Cerebral Malaria: Current Clinical and Immunological Aspects

Evaluating the Antimalarial Potential of d-α-Tocopherol Polyethylene Glycol 1000 Succinate and α-Tocopherol, In Vivo Studies in Plasmodium berghei-Infected Mice and Molecular Docking Insights

Oxidative stress is a pivotal factor in the pathogenesis of malaria, contributing to the development of conditions such as anemia, respiratory complications, and cerebral malaria. To counteract oxidative damage, we evaluated the effects of vitamin E (α-TOH) and d-α-tocopherol polyethylene glycol 1000 succinate (TPGS) supplementation on parasitemia progression, mortality rate, and blood-brain barrier (BBB) permeability in Plasmodium berghei ANKA-infected mice. The mice were divided into four groups: a control group (untreated and uninfected), an infected group (Pb), a TPGS + Pb group, and an α-TOH + Pb group. The results demonstrated that TPGS was more effective than α-TOH, exhibiting a lower parasitemia (9.59%) and mortality (40%) by Day 12 and superior BBB protection in advanced infection stages. These findings suggest that TPGS may represent a promising therapeutic strategy for the management of malaria. Molecular docking analysis indicated that TPGS exhibited the highest binding affinity with plasmepsin 2 (-7.3 kcal/mol), whereas vitamin E demonstrated the strongest binding with plasmepsin 1 (-7.2 kcal/mol).

Mouse NOD/Shi and NSY/Hos strains infected with Plasmodium berghei ANKA are models for experimental cerebral malaria

In humans, cerebral malaria is the most common cause of malaria-related mortality. Mouse C57BL/6 (B6) sub-strains are the major model system for experimental cerebral malaria (ECM) as they show similar pathophysiology to human cerebral malaria after infection with the rodent malaria parasite Plasmodium berghei ANKA. This model system has been used to analyze the molecular mechanisms of cerebral malaria. To develop new mouse models, we analyzed the ECM susceptibility of NOD/Shi (NOD) and NSY/Hos (NSY) strains established from the non-inbred ICR strain. Both NOD and NSY strains exhibited clinical symptoms and pathologies similar to ECM in C57BL/6J (B6J) mice and died within 11 days of infection. Thus, the NOD and NSY strains are susceptible to ECM and may be useful as new ECM models. The ECM susceptibility of both strains is suggested to be due to homozygosity for the cerebral malaria susceptibility allele of the ECM susceptible ICR strain. Although analyses using B6 sub-strains have proposed that complement component 5 (C5) plays an important role in ECM pathogenesis, we found that C5 was not essential as the ECM susceptible NOD strain is C5 deficient. Thus, results obtained from B6 sub-strains may not reflect the full picture of ECM in mice. Comparative analyses of multiple ECM models will contribute to a more accurate identification of the factors essential for ECM.

Host directed immunotherapy for chronic infections and cancer

Host-directed immunotherapy (HDI) is emerging as a transformative strategy in managing chronic diseases by leveraging the host's immune system to combat disease. This innovative approach has shown promise in a range of conditions, including cancer and parasitic infections. In oncology, HDI aims to enhance the body's natural immune response against cancer cells through mechanisms such as immune checkpoint inhibition, monoclonal antibodies, and cytokine therapies. These strategies are designed to boost the immune system's ability to recognize and destroy tumors, improving patient outcomes and offering alternatives to traditional cancer treatments. Similarly, in parasitic infections, HDI focuses on strengthening the host's immune defenses to control and eradicate those infections. For diseases like malaria, leishmaniasis, and Chagas disease, HDI strategies may involve adjuvants or immune modulators that amplify the body's ability to target and eliminate parasites. By optimizing immune responses and reducing reliance on conventional treatments, HDI holds the potential to revolutionize therapeutic approaches across various chronic diseases. This chapter highlights the flexibility and potential of HDI in advancing treatments, offering novel ways for improving patient care and disease management.

