Comparison of expression of p-glycoprotein and its function between wild type and mdr 1 a p-glycoprotein gene knock-out mice

最近的研究表明，mdr1a P-糖蛋白(p-gp)定位于脑毛细血管内皮细胞，在血脑屏障中起着重要的挤出泵作用，对肿瘤细胞具有多药耐药作用。虽然我们以前的报道表明p-gp在豚鼠内耳毛细血管内皮细胞中也有表达，但它在内耳中的功能参与仍不清楚。本研究利用mdrla p-gp基因敲除小鼠[mdrla(-/-)小鼠]和野生型mdrla(+/+)小鼠，研究了p-gp在内耳中的功能。通过RT-PCR分析，在野生型小鼠内耳组织中检测到mdr1a p-gp编码基因。免疫组织化学研究显示，mdrla(+/+)小鼠内耳血-内耳屏障部位的毛细血管内皮细胞有高水平的p-gp表达，而mdrla(-/-)小鼠的内耳毛细血管内皮细胞未见p-gp表达。药代动力学分析显示…与mdrla(+/+)小鼠相比，更多的tdrla(-/-)小鼠表现出对p-gp转运药物如阿霉素(阿霉素)和长春新碱的超敏反应，并且这些药物在内耳的累积增加(1.22-7.71倍)。但给予耳毒性药物顺铂后，p-gp的蓄积量并未增加，说明p-gp对药物的挤压具有选择性。听觉脑干反应的电生理研究显示，只有mdrla(-/-)小鼠在注射阿霉素或长春花碱后，I波和I-V波间潜伏期的阈值移动和延长。此外，在mdrla(+/+)小鼠中，与环孢素A联合给药抑制p-gp功能会导致阿霉素在内耳的积聚增加(2.46倍)，并导致听力障碍。这些结果表明，mdr1a p-gp作为一种外排泵，可以预防p-gp底物药物所致的耳毒性，并参与血-内耳屏障的新的作用机制。较少

Recent studies have shown that mdrla p-glycoprotein (p-gp), which conferred multidrug resistance against tumor cells, was located in the brain capillary endothelial cells and played an important role as an extrusion pump in blood-brain barrier. Although it has been shown from our previous report that p-gp was also expressed in the inner ear capillary endothelial cells of the guinea pig, its functional involvement in the inner ear was remained obscure. The present study investigated the p-gp function in the inner ear using mdrla p-gp gene knock-out mice [mdrla(-/-) mice] and wild type mdrla(+/+) mice. Using RT-PCR analysis, mdrla p-gp-encoding gene was detected in the inner ear tissue of the wild type mice. Immunohistochemical study demonstrated that high level expression of p-gp was detected in the capillary endothelial cells of mdrla(+/+) mice inner ear at the site of blood-inner ear barrier, while no p-gp expression was noted in mdrla(-/-) mice. Pharmacokinetic analyses indicated tha … More t mdrla(-/-) mice displayed hypersensitivity to p-gp transported drugs such as doxorubicin (adriamycin) and vinblastine, and increased accumulation of these drugs in the inner ear (1.22-to 7.71-fold) compared with that in mdrla(+/+) mice. However, increased accumulation was not detected after administering with ototoxic drug cisplatin, indicating that p-gp had a selectivity for extruding drugs. Electrophysiological studies using auditory brainstem response showed threshold shifts and prolongations of wave I and wave I to V interpeak latencies only in mdrla(-/-) mice after administering with adriamycin or vinblastine. Furthermore, inhibition of p-gp function by co-administration with cyclosporin A in mdrla(+/+) mice resulted in increased accumulation (2.46-fold) of adriamycin in the inner ear and hearing impairment . From these results, it was suggested that mdrla p-gp, which acts as an efflux pump, prevented ototoxicity induced by p-gp substrate drugs and contributed to a new functional mechanism in the blood-inner ear barrier. Less