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UBC Theses and Dissertations

In vitro metabolism of 2,2',4,4'-tetrabromodiphenyl ether Moffatt, Sarah


Polybrominated diphenyl ethers (PBDEs) are halogenated aromatic hydrocarbons that have been used as additive flame-retardants in a variety of consumer products since 1965. The widespread use of PBDEs coupled with their high lipophilicity and chemical stability resulted in the ubiquitous distribution of PBDEs in the environment. 2,2',4,4-Tetrabromodiphenyl ether (BDE-47) is among the most prevalent PBDE detected in human, wildlife, and abiotic samples. BDE-47 has been detected in air, sediment, fish, marine mammals, and in human blood, adipose tissue, and breast milk. Laboratory studies have shown that PBDEs can be metabolized by hepatic cytochrome P450 (CYP) enzymes to hydroxylated PBDEs (OH-PBDEs). OH-PBDEs are of toxicological interest as OH-PBDEs show greater affinity for the thyroid hormone receptor than the natural ligand or PBDEs. OH-PBDEs have been detected in blood and feces of rodents treated with BDE-47 and various OH-PBDEs have been found in human plasma. The most common method for the detection and quantification of PBDEs and OH-PBDEs in environmental samples has been gas chromatography-mass spectrometry (GC/MS). GC-based methods are sensitive, but require derivatization of OH-PBDEs. Ultra performance liquid chromatography coupled with mass spectrometry (UPLC/MS) provides an alternative analytical technique that does not require derivatization. Although several UPLC/MS methods have been used to detect and quantify OH-PBDEs, a fully validated UPLC/MS method does not exist. The UPLC/MS method used in the present study was validated to detect and quantify two OH-tri-BDEs and five OH-tetra-BDEs in rat hepatic microsomes. This method was then applied to investigate the biotransformation of BDE-47 using hepatic microsomes prepared from rats that had been pretreated with known CYP enzyme inducers and using a panel of rat recombinant CYP enzymes. Five OH-tetra-BDE metabolites were identified (4-OH-BDE-42, 3-OH-BDE-47, 5-OH-BDE-47, 6-OH-BDE-47, and 4'-OH-BDE-49). The formation of OH-tri-BDEs was not detected. The kinetic parameters of all identified metabolites, with the exception of 6-OH-BDE-47, were determined. Using the rat recombinant enzyme panel, CYP1A1, CYP2A2, CYP2B1, CYP2C6, and CYP3A1 were identified as being involved in the biotransformation of BDE-47.

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