Targeting the redox metabolism of Plasmodium falciparum

Depletion of hepatic glutathione and adenosine by glucocorticoid exposure in Wistar rats is pregnancy-independent

Liver diseases have gained increasing attention due to their substantial impact on health, independently as well as in association with cardio-metabolic disorders. Studies have suggested that glutathione and adenosine assist in providing protection against oxidative stress and inflammation while glucocorticoid (GC) therapy has been associated with chronic inflammatory disorders, even in pregnancy. The implications of Glucocorticoid exposure on maternal health and fetal growth is a concern, however, the possible role of glutathione and adenosine has not been thoroughly investigated. The study therefore hypothesize that exposure to glucocorticoids leads to depletion of hepatic glutathione and adenosine levels, contributing to oxidative stress and tissue injury. Additionally, we aim to investigate whether the effects of glucocorticoids on hepatic health are pregnancy dependent in female rats. Twelve Pregnant and twelve age-matched non-pregnant rats were used for this study; an exogenous administration of glucocorticoid (Dex: 0.2 mg/kg) or vehicle (po) was administered to six pregnant and six non-pregnant rats from gestational day 14 to 19 or for a period of 6 days respectively. Data obtained showed that GC exposure led to a decrease in hepatic glucose-6-phosphate dehydrogenase, glutathione peroxidase, GSH/GSSG ratio and adenosine content in both pregnant and non-pregnant rats. In addition, increased activities of adenosine deaminase and xanthine oxidase, along with increased production of uric acid and increased levels of lactate dehydrogenase, aspartate aminotransferase, alanine transferase, alkaline phosphatase and gamma-glutamyl transferase were observed. In summary, the study indicates that GC-induced liver damage is underlined by depleted hepatic adenosine and glutathione levels as well as elevated markers of tissue inflammation and/or injury. Furthermore, the findings suggest that the effects of GC exposure on hepatic health are pregnancy independent.

Structural and functional characterization of 6-phosphogluconate dehydrogenase in Plasmodium falciparum (3D7) and identification of its potent inhibitors

The malarial parasite Plasmodium falciparum predominantly causes severe malaria and deaths worldwide. Moreover, resistance developed by P. falciparum to frontline drugs in recent years has markedly increased malaria-related deaths in South Asian Countries. Ribulose 5-phosphate and NADPH synthesized by Pentose Phosphate Pathway (PPP) act as a direct precursor for nucleotide synthesis and P. falciparum survival during oxidative challenges in the intra-erythrocytic growth phase . In the present study, we have elucidated the structure and functional characteristics of 6-phosphogluconate dehydrogenase (6PGD) in P. falciparum and have identified potent hits against 6PGD by pharmacophore-based virtual screening with ZINC and ChemBridge databases. Molecular docking and Molecular dynamics simulation, binding free energies (MMGBSA & MMPBSA), and Density Functional Theory (DFT) calculations were integratively employed to validate and prioritize the most potential hits. The 6PGD structure was found to have an open and closed conformation during MD simulation. The apo form of 6PGD was found to be in closed conformation, while a open conformation attributed to facilitating binding of cofactor. It was also inferred from the conformational analysis that the small domain of 6PGD has a high influence in altering the conformation that may aid in open/closed conformation of 6PGD. The top three hits identified using pharmacophore hypotheses were ChemBridge_11084819, ChemBridge_80178394, and ChemBridge_17912340. Though all three hits scored a high glide score, MMGBSA, and favorable ADMET properties, ChemBridge_11084819 and ChemBrdige_17912340 showed higher stability and binding free energy. Moreover, these hits also featured stable H-bond interactions with the active loop of 6PGD with binding free energy comparable to substrate-bound complex. Therefore, the ChemBridge_11084819 and ChemBridge_17912340 moieties demonstrate to have high therapeutic potential against 6PGD in P. falciparum.Communicated by Ramaswamy H. Sarma.

