ToxSci Advance Access originally published online on August 17, 2005
Toxicological Sciences 2005 88(1):127-133; doi:10.1093/toxsci/kfi288
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Published by Oxford University Press 2005.
Differential Expression of CYP1A, 2B, and 3A Genes in the F344 Rat following Exposure to a Polybrominated Diphenyl Ether Mixture or Individual Components
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* Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences (NIEHS), Research Triangle Park, North Carolina 27709; Department of Toxicology, North Carolina State University, Raleigh, North Carolina 27695; and Battelle, Columbus, Ohio 43201
Received May 17, 2005; accepted August 11, 2005
Polybrominated diphenyl ethers (PBDEs), used as flame retardants, have been detected in the environment and in mammalian tissues and fluids. Evidence indicates that PBDE mixtures induce CYPs through aryl hydrocarbon receptor (AhR)-dependent and -independent pathways. The present work has investigated the effects of individual components of a commercial PBDE mixture (DE71) on expression of CYP1A1, a biomarker for activation of the AhR (dioxin-like), and CYP2B and CYP3A, biomarkers for activation of the constitutive androstane and pregnanexreceptors (CAR and PXR), respectively, in the rat. Male F344 rats were dosed orally on three consecutive days with either DE71, PBDE components, 2,2',4,4'-tetraBDE (BDE47), 2,2',4,4',5-pentaBDE (BDE99), 2,2',4,4',5,5'-hexaBDE (BDE153), representative polybrominated dibenzofurans (PBDFs) present in DE71, or reference PCBs. Differential expression of target genes was determined in liver 24 h after the last dose. Quantitative PCR analysis indicated up-regulation of CYP1A1 by DE71; however, the response was weak compared to that for dioxin-like PCB126. Individual PBDE components of DE71 up-regulated CYP1A1 only at the highest administered dose (100 µmol/kg/day). Representative PBDFs efficiently up-regulated CYP1A1; therefore, they, along with other PBDFs and polybrominated dibenzodioxins detected in DE71 and individual PBDE components, may be responsible for most, if not all, dioxin-like properties previously observed for PBDEs. Conversely, PBDEs appear capable of up-regulating CYP2B and CYP3A in rats at doses similar to that for non-dioxin-like PCB153. These results indicate that in vivo PBDE-mediated toxicity would be better categorized by AhR-independent mechanisms, rather than the well-characterized AhR-dependent mechanism associated with exposure to dioxin-like chemicals.
Key Words: polybrominated diphenyl ethers; polybrominated dibenzodioxins and dibenzofurans; polychlorinated biphenyls; persistent organic compounds; gene expression; quantitative RT-PCR.
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