线粒体功能损伤与胰岛素抵抗

胰岛素抵抗在肥胖、代谢综合症、心血管类疾病和2型糖尿病及其并发症等疾病的病理病程中起了重要的作用。近年来,研究发现线粒体功能损伤与胰岛素抵抗有着密切的联系。一些遗传因素、老化现象、ROS生成的增多、线粒体生物合成降低或一些线粒体相关蛋白变化,都可能损伤线粒体功能,而这些因素也都是诱发胰岛素抵抗的主要诱因。了解线粒体损伤与胰岛素抵抗的关系将为胰岛素抵抗的研究和治疗提供新的思路。该文将从遗传因素、老化、ROS、生物合成、UCP、Sirt3等可影响线粒体功能的几个方面阐述线粒体功能损伤与胰岛素抵抗的关系,并介绍胰岛素抵抗治疗中与线粒体相关的药物作用机制。     

Insulin resistance and antidiabetic drugs.

Insulin resistance describes an impaired biological response to insulin, which underpins the development of type 2 (non-insulin-dependent) diabetes mellitus (T2DM). Initially, insulin resistance causes a compensatory hyperinsulinaemia, which gives way to pancreatic beta-cell failure. Insulin resistance and hyperinsulinaemia conspire together in the development of a diverse collection of risk factors for coronary heart disease, namely obesity, T2DM, dyslipidaemia, hypertension, atherosclerosis, and a pro-coagulant state. This collection of factors is commonly found in T2DM patients, and is recognised as the Insulin Resistance Syndrome or Syndrome X. By targeting insulin resistance as a treatment strategy for T2DM, it should be possible to broaden the potential benefits, so that improved glycaemic control is complemented with improvements to other components of Syndrome X. At present, metformin and thiazolidinediones are the only therapies for T2DM that directly address aspects of insulin resistance. Increasing awareness of the clinical implications of insulin resistance, and increasing knowledge of the cellular basis of insulin resistance, provide the rationale and a means for developing an anti-insulin resistance approach to the treatment of T2DM.     

Targeting mitochondrial biogenesis for preventing and treating insulin resistance in diabetes and obesity: Hope from natural mitochondrial nutrients

Insulin resistance is an important feature of type 2 diabetes and obesity. The underlying mechanisms of insulin resistance are still unclear and may involve pathological changes in multiple tissues. Mitochondrial dysfunction, including mitochondrial loss and over-production of oxidants, has been suggested to be involved in the development of insulin resistance. Increasing evidence suggests that targeting mitochondria to protect mitochondrial function as a unique measure, i.e. mitochondrial medicine, could prevent and ameliorate various diseases associated with mitochondrial dysfunction. In this review, we have summarized recent progress in pharmaceutical and nutritional studies of drugs and nutrients to targeting mitochondria by stimulating mitochondrial metabolism (biogenesis and degradation) to improve mitochondrial function and decrease oxidative stress for preventing and ameliorating insulin resistance. We have focused on nutrients from natural sources to stimulating mitochondrial biogenesis in cellular systems and in animal models. The in vitro and in vivo studies, especially our own work on the effects and mechanisms of mitochondrial targeting nutrients or their combinations, may help us to understand the importance and mechanisms of mitochondrial biogenesis in insulin resistance, and provide hope for developing mitochondria-targeting agents for preventing and treating insulin resistance in type 2 diabetes and obesity.     

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.     

Cardiovascular risk in the spectrum of type 2 diabetes mellitus

The clinical importance of the metabolic syndrome is that this group of risk factors greatly increases the likelihood of cardiovascular events, the major source of disease morbidity and mortality in patients with obesity and type 2 diabetes. Recent studies have helped clarify the mechanisms underlying the vascular dysfunction that leads to cardiovascular outcomes in diabetes. This vascular dysfunction is correlated with visceral adiposity, insulin resistance and alterations in the levels of a variety of circulating factors. The vascular effects of overt hyperglycemia also play an important role in diabetes mellitus. Appropriate management of diabetes in the context of the metabolic syndrome requires that we pay close attention to minimizing cardiovascular risk. In this brief review, we will cover several key concepts in the pathophysiology of type 2 diabetes that confer increased cardiovascular risk and influence the choice of oral therapies for this widespread disorder.     

