malonyl-coenzyme-a and Obesity

Metabolic integration of nutrient sensing in the central nervous system has been shown to be an important regulator of adiposity by affecting food intake and peripheral energy expenditure. Modulation of de novo fatty acid synthetic flux by cytokines and nutrient availability plays an important role in this process. Inhibition of hypothalamic fatty acid synthase by pharmacologic or genetic means leads to an increased malonyl-CoA level and suppression of food intake and adiposity. Conversely, the ectopic expression of malonyl-CoA decarboxylase in the hypothalamus is sufficient to promote feeding and adiposity. Based on these and other findings, metabolic intermediates in fatty acid biogenesis, including malonyl-CoA and long-chain acyl-CoAs, have been implicated as signaling mediators in the central control of body weight. Malonyl-CoA has been hypothesized to mediate its effects in part through an allosteric interaction with an atypical and brain-specific carnitine palmitoyltransferase-1 (CPT1c). CPT1c is expressed in neurons and binds malonyl-CoA, however, it does not perform the same biochemical function as the prototypical CPT1 enzymes. Mouse knockout models of CPT1c exhibit suppressed food intake and smaller body weight, but are highly susceptible to weight gain when fed a high-fat diet. Thus, the brain can directly sense and respond to changes in nutrient availability and composition to affect body weight and adiposity.

Topics: Animals; Anti-Obesity Agents; Carnitine O-Palmitoyltransferase; Humans; Hypothalamus; Malonyl Coenzyme A; Obesity

The central nervous system mediates energy balance (energy intake and energy expenditure) in the body; the hypothalamus has a key role in this process. Recent evidence has demonstrated an important role for hypothalamic malonyl CoA in mediating energy balance. Malonyl CoA is generated by the carboxylation of acetyl CoA by acetyl CoA carboxylase and is then either incorporated into long-chain fatty acids by fatty acid synthase, or converted back to acetyl-CoA by malonyl CoA decarboxylase. Increased hypothalamic malonyl CoA is an indicator of energy surplus, resulting in a decrease in food intake and an increase in energy expenditure. In contrast, a decrease in hypothalamic malonyl CoA signals an energy deficit, resulting in an increased appetite and a decrease in body energy expenditure. A number of hormonal and neural orexigenic and anorexigenic signaling pathways have now been shown to be associated with changes in malonyl CoA levels in the arcuate nucleus (ARC) of the hypothalamus. Despite compelling evidence that malonyl CoA is an important mediator in the hypothalamic ARC control of food intake and regulation of energy balance, the mechanism(s) by which this occurs has not been established. Malonyl CoA inhibits carnitine palmitoyltransferase-1 (CPT-1), and it has been proposed that the substrate of CPT-1, long-chain acyl CoA(s), may act as a mediator(s) of appetite and energy balance. However, recent evidence has challenged the role of long-chain acyl CoA(s) in this process, as well as the involvement of CPT-1 in hypothalamic malonyl CoA signaling. A better understanding of how malonyl CoA regulates energy balance should provide novel approaches to targeting intermediary metabolism in the hypothalamus as a mechanism to control appetite and body weight. Here, we review the data supporting an important role for malonyl CoA in mediating hypothalamic control of energy balance, and recent evidence suggesting that targeting malonyl CoA synthesis or degradation may be a novel approach to favorably modify appetite and weight gain.

Topics: AMP-Activated Protein Kinases; Appetite Regulation; Feeding Behavior; Humans; Hypothalamus; Malonyl Coenzyme A; Obesity; Signal Transduction

Obesity is an important contributor to the risk of developing insulin resistance, diabetes, and heart disease. Alterations in tissue levels of malonyl-CoA have the potential to impact on the severity of a number of these disorders. This review will focus on the emerging role of malonyl-CoA as a key "metabolic effector" of both obesity and cardiac fatty acid oxidation. In addition to being a substrate for fatty acid biosynthesis, malonyl-CoA is a potent inhibitor of mitochondrial carnitine palmitoyltransferase (CPT) 1, a key enzyme involved in mitochondrial fatty acid uptake. A decrease in myocardial malonyl-CoA levels and an increase in CPT1 activity contribute to an increase in cardiac fatty acid oxidation. An increase in malonyl-CoA degradation due to increased malonyl-CoA decarboxylase (MCD) activity may be one mechanism responsible for this decrease in malonyl-CoA. Another mechanism involves the inhibition of acetyl-CoA carboxylase (ACC) synthesis of malonyl-CoA, due to AMP-activated protein kinase (AMPK) phosphorylation of ACC. Recent studies have demonstrated a role of malonyl-CoA in the hypothalamus as a regulator of food intake. Increases in hypothalamic malonyl-CoA and inhibition of CPT1 are associated with a decrease in food intake in mice and rats, while a decrease in hypothalamic malonyl-CoA increases food intake and weight gain. The exact mechanism(s) responsible for these effects of malonyl-CoA are not clear, but have been proposed to be due to an increase in the levels of long chain acyl CoA, which occurs as a result of malonyl-CoA inhibition of CPT1. Both hypothalamic and cardiac studies have demonstrated that control of malonyl-CoA levels has an important impact on obesity and heart disease. Targeting enzymes that control malonyl-CoA levels may be an important therapeutic approach to treating heart disease and obesity.

Topics: Acetyl-CoA Carboxylase; Acyl Coenzyme A; AMP-Activated Protein Kinases; Animals; Appetite Regulation; Carnitine O-Palmitoyltransferase; Energy Metabolism; Heart Diseases; Humans; Hypothalamus; Malonyl Coenzyme A; Multienzyme Complexes; Obesity; Protein Serine-Threonine Kinases

New evidence suggests that leptin and other anorexigenic agents reduce appetite by inactivating hypothalamic AMP-activated protein kinase (AMPK), thereby increasing malonyl CoA levels. This preview examines AMP biology and its role in malonyl-CoA generation and attempts to integrate its central actions with its peripheral antilipotoxic actions within the context of leptin physiology in obesity.

Topics: AMP-Activated Protein Kinases; Animals; Eating; Energy Intake; Energy Metabolism; Humans; Hypothalamus; Leptin; Malonyl Coenzyme A; Multienzyme Complexes; Obesity; Protein Serine-Threonine Kinases

An increasing body of evidence has linked AMP-activated protein kinase (AMPK) and malonyl coenzyme A (CoA) to the regulation of energy balance. Thus, factors that activate AMPK and decrease the concentration of malonyl CoA in peripheral tissues, such as exercise, decrease triglyceride accumulation in the adipocyte and other cells. The data reviewed here suggest that this is related to the fact that these factors concurrently increase fatty acid oxidation, decrease the esterification of fatty acids to form glycerolipids, and, by mechanisms still unknown, increase energy expenditure. Malonyl CoA contributes to these events because it is an allosteric inhibitor of carnitine palmitoyltransferase, the enzyme that controls the transfer of long-chain fatty acyl CoA from the cytosol to the mitochondria, where they are oxidized. AMPK activation in turn increases fatty acid oxidation (by effects on enzymes that govern malonyl CoA synthesis and possibly its degradation) and inhibits triglyceride synthesis. It also increases the expression of uncoupling proteins and the transcriptional regulator peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC1alpha), which could possibly increase energy expenditure. Recent studies suggest that the ability of leptin, adiponectin, 5'-aminoimidazole 4-carboxamide riboside (AICAR), adrenergic agonists, and metformin to diminish adiposity may be mediated, at least in part, by AMPK activation in peripheral tissues. In addition, preliminary studies suggest that malonyl CoA and AMPK take part in fuel-sensing and signaling mechanisms in the hypothalamus that could regulate food intake and energy expenditure.

