Cerebral malaria (CM) pathogenesis is due to a complex interaction between the vascular, coagulation and immune systems, and parasite sequestration. By using the experimental cerebral malaria (eCM) model, we reported that pantethine therapy protects all recipients from eCM by inhibiting microparticle (MP) formation and brain vascular leak. ATP-binding cassette A1-deficiency prevents MP formation and all deficient animals are protected from death. Our preliminary data indicate that MP formation is markedly increased during eCM and correlates with clinical symptoms and histological analysis of disease. By using our in vitro model of the human blood brain barrier (BBB), we observed that MPs are potent activators of monocytes and facilitate the adhesion of Plasmodium falciparum-parasitized RBCs (Pf-pRBCs) to human brain endothelial cell (HBEC) monolayers in vitro by adhering to either the pRBCs or HBECs. We subsequently confirmed our results with the 2 models in patients; we reported a marked increase in MPs in patients with CM, and that the numbers of platelet MPs correlated with coma depth and thrombocytopenia. This finding also suggests that MPs function in human CM coagulopathy, which also correlates with the development of CM in patients, and underscores the importance of MPs and coagulopathy in CM pathogenesis in humans. Translation of these findings into adjunctive therapy for human CM requires an improved understanding of the significance of MPs as biomarkers and the identification of other MP-specific targets for intervention. We hypothesize that increased numbers of microparticles (MPs) are elicited during cerebral malaria and MPs function in CM by: (i) eliciting a pro-inflammatory, pro-adhesive, and pro-coagulatory state in the vasculature, and (ii) contributing to the breakdown of the blood brain barrier (BBB). To address this hypothesis, we use two well accepted models: an in vivo model: P. berghei-ANKA infection of mice or eCM and an in vitro model: HBEC monolayers with adherent cell populations (i.e., P. falciparum-parasitized RBCs, platelets, and leukocytes). We propose in aim 1 to assess in vivo the number of MPs, their cellular origin, their surface and intra-MP proteins that contribute to their pro-inflammatory and pro-coagulation properties during eCM. We also in aim 1 determine MP's in vivo kinetics, fate, and whether MPs directly contribute to eCM pathogenesis. Some of these studies would require large numbers of patients compared with 5 animals/ group in eCM because of the identical parasite and host genetics and controlled environment; other studies cannot be ethically performed in humans. By using human cells, we will determine in aim 2 whether Pf-pRBCs are important stimuli for MP production.
In aim 3, we will elucidate whether MPs function directly to disrupt the BBB or whether MPs increase cell (Pf-pRBC, platelet, and leukocyte) adhesion and indirectly disrupt the BBB. The proposed analysis will lead to defined studies in patients to confirm our hypothesis and may ultimately lead to clinical testing of anti-MP adjunctive therapy. These studies are significant because they directly address pathogenic mechanisms of an important but often overlooked disease that kills millions of people and defines the mechanisms to target for a potential adjunctive therapy to rescue those presenting with cerebral malaria from their disease. We are the only group that has proposed this innovative role for MP in CM pathogenesis, provided results from animal models to human models to patient analysis to confirm the hypothesis, identified a potential lead compound, and developed new methods for MP analysis. Our approach is therefore innovative. We have extensive preliminary data to support our studies, indicating that the proposed studies are feasible.
Malaria is a leading cause of morbidity and mortality due to a single infectious agent but there is little consensus regarding the optimal adjunctive treatment of patients presenting with cerebral malaria. We have identified that microparticles are critical for cerebral malaria pathogenesis. By studying how MPs contribute to cerebral malaria pathogenesis, we will improve our understanding of MP as biomarkers and may develop adjunctive therapy for cerebral malaria.