Contribution of Magnetic Resonance Imaging Studies to the Understanding of Cerebral Malaria Pathogenesis

Cerebral malaria (CM), the most lethal clinical syndrome of Plasmodium falciparum infection, mostly affects children under 5 in sub-Saharan Africa. CM is characterized by seizures and impaired consciousness that lead to death in 15-20% of cases if treated quickly, but it is completely fatal when untreated. Brain magnetic resonance imaging (MRI) is an invaluable source of information on the pathophysiology of brain damage, but, due to limited access to scanners in endemic regions, only until very recently have case reports of CM patients studied with advanced MRI methods been published. The murine model of experimental cerebral malaria (ECM) shares many common features with the human disease and has been extensively used to study the pathogenic mechanisms of the neurological syndrome. In vivo MRI studies on this model, the first of which was published in 2005, have contributed to a better understanding of brain lesion formation in CM and identified disease markers that were confirmed by MRI studies published from 2013 onwards in pediatric patients from endemic areas. In this review, we recapitulate the main findings and critically discuss the contributions of MRI studies in the ECM model to the understanding of human CM.

From Genome-wide Association Studies to Functional Variants: ARL14 Cis-regulatory Variants Are Associated With Severe Malaria

BACKGROUND

Genome-wide association studies have identified several nonfunctional tag single-nucleotide polymorphisms (SNPs) associated with severe malaria. We hypothesized that causal SNPs could play a significant role in severe malaria by altering promoter or enhancer activity. Here, we sought to identify such regulatory SNPs.

METHODS

SNPs in linkage disequilibrium with tagSNPs associated with severe malaria were identified and were further annotated using FUMA. Then, SNPs were prioritized using the integrative weighted scoring method to identify regulatory ones. Gene reporter assays were performed to assess the regulatory effect of a region containing candidates. The association between SNPs and severe malaria was assessed using logistic regression models in a Senegalese cohort.

RESULTS

Among 418 SNPs, the best candidates were rs116525449 and rs79644959, which were in full disequilibrium between them, and located within the ARL14 promoter. Our gene reporter assay results revealed that the region containing the SNPs exhibited cell-specific promoter or enhancer activity, while the SNPs influenced promoter activity. We detected an association between severe malaria and those 2 SNPs using the overdominance model and we replicated the association of severe malaria with the tagSNP rs116423146.

CONCLUSIONS

We suggest that these SNPs regulate ARL14 expression in immune cells and the presentation of antigens to T lymphocytes, thus influencing severe malaria development.

Current Status of Malaria Control and Elimination in Africa: Epidemiology, Diagnosis, Treatment, Progress and Challenges

The African continent carries the greatest malaria burden in the world. Falciparum malaria especially has long been the leading cause of death in Africa. Climate, economic factors, geographical location, human intervention and unstable security are factors influencing malaria transmission. Due to repeated infections and early interventions, the proportion of clinically atypical malaria or asymptomatic plasmodium carriers has increased significantly, which easily lead to misdiagnosis and missed diagnosis. African countries have made certain progress in malaria control and elimination, including rapid diagnosis of malaria, promotion of mosquito nets and insecticides, intermittent prophylactic treatment in high-risk groups, artemisinin based combination therapies, and the development of vaccines. Between 2000 and 2022, there has been a 40% decrease in malaria incidence and a 60% reduction in mortality rate in the WHO African Region. However, many challenges are emerging in the fight against malaria in Africa, such as climate change, poverty, substandard health services and coverage, increased outdoor transmission and the emergence of new vectors, and the growing threat of resistance to antimalarial drugs and insecticides. Joint prevention and treatment, identifying molecular determinants of resistance, new drug development, expanding seasonal malaria chemo-prevention intervention population, and promoting the vaccination of RTS, S/AS01 and R21/Matrix-M may help to solve the dilemma. China's experience in eliminating malaria is conducive to Africa's malaria prevention and control, and China-Africa cooperation needs to be constantly deepened and advanced. Our review aims to help the global public develop a comprehensive understanding of malaria in Africa, thereby contributing to malaria control and elimination.

