Impairment of the antioxidant properties of serum albumin in patients with diabetes: protective effects of metformin.

Free radical production is increased during diabetes. Serum albumin is a major antioxidant agent, and structural modification of albumin induced by glucose or free radicals impairs its antioxidant properties. Therefore the aim of the present study was to compare the antioxidant capacities and structural changes in albumin in patients with T2DM (Type 2 diabetes mellitus) treated with MET (metformin) or SU (sulfonylureas) and in healthy control subjects. Structural changes in albumin were studied by fluorescence quenching in the presence of acrylamide. Albumin thiols and fructosamines, reflecting oxidized and glycation-induced changes in serum albumin respectively, were assessed. Structural changes in albumin were demonstrated by a significant decrease in fluorescence quenching in patients with T2DM, with patients treated with MET exhibiting a significant difference in the conformation of albumin compared with patients treated with SU. Oxidation, resulting in a significant decrease in thiol groups and plasma total antioxidant capacity, and glycation, associated with a significant increase in fructosamines, were both found when comparing healthy control subjects with patients with T2DM. When patients treated with MET were compared with those treated with SU, oxidative stress and glycation were found to be significantly lower in MET-treated patients. In conclusion, patients with T2DM have a decrease in the antioxidant properties of serum albumin which may aggravate oxidative stress and, thus, contribute to vascular and metabolic morbidities. Moreover, a significant protection of albumin was found in patients with T2DM treated with MET.