Evidence of blood-brain barrier dysfunction in human cerebral malaria

Linking Cerebral Malaria Pathogenesis to APOE-Mediated Amyloidosis: Observations and Hypothesis

Although most children with cerebral malaria fully recover, more than a fifth of the survivors develop post-discharge neurodevelopmental sequelae suggestive of advanced neuronal injury. However, the cerebral molecular processes initiating neurological dysfunction in cerebral malaria are still debatable. In this article, we explore available data and hypothesise that cerebral malaria might be linked to APOE-mediated amyloidosis, one of the pathological processes associated with Alzheimer's disease. If our hypothesis is tested and found to be true, it could have far-reaching implications for what we know about cerebral malaria pathogenesis.

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.

Lymphatic network drainage resolves cerebral edema and facilitates recovery from experimental cerebral malaria

While brain swelling, associated with fluid accumulation, is a known feature of pediatric cerebral malaria (CM), how fluid and macromolecules are drained from the brain during recovery from CM is unknown. Using the experimental CM (ECM) model, we show that fluid accumulation in the brain during CM is driven by vasogenic edema and not by perivascular cerebrospinal fluid (CSF) influx. We identify that fluid and molecules are removed from the brain extremely quickly in mice with ECM to the deep cervical lymph nodes (dcLNs), predominantly through basal routes and across the cribriform plate and the nasal lymphatics. In agreement, we demonstrate that ligation of the afferent lymphatic vessels draining to the dcLNs significantly impairs fluid drainage from the brain and lowers anti-malarial drug recovery from the ECM syndrome. Collectively, our results provide insight into the pathways that coordinate recovery from CM.

A Phase I trial of Non-invasive Ventilation and seizure prophylaxis with levetiracetam In Children with Cerebral Malaria Trial (NOVICE-M Trial)

Background

African children with cerebral malaria and seizures caused Plasmodium falciparum are at greater risk of poor outcomes including death and neurological sequelae. The agonal events are severe hypoventilation and respiratory arrest often triggered by seizures. We hypothesised that prophylactic anti-seizure medication (ASM) could avert 'spikes' of intracranial pressure during or following seizures and that adequate ventilation could be supported by biphasic Cuirass Ventilation (BCV) which requires no intubation.

Methods

A Phase I trial conducted in Kilifi, Kenya designed to provide data on safety, feasibility and preliminary data on seizure control using prophylactic ASM (levetiracetam) and BCV as non-invasive ventilatory support in children with cerebral malaria. Children aged 3 months to 12-years hospitalised with P falciparum malaria (positive rapid diagnostic test or a malaria slide), a Blantyre Coma Score ≤2 and a history of acute seizures in this illness are eligible for the trial. In a phased evaluation we will study i) BCV alone for respiratory support (n=10); ii) prophylactic LVT: 40mg/kg loading dose then 30mg/kg every 12 hours given via nasogastric tube for 72 hours (or until fully conscious) plus BCV support (n=10) and; iii) prophylactic LVT: 60mg/kg loading dose then 45mg/kg every 12 hours given via nasogastric tube for 72 hours (or until fully conscious) plus BCV support (n=10). Primary outcome measure: cumulative time with a clinically detected seizures or number of observed seizures over 36 hours. Secondary outcomes will be assessed by feasibility or ability to implement BCV, and recovery from coma within 36 hours. Safety endpoints include: aspiration during admission; death at 28 days and 180 days; and de-novo neurological impairments at 180 days.

Conclusions

This is a Phase I trial largely designed to test the feasibility, tolerability and safety of using non-invasive ventilatory support and LVT prophylaxis in cerebral malaria.

Registration

ISRCTN76942974 (5.02.2019); PACTR202112749708968 (20.12.2021).

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Understanding the mechanisms underlying the disruption of the blood-brain barrier in parasitic infections

Parasites have a significant impact on the neurological, cognitive, and mental well-being of humans, with a global population of over 1 billion individuals affected. The pathogenesis of central nervous system (CNS) injury in parasitic diseases remains limited, and prevention and control of parasitic CNS infections remain significant areas of research. Parasites, encompassing both unicellular and multicellular organisms, have intricate life cycles and possess the ability to infect a diverse range of hosts, including the human population. Parasitic illnesses that impact the central and peripheral nervous systems are a significant contributor to morbidity and mortality in low- to middle-income nations. The precise pathways through which neurotropic parasites infiltrate the CNS by crossing the blood-brain barrier (BBB) and cause neurological harm remain incompletely understood. Investigating brain infections caused by parasites is closely linked to studying neuroinflammation and cerebral impairment. The exact molecular and cellular mechanisms involved in this process remain incomplete, but understanding the exact mechanisms could provide insight into their pathogenesis and potentially reveal novel therapeutic targets. This review paper explores the underlying mechanisms involved in the development of neurological disorders caused by parasites, including parasite-derived elements, host immune responses, and modifications in tight junctions (TJs) proteins.

Effects of anti-tau immunotherapy on reactive microgliosis, cerebral endotheliopathy, and cognitive function in an experimental model of cerebral malaria

Cerebral malaria (CM), a potentially fatal encephalopathy caused primarily by infection with Plasmodium falciparum, results in long-term adverse neuro-psychiatric sequelae. Neural cell injury contributes to the neurological deficits observed in CM. Abnormal regulation of tau, an axonal protein pathologically associated with the formation of neurofibrillary lesions in neurodegenerative diseases, has been linked to inflammation and cerebral microvascular compromise and has been reported in human and experimental CM (ECM). Immunotherapy with a monoclonal antibody to pathological tau (PHF-1 mAB) in experimental models of neurodegenerative diseases has been reported to mitigate cognitive decline. We investigated whether immunotherapy with PHF-1 mAB prevented cerebral endotheliopathy, neural cell injury, and neuroinflammation during ECM. Using C57BL/6 mice infected with either Plasmodium berghei ANKA (PbA), which causes ECM, Plasmodium berghei NK65 (PbN), which causes severe malaria, but not ECM, or uninfected mice (Un), we demonstrated that when compared to PbN infection or uninfected mice, PbA infection resulted in significant memory impairment at 6 days post-infection, in association with abnormal tau phosphorylation at Ser202 /Thr205 (pSer202 /Thr205 ) and Ser396-404 (pSer396-404 ) in mouse brains. ECM also resulted in significantly higher expression of inflammatory markers, in microvascular congestion, and glial cell activation. Treatment with PHF-1 mAB prevented PbA-induced cognitive impairment and was associated with significantly less vascular congestion, neuroinflammation, and neural cell activation in mice with ECM. These findings suggest that abnormal regulation of tau protein contributes to cerebral vasculopathy and is critical in the pathogenesis of neural cell injury during CM. Tau-targeted therapies may ameliorate the neural cell damage and subsequent neurocognitive impairment that occur during disease.

