New careers for antioxidants

摘要

It is a remarkable fact that antioxidants are nontoxic compounds that reduce the incidence of cancer. Antioxidant nutrients such as vitamin E, β-carotene, lycopene, and selenium are regularly found to reduce the risk of lung, prostate, stomach, or total cancers, as well as oral precancers, in epidemiologic studies (1). Foods containing these nutrients are similarly effective, as are nondietary antioxidants such as green tea phenols and various Oriental herbal medicines (2). In general, the level of risk reduction is on the order of 0.6, which might encouragingly be extrapolated to (0.6)~n for those of us with n organs at risk. The risk reduction from an anti-oxidant can be 3-fold in the elderly, in smokers, and in subpopulations deficient in a second antioxidant (1). This result suggests that functional redundancy of antioxidant systems is hiding the importance of their biological roles until two actors have been removed, as often happens with gene knockouts. These nutrients, as well as nonnutrient antioxidants such as N-acetyl cysteine, also slow the appearance of tumors in mice (2-4). Why do antioxidants have these effects?