Functional evaluation of polymorphisms in the human ABCB1 gene and the impact on clinical responses of antiepileptic drugs

OBJECTIVEThe ABCB1 haplotype combinations have been demonstrated to be associated with epilepsy treatment outcomes. The aim of this study is to investigate whether ABCB1 haplotype combinations would affect P-glycoprotein (Pgp) function and impact the clinical responses of antiepileptic drugs (AEDs). METHODS AND RESULTSTransport of substrate rhodamine 123 and calcein-AM by human Pgp carrying 12 haplotype combinations of 1236C>T, 2677G>T/A and 3435C>T were assayed in the absence and presence of known inhibitors and AEDs. The inhibitory potency of the tested drugs from the dose–response relationships was cyclosporin A>verapamil> phenytoin> carbamazepine> lamotrigine>phenobarbital>valproic acid, levetiracetam, gabapentin. The silent polymorphisms combination (1236T-3435T) and triple haplotypes (1236T-2677A/T-3435T) resulted in profoundly less effective inhibition against substrates with significantly lower intracellular substrate concentration. These results confirmed that ABCB1 polymorphisms were associated with clinical responses of AEDs. CONCLUSIONOur findings demonstrated that human ABCB1 polymorphisms may alter the interactions between Pgp and substrates, and provided functional evidence for ABCB1 haplotypes-associated epilepsy treatment responses.