Adhesion of Plasmodium falciparum-infected erythrocytes to human cells: molecular mechanisms and therapeutic implications. Expert Rev Mol Med. 2009;11:e16. [PMID: 19467172 PMCID: PMC2878476 DOI: 10.1017/s1462399409001082]

Extant interspecific hybridization among trematodes within the Schistosoma haematobium species complex in Nigeria

BACKGROUND

Natural interspecific hybridization between the human parasite (Schistosoma haematobium [Sh]) and bovine parasites (Schistosoma bovis [Sb], Schistosoma curassoni [Sc]) is increasingly reported in Africa. We developed a multi-locus PCR DNA-Seq strategy that amplifies two unlinked nuclear (transITS, BF) and two linked organellar genome markers (CO1, ND5) to genotype S. haematobium eggs collected from infected people in Ile Oluji/Oke Igbo, Ondo State (an agrarian community) and Kachi, Jigawa State (a pastoral community) in Southwestern and Northern Nigeria, respectively.

PRINCIPAL FINDINGS

Out of a total of 219 urine samples collected, 57 were positive for schistosomes. All patients from Jigawa state possessed an Sh mitochondrial genome and were infected with a genetic profile consistent with an Sh x Sb hybrid based on sequences obtained at CO1, ND5, transITS and BF nuclear markers. Whereas samples collected from Ondo state were more varied. Mitonuclear discordance was observed in all 17 patients, worms possessed an Sb mitochondrial genome but one of four different genetic profiles at the nuclear markers, either admixed (heterozygous between Sh x Sc or Sh x Sb) at both markers (n = 10), Sh at BF and admixed at transITS (Sh x Sc) (n = 5), admixed (Sh x Sc) at BF and homozygous Sc at transITS (n = 1) or homozygous Sh at BF and homozygous Sc at transITS (n = 1).

SIGNIFICANCE

Previous work suggested that zoonotic transmission of S. bovis in pastoral communities, where humans and animals share a common water source, is a driving factor facilitating interspecific hybridization. However, our data showed that all samples were hybrids, with greater diversity identified in Southwestern Nigeria, a non-pastoral site. Further, one patient possessed an S. bovis mitochondrial genome but was homozygous for S. haematobium at BF and homozygous for S. curassoni at transITS supporting at least two separate backcrosses in its origin, suggesting that interspecific hybridization may be an ongoing process.

Biological evaluation of novel side chain containing CQTrICh-analogs as antimalarials and their development as PfCDPK1 kinase inhibitors

The rapid emergence of resistance to existing frontline antimalarial drugs emphasizes a need for the development of target-oriented molecules with novel modes of action. Given the importance of a plant-like Calcium-Dependent Protein Kinase 1 (PfCDPK1) as a stand-alone multistage signalling regulator of P. falciparum, we designed and synthesized 7-chloroquinoline-indole-chalcones tethered with a triazole (CQTrICh-analogs 7 (a-s) and 9) directed towards PfCDPK1. This was accomplished by reacting substituted 1-phenyl-3-(1-(prop-2-yn-1-yl)-1H-indol-3-yl) prop-2-en-1-one and 1-(prop-2-yn-1-yl)-1H-indole-3-carbaldehyde with 4-azido-7-chloroquinoline, respectively via a 'click' reaction. The selected CQTrICh-analogs: 7l and 7r inhibited the growth of chloroquine-sensitive 3D7 strain and -resistant RKL-9 isolate of Plasmodium falciparum, with IC50 values of 2.4 μM & 1.8 μM (7l), and 3.5 μM & 2.7 μM (7r), respectively, and showed no apparent hemolytic activity and cytotoxicity in mammalian cells. Intra-erythrocytic progression studies revealed that the active hybrids: 7l and 7r are effective against the mature stages of the parasite. 7l and 7r were found to stably interact with the catalytically active ATP-binding pocket of PfCDPK1 via energetically favourable H-bonds. The interaction was confirmed in vitro by microscale thermophoresis and kinase assays, which demonstrated that the active hybrids interact with PfCDPK1 and inhibit its kinase activity which is presumably responsible for the parasite growth inhibition. Interestingly, 7l and 7r showed no inhibitory effect on the human kinases, indicating their selectivity for the parasite kinase. We report the antiplasmodial potential of novel kinase-targeting bio-conjugates, a step towards developing pan-kinase inhibitors which is a prerequisite for multistage anti-malarial protection.

An immune memory-structured SIS epidemiological model for hyperdiverse pathogens

A hyperdiverse class of pathogens of humans and wildlife, including the malaria parasite Plasmodium falciparum, relies on multigene families to encode antigenic variation. As a result, high (asymptomatic) prevalence is observed despite high immunity in local populations under high-transmission settings. The vast diversity of "strains" and genes encoding this variation challenges the application of established models for the population dynamics of such infectious diseases. Agent-based models have been formulated to address theory on strain coexistence and structure, but their complexity can limit application to gain insights into population dynamics. Motivated by P. falciparum malaria, we develop an alternative formulation in the form of a structured susceptible-infected-susceptible population model in continuous time, where individuals are classified not only by age, as is standard, but also by the diversity of parasites they have been exposed to and retain in their specific immune memory. We analyze the population dynamics and bifurcation structure of this system of partial-differential equations, showing the existence of alternative steady states and an associated tipping point with transmission intensity. We attribute the critical transition to the positive feedback between parasite genetic diversity and force of infection. Basins of attraction show that intervention must drastically reduce diversity to prevent a rebound to high infection levels. Results emphasize the importance of explicitly considering pathogen diversity and associated specific immune memory in the population dynamics of hyperdiverse epidemiological systems. This statement is discussed in a more general context for ecological competition systems with hyperdiverse trait spaces.

Haematological parameters and their correlation with the degree of malaria parasitaemia among outpatients attending a polyclinic

BACKGROUND

Malaria is a parasitic disease caused by various species of the blood parasite Plasmodium; of all the parasitic diseases, malaria has the highest prevalence and mortality with an estimated 247 million cases and 619,000 deaths recorded worldwide as of 2021. Malaria causes febrile illness with several changes in blood cell parameters. Some of these changes include leucopenia, thrombocytopenia, and anaemia. If these changes could be correlated with the degree of parasitaemia, it can serve as a guide to physicians when treating malaria. This study was therefore aimed at correlating haematological parameters with levels of parasitaemia during malaria infection.

METHODS

The study was a cross-sectional study involving 89 malaria positive patients. About 5 ml of blood was collected from each participant who gave his or her informed consent to partake in the study. A full blood count was performed on their samples to determine their haematological parameters using a haematology auto-analyzer. A parasite count was also performed via microscopy to determine the degree of parasitaemia. The data obtained from the study was entered into a database and statistically analysed using Statistical Package for Social Sciences (SPSS) version 23 and Microsoft Excel 2016.

RESULTS

The study comprised of 89 participants out of which 35 were males and 54 were females with the mean age of 26.15 years. Secondary education participants were the highest with quaternary education the lowest. The highest parasite count recorded was 398,174 parasites/µl of blood, lowest count was 101 with the average being 32,942.32584. There was also a significant positive Pearson's correlation between total WBC and parasitaemia and with the WBC differentials, neutrophils, lymphocytes and monocytes had positive correlations while eosinophils and basophils had negative correlations. Furthermore, platelets, total RBC's, haemoglobin, MCH, MCHC and Hct all showed negative correlations. Linear regression also showed a linear relationship between parasite density and the various haematological parameters.

CONCLUSION

The linear relationship (correlation) between WBC and MCH were the only significant ones at 95% and 99% confidence interval, respectively based on a two-tail t-test. Also, based on the regression analysis, the changes caused by WBC and PLT were the only significant changes at 95% confidence level in a two-tailed t-test.

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.

Erythrocytes: Member of the Immune System that Should Not Be Ignored

Erythrocytes are the most abundant type of cells in the blood and have a relatively simple structure when mature; they have a long life-span in the circulatory system. The primary function of erythrocytes is as oxygen carriers; however, they also play an important role in the immune system. Erythrocytes recognize and adhere to antigens and promote phagocytosis. The abnormal morphology and function of erythrocytes are also involved in the pathological processes of some diseases. Owing to the large number and immune properties of erythrocytes, their immune functions should not be ignored. Currently, research on immunity is focused on immune cells other than erythrocytes. However, research on the immune function of erythrocytes and the development of erythrocyte-mediated applications is of great significance. Therefore, we aimed to review the relevant literature and summarize the immune functions of erythrocytes.

