Erythrocyte and plasma antioxidant activity and subclinical complications in young diabetic patients.

The review article entitled "Oxidative Stress and Diabetic Vascular Complications" accumulates evidence indicating that oxidative stress may play an important role in the etiology of diabetic complications (1). However, there are nearly no studies of diabetic children and adolescents developing subclinical complications. To our knowledge, only Jos et al. (2) have suggested that there is a relationship between retinopathy and decreased glutathione peroxidase activity in young diabetic patients. Very recently, we published a study to verify Joss data in a larger group of patients and to extend the antioxidant parameters and subclinical complications searched for (3). Some biological parameters involved in cell defense against oxygen radicals (plasma vitamins C and E, erythrocyte glutathione peroxidase, glutathione reductase, and superoxide dismutase) were measured in single blood samples from 119 diabetic infants, adolescents, and young adults. Data were studied in relation to residual insulin secretion determined by C-peptide, the level of metabolic control appreciated by glycosylated hemoglobin, lipid abnormalities, and subclinical complications (retinopathy by fluorescein angiography, neuropathy by peroneal motor nerve conduction velocity, and nephropathy by 24-hour microalbuminuria). There was no change in antioxidant parameters with residual insulin secretion. Patients with poor glycemic control and high plasma lipids had higher levels of plasma vitamin E. Patients with nephropathy had lower plasma vitamin C levels, and those with neuropathy showed lower erythrocyte glutathione peroxidase activity. Plasma vitamin C concentrations and erythrocyte glutathione reductase activities were negatively correlated with the age of the patients and the duration of the disease. In conclusion, higher transport capacity of vitamin E probably explains the elevated levels of vitamin E that were observed in patients with high lipid levels and long-lasting illness. The lower levels of vitamin C in the presence of nephropathy may be caused by an increased renal excretion of this vitamin. The reduction of glutathione peroxidase, glutathione reductase activities, and vitamin C levels confirms the existence of an oxidative stress in young type I diabetic patients.