Hyperbaric oxygen prevents early death caused by experimental cerebral malaria

Role of TAM Receptors in Antimalarial Humoral Immune Response

Immune response against malaria and the clearance of Plasmodium parasite relies on germinal-center-derived B cell responses that are temporally and histologically layered. Despite a well-orchestrated germinal center response, anti-Plasmodium immune response seldom offers sterilizing immunity. Recent studies report that certain pathophysiological features of malaria such as extensive hemolysis, hypoxia as well as the extrafollicular accumulation of short-lived plasmablasts may contribute to this suboptimal immune response. In this review, we summarize some of those studies and attempt to connect certain host intrinsic features in response to the malarial disease and the resultant gaps in the immune response.

Hyperbaric oxygen augments susceptibility to C. difficile infection by impairing gut microbiota ability to stimulate the HIF-1α-IL-22 axis in ILC3

Hyperbaric oxygen (HBO) therapy is a well-established method for improving tissue oxygenation and is typically used for the treatment of various inflammatory conditions, including infectious diseases. However, its effect on the intestinal mucosa, a microenvironment known to be physiologically hypoxic, remains unclear. Here, we demonstrated that daily treatment with hyperbaric oxygen affects gut microbiome composition, worsening antibiotic-induced dysbiosis. Accordingly, HBO-treated mice were more susceptible to Clostridioides difficile infection (CDI), an enteric pathogen highly associated with antibiotic-induced colitis. These observations were closely linked with a decline in the level of microbiota-derived short-chain fatty acids (SCFAs). Butyrate, a SCFA produced primarily by anaerobic microbial species, mitigated HBO-induced susceptibility to CDI and increased epithelial barrier integrity by improving group 3 innate lymphoid cell (ILC3) responses. Mice displaying tissue-specific deletion of HIF-1 in RORγt-positive cells exhibited no protective effect of butyrate during CDI. In contrast, the reinforcement of HIF-1 signaling in RORγt-positive cells through the conditional deletion of VHL mitigated disease outcome, even after HBO therapy. Taken together, we conclude that HBO induces intestinal dysbiosis and impairs the production of SCFAs affecting the HIF-1α-IL-22 axis in ILC3 and worsening the response of mice to subsequent C. difficile infection.

Inhibition of γδ T Cells Alleviates Blood-Brain Barrier in Cardiac Arrest and Cardiopulmonary Resuscitation in Mice

Ischemia/reperfusion (I/R) injury is the leading cause of death following cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). γδT cells are suggested to aggravate blood-brain barrier (BBB) injury in various pathological processes. We herein investigate the effects of γδT cells inhibitor (UC7-13D5) against I/R injury post-CA/CPR. C57BL/6 mice were subjected to CA through injection of KCL (70 μL of 0.5 mol/L) and cessation of mechanical ventilation followed by CPR. Flow cytometry was performed to measure the proportion of CD3-positive cells after intraperitoneal injection of 200 μg UC7-13D5 at 6 h, 24 h, and 48 h post-resuscitation into mice. Neurological scores and modified neurological severity scores were assessed to examine neurological functions. Brain edema was estimated via brain water content measurements. Immunohistochemistry of caspase-3 and immunofluorescence staining of claudin-1, ZO-1 and CD31 were performed to detect neuronal apoptosis, BBB integrity and angiogenesis. Microvascular morphology in the cortical area was assessed via H&E staining. Oxidative stress was determined by measuring malondialdehyde, myeloperoxidase, xanthine oxidase, superoxide dismutase, and glutathione peroxidase activities. Western blotting was performed to measure the protein levels of Nuclear factor-E2-related factor 2 (Nrf2) and Heme oxygenase-1 (HO-1). UC7-13D5 effectively depleted γδT cells. Inhibition of γδT cells improved neurological deficits and reduced brain edema post-CA/CPR. γδT cells depletion attenuated neuronal apoptosis, BBB disruption and oxidative stress and promoted angiogenesis following CA/CPR. Inhibition of γδT cells facilitated the activation of the Nrf2/HO-1 pathway in CA/CPR-induced mice. Inhibition of γδT cells alleviates neurological deficits and cerebral edema in mice with CA/CPR by inhibiting neuronal apoptosis, BBB disruption and oxidative stress, and promoting angiogenesis via activation of the Nrf2/HO-1 pathway.

