Rocaglates as dual-targeting agents for experimental cerebral malaria.

Cerebral malaria (CM) is a severe and rapidly progressing complication of infection by parasites that is associated with high rates of mortality and morbidity. Treatment options are currently few, and intervention with artemisinin (Art) has limited efficacy, a problem that is compounded by the emergence of resistance to Art in parasites. Rocaglates are a class of natural products derived from plants of the genus that have been shown to interfere with eukaryotic initiation factor 4A (eIF4A), ultimately blocking initiation of protein synthesis.

Synthetic oleanane triterpenoids enhance blood brain barrier integrity and improve survival in experimental cerebral malaria.

Background: Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection associated with high mortality and neurocognitive impairment in survivors. New anti-malarials and host-based adjunctive therapy may improve clinical outcome in CM. Synthetic oleanane triterpenoid (SO) compounds have shown efficacy in the treatment of diseases where inflammation and oxidative stress contribute to pathogenesis.

CD47-SIRPα Interactions Regulate Macrophage Uptake of Plasmodium falciparum-Infected Erythrocytes and Clearance of Malaria In Vivo.

CD47 engagement by the macrophage signal regulatory protein alpha (SIRPα) inhibits phagocytic activity and protects red blood cells (RBCs) from erythrophagocytosis. The role of CD47-SIRPα in the innate immune response to Plasmodium falciparum infection is unknown. We hypothesized that disruption of SIRPα signaling may enhance macrophage uptake of malaria parasite-infected RBCs.

Chronic HIV infection impairs nonopsonic phagocytosis of malaria parasites.

Malaria-specific immune responses are altered in HIV/malaria-coinfected individuals and are associated with higher parasite burdens and more severe clinical disease. Monocyte/macrophage phagocytosis is a major mechanism of malaria parasite clearance. We hypothesized that phagocytosis of malaria-parasitized erythrocytes is impaired in coinfected individuals and could contribute to the increased parasite burdens observed.

HIV infection deregulates Tim-3 expression on innate cells: combination antiretroviral therapy results in partial restoration.

Background: The Tim-3 receptor has been implicated as a negative regulator of adaptive immune responses and has been linked to T-cell dysfunction in chronic viral infections, such as HIV. Blocking Tim-3 has been proposed as a potential therapeutic intervention in HIV infection. However, a more detailed characterization of Tim-3 expression in the presence of HIV is required before such strategies can be considered.

HIV infection deregulates innate immunity to malaria despite combination antiretroviral therapy.

Objective: Malaria and HIV-1 adversely interact, with HIV-positive individuals suffering higher parasite burdens and worse clinical outcomes. However, the mechanisms underlying these disease interactions are unclear. We hypothesized that HIV coinfection impairs the innate immune response to malaria, and that combination antiretroviral therapy (cART) may restore this response.

ABO blood groups influence macrophage-mediated phagocytosis of Plasmodium falciparum-infected erythrocytes.

Erythrocyte polymorphisms associated with a survival advantage to Plasmodium falciparum infection have undergone positive selection. There is a predominance of blood group O in malaria-endemic regions, and several lines of evidence suggest that ABO blood groups may influence the outcome of P. falciparum infection.

Characterization of a new phosphatase from Plasmodium.

Plasmodium falciparum malaria is the most important parasitic disease worldwide, responsible for an estimated 1 million deaths annually. Two P. falciparum genes code for putative phosphoglycerate mutases (PGMases), a widespread protein group characterized by the involvement of histidine residues in their catalytic mechanism.

Cysteamine, the natural metabolite of pantetheinase, shows specific activity against Plasmodium.

In mice, loss of pantetheinase activity causes susceptibility to infection with Plasmodium chabaudi AS. Treatment of mice with the pantetheinase metabolite cysteamine reduces blood-stage replication of P. chabaudi and significantly increases survival.

Adenosine triphosphate depletion of erythrocytes simulates the phenotype associated with pyruvate kinase deficiency and confers protection against Plasmodium falciparum in vitro.

Background: Erythrocytes from individuals with pyruvate kinase deficiency (PKD) are resistant to invasion by Plasmodium falciparum parasites, and erythrocytes infected with ring-stage parasites are preferentially cleared by macrophages in vitro. However, the underlying molecular basis of protection is unknown. In the present study, we examined adenosine triphosphate (ATP) levels in PKD erythrocytes (ie, erythrocytes from individuals with PKD) and determined whether depletion of ATP in normal erythrocytes would recapitulate the phenotype observed with PKD.

Rosiglitazone modulates the innate immune response to Plasmodium falciparum infection and improves outcome in experimental cerebral malaria.

For severe malarial syndromes such as cerebral malaria, adverse clinical outcomes are often mediated by the immune system rather than caused by the parasite directly. However, few therapeutic agents have been developed to modulate the host's immunopathological responses to infection. Here, we report that the peroxisome proliferator-activated receptor gamma (PPARgamma) agonist rosiglitazone modulated the host response to malaria by enhancing phagocytic clearance of malaria-parasitized erythrocytes and by decreasing inflammatory responses to infection via inhibition of Plasmodium falciparum glycosylphosphatidylinositol-induced activation of the mitogen-activated protein kinase (MAPK) and nuclear factor-kappaB (NF-kappaB) signaling pathways.

