Falciparum Erythrocyte Membrane Protein Research Articles

Mosaic and cocktail capsid-virus-like particle vaccines for induction of antibodies against the EPCR-binding CIDRα1 domain of PfEMP1.

The sequestration of Plasmodium falciparum-infected erythrocytes to the host endothelium is central to the pathogenesis of malaria. The sequestration is mediated by the parasite´s diverse Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) variants, which bind select human receptors on the endothelium. Severe malaria is associated with PfEMP1 binding human endothelial protein C receptor (EPCR) via their CIDRα1 domains. Antibodies binding and inhibiting across the sequence diverse CIDRα1 domains are likely important in acquired immunity against severe malaria. In this study, we explored if immunization with AP205 bacteriophage capsid-virus-like particles (cVLPs) presenting a mosaic of diverse CIDRα1 protein variants would stimulate broadly reactive and inhibitory antibody responses in mice. Three different mosaic cVLP vaccines each composed of five CIDRα1 protein variants with varying degrees of sequence conservation of residues at and near the EPCR binding site, were tested. All mosaic cVLP vaccines induced functional antibodies comparable to those induced by matched cocktails of cVLPs decorated with the single CIDRα1 variant. No broadly reactive responses were observed. However, the vaccines did induce some cross-reactivity and inhibition within the CIDRα1 subclasses included in the vaccines, demonstrating potential use of the cVLP vaccine platform for the design of multivalent vaccines.

Fatty Acid Esters and Acyclic Monoterpenoid from Justicia insularis Leaf Fractions Attenuated Malaria Pathogenesis Through Docking with Plasmodium falciparum Serine Hydroxymethyl Transferase and Plasmodium falciparum Erythrocyte Membrane Protein 1 Proteins

Background Justicia insularis (Acanthaceae) T. Anderson is ethnopharmacologically used in Nigeria for the treatment of diseases including malaria. Therefore, this study was designed to investigate in vivo antiplasmodial effect of J. insularis leaf in Plasmodium berghei-infected mice, characterize its constituents, and carryout in silico studies of its compounds. Methods Standard protocols were followed in the processing of the plant leaves, extraction, fractionation, isolation, and characterization, evaluation of in vivo antiplasmodial assay, retrieval of Plasmodium falciparum serine hydroxymethyl transferase (PfSHMT) and Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP-1) proteins, absorption, distribution, metabolism, excretion, and toxicity (ADMET), and docking studies. Gas chromatography-mass spectrometry (GC-MS) was employed to isolate and characterize the compounds; SWISSADME and ADMET lab 2 enhanced the evaluation of pharmacokinetic properties, PyRx for docking analysis; Biovia discovery studio for 2D visualization, and PyMol software for 3D visualization of the ligand-protein interactions. Results The dichloromethane (61.59%) and ethyl acetate (73.15%) fractions had the best therapeutic indices and compared favorably with chloroquine (81.58%) in the curative antiplasmodial assay. The GC-MS analysis revealed 20 already reported antiplasmodial compounds with hexanoic acid 1,1-dimethylethyl ester, octadecanoic acid docosyl ester, and trans-β-ocimene as the lead compounds based on their binding affinities, permeation of the blood-brain-barrier, non-inhibition of metabolizing enzymes, ease of excretion, non-carcinogenicity, as well as non-violation of Lipinski's criteria. Conclusion Octadecanoic acid docosyl ester and hexanoic acid 1,1-dimethylethyl ester bonded the tetrahydrofolate-binding sites of PfSHMT, caused inhibition of DNA synthesis, and apoptosis, whereas trans-β-ocimene inhibited PfEMP-1, reversed the attachment of parasitized red blood cells to micro-vascular endothelium as their mechanism of action for parasitemia clearance. Moreover, these lead compounds reported for the first time in the dichloromethane and EtoAc fractions of this plant are responsible for the remarkable antiplasmodial activity observed in this study.

