Arginine, Nitric Oxide, and Severe Malaria

描述(由申请人提供)：我们在坦桑尼亚儿童和印度尼西亚成年人中的研究显示，一氧化氮(NO)的产生受损，单核细胞一氧化氮合酶2(NOS2)的表达受损，一氧化氮合酶底物精氨酸水平非常低。我们的结论是，NO和NOS2对严重疟疾的发展具有保护作用。NO在体外对包括恶性疟原虫在内的多种生物具有抗菌作用，并能调节内皮功能(减少细胞黏附分子的表达和寄生虫红细胞的黏附)。精氨酸在一氧化氮合酶作用下可转化为瓜氨酸和一氧化氮，精氨酸酶可转化为鸟氨酸和尿素。在体内，NO的生物利用度会因为NO的生成减少和溶血而降低(红细胞释放的血红蛋白和精氨酸酶分别可以猝灭NO和消耗精氨酸)。我们对印度尼西亚成年人和坦桑尼亚儿童的研究证实，精氨酸在临床疟疾中含量较低。我们还表明，通过异常反应性充血-外周动脉血压测量确定，患有中度疟疾的成年人存在内皮功能障碍。这种反应性充血主要依赖于NO。我们发现内皮功能障碍与血乳酸水平升高、溶血指标和无生物利用度有关。我们的研究表明，这些成年人静脉注射精氨酸是安全的，可以逆转低精氨酸血症，改善内皮功能，增加呼出的NO。还没有人确定疟疾患者成人和儿童低精氨酸血症的确切原因。此外，还没有人评估疟疾儿童的内皮功能障碍及其与精氨酸水平和NO产生的关系。我们假设，低精氨酸血症是精氨酸降解增加和精氨酸合成减少的综合结果；低精氨酸血症导致疟疾相关疾病的发生；一氧化氮生物利用度降低和内皮功能障碍；以及低精氨酸血症在严重疟疾的整体病理生理学中起重要作用。此外，我们假设精氨酸与杀寄生虫的抗疟疾化疗联合使用将在治疗严重疟疾时有用。其具体目的是(1)确定坦桑尼亚儿童临床疟疾中低精氨酸血症的机制；(2)评估疟疾儿童的内皮功能，特别强调与精氨酸水平和一氧化氮产生的关系；(3)对住院的中度严重疟疾儿童进行静脉注射精氨酸的剂量范围研究。疟疾是非洲儿童住院和死亡的最常见原因，即使在接受抗疟疾化疗的儿童中，死亡率也很高。我们的研究将回答有关严重疟疾的病理生理学的重要问题，这项工作可能会导致对这种经常致命的疾病的新的辅助治疗。与公共卫生相关：疟疾导致的全球死亡率高于任何其他寄生虫病。恶性疟原虫是严重疟疾的罪魁祸首，每年估计有150万至270万人死于疟疾。这些死亡大多发生在五岁以下的非洲儿童中。尽管使用了快速杀寄生性抗疟疾化疗，但严重疟疾的病死率仍然很高。辅助治疗(在抗疟疾化疗的基础上增加的治疗)并没有带来任何益处。我们早期的研究表明，精氨酸(通过一氧化氮途径)可能是一种有用的辅助治疗。我们在这里提出的研究将回答与精氨酸和一氧化氮有关的严重疟疾的病理生理学的重要问题，这项工作可能会导致对这种经常致命的疾病的新的辅助治疗。

DESCRIPTION (provided by applicant): Our work in Tanzanian children and Indonesian adults demonstrated impaired production of nitric oxide (NO), impaired mononuclear cell NO synthase 2 (NOS2) expression, and very low levels of the NOS substrate arginine. We concluded that NO and NOS2 are protective against development of severe malaria. NO has antimicrobial effects in vitro against a wide variety of organisms including Plasmodium falciparum, and it can modulate endothelial function (reduction of cell adhesion molecule expression and adherence of parasitized erythrocytes). Arginine can be converted to citrulline and NO by NOS, and to ornithine and urea by arginase. In vivo NO bioavailability can be decreased because of both reduced NO production and hemolysis (hemoglobin and arginase released from erythrocytes can quench NO and consume arginine, respectively). Our studies in Indonesian adults and Tanzanian children confirmed that arginine is low in clinical malaria. We have also shown that adults with moderately severe malaria have endothelial dysfunction as determined by abnormal reactive hyperemia-peripheral arterial tonometry measurements. This reactive hyperemia is primarily dependent on NO. We found that endothelial dysfunction is associated with elevated blood lactate levels, measures of hemolysis, and NO bioavailability. Our studies showed that administration of arginine intravenously to these adults is safe and results in reversion of hypoargininemia, improved endothelial function, and increased exhaled NO. No one has determined the precise cause of hypoargininemia in adults and children who have malaria. Furthermore, no one has evaluated children with malaria for endothelial dysfunction and its relationship to arginine levels and NO production. We hypothesize that hypoargininemia results from a combination of increased arginine degradation and decreased arginine synthesis; that hypoargininemia contributes to the malaria-associated reduced NO bioavailability and endothelial dysfunction; and that hypoargininemia is important in the overall pathophysiology of severe malaria. In addition, we hypothesize that arginine administered in conjunction with parasiticidal antimalarial chemotherapy will be useful in the treatment of severe malaria. The specific aims are to (1) determine the mechanisms of hypoargininemia in clinical malaria in Tanzanian children; (2) to assess endothelial function in children with malaria with a special emphasis on relationships to arginine levels and NO production; and (3) to perform a dose-ranging study of intravenous arginine administration in hospitalized children with moderately severe malaria. Malaria is the most common cause of hospitalization and death in African children, and there is a high rate of death even in those who receive antimalarial chemotherapy. Our studies will answer important questions regarding the pathophysiology of severe malaria, and the work may lead to new adjunctive treatments for this frequently deadly disease. PUBLIC HEALTH RELEVANCE: Malaria causes more global mortality than any other parasitic disease. Plasmodium falciparum is responsible for severe malaria and the estimated 1.5 to 2.7 million deaths that occur from malaria each year. The majority of these deaths occur in African children less than five years of age. Case fatality rates in severe malaria remain high despite the use of rapidly parasiticidal antimalarial chemotherapy. Adjunctive therapies (treatments added to antimalarial chemotherapy) have not been beneficial. Our earlier studies indicate that arginine (through nitric oxide pathways) may be a useful adjunctive therapy. The studies we propose here will answer important questions relative to the pathophysiology of severe malaria regarding arginine and nitric oxide, and the work may lead to new adjunctive treatments for this frequently deadly disease.