Abstract
2,2′,4,4′-Tetra-bromodiphenyl ether (BDE-47), an important congener among polybrominated diphenyl ether (PBDE) compounds, has been predominantly in environmental samples and human tissue. Thyroid disruption is the most sensitive endpoint effect among a number of health effects of exposure to BDE-47 in animals and humans. However, the detailed underlying mechanisms in humans are not well understood. In the present study, human pregnane X receptor (hPXR)-overexpressing HepG2 cell model and a dual-luciferase reporter assay system were constructed to investigate the role of hPXR in BDE-47–induced alterations of expression of metabolic enzymes and TR in vitro. The results showed that hPXR was significantly activated by BDE-47, and expression levels of both mRNA and protein of the thyroid receptor (TR) isoforms TRα1 and TRβ1 were decreased in hPXR-overexpressing HepG2 cells after BDE-47 treatment. However, the increased expression of hepatic microsomal phase I enzyme CYP3A4 and phase II enzymes, UGT1A3 and SULT2A1 were also found. Taken together, the results indicated that BDE-47 was a strong hPXR activator, activation of hPXR played an important role in BDE-47–induced down-regulation of TR, and up-regulations of CYP3A4, UGT1A3, and SULT2A1 participated in the process, which may provide more toxicological evidence on mechanisms of disruption of thyroid hormone induced by BDE-47.
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