Phagocyte-derived reactive oxygen species do not influence the progression of murine blood-stage malaria infections

Vitamin C co-administration with artemether-lumefantrine abrogates chronic stress exacerbated Plasmodium berghei-induced sickness behaviour, inflammatory and oxidative stress responses in mice

This study evaluated the effects of vitamin C and artemether-lumefantrine (AL) on sickness behaviour and oxido-inflammatory response in chronically stressed mice infected with Plasmodium berghei. Sickness behaviour severity was examined with weight and assessment of mice behaviours. Results showed that stress increased parasitaemia in infected mice. Vitamin C co-administration with AL increased parasite clearance over AL alone, and modulated inflammatory cytokines (TNF-α, IL-1β, IL-10, IL-12) and antioxidant parameters in plasma and brain tissue. Conclusively, stress worsens malaria-induced sickness behaviour and up-regulates the inflammatory and oxidative stress response. Co-administration of vitamin C with AL appears to counteract these detrimental effects.

Biogenically synthesized green silver nanoparticles exhibit antimalarial activity

The suboptimal efficacies of existing anti-malarial drugs attributed to the emergence of drug resistance dampen the clinical outcomes. Hence, there is a need for developing novel drug and drug targets. Recently silver nanoparticles (AgNPs) constructed with the leaf extracts of Euphorbia cotinifolia were shown to possess antimalarial activity. Therefore, the synthesized AgNPs from Euphorbia cotinifolia (EcAgNPs) were tested for their parasite clearance activity. We determined the antimalarial activity in the asexual blood stage infection of 3D7 (laboratory strain) P. falciparum. EcAgNPs demonstrated the significant inhibition of parasite growth (EC50 of 0.75 µg/ml) in the routine in vitro culture of P. falciparum. The synthesized silver nanoparticles were seen to induce apoptosis in P. falciparum through increased reactive oxygen species (ROS) ROS production and activated programmed cell death pathways characterized by the caspase-3 and calpain activity. Also, altered transcriptional regulation of Bax/Bcl-2 ratio indicated the enhanced apoptosis. Moreover, inhibited expression of PfLPL-1 by EcAgNPs is suggestive of the dysregulated host fatty acid flux via parasite lipid storage. Overall, our findings suggest that EcAgNPs are a non-toxic and targeted antimalarial treatment, and could be a promising therapeutic approach for clearing malaria infection.

Antimalarial and Immunomodulatory Activities of Tithonia diversifolia (Asteraceae) Leave Flafonoids-Rich Extract Used in Cameroonian Traditional Medecine

Background

Phytochemicals are considered the reliable source for the treatment of infection including malaria. Especially, phenols are known as potentially toxic to the growth and development of pathogens, among which flavonoids are the most extensively studied and play more intensive roles in ethnopharmacology. The immunological effect and role of T. diversifolia flavonoids-rich extract in treatment of malaria have therefore been examined in this study.

Methods

In vitro test against Plasmodium falciparum and 4-day suppressive and Rane's tests against Plasmodium berghei in mice were used to evaluate the antimalarial activities. TNF-α and INF-γ levels, phagocytic tests, and production of oxygen and nitrogen radical were assessed to appreciate the immunomodulatory activity. One-way analysis of variance followed by post hoc Student's t tests was used for data analysis.

Results

T. diversifolia flavonoids-rich extract at the concentrations ranging from 0.0004 mg/ml significantly (p < 0.05) inhibited in a concentration-dependent manner the growth of trophozoite up to 100% inhibition with 0.025 mg/ml at 24 and 48 hrs. Moreover, T. diversifolia flavonoids-rich extract reduced the level of parasitemia and improved in a dose-dependent manner the survival time of infected mice significantly (p < 0.05) compared to their control in 4-day suppressive test as well as in Rane's test. Additionally, T. diversifolia flavonoids-rich extract increased the TNF-α and INF-γ levels in rats infected by P. berghei. Furthermore, the flavonoid-rich extract enhanced weight of spleen in the rats, the metabolic and phagocytic activities of the peritoneal cells, and the concentration of nitric oxide and oxygen radicals in methylprednisolone-immunocompromised rats compared to the control (p < 0.05).

Conclusion

The study has revealed that T. diversifolia flavonoids-rich extract through its antiplasmodial and phagocytic activities is a promising treatment of malaria.