Plasmodium falciparum adapts its investment into replication versus transmission according to the host environment

The malaria parasite life cycle includes asexual replication in human blood, with a proportion of parasites differentiating to gametocytes required for transmission to mosquitoes. Commitment to differentiate into gametocytes, which is marked by activation of the parasite transcription factor ap2-g, is known to be influenced by host factors but a comprehensive model remains uncertain. Here, we analyze data from 828 children in Kilifi, Kenya with severe, uncomplicated, and asymptomatic malaria infection over 18 years of falling malaria transmission. We examine markers of host immunity and metabolism, and markers of parasite growth and transmission investment. We find that inflammatory responses associated with reduced plasma lysophosphatidylcholine levels are associated with markers of increased investment in parasite sexual reproduction (i.e. transmission investment) and reduced growth (i.e. asexual replication). This association becomes stronger with falling transmission and suggests that parasites can rapidly respond to the within-host environment, which in turn is subject to changing transmission.

Pathology of Malaria

Malaria is an acute febrile illness that is caused by infection with Plasmodium spp. parasites. Malaria is a serious illness and sometimes it may be fatal resulting in mortality and morbidity. The clinical picture painted in patients with malarial infection occurs following the release of the merozoites into the bloodstream following the rupture of infected red cells. In the infection with the P. falciparum, the commonest form affecting humans, all stages of red cells are infected making the infection quite severe as compared to infection with other species which infects the old and young red cells only which contributes to a small percentage of red cells. In this chapter, the Authors review the current knowledge about Malaria epidemiology, pathogenesis and anatomic pathology. The diverse clinical pictures as well as the association with genetic conditions and diseases are discussed.

Plasmodium vivax vaccine: What is the best way to go?

Malaria is one of the most devastating human infectious diseases caused by Plasmodium spp. parasites. A search for an effective and safe vaccine is the main challenge for its eradication. Plasmodium vivax is the second most prevalent Plasmodium species and the most geographically distributed parasite and has been neglected for decades. This has a massive gap in knowledge and consequently in the development of vaccines. The most significant difficulties in obtaining a vaccine against P. vivax are the high genetic diversity and the extremely complex life cycle. Due to its complexity, studies have evaluated P. vivax antigens from different stages as potential targets for an effective vaccine. Therefore, the main vaccine candidates are grouped into preerythrocytic stage vaccines, blood-stage vaccines, and transmission-blocking vaccines. This review aims to support future investigations by presenting the main findings of vivax malaria vaccines to date. There are only a few P. vivax vaccines in clinical trials, and thus far, the best protective efficacy was a vaccine formulated with synthetic peptide from a circumsporozoite protein and Montanide ISA-51 as an adjuvant with 54.5% efficacy in a phase IIa study. In addition, the majority of P. vivax antigen candidates are polymorphic, induce strain-specific and heterogeneous immunity and provide only partial protection. Nevertheless, immunization with recombinant proteins and multiantigen vaccines have shown promising results and have emerged as excellent strategies. However, more studies are necessary to assess the ideal vaccine combination and test it in clinical trials. Developing a safe and effective vaccine against vivax malaria is essential for controlling and eliminating the disease. Therefore, it is necessary to determine what is already known to propose and identify new candidates.

CD36-A Host Receptor Necessary for Malaria Parasites to Establish and Maintain Infection

Plasmodium falciparum-infected erythrocytes (PfIEs) present P. falciparum erythrocyte membrane protein 1 proteins (PfEMP1s) on the cell surface, via which they cytoadhere to various endothelial cell receptors (ECRs) on the walls of human blood vessels. This prevents the parasite from passing through the spleen, which would lead to its elimination. Each P. falciparum isolate has about 60 different PfEMP1s acting as ligands, and at least 24 ECRs have been identified as interaction partners. Interestingly, in every parasite genome sequenced to date, at least 75% of the encoded PfEMP1s have a binding domain for the scavenger receptor CD36 widely distributed on host endothelial cells and many other cell types. Here, we discuss why the interaction between PfIEs and CD36 is optimal to maintain a finely regulated equilibrium that allows the parasite to multiply and spread while causing minimal harm to the host in most infections.

Red Blood Cells Oligosaccharides as Targets for Plasmodium Invasion

The key element in developing a successful malaria treatment is a good understanding of molecular mechanisms engaged in human host infection. It is assumed that oligosaccharides play a significant role in Plasmodium parasites binding to RBCs at different steps of host infection. The formation of a tight junction between EBL merozoite ligands and glycophorin receptors is the crucial interaction in ensuring merozoite entry into RBCs. It was proposed that sialic acid residues of O/N-linked glycans form clusters on a human glycophorins polypeptide chain, which facilitates the binding. Therefore, specific carbohydrate drugs have been suggested as possible malaria treatments. It was shown that the sugar moieties of N-acetylneuraminyl-N-acetate-lactosamine and 2,3-didehydro-2-deoxy-N-acetylneuraminic acid (DANA), which is its structural analog, can inhibit P. falciparum EBA-175-GPA interaction. Moreover, heparin-like molecules might be used as antimalarial drugs with some modifications to overcome their anticoagulant properties. Assuming that the principal interactions of Plasmodium merozoites and host cells are mediated by carbohydrates or glycan moieties, glycobiology-based approaches may lead to new malaria therapeutic targets.

Neurological Complications of Malaria

PURPOSE OF REVIEW

To discuss the neurological complications and pathophysiology of organ damage following malaria infection.

RECENT FINDINGS

The principal advancement made in malaria research has been a better understanding of the pathogenesis of cerebral malaria (CM), the most dreaded neurological complication generally caused by Plasmodium falciparum infection. However, no definitive treatment has yet been evolved other than the use of antimalarial drugs and supportive care. The development of severe cerebral edema in CM results from two distinct pathophysiologic mechanisms. First, the development of "sticky" red blood cells (RBCs) leads to cytoadherence, where red blood cells (RBCs) get stuck to the endothelial walls and between themselves, resulting in clogging of the brain microvasculature with resultant hypoxemia and cerebral edema. In addition, the P. falciparum-infected erythrocyte membrane protein 1 (PfEMP1) molecules protrude from the raised knob structures on the RBCs walls and are in themselves made of a combination of human and parasite proteins in a tight complex. Antibodies to surfins, rifins, and stevors from the parasite are also located in the RBC membrane. On the human microvascular side, a range of molecules involved in host-parasite interactions, including CD36 and intracellular adhesion molecule 1, is activated during interaction with other molecules such as endothelial protein C receptor and thrombospondin. As a result, an inflammatory response occurs with the dysregulated release of cytokines (TNF, interleukins 1 and 10) which damage the blood-brain barrier (BBB), causing plasma leakage and brain edema. This second mechanism of CNS injury often involves multiple organs in adult patients in endemic areas but remains localized only to the central nervous system (CNS) among African children. Neurological sequelae may follow both P. falciparum and P. vivax infections. The major brain pathology of CM is brain edema with diffuse brain swelling resulting from the combined effects of reduced perfusion and hypoxemia of cerebral neurons due to blockage of the microvasculature by parasitized RBCs as well as the neurotoxic effect of released cytokines from a hyper-acute immune host reaction. A plethora of additional neurological manifestations have been associated with malaria, including posterior reversible encephalopathy syndrome (PRES), reversible cerebral vasoconstriction syndrome (RCVS), malarial retinopathy, post-malarial neurological syndrome (PMNS), acute disseminated encephalomyelitis (ADEM), Guillain-Barré syndrome (GBS), and cerebellar ataxia. Lastly, the impact of the COVID-19 pandemic on worldwide malaria control programs and the possible threat from co-infections is briefly discussed.

Pathophysiology of Cerebral Malaria: Implications of MSCs as A Regenerative Medicinal Tool

The severe form of malaria, i.e., cerebral malaria caused by Plasmodium falciparum, is a complex neurological syndrome. Surviving persons have a risk of behavioral difficulties, cognitive disorders, and epilepsy. Cerebral malaria is associated with multiple organ dysfunctions. The adhesion and accumulation of infected RBCs, platelets, and leucocytes (macrophages, CD4⁺ and CD8⁺ T cells, and monocytes) in the brain microvessels play an essential role in disease progression. Micro-vascular hindrance by coagulation and endothelial dysfunction contributes to neurological damage and the severity of the disease. Recent studies in human cerebral malaria and the murine model of cerebral malaria indicate that different pathogens as well as host-derived factors are involved in brain microvessel adhesion and coagulation that induces changes in vascular permeability and impairment of the blood-brain barrier. Efforts to alleviate blood-brain barrier dysfunction and de-sequestering of RBCs could serve as adjunct therapies. In this review, we briefly summarize the current understanding of the pathogenesis of cerebral malaria, the role of some factors (NK cells, platelet, ANG-2/ANG-1 ratio, and PfEMP1) in disease progression and various functions of Mesenchymal stem cells. This review also highlighted the implications of MSCs as a regenerative medicine.

