Origin of reactive oxygen species in erythrocytes infected with Plasmodium falciparum

Redox Homeostasis within the Drug-Resistant Malarial Parasite Digestive Vacuole

We have developed a cost-effective strategy for the complete synthesis of azetidinyl coumarin fluorophore derivatives that report changes in physiologic levels of glutathione (GSH), which includes a more cost- effective synthesis of the probe precursor hydroxyl derivative and its subsequent derivatization to promote subcellular localization. We functionalize coumarin derivatives with a cyano side chain similar to a previous strategy (Jiang X. et al., Nature Communications 2017, 8; 16087) and validate the 7-azetidinyl conformation as an explanation for enhanced GSH-dependent coumarin fluorescence. We couple the azetidinyl probe to different mass dextrans using either no linker or a 6C linker and also synthesize a morpholino derivative. We titrate the fluorescence of the different functionalized probes vs [GSH] in vitro. We load one dextran-conjugated probe within the digestive vacuole (DV) of live intraerythrocytic P. falciparum malarial parasites and also measure cytosolic localization of the morpholino probe. Using significantly improved single-cell photometry (SCP) methods, we show that the morpholino probe faithfully reports [GSH] from the live parasite cytosol, while the 70 kDa dextran-conjugated probe reports DV redox homeostasis for control chloroquine-sensitive (CQS) and artemisinin-sensitive (ARTS) transfectant parasites vs their genetically matched chloroquine-resistant (CQR)/artemisinin-sensitive (CQR/ARTS) and CQR artemisinin-resistant (CQR/ARTR) strains, respectively. We quantify rapid changes in DV redox homeostasis for these parasites ± drug pulses under live-cell perfusion conditions. The results are important for understanding the pharmacology of antimalarial drugs and the molecular mechanisms underlying CQR and ARTR phenomena.

Chemical propulsion of hemozoin crystal motion in malaria parasites

Malaria parasites infect red blood cells where they digest host hemoglobin and release free heme inside a lysosome-like organelle called the food vacuole. To detoxify excess heme, parasites form hemozoin crystals that rapidly tumble inside this compartment. Hemozoin formation is critical for parasite survival and antimalarial drug activity, but crystal motion and its underlying mechanism are unexplored. We used quantitative image analysis to determine the timescale of motion, which requires the intact vacuole but does not require the parasite itself. Using single-particle tracking and Brownian dynamics simulations with experimentally derived interaction potentials, we found that hemozoin motion exhibits unexpectedly tight confinement but is much faster than thermal diffusion. Hydrogen peroxide, which is generated at high concentrations in the food vacuole, has been shown to stimulate metallic nanoparticle motion via surface-catalyzed peroxide decomposition that generates propulsive kinetic energy. We observed that peroxide stimulated the motion of isolated crystals in solution and that conditions that suppress peroxide formation slowed hemozoin motion inside parasites. These data suggest that surface-exposed metals on hemozoin catalyze peroxide decomposition to drive crystal motion and strengthen oxidative stress protection during blood-stage infection. This work reveals hemozoin motion in malaria parasites as a biological example of a self-propelled nanoparticle.

Testosterone Modulates Oxidative Stress in a Sexually Dimorphic Manner in CBA/Ca Mice Infected with Plasmodium berghei ANKA

Malaria, the deadliest parasitic disease in the world, is sexually dimorphic, inflammatory, and oxidative. Males experience more severe symptoms and mortality than females do; therefore, the roles of 17β-estradiol and testosterone in this phenomenon have been studied. Both hormones affect oxidative stress, the primary mechanism of Plasmodium elimination. Estradiol has antioxidant activity, but the role of testosterone is controversial. Testosterone increases oxidative stress by reducing superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) activities, which increase lipoperoxidation in the testis. However, the antioxidant properties of testosterone in prostate and nervous tissue have also been reported. The discrepancies are probably because when testosterone levels increase, the aromatase enzyme transforms testosterone into estrogens that possess antioxidant activity, which masks the results. Therefore, it is unknown whether testosterone is involved in the sexual dimorphism that occurs in oxidative stress in malaria. In this work, we administered testosterone and simultaneously inhibited aromatase with letrozole to evaluate the role of testosterone in the sexually dimorphic pattern of oxidative stress that occurs in the blood, spleen, and brain of male and female CBA/Ca mice infected with Plasmodium berghei ANKA (P. berghei ANKA). Testosterone triggers parasitemia in males, who also display more oxidative stress than females in the absence of infection, leading to sexually dimorphic patterns. Interestingly, increasing testosterone levels in infected mice reduced oxidative stress in males and increased oxidative stress in females, reversing or eliminating the dimorphic patterns observed. Oxidative stress varies in each tissue; the brain was the most protected, while the blood was the greatest damaged. Our findings highlight the role of testosterone as a regulator of oxidative stress in a tissue and sex-specific manner; therefore, understanding the role of testosterone in malaria may contribute to the development of sex-specific personalized antimalarial therapies.

Malaria parasite cysteine and aspartic proteases as key drug targets for antimalarial therapy

CONTEXT

Cysteine and aspartic proteases are enzyme families that play crucial roles in the life cycle of Plasmodium, the parasite responsible for malaria. These proteases are involved in vital biological processes, such as hemoglobin degradation within the host's red blood cells, protein turnover, and regulation of parasite development. Inhibiting these proteases with small molecule drugs can block the parasite's growth and survival. Chemically, these enzymes have specific active sites where inhibitors can bind, preventing the breakdown of key proteins, making them attractive targets for the design of novel antimalarial compounds. Understanding the structure and catalytic mechanisms of these proteases is critical for developing selective and potent inhibitors. The degradation of hemoglobin occurs in the parasite's digestive vacuole, and disruption of this process by targeting these proteases can inhibit parasite development, leading to the death of the parasite. Hence, these proteases are critical for maintaining the parasite's metabolic functions, and inhibiting them can disrupt the parasite's life cycle. Malaria remains a major global health problem, particularly in tropical and subtropical regions, where resistance to existing antimalarial drugs, such as chloroquine and artemisinin-based therapies, is an escalating issue. The emergence of drug-resistant Plasmodium strains highlights the urgent need for new therapeutic strategies. Targeting cysteine and aspartic proteases offers a novel approach to antimalarial drug development, as these enzymes are crucial for parasite survival and have not been widely exploited in current therapies. By inhibiting these proteases, researchers aim to develop new antimalarial treatments that could overcome resistance mechanisms and provide more effective options for malaria control and eradication.

METHODS

The application of computational methods such as molecular docking, dynamics simulations, and quantum mechanical calculations, combined with powerful molecular modeling tools, provides a comprehensive framework for discovering and optimizing inhibitors targeting Plasmodium cysteine and aspartic proteases. These methods facilitate the rational design of novel antimalarial drugs, offering a pathway to overcome drug resistance and improve therapeutic outcomes.

Artemisinin-resistant Plasmodium falciparum Kelch13 mutant proteins display reduced heme-binding affinity and decreased artemisinin activation

The potency of frontline antimalarial drug artemisinin (ART) derivatives is triggered by heme-induced cleavage of the endoperoxide bond to form reactive heme-ART alkoxy radicals and covalent heme-ART adducts, which are highly toxic to the parasite. ART-resistant (ART-R) parasites with mutations in the Plasmodium falciparum Kelch-containing protein Kelch13 (PfKekch13) exhibit impaired hemoglobin uptake, reduced yield of hemoglobin-derived heme, and thus decreased ART activation. However, any direct involvement of PfKelch13 in heme-mediated ART activation has not been reported. Here, we show that the purified recombinant PfKelch13 wild-type (WT) protein displays measurable binding affinity for iron and heme, the main effectors for ART activation. The heme-binding property is also exhibited by the native PfKelch13 protein from parasite culture. The two ART-R recombinant PfKelch13 mutants (C580Y and R539T) display weaker heme binding affinities compared to the ART-sensitive WT and A578S mutant proteins, which further translates into reduced yield of heme-ART derivatives when ART is incubated with the heme molecules bound to the mutant PfKelch13 proteins. In conclusion, this study provides the first evidence for ART activation via the heme-binding propensity of PfKelch13. This mechanism may contribute to the modulation of ART-R levels in malaria parasites through a novel function of PfKelch13.

