Insulin therapy improves insulin-stimulated endothelial function in patients with type 2 diabetes and ischemic heart disease

Endothelial Cell Insulin Signaling Regulates CXCR4 (C-X-C Motif Chemokine Receptor 4) and Limits Leukocyte Adhesion to Endothelium

BACKGROUND

An activated, proinflammatory endothelium is a key feature in the development of complications of obesity and type 2 diabetes and can be caused by insulin resistance in endothelial cells.

METHODS

We analyzed primary human endothelial cells by RNA sequencing to discover novel insulin-regulated genes and used endothelial cell culture and animal models to characterize signaling through CXCR4 (C-X-C motif chemokine receptor 4) in endothelial cells.

RESULTS

CXCR4 was one of the genes most potently regulated by insulin, and this was mediated by PI3K (phosphatidylinositol 3-kinase), likely through FoxO1, which bound to the CXCR4 promoter. CXCR4 mRNA in CD31+ cells was 77% higher in mice with diet-induced obesity compared with lean controls and 37% higher in db/db mice than db/+ controls, consistent with upregulation of CXCR4 in endothelial cell insulin resistance. SDF-1 (stromal cell-derived factor-1)-the ligand for CXCR4-increased leukocyte adhesion to cultured endothelial cells. This effect was lost after deletion of CXCR4 by gene editing while 80% of the increase was prevented by treatment of endothelial cells with insulin. In vivo microscopy of mesenteric venules showed an increase in leukocyte rolling after intravenous injection of SDF-1, but most of this response was prevented in transgenic mice with endothelial overexpression of IRS-1 (insulin receptor substrate-1).

CONCLUSIONS

Endothelial cell insulin signaling limits leukocyte/endothelial cell interaction induced by SDF-1 through downregulation of CXCR4. Improving insulin signaling in endothelial cells or inhibiting endothelial CXCR4 may reduce immune cell recruitment to the vascular wall or tissue parenchyma in insulin resistance and thereby help prevent several vascular complications.

Insulin Receptors and Insulin Action in the Heart: The Effects of Left Ventricular Assist Devices

This year, 2022, marks the 100th anniversary of the isolation of human insulin and its administration to patients suffering from diabetes mellitus (DM). Insulin exerts many effects on the human body, including the cardiac tissue. The pathways implicated include the PKB/Akt signaling pathway, the Janus kinase, and the mitogen-activated protein kinase pathway and lead to normal cardiac growth, vascular smooth muscle regulation, and cardiac contractility. This review aims to summarize the existing knowledge and provide new insights on insulin pathways of cardiac tissue, along with the role of left ventricular assist devices on insulin regulation and cardiac function.

Endothelial Dysfunction in Atherosclerotic Cardiovascular Diseases and Beyond: From Mechanism to Pharmacotherapies

The endothelium, a cellular monolayer lining the blood vessel wall, plays a critical role in maintaining multiorgan health and homeostasis. Endothelial functions in health include dynamic maintenance of vascular tone, angiogenesis, hemostasis, and the provision of an antioxidant, anti-inflammatory, and antithrombotic interface. Dysfunction of the vascular endothelium presents with impaired endothelium-dependent vasodilation, heightened oxidative stress, chronic inflammation, leukocyte adhesion and hyperpermeability, and endothelial cell senescence. Recent studies have implicated altered endothelial cell metabolism and endothelial-to-mesenchymal transition as new features of endothelial dysfunction. Endothelial dysfunction is regarded as a hallmark of many diverse human panvascular diseases, including atherosclerosis, hypertension, and diabetes. Endothelial dysfunction has also been implicated in severe coronavirus disease 2019. Many clinically used pharmacotherapies, ranging from traditional lipid-lowering drugs, antihypertensive drugs, and antidiabetic drugs to proprotein convertase subtilisin/kexin type 9 inhibitors and interleukin 1β monoclonal antibodies, counter endothelial dysfunction as part of their clinical benefits. The regulation of endothelial dysfunction by noncoding RNAs has provided novel insights into these newly described regulators of endothelial dysfunction, thus yielding potential new therapeutic approaches. Altogether, a better understanding of the versatile (dys)functions of endothelial cells will not only deepen our comprehension of human diseases but also accelerate effective therapeutic drug discovery. In this review, we provide a timely overview of the multiple layers of endothelial function, describe the consequences and mechanisms of endothelial dysfunction, and identify pathways to effective targeted therapies. SIGNIFICANCE STATEMENT: The endothelium was initially considered to be a semipermeable biomechanical barrier and gatekeeper of vascular health. In recent decades, a deepened understanding of the biological functions of the endothelium has led to its recognition as a ubiquitous tissue regulating vascular tone, cell behavior, innate immunity, cell-cell interactions, and cell metabolism in the vessel wall. Endothelial dysfunction is the hallmark of cardiovascular, metabolic, and emerging infectious diseases. Pharmacotherapies targeting endothelial dysfunction have potential for treatment of cardiovascular and many other diseases.

Insulin's actions on vascular tissues: Physiological effects and pathophysiological contributions to vascular complications of diabetes

Background

Insulin has been demonstrated to exert direct and indirect effects on vascular tissues. Its actions in vascular cells are mediated by two major pathways: the insulin receptor substrate 1/2-phosphoinositide-3 kinase/Akt (IRS1/2/PI3K/Akt) pathway and the Src/mitogen-activated protein kinase (MAPK) pathway, both of which contribute to the expression and distribution of metabolites, hormones, and cytokines.

Scope of review

In this review, we summarize the current understanding of insulin's physiological and pathophysiological actions and associated signaling pathways in vascular cells, mainly in endothelial cells (EC) and vascular smooth muscle cells (VSMC), and how these processes lead to selective insulin resistance. We also describe insulin's potential new signaling and biological effects derived from animal studies and cultured capillary and arterial EC, VSMC, and pericytes. We will not provide a detailed discussion of insulin's effects on the myocardium, insulin's structure, or its signaling pathways' various steps, since other articles in this issue discuss these areas in depth.

Major conclusions

Insulin mediates many important functions on vascular cells via its receptors and signaling cascades. Its direct actions on EC and VSMC are important for transporting and communicating nutrients, cytokines, hormones, and other signaling molecules. These vascular actions are also important for regulating systemic fuel metabolism and energetics. Inhibiting or enhancing these pathways leads to selective insulin resistance, exacerbating the development of endothelial dysfunction, atherosclerosis, restenosis, poor wound healing, and even myocardial dysfunction. Targeted therapies to improve selective insulin resistance in EC and VSMC are thus needed to specifically mitigate these pathological processes.

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Insulin's actions in vascular cells have a significant influence on systemic metabolism.

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Insulin exerts its vascular effects through its receptors and signaling cascades.

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Inhibition or enhancement of different insulin signaling leads to selective insulin resistance.

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Loss of insulin's actions causes endothelial dysfunction and vascular complications in diabetes.

Cellular and Functional Effects of Insulin Based Therapies and Exercise on Endothelium

Endothelial dysfunction is a hallmark of type 2 diabetes that can have severe consequences on vascular function, including hypertension and changes in blood flow, as well as exercise performance. Because endothelium is also the barrier for insulin movement into tissues, it acts as a gatekeeper for transport and glucose uptake. For this reason, endothelial dysfunction is a tempting area for pharmacological and/or exercise intervention with insulin-based therapies. In this review, we describe the current state of drugs that can be used to treat endothelial dysfunction in type 2 diabetes and diabetes-related diseases (e.g., obesity) at the molecular levels, and also discuss their role in exercise.