Ectopic Expression of Plasmodium vivax vir Genes in P. falciparum Affects Cytoadhesion via Increased Expression of Specific var Genes

Plasmodium falciparum-infected erythrocytes (PfIEs) adhere to endothelial cell receptors (ECRs) of blood vessels mainly via PfEMP1 proteins to escape elimination via the spleen. Evidence suggests that P. vivax-infected reticulocytes (PvIRs) also bind to ECRs, presumably enabled by VIR proteins, as shown by inhibition experiments and studies with transgenic P. falciparum expressing vir genes. To test this hypothesis, our study investigated the involvement of VIR proteins in cytoadhesion using vir gene-expressing P. falciparum transfectants. Those VIR proteins with a putative transmembrane domain were present in Maurer's clefts, and some were also present in the erythrocyte membrane. The VIR protein without a transmembrane domain (PVX_050690) was not exported. Five of the transgenic P. falciparum cell lines, including the one expressing PVX_050690, showed binding to CD36. We observed highly increased expression of specific var genes encoding PfEMP1s in all CD36-binding transfectants. These results suggest that ectopic vir expression regulates var expression through a yet unknown mechanism. In conclusion, the observed cytoadhesion of P. falciparum expressing vir genes depended on PfEMP1s, making this experimental unsuitable for characterizing VIR proteins.

Target-Based Virtual Screening of Natural Compounds Identifies a Potent Antimalarial With Selective Falcipain-2 Inhibitory Activity

We employed a comprehensive approach of target-based virtual high-throughput screening to find potential hits from the ZINC database of natural compounds against cysteine proteases falcipain-2 and falcipain-3 (FP2 and FP3). Molecular docking studies showed the initial hits showing high binding affinity and specificity toward FP2 were selected. Furthermore, the enzyme inhibition and surface plasmon resonance assays were performed which resulted in a compound ZINC12900664 (ST72) with potent inhibitory effects on purified FP2. ST72 exhibited strong growth inhibition of chloroquine-sensitive (3D7; EC₅₀ = 2.8 µM) and chloroquine-resistant (RKL-9; EC₅₀ = 6.7 µM) strains of Plasmodium falciparum. Stage-specific inhibition assays revealed a delayed and growth defect during parasite growth and development in parasites treated with ST72. Furthermore, ST72 significantly reduced parasite load and increased host survival in a murine model infected with Plasmodium berghei ANKA. No Evans blue staining in ST72 treatment indicated that ST72 mediated protection of blood–brain barrier integrity in mice infected with P. berghei. ST72 did not show any significant hemolysis or cytotoxicity against human HepG2 cells suggesting a good safety profile. Importantly, ST72 with CQ resulted in improved growth inhibitory activity than individual drugs in both in vitro and in vivo studies.

Design of red blood cell membrane-cloaked dihydroartemisinin nanoparticles with enhanced antimalarial efficacy

Targeting delivery and prolonging action duration of artemisinin drugs are effective strategies for improving antimalarial treatment outcomes. Here, dihydroartemisinin (DHA) loaded poly (lactic-co-glycolic acid) (PLGA) nanoparticles (PDNs) were prepared and further cloaked with red blood cell (RBC) membranes via electrostatic interactions to yield RBC membrane-cloaked PDNs (RPDNs). The prepared RPDNs displayed a notable "core-shell" structure, with a negative surface charge of -29.2 ± 4.19 mV, a relatively uniform size distribution (86.4 ± 2.54 nm, polydispersity index of 0.179 ± 0.011), an average encapsulation efficiency (70.1 ± 0.79%), and a 24-h sustained-release behavior in vitro. Compared with PDNs, RPDNs showed markedly decreased phagocytic activity by RAW 264.7 cells and had prolonged blood circulation duration. The Pearson correlation coefficient of RPDNs distribution in infected red blood cells (iRBCs) was 0.7173, suggesting that RPDNs could effectively target Plasmodium-iRBCs. In PyBy265-infected mice, RPDNs showed a higher inhibition ratio (88.39 ± 2.69%) than PDNs (83.13 ± 2.12%) or DHA (58.74 ± 3.78%), at the same dose of 8.8 μmol/kg. The ED₉₀ of RPDNs (8.13 ± 0.18 μmol/kg) was substantially lower than that of PDNs (14.48 ± 0.23 μmol/kg) and DHA (17.67 ± 3.38 μmol/kg). Furthermore, no apparent abnormalities were detected in routine blood examination, liver function indexes, and pathological analysis of tissue sections of PyBy265-infected mice following RPDNs treatment. In conclusion, the prepared RPDNs exhibited enhanced antimalarial efficacy, prolonged circulation, targeted delivery to Plasmodium-iRBCs, and satisfactory biocompatibility.

A Deadly Embrace: Hemagglutination Mediated by SARS-CoV-2 Spike Protein at Its 22 N-Glycosylation Sites, Red Blood Cell Surface Sialoglycoproteins, and Antibody

Rouleaux (stacked clumps) of red blood cells (RBCs) observed in the blood of COVID-19 patients in three studies call attention to the properties of several enveloped virus strains dating back to seminal findings of the 1940s. For COVID-19, key such properties are: (1) SARS-CoV-2 binds to RBCs in vitro and also in the blood of COVID-19 patients; (2) although ACE2 is its target for viral fusion and replication, SARS-CoV-2 initially attaches to sialic acid (SA) terminal moieties on host cell membranes via glycans on its spike protein; (3) certain enveloped viruses express hemagglutinin esterase (HE), an enzyme that releases these glycan-mediated bindings to host cells, which is expressed among betacoronaviruses in the common cold strains but not the virulent strains, SARS-CoV, SARS-CoV-2 and MERS. The arrangement and chemical composition of the glycans at the 22 N-glycosylation sites of SARS-CoV-2 spike protein and those at the sialoglycoprotein coating of RBCs allow exploration of specifics as to how virally induced RBC clumping may form. The in vitro and clinical testing of these possibilities can be sharpened by the incorporation of an existing anti-COVID-19 therapeutic that has been found in silico to competitively bind to multiple glycans on SARS-CoV-2 spike protein.

A Nanodrug Coated with Membrane from Brain Microvascular Endothelial Cells Protects against Experimental Cerebral Malaria

Human malaria is a global life-threatening infectious disease. Cerebral malaria (CM) induced by Plasmodium falciparum parasites accounts for 90% of malaria deaths. Treating CM is challenging due to inadequate treatment options and the development of drug resistance. We describe a nanoparticle formulation of the antimalarial drug dihydroartemisinin that is coated in a biomimetic membrane derived from brain microvascular endothelial cells (BMECs) and test its therapeutic efficacy in a mouse model of experimental cerebral malaria (ECM). The membrane-coated nanoparticle drug has a prolonged drug-release profile and enhanced dual targeting killing efficacy toward parasites residing in red blood cells (iRBCs) and iRBCs obstructed in the BMECs (for both rodent and human). In a mice ECM model, the nanodrug protects the brain, liver, and spleen from infection-induced damage and improves the survival rate of mice. This so-called nanodrug offers new insight into engineering nanoparticle-based therapeutics for malaria and other parasitic pathogen infections.

Selecting Plasmodium falciparum Infected Erythrocytes for Adhesion to Cell Lines

Plasmodium falciparum expresses variant surface antigens on the surface of mature infected erythrocytes (IEs) for binding to various receptors on host cells (cytoadhesion) to evade host immunity. This enables IEs to sequester in the microvasculature of different organs and tissues of the host, contributing to different outcomes of disease. The in vitro study of cytoadhesion involves the use of IEs and human endothelial cells or other cell lines that express host cell receptors. To enrich for IE populations that bind to certain cell types or receptors, we describe a method for panning mature pigmented trophozoite IEs on cell lines. The method enables coculturing of IEs with cells of interest and the selection of IEs that cytoadhere for continuous culturing. The method serves as a tool for generating IEs with specific cell or cell receptor adhesion phenotypes to allow detailed studies of cytoadhesion interactions.