Cerebral Malaria and Neuronal Implications of Plasmodium Falciparum Infection: From Mechanisms to Advanced Models

Reorganization of host red blood cells by the malaria parasite Plasmodium falciparum enables their sequestration via attachment to the microvasculature. This artificially increases the dwelling time of the infected red blood cells within inner organs such as the brain, which can lead to cerebral malaria. Cerebral malaria is the deadliest complication patients infected with P. falciparum can experience and still remains a major public health concern despite effective antimalarial therapies. Here, the current understanding of the effect of P. falciparum cytoadherence and their secreted proteins on structural features of the human blood-brain barrier and their involvement in the pathogenesis of cerebral malaria are highlighted. Advanced 2D and 3D in vitro models are further assessed to study this devastating interaction between parasite and host. A better understanding of the molecular mechanisms leading to neuronal and cognitive deficits in cerebral malaria will be pivotal in devising new strategies to treat and prevent blood-brain barrier dysfunction and subsequent neurological damage in patients with cerebral malaria.

Oxidative Stress in Malaria: Potential Benefits of Antioxidant Therapy

Malaria is an infectious disease and a serious public health problem in the world, with 3.3 billion people in endemic areas in 100 countries and about 200 million new cases each year, resulting in almost 1 million deaths in 2018. Although studies look for strategies to eradicate malaria, it is necessary to know more about its pathophysiology to understand the underlying mechanisms involved, particularly the redox balance, to guarantee success in combating this disease. In this review, we addressed the involvement of oxidative stress in malaria and the potential benefits of antioxidant supplementation as an adjuvant antimalarial therapy.

NADPH Oxidase: a Possible Therapeutic Target for Cognitive Impairment in Experimental Cerebral Malaria

Long-term cognitive impairment associated with seizure-induced hippocampal damage is the key feature of cerebral malaria (CM) pathogenesis. One-fourth of child survivors of CM suffer from long-lasting neurological deficits and behavioral anomalies. However, mechanisms on hippocampal dysfunction are unclear. In this study, we elucidated whether gp91^phox isoform of nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) (a potent marker of oxidative stress) mediates hippocampal neuronal abnormalities and cognitive dysfunction in experimental CM (ECM). Mice symptomatic to CM were rescue treated with artemether monotherapy (ARM) and in combination with apocynin (ARM + APO) adjunctive based on scores of Rapid Murine Come behavior Scale (RMCBS). After a 30-day survivability period, we performed Barnes maze, T-maze, and novel object recognition cognitive tests to evaluate working and reference memory in all the experimental groups except CM. Sensorimotor tests were conducted in all the cohorts to assess motor coordination. We performed Golgi-Cox staining to illustrate cornu ammonis-1 (CA1) pyramidal neuronal morphology and study overall hippocampal neuronal density changes. Further, expression of NOX2, NeuN (neuronal marker) in hippocampal CA1 and dentate gyrus was determined using double immunofluorescence experiments in all the experimental groups. Mice administered with ARM monotherapy and APO adjunctive treatment exhibited similar survivability. The latter showed better locomotor and cognitive functions, reduced ROS levels, and hippocampal NOX2 immunoreactivity in ECM. Our results show a substantial increase in hippocampal NeuN immunoreactivity and dendritic arborization in ARM + APO cohorts compared to ARM-treated brain samples. Overall, our study suggests that overexpression of NOX2 could result in loss of hippocampal neuronal density and dendritic spines of CA1 neurons affecting the spatial working and reference memory during ECM. Notably, ARM + APO adjunctive therapy reversed the altered neuronal morphology and oxidative damage in hippocampal neurons restoring long-term cognitive functions after CM.

