Nitric oxide protects against microcirculatory complications of malaria

描述(由申请人提供)：我们认为，一氧化氮(NO)的生物利用度低是严重疟疾微循环并发症的中介；寄生虫复制不可避免地释放的无细胞血红蛋白(Hb)导致NO猝灭，以及低精氨酸血症导致NO生物利用度低。血管漏、点状出血和低血压是公认的实验性脑型疟疾(ECM)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中发挥作用。我们的观察表明：(1)在体外循环过程中，游离血红蛋白(Hb)显著升高，(2)游离Hb清除一氧化氮(NO)，(3)在体外循环过程中出现明显的低精氨酸血症，这表明与败血症不同，疟疾休克是由低NO生物利用度引起的。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它在ECM中的血管渗漏中的作用。我们假设的一个关键预测是，外源性NO应该可以预防细胞外基质的发病；事实上，供体给予NO显著地保护动物免受疾病的发展(P=0.003)。显著保护NO供体处理的小鼠，减少血管渗漏、点状出血、低血压，并削弱NO介导的信号转导(cGMP水平)，而在注射生理盐水的对照组中检测到ECM。这些研究将扩展到确定是否没有供体给药保护ECM期间的其他微循环功能障碍，如低组织灌注量和氧合(目标1)。在ECM过程中，寄生的红细胞(PRBC)、血小板和白细胞会发生黏附，缺乏选定的细胞黏附分子可以保护疟疾的发生。我们将把ECM微循环并发症的结果与细胞黏附和eCAM表达联系起来，以确定细胞黏附导致血脑屏障破坏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细胞黏附(目标2)。最终目的将通过生物测定(动脉扩张和静脉漏)和实际测量(无电极)来评估在ECM过程中是否没有生物利用度受到损害，并由保护性的NO供体恢复。ENOS对ECM和NO供体治疗的反应也将被阐明；目前缺乏对体内eNOS对其他疾病(镰状细胞性贫血)期间发生的游离Hb或低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，拟议中的研究还可能导致疟疾的辅助治疗，使数百万儿童免于死亡或认知障碍。这些研究还将解决有关疟疾发病机制的长期争议，例如pRBC黏附是否会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).