title: Oxidation of (+)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene by mouse keratinocytes: evidence for peroxyl radical- and monoxygenase-dependent metabolism.
abstract: The role of prostaglandin H (PGH) synthase and peroxyl radicals as well as cytochrome P-450 in the metabolism of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) was examined in fresh skin keratinocytes isolated from hairless mice. Labeled (+)-BP-7,8-diol was oxidized after incubation with the keratinocytes to syn- and anti-diolepoxides in greater than a 4:1 ratio as estimated by h.p.l.c. analysis of the stable hydrolysis products. Formation of diolepoxides was dependent on cell number and the concentration of BP-7,8-diol. Incubation in the presence of the PGH synthase substrate, 20:4 or the inhibitor, indomethacin did not alter the total formation or the ratio of diolepoxides. However, the addition of butylated hydroxyanisole (1 micron) an inhibitor of peroxyl radical dependent-metabolism significantly inhibited diolepoxide formation. The time course for the formation of the anti-diolepoxide and lipid peroxidation, measured as malondialdehyde was determined. The results suggest an excellent correlation between peroxyl radical and diolepoxide formation. Pretreatment of mice with the cytochrome P-450 inducer, beta-naphthoflavone greatly altered the metabolism of (+)-BP-7,8-diol by keratinocytes. The major metabolite was the syn-diolepoxide with significant formation of two unknown metabolites. Pretreatment of mice with BP-7,8-diol did not induce aryl hydrocarbon hydroxylase activity but did increase the yield of syn-diolepoxide formed from labeled (+)-BP-7,8-diol by 1.5-fold. Our results suggest that peroxyl radical-mediated metabolism is primarily responsible for the oxidation of (+)-BP-7,8-diol in control animals while the cytochrome P-450 system is primarily responsible for oxidation in animals pretreated with inducers.
mesh_terms: D000818:Animals; D002083:Butylated Hydroxyanisole / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D004101:Dihydroxydihydrobenzopyrenes / Q000378:metabolism*; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism*; D005260:Female; D005609:Free Radicals; D066298:In Vitro Techniques; D007633:Keratins; D008054:Lipid Peroxides / Q000378:metabolism*; D051379:Mice; D008812:Mice, Hairless; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011451:Prostaglandin-Endoperoxide Synthases / Q000502:physiology
chemical_list: D004101:Dihydroxydihydrobenzopyrenes; D005609:Free Radicals; D008054:Lipid Peroxides; C017228:benzo(a)pyrene 7,8-dihydrodiol; D002083:Butylated Hydroxyanisole; D007633:Keratins; D003577:Cytochrome P-450 Enzyme System; D011451:Prostaglandin-Endoperoxide Synthases