Characterization of cerebral malaria in the outbred Swiss Webster mouse infected by Plasmodium berghei ANKA

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

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

Investigation of Plasma-Derived Lipidome Profiles in Experimental Cerebral Malaria in a Mouse Model Study

Cerebral malaria (CM), a fatal complication of Plasmodium infection that affects children, especially under the age of five, in sub-Saharan Africa and adults in South-East Asia, results from incompletely understood pathogenetic mechanisms. Increased release of circulating miRNA, proteins, lipids and extracellular vesicles has been found in CM patients and experimental mouse models. We compared lipid profiles derived from the plasma of CBA mice infected with Plasmodium berghei ANKA (PbA), which causes CM, to those from Plasmodium yoelii (Py), which does not. We previously showed that platelet-free plasma (18k fractions enriched from plasma) contains a high number of extracellular vesicles (EVs). Here, we found that this fraction produced at the time of CM differed dramatically from those of non-CM mice, despite identical levels of parasitaemia. Using high-resolution liquid chromatography-mass spectrometry (LCMS), we identified over 300 lipid species within 12 lipid classes. We identified 45 and 75 lipid species, mostly including glycerolipids and phospholipids, with significantly altered concentrations in PbA-infected mice compared to Py-infected and uninfected mice, respectively. Total lysophosphatidylethanolamine (LPE) levels were significantly lower in PbA infection compared to Py infection and controls. These results suggest that experimental CM could be characterised by specific changes in the lipid composition of the 18k fraction containing circulating EVs and can be considered an appropriate model to study the role of lipids in the pathophysiology of CM.

Methylene Blue-Based Combination Therapy with Amodiaquine Prevents Severe Malaria in an Experimental Rodent Model

Untreated malaria can progress rapidly to severe forms (<24 h). Moreover, resistance to antimalarial drugs is a threat to global efforts to protect people from malaria. Given this, it is clear that new chemotherapy must be developed. We contribute new data about using methylene blue (MB) to cure malaria and cerebral malaria in a combined therapy with common antimalarial drugs, including mefloquine (MQ) and amodiaquine (AQ). A C57BL6/J mouse model was used in an experimental cerebral malaria model. Mice were infected with Plasmodium berghei ANKA on Day 0 (D0) and the treatment started on D3 (nearly 1% parasitaemia) with AQ, MQ or MB alone or in combination with AQ or MQ. AQ, MQ and MB alone were unable to prevent cerebral malaria as part of a late chemotherapy. MB-based combination therapies were efficient even if treatment began at a late stage. We found a significant difference in survival rate (p < 0.0001) between MBAQ and the untreated group, but also with the AQ (p = 0.0024) and MB groups (p < 0.0001). All the infected mice treated with MB in combination with AQ were protected from cerebral malaria. Partial protection was demonstrated with MB associated with MQ. In this group, a significant difference was found between MBMQ and the untreated group (p < 0.0001), MQ (p = 0.0079) and MB (p = 0.0039). MB associated with AQ would be a good candidate for preventing cerebral malaria.

Malaria Related Neurocognitive Deficits and Behavioral Alterations

Typical of tropical and subtropical regions, malaria is caused by protozoa of the genus Plasmodium and is, still today, despite all efforts and advances in controlling the disease, a major issue of public health. Its clinical course can present either as the classic episodes of fever, sweating, chills and headache or as nonspecific symptoms of acute febrile syndromes and may evolve to severe forms. Survivors of cerebral malaria, the most severe and lethal complication of the disease, might develop neurological, cognitive and behavioral sequelae. This overview discusses the neurocognitive deficits and behavioral alterations resulting from human naturally acquired infections and murine experimental models of malaria. We highlighted recent reports of cognitive and behavioral sequelae of non-severe malaria, the most prevalent clinical form of the disease worldwide. These sequelae have gained more attention in recent years and therapies for them are required and demand advances in the understanding of neuropathogenesis. Recent studies using experimental murine models point to immunomodulation as a potential approach to prevent or revert neurocognitive sequelae of malaria.

Whole blood transfusion improves vascular integrity and increases survival in artemether-treated experimental cerebral malaria

Pathological features observed in both human and experimental cerebral malaria (ECM) are endothelial dysfunction and changes in blood components. Blood transfusion has been routinely used in patients with severe malarial anemia and can also benefit comatose and acidotic malaria patients. In the present study Plasmodium berghei-infected mice were transfused intraperitoneally with 200 μL of whole blood along with 20 mg/kg of artemether. ECM mice showed severe thrombocytopenia and decreases in hematocrit. Artemether treatment markedly aggravated anemia within 24 h. Whole blood administration significantly prevented further drop in hematocrit and partially restored the platelet count. Increased levels of plasma angiopoietin-2 (Ang-2) remained high 24 h after artemether treatment but returned to normal levels 24 h after blood transfusion, indicating reversal to quiescence. Ang-1 was depleted in ECM mice and levels were not restored by any treatment. Blood transfusion prevented the aggravation of the breakdown of blood brain barrier after artemether treatment and decreased spleen congestion without affecting splenic lymphocyte populations. Critically, blood transfusion resulted in markedly improved survival of mice with ECM (75.9% compared to 50.9% receiving artemether only). These findings indicate that whole blood transfusion can be an effective adjuvant therapy for cerebral malaria.

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.

Dexamethasone increased the survival rate in Plasmodium berghei-infected mice

The present study aimed to evaluate the effects of dexamethasone on the redox status, parasitemia evolution, and survival rate of Plasmodium berghei-infected mice. Two-hundred and twenty-five mice were infected with Plasmodium berghei and subjected to stimulation or inhibition of NO synthesis. The stimulation of NO synthesis was performed through the administration of L-arginine, while its inhibition was made by the administration of dexamethasone. Inducible NO synthase (iNOS) inhibition by dexamethasone promoted an increase in the survival rate of P. berghei-infected mice, and the data suggested the participation of oxidative stress in the brain as a result of plasmodial infection, as well as the inhibition of brain NO synthesis, which promoted the survival rate of almost 90% of the animals until the 15th day of infection, with possible direct interference of ischemia and reperfusion syndrome, as seen by increased levels of uric acid. Inhibition of brain iNOS by dexamethasone caused a decrease in parasitemia and increased the survival rate of infected animals, suggesting that NO synthesis may stimulate a series of compensatory redox effects that, if overstimulated, may be responsible for the onset of severe forms of malaria.

