Alexandre F. Marques

Proteomic Analysis of Trypanosoma cruzi Secretome: Characterization of Two Populations of Extracellular Vesicles and Soluble Proteins

Microorganisms use specialized systems to export virulence factors into host cells. Secretion of effector proteins into the extracellular environment has been described in Trypanosoma cruzi; however, a comprehensive proteomic analysis of the secretome and the secretion mechanisms involved remain elusive. Here, we present evidence that T. cruzi releases proteins associated with vesicles that are formed by at least two different mechanisms. Transmission electron microscopy showed larger vesicles budding from the plasma membrane of noninfective epimastigotes and infective metacyclic trypomastigotes, as well as smaller vesicles within the flagellar pocket of both forms. Parasite conditioned culture supernatant was fractionated and characterized by morphological, immunochemical, and proteomic analyses. Three fractions were obtained by differential ultracentrifugation: the first enriched in larger vesicles resembling ectosomes, the second enriched in smaller vesicles resembling exosomes, and a third fraction enriched in soluble proteins not associated with extracellular vesicles. Label-free quantitative proteomic analysis revealed a rich collection of proteins involved in metabolism, signaling, nucleic acid binding, and parasite survival and virulence. These findings support the notion that T. cruzi uses different secretion pathways to excrete/secrete proteins. Moreover, our results suggest that metacyclic forms may use extracellular vesicles to deliver cargo into host cells.

Improved Proteomic Approach for the Discovery of Potential Vaccine Targets in Trypanosoma cruzi

Chagas disease, caused by Trypanosoma cruzi, is a devastating parasitic infection affecting millions of people. Although many efforts have been made for the development of immunotherapies, there is no available vaccine against this deadly infection. One major hurdle for the rational approach to develop a T. cruzi vaccine is the limited information about the proteins produced by different phylogenetic lineages, strains, and stages of the parasite. Here, we have adapted a 1D nanoHPLC system to perform online 2D LC-MS/MS, using the autosampler to inject the eluting salt solutions in the first dimension separation. The application of this methodology for the proteomic analysis of the infective trypomastigote stage of T. cruzi led to the identification of 1448 nonredundant proteins. Furthermore, about 14% of the identified sequences comprise surface proteins, most of them glycosylphosphatidylinositol (GPI)-anchored and related to parasite pathogenesis. Immunoinformatic analysis revealed thousands of potential peptides with predicted high-binding affinity for major histocompatibility complex (MHC) class I and II molecules. The high diversity of proteins expressed on the trypomastigote surface may have many implications for host-cell invasion and immunoevasion mechanisms triggered by the parasite. Finally, we performed a rational approach to filter potential T-cell epitopes that could be further tested and validated for development of a Chagas disease vaccine.

A synthetic peptide from Trypanosoma cruzi mucin-like associated surface protein as candidate for a vaccine against Chagas disease.

Chagas disease, caused by Trypanosoma cruzi, is responsible for producing significant morbidity and mortality throughout Latin America. The disease has recently become a public health concern to nonendemic regions like the U.S. and Europe. Currently there are no fully effective drugs or vaccine available to treat the disease. The mucin-associated surface proteins (MASPs) are glycosylphosphatidylinositol (GPI)-anchored glycoproteins encoded by a multigene family with hundreds of members. MASPs are among the most abundant antigens found on the surface of the infective trypomastigote stage of T. cruzi, thus representing an attractive target for vaccine development. Here we used immunoinformatics to select a 20-mer peptide with several predicted overlapping B-cell, MHC-I, and MHC-II epitopes, from a MASP family member expressed on mammal-dwelling stages of T. cruzi. The synthetic MASP peptide conjugated to keyhole limpet hemocyanin (MASPpep-KLH) was tested in presence or not of an adjuvant (alum, Al) as a vaccine candidate in the C3H/HeNsd murine model of T. cruzi infection. In considerable contrast to the control groups receiving placebo, Al, or KLH alone or the group immunized with MASPpep-KLH/Al, the group immunized with MASPpep-KLH showed 86% survival rate after challenge with a highly lethal dose of trypomastigotes. As evaluated by quantitative real-time polymerase chain reaction, MASPpep-KLH-immunized animals had much lower parasite load in the heart, liver, and spleen than control animals. Moreover, protected animals produced trypanolytic, protective antibodies, and a cytokine profile conducive to resistance against parasite infection. Finally, in vivo depletion of either CD4(+) or CD8(+) T cells indicated that the latter are critical for protection in mice immunized with MASPpep-KLH. In summary, this new peptide-based vaccine with overlapping B- and T-cell epitopes is able to control T. cruzi infection in mice by priming both humoral and cellular immunity.

Intraspecies variation in Trypanosoma cruzi GPI-mucins: biological activities and differential expression of α-galactosyl residues.

