Toxoplasma gondii relies on both host and parasite isoprenoids and can be rendered sensitive to atorvastatin

The Toxoplasma monocarboxylate transporters are involved in the metabolism within the apicoplast and are linked to parasite survival

The apicoplast is a four-membrane plastid found in the apicomplexans, which harbors biosynthesis and organelle housekeeping activities in the matrix. However, the mechanism driving the flux of metabolites, in and out, remains unknown. Here, we used TurboID and genome engineering to identify apicoplast transporters in Toxoplasma gondii. Among the many novel transporters, we show that one pair of apicomplexan monocarboxylate transporters (AMTs) appears to have evolved from a putative host cell that engulfed a red alga. Protein depletion showed that AMT1 and AMT2 are critical for parasite growth. Metabolite analyses supported the notion that AMT1 and AMT2 are associated with biosynthesis of isoprenoids and fatty acids. However, stronger phenotypic defects were observed for AMT2, including in the inability to establish T. gondii parasite virulence in mice. This study clarifies, significantly, the mystery of apicoplast transporter composition and reveals the importance of the pair of AMTs in maintaining the apicoplast activity in apicomplexans.

Beyond the MEP Pathway: A novel kinase required for prenol utilization by malaria parasites

A proposed treatment for malaria is a combination of fosmidomycin and clindamycin. Both compounds inhibit the methylerythritol 4-phosphate (MEP) pathway, the parasitic source of farnesyl and geranylgeranyl pyrophosphate (FPP and GGPP, respectively). Both FPP and GGPP are crucial for the biosynthesis of several essential metabolites such as ubiquinone and dolichol, as well as for protein prenylation. Dietary prenols, such as farnesol (FOH) and geranylgeraniol (GGOH), can rescue parasites from MEP inhibitors, suggesting the existence of a missing pathway for prenol salvage via phosphorylation. In this study, we identified a gene in the genome of P. falciparum, encoding a transmembrane prenol kinase (PolK) involved in the salvage of FOH and GGOH. The enzyme was expressed in Saccharomyces cerevisiae, and its FOH/GGOH kinase activities were experimentally validated. Furthermore, conditional knockout parasites (Δ-PolK) were created to investigate the biological importance of the FOH/GGOH salvage pathway. Δ-PolK parasites were viable but displayed increased susceptibility to fosmidomycin. Their sensitivity to MEP inhibitors could not be rescued by adding prenols. Additionally, Δ-PolK parasites lost their capability to utilize prenols for protein prenylation. Experiments using culture medium supplemented with whole/delipidated human plasma in transgenic parasites revealed that human plasma has components that can diminish the effectiveness of fosmidomycin. Mass spectrometry tests indicated that both bovine supplements used in culture and human plasma contain GGOH. These findings suggest that the FOH/GGOH salvage pathway might offer an alternate source of isoprenoids for malaria parasites when de novo biosynthesis is inhibited. This study also identifies a novel kind of enzyme related to isoprenoid metabolism.

An updated review of chemical compounds with anti-Toxoplasma gondii activity

The opportunistic apicomplexan parasite Toxoplasma gondii is the etiologic agent for toxoplasmosis, which can infect a widespread range of hosts, particularly humans and warm-blooded animals. The present chemotherapy to treat or prevent toxoplasmosis is deficient and is based on diverse drugs such as atovaquone, trimethoprim, spiramycine, which are effective in acute toxoplasmosis. Therefore, a safe chemotherapy is required for toxoplasmosis considering that its responsible agent, T. gondii, provokes severe illness and death in pregnant women and immunodeficient patients. A certain disadvantage of the available treatments is the lack of effectiveness against the tissue cyst of the parasite. A safe chemotherapy to combat toxoplasmosis should be based on the metabolic differences between the parasite and the mammalian host. This article covers different relevant molecular targets to combat this disease including the isoprenoid pathway (farnesyl diphosphate synthase, squalene synthase), dihydrofolate reductase, calcium-dependent protein kinases, histone deacetylase, mitochondrial electron transport chain, etc.

Transcriptomic and metabolomic analyses reveal the essential nature of Rab1B in Toxoplasma gondii

BACKGROUND

The protozoan parasite Toxoplasma gondii encodes a dozen Rab proteins, which are parts of the small GTPase superfamily and regulate intracellular membrane trafficking. Our previous study showed that depletion of Rab1B caused severe defects regarding parasite growth and morphological structure, yet early defects of endocytic trafficking and vesicle sorting to the rhoptry in T. gondii are not expected to have a strong effect. To understand this discrepancy, we performed an integrated analysis at the level of transcriptomics and metabolomics.

METHODS

In the study, tetracycline-inducible TATi/Ty-Rab1B parasite line treated with ATc at three different time points (0, 18 and 24 h) was used. We first observed the morphological changes caused by Rab1B depletion via transmission electron technology. Then, high-throughput transcriptome along with non-targeted metabolomics were performed to analyze the RNA expression and metabolite changes in the Rab1B-depleted parasite. The essential nature of Rab1B in the parasite was revealed by the integrated omics approach.

RESULTS

Transmission electron micrographs showed a strong disorganization of endo-membranes in the Rab1B-depleted parasites. Our deep analysis of transcriptome and metabolome identified 2181 and 2374 differentially expressed genes (DEGs) and 30 and 83 differentially expressed metabolites (DEMs) at 18 and 24 h of induction in the tetracycline-inducible parasite line, respectively. These DEGs included key genes associated with crucial organelles that contain the rhoptry, microneme, endoplasmic reticulum and Golgi apparatus. The analysis of qRT-PCR verified some of the key DEGs identified by RNA-Seq, supporting that the key vesicular regulator Rab1B was involved in biogenesis of multiple parasite organelles. Functional enrichment analyses revealed pathways related to central carbon metabolisms and lipid metabolisms, such as the TCA cycle, glycerophospholipid metabolism and fatty acid biosynthesis and elongation. Further correlation analysis of the major DEMs and DEGs supported the role of Rab1B in biogenesis of fatty acids (e.g. myrisoleic acid and oleic acid) (R > 0.95 and P < 0.05), which was consistent with the scavenging role in biotin via the endocytic process.

CONCLUSIONS

Rab1B played an important role in parasite growth and morphology, which was supported by the replication assay and transmission electron microscopy observation. Our multi-omics analyses provided detailed insights into the overall impact on the parasite upon depletion of the protein. These analyses reinforced the role of Rab1B in the endocytic process, which has an impact on fatty acid biogenesis and the TCA cycle. Taken together, these findings contribute to our understanding of a key vesicular regulator, Rab1B, on parasite metabolism and morphological formation in T. gondii.

Functional screening reveals Toxoplasma prenylated proteins required for endocytic trafficking and rhoptry protein sorting

In the apicomplexans, endocytosed cargos (e.g., hemoglobin) are trafficked to a specialized organelle for digestion. This follows a unique endocytotic process at the micropore/cytostome in these parasites. However, the mechanism underlying endocytic trafficking remains elusive, due to the repurposing of classical endocytic proteins for the biogenesis of apical organelles. To resolve this issue, we have exploited the genetic tractability of the model apicomplexan Toxoplasma gondii, which ingests host cytosolic materials (e.g., green fluorescent protein[GFP]). We determined an association between protein prenylation and endocytic trafficking, and using an alkyne-labeled click chemistry approach, the prenylated proteome was characterized. Genome editing, using clustered regularly interspaced short palindromic repaet/CRISPR-associated nuclease 9 (CRISPR/Cas9), was efficiently utilized to generate genetically modified lines for the functional screening of 23 prenylated candidates. This identified four of these proteins that regulate the trafficking of endocytosed GFP vesicles. Among these proteins, Rab1B and YKT6.1 are highly conserved but are non-classical endocytic proteins in eukaryotes. Confocal imaging analysis showed that Rab1B and Ras are substantially localized to both the trans-Golgi network and the endosome-like compartments in the parasite. Conditional knockdown of Rab1B caused a rapid defect in secretory trafficking to the rhoptry bulb, suggesting a trafficking intersection role for the key regulator Rab1B. Further experiments confirmed a critical role for protein prenylation in regulating the stability/activity of these proteins (i.e., Rab1B and YKT6.1) in the parasite. Our findings define the molecular basis of endocytic trafficking and reveal a potential intersection function of Rab1B on membrane trafficking in T. gondii. This might extend to other related protists, including the malarial parasites. IMPORTANCE The protozoan Toxoplasma gondii establishes a permissive niche, in host cells, that allows parasites to acquire large molecules such as proteins. Numerous studies have demonstrated that the parasite repurposes the classical endocytic components for secretory sorting to the apical organelles, leaving the question of endocytic transport to the lysosome-like compartment unclear. Recent studies indicated that endocytic trafficking is likely to associate with protein prenylation in malarial parasites. This information promoted us to examine this association in the model apicomplexan T. gondii and to identify the key components of the prenylated proteome that are involved. By exploiting the genetic tractability of T. gondii and a host GFP acquisition assay, we reveal four non-classical endocytic proteins that regulate the transport of endocytosed cargos (e.g., GFP) in T. gondii. Thus, we extend the principle that protein prenylation regulates endocytic trafficking and elucidate the process of non-classical endocytosis in T. gondii and potentially in other related protists.