Topics: Adipose Tissue; AMP-Activated Protein Kinases; Animals; Humans; Malonyl Coenzyme A; Multienzyme Complexes; Obesity; Protein Serine-Threonine Kinases

It is widely held that although obesity and type 2 diabetes are polygenic in origin, the primary defect causing both conditions is insulin resistance, which in turn gives rise to a constellation of other abnormalities, including hyperinsulinemia, dyslipidemia, glucose intolerance, and (in the genetically predisposed) frank hyperglycemia. Explored here is an alternative, albeit speculative, scenario in which hyperinsulinemia and insulin resistance arise either simultaneously or sequentially from some preexisting defect within the leptin signaling pathway. In either case, a central component of the model is that the breakdown of glucose homeostasis that is characteristic of the condition of obesity with type 2 diabetes is secondary to disturbances in lipid dynamics. The possibility is raised that abnormally high concentrations of malonyl-CoA in liver and skeletal muscle suppress the activity of mitochondrial carnitine palmitoyltransferase I and thus fatty acid oxidation in both sites. It is suggested that the buildup of fat within the muscle cell (caused in part by excessive delivery of VLDLs from the liver) interferes with glucose transport or metabolism or both, producing insulin resistance. Elevated circulating concentrations of fatty acids are also implicated in the etiology of type 2 diabetes by virtue of 1) their powerful acute insulinotropic effect, 2) their ability to exacerbate insulin resistance in muscle, and 3) their long-term detrimental action on pancreatic beta-cell function.

Topics: Animals; Carnitine O-Palmitoyltransferase; Diabetes Mellitus, Type 2; Dietary Carbohydrates; Dietary Fats; Energy Metabolism; Fatty Acids; Glucose; Humans; Islets of Langerhans; Liver; Malonyl Coenzyme A; Muscles; Obesity

Widely held theories of the pathogenesis of obesity-associated NIDDM have implicated apparently incompatible events as seminal: 1) insulin resistance in muscle, 2) abnormal secretion of insulin, and 3) increases in intra-abdominal fat. Altered circulating or tissue lipids are characteristic features of obesity and NIDDM. The etiology of these defects is not known. In this perspective, we propose that the same metabolic events, elevated malonyl-CoA and long-chain acyl-CoA (LC-CoA), in various tissues mediate, in part, the pleiotropic alterations characteristic of obesity and NIDDM. We review the evidence in support of the emerging concept that malonyl-CoA and LC-CoA act as metabolic coupling factors in beta-cell signal transduction, linking fuel metabolism to insulin secretion. We suggest that acetyl-CoA carboxylase, which synthesizes malonyl-CoA, a "signal of plenty," and carnitine palmitoyl transferase 1, which is regulated by it, may perform as fuel sensors in the beta-cell, integrating the concentrations of all circulating fuel stimuli in the beta-cell as well as in muscle, liver, and adipose tissue. The target effectors of LC-CoA may include protein kinase C sub-types, complex lipid formation, genes encoding metabolic enzymes or transduction factors, and protein acylation. We support the concept that only under conditions in which both glucose and lipids are plentiful will the metabolic abnormality, which may be termed glucolipoxia, become apparent. If our hypothesis is correct that common signaling abnormalities in the metabolism of malonyl-CoA and LC-CoA contribute to altered insulin release and sensitivity, it offers a novel explanation for the presence of variable combinations of these defects in individuals with differing genetic backgrounds and for the fact that it has been difficult to determine whether one or the other is the primary event.

Topics: Acyl Coenzyme A; Animals; Cytosol; Diabetes Mellitus; Diabetes Mellitus, Type 2; Humans; Insulin; Insulin Secretion; Islets of Langerhans; Malonyl Coenzyme A; Obesity; Signal Transduction

Obesity and diabetes normally cause mitochondrial dysfunction and hepatic lipid accumulation, while fatty acid synthesis is suppressed and malonyl-CoA is depleted in the liver of severe obese or diabetic animals. Therefore, a negative regulatory mechanism might work for the control of mitochondrial fatty acid metabolism that is independent of malonyl-CoA in the diabetic animals. As mitochondrial β-oxidation is controlled by the acetyl-CoA/CoA ratio, and the acetyl-CoA generated in peroxisomal β-oxidation could be transported into mitochondria via carnitine shuttles, we hypothesize that peroxisomal β-oxidation might play a role in regulating mitochondrial fatty acid oxidation and inducing hepatic steatosis under the condition of obesity or diabetes. This study reveals a novel mechanism by which peroxisomal β-oxidation controls mitochondrial fatty acid oxidation in diabetic animals. We determined that excessive oxidation of fatty acids by peroxisomes generates considerable acetyl-carnitine in the liver of diabetic mice, which significantly elevates the mitochondrial acetyl-CoA/CoA ratio and causes feedback suppression of mitochondrial β-oxidation. Additionally, we found that specific suppression of peroxisomal β-oxidation enhances mitochondrial fatty acid oxidation by reducing acetyl-carnitine formation in the liver of obese mice. In conclusion, we suggest that induction of peroxisomal fatty acid oxidation serves as a mechanism for diabetes-induced hepatic lipid accumulation. Targeting peroxisomal β-oxidation might be a promising pathway in improving hepatic steatosis and insulin resistance as induced by obesity or diabetes.

Topics: Acetyl Coenzyme A; Acetylcarnitine; Animals; Diabetes Mellitus, Experimental; Fatty Acids; Fatty Liver; Insulin Resistance; Liver; Malonyl Coenzyme A; Mice; Mice, Obese; Obesity; Oxidation-Reduction

Elevations in circulating levels of branched-chain amino acids (BCAAs) are associated with a variety of cardiometabolic diseases and conditions. Restriction of dietary BCAAs in rodent models of obesity lowers circulating BCAA levels and improves whole-animal and skeletal-muscle insulin sensitivity and lipid homeostasis, but the impact of BCAA supply on heart metabolism has not been studied. Here, we report that feeding a BCAA-restricted chow diet to Zucker fatty rats (ZFRs) causes a shift in cardiac fuel metabolism that favors fatty acid relative to glucose catabolism. This is illustrated by an increase in labeling of acetyl-CoA from [1-

Topics: Acetyl Coenzyme A; Amino Acids, Branched-Chain; Animals; Diet; Glucose; Male; Malonyl Coenzyme A; Metabolomics; Myocardium; Obesity; Palmitates; Protein Kinases; Rats; Rats, Zucker; Triglycerides

Topics: Adipose Tissue, Brown; Animals; Brain; Diabetes Mellitus, Type 2; Feeding Behavior; Gene Expression; Insulin; Leptin; Liver; Male; Malonyl Coenzyme A; Obesity; Rats, Zucker; Thermogenesis; Thinness

Impaired skeletal muscle mitochondrial fatty acid oxidation (mFAO) has been implicated in the etiology of insulin resistance. Carnitine palmitoyltransferase-1 (CPT1) is a key regulatory enzyme of mFAO whose activity is inhibited by malonyl-CoA, a lipogenic intermediate. Whereas increasing CPT1 activity in vitro has been shown to exert a protective effect against lipid-induced insulin resistance in skeletal muscle cells, only a few studies have addressed this issue in vivo. We thus examined whether a direct modulation of muscle CPT1/malonyl-CoA partnership is detrimental or beneficial for insulin sensitivity in the context of diet-induced obesity. By using a Cre-LoxP recombination approach, we generated mice with skeletal muscle-specific and inducible expression of a mutated CPT1 form (CPT1mt) that is active but insensitive to malonyl-CoA inhibition. When fed control chow, homozygous CPT1mt transgenic (dbTg) mice exhibited decreased CPT1 sensitivity to malonyl-CoA inhibition in isolated muscle mitochondria, which was sufficient to substantially increase ex vivo muscle mFAO capacity and whole body fatty acid utilization in vivo. Moreover, dbTg mice were less prone to high-fat/high-sucrose (HFHS) diet-induced insulin resistance and muscle lipotoxicity despite similar body weight gain, adiposity, and muscle malonyl-CoA content. Interestingly, these CPT1mt-protective effects in dbTg-HFHS mice were associated with preserved muscle insulin signaling, increased muscle glycogen content, and upregulation of key genes involved in muscle glucose metabolism. These beneficial effects of muscle CPT1mt expression suggest that a direct modulation of the malonyl-CoA/CPT1 partnership in skeletal muscle could represent a potential strategy to prevent obesity-induced insulin resistance.

