Introducing the NUATEI Consortium: A Mexican Research Program for the Identification of Natural and Synthetic Antimicrobial Compounds for Prevalent Infectious Diseases.

The need for new drugs to treat human infections is a global health concern. Diseases like tuberculosis, trypanosomiasis, amoebiasis, and AIDS remain significant problems, especially in developing countries like Mexico. Despite existing treatments, issues such as resistance and adverse effects drive the search for new alternatives. Herein, we introduce the NUATEI research consortium, made up of experts from the Institute of Biomedical Research at UNAM, who identify and obtain natural and synthetic compounds and test their effects against human pathogens using in vitro and in vivo models. The consortium has evaluated hundreds of natural extracts and compounds against the pathogens causing tuberculosis, trypanosomiasis, amoebiasis, and AIDS, rendering promising results, including a patent with potential for preclinical studies. This paper presents the rationale behind the formation of this consortium, as well as its objectives and strategies, emphasizing the importance of natural and synthetic products as sources of antimicrobial compounds and the relevance of the diseases studied. Finally, we briefly describe the methods of the evaluation of the compounds in each biological model and the main achievements. The potential of the consortium to screen numerous compounds and identify new therapeutic agents is highlighted, demonstrating its significant contribution to addressing these infectious diseases.

A Promising Amphotericin B Derivative Induces Morphological Alterations, Mitochondrial Damage, and Oxidative Stress In Vitro and Prevents Mice from Death Produced by a Virulent Strain of Trypanosoma cruzi.

Chagas Disease is a neglected tropical disease caused by the protozoan parasite Trypanosoma cruzi, affecting 6-8 million people, mainly in Latin America. The medical treatment is based on two compounds, benznidazole and nifurtimox, with limited effectiveness and that produce severe side effects; consequently, there is an urgent need to develop new, safe, and effective drugs. Amphotericin B is the most potent antimycotic known to date. A21 is a derivative of this compound with the property of binding to ergosterol present in cell membranes of some organisms. In the search for a new therapeutic drug against T. cruzi, the objective of this work was to study the in vitro and in vivo effects of A21 derivative on T. cruzi. Our results show that the A21 increased the reactive oxygen species and reduced the mitochondrial membrane potential, affecting the morphology, metabolism, and cell membrane permeability of T. cruzi in vitro. Even more important was finding that in an in vivo murine model of infection, A21 in combination with benznidazole was able to reduce blood parasitemia, diminish the immune inflammatory infiltrate in skeletal muscle and rescue all the mice from death due to a virulent T. cruzi strain.

First Report of Seropositivity to Trypanosoma cruzi in Mexican Afro-Descendants from Guerrero and Oaxaca States.

Mexican Afro-descendant is a population poorly studied in many aspects, between them the infectious diseases that they suffer. This population is mainly found in the country's Pacific (Oaxaca and Guerrero states) and Atlantic (Veracruz) coast. In these regions, a diversity of triatomine vectors of the Chagas disease is found. Also, all the genotypes of Trypanosoma cruzi DTUs have been reported. That is why the present study aimed to study the presence of antibodies against T. cruzi and cardiac pathology associated with the Chagas disease in the Mexican Afro-descendant population of Guerrero and Oaxaca. ELISA, Western blot, and recombinant antigen's ELISA were used to evaluate the seropositivity of these communities. Furthermore, an electrocardiographic study and evaluation of risk factors associated with T. cruzi infection in the Oaxaca and Guerrero populations were conducted. 26.77% of the analyzed population was positive for two serological tests. These percentages are higher than the previously reported for the mestizo population in similar studies. Electrocardiographic results showed cardiac disorder associated with the Chagas disease in the population. Also, risk factors were identified associated with the men's activities in the outdoor working areas.

Role of a 49 kDa Trypanosoma cruzi Mucin-Associated Surface Protein (MASP49) during the Infection Process and Identification of a Mammalian Cell Surface Receptor.