Statin and aspirin use in parasitic infections as a potential therapeutic strategy: A narrative review

Infections, including zoonoses, constitute a threat to human health due to the spread of resistant pathogens. These diseases generate an inflammatory response controlled by a resolving mechanism involving specialized membrane lipid-derived molecules called lipoxins, resolvins, maresins, and protectins. The production of some of these molecules can be triggered by aspirin or statins. Thus, it is proposed that modulation of the host response could be a useful therapeutic strategy, contributing to the management of resistance to antiparasitic agents or preventing drift to chronic, host-damaging courses. Therefore, the present work presents the state of the art on the use of statins or aspirin for the experimental management of parasitic infections such as Chagas disease, leishmaniasis, toxoplasmosis or malaria. The methodology used was a narrative review covering original articles from the last seven years, 38 of which met the inclusion criteria. Based on the publications consulted, modulation of the resolution of inflammation using statins may be feasible as an adjuvant in the therapy of parasitic diseases. However, there was no strong experimental evidence on the use of aspirin; therefore, further studies are needed to evaluate its role inflammation resolution process in infectious diseases.

Antiplasmodial, Trypanocidal, and Genotoxicity In Vitro Assessment of New Hybrid α,α-Difluorophenylacetamide-statin Derivatives

BACKGROUND

Statins present a plethora of pleiotropic effects including anti-inflammatory and antimicrobial responses. A,α-difluorophenylacetamides, analogs of diclofenac, are potent pre-clinical anti-inflammatory non-steroidal drugs. Molecular hybridization based on the combination of pharmacophoric moieties has emerged as a strategy for the development of new candidates aiming to obtain multitarget ligands.

METHODS

Considering the anti-inflammatory activity of phenylacetamides and the potential microbicidal action of statins against obligate intracellular parasites, the objective of this work was to synthesize eight new hybrid compounds of α,α-difluorophenylacetamides with the moiety of statins and assess their phenotypic activity against in vitro models of Plasmodium falciparum and Trypanosoma cruzi infection besides exploring their genotoxicity safety profile.

RESULTS

None of the sodium salt compounds presented antiparasitic activity and two acetated compounds displayed mild anti-P. falciparum effect. Against T. cruzi, the acetate halogenated hybrids showed moderate effect against both parasite forms relevant for human infection. Despite the considerable trypanosomicidal activity, the brominated compound revealed a genotoxic profile impairing future in vivo testing.

CONCLUSIONS

However, the chlorinated derivative was the most promising compound with chemical and biological profitable characteristics, without presenting genotoxicity in vitro, being eligible for further in vivo experiments.

Prenyl Transferases Regulate Secretory Protein Sorting and Parasite Morphology in Toxoplasma gondii

Protein prenylation is an important protein modification that is responsible for diverse physiological activities in eukaryotic cells. This modification is generally catalyzed by three types of prenyl transferases, which include farnesyl transferase (FT), geranylgeranyl transferase (GGT-1) and Rab geranylgeranyl transferase (GGT-2). Studies in malaria parasites showed that these parasites contain prenylated proteins, which are proposed to play multiple functions in parasites. However, the prenyl transferases have not been functionally characterized in parasites of subphylum Apicomplexa. Here, we functionally dissected functions of three of the prenyl transferases in the Apicomplexa model organism Toxoplasma gondii (T. gondii) using a plant auxin-inducible degron system. The homologous genes of the beta subunit of FT, GGT-1 and GGT-2 were endogenously tagged with AID at the C-terminus in the TIR1 parental line using a CRISPR-Cas9 approach. Upon depletion of these prenyl transferases, GGT-1 and GGT-2 had a strong defect on parasite replication. Fluorescent assay using diverse protein markers showed that the protein markers ROP5 and GRA7 were diffused in the parasites depleted with GGT-1 and GGT-2, while the mitochondrion was strongly affected in parasites depleted with GGT-1. Importantly, depletion of GGT-2 caused the stronger defect to the sorting of rhoptry protein and the parasite morphology. Furthermore, parasite motility was observed to be affected in parasites depleted with GGT-2. Taken together, this study functionally characterized the prenyl transferases, which contributed to an overall understanding of protein prenylation in T. gondii and potentially in other related parasites.

The Biomedical Importance of the Missing Pathway for Farnesol and Geranylgeraniol Salvage

Isoprenoids are the output of the polymerization of five-carbon, branched isoprenic chains derived from isopentenyl pyrophosphate (IPP) and its isomer, dimethylallyl pyrophosphate (DMAPP). Isoprene units are consecutively condensed to form longer structures such as farnesyl and geranylgeranyl pyrophosphate (FPP and GGPP, respectively), necessary for the biosynthesis of several metabolites. Polyprenyl transferases and synthases use polyprenyl pyrophosphates as their natural substrates; however, it is known that free polyprenols, such as farnesol (FOH), and geranylgeraniol (GGOH) can be incorporated into prenylated proteins, ubiquinone, cholesterol, and dolichols. Furthermore, FOH and GGOH have been shown to block the effects of isoprenoid biosynthesis inhibitors such as fosmidomycin, bisphosphonates, or statins in several organisms. This phenomenon is the consequence of a short pathway, which was observed for the first time more than 25 years ago: the polyprenol salvage pathway, which works via the phosphorylation of FOH and GGOH. Biochemical studies in bacteria, animals, and plants suggest that this pathway can be carried out by two enzymes: a polyprenol kinase and a polyprenyl-phosphate kinase. However, to date, only a few genes have been unequivocally identified to encode these enzymes in photosynthetic organisms. Nevertheless, pieces of evidence for the importance of this pathway abound in studies related to infectious diseases, cancer, dyslipidemias, and nutrition, and to the mitigation of the secondary effects of several drugs. Furthermore, nowadays it is known that both FOH and GGOH can be incorporated via dietary sources that produce various biological effects. This review presents, in a simplified but comprehensive manner, the most important data on the FOH and GGOH salvage pathway, stressing its biomedical importance The main objective of this review is to bring to light the need to discover and characterize the kinases associated with the isoprenoid salvage pathway in animals and pathogens.

The Heptaprenyl Diphosphate Synthase (Coq1) Is the Target of a Lipophilic Bisphosphonate That Protects Mice against Toxoplasma gondii Infection

Prenyldiphosphate synthases catalyze the reaction of allylic diphosphates with one or more isopentenyl diphosphate molecules to form compounds such as farnesyl diphosphate, used in, e.g., sterol biosynthesis and protein prenylation, as well as longer "polyprenyl" diphosphates, used in ubiquinone and menaquinone biosynthesis. Quinones play an essential role in electron transport and are associated with the inner mitochondrial membrane due to the presence of the polyprenyl group. In this work, we investigated the synthesis of the polyprenyl diphosphate that alkylates the ubiquinone ring precursor in Toxoplasma gondii, an opportunistic pathogen that causes serious disease in immunocompromised patients and the unborn fetus. The enzyme that catalyzes this early step of the ubiquinone synthesis is Coq1 (TgCoq1), and we show that it produces the C35 species heptaprenyl diphosphate. TgCoq1 localizes to the mitochondrion and is essential for in vitro T. gondii growth. We demonstrate that the growth defect of a T. gondii TgCoq1 mutant is rescued by complementation with a homologous TgCoq1 gene or with a (C45) solanesyl diphosphate synthase from Trypanosoma cruzi (TcSPPS). We find that a lipophilic bisphosphonate (BPH-1218) inhibits T. gondii growth at low-nanomolar concentrations, while overexpression of the TgCoq1 enzyme dramatically reduced growth inhibition by the bisphosphonate. Both the severe growth defect of the mutant and the inhibition by BPH-1218 were rescued by supplementation with a long-chain (C30) ubiquinone (UQ6). Importantly, BPH-1218 also protected mice against a lethal T. gondii infection. TgCoq1 thus represents a potential drug target that could be exploited for improved chemotherapy of toxoplasmosis. IMPORTANCE Millions of people are infected with Toxoplasma gondii, and the available treatment for toxoplasmosis is not ideal. Most of the drugs currently used are only effective for the acute infection, and treatment can trigger serious side effects requiring changes in the therapeutic approach. There is, therefore, a compelling need for safe and effective treatments for toxoplasmosis. In this work, we characterize an enzyme of the mitochondrion of T. gondii that can be inhibited by an isoprenoid pathway inhibitor. We present evidence that demonstrates that inhibition of the enzyme is linked to parasite death. In addition, the inhibitor can protect mice against a lethal dose of T. gondii. Our results thus reveal a promising chemotherapeutic target for the development of new medicines for toxoplasmosis.

