Changes in morphology and infectivity of cell culture-derived trypomastigotes of Trypanosoma cruzi

Experimental Trypanosoma cruzi Infection and Chagas Disease-A Word of Caution

The physician Carlos Chagas (1879-1934) described the protozoan parasite Trypanosoma cruzi and discovered a new illness named American trypanosomiases or Chagas disease (Chagas, 1909) [...].

Trypanosoma cruzi pathogenicity involves virulence factor expression and upregulation of bioenergetic and biosynthetic pathways

The molecular repertoire of Trypanosoma cruzi effects its virulence and impacts the clinical course of the resulting Chagas disease. This study aimed to determine the mechanism underlying the pathogenicity of T. cruzi. Two T. cruzi cell lines (C8C3hvir and C8C3lvir), obtained from the clone H510 C8C3 and exhibiting different virulence phenotypes, were used to evaluate the parasite's infectivity in mice. The organ parasite load was analysed by qPCR. The proteomes of both T. cruzi cell lines were compared using nLC-MS/MS. Cruzipain (Czp), complement regulatory protein (CRP), trans-sialidase (TS), Tc-85, and sialylated epitope expression levels were evaluated by immunoblotting. High-virulence C8C3hvir was highly infectious in mice and demonstrated three to five times higher infectivity in mouse myocardial cells than low-virulence C8C3lvir. qPCR revealed higher parasite loads in organs of acute as well as chronically C8C3hvir-infected mice than in those of C8C3lvir-infected mice. Comparative quantitative proteomics revealed that 390 of 1547 identified proteins were differentially regulated in C8C3hvir with respect to C8C3lvir. Amongst these, 174 proteins were upregulated in C8C3hvir and 216 were downregulated in C8C3lvir. The upregulated proteins in C8C3hvir were associated with the tricarboxylic acid cycle, ribosomal proteins, and redoxins. Higher levels of Czp, CRP, TS, Tc-85, and sialylated epitopes were expressed in C8C3hvir than in C8C3lvir. Thus, T. cruzi virulence may be related to virulence factor expression as well as upregulation of bioenergetic and biosynthetic pathways proteins.

Biological and Molecular Effects of Trypanosoma cruzi Residence in a LAMP-Deficient Intracellular Environment

Trypanosoma cruzi invades non-professional phagocytic cells by subverting their membrane repair process, which is dependent on membrane injury and cell signaling, intracellular calcium increase, and lysosome recruitment. Cells lacking lysosome-associated membrane proteins 1 and 2 (LAMP1 and LAMP2) are less permissive to parasite invasion but more prone to parasite intracellular multiplication. Several passages through a different intracellular environment can significantly change T. cruzi's gene expression profile. Here, we evaluated whether one single passage through LAMP-deficient (KO) or wild-type (WT) fibroblasts, thus different intracellular environments, could influence T. cruzi Y strain trypomastigotes' ability to invade L6 myoblasts and WT fibroblasts host cells. Parasites released from LAMP2 KO cells (TcY-L2-/-) showed higher invasion, calcium signaling, and membrane injury rates, for the assays in L6 myoblasts, when compared to those released from WT (TcY-WT) or LAMP1/2 KO cells (TcY-L1/2-/-). On the other hand, TcY-L1/2-/- showed higher invasion, calcium signaling, and cell membrane injury rates, for the assays in WT fibroblasts, compared to TcY-WT and TcY-L1/2-/-. Albeit TcY-WT presented an intermediary invasion and calcium signaling rates, compared to the others, in WT fibroblasts, they induced lower levels of injury, which reinforces that signals mediated by surface membrane protein interactions also have a significant contribution to trigger host cell calcium signals. These results clearly show that parasites released from WT or LAMP KO cells are distinct from each other. Additionally, these parasites' ability to invade the cell may be distinct depending on which cell type they interact with. Since these alterations most likely would reflect differences among parasite surface molecules, we also evaluated their proteome. We identified few protein complexes, membrane, and secreted proteins regulated in our dataset. Among those are some members of MASP, mucins, trans-sialidases, and gp63 proteins family, which are known to play an important role during parasite infection and could correlate to TcY-WT, TcY-L1/2-/-, and TcY-L2-/- biological behavior.

Nicastrin-Like, a Novel Transmembrane Protein from Trypanosoma cruzi Associated to the Flagellar Pocket

Nicastrin (NICT) is a transmembrane protein physically associated with the polytypical aspartyl protease presenilin that plays a vital role in the correct localization and stabilization of presenilin to the membrane-bound γ-secretase complex. This complex is involved in the regulation of a wide range of cellular events, including cell signaling and the regulation of endocytosed membrane proteins for their trafficking and protein processing. Methods: In Trypanosoma cruzi, the causal agent of the Chagas disease, a NICT-like protein (Tc/NICT) was identified with a short C-terminus orthologous to the human protein, a large ectodomain (ECD) with numerous glycosylation sites and a single-core transmembrane domain containing a putative TM-domain (457GSVGA461) important for the γ-secretase complex activity. Results: Using the Spot-synthesis strategy with Chagasic patient sera, five extracellular epitopes were identified and synthetic forms were used to generate rabbit anti-Tc/NICT polyclonal serum that recognized a ~72-kDa molecule in immunoblots of T. cruzi epimastigote extracts. Confocal microscopy suggests that Tc/NICT is localized in the flagellar pocket, which is consistent with data from our previous studies with a T. cruzi presenilin-like protein. Phylogenetically, Tc/NICT was localized within a subgroup with the T. rangeli protein that is clearly detached from the other Trypanosomatidae, such as T. brucei. These results, together with a comparative analysis of the selected peptide sequence regions between the T. cruzi and mammalian proteins, suggest a divergence from the human NICT that might be relevant to Chagas disease pathology. As a whole, our data show that a NICT-like protein is expressed in the infective and replicative stages of T. cruzi and may be considered further evidence for a γ-secretase complex in trypanosomatids.