Trypanosoma cruzi is the etiologic agent of Chagas disease, a parasitic disease of great medical importance on the American continent. Trypomastigote infection's initial step in a mammalian host is vital for the parasite's life cycle. A trypomastigote's surface presents many molecules, some of which have been proposed to be involved in the infection process, including a glycoprotein family called mucin-associated surface proteins (MASPs). This work describes a 49-kDa molecule (MASP49) that belongs to this family and is expressed mainly on the surfaces of amastigotes and trypomastigotes but can be found in extracts and the membrane-enriched fractions of epimastigotes. This protein is partially GPI-anchored to the surface and has a role during the internalization process, since its blockade with specific antibodies decreases parasite entry into Vero cells by 62%. This work shows that MASP49 binds to peritoneal macrophages and rat cardiomyocytes, undergoes glycosylation via galactose N-acetylgalactosamine, and can attach to the macrophage murine C-type lectin receptor (mMGL). These results suggest that MASP49 can be considered a virulence factor in T. cruzi, and a better understanding of its role in the infection process is necessary.

Trypanosoma cruzi blood trypomastigotes induce intense skeletal and cardiac muscle damage and Th1/ Th2 immune response in the acute phase of mice infected by the oral route.

Oral acquisition of Trypanosoma cruzi is a foodborne transmission by juices and fruits contaminated with metacyclic trypomastigotes (MT) or by the ingestion of wild reservoirs infected with blood trypomastigotes (BT). In Mexico, hunting and food consumption of wild animals are current practices, which could represent a risk factor for oral infection in the rural population. In this work, Balb/c mice were inoculated by oral route with BT of a highly virulent T. cruzi Mexican strain (DTU I) to evaluate the establishment of the infection, and the humoral and cellular immune response in the acute phase of the infection. We show that BT induces blood and tissue parasitism producing an inflammatory process in the heart and skeletal muscle and low parasitism and inflammation in the digestive tract of orally infected mice. Besides, in the acute phase, the BT promotes splenomegaly, intense damage in skeletal and cardiac muscles, a humoral response dominated by the IgG isotype, and the expression of pro-inflammatory cytokines.

Structural New Data for Mitochondrial Peroxiredoxin From Trypanosoma cruzi Show High Similarity With Human Peroxiredoxin 3: Repositioning Thiostrepton as Antichagasic Drug.

Trypanosoma cruzi, the causal agent of Chagas disease, has peroxiredoxins (PRXs) expressed in all stages of the parasite and whose function is to detoxify oxidizing agents, such as reactive oxygen species (ROS). These proteins are central for the survival and replication of the parasite and have been proposed as virulence factors. Because of their importance, they have also been considered as possible therapeutic targets, although there is no specific drug against them. One of them, the mitochondrial PRX (TcMPX), is important in the detoxification of ROS in this organelle and has a role in the infectivity of T. cruzi. However, their structural characteristics are unknown, and possible inhibitors have not been proposed. The aim was to describe in detail some structural characteristics of TcMPX and compare it with several PRXs to find possible similarities and repositioning the antibiotic Thiostrepton as a potential inhibitor molecule. It was found that, in addition to the characteristic active site of a 2-cys PRX, this protein has a possible transmembrane motif and motifs involved in resistance to hyper oxidation. The homology model suggests a high structural similarity with human PRX3. This similarity was corroborated by cross-recognition using an anti-human PRX antibody. In addition, molecular docking showed that Thiostrepton, a potent inhibitor of human PRX3, could bind to TcMPX and affect its function. Our results show that Thiostrepton reduces the proliferation of T. cruzi epimastigotes, cell-derived trypomastigotes, and blood trypomastigotes with low cytotoxicity on Vero cells. We also demonstrated a synergic effect of Thriostepton and Beznidazol. The convenience of seeking treatment alternatives against T. cruzi by repositioning compounds as Thiostrepton is discussed.

Differential activity on trypanosomatid parasites of a novel recombinant defensin type 1 from the insect Triatoma (Meccus) pallidipennis.

