Reactive oxygen and nitrogen species in pathogenesis of vascular complications of diabetes

Macrovascular and microvascular diseases are currently the principal causes of morbidity and mortality in subjects with diabetes. Disorders of the physiological signaling functions of reactive oxygen species (superoxide and hydrogen peroxide) and reactive nitrogen species (nitric oxide and peroxynitrite) are important features of diabetes. In the absence of an appropriate compensation by the endogenous antioxidant defense network, increased oxidative stress leads to the activation of stress-sensitive intracellular signaling pathways and the formation of gene products that cause cellular damage and contribute to the vascular complications of diabetes. It has recently been suggested that diabetic subjects with vascular complications may have a defective cellular antioxidant response against the oxidative stress generated by hyperglycemia. This raises the concept that antioxidant therapy may be of great benefit to these subjects. Although our understanding of how hyperglycemia-induced oxidative stress ultimately leads to tissue damage has advanced considerably in recent years, effective therapeutic strategies to prevent or delay the development of this damage remain limited. Thus, further investigation of therapeutic interventions to prevent or delay the progression of diabetic vascular complications is needed.     

Molecular mechanisms of diabetic vascular complications

Diabetic complications are the major causes of morbidity and mortality in patients with diabetes. Microvascular complications include retinopathy, nephropathy and neuropathy, which are leading causes of blindness, end‐stage renal disease and various painful neuropathies; whereas macrovascular complications involve atherosclerosis related diseases, such as coronary artery disease, peripheral vascular disease and stroke. Diabetic complications are the result of interactions among systemic metabolic changes, such as hyperglycemia, local tissue responses to toxic metabolites from glucose metabolism, and genetic and epigenetic modulators. Chronic hyperglycemia is recognized as a major initiator of diabetic complications. Multiple molecular mechanisms have been proposed to mediate hyperglycemia’s adverse effects on vascular tissues. These include increased polyol pathway, activation of the diacylglycerol/protein kinase C pathway, increased oxidative stress, overproduction and action of advanced glycation end products, and increased hexosamine pathway. In addition, the alterations of signal transduction pathways induced by hyperglycemia or toxic metabolites can also lead to cellular dysfunctions and damage vascular tissues by altering gene expression and protein function. Less studied than the toxic mechanisms, hyperglycemia might also inhibit the endogenous vascular protective factors such as insulin, vascular endothelial growth factor, platelet‐derived growth factor and activated protein C, which play important roles in maintaining vascular homeostasis. Thus, effective therapies for diabetic complications need to inhibit mechanisms induced by hyperglycemia’s toxic effects and also enhance the endogenous protective factors. The present review summarizes these multiple biochemical pathways activated by hyperglycemia and the potential therapeutic interventions that might prevent diabetic complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00018.x, 2010)     

The use of vitamin E in type 2 diabetes mellitus

Diabetes mellitus has assumed epidemic proportions in most parts of the world, and it is a major source of morbidity in developed countries. In addition, in several instances, diabetes is associated with a variety of metabolic abnormalities, including abdominal obesity, insulin resistance, hypertension, dyslipidemia, and hyperglycemia. There is considerable evidence that hyperglycemia causes the generation of reactive oxygen species (ROS), ultimately leading to increased oxidative stress in a variety of tissues. In the absence of an appropriate compensatory response by the endogenous antioxidants, such as vitamins C and E, catalase, glutathione, and superoxide dismutase, oxidative stress dominates, resulting in the activation of stress-sensitive intracellular signaling pathways. One of the major consequences is the generation of gene products that cause cellular damage and are ultimately responsible for the late complications of diabetes. The ability of antioxidants to protect against the effects of hyperglycemia in vitro, along with the clinical benefits often reported following antioxidant therapy, supports a causative role of oxidative stress in mediating and/or worsening these abnormalities. This review will focus on the critical assessment of the literature as it relates to the association between oxidative stress and diabetes, followed by the role of oxidative stress in the complications of type 2 diabetes mellitus. Finally, a review of the use of the antioxidant vitamin E will be provided in diabetic patients by assessing and evaluating some of the clinical trials in the literature.     

