Mechanisms of anemia in malaria

Summary Anemia frequently accompanies infections, contributing to adverse outcomes and even death. The mechanisms underlying this complication in different infections appear to be diverse and are, in general, not well-defined. The major infectious disease contributing globally to pediatric anemia is malaria, which is responsible for the majority of anemia-related hospital admissions in endemic areas and is a major cause of death in children. Although malaria is caused by Plasmodium infection of red blood cells (RBC), the main contributing factor to malarial anemia is the loss of uninfected RBC through still largely uncharacterized mechanisms. Therefore, there is a great need for a better understanding of the mechanisms causing malarial anemia that could lead to targeted treatments for this severe complication. We have recently analyzed plasma samples from a cohort of 552 Ugandan children with severe malaria to study the role of Xanthine Oxidase (XO), an oxidative enzyme that is upregulated in the plasma of malaria patients. We have observed a strong association between the levels of XO in plasma and the development of severe malarial anemia in children. Additionally, the levels of XO correlated significantly with biomarkers of hemolysis, suggesting that XO activity may contribute to the loss of uninfected RBC during malaria. In this project, we intend to determine whether there is a causal relation between the increased levels of XO and development of severe malarial anemia by studying the mechanisms underlying XO-induced hemolysis and/or phagocytosis of uninfected RBC in human cells in vitro and in mice models of malaria. In the first aim we will determine the mechanism underlying XO-induced loss of RBC in vitro. We will study the effects of XO from patient plasma on healthy human RBC (or RBC co-cultured with Plasmodium falciparum in vitro) to determine whether XO exposure increases susceptibility to hemolysis, eryptosis and/or phagocytosis by human monocyte/macrophages. In the second aim we will determine role of XO in malaria-induced anemia in a mouse model of infection that reproduces the characteristics human severe malarial anemia: low parasitemia and high, transient loss of uninfected RBC. We will first determine whether ex vivo exposure to XO increases the loss of RBC transferred into mice. We will also use specific inhibitors of XO to determine whether XO activity is a major contributor to anemia. The validation of XO as a contributor to anemia may open new possibilities for much needed adjunctive therapy in malaria and other infection-induced hemolytic anemias.