Characterization of anti-Toxoplasma activity of SDZ 215-918, a cyclosporin derivative lacking immunosuppressive and peptidyl-prolyl-isomerase-inhibiting activity: possible role of a P glycoprotein in Toxoplasma physiology

Glycosylation Analysis of Feline Small Intestine Following Toxoplasma gondii Infection

Simple Summary

Toxoplasma gondii has a serious impact on public health and the economic development of animal husbandry. Glycosylation, especially N-glycosylation, the pattern modification of proteins, is closely related to the biological functions of proteins, and our study used it to analyze glycosylation alterations in the small intestine of cats infected with T. gondii. The results of the present study showed that 56 glycosylated peptides were upregulated and 37 glycosylated peptides were downregulated. Additionally, we also identified eight N-glycosylated proteins of T. gondii including eight N-glycopeptides and eight N-glycosylation sites. Moreover, the protein eEF2 and its corresponding peptide sequence were identified, with GO terms (i.e., cellular process and metabolic process, cell and cell part, and catalytic activity) that were significantly enriched in the T. gondii MAPK pathway. In addition, the Clusters of Orthologous Groups of proteins (COG) function prediction results showed that posttranslational modification, protein turnover, and chaperones (11%) had the highest enrichment for T. gondii. The host proteins ICAM-1 and PPT1 and the endoplasmic reticulum stress pathway may play an important role in the glycosylation of T. gondii-infected hosts. Our study may provide a new target for T. gondii detection to prevent the spread of T. gondii oocysts in the future.

Abstract

Toxoplasma gondii (T. gondii) is responsible for severe human and livestock diseases, huge economic losses, and adversely affects the health of the public and the development of animal husbandry. Glycosylation is a common posttranslational modification of proteins in eukaryotes, and N-glycosylation is closely related to the biological functions of proteins. However, glycosylation alterations in the feline small intestine following T. gondii infection have not been reported. In this study, the experimental group was intragastrically challenged with 600 brain cysts of the Prugniuad (Pru) strain that were collected from infected mice. The cats’ intestinal epithelial tissues were harvested at 10 days post-infection and then sent for protein glycosylation analysis. High-performance liquid chromatography coupled to tandem mass spectrometry was used to analyze the glycosylation alterations in the small intestine of cats infected with T. gondii. The results of the present study showed that 56 glycosylated peptides were upregulated and 37 glycosylated peptides were downregulated in the feline small intestine infected by T. gondii. Additionally, we also identified eight N-glycosylated proteins of T. gondii including eight N-glycopeptides and eight N-glycosylation sites. The protein A0A086JND6_TOXGO (eEF2) and its corresponding peptide sequence were identified in T. gondii infection. Some special GO terms (i.e., cellular process and metabolic process, cell and cell part, and catalytic activity) were significantly enriched, and the Clusters of Orthologous Groups of proteins (COG) function prediction results showed that posttranslational modification, protein turnover, and chaperones (11%) had the highest enrichment for T. gondii. Interestingly, eEF2, a protein of T. gondii, is also involved in the significantly enriched T. gondii MAPK pathway. The host proteins ICAM-1 and PPT1 and the endoplasmic reticulum stress pathway may play an important role in the glycosylation of Toxoplasma-infected hosts. This is the first report showing that T. gondii oocysts can undergo N-glycosylation in the definitive host and that eEF2 is involved, which may provide a new target for T. gondii detection to prevent the spread of T. gondii oocysts in the future.

A Role for Basigin in Toxoplasma gondii Infection

The role of specific host cell surface receptors during Toxoplasma gondii invasion of host cells is poorly defined. Here, we interrogated the role of the well-known malarial invasion receptor, basigin, in T. gondii infection of astrocytes. We found that primary astrocytes express two members of the BASIGIN (BSG) immunoglobulin family, basigin and embigin, but did not express neuroplastin. Antibody blockade of either basigin or embigin caused a significant reduction of parasite infectivity in astrocytes. The specific role of basigin during T. gondii invasion was further examined using a mouse astrocytic cell line (C8-D30), which exclusively expresses basigin. CRISPR-mediated deletion of basigin in C8-D30 cells resulted in decreased T. gondii infectivity. T. gondii replication and invasion efficiency were not altered by basigin deficiency, but parasite attachment to astrocytes was markedly reduced. We also conducted a proteomic screen to identify T. gondii proteins that interact with basigin. Toxoplasma-encoded cyclophilins, the protein 14-3-3, and protein disulfide isomerase (TgPDI) were among the putative basigin-ligands identified. Recombinant TgPDI produced in E. coli bound to basigin and pretreatment of tachyzoites with a PDI inhibitor decreased parasite attachment to host cells. Finally, mutagenesis of the active site cysteines of TgPDI abolished enzyme binding to basigin. Thus, basigin and its related immunoglobulin family members may represent host receptors that mediate attachment of T. gondii to diverse cell types.

P-Glycoprotein Inhibitors Differently Affect Toxoplasma gondii, Neospora caninum and Besnoitia besnoiti Proliferation in Bovine Primary Endothelial Cells

Apicomplexan parasites are obligatory intracellular protozoa. In the case of Toxoplasma gondii, Neospora caninum or Besnoitia besnoiti, to ensure proper tachyzoite production, they need nutrients and cell building blocks. However, apicomplexans are auxotrophic for cholesterol, which is required for membrane biosynthesis. P-glycoprotein (P-gp) is a transmembrane transporter involved in xenobiotic efflux. However, the physiological role of P-gp in cholesterol metabolism is unclear. Here, we analyzed its impact on parasite proliferation in T. gondii-, N. caninum- and B. besnoiti-infected primary endothelial cells by applying different generations of P-gp inhibitors. Host cell treatment with verapamil and valspodar significantly diminished tachyzoite production in all three parasite species, whereas tariquidar treatment affected proliferation only in B. besnoiti. 3D-holotomographic analyses illustrated impaired meront development driven by valspodar treatment being accompanied by swollen parasitophorous vacuoles in the case of T. gondii. Tachyzoite and host cell pre-treatment with valspodar affected infection rates in all parasites. Flow cytometric analyses revealed verapamil treatment to induce neutral lipid accumulation. The absence of a pronounced anti-parasitic impact of tariquidar, which represents here the most selective P-gp inhibitor, suggests that the observed effects of verapamil and valspodar are associated with mechanisms independent of P-gp. Out of the three species tested here, this compound affected only B. besnoiti proliferation and its effect was much milder as compared to verapamil and valspodar.

