Development Of Plasmodium Falciparum Research Articles

Critical role of Erythrocyte Binding-Like protein of the rodent malaria parasite Plasmodium yoelii to establish an irreversible connection with the erythrocyte during invasion

Plasmodium malaria parasites multiply within erythrocytes and possess a repertoire of proteins whose function is to recognize and invade these vertebrate host cells. One such protein involved in erythrocyte invasion is the micronemal protein, Erythrocyte Binding-Like (EBL), which has been studied as a potential target of vaccine development in Plasmodium vivax (PvDBP) and Plasmodium falciparum (EBA-175). In the rodent malaria parasite model Plasmodium yoelii, specific substitutions in the EBL regions responsible for intracellular trafficking (17XL parasite line) or receptor recognition (17X1.1pp. parasite line), paradoxically increase invasion ability and virulence rather than abolish EBL function. Attempts to disrupt the ebl gene locus in the 17XL and 17XNL lines were unsuccessful, suggesting EBL essentiality. To understand the mechanisms behind these potentially conflicting outcomes, we generated 17XL-based transfectants in which ebl expression is suppressed with anhydrotetracycline (ATc) and investigated merozoite behavior during erythrocyte invasion. In the absence of ATc, EBL was secreted to the merozoite surface, whereas following ATc administration parasitemia was negligible in vivo. Merozoites lacking EBL were unable to invade erythrocytes in vitro, indicating that EBL has a critical role for erythrocyte invasion. Quantitative time-lapse imaging revealed that with ATc administration a significant number of merozoites were detached from the erythrocyte after the erythrocyte deformation event and no echinocytosis was observed, indicating that EBL is required for merozoites to establish an irreversible connection with erythrocytes during invasion.

Alpha-Mangostin Effect on Inhibition Development Stadium and Globin Accumulation Against Plasmodium falciparum

α--Mangostin is a widely reported group of Xanthone compounds from the Clusiaceae family of 40 genera and over 1000 species spread across the tropics and subtropics area. The Objective for determine effect of α-mangostin from Garcinia tetrandra Pierre stem bark against development stadium inhibition and globin accumulation of Plasmodium falciparum. Inhibition stadium development assay used based on the Rosenthal method. Plasmodium falciparum parasitic globin accumulation assay. Globin accumulation assay used the highest concentration of in vitro antimalarial test using SDS-PAGE with positive control E-64 and α-mangostin were incubated together with the malaria parasite during 24 h. Result of Inhibition stadium development of Plasmodium falciparum against α-mangostin show inhibition from development stadium of the malaria parasite Plasmodium falciparum, Electrophoresis show globin accumulation from electrophoresis followed by staining using Coomassie brilliant blue. α-mangostin showed inhibition the growth of malaria parasite Plasmodium falciparum with dose 10 μg/ml is expected to occur a large accumulation of globin, which can be viewed both morphologically and by the method of SDS-PAGE.

Ned-19 inhibition of parasite growth and multiplication suggests a role for NAADP mediated signalling in the asexual development of Plasmodium falciparum

BackgroundAlthough malaria is a preventable and curable human disease, millions of people risk to be infected by the Plasmodium parasites and to develop this illness. Therefore, there is an urgent need to identify new anti-malarial drugs. Ca2+ signalling regulates different processes in the life cycle of Plasmodium falciparum, representing a suitable target for the development of new drugs.ResultsThis study investigated for the first time the effect of a highly specific inhibitor of nicotinic acid adenine dinucleotide phosphate (NAADP)-induced Ca2+ release (Ned-19) on P. falciparum, revealing the inhibitory effect of this compound on the blood stage development of this parasite. Ned-19 inhibits both the transition of the parasite from the early to the late trophozoite stage and the ability of the late trophozoite to develop to the multinucleated schizont stage. In addition, Ned-19 affects spontaneous intracellular Ca2+ oscillations in ring and trophozoite stage parasites, suggesting that the observed inhibitory effects may be associated to regulation of intracellular Ca2+ levels.ConclusionsThis study highlights the inhibitory effect of Ned-19 on progression of the asexual life cycle of P. falciparum. The observation that Ned-19 inhibits spontaneous Ca2+ oscillations suggests a potential role of NAADP in regulating Ca2+ signalling of P. falciparum.

