Factors regulating the expression of vascular permeability/vascular endothelial growth factor by human vascular tissues

An increased skin microvessel density is associated with neurovascular complications in type 1 diabetes mellitus

The aim of this study was to assess the blood vessel density and maturity in the skin of adults with type 1 diabetes in relation to the presence of late neurovascular complications. We included 148 patients (87 men) with a median (interquartile range) age of 41 (31-49) and median diabetes duration of 21 (17-30) years. Microvessel (CD133, CD34, CD31 and von Willebrand factor) markers were evaluated by indirect immunohistochemistry assay in material from a skin biopsy. Diabetic retinopathy was diagnosed using direct ophthalmoscopy, and diabetic kidney disease was estimated in people with increased albuminuria and a 10-year duration of diabetes or evidence of diabetic retinopathy . Diabetic peripheral neuropathy diagnosis was based on Toronto definition, cardiac autonomic neuropathy on validated ProSciCard III program. Microvessel density, assessed by CD34 and CD133, was significantly higher in patients with cardiac autonomic neuropathy [160 (125-175) vs 121 (100-154)/1 mm², p = 0.001 and 92 (83-104) vs 79 (63-92)/1 mm², p = 0.007, respectively] and CD34 in patients with diabetic peripheral neuropathy [135 (106-168) vs 121 (95-145)/1 mm², p = 0.018], as compared with subjects without complications. In multivariate logistic regression, density of CD34 and CD133 positive vessels was associated with presence of cardiac autonomic neuropathy [odds ratio 1.016 (95% confidence interval: 1.002-1.029), p = 0.019 and odds ratio 1.037 (95% confidence interval: 1.008-1.067), p = 0.011, respectively]. It was independent from age, sex, diabetes duration, smoking status, body mass index and HbA1c value. Density of CD34 positive vessels was also associated with diabetic peripheral neuropathy, independently from sex and diabetes duration [odds ratio 1.009 (95% confidence interval: 1.001-1.020), p = 0.037]. Skin microvessel density is increased in adults with clinical evidence of neurovascular complications of type 1 diabetes. This is associated with predominance of the vessels of low maturity.

Cerebrovascular complications of diabetes: focus on cognitive dysfunction

The incidence of diabetes has more than doubled in the United States in the last 30 years and the global disease rate is projected to double by 2030. Cognitive impairment has been associated with diabetes, worsening quality of life in patients. The structural and functional interaction of neurons with the surrounding vasculature is critical for proper function of the central nervous system including domains involved in learning and memory. Thus, in this review we explore cognitive impairment in patients and experimental models, focusing on links to vascular dysfunction and structural changes. Lastly, we propose a role for the innate immunity-mediated inflammation in neurovascular changes in diabetes.

New insights into molecular mechanisms of diabetic kidney disease

Diabetic kidney disease remains a major microvascular complication of diabetes and the most common cause of chronic kidney failure requiring dialysis in the United States. Medical advances over the past century have substantially improved the management of diabetes mellitus and thereby have increased patient survival. However, current standards of care reduce but do not eliminate the risk of diabetic kidney disease, and further studies are warranted to define new strategies for reducing the risk of diabetic kidney disease. In this review, we highlight some of the novel and established molecular mechanisms that contribute to the development of the disease and its outcomes. In particular, we discuss recent advances in our understanding of the molecular mechanisms implicated in the pathogenesis and progression of diabetic kidney disease, with special emphasis on the mitochondrial oxidative stress and microRNA targets. Additionally, candidate genes associated with susceptibility to diabetic kidney disease and alterations in various cytokines, chemokines, and growth factors are addressed briefly.