Defensins are one of the major families of antimicrobial peptides (AMPs) that are widely distributed in insects. In Triatomines (Hemiptera: Reduviidae) vectors of Trypanosoma cruzi the causative agent of Chagas disease, two large groups of defensin isoforms have been described: type 1 and type 4. The aim of this study was to analyze the trypanocidal activity of a type 1 recombinant defensin (rDef1.3) identified in Triatoma (Meccus) pallidipennis, an endemic specie from México. The trypanocidal activity of this defensin was evaluated in vitro, against the parasites T. cruzi, T. rangeli, and two species of Leishmania (L. mexicana and L. major) both causative agents of cutaneous leishmaniasis. Our data demonstrated that the defensin was active against all the parasites although in different degrees. The defensin altered the morphology, reduced the viability and inhibited the growth of T.cruzi. When tested against T. rangeli (a parasite that infects a variety of mammalian species), stronger morphological effects where observed. Surprisingly the greatest effects were observed against the two Leishmania species, of which L. major was the parasite most affected with 50% of dead cells or with damaged membranes, in addition of a reduction in its proliferative capacity in culture. These results suggest that rDef1.3 has an important antimicrobial effect against trypanosomatids which cause some of the more important neglected tropical diseases transmitted by insect vectors.

Differential gene expression of virulence factors modulates infectivity of TcI Trypanosoma cruzi strains.

Trypanosoma cruzi is the etiological agent of Chagas disease, whose clinical outcome ranges from asymptomatic individuals to chronic fatal megasyndromes. Despite being central to pathogenesis, the regulation of parasite virulence factors' expression remains largely unknown. In this work, the relative expression of several parasite virulence factors between two TcI strains (Ninoa, low virulence and Qro, high virulence) was assessed by qRT-PCR of total and of polysome-associated mRNA, as well as by western blots. Trypomastigotes were also incubated with specific anti-sense morpholino oligonucleotides to block the translation of a selected virulence factor, calreticulin, in both strains. Ninoa trypomastigotes showed significantly lower levels of trypomastigote-decay acceleration factor, complement regulatory protein, complement C2 receptor inhibitor trispanning, and glycoproteins 82 and 90 mRNAs compared with Qro. There was a significantly lower recruitment of complement regulatory protein and complement C2 receptor inhibitor trispanning mRNAs to polysomes and higher recruitment of MASP mRNA to monosomes in Ninoa strain. Calreticulin mRNA displayed both a higher total mRNA level and recruitment to translationally active polysomes in the Ninoa strain (low virulence) than in the Qro strain (high virulence). When calreticulin was downregulated by ≈ 50% by anti-sense morpholino oligonucleotides, a significant decrease of parasite invasion in mammalian cells was found in both strains. Calreticulin downregulation, however, only increased significantly the activation of the complement system by Ninoa trypomastigotes. These results suggest a role for the regulation of virulence factors' gene expression in the differential virulence among T. cruzi strains. Furthermore, a possible function of calreticulin in parasite invasion not related to its binding to complement factors is shown.

Delivery of Antisense DNA into Pathogenic Parasite Trypanosoma cruzi Using Virus-Like Protein-Based Nanoparticles.

Trypanosoma cruzi, which causes Chagas disease, is one of the most lacerating parasites in terms of health and social impacts. New approaches for its study and treatment are urgently needed since in more than 50 years only two drugs have been approved. Genetic approaches based on antisense oligonucleotides (AONs) are promising; however, to harness their full potential the development of effective carriers is paramount. Here, we report the use of an engineered virus-like protein C-BK12 to transfect AONs into T. cruzi. Using gel electrophoresis, Dynamic Light Scattering, and atomic force microscopy, we found that C-BK12 binds AONs and forms 10-25 nm nanoparticles (NPs), which are very stable when incubated in biological media, only releasing up to 25% of AON. Fluorescence microscopy and qPCR revealed that the NPs successfully delivered AONs into epimastigotes and reduced the expression of a target gene down to 68%. Importantly, the protein did not show cytotoxicity. The combination of high stability and capability to transfect and knock down gene expression without causing cell damage and death makes the protein C-BK12 a promising starting point for the further development of safe and effective carriers to deliver AONs into T. cruzi for biological studies.