Trypanosoma cruzi Presenilin-Like Transmembrane Aspartyl Protease: Characterization and Cellular Localization

The increasing detection of infections of Trypanosoma cruzi, the etiological agent of Chagas disease, in non-endemic regions beyond Latin America has risen to be a major public health issue. With an impact in the millions of people, current treatments rely on antiquated drugs that produce severe side effects and are considered nearly ineffective for the chronic phase. The minimal progress in the development of new drugs highlights the need for advances in basic research on crucial biochemical pathways in T. cruzi to identify new targets. Here, we report on the T. cruzi presenilin-like transmembrane aspartyl enzyme, a protease of the aspartic class in a unique phylogenetic subgroup with T. vivax separate from protozoans. Computational analyses suggest it contains nine transmembrane domains and an active site with the characteristic PALP motif of the A22 family. Multiple linear B-cell epitopes were identified by SPOT-synthesis analysis with Chagasic patient sera. Two were chosen to generate rabbit antisera, whose signal was primarily localized to the flagellar pocket, intracellular vesicles, and endoplasmic reticulum in parasites by whole-cell immunofluorescence. The results suggest that the parasitic presenilin-like enzyme could have a role in the secretory pathway and serve as a target for the generation of new therapeutics specific to the T. cruzi.

Precision Health for Chagas Disease: Integrating Parasite and Host Factors to Predict Outcome of Infection and Response to Therapy

Chagas disease, caused by the infection with the protozoan parasite Trypanosoma cruzi, is clinically manifested in approximately one-third of infected people by inflammatory heart disease (cardiomyopathy) and, to a minor degree, gastrointestinal tract disorders (megaesophagus or megacolon). Chagas disease is a zoonosis transmitted among animals and people through the contact with triatomine bugs, which are found in much of the western hemisphere, including most countries of North, Central and South America, between parallels 45° north (Minneapolis, USA) and south (Chubut Province, Argentina). Despite much research on drug discovery for T. cruzi, there remain only two related agents in widespread use. Likewise, treatment is not always indicated due to the serious side effects of these drugs. On the other hand, the epidemiology and pathogenesis of Chagas disease are both highly complex, and much is known about both. However, it is still impossible to predict what will happen in an individual person infected with T. cruzi, because of the highly variability of parasite virulence and human susceptibility to infection, with no definitive molecular predictors of outcome from either side of the host-parasite equation. In this Minireview we briefly discuss the current state of T. cruzi infection and prognosis and look forward to the day when it will be possible to employ precision health to predict disease outcome and determine whether and when treatment of infection may be necessary.

Vismione B Interferes with Trypanosoma cruzi Infection of Vero Cells and Human Stem Cell-Derived Cardiomyocytes

Traditional African medicine is a source of new molecules that might be useful in modern therapeutics. We tested ten limonoids, six quinones, one xanthone, one alkaloid, and one cycloartane, isolated from four Cameroonian medicinal plants, and one plant-associated endophytic fungus, against Trypanosoma cruzi, the etiological agent of Chagas disease (CD). Vero cells, or human-induced pluripotent stem cells (hiPSC)-derived cardiomyocytes (hiPSC-CM) were infected with T. cruzi trypomastigotes (discrete typing unit types I or II). Infection took place in the presence of drugs, or 24 hours before drug treatment. Forty-eight hours after infection, infection rates and parasite multiplication were evaluated by Giemsa stain. Cell metabolism was measured to determine functional integrity. In Vero cells, several individual molecules significantly affected T. cruzi infection and multiplication with no, or minor, effects on cell viability. Reduced infection rates and multiplication by the quinone vismione B was superior to the commonly used therapeutic benznidazole (BNZ). The vismione B concentration inhibiting 50% of T. cruzi infection (IC₅₀) was 1.3 µM. When drug was applied after infection, anti-Trypanosoma effects of vismione B [10 µM) were significantly stronger than effects of BNZ (23 µM). Furthermore, in hiPSC-CM cultures, infection and multiplication rates in the presence of vismione B (10 µM) were significantly lower than in BNZ (11.5 µM), without showing signs of cytotoxicity. Our data indicate that vismione B is more potent against T. cruzi infection and multiplication than BNZ, with stronger effects on established infection. Vismione B, therefore, might become a promising lead molecule for treatment development for CD.

Plasma membrane repair involvement in parasitic and other pathogen infections

Intracellular pathogens depend on specific mechanisms to be able to gain entry and survive into their host cells. For this, they subvert pathways involved in physiological cellular processes. Here we are going to focus on how two protozoan parasites, Trypanosoma cruzi and Leishmania sp, which may cause severe diseases in humans, use plasma membrane repair (PMR) mechanisms to gain entry in host intracellular environment. T. cruzi is the causative agent of Chagas disease, a disease originally endemic of central and South America, but that has become widespread around the globe. T. cruzi is able to invade any nucleated cell, but muscle cells are usually the main targets during chronic disease. During host cell contact, the parasite interacts with proteins at the host cell surface and may cause damage to their membrane, which has been shown to be responsible for inducing intracellular calcium increase and PMR-related events that culminate with parasite internalization. The same was recently observed for Leishmania sp, when infecting nonprofessional phagocytic cells, such as fibroblasts. Other pathogens, such as viruses or bacteria may also use PMR-related events for invasion and vacuole escape/maturation. In some cases, PMR may also be responsible to modulate pathogen intracellular development. These other PMR roles in pathogen infections will also be briefly discussed.

