Cyclosporine A enhances gluconeogenesis while sirolimus impairs insulin signaling in peripheral tissues after 3 weeks of treatment

Cyclosporine A (CsA) and sirolimus (SRL) are immunosuppressive agents (IA) associated with new-onset diabetes after transplantation (NODAT). This study aims to evaluate the effects of 3-weeks of treatment with either CsA (5 mg/kg BW/day) or SRL (1 mg/kg BW/day) on insulin signaling and expression of markers involved in glucose metabolism in insulin-sensitive tissues, in Wistar rats.     

Osthole improves glucose and lipid metabolism via modulation of PPARα/γ-mediated target gene expression in liver,adipose tissue,and skeletal muscle in fatty liver rats

Context: Osthole may be a dual agonist of peroxisome proliferator-activated receptors (PPAR) α/γ and ameliorate the insulin resistance (IR), but its mechanisms are not yet understood completely.

Objective: We investigated the effects of osthole on PPARα/γ-mediated target genes involved in glucose and lipid metabolism in liver, adipose tissue, and skeletal muscle in fatty liver and IR rats.

Materials and methods: The rat model was established by orally feeding high-fat and high-sucrose emulsion for 9 weeks. The experimental rats were treated with osthole 5–10?mg/kg by gavage after feeding the emulsion for 6 weeks, and were sacrificed 4 weeks after administration.

Results: After treatment with osthole 5–10?mg/kg for 4 weeks, the lipid levels in serum and liver were decreased by 37.9–67.2% and 31.4–38.5% for triglyceride, 33.1–47.5% and 28.5–31.2% for free fatty acid, respectively, the fasting blood glucose, fasting serum insulin, and homeostasis model assessment of IR were also decreased by 17.2–22.7%, 25.9–26.7%, and 37.5–42.8%, respectively. Osthole treatment might simultaneously decrease the sterol regulatory element binding protein-1c, diacylglycerol acyltransferase, and fatty acid synthase mRNA expressions in liver and adipose tissue, and increase the carnitine palmitoyltransferase-1A mRNA expression in liver and glucose transporter-4 mRNA expression in skeletal muscle, especially in the osthole 10?mg/kg group (p?<?0.01).

Discussion and conclusion: Osthole can improve glucose and lipid metabolism in fatty liver and IR rats, and its mechanisms may be associated with synergic modulation of PPARα/γ-mediated target genes involved in glucose and lipid metabolism in liver, adipose tissue, and skeletal muscle.     

Adipocyte-derived exosomal miR-27a induces insulin resistance in skeletal muscle through repression of PPARγ

OBJECTIVE To explore increasingly exosomal serum miR-27 a derived from adipocytes could be taken up by skeletal muscle tissue and induce insulin resistance in skeletal muscle in obese state. METHODS The association between miR-27 a and insulin resistance in skeletal muscle was determined in obese children,high-fat diet-induced miR-27 a knockdown obese mice,db/db mice and C2C12 cells overexpressing miR-27 a.The crosstalk mediated by exosomal miR-27 a between adipose tissue and skeletal muscle was determined in C2C12 cel s incubated with conditioned medium prepared from palmitate-treated 3 T3-L1 adipocytes. RESULTS After knockdown miR-27 a in obese insulin resistance mice,impaired insulin resistance, glucose intolerance and insulin resistance of skeletal muscle were partly restored. In high-fat diet group, the expressions of IRS-1 and GLUT4 in glucose uptake signal pathway of skeletal muscle were significantly decreased, while the expression of IRS-1 and GLUT4 was restored after miR-27 a knockdown. The content of FABP4, a marker specific for exosomes from adipocytes, was detected in sera, skeletal muscle, supernatant of adipocytes and co-cultured C2C12 cells; furthermore,exosomal miR-27 a in serum and adipocyte supernatants were detect, and fluorescence co-localization experiments were conducted to detect whether the exosomal miR-27 a in serum is mainly derived from adipocyte; finally,we used the supernatant of adipose tissue to construct conditioned media to treat with C2C12 cells, and detected whether adipocytes derived exosomal miR-27 a could impaired glucose uptake signaling pathway of skeletal muscle. the expressions of PPARγ silencing high-fat diet induced C57 BL/6 J obese mouse model and adenovirus intervention miR-27 a knockdown model were examined,and a C2C12 cell model overexpressing miR-27 a in the absence or presence with rosiglitazone(PPARγ activator)were established to test glucose consumption, glucose uptake, and glucose uptake signaling pathways of skeletal muscle cells. CONCLUSION These results identify a novel crosstalk signaling pathway between adipose tissue and skeletal muscle in the development of insulin resistance, and indicate that adipose tissue-derived miR-27 a may play a key role in the development of obesity-triggered insulin resistance in skeletal muscle.     

