| Thyroid disrupting chemicals (TDCs) are chemicals that affect thyroid metabolism, either through the hypothalamic-pituitary-thyroid axis or directly via nuclear receptors. Studies found that PCB153is the highest content congeners of PCBs in the biological and human tissues; p,p’-DDE, which the most important metabolite of DDT, the most persistent in the environment and the body, the highest concentration of metabolites, is a sign of the residual period of DDT in environment. The study found that the PCBs and p, p’-DDE can disrupt thyroid functions of humans and experimental animals.In the present study, neonatal Sprague-Dawley (SD) rats were exposed to PCB153and p, p’-DDE at a lower dose, the effects of PCB153and/or p, p’-DDE on rat growth and development, THs, were observed. In addition, The ELISA, Real time-PCR, Western blot and other ways were used to detect possible mechanisms on THs synthesis, secretion, and metabolism, a variety of factors at the level of transcription or translation level. TDCs toxic effects on the thyroid system and its mechanism will provide the knowledge for further study.Part Ⅰ, the effect of PCB153and/or p, p’-DDE on neonatal rats’ thyroid and THsObjective:To investigate the effects of PCB153and/or p, p’-DDE on neonatal rats’ thyroid and THs.Methods:Neonatal pups from postnatal3day to15day were exposed to PCB153and/or p, p’-DDE every other day at the dose of1ml/kg body weight orally. PCB153exposure experiment:solvent control group,0.025mg/kg PCB153,0.25mg/kg PCB153,2.5mg/kg PCB153. p,p’-DDE single and combibation with PCB153experiment:solvent control,0.1mg/kg p,p’-DDE,1mg/kg p,p’-DDE, lOmg/kg p’-DDE,0.25mg/kg PCB153+1mg/kg p,p’-DDE,2.5mg/kg PCB153+10mg/kg p,p’-DDE. Before every exposure, weight of animals was examed in the lactation period; after the exposure, weight of animals once a week; all animals were sacrificed after the body was weight. The thyroid, cerebrum and liver were sperated from the body, weighted; organ coefficients were calculated. ELISA kits for detection of serum TT4, FT4, TT3, FT3, TSH and TRH were used in the present study. Morris water maze navigation test and space exploration experiments to measure animal spatial memory, working memory, and spatial ability.Results:Compared with control group, latency and total distance in navigation test in2.5mg/kg PCB153group were increased significantly, and the difference was statistically significant (P<0.05). At postnatal21, Compared with control group, thyroid-body coefficient is lower in0.25mg/kg PCB153,2.5mg/kg PCB153groups, the difference was statistically significant (P<0.05). Thyroid coefficient were increased in p,p’-DDE groups, the difference was statistically significant (P<0.05); liver organ coefficient increases in2.5mg/kg PCB153+10mg/kg p,p’-DDE, the difference was statistically significant (P<0.05). At PND21, compared with control group, serum TT4, FT3, TT3levels were significantly decreased in0.25mg/kg PCB153,2.5mg/kg PCB153groups, the difference was statistically significant (P<0.05); and so do the TRH level in every exposure group. Compared with control group, serum TT4, FT3(except0.1mg/kg p,p’-DDE group) levels were significantly decreased in every exposure group, and the difference was statistically significant (P<0.05), and so FT4levels in2.5mg/kg PCB153+10mg/kg p,p’-DDE group. At PND50, compared with control group, serum TT4, TT3levels were decreased in each exposed group, the difference was statistically significant (P<0.05), serum FT4levels in2.5mg/kg PCB153group, and FT3, TSH level in0.25mg/kg PCB153,2.5mg/kg PCB153group. But serum TRH levels were significantly increased in PCB153group, the difference was statistically significant (P<0.05). Compared with control group, serum TT4levels were significantly decreased in every exposure group, the difference was statistically significant (P<0.05), so does serum FT4levels in10mg/kg p,p’-DDE. Compared with same dose of PCB153single