Nitric oxide protects against microcirculatory complications of malaria

描述（由申请人提供）：我们建议低一氧化氮（NO）生物利用度介导严重疟疾的微循环并发症；NO被无细胞血红蛋白（Hb）淬灭，这是寄生虫复制不可避免的结果，低精氨酸血症导致NO产量低，导致NO生物利用度低。血管泄漏、点状出血和低血压是众所周知的实验性脑疟疾（ECM）并发症，拟议的研究将确定组织氧合不良是否也通过改变血流量或功能性毛细血管密度在疟疾发病机制中起作用。我们观察到(i)游离血红蛋白（Hb）在ECM期间显著升高，（ii）游离血红蛋白清除一氧化氮（NO）， （iii） ECM期间发生明显的低精氨酸血症，这表明，与败血症相反，疟疾休克是由低NO生物利用度引起的。NO在微循环研究中介导血管泄漏及其发病机制中的作用是一个主要的争议，我们的研究将明确其在ECM血管泄漏中的作用。我们的假设的一个关键预测是外源性NO应该防止ECM发病机制；事实上，一氧化氮给药显著（P=0.003）保护动物免受疾病的发展。明显保护的一氧化氮供体处理小鼠消除了血管渗漏、点状出血、低血压和一氧化氮介导的信号传导（cGMP水平）受损，这些在注射ECM的盐水对照组中检测到。这些研究将进一步扩展，以确定一氧化氮供体给药是否可以防止ECM期间的其他微循环功能障碍，如低组织灌注和低氧合（目的1）。寄生红细胞（prbc）、血小板和白细胞在ECM期间发生粘附，缺乏选定的细胞粘附分子可防止疟疾发病。我们将把ECM的微循环并发症的结果与细胞粘附和eCAM表达联系起来，以确定细胞粘附有助于破坏血脑屏障和发病机制的细胞和分子机制，并确定外源性NO是否以及如何保护ECM细胞粘附（目的2）。最终目的是通过生物测定（小动脉扩张和静脉泄漏）和实际测量（NO电极）来评估在ECM期间NO的生物利用度是否受损，并通过保护性NO供体恢复。eNOS对ECM和NO供体治疗的反应也将被阐明；目前还缺乏对其他疾病（镰状细胞性贫血）中发生的游离Hb或低NO生物利用度的体内eNOS反应的详细了解。除了提供有关微循环的新信息外，拟议的研究可能会导致疟疾的辅助治疗，从而拯救数百万儿童免于死亡或认知受损。这些研究还将解决长期存在的关于疟疾发病机制的争议，如pRBC粘附是否导致缺氧和多器官衰竭（隔离假说）。

DESCRIPTION (provided by applicant): We propose that low nitric oxide (NO) bioavailability mediates the microcirculatory complications of severe malaria; NO quenching by cell-free hemoglobin (Hb) released as an unavoidable consequence of parasite replication and low NO production due to hypoargininemia lead to low NO bioavailability. Vascular leak, petechial hemorrhaging, and hypotension are well recognized complications of experimental cerebral malaria (ECM), and the proposed studies will determine whether poor tissue oxygenation also functions in malaria pathogenesis by altering blood flow or functional capillary density. Our observations that (i) free hemoglobin (Hb) is markedly elevated during ECM, (ii) free Hb scavenges nitric oxide (NO) and (iii) marked hypoargininemia occurs during ECM indicate that, in contrast to sepsis, malaria shock is caused by low NO bioavailability. A major controversy in microcirculation research is the role of NO in mediating vascular leak and pathogenesis, and our proposed studies will define its role in vascular leak during ECM. A key prediction of our hypothesis is that exogenous NO should protect against ECM pathogenesis; indeed, NO donor administration significantly (P=0.003) protects animals from the development of disease. The markedly protected NO donor-treated mice abrogated the vascular leak, petechial hemorrhage, hypotension, and impaired NO mediated signaling (cGMP levels) that were detected in saline-injected controls with ECM. These studies will be extended to define whether NO donor administration protects against other microcirculatory dysfunction during ECM, such as low tissue perfusion and oxygenation (aim 1). Adhesion of parasitized erythrocytes (pRBCs), platelets, and leukocytes occur during ECM and deficiency of selected cell adhesion molecules protects against malaria pathogenesis. We will interrelate the results of the microcirculatory complications of ECM to cell adhesion and eCAM expression to define the cellular and molecular mechanisms whereby cell adhesion contributes to disruption of the blood brain barrier and pathogenesis and identify whether and how exogenous NO protects against ECM cell adhesion (aim 2). The final aim will assess by bioassay (arteriolar dilation, and venular leak) and actual measurement (NO electrode) whether NO bioavailability is impaired during ECM and restored by the protective NO donor. The response of eNOS to ECM and NO donor treatment will also be elucidated; a detailed understanding of in vivo eNOS responses to free Hb or to low NO bioavailability that occurs during other diseases (sickle cell anemia) is currently lacking. Besides providing new information about the microcirculation, the proposed studies may lead to adjunct therapy for malaria that rescues millions of children from death or impaired cognition. These studies will also address long standing controversies about malaria pathogenesis, such as whether pRBC adhesion leads to hypoxia and multi-organ failure (sequestration hypothesis).