Inhaled Nitric Oxide as an Adjunctive Treatment for Cerebral Malaria in Children: A Phase II Randomized Open-Label Clinical Trial

Malaria kills more than half a million people per year, and most are children in sub-Saharan Africa [1]. Cerebral malaria (CM) is a catastrophic sequel of Plasmodium falciparum malaria, with a mortality rate of approximately 20% [2], causing long-term neurological defects in 10% to 24% of survivors [3, 4]. The most effective antiparasitic therapy is intravenous (IV) artesunate, which reduced mortality from 21% to 18% in African children with CM [2]. Several adjunctive therapies have been tested, but none have proven to be effective [5]. Nitric oxide (NO) is an intercellular messenger molecule synthesized by various cell types, including vascular endothelial cells. Nitric oxide is a vasodilator and inhibits platelet aggregation, among numerous other effects [6]. Malaria severity was correlated with reduced levels of biochemical markers of NO production [7]. Physiological markers of reduced NO bioavailability—reduced brachial artery postischemic vasodilation [8, 9] and increased pulmonary arterial pressures [10]—were correlated with increased cell-free hemoglobin levels in patients with severe malaria, reflecting the NO-scavenging property of cell-free hemoglobin. Angiopoietin (Ang)-1 and its antagonist Ang-2 regulate endothelial activation, and serum, plasma, or whole blood levels have been studied as biomarkers of CM severity and disease progression. Angiopoietin-1 levels were reduced and Ang-2 levels were elevated in pediatric CM patients compared with healthy children [11] and uncomplicated malaria patients [12, 13]. Significantly elevated levels of Ang-2 were found in fatal cases of CM and severe malaria [13]. Breathing low concentrations of NO gas reduces pulmonary arterial pressures without producing systemic hypotension in animal models and children [14, 15], and inhaled NO has been safely used to treat persistent pulmonary hypertension and other pulmonary disorders [16, 17] in neonates and infants for over 20 years [18]. In Plasmodium berghei ANKA (PbA)-infected mice (a murine CM model), breathing 40 or 80 parts per million (ppm) of inhaled NO [19, 20] improved survival rates, reduced plasma inflammatory markers, and increased plasma Ang-1 levels. In other studies, inhaled NO reduced cerebral injury in murine models of stroke [21, 22] and traumatic brain injury [23]. Based on the well established clinical safety profile of inhaled NO and its efficacy in experimental models of CM, we conducted an open-label randomized trial of breathing 80 ppm NO versus nitrogen (N2) as an adjunctive therapy to IV artesunate in pediatric CM patients in Uganda. The primary endpoint was to compare the increase of plasma Ang-1 levels over the first 48 hours of treatment in patients breathing either NO or N2. Nitric oxide delivery and safety were monitored and assessed by measuring methemoglobin% (metHb%) and NO metabolites. Although the study was too small to detect significant changes, in-hospital mortality, time to recovery from coma, and neurologic sequelae for up to 6 months after discharge were also determined.