title: Biotransformation of BDE-47 to potentially toxic metabolites is predominantly mediated by human CYP2B6.
abstract: BACKGROUND
  Previous studies have indicated that cytochrome P450s (CYPs) are involved in the metabolism of polybrominated diphenyl ether (PBDE) flame retardants in humans, resulting in the formation of hydroxylated PBDEs (OH-PBDEs) that are potentially more toxic than the parent PBDEs. However, the specific enzymes responsible for the formation of OH-PBDEs are unknown.
  
  
  OBJECTIVE
  The purposes of this study were to characterize the in vitro metabolism of 2,2´,4,4´-tetrabromodiphenyl ether (BDE-47) by human liver microsomes (HLM) and recombinant human CYPs, and to identify the CYP(s) that are active in the oxidative metabolism of BDE-47.
  
  
  METHODS
  Recombinant human CYPs (CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4) were incubated with BDE-47 (20 µM), and the metabolites were measured and characterized using gas chromatography with tandem mass spectrometry (GC-MS/MS). For kinetic studies, CYP2B6 and pooled human liver microsomes (HLMs) were incubated with BDE-47 (0-60 µM).
  
  
  RESULTS
  CYP2B6 was the predominant CYP capable of forming six OH-BDEs, including 3-OH-BDE-47, 5-OH-BDE-47, 6-OH-BDE-47, 4-OH-BDE-42, 4´-OH-BDE-49, and a metabolite tentatively identified as 2´-OH-BDE-66. On the basis of full-scan GC-MS analysis, we hypothesized the formation of two other metabolites: di-OH-tetra-BDE and di-OH-tetrabrominated dioxin. In kinetic studies of BDE-47 metabolism by CYP2B6 and pooled HLMs, we found Km values ranging from 3.8 to 6.4 µM and 7.0 to 11.4 µM, respectively, indicating the high affinity toward the formation of OH-BDEs.
  
  
  CONCLUSIONS
  Our findings support a predominant role of CYP2B6 in the metabolism of BDE-47 to potentially toxic metabolites, including a hypothesized di-OH-tetrabrominated dioxin metabolite. These results will assist future epidemiological studies investigating the potential of PBDEs and their metabolites to produce neurobehavioral/neurodevelopmental disorders.
authors.affiliation: Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA.
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Feo
authors.forename: Michael S
authors.initials: MS
authors.lastname: Gross
authors.forename: Barbara P
authors.initials: BP
authors.lastname: McGarrigle
authors.forename: Ethel
authors.initials: E
authors.lastname: Eljarrat
authors.forename: Damià
authors.initials: D
authors.lastname: Barceló
authors.forename: Diana S
authors.initials: DS
authors.lastname: Aga
authors.forename: James R
authors.initials: JR
authors.lastname: Olson
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D065702:Cytochrome P-450 CYP2B6; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004781:Environmental Exposure; D004785:Environmental Pollutants / Q000493:pharmacokinetics*; D005411:Flame Retardants / Q000493:pharmacokinetics*; D008401:Gas Chromatography-Mass Spectrometry; D055768:Halogenated Diphenyl Ethers / Q000493:pharmacokinetics*; D006801:Humans; D007700:Kinetics; D008862:Microsomes, Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D053719:Tandem Mass Spectrometry
chemical_list: D004785:Environmental Pollutants; D005411:Flame Retardants; D055768:Halogenated Diphenyl Ethers; D011994:Recombinant Proteins; C511295:2,2',4,4'-tetrabromodiphenyl ether; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; D010089:Oxidoreductases, N-Demethylating