Diabetic endothelial dysfunction: effect of free radical scavenging in Type 2 diabetic patients

Coronary endothelial dysfunction and mitochondrial reactive oxygen species in type 2 diabetic mice

Endothelial cell (EC) dysfunction is implicated in cardiovascular diseases, including diabetes. The decrease in nitric oxide (NO) bioavailability is the hallmark of endothelial dysfunction, and it leads to attenuated vascular relaxation and atherosclerosis followed by a decrease in blood flow. In the heart, decreased coronary blood flow is responsible for insufficient oxygen supply to cardiomyocytes and, subsequently, increases the incidence of cardiac ischemia. In this study we investigate whether and how reactive oxygen species (ROS) in mitochondria contribute to coronary endothelial dysfunction in type 2 diabetic (T2D) mice. T2D was induced in mice by a high-fat diet combined with a single injection of low-dose streptozotocin. ACh-induced vascular relaxation was significantly attenuated in coronary arteries (CAs) from T2D mice compared with controls. The pharmacological approach reveals that NO-dependent, but not hyperpolarization- or prostacyclin-dependent, relaxation was decreased in CAs from T2D mice. Attenuated ACh-induced relaxation in CAs from T2D mice was restored toward control level by treatment with mitoTempol (a mitochondria-specific O2(-) scavenger). Coronary ECs isolated from T2D mice exhibited a significant increase in mitochondrial ROS concentration and decrease in SOD2 protein expression compared with coronary ECs isolated from control mice. Furthermore, protein ubiquitination of SOD2 was significantly increased in coronary ECs isolated from T2D mice. These results suggest that augmented SOD2 ubiquitination leads to the increase in mitochondrial ROS concentration in coronary ECs from T2D mice and attenuates coronary vascular relaxation in T2D mice.

Role of K(ATP) channels in β-cell resistance to oxidative stress

The importance of K(ATP) channels in stimulus-secretion coupling of β-cells is well established, although they are not indispensable for the maintenance of glycaemic control. This review article depicts a new role for K(ATP) channels by showing that genetic or pharmacological ablation of these channels protects β-cells against oxidative stress. Increased production of oxidants is a crucial factor in the pathogenesis of type 2 diabetes mellitus (T2DM). T2DM develops when β-cells can no longer compensate for the high demand of insulin resulting from excess fuel intake. Instead β-cells start to secrete less insulin and β-cell mass is diminished by apoptosis. Both, reduction of insulin secretion and β-cell mass induced by oxidative stress, are prevented by deletion or inhibition of K(ATP) channels. These findings may open up new insights into the early treatment of T2DM.

Microvascular reactivity in type 1 diabetics

OBJECTIVE

To evaluate whether differences are present in microvascular response to the schemia induced by dynamic videocapillaroscopy (VCD), through analysis of the measured capillar transverse segment area (CTSA) in patients with type 1 diabetes mellitus (T1DM).

METHODS

The vascular reactivity of the CTSA was studied by VCD, using a reactive hyperemia test in 61 volunteers, being 31 healthy controls without diabetes family history (Group 1) and 30 patients with T1DM without complications (Group 2). The images were captured every two seconds, during reperfusion after one minute induced ischaemia, and they were analyzed by the program Studio Version 8 and Motic Image Plus. The pre-ischemia capillary transverse segment (basal area, BA), the maximum strain post-ischemia (maximum area, MA), and time to achieve it (MAt) were measured during reperfusion, and the increased area percentage (Ap) was estimated.

RESULTS

The mean differences between groups were evaluated by the t-test. The median comparisons between the groups were studied by the Mann-Whitney test. There was no difference in BA between the groups. The Ap was significantly lower among the diabetic patients, and there was a significant increase in the Mat among the patients of Group 2 when compared to Group 1.

CONCLUSIONS

These data suggest that type 1 diabetes provokes earlier endothelial dysfunction, before the onset of clinically detectable degenerative complications. The outcomes from these alterations need further studies.

