P-glycoprotein-mediated efflux of phenobarbital at the blood-brain barrier evidence from transport experiments in vitro

SummaryThe purpose of the present studies was to investigate characteristics of phenobarbital (PB) transport across the blood-brain barrier (BBB). Cultured rat brain microvascular endothelial cells (rBMECs) were used as an in vitro BBB model. Experiments were conducted to examine time-, concentration- and temperature-dependent elements of PB uptake, and the effect of tested agents on the steady-state uptake of PB. PB efflux from rBMECs and the polarised transport of PB were examined to evaluate whether P-glycoprotein (P-gp) was involved in the PB efflux transport across BBB. The results demonstrated that the uptake of PB by rBMECs was in a time-, concentration- and temperature-dependent manner. P-gp modulators, cyclosporin A (CsA), ketoconazole and metabolic inhibitor dinitrophenol, increased the PB steady-state uptake by more than 50% (p < 0.01), and decreased the PB efflux by more than 50% (p < 0.01). Similar results were observed in the uptake and efflux studies of rhodamine-123 by co-administration of CsA. Further results were obtained in the polarised transendothelial transport of PB in the apical to basolateral (A–B) and basolateral to apical (B–A) directions either with or without CsA. The result showed that transport of PB in the B–A direction was significantly greater than the transport in the A–B direction (p < 0.05), and the co-administration of 50 μM CsA almost inhibited P-gp-involved efflux in the rBMECs. Overall, these findings suggest that P-gp may contribute to the efflux transport of PB across BBB.