Expression of Aquaporin-1 and Aquaporin-5 in a Rat Model of High-Altitude Pulmonary Edema and the Effect of Hyperbaric Oxygen Exposure

Objective:

To investigate the therapeutic roles of hyperbaric oxygen exposure on high-altitude pulmonary edema and to determine whether aquaporin-1 and aquaporin-5 were involved in the pathogenesis of HAPE in rats.

Methods:

Rats were divided into 5 groups: The control group, the HAPE group (HAPE model), the HBO group (hyperbaric oxygen exposure), the NBO group (normobaric oxygen exposure), and the NA group (normal air exposure). Western blot and real-time PCR were used to analyze the pulmonary expressions of AQP1 and AQP5. The wet-to-dry (W/D) weight ratio and the morphology of the lung were also examined.

Results:

The lung W/D weight ratio in the HAPE group was increased compared with the control group. The injury score in the HBO group was noticeably lower than that in the control group. The mRNA and proteins expressions of AQP1 and AQP5 were significantly downregulated in the HAPE group.

Conclusions:

Oxygen exposure alleviated high-altitude hypobaric hypoxia-induced lung injury in rats. Additionally, HBO therapy had significant advantage on interstitial HAPE.

Inhibition of hypoxia-associated response and kynurenine production in response to hyperbaric oxygen as mechanisms involved in protection against experimental cerebral malaria

Cerebral malaria (CM) is a multifactorial syndrome involving an exacerbated proinflammatory status, endothelial cell activation, coagulopathy, hypoxia, and accumulation of leukocytes and parasites in the brain microvasculature. Despite significant improvements in malaria control, 15% of mortality is still observed in CM cases, and 25% of survivors develop neurologic sequelae for life-even after appropriate antimalarial therapy. A treatment that ameliorates CM clinical signs, resulting in complete healing, is urgently needed. Previously, we showed a hyperbaric oxygen (HBO)-protective effect against experimental CM. Here, we provide molecular evidence that HBO targets brain endothelial cells by decreasing their activation and inhibits parasite and leukocyte accumulation, thus improving cerebral microcirculatory blood flow. HBO treatment increased the expression of aryl hydrocarbon receptor over hypoxia-inducible factor 1-α (HIF-1α), an oxygen-sensitive cytosolic receptor, along with decreased indoleamine 2,3-dioxygenase 1 expression and kynurenine levels. Moreover, ablation of HIF-1α expression in endothelial cells in mice conferred protection against CM and improved survival. We propose that HBO should be pursued as an adjunctive therapy in CM patients to prolong survival and diminish deleterious proinflammatory reaction. Furthermore, our data support the use of HBO in therapeutic strategies to improve outcomes of non-CM disorders affecting the brain.-Bastos, M. F., Kayano, A. C. A. V., Silva-Filho, J. L., Dos-Santos, J. C. K., Judice, C., Blanco, Y. C., Shryock, N., Sercundes, M. K., Ortolan, L. S., Francelin, C., Leite, J. A., Oliveira, R., Elias, R. M., Câmara, N. O. S., Lopes, S. C. P., Albrecht, L., Farias, A. S., Vicente, C. P., Werneck, C. C., Giorgio, S., Verinaud, L., Epiphanio, S., Marinho, C. R. F., Lalwani, P., Amino, R., Aliberti, J., Costa, F. T. M. Inhibition of hypoxia-associated response and kynurenine production in response to hyperbaric oxygen as mechanisms involved in protection against experimental cerebral malaria.

