Epigenetic and transcriptional regulation of cytokine production by Plasmodium falciparum-exposed monocytes.

Plasmodium falciparum infection causes the most severe form of malaria, where excessive production of proinflammatory cytokines can drive the pathogenesis of the disease. Monocytes play key roles in host defense against malaria through cytokine production and phagocytosis; however, they are also implicated in pathogenesis through excessive proinflammatory cytokine production. Understanding the underlying molecular mechanisms that contribute to inflammatory cytokine production in P. falciparum-exposed monocytes is key towards developing better treatments. Here, we provide molecular evidence that histone 3 lysine 4 (H3K4) methylation is key for inflammatory cytokine production in P. falciparum-exposed monocytes. In an established in vitro system that mimics blood stage infection, elevated proinflammatory TNF and IL-6 cytokine production is correlated with increased mono- and tri-methylated H3K4 levels. Significantly, we demonstrate through utilizing a pharmacological inhibitor of H3K4 methylation that TNF and IL-6 expression can be suppressed in P. falciparum-exposed monocytes. This elucidated epigenetic regulatory mechanism, controlling inflammatory cytokine production, potentially provides new therapeutic options for future malaria treatment.

Fetal Growth Retardation is Associated with High Apoptotic Cells and Low VEGF Expression in Placenta of Malarial Pregnant Mice.

Background: During pregnancy, pregnant women are susceptible to malaria, contributing significantly to maternal and infant mortality. Objective: This research was conducted to study the effect of Plasmodium berghei infection in pregnant mice on fetal growth retardation through placental cell apoptosis and the change of local vascularization. Methods: Eighteen pregnant Balb/c strain mice resulting from simultanously mating were divided into two groups those were nine pregnant mice used as non infected group and nine pregnant mice infected with Plasmodium berghei on day 9th post mating used as infected group respectively. On day 15th of post mating, all of the pregnant mice were killed. Fetal weights were measured using analytic balance. Apoptosis of placental cells and VEGF expression in the placental tissue were measured using immunohistochemistry. Results: Result showed that there was sequestration of parasite-infected red blood cells (PRBCs) in intervillous space. Statistical analysis showed that the fetal weights in infected pregnant mice group was significantly lower than non infected one (p = 0.01), and the placental cell apoptosis in placental tissue of infected pregnant mice was significantly higher than the non infected one (p=0.00).There was also a significant difference on VEGF expression between infected group and non infected group (p= 0,00). Conclusion: Plasmodium berghei infection in pregnant Balb/c mice can cause fetal growth retardation due to high of placental cell apoptosis and low VEGF expression.

Global analysis of putative phospholipases in Plasmodium falciparum reveals an essential role of the phosphoinositide-specific phospholipase C in parasite maturation.

For its replication within red blood cells, the malaria parasite depends on a highly active and regulated lipid metabolism. Enzymes involved in lipid metabolic processes such as phospholipases are, therefore, potential drug targets. Here, using reverse genetics approaches, we show that only 1 out of the 19 putative phospholipases expressed in asexual blood stages of Plasmodium falciparum is essential for proliferation in vitro, pointing toward a high level of redundancy among members of this enzyme family. Using conditional mislocalization and gene disruption techniques, we show that this essential phosphoinositide-specific phospholipase C (PI-PLC, PF3D7_1013500) has a previously unrecognized essential role during intracellular parasite maturation, long before its previously perceived role in parasite egress and invasion. Subsequent lipidomic analysis suggests that PI-PLC mediates cleavage of phosphatidylinositol bisphosphate (PIP2) in schizont-stage parasites, underlining its critical role in regulating phosphoinositide levels in the parasite. IMPORTANCE The clinical symptoms of malaria arise due to repeated rounds of replication of Plasmodium parasites within red blood cells (RBCs). Central to this is an intense period of membrane biogenesis. Generation of membranes not only requires de novo synthesis and acquisition but also the degradation of phospholipids, a function that is performed by phospholipases. In this study, we investigate the essentiality of the 19 putative phospholipase enzymes that the human malaria parasite Plasmodium falciparum expresses during its replication within RBCs. We not only show that a high level of functional redundancy exists among these enzymes but, at the same time, also identify an essential role for the phosphoinositide-specific phospholipase C in parasite development and cleavage of the phospholipid phosphatidylinositol bisphosphate.

