Pathogenesis of cerebral malaria: new diagnostic tools, biomarkers, and therapeutic approaches

A human pluripotent stem cell-derived in vitro model of the blood-brain barrier in cerebral malaria

BACKGROUND

Blood-brain barrier (BBB) disruption is a central feature of cerebral malaria (CM), a severe complication of Plasmodium falciparum (Pf) infections. In CM, sequestration of Pf-infected red blood cells (Pf-iRBCs) to brain endothelial cells combined with inflammation, hemolysis, microvasculature obstruction and endothelial dysfunction mediates BBB disruption, resulting in severe neurologic symptoms including coma and seizures, potentially leading to death or long-term sequelae. In vitro models have advanced our knowledge of CM-mediated BBB disruption, but their physiological relevance remains uncertain. Using human induced pluripotent stem cell-derived brain microvascular endothelial cells (hiPSC-BMECs), we aimed to develop a novel in vitro model of the BBB in CM, exhibiting enhanced barrier properties.

METHODS

hiPSC-BMECs were co-cultured with HB3var03 strain Pf-iRBCs up to 9 h. Barrier integrity was measured using transendothelial electrical resistance (TEER) and sodium fluorescein permeability assays. Localization and expression of tight junction (TJ) proteins (occludin, zonula occludens-1, claudin-5), cellular adhesion molecules (ICAM-1, VCAM-1), and endothelial surface markers (EPCR) were determined using immunofluorescence imaging (IF) and western blotting (WB). Expression of angiogenic and cell stress markers were measured using multiplex proteome profiler arrays.

RESULTS

After 6-h of co-culture with Pf-iRBCs, hiPSC-BMECs showed reduced TEER and increased sodium fluorescein permeability compared to co-culture with uninfected RBCs, indicative of a leaky barrier. We observed disruptions in localization of occludin, zonula occludens-1, and claudin-5 by IF, but no change in protein expression by WB in Pf-iRBC co-cultures. Expression of ICAM-1 and VCAM-1 but not EPCR was elevated in hiPSC-BMECs with Pf-iRBC co-culture compared to uninfected RBC co-culture. In addition, there was an increase in expression of angiogenin, platelet factor-4, and phospho-heat shock protein-27 in the Pf-iRBCs co-culture compared to uninfected RBC co-culture.

CONCLUSION

These findings demonstrate the validity of our hiPSC-BMECs based model of the BBB, that displays enhanced barrier integrity and appropriate TJ protein localization. In the hiPSC-BMEC co-culture with Pf-iRBCs, reduced TEER, increased paracellular permeability, changes in TJ protein localization, increase in expression of adhesion molecules, and markers of angiogenesis and cellular stress all point towards a novel model with enhanced barrier properties, suitable for investigating pathogenic mechanisms underlying BBB disruption in CM.

Oral administration of IPI549 protects mice from neuropathology and an overwhelming inflammatory response during experimental cerebral malaria

Infection with Plasmodium falciparum is often deadly when it results in cerebral malaria, which is associated with neuropathology described as an overwhelming inflammatory response and mechanical obstruction of cerebral microvascular. PI3Kγ is a critical component of intracellular signal transduction and plays a central role in regulating cell chemotaxis, migration, and activation. The purpose of this study was to examine the relationship between inhibiting the PI3Kγ pathway and the outcome of experimental cerebral malaria (ECM) in C57BL/6J mice infected with the mouse malaria parasite, Plasmodium berghei ANKA. We observed that oral administration of the PI3Kγ inhibitor IPI549 after infection completely protected mice from ECM. IPI549 treatment significantly dampened the magnitude of inflammatory responses, with reduced production of pro-inflammatory factors, decreased T cell activation, and altered differentiation of antigen-presenting cells. IPI549 treatment protected the infected mice from neuropathology, as assessed by an observed reduction of pathogenic T cells in the brain. Treating the infected mice with IPI549 three days after parasite inoculation improved the murine blood brain barrier (BBB) integrity and helped the mice pass the onset of ECM. Together, these data indicate that oral administration of the PI3Kγ inhibitor IPI549 has a suppressive role in host inflammation and alleviates cerebral pathology, which supports IPI549 as a new malaria treatment option with potential therapeutic implications for cerebral malaria.

Unravelling mysteries at the perivascular space: a new rationale for cerebral malaria pathogenesis

Cerebral malaria (CM) is a severe neurological complication caused by Plasmodium falciparum parasites; it is characterized by the sequestration of infected red blood cells within the cerebral microvasculature. New findings, combined with a better understanding of the central nervous system (CNS) barriers, have provided greater insight into the players and events involved in CM, including site-specific T cell responses in the human brain. Here, we review the updated roles of innate and adaptive immune responses in CM, with a focus on the role of the perivascular macrophage-endothelium unit in antigen presentation, in the vascular and perivascular compartments. We suggest that these events may be pivotal in the development of CM.

Surface proteome of plasma extracellular vesicles as mechanistic and clinical biomarkers for malaria

PURPOSE

Malaria is a life-threatening mosquito-borne disease caused by Plasmodium parasites, mainly in tropical and subtropical countries. Plasmodium falciparum (P. falciparum) is the most prevalent cause on the African continent and responsible for most malaria-related deaths globally. Important medical needs are biomarkers for disease severity or disease outcome. A potential source of easily accessible biomarkers are blood-borne small extracellular vesicles (sEVs).

METHODS

We performed an EV Array to find proteins on plasma sEVs that are differentially expressed in malaria patients. Plasma samples from 21 healthy subjects and 15 malaria patients were analyzed. The EV array contained 40 antibodies to capture sEVs, which were then visualized with a cocktail of biotin-conjugated CD9, CD63, and CD81 antibodies.

