Baltes Steffen, Gastens Alexandra M, Fedrowitz Maren, Potschka Heidrun, Kaever Volkhard, Löscher Wolfgang
Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine, Bünteweg 17, D-30559 Hannover, Germany.
Neuropharmacology. 2007 Feb;52(2):333-46. doi: 10.1016/j.neuropharm.2006.07.038. Epub 2006 Oct 10.
In view of the important role of P-glycoprotein (Pgp) and other drug efflux transporters for drug distribution and resistance, the identification of compounds as substrates of Pgp-mediated transport is one of the key issues in drug discovery and development, particularly for compounds acting on the central nervous system. In vitro transport assays with Pgp-transfected kidney cell lines are widely used to evaluate the potential of compounds to act as Pgp substrates or inhibitors. Furthermore, such cell lines are also frequently utilized as a substitute for more labor-intensive in vitro or in vivo models of the blood-brain barrier (BBB). Overexpression of Pgp or members of the multidrug resistance protein (MRP) family at the BBB has been implicated in the mechanisms underlying resistance to antiepileptic drugs (AEDs) in patients with epilepsy. Therefore, it is important to know which AEDs are substrates for Pgp or MRPs. In the present study, we used monolayers of polarized MDCKII dog kidney or LLC-PK1 pig kidney cells transfected with cDNA containing either human MDR1, MRP2 or mouse mdr1a and mdr1b sequences to measure the directional transport of AEDs. Cyclosporin A (CsA) and vinblastine were used as reference standards for Pgp and MRP2, respectively. The AEDs phenytoin and levetiracetam were directionally transported by mouse but not human Pgp, whereas CsA was transported by both types of Pgp. Carbamazepine was not transported by any type of Pgp and did not inhibit the transport of CsA. In contrast to vinblastine, none of the AEDs was transported by MRP2 in transfected kidney cells. The data indicate that substrate recognition or transport efficacy by Pgp differs between human and mouse for certain AEDs. Such species differences, which are certainly not restricted to human and mouse, may explain, at least in part, the controversial data which have been previously reported for AED transport by Pgp in preparations from different species. However, because transport efficacy of efflux transporters such as Pgp or MRP2 may not only differ between species but also between tissues, the present data do not exclude that the AEDs examined are weak substrates of Pgp or MRP2 at the human BBB.
鉴于P-糖蛋白（Pgp）和其他药物外排转运体在药物分布和耐药性方面的重要作用，确定化合物是否为Pgp介导转运的底物是药物研发中的关键问题之一，对于作用于中枢神经系统的化合物尤为如此。用转染Pgp的肾细胞系进行体外转运试验，被广泛用于评估化合物作为Pgp底物或抑制剂的潜力。此外，这类细胞系还经常被用作更耗费人力的血脑屏障（BBB）体外或体内模型的替代物。BBB处Pgp或多药耐药蛋白（MRP）家族成员的过表达与癫痫患者对抗癫痫药物（AEDs）耐药的机制有关。因此，了解哪些AEDs是Pgp或MRPs的底物很重要。在本研究中，我们使用转染了含人MDR1、MRP2或小鼠mdr1a和mdr1b序列的cDNA的极化MDCKII犬肾或LLC-PK1猪肾细胞单层来测量AEDs的定向转运。环孢素A（CsA）和长春碱分别用作Pgp和MRP2的参考标准。AEDs苯妥英和左乙拉西坦可被小鼠而非人Pgp定向转运，而CsA可被两种类型的Pgp转运。卡马西平不能被任何类型的Pgp转运，也不抑制CsA的转运。与长春碱不同，在转染的肾细胞中，没有一种AEDs可被MRP2转运。数据表明，对于某些AEDs，人源和鼠源Pgp的底物识别或转运效率存在差异。这种物种差异肯定不限于人和小鼠，这可能至少部分解释了先前报道的不同物种制剂中Pgp对AEDs转运的争议性数据。然而，由于Pgp或MRP2等外排转运体的转运效率不仅可能因物种不同而异，也可能因组织不同而异，因此目前的数据并不排除所检测的AEDs在人BBB处是Pgp或MRP2的弱底物。
