Nitric Oxide (NO) Activity and Diabetic Nephropathy

Experimental data suggest that oxidative stress and endothelial dysfunction are key players in the pathogenesis of diabetic nephropathy. In the last few years the investigators were able to establish a method to assess endothelial function of the renal vasculature in humans and started to systematically study a variety of cardiovascular disorders known to be associated with endothelial dysfunction in other vascular beds, including hypertension, hypercholesterolemia and type-2 diabetes. In patients with type-2 diabetes the investigators could demonstrate that despite unaltered basal and stimulated NO-activity, the renal response to the antioxidant vitamin C was more pronounced compared to control subjects. These data suggest that oxidative stress is increased in the renal vasculature of diabetic patients. Furthermore, NO-activity in diabetic patients appears to be upregulated to compensate for the increase in oxidative stress. This hypothesis is supported by the demonstration of increased endothelial nitric oxide synthase (eNOS) expression in kidney biopsies of diabetic patients. The major focus of the investigators' current research activities is to assess the role of endothelial dysfunction in the very early stages of diabetic nephropathy. To this end, patients with increased fasting glucose or metabolic syndrome will be studied in comparison with an age-matched control group. Endothelial function and the role of oxidative stress will be assessed in the renal vasculature in all groups. In parallel, the investigators will study endothelial function in the forearm by venous occlusion plethysmography and in the retinal vasculature by scanning laser doppler flowmetry to dissect regional differences in the regulation of endothelial function. Further aspects include the role of microalbuminuria, glomerular hyperfiltration, and endogenous inhibitors of NO synthase such as NG,NG-Dimethyl-L-Arginine (ADMA). In a therapeutic approach, the investigators will determine the effects of various antioxidant treatment strategies on endothelial function and their potential role in the prevention of diabetic nephropathy.