Identification of a divalent metal transporter required for cellular iron metabolism in malaria parasites

Plasmodium falciparum malaria parasites invade and multiply inside red blood cells (RBCs), the most iron-rich compartment in humans. Like all cells, P. falciparum requires nutritional iron to support essential metabolic pathways, but the critical mechanisms of iron acquisition and trafficking during RBC infection have remained obscure. Parasites internalize and liberate massive amounts of heme during large-scale digestion of RBC hemoglobin within an acidic food vacuole (FV) but lack a heme oxygenase to release porphyrin-bound iron. Although most FV heme is sequestered into inert hemozoin crystals, prior studies indicate that trace heme escapes biomineralization and is susceptible to nonenzymatic degradation within the oxidizing FV environment to release labile iron. Parasites retain a homolog of divalent metal transporter 1 (DMT1), a known mammalian iron transporter, but its role in P. falciparum iron acquisition has not been tested. Our phylogenetic studies indicate that P. falciparum DMT1 (PfDMT1) retains conserved molecular features critical for metal transport. We localized this protein to the FV membrane and defined its orientation in an export-competent topology. Conditional knockdown of PfDMT1 expression is lethal to parasites, which display broad cellular defects in iron-dependent functions, including impaired apicoplast biogenesis and mitochondrial polarization. Parasites are selectively rescued from partial PfDMT1 knockdown by supplementation with exogenous iron, but not other metals. These results support a cellular paradigm whereby PfDMT1 is the molecular gatekeeper to essential iron acquisition by blood-stage malaria parasites and suggest that therapeutic targeting of PfDMT1 may be a potent antimalarial strategy.

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.

Identification of a divalent metal transporter required for cellular iron metabolism in malaria parasites

Plasmodium falciparum malaria parasites invade and multiply inside red blood cells (RBCs), the most iron-rich compartment in humans. Like all cells, P. falciparum requires nutritional iron to support essential metabolic pathways, but the critical mechanisms of iron acquisition and trafficking during RBC infection have remained obscure. Parasites internalize and liberate massive amounts of heme during large-scale digestion of RBC hemoglobin within an acidic food vacuole (FV) but lack a heme oxygenase to release porphyrin-bound iron. Although most FV heme is sequestered into inert hemozoin crystals, prior studies indicate that trace heme escapes biomineralization and is susceptible to non-enzymatic degradation within the oxidizing FV environment to release labile iron. Parasites retain a homolog of divalent metal transporter 1 (DMT1), a known mammalian iron transporter, but its role in P. falciparum iron acquisition has not been tested. Our phylogenetic studies indicate that P. falciparum DMT1 (PfDMT1) retains conserved molecular features critical for metal transport. We localized this protein to the FV membrane and defined its orientation in an export-competent topology. Conditional knockdown of PfDMT1 expression is lethal to parasites, which display broad cellular defects in iron-dependent functions, including impaired apicoplast biogenesis and mitochondrial polarization. Parasites are selectively rescued from partial PfDMT1 knockdown by supplementation with exogenous iron, but not other metals. These results support a cellular paradigm whereby PfDMT1 is the molecular gatekeeper to essential iron acquisition by blood-stage malaria parasites and suggest that therapeutic targeting of PfDMT1 may be a potent antimalarial strategy.

Host-parasite interaction in severe and uncomplicated malaria infection in ghanaian children

PURPOSE

During malarial infection, both parasites and host red blood cells (RBCs) come under severe oxidative stress due to the production of free radicals. The host system responds in protecting the RBCs against the oxidative damage caused by these free radicals by producing antioxidants. In this study, we investigated the antioxidant enzyme; superoxide dismutase (SOD) activity and cytokine interactions with parasitaemia in Ghanaian children with severe and uncomplicated malaria.

METHODOLOGY

One hundred and fifty participants aged 0-12 years were administered with structured questionnaires. Active case finding approach was used in participating hospitals to identify and interview cases before treatment was applied. Blood samples were taken from each participant and used to quantify malaria parasitaemia, measure haematological parameters and SOD activity. Cytokine levels were measured by commercial ELISA kits. DNA comet assay was used to evaluate the extent of parasite DNA damage due to oxidative stress.

RESULTS

Seventy - Nine (79) and Twenty- Six (26) participants who were positive with malaria parasites were categorized as severe (56.75 × 103 ± 57.69 parasites/µl) and uncomplicated malaria (5.87 × 103 ± 2.87 parasites/µl) respectively, showing significant difference in parasitaemia (p < 0.0001). Significant negative correlation was found between parasitaemia and SOD activity levels among severe malaria study participants (p = 0.0428). Difference in cytokine levels (IL-10) amongst the control, uncomplicated and severe malaria groups was significant (p < 0.0001). The IFN-γ/IL-10 /TNF-α/IL-10 ratio differed significantly between the malaria infected and non- malaria infected study participants. DNA comet assay revealed damage to Plasmodium parasite DNA.

CONCLUSION

Critical roles played by SOD activity and cytokines as anti-parasitic defense during P. falciparum malaria infection in children were established.

Alkaloidal Extracts from Avicennia africana P. Beauv. (Avicenniaceae) Leaf: An Antiplasmodial, Antioxidant, and Erythrocyte Viable

Background

The emergence of drug-resistant parasites impedes disease management and eradication efforts. Hence, a reinvigorated attempt to search for potent lead compounds in the mangroves is imperative.

Aim

This study evaluates in vitro antiplasmodial activity, antioxidant properties, and cytotoxicity of A. africana leaf alkaloidal extracts.

Methods

The A. africana leaves were macerated with 70% ethanol to obtain a total crude extract. Dichloromethane and chloroform-isopropanol (3 : 1, v/v) were used to extract the crude alkaloids and quaternary alkaloids from the total crude. The antiplasmodial activities of the alkaloidal extracts were performed against 3D7 P. falciparum chloroquine-sensitive clone via the SYBR Green I fluorescence assay with artesunate serving as the reference drug. The alkaloidal extracts were further evaluated for antioxidant properties via the total antioxidant capacity (TAC), the total glutathione concentration (GSH), the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, and the ferric-reducing antioxidant power (FRAP) methods. The cytotoxic activity of the alkaloidal extracts was tested on erythrocytes using a 3-(4,5-dimethylthiazol-2-yl)-5-diphenyltetrazolium bromide-MTT assay with little modification. The phytocompounds in the alkaloidal extracts were identified via gas chromatography-mass spectrometry (GC-MS) techniques.

Results

The total crude extract showed good antiplasmodial activity (IC50 = 11.890 µg/mL). The crude and quaternary alkaloidal extracts demonstrated promising antiplasmodial effects with IC50 values of 6.217 and 6.285 µg/mL, respectively. The total crude and alkaloidal extracts showed good antioxidant properties with negligible cytotoxicity on erythrocytes with good selectivity indices. The GC-MS spectral analysis of crude alkaloidal extracts gave indole and isoquinoline alkaloids and several other compounds. Dexrazoxane was found to be the main compound predicted, with an 86% peak area in the quaternary alkaloidal extract.

Conclusion

The crude and quaternary alkaloidal extracts exhibited antiplasmodial activities and ability to inhibit oxidative stress with negligible toxicity on erythrocytes. This may be good characteristics to avoid oxidative stress related to Plasmodium infection in the treatment of malaria.

In vitro and in vivo antimalarial activity of green synthesized silver nanoparticles using Sargassum tenerrimum - a marine seaweed

Green nanotechnology has recently attracted a lot of attention as a potential technique for drug development. In the present study, silver nanoparticles were synthesised by using Sargassum tenerrimum, a marine seaweed crude extract (Ag-ST), and evaluated for antimalarial activity in both in vitro and in vivo models. The results showed that Ag-ST nanoparticles exhibited good antiplasmodial activity with IC50 values 7.71±0.39 µg/ml and 23.93±2.27 µg/ml against P. falciparum and P. berghei respectively. These nanoparticles also showed less haemolysis activity suggesting their possible use in therapeutics. Further, P. berghei infected C57BL/6 mice were used for the four-day suppressive, curative and prophylactic assays where it was noticed that the Ag-ST nanoparticles significantly reduced the parasitaemia and there were no toxic effects observed in the biochemical and haematological parameters. Further to understand its possible toxic effects, both in vitro and in vivo genotoxicological studies were performed which revealed that these nanoparticles are non-genotoxic in nature. The possible antimalarial activity of Ag-ST may be due to the presence of bioactive phytochemicals and silver ions. Moreover, the phytochemicals prevent the nonspecific release of ions responsible for low genotoxicity. Together, the bio-efficacy and toxicology outcomes demonstrated that the green synthesized silver nanoparticles (Ag-ST) could be a cutting-edge alternative for therapeutic applications.