Role of anabolic agents in colorectal carcinogenesis: Myths and realities (Review)

Colorectal cancer (CRC) is one of the four leading causes of cancer‑related mortality worldwide. Even though over the past few decades the global scientific community has made tremendous efforts to understand this entity, many questions remain to be raised on this issue and even more to be answered. Epidemiological findings have unveiled numerous environmental and genetic risk factors, each one contributing to a certain degree to the final account of new CRC cases. Moreover, different trends have been revealed regarding the age of onset of CRC between the two sexes. That, in addition to newly introduced therapeutic approaches for various diseases based on androgens, anti‑androgens and anabolic hormones has raised some concerns regarding their possible carcinogenic effects or their synergistic potential with other substances/risk factors, predisposing the individual to CRC. Notably, despite the intense research on experimental settings and population studies, the conclusions regarding the majority of anabolic substances are ambiguous. Some of these indicate the carcinogenic properties of testosterone, dihydrotestosterone (DHT), growth hormone and insulin‑like growth factor (IGF) and others, demonstrating their neutral nature or even their protective one, as in the case of vitamin D. Thus, the synergistic nature of anabolic substances with other CRC risk factors (such as type 2 diabetes mellitus, metabolic syndrome and smoking) has emerged, suggesting a more holistic approach.

The continuums of impairment in vascular reactivity across the spectrum of cardiometabolic health: A systematic review and network meta-analysis

This study aimed to assess, for the first time, the change in vascular reactivity across the full spectrum of cardiometabolic health. Systematic searches were conducted in MEDLINE and EMBASE databases from their inception to March 13, 2017, including studies that assessed basal vascular reactivity in two or more of the following health groups (aged ≥18 years old): healthy, overweight, obesity, impaired glucose tolerance, metabolic syndrome, or type 2 diabetes with or without complications. Direct and indirect comparisons of vascular reactivity were combined using a network meta-analysis. Comparing data from 193 articles (7226 healthy subjects and 19344 patients), the network meta-analyses revealed a progressive impairment in vascular reactivity (flow-mediated dilation data) from the clinical onset of an overweight status (-0.41%, 95% CI, -0.98 to 0.15) through to the development of vascular complications in those with type 2 diabetes (-4.26%, 95% CI, -4.97 to -3.54). Meta-regressions revealed that for every 1 mmol/l increase in fasting blood glucose concentration, flow-mediated dilation decreased by 0.52%. Acknowledging that the time course of disease may vary between patients, this study demonstrates multiple continuums of vascular dysfunction where the severity of impairment in vascular reactivity progressively increases throughout the pathogenesis of obesity and/or insulin resistance, providing information that is important to enhancing the timing and effectiveness of strategies that aim to improve cardiovascular outcomes.

The effect of basal insulin glargine on the fibrinolytic system and von Willebrand factor in people with dysglycaemia and high risk for cardiovascular events: Swedish substudy of the Outcome Reduction with an Initial Glargine Intervention trial

INTRODUCTION

Fibrinolytic factors, plasminogen activator inhibitor-1, tissue plasminogen activator, tissue plasminogen activator/plasminogen activator-complex and the haemostatic factor von Willebrand factor are known markers of cardiovascular disease. Their plasma levels are adversely affected in patients with dysglycaemia, and glucose normalization with insulin glargine might improve the levels of these factors.

METHODS

Prespecified Swedish substudy of the Outcome Reduction with an Initial Glargine Intervention trial (ClinicalTrials.gov number, NCT00069784). Tissue plasminogen activator activity, tissue plasminogen activator antigen, plasminogen activator inhibitor-1 antigen, tissue plasminogen activator/plasminogen activator inhibitor-1 complex and von Willebrand factor were analysed at study start, after 2 years and at the end of the study (median follow-up of 6.2 years).

RESULTS

Of 129 patients (mean age of 64 ± 7 years, females: 19%), 68 (53%) and 61 (47%) were randomized to the insulin glargine and standard care group, respectively. Allocation to insulin glargine did not significantly affect the studied fibrinolytic markers or von Willebrand factor compared to standard care. Likewise, there were no significant differences in plasminogen activator inhibitor-1, tissue plasminogen activator antigen and von Willebrand factor. During the whole study period, the within-group analysis revealed a curvilinear pattern and significant changes for tissue plasminogen activator/plasminogen activator inhibitor-1 complex, tissue plasminogen activator antigen and von Willebrand factor in the insulin glargine but not in the standard care group.

CONCLUSION

In people with dysglycaemia and other cardiovascular risk factors, basal insulin does not improve the levels of markers of fibrinolysis or von Willebrand factor compared to standard glucose-lowering treatments.

Insulin resistance in vascular endothelial cells promotes intestinal tumour formation

The risk of several cancers, including colorectal cancer, is increased in patients with obesity and type 2 diabetes, conditions characterized by hyperinsulinemia and insulin resistance. Because hyperinsulinemia itself is an independent risk factor for cancer development, we examined tissue-specific insulin action in intestinal tumor formation. In vitro, insulin increased proliferation of primary cultures of intestinal tumor epithelial cells from Apc^Min/+ mice by over 2-fold. Surprisingly, targeted deletion of insulin receptors in intestinal epithelial cells in Apc^Min/+ mice did not change intestinal tumor number or size distribution on either a low or high-fat diet. We therefore asked whether cells in the tumor stroma might explain the association between tumor formation and insulin resistance. To this end, we generated Apc^Min/+ mice with loss of insulin receptors in vascular endothelial cells. Strikingly, these mice had 42% more intestinal tumors than controls, no change in tumor angiogenesis, but increased expression of vascular cell adhesion molecule-1 (VCAM-1) in primary culture of tumor endothelial cells. Insulin decreased VCAM-1 expression and leukocyte adhesion in quiescent tumor endothelial cells with intact insulin receptors and partly prevented increases in VCAM-1 and leukocyte adhesion after treatment with tumor necrosis factor-α. Knockout of insulin receptors in endothelial cells also increased leukocyte adhesion in mesenteric venules and increased the frequency of neutrophils in tumors. We conclude that although insulin is mitogenic for intestinal tumor cells in vitro, its action on tumor cells in vivo is via signals from the tumor microenvironment. Insulin resistance in tumor endothelial cells produces an activated, proinflammatory state that promotes tumorigenesis. Improvement of endothelial dysfunction may reduce colorectal cancer risk in patients with obesity and type 2 diabetes.

