title: Biotransformation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) by human liver microsomes: identification of cytochrome P450 2B6 as the major enzyme involved.
abstract: Polybrominated diphenyl ethers (PBDEs) were widely used flame retardants that have become persistent environmental pollutants. In the present study, we investigated the in vitro oxidative metabolism of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), a major PBDE detected in human tissue and environmental samples. Biotransformation of BDE-47 by pooled and individual human liver microsomes and by human recombinant cytochrome P450 (P450) enzymes was assessed using a liquid chromatography/tandem mass spectrometry-based method. Of the nine hydroxylated metabolites of BDE-47 produced by human liver microsomes, seven metabolites were identified using authentic standards. A monohydroxy-tetrabrominated and a dihydroxy-tetrabrominated metabolite remain unidentified. Kinetic analysis of the rates of metabolite formation revealed that the major metabolites were 5-hydroxy-2,2',4,4'-tetrabromodiphenyl ether (5-OH-BDE-47), 6-hydroxy-2,2',4,4'-tetrabromodiphenyl ether (6-OH-BDE-47), and possibly the unidentified monohydroxy-tetrabrominated metabolite. Among the human recombinant P450 enzymes tested, P450 2B6 was the most active enzyme in the formation of the hydroxylated metabolites of BDE-47. Moreover, the formation of all metabolites of BDE-47 by pooled human liver microsomes was inhibited by a P450 2B6-specific antibody and was highly correlated with P450 2B6-mediated activity in single donor liver microsomes indicating that P450 2B6 was the major P450 responsible for the biotransformation of BDE-47. Additional experiments involving the incubation of liver microsomes with individual monohydroxy-tetrabrominated metabolites in place of BDE-47 demonstrated that 2,4-dibromophenol was a product of BDE-47 and several primary metabolites, but the dihydroxy-tetrabrominated metabolite was not formed by sequential hydroxylation of any of the monohydroxy-tetrabrominated metabolites tested. The present study provides a comprehensive characterization of the oxidative metabolism of BDE-47 by human liver microsomes and P450 2B6.
authors.affiliation: Faculty of Pharmaceutical Sciences, The University of British Columbia , Vancouver, British Columbia, Canada V6T 1Z3.
authors.forename: Claudio A
authors.initials: CA
authors.lastname: Erratico
authors.forename: András
authors.initials: A
authors.lastname: Szeitz
authors.forename: Stelvio M
authors.initials: SM
authors.lastname: Bandiera
mesh_terms: D000906:Antibodies / Q000494:pharmacology; D001711:Biotransformation / Q000187:drug effects; D065702:Cytochrome P-450 CYP2B6 / Q000378:metabolism*; D055768:Halogenated Diphenyl Ethers / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D015394:Molecular Structure; D010084:Oxidation-Reduction
chemical_list: D000906:Antibodies; D055768:Halogenated Diphenyl Ethers; C511295:2,2',4,4'-tetrabromodiphenyl ether; D065702:Cytochrome P-450 CYP2B6