Role of Nitric Oxide in Malaria

This study, conducted by NIH, the University of Bamako in Mali, Africa, and Tulane University will examine the relationships between hemolysis (breakdown of red blood cells), nitric oxide (a gas important in regulating blood vessel dilation and blood flow) and pulmonary hypertension in patients with malaria. Malaria is among the leading causes of death in many of the world s poorest countries. It is caused by a parasite that is transmitted to humans by mosquitoes. Malian children ages 1-5 years are eligible for participation in this study. They include children with asymptomatic infection, uncomplicated disease, and severe disease. Uninfected controls are also included. Upon enrollment, participants have a medical history and physical examination, echocardiogram (ultrasound test of heart function) and blood tests. In addition, all participants (infected children and controls) have repeat evaluations when healthy, approximately 7 to10 days following successful therapy.

Malaria is among the leading infectious causes of death in many of the world s poorest countries. This parasitic mosquito-borne illness produces massive hemolysis in many infected human hosts. While much is known about parasite replication and cytoadherence, very little is known about the impact of hemolysis per se on vascular tone and endothelial function. Crossing a number of medical disciplines beyond the scope of malaria, intriguing new research on inherited hemolytic disorders such as sickle cell disease (SCD) provides clues to pathogenic mechanisms that may be relevant to malaria. Dr. Gladwin (NHLBI) and colleagues have characterized a mechanism of disease, hemolysis-associated endothelial dysfunction, in which red blood cell hemoglobin spills into plasma and reacts with and oxidatively destroys nitric oxide (NO). Additionally, erythrocyte arginase I is released into plasma and catabolizes arginine, the substrate for endothelial NO synthesis. As a result, the profound reduction in NO bioavailability produces vasomotor instability, oxidant stress, inflammation, endothelial adhesion molecule expression, activation of tissue factor, and platelet aggregation. Consistent with shared mechanisms, these same pathways are found to be activated during malarial infection. Chronic hemolysis in hemoglobinopathies also leads to a disease syndrome, hemolysis associated pulmonary hypertension, which develops in all chronic hereditary and acquired hemolytic conditions and is associated with excessive morbidity and mortality. Despite the recent appreciation of these mechanisms, not one study can be found in the literature evaluating pulmonary hypertension in human malaria. This protocol therefore aims to evaluate mechanisms governing interrelationships among malaria, intravascular hemolysis, NO bioavailability, endothelial function, pulmonary hypertension, and evolutionarily selected host polymorphisms that regulate the host response to hemolysis. We will correlate our clinical observations in the field with laboratory assays of hemolysis and nitric oxide bioavailability related to scavenging by cell-free hemoglobin and arginine catabolism. Using a candidate gene approach, we will identify and selectively characterize polymorphisms in genes important for endothelial function, vascular inflammation and disease phenotype. Finally, the characterization of this mechanism in malaria may catalyze the development of novel therapies targeting this pathway, such as sodium nitrite, inhaled nitric oxide gas, and/or recombinant haptoglobin infusions. This international collaboration between scientists at the NIH, University of Bamako, and Tulane University will provide an exclusive opportunity for the rapid transfer of appropriate technology and expertise relevant to the provision of the highest quality care to malaria patients in Mali and the world.