Insulin Downregulates the Transcriptional Coregulator CITED2, an Inhibitor of Proangiogenic Function in Endothelial Cells

In patients with atherosclerotic complications of diabetes, impaired neovascularization of ischemic tissue in the myocardium and lower limb limits the ability of these tissues to compensate for poor perfusion. We identified 10 novel insulin-regulated genes, among them Adm, Cited2, and Ctgf, which were downregulated in endothelial cells by insulin through FoxO1. CBP/p300-interacting transactivator with ED-rich tail 2 (CITED2), which was downregulated by insulin by up to 54%, is an important negative regulator of hypoxia-inducible factor (HIF) and impaired HIF signaling is a key mechanism underlying the impairment of angiogenesis in diabetes. Consistent with impairment of vascular insulin action, CITED2 was increased in cardiac endothelial cells from mice with diet-induced obesity and from db/db mice and was 3.8-fold higher in arterial tissue from patients with type 2 diabetes than control subjects without diabetes. CITED2 knockdown promoted endothelial tube formation and endothelial cell proliferation, whereas CITED2 overexpression impaired HIF activity in vitro. After femoral artery ligation, induction of an endothelial-specific HIF target gene in hind limb muscle was markedly upregulated in mice with endothelial cell deletion of CITED2, suggesting that CITED2 can limit HIF activity in vivo. We conclude that vascular insulin resistance in type 2 diabetes contributes to the upregulation of CITED2, which impairs HIF signaling and endothelial proangiogenic function.

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.

Glycemic variability in type 2 diabetes mellitus: oxidative stress and macrovascular complications

Diabetes mellitus is a world-wide health issue with potential for significant negative health outcomes, including microvascular and macrovascular complications. The relationship of hemoglobin HbA1c and other glycosylation end products (AGEs) to these complications, particularly microvascular disease, is well understood. More recent evidence suggests that glycemic variability may be associated with diabetes macrovascular complications. As HbA1c is better representative of average glucose levels and does not account as well for glycemic variability, hence new methods to assess and treat this variability is needed to reduce incidence of complications. In this chapter, the relationship of glycemic control to diabetes complications will be explored with focus on the mechanisms of tissue damage from this variability along with the oxidative stress. Additionally, treatment strategies to optimize HbA1c and glycemic variability with the goal of reducing risk of complications in persons with diabetes are reviewed.

Tissue-specific insulin signaling, metabolic syndrome, and cardiovascular disease

Impaired insulin signaling is central to development of the metabolic syndrome and can promote cardiovascular disease indirectly through development of abnormal glucose and lipid metabolism, hypertension, and a proinflammatory state. However, insulin's action directly on vascular endothelium, atherosclerotic plaque macrophages, and in the heart, kidney, and retina has now been described, and impaired insulin signaling in these locations can alter progression of cardiovascular disease in the metabolic syndrome and affect development of microvascular complications of diabetes mellitus. Recent advances in our understanding of the complex pathophysiology of insulin's effects on vascular tissues offer new opportunities for preventing these cardiovascular disorders.

Vascular effects of intravenous intralipid and dextrose infusions in obese subjects

Hyperglycemia and elevated free fatty acids (FFA) are implicated in the development of endothelial dysfunction. Infusion of soy-bean oil-based lipid emulsion (Intralipid®) increases FFA levels and results in elevation of blood pressure (BP) and endothelial dysfunction in obese healthy subjects. The effects of combined hyperglycemia and high FFA on BP, endothelial function and carbohydrate metabolism are not known. Twelve obese healthy subjects received four random, 8-h IV infusions of saline, Intralipid 40 mL/h, Dextrose 10% 40 mL/h, or combined Intralipid and dextrose. Plasma levels of FFA increased by 1.03±0.34 mmol/L (p=0.009) after Intralipid, but FFAs remained unchanged during saline, dextrose, and combined Intralipid and dextrose infusion. Plasma glucose and insulin concentrations significantly increased after dextrose and combined Intralipid and dextrose (all, p<0.05) and were not different from baseline during saline and lipid infusion. Intralipid increased systolic BP by 12±9 mmHg (p<0.001) and diastolic BP by 5±6 mmHg (p=0.022),and decreased flow-mediated dilatation (FMD) from baseline by 3.2%±1.4% (p<0.001). Saline and dextrose infusion had neutral effects on BP and FMD. The co-administration of lipid and dextrose decreased FMD by 2.4%±2.1% (p=0.002) from baseline, but did not significantly increase systolic or diastolic BP. Short-term Intralipid infusion significantly increased FFA and BP; in contrast, FFA and BP were unchanged during combined infusion of Intralipid and dextrose. Combined Intralipid and dextrose infusion resulted in endothelial dysfunction similar to Intralipid alone.

Strict glycaemic control improves skin microcirculation in patients with type 2 diabetes: a report from the Diabetes mellitus And Diastolic Dysfunction (DADD) study

BACKGROUND

Microcirculatory and endothelial dysfunction are signs of cardiovascular engagement in patients with type 2 diabetes. This study tested whether glucose normalisation may reverse this.

METHODS

Thirty-nine T2DM patients (age 61±7 years, 58% females) with signs of mild diastolic dysfunction were randomised to strict glucose control based on insulin (I-group; n=21) or oral agents (O-group; n=18) for four months. Skin microcirculation was studied with laser Doppler fluxmetry and endothelial function with brachial artery flow-mediated dilatation.

RESULTS

Glucose control improved (reduction of HbA(1c) I-group = -0.5%; O-group -0.7%; p=0.69). Microcirculation improved in the entire group (n=39) determined by foot laser Doppler fluxmetry (32.2±13.6 vs. 35.3±13.1 perfusion units; p<0.001) and laser Doppler fluxmetry following heating (68.8±34.0 vs. 69.3±25.1 PU; p=0.007). Improvement was more consistent with oral agents than insulin. Endothelial function expressed as flow-mediated dilatation decreased in the I-group (6.0±2.2 to 4.7±3.0%; p=0.037) but remained unchanged in the O-group (4.8±2.3 to 5.0±3.7%; n.s.).

CONCLUSIONS

Glycaemic normalisation improved skin microcirculation but not endothelial function in patients with type 2 diabetes with mild cardiovascular engagement.

Global gene expression profiling displays a network of dysregulated genes in non-atherosclerotic arterial tissue from patients with type 2 diabetes

Background

Generalized arterial alterations, such as endothelial dysfunction, medial matrix accumulations, and calcifications are associated with type 2 diabetes (T2D). These changes may render the vessel wall more susceptible to injury; however, the molecular characteristics of such diffuse pre-atherosclerotic changes in diabetes are only superficially known.

Methods

To identify the molecular alterations of the generalized arterial disease in T2D, DNA microarrays were applied to examine gene expression changes in normal-appearing, non-atherosclerotic arterial tissue from 10 diabetic and 11 age-matched non-diabetic men scheduled for a coronary by-pass operation. Gene expression changes were integrated with GO-Elite, GSEA, and Cytoscape to identify significant biological pathways and networks.

Results

Global pathway analysis revealed differential expression of gene-sets representing matrix metabolism, triglyceride synthesis, inflammation, insulin signaling, and apoptosis. The network analysis showed a significant cluster of dysregulated genes coding for both intra- and extra-cellular proteins associated with vascular cell functions together with genes related to insulin signaling and matrix remodeling.

Conclusions

Our results identify pathways and networks involved in the diffuse vasculopathy present in non-atherosclerotic arterial tissue in patients with T2D and confirmed previously observed mRNA-alterations. These abnormalities may play a role for the arterial response to injury and putatively for the accelerated atherogenesis among patients with diabetes.