Identification of Co-Existing Mutations and Gene Expression Trends Associated With K13-Mediated Artemisinin Resistance in Plasmodium falciparum

Plasmodium falciparum infects millions and kills thousands of people annually the world over. With the emergence of artemisinin and/or multidrug resistant strains of the pathogen, it has become even more challenging to control and eliminate the disease. Multiomics studies of the parasite have started to provide a glimpse into the confounding genetics and mechanisms of artemisinin resistance and identified mutations in Kelch13 (K13) as a molecular marker of resistance. Over the years, thousands of genomes and transcriptomes of artemisinin-resistant/sensitive isolates have been documented, supplementing the search for new genes/pathways to target artemisinin-resistant isolates. This meta-analysis seeks to recap the genetic landscape and the transcriptional deregulation that demarcate artemisinin resistance in the field. To explore the genetic territory of artemisinin resistance, we use genomic single-nucleotide polymorphism (SNP) datasets from 2,517 isolates from 15 countries from the MalariaGEN Network (The Pf3K project, pilot data release 4, 2015) to dissect the prevalence, geographical distribution, and co-existing patterns of genetic markers associated with/enabling artemisinin resistance. We have identified several mutations which co-exist with the established markers of artemisinin resistance. Interestingly, K13-resistant parasites harbor α-ß hydrolase and putative HECT domain-containing protein genes with the maximum number of SNPs. We have also explored the multiple, publicly available transcriptomic datasets to identify genes from key biological pathways whose consistent deregulation may be contributing to the biology of resistant parasites. Surprisingly, glycolytic and pentose phosphate pathways were consistently downregulated in artemisinin-resistant parasites. Thus, this meta-analysis highlights the genetic and transcriptomic features of resistant parasites to propel further exploratory studies in the community to tackle artemisinin resistance.

Cysticidal effect of a pure naphthoquinone on Taenia crassiceps cysticerci

Cysticercosis is a disease caused by the metacestode of the parasite Taenia solium (T. solium). In humans, the most severe complication of the disease is neurocysticercosis. The drug of choice to treat this disease is albendazole; however, the bioavailability and efficacy of the drug are variable. Therefore, new molecules with therapeutic effects against this and other parasitic infections caused by helminths must be developed. Naphthoquinones are naphthalene-derived compounds that possess antibacterial, antifungal, antitumoral, and antiparasitic properties. The aim of this work was to evaluate the in vitro anti-helminthic effect of 2-[(3-chlorophenylamino)phenylmethyl]-3-hydroxy-1,4-naphthoquinone, isolated from a natural source and then synthesized (naphthoquinone 4a), using an experimental model of murine cysticercosis caused by Taenia crassiceps (T. crassiceps). This compound causes paralysis in the cysticerci membrane from day 3 of the in vitro treatment. Additionally, it induces changes in the shape, size, and appearance of the cysticerci and a decrease in the reproduction rate. In conclusion, naphthoquinone 4a has in vitro cysticidal activity on T. crassiceps cysticerci depending on the duration of the treatment and the concentration of the compound. Therefore, it is a promising drug candidate to be used in T. crassiceps and possibly T. solium infections.

Plasmodium falciparum LipB mutants display altered redox and carbon metabolism in asexual stages and cannot complete sporogony in Anopheles mosquitoes

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Apicoplast LipB deletion leads to changed antioxidant expression that precedes and coincides with accelerated differentiation.

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3D7 Plasmodium exhibits changes in glycolysis and tricarboxylic acid cycle activity after deletion of apicoplast LipB.

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When LipB is deleted from NF54 Plasmodium, the resulting parasites cannot complete their development in mosquitoes.

