Vesicles as carriers of virulence factors in parasitic protozoan diseases

Different types of shed vesicles as, for example, exosomes, plasma-membrane-derived vesicles or microparticles, are the focus of intense research in view of their potential role in cell cell communication and under the perspective that they might be good tools for immunotherapy, vaccination or diagnostic purposes. This review discusses ways employed by pathogenic trypanosomatids to interact with the host by shedding vesicles that contain molecules important for the establishment of infection, as opposed to previous beliefs considering them as a waste of cellular metabolism. Trypanosomatids are compared with Apicomplexa, which circulate parasite antigens bound to vesicles shed by host cells. The knowledge of the origin and chemical composition of these different vesicles might lead to the understanding of the mechanisms that determine their biological function. (C) 2012 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.

Leishmania amazonensis Arginase Compartmentalization in the Glycosome Is Important for Parasite Infectivity

In Leishmania, de novo polyamine synthesis is initiated by the cleavage of L-arginine to urea and L-ornithine by the action of arginase (ARG, E.C. 3.5.3.1). Previous studies in L. major and L. mexicana showed that ARG is essential for in vitro growth in the absence of polyamines and needed for full infectivity in animal infections. The ARG protein is normally found within the parasite glycosome, and here we examined whether this localization is required for survival and infectivity. First, the localization of L. amazonensis ARG in the glycosome was confirmed in both the promastigote and amastigote stages. As in other species, arg(-) L. amazonensis required putrescine for growth and presented an attenuated infectivity. Restoration of a wild type ARG to the arg(-) mutant restored ARG expression, growth and infectivity. In contrast, restoration of a cytosol-targeted ARG lacking the glycosomal SKL targeting sequence (arg Delta SKL) restored growth but failed to restore infectivity. Further study showed that the ARG Delta SKL protein was found in the cytosol as expected, but at very low levels. Our results indicate that the proper compartmentalization of L. amazonensis arginase in the glycosome is important for enzyme activity and optimal infectivity. Our conjecture is that parasite arginase participates in a complex equilibrium that defines the fate of L-arginine and that its proper subcellular location may be essential for this physiological orchestration.

Horizontal gene transfer confers fermentative metabolism in the respiratory-deficient plant trypanosomatid Phytomonas serpens

Among trypanosomatids, the genus Phytomonas is the only one specifically adapted to infect plants. These hosts provide a particular habitat with a plentiful supply of carbohydrates. Phytomonas sp. lacks a cytochrome-mediated respiratory chain and Krebs cycle, and ATP production relies predominantly on glycolysis. We have characterised the complete gene encoding a putative pyruvate/indolepyruvate decarboxylase (PDC/IPDC) (548 amino acids) of P. serpens, that displays high amino acid sequence similarity with phytobacteria and Leishmania enzymes. No orthologous PDC/IPDC genes were found in Trypanosoma cruzi or T. brucei. Conservation of the PDC/IPDC gene sequence was verified in 14 Phytomonas isolates. A phylogenetic analysis shows that Phytomonas protein is robustly monophyletic with Leishmania spp. and C. fasciculata enzymes. In the trees this clade appears as a sister group of indolepyruvate decarboxylases of gamma-proteobacteria. This supports the proposition that a horizontal gene transfer event from a donor phytobacteria to a recipient ancestral trypanosome has occurred prior to the separation between Phytomonas. Leishmania and Crithidia. We have measured the PDC activity in P. serpens cell extracts. The enzyme has a Km value for pyruvate of 1.4 mM. The acquisition of a PDC, a key enzyme in alcoholic fermentation, explains earlier observations that ethanol is one of the major end-products of glucose catabolism under aerobic and anaerobic conditions. This represents an alternative and necessary route to reoxidise part of the NADH produced in the highly demanding glycolytic pathway and highlights the importance of this type of event in metabolic adaptation. (C) 2012 Elsevier B.V. All rights reserved.

IN VITRO TRYPANOCIDAL EVALUATION OF PINANE DERIVATIVES FROM ESSENTIAL OILS OF RIPE FRUITS FROM Schinus terebinthifolius RADDI (ANACARDIACEAE)

Essential oils of ripe fruits from Schinus terebinthifolius (Anacardiaceae), obtained using a pilot extractor and a Clevenger apparatus were chemically characterized. Due the high amount of (-)-alpha-pinene in both oils, this monoterpene was tested against the protozoan parasite Trypanosoma cruzi, showing a moderate potential (IC50 63.56 mu g/mL) when compared to benznidazole (IC50 43.14 mu g/mL). Otherwise, (-)-alpha-pinene oxide did not showed anti-trypanosomal activity (IC50 > 400 mu g/mL) while (-)-pinane showed an IC50 of 56.50 mu g/mL. The obtained results indicated that the epoxydation of a-pinene results to the loss of the anti-parasitic activity while its hydrogenation product, contributed slightly to the increased activity.

