Antigenicity and adhesiveness of a Plasmodium vivax VIR-E protein from Brazilian isolates.

BACKGROUND: Plasmodium vivax, the major cause of malaria in Latin America, has a large subtelomeric multigene family called vir. In the P. vivax genome, about 20% of its sequences are vir genes. Vir antigens are grouped in subfamilies according to their sequence similarities and have been shown to have distinct roles and subcellular locations. However, little is known about vir subfamilies, especially when comes to their functions. OBJECTIVE: To evaluate the diversity, antigenicity, and adhesiveness of Plasmodium vivax VIR-E. METHODS: Vir-E genes were amplified from six P. vivax isolates from Manaus, North of Brazil. The presence of naturally acquired antibodies to recombinant PvBrVIR-E and PvAMA-1 was evaluated by ELISA. Binding capacity of recombinant PvBrVIR-E was assessed by adhesion assay to CHO-ICAM1 cells. FINDINGS: Despite vir-E sequence diversity, among those identified sequences, a representative one was chosen to be expressed as recombinant protein. The presence of IgM or IgG antibodies to PvBrVIR-E was detected in 23.75% of the study population while the presence of IgG antibodies to PvAMA-1 antigen was 66.25% in the same population. PvBrVIR-E was adhesive to CHO-ICAM1. MAIN CONCLUSIONS: PvBrVIR-E was antigenic and adhesive to CHO-ICAM1.

Total parasite biomass but not peripheral parasitaemia is associated with endothelial and haematological perturbations in Plasmodium vivax patients.

Plasmodium vivax is the major cause of human malaria in the Americas. How P. vivax infection can lead to poor clinical outcomes, despite low peripheral parasitaemia, remains a matter of intense debate. Estimation of total P. vivax biomass based on circulating markers indicates existence of a predominant parasite population outside of circulation. In this study, we investigate associations between both peripheral and total parasite biomass and host response in vivax malaria. We analysed parasite and host signatures in a cohort of uncomplicated vivax malaria patients from Manaus, Brazil, combining clinical and parasite parameters, multiplexed analysis of host responses, and ex vivo assays. Patterns of clinical features, parasite burden, and host signatures measured in plasma across the patient cohort were highly heterogenous. Further data deconvolution revealed two patient clusters, here termed Vivaxlow and Vivaxhigh. These patient subgroups were defined based on differences in total parasite biomass but not peripheral parasitaemia. Overall Vivaxlow patients clustered with healthy donors and Vivaxhigh patients showed more profound alterations in haematological parameters, endothelial cell (EC) activation, and glycocalyx breakdown and levels of cytokines regulating different haematopoiesis pathways compared to Vivaxlow. Vivaxhigh patients presented more severe thrombocytopenia and lymphopenia, along with enrichment of neutrophils in the peripheral blood and increased neutrophil-to-lymphocyte ratio (NLCR). When patients' signatures were combined, high association of total parasite biomass with a subset of markers of EC activation, thrombocytopenia, and lymphopenia severity was observed. Finally, machine learning models defined a combination of host parameters measured in the circulation that could predict the extent of parasite infection outside of circulation. Altogether, our data show that total parasite biomass is a better predictor of perturbations in host homeostasis in P. vivax patients than peripheral parasitaemia. This supports the emerging paradigm of a P. vivax tissue reservoir, particularly in the haematopoietic niche of bone marrow and spleen.