Topics: Animals; Carnitine O-Palmitoyltransferase; Diet, High-Fat; Dietary Sucrose; Energy Metabolism; Glucose; Insulin Resistance; Male; Malonyl Coenzyme A; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mitochondria, Muscle; Muscle, Skeletal; Mutation; Obesity; Oxygen Consumption; Signal Transduction

Obesity is characterised by lipid accumulation in skeletal muscle, which increases the risk of developing insulin resistance and type 2 diabetes. AMP-activated protein kinase (AMPK) is a sensor of cellular energy status and is activated in skeletal muscle by exercise, hormones (leptin, adiponectin, IL-6) and pharmacological agents (5-amino-4-imidazolecarboxamide ribonucleoside [AICAR] and metformin). Phosphorylation of acetyl-CoA carboxylase 2 (ACC2) at S221 (S212 in mice) by AMPK reduces ACC activity and malonyl-CoA content but the importance of the AMPK-ACC2-malonyl-CoA pathway in controlling fatty acid metabolism and insulin sensitivity is not understood; therefore, we characterised Acc2 S212A knock-in (ACC2 KI) mice.. Whole-body and skeletal muscle fatty acid oxidation and insulin sensitivity were assessed in ACC2 KI mice and wild-type littermates.. ACC2 KI mice were resistant to increases in skeletal muscle fatty acid oxidation elicited by AICAR. These mice had normal adiposity and liver lipids but elevated contents of triacylglycerol and ceramide in skeletal muscle, which were associated with hyperinsulinaemia, glucose intolerance and skeletal muscle insulin resistance.. These findings indicate that the phosphorylation of ACC2 S212 is required for the maintenance of skeletal muscle lipid and glucose homeostasis.

Topics: Acetyl-CoA Carboxylase; Aminoimidazole Carboxamide; AMP-Activated Protein Kinases; Animals; Hypoglycemic Agents; Insulin; Insulin Resistance; Leptin; Lipid Metabolism; Malonyl Coenzyme A; Mice; Muscle, Skeletal; Obesity; Oxidation-Reduction; Phosphorylation; Ribonucleotides

Despite major public health concern, therapy for non-alcoholic fatty liver, the liver manifestation of the metabolic syndrome often associated with insulin resistance (IR), remains elusive. Strategies aiming to decrease liver lipogenesis effectively corrected hepatic steatosis and IR in obese animals. However, they also indirectly increased mitochondrial long-chain fatty acid oxidation (mFAO) by decreasing malonyl-CoA, a lipogenic intermediate, which is the allosteric inhibitor of carnitine palmitoyltransferase 1 (CPT1A), the key enzyme of mFAO. We thus addressed whether enhancing hepatic mFAO capacity, through a direct modulation of liver CPT1A/malonyl-CoA partnership, can reverse an already established hepatic steatosis and IR in obese mice.. Adenovirus-mediated liver expression of a malonyl-CoA-insensitive CPT1A (CPT1mt) in high-fat/high-sucrose (HF/HS) diet-induced or genetically (ob/ob) obese mice was followed by metabolic and physiological investigations.. In association with increased hepatic mFAO capacity, liver CPT1mt expression improved glucose tolerance and insulin response to a glucose load in HF/HS and ob/ob mice, showing increased insulin sensitivity, and corrected IR in ob/ob mice. Surprisingly, hepatic steatosis was not affected in CPT1mt-expressing obese mice, indicating a clear dissociation between hepatic steatosis and IR. Moreover, liver CPT1mt expression rescued HF/HS-induced impaired hepatic insulin signaling at the level of IRS-1, IRS-2, Akt, and GSK-3β, most likely through the observed decrease in the HF/HS-induced accumulation of lipotoxic lipids, oxidative stress, and JNK activation.. Enhancing hepatic mFAO capacity is sufficient to reverse a state of IR and glucose intolerance in obese mice independently of hepatic steatosis.

Topics: Adenoviridae; Adiposity; Animals; Body Weight; Carnitine O-Palmitoyltransferase; Fatty Acids; Fatty Liver; Glucaric Acid; Glucose Intolerance; Insulin Resistance; Lipid Metabolism; Male; Malonyl Coenzyme A; Mice; Mice, Inbred C57BL; Mice, Obese; Mitochondria, Liver; Obesity; Oxidation-Reduction

Excessive ectopic lipid deposition contributes to impaired insulin action in peripheral tissues and is considered an important link between obesity and type 2 diabetes mellitus. Acetyl-CoA carboxylase 2 (ACC2) is a key regulatory enzyme controlling skeletal muscle mitochondrial fatty acid oxidation; inhibition of ACC2 results in enhanced oxidation of lipids. Several mouse models lacking functional ACC2 have been reported in the literature. However, the phenotypes of the different models are inconclusive with respect to glucose homeostasis and protection from diet-induced obesity.. Here, we studied the effects of pharmacological inhibition of ACC2 using as a selective inhibitor the S enantiomer of compound 9c ([S]-9c). Selectivity was confirmed in biochemical assays using purified human ACC1 and ACC2.. (S)-9c significantly increased fatty acid oxidation in isolated extensor digitorum longus muscle from different mouse models (EC(50) 226 nmol/l). Accordingly, short-term treatment of mice with (S)-9c decreased malonyl-CoA levels in skeletal muscle and concomitantly reduced intramyocellular lipid levels. Treatment of db/db mice for 70 days with (S)-9c (10 and 30 mg/kg, by oral gavage) resulted in improved oral glucose tolerance (AUC -36%, p < 0.05), enhanced skeletal muscle 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) uptake, as well as lowered prandial glucose (-31%, p < 0.01) and HbA(1c) (-0.7%, p < 0.05). Body weight, liver triacylglycerol, plasma insulin and pancreatic insulin content were unaffected by the treatment.. In conclusion, the ACC2-selective inhibitor (S)-9c revealed glucose-lowering effects in a mouse model of diabetes mellitus.

Topics: Acetyl-CoA Carboxylase; Animals; Body Weight; Fatty Acids; Glucose; Glycated Hemoglobin; Homeostasis; Insulin Resistance; Male; Malonyl Coenzyme A; Mice; Mice, Inbred NOD; Muscle, Skeletal; Obesity; Triglycerides

Three coenzyme A (CoA) molecular species, i.e., acetyl-CoA, malonyl-CoA, and nonesterified CoA (CoASH), in 13 types of fasted rat tissue were analyzed. A relatively larger pool size of total CoA, consisting of acetyl-CoA, malonyl-CoA, and CoASH, was observed in the medulla oblongata, liver, heart, and brown adipose tissue. Focusing on changes in the CoA pool size in response to the nutrient composition of the diet given, total CoA pools in rats continuously fed a high-fat diet for 4 weeks were significantly higher in the hypothalamus, cerebellum, and kidney, and significantly lower in the liver and skeletal muscle than those of rats fed a high-carbohydrate or high-protein diet. In particular, reductions in the liver were remarkable and were caused by decreased CoASH levels. Consequently, the total CoA pool size was reduced by approximately one-fifth of the hepatic contents of rats fed the other diets. In the hypothalamus, which monitors energy balance, all three CoA molecular species measured were at higher levels when rats were fed the high-fat diet. Thus, it was of interest that feeding rats a high-fat diet affected the behaviors of CoA pools in the hypothalamus, liver, and skeletal muscle, suggesting a significant relationship between CoA pools, especially malonyl-CoA and/or CoASH pools, and lipid metabolism in vivo.

