Biological aspects of the Trypanosoma cruzi (Dm28c clone) intermediate form, between epimastigote and trypomastigote, obtained in modified liver infusion tryptose (LIT) medium

TcSR62, an RNA-binding protein, as a new potential target for anti-trypanocidal agents

Trypanosomatids are parasites of health importance that cause neglected diseases in humans and animals. Chagas' disease, caused by Trypanosoma cruzi, affects 6-7 millions of people worldwide, mostly in Latin America, most of whom do not have access to diagnosis or treatment. Currently, there are no available vaccines, and the antiparasitic drugs used for treatment are often toxic and ineffective for the chronic stage of infection. Therefore, exploration of new therapeutic targets is necessary and highlights the importance of identifying new therapeutic options for the treatment of this disease. Trypanosomatid genes are organized and expressed in a species-specific fashion and many of their regulatory factors remain to be explored, so proteins involved in the regulation of gene expression are interesting candidates as drug targets. Previously, we demonstrated that the TbRRM1 protein from T. brucei is an essential nuclear factor involved in Pol-II transcriptional regulation. TcSR62 is a TbRRM1 orthologous protein in T. cruzi, but little is known about its function. In this study, we used molecular modeling of the RNA-binding domains of the TcSR62 protein and computational molecular docking to identify TcSR62-specific drug candidates. We identified sorafenib tosylate (ST) as a compound with trypanocidal activity. Sorafenib tosylate showed promising half-maximal inhibitory concentration (IC50) for all parasite stages in vitro. Furthermore, overexpression of TcSR62 protein led to ST-resistant parasites, suggesting that the trypanocidal effect might be due to the inhibition of TcSR62 function. These results demonstrate that ST could be repurposed as a novel drug to treat Chagas' disease.

Discovery of 2-aminopyridine Derivatives with Antichagasic and Antileishmanial Activity Using Phenotypic Assays

Background:

Compounds previously studied as anticancer were screened against trypomastigotes to access the bioactivity. The epimastigote form of Trypanosoma cruzi Y strain and the promastigote form of Leishmania amazonensis and Leishmania infantum were used in this work.

Methods:

Cell-based assays were performed to access the bioactivity of the compounds using MTT and the flow cytometry methods.

Results:

Neq0438, Neq0474 and Neq0440 had the highest potency, with EC50 of 39 μM (L. amazonensis), 52 μM (T. cruzi) and 81 μM (T. cruzi), respectively. These molecules were inactive for Balb/C fibroblast cell line at concentrations above 250 μM, showing selectivity for the parasites.

Conclusion:

This is the first report that demonstrates antiparasitic activity for the 2-aminopyridine scaffold, with cross-activity against cancer cells.

Novel [1,2,3]triazolo[1,5-a]pyridine derivatives are trypanocidal by sterol biosynthesis pathway alteration

Aim: To study a new series of [1,2,3]triazolo[1,5-α]pyridine derivatives as trypanocidal agents because current antichagasic pharmacologic therapy is only partially effective. Materials & methods: The effect of the series upon Trypanosoma cruzi epimastigotes and murine macrophages viability, cell cycle, cell death and on the metabolites of the sterol biosynthesis pathway was measured; also, docking in 14α-demethylase was analyzed. Results: Compound 16 inhibits 14α-demethylase producing an imbalance in the cholesterol/ergosterol synthesis pathway, as suggested by a metabolic control and theoretical docking analysis. Consequently, it prevented cell proliferation, stopping the cellular cycle at the G2/M phase, inducing cell death. Conclusion: Although the exact cell death mechanism remained elusive, this series can be used for the further rational design of novel antiparasitic molecules.

Effective Tetradentate Compound Complexes against Leishmania spp. that Act on Critical Enzymatic Pathways of These Parasites

The spectrum and efficacy of available antileishmanial drugs is limited. In the present work we evaluated in vitro the antiproliferative activity of 11 compounds based on tetradentate polyamines compounds against three Leishmania species (L. braziliensis, L. donovani and L. infantum) and the possible mechanism of action. We identified six compounds (3, 5, 6, 7, 8 and 10) effective against all three Leishmania spp both on extracellular and intracellular forms. These six most active leishmanicidal compounds also prevent the infection of host cells. Nevertheless, only compound 7 is targeted against the Leishmania SOD. Meanwhile, on the glucose metabolism the tested compounds have a species-specific effect on Leishmania spp.: L. braziliensis was affected mainly by 10 and 8, L. donovani by 7, and L. infantum by 5 and 3. Finally, the cellular ultrastructure was mainly damaged by 11 in the three Leishmania spp. studied. These identified antileishmania candidates constitute a good alternative treatment and will be further studied.

