title: Sequential metabolism of 2,3,7-trichlorodibenzo-p-dioxin (2,3,7-triCDD) by cytochrome P450 and UDP-glucuronosyltransferase in human liver microsomes.
abstract: Metabolism of polychlorinated dibenzo-p-dioxins by cytochrome P450 (P450) and UDP-glucuronosyltransferase (UGT) was examined using a recombinant enzyme system and human liver microsomes. We analyzed the glucuronidation of 2,3,7-trichlorodibenzo-p-dioxin (2,3,7-triCDD) by rat CYP1A1 expressed in yeast microsomes and human UGT expressed in baculovirus-infected insect cells. Multiple UGT isozymes showed glucuronidation activity toward 8-hydroxy-2,3,7-triCDD (8-OH-2,3,7-triCDD), which was produced by CYP1A1. Of these UGTs, UGT1A1, 1A9, and 2B7, which are constitutively expressed in human livers, showed remarkable activity toward 8-OH-2,3,7-triCDD. The apparent kinetic parameters of glucuronidation, K(m) and k(cat), were estimated to be 0.8 microM and 1.8 min(-1), respectively, for UGT1A1, 0.8 microM and 1.8 min(-1), respectively, for UGT1A9, and 3.9 microM and 7.0 min(-1), respectively, for UGT2B7. In human liver microsomes with NADPH and UDP-glucuronic acid, 2,3,7-triCDD was first converted to 8-OH-2,3,7-triCDD, then further converted to its glucuronide. We compared the ability of 10 human liver microsomes to metabolize 2,3,7-triCDD and observed a significant difference in the glucuronidation of 2,3,7-triCDD that originated from the difference of the P450-dependent hydroxylation of 2,3,7-triCDD.
authors.affiliation: Graduate School of Agrculture, Kyoto University, Kyoto, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kasai
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Sakaki
authors.forename: Raku
authors.initials: R
authors.lastname: Shinkyo
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Ikushiro
authors.forename: Takashi
authors.initials: T
authors.lastname: Iyanagi
authors.forename: Maya
authors.initials: M
authors.lastname: Kamao
authors.forename: Toshio
authors.initials: T
authors.lastname: Okano
authors.forename: Miho
authors.initials: M
authors.lastname: Ohta
authors.forename: Kuniyo
authors.initials: K
authors.lastname: Inouye
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006801:Humans; D008862:Microsomes, Liver / Q000201:enzymology*; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000378:metabolism*; D051381:Rats
chemical_list: D000072317:Polychlorinated Dibenzodioxins; D003577:Cytochrome P-450 Enzyme System; D014453:Glucuronosyltransferase