Ciclosporin and the cat: Current understanding and review of clinical use

Practical relevance: Ciclosporin (CsA) is a systemic immuno-modulatory drug widely used to treat immune-mediated diseases in humans and veterinary species. CsA was registered for use in cats in the USA and Europe in 2011, and is indicated for the treatment of chronic allergic dermatitis at a recommended daily dose of 7 mg/kg PO.

AUDIENCE

This review will be of interest to all veterinarians working with cats, given the wide range of potential applications of CsA and its safety profile. Although the drug is currently only licensed to treat chronic allergic dermatitis in cats, a small number of reports describe its use in non-dermatological conditions. Evidence base: This article reviews the mechanism of action, pharmacokinetics, drug interactions, adverse effects and clinical use of CsA, both for the licensed indication and for off-label use in the feline patient. Information presented has been summarised from the existing literature on CsA, with specific interest in studies carried out in cats. For its licensed indication, chronic allergic dermatitis, evidence provided includes randomised, placebo or prednisolone-controlled studies (EBM grade I) and prospective or retrospective open trials.

Clinically Available Medicines Demonstrating Anti-Toxoplasma Activity

Toxoplasma gondii is an apicomplexan parasite of humans and other mammals, including livestock and companion animals. While chemotherapeutic regimens, including pyrimethamine and sulfadiazine regimens, ameliorate acute or recrudescent disease such as toxoplasmic encephalitis or ocular toxoplasmosis, these drugs are often toxic to the host. Moreover, no approved options are available to treat infected women who are pregnant. Lastly, no drug regimen has shown the ability to eradicate the chronic stage of infection, which is characterized by chemoresistant intracellular cysts that persist for the life of the host. In an effort to promote additional chemotherapeutic options, we now evaluate clinically available drugs that have shown efficacy in disease models but which lack clinical case reports. Ideally, less-toxic treatments for the acute disease can be identified and developed, with an additional goal of cyst clearance from human and animal hosts.

Analysis of cyclosporin A and a set of analogs as inhibitors of a T. cruzi cyclophilin by docking and molecular dynamics

Cyclophilins (CyPs) are enzymes involved in protein folding. In Trypanosoma cruzi (T. cruzi), the most abundantly expressed CyP is the isoform TcCyP19. It has been shown that TcCyP19 is inhibited by the immunosuppressive drug cyclosporin A (CsA) and analogs, which also proved to have potent trypanosomicidal activity in vitro. In this work, we continue and expand a previous study on the molecular interactions of CsA, and a set of analogs modeled in complexes with TcCyP19. The modeled complexes were used to evaluate binding free energies by molecular dynamics (MD), applying the Linear Interaction Energy (LIE) method. In addition, putative binding sites were identified by molecular docking. In our analysis, the binding free energy calculations did not correlate with experimental data. The heterogeneity of the non-bonded energies and the variation in the pattern of hydrogen bonds suggest that the systems may not be suitable for the application of the LIE method. Further, the docking calculations identified two other putative binding sites with comparable scoring energies to the active site, a fact that may also explain the lack of correlation found. Kinetic experiments are needed to confirm or reject the multiple binding sites hypothesis. In the meantime, MD simulations at the alternative sites, employing other methods to compute binding free energies, might be successful at finding good correlations with the experimental data.

Effect of oral administration of cyclosporine on Toxoplasma gondii infection status of cats

OBJECTIVE

To evaluate whether anti-inflammatory doses of cyclosporine activate Toxoplasma gondii in chronically infected cats or potentiate infection in cats exposed for the first time.

ANIMALS

30 T gondii-negative cats.

PROCEDURES

Cats were assigned to 1 of 3 groups (10 cats/group). Group 1 (control) cats were administered a placebo for 126 days; group 2 cats were administered a placebo for 84 days, followed by cyclosporine at 7.5 mg/kg/d, PO, for 42 days; and group 3 cats were administered cyclosporine at 7.5 mg/kg/d, PO, for 126 days. Cats were orally inoculated with T gondii on day 42. Results for fecal flotations, PCR assays, and histologic examinations and IgM and IgG titers were analyzed. Cyclosporine concentrations were measured on selected days.

RESULTS

All cats were infected by T gondii and developed signs of self-limiting gastrointestinal tract infection. Group 3 had the highest incidence and severity of CNS and pulmonary histopathologic findings typical of toxoplasmosis. One cat in group 3 died of systemic toxoplasmosis; that cat had a cyclosporine concentration of 1,690 ng/mL. Group 2 cats infected with T gondii before cyclosporine administration did not have repeated oocyst shedding. Group 3 cats shed fewer oocysts for a shorter time than did control cats of group 1.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of cyclosporine in accordance with the protocol for this study did not potentiate the enteroepithelial phase of T gondii infection. Cats with high cyclosporine blood concentrations at the time of primary T gondii infection may be at risk of developing systemic toxoplasmosis.

Screening for small molecule inhibitors of Toxoplasma gondii

INTRODUCTION

Toxoplasma gondii, the agent that causes toxoplasmosis, is an opportunistic parasite that infects many mammalian species. It is an obligate intracellular parasite that causes severe congenital neurological and ocular disease mostly in immunocompromised humans. The current regimen of therapy includes only a few medications that often lead to hypersensitivity and toxicity. In addition, there are no vaccines available to prevent the transmission of this agent. Therefore, safer and more effective medicines to treat toxoplasmosis are urgently needed.

AREAS COVERED

The author presents in silico and in vitro strategies that are currently used to screen for novel targets and unique chemotypes against T. gondii. Furthermore, this review highlights the screening technologies and characterization of some novel targets and new chemical entities that could be developed into highly efficacious treatments for toxoplasmosis.

EXPERT OPINION

A number of diverse methods are being used to design inhibitors against T. gondii. These include ligand-based methods, in which drugs that have been shown to be efficacious against other Apicomplexa parasites can be repurposed to identify lead molecules against T. gondii. In addition, structure-based methods use currently available repertoire of structural information in various databases to rationally design small-molecule inhibitors of T. gondii. Whereas the screening methods have their advantages and limitations, a combination of methods is ideally suited to design small-molecule inhibitors of complex parasites such as T. gondii.

