Raised plasma fibronectin concentration is related to the presence of diabetic retinopathy

Retinal capillary basement membrane thickening: Role in the pathogenesis of diabetic retinopathy

Vascular basement membrane (BM) thickening has been hailed over half a century as the most prominent histological lesion in diabetic microangiopathy, and represents an early ultrastructural change in diabetic retinopathy (DR). Although vascular complications of DR have been clinically well established, specific cellular and molecular mechanisms underlying dysfunction of small vessels are not well understood. In DR, small vessels develop insidiously as BM thickening occurs. Studies examining high resolution imaging data have established BM thickening as one of the foremost structural abnormalities of retinal capillaries. This fundamental structural change develops, at least in part, from excess accumulation of BM components. Although BM thickening is closely associated with the development of DR, its contributory role in the pathogenesis of DR is coming to light recently. DR develops over several years before clinical manifestations appear, and it is during this clinically silent period that hyperglycemia induces excess synthesis of BM components, contributes to vascular BM thickening, and promotes structural and functional lesions including cell death and vascular leakage in the diabetic retina. Studies using animal models show promising results in preventing BM thickening with subsequent beneficial effects. Several gene regulatory approaches are being developed to prevent excess synthesis of vascular BM components in an effort to reduce BM thickening. This review highlights current understanding of capillary BM thickening development, role of BM thickening in retinal vascular lesions, and strategies for preventing vascular BM thickening as a potential therapeutic strategy in alleviating characteristic lesions associated with DR.

Markers of diabetic nephropathy

It is well established that the detection of microalbuminuria in a patient with diabetes mellitus indicates the presence of glomerular involvement in early renal damage. Recent studies have demonstrated that there is also a tubular component to renal complications of diabetes, as shown by the detection of renal tubular proteins and enzymes in the urine. In fact, tubular involvement may precede glomerular involvement, as several of these tubular proteins and enzymes are detectable even before the appearance of microalbuminuria. This review looks at the studies reported so far on serum and urinary markers of diabetic nephropathy, both glomerular and tubular, and their roles in the early detection of renal damage. The advantages and disadvantages of some of these markers are also discussed. The markers reviewed include (1) glomerular--transferrin, fibronectin, and other components of glomerular extracellular matrix, and (2) tubular--low molecular weight proteins (beta 2 microglobulin, retinol binding protein, alpha 1 microglobulin, urine protein 1), other proteins such as Tamm-Horsfall protein, beta 2 glycoprotein-1, urinary enzymes (N-acetyl-beta-D-glucosaminidase, cholinesterase, gamma glutamyltranspeptidase, alanine aminopeptidase), and tubular brush-border antigen.

Nonenzymatic glycation of fibronectin impairs adhesive and proliferative properties of human vascular smooth muscle cells

Nonenzymatic glycation of proteins is involved in the pathogenesis of diabetes vascular complications. Extracellular matrix proteins are a prominent target for nonenzymatic glycation because of their slow turnover rates. The aim of this study was to investigate the influence of human fibronectin (F) nonenzymatic glycation on adhesion and proliferation of cultured human vascular smooth muscle cells (hVSMC). Incubation of human F with 500 mmol/L D-glucose at 37 degrees C induced a time-dependent increase in fluorescence detectable at 440 nm after excitation at 363 nm. Nonenzymatic glycation did not affect binding of F itself to the plates. Adhesion of hVSMC to F increased with the increase of incubation time of the cells on the protein from 30 minutes up to 120 minutes and remained stable thereafter. Adhesion to glycated fibronectin (GF) was reduced in comparison to control F at all the different adhesion times. Adhesion of hVSMC to GF was reduced when F was exposed to glucose for 4, 9, or 28 days (P=.0417 to .0025), but not when F was exposed for 1 day. Adhesion of hVSMC to GF was reduced compared with adhesion to nonglycated F at all coating concentrations from 0.2 to 10 micrograms/mL (P=.05 to .014). Thus, nonenzymatic glycation of F impairs adhesion of hVSMC in vitro. Proliferation of hVSMC on F increased with increasing concentrations of the protein as coating agent (ANOVA:P<.0001 for both nonglycated F and GF). Proliferation with F glycated for 4, 9, and 28 days was reduced at concentrations of 1, 3, and 10 micrograms/mL as compared with proliferation with nonglycated F (P=.0253 to .0001). Proliferation on F glycated for only 1 day was not significantly reduced. When the number of hVSMC plated on control F was reduced by 25% to take into account the reduced adhesion, the number of cells that proliferated on F was still reduced. In conclusion, nonenzymatic glycation of F impairs adhesive and proliferative properties of hVSMC.

Plasma free N-terminal fibronectin 30-kDa domain as a marker of endothelial dysfunction in type 1 diabetes mellitus

The plasma free N-terminal fibronectin 30-kDa domain was measured in 44 type 1 diabetic patients and in 20 healthy subjects. A significantly raised mean concentration of a free N-terminal fibronectin 30-kDa domain was found in plasma of diabetic patients with proliferative retinopathy as compared with healthy persons (P less than 0.001). A positive correlation was observed between free N-terminal fibronectin 30-kDa domain and von Willebrand factor in plasma of all examined subjects (r = 0.62, P less than 0.01). A similar correlation was present between 30-kDa domain and albuminuria (r = 0.56, P less than 0.01). However, no relationship was found between fibronectin 30-kDa domain and control of diabetes as assessed by fructosamine concentration. The free N-terminal fibronectin 30-kDa domain may be used as a marker of actual endothelial cell dysfunction in diabetes.

