Specificity of age-related carbonylation of plasma proteins in the mouse and rat

The purpose of this study was to determine (1) whether oxidative damage to plasma proteins in mice and rats, accrued during aging and manifested as carbonyl modifications, was selective or random, and (2) whether the putative carbonylated proteins could be used as markers of oxidative stress and aging. The total protein carbonyl content of the plasma significantly increased with age in mice but not in rats. Immunostaining of mouse plasma proteins, resolved by SDS-PAGE to localize carbonyls, revealed that only two specific proteins exhibited an age-associated increase in carbonylation. These proteins with molecular weights of 68 and 75 kDa, were identified as albumin and transferrin, respectively. In the rat, albumin and a 167-kDa protein, alpha1-macroglobulin (alpha-1M), showed significant age-dependent accrual of carbonylation. In the plasma of middle age Rhesus monkeys, in addition to albumin, a 54-kDa protein showed carbonylation. However, neither transferrin nor alpha-1M were carbonylated in the plasma of Rhesus monkey. Albumin was the only protein that showed carbonylation in all the three species examined. Results of this study indicate that age-associated increase in protein carbonylation is a selective and not a random phenomenon. However, the set of proteins that become carbonylated differs in different species.