Pathophysiological implications of insulin resistance on vascular endothelial function

Animal models of insulin resistance: A review

Insulin resistance can be seen as a molecular and genetic mystery, with a role in the pathophysiology of type 2 diabetes mellitus. It is a basis for a number of chronic diseases like hypertension, dyslipidemia, glucose intolerance, coronary heart disease, cerebral vascular disease along with T2DM, thus the key is to cure and prevent insulin resistance. Critical perspicacity into the etiology of insulin resistance have been gained by the use of animal models where insulin action has been modulated by various transgenic and non-transgenic models which is not possible in human studies. The following review comprises the pathophysiology involved in insulin resistance, various factors causing insulin resistance, their screening and various genetic and non-genetic animal models highlighting the pathological and metabolic characteristics of each.

Atorvastatin ameliorates endothelium-specific insulin resistance induced by high glucose combined with high insulin

The aim of the present study was to establish an endothelial cell model of endothelium-specific insulin resistance to evaluate the effect of atorvastatin on insulin resistance-associated endothelial dysfunction and to identify the potential pathway responsible for its action. Cultured human umbilical vein endothelial cells (HUVECs) were pretreated with different concentrations of glucose with, or without, 10‑5 M insulin for 24 h, following which the cells were treated with atorvastatin. The tyrosine phosphorylation of insulin receptor (IR) and insulin receptor substrate-1 (IRS‑1), the production of nitric oxide (NO), the activity and phosphorylation level of endothelial NO synthase (eNOS) on serine1177, and the mRNA levels of endothelin‑1 (ET‑1) were assessed during the experimental procedure. Treatment of the HUVECs with 30 mM glucose and 10‑5 M insulin for 24 h impaired insulin signaling, with reductions in the tyrosine phosphorylation of IR and protein expression of IRS‑1 by almost 75 and 65%, respectively. This, in turn, decreased the activity and phosphorylation of eNOS on serine1177, and reduced the production of NO by almost 80%. By contrast, the mRNA levels of ET‑1 were upregulated. All these changes were ameliorated by atorvastatin. Taken together, these results demonstrated that high concentrations of glucose and insulin impaired insulin signaling leading to endothelial dysfunction, and that atorvastatin ameliorated these changes, acting primarily through the phosphatidylinositol 3-kinase/Akt/eNOS signaling pathway.

Chlorthalidone Improves Endothelial-Mediated Vascular Responses in Hypertension Complicated by Nondiabetic Metabolic Syndrome

Background: The study was conducted to evaluate the vascular effects of chlorthalidone, a distal tubule-acting natriuretic agent, in hypertensive patients with nondiabetic metabolic syndrome, an insulin-resistant condition characterized by endothelial dysfunction and high risk for diabetes mellitus development.

Methods: Thirteen untreated hypertensive patients with Adult Treatment Panel-III-defined nondiabetic metabolic syndrome were assigned to 3-month treatment with chlorthalidone. The end-points were baseline and post-treatment evaluation of (1) forearm blood flow (strain-gauge plethysmography) responses to graded intra-arterial acetylcholine infusion to test endothelial-mediated vasomotor function, with sodium nitroprusside as a control for endothelium-independent vasodilatation; (2) minimum forearm vascular resistance, the ratio of mean blood pressure and maximal blood flow in response to 13-minute arterial occlusion, as a hemodynamic correlate of arteriolar structure; and (3) transcapillary albumin escape rate (the 1-hour decay rate of 125I-albumin, 6-8 μC ev) as a measure of systemic capillary permeability. Additional measurements included baseline and posttreatment lipids, fasting, and postload glucose and insulin as well as the homeostasis model assessment, an index of insulin sensitivity.

Results: Chlorthalidone reduced blood pressure, augmented acetylcholine-mediated vasodilatation, decreased minimum forearm resistance, and slowed the transcapillary albumin escape rate. Metabolic parameters did not change significantly except for an increase in low-density lipoprotein cholesterol levels.

Conclusions: Chlorthalidone improved endothelial function, reversed abnormal arteriolar structure, and slowed albumin permeation in hypertensive patients with nondiabetic metabolic syndrome.

Role of habitual physical activity in modulating vascular actions of insulin

NEW FINDINGS

What is the topic of this review? This review highlights the importance of increased vascular insulin sensitivity for maintaining glycaemic control and cardiovascular health. What advances does it highlight? We discuss the role of habitual physical activity in modulating vascular actions of insulin. Type 2 diabetes and cardiovascular disease commonly coexist. Current evidence suggests that impaired insulin signalling in the vasculature may be a common link between metabolic and cardiovascular diseases, including glycaemic dysregulation and atherosclerosis. Herein, we highlight the importance of the actions of insulin on the vasculature for glycaemic control and arterial health. In addition, we summarize and discuss findings from our group and others demonstrating that increased physical activity may be an effective approach to enhancing vascular insulin sensitivity. Furthermore, in light of the existing literature, we formulate the hypothesis that increased shear stress may be a prime mechanism through which habitual physical activity improves insulin signalling in the vasculature. Ultimately, we propose that targeting vascular insulin resistance may represent a viable strategy for improving glycaemic control and reducing cardiovascular risk in patients with type 2 diabetes.

Recurrent pre-eclampsia in women with metabolic syndrome and low plasma volume: a retrospective cohort study

OBJECTIVE

To determine the prevalence of recurrent pre-eclampsia in women with a history of pre-eclampsia with both metabolic syndrome and low plasma volume postpartum, as compared with women without either entity.

DESIGN

Retrospective cohort study.

SETTING

Three tertiary referral hospitals in the Netherlands.

POPULATION

Women with a history of pre-eclampsia.

METHODS

In 196 women with a history of pre-eclampsia we determined the presence or absence of metabolic syndrome using the World Health Organization criteria and measured plasma volume with the (125) I-human serum albumin indicator dilution technique. We compared the prevalence of recurrent pre-eclampsia in four groups, classified according to presence or absence of metabolic syndrome and low or normal plasma volume, calculating odds ratios (OR), adjusted for confounders.

MAIN OUTCOME MEASURE

Recurrence of pre-eclampsia in the subsequent pregnancy.

RESULTS

The prevalence of recurrent pre-eclampsia was 12% (12/99) in women without metabolic syndrome with normal plasma volume, versus 47% (8/17) in women with both metabolic syndrome and low plasma volume: OR 6.44 (95% CI 2.09-19.90), adjusted OR 7.90 (95% CI 2.30-27.16). Recurrent pre-eclampsia was present in 44% (10/23) and 25% (14/57) of women with isolated metabolic syndrome and low plasma volume, respectively.

CONCLUSIONS

In the concomitant presence of metabolic syndrome and low plasma volume, the prevalence of recurrent pre-eclampsia was nearly 50%, which is four times as high as the prevalence in women without either entity.

TWEETABLE ABSTRACT

Metabolic syndrome and low plasma volume raise the risk of recurrent pre-eclampsia to nearly 50%.

