiveness of net glucose uptake was significantly increased by 56% and 80% at 1 hour and 48 hours after acute exercise. However, 72 hours after acute exercise, the increased insulin responsiveness of net glucose uptake was no longer evident. These results indicate that improved responsiveness of muscle glucose uptake persists for at least 48 hours after two hours of acute intermittent exercise in 15-week-old obese Zucker rats.

Topics: Adipose Tissue; Animals; Biological Transport; Blood Glucose; Body Mass Index; Disease Models, Animal; Glucose; Glycogen; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Muscles; Obesity; Oxygen; Perfusion; Physical Conditioning, Animal; Rats; Rats, Zucker; Time Factors

The effects of 17-beta-oestradiol (E2) and progesterone (P) on insulin sensitivity were determined in oophorectomized (OVX) rats by the euglycaemic hyperinsulinaemic clamp technique combined with measurements of insulin-stimulated 2-deoxy-D-glucose (2-DOG) transport and glycogen synthesis in white and red parts of the gastrocnemius, the extensor digitorum longus and soleus muscles as well as in the liver (only glycogen synthesis). OVX was followed by insulin resistance in the clamp measurements. This was paralleled by a decreased insulin-stimulated content of 2-DOG in muscles, an index of glucose transport. Glycogen synthesis in muscle was also decreased, although to less extent. E2, alone or in combination with P, restored this to values of intact controls, while P alone was followed by insulin resistance. Liver glycogen synthesis was also decreased by OVX but this required combination of E2 and P to be fully restored. It was concluded that particularly E2 plays an important role in the maintenance of normal insulin sensitivity while P alone seems to be followed by insulin resistance, both effects apparently mainly by regulation of glucose uptake in muscle. E2 + P may be of importance for maintenance of normal glycogen synthesis in the liver.

Topics: Animals; Blood Glucose; Body Weight; Deoxyglucose; Estradiol; Estrogens; Female; Glycogen; Insulin; Insulin Resistance; Liver; Muscles; Organ Size; Ovariectomy; Progesterone; Rats; Rats, Sprague-Dawley

The mechanism by which glucocorticoids induce insulin resistance was studied in normal rats administered for 2 days with corticosterone then tested by euglycaemic hyperinsulinaemic clamps. Corticosterone administration induced a slight hyperglycaemia, hyperinsulinaemia and increased non-esterified fatty acid levels. It impaired insulin-stimulated total glucose utilization (corticosterone 15.7 +/- 0.7; controls 24.6 +/- 0.8 mg.kg-1 x min-1), as well as residual hepatic glucose production (corticosterone 4.9 +/- 1.0; controls 2.0 +/- 0.7 mg.kg-1 x min-1). During the clamps, insulin did not decrease the elevated non-esterified fatty acid levels in corticosterone-administered rats (corticosterone 1.38 +/- 0.15, controls 0.22 +/- 0.04 mmol/l). Corticosterone administration decreased the in vivo insulin-stimulated glucose utilization index by individual muscles by 62 +/- 6%, and the de novo glycogen synthesis by 78 +/- 2% (n = 8-9 muscles). GLUT4 protein and mRNA levels were either unchanged or slightly increased by corticosterone administration. Inhibition of lipid oxidation by etomoxir prevented corticosterone-induced muscle but not hepatic insulin resistance. In conclusion, glucocorticoid-induced muscle insulin resistance is due to excessive non-esterified fatty acid oxidation, possibly via increased glucose fatty-acid cycle ultimately inhibiting glucose transport, or via decreased glycogen synthesis, or by a direct effect on glucose transporter translocation or activity or both.

Topics: Animals; Blood Glucose; Carnitine O-Palmitoyltransferase; Corticosterone; Epoxy Compounds; Fatty Acids, Nonesterified; Gluconeogenesis; Glucose; Glucose Clamp Technique; Glucose Transporter Type 4; Glycogen; Hypoglycemic Agents; Insulin; Insulin Resistance; Liver; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscles; Rats; Rats, Zucker; RNA, Messenger

1. Stress is associated with a severe, yet reversible, form of insulin resistance. The aim of this study was to quantify the kinetics of insulin action (sensitivity and responsiveness) on intermediary metabolism during post-surgical stress. 2. We studied nine patients 6-8 h after major uncomplicated surgery, and eight healthy subjects matched for age, weight, glucose tolerance and duration of fast. A three-step isoglycaemic insulin clamp was combined with indirect calorimetry, [6-3H]glucose infusion and the forearm technique. 3. The following significant (P < 0.05 or less) abnormalities were found in the patients. Hepatic glucose production was higher at baseline, and less suppressed by insulin. Whole-body glucose disposal was impaired at all insulin doses (by 33-60%). Glucose oxidation was depressed throughout the dose range but its increments in response to insulin were normal. In contrast, non-oxidative glucose disposal was essentially unresponsive. At all insulin levels, forearm glucose extraction was markedly depressed and forearm lactate release was in excess of concurrent glucose uptake, suggesting ongoing glycogenolysis despite insulin. Total lipolysis (plasma free fatty acid and glycerol levels) promptly responded to insulin but remained higher than in the control subjects throughout. In the forearm, even the highest insulin dose could not suppress net free fatty acid and glycerol release. Total lipid oxidation was increased throughout the insulin range, and calculated direct free fatty acid (as opposed to plasma free fatty acid) oxidation was virtually unaffected by insulin. Protein oxidation was slightly (35%) increased, but was suppressed normally in response to insulin. Energy expenditure was 20% higher at baseline, and failed to rise with insulin. Arterial blood pH values were consistently (if slightly) lower, and net forearm proton release was higher, both at baseline and during insulin infusion. 4. Post-surgical insulin resistance is characterized by normal sensitivity but decreased responsiveness of glucose oxidation, lipolysis and plasma free fatty acid oxidation, whereas glycogen synthesis and direct free fatty acid oxidation are virtually unresponsive. For both glucose and lipid metabolism, the insulin resistance is particularly severe in forearm tissues, in which mild metabolic acidosis may play an additional role.

Topics: Blood Glucose; Calorimetry, Indirect; Dose-Response Relationship, Drug; Fatty Acids, Nonesterified; Female; Forearm; Glycogen; Humans; Insulin; Insulin Resistance; Kinetics; Lipid Metabolism; Male; Middle Aged; Oxidation-Reduction; Postoperative Complications; Potassium; Stress, Physiological

Transgenic mice, containing the chimeric gene obtained by linking the promoter-regulatory region of P-enolpyruvate carboxykinase (PEPCK) gene to the bovine growth hormone structural gene (bGH), were used to investigate the long-term effects of bGH on glucose metabolism. Expression of the PEPCK/bGH gene was markedly enhanced by feeding a diet high in protein and inhibited by a high carbohydrate diet. All transgenic mice had normal levels of blood glucose but were hyperinsulinemic, indicating that they were insulin resistant. The glycogen synthase activity ratios in the muscle and liver of transgenic mice were lower than noted for control animals, and remained unchanged in liver after feeding a standard high carbohydrate or a high protein diet. Similar effects were detected in the activity of glycogen phosphorylase, except that a high carbohydrate diet activated this enzyme in the liver. The activation of glycogen phosphorylase in both muscle and liver correlated with the expression of their genes. These animals had a significant content of glycogen and glucose 6-phosphate, which was related to the levels of glucokinase mRNA in the liver. The concentration of fructose 2,6-bisphosphate in the liver of all fed transgenic mice was lower than noted in livers from fed animals. In addition, a decrease in the hepatic expression of the endogenous genes for PEPCK, tyrosine aminotransferase (TAT), and the glucose transporter GLUT-2 was observed and directly correlated with the expression of bGH. Thus, bGH can control glucose metabolism in vivo, at least in part, by modifying the expression of several genes coding for proteins of importance in carbohydrate metabolism. Taken together, these results indicate a state of insulin resistance caused by chronic exposure of the animals to an elevated concentration of bGH.

Topics: Animals; Blood Glucose; Cattle; Dietary Carbohydrates; Dietary Proteins; Gene Expression; Glucokinase; Gluconeogenesis; Glycogen; Glycolysis; Growth Hormone; Insulin Resistance; Liver; Mice; Mice, Transgenic; Muscles; Phosphoenolpyruvate Carboxykinase (GTP); Recombinant Fusion Proteins; RNA, Messenger

Increased routing of glucose through the hexosamine-biosynthetic pathway has been implicated in the development of glucose-induced insulin resistance of glucose transport in cultured adipocytes. Because both glucosamine and glucose enter this pathway as glucosamine-6-phosphate, we examined the effects of preincubation with glucosamine in isolated rat diaphragms and in fibroblasts overexpressing the human insulin receptor (HIR-cells). In muscles, pre-exposure to glucosamine inhibited subsequent basal and, to a greater extent, insulin-stimulated glucose transport in a time- and dose-dependent manner and abolished the stimulation by insulin of glycogen synthesis. Insulin receptor number, activation of the insulin receptor tyrosine kinase in situ and after solubilization, and the total pool of glucose transporters (GLUT4) were unaffected, and glycogen synthase was activated by glucosamine pretreatment. In HIR-cells, which express GLUT1 and not GLUT4, basal and insulin-stimulated glucose transport were unaffected by glucosamine, but glycogen synthesis was markedly inhibited. Insulin-stimulated activation of protein kinases (MAP and S6) was unaffected, and the fractional velocity and apparent total activity of glycogen synthase was increased in glucosamine-treated HIR-cells. In pulse-labeling studies, addition of glucosamine during the chase prolonged processing of insulin proreceptors to receptors and altered the electrophoretic mobility of proreceptors and processed alpha-subunits, consistent with altered glycosylation. Glucosamine-induced insulin resistance of glucose transport appears to be restricted to GLUT4-expressing cells, i.e., skeletal muscle and adipocytes; it may reflect impaired translocation of GLUT4 to the plasmalemma. The glucosamine-induced imbalance in UDP sugars, i.e., increased UDP-N-acetylhexosamines and decreased UDP-glucose, may alter glycosylation of critical proteins and limit the flux of glucose into glycogen.

Topics: Animals; Biological Transport; Fibroblasts; Glucosamine; Glucose; Glucose Transporter Type 4; Glycogen; Glycogen Synthase; In Vitro Techniques; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscles; Rats; Rats, Wistar; Receptor, Insulin

To evaluate the long-held concept that acidic guanidines lack glycemic effects, guanidinoalkanoic acids and the biguanide metformin (positive control) were administered to KKAy mice, a model of noninsulin-dependent diabetes. Two acidic guanidines, 3-guanidinopropionic acid (3-GPA) and guanidinoacetic acid, decreased the plasma glucose level; other compounds were ineffective. 3-GPA was more potent than even metformin. Insulin suppression tests in KKAy mice indicated that improved insulin sensitivity was the mode of action for 3-GPA. Glycemic effects in KKAy mice resulted from increased glucose disposal whereas gluconeogenesis, hepatic glycogen content and intestinal glucose absorption were unchanged. 3-GPA's glycemic effect was corroborated in two other models of noninsulin-dependent diabetes. In ob/ob mice, the compound reduced hyperglycemia, polyuria, glycosuria and hyperinsulinemia. In insulin-resistant rhesus monkeys, it increased the disappearance of i.v. glucose. The glycemic action of 3-GPA required the presence of some circulating insulin as well as hyperglycemia because the compound was ineffective in normoglycemic mice, insulinopenic Chinese hamsters and streptozotocin-diabetic rats. These data indicate that acidic guanidine derivatives can ameliorate hyperglycemia in animal models of noninsulin-dependent diabetes. Because acidic derivatives uniquely lack the propensity of guanidine compounds for inducing lactic acidosis, our finding suggests a new approach for developing improved antidiabetes compounds from this chemical class.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Gluconeogenesis; Glucose; Glycogen; Guanidines; Hyperglycemia; Insulin; Insulin Resistance; Intestinal Absorption; Liver Glycogen; Macaca mulatta; Male; Metformin; Mice; Mice, Inbred C57BL; Mice, Obese; Muscles; Propionates; Structure-Activity Relationship

Diabetes in patients with pancreatic cancer occurs in 70% to 80% of the patients and is characterized by high plasma levels of insulin. In type II diabetes that is not associated with pancreatic cancer, peripheral insulin resistance and impaired muscle glycogen synthesis are major pathogenic factors. We investigated peripheral insulin sensitivity in patients with pancreatic cancer before and after tumor removal. The effects of pancreatic tumor extracts on glycogen synthesis in skeletal muscle in vitro and the tumor content of pancreatic islet hormones were also investigated. Marked peripheral insulin resistance was found in the patients with pancreatic cancer and was more pronounced in the diabetic patients than in the nondiabetic patients. Insulin sensitivity was not correlated with weight loss, tumor size, or bilirubin levels but improved after surgery. Tumor extracts from diabetic patients with pancreatic cancer caused a marked reduction of glycogen synthesis in skeletal muscle in vitro. All tumors contained islet hormones but not in concentrations sufficient to explain the effect on glycogen synthesis. These findings indicate that a diabetogenic factor associated with pancreatic adenocarcinomas could be involved in the development of the profound peripheral insulin resistance and thereby could contribute to the high incidence of diabetes observed in patients with pancreatic cancer.

Topics: Aged; Animals; Carcinoma, Intraductal, Noninfiltrating; Diabetes Complications; Female; Glucose Clamp Technique; Glycogen; Humans; Insulin Resistance; Male; Muscles; Pancreatic Hormones; Pancreatic Neoplasms; Radioimmunoassay; Rats; Rats, Wistar

Amylin and calcitonin gene-related peptide (CGRP) inhibited insulin-stimulated 2-deoxyglucose uptake in L6 myocytes and isolated soleus muscle. Both peptides were maximally active at 10 pM in L6 cells and inhibited insulin action by 40-50%. In soleus muscle amylin and CGRP inhibited insulin-stimulated uptake by 65-85%. Amylin competed with 125I-CGRP for binding to L6 cells but with 100-fold lower potency than CGRP. Occupancy of the CGRP receptor in L6 cells is coupled to adenylyl cyclase. Amylin increased the cellular content of adenosine 3',5'-cyclic monophosphate (cAMP), but consistent with binding, amylin was 100-fold less potent than CGRP. In soleus muscle, 100 nM amylin, which maximally inhibited 2-deoxyglucose uptake, had no effect cAMP content, whereas CGRP at the same concentration increased cAMP by 50%. The effect of CGRP on cAMP levels was completely suppressed by the competitive antagonist, CGRP-(8-37). In contrast, the suppression of insulin-stimulated glycogen synthesis or 2-deoxyglucose uptake by amylin was unaffected by 1 microM CGRP-(8-37). Our results demonstrate that the inhibition of insulin-stimulated glucose transport by amylin is independent of cAMP and may be mediated by a unique receptor that is distinct from the adenylyl cyclase-coupled CGRP receptor.