Rhoptry neck protein 4 plays important roles during Plasmodium sporozoite infection of the mammalian liver.

During invasion, Plasmodium parasites secrete proteins from rhoptry and microneme apical end organelles, which have crucial roles in attaching to and invading target cells. A sporozoite stage-specific gene silencing system revealed that rhoptry neck protein 2 (RON2), RON4, and RON5 are important for sporozoite invasion of mosquito salivary glands. Here, we further investigated the roles of RON4 during sporozoite infection of the liver in vivo. Following intravenous inoculation of RON4-knockdown sporozoites into mice, we demonstrated that sporozoite RON4 has multiple functions during sporozoite traversal of sinusoidal cells and infection of hepatocytes. In vitro infection experiments using a hepatoma cell line revealed that secreted RON4 is involved in sporozoite adhesion to hepatocytes and has an important role in the early steps of hepatocyte infection. In addition, in vitro motility assays indicated that RON4 is required for sporozoite attachment to the substrate and the onset of migration. These findings indicate that RON4 is crucial for sporozoite migration toward and invasion of hepatocytes via attachment ability and motility.IMPORTANCEMalarial parasite transmission to mammals is established when sporozoites are inoculated by mosquitoes and migrate through the bloodstream to infect hepatocytes. Many aspects of the molecular mechanisms underpinning migration and cellular invasion remain largely unelucidated. By applying a sporozoite stage-specific gene silencing system in the rodent malarial parasite, Plasmodium berghei, we demonstrated that rhoptry neck protein 4 (RON4) is crucial for sporozoite infection of the liver in vivo. Combined with in vitro investigations, it was revealed that RON4 functions during a crossing of the sinusoidal cell layer and invading hepatocytes, at an early stage of liver infection, by mediating the sporozoite capacity for adhesion and the onset of motility. Since RON4 is also expressed in Plasmodium merozoites and Toxoplasma tachyzoites, our findings contribute to understanding the conserved invasion mechanisms of Apicomplexa parasites.

Cysteine Residues in Region 6 of the Plasmodium yoelii Erythrocyte-Binding-like Ligand That Are Related to Its Localization and the Course of Infection.

Plasmodium malaria parasites use erythrocyte-binding-like (EBL) ligands to invade erythrocytes in their vertebrate host. EBLs are released from micronemes, which are secretory organelles located at the merozoite apical end and bind to erythrocyte surface receptors. Because of their essential nature, EBLs have been studied as vaccine candidates, such as the Plasmodium vivax Duffy binding protein. Previously, we showed through using the rodent malaria parasite Plasmodium yoelii that a single amino acid substitution within the EBL C-terminal Cys-rich domain (region 6) caused mislocalization of this molecule and resulted in alteration of the infection course and virulence between the non-lethal 17X and lethal 17XL strains. In the present study, we generated a panel of transgenic P. yoelii lines in which seven of the eight conserved Cys residues in EBL region 6 were independently substituted to Ala residues to observe the consequence of these substitutions with respect to EBL localization, the infection course, and virulence. Five out of seven transgenic lines showed EBL mislocalizations and higher parasitemias. Among them, three showed increased virulence, whereas the other two did not kill the infected mice. The remaining two transgenic lines showed low parasitemias similar to their parental 17X strain, and their EBL localizations did not change. The results indicate the importance of Cys residues in EBL region 6 for EBL localization, parasite infection course, and virulence and suggest an association between EBL localization and the parasite infection course.

PfATP4 inhibitors in the Medicines for Malaria Venture Malaria Box and Pathogen Box block the schizont-to-ring transition by inhibiting egress rather than invasion.

