Human serum albumin, a negative acute phase reactant and marker of nutritive status, presents at high concentrations in plasma. Albumin has always been used in many clinical states especially to improve circulatory failure. It has been showed that albumin is involved in many bioactive functions such as regulation of plasma osmotic pressure, binding and transport of various endogenous or exogenous compounds, and finally extracellular antioxidant defenses. Molecules like transferrin, caeruloplasmin, haptoglobin, uric acid, bilirubin, alpha-tocopherol, glucose, and albumin constitute extracellular antioxidant defenses in blood plasma but albumin is the most potent one. Most of the antioxidant properties of albumin can be attributed to its unique biochemical structure. The protein possesses antioxidant properties such as binding copper tightly and iron weakly, scavenging free radicals, e.g., hypochlorous acid (HOCl) and Peroxynitrite (ONOOH) and providing thiol group (-SH). Whether it is chronic or acute, during many pathological conditions, biomarkers of oxidative protein damage increase and this observation continues with considerable oxidation of human serum albumin. There is an important necessity to specify its interactions with Reactive Oxygen Species. Generally, it may lower the availability of pro-oxidants and be preferentially oxidized to protect other macromolecules but all these findings make it necessary that researchers give a more detailed explanation of albumin and its relations with oxidative stress.

In this study, we evaluated protein oxidation in 84 patients with Type 2 diabetes with no complications and in 61 healthy volunteers who formed the control group, whose ages matched those of the patients. We determined plasma carbonyl and plasma thiol levels as markers of oxidative protein damage and erythrocyte glutathione, plasma ceruloplasmin and transferrin as markers of free radical scavengers. The concentrations (mean ± SD) of both of plasma carbonyl (1.24 ± 0.46 vs. 0.72 ± 0.17 nmole/mg protein; p < 0.0001) and lipid hydroperoxides (1.8 ± 0.63 vs. 1.3 ± 0.21 µtmole/l; p<0.0001) were increased, and the concentration of plasma transferrin (3.85 ± 0.65 vs. 4.59 ± 0.79 g/I; p < 0.05) was decreased, respectively, in Type 2 diabetic patients compared with those of the controls. There were no significant differences in the concentrations of plasma thiol (0.0064 ± 0.001 vs. 0.0068 ± 0.001 µimole/mg protein), erythrocyte glutathione (2.54 ± 0.57 vs. 2.65 ± 0.56 mg/g Hb), plasma ceruloplasmin (548 ± 107.30 vs. 609 ± 93.34 mg/l) between the patients and the controls. These changes observed in diabetic patients contribute to the imbalance in the redox status of the plasma. We attribute this imbalance to oxidative protein damage in Type 2 diabetic patients clinically free of complications.