Increased protein carbonylation of red blood cell membrane in diabetic retinopathy

We investigated the protein carbonylation of red blood cell (RBC) membrane in type 2 diabetic patients and the potential implication of carbonyl/oxidative stress in reflecting disease severity. Sixty-four diabetic patients with or without retinopathy of variable clinical severity (Groups DR and DM, respectively) and 20 healthy controls were included in the study. Protein carbonyls were determined in RBC membranes by immunoblotting. Compared to healthy volunteers, the RBC membranes of diabetic patients were characterized by significantly increased levels of carbonylated proteins. The carbonylation of Group DR was higher compared to that of Group DM. The subgroup of patients with proliferative retinopathy exhibited a trend towards a significant increase in protein carbonyls, compared to both free-of-retinopathy diabetic cases and non-proliferative diabetic retinopathy cases. The correlation between the chemical modifications of the erythrocyte membrane proteins and the clinical severity of diabetic retinopathy suggests a potential utility of membrane carbonylation as a marker and risk factor in the development of retinopathy.