Topics: Amyloid; Animals; Biological Transport; Calcitonin Gene-Related Peptide; Cell Line; Cyclic AMP; Deoxyglucose; Glycogen; Insulin; Insulin Resistance; Islet Amyloid Polypeptide; Kinetics; Male; Muscles; Peptide Fragments; Rats; Rats, Sprague-Dawley; Receptors, Calcitonin; Receptors, Cell Surface

It was shown that 15-min electrical stimulation of the rat sciatic nerve greatly increases the in vitro measured sensitivity of lactate formation, glucose transport, and glycogen synthesis to insulin, impaired by previous tenotomy. The insulin sensitivity of all these processes was, however, still below that found in the stimulated intact soleus muscle. Extending the stimulation up to 30 min did not cause any further changes in insulin sensitivity either in tenotomized or in intact muscles.

Topics: Achilles Tendon; Animals; Biological Transport; Deoxyglucose; Electric Stimulation; Glycogen; Insulin Resistance; Lactates; Male; Movement; Muscles; Rats; Rats, Wistar

Two insulin mediators, inositol phosphoglycans, were isolated from bovine liver by methods previously developed for rat liver, i.e. chromatography on an AG 1 x 8 ion exchange column and selective elution with HCl at pH 2.0 and 1.3. The pH 2.0 mediator containing D-chiroinositol stimulated pyruvate dehydrogenase phosphatase, whereas the pH 1.3 mediator containing myo-inositol inhibited cAMP-dependent protein kinase. Each mediator was further purified by thin layer and Bio-Gel P4 column chromatography and injected ip into normal fed rats together with [U-14C]glucose. After 2.5 h, diaphragms were removed, and glycogen isolated. Insulin mediators, like insulin, stimulated [U-14C]glucose incorporation into glycogen by 150-160% in a dose-dependent manner in the nanomolar range. Mediators injected iv in the nanomolar range into low dose streptozotocin-diabetic rats decreased plasma glucose 30-45% in 30-60 min, with a return to basal concentrations after 150-180 min. These in vivo insulin-like effects of mediator were observed without changes in serum insulin concentrations. The pH 2.0 mediator was 50-100 times more active (per nmol organic phosphate) than the pH 1.3 mediator in the ip diaphragm glycogenesis assay. Mediator effects on diaphragm were completely blocked by preincubation with an immunopurified inositol phosphoglycan antibody. Both mediators were equally active iv in lowering plasma glucose (per nmol inositol) at concentrations comparable to those of insulin.

Topics: Animals; Blood Glucose; Cattle; Diabetes Mellitus, Experimental; Glucose; Glycogen; Hydrogen-Ion Concentration; Inositol; Insulin; Insulin Resistance; Isomerism; Liver; Male; Muscles; Protein Kinases; Rats; Rats, Sprague-Dawley; Reference Values; Sugar Phosphates

Calcitonin gene-related peptide (CGRP) is a neuropeptide that is released at the neuromuscular junction in response to nerve excitation. To examine the relationship between plasma CGRP concentration and intracellular glucose metabolism in conscious rats, we performed insulin (22 pmol.kg-1.min-1) clamp studies combined with the infusion of 0, 20, 50, 100, 200, and 500 pmol.kg-1.min-1 CGRP (plasma concentrations ranging from 2 x 10(-11) to 5 x 10(-9) M). CGRP antagonized insulin's suppression of hepatic glucose production at plasma concentrations (approximately 10(-10) M) that are only two- to fivefold its basal portal concentration. Insulin-mediated glucose disposal was decreased by 20-32% when CGRP was infused at 50 pmol.kg-1.min-1 (plasma concentration 3 x 10(-10) M) or more. The impairment in insulin-stimulated glycogen synthesis in skeletal muscle accounted for all of the CGRP-induced decrease in glucose disposal, while whole body glycolysis was increased despite the reduction in total glucose uptake. The muscle glucose 6-phosphate concentration progressively increased during the CGRP infusions. CGRP inhibited insulin-stimulated glycogen synthase in skeletal muscle with a 50% effective dose of 1.9 +/- 0.36 x 10(-10) M. This effect on glycogen synthase was due to a reduction in enzyme affinity for UDP-glucose, with no changes in the maximal velocity. In vitro CGRP stimulated both hepatic and skeletal muscle adenylate cyclase in a dose-dependent manner. These data suggest that 1) CGRP is a potent antagonist of insulin at the level of muscle glycogen synthesis and hepatic glucose production; 2) inhibition of glycogen synthase is its major biochemical action in skeletal muscle; and 3) these effects are present at concentrations of the peptide that may be in the physiological range for portal vein and skeletal muscle. These data underscore the potential role of CGRP in the physiological modulation of intracellular glucose metabolism.

Topics: Adenylyl Cyclases; Animals; Calcitonin Gene-Related Peptide; Catecholamines; Consciousness; Glucose; Glycogen; Glycogen Synthase; Glycolysis; Insulin; Insulin Resistance; Liver; Male; Muscles; Phosphorylases; Rats; Rats, Sprague-Dawley

An inositol-phosphate glycan (InsP glycan), which is the polar head group of an insulin-sensitive glycosyl-phosphatidylinositol (glycosyl-PtdIns), has been reported to mimic some insulin actions when added to different types of cells. In connection with this, a specific, time-dependent and energy-dependent transport system for this InsP glycan has been identified in isolated rat hepatocytes [Alvarez, J. F., Sánchez-Arias, J. A., Guadaño, A., Estevez, F., Varela, I., Felíu, J. E. & Mato, J.M. (1991) Biochem. J. 274, 369-374]. Here we have investigated the glycosyl-PtdIns-dependent insulin-signalling system in hepatocytes isolated from either 3-month-old or 24-month-old rats. Aging reduced the stimulatory effect of insulin on [U-14C]glucose incorporation into glycogen, caused a significant decrease in basal glycosyl-PtdIns levels and blocked the insulin-mediated hydrolysis of this lipid. In 24-month-old rats, we also observed a diminution in the rate of hepatocyte InsP-glycan uptake and a marked reduction of the stimulatory effect of this compound on glycogen synthesis. These results support the hypothesis that insulin resistance associated with aging is accompanied by an impairment of the glycosyl-PtdIns-dependent cellular signalling system.

Topics: Aging; Animals; Glucose; Glycogen; Glycosylphosphatidylinositols; Insulin; Insulin Resistance; Liver; Male; Rats; Rats, Wistar; Signal Transduction

It is not generally known whether impaired stimulation of muscle glucose metabolism in insulin-resistant states is specific to insulin stimulation. Our aim was to examine whether glucose uptake responded normally to exercise and postexercise recovery in insulin-resistant high-fat-fed (HFF) rats. Three-week HFF or Chow-fed [control (Con)] adult rats were studied 5 days after cannulation. Before, during, or immediately after (recovery) 50 min of treadmill exercise, bolus 2-deoxy-[3H]glucose and [14C]glucose were administered to estimate muscle glucose uptake (R'g) and glycogen incorporation rates. Mean exercise and recovery plasma glucose levels were similar in HFF and Con rats. In hindlimb muscles sampled, exercise and recovery R'g were similar in HFF and Con (e.g., red quadriceps exercise 104 +/- 13 vs. 113 +/- 8, recovery 45.3 +/- 3.9 vs. 47.7 +/- 4.5 mumol.100 g-1.min-1, respectively). Moreover, muscle glucose transporter (GLUT-4) content was not reduced in HFF rats. Glycogen resynthesis accounted almost entirely for R'g during recovery and was equivalent between groups. We conclude that impaired muscle glucose uptake and glycogen synthesis in HFF rats are characteristic of insulin but not of exercise or postexercise stimulation.

Topics: Analysis of Variance; Animals; Blood Glucose; Glucose; Glucose Clamp Technique; Glycogen; Insulin; Insulin Resistance; Male; Motor Activity; Muscles; Physical Exertion; Rats; Rats, Wistar

Reduction of physical activity due to disease or environmental restraints, such as total bed rest or exposure to spaceflight, leads to atrophy of skeletal muscle and is frequently accompanied by alterations in food intake and the concentration of metabolic regulatory hormones such as insulin. Hindlimb suspension of laboratory rats, as a model for microgravity, also shows marked atrophy of gravity dependent muscles along with a reduced gain in body weight. Suspended rats exhibit enhanced sensitivity to insulin-induced glucose uptake when compared with normal control rats and resistance to insulin action when compared with control rats matched similarly for reduced body weight gain. These changes are accompanied by decreased insulin binding and tyrosine kinase activity in soleus but not plantaris muscle, unchanged glucose uptake by perfused hindlimb and decreased sensitivity but not responsiveness to insulin-induced suppression of net proteolysis in hindlimb skeletal muscle. These findings suggest that loss of insulin sensitivity during muscle atrophy is associated with decreased insulin binding and tyrosine kinase activity in atrophied soleus muscle along with decreased sensitivity to the effects of insulin on suppressing net protein breakdown but not on enhancing glucose uptake by perfused hindlimb.

Topics: Animals; Body Weight; Glucose; Glycogen; Hindlimb; Immobilization; Insulin; Insulin Resistance; Liver; Liver Glycogen; Male; Muscle, Skeletal; Muscular Atrophy; Protein-Tyrosine Kinases; Rats; Rats, Sprague-Dawley; Receptor, Insulin; Weightlessness Simulation

The circadian rhythm of glycogen metabolism in liver and skeletal muscle was studied in lean and gold thioglucose (GTG) induced-obese mice. The active forms of glycogen synthase (GSI) and phosphorylase (GPa) and the total activity of these enzymes were measured every three hours over a 24 h period in mice fed ad libitum. Hepatic and muscle glycogen content displayed a marked diurnal rhythm that was similar in lean and obese mice. In skeletal muscle the glycogen content, GSI and GPa were not significantly different in lean and obese animals over the 24 h period. The activities of muscle GSI and GPa were constant in both groups despite the diurnal variation in the muscle glycogen content. The absence of an increase in the glycogen content of skeletal muscle despite the pronounced hyperinsulinemia and hyperglycemia in the obese mice, may indicate the degree of insulin resistance in this tissue or the maximal capacity of muscle tissue to store glycogen. In liver, glycogen concentration and total glycogen storage were higher in obese mice. Unlike muscle, both hepatic GSI and GPa underwent significant changes in activity over the 24 h period. Hepatic GSI was lower and GPa was higher in obese mice. The circadian rhythm in enzyme activities was independent of both blood glucose and insulin levels. The total glycogen storage and the activities of total phosphorylase and GPa were significantly increased in the liver from GTG obese mice over a 24 h period and could be implicated in the development of insulin resistance and glucose intolerance in this model of obesity.

Topics: Animals; Aurothioglucose; Blood Glucose; Circadian Rhythm; Eating; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Liver; Liver Glycogen; Male; Mice; Mice, Inbred CBA; Muscles; Obesity; Organ Size; Phosphorylases

In order to examine the effects of testosterone (T) on insulin sensitivity, male rats were castrated or sham-operated, and exposed to low or high doses of T to substitute normal or to produce high serum T concentrations. Insulin sensitivity was followed by euglycaemic, hyperinsulinaemic glucose clamp measurements. An index of insulin-stimulated glucose transport was obtained in the white gastrocnemius (WG), extensor digitorum longus (EDL), red gastrocnemius (RG) and soleus (SOL) muscles after a bolus dose of [2-3H]deoxyglucose (2-DOG) when steady state was obtained in the clamp measurements. Glycogen synthesis was followed similarly with [U-14C]glucose as a labelled precursor after isolation of glycogen in the muscles mentioned, and in the liver. Castration and high T were followed by a marked insulin resistance in the clamp measurements. This was paralleled by a diminished insulin stimulation of glucose incorporation into glycogen down to about 50% of control values, apparently equally pronounced in all muscles but not found in liver glycogen synthesis. 2-DOG uptake was diminished by castration in the WG and RG muscles but was unaffected by high doses of T. Substitution of castrated rats with a low dose of T, restoring their serum T concentrations to the normal range, completely abolished these perturbations of insulin sensitivity. It is concluded that T is an important regulator of muscular insulin sensitivity, which seems to be highest in a 'window' of normal serum T concentrations.

Topics: Animals; Corticosterone; Deoxyglucose; Glucose; Glycogen; Insulin Resistance; Kinetics; Male; Muscles; Orchiectomy; Rats; Rats, Sprague-Dawley; Testis; Testosterone

To examine the mechanisms of hyperglycemia-induced insulin resistance, eight insulin-dependent (type I) diabetic men were studied twice, after 24 h of hyperglycemia (mean blood glucose 20.0 +/- 0.3 mM, i.v. glucose) and after 24 h of normoglycemia (7.1 +/- 0.4 mM, saline) while receiving identical diets and insulin doses. Whole-body and forearm glucose uptake were determined during a 300-min insulin infusion (serum free insulin 359 +/- 22 and 373 +/- 29 pM, after hyper- and normoglycemia, respectively). Muscle biopsies were taken before and at the end of the 300-min insulin infusion. Plasma glucose levels were maintained constant during the 300-min period by keeping glucose for 150 min at 16.7 +/- 0.1 mM after 24-h hyperglycemia and increasing it to 16.5 +/- 0.1 mM after normoglycemia and by allowing it thereafter to decrease in both studies to normoglycemia. During the normoglycemic period (240-300 min), total glucose uptake (25.0 +/- 2.8 vs. 33.8 +/- 3.9 mumol.kg-1 body wt.min-1, P less than 0.05) was 26% lower, forearm glucose uptake (11 +/- 4 vs. 18 +/- 3 mumol.kg-1 forearm.min-1, P less than 0.05) was 35% lower, and nonoxidative glucose disposal (8.9 +/- 2.2 vs. 19.4 +/- 3.3 mumol.kg-1 body wt-1min-1, P less than 0.01) was 54% lower after 24 h of hyper- and normoglycemia, respectively. Glucose oxidation rates were similar. Basal muscle glycogen content was similar after 24 h of hyperglycemia (234 +/- 23 mmol/kg dry muscle) and normoglycemia (238 +/- 22 mmol/kg dry muscle). Insulin increased muscle glycogen to 273 +/- 22 mmol/kg dry muscle after 24 h of hyperglycemia and to 296 +/- 33 mmol/kg dry muscle after normoglycemia (P less than 0.05 vs. 0 min for both). Muscle ATP, free glucose, glucose-6-phosphate, and fructose-6-phosphate concentrations were similar after both 24-h treatment periods and did not change in response to insulin. We conclude that a marked decrease in whole-body, muscle, and nonoxidative glucose disposal can be induced by hyperglycemia alone.

