Perinatal exposure to an environmentally-relevant mixture of BFRs and ovarian gene expression in the adult rat

Brominated flame retardants (BFRs), including polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDD), leach out from consumer products into the environment. Exposure to BFRs has been associated with effects on endocrine homeostasis. To test the hypothesis that in utero and lactational exposure to BFRs may affect the reproductive system of female offspring, adult female Sprague-Dawley rats were fed nominal doses (0, 0.06, 20, or 60 mg/kg/day) of a BFR dietary mixture formulated to mimic the levels of congeners in house dust from prior to mating until weaning. Vaginal opening and the day of first estrus occurred at a significantly earlier age among offspring from the 20 mg/kg/day BFR group, indicating that the onset of puberty was advanced. Histological analysis of ovaries from post-natal day 46 offspring revealed an increase in the incidence of multi-oocyte follicles. Toxicogenomics analysis of ovarian gene expression identified upstream regulators, including HIF1A, CREB1, EGF, the β-estradiol and PPARA pathways, predicted to be downregulated in the 20 mg/kg/day or the 60 mg/kg/day group and to contribute to the gene expression patterns observed. Thus, perinatal exposure to BFRs dysregulated ovarian folliculogenesis and signaling pathways that are fundamental for ovarian function. For each of the 4 treatment groups (0, 0.06, 20 and 60 mg/kg/day), RNA was extracted from the ovaries of 5-6 animals from independent litters. One animal in the low group was found to be an outlier and was removed (Ovary_PND46_0.06_rep4)

溴化阻燃剂（Brominated flame retardants, BFRs）包括多溴二苯醚（polybrominated diphenyl ethers, PBDEs）与六溴环十二烷（hexabromocyclododecane, HBCDD），可从消费品中浸出并进入环境。暴露于BFRs已被证实会干扰内分泌稳态。为验证「子宫内与哺乳期暴露于BFRs可能影响雌性子代生殖系统」这一科学假说，本研究将成年雌性斯普拉格-道利大鼠（Sprague-Dawley rats）喂食标称剂量分别为0、0.06、20、60 mg/kg/天的BFRs膳食混合物，该配方模拟了交配前室内灰尘中BFRs同系物的水平，染毒周期从交配前持续至子代断乳。结果显示，20 mg/kg/天BFRs暴露组的雌性子代，其阴道开口时间与初次动情期出现日期均显著提前，提示青春期启动被提前。对出生后第46天子代的卵巢进行组织学分析，发现多卵母细胞卵泡的发生率显著升高。通过卵巢基因表达的毒理基因组学（Toxicogenomics）分析，本研究鉴定出包括缺氧诱导因子1α（HIF1A）、环腺苷酸应答元件结合蛋白1（CREB1）、表皮生长因子（EGF）、β-雌二醇（β-estradiol）通路以及过氧化物酶体增殖物激活受体α（PPARA）在内的上游调控因子；预测结果显示，上述调控因子在20 mg/kg/天或60 mg/kg/天暴露组中呈下调状态，并与观测到的基因表达模式密切相关。综上，围产期暴露于BFRs会失调卵巢卵泡发生过程及维持卵巢功能必需的信号通路。本研究的4个处理组（0、0.06、20、60 mg/kg/天）中，分别从5-6只来自独立产仔的雌性大鼠卵巢中提取核糖核酸（RNA）。低剂量组中有1只样本被判定为异常值并被移除（Ovary_PND46_0.06_rep4）