C5 deficiency and C5a or C5aR blockade protects against cerebral malaria.

Experimental infection of mice with Plasmodium berghei ANKA (PbA) provides a powerful model to define genetic determinants that regulate the development of cerebral malaria (CM). Based on the hypothesis that excessive activation of the complement system may confer susceptibility to CM, we investigated the role of C5/C5a in the development of CM. We show a spectrum of susceptibility to PbA in a panel of inbred mice; all CM-susceptible mice examined were found to be C5 sufficient, whereas all C5-deficient strains were resistant to CM.

Pyruvate kinase deficiency and malaria.

Malaria that is caused by Plasmodium falciparum is a significant global health problem. Genetic characteristics of the host influence the severity of disease and the ultimate outcome of infection, and there is evidence of coevolution of the plasmodium parasite with its host. In humans, pyruvate kinase deficiency is the second most common erythrocyte enzyme disorder.

HIV impairs opsonic phagocytic clearance of pregnancy-associated malaria parasites.

Background: Primigravid (PG) women are at risk for pregnancy-associated malaria (PAM). Multigravid (MG) women acquire protection against PAM; however, HIV infection impairs this protective response. Protection against PAM is associated with the production of IgG specific for variant surface antigens (VSA-PAM) expressed by chondroitin sulfate A (CSA)-adhering parasitized erythrocytes (PEs).

Disruption of CD36 impairs cytokine response to Plasmodium falciparum glycosylphosphatidylinositol and confers susceptibility to severe and fatal malaria in vivo.

CD36 is a scavenger receptor that has been implicated in malaria pathogenesis as well as innate defense against blood-stage infection. Inflammatory responses to Plasmodium falciparum GPI (pfGPI) anchors are believed to play an important role in innate immune response to malaria. We investigated the role of CD36 in pfGPI-induced MAPK activation and proinflammatory cytokine secretion.

Placental chondroitin sulfate A-binding malarial isolates evade innate phagocytic clearance.

Pregnancy-associated malaria is characterized by the accumulation of parasitized erythrocytes (PEs) and monocytes in the placenta, and they are believed to directly contribute to adverse birth outcomes. Although most parasite isolates adhere to CD36, placental isolates express novel variant surface antigens (VSAs) and bind to chondroitin sulfate A (CSA). CSA-binding PEs are rarely observed outside of pregnancy, and most primigravid women lack immunity and must rely on innate immune mechanisms to clear these placental parasite variants.

Nonopsonic phagocytosis of erythrocytes infected with ring-stage Plasmodium falciparum.

Ring-stage parasitized erythrocytes (RPEs) were demonstrated to interact with effector cells of the innate immune system. With receptor blockade studies and CD36-null macrophages, human and murine macrophages were shown to phagocytose RPEs through the pattern recognition receptor CD36. These in vitro data implicate scavenger receptors in the clearance of RPEs.

Enhanced phagocytosis of ring-parasitized mutant erythrocytes: a common mechanism that may explain protection against falciparum malaria in sickle trait and beta-thalassemia trait.

High frequency of erythrocyte (red blood cell [RBC]) genetic disorders such as sickle cell trait, thalassemia trait, homozygous hemoglobin C (Hb-C), and glucose-6-phosphate dehydrogenase (G6PD) deficiency in regions with high incidence of Plasmodium falciparum malaria and case-control studies support the protective role of those conditions. Protection has been attributed to defective parasite growth or to enhanced removal of the parasitized RBCs. We suggested enhanced phagocytosis of rings, the early intraerythrocytic form of the parasite, as an alternative explanation for protection in G6PD deficiency.

The Haldane malaria hypothesis: facts, artifacts, and a prophecy.

Heterozygous thalassemia and sickle cell disease produce mild hematological symptoms but provide protection against malaria mortality and severe malaria symptoms. Two explanations for resistance are considered in the literature - impaired growth of the parasite or enhanced removal by the host immune cells. A critical overview of studies that connect malaria resistance with impaired intra-erythrocytic growth is presented.

Innate immunity to malaria caused by Plasmodium falciparum.

Malaria, a widespread disease caused by protozoa of the genus Plasmodium, contributes to the death of more than 2 million people each year. Resistance to antimalarial drugs is increasing, and an effective vaccine has not yet been designed. In the search for alternative means to control malaria infections, especially those caused by the most lethal species of malaria parasite, Plasmodium falciparum, our attention has turned to elucidating the relationships of the parasite and human host at the molecular level.

16alpha-bromoepiandrosterone, an antimalarial analogue of the hormone dehydroepiandrosterone, enhances phagocytosis of ring stage parasitized erythrocytes: a novel mechanism for antimalarial activity.

Dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEA-S), which are the most abundant hormones secreted by the adrenal cortex and are present in plasma at approximately 6 micro M, as well as their analogue, 16alpha-bromoepiandrosterone (EPI), exerted antimalarial activities against two chloroquine-sensitive Plasmodium falciparum strains (Palo Alto, 50% inhibitory concentration [IC(50)] of EPI, 4.8 +/- 0.68 micro M; T996/86, IC(50) of EPI, 7.