Disruption of thyroid endocrine in zebrafish exposed to BDE-209

Polybrominated diphenyl ethers (PBDs) could adversely affect the thyroid endocrine system; previous studies report that BDE-209 has the potential effect on the fish thyroid endocrine system. In this study, we aimed to verify the bioconcentration and metabolism of BDE-209 in zebrafish. One day post-fertilization (dpf) zebrafish embryos were treated with different concentrations of BDE-209 (0, 0.01, 0.1 and 1 mg/L) until 10 dpf. BDE-209 was obviously accumulated in the zebrafish after 10 days exposure, and the metabolic products such as octa-BDE and nona-BDE were detected. After treated with BDE-209, the triiodthyronine (T3) and thyroxine (T4) levels were significantly decreased, suggesting that exposure to BDE-209 could disrupt the thyroid endocrine system in zebrafish. The transcriptional expression of genes involved in the hypothalamic-pituitary-thyroid (HPT) axis was altered. The mRNA expression levels of corticotrophin-releasing hormone (CRH) and thyroid-stimulating hormone (TSHβ) were significantly increased. The mRNA expression of pax8 and nkx2.1 which regulate thyroid development and synthesis were also increased. These data indicated that BDE-209 could disrupt the thyroid endocrine system in zebrafish, which could be assessed by hypothalamic-pituitary-thyroid axis.