Endothelial activation and dysregulation in malaria: a potential target for novel therapeutics

The critical role of endothelial cell in the toxicity associated with chimeric antigen receptor T cell therapy and intervention strategies

Chimeric antigen receptor (CAR)-T cell therapy has shown promising results in patients with hematological malignancies. However, many patients still have poor prognoses or even fatal outcomes due to the life-threatening toxicities associated with the therapy. Moreover, even after improving the known influencing factors (such as number or type of CAR-T infusion) related to CAR-T cell infusion, the results remain unsatisfactory. In recent years, it has been found that endothelial cells (ECs), which are key components of the organization, play a crucial role in various aspects of immune system activation and inflammatory response. The levels of typical markers of endothelial activation positively correlated with the severity of cytokine release syndrome (CRS) and immune effector cell-associated neurotoxic syndrome (ICANS), suggesting that ECs are important targets for intervention and toxicity prevention. This review focuses on the critical role of ECs in CRS and ICANS and the intervention strategies adopted.

Exploring adjunctive therapies for cerebral malaria

Cerebral malaria (CM) is one of the most severe complications of malaria infection characterized by coma and neurological effects. Despite standardized treatment of malaria infection with artemisinin-based combination therapies (ACT), the mortality rate is still high, and it primarily affects pediatric patients. ACT reduces parasitemia but fails to adequately target the pathogenic mechanisms underlying CM, including blood-brain-barrier (BBB) disruption, endothelial activation/dysfunction, and hyperinflammation. The need for adjunctive therapies to specifically treat this form of severe malaria is critical as hundreds of thousands of people continue to die each year from this disease. Here we present a summary of some potential promising therapeutic targets and treatments for CM, as well as some that have been tested and deemed ineffective or, in some cases, even deleterious. Further exploration into these therapeutic agents is warranted to assess the effectiveness of these potential treatments for CM patients.

Coenzyme Q10 exhibits anti-inflammatory and immune-modulatory thereby decelerating the occurrence of experimental cerebral malaria

Cerebral Malaria (CM) is associated with the complex neurological syndrome, whose pathology is mediated by severe inflammatory processes following infection with Plasmodium falciparum. Coenzyme-Q10 (Co-Q10) is a potent anti-inflammatory, anti-oxidant, and anti-apoptotic agent with numerous clinical applications. The aim of this study was to elucidate the role of oral administration of Co-Q10 on the initiation or regulation of inflammatory immune response during experimental cerebral malaria (ECM). For this purpose, the pre-clinical effect of Co-Q10 was evaluated in C57BL/6 J mice infected with Plasmodium berghei ANKA (PbA). Treatment with Co-Q10 resulted in the reduction of infiltrating parasite load, greatly improved the survival rate of PbA-infected mice that occurred independent of parasitaemia and prevented PbA-induced disruption of the blood-brain barrier (BBB) integrity. Exposure to Co-Q10 resulted in the reduction of infiltration of effector CD8 + T cells in the brain and secretion of cytolytic Granzyme B molecules. Notably, Co-Q10-treated mice had reduced levels of CD8 +T cell chemokines CXCR3, CCR2, and CCR5 in the brain following PbA-infection. Brain tissue analysis showed a reduction in the levels of inflammatory mediators TNF- α, CCL3, and RANTES in Co-Q10 administered mice. In addition, Co-Q10 modulated the differentiation and maturation of both splenic and brain dendritic cells and cross-presentation (CD8α+DCs) during ECM. Remarkably, Co-Q10 was very effective in decreasing levels of CD86, MHC-II, and CD40 in macrophages associated with ECM pathology. Exposure to Co-Q10 resulted in increased expression levels of Arginase-1 and Ym1/chitinase 3-like 3, which is linked to ECM protection. Furthermore, Co-Q10 supplementation prevented PbA-induced depletion of Arginase and CD206 mannose receptor levels. Co-Q10 abrogated PbA-driven elevation in pro-inflammatory cytokines IL-1β, IL-18, and IL-6 levels. In conclusion, the oral supplementation with Co-Q10 decelerates the occurrence of ECM by preventing lethal inflammatory immune responses and dampening genes associated with inflammation and immune-pathology during ECM, and offers an inimitable opening for developing an anti-inflammatory agent against cerebral malaria.

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.

Immune and endothelial activation markers and risk stratification of childhood pneumonia in Uganda: A secondary analysis of a prospective cohort study

BACKGROUND

Despite the global burden of pneumonia, reliable triage tools to identify children in low-resource settings at risk of severe and fatal respiratory tract infection are lacking. This study assessed the ability of circulating host markers of immune and endothelial activation quantified at presentation, relative to currently used clinical measures of disease severity, to identify children with pneumonia who are at risk of death.

METHODS AND FINDINGS

We conducted a secondary analysis of a prospective cohort study of children aged 2 to 59 months presenting to the Jinja Regional Hospital in Jinja, Uganda between February 2012 and August 2013, who met the Integrated Management of Childhood Illness (IMCI) diagnostic criteria for pneumonia. Circulating plasma markers of immune (IL-6, IL-8, CXCL-10/IP-10, CHI3L1, sTNFR1, and sTREM-1) and endothelial (sVCAM-1, sICAM-1, Angpt-1, Angpt-2, and sFlt-1) activation measured at hospital presentation were compared to lactate, respiratory rate, oxygen saturation, procalcitonin (PCT), and C-reactive protein (CRP) with a primary outcome of predicting 48-hour mortality. Of 805 children with IMCI pneumonia, 616 had severe pneumonia. Compared to 10 other immune and endothelial activation markers, sTREM-1 levels at presentation had the best predictive accuracy in identifying 48-hour mortality for children with pneumonia (AUROC 0.885, 95% CI 0.841 to 0.928; p = 0.03 to p < 0.001) and severe pneumonia (AUROC 0.870, 95% CI 0.824 to 0.916; p = 0.04 to p < 0.001). sTREM-1 was more strongly associated with 48-hour mortality than lactate (AUROC 0.745, 95% CI 0.664 to 0.826; p < 0.001), respiratory rate (AUROC 0.615, 95% CI 0.528 to 0.702; p < 0.001), oxygen saturation (AUROC 0.685, 95% CI 0.594 to 0.776; p = 0.002), PCT (AUROC 0.650, 95% CI 0.566 to 0.734; p < 0.001), and CRP (AUROC 0.562, 95% CI 0.472 to 0.653; p < 0.001) in cases of pneumonia and severe pneumonia. The main limitation of this study was the unavailability of radiographic imaging.

CONCLUSIONS

In this cohort of Ugandan children, sTREM-1 measured at hospital presentation was a significantly better indicator of 48-hour mortality risk than other common approaches to risk stratify children with pneumonia. Measuring sTREM-1 at clinical presentation may improve the early triage, management, and outcome of children with pneumonia at risk of death.

TRIAL REGISTRATION

The trial was registered at clinicaltrial.gov (NCT04726826).

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.

Experimental Models to Study the Pathogenesis of Malaria-Associated Acute Respiratory Distress Syndrome

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is increasingly gaining recognition as a severe malaria complication because of poor prognostic outcomes, high lethality rate, and limited therapeutic interventions. Unfortunately, invasive clinical studies are challenging to conduct and yields insufficient mechanistic insights. These limitations have led to the development of suitable MA-ARDS experimental mouse models. In patients and mice, MA-ARDS is characterized by edematous lung, along with marked infiltration of inflammatory cells and damage of the alveolar-capillary barriers. Although, the pathogenic pathways have yet to be fully understood, the use of different experimental mouse models is fundamental in the identification of mediators of pulmonary vascular damage. In this review, we discuss the current knowledge on endothelial activation, leukocyte recruitment, leukocyte induced-endothelial dysfunction, and other important findings, to better understand the pathogenesis pathways leading to endothelial pulmonary barrier lesions and increased vascular permeability. We also discuss how the advances in imaging techniques can contribute to a better understanding of the lung lesions induced during MA-ARDS, and how it could aid to monitor MA-ARDS severity.