Plasmodium vivax Infection Alters Mitochondrial Metabolism in Human Monocytes

Monocytes play an important role in the host defense against Plasmodium vivax as the main source of inflammatory cytokines and mitochondrial reactive oxygen species (mROS). Here, we show that monocyte metabolism is altered during human P. vivax malaria, with mitochondria playing a major function in this switch. The process involves a reprograming in which the cells increase glucose uptake and produce ATP via glycolysis instead of oxidative phosphorylation. P. vivax infection results in dysregulated mitochondrial gene expression and in altered membrane potential leading to mROS increase rather than ATP production. When monocytes were incubated with P. vivax-infected reticulocytes, mitochondria colocalized with phagolysosomes containing parasites representing an important source mROS. Importantly, the mitochondrial enzyme superoxide dismutase 2 (SOD2) is simultaneously induced in monocytes from malaria patients. Taken together, the monocyte metabolic reprograming with an increased mROS production may contribute to protective responses against P. vivax while triggering immunomodulatory mechanisms to circumvent tissue damage. IMPORTANCE Plasmodium vivax is the most widely distributed causative agent of human malaria. To achieve parasite control, the human immune system develops a substantial inflammatory response that is also responsible for the symptoms of the disease. Among the cells involved in this response, monocytes play an important role. Here, we show that monocyte metabolism is altered during malaria, with its mitochondria playing a major function in this switch. This change involves a reprograming process in which the cells increase glucose uptake and produce ATP via glycolysis instead of oxidative phosphorylation. The resulting altered mitochondrial membrane potential leads to an increase in mitochondrial reactive oxygen species rather than ATP. These data suggest that agents that change metabolism should be investigated and used with caution during malaria.

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.

Synthesis and biological evaluation of Val-Val dipeptide-sulfonamide conjugates

Novel Val-Val dipeptide-benzenesulfonamide conjugates were reported in this study. These were achieved by a condensation reaction of p-substituted benzenesulfonamoyl alkanamides with 2-amino-4-methyl-N-substituted phenyl butanamide using classical peptide-coupling reagents. The compounds were characterized using Fourier transform infrared, ¹ H-nuclear magnetic resonance (NMR), ¹³ C-NMR, and electrospray ionization-high-resolution mass spectrometry spectroscopic techniques. As predicted from in silico studies, the Val-Val dipeptide-benzenesulfonamide conjugates exhibited antimalarial and antioxidant properties that were analogous to the standard drug. The synthesized compounds were evaluated for in vivo antimalarial activity against Plasmodium berghei. The hematological analysis was also conducted on the synthesized compounds. At 50 mg/kg body weight, compounds 8a, 8d, and 8g-i inhibited the multiplication of the parasite by 48-54% on Day 7 of posttreatment exposure, compared with the 67% reduction with artemisinin. All the synthesized dipeptides had a good antioxidant property, but it was less when compared with vitamin C. The dipeptides reported herein showed the ability to reduce oxidative stress arising from the malaria parasite.

Erythrocyte Lipid and Antioxidant Changes in <i>Plasmodium falciparum</i>-infected Children Attending Mother and Child Hospital in Akure, Nigeria

BACKGROUND AND OBJECTIVE

Understanding the molecular and cellular pathways activated in response to Plasmodium falciparum infection is crucial for the development of pharmacological intervention to malaria. The present study was designed to evaluate the lipid components and the oxidative status of erythrocyte obtained from children under 5 years infected with Plasmodium falciparum.

MATERIALS AND METHODS

Parasitemia was assessed prior and after treatment with antimalarial, erythrocyte lipid profile, levels of lipid peroxidation and antioxidant status (reduced glutathione, GSH; superoxide dismutase, SOD; catalase and glutathione peroxidase, GPx) were measured.

RESULTS

Results obtained showed that in Plasmodium infected erythrocyte, the total phospholipids, cholesterol and LDL-cholesterol concentrations were significantly elevated beyond the normal level. In addition, an upsurge in erythrocyte oxidant (lipid peroxide) status with a concomitant downregulation of the antioxidant status (GSH concentration and SOD, catalase and GPx activities) was observed in P. falciparum-infected children. However, following a three-day treatment with artemisinin combination drugs, there was a significant reduction in erythrocyte phospholipids, total cholesterol and LDL-cholesterol concentration as well as lipid peroxide levels. Significant augmentation in erythrocyte antioxidant status (GSH, SOD, catalase and GPx) were also observed after treatment with antimalarials.

CONCLUSION

This study demonstrated that erythrocyte lipids and oxidative status are usually altered in Plasmodium falciparum-infected children. Thus, monitoring erythrocyte lipid profile and oxidative status could offer a viable diagnostic strategy in early detection of malaria in children.

