guanosine-triphosphate and Insulin-Resistance

The characterisation of receptor sites of hormones to various tissues in vivo and in vitro have introduced new insights for the evaluation of pathogenic mechanisms involved in endocrine and metabolic human diseases. Disorders at the receptor level are characterized by changes in the number of receptor sites, the affinity of the hormone to its specific receptors or by generation of anti-receptor antibodies, which impair hormone binding procedures or post-receptor metabolism. Altered receptor physiology may be of an important value as well for diagnosis and treatment of endocrine, metabolic and neoplastic diseases as for the understanding of their pathogenetic mechanisms.

Topics: Acanthosis Nigricans; Adenosine Triphosphate; Adenylyl Cyclases; Antibodies; Binding, Competitive; Cyclic AMP; Diabetes Complications; Endocrine System Diseases; Enzyme Activation; Graves Disease; Guanosine Triphosphate; Humans; Hypercholesterolemia; Insulin; Insulin Resistance; Lipoproteins, LDL; Metabolic Diseases; Myasthenia Gravis; Obesity; Receptors, Androgen; Receptors, Cell Surface; Receptors, Neurotransmitter

Non‑alcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, insulin resistance and inflammation; however, the exact pathogenesis of NAFLD is not fully understood. Green tea polyphenols (GTP) exhibit beneficial effects against metabolic syndrome. However, the effect of GTP on NAFLD remains largely unknown. The aim of the present study was to investigate the effects of GTP on NAFLD in high‑fat diet (HFD)‑induced rats. The NAFLD rat model was induced with a HFD for 8 weeks. A total of 30 adult male Sprague Dawley rats were randomly divided into three groups: i) Normal control group; ii) HFD group; and iii) HFD with GTP group. Hematoxylin and eosin and Oil Red O analyses were performed. The levels of alanine aminotransferase (ALT), aspartate amino-transferase (AST) and inflammatory cytokines in the serum, as well as oxidative stress markers and hepatic lipids in the liver were measured. In addition, parameters associated with glucose metabolism were also assessed. Western blotting and RT‑qPCR were used to determine the expression levels of 5' adenosine monophosphate‑activated protein kinase (AMPK). HFD‑induced rats exhibited features associated with NAFLD. GTP intervention significantly reduced serum ALT and AST levels. Fasting serum glucose, insulin resistance and hepatic lipid levels were all decreased in the GTP‑treated rats. GTP also significantly decreased the levels of TNF‑α, IL‑6 and malondialdehyde. In contrast, superoxide dismutase levels were increased in the liver. Furthermore, GTP also significantly increased phosphorylation of AMPK and attenuated histopathological changes indicative of injury in liver tissue. GTP has a protective effect on HFD‑induced hepatic steatosis, insulin resistance and inflammation, and the underlying mechanism may involve the AMPK pathway.

Topics: AMP-Activated Protein Kinases; Animals; Blood Glucose; Body Weight; Diet, High-Fat; Fatty Liver; Guanosine Triphosphate; Insulin; Insulin Resistance; Lipid Metabolism; Liver Function Tests; Male; Plant Extracts; Polyphenols; Rats; Tea

The mechanism of TNF-α-induced insulin resistance has remained unresolved with evidence for down-regulation of insulin effector targets effects or blockade of proximal as well as distal insulin signaling events depending upon the dose, time, and cell type examined. To address this issue we examined the acute actions of TNF-α in differentiated 3T3L1 adipocytes. Acute (5-15 min) treatment with 20 ng/ml (~0.8 nm) TNF-α had no significant effect on IRS1-associated phosphatidylinositol 3-kinase. In contrast, TNF-α increased insulin-stimulated cyclin-dependent kinase-5 (CDK5) phosphorylation on tyrosine residue 15 through an Erk-dependent pathway and up-regulated the expression of the CDK5 regulator protein p35. In parallel, TNF-α stimulation also resulted in the phosphorylation and GTP loading of the Rho family GTP-binding protein, TC10α. TNF-α enhanced the depolymerization of cortical F-actin and inhibited insulin-stimulated glucose transporter-4 (GLUT4) translocation. Treatment with the MEK inhibitor, PD98059, blocked the TNF-α-induced increase in CDK5 phosphorylation and the depolymerization of cortical F-actin. Conversely, siRNA-mediated knockdown of CDK5 or treatment with the MEK inhibitor restored the impaired insulin-stimulated GLUT4 translocation induced by TNF-α. Furthermore, siRNA-mediated knockdown of p44/42 Erk also rescued the TNF-α inhibition of insulin-stimulated GLUT4 translocation. Together, these data demonstrate that TNF-α-mediated insulin resistance of glucose uptake can occur through a MEK/Erk-dependent activation of CDK5.

Topics: 3T3-L1 Cells; Actins; Animals; Cyclin-Dependent Kinase 5; Flavonoids; Glucose Transporter Type 4; Guanosine Diphosphate; Guanosine Triphosphate; Insulin Receptor Substrate Proteins; Insulin Resistance; Mice; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Phosphatidylinositol 3-Kinases; Phosphorylation; Polymerization; Receptor, Insulin; rho GTP-Binding Proteins; RNA Interference; Tumor Necrosis Factor-alpha