Melatonin Prevents Brain Damage and Neurocognitive Impairment Induced by Plasmodium Berghei ANKA Infection in Murine Model of Cerebral Malaria

Cerebral malaria is characterized by permanent cognitive impairments in Plasmodium-infected children. Antimalarial therapies show little effectiveness to avoid neurological deficits and brain tissue alterations elicited by severe malaria. Melatonin is a well-recognized endogenous hormone involved in the control of brain functions and maintenance of blood–brain barrier integrity. The current study has evaluated the effect of melatonin on the histological alterations, blood–brain barrier leakage, and neurocognitive impairments in mice developing cerebral malaria. Swiss mice infected with Plasmodium berghei ANKA strain was used as cerebral malaria model. Melatonin treatment (5 and 10 mg/kg) was performed for four consecutive days after the infection, and data have shown an increased survival rate in infected mice treated with melatonin. It was also observed that melatonin treatment blocked brain edema and prevented the breakdown of blood–brain barrier induced by the Plasmodium infection. Furthermore, hematoxylin and eosin staining revealed that melatonin mitigates the histological alterations in Plasmodium-infected animals. Melatonin was also able to prevent motor and cognitive impairments in infected mice. Taken together, these results show for the first time that melatonin treatment prevents histological brain damages and neurocognitive alterations induced by cerebral malaria.

Association of cerebral malaria and TNF-α levels: a systematic review

Background

Cerebral malaria is the most severe form of infection with Plasmodium falciparum characterized by a highly inflammatory response. This systematic review aimed to investigate the association between TNF-α levels and cerebral malaria.

Methods

This review followed the Preferred Reporting of Systematic Review and Meta-analyses (PRISMA) guidelines. The search was performed at PubMed, LILACS, Scopus, Web of Science, The Cochrane Library, OpenGrey and Google Scholar. We have included studies of P. falciparum-infected humans with or without cerebral malaria and TNF-α dosage level. All studies were evaluated using a risk of bias tool and the GRADE approach.

Results

Our results have identified 2338 studies, and 8 articles were eligible according to this systematic review inclusion criteria. Among the eight articles, five have evaluated TNF- α plasma dosage, while two have evaluated at the blood and one at the brain (post-Morten). Among them, only five studies showed higher TNF-α levels in the cerebral malaria group compared to the severe malaria group. Methodological problems were identified regarding sample size, randomization and blindness, but no risk of bias was detected.

Conclusion

Although the results suggested that that TNF-α level is associated with cerebral malaria, the evidence is inconsistent and imprecise. More observational studies evaluating the average TNF-alpha are needed.

Infectivity and Screening of Anti-piperaquine Genes in Mice Infected with Piperaquine-Sensitive and Piperaquine-Resistant Plasmodium berghei

BACKGROUND

Piperaquine (PQ) is one of the major components of artemisinin-based combination therapy for malaria. However, the mechanism of PQ resistance has remained unclear.

METHODS

In this study, we infected mice with PQ-resistant Plasmodium berghei ANKA strain line (PbPQR) or PQ-sensitive P. berghei ANKA strain line (PbPQS) and their survival rates, parasitemia, and spleen sizes were compared. In addition, we constructed genomic DNA subtractive library of spleens from the infected mice, and screened the potential PQ-resistant related genes from genomic DNA of PbPQR line using the representational difference analysis (RDA) method. Clones of the subtractive library were screened by PCR, and related genes were sequenced and analyzed using BLAST software of NCBI.

RESULTS

Compared to PbPQS-infected mice, PbPQR-infected mice survived significantly longer, and had significantly lowered parasitemia rate and significantly increased splenomegaly. Among the total of 502 clones picked, 494 were sequenced and 96 unique PCR fragments were obtained; in which 24 DNA fragments were homologous to chromosomes related to immune function of mice. ORF Finder blasting showed that at the protein level, 26 encoded proteins were homologous to 18 hypothetical PbANKA proteins and 13 encoded proteins were homologous to "ferlin-like protein" family of PbANKA. In addition, there were more immune-related DNA molecules, ubiquitous PbANKA homology at the ORF fragment level, and enriched ferlin-like protein families identified from PbPQR-infected mice than those from PbPQS-infected mice.

CONCLUSION

These findings suggest that PbPQR may induce stronger protective immune response than that of PbPQS in infected mice.

Maternal and fetal outcome of pregnancy in Swiss mice infected with Plasmodium berghei ANKAGFP

Malaria in pregnant women is associated with risk of maternal and perinatal morbidity and mortality, and there are few antimalarial drugs considered safe to treat them, so it is necessary to develop safer antimalarial medicines. The goal of this study was to develop an animal model for human malaria during pregnancy by characterizing the maternal and fetal outcomes in malaria infected Swiss mice. For that, in the present study, we evaluated the outcome of pregnancy in Swiss mice infected with Plasmodium berghei ANKA^GFP. We observed a reduction of fetal body weight and signs of skeletal ossification retardation in the offspring of mice infected on GD 12. The group of mice infected with malaria presented premature deliveries and histopathology changes consistent with placental malaria. Our study suggests that Swiss Webster mice infected with P. berghei ANKA^GFP on GD 12 might be a valuable model to investigate the safety and the efficacy of new antimalarial drugs indicated to pregnant women.

Targeting the Hexosamine Biosynthetic Pathway Prevents Plasmodium Developmental Cycle and Disease Pathology in Vertebrate Host

Cerebral malaria (CM) is a clinical syndrome involving irreversible and lethal signs of brain injury associated to infection by parasites of the genus Plasmodium. The pathogenesis of CM derives from infection-induced proinflammatory cytokines associated with cytoadherence of parasitized red blood cells to brain microvasculature. Glycoconjugates are very abundant in the surface of Plasmodium spp., and are critical mediators of parasite virulence in host–pathogen interactions. Herein, we show that 6-Diazo-5-oxo-L-norleucine (DON) therapeutically used for blocking hexosamine biosynthetic pathway leads to recovery in experimental murine cerebral malaria. DON-induced protection was associated with decreased parasitism, which severely reduced Plasmodium transmission to mosquitoes. These findings point to a potential use of DON in combination therapies against malaria.

Reversal of cerebrovascular constriction in experimental cerebral malaria by L-arginine

Vascular dysfunction associated with low nitric oxide (NO) biavailability and low plasma L-arginine levels is observed in both human and experimental cerebral malaria (ECM). In ECM, cerebrovascular constriction results in decreased pial blood flow and hypoxia, and administration of NO donors reverses constriction and increases survival. Supplementation of L-arginine, the substrate for NO synthesis by NO synthases, has been considered as a strategy to improve vascular health and act as adjunctive therapy in human severe malaria. We investigated the effect of L-arginine supplementation on pial vascular tonus of mice with ECM after direct superfusion on the brain surface or systemic delivery. Pial arteriolar diameters of Plasmodium berghei-infected mice with implanted cranial windows were measured using intravital microscopy methods, before and after L-arginine administration. Systemic delivery of L-arginine was performed intravenously, at 10, 50, 100 and 200 mg/kg, as bolus injection or slowly through osmotic pumps, combined or not with artesunate. Direct superfusion of L-arginine (10^-7M, 10^-5M and 10^-3M) on the brain surface of mice with ECM resulted in immediate, consistent and dose-dependent dilation of pial arterioles. ECM mice showed marked cerebrovascular constriction that progressively worsened over a 24 h-period after subcutaneous saline bolus administration. L-arginine administration prevented the worsening in pial constriction at all the doses tested, and at 50 mg/kg and 100 mg/kg it induced temporary reversal of vasoconstriction. Slow, continuous delivery of L-arginine by osmotic pumps, or combined bolus administration of artesunate with L-arginine, also prevented worsening of pial constriction and resulted in improved survival of mice with ECM. L-arginine ameliorates pial vasoconstriction in mice with ECM.