Atypical activation of dendritic cells by Plasmodium falciparum

Dendritic cells (DCs) are activated by pathogens to initiate and shape immune responses. We found that the activation of DCs by Plasmodium falciparum, the main causative agent of human malaria, induces a highly unusual phenotype by which DCs up-regulate costimulatory molecules and secretion of chemokines, but not of cytokines typical of inflammatory responses (IL-1β, IL-6, IL-10, TNF). Similar results were obtained with DCs obtained from malaria-naïve US donors and malaria-experienced donors from Mali. Contact-dependent cross-talk between the main DC subsets, plasmacytoid and myeloid DCs (mDCs) was necessary for increased chemokine and IFN-α secretion in response to the parasite. Despite the absence of inflammatory cytokine secretion, mDCs incubated with P. falciparum-infected erythrocytes activated antigen-specific naïve CD4⁺ T cells to proliferate and secrete Th1-like cytokines. This unexpected response of human mDCs to P. falciparum exhibited a transcriptional program distinct from a classical LPS response, pointing to unique P. falciparum-induced activation pathways that may explain the uncharacteristic immune response to malaria.

Pathophysiological Mechanisms in Gaseous Therapies for Severe Malaria

Over 200 million people worldwide suffer from malaria every year, a disease that causes 584,000 deaths annually. In recent years, significant improvements have been achieved on the treatment of severe malaria, with intravenous artesunate proving superior to quinine. However, mortality remains high, at 8% in children and 15% in adults in clinical trials, and even worse in the case of cerebral malaria (18% and 30%, respectively). Moreover, some individuals who do not succumb to severe malaria present long-term cognitive deficits. These observations indicate that strategies focused only on parasite killing fail to prevent neurological complications and deaths associated with severe malaria, possibly because clinical complications are associated in part with a cerebrovascular dysfunction. Consequently, different adjunctive therapies aimed at modulating malaria pathophysiological processes are currently being tested. However, none of these therapies has shown unequivocal evidence in improving patient clinical status. Recently, key studies have shown that gaseous therapies based mainly on nitric oxide (NO), carbon monoxide (CO), and hyperbaric (pressurized) oxygen (HBO) alter vascular endothelium dysfunction and modulate the host immune response to infection. Considering gaseous administration as a promising adjunctive treatment against severe malaria cases, we review here the pathophysiological mechanisms and the immunological aspects of such therapies.

Early IFN-γ production together with decreased expression of TLR3 and TLR9 characterizes EAE development conditional on the presence of myelin

Experimental autoimmune encephalomyelitis (EAE) is a model for the study of multiple sclerosis, which is an inflammatory and demyelinating disease of the central nervous system (CNS). Despite increased efforts to elucidate the function of toll-like receptors (TLRs) in autoimmune diseases of the CNS, the relative contribution of other factors, including the immunomodulatory properties of TLR signaling, role of the innate response and the presence or absence of myelin peptides remain unclear. The aim was to evaluate TLR expression in the CNS during EAE development by investigating the expression of TLRs in the initial phase of EAE and establishing correlations with the modulation of inflammatory factors. Mice were subcutaneously immunized at the tail base with 100 μg of myelin oligodendrocyte glycoprotein peptide (MOG35-55), emulsified in complete Freund's adjuvant (CFA) supplemented with 400 μg of attenuated Mycobacterium tuberculosis H37RA. Pertussis toxin (300 ng per animal) was intraperitoneally injected on the day of immunization and 48 h later. Another group (MOG(-)) received an equal emulsion of CFA and M. tuberculosis, without MOG35-55, and the same protocol of Pertussis toxin. The immunized mice presented signs of disease with increased IFN-γ production and presence of NK cells on Day 2 postimmunization and reduced the expression of TLR-3 and TLR-9. In the spinal cord, CCL5 and CCL20 were higher in EAE. This study establishes a correlation between TLR-3 and TLR-9 expression with the development of EAE. In addition, evidence of a role for the myelin peptide in targeting the innate inflammatory response to the CNS is presented.