Topics: Adenosine Triphosphate; Adult; Biopsy; Blood Glucose; Circadian Rhythm; Diabetes Mellitus, Type 1; Energy Metabolism; Fatty Acids, Nonesterified; Fructosephosphates; Glucose-6-Phosphate; Glucosephosphates; Glycogen; Growth Hormone; Humans; Hydrocortisone; Hyperglycemia; Insulin; Insulin Resistance; Lactates; Male; Muscles; Osmolar Concentration; Oxidation-Reduction; Potassium; Serum Albumin

The effects of cortisol on insulin sensitivity were examined in rats with the euglycaemic, hyperinsulinaemic clamp technique. Uptake of 2-deoxyglucose and incorporation of glucose into glycogen was followed in the white gastrocnemius, extensor digitorum longus, red gastrocnemius and soleus muscles as well as the liver (only glycogen synthesis). Maximal velocity and fractional velocity of the insulin-sensitive part of glycogen synthase (FV %) was measured in the muscles, as well as muscle fibre composition and capillary density. After 24 h exposure to cortisol, insulin sensitivity was diminished in the clamp measurements. This was paralleled by a decrease in glycogen synthesis in the most insulin-sensitive red gastrocnemius and Soleus muscles, but not in the white gastrocnemius or extensor digitorum longus muscles or the liver, and no effect was seen on 2-deoxyglucose uptake in muscles. FV % was markedly inhibited in all muscles. After 48 h exposure to cortisol, glycogen synthesis was markedly inhibited in all muscles, and 2-deoxyglucose uptake in all except the least insulin-sensitive muscle, WG. No changes in muscle morphology were found. These results suggest that the insulin resistance caused by cortisol is elicited in a stepwise manner, starting with an inhibition in the glycogen synthesis system in insulin-sensitive muscles, later including all muscles as well as 2-deoxyglucose uptake. This occurs without changes in morphology.

Topics: Animals; Biological Transport, Active; Deoxyglucose; Female; Glycogen; Glycogen Synthase; Hydrocortisone; Insulin Resistance; Muscles; Rats; Rats, Inbred Strains

Insulin action was studied in rats with CCl4/phenobarbital-induced cirrhosis of the liver using the euglycemic hyperinsulinemic clamp technique coupled with isotopic measurement of individual tissue glucose uptake, glycogen formation, and lipogenesis. In cirrhotic rats, dose response curves showed a reduction of insulin-stimulated total body glucose disposal of about 30%. Insulin action on tissue glucose uptake and initial phosphorylation (assessed with [3H]2-deoxyglucose) were unchanged; however, incorporation of [14C]glucose into lipids and particularly into glycogen was reduced substantially (being most pronounced in skeletal muscle and diaphragm) at maximally as well as half-maximally effective serum insulin concentrations during euglycemic clamping. At identical IV insulin infusion rates, steady-state serum insulin concentrations were elevated up to fourfold in cirrhotic animals. Antilipolytic action of insulin was unaltered. These data suggest that the principal metabolic pathway affected in insulin resistance of rats with experimental cirrhosis appeared to be insulin-stimulated glycogen formation in muscle tissues.

Topics: Adipose Tissue; Animals; Carbon Tetrachloride; Deoxyglucose; Epididymis; Glucose; Glucose Clamp Technique; Glycogen; Insulin; Insulin Resistance; Lipids; Lipolysis; Liver Cirrhosis, Experimental; Male; Rats; Rats, Inbred Strains

The experimental evidence supporting a direct role for hyperinsulinemia as a cause of insulin resistance remains equivocal. Amylin, an islet beta-cell peptide cosecreted with insulin in response to nutrient stimuli, causes insulin resistance when infused into intact animals or applied to isolated skeletal muscles. We compared measures of amylin and insulin gene expression between control and genetically obese, insulin-resistant Lister Albany/NIH-(LA/N-cp) rats. Pancreatic amylin messenger RNA levels were increased 7.8 +/- 0.7-fold (mean +/- SEM), and plasma amylin-like immunoreactive material was increased 10.9 +/- 1.1-fold (LA/N-lean, 14 +/- 4 pM; LA/N-cp, 153 +/- 16 pM; p less than 0.0001) in obese rats. Pancreatic insulin I mRNA levels were increased 7.4 +/- 0.5-fold, and plasma insulin levels 20.0 +/- 5.0-fold, in these rats (LA/N-lean, 308 +/- 84 pM; LA/N-cp 6,120 +/- 1,540 pM; p less than 0.0001). The EC50 for insulin-stimulated incorporation of glucose into glycogen was about fourfold higher in muscles isolated from obese rats. The present results, coupled with previous observations, support the hypothesis that hyperamylinemia, rather than hyperinsulinemia per se, could have directly caused the insulin resistance in the obese LA/N-cp rats. Hyperamylinemia needs to be considered in future experimental studies probing the relation between hyperinsulinemia and insulin resistance.

Topics: Amyloid; Animals; Blood Glucose; Glucose Tolerance Test; Glycogen; Hyperinsulinism; Insulin; Insulin Resistance; Islet Amyloid Polypeptide; Muscles; Obesity; Rats; Rats, Inbred Strains; RNA, Messenger

The effect of okadaic acid, an inhibitor of protein phosphatases-1 and -2A, was studied on glucose transport and metabolism in soleus muscles isolated from lean and insulin-resistant obese mice. In muscles from lean mice, the uptake of 2-deoxyglucose, an index of glucose transport and phosphorylation, was increased by okadaic acid in a concentration-dependent manner. At 5 microM, okadaic acid was as efficient as a maximally effective insulin concentration. Glucose metabolism (glycolysis and glycogen synthesis) was also measured. Whereas glycolysis was stimulated by okadaic acid, glycogen synthesis was unchanged. When okadaic acid and insulin were added together in the incubation medium, the rates of glucose transport, glycolysis, and glycogen synthesis were similar to those obtained with insulin alone, whether maximal or submaximal insulin concentrations were used. Furthermore, okadaic acid did not activate the kinase activity of the insulin receptor studied in an acellular system or in intact muscles. These results indicate that a step in the insulin-induced stimulation of muscle glucose transport involves a serine/threonine phosphorylation event that is regulated by protein phosphatases-1 and/or -2A. In muscles of insulin-resistant obese mice, the absolute values of deoxyglucose uptake stimulated by okadaic acid were lower than in muscles from lean mice. However, the okadaic acid effect, expressed as a fold stimulation, was normal. These observations suggest that in the insulin-resistant state linked to obesity, the serine/threonine phosphorylation event is likely occurring normally, but a defect at the level of the glucose transporter itself would prevent a normal response to insulin or okadaic acid.

Topics: Animals; Biological Transport; Carrier Proteins; Ethers, Cyclic; Glucose; Glycogen; Glycolysis; Insulin Resistance; Intracellular Signaling Peptides and Proteins; Mice; Muscle Proteins; Muscles; Obesity; Okadaic Acid; Phosphoprotein Phosphatases; Phosphorylation; Protein-Tyrosine Kinases; Proteins; Receptor, Insulin

Exercise training reduces the muscle insulin resistance of the obese Zucker rat. The purpose of the present study was to determine whether the magnitude of this training response is exercise intensity specific. Obese Zucker rats were randomly divided into sedentary (SED), low-intensity (LI), and high-intensity (HI) exercise groups. For the LI rats, exercise training consisted of running on a rodent treadmill at 18 m/min up an 8% grade for 90 min. Rats in the HI group ran at 24 m/min up an 8% grade for four 17-min bouts with 3 min between bouts. Both exercise groups performed the same amount of work and trained 5 days/wk for 7 wk. To evaluate muscle insulin resistance, rat hindlimbs were perfused for 30 min with perfusate containing 6 mM glucose (0.15 mu Ci of D-[14C(U)] glucose/ml) and either a maximal (10.0 mU/ml) or a submaximal (0.50 mU/ml) insulin concentration. Perfusions were performed 48-56 h after the last exercise bout and a 12-h fast. In the presence of 0.5 mU/ml insulin, the rate of muscle glucose uptake was found to be significantly faster for the HI (9.56 +/- 0.66 mumol.h-1.g-1) than for the LI (7.72 +/- 0.65 mumol.h-1.g-1) and SED (6.64 +/- 0.44 mumol.h-1.g-1) rats. The difference in glucose uptake between the LI and SED rats was not significant. In the presence of 10.0 mU/ml insulin, the rate of glucose uptake was significantly faster for the HI (16.43 +/- 1.02 mumol.h-1.g-1) than for the LI rats (13.76 +/- 0.84 mumol.h-1.g-1) and significantly faster for the LI than for the SED rats (11.02 +/- 0.35 mumol.h-1.g-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Biological Transport, Active; Female; Glucose; Glycogen; Insulin Resistance; Muscles; Obesity; Physical Conditioning, Animal; Physical Exertion; Rats; Rats, Zucker

We examined the in vivo mechanisms of amylin-induced resistance in concious rats (n = 18). During 180-min euglycemic insulin-clamp (21.5 pmol.kg-1.min-1) studies, amylin (50, 200, or 500 pmol.kg-1.min-1; plasma concentration from 3 x 10(-10) to 9 x 10(-9) M) infusion determined a 19-27% reduction in glucose uptake (117.8 +/- 7.0 vs. 145.8 +/- 11.0, 107.1 +/- 9.2 vs. 145.1 +/- 6.7, and 105.0 +/- 7.2 vs. 144.4 +/- 7.0 mumol.kg-1.min-1 at 50, 200, or 500 pmol.kg-1.min-1, respectively, P less than 0.01) versus insulin alone, whereas 10-pmol.kg-1.min-1 amylin infusion (plasma concn 5 x 10(-11) M) failed to affect insulin-mediated glucose disposal. After amylin infusion, the contribution of whole-body glycolysis to overall glucose disposal increased from 43-48 to 62-79%, whereas muscle glycogen synthesis decreased significantly at all peptide concentrations greater than 3 x 10(-10) M, completely accounting for the decrease in glucose uptake. Skeletal muscle glucose-6-phosphate concentration rose from 0.219 +/- 0.038 mumol/g (insulin alone) to 0.350 +/- 0.018, 0.440 +/- 0.020, and 0.505 +/- 0.035 mumol/g (insulin plus amylin at 50, 200, or 500 pmol.kg-1.min-1, P less than 0.01). Suppression of hepatic glucose production by insulin was unaffected by a 50-pmol.kg-1.min-1 amylin infusion (18.5 +/- 4.3 vs. 21.7 +/- 2.9 mumol.kg-1.min-1), whereas it was slightly but significantly impaired by amylin infusion at 200 pmol.kg-1.min-1 (17.8 +/- 3.9 vs. 24.7 +/- 4.5 mumol.kg-1.min-1, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Amyloid; Animals; Blood Glucose; Glycogen; Insulin; Insulin Infusion Systems; Insulin Resistance; Islet Amyloid Polypeptide; Liver; Male; Muscles; Rats; Rats, Inbred Strains; Reference Values

Topics: Glucose; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Kidney Failure, Chronic; Liver; Receptor, Insulin; Renal Dialysis

Topics: Adrenocortical Hyperfunction; Animals; Cushing Syndrome; Glucocorticoids; Gluconeogenesis; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Insulin Secretion; Liver; Receptor, Insulin

1. The insulin-like effects of orthovanadate (10 mM) and peroxides of vanadate (peroxovanadates, at 1 mM) on rates of lactate formation, glucose oxidation and glycogen synthesis were measured in incubated soleus-muscle preparations isolated from non-obese Wistar rats and lean (fa/?) or insulin-resistant obese Zucker (fa/fa) rats. 2. The stimulation of the rates of lactate formation and glucose oxidation by either orthovanadate or peroxovanadates was of similar magnitude to the stimulation by a maximally effective concentration of insulin (1000 microunits/ml). 3. Peroxovanadates, but not orthovanadate, maximally stimulated the rate of glycogen synthesis in incubated soleus muscles isolated from Wistar rats. 4. When soleus-muscle preparations were incubated in the presence of both insulin (1000 microunits/ml) and peroxovanadates (1 mM), this did not result in a synergistic increase in the rate of total glucose utilization as compared with either agent alone. 5. Soleus muscles isolated from obese (fa/fa) Zucker rats exhibited a decrease in response to a physiologically relevant concentration of insulin (100 microunits/ml). Peroxovanadates, at 1 mM, maximally stimulated the rate of glycogen synthesis in soleus muscles isolated from obese (fa/fa) Zucker rats. 6. The findings indicate that peroxovanadates are useful and important agents for investigating the mechanism of action of insulin in skeletal muscle.

Topics: Animals; Glucose; Glycogen; Glycolysis; In Vitro Techniques; Insulin; Insulin Resistance; Lactates; Male; Muscles; Obesity; Rats; Rats, Inbred Strains; Rats, Zucker; Vanadates

This study examines the effects of a relatively selective alpha 2-adrenoceptor antagonist, 8-(L-piperazinyl)imado-[1,2-alpha] pyrazine (compound A), and the preferential alpha 2-agonist clonidine on blood glucose, glucose tolerance, and plasma insulin levels in the C57BL/6J ob/ob mouse and its lean littermate. While clonidine raised blood glucose levels and impaired glucose tolerance, oral administration of compound A resulted in decreased blood glucose levels, as well as improved glucose tolerance in ob/ob mice. Insulin levels in ob/ob mice treated with clonidine were significantly reduced, while compound A raised insulin levels threefold and blocked the effects of clonidine when co-administered to the same animals. Clonidine-induced hyperglycemia in lean littermates was not accompanied by a decrease in insulin levels, while a small but significant increase in insulin levels was observed by compound A administration. Glycogen synthesis in diaphragm of ob/ob mice was enhanced after oral administration of compound A and was accompanied by an increase in plasma insulin levels. Concomitant treatment with a potent somatostatin analog to inhibit insulin release blocked the effects of the alpha 2-adrenoceptor antagonist, compound A. These observations suggest that the alpha 2-antagonist studied, increased plasma insulin levels with an accompanying reduction in blood glucose and an improvement in glucose tolerance in a genetic model of insulin resistance. Differential sensitivity to alpha 2-agonist in these genetically obese mice, ob/ob, was demonstrated by decreased insulin levels due to clonidine administration.

Topics: Administration, Oral; Adrenergic alpha-Antagonists; Animals; Blood Glucose; Clonidine; Diaphragm; Glucose Tolerance Test; Glycogen; Insulin; Insulin Resistance; Male; Mice; Mice, Obese; Piperazines; Pyrazines; Somatostatin

We searched for metabolic crossover points in muscle glucose metabolite profiles during maintenance of matched glucose fluxes across forearm muscle in insulin-resistant type I (insulin-dependent) diabetic patients and nondiabetic subjects. To classify subjects as insulin sensitive or insulin resistant, whole-body and forearm glucose disposal, oxidative and nonoxidative glucose disposal (indirect calorimetry), and glycogen synthesis (muscle glycogen content in needle biopsies) were measured under euglycemic conditions at two insulin concentrations. Whole-body and forearm muscle glucose disposal were significantly reduced in diabetic patients compared with control subjects. The reduction in total glucose disposal was due to similar relative reductions in oxidative and nonoxidative glucose disposal, pointing toward rate limitation early in glucose metabolism. The defect in nonoxidative glucose disposal was at least partly due to a defect in muscle glycogen synthesis, because muscle glycogen content failed to increase in response to an increase in the plasma insulin concentration in the diabetic patients. The most-insulin-resistant type 1 diabetic patients were restudied under conditions where, by glucose mass action, whole-body glucose disposal was forced to be similar to that in the control subjects. Matching glucose fluxes in the two groups resulted in similar rates of forearm and whole-body oxidative and nonoxidative glucose disposal and muscle glycogen synthesis, but it did not result in accumulation of free intracellular glucose, glucose-6-phosphate, glucose-1-phosphate, fructose-6-phosphate, or lactate in muscle. These data imply that the rate-limiting defect for glucose disposal in skeletal muscle of type I diabetic patients is at the level of glucose transport.