Increased of Spleen White Pulp Diameter Post Dbl2β-Pfemp1 Recombinant Protein Injection in Wistar Rats: Pre-Clinical Study for Malaria Vaccine Development

Malaria is a major infectious disease worldwide, and vaccination is essential for disease control. The Plasmodium falciparum Erythrocyte Membrane Protein-1 (PfEMP1) is a potential malaria vaccine candidate due to its involvement in pathogenesis. Injection of DBL2β-PfEMP1 recombinant protein in animal models induces IgG and CD4+ production and inhibits binding with host endothelial receptors. This study aimed to analyze the spleen immune response by measuring the white pulp diameter. The experimental study used Wistar rats (Rattus norvegicus) that were divided into four groups, a control group and three treatment groups, which were injected with 100, 150, and 200 μg of DBL2β-PfEMP1 protein. Injection was done thrice with three-week intervals (days 0, 21, and 42). On day 56, rats were euthanized, and spleens were prepared for histology examination. The white pulp diameter increased along with increasing the dose of protein. The ANOVA test showed a significant difference between groups (p=0.001). The posthoc Bonferroni test showed a significant difference between the control and the 150 and 200 μg groups and the 100 μg and 200 μg groups. In conclusion, the DBL2β-PfEMP1 recombinant protein injection increased the spleen white pulp diameter in Wistar rats, and the 200 μg dose resulted in the highest increase.

Detection of naturally acquired, strain-transcending antibodies against rosetting Plasmodium falciparum strains in humans.

Strain-transcending antibodies against virulence-associated subsets of P. falciparum-infected erythrocyte surface antigens could protect children from severe malaria. However, the evidence supporting the existence of such antibodies is incomplete and inconsistent. One subset of surface antigens associated with severe malaria, rosette-mediating Plasmodium falciparum Erythrocyte Membrane Protein one (PfEMP1) variants, cause infected erythrocytes to bind to uninfected erythrocytes to form clusters of cells (rosettes) that contribute to microvascular obstruction and pathology. Here, we tested plasma from 80 individuals living in malaria-endemic regions for IgG recognition of the surface of four P. falciparum rosetting strains using flow cytometry. Broadly reactive plasma samples were then used in antibody elution experiments in which intact IgG was eluted from the surface of infected erythrocytes and transferred to heterologous rosetting strains to look for strain-transcending antibodies. We found that seroprevalence (percentage of positive plasma samples) against allopatric rosetting strains was high in adults (63%-93%) but lower in children (13%-48%). Strain-transcending antibodies were present in nine out of eleven eluted antibody experiments, with six of these recognizing multiple heterologous rosetting parasite strains. One eluate had rosette-disrupting activity against heterologous strains, suggesting PfEMP1 as the likely target of the strain-transcending antibodies. Naturally acquired strain-transcending antibodies to rosetting P. falciparum strains in humans have not been directly demonstrated previously. Their existence suggests that such antibodies could play a role in clinical protection and raises the possibility that conserved epitopes recognized by strain-transcending antibodies could be targeted therapeutically by monoclonal antibodies or vaccines.

Endothelial Protein C Receptor and Its Impact on Rheumatic Disease.

Endothelial Protein C Receptor (EPCR) is a key regulator of the activated protein C anti-coagulation pathway due to its role in the binding and activation of this protein. EPCR also binds to other ligands such as Factor VII and X, γδ T-cells, plasmodium falciparum erythrocyte membrane protein 1, and Secretory group V Phospholipases A2, facilitating ligand-specific functions. The functions of EPCR can also be regulated by soluble (s)EPCR that competes for the binding sites of membrane-bound (m)EPCR. sEPCR is created when mEPCR is shed from the cell surface. The propensity of shedding alters depending on the genetic haplotype of the EPCR gene that an individual may possess. EPCR plays an active role in normal homeostasis, anti-coagulation pathways, inflammation, and cell stemness. Due to these properties, EPCR is considered a potential effector/mediator of inflammatory diseases. Rheumatic diseases such as rheumatoid arthritis and systemic lupus erythematosus are autoimmune/inflammatory conditions that are associated with elevated EPCR levels and disease activity, potentially driven by EPCR. This review highlights the functions of EPCR and its contribution to rheumatic diseases.