Involvement of cyclophilin B in the replication of Japanese encephalitis virus

Japanese encephalitis virus (JEV) is a mosquito-borne RNA virus that belongs to the Flaviviridae family. In this study, we have examined the effect of cyclosporin A (CsA) on the propagation of JEV. CsA exhibited potent anti-JEV activity in various mammalian cell lines through the inhibition of CypB. The propagation of JEV was impaired in the CypB-knockdown cells and this reduction was cancelled by the expression of wild-type but not of peptidylprolyl cis-trans isomerase (PPIase)-deficient CypB, indicating that PPIase activity of CypB is critical for JEV propagation. Infection of pseudotype viruses bearing JEV envelope proteins was not impaired by the knockdown of CypB, suggesting that CypB participates in the replication but not in the entry of JEV. CypB was colocalized and immunoprecipitated with JEV NS4A in infected cells. These results suggest that CypB plays a crucial role in the replication of JEV through an interaction with NS4A.

Molecular aspects of cyclophilins mediating therapeutic actions of their ligands

Cyclosporine A (CsA) is an immunosuppressive cyclic peptide that binds with a high affinity to 18 kDa human cyclophilin-A (hCyPA). CsA and its several natural derivatives have some pharmacological potential in treatment of diverse immune disorders. More than 20 paralogues of CyPA are expressed in the human body while expression levels and functions of numerous ORFs encoding cyclophilin-like sequences remain unknown. Certain derivatives of CsA devoid of immunosuppressive activity may have some potential in treatments of Alzheimer diseases, Hepatitis C and HIV infections, amyotrophic lateral sclerosis, congenital muscular dystrophy, asthma and various parasitic infections. Here, we discuss structural and functional aspects of the human cyclophilins and their interaction with various intra-cellular targets that can be under the control of CsA or its complexes with diverse cyclophilins that are selectively expressed in different cellular compartments. Some molecular aspects of the cyclophilins expressed in parasites invading humans and causing diseases were also analyzed.

Thiazole, oxadiazole, and carboxamide derivatives of artemisinin are highly selective and potent inhibitors of Toxoplasma gondii

We have prepared 23 new dehydroartemisinin (DART) trioxane derivatives (11 thiazoles, 2 oxadiazoles, and 10 carboxamides) and have screened them for in vitro activity in the Toxoplasma lytic cycle. Fifteen (65%) of the derivatives were noncytotoxic to host cells (TD(50) > or = 320 microM). Eight thiazole derivatives and two carboxamide derivatives displayed effective inhibition of Toxoplasma growth (IC(50) = 0.25-0.42 microM), comparable in potency to artemether (IC(50) = 0.31 microM) and >100 times more inhibitory than the currently employed front-line drug trimethoprim (IC(50) = 46 microM). The thiazoles as a group were more effective than the other derivatives at inhibiting growth of extracellular as well as intracellular parasites. Unexpectedly, two thiazole trioxanes (5 and 6) were parasiticidal; both inhibited parasite replication irreversibly after parasite exposure to 10 microM of drug for 24 h, whereas the standard trioxane drugs artemisinin and artemether were not parasiticidal. Some of the new derivatives of artemisinin described here represent effective anti-Toxoplasma trioxanes as well as molecular probes for elucidating the mechanism of action of the DART class of artemisinin derivatives.

The P-glycoprotein inhibitor GF120918 modulates Ca2+-dependent processes and lipid metabolism in Toxoplasma gondii

Up-regulation of the membrane-bound efflux pump P-glycoprotein (P-gp) is associated with the phenomenon of multidrug-resistance in pathogenic organisms, including protozoan parasites. In addition, P-gp plays a role in normal physiological processes, however our understanding of these P-gp functions remains limited. In this study we investigated the effects of the P-gp inhibitor GF120918 in Toxoplasma gondii, a model apicomplexan parasite and an important human pathogen. We found that GF120918 treatment severely inhibited parasite invasion and replication. Further analyses of the molecular mechanisms involved revealed that the P-gp inhibitor modulated parasite motility, microneme secretion and egress from the host cell, all cellular processes known to depend on Ca²⁺ signaling in the parasite. In support of a potential role of P-gp in Ca²⁺-mediated processes, immunoelectron and fluorescence microscopy showed that T. gondii P-gp was localized in acidocalcisomes, the major Ca²⁺ storage in the parasite, at the plasma membrane, and in the intravacuolar tubular network. In addition, metabolic labeling of extracellular parasites revealed that inhibition or down-regulation of T. gondii P-gp resulted in aberrant lipid synthesis. These results suggest a crucial role of T. gondii P-gp in essential processes of the parasite biology and further validate the potential of P-gp activity as a target for drug development.

Synthesis and evaluation of 4-acyl-2-thiazolylhydrazone derivatives for anti-Toxoplasma efficacy in vitro

A new series of 4-acyl-2-thiazolylhydrazone derivatives was synthesized and screened for its in vitro activity against Toxoplasma gondii. We evaluated parasite growth inhibition and cytotoxicity, inhibition of replication, and inhibition of parasite invasion of host cells. The biological results indicated that some substances had an antiproliferative effect against intracellular T. gondii tachyzoites cultivated in vitro.

In silico analysis of the cyclophilin repertoire of apicomplexan parasites

Background

Cyclophilins (Cyps) are peptidyl cis/trans isomerases implicated in diverse processes such as protein folding, signal transduction, and RNA processing. They are also candidate drug targets, in particular for the immunosuppressant cyclosporine A. In addition, cyclosporine is known to exhibit anti-parasitic effects on a wide range of organisms including several apicomplexa. In order to obtain new non-immunosuppressive drugs targeting apicomplexan cyclophilins, a profound knowledge of the cyclophilin repertoire of this phylum would be necessary.

Results

BLAST and maximum likelihood analyses identified 16 different cyclophilin subfamilies within the genomes of Cryptosporidium hominis, Toxoplasma gondii, Plasmodium falciparum, Theileria annulata, Theileria parva, and Babesia bovis. In addition to good statistical support from the phylogenetic analysis, these subfamilies are also confirmed by comparison of cyclophilin domain architecture. Within an individual genome, the number of different Cyp genes that could be deduced varies between 7–9 for Cryptosporidia and 14 for T. gondii. Many of the putative apicomplexan cyclophilins are predicted to be nuclear proteins, most of them presumably involved in RNA processing.