Trypanosoma cruzi TcSMUG L-surface mucins promote development and infectivity in the triatomine vector Rhodnius prolixus

BACKGROUND

TcSMUG L products were recently identified as novel mucin-type glycoconjugates restricted to the surface of insect-dwelling epimastigote forms of Trypanosoma cruzi, the etiological agent of Chagas disease. The remarkable conservation of their predicted mature N-terminal region, which is exposed to the extracellular milieu, suggests that TcSMUG L products may be involved in structural and/or functional aspects of the interaction with the insect vector.

METHODOLOGY AND PRINCIPAL FINDINGS

Here, we investigated the putative roles of TcSMUG L mucins in both in vivo development and ex vivo attachment of epimastigotes to the luminal surface of the digestive tract of Rhodnius prolixus. Our results indicate that the exogenous addition of TcSMUG L N-terminal peptide, but not control T. cruzi mucin peptides, to the infected bloodmeal inhibited the development of parasites in R. prolixus in a dose-dependent manner. Pre-incubation of insect midguts with the TcSMUG L peptide impaired the ex vivo attachment of epimastigotes to the luminal surface epithelium, likely by competing out TcSMUG L binding sites on the luminal surface of the posterior midgut, as revealed by fluorescence microscopy.

CONCLUSION AND SIGNIFICANCE

Together, these observations indicate that TcSMUG L mucins are a determinant of both adhesion of T. cruzi epimastigotes to the posterior midgut epithelial cells of the triatomine, and the infection of the insect vector, R. prolixus.

Trypanosoma cruzi: effects of heat shock on ecto-ATPase activity

In this work, we demonstrate that Trypanosoma cruzi Y strain epimastigotes exhibit Mg2+-dependent ecto-ATPase activity that is stimulated by heat shock. When the epimastigotes were incubated at 37°C for 2h, the ecto-ATPase activity of the cells was 43.95±0.97 nmol Pi/h×10(7) cells, whereas the ecto-ATPase activity of cells that were not exposed to heat shock stress was 16.97±0.30 nmol Pi/h×10(7) cells. The ecto-ATPase activities of cells, that were exposed or not exposed to heat shock stress had approximately the same Km values (2.25±0.26 mM ATP and 1.55±0.23 mM ATP, respectively) and different Vmax values. The heat-shocked cells had higher Vmax values (54.38±3.07 nmol Pi/h×10(7) cells) than the cells that were not exposed to heat shock (19.38±1.76 nmol Pi/h×10(7) cells). We also observed that the ecto-phosphatase and ecto-5'nucleotidase activities of cells that had been incubated at 28°C or 37°C were the same. Interestingly, cycloheximide, an inhibitor of protein synthesis, suppressed the heat shock effect of ecto-ATPase activity on T. cruzi. The Mg2+-dependent ecto-ATPase activity from the Y strain (high virulence) was approximately 2-fold higher than that of Dm28c (a clone with low virulence). In addition, these two strains presented different responses to heat shock with regard to their ecto-ATPase activities; Y strain epimastigotes had a stimulation of 2.52-fold while the Dm28c strain had a 1.71-fold stimulation. In this context, the virulent trypomastigote form of T. cruzi, Dm28c, had an ecto-ATPase activity that was more than 7-fold higher (66.67±5.98 nmol Pi/h×10(7) cells) than that of the insect epimastigote forms (8.91±0.76 nmol Pi/h×10(7) cells). This difference increased to approximately 10-fold when both forms were subjected to heat shock stress (181.14±16.48 nmol Pi/h×10(7) cells for trypomastigotes and 16.71±1.17 nmol Pi/h×10(7) cells for epimastigotes at 37°C). The ecto-ATPase activity of a plasma membrane-enriched fraction obtained from T. cruzi epimastigotes was not increased by heat treatment, which suggested that cytoplasmic components had an influence on enzyme activation by heat shock stress.