Epidemiological studies indicate that the consumption of green tea polyphenols (GTP) may reduce the risk of coronary artery disease. To explore the underlying mechanisms of action at the molecular level, we examined the effects of GTP on the cardiac mRNA and protein levels of genes involved in insulin and lipid metabolism and inflammation. In rats fed a high-fructose diet, supplementation with GTP (200 mg/kg BW daily dissolved in distilled water) for 6 wk, reduced systemic blood glucose, plasma insulin, retinol-binding protein 4, soluble CD36, cholesterol, triglycerides, free fatty acids and LDL-C levels, as well as the pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and IL-6. GTP did not affect food intake, bodyweight and heart weight. In the myocardium, GTP also increased the insulin receptor (Ir), insulin receptor substrate 1 and 2 (Irs1 and Irs2), phosphoinositide-3-kinase (Pi3k), v-akt murine thymoma viral oncogene homolog 1 (Akt1), glucose transporter 1 and 4 (Glut1 and Glut4) and glycogen synthase 1 (Gys1) expression but inhibited phosphatase and tensin homolog deleted on chromosome ten (Pten) expression and decreased glycogen synthase kinase 3beta (Gsk3beta) mRNA expression. The sterol regulatory element-binding protein-1c (Srebp1c) mRNA, microsomal triglyceride transfer protein (Mttp) mRNA and protein, Cd36 mRNA and cluster of differentiation 36 protein levels were decreased and peroxisome proliferator-activated receptor (Ppar)gamma mRNA levels were increased. GTP also decreased the inflammatory factors: Tnf, Il1b and Il6 mRNA levels, and enhanced the anti-inflammatory protein, zinc-finger protein, protein and mRNA expression. In summary, consumption of GTP ameliorated the detrimental effects of high-fructose diet on insulin signaling, lipid metabolism and inflammation in the cardiac muscle of rats.

Topics: Animals; Blood Glucose; Body Weight; CD36 Antigens; Flavonoids; Gene Deletion; Gene Expression Regulation; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Guanosine Triphosphate; Inflammation; Insulin; Insulin Resistance; Muscle Proteins; Myocardium; Organ Size; Phenols; Polyphenols; Rats; Retinol-Binding Proteins, Plasma; RNA, Messenger; Tea

In fetal brown adipocyte primary cultures, insulin rapidly (at 5 min) induced tyrosine phosphorylation of the insulin receptor beta-subunit; this effect was maximal at physiological concentrations (1 nM). Insulin also stimulated insulin receptor substrate-1 tyrosine phosphorylation and subsequently activated phosphatidylinositol 3-kinase. Moreover, a 3-fold increase in the Ras.GTP active form and a 6-fold increase in Raf-1 kinase activity were induced after insulin stimulation. An immortalized brown adipocyte cell line (by permanent simian virus 40 large T antigen and pMEXneo cotransfection) showed a reduced maximal responsiveness to insulin in the same range of insulin concentrations studied (1-100 nM). Transformed brown adipocyte cell line (by permanent simian virus 40 large T antigen and pMEXneo H-ras(lys12) cotransfection) developed insulin resistance upstream from Ras, showing an impairment in the insulin receptor autophosphorylation, and in insulin receptor substrate-1 tyrosine phosphorylation and its association with phosphatidylinositol 3-kinase upon treatment with 1 nM insulin, although insulin receptor number and affinity (Kd) remained unaltered. This lack of effect was ameliorated upon treatment with higher insulin concentrations, in a dose-dependent manner. However, downstream from Ras, events such as formation of the Ras.GTP active form, and Raf-1 kinase and 12-O-tetradecanoylphorbol-13-acetate response element-chloramphenicol transferase (transiently transfected) activities were overstimulated, compared with those in primary and immortalized cells, in an insulin-independent manner. Wheat-germ lectin-purified receptors from H-ras(lys12)-transformed brown adipocytes showed a marked phosphorylation in the basal state, which was suppressed by serine-threonine phosphatase pretreatment. Moreover, alkaline phosphatase pretreatment restored the tyrosine kinase activity of the receptor in response to insulin. We conclude that the decreased tyrosine autophosphorylation rate of the insulin receptor from H-ras(lys12)-transformed brown adipocytes is a consequence of its basal serine/threonine phosphorylation, resulting in severe insulin resistance.

Topics: Adipocytes; Adipose Tissue, Brown; Alkaline Phosphatase; Animals; Blotting, Western; Cell Line, Transformed; Dose-Response Relationship, Drug; Fetus; Guanosine Triphosphate; Insulin; Insulin Resistance; Phosphorylation; Precipitin Tests; Protein Serine-Threonine Kinases; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-raf; Proto-Oncogene Proteins p21(ras); Rats; Rats, Wistar; Receptor, Insulin; Serine; Signal Transduction; Tetradecanoylphorbol Acetate; Threonine; Transfection

Hemorrhagic shock in rats was produced by bleeding the animals to a mean arterial pressure of 40 mmHg, which was maintained for 2 h. Muscles from these animals ('shock' muscles) demonstrated basal glucose uptake values unchanged from control values but, unlike the control muscles, the "shock' muscles showed resistance to the stimulation of glucose uptake by insulin. Infusion of ATP-MgCl2, ADP-MgCl2, adenosine-MgCl2, or GTP-MgCl2 to animals following shock had no effect on basal glucose uptake; however, ATP-MgCl2 but not the other nucleotides permitted insulin to exert its stimulatory effect on such muscles. An optimal insulin effect in ATP-MgCl2 treated 'shock' muscles occurred at an insulin concentration of u.001 U/ml, which is also the concentration required to produce optimal insulin effect in control muscles. Following 1-h incubation in Krebs-HCO3 medium, intracellular ATP contents of 'shock' muscles were about 50% lower than in control muscles. Treatment with ATP-MgCl2 following shock, however, resulted in ATP contents in such muscles similar to those in control muscles. Possible mechanisms for this reversal of insulin resistance by in vivo infusion of ATP-MgCl2 in shock are discussed.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Animals; Glucose; Guanosine Triphosphate; Insulin; Insulin Resistance; Muscles; Nucleotides; Rats; Shock, Hemorrhagic