Citrulline protects mice from experimental cerebral malaria by ameliorating hypoargininemia, urea cycle changes and vascular leak

Clinical and model studies indicate that low nitric oxide (NO) bioavailability due in part to profound hypoargininemia contributes to cerebral malaria (CM) pathogenesis. Protection against CM pathogenesis may be achieved by altering the diet before infection with Plasmodium falciparum infection (nutraceutical) or by administering adjunctive therapy that decreases CM mortality (adjunctive therapy). This hypothesis was tested by administering citrulline or arginine in experimental CM (eCM). We report that citrulline injected as prophylaxis immediately post infection (PI) protected virtually all mice by ameliorating (i) hypoargininemia, (ii) urea cycle impairment, and (iii) disruption of blood brain barrier. Citrulline prophylaxis inhibited plasma arginase activity. Parasitemia was similar in citrulline- and vehicle control-groups, indicating that protection from pathogenesis was not due to decreased parasitemia. Both citrulline and arginine administered from day 1 PI in the drinking water significantly protected mice from eCM. These observations collectively indicate that increasing dietary citrulline or arginine decreases eCM mortality. Citrulline injected ip on day 4 PI with quinine-injected ip on day 6 PI partially protected mice from eCM; citrulline plus scavenging of superoxide with pegylated superoxide dismutase and pegylated catalase protected all recipients from eCM. These findings indicate that ameliorating hypoargininemia with citrulline plus superoxide scavenging decreases eCM mortality.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

Myeloperoxidase Attenuates Pathogen Clearance during Plasmodium yoelii Nonlethal Infection

Myeloperoxidase (MPO), a leukocyte-derived enzyme mainly secreted by activated neutrophils, is known to be involved in the immune response during bacterial and fungal infection and inflammatory diseases. Nevertheless, the role of MPO in a parasitic disease like malaria is unknown. We hypothesized that MPO contributes to parasite clearance. To address this hypothesis, we used Plasmodium yoelii nonlethal infection in wild-type and MPO-deficient mice as a murine malaria model. We detected high MPO plasma levels in wild-type mice with Plasmodium yoelii infection. Unexpectedly, infected MPO-deficient mice did not show increased parasite loads but were able to clear the infection more rapidly than wild-type mice. Additionally, the presence of neutrophils at the onset of infection seemed not to be essential for the control of the parasitemia. The effect of decreased parasite levels in MPO-deficient mice was absent from animals lacking mature T and B cells, indicating that this effect is most likely dependent on adaptive immune response mechanisms. Indeed, we observed increased gamma interferon and tumor necrosis factor alpha production by T cells in infected MPO-deficient mice. Together, these results suggest that MPO modulates the adaptive immune response during malaria infection, leading to an attenuated parasite clearance.

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.

Protective immunity against malaria after vaccination

A good understanding of the immunological correlates of protective immunity is an important requirement for the development of effective vaccines against malaria. However, this concern has received little attention even in the face of two decades of intensive vaccine research. Here, we review the immune response to blood-stage malaria, with a particular focus on the type of vaccine most likely to induce the kind of response required to give strong protection against infection.

Are reactive oxygen species always detrimental to pathogens?

Reactive oxygen species (ROS) are deadly weapons used by phagocytes and other cell types, such as lung epithelial cells, against pathogens. ROS can kill pathogens directly by causing oxidative damage to biocompounds or indirectly by stimulating pathogen elimination by various nonoxidative mechanisms, including pattern recognition receptors signaling, autophagy, neutrophil extracellular trap formation, and T-lymphocyte responses. Thus, one should expect that the inhibition of ROS production promote infection. Increasing evidences support that in certain particular infections, antioxidants decrease and prooxidants increase pathogen burden. In this study, we review the classic infections that are controlled by ROS and the cases in which ROS appear as promoters of infection, challenging the paradigm. We discuss the possible mechanisms by which ROS could promote particular infections. These mechanisms are still not completely clear but include the metabolic effects of ROS on pathogen physiology, ROS-induced damage to the immune system, and ROS-induced activation of immune defense mechanisms that are subsequently hijacked by particular pathogens to act against more effective microbicidal mechanisms of the immune system. The effective use of antioxidants as therapeutic agents against certain infections is a realistic possibility that is beginning to be applied against viruses.

Host matrix metalloproteinases in cerebral malaria: new kids on the block against blood-brain barrier integrity?

Cerebral malaria (CM) is a life-threatening complication of falciparum malaria, associated with high mortality rates, as well as neurological impairment in surviving patients. Despite disease severity, the etiology of CM remains elusive. Interestingly, although the Plasmodium parasite is sequestered in cerebral microvessels, it does not enter the brain parenchyma: so how does Plasmodium induce neuronal dysfunction? Several independent research groups have suggested a mechanism in which increased blood–brain barrier (BBB) permeability might allow toxic molecules from the parasite or the host to enter the brain. However, the reported severity of BBB damage in CM is variable depending on the model system, ranging from mild impairment to full BBB breakdown. Moreover, the factors responsible for increased BBB permeability are still unknown. Here we review the prevailing theories on CM pathophysiology and discuss new evidence from animal and human CM models implicating BBB damage. Finally, we will review the newly-described role of matrix metalloproteinases (MMPs) and BBB integrity. MMPs comprise a family of proteolytic enzymes involved in modulating inflammatory response, disrupting tight junctions, and degrading sub-endothelial basal lamina. As such, MMPs represent potential innovative drug targets for CM.