Pathogenesis of Plasmodium berghei ANKA infection in the gerbil (Meriones unguiculatus) as an experimental model for severe malaria

Background: As the quest to eradicate malaria continues, there remains a need to gain further understanding of the disease, particularly with regard to pathogenesis. This is facilitated, apart from in vitro and clinical studies, mainly via in vivo mouse model studies. However, there are few studies that have used gerbils (Meriones unguiculatus) as animal models. Thus, this study is aimed at characterizing the effects of Plasmodium berghei ANKA (PbA) infection in gerbils, as well as the underlying pathogenesis. Methods: Gerbils, 5-7 weeks old were infected by PbA via intraperitoneal injection of 1 × 10⁶ (0.2 mL) infected red blood cells. Parasitemia, weight gain/loss, hemoglobin concentration, red blood cell count and body temperature changes in both control and infected groups were monitored over a duration of 13 days. RNA was extracted from the brain, spleen and whole blood to assess the immune response to PbA infection. Organs including the brain, spleen, heart, liver, kidneys and lungs were removed aseptically for histopathology. Results: Gerbils were susceptible to PbA infection, showing significant decreases in the hemoglobin concentration, RBC counts, body weights and body temperature, over the course of the infection. There were no neurological signs observed. Both pro-inflammatory (IFNγ and TNF) and anti-inflammatory (IL-10) cytokines were significantly elevated. Splenomegaly and hepatomegaly were also observed. PbA parasitized RBCs were observed in the organs, using routine light microscopy and in situ hybridization. Conclusion: Gerbils may serve as a good model for severe malaria to further understand its pathogenesis.

Increased Plasmodium falciparum Parasitemia in Non-splenectomized Saimiri sciureus Monkeys Treated with Clodronate Liposomes

A major constraint in the study of Plasmodium falciparum malaria, including vaccine development, lies on the parasite's strict human host specificity and therefore the shortage of animal experimental models able to harbor human plasmodia. The best experimental models are neo-tropical primates of the genus Saimiri and Aotus, but they require splenectomy to reduce innate defenses for achieving high and consistent parasitemias, an important limitation. Clodronate-liposomes (CL) have been successfully used to deplete monocytes/macrophages in several experimental models. We investigated whether a reduction in the numbers of phagocytic cells by CL would improve the development of P. falciparum parasitemia in non-splenectomized Saimiri sciureus monkeys. Depletion of S. sciureus splenocytes after in vitro incubation with CL was quantified using anti-CD14 antibodies and flow cytometry. Non-infected and P. falciparum-infected S. sciureus were injected intravenously twice a week with either CL at either 0.5 or 1 mL (5 mg/mL) or phosphate buffered saline (PBS). Animals were monitored during infection and treated with mefloquine. After treatment and euthanasia, spleen and liver were collected for histological analysis. In vitro CL depleted S. sciureus splenic monocyte/macrophage population in a dose- and time-dependent manner. In vivo, half of P. falciparum-infected S. sciureus treated with CL 0.5 mL, and two-thirds of those treated with CL 1 mL developed high parasitemias requiring mefloquine treatment, whereas all control animals were able to self-control parasitemia without the need for antimalarial treatment. CL-treated infected S. sciureus showed a marked decrease in the degree of splenomegaly despite higher parasitemias, compared to PBS-treated animals. Histological evidence of partial monocyte/macrophage depletion, decreased hemozoin phagocytosis and decreased iron recycling was observed in both the spleen and liver of CL-treated infected S. sciureus. CL is capable of promoting higher parasitemia in P. falciparum-infected S. sciureus, associated with evidence of partial macrophage depletion in the spleen and liver. Macrophage depletion by CL is therefore a practical and viable alternative to surgical splenectomy in this experimental model.

Controlled release of artemisone for the treatment of experimental cerebral malaria

Background

Cerebral malaria (CM) is a leading cause of malarial mortality resulting from infection by Plasmodium falciparum. Treatment commonly involves adjunctive care and injections or transfusion of artemisinins. All artemisinins that are in current use are metabolized to dihydroxyartemisinin (DHA), to which there is already some parasite resistance. We used artemisone, a derivative that does not convert to DHA, has improved pharmacokinetics and anti-plasmodial activity and is also anti-inflammatory (an advantage given the immunopathological nature of CM).

Methods

We examined controlled artemisone release from biodegradable polymers in a mouse CM model. This would improve treatment by exposing the parasites for a longer period to a non-toxic drug concentration, high enough to eliminate the pathogen and prevent CM. The preparations were inserted into mice as prophylaxis, early or late treatment in the disease course.

Results

The most efficient formulation was a rigid polymer, containing 80 mg/kg artemisone, which cured all of the mice when used as early treatment and 60% of the mice when used as a very late treatment (at which stage all control mice would die of CM within 24 h). In those mice that were not completely cured, relapse followed a latent period of more than seven days. Prophylactic treatment four days prior to the infection prevented CM. We also measured the amount of artemisone released from the rigid polymers using a bioassay with cultured P. falciparum. Significant amounts of artemisone were released throughout at least ten days, in line with the in vivo prophylactic results.

Conclusions

Overall, we demonstrate, as a proof-of-concept, a controlled-sustained release system of artemisone for treatment of CM. Mice were cured or if treated at a very late stage of the disease, depicted a delay of a week before death. This delay would enable a considerable time window for exact diagnosis and appropriate additional treatment. Identical methods could be used for other parasites that are sensitive to artemisinins (e.g. Toxoplasma gondii and Neospora caninum).

Endothelin-1 Treatment Induces an Experimental Cerebral Malaria-Like Syndrome in C57BL/6 Mice Infected with Plasmodium berghei NK65

Plasmodium berghei ANKA infection of C57BL/6 mice is a widely used model of experimental cerebral malaria (ECM). By contrast, the nonneurotropic P. berghei NK65 (PbN) causes severe malarial disease in C57BL/6 mice but does not cause ECM. Previous studies suggest that endothelin-1 (ET-1) contributes to the pathogenesis of ECM. In this study, we characterize the role of ET-1 on ECM vascular dysfunction. Mice infected with 10⁶ PbN-parasitized red blood cells were treated with either ET-1 or saline from 2 to 8 days postinfection (dpi). Plasmodium berghei ANKA-infected mice served as the positive control. ET-1-treated PbN-infected mice exhibited neurological signs, hypothermia, and behavioral alterations characteristic of ECM, dying 4 to 8 dpi. Parasitemia was not affected by ET-1 treatment. Saline-treated PbN-infected mice did not display ECM, surviving until 12 dpi. ET-1-treated PbN-infected mice displayed leukocyte adhesion to the vascular endothelia and petechial hemorrhages throughout the brain at 6 dpi. Intravital microscopic images demonstrated significant brain arteriolar vessel constriction, decreased functional capillary density, and increased blood-brain barrier permeability. These alterations were not present in either ET-1-treated uninfected or saline-treated PbN-infected mice. In summary, ET-1 treatment of PbN-infected mice induced an ECM-like syndrome, causing brain vasoconstriction, adherence of activated leukocytes in the cerebral microvasculature, and blood-brain barrier leakage, indicating that ET-1 is involved in the genesis of brain microvascular alterations that are the hallmark of ECM.