exposure group, serum TT3、FT3level was significantly increased in0.25mg/kg PCB153+lmg/kg p,p’-DDE,2.5mg/kg PCB153+10mg/kg p,p’-DDE group, and the difference was statistically significant (P<0.05). An interaction was found between PCB153and p, p’-DDE combined exposure on serum the FT3level (F=9.49, P<0.05).Conclusion:PCB153and/or p, p’-DDE exposure could disrupt the growth and development of the thyroids of rats. PCB153and/or p, p’-DDE exposure will disrupt the thyroid hormone homeostasis. PCB153might be harmful to the ability of learning, spatial memory of rats.Part Ⅱ, potential mechanisms of PCB153and/or p, p’-DDE on rats’ thyroid hormone homeostasisObjective:The present study was designed to investigate potential mechanism of PCB153and/or p, p’-DDE on thyroid hormone homeostasis.Methods:ELISA kit for detection of serum NIS, TG, TPO, TTR, ROS, MDA, GSH-PX, SOD levels. RT-PCR were used to detect the rat (postnatal day50) hepatic mRNA expression levels of TR (TRal, TRβ1, TRβ2), deiodinase (D1, D2), liver tissue metabolic enzymes (CYP1A1, CYP2B3, UGT1A1, UGT1A9), thyroid hormone transmembrane transport protein (MCT8), retinoid X receptor (RXR alpha), ERK1/2signal pathway (Kras1, KRafl, MEK1, ERK1, ERK2), Western blot to detect the rat hepatic protein expression level of TRβ1, RXRa, total ERK1/2, phosphorylation of ERK1/2protein.Results:At PND21, compared with control group, serum TPO levels decreased significantly in PCB153group, and the difference was statistically significant (P<0.05), and so does the serum NIS in0.25mg/kg and2.5mg/kg PCB153groups. Gender differences were tested in PCB153groups on serum TG and TTR levels, compared with the control group of the same gender, TG and TTR levels were decreased in0.25mg/kg PCB153and2.5mg/kg PCB153group, the difference was statistically significant (P<0.05). Compared with the control group, serum levels of ROS, MDA were increased in each PCB153group, the difference was statistically significant (P<0.05); but serum GSH-PX, SOD levels were decreased in0.25mg/kg PCB153,2.5mg/kg PCB153group, the difference was statistically significant (P<0.05). Compared with control group, serum ROS levels (except0.1mg/kg p, p’-DDE group) were significantly increased in p,p’-DDE group, the difference was statistically significant (P<0.05). At PND50, compared with control group, serum TPO levels were significantly decreased in PCB153group, serum TG levels in10mg/kg p,p’-DDE group, and the difference was statistically significant (P<0.05). Gender differences were found in serum TTR in PCB153group, compared with control group of the same gender, serum TTR levels were decreased significantly in0.25mg/kg PCB153,2.5mg/kg PCB153female group, and the difference was statistically significant (P<0.05). Compared with control group, serum levels of ROS and MDA levels were increased in PCB153group, the difference was statistically significant (P<0.05); serum GSH-PX, SOD levels were significantly decreased in PCB153group, the difference was statistically significant (P<0.05).Compared with control group of the same gender, in male rats, the mRNA expression levels of TRα1in each PCB153group, lOmg/kg p,p’-DDE group, TRβ1in PCB153group (except0.25mg/kg group), p,p’-DDE group (except lmg/kg p,p’-DDE group), TRβ2in each p,p’-DDE group and combination groups were significantly increased, difference was statistically significant (P<0.05). In female rats, mRNA expression levels of TRal in2.5mg/kg PCB153group, TRβ1in10mg/kg p,p’-DDE group, TRβ2in2.5mg/kg PCB153, each p,p’-DDE group (except1mg/kg p, p’-DDE exposure group) and combination groups were significantly increased, difference was statistically significant (P<0.05). An interaction was found between PCB153and p,p’-DDE exposure on mRNA expression levels of TRβ1(F=10.00, P<0.05).Compared with control group of the same gender, in male rats, the mRNA expression levels of D1in each PCB153group, p, p’-DDE group and combination groups, D2in2.5mg/kg