Antioxidant potential of a polyherbal antimalarial as an indicator of its therapeutic value

Nefang is a polyherbal product composed of Mangifera indica (bark and leaf), Psidium guajava, Carica papaya, Cymbopogon citratus, Citrus sinensis, and Ocimum gratissimum (leaves), used for the treatment of malaria. Compounds with antioxidant activity are believed to modulate plasmodial infection. Antioxidant activity of the constituent aqueous plants extracts, in vitro, was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH), total phenolic content (TPC), and ferric reducing antioxidant power (FRAP) methods and, in vivo, Nefang (100 and 500 mg kg⁻¹) activity was evaluated in carbon tetrachloride-induced oxidative stressed Wistar rats. Superoxide dismutase, catalase activities, and lipid peroxidation by the malondialdehyde and total proteins assays were carried out. P. guajava, M. indica leaf, and bark extracts had the highest antioxidant properties in all three assays, with no statistically significant difference. Rats treated with the carbon tetrachloride had a statistically significant decrease in levels of triglycerides, superoxide dismutase, and catalase (P < 0.05) and increase in malondialdehyde activity, total protein levels, and liver and renal function markers, whereas rats treated with Nefang showed increased levels in the former and dose-dependent decrease towards normal levels in the later. These results reveal the constituent plants of Nefang that contribute to its in vivo antioxidant potential. This activity is a good indication of the therapeutic potential of Nefang.

A novel chitosan based antimalarial drug delivery against Plasmodium berghei infection

Chitosan is a natural polysaccharide that has attracted significant scientific interest during the last two decades and chitosan based nanodrug delivery systems seem to be a hopeful and viable strategy for improving disease treatment. This study aims to evaluate the potency of the polymer based nanochloroquine in application for attenuation of Plasmodium berghei infection in Swiss mice and effectiveness against the parasite induced oxidative stress and deoxyribo nucleic acid (DNA) damage in lymphocytes. Nanoparticle was prepared by ionotropic gelation between chitosan and sodium tripolyphosphate. The chloroquine was treated by the actual drug content of effective nanochloroquine and the nanodrug was charged with its effective dose for fifteen days, after successive infection development in Swiss mice. Gimsa staining of thin smear and flow cytometry analysis was pursued to reveal the parasitemia. Different oxidative markers, inflammatory markers, antioxidant enzymes level and also lymphocytic deoxyribo nucleic acid damage study were performed. The present study reveals the potency of the nanodrug which has been found as more prospective than only chloroquine treatment to combat the parasite infection, oxidative stress as well as inflammation and DNA damage. From the study, we conclude this nanodrug may be applicable as potent therapeutic agent than only chloroquine.

Oxidative stress in malaria

Malaria is a significant public health problem in more than 100 countries and causes an estimated 200 million new infections every year. Despite the significant effort to eradicate this dangerous disease, lack of complete knowledge of its physiopathology compromises the success in this enterprise. In this paper we review oxidative stress mechanisms involved in the disease and discuss the potential benefits of antioxidant supplementation as an adjuvant antimalarial strategy.

Twofold cost of reproduction: an increase in parental effort leads to higher malarial parasitaemia and to a decrease in resistance to oxidative stress

Parental effort is usually associated with high metabolism that could lead to an increase in the production of reactive oxidative species giving rise to oxidative stress. Since many antioxidants involved in the resistance to oxidative stress can also enhance immune function, an increase in parental effort may diminish the level of antioxidants otherwise involved in parasite resistance. In the present study, we performed brood size manipulation in a population of great tits (Parus major) to create different levels of parental effort. We measured resistance to oxidative stress and used a newly developed quantitative PCR assay to quantify malarial parasitaemia. We found that males with an enlarged brood had significantly higher level of malarial parasites and lower red blood cell resistance to free radicals than males rearing control and reduced broods. Brood size manipulation did not affect female parasitaemia, although females with an enlarged brood had lower red blood cell resistance than females with control and reduced broods. However, for both sexes, there was no relationship between the level of parasitaemia and resistance to oxidative stress, suggesting a twofold cost of reproduction. Our results thus suggest the presence of two proximate and independent mechanisms for the well-documented trade-off between current reproductive effort and parental survival.

