Cyclosporin A: antiparasite drug, modulator of the host-parasite relationship and immunosuppressant

Evaluating the potential of non-immunosuppressive cyclosporin analogs for targeting Toxoplasma gondii cyclophilin: Insights from structural studies

Toxoplasmosis persists as a prevalent disease, facing challenges from parasite resistance and treatment side effects. Consequently, identifying new drugs by exploring novel protein targets is essential for effective intervention. Cyclosporin A (CsA) possesses antiparasitic activity against Toxoplasma gondii, with cyclophilins identified as possible targets. However, CsA immunosuppressive nature hinders its use as an antitoxoplasmosis agent. Here, we evaluate the potential of three CsA derivatives devoid of immunosuppressive activity, namely, NIM811, Alisporivir, and dihydrocyclosporin A to target a previously characterized cyclophilin from Toxoplasma gondii (TgCyp23). We determined the X-ray crystal structures of TgCyp23 in complex with the three analogs and elucidated their binding and inhibitory properties. The high resolution of the structures revealed the precise positioning of ligands within the TgCyp23 binding site and the details of protein-ligand interactions. A comparison with the established ternary structure involving calcineurin indicates that substitutions at position 4 in CsA derivatives prevent calcineurin binding. This finding provides a molecular explanation for why CsA analogs can target Toxoplasma cyclophilins without compromising the human immune response.

Repurposing the Medicines for Malaria Venture's COVID Box to discover potent inhibitors of Toxoplasma gondii, and in vivo efficacy evaluation of almitrine bismesylate (MMV1804175) in chronically infected mice

Toxoplasmosis, caused by the obligate intracellular parasite Toxoplasma gondii, affects about one-third of the world's population and can cause severe congenital, neurological and ocular issues. Current treatment options are limited, and there are no human vaccines available to prevent transmission. Drug repurposing has been effective in identifying anti-T. gondii drugs. In this study, the screening of the COVID Box, a compilation of 160 compounds provided by the "Medicines for Malaria Venture" organization, was conducted to explore its potential for repurposing drugs to combat toxoplasmosis. The objective of the present work was to evaluate the compounds' ability to inhibit T. gondii tachyzoite growth, assess their cytotoxicity against human cells, examine their absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties, and investigate the potential of one candidate drug through an experimental chronic model of toxoplasmosis. Early screening identified 29 compounds that could inhibit T. gondii survival by over 80% while keeping human cell survival up to 50% at a concentration of 1 μM. The Half Effective Concentrations (EC50) of these compounds ranged from 0.04 to 0.92 μM, while the Half Cytotoxic Concentrations (CC50) ranged from 2.48 to over 50 μM. Almitrine was chosen for further evaluation due to its favorable characteristics, including anti-T. gondii activity at nanomolar concentrations, low cytotoxicity, and ADMET properties. Administering almitrine bismesylate (Vectarion®) orally at dose of 25 mg/kg/day for ten consecutive days resulted in a statistically significant (p < 0.001) reduction in parasite burden in the brains of mice chronically infected with T. gondii (ME49 strain). This was determined by quantifying the RNA of living parasites using real-time PCR. The presented results suggest that almitrine may be a promising drug candidate for additional experimental studies on toxoplasmosis and provide further evidence of the potential of the MMV collections as a valuable source of drugs to be repositioned for infectious diseases.

Structural Basis for Cyclosporin Isoform-Specific Inhibition of Cyclophilins from Toxoplasma gondii

Cyclosporin (CsA) has antiparasite activity against the human pathogen Toxoplasma gondii. A possible mechanism of action involves CsA binding to T. gondii cyclophilins, although much remains to be understood. Herein, we characterize the functional and structural properties of a conserved (TgCyp23) and a more divergent (TgCyp18.4) cyclophilin isoform from T. gondii. While TgCyp23 is a highly active cis-trans-prolyl isomerase (PPIase) and binds CsA with nanomolar affinity, TgCyp18.4 shows low PPIase activity and is significantly less sensitive to CsA inhibition. The crystal structure of the TgCyp23:CsA complex was solved at the atomic resolution showing the molecular details of CsA recognition by the protein. Computational and structural studies revealed relevant differences at the CsA-binding site between TgCyp18.4 and TgCyp23, suggesting that the two cyclophilins might have distinct functions in the parasite. These studies highlight the extensive diversification of TgCyps and pave the way for antiparasite interventions based on selective targeting of cyclophilins.

Cyclosporine A increases the intensity of Toxocara canis infection in swiss mice

Toxocariasis is a zoonotic disease of worldwide distribution. The connection between parasitic diseases and conditions that depress the immune system, such as the use of immunosuppressive drugs, has been studied. The purpose of this study was to evaluate the effect of Cyclosporine A (CsA) on the intensity of infection, humoral response and gene transcription of interleukins IL-4, IL-10 and IL-12 in mice experimentally infected with Toxocara canis. To this end, mice were divided into two groups treated with CsA (G1: 10 mg/Kg and G2: 50 mg/kg), the G3 and G4 group received PBS. After the last administration of the drug or PBS (orally every 48 hours for 15 days), groups G1, G2 and G3 were inoculated with 1200 eggs of T. canis. Was collected blood samples on days zero, 15 and 30 days post-inoculation (PI), for ELISA test and the mice were euthanized 30 days PI. The organs and striated muscle tissue were collected for the recovery of larvae. The splenocytes were analyzed by RT-PCR. The intensity of infection in the mice treated with 50 mg/kg of CsA was 65.5% higher than in the control group (p=0.001). An analysis of the kinetics of anti-Toxocara antibody revealed that the groups treated with CsA showed significantly higher mean levels of antibodies on day 15 PI. The transcription of the three tested interleukins showed no statistical difference between G2 and G3 (control). It was concluded that the immunosuppression triggered by CsA (50 mg/Kg) favored the establishment of a larger number of T. canis larvae without, however, altering immunoglobulin production and IL-4, IL-10 and IL-12 transcription on day 30 PI.

Evaluation of in vitro antileishmanial efficacy of cyclosporin A and its non-immunosuppressive derivative, dihydrocyclosporin A

Background

New therapeutic drugs are urgently needed against visceral leishmaniasis because current drugs, such as pentavalent antimonials and miltefosine, produce severe side effects and development of resistance. Whether cyclosporine A (CsA) and its derivatives can be used as therapeutic drugs for visceral leishmaniasis has been controversial for many years.