Malaria is still one of the most important global infectious diseases. Emergence of drug resistance and a shortage of new efficient antimalarials continue to hamper a malaria eradication agenda. Malaria parasites are highly sensitive to changes in the redox environment. Understanding the mechanisms regulating parasite redox could contribute to the design of new drugs. Malaria parasites have a complex network of redox regulatory systems housed in their cytosol, in their mitochondrion and in their plastid (apicoplast). While the roles of enzymes of the thioredoxin and glutathione pathways in parasite survival have been explored, the antioxidant role of α-lipoic acid (LA) produced in the apicoplast has not been tested. To take a first step in teasing a putative role of LA in redox regulation, we analysed a mutant Plasmodium falciparum (3D7 strain) lacking the apicoplast lipoic acid protein ligase B (lipB) known to be depleted of LA. Our results showed a change in expression of redox regulators in the apicoplast and the cytosol. We further detected a change in parasite central carbon metabolism, with lipB deletion resulting in changes to glycolysis and tricarboxylic acid cycle activity. Further, in another Plasmodium cell line (NF54), deletion of lipB impacted development in the mosquito, preventing the detection of infectious sporozoite stages. While it is not clear at this point if the observed phenotypes are linked, these findings flag LA biosynthesis as an important subject for further study in the context of redox regulation in asexual stages, and point to LipB as a potential target for the development of new transmission drugs.

Pharmacokinetics and Ex Vivo Antimalarial Activity of Artesunate-Amodiaquine plus Methylene Blue in Healthy Volunteers

High rates of artemisinin-based combination therapy (ACT) failures in the treatment of Plasmodium falciparum malaria in Southeast Asia have led to triple-drug strategies to extend the useful life of ACTs. In this study, we determined whether methylene blue [MB; 3,7-bis(dimethylamino)phenothiazin-5-ium chloride hydrate] alters the pharmacokinetics of artesunate-amodiaquine (ASAQ) and enhances the ex vivo antimalarial activity of ASAQ. In an open-label, randomized crossover design, a single oral dose of ASAQ (200 mg AS/540 mg AQ) alone or with MB (325 mg) was administered to 15 healthy Vietnamese volunteers. Serial blood samples were collected up to 28 days after dosing. Pharmacokinetic properties of the drugs were determined by noncompartmental analysis. After drug administration, plasma samples from seven participants were assessed for ex vivo antimalarial activity against the artemisinin-sensitive MRA1239 and the artemisinin-resistant MRA1240 P. falciparum lines, in vitro MB significantly increased the mean area under the curve of the active metabolite of AS, dihydroartemisinin (1,246 ± 473 versus 917 ± 405 ng·h/ml, P = 0.009) but did not alter the pharmacokinetics of AQ, AS, or desethylamodiaquine. Comparing the antimalarial activities of the plasma samples from the participants collected up to 48 h after ASAQ plus MB (ASAQ+MB) and ASAQ dosing against the MRA1239 and MRA1240 lines, MB significantly enhanced the blood schizontocidal activity of ASAQ by 2.0-fold and 1.9-fold, respectively. The ring-stage survival assay also confirmed that MB enhanced the ex vivo antimalarial activity of ASAQ against MRA1240 by 2.9-fold to 3.8-fold, suggesting that the triple-drug combination has the potential to treat artemisinin-resistant malaria and for malaria elimination. (This study has been registered in the Australian New Zealand Clinical Trials Registry [https://anzctr.org.au/] under registration number ACTRN12612001298808.).

Signaling Response to Transient Redox Stress in Human Isolated T Cells: Molecular Sensor Role of Syk Kinase and Functional Involvement of IL2 Receptor and L-Selectine

Reactive oxygen species (ROS) are central effectors of inflammation and play a key role in cell signaling. Previous reports have described an association between oxidative events and the modulation of innate immunity. However, the role of redox signaling in adaptive immunity is still not well understood. This work is based on a novel investigation of diamide, a specific oxidant of sulfhydryl groups, and it is the first performed in purified T cell tyrosine phosphorylation signaling. Our data show that ex vivo T cells respond to –SH group oxidation with a distinctive tyrosine phosphorylation response and that these events elicit specific cellular responses. The expression of two essential T-cell receptors, CD25 and CD62L, and T-cell cytokine release is also affected in a specific way. Experiments with Syk inhibitors indicate a major contribution of this kinase in these phenomena. This pilot work confirms the presence of crosstalk between oxidation of cysteine residues and tyrosine phosphorylation changes, resulting in a series of functional events in freshly isolated T cells. Our experiments show a novel role of Syk inhibitors in applying their anti-inflammatory action through the inhibition of a ROS-generated reaction.