Course of Plasmodium infection studied using 2D-COS on human erythrocytes

BACKGROUND

The threat of malaria is still present in the world. Recognizing the type of parasite is important in determining a treatment plan. The golden routine involves microscopic diagnostics of Giemsa-stained thin blood smears, however, alternative methods are also constantly being sought, in order to gain an additional insight into the course of the disease. Spectroscopic methods, e.g., Raman spectroscopy, are becoming increasingly popular, due to the non-destructive nature of these techniques.

METHODS

The study included patients hospitalized for malaria caused by Plasmodium falciparum or Plasmodium vivax, in the Department of Infectious Diseases at the University Hospital in Krakow, Poland, as well as healthy volunteers. The aim of this study was to assess the possibility of using Raman spectroscopy and 2D correlation (2D-COS) spectroscopy in understanding the structural changes in erythrocytes depending on the type of attacking parasite. EPR spectroscopy and two-trace two-dimensional (2T2D) correlation was also used to examine the specificity of paramagnetic centres found in the infected human blood.

RESULTS

Two-dimensional (2D) correlation spectroscopy facilitates the identification of the hidden relationship, allowing for the discrimination of Raman spectra obtained during the course of disease in human red blood cells, infected by P. falciparum or P. vivax. Synchronous cross-peaks indicate the processes taking place inside the erythrocyte during the export of the parasite protein towards the cell membrane. In contrast, moieties that generate asynchronous 2D cross-peaks are characteristic of the respective ligand-receptor domains. These changes observed during the course of the infection, have different dynamics for P. falciparum and P. vivax, as indicated by the asynchronous correlation cross-peaks. Two-trace two-dimensional (2T2D) spectroscopy, applied to EPR spectra of blood at the beginning of the infection, showed differences between P. falciparum and P. vivax.

CONCLUSIONS

A unique feature of 2D-COS is the ability to discriminate the collected Raman and EPR spectra. The changes observed during the course of a malaria infection have different dynamics for P. falciparum and P. vivax, indicated by the reverse sequence of events. For each type of parasite, a specific recycling process for iron was observed in the infected blood.

Influence of Cucurbiturils on the Production of Reactive Oxygen Species by T- and B-Lymphocytes, Platelets and Red Blood Cells

Reactive oxygen species (ROS) are highly reactive chemical molecules containing oxygen. ROS play an important role in signaling and cell homeostasis at low and moderate concentrations. ROS could be a cause of damage to proteins, nucleic acids, lipids, membranes and organelles at high concentrations. There are a lot of cells that can produce ROS to maintain functional activity. It is known that metal nanoparticles can increase production of ROS in cells. However, the effect of cucurbiturils on ROS production is still unknown. In our study, we evaluated production of ROS by the immune (T-, B-lymphocytes, NK-cells) and non-immune cells (red blood cells, platelets), as well as tumor cells line (1301, K562) after treatment with cucurbiturils in vitro. Assessment of reactive oxide species (ROS) were provided by using dihydrorhodamine 123 (DHR 123). Fluorescence intensity and percentage DHR123 were measured by flow cytometry. Platelets, erythrocytes and activated T-helpers were changed the level of ROS production in response to stimulation with cucurbiturils. It was found that the percentage of these ROS-producing cells was reduced by cucurbiturils. Thus, cucurbiturils may affect the production of ROS by cells, but further research is needed in this area.

Luffa cylindrica (Linn. M. J. Roem) Reduces Oxidative Stress In Vivo in Plasmodium berghei-Infected Albino Mice

Background: Malaria is endemic in sub-Saharan Africa, and oxidative stress has been implicated in malaria disease. Luffa cylindrica is an ethnomedicinal plant used to treat various diseases, including malaria. The oxidative stress-reducing potential of L. cylindrica in malaria-disease state of Plasmodium berghei NK-65 parasite-infected mice was carried out in vivo.

Methods: Mice were infected with P. berghei NK-65, and the effect of administration of methanolic leaves extract (100, 200, and 400 mg/kg b.w) of L. cylindrica on percentage parasitemia in blood smear, antioxidant enzymes (catalase CAT, superoxide dismutase SOD, glutathione-s-transferase GST), non-enzymatic antioxidant (reduced glutathione GSH) and malondialdehyde concentration in tissues (plasma, liver, kidneys, and spleen) of mice was investigated and compared to chloroquine and artesunate as reference antimalarial drugs. Phytochemical constituents of the extract were determined by standard methods.

Results: Saponins, tannins, terpenes, phenolics, flavonoids, alkaloids, and glycosides were the phytochemical constituents identified in the extract. The extract at three doses (100, 200, and 400 mg/kg b.w.) investigated caused a significant reduction (p < 0.05) of parasite growth with over 90% reduction in parasitemia level in mice infected with the parasite. The extract also ameliorated oxidative stress in mice by significantly (p < 0.05) increasing the activities of CAT, SOD, and GST in the studied tissues of mice. The level of malondialdehyde, a marker of oxidative stress in mice, was also significantly (p < 0.05) reduced by the extract. The results were comparable with chloroquine- and artesunate-treated groups.

Conclusion: The study concludes that L. cylindrica is an effective therapy for treating malaria and for the management of its oxidative stress-related complications due to its antioxidant properties.

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.

Impact of Oxidative Stress on Risk of Death and Readmission in African Children With Severe Malaria: A Prospective Observational Study

BACKGROUND

We hypothesized that oxidative stress in Ugandan children with severe malaria is associated with mortality.

METHODS

We evaluated biomarkers of oxidative stress in children with cerebral malaria (CM, n = 77) or severe malarial anemia (SMA, n = 79), who were enrolled in a randomized clinical trial of immediate vs delayed iron therapy, compared with community children (CC, n = 83). Associations between admission biomarkers and risk of death during hospitalization or risk of readmission within 6 months were analyzed.

RESULTS

Nine children with CM and none with SMA died during hospitalization. Children with CM or SMA had higher levels of heme oxygenase-1 (HO-1) (P < .001) and lower superoxide dismutase (SOD) activity than CC (P < .02). Children with CM had a higher risk of death with increasing HO-1 concentration (odds ratio [OR], 6.07 [95% confidence interval {CI}, 1.17-31.31]; P = .03) but a lower risk of death with increasing SOD activity (OR, 0.02 [95% CI, .001-.70]; P = .03). There were no associations between oxidative stress biomarkers on admission and risk of readmission within 6 months of enrollment.

CONCLUSIONS

Children with CM or SMA develop oxidative stress in response to severe malaria. Oxidative stress is associated with higher mortality in children with CM but not with SMA.

CLINICAL TRIALS REGISTRATION

NCT01093989.

Eryptosis as a New Insight in Malaria Pathogenesis

Eryptosis is a programmed cell death-like process that occurs in red blood cells. Although the red blood cells are anucleated, there are similarities between eryptosis and apoptosis, such as increased calcium efflux, calpain activation, phosphatidylserine exposure, cell blebbing and cell shrinkage. Eryptosis occurs physiologically in red blood cells, as a consequence of the natural senescence process of these cells, but it can also be stimulated in pathological situations such as metabolic syndromes, uremic syndromes, polycythemia vera, anemias such as sickle cell anemia and thalassemia, and infectious processes including Plasmodium infection. Infection-induced eryptosis is believed to contribute to damage caused by Plasmodium, but it’s still a topic of debate in the literature. In this review, we provided an overview of eryptosis mechanisms and its possible pathogenic role in malaria.

Docosahexaenoic acid is potent against the growth of mature stages of Plasmodium falciparum; inhibition of hematin polymerization a possible target

The present study investigates the potential effect of externally added unsaturated fatty acids on P. falciparum growth. Our results indicate that polyunsaturated fatty acids (PUFAs) inhibit the growth of Plasmodium in proportional to their degree of unsaturation. At higher concentration the PUFA Docosahexaenoic acid (DHA) induces pyknotic nuclei in infected erythrocytes. When Plasmodium stages were treated transiently with DHA, the ring stage culture recovered from the drug effect and parasitemia was increased post DHA removal with delayed growth of 12 h, compared to untreated control. Schizont stage treated culture displayed a 36 h delay in growth to infect fresh erythrocytes signifying its recovery is less than the ring stage. However the trophozoite stage failed to recover and showed a decrease in parasitemia, similar to that of continuous treated culture. PUFAs inhibited β- hematin polymerization by binding to free heme derived from hemoglobin degradation. Digestive vacuole neutral lipid bodies, which are pivotal for β- hematin polymerization, decreased and subsequently abrogated with increasing concentration of DHA in trophozoite stage treated culture. Our study concludes that DHA interacts with heme monomers and inhibits the β- hematin polymerization and growth of mature stages i.e., trophozoite and schizont stages of plasmodium.