Targeting the liver in the metabolic syndrome: evidence from animal models

The metabolic syndrome is an emerging global epidemic characterized by clustering of metabolic abnormalities leading to increased cardiovascular risk: glucose intolerance or type 2 diabetes, dyslipidemia, hypertension, and "central" obesity. Scientists are decoding and piecing together the molecular texture underlying the metabolic syndrome: insulin resistance and dyslipidemia stand out as central pathophysiological events. In this picture, the liver rises as the leading organ in the maintenance of metabolic fitness; it serves as the first relay station for processing dietary information, and encloses the whole biochemical machinery for both glucose and lipid storage and disposal. In addition, the liver is a target of the different endocrine molecules secreted by pancreatic beta-cells and adipose tissue. Evidence collected in animal models supports the central role of the liver in the metabolic syndrome. While specific bereft of insulin sensitivity in skeletal muscle and adipose tissue fails to induce diabetes at certain extent, this is constantly the outcome in case of hepatic insulin resistance. Also, dyslipidemia is currently interpreted as the result of increased flux of free fatty acids to the liver with ensuing misbalance of lipoprotein synthesis and removal. In this review we bring together recent advances in the field of lipid sensing nuclear receptors, adipokines and other molecules responsible for metabolic fitness, and provide a putative coherent frame to conceive the pathophysiology of the metabolic syndrome.     

2型糖尿病大鼠模型GLUT4 mRNA表达的研究

目的：研究葡萄糖转运体4（GLUT4）mRNA表达在2型糖尿病胰岛素抵抗中的分子机制。方法：采用高脂高糖饲养，一次性腹腔注射链脲佐菌素（STZ）制备2型糖尿病大鼠模型。逆转录聚合酶链反应（RT-PCR）分析大鼠骨骼肌、心肌和脂肪组织中GLUT4 mRNA的表达量变化与差别。结果：正常对照组和2型糖尿病大鼠模型组GLUT4 mRNA在骨骼肌中有相对较高表达，在心肌中表达次之，在脂肪组织中表达相对偏低。2型糖尿病大鼠模型组骨骼肌中GLUT4 mRNA表达量只有对照组骨骼肌的48％、心肌的44％、脂肪组织的38％。结论：GLUT4 mRNA表达量下降导致骨骼肌、心肌和脂肪组织对葡萄糖摄取利用减少是胰岛素抵抗的重要分子基础，是诱发2型糖尿病原因之一。     

Nobiletin improves hyperglycemia and insulin resistance in obese diabetic ob/ob mice

Nobiletin is a polymethoxylated flavone found in certain citrus fruits that exhibits various pharmacological effects including anti-inflammatory, antitumor and neuroprotective properties. The present study investigated the effects of nobiletin on insulin sensitivity in obese diabetic ob/ob mice, and the possible mechanisms involved. The ob/ob mice were treated with nobiletin (200 mg/kg) for 5 weeks. Nobiletin significantly improved the plasma glucose levels, homeostasis model assessment index, glucose tolerance in an oral glucose tolerance test and plasma adiponectin levels. In white adipose tissue (WAT), nobiletin significantly decreased the mRNA expression levels of inflammatory adipokines such as interleukin (IL)-6 and monocyte chemoattractant protein (MCP)-1 and increased the mRNA expression levels of adiponectin, peroxisome proliferator-activated receptor (PPAR)-γ and its target genes. At the same time, nobiletin increased the glucose transporter (Glut) 4 expression levels in the whole plasma membrane, and Glut1 and phospho-Akt expression in the whole cell lysates in WAT and muscle. Nobiletin also increased Glut4 protein expression level in the whole cell lysates of the muscle. Taken together, the present results suggest that nobiletin improved the hyperglycemia and insulin resistance in obese diabetic ob/ob mice by regulating expression of Glut1 and Glut4 in WAT and muscle, and expression of adipokines in WAT.     