PfCDPK1 mediated signaling in erythrocytic stages of Plasmodium falciparum

Calcium Dependent Protein Kinases are key effectors of calcium signaling in malaria parasite. PfCDPK1 is critical for asexual development of Plasmodium falciparum, but its precise function and substrates remain largely unknown. Using a conditional knockdown strategy, we here establish that this kinase is critical for the invasion of host erythrocytes. Furthermore, using a multidisciplinary approach involving comparative phosphoproteomics we gain insights into the underlying molecular mechanisms. We identify substrates of PfCDPK1, which includes proteins of Inner Membrane Complex and glideosome-actomyosin motor assembly. Interestingly, PfCDPK1 phosphorylates PfPKA regulatory subunit (PfPKA-R) and regulates PfPKA activity in the parasite, which may be relevant for the process of invasion. This study delineates the signaling network of PfCDPK1 and sheds light on mechanisms via which it regulates invasion.

Platelets activate a pathogenic response to blood-stage Plasmodium infection but not a protective immune response

AbstractClinical studies indicate that thrombocytopenia correlates with the development of severe falciparum malaria, suggesting that platelets either contribute to control of parasite replication, possibly as innate parasite killer cells or function in eliciting pathogenesis. Removal of platelets by anti-CD41 mAb treatment, platelet inhibition by aspirin, and adoptive transfer of wild-type (WT) platelets to CD40-KO mice, which do not control parasite replication, resulted in similar parasitemia compared with control mice. Human platelets at a physiologic ratio of 1 platelet to 9 red blood cells (RBCs) did not inhibit the in vitro development or replication of blood-stage Plasmodium falciparum. The percentage of Plasmodium-infected (iRBCs) with bound platelets during the ascending parasitemia in Plasmodium chabaudi– and Plasmodium berghei–infected mice and the 48-hour in vitro cycle of P falciparum was <10%. P chabaudi and P berghei iRBCs with apoptotic parasites (TdT+) exhibited minimal platelet binding (<5%), which was similar to nonapoptotic iRBCs. These findings collectively indicate platelets do not kill bloodstage Plasmodium at physiologically relevant effector-to-target ratios. P chabaudi primary and secondary parasitemia was similar in mice depleted of platelets by mAb-injection just before infection, indicating that activation of the protective immune response does not require platelets. In contrast to the lack of an effect on parasite replication, adoptive transfer of WT platelets to CD40-KO mice, which are resistant to experimental cerebral malaria, partially restored experimental cerebral malaria mortality and symptoms in CD40-KO recipients, indicating platelets elicit pathogenesis and platelet CD40 is a key molecule.

Investigating the Osmotic Component in Mechanisms of Malaria Parasite Plasmodium Falciparum Egress and Invasion of Human Red Blood Cells

Human red blood cells (RBC) experience a transient echinocytic shape change immediately after parasite invasion and another within the last minutes before parasite egress when infected RBC seems to round up. The rapidity of shape changes in both events makes an osmotic mechanism a likely candidate. Indeed, it was shown that the rate of parasite egress is influenced by the osmolarity of the culture medium, suggesting the involvement of ion channels in the egress program and Aquaporin 1, a RBC water channel, was implicated in the initiation of the intraerythrocytic development of Plasmodium falciparum. Currently available methods are able to resolve infected red blood cell volume at the various stages of the 48h plasmodium developmental cycle, yet lack time resolution to capture fast-progressing events such as parasite egress and invasion of RBC. To gain insight into the putative osmotic component of these processes, we tested the suitability of a recently developed method for volume measurements of live cells, based on fluorescence exclusion, for volume evaluation in RBC during fast egress-invasion events in vitro. We show that volumes can be captured with video rate speed, high throughput, and sensitivity to relative changes of 0.3 µm3. We conclude that the fluorescence exclusion method is well suited for testing parasite egress-invasion events in real time and studying multiple individual events in the same cell suspension. Preliminary volume measurements of infected erythrocytes approaching parasite egress will be presented.

