Effect of insulin therapy on endothelium-dependent dilation in type 2 diabetes mellitus

Insulin Therapy, Glycemic Control, and Cardiovascular Risk Factors in Young Latin Americans with Type 2 Diabetes Mellitus

BACKGROUND

Type 2 diabetes has been linked to an increased risk of cardiovascular (CV) disease, but this risk has not been well documented in young patients, especially of Latin American descent. Also, the potential CV benefits of insulin therapy have not been evaluated in young patients with type 2 diabetes. The objectives of this study were to determine any gender-related difference in the presence of CV risk factors in young Latin Americans with poorly controlled type 2 diabetes and the effect of intensive insulin therapy on these CV risk factors.

METHODS AND RESULTS

Fifty-seven Latin American patients with type 2 diabetes between the ages 18 and 45 years were evaluated at baseline. All women were premenopausal and had regular menstrual periods. The mean body mass index (BMI) was > 30 kg/m2 in both genders. Percent body fat, percent hemoglobin A1c, and lipoprotein profiles were similar between genders. Highly sensitive C-reactive protein (CRP) levels were elevated and similar between genders (p = .4). Leukocyte adhesion molecules (intercellular adhesion molecule 1, vascular adhesion molecule 1, E-selectin) and monocyte chemoattractant protein 1 were elevated, whereas adiponectin levels were below normal in both gender groups. Urinary albumin excretion was similar between genders and did not show any relationship with any of the variables. In women, there was a direct relationship between waist circumference and high-sensitivity CRP levels (rho = .53, p = .01). No other significant relationships were observed. Eighteen Latin American patients with type 2 diabetes completed up to 104 weeks of post-intervention with insulin monotherapy. In these patients, glycemic, lipoprotein, and anthropometric measurements were obtained every 12 weeks. Highly sensitive CRP, leukocyte adhesion molecules, and urinary albumin excretion, among other tests, were obtained every 52 weeks. At 52 and 104 weeks, body weight, BMI, waist circumference, and percent body fat increased in a parallel and significant manner. Despite a significant decrease in percent hemoglobin A1c (22.2%; p = < .0001), lipid and lipoprotein profiles, highly sensitive CRP, leukocyte adhesion molecules, and other nontraditional CV risk factors did not change significantly.

CONCLUSIONS

In young, obese, Latino type 2 diabetic patients, improvement in glycemic control with insulin monotherapy was not associated with a parallel improvement in markers of vascular inflammation. Premenopausal Latino women with uncontrolled type 2 diabetes have CV risks comparable to Latino diabetic men of the same age. Obesity and underlying insulin resistance may counteract the potential CV benefits associated with insulin therapy in lean diabetic patients. Weight loss could be a potential therapeutic modality to improve CV risk in Latino type 2 diabetic patients, especially women.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

Endothelial dysfunction in diabetes: pathogenesis, significance, and treatment

Type 2 diabetes (T2D) markedly increases the risk of cardiovascular disease. Endothelial dysfunction (ED), an early indicator of diabetic vascular disease, is common in T2D and independently predicts cardiovascular risk. Although the precise pathogenic mechanisms for ED in T2D remain unclear, at inception they probably involve uncoupling of both endothelial nitric oxide synthase activity and mitochondrial oxidative phosphorylation, as well as the activation of vascular nicotinamide adenine dinucleotide phosphate oxidase. The major contributing factors include dyslipoproteinemia, oxidative stress, and inflammation. Therapeutic interventions are designed to target these pathophysiological factors that underlie ED. Therapeutic interventions, including lifestyle changes, antiglycemic agents and lipid-regulating therapies, aim to correct hyperglycemia and atherogenic dyslipidemia and to improve ED. However, high residual cardiovascular risk is seen in both research and clinical practice settings. Well-designed studies of endothelial function in appropriately selected volunteers afford a good opportunity to test new therapeutic interventions, paving the way for clinical trials and utilization in the care of the diabetic patient. However, based on the results from a recent clinical trial, niacin should not be added to a statin in individuals with low high-density lipoprotein cholesterol and very well controlled low-density lipoprotein cholesterol.

The influence of fenofibrate on lipid profile, endothelial dysfunction, and inflammatory markers in type 2 diabetes mellitus patients with typical and mixed dyslipidemia

BACKGROUND

Type 2 diabetes is associated with early development of endothelial dysfunction. Patients present with typical dyslipidemia (predominantly high levels of triglycerides [TG] and low levels of high-density lipoprotein cholesterol [HDL-C]) or mixed hypercholesterolemia (high levels of low-density lipoprotein cholesterol [LDL-C] and TG with low HDL-C). Normal levels include LDL-C < 100 mg/dL, TG < 135 mg/dL, and HDL-C > 40 mg/dL for men and >50 mg/dL for women.

OBJECTIVE

To determine the effects of 8 weeks' administration of fenofibrate on inflammatory markers, metabolic parameters, and endothelial dysfunction.

METHODS

We administered micronized fenofibrate (Laboratories Fourneir S.A Dijon, France) daily for 8 weeks to 40 dyslipidemic, type 2 diabetes patients with equal numbers in each arm of the typical or mixed dyslipidemia groups. Noninvasive endothelial function assessments were performed and serum inflammatory markers obtained before and after treatment.

RESULTS

The typical group demonstrated significantly greater TG reduction and HDL-C increment, ie, 56% vs, 21.3% (P < .005) and 21% vs. 7.6% (P = .001), respectively, compared with the mixed group. There was greater LDL-C reduction within the mixed group compared with the typical group 21.0% vs. 2.2% (P < .05). Endothelial dysfunction was present in both groups at baseline. After treatment, the typical group demonstrated significant improvement in resting brachial diameter (3.9 mm [interquartile range {IQR} 3.3-4.7] to 4.2 mm [IQR 3.4-4.8], P = .001) compared with no change within the mixed group (3.6 mm [IQR 3.1-5.4] to 3.7 mm [IQR 3.1-5.3], P = .26). Flow-mediated diameter improved significantly in both groups. The mixed group had significantly greater levels of hs-CRP at baseline but no changes throughout the study. The mixed group demonstrated an increase in vascular adhesion molecule-1 from 706 ng/mL (IQR 566-1195) to 845 ng/mL (637-1653; P = .01), a reduction of tumor necrosis factor-α from 7.0 pg/mL (IQR 1.0-43.5) to 2.5 pg/mL (IQR 1.5-13.5; P = .04) throughout the study.