The ferredoxin redox system - an essential electron distributing hub in the apicoplast of Apicomplexa

The apicoplast, a relict plastid found in most species of the phylum Apicomplexa, harbors the ferredoxin redox system which supplies electrons to enzymes of various metabolic pathways in this organelle. Recent reports in Toxoplasma gondii and Plasmodium falciparum have shown that the iron-sulfur cluster (FeS)-containing ferredoxin is essential in tachyzoite and blood-stage parasites, respectively. Here we review ferredoxin's crucial contribution to isoprenoid and lipoate biosynthesis as well as tRNA modification in the apicoplast, highlighting similarities and differences between the two species. We also discuss ferredoxin's potential role in the initial reductive steps required for FeS synthesis as well as recent evidence that offers an explanation for how NADPH required by the redox system might be generated in Plasmodium spp.

Modulation of autophagy as a therapeutic strategy for Toxoplasma gondii infection

Toxoplasma gondii infection is a severe health threat that endangers billions of people worldwide. T. gondii utilizes the host cell membrane to form a parasitophorous vacuole (PV), thereby fully isolating itself from the host cell cytoplasm and making intracellular clearance difficult. PV can be targeted and destroyed by autophagy. Autophagic targeting results in T. gondii killing via the fusion of autophagosomes and lysosomes. However, T. gondii has developed many strategies to suppress autophagic targeting. Accordingly, the interplay between host cell autophagy and T. gondii is an emerging area with important practical implications. By promoting the canonical autophagy pathway or attenuating the suppression of autophagic targeting, autophagy can be effectively utilized in the development of novel therapeutic strategies against T gondii. Here, we have illustrated the complex interplay between host cell mediated autophagy and T. gondii. Different strategies to promote autophagy in order to target the parasite have been elucidated. Besides, we have analyzed some potential new drug molecules from the DrugBank database using bioinformatics tools, which can modulate autophagy. Various challenges and opportunities focusing autophagy mediated T. gondii clearance have been discussed, which will provide new insights for the development of novel drugs against the parasite.

Disrupting the plastidic iron-sulfur cluster biogenesis pathway in Toxoplasma gondii has pleiotropic effects irreversibly impacting parasite viability

Like many other apicomplexan parasites, Toxoplasma gondii contains a plastid harboring key metabolic pathways, including the sulfur utilization factor (SUF) pathway that is involved in the biosynthesis of iron-sulfur clusters. These cofactors are crucial for a variety of proteins involved in important metabolic reactions, potentially including plastidic pathways for the synthesis of isoprenoid and fatty acids. It was shown previously that impairing the NFS2 cysteine desulfurase, involved in the first step of the SUF pathway, leads to an irreversible killing of intracellular parasites. However, the metabolic impact of disrupting the pathway remained unexplored. Here, we generated another mutant of this pathway, deficient in the SUFC ATPase, and investigated in details the phenotypic consequences of TgNFS2 and TgSUFC depletion on the parasites. Our analysis confirms that Toxoplasma SUF mutants are severely and irreversibly impacted in division and membrane homeostasis, and suggests a defect in apicoplast-generated fatty acids. However, we show that increased scavenging from the host or supplementation with exogenous fatty acids do not fully restore parasite growth, suggesting that this is not the primary cause for the demise of the parasites and that other important cellular functions were affected. For instance, we also show that the SUF pathway is key for generating the isoprenoid-derived precursors necessary for the proper targeting of GPI-anchored proteins and for parasite motility. Thus, we conclude plastid-generated iron-sulfur clusters support the functions of proteins involved in several vital downstream cellular pathways, which implies the SUF machinery may be explored for new potential anti-Toxoplasma targets.

Parasite powerhouse: A review of the Toxoplasma gondii mitochondrion

Toxoplasma gondii is a member of the apicomplexan phylum, a group of single-celled eukaryotic parasites that cause significant human morbidity and mortality around the world. T. gondii harbors two organelles of endosymbiotic origin: a non-photosynthetic plastid, known as the apicoplast, and a single mitochondrion derived from the ancient engulfment of an α-proteobacterium. Due to excitement surrounding the novelty of the apicoplast, the T. gondii mitochondrion was, to a certain extent, overlooked for about two decades. However, recent work has illustrated that the mitochondrion is an essential hub of apicomplexan-specific biology. Development of novel techniques, such as cryo-electron microscopy, complexome profiling, and next-generation sequencing have led to a renaissance in mitochondrial studies. This review will cover what is currently known about key features of the T. gondii mitochondrion, ranging from its genome to protein import machinery and biochemical pathways. Particular focus will be given to mitochondrial features that diverge significantly from the mammalian host, along with discussion of this important organelle as a drug target.

Toxoplasma gondii apicoplast-resident ferredoxin is an essential electron transfer protein for the MEP isoprenoid-biosynthetic pathway

Apicomplexan parasites, such as Toxoplasma gondii, are unusual in that each cell contains a single apicoplast, a plastid-like organelle that compartmentalizes enzymes involved in the essential 2C-methyl-D-erythritol 4-phosphate pathway of isoprenoid biosynthesis. The last two enzymatic steps in this organellar pathway require electrons from a redox carrier. However, the small iron-sulfur cluster-containing protein ferredoxin, a likely candidate for this function, has not been investigated in this context. We show here that inducible knockdown of T. gondii ferredoxin results in progressive inhibition of growth and eventual parasite death. Surprisingly, this phenotype is not accompanied by ultrastructural changes in the apicoplast or overall cell morphology. The knockdown of ferredoxin was instead associated with a dramatic decrease in cellular levels of the last two metabolites in isoprenoid biosynthesis, 1-hydroxy-2-methyl-2-(E)- butenyl-4-pyrophosphate, and isomeric dimethylallyl pyrophosphate/isopentenyl pyrophosphate. Ferredoxin depletion was also observed to impair gliding motility, consistent with isoprenoid metabolites being important for dolichol biosynthesis, protein prenylation, and modification of other proteins involved in motility. Significantly, pharmacological inhibition of isoprenoid synthesis of the host cell exacerbated the impact of ferredoxin depletion on parasite replication, suggesting that the slow onset of parasite death after ferredoxin depletion is because of isoprenoid scavenging from the host cell and leading to partial compensation of the depleted parasite metabolites upon ferredoxin knockdown. Overall, these findings show that ferredoxin has an essential physiological function as an electron donor for the 2C-methyl-D-erythritol 4-phosphate pathway and is a potential drug target for apicomplexan parasites.

A plastid two-pore channel essential for inter-organelle communication and growth of Toxoplasma gondii

Two-pore channels (TPCs) are a ubiquitous family of cation channels that localize to acidic organelles in animals and plants to regulate numerous Ca²⁺-dependent events. Little is known about TPCs in unicellular organisms despite their ancient origins. Here, we characterize a TPC from Toxoplasma gondii, the causative agent of toxoplasmosis. TgTPC is a member of a novel clad of TPCs in Apicomplexa, distinct from previously identified TPCs and only present in coccidians. We show that TgTPC localizes not to acidic organelles but to the apicoplast, a non-photosynthetic plastid found in most apicomplexan parasites. Conditional silencing of TgTPC resulted in progressive loss of apicoplast integrity, severely affecting growth and the lytic cycle. Isolation of TPC null mutants revealed a selective role for TPCs in replication independent of apicoplast loss that required conserved residues within the pore-lining region. Using a genetically-encoded Ca²⁺ indicator targeted to the apicoplast, we show that Ca²⁺ signals deriving from the ER but not from the extracellular space are selectively transmitted to the lumen. Deletion of the TgTPC gene caused reduced apicoplast Ca²⁺ uptake and membrane contact site formation between the apicoplast and the ER. Fundamental roles for TPCs in maintaining organelle integrity, inter-organelle communication and growth emerge.

The metabolic pathways and transporters of the plastid organelle in Apicomplexa

The apicoplast is the relict of a plastid organelle found in several disease-causing apicomplexan parasites such as Plasmodium spp. and Toxoplasma gondii. In these organisms, the organelle has lost its photosynthetic capability but harbours several fitness-conferring or essential metabolic pathways. Although maintaining the apicoplast and fuelling the metabolic pathways within requires the challenging constant import and export of numerous metabolites across its four membranes, only few apicoplast transporters have been identified to date, most of which are orphan transporters. Here we review the roles of metabolic pathways within the apicoplast and what is currently known about the few identified apicoplast metabolite transporters. We discuss what metabolites must get in and out of the apicoplast, the many transporters that are yet to be discovered, and what role these might play in parasite metabolism and as putative drug targets.