Disrupting Mosquito Reproduction and Parasite Development for Malaria Control.

The control of mosquito populations with insecticide treated bed nets and indoor residual sprays remains the cornerstone of malaria reduction and elimination programs. In light of widespread insecticide resistance in mosquitoes, however, alternative strategies for reducing transmission by the mosquito vector are urgently needed, including the identification of safe compounds that affect vectorial capacity via mechanisms that differ from fast-acting insecticides. Here, we show that compounds targeting steroid hormone signaling disrupt multiple biological processes that are key to the ability of mosquitoes to transmit malaria. When an agonist of the steroid hormone 20-hydroxyecdysone (20E) is applied to Anopheles gambiae females, which are the dominant malaria mosquito vector in Sub Saharan Africa, it substantially shortens lifespan, prevents insemination and egg production, and significantly blocks Plasmodium falciparum development, three components that are crucial to malaria transmission. Modeling the impact of these effects on Anopheles population dynamics and Plasmodium transmission predicts that disrupting steroid hormone signaling using 20E agonists would affect malaria transmission to a similar extent as insecticides. Manipulating 20E pathways therefore provides a powerful new approach to tackle malaria transmission by the mosquito vector, particularly in areas affected by the spread of insecticide resistance.

Molecular expression of aquaporin mRNAs in the northern house mosquito, Culex pipiens

Aquaporins (AQPs) are a family of membrane-bound proteins, originally described as water-channels, that broadly exist in prokaryotic and eukaryotic cells. However, some AQPs can transport small molecules (e.g. urea, glycerol) along with or preferentially to water. Previous work in the mosquitoes Aedes aegypti and Anopheles gambiae have characterized the molecular expression of one or more AQP genes and shown that they are involved in water homeostasis after blood feeding, tolerance to dehydration and heat stresses, and development of Plasmodium falciparum in the mosquito. However, the molecular expression of AQPs in the northern house mosquito Culex pipiens, the primary vector of West Nile virus, is presently unknown. Here we characterize the relative mRNA expression of six AQP genes in C. pipiens. We used quantitative RT-PCR (qPCR) to compare AQP mRNA levels 1) among different life stages and sexes, 2) between blood fed and non-blood fed adult females, 3) between adult females injected with phosphate-buffered saline (PBS) and non-injected females, and 4) between adult females exposed to a low vs. high relative humidity. We found that: 1) four AQP mRNAs (Drip, Bib, Eglp1, Aqp12L) were differentially expressed between larval and adult life stages, but not between sexes; 2) after a blood meal, the expression of two AQP mRNAs (Drip and Aqp12L) were down-regulated and one AQP mRNA (Eglp2) was up-regulated; 3) the expression of two AQP mRNAs (Drip and Prip) were down-regulated and one AQP mRNA (Eglp1) was up regulated after injecting the hemolymph of mosquitoes with PBS; and 4) the expression of Prip and Eglp2 mRNAs were both down-regulated in response to a low relative humidity. Our study is the first to characterize the molecular expression patterns of AQPs in C. pipiens, thus providing a foundation for future research elucidating the physiological and functional roles of AQPs in this important disease vector.

Widespread occurrence of lysine methylation in Plasmodium falciparum proteins at asexual blood stages.