CONCLUSIONS

We effectively compared 8 weeks of fenofibrate therapy in type 2 diabetics with contrasting lipid abnormalities. The typical dyslipidemia group showed significantly greater lipid improvements compared with the mixed dyslipidemia group. Both groups had improvements in endothelial functions that were independent of the lipid levels. We concluded that fibrate therapy in type 2 diabetics is beneficial, especially those with typical dyslipidemia and extends beyond its lipid lowering properties.

Rosiglitazone improves endothelial function in patients with type 2 diabetes treated with insulin

An increased incidence of myocardial infarction with rosiglitazone in patients with type 2 diabetes mellitus (T2DM) has been reported. This study aimed to assess the effect of rosiglitazone on endothelial function, assessed by flow-mediated dilation (FMD), in 34 patients with advanced T2DM treated with insulin without known cardiovascular disease. Patients were randomised into two groups: no additional treatment was given in 17 patients, while 17 patients were given rosiglitazone for 6 months. Addition of rosiglitazone significantly reduced glycosylated haemoglobin (HbA(1c)) (p < 0.0005) and fasting glucose (p < 0.05) and improved FMD (p < 0.005). No significant changes were observed in the insulin-only group. The single independent predictor of FMD improvement was rosiglitazone treatment (p = 0.048). These results show that, in patients with advanced T2DM treated with insulin, addition of rosiglitazone may have a beneficial effect on endothelial function. Further research is needed to investigate why this beneficial effect does not translate into improved cardiovascular prognosis in these patients.

Insulin therapy does not interfere with venous endothelial function evaluation in patients with type 2 diabetes mellitus

INTRODUCTION

Endothelium-dependent dilation is improved in insulin-treated diabetic patients, but this effect is probably due to improved glycemic control. The objective of the present study was to compare endothelium-dependent dilation in patients with well-controlled type 2 diabetes who are or are not using insulin as part of their therapy.

METHODS

We studied 27 patients with type 2 diabetes (11 women, 60.3 years ± 6 years, with HbA1c < 7% and no nephropathy), including 16 patients treated with anti-diabetic agents (No-Ins, 8 women) and 11 patients treated with insulin alone or in combination with anti-diabetic agents (Ins, 3 women). Endothelial function was evaluated by the dorsal hand vein technique, which measures changes in vein diameter in response to phenylephrine, acetylcholine (endothelium-dependent vasodilation) and sodium nitroprusside (endothelium-independent vasodilation).

RESULTS

Age, systolic blood pressure (No-Ins: 129.4 mmHg ± 11.8 mmHg, Ins: 134.8 mmHg ± 12.0 mmHg; P= 0.257), HbA1c, lipids and urinary albumin excretion rate [No-Ins: 9 mg/24 h (0-14.1 mg/24 h) vs. Ins: 10.6 mg/24 h (7.5-14.4 mg/24 h), P=0.398] were similar between groups. There was no difference between endothelium-dependent vasodilation of the No-Ins group (59.3% ± 26.5%) vs. the Ins group (54.0% ± 16.3%; P=0.526). Endothelium-independent vasodilation was also similar between the No-Ins (113.7% ± 35.3%) and Ins groups (111.9% ± 28.5%; P=0.888).

CONCLUSIONS

Subcutaneous insulin therapy does not interfere with venous endothelial function in type 2 diabetes when glycemic and blood pressure control are stable.

Influence of visceral obesity and liver fat on vascular structure and function in obese subjects

Endothelial dysfunction and increased intima-media thickness (IMT) have been found in obese patients. Both regional fat distribution and liver steatosis may influence these markers of subclinical atherosclerosis. We sought to determine the interrelationships of endothelial function, carotid IMT, visceral and subcutaneous adipose tissue accumulation, and liver steatosis in severely obese subjects. In 64 severely obese patients (BMI 42.3 +/- 4.3 kg/m(2)), we determined (i) endothelial function as flow-mediated dilation (FMD) of the brachial artery, (ii) carotid IMT, (iii) visceral fat diameter, and (iv) degree of liver steatosis using ultrasound. FMD was associated inversely with visceral fat diameter and degree of steatosis (r = -0.577, P < 0.0001 and r = -0.523, P < 0.0001, respectively). Carotid IMT correlated with visceral fat mass (r = 0.343, P = 0.007) but not with liver steatosis. After adjustment for conventional cardiovascular risk factors, FMD was predicted independently by the visceral fat diameter, age, and sex (r(2) = 0.48, P < 0.0001), but not by the degree of liver steatosis or plasma adiponectin levels. In contrast, age and sex were the only predictors of IMT (r(2) = 0.33, P < 0.001). In obese patients, visceral fat diameter is a major determinant of endothelial dysfunction, independent of traditional risk factors or the degree of liver steatosis and plasma adiponectin. Measurement of visceral fat diameter by ultrasound is a novel and simple method to identify subjects with an increased risk for atherosclerosis within an obese population.