In vitro Effect of Harmine Alkaloid and Its N-Methyl Derivatives Against Toxoplasma gondii

Toxoplasmosis is one of the most prevalent and neglected zoonotic global diseases caused by Toxoplasma gondii. The current pharmacological treatments show clinical limitations, and therefore, the search for new drugs is an urgent need in order to eradicate this infection. Due to their intrinsic biological activities, β-carboline (βC) alkaloids might represent a good alternative that deserves further investigations. In this context, the in vitro anti-T. gondii activity of three βCs, harmine (1), 2-methyl-harminium (2), and 9-methyl-harmine (3), was evaluated herein. Briefly, the three alkaloids exerted direct effects on the parasite invasion and/or replication capability. Replication rates of intracellular treated tachyzoites were also affected in a dose-dependent manner, at noncytotoxic concentrations for host cells. Additionally, cell cycle analysis revealed that both methyl-derivatives 2 and 3 induce parasite arrest in S/M phases. Compound 3 showed the highest irreversible parasite growth inhibition, with a half maximal inhibitory concentration (IC50) value of 1.8 ± 0.2 μM and a selectivity index (SI) of 17.2 at 4 days post infection. Due to high replication rates, tachyzoites are frequently subjected to DNA double-strand breaks (DSBs). This highly toxic lesion triggers a series of DNA damage response reactions, starting with a kinase cascade that phosphorylates a large number of substrates, including the histone H2A.X to lead the early DSB marker γH2A.X. Western blot studies showed that basal expression of γH2A.X was reduced in the presence of 3. Interestingly, the typical increase in γH2A.X levels produced by camptothecin (CPT), a drug that generates DSB, was not observed when CPT was co-administered with 3. These findings suggest that 3 might disrupt Toxoplasma DNA damage response.

Rosuvastatin revert memory impairment and anxiogenic-like effect in mice infected with the chronic ME-49 strain of Toxoplasma gondii

The aim of this study was to investigate the effect of rosuvastatin treatment on memory impairment, and anxiogenic-like effects in mice chronically infected with Toxoplasma gondii. For this, Balb/c mice were infected orally with chronic ME-49 strain of Toxoplasma gondii. Oral treatment with rosuvastatin (40mg/kg/day) started on the 51^st day post-infection and was performed daily for 21 days. After completion of treatment, anxiety-like effects and locomotion were investigated in the open field (OF) test, whereas novel object recognition (NOR) test was used for evaluation of short- and long-term memory. At the end of the experiments, the brain was collected for Toxoplasma gondii DNA quantification and histopathological analysis. Infection with ME-49 strain decreased the time spent in the center of OF, indicating an anxiogenic effect, without affecting total and peripheral locomotion. Rosuvastatin treatment inhibited the change in the center time. Besides, pharmacological treatment increased total and central locomotion in both non-infected and infected animals. Infection also impaired both short- and long-term memory in the NOR test, and these effects were reverted by rosuvastatin treatment. In addition to effects in behavioral changes, rosuvastatin also reduced parasite load in the brain and attenuated signs of brain inflammation such as perivascular cuffs, inflammatory cell infiltration and tissue damage. These findings indicate for the first time the efficacy of rosuvastatin in treatment of memory impairment and anxiogenic effect evoked by infection with Toxoplasma gondii. These effects might be mediated by reduced cyst load, which in turn decrease inflammation and damage in the brain.

Control of human toxoplasmosis

Toxoplasmosis is caused by Toxoplasma gondii, an apicomplexan parasite that is able to infect any nucleated cell in any warm-blooded animal. Toxoplasma gondii infects around 2 billion people and, whilst only a small percentage of infected people will suffer serious disease, the prevalence of the parasite makes it one of the most damaging zoonotic diseases in the world. Toxoplasmosis is a disease with multiple manifestations: it can cause a fatal encephalitis in immunosuppressed people; if first contracted during pregnancy, it can cause miscarriage or congenital defects in the neonate; and it can cause serious ocular disease, even in immunocompetent people. The disease has a complex epidemiology, being transmitted by ingestion of oocysts that are shed in the faeces of definitive feline hosts and contaminate water, soil and crops, or by consumption of intracellular cysts in undercooked meat from intermediate hosts. In this review we examine current and future approaches to control toxoplasmosis, which encompass a variety of measures that target different components of the life cycle of T. gondii. These include: education programs about the parasite and avoidance of contact with infectious stages; biosecurity and sanitation to ensure food and water safety; chemo- and immunotherapeutics to control active infections and disease; prophylactic options to prevent acquisition of infection by livestock and cyst formation in meat; and vaccines to prevent shedding of oocysts by definitive feline hosts.

The NTP generating activity of pyruvate kinase II is critical for apicoplast maintenance in Plasmodium falciparum

The apicoplast of Plasmodium falciparum parasites is believed to rely on the import of three-carbon phosphate compounds for use in organelle anabolic pathways, in addition to the generation of energy and reducing power within the organelle. We generated a series of genetic deletions in an apicoplast metabolic bypass line to determine which genes involved in apicoplast carbon metabolism are required for blood-stage parasite survival and organelle maintenance. We found that pyruvate kinase II (PyrKII) is essential for organelle maintenance, but that production of pyruvate by PyrKII is not responsible for this phenomenon. Enzymatic characterization of PyrKII revealed activity against all NDPs and dNDPs tested, suggesting that it may be capable of generating a broad range of nucleotide triphosphates. Conditional mislocalization of PyrKII resulted in decreased transcript levels within the apicoplast that preceded organelle disruption, suggesting that PyrKII is required for organelle maintenance due to its role in nucleotide triphosphate generation.

Functional and Computational Genomics Reveal Unprecedented Flexibility in Stage-Specific Toxoplasma Metabolism

To survive and proliferate in diverse host environments with varying nutrient availability, the obligate intracellular parasite Toxoplasma gondii reprograms its metabolism. We have generated and curated a genome-scale metabolic model (iTgo) for the fast-replicating tachyzoite stage, harmonized with experimentally observed phenotypes. To validate the importance of four metabolic pathways predicted by the model, we have performed in-depth in vitro and in vivo phenotyping of mutant parasites including targeted metabolomics and CRISPR-Cas9 fitness screening of all known metabolic genes. This led to unexpected insights into the remarkable flexibility of the parasite, addressing the dependency on biosynthesis or salvage of fatty acids (FAs), purine nucleotides (AMP and GMP), a vitamin (pyridoxal-5P), and a cofactor (heme) in both the acute and latent stages of infection. Taken together, our experimentally validated metabolic network leads to a deeper understanding of the parasite's biology, opening avenues for the development of therapeutic intervention against apicomplexans.

Rosuvastatin reduced brain parasite burden in a chronic toxoplasmosis in vivo model and influenced the neuropathological pattern of ME-49 strain

This study evaluated the effects of rosuvastatin in vivo on toxoplasmosis chronic infection. Thirty-five Swiss mice were orally infected (ME-49 strain). After 50 days, the mice were separated into five groups: GI - non-infected, GII - infected, GIII - infected and treated with pyrimethamine and sulfadiazine (12.5 + 50 mg kg-1 body weight day-1), GIV and GV - infected and treated with rosuvastatin 10 and 40 mg kg-1 body weight day-1, respectively. After 21 days, we collected blood, liver, lungs, femoral biceps and brain were removed for Toxoplasma gondii DNA quantification by qPCR and histopathological analysis. GIV and GV did not present premature death or clinical changes, and the hepatic enzyme levels were lower compared to GI. Toxoplasma gondii DNA was detected mainly in brain and muscle, but the parasite load was significantly lower in GV compared to GII brains (P < 0.05). Histopathological changes were observed in brains, with T. gondii cysts as well as an inflammatory condition, including necrosis areas in GII and GIII. These data confirm active infection with tissue injury. This inflammatory condition was attenuated in the groups treated with rosuvastatin, especially R40 (GV). Our findings demonstrated the in vivo action of rosuvastatin in reducing cerebral parasitic load and indicate that this drug may interfere in chronic toxoplasmosis.

A Metabolic Dependency for Host Isoprenoids in the Obligate Intracellular Pathogen Rickettsia parkeri Underlies a Sensitivity to the Statin Class of Host-Targeted Therapeutics

Obligate intracellular pathogens, which include viruses as well as certain bacteria and eukaryotes, are a subset of infectious microbes that are metabolically dependent on and unable to grow outside an infected host cell because they have lost or lack essential biosynthetic pathways. In this study, we describe a metabolic dependency of the bacterial pathogen Rickettsia parkeri on host isoprenoid molecules that are used in the biosynthesis of downstream products, including cholesterol, steroid hormones, and heme. Bacteria make products from isoprenoids, such as an essential lipid carrier for making the bacterial cell wall. We show that bacterial metabolic dependency can represent a potential Achilles’ heel and that inhibiting host isoprenoid biosynthesis with the FDA-approved statin class of drugs inhibits bacterial growth by interfering with the integrity of the cell wall. This work supports the potential to treat infections by obligate intracellular pathogens through inhibition of host biosynthetic pathways that are susceptible to parasitism.