Mammea type coumarins isolated from Calophyllum brasiliense induced apoptotic cell death of Trypanosoma cruzi through mitochondrial dysfunction, ROS production and cell cycle alterations.

Chagas Disease is a neglected tropical disease caused by the protozoan parasite Trypanosoma cruzi which affects 6-8 million people, mostly in Latin America. The medical treatment is based on two nitroimidazole compounds, which have limited effectiveness in the chronic phase of the disease and produce several adverse effects; consequently, there is an urgent need to develop new, safe, and effective drugs. Previous reports had shown that natural coumarins, especially mammea A/BA isolated from the tropical tree Calophyllum brasiliense, is a promissory molecule for developing new drugs, due to its potent activity, higher than benznidazole, selectivity, and its low toxicity in mice. However, its mode of action is still unknown. In the present work, we evaluated the mechanism of action of the coumarin mammea A/BA (93.6%), isolated from the tropical tree C. brasiliense on Querétaro strain (Tc1) of T. cruzi. This compound was tested in vitro on epimastigotes and trypomastigotes of T. cruzi for intracellular esterase activity, plasma membrane integrity, phosphatidylserine exposure, ROS production, mitochondrial membrane potential, caspase-like activity, DNA integrity, cell cycle and autophagy. Mammea A/BA showed a 50% lethal concentration (LC50) of 85.8 and 36.9 µM for epimastigotes and trypomastigotes respectively. It affected intracellular esterase activity, produced important plasma membrane damage and induced phosphatidylserine exposure. An increase in reactive oxygen species (ROS) and decrease in mitochondrial membrane potential were detected. Caspase-like activity was present in both parasite forms producing DNA integrity damage. This compound also induced a cell cycle arrest in the G1 phase and the presence of autophagy vacuoles. The above data suggest that mammea A/BA induce cell death of T. cruzi by autophagy and apoptosis-like phenomena and support our suggestion that mammea A/BA could be a promising molecule for the development of new drugs to treat Chagas Disease.

Hopane-type triterpenes from Cnidoscolus spinosus and their bioactivities.

Chemical investigation of the aerial parts of Cnidoscolus spinosus resulted in the isolation of relatively infrequent hopane-type triterpenes, 3ß-acetoxy-hop-22(29)-ene (1), first reported here as natural product, together with 3-oxo-hop-22(29)-ene (2), and 3ß-hydroxy-hop-22(29)-ene (3). ß-Amyrin palmitate and three phytosterols were also characterized. The structures of the compounds were established using spectroscopic methods, and those of 1 and 2 were confirmed by crystallographic analysis. Selected biological activities for the isolated hopane-type triterpenes were tested through a series of assays for determining the cytotoxic, anti-inflammatory, α-glucosidase inhibition and antiparasitic activities. Compounds 1-3 did not show cytotoxic activity, compound 1 displayed an important inhibitory effect in the mouse ear induced inflammation assay, and significantly inhibited the yeast α-glucosidase activity in vitro and in silico. Additionally, compounds 2 and 3 showed marginal activities against Trypanosoma cruzi and Leishmania mexicana. Therefore, the bioactivities of hopane-type triterpenes deserve further investigation, particularly their anti-inflammatory properties.

Coumarins isolated from Calophyllum brasiliense produce ultrastructural alterations and affect in vitro infectivity of Trypanosoma cruzi.

