Transporter Expression in Response to Hepatotoxicants

描述(申请人提供)：药物毒性是急性肝功能衰竭的头号原因，而肝脏毒性是药物退出美国市场或停止临床开发的最常见原因。有趣的是，在啮齿动物身上的研究表明，在亚致死剂量的肝脏毒物如对乙酰氨基酚(APAP)和四氯化碳(CCl4)后，肝脏获得了对化学损伤的抵抗力。在使用APAP的人类患者中也可以看到类似的耐受性。目前，这种弹性的机制尚不清楚。它可能涉及对接触肝毒物质引发的氧化和炎症信号的代偿性变化。更好地理解这一现象很重要，因为它可能是急性肝损伤患者临床相关药物-疾病相互作用的一个来源。转运蛋白介导的外源物质流入和流出的改变可能与肝毒抗药性有关。该实验室的初步数据显示，在接受APAP和CCI4治疗的小鼠中，许多多药耐药蛋白(MRPs)的基因和蛋白表达发生了显著变化。我们假设，在化学性肝损伤过程中，MRP转运体表达的变化是肝细胞对随后的肝毒攻击产生抵抗力的一种代偿机制。我们建议首先通过研究APAP和CCI4治疗后肝脏MRP表达和定位的时间和区域变化来检验这一假设。然后，我们将确定炎性介质是否通过调节细胞因子的来源来促进这种反应。最后的实验将检验转录因子-E2 P45相关因子2(Nrf2)在缺乏Nrf2的小鼠损伤和从APAP和CC4治疗中恢复过程中调节转运蛋白基因表达的作用。NRF2协调调节药物代谢和解毒基因的表达。它在监管MRP方面的作用尚未得到调查。拟议的研究有望证明，暴露于肝毒剂后肝脏运输蛋白表达的变化代表了一种适应过程，可以防止某些化学物质的积累。这种适应性反应可能是肝细胞在损伤和再生期间存活所必需的。在建议中描述的实验条件下对运输蛋白表达的全面表征与人类健康密切相关。这一信息应该为我们提供急性肝损伤患者对药物的潜在易感性的指示：需要转运蛋白功能才能从肝脏排泄，和/或b)。产生炎症和损伤的介质，这些介质可以通过转运蛋白的作用消除。

DESCRIPTION (provided by applicant): Drug toxicity is the number one cause of acute liver failure, and hepatotoxicity is the most common reason why drugs are withdrawn from the US market or are stopped from clinical development. Interestingly, studies in rodents show that the liver acquires resistance to chemical injury following sub-lethal administration of hepatotoxicants such as acetaminophen (APAP) and carbon tetrachloride (CCl4). Similar tolerance is seen in a subset of human patients that use APAP. Currently, the mechanism of this resiliency is not known. It likely involves compensatory changes in response to oxidative and inflammatory signals triggered by hepatotoxicant exposure. A better understanding of this phenomenon is important since it may represent a source of clinically relevant drug-disease interactions in individuals with acute liver injury. Changes in transport protein-mediated influx and efflux of xenobiotics could contribute to hepatotoxicant resistance. Preliminary data from this laboratory show significant changes in gene and protein expression for a number of multidrug resistance proteins (Mrps) in mice receiving APAP and CCI4 treatment. We hypothesized that changes in expression of Mrp transporters during chemical-induced liver injury is a compensatory mechanism by which hepatocytes acquire resistance to subsequent hepatotoxicant challenge. We propose to test this hypothesis by first, investigating the temporal and zonal changes in expression and localization of hepatic Mrps following APAP and CCI4 treatment. Then, we will determine if inflammatory mediators contribute to this response by modulating cellular sources of cytokines. The final experiments will examine the role of the transcription factor-E2 p45-related factor 2 (Nrf2) in regulating transporter gene expression in mice lacking Nrf2 during injury and recovery from APAP and CC4 treatment. Nrf2 coordinately regulates the expression of drug metabolizing and detoxification genes. Its role in regulating Mrps has not been investigated. The proposed studies are expected to demonstrate that changes in liver transport protein expression following hepatotoxicant exposure represent an adaptation process that prevents accumulation of certain chemicals. This adaptive response may be essential for hepatocyte survival during periods of injury and regeneration. A comprehensive characterization of transport protein expression under the experimental conditions described in the proposal is of great relevance to human health. This information should give us an indication of the potential susceptibility of individuals with acute liver injury to pharmaceuticals that: a.) require transporter function for their excretion from the liver, and/or b). generate mediators of inflammation and injury that can be eliminated via transporter action.