Topics: Acetyl Coenzyme A; Animals; Body Weight; Coenzyme A; Diet, High-Fat; Energy Intake; Hypothalamus; Lipid Metabolism; Liver; Male; Malonyl Coenzyme A; Muscle, Skeletal; Obesity; Organ Specificity; Rats; Rats, Wistar; Tissue Distribution; Weight Gain

Leptin directly acts on peripheral tissues and alters energy metabolism in obese mice. It also has acute beneficial effects on these tissues via its hypothalamic action. However, it is not clear what effect chronic intracerebroventrical (ICV) leptin administration has on cardiac energy metabolism. We examined the effects of chronic ICV leptin on glucose and fatty acid metabolism in isolated working hearts from high-fat-fed and low-fat-fed mice. Mice were fed a high-fat (60% calories from fat) or low-fat (10% calories from fat) diet for 8 weeks before ICV leptin (5 [mu]g/d) for 7 days. In low-fat-fed mice, leptin increased glucose oxidation rates in isolated working hearts when compared with control [203 +/- 21 vs. 793 +/- 93 nmol[middle dot](g dry weight)-1[middle dot]min-1]. In high-fat-fed mice leptin inhibited fatty acid oxidation [476 +/- 73 vs. 251 +/- 38 nmol[middle dot](g[middle dot]dry[middle dot]wt)-1[middle dot]min-1]. The increase in glucose oxidation in low-fat-fed mice was accompanied by increased pyruvate dehydrogenase activity. In high-fat-fed mice, leptin increased cardiac malonyl coenzyme A levels, secondary to a decrease in malonyl coenzyme A decarboxylase expression. These results suggest that ICV leptin alters cardiac energy metabolism opposite to its peripheral effects and that these effects differ depending on energy substrate supply to the mice.

Topics: Animals; Body Weight; Carboxy-Lyases; Dietary Fats; Energy Intake; Energy Metabolism; Glucose; Hypothalamus; Infusions, Intraventricular; Leptin; Lipid Metabolism; Male; Malonyl Coenzyme A; Mice; Mice, Inbred C57BL; Mice, Obese; Myocardium; Obesity; Oxidation-Reduction; Random Allocation

Inhibition of acetyl-CoA carboxylases has the potential for modulating long chain fatty acid biosynthesis and mitochondrial fatty acid oxidation. Hybridization of weak inhibitors of ACC2 provided a novel, moderately potent but lipophilic series. Optimization led to compounds 33 and 37, which exhibit potent inhibition of human ACC2, 10-fold selectivity over inhibition of human ACC1, good physical and in vitro ADME properties and good bioavailability. X-ray crystallography has shown this series binding in the CT-domain of ACC2 and revealed two key hydrogen bonding interactions. Both 33 and 37 lower levels of hepatic malonyl-CoA in vivo in obese Zucker rats.

Topics: Acetyl-CoA Carboxylase; Animals; Crystallography, X-Ray; Diabetes Mellitus, Type 2; Drug Design; Enzyme Inhibitors; Fatty Acids; Humans; Liver; Male; Malonyl Coenzyme A; Mice; Mice, Inbred C57BL; Models, Molecular; Obesity; Rats; Rats, Zucker; Small Molecule Libraries; Structure-Activity Relationship

Deletion of acetyl CoA carboxylase-2 (Acc2) reportedly causes leanness in the setting of hyperphagia. To determine the cellular basis for these effects, we generated a mouse model in which Acc2 can be selectively deleted by the action of Cre recombinase. Deletion of Acc2 from skeletal muscle, the predominant site of Acc2 expression, had no effect on body weight, food intake, or body composition. When Acc2 was inactivated in the germline, Acc2 knockout (Acc2KO) mice displayed no differences in body weight, food intake, body composition, or glucose homeostasis as compared to controls on chow or high fat diet. Total malonyl CoA content and fatty acid oxidation rates in skeletal muscle of Acc2KO mice were unchanged, suggesting metabolic compensation in response to the loss of Acc2. The limited impact of Acc2 deletion on energy balance raises the possibility that selective pharmacological inhibition of Acc2 for the treatment of obesity may be ineffective.

Topics: Acetyl-CoA Carboxylase; Alleles; Animals; Body Composition; Body Weight; Exons; Gene Deletion; Genotype; Integrases; Malonyl Coenzyme A; Mice; Mice, Knockout; Muscle, Skeletal; Obesity; Phenotype

Interest in the pathophysiological relevance of intramuscular triacylglycerol (IMTG) accumulation has grown from numerous studies reporting that abnormally high glycerolipid levels in tissues of obese and diabetic subjects correlate negatively with glucose tolerance. Here, we used a hindlimb perfusion model to examine the impact of obesity and elevated IMTG levels on contraction-induced changes in skeletal muscle fuel metabolism. Comprehensive lipid profiling was performed on gastrocnemius muscles harvested from lean and obese Zucker rats immediately and 25 min after 15 min of one-legged electrically stimulated contraction compared with the contralateral control (rested) limbs. Predictably, IMTG content was grossly elevated in control muscles from obese rats compared with their lean counterparts. In muscles of obese (but not lean) rats, contraction resulted in marked hydrolysis of IMTG, which was then restored to near resting levels during 25 min of recovery. Despite dramatic phenotypical differences in contraction-induced IMTG turnover, muscle levels of diacylglycerol (DAG) and long-chain acyl-CoAs (LCACoA) were surprisingly similar between groups. Tissue profiles of acylcarnitine metabolites suggested that the surfeit of IMTG in obese rats fueled higher rates of fat oxidation relative to the lean group. Muscles of the obese rats had reduced lactate levels immediately following contraction and higher glycogen resynthesis during recovery, consistent with a lipid-associated glucose-sparing effect. Together, these findings suggest that contraction-induced mobilization of local lipid reserves in obese muscles promotes beta-oxidation, while discouraging glucose utilization. Further studies are necessary to determine whether persistent oxidation of IMTG-derived fatty acids contributes to systemic glucose intolerance in other physiological settings.

Topics: Acetyl-CoA Carboxylase; Animals; Biological Transport; Carnitine; Glucose; Glycogen; Lactic Acid; Lipids; Malonyl Coenzyme A; Muscle Contraction; Muscle, Skeletal; Obesity; Pyruvic Acid; Rats; Rats, Zucker; Sciatic Nerve; Triglycerides

Given the success in engineering synthetic phenotypes in microbes and mammalian cells, constructing non-native pathways in mammals has become increasingly attractive for understanding and identifying potential targets for treating metabolic disorders. Here, we introduced the glyoxylate shunt into mouse liver to investigate mammalian fatty acid metabolism. Mice expressing the shunt showed resistance to diet-induced obesity on a high-fat diet despite similar food consumption. This was accompanied by a decrease in total fat mass, circulating leptin levels, plasma triglyceride concentration, and a signaling metabolite in liver, malonyl-CoA, that inhibits fatty acid degradation. Contrary to plants and bacteria, in which the glyoxylate shunt prevents the complete oxidation of fatty acids, this pathway when introduced in mice increases fatty acid oxidation such that resistance to diet-induced obesity develops. This work suggests that using non-native pathways in higher organisms to explore and modulate metabolism may be a useful approach.