The Use of Vitamin E in Type 2 Diabetes Mellitus

Diabetes mellitus has assumed epidemic proportions in most parts of the world, and it is a major source of morbidity in developed countries. In addition, in several instances, diabetes is associated with a variety of metabolic abnormalities, including abdominal obesity, insulin resistance, hypertension, dyslipidemia, and hyperglycemia. There is considerable evidence that hyperglycemia causes the generation of reactive oxygen species (ROS), ultimately leading to increased oxidative stress in a variety of tissues. In the absence of an appropriate compensatory response by the endogenous antioxidants, such as vitamins C and E, catalase, glutathione, and superoxide dismutase, oxidative stress dominates, resulting in the activation of stress-sensitive intracellular signaling pathways. One of the major consequences is the generation of gene products that cause cellular damage and are ultimately responsible for the late complications of diabetes. The ability of antioxidants to protect against the effects of hyperglycemia in vitro, along with the clinical benefits often reported following antioxidant therapy, supports a causative role of oxidative stress in mediating and/or worsening these abnormalities. This review will focus on the critical assessment of the literature as it relates to the association between oxidative stress and diabetes, followed by the role of oxidative stress in the complications of type 2 diabetes mellitus. Finally, a review of the use of the antioxidant vitamin E will be provided in diabetic patients by assessing and evaluating some of the clinical trials in the literature.     

Oxidative stress: A cause and therapeutic target of diabetic complications

Oxidative stress is defined as excessive production of reactive oxygen species (ROS) in the presence of diminished anti‐oxidant substances. Increased oxidative stress could be one of the common pathogenic factors of diabetic complications. However, the mechanisms by which hyperglycemia increases oxidative stress are not fully understood. In this review, we focus on the impact of mitochondrial derived ROS (mtROS) on diabetic complications and suggest potential therapeutic approaches to suppress mtROS. It has been shown that hyperglycemia increases ROS production from mitochondrial electron transport chain and normalizing mitochondrial ROS ameliorates major pathways of hyperglycemic damage, such as activation of polyol pathway, activation of PKC and accumulation of advanced glycation end‐products (AGE). Additionally, in subjects with type 2 diabetes, we found a positive correlation between HbA1c and urinary excretion of 8‐hydroxydeoxyguanosine (8‐OHdG), which reflects mitochondrial oxidative damage, and further reported that 8‐OHdG was elevated in subjects with diabetic micro‐ and macro‐ vascular complications. We recently created vascular endothelial cell‐specific manganese superoxide dismutase (MnSOD) transgenic mice, and clarified that overexpression of MnSOD in endothelium could prevent diabetic retinopathy in vivo. Furthermore, we found that metformin and pioglitazone, both of which have the ability to reduce diabetic vascular complications, could ameliorate hyperglycemia‐induced mtROS production by the induction of PPARγ coactivator‐1α (PGC‐1α) and MnSOD and/or activation of adenosine monophosphate (AMP)‐activated protein kinase (AMPK). We also found that metformin and pioglitazone promote mitochondrial biogenesis through the same AMPK–PGC‐1α pathway. Taking these results, mtROS could be the key initiator of and a therapeutic target for diabetic vascular complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00013.x, 2010)     

Mass spectrometric quantification of amino acid oxidation products identifies oxidative mechanisms of diabetic end-organ damage

Diabetes mellitus is increasingly prevalent worldwide. Diabetic individuals are at markedly increased risk for premature death due to cardiovascular disease. Furthermore, substantial morbidity results from microvascular complications which include retinopathy, nephropathy, and neuropathy. Clinical studies involving diabetic patients have suggested that degree of diabetic hyperglycemia correlates with risk of complications. Recent evidence implicates a central role for oxidative stress and vascular inflammation in all forms of insulin resistance, obesity, diabetes and its complications. Although, glucose promotes glycoxidation reactions in vitro and products of glycoxidation and lipoxidation are elevated in plasma and tissue in diabetics, the exact relationships among hyperglycemia, the diabetic state, and oxidative stress are not well-understood. Using a combination of in vitro and in vivo experiments, we have identified amino acid oxidation markers that serve as molecular fingerprints of specific oxidative pathways. Quantification of these products utilizing highly sensitive and specific gas chromatography/mass spectrometry in animal models of diabetic complications and in humans has provided insights in oxidative pathways that result in diabetic complications. Our studies strongly support the hypothesis that unique oxidants are generated in the microenvironment of tissues vulnerable to diabetic damage. Potential therapies interrupting these reactive pathways in target tissue are likely to be beneficial in preventing diabetic complications.     