Gram-negative bacteria in the order Rickettsiales have an obligate intracellular growth requirement, and some species cause human diseases such as typhus and spotted fever. The bacteria have evolved a dependence on essential nutrients and metabolites from the host cell as a consequence of extensive genome reduction. However, it remains largely unknown which nutrients they acquire and whether their metabolic dependency can be exploited therapeutically. Here, we describe a genetic rewiring of bacterial isoprenoid biosynthetic pathways in the Rickettsiales that has resulted from reductive genome evolution. Furthermore, we investigated whether the spotted fever group Rickettsia species Rickettsia parkeri scavenges isoprenoid precursors directly from the host. Using targeted mass spectrometry, we found that infection caused decreases in host isoprenoid products and concomitant increases in bacterial isoprenoid metabolites. Additionally, we report that treatment of infected cells with statins, which inhibit host isoprenoid synthesis, prohibited bacterial growth. We show that growth inhibition correlates with changes in bacterial size and shape that mimic those caused by antibiotics that inhibit peptidoglycan biosynthesis, suggesting that statins lead to an inhibition of cell wall synthesis. Altogether, our results describe a potential Achilles’ heel of obligate intracellular pathogens that can potentially be exploited with host-targeted therapeutics that interfere with metabolic pathways required for bacterial growth.

IMPORTANCE Obligate intracellular pathogens, which include viruses as well as certain bacteria and eukaryotes, are a subset of infectious microbes that are metabolically dependent on and unable to grow outside an infected host cell because they have lost or lack essential biosynthetic pathways. In this study, we describe a metabolic dependency of the bacterial pathogen Rickettsia parkeri on host isoprenoid molecules that are used in the biosynthesis of downstream products, including cholesterol, steroid hormones, and heme. Bacteria make products from isoprenoids, such as an essential lipid carrier for making the bacterial cell wall. We show that bacterial metabolic dependency can represent a potential Achilles’ heel and that inhibiting host isoprenoid biosynthesis with the FDA-approved statin class of drugs inhibits bacterial growth by interfering with the integrity of the cell wall. This work supports the potential to treat infections by obligate intracellular pathogens through inhibition of host biosynthetic pathways that are susceptible to parasitism.

Prenylquinones in Human Parasitic Protozoa: Biosynthesis, Physiological Functions, and Potential as Chemotherapeutic Targets

Human parasitic protozoa cause a large number of diseases worldwide and, for some of these diseases, there are no effective treatments to date, and drug resistance has been observed. For these reasons, the discovery of new etiological treatments is necessary. In this sense, parasitic metabolic pathways that are absent in vertebrate hosts would be interesting research candidates for the identification of new drug targets. Most likely due to the protozoa variability, uncertain phylogenetic origin, endosymbiotic events, and evolutionary pressure for adaptation to adverse environments, a surprising variety of prenylquinones can be found within these organisms. These compounds are involved in essential metabolic reactions in organisms, for example, prevention of lipoperoxidation, participation in the mitochondrial respiratory chain or as enzymatic cofactors. This review will describe several prenylquinones that have been previously characterized in human pathogenic protozoa. Among all existing prenylquinones, this review is focused on ubiquinone, menaquinone, tocopherols, chlorobiumquinone, and thermoplasmaquinone. This review will also discuss the biosynthesis of prenylquinones, starting from the isoprenic side chains to the aromatic head group precursors. The isoprenic side chain biosynthesis maybe come from mevalonate or non-mevalonate pathways as well as leucine dependent pathways for isoprenoid biosynthesis. Finally, the isoprenic chains elongation and prenylquinone aromatic precursors origins from amino acid degradation or the shikimate pathway is reviewed. The phylogenetic distribution and what is known about the biological functions of these compounds among species will be described, as will the therapeutic strategies associated with prenylquinone metabolism in protozoan parasites.

Pravastatin and Simvastatin Pretreatment in Combination with Pyrimethamine and Sulfadiazine Reduces Infection Process of Toxoplasma gondii Tachyzoites (RH Strain) in HeLa Cells

PURPOSE

Toxoplasma gondii is a protozoan from phylum Apicomplexa, which causes the toxoplasmosis infection; this one exhibits an apicoplast organelle which assists in the metabolism of isoprenoids and other pivotal mediators for the parasite survival. Statins are drugs that inhibit cholesterol synthesis, blocking the conversion of the substrate HMG-CoA to mevalonate, thus preventing the initial processes of the biosynthesis of these precursors, both in humans and parasite. Our goal was to verify whether the Toxoplasma gondii (RH strain) tachyzoites form pretreated with pravastatin and simvastatin in association with pyrimethamine and sulfadiazine at low concentrations could affect the infection processes, suggesting direct action on protozoa intracellular proliferation through the inhibition of isoprenoids in the parasite's apicoplast.

METHODS

To have the adhesion, infection, and parasite proliferation during experimental infection investigated, HeLa cells (10⁵) were subjected to a 24-hour infection by T. gondii tachyzoites forms of RH strain (5 × 10⁵) pretreated for 30 min with pravastatin and/or simvastatin combined or not with pyrimethamine and sulfadiazine.

RESULTS

Combined with conventional drugs at low concentrations pravastatin and simvastatin inhibit the adhesion, invasion, and intracellular proliferation of T. gondii in HeLa cells which are similar to the positive control.

CONCLUSION

Pravastatin and simvastatin in association with pyrimethamine and sulfadiazine at low concentrations can be regarded as a promising, effective alternative to toxoplasmosis treatment with reduced side effects.

An Open-Format Enteroid Culture System for Interrogation of Interactions Between Toxoplasma gondii and the Intestinal Epithelium

When transmitted through the oral route, Toxoplasma gondii first interacts with its host at the small intestinal epithelium. This interaction is crucial to controlling initial invasion and replication, as well as shaping the quality of the systemic immune response. It is therefore an attractive target for the design of novel vaccines and adjuvants. However, due to a lack of tractable infection models, we understand surprisingly little about the molecular pathways that govern this interaction. The in vitro culture of small intestinal epithelium as 3D enteroids shows great promise for modeling the epithelial response to infection. However, the enclosed luminal space makes the application of infectious agents to the apical epithelial surface challenging. Here, we have developed three novel enteroid-based techniques for modeling T. gondii infection. In particular, we have adapted enteroid culture protocols to generate collagen-supported epithelial sheets with an exposed apical surface. These cultures retain epithelial polarization, and the presence of fully differentiated epithelial cell populations. They are susceptible to infection with, and support replication of, T. gondii. Using quantitative label-free mass spectrometry, we show that T. gondii infection of the enteroid epithelium is associated with up-regulation of proteins associated with cholesterol metabolism, extracellular exosomes, intermicrovillar adhesion, and cell junctions. Inhibition of host cholesterol and isoprenoid biosynthesis with Atorvastatin resulted in a reduction in parasite load only at higher doses, indicating that de novo synthesis may support, but is not required for, parasite replication. These novel models therefore offer tractable tools for investigating how interactions between T. gondii and the host intestinal epithelium influence the course of infection.

Delayed Death by Plastid Inhibition in Apicomplexan Parasites

The discovery of a plastid in apicomplexan parasites was hoped to be a watershed moment in the treatment of parasitic diseases as it revealed drug targets that are implicitly divergent from host molecular processes. Indeed, this organelle, known as the apicoplast, has since been a productive therapeutic target for pharmaceutical interventions against infections by Plasmodium, Toxoplasma, Babesia, and Theileria. However, some inhibitors of the apicoplast are restricted in their treatment utility because of their slow-kill kinetics, and this characteristic is called the delayed death effect. Here we review the recent genetic and pharmacological experiments that interrogate the causes of delayed death and explore the foundation of this phenomenon in Plasmodium and Toxoplasma parasites.

Synthesis and biological evaluation of 1-alkylaminomethyl-1,1-bisphosphonic acids against Trypanosoma cruzi and Toxoplasma gondii

As an extension of our project aimed at the search for new chemotherapeutic agents against Chagas disease and toxoplasmosis, several 1,1-bisphosphonates were designed, synthesized and biologically evaluated against Trypanosoma cruzi and Toxoplasma gondii, the etiologic agents of these diseases, respectively. In particular, and based on the antiparasitic activity exhibited by 2-alkylaminoethyl-1,1-bisphosphonates targeting farnesyl diphosphate synthase, a series of linear 2-alkylaminomethyl-1,1-bisphosphonic acids (compounds 21-33), that is, the position of the amino group was one carbon closer to the gem-phosphonate moiety, were evaluated as growth inhibitors against the clinically more relevant dividing form (amastigotes) of T. cruzi. Although all of these compounds resulted to be devoid of antiparasitic activity, these results were valuable for a rigorous SAR study. In addition, unexpectedly, the synthetic designed 2-cycloalkylaminoethyl-1,1-bisphosphonic acids 47-49 were free of antiparasitic activity. Moreover, long chain sulfur-containing 1,1-bisphosphonic acids, such as compounds 54-56, 59, turned out to be nanomolar growth inhibitors of tachyzoites of T. gondii. As many bisphosphonate-containing molecules are FDA-approved drugs for the treatment of bone resorption disorders, their potential nontoxicity makes them good candidates to control American trypanosomiasis and toxoplasmosis.