The cation efflux pump Plasmodium falciparum ATPase 4 (PfATP4) maintains Na+ homeostasis in malaria parasites and has been implicated in the mechanism of action of many structurally diverse antimalarial agents, including >7% of the antimalarial compounds in the Medicines for Malaria Venture's 'Malaria Box' and 'Pathogen Box'. Recent screens of the 'Malaria Box' and 'Pathogen Box' revealed that many PfATP4 inhibitors prevent parasites from exiting their host red blood cell (egress) or entering new host cells (invasion), suggesting that these compounds may have additional molecular targets involved in egress or invasion. Here, we demonstrate that five PfATP4 inhibitors reduce egress but not invasion. These compounds appear to inhibit egress by blocking the activation of protein kinase G, an enzyme that, once stimulated, rapidly activates parasite egress. We establish a direct link between egress and PfATP4 function by showing that the inhibition of egress is attenuated in a Na+-depleted environment and in parasites with a mutation in pfatp4. Finally, we show that PfATP4 inhibitors induce host cell lysis when administered prior to the completion of parasite replication. Since host cell lysis mimics egress but is not followed by invasion, this phenomenon likely explains why several PfATP4 inhibitors were previously classified as invasion inhibitors. Collectively, our results confirm that PfATP4-mediated Na+ efflux is critical to the regulation of parasite egress.

Red Blood Cells Oligosaccharides as Targets for Plasmodium Invasion.

The key element in developing a successful malaria treatment is a good understanding of molecular mechanisms engaged in human host infection. It is assumed that oligosaccharides play a significant role in Plasmodium parasites binding to RBCs at different steps of host infection. The formation of a tight junction between EBL merozoite ligands and glycophorin receptors is the crucial interaction in ensuring merozoite entry into RBCs. It was proposed that sialic acid residues of O/N-linked glycans form clusters on a human glycophorins polypeptide chain, which facilitates the binding. Therefore, specific carbohydrate drugs have been suggested as possible malaria treatments. It was shown that the sugar moieties of N-acetylneuraminyl-N-acetate-lactosamine and 2,3-didehydro-2-deoxy-N-acetylneuraminic acid (DANA), which is its structural analog, can inhibit P. falciparum EBA-175-GPA interaction. Moreover, heparin-like molecules might be used as antimalarial drugs with some modifications to overcome their anticoagulant properties. Assuming that the principal interactions of Plasmodium merozoites and host cells are mediated by carbohydrates or glycan moieties, glycobiology-based approaches may lead to new malaria therapeutic targets.

The PTEX Pore Component EXP2 Is Important for Intrahepatic Development during the Plasmodium Liver Stage.

During vertebrate infection, obligate intracellular malaria parasites develop within a parasitophorous vacuole, which constitutes the interface between the parasite and its hepatocyte or erythrocyte host cells. To traverse this barrier, Plasmodium spp. utilize a dual-function pore formed by EXP2 for nutrient transport and, in the context of the PTEX translocon, effector protein export across the vacuole membrane. While critical to blood-stage survival, less is known about EXP2/PTEX function in the liver stage, although major differences in the export mechanism are suggested by absence of the PTEX unfoldase HSP101 in the intrahepatic vacuole. Here, we employed the glucosamine-activated glmS ribozyme to study the role of EXP2 during Plasmodium berghei liver-stage development in hepatoma cells. Insertion of the glmS sequence into the exp2 3' untranslated region (UTR) enabled glucosamine-dependent depletion of EXP2 after hepatocyte invasion, allowing separation of EXP2 function during intrahepatic development from a recently reported role in hepatocyte invasion. Postinvasion EXP2 knockdown reduced parasite size and largely abolished expression of the mid- to late-liver-stage marker LISP2. As an orthogonal approach to monitor development, EXP2-glmS parasites and controls were engineered to express nanoluciferase. Activation of glmS after invasion substantially decreased luminescence in hepatoma monolayers and in culture supernatants at later time points corresponding to merosome detachment, which marks the culmination of liver-stage development. Collectively, our findings extend the utility of the glmS ribozyme to study protein function in the liver stage and reveal that EXP2 is important for intrahepatic parasite development, indicating that PTEX components also function at the hepatocyte-parasite interface. IMPORTANCE After the mosquito bite that initiates a Plasmodium infection, parasites first travel to the liver and develop in hepatocytes. This liver stage is asymptomatic but necessary for the parasite to transition to the merozoite form, which infects red blood cells and causes malaria. To take over their host cells, avoid immune defenses, and fuel their growth, these obligately intracellular parasites must import nutrients and export effector proteins across a vacuole membrane in which they reside. In the blood stage, these processes depend on a translocon called PTEX, but it is unclear if PTEX also functions during the liver stage. Here, we adapted the glmS ribozyme to control expression of EXP2, the membrane pore component of PTEX, during the liver stage of the rodent malaria parasite Plasmodium berghei. Our results show that EXP2 is important for intracellular development in the hepatocyte, revealing that PTEX components are also functionally important during liver-stage infection.