Oxidative stress in early diabetic nephropathy: fueling the fire

Diabetic nephropathy is a major microvascular complication of diabetes mellitus and the most common cause of end-stage renal disease worldwide. The treatment costs of diabetes mellitus and its complications represent a huge burden on health-care expenditures, creating a major need to identify modifiable factors concerned in the pathogenesis and progression of diabetic nephropathy. Chronic hyperglycemia remains the primary cause of the metabolic, biochemical and vascular abnormalities in diabetic nephropathy. Promotion of excessive oxidative stress in the vascular and cellular milieu results in endothelial cell dysfunction, which is one of the earliest and most pivotal metabolic consequences of chronic hyperglycemia. These derangements are caused by excessive production of advanced glycation end products and free radicals and by the subjugation of antioxidants and antioxidant mechanisms. An increased understanding of the role of oxidative stress in diabetic nephropathy has lead to the exploration of a number of therapeutic strategies, the success of which has so far been limited. However, judicious and timely use of current therapies to maintain good glycemic control, adequate blood pressure and lipid levels, along with lifestyle measures such as regular exercise, optimization of diet and smoking cessation, may help to reduce oxidative stress and endothelial cell dysfunction and retard the progression of diabetic nephropathy until more definitive therapies become available.     

氧化应激与糖尿病血管并发症的关系

糖尿病是一种与代谢相关的慢性疾病,可引起相关的血管损伤.糖尿病并发症发病机理十分复杂,而氧化应激（OS）是引起糖尿病血管并发症的重要机制之一.OS可引起体内糖代谢障碍和脂质代谢紊乱,引发高血糖和炎症反应,损伤组织器官,并加速糖尿病血管并发症的发生和发展,可导致动脉粥样硬化（AS）、内皮血管损伤等,严重影响日常生活,其心血管并发症是导致患者死亡的主要原因之一.正确的认识、评价和治疗OS,可能对糖尿病血管并发症的研究具有重要意义.     

Oxidative stress and diabetic cardiomyopathy: a brief review

Diabetes is a serious public health problem. Improvements in the treatment of noncardiac complications from diabetes have resulted in heart disease becoming a leading cause of death in diabetic patients. Several cardiovascular pathological consequences of diabetes such as hypertension affect the heart to varying degrees. However, hyperglycemia, as an independent risk factor, directly causes cardiac damage and leads to diabetic cardiomyopathy. Diabetic cardiomyopathy can occur independent of vascular disease, although the mechanisms are largely unknown. Previous studies have paid little attention to the direct effects of hyperglycemia on cardiac myocytes, and most studies, especially in vitro, have mainly focused on the molecular mechanisms underlying pathogenic alterations in vascular smooth-muscle cells and endothelial cells. Thus, a comprehensive understanding of the mechanisms of diabetic cardiomyopathy is urgently needed to develop approaches for the prevention and treatment of diabetic cardiac complications. This review provides a survey of current understanding of diabetic cardiomyopathy. Current consensus is that hyperglycemia results in the production of reactive oxygen and nitrogen species, which leads to oxidative myocardial injury. Alterations in myocardial structure and function occur in the late stage of diabetes. These chronic alterations are believed to result from acute cardiac responses to suddenly increased glucose levels at the early stage of diabetes. Oxidative stress, induced by reactive oxygen and nitrogen species derived from hyperglycemia, causes abnormal gene expression, altered signal transduction, and the activation of pathways leading to programmed myocardial cell deaths. The resulting myocardial cell loss thus plays a critical role in the development of diabetic cardiomyopathy. Advances in the application of various strategies for targeting the prevention of hyperglycemia-induced oxidative myocardial injury may be fruitful.     

Oxidative Stress,Diabetes, and Diabetic Complications

Oxidative stress is considered to be the main cause for several chronic diseases including diabetes. Through hyperglycemia, hyperlipidemia, hypertension and possible iron dyshomeostasis, diabetes induces oxidative stress that causes damage to multiple organs, leading to various complications. Therefore, antioxidant therapy may be an interesting approach to prevent diabetes and diabetic complications. Metallothionein as a potent antioxidant was found to significantly protect heart and kidney against diabetes-induced pathophysiological changes. Zinc as an important trace element and a metallothionein inducer was found to have same protective function. Since diabetes would impair defensive system, including growth factor reduction, exogenous supplementation of fibroblast growth factor (FGF) significantly prevented diabetes-induced cardiac oxidative damage and wound healing impairment. These studies suggest that protective agents such as metallothionein, zinc and FGFs play an important role in preventing the development of diabetes and diabetic complications.     

