肝损伤引起脑内药物转运体-药物代谢酶联盟失衡及其对脑内药物处置改变的贡献

Brain disposition of drugs and endogenous substances is highly dependent on orderly coordination of drug transporters and drug metabolism enzymes (i.e. brain transporter-enzyme interplay). Based on the facts that liver failure remarkably altered expression of drug transporters (P-GP, BCRP, Oat3 and Oct3) and enzymes (Cyp2d4 and Ugt1a) and increased levels of some endogenous substances (such as tryptophan, 5-hydroxytryptamine, dopamine and 5-hydroxyindoleacetic acid) in brain, we proposed following hypothesis. “Liver failure altered expression and function of drug transporters and enzymes in brain, leading to disturbance of transporter-enzyme interplay, in turn altering brain disposition of drugs and their CNS efficacy. Extent of the alterations was integrated effects of the altered drug transporters and enzymes”. Here, we used liver failure rats induced by thioacetamide and bile duct-ligation as well as in vitro cell model to investigate: 1. alterations in expression and function of drug transporters (P-GP, BCRP, Oat3 and Oct3) and enzymes (Cyp2d4 and Ugt1a) in brain by liver failure and their mechanisms which were involved in these alterations; 2. indidivual contribution of alterations in drug transporters and enzymes by liver failure to the alterations in brain disposition of drugs (such as venlafaxine) and CNS activity as well as their integrated effect; 3. contribution of the disordered transporter-enzyme interplay to disturbance of some endogenous substances (such as tryptophan and 5-hydroxytryptamine) in brain. These results may also highlight roles of the disordered transporter-enzyme interplay in hepatic encephalopathy, prediction of brain disposition of drugs and their central adverse reactions.

药物/内源性物质脑内处置高度依赖于脑内药物转运体和代谢酶间有序协同作用（脑药物转运体-代谢酶联盟）。鉴于肝损伤显著改变脑内药物转运体(P-GP、BCRP、Oat3和Oct3)和代谢酶（Cyp2d4和Ugt1a）表达，以及增加脑内5-羟色胺、色氨酸、多巴胺和5-吲哚乙酸等浓度的事实，提出肝损伤改变脑内药物转运体和代谢酶的功能与表达，引起脑药物转运体-代谢酶联盟失衡，进而改变脑内药物处置和中枢活性，其改变程度是药物转运体和代谢酶改变整合效应的推论。以上述药物转运体和代谢酶为靶点，用硫代乙酰胺和胆管结扎诱导肝损伤大鼠，结合细胞实验，研究：①肝损伤引起脑药物转运体-代谢酶联盟失衡及机制；②脑内药物转运体和代谢酶改变各自对文拉法辛等药物脑内处置贡献和整合效应；③这种联盟失衡对脑内5-羟色胺等物质浓度紊乱的贡献。其成果有助于阐明脑药物转运体-代谢酶失衡在肝性脑病中作用，药物脑内处置和中枢不良反应预测。

脑药物转运体和代谢酶参与脑内药物处置和一些内源性物质平衡调控。用胆管结扎(BDL)大鼠研究:1)血脑屏障(BBB)上BCRP功能与表达下调对齐多夫定脑分布和中枢毒性影响；2)BDL反向调节BBB上BCRP和P-gp功能与表达机制；3)BDL上调BBB上LAT1功能与表达机制及与脑内色氨酸和苯丙氨酸浓度升高关系; 4)BDL差异性改变肠、肝和肾OCTs机制及对二甲双胍药动学影响；5)肝缺血/再灌(HIR)损伤BBB机制；6)脑内DA浓度增加机制及与精神异常关系；7)文拉法辛上调COMT表达机制和临床意义。8)BDL下调脑UGT1A6功能与表达机制及对脑内5-HT浓度增加贡献。结果：1)肝损伤显著下调BBB上BCRP功能与表达，增加齐多夫定脑分布和中枢毒性；2)BDL上调BBB上P-gp功能和下调BCRP功能，这与P-gp膜蛋白上调和BCRP膜蛋白降低一致。BDL上调ERM和ezrin膜蛋白表达，降低radixin膜蛋白表达。BBB细胞结果显示胆红素+氨上调ezrin和P-gp膜蛋白表达，降低radixin和BCRP膜蛋白表达。沉默ezrin下调P-gp膜蛋白表达，逆转胆红素+氨诱导作用。沉默radixin下调BCRP膜蛋白表达。3)BDL上调BBB上LAT1功能与表达，升高脑内色氨酸和苯丙氨酸浓度。胆红素激活AhR上调LAT1表达；4)BDL下调肠OCT2和肝OCT1蛋白表达，上调肾和肝OCT2蛋白表达。这与肠胆酸盐浓度降低和血浆胆红素浓度升高有关。胆酸盐和胆红素激活FXR调节OCTs蛋白表达。肠、肝和肾OCTs表达改变显著影响二甲双胍药动学，可用半生理模型分析各转运体对二甲双胍药动学贡献。5)HIR损伤BBB源于肝脏释放大量精氨酸酶，剥夺精氨酸，抑制脑血管内皮细胞增殖。6)BDL大鼠出现肝性脑病样症状，脑内DA浓度升高和酪氨酸羟化酶(HT)表达增加。胆红素激活NF-kB通路上调HT表达。7)文拉法辛引起动物精神异常，诱导脑内COMT表达和降低S-腺苷甲硫氨酸(SAM)浓度。托卡朋和SAM可逆转文拉法辛所致精神异常，提示文拉法辛通过诱导脑COMT表达降低SAM浓度诱发精神异常。8)UGT1A6参与脑内5-HT代谢，BDL显著降低脑UGT1A6活性与表达，是脑内5-HT浓度升高主要原因。该成果有助于诠释脑内药物转运体和代谢酶在肝性脑病中作用，预测药物脑内处置和中枢毒性。

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