Plasma fibronectin in normolipidaemic and hyperlipidaemic uraemic patients treated with haemodialysis

Plasma fibronectin (PF) concentrations, were investigated in normolipidaemic and hyperlipidaemic (type IV) patients with chronic renal failure treated with hemodialysis (n = 29) and in controls (n = 34). Mean PF was significantly reduced in both subsets of dialysed patients. Among the hemodialysed patients the presence of hyperlipidaemia did not modify PF levels, which resulted, on the contrary, significantly higher in hyperlipidaemic controls as compared with the normolipidaemic group. In controls, according to a multivariate analysis model, PF was directly related with age and inversely with HDL-cholesterol. In the hemodialysed patients total cholesterol was the unique significant PF related variate, being this group, therefore, characterized by the lack of any inverse relation between PF and HDL-cholesterol. Finally, no PF modifications were observed in hemodialyzed patients affected by arterial hypertension or clinically evident atherosclerotic lesions.

Plasmatic levels of fibronectin in diabetics with and without retinopathy. Correlation with some hormonal and metabolic parameters

Fibronectin is a high molecular weight alpha-2-glycoprotein. Its peculiar role in the structure of connective tissue, together with its wide involvement in coagulative dynamics, justified the increasing interest for fibronectin in the pathogenesis of diabetic disease and its vascular sequelae. In the present work, we evaluated the levels of plasma fibronectin (PF) in diabetics with and without retinopathy, and studied the possible correlation between the glycoprotein and some hormonal and metabolic parameters, expression of glycometabolic balance. We examined 26 type I and 24 type II diabetics, further divided into retinopathics and not retinopathics, and 43 normal subjects. We did not find any significant difference in PF levels either between normals and diabetics, or between type I and type II patients, or between retinopathics and not retinopathics. PF was significantly correlated to age, both in normals and in diabetics. Diabetic patients showed a significant positive correlation of PF to total cholesterol (r = 0.56; p less than 0.05) and triglycerides (r = 0.36; p less than 0.05). This seems to suggest, although indirectly, the existence of a relationship between the levels of PF and the degree of large vessel involvement. No significant correlation was found with HbA1c, beta-OH, AcAc, lactate, pyruvate, C-peptide, total and free insulin or GH. We further indicated an inverse correlation between PF and plasma glucagon (IRG). Very low levels of PF are commonly associated with high IRG plasma values during acute energy deprivation such as prolonged fasting and ketoacidotic coma. Therefore, PF levels might represent an index of latent to overt energy depletion.

Plasma fibronectin as an indicator of microvascular damage in diabetic patients. Rapid and sensitive evaluation by a radial immunodiffusion technique

Plasma fibronectin might be considered as an indicator of early and advanced microvascular damage in diabetic patients. We have therefore studied plasma fibronectin, using a radial immunodiffusion technique (LC-Partigen Fibronectin), in insulin-dependent and non-insulin-dependent diabetic patients with and without microangiopathic and neurological complications, i.e. retinopathy, nephropathy and autonomic and peripheral neuropathy. Steady and progressive increases of plasma fibronectin levels in association with the worsening of both diabetic retinopathy and nephropathy have been observed. However, significant variations of plasma fibronectin levels were already found in diabetic patients without microangiopathy when compared with healthy control subjects. Fibronectin levels were also higher in diabetic patients with autonomic and peripheral neuropathy than in control subjects and diabetic patients without neurological changes. The evaluation of plasma fibronectin by a specific radial immunodiffusion procedure might represent an important approach in the study and prevention of diabetic microcirculatory disorders.

Plasma fibronectin, von Willebrand factor antigen, and blood rheology. Association with diabetic microvascular disease

Plasma fibronectin might play a role in the pathogenesis and progression of diabetic microvascular disease. To test this hypothesis we measured plasma fibronectin, von Willebrand factor antigen, fibrinogen, erythrocyte filtrability, whole-blood viscosity, proteinuria and albuminuria in 25 control subjects and 29 diabetic patients with and without microvascular complications. Plasma fibronectin was significantly higher in the diabetic patients, especially in those with retinopathy and nephropathy. A significant correlation between fibronectin and von Willebrand factor antigen was found in both patients with and without microangiopathy (p less than 0.001). In diabetic patients with and without microvascular complications, several significant correlations were found between increased fibronectin levels and reduced erythrocyte filtrability (p less than 0.001) and between the increase of fibronectin and whole-blood viscosity (p less than 0.001). Furthermore, a significant correlation was found between plasma fibronectin levels, proteinuria (p less than 0.001) and albuminuria (p less than 0.001). The relationship between plasma fibronectin and changes of blood rheology may be important for the occurrence and progression of diabetic microangiopathy.