Aloe vera gel alleviates cardiotoxicity in streptozocin-induced diabetes in rats

Objectives

Persistent hyperglycaemia results in oxidative stress along with the generation of oxygen free radicals and appears to be an important factor in the production of secondary complications in diabetes. The aim of this work was to evaluate markers of oxidative stress in heart tissue along with the protective, antioxidant and antidiabetic activity of 30% Aloe vera gel in diabetic rats.

Methods

Streptozocin was given as a single intravenous injection and 30% Aloe vera gel was given in two doses for 20 days, orally. Blood glucose, glycosylated haemoglobin, blood reduced glutathione, serum lactate dehydrogenase and serum creatine kinase levels were measured on day 21 after drug treatment. Heart rate and mean blood pressure were recorded at the end of the study. Different biochemical variables were evaluated in the heart tissue, including thiobarbituric acid reactive substance (TBARS), reduced glutathione, superoxide dismutase and catalase in diabetic and in Aloe vera-treated diabetic rats.

Key findings

In streptozocin diabetic rats, the TBARS level was increased significantly, superoxide dismutase and reduced glutathione significantly decreased, and the catalase level was significantly increased. Aloe vera 30% gel (200 mg/kg) treatment in diabetic rats reduced the increased TBARS and maintained the superoxide dismutase and catalase activity up to the normal level. Aloe vera gel increased reduced glutathione by four times in diabetic rats.

Conclusions

Aloe vera gel at 200 mg/kg had significant antidiabetic and cardioprotective activity.

Effect of caloric restriction with and without exercise training on oxidative stress and endothelial function in obese subjects with type 2 diabetes

AIM

Effects of dietary weight loss on endothelial function, particularly when combined with exercise training, is largely unknown in type 2 diabetes. We sought to determine whether aerobic exercise training provided any additional improvements in endothelial function, oxidative stress or other established markers of cardiovascular risk when combined with an energy-restricted diet in patients with type 2 diabetes.

METHODS

In a parallel study design, 29 sedentary, overweight and obese patients with type 2 diabetes (age 52.4 +/- 1.4 years and BMI 34.2 +/- 0.9 kg/m(2)) were randomized to a 12-week moderate energy-restricted diet (~5000 kJ/day and approximately 30% energy deficit) with or without aerobic exercise training [diet only (D), n = 16 and diet plus exercise (DE), n = 13]. Body weight, cardiovascular risk markers, malondialdehyde (MDA, oxidative stress marker), 24-h urinary nitrate/nitrite and flow-mediated dilatation (FMD) of the brachial artery were measured pre- and postintervention.

RESULTS

Both interventions reduced body weight (D 8.9%, DE 8.5%, time effect p < 0.001). Significant reductions in body fat, waist circumference, blood pressure, glycated haemoglobin, glucose, insulin resistance, lipids and MDA and increases in urinary nitrite/nitrate were observed in both groups (time effect p < or = 0.05); however, these changes were not different between treatments. At baseline, FMD was similar in both groups (D 2.5 +/- 0.9%, DE 4.2 +/- 1.2%; p = 0.25) and did not change after the interventions (p = 0.59).

CONCLUSIONS

These results suggest that lifestyle interventions incorporating diet with or without exercise improve glycaemic control, reduce oxidative stress and improve other cardiovascular risk factors but do not improve FMD in obese subjects with type 2 diabetes.

Interleukin-6 and Oxidative Stress in Plasma of Alloxan-Induced Diabetic Rabbits after Pioglitazone Treatment

There is evidence that oxidative stress might be implicated in promoting a state of systemic inflammation in diabetic patients. Understanding the role of reactive oxygen species in the inflammatory response in diabetes becomes essential in finding preventive treatments. Pioglitazone is a new oral antidiabetic agent with potent antioxidant and anti-inflammatory properties. The drug is a high affinity ligand of peroxisome proliferator-activated receptor gamma. This receptor seems to be involved in the control of inflammation by modulating the production of inflammatory mediators. In the present study, the changes in some markers of enhanced oxidative stress and in the level of pro-inflammatory interleukin-6 (IL-6) were examined in plasma of diabetic rabbits after 4 and 8 weeks of pioglitazone treatment. Ascorbic acid (AA) concentration and total antioxidant status (TAS) in plasma of diabetic animals were diminished and significantly elevated after pioglitazone treatment (p < 0.05). Protein carbonyl groups (PCG) content and IL-6 concentration were elevated in plasma of diabetic animals and significantly diminished after pioglitazone treatment. The results obtained in the present study confirm the relations of cytokine systems with oxidative stress in plasma of diabetic subjects. They also suggest the antioxidative and antinflammatory properties of pioglitazone.