Transcriptional responses of brain endothelium to Plasmodium falciparum patient-derived isolates in vitro

A hallmark of cerebral malaria (CM) is sequestration of Plasmodium falciparum-infected erythrocytes (IE) within the brain microvasculature. Binding of IE to endothelium reduces microvascular flow and, combined with an inflammatory response, perturbs endothelial barrier function, resulting in breakdown of the blood-brain barrier (BBB). Cytoadherence leads to activation of the endothelium and alters a range of cell processes affecting signaling pathways, receptor expression, coagulation, and disruption of BBB integrity. Here, we investigated whether CM-derived parasites elicit differential effects on human brain microvascular endothelial cells (HBMECs), as compared to uncomplicated malaria (UM)-derived parasites. Patient-derived IE from UM and CM clinical cases, as well as non-binding skeleton-binding protein 1 knockout parasites, were overlaid onto tumour necrosis factor (TNF)-activated HBMECs. Gene expression analysis of endothelial responses was performed using probe-based assays of a panel of genes involved in inflammation, apoptosis, endothelial barrier function, and prostacyclin synthesis pathway. We observed a significant effect on endothelial transcriptional responses in the presence of IE, yet there was no significant correlation between HBMEC responses and type of clinical syndrome (UM or CM). Furthermore, there was no correlation between HBMEC gene expression and both binding itself and level of IE binding to HBMECs, as we detected the same change in endothelial responses when employing both binding and non-binding parasites. Our results suggest that interaction of IE with endothelial cells in this co-culture model induces some endothelial responses that are independent of clinical origin and independent of the expression of the major variant antigen Plasmodium falciparum erythrocyte membrane protein 1 on the IE surface.

IMPORTANCE

Cerebral malaria (CM) is the most prevalent and deadly complication of severe Plasmodium falciparum infection. A hallmark of this disease is sequestration of P. falciparum-infected erythrocytes (IE) in brain microvasculature that ultimately results in breakdown of the blood-brain barrier. Here, we compared the effect of P. falciparum parasites derived from uncomplicated malaria (UM) and CM cases on the relative gene expression of human brain microvascular endothelial cells (HBMECs) for a panel of genes. We observed a significant effect on the endothelial transcriptional response in the presence of IE, yet there is no significant correlation between HBMEC responses and the type of clinical syndrome (UM or CM). Furthermore, there was no correlation between HBMEC gene expression and both binding itself and the level of IE binding to HBMECs. Our results suggest that interaction of IE with endothelial cells induces endothelial responses that are independent of clinical origin and not entirely driven by surface Plasmodium falciparum erythrocyte membrane protein 1 expression.

Neurons upregulate PD-L1 via IFN/STAT1/IRF1 to alleviate damage by CD8+ T cells in cerebral malaria

BACKGROUND

Cerebral malaria (CM) is the most lethal complication of malaria, and survivors usually endure neurological sequelae. Notably, the cytotoxic effect of infiltrating Plasmodium-activated CD8+ T cells on cerebral microvasculature endothelial cells is a prominent feature of the experimental CM (ECM) model with blood-brain barrier disruption. However, the damage effect of CD8+ T cells infiltrating the brain parenchyma on neurons remains unclear. Based on the immunosuppressive effect of the PD-1/PD-L1 pathway on T cells, our previous study demonstrated that the systemic upregulation of PD-L1 to inhibit CD8+ T cell function could effectively alleviate the symptoms of ECM mice. However, it has not been reported whether neurons can suppress the pathogenic effect of CD8+ T cells through the PD-1/PD-L1 negative immunomodulatory pathway. As the important inflammatory factor of CM, interferons can induce the expression of PD-L1 via different molecular mechanisms according to the neuro-immune microenvironment. Therefore, this study aimed to investigate the direct interaction between CD8+ T cells and neurons, as well as the mechanism of neurons to alleviate the pathogenic effect of CD8+ T cells through up-regulating PD-L1 induced by IFNs.