Harnessing the Potential of miRNAs in Malaria Diagnostic and Prevention

Despite encouraging progress over the past decade, malaria remains a major global health challenge. Its severe form accounts for the majority of malaria-related deaths, and early diagnosis is key for a positive outcome. However, this is hindered by the non-specific symptoms caused by malaria, which often overlap with those of other viral, bacterial and parasitic infections. In addition, current tools are unable to detect the nature and degree of vital organ dysfunction associated with severe malaria, as complications develop silently until the effective treatment window is closed. It is therefore crucial to identify cheap and reliable early biomarkers of this wide-spectrum disease. microRNAs (miRNAs), a class of small non-coding RNAs, are rapidly released into the blood circulation upon physiological changes, including infection and organ damage. The present review details our current knowledge of miRNAs as biomarkers of specific organ dysfunction in patients with malaria, and both promising candidates identified by pre-clinical models and important knowledge gaps are highlighted for future evaluation in humans. miRNAs associated with infected vectors are also described, with a view to expandind this rapidly growing field of research to malaria transmission and surveillance.

The Future in Sensing Technologies for Malaria Surveillance: A Review of Hemozoin-Based Diagnosis

Early and effective malaria diagnosis is vital to control the disease spread and to prevent the emergence of severe cases and death. Currently, malaria diagnosis relies on optical microscopy and immuno-rapid tests; however, these require a drop of blood, are time-consuming, or are not specific and sensitive enough for reliable detection of low-level parasitaemia. Thus, there is an urge for simpler, prompt, and accurate alternative diagnostic methods. Particularly, hemozoin has been increasingly recognized as an attractive biomarker for malaria detection. As the disease proliferates, parasites digest host hemoglobin, in the process releasing toxic haem that is detoxified into an insoluble crystal, the hemozoin, which accumulates along with infection progression. Given its magnetic, optical, and acoustic unique features, hemozoin has been explored for new label-free diagnostic methods. Thereby, herein, we review the hemozoin-based malaria detection methods and critically discuss their challenges and potential for the development of an ideal diagnostic device.

Insilico Functional Analysis of Genome-Wide Dataset From 17,000 Individuals Identifies Candidate Malaria Resistance Genes Enriched in Malaria Pathogenic Pathways

Recent genome-wide association studies (GWASs) of severe malaria have identified several association variants. However, much about the underlying biological functions are yet to be discovered. Here, we systematically predicted plausible candidate genes and pathways from functional analysis of severe malaria resistance GWAS summary statistics (N = 17,000) meta-analysed across 11 populations in malaria endemic regions. We applied positional mapping, expression quantitative trait locus (eQTL), chromatin interaction mapping, and gene-based association analyses to identify candidate severe malaria resistance genes. We further applied rare variant analysis to raw GWAS datasets (N = 11,000) of three malaria endemic populations including Kenya, Malawi, and Gambia and performed various population genetic structures of the identified genes in the three populations and global populations. We performed network and pathway analyses to investigate their shared biological functions. Our functional mapping analysis identified 57 genes located in the known malaria genomic loci, while our gene-based GWAS analysis identified additional 125 genes across the genome. The identified genes were significantly enriched in malaria pathogenic pathways including multiple overlapping pathways in erythrocyte-related functions, blood coagulations, ion channels, adhesion molecules, membrane signalling elements, and neuronal systems. Our population genetic analysis revealed that the minor allele frequencies (MAF) of the single nucleotide polymorphisms (SNPs) residing in the identified genes are generally higher in the three malaria endemic populations compared to global populations. Overall, our results suggest that severe malaria resistance trait is attributed to multiple genes, highlighting the possibility of harnessing new malaria therapeutics that can simultaneously target multiple malaria protective host molecular pathways.

Targeting the CD146/Galectin-9 axis protects the integrity of the blood-brain barrier in experimental cerebral malaria

Cerebral malaria (CM) is a life-threatening diffuse encephalopathy caused by Plasmodium falciparum, in which the destruction of the blood-brain barrier (BBB) is the main cause of death. However, increasing evidence has shown that antimalarial drugs, the current treatment for CM, do little to protect against CM-induced BBB damage. Therefore, a means to alleviate BBB dysfunction would be a promising adjuvant therapy for CM. The adhesion molecule CD146 has been reported to be expressed in both endothelial cells and proinflammatory immune cells and mediates neuroinflammation. Here, we demonstrate that CD146 expressed on BBB endothelial cells but not immune cells is a novel therapeutic target in a mouse model of experimental cerebral malaria (eCM). Endothelial CD146 is upregulated during eCM development and facilitates the sequestration of infected red blood cells (RBCs) and/or proinflammatory lymphocytes in CNS blood vessels, thereby promoting the disruption of BBB integrity. Mechanistic studies showed that the interaction of CD146 and Galectin-9 contributes to the aggregation of infected RBCs and lymphocytes. Deletion of endothelial CD146 or treatment with the anti-CD146 antibody AA98 prevents severe signs of eCM, such as limb paralysis, brain vascular leakage, and death. In addition, AA98 combined with the antiparasitic drug artemether improved the cognition and memory of mice with eCM. Taken together, our findings suggest that endothelial CD146 is a novel and promising target in combination with antiparasitic drugs for future CM therapies.

Multi-functional antibody profiling for malaria vaccine development and evaluation

INTRODUCTION

A vaccine would greatly accelerate current global efforts toward malaria elimination. While a partially efficacious vaccine has been achieved for Plasmodium falciparum, a major bottleneck in developing highly efficacious vaccines is a lack of reliable correlates of protection, and the limited application of assays that quantify functional immune responses to evaluate and down-select vaccine candidates in pre-clinical studies and clinical trials.

AREAS COVERED

In this review, we describe the important role of antibodies in immunity against malaria and detail the nature and functional activities of antibodies against the malaria-causing parasite. We highlight the growing understanding of antibody effector functions against malaria and in vitro assays to measure these functional antibody responses. We discuss the application of these assays to quantify antibody functions in vaccine development and evaluation.

EXPERT OPINION

It is becoming increasingly clear that multiple antibody effector functions are involved in immunity to malaria. Therefore, we propose that evaluating vaccine candidates needs to move beyond individual assays or measuring IgG magnitude alone. Instead, vaccine evaluation should incorporate the full breadth of antibody response types and harness a wider range of assays measuring functional antibody responses. We propose a 3-tier approach to implementing assays to inform vaccine evaluation.

Single-Cell RNA Sequencing Reveals Cellular Heterogeneity and Stage Transition under Temperature Stress in Synchronized Plasmodium falciparum Cells

The malaria parasite has a complex life cycle exhibiting phenotypic and morphogenic variations in two different hosts by existing in heterogeneous developmental states. To investigate this cellular heterogeneity of the parasite within the human host, we performed single-cell RNA sequencing of synchronized Plasmodium cells under control and temperature treatment conditions. Using the Malaria Cell Atlas (https://www.sanger.ac.uk/science/tools/mca) as a guide, we identified 9 subtypes of the parasite distributed across known intraerythrocytic stages. Interestingly, temperature treatment results in the upregulation of the AP2-G gene, the master regulator of sexual development in a small subpopulation of the parasites. Moreover, we identified a heterogeneous stress-responsive subpopulation (clusters 5, 6, and 7 [∼10% of the total population]) that exhibits upregulation of stress response pathways under normal growth conditions. We also developed an online exploratory tool that will provide new insights into gene function under normal and temperature stress conditions. Thus, our study reveals important insights into cell-to-cell heterogeneity in the parasite population under temperature treatment that will be instrumental toward a mechanistic understanding of cellular adaptation and population dynamics in Plasmodium falciparum. IMPORTANCE The malaria parasite has a complex life cycle exhibiting phenotypic variations in two different hosts accompanied by cell-to-cell variability that is important for stress tolerance, immune evasion, and drug resistance. To investigate cellular heterogeneity determined by gene expression, we performed single-cell RNA sequencing (scRNA-seq) of about 12,000 synchronized Plasmodium cells under physiologically relevant normal (37°C) and temperature stress (40°C) conditions phenocopying the cyclic bouts of fever experienced during malarial infection. In this study, we found that parasites exhibit transcriptional heterogeneity in an otherwise morphologically synchronized culture. Also, a subset of parasites is continually committed to gametocytogenesis and stress-responsive pathways. These observations have important implications for understanding the mechanisms of drug resistance generation and vaccine development against the malaria parasite.