Topics: Adult; Biological Transport; Diabetes Mellitus, Type 1; Glucose; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Resistance; Metabolic Clearance Rate; Muscles; Oxidation-Reduction

Diets high in saturated fat and simple carbohydrate result in an insulin-resistant state, while training increases insulin sensitivity. Insulin resistance was induced by feeding a high-fat, high-sucrose (HFS) diet to 4-week-old female Sprague-Dawley rats. A control diet (low-fat, complex-carbohydrate) was fed to another group for comparison. During the 4-week dietary treatment, half of each group was trained by treadmill running (2 h day-1, 6 days week-1m 30 m min-1, 0% grade). At the end of this 4-week experimental period, hindquarter perfusions were performed at either basal (0) or maximal (100 nM) insulin concentrations to determine glucose uptake, glycogen synthesis, total glycogen content and the activity of several enzymes. Insulin (100 nM) significantly increased glucose uptake and glycogen synthesis in all four groups (CON-UN, CON-TR, HFS-UN, HFS-TR, where CON, UN and TR refer to control, untrained and trained respectively). HFS feeding significantly decreased (P less than 0.002) glucose uptake (mumol g-1 h-1) with maximal insulin stimulation, while training significantly increased uptake (P less than 0.01) at both insulin concentrations. Glycogen synthesis was also increased by training (P less than 0.05) at both insulin concentrations, but accounted for only 25-28% of the glucose uptake. Although training improved the insulin resistance caused by the HFS diet, glucose uptake in the HFS-TR group was still significantly lower than the CON-TR group. Changes in glycogen synthesis are not great enough to account for the decrease or increase in glucose uptake found in the HFS-fed or trained animals.

Topics: Animals; Body Weight; Dietary Carbohydrates; Dietary Fats; Dose-Response Relationship, Drug; Female; Glucose; Glycogen; Hexokinase; Insulin; Insulin Resistance; Phosphofructokinase-1; Physical Conditioning, Animal; Rats; Rats, Inbred Strains

Because skeletal muscle plays a major role in glucose disposal, it may be the primary site of insulin resistance in non-insulin-dependent diabetes mellitus (NIDDM). Rates of glycogen synthesis (GS), glucose utilization via glycolysis, glycolytic utilization (GU), and glucose transport (GT) were studied in epitrochlearis muscles (EMs) obtained from 10-wk-old nonfasted Sprague-Dawley rats in which NIDDM was neonatally induced with streptozocin. Plasma glucose in NIDDM rats was elevated (P less than 0.001), whereas plasma insulin was similar in NIDDM and control rats. No differences in muscle weight, protein, glycogen, ATP, phosphocreatine, lactate, lactate-pyruvate ratios, or glucose-6-phosphate were noted in EMs of control and NIDDM rats. EMs were incubated in medium containing 5.6 or 11.2 mM glucose with tracer D-[5-3H]glucose and insulin from 0 to 7.18 x 10(-7) M for 1 or 2 h, and GS, GT, and GU were evaluated. Similar rates of basal (non-insulin-mediated) and insulin-stimulated GS, GU, and GT were observed in EMs of NIDDM and control rats incubated in 5.6 mM glucose for 2 h. Insulin dose-response curves revealed similar sensitivities and responsiveness. Increasing glucose concentration (from 5.6 to 11.2 mM) induced significant increases in basal rates of GS, GU, and GT in EMs of control but not NIDDM rats. Insulin dose-response curves for GS and GT revealed decreased sensitivity and no change in responsiveness in EMs of control and NIDDM rats, even though GU of EMs of NIDDM rats was significantly lower at basal and all other insulin concentrations. These data revealed that both insulin resistance and glucose resistance contribute to the impaired glucose metabolism in EMs of the NIDDM rat.

Topics: Adenosine Triphosphate; Animals; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Glucose; Glucosephosphates; Glycogen; Humerus; Insulin; Insulin Resistance; Lactates; Lactic Acid; Muscles; Organ Size; Phosphocreatine; Proteins; Pyruvates; Pyruvic Acid; Rats; Rats, Inbred Strains

The ability of the biguanide hypoglycemic agent metformin to improve the acute effects of insulin on glucose and/or lipid metabolism was investigated in both insulin-responsive and insulin-resistant cultured rat hepatocytes: (1) metformin (20 micrograms/mL, 16 hours) increased the insulin-dependent stimulation of glycogen and lipid synthesis through an exclusive enhancement of the responsiveness without modification of the cell sensitivity to the hormone; (2) metformin neither altered basal glycogenesis from [U-14C]glucose and basal lipogenesis from [1-14C]acetate nor insulin binding. These results indicate the ability of this drug to selectively potentiate the acute action of insulin at a postreceptor step in normal liver cells. A prolonged incubation with insulin (16 hours, 5 x 10(-7) mol/L) led the hepatocytes to a state of resistance evidenced by a 50% decrease in their maximal responsiveness and sensitivity to a subsequent acute stimulation by the hormone, as assessed on lipogenesis. Addition of metformin (20 micrograms/mL) during the overnight incubation of hepatocytes with insulin prevented the decrease in cell responsiveness and sensitivity to the hormone for the stimulation of lipogenesis, thus showing that metformin was able to hamper the development of the resistant state to the hormone in this pathway. These results strongly suggest that metformin improves type 2 diabetes through an effect at the hepatic level on both insulin action and insulin-induced resistance.

Topics: Animals; Cells, Cultured; Dose-Response Relationship, Drug; Drug Synergism; Female; Glycogen; Insulin; Insulin Resistance; Lipid Metabolism; Liver; Metformin; Rats; Rats, Inbred Strains; Receptor, Insulin

Intact or oophorectomized (OVX) female rats were given moderate doses of testosterone for 12 wk. Insulin-stimulated glucose transport with submaximal insulin concentrations was studied with the euglycemic clamp technique. Glycogen synthesis and 2-deoxy-D-glucose uptake were measured during the clamp in the extensor digitorum longus, white and red portions of the gastrocnemius, and in the soleus muscles by tracer technique. Testosterone treatment resulted in elevations of circulating testosterone, increased plasma insulin concentrations, and a marked decrease in insulin-stimulated glucose transport. In control animals, glycogen synthesis and 2-deoxy-D-glucose transport increased with increasing concentrations of type 1 fibers. Testosterone inhibited glycogen synthesis and 2-deoxy-D-glucose transport to approximately 50% in all muscles except 2-deoxy-D-glucose transport in intact rats. Glycogen synthesis in the liver was not affected. Testosterone administration also resulted in changes in muscle morphology. The relative number of type 1 fibers decreased, whereas type 2 fibers increased. This was most pronounced in red muscles. There was also a decrease in capillary density after testosterone treatment. It was concluded that testosterone administered to female rats is followed by marked insulin resistance. This is correlated to alterations in muscle morphology with fewer type 1 fibers and a lower degree of capillarization, which are both known to be characteristics of insulin-insensitive muscles.

Topics: Animals; Capillaries; Female; Glucose; Glucose Clamp Technique; Glycogen; Insulin; Insulin Resistance; Liver; Liver Glycogen; Muscles; Organ Size; Ovariectomy; Rats; Rats, Inbred Strains; Reference Values; Testosterone

There are three major hormone classes--peptide, steroid, and the newly defined growth factors--each with its own system for signal transduction in the cell. Two interdependent theses are proposed for the peptide hormone: that incoming signal transduction requires coupling to a G protein in a second-messenger pathway, and that second-messenger redundancy assures checks and balances in cell regulation.

Topics: Adult; Animals; Cell Communication; Cyclic AMP; Dogs; Female; Glucagon; Glycogen; Homeostasis; Hormones; Humans; Infant, Newborn; Insulin; Insulin Resistance; Male; Peptides; Protein Kinases; Second Messenger Systems; Signal Transduction

To examine subcellular mechanisms behind the pathogenesis of peripheral insulin resistance in chronic uremic patients, insulin receptor function and glycogen synthase activity were studied in biopsies of skeletal muscle obtained during renal transplant surgery in 9 non-diabetic uremic patients. The results were compared with values obtained in an age- and sex-matched group of subjects with normal renal function, undergoing surgery for urological or gynecological diseases. The recovery of solubilized, wheat germ agglutinin-purified insulin receptors from skeletal muscle was increased among the uremic patients: 49.3 +/- 6.1 vs 31.4 +/- 2.8 fmol/100 mg muscle in healthy controls (p less than 0.03). Basal as well as insulin-stimulated kinase activities of the insulin receptors, expressed as phosphorylation of the synthetic peptide poly(Glu-Tyr(4:1] were similar. In addition, the maximal activity of the glycogen synthase was enhanced in uremic muscle: 26.6 +/- 2.8 vs 19.5 +/- 1.8 nmol.(mg protein)-1.min-1 (p less than 0.05), whereas the half-maximal activation constant for glucose-6-phosphate was identical in the two groups. Likewise, the muscle glycogen concentrations were similar in the uremic patients and the normal controls. In conclusion, our data suggest that neither impaired insulin receptor function nor a reduced maximal glycogen synthase activity of skeletal muscle are involved in the pathogenesis of the insulin resistance of patients with chronic renal failure.

Topics: Adult; Female; Glycogen; Glycogen Synthase; Humans; Insulin Resistance; Kidney Failure, Chronic; Male; Middle Aged; Muscles; Protein-Tyrosine Kinases; Receptor, Insulin

The role of an increased sympathetic activation in the development of insulin resistance in diabetic skeletal muscle was investigated. Epitrochlearis muscles from rats with streptozocin-induced diabetes and from controls were incubated in vitro for 0.5-12.0 h. Diabetes decreased maximal insulin-stimulated (20 mU/ml) glucose transport capacity by 60% (P less than .001), but this decreased insulin responsiveness returned to normal on in vitro incubation (3.79 +/- 0.59 before vs. 8.92 +/- 0.64 mumol.ml-1.h-1 after 12 h of incubation). The reversal of decreased insulin responsiveness in diabetic muscles did not require the presence of insulin and was not affected by the presence of 5.0 x 10(-8) M of epinephrine. However, it was possible to partially prevent the development of insulin resistance with regard to glucose transport by treating the rats with the beta-adrenergic antagonist propranolol (0.5 mg/kg) every 12 h during the entire 72-h period in which the animals were kept diabetic (insulin responsiveness was 3.16 +/- 0.40 mumol.ml-1.h-1 for saline-injected group vs. 5.55 +/- 0.46 mumol.ml-1.h-1 for propranolol-treated group). This effect was not present after a single injection of the drug 2 h before the experiment or when propranolol treatment was withdrawn 12 h before the experiment. The beta-adrenergic blockade markedly reduced the plasma concentration of free fatty acids (0.5 +/- 0.01 mumol/ml for propranolol-treated rats vs. 1.1 +/- 0.1 mumol/ml for saline-treated rats; P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adrenergic beta-Antagonists; Animals; Biological Transport; Blood Glucose; Catecholamines; Diabetes Mellitus, Experimental; Epinephrine; Fatty Acids, Nonesterified; Glucagon; Glucose; Glycogen; Insulin; Insulin Resistance; Male; Muscles; Propranolol; Rats; Rats, Inbred Strains; Streptozocin

We examined whether chronic exercise prevents insulin resistance developing in the high-fat-fed (HFF) rat, a model that otherwise develops profound peripheral insulin resistance. Insulin action (euglycemic clamp plus 2-[3H]deoxy-D-glucose-[14C]glucose tracer technique) was examined after 3 wk in sedentary control and sedentary or wheel cage exercise-trained HFF rats. At the whole body level, a reduction in peripheral insulin potency in HFF rats was prevented by concomitant chronic exercise; the 30-40% reduction in insulin-stimulated whole body net glucose utilization in sedentary HFF rats was abolished. Responses in individual muscles, however, suggested that the chronic exercise effect may be a compensation for, rather than a correction of insulin resistance induced by a high-fat diet; in six of eight muscles examined it produced an upward additive shift rather than a left shift in insulin dose response. Chronic exercise increased both muscle glycolytic flux and glycogen storage rates in the HFF rats, suggesting that glucose transport may be involved. We conclude that increased physical activity is beneficial in counteracting high-fat diet-induced insulin resistance. Different processes appear to be involved in the development of diet-induced insulin resistance in muscle and its amelioration by regular exercise.

Topics: Animals; Blood Glucose; Body Weight; Dietary Fats; Glycogen; Glycolysis; Insulin; Insulin Resistance; Liver Glycogen; Male; Muscles; Organ Specificity; Physical Conditioning, Animal; Physical Exertion; Rats; Rats, Inbred Strains; Reference Values

Seven endurance-trained subjects [maximal O2 consumption (VO2max) 64 +/- 1 (SE) ml.min-1.kg-1] were subjected to three sequential hyperinsulinemic euglycemic clamps 15 h after having performed their last training session (T). Results were compared with findings in seven untrained subjects (VO2max 44 +/- 2 ml.min-1.kg-1) studied both at rest (UT) and after 60 min of bicycle exercise at 150 W (UT-ex). In T and UT-ex compared with UT, sensitivity for insulin-mediated whole-body glucose uptake was higher [insulin concentrations eliciting half-maximal glucose uptake being 44 +/- 2 (T) and 43 +/- 4 (UT-ex) vs. 52 +/- 3 microU/ml (UT), P less than 0.05] and responsiveness was higher [13.4 +/- 1.2 (T) and 10.9 +/- 0.7 (UT-ex) vs. 9.5 +/- 0.7 mg.min-1.kg-1 (UT), P less than 0.05]. Furthermore, responsiveness was higher (P less than 0.05) in T than in UT-ex. Insulin-stimulated O2 uptake and maximal glucose oxidation rate were higher in T than in UT and UT-ex. Insulin-stimulated conversion or glucose to glycogen and muscle glycogen synthase was higher in T than in UT and UT-ex. However, glycogen storage in vastus lateralis muscle was found only in UT-ex. No change in any glucoregulatory hormone or metabolite could explain the increased insulin action in trained subjects. It is concluded that physical training induces an adaptive increase in insulin responsiveness of whole-body glucose uptake, which does not reflect increased glycogen deposition in muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Biological Transport, Active; Blood Glucose; Dose-Response Relationship, Drug; Glucose; Glycogen; Hormones; Humans; Insulin; Insulin Resistance; Liver; Male; Muscles; Physical Endurance

Lithium salts are commonly used in psychiatric patients and have been shown to have an insulinlike action in vitro. To define the impact of lithium ion on in vivo glucose metabolism, the effect of 2 wk of lithium treatment on plasma glucose and insulin concentrations, insulin-mediated glucose disposal, and skeletal muscle glycogen synthesis in normal and diabetic rats was examined. Our results demonstrated the ability of lithium ions to completely restore insulin sensitivity to normal in diabetic rats. The insulin-mimetic activity of the cation seems to be highly specific for the glycogenic pathway in skeletal muscle. These results raise the possibility that lithium ion may prove effective in reversing the defect in glycogen storage that characterizes non-insulin-dependent diabetes mellitus in humans.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Experimental; Glucose; Glycogen; Insulin; Insulin Resistance; Lithium; Male; Rats; Rats, Inbred Strains

To investigate the effect of chronic pancreatitis (CP) on in vitro hepatic sensitivity to insulin, the suppression of glucagon-stimulated hepatic glucose production (HGP) by insulin was examined during isolated liver perfusion (ILP) in CP and sham-operated rats. CP was induced at laparotomy by infusion of 50 microliters 99% oleic acid into the common bile duct during temporary occlusion of the proximal hepatic duct in 250- to 350-g Sprague-Dawley rats. Eight to sixteen weeks later, single-pass ILP was performed on fed animals. Glucagon (100 pg/ml) was infused for 30 min; the final 20 min of perfusion was performed with (a) no insulin, (b) 25 microU/ml insulin, or (c) 100 microU/ml insulin. CP and sham rats demonstrated comparable HGP responses to glucagon during the 0- to 10-min period (5.2 +/- 0.5 vs 5.9 +/- 0.5 mg/g/min, P = NS). CP rats demonstrated an HGP response to glucagon alone more evanescent than that in sham rats (20-30 min of HGP, 6.6 +/- 0.6 vs 9.5 +/- 0.4 mg/g/min, P less than 0.05). Sham rats showed a dose-dependent inhibition of HGP by insulin, however (percentage 20-30 min of HGP/0-10 min of HGP for 0, 25, and 100 microU/ml insulin: 166 +/- 12, 125 +/- 7, and 101 +/- 5%, P less than 0.01), whereas CP rats showed no effect of insulin (130 +/- 6, 123 +/- 7, 134 +/- 7%, P = NS). Pre- and postperfusion liver glycogen contents revealed comparable decreases in liver glycogen in both groups: insulin inhibition of HGP in sham rats was accompanied by higher postperfusion glycogen content. These data demonstrate a loss of insulin-mediated suppression of hepatic glucose production in livers obtained from pancreatitic rats. We conclude that CP is accompanied by a primary hepatic resistance to insulin; this defect may play a role in the etiology of pancreatogenic diabetes.