In vitro metabolic effects of gliclazide and glibenclamide in the rat

The actions of gliclazide and glibenclamide on glucose uptake and glycogen deposition by rat hemidiaphragm and glucose utilization by rat epididymal adipose tissue have been examined in vitro. Neither drug exerted an insulin-like action on muscle or adipose tissue with respect to glucose uptake, glycogen deposition or glucose utilization. Neither gliclazide nor glibenclamide augmented the stimulating action of insulin on glucose uptake or glycogen deposition in the rat hemidiaphragm. In a high concentration (1 microgram ml-1), but not in lower concentrations, glibenclamide enhanced the action of insulin in stimulating glucose utilization by rat epididymal adipose tissue. Gliclazide was without any significant effect. Twenty eight day oral treatment with gliclazide did not increase basal or insulin-stimulated glucose uptake or glycogen deposition in rat hemidiaphragm muscle or glucose utilization by epididymal adipose tissue. It is concluded that in normal rats sulphonylureas do not exert important insulin-like actions or insulin potentiating effects.     

PPAR- γ agonist in treatment of diabetes: cardiovascular safety considerations

The peroxisome proliferator-activated receptors (PPARs) are nuclear fatty acid receptors, which contain a type II zinc finger DNA binding motif and a hydrophobic ligand binding pocket. These receptors are thought to play an important role in metabolic diseases such as obesity, insulin resistance, and coronary artery disease. Three subtypes of PPAR receptors have been described: PPARα, PPARδ/β, and PPARγ. PPARα is found in the liver, muscle, kidney, and heart. In the liver, its role is to up-regulate genes involved in fatty acid uptake, binding, β-oxidation and electron transport, and oxidative phosphorylation in subcutaneous fat but not in skeletal muscle. PPARδ/β is expressed in many tissues but markedly in brain, adipose tissue, and skin. PPARγ has high expression in fat, low expression in the liver, and very low expression in the muscle. The thiazolidinediones (TZD) are synthetic ligands of PPARγ. By activating a number of genes in tissues, PPARγ increases glucose and lipid uptake, increases glucose oxidation, decreases free fatty acid concentration, and decreases insulin resistance. Although, there is a rationale for the use of TZDs in patients with type 2 diabetes mellitus, clinical studies have produced conflicting data. While currently used TZDs are clearly associated with heart failure (HF) worsening; with regards to cardiovascular outcomes, pioglitazone seems to be related to a trend toward reduction in cardiovascular morbidity and mortality, whereas rosiglitazone may actually increase risk of cardiovascular events. We review the existing literature on TZDs and discuss role and cardiovascular safety of these agents for the contemporary treatment of diabetes. Other side effects of these agents i.e. increase in osteoporosis and possible risk of bladder cancer is also discussed.     

Central role of the adipocyte in insulin resistance

Mechanisms of insulin resistance in subjects at risk for type 2 diabetes remain to be elucidated. Insulin acts slowly in vivo, but rapidly in vitro, suggesting that the pathway insulin traverses from B-cell to insulin sensitive tissue may be altered in diabetes. An important component of that pathway is transport of insulin across the capillary endothelium. Several groups have demonstrated that insulin resistance may result from reduced capillary permeability to insulin--it remains to be determined whether reduced permeability contributes to insulin resistance in any stage leading to type 2 diabetes. Interestingly, the transport of insulin across the endothelial barrier not only limits the rate of insulin to stimulate glucose uptake by skeletal muscle, but appears also to determine the rate at which insulin suppresses liver glucose output. Because the liver circulation is fenestrated, it is not possible that insulin transport into the liver is the rate determining step for suppression of liver glucose output. An alternative hypothesis was considered--that insulin is transported into an extrahepatic tissue. A "second signal" is generated by the extrahepatic tissue, the signal is released into the blood, and the signal in turn controls hepatic glucose output. Several lines of evidence suggest that the second signal is free fatty acids (FFA): 1) There is a strong correlation between FFA and liver glucose output under a variety of experimental conditions. 2) If FFA are maintained at basal concentrations during insulin administration, glucose output fails to decline. 3) If FFA are reduced independent of insulin administration, glucose output is reduced. These three points support the concept that insulin, by regulating adipocyte lipolysis, controls liver glucose production. Thus, the adipocyte is a critical mediator between insulin and liver glucose output. Evidence that FFA also suppress skeletal muscle glucose uptake and insulin secretion from the B-cell supports the overall central role of the adipocyte in the regulation of glycemia. Insulin resistance at the fat cell may be an important component of the overall regulation of glycemia because of the relationships between FFA and glucose production, glucose uptake, and insulin release. It is possible that insulin resistance at the adipocyte itself can be a major cause of the dysregulation of carbohydrate metabolism in the prediabetic state.     