Establishment of a murine model of cerebral malaria in KunMing mice infected with Plasmodium berghei ANKA

Malaria remains one of the most devastating diseases. Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection resulting in high mortality and morbidity worldwide. Analysis of precise mechanisms of CM in humans is difficult for ethical reasons and animal models of CM have been employed to study malaria pathogenesis. Here, we describe a new experimental cerebral malaria (ECM) model with Plasmodium berghei ANKA infection in KunMing (KM) mice. KM mice developed ECM after blood-stage or sporozoites infection, and the development of ECM in KM mice has a dose-dependent relationship with sporozoites inoculums. Histopathological findings revealed important features associated with ECM, including accumulation of mononuclear cells and red blood cells in brain microvascular, and brain parenchymal haemorrhages. Blood-brain barrier (BBB) examination showed that BBB disruption was present in infected KM mice when displaying clinical signs of CM. In vivo bioluminescent imaging experiment indicated that parasitized red blood cells accumulated in most vital organs including heart, lung, spleen, kidney, liver and brain. The levels of inflammatory cytokines interferon-gamma, tumour necrosis factor-alpha, interleukin (IL)-17, IL-12, IL-6 and IL-10 were all remarkably increased in KM mice infected with P. berghei ANKA. This study indicates that P. berghei ANKA infection in KM mice can be used as ECM model to extend further research on genetic, pharmacological and vaccine studies of CM.

Early prediction of cerebral malaria by (1)H NMR based metabolomics

BACKGROUND

Cerebral malaria (CM) is a life-threatening disease, caused mainly by Plasmodium falciparum in humans. In adults only 1-2% of P. falciparum-infected hosts transit to the cerebral form of the disease while most exhibit non-cerebral malaria (NCM). The perturbed metabolic pathways of CM and NCM have been reported. Early marker(s) of CM is(are) not known and by the time a patient exhibits the pathological symptoms of CM, the disease has progressed. Murine CM, like the human disease, is difficult to assign to specific animals at early stage and hence the challenge to treat CM at pre-clinical stage of the disease. This is the first report of prediction of CM in mice using a novel strategy based on (1)H nuclear magnetic resonance (NMR)-based metabolomics.

METHODS

Mice were infected with malarial parasites, and serum was collected from all the animals (CM/NCM) before CM symptoms were apparent. The assignment of mice as NCM/CM at an early time point is based on their symptoms at days 8-9 post-infection (pi). The serum samples were subjected to (1)H NMR-based metabolomics. (1)H NMR spectra of the serum samples, collected at various time points (pi) in multiple sets of experiments, were subjected to multivariate analyses.

RESULTS

The results from orthogonal partial least square discriminant analyses (OPLS-DA) suggest that the animals with CM start to diverge out in metabolic profile and were distinct on day 4 pi, although by physical observation they were indistinguishable from the NCM. The metabolites that appeared to contribute to this distinction were serum lipids and lipoproteins, and 14-19% enhancement was observed in mice afflicted with CM. A cut-off of 14% change of total lipoproteins in serum predicts 54-71% CM in different experiments at day 4 pi.

CONCLUSION

This study clearly demonstrates the possibility of differentiating and identifying animals with CM at an early, pre-clinical stage. The strategy, based on metabolite profile of serum, tested with different batches of animals in both the sex and across different times of the year, is found to be robust. This is the first such study of pre-clinical prognosis of CM.

Increased CD11b and Hypoxia-Inducible Factors-1alpha Expressions in the Lung Tissue and Surfactant Protein-D Levels in Serum Are Related with Acute Lung Injury in Severe Malaria of C57BL/6 Mice

BACKGROUND

We aimed to reveal the role of CD11b and hypoxia-inducible factors-1alpha (HIF-1α) expressions on monocytes and alveolar macrophages of lung tissue, and the levels of serum surfactant protein-D (SP-D) in severe malaria-associated acute lung injury (ALI).

METHODS

The C57BL/6 mice were divided into control group, renal malaria group (inoculated with 10⁶Plasmodium berghei ANKA), and cerebral malaria group (inoculated with 10⁷P. berghei ANKA). The expressions of CD11b and HIF-1α in lung tissue were observed by immunohistochemistry, and serum SP-D levels were measured by ELISA. This study was conducted from June 2014 to February 2015 in the Laboratory of Parasitology, Faculty of Medicine, Universitas Brawijaya, Malang.

RESULTS

The CD11b expression on pulmonary tissue of renal and cerebral malaria mice were significantly higher than control mice (P=0.002; P=0.002), as well as the HIF-1α expression on pulmonary tissue (P=0.002; P=0.002). The level of serum SP-D in renal malaria and cerebral malaria mice were significantly higher than control mice (P=0.002; P=0.002). We found a strong correlation between the expression of CD11b and HIF-1α in lung tissue (r=0.937, P=0.000), as well as between CD11b expression and serum SP-D levels (r=0.907, P=0.000) and between HIF-1α expression and serum SP-D levels (r=0.913, P=0.000).

CONCLUSION

Severe malaria-associated ALI increased the expression of CD11b and HIF-1α in the lung tissue and increased serum SP-D levels of C57BL/6 mice significantly.

Indocyanine Green Liposomes for Diagnosis and Therapeutic Monitoring of Cerebral Malaria

Cerebral malaria (CM) is a major cause of death of Plasmodium falciparum infection. Misdiagnosis of CM often leads to treatment delay and mortality. Conventional brain imaging technologies are rarely applicable in endemic areas. Here we address the unmet need for a simple, non-invasive imaging methodology for early diagnosis of CM. This study presents the diagnostic and therapeutic monitoring using liposomes containing the FDA-approved fluorescent dye indocyanine green (ICG) in a CM murine model. Increased emission intensity of liposomal ICG was demonstrated in comparison with free ICG. The Liposomal ICG's emission was greater in the brains of the infected mice compared to naïve mice and drug treated mice (where CM was prevented). Histological analyses suggest that the accumulation of liposomal ICG in the cerebral vasculature is due to extensive uptake mediated by activated phagocytes. Overall, liposomal ICG offers a valuable diagnostic tool and a biomarker for effectiveness of CM treatment, as well as other diseases that involve inflammation and blood vessel occlusion.