Probing cerebral malaria inflammation in 3D human brain microvessels

Sequestration of Plasmodium falciparum-infected erythrocytes (IEs) in the brain microcirculation is a hallmark of cerebral malaria (CM), which leads to endothelial activation, brain swelling, and death. Here, we probed CM inflammation in a perfusable 3D human brain microvessel model. 3D brain microvessels supported in vivo-like capacities for parasite binding and maturation in situ, leading to a distinct inflammatory response from the pro-inflammatory cytokine tumor necrosis factor α (TNF-α). By combining transcriptional analysis, imaging, and leukocyte perfusion, we showed that whereas TNF-α promotes a reversible inflammatory phenotype with widespread leukocyte recruitment, parasites induce unique stress response pathways and cause localized cell adhesivity changes, focal endothelial disruptions, and apoptosis. Furthermore, parasites modified the temporal kinetics of the TNF transcriptional response, suggesting augmented inflammatory damage with the two sequential stimuli. Our findings offer mechanistic insights into CM biology in a 3D brain microvessel mimetic platform and suggest that multiple events intersect to promote brain barrier inflammation in CM.

Increased brain microvascular hemoglobin concentrations in children with cerebral malaria

Brain swelling is associated with death from cerebral malaria, but it is unclear whether brain swelling is caused by cerebral edema or vascular congestion-two pathological conditions with distinct effects on tissue hemoglobin concentrations. We used near-infrared spectroscopy (NIRS) to noninvasively study cerebral microvascular hemoglobin concentrations in 46 Malawian children with cerebral malaria. Cerebral malaria was defined by the presence of the malaria parasite Plasmodium falciparum on a blood smear, a Blantyre coma score of 2 or less, and retinopathy. Children with uncomplicated malaria (n = 33) and healthy children (n = 29) were enrolled as comparators. Cerebral microvascular hemoglobin concentrations were higher among children with cerebral malaria compared with those with uncomplicated malaria [median (25th, 75th): 145.2 (95.2, 190.0) μM versus 82.9 (65.7, 105.4) μM, P = 0.008]. Cerebral microvascular hemoglobin concentrations correlated with brain swelling score determined by MRI (r = 0.37, P = 0.03). Fluctuations in cerebral microvascular hemoglobin concentrations over a 30-min time period were characterized using detrended fluctuation analysis (DFA). DFA determined self-similarity of the cerebral microvascular hemoglobin concentration signal to be lower among children with cerebral malaria compared with those with uncomplicated malaria [0.63 (0.54, 0.70) versus 0.91 (0.82, 0.94), P < 0.0001]. The lower self-similarity of the hemoglobin concentration signal in children with cerebral malaria suggested impaired regulation of cerebral blood flow. The elevated cerebral tissue hemoglobin concentration and its correlation with brain swelling suggested that excess blood volume, potentially due to vascular congestion, may contribute to brain swelling in cerebral malaria.

Perillyl alcohol modulates activation, permeability and integrity of human brain endothelial cells induced by Plasmodium falciparum

BACKGROUND

Cerebral malaria (CM) is a severe immunovasculopathy caused for Plasmodium falciparum infection, which is characterised by the sequestration of parasitised red blood cells (pRBCs) in brain microvessels. Previous studies have shown that some terpenes, such as perillyl alcohol (POH), exhibit a marked efficacy in preventing cerebrovascular inflammation, breakdown of the brain-blood barrier (BBB) and brain leucocyte accumulation in experimental CM models.

OBJECTIVE

To analyse the effects of POH on the endothelium using human brain endothelial cell (HBEC) monolayers co-cultured with pRBCs.

METHODOLOGY

The loss of tight junction proteins (TJPs) and features of endothelial activation, such as ICAM-1 and VCAM-1 expression were evaluated by quantitative immunofluorescence. Microvesicle (MV) release by HBEC upon stimulation by P. falciparum was evaluated by flow cytometry. Finally, the capacity of POH to revert P. falciparum-induced HBEC monolayer permeability was examined by monitoring trans-endothelial electrical resistance (TEER).

FINDINGS

POH significantly prevented pRBCs-induced endothelial adhesion molecule (ICAM-1, VCAM-1) upregulation and MV release by HBEC, improved their trans-endothelial resistance, and restored their distribution of TJPs such as VE-cadherin, Occludin, and JAM-A.

CONCLUSIONS

POH is a potent monoterpene that is efficient in preventing P. falciparum-pRBCs-induced changes in HBEC, namely their activation, increased permeability and alterations of integrity, all parameters of relevance to CM pathogenesis.

Cerebrospinal fluid biomarkers provide evidence for kidney-brain axis involvement in cerebral malaria pathogenesis

Introduction

Cerebral malaria is one of the most severe manifestations of malaria and is a leading cause of acquired neurodisability in African children. Recent studies suggest acute kidney injury (AKI) is a risk factor for brain injury in cerebral malaria. The present study evaluates potential mechanisms of brain injury in cerebral malaria by evaluating changes in cerebrospinal fluid measures of brain injury with respect to severe malaria complications. Specifically, we attempt to delineate mechanisms of injury focusing on blood-brain-barrier integrity and acute metabolic changes that may underlie kidney-brain crosstalk in severe malaria.

Methods

We evaluated 30 cerebrospinal fluid (CSF) markers of inflammation, oxidative stress, and brain injury in 168 Ugandan children aged 18 months to 12 years hospitalized with cerebral malaria. Eligible children were infected with Plasmodium falciparum and had unexplained coma. Acute kidney injury (AKI) on admission was defined using the Kidney Disease: Improving Global Outcomes criteria. We further evaluated blood-brain-barrier integrity and malaria retinopathy, and electrolyte and metabolic complications in serum.

Results

The mean age of children was 3.8 years (SD, 1.9) and 40.5% were female. The prevalence of AKI was 46.3% and multi-organ dysfunction was common with 76.2% of children having at least one organ system affected in addition to coma. AKI and elevated blood urea nitrogen, but not other measures of disease severity (severe coma, seizures, jaundice, acidosis), were associated with increases in CSF markers of impaired blood-brain-barrier function, neuronal injury (neuron-specific enolase, tau), excitatory neurotransmission (kynurenine), as well as altered nitric oxide bioavailability and oxidative stress (p < 0.05 after adjustment for multiple testing). Further evaluation of potential mechanisms suggested that AKI may mediate or be associated with CSF changes through blood-brain-barrier disruption (p = 0.0014), ischemic injury seen by indirect ophthalmoscopy (p < 0.05), altered osmolality (p = 0.0006) and through alterations in the amino acids transported into the brain.

Conclusion

In children with cerebral malaria, there is evidence of kidney-brain injury with multiple potential pathways identified. These changes were specific to the kidney and not observed in the context of other clinical complications.