Homeostasis of extracellular ATP in uninfected RBCs from a Plasmodium falciparum culture and derived microparticles.

Plasmodium falciparum, a dangerous parasitic agent causing malaria, invades human red blood cells (RBCs), causing hemolysis and microvascular obstruction. These and other pathological processes of malaria patients are due to metabolic and structural changes occurring in uninfected RBCs. In addition, infection activates the production of microparticles (MPs). ATP and byproducts are important extracellular ligands modulating purinergic signaling within the intravascular space. Here, we analyzed the contribution of uninfected RBCs and MPs to the regulation of extracellular ATP (eATP) of RBCs, which depends on the balance between ATP release by specific transporters and eATP hydrolysis by ectonucleotidases. RBCs were cultured with P. falciparum for 24-48 h prior to experiments, from which uninfected RBCs and MPs were purified. On-line luminometry was used to quantify the kinetics of ATP release. Luminometry, colorimetry and radioactive methods were used to assess the rate of eATP hydrolysis by ectonucleotidases. Rates of ATP release and eATP hydrolysis were also evaluated in MPs. Uninfected RBCs challenged by different stimuli displayed a strong and transient activation of ATP release, together with an elevated rate of eATP hydrolysis. MPs contained ATP in their lumen, which was released upon vesicle rupture, and were able to hydrolyze eATP. Results suggest that uninfected RBCs and MPs can act as important determinants of eATP regulation of RBCs during malaria. The comparison of eATP homeostasis in infected RBCs, ui-RBCs, and MPs allowed us to speculate on the impact of P. falciparum infection on intravascular purinergic signaling and the control of the vascular caliber by RBCs.

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.

High-resolution structures of malaria parasite actomyosin and actin filaments.

Malaria is responsible for half a million deaths annually and poses a huge economic burden on the developing world. The mosquito-borne parasites (Plasmodium spp.) that cause the disease depend upon an unconventional actomyosin motor for both gliding motility and host cell invasion. The motor system, often referred to as the glideosome complex, remains to be understood in molecular terms and is an attractive target for new drugs that might block the infection pathway. Here, we present the high-resolution structure of the actomyosin motor complex from Plasmodium falciparum. The complex includes the malaria parasite actin filament (PfAct1) complexed with the class XIV myosin motor (PfMyoA) and its two associated light-chains. The high-resolution core structure reveals the PfAct1:PfMyoA interface in atomic detail, while at lower-resolution, we visualize the PfMyoA light-chain binding region, including the essential light chain (PfELC) and the myosin tail interacting protein (PfMTIP). Finally, we report a bare PfAct1 filament structure at improved resolution.

Ferroptosis plays an essential role in the antimalarial mechanism of low-dose dihydroartemisinin.

The activation of artemisinin and its derivatives (ARTs) to generate ROS and other free radicals is mainly heme- or ferrous iron-dependent. ARTs induce ferroptosis in tumor cells, although the involvement of ferroptosis in malaria remains unclear. We found that three typical inducers of ferroptosis (erastin, RSL3 and sorafenib) could effectively mimic DHA inhibition on the growth of blood-stage parasites, which exhibited synergistic or nearly additive interactions in vitro with DHA, while the combination of DHA with ferroptosis inhibitors (deferoxamine, liproxstatin-1) had an obvious antagonistic effect. DHA, similar to ferroptosis inducers, can simultaneously induce the accumulation of ferroptosis-associated cellular labile iron and lipid peroxide. However, deferoxamine and liproxstatin-1 reduced the increase in ferrous iron and lipid peroxide caused by DHA. These results suggested that ferroptosis might be an effective way to induce cell death in parasites and could be a primary mechanism by which DHA kills parasites, with almost 50% contribution at low concentrations. These results provide a new strategy for antimalarial drug screening and clinical medication guidance.