Antimalarial Properties of Dunnione Derivatives as NQO2 Substrates

Dunnione, a natural product isolated from the leaves of Streptocarpus dunnii (Gesneriaceae), acts as a substrate for quinone-reductases that may be associated with its antimalarial properties. Following our exploration of reactive oxygen species-producing compounds such as indolones, as possible new approaches for the research of new ways to treat this parasitosis, we explored derivatives of this natural product and their possible antiplasmodial and antimalarial properties, in vitro and in vivo, respectively. Apart from one compound, all the products tested had weak to moderate antiplasmodial activities, the best IC₅₀ value being equal to 0.58 µM. In vivo activities in the murine model were moderate (at a dose of 50 mg/kg/mice, five times higher than the dose of chloroquine). These results encourage further pharmacomodulation steps to improve the targeting of the parasitized red blood cells and antimalarial activities.

Plasmodium falciparum PFI1625c offers an opportunity to design potent anti-malarials: Biochemical characterization and testing potentials in drug discovery

Putative PFI1625c was cloned, over-expressed and purified to homogeneity. It is a 56.2 kDa monomeric protease which preferentially catalyzes the degradation of gelatin with a K_m = 30μM. It is a slow acting enzyme with optimal pH 8.5 and temperature 37 °C, and activity is sensitive to metalloprotease inhibitor 1,10-phenanthroline. PFI1625c active site was probed with a series of heterocyclic compounds and three molecules namely, BNPC-Inh2, DDBM-Inh1 and BHPM-Inh1 from the series were inhibiting PFI1625c protease activity. These heterocyclic compounds were found to irreversible inhibiting PFI1625c protease activity. Parasite culture was treated with these inhibitors and PFI1625c isolated from culture was found to be inactive without affecting other gelatinases present in the parasite. These inhibitors were used to generate chemically knockout PFI1625c in the parasite. PFI1625c knockout parasite remained at ring stage and was unable to complete its erythrocytic schizogony. Also, these knockout parasites were incapable to multiply. More careful analysis indicate these parasites develop oxidative stress as evident by the increase in lipid peroxidation, protein-carbonyl and a decrease of GSH level. In summary, the current study has employed biochemical, computational and pharmacological approaches to explore the role of PFI1625c in the parasite, its utility as a potential drug target to develop anti-malarials.

Glucose 6-phosphate dehydrogenase 6-phosphogluconolactonase: characterization of the Plasmodium vivax enzyme and inhibitor studies

BACKGROUND

Since malaria parasites highly depend on ribose 5-phosphate for DNA and RNA synthesis and on NADPH as a source of reducing equivalents, the pentose phosphate pathway (PPP) is considered an excellent anti-malarial drug target. In Plasmodium, a bifunctional enzyme named glucose 6-phosphate dehydrogenase 6-phosphogluconolactonase (GluPho) catalyzes the first two steps of the PPP. PfGluPho has been shown to be essential for the growth of blood stage Plasmodium falciparum parasites.

METHODS

Plasmodium vivax glucose 6-phosphate dehydrogenase (PvG6PD) was cloned, recombinantly produced in Escherichia coli, purified, and characterized via enzyme kinetics and inhibitor studies. The effects of post-translational cysteine modifications were assessed via western blotting and enzyme activity assays. Genetically encoded probes were employed to study the effects of G6PD inhibitors on the cytosolic redox potential of Plasmodium.

