The Thyroid-Disrupting Effects Of Several Typical Contaminants On Zebrafish

In this study, two chloroacetamides butachlor, acetochlor (ACT) and three synthetic pyrethroids (SPs) including permethrin (PM), bifenthrin (BF) and λ-cyhalothrin (λ-CH) as well as one of anti-inflammatory drugs (naproxen, NPX) were chosen as representative compounds. We investigated their mechanism of toxicity according to their endocrine disrupting effects using zebrafish as a model organism. Firstly, we studied the developmental toxicity, estrogen effects and immunetoxicity of butachlor as well as their mechanisms from the perspective of the interaction of endocrine disrupting effects and immunotoxicity. And the enantioselectivity on the developmental toxicity, thyroid toxicity and immunetoxicity of ACT as well as their mechanisms were further explored. Secondly, we established the dynamics of uptake and elimination of three SPs in zebraifsh eleutheroembryos from the perspective of bioaccumulation, and on this basis, we studied their effects on the thyroid hormone levels and gene transcription in the hypothalamic-pituitary-thyroid (HPT) axis. Finally, we compared the differences in metabolic, thyroid disruption and bioaccumulation between 96h and60d of exposure21-d juvenile zebrafish to NPX from the perspective of the toxic effects of short-term and long-term exposure.The results are as follows:(1) Butachlor significantly reduced embryo survival and hatching rate, and resulted in a series of malformations, including yolk sac edema, pericardial edema and crooked body. The transcription of genes related to the innate immune system (IL-1β, CC-chem and IL-8) and Vtgl were significantly up-regulated. The embryo enantioselectivity toxicities of ACT were observed in the development of zebrafish. ACT could alter the transcription of genes of HPT axis (TRa, TRβ, Dio2and TSHβ) and the (+)-S-ACT showed more strong thyroid-disrupting effect than (-)-R-ACT. However, as for the genes related to the innate immune system (IL-1β, CC-chem, CXCL-Clc and IL-8), the (-)-R-ACT showed more strong effect than (+)-S-ACT. The results suggested that the endocrine-disrupting effect of chloroacetamides on fish had a certain relationship with immunotoxicity, and exhibiting enantioselectivity toxicity.(2) During the uptake period, eleutheroembryo concentrations of the three SPs increased quickly with uptake curves that were linear (R2>0.85). The bioaccumulation factors ranged from140.5to586.7. The elimination of SPs was slowly and followed the first-order process. The elimination rate constants (k) ranged from0.018h-1to0.0533h-1and the half-life (t1/2) ranged from13.0h to38.5h. The selective enrichment and elimination of PM isomers were observed. PM and λ-CH resulted in a significant decrease in body weight. Three SPs altered the level of thyroid hormone and the transcriptions of genes of the HPT axis, which plays an important role in the transport, synthesis, metabolism of thyroid hormone. SPs could be accumulated in zebrafish and the bioaccumulation of them is concentration dependent. These results indicated that SPs had a significant bioaccumulation effect in zebrafish and thyroid-disrupting effect.(3) Short-term exposure (96h) of NPX induced the expression of CYP1A, CYP2J26, TRs, while long-term exposure (60d) of NPX significantly inhibited the expression of CYP2J26, CYP3A, TRs and Dio2, and existed a significant bioaccumulation effect. The above results show that there is a significant differences in short-term and long-term effects. The endocrine-disrupting effect of NPX were closely related to their metabolism and accumulation.