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The generation of oxidation products of benzo[a]pyrene by lipid peroxidation: a study using gamma-irradiation.

The role which active oxygen and radicals generated by the peroxidation of unsaturated fatty acids could play in the oxidation of benzo[a]pyrene has been studied using gamma-irradiation. Irradiation of benzo[a]pyrene resulted in the formation of benzo[a]pyrene 1,6-, 3,6- and 6,12-quinones and other more polar products which were analysed by h.p.l.c. OH. radicals are believed to be involved in this oxidation. The presence of polyunsaturated fatty acids and polyunsaturated lipids stimulated the formation of benzo[a]pyrene products following gamma-irradiation. Oxidation of benzo[a]pyrene also occurred over a period of days in the presence of autoxidising mackerel oil. The rate of benzo[a]pyrene oxidation was related to the extent of lipid peroxidation as determined by malonaldehyde formation. Malonaldehyde production as a result of peroxidising lipids was inhibited by benzo[a]pyrene which suggested that benzo[a]pyrene reacted directly with lipid peroxy radicals or hydroperoxides generated in the process of lipid peroxidation. These results demonstrate that oxidation products of the peroxidation of lipids and fatty acids are able to react directly with benzo[a]pyrene to form products including benzo[a]pyrene quinones without the presence of enzymes such as the cytochrome P-450 mixed function oxidase system and prostaglandin synthetase. It is possible that benzo[a]pyrene may be activated by these types of reactions in vivo or in vitro when benzo[a]pyrene is in contact with polyunsaturated lipids in foodstuffs or the intestinal lumen and peroxidation of unsaturated fats may play an important role in human carcinogenesis.