Topics: Animals; Body Fat Distribution; Cell Line, Tumor; Dietary Fats; Energy Metabolism; Fatty Acids; Female; Gluconeogenesis; Glyoxylates; Humans; Isocitrate Lyase; Leptin; Malate Synthase; Male; Malonyl Coenzyme A; Mice; Mice, Inbred C57BL; Obesity; Respiratory Function Tests; Triglycerides

Leptin stimulates fatty acid oxidation via the phosphorylation of AMPK (AMP-activated protein kinase) and ACC (acetyl-CoA carboxylase). Obesity is associated with resistance to the effects of leptin. We determined the action of leptin on AMPKalpha and ACCbeta phosphorylation and lipid metabolism in soleus (SOL) and extensor digitorum longus (EDL) muscles from lean and obese Wistar rats after 1 and 100 nM leptin. Both leptin doses stimulated phosphorylation of AMPKalpha and ACCbeta (P

Topics: Acetyl-CoA Carboxylase; Acyl Coenzyme A; Adipose Tissue; AMP-Activated Protein Kinases; Animals; Body Weight; Dietary Fats; Disease Models, Animal; Dose-Response Relationship, Drug; Energy Metabolism; Enzyme Activation; Fatty Acids; Glycolysis; Humans; Insulin; Leptin; Male; Malonyl Coenzyme A; Multienzyme Complexes; Muscle Fibers, Skeletal; Muscle, Skeletal; Obesity; Oxidation-Reduction; Phosphorylation; Protein Serine-Threonine Kinases; Rats; Rats, Wistar

The lipid peroxidation product 4-hydroxynonenal (4-HNE) is a signaling mediator with wide-ranging biological effects. In this paper, we report that disruption of mGsta4, a gene encoding the 4-HNE-conjugating enzyme mGSTA4-4, causes increased 4-HNE tissue levels and is accompanied by age-dependent development of obesity which precedes the onset of insulin resistance in 129/sv mice. In contrast, mGsta4 null animals in the C57BL/6 genetic background have normal 4-HNE levels and remain lean, indicating a role of 4-HNE in triggering or maintaining obesity. In mGsta4 null 129/sv mice, the expression of the acetyl-CoA carboxylase (ACC) transcript is enhanced several-fold with a concomitant increase in the tissue level of malonyl-CoA. Also, mitochondrial aconitase is partially inhibited, and tissue citrate levels are increased. Accumulation of citrate could lead to allosteric activation of ACC, further augmenting malonyl-CoA levels. Aconitase may be inhibited by 4-HNE or by peroxynitrite generated by macrophages which are enriched in white adipose tissue of middle-aged mGsta4 null 129/sv mice and, upon lipopolysaccharide stimulation, produce more reactive oxygen species and nitric oxide than macrophages from wild-type mice. Excessive malonyl-CoA synthesized by the more abundant and/or allosterically activated ACC in mGsta4 null mice leads to fat accumulation by the well-known mechanisms of promoting fatty acid synthesis and inhibiting fatty acid beta-oxidation. Our findings complement the recent report that obesity causes both a loss of mGSTA4-4 and an increase in the level of 4-HNE [Grimsrud, P. A., et al. (2007) Mol. Cell. Proteomics 6, 624-637]. The two reciprocal processes are likely to establish a positive feedback loop that would promote and perpetuate the obese state.

Topics: Acetyl-CoA Carboxylase; Aconitate Hydratase; Aging; Aldehydes; Animals; Antigens, CD; Antigens, Differentiation, Myelomonocytic; Blood Glucose; Citric Acid; Female; Glucose Tolerance Test; Glutathione Transferase; Insulin Resistance; Lipid Peroxidation; Male; Malonyl Coenzyme A; Mice; Mice, Inbred C57BL; Obesity; Reactive Oxygen Species

Peroxisomal oxidation yields metabolites that are more efficiently utilized by mitochondria. This is of potential clinical importance because reduced fatty acid oxidation is suspected to promote excess lipid accumulation in obesity-associated insulin resistance. Our purpose was to assess peroxisomal contributions to mitochondrial oxidation in mixed gastrocnemius (MG), liver, and left ventricle (LV) homogenates from lean and fatty (fa/fa) Zucker rats. Results indicate that complete mitochondrial oxidation (CO(2) production) using various lipid substrates was increased approximately twofold in MG, unaltered in LV, and diminished approximately 50% in liver of fa/fa rats. In isolated mitochondria, malonyl-CoA inhibited CO(2) production from palmitate 78%, whereas adding isolated peroxisomes reduced inhibition to 21%. These data demonstrate that peroxisomal products may enter mitochondria independently of CPT I, thus providing a route to maintain lipid disposal under conditions where malonyl-CoA levels are elevated, such as in insulin-resistant tissues. Peroxisomal metabolism of lignoceric acid in fa/fa rats was elevated in both liver and MG (LV unaltered), but peroxisomal product distribution varied. A threefold elevation in incomplete oxidation was solely responsible for increased hepatic peroxisomal oxidation (CO(2) unaltered). Alternatively, only CO(2) was detected in MG, indicating that peroxisomal products were exclusively partitioned to mitochondria for complete lipid disposal. These data suggest tissue-specific destinations for peroxisome-derived products and emphasize a potential role for peroxisomes in skeletal muscle lipid metabolism in the obese, insulin-resistant state.

Topics: Animals; Disease Models, Animal; Epoxy Compounds; Glucose Tolerance Test; Hypoglycemic Agents; Insulin Resistance; Lipids; Liver; Male; Malonyl Coenzyme A; Mitochondria, Liver; Mitochondria, Muscle; Obesity; Oxidation-Reduction; Peroxisomes; Rats; Rats, Sprague-Dawley; Rats, Zucker

Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the first committed step in triacylglycerol (TAG) and phospholipid biosynthesis. GPAT activity has been identified in both ER and mitochondrial subcellular fractions. The ER activity dominates in most tissues except in liver, where the mitochondrial isoform (mtGPAT) can constitute up to 50% of the total activity. To study the in vivo effects of hepatic mtGPAT overexpression, mice were transduced with adenoviruses expressing either murine mtGPAT or a catalytically inactive variant of the enzyme. Overexpressing mtGPAT resulted in massive 12- and 7-fold accumulation of liver TAG and diacylglycerol, respectively but had no effect on phospholipid or cholesterol ester content. Histological analysis showed extensive lipid accumulation in hepatocytes. Furthermore, mtGPAT transduction markedly increased adipocyte differentiation-related protein and stearoyl-CoA desaturase-1 (SCD-1) in the liver. In line with increased SCD-1 expression, 18:1 and 16:1 in the hepatic TAG fraction increased. In addition, mtGPAT overexpression decreased ex vivo fatty acid oxidation, increased liver TAG secretion rate 2-fold, and increased plasma TAG and cholesterol levels. These results support the hypothesis that increased hepatic mtGPAT activity associated with obesity and insulin resistance contributes to increased TAG biosynthesis and inhibition of fatty acid oxidation, responses that would promote hepatic steatosis and dyslipidemia.

Topics: Amino Acid Substitution; Animals; Carbohydrates; Diglycerides; Enzyme Induction; Fatty Acids; Fatty Liver; Glycerol-3-Phosphate O-Acyltransferase; Insulin Resistance; Lipids; Male; Malonyl Coenzyme A; Mass Spectrometry; Mice; Mice, Inbred C57BL; Mitochondria, Liver; Obesity; Oxidation-Reduction; Phospholipids; Recombinant Fusion Proteins; RNA, Messenger; Triglycerides

In animals, liver and white adipose are the main sites for the de novo fatty acid synthesis. Deletion of fatty acid synthase or acetyl-CoA carboxylase (ACC) 1 in mice resulted in embryonic lethality, indicating that the de novo fatty acid synthesis is essential for embryonic development. To understand the importance of de novo fatty acid synthesis and the role of ACC1-produced malonyl-CoA in adult mouse tissues, we generated liver-specific ACC1 knockout (LACC1KO) mice. LACC1KO mice have no obvious health problem under normal feeding conditions. Total ACC activity and malonyl-CoA levels were approximately 70-75% lower in liver of LACC1KO mice compared with that of the WT mice. In addition, the livers of LACC1KO mice accumulated 40-70% less triglycerides. Unexpectedly, when fed fat-free diet for 10 days, there was significant up-regulation of PPARgamma and several enzymes in the lipogenic pathway in the liver of LACC1KO mice compared with the WT mice. Despite the significant up-regulation of the lipogenic enzymes, including a >2-fold increase in fatty acid synthase mRNA, protein, and activity, there was significant decrease in the de novo fatty acid synthesis and triglyceride accumulation in the liver. However, there were no significant changes in blood glucose and fasting ketone body levels. Hence, reducing cytosolic malonyl-CoA and, therefore, the de novo fatty acid synthesis in the liver, does not affect fatty acid oxidation and glucose homeostasis under lipogenic conditions.