Mammalian cellular culture models of Trypanosoma cruzi infection: a review of the published literature

Cellular culture infection with Trypanosoma cruzi is a tool used to dissect the biological mechanisms behind Chagas disease as well as to screen potential trypanocidal compounds. Data on these models are highly heterogeneous, which represents a challenge when attempting to compare different studies. The purpose of this review is to provide an overview of the cell culture infectivity assays performed to date. Scientific journal databases were searched for articles in which cultured cells were infected with any Trypanosoma cruzi strain or isolate regardless of the study’s goal. From these articles the cell type, parasite genotype, culture conditions and infectivity results were extracted. This review represents an initial step toward the unification of infectivity model data. Important differences were detected when comparing the pathophysiology of Chagas disease with the experimental conditions used in the analyzed studies. While Trypanosoma cruzi preferentially infects stromal cells in vivo, most of the assays employ epithelial cell lines. Furthermore, the most commonly used parasite strain (Tulahuen-TcVI) is associated with chagasic cardiomyopathy only in the Southern Cone of South America. Suggestions to overcome these discrepancies include the use of stromal cell lines and parasite genotypes associated with the known characteristics of the natural history of Chagas disease.

Cellular analysis of host cell infection by different developmental stages of Trypanosoma cruzi

Trypanosoma cruzi is an obligate intracellular parasite that infects phagocytic and non-phagocytic mammalian cells by a complex process that appears to involve several discrete steps. Even though the infection process was described many years ago, the molecular mechanisms involved remain poorly understood. As fluorescent proteins have proven to be excellent tools for live-cell imaging, we used EGFP- and DsRed1-1-transfected trypomastigotes, amastigotes and epimastigotes to study the infection process in living cells. Contrary to what has been reported, our results showed that epimastigotes are as infective as trypomastigotes and amastigotes. Besides, differences in replication, differentiation and parasite release times were observed among the stages. Our results suggest that the different developmental stages use distinct attachment and invasion mechanisms. We propose that fluorescent-based plasmid expression systems are good models for studying the infection process of intracellular microorganisms and could offers insights about the molecular mechanisms involved.

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.

Trypanosoma cruzi-fibroblastic cell interactions necessary for cellular invasion

Detailed knowledge of the mechanism by which vertebrate cells are invaded by the haemoflagellated parasite Trypanosoma cruzi is of paramount importance for understanding one of the early events in the life cycle of this obligatory intracellular parasite. The ability to infect vertebrate fibroblastic cells was found to be only partially expressed in trypomastigotes that were recently liberated from cell cultures. These trypomastigotes could increase by several fold their capability for adhesion and infection by a time-dependent in vitro process. This activation phenomenon was used to study how certain inhibitors of macromolecular biosynthesis (actinomycin D, puromycin, tunicamycin), proteases, protease inhibitors, and a combination of them, acted on adhesion and infection. The effect of exposing the parasites and, independently, the host fibroblasts to various lectins and carbohydrates was also investigated. Most of these treatments either inhibited or stimulated adhesion and infection. Exposure of fibroblastic cells to trypsin and to drugs altering the cytoskeleton impaired their susceptibility to infection. Tunicamycin blocked the recovery of infection, but not of adhesion, in trypsinized cells. The results obtained have been interpreted as indicating that the process of fibroblast infection by T. cruzi trypomastigotes occurs through two distinct and independent steps (adhesion and penetration), mediated by components of both the parasite and the host cell. The parasite components seem to be: (a) a lectin-like protein involved in adhesion; (b) an activating inducible system, probably of proteolytic nature, which enhances parasite adhesion; and (c) a tunicamycin-sensitive glycoprotein, related to penetration only. As for the fibroblastic cell components, these are postulated to be two glycoproteins (one insensitive and the other sensitive to tunicamycin), which are involved in the steps of parasite attachment and penetration, respectively.

Roles of naturally occurring protease inhibitors in the modulation of host cell signaling and cellular invasion by Trypanosoma cruzi

Trypanosoma cruzi trypomastigotes rely on the structural diversity of the cruzipain family of cysteine proteases to infect and multiply in nonprofessional phagocytic cells. Herein, we will review studies demonstrating that the interplay of cruzipain with peptidase inhibitors modulate infection outcome in a variety of experimental settings. Studies with a panel of T. cruzi strains showed that parasite ability to invade human smooth muscle cells is influenced by the balance between cruzipain and chagasin, a tight binding endogenous inhibitor of papain-like cysteine proteases. Analysis of T. cruzi interaction with endothelial cells and cardiomyocytes indicated that parasite-induced activation of bradykinin receptors drive host cell invasion by [Ca2+]I-dependent pathways. Clues about the mechanisms underlying kinin generation in vivo by trypomastigotes came from analysis of the dynamics of edematogenic inflammation. Owing to plasma extravasation, the blood-borne kininogens accumulate in peripheral sites of infection. Upon diffusion in peripheral tissues, kininogens (i.e., type III cystatins) bind to heparan sulphate chains, thus constraining interactions of the cystatin-like inhibitory domains with cruzipain. The cell bound kininogens are then turned into facile substrates for cruzipain, which liberates kinins in peripheral tissues. Subjected to tight-regulation by kinin-degrading metallopeptidases, such as angiotensin converting enzyme, the short-lived kinin peptides play a dual role in the host-parasite balance. Rather than unilaterally stimulating pathogen infectivity via bradykinin receptors, the released kinins potently induce dendritic cell maturation, thus stimulating type 1 immune responses. In conclusion, the studies reviewed herein illustrate how regulation of parasite proteases may affect host-parasite equilibrium in the course of IT cruzi infection.