Bioactivity of Farnesyltransferase Inhibitors Against Entamoeba histolytica and Schistosoma mansoni

The protozoan parasite Entamoeba histolytica can induce amebic colitis and amebic liver abscess. First-line drugs for the treatment of amebiasis are nitroimidazoles, particularly metronidazole. Metronidazole has side effects and potential drug resistance is a concern. Schistosomiasis, a chronic and painful infection, is caused by various species of the Schistosoma flatworm. There is only one partially effective drug, praziquantel, a worrisome situation should drug resistance emerge. As many essential metabolic pathways and enzymes are shared between eukaryotic organisms, it is possible to conceive of small molecule interventions that target more than one organism or target, particularly when chemical matter is already available. Farnesyltransferase (FT), the last common enzyme for products derived from the mevalonate pathway, is vital for diverse functions, including cell differentiation and growth. Both E. histolytica and Schistosoma mansoni genomes encode FT genes. In this study, we phenotypically screened E. histolytica and S. mansoni in vitro with the established FT inhibitors, lonafarnib and tipifarnib, and with 125 tipifarnib analogs previously screened against both the whole organism and/or the FT of Trypanosoma brucei and Trypanosoma cruzi. For E. histolytica, we also explored whether synergy arises by combining lonafarnib and metronidazole or lonafarnib with statins that modulate protein prenylation. We demonstrate the anti-amebic and anti-schistosomal activities of lonafarnib and tipifarnib, and identify 17 tipifarnib analogs with more than 75% growth inhibition at 50 μM against E. histolytica. Apart from five analogs of tipifarnib exhibiting activity against both E. histolytica and S. mansoni, 10 additional analogs demonstrated anti-schistosomal activity (severe degenerative changes at 10 μM after 24 h). Analysis of the structure-activity relationship available for the T. brucei FT suggests that FT may not be the relevant target in E. histolytica and S. mansoni. For E. histolytica, combination of metronidazole and lonafarnib resulted in synergism for growth inhibition. Also, of a number of statins tested, simvastatin exhibited moderate anti-amebic activity which, when combined with lonafarnib, resulted in slight synergism. Even in the absence of a definitive molecular target, identification of potent anti-parasitic tipifarnib analogs encourages further exploration while the synergistic combination of metronidazole and lonafarnib offers a promising treatment strategy for amebiasis.

Farnesyl pyrophosphate synthase is essential for the promastigote and amastigote stages in Leishmania major

Isoprenoid synthesis provides a diverse class of biomolecules including sterols, dolichols, ubiquinones and prenyl groups. The enzyme farnesyl pyrophosphate synthase (FPPS) catalyzes the formation of farnesyl pyrophosphate, a key intermediate for the biosynthesis of all isoprenoids. In Leishmania, FPPS is considered the main target of nitrogen containing bisphosphonates, yet the essentiality of this enzyme remains untested. Using a facilitated knockout approach, we carried out the genetic analysis of FPPS in Leishmania major. Our data indicated that chromosomal null mutants for FPPS could only be generated in presence of an episomally expressed FPPS. Long-term retention of the episome by the chromosomal FPPS-null mutants in culture and in infected BALB/c mice suggests that FPPS is indispensable. In addition, applying negative selection pressure failed to induce the loss of ectopic FPPS in the chromosomal FPPS-null mutants, although it led to significant growth delay in culture and in mice. Together, our findings have confirmed the essentiality of FPPS in both promastigotes and amastigotes in L. major and thus validate its potential as a drug target for the treatment of cutaneous leishmaniasis.

Host Cell Metabolism Contributes to Delayed-Death Kinetics of Apicoplast Inhibitors in Toxoplasma gondii

Toxoplasma gondii and related human parasites contain an essential plastid organelle called the apicoplast. Clinically used antibiotics and other inhibitors that disrupt apicoplast biogenesis cause a mysterious “delayed-death” phenotype in which parasite growth is unaffected during the first lytic cycle of inhibitor treatment but is severely inhibited in the second lytic cycle even after drug removal.

Toxoplasma gondii and related human parasites contain an essential plastid organelle called the apicoplast. Clinically used antibiotics and other inhibitors that disrupt apicoplast biogenesis cause a mysterious “delayed-death” phenotype in which parasite growth is unaffected during the first lytic cycle of inhibitor treatment but is severely inhibited in the second lytic cycle even after drug removal. Critical to understanding the complex downstream cellular effects of these drug classes are the timing of apicoplast loss during inhibitor treatment and how it relates to this peculiar growth phenotype. Here we show that, upon treatment with diverse classes of apicoplast inhibitors, newly replicated T. gondii parasites in the first lytic cycle initially form apicoplasts with defects in protein import or genome replication and eventually fail to inherit the apicoplast altogether. Despite the accumulation of parasites with defective or missing apicoplasts, growth is unaffected during the first lytic cycle, as previously observed. Strikingly, concomitant inhibition of host cell isoprenoid biosynthesis results in growth inhibition in the first lytic cycle and unmasks the apicoplast defects. These results suggest that defects in and even the complete loss of the apicoplast in T. gondii are partially rescued by scavenging of host cell metabolites, leading to death that is delayed. Our findings uncover host cell interactions that can alleviate apicoplast inhibition and highlight key differences in delayed-death inhibitors between T. gondii and Plasmodium falciparum.

Metabolic interactions between Toxoplasma gondii and its host

Toxoplasma gondii is an obligate intracellular parasite belonging to the phylum Apicomplexa that infects all warm-blooded animals, including humans. T. gondii can replicate in every nucleated host cell by orchestrating metabolic interactions to derive crucial nutrients. In this review, we summarize the current status of known metabolic interactions of T. gondii with its host cell and discuss open questions and promising experimental approaches that will allow further dissection of the host-parasite interface and discovery of ways to efficiently target both tachyzoite and bradyzoite forms of T. gondii, which are associated with acute and chronic infection, respectively.

Atorvastatin: In-Vivo Synergy with Metronidazole as Anti-Blastocystis Therapy

Blastocystis is an enteric Straminopile in tropical, subtropical and developing countries. Metronidazole has been a chemotheraputic for blastocystosis. Failures in its regimens were reported and necessitate new studies searching for alternative therapeutic agents. Aim of current study is to investigate potential effects of Atorvastatin (AVA) compared to the conventional chemotherapeutic MTZ in experimentally Blastocystis-infected mice. Anti-Blastocystis efficacy of AVA was evaluated parasitologically, histopathologically and by transmission electron microscopy using MTZ (10 mg/kg) as a control. Therapeutic efficacy of AVA was apparently dose-dependent. Regimens of AVA (20 and 40 mg/kg) proved effective against Blastocystis infections with high reduction in Blastocystis shedding (93.4–97.9%) compared to MTZ (79.3%). The highest reductions (98.1% and 99.4%) were recorded in groups of combination treatments AVA 20–40 mg/kg and MTZ 10 mg/kg. Blastocystis was nearly eradicated by the 20th day post infection. Genotype analysis revealed that genotype I was most susceptible, genotype III was less. Histopathologic and ultrastructural studies revealed apoptotic changes in Blastocystis and significant improvement of intestinal histopathological changes more remarkable in combinational therapy groups. Thus, the present study offers AVA as a potential candidate for Blastocystis therapy combined with MTZ.

Synergistic Activity between Statins and Bisphosphonates against Acute Experimental Toxoplasmosis

Bisphosphonates are widely used for the treatment of bone disorders. These drugs also inhibit the growth of a variety of protozoan parasites, such as Toxoplasma gondii, the etiologic agent of toxoplasmosis. The target of the most potent bisphosphonates is the isoprenoid biosynthesis pathway enzyme farnesyl diphosphate synthase (FPPS). Based on our previous work on the inhibitory effect of sulfur-containing linear bisphosphonates against T. gondii, we investigated the potential synergistic interaction between one of these derivatives, 1-[(n-heptylthio)ethyl]-1,1-bisphosphonate (C7S), and statins, which are potent inhibitors of the host 3-hydroxy-3-methyl glutaryl-coenzyme A reductase (3-HMG-CoA reductase). C7S showed high activity against the T. gondii bifunctional farnesyl diphosphate (FPP)/geranylgeranyl diphosphate (GGPP) synthase (TgFPPS), which catalyzes the formation of FPP and GGPP (50% inhibitory concentration [IC₅₀] = 31 ± 0.01 nM [mean ± standard deviation]), and modest effect against the human FPPS (IC₅₀ = 1.3 ± 0.5 μM). We tested combinations of C7S with statins against the in vitro replication of T. gondii We also treated mice infected with a lethal dose of T. gondii with similar combinations. We found strong synergistic activities when using low doses of C7S, which were stronger in vivo than when tested in vitro We also investigated the synergism of several commercially available bisphosphonates with statins both in vitro and in vivo Our results provide evidence that it is possible to develop drug combinations that act synergistically by inhibiting host and parasite enzymes in vitro and in vivo.