Post-transcriptional and post-translational modifications play a major role in Plasmodium life cycle regulation. Lysine methylation of histone proteins is well documented in several organisms, however in recent years lysine methylation of proteins outside histone code is emerging out as an important post-translational modification (PTM). In the present study we have performed global analysis of lysine methylation of proteins in asexual blood stages of Plasmodium falciparum development. We immunoprecipitated stage specific Plasmodium lysates using anti-methyl lysine specific antibodies that immunostained the asexual blood stage parasites. Using liquid chromatography and tandem mass spectrometry analysis, 570 lysine methylated proteins at three different blood stages were identified. Analysis of the peptide sequences identified 605 methylated sites within 422 proteins. Functional classification of the methylated proteins revealed that the proteins are mainly involved in nucleotide metabolic processes, chromatin organization, transport, homeostatic processes and protein folding. The motif analysis of the methylated lysine peptides reveals novel motifs. Many of the identified lysine methylated proteins are also interacting partners/substrates of PfSET domain proteins as revealed by STRING database analysis. Our findings suggest that the protein methylation at lysine residues is widespread in Plasmodium and plays an important regulatory role in diverse set of the parasite pathways.

Iron and malaria: a dangerous liaison?

Malaria increases the burden of anemia in low-income countries, where, according to 2012 data from the World Health Organization, 40% of children are anemic. Moreover, iron is a cofactor for Plasmodium falciparum development, raising fears that iron supplementation might be harmful in patients with P. falciparum infection. The primary objective of this narrative review is to describe current knowledge on the iron-malaria association, including recent findings and substantive qualitative results. Between 2012 and 2016 the MEDLINE database was searched for literature published about malaria and iron levels. Observational studies reported some protection of iron supplementation against malaria among iron-deficient children, while older clinical trials reported increased susceptibility to malaria among iron-supplemented children. However, iron supplements were not significantly associated with increased malaria risk in recent clinical trials or in a 2016 Cochrane review. Evidence of an iron-malaria association is limited by the following factors: the protective effect of control interventions, the limited follow-up of children, and the lack of homogenous iron indicators. The effects of previous health status and possible thresholds in iron levels should be investigated using a gold-standard combination of iron markers. Moreover, the benefits of iron supplementation require further evaluation.

Characterization and expression analysis of gene encoding heme peroxidase HPX15 in major Indian malaria vector Anopheles stephensi (Diptera: Culicidae)

The interaction of mosquito immune system with Plasmodium is critical in determining the vector competence. Thus, blocking the crucial mosquito molecules that regulate parasite development might be effective in controlling the disease transmission. In this study, we characterized a full-length AsHPX15 gene from the major Indian malaria vector Anopheles stephensi. This gene is true ortholog of Anopheles gambiae heme peroxidase AgHPX15 (AGAP013327), which modulates midgut immunity and regulates Plasmodium falciparum development. We found that AsHPX15 is highly induced in mosquito developmental stages and blood fed midguts. In addition, this is a lineage-specific gene that has identical features and 65–99% amino acids identity with other HPX15 genes present in eighteen worldwide-distributed anophelines. We discuss that the conserved HPX15 gene might serve as a common target to manipulate mosquito immunity and arresting Plasmodium development inside the vector host.

Exposure to deltamethrin affects development of Plasmodium falciparum inside wild pyrethroid resistant Anopheles gambiae s.s. mosquitoes in Uganda.

BackgroundPyrethroid resistance in African vector mosquitoes is a threat to malaria control. Resistant mosquitoes can survive insecticide doses that would normally be lethal. We studied effects of such doses on Plasmodium falciparum development inside kdr-resistant Anopheles gambiae s.s. in Uganda.MethodsWe collected An. gambiae s.s. homozygous for kdr-L1014S mutation, fed them on blood samples from 42 P. falciparum-infected local patients, then exposed them either to nets treated with sub-lethal doses of deltamethrin or to untreated nets. After seven days, we dissected 692 mosquitoes and examined their midguts for oocysts. Prevalence (proportion infected) and intensity of infection (number of oocysts per infected mosquito) were recorded for each group.ResultsBoth prevalence and intensity of infection were significantly reduced in deltamethrin-exposed mosquitoes, compared to those exposed to untreated nets. With low doses (2.5–5.0 mg/m2), prevalence was reduced by 59 % (95 % CI = 22 %-78 %) and intensity by 41 % (95 % CI = 25 %-54 %). With high doses (10–16.7 mg/m2), prevalence was reduced by 80 % (95 % CI = 67 %-88 %) and intensity by 34 % (95 % CI = 20 %-46 %).ConclusionsWe showed that, with locally-sampled parasites and mosquitoes, doses of pyrethroids that are sub-lethal for resistant mosquitoes can interfere with parasite development inside mosquitoes. This mechanism could enable pyrethroid-treated nets to prevent malaria transmission despite increasing vector resistance.