Plasmodium falciparum SET2 domain is allosterically regulated by its PHD-like domain to methylate at H3K36

The antigenic variation is an essential mechanism employed by the malaria parasite to establish a chronic infection in humans. Three major virulent proteins EMP1, RIFINs, and STEVOR have been implicated in contributing to the antigenic variation process and are encoded by multigene families in Plasmodium spp. The key virulence factor PfEMP1 is encoded by var genes, and it exhibits a mutually exclusive transcriptional switching between var genes, ensuring an individual parasite only transcribes a single var gene at a time. Expression of var genes is tightly regulated by two histone epigenetic methylation marks H3K36me3 and H3K9me3, of which the H3K36me3 mark is highly enriched on transcription start sites (TSSs) of suppressed var genes in P. falciparum. However, the mechanisms of H3K36me3 mark propagation on all the 59 var genes of P. falciparum are not known. Here, we have identified a PHD (Plant Homeodomain-like Domain) like domain present within the PfSET2 protein that specifically binds to the H3K36me2 mark, an intermediate product of the H3K36me3 mark formation on the nucleosome. Surprisingly, we have found that PHD - H3K36me2 interaction leads to stimulation of SET2 domain activity on the nucleosome substrates. The allosteric stimulation of the PfSET2 domain by PHD-like domain present within the same protein suggests a novel mechanism of H3K36me3 mark propagation on var genes of P. falciparum. This study proposes allosteric regulation of PfSET2 protein by H3K36me2 mark as an essential mechanism of var genes suppression to ensure successful antigenic variation by the malaria parasite.

Insecticide-treated net ownership, utilization and knowledge of malaria in children residing in Batoke-Limbe, Mount Cameroon area: effect on malariometric and haematological indices

Background

Insecticide-treated nets (ITNs) are the most widely used interventions for malaria control in Africa. The aim of this study was to assess the ownership and utilization of ITNs and the knowledge of malaria and their effects on malariometric and haematological indices in children living in the Mount Cameroon area.

Methods

A community-based cross-sectional study involving a total of 405 children aged between 6 months and 14 years living in Batoke–Limbe was carried out between July and October 2017. A semi-structured questionnaire was used to document demographic status, knowledge on malaria and ITN ownership and usage. Venous blood sample was collected from each child to determine the prevalence and intensity of parasitaemia by Giemsa-stained microscopy and full blood count by auto haematology analysis to obtain white blood cell (WBC) and red blood cell (RBC) counts, haemoglobin (Hb) level, haematocrit (Hct), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC). A multilinear regression model was used to determine the relationship between haematological parameter as dependent variable and the independent variables.

Results

The overall prevalence of parasitaemia, anaemia, knowledge about malaria, ITN ownership, usage and effective usage was 46.7%, 54.7%, 40.7%, 78.8%, 50.9% and 29.9%, respectively. The prevalence of parasitaemia was significantly higher (P < 0.001) in children who ineffectively utilized ITNs (54.9%) than effective users (27.3%). Having knowledge of malaria, negatively correlated with WBC counts (P = 0.005), but positively correlated with Hb levels (P < 0.001), RBC counts (P < 0.001), Hct (P < 0.001), MCV (P < 0.001) and MCH (P < 0.001). ITN use positively correlated with WBC counts (P = 0.005) but negatively with Hb levels (P = 0.004), RBC counts (P = 0.006), and MCH (P < 0.001). Meanwhile, parasitaemia negatively correlated with Hb levels (P = 0.004), RBC counts (P = 0.01), Hct (P = 0.04) and MCHC (P = 0.015).

Conclusion

There is need for more sensitization on the benefits of using the ITNs to meet up with the intended and expected impact of the free distribution of ITNs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03860-6.

Plasma MicroRNA Profiling of Plasmodium falciparum Biomass and Association with Severity of Malaria Disease

Severe malaria (SM) is a major public health problem in malaria-endemic countries. Sequestration of Plasmodium falciparum–infected erythrocytes in vital organs and the associated inflammation leads to organ dysfunction. MicroRNAs (miRNAs), which are rapidly released from damaged tissues into the host fluids, constitute a promising biomarker for the prognosis of SM. We applied next-generation sequencing to evaluate the differential expression of miRNAs in SM and in uncomplicated malaria (UM. Six miRNAs were associated with in vitro P. falciparum cytoadhesion, severity in children, and P. falciparum biomass. Relative expression of hsa-miR-4497 quantified by TaqMan-quantitative reverse transcription PCR was higher in plasma of children with SM than those with UM (p<0.048) and again correlated with P. falciparum biomass (p = 0.033). These findings suggest that different physiopathological processes in SM and UM lead to differential expression of miRNAs and pave the way for future studies to assess their prognostic value in malaria.

The role of upstream open reading frames in translation regulation in the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii

During their complex life cycles, the Apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii employ several layers of regulation of their gene expression. One such layer is mediated at the level of translation through upstream open reading frames (uORFs). As uORFs are found in the upstream regions of a majority of transcripts in both the parasites, it is essential that their roles in translational regulation be appreciated to a greater extent. This review provides a comprehensive summary of studies that show uORF-mediated gene regulation in these parasites and highlights examples of clinically and physiologically relevant genes, including var2csa in P. falciparum, and ApiAT1 in T. gondii, that exhibit uORF-mediated regulation. In addition to these examples, several studies that use bioinformatics, transcriptomics, proteomics and ribosome profiling also indicate the possibility of widespread translational regulation by uORFs. Further analysis of these genome-wide datasets, taking into account uORFs associated with each gene, will reveal novel genes involved in key biological pathways such as cell-cycle progression, stress-response and pathogenicity. The cumulative evidence from studies presented in this review suggests that uORFs will play crucial roles in regulating gene expression during clinical disease caused by these important human pathogens.

Elevated Levels of the Endothelial Molecules ICAM-1, VEGF-A, and VEGFR2 in Microscopic Asymptomatic Malaria

Background

In malaria, clinical disease has been associated with increased levels of endothelial activation due to the sequestration of infected erythrocytes. However, the levels and impact of endothelial activation and pro-angiogenic molecules such as vascular endothelial growth factor (VEGF)–A and its receptor vascular endothelial growth factor receptor 2 (VEGFR2) in asymptomatic malaria have not been well characterized.

Methods

Blood samples were obtained from community children for malaria diagnosis using microscopy and polymerase chain reaction. A multiplex immunoassay was used to determine the levels of intracellular adhesion molecule (ICAM)–1, vascular endothelial growth factor (VEGF)–A, and VEGFR2 in the plasma of children with microscopic or submicroscopic asymptomatic parasitemia and compared with levels in uninfected controls.

Results

Levels of ICAM-1, VEGF-A, and VEGFR2 were significantly increased in children with microscopic asymptomatic parasitemia compared with uninfected controls. Also, levels of VEGF-A were found to be inversely associated with age. Additionally, a receiver operating characteristic analysis revealed that plasma levels of ICAM-1 (area under the curve [AUC], 0.72) showed a moderate potential in discriminating between children with microscopic malaria from uninfected controls when compared with VEGF-A (AUC, 0.67) and VEGFR2 (AUC, 0.69).

Conclusions

These data imply that endothelial activation and pro-angiogenic growth factors could be one of the early host responders during microscopic asymptomatic malaria and may play a significant role in disease pathogenesis.

Red blood cell adhesion to ICAM-1 is mediated by fibrinogen and is associated with right-to-left shunts in sickle cell disease

Sickle cell disease (SCD), which afflicts 100 000 Americans, as well as millions worldwide, is associated with anemia, lifelong morbidity, and early mortality. Abnormal adhesion of sickle red blood cells (RBCs) to activated vascular endothelium may contribute acutely to the initiation of painful vaso-occlusive crises and chronically to endothelial damage in SCD. Sickle RBCs adhere to activated endothelium through several adhesion mechanisms. In this study, using whole blood from 17 people with heterozygous SCD (HbS variant) and 55 people with homozygous SCD (HbSS) analyzed in an in vitro microfluidic assay, we present evidence for the adhesion of sickle RBCs to immobilized recombinant intercellular adhesion molecule 1 (ICAM-1). We show that sickle RBC adhesion to ICAM-1 in vitro is associated with evidence of hemolysis in vivo, marked by elevated lactate dehydrogenase levels, reticulocytosis, and lower fetal hemoglobin levels. Further, RBC adhesion to ICAM-1 correlates with a history of intracardiac or intrapulmonary right-to-left shunts. Studies of potential ICAM-1 ligands on RBC membranes revealed that RBC-ICAM-1 interactions were mediated by fibrinogen bound to the RBC membrane. We describe, for the first time, RBC rolling behavior on ICAM-1 under high shear rates. Our results suggest that firm adhesion of sickle RBCs to ICAM-1 most likely occurs in postcapillary venules at low physiological shear rates, which is facilitated by initial rolling in high shear regions (eg, capillaries). Inhibition of RBC and ICAM-1 interactions may constitute a novel therapeutic target in SCD.