Topics: Animals; Blood Glucose; Chronic Disease; Glucagon; Glucose; Glycogen; Insulin; Insulin Resistance; Liver; Male; Pancreatitis; Perfusion; Rats; Rats, Inbred Strains

Insulin-mediated glucose metabolism was examined in vivo and in vitro in a chronically uremic (4-week) rat model established by a 90% nephrectomy. Using the euglycemic insulin clamp technique, uremic rats demonstrated a 28% reduction (P less than .01) in total body glucose disposal compared with pair-fed controls. Suppression of hepatic glucose production by insulin was not impaired. The ability of insulin to promote glycogen synthesis by the soleus muscle in vitro was normal in uremic rats. In contrast, the ability of insulin to enhance both glycolysis and glucose oxidation by the soleus muscle was significantly reduced (P less than .01) in uremic rats. These results provide evidence that at least two intracellular metabolic defects, ie, in the glycolytic and glucose oxidative pathways, contribute to the insulin resistance of chronic uremia.

Topics: Animals; Glucose; Glycogen; Glycolysis; Insulin; Insulin Resistance; Liver; Male; Muscles; Oxidation-Reduction; Rats; Rats, Inbred Strains; Uremia

Insulin action was assessed by using the hyperinsulinemic (approximately 800 pmol/L) euglycemic clamp in rats fed equal amounts of glucose or fructose (35% of calories) for 4 wk. The glucose infusion rate required to maintain euglycemia was decreased in fructose-fed animals (14.6 +/- 1.4 vs 21.8 +/- 1.1 for glucose-fed rats, p less than 0.001) with this whole-body effect contributed to equally by an impairment in hepatic insulin action and a reduction in peripheral glucose disposal in a range of tissues. There was no difference in basal glucose turnover, energy expenditure, or postprandial blood glucose and insulin responses to the diets. In the fructose-fed rats there was an increase in fasting triglyceride levels by 2 wk. Euglycemic clamp glucose disposal correlated positively and clamp hepatic glucose output correlated negatively with fasting triglyceride levels. In summary, fructose but not glucose feeding led to impaired insulin action in both the liver and peripheral tissues, effects that may depend on antecedent circulating triglyceride levels.

Topics: Animals; Blood Glucose; Dietary Carbohydrates; Energy Metabolism; Fructose; Glucose; Glycogen; Insulin; Insulin Resistance; Kinetics; Liver; Male; Muscles; Rats; Rats, Inbred Strains; Triglycerides

Adult cats determined by clinical laboratory evaluations to be normal, impaired glucose tolerant, or overtly diabetic were used to explore prospectively the relationships among pancreatic beta cell islet amyloid polypeptide (IAPP) immunoreactivity, islet amyloid (IA) deposition, and diabetogenesis. IAPP-derived IA was found in 11 of 14 (79%) diabetic cats, in four of nine (44%) impaired glucose tolerant cats, and in two of eight (25%) normal adult cats. The presence of IA even in very small amounts, therefore, predicts a very high probability (88%) that an animal has either impaired glucose tolerance or overt DM. Although all overtly diabetic cats had a marked decrease or absence of beta cell IAPP immunoreactivity, six of six cats with impaired glucose tolerance retained IAPP immunoreactivity with 1:15,000 dilutions of antisynthetic IAPP 7-17, whereas only one of seven normal cats had IAPP immunoreactivity beyond 1:10,000 dilutions. These findings suggest that increased IAPP production preceding the development of overt DM is linked to the progressive formation of insoluble IA deposits that are apparent in most overtly diabetic individuals. Of most importance, in that IAPP has been reported to inhibit both basal and insulin-stimulated rates of glycogen synthesis, is the possibility that increased production and release of IAPP by pancreatic beta cells plays a key role in the development of the insulin resistance and impaired glucose tolerance, both of which occur in Type 2 DM.

Topics: Amyloid; Animals; Cats; Diabetes Mellitus, Type 2; Glucose; Glucose Tolerance Test; Glycogen; Immunohistochemistry; Insulin Resistance; Islets of Langerhans; Peptides

In order to study the effect of corticosteroids on energy metabolism in immunosuppressed patients after kidney transplantation, we have examined glucose utilization, energy expenditure, and lean body mass in 10 kidney-transplanted patients receiving steroids (methylprednisolone 8.2 +/- 1.5 mg/day) and in 10 healthy age- and weight-matched control subjects. Glucose utilization was measured during euglycemic insulin clamp in combination with indirect calorimetry and infusion of [3H-3]-glucose, while beta-cell function was measured during a hyperglycemic clamp. The kidney-transplanted patients were resistant to the glucoregulatory effect of insulin, as demonstrated by a 25% reduction in total glucose disposal compared to control subjects. This defect was almost completely accounted for by a defect in storage of glucose as glycogen (3.3 +/- 0.5 vs. 5.0 +/- 0.5 mg/kg LBM min; P less than 0.05). The reduction in nonoxidative glucose disposal was associated with reduced lean body mass and incapacity to release energy as heat after infusion of insulin, i.e. thermogenic defect. In contrast, oxidation of glucose and lipids was not influenced by steroid therapy. Furthermore, suppression of hepatic glucose production was normal, and insulin secretion was normally enhanced in relation to the degree of insulin resistance in the steroid-treated patients. In conclusion, steroid-induced insulin resistance in kidney-transplanted patients is due to alterations in the nonoxidative pathway of glucose metabolism. These findings raise the question of whether steroid therapy directly influences glycogen synthase in man.

Topics: Adrenal Cortex Hormones; Blood Glucose; Body Temperature Regulation; Energy Metabolism; Glycogen; Humans; Insulin Resistance; Islets of Langerhans; Kidney Transplantation; Lipid Metabolism; Liver

Insulin resistance occurs in a variety of conditions, including diabetes, obesity and essential hypertension, but its underlying molecular mechanisms are unclear. In type 2 (non-insulin-dependent) diabetes mellitus, it is insulin-resistance in skeletal muscle, the chief site of insulin-mediated glucose disposal in humans, that predominantly accounts for the low rates of glucose clearance from the blood, and hence for impaired glucose tolerance. Human type 2 diabetes is characterized by a decrease in non-oxidative glucose storage (muscle glycogen synthesis), and by the deposition of amyloid in the islets of Langerhans. Amylin is a 37-amino-acid peptide which is a major component of islet amyloid and has structural similarity to human calcitonin gene-related peptide-2 (CGRP-2; ref. 8). CGRP is a neuropeptide which may be involved in motor activity in skeletal muscle. We now report that human pancreatic amylin and rat CGRP-1 are potent inhibitors of both basal and insulin-stimulated rates of glycogen synthesis in stripped rat soleus muscle in vitro. These results may provide a basis for a new understanding of the molecular mechanisms that cause insulin resistance in skeletal muscle.

Topics: Amyloid; Animals; Calcitonin; Calcitonin Gene-Related Peptide; Dose-Response Relationship, Drug; Glycogen; In Vitro Techniques; Insulin; Insulin Resistance; Islet Amyloid Polypeptide; Lactates; Male; Muscles; Neuropeptides; Rats; Rats, Inbred Strains

Topics: Animals; Glucose; Glycogen; Glycolysis; Insulin; Insulin Resistance; Muscles; Obesity; Rats; Rats, Zucker

The present study was performed to investigate as to whether peripheral insulin resistance exists in spontaneously hypertensive rats (SHR). After a 12 h fasting period, SHR had significantly higher serum glucose and higher plasma glucagon values in comparison to normotensive control rats (WKY). There was a tendency for higher serum insulin concentrations as well, but this difference did not reach significance. After oral glucose loading or glucose/insulin administration, serum glucose and insulin levels were also higher in SHR compared to WKY rats. Muscle glycogen and glucose concentrations were identical in fasted SHR and WKY rats. With an oral glucose load or glucose/insulin treatment there was a significant increase in muscle glycogen, whereas glucose values declined in skeletal muscle. Both total (a+b-form) phosphorylase activity as well as the active a-form of the enzyme were similar in skeletal muscle of SHR and WKY rats. Glucose/insulin administration or oral glucose loading induced a considerable reduction of both a+b-form and a-form activities. The decrease in muscle phosphorylase activities was almost identical in both groups of animals. There was also a comparable activity of muscle glycogen synthetase activity in all groups of rats. Despite subtile changes of glucose, glucagon and to a lesser degree insulin levels which would be suggestive of insulin resistance, the data obtained from skeletal muscle argue against peripheral insulin resistance in spontaneously hypertensive rats.

Topics: Animals; Blood Glucose; Glycogen; Glycogen Synthase; Hypertension; Insulin; Insulin Resistance; Male; Muscles; Phosphorylases; Rats; Rats, Inbred SHR; Rats, Inbred WKY

Denervated (1-10 days) rat epitrochlearis muscles were isolated, and basal and insulin-stimulated protein and glucose metabolism were studied. Although basal rates of glycolysis and glucose transport were increased in 1-10-day-denervated muscles, basal glycogen-synthesis rates were unaltered and glycogen concentrations were decreased. Basal rates of protein degradation and synthesis were increased in 1-10-day-denervated muscles. The increase in degradation was greater than that in synthesis, resulting in muscle atrophy. Increased rates of proteolysis and glycolysis were accompanied by elevated release rates of leucine, alanine, glutamate, pyruvate and lactate from 3-10-day-denervated muscles. ATP and phosphocreatine were decreased in 3-10-day-denervated muscles. Insulin resistance of glycogen synthesis occurred in 1-10-day denervated muscles. Insulin-stimulated glycolysis and glucose transport were inhibited by day 3 of denervation, and recovered by day 10. Inhibition of insulin-stimulated protein synthesis was observed only in 3-day-denervated muscles, whereas regulation by insulin of net proteolysis was unaffected in 1-10-day-denervated muscles. Thus the results demonstrate enhanced glycolysis, proteolysis and protein synthesis, and decreased energy stores, in denervated muscle. They further suggest a defect in insulin's action on protein synthesis in denervated muscles as well as on glucose metabolism. However, the lack of concurrent changes in all insulin-sensitive pathways and the absence of insulin-resistance for proteolysis suggest multiple and specific cellular defects in insulin's action in denervated muscle.

Topics: Adenosine Triphosphate; Amino Acids; Animals; Female; Glucose; Glycogen; Glycolysis; In Vitro Techniques; Insulin Resistance; Muscle Denervation; Muscle Proteins; Muscles; Organ Size; Phosphocreatine; Rats; Rats, Inbred Strains

Six men with a low rate of insulin-stimulated, non-oxidative carbohydrate disposal (storage) and six with a high storage rate were recruited for study of the fate of insulin-stimulated glucose uptake. [3-3H]glucose was infused before and during a 4-h hyperinsulinemic euglycemic clamp procedure in a dosage regimen designed to maintain a constant specific activity. From the disposition of label, the rate of insulin-mediated glucose incorporation into glycogen in the low-storage subjects was one-fourth that of the high-storage subjects (P less than .02). The insulin-mediated increase in muscle glycogen synthase activity in the low-storage subjects was one-fourth that of the high-storage subjects (P less than .05), suggesting the possibility of a causal relationship. In the high-storage but not the low-storage subjects, the rate of glycolysis inferred from the appearance of metabolized tritium in body water exceeded the carbohydrate oxidation rate (P less than .002). This suggests that in these subjects there is a significant fraction of glycolysis that is not oxidized and that this component of carbohydrate metabolism therefore contributes to storage.

Topics: Adult; Body Composition; Calorimetry; Glucose; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Male; Muscles; Racial Groups

We studied the binding and action of insulin in cultured fibroblasts from six patients with lipoatrophic diabetes and marked in vivo insulin resistance and from seven control subjects. The binding of insulin was not altered, which corresponds well with studies with circulating erythrocytes. Similarly, the action of the hormone on amino acid uptake (estimated by active transport of aminoisobutyric acid) was comparable in patient and control cells. Conversely, studies concerning the effect of insulin on glucose transport (estimated by facilitated diffusion of 2-deoxyglucose) or glycogen synthesis (estimated by incorporation of glucose into cellular glycogen) revealed the presence of heterogeneous alterations among the different patient cell lines. However, although the nature of the defect(s) varied among the patients, alterations in glucose metabolism were present in all cases. These data suggest the presence of primary postbinding defects in glucose cellular pathways that give rise to insulin resistance in cells from lipoatrophic diabetic patients.

Topics: Adolescent; Adult; Amino Acids; Cells, Cultured; Child; Diabetes Mellitus, Lipoatrophic; Fibroblasts; Glucose; Glycogen; Humans; Infant; Insulin; Insulin Resistance; Receptor, Insulin

The ability of glucose and insulin to modify insulin-stimulated glucose transport and uptake was investigated in perfused skeletal muscle. Here we report that perfusion of isolated rat hindlimbs for 5 h with 12 mM-glucose and 20,000 microunits of insulin/ml leads to marked, rapidly developing, impairment of insulin action on muscle glucose transport and uptake. Thus maximal insulin-stimulated glucose uptake at 12 mM-glucose decreased from 34.8 +/- 1.9 to 11.5 +/- 1.1 mumol/h per g (mean +/- S.E.M., n = 10) during 5 h perfusion. This decrease in glucose uptake was accompanied by a similar change in muscle glucose transport as measured by uptake of 3-O-[14C]-methylglucose. Simultaneously, muscle glycogen stores increased to 2-3.5 times initial values, depending on fibre type. Perfusion for 5 h in the presence of glucose but in the absence of insulin decreased subsequent insulin action on glucose uptake by 80% of the effect of glucose with insulin, but without an increase in muscle glycogen concentration. Perfusion for 5 h with insulin but without glucose, and with subsequent addition of glucose back to the perfusate, revealed glucose uptake and transport similar to initial values obtained in the presence of glucose and insulin. The data indicate that exposure to a moderately increased glucose concentration (12 mM) leads to rapidly developing resistance of skeletal-muscle glucose transport and uptake to maximal insulin stimulation. The effect of glucose is enhanced by simultaneous insulin exposure, whereas exposure for 5 h to insulin itself does not cause measurable resistance to maximal insulin stimulation.