Methods

In this study, we evaluated the efficacy of CsA and its derivative, dihydrocyclosporin A (DHCsA-d), against promastigotes and intracellular amastigotes of Leishmania donovani. Sodium stibogluconate (SSG) was used as a positive control.

Results

Our results showed that DHCsA-d was able to inhibit the proliferation of L. donovani promastigotes (IC₅₀: 21.24 μM and 12.14 μM at 24 h and 48 h, respectively) and intracellular amastigotes (IC₅₀: 5.23 μM and 4.84 μM at 24 and 48 h, respectively) in vitro, but CsA treatment increased the number of amastigotes in host cells. Both DHCsA-d and CsA caused several alterations in the morphology and ultrastructure of L. donovani, especially in the mitochondria. However, DHCsA-d showed high cytotoxicity towards cells of the mouse macrophage cell line RAW264.7, with CC50 values of 7.98 μM (24 h) and 6.65 μM (48 h). Moreover, DHCsA-d could increase IL-12, TNF-α and IFN-γ production and decrease the levels of IL-10, IL-4, NO and H₂O₂ in infected macrophages. On the contrary, CsA decreased IL-12, TNF-α, and IFN-γ production and increased the levels of IL-10, IL-4, NO and H₂O₂ in infected macrophages. The expression of L. donovani cyclophilin A (LdCyPA) in promastigotes and intracellular amastigotes and the expression of cyclophilin A (CyPA) in RAW 264.7 cells were found to be significantly downregulated in the CsA-treated group compared to those in the untreated group. However, no significant changes in LdCyPA and CyPA levels were found after DHCsA-d or SSG treatment.

Conclusions

Our findings initially resolved the dispute regarding the efficacy of CsA and DHCsA-d for visceral leishmaniasis treatment. CsA showed no significant inhibitory effect on intracellular amastigotes. DHCsA-d significantly inhibited promastigotes and intracellular amastigotes, but it was highly cytotoxic. Therefore, CsA and DHCsA-d are not recommended as antileishmanial drugs.

A Functional Analysis of the Cyclophilin Repertoire in the Protozoan Parasite Trypanosoma Cruzi

Trypanosoma cruzi is the etiological agent of Chagas disease. It affects eight million people worldwide and can be spread by several routes, such as vectorborne transmission in endemic areas and congenitally, and is also important in non-endemic regions such as the United States and Europe due to migration from Latin America. Cyclophilins (CyPs) are proteins with enzymatic peptidyl-prolyl isomerase activity (PPIase), essential for protein folding in vivo. Cyclosporin A (CsA) has a high binding affinity for CyPs and inhibits their PPIase activity. CsA has proved to be a parasiticidal drug on some protozoa, including T. cruzi. In this review, we describe the T. cruzi cyclophilin gene family, that comprises 15 paralogues. Among the proteins isolated by CsA-affinity chromatography, we found orthologues of mammalian CyPs. TcCyP19, as the human CyPA, is secreted to the extracellular environment by all parasite stages and could be part of a complex interplay involving the parasite and the host cell. TcCyP22, an orthologue of mitochondrial CyPD, is involved in the regulation of parasite cell death. Our findings on T. cruzi cyclophilins will allow further characterization of these processes, leading to new insights into the biology, the evolution of metabolic pathways, and novel targets for anti-T. cruzi control.

Helminths in organ transplantation

With transplantation becoming an increasingly routine form of treatment for diverse populations, and with international travel becoming ever more accessible and affordable, the danger of transplantation-mediated helminth infections, exacerbated by coincident immunosuppression, must be considered. In this Review, we attempt to catalogue all clinically-relevant helminthiases that have been reported to coincide with transplantation, whether by transplantation-mediated transmission, reactivation of latent infections in an immunosuppressed context, or possible de-novo infection during the immunosuppressed peritransplant period. Helminthiasis has been reported in cases of kidney, liver, bowel, pancreas, heart, lung, and stem-cell transplant, and blood transfusion. For each helminthiasis, known risk factors, symptoms, and suggested options for screening and treatment are given. We conclude that helminths are a small but important and potentially severe source of disease after transplantation, and, with options for diagnosis and treatment, these pathogens warrant greater consideration during organ implantation. The achievement of immunological tolerance using helminth-derived products is also an exciting future prospect.

Effect of 2,3,7,8-Tetrachloro-di-benzo-p-dioxin on T Cell Subpopulations in the Thymus and Spleen of Mice with Chronic Toxoplasma gondii Infection

In the current study, the effect of exposure to the environmental pollutant, 2,3,7,8-tetrachloro-di-benzo- p-dioxin (TCDD), on mice having chronic infection with Toxoplasma gondii was investigated. For this purpose, four groups of mice were used—mice treated with vehicle, mice treated with TCDD alone, mice infected with T. gondii alone, and mice receiving a combination of TCDD treatment and T. gondii infection. Histological examination and tissue cyst enumeration were performed to indicate the level of infection of the brain. The immune status was studied by enumerating the cellularity as well as the percentages and absolute numbers of the lymphocyte subsets based on the expression of CD4 and CD8 markers in the thymus and spleen. Our studies demonstrated that there was a significant decrease in the total number of thymocytes in TCDD-treated mice that were either uninfected or infected with T. gondii when compared to vehicle controls. However, there was no significant difference observed in thymic cellularity in mice that were infected with T. gondii alone when compared to the uninfected vehicle controls. In addition, the ratio and the total numbers of CD4+, CD8+, CD4–CD8–(double negative, DN) and CD4+CD8+ (double positive, DP) T cell subsets in the thymus from various groups were determined. There was no change in the percentages of T cell subsets in TCDD-treated mice or T. gondii-infected mice when compared to the vehicle controls. However, there was a decrease in the percentage of DPT cells and an increase in the DN and CD8+ T cells in mice that received a combination of TCDD-treatment and T. gondii infection when compared to mice receiving the vehicle or TCDD-treatment alone or infection with T. gondii alone. There was also a decrease in the absolute numbers of the DP and CD4+ T cells and an increase in the CD8+ T cells in the thymus of mice receiving the combination of TCDD-treatment and T. gondii infection when compared to vehicle controls. The splenic cellularity as well as the percentage and absolute numbers of the CD4+ and CD8+ T cell subsets and the non-T cells were not altered in all the groups tested. The natural history of T. gondii infection was not altered following TCDD treatment as demonstrated by no significant differences in brain lesion scores and the number of tissue cysts in the brains of these mice.