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

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

Hypoxia promotes liver-stage malaria infection in primary human hepatocytes in vitro

Homeostasis of mammalian cell function strictly depends on balancing oxygen exposure to maintain energy metabolism without producing excessive reactive oxygen species. In vivo, cells in different tissues are exposed to a wide range of oxygen concentrations, and yet in vitro models almost exclusively expose cultured cells to higher, atmospheric oxygen levels. Existing models of liver-stage malaria that utilize primary human hepatocytes typically exhibit low in vitro infection efficiencies, possibly due to missing microenvironmental support signals. One cue that could influence the infection capacity of cultured human hepatocytes is the dissolved oxygen concentration. We developed a microscale human liver platform comprised of precisely patterned primary human hepatocytes and nonparenchymal cells to model liver-stage malaria, but the oxygen concentrations are typically higher in the in vitro liver platform than anywhere along the hepatic sinusoid. Indeed, we observed that liver-stage Plasmodium parasite development in vivo correlates with hepatic sinusoidal oxygen gradients. Therefore, we hypothesized that in vitro liver-stage malaria infection efficiencies might improve under hypoxia. Using the infection of micropatterned co-cultures with Plasmodium berghei, Plasmodium yoelii or Plasmodium falciparum as a model, we observed that ambient hypoxia resulted in increased survival of exo-erythrocytic forms (EEFs) in hepatocytes and improved parasite development in a subset of surviving EEFs, based on EEF size. Further, the effective cell surface oxygen tensions (pO₂) experienced by the hepatocytes, as predicted by a mathematical model, were systematically perturbed by varying culture parameters such as hepatocyte density and height of the medium, uncovering an optimal cell surface pO₂ to maximize the number of mature EEFs. Initial mechanistic experiments revealed that treatment of primary human hepatocytes with the hypoxia mimetic, cobalt(II) chloride, as well as a HIF-1α activator, dimethyloxalylglycine, also enhance P. berghei infection, suggesting that the effect of hypoxia on infection is mediated in part by host-dependent HIF-1α mechanisms.

Cerebral tissue oxygenation impairment during experimental cerebral malaria

Ischemia and hypoxia have been implicated in cerebral malaria (CM) pathogenesis, although direct measurements of hypoxia have not been conducted. C57BL/6 mice infected with Plasmodium berghei ANKA (PbA) develop a neurological syndrome known as experimental cerebral malaria (ECM), whereas BALB/c mice are resistant to ECM. In this study, intravital microscopy methods were used to quantify hemodynamic changes, vascular/tissue oxygen (O₂) tension (PO₂), and perivascular pH in vivo in ECM and non-ECM models, employing a closed cranial window model. ECM mice on day 6 of infection showed marked decreases in pial blood flow, vascular (arteriolar, venular), and perivascular PO₂, perivascular pH, and systemic hemoglobin levels. Changes were more dramatic in mice with late-stage ECM compared with mice with early-stage ECM. These changes led to drastic decreases in O₂ delivery to the brain tissue. In addition, ECM animals required a greater PO₂ gradient to extract the same amount of O₂ compared with non-infected animals, as the pial tissues extract O₂ from the steepest portion of the blood O₂ equilibrium curve. ECM animals also showed increased leukocyte adherence in postcapillary venules, and the intensity of adhesion was inversely correlated with blood flow and O₂ extraction. PbA-infected BALB/c mice displayed no neurological signs on day 6 and while they did show changes similar to those observed in C57BL/6 mice (decreased pial blood flow, vascular/tissue PO₂, perivascular pH, hemoglobin levels), non-ECM animals preserved superior perfusion and oxygenation compared with ECM animals at similar anemia and parasitemia levels, resulting in better O₂ delivery and O₂ extraction by the brain tissue. In conclusion, direct quantitative assessment of pial hemodynamics and oxygenation in vivo revealed that ECM is associated with severe progressive brain tissue hypoxia and acidosis.

The role of platelet-activating factor receptor (PAFR) in lung pathology during experimental malaria

Malaria-associated lung pathology has been a neglected area in the study of malaria complications. Platelet-activating factor (PAF) is an inflammatory mediator involved in lung inflammation. Using mice lacking the PAF receptor (PAFR(-/-)) we investigated the relevance of signaling through the PAFR for the lung inflammatory process triggered by Plasmodium berghei ANKA (PbA) strain infection. In PAFR(-/-) mice, pulmonary inflammation was markedly reduced as demonstrated by histology, production of certain pro-inflammatory mediators, accumulation of macrophage and CD8+ T cells in the lung parenchyma and the virtual absence of changes in vascular permeability. Therefore, PAFR activation is crucial in the pathogenesis of pulmonary damage associated with PbA infection in C57Bl/6 mice.

