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.

Structural alterations of the erythrocyte membrane proteins in diabetic retinopathy.

BACKGROUND: Several rheological disorders of the erythrocytes, such as increased aggregation and decreased deformability, have been observed in diabetes mellitus and have been implicated in the development of diabetic microangiopathy. Structural alterations of the erythrocyte membrane proteins caused by the diabetic process may be at the origin of those observations. In the present study, we searched for erythrocyte membrane protein alterations in diabetic retinopathy. METHODS: We examined peripheral blood samples from 40 type-2 diabetic patients with diabetic retinopathy of variable severity (19 males and 21 females, mean age 66.8 years, Group A) and we compared them with samples from 19 type-2 diabetic patients without diabetic retinopathy (13 males and six females, mean age 66.5 years, Group B) and 16 healthy volunteers (eight males and eight females, mean age 65.6 years, Group C). Erythrocyte membrane ghosts from all samples were subjected to SDS-PAGE, and the electrophoretic pattern of transmembrane and cytoskeletal proteins was analysed for each sample. The protein quantification of each electrophoretic band was accomplished through scanning densitometry. RESULTS: No significant deviations from normal electrophoresis were observed in Groups B and C, apart from an increase in band 8 in two samples from Group B (11%). In contrast, in 14 samples from Group A (35%) we detected increases in protein band 8 and/or membrane-bound haemoglobin along with a decrease in spectrin. Moreover, increased mobility of band 3, an aberrant high molecular weight (MW) (> 255 kDa) band and a low MW (42 kDa) band were evident in ten samples from Group A (25%). Glycophorins were altered in 46% of Group-A patients versus 38% of Group-B patients. Females and patients with long duration of diabetes presented more electrophoretic abnormalities. CONCLUSIONS: Structural alterations of the erythrocyte membrane proteins are shown for the first time in association with diabetic retinopathy. Their detection may serve as a blood marker for the development of diabetic microangiopathy. Further studies are needed to assess whether pharmaceutical intervention to the rheology of erythrocytes can prevent or alleviate microvascular diabetic complications.