Conclusion

The genomes of apicomplexa harbor a cyclophilin repertoire that is at least as complex as that of most fungi. The identification of Cyp subfamilies that are specific for lower eukaryotes, apicomplexa, or even the genus Plasmodium is of particular interest since these subfamilies are not present in host cells and might therefore represent attractive drug targets.

Host cell P-glycoprotein is essential for cholesterol uptake and replication of Toxoplasma gondii

P-glycoprotein (P-gp) is a membrane-bound efflux pump that actively exports a wide range of compounds from the cell and is associated with the phenomenon of multidrug resistance. However, the role of P-gp in normal physiological processes remains elusive. Using P-gp-deficient fibroblasts, we showed that P-gp was critical for the replication of the intracellular parasite Toxoplasma gondii but was not involved in invasion of host cells by the parasite. Importantly, we found that the protein participated in the transport of host-derived cholesterol to the intracellular parasite. T. gondii replication in P-gp-deficient host cells not only resulted in reduced cholesterol content in the parasite but also altered its sphingolipid metabolism. In addition, we found that different levels of P-gp expression modified the cholesterol metabolism in uninfected fibroblasts. Collectively our findings reveal a key and previously undocumented role of P-gp in host-parasite interaction and suggest a physiological role for P-gp in cholesterol trafficking in mammalian cells.

Artemisinin derivatives inhibit Toxoplasma gondii in vitro at multiple steps in the lytic cycle

OBJECTIVES

We sought to improve upon the usefulness of artemisinins as anti-Toxoplasma agents by synthesizing new unsaturated, carba derivatives and then testing them for in vitro efficacy against three steps of the lytic cycle of Toxoplasma gondii tachyzoites.

METHODS

Novel derivatives of ART were synthesized and then tested for in vitro antiparasitic activity using T. gondii tachyzoites constitutively expressing beta-galactosidase and human fibroblast host cells. Compounds were evaluated for parasite growth inhibition and cytotoxicity, inhibition of replication and inhibition of parasite invasion of host cells.

RESULTS

Five of the seven new derivatives, 3a-c, 3e and 3f, effectively inhibited T. gondii growth (IC50=1.0-4.4 microM); however, only three of these proved to be relatively non-cytotoxic (TD50>or=200 microM). The same five derivatives also inhibited tachyzoite replication, and attachment to and invasion of host cells as effectively as or better than the parent compound ART. In addition, one of the derivatives incapable of inhibiting growth, deoxy-3a, was found to inhibit parasite invasion.

CONCLUSIONS

These new artemisinin derivatives have the ability to inhibit multiple steps of T. gondii's lytic cycle. Synthetic unsaturated, carba derivatives of ART have potential as therapeutic agents for the prevention and treatment of toxoplasmosis in humans.

Molecular characterization and expression analysis of a P-glycoprotein homologue in Toxoplasma gondii

ATP-binding cassette (ABC) transporters represent an important family of membrane proteins involved in drug resistance and other biological activities. The present study reports on the characterization of a P-glycoprotein (Pgp), TgABC.B1, in the protozoan parasite Toxoplasma gondii. The protein encoded by the TgABC.B1 gene displays the typical (TMD-NBD)2 structural organization of the "full" ABC transporter and shows significant identity and similarity with two apicomplexan Pgps; Pgh1 in Plasmodium falciparum and CpABC3 in Cryptosporidium parvum. The TgABC.B1 gene is a single copy gene transcribed into a full-length mRNA of 4.3kb and expressed as a protein of approximately 150kDa, which cellular localization revealed a membrane-associated labelling in tachyzoites. The TgABC.B1 gene is constitutively expressed in the three major T. gondii genotypes but demonstrated a higher expression in virulent type I, at both transcriptional and translational levels. Further characterization of this Pgp-like protein will increase our knowledge of the membrane transport system in this parasite and could result in the identification of a new therapeutic target in Toxoplasma.

Novel paradigms for drug discovery: computational multitarget screening

An established paradigm in current drug development is (i) to identify a single protein target whose inhibition is likely to result in the successful treatment of a disease of interest; (ii) to assay experimentally large libraries of small-molecule compounds in vitro and in vivo to identify promising inhibitors in model systems; and (iii) to determine whether the findings are extensible to humans. This complex process, which is largely based on trial and error, is risk-, time- and cost-intensive. Computational (virtual) screening of drug-like compounds simultaneously against the atomic structures of multiple protein targets, taking into account protein-inhibitor dynamics, might help to identify lead inhibitors more efficiently, particularly for complex drug-resistant diseases. Here we discuss the potential benefits of this approach, using HIV-1 and Plasmodium falciparum infections as examples. We propose a virtual drug discovery 'pipeline' that will not only identify lead inhibitors efficiently, but also help minimize side-effects and toxicity, thereby increasing the likelihood of successful therapies.

Anti-Trypanosoma cruzi effects of cyclosporin A derivatives: possible role of a P-glycoprotein and parasite cyclophilins

Cyclophilins are target molecules for cyclosporin A (CsA), an immunosuppressive antimicrobial drug. We have previously reported the in vitro anti-Trypanosoma cruzi activity of H-7-94 and F-7-62 non-immunosuppressive CsA analogues. In this work, we continue the study of the parasiticidal effect of H-7-94 and F-7-62 CsA analogues in vitro and in vivo and we analyse 3 new CsA derivatives: MeIle-4-CsA (NIM 811), MeVal-4-CsA (MeVal-4) and D-MeAla-3-EtVal-4-CsA, (EtVal-4). The most efficient anti-T. cruzi effect was observed with H-7-94, F-7-62 and MeVal-4 CsA analogues evidenced as inhibition of epimastigote proliferation, trypomastigote penetration, intracellular amastigote development and in vivo T. cruzi infection. This trypanocidal activity could be due to inhibition of the peptidyl prolyl cis-trans isomerase activity on the T. cruzi recombinant cyclophilins tested. Furthermore, CsA and F-7-62 derivative inhibited the efflux of rhodamine 123 from T. cruzi epimastigotes, suggesting an interference with a P-glycoprotein activity. Moreover, H-7-94 and F-7-62 CsA analogues were not toxic as shown by cell viability and by aminopyrine-N-demethylase activity on mammalian cells. Our results show that H-7-94, F-7-62 and MeVal-4 CsA analogues expressed the highest inhibiting effects on T. cruzi, being promissory parasiticidal drugs worthy of further studies.