Insulin glargine reduces carotid intimal hyperplasia after balloon catheter injury in Zucker fatty rats possibly by reduction in oxidative stress

Diabetes and impaired glucose tolerance are associated with increased cardiovascular disease morbidity and mortality particularly after vascular injury. Since insulin is frequently used in such patients, the effect of glulisine (short acting) and glargine (long acting) were tested in Zucker fatty rat carotid artery subjected to balloon catheter injury. Insulin-resistant Zucker fatty rats were sc injected 0.45 mg/kg/d of glargine (once) or glulisine (twice) for 1 week before, and 3 weeks after balloon injury. Fasting and postprandial glucose was measured twice weekly. Injured and uninjured carotid arteries, liver, and aorta were harvested after 3 weeks of injury. Carotid sections were H&E stained for measuring intima/media ratio or immunostained for nitrotyrosine. Serum and aortic protein were analyzed for IGF-1 and 8-isoprostane, respectively. Carotid intima/media ratio was significantly reduced in the glargine group [0.9 +/- 0.1-control; 0.6 +/- 0.1-glulisine; 0.4 +/- 0.1-glargine, P < 0.05]. Serum IGF-1 levels were higher in both insulins, but significant only in glargine group [567 +/- 121 (ng/ml)-control; 1059 +/- 150 (ng/ml)-glargine; P < 0.05]. The aortic 8-isoprostane levels decreased significantly in the glargine group [(921 vs. 2566 pg/mg protein; P < 0.05]. Compared to control nitrotyrosine staining intensity was significantly lower in both groups of insulin-treated rats; the lowest level was in the glargine group. Insulin glargine attenuates carotid intimal hyperplasia in nondiabetic Zucker fatty rat independent of glucose levels and support a valuable function for insulin in vascular disease that merits additional investigations.

Impaired endothelial function and insulin action in first-degree relatives of patients with type 2 diabetes mellitus

First-degree relatives (FDR) of patients with type 2 diabetes mellitus are at increased risk of developing type 2 diabetes mellitus. We studied if endothelial dysfunction of the resistance vessels is present and may coexist with metabolic insulin resistance in FDR. Male FDR (n = 13; 26 +/- 1 years; body mass index, 25 +/- 1 kg m(2) [mean +/- SEM]) and matched control subjects (CON) (n = 22; 25 +/- 1 years; body mass index, 24 +/- 1 kg m(2)) were studied by hyperinsulinemic (40 mU min(-1)m(-2)) isoglycemic clamp combined with brachial arterial and deep venous catheterization of the forearm. Forearm blood flow (FBF) was measured by venous occlusion plethysmography upon stimulation with systemic hyperinsulinemia (291 +/- 11 pmol/L, pooled data from both groups) and upon intraarterial infusion of adenosine (ADN) and acetylcholine (ACH) +/- hyperinsulinemia. Forearm blood flow response to ADN and ACH was less in FDR vs CON (P < .05); systemic hyperinsulinemia added to the FBF effect of ADN in CON (P < .05) but not in FDR. In addition, FDR demonstrated impaired FBF to hyperinsulinemia (2.1 +/- 0.2 vs 4.0 +/- 0.6 mL 100 mL(-1) min(-1)) in FDR and CON, respectively (P < .05). Both M-value (5.0 +/- 0.7 vs 7.0 +/- 0.5 mg min(-1) kg(-1)) and forearm glucose clearance (0.6 +/- 0.1 vs 1.4 +/- 0.4 mL 100 mL(-1)min(-1)) were diminished in FDR compared with CON (all P < .05). FDR demonstrated endothelial dysfunction of the resistance vessels in addition to impaired insulin-stimulated increase in bulk flow. Moreover, FDR demonstrated whole-body insulin resistance as well as decreased basal and insulin-stimulated forearm glucose uptake. It remains to be established whether FDR also demonstrate impaired insulin-stimulated microvascular function.

Rosiglitazone, but not glimepiride, improves myocardial diastolic function in association with reduction in oxidative stress in type 2 diabetic patients without overt heart disease

The effects of thiazolidinediones on cardiac function are controversial in humans with type 2 diabetes (T2DM) and in animals. Given the high prevalence and prognostic relevance of diastolic myocardial dysfunction in T2DM, we tested the hypothesis that by reducing oxidative stress rosiglitazone, but not glimepiride, may improve diastolic function. This randomised cross-over study investigated 12 metformin-treated T2DM patients without cardiovascular disease before and after 16 weeks of additional therapy with rosiglitazone (8 mg daily) or glimepiride (3 mg daily). Systolic and diastolic myocardial velocity (E') were assessed with tissue Doppler. In spite of similar non-significant lowering of glycosylated haemoglobin (HbA1C), rosiglitazone, but not glimepiride, significantly improved E' (p=0.04), reduced malondialdehyde (p=0.028), lowered high-sensitivity C-reactive protein (hsCRP) (p=0.019), and increased adiponectin (p=0.002). For rosiglitazone, multivariate regression analysis revealed malondialdehyde reduction as an independent determinant of treatment-induced improvement in E'. The rosiglitazone-induced improvements of diastolic function and oxidative stress may be of prognostic relevance in choosing therapy for T2DM patients without overt heart disease.

Effects of oral glucose load on endothelial function and on insulin and glucose fluctuations in healthy individuals

Background/aims. Postprandial hyperglycemia, an independent risk factor for cardiovascular disease, is accompanied by endothelial dysfunction. We studied the effect of oral glucose load on insulin and glucose fluctuations, and on postprandial endothelial function in healthy individuals in order to better understand and cope with the postprandial state in insulin resistant individuals. Methods. We assessed post-oral glucose load endothelial function (flow mediated dilation), plasma insulin, and blood glucose in 9 healthy subjects. Results. The largest increases in delta FMD values (fasting FMD value subtracted from postprandial FMD value) occurred at 3 hours after both glucose or placebo load, respectively: 4.80 ± 1.41 (P = .009) and 2.34 ± 1.47 (P = .15). Glucose and insulin concentrations achieved maximum peaks at one hour post-glucose load. Conclusion. Oral glucose load does not induce endothelial dysfunction in healthy individuals with mean insulin and glucose values of 5.6 mmol/L and 27.2 mmol/L, respectively, 2 hours after glucose load.

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.

The role of angiotensin II type 1 receptor blockers in the prevention and management of diabetes mellitus

Angiotensin II Receptor blockers (ARBs) are an important addition to the current range of medications available for treating a wide spectrum of diseases including cardiovascular diseases. Coronary heart disease (CHD) is the most common cause of death in the United Kingdom and worldwide. More importantly, the presence of the metabolic syndrome and the likelihood of diabetes mellitus taking on epidemic proportions in the years to come all threaten to maintain the mortality rate due to CHD. This review article focuses on the clinical studies that have helped define the trends in the usage of these agents in the prevention and treatment of diabetes mellitus and its complications and also explores possible mechanisms of action and future developments.

