Levels of carbonyl groups in plasma proteins of type 2 diabetes mellitus subjects

Carbonyl groups result from protein oxidation and their level in tissues an d plasma is a relatively stable marker of oxidative damage. Carbonyl conten t of plasma proteins in 43 type 2 diabetic subjects, 30-87 years of age (25 males and 18 females) and in 20 age-matched healthy controls (31-89 years of age, 12 males and 8 females) was evaluated with 2,4-dinitro-phenyl-hydra zine method. In both groups, lipids, tocopherols (HPLC) and glycated hemogl obin (HPLC) were studied. Fasting blood glucose, glycated hemoglobin and lipids were significantly hi gher in the diabetic group; carbonyl content and alpha-tocopherol were slig htly, but not significantly higher in the diabetic group (1.06 +/- 0.03 vs. 0.97 +/- 0.04 nmol/mg protein, 27.07 +/- 2.82 vs. 31.55 +/- 2.11 mu mol/l, respectively). Significant relationships between age and lipids, alpha-toc opherol and proteins were found in controls, but not in diabetics. Alpha-to copherol correlated with lipids in both groups; glycated hemoglobin, a mark er of glycemic control, was related to lipids, alpha-tocopherol and protein carbonyl groups in diabetics, while only the correlation with carbonyls wa s found in controls. These results suggest that impaired glycemic control is connected to protei n oxidation. Glycation cascade also releases free radicals, becoming respon sible for further oxidative attacks. In conclusion, increased oxidative str ess, if any, in the diabetic group, is doubtlessly induced by hyperglycemia , and the tocopherols are not seriously affected by a worsening of the meta bolic control.