Antiparasitical chemotherapy in Chagas' disease cardiomyopathy: current evidence

Chronic chagasic cardiomyopathy affects 20% of Chagas disease patients. At present, Chagas disease chemotherapy uses nitrofurans, benznidazole (Rochagan (R), Rodanil (R), Roche) or nifurtimox (Lampit (R), Bayer). Treatment during acute and recent chronic phases in childhood effects 71.5% and 57.6%, respectively, of parasitological cure. However, in clinical trials during the late chronic phase, only 5.9% of parasitological cure were achieved. This review focuses on the benefit from aetiological treatment to avoid, stop or revert myocarditis. Divergent data gathered from clinical practice are not convincing to support prescription of aetiological treatment as routine for indeterminate and cardiac chronic patients.

Myocardial Chemokine Expression and Intensity of Myocarditis in Chagas Cardiomyopathy Are Controlled by Polymorphisms in CXCL9 and CXCL10

Background: Chronic Chagas cardiomyopathy (CCC), a life-threatening inflammatory dilated cardiomyopathy, affects 30% of the approximately 8 million patients infected by Trypanosoma cruzi. Even though the Th1 T cell-rich myocarditis plays a pivotal role in CCC pathogenesis, little is known about the factors controlling inflammatory cell migration to CCC myocardium. Methods and Results: Using confocal immunofluorescence and quantitative PCR, we studied cell surface staining and gene expression of the CXCR3, CCR4, CCR5, CCR7, CCR8 receptors and their chemokine ligands in myocardial samples from end-stage CCC patients. CCR5+, CXCR3+, CCR4+, CCL5+ and CXCL9+ mononuclear cells were observed in CCC myocardium. mRNA expression of the chemokines CCL5, CXCL9, CXCL10, CCL17, CCL19 and their receptors was upregulated in CCC myocardium. CXCL9 mRNA expression directly correlated with the intensity of myocarditis, as well as with mRNA expression of CXCR3, CCR4, CCR5, CCR7, CCR8 and their ligands. We also analyzed single-nucleotide polymorphisms for genes encoding the most highly expressed chemokines and receptors in a cohort of Chagas disease patients. CCC patients with ventricular dysfunction displayed reduced genotypic frequencies of CXCL9 rs10336 CC, CXCL10 rs3921 GG, and increased CCR5 rs1799988CC as compared to those without dysfunction. Significantly, myocardial samples from CCC patients carrying the CXCL9/CXCL10 genotypes associated to a lower risk displayed a 2-6 fold reduction in mRNA expression of CXCL9, CXCL10, and other chemokines and receptors, along with reduced intensity of myocarditis, as compared to those with other CXCL9/CXCL10 genotypes. Conclusions: Results may indicate that genotypes associated to reduced risk in closely linked CXCL9 and CXCL10 genes may modulate local expression of the chemokines themselves, and simultaneously affect myocardial expression of other key chemokines as well as intensity of myocarditis. Taken together our results may suggest that CXCL9 and CXCL10 are master regulators of myocardial inflammatory cell migration, perhaps affecting clinical progression to the life-threatening form of CCC.

Ubiquitin proteasome system and the atypical kinase PfPK7 are involved in melatonin signaling in Plasmodium falciparum

We previously reported that melatonin modulates the Plasmodium falciparum erythrocytic cycle by increasing schizont stage population as well as diminishing ring stage population. In addition, the importance of calcium and cAMP in melatonin signaling pathway in P. falciparum was also demonstrated. Nevertheless, the molecular effectors of the indoleamine signaling pathway remain elusive. We now demonstrate by real-time PCR that melatonin treatment up-regulates genes related to ubiquitin/proteasome system (UPS) components and that luzindole, a melatonin receptor antagonist, inhibits UPS transcription modulation. We also show that protein kinase PfPK7, a P. falciparum orphan kinase, plays a crucial role in the melatonin transduction pathway, since following melatonin treatment of P. falciparum parasites where pfpk7 gene is disrupted (pfpk7- parasites) (i) the ratio of asexual stages remain unchanged, (ii) the increase in cytoplasmatic calcium in response to melatonin was strongly diminished and (iii) up-regulation of UPS genes did not occur. The wild-type melatonin-induced alterations in cell cycle features, calcium rise and UPS gene transcription were restored by re-introduction of a functional copy of the pfpk7 gene in the pfpk7- parasites.