The Leishmania donovani chaperone cyclophilin 40 is essential for intracellular infection independent of its stage-specific phosphorylation status

During its life cycle, the protozoan pathogen Leishmania donovani is exposed to contrasting environments inside insect vector and vertebrate host, to which the parasite must adapt for extra- and intracellular survival. Combining null mutant analysis with phosphorylation site-specific mutagenesis and functional complementation we genetically tested the requirement of the L. donovani chaperone cyclophilin 40 (LdCyP40) for infection. Targeted replacement of LdCyP40 had no effect on parasite viability, axenic amastigote differentiation, and resistance to various forms of environmental stress in culture, suggesting important functional redundancy to other parasite chaperones. However, ultrastructural analyses and video microscopy of cyp40-/- promastigotes uncovered important defects in cell shape, organization of the subpellicular tubulin network and motility at stationary growth phase. More importantly, cyp40-/- parasites were unable to establish intracellular infection in murine macrophages and were eliminated during the first 24 h post infection. Surprisingly, cyp40-/- infectivity was restored in complemented parasites expressing a CyP40 mutant of the unique S274 phosphorylation site. Together our data reveal non-redundant CyP40 functions in parasite cytoskeletal remodelling relevant for the development of infectious parasites in vitro independent of its phosphorylation status, and provide a framework for the genetic analysis of Leishmania-specific phosphorylation sites and their role in regulating parasite protein function.

Effects of praziquantel and sanguinarine on expression of immune genes and susceptibility to Aeromonas hydrophila in goldfish (Carassius auratus) infected with Dactylogyrus intermedius

Praziquantel and sanguinarine have been demonstrated positive therapeutic effects on monogenean Dactylogyrus intermedius; however, few studies have considered the post impacts of these antiparasitic chemicals on host after repelling the parasites. The changes of expression of selected immune genes (CCL-1, CXCL-8, IL-1β-1, IL-1β-2, TNFα-1, TNFα-2 and TGF-β) in gill, kidney and spleen and bacterial loads of Aeromonas hydrophila in gill, kidney, spleen and liver following bath administration of these antiparasitic chemicals were evaluated. The results showed that praziquantel and sanguinarine up-regulated to varying degrees of CXCL-8, IL-1β-1, IL-1β-2, TNFα-1 and TNFα-2 in gill, kidney and spleen. They both decreased the CCL-1 expression in gill while increased it in kidney and spleen. However, in all the tested tissues, the expression of TGF-β decreased in praziquantel treated goldfish whereas that increased in sanguinarine treated goldfish. The A. hydrophila challenge test showed that the praziquantel treatment enhanced the susceptibility to A. hydrophila while sanguinarine treatment decreased the susceptibility, as compared with the non-treated group. Overall, the results indicate that bath administration of praziquantel and sanguinarine modulates the immune related genes in goldfish and these may, to some extent, affect their ability to resist bacterial pathogens.

Cyclosporin A--a review on fermentative production, downstream processing and pharmacological applications

In present times, the immunosuppressants have gained considerable importance in the world market. Cyclosporin A (CyA) is a cyclic undecapeptide with a variety of biological activities including immunosuppressive, anti-inflammatory, antifungal and antiparasitic properties. CyA is produced by various types of fermentation techniques using Tolypocladium inflatum. In the present review, we discuss the biosynthetic pathway, fermentative production, downstream processing and pharmacological activities of CyA.

Design and synthesis of conformationally constrained cyclophilin inhibitors showing a cyclosporin-A phenotype in C. elegans

Cyclophilin A (CypA) is a member of the immunophilin family of proteins and receptor for the immunosuppressant drug cyclosporin A (CsA). Here we describe the design and synthesis of a new class of small-molecule inhibitors for CypA that are based upon a dimedone template. Electrospray mass spectrometry is utilised as an initial screen to quantify the protein affinity of the ligands. Active inhibitors and fluorescently labelled derivatives are then used as chemical probes for investigating the biological role of cyclophilins in the nematode Caenorhabditis elegans.

Cyclosporin A treatment of Leishmania donovani reveals stage-specific functions of cyclophilins in parasite proliferation and viability

Background

Cyclosporin A (CsA) has important anti-microbial activity against parasites of the genus Leishmania, suggesting CsA-binding cyclophilins (CyPs) as potential drug targets. However, no information is available on the genetic diversity of this important protein family, and the mechanisms underlying the cytotoxic effects of CsA on intracellular amastigotes are only poorly understood. Here, we performed a first genome-wide analysis of Leishmania CyPs and investigated the effects of CsA on host-free L. donovani amastigotes in order to elucidate the relevance of these parasite proteins for drug development.

Methodology/Principal Findings

Multiple sequence alignment and cluster analysis identified 17 Leishmania CyPs with significant sequence differences to human CyPs, but with highly conserved functional residues implicated in PPIase function and CsA binding. CsA treatment of promastigotes resulted in a dose-dependent inhibition of cell growth with an IC50 between 15 and 20 µM as demonstrated by proliferation assay and cell cycle analysis. Scanning electron microscopy revealed striking morphological changes in CsA treated promastigotes reminiscent to developing amastigotes, suggesting a role for parasite CyPs in Leishmania differentiation. In contrast to promastigotes, CsA was highly toxic to amastigotes with an IC50 between 5 and 10 µM, revealing for the first time a direct lethal effect of CsA on the pathogenic mammalian stage linked to parasite thermotolerance, independent from host CyPs. Structural modeling, enrichment of CsA-binding proteins from parasite extracts by FPLC, and PPIase activity assays revealed direct interaction of the inhibitor with LmaCyP40, a bifunctional cyclophilin with potential co-chaperone function.

Conclusions/Significance

The evolutionary expansion of the Leishmania CyP protein family and the toxicity of CsA on host-free amastigotes suggest important roles of PPIases in parasite biology and implicate Leishmania CyPs in key processes relevant for parasite proliferation and viability. The requirement of Leishmania CyP functions for intracellular parasite survival and their substantial divergence form host CyPs defines these proteins as prime drug targets.

