title: Different mechanisms for inhibition of human cytochromes P450 1A1, 1A2, and 1B1 by polycyclic aromatic inhibitors.
abstract: We have previously shown that several polycyclic aromatic hydrocarbons (PAHs) strongly inhibit their own and other PAH metabolism catalyzed by cytochrome P450 (P450) 1A1, 1A2, and 1B1 [Shimada, T., and Guengerich, F. P. (2006) Chem. Res. Toxicol. 19, 288-294]. In the present study, we examined mechanisms of how PAHs inhibit these P450 enzymes by using 7-ethoxyresorufin O-deethylation (EROD) as a model reaction. First, we examined mechanisms of inhibition of P450 1A1, 1A2, and 1B1 by the synthetic model inhibitors 1-(1-propynyl)pyrene (1PP), 1-ethynylpyrene (1EP), 2-ethynylpyrene (2EP), and 4-(1-propynyl)biphenyl (4Pbi). Both 1PP and 1EP inhibited P450 1A1 in a mechanism-based manner, but P450 1B1 and 1A2 were directly inhibited by 1PP and 1EP. Interestingly, P450 1B1 inactivated 1PP and 1EP to products that were not inhibitory to P450 1B1. 4Pbi was a mechanism-based inhibitor of P450 1A1 and 1B1, but 2EP directly inhibited these P450s. All four of the inhibitors directly inhibited P450 1A2. We also found that benzo[a]pyrene and seven other PAH compounds tested inhibited P450 1A2 in a mechanism-based manner, but fluoranthene directly inhibited P450 1A2. All of the nine PAHs examined were direct inhibitors of P450 1A1 and P450 1B1. These results suggest different mechanisms of inhibition of P450 1A1, 1A2, and 1B1 by PAHs and related chemicals and that interactions between P450 enzymes and PAH inhibitors are involved in differences in inhibition of the enzymes.
authors.affiliation: Department of Chemical Biology, Osaka City University Medical School, Abeno-ku, Osaka 545-8585, Japan. shimada@msic.med.osaka-cu.ac.jp
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Shimada
authors.forename: Norie
authors.initials: N
authors.lastname: Murayama
authors.forename: Kazushi
authors.initials: K
authors.lastname: Okada
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Funae
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamazaki
authors.forename: F Peter
authors.initials: FP
authors.lastname: Guengerich
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002384:Catalysis; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065633:Cytochrome P-450 CYP1B1; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D010078:Oxazines / Q000378:metabolism; D011084:Polycyclic Aromatic Hydrocarbons / Q000494:pharmacology*
chemical_list: D065609:Cytochrome P-450 CYP1A2 Inhibitors; D004791:Enzyme Inhibitors; D010078:Oxazines; D011084:Polycyclic Aromatic Hydrocarbons; C007649:ethoxyresorufin; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D065633:Cytochrome P-450 CYP1B1