Nitric Oxide and Microvascular Dysfunction in Severe Malaria

 描述（由申请人提供）：我们已经表明，一氧化氮（NO）对严重恶性疟疾的发展和死亡具有保护作用，并且NO在恶性疟疾中的生物利用度非常低。内皮功能障碍和低NO生物利用度是严重疟疾的中心特征。我们试图了解重症疟疾发病机制中微血管功能受损的原因，并开发增加内皮细胞NO的预防性治疗方法，以期改善重症疟疾的微血管灌注和临床结局。患有严重疟疾的儿童和成人的低NO生物利用度是死亡率的独立预测因子。我们的工作已经确定了一些导致NO减少的过程，但内皮糖萼损失在疟疾中的作用尚未研究。糖萼是内皮细胞腔侧的一种凝胶样层，其作为响应于来自流动血液的剪切应力的内皮细胞NO合成酶（NOS）产生NO的关键转导传感器。已知糖萼在某些疾病的急性炎症中早期丢失。我们发现，用NO前体精氨酸治疗成人疟疾只能暂时和部分纠正NO缺乏和内皮功能障碍。我们认为使用NO前药如亚硝酸钠将纠正NO缺乏和内皮功能障碍。在酸中毒和缺氧组织中，亚硝酸盐通过脱氧血红蛋白转化为NO，使其成为特别有吸引力的NOS非依赖性候选药物。假设1.患有严重恶性疟疾的儿童有内皮糖萼完整性的丧失，这种丧失与疾病的严重程度和NO依赖性微血管功能障碍成正比。目标1.我们将确定内皮糖萼破坏、内皮NO生物利用度和功能障碍与疟疾疾病严重程度之间的关系。使用侧流暗场成像和生化检测，我们将检查微血管糖萼分解，并确定其与内皮NO生物利用度，微血管功能和疾病严重程度的坦桑尼亚儿童中重度恶性疟疾。假设2.恶性疟患儿血管对NO的反应与糖萼完整性无关目标2.我们将确定恶性疟疾和受损内皮糖萼的儿童是否对外源性NO（亚硝酸盐）有有益的血管反应。如果这些儿童的血管功能对外源性NO（亚硝酸盐）的反应没有改善，这将表明完整的糖萼是必要的 这不仅是因为它能够抵抗剪切应力以诱导内皮NO的产生，而且是因为血管对外源性NO的反应。这项研究将为我们提供关于疟疾中与糖萼损伤有关的血管功能障碍的发展机制的重要信息。它还可能为测试外源性NO来源提供明确的理由（例如，亚硝酸盐）作为恶性疟疾的预防治疗。1

 DESCRIPTION (provided by applicant): We have shown that nitric oxide (NO) is protective against the development of severe falciparum malaria and death, and that NO bioavailability is very low in falciparum malaria. Endothelial dysfunction and low NO bioavailability are central features of severe malaria. We seek to understand the causes of impaired microvascular function in the pathogenesis of severe malaria and to develop adjunctive therapies that increase endothelial cell NO in hopes of improving microvascular perfusion and clinical outcomes in severe malaria. The low NO bioavailability in children and adults with severe malaria is an independent predictor of mortality. Our work has identified a number of processes leading to the reduced NO, but the role of endothelial glycocalyx loss in malaria has not been investigated. The glycocalyx is a gel-like layer lining the luminal side of the endothelium that serves as the key transduction sensor for endothelial cell NO production by NO synthase (NOS) in response to shear stress from flowing blood. Glycocalyx is known to be lost early in acute inflammation in some disorders. We showed that treatment of adults with malaria with the NO precursor arginine only temporarily and partially corrects the NO deficiency and endothelial dysfunction. We consider that use of an NO prodrug such as sodium nitrite will correct both the NO deficiency and endothelial dysfunction. Nitrite is converted to NO by deoxyhemoglobin in acidotic and hypoxic tissues making it an especially appealing NOS-independent candidate drug. Hypothesis 1. Children with severe falciparum malaria have loss of integrity of the endothelial glycocalyx, and this loss is proportional to disease severity and NO-dependent microvascular dysfunction. Aim 1. We will determine the relationship between endothelial glycocalyx breakdown, endothelial NO bioavail- ability & dysfunction, and malaria disease severity. Using sidestream dark-field imaging and biochemical assays, we will examine microvascular glycocalyx breakdown and determine its relationship to endothelial NO bioavailability, microvascular function, and disease severity in Tanzanian children with moderately severe falciparum malaria. Hypothesis 2. Vascular response to NO is independent of glycocalyx integrity in children with falciparum malaria. Aim 2. We will determine if children with falciparum malaria and damaged endothelial glycocalyx have beneficial vascular responses to exogenous NO (nitrite). If there is no improvement in vascular function in response to exogenous NO (nitrite) in these children, this will indicate that an intact glycocalyx is necessary not only for its ability to transduce shear stress to induce endothelial NO production, but also fo the vessel to respond to exogenous NO. This study will give us important information regarding the mechanism(s) of development of vascular dysfunction in malaria with respect to glycocalyx damage. It will also likely provide a clear rationale for testing exogenous NO sources (e.g., nitrite) as adjunctive therapies for falciparum malaria. 1