The Effect of Sodium Nitrite on Acute Hemolysis in a Canine Model

本研究的主要目的是确定静脉注射亚硝酸钠在犬急性血管内溶血模型中的治疗价值。一氧化氮(NO)是一种血管扩张剂，由血管内皮细胞持续产生。循环中可利用的NO的数量部分地受NO与血红蛋白结合的调节。血红蛋白通常包含在红细胞中，与一氧化氮的反应速度相对较慢。然而，循环内红细胞的破坏(血管内溶血)会导致血红蛋白(无细胞血红蛋白)从红细胞释放到循环中。在溶血过程中释放到循环中的无细胞血红蛋白与NO的结合速度比红细胞内的血红蛋白快得多。这种NO与无细胞血红蛋白的快速结合破坏了循环内NO的正常平衡，并导致可用的NO数量减少。这种可利用的NO数量的减少会导致血管收缩，随后导致血流量减少和器官损伤。静脉注射亚硝酸钠可以与无细胞血红蛋白结合，并可能阻止无细胞血红蛋白与NO结合。如果亚硝酸盐能阻止无细胞血红蛋白与NO结合，它可能会防止溶血过程中发生的血管收缩和器官损伤。 在低强度和高强度低张血管内溶血的犬模型中，我们研究了输注亚硝酸盐后的血流动力学反应。溶血增加了体动脉和肺动脉压，增加了体循环血管阻力。溶血还抑制NO供体硝普钠对NO依赖的肺和全身血管的扩张。与硝普钠相比，亚硝酸盐不仅抑制溶血相关的血管收缩，而且在血浆血红蛋白浓度为25微米时增强血管扩张，显示出独特的作用。我们还观察到血浆血红蛋白水平和亚硝酸盐之间的相互作用，以增强硝普钠诱导的肺循环和体循环的血管扩张。利用线粒体NO传感器系统在体外重现体内血红蛋白的亚硝酸还原酶活性。亚硝酸盐输注可以在保持氧气输送的同时促进血红蛋白生成NO；这一效应可以被利用来治疗溶血性疾病和为以血红蛋白为基础的血液替代品解毒。

The primary goal of this study was to determine the therapeutic value of intravenous sodium nitrite in a canine model of acute intravascular hemolysis. Nitric oxide (NO) is a vasodilator which is constantly produced by the vascular endothelium. The amount of NO available in the circulation is, in part, regulated by the binding of NO to hemoglobin. Hemoglobin is normally contained within the red blood cell and reacts with nitric oxide at a relatively slow rate. However, the destruction of red blood cells within the circulation (intravascular hemolysis) causes the release of hemoglobin (cell-free hemoglobin) from the red blood cell into the circulation. The cell-free hemoglobin released into the circulation during hemolysis binds to NO at a much faster rate than hemoglobin within the red blood cell. This rapid binding of NO by cell-free hemoglobin disrupts the normal balance of NO within the circulation and leads to a decrease in the amount of NO available. This decrease in the amount of available NO leads to vasoconstriction and subsequently to decreased blood flow and organ injury. Intravenous sodium nitrite can bind to cell-free hemoglobin and may prevent the cell-free hemoglobin from binding to NO. If the nitrite can prevent the cell-free hemoglobin from binding NO, it may prevent the vasoconstriction and organ injury that occurs during hemolysis. In a canine model of low and high intensity hypotonic intravascular hemolysis, we characterized the hemodynamic responses to nitrite infusions. Hemolysis increased systemic and pulmonary arterial pressures and systemic vascular resistance. Hemolysis also inhibited NO-dependent pulmonary and systemic vasodilation by the NO-donor sodium nitroprusside. Compared with nitroprusside, nitrite demonstrated unique effects by not only inhibiting hemolysis-associated vasoconstriction, but also by potentiating vasodilation at plasma hemoglobin concentrations <25 microM. We also observed as interaction between plasma hemoglobin level and nitrite to augment nitroprusside-induced vasodilation of the pulmonary and systemic circulation. This nitrite reductase activity of hemoglobin in vivo was recapitulated in vitro using a mitochondrial NO sensor system. Nitrite infusions may promote NO generation from hemoglobin while maintaining oxygen delivery; this effect could be harnessed to treat hemolytic conditions and to detoxify the hemoglobin-based blood substitutes.