The glycosylphosphatidylinositol (GPI)-anchored mucins of Trypanosoma cruzi trypomastigotes play an important immunomodulatory role during the course of Chagas disease. Here, some biological activities of tGPI-mucins from four T. cruzi isolates, including benznidazole-susceptible (BZS-Y), benznidazole-resistant (BZR-Y), CL, and Colombiana, were evaluated. GPI-mucins were able to differentially trigger the production of interleukin-12 and nitric oxide in BALB/c macrophages and modulate LLC-MK2 cell invasion. The significance of these variations was assessed after analysis of the terminal α-galactosyl residues. Enzymatic treatment with α-galactosidase indicated a differential expression of O-linked α-galactosyl residues among the strains, with higher expression of this sugar in BZS-Y and BZR-Y T. cruzi populations followed by Colombiana and CL. Unweighted pair group method analysis of the carbohydrate anchor profile and biological parameters allowed the clustering of two groups. One group includes Y and CL strains (T. cruzi II and VI), and the other group is represented by Colombiana strain (T. cruzi I).

Potential use of synthetic α-galactosyl-containing glycotopes of the parasite Trypanosoma cruzi as diagnostic antigens for Chagas disease†

A synthetic glycoarray containing non-reducing α-galactopyranosyl moieties related to mucin O-glycans of the parasite Trypanosoma cruzi was evaluated by a chemiluminescent enzyme-linked immunosorbent assay with sera from patients with chronic Chagas disease. Our data revealed the disaccharide Galα(1,3)Galβ as the immunodominant glycotope, which may eventually be employed as a diagnostic antigen for Chagas disease.

Amblyomma sculptum tick saliva: α-Gal identification, antibody response and possible association with red meat allergy in Brazil

The anaphylaxis response is frequently associated with food allergies, representing a significant public health hazard. Recently, exposure to tick bites and production of specific IgE against α-galactosyl (α-Gal)-containing epitopes has been correlated to red meat allergy. However, this association and the source of terminal, non-reducing α-Gal-containing epitopes have not previously been established in Brazil. Here, we employed the α-1,3-galactosyltransferase knockout mouse (α1,3-GalT-KO) model and bacteriophage Qβ-virus like particles (Qβ-VLPs) displaying Galα1,3Galβ1,4GlcNAc (Galα3LN) epitopes to investigate the presence of α-Gal-containing epitopes in the saliva of Amblyomma sculptum, a species of the Amblyomma cajennense complex, which represents the main tick that infests humans in Brazil. We confirmed that the α-1,3-galactosyltransferase knockout animals produce significant levels of anti-α-Gal antibodies against the Galα1,3Galβ1,4GlcNAc epitopes displayed on Qβ-virus like particles. The injection of A. sculptum saliva or exposure to feeding ticks was also found to induce both IgG and IgE anti-α-Gal antibodies in α-1,3-galactosyltransferase knockout mice, thus indicating the presence of α-Gal-containing epitopes in the tick saliva. The presence of α-Gal-containing epitopes was confirmed by ELISA and immunoblotting following removal of terminal α-Gal epitopes by α-galactosidase treatment. These results suggest for the first known time that bites from the A. sculptum tick may be associated with the unknown etiology of allergic reactions to red meat in Brazil.

Synthesis of Galα(1,3)Galβ(1,4)GlcNAcα-, Galβ(1,4)GlcNAcα- and GlcNAc-containing neoglycoproteins and their immunological evaluation in the context of Chagas disease.

The protozoan parasite, Trypanosoma cruzi, the etiologic agent of Chagas disease (ChD), has a cell surface covered by immunogenic glycoconjugates. One of the immunodominant glycotopes, the trisaccharide Galα(1,3)Galβ(1,4)GlcNAcα, is expressed on glycosylphosphatidylinositol-anchored mucins of the infective trypomastigote stage of T. cruzi and triggers high levels of protective anti-α-Gal antibodies (Abs) in infected individuals. Here, we have efficiently synthesized the mercaptopropyl glycoside of that glycotope and conjugated it to maleimide-derivatized bovine serum albumin (BSA). Chemiluminescent-enzyme-linked immunosorbent assay revealed that Galα(1,3)Galβ(1,4)GlcNAcα-BSA is recognized by purified anti-α-Gal Abs from chronic ChD patients ∼230-fold more strongly than by anti-α-Gal Abs from sera of healthy individuals (NHS anti-α-Gal). Similarly, the pooled sera of chronic Chagas disease patients (ChHSP) recognized Galα(1,3)Galβ(1,4)GlcNAcα ∼20-fold more strongly than pooled NHS. In contrast, the underlying disaccharide Galβ(1,4)GlcNAcα and the monosaccharide GlcNAcα or GlcNAcβ conjugated to BSA are poorly or not recognized by purified anti-α-Gal Abs or sera from Chagasic patients or healthy individuals. Our results highlight the importance of the terminal Galα moiety for recognition by Ch anti-α-Gal Abs and the lack of Abs against nonself Galβ(1,4)GlcNAcα and GlcNAcα glycotopes. The substantial difference in binding of Ch vs. NHS anti-α-Gal Abs to Galα(1,3)Galβ(1,4)GlcNAcα-BSA suggests that this neoglycoprotein (NGP) might be suitable for experimental vaccination. To this end, the Galα(1,3)Galβ(1,4)GlcNAcα-BSA NGP was then used to immunize α1,3-galactosyltransferase-knockout mice, which produced antibody titers 40-fold higher as compared with pre-immunization titers. Taken together, our results indicate that the synthetic Galα(1,3)Galβ(1,4)GlcNAcα glycotope coupled to a carrier protein could be a potential diagnostic and vaccine candidate for ChD.