Oxidative stress in the pathogenesis of diabetic neuropathy

Oxidative stress results from a cell or tissue failing to detoxify the free radicals that are produced during metabolic activity. Diabetes is characterized by chronic hyperglycemia that produces dysregulation of cellular metabolism. This review explores the concept that diabetes overloads glucose metabolic pathways, resulting in excess free radical production and oxidative stress. Evidence is presented to support the idea that both chronic and acute hyperglycemia cause oxidative stress in the peripheral nervous system that can promote the development of diabetic neuropathy. Proteins that are damaged by oxidative stress have decreased biological activity leading to loss of energy metabolism, cell signaling, transport, and, ultimately, to cell death. Examination of the data from animal and cell culture models of diabetes, as well as clinical trials of antioxidants, strongly implicates hyperglycemia-induced oxidative stress in diabetic neuropathy. We conclude that striving for superior antioxidative therapies remains essential for the prevention of neuropathy in diabetic patients.     

Can diabetic neuropathy be prevented?

The incidence of diabetes and its complication have rapidly increased. Decreased quality of life and increased mortality are the major problems of people with diabetes. These problems are mainly caused by chronic complications. The incidence of diabetic neuropathy, which is one of these chronic complications, approaches 50% in most diabetic patients. The intensive metabolic management alone cannot completely prevent the development and progression of diabetic complications. Therefore, blocking and management of pathogenic mechanism of complication are required. Pathogenesis of diabetic neuropathy has multifactorial causes. Diabetic neuropathy is thought to occur both from direct hyperglycemia-induced damage to the nerve parenchyma and from neuronal ischemia brought about indirectly by hyperglycemia-induced decreases in neurovascular flow. The effects of hyperglycemia get converted to neuronal dysfunction via at least three secondary biochemical pathways: the polyol pathway, non-enzymatic glycation of proteins, oxidative stress and protein kinase C, and the interactions between them. Because of these interactions, interference with one of these biochemical pathways could either worsen or attenuate the effects of the others. So, the use of therapeutic intervention of these pathways is inevitable and valid to prevent the progression of diabetic neuropathy. As yet, a satisfactory and fundamental, preventive, and therapeutic method is not available with us to prevent progression. So, we will introduce the earlier diagnostic methods of diabetic neuropathy and will discuss the advantages and limitations of each method.     

高糖代谢记忆与糖尿病并发症

高糖"代谢记忆"是影响糖尿病并发症的重要因素,早期血糖控制情况可对并发症产生持久影响.氧化应激和晚期槠基化终末产物(AGEs)是形成高糖"代谢记忆"的基础,同时也是高糖"代谢记忆"参与糖尿病并发症的主要途径.在氧化应激途径中,活性氧簇(ROS)激活与糖尿病并发症相关;在AGEs途径中,AGEs引发的后续效应介导并发症的发生.减弱氧化应激和AGEs的作用,清除有害的代谢记忆,有望成为延缓糖尿病慢性并发症的治疗措施.     

Control of hyperglycemia significantly improves oxidative stress profile of pancreatic islets

Pancreatic islets are known to express low levels of antioxidant enzymes compared to other tissues and are therefore vulnerable to oxidative stress. Enhancing antioxidant defense mechanisms in pancreatic islets help them to cope better with oxidative stress. Persistent hyperglycemia under diabetic condition leads to continuous generation of reactive oxygen species, and different tissues exposed to this are oxidatively damaged depending on their antioxidant defense. Since islet cells are very poor in their antioxidant defense, our interest was to assess their antioxidant profile under normal, diabetic, insulin treated diabetic and untreated diabetic condition. On one hand, antioxidant defense was measured in terms of antioxidant enzymes and antioxidant molecules while on the other, damage caused to biomolecules was estimated. Our data demonstrate that oxidative damage to all biomolecules increased in islets cultured from diabetic animals, which enhanced further in islets from untreated diabetic animals. Insulin treatment significantly improved oxidative stress profile of islets indicating that the control of hyperglycemia leads to improvement in oxidative stress profile.     