METHODS

Using the ECM model of C57BL/6J mice infected with Plasmodium berghei ANKA (PbA), morphological observations were conducted in vivo by electron microscope and IF staining. The interaction between the ECM CD8+ T cells (immune magnetic bead sorting from spleen of ECM mice) and primary cultured cortical neurons in vitro was observed by IF staining and time-lapse photography. RNA-seq was performed to analyze the signaling pathway of PD-L1 upregulation in neurons induced by IFNβ or IFNγ, and verified through q-PCR, WB, IF staining, and flow cytometry both in vitro and in vivo using IFNAR or IFNGR gene knockout mice. The protective effect of adenovirus-mediated PD-L1 IgGFc fusion protein expression was verified in ECM mice with brain stereotaxic injection in vivo and in primary cultured neurons via viral infection in vitro.

RESULTS

In vivo, ECM mice showed infiltration of activated CD8+ T cells and neuronal injury in the brain parenchyma. In vitro, ECM CD8+ T cells were in direct contact with neurons and induced axonal damage, as an active behavior. The PD-L1 protein level was elevated in neurons of ECM mice and in primary cultured neurons induced by IFNβ, IFNγ, or ECM CD8+ T cells in vitro. Furthermore, the IFNβ or IFNγ induced neuronal expression of PD-L1 was mediated by increasing STAT1/IRF1 pathway via IFN receptors. The increase of PD-L1 expression in neurons during PbA infection was weakened after deleting the IFNAR or IFNGR. Increased PD-L1 expression by adenovirus partially protected neurons from CD8+ T cell-mediated damage both in vitro and in vivo.

CONCLUSION

Our study demonstrates that both type I and type II IFNs can induce neurons to upregulate PD-L1 via the STAT1/IRF1 pathway mediated by IFN receptors to protect against activated CD8+ T cell-mediated damage, providing a targeted pathway to alleviate neuroinflammation during ECM.

Cerebral malaria pathogenesis: Dissecting the role of CD4+ and CD8+ T-cells as major effectors in disease pathology

Cerebral malaria (CM) is a severe complication of Plasmodium falciparum (P. falciparum) infection, with complex pathogenesis involving multiple factors, including the host's immunological response. T lymphocytes, specifically CD4+ T helper cells and CD8+ cytotoxic T cells, are crucial in controlling parasite growth and activating cells for parasite clearance via cytokine secretion. Contrary to this, reports also suggest the pathogenic nature of T lymphocytes as they are often involved in disease progression and severity. CD8+ cytotoxic T cells migrate to the host's brain vasculature, disrupting the blood-brain barrier and causing neurological manifestations. CD4+ T helper cells on the other hand play a variety of functions as they differentiate into different subtypes which may function as pro-inflammatory or anti-inflammatory. The excessive pro-inflammatory response in CM can lead to multi-organ failure, necessitating a check mechanism to maintain immune homeostasis. This is achieved by regulatory T cells and their characteristic cytokines, which counterbalance the pro-inflammatory immune response. Maintaining a critical balance between pro and anti-inflammatory responses is crucial for determining disease outcomes in CM. A slight change in this balance may contribute to a disease severity owing to an extreme inflammatory response or unrestricted parasite growth, a potential target for designing immunotherapeutic treatment approaches. The review briefly discusses the pathogenesis of CM and various mechanisms responsible for the disruption of the blood-brain barrier. It also highlights the role of different T cell subsets during infection and emphasizes the importance of balance between pro and anti-inflammatory T cells that ultimately decides the outcome of the disease.

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.

Human ApoE2 protects mice against Plasmodium berghei ANKA experimental cerebral malaria

IMPORTANCE

Cerebral malaria (CM) is the deadliest complication of malaria infection with an estimated 15%-25% mortality. Even with timely and effective treatment with antimalarial drugs such as quinine and artemisinin derivatives, survivors of CM may suffer long-term cognitive and neurological impairment. Here, we show that human apolipoprotein E variant 2 (hApoE2) protects mice from experimental CM (ECM) via suppression of CD8+ T cell activation and infiltration to the brain, enhanced cholesterol metabolism, and increased IFN-γ production, leading to reduced endothelial cell apoptosis, BBB disruption, and ECM symptoms. Our results suggest that hApoE can be an important factor for risk assessment and treatment of CM in humans.