BACKGROUND: The current drugs for Chagas Disease caused by the protozoan Trypanosoma cruzi have limited therapeutic potential and are associated with serious side effects. Natural products can aid to develop new chemotherapeutic agents. Several natural coumarins, especially Mammea A/BA, have shown significant activity against T. cruzi and low toxicity on human lymphocytes, but its effectivity on a wide range of strains need to be tested, as well as to deepen in their mode of action and safety. HYPOTHESIS/PURPOSE: To discern the effects and explore the action mechanisms of mammea A/BA and a mixture of mammea coumarins isolated from Calophyllum brasiliense on Mexican strains of T. cruzi belonging to different genotypes and compare its effectivity with the drug benznidazole. STUDY DESIGN: We evaluated the trypanocidal activity in vitro of mammea A/BA (93.6%), and a mixture of coumarins, mammea A/BA + A/BB + A/BD (86:10:1%) on Mexican T. cruzi strains belonging to different genotypes Ninoa, Querétaro (TcI) and Ver6 (TcVI). MATERIAL AND METHODS: Mammea A/BA and the mixture of coumarins, were isolated from Calophyllum brasiliense, identified by proton NMR and purity determined by HPLC. The in vitro trypanocidal activity was evaluated on mobility, growth recovery, morphology and infectivity of T. cruzi. The cytotoxicity on mammalian cells was compared with benznidazole. The ultrastructure of the treated epimastigotes was analyzed by transmission electron microscopy (TEM). RESULTS: Mammea A/BA and the mixture of coumarins showed high trypanocidal activity, affecting the mobility, growth recovery, morphology, ultrastructure of epimastigotes, and drastically reduce trypomastigotes infectivity on Vero cells. These substances were four times more potent than benznidazole and showed low cytotoxicity and high selectivity index. The TEM showed severe alterations on the plasmatic membrane, nuclear envelope, as well as, mitochondrial swelling, that leads to the death of parasites. CONCLUSION: Mammea A/BA (93.6%) and a mixture of mammea A/BA + A/BB and A/BD (86: 10: 1%) isolated from the tropical tree C. brasiliense showed higher trypanocidal activity than the current drug benznidazole on three Mexican strains of T. cruzi. These compounds induced severe physiological and morphological alterations. These results suggest their possible use in preclinical studies.

Immune reactivity to Trypanosoma cruzi chimeric proteins for Chagas disease diagnosis in immigrants living in a non-endemic setting.

BACKGROUND: Chronic Chagas Disease (CD) diagnosis is based on serological methods employing crude, semipurified or recombinant antigens, which may result in low sensitivity or cross-reactivity. To reduce these restrictions, we developed a strategy involving use of molecules containing repetitive fragments of Trypanosoma cruzi conserved proteins. Diagnostic performance of IBMP-8.1 and IBMP-8.4 chimeric antigens (Molecular Biology Institute of Paraná - IBMP in Portuguese acronym) was assessed to diagnose T. cruzi-infected and non-infected immigrants living in Barcelona (Spain), a non-endemic setting for Chagas disease. METHODS: Reactivity of IBMP-8.1 and IBMP-8.4 was assessed using an in-house automated ELISA with 347 positive and 331 negative individuals to Chagas disease. Antigenic cross-reactivity was measured with sera samples from pregnant women with Toxoplasma gondii (n = 98) and Zika virus (n = 75) antibodies. RESULTS: The area under the curve values was 1 and 0.99 for the IBMP-8.1 and IBMP-8.4 proteins, respectively, demonstrating excellent diagnostic accuracy. The reactivity index was higher for IBMP-8.1 than IBMP-8.4 in positive samples and no significant difference in reactivity index was observed in negative samples. Sensitivity ranged from 99.4% for IBMP-8.1 to 99.1% for IBMP-8.4 and was not statistically different. Specificity for IBMP-8.1 reached 100 and 99.7% for IBMP-8.4, both nearly 100% accurate. No antigenic cross-reactivity was observed and reactivity index was similar to that for negative Chagas disease individuals. CONCLUSIONS: Our results showed an outstanding performance of IBMP-8.1 and IBMP-8.4 chimeric antigens by ELISA and suggest both chimeric antigens could also be used for Chagas disease diagnosis in immigrants living in non-endemic settings.

First report of family clusters of Chagas disease seropositive blood donors in Mexico City and their epidemiological relevance.