Visceral leishmanisasis, also known as Kala Azar, is caused by the protozoan parasite Leishmania donovani. The L. donovani infectious cycle comprises two developmental stages, a motile promastigote stage that proliferates inside the digestive tract of the phlebotomine insect host, and a non-motile amastigote stage that differentiates inside the macrophages of mammalian hosts. Intracellular parasite survival in mouse and macrophage infection assays has been shown to be strongly compromised in the presence of the inhibitor cyclosporin A (CsA), which binds to members of the cyclophilin (CyP) protein family. It has been suggested that the toxic effects of CsA on amastigotes occurs indirectly via host cyclophilins, which may be required for intracellular parasite development and growth. Using a host-free L. donovani culture system we revealed for the first time a direct and stage-specific effect of CsA on promastigote growth and amastigote viability. We provided evidence that parasite killing occurs through a heat sensitivity mechanism likely due to direct inhibition of the co-chaperone cyclophilin 40. Our data allow important new insights into the function of the Leishmania CyP protein family in differentiation, growth, and intracellular survival, and define this class of molecules as important drug targets.

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.

Protein Ser/Thr phosphatases of parasitic protozoa

Protein phosphorylation is an important mechanism implicated in physiology of any organism, including parasitic protozoa. Enzymes that control protein phosphorylation (kinases and phosphatases) are considered promising targets for drug development. This review attempts to provide the first account of the current understanding of the structure, regulation and biological functions of protein Ser/Thr phosphatases in unicellular parasites. We have examined the complements of phosphatases ("phosphatomes") of the PPP and PPM families in several species of Apicomplexa (including malaria parasite Plasmodium), as well as Giardia lamblia, Entamoeba histolytica, Trichomonas vaginalis and a microsporidium Encephalitozoon cuniculi. Apicomplexans have homologues (in most cases represented by single isoforms) of all human PPP subfamilies. Some apicomplexan PPP phosphatases have no orthologues in their vertebrate hosts, including a previously unrecognised group of pseudo-phosphatases with putative Ca(2+)-binding domains, which we designate as EFPP. We also describe the presence of previously undetected Zn finger motifs in PPEF phosphatases from kinetoplastids, and a likely case of convergent evolution of tetratricopeptide repeat domain-containing phosphatases in G. lamblia. Among the parasites examined, E. cuniculi has the smallest Ser/Thr phosphatome (5 PPP and no PPM), while T. vaginalis shows the largest expansion of the PPP family (169 predicted phosphatases). Most protozoan PPM phosphatases cluster separately from human sequences. The structural peculiarities or absence of human orthologues of a number of protozoan protein Ser/Thr phosphatases makes them potentially suitable targets for chemotherapy and thus warrants their functional assessment.

Functional analysis of Leishmania major cyclophilin

A potent immunosuppressive drug cyclosporin A (CsA) is known to inhibit human cell infection by the pathogenic protozoan parasite Leishmania major both in vitro and in vivo. The proposed mechanism of action involves CsA binding to Leishmania major-expressed cyclophilin and subsequent down-regulation of signaling events necessary for establishing productive infection. Recently, we identified a ubiquitously expressed membrane protein, CD147, as a signaling receptor for extracellular cyclophilins in mammalian cells. Here we demonstrate that, while being enzymatically active, the Leishmania cyclophilin, unlike its human homologue, does not interact with CD147 on the cell surface of target cells. CD147 facilitates neither Leishmania binding nor infection. Primary structure and biochemical analyses revealed that the parasite's cyclophilin is defective in heparan binding, an event required for signaling interaction between CD147 and human cyclophilin. When the heparan-binding motif was reconstituted in Leishmania cyclophilin, it regained the CD147-dependent signaling activity. These results underscore a critical role of cyclophilin-heparan interactions in CD147-mediated signaling events and argue against the role of Leishmania cyclophilin in parasite binding to target cells.

The Three-dimensional Structure of Two Redox States of Cyclophilin A from Schistosoma mansoni

Treatment of schistosomiasis, a widespread human parasitic disease caused by the helminth parasites of the genus Schistosoma, relies mainly on one chemotherapeutic agent, praziquantel, although several other compounds exert anti-parasitic effects. One such compound is the immunosuppressant cyclosporin A, which has been shown to significantly diminish worm burden in mice infected with Schistosoma mansoni. Given the well established interaction between cyclosporin A and the cyclophilin superfamily of peptidylprolyl cis-trans isomerases, we solved the structure of cyclophilin A from S. mansoni (SmCypA) by x-ray crystallography in the reduced and oxidized states at 1.5 and 1.8 A of resolution, respectively. Oxidized SmCypA contains a disulfide bridge between two C-terminal cysteines (Cys-122 and Cys-126). This is the first example of a cyclophilin containing this disulfide bridge. Parallel functional studies suggest a mechanism for regulation of SmCypA activity via oxidation of its thiol groups; in fact, whereas oxidized SmCypA is inactive, reduced SmCypA is an efficient isomerase active at nanomolar levels with a k(cat)/K(m) of 1.1 x 10(7) M(-1) s(-1), and it is inhibited by cyclosporin A (IC(50) of 14 +/- 4 nM). The lack of conservation of this cysteine couple within the CypA superfamily, their close proximity to the active site, and the importance of thiol groups for peptidyl-prolyl cis-trans isomerase activity render this structural feature a challenge for the development of alternative and more effective anti-schistosomiasis inhibitors and may in addition imply an alternative function of SmCypA in the schistosome.

Enzymes: An integrated view of structure, dynamics and function

Microbes utilize enzymes to perform a variety of functions. Enzymes are biocatalysts working as highly efficient machines at the molecular level. In the past, enzymes have been viewed as static entities and their function has been explained on the basis of direct structural interactions between the enzyme and the substrate. A variety of experimental and computational techniques, however, continue to reveal that proteins are dynamically active machines, with various parts exhibiting internal motions at a wide range of time-scales. Increasing evidence also indicates that these internal protein motions play a role in promoting protein function such as enzyme catalysis. Moreover, the thermodynamical fluctuations of the solvent, surrounding the protein, have an impact on internal protein motions and, therefore, on enzyme function. In this review, we describe recent biochemical and theoretical investigations of internal protein dynamics linked to enzyme catalysis. In the enzyme cyclophilin A, investigations have lead to the discovery of a network of protein vibrations promoting catalysis. Cyclophilin A catalyzes peptidyl-prolyl cis/trans isomerization in a variety of peptide and protein substrates. Recent studies of cyclophilin A are discussed in detail and other enzymes (dihydrofolate reductase and liver alcohol dehydrogenase) where similar discoveries have been reported are also briefly discussed. The detailed characterization of the discovered networks indicates that protein dynamics plays a role in rate-enhancement achieved by enzymes. An integrated view of enzyme structure, dynamics and function have wide implications in understanding allosteric and co-operative effects, as well as protein engineering of more efficient enzymes and novel drug design.