An in vitro study on the differentiated metabolic mechanism of chloroquine-resistant Plasmodium falciparum using high-resolution metabolomics

Chloroquine (CQ) is an important drug used therapeutically for treatment of malaria. However, due to limited number of studies on metabolic targets of chloroquine (CQ), it is difficult to attribute mechanisms underlying resistance associated with usage of this drug. The present study aimed to investigate the metabolic signatures of CQ-resistant Plasmodium falciparum (PfDd2) compared to CQ-sensitive Plasmodium falciparum (Pf3D7). Both Pf3D7 and PfDd2 were treated with CQ at 200 nM for 48 hr; thereafter, the harvested red blood cells (RBCs) and media were subjected to microscopy and high-resolution metabolomics (HRM). Glutathione, γ-L-glutamyl-L-cysteine, spermidine, inosine monophosphate, alanine, and fructose-1,6-bisphosphate were markedly altered in PfDd2 of RBC. In the media, cysteine, cysteic acid, spermidine, phenylacetaldehyde, and phenylacetic acid were significantly altered in PfDd2. These differential metabolic signatures related signaling pathways of PfDd2, such as oxidative stress pathway and glycolysis may provide evidence for understanding the resistance mechanism and pathogenesis of the CQ-resistant parasite.

Biomarkers of cellular aging during a controlled human malaria infection

Cellular aging is difficult to study in individuals with natural infection, given the diversity of symptom duration and clinical presentation, and the high interference of aging-related processes with host and environmental factors. To address this challenge, we took advantage of the controlled human malaria infection (CHMI) model. This approach allowed us to characterize the relationship among cellular aging markers prior, during and post malaria pathophysiology in humans, controlling for infection dose, individual heterogeneity, previous exposure and co-infections. We demonstrate that already low levels of Plasmodium falciparum impact cellular aging by inducing high levels of inflammation and redox-imbalance; and that cellular senescence reversed after treatment and parasite clearance. This study provides insights into the complex relationship of telomere length, cellular senescence, telomerase expression and aging-related processes during a single malaria infection.

An SR protein is essential for activating DNA repair in malaria parasites

Plasmodium falciparum, the parasite responsible for the deadliest form of human malaria, replicates within the erythrocytes of its host, where it encounters numerous pressures that cause extensive DNA damage, which must be repaired efficiently to ensure parasite survival. Malaria parasites, which have lost the non-homologous end joining (NHEJ) pathway for repairing DNA double-strand breaks, have evolved unique mechanisms that enable them to robustly maintain genome integrity under such harsh conditions. However, the nature of these adaptations is unknown. We show that a highly conserved RNA splicing factor, P. falciparum (Pf)SR1, plays an unexpected and crucial role in DNA repair in malaria parasites. Using an inducible and reversible system to manipulate PfSR1 expression, we demonstrate that this protein is recruited to foci of DNA damage. Although loss of PfSR1 does not impair parasite viability, the protein is essential for their recovery from DNA-damaging agents or exposure to artemisinin, the first-line antimalarial drug, demonstrating its necessity for DNA repair. These findings provide key insights into the evolution of DNA repair pathways in malaria parasites as well as the ability of the parasite to recover from antimalarial treatment.

Summary: There is an unexpected role for the alternative splicing factor PfSR1 in activating the DNA damage response in the human malaria parasite Plasmodium falciparum.

Synergistic Action between PfHsp90 Inhibitor and PfRad51 Inhibitor Induces Elevated DNA Damage Sensitivity in the Malaria Parasite

The DNA recombinase Rad51 from the human malaria parasite Plasmodium falciparum has emerged as a potential drug target due to its central role in the homologous recombination (HR)-mediated double-strand break (DSB) repair pathway. Inhibition of the ATPase and strand exchange activity of P. falciparum Rad51 (PfRad51) by a small-molecule inhibitor, B02 [3-(phenylmethyl)-2-[(1E)-2-(3-pyridinyl)ethenyl]-4(3H)-quinazolinone], renders the parasite more sensitive to genotoxic agents. Here, we investigated whether the inhibition of the molecular chaperone PfHsp90 potentiates the antimalarial action of B02. We found that the PfHsp90 inhibitor 17-AAG [17-(allylamino)-17-demethoxygeldanamycin] exhibits strong synergism with B02 in both drug-sensitive (strain 3D7) and multidrug-resistant (strain Dd2) P. falciparum parasites. 17-AAG causes a greater than 200-fold decrease in the half-maximal inhibitory concentration (IC50) of B02 in 3D7 parasites. Our results provide mechanistic insights into such profound synergism between 17-AAG and B02. We report that PfHsp90 physically interacts with PfRad51 and promotes the UV irradiation-induced DNA repair activity of PfRad51 by controlling its stability. We find that 17-AAG reduces PfRad51 protein levels by accelerating proteasomal degradation. Consequently, PfHsp90 inhibition renders the parasites more susceptible to the potent DNA-damaging agent methyl methanesulfonate (MMS) in a dose-dependent manner. Thus, our study provides a rationale for targeting PfHsp90 along with the recombinase PfRad51 for controlling malaria propagation.

Structure-Based Identification and Functional Characterization of a Lipocalin in the Malaria Parasite Plasmodium falciparum

Proteins of the lipocalin family are known to bind small hydrophobic ligands and are involved in various physiological processes ranging from lipid transport to oxidative stress responses. The genome of the malaria parasite Plasmodium falciparum contains a single protein PF3D7_0925900 with a lipocalin signature. Using crystallography and small-angle X-ray scattering, we show that the protein has a tetrameric structure of typical lipocalin monomers; hence we name it P. falciparum lipocalin (PfLCN). We show that PfLCN is expressed in the intraerythrocytic stages of the parasite and localizes to the parasitophorous and food vacuoles. Conditional knockdown of PfLCN impairs parasite development, which can be rescued by treatment with the radical scavenger Trolox or by temporal inhibition of hemoglobin digestion. This suggests a key function of PfLCN in counteracting oxidative stress-induced cell damage during multiplication of parasites within erythrocytes.

Dual RNA Sequencing Meta-analysis in Plasmodium Infection Identifies Host-Parasite Interactions

Dual RNA sequencing (RNA-Seq) is the simultaneous transcriptomic analysis of interacting symbionts, for example, in malaria. Potential cross-species interactions identified by correlated gene expression might highlight interlinked signaling, metabolic, or gene regulatory pathways in addition to physically interacting proteins. Often, malaria studies address one of the interacting organisms-host or parasite-rendering the other "contamination." Here we perform a meta-analysis using such studies for cross-species expression analysis. We screened experiments for gene expression from host and Plasmodium. Out of 171 studies in Homo sapiens, Macaca mulatta, and Mus musculus, we identified 63 potential studies containing host and parasite data. While 16 studies (1,950 samples) explicitly performed dual RNA-Seq, 47 (1,398 samples) originally focused on one organism. We found 915 experimental replicates from 20 blood studies to be suitable for coexpression analysis and used orthologs for meta-analysis across different host-parasite systems. Centrality metrics from the derived gene expression networks correlated with gene essentiality in the parasites. We found indications of host immune response to elements of the Plasmodium protein degradation system, an antimalarial drug target. We identified well-studied immune responses in the host with our coexpression networks, as our approach recovers known broad processes interlinked between hosts and parasites in addition to individual host and parasite protein associations. The set of core interactions represents commonalities between human malaria and its model systems for prioritization in laboratory experiments. Our approach might also allow insights into the transferability of model systems for different pathways in malaria studies.IMPORTANCE Malaria still causes about 400,000 deaths a year and is one of the most studied infectious diseases. The disease is studied in mice and monkeys as lab models to derive potential therapeutic intervention in human malaria. Interactions between Plasmodium spp. and its hosts are either conserved across different host-parasite systems or idiosyncratic to those systems. Here we use correlation of gene expression from different RNA-Seq studies to infer common host-parasite interactions across human, mouse, and monkey studies. First, we find a set of very conserved interactors, worth further scrutiny in focused laboratory experiments. Second, this work might help assess to which extent experiments and knowledge on different pathways can be transferred from models to humans for potential therapy.