Malaria Parasite Plasmodium falciparum Proteins on the Surface of Infected Erythrocytes as Targets for Novel Drug Discovery

Specific adhesion (sequestration) of Plasmodium falciparum parasite-infected erythrocytes (IEs) in deep vascular beds can cause severe complications resulting in death. This review describes our work on the discovery, characterization, and optimization of novel inhibitors that specifically prevent adhesion of IEs to the host vasculature during severe malaria, especially its placental and cerebral forms. The main idea of using anti-adhesion drugs in severe malaria is to release sequestered parasites (or prevent additional sequestration) as quickly as possible. This may significantly improve the outcomes for patients with severe malaria by decreasing local and systemic inflammation associated with the disease and reestablishing the microvascular blood flow. To identify anti-malarial adhesion-inhibiting molecules, we have developed a high-throughput (HT) screening approach and found a number of promising leads that can be further developed into anti-adhesion drugs providing an efficient adjunct therapy against severe forms of malaria.

Predictive role of endothelial cell activation in cytokine release syndrome after chimeric antigen receptor T cell therapy for acute lymphoblastic leukaemia

CD19-target chimeric antigen receptor (CAR)-T cell therapy is highly effective for relapsed/refractory (R/R) acute lymphoblastic leukaemia (ALL), but is often complicated by cytokine release syndrome (CRS), which is potentially life-threatening. Endothelial cells are the core regulator of CRS in many infectious diseases and may also play a key role after CAR-T cell therapy. We provided a detailed clinical, laboratory description and endothelial cell activation biomarkers in patients with CRS. Endothelial cell activation was associated with occurrence, development and severity of CRS, manifested by decreased serum angiopoietin (Ang)-1 levels and increased levels of von Willebrand Factor (VWF), Ang-2, Ang-2:Ang-1, sE-selectin, soluble intercellular adhesion molecule (sICAM-1) and soluble vascular cell adhesion molecule (sVCAM)-1. Besides, the endothelial activation was correlated with the hepatic, kidney and hematopoietic dysfunction in CRS patients. After infusion of CAR-T cells, we detected changes of endothelial activation-related biomarkers within 36 hours in patients who subsequently developed CRS, especially severe CRS. Using top tree models, we could predict which patients would develop CRS, especially severe CRS, or identify the severity of CRS by certain biomarkers of endothelial activation. These data provide a new idea and will help identify new targets for early intervention and prevention of CRS.

Acute Phase Responses Vary Between Children of HbAS and HbAA Genotypes During Plasmodium falciparum Infection

Purpose

Haemoglobin genotype S is known to offer protection against Plasmodium falciparum infections but the mechanism underlying this protection is not completely understood. Associated changes in acute phase proteins (APPs) during Plasmodium falciparum infections between Haemoglobin AA (HbAA) and Haemoglobin AS (HbAS) individuals also remain unclear. This study aimed to evaluate changes in three APPs and full blood count (FBC) indices of HbAA and HbAS children during Plasmodium falciparum infection.

Methods

Venous blood was collected from three hundred and twenty children (6 months to 15 years) in Begoro in Fanteakwa District of Ghana during a cross-sectional study. Full blood count (FBC) indices were measured and levels of previously investigated APPs in malaria patients; C-reactive protein (CRP), ferritin and transferrin measured using Enzyme-Linked Immunosorbent Assays.

Results

Among the HbAA and HbAS children, levels of CRP and ferritin were higher in malaria positive children as compared to those who did not have malaria. The mean CRP levels were significantly higher among HbAA children (p=0.2e-08) as compared to the HbAS children (p=0.43). Levels of transferrin reduced in both HbAA and HbAS children with malaria, but the difference was only significant among HbAA children (p=0.0038), as compared to the HbAS children. No significant differences were observed in ferritin levels between HbAA and HbAS children in both malaria negative (p=0.76) and positive (p=0.26) children. Of the full blood count indices measured, red blood cell count (p=0.044) and haemoglobin (Hb) levels (p=0.017) differed between HbAA and HbAS in those without malaria, with higher RBC counts and lower Hb levels found in HbAS children. In contrast, during malaria, lymphocyte and platelet counts were elevated, whilst granulocytes and Mean Cell Haematocrit counts were reduced among children of the HbAS genotypes.

Conclusion

Significant changes in APPs were found in HbAA children during malaria as compared to HbAS children, possibly due to differences in malaria-induced inflammation levels. This suggests that the HbAS genotype is associated with better control of P. falciparum infection-induced inflammatory response than HbAA genotype.

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.

The Malaria-High Blood Pressure Hypothesis: Revisited

Malaria etiologies with pathophysiological similarities to hypertension currently constitute a major subject of research. The malaria-high blood pressure hypothesis is strongly supported by observations of the increasing incidence of hypertension in malaria-endemic, low- and middle-income countries with poor socioeconomic conditions, particularly in sub-Saharan African countries. Malnutrition and low birth weight with persistent symptomatic malaria presentations in pregnancy correlate strongly with the development of preeclampsia, gestational hypertension and subsequent hypertension in adult life. Evidence suggest that the link between malaria infection and high blood pressure involves interactions between malaria parasites and erythrocytes, the inflammatory process, effects of the infection during pregnancy; effects on renal and vascular functions as well as effects in sickle cell disease. Possible mechanisms which provide justification for the malaria-high blood pressure hypothesis include the following: endothelial dysfunction (reduced nitric oxide (NO) levels), impaired release of local neurotransmitters and cytokines, decrease in vascular smooth muscle cell viability and/or alterations in cellular calcium signaling leading to enhanced vascular reactivity, remodeling, and cardiomyopathies, deranged homeostasis through dehydration, elevated intracellular mediators and proinflammatory cytokine responses, possible genetic regulations, activation of the renin-angiotensin-aldosterone system mechanisms and renal derangements, severe anemia and hemolysis, renal failure, and end organ damage. Two key mediators of the malaria-high blood pressure association are: endothelial dysfunction (reduced NO) and increased angiotensin-converting enzyme activity/angiotensin II levels. Sickle cell disease is associated with protection against malaria infection and reduced blood pressure. In this review, we present the state of knowledge about the malaria-blood pressure hypothesis and suggest insights for future studies.

Acute kidney injury due to acute cortical necrosis following vivax malaria

Malaria is a parasitic infection of global importance but has a high prevalence in the developing countries. Renal failure is a common complication of severe Plasmodium falciparum malaria and has been reported in up to 40% of all cases. Acute kidney injury (AKI), however, is not commonly associated with Plasmodium vivax infection. In those patients who develop AKI following P. vivax infection, the cause is commonly attributed to mixed undiagnosed falciparum infection or coexistent sepsis, dehydration, or hypotension. Infrequently, an association of P. vivax infection with thrombotic microangiopathy (TMA) has been reported. The purpose of this report is to describe renal failure due to TMA following malaria caused by P. vivax. A 24-year-old female presented with a history of fever and jaundice of two weeks duration followed by progressive oliguria and swelling of the face and feet five days after the onset of fever. The evaluation revealed normal blood pressure, anemia, thrombocytopenia, azotemia, unconjugated hyperbilirubinemia with mildly elevated transaminases, and elevated lactate dehydrogenase. Peripheral smear was positive for P. vivax, and schistocytes were seen. She was given intravenous artesunate followed by oral primaquine for 14 days. Urine examination showed proteinuria and microscopic hematuria. She remained oliguric and dialysis dependent, and her kidney biopsy revealed patchy cortical necrosis involving 40% of sampled cortex with widespread fibrinoid necrosis of the vessel wall, red blood cell fragmentation, and luminal thrombotic occlusion. Hemodialysis was discontinued after three weeks when there was the improvement of renal function over time, and her serum creatinine decreased to 2.2 mg/dL by six weeks. Patients with P. vivax malaria developing renal failure may have TMA. Renal biopsy, if performed early in the course of the disease, may identify TMA and institution of plasma exchange in such patients could help in early recovery.

