十溴联苯醚(BDE 209)暴露对孕期大鼠和胎鼠甲状腺激素干扰效应研究

In utero Exposure to Decabromodiphenyl Ether(BDE 209)Induced Thy-roid Hormone Disturbance in Maternal and Fetal Rats

为探讨孕期十溴联苯醚(BDE 209)暴露对孕期羊水和胎鼠循环甲状腺激素(TH)的影响及其对胎脑发育的损害作用,将24只Wistar雌性大鼠随机分为对照组、BDE 209低剂量组(100 mg·kg^(-1) bw)和高剂量组(300 mg·kg^(-1) bw),与雄鼠合笼,经阴道涂片确认受孕后,在孕1 d给予BDE 209经口持续灌胃染毒至孕15 d(GD15)和孕20 d(GD20)。在GD15和GD20这2个时间点麻醉母鼠后剥离胎鼠称取体质量;应用酶联免疫吸附剂测定(ELISA)检测GD15、GD20羊水及GD20胎鼠循环TH水平,包括总三碘甲状腺原氨酸(TT3)、血清游离三碘甲腺原氨酸(FT3)、血清总甲状腺素(TT4)、游离甲状腺素(FT4)和促甲状腺激素(TSH)水平;应用实时荧光定量PCR(RT-qPCR)法检测胎脑促甲状激素释放激素(thyrotropin-releasing hormone,Trh)基因相对表达;应用苏木精-伊红染色(HE染色)观察GD20胎脑形态学改变。结果表明:(1)高剂量BDE 209可引起胎鼠体质量异常改变。(2)BDE 209可引起孕期羊水和孕后期胎鼠循环TH水平紊乱,表现为GD15时,BDE 209可引起羊水FT3下降、TT4和TSH增高,但未见统计学意义;低、高剂量BDE 209均可引起羊水FT4水平升高(P<0.05或P<0.01),且具有剂量依赖性。GD20时,与GD15相比,对照组羊水TH水平有所变化,FT3和TT4水平均明显增高,而TSH水平有所降低;低、高剂量BDE 209引起FT3显著降低(P<0.05),FT4在高剂量组升高(P<0.05);低、高剂量BDE 209引起TSH水平显著升高(P<0.05)。GD20时,胎鼠血清TH变化与同时期羊水中的基本一致,BDE 209可致胎鼠血清FT3和TT4下降,虽然没有显著性差异,胎鼠血清TSH水平增高,尤其在高剂量组(P<0.05)。(3)BDE 209可导致孕育中胎脑Trh基因表达下调(P<0.05),并随着孕期进程而加重。(4)病理学观察发现BDE 209可引起孕末期胎鼠脑细胞结构发生变化,使细胞数量减少,脑组织出现萎缩。综上,孕期BDE 209暴露可影响胚胎大鼠生长发育;引起羊水TH水平紊乱、胚胎大鼠循环TH水平紊乱以及胚胎脑组织Trh基因表达抑制,导致脑组织结构产生病理改变。这些可能是BDE 209致子代发育神经毒性的病理基础。

To investigate the effects of exposure to decabromodiphenyl ether(BDE 209)during pregnancy on thyroid hormone(TH)disturbance in fetal rats and its role in developmental neurotoxicity,24 Wistar female rats were randomly divided into control(peanut oil only)and two experimental groups(BDE 209 resolved in peanut oil at 100 mg·kg^(-1) bw or 300 mg·kg^(-1) bw).The female rats were placed with the male rats periodically.After pregnancy was confirmed by vaginal smear,all pregnant rats were either fed through oral gavage with BDE 209 or peanut oil at the first day of gestation until the 15th day of gestation(GD15)and the 20th day of gestation(GD20).At each time point,the fetal rats were removed from the maternal uterus and the body mass were recorded;the amniotic fluid and the peripheral blood of the fetal rats were collected for TH hormone evaluation by enzyme-linked immunosorbent assay(ELISA);the fetal brain tissues were collected and the expression of thyrotropin-releasing hormone(Trh)gene was detected by real time-quantitative PCR(RT-qPCR);the pathological changes of fetal brain tissues were also evaluated by hematoxylin and eosin(HE)staining.Results show that:(1)High dose BDE 209 exposure could affect the growth of the fetal rats.(2)BDE 209 could cause TH disorder in amniotic fluid during pregnancy and in the circulation of the fetal rats as described below.On GD15,BDE 209 decreased the level of free triiodothylamine in serum(FT3),increased the level of total serum thyroxine(TT4)and thyroid stimulating hormone(TSH)in amniotic fluid,although no statistical significance was found;both low and high doses of BDE 209 could increase the level of FT4 in amniotic fluid(P<0.05 or P<0.01)with a dose-response dependence.On GD20,com-pared with GD15,the basal TH level of amniotic fluid was changed,that is,FT3 and TT4 levels were significantly increased,while TSH level was decreased;low and high dose BDE 209 significantly decreased the level of FT3(P<0.05),the level of free thyroxine(FT4)index increased in the high dose group(P<0.05);the level of TSH signifi-cantly increased at low and high dose group of BDE 209(P<0.05).On GD20,the change of serum TH in fetal rats was basically consistent with that in amniotic fluid at the same period,that is,BDE 209 could cause the level of serum FT3 and TT4 decreased in fetal rats,although no significant difference was detected;the serum TSH level of fetal rats increased,especially in the high dose group(P<0.05).(3)BDE 209 resulted in the down-regulation of Trh gene expression in gestational fetal brain(P<0.05).(4)Pathological examinations showed that the neural injuries by BDE 209 in the fetal rats at the end of pregnancy may result in decreased cell numbers and atrophy of brain tissue.BDE 209 exposure during pregnancy can affect the growth and development of fetal rats,lead to TH disorder in amniotic fluid,TH disorder in circulation of fetal rats,and abnormal gene expression of fetal brain Trh,and result in brain tissue morphological deformity.These alterations may underlie the BDE 209-mediated developmental neurotoxicity in offspring.