In vitro metabolic effects of gliclazide and glibenclamide in the rat

The actions of gliclazide and glibenclamide on glucose uptake and glycogen deposition by rat hemidiaphragm and glucose utilization by rat epididymal adipose tissue have been examined in vitro. Neither drug exerted an insulin-like action on muscle or adipose tissue with respect to glucose uptake, glycogen deposition or glucose utilization. Neither gliclazide nor glibenclamide augmented the stimulating action of insulin on glucose uptake or glycogen deposition in the rat hemidiaphragm. In a high concentration (1 μgg ml^?1), but not in lower concentrations, glibenclamide enhanced the action of insulin in stimulating glucose utilization by rat epididymal adipose tissue. Gliclazide was without any significant effect. Twenty eight day oral treatment with gliclazide did not increase basal or insulin-stimulated glucose uptake or glycogen deposition in rat hemidiaphragm muscle or glucose utilization by epididymal adipose tissue. It is concluded that in normal rats sulphonylureas do not exert important insulin-like actions or insulin potentiating effects.     

噻唑烷二酮类不良反应研究进展

噻唑烷二酮类胰岛素增敏剂通过增加外周组织对胰岛素的敏感性而改善胰岛素抵抗,降低血胰岛素水平、减少胰岛素用量,降低血糖和HbAlc,提高HDL-C水平,保护胰岛β细胞功能;还能对抗多种心血管疾病危险因子的损害,有益于糖尿病大血管和微血管并发症的防治.然而近年来有关噻唑烷二酮类药物不良反应的报道越来越多,部分病人甚至因此而停药.笔者综述噻唑烷二酮类药物不良反应.     

Glucose uptake stimulator YM‐138552 activates gene expression and translocation of glucose transporter isotype 4

In this study, we examined the effect of YM‐138552 on the glucose uptake, gene expression, and transport activities of the insulin‐regulatable glucose transporter isotype 4 (Glut4) in skeletal muscle cells. YM‐138552 stimulated medium glucose consumption in a dose‐dependent manner (EC₅₀ = 0.07 μM) in myoblast muscle C2C12 cells under differentiation conditions with 2% horse serum supplement. The stimulatory effect of glucose consumption was verified by radiolabeled 2‐DG uptake assay. The compound showed dose‐dependent stimulation of 2‐DG uptake in G8 myoblast muscle cells up to a 1 μM concentration (EC₅₀ = 0.19 μM). To investigate the mechanism of glucose uptake stimulation by YM‐138552, the mRNA level of Glut4 was determined using real‐time quantitative RT‐PCR. The Glut4 mRNA level expressed in C2C12 cells treated with YM‐138552 increased up to at least 24 h (227% vs. control), after which it gradually decreased to the initial level at 36 h. In addition, we established that C2C12 cells stably expressed the myc‐tagged Glut4 protein (C2C12‐Glut4myc) and measured the Glut4 translocation activity. The Glut4 translocation activity was stimulated by treatment of YM‐138552 without insulin in a dose‐dependent manner (EC₅₀ = 0.62 μM), and no insulin effect (100 nM) was observed. This suggests that YM‐138552 has an insulin‐like effect. These results suggest that the stimulation of glucose uptake by YM‐138552 in muscle cells was partly due to upregulation of the Glut4 gene expression and its translocation activation. Our findings on the in vitro effects of YM‐138552 glucose uptake stimulation through the Glut4 transporter may suggest a direction for the development of new drugs for the treatment of NIDDM. Drug Dev. Res. 51:43–48, 2000. © 2000 Wiley‐Liss, Inc.     