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.

The effect of immunosuppression with Cyclosporin A on the development of sheep scab

The present study confirms that following infection with the ectoparasitic sheep scab mite, Psoroptes ovis, there is a rapid (within 24 h) inflammatory influx of eosinophils and apoptosis of the keratinocytes at the site of infection. In order to investigate whether these inflammatory reactions are important in the maintenance of mite infection, a group of animals were treated daily after the establishment of infection with the potent anti-inflammatory drug, Cyclosporin A. The course of infection was monitored by determining the lesion area and mite numbers, systemic antibody and blood eosinophils, as well as the inflammatory cells and T cell sub-populations within the lesion throughout the 6-week duration of the experiment. These parameters were compared with those in a similar infected control (non-treated) group. In control infected animals, the lesion area and mite numbers increased steadily throughout the 6-week period. In contrast, lesion area and mite numbers were severely depressed in the group which received Cyclosporin A. Local and systemic eosinophils, and systemic antibody were also significantly reduced in the drug treated animals, compared to controls. Surprisingly however, the number of lesional pan T cells, T helper cells, gammadeltaT cells and dendritic cells in Cyclosporin A treated animals were either the same, or significantly (P < 0.05) enhanced when compared to the control infected animals at the termination of the experiment. The results will be discussed in terms of the role of the dermal inflammatory response in the establishment and maintenance of the sheep scab mite.

Cyclophilin nomenclature problems, or, 'a visit from the sequence police'

Why is agreement on one particular name for each gene important? As one genome after another becomes sequenced, it is imperative to consider the complexity of genes, genetic architecture, gene expression, gene-gene and gene-product interactions and evolutionary relatedness across species. To agree on a particular gene name not only makes one's own research easier, it aids automated text-mining algorithms and search engines, which are increasingly employed to find relationships in the millions of abstracts in the medical research literature and sequence databases. A common nomenclature system will also be helpful to the present generation, as well as future generations, of graduate students and postdoctoral fellows who are about to enter genomics research. In this paper, the authors present some problems that arose when two separate research communities decided to choose the same root, CYP, for naming their gene families. They then offer a logical solution, by renaming the cyclophilin genes with a common root, such a cyn- in Caenorhabditis and CYN- in mammals (Cyn in mouse), and using evolutionary divergence to cluster genes of the highest level of relatedness.

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.

Efeitos da ciclosporina A e betametasona na toxocaríase murina experimental

Estudou-se o efeito de ciclosporina A ou betametasona em camundongos experimentalmente infectados por larvas de Toxocara canis administrados 15 dias antes ou 45 dias após infecção por esse ascarídeo. Nos animais infectados determinou-se a cinética da resposta humoral por IgG 60 e 90 dias após infecção por meio de pesquisa de anticorpos anti-Toxocara, utilizando teste imunoenzimático, em amostras de sangue obtidas por punção do plexo orbitário. No 90º dia após a infecção todos os animais sobreviventes foram sacrificados e submetidos a digestão ácida da carcaça, pulmões, fígado e cérebro para recuperação de larvas de Toxocara canis encistadas nesses órgãos. Observou-se retardo na produção de anticorpos IgG anti-Toxocara nos animais tratados com ciclosporina A ou betametasona 15 dias antes da infecção, além de aumento significativo na quantidade de larvas de Toxocara canis recuperadas no grupo de animais que foi tratado com ciclosporina A 15 dias antes da infecção pelo ascarídeo.

Enzymes involved in the biogenesis of the nematode cuticle

Nematodes include species that are significant parasites of man, his domestic animals and crops, and cause chronic debilitating diseases in the developing world; such as lymphatic filariasis and river blindness caused by filarial species. Around one third of the World's population harbour parasitic nematodes; no vaccines exist for prevention of infection, limited effective drugs are available and drug resistance is an ever-increasing problem. A critical structure of the nematode is the protective cuticle, a collagen-rich extracellular matrix (ECM) that forms the exoskeleton, and is critical for viability. This resilient structure is synthesized sequentially five times during nematode development and offers protection from the environment, including the hosts' immune response. The detailed characterization of this complex structure; it's components, and the means by which they are synthesized, modified, processed and assembled will identify targets that may be exploited in the future control of parasitic nematodes. This review will focus on the nematode cuticle. This structure is predominantly composed of collagens, a class of proteins that are modified by a range of co- and post-translational modifications prior to assembly into higher order complexes or ECMs. The collagens and their associated enzymes have been comprehensively characterized in vertebrate systems and some of these studies will be addressed in this review. Conversely, the biosynthesis of this class of essential structural proteins has not been studied in such detail in the nematodes. As with all morphogenetic, functional and developmental studies in the Nematoda phylum, the free-living species Caenorhabditis elegans has proven to be invaluable in the characterization of the cuticle and the cuticle collagen gene family, and is now proving to be an excellent model in the study of cuticle collagen biosynthetic enzymes. This model system will be the main focus of this review.

Review of the properties and mechanisms of action of cyclosporine with an emphasis on dermatological therapy in dogs, cats and people

Cyclosporine is being increasingly used in veterinary medicine. It is a potent suppressor of T cell induction and proliferation, and has a wide variety of anti-inflammatory and antiproliferative effects, downregulating effects on antigen presentation, and variable effects on parasites. This paper reviews its properties and mechanisms of action with particular reference to its use in the treatment of dermatological conditions in dogs, cats and people.