[Cell-host-parasite interactions: biodiversity, pathogenesis, environment]

The apicomplexan Toxoplasma gondii, an obligate intracellular parasite, can infect humans and a wide range of vertebrates leading to toxoplasmosis. This generally benign affection can causes severe life-threatening disease, particularly in immunocompromised patients and in children with congenital toxoplasmosis. Our research team works on cell-host-parasite interactions by studying biodiversity, pathogenic mechanisms and environment. We search to identify prognostic factors of disease and markers of resistance. This project is an integral part of our Research Institute (IFR53) which receives support from the Toxoplasma Biological Resource Center for constituting a bank of well characterized toxoplasma isolates for genotyping, clinical and epidemiological data. The involvement of metalloproteinases implicated during monocytic cell invasion and identification of ABC transporter proteins in T. gondii, factors implicated in resistance, need to be explored.

Peptidyl-prolyl cis-trans isomerases (immunophilins) and their roles in parasite biochemistry, host-parasite interaction and antiparasitic drug action

Immunophilin is the collective name given to the cyclophilin and FK506-binding protein families. As the name suggests, these include the major binding proteins of certain immunosuppressive drugs: cyclophilins for the cyclic peptide cyclosporin A and FK506-binding proteins for the macrolactones FK506 and rapamycin. Both families, although dissimilar in sequence, possess peptidyl-prolyl cis-trans isomerase activity in vitro and can play roles in protein folding and transport, RNA splicing and the regulation of multi-protein complexes in cells. In addition to enzymic activity, many immunophilins act as molecular chaperones. This property may be conferred by the isomerase domain and/or by additional domains. Recent years have seen a great increase in the number of known immunophilin genes in parasitic protozoa and helminths and in many cases their products have been characterised biochemically and their temporal and spatial expression patterns have been examined. Some of these genes represent novel types: one example is a Toxoplasma gondii gene encoding a protein with both cyclophilin and FK506-binding protein domains. Likely roles in protein folding and oligomerisation, RNA splicing and sexual differentiation have been suggested for parasite immunophilins. In addition, unexpected roles in parasite virulence (Mip FK506-binding protein of Trypanosoma cruzi) and host immuno-modulation (e.g. 18-kDa cyclophilin of T. gondii) have been established. Furthermore, in view of the potent antiparasitic activities of cyclosporins, macrolactones and non-immunosuppressive derivatives of these compounds, immunophilins may mediate drug action and/or may themselves represent potential drug targets. Investigation of the mechanisms of action of these agents may lead to the design of potent and selective antimalarial and other antiparasitic drugs. This review discusses the properties of immunophilins in parasites and the 'animal model'Caenorhabditis elegans and relates these to our understanding of the roles of these proteins in cellular biochemistry, host-parasite interaction and the antiparasitic mechanisms of the drugs that bind to them.

Cyclophilin B is a functional regulator of hepatitis C virus RNA polymerase

Viruses depend on host-derived factors for their efficient genome replication. Here, we demonstrate that a cellular peptidyl-prolyl cis-trans isomerase (PPIase), cyclophilin B (CyPB), is critical for the efficient replication of the hepatitis C virus (HCV) genome. CyPB interacted with the HCV RNA polymerase NS5B to directly stimulate its RNA binding activity. Both the RNA interference (RNAi)-mediated reduction of endogenous CyPB expression and the induced loss of NS5B binding to CyPB decreased the levels of HCV replication. Thus, CyPB functions as a stimulatory regulator of NS5B in HCV replication machinery. This regulation mechanism for viral replication identifies CyPB as a target for antiviral therapeutic strategies.

Inhibitory effect of aureobasidin A on Toxoplasma gondii

The apicomplexan parasite Toxoplasma gondii is a leading opportunistic pathogen associated with AIDS and congenital birth defects. Due to the need for identifying new parasite-specific treatments, the possibility of targeting sphingolipid biosynthesis in the parasite was investigated. Aureobasidin A, an inhibitor of the enzyme synthesizing the sphingolipid inositol phosphorylceramide, which is present in fungi, plants, and some protozoa but absent in mammalian cells, was found to block in vitro T. gondii replication without affecting host cell metabolism. Aureobasidin A treatment did not induce tachyzoite to bradyzoite stage conversion in T. gondii but resulted in a loss of intracellular structures and vacuolization within the parasite. In addition, aureobasidin A inhibited sphingolipid synthesis in T. gondii. Sphingolipid biosynthetic pathways may therefore be considered targets for the development of anti-T. gondii agents.

In vitro anti-parasitic activity of Cyclosporin A analogs on Trypanosoma cruzi

Cyclosporin A (CsA) nonimmunosuppressive analogs were evaluated against Trypanosoma cruzi and on TcCyP19, a cyclophilin of 19 kDa. Two out of eight CsA analogs, H-7-94 and F-7-62 showed the best anti-parasitic effects on all in vitro assays. Their IC(50) values were 0.82 and 3.41 microM, respectively, compared to CsA IC(50) value 5.39 microM on epimastigote proliferation; and on trypomastigote lysis their IC(50) values were 0.97 and 2.66 microM compared to CsA IC(50) value 7.19 microM. H-7-94 and F-7-62 were also more effective than CsA in inhibiting trypomastigote infection. The enzymatic activity of TcCyP19 was inhibited by all CsA derivatives, suggesting this target is involved in the trypanocidal effects observed.

Cyclosporin A inhibits calcineurin (phosphatase 2B) and P-glycoprotein activity in Entamoeba histolytica

Cyclosporin A (CsA) inhibits the proliferation of several protozoan parasites through blocking the activity of calcineurin (Cn) or P-glycoproteins (Pgp). We report here, that inhibition of the proliferation of Entamoeba histolytica trophozoites, the causal agent of human amebiasis, is due to interference of the phosphatase activity of Cn, in a similar fashion to the effect of this immunosuppressive drug on T lymphocytes. The non-immunosuppressive CsA analog PSC-833, which binds Pgp without interfering the function of Cn, did not inhibit the proliferation of HM1:IMSS trophozoites. Moreover, phosphatase activity of amebic Cn, detected using the phosphopeptide RII, was drastically affected by incubation with CsA, but not with PSC-833. On the other hand, both drugs were also tested on clone C2 trophozoites, which grow in the presence of emetine due to over-expression of Pgp. The effect of CsA was similar to that observed on HM1:IMSS trophozoites, whereas PSC-833 only affected the proliferation and viability of clone C2 when the trophozoites were grown in the presence of 40 microM of emetine, suggesting an interference of the Pgp activity. This suggestion was confirmed by results from experiments of Pgp-dependent effux of rhodamine from pre-loaded trophozoites, in the presence of either of these drugs. Therefore, CsA inhibition of E. histolytica trophozoite proliferation is more likely due to Cn than Pgp activity inhibition.