New insights into microvascular injury to inform enhanced diagnostics and therapeutics for severe malaria

Severe malaria (SM) has high mortality and morbidity rates despite treatment with potent antimalarials. Disease onset and outcome is dependent upon both parasite and host factors. Infected erythrocytes bind to host endothelium contributing to microvascular occlusion and dysregulated inflammatory and immune host responses, resulting in endothelial activation and microvascular damage. This review focuses on the mechanisms of host endothelial and microvascular injury. Only a small percentage of malaria infections (≤1%) progress to SM. Early recognition and treatment of SM can improve outcome, but we lack triage tools to identify SM early in the course of infection. Current point-of-care pathogen-based rapid diagnostic tests do not address this critical barrier. Immune and endothelial activation have been implicated in the pathobiology of SM. We hypothesize that measuring circulating mediators of these pathways at first clinical presentation will enable early triage and treatment of SM. Moreover, that host-based interventions that modulate these pathways will stabilize the microvasculature and improve clinical outcome over that of antimalarial therapy alone.

Biosensors for Detection of Human Placental Pathologies: A Review of Emerging Technologies and Current Trends

Substantial growth in the biosensor research has enabled novel, sensitive and point-of-care diagnosis of human diseases in the last decade. This paper presents an overview of the research in the field of biosensors that can potentially predict and diagnosis of common placental pathologies. A survey of biomarkers in maternal circulation and their characterization methods is presented, including markers of oxidative stress, angiogenic factors, placental debris, and inflammatory biomarkers that are associated with various pathophysiological processes in the context of pregnancy complications. Novel biosensors enabled by microfluidics technology and nanomaterials is then reviewed. Representative designs of plasmonic and electrochemical biosensors for highly sensitive and multiplexed detection of biomarkers, as well as on-chip sample preparation and sensing for automatic biomarker detection are illustrated. New trends in organ-on-a-chip based placental disease models are highlighted to illustrate the capability of these in vitro disease models in better understanding the complex pathophysiological processes, including mass transfer across the placental barrier, oxidative stress, inflammation, and malaria infection. Biosensor technologies that can be potentially embedded in the placental models for real time, label-free monitoring of these processes and events are suggested. Merger of cell culture in microfluidics and biosensing can provide significant potential for new developments in advanced placental models, and tools for diagnosis, drug screening and efficacy testing.

Critical Roles of Endogenous Glucocorticoids for Disease Tolerance in Malaria

During malaria, the hypothalamic-pituitary-adrenal (HPA) axis is activated and glucocorticoid (GC) levels are increased, but their essential roles have been largely overlooked. GCs are decisive for systemic regulation of vital processes such as immune responses, vascular function, and metabolism, which are crucial in malaria. Here, we introduce GCs in general, followed by their versatile roles for disease tolerance in malaria. A complementary comparison is provided with their role in sepsis. Finally, potential translational implications are considered. The failed clinical trials of dexamethasone against cerebral malaria in the past have diminished the interest in GCs in malaria. However, the issue of relative corticosteroid insufficiency has barely been explored in malaria patients, but may hold promise for a better understanding and treatment of specific malaria complications.

Activation of Mast Cells Promote Plasmodium berghei ANKA Infection in Murine Model

Malaria, a mosquito-borne infectious disease, is a severe health problem worldwide. As reported, some anti-malarial drugs with anti-parasitic properties also block mast cells (MCs) activities. It is hypothesized that MCs activity may be correlated with the pathogenesis of malaria. Thus, the role of MCs on malarial pathogenesis and the involved physiological action and pathways need to be further investigated. This study aimed to investigate the effect of MCs activation on malaria disease severity using KunMing mice with Plasmodium berghei ANKA (PbANKA) infection treated with MCs degranulator (compound 48/80, C48/80) or MCs stabilizer (disodium cromoglycate, DSCG). PbANKA infection caused a dramatic increase in MCs density and level of MCs degranulation in cervical lymph node (CLN) and skin. Compared with infected control, C48/80 treatment had shortened survival time, increased parasitemia, exacerbated liver inflammation and CLN hyperplasia, accompanied with increase in vascular leakage and leukocyte number. The infected mice with C48/80 treatment also elevated the release of CCL2, CXCL1, and MMP-9 from MCs in CLN and skin, and TNF-α, IFN-γ, CCR2, and CXCR2 mRNA expression in CLN and liver. In contrast, the infected mice treated with DSCG showed longer survival time, lower parasitemia, improved liver inflammation and CLN hyperplasia, followed by a decline of vascular leakage and leukocyte number. Decreased MCs-derived CCL2, CXCL1, and MMP-9 from CLN and skin, mRNA expression in CLN and liver (TNF-α, IFN-γ, CCR2, and CXCR2) were also observed in infected mice with DSCG treatment. Our data indicated that MCs activation may facilitate the pathogenesis of PbANKA infection.

Integrated fever management: disease severity markers to triage children with malaria and non-malarial febrile illness

Febrile symptoms in children are a leading cause of health-care seeking behaviour worldwide. The majority of febrile illnesses are uncomplicated and self-limited, without the need for referral or hospital admission. However, current diagnostic tools are unable to identify which febrile children have self-limited infection and which children are at risk of progressing to life-threatening infections, such as severe malaria. This paper describes the need for a simple community-based tool that can improve the early recognition and triage of febrile children, with either malarial or non-malarial illness, at risk of critical illness. The integration of a disease severity marker into existing malaria rapid diagnostic tests (RDT) could enable detection of children at risk of severe infection in the hospital and community, irrespective of aetiology. Incorporation of a disease severity marker could inform individualized management and early triage of children at risk of life-threatening infection. A child positive for both malaria and a disease severity marker could be prioritized for urgent referral/admission and parenteral therapy. A child positive for malaria and negative for a disease severity marker could be managed conservatively, as an out-patient, with oral anti-malarial therapy. An RDT with a disease severity marker could facilitate an integrated community-based approach to fever syndromes and improve early recognition, risk stratification, and prompt treatment of severe malaria and other life-threatening infections.

Glucose metabolism mediates disease tolerance in cerebral malaria

Sickness behaviors are a conserved set of stereotypic responses to inflammatory diseases. We recently demonstrated that interfering with inflammation-induced anorexia led to metabolic changes that had profound effects on survival of acute inflammatory conditions. We found that different inflammatory states needed to be coordinated with corresponding metabolic programs to actuate tissue-protective mechanisms. Survival of viral inflammation required intact glucose utilization pathways, whereas survival of bacterial inflammation required alternative fuel substrates and ketogenic programs. We thus hypothesized that organismal metabolism would be important in other classes of infectious inflammation and sought to understand its role in the prototypic parasitic disease malaria. Utilizing the cerebral malaria model, Plasmodium berghei ANKA (PbA) infection in C57BL/6J male mice, we unexpectedly found that inhibition of glycolysis using 2-deoxy glucose (2DG) conferred protection from cerebral malaria. Unlike vehicle-treated animals, 2DG-treated animals did not develop cerebral malaria and survived until ultimately succumbing to fatal anemia. We did not find any differences in parasitemia or pathogen load in affected tissues. There were no differences in the kinetics of anemia. We also did not detect differences in immune infiltration in the brain or in blood-brain barrier permeability. Rather, on pathological analyses performed on the entire brain, we found that 2DG prevented the formation of thrombi and thrombotic complications. Using thromboelastography (TEG), we found that 2DG-treated animals formed clots that were significantly less strong and stable. Together, these data suggest that glucose metabolism is involved in inflammation-induced hemostasis and provide a potential therapeutic target in treatment of cerebral malaria.