Generation and analysis of expressed sequence tags from Trypanosoma cruzi trypomastigote and amastigote cDNA libraries

We have generated 2771 expressed sequence tags (ESTs) from two cDNA libraries of Trypanosoma cruzi CL-Brener. The libraries were constructed from trypomastigote and amastigotes, using a spliced leader primer to synthesize the cDNA second strand, thus selecting for full-length cDNAs. Since the libraries were not normalized nor pre-screened, we compared the representation of transcripts between the two using a statistical test and identify a subset of transcripts that show apparent differential representation. A non-redundant set of 1619 reconstructed transcripts was generated by sequence clustering. This dataset was used to perform similarity searches against protein and nucleotide databases. Based on these searches, 339 sequences could be assigned a putative identity. One thousand one-hundred and sixteen sequences in the non-redundant clustered dataset (68.8%) are new expression tags, not represented in the T. cruzi epimastigote ESTs that are in the public databases. Additional information is provided online at http://genoma.unsam.edu.ar/projects/tram. To the best of our knowledge these are the first ESTs reported for the life cycle stages of T. cruzi that occur in the vertebrate host.

Morphological comparison of axenic amastigogenesis of trypomastigotes and metacyclic forms of Trypanosoma cruzi

Amastigogenesis occurs first when metacyclic trypomastigotes from triatomine urine differentiate into amastigotes inside mammalian host cells and a secondary process when tissue-derived trypomastigotes invade new cells and differentiate newly to amastigotes. Using scanning electron microscopy, we compared the morphological patterns manifested by trypomastigotes and metacyclic forms of Trypanosoma cruzi during their axenic-transformation to amastigotes in acidic medium at 37 C. We show here that in culture MEMTAU medium, secondary and primary axenic amastigogenesis display different morphologies. As already described, we also observed a high differentiation rate of trypomastigotes into amastigotes. Conversely, the transformation rate of in vitro-induced-metacyclic trypomastigotes to amastigotes was significantly slower and displayed distinct patterns of transformation that seem environment-dependent. Morphological comparisons of extracelullar and intracellular amastigotes showed marked similarities, albeit some differences were also detected. SDS-PAGE analyses of protein and glycoprotein from primary and axenic extracelullar amastigotes showed similarities in glycopeptide profiles, but variations between their proteins demonstrated differences in their respective macromolecular constitutions. The data indicate that primary and axenic secondary amastigogenesis of T. cruzi may be the result of different developmental processes and suggest that the respective intracellular mechanisms driving amastigogenesis may not be the same.

Production of amastigotes from metacyclic trypomastigotes of Trypanosoma cruzi

Attempts to recreate all the developmental stages of Trypanosoma cruzi in vitro have thus far been met with partial success. It is possible, for instance, to produce trypomastigotes in tissue culture and to obtain metacyclic trypomastigotes in axenic conditions. Even though T. cruzi amastigotes are known to differentiate from trypomastigotes and metacyclic trypomastigotes, it has only been possible to generate amastigotes in vitro from the tissue-culture-derived trypomastigotes. The factors and culture conditions required to trigger the transformation of metacyclic trypomastigotes into amastigotes are as yet undetermined. We show here that pre-incubation of metacyclic trypomastigotes in culture (MEMTAU) medium at 37 degrees C for 48 h is sufficient to commit the parasites to the transformation process. After 72 h of incubation in fresh MEMTAU medium, 90% of the metacyclic parasites differentiate into forms that are morphologically indistinguishable from normal amastigotes. SDS-PAGE, Western blot and PAABS analyses indicate that the transformation of axenic metacyclic trypomastigotes to amastigotes is associated with protein, glycoprotein and antigenic modifications. These data suggest that (a) T. cruzi amastigotes can be obtained axenically in large amounts from metacyclic trypomastigotes, and (b) the amastigotes thus obtained are morphological, biological and antigenically similar to intracellular amastigotes. Consequently, this experimental system may facilitate a direct, in vitro assessment of the mechanisms that enable T. cruzi metacyclic trypomastigotes to transform into amastigotes in the cells of mammalian hosts.

Inhibition of HSP90 in Trypanosoma cruzi induces a stress response but no stage differentiation

The 90-kDa heat shock proteins (HSP90) are important in the regulation of numerous intracellular processes in eukaryotic cells. In particular, HSP90 has been shown to be involved in the control of the cellular differentiation of the protozoan parasite Leishmania donovani. We investigated the role of HSP90 in the related parasite Trypanosoma cruzi by inhibiting its function using geldanamycin (GA). GA induced a dose-dependent increase in heat shock protein levels and a dose-dependent arrest of proliferation. Epimastigotes were arrested in G(1) phase of the cell cycle, but no stage differentiation occurred. Blood form trypomastigotes showed conversion towards spheromastigote-like forms when they were cultivated with GA, but differentiation into epimastigotes was permanently blocked. We conclude that, similar to leishmanial HSP90, functional HSP90 is essential for cell division in T. cruzi and serves as a feedback inhibitor in the cellular stress response. In contrast to L. donovani cells, however, T. cruzi cells treated with GA do not begin to differentiate into relevant life cycle stages.

Trypanosoma cruzi: in vitro phosphorylation of tubulin by a protein kinase CK2-like enzyme

One predominant 55-kDa polypeptide was phosphorylated in vitro in Trypanosoma cruzi homogenates prepared from three differentiation stages: epimastigotes, trypomastigotes, and spheromastigotes. Anti-alpha and anti-beta tubulin monoclonal antibodies immunoprecipitated the phosphorylated 55-kDa polypeptide from epimastigote extracts. Phosphoserine was the only residue phosphorylated in vitro in the 55-kDa polypeptide and in immunoprecipitated alpha tubulin. The phosphorylation of both the 55-kDa polypeptide and exogenously added casein was inhibited with GTP, heparin, and 2,3-bisphosphoglycerate in a dose-dependent manner, indicating the involvement of a CK2-like protein kinase. Moreover, when tubulin was isolated from an epimastigote homogenate by ultracentrifugation, followed by DEAE-Sephacel chromatography, a protein kinase that phosphorylated tubulin and casein co-purified with this cytoskeletal component. This result suggests an association between tubulin and its corresponding protein kinase in T. cruzi.

