Alpha and Beta Isomers of Tetrabromoethylcyclohexane (TBECH) Flame Retardant: Depletion and Metabolite Formation In Vitro Using a Model Rat Microsomal Assay

The metabolism of α- and β-isomers of the flame retardant chemical tetrabromoethylcyclohexane (TBECH) was investigated using a model in vitro enzyme-mediated biotransformation assay based on rat liver microsomes. In enzymatically active assays, concentrations of both α- and β-TBECH isomers were equa...

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Bibliographic Details
Published in:Environmental science & technology 2012-09, Vol.46 (18), p.10263-10270
Main Authors: Chu, Shaogang, Gauthier, Lewis T, Letcher, Robert J
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
Chemical and industrial products toxicology. Toxic occupational diseases
Chemical compounds
Cyclohexanes - analysis
Cyclohexanes - metabolism
Environmental Pollutants - analysis
Environmental Pollutants - metabolism
Environmental science
Enzymes
Flame retardants
Flame Retardants - analysis
Flame Retardants - metabolism
Gas Chromatography-Mass Spectrometry
Isomerism
Medical sciences
Metabolism
Metabolites
Microsomes, Liver - metabolism
Models, Molecular
Rats
Rodents
Tandem Mass Spectrometry
Toxicology
Various organic compounds
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Summary:The metabolism of α- and β-isomers of the flame retardant chemical tetrabromoethylcyclohexane (TBECH) was investigated using a model in vitro enzyme-mediated biotransformation assay based on rat liver microsomes. In enzymatically active assays, concentrations of both α- and β-TBECH isomers were equally depleted by about 40% and in a time-dependent fashion over a 60-min assay incubation period, and determined by GC-MS(ECNI) analysis. No such depletion was observed in nonenzymatically active control assays. After the full 60-min assay incubation period, debrominated TBECH metabolites were not detected by GC-MS(ECNI), and suggested that enzyme-mediated debromination of TBECH did not occur via cyctochrome P450 enzyme-mediated catalysis or that the rate of TBECH metabolism in vitro was too slow. In the enzymatically active assays, but not in the nonezymatically active control assays, α- and β-monohydroxy-TBECH (OH-TBECH), dihydroxy-TBECH ((OH)2-TBECH), and some additional compounds with molecular formulas of C8H13Br3O2 and C8H11Br3O2 were identified by LC-Q-ToF-MS. Two unique sets of OH-TBECH and (OH)2-TBECH metabolites were derived from both α- and β-TBECH isomers. The LC-ESI(−)-MS/MS peak areas of all four OH-TBECH and (OH)2-TBECH metabolites increased at a comparable rate in a time-dependent manner over a 60-min assay incubation period. This study demonstrated that metabolism via hydroxylation can occur in vitro for α- and β-TBECH. These results underscore the importance of understanding the biological fate of TBECH and the possible implications on the health and TBECH levels in exposed wildlife and in the environment.
ISSN:0013-936X
1520-5851
DOI:10.1021/es301546h