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Title
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Biotransformation of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) by human liver microsomes : identification of cytochrome P450 2B6 as the major enzyme involved
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Author
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Abstract
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| 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. |
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Language
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English
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Source (journal)
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Chemical research in toxicology / American Chemical Society. - Washington, D.C.
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Publication
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Washington, D.C.
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2013
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ISSN
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0893-228X
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DOI
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10.1021/TX300522U
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Volume/pages
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26
:5
(2013)
, p. 721-731
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ISI
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000319720500011
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Full text (Publisher's DOI)
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