Hemozoin (beta-hematin) Formation Inhibitors: Promising Target for the Development of New Antimalarials: Current Update and Future Prospect.

BACKGROUND: Malaria is responsible for social and economic burden in most lowincome malaria-affected countries. Thus, newer antimalarials are needed to tackle morbidities and mortalities associated with the drug-resistant malarial strains. Haemoglobin digestion inside the food vacuole of malarial parasite would lead to producing redox-active and toxic-free heme. The detoxification process adopted by Plasmodium sp. would give rise to hemozoin (Hz) (betahematin) formation. Targeting the pathway of hemozoin formation is considered a validated target for the discovery of newer antimalarials. OBJECTIVE: This study aims to collect detailed information about aspects of hemozoin (Hz) (betahematin) inhibitors. METHODS: A systemic search has been carried out using PubMed, Google Scholar, CNKI, etc., for relevant studies having the keyword, 'hemozoin or beta-hematin' for almost the last 2 decades (2000-2021). RESULTS: This review tries to summarize all the recent advancements made for the developments of synthetic, natural isolated phytoconstituents and plant extracts inhibiting the hemozoin (betahematin) formation. CONCLUSION: Thus they would act as promising antimalarial candidates in the near future.

Activity of Anti-Microbial Peptides (AMPs) against Leishmania and Other Parasites: An Overview.

Anti-microbial peptides (AMPs), small biologically active molecules, produced by different organisms through their innate immune system, have become a considerable subject of interest in the request of novel therapeutics. Most of these peptides are cationic-amphipathic, exhibiting two main mechanisms of action, direct lysis and by modulating the immunity. The most commonly reported activity of AMPs is their anti-bacterial effects, although other effects, such as anti-fungal, anti-viral, and anti-parasitic, as well as anti-tumor mechanisms of action have also been described. Their anti-parasitic effect against leishmaniasis has been studied. Leishmaniasis is a neglected tropical disease. Currently among parasitic diseases, it is the second most threating illness after malaria. Clinical treatments, mainly antimonial derivatives, are related to drug resistance and some undesirable effects. Therefore, the development of new therapeutic agents has become a priority, and AMPs constitute a promising alternative. In this work, we describe the principal families of AMPs (melittin, cecropin, cathelicidin, defensin, magainin, temporin, dermaseptin, eumenitin, and histatin) exhibiting a potential anti-leishmanial activity, as well as their effectiveness against other microorganisms.

STK35L1 regulates host cell cycle-related genes and is essential for Plasmodium infection during the liver stage of malaria.

Protein kinases of both the parasite and the host are crucial in parasite invasion and survival and might act as drug targets against drug-resistant malaria. STK35L1 was among the top five hits in kinome-wide screening, suggesting its role in malaria's liver stage. However, the role of host STK35L1 in malaria remains elusive. In this study, we found that STK35L1 was highly upregulated during the infection of Plasmodium berghei (P. berghei) in HepG2 cells and mice liver, and knockdown of STK35L1 remarkably suppressed the sporozoites' infection in HepG2 cells. We showed that STAT3 is upregulated and phosphorylated during P. berghei sporozoites' infection, and STAT3 activation is required for both the upregulation of STK35L1 and STAT3. Furthermore, we found that ten cell cycle genes were upregulated in the sporozoite-infected hepatocytes. Knockdown of STK35L1 inhibited the basal expression of these genes except CDKN3 and GTSE1 in HepG2 cells. Thus, we identified STK35L1 as a host kinase that plays an obligatory role in malaria's liver stage and propose that it may serve as a potential drug target against drug-resistant malaria.

PET Imaging of Translocator Protein as a Marker of Malaria-Associated Lung Inflammation.

