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, Km and kcat, were estimated to be 0.8 μM and 1.8 min-1, respectively, for UGT1A1, 0.8 μM and 1.8 min-1, respectively, for UGT1A9, and 3.9 μM 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.
Footnotes
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This work was partly supported by Health Science Research grants from the Ministry of Health Labour and Welfare of Japan and a grant-in-aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan.
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ABBREVIATIONS: PCDD, polychlorinated dibenzo-p-dioxin; 2,3,7,8-tetraCDD, 2,3,7,8-tetrachloro-dibenzo-p-dioxin; DD, dibenzodioxin; DCDD, dichlorinated dibenzo-p-dioxin; P450, cytochrome P450; UGT, UDP-glucuronosyltransferase; Glc-UA, glucuronic acid; 8-OH-2,3,7-triCDD, 8-hydroxy-2,3,7-trichloro-dibenzo-p-dioxin; 2,3,7-triCDD, 2,3,7-trichloro-dibenzo-p-dioxin; MBP, maltose binding protein; kDa, kilodalton(s); HPLC, high-performance liquid chromatography; GC, gas chromatography; MS, mass spectrometry; PCDF, polychlorinated dibenzofuran.
- Received January 12, 2004.
- Accepted May 7, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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