In vitro model of brain endothelial cell barrier reveals alterations induced by Plasmodium blood stage factors

Cerebral malaria (CM) is a severe neurological condition caused by Plasmodium falciparum. Disruption of the brain-blood barrier (BBB) is a key pathological event leading to brain edema and vascular leakage in both humans and in the mouse model of CM. Interactions of brain endothelial cells with infected red blood cells (iRBCs) and with circulating inflammatory mediators and immune cells contribute to BBB dysfunction in CM. Adjunctive therapies for CM aim at preserving the BBB to prevent neurologic deficits. Experimental animal and cellular models are essential to develop new therapeutic strategies. However, in mice, the disease develops rapidly, which offers a very narrow time window for testing the therapeutic potential of drugs acting in the BBB. Here, we establish a brain endothelial cell barrier whose disturbance can be monitored by several parameters. Using this system, we found that incubation with iRBCs and with extracellular particles (EPs) released by iRBCs changes endothelial cell morphology, decreases the tight junction protein zonula occludens-1 (ZO-1), increases the gene expression of the intercellular adhesion molecule 1 (ICAM-1), and induces a significant reduction in transendothelial electrical resistance (TEER) with increased permeability. We propose this in vitro experimental setup as a straightforward tool to investigate molecular interactions and pathways causing endothelial barrier dysfunction and to test compounds that may target BBB and be effective against CM. A pre-selection of the effective compounds that strengthen the resistance of the brain endothelial cell barrier to Plasmodium-induced blood factors in vitro may increase the likelihood of their efficacy in preclinical disease mouse models of CM and in subsequent clinical trials with patients.

Mouse Models for Unravelling Immunology of Blood Stage Malaria

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

Plasmodium falciparum and TNF-α Differentially Regulate Inflammatory and Barrier Integrity Pathways in Human Brain Endothelial Cells

Cerebral malaria is a severe complication of Plasmodium falciparum infection characterized by the loss of blood-brain barrier (BBB) integrity, which is associated with brain swelling and mortality in patients. P. falciparum-infected red blood cells and inflammatory cytokines, like tumor necrosis factor alpha (TNF-α), have been implicated in the development of cerebral malaria, but it is still unclear how they contribute to the loss of BBB integrity. Here, a combination of transcriptomic analysis and cellular assays detecting changes in barrier integrity and endothelial activation were used to distinguish between the effects of P. falciparum and TNF-α on a human brain microvascular endothelial cell (HBMEC) line and in primary human brain microvascular endothelial cells. We observed that while TNF-α induced high levels of endothelial activation, it only caused a small increase in HBMEC permeability. Conversely, P. falciparum-infected red blood cells (iRBCs) led to a strong increase in HBMEC permeability that was not mediated by cell death. Distinct transcriptomic profiles of TNF-α and P. falciparum in HBMECs confirm the differential effects of these stimuli, with the parasite preferentially inducing an endoplasmic reticulum stress response. Our results establish that there are fundamental differences in the responses induced by TNF-α and P. falciparum on brain endothelial cells and suggest that parasite-induced signaling is a major component driving the disruption of the BBB during cerebral malaria, proposing a potential target for much needed therapeutics.

Neurological Complications of Malaria

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Cerebral malaria - modelling interactions at the blood-brain barrier in vitro

The blood–brain barrier (BBB) is a continuous endothelial barrier that is supported by pericytes and astrocytes and regulates the passage of solutes between the bloodstream and the brain. This structure is called the neurovascular unit and serves to protect the brain from blood-borne disease-causing agents and other risk factors. In the past decade, great strides have been made to investigate the neurovascular unit for delivery of chemotherapeutics and for understanding how pathogens can circumvent the barrier, leading to severe and, at times, fatal complications. One such complication is cerebral malaria, in which Plasmodium falciparum-infected red blood cells disrupt the barrier function of the BBB, causing severe brain swelling. Multiple in vitro models of the BBB are available to investigate the mechanisms underlying the pathogenesis of cerebral malaria and other diseases. These range from single-cell monolayer cultures to multicellular BBB organoids and highly complex cerebral organoids. Here, we review the technologies available in malaria research to investigate the interaction between P. falciparum-infected red blood cells and the BBB, and discuss the advantages and disadvantages of each model.

Summary: This Review discusses the available in vitro models to investigate the impact of adhesion of Plasmodium falciparum-infected red blood cells on the blood–brain barrier, a process associated with cerebral malaria.

Neuroimmunology of Common Parasitic Infections in Africa

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

The Potential Roles of Glial Cells in the Neuropathogenesis of Cerebral Malaria

Cerebral malaria (CM) is a severe neurological complication of malaria caused by the Plasmodium falciparum parasite. It is one of the leading causes of death in children under 5 years of age in Sub-Saharan Africa. CM is associated with blood-brain barrier disruption and long-term neurological sequelae in survivors of CM. Despite the vast amount of research on cerebral malaria, the cause of neurological sequelae observed in CM patients is poorly understood. In this article, the potential roles of glial cells, astrocytes, and microglia, in cerebral malaria pathogenesis are reviewed. The possible mechanisms by which glial cells contribute to neurological damage in CM patients are also examined.

Cerebral malaria: insight into pathology from optical coherence tomography

We aimed to investigate structural retinal changes in malarial retinopathy (MR) using hand-held optical coherence tomography (HH-OCT) to assess its diagnostic potential. Children with MR (n = 43) underwent ophthalmoscopy, fluorescein angiography and HH-OCT during admission, 1-month (n = 31) and 1-year (n = 8) post-discharge. Controls were comatose patients without malaria (n = 6) and age/sex-matched healthy children (n = 43). OCT changes and retinal layer thicknesses were compared. On HH-OCT, hyper-reflective areas (HRAs) were seen in the inner retina of 81% of MR patients, corresponding to ischaemic retinal whitening on fundus photography. Cotton wool spots were present in 37% and abnormal hyper-reflective dots, co-localized to capillary plexus, in 93%. Hyper-reflective vessel walls were present in 84%, and intra-retinal cysts in 9%. Vascular changes and cysts resolved within 48 h. HRAs developed into retinal thinning at 1 month (p = 0.027) which was more pronounced after 1 year (p = 0.009). Ischaemic retinal whitening is located within inner retinal layers, distinguishing it from cotton wool spots. Vascular hyper-reflectivity may represent the sequestration of parasitized erythrocytes in vessels, a key CM feature. The mechanisms of post-ischemic retinal atrophy and cerebral atrophy with cognitive impairment may be similar in CM survivors. HH-OCT has the potential for monitoring patients, treatment response and predicting neurological deficits.

Childhood Mortality After Fluid Bolus With Septic or Severe Infection Shock: A Systematic Review and Meta-Analysis

BACKGROUND

A considerable debate on whether fluid bolus could decrease childhood mortality in pediatric patients with septic or severe infection shock is still unresolved. A systematic review and meta-analysis was conducted to investigate the mortality rates after fluid bolus among children with septic or severe infection shock.

METHODS

A systematic electronic search of PubMed, MEDLINE, Cochrane Library, and EMBASE databases was conducted to identify relevant published studies till March 30, 2020.