Cognitive dysfunction is sustained after rescue therapy in experimental cerebral malaria, and is reduced by additive antioxidant therapy

Neurological impairments are frequently detected in children surviving cerebral malaria (CM), the most severe neurological complication of infection with Plasmodium falciparum. The pathophysiology and therapy of long lasting cognitive deficits in malaria patients after treatment of the parasitic disease is a critical area of investigation. In the present study we used several models of experimental malaria with differential features to investigate persistent cognitive damage after rescue treatment. Infection of C57BL/6 and Swiss (SW) mice with Plasmodium berghei ANKA (PbA) or a lethal strain of Plasmodium yoelii XL (PyXL), respectively, resulted in documented CM and sustained persistent cognitive damage detected by a battery of behavioral tests after cure of the acute parasitic disease with chloroquine therapy. Strikingly, cognitive impairment was still present 30 days after the initial infection. In contrast, BALB/c mice infected with PbA, C57BL6 infected with Plasmodium chabaudi chabaudi and SW infected with non lethal Plasmodium yoelii NXL (PyNXL) did not develop signs of CM, were cured of the acute parasitic infection by chloroquine, and showed no persistent cognitive impairment. Reactive oxygen species have been reported to mediate neurological injury in CM. Increased production of malondialdehyde (MDA) and conjugated dienes was detected in the brains of PbA-infected C57BL/6 mice with CM, indicating high oxidative stress. Treatment of PbA-infected C57BL/6 mice with additive antioxidants together with chloroquine at the first signs of CM prevented the development of persistent cognitive damage. These studies provide new insights into the natural history of cognitive dysfunction after rescue therapy for CM that may have clinical relevance, and may also be relevant to cerebral sequelae of sepsis and other disorders.

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

Plasmodium berghei ANKA (PbA) infection in susceptible inbred mouse strains is the most commonly used experimental model to study pathogenesis of cerebral malaria (CM). Indeed, many concepts on mechanisms related to this complication have arisen from works using this model. Although inbred strains present several advantages and are indicated for most studies, the use of outbred models can show unique usefulness in a number of approaches such as fine post-quantitative trait loci mapping and discovery of genes relevant to CM susceptibility or resistance, as well as pharmacological and vaccine studies. Here we describe the features of PbA infection and CM incidence, and characterize the associated multiorgan pathology in the outbred Swiss Webster mouse. This model showed a sizeable (62.7%) and reproducible incidence of CM demonstrated by clinical signs and histopathological changes in brain (microhaemorrhages, oedema and vessel plugging by mononuclear cells). Major pathological changes were also observed in lungs, liver, thymus and spleen, analogous to those observed in inbred strains. Parasitaemia levels were associated with the risk of CM development, the risk being significantly higher in mice showing higher values of parasitaemia on days 6-7 of infection. This outbred CM model is then suitable for genetic, vaccine and drug studies targeting this malaria complication.

Effect of indoleamine dioxygenase-1 deficiency and kynurenine pathway inhibition on murine cerebral malaria

Cerebral malaria (CM) can be a fatal manifestation of Plasmodium falciparum infection. In this study, two different approaches were used to examine the role of indoleamine 2,3-dioxygenase-1 (IDO-1) and its metabolites in the development of murine CM. Mice genetically deficient in IDO-1 were not protected against CM, but partial protection was observed in C57BL/6 mice treated with Ro 61-8048, an inhibitor of kynurenine-3-hydroxylase. This protection was associated with suppressed levels of picolinic acid (PA) within the brain, but not with changes in the levels of kynurenic acid (KA) or quinolinic acid (QA). These data suggest that although IDO-1 is not directly involved in the pathogenesis of CM in C57BL/6 mice, the production of the kynurenine pathway metabolite PA may contribute to the development of murine CM.

A central role for free heme in the pathogenesis of severe malaria: the missing link?