BACKGROUND: Chagas disease is an important health problem in Latin America. Relatives of T. cruzi seropositive donors could also test positive in serological assays. Therefore, the study of Chagas diseases in family clusters has become important to accurately evaluate the problem that this infectious disease represents. OBJECTIVE: to investigate family cluster from blood donors, their serological, clinical and epidemiological status. METHODS: 53 family clusters consisting of index case and a variable number of relatives were studied. All the participants had ELISA and Western blot assays, as well as, clinical tests including an electrocardiogram and chest x ray. RESULTS: We found that 24.52% of the family clusters had at least one T. cruzi seropositive family member, in addition to the blood donor. Importantly, 20.75% of the index cases and 5.0% of the relatives presented pathological manifestations associated to Chagas disease. Several epidemiological conditions are associated to being T. cruzi seropositive. CONCLUSION: blood donor's family clusters have several seropositive to T. cruzi members. Mother-child pairs were also seropositive, suggesting vertical transmition. Pathological symptom associated to Chagas Diseases were present in index cases and family member. These results highlight the importance of studying family clusters to clarify the true magnitude of Chagas disease in Mexico.

Glycosylation on proteins of the intestine and perimicrovillar membrane of Triatoma (Meccus) pallidipennis, under different feeding conditions.

Trypanosoma cruzi, the causative agent of Chagas disease, interacts with molecules in the midgut of its insect vector to multiply and reach the infective stage. Many studies suggest that the parasite binds to midgut-specific glycans. We identified several glycoproteins expressed in the intestine and perimicrovillar membrane (PMM) of Triatoma (Meccus) pallidipennis under different feeding conditions. In order to assess changes in protein-linked glycans, we performed lectin and immunoblot analyses on glycoprotein extracts from these intestinal tissues using well-characterized lectins, and an antibody, which collectively recognize a wide range of different glycans epitopes. We observed that the amount and composition of proteins and glycoproteins associated with different glycans structures changed over time in the intestines and PMM under different physiological conditions. PMM extracts contained a wide variety of glycoproteins with different sugar residues, including abundant high-mannose and complex sialylated glycans. We propose that these molecules could be involved in the process of parasite-vector interactions.

Variability of defensin genes from a Mexican endemic Triatominae: Triatoma (Meccus) pallidipennis (Hemiptera: Reduviidae).

Chagas disease remains a serious health problem for countries where the most common mode of transmission is infection contracted from the feces of a Triatominae insect vector. In México, 32 species of Triatoma have been identified; amongst them, Triatoma (Meccus) pallidipennis is an endemic species reported to have high percentages of infection with T. cruzi Defensins, cysteine-rich cationic peptides, are a family of antimicrobial peptides (AMPs); the synthesis of these molecules is crucial for insect's immune defense. In the present study, the genes encoding defensins in T. pallidipennis were sequenced with the purpose of identifying the variability of these genes in a Mexican vector of T. cruzi We found 12 different genes encoding three mature peptides, all of which had the typical folding of a functional insect defensin. In this work two Defensins type 1 and one type 4 were identified. The pro-peptide domain was highly variable and the mature peptide was not. This is the first report focus on variability of defensins from an epidemiologically important Triatoma in Mexico.

Computational Methods to Discover Compounds for the Treatment of Chagas Disease.

Infectious diseases continue to be a major public health. Among these diseases, American trypanosomiasis or Chagas disease (CD) is a major cause of morbidity and death for millions of people in Latin America. The two drugs currently available for the treatment of CD have poor efficacy and major side effects. Thus, there is a pressing need to develop safe and effective drugs against this disease. Herein we review the diversity and coverage of chemical space of compounds tested as inhibitors of Trypanosoma cruzi, a parasite causing CD. We also review major molecular targets currently pursued to kill the parasite and recent computational approaches to identify inhibitors for such targets.

Complement system contributes to modulate the infectivity of susceptible TcI strains of Trypanosoma cruzi.