Antigenicity and adhesiveness of a Plasmodium vivax VIR-E protein from Brazilian isolates

BACKGROUND Plasmodium vivax, the major cause of malaria in Latin America, has a large subtelomeric multigene family called vir. In the P. vivax genome, about 20% of its sequences are vir genes. Vir antigens are grouped in subfamilies according to their sequence similarities and have been shown to have distinct roles and subcellular locations. However, little is known about vir subfamilies, especially when comes to their functions. OBJECTIVE To evaluate the diversity, antigenicity, and adhesiveness of Plasmodium vivax VIR-E. METHODS Vir-E genes were amplified from six P. vivax isolates from Manaus, North of Brazil. The presence of naturally acquired antibodies to recombinant PvBrVIR-E and PvAMA-1 was evaluated by ELISA. Binding capacity of recombinant PvBrVIR-E was assessed by adhesion assay to CHO-ICAM1 cells. FINDINGS Despite vir-E sequence diversity, among those identified sequences, a representative one was chosen to be expressed as recombinant protein. The presence of IgM or IgG antibodies to PvBrVIR-E was detected in 23.75% of the study population while the presence of IgG antibodies to PvAMA-1 antigen was 66.25% in the same population. PvBrVIR-E was adhesive to CHO-ICAM1. MAIN CONCLUSIONS PvBrVIR-E was antigenic and adhesive to CHO-ICAM1.

Tafenoquine for the prophylaxis, treatment and elimination of malaria: eagerness must meet prudence.

Malaria puts more than 3 billion people at risk of infection and causes high morbidity and mortality. Plasmodium vivax forms hypnozoites, which may initiate recurrences, even in the absence of reinfection or superinfection. Until recently, the only drug available for eliminating hypnozoites was primaquine (PQ), which, given its short half-life, requires a relatively long course of treatment. Tafenoquine (TQ) is a PQ analog with a longer half-life. This enables radical cure of malaria with a single dose and overcomes adherence issues associated with PQ, thereby increasing effectiveness in real-life settings. Clinical studies have provided sound evidence for TQ's safety and efficacy against malaria, which recently led to its approval by the US FDA. Here, we review aspects of TQ, including how to avoid hemolytic anemia in G6PD deficient patients. We believe that TQ promises to be a major advance toward malaria elimination.

Chalcones as a basis for computer-aided drug design: innovative approaches to tackle malaria.

Aim: Computer-aided drug design approaches were applied to identify chalcones with antiplasmodial activity. Methodology: The virtual screening was performed as follows: structural standardization of in-house database of chalcones; identification of potential Plasmodium falciparum protein targets for the chalcones; homology modeling of the predicted P. falciparum targets; molecular docking studies; and in vitro experimental validation. Results: Using these models, we prioritized 16 chalcones with potential antiplasmodial activity, for further experimental evaluation. Among them, LabMol-86 and LabMol-87 showed potent in vitro antiplasmodial activity against P. falciparum, while LabMol-63 and LabMol-73 were potent inhibitors of Plasmodium berghei progression into mosquito stages. Conclusion: Our results encourage the exploration of chalcones in hit-to-lead optimization studies for tackling malaria.

A new heparan sulfate from the mollusk Nodipecten nodosus inhibits merozoite invasion and disrupts rosetting and cytoadherence of Plasmodium falciparum.

BACKGROUND: Despite treatment with effective antimalarial drugs, the mortality rate is still high in severe cases of the disease, highlighting the need to find adjunct therapies that can inhibit the adhesion of Plasmodium falciparum-infected erythrocytes (Pf-iEs). OBJECTIVES: In this context, we evaluated a new heparan sulfate (HS) from Nodipecten nodosus for antimalarial activity and inhibition of P. falciparum cytoadhesion and rosetting. METHODS: Parasite inhibition was measured by SYBR green using a cytometer. HS was assessed in rosetting and cytoadhesion assays under static and flow conditions using Chinese hamster ovary (CHO) and human lymphatic endothelial cell (HLEC) cells expressing intercellular adhesion molecule-1 (ICAM1) and chondroitin sulfate A (CSA), respectively. FINDINGS: This HS inhibited merozoite invasion similar to heparin. Moreover, mollusk HS decreased cytoadherence of P. falciparum to CSA and ICAM-1 on the surface of endothelial cells under static and flow conditions. In addition, this glycan efficiently disrupted rosettes. CONCLUSIONS: These findings support a potential use for mollusk HS as adjunct therapy for severe malaria.