Reversal of chloroquine resistance in Plasmodium falciparum using combinations of chemosensitizers

Research into chloroquine resistance reversal in Plasmodium falciparum has revealed a widespread range of functionally and structurally diverse chemosensitizers. However, nearly all of these chemosensitizers reverse resistance optimally only at concentrations that are toxic to humans. Verapamil, desipramine, and trifluoperazine were shown to potentiate chloroquine accumulation in a chloroquine-resistant (CQ(r)) strain of P. falciparum, while progesterone, ivermectin, and cyclosporin A were not shown to potentiate chloroquine accumulation. The simultaneous use of two or even three of these chemosensitizers at concentrations within their therapeutic ranges in humans displayed an additive effect in potentiating chloroquine accumulation in the CQ(r) strain. The levels of resistance reversal achieved with these multiple combinations were comparable to those achieved with high concentrations of the single agents used to enhance the activity of chloroquine. No chemosensitizer, whether used singly or in combination, potentiated any change in chloroquine accumulation or a shift in the 50% inhibitory concentration for the chloroquine-sensitive strain. The use of combinations of chemosensitizers at concentrations not toxic to humans could effectively reverse chloroquine resistance without the marked toxicity from the use of a single agent at high concentrations. This cocktail of chemosensitizers may serve as a viable treatment to restore the efficacy of chloroquine in patients with malaria.

Lack of abundance of cytoplasmic cyclosporin A-binding protein renders free-living Leishmania donovani resistant to cyclosporin A

The majority of the effects of cyclosporin A (CsA) on cells is caused by the inhibition of phosphatase activity of calcineurin (CN) by the cyclophilin A (CyPA)-CsA complex formed in the cytoplasm. Although CsA inhibits the proliferation of a large number of parasites, not all are susceptible. The presence of structurally altered CyPA with lower affinity for CsA had been suggested to be the cause of resistance. We report here the identification and cloning of a high affinity CsA-binding protein (LdCyP) from Leishmania donovani, a trypanosomatid parasite that is naturally resistant to CsA. The translated LdCyP consists of 187 amino acids with a cleavable 21-amino acid hydrophobic NH(2)-terminal extension. Modeling studies confirmed that all the residues of human CyPs responsible for interaction with CsA are sequentially and conformationally conserved in LdCyP. The purified recombinant protein displayed biochemical parameters comparable to human CyPs. Reverse transcription-polymerase chain reaction analysis confirmed that LdCyP was abundantly expressed. Immunoblot experiments and direct CsA binding studies revealed that LdCyP located in the subcellular organelles constituted the bulk of the CsA binding activity present in L. donovani, whereas the level of binding activity in the cytosol was conspicuously low. CsA selectively facilitated the secretion of LdCyP in the culture medium. Based on these results, it is concluded that the insensitivity of L. donovani to CsA is probably due to the paucity of CsA binding activity in the cytoplasm of the parasite. We suggest that LdCyP, located in the secretory pathway, may function as a chaperone by binding to membrane proteins rather than as the mediator of CN inhibition.

Emerging parasite zoonoses: the role of host-parasite relationship

Human-parasite relationships have played an essential role in the emergence or re-emergence of some parasitic diseases. These interactions are due to numerous causes. Some are linked to humans (immunodeficiencies due to AIDS among other causes, treatments, nosocomial contaminations, genetic predisposition), others concern the parasite (particular genotypes having modified their parasitic specificity). Several of these causes were predominant in the emergence of parasitoses such as cryptosporidiasis, microsporidioses or, to a certain point, pneumocystosis, the transmission of which has become zoonotic or even anthroponotic, inter-human. Re-emergent diseases (toxoplasmosis, leishmaniasis, giardiasis, strongyloidiasis, scabies) had already been described in human pathology, but their frequency or symptomatology have been drastically modified. In this case also, the unbalanced host-parasite relationship is largely responsible but it can not be dissociated from other causes, especially environmental and nutritional.

Identification of potential vaccine and drug target candidates by expressed sequence tag analysis and immunoscreening of Onchocerca volvulus larval cDNA libraries

The search for appropriate vaccine candidates and drug targets against onchocerciasis has so far been confronted with several limitations due to the unavailability of biological material, appropriate molecular resources, and knowledge of the parasite biology. To identify targets for vaccine or chemotherapy development we have undertaken two approaches. First, cDNA expression libraries were constructed from life cycle stages that are critical for establishment of Onchocerca volvulus infection, the third-stage larvae (L3) and the molting L3. A gene discovery effort was then initiated by random expressed sequence tag analysis of 5,506 cDNA clones. Cluster analyses showed that many of the transcripts were up-regulated and/or stage specific in either one or both of the cDNA libraries when compared to the microfilariae, L2, and both adult stages of the parasite. Homology searches against the GenBank database facilitated the identification of several genes of interest, such as proteinases, proteinase inhibitors, antioxidant or detoxification enzymes, and neurotransmitter receptors, as well as structural and housekeeping genes. Other O. volvulus genes showed homology only to predicted genes from the free-living nematode Caenorhabditis elegans or were entirely novel. Some of the novel proteins contain potential secretory leaders. Secondly, by immunoscreening the molting L3 cDNA library with a pool of human sera from putatively immune individuals, we identified six novel immunogenic proteins that otherwise would not have been identified as potential vaccinogens using the gene discovery effort. This study lays a solid foundation for a better understanding of the biology of O. volvulus as well as for the identification of novel targets for filaricidal agents and/or vaccines against onchocerciasis based on immunological and rational hypothesis-driven research.

Biochemical and structural characterization of a divergent loop cyclophilin from Caenorhabditis elegans

Cyclophilin 3 (CYP-3) is one of the most abundantly expressed cyclophilin isoforms in the free living nematode Caenorhabditis elegans. The detailed post-embryonic expression pattern of the cyp-3 transcript is unusual, peaking during early larval development. The spatial expression pattern was examined via reporter gene analysis demonstrating that the cyp-3 transcript is exclusively expressed in the single anterior excretory cell. Recombinant cyclophilin 3 has been purified, crystallized and solved to a resolution of 1.8 A. The peptidyl-prolyl isomerase activity of CYP-3 has been characterized against the substrate N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide, and gives a k(cat)/K(m) value of 2.4 x 10(6) M(-1) s(-1). The immunosuppressive drug cyclosporin A binds and inhibits CYP-3 with an IC(50) value of 16 nM, comparable with the range of values found for human cyclophilin A. The x-ray structure shows that the overall fold and active site geometry is similar to other cyclophilin structures. There are however a number of distinctive features, and we use this structure and amino acid sequence alignment analysis to identify a subgroup of "divergent-loop cyclophilins". This subgroup has a number of uniquely conserved features: an additional loop between residues 48 and 54 (KSGKPLH); two cysteine residues (Cys(40) and Cys(168)) that are in close proximity but remain in the unoxidized form, and two other conserved residues, His(54) and Glu(83). We suggest that these features are functionally important for the role played by this class of cyclophilins during cellular responses to stress caused by changes in the redox environment or by up-regulation of cellular activity. This study represents a detailed biological, biochemical, and structural characterization of a single cyclophilin isoform in the model organism Caenorhabditis elegans.