Targeting the IL33-NLRP3 axis improves therapy for experimental cerebral malaria

Cerebral malaria (CM) is a serious neurological complication caused by Plasmodium falciparum infection. Currently, the only treatment for CM is the provision of antimalarial drugs; however, such treatment by itself often fails to prevent death or development of neurological sequelae. To identify potential improved treatments for CM, we performed a nonbiased whole-brain transcriptomic time-course analysis of antimalarial drug chemotherapy of murine experimental CM (ECM). Bioinformatics analyses revealed IL33 as a critical regulator of neuroinflammation and cerebral pathology that is down-regulated in the brain during fatal ECM and in the acute period following treatment of ECM. Consistent with this, administration of IL33 alongside antimalarial drugs significantly improved the treatment success of established ECM. Mechanistically, IL33 treatment reduced inflammasome activation and IL1β production in microglia and intracerebral monocytes in the acute recovery period following treatment of ECM. Moreover, treatment with the NLRP3-inflammasome inhibitor MCC950 alongside antimalarial drugs phenocopied the protective effect of IL33 therapy in improving the recovery from established ECM. We further showed that IL1β release from macrophages was stimulated by hemozoin and antimalarial drugs and that this was inhibited by MCC950. Our results therefore demonstrate that manipulation of the IL33-NLRP3 axis may be an effective therapy to suppress neuroinflammation and improve the efficacy of antimalarial drug treatment of CM.

Adjunctive therapy for severe malaria: a review and critical appraisal

BACKGROUND

Despite recent efforts and successes in reducing the malaria burden globally, this infection still accounts for an estimated 212 million clinical cases, 2 million severe malaria cases, and approximately 429,000 deaths annually. Even with the routine use of effective anti-malarial drugs, the case fatality rate for severe malaria remains unacceptably high, with cerebral malaria being one of the most life-threatening complications. Up to one-third of cerebral malaria survivors are left with long-term cognitive and neurological deficits. From a population point of view, the decrease of malaria transmission may jeopardize the development of naturally acquired immunity against the infection, leading to fewer total cases, but potentially an increase in severe cases. The pathophysiology of severe and cerebral malaria is not completely understood, but both parasite and host determinants contribute to its onset and outcomes. Adjunctive therapy, based on modulating the host response to infection, could help to improve the outcomes achieved with specific anti-malarial therapy.

RESULTS AND CONCLUSIONS

In the last decades, several interventions targeting different pathways have been tested. However, none of these strategies have demonstrated clear beneficial effects, and some have shown deleterious outcomes. This review aims to summarize evidence from clinical trials testing different adjunctive therapy for severe and cerebral malaria in humans. It also highlights some preclinical studies which have evaluated novel strategies and other candidate therapeutics that may be evaluated in future clinical trials.

Dysregulation of angiopoietin-1 plays a mechanistic role in the pathogenesis of cerebral malaria

Cerebral malaria is a leading cause of global morbidity and mortality. Interventions targeting the underlying pathophysiology of cerebral malaria may improve outcomes compared to treatment with antimalarials alone. Microvascular leak plays an important role in the pathogenesis of cerebral malaria. The angiopoietin (Ang)-Tie-2 system is a critical regulator of vascular function. We show that Ang-1 expression and soluble Tie-2 expression were associated with disease severity and outcome in a prospective study of Ugandan children with severe malaria and in a preclinical murine model of experimental cerebral malaria. Ang-1 was necessary for maintenance of vascular integrity and survival in a mouse model of cerebral malaria. Therapeutic administration of Ang-1 preserved blood-brain barrier integrity and, in combination with artesunate treatment, improved survival beyond that with artesunate alone. These data define a role for dysregulation of the Ang-Tie-2 axis in the pathogenesis of cerebral malaria and support the evaluation of Ang-Tie-2-based interventions as potential adjunctive therapies for treating severe malaria.

A single rapamycin dose protects against late-stage experimental cerebral malaria via modulation of host immunity, endothelial activation and parasite sequestration

Background

Maladaptive immune responses during cerebral malaria (CM) result in high mortality despite opportune anti-malarial chemotherapy. Rapamycin, an FDA-approved immunomodulator, protects against experimental cerebral malaria (ECM) in mice through effects on the host. However, the potential for reduced adaptive immunity with chronic use, combined with an incomplete understanding of mechanisms underlying protection, limit translational potential as an adjunctive therapy in CM.

Results

The results presented herein demonstrate that a single dose of rapamycin, provided as late as day 4 or 5 post-infection, protected mice from ECM neuropathology and death through modulation of distinct host responses to infection. Rapamycin prevented parasite cytoadherence in peripheral organs, including white adipose tissue, via reduction of CD36 expression. Rapamycin also altered the splenic immune response by reducing the number of activated T cells with migratory phenotype, while increasing local cytotoxic T cell activation. Finally, rapamycin reduced brain endothelial ICAM-1 expression concomitant with reduced brain pathology. Together, these changes potentially contributed to increased parasite elimination while reducing CD8 T cell migration to the brain.

Conclusions

Rapamycin exerts pleotropic effects on host immunity, vascular activation and parasite sequestration that rescue mice from ECM, and thus support the potential clinical use of rapamycin as an adjunctive therapy in CM.

S-Nitrosoglutathione Reductase Deficiency Confers Improved Survival and Neurological Outcome in Experimental Cerebral Malaria

Artesunate remains the mainstay of treatment for cerebral malaria, but it is less effective in later stages of disease when the host inflammatory response and blood-brain barrier integrity dictate clinical outcomes. Nitric oxide (NO) is an important regulator of inflammation and microvascular integrity, and impaired NO bioactivity is associated with fatal outcomes in malaria. Endogenous NO bioactivity in mammals is largely mediated by S-nitrosothiols (SNOs). Based on these observations, we hypothesized that animals deficient in the SNO-metabolizing enzyme, S-nitrosoglutathione reductase (GSNOR), which exhibit enhanced S-nitrosylation, would have improved outcomes in a preclinical model of cerebral malaria. GSNOR knockout (KO) mice infected with Plasmodium berghei ANKA had significantly delayed mortality compared to WT animals (P < 0.0001), despite higher parasite burdens (P < 0.01), and displayed markedly enhanced survival versus the wild type (WT) when treated with the antimalarial drug artesunate (77% versus 38%; P < 0.001). Improved survival was associated with higher levels of protein-bound NO, decreased levels of CD4⁺ and CD8⁺ T cells in the brain, improved blood-brain barrier integrity, and improved coma scores, as well as higher levels of gamma interferon. GSNOR KO animals receiving WT bone marrow had significantly reduced survival following P. berghei ANKA infection compared to those receiving KO bone barrow (P < 0.001). Reciprocal transplants established that survival benefits of GSNOR deletion were attributable primarily to the T cell compartment. These data indicate a role for GSNOR in the host response to malaria infection and suggest that strategies to disrupt its activity will improve clinical outcomes by enhancing microvascular integrity and modulating T cell tissue tropism.

miR-155 Modifies Inflammation, Endothelial Activation and Blood-Brain Barrier Dysfunction in Cerebral Malaria

miR-155 has been shown to participate in host response to infection and neuro-inflammation via negative regulation of blood-brain-barrier (BBB) integrity and T cell function. We hypothesized that miR-155 may contribute to the pathogenesis of cerebral malaria (CM). To test this hypothesis, we used a genetic approach to modulate miR-155 expression in an experimental model of cerebral malaria (ECM). In addition, an engineered endothelialized microvessel system and serum samples from Ugandan children with CM were used to examine an anti-miR-155 as a potential adjunctive therapeutic for severe malaria. Despite higher parasitemia, survival was significantly improved in miR-155^-/- mice vs. wild-type littermate mice in ECM. Improved survival was associated with preservation of BBB integrity and reduced endothelial activation, despite increased levels of pro-inflammatory cytokines. Pre-treatment with antagomir-155 reduced vascular leak induced by human CM sera in an ex vivo endothelial microvessel model. These data provide evidence supporting a mechanistic role for miR-155 in host response to malaria via regulation of endothelial activation, microvascular leak and BBB dysfunction in CM.