Therapeutic regulation of endothelial dysfunction in type 2 diabetes mellitus

Endothelial dysfunction is universal in diabetes, being intimately involved with the development of cardiovascular disease. The pathogenesis of endothelial dysfunction in diabetes is complex. It is initially related to the effects of fatty acids and insulin resistance on 'uncoupling' of both endothelial nitric oxide synthase activity and mitochondrial function. Oxidative stress activates protein kinase C (PKC), polyol, hexosamine and nuclear factor kappa B pathways, thereby aggravating endothelial dysfunction. Improvements in endothelial function in the peripheral circulation in diabetes have been demonstrated with monotherapies, including statins, fibrates, angiotensin-converting enzyme (ACE) inhibitors, metformin and fish oils. These observations are supported by large clinical end point trials. Other studies show benefits with certain antioxidants, L-arginine, folate, PKC-inhibitors, peroxisome proliferator activated receptor (PPAR)-alpha and -gamma agonists and phosphodiesterase (PDE-5) inhibitors. However, the benefits of these agents remain to be shown in clinical end point trials. Combination treatments, for example, statins plus ACE inhibitors and statins plus fibrates, have also been demonstrated to have additive benefits on endothelial function in diabetes, but there are no clinical outcome data to date. Measurement of endothelial dysfunction in cardiovascular research can provide fresh opportunities for exploring the mechanism of benefit of new therapeutic regimens and for planning and designing large clinical trials.

Endothelial function varies according to insulin resistance disease type

OBJECTIVE

We examined the relationship between insulin resistance and vascular function in three insulin-resistant states (type 2 diabetes, non-HIV lipodystrophic diabetes, and nondiabetic polycystic ovary syndrome [PCOS]) and in healthy control subjects.

RESEARCH DESIGN AND METHODS

The population included 12 women with type 2 diabetes, 6 with lipodystrophic diabetes, 10 with PCOS, and 19 healthy female subjects. Metabolic measures included insulin sensitivity by the homeostasis model assessment, lipids, free fatty acids, and adiponectin. High-resolution B-mode ultrasound was used to determine endothelium-dependent and -independent vasodilation.

RESULTS

Type 2 diabetic, liposdystrophic, and PCOS subjects were insulin resistant compared with control subjects (P = 0.001). Flow-mediated vasodilation was reduced in diabetic (3.4 +/- 1.3%) compared with control (7.3 +/- 1.1%) subjects but not in lipodystrophic (7.7 +/- 1.2%) or PCOS (9.9 +/- 0.7%) subjects (P = 0.005). Nitroglycerin-mediated vasodilation was attenuated in both diabetic (15.2 +/- 2.0%) and lipodystrophic (16.7 +/- 3.6%) subjects compared with healthy control (24.6 +/- 2.4%) and PCOS (23.2 +/- 1.8%) subjects (P = 0.019). Insulin resistance, free fatty acids, adiponectin, or C-reactive protein did not associate with vascular dysfunction.

CONCLUSIONS

Among these different types of patients with insulin resistance, we found abnormal endothelium-dependent vasodilation only in the patients with type 2 diabetes. We postulate that variations in the mechanism of insulin resistance may affect endothelial function differently than glucose homeostasis.

Positive family history of coronary artery disease is associated with reduced myocardial vasoreactivity in healthy men

OBJECTIVE

Positive family history as a risk factor for coronary artery disease seems to be most important in subjects who otherwise are at low risk. We examined the association between family history of coronary artery disease and myocardial vasoreactivity in healthy men.

METHODS

35 non-smoking healthy men (age 35+/-7 years) were studied: 16 had positive family history of coronary artery disease and 19 had negative family history. The myocardial blood flow measurements were performed basally and during adenosine infusion (140 mug/kg/min) with and without simultaneous physiological hyperinsulinemia (insulin infusion at a rate of 1 mU/kg/min) using positron emission tomography and O-15-water.

RESULTS

Basal myocardial blood flow was similar between the subjects with positive and negative family history of coronary artery disease (0.79+/-0.19 and 0.79+/-0.21 mL g(-1) min(-1), NS). Adenosine stimulated flow was significantly reduced in subjects with positive family history (3.0+/-0.5 vs 4.0+/-1.2 mL g(-1) min(-1), respectively, p=0.003). During physiological hyperinsulinemia adenosine stimulated flow was further enhanced in both groups but significantly blunted in subjects with positive family history (3.7+/-0.9 vs 5.2+/-1.5 mL g(-1) min(-1), respectively, p=0.001). These differences remained significant after simultaneous controlling for age, BMI, HbA1c, LDL-cholesterol, HDL-cholesterol and blood pressure (p=0.002).

CONCLUSIONS

Healthy non-smoking men with positive family history of coronary artery disease are characterized by impaired myocardial vasoreactivity.

Correction of endothelial dysfunction in diabetic female rats by tetrahydrobiopterin and chronic insulin

Diabetes-induced vascular dysfunction has mainly been studied in males. However, the mechanisms involved may not correspond to those in females. Here we analyzed the effects of tetrahydrobiopterin (BH(4)) and chronic insulin on the physiology of mesenteric arterioles of alloxan-diabetic female rats. The parameters studied were the mesenteric arteriolar reactivity (intravital microscopy), nitric oxide synthase (NOS) activity (conversion of L-arginine to L-citrulline), eNOS gene expression (RT-PCR), NO production (diaminofluorescein), reactive oxygen species (ROS) generation (intravital fluorescence microscopy) and Cu/Zn superoxide dismutase (SOD) activity (spectrophotometry) and gene expression (RT-PCR). The reduced endothelium-dependent vasodilation of diabetic females was corrected by both BH(4) and insulin. NOS activity was decreased by diabetes, but insulin did not correct it. However, NOS expression was not modified by either diabetes or insulin. Arterioles of diabetic rats exhibited lower NO production, which was fully corrected by BH(4) and only partially by insulin. ROS generation was increased in diabetic rats, and both BH(4) and insulin normalized it. Diabetes did not change SOD activity and gene expression. However, insulin increased SOD activity but not its expression. Our data suggest that, similarly to males, endothelial dysfunction in female diabetic rats involves an altered ROS/NO imbalance. In contrast to males, however, insulin does not regulate NOS in the microcirculation of diabetic females.