Structural and Functional Analysis of a Platelet-Activating Lysophosphatidylcholine of Trypanosoma cruzi

Background Trypanosoma cruzi is the causative agent of the life-threatening Chagas disease, in which increased platelet aggregation related to myocarditis is observed. Platelet-activating factor (PAF) is a potent intercellular lipid mediator and second messenger that exerts its activity through a PAF-specific receptor (PAFR). Previous data from our group suggested that T. cruzi synthesizes a phospholipid with PAF-like activity. The structure of T. cruzi PAF-like molecule, however, remains elusive. Methodology/Principal findings Here, we have purified and structurally characterized the putative T. cruzi PAF-like molecule by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). Our ESI-MS/MS data demonstrated that the T. cruzi PAF-like molecule is actually a lysophosphatidylcholine (LPC), namely sn-1 C18:1(delta 9)-LPC. Similar to PAF, the platelet-aggregating activity of C18:1-LPC was abrogated by the PAFR antagonist, WEB 2086. Other major LPC species, i.e., C16:0-, C18:0-, and C18:2-LPC, were also characterized in all T. cruzi stages. These LPC species, however, failed to induce platelet aggregation. Quantification of T. cruzi LPC species by ESI-MS revealed that intracellular amastigote and trypomastigote forms have much higher levels of C18:1-LPC than epimastigote and metacyclic trypomastigote forms. C18:1-LPC was also found to be secreted by the parasite in extracellular vesicles (EV) and an EV-free fraction. A three-dimensional model of PAFR was constructed and a molecular docking study was performed to predict the interactions between the PAFR model and PAF, and each LPC species. Molecular docking data suggested that, contrary to other LPC species analyzed, C18:1-LPC is predicted to interact with the PAFR model in a fashion similar to PAF. Conclusions/Significance Taken together, our data indicate that T. cruzi synthesizes a bioactive C18:1-LPC, which aggregates platelets via PAFR. We propose that C18:1-LPC might be an important lipid mediator in the progression of Chagas disease and its biosynthesis could eventually be exploited as a potential target for new therapeutic interventions.

Evaluation of a chemiluminescent enzyme-linked immunosorbent assay for the diagnosis of Trypanosoma cruzi infection in a nonendemic setting

The disappearance of lytic, protective antibodies (Abs) from the serum of patients with Chagas disease is accepted as a reliable indicator of parasitological cure. The efficiency of a chemiluminescent enzyme-linked immunosorbent assay based on a purified, trypomastigote-derived glycosylphosphatidylinositol-anchored mucin antigen for the serologic detection of lytic Abs against Trypanosoma cruzi was evaluated in a nonendemic setting using a panel of 92 positive and 58 negative human sera. The technique proved to be highly sensitive {100%; 95% confidence interval (CI) = 96-100} and specific (98.3%; 95% CI = 90.7-99.7), with a kappa score of 0.99. Therefore, this assay can be used to detect active T. cruzi infection and to monitor trypanosomicidal treatment.

Altered Hypercoagulability Factors in Patients with Chronic Chagas Disease: Potential Biomarkers of Therapeutic Response

Thromboembolic events were described in patients with Chagas disease without cardiomyopathy. We aim to confirm if there is a hypercoagulable state in these patients and to determine if there is an early normalization of hemostasis factors after antiparasitic treatment. Ninety-nine individuals from Chagas disease-endemic areas were classified in two groups: G1, with T.cruzi infection (n = 56); G2, healthy individuals (n = 43). Twenty-four hemostasis factors were measured at baseline. G1 patients treated with benznidazole were followed for 36 months, recording clinical parameters and performance of conventional serology, chemiluminescent enzyme-linked immunosorbent assay (trypomastigote-derived glycosylphosphatidylinositol-anchored mucins), quantitative polymerase chain reaction, and hemostasis tests every 6-month visits. Prothrombin fragment 1+2 (F1+2) and endogenous thrombin potential (ETP) were abnormally expressed in 77% and 50% of infected patients at baseline but returned to and remained at normal levels shortly after treatment in 76% and 96% of cases, respectively. Plasmin-antiplasmin complexes (PAP) were altered before treatment in 32% of G1 patients but normalized in 94% of cases several months after treatment. None of the patients with normal F1+2 values during follow-up had a positive qRT-PCR result, but 3/24 patients (13%) with normal ETP values did. In a percentage of chronic T. cruzi infected patients treated with benznidazole, altered coagulation markers returned into normal levels. F1+2, ETP and PAP could be useful markers for assessing sustained response to benznidazole.