Plasmodium knowlesi: a relevant, versatile experimental malaria model

The primate malaria Plasmodium knowlesi has a long-standing history as an experimental malaria model. Studies using this model parasite in combination with its various natural and experimental non-human primate hosts have led to important advances in vaccine development and in our understanding of malaria invasion, immunology and parasite-host interactions. The adaptation to long-term in vitro continuous blood stage culture in rhesus monkey, Macaca fascicularis and human red blood cells, as well as the development of various transfection methodologies has resulted in a highly versatile experimental malaria model, further increasing the potential of what was already a very powerful model. The growing evidence that P. knowlesi is an important human zoonosis in South-East Asia has added relevance to former and future studies of this parasite species.

Exploring experimental cerebral malaria pathogenesis through the characterisation of host-derived plasma microparticle protein content

Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection responsible for thousands of deaths in children in sub-Saharan Africa. CM pathogenesis remains incompletely understood but a number of effectors have been proposed, including plasma microparticles (MP). MP numbers are increased in CM patients’ circulation and, in the mouse model, they can be localised within inflamed vessels, suggesting their involvement in vascular damage. In the present work we define, for the first time, the protein cargo of MP during experimental cerebral malaria (ECM) with the overarching hypothesis that this characterisation could help understand CM pathogenesis. Using qualitative and quantitative high-throughput proteomics we compared MP proteins from non-infected and P. berghei ANKA-infected mice. More than 360 proteins were identified, 60 of which were differentially abundant, as determined by quantitative comparison using TMT^TM isobaric labelling. Network analyses showed that ECM MP carry proteins implicated in molecular mechanisms relevant to CM pathogenesis, including endothelial activation. Among these proteins, the strict association of carbonic anhydrase I and S100A8 with ECM was verified by western blot on MP from DBA/1 and C57BL/6 mice. These results demonstrate that MP protein cargo represents a novel ECM pathogenic trait to consider in the understanding of CM pathogenesis.

Systematic review of the role of angiopoietin-1 and angiopoietin-2 in Plasmodium species infections: biomarkers or therapeutic targets?

BACKGROUND

Levels of both angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) correlate with malaria disease severity and are proposed as biomarkers and possible therapeutic targets. To establish their role in malaria, a systematic review was performed of the literature on Ang-1 and Ang-2 with regard to their potential as biomarkers in malaria and discuss their possible place in adjuvant treatment regimens.

METHODS

Ten electronic databases were systematically searched to identify studies investigating Ang-1 and Ang-2 in human and murine malaria in both clinical and experimental settings. Information about the predictive value of Ang-1 and Ang-2 for disease severity and their regulatory changes in interventional studies were extracted.

RESULTS

Some 579 studies were screened; 26 were included for analysis. In all five studies that determined Ang-1 levels and in all 11 studies that determined Ang-2 in different disease severity states in falciparum malaria, a decline in Ang-1 and an increase of Ang-2 levels was associated with increasing disease severity. All nine studies that determined angiopoietin levels in Plasmodium falciparum patients to study their ability as biomarkers could distinguish between multiple disease severity states; the more the disease severity states differed, the better they could be distinguished. Five studies differentiating malaria survivors from non-survivors with Ang-2 as marker found an AUROC in a range of 0.71-0.83, which performed as well or better than lactate. Prophylactic administration of FTY720, rosiglitazone or inhalation of nitric oxide (NO) during malaria disease in mice resulted in an increase in Ang-1, a decrease in Ang-2 and an increased survival. For rosiglitazone, a decrease in Ang-2/Ang-1 ratio was observed after post-infection treatment in mice and humans with malaria, but for inhalation of NO, an effect on Ang-1 and survival was only observed in mice.

CONCLUSION

Both Ang-1 and Ang-2 levels correlate with and can distinguish between malaria disease severity states within the group of malaria-infected patients. However, distinct comparisons of disease severity states were made in distinct studies and not all distinctions made had clinical relevance. Changes in levels of Ang-1 and Ang-2 might also reflect treatment effectiveness and are promising therapeutic targets as part of multi-targeted therapy.

Treating the host response to emerging virus diseases: lessons learned from sepsis, pneumonia, influenza and Ebola

There is an ongoing threat of epidemic or pandemic diseases that could be caused by influenza, Ebola or other emerging viruses. It will be difficult and costly to develop new drugs that target each of these viruses. Statins and angiotensin receptor blockers (ARBs) have been effective in treating patients with sepsis, pneumonia and influenza, and a statin/ARB combination appeared to dramatically reduce mortality during the recent Ebola outbreak. These drugs target (among other things) the endothelial dysfunction found in all of these diseases. Most scientists work on new drugs that target viruses, and few accept the idea of treating the host response with generic drugs. A great deal of research will be needed to show conclusively that these drugs work, and this will require the support of public agencies and foundations. Investigators in developing countries should take an active role in this research. If the next Public Health Emergency of International Concern is caused by an emerging virus, a "top down" approach to developing specific new drug treatments is unlikely to be effective. However, a "bottom up" approach to treatment that targets the host response to these viruses by using widely available and inexpensive generic drugs could reduce mortality in any country with a basic health care system. In doing so, it would make an immeasurable contribution to global equity and global security.

Angiotensin receptors and β-catenin regulate brain endothelial integrity in malaria

Cerebral malaria is characterized by cytoadhesion of Plasmodium falciparum-infected red blood cells (Pf-iRBCs) to endothelial cells in the brain, disruption of the blood-brain barrier, and cerebral microhemorrhages. No available antimalarial drugs specifically target the endothelial disruptions underlying this complication, which is responsible for the majority of malaria-associated deaths. Here, we have demonstrated that ruptured Pf-iRBCs induce activation of β-catenin, leading to disruption of inter-endothelial cell junctions in human brain microvascular endothelial cells (HBMECs). Inhibition of β-catenin-induced TCF/LEF transcription in the nucleus of HBMECs prevented the disruption of endothelial junctions, confirming that β-catenin is a key mediator of P. falciparum adverse effects on endothelial integrity. Blockade of the angiotensin II type 1 receptor (AT1) or stimulation of the type 2 receptor (AT2) abrogated Pf-iRBC-induced activation of β-catenin and prevented the disruption of HBMEC monolayers. In a mouse model of cerebral malaria, modulation of angiotensin II receptors produced similar effects, leading to protection against cerebral malaria, reduced cerebral hemorrhages, and increased survival. In contrast, AT2-deficient mice were more susceptible to cerebral malaria. The interrelation of the β-catenin and the angiotensin II signaling pathways opens immediate host-targeted therapeutic possibilities for cerebral malaria and other diseases in which brain endothelial integrity is compromised.

Alterations in Systemic Extracellular Heme and Hemopexin Are Associated With Adverse Clinical Outcomes in Ugandan Children With Severe Malaria

Background. Malaria remains a major cause of global mortality. Extracellular heme, released during malaria-induced hemolysis, mediates a number of pathogenic processes associated with vascular and organ injury. Hemopexin (hpx) facilitates the degradation of extracellular heme. In this study, we explore the hypothesis that dysregulation of the heme-hpx axis is associated with disease severity, acute kidney injury (AKI), and outcome.

Methods. Plasma levels of hemin and hpx (at admission, day 3, and day 14) were assessed in children with severe malaria in Jinja, Uganda.