Metabolic syndrome and endothelial dysfunction

The incidence of metabolic syndrome is rapidly increasing in the United States. Metabolic syndrome is associated with increased cardiovascular morbidity and mortality, and endothelial dysfunction is an early pathogenetic event in the metabolic syndrome. Endothelial dysfunction of either the coronary, the peripheral, or the cerebral vasculature is a predictor of vascular events and appears to be a marker of uncontrolled atherosclerotic risk that adds to the burden of the genetic predisposition to cardiovascular disease. Clinically and experimentally, endothelial dysfunction can be restored by several agents, including blockers/inhibitors of the renin-angiotensin-aldosterone system, as well as statins. Nevertheless, it would be premature, and most likely inappropriate, to use improvement of endothelial function as a surrogate end point to predict reduction in cardiovascular morbidity and mortality. However, a clear understanding of the mechanisms of endothelial dysfunction in the metabolic syndrome may allow the development of preventive and early therapeutic measures targeting cardiovascular disease.

Dysregulation of the endothelial nitric oxide synthase–soluble guanylate cyclase pathway is normalized by insulin in the aorta of diabetic rat

Antiatherogenic effects of nitric oxide (NO) are mediated by activation of soluble guanylate cyclase (sGC) and are impaired by diabetes in animals and humans. We investigated whether uncontrolled diabetes and insulin therapy effect expression and function of the main enzymes of the endothelial nitric oxide (eNOS)-sGC signaling pathway in vivo. Expression and function of eNOS, sGC and protein kinase G (PKG) were studied by Western blot analysis and vasorelaxation to NO-donor in thoracic aortas from control (CON) and streptozotocin (SZT)-induced diabetic rats during uncontrolled diabetes (DM) and insulin treatment (INS) for 8 weeks. Protein level of eNOS was increased (+300%, P < 0.05), while sGC (-50%) and PKG (-65%) proteins were reduced (P < 0.03) in aortas of DM. Insulin treatment normalized these defects resulting in eNOS, sGC and PKG aortic protein content comparable to control. In aortic rings, diethylamine NONOate (DEA-NONOate)-induced vasorelaxation was attenuated (P< or =0.05) in DM compared to control and returned to normal in INS. Thus, experimental diabetes decreases sGC and PKG expression and their NO-dependent activation in aorta despite overexpression of eNOS. These abnormalities are normalized by insulin treatment and improved metabolic control.

Hyperglycemia reduces survival and impairs function of circulating blood-derived progenitor cells

OBJECTIVE

Function and availability of circulating progenitor cells (CPC) have been shown to be impaired in patients with diabetes mellitus (DM). Therefore, the aim of the present study was to analyze possible mechanisms leading to the reduction of CPC amount and function.

METHODS AND RESULTS

Peripheral blood mononuclear cells (MNCs) of healthy donors (n=15) were cultivated under hyperglycemia (HG) conditions (12 mmol/L D-Glucose) or in osmotic control medium (Con) (5 mmol/L D-Glucose plus 7 mmol/L L-Glucose) for 7 days. CPC amount was determined by uptake of acetylated low-density lipoprotein and lectin binding. On the functional level, cell cycle status, nitric oxide (NO) production, and migrational and integrative capacity of CPCs were assessed. HG conditions caused a significant decrease in CPC amount derived from healthy MNCs. Furthermore, HG conditions led to a functional impairment, reflected in a decreased NO production and matrix metalloproteinase (MMP)-9 activity, as well as an impairment of the migrational and integrative capacities.

CONCLUSIONS

HG, a main feature of DM, affects important functional characteristics of CPCs. These results may provide further insight into the pathomechanism of endothelial dysfunction in HG.

Mechanisms, Significance and Treatment of Vascular Dysfunction in Type 2 Diabetes Mellitus

Endothelial dysfunction and increased arterial stiffness occur early in the pathogenesis of diabetic vasculopathy. They are both powerful independent predictors of cardiovascular risk. Advances in non-invasive methodologies have led to widespread clinical investigation of these abnormalities in diabetes mellitus, generating a wealth of new knowledge concerning the mechanisms of vascular dysfunction, risk factor associations and potential treatment targets. Endothelial dysfunction primarily reflects decreased availability of nitric oxide (NO), a critical endothelium-derived vasoactive factor with vasodilatory and anti-atherosclerotic properties. Techniques for assessing endothelial dysfunction include ultrasonographic measurement of flow-mediated vasodilatation of the brachial artery and plethysmography measurement of forearm blood flow responses to vasoactive agents. Arterial stiffness may be assessed using pulse wave analysis to generate measures of pulse wave velocity, arterial compliance and wave reflection. The pathogenesis of endothelial dysfunction in type 2 diabetes is multifactorial, with principal contributors being oxidative stress, dyslipidaemia and hyperglycaemia. Elevated blood glucose levels drive production of reactive oxidant species (ROS) via multiple pathways, resulting in uncoupling of mitochondrial oxidative phosphorylation and endothelial NO synthase (eNOS) activity, reducing NO availability and generating further ROS. Hyperglycaemia also contributes to accelerated arterial stiffening by increasing formation of advanced glycation end-products (AGEs), which alter vessel wall structure and function. Diabetic dyslipidaemia is characterised by accumulation of triglyceride-rich lipoproteins, small dense low-density lipoprotein (LDL) particles, reduced high-density lipoprotein (HDL)-cholesterol and increased postprandial free fatty acid flux. These lipid abnormalities contribute to increasing oxidative stress and may directly inhibit eNOS activity. Although lipid-regulating agents such as HMG-CoA reductase inhibitors (statins), fibric acid derivatives (fibrates) and fish oils are used to treat diabetic dyslipidaemia, their impact on vascular function is less clear. Studies in type 2 diabetes have yielded inconsistent results, but this may reflect sampling variation and the potential over-riding influence of oxidative stress, dysglycaemia and insulin resistance on endothelial dysfunction. Results of positive intervention trials suggest that improvement in vascular function is mediated by both lipid and non-lipid mechanisms, including anti-inflammatory, anti-oxidative and direct effects on the arterial wall. Other treatments, such as renin-angiotensin-aldosterone system antagonists, insulin sensitisers and lifestyle-based interventions, have shown beneficial effects on vascular function in type 2 diabetes. Novel approaches, targeting eNOS and AGEs, are under development, as are new lipid-regulating therapies that more effectively lower LDL-cholesterol and raise HDL-cholesterol. Combination therapy may potentially increase therapeutic efficacy and permit use of lower doses, thereby reducing the risk of adverse drug effects and interactions. Concomitant treatments that specifically target oxidative stress may also improve endothelial dysfunction in diabetes. Vascular function studies can be used to explore the therapeutic potential and mechanisms of action of new and established interventions, and provide useful surrogate measures for cardiovascular endpoints in clinical trials.

