Isbell T Scott, Gladwin Mark T, Patel Rakesh P
Department of Pathology, and Center for Free Radical Biology, University of Alabama at Birmingham, Alabama 35296, USA.
Am J Physiol Heart Circ Physiol. 2007 Oct;293(4):H2565-72. doi: 10.1152/ajpheart.00759.2007. Epub 2007 Aug 31.
Nitrite reacts with deoxyhemoglobin to generate nitric oxide (NO). This reaction has been proposed to contribute to nitrite-dependent vasodilation in vivo and potentially regulate physiological hypoxic vasodilation. Paradoxically, while deoxyhemoglobin can generate NO via nitrite reduction, both oxyhemoglobin and deoxyhemoglobin potently scavenge NO. Furthermore, at the very low O(2) tensions required to deoxygenate cell-free hemoglobin solutions in aortic ring bioassays, surprisingly low doses of nitrite can be reduced to NO directly by the blood vessel, independent of the presence of hemoglobin; this makes assessments of the role of hemoglobin in the bioactivation of nitrite difficult to characterize in these systems. Therefore, to study the O(2) dependence and ability of deoxhemoglobin to generate vasodilatory NO from nitrite, we performed full factorial experiments of oxyhemoglobin, deoxyhemoglobin, and nitrite and found a highly significant interaction between hemoglobin deoxygenation and nitrite-dependent vasodilation (P < or = 0.0002). Furthermore, we compared the effect of hemoglobin oxygenation on authentic NO-dependent vasodilation using a NONOate NO donor and found that there was no such interaction, i.e., both oxyhemoglobin and deoxyhemoglobin inhibited NO-mediated vasodilation. Finally, we showed that another NO scavenger, 2-carboxyphenyl-4,4-5,5-tetramethylimidazoline-1-oxyl-3-oxide, inhibits nitrite-dependent vasodilation under normoxia and hypoxia, illustrating the uniqueness of the interaction of nitrite with deoxyhemoglobin. While both oxyhemoglobin and deoxyhemoglobin potently inhibit NO, deoxyhemoglobin exhibits unique functional duality as an NO scavenger and nitrite-dependent NO generator, suggesting a model in which intravascular NO homeostasis is regulated by a balance between NO scavenging and NO generation that is dynamically regulated by hemoglobin's O(2) fractional saturation and allosteric nitrite reductase activity.
亚硝酸盐与脱氧血红蛋白反应生成一氧化氮（NO）。有人提出该反应有助于体内亚硝酸盐依赖性血管舒张，并可能调节生理性低氧性血管舒张。矛盾的是，虽然脱氧血红蛋白可通过亚硝酸盐还原生成NO，但氧合血红蛋白和脱氧血红蛋白都能有效清除NO。此外，在主动脉环生物测定中使无细胞血红蛋白溶液脱氧所需的极低氧张力下，令人惊讶的是，低剂量亚硝酸盐可直接被血管还原为NO，而与血红蛋白的存在无关；这使得在这些系统中难以确定血红蛋白在亚硝酸盐生物活化中的作用。因此，为了研究脱氧血红蛋白从亚硝酸盐生成血管舒张性NO的氧依赖性和能力，我们对氧合血红蛋白、脱氧血红蛋白和亚硝酸盐进行了全因子实验，发现血红蛋白脱氧与亚硝酸盐依赖性血管舒张之间存在高度显著的相互作用（P≤0.0002）。此外，我们使用NONOate NO供体比较了血红蛋白氧合对真正的NO依赖性血管舒张的影响，发现不存在这种相互作用，即氧合血红蛋白和脱氧血红蛋白均抑制NO介导的血管舒张。最后，我们表明另一种NO清除剂2-羧基苯基-4,4,5,5-四甲基咪唑啉-1-氧基-3-氧化物在常氧和低氧条件下抑制亚硝酸盐依赖性血管舒张，说明了亚硝酸盐与脱氧血红蛋白相互作用的独特性。虽然氧合血红蛋白和脱氧血红蛋白都能有效抑制NO，但脱氧血红蛋白作为NO清除剂和亚硝酸盐依赖性NO生成剂表现出独特的功能二元性，这表明一种模型，即血管内NO稳态由NO清除和生成之间的平衡调节，该平衡由血红蛋白的氧分数饱和度和变构亚硝酸盐还原酶活性动态调节。