Thioredoxin reductase from Toxoplasma gondii: an essential virulence effector with antioxidant function

Thioredoxin reductase (TR) can help pathogens resist oxidative-burst injury from host immune cells by maintaining a thioredoxin-reduction state during NADPH consumption. TR is a necessary virulence factor that enables the persistent infection of some parasites. We performed bioinformatics analyses and biochemical assays to characterize the activity, subcellular localization, and genetic ablation of Toxoplasma gondii TR (TgTR), to shed light on its biologic function. We expressed the TgTR protein with an Escherichia coli expression system and analyzed its enzyme activity, reporting a K_m for the recombinant TgTR of 11.47-15.57 μM, using NADPH as a substrate, and 130.48-151.09 μM with dithio-bis-nitrobenzoic acid as a substrate. The TgTR sequence shared homology with that of TR, but lacked a selenocysteine residue in the C-terminal region and was thought to contain 2 flavin adenine dinucleotide (FAD) domains and 1 NADPH domain. In addition, immunoelectron microscopy results showed that TgTR was widely dispersed in the cytoplasm, and we observed that parasite antioxidant capacity, invasion efficiency, and proliferation were decreased in TR-knockout (TR-KO) strains in vitro, although this strain still stimulated the release of reactive oxygen species release in mouse macrophages while being more sensitive to H₂O₂ toxicity in vitro Furthermore, our in vivo results revealed that the survival time of mice infected with the TR-KO strain was significantly prolonged relative to that of mice infected with the wild-type strain. These results suggest that TgTR plays an important role in resistance to oxidative damage and can be considered a virulence factor associated with T. gondii infection.-Xue, J., Jiang, W., Chen, Y., Gong, F., Wang, M., Zeng, P., Xia, C., Wang, Q., Huang, K. Thioredoxin reductase from Toxoplasma gondii: an essential virulence effector with antioxidant function.

Plant hormone cytokinins control cell cycle progression and plastid replication in apicomplexan parasites

Cytokinins are plant hormones that are involved in regulation of cell proliferation, cell cycle progression, and cell and plastid development. Here, we show that the apicomplexan parasites Toxoplasma gondii and Plasmodium berghei, an opportunistic human pathogen and a rodent malaria agent, respectively, produce cytokinins via a biosynthetic pathway similar to that in plants. Cytokinins regulate the growth and cell cycle progression of T. gondii by mediating expression of the cyclin gene TgCYC4. A natural form of cytokinin, trans-zeatin (t-zeatin), upregulated expression of this cyclin, while a synthetic cytokinin, thidiazuron, downregulated its expression. Immunofluorescence microscopy and quantitative PCR analysis showed that t-zeatin increased the genome-copy number of apicoplast, which are non-photosynthetic plastid, in the parasite, while thidiazuron led to their disappearance. Thidiazuron inhibited growth of T. gondii and Plasmodium falciparum, a human malaria parasite, suggesting that thidiazuron has therapeutic potential as an inhibitor of apicomplexan parasites.

Pravastatin and simvastatin inhibit the adhesion, replication and proliferation of Toxoplasma gondii (RH strain) in HeLa cells

The conventional treatment for toxoplasmosis with pyrimethamine and sulfadiazine shows toxic effects to the host, and it is therefore necessary to search for new drugs. Some studies suggest the use of statins, which inhibit cholesterol synthesis in humans and also the initial processes of isoprenoid biosynthesis in the parasite. Thus, the objective of this study was to evaluate the activity of the statins pravastatin and simvastatin in HeLa cells infected in vitro with the RH strain of T. gondii. HeLa cells (1×10⁵) were infected with T. gondii tachyzoites (5×10⁵) following two different treatment protocols. In the first protocol, T. gondii tachyzoites were pretreated with pravastatin (50 and 100μg/mL) and simvastatin (1.56 and 3.125μg/mL) for 30min prior to infection. In the second, HeLa cells were first infected (5×10⁵) with tachyzoites and subsequently treated with pravastatin and simvastatin for 24h at the concentrations noted above. Initially, we evaluated the cytotoxicity of drugs by the MTT assay, number of tachyzoites adhered to cells, number of infected cells, and viability of tachyzoites by trypan blue exclusion. The supernatant of the cell cultures was collected post-treatment for determination of the pattern of Th1/Th2/Th17 cytokines by cytometric bead array. There was no cytotoxicity to HeLa cells with 50 and 100μg/mL pravastatin and 1.56 and 3.125μg/mL simvastatin. There was no change in the viability of tachyzoites that received pretreatment. Regarding the pre- and post-treatment of the cells with pravastatin and simvastatin alone, there was a reduction in adhesion, invasion and proliferation of cells to T. gondii. As for the production of cytokines, we found that IL-6 and IL-17 were significantly reduced in cells infected with T. gondii and treated with pravastatin and simvastatin, when compared to control. Based on these results, we can infer that pravastatin and simvastatin alone possess antiproliferative effects on tachyzoites forms of T. gondii, giving these drugs new therapeutic uses.

In Vitro and In Vivo Activities of Sulfur-Containing Linear Bisphosphonates against Apicomplexan Parasites

We tested a series of sulfur-containing linear bisphosphonates against Toxoplasma gondii, the etiologic agent of toxoplasmosis. The most potent compound (compound 22; 1-[(n-decylsulfonyl)ethyl]-1,1-bisphosphonic acid) is a sulfone-containing compound, which had a 50% effective concentration (EC₅₀) of 0.11 ± 0.02 μM against intracellular tachyzoites. The compound showed low toxicity when tested in tissue culture with a selectivity index of >2,000. Compound 22 also showed high activity in vivo in a toxoplasmosis mouse model. The compound inhibited the Toxoplasma farnesyl diphosphate synthase (TgFPPS), but the concentration needed to inhibit 50% of the enzymatic activity (IC₅₀) was higher than the concentration that inhibited 50% of growth. We tested compound 22 against two other apicomplexan parasites, Plasmodium falciparum (EC₅₀ of 0.6 ± 0.01 μM), the agent of malaria, and Cryptosporidium parvum (EC₅₀ of ∼65 μM), the agent of cryptosporidiosis. Our results suggest that compound 22 is an excellent novel compound that could lead to the development of potent agents against apicomplexan parasites.

A Systematic Review of In vitro and In vivo Activities of Anti-Toxoplasma Drugs and Compounds (2006-2016)

The currently available anti-Toxoplasma agents have serious limitations. This systematic review was performed to evaluate drugs and new compounds used for the treatment of toxoplasmosis. Data was systematically collected from published papers on the efficacy of drugs/compounds used against Toxoplasma gondii (T. gondii) globally during 2006-2016. The searched databases were PubMed, Google Scholar, Science Direct, ISI Web of Science, EBSCO, and Scopus. One hundred and eighteen papers were eligible for inclusion in this systematic review, which were both in vitro and in vivo studies. Within this review, 80 clinically available drugs and a large number of new compounds with more than 39 mechanisms of action were evaluated. Interestingly, many of the drugs/compounds evaluated against T. gondii act on the apicoplast. Therefore, the apicoplast represents as a potential drug target for new chemotherapy. Based on the current findings, 49 drugs/compounds demonstrated in vitro half-maximal inhibitory concentration (IC50) values of below 1 μM, but most of them were not evaluated further for in vivo effectiveness. However, the derivatives of the ciprofloxacin, endochin-like quinolones and 1-[4-(4-nitrophenoxy) phenyl] propane-1-one (NPPP) were significantly active against T. gondii tachyzoites both in vitro and in vivo. Thus, these compounds are promising candidates for future studies. Also, compound 32 (T. gondii calcium-dependent protein kinase 1 inhibitor), endochin-like quinolones, miltefosine, rolipram abolish, and guanabenz can be repurposed into an effective anti-parasitic with a unique ability to reduce brain tissue cysts (88.7, 88, 78, 74, and 69%, respectively). Additionally, no promising drugs are available for congenital toxoplasmosis. In conclusion, as current chemotherapy against toxoplasmosis is still not satisfactory, development of well-tolerated and safe specific immunoprophylaxis in relaxing the need of dependence on chemotherapeutics is a highly valuable goal for global disease control. However, with the increasing number of high-risk individuals, and absence of a proper vaccine, continued efforts are necessary for the development of novel treatment options against T. gondii. Some of the novel compounds reviewed here may represent good starting points for the discovery of effective new drugs. In further, bioinformatic and in silico studies are needed in order to identify new potential toxoplasmicidal drugs.