RESULTS

Here the recombinant production and characterization of PvG6PD, the C-terminal and NADPH-producing part of PvGluPho, is described. A comparison with PfG6PD (the NADPH-producing part of PfGluPho) indicates that the P. vivax enzyme has higher K_M values for the substrate and cofactor. Like the P. falciparum enzyme, PvG6PD is hardly affected by S-glutathionylation and moderately by S-nitrosation. Since there are several naturally occurring variants of PfGluPho, the impact of these mutations on the kinetic properties of the enzyme was analysed. Notably, in contrast to many human G6PD variants, the mutations resulted in only minor changes in enzyme activity. Moreover, nanomolar IC₅₀ values of several compounds were determined on P. vivax G6PD (including ellagic acid, flavellagic acid, and coruleoellagic acid), inhibitors that had been previously characterized on PfGluPho. ML304, a recently developed PfGluPho inhibitor, was verified to also be active on PvG6PD. Using genetically encoded probes, ML304 was confirmed to disturb the cytosolic glutathione-dependent redox potential of P. falciparum blood stage parasites. Finally, a new series of novel small molecules with the potential to inhibit the falciparum and vivax enzymes were synthesized, resulting in two compounds with nanomolar activity.

CONCLUSION

The characterization of PvG6PD makes this enzyme accessible to further drug discovery activities. In contrast to naturally occurring G6PD variants in the human host that can alter the kinetic properties of the enzyme and thus the redox homeostasis of the cells, the naturally occurring PfGluPho variants studied here are unlikely to have a major impact on the parasites' redox homeostasis. Several classes of inhibitors have been successfully tested and are presently being followed up.

(-)-Epigallocatechin-3-Gallate Inhibits the Chaperone Activity of Plasmodium falciparum Hsp70 Chaperones and Abrogates Their Association with Functional Partners

Heat shock proteins (Hsps), amongst them, Hsp70 and Hsp90 families, serve mainly as facilitators of protein folding (molecular chaperones) of the cell. The Hsp70 family of proteins represents one of the most important molecular chaperones in the cell. Plasmodium falciparum, the main agent of malaria, expresses six Hsp70 isoforms. Two (PfHsp70-1 and PfHsp70-z) of these localize to the parasite cytosol. PHsp70-1 is known to occur in a functional complex with another chaperone, PfHsp90 via a co-chaperone, P. falciparum Hsp70-Hsp90 organising protein (PfHop). (-)-Epigallocatechin-3-gallate (EGCG) is a green tea constituent that is thought to possess antiplasmodial activity. However, the mechanism by which EGCG exhibits antiplasmodial activity is not fully understood. A previous study proposed that EGCG binds to the N-terminal ATPase domain of Hsp70. In the current study, we overexpressed and purified recombinant forms of two P. falciparum cytosol localized Hsp70s (PfHsp70-1 and PfHsp70-z), and PfHop, a co-chaperone of PfHsp70-1. Using the surface plasmon resonance approach, we demonstrated that EGCG directly binds to the two Hsp70s. We further observed that binding of EGCG to the two proteins resulted in secondary and tertiary conformational changes. In addition, EGCG inhibited the ATPase and chaperone function of the two proteins. Furthermore, EGCG abrogated association of the two Hsp70s with their functional partners. Using parasites cultured in vitro at the blood stages, we observed that 2.9 µM EGCG suppressed 50% P. falciparum parasite growth (IC₅₀). Our findings demonstrate that EGCG directly binds to PfHsp70-1 and PfHsp70-z to inhibit both the ATPase and chaperone functions of the proteins. Our study constitutes the first direct evidence suggesting that the antiplasmodial activity of EGCG is at least in part accounted for by its inhibition of Hsp70 function.

A phenolic glycoside from Flacourtia indica induces heme mediated oxidative stress in Plasmodium falciparum and attenuates malaria pathogenesis in mice

BACKGROUND

Flacourtia indica is especially popular among the various communities of many African countries where it is being used traditionally for the treatment of malaria. In our previous report, we have identified some phenolic glycosides from the aerial parts of F. indica as promising antiplasmodial agents under in vitro conditions.

PURPOSE

Antimalarial bioprospection of F. indica derived phenolic glycoside in Swiss mice (in vivo) with special emphasis on its mode of action.

METHODS

Chloroquine sensitive strain of Plasmodium falciparum was routinely cultured and used for the in vitro studies. The in vivo antimalarial potential of phenolic glycoside was evaluated against P. berghei in Swiss mice through an array of parameters viz., hematological, biochemical, chemo-suppression and mean survival time.