Cryptosporidium parvum: effect of multi-drug reversing agents on the expression and function of ATP-binding cassette transporters

In the present study, the gene expression of three multidrug resistance (MDR) and resistance-associated protein (MRP) transport proteins or efflux pumps was characterized and the phenotypic evidence for such pumps was demonstrated in cultured Madin-Darby canine kidney (MDCK) cells. A gradient for the fluorescent probe calcein was established between parasite and host cell suggestive of a parasite extrusion pump at the parasite-host interface. This gradient was decreased in a glucose-free medium containing 2-deoxyglucose or 3-O-methylglucose, by probenecid, and by the isoflavonoid, narigenin, suggesting that the calcein extrusion was energy-dependent and involved an MRP-like pump. While neither MDR or MRP inhibiters significantly affected transcript levels of any of the ABC transporters, transcript levels of the Cryptosporidium parvum ABC protein (CpABC1), an MRP transporter, were consistently expressed 4 logs higher than either CpABC3 or CpABC2, suggesting a prominent role in the intracellular stages of the parasite.

P-glycoprotein inhibitors modulate accumulation and efflux of xenobiotics in extra and intracellular Toxoplasma gondii

We examined xenobiotic transport and the effects of P-glycoprotein (Pgp) inhibitors on efflux function in Toxoplasma gondii tachyzoites. The fluorescence emission of JC-1 and daunorubicin (Pgp substrates) was determined in both extracellular tachyzoites and T. gondii-infected human KB cells. Dye accumulation and efflux were modulated by verapamil (Vp) and cyclosporin A (CsA), both of which are Pgp inhibitors. Red JC-1 emission was measured from 10(6) extracellular tachyzoites, using spectrofluorometry. The increase in red emission was significant from 1 microM concentration of both drugs and was higher with CsA than with Vp. Compared with untreated tachyzoites, JC-1 efflux was inhibited by 3 microM CsA and 3 microM Vp. With intracellular tachyzoites, the fluorescence distribution of daunorubicin (DNR) between the parasitophorous vacuole and the host cell was modulated by Vp and CsA. In media free of CsA and Vp, DNR emission inside intracellular tachyzoites was very weak, as observed by confocal microscopy. In the presence of CsA or Vp, DNR emission was markedly enhanced in tachyzoites but not in the whole vacuole. The modulation of DNR uptake seems to involve the tachyzoite membrane rather than the parasitophorous vacuole or host cell membranes. It suggests that Vp would inhibit the DNR efflux from intracellular tachyzoites through a transitory effect. In conclusion, these two Pgp inhibitors increase both extracellular and intracellular dye accumulation in living T. gondii, pointing to the existence of a transmembrane transport mediated by a Pgp homologue located on the parasite membrane complex.

Fungicidal synergism of fluconazole and cyclosporine in Candida albicans is not dependent on multidrug efflux transporters encoded by the CDR1, CDR2, CaMDR1, and FLU1 genes

The combination of fluconazole (FLC) and cyclosporine (CY) is fungicidal in FLC-susceptible C. albicans (O. Marchetti, P. Moreillon, M. P. Glauser, J. Bille, and D. Sanglard, Antimicrob. Agents Chemother. 44:2373-2381, 2000). The mechanism of this synergism is unknown. CY has several cellular targets including multidrug efflux transporters. The hypothesis that CY might inhibit FLC efflux was investigated by comparing the effect of FLC-CY in FLC-susceptible parent CAF2-1 (FLC MIC, 0.25 mg/liter) and in FLC-hypersusceptible mutant DSY1024 (FLC MIC, 0.03 mg/liter), in which the CDR1, CDR2, CaMDR1, and FLU1 transporter genes have been selectively deleted. We postulated that a loss of the fungicidal effect of FLC-CY in DSY1024 would confirm the roles of these efflux pumps. Time-kill curve studies showed a more potent fungistatic effect of FLC (P = 0.05 at 48 h with an inoculum of 10(3) CFU/ml) and a more rapid fungicidal effect of FLC-CY (P = 0.05 at 24 h with an inoculum of 10(3) CFU/ml) in the FLC-hypersusceptible mutant compared to those in the parent. Rats with experimental endocarditis were treated for 2 or 5 days with high-dose FLC, high-dose CY, or both drugs combined. FLC monotherapy for 5 days was more effective against the hypersusceptible mutant than against the parent. However, the addition of CY to FLC still conferred a therapeutic advantage in animals infected with mutant DSY1024, as indicated by better survival (P = 0.04 versus the results obtained with FLC) and sterilization of valves and kidneys after a very short (2-day) treatment (P = 0.009 and 0.002, respectively, versus the results obtained with FLC). Both in vitro and in vivo experiments consistently showed that the deletion of the four membrane transporters in DSY1024 did not result in loss of the fungicidal effect of FLC-CY. Yet, the accelerated killing in the mutant suggested a "dual-hit" mechanism involving FLC hypersusceptibility due to the efflux pump elimination and fungicidal activity conferred by CY. Thus, inhibition of multidrug efflux transporters encoded by CDR1, CDR2, CaMDR1, and FLU1 genes is not responsible for the fungicidal synergism of FLC-CY. Other cellular targets must be considered.

Cryptosporidiosis and the challenges of chemotherapy

Cryptosporidium parvum is a protozoan parasite that infects the epithelial cells of the small intestine causing diarrheal illness in humans. Cryptosporidium has a worldwide distribution and is considered an emerging zoonosis. Despite intensive efforts to develop workable experimental models, and the evaluation of over 200 chemotherapeutic agents, adequate therapies to clear the host of these parasites are still lacking. The reasons for the lack of drug efficacy are probably manifold and may include the unusual location of the parasite in the host cell, distinct structural and biochemical composition, or its ability to either block import or rapidly efflux drug molecules. Understanding some of the basic mechanisms by which drugs are transported to the parasite and identifying unique targets is a first step in developing effective therapeutic agents.