RESULTS

We detected significant differences in the protein decoration of sEVs between healthy subjects and malaria patients. We found CD106 to be the best discrimination marker based on receiver operating characteristic (ROC) analysis with an area under the curve of > 0.974. Additional ensemble feature selection revealed CD106, Osteopontin, CD81, major histocompatibility complex class II DR (HLA-DR), and heparin binding EGF like growth factor (HBEGF) together with thrombocytes to be a feature panel for discrimination between healthy and malaria. TNF-R-II correlated with HLA-A/B/C as well as CD9 with CD81, whereas Osteopontin negatively correlated with CD81 and CD9. Pathway analysis linked the herein identified proteins to IFN-γ signaling.

CONCLUSION

sEV-associated proteins can discriminate between healthy individuals and malaria patients and are candidates for future predictive biomarkers.

TRIAL REGISTRATION

The trial was registered in the Deutsches Register Klinischer Studien (DRKS-ID: DRKS00012518).

Increased Neutrophil Percentage and Neutrophil-T Cell Ratio Precedes Clinical Onset of Experimental Cerebral Malaria

Newly emerging data suggest that several neutrophil defense mechanisms may play a role in both aggravating and protecting against malaria. These exciting findings suggest that the balance of these cells in the host body may have an impact on the pathogenesis of malaria. To fully understand the role of neutrophils in severe forms of malaria, such as cerebral malaria (CM), it is critical to gain a comprehensive understanding of their behavior and functions. This study investigated the dynamics of neutrophil and T cell responses in C57BL/6 and BALB/c mice infected with Plasmodium berghei ANKA, murine models of experimental cerebral malaria (ECM) and non-cerebral experimental malaria, respectively. The results demonstrated an increase in neutrophil percentage and neutrophil-T cell ratios in the spleen and blood before the development of clinical signs of ECM, which is a phenomenon not observed in the non-susceptible model of cerebral malaria. Furthermore, despite the development of distinct forms of malaria in the two strains of infected animals, parasitemia levels showed equivalent increases throughout the infection period evaluated. These findings suggest that the neutrophil percentage and neutrophil-T cell ratios may be valuable predictive tools for assessing the dynamics and composition of immune responses involved in the determinism of ECM development, thus contributing to the advancing of our understanding of its pathogenesis.

Pathogenesis of Cerebral Malaria: New Trends and Insights for Developing Adjunctive Therapies

No specific or adjunctive therapies exist to treat cerebral malaria (CM) as of date. CM is a neuropathological manifestation of the malaria infection in humans, caused by the hemoparasitic pathogen Plasmodium falciparum. Driven through a multitude of virulence factors, varied immune responses, variations in brain swelling with regard to the age of patients, parasite biomass, and parasite-typing, the essential pathogenetic mechanisms underlying clinical CM have remained elusive. However, a recent series of studies based on molecular, immunologic, and advanced neuroradiologic and machine-learning approaches have unraveled new trends and insights to better understand and focus on the key determinants of CM in humans. This could possibly be the beginning of the design of new and effective adjunctive therapies that may not be common or applicable to the entire malarious world, but that could, rather, be specific to the variations in the determinants of CM.

Identifying effective diagnostic biomarkers for childhood cerebral malaria in Africa integrating coexpression analysis with machine learning algorithm

BACKGROUND

Cerebral malaria (CM) is a manifestation of malaria caused by plasmodium infection. It has a high mortality rate and severe neurological sequelae, existing a significant research gap and requiring further study at the molecular level.

METHODS

We downloaded the GSE117613 dataset from the Gene Expression Omnibus (GEO) database to determine the differentially expressed genes (DEGs) between the CM group and the control group. Weighted gene coexpression network analysis (WGCNA) was applied to select the module and hub genes most relevant to CM. The common genes of the key module and DEGs were selected to perform further analysis. The least absolute shrinkage and selection operator (LASSO) logistic regression and support vector machine recursive feature elimination (SVM-RFE) were applied to screen and verify the diagnostic markers of CM. Eventually, the hub genes were validated in the external dataset. Gene set enrichment analysis (GSEA) was applied to investigate the possible roles of the hub genes.

RESULTS

The GO and KEGG results showed that DEGs were enriched in some neutrophil-mediated pathways and associated with some lumen structures. Combining LASSO and the SVM-RFE algorithms, LEF1 and IRAK3 were identified as potential hub genes in CM. Through the GSEA enrichment results, we found that LEF1 and IRAK3 participated in maintaining the integrity of the blood-brain barrier (BBB), which contributed to improving the prognosis of CM.

CONCLUSIONS

This study may help illustrate the pathophysiology of CM at the molecular level. LEF1 and IRAK3 can be used as diagnostic biomarkers, providing new insight into the diagnosis and prognosis prediction in pediatric CM.

Diagnosis of cerebral malaria: Tools to reduce Plasmodium falciparum associated mortality

Cerebral malaria (CM) is a major cause of mortality in Plasmodium falciparum (Pf) infection and is associated with the sequestration of parasitised erythrocytes in the microvasculature of the host's vital organs. Prompt diagnosis and treatment are key to a positive outcome in CM. However, current diagnostic tools remain inadequate to assess the degree of brain dysfunction associated with CM before the window for effective treatment closes. Several host and parasite factor-based biomarkers have been suggested as rapid diagnostic tools with potential for early CM diagnosis, however, no specific biomarker signature has been validated. Here, we provide an updated review on promising CM biomarker candidates and evaluate their applicability as point-of-care tools in malaria-endemic areas.

