MRP2 mediated defense against oxidative stress in liver

肝脏中的氧化应激有时伴随着胆汁淤积。多药耐药相关蛋白2/三磷酸腺苷结合盒转运体家族2(MRP2/Abcc2)是一种参与胆盐非依赖性胆汁流动的胆汁转运蛋白家族，在EA诱导的大鼠肝脏急性氧化应激状态下，其内在化过程已被我们所描述。然而，信号转导途径和调控分子仍有待研究。在这项研究中，我们利用分离的大鼠肝细胞偶联(IRCHs)来研究电针诱导MRP2内化的机制。经电针治疗后，MRP2指数显著降低，其定义为IRCHs中MRP2阳性小管膜染色与细胞核数目之比。通过使用该系统，我们发现电针依次降低GSH、Ca~(2+)和Gt~(2+)的升高，NO的产生，nPKC的激活，最终导致选择性的MRP2内化。此外，我们还展示了一种非类固醇抗炎药物，萘普生诱导的氧化应激也会导致GSH向胆汁中排泄减少而导致胆汁淤积。由于GSH本身被认为是MRP2的良好底物，我们认为MRP2的内化也导致了萘普生诱导的胆汁淤积。最后，这些新的发现可能能够解决药物性肝炎和衰老引起的胆汁淤积的机制。

Oxidative stress in the liver is sometimes accompanied by cholestasis. We have described the internalization of multidrug resistance-associated protein 2/ ATP-binding cassette transporter family 2 (Mrp2/Abcc2), a biliary transporter involved in bile-salt-independent bile flow, under ethacrynic acid (EA)-induced acute oxidative stress in rat liver. However, the signaling pathway and regulatory molecules have been remained to be investigated. In this research, we investigated the mechanism of EA-induced Mrp2 internalization using isolated rat hepatocyte couplets (IRCHs). The Mrp2-index, defined as the ratio of Mrp2 positive canalicular membrane staining in IRCHs per number of cell nuclei, was significantly reduced by treatment with EA. By using this system, we have found EA produced a reduction in GSH,Ca^<2+> elevation, NO production, nPKC activation in a sequential manner, finally leading to selective Mrp2 internalization. In addition to this, we demonstrated one of the non-steroidal anti-inflammatory drugs, Naproxen induced oxidative stress also leads to cholestasis caused by decrease excretion of GSH into bile. As GSH itself is known to be a good substrate of Mrp2, we thought Mrp2 internalization also caused Naproxen-induced cholestasis. Finally, these new findings might be able to solve the mechanism of cholestasis caused by drug-induced hepatitis and aging.