RESULTS

A total of 19 studies with 9,321 severe sepsis or septic shock pediatric patients were included and exhibited an acceptable quality. Of the 17 studies that reported mortality at 48 h, no bolus group decreased the mortality rate when compared with bolus group with a risk ratio (RR) of 0.74 [95% confidence interval (CI) = 0.62-0.88, P < 0.01], and showed no heterogeneity (I2 = 0%). Similar results were observed on colloids and crystalloids solution in malaria shock cases with a RR of 0.79 (95% CI = 0.62-1.02). For the subgroup of general shock patients, no significant difference was shown with an RR of 0.79 (95% CI = 0.62-1.02, P = 0.07) and no significant heterogeneity (I2 = 0%). Two studies reported mortality at week 4 and pooled results indicated that no bolus group was protective against mortality when compared with bolus group with RR of 0.71 (95% CI = 0.57-0.88, I2 = 0%).

CONCLUSION

For the mortality at 48 h, the no bolus group showed decreased mortality when compared with the bolus group, especially in the malaria group. Similar results were found in the colloids and crystalloids solution in patients with malaria shock. Meta-analysis studies with long-term follow-up period and larger sample size are warranted to address the conclusion in the future.

Perillyl alcohol reduces parasite sequestration and cerebrovascular dysfunction during experimental cerebral malaria

Cerebral malaria (CM) is a severe immunovasculopathy which presents high mortality rate (15-20%), despite the availability of artemisinin-based therapy. More effective immunomodulatory and/or antiparasitic therapies are urgently needed. Experimental Cerebral Malaria (ECM) in mice is used to elucidate aspects involved in this pathology since manifests many of the neurological features of CM. In the present study, we evaluated the potential mechanisms involved in the protection afforded by perillyl alcohol (POH) in mouse strains susceptible to CM caused by Plasmodium berghei ANKA (PbA) infection through intranasal preventive treatment. Additionally, to evaluate the interaction of POH with the cerebral endothelium using an in vitro model of human brain endothelial cells (HBEC). Pharmacokinetic approaches demonstrated constant and prolonged levels of POH in the plasma and brain after a single intranasal dose. Treatment with POH effectively prevented vascular dysfunction. Furthermore, treatment with POH reduced the endothelial cell permeability and PbA s in the brain and spleen. Finally, POH treatment decreased the accumulation of macrophages and T and B cells in the spleen and downregulated the expression of endothelial adhesion molecules (ICAM-1, VCAM-1, and CD36) in the brain. POH is a potent monoterpene that prevents cerebrovascular dysfunction in vivo and in vitro, decreases parasite sequestration, and modulates different processes related to the activation, permeability, and integrity of the blood brain barrier (BBB), thereby preventing cerebral oedema and inflammatory infiltrates.

CD8+ T cells target cerebrovasculature in children with cerebral malaria

BACKGROUNDCerebral malaria (CM) accounts for nearly 400,000 deaths annually in African children. Current dogma suggests that CM results from infected RBC (iRBC) sequestration in the brain microvasculature and resulting sequelae. Therapies targeting these events have been unsuccessful; findings in experimental models suggest that CD8+ T cells drive disease pathogenesis. However, these data have largely been ignored because corroborating evidence in humans is lacking. This work fills a critical gap in our understanding of CM pathogenesis that is impeding development of therapeutics.METHODSUsing multiplex immunohistochemistry, we characterized cerebrovascular immune cells in brain sections from 34 children who died from CM or other causes. Children were grouped by clinical diagnosis (CM+ or CM-), iRBC sequestration (Seqhi, Seqlo, Seq0) and HIV status (HIV+ or HIV-).RESULTSWe identified effector CD3+CD8+ T cells engaged on the cerebrovasculature in 69% of CM+ HIV- children. The number of intravascular CD3+CD8+ T cells was influenced by CM status (CM+ > CM-, P = 0.004) and sequestration level (Seqhi > Seqlo, P = 0.010). HIV coinfection significantly increased T cell numbers (P = 0.017) and shifted cells from an intravascular (P = 0.004) to perivascular (P < 0.0001) distribution.CONCLUSIONWithin the studied cohort, CM is associated with cerebrovascular engagement of CD3+CD8+ T cells, which is exacerbated by HIV coinfection. Thus, CD3+CD8+ T cells are highly promising targets for CM adjunctive therapy, opening new avenues for the treatment of this deadly disease.FUNDINGThis research was supported by the Intramural Research Program of the National Institutes of Health.

Fibrinogen: A potential biomarker for predicting disease severity in multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. The exact pathogenesis behind the development of MS is unknown. This study aims to elucidate the role of fibrinogen in MS pathology and discuss candidacy as a biomarker for disease management.

METHOD

The method applied is a systematic literature review on the bio-medical database PubMed.

RESULTS

This study found that even though the role of fibrinogen in disease development has been studied considerably, clinical application as a viable biomarker has not yet been achieved conclusively in human studies.

CONCLUSION

Recent evidence points toward fibrinogen and its degradation products playing a possible role in the disease pathogenesis Further research is needed to convincingly evaluate fibrinogen as a practical biomarker for diagnostic use or for assessing disease severity.

Advancing brain barriers RNA sequencing: guidelines from experimental design to publication

BACKGROUND

RNA sequencing (RNA-Seq) in its varied forms has become an indispensable tool for analyzing differential gene expression and thus characterization of specific tissues. Aiming to understand the brain barriers genetic signature, RNA seq has also been introduced in brain barriers research. This has led to availability of both, bulk and single-cell RNA-Seq datasets over the last few years. If appropriately performed, the RNA-Seq studies provide powerful datasets that allow for significant deepening of knowledge on the molecular mechanisms that establish the brain barriers. However, RNA-Seq studies comprise complex workflows that require to consider many options and variables before, during and after the proper sequencing process.

MAIN BODY

In the current manuscript, we build on the interdisciplinary experience of the European PhD Training Network BtRAIN ( https://www.btrain-2020.eu/ ) where bioinformaticians and brain barriers researchers collaborated to analyze and establish RNA-Seq datasets on vertebrate brain barriers. The obstacles BtRAIN has identified in this process have been integrated into the present manuscript. It provides guidelines along the entire workflow of brain barriers RNA-Seq studies starting from the overall experimental design to interpretation of results. Focusing on the vertebrate endothelial blood-brain barrier (BBB) and epithelial blood-cerebrospinal-fluid barrier (BCSFB) of the choroid plexus, we provide a step-by-step description of the workflow, highlighting the decisions to be made at each step of the workflow and explaining the strengths and weaknesses of individual choices made. Finally, we propose recommendations for accurate data interpretation and on the information to be included into a publication to ensure appropriate accessibility of the data and reproducibility of the observations by the scientific community.

CONCLUSION

Next generation transcriptomic profiling of the brain barriers provides a novel resource for understanding the development, function and pathology of these barrier cells, which is essential for understanding CNS homeostasis and disease. Continuous advancement and sophistication of RNA-Seq will require interdisciplinary approaches between brain barrier researchers and bioinformaticians as successfully performed in BtRAIN. The present guidelines are built on the BtRAIN interdisciplinary experience and aim to facilitate collaboration of brain barriers researchers with bioinformaticians to advance RNA-Seq study design in the brain barriers community.