Vascular dysfunction as a target for adjuvant therapy in cerebral malaria

Cerebral malaria (CM) is a life-threatening complication of Plasmodium falciparum malaria that continues to be a major global health problem. Brain vascular dysfunction is a main factor underlying the pathogenesis of CM and can be a target for the development of adjuvant therapies for the disease. Vascular occlusion by parasitised red blood cells and vasoconstriction/vascular dysfunction results in impaired cerebral blood flow, ischaemia, hypoxia, acidosis and death. In this review, we discuss the mechanisms of vascular dysfunction in CM and the roles of low nitric oxide bioavailability, high levels of endothelin-1 and dysfunction of the angiopoietin-Tie2 axis. We also discuss the usefulness and relevance of the murine experimental model of CM by Plasmodium berghei ANKA to identify mechanisms of disease and to screen potential therapeutic interventions.

N-acetyl cysteine and mushroom Agaricus sylvaticus supplementation decreased parasitaemia and pulmonary oxidative stress in a mice model of malaria

Background

Malaria infection can cause high oxidative stress, which could lead to the development of severe forms of malaria, such as pulmonary malaria. In recent years, the role of reactive oxygen species in the pathogenesis of the disease has been discussed, as well as the potential benefit of antioxidants supplementation. The aim of this study was to investigate the effects of N-acetyl cysteine (NAC) or mushroom Agaricus sylvaticus supplementation on the pulmonary oxidative changes in an experimental model of malaria caused by Plasmodium berghei strain ANKA.

Methods

Swiss male mice were infected with P. berghei and treated with NAC or AS. Samples of lung tissue and whole blood were collected after one, three, five, seven or ten days of infection for the assessment of thiobarbituric acid reactive substances (TBARS), trolox equivalent antioxidant capacity (TEAC), nitrites and nitrates (NN) and to assess the degree of parasitaemia.

Results

Although parasitaemia increased progressively with the evolution of the disease in all infected groups, there was a significant decrease from the seventh to the tenth day of infection in both antioxidant-supplemented groups. Results showed significant higher levels of TEAC in both supplemented groups, the highest occurring in the group supplemented with A. sylvaticus. In parallel, TBARS showed similar levels among all groups, while levels of NN were higher in animals supplemented with NAC in relation to the positive control groups and A. sylvaticus, whose levels were similar to the negative control group.

Conclusion

Oxidative stress arising from plasmodial infection was attenuated by supplementation of both antioxidants, but A. sylvaticus proved to be more effective and has the potential to become an important tool in the adjuvant therapy of malaria.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0717-0) contains supplementary material, which is available to authorized users.

Interleukin-18 Antagonism Improved Histopathological Conditions of Malaria Infection in Mice

BACKGROUND

Interleukin 18 (IL-18) exerts pleiotropic roles in many inflammatory-related diseases including parasitic infection. Previous studies have demonstrated the promising therapeutic potential of modulating IL-18 bioactivity in various pathological conditions. However, its involvement during malaria infection has yet to be established. In this study, we demonstrated the effect of modulating IL-18 on the histopathological conditions of malaria infected mice.

METHODS

Plasmodium berghei ANKA infection in male ICR mice was used as a model for malaria infection. Modulation of IL-18 release was carried out by treatment of malarial mice with recombinant mouse IL-18 (rmIL-18) and recombinant mouse IL-18 Fc chimera (rmIL-18Fc) intravenously. Histopathological study and analysis were performed on major organs including brain, liver, spleen, lungs and kidney.

RESULTS

Treatment with rmIL-18Fc resulted in significant improvements on the histopathological conditions of the organs in malaria-infected mice.

CONCLUSION

IL-18 is an important mediator of malaria pathogenesis and targeting IL-18 could prove beneficial in malaria-infected host.

A chronic scheme of cranial window preparation to study pial vascular reactivity in murine cerebral malaria

OBJECTIVE

The acute implantation of a cranial window for studying cerebroarteriolar reactivity in living animals involves a highly surgically invasive craniotomy procedure at the time of experimentation, which limits its application in severely ill animals such as in the experimental murine model of cerebral malaria (ECM). To overcome this problem, a chronic window implantation scheme was designed and implemented.

METHODS

A partial craniotomy is first performed by creating a skull bone flap in the healthy mice, which are then left to recover for one to two weeks, followed by infection to induce ECM. Uninfected animals are utilized as control. When cranial superfusion is needed, the bone flap is retracted and window implantation completed by assembling a perfusion chamber for compound delivery to the exposed brain surface. The presurgical step is intended to minimize surgical trauma on the day of experimentation.

RESULTS

Chronic preparations in uninfected mice exhibited remarkably improved stability over acute ones by significantly reducing periarteriolar tissue damage and enhancing cerebroarteriolar dilator responses. The chronic scheme was successfully implemented in ECM mice, which unveiled novel preliminary insights into impaired cerebroarteriolar reactivity and eNOS dysfunction.

CONCLUSION

The chronic scheme presents an innovative approach for advancing our mechanistic understanding on cerebrovascular dysfunction in ECM.

Metabolic perturbations of kidney and spleen in murine cerebral malaria: (1)H NMR-based metabolomic study

A significant fraction of global population is under the threat of malaria. Majority of annual death is due to the more complicated form of the infection i.e. the cerebral form, also known as Cerebral Malaria (CM). Host parasite interaction is known to cause a cascade of events in various tissues like brain, liver, kidney, and spleen. We have employed (1)H NMR based metabolomics to understand the specific perturbations of various tissues in CM. In our previous paper we have delineated the differences between CM vis-a-vis non-cerebral malaria (NCM) mice in serum, liver and brain. In this paper we focus on their differences of metabolic profile in kidney and spleen as kidney dysfunction and splenomegaly are known to be associated to neurological outcome of the disease. Moreover we have also looked into how the biological compartments (kidney, spleen and serum) interact with each other. The various metabolites involved in such interactions and their correlational aspects across the compartments have been studied in CM, NCM and control mice. The idea was to find out the specific pathways that are altered in CM mice. Our results demonstrate that both the kidney as well as spleen metabolism are differentially perturbed in CM with respect to NCM. The results point out that glutamate levels are decreased in CM mice with respect to NCM mice both in case of spleen and kidney while creatine, myo-inositol and betaine levels are increased in kidney of CM mice with respect to NCM mice. From the analysis of Multiway Principal Component Analysis (MPCA) we see that lipid metabolism and TCA cycle is altered in kidney and spleen.