Expression of alpha- and beta-tubulin genes during growth of Trypanosoma cruzi epimastigotes

The expression of tubulin genes was studied during the growth of epimastigotes of Trypanosoma cruzi. Northern blot analysis showed that there was a decrease in the levels of alpha- and beta-tubulin mRNAs as epimastigotes changed from the logarithmic to the stationary phase. The changes were associated with a similar decrease in the rates of transcription for both of these genes as measured by run-on assays using permeabilized parasites. In contrast to these results, ubiquitin transcription increased slightly. The levels of alpha-tubulin protein per parasite also decreased in stationary compared with logarithmic phase epimastigotes, in close agreement with the decrease in transcription. However, beta-tubulin protein levels did not change significantly. Our results thus indicated that during the growth of epimastigotes, the expression of alpha-tubulin is controlled partially at the transcriptional level. On the other hand, the experiments also suggested that beta-tubulin expression is controlled at a post-transcriptional level.

Alterations in the surface charge of heart muscle cells during interaction with Trypanosoma cruzi

The surface charge of heart muscle cells (HMC) and Trypanosoma cruzi trypomastigotes was estimated during their interaction by means of zeta potential (ZP). Metacyclic and bloodstream trypomastigote, but not amastigote forms, are able to decrease the surface charge of HMC as well as other nonphagocytic cells. However, no alteration could be detected on T. cruzi-infected macrophage cell line. Trypomastigote forms collected from the supernatant after 20 h of contact with HMC also have their ZP value decreased. The analysis of the surface components of both the parasite and HMC involved in such interaction was also carried out. Assays concerning the kinetics of the cell-parasite interaction demonstrated the influence of parasite surface anionogenicity during its interaction with HMC. The binding of bloodstream forms to HMC was enhanced after their incubation with cationized ferritin (CF), whereas phospholipase C and neuraminidase treatments improved and trypsin treatment inhibited parasite uptake in HMC. Conversely, the incubation of HMC with phospholipase C impaired, and with trypsin enhanced, the interiorization of the parasites. These results suggest that trypomastigote forms of T. cruzi may process the surface of HMC and its own surface either by removing molecules or by exposing ligands for their internalization.

Trypanosoma cruzi glutathione-binding proteins: immunogenicity during human and experimental Chagas' disease

Following purification by affinity chromatography, three glutathione-binding proteins (TcGBP) of 45, 30, and 25 kDa were co-purified from Trypanosoma cruzi epimastigotes. Using 1-chloro-2,4 dinitrobenzene as substrate, a glutathione S-transferase activity of 70 nmol/min/mg of proteins was detected in the GSH binding fraction. An increased expression of TcGBP and total GST activity was observed upon incubation of parasites with phenobarbital, which is an inducer of GST synthesis. Immunofluorescence and electron microscopic experiments demonstrated that TcGBP were expressed by all developmental stages of the parasite, including infective forms. The expression of these proteins by intracellular dividing amastigotes could be in favour of a potential defensive role of these molecules against host attack. Results obtained by immunoprecipitation of in vitro translation products using anti-TcGBP antisera suggested that these three polypeptides are not glycosylated. In addition, antibodies directed against the TcGBP were found in a high proportion of T. cruzi-infected chronic chagasic patients' sera and in sera of chronically infected BALB/c mice. In contrast, acute chagasic patients' sera and acute-phase mouse sera were found to be poorly reactive with these proteins. Our results identify a new class of potential target antigens, which may be essential for the development of T. cruzi in its host. Their protective role in experimental models deserves to be investigated.

Binding of antibody and resistance to lysis of trypomastigotes of Trypanosoma cruzi

Epimastigote forms of Trypanosoma cruzi are readily lysed by complement via the alternative pathway. Neither fibroblast-derived trypomastigotes nor blood-form trypomastigotes are lysed by complement alone and few (less than 30% of the Brazil strain) are lysed in the presence of parasite-specific antibody and complement. The mechanism by which trypomastigotes resist antibody-dependent, complement-mediated lysis is not clearly understood. In the present study, we have utilized flow cytometric analysis to examine the binding of parasite-specific antibody to epimastigotes, fibroblast-derived trypomastigotes and blood-form trypomastigotes of a Brazil strain of T. cruzi. We also determined the extent of lysis of these parasites in the presence of complement utilizing propidium iodide to determine cell death. It was found that all epimastigotes bind approximately the same amount of antibody but that there are subpopulations of trypomastigotes which bind antibody to varying degrees. When these subpopulations were sorted, and treated with complement, lysis was only minimally increased in the population of parasites which bound significantly greater amounts of antibody.