Common virulence gene expression in adult first-time infected malaria patients and severe cases

Sequestration of Plasmodium falciparum(P. falciparum)-infected erythrocytes to host endothelium through the parasite-derived P. falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion proteins is central to the development of malaria pathogenesis. PfEMP1 proteins have diversified and expanded to encompass many sequence variants, conferring each parasite a similar array of human endothelial receptor-binding phenotypes. Here, we analyzed RNA-seq profiles of parasites isolated from 32 P. falciparum-infected adult travellers returning to Germany. Patients were categorized into either malaria naive (n = 15) or pre-exposed (n = 17), and into severe (n = 8) or non-severe (n = 24) cases. For differential expression analysis, PfEMP1-encoding var gene transcripts were de novo assembled from RNA-seq data and, in parallel, var-expressed sequence tags were analyzed and used to predict the encoded domain composition of the transcripts. Both approaches showed in concordance that severe malaria was associated with PfEMP1 containing the endothelial protein C receptor (EPCR)-binding CIDRα1 domain, whereas CD36-binding PfEMP1 was linked to non-severe malaria outcomes. First-time infected adults were more likely to develop severe symptoms and tended to be infected for a longer period. Thus, parasites with more pathogenic PfEMP1 variants are more common in patients with a naive immune status, and/or adverse inflammatory host responses to first infections favor the growth of EPCR-binding parasites.

Prevalence of Cardiovascular Complications in Malaria: A Systematic Review and Meta-Analysis

Recent studies have suggested that malaria may affect the cardiovascular system. The aim of this systematic review and meta-analysis was to determine the prevalence of cardiovascular complications in symptomatic malaria patients. We searched databases such as Pubmed, Embase, Cochrane, and Web of Science (January 1950-April 2020) for studies reporting on cardiovascular complications in adults and children with malaria. Cardiovascular complications were defined as abnormalities in electrocardiogram (ECG), cardiac biomarkers, and echocardiography on admission or during outpatient examination. Studies of patients with known heart disease or cardiovascular evaluation performed after the start of intravenous antimalarial medication were excluded. The study was registered in International Prospective Register of Systematic Reviews (PROSPERO) (No.: CRD42020167672). The literature search yielded 1,243 studies, and a total of 43 studies with symptomatic malaria patients were included. Clinical studies (n = 12 adults; n = 5 children) comprised 3,117 patients, of which a majority had Plasmodium falciparum (n = 15) and were diagnosed with severe malaria (n = 13). In random-effects models of adults, the pooled prevalence estimate for any cardiovascular complication was 7% (95% CI: 5-9). No meta-analysis was conducted in children, but the range of abnormal ECG was 0-8%, cardiac biomarkers 0-57%, and echocardiography 4-9%. We analyzed 33 cases (n = 10 postmortem), in which the most common cardiovascular pathologies were myocarditis and acute coronary syndrome. All histopathological studies found evidence of parasitized red blood cells in the myocardium. Cardiovascular complications are not uncommon in symptomatic adults and children with malaria. Additional studies investigating malaria and cardiovascular disease are encouraged.

Adipose tissue parasite sequestration drives leptin production in mice and correlates with human cerebral malaria

Circulating levels of the adipokine leptin are linked to neuropathology in experimental cerebral malaria (ECM), but its source and regulation mechanism remain unknown. Here, we show that sequestration of infected red blood cells (iRBCs) in white adipose tissue (WAT) microvasculature increased local vascular permeability and leptin production. Mice infected with parasite strains that fail to sequester in WAT displayed reduced leptin production and protection from ECM. WAT sequestration and leptin induction were lost in CD36KO mice; however, ECM susceptibility revealed sexual dimorphism. Adipocyte leptin was regulated by the mechanistic target of rapamycin complex 1 (mTORC1) and blocked by rapamycin. In humans, although Plasmodium falciparum infection did not increase circulating leptin levels, iRBC sequestration, tissue leptin production, and mTORC1 activity were positively correlated with CM in pediatric postmortem WAT. These data identify WAT sequestration as a trigger for leptin production with potential implications for pathogenesis of malaria infection, prognosis, and treatment.

An antigenic diversification threshold for falciparum malaria transmission at high endemicity

In malaria and several other important infectious diseases, high prevalence occurs concomitantly with incomplete immunity. This apparent paradox poses major challenges to malaria elimination in highly endemic regions, where asymptomatic Plasmodium falciparum infections are present across all age classes creating a large reservoir that maintains transmission. This reservoir is in turn enabled by extreme antigenic diversity of the parasite and turnover of new variants. We present here the concept of a threshold in local pathogen diversification that defines a sharp transition in transmission intensity below which new antigen-encoding genes generated by either recombination or migration cannot establish. Transmission still occurs below this threshold, but diversity of these genes can neither accumulate nor recover from interventions that further reduce it. An analytical expectation for this threshold is derived and compared to numerical results from a stochastic individual-based model of malaria transmission that incorporates the major antigen-encoding multigene family known as var. This threshold corresponds to an “innovation” number we call R_div; it is different from, and complementary to, the one defined by the classic basic reproductive number of infectious diseases, R₀, which does not readily is better apply under large and dynamic strain diversity. This new threshold concept can be exploited for effective malaria control and applied more broadly to other pathogens with large multilocus antigenic diversity.

The vast diversity of the falciparum malaria parasite, as seen by the immune system of hosts in high transmission regions, underlies both high prevalence of asymptomatic infections and partial protection to re-infection despite previous exposure. This large antigenic diversity of the parasite challenges control and elimination efforts. We propose a threshold quantity for antigenic innovation, we call R_div, measuring the potential of transmission to accumulate new antigenic variants over time. When R_div is pushed below one by reduced transmission intensity, new genes encoding this variation can no longer accumulate, resulting in a lower number of strains and facilitating further intervention. This innovation number can be applied to other infectious diseases with fast turnover of antigens, where large standing diversity similarly opposes successful intervention.

Epstein-Barr virus infection modulates blood-brain barrier cells and its co-infection with Plasmodium falciparum induces RBC adhesion

Plasmodium falciparum infection-mediated Epstein-Barr virus (EBV) reactivation is well established in malaria-endemic countries. We hypothesize that, during malaria onset, the reactivated EBV can infect human brain microvascular endothelial cells (HBECs). This may cause severe cerebral manifestations. We infected HBECs with EBV in vitro. The subsequent gene expression pattern of EBV, inflammatory and endothelial markers was analysed using qRT-PCR. Further, a wound-healing assay for cells maintaining blood-brain barrier (BBB) integrity was performed to investigate the effect of EBV-infected HBECs secretions. The RBC adhesion assay was conducted to assess RBC attachment onto HBECs during EBV and P. falciparum mono- and co-infection. Our experiments revealed that EBV infection of HBECs significantly elevated several inflammatory (TNFα, CCL2) and endothelial (integrin β3, PECAM, VEGFA, VWF, claudin-5, cx37) markers. The EBV-infected HBECs secretion significantly reduced migration of HBECs, glial and neuronal cells. Additionally, EBV-P. falciparum co-infection significantly (P < 0.05) enhanced RBC adhesion to HBECs compared to mono-infection scenarios. Conclusively, the EBV infection of HBECs led to endothelial activation and modulated the BBB microenvironment. The EBV-P. falciparum co-infection scenario increased RBC adhesion on ECs which is a hallmark of cerebral malaria. Together with malaria, EBV infection can aid in exacerbation of cerebral malaria pathology.

Analysis of the Interaction Between Plasmodium falciparum-Infected Erythrocytes and Human Endothelial Cells Using a Laminar Flow System, Bioinformatic Tracking and Transcriptome Analysis

During malaria infection, the endothelial lining of the small blood vessels of the brain and other vital organs is strongly stimulated. This leads to fatal complications and poor prognosis of the infection. It is believed that two main reasons are responsible for this pathology, namely the cytoadhesion of Plasmodium falciparum-infected erythrocytes (IEs) on the one hand and the proinflammatory products released by the IEs which activate the endothelial cells (ECs) on the other hand. Until recently, most of the studies that characterized the activation of ECs were performed under static conditions, which do not reflect the real sequelae in vivo. In this chapter, we present a system, which allows authentic simulation of the IEs-ECs interactions during P. falciparum infection.The main idea of the system is to provide an adequate shear stress over the ECs during the cytoadhesion and stimulation with IEs, which provides a better basis for the investigation of the cytoadhesion pathology through analyzing the ECs' transcriptome after stimulation. On the other hand, analyzing the transcriptome of the IEs might also give deeper analysis of their response to shear stress. Deep understanding of these events might help in the development of novel treatment strategies that interfere with this cell-cell interaction.