Assessment of Neutrophil Gelatinase-Associated Lipocalin (NGAL) and Retinol-Binding Protein 4 (RBP4) in Type 2 Diabetic Patients with Nephropathy

Diabetic nephropathy (DN) is one of the most serious microvascular complications of diabetes. The study aims to evaluate the diagnostic value of serum neutrophil gelatinase-associated lipocalin (NGAL) and retinol-binding protein 4 (RBP4) as biomarkers for early detection of nephropathy in type 2 diabetic patients. The current study was performed on 150 type 2 diabetic patients. These patients were classified into three equal groups according to their albumin/creatinine ratio (ACR), including patients with normoalbuminuria (ACR <30 mg/g creatinine), patients with microalbuminuria (ACR = 30-300 mg/g creatinine), and patients with macroalbuminuria (ACR >300 mg/g creatinine). Fifty apparently healthy subjects matching the same age and socioeconomic status with diabetic subjects were selected as a control group. The plasma glucose, insulin, glycosylated hemoglobin (HbA1c), homeostasis model assessment of insulin resistance (HOMA-IR), lipid profile, urea, creatinine, cystatin C, glomerular filtration rate (GFR), NGAL, and RBP4 were measured in the studied groups. Significantly elevated NGAL and RBP4 levels were observed in micro- and macroalbuminuric diabetic groups when compared to the control and normoalbuminuric diabetic groups. NGAL and RBP4 were found to correlate positively with duration of diabetes, systolic and diastolic blood pressure, glucose, HbA1c, HOMA-IR, triacylglycerol, and ACR, but correlate inversely with GFR in DN groups. Receiver operating characteristic curves revealed that for early detection of DN, the best cutoff values to discriminate DN and diabetic without nephropathy groups were 91.5 ng/mL for NGAL with 87% sensitivity, 74% specificity, and area under the curve (AUC) = 0.881; 24.5 ng/mL for RBP4 with 84% sensitivity, 90% specificity, and AUC = 0.912; and 37.5 mg/g creatinine for ACR with 89% sensitivity, 72% specificity, and AUC = 0.819. RBP4 is more specific (90% specificity) than NGAL (74% specificity) and ACR (72% specificity). Therefore, RBP4 marker may serve as a tool to follow-up clinical monitoring of the development and progression of DN.

Clinical and Biochemical Markers of Cardiovascular Structure and Function in Women With the Metabolic Syndrome

The pathobiological impact of individual components of the metabolic syndrome (MS) on cardiac structural and functional parameters in women with isolated MS is not known. The objectives of this study were (1) to compare biochemical (prothrombotic, lipogenic, and inflammatory) and imaging (carotid intima-media thickening and basic cardiac structural measurements) markers in women with and without MS and (2) to examine if any of these markers associated or predicted cardiac structural differences between the 2 groups. This cross-sectional pilot study included 88 women with MS and 35 women without it. MS was defined according to the National Cholesterol Education Program Adult Treatment Panel III criteria. Patients with diagnosis of diabetes were excluded. Compared with healthy subjects, women with MS had higher levels of intercellular adhesion molecule, myeloperoxidase, C-reactive protein, plasminogen activator inhibitor-1, leptin, apolipoprotein-B, and lower levels of apolipoprotein-A1 (p <0.001 for all). They also had higher mean ventricular septum, posterior wall thickness, left ventricular (LV) mass, carotid intima-media thickness (p <0.001 for all), and left atrial diameter (p = 0.015). In multivariable regression models, waist circumference and systolic blood pressure (BP) were significant predictors of: ventricular septum (p = 0.005 and p = 0.001, respectively), posterior wall thickness (p = 0.008 and p = 0.040, respectively), and LV mass (p <0.001 and p = 0.013, respectively). Significant predictors for carotid intima-media thickness were systolic BP, glucose, and leptin (p <0.0001, p = 0.034, and p = 0.002, respectively). In conclusion, there are significant clinical, biochemical, and cardiovascular structural differences in women with isolated MS compared with those without. Waist circumference and systolic BP had the strongest association with cardiac structural differences in this group of women.

Role of sphingosine-1-phosphate receptor 1 and sphingosine-1-phosphate receptor 2 in hyperglycemia-induced endothelial cell dysfunction

The hyperglycemia-induced production of oxidative stress results in endothelial cell dysfunction. Previous studies have demonstrated that sphingosine-1-phosphate (S1P) regulates an array of biological activities in endothelial cells mediated by sphingosine-1-phosphate receptors (S1PRs). However, the role of S1PR-mediated signaling pathways in hyperglycemia-induced endothelial cell dysfunction is currently unknown. In the present study, we aimed to explore the role of S1PRs in endothelial cell dysfunction. For this purpose, hyperglycemia-induced oxidative stress was examined using human umbilical vein endothelial cells (HUVECs) cultured with either normal (5.6 mM) or high (25 mM) levels of glucose. The levels of reactive oxygen species (ROS) and nitric oxide (NO) were determined by flow cytometric (FCM) analysis and nitrate reductase, respectively. Endothelial morphogenesis assay was performed in three-dimensional Matrigel. The mRNA and protein expression levels of S1PRs in the HUVECs were determined by RT-qPCR and western blot analysis, respectively. In addition, ROS, NO and endothelial morphogenesis assays were conducted using the high glucose-treated endothelial cells transfected with adenoviral vector expressing exogenous S1PR1 gene (pAd-S1PR1) or with adenoviral vector expressing S1PR2-specific shRNA (pAd-shRNA-S1PR2). The expression levels of S1PR1 and S1PR2 in the endothelial cells treated with high levels of glucose decreased and increased, respectively. However, the effects of high levels of glucose on S1PR3 were minimal. In addition, high levels of glucose enhanced ROS generation and markedly reduced NO generation and morphogenetic responses. Nevertheless, all the aforementioned changes were completely reversed by transfection with pAd-S1PR1 or pAd-shRNA-S1PR2, which increased S1PR1 and decreased S1PR2 expression, respectively. It can thus be concluded that S1PR1 and S1PR2 play crucial roles in hyperglycemia-induced endothelial cell dysfunction.

Contemporary treatment strategies for Type 2 diabetes-related macrovascular disease

Type 2 diabetes mellitus poses a major challenge to healthcare providers in the coming years as its prevalence increases across the globe. The disease doubles the risk of cardiovascular morbidity and mortality, with 70% of sufferers dying from a cardiac cause. Large clinical trials of current glucose-lowering therapies for Type 2 diabetes have shown no benefit in reducing the risk of macrovascular events. Blood pressure control, angiotensin-converting enzyme inhibitor therapy and improvement of dyslipidemia with statins have proven benefit in reducing cardiovascular risk in Type 2 diabetes. A growing understanding of the importance of pathological processes including endothelial dysfunction, abnormal growth factor biology, oxidative stress, dysregulation of adipokines and deficient vascular repair and regeneration in insulin-resistant states promises new treatments to combat the problem.

Carotid artery intima-media thickness and erectile dysfunction in patients with metabolic syndrome

Background

Metabolic syndrome (MS) has become a pandemic in Turkey, as is the case globally. Increase in carotid artery intima-media thickness (CIMT) and erectile dysfunction (ED) may be evident before the clinical signs of cardiovascular disease appear. We aimed to investigate the prevalence of increased CIMT and ED as markers of atherosclerotic disease in patients with MS.

Material/Methods

Thirty-two patients with MS and 29 healthy controls were included. Anthropometric and biochemical parameters, along with total testosterone (TT), high sensitive C-reactive protein (hs-CRP), were recorded. Carotid artery intima-media thickness was measured. Erectile dysfunction was assessed with International Index of Erectile Function.

Results

Patients with MS had higher BMI, fasting plasma glucose, post-prandial plasma glucose, insulin, HOMA-IR, total cholesterol, triglycerides, hs-CRP, and CIMT, whereas TT levels were lower (p<0.0001). The prevalence and severity of erectile dysfunction were higher in patients with MS (p<0.0001). Erectile dysfunction scores correlated inversely with CIMT. MS patients with ED were older and had higher CIMT compared to those without ED. Increase in age and HOMA and decrease in TT increased the risk of ED. When KIMT exceeding the 95^th percentile of healthy controls was accepted as a risk factor for CVD, presence of ED was the only determinant for this increase.

Conclusions

Erectile dysfunction was more prevalent and severe in patients with MS and correlated with subclinical endothelial dysfunction. Total testosterone deficiency was prominent among MS patients. Presence of ED points to an increased risk of cardiovascular disease when MS is present.

