Platelet protein kinase C isoform content in type 2 diabetes complicated with retinopathy and nephropathy

It has been reported that platelet aggregation in diabetic patients with mi croangiopathy is increased compared with healthy subjects. Chronic hypergly cemia is known to cause an increase in diacylglycerol level in various tiss ues. We examine whether protein kinase C (PKC) isoform content in platelets from diabetic patients is increased compared with healthy subjects, as pre viously described in the retina, aorta, and heart of diabetic rats. Platele t PKC alpha, beta and zeta immunoreactivity in cytosol, membrane and cytosk eleton (CS) fractions were analyzed by immunoblotting in 20 type 2 diabetic patients (who had been treated with diet alone, sulphonylureas or insulin, and whose condition was complicated with retinopathy, nephropathy, neuropa thy and/or macroangiopathy) and in five healthy subjects. PKC alpha, beta a nd zeta immunoreactivity in cytosol, membrane and CS fractions in platelets from diabetic subjects were not significantly higher than those from healt hy subjects. However, platelet PKC beta immunoreactivity in cytosol fractio n was significantly higher in diabetic patients with normal serum creatinin e (Cr) level than in diabetic patients with abnormal Cr level (Cr greater t han or equal to 1.5 mg/dl) or in healthy subjects. Moreover, significant ne gative correlation between PKC beta immunoreactivity in cytosol fraction of platelets and serum Cr level was found in diabetic patients (P < 0.05). To clarify the effect of treatment for diabetes, PKC isoform immunoreactivity in platelets was measured in type 2 diabetic patients treated with diet al one, sulphonylurea or insulin treatment. Serum creatinine level in diabetic patients with insulin treatment was significantly higher than in diabetic patients with sulphonylurea treatment and diet alone. In addition, PKC<beta > immunoreactivity in diabetic patients with insulin treatment was signific antly suppressed compared with that in patients treated by sulphonylurea tr eatment. These results suggest that chronic hyperglycemia may activate plat elet PKC beta isoform, and that insulin treatment may decrease platelet PKC beta activity. Finally, not only PKC beta antagonists, but also glycemic c ontrol by insulin may prevent development of diabetic microangiopathy.