Reactive Oxygen Species and Other Mediators of Phototoxic Damage
Environmental factors are major causes of cancer. In addition to xenobiotics also radiation may have importance in carcinogenesis as an association has been demonstrated e.g. between skin cancers and exposure to UV light. Although the exact mechanisms how environmental agents cause cancer are partially unknown, a 3-stage model including initiation, promotion and progression of cancer is generally accepted. Usually chemicals are metabolized into reactive intermediates reacting with cellular macromolecules to initiate cancer or they may act as tumor promoters when the mechanisms have not been explored. Some xenobiotics may be metabolized into free radicals which may attack on DNA and initiate cancer or these free radicals may act on other components such as oxygen to activate it into active forms which may act as tumor initiators or promoters. It is well known that radiation may cause DNA damage via the formation of hydroxyl radicals. Hydrogen peroxide causes DNA strand breakage and liberation of DNA bases as well as chemical alterations of bases. Superoxide anion causes single-strand scissions.
KeywordsSinglet Oxygen Active Oxygen Species Free Radical Reaction Dietary Lipid Level Phototoxic Reaction
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