Genetics of cerebral malaria: pathogenesis, biomarkers and emerging therapeutic interventions

Background

Cerebral malaria (CM) is a preeminent cause of severe disease and premature deaths in Sub-Saharan Africa, where an estimated 90% of cases occur. The key features of CM are a deep, unarousable coma that persists for longer than 1 h in patients with peripheral Plasmodium falciparum and no other explanation for encephalopathy. Significant research efforts on CM in the last few decades have focused on unravelling the molecular underpinnings of the disease pathogenesis and the identification of potential targets for therapeutic or pharmacologic intervention. These efforts have been greatly aided by the generation and study of mouse models of CM, which have provided great insights into key events of CM pathogenesis, revealed an interesting interplay of host versus parasite factors that determine the progression of malaria to severe disease and exposed possible targets for therapeutic intervention in severe disease.

Main Body

This paper reviews our current understanding of the pathogenic and immunologic factors involved in CM. We present the current view of the roles of certain gene products e.g., the var gene, ABCA-1, ICAM-1, TNF-alpha, CD-36, PfEMP-1 and G6PD, in CM pathogenesis. We also present alterations in the blood–brain barrier as a consequence of disease proliferation as well as complicated host and parasite interactions, including the T-cell immune reaction, reduced deformation of erythrocytes and cytoadherence. We further looked at recent advances in cerebral malaria treatment interventions by emphasizing on biomarkers, new diagnostic tools and emerging therapeutic options.

Conclusion

Finally, we discuss how the current understanding of some of these pathogenic and immunologic factors could inform the development of novel therapeutic interventions to fight CM.

Mouse Models for Unravelling Immunology of Blood Stage Malaria

Malaria comprises a spectrum of disease syndromes and the immune system is a major participant in malarial disease. This is particularly true in relation to the immune responses elicited against blood stages of Plasmodium-parasites that are responsible for the pathogenesis of infection. Mouse models of malaria are commonly used to dissect the immune mechanisms underlying disease. While no single mouse model of Plasmodium infection completely recapitulates all the features of malaria in humans, collectively the existing models are invaluable for defining the events that lead to the immunopathogenesis of malaria. Here we review the different mouse models of Plasmodium infection that are available, and highlight some of the main contributions these models have made with regards to identifying immune mechanisms of parasite control and the immunopathogenesis of malaria.

Neurotransmitters and molecular chaperones interactions in cerebral malaria: Is there a missing link?

Plasmodium falciparum is responsible for the most severe and deadliest human malaria infection. The most serious complication of this infection is cerebral malaria. Among the proposed hypotheses that seek to explain the manifestation of the neurological syndrome in cerebral malaria is the vascular occlusion/sequestration/mechanic hypothesis, the cytokine storm or inflammatory theory, or a combination of both. Unfortunately, despite the increasing volume of scientific information on cerebral malaria, our understanding of its pathophysiologic mechanism(s) is still very limited. In a bid to maintain its survival and development, P. falciparum exports a large number of proteins into the cytosol of the infected host red blood cell. Prominent among these are the P. falciparum erythrocytes membrane protein 1 (PfEMP1), P. falciparum histidine-rich protein II (PfHRP2), and P. falciparum heat shock proteins 70-x (PfHsp70-x). Functional activities and interaction of these proteins with one another and with recruited host resident proteins are critical factors in the pathology of malaria in general and cerebral malaria in particular. Furthermore, several neurological impairments, including cognitive, behavioral, and motor dysfunctions, are known to be associated with cerebral malaria. Also, the available evidence has implicated glutamate and glutamatergic pathways, coupled with a resultant alteration in serotonin, dopamine, norepinephrine, and histamine production. While seeking to improve our understanding of the pathophysiology of cerebral malaria, this article seeks to explore the possible links between host/parasite chaperones, and neurotransmitters, in relation to other molecular players in the pathology of cerebral malaria, to explore such links in antimalarial drug discovery.

Cerebral malaria induced by plasmodium falciparum: clinical features, pathogenesis, diagnosis, and treatment

Cerebral malaria (CM) caused by Plasmodium falciparum is a fatal neurological complication of malaria, resulting in coma and death, and even survivors may suffer long-term neurological sequelae. In sub-Saharan Africa, CM occurs mainly in children under five years of age. Although intravenous artesunate is considered the preferred treatment for CM, the clinical efficacy is still far from satisfactory. The neurological damage induced by CM is irreversible and lethal, and it is therefore of great significance to unravel the exact etiology of CM, which may be beneficial for the effective management of this severe disease. Here, we review the clinical characteristics, pathogenesis, diagnosis, and clinical therapy of CM, with the aim of providing insights into the development of novel tools for improved CM treatments.

Angiogenic and angiostatic factors present in the saliva of malaria patients

Background

Malaria related mortality is associated with significant deregulation of host inflammatory factors such as interferon-inducible protein 10, a member of the CXC or α-subfamily (CXCL10), and host angiogenic factors such as angiopoietin 1 (Ang-1) and angiopoietin 2 (Ang-2). However, detection of these factors in malaria patients requires the drawing of blood, which is invasive and increases the risk of accidental blood-borne infections. There has been an increased interest in the use of saliva as the body fluid of choice for the diagnosis of many infectious diseases including malaria. Here, saliva levels of CXCL10, Ang-1, and Ang-2 previously shown to be predictive of severe malaria in malaria patients in Ghana were assessed in malaria patients.