Insulin- and growth factor-resistance impairs vascular regeneration in diabetes mellitus

Diabetes and pre-diabetes are major contributors to cardiovascular mortality and morbidity. Insulin resistance is a key pathophysiological determinant of the metabolic and vascular abnormalities noted in these disorders. Ineffective vascular repair is likely to be an important contributor to the development of endothelial dysfunction, and subsequently atherosclerosis, in patients with diabetes. Beyond the systemic effects of the insulin resistant phenotype, including factors such as dysglycaemia and inflammation, cellular insulin resistance is emerging as an important factor in diabetic vascular disease. Disordered signal transduction via the PI3-kinase/Akt and MAP-kinase cascades is a hallmark of cellular insulin resistance, and such changes have been linked with both endothelial dysfunction and impaired angiogenesis. In this review we highlight the importance of insulin resistance to vascular repair and regeneration, discuss important cross-talk between the intracellular signalling of insulin and key pro-angiogenic molecules, and link these concepts to common patterns of vascular disease.     

Vascular effects of insulin

Insulin as a vascular hormone, apart from its effect on intermediary metabolism, has been considered to play an important role in cardiovascular regulation and pathophysiology of cardiovascular diseases such as essential hypertension, congestive cardiac failure and atherosclerosis. Insulin induces pressor effects by mechanisms of increased sympathetic activity, renal sodium retention and proliferation of vascular smooth muscle cells. On the other hand, accumulating evidence indicates that insulin decreases vascular resistance and increases organ blood flow especially in skeletal muscle tissue, indicating that insulin is a vasodilator. Several mechanisms underlying insulin-induced vasodilation have been proposed. Insulin enhances calcium efflux from vascular smooth muscle cells by activating the plasma membrane Ca(2+)-ATPase and causes hyperpolarization by stimulating Na+, K(+)-ATPase and sodium/potassium pump. Insulin also stimulates nitric oxide (NO) synthase and increases release of NO from vascular endothelium to cause vasodilation. An increase in cyclic AMP levels is induced by insulin, via activation of insulin receptors, beta-adrenoceptors and calcitonin gene-related peptide receptors. However, main cause of mechanisms mediating the vasodilation remain obscure. Hypertension is associated with insulin resistance and hyperinsulinemia. Insulin resistance may contribute to hypertension by sympathetic overactivity, endothelium dysfunction and decreased vasodilator action of insulin. Therefore, insulin must be considered a vasoactive peptide and more investigations are needed to better understand the full significance of the hemodynamic effect of insulin.     

线粒体脂质过载与胰岛素抵抗

胰岛素抵抗(insulin resistance,IR)是肥胖和2型糖尿病的共同病理基础,虽然引起IR的具体机制仍不明确,但是近年来人们认为脂质剩余可能是其分子基础之一.线粒体是调控代谢的重要细胞器,胰岛素靶细胞线粒体脂质过载导致线粒体功能障碍在IR发生发展中具有重要作用,且两者互为影响.因此,减轻线粒体脂质过载有利于防治IR,为治疗2型糖尿病提供新的思路.     

Molecular mechanisms for vascular injury in the metabolic syndrome

The metabolic syndrome is strongly associated with insulin resistance and has been recognized as a cluster of risk factors for cardiovascular diseases such as visceral obesity, hypertension, diabetes and dyslipidemia. Recently, insulin resistance in the absence of overt diabetes or the metabolic syndrome itself has been shown to be associated with endothelial dysfunction, one of the initial steps in the process of atherosclerosis. In the present article we review the molecular mechanisms by which the metabolic syndrome causes endothelial dysfunction and subsequently promotes atherosclerosis. We also discuss promising therapeutic strategies that specifically target the mechanisms responsible for vascular alterations in the metabolic syndrome.     