Glycophorin B-PfEMP1 interaction mediates robust rosetting in Plasmodium falciparum

P. falciparumerythrocyte membrane protein 1 (PfEMP1) is the major parasite protein responsible for rosetting by binding to host receptors such as heparan sulfate, CR1 on RBC surface. Usually monomeric protein-carbohydrate interactions are weak [1], therefore PfEMP1 binds to plasma proteins like IgM or α2-macroglobulin that facilitate its clustering on parasitized RBC surface and augment rosetting [2,3]. We show that 3D7A expresses PfEMP1, PF3D7_0412900, and employs its CIDRγ2 domain to interact with glycophorin B on uninfected RBC to form large rosettes but more importantly even in the absence of plasma proteins. Overall, we established the role of PF3D7_0412900 in rosetting as antibodies against CIDRγ2 domain reduced rosetting and also identified its receptor, glycophorin B which could provide clue why glycophorin B null phenotype, S-s-U- RBCs prevalent in malaria endemic areas is protective against severe malaria.

A novel computational pipeline for var gene expression augments the discovery of changes in the Plasmodium falciparum transcriptome during transition from in vivo to short-term in vitro culture

The pathogenesis of severe Plasmodium falciparum malaria involves cytoadhesive microvascular sequestration of infected erythrocytes, mediated by P. falciparum erythrocyte membrane protein 1 (PfEMP1). PfEMP1 variants are encoded by the highly polymorphic family of var genes, the sequences of which are largely unknown in clinical samples. Previously, we published new approaches for var gene profiling and classification of predicted binding phenotypes in clinical P. falciparum isolates (Wichers et al., 2021), which represented a major technical advance. Building on this, we report here a novel method for var gene assembly and multidimensional quantification from RNA-sequencing that outperforms the earlier approach of Wichers et al., 2021, on both laboratory and clinical isolates across a combination of metrics. Importantly, the tool can interrogate the var transcriptome in context with the rest of the transcriptome and can be applied to enhance our understanding of the role of var genes in malaria pathogenesis. We applied this new method to investigate changes in var gene expression through early transition of parasite isolates to in vitro culture, using paired sets of ex vivo samples from our previous study, cultured for up to three generations. In parallel, changes in non-polymorphic core gene expression were investigated. Modest but unpredictable var gene switching and convergence towards var2csa were observed in culture, along with differential expression of 19% of the core transcriptome between paired ex vivo and generation 1 samples. Our results cast doubt on the validity of the common practice of using short-term cultured parasites to make inferences about in vivo phenotype and behaviour.

A novel computational pipeline for var gene expression augments the discovery of changes in the Plasmodium falciparum transcriptome during transition from in vivo to short-term in vitro culture.

The pathogenesis of severe Plasmodium falciparum malaria involves cytoadhesive microvascular sequestration of infected erythrocytes, mediated by P. falciparum erythrocyte membrane protein 1 (PfEMP1). PfEMP1 variants are encoded by the highly polymorphic family of var genes, the sequences of which are largely unknown in clinical samples. Previously, we published new approaches for var gene profiling and classification of predicted binding phenotypes in clinical P. falciparum isolates (Wichers et al., 2021), which represented a major technical advance. Building on this, we report here a novel method for var gene assembly and multidimensional quantification from RNA-sequencing that outperforms the earlier approach of Wichers et al., 2021, on both laboratory and clinical isolates across a combination of metrics. Importantly, the tool can interrogate the var transcriptome in context with the rest of the transcriptome and can be applied to enhance our understanding of the role of var genes in malaria pathogenesis. We applied this new method to investigate changes in var gene expression through early transition of parasite isolates to in vitro culture, using paired sets of ex vivo samples from our previous study, cultured for up to three generations. In parallel, changes in non-polymorphic core gene expression were investigated. Modest but unpredictable var gene switching and convergence towards var2csa were observed in culture, along with differential expression of 19% of the core transcriptome between paired ex vivo and generation 1 samples. Our results cast doubt on the validity of the common practice of using short-term cultured parasites to make inferences about in vivo phenotype and behaviour.

PfEMP1 and var genes - Still of key importance in Plasmodium falciparum malaria pathogenesis and immunity.

The most severe form of malaria, caused by infection with Plasmodium falciparum parasites, continues to be an important cause of human suffering and poverty. The P. falciparum erythrocyte membrane protein 1 (PfEMP1) family of clonally variant antigens, which mediates the adhesion of infected erythrocytes to the vascular endothelium in various tissues and organs, is a central component of the pathogenesis of the disease and a key target of the acquired immune response to malaria. Much new knowledge has accumulated since we published a systematic overview of the PfEMP1 family almost ten years ago. In this chapter, we therefore aim to summarize research progress since 2015 on the structure, function, regulation etc. of this key protein family of arguably the most important human parasite. Recent insights regarding PfEMP1-specific immune responses and PfEMP1-specific vaccination against malaria, as well as an outlook for the coming years are also covered.