4-Chlorothymol Exerts Antiplasmodial Activity Impeding Redox Defense System in Plasmodium falciparum

Malaria remains one of the major health concerns due to the resistance of Plasmodium species toward the existing drugs warranting an urgent need for new antimalarials. Thymol derivatives were known to exhibit enhanced antimicrobial activities; however, no reports were found against Plasmodium spp. In the present study, the antiplasmodial activity of thymol derivatives was evaluated against chloroquine-sensitive (NF-54) and -resistant (K1) strains of Plasmodium falciparum. Among the thymol derivatives tested, 4-chlorothymol showed potential activity against sensitive and resistant strains of P. falciparum. 4-Chlorothymol was found to increase the reactive oxygen species and reactive nitrogen species level. Furthermore, 4-chlorothymol could perturb the redox balance by modulating the enzyme activity of GST and GR. 4-Chlorothymol also showed synergy with chloroquine against chloroquine-resistant P. falciparum. 4-Chlorothymol was found to significantly suppress the parasitemia and increase the mean survival time in in vivo assays. Interestingly, in in vivo assay, 4-chlorothymol in combination with chloroquine showed higher chemosuppression as well as enhanced mean survival time at a much lower concentration as compared to individual doses of chloroquine and 4-chlorothymol. These observations clearly indicate the potential use of 4-chlorothymol as an antimalarial agent, which may also be effective in combination with the existing antiplasmodial drugs against chloroquine-resistant P. falciparum infection. In vitro cytotoxicity/hemolytic assay evidently suggests that 4-chlorothymol is safe for further exploration of its therapeutic properties.

In vitro and in vivo antiplasmodial activity of hydroethanolic bark extract of Bridelia atroviridis müll. Arg. (Euphorbiaceae) and lc-ms-based phytochemical analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Malaria is a life-threatening health problem worldwide and treatment remains a major challenge. Natural products from medicinal plants are credible sources for better anti-malarial drugs.

AIM OF THE STUDY

This study aimed at assessing the in vitro and in vivo antiplasmodial activities of the hydroethanolic extract of Bridelia atroviridis bark.

MATERIALS AND METHODS

The phytochemical characterization of Bridelia atroviridis extract was carried out by High-Performance Liquid Chromatography-Mass spectrometry (HPLC-MS). The cytotoxicity test on Vero cells was carried out using the resazurin-based assay while the in vitro antiplasmodial activity was determined on Plasmodium falciparum (Dd2 strain, chloroquine resistant) using the SYBR green I-based fluorescence assay. The in vivo assay was performed on Plasmodium berghei-infected rats daily treated for 5 days with distilled water (10 mL/kg) for malaria control, 25 mg/kg of chloroquine sulfate for positive control and 50, 100 and 200 mg/kg of B. atroviridis extract for the three test groups. Parasitaemia was daily monitored using 10% giemsa-staining thin blood smears. At the end of the treatment, animals were sacrificed, blood was collected for hematological and biochemical analysis while organs were removed for biochemical and histopathological analyses.

RESULTS

The HPLC-MS analysis data of B. atroviridis revealed the presence of bridelionoside D, isomyricitrin, corilagin, myricetin and 5 others compounds not yet identified. Bridelia atroviridis exhibited good in vitro antiplasmodial activity with the IC₅₀ evaluated at 8.08 μg/mL and low cytotoxicity with the median cytotoxic concentration (CC₅₀) higher than 100 μg/mL. B. atroviridis extract significantly reduced the parasitemia (p < 0.05) with an effective dose-50 (ED-50) of 89 mg/kg. B. atroviridis also prevented anemia, leukocytosis and liver and kidneys impairment by decrease of transaminases, ALP, creatinine, uric acid, and triglycerides concentrations. As well, B. atroviridis extract decreased some pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) levels and significantly improved the anti-inflammatory status (P < 0.01) of infected animals marked by a decrease of IL-10 concentration. These results were further confirmed by the improved of antioxidant status and the quasi-normal microarchitecture of the liver, kidneys and spleen in test groups. Overall, the hydroethanolic bark extract of Bridelia atroviridis demonstrated antimalarial property and justified its use in traditional medicine to manage malaria disease.

Biomarkers of disease severity in vivax malaria

Severe complications have been observed and established for Plasmodium falciparum as well as P. vivax infections worldwide. Although P. vivax infection is not fully acknowledged as malignant malaria, recently life-threatening complications have been reported to occur in many studies. The recognition of biomarkers with excellent sensitivity and reliability plays a prime role in disease management. Acute inflammatory response and oxidative stress are observed in malaria due to the production of reactive oxygen species. Lipid and protein oxidative injuries are prospective biomarkers for disease severity owing to the damage caused by the parasite. We have tried to find out whether protein carbonylation (PC), lipid peroxidation (LPO) and superoxide dismutase (SOD) could suffice as a biomarker for severe vivax malaria or not. Blood samples were collected from the individuals attending Jawaharlal Nehru Medical College of Aligarh Muslim University during the wet season of malaria transmission. Microscopy and rapid diagnostic kits were used as a tool for malaria diagnosis. A total of 214 subjects were enrolled for the study: 30 febrile controls and 184 subjects with vivax malaria. Protein carbonylation and lipid peroxidation were found to be directly associated with parasite count and total antioxidant status (TAS). Increase in oxidative stress was also observed in severe vivax malaria patients. Levels of uric acid and bilirubin too were raised in complicated cases. Protein carbonylation was found to be a more reliable indicator of vivax malaria severity than lipid peroxidation.

Redox interactome in malaria parasite Plasmodium falciparum

The malaria-causing parasite Plasmodium falciparum is a severe threat to human health across the globe. This parasite alone causes the highest morbidity and mortality than any other species of Plasmodium. The parasites dynamically multiply in the erythrocytes of the vertebrate hosts, a large number of reactive oxygen species that damage biological macromolecules are produced in the cell during parasite growth. To relieve this intense oxidative stress, the parasite employs an NADPH-dependent thioredoxin and glutathione system that acts as an antioxidant and maintains redox status in the parasite. The mutual interaction of both redox proteins is involved in various biological functions and the survival of the erythrocytic stage of the parasite. Since the Plasmodium species is deficient in catalase and classical glutathione peroxidase, so their redox balance relies on a complex set of five peroxiredoxins, differentially positioned in the cytosol, mitochondria, apicoplast, and nucleus with partly overlapping substrate preferences. Moreover, Plasmodium falciparum possesses a set of members belonging to the thioredoxin superfamily, such as three thioredoxins, two thioredoxin-like proteins, one dithiol, three monocysteine glutaredoxins, and one redox-active plasmoredoxin with largely redundant functions. This review paper aims to discuss and encapsulate the biological function and current knowledge of the functional redox network of Plasmodium falciparum.

Ascorbic acid coadministration with artesunate–amodiaquine, up-regulated antioxidant enzymes gene expression in bone marrow cells and elicited biochemical changes in Plasmodium berghei-infected mice

One of the hallmarks of malaria infection is oxidative stress. This study was aimed at investigating the potential effects of coadministering a therapeutic dose of artesunate–amodiaquine (AS/AQ) with Vitamin C (Vit C) orally on some biochemical parameters and antioxidant enzymes gene expression in bone marrow cells of Plasmodium berghei-infected mice. Thirty male Swiss albino mice were divided into five groups of six mice each as follows: Basal control (not infected with P. berghei), Untreated (P. berghei-infected without treatment), Vit C, AS/AQ and AS/AQ + Vit C combination treated mice. Treatment was done twice daily for three consecutive days. Complete parasite clearance was observed on the second day of treatment in AS/AQ and AS/AQ + Vit C combination treated P. berghei-infected mice. Serum albumin and bilirubin levels were higher in the AS/AQ + Vit C combination treated P. berghei-infected mice compared with those treated with AS/AQ only. Artesunate–amodiaquine + Vit C combination increased superoxide dismutase activity and reduced hydrogen peroxide and malondialdehyde levels in P. berghei-infected mice when compared with the mice treated with only AS/AQ. Furthermore, AS/AQ + Vit C combination significantly up-regulated catalase and glutathione peroxidase-1 (GPx-1) mRNA expression compared with the mice treated with only AS/AQ. This is the first report linking AS/AQ to antioxidant enzyme gene expression in bone marrow cells. Our findings showed that AS/AQ and Vit C coadministration may be beneficial as it ameliorated oxidative stress and up-regulated antioxidant enzyme gene expression in P. berghei-infected mice.

Characterisation of plasmodial transketolases and identification of potential inhibitors: an in silico study

BACKGROUND

Plasmodial transketolase (PTKT) enzyme is one of the novel pharmacological targets being explored as potential anti-malarial drug target due to its functional role and low sequence identity to the human enzyme. Despite this, features contributing to such have not been exploited for anti-malarial drug design. Additionally, there are no anti-malarial drugs targeting PTKTs whereas the broad activity of these inhibitors against PTKTs from other Plasmodium spp. is yet to be reported. This study characterises different PTKTs [Plasmodium falciparum (PfTKT), Plasmodium vivax (PvTKT), Plasmodium ovale (PoTKT), Plasmodium malariae (PmTKT) and Plasmodium knowlesi (PkTKT) and the human homolog (HsTKT)] to identify key sequence and structural based differences as well as the identification of selective potential inhibitors against PTKTs.