Regulation of Trypanosoma cruzi infectivity by alpha- and beta-adrenergic agonists: desensitization produced by prolonged treatments or increasing agonist concentrations

We previously reported that blood forms of Trypanosoma cruzi express alpha- and beta-adrenergic receptors and that binding of specific agonists to these receptors modifies the infective capacity of the parasite in vitro. The present study has revealed that the inhibitory effect of the beta-adrenergic agonist L-isoproterenol and the stimulatory effect of the alpha-adrenergic agonist L-phenylephrine are not produced when the parasite is subjected to prolonged exposure to otherwise effective doses of these agonists or when supraoptimal doses of these agonists are used. We refer to these phenomena as 'desensitization' because of their analogy with vertebrate cells becoming desensitized by prolonged exposure to, or relatively high concentrations of, adrenergic agonists. At a constant agonist concentration, T. cruzi desensitization was time-dependent and, when the time of parasite treatment with the agonists was not changed, the higher concentrations of the agonist tested were the most effective in producing desensitization. The reduced infectivity resulting from treatment with optimal doses of L-isoproterenol was accompanied by elevated levels of cyclic adenosine monophosphate (cAMP) which were not detectable when L-isoproterenol concentrations producing desensitization were used. This finding implicated cAMP as a likely second signal in the inhibitory mechanisms of this agonist. No significant change in cAMP was detectable in parasites treated with L-phenylephrine, leaving open the question about how optimal doses of this alpha-adrenergic agonist enhance T. cruzi infectivity. Parasite responsiveness to alpha- and beta-adrenergic agonists as well as the desensitization effects define a system which regulates infectivity and could be modified at the host tissue level by naturally occurring agonists.

Immunocytochemical localization of neuraminidase in Trypanosoma cruzi

A polyclonal antibody obtained against neuraminidase purified from Trypanosoma cruzi was used for the localization of the protein in whole cells by immunofluorescence microscopy and in thin sections of parasites (epimastigote, amastigote, and trypomastigote forms) embedded at a low temperature in Lowicryl K4M resin. The intensity of labeling, as evaluated by the number of gold particles associated with the parasite, varied according to the protozoan developmental stage. In the noninfective epimastigote forms, labeling of the cell surface was very weak. However, an intense labeling of some cytoplasmic vacuoles was observed. Labeling of the surfaces of most of the trypomastigote forms was weak, while gold particles were seen in association with the flagellar pockets of these forms, which suggests that the enzyme is secreted through this region. Intense labeling of the surfaces of many, but not all, transition forms between trypomastigote and amastigote forms was observed. Amastigote forms found in the supernatant of infected cell cultures had their surfaces intensely labeled, while few particles were seen on the surfaces of intracellular amastigotes. The results obtained are discussed in relation to the role played by T. cruzi neuraminidase in the process of parasite-host cell interaction.

Complement component C1q enhances invasion of human mononuclear phagocytes and fibroblasts by Trypanosoma cruzi trypomastigotes

Internalization and infectivity of Trypanosoma cruzi trypomastigotes by macrophages is enhanced by prior treatment of parasites with normal human serum. Heating serum or removing C1q from serum abrogates the enhancement, but augmentation of attachment and infectivity is restored by addition of purified C1q to either serum source. Although both noninfective epimastigotes (Epi) and vertebrate-stage tissue culture trypomastigotes (TCT) bind C1q in saturable fashion at 4 degrees C, internalization by monocytes and macrophages of TCT but not Epi-bearing C1q is enhanced in comparison to untreated parasites. Adherence of human monocytes and macrophages to surfaces coated with C1q also induces a marked enhancement of the internalization of native TCT. C1q enhances attachment of both Epi and TCT to human foreskin fibroblasts, but only when C1q is on the parasite and not when the fibroblasts are plated on C1q-coated surfaces. Only TCT coated with C1q show enhanced invasion into fibroblasts. Although trypomastigotes produce an inhibitor of the complement cascade which limits C3 deposition during incubation in normal human serum, C1q binds to the parasite and enhances entry of trypomastigotes into target cells.

Antiproliferative synergism of the allylamine SF 86-327 and ketoconazole on epimastigotes and amastigotes of Trypanosoma (Schizotrypanum) cruzi

We have investigated the growth-inhibitory effects of two ergosterol biosynthesis inhibitors, the dioxolane imidazole ketoconazole and the allylamine SF 86-327, alone and in combination, on the proliferative stages of Trypanosoma (Schizotrypanum) cruzi, the causative agent of Chagas' disease. Proliferation of epimastigotes in liver infusion-tryptose medium at 28 degrees C was immediately arrested by any of these drugs at greater than or equal to 3 x 10(-5) M; cell lysis occurred 24 h later. Below that concentration, SF 86-327 at concentrations down to 1 x 10(-6) M stopped growth after 48 h. In contrast, ketoconazole slowed cell growth only moderately, but proliferation finally stopped and cell lysis occurred after 120 h at 3 x 10(-6) M. Synergistic effects could be observed when the two drugs were used in combination: the concentration of SF 86-327 required to reduce the cell growth to 25% of controls in 144 h was reduced 33-fold in the presence of 1 x 10(-6) M ketoconazole, which by itself reduced growth only by 30%. Amastigotes, proliferating in Vero cells at 37 degrees C, were much more susceptible to both drugs, but ketoconazole was definitely a more potent antiparasitic agent than the allylamine in this system: whereas the concentration of SF 86-327 required to reduce the number of infected cells to 50% of controls was 1 x 10(-7) M and that required to completely eradicate the parasite was 3 x 10(-6) M, for ketoconazole these concentrations were 1 x 10(-10) M and 1 x 10(-8) M, respectively. Again, strong synergistic effects were observed when the drugs were used in combination: the concentration of SF 86-327 required to reduce the number of infected cells to 50% of controls was 100-fold lower in the presence of 10(-11) M ketoconazole, which by itself had no effects on amastigote proliferation. The parasite was completely eradicated when the drugs were used in combination at concentrations as low as 10(-9) M. Synergy of the antiproliferative effects of the drugs on both froms of the parasite was further demonstrated by concave isobolograms. On the other hand, SF 86-327 at 10(-5) M had no effects on the proliferation of Vero cells, whereas ketoconazole at 10(-7) M reduced the proliferation of these cells by 50%.