Accelerator or Brake: Immune Regulators in Malaria

Malaria is a life-threatening infectious disease, affecting over 250 million individuals worldwide each year, eradicating malaria has been one of the greatest challenges to public health for a century. Growing resistance to anti-parasitic therapies and lack of effective vaccines are major contributing factors in controlling this disease. However, the incomplete understanding of parasite interactions with host anti-malaria immunity hinders vaccine development efforts to date. Recent studies have been unveiling the complexity of immune responses and regulators against Plasmodium infection. Here, we summarize our current understanding of host immune responses against Plasmodium-derived components infection and mainly focus on the various regulatory mechanisms mediated by recent identified immune regulators orchestrating anti-malaria immunity.

Inhibition of Hemoglobin Degrading Protease Falcipain-2 as a Mechanism for Anti-Malarial Activity of Triazole-Amino Acid Hybrids

BACKGROUND

Novel drug development against malaria parasite over old conventional antimalarial drugs is essential due to rapid and indiscriminate use of drugs, which led to the emergence of resistant strains.

METHODS

In this study, previously reported triazole-amino acid hybrids (13-18) are explored against Plasmodium falciparum as antimalarial agents. Among six compounds, 15 and 18 exhibited antimalarial activity against P. falciparum with insignificant hemolytic activity and cytotoxicity towards HepG2 mammalian cells. In molecular docking studies, both compounds bind into the active site of PfFP-2 and block its accessibility to the substrate that leads to the inhibition of target protein further supported by in vitro analysis.

RESULTS

Antimalarial half-maximal inhibitory concentration (IC50) of 15 and 18 compounds were found to be 9.26 μM and 20.62 μM, respectively. Blood stage specific studies showed that compounds, 15 and 18 are effective at late trophozoite stage and block egress pathway of parasites. Decreased level of free monomeric heme was found in a dose dependent manner after the treatment with compounds 15 and 18, which was further evidenced by the reduction in percent of hemoglobin hydrolysis. Compounds 15 and 18 hindered hemoglobin degradation via intra- and extracellular cysteine protease falcipain-2 (PfFP-2) inhibitory activity both in in vitro and in vivo in P. falciparum.

CONCLUSION

We report antimalarial potential of triazole-amino acid hybrids and their role in the inhibition of cysteine protease PfFP-2 as its mechanistic aspect.

Haplotype of RNASE 3 polymorphisms is associated with severe malaria in an Indian population

Severe malaria (SM) caused by Plasmodium falciparum (Pf) infection has been associated with life-threatening anemia, metabolic acidosis, cerebral malaria and multiorgan dysfunction. It may lead to death if not treated promptly. RNASE 3 has been linked to Pf growth inhibition and its polymorphisms found associated with SM and cerebral malaria in African populations. This study aimed to assess the association of RNASE 3 polymorphisms with SM in an Indian population. RNASE 3 gene and flanking regions were amplified followed by direct DNA sequencing in 151 Indian patients who visited Wenlock District Government Hospital, Mangalore, Karnataka, India. Allele, genotype and haplotype frequencies were compared between patients with SM (n = 47) and uncomplicated malaria (UM; n = 104). Homozygous mutant genotype was only found for rs2233860 (+ 499G > C) polymorphism (< 1% frequency). No significant genetic associations were found for RNASE 3 polymorphism genotypes and alleles in Indian SM patients using the Fisher's exact test. C-G-G haplotype of rs2233859 (− 38C > A), rs2073342 (+ 371C > G) and rs2233860 (+ 499G > C) polymorphisms was correlated significantly with SM patients (OR = 3.03; p = 0.008) after Bonferroni correction. A haplotype of RNASE 3 gene was found associated with an increased risk of SM and confirming that RNASE 3 gene plays a role in susceptibility to SM.

Teratogen update: Malaria in pregnancy and the use of antimalarial drugs in the first trimester

Malaria is a particular problem in pregnancy because of enhanced sensitivity, the possibility of placental malaria, and adverse effects on pregnancy outcome. Artemisinin-containing combination therapies (ACTs) are the most effective antimalarials known. WHO recommends 7-day quinine therapy for uncomplicated Plasmodium falciparum malaria in the first trimester despite the superior tolerability and efficacy of 3-day ACT regimens because artemisinins caused embryolethality and/or cardiovascular malformations at relatively low doses in rats, rabbits, and monkeys. The developmental toxicity of artesunate, artemether, and DHA were similar in rats but artesunate was embryotoxic at lower doses in rabbits (5 mg/kg/day) than artemether (no effect level = 25 mg/kg/day). In clinical studies in Africa, treatment with artemether-lumefantrine in the first trimester was observed to be highly efficacious and the miscarriage rate (≤3.1%) was similar to no antimalarial treatment (2.6%). When data from the first-trimester use of largely artesunate-based therapies in Thailand were pooled together, there was no difference in miscarriage rate compared to quinine. However, individually, artesunate-mefloquine was associated with a higher miscarriage rate (15/71 = 21%) compared to other artemisinin-based therapies including 7-day artesunate + clindamycin (2/50 = 4%) and quinine (92/842 = 11%). Thus, appropriate statistical comparisons of individual ACT groups are needed prior to assuming that they all have the same risk for developmental toxicity. Current limitations in the assessment of the safety of ACTs in the first trimester are a lack of exposures early in gestation (gestational weeks 6-7), limited postnatal evaluation for cardiovascular malformations, and the pooling of all ACTs for the assessment of risk.

A case of Falciparum malaria presenting with features of functional bowel obstruction

Malaria is the most common tropical disease in Sudan, which is caused by an infection with Plasmodium protozoa transmitted by an infective female Anopheles mosquito. Headache, fever, cough, fatigue, malaise, shaking chills, arthralgia and myalgia are the cardinal features of malaria, but occasionally, it has an atypical presentation. Intestinal obstruction as a complication is an extremely rare presentation. Here within, we describe a 28-year-old Sudanese man who has presented with of colicky abdominal pain, absolute constipation for two days and fever. Blood film for malaria was positive for Plasmodium falciparum. Intravenous artesunate injections have resulted in the resolution of symptoms of bowel obstruction. In conclusion, malaria should be suspected in any febrile patient with the features of bowel obstruction especially in an endemic area or if the patient has recently travelled to an endemic area with malaria. Treatment of malaria will result in the resolution of symptoms of functional bowel obstruction.

Sphingosine 1-Phosphate in Malaria Pathogenesis and Its Implication in Therapeutic Opportunities

Sphingosine 1-Phosphate (S1P) is a bioactive lipid intermediate in the sphingolipid metabolism, which exist in two pools, intracellular and extracellular, and each pool has a different function. The circulating extracellular pool, specifically the plasma S1P is shown to be important in regulating various physiological processes related to malaria pathogenesis in recent years. Although blood cells (red blood cells and platelets), vascular endothelial cells and hepatocytes are considered as the important sources of plasma S1P, their extent of contribution is still debated. The red blood cells (RBCs) and platelets serve as a major repository of intracellular S1P due to lack, or low activity of S1P degrading enzymes, however, contribution of platelets toward maintaining plasma S1P is shown negligible under normal condition. Substantial evidences suggest platelets loss during falciparum infection as a contributing factor for severe malaria. However, platelets function as a source for plasma S1P in malaria needs to be examined experimentally. RBC being the preferential site for parasite seclusion, and having the ability of trans-cellular S1P transportation to EC upon tight cell-cell contact, might play critical role in differential S1P distribution and parasite growth. In the present review, we have summarized the significance of both the S1P pools in the context of malaria, and how the RBC content of S1P can be channelized in better ways for its possible implication in therapeutic opportunities to control malaria.

Identification and structure-activity relationship (SAR) studies of carvacrol derivatives as potential anti-malarial against Plasmodium falciparum falcipain-2 protease

In an effort to develop a potent anti-malarial agent against Plasmodium falciparum, a structure-guided virtual screening using an in-house library comprising 652 compounds was performed. By docking studies, we identified two compounds (JMI-105 and JMI-346) which formed significant non-covalent interactions and fit well in the binding pocket of PfFP-2. We affirmed this observation by MD simulation studies. As evident by the biochemical analysis, such as enzyme inhibition assay, Surface Plasmon Resonance (SPR), live-cell imaging and hemozoin inhibition, JMI-105 and JMI-346 at 25 µM concentration showed an inhibitory effect on purified PfFP-2. JMI-105 and JMI-346 inhibited the growth of CQ^S (3D7; IC₅₀ = 8.8 and 13 µM) and CQ^R (RKL-9; IC₅₀ = 14.3 and 33 µM) strains of P. falciparum. Treatment with compounds resulted in defect in parasite growth and development. No significant hemolysis or cytotoxicity towards human cells was observed suggesting that these molecules are non-toxic. We pursued, structural optimization on JMI-105 and in the process, SAR oriented derivatives (5a-5l) were synthesized and evaluated for growth inhibition potential. JMI-105 significantly decreased parasitemia and prolonged host survival in a murine model with P. berghei ANKA infection. The compounds (JMI-105 and JMI-346) against PfFP-2 have the potential to be used as an anti-malarial agent.

