title: Primary role of cytochrome P450 2B6 in the oxidative metabolism of 2,2',4,4',6-pentabromodiphenyl ether (BDE-100) to hydroxylated BDEs.
abstract: Human exposure to polybrominated diphenyl ethers (PBDEs) through various routes poses deleterious health effects. PBDEs are biotransformed into hydroxylated metabolites (OH-BDEs) via cytochrome P450s (P450s), which may add to their neurotoxic effects. This study characterizes the in vitro metabolism of 2,2',4,4',6-pentabromodiphenyl ether (BDE-100), one of the most abundant PBDE congeners found in humans, by recombinant human P450s and pooled human liver microsomes (HLMs). Ten recombinant P450s were individually incubated with BDE-100 to monitor P450-specific metabolism. P450 2B6 was found to be the predominant enzyme responsible for nearly all formation of six mono-OH-pentaBDE and two di-OH-pentaBDE metabolites. Four metabolites were identified as 3-hydroxy-2,2',4,4',6-pentabromodiphenyl ether (3-OH-BDE-100), 5'-hydroxy-2,2',4,4',6-pentabromodiphenyl ether (5'-OH-BDE-100), 6'-hydroxy-2,2',4,4',6-pentabromodiphenyl ether (6'-OH-BDE-100), and 4'-hydroxy-2,2',4,5',6-pentabromodiphenyl ether (4'-OH-BDE-103) through use of reference standards. The two remaining mono-OH-pentaBDE metabolites were hypothesized using mass spectral fragmentation characteristics of derivatized OH-BDEs, which allowed prediction of an ortho-OH-pentaBDE and a para-OH-pentaBDE positional isomer. Additional information based on theoretical boiling point calculations using COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) and experimental chromatographic retention times were used to identify the hypothesized metabolites as 2'-hydroxy-2,3',4,4',6-pentabromodiphenyl ether (2'-OH-BDE-119) and 4-hydroxy-2,2',4',5,6-pentabromodiphenyl ether (4-OH-BDE-91), respectively. Kinetic studies of BDE-100 metabolism using P450 2B6 and HLMs revealed Km values ranging from 4.9 to 7.0 μM and 6-10 μM, respectively, suggesting a high affinity toward the formation of OH-BDEs. Compared to the metabolism of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) reported in previous studies, BDE-100 appears to be more slowly metabolized by P450s due to the presence of a third ortho-substituted bromine atom.
authors: †Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260, United States.
authors: Michael S
authors: MS
authors: Gross
authors: †Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260, United States.
authors: Deena M
authors: DM
authors: Butryn
authors: ‡Department of Pharmacology and Toxicology and Department of Epidemiology and Environmental Health, University at Buffalo, The State University of New York, Buffalo, New York 14214, United States.
authors: Barbara P
authors: BP
authors: McGarrigle
authors: †Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260, United States.
authors: Diana S
authors: DS
authors: Aga
authors: ‡Department of Pharmacology and Toxicology and Department of Epidemiology and Environmental Health, University at Buffalo, The State University of New York, Buffalo, New York 14214, United States.
authors: James R
authors: JR
authors: Olson
mesh_terms: D065702:Cytochrome P-450 CYP2B6 / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D010084:Oxidation-Reduction; D011075:Polybrominated Biphenyls / Q000633:toxicity*
chemical_list: D011075:Polybrominated Biphenyls; C517827:pentabrominated diphenyl ether 100; D065702:Cytochrome P-450 CYP2B6