The GTPase TcRjl of the human pathogen Trypanosoma cruzi is involved in the cell growth and differentiation

The protozoan parasite Trypanosoma cruzi, the etiological agent of Chagas Disease, undergoes through a complex life cycle where rounds of cell division and differentiation occur initially in the gut of triatominae vectors and, after transmission, inside of infected cells in vertebrate hosts. Members of the Ras superfamily of GTPases are molecular switches which play pivotal regulatory functions in cell growth and differentiation. We have previously described a novel GTPase in T. cruzi, TcRjl, which belongs to the RJL family of Ras-related GTP binding proteins. Here we show that most of TcRjl protein is found bound to GTP nucleotides and may be locked in this stage. In addition, we show that TcRjl is located close to the kinetoplast, in a region corresponding possibly to flagellar pocket of the parasite and the expression of a dominant-negative TcRjl construct (TcRjlS37N) displays a significative growth phenotype in reduced serum medium. Remarkably, overexpression of TcRjl inhibits differentiation of epimastigotes to trypomastigote forms and promotes the accumulation of intermediate differentiation stages. Our data suggest that TcRjl might play a role in the control of the parasite growth and differentiation.

Involvement of sulfated glycosaminoglycans on the development and attachment of Trypanosoma cruzi to the luminal midgut surface in the vector, Rhodnius prolixus

In the present study, we investigated the involvement of sulfated glycosaminoglycans in both the in vivo development and adhesion of T. cruzi epimastigotes to the luminal surface of the digestive tract of the insect vector, Rhodnius prolixus. Pre-incubation of T. cruzi, Dm 28c epimastigotes with heparin, chondroitin 4-sulfate, chondroitin 6-sulfate or protamine chloridrate inhibited in vitro attachment of parasites to the insect midgut. Enzymatic removal of heparan sulfate moieties by heparinase I or of chondroitin sulfate moieties by chondroitinase AC from the insect posterior midgut abolished epimastigote attachment in vitro. These treatments also reduced the labelling of anionic sites exposed at the luminal surface of the perimicrovillar membranes in the triatomine midgut epithelial cells. Inclusion of chondroitin 4-sulfate or chondroitin 6-sulfate and to a lesser extent, heparin, in the T. cruzi-infected bloodmeal inhibited the establishment of parasites in R. prolixus. These observations indicate that sulfated glycosaminoglycans are one of the determinants for both adhesion of the T. cruzi epimastigotes to the posterior midgut epithelial cells of the triatomine and the parasite infection in the insect vector, R. prolixus.

Improved method for in vitro secondary amastigogenesis of Trypanosoma cruzi: morphometrical and molecular analysis of intermediate developmental forms

Trypanosoma cruzi undergoes a biphasic life cycle that consists of four alternate developmental stages. In vitro conditions to obtain a synchronic transformation and efficient rates of pure intermediate forms (IFs), which are indispensable for further biochemical, biological, and molecular studies, have not been reported. In the present study, we established an improved method to obtain IFs from secondary amastigogenesis. During the transformation kinetics, we observed progressive decreases in the size of the parasite body, undulating membrane and flagellum that were concomitant with nucleus remodeling and kinetoplast displacement. In addition, a gradual reduction in parasite movement and acquisition of the amastigote-specific Ssp4 antigen were observed. Therefore, our results showed that the in vitro conditions used obtained large quantities of highly synchronous and pure IFs that were clearly distinguished by morphometrical and molecular analyses. Obtaining these IFs represents the first step towards an understanding of the molecular mechanisms involved in amastigogenesis.

Novel mitochondrial complex II isolated from Trypanosoma cruzi is composed of 12 peptides including a heterodimeric Ip subunit

Mitochondrial respiratory enzymes play a central role in energy production in aerobic organisms. They differentiated from the alpha-proteobacteria-derived ancestors by adding noncatalytic subunits. An exception is Complex II (succinate: ubiquinone reductase), which is composed of four alpha-proteobacteria-derived catalytic subunits (SDH1-SDH4). Complex II often plays a pivotal role in adaptation of parasites in host organisms and would be a potential target for new drugs. We purified Complex II from the parasitic protist Trypanosoma cruzi and obtained the unexpected result that it consists of six hydrophilic (SDH1, SDH2N, SDH2C, and SDH5-SDH7) and six hydrophobic (SDH3, SDH4, and SDH8-SDH11) nucleus-encoded subunits. Orthologous genes for each subunit were identified in Trypanosoma brucei and Leishmania major. Notably, the iron-sulfur subunit was heterodimeric; SDH2N and SDH2C contain the plant-type ferredoxin domain in the N-terminal half and the bacterial ferredoxin domain in the C-terminal half, respectively. Catalytic subunits (SDH1, SDH2N plus SDH2C, SDH3, and SDH4) contain all key residues for binding of dicarboxylates and quinones, but the enzyme showed the lower affinity for both substrates and inhibitors than mammalian enzymes. In addition, the enzyme binds protoheme IX, but SDH3 lacks a ligand histidine. These unusual features are unique in the Trypanosomatida and make their Complex II a target for new chemotherapeutic agents.