Results. The ratio of heme to hpx was higher at admission and decreased with recovery (median, 0.043 [interquartile range {IQR}, 0.007–0.239] on day 1, 0.024 [IQR, 0.005–0.126] on day 3, and 0.008 [IQR, 0.002–0.022] on day 14; P < .001). Ratios of heme to hpx at admission were higher in children with as compared to those without severe anemia (median, 0.124 [IQR, 0.024–0.431] vs 0.016 [IQR, 0.003–0.073]; P < .0001), children with as compared to those without respiratory distress (median, 0.063 [IQR, 0.017–0.413] vs 0.020 [IQR, 0.004–0.124]; P < .01), and children with as opposed to those without stage 3 AKI (median, 0.354 [IQR, 0.123–2.481] vs 0.037 [IQR, 0.005–0.172], P < .01). The heme to hpx ratio at admission was associated with 6-month mortality (median, 0.148 [IQR, 0.042–0.500] vs 0.039 [IQR, 0.007–0.172]; P = .012).

Conclusions. The ratio of heme to hpx is associated with disease severity and adverse clinical outcomes in Ugandan children, and dysregulation of the heme axis may contribute to malaria pathogenesis.

Cerebral malaria--clinical manifestations and pathogenesis

One of the most common central nervous system diseases in tropical countries is cerebral malaria (CM). Malaria is a common protozoan infection that is responsible for enormous worldwide mortality and economic burden on the society. Episodes of Plasmodium falciparum (Pf) caused CM may be lethal, while survivors are likely to suffer from persistent debilitating neurological deficits, especially common in children. In this review article, we have summarized the various symptoms and manifestations of CM in children and adults, and entailed the molecular basis of the disease. We have also emphasized how pathogenesis of the disease is effected by the parasite and host responses including blood brain barrier (BBB) disruption, endothelial cell activation and apoptosis, nitric oxide bioavailability, platelet activation and apoptosis, and neuroinflammation. Based on a few recent studies carried out in experimental mouse malaria models, we propose a basis for the neurological deficits and sequelae observed in human cerebral malaria, and summarize how existing drugs may improve prognosis in affected individuals.

The immunological balance between host and parasite in malaria

Coevolution of humans and malaria parasites has generated an intricate balance between the immune system of the host and virulence factors of the parasite, equilibrating maximal parasite transmission with limited host damage. Focusing on the blood stage of the disease, we discuss how the balance between anti-parasite immunity versus immunomodulatory and evasion mechanisms of the parasite may result in parasite clearance or chronic infection without major symptoms, whereas imbalances characterized by excessive parasite growth, exaggerated immune reactions or a combination of both cause severe pathology and death, which is detrimental for both parasite and host. A thorough understanding of the immunological balance of malaria and its relation to other physiological balances in the body is of crucial importance for developing effective interventions to reduce malaria-related morbidity and to diminish fatal outcomes due to severe complications. Therefore, we discuss in this review the detailed mechanisms of anti-malarial immunity, parasite virulence factors including immune evasion mechanisms and pathogenesis. Furthermore, we propose a comprehensive classification of malaria complications according to the different types of imbalances.

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

Cerebral malaria is a severe neuropathological complication of Plasmodium falciparum infection. It results in high mortality and post-recovery neuro-cognitive disorders in children, even after appropriate treatment with effective anti-parasitic drugs. While the complete landscape of the pathogenesis of cerebral malaria still remains to be elucidated, numerous innovative approaches have been developed in recent years in order to improve the early detection of this neurological syndrome and, subsequently, the clinical care of affected patients. In this review, we briefly summarize the current understanding of cerebral malaria pathogenesis, compile the array of new biomarkers and tools available for diagnosis and research, and describe the emerging therapeutic approaches to tackle this pathology effectively.

Endothelial-Leukocyte Interaction in Severe Malaria: Beyond the Brain

Malaria is the most important parasitic disease worldwide, accounting for 1 million deaths each year. Severe malaria is a systemic illness characterized by dysfunction of brain tissue and of one or more peripheral organs as lungs and kidney. The most severe and most studied form of malaria is associated with cerebral complications due to capillary congestion and the adhesion of infected erythrocytes, platelets, and leukocytes to brain vasculature. Thus, leukocyte rolling and adhesion in the brain vascular bed during severe malaria is singular and distinct from other models of inflammation. The leukocyte/endothelium interaction and neutrophil accumulation are also observed in the lungs. However, lung interactions differ from brain interactions, likely due to differences in the blood-brain barrier and blood-air barrier tight junction composition of the brain and lung endothelium. Here, we review the importance of endothelial dysfunction and the mechanism of leukocyte/endothelium interaction during severe malaria. Furthermore, we hypothesize a possible use of adjunctive therapies to antimalarial drugs that target the interaction between the leukocytes and the endothelium.

Microvascular obstruction and endothelial activation are independently associated with the clinical manifestations of severe falciparum malaria in adults: an observational study

BACKGROUND

Microvascular obstruction and endothelial dysfunction have both been linked to tissue hypoperfusion in falciparum malaria, but their relative contributions to the disease's pathogenesis and outcome are unknown.

METHODS

Microvascular blood flow was quantified in adults with severe falciparum malaria on their admission to hospital; plasma biomarkers of endothelial function were measured simultaneously. The relationship between these indices and the patients' clinical findings and in-hospital course was examined.

RESULTS

Microvascular obstruction was observed in 119/142 (84 %) patients; a median (interquartile range (IQR)) of 14.9 % (6.6-34.9 %) of capillaries were obstructed in patients that died versus 8.3 % (1.7-26.6 %) in survivors (P = 0.039). The proportion of obstructed capillaries correlated with the estimated parasite biomass (rs = 0.25, P = 0.004) and with plasma lactate (rs = 0.38, P <0.0001), the strongest predictor of death in the series. Plasma angiopoietin-2 (Ang-2) concentrations were markedly elevated suggesting widespread endothelial activation; the median (IQR) Ang-2 concentration was 21.9 ng/mL (13.4-29.4 ng/mL) in patients that died versus 14.9 ng/mL (9.8-29.3 ng/mL) in survivors (P = 0.035). Ang-2 concentrations correlated with estimated parasite biomass (rs = 0.35, P <0.001) and plasma lactate (rs = 0.37, P <0.0001). Microvascular obstruction and Ang-2 concentrations were not significantly correlated with each other (rs = 0.17, P = 0.06), but were independently associated with plasma lactate (P <0.001 and P = 0.002, respectively).

CONCLUSIONS

Microvascular obstruction and systemic endothelial activation are independently associated with plasma lactate, the strongest predictor of death in adults with falciparum malaria. This supports the hypothesis that the two processes make an independent contribution to the pathogenesis and clinical manifestations of the disease.

Lipoxin A4 attenuates endothelial dysfunction during experimental cerebral malaria

A breakdown of the brain-blood barrier (BBB) due to endothelial dysfunction is a primary feature of cerebral malaria (CM). Lipoxins (LX) are specialized pro-resolving mediators that attenuate endothelial dysfunction in different vascular beds. It has already been shown that LXA4 prolonged Plasmodium berghei-infected mice survival by a mechanism that depends on inhibiting IL-12 production and CD8(+)IFN-γ(+) T cells in brain tissue; however, the effects of this treatment on endothelial dysfunction induced during experimental cerebral malaria (ECM) remains to be elucidated. Herein, we investigate the role of LXA4 on endothelial dysfunction during ECM. The treatment of P. berghei-infected mice with LXA4 prevented BBB breakdown and ameliorated behavioral symptoms but did not modulate TNF-α production. In addition, microcirculation analysis showed that treatment with LXA4 significantly increased functional capillary density in brains of P. berghei-infected C57BL/6 mice. Furthermore, histological analyses of brain sections demonstrated that exogenous LXA4 reduced capillary congestion that was accompanied by reduced ICAM-1 expression in the brain tissue. In agreement, LXA4 treatment of endothelial cells stimulated by Plasmodium berghei (Pb)- or Plasmodium falciparum (Pf)-parasitized red blood cells (RBCs) inhibited ICAM-1 expression. Additionally, LXA4 treatment restored the expression of HO-1 that is reduced during ECM. As well, LXA4 treatment inhibits PbRBC and PfRBC adhesion to endothelial cells that was reversed by the use of an HO-1 inhibitor (ZnPPIX). Our results demonstrate for the first time that LXA4 ameliorates endothelial dysfunction during ECM by modulating ICAM-1 and HO-1 expression in brain tissue.

