Glucose and free radicals impair the antioxidant properties of serum albumin

Epidemiological data consistently show that reduced levels of serum albumin , which is the most abundant protein in plasma, are associated with an incr eased mortality risk. Various biological properties evidenced by direct eff ects of the albumin molecule may explain its beneficial effects. The presen t work aimed to investigate in vitro whether glycation or free radicals or both factors would affect the antioxidant properties of bovine serum albumi n (BSA), Glycation was performed by long-term incubations (60 days) of BSA with increasing concentrations of glucose (up to 500 mmol/l) at 37 degrees C, Minimally oxidized BSA was obtained after controlled incubations of dial yzed BSA samples with a water-soluble free radical generator [2,2' azo-bis( 2-amidinopropane) HCl], The glycation-mediated modifications and the free r adical-induced conformational changes of BSA were monitored using intrinsic fluorescence measurements of the tryptophan residues and acrylamide as a q uenching agent. Thiol groups, Amadori glycophore contents, and boronate bin ding were also measured. We found that the changes observed in the conforma tion of the BSA molecule were associated with modifications of its antioxid ant properties. The latter were studied by the copper-mediated oxidation of human low density lipoproteins and the free radical-induced blood hemolysi s test. Our data support the concept that oxidative-induced BSA modificatio ns are important determinants in the antioxidant properties of BSA, Glycate d BSA still behaved as an antioxidant but became pro-oxidant in the presenc e of copper, probably by generating oxygenated species. These data confirm the key role of metals ions in this process. Although these results warrant further in vivo investigations, we propose that, considering the poor gluc ose control found in diabetics as well as the key role of oxidative stress in vascular complications, glycation-mediated and free radical-induced impa irment of the antioxidant properties of albumin might be important paramete rs in vascular complications encountered in diabetes.