Aleksunes Lauren M, Campion Sarah N, Goedken Michael J, Manautou José E
Department of Pharmaceutical Sciences, University of Connecticut, Storrs, Connecticut 06269, USA.
Toxicol Sci. 2008 Aug;104(2):261-73. doi: 10.1093/toxsci/kfn093. Epub 2008 May 8.
Treatment with hepatotoxicants such as acetaminophen (APAP) causes resistance to a second, higher dose of the same toxicant (autoprotection). APAP induces hepatic mRNA and protein levels of the multidrug resistance-associated proteins (Mrp) transporters in mice and humans. Basolateral efflux transporters Mrp3 and Mrp4 are the most significantly induced. We hypothesized that upregulation of Mrp3 and Mrp4 is one mechanism by which hepatocytes become resistant to a subsequent higher dose of APAP by limiting accumulation of xeno-, endobiotics, and byproducts of hepatocellular injury. The purpose of this study was to evaluate Mrp3 and Mrp4 expression in proliferating hepatocytes in a mouse model of APAP autoprotection. Plasma and livers were collected from male C57BL/6J mice treated with APAP 400 mg/kg for determination of hepatotoxicity and protein expression. Maximal Mrp3 and Mrp4 induction occurred 48 h after APAP. Mrp4 upregulation occurred selectively in proliferating hepatocytes. Additional groups of APAP-pretreated mice were challenged 48 h later with a second, higher dose of APAP. APAP-pretreated mice had reduced hepatotoxicity after APAP challenge compared to those pretreated with vehicle. A more rapid recovery of glutathione (GSH) in APAP-pretreated mice corresponded with increases in GSH synthetic enzymes. Interestingly, mice pretreated and challenged with APAP had dramatic increases in Mrp4 expression as well as enhanced hepatocyte proliferation. Inhibition of hepatocyte replication with colchicine not only restored sensitivity of APAP-pretreated mice to injury, but also blocked Mrp4 induction. Mrp4 overexpression may be one phenotypic property of proliferating hepatocytes that protects against subsequent hepatotoxicant exposure by mechanisms that are presently unknown.
用对乙酰氨基酚（APAP）等肝毒性物质进行处理会使机体对第二次更高剂量的相同毒性物质产生抗性（自身保护）。APAP可诱导小鼠和人类肝脏中多药耐药相关蛋白（Mrp）转运体的mRNA和蛋白质水平升高。基底外侧外排转运体Mrp3和Mrp4的诱导最为显著。我们推测，Mrp3和Mrp4的上调是肝细胞通过限制外源性物质、内源性物质和肝细胞损伤副产物的蓄积而对后续更高剂量APAP产生抗性的一种机制。本研究的目的是在APAP自身保护的小鼠模型中评估增殖肝细胞中Mrp3和Mrp4的表达。收集用400 mg/kg APAP处理的雄性C57BL/6J小鼠的血浆和肝脏，用于测定肝毒性和蛋白质表达。APAP处理后48小时，Mrp3和Mrp4的诱导达到最大值。Mrp4的上调选择性地发生在增殖肝细胞中。48小时后，用另一更高剂量的APAP对另外几组经APAP预处理的小鼠进行攻击。与用赋形剂预处理的小鼠相比，经APAP预处理的小鼠在接受APAP攻击后肝毒性降低。经APAP预处理的小鼠中谷胱甘肽（GSH）的更快恢复与GSH合成酶的增加相对应。有趣的是，经APAP预处理并接受攻击的小鼠中，Mrp4表达显著增加，同时肝细胞增殖增强。用秋水仙碱抑制肝细胞复制不仅恢复了经APAP预处理的小鼠对损伤的敏感性，还阻断了Mrp4的诱导。Mrp4的过表达可能是增殖肝细胞的一种表型特性，其通过目前未知的机制保护机体免受后续肝毒性物质的暴露。