Identification of NF-AT-like transcription factor in Schistosoma mansoni: its possible involvement in the antiparasitic action of cyclosporin A

Cyclosporin A (CsA) has been found to exert potent anti-parasite activity against a wide range of protozoan and helminth parasites. In schistosomes, evidence has been accumulated to propose that the drug damages parasites by mechanisms independent of its immunosuppressive properties. Moreover, the absence of correlation between anti-schistosomal properties and inhibition of peptidyl-prolyl cis-trans isomerase activity of cyclophilins (CsA receptors) for various drug analogs, argued against a direct implication of cyclophilins in the lethal effect of CsA. We describe, in S. mansoni, the existence of NF-AT-like transcription factors, a protein family already characterized by its sensitivity to CsA. The observation that CsA treatment of S. mansoni larvae inhibited the expression of the Sm28GST protein and the characterization of a functional NF-AT-like site in the gene encoding this protein, provide new insights in the understanding of the antischistosomal effect of CsA. Our results also support the hypothesis that the regulatory function of NF-AT-like proteins might be responsible for parasite development and survival in the host and open new perspectives in studies of helminth biology.

Mucosal mast cell responses and release of mast cell protease-I in infections of mice with Hymenolepis diminuta and H. microstoma: modulation by cyclosporin A

The dynamics of intestinal mucosal mast cells and the major mucosal mast cell protease were followed during the course of laboratory infections of mice with Hymenolepis diminuta and H. microstoma. The effects of the drug cyclosporin A (CsA), which is both immunosuppressive and selectively anthelmintic depending upon dose regime, were determined. In H. diminuta infections worm expulsion occurred around day 9 and coincided with peak mastocytosis and peak mMCP-I concentrations in tissues and serum. Immunosuppressive treatment with CsA prevented worm expulsion, permitting some individuals to reach maturity, and abrogated mast cell proliferation and mMCP-I production and release. By contrast, H. microstoma infections persisted for 64 days in spite of a considerable mastocyosis in both intestine and bile duct tissues accompanied by a high level of mMCP-I in tissues and serum. A subimmunosuppressive regime of CsA had only limited effects on worms and mast cell numbers and activity. Together these data shed light on the variable mast cell response to gastrointestinal infections and on the potential significance of parasite location in evasion of mast cell action. Use of CsA reveals the contributions of both T cell-dependent mechanisms, including mast cell proliferation and activation, and T cell-independent events in regulating intestinal helminth infections.

Crystal structure of the cyclophilin-like domain from the parasitic nematode Brugia malayi

Cyclophilins are a family of proteins that exhibit peptidyl-prolyl cis-trans isomerase activity and bind the immunosuppressive agent cyclosporin A (CsA). Brugia malayi is a filarial nematode parasite of humans, for which a cyclophilin-like domain was identified at the N-terminal of a protein containing 843 amino acid residues. There are two differences in sequence in the highly conserved CsA binding site: A histidine and a lysine replace a tryptophan and an alanine, respectively. The crystal structure of this domain has been determined by the molecular replacement method and refined to an R-factor of 16.9% at 2.15 A resolution. The overall structure is similar to other cyclophilins; however, major differences occur in two loops. Comparison of the CsA binding site of this domain with members of the cyclophilin family shows significant structural differences, which can account for the reduced sensitivity of the Brugia malayi protein to inhibition by CsA.

Immunosuppressive and antiparasitic effects of cyclosporin A on Hymenolepis nana infection in mice

The effect of cyclosporin A, which is known to act both as immunosuppressant and as an antiparasitic drug in many host-parasite systems, was examined in a mouse-Hymenolepis nana system. When BDF1 mice were injected s.c. with cyclosporin A (100 mg kg-1 day-1) every 48 h from 11 days p.i. with eggs, expulsion of the adult worms from the intestines of mice was prevented completely until at least 30 days p.i. Worm burden, dry weight and the number of gravid proglottids were not significantly reduced. By contrast, in untreated mice most of the worms were eliminated by 19 days p.i. The drug also completely abolished acquired resistance to a challenge infection with eggs when mice were injected s.c. with cyclosporin A (100 mg kg-1 day-1) around the time of challenge infection (Days -2, -1, 0, 1 and 2 relative to challenge). Such immunosuppressive effects of cyclosporin A on worm expulsion and protective immunity to reinfection were similar to those of another immunosuppressant, cyclophosphamide. As for the antiparasitic action of cyclosporin A against H. nana, a smaller number of cysticercoids developed from eggs in mice given cyclosporin A (100 mg kg-1 day-1) for 5 days beginning 1 day before infection, than in untreated controls.

The X-ray structure of a divergent cyclophilin from the nematode parasite Brugia malayi

A structure of residues 1-177 of the cyclophilin domain of a large divergent cyclophilin from the filarial nematode parasite Brugia malayi has been crystallised and solved in two different crystal forms. The active site has a similar structure to that of human cyclophilin A. Two of the 13 residues important in forming the human cyclophilin A/cyclosporin A complex are altered in the B. malayi cyclophilin and explain the relatively poor inhibition of peptidyl prolyl isomerase activity by cyclosporin A.

Opportunistic properties of Nosema algerae (Microspora), a mosquito parasite, in immunocompromised mice

In the last ten years microsporidia have been recognized as opportunistic pathogens in AIDS patients. The sources of infection and the mechanisms of transmission of these organisms in humans are mostly uncertain. Transmission of invertebrate microsporidia to mammals is normally considered impossible, temperature being a limiting factor for development. Mice treated with cortisone acetate and with cyclosporin A, respectively, as well as athymic nice were injected intravenously, intranasally, perorally and subcutaneously with spores of Nosema algerae, a microsporidian species of culicine mosquitoes. No infection could be detected in tissue samples of cortisone acetate and cyclosporin A treated mice. However, the experimental inoculation of spores into the tail and foot of athymic mice caused severe infection in skeletal muscles and the connective tissue. In some tails, nerve tissue and bone marrow were also infected. Vegetative stages and spores were seen in direct contact to host cell cytoplasma. For the first time the prolonged and progressive development of an invertebrate microsporidium in a mammalian host is shown. The possibility of invertebrate microsporidia as a source of human microsporidiosis should now be taken into consideration.

