Platelet antioxidant enzymes in insulin-dependent diabetes mellitus

The measurement of the peroxidase scavenging system represented by the activities of superoxide dismutase (SOD), catalase and glutathione peroxidase (GSH-Px) in blood cells of diabetic patients has, in the past, given equivocal results. Likewise, the role of these intracellular enzymatic scavengers against the oxidative stress of diabetes-associated microangiopathic complications is unknown.

Choosing platelets as cell model (as commonly done in previous studies), the aim of this study was to relate the platelet content of SOD, catalase and GSH-Px to the presence of diabetes, as well as to the presence of nephropathy and retinopathy in 35 insulin-dependent diabetic patients, as compared to 10 age-matched control subjects.

The enzymatic activities were not changed in diabetic patients in comparison with healthy controls. After stratifying patients according to presence of nephropathy (24-h urinary albumin excretion rate persistently > or =20 microg min(-1)) or retinopathy, the group of albuminuric patients was characterized by a significant decrease in SOD activity as compared to those in the normoalbuminuric range (4.36+/-1.06 vs. 6.81+/-2.26 mU 10(-9) platelets; p=0.01). Catalase and GSH-Px did not change. No modification in platelet enzyme activities has been found in diabetic subjects with retinopathy.

These results suggest that diabetic nephropathy, at least in its early stage, may be related to an altered redox state of platelets, as tested by the reduction in SOD activity, thus, indicating that the renal damage in these patients may be associated to a selective increase in platelet susceptibility to variation in the redox state.