Metabolic syndrome-interdependence of the cardiovascular and metabolic pathways

The metabolic syndrome is a worldwide epidemic, setting the stage for type 2 diabetes and its microvascular complications, and acceleration of macrovascular disease. Insulin resistance, hyperglycemia, dyslipidemia, hypertension, thrombotic disorders and adiposity define the metabolic syndrome and contribute to endothelial dysfunction and, subsequently, to accelerated atherosclerosis. Angiotensin II contributes to the development and progression of cardiovascular and renal endpoints and, as such, angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors demonstrate a protective effect. Ligands for the peroxisome proliferator-activated receptor gamma (PPAR gamma), appear to impact favourably on atherosclerosis through both direct and indirect mechanisms. In humans, these ligands improve endothelial function, attenuate albuminuria and hypertension, and potentially prevent conversion of prediabetes to type 2 diabetes. Statins also have proven benefit in decreasing overall cardiovascular and stroke mortality and morbidity. The combination of angiotensin II blockade, statin therapy and PPAR gamma activation might emerge as an important global therapeutic strategy in the metabolic syndrome and diabetes. Further studies are needed to determine whether they have synergistic effects to protect the vasculature.     

Potential pathogenic inflammatory mechanisms of endothelial dysfunction induced by type 2 diabetes mellitus

Insulin resistance and the vascular complications of diabetes include activation of the inflammation cascade, endothelial dysfunction, and oxidative stress. The comorbidities of diabetes, namely obesity, insulin resistance, hyperglycemia, hypertension and dyslipidemia collectively aggravate these processes while antihyperglycemic interventions tend to correct them. Increased C-reactive protein, interleukin 6, tumor necrosis factor alpha and especially interstitial cellular adhesion molecule-1, vascular cellular adhesion molecule-1, and E-selectin are associated with cardiovascular and non-cardiovascular complications of both type 1 and type 2 diabetes. We sought to review the clinical implications of the inflammation theory, including the relevance of inflammation markers as predictors of type 2 diabetes in clinical studies, and the potential treatments of diabetes, inferred from the pathophysiology.     

胰岛素抵抗与血管内皮细胞释放一氧化氮关系的研究进展

胰岛素抵抗(IR)是产生2型糖尿病、心血管疾病、高脂血症、高尿酸血症及代谢综合症的共同病理基础。IR产生机制尚未阐明,现已证实胰岛素抵抗会伴有内皮细胞功能紊乱,血管内皮受损是微血管和大血管病变的重要因素,并且内皮损伤伴有一氧化氮合酶(NOS)功能和一氧化氮(NO)释放紊乱。本综述将讨论内皮功能障碍和胰岛素抵抗的相关病理生理学机制,并确定检查内皮细胞中NO的释放量是否能确定患者患有胰岛素抵抗及伴有并发症,为临床检验提供依据。     

Renin–angiotensin system inhibitor and statins combination therapeutics – what have we learnt?

Hypercholesterolemia and hypertension are the most common risk factors for cardiovascular disease (CVD). Updated guidelines emphasize target reduction of overall cardiovascular risks. Hypercholesterolemia and hypertension have a synergistic deleterious effect on insulin resistance and endothelial dysfunction. Unregulated renin–angiotensin system (RAS) is important in the pathogenesis of atherosclerosis. Statins are the most important in patients with hypercholesterolemia to prevent CVD by lowering low-density lipoprotein-cholesterol, improving endothelial dysfunction, and other anti-atherosclerotic effects. Unfortunately, statin therapy dose-dependently causes insulin resistance and increases the risk of type 2 diabetes mellitus. RAS inhibitors improve both endothelial dysfunction and insulin resistance in addition to blood pressure lowering. Further, cross-talk between hypercholesterolemia and RAS exists at multiple steps of insulin resistance and endothelial dysfunction. In this regard, combined therapy with statins and RAS inhibitors demonstrates additive/synergistic beneficial effects on endothelial dysfunction and insulin resistance in addition to lowering both cholesterol levels and blood pressure and it did reduce cardiovascular events when compared with either monotherapy in patients. This is mediated by both distinct and interrelated mechanisms. Therefore, combined therapy with statins and RAS inhibitors may be important in developing optimal management strategies in patients with hypertension, hypercholesterolemia, diabetes, metabolic syndrome or obesity to prevent or treat CVD.     

