Inhibition of the Induction of Cancer by Antioxidants

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Abstract
Free radicals are now known to play an important role in many diseases including aging (Slaga, 1989; Halliwell, 1993). The importance of free radicals in radiation carcinogenesis and free radicals and electrophiles in chemical carcinogenesis is also well recognized. Free radicals and reactive oxygen species are continuously produced in vivo. Consequently, organisms have evolved that possess not only antioxidant and electrophile defense systems to protect against them, but also repair systems that prevent the accumulation of oxidatively-damaged molecules (Halliwell, 1993). Since increased free radical levels and levels of electrophilic compounds have been associated with many disease conditions, antioxidants, free radical scavengers, and electrophilic scavengers may be very useful in cancer prevention, cardiovascular disease prevention, immune function augmentation, and increasing the life span of man. Antioxidant enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase, are preventive antioxidants, because they eliminate species involved in the initiation of free radical chain reactions; while small molecule antioxidants, such as ascorbate, the tocopherols, glutathione, and reduced co-enzyme Q10 can repair oxidizing radicals directly and therefore are chain-breaking antioxidants. It is well known that ascorbate and tocopherols function synergistically to protect membrane lipids from damage (Buettner, 1993). Other molecules such as metal ion binding proteins, b-carotene, bilirubin, and urate are also very important antioxidants (Halliwell, 1993).