The role of advanced oxidation protein products and total thiols in diabetic retinopathy.

PURPOSE This study aimed to investigate the role of protein peroxidation by detecting the serum levels of advanced oxidation protein products (AOPP), a novel marker for the degree of oxidative damage to proteins, and total thiol as a marker of antioxidant status in diabetic patients with or without diabetic retinopathy (DR) and to compare the results with those of control subjects. METHODS The study groups consisted of two separate subgroups: 1) 37 patients (14 male, 23 female) with noninsulin-dependent diabetes mellitus (NIDDM) showing diabetic retinopathy (DR) and 2) 20 patients with NIDDM and without any signs of DR (9 male, 11 female); 26 healthy non-diabetic control subjects (15 male, 11 female) were selected from the patients attending our department for refractive disorders. Venous blood samples of all participants were collected in the morning after an overnight fast, and serum samples storedat -70 degrees C until assay for AOPP, and total thiol. RESULTS AOPP levels were significantly higher in diabetic patients with (210.9+/-73.0 micronmol/L) or without DR (222.7+/-94.4 micronmol/L) when compared to those of controls (152.4+/-72.04 micronmol/L) (p=0.004). Even though the difference was not statistically significant (p=0.095), total thiol levels in cases with DR (278.7+/-139.1 micronmol/L) were lower than those without DR (334.0+/-129.4 micronmol/L) and controls (353.2+/-145.6 micronmol/L). Correlation tests did not reveal any association between these parameters and age, sex, or duration of DM. CONCLUSIONS The present study suggests that increased protein oxidation may contribute to the pathogenesis of DR.