METHODS

A sequence-based study was carried out using multiple sequence alignment, phylogenetic tree calculations and motif discovery analysis. Additionally, TKT models of PfTKT, PmTKT, PoTKT, PmTKT and PkTKT were modelled using the Saccharomyces cerevisiae TKT structure as template. Based on the modelled structures, molecular docking using 623 South African natural compounds was done. The stability, conformational changes and detailed interactions of selected compounds were accessed viz all-atom molecular dynamics (MD) simulations and binding free energy (BFE) calculations.

RESULTS

Sequence alignment, evolutionary and motif analyses revealed key differences between plasmodial and the human TKTs. High quality homodimeric three-dimensional PTKTs structures were constructed. Molecular docking results identified three compounds (SANC00107, SANC00411 and SANC00620) which selectively bind in the active site of all PTKTs with the lowest (better) binding affinity ≤ - 8.5 kcal/mol. MD simulations of ligand-bound systems showed stable fluctuations upon ligand binding. In all systems, ligands bind stably throughout the simulation and form crucial interactions with key active site residues. Simulations of selected compounds in complex with human TKT showed that ligands exited their binding sites at different time steps. BFE of protein-ligand complexes showed key residues involved in binding.

CONCLUSIONS

This study highlights significant differences between plasmodial and human TKTs and may provide valuable information for the development of novel anti-malarial inhibitors. Identified compounds may provide a starting point in the rational design of PTKT inhibitors and analogues based on these scaffolds.

Expression of 4-Hydroxynonenal (4-HNE) and Heme Oxygenase-1 (HO-1) in the Kidneys of Plasmodium berghei-Infected Mice

Acute kidney injury (AKI) is one of the most serious complications of severe Plasmodium falciparum malaria, but the exact pathogenic mechanisms of AKI in P. falciparum infection have not been clearly elucidated. We hypothesized that oxidative stress is a potential mediator of acute tubular necrosis in P. falciparum-infected kidneys. Therefore, this study aimed to investigate the histopathological changes and markers of oxidative stress in kidney tissues from mice with experimental malaria. DBA/2 mice were divided into two groups: the mice in the malaria-infected group (n = 10) were intraperitoneally injected with 1 × 10⁶P. berghei ANKA-infected red blood cells, and the mice in the control group (n = 10) were intraperitoneally injected with a single dose of 0.85% normal saline. Kidney sections were collected and used for histopathological examination and the investigation of 4-hydroxynonenal (4-HNE) and heme oxygenase-1 (HO-1) expression through immunohistochemistry staining. The histopathology study revealed that the P. berghei-infected kidneys exhibited a greater area of tubular necrosis than those of the control group (p < 0.05). The positive staining scores for 4-HNE and HO-1 expression in tubular epithelial cells of the P. berghei-infected group were significantly higher than those found for the control group (p < 0.05). In addition, significant positive correlations were found between the tubular necrosis score and the positive staining scores for 4-HNE and HO-1 in the kidneys from the P. berghei-infected group. In conclusion, this finding demonstrates that increased expression of 4-HNE and HO-1 might be involved in the pathogenesis of acute tubular damage in the kidneys during malaria infection. Our results provide new insights into the pathogenesis of malaria-associated AKI and might provide guidelines for the future development of a therapeutic intervention for malaria.

In Vivo Imaging with Genetically Encoded Redox Biosensors

Redox reactions are of high fundamental and practical interest since they are involved in both normal physiology and the pathogenesis of various diseases. However, this area of research has always been a relatively problematic field in the context of analytical approaches, mostly because of the unstable nature of the compounds that are measured. Genetically encoded sensors allow for the registration of highly reactive molecules in real-time mode and, therefore, they began a new era in redox biology. Their strongest points manifest most brightly in in vivo experiments and pave the way for the non-invasive investigation of biochemical pathways that proceed in organisms from different systematic groups. In the first part of the review, we briefly describe the redox sensors that were used in vivo as well as summarize the model systems to which they were applied. Next, we thoroughly discuss the biological results obtained in these studies in regard to animals, plants, as well as unicellular eukaryotes and prokaryotes. We hope that this work reflects the amazing power of this technology and can serve as a useful guide for biologists and chemists who work in the field of redox processes.

Insight into hydroxyl radical-mediated cleavage of caged methylene blue: the role of Fenton's catalyst for antimalarial hybrid drug activation

Methylene blue with a 10-N carbamoyl linkage was reported to be a hydroxyl radical triggered cleavable ligand. Probed by this platform, hemoproteins were demonstrated to be a much more efficient Fenton's catalyst than commonly used inorganic Fe(ii) salts. The applicability of this ligand was demonstrated through the capability of being triggered by elevated reactive oxygen species levels at diseased tissue, with malaria-parasitized erythrocytes as an in vitro model.

In vitro and in vivo analysis of the anti-plasmodial activity of ethanol extract of Phyllanthus nivosus W. Bull leaf

Antimalarial agents are necessary tools in the global malaria eradication agenda and plants used traditionally in the treatment of malaria are indispensable sources of antimalarial compounds. The aim of this study was to evaluate the antiplasmodial potential of Phyllanthus nivosus leaf. In vitro antiplasmodial assay was conducted using Plasmodium falciparum infected erythrocytes incubated at 37 °C in modified RPMI 1640 culture media. The inhibitory effect of the ethanol extract on plasmodium lactate dehydrogenase (pLDH) activity was determined as a measure of antiplasmodial activity. In vivo study was done using mice infected with chloroquine sensitive P. berghei (NK-65 strain). Parasitemia, packed cell volume (PCV), hemoglobin (Hb) and liver lipid peroxidation (MDA) levels were determined after a 4 day treatment. Chloroquine was used as standard drug for both assays. The extract reduced pLDH activity by 39.52, 42.07 and 43.87% at 12, 25 and 50 μg/mL respectively. 100 and 200 mg/kg body weight of extract and 10 mg/kg chloroquine suppressed parasitemia of infected mice by 82.76, 81.11 and 86.87% respectively. Furthermore, the extract significantly reduced (p < 0.05) the elevated MDA level and reversed PCV and Hb levels of infected mice to normal values. Phytochemical screening of the extract revealed the presence of alkaloids, tannins, flavonoids, cardiac glycosides, anthraquinones, steroids and terpenes. Gas chromatography-mass spectrometry (GC-MS) analysis showed the presence of ten compounds, the most abundant of which is Methyl linoleate (35.77%). This study demonstrated that P. nivosus leaf possesses antimalarial potential and contains bioactive compounds that could be beneficial in the development of new antimalarial agents.

Combining Stage Specificity and Metabolomic Profiling to Advance Antimalarial Drug Discovery

We report detailed susceptibility profiling of asexual blood stages of the malaria parasite Plasmodium falciparum to clinical and experimental antimalarials, combined with metabolomic fingerprinting. Results revealed a variety of stage-specific and metabolic profiles that differentiated the modes of action of clinical antimalarials including chloroquine, piperaquine, lumefantrine, and mefloquine, and identified late trophozoite-specific peak activity and stage-specific biphasic dose-responses for the mitochondrial inhibitors DSM265 and atovaquone. We also identified experimental antimalarials hitting previously unexplored druggable pathways as reflected by their unique stage specificity and/or metabolic profiles. These included several ring-active compounds, ones affecting hemoglobin catabolism through distinct pathways, and mitochondrial inhibitors with lower propensities for resistance than either DSM265 or atovaquone. This approach, also applicable to other microbes that undergo multiple differentiation steps, provides an effective tool to prioritize compounds for further development within the context of combination therapies.

Sickle Cell Trait Induces Oxidative Damage on Plasmodium falciparum Proteome at Erythrocyte Stages

The presence of hemoglobin A-S (HbAS) in erythrocytes has been related to the high production of reactive oxygen species (ROS) and an increased in intracellular oxidative stress that affects the progress of Plasmodium erythrocytic cycle life and attenuates its serious clinical symptoms. Nevertheless, oxidative effects on P. falciparum proteome across the intraerythrocytic cycle in the presence of HbAS traits have not been described yet. Here, an immune dot-blot assay was used to quantify the carbonyl index (C.I) on P. falciparum 3D7 proteome at the different asexual erythrocytic stages. Protein carbonylation on parasites cultivated in erythrocytes from two donors with HbAS increased 5.34 ± 1.42 folds at the ring stage compared to control grown in hemoglobin A-A (HbAA) red blood cells. Whereas at trophozoites and schizonts stages were augmented 2.80 ± 0.52 and 3.05 ± 0.75 folds, respectively. Besides proteins involved in processes of the stress response, recognition and invasion were identified from schizonts carbonylated bands by combining SDS-PAGE with MALDI-TOF-TOF analysis. Our results reinforce the hypothesis that such oxidative modifications do not appear to happen randomly, and the sickle cell trait affects mainly a small fraction of parasite proteins particularly sensitive to ROS.

