calcein-am and Epilepsy

About 70% of the patients suffering from temporal lobe epilepsy (TLE) are resistant to currently available antiepileptic drugs (AEDs). For them one therapeutic option to achieve seizure control is to undergo epilepsy surgery. Expression of multidrug transporters is upregulated in resected tissue specimens from TLE patients, as well as in animal models of chronic epilepsy, which might lead to altered tissue availability of AEDs and therefore contribute to drug refractoriness. Here we describe a functional test of multidrug transporter activity in brain slices from TLE patients based on intracellular accumulation of the fluorescent multidrug transporter substrate calcein and compare functional data to the expression pattern of multidrug transporters. The rate of cytosolic calcein fluorescence increase was altered by inhibitors of multidrug transport such as probenecid (400 μM) and verapamil (40 μM) in a subset of slices, indicating the presence of functional multidrug transport proteins in human epileptic tissue. Interestingly, there were differences between the expression pattern of multidrug transporters and their ability to remove calcein-AM. Consequently, in vitro studies on multidrug transporters should always include functional tests of their activity as expression alone is not necessarily conclusive.

Topics: Adjuvants, Pharmaceutic; Anticonvulsants; ATP Binding Cassette Transporter, Subfamily B, Member 1; Epilepsy; Fluoresceins; Gene Expression Regulation; Hippocampus; Humans; In Vitro Techniques; Multidrug Resistance-Associated Proteins; Neocortex; Nerve Tissue Proteins; Neurons; Probenecid; Verapamil

Resistance to antiepileptic drugs (AEDs) is one of the most serious problems in the treatment of epilepsy. Accumulating experimental evidence suggests that increased expression of the drug efflux transporter P-glycoprotein (Pgp) at the blood-brain barrier may be involved in the mechanisms leading to AED resistance. In addition to Pgp, increased expression of several multidrug resistance-associated proteins (MRPs) has been determined in epileptogenic brain regions of patients with pharmacoresistant epilepsy. However, it is not known whether AEDs are substrates for MRPs. In the present experiments, we evaluated whether common AEDs are transported by human MRPs (MRP1, 2 and 5) that are overexpressed in AED resistant epilepsy. For this purpose, we used a highly sensitive assay (concentration equilibrium transport assay; CETA) in polarized kidney cell lines (LLC, MDCKII) transfected with human MRPs. The assay was validated by known MRP substrates, including calcein-AM (MRP1), vinblastine (MRP2) and chloromethylfluorescein diacetate (CMFDA; MRP5). The directional transport determined with these drugs in MRP-transfected cell lines could be blocked with the MRP inhibitor MK571. However, in contrast to transport of known MRP substrates, none of the common AEDs (carbamazepine, valproate, levetiracetam, phenytoin, lamotrigine and phenobarbital) used in this study was transported by MRP1, MRP2 or MRP5. A basolateral-to-apical transport of valproate, which could be inhibited by MK571 and probenecid, was determined in LLC cells (both wildtype and transfected), but the specific transporter involved was not identified. The data indicate that common AEDs are not substrates for human MRP1, MRP2 or MRP5, at least in the in vitro models used in this study.

Topics: Anticonvulsants; Biological Transport; Cell Line; Central Nervous System Agents; Epilepsy; Fluoresceins; Humans; Multidrug Resistance-Associated Protein 2; Multidrug Resistance-Associated Proteins; Propionates; Quinolines; Reproducibility of Results; Transfection; Vinblastine

The 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).. Transport 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.. Our 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.

Topics: Anticonvulsants; ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; Base Sequence; Cells, Cultured; Dose-Response Relationship, Drug; Drug Resistance; Epilepsy; Fluoresceins; Fluorescent Dyes; Humans; Polymorphism, Single Nucleotide; Prognosis; Rhodamine 123