Endothelial dysfunction and diabetes: effects on angiogenesis, vascular remodeling, and wound healing

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by inappropriate hyperglycemia due to lack of or resistance to insulin. Patients with DM are frequently afflicted with ischemic vascular disease or wound healing defect. It is well known that type 2 DM causes amplification of the atherosclerotic process, endothelial cell dysfunction, glycosylation of extracellular matrix proteins, and vascular denervation. These complications ultimately lead to impairment of neovascularization and diabetic wound healing. Therapeutic angiogenesis remains an attractive treatment modality for chronic ischemic disorders including PAD and/or diabetic wound healing. Many experimental studies have identified better approaches for diabetic cardiovascular complications, however, successful clinical translation has been limited possibly due to the narrow therapeutic targets of these agents or the lack of rigorous evaluation of pathology and therapeutic mechanisms in experimental models of disease. This paper discusses the current body of evidence identifying endothelial dysfunction and impaired angiogenesis during diabetes.

The effect of chronic heart failure and type 2 diabetes on insulin-stimulated endothelial function is similar and additive

Aim

Chronic heart failure is associated with endothelial dysfunction and insulin resistance. The aim of this investigation was to study insulin-stimulated endothelial function and glucose uptake in skeletal muscles in patients with heart failure in comparison to patients with type 2 diabetes.

Methods

Twenty-three patients with systolic heart failure and no history of diabetes, seven patients with both systolic heart failure and type 2 diabetes, 19 patients with type 2 diabetes, and ten healthy controls were included in the study. Endothelial function was studied by venous occlusion plethysmography. Insulin-stimulated endothelial function was assessed after intra-arterial infusion of insulin followed by co-infusion with serotonin in three different dosages. Forearm glucose uptake was measured during the insulin infusion.

Results

Patients with systolic heart failure had impaired insulin-stimulated endothelial function. The percentage increase in blood flow during co-infusion with insulin and serotonin dose response study was 24.74% ± 6.16%, 23.50% ± 8.32%, and 22.29% ± 10.77% at the three doses respectively, compared to the healthy control group 45.96% ± 11.56%, 67.40% ± 18.11% and 84.57% ± 25.73% (P = 0.01). Insulin-stimulated endothelial function was similar in heart failure patients and patients with type 2 diabetes, while it was further deteriorated in patients suffering from both heart failure and diabetes with a percentage increase in blood flow of 19.15% ± 7.81%, −2.35% ± 11.76%, and 5.82% ± 17.70% at the three doses of serotonin, respectively. Forearm glucose uptake was impaired in patients with heart failure compared to healthy controls (P = 0.03) and tended to be further impaired by co-existence of diabetes (P = 0.08).

Conclusion

Systolic heart failure and type 2 diabetes result in similar vascular insulin resistance and reduced muscular insulin-stimulated glucose uptake. The effects of systolic heart failure and type 2 diabetes appear to be additive.

Endothelial function is unaffected by changing between carvedilol and metoprolol in patients with heart failure--a randomized study

Background

Carvedilol has been shown to be superior to metoprolol tartrate to improve clinical outcomes in patients with heart failure (HF), yet the mechanisms responsible for these differences remain unclear. We examined if there were differences in endothelial function, insulin stimulated endothelial function, 24 hour ambulatory blood pressure and heart rate during treatment with carvedilol, metoprolol tartrate and metoprolol succinate in patients with HF.

Methods

Twenty-seven patients with mild HF, all initially treated with carvedilol, were randomized to a two-month treatment with carvedilol, metoprolol tartrate or metoprolol succinate. Venous occlusion plethysmography, 24-hour blood pressure and heart rate measurements were done before and after a two-month treatment period.

Results

Endothelium-dependent vasodilatation was not affected by changing from carvedilol to either metoprolol tartrate or metoprolol succinate. The relative forearm blood flow at the highest dose of serotonin was 2.42 ± 0.33 in the carvedilol group at baseline and 2.14 ± 0.24 after two months continuation of carvedilol (P = 0.34); 2.57 ± 0.33 before metoprolol tartrate treatment and 2.42 ± 0.55 after treatment (p = 0.74) and in the metoprolol succinate group 1.82 ± 0.29 and 2.10 ± 0.37 before and after treatment, respectively (p = 0.27). Diurnal blood pressures as well as heart rate were also unchanged by changing from carvedilol to metoprolol tartrate or metoprolol succinate.

Conclusion

Endothelial function remained unchanged when switching the beta blocker treatment from carvedilol to either metoprolol tartrate or metoprolol succinate in this study, where blood pressure and heart rate also remained unchanged in patients with mild HF.

Trial registration

Current Controlled Trials NCT00497003

Protein kinase C inhibition ameliorates functional endothelial insulin resistance and vascular smooth muscle cell hypersensitivity to insulin in diabetic hypertensive rats

OBJECTIVE

Insulin resistance, diabetes, and hypertension are considered elements of metabolic syndrome which is associated with vascular dysfunction. We investigated whether inhibition of protein kinase C (PKC) would affect vascular function in diabetic hypertensive (DH) rats.

METHODS

A combination of type 2 diabetes and arterial hypertension was produced in male Sprague Dawley rats by intrauterine protein deprivation (IUPD) followed by high salt diet. At the age of 32 weeks, DH rats were treated for 2 weeks with the angiotensin-converting enzyme inhibitor captopril (Capto, 30 mg/kg), PKC inhibitor ruboxistaurin (RBX, 50 mg/kg) or vehicle (n = 8 per group) and blood pressure was monitored using telemetry. At the end of experiments, femoral arteries were dissected, and vascular reactivity was evaluated with isovolumic myography.

RESULTS

The IUPD followed by high salt diet resulted in significant elevation of plasma glucose, plasma insulin, and blood pressure. Endothelium-dependent vascular relaxation in response to acetylcholine was blunted while vascular contraction in response to phenylephrine was enhanced in the DH rats. Neither Capto nor RBX restored endothelium-dependent vascular relaxation while both suppressed vascular contraction. Ex-vivo incubation of femoral arteries from control rats with insulin induced dose-response vasorelaxation while insulin failed to induce vasorelaxation in the DH rat arteries. In the control arteries treated with endothelial nitric oxide synthase inhibitor L-NAME, insulin induced vasoconstriction that was exacerbated in DH rats. Capto and RBX partially inhibited insulin-stimulated vascular contraction.

CONCLUSION

These findings suggest that PKC inhibition ameliorates functional endothelial insulin resistance and smooth muscle cell hypersensitivity to insulin, but does not restore acetylcholine-activated endothelium-dependent vasodilation in DH rats.

Impact of previous insulin therapy on the prognosis of diabetic patients with acute coronary syndromes

OBJECTIVE: To determine whether previous insulin treatment independently influences subsequent outcomes in diabetic patients with ACS (acute coronary syndromes). SUBJECTS AND METHODS: 375 diabetic patients with ACS, divided in 2 groups: Group A (n = 69) - previous insulin and Group B (n = 306) - without previous insulin. Predictors of 1-year mortality and major adverse cardiac events (MACE) were analyzed by Cox regression analysis. RESULTS: Group A had more previous stroke (17.4% vs. 9.2%, p = 0.047) and peripheral artery disease (13.0% vs. 3.6%, p = 0.005). They had significantly higher admission glycemia and lower LDL cholesterol. There were no significant differences in the type of ACS, in 1-year mortality (18.2% vs. 10.4%, p = 0.103) or MACE (32.1% vs. 23.0%, p = 0.146) between groups. In multivariate analysis, insulin treatment was neither an independent predictor of 1-year mortality nor of MACE. CONCLUSION: Despite the more advanced atherosclerotic disease, diabetics under insulin had similar outcomes to those without insulin. Insulin may protect diabetics from the expected poor adverse outcome of an advanced atherosclerotic disease.

