title: Fatty acid hydroperoxides support cytochrome P450 2S1-mediated bioactivation of benzo[a]pyrene-7,8-dihydrodiol.
abstract: In the accompanying report (p. 1031), we showed that a novel dioxin-inducible cytochrome P450, CYP2S1, efficiently metabolizes benzo[a]pyrene-trans-7,8-dihydrodiol (BaP-7,8-diol) into the highly mutagenic and carcinogenic benzo[a]pyrene-r-7,t-8-dihydrodiol-t-9,10-epoxide (BaP-diol-t-epoxide), using cumene hydroperoxide in lieu of NADPH/O(2). Lipid hydroperoxide-supported P450 oxidation has been reported in several cases. However, it has not yet been described for the bioactivation of BaP-7,8-diol. In this report, we demonstrate that CYP2S1 can use various fatty acid hydroperoxides to support epoxidation of BaP-7,8-diol at a much higher rate than with cumene hydroperoxide. Kinetic analyses with several fatty acid hydroperoxides revealed that 13S-hydroperoxy-9Z,11E-octadecadienoic acid (13-HpODE) was the most potent oxidant tested (K(m), 3.4 +/- 0.8 microM; turnover, 4.51 +/- 0.13 min(-1)), followed by 12S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (K(m), 2.8 +/- 0.7 microM; turnover, 3.7 +/- 0.1 min(-1)), 5S-hydroperoxy-6E,8Z,11Z,14Z-eicosatetraenoic acid (K(m), 2.7 +/- 0.8 microM; turnover, 3.69 +/- 0.09 min(-1)), and 15S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (K(m), 11.6 +/- 0.3 microM; turnover, 0.578 +/- 0.030 min(-1)). The antioxidant butylated hydroxyanisole inhibited CYP2S1-catalyzed epoxidation by 100%, suggesting that epoxidation proceeds by a free radical mechanism. Other cytochromes P450, including CYP1A1, CYP1B1, CYP1A2, and CYP3A4, were also able to epoxidize BaP-7,8-diol using various fatty acid hydroperoxides, although at slower rates than CYP2S1. The cytotoxicity of BaP-7,8-diol significantly increased in mammalian cells overexpressing CYP2S1, and BaP-diol-t-epoxide formation in these cells also increased in the presence of 13-HpODE. Together, these results suggest that fatty acid hydroperoxides can serve as physiological cofactors in supporting in vivo CYP2S1-catalyzed oxidation of BaP-7,8-diol, and that fatty acid hydroperoxides and CYP2S1 may play important roles in benzo[a]pyrene-induced carcinogenesis.
authors.affiliation: Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Bui
authors.forename: Erin L
authors.initials: EL
authors.lastname: Hsu
authors.forename: Oliver
authors.initials: O
authors.lastname: Hankinson
mesh_terms: D000818:Animals; D001711:Biotransformation; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D004101:Dihydroxydihydrobenzopyrenes / Q000737:chemistry / Q000378:metabolism*; D004785:Environmental Pollutants / Q000378:metabolism; D006801:Humans; D008054:Lipid Peroxides / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D010084:Oxidation-Reduction
chemical_list: D004101:Dihydroxydihydrobenzopyrenes; D004785:Environmental Pollutants; D008054:Lipid Peroxides; C017228:benzo(a)pyrene 7,8-dihydrodiol; D003577:Cytochrome P-450 Enzyme System; C422564:CYP2S1 protein, human