Topics: Animals; Biological Transport; Female; Glucose; Glycogen; Insulin Resistance; Muscles; Rats; Rats, Inbred Strains

We studied glucose metabolism in non-insulin-dependent diabetic (NIDDM) men with and without glycogen-depleting cycle exercise 12 h beforehand and have compared the results to our previous data in lean and obese subjects. Rates of total glucose utilization, glucose oxidation, nonoxidative glucose disposal (NOGD), glucose metabolic clearance rate (MCR), and endogenous glucose production (EGP) were determined with a "two-level" insulin-clamp technique (100-min infusions at 40 and 400 mU X m-2 X min-1) combined with indirect calorimetry and D-3-[3H]glucose infusion. Muscle biopsy specimens from vastus lateralis were analyzed for glycogen content and glycogen synthase activity before and after insulin infusions. After exercise, NIDDM subjects had muscle glycogen concentrations comparable with those of lean and obese subjects. The activation of glycogen synthase both by prior exercise and insulin infusion was similar to lean controls. After exercise, total glucose disposal was significantly increased during the 40-mU X m-2 X min-1 infusion (P less than .05), but the increase observed during the 400-mU X m-2 X min-1 infusion was not significant. These increases after exercise were the result of significantly higher NOGD during both levels of insulin infusion. The MCR of glucose during both insulin infusions was reduced in NIDDM compared with lean subjects but was very similar to that in obese nondiabetics. Basal EGP was significantly reduced on the morning after exercise (4.03 +/- 0.27 vs. 3.21 +/- 0.21 mg x kg-1 fat-free mass x min-1) (P less than .05) and associated with significant reductions of fasting plasma glucose (197 +/- 12 vs. 164 +/- 9 mg/dl).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Blood Glucose; C-Peptide; Diabetes Mellitus, Type 2; Glucose; Glycogen; Glycogen Synthase; Humans; Insulin; Insulin Resistance; Male; Muscles; Physical Exertion

To assess a suitable model for the study of the mechanisms of development of insulin resistance in vivo, liver and muscle glycogen levels (as a metabolic index of tissue insulin sensitivity) were investigated in rats with functioning islet cell adenomas induced by streptozotocin and nicotinamide. These rats have basal moderate hyperinsulinemia and hypoglycemia and show a remarkable increase in insulin secretion after glucose administration. Plasma glucagon concentrations are normal. Nevertheless, in tumor-bearing rats, a reduction of tissue glycogen stores occurs, related to plasma glucose concentrations, and liver glycogen fails to increase even after a glucose load. The lack of excess fat in tumor-bearing rats also suggests a certain insulin insensitivity of the adipose tissue and distinguishes this model of chronic hyperinsulinism from other reported models, such as genetically obese animals.

Topics: Adrenal Glands; Animals; Blood Glucose; Chronic Disease; Disease Models, Animal; Glucagon; Glycogen; Hyperinsulinism; Insulin; Insulin Resistance; Liver; Male; Muscles; Organ Size; Rats; Rats, Inbred Strains

Skeletal muscle rapidly develops severe insulin resistance following denervation, although insulin binding is unimpaired. Insulin-stimulated receptor tyrosyl kinase activity was studied in intact and 24-h denervated rat hind limb muscles using three preparations: (a) solubilized insulin receptors incubated +/- insulin with gamma-[32P]ATP and histone H2b; (b) soleus muscles prelabeled in vitro with [32P]phosphate with subsequent insulin-stimulated phosphorylation of the receptor in situ; (c) assessment of in vivo activation of muscle receptor tyrosyl kinase by insulin. The latter was achieved by solubilizing muscle insulin receptors in the presence of phosphoprotein phosphatase and kinase inhibitors and measuring receptor-catalyzed histone H2b phosphorylation in the presence of limiting (5 microM) gamma-[32P]ATP. Receptors isolated 5 and 30 min after intravenous insulin injection catalyzed 32P incorporation into histone H2b twice as fast as those from saline-treated controls; insulin stimulated histone H2b labeling exclusively on tyrosine. In vivo activation was demonstrated using solubilized and insulin-agarose-bound receptors. Autophosphorylation of the beta-subunit and receptor tyrosyl kinase activity toward histone H2b was stimulated by insulin in denervated muscles as in controls, although the biological response to insulin, in vitro and in vivo, was markedly impaired after denervation, suggesting a postreceptor defect. The method developed to assess insulin-stimulated receptor activation in vivo seems useful in characterizing mechanisms of insulin resistance.

Topics: Animals; Enzyme Activation; Glycogen; Insulin; Insulin Resistance; Kinetics; Male; Muscle Denervation; Muscles; Phosphorylation; Protamine Kinase; Protein-Tyrosine Kinases; Rats; Rats, Inbred Strains; Receptor, Insulin; Ribonucleotides

We studied the effect of the duration of diabetic state on insulin action in skeletal muscle by measuring insulin binding, 2-deoxyglucose uptake, and intracellular glucose metabolism in isolated soleus muscles from streptozotocin-induced diabetic rats. Insulin binding to soleus muscles from diabetic rats was increased over that from controls. Glucose transport activity was determined by measuring the 2-deoxyglucose uptake at the concentration of 1 mmol/L at 25 degrees C. In the rats with diabetes of one week duration, insulin-stimulated 2-deoxyglucose uptake was not impaired, whereas basal 2-deoxyglucose uptake was decreased. However, the diabetic rats with two weeks duration revealed a 35.6% decrease in the insulin-stimulated 2-deoxyglucose uptake. Furthermore, four week duration of diabetic state led to a 60% decrease both in basal and insulin-stimulated 2-deoxyglucose uptake. Total glucose utilization was estimated as the total amount of glucose incorporated into muscle and lactate released into the medium following incubation at 37 degrees C, with 5 mmol/L glucose. The diabetic rats with one week duration did not demonstrate any changes in total glucose utilization both in basal and insulin-stimulated state. However more than two weeks duration of diabetes led to a 30% to 35% decrease both in basal and insulin-stimulated total glucose utilization, similar to the findings in the 2-deoxyglucose uptake study. We concluded that prolonged insulinopenia led to decreased glucose transport and intracellular glucose metabolism and resulted in insulin resistance in skeletal muscles.

Topics: Animals; Deoxyglucose; Diabetes Mellitus, Experimental; Glucose; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Male; Muscles; Rats; Rats, Inbred Strains; Receptor, Insulin

We have studied the regulation of glycogen metabolism by insulin in the insulin-sensitive nonfusing muscle cell line BC3H-1. The basal percentage of glycogen synthase I activity was not altered by insulin alone at any concentration, time of exposure, or age of cells tested. The addition of glucose or 2-deoxyglucose to the glucose- and serum-free incubation medium caused a 2-fold increase in glycogen synthase I activity over basal levels, and the effect was enhanced to 3-fold if insulin was added to the medium. Glycogen phosphorylase a activity was not altered by incubation in the presence of insulin, but was lowered by the addition of 2-deoxyglucose. This effect was also enhanced in the presence of insulin. The effect of exogenously added sugar occurred only if a 6-phosphorylatable hexose was used. The effect seen with 2-deoxyglucose was stable to Sephadex G-25 desalting, suggesting that activation of glycogen synthase was the result of a stable (covalent) modification of the enzyme. We were also able to demonstrate the presence of glucose-6-phosphate-activatable glycogen synthase phosphatase activity in the myocytes. The effect of 2-deoxyglucose in the presence or absence of insulin could be completely reversed by including cytochalasin B in the medium, suggesting that both the effect of hexose and the insulin enhancement of its effect were entirely dependent on carrier-mediated hexose uptake. Four insulin-mimetic agents, H2O2 Concanavalin A, Na orthovanadate, and antiinsulin receptor B2 serum, were also tested. Despite different mechanisms of action, each agent qualitatively mimicked insulin in the myocytes. All stimulated hexose transport, glucose incorporation into glycogen, and hexose-dependent activation of glycogen synthase in a manner not additive with insulin, but none increased basal glycogen synthase I activity in the absence of hexose. These results suggest that although insulin is capable of regulating glycogen metabolism both by increasing the uptake of sugar and by altering the activation state of glycogen synthase and phosphorylase, these effects are entirely due to the stimulation of hexose uptake, and hexose-independent actions of insulin are absent in BC3H-1 cells.

Topics: 3-O-Methylglucose; Animals; Cell Line; Concanavalin A; Deoxyglucose; Glucosephosphate Dehydrogenase; Glycogen; Glycogen Synthase; Glycogen-Synthase-D Phosphatase; Hexoses; Hydrogen Peroxide; Insulin; Insulin Resistance; Methylglucosides; Mice; Muscles; Neoplasms, Experimental; Vanadates; Vanadium

A lipoprotein-induced resistance to the action of insulin has been postulated. To test this hypothesis, cultured rat-derived hepatoma cells, designated FAO, and human-derived hepatoma cells, designated HEP-G2, were incubated for 20 h in the presence or absence of lipoprotein; specific 125I-insulin receptor binding and labeled glucose incorporation into glycogen were then measured. Very low density lipoproteins (d less than 1.006 g/ml) in physiologic (0.5 mg/ml) or pathophysiologic (5 mg/ml) concentrations did not modify insulin receptor binding of FAO or HEP-G2 cells. This was true for very low density lipoproteins derived from normal human, diabetic human, and streptozotocin-diabetic rat plasma. Low density lipoproteins (d = 1.019 - 1.063 g/ml) isolated from normal human plasma similarly failed to modify insulin receptor binding. Concerning insulin action, the different very low density lipoprotein preparations did not modulate either basal or insulin-stimulated glucose incorporation into glycogen of the cells. Thus, very low density lipoproteins and low density lipoproteins did not induce insulin resistance in cultured hepatoma cells either at the insulin receptor level or at the post-receptor level.

Topics: Animals; Cells, Cultured; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Lipoproteins; Lipoproteins, LDL; Lipoproteins, VLDL; Liver; Liver Neoplasms, Experimental; Rats; Receptor, Insulin

Topics: Adenosine; Animals; Glycogen; Insulin; Insulin Resistance; Lactates; Male; Muscles; Rats; Rats, Inbred Strains; Tendons

In order to delineate the sequence of development of the metabolic changes in the obese-hyperglycaemic syndrome in the NZO mouse, the uptake of 2-deoxyglucose, glucose utilization and glycogen synthesis by isolated soleus muscle in the absence and presence of graded doses of insulin was measured, and related to the gain in body weight and development of hyperinsulinaemia and hyperglycaemia. It was found that the NZO mice were hyperglycaemic and hyperinsulinaemic compared to an unrelated control strain (Balb c) from the earliest age studied (4 weeks). At 4-6 weeks, 2-deoxyglucose uptake and glucose utilization in the absence of insulin were decreased but the sensitivity and responsiveness to added insulin were comparable to those in the control strain. By 11 weeks, the responsiveness to added insulin was markedly impaired, an abnormality also seen at 52 weeks. Abnormal binding of insulin to its receptors was insufficient explanation for the observed changes. It is concluded that hyperinsulinaemia and hyperglycaemia develop early in NZO mice. Basal glucose transport and glucose utilization by isolated soleus muscle are also decreased from an early age, but decreased responsiveness to insulin in the soleus muscle is secondary and to insulin in the soleus muscle is secondary and relatively late manifestations of the syndrome.

Topics: Animals; Biological Transport, Active; Deoxyglucose; Female; Glucose; Glycogen; Hyperglycemia; Hyperinsulinism; In Vitro Techniques; Insulin Resistance; Mice; Mice, Inbred BALB C; Mice, Obese; Muscles; Obesity

Two treatments that increase skeletal muscle insulin action are exercise training and high-carbohydrate diet. The purpose of the present study was to determine whether exercise training and a diet high in carbohydrates could function synergistically to reduce the muscle insulin resistance in the obese Zucker rat. Obese rats 4 wk of age were randomly assigned to an exercise or sedentary group. Each group was subdivided by diet with one-half of the rats fed a high-carbohydrate diet and one-half fed a high-fat diet. Lean Zucker rats fed the high-fat diet were used as controls. Muscle insulin resistance was assessed during hindlimb perfusion with a submaximally stimulating concentration of insulin. Exercise training and the high-carbohydrate diet increased the rate of muscle glucose uptake in the obese rat by 46 and 53%, respectively. More importantly, the combined effect of exercise training and high-carbohydrate diet was greater than the sum of their individual effects. Glycogen synthesis paralleled glucose uptake and was the major pathway for intracellular glucose disposal. Muscle glucose uptake for exercise-trained, high-carbohydrate fed obese rats was comparable with that of lean controls. It is concluded that exercise training and the high-carbohydrate diet functioned synergistically to reduce the muscle insulin resistance in the obese rat.

Topics: Animals; Dietary Carbohydrates; Glucose; Glycogen; Hexokinase; Insulin Resistance; Lactates; Lactic Acid; Muscles; Obesity; Oxidation-Reduction; Physical Conditioning, Animal; Rats; Rats, Zucker

Young lean (Fa/?) and obese (fa/fa) rats were treated with the thermogenic beta-adrenoceptor agonist, BRL 26830, for 3 weeks. In lean rats this treatment had no effect on body weight but there was a marked increase in the insulin sensitivity of soleus muscle strips with respect to glycolytic rate. Treatment of obese rats with BRL 26830 produced a small but not significant decrease in body weight but the sensitivity of both glycolysis and glycogen synthesis to insulin was increased so that muscles of treated obese rats showed similar insulin sensitivity to untreated lean rats. It is suggested that such changes are unlikely to be merely a secondary consequence of an anti-obesity action.