Topics: Acetyl-CoA Carboxylase; Animal Feed; Animals; Dietary Fats; Gene Deletion; Gene Expression Regulation; Glucose; Homeostasis; Lipid Metabolism; Liver; Malonyl Coenzyme A; Mice; Mice, Inbred C57BL; Mice, Knockout; Obesity; Rats; Triglycerides; Up-Regulation

In humans and animal models, increased intramuscular lipid (IML) stores have been implicated in insulin resistance. Malonyl-CoA plays a critical role in cellular lipid metabolism both by serving as a precursor in the synthesis of lipids and by inhibiting lipid oxidation. In muscle, Malonyl-CoA acts primarily as a negative allosteric regulator of carnitine palmitoyl transferase-1 (CPT1) activity, thereby blocking the transport of long chain fatty acyl CoAs into the mitochondria for oxidation. In muscle, increased malonyl-CoA, decreased muscle CPT1 activity, and increased IML have all been reported in obesity. In order to determine whether malonyl-CoA synthesis might be under transcriptional as well as biochemical regulation, we measured mRNA content of several key genes that contribute to the cellular metabolism of malonyl-CoA in muscle biopsies from lean to morbidly obese subjects. Employing quantitative real-time PCR, we determined that expression of mitochondrial acetyl-CoA carboxylase 2 (ACC2) was increased by 50% with obesity (P < 0.05). In both lean and obese subjects, expression of mitochondrial ACC2 was 20-fold greater than that of cytoplasmic ACC1, consistent with their hypothesized roles in synthesizing malonyl-CoA from acetyl-CoA for CPT1 regulation and lipogenesis, respectively. In addition, in both lean and obese subjects, expression of malonyl-CoA decarboxylase was approximately 40-fold greater than fatty acid synthase, consistent with degradation, rather than lipogenesis, being the primary fate of malonyl-CoA in human muscle. No other genes showed signs of increased mRNA content with obesity, suggesting that there may be selective transcriptional regulation of malonyl-CoA metabolism in human obesity.

Topics: Acetyl-CoA Carboxylase; Adult; Animals; Biopsy; Carboxy-Lyases; Carnitine O-Palmitoyltransferase; Fatty Acid Synthases; Gene Expression Regulation, Enzymologic; Humans; Isoenzymes; Malonyl Coenzyme A; Muscle, Skeletal; Obesity; Pyruvate Carboxylase; Sterol Regulatory Element Binding Protein 1

Topics: Acetyl-CoA Carboxylase; Adipocytes; Adipose Tissue; Animals; Cell Cycle Proteins; Energy Intake; Energy Metabolism; Enzyme Activation; Fasting; Fatty Acids; Hepatocytes; Insulin; Insulin Resistance; Lipid Metabolism; Lipogenesis; Liver; Malonyl Coenzyme A; Mice; Models, Biological; Nuclear Proteins; Obesity; Oxidation-Reduction; Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction; Ubiquitin; Ubiquitin-Protein Ligases

Increased accumulation of fatty acids and their derivatives can impair insulin-stimulated glucose disposal by skeletal muscle. To characterize the nature of the defects in lipid metabolism and to evaluate the effects of thiazolidinedione treatment, we analyzed the levels of triacylglycerol, long-chain fatty acyl-coA, malonyl-CoA, fatty acid oxidation, AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase (ACC), malonyl-CoA decarboxylase, and fatty acid transport proteins in muscle biopsies from nondiabetic lean, obese, and type 2 subjects before and after an euglycemic-hyperinsulinemic clamp as well as pre-and post-3-month rosiglitazone treatment. We observed that low AMPK and high ACC activities resulted in elevation of malonyl-CoA levels and lower fatty acid oxidation rates. These conditions, along with the basal higher expression levels of fatty acid transporters, led accumulation of long-chain fatty acyl-coA and triacylglycerol in insulin-resistant muscle. During the insulin infusion, muscle fatty acid oxidation was reduced to a greater extent in the lean compared with the insulin-resistant subjects. In contrast, isolated muscle mitochondria from the type 2 subjects exhibited a greater rate of fatty acid oxidation compared with the lean group. All of these abnormalities in the type 2 diabetic group were reversed by rosiglitazone treatment. In conclusion, these studies have shown that elevated malonyl-CoA levels and decreased fatty acid oxidation are key abnormalities in insulin-resistant muscle, and, in type 2 diabetic patients, thiazolidinedione treatment can reverse these abnormalities.

Topics: Acetyl-CoA Carboxylase; Acyl Coenzyme A; Adult; AMP-Activated Protein Kinases; Carboxy-Lyases; Diabetes Mellitus, Type 2; Fatty Acid Transport Proteins; Fatty Acids; Female; Glucose Clamp Technique; Humans; Hypoglycemic Agents; Insulin Resistance; Lipids; Male; Malonyl Coenzyme A; Middle Aged; Mitochondria, Muscle; Multienzyme Complexes; Muscle, Skeletal; Obesity; Oxidation-Reduction; Protein Serine-Threonine Kinases; Rosiglitazone; Thiazolidinediones; Triglycerides

Plasma leptin and growth hormone (GH) profile and pulsatility have been studied in morbidly obese subjects before and 14 months after bilio-pancreatic diversion (BPD), a bariatric technique producing massive lipid malabsorption. The maximum leptin diurnal variation (acrophase) decreased (10.27+/-1.70 vs. 22.60+/-2.79 ng x ml(-1); P=0.001), while its pulsatility index (PI) increased (1.084+/-0.005 vs. 1.050+/-0.004 ng x ml(-1) x min(-1); P=0.02) after BPD. Plasma GH acrophase increased (P=0.0001) from 0.91+/-0.20 to 4.58+/-0.80 microg x l(-1) x min(-1) after BPD as well as GH PI (1.70+/-0.13 vs. 1.20+/-0.04 microg x l(-1) x min(-1); P=0.024). Whole-body glucose uptake (M), assessed by euglycemic-hyperinsulinemic clamp, almost doubled after BPD (from 0.274+/-0.022 to 0.573+/-0.027 mmol x kgFFM(-1) x min(-1); P<0.0001), while 24 h lipid oxidation was significantly (P<0.0001) reduced (131.94+/-35.58 vs. 44.56+/-15.10 g). However, the average lipid oxidation was 97.2+/-3.1% (P<0.01) of the metabolizable lipid intake after the bariatric operation, while it was 69.2+/-8.5% before. After the operation, skeletal muscle ACC2 mRNA decreased (P<0.0001) from 452.82+/-76.35 to 182.45+/-40.69% of cyclophilin mRNA as did the malonyl-CoA (from 0.28+/-0.02 to 0.16+/-0.01 nmol x g(-1); P<0.0001). Leptin changes negatively correlated with M changes (R2=0.69, P<0.001). In a stepwise regression (R2=0.87, P=0.0055), only changes in 24 h free fatty acids (B=0.105+/-0.018, P=0.002) and glucose/insulin ratio (B=0.247+/-0.081, P=0.029) were the best predictors of leptin variations. In conclusion, the reversion of insulin resistance after BPD might allow reversal of leptin resistance, restoration of leptin pulsatility, and consequent inhibition of ACC2 mRNA expression, translating to a reduced synthesis of malonyl-CoA, which, in turn, results in increased fatty acid oxidation. Finally, since leptin inhibits GH secretion, a reduction of circulating leptin levels might have produced an increase in GH secretion, as observed in our series.