Experimental cerebral malaria pathogenesis--hemodynamics at the blood brain barrier

Cerebral malaria claims the lives of over 600,000 African children every year. To better understand the pathogenesis of this devastating disease, we compared the cellular dynamics in the cortical microvasculature between two infection models, Plasmodium berghei ANKA (PbA) infected CBA/CaJ mice, which develop experimental cerebral malaria (ECM), and P. yoelii 17XL (PyXL) infected mice, which succumb to malarial hyperparasitemia without neurological impairment. Using a combination of intravital imaging and flow cytometry, we show that significantly more CD8(+) T cells, neutrophils, and macrophages are recruited to postcapillary venules during ECM compared to hyperparasitemia. ECM correlated with ICAM-1 upregulation on macrophages, while vascular endothelia upregulated ICAM-1 during ECM and hyperparasitemia. The arrest of large numbers of leukocytes in postcapillary and larger venules caused microrheological alterations that significantly restricted the venous blood flow. Treatment with FTY720, which inhibits vascular leakage, neurological signs, and death from ECM, prevented the recruitment of a subpopulation of CD45(hi) CD8(+) T cells, ICAM-1(+) macrophages, and neutrophils to postcapillary venules. FTY720 had no effect on the ECM-associated expression of the pattern recognition receptor CD14 in postcapillary venules suggesting that endothelial activation is insufficient to cause vascular pathology. Expression of the endothelial tight junction proteins claudin-5, occludin, and ZO-1 in the cerebral cortex and cerebellum of PbA-infected mice with ECM was unaltered compared to FTY720-treated PbA-infected mice or PyXL-infected mice with hyperparasitemia. Thus, blood brain barrier opening does not involve endothelial injury and is likely reversible, consistent with the rapid recovery of many patients with CM. We conclude that the ECM-associated recruitment of large numbers of activated leukocytes, in particular CD8(+) T cells and ICAM(+) macrophages, causes a severe restriction in the venous blood efflux from the brain, which exacerbates the vasogenic edema and increases the intracranial pressure. Thus, death from ECM could potentially occur as a consequence of intracranial hypertension.

Strong type 1, but impaired type 2, immune responses contribute to Orientia tsutsugamushi-induced pathology in mice

Scrub typhus is a neglected, but important, tropical disease, which puts one-third of the world's population at risk. The disease is caused by Orientia tsutsugamushi, an obligately intracellular Gram-negative bacterium. Dysregulation in immune responses is known to contribute to disease pathogenesis; however, the nature and molecular basis of immune alterations are poorly defined. This study made use of a newly developed murine model of severe scrub typhus and focused on innate regulators and vascular growth factors in O. tsutsugamushi-infected liver, lungs and spleen. We found no activation or even reduction in base-line expression for multiple molecules (IL-7, IL-4, IL-13, GATA3, ROR-γt, and CXCL12) at 2, 6 and 10 days post-infection. This selective impairment in type 2-related immune responses correlated with a significant activation of the genes for IL-1β, IL-6, IL-10, TNF-α, IFN-γ, as well as CXCR3- and CXCR1-related chemokines in inflamed tissues. The elevated angiopoietin (Ang)-2 expression and Ang-2/Ang-1 ratios suggested excessive inflammation and the loss of endothelial integrity. These alterations, together with extensive recruitment of myeloperoxidase (MPO)-expressing neutrophils and the influx of CD3+ T cells, contributed to acute tissue damage and animal death. This is the first report of selective alterations in a panel of immune regulators during early O. tsutsugamushi infection in intravenously inoculated C57BL/6 mice. Our findings shed new light on the pathogenic mechanisms associated with severe scrub typhus and suggest potential targets for therapeutic investigation.

CD36 and malaria: friends or foes? A decade of data provides some answers

The past 10 years have generated new insights into the complex interaction between CD36 (cluster of differentiation 36) and malaria. These range from the crystallization of the CD36 homolog, LIMPII (lysosomal integral membrane protein II), permitting modeling of CD36 and its binding to diverse ligands, to cell biology-based studies of CD36 and large population genetic studies assessing the association of CD36 polymorphisms and malarial disease severity. Collectively these lines of evidence indicate that a receptor other than CD36 is associated with severity. CD36 plays an important role in innate immunity and in the phagocytic uptake of multiple pathogens including malaria. CD36 polymorphisms lack association with severity, and isolates that cause severe disease primarily bind to endothelial protein C receptor (EPCR) rather than to CD36.

Pathogenesis of cerebral malaria--inflammation and cytoadherence

Despite decades of research on cerebral malaria (CM) there is still a paucity of knowledge about what actual causes CM and why certain people develop it. Although sequestration of P. falciparum infected red blood cells has been linked to pathology, it is still not clear if this is directly or solely responsible for this clinical syndrome. Recent data have suggested that a combination of parasite variant types, mainly defined by the variant surface antigen, P. falciparum erythrocyte membrane protein 1 (PfEMP1), its receptors, coagulation and host endothelial cell activation (or inflammation) are equally important. This makes CM a multi-factorial disease and a challenge to unravel its causes to decrease its detrimental impact.

Immunobiology of Plasmodium in liver and brain

Malaria remains one of the most serious health problems globally, but our understanding of the biology of the parasite and the pathogenesis of severe disease is still limited. Multiple cellular effector mechanisms that mediate parasite elimination from the liver have been described, but how effector cells use classical granule-mediated cytotoxicity to attack infected hepatocytes and how cytokines and chemokines spread via the unique fluid pathways of the liver to reach the parasites over considerable distances remains unknown. Similarly, a wealth of information on cerebral malaria (CM), one of the most severe manifestations of the disease, was gained from post-mortem analyses of human brain and murine disease models, but the cellular processes that ultimately cause disease are not fully understood. Here, we discuss how imaging of the local dynamics of parasite infection and host response as well as consideration of anatomical and physiological features of liver and brain can provide a better understanding of the initial asymptomatic hepatic phase of the infection and the cascade of events leading to CM. Given the increasing drug resistance of both parasite and vector and the unavailability of a protective vaccine, the urgency to reduce the tremendous morbidity and mortality associated with severe malaria is obvious.

PPARγ agonists improve survival and neurocognitive outcomes in experimental cerebral malaria and induce neuroprotective pathways in human malaria

Cerebral malaria (CM) is associated with a high mortality rate, and long-term neurocognitive impairment in approximately one third of survivors. Adjunctive therapies that modify the pathophysiological processes involved in CM may improve outcome over anti-malarial therapy alone. PPARγ agonists have been reported to have immunomodulatory effects in a variety of disease models. Here we report that adjunctive therapy with PPARγ agonists improved survival and long-term neurocognitive outcomes in the Plasmodium berghei ANKA experimental model of CM. Compared to anti-malarial therapy alone, PPARγ adjunctive therapy administered to mice at the onset of CM signs, was associated with reduced endothelial activation, and enhanced expression of the anti-oxidant enzymes SOD-1 and catalase and the neurotrophic factors brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the brains of infected mice. Two months following infection, mice that were treated with anti-malarials alone demonstrated cognitive dysfunction, while mice that received PPARγ adjunctive therapy were completely protected from neurocognitive impairment and from PbA-infection induced brain atrophy. In humans with P. falciparum malaria, PPARγ therapy was associated with reduced endothelial activation and with induction of neuroprotective pathways, such as BDNF. These findings provide insight into mechanisms conferring improved survival and preventing neurocognitive injury in CM, and support the evaluation of PPARγ agonists in human CM.

Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection that is associated with long-term neurocognitive impairment in about a third of survivors even when optimal anti-malarial therapy is used. Since both the parasite and the host immune response to infection play a role in the development of CM, adjunctive therapies that modulate the host response, given in conjunction with anti-parasitic therapy, may improve survival and prevent neurocognitive injury. Here we examine the effects of PPARγ agonists on neurocongitive injury using a mouse model of CM. We demonstrate that PPARγ agonists, when administered with anti-malarials, protected mice from developing brain atrophy and neurocognitive impairment. This was associated with induction of anti-oxidant and neuroprotective pathways in the brains of infected mice. We also observed the same neuroprotective pathways induced in patients with falciparum malaria that received PPARγ adjunctive therapy. Our findings suggest that PPARγ agonists may be valuable in the treatment and prevention of CM-induced neurocognitive injury, and support the testing of PPARγ agonists in patients with CM.

Stuck in a rut? Reconsidering the role of parasite sequestration in severe malaria syndromes

Severe malaria defines individuals at increased risk of death from their infection. Proposed pathogenic mechanisms include parasite sequestration, inflammation, and endothelial dysfunction. Severe malaria is not a single entity, manifesting with distinct syndromes such as severe anemia, severe respiratory distress or coma, each characterized by differences in epidemiology, underlying biology, and risk of death. The relative contribution of the various pathogenic mechanisms may differ between syndromes, and this is supported by accumulating evidence, which challenges sequestration as the initiating event. Here we propose that high parasite biomass is the common initiating feature, but subtle variations in the interaction between the host and parasite exist, and understanding these differences may be crucial to improve outcomes in patients with severe malaria.

Potential efficacy of citicoline as adjunct therapy in treatment of cerebral malaria

Cerebral malaria (CM) is characterized by a dysregulated immune response that results in endothelial membrane destabilization and increased microparticle (MP) production. Citicoline (CTC) is a membrane stabilizer used for the treatment of neurological disorders. We evaluated the efficacy of CTC as adjunct therapy to aid recovery from experimental CM. We show that CTC reduces MP production in vitro; in combination with artesunate in vivo, confers partial protection against CM; and prolongs survival.

Cytoadherence of Plasmodium berghei-infected red blood cells to murine brain and lung microvascular endothelial cells in vitro

Sequestration of infected red blood cells (iRBC) within the cerebral and pulmonary microvasculature is a hallmark of human cerebral malaria (hCM). The interaction between iRBC and the endothelium in hCM has been studied extensively and is linked to the severity of malaria. Experimental CM (eCM) caused by Plasmodium berghei ANKA reproduces most features of hCM, although the sequestration of RBC infected by P. berghei ANKA (PbA-iRBC) has not been completely delineated. The role of PbA-iRBC sequestration in the severity of eCM is not well characterized. Using static and flow cytoadherence assays, we provide the first direct in vitro evidence for the binding of PbA-iRBC to murine brain and lung microvascular endothelial cells (MVEC). We found that basal PbA-iRBC cytoadherence to MVECs was significantly higher than that of normal red blood cells (NRBC) and of RBC infected with P. berghei K173 (PbK173-iRBC), a strain that causes noncerebral malaria (NCM). MVEC prestimulation with tumor necrosis factor (TNF) failed to promote any further significant increase in mixed-stage iRBC adherence. Interestingly, enrichment of the blood for mature parasites significantly increased PbA-iRBC binding to the MVECs prestimulated with TNF, while blockade of VCAM-1 reduced this adhesion. Our study provides evidence for the firm, flow-resistant binding to endothelial cells of iRBC from strain ANKA-infected mice, which develop CM, and for less binding of iRBC from strain K173-infected mice, which develop NCM. An understanding of P. berghei cytoadherence may help elucidate the importance of sequestration in the development of CM and aid the development of antibinding therapies to help reduce the burden of this syndrome.

Hemoglobinopathies: slicing the Gordian knot of Plasmodium falciparum malaria pathogenesis

Plasmodium falciparum malaria kills over 500,000 children every year and has been a scourge of humans for millennia. Owing to the co-evolution of humans and P. falciparum parasites, the human genome is imprinted with polymorphisms that not only confer innate resistance to falciparum malaria, but also cause hemoglobinopathies. These genetic traits—including hemoglobin S (HbS), hemoglobin C (HbC), and α-thalassemia—are the most common monogenic human disorders and can confer remarkable degrees of protection from severe, life-threatening falciparum malaria in African children: the risk is reduced 70% by homozygous HbC and 90% by heterozygous HbS (sickle-cell trait). Importantly, this protection is principally present for severe disease and largely absent for P. falciparum infection, suggesting that these hemoglobinopathies specifically neutralize the parasite's in vivo mechanisms of pathogenesis. These hemoglobin variants thus represent a “natural experiment” to identify the cellular and molecular mechanisms by which P. falciparum produces clinical morbidity, which remain partially obscured due to the complexity of interactions between this parasite and its human host. Multiple lines of evidence support a restriction of parasite growth by various hemoglobinopathies, and recent data suggest this phenomenon may result from host microRNA interference with parasite metabolism. Multiple hemoglobinopathies mitigate the pathogenic potential of parasites by interfering with the export of P. falciparum erythrocyte membrane protein 1 (PfEMP1) to the surface of the host red blood cell. Few studies have investigated their effects upon the activation of the innate and adaptive immune systems, although recent murine studies suggest a role for heme oxygenase-1 in protection. Ultimately, the identification of mechanisms of protection and pathogenesis can inform future therapeutics and preventive measures. Hemoglobinopathies slice the “Gordian knot” of host and parasite interactions to confer malaria protection, and offer a translational model to identify the most critical mechanisms of P. falciparum pathogenesis.

Comparison of parasite sequestration in uncomplicated and severe childhood Plasmodium falciparum malaria

Objectives

To determine whether sequestration of parasitized red blood cells differs between children with uncomplicated and severe Plasmodium falciparum malaria.

Methods

We quantified circulating-, total- and sequestered-parasite biomass, using a mathematical model based on plasma concentration of P. falciparum histidine rich protein 2, in Gambian children with severe (n = 127) and uncomplicated (n = 169) malaria.

Results

Circulating- and total-, but not sequestered-, parasite biomass estimates were significantly greater in children with severe malaria than in those with uncomplicated malaria. Sequestered biomass estimates in children with hyperlactataemia or prostration were similar to those in uncomplicated malaria, whereas sequestered biomass was higher in patients with severe anaemia, and showed a trend to higher values in cerebral malaria and fatal cases. Blood lactate concentration correlated with circulating- and total-, but not sequestered parasite biomass. These findings were robust after controlling for age, prior antimalarial treatment and clonality of infection, and over a realistic range of variation in model parameters.

Conclusion

Extensive sequestration is not a uniform requirement for severe paediatric malaria. The pathophysiology of hyperlactataemia and prostration appears to be unrelated to sequestered parasite biomass. Different mechanisms may underlie different severe malaria syndromes, and different therapeutic strategies may be required to improve survival.

Biomarkers of endothelial activation/dysfunction in infectious diseases

Endothelial dysfunction contributes to the pathogenesis of a variety of potentially serious infectious diseases and syndromes, including sepsis and septic shock, hemolytic-uremic syndrome, severe malaria, and dengue hemorrhagic fever. Because endothelial activation often precedes overt endothelial dysfunction, biomarkers of the activated endothelium in serum and/or plasma may be detectable before classically recognized markers of disease, and therefore, may be clinically useful as biomarkers of disease severity or prognosis in systemic infectious diseases. In this review, the current status of mediators of endothelial cell function (angiopoietins-1 and -2), components of the coagulation pathway (von Willebrand Factor, ADAMTS13, and thrombomodulin), soluble cell-surface adhesion molecules (soluble E-selectin, sICAM-1, and sVCAM-1), and regulators of vascular tone and permeability (VEGF and sFlt-1) as biomarkers in severe infectious diseases is discussed in the context of sepsis, E. coli O157:H7 infection, malaria, and dengue virus infection.