Profiles of global mutations in the human intercellular adhesion molecule-1 (ICAM-1) shed light on population-specific malaria susceptibility

Plasmodium falciparum is responsible for malaria-related morbidity and mortality. PfEMP1 (P. falciparum erythrocyte membrane protein 1) mediates infected erythrocytes adhesion to various surface vascular receptors, including intercellular adhesion molecule-1 (ICAM-1), associating this interaction with severe malaria in several studies. Genetic variation in host ICAM-1 plays a significant role in determining susceptibility to malaria infection via clinical phenotypes such as the ICAM-1Kilifi variant which has been reported to be associated with susceptibility in populations. Our genomic and structural analysis of single nucleotide polymorphisms (SNPs) in ICAM-1 revealed 9 unique mutations each in its distinct A-type and BC-type PfEMP1 DBLβ-interacting regions. These mutations are noted in only a few field isolates and mainly in the African/African American population. The ICAM-1Kilifi variant lies in a flexible loop proximal to the DBLβ-interacting region. This analysis will assist in establishing functional correlations of reported global mutations via experimental and clinical studies and in the tailored design of population-specific genetic surveillance studies. Understanding host polymorphism as an evolutionary force in diverse populations can help to predict predisposition to disease severity and will contribute towards laying the framework for designing population-specific personalized medicines for severe malaria.

SEVUparin as a potential Adjunctive Treatment in children with severe malaria: A phase I trial safety and dose finding trial (SEVUSMAART)

Background Even on the best antimalarial treatments (injectable artesunate) African children with severe malaria have poor outcomes with most deaths occurring early in the course of hospital admission (<24hours). Lactic acidosis, largely due to impairment of the microcirculatory flow due to parasite sequestration, is a main risk factor for poor outcome. There are no adjuvant treatments for severe malaria that target this complication. Sevuparin, a heparin-like drug, binds to Plasmodium falciparum erythrocyte membrane protein blocking merozoite invasion, preventing cytoadherence and transiently de-sequestering infected erythrocytes. Leading to improved microcirculatory flow by reversing/preventing parasite sequestration. If given early during admission this could result in improvements in outcomes . Sevuparin has been shown to be safe and well tolerated in adults with only some mild transient effects on activated partial thromboplastin time (APTT) were reported, without clinical consequences. Methods A Phase I trial designed to provide data on safety, dosing, feasibility of sevuparin as an adjuvant therapy in Kenya and Zambian children with severe malaria complicated by lactic acidosis (> 2mmol/l). Three intravenous doses will be given at admission (0 hours), 8 and 16 hours. APPT will be measured 1 hour after each dose (to assess maximum toxicity). Studying 20 children will allow sufficient data on safety to be generated across a range of doses to identify the maximum tolerated dose (MTD) using the Continual Reassessment Method, which adapts or informs subsequent doses for each child based on the data from previously enrolled children. The MTD will be identified based on the dose-toxicity model updated by each previous patient’s APTT results using standard methods. Conclusions The results of the Phase I trial will identify the final dose to be tested in a Phase II trial in terms of both efficacy and safety outcomes. Registration PACTR number: 202007890194806 (date 20/07/2020) ISRCTN32271864 (date 28/07/2021)

Profiling the Plasmodium falciparum Erythrocyte Membrane Protein 1-Specific Immununoglobulin G Response Among Ghanaian Children With Hemoglobin S and C.

Members of the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family are important targets for protective immunity. Abnormal display of PfEMP1 on the surfaces of infected erythrocytes (IEs) and reduced cytoadhesion have been demonstrated in hemoglobin (Hb) AS and HbAC, inherited blood disorders associated with protection against severe P. falciparum malaria. We found that Ghanaian children with HbAS had lower levels of immunoglobulin G against several PfEMP1 variants and that this reactivity increased more slowly with age than in their HbAA counterparts. Moreover, children with HbAS have lower total parasite biomass than those with HbAA at comparable peripheral parasitemias, suggesting impaired cytoadhesion of HbAS IEs in vivo and likely explaining the slower acquisition of PfEMP1-specific immunoglobulin G in this group. In contrast, the function of acquired antibodies was comparable among Hb groups and appears to be intact and sufficient to control parasitemia via opsonization and phagocytosis of IEs.