Endothelial nitric oxide synthase transgenic models of endothelial dysfunction

Endothelial production of nitric oxide is critical to the regulation of vascular responses, including vascular tone and regional blood flow, leukocyte-endothelial interactions, platelet adhesion and aggregation, and vascular smooth muscle cell proliferation. A relative deficiency in the amount of bioavailable vascular NO results in endothelial dysfunction, with conditions that are conducive to the development of atherosclerosis: thrombosis, inflammation, neointimal proliferation, and vasoconstriction. This review focuses on mouse models of endothelial dysfunction caused by direct genetic modification of the endothelial nitric oxide synthase (eNOS) gene. We first describe the cardiovascular phenotypes of eNOS knockout mice, which are a model of total eNOS gene deficiency and thus the ultimate model of endothelial dysfunction. We then describe S1177A and S1177D eNOS mutant mice as mouse models with altered eNOS phosphorylation and therefore varying degrees of endothelial dysfunction. These include transgenic mice that carry the eNOS S1177A and S1177D transgenes, as well as knockin mice in which the endogenous eNOS gene has been mutated to carry the S1177A and S1177D mutations. Together, eNOS knockout mice and eNOS S1177 mutant mice are useful tools to study the effects of total genetic deficiency of eNOS as well as varying degrees of endothelial dysfunction caused by eNOS S1177 phosphorylation.

Metoprolol compared to carvedilol deteriorates insulin-stimulated endothelial function in patients with type 2 diabetes - a randomized study

AIM

Studies of beta blockade in patients with type 2 diabetes have shown inferiority of metoprolol treatment compared to carvedilol on indices of insulin resistance. The aim of this study was to examine the effect of metoprolol versus carvedilol on endothelial function and insulin-stimulated endothelial function in patients with type 2 diabetes.

METHOD

24 patients with type 2 diabetes were randomized to receive either 200 mg metoprolol succinate or 50 mg carvedilol daily. Endothelium-dependent vasodilation was assessed by using venous occlusion plethysmography with increasing doses of intra-arterial infusions of the agonist serotonin. Insulin-stimulated endothelial function was assessed after co-infusion of insulin for sixty minutes. Vaso-reactivity studies were done before and after the two-month treatment period.

RESULTS

Insulin-stimulated endothelial function was deteriorated after treatment with metoprolol, the percentage change in forearm blood-flow was 60.19% +/- 17.89 (at the highest serotonin dosages) before treatment and -33.80% +/- 23.38 after treatment (p = 0.007). Treatment with carvedilol did not change insulin-stimulated endothelial function. Endothelium-dependent vasodilation without insulin was not changed in either of the two treatment groups.

CONCLUSION

This study shows that vascular insulin sensitivity was preserved during treatment with carvedilol while blunted during treatment with metoprolol in patients with type 2 diabetes.

TRIAL REGISTRATION

Current Controlled Trials NCT00497003.

Loss of insulin signaling in vascular endothelial cells accelerates atherosclerosis in apolipoprotein E null mice

To determine whether insulin action on endothelial cells promotes or protects against atherosclerosis, we generated apolipoprotein E null mice in which the insulin receptor gene was intact or conditionally deleted in vascular endothelial cells. Insulin sensitivity, glucose tolerance, plasma lipids, and blood pressure were not different between the two groups, but atherosclerotic lesion size was more than 2-fold higher in mice lacking endothelial insulin signaling. Endothelium-dependent vasodilation was impaired and endothelial cell VCAM-1 expression was increased in these animals. Adhesion of mononuclear cells to endothelium in vivo was increased 4-fold compared with controls but reduced to below control values by a VCAM-1-blocking antibody. These results provide definitive evidence that loss of insulin signaling in endothelium, in the absence of competing systemic risk factors, accelerates atherosclerosis. Therefore, improving insulin sensitivity in the endothelium of patients with insulin resistance or type 2 diabetes may prevent cardiovascular complications.

Role of protein kinase C in diabetic complications

Hyperglycemia is an important factor in the development of macrovascular and microvascular complications in all diabetic patients. Several hypotheses have been postulated to explain the adverse effect of hyperglycemia on the vasculature; and one of these hypotheses is the activation of specific isoforms of protein kinase C (PKC) by diabetes. In this review, we summarize the molecular mechanisms of PKC activation and its relationship to diabetic complications. PKC activity regulates vascular permeability, contractility, extracellular matrix synthesis, hormone receptor turnover and proliferation, cell growth, angiogenesis, cytokine activation and leukocyte adhesion. All of these properties are abnormal in diabetes and are correlated with increased diacylglycerol-PKC pathway and PKCα, β1/2 and δ isoforms activation in the retina, aorta, heart and renal glomeruli.

Is there a link between glucose levels and heart failure? An update

It has been well documented that there is an increased prevalence of standard cardiovascular (CV) risk factors in association with diabetes and with diabetes-related abnormalities. Hyperglycemia, in particular, also plays an important role. Heart failure (HF) has become a frequent manifestation of cardiovascular disease (CVD) among individuals with diabetes mellitus. Epidemiological studies suggest that the effect of hyperglycemia on HF risk is independent of other known risk factors. Analysis of datasets from populations including individuals with dysglycemia suggests the pathogenic role of hyperglycemia on left ventricular function and on the natural history of HF. Despite substantial epidemiological evidence of the relationship between diabetes and HF, data from available interventional trials assessing the effect of a glucose-lowering strategy on CV outcomes are limited. To provide some insight into these issues, we describe in this review the recent important data to understand the natural course of CV disease in diabetic individuals and the role of hyperglycemia at different times in the progression of HF.

Insulin and non-insulin mediated vasodilation and glucose uptake in patients with type 2 diabetes

AIMS

The objective was to re-examine endothelial function, insulin mediated vasodilation and glucose extraction in the forearm of patients with type 2 diabetes (T2DM) and matched control subjects (CON) to investigate whether blood flow impairments result from diabetes per se or from concurrent disease.

METHODS

18 subjects (10 with T2DM, 8 CON) had graded brachial artery infusions of endothelial dependent (acetylcholine: 15, 30, 60 microg/min), endothelial independent (sodium nitroprusside: 1, 3, 10 microg/min) and partially endothelial mediated (adenosine: 50, 150, 500 microg/min) vasodilators. The protocol was repeated during a hyperinsulinemic clamp. Forearm blood flow and glucose extraction were measured at each dose of vasodilator (with/without insulin). Measurements were also taken in the control arm, reflecting systemic insulin infusion only.

RESULTS

Non-insulin mediated increases in bulk forearm blood flow were similar in T2DM and CON. However, insulin mediated forearm blood flow responses and glucose extraction were lower in T2DM versus CON.

CONCLUSION

The vasodilatory effect of insulin is impaired in T2DM although bulk flow capacity is maintained. Insulin mediated glucose extraction is reduced during concomitant maximal stimulation of forearm blood flow with endothelial-dependent vasodilators, despite maintaining flow. This is consistent with previous work that associates T2DM with impaired insulin mediated capillary recruitment.

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.