Malaria inflammation by xanthine oxidase-produced reactive oxygen species

Malaria is a highly inflammatory disease caused by Plasmodium infection of host erythrocytes. However, the parasite does not induce inflammatory cytokine responses in macrophages in vitro and the source of inflammation in patients remains unclear. Here, we identify oxidative stress, which is common in malaria, as an effective trigger of the inflammatory activation of macrophages. We observed that extracellular reactive oxygen species (ROS) produced by xanthine oxidase (XO), an enzyme upregulated during malaria, induce a strong inflammatory cytokine response in primary human monocyte-derived macrophages. In malaria patients, elevated plasma XO activity correlates with high levels of inflammatory cytokines and with the development of cerebral malaria. We found that incubation of macrophages with plasma from these patients can induce a XO-dependent inflammatory cytokine response, identifying a host factor as a trigger for inflammation in malaria. XO-produced ROS also increase the synthesis of pro-IL-1β, while the parasite activates caspase-1, providing the two necessary signals for the activation of the NLRP3 inflammasome. We propose that XO-produced ROS are a key factor for the trigger of inflammation during malaria.

Lacking catalase, a protistan parasite draws on its photosynthetic ancestry to complete an antioxidant repertoire with ascorbate peroxidase

Background

Antioxidative enzymes contribute to a parasite’s ability to counteract the host’s intracellular killing mechanisms. The facultative intracellular oyster parasite, Perkinsus marinus, a sister taxon to dinoflagellates and apicomplexans, is responsible for mortalities of oysters along the Atlantic coast of North America. Parasite trophozoites enter molluscan hemocytes by subverting the phagocytic response while inhibiting the typical respiratory burst. Because P. marinus lacks catalase, the mechanism(s) by which the parasite evade the toxic effects of hydrogen peroxide had remained unclear. We previously found that P. marinus displays an ascorbate-dependent peroxidase (APX) activity typical of photosynthetic eukaryotes. Like other alveolates, the evolutionary history of P. marinus includes multiple endosymbiotic events. The discovery of APX in P. marinus raised the questions: From which ancestral lineage is this APX derived, and what role does it play in the parasite’s life history?

Results

Purification of P. marinus cytosolic APX activity identified a 32 kDa protein. Amplification of parasite cDNA with oligonucleotides corresponding to peptides of the purified protein revealed two putative APX-encoding genes, designated PmAPX1 and PmAPX2. The predicted proteins are 93% identical, and PmAPX2 carries a 30 amino acid N-terminal extension relative to PmAPX1. The P. marinus APX proteins are similar to predicted APX proteins of dinoflagellates, and they more closely resemble chloroplastic than cytosolic APX enzymes of plants. Immunofluorescence for PmAPX1 and PmAPX2 shows that PmAPX1 is cytoplasmic, while PmAPX2 is localized to the periphery of the central vacuole. Three-dimensional modeling of the predicted proteins shows pronounced differences in surface charge of PmAPX1 and PmAPX2 in the vicinity of the aperture that provides access to the heme and active site.

Conclusions

PmAPX1 and PmAPX2 phylogenetic analysis suggests that they are derived from a plant ancestor. Plant ancestry is further supported by the presence of ascorbate synthesis genes in the P. marinus genome that are similar to those in plants. The localizations and 3D structures of the two APX isoforms suggest that APX fulfills multiple functions in P. marinus within two compartments. The possible role of APX in free-living and parasitic stages of the life history of P. marinus is discussed.

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1465-5) contains supplementary material, which is available to authorized users.

Severe oxidative stress in sickle cell disease patients with uncomplicated Plasmodium falciparum malaria in Kampala, Uganda

BACKGROUND

Oxidative stress plays a vital role in the pathogenesis of both Sickle Cell Disease (SCD) and Plasmodium falciparum malaria. However, there are limited studies on the effect of P. falciparum malaria infection on oxidative stress in SCD patients.

METHODS

A cross-sectional study was undertaken to compare levels of biomarkers of oxidative stress in isolates from SCD patients with uncomplicated P.falciparum malaria. The biomarkers namely: malondialdehyde (MDA), reduced glutathione (GSH), catalase (CAT) and glutathione peroxidase (GPx) were determined in plasma samples from SCD malaria positive, malaria positive, SCD malaria negative and healthy control participants. The genetic diversity of P.falciparum was determined by nested polymerase chain reaction of merozoite surface protein-2 (MSP-2) gene.

RESULTS

Out of 207 participants, 54 (26%) were SCD malaria positive, 51 (24%) malaria positive, 51 (24%) SCD controls and 51 (24%) healthy control individuals. The mean concentration of MDA was significantly higher in SCD malaria positive than SCD controls (P < 0.0001). In contrast, the mean concentration of GSH (P < 0.0001) and GPx (P < 0.0001) were significantly lower in SCD malaria than SCD controls. Although not significantly different, the mean concentration of MDA was higher (P = 0.0478), but the geometric mean parasite density (P = 0.2430) and multiplicity of infection (P = 0.3478) were lower in SCD malaria samples than in malaria samples. The most prevalent MSP2 allelic family was IC3D7 in SCD malaria (72%) and Malaria (76%) samples. The biomarkers of oxidative stress were not significantly different between IC3D7 and FC27 allelic families of MSP2.

CONCLUSION

We identified severe oxidative stress in Sickle cell disease patients with uncomplicated P.falciparum malaria.

The malaria toxin hemozoin induces apoptosis in human neurons and astrocytes: Potential role in the pathogenesis of cerebral malaria

Malaria, caused by an intracellular protozoan parasite of the genus Plasmodium, is one of the most important infectious diseases worldwide. In 2017, a total of 219 millions cases were reported with 435,000 deaths related to malaria. A major complication of malaria infection is cerebral malaria (CM), characterized by enhanced blood-brain barrier permeability, leukocyte infiltration and/or activation, and neuronal dropout resulting in coma and death in significant numbers of individuals, especially children. Despite the high incidence and mortality, the pathogenesis of cerebral malaria is not well characterized. Hemozoin (HMZ) or "malaria pigment," a by-product of intraerythrocytic parasite-mediated hemoglobin catabolism, is released into the bloodstream after lysis of the host infected erythrocyte. The effects of HMZ on brain cells has not been studied due to the contamination/adhesion/aggregation of the HMZ with host and toxic parasitic factors. We now demonstrate that extracellular purified HMZ is taken up by human neurons and astrocytes, resulting in cellular dysfunction and toxicity. These findings contribute to a better understanding of the neuropathogenesis of CM and provide evidence that HMZ accumulation in the bloodstream could result in CNS compromise. Thus, alternative approaches to reducing circulating HMZ could serve as a potential treatment.

Phosphoglycolate phosphatase is a metabolic proofreading enzyme essential for cellular function in Plasmodium berghei

Plasmodium falciparum (Pf) 4-nitrophenylphosphatase has been shown previously to be involved in vitamin B1 metabolism. Here, conducting a BLASTp search, we found that 4-nitrophenylphosphatase from Pf has significant homology with phosphoglycolate phosphatase (PGP) from mouse, human, and yeast, prompting us to reinvestigate the biochemical properties of the Plasmodium enzyme. Because the recombinant PfPGP enzyme is insoluble, we performed an extended substrate screen and extensive biochemical characterization of the recombinantly expressed and purified homolog from Plasmodium berghei (Pb), leading to the identification of 2-phosphoglycolate and 2-phospho-L-lactate as the relevant physiological substrates of PbPGP. 2-Phosphoglycolate is generated during repair of damaged DNA ends, 2-phospho-L-lactate is a product of pyruvate kinase side reaction, and both potently inhibit two key glycolytic enzymes, triosephosphate isomerase and phosphofructokinase. Hence, PGP-mediated clearance of these toxic metabolites is vital for cell survival and functioning. Our results differ significantly from those in a previous study, wherein the PfPGP enzyme has been inferred to act on 2-phospho-D-lactate and not on the L isomer. Apart from resolving the substrate specificity conflict through direct in vitro enzyme assays, we conducted PGP gene knockout studies in P. berghei, confirming that this conserved metabolic proofreading enzyme is essential in Plasmodium In summary, our findings establish PbPGP as an essential enzyme for normal physiological function in P. berghei and suggest that drugs that specifically inhibit Plasmodium PGP may hold promise for use in anti-malarial therapies.