Cerebral malaria and the story of Quinine and the Fever Trees

Cinchona bark was first recorded as a cure for malaria by the Spanish in Peru around 1630. A Spanish missionary allegedly learned of the treatment from the Indian natives. Cerebral malaria caused by Plasmodium falciparum is life threatening and one of the commonest encephalopathies in the world. Quinine was the first effective treatment, discovered in the bark of quina-quina, cinchona, ‘the fever tree’ in Peru in 1633. Many tales – many fanciful – relate to its early use. Foremost of the discoverers in 1735 was a group of French scientists in an expedition to Peru directed by the Parisian Academie Royale des Sciences. It was then widely exported and employed in Spain, Italy and Britain to become the standard treatment.

ZBTB7B (ThPOK) Is Required for Pathogenesis of Cerebral Malaria and Protection against Pulmonary Tuberculosis

We used a genome-wide screen in N-ethyl-N-nitrosourea (ENU)-mutagenized mice to identify genes in which recessive loss-of-function mutations protect against pathological neuroinflammation. We identified an R367Q mutation in the ZBTB7B (ThPOK) protein in which homozygosity causes protection against experimental cerebral malaria (ECM) caused by infection with Plasmodium berghei ANKA. Zbtb7b^R367Q homozygous mice show a defect in the lymphoid compartment expressed as severe reduction in the number of single-positive CD4 T cells in the thymus and in the periphery, reduced brain infiltration of proinflammatory leukocytes in P. berghei ANKA-infected mice, and reduced production of proinflammatory cytokines by primary T cells ex vivo and in vivo Dampening of proinflammatory immune responses in Zbtb7b^R367Q mice is concomitant to increased susceptibility to infection with avirulent (Mycobacterium bovis BCG) and virulent (Mycobacterium tuberculosis H37Rv) mycobacteria. The R367Q mutation maps to the first DNA-binding zinc finger domain of ThPOK and causes loss of base contact by R367 in the major groove of the DNA, which is predicted to impair DNA binding. Global immunoprecipitation of ThPOK-containing chromatin complexes coupled to DNA sequencing (ChIP-seq) identified transcriptional networks and candidate genes likely to play key roles in CD4⁺ CD8⁺ T cell development and in the expression of lineage-specific functions of these cells. This study highlights ThPOK as a global regulator of immune function in which alterations may affect normal responses to infectious and inflammatory stimuli.

Differential Expression of CD31 and Von Willebrand Factor on Endothelial Cells in Different Regions of the Human Brain: Potential Implications for Cerebral Malaria Pathogenesis

Cerebral microvascular endothelial cells (CMVECs) line the vascular system of the brain and are the chief cells in the formation and function of the blood brain barrier (BBB). These cells are heterogeneous along the cerebral vasculature and any dysfunctional state in these cells can result in a local loss of function of the BBB in any region of the brain. There is currently no report on the distribution and variation of the CMVECs in different brain regions in humans. This study investigated microcirculation in the adult human brain by the characterization of the expression pattern of brain endothelial cell markers in different brain regions. Five different brain regions consisting of the visual cortex, the hippocampus, the precentral gyrus, the postcentral gyrus, and the rhinal cortex obtained from three normal adult human brain specimens were studied and analyzed for the expression of the endothelial cell markers: cluster of differentiation 31 (CD31) and von-Willebrand-Factor (vWF) through immunohistochemistry. We observed differences in the expression pattern of CD31 and vWF between the gray matter and the white matter in the brain regions. Furthermore, there were also regional variations in the pattern of expression of the endothelial cell biomarkers. Thus, this suggests differences in the nature of vascularization in various regions of the human brain. These observations also suggest the existence of variation in structure and function of different brain regions, which could reflect in the pathophysiological outcomes in a diseased state.

Cerebral Plasmodium falciparum malaria: The role of PfEMP1 in its pathogenesis and immunity, and PfEMP1-based vaccines to prevent it

Malaria, a mosquito-borne infectious disease caused by parasites of the genus Plasmodium continues to be a major health problem worldwide. The unicellular Plasmodium-parasites have the unique capacity to infect and replicate within host erythrocytes. By expressing variant surface antigens Plasmodium falciparum has evolved to avoid protective immune responses; as a result in endemic areas anti-malaria immunity develops gradually over many years of multiple and repeated infections. We are studying the role of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) expressed by asexual stages of P. falciparum responsible for the pathogenicity of severe malaria. The immunopathology of falciparum malaria has been linked to cyto-adhesion of infected erythrocytes to specific host receptors. A greater appreciation of the PfEMP1 molecules important for the development of protective immunity and immunopathology is a prerequisite for the rational discovery and development of a safe and protective anti-disease malaria vaccine. Here we review the role of ICAM-1 and EPCR receptor adhering falciparum-parasites in the development of severe malaria; we discuss our current research to understand the factors involved in the pathogenesis of cerebral malaria and the feasibility of developing a vaccine targeted specifically to prevent this disease.

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

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

Brain Endothelium: The "Innate Immunity Response Hypothesis" in Cerebral Malaria Pathogenesis

Cerebral malaria (CM) is a life-threatening neurological syndrome caused by Plasmodium falciparum infection afflicting mainly children in Africa. Current pathogenesis models implicate parasite and host-derived factors in impairing brain vascular endothelium (BVE) integrity. Sequestration of Plasmodium-infected red blood cells (iRBCs) in brain microvessels is a hallmark of CM pathology. However, the precise mechanisms driving loss of blood-brain barrier (BBB) function with consequent brain injury are still unsettled and it is plausible that distinct pathophysiology trajectories are involved. Studies in humans and in the mouse model of CM indicate that inflammatory reactions intertwined with microcirculatory and coagulation disturbances induce alterations in vascular permeability and impair BBB integrity. Yet, the role of BVE as initiator of immune responses against parasite molecules and iRBCs is largely unexplored. Brain endothelial cells express pattern recognition receptors (PRR) and are privileged sensors of blood-borne infections. Here, we focus on the hypothesis that innate responses initiated by BVE and subsequent interactions with immune cells are critical to trigger local effector immune functions and induce BBB damage. Uncovering mechanisms of BVE involvement in sensing Plasmodium infection, recruiting of immune cells and directing immune effector functions could reveal pharmacological targets to promote BBB protection with potential applications in CM clinical management.

Brain swelling is independent of peripheral plasma cytokine levels in Malawian children with cerebral malaria

Background

Cerebral malaria (CM) is often fatal, and severe brain swelling is a predictor of CM-related mortality. CM is characterized by elevated circulating pro-inflammatory cytokines TNF and IFN-γ and anti-inflammatory cytokine IL-10, however whether cytokine levels correlate with brain swelling severity is unknown. This study therefore was conducted to investigate the relationship between cytokine levels and brain swelling severity in children presenting with CM.

