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

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.

Rheopheresis in patients with ischemic diabetic foot syndrome: results of an open label prospective pilot trial

Rheopheresis is a specific application of membrane differential filtration, synonymous with double filtration plasmapheresis, for extracorporeal hemorheotherapy. Safety and efficacy of Rheopheresis for wound healing and skin oxygenation were investigated in patients with ischemic diabetic foot syndrome. Eight patients with type 2 diabetes mellitus and non-healing foot ulcers caused by severe ischemic diabetic foot syndrome were treated by a series of seven Rheopheresis sessions in a time span of 11 weeks. Wound healing had not been detectable under conditions of standardized wound care during at least 2 months. Wound status was classified by its morphology, severity and location, according to the criteria of Wagner. Transcutaneous oxygen pressure (tcPO2), laser Doppler flowmetry and vital capillary microscopy were repeatedly performed to monitor the effects of the Rheopheresis treatment series on microcirculation and skin blood flow. Laboratory parameters of blood rheology, endothelial function and inflammatory state were measured in addition to safety parameters. In four patients (baseline Wagner stage 2), Rheopheresis accelerated wound healing of foot ulcers and was associated with an improvement of Wagner stage and a pronounced increase in tcPO2. In two patients (baseline Wagner stage 2), wound healing was unchanged but mean tcPO2 increased, allowing successful minor amputation. Values of tcPO2 remained stable and enhanced for the 3 months follow-up period. In two patients (baseline Wagner stage 4 or 5), no improvements in foot lesions were observed within the treatment period. As an adjunct therapeutic option, Rheopheresis may preserve a functional lower extremity, delay amputation or reduce the extent of amputation.

Comparison of laser-Doppler flowmetry with biochemical indicators of endothelial dysfunction related to early microangiopathy in Type 1 diabetic patients

The aim of this study was to compare biochemical markers of endothelial activation with microcirculation measured by laser-Doppler flowmetry in Type 1 diabetic patients with or without microangiopathy. A total of 44 Type 1 diabetic patients were subdivided into those with (n=24) and without (n=20) microangiopathy according to ophthalmological findings and the presence or absence of microalbuminuria. The control group consisted of 25 healthy people of comparable age, sex, and body mass index. Postocclusive reactive hyperemia (PORH) and thermal hyperemia (TH, at 44 degrees C) were measured at the forearm. Serum N-acetyl-beta-glucosaminidase (NAG) activity, serum E-selectin, and ICAM-1 concentrations were used as biochemical markers of endothelial dysfunction. A significantly lower velocity of perfusion increase during postocclusive hyperemia (PORH(max) x t(1)(-1)) and during thermal hyperemia (TH(max) x t(2)(-1)) (P<.01) were accompanied by higher serum NAG activity (20.9+/-4.6 vs. 16.3+/-2.5 U l(-1), P<.01) in diabetic patients with microangiopathy as compared to healthy persons. An inverse relationship was found between PORH(max) x t(1)(-1) and NAG (r=-.33) results in diabetic patients. In addition, higher mean values of serum NAG activity, E-selectin, and ICAM-1 concentrations were associated with significantly lower values of microcirculation parameters (PORH(max) x t(2)(-1) and TH(max) x t(2)(-1)) in six patients without microangiopathy who had at least one of the above biochemical markers higher than mean+2 S.D. range. We suggest that serum NAG activity, E-selectin, and ICAM-1 concentrations may be used together with laser-Doppler flowmetry in Type 1 diabetic patients as early indicators of vascular changes in very early stage of diabetic microangiopathy.