Endothelial dysfunction in metabolic and vascular disorders

Vascular endothelium has important regulatory functions in the cardiovascular system and a pivotal role in the maintenance of vascular health and metabolic homeostasis. It has long been recognized that endothelial dysfunction participates in the pathogenesis of atherosclerosis from early, preclinical lesions to advanced, thrombotic complications. In addition, endothelial dysfunction has been recently implicated in the development of insulin resistance and type 2 diabetes mellitus (T2DM). Considering that states of insulin resistance (eg, metabolic syndrome, impaired fasting glucose, impaired glucose tolerance, and T2DM) represent the most prevalent metabolic disorders and risk factors for atherosclerosis, it is of considerable scientific and clinical interest that both metabolic and vascular disorders have endothelial dysfunction as a common background. Importantly, endothelial dysfunction has been associated with adverse outcomes in patients with established cardiovascular disease, and a growing body of evidence indicates that endothelial dysfunction also imparts adverse prognosis in states of insulin resistance. In this review, we discuss the association of insulin resistance and T2DM with endothelial dysfunction and vascular disease, with a focus on the underlying mechanisms and prognostic implications of the endothelial dysfunction in metabolic and vascular disorders. We also address current therapeutic strategies for the improvement of endothelial dysfunction.

Effects of metformin and exercise training, alone or in association, on cardio-pulmonary performance and quality of life in insulin resistance patients

Background

Metformin (MET) therapy exerts positive effects improving glucose tolerance and preventing the evolution toward diabetes in insulin resistant patients. It has been shown that adding MET to exercise training does not improve insulin sensitivity. The aim of this study was to determine the effect of MET and exercise training alone or in combination on maximal aerobic capacity and, as a secondary end-point on quality of life indexes in individuals with insulin resistance.

Methods

75 insulin resistant patients were enrolled and subsequently assigned to MET (M), MET with exercise training (MEx), and exercise training alone (Ex). 12-weeks of supervised exercise-training program was carried out in both Ex and MEx groups. Cardiopulmonary exercise test and SF-36 to evaluate Health-Related Quality of Life (HRQoL) was performed at basal and after 12-weeks of treatment.

Results

Cardiopulmonary exercise test showed a significant increase of peak VO2 in Ex and MEx whereas M showed no improvement of peak VO2 (∆ VO2 [CI 95%] Ex +0.26 [0.47 to 0.05] l/min; ∆ VO2 MEx +0.19 [0.33 to 0.05] l/min; ∆ VO2 M -0.09 [-0.03 to -0.15] l/min; M vs E p < 0.01; M vs MEx p < 0.01; MEx vs Ex p = ns). SF-36 highlighted a significant increase in general QoL index in the MEx (58.3 ± 19 vs 77.3 ± 16; p < 0.01) and Ex (62.1 ± 17 vs 73.7 ± 12; p < 0.005) groups.

Conclusions

We evidenced that cardiopulmonary negative effects showed by MET therapy may be counterbalanced with the combination of exercise training. Given that exercise training associated with MET produced similar effects to exercise training alone in terms of maximal aerobic capacity and HRQoL, programmed exercise training remains the first choice therapy in insulin resistant patients.

Endothelial Insulin Resistance Protects the Heart Against Prolonged Ischemia–Reperfusion Injury But Does Not Prevent Insulin Transport Across the Endothelium in a Mouse Langendorff Model

Aim:

The endothelium plays an important role in the maintenance of cardiovascular homeostasis in healthy individuals. Insulin resistance can lead to the development of endothelial dysfunction, which is an important step in the pathogenesis of atherosclerosis. We investigated specifically whether the presence of vascular insulin resistance and endothelial dysfunction has any influence on the myocardial tolerance to ischemia–reperfusion (IR) injury, using Endothelial Specific Mutant Insulin Receptor Over-expressing (ESMIRO) mice, which exhibit vascular insulin resistance and vascular dysfunction.

Methods:

ESMIRO or wild-type (WT) littermate mouse hearts were isolated and perfused on a Langendorff apparatus. These were subjected to either 35-minute or 45-minute ischemia followed by reperfusion, after which infarct size was determined. The ability of insulin to activate its target kinase pathway, that is, phosphoinositide 3 (PI3) kinase/protein kinase B (AKT) in ESMIRO hearts was also assessed by Western blot analysis.

Results:

Compared to 35-minute ischemia, the extended 45-minute ischemic protocol significantly exacerbated myocardial infarction in WT mice, (56% ± 4%, n = 6 vs 32% ± 4%, n = 9; P < .01) but not in ESMIRO littermates (34% ± 7%, n = 6 vs 32% ± 3%, n = 9; not significant), suggesting some form of protective phenotype. Insulin treatment was associated with a significant increase in AKT phosphorylation in the myocardium in both the ESMIRO mice and WT littermates, and this was attenuated in both by inhibition of PI3 kinase using LY294002. Thus, insulin was able to directly activate PI3 kinase/AKT in the myocardium despite the absence of functional endothelial insulin receptors in the ESMIRO mice.

Conclusion:

(1) Insulin at pharmacologic concentrations can be transported across the endothelium independent of vascular insulin receptors and (2) vascular insulin resistance and/or endothelial dysfunction are protective against prolonged IR injury in the Langendorff model.

Nitric oxide, oxidative stress, and p66Shc interplay in diabetic endothelial dysfunction

Increased oxidative stress and reduced nitric oxide (NO) bioavailability play a causal role in endothelial cell dysfunction occurring in the vasculature of diabetic patients. In this review, we summarized the molecular mechanisms underpinning diabetic endothelial and vascular dysfunction. In particular, we focused our attention on the complex interplay existing among NO, reactive oxygen species (ROS), and one crucial regulator of intracellular ROS production, p66Shc protein.

Melatonin administration decreases adipogenesis in the liver of ob/ob mice through autophagy modulation

Despite efforts to curb the incidence of obesity and its comorbidities, this condition remains the fifth leading cause of death worldwide. To identify ways to reduce this global effect, we investigated the actions of daily melatonin administration on oxidative stress parameters and autophagic processes as a possible treatment of obesity in ob/ob mice. The involvement of melatonin in many physiological functions, such as the regulation of seasonal body weight variation, glucose uptake, or adiposity, and the role of this indoleamine as an essential antioxidant, has become the focus of numerous anti-obesity studies. Here, we examined the oxidative status in the livers of obese melatonin-treated and untreated mice, observing a decrease in the oxidative stress levels through elevated catalase activity. ROS-mediated autophagy was downregulated in the liver of melatonin-treated animals and was accompanied by significant accumulation of p62. Autophagy is closely associated with adipogenesis; in this study, we report that melatonin-treated obese mice also showed reduced adiposity, as demonstrated by diminished body weight and reduced peroxisome proliferator-activated receptor gamma expression. Based on these factors, it is reasonable to assume that oxidative stress and autophagy play important roles in obesity, and therefore, melatonin could be an interesting target molecule for the development of a potential therapeutic agent to curb body weight.

Uncoupling of eNOS contributes to redox-sensitive leukocyte recruitment and microvascular leakage elicited by methylglyoxal

Elevated levels of the glycolysis metabolite methylglyoxal (MG) have been implicated in impaired leukocyte-endothelial interactions and vascular complications in diabetes, putative mechanisms of which remain elusive. Uncoupling of endothelial nitric oxide synthase (eNOS) was shown to be involved in endothelial dysfunction in diabetes. Whether MG contributes to these effects has not been elucidated. By using intravital microscopy in vivo, we demonstrate that MG-triggered reduction in leukocyte rolling velocity and increases in rolling flux, adhesion, emigration and microvascular permeability were significantly abated by scavenging reactive oxygen species (ROS). In murine cremaster muscle, MG treatment reduced tetrahydrobiopterin (BH4)/total biopterin ratio, increased arginase expression and stimulated ROS and superoxide production. The latter was significantly blunted by ROS scavengers Tempol (300μM) or MnTBAP (300μM), by BH4 supplementation (100μM) or by NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 20μM). In these tissues and cultured murine and human primary endothelial cells, MG increased eNOS monomerization and decreased BH4/total biopterin ratio, effects that were significantly mitigated by supplementation of BH4 or its precursor sepiapterin but not by L-NAME or tetrahydroneopterin, indicative of MG-triggered eNOS uncoupling. MG treatment further decreased the expression of guanosine triphosphate cyclohydrolase I in murine primary endothelial cells. MG-induced leukocyte recruitment was significantly attenuated by supplementation of BH4 or sepiapterin or suppression of superoxide by L-NAME confirming the role of eNOS uncoupling in MG-elicited leukocyte recruitment. Together, our study uncovers eNOS uncoupling as a pivotal mechanism in MG-induced oxidative stress, microvascular hyperpermeability and leukocyte recruitment in vivo.