Cerebral malaria: we have come a long way

Despite decades of research, cerebral malaria remains one of the most serious complications of Plasmodium infection and is a significant burden in Sub-Saharan Africa, where, despite effective antiparasitic treatment, survivors develop long-term neurological sequelae. Although much remains to be discovered about the pathogenesis of cerebral malaria, The American Journal of Pathology has been seminal in presenting original research from both human and experimental models. These studies have afforded significant insight into the mechanism of cerebral damage in this devastating disease. The present review highlights information gleaned from these studies, especially in terms of their contributions to the understanding of cerebral malaria.

CNS hypoxia is more pronounced in murine cerebral than noncerebral malaria and is reversed by erythropoietin

Cerebral malaria (CM) is associated with high mortality and risk of sequelae, and development of adjunct therapies is hampered by limited knowledge of its pathogenesis. To assess the role of cerebral hypoxia, we used two experimental models of CM, Plasmodium berghei ANKA in CBA and C57BL/6 mice, and two models of malaria without neurologic signs, P. berghei K173 in CBA mice and P. berghei ANKA in BALB/c mice. Hypoxia was demonstrated in brain sections using intravenous pimonidazole and staining with hypoxia-inducible factor-1α-specific antibody. Cytopathic hypoxia was studied using poly (ADP-ribose) polymerase-1 (PARP-1) gene knockout mice. The effect of erythropoietin, an oxygen-sensitive cytokine that mediates protection against CM, on cerebral hypoxia was studied in C57BL/6 mice. Numerous hypoxic foci of neurons and glial cells were observed in mice with CM. Substantially fewer and smaller foci were observed in mice without CM, and hypoxia seemed to be confined to neuronal cell somas. PARP-1-deficient mice were not protected against CM, which argues against a role for cytopathic hypoxia. Erythropoietin therapy reversed the development of CM and substantially reduced the degree of neural hypoxia. These findings demonstrate cerebral hypoxia in malaria, strongly associated with cerebral dysfunction and a possible target for adjunctive therapy.

Oxygen therapy for cerebral malaria

Malaria is an important global health issue, killing nearly one million people worldwide each year. There is a disproportionate disease burden, since 89% of cases are of African origin, and 85% of deaths worldwide occur in children under 5 years of age of age.(1) Cerebral malaria (CM) is the most serious complication of infection. Despite prompt anti-malarial treatment, fatalities remain high - mortality rates while undergoing treatment with Artemisinin or quinine-based therapy reach 15% and 22% respectively.(2) There is, therefore, a need to develop an adjunct therapy to preserve neurological function during the treatment period. Recent experimental research has indicated hyperbaric oxygenation (HBO) to be a rational and effective adjunct therapy.(3) This article examines the current understanding of CM, and the possible benefits provided by HBO therapy.

Regulatory T cell induction during Plasmodium chabaudi infection modifies the clinical course of experimental autoimmune encephalomyelitis

Background

Experimental autoimmune encephalomyelitis (EAE) is used as an animal model for human multiple sclerosis (MS), which is an inflammatory demyelinating autoimmune disease of the central nervous system characterized by activation of Th1 and/or Th17 cells. Human autoimmune diseases can be either exacerbated or suppressed by infectious agents. Recent studies have shown that regulatory T cells play a crucial role in the escape mechanism of Plasmodium spp. both in humans and in experimental models. These cells suppress the Th1 response against the parasite and prevent its elimination. Regulatory T cells have been largely associated with protection or amelioration in several autoimmune diseases, mainly by their capacity to suppress proinflammatory response.