Early growth response factor-1 mediates insulin-inducible vascular endothelial cell proliferation and regrowth after injury

Hyperinsulinemia in diabetes mellitus is a significant risk factor in the development of atherosclerosis and early restenosis after balloon angioplasty. These manifestations could be mediated by the ability of insulin to potentiate the cellular proliferative and reparative response of vascular cell types to local stimuli. Here we demonstrate that insulin stimulates DNA synthesis in aortic endothelial cells. Reverse transcription-polymerase chain reaction and Northern blotting revealed that insulin induces the expression and transcriptional activity of the immediate early gene and zinc finger transcription protein, early growth response factor-1 (Egr-1). Western immunoblot analysis revealed that insulin-inducible Egr-1 expression was inhibited using phosphorothioate-specific antisense oligonucleotides targeting Egr-1 mRNA. These agents blocked endothelial cell DNA synthesis stimulated by insulin in a dose-dependent manner and inhibited the capacity of insulin to potentiate the reparative response of endothelial cells to mechanical injury in vitro. These oligonucleotides also attenuated wound repair in smooth muscle cells. DNA synthesis induced by insulin was suppressed by inhibitors of two upstream activators of Egr-1, extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-phosphate (PI 3-K), whereas p38 kinase inhibitors had no effect. These present findings demonstrate that insulin-inducible DNA synthesis and repair after injury are processes critically dependent upon the activation of Egr-1. Additionally, they implicate this transcription factor as a potential target for the inhibition of restenosis in diabetics.

Diabetes and endothelial dysfunction: a clinical perspective

The main etiology for mortality and a great percent of morbidity in patients with diabetes mellitus is atherosclerosis. A hypothesis for the initial lesion of atherosclerosis is endothelial dysfunction, defined pragmatically as changes in the concentration of the chemical messengers produced by the endothelial cell and/or by blunting of the nitric oxide-dependent vasodilatory response to acetylcholine or hyperemia. Endothelial dysfunction has been documented in patients with diabetes and in individuals with insulin resistance or at high risk for developing type 2 diabetes. Factors associated with endothelial dysfunction in diabetes include activation of protein kinase C, overexpression of growth factors and/or cytokines, and oxidative stress. Several therapeutic interventions have been tested in clinical trials aimed at improving endothelial function in patients with diabetes. Insulin sensitizers may have a beneficial effect in the short term, but the virtual absence of trials with cardiovascular end-points preclude any definitive conclusion. Two trials offer optimism that treatment with ACE inhibitors may have a positive impact on the progression of atherosclerosis. Although widely used, the effect of hypolipidemic agents on endothelial function in diabetes is not clear. The role of antioxidant therapy is controversial. No data have been published regarding the effects of hormonal replacement therapy on endothelial dysfunction in postmenopausal women with type 2 diabetes.

Oxidative stress and lipids in diabetes: a role in endothelium vasodilator dysfunction?

Endothelial dysfunction is a key feature of diabetes mellitus and is thought to be the major cause of vascular complications associated with the disease. The vascular endothelium demonstrates impaired synthesis of vasodilators and increased release of procoagulants and vasoconstrictors, defects which theoretically could explain the increased incidence of atherosclerosis and hypertension found within this patient group. The pathways mediating endothelial cell layer dysfunction are unknown, although many candidates have been proposed. This review concentrates on the hypothesis that increased oxidative stress combined with abnormal plasma lipid composition leads to reduced synthesis of endothelial vasodilators and hence endothelial dysfunction. Free radical generation is undoubtedly raised in diabetes but the evidence for decreased antioxidant status is debatable. The role of antioxidant and lipid-lowering therapy is considered, but few studies have directly investigated the effect of treatment on vascular function. Concern arises from individual studies of vitamin E in diabetic animals which have proved deleterious. Current literature implies that a combination therapy of vitamin E and vitamin C may be beneficial, but this needs to be investigated further in both animal and human diabetes.