Leishmanicidal activity of an alkenylphenol from Piper malacophyllum is related to plasma membrane disruption

Leishmaniasis and Chagas disease are parasitic protozoan infections that affect the poorest population in the world, causing high mortality and morbidity. As a result of highly toxic and long-duration treatments, novel, safe and more efficacious drugs are essential. In this work, the methanol (MeOH) extract from the leaves of Piper malacophyllum (Piperaceae) was fractioned to afford one alkenylphenol, which was characterized as 4-[(3'E)-decenyl]phenol (gibbilimbol B) by spectroscopic methods. Anti-protozoan in vitro assays demonstrated for the first time that Leishmania (L.) infantum chagasi was susceptible to gibbilimbol B. with an in vitro EC50 of 23 mu g/mL against axenic promastigotes and an EC50 of 22 mu g/mL against intracellular amastigotes. Gibbilimbol B was also tested for anti-trypanosomal activity (Trypanosoma cruzi) and showed an EC50 value of 17 mu g/mL against trypomastigotes. To evaluate the cytotoxic parameters, this alkenylphenol was tested in vitro against NCTC cells, showing a CC50 of 59 mu g/mL and absent hemolytic activity at the highest concentration of 75 mu g/mL. Using the fluorescent probe SYTOX Green suggested that the alkenylphenol disrupted the Leishmania plasma membrane upon initial incubation. Further drug design studies aiming at derivatives could be a promising tool for the development of new therapeutic agents for leishmaniasis and Chagas disease. (C) 2012 Elsevier Inc. All rights reserved.

Fumarate hydratase isoforms of Leishmania major: Subcellular localization, structural and kinetic properties

Fumarate hydratases (FHs; EC 4.2.1.2) are enzymes that catalyze the reversible hydration of fumarate to S-malate. Parasitic protists that belong to the genus Leishmania and are responsible for a complex of vector-borne diseases named leishmaniases possess two genes that encode distinct putative FH enzymes. Genome sequence analysis of Leishmania major Friedlin reveals the existence of genes LmjF24.0320 and LmjF29.1960 encoding the putative enzymes LmFH-1 and LmFH-2, respectively. In the present work, the FH activity of both L. major enzymes has been confirmed. Circular dichroism studies suggest important differences in terms of secondary structure content when comparing LmFH isoforms and even larger differences when comparing them to the homologous human enzyme. CD melting experiments revealed that both LmFH isoforms are thermolabile enzymes. The catalytic efficiency under aerobic and anaerobic environments suggests that they are both highly sensitive to oxidation and damaged by oxygen. Intracellular localization studies located LmFH-1 in the mitochondrion, whereas LmFH-2 was found predominantly in the cytosol with possibly also some in glycosomes. The high degree of sequence conservation in different Leishmania species, together with the relevance of FH activity for the energy metabolism in these parasites suggest that FHs might be exploited as targets for broad-spectrum antileishmanial drugs. (c) 2012 Elsevier B.V. All rights reserved.

Solid Dispersion of Ursolic Acid in Gelucire 50/13: a Strategy to Enhance Drug Release and Trypanocidal Activity

Solid dispersions (SDs) are an approach to increasing the water solubility and bioavailability of lipophilic drugs such as ursolic acid (UA), a triterpenoid with trypanocidal activity. In this work, Gelucire 50/13, a surfactant compound with permeability-enhancing properties, and silicon dioxide, a drying adjuvant, were employed to produce SDs with UA. SDs and physical mixtures (PMs) in different drug/carrier ratios were characterized and compared using differential scanning calorimetry, hot stage microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), particle size, water solubility values, and dissolution profiles. Moreover, LLC-MK2 fibroblast cytotoxicity and trypanocidal activity evaluation were performed to determine the potential of SD as a strategy to improve UA efficacy against Chagas disease. The results demonstrated the conversion of UA from the crystalline to the amorphous state through XRD. FTIR experiments provided evidence of intermolecular interactions among the drug and carriers through carbonyl peak broadening in the SDs. These findings helped explain the enhancement of water solubility from 75.98 mu g/mL in PMs to 293.43 mu g/mL in SDs and the faster drug release into aqueous media compared with pure UA or PMs, which was maintained after 6 months at room temperature. Importantly, improved SD dissolution was accompanied by higher UA activity against trypomastigote forms of Trypanosoma cruzi, but not against mammalian fibroblasts, enhancing the potential of UA for Chagas disease treatment.

Structure- and Ligand-Based Structure-Activity Relationships for a Series of Inhibitors of Aldolase

Aldolase has emerged as a promising molecular target for the treatment of human African trypanosomiasis. Over the last years, due to the increasing number of patients infected with Trypanosoma brucei, there is an urgent need for new drugs to treat this neglected disease. In the present study, two-dimensional fragment-based quantitative-structure activity relationship (QSAR) models were generated for a series of inhibitors of aldolase. Through the application of leave-one-out and leave-many-out cross-validation procedures, significant correlation coefficients were obtained (r(2) = 0.98 and q(2) = 0.77) as an indication of the statistical internal and external consistency of the models. The best model was employed to predict pK(i) values for a series of test set compounds, and the predicted values were in good agreement with the experimental results, showing the power of the model for untested compounds. Moreover, structure-based molecular modeling studies were performed to investigate the binding mode of the inhibitors in the active site of the parasitic target enzyme. The structural and QSAR results provided useful molecular information for the design of new aldolase inhibitors within this structural class.