Changes in lipid composition during sexual development of the malaria parasite Plasmodium falciparum.

BackgroundThe development of differentiated sexual stages (gametocytes) within human red blood cells is essential for the propagation of the malaria parasite, since only mature gametocytes will survive in the mosquito’s midgut. Hence gametocytogenesis is a pre-requisite for transmission of the disease. Physiological changes involved in sexual differentiation are still enigmatic. In particular the lipid metabolism—despite being central to cellular regulation and development—is not well explored.MethodsHere the lipid profiles of red blood cells infected with the five different sexual stages of Plasmodium falciparum were analysed by mass spectrometry and compared to those from uninfected and asexual trophozoite infected erythrocytes.ResultsFundamental differences between erythrocytes infected with the different parasite stages were revealed. In mature gametocytes many lipids that decrease in the trophozoite and early gametocyte infected red blood cells are regained. In particular, regulators of membrane fluidity, cholesterol and sphingomyelin, increased significantly during gametocyte maturation. Neutral lipids (serving mainly as caloriometric reserves) increased from 3 % of total lipids in uninfected to 27 % in stage V gametocyte infected red blood cells. The major membrane lipid class (phospholipids) decreased during gametocyte development.ConclusionsThe lipid profiles of infected erythrocytes are characteristic for the particular parasite life cycle and maturity stages of gametocytes. The obtained lipid profiles are crucial in revealing the lipid metabolism of malaria parasites and identifying targets to interfere with this deadly disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1130-z) contains supplementary material, which is available to authorized users.

Biliverdin targets enolase and eukaryotic initiation factor 2 (eIF2α) to reduce the growth of intraerythrocytic development of the malaria parasite Plasmodium falciparum.

In mammals, haem degradation to biliverdin (BV) through the action of haem oxygenase (HO) is a critical step in haem metabolism. The malaria parasite converts haem into the chemically inert haemozoin to avoid toxicity. We discovered that the knock-out of HO in P. berghei is lethal; therefore, we investigated the function of biliverdin (BV) and haem in the parasite. Addition of external BV and haem to P. falciparum-infected red blood cell (RBC) cultures delays the progression of parasite development. The search for a BV molecular target within the parasites identified P. falciparum enolase (Pf enolase) as the strongest candidate. Isothermal titration calorimetry using recombinant full-length Plasmodium enolase suggested one binding site for BV. Kinetic assays revealed that BV is a non-competitive inhibitor. We employed molecular modelling studies to predict the new binding site as well as the binding mode of BV to P. falciparum enolase. Furthermore, addition of BV and haem targets the phosphorylation of Plasmodium falciparum eIF2α factor, an eukaryotic initiation factor phosphorylated by eIF2α kinases under stress conditions. We propose that BV targets enolase to reduce parasite glycolysis rates and changes the eIF2α phosphorylation pattern as a molecular mechanism for its action.

