Role of Dietary Antioxidants in Protection against Oxidative Damage

Abstract

Recently, much attention has been focused on studies which suggest the involvement of active oxygens and free radicals in a variety of pathological events, cancer, and even the aging process (21,30). Oxygen is indispensable for aerobic organisms including, of course, human beings; however, it is believed that oxygen also may be responsible for undesired phenomena (4). In particular, oxygen species such as hydrogen peroxide, superoxide anion radical and singlet oxygen, and other radicals, are proposed as agents attacking polyunsaturated fatty acid in cell membranes, giving rise to lipid peroxidation (3). Several reports have suggested that lipid peroxidation may result in destabilization and disintegration of cell membranes, leading to liver injury and other diseases, and finally, to aging and susceptibility to cancer. However, normal cell membranes do not undergo lipid peroxidation so severely in vivo because of the extremely efficient protective mechanisms against damage caused by active oxygens and free radicals. Such systems include enzymatic inactivation by, for example, superoxide dismutase, glutathione-peroxidase and catalase, as well as nonenzymatic protection of polyunsaturated fatty acid by physiological and biological antioxidants such as vitamin E, vitamin C, s-carotene, and uric acid (2). More recently, bilirubin (35) and carnocine (18) have been reported as being biologically significant antioxidants. In addition, several antioxidants have been reported to play an important role in the prevention of carcinogenesis related to active oxygen radicals, and in some cases, to extend the life span of animals (8).