Insulin resistance in obesity as the underlying cause for the metabolic syndrome

The metabolic syndrome affects more than a third of the US population, predisposing to the development of type 2 diabetes and cardiovascular disease. The 2009 consensus statement from the International Diabetes Federation, American Heart Association, World Heart Federation, International Atherosclerosis Society, International Association for the Study of Obesity, and the National Heart, Lung, and Blood Institute defines the metabolic syndrome as 3 of the following elements: abdominal obesity, elevated blood pressure, elevated triglycerides, low high-density lipoprotein cholesterol, and hyperglycemia. Many factors contribute to this syndrome, including decreased physical activity, genetic predisposition, chronic inflammation, free fatty acids, and mitochondrial dysfunction. Insulin resistance appears to be the common link between these elements, obesity and the metabolic syndrome. In normal circumstances, insulin stimulates glucose uptake into skeletal muscle, inhibits hepatic gluconeogenesis, and decreases adipose-tissue lipolysis and hepatic production of very-low-density lipoproteins. Insulin signaling in the brain decreases appetite and prevents glucose production by the liver through neuronal signals from the hypothalamus. Insulin resistance, in contrast, leads to the release of free fatty acids from adipose tissue, increased hepatic production of very-low-density lipoproteins and decreased high-density lipoproteins. Increased production of free fatty acids, inflammatory cytokines, and adipokines and mitochondrial dysfunction contribute to impaired insulin signaling, decreased skeletal muscle glucose uptake, increased hepatic gluconeogenesis, and β cell dysfunction, leading to hyperglycemia. In addition, insulin resistance leads to the development of hypertension by impairing vasodilation induced by nitric oxide. In this review, we discuss normal insulin signaling and the mechanisms by which insulin resistance contributes to the development of the metabolic syndrome.     

Insulin therapy stimulates lipid synthesis and improves endocrine functions of adipocytes in dietary obese C57BL/6 mice

Aim:

To evaluate whether insulin intervention could affect the metabolic and endocrine functions of adipose tissue.

Methods:

C57BL/6 mice were fed on a high-fat-diet for 12−16 weeks to induce insulin resistance. Insulin intervention was administered in the high-fat-diet mice for 4 weeks at 12 weeks (early insulin treatment) or 16 weeks (late insulin treatment). Intraperitoneal glucose tolerance tests were performed before and after insulin treatment. Expression levels of factors involved in the triglyceride synthesis and endocrine functions of adipose tissue including phosphoenolpyruvate carboxykinase (PEPCK-C), fatty acid synthase (FAS), aquaporin 7 (AQP7), adiponectin, visfatin, and interleukin-6 (IL-6) were determined by Western blot.

Results:

In the obese mice, glucose tolerance was impaired; triglyceride content was increased in the liver tissue; protein expression of FAS and adiponectin was decreased; expression of visfatin was increased in adipose tissue. After 4-week insulin treatment, glucose tolerance was improved; triglyceride content was decreased in the liver and skeletal muscle; expression of PEPCK-C, FAS, and adiponectin was increased in the adipose tissue; IL-6 and AQP7 expression was reduced in the fat. Early insulin treatment had better effect in increasing the expression of FAS and PEPCK-C and decreasing the expression of IL-6.

Conclusion:

These results indicate that insulin can target adipocytes for improvement of insulin sensitivity through stimulating triglyceride synthesis and partly improving endocrine functions.     

Effects of losartan in combination with or without exercise on insulin resistance in Otsuka Long–Evans Tokushima Fatty rats

Hypertension often complicates type 2 diabetes mellitus, and angiotensin converting enzyme inhibitor treatment has been shown to improve insulin resistance in such cases. However, the effect of angiotensin II type-1 (AT₁) receptor antagonists on insulin resistance is still controversial. To gain further information on this effect, we examined the effect of losartan on insulin resistance in Otsuka Long–Evans Tokushima Fatty (OLETF) rats, a model of type 2 diabetes mellitus. Losartan administration alone lowered systolic blood pressure, but did not improve oral glucose tolerance test or insulin resistance in OLETF rats. However, the administration of losartan with exercise significantly improved both systolic blood pressure and insulin resistance relative to control OLETF rats. On the other hand, losartan treatment, regardless of exercise, increased glucose uptake in excised soleus muscle and fat cells. To explore the beneficial effect of losartan on skeletal muscle glucose uptake, we examined intracellular signaling of soleus muscle. Although Akt activity and glucose transporter type 4 (GLUT4) expressions were not affected by losartan with or without exercise, extracellular signal-regulated kinase (ERK1/2) and p38 mitogen-activated protein (MAP) kinase activities were increased by both interventions. These results indicate that angiotensin AT₁ receptor antagonist improved local insulin resistance, but not systemic insulin resistance. These findings may explain the controversy over the effect of angiotensin AT₁ receptor antagonists on insulin resistance in clinical use. The enhancing effect of angiotensin AT₁ receptor antagonist on skeletal muscle glucose uptake may be attributable to MAP kinase activation or other mechanisms rather than phosphatidylinositol 3-kinase activation.     