Malaria, the disease caused by Plasmodium infection, is endemic to poverty in so-called underdeveloped countries. Plasmodium falciparum, the main infectious Plasmodium species in sub-Saharan countries, can trigger the development of severe malaria, including cerebral malaria, a neurological syndrome that claims the lives of more than one million children (<5 years old) per year. Attempts to eradicate Plasmodium infection, and in particular its lethal outcomes, have so far been unsuccessful. Using well-established rodent models of malaria infection, we found that survival of a Plasmodium-infected host is strictly dependent on the host's ability to up-regulate the expression of heme oxygenase-1 (HO-1 encoded by the gene Hmox1). HO-1 is a stress-responsive enzyme that catabolizes free heme into biliverdin, via a reaction that releases Fe and generates the gas carbon monoxide (CO). Generation of CO through heme catabolism by HO-1 prevents the onset of cerebral malaria. The protective effect of CO is mediated via its binding to cell-free hemoglobin (Hb) released from infected red blood cells during the blood stage of Plasmodium infection. Binding of CO to cell-free Hb prevents heme release and thus generation of free heme, which we found to play a central role in the pathogenesis of cerebral malaria. We will address hereby how defense mechanisms that prevent the deleterious effects of free heme, including the expression of HO-1, impact on the pathologic outcome of Plasmodium infection and how these may be used therapeutically to suppress its lethal outcomes.

Chemokine gene expression during fatal murine cerebral malaria and protection due to CXCR3 deficiency

Cerebral malaria (CM) can be a fatal manifestation of Plasmodium falciparum infection. Using murine models of malaria, we found much greater up-regulation of a number of chemokine mRNAs, including those for CXCR3 and its ligands, in the brain during fatal murine CM (FMCM) than in a model of non-CM. Expression of CXCL9 and CXCL10 RNA was localized predominantly to the cerebral microvessels and in adjacent glial cells, while expression of CCL5 was restricted mainly to infiltrating lymphocytes. The majority of mice deficient in CXCR3 were found to be protected from FMCM, and this protection was associated with a reduction in the number of CD8+ T cells in brain vessels as well as reduced expression of perforin and FasL mRNA. Adoptive transfer of CD8+ cells from C57BL/6 mice with FMCM abrogated this protection in CXCR3-/- mice. Moreover, there were decreased mRNA levels for the proinflammatory cytokines IFN-gamma and lymphotoxin-alpha in the brains of mice protected from FMCM. These data suggest a role for CXCR3 in the pathogenesis of FMCM through the recruitment and activation of pathogenic CD8+ T cells.

Macrophage-mediated but gamma interferon-independent innate immune responses control the primary wave of Plasmodium yoelii parasitemia

In most models of blood-stage malaria infection, proinflammatory immune responses are required for control of infection and elimination of parasites. We hypothesized therefore that the fulminant infections caused in mice by the lethal strain of Plasmodium yoelii (17XL) might be due to failure to activate a sufficient inflammatory response. Here we have compared the adaptive CD4+ T-cell and innate immune response to P. yoelii 17XL with that induced by the self-resolving, nonlethal strain of P. yoelii, 17X(NL). During the first 7 to 9 days of infection, splenic effector CD4+ T-cell responses were similar in mice with lethal and nonlethal infections with similar levels of activation in vivo and equivalent proliferation in vitro following mitogenic stimulation. Nonspecific T-cell hyporesponsiveness was observed at similar levels during both infections and was due, in part, to suppression mediated by CD11b+ cells. Importantly, however, RAG-/- mice were able to control the initial growth phase of nonlethal P. yoelii infection as effectively as wild-type mice, indicating that T cells and/or B cells play little, if any, role in control of the primary peak of parasitemia. Somewhat unexpectedly, we could find no clear role for either NK cells or gamma interferon (IFN-gamma) in controlling primary P. yoelii infection. In contrast, depletion of monocytes/macrophages exacerbated parasite growth and anemia during both lethal and nonlethal acute P. yoelii infections, indicating that there is an IFN-gamma-, NK cell-, and T-cell-independent pathway for induction of effector macrophages during acute malaria infection.

Gene-knockout mice in malaria research: useful or misleading?

Gene-knockout mice have been extensively used in the study of several malaria-induced pathologies. Some investigators believe that the deficient, infected mice mimic disease aspects produced in the absence of the target gene, but others believe that the deficient mice models mainly explain the effects of compensatory, related molecules. Comparison of some of the most relevant knockout mouse studies for understanding cerebral malaria and parasitemia and their related human reports shows that gene-knockout mice are useful tools that support conclusions from human genetic studies. These mice have helped to indicate new resistance genes against human malaria and have provided valuable information about mechanisms of malaria resistance in mice.