The Role of Megalin in the Transport of Gentamicin Across BeWo Cells, an In Vitro Model of the Human Placenta

Aminoglycosides (AG) are known to readily cross the placenta, although the mechanisms responsible for placental transport have not been characterized. Megalin is expressed in human placenta, and it is reasonable to speculate, given its role in renal AG uptake, that it is similarly involved in placental transport. However, the role of megalin in placental AG uptake has not been established. An in vitro model to study megalin-mediated placental transport has also not been previously described. The objectives of this study, therefore, were to evaluate the human choriocarcinoma (BeWo) cell line as a model to study megalin-mediated placental transport and to assess the uptake kinetics of gentamicin, an AG antibiotic, using this in vitro model. BeWo cells were grown on Transwell® plates, and megalin expression and functional activity were assessed. Uptake of (3)H-gentamicin was also evaluated in the presence and absence of megalin inhibitors. Expression of megalin protein and mRNA in BeWo cells were confirmed via immunoblot and qPCR analysis. Uptake of fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (BSA) (a megalin substrate) was time-, concentration-, and temperature-dependent consistent with a transporter-mediated process. FITC-BSA uptake was also significantly reduced in the presence of unlabeled gentamicin (a megalin substrate) and sodium maleate (to induce megalin shedding) suggesting that megalin is functionally active in BeWo cells. Gentamicin uptake exhibited time and temperature dependence, saturability and Michaelis-Menten kinetics, all of which suggest a transporter-mediated process. Gentamicin uptake was also significantly reduced in the presence of the megalin inhibitors RAP and EDTA suggesting that megalin is likely involved in gentamicin uptake.