The tubulin genes of Trypanosoma cruzi

The organization of the alpha- and beta-tubulin genes in the genome of Trypanosoma cruzi have been analysed by Southern blotting using tubulin probes derived from Trypanosoma brucei. The tubulin array appears to be more complex in this organism than in other members of the same family. Some tubulin genes are tightly clustered in an alternating (alpha-beta)n array with a basic repeat unit length of 4.3 kb. However, other pairs of alternating alpha- and beta-tubulin sequences appear to be physically separated from the basic group. This finding indicates that the tubulin gene cluster present in T. cruzi is less perfectly conserved than in T. brucei. T. (Herpetosoma) rangeli is similar to T. (Schizotrypanum) cruzi in its tubulin gene organization whereas most of these genes are tandemly clustered in the genome of T. (Trypanozoon) evansi, with a basic repeat unit length of 3.6 kb as previously described for T. (Trypanozoon) brucei. Two overlapping recombinant clones containing T. cruzi tubulin sequences have been isolated from a genomic cosmid library of T. cruzi epimastigotes using the T. brucei tubulin probes. Partial sequencing of the T. cruzi beta-tubulin gene has confirmed its identity and shows more than 70% homology with the sea urchin, chicken and T. b. rhodesiense beta-tubulin reported gene sequences. Analysis of tubulin gene organization through the parasite life cycle does not show evidence of major rearrangements within the repeat unit. Several T. cruzi strains and cloned lines whilst sharing the 4.3-kb tubulin repeat unit, exhibited very variable tubulin gene organization with tubulin probes. These striking differences in the organization of this structural gene among T. cruzi strains and cloned lines suggest that the heterogeneity previously reported in parasite populations may be related to a very dynamic, diploid genome.

Stage-specific surface antigens expressed during the morphogenesis of vertebrate forms of Trypanosoma cruzi

The origin of Trypanosoma cruzi slender and broad forms found in the circulation of the mammalian host has remained obscure and, unlike what has been proposed for African trypanosomes, no precise form-function relationship has been ascribed to them. We show here that parasites circulating in the blood of infected animals display a high degree of polymorphism. Around 10% of the forms found circulating in mice during the acute phase of infection were amastigotes, and the other 90% included slender and broad trypomastigotes and intermediate forms between amastigotes and trypomastigotes. Slender trypomastigotes, from blood or cell culture, undergo extracellularly morphological rearrangements in which the parasites become gradually broader and transform into amastigotes. By scanning electron microscopy a progressive internalization of the flagellum and reorganization of the cell shape in a helical fashion were observed in parasites undergoing transformation. After 48 hr of extracellular incubation the parasite population consisted exclusively of amastigotes with a short protruding flagellum. The morphological changes were associated with the expression of different surface antigens defined by monoclonal antibodies: the trypomastigote-specific antigens Ssp-1 (a 100-120-150-Mr glycoprotein), Ssp-2 (a 70-Mr glycoprotein), Ssp-3 (undefined), and Ssp-4, an amastigote-specific surface antigen. Ssp-4 was also detected on intracellular amastigotes (in vitro and in vivo). We conclude that trypomastigotes are programmed to develop into amastigotes whether or not they enter cells, and that the differentiation can occur in the blood of the vertebrate host. These findings raise some questions regarding conventional views on the life cycle of T. cruzi.

Trypanosomatid hydrogen peroxide [corrected] metabolism

The rate of whole cell H2O2 metabolism in several salivarian and stercorarian trypanosomes and Leishmania species was measured. These cells metabolized H2O2 at rates between 2.3 and 48.2 nmol/10(8) cells per min depending upon the species employed. H2O2 metabolism was largely insensitive to NaN3, implying that typical catalase and peroxidase haemoproteins are not important in H2O2 metabolism. The metabolism of H2O2, however, was almost completely inhibited by N-ethylmaleimide. In representative species, H2O2 metabolism was shown to occur through a trypanothione-dependent mechanism.

The interaction of a Trypanosoma cruzi surface protein with Vero cells and its relationship with parasite adhesion

Previous studies have shown that adhesion to fibroblastic cells of cell culture-derived trypomastigotes of Trypanosoma cruzi probably occurs through a ligand-receptor interaction. The results now obtained indicate that solubilization with a mild detergent ('Chaps', 0.8%) of 125I-surface proteins of trypomastigotes, followed by detergent removal and interaction of the solubilized proteins with a monolayer of intact Vero cells, brings about binding to the cells of a parasite surface protein, which exhibits a molecular weight of 83,000 and isoelectric point of 8.1-8.6 upon two-dimensional polyacrylamide gel electrophoresis. This polypeptide was detected in extracts of highly adherent, extracellularly incubated parasites, but not in extracts of poorly adhesive, recently released trypomastigotes. The detergent-free extracts of incubated trypomastigotes inhibit attachment of live parasites to Vero cells, while extracts of fresh trypomastigotes are nearly ineffective. Binding of the parasite polypeptide to the cells is stimulated by parasite trypsinization or activation in the presence of tunicamycin, and it is inhibited by the presence of mannan or by Vero cell trypsinization, thus showing a similar behaviour to that observed for parasite attachment to Vero cells under these conditions. These results suggest that the surface membranes of activated, highly adherent T. cruzi trypomastigotes contain an 83 kDa polypeptide which acts as a lectin-like protein that can interact with the surface of Vero fibroblasts, probably through mannose residues of a glycoprotein receptor of the host cell.

