title: Identification of human hepatic cytochrome P450 enzymes involved in the metabolism of 8-prenylnaringenin and isoxanthohumol from hops (Humulus lupulus L.).
abstract: The female flowers of hops (Humulus lupulus L.) are used in the brewing of beer and are under investigation for use in dietary supplements for the management of menopausal symptoms in women. Hop extracts contain the weakly estrogenic compound isoxanthohumol (IX), proestrogenic xanthohumol, and the potent estrogen 8-prenylnaringenin (8PN). Because IX can be metabolized in the human liver to form 8PN, the specific cytochrome P450 (P450) enzymes responsible for this O-demethylation reaction were identified. In addition, the enzymes that convert IX and 8PN to their most abundant metabolites were identified because these metabolic pathways might also affect the estrogenicity of hop preparations. Specifically, the P450 enzymes that catalyze the oxidation of the prenyl side chains of IX and 8PN into trans- or cis-alcohols were investigated. Human liver microsomes and monoclonal antibodies that inhibit specific P450 enzymes were used in combination with liquid chromatography/mass spectrometry to identify the enzymes responsible for these transformations. CYP2C19 was found to catalyze the formation of both cis- and trans-alcohols of the prenyl side chain of 8PN with K(m) values of 14.8 +/- 3.2 and 16.6 +/- 4.6 microM, respectively. CYP2C8 converted 8PN regioselectively to the trans-alcohol of the prenyl group with a K(m) of 3.7 +/- 0.9 microM. Finally, CYP1A2 was found to catalyze the O-demethylation of IX to generate 8PN, with a K(m) value of 17.8 +/- 3.7 microM. These results suggest that the estrogenicity of hop constituents in vivo will depend in part on metabolic conversion that may show individual variation.
authors.affiliation: Department of Medicinal Chemistry and Pharmacognosy, University of Illinois College of Pharmacy, University of Illinois at Chicago/National Institutes of Health Center for Botanical Dietary Supplements Research, IL 60612-7231, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Guo
authors.forename: Dejan
authors.initials: D
authors.lastname: Nikolic
authors.forename: Lucas R
authors.initials: LR
authors.lastname: Chadwick
authors.forename: Guido F
authors.initials: GF
authors.lastname: Pauli
authors.forename: Richard B
authors.initials: RB
authors.lastname: van Breemen
mesh_terms: D000911:Antibodies, Monoclonal; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D019388:Cytochrome P-450 CYP1A2 / Q000276:immunology / Q000378:metabolism*; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065731:Cytochrome P-450 CYP2C19; D065727:Cytochrome P-450 CYP2C8; D003640:Dealkylation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D044950:Flavanones / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D027582:Humulus / Q000737:chemistry*; D006900:Hydroxylation; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D009853:Omeprazole / Q000494:pharmacology; D011794:Quercetin / Q000494:pharmacology; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D044004:Xanthones / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: C119737:8-prenylnaringenin; D000911:Antibodies, Monoclonal; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D004791:Enzyme Inhibitors; D044950:Flavanones; D044004:Xanthones; C512910:isoxanthohumol; D011794:Quercetin; D013806:Theophylline; C050131:furafylline; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C504573:CYP1A2 protein, human; C045793:CYP2C19 protein, human; C450259:CYP2C8 protein, human; D019388:Cytochrome P-450 CYP1A2; D065731:Cytochrome P-450 CYP2C19; D065727:Cytochrome P-450 CYP2C8; D009853:Omeprazole