title: Theoretical calculation of triazolam hydroxylation and endogenous steroid inhibition in the active site of CYP3A4.
abstract: CYP3A4 has unusual kinetic characteristics because it has a large active site. CYP3A4 produced more 4-hydroxytriazolam than alpha-hydroxytriazolam at concentrations of more than 60 muM triazolam, and different steroids had different inhibitory effects on the system. To clarify these interesting observations, the interactions between substrate and substrate/steroid were investigated by theoretical calculations. When two triazolam molecules were docked into the active site, the distance between the O-atom and the 4-hydroxylated site was less than the distance to the alpha-hydroxylated site because of interaction between the two triazolam molecules. Estradiol inhibited both alpha- and 4-hydroxytriazolam formation by 50%. Dehydroepiandrosterone (DHEA) inhibited alpha-hydroxylation more than 4-hydroxytriazolam formation, whereas aldosterone had no effect. When one triazolam molecule and one steroid molecule were simultaneously docked, estradiol increased the distance between the O-atom and the two hydroxylated sites, DHEA only increased the distance between the O-atom and alpha-hydroxylated site, and aldosterone did not change the distances. The relevant angles of Fe-O-C in the hydroxylated site of triazolam also widened, together with increased distance. These findings indicate that formation of a substrate and substrate/effector complex in the active site may be a factor for determining the enzyme kinetic parameters of CYP3A4.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1, Inohana, Chuo-ku, Chiba 260-8675, Japan.
authors.forename: Nao
authors.initials: N
authors.lastname: Torimoto
authors.forename: Itsuko
authors.initials: I
authors.lastname: Ishii
authors.forename: Masayuki
authors.initials: M
authors.lastname: Hata
authors.forename: Yukari
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Nakamura
authors.forename: Noritaka
authors.initials: N
authors.lastname: Ariyoshi
authors.forename: Mitsukazu
authors.initials: M
authors.lastname: Kitada
mesh_terms: D001665:Binding Sites; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000378:metabolism*; D003687:Dehydroepiandrosterone / Q000502:physiology*; D006801:Humans; D006900:Hydroxylation; D014229:Triazolam / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D014229:Triazolam; D003687:Dehydroepiandrosterone; D003577:Cytochrome P-450 Enzyme System; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human