title: Effects of endogenous steroids on CYP3A4-mediated drug metabolism by human liver microsomes.
abstract: In the present study, we investigated the effects of 14 endogenous steroids on the CYP3A4-mediated drug metabolism by human liver microsomes in vitro. Nevirapine (NVP) 2-, 12-hydroxylations, carbamazepine (CBZ) 10,11-epoxidation, triazolam (TZM) 1'-, 4-hydroxylations, erythromycin (EM) N-demethylation, and 2-sulphamoylacetylphenol (SMAP) formation from zonisamide (ZNS) were investigated. The activities of the NVP 2-, 12-hydroxylations, the CBZ 10,11-epoxidation, and the TZM 4-hydroxylation were activated by endogenous androgens, such as androstenedione (AND), testosterone, and dehydroepiandrosterone. However, these androgens inhibited EM N-demethylation, TZM 1'-hydroxylation, and SMAP formation. To understand the mechanisms of these effects of androgens on CYP3A4 activities, we performed a kinetic analysis of the metabolism of CBZ and ZNS in the presence or absence of AND using the modified two-site equation model. The addition of AND to the reaction mixture caused a drastic increase in the activity of CBZ 10,11-epoxidase, especially at a low substrate concentration, and resulted in a change in the kinetics from the sigmoid to Michaelis-Menten type. On the other hand, the metabolism of ZNS was strongly inhibited by AND, although no allosteric change was observed in this case. These data demonstrate that endogenous steroids, especially androgens, strongly affect CYP3A4-mediated drug metabolism in vitro. The postulated mechanisms of the interactions between AND and CBZ or ZNS are discussed.
authors.affiliation: Division of Pharmacy, Chiba University Hospital, Chuo-ku, Chiba, Japan.
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Nakamura
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Nakasa
authors.forename: Itsuko
authors.initials: I
authors.lastname: Ishii
authors.forename: Noritaka
authors.initials: N
authors.lastname: Ariyoshi
authors.forename: Takashi
authors.initials: T
authors.lastname: Igarashi
authors.forename: Shigeru
authors.initials: S
authors.lastname: Ohmori
authors.forename: Mitsukazu
authors.initials: M
authors.lastname: Kitada
mesh_terms: D000328:Adult; D002220:Carbamazepine / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004852:Epoxy Compounds / Q000378:metabolism; D004917:Erythromycin / Q000378:metabolism; D006801:Humans; D006900:Hydroxylation; D066298:In Vitro Techniques; D007555:Isoxazoles / Q000378:metabolism; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects* / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019829:Nevirapine / Q000378:metabolism; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D010636:Phenols / Q000378:metabolism; D013256:Steroids / Q000494:pharmacology*; D013449:Sulfonamides / Q000378:metabolism; D014229:Triazolam / Q000378:metabolism; D000078305:Zonisamide
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D004852:Epoxy Compounds; D007555:Isoxazoles; D004364:Pharmaceutical Preparations; D010636:Phenols; D013256:Steroids; D013449:Sulfonamides; D014229:Triazolam; D002220:Carbamazepine; D000078305:Zonisamide; D004917:Erythromycin; C077805:2-sulfamoylacetylphenol; D003577:Cytochrome P-450 Enzyme System; D019829:Nevirapine; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human