Sequential metabolism of 2,3,7-trichlorodibenzo-p-dioxin (2,3,7-triCDD) by cytochrome P450 and UDP-glucuronosyltransferase in human liver microsomes.
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.
Kasai
Noriyuki
N
Graduate School of Agrculture, Kyoto University, Kyoto, Japan.
Sakaki
Toshiyuki
T
Shinkyo
Raku
R
Ikushiro
Shin-Ichi
S
Iyanagi
Takashi
T
Kamao
Maya
M
Okano
Toshio
T
Ohta
Miho
M
Inouye
Kuniyo
K
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
D000072317:Polychlorinated Dibenzodioxins; D003577:Cytochrome P-450 Enzyme System; D014453:Glucuronosyltransferase