Early changes of serum N-acetyl-beta-glucosaminidase, tissue plasminogen activator and erythrocyte superoxide dismutase in relation to retinopathy in type 1 diabetes mellitus

Biochemical markers of early changes that are characteristic for diabetic microangiopathy are not completely understood. We investigated activities of serum N-acetyl-beta-glucosaminidase (NAG), tissue plasminogen activator and erythrocyte superoxide dismutase in well defined groups of type 1 diabetic patients. Patients were selected on the basis of 4 year follow-up observation. Forty-two type 1 diabetic patients were subdivided into those without retinopathy (n = 13) throughout the study, those with newly developed or worsened retinopathy (n = 12) during 4 years and those with retinopathy already established at the beginning of the study and without evidence of its progression (n = 17). All diabetic patients had albustix-negative urine. A significant increase of the mean serum NAG activity during 4 years was found only in patients without retinopathy (P < 0.01) whereas no changes of the altered enzyme activities were present in patients with developing and established retinopathy. The mean activity of tissue plasminogen activator was elevated in all groups of diabetic patients compared with healthy subjects (P < 0.001). A significant positive correlation was found between plasminogen activator and serum NAG (r = 0.51, P < 0.01). Erythrocyte superoxide dismutase was higher in diabetic patients than in healthy persons (P < 0.01) but no differences were observed between the patients with or without retinopathy. Superoxide dismutase positively correlated with NAG (r = 0.57, P < 0.01). We conclude that early functional changes precede a morphological development of diabetic retinopathy as was evident from the altered enzyme activities.

Localization of two binding domains for thrombospondin within fibronectin

Thrombospondin is a major glycoprotein of the platelet alpha-granule and is secreted during platelet activation. Several protease-resistant domains of thrombospondin mediate its interactions with components of the extracellular matrix including fibronectin, collagen, heparin, laminin, and fibrinogen. Thrombospondin, as well as fibronectin, is composed of several discretely located biologically active domains. We have characterized the thrombospondin binding domains of plasma fibronectin and determined the binding affinities of the purified domains; fibronectin has at least two binding sites for thrombospondin. Thrombospondin bound specifically to the 29-kDa amino-terminal heparin binding domain of fibronectin as well as to the 31-kDa non-heparin binding domain located within the larger 40-kDa carboxy-terminal fibronectin domain generated by chymotrypsin proteolysis. Platelet thrombospondin interacted with plasma fibronectin in a specific and saturable manner in blot binding as well as solid-phase binding assays. These interactions were independent of divalent cations. Thrombospondin bound to the 29-kDa fibronectin heparin binding domain with a Kd of 1.35 x 10(-9) M. The Kd for the 31-kDa domain of fibronectin was 2.28 x 10(-8) M. The 40-kDa carboxy-terminal fragment bound with a Kd of 1.65 x 10(-8) M. Heparin, which binds to both proteins, inhibited thrombospondin binding to the amino-terminal domain of fibronectin by more than 70%. The heparin effect was less pronounced with the non-heparin binding carboxy-terminal domain of fibronectin. By contrast, the binding affinity of the thrombospondin 150-kDa domain, which itself lacked heparin binding, was not affected by the presence of heparin. Based on these data, we conclude that thrombospondin binds with different affinities to two distinct domains in the fibronectin molecule.

A six-year follow-up of the relationship between N-acetyl-beta-glucosaminidase and albuminuria in relation to retinopathy

Fifty patients with Type 1 diabetes mellitus were observed over 6 years. Serum and urinary N-acetyl-beta-glucosaminidase (NAG) activity, and albuminuria were measured in groups of patients subdivided according to ophthalmological findings. Significantly higher mean serum NAG activity was found at the beginning of the study in patients who later developed diabetic retinopathy in comparison with those who did not (geometric mean (2SD range) 19.7 (12.4-31.2) vs 14.4 (9.5-22.7) U l-1, p less than 0.01). Urinary NAG activity was significantly higher in all groups of diabetic patients than in healthy control subjects (p less than 0.05). A significant increase in albumin:creatinine ratio during the study was found in patients with newly developed diabetic retinopathy compared with patients who did not (at 6 years 1.33 (0.40-4.43) vs 0.75 (0.24-2.31) g mol-1, p less than 0.01). No differences in either biochemical variable were found between hypertensive and normotensive diabetic patients at the end of the study. The results suggest that both serum NAG activity and albuminuria may serve as early functional indicators of diabetic retinopathy.