Antimalarial potentials of Stemonocoleus micranthus Harms (leguminoseae) stem bark in Plasmodium berghei infected mice

Background

Malaria is a leading cause of death in Nigeria.

Aim

Antimalarial activity of Stemonocoleus micranthus stem bark was evaluated in mice with an objective to finding scientific evidence for its use as antimalarial remedy in South-east Nigeria.

Methods

Antiplasmodial activities of hydro-methanolic extract and solvent fractions (hexane, chloroform, ethyl acetate and aqueous) of S. micranthus stem bark against chloroquine-sensitive Plasmodium berghei infected mice were determined using suppressive and curative procedures. Chloroquine was used as positive control. In vitro models, DPPH (1, 1-diphenyl-2- picrylhydrazyl) radical scavenging, FRAP (ferric reducing antioxidant power) and TPC (total phenolic content) were used to assay antioxidant activity of the test samples. Phytoconstituents of the active fractions were analysed by GC-MS.

Results

Chemosuppressive effect exerted by extract (50, 100, 200, 400 mg kg⁻¹) and fractions (20, 40, 80 mg kg⁻¹) ranged between 54.14 – 67.73% and 59.41–94.51% respectively. Curative effects was also dose dependent. In both models, ethyl acetate was the active fraction. At low doses the animals lived longer but not protected (D₀ – D₂₉). At high doses, extract (400 mg kg⁻¹), active fractions (80 mg kg⁻¹) and chloroquine (5 mg kg⁻¹) the animals were fully protected.

The extract and fractions exhibited antioxidant potentials which could have contributed individually or synergistically to antimalarial activities reported in this study. Oral LD₅₀ was estimated to be greater than 4000 mg kg⁻¹, in mice.

Conclusion

The results of this study may have provided support on traditional therapeutic use of the plant in treatment of malaria.

The sickle cell trait affects contact dynamics and endothelial cell activation in Plasmodium falciparum-infected erythrocytes

Sickle cell trait, a common hereditary blood disorder, protects carriers from severe disease in infections with the human malaria parasite Plasmodium falciparum. Protection is associated with a reduced capacity of parasitized erythrocytes to cytoadhere to the microvascular endothelium and cause vaso-occlusive events. However, the underpinning cellular and biomechanical processes are only partly understood and the impact on endothelial cell activation is unclear. Here, we show, by combining quantitative flow chamber experiments with multiscale computer simulations of deformable cells in hydrodynamic flow, that parasitized erythrocytes containing the sickle cell haemoglobin displayed altered adhesion dynamics, resulting in restricted contact footprints on the endothelium. Main determinants were cell shape, knob density and membrane bending. As a consequence, the extent of endothelial cell activation was decreased. Our findings provide a quantitative understanding of how the sickle cell trait affects the dynamic cytoadhesion behavior of parasitized erythrocytes and, in turn, endothelial cell activation.

Manipulating Eryptosis of Human Red Blood Cells: A Novel Antimalarial Strategy?

Malaria is a major global health burden, affecting over 200 million people worldwide. Resistance against all currently available antimalarial drugs is a growing threat, and represents a major and long-standing obstacle to malaria eradication. Like many intracellular pathogens, Plasmodium parasites manipulate host cell signaling pathways, in particular programmed cell death pathways. Interference with apoptotic pathways by malaria parasites is documented in the mosquito and human liver stages of infection, but little is known about this phenomenon in the erythrocytic stages. Although mature erythrocytes have lost all organelles, they display a form of programmed cell death termed eryptosis. Numerous features of eryptosis resemble those of nucleated cell apoptosis, including surface exposure of phosphatidylserine, cell shrinkage and membrane ruffling. Upon invasion, Plasmodium parasites induce significant stress to the host erythrocyte, while delaying the onset of eryptosis. Many eryptotic inducers appear to have a beneficial effect on the course of malaria infection in murine models, but major gaps remain in our understanding of the underlying molecular mechanisms. All currently available antimalarial drugs have parasite-encoded targets, which facilitates the emergence of resistance through selection of mutations that prevent drug-target binding. Identifying host cell factors that play a key role in parasite survival will provide new perspectives for host-directed anti-malarial chemotherapy. This review focuses on the interrelationship between Plasmodium falciparum and the eryptosis of its host erythrocyte. We summarize the current knowledge in this area, highlight the different schools of thoughts and existing gaps in knowledge, and discuss future perspectives for host-directed therapies in the context of antimalarial drug discovery.

Probucol induces the generation of lipid peroxidation products in erythrocytes and plasma of male cynomolgus macaques

We previously reported that probucol, a lipid lowering agent, protected mice from malaria infection via depletion in plasma α-tocopherol. The antioxidant α-tocopherol in host circulation is necessary for the malaria parasites to protect themselves from oxidative stress in erythrocytes where high amounts of reactive oxygen species are generated. To assess the potential for the clinical application of probucol as an anti-malarial therapy, it was necessary to determine the effects of probucol by using primate experiments. Here we verified that probucol induces an α-tocopherol decrement in cynomolgus macaque erythrocytes and plasma. After 2 weeks of probucol administration at doses of 200 or 400 mg/kg/day, the α-tocopherol contents in erythrocytes tended to decrease. The contents of hydroxyoctadecadienoic acids and 7β-hydroxycholesterol, peroxidation products derived from linoleic acid and cholesterol, respectively, increased in erythrocytes. On the other hand, plasma α-tocopherol concentration showed a marginal decrement. Plasma lipid peroxidation products were transiently increased in the early stages of probucol administration. No adverse effects were observed throughout the experiment, although the dosage of probucol was higher than the clinical maximum dosage. Considering that malaria proliferates in erythrocytes, probucol-induced disruption of redox homeostasis in erythrocytes could be effective in the inhibition of parasite proliferation.

Oxidative stress, eryptosis and anemia: a pivotal mechanistic nexus in systemic diseases

The average lifespan of circulating erythrocytes usually exceeds hundred days. Prior to that, however, erythrocytes may be exposed to oxidative stress in the circulation which could cause injury and trigger their suicidal death or eryptosis. Oxidative stress activates Ca²⁺ -permeable nonselective cation channels in the cell membrane, thus, stimulating Ca²⁺ entry and subsequent cell membrane scrambling resulting in phosphatidylserine exposure and activation of Ca²⁺ -sensitive K⁺ channels leading to K⁺ exit, hyperpolarization, Cl^- exit, and ultimately cell shrinkage due to loss of KCl and osmotically driven water. While the mechanistic link between oxidative stress and anemia remains ill-defined, several diseases such as diabetes, hepatic failure, malignancy, chronic kidney disease and inflammation have been identified to display both increased oxidative stress as well as eryptosis. Recent compelling evidence suggests that oxidative stress is an important perpetrator in accelerating erythrocyte loss in different systemic conditions and an underlying mechanism for anemia associated with these pathological states. In the present review, we discuss the role of oxidative stress in reducing erythrocyte survival and provide novel insights into the possible use of antioxidants as putative antieryptotic and antianemic agents in a variety of systemic diseases.

Antimicrobial effects of N-benzyloxycarbonyl-S-(2,4-dinitrophenyl) glutathione diesters against chloroquinine sensitive (NF54) and resistant (K1) strains of Plasmodium falciparum

N-Benzyloxycarbony-S-(2,4-dinitrophenyl)glutathione diesters have been investigated for antimalarial activity against chloroquinine sensitive (NF54) and resistant (K1) strains of P. falciparum. Both strains appear equally susceptible to inhibition by compounds 1-4, with an IC₅₀ ∼ 4.92-6.97 μM, consistent with the target of these compounds being the PfMRP transporter. Against the NF54 strain, diester derivatives containing ethyl side chains showed lower in vitro activity than those with methyl side chains 1-4, IC₅₀ ∼ 5.7-6.97 μM with the exception of compound 5 (IC₅₀ > 25 μM). The cytotoxicity of compounds with log P ∼ 3.9-5.8 were lower against the murine L6 cell line than compounds with a higher log P > 5.8 that were toxic. Overall the cytotoxicity of compounds 1-7 were lower against KB cells than against the L6 cell line with the exception of compound 4, which showed a higher relative toxicity.