Vascular endothelial growth factors and vascular permeability

Vascular endothelial growth factors (VEGFs) are key regulators of permeability. The principal evidence behind how they increase vascular permeability in vivo and in vitro and the consequences of that increase are addressed here. Detailed analysis of the published literature has shown that in vivo and in vitro VEGF-mediated permeability differs in its time course, but has common involvement of many specific signalling pathways, in particular VEGF receptor-2 activation, calcium influx through transient receptor potential channels, activation of phospholipase C gamma and downstream activation of nitric oxide synthase. Pathways downstream of endothelial nitric oxide synthase appear to involve the guanylyl cyclase-mediated activation of the Rho–Rac pathway and subsequent involvement of junctional signalling proteins such as vascular endothelial cadherin and the tight junctional proteins zona occludens and occludin linked to the actin cytoskeleton. The signalling appears to be co-ordinated through spatial organization of the cascade into a signalplex, and arguments for why this may be important are considered. Many proteins have been identified to be involved in the regulation of vascular permeability by VEGF, but still the mechanisms through which these are thought to interact to control permeability are dependent on the experimental system, and a synthesis of existing data reveals that in intact vessels the co-ordination of the pathways is still not understood.

Diabetes is a vascular disease: the role of endothelial dysfunction in pathophysiology of cardiovascular disease in diabetes

Diabetes is a vascular disease. Endothelial dysfunction is the initial process in vascular manifestations of diabetes mellitus (DM). There are multiple pathways involved in the pathophysiologic process related to endothelial dysfunction in DM. Most of these abnormalities occur secondary to insulin resistance. In this article the role of insulin, glucose,dyslipidemia, oxidative stress and various cellular mechanisms related to endothelial dys-function in diabetes are discussed in detail.

Modulatory effects of HMG-CoA reductase inhibitors in diabetic microangiopathy

3-hydroxy-3-methyl-glutaryl CoA (HMG-CoA) reductase inhibitors or statins are competitive inhibitors of the rate-limiting enzyme in cholesterol biosynthesis. Several large landmark clinical studies have shown a marked reduction of cardiovascular mortality and morbidity in patients treated with statins. Because of the strong association between serum cholesterol levels and coronary artery disease, investigators initially assumed that the predominant beneficial effects of statins result from their lipid-lowering properties. However, more recent observations have suggested that the clinical benefits of statins may be in part independent of their cholesterol-lowering effects. The pleiotropic or cholesterol-independent effects of statins might result from preventing the production of isoprenoids. Isoprenoids serve as important lipid attachments for the post-translational modification of a variety of proteins such as small GTP binding proteins implicated in intracellular signaling. The list of different pleiotropic effects of statins is still growing and, among others, includes the modulatory effects of statins on endothelial function, oxidative stress, coagulation, plaque stability, and inflammation. The pleiotropic effects of statins represent an area of great interest in prevention and therapy of cardiovascular and other chronic diseases. An area of particular interest is the potential beneficial effects of statins in diabetes and its micro/macrovascular complications. This review summarizes our current understanding of the pleiotropic effects of statins in diabetes and the modulatory effects of statins in various pathobiological pathways involved in diabetes and its complications.

Mechanisms of endothelial dysfunction in the metabolic syndrome

Cardiovascular disease is a leading cause of death and disability in patients with diabetes or metabolic syndrome (MS). The available data suggest that many patients with diabetes or MS already have vascular abnormalities by the time they are diagnosed with their metabolic disorder. Endothelial dysfunction (ED), which is one of the initial steps in the process of vascular disease, is often present in patients with diabetes or MS. Although the precise mechanism(s) by which diabetes or MS causes ED remains to be elucidated, several possibilities exist. Hyperglycemia, hyperinsulinemia, increased oxidative stress, and diabetic dyslipidemia can all contribute to ED individually or in concert with one another. ED in the setting of diabetes or MS can subsequently result in the activation of a variety of pathways that alter vascular function and participate in the process of vascular remodeling and atherosclerosis. Because insulin resistance is the predominant mechanism responsible for various perturbations seen in MS or diabetes, it is essential to develop a therapeutic strategy that can improve insulin sensitivity with the hope that such interventions would reduce the risk of future cardiovascular events.