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is a severe complication of malaria that occurs despite effective antimalarial treatment. Currently, noninvasive imaging procedures such as chest X-rays are used to assess edema in established MA-ARDS, but earlier detection methods are needed to reduce morbidity and mortality. The early stages of MA-ARDS are characterized by the infiltration of leukocytes, in particular monocytes/macrophages; thus, monitoring of immune infiltrates may provide a useful indicator of early pathology. In this study, Plasmodium berghei ANKA-infected C57BL/6 mice, a rodent model of MA-ARDS, were longitudinally imaged using the 18-kDa translocator protein (TSPO) imaging agent [18F]FEPPA as a marker of macrophage accumulation during the development of pathology and in response to combined artesunate and chloroquine diphosphate (ART+CQ) therapy. [18F]FEPPA uptake was compared to blood parasitemia levels and to levels of pulmonary immune cell infiltrates by using flow cytometry. Infected animals showed rapid increases in lung retention of [18F]FEPPA, correlating well with increases in blood parasitemia and pulmonary accumulation of interstitial inflammatory macrophages and major histocompatibility complex class II (MHC-II)-positive alveolar macrophages. Treatment with ART+CQ abrogated this increase in parasitemia and significantly reduced both lung uptake of [18F]FEPPA and levels of macrophage infiltrates. We conclude that retention of [18F]FEPPA in the lungs is well correlated with changes in blood parasitemia and levels of lung-associated macrophages during disease progression and in response to ART+CQ therapy. With further development, TSPO biomarkers may have the potential to accurately assess the early onset of MA-ARDS.

Mesenchymal Stem Cells: A Novel Therapeutic Approach to Enhance Protective Immunomodulation and Erythropoietic Recovery in Malaria.

Mesenchymal stem cells (MSCs) are self-renewing, multi-potent heterogeneous stem cells that display strong tissue protective and restorative properties by differentiating into cells of the mesodermal lineages. In addition to multi-lineage differentiation capacity, MSCs play important roles in regulating immune responses, inflammation, and tissue regeneration. MSCs play a role in the outcome of the pathogenesis of several infectious diseases. A unique subset of MSCs accumulates in secondary lymphoid organs during malaria disease progression. These MSCs counteract the capacity of malaria parasites to subvert activating co-stimulatory molecules and to regulate expression of negative co-stimulatory molecules on T lymphocytes. Consequently, MSCs have the capacity to restore the functions of CD34+ haematopoietic cells and CD4+ and CD8+ T cells during malaria infection. These observations suggest that cell-based therapeutics for intervention in malaria may be useful in achieving sterile clearance and preventing disease reactivation. In addition, MSCs provide host protection against malaria by reprogramming erythropoiesis through accelerated formation of colony-forming-units-erythroid (CFU-E) cells in the bone marrow. These findings suggest that MSCs are positive regulators of erythropoiesis, making them attractive targets for treatment of malarial anemia. MSC-based therapies, unlike anti-malarial drugs, display therapeutic effects by targeting a large variety of cellular processes rather than a single pathway. In the present review we focus on these recent research findings and discuss clinical applications of MSC-based therapies for malaria.

17ß-Estradiol Is Involved in the Sexual Dimorphism of the Immune Response to Malaria.

Malaria is the leading cause of parasitic infection-related death globally. Additionally, malaria-associated mortality is higher in men than in women, and this sexual dimorphism reflects differences in innate and adaptive immune responses that are influenced by sex hormones. Normally, females develop more robust immune responses against parasites than males. However, most clinical and laboratory studies related to the immune response to malaria do not consider sex as a variable, and relatively few studies have compared the sex-dependent role of 17ß-estradiol in this process. In this study, we decreased in vivo the levels of 17ß-estradiol by gonadectomy or administered 17ß-estradiol to intact or gonadectomized male and female CBA/Ca mice infected with Plasmodium berghei ANKA. Subsequently, we assessed the effects of 17ß-estradiol on parasite load; the percentages of different immune cells in the spleen; the plasma levels of antibodies and pro- and anti-inflammatory cytokines; and the mRNA expression levels of cytokine-encoding genes in the brain. The results showed that the administration of 17ß-estradiol increased parasitemia and decreased body weight in intact female mice. Moreover, intact females exhibited higher levels of CD8+ T cells and lower levels of NK1.1+ cells than their male counterparts under the same condition. Gonadectomy increased IFN-γ and decreased TNF-α concentrations only in intact female mice. Additionally, IL-10 levels were higher in intact females than in their male counterparts. Finally, the mRNA expression levels of cytokines coding genes in the brain showed a dimorphic pattern, i.e., gonadectomy upregulated Tnf, Il1b, and Il10 expression in males but not in females. Our findings explain the sexual dimorphism in the immune response to malaria, at least in part, and suggest potential sex-dependent implications for the efficacy of vaccines or drugs targeting malaria.