A new hypothesis on the manifestation of cerebral malaria: the secret is in the liver

Despite the abundance of information on cerebral malaria (CM), the pathogenesis of this disease is not completely understood. At present, two nonexclusive dominant hypotheses exist to explain how the neurological syndrome manifests: the sequestration (or mechanical) hypothesis and the inflammatory hypothesis. The sequestration hypothesis states that sequestration of Plasmodium falciparum-parasitized red blood cells (pRBCs) to brain capillary endothelia causes obstruction of capillary blood flow followed by brain tissue anoxia and coma. The inflammatory hypothesis postulates that P. falciparum infection releases toxic molecules in the circulation, inducing an imbalanced systemic inflammatory response that leads to coagulopathy, brain endothelial cell dysfunction, accumulation of leukocytes in the brain microcirculation, blood brain barrier (BBB) leakage, cerebral vasoconstriction, edema, and coma. However, both hypotheses, even when considered together, are not sufficient to fully explain the pathogenesis of CM. Here, we propose that the development of acute liver failure (ALF) together with BBB breakdown are the necessary and sufficient conditions for the genesis of CM. ALF is characterized by coagulopathy and hepatic encephalopathy (HE) in a patient without pre-existing liver disease. Signs of hepatic dysfunction have been shown to occur in 2.5-40% of CM patients. In addition, recent studies with murine models demonstrated that mice presenting experimental cerebral malaria (ECM) had hepatic damage and brain metabolic changes characteristic of HE. However, the occurrence of CM in patients with mild or without apparent hepatocellular liver damage and the presence of liver damage in non-CM murine models indicate that the development of ALF during malaria infection is not the single factor responsible for neuropathology. To solve this problem, we also propose that BBB breakdown contributes to the pathogenesis of CM and synergizes with hepatic failure to cause neurological signs and symptoms. BBB dysfunction would thus occur in CM by a mechanism similar to the one occurring in sepsis and is in agreement with the inflammatory hypothesis. Nevertheless, differently from in the inflammatory hypothesis, BBB leakage would facilitate the penetration of ammonia and other toxins into the brain parenchyma, but would not be sufficient to cause CM when occurring alone. We believe our hypothesis better explains the pathogenesis of CM, does not have problems to deal with the exception data not explained by the previous hypotheses, and reveals new targets for adjunctive therapy.

Nitric oxide synthase dysfunction contributes to impaired cerebroarteriolar reactivity in experimental cerebral malaria

Cerebrovascular dysfunction plays a key role in the pathogenesis of cerebral malaria. In experimental cerebral malaria (ECM) induced by Plasmodium berghei ANKA, cerebrovascular dysfunction characterized by vascular constriction, occlusion and damage results in impaired perfusion and reduced cerebral blood flow and oxygenation, and has been linked to low nitric oxide (NO) bioavailability. Here, we directly assessed cerebrovascular function in ECM using a novel cranial window method for intravital microscopy of the pial microcirculation and probed the role of NOS isoforms and phosphorylation patterns in the impaired vascular responses. We show that pial arteriolar responses to endothelial NOS (eNOS) and neuronal NOS (nNOS) agonists (Acetylcholine (ACh) and N-Methyl-D-Aspartate (NMDA)) were blunted in mice with ECM, and could be partially recovered by exogenous supplementation of tetrahydrobiopterin (BH4). Pial arterioles in non-ECM mice infected by Plasmodium berghei NK65 remained relatively responsive to the agonists and were not significantly affected by BH4 treatment. These findings, together with the observed blunting of NO production upon stimulation by the agonists, decrease in total NOS activity, augmentation of lipid peroxidation levels, upregulation of eNOS protein expression, and increase in eNOS and nNOS monomerization in the brain during ECM development strongly indicate a state of eNOS/nNOS uncoupling likely mediated by oxidative stress. Furthermore, the downregulation of Serine 1176 (S1176) phosphorylation of eNOS, which correlated with a decrease in cerebrovascular wall shear stress, implicates hemorheological disturbances in eNOS dysfunction in ECM. Finally, pial arterioles responded to superfusion with the NO donor, S-Nitroso-L-glutathione (GSNO), but with decreased intensity, indicating that not only NO production but also signaling is perturbed during ECM. Therefore, the pathological impairment of eNOS and nNOS functions contribute importantly to cerebrovascular dysfunction in ECM and the recovery of intrinsic functionality of NOS to increase NO bioavailability and restore vascular health represents a target for ECM treatment.

Slow and continuous delivery of a low dose of nimodipine improves survival and electrocardiogram parameters in rescue therapy of mice with experimental cerebral malaria

BACKGROUND

Human cerebral malaria (HCM) is a life-threatening complication caused by Plasmodium falciparum infection that continues to be a major global health problem despite optimal anti-malarial treatment. In the experimental model of cerebral malaria (ECM) by Plasmodium berghei ANKA, bolus administration of nimodipine at high doses together with artemether, increases survival of mice with ECM. However, the dose and administration route used is associated with cardiovascular side effects such as hypotension and bradycardia in humans and mice, which could preclude its potential use as adjunctive treatment in HCM.

METHODS

In the present study, alternative delivery systems for nimodipine during late-stage ECM in association with artesunate were searched to define optimal protocols to achieve maximum efficacy in increasing survival in rescue therapy while causing the least cardiac side effects. The baseline electrocardiogram (ECG) and arterial pressure characteristics of uninfected control animals and of mice with ECM and its response upon rescue treatment with artesunate associated or not with nimodipine is also analysed.

RESULTS

Nimodipine, given at 0.5 mg/kg/day via a slow and continuous delivery system by osmotic pumps, increases survival of mice with ECM when used as adjunctive treatment to artesunate. Mice with ECM showed hypotension and ECG changes, including bradycardia and increases in PR, QRS, QTc and ST interval duration. ECM mice also show increased QTc dispersion, heart rate variability (HRV), RMSSD, low frequency (LF) and high frequency (HF) bands of the power spectrum. Both sympathetic and parasympathetic inputs to the heart were increased, but there was a predominance of sympathetic tone as demonstrated by an increased LF/HF ratio. Nimodipine potentiated bradycardia when given by bolus injection, but not when via osmotic pumps. In addition, nimodipine shortened PR duration and improved HRV, RMSSD, LF and HF powers in mice with ECM. In addition, nimodipine did not increased hypotension or decreased the speed of arterial pressure recovery when used in rescue therapy with artesunate.

CONCLUSIONS

These data show that slow and continuous delivery of lower doses of nimodipine improves survival of mice with ECM in rescue therapy with artesunate while showing a safer profile in terms of cardiovascular effects.

Measurement of the uniaxial mechanical properties of rat brains infected by Plasmodium berghei ANKA

Degenerative and demyelinating diseases are known to alter the mechanical properties of brain tissue. While few studies have characterized these biomechanical changes, it is clear that accurate characterization of the mechanical properties of diseased brain tissue could be a substantial asset to neuronavigation and surgery simulation through haptic devices. In this study, samples of brain tissue from rats infected with Plasmodium berghei ANKA, an African murine malaria parasite, are evaluated using a uniaxial tensile test machine. Infected brains having different levels of parasitemia are mounted on the testing machine and extended until failure of the tissue. The stress–strain curve of each sample is obtained and compared to healthy rat brain tissue. Young’s modulus of each sample is extracted from the Hookean part of the stress–strain diagram. Young’s modulus of rats’ brain shows considerable difference among the samples having various levels of parasitemia compared with the controls. For instance, the brains with 0% (control), 1.5%, and 9% parasitemia showed a Young’s modulus of 46.15, 54.54, and 266.67 kPa, respectively. This suggests sequestration of the stiffened and less deformable parasitized red blood cells in the brain microvasculature.