Methods

A total of 195 Malawian children presenting with CM were recruited and had the concentrations of plasma cytokines determined and compared to brain swelling severity, determined by MRI examination, and graded as severe, moderate, mild or none.

Results

Levels of IL-1β, IL-6, IL-8 and IL-10 did not differ between CM patients with and without severe brain swelling. Compared to children without brain swelling, IL-12 levels were higher in children with severe swelling (p < 0.01, no swelling 1 pg/mL, IQR [1] vs. severe swelling 18.7 pg/mL, IQR [1–27]), whereas TNF concentrations were higher in children with moderate brain swelling compared to children with no swelling (p < 0.01, no swelling 3 pg/mL, IQR [1–20] vs. moderate swelling 24 pg/mL, IQR [8–58]. Multivariate analysis showed that no single cytokine independently predicted brain swelling.

Conclusion

Severe brain swelling in paediatric CM was independent of tested blood pro-inflammatory and anti-inflammatory cytokines which are markers of systemic inflammation.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2590-0) contains supplementary material, which is available to authorized users.

Opportunities for Host-targeted Therapies for Malaria

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

Tight junction structure, function, and assessment in the critically ill: a systematic review

BACKGROUND

Epithelial and endothelial barrier integrity, essential for homeostasis, is maintained by cellular boarder structures known as tight junctions (TJs). In critical illness, TJs may become disrupted, resulting in barrier dysfunction manifesting as capillary leak, pulmonary edema, gut bacterial translocation, and multiple organ failure. We aim to provide a clinically focused overview of TJ structure and function and systematically review and analyze all studies assessing markers of endothelial and epithelial TJ breakdown correlated with clinical outcomes in critically ill humans.

METHODS

We systematically searched MEDLINE, EMBASE, and PubMed. Additional articles were identified by targeted searches. We included studies that looked at the relationship between biomarkers of endothelial or epithelial TJ structure or function and critical illness. Results were qualitatively analyzed due to sample size and heterogeneity.

RESULTS

A total of 5297 abstracts met search criteria, of which 150 articles met requirements for full text review. Of these, 30 studies met inclusion criteria. Fifteen of the 30 reports investigated proteins of endothelial tight junctions and 15 investigated epithelial TJ markers, exclusively in the gastrointestinal epithelium. No studies investigated TJ-derived proteins in primary cardiac or pulmonary pathology.

CONCLUSIONS

TJ integrity is essential for homeostasis. We identified multiple studies that indicate TJs are disrupted by critical illness. These studies highlight the significance of barrier disruption across many critical disease states and correlate TJ-associated markers to clinically relevant outcomes. Further study on the role of multiple tissue-specific claudins, particularly in the setting of respiratory or cardiac failure, may lead to diagnostic and therapeutic advances.

SYSTEMATIC REVIEW REGISTRATION

This systematic review is registered in the PROSPERO database: CRD42017074546 .

Cerebral Malaria in Mouse and Man

Cerebral malaria (CM) is an acute encephalopathy caused by the malaria parasite Plasmodium falciparum, which develops in a small minority of infected patients and is responsible for the majority of deaths in African children. Despite decades of research on CM, the pathogenic mechanisms are still relatively poorly defined. Nevertheless, many studies in recent years, using a combination of animal models, in vitro cell culture work, and human patients, provide significant insight into the pathologic mechanisms leading to CM. In this review, we summarize recent findings from mouse models and human studies on the pathogenesis of CM, understanding of which may enable development of novel therapeutic approaches.

Bridging barriers: a comparative look at the blood-brain barrier across organisms

This review by O'Brown et al. discusses the cellular nature of the blood–brain barrier (BBB) and the conservation and variation of BBB function across taxa. It compares the BBB across organisms in order to provide insight into the human BBB both under normal physiological conditions and in neurological diseases.

The blood–brain barrier (BBB) restricts free access of molecules between the blood and the brain and is essential for regulating the neural microenvironment. Here, we describe how the BBB was initially characterized and how the current field evaluates barrier properties. We next detail the cellular nature of the BBB and discuss both the conservation and variation of BBB function across taxa. Finally, we examine our current understanding of mouse and zebrafish model systems, as we expect that comparison of the BBB across organisms will provide insight into the human BBB under normal physiological conditions and in neurological diseases.

Elimination of intravascular thrombi prevents early mortality and reduces gliosis in hyper-inflammatory experimental cerebral malaria

BACKGROUND

Cerebral malaria (CM) is the most lethal outcome of Plasmodium infection. There are clear correlations between expression of inflammatory cytokines, severe coagulopathies, and mortality in human CM. However, the mechanisms intertwining the coagulation and inflammation pathways, and their roles in CM, are only beginning to be understood. In mice with T cells deficient in the regulatory cytokine IL-10 (IL-10 KO), infection with Plasmodium chabaudi leads to a hyper-inflammatory response and lethal outcome that can be prevented by anti-TNF treatment. However, inflammatory T cells are adherent within the vasculature and not present in the brain parenchyma, suggesting a novel form of cerebral inflammation. We have previously documented behavioral dysfunction and microglial activation in infected IL-10 KO animals suggestive of neurological involvement driven by inflammation. In order to understand the relationship of intravascular inflammation to parenchymal dysfunction, we studied the congestion of vessels with leukocytes and fibrin(ogen) and the relationship of glial cell activation to congested vessels in the brains of P. chabaudi-infected IL-10 KO mice.

METHODS

Using immunofluorescence microscopy, we describe severe thrombotic congestion in these animals. We stained for immune cell surface markers (CD45, CD11b, CD4), fibrin(ogen), microglia (Iba-1), and astrocytes (GFAP) in the brain at the peak of behavioral symptoms. Finally, we investigated the roles of inflammatory cytokine tumor necrosis factor (TNF) and coagulation on the pathology observed using neutralizing antibodies and low-molecular weight heparin to inhibit both inflammation and coagulation, respectively.

RESULTS

Many blood vessels in the brain were congested with thrombi containing adherent leukocytes, including CD4 T cells and monocytes. Despite containment of the pathogen and leukocytes within the vasculature, activated microglia and astrocytes were prevalent in the parenchyma, particularly clustered near vessels with thrombi. Neutralization of TNF, or the coagulation cascade, significantly reduced both thrombus formation and gliosis in P. chabaudi-infected IL-10 KO mice.

CONCLUSIONS

These findings support the contribution of cytokines, coagulation, and leukocytes within the brain vasculature to neuropathology in malaria infection. Strikingly, localization of inflammatory leukocytes within intravascular clots suggests a mechanism for interaction between the two cascades by which cytokines drive local inflammation without considerable cellular infiltration into the brain parenchyma.