Methods

This study was conducted in the Shai-Osudoku District Hospital in Dodowa, Accra, Ghana and the study population comprised 119 malaria patients and 94 non-malaria subjects. The non-malaria subjects are healthy community participants with no malaria infection. Plasma and saliva levels of CXCL10, Ang-1 and Ang-2 of the study participants were measured using an enzyme-linked immunoassay. Complete blood counts of each participant were measured with a haematology autoanalyzer. Pearson correlation was used to evaluate the correlation between plasma and saliva levels of each biomarker in malaria patients. A p-value of < 0.05 was considered significant. Box plots of median biomarker concentrations were plotted. SPSS version 14.2 software was used for statistical analysis.

Results

The non-malaria subjects had a median age of 29 years compared to 23 years for malaria patients (p = 0.001). Among the malaria patients, there was a strong significant relationship between CXCL10 (R² = 0.7, p < 0.0001) and Ang-1 (R² = 0.7, p < 0.0001). Malaria patients had lower saliva levels of Ang-1 (p = 0.009) and higher saliva levels of CXCL10 (p = 0.004) and Ang-2 (p = 0.001) compared to non-malaria subjects.

Conclusions

This study provides the first evidence of elevated levels of CXCL10 and Ang-2 in the saliva of malaria patients. Detection of CXCL10, Ang-1 and Ang-2 in saliva may have a potential application for non-invasive malaria diagnosis.

Treatment Reducing Endothelial Activation Protects against Experimental Cerebral Malaria

Cerebral malaria (CM) is the most severe neurological complication of malaria caused by Plasmodium falciparum infection. The available antimalarial drugs are effective at clearing the parasite, but the mortality rate remains as high as 20% of CM cases. At the vascular level, CM is characterized by endothelial activation and dysfunction. Several biomarkers of endothelial activation have been associated with CM severity and mortality, making the brain vascular endothelium a potential target for adjunctive therapies. Statins and Angiotensin II Receptor Blockers (ARBs) are drugs used to treat hypercholesterolemia and hypertension, respectively, that have shown endothelial protective activity in other diseases. Here, we used a combination of a statin (atorvastatin) and an ARB (irbesartan) as adjunctive therapy to conventional antimalarial drugs in a mouse experimental model of CM. We observed that administration of atorvastatin–irbesartan combination decreased the levels of biomarkers of endothelial activation, such as the von Willebrand factor and angiopoietin-1. After mice developed neurological signs of CM, treatment with the combination plus conventional antimalarial drugs increased survival rates of animals 3–4 times compared to treatment with antimalarial drugs alone, with animals presenting lower numbers and smaller hemorrhages in the brain. Taken together, our results support the hypothesis that inhibiting endothelial activation would greatly reduce the CM-associated pathology and mortality.

Cerebral Malaria: Current Clinical and Immunological Aspects

This review focuses on current clinical and immunological aspects of cerebral malaria induced by Plasmodium falciparum infection. Albeit many issues concerning the inflammatory responses remain unresolved and need further investigations, current knowledge of the underlying molecular mechanisms is highlighted. Furthermore, and in the light of significant limitations in preventative diagnosis and treatment of cerebral malaria, this review mainly discusses our understanding of immune mechanisms in the light of the most recent research findings. Remarkably, the newly proposed CD8+ T cell-driven pathophysiological aspects within the central nervous system are summarized, giving first rational insights into encouraging studies with immune-modulating adjunctive therapies that protect from symptomatic cerebral participation of Plasmodium falciparum infection.

Carbon dots and Methylene blue facilitated photometric quantification of Hemoglobin

Early detection and monitoring of any abnormality of Hemoglobin (Hb) concentration in whole blood samples are important as this may be related to anemia, leukemia, dengue, etc. To facilitate quantitative detection and to monitor the hemoglobin level in the blood, we attempt to develop a low-cost, portable point of care (POC) device based on the spectrophotometric principle. Optical sensitivities of carbon quantum dots (CDs) are found to be highly responsive, while there is a selective reaction between Hb and reduced form of Methylene Blue (MB_red). The interaction of Hb, MB_red, and CDs is delineated using UV-Visible (UV-Vis) spectroscopy. CDs have a characteristic UV-Vis peak at ∼ 347 nm, and it shows a gradual increase in intensity with a slight red shift (∼355 nm) on the progressive increase in Hb concentration. Simultaneously, the colorless MB_red is oxidized to its blue oxidized form MB_ox and its characteristic peak starts reappearing at ∼ 663 nm. These responses are exploited to quantify Hb concentration with a limit of detection (LOD) as low as ∼ 2 g dL^-1 in a developed POC device, and the results are validated with the clinical data obtained from a local hospital with reasonably good agreement. This photometric detection approach can be adopted for other quantitative biosensors.

Neuroimmunology of Common Parasitic Infections in Africa

Parasitic infections of the central nervous system are an important cause of morbidity and mortality in Africa. The neurological, cognitive, and psychiatric sequelae of these infections result from a complex interplay between the parasites and the host inflammatory response. Here we review some of the diseases caused by selected parasitic organisms known to infect the nervous system including Plasmodium falciparum, Toxoplasma gondii, Trypanosoma brucei spp., and Taenia solium species. For each parasite, we describe the geographical distribution, prevalence, life cycle, and typical clinical symptoms of infection and pathogenesis. We pay particular attention to how the parasites infect the brain and the interaction between each organism and the host immune system. We describe how an understanding of these processes may guide optimal diagnostic and therapeutic strategies to treat these disorders. Finally, we highlight current gaps in our understanding of disease pathophysiology and call for increased interrogation of these often-neglected disorders of the nervous system.

