Hinchman C A, Rebbeor J F, Ballatori N
Department of Environmental Medicine, University of Rochester School of Medicine, Rochester, New York 14642, USA.
Am J Physiol. 1998 Oct;275(4):G612-9. doi: 10.1152/ajpgi.1998.275.4.G612.
The role of the liver in the disposition of circulating mercapturic acids was examined in anesthetized rats and in the isolated perfused rat liver using S-2,4-dinitrophenyl-N-acetylcysteine (DNP-NAC) as the model compound. When DNP-NAC was infused into the jugular vein (150 or 600 nmol over 60 min) it was rapidly and nearly quantitatively excreted as DNP-NAC into bile (42-36% of the dose) and urine (48-62% of dose). Some minor metabolites were detected in bile (<4%), with the major metabolite coeluting on HPLC with the DNP conjugate of glutathione (DNP-SG). Isolated rat livers perfused single pass with 3 microM DNP-NAC removed 72 +/- 9% of this mercapturic acid from perfusate. This rapid DNP-NAC uptake was unaffected by sodium omission, or by L-cysteine, L-glutamate, L-cystine, or N-acetylated amino acids, but was decreased by inhibitors of hepatic sinusoidal organic anion transporters (oatp), indicating that DNP-NAC is a substrate for these transporters. The DNP-NAC removed from perfusate was promptly excreted into bile, eliciting a dose-dependent choleresis. DNP-NAC itself constituted approximately 75% of the total dose recovered in bile, reaching a concentration of 9 mM when livers were perfused in a recirculating mode with an initial DNP-NAC concentration of 250 microM. Other biliary metabolites included DNP-SG, DNP-cysteinylglycine, and DNP-cysteine. DNP-SG was likely formed by a spontaneous retro-Michael reaction between glutathione and DNP-NAC. Subsequent degradation of DNP-SG by biliary gamma-glutamyltranspeptidase and dipeptidase activities accounts for the cysteinylglycine and cysteine conjugates, respectively. These findings indicate the presence of efficient hepatic mechanisms for sinusoidal uptake and biliary excretion of circulating mercapturic acids in rat liver and demonstrate that the liver plays a role in their whole body elimination.
以S-2,4-二硝基苯基-N-乙酰半胱氨酸（DNP-NAC）作为模型化合物，在麻醉大鼠和离体灌注大鼠肝脏中研究了肝脏在循环中硫醇尿酸处置中的作用。当将DNP-NAC注入颈静脉（60分钟内注入150或600纳摩尔）时，它会迅速且几乎定量地以DNP-NAC形式排泄到胆汁（占剂量的42%-36%）和尿液（占剂量的48%-62%）中。在胆汁中检测到一些次要代谢产物（<4%），主要代谢产物在高效液相色谱（HPLC）上与谷胱甘肽的DNP共轭物（DNP-SG）共洗脱。用3微摩尔DNP-NAC单次灌注离体大鼠肝脏，可从灌注液中去除72±9%的这种硫醇尿酸。这种快速的DNP-NAC摄取不受钠缺失、L-半胱氨酸、L-谷氨酸、L-胱氨酸或N-乙酰化氨基酸的影响，但会被肝窦有机阴离子转运体（oatp）抑制剂降低，这表明DNP-NAC是这些转运体的底物。从灌注液中去除的DNP-NAC会迅速排泄到胆汁中，引发剂量依赖性胆汁分泌。DNP-NAC本身约占胆汁中回收总剂量的75%，当肝脏以再循环模式灌注，初始DNP-NAC浓度为250微摩尔时，其浓度达到9毫摩尔。其他胆汁代谢产物包括DNP-SG、DNP-半胱氨酰甘氨酸和DNP-半胱氨酸。DNP-SG可能是由谷胱甘肽与DNP-NAC之间的自发逆迈克尔反应形成的。随后，胆汁中的γ-谷氨酰转肽酶和二肽酶活性分别对DNP-SG进行降解，从而产生半胱氨酰甘氨酸和半胱氨酸共轭物。这些发现表明，大鼠肝脏中存在有效的肝脏机制，用于肝窦摄取和胆汁排泄循环中的硫醇尿酸，并证明肝脏在其全身消除中发挥作用。