The postprandial state does not impair endothelial function in women with type 2 diabetes irrespective of glycaemic control

AIMS/HYPOTHESIS

The postprandial state has been shown to be associated with endothelial dysfunction, a predictor of cardiovascular morbidity. In type 2 diabetes, postprandial metabolic excursions are prolonged and exaggerated, but less pronounced if glycaemic control is optimised. We investigated the impact of improved glycaemic control on endothelial function in the postprandial state.

METHODS

We studied 19 postmenopausal women with type 2 diabetes and ten non-diabetic subjects. Participants with diabetes were re-studied 3 months after intensive glucose regulation. We measured forearm blood flow by strain gauge plethysmography during rest, during acetylcholine infusion and post ischaemia in the fasting state, and again 3 hours after a mixed meal (660 kcal, 55% fat).

RESULTS

Endothelium-dependent vasodilation was impaired in the diabetic group (p<0.005) and improved following an HbA1c reduction of 0.96% (p<0.05 for high-dose acetylcholine infusion). Postprandial metabolic excursions were higher in the diabetic group (p<0.001, p<0.01 and p<0.05 for glucose, insulin and triglycerides respectively). Resting forearm blood flow increased in all groups after the meal (p<0.005). There was no difference in fasting and postprandial endothelium-dependent vasodilation before and after improved glucose regulation in either group.

CONCLUSIONS/INTERPRETATION

The postprandial state does not impair endothelial function in non-diabetic women and does not make pre-existing endothelial dysfunction worse in women with type 2 diabetes, irrespective of glycaemic control.

Nontraditional risk factors for cardiovascular disease in diabetes

People with type 2 diabetes are disproportionately affected by cardiovascular disease (CVD), compared with those without diabetes. Traditional risk factors do not fully explain this excess risk, and other "nontraditional" risk factors may be important. This review will highlight the importance of nontraditional risk factors for CVD in the setting of type 2 diabetes and discuss their role in the pathogenesis of the excess CVD morbidity and mortality in these patients. We will also discuss the impact of various therapies used in patients with diabetes on nontraditional risk factors.

The Role of Exercise in the Treatment of Cardiovascular Disease Associated with Type 2 Diabetes Mellitus

The role of exercise training in the prevention and treatment of type 2 diabetes mellitus has been studied extensively over the past two decades. Although the primary treatment aim for patients with type 2 diabetes is metabolic control, the morbidity and mortality associated with the disease is more a function of cardiovascular disease. As exercise is associated with favourable reductions in the risk for cardiovascular disease in other high-risk populations, here we explore the role of exercise in the treatment of cardiovascular maladaptations associated with type 2 diabetes. The cardiovascular adaptation to type 2 diabetes is characterised by hypertrophy, stiffening and loss of functional reserve. Clinically, the cardiovascular adaptations to the diabetic state are associated with an increased risk for cardiovascular disease. Functionally, these adaptations have been shown to contribute to a reduced exercise capacity, which may explain the reduced cardiovascular fitness observed in this population. Exercise training is associated with improved exercise capacity in various populations, including type 2 diabetes. Several structural and functional adaptations within the cardiovascular system following exercise training could explain these findings, such as reductions in ventricular and vascular structural hypertrophy and compliance coupled with increased functional reserve. Although these cardiovascular adaptations to aerobic exercise training have been well documented in older populations with similar decrements in cardiovascular fitness and function, they have yet to be examined in patients with type 2 diabetes. For this reason, we contend that exercise training may be an excellent therapeutic adjunct in the treatment of diabetic cardiovascular disease.

Glargine and regular human insulin similarly acutely enhance endothelium-dependent vasodilatation in normal subjects

OBJECTIVE

Human insulin enhances the vasodilatory effect of acetylcholine (ACh), an endothelium-dependent vasodilator, in normal subjects. Structural changes in a long-acting insulin analog, insulin glargine, may change its binding properties to insulin receptor and structurally homologous receptors, such as the insulin-like growth factor-1 receptor, and thereby alter its vascular effects. In the present study, we compared effects of glargine and regular human insulin on blood flow responses to endothelium-dependent and endothelium-independent vasoactive agents in vivo in normal subjects.