Role of P glycoprotein in the course and treatment of Encephalitozoon microsporidiosis

Encephalitozoon microsporidia are obligate intracellular protozoan parasites that proliferate and differentiate within a parasitophorous vacuole inside host cells that are usually epithelial in nature. Isolates of the three species of the Encephalitozoon microsporidia, E. cuniculi, E. hellem, and E. intestinalis, were obtained from AIDS patients and cultured in green monkey (E6) kidney cells. Anti-P-glycoprotein (anti-Pgp) and anti-multidrug resistance-associated protein (anti-MRP) monoclonal antibodies were used to probe for multidrug resistance (MDR) pump epitopes and verapamil- or cyclosporin A- and probenecid-modulated intracellular calcein fluorescence were used to assess the expression of Pgp and MRP respectively in uninfected and infected cells. Pgp, but not MRP, was detected immunocytochemically and by verapamil- and cyclosporin A-potentiated intracellular fluorescence in both host cells and parasite developing stages. When an in vitro infection assay was employed, verapamil and cyclosporin A acted as chemosensitizing agents for the antiparasitic drug albendazole. These observations suggest that inhibiting host cell and perhaps parasite MDR pumps may increase the efficacy of antiparasitic agents in these and other microsporidia species.

Fluconazole plus cyclosporine: a fungicidal combination effective against experimental endocarditis due to Candida albicans

Recent observations demonstrated that fluconazole plus cyclosporine (Cy) synergistically killed Candida albicans in vitro. This combination was tested in rats with C. albicans experimental endocarditis. The MICs of fluconazole and Cy for the test organism were 0.25 and >10 mg/liter, respectively. Rats were treated for 5 days with either Cy, amphotericin B, fluconazole, or fluconazole-Cy. Although used at high doses, the peak concentrations of fluconazole in the serum of rats (up to 4.5 mg/liter) were compatible with high-dose fluconazole therapy in humans. On the other hand, Cy concentrations in serum (up to 4.5 mg/liter) were greater than recommended therapeutic levels. Untreated rats demonstrated massive pseudohyphal growth in both the vegetations and the kidneys. However, only the kidneys displayed concomitant polymorphonuclear infiltration. The therapeutic results reflected this dissociation. In the vegetations, only the fungicidal fluconazole-Cy combination significantly decreased fungal densities compared to all groups, including amphotericin B (P < 0.0001). In the kidneys, all regimens except the Cy regimen were effective, but fluconazole-Cy remained superior to amphotericin B and fluconazole alone in sterilizing the organs (P < 0.0001). While the mechanism responsible for the fluconazole-Cy interaction is hypothetical, this observation opens new perspectives for fungicidal combinations between azoles and other drugs.

Potent synergism of the combination of fluconazole and cyclosporine in Candida albicans

Several types of drugs currently used in clinical practice were screened in vitro for their potentiation of the antifungal effect of the fungistatic agent fluconazole (FLC) on Candida albicans. These drugs included inhibitors of multidrug efflux transporters, antimicrobial agents, antifungal agents, and membrane-active compounds with no antimicrobial activity, such as antiarrhythmic agents, proton pump inhibitors, and platelet aggregation inhibitors. Among the drugs tested in an agar disk diffusion assay, cyclosporine (Cy), which had no intrinsic antifungal activity, showed a potent antifungal effect in combination with FLC. In a checkerboard microtiter plate format, however, it was observed that the MIC of FLC, as classically defined by the NCCLS recommendations, was unchanged when FLC and Cy were combined. Nevertheless, if a different reading endpoint corresponding to the minimal fungicidal concentration needed to decrease viable counts by at least 3 logs in comparison to the growth control was chosen, the combination was synergistic (fractional inhibitory concentration index of <1). This endpoint fitted to the definition of MIC-0 (optically clear wells) and reflected the absence of the trailing effect, which is the result of a residual growth at FLC concentrations greater than the MIC. The MIC-0 values of FLC and Cy tested alone in C. albicans were >32 and >10 microg/ml, respectively, and decreased to 0.5 and 0.625 microg/ml when the two drugs were combined. The combination of 0.625 microg of Cy per ml with supra-MICs of FLC resulted in a potent antifungal effect in time-kill curve experiments. This effect was fungicidal or fungistatic, depending on the C. albicans strain used. Since the Cy concentration effective in vitro is achievable in vivo, the combination of this agent with FLC represents an attractive perspective for the development of new management strategies for candidiasis.

Toxoplasma gondii exploits host low-density lipoprotein receptor-mediated endocytosis for cholesterol acquisition

The obligate intracellular protozoan Toxoplasma gondii resides within a specialized parasitophorous vacuole (PV), isolated from host vesicular traffic. In this study, the origin of parasite cholesterol was investigated. T. gondii cannot synthesize sterols via the mevalonate pathway. Host cholesterol biosynthesis remains unchanged after infection and a blockade in host de novo sterol biosynthesis does not affect parasite growth. However, simultaneous limitation of exogenous and endogenous sources of cholesterol from the host cell strongly reduces parasite replication and parasite growth is stimulated by exogenously supplied cholesterol. Intracellular parasites acquire host cholesterol that is endocytosed by the low-density lipoprotein (LDL) pathway, a process that is specifically increased in infected cells. Interference with LDL endocytosis, with lysosomal degradation of LDL, or with cholesterol translocation from lysosomes blocks cholesterol delivery to the PV and significantly reduces parasite replication. Similarly, incubation of T. gondii in mutant cells defective in mobilization of cholesterol from lysosomes leads to a decrease of parasite cholesterol content and proliferation. This cholesterol trafficking to the PV is independent of the pathways involving the host Golgi or endoplasmic reticulum. Despite being segregated from the endocytic machinery of the host cell, the T. gondii vacuole actively accumulates LDL-derived cholesterol that has transited through host lysosomes.

Antibiotics for the treatment of rheumatologic syndromes

Design of rational therapy depends on knowledge of the causes of the disease, which is knowledge often lacking in rheumatology. There have been theories of infectious causes of many rheumatologic diseases but no proof. The seductive possibility of an infectious etiology has led to the use of antibiotics for treating these diseases. This article reviews the effectiveness of antibiotics against rheumatologic syndromes, including rheumatoid arthritis and Lyme disease.