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.

Neuroimmunological blood brain barrier opening in experimental cerebral malaria

Plasmodium falciparum malaria is responsible for nearly one million annual deaths worldwide. Because of the difficulty in monitoring the pathogenesis of cerebral malaria in humans, we conducted a study in various mouse models to better understand disease progression in experimental cerebral malaria (ECM). We compared the effect on the integrity of the blood brain barrier (BBB) and the histopathology of the brain of P. berghei ANKA, a known ECM model, P. berghei NK65, generally thought not to induce ECM, P. yoelii 17XL, originally reported to induce human cerebral malaria-like histopathology, and P. yoelii YM. As expected, P. berghei ANKA infection caused neurological signs, cerebral hemorrhages, and BBB dysfunction in CBA/CaJ and Swiss Webster mice, while Balb/c and A/J mice were resistant. Surprisingly, PbNK induced ECM in CBA/CaJ mice, while all other mice were resistant. P. yoelii 17XL and P. yoelii YM caused lethal hyperparasitemia in all mouse strains; histopathological alterations, BBB dysfunction, or neurological signs were not observed. Intravital imaging revealed that infected erythrocytes containing mature parasites passed slowly through capillaries making intimate contact with the endothelium, but did not arrest. Except for relatively rare microhemorrhages, mice with ECM presented no obvious histopathological alterations that would explain the widespread disruption of the BBB. Intravital imaging did reveal, however, that postcapillary venules, but not capillaries or arterioles, from mice with ECM, but not hyperparasitemia, exhibit platelet marginalization, extravascular fibrin deposition, CD14 expression, and extensive vascular leakage. Blockage of LFA-1 mediated cellular interactions prevented leukocyte adhesion, vascular leakage, neurological signs, and death from ECM. The endothelial barrier-stabilizing mediators imatinib and FTY720 inhibited vascular leakage and neurological signs and prolonged survival to ECM. Thus, it appears that neurological signs and coma in ECM are due to regulated opening of paracellular-junctional and transcellular-vesicular fluid transport pathways at the neuroimmunological BBB.

Plasmodium falciparum, the deadliest of all human malaria parasites, can cause cerebral malaria, a severe and frequently fatal complication of this devastating disease. Young children are predominantly at risk and may progress rapidly from the first signs of neurological involvement to coma and death. Here we used a murine model for high-resolution in vivo imaging to demonstrate that cerebral malaria, but not high parasitemia and severe anemia, is associated with extensive leakage of fluid from cerebral blood vessels into the brain tissue. This vascular leakage occurs downstream from the capillary bed, at the neuroimmunological blood brain barrier, a site recently recognized as the immune cell entry point into the brain during neuroinflammation. Vascular leakage is closely associated with the appearance of neurological signs suggesting that the ultimate cause of brain edema, coma and death in cerebral malaria is a widespread opening of the neuroimmunological blood brain barrier. Indeed, vascular leakage, neurological signs, and death from ECM can be prevented with endothelial barrier-stabilizing drugs. Based on the unique role of this anatomical feature in neuroinflammation, our findings are expected to have implications for other infectious diseases and autoimmune disorders of the central nervous system.

Histopathological studies in two strains of semi-immune mice infected with Plasmodium berghei ANKA after chronic exposure

To mimic a human malaria infection in the endemic condition, two strains of mice (Balb/c and CBA) were infected and treated several times to generate so-called semi-immune status. As previously reported, neither mice (Balb/c and CBA) strain showed cerebral malaria, even in the susceptible C57BL/6 (B6). The significant difference between the mice strains in our previous study was the rate of destruction of uninfected red blood cells (uRBCs) at infection. After the established repeated cycles of infection and treatment and the final challenge with 10(4) Plasmodium berghei ANKA until minimum Hb, Balb/c and CBA mice were sacrificed. The spleen, liver, brain, kidney, lung, heart, and muscle were removed, stained with hematoxylin-eosin and analyzed with light microscopy. Previous observation suggested that Balb/c destroyed uRBC at much higher rate than the other strains although the parasitemia was very low. Pathological investigation carried out in this study revealed that this destruction was mainly contributed by the uRBCs as no parasite sequestration was observed in any of the organs. However, malaria pigment deposition was observed in spleen and liver of all the semi-immune mice strains. This histopathological study in the severe malaria anemia model, which is difficult to conduct in humans, will be helpful in taking into account different responses to malaria infection when designing therapeutic interventions and vaccine studies.

Sequestration and tissue accumulation of human malaria parasites: can we learn anything from rodent models of malaria?

The sequestration of Plasmodium falciparum–infected red blood cells (irbcs) in the microvasculature of organs is associated with severe disease; correspondingly, the molecular basis of irbc adherence is an active area of study. In contrast to P. falciparum, much less is known about sequestration in other Plasmodium parasites, including those species that are used as models to study severe malaria. Here, we review the cytoadherence properties of irbcs of the rodent parasite Plasmodium berghei ANKA, where schizonts demonstrate a clear sequestration phenotype. Real-time in vivo imaging of transgenic P. berghei parasites in rodents has revealed a CD36-dependent sequestration in lungs and adipose tissue. In the absence of direct orthologs of the P. falciparum proteins that mediate binding to human CD36, the P. berghei proteins and/or mechanisms of rodent CD36 binding are as yet unknown. In addition to CD36-dependent schizont sequestration, irbcs accumulate during severe disease in different tissues, including the brain. The role of sequestration is discussed in the context of disease as are the general (dis)similarities of P. berghei and P. falciparum sequestration.

Persistent cognitive and motor deficits after successful antimalarial treatment in murine cerebral malaria

Human cerebral malaria causes neurological and behavioral deficits which persist long after resolution of infection and clearance of parasites with antimalarial drugs. Previously, we demonstrated that during active infection, mice with cerebral malaria demonstrated negative behavioral outcomes. Here we used a chloroquine treatment model of cerebral malaria to determine whether these abnormal outcomes would be persistent in the mouse model. C57BL/6 mice were infected with Plasmodium berghei ANKA, and treated for ten days. After cessation of chloroquine, a comprehensive assessment of cognitive and motor function demonstrated persistence of abnormal behavioral outcomes, 10 days after successful eradication of parasites. Furthermore, these deficits were still evident forty days after cessation of chloroquine, indicating persistence long after successful treatment, a hallmark feature of human cerebral malaria. Thus, cognitive tests similar to those used in these mouse studies could facilitate the development of adjunctive therapies that can ameliorate adverse neurological outcomes in human cerebral malaria.