Sequential dysregulated plasma levels of angiopoietins (ANG-2 and ratios of ANG-2/ANG-1) are associated with malaria severity and mortality among hospital admitted cases in South Bastar Region of Chhattisgarh, Central India

Cerebral malaria (CM) is one of the most severe forms of P. falciparum infection, with an associated high case-fatality rate. Angiopoietins (ANG-1 and ANG-2) are important biomarkers of endothelial activation and dysfunction. This study was carried out in Maharani Hospital and associated Medical College, Jagdalpur, CG, Central India from 2010 to 2014. Based on the treatment recovery patterns, cases (n = 65) were classified as mild malaria with rapid recovery (MM-RR), n= 14; non-cerebral severe malaria with moderately fast recovery (NCSM-MFR), n= 9; CM survivors with slow recovery (CMS-SR), n= 36 and deteriorated CM non-survivors (Det-CMNS), n= 6. Plasma levels (pg/ml) of ANG-1 and ANG-2 were measured by ELISA in all the samples at the time of hospital admission and 48 hours of treatment. Levels were also measured in available samples at the third time point (time of discharge for survivors or 72 hours post-treatment in fatal cases). Data analysis was done by appropriate statistical tests using Stata 11.0 and SPSS 25.0 software. At the time of admission, ANG-2 and ratios of ANG-2/ANG-1 significantly distinguished Det-CMNS cases from MM-RR and NCSM-MFR cases with good AUC scores (0.8-0.9). Further, Det-CMNS cases could also be distinguished from MM-RR, NCSM-MFR, and CMS-SR cases by ANG-2 (AUC scores 0.9) and ratios of ANG-2/ANG-1 (AUC: 0.8-0.9) at 48 hours of treatment. Paired analysis of sequential measurement of angiopoietins revealed that compared to admission levels, the ratios of ANG-2/ANG-1 significantly declined 48 hours after treatment in MM-RR (p= 0.041), NCSM-MFR (p= 0.050), and CMS-SR (p= 0.0002) cases but not in cases of Det-CMNS (p= 0.916). In conclusion, plasma levels of ANG-2 and ratios of ANG-2/ANG-1 may serve as good biomarkers to distinguish the malaria severity at the time of hospital admission and recovery patterns upon treatment in Central India.

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.

Neglected and (re-)emergent infections of the CNS i n low-/middle-income countries

Low- and middle-income countries (LMIC) have suffered from long-term health system deficiencies, worsened by poor living conditions, lack of sanitation, a restricted access to health facilities and running water, overcrowding, and overpopulation. These factors favor human displacement and deepen marginalization; consequently, their population endures a high burden of infectious diseases. In this context, the current epidemiological landscape and its impact on health and economic development are not promissory, despite the commitment by the international community to eradicate neglected tropical infections - especially tuberculosis and malaria, by 2030. Neglected and (re)-emerging infectious diseases affecting the central nervous system (CNS) are a major public health concern in these countries, as they cause a great morbidity and mortality; furthermore, survivors often suffer from severe neurological disabilities. Herein, we present a retrospective review focused on some neglected and (re)-emerging infectious diseases, including neurocysticercosis, malaria, rabies, West Nile virus encephalitis, tuberculosis, neuroborreliosis, and SARS-CoV-2 in LMIC. A retrospective review of studies on selected neglected and (re)-emerging infectious diseases in LMIC was performed, including reports by the World Health Organization (WHO) published within the last five years. Data on infection by SARS-CoV-2 were provided by the John Hopkins University Coronavirus Resource Center. CNS neglected and (re)-emerging infectious diseases remain as important causes of disease in LMIC. An alarming increase in the prevalence of malaria, tuberculosis, and cysticercosis is observed in the region, compounded by the recent COVID-19 pandemic. The WHO is currently supporting programs/efforts to cope with these diseases. Herein, we highlight the epidemiological burden of some CNS infections in LMIC, and their clinical and neuroimaging features, to facilitate an accurate diagnosis, considering that most of these diseases will not be eradicated in the short term; instead, their incidence will likely increase along with poverty, inequality, and related socioeconomic problems.

G6pd-Deficient Mice Are Protected From Experimental Cerebral Malaria and Liver Injury by Suppressing Proinflammatory Response in the Early Stage of Plasmodium berghei Infection

Epidemiological studies provide compelling evidence that glucose-6-phosphate dehydrogenase (G6PD) deficiency individuals are relatively protected against Plasmodium parasite infection. However, the animal model studies on this subject are lacking. Plus, the underlying mechanism in vivo is poorly known. In this study, we used a G6pd-deficient mice infected with the rodent parasite Plasmodium berghei (P.berghei) to set up a malaria model in mice. We analyzed the pathological progression of experimental cerebral malaria (ECM) and acute liver injury in mice with different G6pd activity infected with P.berghei. We performed dual RNA-seq for host-parasite transcriptomics and validated the changes of proinflammatory response in the murine model. G6pd-deficient mice exhibited a survival advantage, less severe ECM and mild liver injury compared to the wild type mice. Analysis based on dual RNA-seq suggests that G6pd-deficient mice are protected from ECM and acute liver injury were related to proinflammatory responses. Th1 differentiation and dendritic cell maturation in the liver and spleen were inhibited in G6pd-deficient mice. The levels of proinflammatory cytokines were reduced, chemokines and vascular adhesion molecules in the brain were significantly down-regulated, these led to decreased cerebral microvascular obstruction in G6pd-deficient mice. We generated the result that G6pd-deficiency mediated protection against ECM and acute liver injury were driven by the regulatory proinflammatory responses. Furthermore, bioinformatics analyses showed that P.berghei might occur ribosome loss in G6pd-deficient mice. Our findings provide a novel perspective of the underlying mechanism of G6PD deficiency mediated protection against malaria in vivo.