Endothelial dysfunction and cardiovascular risk factors

The endothelium plays an integral role in the regulation of vascular tone, platelet activity, leukocyte adhesion, and thrombosis and is intimately involved in the development of atherosclerosis. Endothelial dysfunction has been observed in patients with established coronary artery disease or coronary risk factors, both in the coronary and peripheral vasculature. Therapeutic interventions with lipid-lowering drugs, ACE inhibitors, physical activity, and antioxidant agents have been shown to improve endothelial function in coronary and peripheral vessels. This systemic manifestation and improvement of endothelial function suggests that a common mechanism may contribute to endothelial dysfunction in the coronary and peripheral circulation.

TARGET AUDIENCE

Internist, Cardiologists, Family physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to define the participation of cardiovascular risk factors in the various complications associated with endothelial dysfunction.

A randomized trial of the impact of strict glycaemic control on myocardial diastolic function and perfusion reserve: a report from the DADD (Diabetes mellitus And Diastolic Dysfunction) study

AIMS

Myocardial diastolic dysfunction (MDD) and impaired coronary flow reserve (CFR) are early signs of myocardial involvement in patients with diabetes. The important question of whether this may be reversed by glucose normalization has not been tested in a controlled clinical trial. We hypothesized that strict glycaemic control, particularly if insulin based, will improve MDD and CFR.

METHODS AND RESULTS

Thirty-nine type 2 diabetes patients (mean age 61.0 +/- 7 years) with signs of diastolic dysfunction were randomly assigned to strict metabolic control by insulin (I-group; n = 21) or oral glucose lowering agents (O-group; n = 18). MDD and CFR were studied with Doppler-echocardiography including Tissue Doppler Imaging and myocardial contrast enhanced echocardiography. Fasting glucose (I-group = -2.2 +/- 2.1; O-group -1.5 +/- 0.8 mmol/L) and HbA(1c) were normalized (-0.6 +/- 0.4 and -0.7 +/- 0.4%, respectively) in both groups, but this did not significantly improve MDD in either of the groups (P = 0.65). There was no difference in CFR before and after improved glycaemic control.

CONCLUSION

The hypothesis that strict glycaemic control would reverse early signs of MDD and improve CFR in patients with type 2 diabetes could not be confirmed, despite achieved normalization. Whether it is possible to influence a more pronounced diastolic dysfunction, particularly in less well-controlled diabetic patients, remains to be established.

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.

Effect of Shengmai injection on vascular endothelial and heart functions in patients with coronary heart disease complicated with diabetes mellitus

OBJECTIVE

To study the effect of Shengmai injection (, SMI) on vascular endothelial and heart functions in coronary heart disease patients complicated with diabetes mellitus (CHD-DM).

METHODS

One hundred and twenty patients with CHD-DM, their diagnosis confirmed by coronary arteriography, were equally randomized into a control group treated with conventional treatment and a treated group treated with conventional treatment plus SMI. The changes in blood levels of nitric oxide (NO), endothelin-1 (ET-1) and angiotensin II (Ang II), as well as endothelium-dependent vascular dilating function and heart function in the patients were observed before treatment and after the 3-week treatment.

RESULTS

After being treated with SMI for 3 weeks, in the treated group, blood level of NO was raised significantly from 69.8 + or - 33.1 micro mol/L to 120.1 + or - 50.8 micro mol/L, and ET-1 was lowered from 70.1 + or - 32.1 ng/L to 46.2 + or - 21.3 ng/L, respectively (P<0.01); that of Ang II was lowered from 81.3 + or - 24.3 ng/L to 50.2 + or - 27.3 ng/L (P<0.01); brachial arterial post-congestion blood flow increasing rate was raised from 389.4 + or - 26.3% to 459.3 + or - 27.8% (P<0.01); and the improvement in heart function as seen through the ejection fraction (EF) was increased from 44 + or - 5% to 68 + or - 6% (P<0.01), all the changes being more significant than those in the control group (all P<0.01).

CONCLUSION

SMI can improve not only the endothelial function in CHD-DM patients, but also heart contraction significantly.

An integrated view of insulin resistance and endothelial dysfunction

Endothelial dysfunction and insulin resistance are frequently comorbid states. Vasodilator actions of insulin are mediated by phosphatidylinositol 3-kinase (PI3K)-dependent signaling pathways that stimulate production of nitric oxide from vascular endothelium. This helps to couple metabolic and hemodynamic homeostasis under healthy conditions. In pathologic states, shared causal factors, including glucotoxicity, lipotoxicity, and inflammation selectively impair PI3K-dependent insulin signaling pathways that contribute to reciprocal relationships between insulin resistance and endothelial dysfunction. This article discusses the implications of pathway-selective insulin resistance in vascular endothelium, interactions between endothelial dysfunction and insulin resistance, and therapeutic interventions that may simultaneously improve both metabolic and cardiovascular physiology in insulin-resistant conditions.

Insulin stimulates the clonogenic potential of angiogenic endothelial progenitor cells by IGF-1 receptor-dependent signaling

Endothelial progenitor cells (EPCs) have been shown to be involved in vascular regeneration and angiogenesis in experimental diabetes. Because insulin therapy mobilizes circulating progenitor cells, we studied the effects of insulin on outgrowth of EPCs from peripheral blood mononuclear cells of healthy volunteers and patients with type 2 diabetes. Insulin increased the formation of EPC colony-forming units in a dose-dependent manner, half-maximal at 1.5 nM and peaking at 15 nM. Inhibiting the insulin receptor with neutralizing antibodies or antisense oligonucleotides had no effect on EPC outgrowth.(1) In contrast, targeting the human insulin-like growth factor 1 (IGF-1) receptor with neutralizing antibodies significantly suppressed insulin-induced outgrowth of EPCs from both healthy controls and patients with type 2 diabetes. This IGF-1 receptor-mediated insulin effect on EPC growth was at least in part dependent on MAP kinases(2) and was abrogated when extracellular signal-regulated kinase 1/2 (Erk1/2) and protein kinase 38 (p38) activity was inhibited. To study the functional relevance of the observed insulin effects, we studied EPC-induced tube formation of bovine endothelial cells in vitro. Insulin-stimulated EPCs incorporated into the endothelial tubes and markedly enhanced tube formation. In conclusion, this is the first study showing an insulin-mediated activation of the IGF-1 receptor leading to an increased clonogenic and angiogenic potential of EPCs in vitro.

Sustained benefits in vascular function through flavanol-containing cocoa in medicated diabetic patients a double-masked, randomized, controlled trial

OBJECTIVES

Our goal was to test feasibility and efficacy of a dietary intervention based on daily intake of flavanol-containing cocoa for improving vascular function of medicated diabetic patients.

BACKGROUND

Even in fully medicated diabetic patients, overall prognosis is unfavorable due to deteriorated cardiovascular function. Based on epidemiological data, diets rich in flavanols are associated with a reduced cardiovascular risk.

METHODS

In a feasibility study with 10 diabetic patients, we assessed vascular function as flow-mediated dilation (FMD) of the brachial artery, plasma levels of flavanol metabolites, and tolerability after an acute, single-dose ingestion of cocoa, containing increasing concentrations of flavanols (75, 371, and 963 mg). In a subsequent efficacy study, changes in vascular function in 41 medicated diabetic patients were assessed after a 30-day, thrice-daily dietary intervention with either flavanol-rich cocoa (321 mg flavanols per dose) or a nutrient-matched control (25 mg flavanols per dose). Both studies were undertaken in a randomized, double-masked fashion. Primary and secondary outcome measures included changes in FMD and plasma flavanol metabolites, respectively.