Inhibition of malaria parasite Plasmodium falciparum development by crotamine, a cell penetrating peptide from the snake venom

We show here that crotamine, a polypeptide from the South American rattlesnake venom with cell penetrating and selective anti-fungal and anti-tumoral properties, presents a potent anti-plasmodial activity in culture. Crotamine inhibits the development of the Plasmodium falciparum parasites in a dose-dependent manner [IC50 value of 1.87μM], and confocal microscopy analysis showed a selective internalization of fluorescent-labeled crotamine into P. falciparum infected erythrocytes, with no detectable fluorescence in uninfected healthy erythrocytes. In addition, similarly to the crotamine cytotoxic effects, the mechanism underlying the anti-plasmodial activity may involve the disruption of parasite acidic compartments H+ homeostasis. In fact, crotamine promoted a reduction of parasites organelle fluorescence loaded with the lysosomotropic fluorochrome acridine orange, in the same way as previously observed mammalian tumoral cells. Taken together, we show for the first time crotamine not only compromised the metabolism of the P. falciparum, but this toxin also inhibited the parasite growth. Therefore, we suggest this snake polypeptide as a promising lead molecule for the development of potential new molecules, namely peptidomimetics, with selectivity for infected erythrocytes and ability to inhibit the malaria infection by its natural affinity for acid vesicles.

Ascorbic acid co-administration with artemisinin based combination therapies in falciparum malaria.

Malaria infection poses a serious public health problem in endemic countries. As per World Malaria Report 2015, it is estimated that 3.2 billion people in 97 countries are at risk of being infected with malaria; 214 million cases of malaria with 4,38,000 malaria induced deaths are reported during the year1. Clinical consequences of malaria result primarily from parasitic invasion of red blood cells (RBCs). Inside the RBCs, the parasite metabolizes the host haemoglobin in the acidic environment of the parasite's food vacuole. This leads to production of free haem which contains Fe2+ atoms that can catalyze Fenton and Haber-Weiss reactions, generating the radicals which can cause extensive molecular damage2. Haemolysis of infected red cells releases free haem which may be responsible for an external oxidative stress on both infected and non-infected RBCs2 and may be one of the factors contributing to destruction of normal red cells. Presence of pro-oxidants in plasma of patients suffering from acute falciparum malaria has been demonstrated by measurement of the erythrocyte thiobarbituric acid-reactive substance concentrations3. The parasite develops antioxidant mechanisms partly through reducing its own generation of reactive oxygen species and partly through increased synthesis of reduced glutathione and thioredoxin reductase system2. During intraerythrocytic development of Plasmodium falciparum, a large number of parasite proteins move beyond its own plasma membrane and associate with RBC membrane cytoskeletal proteins. Parasite and host red cell cytoskeletal protein interactions lead to formation of large molecular complexes which appear as electron dense “knobs” on the RBC surface. These changes lead to alterations in the rheological properties of infected red cells which become less deformable and more adhesive4.

An assay to probe Plasmodium falciparum growth, transmission stage formation and early gametocyte development.

Conversion from asexual proliferation to sexual differentiation initiates the production of the gametocyte, which is the malaria parasite stage required for human-to-mosquito transmission. This protocol describes an assay designed to probe the effect of drugs or other perturbations on asexual replication, sexual conversion and early gametocyte development in the major human malaria parasite Plasmodium falciparum. Synchronized asexually replicating parasites are induced for gametocyte production by the addition of conditioned medium, and they are then exposed to the treatment of interest during sexual commitment or at any subsequent stage of early gametocyte development. Flow cytometry is used to measure asexual proliferation and gametocyte production via DNA dye staining and the gametocyte-specific expression of a fluorescent protein, respectively. This screening approach may be used to identify and evaluate potential transmission-blocking compounds and to further investigate the mechanism of sexual conversion in malaria parasites. The full protocol can be completed in 11 d.

Molecular interaction of selected phytochemicals under the charged environment of Plasmodium falciparum chloroquine resistance transporter (PfCRT) model

Phytochemicals of Catharanthus roseus Linn. and Tylophora indica have been known for their inhibition of malarial parasite, Plasmodium falciparum in cell culture. Resistance to chloroquine (CQ), a widely used antimalarial drug, is due to the CQ resistance transporter (CRT) system. The present study deals with computational modeling of Plasmodium falciparum chloroquine resistance transporter (PfCRT) protein and development of charged environment to mimic a condition of resistance. The model of PfCRT was developed using Protein homology/analogy engine (PHYRE ver 0.2) and was validated based on the results obtained using PSI-PRED. Subsequently, molecular interactions of selected phytochemicals extracted from C. roseus Linn. and T. indica were studied using multiple-iterated genetic algorithm-based docking protocol in order to investigate the translocation of these legends across the PfCRT protein. Further, molecular dynamics studies exhibiting interaction energy estimates of these compounds within the active site of the protein showed that compounds are more selective toward PfCRT. Clusters of conformations with the free energy of binding were estimated which clearly demonstrated the potential channel and by this means the translocation across the PfCRT is anticipated.