Natural immunity to malaria preferentially targets the endothelial protein C receptor-binding regions of PfEMP1s.

Antibody responses to variant surface antigens (VSAs) produced by the malaria parasite Plasmodium falciparum may contribute to age-related natural immunity to severe malaria. One VSA family, P. falciparum erythrocyte membrane protein-1 (PfEMP1), includes a subset of proteins that binds endothelial protein C receptor (EPCR) in human hosts and potentially disrupts the regulation of inflammatory responses, which may lead to the development of severe malaria. We probed peptide microarrays containing segments spanning five PfEMP1 EPCR-binding domain variants with sera from 10 Malian adults and 10 children to determine the differences between adult and pediatric immune responses. We defined serorecognized peptides and amino acid residues as those that elicited a significantly higher antibody response than malaria-naïve controls. We aimed to identify regions consistently serorecognized among adults but not among children across PfEMP1 variants, potentially indicating regions that drive the development of immunity to severe malaria. Adult sera consistently demonstrated broader and more intense serologic responses to constitutive PfEMP1 peptides than pediatric sera, including peptides in EPCR-binding domains. Both adults and children serorecognized a significantly higher proportion of EPCR-binding peptides than peptides that do not directly participate in receptor binding, indicating a preferential development of serologic responses at functional residues. Over the course of a single malaria transmission season, pediatric serological responses increased between the start and the peak of the season, but waned as the transmission season ended. IMPORTANCE Severe malaria and death related to malaria disproportionately affect sub-Saharan children under 5 years of age, commonly manifesting as cerebral malaria and/or severe malarial anemia. In contrast, adults in malaria-endemic regions tend to experience asymptomatic or mild disease. Our findings indicate that natural immunity to malaria targets specific regions within the EPCR-binding domain, particularly peptides containing EPCR-binding residues. Epitopes containing these residues may be promising targets for vaccines or therapeutics directed against severe malaria. Our approach provides insight into the development of natural immunity to a binding target linked to severe malaria by characterizing an "adult-like" response as recognizing a proportion of epitopes within the PfEMP1 protein, particularly regions that mediate EPCR binding. This "adult-like" response likely requires multiple years of malaria exposure, as increases in pediatric serologic response over a single malaria transmission season do not appear significant.

VAR2CSA protein for malaria vaccine or anticancer drug delivery? A review of preclinical and clinical research

Variant surface antigen 2- chondroitin sulfate A (VAR2CSA) is a protein belonging to the Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) family. Since the discovery of the protein, various studies have been carried out to utilize VAR2CSA in the clinical field. The typical application is the development of malaria vaccines and anticancer drug carriers based on VAR2CSA. Will anticancer drugs (with VAR2CSA vehicle) work effectively in patients who have already received the VAR2CSA-based malaria vaccine? Given that theoretically, the presence of antibodies triggered by the VAR2CSA vaccine might be against anticancer drugs delivered by VAR2CSA. Therefore, a review regarding the development of research on VAR2CSA, especially as a vaccine or anticancer drug vehicle, is needed. This paper provides an overview of current knowledge about VAR2CSA including its structure and function, biochemical aspects, research approaches both in vitro, ex vivo and in vivo, and the development of potential studies of VAR2CSA in the field of medicine. The literature search was carried out systematically from the PubMed database with the keywords “VAR2CSA”, “VAR2CSA” AND “vaccine”, "VAR2CSA" AND "drug delivery", "VAR2CSA" AND "cancer", "VAR2CSA" AND "placental malaria", "VAR2CSA" AND "review". A Study of VAR2CSA shows promising results, especially in the development of VAR2CSA as the main candidate for the placental malaria vaccine and anticancer drug carrier. Current findings reveal that both studies will carry out clinical trials soon. However, limitations of the study should be considered in future clinical applications for more effective cancer treatment, such as the administration of anticancer drugs by VAR2CSA vehicles on patients who have already received VAR2CSA-based antimalarial vaccines. Furthermore, an example of promising future research is leveraging other domains of VAR2CSA that have not been explored yet.