Antiparasitic Activity of Sulfur- and Fluorine-Containing Bisphosphonates against Trypanosomatids and Apicomplexan Parasites

Based on crystallographic data of the complexes 2-alkyl(amino)ethyl-1,1-bisphosphonates-Trypanosoma cruzi farnesyl diphosphate synthase, some linear 1,1-bisphosphonic acids and other closely related derivatives were designed, synthesized and biologically evaluated against T. cruzi, the responsible agent of Chagas disease and against Toxoplasma gondii, the etiologic agent of toxoplasmosis and also towards the target enzymes farnesyl pyrophosphate synthase of T. cruzi (TcFPPS) and T gondii (TgFPPS), respectively. The isoprenoid-containing 1,1-bisphosphonates exhibited modest antiparasitic activity, whereas the linear α-fluoro-2-alkyl(amino)ethyl-1,1-bisphosphonates were unexpectedly devoid of antiparasitic activity. In spite of not presenting efficient antiparasitic activity, these data turned out to be very important to establish a structural activity relationship.

Activity of Fluorine-Containing Analogues of WC-9 and Structurally Related Analogues against Two Intracellular Parasites: Trypanosoma cruzi and Toxoplasma gondii

Two obligate intracellular parasites, Trypanosoma cruzi, the agent of Chagas disease, and Toxoplasma gondii, an agent of toxoplasmosis, upregulate the mevalonate pathway of their host cells upon infection, which suggests that this host pathway could be a potential drug target. In this work, a number of compounds structurally related to WC-9 (4-phenoxyphenoxyethyl thiocyanate), a known squalene synthase inhibitor, were designed, synthesized, and evaluated for their effect on T. cruzi and T. gondii growth in tissue culture cells. Two fluorine-containing derivatives, the 3-(3-fluorophenoxy)- and 3-(4-fluorophenoxy)phenoxyethyl thiocyanates, exhibited half-maximal effective concentration (EC50 ) values of 1.6 and 4.9 μm, respectively, against tachyzoites of T. gondii, whereas they showed similar potency to WC-9 against intracellular T. cruzi (EC50 values of 5.4 and 5.7 μm, respectively). In addition, 2-[3- (phenoxy)phenoxyethylthio]ethyl-1,1-bisphosphonate, which is a hybrid inhibitor containing 3-phenoxyphenoxy and bisphosphonate groups, has activity against T. gondii proliferation at sub-micromolar levels (EC50 =0.7 μm), which suggests a combined inhibitory effect of the two functional groups.

Review of Experimental Compounds Demonstrating Anti-Toxoplasma Activity

Toxoplasma gondii is a ubiquitous apicomplexan parasite capable of infecting humans and other animals. Current treatment options for T. gondii infection are limited and most have drawbacks, including high toxicity and low tolerability. Additionally, no FDA-approved treatments are available for pregnant women, a high-risk population due to transplacental infection. Therefore, the development of novel treatment options is needed. To aid this effort, this review highlights experimental compounds that, at a minimum, demonstrate inhibition of in vitro growth of T. gondii When available, host cell toxicity and in vivo data are also discussed. The purpose of this review is to facilitate additional development of anti-Toxoplasma compounds and potentially to extend our knowledge of the parasite.

Topical Simvastatin as Host-Directed Therapy against Severity of Cutaneous Leishmaniasis in Mice

We recently demonstrated that statins mediate protection against intracellular pathogens, Mycobacterium tuberculosis and Listeria monocytogenes in mice. Here, we investigated the immunomodulatory potential of simvastatin as a topical or systemic host-directed drug therapy in controlling inflammatory responses in an experimental mouse model of cutaneous leishmaniasis caused by Leishmania major (LV39). In an ear infection model, topical application of simvastatin directly on established lesions significantly reduced severity of the disease reflected by ear lesion size and ulceration. The host protective effect was further accompanied by decreased parasite burden in the ear and draining lymph nodes in both BALB/c and C57BL/6 mice. Pre-treatment of these mice on a low-fat cholesterol diet and systemic simvastatin also reduced footpad swelling, as well as parasite burdens and ulceration/necrosis in the more robust footpad infection model, demonstrating the prophylactic potential of simvastatin for cutaneous leishmaniasis. Mechanistically, following L. major infection, simvastatin-treated primary macrophages responded with significantly reduced cholesterol levels and increased production of hydrogen peroxide. Furthermore, simvastatin-treated macrophages displayed enhanced phagosome maturation, as revealed by increased LAMP-3 expression in fluorescent microscopy and Western blot analysis. These findings demonstrate that simvastatin treatment enhances host protection against L. major by increasing macrophage phagosome maturation and killing effector functions.

Drug Repurposing Screening Identifies Novel Compounds That Effectively Inhibit Toxoplasma gondii Growth

The urgent need to develop new antimicrobial therapies has spawned the development of repurposing screens in which well-studied drugs and other types of compounds are tested for potential off-label uses. As a proof-of-principle screen to identify compounds effective against Toxoplasma gondii, we screened a collection of 1,120 compounds for the ability to significantly reduce Toxoplasma replication. A total of 94 compounds blocked parasite replication with 50% inhibitory concentrations of <5 µM. A significant number of these compounds are established inhibitors of dopamine or estrogen signaling. Follow-up experiments with the dopamine receptor inhibitor pimozide revealed that the drug impacted both parasite invasion and replication but did so independently of inhibition of dopamine or other neurotransmitter receptor signaling. Tamoxifen, which is an established inhibitor of the estrogen receptor, also reduced parasite invasion and replication. Even though Toxoplasma can activate the estrogen receptor, tamoxifen inhibits parasite growth independently of this transcription factor. Tamoxifen is also a potent inducer of autophagy, and we find that the drug stimulates recruitment of the autophagy marker light chain 3-green fluorescent protein onto the membrane of the vacuolar compartment in which the parasite resides and replicates. In contrast to other antiparasitic drugs, including pimozide, tamoxifen treatment of infected cells leads to a time-dependent elimination of intracellular parasites. Taken together, these data suggest that tamoxifen restricts Toxoplasma growth by inducing xenophagy or autophagic destruction of this obligate intracellular parasite. IMPORTANCE There is an urgent need to develop new therapies to treat microbial infections, and the repurposing of well-characterized compounds is emerging as one approach to achieving this goal. Using the protozoan parasite Toxoplasma gondii, we screened a library of 1,120 compounds and identified several compounds with significant antiparasitic activities. Among these were pimozide and tamoxifen, which are well-characterized drugs prescribed to treat patients with psychiatric disorders and breast cancer, respectively. The mechanisms by which these compounds target these disorders are known, but we show here that these drugs kill Toxoplasma through novel pathways, highlighting the potential utility of off-target effects in the treatment of infectious diseases.

Lytic Cycle of Toxoplasma gondii: 15 Years Later

Toxoplasmosis is the clinical and pathological consequence of acute infection with the obligate intracellular apicomplexan parasite Toxoplasma gondii. Symptoms result from tissue destruction that accompanies lytic parasite growth. This review updates current understanding of the host cell invasion, parasite replication, and eventual egress that constitute the lytic cycle, as well as the ways T. gondii manipulates host cells to ensure its survival. Since the publication of a previous iteration of this review 15 years ago, important advances have been made in our molecular understanding of parasite growth and mechanisms of host cell egress, and knowledge of the parasite's manipulation of the host has rapidly progressed. Here we cover molecular advances and current conceptual frameworks that include each of these topics, with an eye to what may be known 15 years from now.

Aryloxyethyl Thiocyanates Are Potent Growth Inhibitors of Trypanosoma cruzi and Toxoplasma gondii

As a part of our project aimed at searching for new safe chemotherapeutic agents against parasitic diseases, several compounds structurally related to the antiparasitic agent WC-9 (4-phenoxyphenoxyethyl thiocyanate), which were modified at the terminal phenyl ring, were designed, synthesized, and evaluated as growth inhibitors against Trypanosoma cruzi, the etiological agent of Chagas disease, and Toxoplasma gondii, the parasite responsible of toxoplasmosis. Most of the synthetic analogues exhibited similar antiparasitic activity and were slightly more potent than our lead WC-9. For example, two trifluoromethylated derivatives exhibited ED50 values of 10.0 and 9.2 μM against intracellular T. cruzi, whereas they showed potent action against tachyzoites of T. gondii (ED50 values of 1.6 and 1.9 μM against T. gondii). In addition, analogues of WC-9 in which the terminal aryl group is in the meta position with respect to the alkyl chain bearing the thiocyanate group showed potent inhibitory action against both T. cruzi and T. gondii at the very low micromolar range, which suggests that a para-phenyl substitution pattern is not necessary for biological activity.