Peripheral non-enzymatic antioxidant changes with human aging: a selective status report

Oxidative stress is thought to be involved in the aging process in aerobic organisms and to play a role in the pathogenesis of several disease states. Since free radicals are extremely reactive, shortly half-lived and therefore very difficult to measure directly, oxidative stress has been mainly studied through the search of indirect biomarkers of free radical-induced damage. In aerobic organisms, oxidative damage to tissues and organs is prevented by a network of defenses which includes antioxidant and repairing enzymes as well as small molecules with scavenging ability, such as antioxidant vitamins. For these reasons, the assay of antioxidant vitamins and of small molecular free radical scavengers in biological milieus may be used, if appropriately performed, to quantify the defense status against oxidative damage and to provide an indirect estimate of free radical production in aging humans. Since several conflicting data have been reported in this area, this review is aimed to summarize the existing evidence and possible faults of the research focusing on the role of plasma concentrations of small-molecular, non-enzymatic antioxidants in the process of senescence in healthy humans.