Cellular and molecular mechanisms of endothelial dysfunction in diabetes

In healthy individuals, the vascular endothelium regulates an intricate balance of factors that maintain vascular homeostasis and normal arterial function. Functional disruption of the endothelium is known to be an early event that underlies the development of subsequent cardiovascular disease (CVD) including atherosclerosis and coronary heart disease. In addition, the rising global epidemic of type 2 diabetes is a significant problem conferring a significantly higher risk of CVD to individuals in whom endothelial dysfunction is also notable. This review first summarises the role of endothelium in health and explores and evaluates the impact of diabetes on endothelial function. The characteristic features of insulin resistance and other metabolic disturbances that may underlie long-term changes in vascular endothelial function (metabolic memory) are described along with proposed cellular, molecular and epigenetic mechanisms. Through understanding the underlying mechanisms, novel targets for future therapies to restore endothelial homeostasis and 'drive' a reparative cellular phenotype are explored.

Physical inactivity, insulin resistance, and the oxidative-inflammatory loop

Epidemiological data indicate that physical inactivity, a main factor of global energetic imbalance, is involved in the worldwide epidemic of obesity and metabolic disorders such as insulin resistance. Although the complex pathogenesis of insulin resistance is not fully understood, literature data accumulated during the past decades clearly indicate that the activation of the oxidative-inflammatory loop plays a major role. By activating the oxidative-inflammatory loop in insulin-sensitive tissues, fat gain and adipose tissue dysfunction likely contribute to induce insulin resistance during chronic and prolonged physical inactivity. However, in the past years, evidence has emerged showing that early insulin resistance also occurs after very short-term exposure to physical inactivity (1-7 days) without any fat gain or energetic imbalance. The possible role of liver disturbances or endothelial dysfunction is suggested, but further studies are necessary to really conclude. Inactive skeletal muscle probably constitutes the primary triggering tissue for the development of early insulin resistance. In the present review, we discuss on the current knowledge about the effect of physical inactivity on whole-body and peripheral insulin sensitivity, and how local inflammation and oxidative stress arising with physical inactivity could potentially induce insulin resistance. We assume that early muscle insulin resistance allows the excess nutrients to shift in the storage tissues to withstand starvation through energy storage. We also consider when chronic and prolonged, physical inactivity over an extended period of time is an underestimated contributor to pathological insulin resistance and hence indirectly to numerous chronic diseases.

Methylglyoxal modulates endothelial nitric oxide synthase-associated functions in EA.hy926 endothelial cells

BACKGROUND

Increased levels of the sugar metabolite methylglyoxal (MG) in vivo were shown to participate in the pathophysiology of vascular complications in diabetes. Alterations of endothelial nitric oxide synthase (eNOS) activity by hypophosphorylation of the enzyme and enhanced monomerization are found in the diabetic milieu, and the regulation of this still remains undefined. Using various pharmacological approaches, we elucidate putative mechanisms by which MG modulates eNOS-associated functions of MG-stimulated superoxide O₂•⁻ production, phosphorylation status and eNOS uncoupling in EA.hy926 human endothelial cells.

METHODS

In cultured EA.hy926 endothelial cells, the effects of MG treatment, tetrahydrobiopterin (BH4; 100 μM) and sepiapterin (20 μM) supplementation, NOS inhibition by N(G)-nitro-L-arginine methyl ester (L-NAME; 50 μM), and inhibition of peroxynitrite (ONOO⁻) formation (300 μM Tempol plus 50 μM L-NAME) on eNOS dimer/monomer ratios, Ser-1177 eNOS phosphorylation and 3-nitrotyrosine (3NT) abundance were quantified using immunoblotting. O₂•⁻-dependent fluorescence was determined using a commercially available kit and tissue biopterin levels were measured by fluorometric HPLC analysis.

RESULTS

In EA.hy926 cells, MG treatment significantly enhanced O₂•⁻ generation and 3NT expression and reduced Ser-1177 eNOS phosphorylation, eNOS dimer/monomer ratio and cellular biopterin levels indicative of eNOS uncoupling. These effects were significantly mitigated by administration of BH4, sepiapterin and suppression of ONOO⁻ formation. L-NAME treatment significantly blunted eNOS-derived O₂•⁻ generation but did not modify eNOS phosphorylation or monomerization.

CONCLUSION

MG triggers eNOS uncoupling and hypophosphorylation in EA.hy926 endothelial cells associated with O₂•⁻ generation and biopterin depletion. The observed effects of the glycolysis metabolite MG presumably account, at least in part, for endothelial dysfunction in diabetes.

Endothelial dysfunction - a major mediator of diabetic vascular disease

The vascular endothelium is a multifunctional organ and is critically involved in modulating vascular tone and structure. Endothelial cells produce a wide range of factors that also regulate cellular adhesion, thromboresistance, smooth muscle cell proliferation, and vessel wall inflammation. Thus, endothelial function is important for the homeostasis of the body and its dysfunction is associated with several pathophysiological conditions, including atherosclerosis, hypertension and diabetes. Patients with diabetes invariably show an impairment of endothelium-dependent vasodilation. Therefore, understanding and treating endothelial dysfunction is a major focus in the prevention of vascular complications associated with all forms of diabetes mellitus. The mechanisms of endothelial dysfunction in diabetes may point to new management strategies for the prevention of cardiovascular disease in diabetes. This review will focus on the mechanisms and therapeutics that specifically target endothelial dysfunction in the context of a diabetic setting. Mechanisms including altered glucose metabolism, impaired insulin signaling, low-grade inflammatory state, and increased reactive oxygen species generation will be discussed. The importance of developing new pharmacological approaches that upregulate endothelium-derived nitric oxide synthesis and target key vascular ROS-producing enzymes will be highlighted and new strategies that might prove clinically relevant in preventing the development and/or retarding the progression of diabetes associated vascular complications.

Insulin-mediated activation of the L-arginine nitric oxide pathway in man, and its impairment in diabetes

Aims/Hypothesis

Impaired L-arginine transport has been reported in cardiovascular diseases, providing a possible mechanism for reduced nitric oxide (NO) production. Given that cardiovascular diseases are also associated with insulin resistance, and insulin is known to induce vasodilation via a NO-dependent pathway, we hypothesised that abnormal insulin modulation of L-arginine transport may contribute to vascular dysfunction in diabetes.

Methods

Forearm blood flow (FBF) responses to insulin and sodium nitroprusside (SNP) were measured in control and type 2 diabetic volunteers using venous occlusion plethysmography. Effects of intra-arterial insulin on the forearm veno-arterial flux of arginine and related amino acids were determined by HPLC. The effect of locally delivered insulin on arginine transport was assessed during an intra-arterial infusion of [4,5-³H] L-arginine.

Results

In controls, intrabrachial infusion of 5 mUnits/min insulin lead to a progressive rise in FBF (p<0.001) while this was not evident in diabetics. In support of this observation, we observed a concomitant, significant increase in the flux of N-hydroxy-L-arginine (the NO precursor) in controls (baseline vs. 60 mins insulin: 16.2±12.2 vs. 33.0±13.1 nmol/100 ml tissue/min; p<0.01), whilst no increase was observed in diabetics. Moreover, insulin augmented the clearance of [³H]L-arginine from the forearm circulation in controls (baseline vs insulin: 123±22 vs. 150±28 ml/min; p<0.05) but not in diabetics.

Conclusion

These findings suggest that insulin resistance may contribute substantially to the onset and development of cardiovascular disease in type 2 diabetics via abnormal insulin-mediated regulation of L-arginine transport.

Vascular risk in women with a history of severe preeclampsia

BACKGROUND. To assess markers of vascular dysfunction and risk in postpartum women with a history of severe preeclampsia.