The antiparasite effects of cyclosporin A: possible drug targets and clinical applications

1. The immunosuppressive drug cyclosporin A, and some of its nonimmunosuppressive derivatives, are potent inhibitors of a range of parasites of humans. 2. Cyclosporin A and the structurally unrelated immunosuppressant FK506 are known to act on T-lymphocytes as complexes with their binding proteins, cyclophilins and FKBPs, respectively. 3. Cyclophilins and FKBPs have been structurally identified in a number of parasites and, in some instances, are believed to play roles in the antiparasitic actions of these drugs. 4. Nonimmunosuppressive cyclosporins and FK506 derivatives may have clinical potential in certain parasitic diseases, especially malaria and schistosomiasis, and identification of the targets of these drugs in parasites may lead to development of novel chemotherapeutic agents.

Cloning and biochemical characterization of the cyclophilin homologues from the free-living nematode Caenorhabditis elegans

Cyclosporin A (CsA) is the most widely used immunosuppressive agent, whose properties are exerted via an interaction with cyclophilin, resulting in down-regulation of signal-transduction events in the T-cell. Cyclophilin is identical with peptidylprolyl cis-trans isomerase (PPI; EC 5.2.1.8), an enzyme which catalyses the isomerization between the two proline conformations in proteins, thereby acting as a catalyst in protein-folding events. Several reports indicate that CsA has potent anti-parasitic activity, effective against both protozoan and helminth species. In order to understand the various biological roles that cyclophilins play we have initiated a study of these proteins in the genetically tractable nematode Caenorhabditis elegans. Here we describe the cloning and characterization of 11 cyclophilin genes (cyp-1 to -11) derived from this nematode; this is currently the greatest number of isoforms described in a single species. Southern blotting and physical mapping indicated that these genes are dispersed throughout the nematode genome. A high degree of conservation exists between several isoforms, which also share characteristics with the ubiquitous isoforms previously described. The remaining isoforms are divergent, having altered CsA-binding domains and additional non-cyclophilin domains, which may impart compartmental specificity. Ten of these isoforms have been expressed in Escherichia coli, and the resultant fusion proteins have been examined biochemically for PPI activity, which they all possess. Isomerase activity is highest in the conserved and lowest in divergent isoforms, perhaps indicating a more specific substrate for the latter. Analysis of the C. elegans cyp genes will provide answers as to the roles played by cyclophilins in protein folding and signal transduction.

Hymenolepis diminuta and H. microstoma: uptake of cyclosporin A and drug binding to parasite cyclophilins

Cyclosporin A (CsA) acts as a powerful immunosuppressant through its binding to the cytosolic isomerase, cyclophilin (CyP), forming a complex which inhibits the phosphatase activity of calcineurin. The drug is also selectively anti-parasitic but its mode of action remains unknown. The mouse tapeworm, Hymenolepis microstoma is sensitive to CsA, but the rat tapeworm, H. diminuta is not susceptible either in rats, mice or in vitro. Using these two tapeworm models, the uptake and binding of CsA were examined in relation to parasite cyclophilins. Uptake and compartmentalization of the drug were markedly different in the two species: H. microstoma takes up more drug than does H. diminuta and sequesters more drug into intracellular compartments. Characterization of cyclophilins using both CsA binding and isomerase activity assays reveals that H. microstoma possesses two cyclophilin isoforms (M(r) 17,700 and 21,400) with isomerase activity that is inhibited by CsA. using identical assays, we have been unable to demonstrate CsA-binding proteins or CsA-sensitive isomerase activity in H. diminuta. These data suggest that the anthelmintic action of CsA relates in some way to the presence and function of parasite cyclophilins.

Parasite cyclophilins and antiparasite activity of cyclosporin A

Cyclosporin A (CsA) was initially developed as an immunosuppressive drug. In the past several years, it has been shown to possess antiparasite activity independent of the immune system. It is not known how the drug exerts these antiparasite effects, or why it is stage and/or species specific. The answers may lie in the enzymatic function of cyclophilins. The cyclophilins are a growing family of proteins that exhibit peptidyl-prolyl cis-trans isomerase (PPiase) activity and bid CsA to varying degrees. PPiases have been shown to play a role in the folding of many essential proteins. Antony Page, Sanjay Kumar and Clotilde Carlow here review parasite cyclophilins and their association with CsA. The possible biological function of parasite cyclophilins and their potential role in future drug discovery are also discussed.

Clethrionomys glareolus, but not Apodemus flavicollis, acquires resistance to Ixodes ricinus L., the main European vector of Borrelia burgdorferi

The European rodents Clethrionomys glareolus (bank vole) and Apodemus flavicollis (yellow-necked-mouse) are important hosts of the tick species Ixodes ricinus, the main European vector of Borrelia burgdorferi. We have addressed the question whether or not these tick hosts develop resistance to I. ricinus larvae. C. glareolus and A. flavicollis were exposed to 40 I. ricinus larvae for five consecutive times at two week intervals. Resistance was tested by the following parameters: percentage of ticks fully engorged, time of attachment, engorgement index, percentage of recovered ticks and proportion of larvae moulting to nymphs. Repeated infestation of C. glareolus resulted in progressive and significant reductions in the percentage of fully engorged ticks, the time of attachment of partially engorged ticks, the scutal index of partially engorged ticks and the moulting success. In contrast, repeatedly infested A. flavicollis did not acquire resistance to larval I. ricinus. Effects of resistance in C. glareolus could be partially disrupted by treatment with the immunosuppressive agent, cyclosporin A (CsA), indicating that T helper cells participate in the immune responses to tick bites. The data suggest that acquired immunity to I. ricinus larvae in C. glareolus is a density-dependent factor regulating natural tick burdens and that it may have an impact on the transmission cycle of B. burgdorferi in Central Europe.