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.

Malaria link of hypertension: a hidden syndicate of angiotensin II, bradykinin and sphingosine 1-phosphate

In malaria-endemic countries, the burden of hypertension is on the rise. Although malaria and hypertension seem to have no direct link, several studies in recent years support their possible link. Three bioactive molecules such as angiotensin II (Ang II), bradykinin (BK) and sphingosine 1-phosphate (S1P) are crucial in regulating blood pressure. While the increased level of Ang II and S1P are responsible for inducing hypertension, BK is arthero-protective and anti-hypertensive. Therefore, in the present review, based on available literatures we highlight the present knowledge on the production and bioavailability of these molecules, the mechanism of their regulation of hypertension, and patho-physiological role in malaria. Further, a possible link between malaria and hypertension is hypothesized through various arguments based on experimental evidence. Understanding of their mechanisms of blood pressure regulation during malaria infection may open up avenues for drug therapeutics and management of malaria in co-morbidity with hypertension.

Conus venom fractions inhibit the adhesion of Plasmodium falciparum erythrocyte membrane protein 1 domains to the host vascular receptors

Using high-throughput BioPlex assays, we determined that six fractions from the venom of Conus nux inhibit the adhesion of various recombinant PfEMP-1 protein domains (PF08_0106 CIDR1α3.1, PF11_0521 DBL2β3, and PFL0030c DBL3X and DBL5e) to their corresponding receptors (CD36, ICAM-1, and CSA, respectively). The protein domain-receptor interactions permit P. falciparum-infected erythrocytes (IE) to evade elimination in the spleen by adhering to the microvasculature in various organs including the placenta. The sequences for the main components of the fractions, determined by tandem mass spectrometry, yielded four T-superfamily conotoxins, one (CC-Loop-CC) with I-IV, II-III connectivity and three (CC-Loop-CX_aaC) with a I-III, II-IV connectivity. The 3D structure for one of the latter, NuxVA = GCCPAPLTCHCVIY, revealed a novel scaffold defined by double turns forming a hairpin-like structure stabilized by the two disulfide bonds. Two other main fraction components were a miniM conotoxin, and a O2-superfamily conotoxin with cysteine framework VI/VII. This study is the first one of its kind suggesting the use of conotoxins for developing pharmacological tools for anti-adhesion adjunct therapy against malaria. Similarly, mitigation of emerging diseases like AIDS and COVID-19, can also benefit from conotoxins as inhibitors of protein-protein interactions as treatment. BIOLOGICAL SIGNIFICANCE: Among the 850+ species of cone snail species there are hundreds of thousands of diverse venom exopeptides that have been selected throughout several million years of evolution to capture prey and deter predators. They do so by targeting several surface proteins present in target excitable cells. This immense biomolecular library of conopeptides can be explored for potential use as therapeutic leads against persistent and emerging diseases affecting non-excitable systems. We aim to expand the pharmacological reach of conotoxins/conopeptides by revealing their in vitro capacity to disrupt protein-protein and protein-polysaccharide interactions that directly contribute to pathology of Plasmodium falciparum malaria. This is significant for severe forms of malaria, which might be deadly even after treated with current parasite-killing drugs because of persistent cytoadhesion of P. falciparum infected erythrocytes even when parasites within red blood cells are dead. Anti-adhesion adjunct drugs would de-sequester or prevent additional sequestration of infected erythrocytes and may significantly improve survival of malaria patients. These results provide a lead for further investigations into conotoxins and other venom peptides as potential candidates for anti-adhesion or blockade-therapies. This study is the first of its kind and it suggests that conotoxins can be developed as pharmacological tools for anti-adhesion adjunct therapy against malaria. Similarly, mitigation of emerging diseases like AIDS and COVID-19, can also benefit from conotoxins as potential inhibitors of protein-protein interactions as treatment.

[Infection associated cerebral vasculitis]

Infections are a frequent cause of cerebral vasculitis, important to diagnose because a specific treatment may be required. Infection-associated vasculitis can be caused by angiotropic pathogens (varicella zoster virus, syphilis, aspergillus). They can be associated with subarachnoidal meningitis (tuberculosis, pyogenic meningitis, cysticercosis). They can appear contiguously to sinuses or orbital infection (aspergillosis, mucormycosis). Finally, they also may be due to an immune mechanism in the context of chronic infections (hepatitis B virus, hepatitis C virus, human immunodeficiency virus). Cerebral vasculitis are severe conditions and their prognosis is directly linked to early recognition and diagnosis. Infectious causes must therefore be systematically considered ahead of cerebral vasculitis, and the appropriate investigations must be determined according to the patient's clinical context. We propose here an update on the infectious causes of cerebral vasculitis, their diagnosis modalities, and therapeutic options.

Neurological disorder and psychosocial aspects of cerebral malaria: what is new on its pathogenesis and complications? A minireview

Recently, malaria is remain considered as the most prevalent infectious disease, affecting the human health globally. High morbidity and mortality worldwide is often allied with cerebral malaria (CM) based disorders of the central nervous system, especially across many tropical and sub-tropical regions. These disorders are characterised by the infection of Plasmodium species, which leads to acute or chronic neurological disorders, even after having active/effective antimalarial drugs. Furthermore, even during the treatment, individual remain sensitive for neurological impairments in the form of decrease blood flow and vascular obstruction in brain including many more other changes. This review briefly explains and update on the epidemiology, burden of disease, pathogenesis and role of CM in neurological disorders with behaviour and function in mouse and human models. Moreover, the social stigma, which plays an important role in neurological disorders and a factor for assessing CM, is also discussed in this review.