The effects of p-chloromercuriphenylsulfonic acid on Trypanosoma cruzi infection of mammalian host cells in vitro

Treatment of Trypanosoma cruzi blood trypomastigotes with p-chloromercuriphenylsulfonic acid (PCMS) increased the association of the parasite with either mouse resident peritoneal macrophages or rat heart myoblasts in vitro. The effect was evidenced by elevation of both the percentage of host cells with parasites and the number of flagellates per 100 cells. The effect of PCMS appeared to be largely on the process of parasite penetration rather than surface binding as it was seen at 37 degrees C but not at 4 degrees C. A short pretreatment time, 5 min, was sufficient to elicit the enhancement, suggesting that the primary effect of PCMS might be at the parasite's cell surface. The PCMS effect was reversible as the parasite returned to normal levels of association with the host cells in less than 4 h after removal of excess PCMS. That sulfhydryl groups were involved in the PCMS effect was indicated by the abilities of excess cysteine and glutathione to block it. These results suggest a role for free sulfhydryl groups on the parasite surface in the process of host cell invasion.

The effect of fetuin and other sialoglycoproteins on the in vitro penetration of Trypanosoma cruzi trypomastigotes into fibroblastic cells

Heat-inactivated calf-, human-, and especially fetal calf serum stimulate infection of Vero cells by cell culture-derived trypomastigotes of Trypanosoma cruzi: the stimulatory effect is more marked with extracellular activated parasites or trypsinized trypomastigotes than with recently released parasites. The augmented invasion is not the consequence of a stimulation of attachment of trypomastigotes to host cells. Various sialoglycoproteins like fetuin, transferrin, fibrinogen, alpha-1-antitrypsin, mucin and goat-IgG are also effective in enhancing in vitro infectivity. Colominic acid also stimulates invasion, but other non-sialic polyanionic compounds are either ineffective (chondroitin sulfate, poly-aspartic acid) or inhibitory (heparin, phytic acid, myo-inositol hexasulfate). Fetuin, the best stimulatory compound tested, gives half-maximal activation with approximately 0.03 mg ml-1, and total activation with 0.5-1 mg ml-1. The enhancement of infectivity is time-dependent (2-3 h for maximal activation) at 37 degrees C and does not occur at 0 degrees C. Desialidated-fetuin or -fetal calf serum do not stimulate infectivity at all. Treatment with fetuin of parasites alone (or Vero cells alone), followed by removal of free fetuin and by interaction with untreated Vero cells (or parasites) indicates that the stimulation effect of fetuin occurs mainly on the trypomastigotes. No specific binding of [125I]fetuin to the parasites could be demonstrated, and incubation with exogenous neuraminidase of trypomastigotes previously activated by fetuin, reverses nearly completely the stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible role of cAMP in the differentiation of Trypanosoma cruzi

To assess the possible action of cAMP on the cell differentiation of Trypanosoma cruzi, we determined both cAMP levels and cAMP-binding activities of epimastigotes and trypomastigotes of this parasite. Trypomastigotes showed a 4-fold higher cAMP content and a 2.5-fold increase in the specific activity of a cAMP-binding protein with identical properties to that of epimastigotes. The high levels of cAMP present in trypomastigotes strongly suggest a role of this cyclic nucleotide on the differentiation of T. cruzi.

Trypanosoma cruzi: polypeptide markers of epimastigotes and trypomastigotes

We compared the major polypeptides of epimastigotes and trypomastigotes of T. cruzi, by submitting total parasite lysates to electrophoresis in polyacrylamide gels (SDS-PAGE), protein staining with Coomassie brilliant blue, laser densitometry, or immunoblotting with sera derived from infected individuals (Chagas' disease). Epimastigotes and trypomastigotes displayed extensive homology, the differences being quantitative, except for a trypomastigote-specific band of Mr 75,000 which reacted with chagasic sera. Immunoblotting with chagasic sera confirmed the electrophoretic homology of epimastigotes and trypomastigotes. Upon antigenic dilution, a cluster of antigenic bands in the range of Mr 150,000 to 75,000 prevailed in the trypomastigotes, whereas the epimastigotes displayed more abundance of antigenic bands in the range of Mr 72,000 to 36,000.

The effect of proteolytic enzymes and protease inhibitors on the interaction Trypanosoma cruzi-fibroblasts

It has been shown previously that the capability to adhere to and infect fibroblastic cells by Trypanosoma cruzi is expressed only partially in trypomastigotes recently liberated from infected fibroblasts, but these parasites can increase several-fold their adhesion and infectivity by a time-dependent extracellular incubation. It is now shown that polyacrylamide gel electrophoresis patterns of 125I-labelled surface proteins of the parasites change during the activation process and that protease inhibitors of diverse specificity can block both these changes and the development of adhesion and infectivity. Treatment of fresh trypomastigotes with different proteases increases immediately adhesion and infection. The effect of trypsin has been studied in detail and it was found that this protease stimulates adhesion 4- to 6-fold, even in trypomastigotes obtained and assayed in the absence of serum. Trypomastigotes incubated for various periods and then exposed to trypsin increase their adhesion to values similar to those attained by prolonged incubation of trypomastigotes alone, but infection is stimulated in fresh trypomastigotes only. Trypomastigotes whose development of activation has been inhibited either by protease inhibitors, puromycin, and tunicamycin, and are thereafter trypsinized, show respectively, that: adhesion and infection are restored immediately to the same high values obtained when untreated controls are trypsinized, adhesion is restored, but not infection, and infection is not restored. These results suggest that the adhesion step of T. cruzi trypomastigotes to fibroblastic cells depends on a membrane protein(s) that is (are) already present in an inactive or hidden form in parasites recently liberated from infected fibroblasts. Upon extracellular maturation of these trypomastigotes this proteins(s) is activated or unmasked, probably through an endogenous proteolytic process, whose expression requires protein synthesis. The penetration step requires biosynthesis of a tunicamycin-sensitive glycoprotein(s) of the parasite and its full expression necessitates serum.