Control of hyperglycemia significantly improves oxidative stress profile of pancreatic islets

Pancreatic islets are known to express low levels of antioxidant enzymes compared to other tissues and are therefore vulnerable to oxidative stress. Enhancing antioxidant defense mechanisms in pancreatic islets help them to cope better with oxidative stress. Persistent hyperglycemia under diabetic condition leads to continuous generation of reactive oxygen species, and different tissues exposed to this are oxidatively damaged depending on their antioxidant defense. Since islet cells are very poor in their antioxidant defense, our interest was to assess their antioxidant profile under normal, diabetic, insulin treated diabetic and untreated diabetic condition. On one hand, antioxidant defense was measured in terms of antioxidant enzymes and antioxidant molecules while on the other, damage caused to biomolecules was estimated. Our data demonstrate that oxidative damage to all biomolecules increased in islets cultured from diabetic animals, which enhanced further in islets from untreated diabetic animals. Insulin treatment significantly improved oxidative stress profile of islets indicating that the control of hyperglycemia leads to improvement in oxidative stress profile.     

Meal-induced oxidative stress and low-density lipoprotein oxidation in diabetes: the possible role of hyperglycemia

Oxidative stress and its contribution to low-density lipoprotein (LDL) oxidation have been implicated in the pathogenesis of vascular diabetic complications. However, the relationship between hyperglycemia, hyperinsulinemia, hyperlipidemia, and oxidative stress is still debated. If plasma glucose and/or insulin and/or lipid are some of the most important determinants of oxidative stress in diabetes, then their typical postprandial elevations in diabetes would be expected to favor oxidative stress and LDL oxidation. To test this hypothesis, in type 2 diabetic patients, we evaluated the effects of two different standard meals designed to produce different levels of postprandial hyperglycemia on the plasma oxidative status and LDL oxidation. The meals were administered in randomized order to each of 10 type 2 diabetic patients. Blood samples were collected at baseline and 60 and 120 minutes after the meals. In every sample, plasma levels of glucose, insulin, cholesterol, triglycerides, nonesterified fatty acids (NEFAs), malondialdehyde (MDA), and the total radical-trapping antioxidant parameter (TRAP) were measured. LDL susceptibility to oxidation was evaluated at baseline and after 120 minutes. Plasma glucose, insulin, triglycerides, and MDA increased and NEFAs and TRAP significantly decreased after either meal. The variations in plasma glucose, MDA, and TRAP were significantly greater and LDL was more susceptible to oxidation after the meal that produced a significantly higher degree of hyperglycemia. These results suggest that postprandial hyperglycemia may contribute to oxidative stress in diabetic patients, providing a mechanistic link between hyperglycemia and diabetic vascular disease.     

Insulin resistance and postprandial hyperglycemia the bad companions in natural history of diabetes: effects on health of vascular tree

In diabetic patients the incidence of cardiovascular diseases (CVD) is higher compared with those without diabetes. This elevated incidence may be due to an increased prevalence of established risk factors, such as obesity, dyslipidemia and hypertension. However, several other determinants must be considered. Attention must be paid to the role that specific factors strictly related to diabetes, insulin-resistance and post-prandial hyperglycemia, play in the etiopathogenesis of CVD, as for example atherosclerosis. This review acknowledges the incidence of diabetes on cardiovascular diseases and atherosclerosis from endothelial dysfunction to plaque destabilization, suggesting that insulin resistance and postprandial hyperglycemia should be considered keys in the generation of these worst diabetic cardiovascular outcomes. It finds in hyperglycemia the primum movens that mediates the cascade of vascular damaging events from the beginning of ROS formation to plaque rupture, through increased inflammation. It also adds insights of why diverse therapeutic interventions, which have in common the ability to reduce oxidative stress and inflammation, can impede or delay the onset of complication of atherosclerosis in diabetic patients.     

Endothelial dysfunction in type 2 diabetes: effect of antioxidants.

Individuals with insulin resistance and diabetes mellitus have increased cardiovascular morbidity and mortality, caused in part by vascular complications. Endothelial dysfunction has been implicated in the pathogenesis of vascular diabetic disease. This abnormal function of the vasculature precedes cardiovascular disease and is associated with impaired endothelium-dependent vasorelaxation. The main etiology of the increased mortality and morbidity of type 2 diabetic patients is atherosclerosis. Increased production of free radicals is associated with the pathophysiology of diabetes, resulting in oxidative damage to lipids and proteins. Reduction of oxidative stress in diabetic patients may delay the onset of atherogenesis and the appearance of micro- and macrovascular complications. Alpha-lipoic acid (LA) is a multifunctional antioxidant that has been shown to have beneficial effects on polyneuropathy and on markers of oxidative stress in various tissues. This study was conducted to investigate the effects of LA on endothelial function in diabetic and hyperlipidemic animal models. Carbohydrate and lipid metabolism, endothelial function, plasma malondialdehyde (MDA) and urinary 8-hydroxydeoxyguanosine (8-OHdG) were assessed in non-diabetic controls (Wistar rats), untreated diabetic Goto-Kakizaki (GK) rats and, atherogenic diet (AD)-fed GK rats (fed with atherogenic diet only, treated with alpha-lipoic acid and treated with vehicle, for 3 months). AD resulted in a 3-fold increase in both total and non-HDL serum cholesterol levels and in a 2-fold increase triglyceride levels while endothelial function was significantly reduce MDA and 8-OHdG levels were higher in the GK and GK hyperlipidemic groups and were completely reversed by the antioxidant. Hyperlipidemic GK diabetic rats showed significantly reduced endothelial function that was partially improved with LA. Furthermore, lipoic acid significantly reduced serum cholesterol levels, without lowering HDL cholesterol. Alpha-lipoic acid supplementation represents an achievable adjunct therapy to improve endothelial function and reduce oxidative stress, factors that are implicated in the pathogenesis of atherosclerosis in diabetes.     

