Prenatal ethanol exposure increases maternal bile acids through placental transport pathway

High maternal serum bile acid level is common and sometimes harmful to the gravida. This study aimed to confirm the bile acid phenotypic change caused by prenatal ethanol exposure (PEE) and elucidate its placental mechanism. Pregnant Wistar rats were administered intragastrically with ethanol 4 g/kg.d from gestational day 9-20. Total bile acids (TBA) were detected in maternal, fetal serum and placental tissues, increasing significantly in the serum but no significant change in the placental tissues. Meta-analysis was performed and verified the efficacy of the PEE-induced model based on published data from several relevant studies. Mining of microarray data from human and rat placental sources identified the involvement of bile acid metabolism and its significant genes, which were verified by RT-qPCR and western blotting on tissues and treated BeWo cells with the administration of FXR/PXR siRNAs or FXR/PXR agonists. Our examination, consistent with microarray data and wet experiments, showed that organic anion transporter polypeptide-related protein 2B1 (Oatp2b1), multidrug resistance-associated proteins 3 (Mrp3) and breast cancer resistance protein (Bcrp) expression were increased, while nuclear receptor farnesoid X receptor (Fxr) was decreased but pregnane X receptor (Pxr) was increased. Furthermore, the interventional experiments confirmed that FXR regulated Bcrp while PXR regulated Oatp2b1 and Mrp3. In summary, PEE could induce high bile acid level in maternal serum and its mechanism is associated with the high expression of BCRP/MRP3/OATP2B1 in the placenta through up-regulating PXR and down-regulating FXR, thereby leading to an excessive bile acid transport to maternal blood via the placenta. Our study provides a novel perspective in terms of placenta, explaining the increased maternal blood bile acids under the toxicity of PEE.

Automated summary

This study confirmed that high maternal serum bile acid level is caused by prenatal ethanol exposure, with the up-regulation of BCRP/MRP3/OATP2B1 in the placenta through PXR up-regulation and FXR down-regulation leading to excessive bile acid transport to maternal blood.