We have shown that nitric oxide (NO) is protective against the development of severe falciparum malaria and death, and that NO bioavailability is very low in falciparum malaria. Endothelial dysfunction and low NO bioavailability are central features of severe malaria. We seek to understand the causes of impaired microvascular function in the pathogenesis of severe malaria and to develop adjunctive therapies that increase endothelial cell NO in hopes of improving microvascular perfusion and clinical outcomes in severe malaria. The low NO bioavailability in children and adults with severe malaria is an independent predictor of mortality. Our work has identified a number of processes leading to the reduced NO, but the role of endothelial glycocalyx loss in malaria has not been investigated. The glycocalyx is a gel-like layer lining the luminal side of the endothelium that serves as the key transduction sensor for endothelial cell NO production by NO synthase (NOS) in response to shear stress from flowing blood. Glycocalyx is known to be lost early in acute inflammation in some disorders. We showed that treatment of adults with malaria with the NO precursor arginine only temporarily and partially corrects the NO deficiency and endothelial dysfunction. We consider that use of an NO prodrug such as sodium nitrite will correct both the NO deficiency and endothelial dysfunction. Nitrite is converted to NO by deoxyhemoglobin in acidotic and hypoxic tissues making it an especially appealing NOS-independent candidate drug. Hypothesis 1. Children with severe falciparum malaria have loss of integrity of the endothelial glycocalyx, and this loss is proportional to disease severity and NO-dependent microvascular dysfunction.
Aim 1. We will determine the relationship between endothelial glycocalyx breakdown, endothelial NO bioavail- ability & dysfunction, and malaria disease severity. Using sidestream dark-field imaging and biochemical assays, we will examine microvascular glycocalyx breakdown and determine its relationship to endothelial NO bioavailability, microvascular function, and disease severity in Tanzanian children with moderately severe falciparum malaria. Hypothesis 2. Vascular response to NO is independent of glycocalyx integrity in children with falciparum malaria.
Aim 2. We will determine if children with falciparum malaria and damaged endothelial glycocalyx have beneficial vascular responses to exogenous NO (nitrite). If there is no improvement in vascular function in response to exogenous NO (nitrite) in these children, this will indicate that an intact glycocalyx is necessary not only for its ability to transduce shear stress to induce endothelial NO production, but also fo the vessel to respond to exogenous NO. This study will give us important information regarding the mechanism(s) of development of vascular dysfunction in malaria with respect to glycocalyx damage. It will also likely provide a clear rationale for testing exogenous NO sources (e.g., nitrite) as adjunctive therapies for falciparum malaria. 1
There were more than 225 million cases of malaria with approximately 781,000 deaths in 2012 worldwide. There is a great need for better ways to prevent and treat malaria. For example, up to 20% of those with severe malaria die despite our best therapies. Our proposed studies of microvascular dysfunction in severe malaria should give us novel insights into disease causation, and lead to new prevention & treatment. (End of Abstract)