High-Throughput Antibody Profiling Identifies Targets of Protective Immunity against P. falciparum Malaria in Thailand.

Malaria poses a significant global health challenge, resulting in approximately 600,000 deaths each year. Individuals living in regions with endemic malaria have the potential to develop partial immunity, thanks in part to the presence of anti-plasmodium antibodies. As efforts are made to optimize and implement strategies to reduce malaria transmission and ultimately eliminate the disease, it is crucial to understand how these interventions impact naturally acquired protective immunity. To shed light on this, our study focused on assessing antibody responses to a carefully curated library of P. falciparum recombinant proteins (n = 691) using samples collected from individuals residing in a low-malaria-transmission region of Thailand. We conducted the antibody assays using the AlphaScreen system, a high-throughput homogeneous proximity-based bead assay that detects protein interactions. We observed that out of the 691 variable surface and merozoite stage proteins included in the library, antibodies to 268 antigens significantly correlated with the absence of symptomatic malaria in an univariate analysis. Notably, the most prominent antigens identified were P. falciparum erythrocyte membrane protein 1 (PfEMP1) domains. These results align with our previous research conducted in Uganda, suggesting that similar antigens like PfEMP1s might play a pivotal role in determining infection outcomes in diverse populations. To further our understanding, it remains critical to conduct functional characterization of these identified proteins, exploring their potential as correlates of protection or as targets for vaccine development.

Endothelial protein C receptor binding induces conformational changes to severe malaria-associated group A PfEMP1

Severe Plasmodium falciparum malaria infections are caused by microvascular sequestration of parasites binding to the human endothelial protein C receptor (EPCR) via the multi-domain P. falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion ligands. Using cryogenic electron microscopy (Cryo-EM) and PfEMP1 sequence diversity analysis, we found that group A PfEMP1 CIDRα1 domains interact with the adjacent DBLα1 domain through central, conserved residues of the EPCR-binding site to adopt a compact conformation. Upon EPCR binding, the DBLα1 domain is displaced, and the EPCR-binding helix of CIDRα1 is turned, kinked, and twisted to reach a rearranged, stable EPCR-bound conformation. The unbound conformation and the required transition to the EPCR-bound conformation may represent a conformational masking mechanism of immune evasion for the PfEMP1 family.

Knobs, Adhesion, and Severe Falciparum Malaria.

Plasmodium falciparum can cause a severe disease with high mortality. A major factor contributing to the increased virulence of P. falciparum, as compared to other human malarial parasites, is the sequestration of infected erythrocytes in the capillary beds of organs and tissues. This sequestration is due to the cytoadherence of infected erythrocytes to endothelial cells. Cytoadherence is primarily mediated by a parasite protein expressed on the surface of the infected erythrocyte called P. falciparum erythrocyte membrane protein-1 (PfEMP1). PfEMP1 is embedded in electron-dense protuberances on the surface of the infected erythrocytes called knobs. These knobs are assembled on the erythrocyte membrane via exported parasite proteins, and the knobs function as focal points for the cytoadherence of infected erythrocytes to endothelial cells. PfEMP1 is a member of the var gene family, and there are approximately 60 antigenically distinct PfEMP1 alleles per parasite genome. Var gene expression exhibits allelic exclusion, with only a single allele being expressed by an individual parasite. This results in sequential waves of antigenically distinct infected erythrocytes and this antigenic variation allows the parasite to establish long-term chronic infections. A wide range of endothelial cell receptors can bind to the various PfEMP1 alleles, and thus, antigenic variation also results in a change in the cytoadherence phenotype. The cytoadherence phenotype may result in infected erythrocytes sequestering in different tissues and this difference in sequestration may explain the wide range of possible clinical manifestations associated with severe falciparum malaria.

Design and Molecular Docking Studies of N-Mannich Base Derivatives of Primaquine Bearing Isatin on the Targets involved in the Pathophysiology of Cerebral Malaria.