The role of oxidative stress in the pathogenesis of type 2 diabetes mellitus micro- and macrovascular complications: avenues for a mechanistic-based therapeutic approach

A growing body of evidence suggests that oxidative stress plays a key role in the pathogenesis of micro- and macrovascular diabetic complications. The increased oxidative stress in subjects with type 2 diabetes is a consequence of several abnormalities, including hyperglycemia, insulin resistance, hyperinsulinemia, and dyslipidemia, each of which contributes to mitochondrial superoxide overproduction in endothelial cells of large and small vessels as well as the myocardium. The unifying pathophysiological mechanism that underlies diabetic complications could be explained by increased production of reactive oxygen species (ROS) via: (1) the polyol pathway flux, (2) increased formation of advanced glycation end products (AGEs), (3) increased expression of the receptor for AGEs, (4) activation of protein kinase C isoforms, and (5) overactivity of the hexosamine pathway. Furthermore, the effects of oxidative stress in individuals with type 2 diabetes are compounded by the inactivation of two critical anti-atherosclerotic enzymes: endothelial nitric oxide synthase and prostacyclin synthase. Of interest, the results of clinical trials in patients with type 2 diabetes in whom intensive management of all the components of the metabolic syndrome (hyperglycemia, hypercholesterolemia, and essential hypertension) was attempted (with agents that exert a beneficial effect on serum glucose, serum lipid concentrations, and blood pressure, respectively) showed a decrease in adverse cardiovascular end points. The purpose of this review is (1) to examine the mechanisms that link oxidative stress to micro- and macrovascular complications in subjects with type 2 diabetes and (2) to consider the therapeutic opportunities that are presented by currently used therapeutic agents which possess antioxidant properties as well as new potential antioxidant substances.     

The link between metabolic abnormalities and endothelial dysfunction in type 2 diabetes: an update

Despite abundant clinical evidence linking metabolic abnormalities to diabetic vasculopathy, the molecular basis of individual susceptibility to diabetic vascular complications is still largely undetermined. Endothelial dysfunction in diabetes-associated vascular complications is considered an early stage of vasculopathy and has attracted considerable research interests. Type 2 diabetes is characterized by metabolic abnormalities, such as hyperglycemia, excess liberation of free fatty acids (FFA), insulin resistance and hyperinsulinemia. These abnormalities exert pathological impact on endothelial function by attenuating endothelium-mediated vasomotor function, enhancing endothelial apoptosis, stimulating endothelium activation/endothelium–monocyte adhesion, promoting an atherogenic response and suppressing barrier function. There are multiple signaling pathways contributing to the adverse effects of glucotoxicity on endothelial function. Insulin maintains the normal balance for release of several factors with vasoactive properties. Abnormal insulin signaling in the endothelium does not affect the whole-body glucose metabolism, but impairs endothelial response to insulin and accelerates atherosclerosis. Excessive level of FFA is implicated in the pathogenesis of insulin resistance. FFA induces endothelial oxidative stress, apoptosis and inflammatory response, and inhibits insulin signaling. Although hyperglycemia, insulin resistance, hyperinsulinemia and dyslipidemia independently contribute to endothelial dysfunction via various distinct mechanisms, the mutual interactions may synergistically accelerate their adverse effects. Oxidative stress and inflammation are predicted to be among the first alterations which may trigger other downstream mediators in diabetes associated with endothelial dysfunction. These mechanisms may provide insights into potential therapeutic targets that can delay or reverse diabetic vasculopathy.