title: Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human CYP1B1 genetic variants.
abstract: Human cytochrome P450 1B1 (CYP1B1) plays a critical role in the metabolic activation of a variety of procarcinogens, including 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). The existence of human CYP1B1 missense genetic variants has been demonstrated, but their activities in metabolizing PhIP are unknown. In this study, we expressed 15 naturally occurring CYP1B1 variants (with either single or multiple amino acid substitutions) and determined their activity changes in metabolizing PhIP to its two major metabolites, 2-hydroxyamino-PhIP and 4'-hydroxy-PhIP. Although the PhIP-metabolizing activities of four variants (Ala(119)Ser, Pro(379)Leu, Ala(443)Gly, Arg(48)Gly/Leu(432)Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp(57)Cys, Gly(61)Glu, Arg(48)Gly/Ala(119)Ser, Arg(48)Gly/Ala(119)Ser/Leu(432)Val, Arg(48)Gly/Ala(119)Ser/Leu(432)Val/Ala(443)Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (V(max)/K(m)) for both N- and 4-hydroxylation of PhIP. Six variants (Gly(365)Trp, Glu(387)Lys, Arg(390)His, Pro(437)Leu, Asn(453)Ser, Arg(469)Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp(365), Lys(387), and His(390) variants and was not detectable for the Ser(453) variant. In contrast, there was no difference between the Trp(469) variant and the wild-type in the microsomal CYP1B1 protein level and P450 content but the Trp(469) variant totally lost its metabolic activity toward PhIP. The Leu(437) variant also had a substantial amount of CYP1B1 protein in the microsomes, but there was a lack of detectable P450 peak and activity. Our results should be useful in selecting appropriate CYP1B1 variants as cancer susceptibility biomarkers for human population studies related to PhIP exposure.
authors.affiliation: School of Public Health, University of Medicine and Dentistry of New Jersey, Room 385, 683 Hoes Lane West, Piscataway, NJ 08854, USA.
authors.forename: Jing-Fen
authors.initials: JF
authors.lastname: Han
authors.forename: Xiao-Yang
authors.initials: XY
authors.lastname: He
authors.forename: Jason S
authors.initials: JS
authors.lastname: Herrington
authors.forename: Lori A
authors.initials: LA
authors.lastname: White
authors.forename: Jun-Feng
authors.initials: JF
authors.lastname: Zhang
authors.forename: Jun-Yan
authors.initials: JY
authors.lastname: Hong
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D002460:Cell Line; D065633:Cytochrome P-450 CYP1B1; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism*; D014644:Genetic Variation / Q000235:genetics*; D006801:Humans; D007093:Imidazoles / Q000737:chemistry / Q000378:metabolism*; D007313:Insecta; D053858:Metabolic Networks and Pathways / Q000502:physiology; D008861:Microsomes / Q000378:metabolism; D051381:Rats; D013045:Species Specificity
chemical_list: D007093:Imidazoles; D003577:Cytochrome P-450 Enzyme System; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; C585499:Cyp1b1 protein, rat; D065633:Cytochrome P-450 CYP1B1