Methodology/Principal Findings

In this study, we verified that CD4⁺CD25⁺ regulatory T cells (T regs) generated during malaria infection (6 days after EAE induction) interfere with the evolution of EAE. We observed a positive correlation between the reduction of EAE clinical symptoms and an increase of parasitemia levels. Suppression of the disease was also accompanied by a decrease in the expression of IL-17 and IFN-γ and increases in the expression of IL-10 and TGF-β1 relative to EAE control mice. The adoptive transfer of CD4⁺CD25⁺ cells from P. chabaudi-infected mice reduced the clinical evolution of EAE, confirming the role of these T regs.

Conclusions/Significance

These data corroborate previous findings showing that infections interfere with the prevalence and evolution of autoimmune diseases by inducing regulatory T cells, which regulate EAE in an apparently non-specific manner.

Global response of Plasmodium falciparum to hyperoxia: a combined transcriptomic and proteomic approach

Background

Over its life cycle, the Plasmodium falciparum parasite is exposed to different environmental conditions, particularly to variations in O₂ pressure. For example, the parasite circulates in human venous blood at 5% O₂ pressure and in arterial blood, particularly in the lungs, at 13% O₂ pressure. Moreover, the parasite is exposed to 21% O₂ levels in the salivary glands of mosquitoes.

Methods

To study the metabolic adaptation of P. falciparum to different oxygen pressures during the intraerythrocytic cycle, a combined approach using transcriptomic and proteomic techniques was undertaken.

Results

Even though hyperoxia lengthens the parasitic cycle, significant transcriptional changes were detected in hyperoxic conditions in the late-ring stage. Using PS 6.0™ software (Ariadne Genomics) for microarray analysis, this study demonstrate up-expression of genes involved in antioxidant systems and down-expression of genes involved in the digestive vacuole metabolism and the glycolysis in favour of mitochondrial respiration. Proteomic analysis revealed increased levels of heat shock proteins, and decreased levels of glycolytic enzymes. Some of this regulation reflected post-transcriptional modifications during the hyperoxia response.

Conclusions

These results seem to indicate that hyperoxia activates antioxidant defence systems in parasites to preserve the integrity of its cellular structures. Moreover, environmental constraints seem to induce an energetic metabolism adaptation of P. falciparum. This study provides a better understanding of the adaptive capabilities of P. falciparum to environmental changes and may lead to the development of novel therapeutic targets.

A rapid murine coma and behavior scale for quantitative assessment of murine cerebral malaria

Background

Cerebral malaria (CM) is a neurological syndrome that includes coma and seizures following malaria parasite infection. The pathophysiology is not fully understood and cannot be accounted for by infection alone: patients still succumb to CM, even if the underlying parasite infection has resolved. To that effect, there is no known adjuvant therapy for CM. Current murine CM (MCM) models do not allow for rapid clinical identification of affected animals following infection. An animal model that more closely mimics the clinical features of human CM would be helpful in elucidating potential mechanisms of disease pathogenesis and evaluating new adjuvant therapies.

Methodology/Principal Findings

A quantitative, rapid murine coma and behavior scale (RMCBS) comprised of 10 parameters was developed to assess MCM manifested in C57BL/6 mice infected with Plasmodium berghei ANKA (PbA). Using this method a single mouse can be completely assessed within 3 minutes. The RMCBS enables the operator to follow the evolution of the clinical syndrome, validated here by correlations with intracerebral hemorrhages. It provides a tool by which subjects can be identified as symptomatic prior to the initiation of trial treatment.

Conclusions/Significance

Since the RMCBS enables an operator to rapidly follow the course of disease, label a subject as affected or not, and correlate the level of illness with neuropathologic injury, it can ultimately be used to guide the initiation of treatment after the onset of cerebral disease (thus emulating the situation in the field). The RMCBS is a tool by which an adjuvant therapy can be objectively assessed.

