P-glycoprotein (P-gp), encoded by the MDR1 (multidrug resistance 1) gene, involves in the efflux of multiple compounds, such as certain antiepileptic drugs. The aim of this research was to observe the impacts of MDR1 (C3435T) variant on the efflux of phenytoin, carbamazepine, valproate, and phenobarbital in vitro. Stable recombinant LLC-PK1 cell systems transfected with MDR1_3435C (wild-type allele) and MDR1_3435T (variant allele) were constructed. The influences of MDR1 (C3435T) variant on the sensitivity, intracellular accumulation, and transepithelial permeability of antiepileptic drugs were assessed. The recombinant MDR1_3435T cells showed higher resistance to carbamazepine compared with MDR1_3435C cells in the cytotoxicity assay (p < 0.01). The intracellular accumulation of carbamazepine was significantly decreased in cells transfecting with MDR1_3435T allele when compared with recombinant MDR1_3435C cells (p < 0.01). These results also indicate that the efflux activity of P-gp-mediated carbamazepine in recombinant MDR1_3435T cells was greatly increased compared with MDR1_3435C cells (p < 0.01), whereas the transport ability of P-gp-dependent phenobarbital in recombinant MDR1_3435T cells was significantly lower than MDR1_3435C cells (p < 0.01). However, the effects of MDR1 (C3435T) polymorphism on the resistance, intracellular accumulation, and efflux of phenytoin and valproate were not found in this study. MDR1_3435T variant allele might be more efficient to transport carbamazepine, whereas reduces the efflux activity of P-gp-mediated phenobarbital. Collectively, MDR1 (C3435T) polymorphism might impact the P-gp activity and antiepileptic agents efflux with drug specificity.

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