P-glycoprotein is functionally expressed in the placenta-derived bovine caruncular epithelial cell line 1 (BCEC-1)

Drug treatment is critical in pregnant cows due to the possibility of a maternal-to-fetal drug transfer across the placenta. Since the (syn)epitheliochorial bovine placental barrier includes an intact uterine epithelium, which in general limits drug transfer to the fetal trophoblast, the establishment of a species- and organ-specific in vitro model like the bovine caruncular epithelial cell line 1 (BCEC-1) for testing bovine placental drug transport is desirable. P-glycoprotein (P-gp or ABCB1) is an important efflux carrier that limits drug permeability across blood-tissue barriers such as the placenta and transports a wide range of structurally unrelated compounds including many drugs commonly used in veterinary medicine. The aim of the present study was to elucidate the suitability of BCEC-1 as an appropriate in vitro model for P-gp mediated drug transport in the bovine placenta. P-gp mRNA expression was detected by RT-PCR in BCEC-1 and placental tissue. Additionally, the carrier protein was localised in the apical membrane of BCEC-1 by immunofluorescence staining with the mouse monoclonal antibody C494. Drug transport in BCEC-1 was investigated by FACS analysis using the fluorescent P-gp substrate Rhodamine 123. Inhibition of Rhodamine 123 efflux by the P-gp inhibitors Verapamil and PSC833 confirmed functional expression of P-gp in BCEC-1. Furthermore, transport measurements in the transwell-system revealed a basal-to-apical net flux of the P-gp substrate digoxin at concentrations ranging from 10nM to 10 μM. This transwell digoxin flux was inhibited by Verapamil. In conclusion, P-gp is functionally expressed in BCEC-1 and mediates a basal-to-apical flux of digoxin indicating dominant apical localization of P-gp in this cell culture model. Therefore, BCEC-1 may be an appropriate in vitro model to study drug transport across the maternal epithelium as part of the epitheliochorial placental barrier of the cow.