Topics: Animals; Blood Glucose; Ethanolamines; Glycogen; Insulin Resistance; Lactates; Lactic Acid; Male; Muscles; Obesity; Rats; Rats, Zucker; Receptors, Adrenergic, beta

Madin-Darby canine kidney (MDCK) cells were previously shown to have few or no plasma membrane insulin binding sites (Hofmann et al: J Biol Chem 258:11774, 1983]. Accordingly, neither insulin-stimulated incorporation of [14C]glucose into glycogen, nor insulin-induced uptake of radiolabeled alpha-aminoisobutyrate ([3H]AIB) could be demonstrated. To probe for receptors, MDCK cultures were surface-labeled with Na125I or were labeled with [35S]methionine. When solubilized cells were immunoprecipitated with sera containing antibodies to the insulin receptor, and immunoprecipitates were analyzed on SDS-gel electrophoresis, no evidence for insulin receptor components was found. Also, when intact MDCK cells wee incubated first with serum containing antibodies to the insulin receptor and then with 125I-protein A, no radiolabeling of insulin receptors occurred. Various agents reported to have insulin-like activity were tested on MDCK cells. The insulinomimetic lectins concanavalin A and wheat germ agglutinin as well as hydrogen peroxide enhanced incorporation of [14C]glucose into glycogen and induced stimulated [3H]AIB uptake, whereas trypsin, vanadate, and serum containing antibodies to the insulin receptor were without effects. Altogether, these results showed that MDCK cells had few or no insulin receptors and were correspondingly insulin-insensitive. However, since insulin-associated responses could be elicited by some insulin mimickers, the post-receptor limb of response in MDCK cells was apparently intact.

Topics: Animals; Cell Line; Cell Membrane; Concanavalin A; Dogs; Glucose; Glycogen; Hydrogen Peroxide; Immune Sera; Immunosorbent Techniques; Insulin; Insulin Resistance; Kidney; Lectins; Receptor, Insulin; Trypsin; Vanadates; Vanadium; Wheat Germ Agglutinins

The mechanisms underlying the abnormal insulin-mediated muscle glucose metabolism occurring in acute uremia (ARF) have not been identified. To characterize the defects, insulin dose-response curves for glucose uptake, glycogen synthesis, glucose oxidation, glycolysis, and lactate release were measured in incubated rat epitrochlearis muscles. ARF did not affect insulin sensitivity, but decreased the responsiveness to insulin of glucose uptake, glycogen synthesis, and glucose oxidation. Glycogen synthesis was subnormal at all levels of insulin and at the maximal insulin concentration; it was 54% lower in muscles of ARF compared to control rats. This inhibition of glycogen synthesis in ARF could be caused by a 23% decrease in the total activity of muscle glycogen synthase and the percentage of enzyme in the activated form. Glycogen phosphorylase activity was unchanged by ARF. ARF also increased the ratio of muscle lactate release to glucose uptake at concentrations of insulin from 10 to 10(4) microU/ml. In the absence and presence of insulin, muscle protein degradation was increased by ARF. In individual muscles incubated with insulin, the rate of proteolysis was correlated with the ratio of lactate release to glucose uptake (r = + 0.82; P less than 0.01). From the insulin dose-response relationships and changes in enzyme activities, we conclude that ARF increases protein degradation in muscle and causes abnormal insulin-mediated glucose metabolism. The abnormalities in glucose metabolism are caused by changes in post-receptor events.

Topics: Animals; Biological Transport, Active; Glucose; Glycogen; Insulin; Insulin Resistance; Lactates; Lactic Acid; Male; Muscles; Proteins; Rats; Rats, Inbred Strains; Uremia

The effect of work-induced hypertrophy (without any concomitant change in circulating parameters) on skeletal muscle metabolism was studied in lean mice and in gold-thioglucose-obese mice. Soleus muscle was functionally overloaded in one leg by tenotomy of gastrocnemius muscle 4 days before muscle isolation, muscle in the other leg being used as control. Basal deoxyglucose uptake and glycolysis were markedly increased in overloaded muscles compared with control muscles, together with a ten-fold increase in fructose 2-6 bisphosphate content. In the presence of maximally effective insulin concentrations, deoxyglucose uptake and glycolysis were identical in overloaded and control muscles of lean mice, while the effects of overload and insulin were partly additive in muscles of gold-thioglucose-obese mice. The sensitivity to insulin and insulin binding to muscles were not modified in overloaded muscles. Insulin-stimulated glycogenogenesis was decreased by about 50% probably due to a lower amount of glycogen synthase in overloaded than in control muscles. Thus, in muscles of gold-thioglucose-obese mice work-induced hypertrophy increased the response to maximal insulin concentrations without modifying the altered insulin sensitivity and decreased insulin binding.

Topics: Animals; Aurothioglucose; Body Weight; Deoxyglucose; Fructosediphosphates; Glycogen; Glycolysis; Hypertrophy; Insulin; Insulin Resistance; Male; Mice; Muscles; Obesity; Physical Exertion

The effects of prior high-intensity cycle exercise (85% VO2 max) to muscular exhaustion on basal and insulin-stimulated glucose metabolism were studied in obese, insulin-resistant, and normal subjects. Six obese (30.4% fat) and six lean (14.5% fat) adult males underwent two separate, two-level hyperinsulinemic-euglycemic clamp studies (100-min infusions at 40 and 400 mU/m2/min), with and without exercise 12 h earlier. Carbohydrate oxidation was estimated by indirect calorimetry using a ventilated hood system, and endogenous glucose production by D-(3-3H)-glucose infusion. Glycogen content and glycogen synthase activity (GS %l) were measured in vastus lateralis muscle biopsies before and at the end of each insulin clamp procedure. After exercise, the obese and lean subjects had comparably low muscle glycogen concentrations (0.10 versus 0.08 mg/g protein, respectively), and equal activation of muscle GS activity (54.4 versus 45.3 GS %l, respectively). In the obese subjects, insulin-stimulated glucose disposal was increased significantly, but not totally corrected to normal. In both groups there was a comparable increase in nonoxidative glucose disposal (NOGD), whereas glucose oxidation was decreased and lipid oxidation was increased. Thus, the major effect of prior exercise was to increase insulin-stimulated glucose disposal in the obese subjects and to alter the pathways of glucose metabolism to favor NOGD and decrease glucose oxidation. No correlation was found between the exercise-induced increase in GS %l and NOGD, except in the normal subjects during maximal insulin stimulation. Thus, glycogen synthase activity does not appear to be rate-limiting for NOGD at physiologic insulin concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Blood Glucose; C-Peptide; Glucose; Glucose Tolerance Test; Glycogen; Glycogen Synthase; Humans; Hyperinsulinism; Insulin; Insulin Resistance; Male; Muscles; Obesity; Oxidation-Reduction; Physical Exertion; Urea

The effects of an exercise-induced muscle glycogen reduction and an elevated muscle glycogen concentration on glucose tolerance and the insulin response to an oral glucose tolerance test (GTT) were examined. GTTs were administered to seven male subjects after 3 days on a mixed diet (C), after exhaustive exercise and 1 day on a high-fat protein diet (L-FP), after exhaustive exercise and 1 day on a mixed diet (L-M), and after exhaustive exercise and 3 days on a high-carbohydrate diet (H-CHO). The L-M treatment resulted in a significant reduction in muscle glycogen (C, 79.6 +/- 4.2 mmol/kg wet wt vs. L-M, 53.9 +/- 1.2 mmol/kg wet wt) and a 31.7% reduction in the insulin-glucose (IG) index, a measure of insulin sensitivity in vivo. Muscle glycogen was also significantly reduced by the L-FP treatment (49.1 +/- 2.4 mmol/kg wet wt), but there was no change in the IG index. Preventing a decrease in the IG index during the L-FP treatment may have been a result of elevated free fatty acids (67%) and ketones (552%) prior to the GTT. Muscle glycogen was significantly increased by the H-CHO treatment (124.8 +/- 11.1 mmol/kg wet wt); however, the IG index was not different from that of the C treatment. The results suggest that an exercise-induced reduction in muscle glycogen can improve insulin sensitivity in vivo but that this effect is diet dependent.

Topics: Adult; Blood Glucose; Dietary Carbohydrates; Dietary Fats; Dietary Proteins; Glucose Tolerance Test; Glycogen; Humans; Insulin Resistance; Lactates; Male; Muscles; Physical Exertion

Rats were fasted 24, 48 or 72 hours to determine the effect of several days without food on glycogen synthase and synthase phosphatase activity in heart. The basal percentage of synthase I decreased gradually from approximately 20% in fed animals to approximately 6% in rats starved for 72 hours. Glycogen increased progressively from 4.6 mg/g wet weight in fed rats to 7.6 mg/g wet weight in 72-hour starved rats. Thus, there was an inverse relationship between the glycogen concentration and the basal percentage of synthase I. The total synthase phosphatase activity measured at a standardized glycogen concentration decreased 50% by 24 hours of starvation and then was unchanged up to 72 hours. The 50% decrease in phosphatase activity correlated directly with insulin concentration in rats fasted 24-72 hours. The rapid stimulatory effect of insulin on synthase activity observed in fed rats was delayed in rats starved 24 and 48 hours. This correlated with a progressively slower synthase phosphatase response to insulin. The stimulatory effect of insulin was lost completely in 72-hour fasted rats. The proposed mechanism for the delayed response in rats starved 24 and 48 hours and lack of response in rats starved 72 hours is insulin resistance. The mechanism remains to be elucidated.

Topics: Animals; Blood Glucose; Glycogen; Glycogen Synthase; Glycogen-Synthase-D Phosphatase; Insulin; Insulin Resistance; Male; Myocardium; Phosphoprotein Phosphatases; Rats; Starvation; Time Factors

Transfer of young rats from a maintenance diet to a breeding diet plus 10% sucrose in the drinking water for 4 weeks caused the development of insulin resistance. Inclusion of the enzyme adenosine deaminase or the adenosine-receptor antagonist 8-phenyltheophylline caused a marked increase in the sensitivity of the soleus-muscle strips isolated from the diet-induced insulin-resistant rats: the concentration of insulin giving 50% of maximum response of glycolysis shifted from 500 to less than 20 microunits/ml.

Topics: Adenosine Deaminase; Animals; Dietary Carbohydrates; Glycogen; Insulin; Insulin Resistance; Lactates; Lactic Acid; Male; Muscles; Nucleoside Deaminases; Rats; Rats, Inbred Strains; Sucrose; Theophylline

Insulin-stimulated glucose utilization was estimated in vivo in 1.5-, 4-, and 12-mo-old rats with an insulin suppression test wherein the height of the steady-state plasma glucose ( SSPG ) concentration, at similar steady-state plasma insulin levels, provides a direct reflection of the efficiency of insulin-stimulated glucose disposal. In parallel studies, the effect of age on in vitro insulin-stimulated glucose uptake was assessed in perfused hindlimb preparations. In addition, changes in the activity of enzymes that regulate muscle glycolysis, glycogenesis, and glycogenolysis were determined in isolated soleus muscle. The results indicated that rats got heavier as they became older, and changes in weight were associated with parallel increases in mean (+/- SE) SSPG concentrations as rats grew from 1.5 (56 +/- 3 mg/dl) to 4 (172 +/- 6 mg/dl) to 12 mo of age (194 +/- 8 mg/dl). The age-related decline in in vivo insulin action was associated with a reduction in insulin action on muscle, and maximal insulin-stimulated glucose uptake by perfused hindlimbs of 12-mo-old rats was approximately 50% of the value seen with perfused hindlimbs from 1.5-mo-old rats. Soleus muscle enzyme activity also varied with age, with significant increases in glycogen synthase and decreases in glycogen phosphorylase documented. Furthermore, muscle glycogen phosphorylase activity, which fell during an insulin infusion in 1.5-mo-old rats, did not change when 12-mo-old rats were infused at comparable insulin levels. Finally, glycogen content was significantly increased (P less than 0.01) in soleus muscle from 12-mo-old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Aging; Animals; Blood Glucose; Body Composition; Epinephrine; Glycogen; Glycogen Synthase; Hindlimb; Insulin; Insulin Resistance; Kinetics; Male; Muscle Development; Muscles; Perfusion; Propranolol; Rats; Rats, Inbred Strains

The effect of short-term denervation on the response to insulin was studied in isolated rat soleus and extensor digitorum longus (EDL) muscles 6 and 24 h after severing one sciatic nerve. Impaired insulin sensitivity and response occurred within 6 h postdenervation in solei. After 24 h, EDL of fed and fasted rats and solei of fed rats showed no stimulation of glycogen synthesis even with supraphysiological doses, whereas solei of fasted rats showed markedly decreased sensitivity and response to insulin. Insulin resistance of glycogen synthesis represented impaired stimulation of glucose transport and impaired glucose-independent activation of glycogen synthase by insulin. Changes in initial glycogen content of muscles did not correlate with insulin resistance. Insulin binding after denervation showed only minimum impairment and did not account for the marked insulin resistance. The response of denervated solei to epinephrine was unimpaired. Insulin resistance, which develops early after denervation in red and white muscles, represents primarily a defect in receptor-function coupling, suggesting that in muscle, nervous stimuli and/or contractile activity modulate signal transmission by the occupied insulin receptor.

Topics: Animals; Deoxyglucose; Epinephrine; Glucose; Glucose-6-Phosphate; Glucosephosphates; Glycogen; Glycogen Synthase; Insulin; Insulin Resistance; Male; Muscle Denervation; Muscles; Rats; Rats, Inbred Strains; Receptor, Insulin; Sciatic Nerve; Time Factors

Topics: Animals; Body Weight; Female; Glucose Tolerance Test; Glycogen; Hypoxia; Insulin Resistance; Muscles; Rats

Topics: Adenosine Triphosphate; Animals; Burns; Glucose; Glycogen; Hindlimb; Insulin; Insulin Resistance; Male; Muscles; Rats; Rats, Inbred Strains; Time Factors

Topics: Adipose Tissue; Animals; Female; Glucose; Glycogen; Insulin Resistance; Male; Muscles; Pregnancy; Pregnancy, Animal; Progesterone; Rats

Topics: Acute Disease; Animals; Dietary Proteins; Enzyme Activation; Fasting; Glycogen; Glycogen Synthase; Insulin Resistance; Kinetics; Lactates; Muscles; Nephrectomy; Phosphorylases; Rats; Serine; Uremia

1. The effect of insulin upon glucose transport and metabolism in soleus muscles of genetically obese (fa/fa) and heterozygote lean Zucker rats was investigated at 5-6 weeks and 10-11 weeks of age. Weight-standardized strips of soleus muscles were used rather than the intact muscle in order to circumvent problems of diffusion of substrates. 2. In younger obese rats (5-6 weeks), plasma concentrations of immunoreactive insulin were twice those of controls, whereas their circulating triacylglycerol concentrations were normal. Insulin effects upon 2-deoxyglucose uptake and glucose metabolism by soleus muscles of these rats were characterized by both a decreased sensitivity and a decrease in the maximal response of this tissue to the hormone. 3. In older obese rats (10-11 weeks), circulating concentrations of insulin and triacylglycerols were both abnormally elevated. A decrease of 25-35% in insulin-binding capacity to muscles of obese rats was observed. The soleus muscles from the older obese animals also displayed decreased sensitivity and maximal response to insulin. However, at a low insulin concentration (0.1m-i.u./ml), 2-deoxyglucose uptake by muscles of older obese rats was stimulated, but such a concentration was ineffective in stimulating glucose incorporation into glycogen, and glucose metabolism by glycolysis. 4. Endogenous lipid utilization by muscle was calculated from the measurements of O(2) consumption, and glucose oxidation to CO(2). The rate of utilization of fatty acids was normal in muscles of younger obese animals, but increased in those of the older obese rats. Increased basal concentrations of citrate, glucose 6-phosphate and glycogen were found in muscles of older obese rats and may reflect intracellular inhibition of glucose metabolism as a result of increased lipid utilization. 5. Thus several abnormalities are responsible for insulin resistance of muscles from obese Zucker rats among which we have observed decreased insulin binding, decreased glucose transport and increased utilization of endogenous fatty acid which could inhibit glucose utilization.