BACKGROUND: Trypanosoma cruzi is a protozoan parasite and an etiological agent of Chagas disease. There is a wide variability in the clinical outcome of its infection, ranging from asymptomatic individuals to those with chronic fatal mega syndromes. Both parasite and host factors, as well as their interplay, are thought to be involved in the process. OBJECTIVES: To evaluate the resistance to complement-mediated killing in two T. cruzi TcI strains with differential virulence and the subsequent effect on their infectivity in mammalian cells. METHODS: Tissue-culture derived trypomastigotes of both strains were incubated in guinea pig serum and subjected to flow cytometry in order to determine their viability and complement activations. Trypomastigotes were also incubated on host cells monolayers in the presence of serum, and infectivity was evaluated under different conditions of complement pathway inhibition. Relative expression of the main parasite-specific complement receptors between the two strains was assessed by quantitative real-time polymerase chain reaction. FINDINGS: In this work, we showed that two TcI strains, one with lower virulence (Ninoa) compared to the other (Qro), differ in their resistance to the lytic activity of complement system, hence causing a compromised ability of Ninoa strain to invade mammalian cells. These results correlate with the three-fold lower messenger RNA (mRNA) levels of complement regulatory protein (CRP), trypomastigote-decay acceleration factor (T-DAF), and complement C2 receptor inhibitor trispanning (CRIT) in Ninoa compared to those in Qro. On the other hand, calreticulin (CRT) mRNA and surface protein levels were higher in Ninoa strain and promoted its infectivity when the lectin pathway of the complement system was inhibited. MAIN CONCLUSIONS: This work suggests the complex interplay of CRP, T-DAF, CRIT, and CRT, and the diagnostic value of mRNA levels in the assessment of virulence potential of T. cruzi strains, particularly when dealing with isolates with similar genetic background.

Complement system contributes to modulate the infectivity of susceptible TcI strains of Trypanosoma cruzi

BACKGROUND Trypanosoma cruzi is a protozoan parasite and an etiological agent of Chagas disease. There is a wide variability in the clinical outcome of its infection, ranging from asymptomatic individuals to those with chronic fatal mega syndromes. Both parasite and host factors, as well as their interplay, are thought to be involved in the process. OBJECTIVES To evaluate the resistance to complement-mediated killing in two T. cruzi TcI strains with differential virulence and the subsequent effect on their infectivity in mammalian cells. METHODS Tissue-culture derived trypomastigotes of both strains were incubated in guinea pig serum and subjected to flow cytometry in order to determine their viability and complement activations. Trypomastigotes were also incubated on host cells monolayers in the presence of serum, and infectivity was evaluated under different conditions of complement pathway inhibition. Relative expression of the main parasite-specific complement receptors between the two strains was assessed by quantitative real-time polymerase chain reaction. FINDINGS In this work, we showed that two TcI strains, one with lower virulence (Ninoa) compared to the other (Qro), differ in their resistance to the lytic activity of complement system, hence causing a compromised ability of Ninoa strain to invade mammalian cells. These results correlate with the three-fold lower messenger RNA (mRNA) levels of complement regulatory protein (CRP), trypomastigote-decay acceleration factor (T-DAF), and complement C2 receptor inhibitor trispanning (CRIT) in Ninoa compared to those in Qro. On the other hand, calreticulin (CRT) mRNA and surface protein levels were higher in Ninoa strain and promoted its infectivity when the lectin pathway of the complement system was inhibited. MAIN CONCLUSIONS This work suggests the complex interplay of CRP, T-DAF, CRIT, and CRT, and the diagnostic value of mRNA levels in the assessment of virulence potential of T. cruzi strains, particularly when dealing with isolates with similar genetic background.

Ultrastructural and physiological changes induced by different stress conditions on the human parasite Trypanosoma cruzi.

Trypanosoma cruzi is the etiological agent of Chagas disease. The life cycle of this protozoan parasite is digenetic because it alternates its different developmental forms through two hosts, a vector insect and a vertebrate host. As a result, the parasites are exposed to sudden and drastic environmental changes causing cellular stress. The stress response to some types of stress has been studied in T. cruzi, mainly at the molecular level; however, data about ultrastructure and physiological state of the cells in stress conditions are scarce or null. In this work, we analyzed the morphological, ultrastructural, and physiological changes produced on T. cruzi epimastigotes when they were exposed to acid, nutritional, heat, and oxidative stress. Clear morphological changes were observed, but the physiological conditions varied depending on the type of stress. The maintenance of the physiological state was severely affected by heat shock, acidic, nutritional, and oxidative stress. According to the surprising observed growth recovery after damage by stress alterations, different adaptations from the parasite to these harsh conditions were suggested. Particular cellular death pathways are discussed.