Vos T A, Hooiveld G J, Koning H, Childs S, Meijer D K, Moshage H, Jansen P L, Müller M
Groningen Institute for Drug Studies, University Center for Pharmacy, University Hospital Groningen, Groningen, the Netherlands.
Hepatology. 1998 Dec;28(6):1637-44. doi: 10.1002/hep.510280625.
Endotoxin-induced cholestasis is mainly caused by an impaired canalicular secretion. Mrp2, the canalicular multispecific organic anion transporter, is strongly down-regulated in this situation, and canalicular bile salt secretion is also reduced. We hypothesized that other adenosine triphosphate-binding cassette (ABC) transporters may compensate for the decreased transport activity to protect the cell from cytokine-induced oxidative damage. Therefore, we examined the expression of ABC-transport proteins in membrane fractions of whole liver and of isolated hepatocytes of endotoxin-treated rats and performed reverse-transcriptase polymerase chain reaction (RT-PCR) on mRNA isolated from these livers. In addition, the localization of these transporters was examined using confocal scanning laser microscopy. By 6 hours after endotoxin administration, we found a clear increase of mrp1 mRNA and protein, whereas mrp2 mRNA and protein were decreased. This was confirmed in isolated hepatocytes. In addition, mdr1b mRNA was strongly increased, whereas mdr1a and mdr2 mRNA did not change significantly. Both the mRNA and protein levels of the sister of P-glycoprotein (spgp), the recently cloned bile salt transporter, decreased. After endotoxin treatment, the normally sharply delineated canalicular staining of mrp2 and spgp had changed to a fuzzy pattern, suggesting localization in a subapical compartment. We conclude that endotoxin-induced cholestasis is caused by decreased mrp2 and spgp levels, as well as an abnormal localization of these proteins. The simultaneous up-regulation of mrp1 and mdr1b may confer resistance to hepatocytes against cytokine-induced metabolic stress.
内毒素诱导的胆汁淤积主要由胆小管分泌受损引起。多特异性有机阴离子转运体Mrp2在这种情况下会强烈下调，同时胆小管胆汁盐分泌也会减少。我们推测其他三磷酸腺苷结合盒（ABC）转运体可能会补偿转运活性的降低，以保护细胞免受细胞因子诱导的氧化损伤。因此，我们检测了内毒素处理大鼠的全肝和分离肝细胞的膜组分中ABC转运蛋白的表达，并对从这些肝脏中分离的mRNA进行了逆转录聚合酶链反应（RT-PCR）。此外，使用共聚焦扫描激光显微镜检查了这些转运体的定位。在内毒素给药后6小时，我们发现mrp1 mRNA和蛋白明显增加，而mrp2 mRNA和蛋白减少。这在分离的肝细胞中得到了证实。此外，mdr1b mRNA强烈增加，而mdr1a和mdr2 mRNA没有明显变化。最近克隆的胆汁盐转运体P-糖蛋白的姐妹蛋白（spgp）的mRNA和蛋白水平均下降。内毒素处理后，mrp2和spgp通常清晰的胆小管染色变为模糊模式，提示定位于顶端下区室。我们得出结论，内毒素诱导的胆汁淤积是由mrp2和spgp水平降低以及这些蛋白的异常定位引起的。mrp1和mdr1b的同时上调可能赋予肝细胞对细胞因子诱导的代谢应激的抗性。