A new heparan sulfate from the mollusk Nodipecten nodosus inhibits merozoite invasion and disrupts rosetting and cytoadherence of Plasmodium falciparum

BACKGROUND Despite treatment with effective antimalarial drugs, the mortality rate is still high in severe cases of the disease, highlighting the need to find adjunct therapies that can inhibit the adhesion of Plasmodium falciparum-infected erythrocytes (Pf-iEs). OBJECTIVES In this context, we evaluated a new heparan sulfate (HS) from Nodipecten nodosus for antimalarial activity and inhibition of P. falciparum cytoadhesion and rosetting. METHODS Parasite inhibition was measured by SYBR green using a cytometer. HS was assessed in rosetting and cytoadhesion assays under static and flow conditions using Chinese hamster ovary (CHO) and human lymphatic endothelial cell (HLEC) cells expressing intercellular adhesion molecule-1 (ICAM1) and chondroitin sulfate A (CSA), respectively. FINDINGS This HS inhibited merozoite invasion similar to heparin. Moreover, mollusk HS decreased cytoadherence of P. falciparum to CSA and ICAM-1 on the surface of endothelial cells under static and flow conditions. In addition, this glycan efficiently disrupted rosettes. CONCLUSIONS These findings support a potential use for mollusk HS as adjunct therapy for severe malaria.

On cytoadhesion of Plasmodium vivax: raison d'être?

It is generally accepted that Plasmodium vivax, the most widely distributed human malaria parasite, causes mild disease and that this species does not sequester in the deep capillaries of internal organs. Recent evidence, however, has demonstrated that there is severe disease, sometimes resulting in death, exclusively associated with P. vivax and that P. vivax-infected reticulocytes are able to cytoadhere in vitro to different endothelial cells and placental cryosections. Here, we review the scarce and preliminary data on cytoadherence in P. vivax, reinforcing the importance of this phenomenon in this species and highlighting the avenues that it opens for our understanding of the pathology of this neglected human malaria parasite.

Immunogenic properties of a recombinant fusion protein containing theC-terminal 19 kDa of Plasmodium falciparum merozoite surface protein-1 and the innate immunity agonist FliC flagellin of Salmonella Typhimurium

In a recent study, we demonstrated the immunogenic properties of a new malaria vaccine polypeptidebased on a 19 kDa C-terminal fragment of the merozoite surface protein-1 (MSP119) from Plasmodiumvivax and an innate immunity agonist, the Salmonella enterica serovar Typhimurium flagellin (FliC).Herein, we tested whether the same strategy, based on the MSP119 component of the deadly malariaparasite Plasmodium falciparum, could also generate a fusion polypeptide with enhanced immunogenicity.The His6FliC-MSP119 fusion protein was expressed from a recombinant Escherichia coli and showedpreserved in vitro TLR5-binding activity. In contrast to animals injected with His6MSP119, mice subcutaneouslyimmunised with the recombinant His6FliC-MSP119 developed strong MSP119-specific systemicantibody responses with a prevailing IgG1 subclass. Incorporation of other adjuvants, such as CpG ODN1826, complete and incomplete Freund’s adjuvants or Quil-A, improved the IgG responses after the second,but not the third, immunising dose. It also resulted in a more balanced IgG subclass response, asevaluated by the IgG1/IgG2c ratio, and higher cell-mediated immune response, as determined by thedetection of antigen-specific interferon- secretion by immune spleen cells. MSP119-specific antibodiesrecognised not only the recombinant protein, but also the native protein expressed on the surface of P.falciparum parasites. Finally, sera from rabbits immunised with the fusion protein alone inhibited the invitro growth of three different P. falciparum strains. In summary, these results extend our previous observationsand further demonstrate that fusion of the innate immunity agonist FliC to Plasmodium antigensis a promising alternative to improve their immunogenicity