Hepatic Transcriptomic Responses in Pregnant and Non-pregnant Rats Exposed to HFPO-DA: Analyses to Inform the Role of Maternal Effects on Neonatal Toxicity

Like other per- and polyfluoroalkyl substances (PFAS), toxicity studies for short-chain HFPO-DA (ammonium, 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate) indicate the liver is the primary target of toxicity in rodents. However, neonatal mortality and decreased birth weight were also reported in rats following oral exposure to HFPO-DA in utero. Exposure-related effects in neonatal rats including hypoglycemia, decreased liver glycogen, and perturbed hepatic gene expression of glucose metabolism and peroxisome proliferator activated receptor (PPAR) pathways also accompanied these findings. A putative rodent-specific adverse outcome pathway (AOP) network was recently developed using these endpoints and assessed for its applicability to PFAS. AOP 1 in this putative AOP network consists of PPARα activation as one of multiple initiating events, and placental insufficiency, neonatal hepatic glycogen deficit, and hypoglycemia as key events leading to neonatal mortality and lower birth weight. To further inform AOP 1 of this putative AOP network and investigate whether this altered carbohydrate metabolism liver phenotype observed in rat neonates also occurs in HFPO-DA-exposed pregnant and non-pregnant adult rats, transcriptomic analysis and glycogen staining were performed on female rat livers from a 15-d developmental or 90-d subchronic toxicity study. HFPO-DA-mediated changes in hepatic gene expression in female rats were consistent with PPARï�¡ signaling. Changes in hepatic glycogen content and glucose metabolism-related gene expression were independent of HFPO-DA exposure, indicating that the altered carbohydrate metabolism phenotype observed in neonatal livers does not occur in adult female rats, regardless of pregnancy status. Therefore, key events in this AOP for neonatal mortality and lower birthweight are likely to directly affect the perinatal rat and are not expected to affect the maternal rat liver. Findings from this study were consistent with previous mechanistic studies supporting the rodent-specific PPARα mode of action for HFPO-DA-mediated liver effects in rodents.与其他全和多氟烷基物质（per- and polyfluoroalkyl substances, PFAS）类似，针对短链HFPO-DA（2,3,3,3-四氟-2-(七氟丙氧基)丙酸铵，ammonium, 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate）的毒性研究表明，肝脏是啮齿类动物中毒性作用的主要靶器官。不过，大鼠经宫内暴露于HFPO-DA后，可出现新生儿死亡率升高及出生体重降低的现象。伴随上述现象的还有新生大鼠的暴露相关效应，包括低血糖、肝糖原减少，以及糖代谢与过氧化物酶体增殖物激活受体（peroxisome proliferator activated receptor, PPAR）通路的肝脏基因表达紊乱。 近期研究人员基于上述检测终点构建了一套假定的啮齿类特异性不良结局途径（adverse outcome pathway, AOP）网络，并对其适用于PFAS的可行性进行了评估。该假定AOP网络中的AOP 1以过氧化物酶体增殖物激活受体α（peroxisome proliferator activated receptor α, PPARα）激活作为多个起始事件之一，并将胎盘功能不全、新生大鼠肝糖原缺乏及低血糖作为导致新生大鼠死亡率升高与出生体重降低的关键事件。 为进一步完善该假定AOP网络中的AOP 1，并探究大鼠新生个体中观察到的糖代谢肝脏表型改变是否同样会出现在经HFPO-DA暴露的怀孕及非怀孕成年大鼠中，研究人员针对两项试验中的雌性大鼠肝脏样本开展了相关实验：一项为为期15天的发育毒性试验，另一项为90天亚慢性毒性试验，并对样本进行了转录组学分析与糖原染色。 HFPO-DA介导的雌性大鼠肝脏基因表达变化与PPARα信号通路特征相符。但肝糖原含量与糖代谢相关基因表达的变化与HFPO-DA暴露无关，这表明新生大鼠肝脏中观察到的糖代谢表型改变并不会出现在成年雌性大鼠中，无论其是否处于妊娠状态。 因此，该AOP中与新生大鼠死亡率升高及出生体重降低相关的关键事件，很可能仅直接作用于围产期大鼠，预计不会对孕鼠肝脏产生影响。本研究结果与此前的机制研究一致，均支持HFPO-DA介导的啮齿类动物肝脏毒性效应存在啮齿类特异性PPARα作用模式。