Topics: Acetyl-CoA Carboxylase; Adult; Area Under Curve; Biliopancreatic Diversion; Circadian Rhythm; Energy Metabolism; Fatty Acids, Nonesterified; Female; Glucose; Glucose Clamp Technique; Human Growth Hormone; Humans; Hydrocortisone; Insulin; Insulin Resistance; Leptin; Malonyl Coenzyme A; Muscle, Skeletal; Obesity; RNA, Messenger

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

Topics: Acetyl Coenzyme A; Dietary Carbohydrates; Humans; Hyperinsulinism; Lipid Metabolism; Lipids; Malonyl Coenzyme A; Obesity; Research

Abdominal obesity and physical inactivity are associated with insulin resistance in humans and contribute to the development of type 2 diabetes. Likewise, sustained increases in the concentration of malonyl coenzyme A (CoA), an inhibitor of fatty-acid oxidation, have been observed in muscle in association with insulin resistance and type 2 diabetes in various rodents. In the present study, we assessed whether these factors are present in a defined population of slightly overweight (body mass index, 26.2 kg/m2), insulin-resistant patients with type 2 diabetes. Thirteen type 2 diabetic men and 17 sex-, age-, and body mass index-matched control subjects were evaluated. Insulin sensitivity was assessed during a two-step euglycemic insulin clamp (infusion of 0.25 and 1.0 mU/kg x min). The rates of glucose administered during the low-dose insulin clamp were 2.0 +/- 0.2 vs. 0.7 +/- 0.2 mg/kg body weight x min (P < 0.001) in the control and diabetic subjects, respectively; rates during the high-dose insulin clamp were 8.3 +/- 0.7 vs. 4.6 +/- 0.4 mg/kg body weight x min (P < 0.001) for controls and diabetic subjects. The diabetic patients had a significantly lower maximal oxygen uptake than control subjects (29.4 +/- 1.0 vs. 33.4 +/- 1.4 ml/kg x min; P = 0.03) and a greater total body fat mass (3.7 kg), mainly due to an increase in truncal fat (16.5 +/- 0.9 vs. 13.1 +/- 0.9 kg; P = 0.02). The plasma concentration of free fatty acid and the rate of fatty acid oxidation during the clamps were both higher in the diabetic subjects than the control subjects (P = 0.002-0.007). In addition, during the high-dose insulin clamp, the increase in cytosolic citrate and malate in muscle, which parallels and regulates malonyl CoA levels, was significantly less in the diabetic patients (P < 0.05 vs. P < 0.001). Despite this, a similar increase in the concentration of malonyl CoA was observed in the two groups, suggesting an abnormality in malonyl CoA regulation in the diabetic subjects. In conclusion, the results confirm that insulin sensitivity is decreased in slightly overweight men with mild type 2 diabetes and that this correlates closely with an increase in truncal fat mass and a decrease in physical fitness. Whether the unexpectedly high levels of malonyl CoA in muscle, together with the diminished suppression of plasma free fatty acid, explains the insulin resistance of the diabetic patients during the clamp remains to be determined.

Topics: Diabetes Mellitus; Diabetes Mellitus, Type 2; Dose-Response Relationship, Drug; Fatty Acids, Nonesterified; Glucose; Glucose Clamp Technique; Humans; Infusions, Intravenous; Insulin Resistance; Male; Malonyl Coenzyme A; Middle Aged; Obesity; Oxidation-Reduction; Physical Fitness

Topics: Animals; Down-Regulation; Eating; Energy Metabolism; Humans; Hypothalamus; Liver; Malonyl Coenzyme A; Obesity; Oxidative Stress; Reactive Oxygen Species; Stearoyl-CoA Desaturase; Weight Loss

C75, a known inhibitor of fatty acid synthase is postulated to cause significant weight loss through decreased hypothalamic neuropeptide Y (NPY) production. Peripherally, C75, an alpha-methylene-gamma-butyrolactone, reduces adipose tissue and fatty liver, despite high levels of malonyl-CoA. To investigate this paradox, we studied the effect of C75 on fatty acid oxidation and energy production in diet-induced obese (DIO) mice and cellular models. Whole-animal calorimetry showed that C75-treated DIO mice had a 50% greater weight loss, and a 32.9% increased production of energy because of fatty acid oxidation, compared with paired-fed controls. Etomoxir, an inhibitor of carnitine O-palmitoyltransferase-1 (CPT-1), reversed the increased energy expenditure in DIO mice by inhibiting fatty acid oxidation. C75 treatment of rodent adipocytes and hepatocytes and human breast cancer cells increased fatty acid oxidation and ATP levels by increasing CPT-1 activity, even in the presence of elevated concentrations of malonyl-CoA. Studies in human cancer cells showed that C75 competed with malonyl-CoA, as measured by CPT-1 activity assays. Thus, C75 acts both centrally to reduce food intake and peripherally to increase fatty acid oxidation, leading to rapid and profound weight loss, loss of adipose mass, and resolution of fatty liver. The pharmacological stimulation of CPT-1 activity is a novel finding. The dual action of the C75 class of compounds as fatty acid synthase inhibitors and CPT-1 agonists has therapeutic implications in the treatment of obesity and type II diabetes.

Topics: 3T3 Cells; 4-Butyrolactone; Adenosine Triphosphate; Adipocytes; Animals; Carnitine O-Palmitoyltransferase; Diet; Energy Metabolism; Enzyme Inhibitors; Epoxy Compounds; Fatty Acid Synthases; Fatty Acids; Humans; Male; Malonyl Coenzyme A; Mice; Mice, Inbred C57BL; Obesity; Oxidation-Reduction; Tumor Cells, Cultured; Weight Loss

Topics: 4-Butyrolactone; Adipose Tissue; Animals; Carnitine O-Palmitoyltransferase; Cell Size; Cerulenin; Energy Intake; Fatty Acids; Ghrelin; Humans; Malonyl Coenzyme A; Obesity; Peptide Hormones; Peptides

A multidisciplinary team may have discovered an important new weapon in the battle of the bulge. On page 2379 of this issue, the team reports that a molecule that is needed for fat synthesis in the body may play a key role in appetite signaling in the brain. Moreover, the investigators produced a synthetic inhibitor of this molecule that spurred a dramatic drop in appetite and weight in mice.

Topics: Animals; Appetite; Appetite Depressants; Brain; Enzyme Inhibitors; Fasting; Fatty Acid Synthases; Humans; Liver; Malonyl Coenzyme A; Mice; Neuropeptide Y; Obesity; RNA, Messenger; Weight Loss

In liver, insulin and glucose acutely increase the concentration of malonyl-CoA by dephosphorylating and activating acetyl-CoA carboxylase (ACC). In contrast, in incubated rat skeletal muscle, they appear to act by increasing the cytosolic concentration of citrate, an allosteric activator of ACC, as reflected by increases in the whole cell concentrations of citrate and malate [Saha, A. K., D. Vavvas, T. G. Kurowski, A. Apazidis, L. A. Witters, E. Shafrir, and N. B. Ruderman. Am. J. Physiol. 272 (Endocrinol. Metab. 35): E641-E648, 1997]. We report here that sustained increases in plasma insulin and glucose may also increase the concentration of malonyl-CoA in rat skeletal muscle in vivo by this mechanism. Thus 70 and 125% increases in malonyl-CoA induced in skeletal muscle by infusions of glucose for 1 and 4 days, respectively, and a twofold increase in its concentration during a 90-min euglycemic-hyperinsulinemic clamp were all associated with significant increases in the sum of whole cell concentrations of citrate and/or malate. Similar correlations were observed in muscle of the hyperinsulinemic fa/fa rat, in denervated muscle, and in muscle of rats infused with insulin for 5 h. In muscle of 48-h-starved rats 3 and 24 h after refeeding, increases in malonyl-CoA were not accompanied by consistent increases in the concentrations of malate or citrate. However, they were associated with a decrease in the whole cell concentration of long-chain fatty acyl-CoA (LCFA-CoA), an allosteric inhibitor of ACC. The results suggest that increases in the concentration of malonyl-CoA, caused in rat muscle in vivo by sustained increases in plasma insulin and glucose or denervation, may be due to increases in the cytosolic concentration of citrate. In contrast, during refeeding after starvation, the increase in malonyl-CoA in muscle is probably due to another mechanism.