RESULTS

2-(6-benzoyl-β-d-glucopyranosyloxy)-7-(1α, 2α, 6α-trihydroxy-3-oxocyclohex-4-enoyl)-5-hydroxybenzyl alcohol (CPG), a phenolic glycoside isolated from the aerial parts of F. indica was found to exhibit promising antiplasmodial activity by arresting the P. falciparum growth at the trophozoite stage. Spectroscopic investigations reveal that CPG possesses a strong binding affinity with free heme moieties. In addition, these interactions lead to the inhibition of heme polymerization in malaria parasite, augmenting oxidative stress, and delaying the rapid growth of parasite. Under in-vivo condition, CPG exhibited significant antimalarial activity against P. berghei at 50 and 75mg/kg body weight through chemo-suppression of parasitemia and ameliorating the parasite induced inflammatory and oxidative (hepatic) imbalance in the experimental mice.

CONCLUSION

CPG was found to be a potential antimalarial constituent of F. indica with an explored mechanism of action, which also offers the editing choices for developing CPG based antimalarial chemotypes.

Role of Quinone Reductase 2 in the Antimalarial Properties of Indolone-Type Derivatives

Indolone-N-oxides have antiplasmodial properties against Plasmodium falciparum at the erythrocytic stage, with IC₅₀ values in the nanomolar range. The mechanism of action of indolone derivatives involves the production of free radicals, which follows their bioreduction by an unknown mechanism. In this study, we hypothesized that human quinone reductase 2 (hQR2), known to act as a flavin redox switch upon binding to the broadly used antimalarial chloroquine, could be involved in the activity of the redox-active indolone derivatives. Therefore, we investigated the role of hQR2 in the reduction of indolone derivatives. We analyzed the interaction between hQR2 and several indolone-type derivatives by examining enzymatic kinetics, the substrate/protein complex structure with X-ray diffraction analysis, and the production of free radicals with electron paramagnetic resonance. The reduction of each compound in cells overexpressing hQR2 was compared to its reduction in naïve cells. This process could be inhibited by the specific hQR2 inhibitor, S29434. These results confirmed that the anti-malarial activity of indolone-type derivatives was linked to their ability to serve as hQR2 substrates and not as hQR2 inhibitors as reported for chloroquine, leading to the possibility that substrate of hQR2 could be considered as a new avenue for the design of new antimalarial compounds.

The Redox Cycler Plasmodione Is a Fast-Acting Antimalarial Lead Compound with Pronounced Activity against Sexual and Early Asexual Blood-Stage Parasites

Previously, we presented the chemical design of a promising series of antimalarial agents, 3-[substituted-benzyl]-menadiones, with potent in vitro and in vivo activities. Ongoing studies on the mode of action of antimalarial 3-[substituted-benzyl]-menadiones revealed that these agents disturb the redox balance of the parasitized erythrocyte by acting as redox cyclers-a strategy that is broadly recognized for the development of new antimalarial agents. Here we report a detailed parasitological characterization of the in vitro activity profile of the lead compound 3-[4-(trifluoromethyl)benzyl]-menadione 1c (henceforth called plasmodione) against intraerythrocytic stages of the human malaria parasite Plasmodium falciparum We show that plasmodione acts rapidly against asexual blood stages, thereby disrupting the clinically relevant intraerythrocytic life cycle of the parasite, and furthermore has potent activity against early gametocytes. The lead's antiplasmodial activity was unaffected by the most common mechanisms of resistance to clinically used antimalarials. Moreover, plasmodione has a low potential to induce drug resistance and a high killing speed, as observed by culturing parasites under continuous drug pressure. Drug interactions with licensed antimalarial drugs were also established using the fixed-ratio isobologram method. Initial toxicological profiling suggests that plasmodione is a safe agent for possible human use. Our studies identify plasmodione as a promising antimalarial lead compound and strongly support the future development of redox-active benzylmenadiones as antimalarial agents.