Endothelial dysfunction in diabetes mellitus

Diabetes mellitus is associated with an increased risk of cardiovascular disease, even in the presence of intensive glycemic control. Substantial clinical and experimental evidence suggest that both diabetes and insulin resistance cause a combination of endothelial dysfunctions, which may diminish the anti-atherogenic role of the vascular endothelium. Both insulin resistance and endothelial dysfunction appear to precede the development of overt hyperglycemia in patients with type 2 diabetes. Therefore, in patients with diabetes or insulin resistance, endothelial dysfunction may be a critical early target for preventing atherosclerosis and cardiovascular disease. Microalbuminuria is now considered to be an atherosclerotic risk factor and predicts future cardiovascular disease risk in diabetic patients, in elderly patients, as well as in the general population. It has been implicated as an independent risk factor for cardiovascular disease and premature cardiovascular mortality for patients with type 1 and type 2 diabetes mellitus, as well as for patients with essential hypertension. A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. The role of chronic hyperglycemia in the development of diabetic microvascular complications and in neuropathy has been clearly established. However, the biochemical or cellular links between elevated blood glucose levels, and the vascular lesions remain incompletely understood. A number of trials have demonstrated that statins therapy as well as angiotensin converting enzyme inhibitors is associated with improvements in endothelial function in diabetes. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes. In the present review we provide the up to date details on this subject.

Metabolic syndrome therapy: prevention of vascular injury by antidiabetic agents

More than 65 million Americans are currently obese. Type 2 diabetes mellitus, frequently seen in obese subjects, affects 17 million adults in the United States, with a continuous and alarmingly increasing rate. To prevent development of diabetes in those who are at high risk, it is recommended to optimize meal planning and enhance physical activity to make sustained weight reduction possible. In addition to lifestyle changes, various oral antidiabetic agents are available, with diverse mechanisms of action. Some target defective insulin secretion (sulphonylureas, benzoic acid derivatives) or glucose absorption (glycosidase inhibitors), whereas others target insulin resistance (metformin, thiazolidinediones). Patients with metabolic syndrome and diabetes have an increased risk for cardiovascular disease linked to a higher prevalence of hypertension, dyslipidemia, microalbuminuria, and altered hemostasis--parameters that may be modified by antidiabetic agents. In this article, we review the oral agents used to treat type 2 diabetes and the metabolic syndrome, and their effects on vascular tissue.

Antioxidative and anti-inflammatory effects of repaglinide in plasma of diabetic animals

Oxidative stress, defined as an imbalance between the production of reactive oxygen species (ROS) and antioxidant defense, is considered to be an important pathogenic factor in diabetes mellitus and its complications. In diabetic state, ROS might also be implicated in promoting a state of systemic inflammation. Recently, it was demonstrated that antioxidant therapy could be used to stop the initiation and propagation of this inflammatory response. Repaglinide is a new oral antidiabetic agent with a possible antioxidant activity. Therefore, in the present study, a possible therapeutic value of repaglinide in ameliorating the oxidative and inflammatory processes was tested in diabetic animals. In the study, the levels of total antioxidant status (TAS), ascorbic acid (AA), protein carbonyl groups (PCG) and interleukin-6 (IL-6) were determined in plasma of diabetic rabbits after 4 and 8 weeks of repaglinide treatment (1mg daily). Ex vivo analysis revealed that there were significant differences in these markers between hyperglycemic and control animals (P<0.05). Some of these parameters were ameliorated by repaglinide treatment. In diabetic rabbits treated with repaglinide, protein oxidation was diminished by 17.8% after 8 weeks of experiment. The level of AA in plasma of diabetic treated animals was higher than in non-treated diabetic groups (by 9.4 and 22.6% after 4 and 8 weeks, respectively). In diabetic treated animals, the TAS level was also significantly increased (by 23.6 and 16.7%). However, in diabetic rabbits, repaglinide did not affect the concentration of IL-6.