Antiplasmodial and interferon-gamma-modulating activities of the aqueous extract of stone breaker (Phyllanthus niruri Linn.) in malaria infection

Plasmodium falciparum parasites are the primary cause of malaria across Africa. The problem of drug resistance to malaria is ever growing and novel therapeutic strategies need to be developed, particularly those targeting the parasite and also the host or host-pathogen interaction. Previous studies have shown that the development of cerebral malaria (CM) is related to dysregulation of the immune system in a murine malaria model of experimental cerebral malaria. It involves a complex interaction of events and interferon-gamma seems to be the unifying factor. Therefore, the antiplasmodial activity targeting the parasite and immunomodulatory strategies that reduce overall host inflammation, with IFN-γ in focus, could delay CM onset and prove beneficial in malaria infection therapy. Phyllanthus niruri is used to treat fever and other symptoms of malaria in Nigeria. Its modes of action as an anti-malarial remedy have not been exhaustively investigated. This study therefore examined the aqueous extract of P. niruri (PE) for its antiplasmodial activity in vitro using the Plasmodium falciparum HB3 strain. Furthermore, in vivo murine malaria model using the Plasmodium berghei ANKA strain was used to investigate its anti-malarial effects. We showed that PE has multiple anti-malarial effects, including anti-parasitic and host immunomodulatory activities. Co-culture of P. falciparum with PE and some of its phytoconstituents drastically reduced parasite number. PE also decreased parasitemia, and increased the survival of infected mice. We also observed that the integrity of the blood-brain barrier was maintained in the PE-treated mice. The results confirmed that PE showed moderate antiplasmodial activity. In vivo murine malaria model using P. berghei ANKA for experimental cerebral malaria revealed that PE suppressed parasite growth, and modulate the production of interferon-gamma. The findings demonstrate that PE affects malaria progression, targeting parasites and host cells.

Post-malarial neurological syndrome in a Gambian adult residing in the Gambia: a case report and a review of literature

BACKGROUND

Post malarial neurological syndrome (PMNS) occurs as a sequel of cerebral malaria which is the most deadly form of severe malaria. In holo-endemic regions (areas of high malarial transmission) all forms of severe malaria as well as cerebral malaria usually occur in children and those who are semi or non-immune like pregnant women, migrants as well as tourists. It also occurs in hypo-endemic regions (areas of limited malarial transmission with low immunity) and malaria- free zones. Survivors however may have neurologic complications after recovery. PMNS has been reported in many parts of the world. Being a sequel to cerebral malaria, it is uncommon in adults who were born and reside in a holo-endemic region all their lives.

CASE REPORT

This is the case of an 18 year old Gambian who has lived in The Gambia all his life that had PMNS five days after recovery from cerebral malaria.

METHODS

This was a predominantly web based literature search. The search comprise all case reports, original articles and reviews on PMNS or neurological deficits associated with malaria or noted after malaria infection. The search engines used were Google, Yahoo and Google scholar.

RESULTS

A total of 62 papers were found. These were used for this review of the literature.

CONCLUSION

Cerebral malaria also occurs in adults in holo-endemic areas though rare and some of the survivors may develop PMNS. It is commoner in the youth age group. There is need for further studies since the youth may be a possible new 'vulnerable group' in holoendemic areas. This may lead to the widening the targeted group for malaria control in the regions of high malarial transmission.

Automated malarial retinopathy detection using transfer learning and multi-camera retinal images

Cerebral malaria (CM) is a fatal syndrome found commonly in children less than 5 years old in Sub-saharan Africa and Asia. The retinal signs associated with CM are known as malarial retinopathy (MR), and they include highly specific retinal lesions such as whitening and hemorrhages. Detecting these lesions allows the detection of CM with high specificity. Up to 23% of CM, patients are over-diagnosed due to the presence of clinical symptoms also related to pneumonia, meningitis, or others. Therefore, patients go untreated for these pathologies, resulting in death or neurological disability. It is essential to have a low-cost and high-specificity diagnostic technique for CM detection, for which We developed a method based on transfer learning (TL). Models pre-trained with TL select the good quality retinal images, which are fed into another TL model to detect CM. This approach shows a 96% specificity with low-cost retinal cameras.