Elucidation of physiological role of nitric oxide (NO) and cytokines in endotoxemia

首先，我们研究了体内一氧化氮（NO）在内毒素（LPS）引起的肝脏药物代谢酶活性降低中的作用。腹腔注射LPS（1 mg/kg）可显著降低AP的全身清除率，反映肝脏药物代谢酶活性降低，并显著增加血浆中亚硝酸盐和硝酸盐（NOx）水平。iNOS抑制剂（10 mg/kg）逆转了这种降低的AP清除率并降低了血浆中的NOx水平。NO供体（FK-409）也降低AP的全身清除率。这些结果强烈地表明，过量的NO在LPS诱导的肝脏P450介导的药物代谢酶活性降低中起关键作用。这些结果警告说，革兰氏阴性细菌感染可能会增加一些药物的副作用的风险，特别是那些主要由肝脏代谢的药物，并表明更有选择性的iNOS抑制剂可能是有用的药物，用于改善这些内毒素诱导的变化。其次，我们研究了LPS对P-糖蛋白（P-gp）介导的体内胆肾转运的影响。LPS可显著降低P-gp底物罗丹明123（Rho）在胆、肾中的排泄，TNF-α抑制剂可保护LPS诱导的Rho在胆、肾中的清除率，而iNO抑制剂则无此作用。结果发现，这些减少是由于TNF-α在血浆中的过量产生，而不是由NO的过量产生。此外，这些减少与LPS诱导的肝脏和肾脏中mdr 1a mRNA表达的减少密切相关。本研究表明，LPS通过降低mdr 1a mRNA的表达，显著降低P-gp介导的胆肾转运，可能是由于LPS释放的细胞因子TNF-α。

First, we investigated the role of nitric oxide (NO) in the decrease in hepatic drug-metabolizing enzyme activity caused by endotoxin (LPS) in vivo. Intraperitoneal injection of LPS (1 mg/kg) dramatically decreased the systemic clearance of AP, reflecting reduced hepatic drug-metabolizing enzyme activity, and significantly increased the level of nitrite and nitrate (NOx) in the plasma. iNOS inhibitor (10 mg/kg) reversed this decreasing AP clearance and reduced the level of NOx in plasma. The NO donor (FK-409) also decreased the systemic clearance of AP.These findings strongly suggest that excess NO plays a key role in the LPS-induced decreases in hepatic P450-mediated drug-metabolizing enzyme activity. These results caution that gram-negative bacterial infection may increase the risk of the side effects of some drugs, especially those which are metabolized mainly by the liver, and suggest that more selective iNOS inhibitors may be useful drugs for ameliorating these endotoxin-induced changes. Second, we investigated the effect of LPS on P-glycoprotein (P-gp)-mediated biliary and renal transport in vivo. LPS dramatically decreased both biliary and renal excretion of the P-gp substrate rhodamine 123 (Rho) 6 h after injection of LPS.TNF-α inhibitor, but not iNO inhibitor, protected LPS-induced decreases in the biliary and renal clearance of Rho. It was found that these decreases are caused by overproduction of TNF-α in plasma, but not by overproduction of NO.In addition, these decreases were correlated well with LPS-induced decreases in the expression of mdr1a mRNA in both livers and kidneys. This study suggests that LPS dramatically decreases P-gp-mediated biliary and renal transport by decreasing the expression of mdr1a mRNA, probably due to LPS-released cytokine, TNF-α.