Aim: 

Our work contributes to the understanding of the mechanisms of drug resistance in epilepsies. This study aimed to investigate i) the levels of expression of P-glycoprotein (P-gp), and multidrug resistance-associated proteins (MRP)1 and 2, ii) the activation of the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR), and iii) the relationship between increased P-gp and MRPs expression and PXR and CAR activation, in immortalized rat brain microvascular endothelial cell lines, GPNT and RBE4, following treatment with the antiepileptic drugs (AEDs), topiramate, phenobarbital, carbamazepine, tiagabine, levetiracetam, and phenytoin.

Methods: 

The confluent GPNT and RBE4 cells were treated with topiramate (100 mM), phenobarbital (300 mM), carbamazepine (100 mM), phenytoin (100 mM), levetiracetam (300 mM) and tiagabine (30 mM) for 72 hrs, adding the same amount of DMSO (0.1%) except controls. To verify the relationship between P-gp and MRPs expression and PXR and CAR activity, some cell cultures were treated with dexamethasone (1 mM), increasing P-gp efflux pump activity, cyclosporine A (5 mM), inhibitor of P-gp, phorbol 12-myristate 13-acetate (100 nM), repressing the activity of PXR, and S-5-isoquinolinesulfonic acid 4-[2-[(5-isoquinolinylsulfonyl) methylamino]-3-oxo-3-(4-phenyl-1-piperazinyl)propyl]phenylester1-[N,O-bis(5-Isoquinolinesulfonyl)-N-methyl-Ltyrosyl]-4-phenylpiperazine (KN-62, 10 mM), repressing CAR activity. The expression of proteins was determined by Western blot analysis.

Results: 

Carbamazepine, phenobarbital and phenytoin induced the highest levels of P-gp and MPRs expression that was associated with increased activation of PXR and CAR receptors as compared to levetiracetam, tiagabine and topiramate.

Conclusions: 

P-gp and MRPs are differently overexpressed in GPNT and RBE4 by various AEDs and both PXR and CAR are involved in the drug-resistant epilepsy induced by carbamazepine, phenobarbital and phenytoin.