Combating multi-drug resistant malaria parasite by inhibiting falcipain-2 and heme-polymerization: Artemisinin-peptidyl vinyl phosphonate hybrid molecules as new antimalarials.

Artemisinin-based combination therapies (ACTs) have been able to reduce the clinical and pathological malaria cases in endemic areas around the globe. However, recent reports have shown a progressive decline in malaria parasite clearance in South-east Asia after ACT treatment, thus envisaging a need for new artemisinin (ART) derivatives and combinations. To address the emergence of drug resistance to current antimalarials, here we report the synthesis of artemisinin-peptidyl vinyl phosphonate hybrid molecules that show superior efficacy than artemisinin alone against chloroquine-resistant as well as multidrug-resistant Plasmodium falciparum strains with EC50 in pico-molar ranges. Further, the compounds effectively inhibited the survival of ring-stage parasite for laboratory-adapted artemisinin-resistant parasite lines as compared to artemisinin. These hybrid molecules showed complete parasite clearance in vivo using P. berghei mouse malaria model in comparison to artemisinin alone. Studies on the mode of action of hybrid molecules suggested that these artemisinin-peptidyl vinyl phosphonate hybrid molecules possessed dual activities: inhibited falcipain-2 (FP-2) activity, a P. falciparum cysteine protease involved in hemoglobin degradation, and also blocked the hemozoin formation in the food-vacuole, a step earlier shown to be blocked by artemisinin. Since these hybrid molecules blocked multiple steps of a pathway and showed synergistic efficacies, we believe that these lead compounds can be developed as effective antimalarials to prevent the spread of resistance to current antimalarials.

Plasmodium infection prevents recurrence and metastasis of hepatocellular carcinoma possibly via inhibition of the epithelial­mesenchymal transition.

Postoperative recurrence causes a high mortality rate among patients with hepatocellular carcinoma (HCC). The current study aimed to determine the effects of Plasmodium infection on HCC metastasis and recurrence. The antitumor effects of Plasmodium infection were determined using two murine orthotopic HCC models: The non­resection model and the resection model. Tumour tissues derived from tumour­bearing mice treated with or without Plasmodium infection were harvested 15 days post­tumour inoculation. The expression levels of biomarkers related to epithelial­mesenchymal transition (EMT) and molecules associated with CC­chemokine receptor 10 (CCR10)­mediated PI3K/Akt/GSK­3ß/Snail signalling were identified using reverse transcription­quantitative PCR and western blotting. The results demonstrated that Plasmodium infection significantly suppressed the progression, recurrence and metastasis of HCC in the two mouse models. The expression levels of E­cadherin were significantly higher in the Plasmodium­treated group compared with that in the control group, whereas the expression levels of Vimentin and Snail were significantly lower in the Plasmodium­treated group. Furthermore, Plasmodium infection inhibited the activation of Akt and GSK­3ß in the tumour tissues by downregulating the expression levels of CCR10 and subsequently suppressing the accumulation of Snail, which may contribute to the suppression of EMT and the prevention of tumour recurrence and metastasis. In conclusion, the results of the present study demonstrated that Plasmodium infection inhibited the recurrence and metastasis and improved the prognosis of HCC by suppressing CCR10­mediated PI3K/Akt/GSK­3ß/Snail signalling and preventing the EMT. These results may be important for the development of novel therapies for HCC recurrence and metastasis, especially for patients in the perioperative period.