METHODS AND RESULTS

Ten healthy men (age: 33+/-9 years [mean+/-SD]; BMI: 23+/-2 kg/m2) were studied on two separate occasions in a double-blind, randomized, crossover fashion. In each study, blood flow responses to intrabrachial artery infusions of ACh and SNP were determined during infusion of saline and intravenously maintained normoglycemic hyperinsulinemia. Hyperinsulinemia (120 minutes; infusion rate: 1 mU/kg per minute) was created by infusing either insulin glargine or human regular insulin. Glargine and human regular insulin similarly stimulated whole-body glucose metabolism and suppressed serum free-fatty acid (FFA) concentrations. Endothelium-independent blood flow responses to low (3 microg/min) and high (10 microg/min) doses of SNP were unaffected by insulin glargine (12.2+/-2.6 versus 13.4+/-4.6 and 19.1+/-4.2 versus 19.6+/-5.1 mL/dL per minute, saline versus insulin, low- and high-dose) and regular human insulin (11.2+/-3.4 versus 12.0+/-5.2 and 16.8+/-5.7 versus 18.4+/-7.7 mL/dL per minute, respectively). In contrast, endothelium-dependent blood flow responses to low (7.5 microg/min) and high (15 microg/min) doses of ACh increased significantly and similarly by insulin glargine, 13.9+/-4.8 versus 19.3+/-6.5 mL/dL per minute (saline versus insulin, +39%, P<0.01) for low-dose ACh and 17.3+/-6.3 versus 23.2+/-9.2 mL/dL per minute (+34%; P<0.02) for high-dose ACh, and regular human insulin, 11.5+/-6.0 versus 15.8+/-8.0 mL/dL per minute (+38%; P<0.05) and 14.0+/-7.5 versus 21.1+/-10.4 mL/dL per minute (+51%; P<0.01).

CONCLUSIONS

Insulin glargine and regular human insulin have similar acute stimulatory effects on endothelium-dependent vasodilation in humans.

Insulin resistance and endothelial dysfunction

Insulin has multiple metabolic actions, including effects on blood vessels. Insulin normally increases blood flow by a mechanism which involves generation of nitric oxide (NO) via the arginine-NO pathway. Although insulin itself is a weak and physiologically unimportant vasodilatator, it appears to markedly potentiate endothelium-dependent vasodilatation. Therefore, anything that impairs insulin action in endothelial cells can be expected to be associated with endothelial dysfunction, i.e. loss of NO bioactivity in the vessel wall. Consistent with the idea that insulin resistance and endothelial dysfunction frequently coexist, all insulin-resistant conditions examined to date have been associated with endothelial dysfunction. However, the latter can also be caused by factors other than insulin resistance-such as a high concentration of low-density lipoprotein (LDL) cholesterol. Therapies which reverse insulin resistance-such as exercise, insulin and inhibitors of the renin-angiotensin-aldosterone (RAA) axis-also reverse endothelial dysfunction, which may thus be an inherent feature of insulin resistance.

Restoration of endothelial function by increasing high-density lipoprotein in subjects with isolated low high-density lipoprotein

BACKGROUND

Loss-of-function mutations in the ATP-binding cassette (ABCA)-1 gene locus are the underlying cause for familial hypoalphalipoproteinemia, providing a human isolated low-HDL model. In these familial hypoalphalipoproteinemia subjects, we evaluated the impact of isolated low HDL on endothelial function and the vascular effects of an acute increase in HDL.

METHODS AND RESULTS

In 9 ABCA1 heterozygotes and 9 control subjects, vascular function was assessed by venous occlusion plethysmography. Forearm blood flow responses to the endothelium-dependent and -independent vasodilators serotonin (5HT) and sodium nitroprusside, respectively, and the inhibitor of nitric oxide synthase NG-monomethyl-l-arginine (L-NMMA) were measured. Dose-response curves were repeated after systemic infusion of apolipoprotein A-I/phosphatidylcholine (apoA-I/PC) disks. At baseline, ABCA1 heterozygotes had decreased HDL levels (0.4+/-0.2 mmol/L; P<0.05), and their forearm blood flow responses to both 5HT (maximum, 49.0+/-10.4%) and L-NMMA (maximum, -22.8+/-22.9%) were blunted compared with control subjects (both P< or =0.005). Infusion of apoA-I/PC disks increased plasma HDL to 1.3+/-0.4 mmol/L in ABCA1 heterozygotes, which resulted in complete restoration of vasomotor responses to both 5HT and L-NMMA (both P</=0.001). Endothelium-independent vasodilation remained unaltered throughout the protocol.

CONCLUSIONS

In ABCA1 heterozygotes, isolated low HDL is associated with endothelial dysfunction, attested to by impaired basal and stimulated NO bioactivity. Strikingly, both parameters were completely restored after a single, rapid infusion of apoA-I/PC. These findings indicate that in addition to its long-term role within reverse cholesterol transport, HDL per se also exerts direct beneficial effects on the arterial wall.

Factors affecting progression of renal failure in patients with type 2 diabetes

OBJECTIVE

Hyperglycemia and hypertension are known to be risk factors for the development of proteinuria in patients with diabetes. Little is known, however, about predictors of progression of renal failure in diabetic patients.

RESEARCH DESIGN AND METHODS

We investigated factors affecting progression of renal failure by measuring the doubling of serum creatinine (s-Cr) as an end point in a cohort of 85 type 2 diabetic patients with chronic renal insufficiency/failure (s-Cr >1.5 and <3.7 mg/dl, 61 +/- 11 years old, 51 men and 34 women, mean s-Cr 2.3 +/- 0.6 mg/dl).

RESULTS

The survey period (mean +/- SD) was 14.2 +/- 10.8 months. The cumulative incidence of the end point in patients with insulin therapy (n = 41) was significantly lower than that in patients without it (n = 44) (P = 0.0022, P values by log-rank test). Multivariate Cox analysis revealed insulin therapy (hazard ratio [HR] 0.435, 95% CI 0.252-0.750, P = 0.0027), serum albumin (0.484, 284-0.823, P = 0.0074), mean blood pressure (1.023, 1.004-1.043, P = 0.017), and hemoglobin (0.841, 0.728-0.972, P = 0.0194) to be independent and significant predictors of progression to renal failure, whereas HbA(1c) or serum cholesterol were not.

CONCLUSION

In type 2 diabetic patients with renal failure, hypoalbuminemia, anemia, higher mean blood pressure, and lack of use of insulin predict rapid progression of renal failure, but HbA(1c) does not, and insulin therapy may be possibly an indicator of the delay in progression of renal failure.

