| ObjectiveTo study the toxic effects of long-term exposure to environmental doses of Triclosan?TCS?on thyroid axis and oxidative stress in zebrafish,simultaneous assessment of toxic effects of triclosan on offspring.MethodsPer500 normal-developed zebrafish eggs were assigned to one control group and three exposure groups.The control group was aerated tap water culture.TheexposedTCSconcentrationswere1?g·L-1,3?g·L-1,and10?g·L-1,respectively.with three parallels in each experimental group.During the exposure period,observations of zebrafish deaths,swimming conditions,food intake and recorded.Samples were taken after 30d,60d and180d culture.The TCS content in zebrafish was detected by HPLC-MS/MS and the enrichment factor was calculated.Enzyme linked immunosorbent assay?Elisa?and kit method were used to detect thyroid hormone level and oxidative stress enzyme activity in zebrafish.240 four-month-old zebrafish with normal development were purchased in the flower and bird market and randomly assigned to a control group and three exposure groups.The experimental settings of the control group and the exposed group were the same as above,and each experimental group was set to have three parallels.After 60 days of exposure,the thyroid axis-related genes of adult zebrafish were detected by RT-PCR.The remaining adult zebrafish spawn in the same group and continue to expose the normally developed fish eggs after fertilization,The offspring of each concentration group were divided into two parts,one was exposed to the same concentration of TCS as their parents,the other was cultured with aerated tap water.After 120 hours of exposure,RT-PCR was used to detect the genes related to thyroid axis of juvenile zebrafish.All the test results were input SPSS22.0,and the difference of groups were compared byANOVA,?=0.05.ResultsIn the exposure period,the mortality of zebrafish,body length and body weight,fatness and growth factor were normal;TCS content in zebrafish with prolonged exposure time increased;exposure at high concentrations,decreased content of thyroid hormone T4 in zebrafish,T3 content increased,FT4 content decreased,the difference was statistically significant?P<0.05?;The kit detected the oxidative stress injury of zebrafish.The content of SOD and GSH decreased and the content of MDA increased in the early stage of zebrafish development.The difference was statistically significant?P<0.05?.After the zebrafish developed,the oxidative stress system returned to normal.After 60 days of TCS exposure,the expression of NIS and TG genes in adultzebrafishwasup-regulated,UGT1abgeneexpressionwas down-regulated,and the difference was statistically significant?P<0.05?.The thyroid axis-related genes of the offspring zebrafish were detected,The expression of TSH,TG,NIS,Nkx2.1 and Pax8 genes was down-regulated,and the expression of DIO2 gene was up-regulated.The difference was statistically significant?P<0.05?.ConclusionsTCS has a strong enrichment ability in zebrafish and can easily accumulate in the body.Higher concentration of TCS can affect the gene regulation related to thyroid hormone synthesis,transport,metabolism and so on,thus affecting the thyroid hormone level.Affecting the homeostasis of thyroid hormone;In the early stages of zebrafish growth,higher concentrations of TCS can cause oxidative damage to zebrafish,but no lethal toxicity. |
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