Topics: Acetyl-CoA Carboxylase; Animals; Citric Acid; Cytosol; Food; Insulin; Malates; Male; Malonyl Coenzyme A; Muscle Denervation; Muscle, Skeletal; Obesity; Osmolar Concentration; Rats; Rats, Sprague-Dawley; Rats, Wistar; Starvation

This study was designed to examine whether n-3 and n-6 polyunsaturated fatty acids at a very low dietary level (about 0.2%) would alter liver activities in respect to fatty acid oxidation. Obese Zucker rats were used because of their low level of fatty acid oxidation, which would make increases easier to detect. Zucker rats were fed diets containing different oil mixtures (5%, w/w) with the same ratio of n-6/n-3 fatty acids supplied either as fish oil or arachidonic acid concentrate. Decreased hepatic triacylglycerol levels were observed only with the diet containing fish oil. In mitochondrial outer membranes, which support carnitine palmitoyltransferase I activity, cholesterol content was similar for all diets, while the percentage of 22:6n-3 and 20:4n-6 in phospholipids was enhanced about by 6 and 3% with the diets containing fish oil and arachidonic acid, respectively. With the fish oil diet, the only difference found in activities related to fatty acid oxidation was the lower sensitivity of carnitine palmitoyltransferase I to malonyl-CoA inhibition. With the diet containing arachidonic acid, peroxisomal fatty acid oxidation and carnitine palmitoyltransferase I activity were markedly depressed. Compared with the control diet, the diets enriched in fish oil and in arachidonic acid gave rise to a higher specific activity of aryl-ester hydrolase in microsomal fractions. We suggest that slight changes in composition of n-3 or n-6 polyunsaturated fatty acids in mitochondrial outer membranes may alter carnitine palmitoyltransferase I activity.

Topics: Animals; Carboxylic Ester Hydrolases; Carnitine O-Palmitoyltransferase; Dietary Fats, Unsaturated; Fatty Acids, Omega-3; Fatty Acids, Omega-6; Fatty Acids, Unsaturated; Lipid Metabolism; Male; Malonyl Coenzyme A; Mice; Microsomes, Liver; Mitochondria, Liver; Monoamine Oxidase; Obesity; Palmitoyl Coenzyme A; Rats; Rats, Zucker; Subcellular Fractions; Urate Oxidase

Insulin resistance is present in liver and muscle of subjects with type 2 diabetes and obesity. Recent studies suggest that such insulin resistance could be related to abnormalities in lipid-mediated signal transduction; however, the nature of these abnormalities is unclear. To examine this question further, tissue levels of diacylglycerol (DAG), malonyl-CoA, and triglyceride (TG) were determined in liver and soleus muscle of obese insulin-resistant KKAy mice and lean C57 BL control mice. In addition, the effects of treatment with pioglitazone, an antidiabetic agent that acts by increasing insulin sensitivity in muscle, liver, and other tissues, were assessed. The KKAy mice were hyperglycemic (407 vs. 138 mg/dl), hypertriglyceridemic (337 vs. 109 mg/dl), hyperinsulinemic (631 vs. 15 mU/ml), and weighed more (42 vs. 35 g) than the control mice. They also had 1.5- to 2.0-fold higher levels of malonyl-CoA in both liver and muscle, higher DAG (twofold) and TG (1.3-fold) levels in muscle, and higher TG (threefold), but not DAG, levels. Treatment of the KKAy mice with pioglitazone for 4 days decreased plasma glucose, TGs, and insulin by approximately 50% and restored hepatic and muscle malonyl-CoA levels to control values. In contrast, pioglitazone increased hepatic and muscle DAG levels two- or threefold. It has no effect on muscle or hepatic TG content, and it slightly increased hepatic TGs in the control group. The results indicate that abnormalities in tissue lipids occur in both liver and muscle of the KKAy mouse and that they are differentially altered when insulin sensitivity is enhanced by treatment with pioglitazone.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood; Diglycerides; Hypoglycemic Agents; Insulin Resistance; Lipid Metabolism; Liver; Male; Malonyl Coenzyme A; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Muscles; Obesity; Pioglitazone; Thiazoles; Thiazolidinediones

Hepatic mitochondrial carnitine palmitoyltransferase (CPT) properties, beta-oxidation of palmitoyl-CoA and membrane polarization were measured in lean and obese Zucker rats. The Vmax. of the 'outer' carnitine palmitoyltransferase ('CPT-A') increased with starvation, with no change in the Km for either carnitine or palmitoyl-CoA. The Ki for malonyl-CoA increased with starvation in lean rats, but not in obese rats. The Vmax. of the 'inner' enzyme ('CPT-B'), as measured by using inverted submitochondrial vesicles, increased with starvation in obese rats only, with no change in the Km for either carnitine or palmitoyl-CoA. The Ki for malonyl-CoA was 2-5-fold higher in inverted vesicles than in intact mitochondria, and showed no alteration with starvation. The activities of both enzymes correlated positively with each other and with beta-oxidation, and inversely with membrane polarization. Malonyl-CoA had little effect on gross membrane fluidity in the Zucker rat, as reflected by diphenylhexatriene fluorescence polarization. The results indicate that both enzymes are related and respond similarly to alterations in membrane fluidity. Membrane fluidity may provide a mechanism for co-ordinated control of CPT activity on both sides of the mitochondrial inner membrane.

Topics: Acyltransferases; Animals; Carnitine O-Palmitoyltransferase; Fluorescence Polarization; Intracellular Membranes; Isoenzymes; Kinetics; Malonyl Coenzyme A; Mitochondria, Liver; Obesity; Oxidation-Reduction; Rats; Rats, Zucker; Starvation

The relationship between lipogenesis and ketogenesis and the concentration of malonyl coenzyme A (CoA) was investigated in hepatocytes from adult obese Zucker rats and their lean littermates fed either a control low-fat diet or a high-fat diet (30% lard in weight). With the control diet, lipogenesis--although strongly inhibited in the presence of either 1 mmol/L oleate, 10(-6) mol/L glucagon or 0.1 mmol/L TOFA (a hypolipidemic drug)--remained about fifteen-fold higher in the obese rats than in the lean rats. In contrast, ketogenesis under some conditions (oleate + TOFA) was not significantly lower (30%) as compared with the lean rats. After adaptation to the high-fat diet, lipogenesis was depressed fourfold in the lean rats and ninefold in the obese ones; however its magnitude remained significantly higher in the latter, namely at a value close to that measured in control-fed lean rats. Ketogenesis was comparable in lean and obese rats and much higher in the presence of 1 mmol/L oleate than of 0.3 mmol/L oleate, whereas lipogenesis did not vary with increasing oleate concentration in the medium. Acetyl-CoA carboxylase activity measured in liver homogenates was higher in the obese group, but was stepwise inhibited by increasing concentrations of oleyl-CoA regardless of the diet for both lean and obese rats, thus showing no abnormality of in vitro responsiveness to this inhibitor. With the control diet, hepatocyte malonyl-CoA levels were significantly higher in the obese rats, both in the basal state and after inhibition of lipogenesis by oleate and TOFA.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acetyl-CoA Carboxylase; Acyl Coenzyme A; Animals; Dietary Fats; Glucagon; In Vitro Techniques; Ketone Bodies; Lactates; Lipids; Liver; Male; Malonyl Coenzyme A; Obesity; Oleic Acid; Oleic Acids; Pyruvates; Rats; Rats, Zucker

Carnitine acyltransferase of liver mitochondria prepared from obese Zucker rats has a higher sensitivity to inhibition by malonyl-CoA compared with carnitine acyltransferase of mitochondria prepared from lean Zucker rats.

Topics: Acyl Coenzyme A; Acyltransferases; Animals; Carnitine Acyltransferases; Fatty Acids; Male; Malonyl Coenzyme A; Mitochondria, Liver; Obesity; Rats; Rats, Zucker