Endothelial nitric oxide synthase gene intron 4 polymorphism in type 2 diabetes mellitus

INTRODUCTION

Endothelial nitric oxide synthase (ecNOS) is a key regulator of vascular nitric oxide production. Polymorphism in intron 4 of the ecNOS gene is implicated in cardiovascular and renal diseases. We investigated a potential involvement of this polymorphism in the development of type 2 diabetes mellitus and its renal complications.

METHODS

This preliminary study involved 410 individuals with type 2 diabetes and 330 healthy control subjects. From the diabetes group 178 patients had diabetic nephropathy. All subjects were genotyped for the ecNOS4 polymorphism by the polymerase chain reaction (PCR) followed by gel electrophoresis. Genotype and allele frequencies were compared between diabetes patients with and without nephropathy and the control group. All calculations were performed using the Statistical Package for the Social Sciences (SPSS, Inc., Chicago, IL, USA) for Windows 5.0. The chi-square test and Fisher's exact test were used for case-control comparisons. The Kruskal-Wallis test was used for the comparison of subgroups of patients with diabetes.

RESULTS

The analysis revealed that patients with diabetes, regardless of their nephropathy status, were significantly different in genotype distribution and 4a allele frequencies compared with controls (p < 0.05). The frequency of aa genotype was 8.2% in diabetic patients without nephropathy, 8.4% with those with nephropathy and 1.2% in controls. The 4a allele showed a significant effect on diabetic nephropathy, with odds ratio of 2.24 (95% confidence interval 1.12-3.40). There were no significant differences in the 4a allele frequency between the normotensive and hypertensive patients with diabetes.

CONCLUSION

Our results suggest that the ecNOS gene polymorphism can serve as a useful genetic marker of increased susceptibility to type 2 diabetes and its renal complications.

Endothelial nitric oxide synthase gene intron 4 polymorphism in type 2 diabetes mellitus

INTRODUCTION

Endothelial nitric oxide synthase (ecNOS) is a key regulator of vascular nitric oxide production. Polymorphism in intron 4 of the ecNOS gene is implicated in cardiovascular and renal diseases. We investigated a potential involvement of this polymorphism in the development of type 2 diabetes mellitus and its renal complications.

METHODS

This preliminary study involved 410 individuals with type 2 diabetes and 330 healthy control subjects. From the diabetes group 178 patients had diabetic nephropathy. All subjects were genotyped for the ecNOS4 polymorphism by the polymerase chain reaction (PCR) followed by gel electrophoresis. Genotype and allele frequencies were compared between diabetes patients with and without nephropathy and the control group. All calculations were performed using the Statistical Package for the Social Sciences (SPSS, Inc., Chicago, IL, USA) for Windows 5.0. The chi-square test and Fisher's exact test were used for case-control comparisons. The Kruskal-Wallis test was used for the comparison of subgroups of patients with diabetes.

RESULTS

The analysis revealed that patients with diabetes, regardless of their nephropathy status, were significantly different in genotype distribution and 4a allele frequencies compared with controls (p < 0.05). The frequency of aa genotype was 8.2% in diabetic patients without nephropathy, 8.4% with those with nephropathy and 1.2% in controls. The 4a allele showed a significant effect on diabetic nephropathy, with odds ratio of 2.24 (95% confidence interval 1.12-3.40). There were no significant differences in the 4a allele frequency between the normotensive and hypertensive patients with diabetes.

CONCLUSION

Our results suggest that the ecNOS gene polymorphism can serve as a useful genetic marker of increased susceptibility to type 2 diabetes and its renal complications.