RESULTS

A single ingestion of flavanol-containing cocoa was dose-dependently associated with significant acute increases in circulating flavanols and FMD (at 2 h: from 3.7 +/- 0.2% to 5.5 +/- 0.4%, p < 0.001). A 30-day, thrice-daily consumption of flavanol-containing cocoa increased baseline FMD by 30% (p < 0.0001), while acute increases of FMD upon ingestion of flavanol-containing cocoa continued to be manifest throughout the study. Treatment was well tolerated without evidence of tachyphylaxia. Endothelium-independent responses, blood pressure, heart rate, and glycemic control were unaffected.

CONCLUSIONS

Diets rich in flavanols reverse vascular dysfunction in diabetes, highlighting therapeutic potentials in cardiovascular disease.

Effects of glucose tolerance on the changes provoked by glucose ingestion in microvascular function

AIMS/HYPOTHESIS

Hyperglycaemia and hyperinsulinaemia have opposite effects on endothelium-dependent vasodilatation in microcirculation, but the net effect elicited by glucose ingestion and the separate influence of glucose tolerance are unknown.

METHODS

In participants with normal glucose tolerance (NGT), impaired glucose tolerance (IGT) or diabetic glucose tolerance, multiple plasma markers of both oxidative stress and endothelial activation, and forearm vascular responses (plethysmography) to intra-arterial acetylcholine (ACh) and sodium nitroprusside (SNP) infusions were measured before and after glucose ingestion. In another IGT group, we evaluated the time-course of the skin vascular responses (laser Doppler) to ACh and SNP (by iontophoresis) 1, 2 and 3 h into the OGTT; the plasma glucose profile was then reproduced by means of a variable intravenous glucose infusion and the vascular measurements repeated.

RESULTS

Following oral glucose, plasma antioxidants were reduced by 5% to 10% (p < 0.01) in all patient groups. The response to acetylcholine was not affected by glucose ingestion in any group, while the response to SNP was attenuated, particularly in the IGT group. The ACh:SNP ratio was slightly improved therefore in all groups, even in diabetic participants, in whom it was impaired basally. A time-dependent improvement in ACh:SNP ratio was also observed in skin microcirculation following oral glucose; this improvement was blunted when matched hyperglycaemia was coupled with lower hyperinsulinaemia (intravenous glucose).

CONCLUSIONS/INTERPRETATION

Regardless of glucose tolerance, oral glucose does not impair endothelium-dependent vasodilatation either in resistance arteries or in the microcirculation, despite causing increased oxidative stress; the endogenous insulin response is probably responsible for countering any inhibitory effect on vascular function.

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.

Addition of pioglitazone and ramipril to intensive insulin therapy in type 2 diabetic patients improves vascular dysfunction by different mechanisms

OBJECTIVE

We examined the relationship between glycemic control, vascular reactivity, and inflammation in type 2 diabetic subjects.

RESEARCH DESIGN AND METHODS

Thirty subjects with type 2 diabetes were initiated on intensive insulin therapy (continuous subcutaneous insulin infusion [n = 12] or multiple daily injections [n = 18]) and then randomized to either pioglitazone (PIO group;45 mg/day), ramipril (RAM group; 10 mg/day), or placebo (PLC group) for 36 weeks. Euglycemic-hyperinsulinemic clamp was used to quantify insulin resistance, and plethysmography was used to assess changes in forearm blood flow (FBF) after 1) 5 min of reactive hyperemia and 2) brachial artery infusion of acetylcholine (7.5, 15, and 30 microg/min) and sodium nitroprusside (3 and 10 microg/min).

RESULTS

The decreases in A1C (approximately 9.0-7.0%) and fasting plasma glucose (approximately 190-128 mg/dl) were equal in all groups. In the PIO group, glucose disposal increased from 3.1 to 4.7 mg x kg(-1) x min(-1), and there was a greater decrease in plasma triglycerides ( approximately 148 vs. 123 mg/dl) and free fatty acids (approximately 838 vs. 595 mEq/l) compared with the RAM or PLC groups (P < 0.05). Plasma adiponectin doubled with pioglitazone treatment (6.2 +/- 0.7 to 13.1 +/- 1.8 microg/ml), while endothelin-1 decreased only with ramipril treatment (2.5 +/- 0.2 to 1.1 +/- 0.2 pg/ml) (P < 001). The increase in FBF during reactive hyperemia (215%) and acetylcholine (from 132 to 205%, 216 to 262%, and 222 to 323%) was greater in the PIO versus RAM or PLC groups. In contrast, FBF during sodium nitroprusside treatment was greater in the RAM group (141-221% and 218-336%) compared with the PIO or PLC groups (all P < 0.05).

CONCLUSIONS

Addition of pioglitazone or ramipril to intensive insulin therapy in type 2 diabetes further improves vascular dysfunction. Pioglitazone enhances endothelial-mediated vasodilation, whereas ACE inhibition enhances endothelial-independent vasodilation. These different vascular effects, combined with the observation that pioglitazone decreases free fatty acids and triglycerides and increases adiponectin, while ramipril reduces endothelin-1, suggest that different mechanisms underlie the vascular responses.

Cardiovascular actions of insulin

Insulin has important vascular actions to stimulate production of nitric oxide from endothelium. This leads to capillary recruitment, vasodilation, increased blood flow, and subsequent augmentation of glucose disposal in classical insulin target tissues (e.g., skeletal muscle). Phosphatidylinositol 3-kinase-dependent insulin-signaling pathways regulating endothelial production of nitric oxide share striking parallels with metabolic insulin-signaling pathways. Distinct MAPK-dependent insulin-signaling pathways (largely unrelated to metabolic actions of insulin) regulate secretion of the vasoconstrictor endothelin-1 from endothelium. These and other cardiovascular actions of insulin contribute to coupling metabolic and hemodynamic homeostasis under healthy conditions. Cardiovascular diseases are the leading cause of morbidity and mortality in insulin-resistant individuals. Insulin resistance is typically defined as decreased sensitivity and/or responsiveness to metabolic actions of insulin. This cardinal feature of diabetes, obesity, and dyslipidemia is also a prominent component of hypertension, coronary heart disease, and atherosclerosis that are all characterized by endothelial dysfunction. Conversely, endothelial dysfunction is often present in metabolic diseases. Insulin resistance is characterized by pathway-specific impairment in phosphatidylinositol 3-kinase-dependent signaling that in vascular endothelium contributes to a reciprocal relationship between insulin resistance and endothelial dysfunction. The clinical relevance of this coupling is highlighted by the findings that specific therapeutic interventions targeting insulin resistance often also ameliorate endothelial dysfunction (and vice versa). In this review, we discuss molecular mechanisms underlying cardiovascular actions of insulin, the reciprocal relationships between insulin resistance and endothelial dysfunction, and implications for developing beneficial therapeutic strategies that simultaneously target metabolic and cardiovascular diseases.

Impaired tissue responsiveness to organic nitrates and nitric oxide: a new therapeutic frontier?

