Development of artificial oxygen carriers under consideration of microvascular homeostasis

本研究旨在研究一种候选人工氧载体——脂质体包裹血红蛋白（HbV）在脓毒症条件下对肝脏微血管血流动力学的影响，以及血红素加氧酶（HO）的气态产物一氧化碳（CO）在内毒素肝脏血红素分子分解代谢过程中改善肝胆功能障碍的作用。在内毒素中毒大鼠灌注肝脏中监测血管阻力和胆红素α （ho源性CO生成的指标）的胆通量。肝脏灌注能捕获NO和CO的HbO_2或能捕获NO但不能捕获CO的metHb。在内毒素预处理的肝脏中，诱导的NO合成酶和HO-1过量产生NO和CO， HbO_2引起明显的血管收缩和胆汁淤积。这些变化不是由NO合成酶抑制剂氨基胍单独复制的，而是由共同施用锌原卟啉- ix，一种HO抑制剂。CO的补充减弱了氨基胍和原卟啉锌- ix引起的事件，表明这些血管松弛气体的同时消除是hbo_2诱导变化的机制之一。这一观点得到了下述观察的支持：甲氧麻黄素不会引起任何胆汁淤积；该试剂捕获NO，但通过HO-1快速降解血红素引发CO过量生产。另一方面，HbV仅表现出轻微的窦静脉通畅变化，而没有引起任何明显的窦静脉血供减少。这些结果表明，内源性CO对应激条件下血红素超载引起的肝胆功能障碍具有保护作用，因此应限制候选载体的外渗，以保持疾病空间中最佳的CO浓度。

This study aimed to examine effects of liposome-encapsulated hemoglobin (HbV), a candidate artificial oxygn carrier, on hepatic microvascular hemodynamics under septic conditions, and roles of CO, the gaseous product of heme oxygenase (HO), in ameliorating hepatobiliary dysfunction during catabolism of heme molecules in endotoxemic livers. Vascular resistance and biliary flux of bilirubin-Ixα, an index of HO-derived CO generation, were monitored in perfused livers of endotoxemic rats. Livers were perfused with HbO_2 which captures NO and CO, or metHb, a reagent trapping NO but not CO. Effexts of HbV were also examined. In endotoxin-pretreated livers where inducible NO synthase and HO-1 overproduced NO and CO, HbO_2 caused marked vasoconstriction and cholestasis. These changes were not reproduced by the NO synthase inhibitor aminoguanidine alone, but by co-administration of zinc protoporphyrin-IX, an HO inhibitor. CO supplementation attenuated the events caused by aminoguanidine plus zinc protoporphyrin-IX, suggesting that simultaneous elimination of these vasorelaxing gases accounts for a mechanism for HbO_2-induced changes. This concept was supported by observation that metHb did not cause any cholestasis; the reagent captures NO but triggers CO overproduction through rapid degradation of the heme by HO-1. On the other hand, HbV exhibited only minor changes in sinusoidal patency without eliciting any notable reduction of sinusoidal blood supply. These results suggest protective roles of endogenous CO against hepatobiliary dysfunction caused by heme overloading under stress conditions, and thus extravasation of the candidate carrier should be limited to maintain optimal CO concentrations in the space of Disse.