TDCPP exposure affects the concentrations of thyroid hormones in zebrafish

Previous studies show that TDCPP may interrupt the thyroid endocrine system, however, the potential mechanisms involved in these processes were largely unknown. In this study, zebrafish embryos/larvae were exposed to TDCPP until 120 hpf, by which time most of the organs of the larvae have completed development. In this study, the effects of TDCPP on HPT axis were examined and the thyroid hormone levels were measured after TDCPP treatment. Zebrafish (Danio rerio) embryos were treated with a series concentration of TDCPP (10, 20, 40, 80, 160 and 320 g/L) from 1 day post-fertilization (dpf) to 5 dpf. Exposure concentrations of TDCPP were determined based on the survival rates in each group. Total mRNA were isolated, first-strand cDNA were synthesis and qPCR were performed to detect the mRNA expression levels in hypothalamic-pituitary-thyroid (HPT) axis. The mRNA expression levels of genes involved in thyroid hormone homeostasis were increased in the TDCPP-treated larvae. The mRNA levels of genes involved in thyroid hormone synthesis were also increased in the embryos treated with TDCPP. Furthermore, exposure to TDCPP led to a dose-dependent effect on zebrafish development, including diminished hatching and survival rates, increased malformation. TDCPP treatment significantly reduced the T4 concentration in the 5 dpf zebrafish larvae, but increased the concentration of T3, suggesting the function of thyroid endocrine were interrupted in the TDCPP-exposed zebrafish. Taken together, these data indicated that TDCPP affected the thyroid hormone levels in the zebrafish larvae and could increased the mRNA expression levels of genes related to HPT axis, which further impaired the endocrine homeostasis and thyroid system.