Topics: Animals; Deoxyglucose; Female; Glucose; Glycogen; Glycolysis; In Vitro Techniques; Insulin; Insulin Resistance; Intracellular Fluid; Muscles; Obesity; Oxygen Consumption; Rats; Receptor, Insulin

To investigate whether skeletal muscle is resistant to insulin in insulinopenic states, insulin binding and biological effects on glucose utilization were studied in isolated soleus muscles from 24- or 48-h-fasted mice and from streptozotocin-diabetic mice. Both 48-h fasting and diabetes led to an increase in insulin binding at insulin concentrations <3.4 nM. In both states, submaximal concentrations of insulin were also more effective in stimulating muscle 2-deoxyglucose uptake and glycogen synthesis, and in activating glycogen synthase. This resulted in a two- to fourfold leftward shift in the insulin dose-response curves in muscles from both groups compared with control. No change in insulin binding or biological effects was detected in muscles from 24-h-fasted mice. Maximal insulin effectiveness on 2-deoxyglucose uptake and glycolysis was either unchanged or only slightly enhanced in 48-h-fasted mice and in diabetic animals, compared with controls. Maximal insulin effects on glycogen synthesis and glycogen synthase activation were unaltered by fasting or diabetes. Basal glucose uptake and glycolysis were similar in all groups of mice. In conclusion, when soleus muscles from 48-h-fasted mice and from diabetic mice are compared with controls it can be observed that, (a) at low insulin concentrations insulin binding is increased and insulin effectiveness in stimulating glucose transport and metabolism is enhanced; (b) biological responses to maximally effective insulin concentrations are either unaltered or slightly increased; (c) basal rates of glucose transport and metabolism are essentially unaltered. These results indicate that in insulinopenic states soleus muscle is not insulin resistant in vitro but is hypersensitive to low concentrations of insulin, and normally responsive to maximally effective doses of the hormone.

Topics: Animals; Deoxyglucose; Diabetes Mellitus, Experimental; Enzyme Activation; Fasting; Glucose; Glycogen; Glycogen Synthase; Glycolysis; Hindlimb; Insulin; Insulin Resistance; Mice; Muscle Proteins; Muscles; Receptor, Insulin; Streptozocin

1. The effect of insulin (0.5, 10 and 50 munits/ml of perfusate) on glucose uptake and disposal in skeletal muscle was studied in the isolated perfused hindquarter of obese (fa/fa) and lean (Fa/Fa) Zucker rats and Osborne-Mendel rats. 2. A concentration of 0.5 munit of insulin/ml induced a significant increase in glucose uptake (approx. 2.5 mumol/min per 30 g of muscle) in lean Zucker rats and in Osborne-Mendel rats, and 10 munits of insulin/ml caused a further increase to approx. 6 mumol/min per 30 g of muscle; but 50 munits of insulin/ml had no additional stimulatory effect. In contrast, in obese Zucker rats only 10 and 50 munits of insulin/ml had a stimulatory effect on glucose uptake, the magnitude of which was decreased by 50-70% when compared with either lean control group. Since under no experimental condition tested was an accumulation of free glucose in muscle-cell water observed, the data suggest an impairment of insulin-stimulated glucose transport across the muscle-cell membrane in obese Zucker rats. 3. The intracellular disposal of glucose in skeletal muscle of obese Zucker rats was also insulin-insensitive: even at insulin concentrations that clearly stimulated glucose uptake, no effect of insulin on lactate oxidation (nor an inhibitory effect on alanine release) was observed; [14C]glucose incorporation into skeletal-muscle lipids was stimulated by 50 munits of insulin/ml, but the rate was still only 10% of that observed in lean Zucker rats. 4. The data indicate that the skeletal muscle of obese Zucker rats is insulin-resistant with respect to both glucose-transport mechanisms and intracellular pathways of glucose metabolism, such as lactate oxidation. The excessive degree of insulin-insensitivity in skeletal muscle of obese Zucker rats may represent a causal factor in the development of the glucose intolerance in this species.

Topics: Adipose Tissue; Animals; Body Composition; Diabetes Mellitus; Female; Glucose; Glycogen; In Vitro Techniques; Insulin; Insulin Resistance; Muscles; Obesity; Perfusion; Rats

Autoantibodies against the insulin receptor are found in the serum of some patients with severe insulin resistance. The effects of one of these sera on insulin binding and on glucose transport and metabolism were investigated in the isolated mouse soleus muscle. Preincubation of muscles with the patient's serum resulted in an inhibition of subsequent 125I-insulin binding (half-maximal effect at 1:500 dilution) and in a two to three-fold stimulation of glucose transport and metabolism (half-maximal effect at 1:2000 dilution). The insulin-like effects were blocked by anti-human IgG, but not by anti-insulin antibodies. The magnitude of the serum effects on 2-deoxyglucose uptake and glycolysis was similar to that of insulin, but the effect on glycogen synthesis was smaller than that of insulin. It is suggested that the patient's serum and insulin promote glucose transport and glycolysis through a common pathway, but act differently on glycogen synthesis.

Topics: Animals; Autoantibodies; Biological Transport; Glucose; Glycogen; Glycolysis; Insulin Resistance; Male; Mice; Mice, Obese; Muscles; Receptor, Insulin

Acute insulin resistance developed after scald injury in the mouse. After 2h plasma glucose and insulin concentrations were each raised about two-fold. Glucose metabolism was studied in vitro in soleus muscles isolated at this time. Glycolysis and glycogen synthesis, and their stimulation by insulin, were unchanged in muscles from scalded mice, and insulin-stimulated transport of 2-deoxyglucose slightly increased, showing that the insulin resistance seen in vivo is not maintained in isolated tissues. Binding of insulin to liver cell membranes prepared from scalded mice was unaltered, whilst that of glucagon was slightly but significantly reduced, showing that changes in polypeptide-hormone receptors can occur within this short time. It was concluded that the acute loss of sensitivity to insulin after injury does not result from a change in insulin receptor sites and presumably reflects an impairment of glucose metabolism in vivo mediated by circulating hormones.

Topics: Animals; Biological Transport; Burns; Cell Membrane; Deoxyglucose; Glucose; Glycogen; Glycolysis; Insulin Resistance; Liver; Male; Mice; Muscles; Receptor, Insulin

In the presence of 5mM glucose insulin only modestly activated rates of glucose uptake by rat epitrochlearis muscles while the rate of glycogen formation from D(U-14C) glucose was markedly stimulated by the hormone. No effect of insulin on lactate output could be detected under these conditions. The activation of labeled glycogen formation by insulin occurred in a dose-dependent manner and a maximal effect was noted at hormone concentrations greater than 4 mU/ml. However, glycogen accumulation by epitrochlearis muscles obtained from old, spontaneously obese rats was activated by only 38 +/- 15% by a supermaximal insulin concentration (200 mU/ml) compared to a 123 +/- 43% stimulation observed in muscles from small rats. This impaired responsiveness to the hormone could not be explained by inhibition of the glycogen synthetase system by increased amounts of endogenous glycogen in the epitrochlearis muscle of spontaneously obese rats. The magnitude of this resistance greatly exceeds the modest reduction in insulin receptor number reported for msucle membranes in obese rats which suggests that other defective cellular components contribute to this syndrome.

Topics: Animals; Dose-Response Relationship, Drug; Glucose; Glycogen; Insulin; Insulin Resistance; Lactates; Male; Muscles; Obesity; Rats; Starvation

Effects of insulin (1 mU/ml) on diaphragms removed from older-obese (70--110 days, 350--520 g) male Sprague-Dawley rats were compared to responses on muscle removed from younger-lean (27--36 days, 80--150 g) animals. Insulin antagonism on glucose transport (2DG uptake), glucose uptake, glycogen synthesis, glycolysis (lactate production), and glucose oxidation was demonstrated in tissue from the older-obese rats. Extracellular water spaces (measured with inulin-H3) were significantly decreased in these tissue. To determine if insulin antagonism of glucose transport could be secondary to inhibition of a rate-limiting reaction in the Embden-Meyerhof pathway with a subsequent negative feedback on transport, both tissue levels of glycolytic intermediates and oxidation of intracellular lipids were measured. No free intracellular glucose was found in diaphragms from either group of rats. Levels of G-6-P, F-6-P, F-1, 6-diP, PEP, and pyruvate were all lower in muscle from the older-obese animals. Incorporation of C14-FFA into tissue TG was slightly, but significantly, lower in this same tissue. Oxidation of intracellular TG and PL was similar in the two groups. In conclusion, diaphragms from older-obese rats manifest insulin antagonism of glucose transport that is probably responsible for the diminished hormonal effect on glucose uptake and the intracellular pathways of glycogen synthesis, glycolysis, and glucose oxidation. This inhibition of insulin action cannot be accounted for by changes in glycolytic intermediates causing a negative feedback on transport or enhanced lipid oxidation and therefore should be considered primary. The relative effects of age and obesity will need to be evaluated in future studies.

Topics: Aging; Animals; Biological Transport, Active; Deoxyglucose; Diaphragm; Disease Models, Animal; Glucose; Glycogen; Glycolysis; Insulin; Insulin Resistance; Lactates; Lipid Metabolism; Male; Muscle Development; Obesity; Rats

The glycogen storage in rat skeletal muscle is reduced after a 20% third degree burn. The reason is probably a relative deficiency of insulin caused by insulin resistance at the tissue level. Posttraumatically increased sympatho-adrenal function has been suspected to cause this insulin resistance. In an earlier study, however, it has been shown that adrenal demedullation has no effect on the glycogen storage. In the present investigation an attempt was made to assess the importance of the increased peripheric sympathetic activity. Muscle glycogen, serum insulin and blood glucose were determined at the end of a glucose infusion after infliction of a burn both in 6-hydroxy-dopamine treated rats and rats with an intact peripheric sympathetic nervous system. It was found that a chemical sympathectomy did not improve the glycogen storage. The result indicates that the increased activity of the sympatho-adrenal system after a burn is not the main cause of the reduced skeletal muscle glycogen storage.

Topics: Animals; Burns; Glycogen; Insulin; Insulin Resistance; Male; Muscle, Skeletal; Rats; Rats, Sprague-Dawley; Sympathectomy, Chemical

Topics: Adipose Tissue; Animals; Blood Glucose; Body Weight; Carbon Radioisotopes; Dose-Response Relationship, Drug; Fatty Acids; Glucocorticoids; Glucose; Glycogen; Growth Hormone; Insulin; Insulin Resistance; Insulin Secretion; Lipid Metabolism; Male; Methylprednisolone; Proteins; Rats; Time Factors

Topics: Adipose Tissue; Animals; Blood Glucose; Carbon Dioxide; Carbon Isotopes; Diaphragm; Glucose; Glycogen; Hyperinsulinism; In Vitro Techniques; Insulin; Insulin Resistance; Insulin Secretion; Islets of Langerhans; Male; Obesity; Rats; Rodent Diseases

Topics: Adipose Tissue; Animals; Blood Glucose; Carbon Dioxide; Carbon Isotopes; Diaphragm; Electroshock; Fatty Acids; Glucose; Glycogen; Hypothalamus; In Vitro Techniques; Insulin; Insulin Resistance; Lipids; Male; Muscles; Obesity; Radioimmunoassay; Rats

Topics: Adipose Tissue; Aging; Animals; Carbon Isotopes; Diaphragm; Diet; Epididymis; Esters; Fatty Acids; Glucose; Glycerides; Glycerol; Glycogen; In Vitro Techniques; Insulin; Insulin Resistance; Male; Muscles; Rats; Stimulation, Chemical; Triglycerides

Topics: Adipose Tissue; Adult; Aged; Body Weight; Carbon Dioxide; Carbon Isotopes; Female; Glucose; Glycogen; Humans; Insulin; Insulin Resistance; Lipid Metabolism; Male; Middle Aged; Muscles; Obesity

Topics: Adipose Tissue; Animals; Blood Glucose; Body Weight; Carbon Dioxide; Carbon Isotopes; Diaphragm; Diet; Epididymis; Glucose; Glycogen; Hyperglycemia; In Vitro Techniques; Insulin; Insulin Resistance; Male; Mice; Mice, Inbred Strains; Muscles; Obesity; Parabiosis; Triglycerides

Topics: Child; Diabetes Mellitus; Glycogen; Humans; Insulin; Insulin Resistance; Islets of Langerhans; Pancreas

Topics: Adipose Tissue; Animals; Blood Glucose; Body Weight; Carbon Dioxide; Carbon Isotopes; Diaphragm; Diet Therapy; Glucose; Glycogen; Hyperglycemia; In Vitro Techniques; Insulin; Insulin Resistance; Mice; Muscles; Obesity

Topics: Adult; Aged; Female; Glucose Tolerance Test; Glycogen; Humans; Insulin; Insulin Resistance; Kidney Failure, Chronic; Male; Middle Aged; Pyelonephritis

Topics: Adipose Tissue; Animals; Blood Glucose; Carbon Isotopes; Diaphragm; Glucose; Glycogen; Injections, Intraperitoneal; Insulin; Insulin Resistance; Male; Methods; Mice; Muscles; Obesity

Topics: Animals; Blood Glucose; Glycogen; Hydrazines; Insulin Resistance; Liver Glycogen; Monoamine Oxidase Inhibitors; Muscles; Rabbits; Rats; Species Specificity

Topics: Animals; Biological Assay; Carbon Isotopes; Cattle; Diabetes Mellitus; Diaphragm; Endopeptidases; Glucose; Glycogen; Injections, Intraperitoneal; Insulin; Insulin Resistance; Pancreatic Extracts; Rats; Serum Albumin, Bovine

Some biological effects of hypoglycin-A, a compound isolated from the fruit of Blighia sapida, have been investigated. Administration of this compound to animals caused drowsiness progressing to coma, and when large doses were given the animals died. For the rat, the oral and intraperitoneal LD50 values were 98 and 97 mg./kg. respectively. Fasting increased the toxicity considerably. The most outstanding biochemical change produced by hypoglycin-A was a delayed hypoglycaemia, the depth of which was related to the dose. The hypoglycaemia was preceded by exhaustion of liver glycogen. There were also smaller decreases in the glycogen stores of the heart, skeletal muscle and kidney, without any increase in blood pyruvate or lactate. Hypoglycin-A lessened the effect of adrenaline on blood glucose and decreased both glucose tolerance and insulin sensitivity. Hypoglycin-A also decreased the oxygen consumption and carbon dioxide production of the intact rat. All these effects are consistent with the hypothesis that the primary action of hypoglycin-A is the interference with glycogen production by the liver.

Topics: Animals; Blighia; Blood Glucose; Fruit; Glycogen; Hypoglycemic Agents; Hypoglycins; Insulin Resistance; Liver; Peptides; Rats

Topics: Diabetes Mellitus; Glycogen; Glycogenolysis; Humans; Insulin; Insulin Resistance; Liver