Effects of thiazolidinediones on cardiovascular risk factors

The thiazolidinediones are the insulin sensitizers used in the management of Type 2 diabetes mellitus. These drugs can potentially decrease the risk of cardiovascular disease by correcting the different components of the insulin resistance syndrome.

Effects of insulin lispro and chronic vitamin C therapy on postprandial lipaemia, oxidative stress and endothelial function in patients with type 2 diabetes mellitus

BACKGROUND

Insulin therapy may influence cardiovascular disease (CVD) and lipid metabolism in type 2 diabetes (T2D). Exaggerated postprandial lipaemia (PPL) is a feature of diabetic dyslipidaemia affecting CVD via enhanced oxidative stress (OS) and endothelial dysfunction. We assessed endothelial function and OS during PPL following insulin and vitamin C. Twenty (17 M) T2D patients were studied (mean Hba1c 8.4%) at baseline, following 6 weeks of insulin lispro (0.2 Iu kg-1) and vitamin C 1-g daily. Eight-h lipid and glucose profiles were measured following a fatty meal. Endothelial function (flow-mediated vasodilatation: FMD) and OS were measured at fasting, 4 h and 8 h.

MATERIALS AND METHODS

Glucose, body mass index, and total and LDL cholesterol remained unchanged. FMD improved. Placebo group: fasting, 1.1 +/- 1.2 to 4.2 +/- 1.1% (P < 0.001); 4-h, 0.3 +/- 1.2 to 3.1 +/- 0.9% (P < 0.01); 8-h, 0.7 +/- 1.1 to 3.76 +/- 1.1% (P < 0.001). Vitamin C group: fasting, 0.9 +/- 1.1 to 6.1 +/- 1.3% (P < 0.001); 4-h, 0.7 +/- 1.5 to 4.9 +/- 2.1% (P < 0.001); 8-h, 0.8 +/- 0.9 to 5.8 +/- 0.6% (P < 0.01). Post-prandial lipaemia was attenuated: TG area-under-curve (mmol L-1 8 h-1), 52.6 +/- 11 to 39.1 +/- 12.5 (placebo group), P < 0.02; and 56.9 +/- 8 to 40.1 +/- 10.3 (vitamin C group), P < 0.02. Oxidative stress was reduced, with greater changes in the vitamin C group.

CONCLUSION

Insulin may thus exert vascular benefits in T2D, by modifying fasting and postprandial lipid metabolism resulting in reduced OS and improved EF. Vitamin C therapy may augment the vascular benefits of insulin in T2D through additional effects on OS and EF.

Insulin as an anti-inflammatory and antiatherosclerotic hormone

Fasting hyperinsulinemia is associated with an increased risk of atherosclerotic complications, namely heart attack and stroke, which has led to the concept that insulin may promote atherosclerosis despite the absence of any evidence that insulin is atherogenic either in humans or in experimental models. Recent evidence shows that insulin exerts vasodilatory, antiplatelet, and anti-inflammatory effects at the cellular level in vitro and in humans in vivo. Because atherosclerosis is an inflammatory process, insulin is probably antiatherosclerotic in the long-term. Recent data on experimental atherosclerosis in mice show that (a) insulin administration reduces the number and the size of atherosclerotic lesions in apolipoprotein E null mice; and (b) in insulin receptor substrate-2 null mice, the interruption in insulin signal transduction results in enhanced atherogenicity. The use of a low dose of insulin infusion in patients with acute myocardial infarction (AMI) has been shown to markedly improve clinical outcomes both in diabetic and nondiabetic patients. The authors' most recent data show that a low-dose infusion of insulin in patients with AMI induces a reduction in inflammation (C-reactive protein and serum amyloid A) and oxidative stress and may have a role in myocardial protection. The authors conclude that insulin is both anti-inflammatory and antiatherogenic and may be of use in the treatment of cardiovascular inflammatory conditions, including AMI.

Augmentation index as a measure of peripheral vascular disease state

Pulse pressure, especially in central arteries, is an independent predictor of adverse cardiovascular events in patients with increased elastic artery stiffness (or elastance). The central arterial pressure wave is composed of a forward traveling wave generated by left ventricular ejection and a later arriving reflected wave from the periphery. Increased stiffness of elastic arteries is the primary cause of increased pulse pressure in subjects with degeneration and hyperplasia of the arterial wall. As stiffness increases, transmission velocity of both forward and reflected waves increase, which causes the reflected wave to arrive earlier in the central aorta and augments pressure in late systole [ie, augmentation index = (augmented pressure/pulse pressure) increases]. These changes in wave reflection properties are associated with vascular disease and aging and cause an increase in left ventricular afterload, myocardial mass, and oxygen consumption. Vasoactive drugs have little direct effect on large elastic arteries but can markedly change wave reflection amplitude and augmentation index by altering stiffness of the muscular arteries and modifying transmission velocity of the reflected wave from the periphery to the heart. This change in amplitude and timing of the reflected wave causes a generalized change in central arterial systolic and pulse pressure that is not detected by cuff pressure measurements in the brachial artery.

Vascular reactivity in diabetes mellitus

Cardiovascular disease is responsible for 70% of the deaths in diabetes mellitus. Endothelial dysfunction occurs early in atherosclerosis and can now be assessed accurately and reproducibly by noninvasive means. Hyperglycemia, insulin resistance, microvascular complications, and coexistent conditions have been shown to impair endothelial function in diabetes. Resistance to insulin's vasodilatory effect and increased free radical generation are probable mechanisms responsible for the endothelial dysfunction in this state. Improvement in glycemic control, insulin and insulin sensitizers, cholesterol lowering, hypolipidemic agents, angiotensin-converting enzyme inhibitors, and angiotensin II receptor blockers have improved clinical cardiovascular outcomes and have also been shown to improve endothelial function. Strategies designed to assess and improve endothelial function may be further beneficial in terms of cardiovascular outcomes in diabetes mellitus, and need to be tested in a clinical setting.