Mechanical disruption of the blood-brain barrier following experimental concussion

Although concussion is now recognized as a major health issue, its non-lethal nature has limited characterization of the underlying pathophysiology. In particular, potential neuropathological changes have typically been inferred from non-invasive techniques or post-mortem examinations of severe traumatic brain injury (TBI). Here, we used a swine model of head rotational acceleration based on human concussion to examine blood-brain barrier (BBB) integrity after injury in association with diffuse axonal injury and glial responses. We then determined the potential clinical relevance of the swine concussion findings through comparisons with pathological changes in human severe TBI, where post-mortem examinations are possible. At 6-72 h post-injury in swine, we observed multifocal disruption of the BBB, demonstrated by extravasation of serum proteins, fibrinogen and immunoglobulin-G, in the absence of hemorrhage or other focal pathology. BBB disruption was observed in a stereotyped distribution consistent with biomechanical insult. Specifically, extravasated serum proteins were frequently observed at interfaces between regions of tissue with differing material properties, including the gray-white boundary, periventricular and subpial regions. In addition, there was substantial overlap of BBB disruption with regions of axonal pathology in the white matter. Acute perivascular cellular uptake of blood-borne proteins was observed to be prominent in astrocytes (GFAP-positive) and neurons (MAP-2-positive), but not microglia (IBA1-positive). Parallel examination of human severe TBI revealed similar patterns of serum extravasation and glial uptake of serum proteins, but to a much greater extent than in the swine model, attributed to the higher injury severity. These data suggest that BBB disruption represents a new and important pathological feature of concussion.

Fibrinogen in neurological diseases: mechanisms, imaging and therapeutics

The blood coagulation protein fibrinogen is deposited in the brain in a wide range of neurological diseases and traumatic injuries with blood-brain barrier (BBB) disruption. Recent research has uncovered pleiotropic roles for fibrinogen in the activation of CNS inflammation, induction of scar formation in the brain, promotion of cognitive decline and inhibition of repair. Such diverse roles are possible in part because of the unique structure of fibrinogen, which contains multiple binding sites for cellular receptors and proteins expressed in the nervous system. The cellular and molecular mechanisms underlying the actions of fibrinogen are beginning to be elucidated, providing insight into its involvement in neurological diseases, such as multiple sclerosis, Alzheimer disease and traumatic CNS injury. Selective drug targeting to suppress the damaging functions of fibrinogen in the nervous system without affecting its beneficial effects in haemostasis opens a new fibrinogen therapeutics pipeline for neurological disease.

Endothelial Activation: The Ang/Tie Axis in Sepsis

Sepsis, a dysregulated host response to infection that causes life-threatening organ dysfunction, is a highly heterogeneous syndrome with no specific treatment. Although sepsis can be caused by a wide variety of pathogenic organisms, endothelial dysfunction leading to vascular leak is a common mechanism of injury that contributes to the morbidity and mortality associated with the syndrome. Perturbations to the angiopoietin (Ang)/Tie2 axis cause endothelial cell activation and contribute to the pathogenesis of sepsis. In this review, we summarize how the Ang/Tie2 pathway is implicated in sepsis and describe its prognostic as well as therapeutic utility in life-threatening infections.

Brain vascular heterogeneity: implications for disease pathogenesis and design of in vitro blood-brain barrier models

The vertebrate blood–brain barrier (BBB) is composed of cerebral microvascular endothelial cells (CEC). The BBB acts as a semi-permeable cellular interface that tightly regulates bidirectional molecular transport between blood and the brain parenchyma in order to maintain cerebral homeostasis. The CEC phenotype is regulated by a variety of factors, including cells in its immediate environment and within functional neurovascular units. The cellular composition of the brain parenchyma surrounding the CEC varies between different brain regions; this difference is clearly visible in grey versus white matter. In this review, we discuss evidence for the existence of brain vascular heterogeneity, focusing on differences between the vessels of the grey and white matter. The region-specific differences in the vasculature of the brain are reflective of specific functions of those particular brain areas. This BBB-endothelial heterogeneity may have implications for the course of pathogenesis of cerebrovascular diseases and neurological disorders involving vascular activation and dysfunction. This heterogeneity should be taken into account when developing BBB-neuro-disease models representative of specific brain areas.

Cerebral malaria induces electrophysiological and neurochemical impairment in mice retinal tissue: possible effect on glutathione and glutamatergic system

Background

Cerebral malaria (CM) is a severe complication resulting from Plasmodium falciparum infection. This condition has usually been associated with cognitive, behavioural and motor dysfunctions, being the retinopathy the most serious consequence resulting from the disease. The pathophysiological mechanisms underlying this complication remain incompletely understood. Several experimental models of CM have already been developed in order to clarify those mechanisms related to this syndrome. In this context, the present work has been performed to investigate which possible electrophysiological and neurochemistry alterations could be involved in the CM pathology.

Methods

Experimental CM was induced in Plasmodium berghei-infected male and female C57Bl/6 mice. The survival and neurological symptoms of CM were registered. Brains and retina were assayed for TNF levels and NOS2 expression. Electroretinography measurements were recorded to assessed a- and b-wave amplitudes and neurochemicals changes were evaluated by determination of glutamate and glutathione levels by HPLC.

Results

Susceptible C57Bl/6 mice infected with ≈ 10⁶ parasitized red blood cells (P. berghei ANKA strain), showed a low parasitaemia, with evident clinical signs as: respiratory failure, ataxia, hemiplegia, and coma followed by animal death. In parallel to the clinical characterization of CM, the retinal electrophysiological analysis showed an intense decrease of a- and-b-wave amplitude associated to cone photoreceptor response only at the 7 days post-infection. Neurochemical results demonstrated that the disease led to a decrease in the glutathione levels with 2 days post inoculation. It was also demonstrated that the increase in the glutathione levels during the infection was followed by the increase in the ³H-glutamate uptake rate (4 and 7 days post-infection), suggesting that CM condition causes an up-regulation of the transporters systems. Furthermore, these findings also highlighted that the electrophysiological and neurochemical alterations occurs in a manner independent on the establishment of an inflammatory response, once tumour necrosis factor levels and inducible nitric oxide synthase expression were altered only in the cerebral tissue but not in the retina.

Conclusions

In summary, these findings indicate for the first time that CM induces neurochemical and electrophysiological impairment in the mice retinal tissue, in a TNF-independent manner.

Finding a Balance between Protection and Pathology: The Dual Role of Perforin in Human Disease

Perforin is critical for controlling viral infection and tumor surveillance. Clinically, mutations in perforin are viewed as unfavorable, as lack of this pore-forming protein results in lethal, childhood disease, familial hemophagocytic lymphohistiocytosis type 2 (FHL 2). However, many mutations in the coding region of PRF1 are not yet associated with disease. Animal models of viral-associated blood–brain barrier (BBB) disruption and experimental cerebral malaria (ECM) have identified perforin as critical for inducing pathologic central nervous system CNS vascular permeability. This review focuses on the role of perforin in both protecting and promoting human disease. It concludes with a novel hypothesis that diversity observed in the PRF1 gene may be an example of selective advantage that protects an individual from perforin-mediated pathology, such as BBB disruption.