METHODS

Carotid intima-media thickness (CIMT) and brachial artery flow-mediated dilatation (FMD) measured by ultrasonography, and lipid profile and insulin resistance evaluated by biochemical assays were compared between 34 women with a history of severe preeclampsia and 42 women with a prior normal pregnancy at least 12-24 months postpartum.

RESULTS

CIMT was higher and FMD lower in the preeclamptic than in the control group. We found a significant inverse correlation between CIMT and FMD in the preeclamptic group, but no difference in lipid profiles and insulin resistance between the groups.

CONCLUSIONS

Women with a history of severe preeclampsia exhibit early structural and functional preatherosclerotic vascular impairment, which might explain their higher risk of future cardiovascular disease.

Postprandial reactive hypoglycaemia: varying presentation patterns on extended glucose tolerance tests and possible therapeutic approaches

Reactive hypoglycemia is a state characterised by sympathetic or neuroglycopenic symptoms associated with hypoglycaemia in the postprandial state resulting in considerable distress to the patient. It is our practice to carry out either extended glucose tolerance tests (eGTTs) or mixed meal tests in these patients. We describe two patients who experienced hypoglycaemic symptoms early and late during eGTT. The patient who experienced symptoms early, in contrast to the patient who presented with late symptoms, did not possess any characteristics of the metabolic syndrome. Based on clinical symptoms, glucose, insulin, and free fatty acid (FFA) levels, we speculate on possible mechanisms that may have accounted for each of their presentation patterns. We then discuss low glycaemic index diet which will be the mainstay of management.

The IGF-1 receptor and regulation of nitric oxide bioavailability and insulin signalling in the endothelium

The insulin-like growth factor-1 receptor (IGF-1R), like the insulin receptor (IR), plays a significant role in determining bioavailability of the critical signalling molecule nitric oxide (NO) and hence, modulates endothelial cell function, particularly in response to stimulation with insulin. In particular, the ability of the IGF-1R to form hybrid receptors with the IR appears to be highly significant in determining the sensitivity of the endothelial cell to insulin. This review will examine the structure of the IGF-1R and how this, with particular reference to the ability of the IGF-1R and the IR to form hybrid receptors, may have an effect both on endothelial cell function and the development of cardiovascular disease.

Cell-specific insulin resistance: implications for atherosclerosis

Insulin resistance is increasingly acknowledged as an independent risk factor for cardiovascular disease. Despite this, our understanding of the cellular and molecular mechanisms that might account for this relationship remain incompletely understood. A key challenge has been in distinguishing between a 'whole-body' milieu of inflammation and oxidative stress from the ramifications of cell-specific resistance to insulin. Transgenic models have now begun to explore the cellular influences of insulin resistance on vascular biology, with novel implications for atherosclerosis across a range of cells including endothelial cells, endothelial progenitor cells, vascular smooth muscle cells, macrophages and fibroblasts. Emerging data from these models have also begun to challenge conventional dogma. In particular, the findings across various cell types are disparate with some even implying a protective influence on vascular biology. We now review these data, highlighting recent advances in our understanding of cellular resistance to insulin as well as those areas where there remains a paucity of data.

Endothelial dysfunction and insulin resistance

In this article, we review several mechanisms by which insulin resistance is related to endothelial dysfunction. The mechanisms we discuss may explain the high prevalence of cardiovascular disease found in people with the metabolic syndrome and diabetes mellitus.

In vivo nitric oxide synthesis, insulin sensitivity, and asymmetric dimethylarginine in obese subjects without and with metabolic syndrome

Metabolic syndrome (MetSyn) is associated with impaired endothelial function. Here the association between nitric oxide (NO) production and insulin sensitivity (Si) in obese subjects with and without MetSyn was evaluated. The relationship between NO production and asymmetric dimethylarginine (ADMA) was also explored. Seven healthy normal-weight subjects (male/female [M/F], 3/4; age, 27.4 ± 10.9 years; body mass index [BMI], 21.9 ± 2.2 kg/m(2)), 7 obese subjects without MetSyn (M/F, 1/6; age, 48.0 ± 8.0 years; BMI, 34.5 ± 2.3 kg/m(2)), and 7 with MetSyn (M/F, 3/4; age, 48.0 ± 10.7 years; BMI, 33.4 ± 2.9 kg/m(2)) were recruited. Body composition and cardiometabolic functions (blood pressure, glucose, insulin, triglycerides, total cholesterol, high-density lipoprotein, ADMA) were measured. A frequent sampling intravenous glucose tolerance test was performed to measure Si. A novel stable isotopic method was used to measure in vivo rates of NO production. The NO production was lower in obese subjects with MetSyn compared with normal-weight subjects and obese subjects without MetSyn. Similarly, Si was significantly lower in obesity, both without and with MetSyn, compared with the control group. A significant direct association was found between NO synthesis and Si (ρ = 0.47, P = .03). Circulating levels of ADMA were significantly higher in the obese group with MetSyn. A nonsignificant negative trend between ADMA and NO synthesis was observed. The association between Si and NO production suggests a close mechanistic link between endothelial function and insulin signaling. The results may be highly informative for the development of controlled longitudinal interventions to improve endothelial and metabolic regulation.

Increasing plasma free fatty acids in healthy subjects induces aortic distensibility changes seen in obesity

BACKGROUND

Elevated free fatty acid (FFA) levels are known to impair aortic elastic function. In obesity, FFA levels are elevated and aortic distensibility (AD) reduced in a pattern that predominantly affects the distal aorta. Despite this, the role of FFAs in obesity-related aortic stiffness remains unclear.

METHODS AND RESULTS

Using vascular MRI, we aimed to determine if (1) FFA level correlated with AD in obesity; and (2) whether elevating FFA acutely and subacutely in normal-weight subjects reproduced the distal pattern of AD change in obesity. To do this, regional AD was recorded in 35 normal-weight and 70 obese subjects and then correlated with FFA levels. When compared with normal weight, obesity was associated with reduced AD in a pattern predominantly affecting the distal aorta (ascending aorta by -22%, proximal descending aorta by -25%, and abdominal aorta by -35%; P<0.001). After controlling for age, blood pressure, and body mass index, FFA levels remained negatively correlated with abdominal AD (r=-0.43, P<0.01). In 2 further normal-weight groups, AD was recorded before and after elevation of FFA levels with intralipid infusion (by +535%, n=9) and a 5-day high-fat, low-carbohydrate diet (by +48%, n=14).

CONCLUSIONS

Both intralipid infusion and a low-carbohydrate diet resulted in reduced abdominal AD (infusion -22%, diet -28%; both P<0.05), reproducing the distal pattern AD reduction seen in obesity. These findings suggest that elevated FFA impair AD in obesity and provide a potential therapeutic target to improve aortic elastic function in obesity.

Maternal high-fat diet impacts endothelial function in nonhuman primate offspring

OBJECTIVE:

The link between maternal under-nutrition and cardiovascular disease (CVD) in the offspring later in life is well recognized, but the impact of maternal over-nutrition on the offspring's cardiovascular function and subsequent risk for CVD later in life remains unclear. Here, we investigated the impact of maternal exposure to a high-fat/calorie diet (HFD) during pregnancy and early postnatal period on endothelial function of the offspring in a nonhuman primate model.

METHODS:

Offspring, naturally born to either a control (CTR) diet (14% fat calories) or a HFD (36% fat calories) consumption dam, were breast-fed until weaning at about 8 months of age. After weaning, the offspring were either maintained on the same diet (CTR/CTR, HFD/HFD), or underwent a diet switch (CTR/HFD, HFD/CTR). Blood samples and arterial tissues were collected at necropsy when the animals were about 13 months of age.

RESULTS:

HFD/HFD juveniles displayed an increased plasma insulin level and glucose-stimulated insulin secretion in comparison with CTR/CTR. In abdominal aorta, but not the renal artery, acetylcholine-induced vasorelaxation was decreased remarkably for HFD/HFD juveniles compared with CTR/CTR. HFD/HFD animals also showed a thicker intima wall and an abnormal vascular-morphology, concurrent with elevated expression levels of several markers related to vascular inflammation and fibrinolytic function. Diet-switching animals (HFD/CTR and CTR/HFD) displayed modest damage on the abdominal vessel.