Perforin: structure, function, and role in human immunopathology

The secretory granule-mediated cell death pathway is the key mechanism for elimination of virus-infected and transformed target cells by cytotoxic lymphocytes. The formation of the immunological synapse between an effector and a target cell leads to exocytic trafficking of the secretory granules and the release of their contents, which include pro-apoptotic serine proteases, granzymes, and pore-forming perforin into the synapse. There, perforin polymerizes and forms a transmembrane pore that allows the delivery of granzymes into the cytosol, where they initiate various apoptotic death pathways. Unlike relatively redundant individual granzymes, functional perforin is absolutely essential for cytotoxic lymphocyte function and immune regulation in the host. Nevertheless, perforin is still the least studied and understood cytotoxic molecule in the immune system. In this review, we discuss the current state of affairs in the perforin field: the protein's structure and function as well as its role in immune-mediated diseases.

Possible role of heme oxygenase-1 and prostaglandins in the pathogenesis of cerebral malaria: heme oxygenase-1 induction by prostaglandin D(2) and metabolite by a human astrocyte cell line

Astrocytes are the most abundant cells in the central nervous system that play roles in maintaining the blood-brain-barrier and in neural injury, including cerebral malaria, a severe complication of Plasmodium falciparum infection. Prostaglandin (PG) D(2) is abundantly produced in the brain and regulates the sleep response. Moreover, PGD(2) is a potential factor derived from P. falciparum within erythrocytes. Heme oxygenase-1 (HO-1) is catalyzing enzyme in heme breakdown process to release iron, carbon monoxide, and biliverdin/bilirubin, and may influence iron supply to the P. falciparum parasites. Here, we showed that treatment of a human astrocyte cell line, CCF-STTG1, with PGD(2) significantly increased the expression levels of HO-1 mRNA by RT-PCR. Western blot analysis showed that PGD(2) treatment increased the level of HO-1 protein, in a dose- and time-dependent manner. Thus, PGD(2) may be involved in the pathogenesis of cerebral malaria by inducing HO-1 expression in malaria patients.

Murine cerebral malaria is associated with a vasospasm-like microcirculatory dysfunction, and survival upon rescue treatment is markedly increased by nimodipine

Brain hemodynamics in cerebral malaria (CM) is poorly understood, with apparently conflicting data showing microcirculatory hypoperfusion and normal or even increased blood flow in large arteries. Using intravital microscopy to assess the pial microvasculature through a closed cranial window in the murine model of CM by Plasmodium berghei ANKA, we show that murine CM is associated with marked decreases (mean: 60%) of pial arteriolar blood flow attributable to vasoconstriction and decreased blood velocity. Leukocyte sequestration further decreased perfusion by narrowing luminal diameters in the affected vessels and blocking capillaries. Remarkably, vascular collapse at various degrees was observed in 44% of mice with CM, which also presented more severe vasoconstriction. Coadministration of artemether and nimodipine, a calcium channel blocker used to treat postsubarachnoid hemorrhage vasospasm, to mice presenting CM markedly increased survival compared with artemether plus vehicle only. Administration of nimodipine induced vasodilation and increased pial blood flow. We conclude that vasoconstriction and vascular collapse play a role in murine CM pathogenesis and nimodipine holds potential as adjunctive therapy for CM.

Advances in the management of cerebral malaria in adults

PURPOSE OF REVIEW

Cerebral malaria continues to be a substantial cause of death and disability worldwide. Although many studies deal with cerebral malaria in children, only very few pertain to adults. Presence of multiorgan failure makes the prognosis poor. Various mechanisms in the pathogenesis of cerebral malaria and the role of adjuvant therapy will be discussed.

RECENT FINDINGS

Artemisinin-based therapies have improved antiparasitic treatment, but in-hospital mortality still remains high, as do neurological sequelae. Several recent studies have given new insights in the pathophysiology of cerebral malaria particularly the role of immune mechanisms in disease progression. Recent findings have identified several potential candidates for adjuvant neuroprotective treatment. Recombinant human erythropoietin has shown beneficial effect in experimental cerebral malaria and will soon enter into large clinical trials.

SUMMARY

Advances have been made in terms of antiparasitic treatment, but the identification of a well tolerated and effective adjuvant treatment to increase survival and reduce brain damage is still pending. The search for new approaches is a major challenge, not least of which is that mechanisms of malaria pathogenesis remain incompletely understood. The paper reviews newer information on pathogenesis and strategies in the management of cerebral malaria in adults.