Antifungal activities of antineoplastic agents: Saccharomyces cerevisiae as a model system to study drug action

Recent evolutionary studies reveal that microorganisms including yeasts and fungi are more closely related to mammals than was previously appreciated. Possibly as a consequence, many natural-product toxins that have antimicrobial activity are also toxic to mammalian cells. While this makes it difficult to discover antifungal agents without toxic side effects, it also has enabled detailed studies of drug action in simple genetic model systems. We review here studies on the antifungal actions of antineoplasmic agents. Topics covered include the mechanisms of action of inhibitors of topoisomerases I and II; the immunosuppressants rapamycin, cyclosporin A, and FK506; the phosphatidylinositol 3-kinase inhibitor wortmannin; the angiogenesis inhibitors fumagillin and ovalicin; the HSP90 inhibitor geldanamycin; and agents that inhibit sphingolipid metabolism. In general, these natural products inhibit target proteins conserved from microorganisms to humans. These studies highlight the potential of microorganisms as screening tools to elucidate the mechanisms of action of novel pharmacological agents with unique effects against specific mammalian cell types, including neoplastic cells. In addition, this analysis suggests that antineoplastic agents and derivatives might find novel indications in the treatment of fungal infections, for which few agents are presently available, toxicity remains a serious concern, and drug resistance is emerging.

CpABC, a Cryptosporidium parvum ATP-binding cassette protein at the host-parasite boundary in intracellular stages

The intracellular parasite Cryptosporidium parvum develops inside a vacuole at the apex of its epithelial host cell. The developing parasite is separated from the host cell cytoplasm by a zone of attachment that consists of an extensively folded membranous structure known as the feeder organelle. It has been proposed that the feeder organelle is the site of regulation of transport of nutrients and drugs into the parasite. In this report, we localize an approximately 200-kDa integral membrane protein, CpABC, from Cryptosporidium parvum to the host-parasite boundary, possibly the feeder organelle. The predicted amino acid sequence of CpABC has significant structural similarity with the cystic fibrosis conductance regulator and the multidrug resistance protein subfamily of ATP-binding cassette proteins. This is an example of a parasite-encoded transport protein localized at the parasite-host interface of an intracellular protozoan.

Detailed characterization of a cyclophilin from the human malaria parasite Plasmodium falciparum

Cyclosporin (Cs) A has pronounced antimalarial activity in vitro and in vivo. In other organisms, the drug is thought to exert its effects either by inhibiting the peptidylprolyl cis/trans isomerase activity of cyclophilin (CyP) or by forming a CyP-CsA complex that inhibits the phosphatase activity of calcineurin. We have cloned and overexpressed in Escherichia coli a gene encoding a CyP from Plasmodium falciparum (PfCyP19) that is located on chromosome 3. The sequence of PfCyP19 shows remarkable sequence identity with human CyPA and, unlike the two previously identified CyPs from P. falciparum, PfCyP19 has no signal peptide or N-terminal sequence extension, suggesting a cytosolic localization. All the residues implicated in the recognition of the synthetic substrate N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide are conserved, resulting in characteristically high Michaelis-Menten and specificity constants (Km>>120 microM, kcat/Km=1.2x10(7) M-1.s-1 respectively). As the first line in the functional characterization of this enzyme, we have assessed its binding affinity for CsA. In accordance with its tryptophan-containing CsA-binding domain, PfCyP19 binds CsA with high affinity (Kd=13 nM, Ki=6.9 nM). Twelve CsA analogues were also found to possess Ki values similar to CsA, with the notable exceptions of Val2-Cs (Ki=218 nM) and Thr2-Cs (Ki=690 nM). The immunosuppressants rapamycin and FK506 were inactive as inhibitors, consistent with other members of the CyP family of rotamases. The CsA analogues were also assessed as inhibitors of P. falciparum growth in vitro. Although their antimalarial activity did not correlate with inhibition of enzyme activity, residues 3 and 4 of CsA appeared to be important for inhibition of parasite growth and residues 1 and 2 for PfCyP19 inhibition. We propose that a malarial CyP-CsA complex presents residues 3 and 4 as part of an 'effector surface' for recognition by a downstream target, similar to the proposed mechanism for T-cell immunosuppression.

Cyclosporin analogs inhibit in vitro growth of Cryptosporidium parvum

Cyclosporine and nonimmunosuppressive cyclosporin (CS) analogs were demonstrated to be potent inhibitors of the growth of the intracellular parasite Cryptosporidium parvum in short-term (48-h) in vitro cultures. Fifty-percent inhibitory concentrations (IC50s) were 0.4 microM for SDZ 033-243, 1.0 microM for SDZ PSC-833, and 1.5 microM for cyclosporine. Two other analogs were less effective than cyclosporine: the IC50 of SDZ 205-549 was 5 microM, and that of SDZ 209-313 was 7 microM. These were much lower than the IC50 of 85 microM of paromomycin, a standard positive control for in vitro drug assays for this parasite. In addition, intracellular growth of excysted sporozoites that had been incubated for 1 h in cyclosporine was significantly reduced, suggesting that the drug can inhibit sporozoite invasion. The cellular activities of the CS analogs used have been characterized for mammalian cells and protozoa. The two analogs that were most active in inhibiting C. parvum, SDZ PSC-833 and SDZ 033-243, bind weakly to cyclophilin, a peptidyl proline isomerase which is the primary target of cyclosporine and CS analogs. However, they are potent modifiers of the activity of the P glycoproteins/ multidrug resistance (MDR) transporters, members of the ATP-binding cassette (ABC) superfamily. Hence, both cyclophilin and some ABC transporters may be targets for this class of drugs, although drugs that preferentially interact with the latter are more potent. Cyclosporine (0.5 microM) had no significant chemosensitizing activity. That is, it did not significantly increase sensitivity to paromomycin, suggesting that an ABC transporter is not critical in the efflux of this drug. Cyclosporine at concentrations up to 50 microM was not toxic to host Caco-2 cells in the CellTiter 96 assay. The results of this study complement those of studies of the inhibitory effect of cyclosporine and CS analogs on other apicomplexan parasites, Plasmodium falciparum, Plasmodium vivax, and Toxoplasma gondii.