Sies H, Stahl W, Sundquist A R
Institut für Physiologische Chemie I, Universität Düsseldorf, Germany.
Ann N Y Acad Sci. 1992 Sep 30;669:7-20. doi: 10.1111/j.1749-6632.1992.tb17085.x.
Tocopherols and tocotrienols (vitamin E) and ascorbic acid (vitamin C) as well as the carotenoids react with free radicals, notably peroxyl radicals, and with singlet molecular oxygen (1O2), this being the basis of their function as antioxidants. RRR-alpha-tocopherol is the major peroxyl radical scavenger in biological lipid phases such as membranes or low-density lipoproteins (LDL). L-Ascorbate is present in aqueous compartments (e.g. cytosol, plasma, and other body fluids) and can reduce the tocopheroxyl radical; it also has a number of metabolically important cofactor functions in enzyme reactions, notably hydroxylations. Upon oxidation, these micronutrients need to be regenerated in the biological setting, hence the need for further coupling to nonradical reducing systems such as glutathione/glutathione disulfide, dihydrolipoate/lipoate, or NADPH/NADP+ and NADH/NAD+. Carotenoids, notably beta-carotene and lycopene as well as oxycarotenoids (e.g. zeaxanthin and lutein), exert antioxidant functions in lipid phases by free-radical or 1O2 quenching. There are pronounced differences in tissue carotenoid patterns, extending also to the distribution between the all-trans and various cis isomers of the respective carotenoids. Antioxidant functions are associated with lowering DNA damage, malignant transformation, and other parameters of cell damage in vitro as well as epidemiologically with lowered incidence of certain types of cancer and degenerative diseases, such as ischemic heart disease and cataract. They are of importance in the process of aging. Reactive oxygen species occur in tissues and cells and can damage DNA, proteins, carbohydrates, and lipids. These potentially deleterious reactions are controlled in part by antioxidants that eliminate prooxidants and scavenge free radicals. Their ability as antioxidants to quench radicals and 1O2 may explain some anticancer properties of the carotenoids independent of their provitamin A activity, but other functions may play a role as well. Tocopherols are the most abundant and efficient scavengers of peroxyl radicals in biological membranes. The water-soluble antioxidant vitamin C can reduce tocopheroxyl radicals directly or indirectly and thus support the antioxidant activity of vitamin E; such functions can be performed also by other appropriate reducing compounds such as glutathione (GSH) or dihydrolipoate. The biological efficacy of the antioxidants is also determined by their biokinetics.
生育酚和生育三烯酚（维生素E）、抗坏血酸（维生素C）以及类胡萝卜素可与自由基，尤其是过氧自由基，以及单线态分子氧（1O2）发生反应，这是它们作为抗氧化剂发挥功能的基础。RRR-α-生育酚是生物脂质相（如细胞膜或低密度脂蛋白（LDL））中的主要过氧自由基清除剂。L-抗坏血酸盐存在于水性区室（如胞质溶胶、血浆和其他体液）中，可还原生育酚自由基；它在酶反应中还具有许多重要的代谢辅助因子功能，尤其是羟化作用。在氧化后，这些微量营养素需要在生物环境中再生，因此需要进一步与非自由基还原系统（如谷胱甘肽/谷胱甘肽二硫化物、二氢硫辛酸/硫辛酸或NADPH/NADP+和NADH/NAD+）偶联。类胡萝卜素，尤其是β-胡萝卜素、番茄红素以及氧化类胡萝卜素（如玉米黄质和叶黄素），通过自由基或1O2猝灭在脂质相中发挥抗氧化功能。组织类胡萝卜素模式存在显著差异，这也延伸到了各自类胡萝卜素的全反式异构体和各种顺式异构体之间的分布。抗氧化功能与降低体外DNA损伤、恶性转化以及其他细胞损伤参数相关，在流行病学上也与某些类型癌症和退行性疾病（如缺血性心脏病和白内障）的发病率降低相关。它们在衰老过程中很重要。活性氧在组织和细胞中产生，可损伤DNA、蛋白质、碳水化合物和脂质。这些潜在的有害反应部分由消除促氧化剂和清除自由基的抗氧化剂控制。它们作为抗氧化剂猝灭自由基和1O2的能力可能解释了类胡萝卜素一些与它们的维生素A原活性无关的抗癌特性，但其他功能可能也发挥了作用。生育酚是生物膜中最丰富、最有效的过氧自由基清除剂。水溶性抗氧化剂维生素C可直接或间接还原生育酚自由基，从而支持维生素E的抗氧化活性；其他合适的还原化合物（如谷胱甘肽（GSH）或二氢硫辛酸）也可发挥此类功能。抗氧化剂的生物学功效还取决于它们的生物动力学。