Cytokines and Chemokines in Cerebral Malaria Pathogenesis

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

Hydrogen sulfide protects against the development of experimental cerebral malaria in a C57BL/6 mouse model

Hydrogen sulfide (H2S) has anti‑inflammatory and neuroprotective properties, particularly during pathological processes. Experimental cerebral malaria (ECM), which is caused by vascular leakage into the brain, is characterized by inflammation, neurological deficits and cerebral hemorrhage. The present study investigated the correlation between ECM genesis and the levels of H2S. The results indicated that the levels of H2S derived from the brain decreased over time following ECM infection, and that the low H2S bioavailability was partially caused by decreased expression of the H2S generating enzyme, cystathionine‑β‑synthase. Administration of NaHS (an exogenous donor of H2S) provided protection against ECM. NaHS inhibited the destruction of the blood brain barrier and the secretion of proinflammatory biomarkers, including interluekin‑18, matrix metalloproteinase‑9 and serum cluster of differentiation 40 into the brain during ECM. In conclusion, these results suggested that low levels of H2S in brain contributed to the progression of ECM, and that H2S donor administration may represent a potential protective therapy against ECM.

Magnetic Resonance Imaging of Cerebral Malaria Patients Reveals Distinct Pathogenetic Processes in Different Parts of the Brain

The pathophysiology and molecular mechanisms underlying cerebral malaria (CM) are still poorly understood. Recent neuroimaging studies demonstrated that brain swelling is a common feature in CM and a major contributor to death in pediatric patients. Consequently, determining the precise mechanisms responsible for this swelling could open new adjunct therapeutic avenues in CM patients. Using an MRI scanner with a higher resolution than the ones used in previous reports, we identified two distinct origins of brain swelling in both adult and pediatric patients from India, occurring in distinct parts of the brain. Our results support the hypothesis that both endothelial dysfunction and microvascular obstruction by Plasmodium falciparum-infected erythrocytes make independent contributions to the pathogenesis of CM, providing opportunities for novel therapeutic interventions.

The mechanisms underlying the rapidly reversible brain swelling described in patients with cerebral malaria (CM) are unknown. Using a 1.5-Tesla (T) magnetic resonance imaging (MRI) scanner, we undertook an observational study in Rourkela, India, of 11 Indian patients hospitalized with CM and increased brain volume. Among the 11 cases, there were 5 adults and 6 children. All patients had reduced consciousness and various degrees of cortical swelling at baseline. The latter was predominately posterior in distribution. The findings on diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) maps were consistent with vasogenic edema in all cases. Reversibility after 48 to 72 h was observed in >90% of cases. DWI/ADC mismatch suggested the additional presence of cytotoxic edema in the basal nuclei of 5 patients; all of these had perfusion parameters consistent with vascular engorgement and not with ischemic infarcts. Our results suggest that an impairment of the blood-brain barrier is responsible for the brain swelling in CM. In 5 cases, vasogenic edema occurred in conjunction with changes in the basal nuclei consistent with venous congestion, likely to be caused by the sequestration of Plasmodium falciparum-infected erythrocytes. While both mechanisms have been individually postulated to play an important role in the development of CM, this is the first demonstration of their concurrent involvement in different parts of the brain. The clinical and radiological characteristics observed in the majority of our patients are consistent with posterior reversible encephalopathy syndrome (PRES), and we show for the first time a high frequency of PRES in the context of CM.

IMPORTANCE The pathophysiology and molecular mechanisms underlying cerebral malaria (CM) are still poorly understood. Recent neuroimaging studies demonstrated that brain swelling is a common feature in CM and a major contributor to death in pediatric patients. Consequently, determining the precise mechanisms responsible for this swelling could open new adjunct therapeutic avenues in CM patients. Using an MRI scanner with a higher resolution than the ones used in previous reports, we identified two distinct origins of brain swelling in both adult and pediatric patients from India, occurring in distinct parts of the brain. Our results support the hypothesis that both endothelial dysfunction and microvascular obstruction by Plasmodium falciparum-infected erythrocytes make independent contributions to the pathogenesis of CM, providing opportunities for novel therapeutic interventions.

Elevated cerebrospinal fluid tumour necrosis factor is associated with acute and long-term neurocognitive impairment in cerebral malaria

Systemic tumour necrosis factor-α (TNF-α) may contribute to the pathogenesis of cerebral malaria (CM) by promoting endothelial activation and parasite sequestration. However, less is known about the role of central nervous system (CNS) TNF-α in CM. We assessed plasma (n=249) and cerebrospinal fluid (CSF) (n=167) TNF-α levels in Ugandan children with CM, plasma TNF-α in Ugandan community control children (n=198) and CSF TNF-α in North American control children who had recovered from leukaemia (n=13). Plasma and CSF TNF-α were measured by magnetic bead assay. We compared plasma and CSF TNF-α levels in children with CM to mortality, acute and chronic neurologic deficits and long-term neurocognitive impairment. Plasma and CSF TNF-α levels were higher in CM than control children (P<.0001 for both). CSF TNF-α levels were higher in children who had neurologic deficits at discharge or 6-month follow-up (P≤.05 for both). Elevated CSF but not plasma TNF-α was associated with longer coma duration (Spearman's rho .18, P=.02) and deficits in overall cognition in children 5 years and older (β coefficient -.74, 95% CI -1.35 to -0.13, P=.02). The study findings suggest that CNS TNF-α may be involved in the development of acute and chronic neurologic and cognitive sequelae in children with CM.

A quantitative brain map of experimental cerebral malaria pathology

The murine model of experimental cerebral malaria (ECM) has been utilised extensively in recent years to study the pathogenesis of human cerebral malaria (HCM). However, it has been proposed that the aetiologies of ECM and HCM are distinct, and, consequently, no useful mechanistic insights into the pathogenesis of HCM can be obtained from studying the ECM model. Therefore, in order to determine the similarities and differences in the pathology of ECM and HCM, we have performed the first spatial and quantitative histopathological assessment of the ECM syndrome. We demonstrate that the accumulation of parasitised red blood cells (pRBCs) in brain capillaries is a specific feature of ECM that is not observed during mild murine malaria infections. Critically, we show that individual pRBCs appear to occlude murine brain capillaries during ECM. As pRBC-mediated congestion of brain microvessels is a hallmark of HCM, this suggests that the impact of parasite accumulation on cerebral blood flow may ultimately be similar in mice and humans during ECM and HCM, respectively. Additionally, we demonstrate that cerebrovascular CD8+ T-cells appear to co-localise with accumulated pRBCs, an event that corresponds with development of widespread vascular leakage. As in HCM, we show that vascular leakage is not dependent on extensive vascular destruction. Instead, we show that vascular leakage is associated with alterations in transcellular and paracellular transport mechanisms. Finally, as in HCM, we observed axonal injury and demyelination in ECM adjacent to diverse vasculopathies. Collectively, our data therefore shows that, despite very different presentation, and apparently distinct mechanisms, of parasite accumulation, there appear to be a number of comparable features of cerebral pathology in mice and in humans during ECM and HCM, respectively. Thus, when used appropriately, the ECM model may be useful for studying specific pathological features of HCM.