Abstract
Dietary antioxidants are expected to exert their physiological functions in vivo by regulating oxidative stress responsible for aging and aging-related degenerative diseases. However, evaluation of their effectiveness in humans is difficult because their bioavailability is still largely unknown. To resolve this problem, integrated studies from experiments using cultured cells to human clinical trials should be carried out with regard to the absorption, distribution, metabolism, excretion and behavior of dietary antioxidants at the target site. We attempted to evaluate the effectiveness of carotenoids and flavonoids for prevention of a variety of oxidative stress-related diseases from the viewpoint of their action as direct antioxidants and/or tuning factors for the cellular redox signaling pathway. It is likely that β-carotene accumulates in the skin in its original form and acts as a direct singlet oxygen quencher. Quercetin seems to require a deconjugation reaction from its conjugated metabolites to active aglycone in order to exert its physiological function in vivo, because this flavonoid is obligatorily converted to its conjugated metabolites during intestinal absorption. We proposed some plausible mechanisms for the prevention of atherosclerosis, depression and disuse muscle atrophy. These would be helpful for assessing the effectiveness of dietary antioxidants in human clinical trials.