Malaria is considered one of the life-threatening mosquito-borne infectious diseases responsible for approximately more than 4,00,000 deaths every year all over the world. Plasmodium falciparum and Plasmodium vivax are widespread species, but infections caused by the former are of great concern. Among the various forms of infections associated with Plasmodium falciparum, cerebral malaria (CM) is the most severe neurological complication, accounting for almost 13% of all malariarelated mortality. The development of effective therapeutics is urgently needed to overcome the fatality of this dreadful disease. The present work attempted to design and virtually screen a chemical library of 75 molecules (N-Mannich base derivatives of primaquine bearing isatin moiety as heterocyclic) by molecular docking studies against anti-malarial target proteins-Cystein Protease Falcipain-2; Dipeptidyl Aminopeptidase- 1; Dipeptidyl Aminopeptidase-3 and Glycogen synthase Kinase-3β receptors, for evaluating their anti-malarial potential. Among all studied anti-malarial target receptors, the designed molecules showed an overall higher affinity for Dipeptidyl Aminopeptidase-3. Furthermore, the molecules were analyzed for binding affinity and drug-like properties using Lipinski rules, and 30 best hits were shortlisted and analyzed for the pharmacokinetic profile. Two of these hits were found to be more toxic than primaquine, hence were omitted in further analysis. Later, these 28 hits were docked against two target proteins, (a) Plasmodium falciparum erythrocyte membrane protein-1 and (b) Intracellular adhesion molecule-1, to determine their efficiency against cerebral malaria, and the results were recorded. Analysis of docking results led to the identification of the 8 studied molecules as lead molecules which were selected for chemical synthesis, in vivo studies, and further preclinical evaluation. The molecule DSR 11 was predicted as the most appropriate lead molecule for anti-CM activity in the present investigation apart from the other seven molecules (DSR4, DSR26, DSR38, DSR40, DSR49, DSR56, and DSR70).

Antibody to Plasmodium falciparum Variant Surface Antigens, var Gene Transcription, and ABO Blood Group in Children With Severe or Uncomplicated Malaria.

Antibodies to variant surface antigens (VSAs) such as Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) may vary with malaria severity. The influence of ABO blood group on antibody development is not understood. Immunoglobulin G antibodies to VSAs in Papua New Guinean children with severe (n = 41) or uncomplicated (n = 30) malaria were measured by flow cytometry using homologous P falciparum isolates. Isolates were incubated with ABO-matched homologous and heterologous acute and convalescent plasma. RNA was used to assess var gene transcription. Antibodies to homologous, but not heterologous, isolates were boosted in convalescence. The relationship between antibody and severity varied by blood group. Antibodies to VSAs were similar in severe and uncomplicated malaria at presentation, higher in severe than uncomplicated malaria in convalescence, and higher in children with blood group O than other children. Six var gene transcripts best distinguished severe from uncomplicated malaria, including UpsA and 2 CIDRα1 domains. ABO blood group may influence antibody acquisition to VSAs and susceptibility to severe malaria. Children in Papua New Guinea showed little evidence of acquisition of cross-reactive antibodies following malaria. Var gene transcripts in Papua New Guinean children with severe malaria were similar to those reported from Africa.

Structural and genomic analysis of single nucleotide polymorphisms in human host factor endothelial protein C receptor (EPCR) reveals complex interplay with malaria parasites.

Plasmodium parasites responsible for malaria follow a complex life cycle of which half takes place inside the human host. Parasites present diverse antigens at different stages of their life cycle and interact with many surface molecules to attach to and enter host cells. The CIDRα1 domain of Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) in infected erythrocytes adheres to one such vascular receptor endothelial protein C receptor (EPCR). EPCR is implicated in the pathogenesis of severe malaria as preferential binding of CIDRα1 to endothelium results in widespread sequestration of infected erythrocytes leading to endothelium inflammation and severe disease. A single EPCR variant S219G is clinically reported to provide protection from severe malaria. In this work, we have collated all single nucleotide polymorphisms (SNPs) in EPCR from dbSNP. We structurally mapped the SNPs on the three-dimensional complex of EPCR and PfEMP1 CIDRα1. Analysis shows that most EPCR mutations lie on the receptor surface and are non-conservative. Of the 11 mutations in the CIDRα1-interaction region of EPCR, S88P, L96V/I, and R98L/H/P/C are seen with comparably higher occurrences in diverse populations. Our structural analysis details a framework of the interactions between the parasite ligand and host factor EPCR. These structural glimpses provide a blueprint for designing both field-based variant sequencing studies and vaccine development.