Erg mediates downregulation of claudin-5 in the brain endothelium of a murine experimental model of cerebral malaria

Cerebral malaria (CM) is a severe complication with brain vascular hyperpermeability. Claudin-5 is the major component of tight junctions. To investigate the expression of claudin-5 in CM, we established a murine experimental cerebral malaria (ECM) model and an in vitro model by treating murine brain endothelial cells (bEnd3) with plasma from ECM mice. Expression of claudin-5 and the ETS transcription factor Erg was reduced in the brain endothelium of ECM mice. In bEnd3 cells exposed to ECM plasma, decreased expression of claudin-5 and Erg, and increased permeability were observed. Silencing of Erg significantly reduced Cldn5 expression. ChIP assays indicated that Erg binds to the -813 ETS motif of the murine Cldn5 gene promoter, and the binding is decreased by treatment with ECM plasma.

Experimental severe malaria is resolved by targeting newly-identified monocyte subsets using immune-modifying particles combined with artesunate

Current treatment of severe malaria and associated cerebral malaria (CM) and respiratory distress syndromes are directed primarily at the parasite. Targeting the parasite has only partial efficacy in advanced infection, as neurological damage and respiratory distress are due to accumulation of host blood cells in the brain microvasculature and lung interstitium. Here, computational analysis identifies Ly6C^lo monocytes as a major component of the immune infiltrate in both organs in a preclinical mouse model. Specifically targeting Ly6C^lo monocyte precursors, identified by adoptive transfer, with immune-modifying particles (IMP) prevents experimental CM (ECM) in 50% of Plasmodium berghei ANKA-infected mice in early treatment protocols. Furthermore, treatment at onset of clinical ECM with 2 doses of a novel combination of IMP and anti-malarial drug artesunate results in 88% survival. This combination confers protection against ECM and mortality in late stage severe experimental malaria and provides a viable advance on current treatment regimens.

Opportunities for Host-targeted Therapies for Malaria

Despite the recent successes of artemisinin-based antimalarial drugs, many still die from severe malaria, and eradication efforts are hindered by the limited drugs currently available to target transmissible gametocyte parasites and liver-resident dormant Plasmodium vivax hypnozoites. Host-targeted therapy is a new direction for infectious disease drug development and aims to interfere with host molecules, pathways, or networks that are required for infection or that contribute to disease. Recent advances in our understanding of host pathways involved in parasite development and pathogenic mechanisms in severe malaria could facilitate the development of host-targeted interventions against Plasmodium infection and malaria disease. This review discusses new opportunities for host-targeted therapeutics for malaria and the potential to harness drug polypharmacology to simultaneously target multiple host pathways using a single drug intervention.

Triaryl Pyrazole Toll-Like Receptor Signaling Inhibitors: Structure-Activity Relationships Governing Pan- and Selective Signaling Inhibitors

The immune system uses members of the toll-like receptor (TLR) family to recognize a variety of pathogen- and host-derived molecules in order to initiate immune responses. Although TLR-mediated, pro-inflammatory immune responses are essential for host defense, prolonged and exaggerated activation can result in inflammation pathology that manifests in a variety of diseases. Therefore, small-molecule inhibitors of the TLR signaling pathway might have promise as anti-inflammatory drugs. We previously identified a class of triaryl pyrazole compounds that inhibit TLR signaling by modulation of the protein-protein interactions essential to the pathway. We have now systematically examined the structural features essential for inhibition of this pathway, revealing characteristics of compounds that inhibited all TLRs tested (pan-TLR signaling inhibitors) as well as compounds that selectively inhibited certain TLRs. These findings reveal interesting classes of compounds that could be optimized for particular inflammatory diseases governed by different TLRs.

Differentially expressed microRNAs in experimental cerebral malaria and their involvement in endocytosis, adherens junctions, FoxO and TGF-β signalling pathways

Cerebral malaria (CM) is the most severe manifestation of infection with Plasmodium, however its pathogenesis is still not completely understood. microRNA (miRNA) have been an area of focus in infectious disease research, due to their ability to affect normal biological processes, and have been shown to play roles in various viral, bacterial and parasitic infections, including malaria. The expression of miRNA was studied following infection of CBA mice with either Plasmodium berghei ANKA (causing CM), or Plasmodium yoelii (causing severe but non-cerebral malaria (NCM)). Using microarray analysis, miRNA expression was compared in the brains of non-infected (NI), NCM and CM mice. Six miRNA were significantly dysregulated between NCM and CM mice, and four of these, miR-19a-3p, miR-19b-3p, miR-142-3p and miR-223-3p, were further validated by qPCR assays. These miRNA are significantly involved in several pathways relevant to CM, including the TGF-β and endocytosis pathways. Dysregulation of these miRNA during CM specifically compared with NCM suggests that these miRNA, through their regulation of downstream targets, may be vitally involved in the neurological syndrome. Our data implies that, at least in the mouse model, miRNA may play a regulatory role in CM pathogenesis.

Case Report: A Case of Severe Cerebral Malaria Managed with Therapeutic Hypothermia and Other Modalities for Brain Edema

Malarial infections are uncommon in the United States and almost all reported cases stem from recent travelers coming from endemic countries. Cerebral malaria (CM) is a severe form of the disease usually affecting children and individuals with limited immunity. Despite proper management, mortality from CM can reach up to 25%, especially when it is associated with brain edema. Inefficient management of the edema may result in brain herniation and death. Uniform guidelines for management of CM-associated brain edema are lacking. In this report, we present a case of CM with associated severe brain edema that was successfully managed using a unique combination of therapeutic hypothermia, hypertonic saline, mannitol, and hyperventilation along with the antimalarial drugs quinidine and doxycycline. Our use of hypothermia was based on its proven benefit for improving neurological outcomes in post-cardiac arrest patients and previous in vitro research, suggesting its potential inhibitory role on malaria growth.