Integrated cytokine and metabolic analysis of pathological responses to parasite exposure in rodents

Parasitic infections cause a myriad of responses in their mammalian hosts, on immune as well as on metabolic level. A multiplex panel of cytokines and metabolites derived from four parasite-rodent models, namely, Plasmodium berghei−mouse, Trypanosoma brucei brucei−mouse, Schistosoma mansoni−mouse, and Fasciola hepatica−rat were statistically coanalyzed. ¹H NMR spectroscopy and multivariate statistical analysis were used to characterize the urine and plasma metabolite profiles in infected and noninfected animals. Each parasite generated a unique metabolic signature in the host. Plasma cytokine concentrations were obtained using the ‘Meso Scale Discovery’ multi cytokine assay platform. Multivariate data integration methods were subsequently used to elucidate the component of the metabolic signature which is associated with inflammation and to determine specific metabolic correlates with parasite-induced changes in plasma cytokine levels. For example, the relative levels of acetyl glycoproteins extracted from the plasma metabolite profile in the P. berghei-infected mice were statistically correlated with IFN-γ, whereas the same cytokine was anticorrelated with glucose levels. Both the metabolic and the cytokine data showed a similar spatial distribution in principal component analysis scores plots constructed for the combined murine data, with samples from all infected animals clustering according to the parasite species and whereby the protozoan infections (P. berghei and T. b. brucei) grouped separately from the helminth infection (S. mansoni). For S. mansoni, the main infection-responsive cytokines were IL-4 and IL-5, which covaried with lactate, choline, and d-3-hydroxybutyrate. This study demonstrates that the inherently differential immune response to single- and multicellular parasites not only manifests in the cytokine expression, but also consequently imprints on the metabolic signature, and calls for in-depth analysis to further explore direct links between immune features and biochemical pathways.

Parasitic infections cause a myriad of responses in their mammalian hosts, including a range of immune reactions and metabolic perturbations. Here, a multiplex panel of cytokines and metabolites derived from four parasite-rodent models, namely, Plasmodium berghei−mouse, Trypanosoma brucei brucei−mouse, Schistosoma mansoni−mouse, and Fasciola hepatica−rat were statistically coanalyzed. ¹H NMR spectroscopy and multivariate statistical analysis were used to characterize the urine and plasma metabolite profiles in infected and noninfected control animals.

Artemisone effective against murine cerebral malaria

Background

Artemisinins are the newest class of drug approved for malaria treatment. Due to their unique mechanism of action, rapid effect on Plasmodium, and high efficacy in vivo, artemisinins have become essential components of malaria treatment. Administration of artemisinin derivatives in combination with other anti-plasmodials has become the first-line treatment for uncomplicated falciparum malaria. However, their efficiency in cases of cerebral malaria (CM) remains to be determined.

Methods

The efficacy of several artemisinin derivatives for treatment of experimental CM was evaluated in ICR or C57BL/6 mice infected by Plasmodium berghei ANKA. Both mouse strains serve as murine models for CM.

Results

Artemisone was the most efficient drug tested, and could prevent death even when administered at relatively late stages of cerebral pathogenesis. No parasite resistance to artemisone was detected in recrudescence. Co-administration of artemisone together with chloroquine was more effective than monotherapy with either drug, and led to complete cure. Artemiside was even more effective than artemisone, but this substance has yet to be submitted to preclinical toxicological evaluation.

Conclusions

Altogether, the results support the use of artemisone for combined therapy of CM.

Algorithms to predict cerebral malaria in murine models using the SHIRPA protocol

Background

Plasmodium berghei ANKA infection in C57Bl/6 mice induces cerebral malaria (CM), which reproduces, to a large extent, the pathological features of human CM. However, experimental CM incidence is variable (50-100%) and the period of incidence may present a range as wide as 6-12 days post-infection. The poor predictability of which and when infected mice will develop CM can make it difficult to determine the causal relationship of early pathological changes and outcome. With the purpose of contributing to solving these problems, algorithms for CM prediction were built.

Methods

Seventy-eight P. berghei-infected mice were daily evaluated using the primary SHIRPA protocol. Mice were classified as CM+ or CM- according to development of neurological signs on days 6-12 post-infection. Logistic regression was used to build predictive models for CM based on the results of SHIRPA tests and parasitaemia.

Results

The overall CM incidence was 54% occurring on days 6-10. Some algorithms had a very good performance in predicting CM, with the area under the receiver operator characteristic (_auROC) curve ≥ 80% and positive predictive values (PV+) ≥ 95, and correctly predicted time of death due to CM between 24 and 72 hours before development of the neurological syndrome (_auROC = 77-93%; PV+ = 100% using high cut off values). Inclusion of parasitaemia data slightly improved algorithm performance.

Conclusion

These algorithms work with data from a simple, inexpensive, reproducible and fast protocol. Most importantly, they can predict CM development very early, estimate time of death, and might be a valuable tool for research using CM murine models.

Inflammatory changes in the central nervous system are associated with behavioral impairment in Plasmodium berghei (strain ANKA)-infected mice

Experimental cerebral malaria is a neuroinflammatory condition that results from the host immune response to the parasite. Using intravital microscopy, we investigated leukocyte recruitment in the brain microcirculation and the temporal relationship of this process to the behavioral changes observed in Plasmodium berghei (strain ANKA)-infected C57Bl/6 mice. We found that leukocyte recruitment was increased from day 5 post-infection (p.i.) onwards. Histopathological changes and increased levels of inflammatory cytokines in the brain were also observed. Behavioral performance evaluated by the SHIRPA protocol showed functional impairment from day 6 p.i. onwards. Thus, early leukocyte migration into the brain and associated inflammatory changes may be involved in neurological impairment in parasite-infected C57Bl/6 mice.

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.

Schistosoma mansoni infection reduces the incidence of murine cerebral malaria

BACKGROUND

Plasmodium and Schistosoma are two of the most common parasites in tropical areas. Deregulation of the immune response to Plasmodium falciparum, characterized by a Th1 response, leads to cerebral malaria (CM), while a Th2 response accompanies chronic schistosomiasis.

METHODS

The development of CM was examined in mice with concomitant Schistosoma mansoni and Plasmodium berghei ANKA infections. The effect of S. mansoni egg antigen injection on disease development and survival was also determined. Cytokine serum levels were estimated using ELISA. Statistical analysis was performed using t-test.

RESULTS

The results demonstrate that concomitant S. mansoni and P. berghei ANKA infection leads to a reduction in CM. This effect is dependent on infection schedule and infecting cercariae number, and is correlated with a Th2 response. Schistosomal egg antigen injection delays the death of Plasmodium-infected mice, indicating immune involvement.

CONCLUSIONS

This research supports previous claims of a protective effect of helminth infection on CM development. The presence of multiple parasitic infections in patients from endemic areas should therefore be carefully noted in clinical trials, and in the development of standard treatment protocols for malaria. Defined helminth antigens may be considered for alleviation of immunopathological symptoms.