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Interaction of BDE-47 and its Hydroxylated Metabolite 6-OH-BDE-47 with the Human ABC Efflux Transporters P-gp and BCRP: Considerations for Human Exposure and Risk Assessment
Marchitti, S., Chris Mazur, C. Dillingham, S. Rawat, A. Sharma, J. Zastre, AND J. Kenneke. Interaction of BDE-47 and its Hydroxylated Metabolite 6-OH-BDE-47 with the Human ABC Efflux Transporters P-gp and BCRP: Considerations for Human Exposure and Risk Assessment. SOT 2016, New Orleans, LA, March 13 - 17, 2016.
ATP binding cassette (ABC) transporters, including P-glycoprotein (P-gp; also known as MDR1, ABCB1) and breast cancer resistance protein (BCRP; also known as ABCG2), are membrane-bound proteins that mediate the cellular efflux of xenobiotics as an important defense against chemical toxins. Exposure to various environmental chemicals, including brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs), can result in changes in the gene expression of these transport proteins, however, little information exists on how environmental chemicals (e.g., PBDEs) and their metabolites interact with ABC transporters. The purpose of the present study was to assess the interaction of BDE-47 and its hydroxylated metabolite, 6-OH-BDE-47, with P-gp and BCRP, using MDR1- and BCRP-expressing membrane vesicles and stably transfected NIH-3T3-MDR1 and MDCK-BCRP cell lines. Results from membrane vesicle assays measuring P-gp-mediated transport of probe substrates demonstrated that, while the parent compound BDE-47 had no measurable effect on P-gp activity, 6-OH-BDE-47 was a potent P-gp inhibitor (IC50 = 11.7 μM). BDE-47 was found to inhibit BCRP activity in a dose response manner, however, 6-OH-BDE-47 was a stronger inhibitor [IC50 = 45.9 μM (BDE-47) vs. IC50 = 9.4 μM (6-OH-BDE-47)]. Active (ATPdependent) transport of BDE-47 and 6-OH-BDE-47 was not detected in membrane vesicles. In addition, no significant protection against these compounds was observed in cytotoxicity assays performed on P-gp and BCRP over-expressing cell lines (NIH-3T3-MDR1 and MDCKBCRP, respectively). Collectively, these data indicate that neither BDE-47 nor 6-OH-BDE-47 are substrates of P-gp or BCRP. Intracellular concentrations of radiolabeled P-gp and BCRP substrates [(3H)-paclitaxel and (3H)-prazosin, respectively] were significantly higher (indicating less efflux) in both NIH-3T3-MDR1 and MDCK-BCRP cells in the presence of 6-OH-BDE-47, but not BDE-47, as compared to control cells. To our knowledge, these results are the first to show that the BDE-47 metabolite 6-OH-BDE-47 is a strong inhibiter of both P-gp and BCRP. Thus, some of the biological effects that have been attributed in the past to BDE-47 in biological systems may, in fact, be due to its metabolite 6-OH-BDE-47. Implications for xenobiotic efflux and considerations for human exposure and risk assessment are discussed.
To be presented at Society of Toxicology (SOT) conference, New Orleans, LA March 13-17, 2016.
Record Details:Record Type: DOCUMENT (PRESENTATION/POSTER)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL EXPOSURE RESEARCH LAB
ECOSYSTEMS RESEARCH DIVISION