Reactive oxygen species and insulin‐resistant cardiomyopathy

1. The prevalence of insulin resistance has increased markedly in the past decade and is known to be associated with cardiovascular risk. Evidence of an insulin‐resistant cardiomyopathy, independent of pressure or volume loading influences, is now emerging. 2. Cardiac oxidative stress is often observed coincident with insulin resistance and there is accumulating evidence that reactive oxygen species (ROS) mediate deleterious effects in the insulin‐resistant heart. It is established that ROS modification of signalling proteins can adversely modulate cellular processes, leading to cardiac growth remodelling and dysfunction. The mechanisms of ROS‐induced damage in insulin‐resistant cardiomyopathy are yet to be fully elucidated. 3. A number of different animal models have been used to study cardiac insulin resistance, including high‐sugar dietary interventions, genetically modified diabetic mice and streptozotocin‐induced diabetes. Mechanistic studies manipulating cardiac anti‐oxidant levels, either endogenously or exogenously, in these models have demonstrated a role for ROS in the cardiac manifestations associated with insulin resistance. 4. The present review summarizes the cardiac‐specific characteristics of insulin resistance, the features of cardiac metabolism relevant to ROS generation and ROS‐mediated cardiomyocyte damage pathways. In vivo studies in which a combination of genetic and environmental variables have been manipulated are considered. These studies provide particular insights into the induction and suppression of insulin‐resistant cardiomyopathy.     

Optimisation of the management of patients with coronary heart disease and type 2 diabetes mellitus

Type 2 diabetes mellitus is a prevalent disease in Westernised society, and more than 50% of individuals with diabetes mellitus die from cardiovascular causes. The underlying metabolic defect of type 2 diabetes mellitus is a combination of insulin resistance and decreased secretion of insulin by pancreatic beta-cells. Insulin resistance commonly precedes the onset of type 2 diabetes mellitus and is usually associated with a metabolic syndrome including hypertension, dyslipidaemia and obesity. Treatment of known cardiovascular risk factors, including hyperglycaemia, dyslipidaemia, hypertension and smoking, plays a key role in delaying the onset and progression of coronary heart disease (CHD) and other forms of atherosclerosis in patients with diabetes mellitus. Sulphonylureas should be used with caution in patients with CHD but aspirin (acetylsalicylic acid), beta-blockers and ACE inhibitors play an important role in the medical management of patients with established coronary artery disease and diabetes mellitus. Patients with diabetes mellitus represent a higher risk group of patients after both percutaneous and surgical coronary revascularisation and the decision regarding the choice of revascularisation procedure should take into account angiographic characteristics, clinical status and patient preference. Patients presenting with diabetes mellitus and acute myocardial infarction should be considered for reperfusion therapy with either urgent thrombolytic therapy or primary percutaneous coronary intervention.     

游离脂肪酸与骨骼肌胰岛素抵抗的研究进展

胰岛素抵抗与肥胖、2型糖尿病、高血压、脂代谢紊乱、异常血凝及纤溶等代谢综合征的发生和发展密切相关。虽然胰岛素抵抗发生机制尚不完全清楚,但大量研究表明游离脂肪酸在机体胰岛素抵抗,特别是骨骼肌胰岛素抵抗方面发挥重要作用。本文就游离脂肪酸引起骨骼肌胰岛素抵抗的作用及其机制进行综述,以期为胰岛素抵抗的改善及治疗带来新的手段。     

The pleiotropic effects of ARB in vascular endothelial progenitor cells

Angiotensin II regulates blood pressure and contributes to endothelial dysfunction and the progression of atherosclerosis. Bone marrow-derived endothelial progenitor cells (EPCs) in peripheral blood contribute to postnatal vessel repair and neovascularization. Impaired EPC function in patients with hypertension and diabetes inhibits the endogenous repair of vascular lesions and leads to the progression of atherosclerosis. The number of EPCs in peripheral blood is inversely correlated with mortality and the occurrence of cardiovascular events. Angiotensin II-mediated signaling is implicated in oxidative stress, inflammation and insulin resistance, factors that cause EPC dysfunction. Blockade of the angiotensin II type 1 receptor may therefore present a new therapeutic target for enhancing EPC function.     