Polymorphisms of the vascular endothelial growth factor and susceptibility to diabetic microvascular complications in patients with type 1 diabetes mellitus

There is increasing evidence implicating genetic factors in the susceptibility to diabetic microvascular complications. Recent studies suggest that increased expression of the cytokine vascular endothelial growth factor (VEGF) may play a role in the pathogenesis of diabetic complications. A number of polymorphisms in the promoter region of the VEGF gene have been identified. The aim was to investigate whether an 18 base pair (bp) deletion (D)/insertion (I) polymorphism at position -2549 in the promoter region of the VEGF gene is associated with the susceptibility to diabetic microvascular complications. Two hundred and thirty-two patients with type 1 diabetes mellitus (T1DM) and 141 normal healthy controls were studied. The D/D genotype was significantly increased in those patients with nephropathy (n=102) compared to those with no complications after 20 years duration of diabetes (uncomplicated, n=66) (40.2% vs. 22.7%, respectively, chi(2)=5.5, P<.05). The combination of polymorphisms of VEGF together with the aldose reductase (ALR2) gene showed that in the nephropaths, 8 of the 83 subjects had the VEGF I allele together with the Z+2 5'ALR2 allele compared with 27 of the 62 uncomplicated patients (chi(2)=26.7, P<.00001). The functional role of the D/I polymorphism was examined by cloning the region into a luciferase reporter assay system and transient transfection into HepG2 cells. The construct containing the 18 bp deletion had a 1.95-fold increase in transcriptional activity compared with its counterpart that had the insert (P<.01). These results suggest that polymorphisms in the promoter region of the VEGF gene together with the ALR2 may be associated with the pathogenesis of diabetic nephropathy.

Protein kinase C and the development of diabetic vascular complications

Hyperglycemic control in diabetes is key to preventing the development and progression of vascular complications such as retinopathy, nephropathy and neuropathy. Increased activation of the diacylglycerol (DAG)-protein kinase C (PKC) signal transduction pathway has been identified in vascular tissues from diabetic animals, and in vascular cells exposed to elevated glucose. Vascular abnormalities associated with glucose-induced PKC activation leading to increased synthesis of DAG include altered vascular blood flow, extracellular matrix deposition, basement membrane thickening, increased permeability and neovascularization. Preferential activation of the PKCbeta isoform by elevated glucose is reported to occur in a variety of vascular tissues. This has lead to the development of LY333531, a PKCbeta isoform specific inhibitor, which has shown potential in animal models to be an orally effective and nontoxic therapy able to produce significant improvements in diabetic retinopathy, nephropathy, neuropathy and cardiac dysfunction. Additionally, the antioxidant vitamin E has been identified as an inhibitor of the DAG-PKC pathway, and shows promise in reducing vascular complications in animal models of diabetes. Given the overwhelming evidence indicating a role for PKC activation in contributing to the development of diabetic vascular complications, pharmacological therapies that can modulate this pathway, particularly with PKC isoform selectivity, show great promise for treatment of vascular complications, even in the presence of hyperglycemia.

A potential role for angiotensin II-induced vascular endothelial growth factor expression in the pathogenesis of diabetic nephropathy?

Diabetic nephropathy often co-exists with other manifestations of microangiopathy, in particular retinopathy. Recent clinical evidence suggests that inhibition of the renin-angiotensin system in humans can delay the development and/or progression of diabetic nephropathy and perhaps also retinopathy. The benefits of this therapeutic strategy may in part be explained by inhibition of the nonhaemodynamic actions of angiotensin II (Ang II). The recognized nonhaemodynamic actions of Ang II include the augmented release of many growth factors. Ang II can stimulate the release of vascular endothelial growth factor (VEGF) from human vascular tissues. VEGF is a family of potent cytokines which act to induce angiogenesis and markedly increase microvascular permeability. VEGF is abundantly expressed in the renal glomerulus, specifically within the podocyte, where its function is unknown. VEGF is also expressed in the retina and increased retinal VEGF expression occurs in diabetes and has been implicated in the pathogenesis of diabetic retinopathy. This review considers the potential clinical significance of Ang II-induced VEGF expression, if any, in the pathogenesis of diabetic nephropathy and retinopathy.