Identification of a thioredoxin reductase from Babesia microti during mammalian infection

Babesia microti is the primary causative agent of human babesiosis worldwide and associated with increased human health risks and the safety of blood supply. The parasite replicates in the host's red blood cells, thus, in order to counteract the oxidative stress and toxic effects, parasites employ a thioredoxin (Trx) system to maintain a redox balance. Since thioredoxin reductase (TrxR) plays a critical role in the system, in this study, we report the cloning, expression, and functional characterization of a novel TrxR from B. microti (BmiTrxR). The complete gene BmiTrxR was obtained by amplifying the 5' and 3' regions of messenger RNA (mRNA) by RACE. The full-length complementary DNA (cDNA) of BmiTrxR was 1766 bp and contained an intact open reading frame with 1662 bp that encoded a polypeptide with 553 amino acids. Molecular weight of the predicted protein was 58.4 kDa with an isoelectric point of 6.95, similar to high molecular weight TrxR. The recombinant protein of BmiTrxR was expressed in a His-fused soluble form in Escherichia coli. The native protein BmiTrxR was identified with the mouse anti-BmiTrxR polyclonal serum by western blotting and IFAT. Moreover, the enzyme showed a disulfide reductase activity using DTNB as substrate and catalyzed the NADPH-dependent reduction of Trx. Auranofin, a known inhibitor of TrxR, completely abrogated the activity of the recombinant enzyme in vitro. These results not only contribute to the understanding of redox pathway in this parasite but also suggest that BmiTrxR could be a potential target for the development of novel strategies to control B. microti thus reducing the incidence of babesiosis.

Oxidative stress control by apicomplexan parasites

Apicomplexan parasites cause infectious diseases that are either a severe public health problem or an economic burden. In this paper we will shed light on how oxidative stress can influence the host-pathogen relationship by focusing on three major diseases: babesiosis, coccidiosis, and toxoplasmosis.

Inference of the oxidative stress network in Anopheles stephensi upon Plasmodium infection

Ookinete invasion of Anopheles midgut is a critical step for malaria transmission; the parasite numbers drop drastically and practically reach a minimum during the parasite's whole life cycle. At this stage, the parasite as well as the vector undergoes immense oxidative stress. Thereafter, the vector undergoes oxidative stress at different time points as the parasite invades its tissues during the parasite development. The present study was undertaken to reconstruct the network of differentially expressed genes involved in oxidative stress in Anopheles stephensi during Plasmodium development and maturation in the midgut. Using high throughput next generation sequencing methods, we generated the transcriptome of the An. stephensi midgut during Plasmodium vinckei petteri oocyst invasion of the midgut epithelium. Further, we utilized large datasets available on public domain on Anopheles during Plasmodium ookinete invasion and Drosophila datasets and arrived upon clusters of genes that may play a role in oxidative stress. Finally, we used support vector machines for the functional prediction of the un-annotated genes of An. stephensi. Integrating the results from all the different data analyses, we identified a total of 516 genes that were involved in oxidative stress in An. stephensi during Plasmodium development. The significantly regulated genes were further extracted from this gene cluster and used to infer an oxidative stress network of An. stephensi. Using system biology approaches, we have been able to ascertain the role of several putative genes in An. stephensi with respect to oxidative stress. Further experimental validations of these genes are underway.

Preparation of rotenone derivatives and in vitro analysis of their antimalarial, antileishmanial and selective cytotoxic activities

Six derivatives of the known biopesticide rotenone were prepared by several chemical transformations. Rotenone and its derivatives showed differential in vitro antiparasitic activity and selective cytotoxicity. In general, compounds were more active against Plasmodium falciparum than Leishmania panamensis. Rotenone had an EC₅₀ of 19.0 µM against P. falciparum, and 127.2 µM against L. panamensis. Although chemical transformation does not improve its biological profile against P. falciparum, three of its derivatives showed a significant level of action within an adequate range of activity with EC₅₀ values < 50.0 µM. This antiplasmodial activity was not due to red blood cell hemolysis, since LC₅₀ was >>400 µM. On the other hand, all derivatives displayed a non-specific cytotoxicity on several cell lines and primary human cell cultures.