Cytokines and Chemokines in Cerebral Malaria Pathogenesis

Cerebral malaria is among the major causes of malaria-associated mortality and effective adjunctive therapeutic strategies are currently lacking. Central pathophysiological processes involved in the development of cerebral malaria include an imbalance of pro- and anti-inflammatory responses to Plasmodium infection, endothelial cell activation, and loss of blood-brain barrier integrity. However, the sequence of events, which initiates these pathophysiological processes as well as the contribution of their complex interplay to the development of cerebral malaria remain incompletely understood. Several cytokines and chemokines have repeatedly been associated with cerebral malaria severity. Increased levels of these inflammatory mediators could account for the sequestration of leukocytes in the cerebral microvasculature present during cerebral malaria, thereby contributing to an amplification of local inflammation and promoting cerebral malaria pathogenesis. Herein, we highlight the current knowledge on the contribution of cytokines and chemokines to the pathogenesis of cerebral malaria with particular emphasis on their roles in endothelial activation and leukocyte recruitment, as well as their implication in the progression to blood-brain barrier permeability and neuroinflammation, in both human cerebral malaria and in the murine experimental cerebral malaria model. A better molecular understanding of these processes could provide the basis for evidence-based development of adjunct therapies and the definition of diagnostic markers of disease progression.

Dynamic interactions of Plasmodium spp. with vascular endothelium

Plasmodial species are protozoan parasites that infect erythrocytes. As such, they are in close contact with microvascular endothelium for most of the life cycle in the mammalian host. The host-parasite interactions of this stage of the infection are responsible for the clinical manifestations of the disease that range from a mild febrile illness to severe and frequently fatal syndromes such as cerebral malaria and multi-organ failure. Plasmodium falciparum, the causative agent of the most severe form of malaria, is particularly predisposed to modulating endothelial function through either direct adhesion to endothelial receptor molecules, or by releasing potent host and parasite products that can stimulate endothelial activation and/or disrupt barrier function. In this review, we provide a critical analysis of the current clinical and laboratory evidence for endothelial dysfunction during severe P. falciparum malaria. Future investigations using state-of-the-art technologies such as mass cytometry and organs-on-chips to further delineate parasite-endothelial cell interactions are also discussed.

Natural Mosquito-Pathogen Hybrid IgG4 Antibodies in Vector-Borne Diseases: A Hypothesis

Chronic exposure to antigens may favor the production of IgG4 antibodies over other antibody types. Recent studies have shown that up to a 30% of normal human IgG4 is bi-specific and is able to recognize two antigens of different nature. A requirement for this specificity is the presence of both eliciting antigens in the same time and at the same place where the immune response is induced. During transmission of most vector-borne diseases, the pathogen is delivered to the vertebrate host along with the arthropod saliva during blood feeding and previous studies have shown the existence of IgG4 antibodies against mosquito salivary allergens. However, there is very little ongoing research or information available regarding IgG4 bi-specificity with regard to infectious disease, particularly during immune responses to vector-borne diseases, such as malaria, filariasis, or dengue virus infection. Here, we provide background information and present our hypothesis that IgG4 may not only be a useful tool to measure exposure to infected mosquito bites, but that these bi-specific antibodies may also play an important role in modulation of the immune response against malaria and other vector-borne diseases in endemic settings.

Severe malaria: what's new on the pathogenesis front?

Plasmodium falciparum causes the most severe and fatal form of malaria in humans with over half a million deaths each year. Cerebral malaria, a complex neurological syndrome of severe falciparum malaria, is often fatal and represents a major public health burden. Despite vigorous efforts, the pathophysiology of cerebral malaria remains to be elucidated, thereby hindering the development of adjunctive therapies. In recent years, multidisciplinary and collaborative approaches have led to groundbreaking progress both in the laboratory and in the field. Here we review the latest breakthroughs in severe malaria pathogenesis, with a specific focus on new pathogenetic mechanisms leading to cerebral malaria. The most recent findings point towards specific parasite phenotypes targeting brain microvasculature, endothelial dysfunction and subsequent oedema-induced brain swelling.

Potential cerebral malaria therapy: intramuscular arteether and vitamin D co-administration

Cerebral malaria (CM) shows lethality rate of 15–25% despite effective antimalarial chemotherapy. The effective adjunct treatment to counteract the CM pathogenesis is urgently required. In murine CM model, most interventions studied till date are administered before the onset of CM symptoms, which belittle its translational value to human. We studied intramuscular arteether–vitamin D (ART–VD) combination treatment for CM outcome improvement after the onset of neurological symptoms. The intramuscular dose of 50 µg kg−1 VD for 3 days combined with a loading dose of 25 mg kg−1α/β arteether followed by 12·5 mg kg−1 dose for two consecutive days led to significant improvement in survival (73% in combination group vs 29 and 0% in arteether and VD monotherapy, respectively) and clinical recovery. The treatment in all the groups partially restored the blood–brain barrier integrity and reduced the level of serum proinflammatory cytokines tumour necrosis factor-α and interferon-γ. The brain transcripts of inflammatory chemokines viz. CXCL10, CXCL9, CCL4 and CCL5 and T cell migration in the brain microvasculature were significantly diminished in all the treatment groups. ART–VD treatment significantly reduced intercellular cell adhesion molecule-1 expression. Taken together, our findings show that coordinated actions of ART–VD improve the outcome of experimental CM.