title: Evaluation of transport of common antiepileptic drugs by human multidrug resistance-associated proteins (MRP1, 2 and 5) that are overexpressed in pharmacoresistant epilepsy.
abstract: 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.
authors.affiliation: Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine, Bünteweg 17, D-30559 Hannover, Germany.
authors.forename: Carlos
authors.initials: C
authors.lastname: Luna-Tortós
authors.forename: Maren
authors.initials: M
authors.lastname: Fedrowitz
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Löscher
mesh_terms: D000927:Anticonvulsants / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D002491:Central Nervous System Agents / Q000493:pharmacokinetics / Q000494:pharmacology; D004827:Epilepsy / Q000378:metabolism*; D005452:Fluoresceins / Q000493:pharmacokinetics; D006801:Humans; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D011422:Propionates / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D015203:Reproducibility of Results; D014162:Transfection; D014747:Vinblastine / Q000493:pharmacokinetics
chemical_list: D000927:Anticonvulsants; D002491:Central Nervous System Agents; D005452:Fluoresceins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011422:Propionates; D011804:Quinolines; D014747:Vinblastine; C000715087:ABCC2 protein, human; C120809:ABCC5 protein, human; C069306:5-chloromethylfluorescein; C085925:calcein AM; C059141:verlukast; C421109:multidrug resistance-associated protein 1