Generation, validation and humanisation of a novel insulin resistant cell model

Insulin resistance is a characteristic of type 2 diabetes and is a major independent risk factor for progression to the disease. In particular, insulin resistance associates with increased body fat and almost certainly contributes to the dramatic increase in risk of type 2 diabetes associated with obesity. Therefore, in order to design truly effective insulin sensitising agents, targeted at the mechanism of disease development, we aimed to generate an obesity-related insulin resistant cell model. Rat hepatoma cells were grown in the presence of serum isolated from obese rodents or obese human volunteers, and the insulin sensitivity of the cells monitored over time by measuring a well-characterised insulin regulated gene promoter. Higher insulin concentrations were required to fully repress the gene in the cells grown in obese rodent serum compared with those grown in serum from lean rodents (almost a 10-fold shift in insulin sensitivity). This was reversed by restoration of normal growth medium, while the insulin resistance was prevented by pioglitazone or metformin. Meanwhile, growth of cells in serum collected from obese human volunteers with diabetes also reduced the insulin sensitivity of the rat cells. No clinical marker predicted the degree of insulin resistance that was generated by the human serum. We have developed a novel insulin resistant cell model for the study of the molecular development of obesity-linked insulin resistance, screen for compounds to overcome obesity-related insulin resistance and potentially search for novel serum biomarkers of insulin resistance.     

Thematic issue-topic--diabetic cardiovascular disease--an unmet medical need: emerging targets and therapies-introduction to the special issue

The major cause of death and complications in patients with type 2 diabetes is cardiovascular disease. Cardiovascular complications that are often associated with diabetes include heart failure, acute myocardial infarction (MI), peripheral vascular disease, and cerebrovascular disease. More than 60% of all patients with type 2 diabetes die of cardiovascular disease, and an even greater percentage have serious complications. The impact of glucose lowering on cardiovascular complications is a hotly debated issue and recent large clinical trials, the Action in Diabetes and Vascular Disease (ADVANCE), Action to Control Cardiovascular Risk in Diabetes (ACCORD) and Veterans Affairs Diabetes Trial (VADT) reported no significant decrease in cardiovascular events with intensive glucose control. Risk remains high even after correcting diabetes-associated dyslipidemia (high triglycerides and low HDL). Several mechanisms are likely to contribute to the accelerated atherosclerosis and increased cardiovascular disease risk seen in type 2 diabetics. Of these, postprandial hyperglycemia/lipemia, insulin resistance and inflammation may be the most important and under controlled contributing factors to vascular disease. The goal of this thematic issue is to address limitations of current therapies and review emerging research and therapeutic approaches that target inflammation, insulin resistance and other pathological mechanisms that contribute to cardiovascular disease in diabetes.     

Molecular mechanisms of diabetes and atherosclerosis: role of adiponectin

Type 2 diabetes mellitus (T2DM) is a disease characterized by inadequate beta-cell response due to progressive insulin resistance that typically accompanies physical inactivity and weight gain. T2DM is associated with substantial morbidity and mortality related to the associated atherosclerotic cardiovascular risks and diabetic vasculopathies, including microangiopathies (e.g., blindness and renal failure) and macroangiopathies (atherosclerosis). The increasing global prevalence of T2DM is linked to the rising rates of obesity, especially abdominal obesity. Visceral fat accumulation is upstream of obesity-related disorders including atherosclerotic cardiovascular disease (ACVD), and is associated with impaired insulin sensitivity and atherosclerosis through dysregulated production of adipocytokines, especially hypoadiponectinemia. This review article discusses the pathophysiological mechanisms responsible for T2DM and atherosclerosis, focusing on adiponectin. Clinical and experimental studies have shown that hypoadiponectinemia contributes to a variety of life style-related diseases including T2DM and atherosclerosis. It is likely that life-style modification, visceral fat reduction and use of medications that increase serum adiponectin levels (e.g., rimonabant, thiazolidinediones, fibrates, angiotensin receptor blocker and mineralocorticoid receptor blockade) when provided in combination can improve hypoadiponectinemia and thus prevent the development of life style-related diseases including T2DM and ACVD.