Hoffmann Katrin, Gastens Alexandra M, Volk Holger A, Löscher Wolfgang
Department of Pharmacology, Toxicology, and Pharmacy, University of Veterinary Medicine, Bünteweg 17, D-30559 Hannover, Germany.
Epilepsy Res. 2006 Apr;69(1):1-14. doi: 10.1016/j.eplepsyres.2005.12.005. Epub 2006 Feb 28.
Multidrug resistance proteins (MRPs; symbol ABCC) are membrane glycoproteins that mediate the ATP-dependent export of a wide range of substrates from cells and thereby affect the bioavailability and disposition of many drugs. MRP2 (ABCC2) is expressed on the apical domain of hepatocytes, enterocytes of the proximal small intestine, and proximal renal tubular cells, but its location in the brain is a matter of debate. Most previous studies failed to determine MRP2 mRNA or protein in the brain or cell preparations from the brain of different species including humans. Based on our previous experience with the drug efflux transporter P-glycoprotein, we evaluated whether the immunohistochemical determination of MRP2 expression is sensitive to fixation and staining variables. Furthermore, we examined whether the MRP2 protein is overexpressed after experimentally induced seizures in rats, using the pilocarpine model of temporal lobe epilepsy. The MRP2 expression in the liver was used as positive control. MRP2 deficient TR- rats were used as negative controls. Despite various modifications in tissue fixation and immunohistochemical staining as well as use of different commercially available MRP2 antibodies, we never observed any unequivocal MRP2 staining in the brain of normal rats. However, after a pilocarpine-induced convulsive status epilepticus, clear MRP2 staining became visible in brain capillary endothelial cells and, less frequently, perivascular astroglia and neurons in various brain regions. In view of our recent data on brain access of antiepileptic drugs in MRP2 deficient TR- rats, seizure-induced over-expression of MRP2 in the blood-brain barrier is likely to impair drug penetration into the brain, thereby contributing to drug resistance in epilepsy.
多药耐药蛋白（MRPs；符号ABCC）是膜糖蛋白，介导多种底物从细胞的ATP依赖性输出，从而影响许多药物的生物利用度和处置。MRP2（ABCC2）表达于肝细胞的顶端结构域、近端小肠的肠上皮细胞和近端肾小管细胞，但它在脑中的定位仍存在争议。以前的大多数研究未能在包括人类在内的不同物种的脑或脑制备细胞中检测到MRP2 mRNA或蛋白。基于我们之前对药物外排转运体P-糖蛋白的经验，我们评估了MRP2表达的免疫组织化学测定对固定和染色变量是否敏感。此外，我们使用颞叶癫痫的毛果芸香碱模型，研究了大鼠实验性诱导癫痫发作后MRP2蛋白是否过表达。肝脏中的MRP2表达用作阳性对照。MRP2缺陷的TR-大鼠用作阴性对照。尽管在组织固定和免疫组织化学染色方面进行了各种改进，以及使用了不同的市售MRP2抗体，但我们在正常大鼠脑中从未观察到任何明确的MRP2染色。然而，在毛果芸香碱诱导的惊厥性癫痫持续状态后，在脑毛细血管内皮细胞中可见清晰的MRP2染色，在不同脑区的血管周围星形胶质细胞和神经元中较少见。鉴于我们最近关于MRP2缺陷的TR-大鼠中抗癫痫药物脑内通透性的数据，癫痫发作诱导的血脑屏障中MRP2的过表达可能会损害药物进入脑内，从而导致癫痫耐药。