CONCLUSION:

Our data indicate that maternal HFD exposure impairs offspring's endothelial function. Both early programming events and postweaning diet contribute to the abnormalities that could be reversed partially by diet intervention.

Chronic kidney disease, insulin resistance, and incident diabetes in older adults

BACKGROUND AND OBJECTIVES

Insulin resistance is a complication of advanced CKD. Insulin resistance is less well characterized in earlier stages of CKD. The response of the pancreatic β cell, effects on glucose tolerance, and risk of diabetes are not clear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Cardiovascular Health Study included 4680 adults without baseline diabetes. The Chronic Kidney Disease Epidemiology Collaboration creatinine equation was used to obtain the estimated GFR (eGFR). Insulin resistance was evaluated as fasting insulin concentration. The insulin sensitivity index, β cell function, and glucose tolerance were assessed by oral glucose tolerance testing. Incident diabetes was defined as fasting glucose ≥126 mg/dl, nonfasting glucose ≥200 mg/dl, or use of glucose-lowering medications.

RESULTS

Mean age was 72.5 years (range, 65-98 years). Mean eGFR was 72.2 (SD 17.1) ml/min per 1.73 m(2). After adjustment, each 10 ml/min per 1.73 m(2) lower eGFR was associated with a 2.2% higher fasting insulin concentration (95% confidence interval [CI], 1.4%, 2.9%; P<0.001) and a 1.1% lower insulin sensitivity index (95% CI, 0.03%, 2.2%; P=0.04). Surprisingly, eGFR was associated with an augmented β cell function index (P<0.001), lower 2-hour glucose concentration (P=0.002), and decreased risk of glucose intolerance (P=0.006). Over a median 12 years' follow-up, 437 participants (9.3%) developed diabetes. eGFR was not associated with the risk of incident diabetes.

CONCLUSIONS

Among older adults, lower eGFR was associated with insulin resistance. However, with lower eGFR, β cell function was appropriately augmented and risks of impaired glucose tolerance and incident diabetes were not increased.

Increased atherothrombotic burden in patients with diabetes mellitus and acute coronary syndrome: a review of antiplatelet therapy

Patients with diabetes mellitus presenting with acute coronary syndrome have a higher risk of cardiovascular complications and recurrent ischemic events when compared to nondiabetic counterparts. Different mechanisms including endothelial dysfunction, platelet hyperactivity, and abnormalities in coagulation and fibrinolysis have been implicated for this increased atherothrombotic risk. Platelets play an important role in atherogenesis and its thrombotic complications in diabetic patients with acute coronary syndrome. Hence, potent platelet inhibition is of paramount importance in order to optimise outcomes of diabetic patients with acute coronary syndrome. The aim of this paper is to provide an overview of the increased thrombotic burden in diabetes and acute coronary syndrome, the underlying pathophysiology focussing on endothelial and platelet abnormalities, currently available antiplatelet therapies, their benefits and limitations in diabetic patients, and to describe potential future therapeutic strategies to overcome these limitations.

Insulin resistance, metabolic stress, and atherosclerosis

Atherosclerosis, a pathological process that underlies the development of cardiovascular disease, is the primary cause of morbidity and mortality in patients with type 2 diabetes mellitus (T2DM). T2DM is characterized by hyperglycemia and insulin resistance (IR), in which target tissues fail to respond to insulin. Systemic IR is associated with impaired insulin signaling in the metabolic tissues and vasculature. Insulin receptor is highly expressed in the liver, muscle, pancreas, and adipose tissue. It is also expressed in vascular cells. It has been suggested that insulin signaling in vascular cells regulates cell proliferation and vascular function. In this review, we discuss the association between IR, metabolic stress, and atherosclerosis with focus on 1) tissue and cell distribution of insulin receptor and its differential signaling transduction and 2) potential mechanism of insulin signaling impairment and its role in the development of atherosclerosis and vascular function in metabolic disorders including hyperglycemia, hypertension, dyslipidemia, and hyperhomocysteinemia. We propose that insulin signaling impairment is the foremost biochemical mechanism underlying increased cardiovascular morbidity and mortality in atherosclerosis, T2DM, and metabolic syndrome.

The Association of Hypertension with Obesity and Metabolic Abnormalities among Chinese Children

A total of 8898 Chinese children (4580 boys and 4318 girls) aged 7–13 years in 6 cities of east China were recruited. Data on height, weight, waist circumference, blood pressure, serum lipid profiles, glucose, and insulin were collected. The overall prevalence of hypertension was 11.1%. Overweight and obese children had a higher risk of developing hypertension than their counterparts (29.1%, 17.4%, and 7.8%, resp.) (P = 0.0001). The means levels of triglycerides, glucose, insulin, and HOMA-IR (1.0 mmol/L, 4.5 mmol/L, 8.4 mU/mL and 1.7, resp.) among hypertensive children were all significantly higher than their normotensive counterparts (0.8 mmol/L, 4.5 mmol/L, 5.9 mU/mL, and 1.2, resp.) (P = 0.0001). Compared with the healthy children, the risk (odds ratio, OR) of having hypertension among children with high triglycerides, hyperglycemia, and metabolic syndrome was 1.4 (95% confidence interval (CI): 1.0–2.0, P = 0.0334), 1.5 (95% CI: 0.9–2.5, P = 0.0890), and 2.8 (95%CI: 1.5–5.4, P = 0.0014), respectively, after controlling for age, gender, BMI, income level, parents' education level and puberty. In conclusion, overweight and obese children have higher risk of having hypertension and children with dyslipidemia, hyperglycemia, and metabolic syndrome and higher HOMA-IR have higher risk of developing hypertension.

Insulin resistance increases the occurrence of new cardiovascular events in patients with manifest arterial disease without known diabetes. the SMART study

Background

Insulin resistance is accompanied by a cluster of metabolic changes, often referred to as metabolic syndrome. Metabolic syndrome is associated with an increased cardiovascular risk in patients with manifest arterial disease. We investigated whether insulin resistance is associated with an increased risk for cardiovascular events in patients with manifest arterial disease without known diabetes and whether this can be explained by the components of the metabolic syndrome or by inflammation.

Methods

Prospective cohort study in 2611 patients with manifest arterial disease without known diabetes. Homeostasis model of insulin resistance (HOMA-IR) was used to quantify insulin resistance. The relation of HOMA-IR with cardiovascular events (vascular death, myocardial infarction or stroke) and all cause mortality was assessed with Cox regression analysis. In additional models adjustments were performed for the single components constituting the metabolic syndrome and for inflammation.

Results

HOMA-IR increases with the number of metabolic syndrome components (mean HOMA-IR ± SD in groups with 0, 1, 2, 3, 4 and 5 metabolic syndrome components: 1.4 ± 0.7; 1.8 ± 1.2; 2.4 ± 1.5; 3.1 ± 1.8; 4.0 ± 2.6; and 5.6 ± 3.6 respectively). High HOMA-IR was independently associated with an increased risk of cardiovascular events (tertile 2 vs. 1 HR 1.92; 95%CI 1.20-3.08) (tertile 3 vs.1 HR 1.78; 95%CI 1.10-2.89) and with all cause mortality (tertile 2 vs. 1 HR 1.80; 95%CI 1.04-3.10) (tertile 3 vs.1 HR 1.56; 95%CI 0.88-2.75). These relations were not influenced by the individual components of metabolic syndrome or by inflammation.

Conclusions

In patients with manifest arterial disease without known diabetes, insulin resistance increases with the number of metabolic syndrome components, and elevated insulin resistance increases the risk of new cardiovascular events.

