Development of artificial oxygen carriers under consideration of microvascular homeostasis

本研究旨在探讨脂质体包裹血红蛋白（HbV）对感染性肝损伤时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CO在改善内毒素血症肝脏血红素分子代谢时肝胆功能障碍中的作用。在内毒素血症大鼠的灌注肝脏中监测血管阻力和胆固醇-Ix α的胆汁流量，这是HO衍生的CO产生的指标。用能捕获NO和CO的HbO_2或能捕获NO而不捕获CO的metHb灌流肝脏，并检测HbV的影响。在诱导型NO合酶和HO-1过度产生NO和CO的内毒素预处理的肝脏中，HbO_2引起显著的血管收缩和胆汁淤积。这些变化并没有再现单独的NO合酶抑制剂氨基胍，但通过共同管理的锌原卟啉-IX，HO抑制剂。补充CO可减弱氨基胍和锌原卟啉-IX引起的事件，表明这些舒张血管气体的同时消除是HbO_2引起的变化的机制。这一概念得到了metHb不会引起任何胆汁淤积的观察结果的支持;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仅表现出窦状隙通畅性的微小变化，而未引起窦状隙血液供应的任何显著减少。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，因此候选载体的外渗应受到限制，以维持Disse空间中的最佳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.