Nitric oxide protects against microcirculatory complications of malaria

描述（由申请人提供）：我们提出低一氧化氮（NO）生物利用度介导严重疟疾的微循环并发症;作为寄生虫复制的不可避免的结果而释放的无细胞血红蛋白（Hb）和低NO产生（由于低维生素B2血症）导致NO生物利用度低，从而使NO淬灭。血管渗漏、瘀点渗出和低血压是实验性脑型疟疾（ECM）公认的并发症，拟议的研究将确定组织氧合不良是否也通过改变血流或功能性毛细血管密度在疟疾发病机制中起作用。我们的观察，（i）游离血红蛋白（Hb）是显着升高，在ECM期间，（ii）游离血红蛋白清除一氧化氮（NO）和（iii）显着的低谷氨酰胺血症发生在ECM表明，与败血症，疟疾休克是由低NO生物利用度。微循环研究中的一个主要争议是NO在介导血管渗漏和发病机制中的作用，我们提出的研究将确定其在ECM过程中的血管渗漏中的作用。我们的假设的一个关键预测是，外源性NO应保护ECM发病机制，确实，NO供体管理显着（P=0.003）保护动物从疾病的发展。显著保护的NO供体处理的小鼠废除了血管渗漏、点状出血、低血压和受损的NO介导的信号传导（cGMP水平），这些在用ECM注射盐水的对照中检测到。这些研究将被扩展以确定NO供体施用是否在ECM期间防止其他微循环功能障碍，例如低组织灌注和氧合（目的1）。在ECM期间发生寄生红细胞（pRBC）、血小板和白细胞的粘附，并且所选细胞粘附分子的缺乏保护免受疟疾发病机制。我们将ECM的微循环并发症的结果与细胞粘附和eCAM表达相互关联，以定义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）。最终目的将通过生物测定（小动脉扩张和小静脉渗漏）和实际测量（NO电极）来评估NO生物利用度是否在ECM期间受损并通过保护性NO供体恢复。eNOS对ECM和NO供体治疗的反应也将得到阐明;目前缺乏对体内eNOS对游离Hb或对其他疾病（镰状细胞性贫血）期间发生的低NO生物利用度的反应的详细了解。除了提供有关微循环的新信息外，拟议中的研究可能会导致疟疾的辅助治疗，挽救数百万儿童的死亡或认知受损。这些研究还将解决长期存在的关于疟疾发病机制的争议，例如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).