Nitric oxide (NO) is a physiologically important modulator of both vasomotor tone and platelet aggregability. These effects of NO are predominantly mediated by cyclic guanosine-3,'5'-monophosphate (cGMP) via activation of soluble guanylate cyclase. However, in patients with ischemic heart disease, platelets and coronary/peripheral arteries are hyporesponsive to the antiaggregatory and vasodilator effects of NO donors. NO resistance is also associated with a number of coronary risk factors and presents in different disease states. It correlates with conventional measures of "endothelial dysfunction," and represents a multifaceted disorder, in which smooth muscle and platelet NO resistance are equally important, as sites of abnormal NO-driven physiology. NO resistance results largely from a combination of "scavenging" of NO by superoxide anion radical (O(2)(-)) and of (reversible) inactivation of soluble guanylate cyclase. It constitutes an impaired physiological response to endogenous NO (endothelium-derived relaxing factor, EDRF) and, as such, may contribute to the increased risk of ischemic events. Impairment in responsiveness to NO in ischemic patients implies a potential problem that those patients, in greatest need of nitrate therapy, may be least likely to respond. The prognostic impact of NO resistance at vascular and platelet levels has been demonstrated in patients with ischemic heart disease, and it has been shown that a number of agents (angiotensin-converting enzyme [ACE] inhibitors, perhexiline, insulin, and possibly statins) ameliorate this anomaly. The current review examines different aspects of the "NO resistance" phenomenon and discusses some related methodological issues.

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.

Angiotensin II type 1 receptor blockade improves hyperglycemia-induced endothelial dysfunction and reduces proinflammatory cytokine release from leukocytes

Angiotensin II and glucose share components of their intracellular redox signaling pathways in endothelial and inflammatory cells. We hypothesized that valsartan, an angiotensin II blocker, attenuates hyperglycemia-induced endothelial dysfunction and downregulates release of proinflammatory cytokines from leukocytes. A sustained hyperglycemic clamp (12 mmol/L) to induce endothelial dysfunction was performed in healthy volunteers before and after 4 weeks of treatment with 160 mg of valsartan. Brachial artery flow-mediated vasodilation (FMD), lipopolysaccharide-induced release of interleukin-6 and TNF-alpha from peripheral blood leukocytes ex vivo, and circulating proinflammatory cytokines were determined before and during the clamp. The hyperglycemic clamp induced a decrease in FMD from 9.2 +/- 0.8 (t = 0 hr) to 4.4+/- 0.5 (t = 2 hr), 3.8 +/- 0.5 (t = 4 hr), and 4.8 +/- 0.5% (t = 22 hr) during the clamp. Valsartan attenuated endothelial dysfunction [FMD 7.0 +/- 0.7 (t = 2 hr), 6.1 +/- 0.7 (t = 4 hr), 6.2 +/- 0.6% (t = 22 hr); P < 0.005] and decreased the release of interleukin-6 and TNF-alpha from leukocytes both before and during the clamp (P < 0.05). Valsartan improves hyperglycemia-induced endothelial dysfunction and reduces the cytokine response to an inflammatory stimulus. A pathophysiological link between the effects of hyperglycemia and the renin-angiotensin system on endothelium and peripheral blood leukocytes may underlie the beneficial effects of inhibitors of the renin-angiotensin system on cardiovascular outcome in patients with diabetes mellitus.

Off-pump CABG in diabetic patients: does insulin dependency matter?

BACKGROUND

We aimed to analyze influence of insulin dependency on short-term outcomes after OPCAB in patients with diabetes.

METHODS

Retrospective cohort study was planned based on chart review. Study population consisted of 148 diabetic cases (63 insulin-dependent diabetics in group I and 85 non-insulin-dependent diabetics in group II). Patients' preoperative data and risk factors for adverse outcomes are analysed. The primary endpoint was all causes of mortality during the in-hospital course. Preestablished secondary endpoints included all major postoperative complications, including non-fatal acute myocardial infarction, non-fatal stroke, sepsis, shock, mediastinitis, respiratory insufficiency, and renal insufficiency, and minor postoperative complications, including mechanical ventilation for more than 24 hours, inotropic support, reoperation for bleeding, and necessity of blood transfusion. Additional analysis was performed on the duration of stay in the intensive care unit and overall hospital stay.

RESULTS

Group I patients were significantly more likely to have hypertension (87.3% versus 82.5%, p=0.023), they also had a trend toward higher prevalence of hypercholesterolemia (71.4% versus 68.6%, p=0.092) and body mass index (28.1+/-4.2 versus 26.9+/-3.7, p=0.085). Angiographic characteristics and number of distal anastomosis were similar in the two groups. There was no significant difference in mortality during the in-hospital course as the primary endpoint. However, analysis in secondary endpoints revealed that group I patients were significantly more likely to have stroke (3.1% versus 2.3%, p=0.027), sternal wound infection (4.7% versus 3.4%, p=0.036) and atrial arrhythmia (28.3% versus 20.9%, p=0.021). Moreover, group I patients were significantly more likely to stay longer than 2 days in ICU (14.2% versus 11.6%, p=0.038). Higher prevalence of renal dysfunction was also observed in group I patients (7.9% versus 6.9%, p=0.069).

CONCLUSION

Similar to insulin dependent diabetes who had on-pump CABG, insulin dependent diabetes develop higher rate of major postoperative complications and stay longer in ICU after off-pump CABG.

Why and how to use insulin therapy earlier in the management of type 2 diabetes

Most patients with type 2 diabetes are inadequately controlled on their current therapy. Suboptimal glycemic control can have devastating consequences, such as retinopathy, nephropathy, neuropathy, and cardiovascular disease that may ultimately lead to mortality. Most patients eventually need insulin therapy, and initiating insulin earlier in the course of type 2 diabetes may lead to optimal glycemic control and prevent or delay diabetes-related complications. Although insulin therapy is the most effective method of managing hyperglycemia, it is often delayed owing to concerns about the complexity and inconvenience of treatment regimens; fear of injections, hypoglycemia or weight gain; and the time required to learn how to effectively manage insulin therapy. The development of insulin analogs, biphasic insulin analogs, and more convenient insulin delivery systems may make insulin therapy more manageable and help more patients achieve their treatment goals.

Mechanisms of Disease: endothelial dysfunction in insulin resistance and diabetes

Endothelial dysfunction is one manifestation of the many changes induced in the arterial wall by the metabolic abnormalities accompanying diabetes and insulin resistance. In type 1 diabetes, endothelial dysfunction is most consistently found in advanced stages of the disease. In other patients, it is associated with nondiabetic insulin resistance and probably precedes type 2 diabetes. In obesity and insulin resistance, increased secretion of proinflammatory cytokines and decreased secretion of adiponectin from adipose tissue, increased circulating levels of free fatty acids, and postprandial hyperglycemia can all alter gene expression and cell signaling in vascular endothelium, cause vascular insulin resistance, and change the release of endothelium-derived factors. In diabetes, sustained hyperglycemia causes increased intracellular concentrations of glucose metabolites in endothelial cells. These changes cause mitochondrial dysfunction, increased oxidative stress, and activation of protein kinase C. Dysfunctional endothelium displays activation of vascular NADPH oxidase, uncoupling of endothelial nitric oxide synthase, increased expression of endothelin 1, a changed balance between the production of vasodilator and vasoconstrictor prostanoids, and induction of adhesion molecules. This review describes how these and other changes influence endothelium-dependent vasodilation in patients with insulin resistance and diabetes. The clinical utility of endothelial function testing and future therapeutic targets is also discussed.