In vitro anti-Plasmodium falciparum properties of the full set of human secreted phospholipases A2.

We have previously shown that secreted phospholipases A2 (sPLA2s) from animal venoms inhibit the in vitro development of Plasmodium falciparum, the agent of malaria. In addition, the inflammatory-type human group IIA (hGIIA) sPLA2 circulates at high levels in the serum of malaria patients. However, the role of the different human sPLA2s in host defense against P. falciparum has not been investigated. We show here that 4 out of 10 human sPLA2s, namely, hGX, hGIIF, hGIII, and hGV, exhibit potent in vitro anti-Plasmodium properties with half-maximal inhibitory concentrations (IC50s) of 2.9 ± 2.4, 10.7 ± 2.1, 16.5 ± 9.7, and 94.2 ± 41.9 nM, respectively. Other human sPLA2s, including hGIIA, are inactive. The inhibition is dependent on sPLA2 catalytic activity and primarily due to hydrolysis of plasma lipoproteins from the parasite culture. Accordingly, purified lipoproteins that have been prehydrolyzed by hGX, hGIIF, hGIII, and hGV are more toxic to P. falciparum than native lipoproteins. However, the total enzymatic activities of human sPLA2s on purified lipoproteins or plasma did not reflect their inhibitory activities on P. falciparum. For instance, hGIIF is 9-fold more toxic than hGV but releases a lower quantity of nonesterified fatty acids (NEFAs). Lipidomic analyses of released NEFAs from lipoproteins demonstrate that sPLA2s with anti-Plasmodium properties are those that release polyunsaturated fatty acids (PUFAs), with hGIIF being the most selective enzyme. NEFAs purified from lipoproteins hydrolyzed by hGIIF were more potent at inhibiting P. falciparum than those from hGV, and PUFA-enriched liposomes hydrolyzed by sPLA2s were highly toxic, demonstrating the critical role of PUFAs. The selectivity of sPLA2s toward low- and high-density (LDL and HDL, respectively) lipoproteins and their ability to directly attack parasitized erythrocytes further explain their anti-Plasmodium activity. Together, our findings indicate that 4 human sPLA2s are active against P. falciparum in vitro and pave the way to future investigations on their in vivo contribution in malaria pathophysiology.

Triaging informative cis-regulatory elements for the combinatorial control of temporal gene expression during Plasmodium falciparum intraerythrocytic development.

BackgroundOver 2700 genes are subject to stage-specific regulation during the intraerythrocytic development of the human malaria parasite Plasmodium falciparum. Bioinformatic analyses have identified a large number of over-represented motifs in the 5′ flanking regions of these genes that may act as cis-acting factors in the promoter-based control of temporal expression. Triaging these lists to provide candidates most likely to play a role in regulating temporal expression is challenging, but important if we are to effectively design in vitro studies to validate this role.MethodsWe report here the application of a repeated search of variations of 5′ flanking sequences from P. falciparum using the Finding Informative Regulatory Elements (FIRE) algorithm.ResultsOur approach repeatedly found a short-list of high scoring DNA motifs, for which cognate specific transcription factors were available, that appear to be typically associated with upregulation of mRNA accumulation during the first half of intraerythrocytic development.ConclusionsWe propose these cis-trans interactions may provide a combinatorial promoter-based control of gene expression to complement more global mechanisms of gene regulation that can account for temporal control during the second half of intraerythrocytic development.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-0701-0) contains supplementary material, which is available to authorized users.