Insulin resistance, hyperinsulinemia, dyslipidemia, hypertension, and accelerated atherosclerosis.

Hypertension is only one component of a multifaceted metabolic-hemodynamic complex that also includes obesity, subtle and overt glucose intolerance, dyslipidemia, enhanced vascular resistance and accelerated atherosclerosis. Results of a number of studies in the past 5 years have shown that even nonobese, nondiabetic individuals with hypertension display insulin resistance, which is located in peripheral tissues (primarily skeletal muscle), is limited to nonoxidative pathways of glucose disposal, and appears to be directly correlated with the severity of hypertension. Insulin resistance and associated hyperinsulinemia in hypertensive individuals are also associated with increased plasma triglyceride levels and decreased high-density lipoprotein concentrations, which likely contributes to enhanced atherosclerosis. Hyperinsulinemia may directly promote atherosclerosis by enhancing LDL-cholesterol accumulation in vessel walls, vascular smooth muscle migration, and proliferation, augmenting connective tissue synthesis in the vascular wall, and decreasing the regression of lipid plaques. The enhanced peripheral vascular resistance that characterizes insulin resistance/hyperinsulinemic states may be related to decreased vascular smooth muscle responses to insulin, which normally modulates (attenuates) vascular contractile responses to vasoactive agents.     

A cellular assay for measuring the modulation of glucose production in H4IIE cells

Type II diabetes and its associated complications are a major health concern of the developed world. One of the hallmarks of diabetes is insulin resistance, where secreted insulin no longer has any effect on its target tissues, namely, liver, muscle, and fat. An important therapeutic strategy is to modulate blood glucose levels using pharmacological agents. Glycogen synthase kinase-3 (GSK3) is a serine-threonine protein kinase that plays important roles in regulating glucose metabolism. It is a key negative regulator of insulin action and is an important contributing factor to insulin resistance in liver, muscle, and adipose tissue. We describe the development of a cell-based assay designed to measure glucose production in rat hepatoma cell line H4IIE liver cells in response to treatment with small molecule inhibitors, including GSK3 inhibitors. The assay is set up in a 96-well format, and glucose production is assessed using a convenient fluorescence-based readout. This disease-relevant cellular assay is a valuable tool for the progression of small molecules that modulate glucose production.     

Section Review: Oncologic,Endocrine & Metabolic: Thiazolidinediones

To date, the treatment of Non-Insulin Dependent Diabetes Mellitus (NIDDM) has focused primarily on attempts to correct some of the metabolic abnormalities commonly associated with the disease. Insulin and/or insulin secretagogues, such as sulphonylureas, are frequently used to lower blood sugar; however, there is a significant risk of hypoglycaemia. Moreover, the use of insulin or insulin secretagogues in patients who are already hyperinsulinaemic may accelerate some of the cardiovascular complications of NIDDM, and further aggravate insulin resistance. Other therapeutic strategies have focused on aberrations in glucose metabolism or absorption, including biguanides, such as metformin, or glucosidase inhibitors, such as acarbose. While these agents have been efficacious to a degree, they do not have a direct impact on the underlying pathology of insulin resistance. A novel therapeutic strategy involves the use of insulin-sensitising agents, such as the thiazolidinediones. These compounds appear to improve insulin resistance by enhancing insulin action in skeletal muscle, liver and adipose tissue. Recent preclinical studies have revealed key insights into the potential mechanism of action of the thiazolidinediones. Furthermore, the emerging clinical experience with one of these agents, troglitazone, is substantiating the benefits of these agents in insulin-resistant diseases.