Influence of blood group, Glucose-6-phosphate dehydrogenase and Haemoglobin genotype on Falciparum malaria in children in Vihiga highland of Western Kenya

Background

Genetic diversity of ABO blood, glucose-6-phosphate dehydrogenase (G6PD) deficiency and haemoglobin type and their ability to protect against malaria vary geographically, ethnically and racially. No study has been carried out in populations resident in malaria regions in western Kenya.

Method

A total of 574 malaria cases (severe malaria anaemia, SMA = 137 and non-SMA = 437) seeking treatment at Vihiga County and Referral Hospital in western Kenya, were enrolled and screened for ABO blood group, G6PD deficiency and haemoglobin genotyped in a hospital-based cross-sectional study.

Result

When compared to blood group O, blood groups A, AB and B were not associated with SMA (P = 0.380, P = 0.183 and P = 0.464, respectively). Further regression analysis revealed that the carriage of the intermediate status of G6PD was associated with risk to SMA (OR = 1.52, 95%CI = 1.029–2.266, P = 0.035). There was, however, no association between AS and SS with severe malaria anaemia. Co-occurrence of both haemoglobin type and G6PD i.e. the AA/intermediate was associated with risk to SMA (OR = 1.536, 95%CI = 1.007–2.343, P = 0.046) while the carriage of the AS/normal G6PD was associated with protection against SMA (OR = 0.337, 95%CI = 0.156–0.915, P = 0.031).

Conclusion

Results demonstrate that blood group genotypes do not have influence on malaria disease outcome in this region. Children in Vihiga with blood group O have some protection against malaria. However, the intermediate status of G6PD is associated with risk of SMA. Further, co-inheritance of sickle cell and G6PD status are important predictors of malaria disease outcome. This implies combinatorial gene function in influencing disease outcome.

Genome wide distribution of G-quadruplexes and their impact on gene expression in malaria parasites

Mechanisms of transcriptional control in malaria parasites are still not fully understood. The positioning patterns of G-quadruplex (G4) DNA motifs in the parasite's AT-rich genome, especially within the var gene family which encodes virulence factors, and in the vicinity of recombination hotspots, points towards a possible regulatory role of G4 in gene expression and genome stability. Here, we carried out the most comprehensive genome-wide survey, to date, of G4s in the Plasmodium falciparum genome using G4Hunter, which identifies G4 forming sequences (G4FS) considering their G-richness and G-skewness. We show an enrichment of G4FS in nucleosome-depleted regions and in the first exon of var genes, a pattern that is conserved within the closely related Laverania Plasmodium parasites. Under G4-stabilizing conditions, i.e., following treatment with pyridostatin (a high affinity G4 ligand), we show that a bona fide G4 found in the non-coding strand of var promoters modulates reporter gene expression. Furthermore, transcriptional profiling of pyridostatin-treated parasites, shows large scale perturbations, with deregulation affecting for instance the ApiAP2 family of transcription factors and genes involved in ribosome biogenesis. Overall, our study highlights G4s as important DNA secondary structures with a role in Plasmodium gene expression regulation, sub-telomeric recombination and var gene biology.

Do Blood Group Antigens and the Red Cell Membrane Influence Human Immunodeficiency Virus Infection?

The expression of blood group antigens varies across human populations and geographical regions due to natural selection and the influence of environment factors and disease. The red cell membrane is host to numerous surface antigens which are able to influence susceptibility to disease, by acting as receptors for pathogens, or by influencing the immune response. Investigations have shown that Human Immunodeficiency Virus (HIV) can bind and gain entry into erythrocytes, and therefore it is hypothesized that blood groups could play a role in this process. The ABO blood group has been well studied. However, its role in HIV susceptibility remains controversial, while other blood group antigens, and the secretor status of individuals, have been implicated. The Duffy antigen is a chemokine receptor that is important in the inflammatory response. Those who lack this antigen, and type as Duffy null, could therefore be susceptible to HIV infection, especially if associated with neutropenia. Other antigens including those in the Rh, Lutheran and OK blood group systems have all been shown to interact with HIV. More recently, experiments show that cells which overexpress the P^k antigen appear to be protected against infection. These reports all demonstrate that red cell antigens interact and influence HIV infection. However, as the red cell membrane is complex and the pathogenesis of HIV multi-factorial, the role of blood group antigens cannot be studied in isolation.

Adhesion between P. falciparum infected erythrocytes and human endothelial receptors follows alternative binding dynamics under flow and febrile conditions

Characterizing the adhesive dynamics of Plasmodium falciparum infected erythrocytes (IEs) to different endothelial cell receptors (ECRs) in flow is a big challenge considering available methods. This study investigated the adhesive dynamics of IEs to five ECRs (CD36, ICAM-1, P-selectin, CD9, CSA) using simulations of in vivo-like flow and febrile conditions. To characterize the interactions between ECRs and knobby and knobless IEs of two laboratory-adapted P. falciplarum isolates, cytoadhesion analysis over time was performed using a new tracking bioinformatics method. The results revealed that IEs performed rolling adhesion exclusively over CD36, but exhibited stationary binding to the other four ECRs. The absence of knobs affected rolling adhesion both with respect to the distance travelled by IEs and their velocity. Knobs played a critical role at febrile temperatures by stabilizing the binding interaction. Our results clearly underline the complexity of the IE-receptor interaction and the importance of knobs for the survival of the parasite at fever temperatures, and lead us to propose a new hypothesis that could open up new strategies for the treatment of malaria.

Association of EPCR Polymorphism rs867186-GG With Severity of Human Malaria

Background

Cerebral malaria (CM) is characterized by the sequestration of Plasmodium-infected erythrocytes (pRBCs) to host brain microvasculature beds via P. falciparum erythrocyte membrane protein 1 (PfEMP1). Under normal conditions, activated protein C (APC) bound to endothelial protein C receptor (EPCR) has cytoprotective properties via the activation of protease-activated receptor 1 (PAR1). During malaria infection, pRBCs transports PfEMP1 to the membranes to bind EPCR in the same region as APC. As a result, APC is less capable of inducing cytoprotective effects via PAR1. Two studies involving adult malaria patients revealed that EPCR rs867186-GG allele is associated with protection against severe malaria, while three other studies involving child malaria patients could not show association between EPCR rs867186-GG genotype and severe malaria or increased mortality among children with CM.

Methods

We examined the association between the EPCR rs867186-GG genotype and the protection against cerebral malaria. Peripheral blood samples were collected from 47 malaria patients and 34 healthy individuals from a study conducted from 2004 to 2007 at the NSCB Medical College Hospital in India. CM and malaria-associated complications were defined based on WHO criteria. Genomic DNA was isolated from the peripheral blood mononuclear cells. Primer sequences were designed to contain rs867186 of the PROCR gene (NM 006404) and were used to amplify a 660 bp product as described before. PCR products were purified, and DNA sequences were determined by Sanger Sequencing (Genewiz, NJ). Nonparametric tests were used to compare the groups. To analyze differences in allele frequencies, we used chi-squared or Fisher's exact tests for categorical variables if the expected values were less than 5. P-value <0.05 was considered statistically significant.

Results

Our results showed significantly higher rates of AG and GG genotypes in CM patients compared to mild malaria (P = 0.0034).

Conclusion

Our results indicate that rs867186-GG or rs867186-AG genotypes are not associated with protection against HCM.

Protective Immunity against Severe Malaria in Children Is Associated with a Limited Repertoire of Antibodies to Conserved PfEMP1 Variants

Extreme diversity of the major Plasmodium falciparum antigen, PfEMP1, poses a barrier to identifying targets of immunity to malaria. Here, we used protein microarrays containing hundreds of variants of the DBLα domain of PfEMP1 to cover the diversity of Papua New Guinean (PNG) parasites. Probing the plasma of a longitudinal cohort of malaria-exposed PNG children showed that group 2 DBLα antibodies were moderately associated with a lower risk of uncomplicated malaria, whereas individual variants were only weakly associated with clinical immunity. In contrast, antibodies to 85 individual group 1 and 2 DBLα variants were associated with a 70%-100% reduction in severe malaria. Of these, 17 variants were strong predictors of severe malaria. Analysis of full-length PfEMP1 sequences from PNG samples shows that these 17 variants are linked to pathogenic CIDR domains. This suggests that whereas immunity to uncomplicated malaria requires a broad repertoire of antibodies, immunity to severe malaria targets a subset of conserved variants. These findings provide insights into antimalarial immunity and potential antibody biomarkers for disease risk.