Li Guo-Xing, Pei Qiu-Ling, Gao Yi, Liu Ke-Ming, Nie Ji-Sheng, Han Guang, Qiu Yu-Lan, Zhang Wen-Ping
Tianjin Centers for Disease Control and Prevention, Hedong District, Tianjin, PR China.
Exp Toxicol Pathol. 2007 Aug;58(6):447-53. doi: 10.1016/j.etp.2007.02.001. Epub 2007 Apr 30.
Arsenic is a double-edged sword to human health. The excretion of various organic anions into bile is mediated by an adenosine triphosphate-dependent conjugate export pump, which has been identified as the canalicular isoform of the multidrug resistance protein 2 (Mrp2). It has been proved that Mrp2 can transport arsenite in vitro, but its effects in vivo are not clear. The aim of this study was to investigate whether Mrp2 plays a role in exportation of arsenic in vivo and its protective effects on liver function. Mrp2 protein level in rat liver was determined by Western blot analysis. Total arsenic concentrations in whole blood and bile were measured using hydride generation atomic absorption spectrometry. Alanine aminotransferase (ALT) activity, aspartate aminotransferase activity (AST), glutathione peroxidase (GSH-PX) activity, malon dialdehyde (MDA) and total bilirubin were measured by biochemical assays. The morphological changes were observed by electron microscopy. Total arsenic levels in blood and bile of arsenite-treated rats were significantly higher than those of control rats (P<0.05) at all three different time points. The overexpression of Mrp2 was 36.61%, 32.36% and 12.73% at 2, 4 and 6 weeks, respectively (percentage of controls, P<0.05), which was significantly higher than controls. A positive correlation between Mrp2 expression level and total arsenic concentration in bile indicated that Mrp2 accelerated the transport of arsenic. Electron microscopy showed that microvilli of bile canaliculi became swollen and sparse. ALT and AST activities in serum were markedly raised at 6 weeks. MDA level in serum increased (P<0.05) and GSH-PX activity in serum decreased except for 2 weeks. Damage of liver function became worse following decreased expression of Mrp2. In conclusion, overexpression of Mrp2 may explain increased biliary excretion of arsenic and it may protect liver function.
砷对人类健康是一把双刃剑。各种有机阴离子向胆汁中的排泄由一种三磷酸腺苷依赖性共轭物输出泵介导，该泵已被鉴定为多药耐药蛋白2（Mrp2）的胆小管异构体。已证明Mrp2在体外可转运亚砷酸盐，但其在体内的作用尚不清楚。本研究的目的是探讨Mrp2在体内砷的输出中是否起作用及其对肝功能的保护作用。通过蛋白质免疫印迹分析测定大鼠肝脏中Mrp2蛋白水平。采用氢化物发生原子吸收光谱法测定全血和胆汁中的总砷浓度。通过生化分析测定丙氨酸转氨酶（ALT）活性、天冬氨酸转氨酶活性（AST）、谷胱甘肽过氧化物酶（GSH-PX）活性、丙二醛（MDA）和总胆红素。通过电子显微镜观察形态学变化。在所有三个不同时间点，亚砷酸盐处理大鼠血液和胆汁中的总砷水平均显著高于对照大鼠（P<0.05）。在第2、4和6周时，Mrp2的过表达分别为36.61%、32.36%和12.73%（相对于对照组的百分比，P<0.05），显著高于对照组。Mrp2表达水平与胆汁中总砷浓度之间呈正相关，表明Mrp2加速了砷的转运。电子显微镜显示胆小管微绒毛肿胀且稀疏。在第6周时，血清中ALT和AST活性显著升高。除第2周外，血清中MDA水平升高（P<0.05），血清中GSH-PX活性降低。随着Mrp2表达降低，肝功能损害加重。总之，Mrp2的过表达可能解释了砷胆汁排泄增加的现象，并且可能保护肝功能。