1,3-Azoles from ortho-naphthoquinones: Synthesis of aryl substituted imidazoles and oxazoles and their potent activity against Mycobacterium tuberculosis

Twenty-three naphthoimidazoles and six naphthoxazoles were synthesised and evaluated against susceptible and rifampicin- and isoniazid-resistant strains of Mycobacterium tuberculosis. Among all the compounds evaluated, fourteen presented MIC values in the range of 0.78 to 6.25 mu g/mL against susceptible and resistant strains of M. tuberculosis, Five structures were solved by X-ray crystallographic analysis. These substances are promising antimycobacterial prototypes. (C) 2012 Elsevier Ltd. All rights reserved.

Pathogen-Induced Proapoptotic Phenotype and High CD95 (Fas) Expression Accompany a Suboptimal CD8(+) T-Cell Response: Reversal by Adenoviral Vaccine

MHC class la-restricted CD8(+) T cells are important mediators of the adaptive immune response against infections caused by intracellular microorganisms. Whereas antigen-specific effector CD8(+) T cells can clear infection caused by intracellular pathogens, in some circumstances, the immune response is suboptimal and the microorganisms survive, causing host death or chronic infection. Here, we explored the cellular and molecular mechanisms that could explain why CD8(+) T-cell-mediated immunity during infection with the human protozoan parasite Trypanosoma cruzi is not optimal. For that purpose, we compared the CD8(+) T-cell mediated immune responses in mice infected with T. cruzi or vaccinated with a recombinant adenovirus expressing an immunodominant parasite antigen. Several functional and phenotypic characteristics of specific CD8(+) T cells overlapped. Among few exceptions was an accelerated expansion of the immune response in adenoviral vaccinated mice when compared to infected ones. Also, there was an upregulated expression of the apoptotic-signaling receptor CD95 on the surface of specific T cells from infected mice, which was not observed in the case of adenoviral-vaccinated mice. Most importantly, adenoviral vaccine provided at the time of infection significantly reduced the upregulation of CD95 expression and the proapoptotic phenotype of pathogen-specific CD8(+) cells expanded during infection. In parallel, infected adenovirus-vaccinated mice had a stronger CD8(+) T-cell mediated immune response and survived an otherwise lethal infection. We concluded that a suboptimal CD8(+) T-cell response is associated with an upregulation of CD95 expression and a proapoptotic phenotype. Both can be blocked by adenoviral vaccination.

Design and synthesis of new (E)-cinnamic N-acylhydrazones as potent antitrypanosomal agents

We report herein the synthesis and trypanocidal profile of new (E)-cinnamic N-acylhydrazones (NAHs) designed by exploiting molecular hybridization between the potent cruzain inhibitors (E)-1-(benzo[d] 11,3)dioxol-5-yl)-3-(4-bromophenyl)prop-2-en-1-one and (E)-3-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene)-7-methoxy-2-naphthohydrazide. These derivatives were evaluated against both amastigote and trypomastigote forms of Trypanosoma cruzi and lead us to identify two compounds that were approximately two times more active than the reference drug, benznidazole, and with good cytotoxic index. Although designed as cruzain inhibitors, the weak potency displayed by the best cinnamyl NAH derivatives indicated that another mechanism of action was likely responsible for their trypanocide action. (C) 2012 Elsevier Masson SAS. All rights reserved.

Characterization of anti-silencing factor 1 in Leishmania major

Anti-silencing factor 1 (ASF1) is a histone chaperone that contributes to the histone deposition during nucleosome assembly in newly replicated DNA. It is involved in chromatin disassembly, transcription activation and in the cellular response to DNA damage. In Leishmania major the ASF1 gene (LmASF1) is located in chromosome 20 and codes for a protein showing 67% of identity with the Trypanosoma brucei TbASF1a. Compared to orthologous proteins, LmASF1 conserves the main residues relevant for its various biological functions. To study ASF1 in Leishmania we generated a mutant overexpressing LmASF1 in L. major. We observed that the excess of LmASF1 impaired promastigotes growth rates and had no impact on cell cycle progress. Differently from yeast, ASF1 overproduction in Leishmania did not affect expression levels of genes located on telomeres, but led to an upregulation of proteins involved in chromatin remodelling and physiological stress, such as heat shock proteins, oxidoreductase activity and proteolysis. In addition, we observed that LmASF1 mutant is more susceptible to the DNA damaging agent, methyl methane sulphonate, than the control line. Therefore, our study suggests that ASF1 from Leishmania pertains to the chromatin remodelling machinery of the parasite and acts on its response to DNA damage.