Suppression of eNOS-derived superoxide by caveolin-1: a biopterin-dependent mechanism

In the vasculature, nitric oxide (NO) is generated by endothelial NO synthase (eNOS) in a calcium/calmodulin-dependent reaction. In the absence of the requisite eNOS cofactor tetrahydrobiopterin (BH(4)), NADPH oxidation is uncoupled from NO generation, leading to the production of superoxide. Although this phenomenon is apparent with purified enzyme, cellular studies suggest that formation of the BH(4) oxidation product, dihydrobiopterin, is the molecular trigger for eNOS uncoupling rather than BH(4) depletion alone. In the current study, we investigated the effects of both BH(4) depletion and oxidation on eNOS-derived superoxide production in endothelial cells in an attempt to elucidate the molecular mechanisms regulating eNOS oxidase activity. Results demonstrated that pharmacological depletion of endothelial BH(4) does not result in eNOS oxidase activity, whereas BH(4) oxidation gave rise to significant eNOS-oxidase activity. These findings suggest that the endothelium possesses regulatory mechanisms, which prevent eNOS oxidase activity from pterin-free eNOS. Using a combination of gene silencing and pharmacological approaches, we demonstrate that eNOS-caveolin-1 association is increased under conditions of reduced pterin bioavailability and that this sequestration serves to suppress eNOS uncoupling. Using small interfering RNA approaches, we demonstrate that caveolin-1 gene silencing increases eNOS oxidase activity to 85% of that observed under conditions of BH(4) oxidation. Moreover, when caveolin-1 silencing was combined with a pharmacological inhibitor of AKT, BH(4) depletion increased eNOS-derived superoxide to 165% of that observed with BH(4) oxidation. This study identifies a critical role of caveolin-1 in the regulation of eNOS uncoupling and provides new insight into the mechanisms through which disease-associated changes in caveolin-1 expression may contribute to endothelial dysfunction.

Endothelin-1 reduces glucose uptake in human skeletal muscle in vivo and in vitro

OBJECTIVE

Endothelin (ET)-1 is a vasoconstrictor and proinflammatory peptide that may interfere with glucose uptake. Our objective was to investigate whether exogenous ET-1 affects glucose uptake in the forearm of individuals with insulin resistance and in cultured human skeletal muscle cells.

RESEARCH DESIGN AND METHODS

Nine male subjects (aged 61 ± 3 years) with insulin resistance (M value <5.5 mg/kg/min or a homeostasis model assessment of insulin resistance index >2.5) participated in a protocol using saline infusion followed by ET-1 infusion (20 pmol/min) for 2 h into the brachial artery. Forearm blood flow (FBF), endothelium-dependent vasodilatation, and endothelium-independent vasodilatation were assessed. Molecular signaling and glucose uptake were determined in cultured skeletal muscle cells.

RESULTS

ET-1 decreased forearm glucose uptake (FGU) by 39% (P < 0.05) after the 2-h infusion. ET-1 reduced basal FBF by 36% after the 2-h infusion (P < 0.05) and impaired both endothelium-dependent vasodilatation (P < 0.01) and endothelium-independent vasodilatation (P < 0.05). ET(A) and ET(B) receptor expression was detected on cultured skeletal muscle cells. One-hour ET-1 incubation increased glucose uptake in cells from healthy control subjects but not from type 2 diabetic patients. Incubation with ET-1 for 24 h reduced glucose uptake in cells from healthy subjects. ET-1 decreased insulin-stimulated Akt phosphorylation and increased phosphorylation of insulin receptor substrate-1 serine 636.

CONCLUSIONS

ET-1 not only induces vascular dysfunction but also acutely impairs FGU in individuals with insulin resistance and in skeletal muscle cells from type 2 diabetic subjects. These findings suggest that ET-1 may contribute to the development of insulin resistance in skeletal muscle in humans.

Suppression of eNOS-derived superoxide by caveolin-1: a biopterin-dependent mechanism

In the vasculature, nitric oxide (NO) is generated by endothelial NO synthase (eNOS) in a calcium/calmodulin-dependent reaction. In the absence of the requisite eNOS cofactor tetrahydrobiopterin (BH(4)), NADPH oxidation is uncoupled from NO generation, leading to the production of superoxide. Although this phenomenon is apparent with purified enzyme, cellular studies suggest that formation of the BH(4) oxidation product, dihydrobiopterin, is the molecular trigger for eNOS uncoupling rather than BH(4) depletion alone. In the current study, we investigated the effects of both BH(4) depletion and oxidation on eNOS-derived superoxide production in endothelial cells in an attempt to elucidate the molecular mechanisms regulating eNOS oxidase activity. Results demonstrated that pharmacological depletion of endothelial BH(4) does not result in eNOS oxidase activity, whereas BH(4) oxidation gave rise to significant eNOS-oxidase activity. These findings suggest that the endothelium possesses regulatory mechanisms, which prevent eNOS oxidase activity from pterin-free eNOS. Using a combination of gene silencing and pharmacological approaches, we demonstrate that eNOS-caveolin-1 association is increased under conditions of reduced pterin bioavailability and that this sequestration serves to suppress eNOS uncoupling. Using small interfering RNA approaches, we demonstrate that caveolin-1 gene silencing increases eNOS oxidase activity to 85% of that observed under conditions of BH(4) oxidation. Moreover, when caveolin-1 silencing was combined with a pharmacological inhibitor of AKT, BH(4) depletion increased eNOS-derived superoxide to 165% of that observed with BH(4) oxidation. This study identifies a critical role of caveolin-1 in the regulation of eNOS uncoupling and provides new insight into the mechanisms through which disease-associated changes in caveolin-1 expression may contribute to endothelial dysfunction.

Suppression of eNOS-derived superoxide by caveolin-1: a biopterin-dependent mechanism

In the vasculature, nitric oxide (NO) is generated by endothelial NO synthase (eNOS) in a calcium/calmodulin-dependent reaction. In the absence of the requisite eNOS cofactor tetrahydrobiopterin (BH(4)), NADPH oxidation is uncoupled from NO generation, leading to the production of superoxide. Although this phenomenon is apparent with purified enzyme, cellular studies suggest that formation of the BH(4) oxidation product, dihydrobiopterin, is the molecular trigger for eNOS uncoupling rather than BH(4) depletion alone. In the current study, we investigated the effects of both BH(4) depletion and oxidation on eNOS-derived superoxide production in endothelial cells in an attempt to elucidate the molecular mechanisms regulating eNOS oxidase activity. Results demonstrated that pharmacological depletion of endothelial BH(4) does not result in eNOS oxidase activity, whereas BH(4) oxidation gave rise to significant eNOS-oxidase activity. These findings suggest that the endothelium possesses regulatory mechanisms, which prevent eNOS oxidase activity from pterin-free eNOS. Using a combination of gene silencing and pharmacological approaches, we demonstrate that eNOS-caveolin-1 association is increased under conditions of reduced pterin bioavailability and that this sequestration serves to suppress eNOS uncoupling. Using small interfering RNA approaches, we demonstrate that caveolin-1 gene silencing increases eNOS oxidase activity to 85% of that observed under conditions of BH(4) oxidation. Moreover, when caveolin-1 silencing was combined with a pharmacological inhibitor of AKT, BH(4) depletion increased eNOS-derived superoxide to 165% of that observed with BH(4) oxidation. This study identifies a critical role of caveolin-1 in the regulation of eNOS uncoupling and provides new insight into the mechanisms through which disease-associated changes in caveolin-1 expression may contribute to endothelial dysfunction.

The metabolic syndrome and mind-body therapies: a systematic review

The metabolic syndrome, affecting a substantial and increasing percentage of the worldwide population, is comprised of a cluster of symptoms associated with increased risk of type 2 diabetes, cardiovascular disease, and other chronic conditions. Mind-body modalities based on Eastern philosophy, such as yoga, tai chi, qigong, and meditation, have become increasingly popular worldwide. These complementary therapies have many reported benefits for improving symptoms and physiological measures associated with the metabolic syndrome. However, clinical trial data concerning the effectiveness of these practices on the syndrome as a whole have not been evaluated using a systematic and synthesizing approach. A systematic review was conducted to critically evaluate the data from clinical trials examining the efficacy of mind-body therapies as supportive care modalities for management of the metabolic syndrome. Three clinical trials addressing the use of mind-body therapies for management of the metabolic syndrome were identified. Findings from the studies reviewed support the potential clinical effectiveness of mind-body practices in improving indices of the metabolic syndrome.