PCB153group was significantly increased, the difference was statistically significant (P<0.05). In female rats, the mRNA expression levels of D2in0.25mg/kg PCB153,2.5mg/kg PCB153,1mg/kg p,p’-DDE,10mg/kg p,p’-DDE,2.5mg/kg PCB153+10mg/kg p, p’-DDE group, were significantly increased, the difference was statistically significant (P<0.05).Compared with control group of the same gender, in male rats, the mRNA expression levels of CYP1A1in each PCB153group, UGT1A1in each PCB153group, p, p’-DDE group, UGT1A9in0.025mg/kg PCB153,2.5mg/kg PCB153group, each p,p’-DDE groups, CYP2B3in0.025mg/kg PCB153,2.5mg/kg PCB153group, each p, p’-DDE group were significantly increased, the difference was statistically significant (P<0.05); In female rats, the mRNA expression levels of CYP1A1in p, p’-DDE group, UGT1A1in2.5mg/kg PCB153, UGT1A9in2.5mg/kg PCB153, lOmg/kg p, p’-DDE group were significantly increased, the difference was statistically significant (P<0.05). An interaction was found between PCB153and p,p’-DDE combination exposure on mRNA expression levels of CYP1A1(F=10.28, P<0.05).Compared with control group of the same gender, in male rats, the mRNA expression levels of MCT8in each PCB153group,1mg/kg p,p’-DDE,10mg/kg p,p’-DDE group, RXRa in each PCB153group,10mg/kg p,p’-DDE group were significantly increased, the difference was statistically significant (P<0.05); In female rats, the mRNA expression levels of MCT8in lOmg/kg p,p’-DDE group were significantly decreased, the difference was statistically significant (P<0.05), the mRNA expression levels of RXRa in each PCB153group were significantly increased, the difference was statistically significant (P<0.05).Compared with control group of the same gender, in male rats, the mRNA expression levels of Krasl in lOmg/kg p,p’-DDE group, Krafl in0.25mg/kg PCB153and10mg/kg p, p’-DDE group, ERK1in10mg/kg p,p’-DDE group, ERK2in0.1mg/kg p,p’-DDE, lOmg/kg p,p’-DDE group were significantly increased, and the difference was statistically significant (P<0.05), and the mRNA expression levels of MEK1in each PCB153group were decreased, but in0mg/kg p,p’-DDE group significantly increased, the difference was statistically significant (P<0.05). In female rats, the mRNA expression levels of Krasl in lmg/kg p,p’-DDE group, Krafl in2.5mg/kg PCB153group, MEK1in lmg/kg p,p’-DDE exposure group, were significantly increased, the difference was statistically significant (P<0.05). interactions was found between PCB153and p,p’-DDE combination exposure on mRNA expression levels of Krafl, Krasl, MEK1(F=8.33,6.53,8.19, P<0.05).Compared with control group of the same gender, in male rats, the protein expression levels of total ERK1/2in0.025mg/kg PCB153,2.5mg/kg PCB153,10mg/kg p,p’-DDE group, p-ERK1/2in2.5mg/kg PCB153,10mg/kg p,p’-DDE group, TRβ1in2.5mg/kg PCB153+10mg/kg p,p’-DDE group, RXRa in2.5mg/kg PCB153+10mg/kg p,p’-DDE were significantly increased, and difference was statistically significant (P<0.05). In female rats, the protein expression levels of RXRa in2.5mg/kg PCB153+10mg/kg p,p’-DDE group were significantly increased, the difference was statistically significant (P<0.05).Conclusion:1) PCB153exposure can inhibit the serum levels of TPO, NIS, TG while p, p’-DDE inhibit that of TPO, which could disrupt the synthesis of thyroid hormones.2) PCB153exposure can inhibit the serum levels of TTR, disrupting the thyroid hormone transporter in the blood.3) PCB153and p,p’-DDE can upregulate hepatic mRNA expression of MCT8in male rats.4) PCB153and p,p’-DDE can upregulate hepatic mRNA expression of deiodinase gene and hepatic metabolic enzymes disrupting the thyroid hormone metabolism.5)PCB153and p,p’-DDE can upregulate hepatic mRNA expression of TR, and the nuclear receptor RXRa to disrupt thyroid hormone homeostasis.6) PCB153and p, p’-DDE change oxidative stress level of body in the rats, and activated ERK1/2signaling pathways. |
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