Astragaloside IV improves metabolic syndrome and endothelium dysfunction in fructose-fed rats

The prevalence of metabolic syndrome has increased in modern society and the condition is proving to be a common precursor of cardiovascular disease. The aim of the present study was to investigate whether astragaloside IV, a major active constituent of Astragalus membranaceus (Fisch) Bge., is able to prevent the development of hypertension and endothelial dysfunction in fructose-fed rats. Rats were fed with 10% fructose in their drinking water for 8 weeks. From the beginning of week 5, two groups of fructose-fed rats were treated with 0.5 or 2 mg/kg, i.p., astragaloside IV. Another group of fructose-fed rats, injected with the same volume of vehicle (dimethylsulfoxide, DMSO) from week 5, served as the control group. At the end of the treatment period, blood pressure, blood glucose, glucose tolerance, blood insulin and lipids were determined. In addition, in vitro experiments were conducted at the end of the eight week treatment period to evaluate endothelium-dependent aortic vasorelaxation, as well as myocardial and aortic tissue levels of nitrate and nitrite (NOx) and cGMP. Fructose-fed rats developed clustering signs of metabolic syndrome, such as increased bodyweight, mild hypertension, hyperinsulinaemia, hypertriglyceridaemia, impaired glucose tolerance and impaired endothelium-dependent vasorelaxation. Administration of astragaloside IV reduced blood pressure and triglyceride levels in fructose-fed rats and high dose of astragaloside IV also improved glucose tolerance and endothelium-dependent vasorelaxation. The astragaloside IV-induced improvement in vasorelaxation was associated with increased levels of aortic NOx and cGMP and was abrogated by blockade of nitric oxide synthase with NG-nitro-l-arginine methyl ester (l-NAME). On the basis of its favourable effects on lipid metabolism, endothelium-dependent vasorelaxation and the nitric oxide–cGMP-related pathway, astragaloside IV may be useful in ameliorating food-induced metabolic syndrome.

The role of IGF-1 resistance in obesity and type 2 diabetes-mellitus-related insulin resistance and vascular disease

IMPORTANCE OF THE FIELD

The insulin-resistant conditions of type 2 diabetes mellitus (T2DM) and obesity are a major cause of cardiovascular disease on a global scale. These disorders are not only a cause of ill health but are a huge financial drain on healthcare systems. T2DM leads to an increased risk of cardiovascular mortality equivalent to over 10 years of ageing while obesity independent of T2DM also leads to a substantially increased risk of acute myocardial infarction. Recent trials of therapeutic agents and approaches to preventing the cardiovascular complications of type 2 diabetes have been disappointing.

AREAS COVERED IN THIS REVIEW

The role of insulin resistance in the endothelium in the regulation of the anti-atherosclerotic signalling molecule NO and a potential important role for IGF-1 in vascular NO production.

WHAT THE READER WILL GAIN

A comprehensive understanding of how insulin and IGF-1 regulate vascular function and the effect of type 2 diabetes on these pathways.

TAKE HOME MESSAGE

The roles of insulin and IGF-1 in vascular function are complex and intimately related. Nevertheless IGF-1 signalling in the arterial wall has the potential to be manipulated to protect the vasculature against the development of atherosclerosis and its devastating complications.

Pathogenesis and clinical physiology of hypertension

Significant advances have been made in understanding the pathogenesis and clinical physiology of primary hypertension. This article presents an overview of the physiology of normal blood pressure control and the pathophysiologic mechanisms that predispose individuals and populations to primary hypertension. The role of genetics, environment, and the gene-environment interaction is discussed. The spectrum of changes in physiologic states that result in chronic increases of arterial blood pressure are reviewed. The nature and characteristics of feedback loops and the primary modulating systems, the central and peripheral nervous systems, and circulating and tissue hormones are reviewed. The role of the endothelium of the artery and its production of endothelin, nitric oxide, angiotensin II, as well as other vasoactive substances in response to various stimuli, is also discussed. A unifying pathway for the development of hypertension and the practical implications for the prevention and control of hypertension are discussed.

Novel iodinated tracers, MIBG and BMIPP, for nuclear cardiology

With the rapid growth of molecular biology, in vivo imaging of such molecular process (i.e., molecular imaging) has been well developed. The molecular imaging has been focused on justifying advanced treatments and for assessing the treatment effects. Most of molecular imaging has been developed using PET camera and suitable PET radiopharmaceuticals. However, this technique cannot be widely available and we need alternative approach. ¹²³I-labeled compounds have been also suitable for molecular imaging using single-photon computed tomography (SPECT) ¹²³I-labeled meta-iodobenzylguanidine (MIBG) has been used for assessing severity of heart failure and prognosis. In addition, it has a potential role to predict fatal arrhythmia, particularly for those who had and are planned to receive implantable cardioverter-defibrillator treatment. ¹²³I-beta-methyl-iodophenylpentadecanoic acid (BMIPP) plays an important role for identifying ischemia at rest, based on the unique capability to represent persistent metabolic alteration after recovery of ischemia, so called ischemic memory. Since BMIPP abnormalities may represent severe ischemia or jeopardized myocardium, it may permit risk analysis in CAD patients, particularly for those with chronic kidney disease and/or hemodialysis patients. This review will discuss about recent development of these important iodinated compounds.

Hypertension, obesity, and inflammation: the complex designs of a deadly trio

Hypertension is a powerful risk factor for cardiovascular disease and frequently occurs in conjunction with obesity and the metabolic syndrome. Recent research into the underlying pathophysiologic processes common to these entities has uncovered the role of a heightened inflammatory state signified by a host of circulating biocytokines. Systemic and local hormonal effectors, such as angiotensin II and aldosterone, interact with inflammatory and oxidative stress to augment endothelial damage in a complex manner. The kidneys play a prominent role in the renin-angiotensin cascade and the abnormal pressor response that ensues. Insulin resistance underlies the pathogenesis of obesity and the metabolic syndrome. The interplay of hypertension, insulin resistance, and obesity vastly enhances the noxious influence of inflammation on the vasculature, promoting deleterious immune adaptations and ultimately increasing atherosclerotic risk. Although certain classes of available pharmacologic agents already address the altered endovascular and humoral dynamics in hypertension, a better understanding of the proinflammatory picture holds promise of targeted treatment modalities in future.

Risk stratification for cardiac death in hemodialysis patients without obstructive coronary artery disease

The incidence of cardiac death is higher among patients receiving dialysis compared with the general population. Although obstructive coronary artery disease is involved in cardiac deaths in the general population, deaths in hemodialysis patients occur in the apparent absence of obstructive coronary artery disease. To study this further, we prospectively enrolled 155 patients receiving hemodialysis after angiography had confirmed the absence of obstructive coronary lesions. All patients were examined by single-photon emission computed tomography using the iodinated fatty acid analog, BMIPP, the uptake of which was graded in 17 standard myocardial segments and assessed as summed scores. Insulin resistance was determined using the homeostasis model assessment index of insulin resistance (HOMA-IR). During a mean follow-up of 5.1 years, 42 patients died of cardiac events. Stepwise Cox hazard analysis associated cardiac death with reduced BMIPP uptake and increased insulin resistance. Patients were assigned to subgroups based on BMIPP summed scores and HOMA-IR cutoff values for cardiac death of 12 and 5.1, respectively, determined by receiver operating characteristic analysis. Cardiac death-free survival rates at 5 years were the lowest (32.2%) in the subgroup with both a summed score and assessment equal to or above the cutoff values compared with any other combination (52.9-98.7%) above, equal to, or below the thresholds. Thus, impaired myocardial fatty acid metabolism and insulin resistance may be associated with cardiac death among hemodialysis patients without obstructive coronary artery disease.