Increased production of reactive oxygen species by cells from mice acutely infected with Trypanosoma cruzi

Gasdermins in Innate Host Defense Against Entamoeba histolytica and Other Protozoan Parasites

Gasdermins (GSDMs) are a group of proteins that are cleaved by inflammatory caspases to induce pore formation in the plasma membrane to cause membrane permeabilization and lytic cell death or pyroptosis. All GSDMs share a conserved structure, containing a cytotoxic N-terminal (NT) pore-forming domain and a C-terminal (CT) repressor domain. Entamoeba histolytica (Eh) in contact with macrophages, triggers outside-in signaling to activate inflammatory caspase-4/1 via the noncanonical and canonical pathway to promote cleavage of gasdermin D (GSDMD). Cleavage of GSDMD removes the auto-inhibition that masks the active pore-forming NT domain in the full-length protein by interactions with GSDM-CT. The cleaved NT-GSDMD monomers then oligomerize to form pores in the plasma membrane to facilitate the release of IL-1β and IL-18 with a measured amount of pyroptosis. Pyroptosis is an effective way to counteract intracellular parasites, which exploit replicative niche to avoid killing. To date, most GSDMs have been verified to perform pore-forming activity and GSDMD-induced pyroptosis is rapidly emerging as a mechanism of anti-microbial host defence. Here, we review our comprehensive and current knowledge on the expression, activation, biological functions, and regulation of GSDMD cleavage with emphases on physiological scenario and related dysfunctions of each GSDM member as executioner of cell death, cytokine secretion and inflammation against Eh and other protozoan parasitic infections.

A terpenoid-rich extract from Clethra fimbriata exhibits anti-Trypanosoma cru zi activity and induces T cell cytokine production

Chagas disease, a worldwide public health concern, is a chronic infection caused by Trypanosoma cruzi. Considering T. cruzi chronic persistence correlates with CD4⁺ and CD8⁺ T cell dysfunction and the safety and efficacy profiles of Benznidazol and Nifurtimox, the two drugs currently used for its etiological treatment, are far from ideal, the search of new trypanocidal treatment options is a highly relevant issue. Therefore, the objective of this work was to evaluate the trypanocidal effect and cytokine production induction of three extracts (hexane, dichloromethane and hydroalcoholic) obtained from Clethra fimbriata, a plant traditionally used as a febrifuge in Colombia. Additionally, the extracts’ major components with the highest trypanocidal activity were determined. It was evidenced C. fimbriata hexane extract exhibited the highest activity capable of inhibiting the three parasite developmental stages with an IC₅₀/EC₅₀ of 153.9 ± 29.5 (epimastigotes), 39.3 ± 7.2 (trypomastigotes), and 45.6 ± 10.5 (amastigotes) μg/mL, presenting a low cytotoxicity in VERO cells with a selectivity index ranging from 6.49 to 25.4. Moreover, this extract induced trypomastigote apoptotic death and inhibited parasite cell infection. The extract also induced IFN-γ and TNF production in CD4⁺ and CD8⁺ T cells, as well as de novo production of the cytotoxic molecules granzyme B and perforin in CD8⁺ T cells from healthy donors. Fatty acids and terpenes represented C. fimbriata key compounds. Thus, the trypanocidal activity and cytokine production induction of the hexane extract may be associated with terpene presence, particularly, triterpenes.

Induction of Effective Immunity against Trypanosoma cruzi

Chagas disease, caused by Trypanosoma cruzi, is a major public health issue. Limitations in immune responses to natural T. cruzi infection usually result in parasite persistence with significant complications. A safe, effective, and reliable vaccine would reduce the threat of T. cruzi infections; however, no suitable vaccine is currently available due to a lack of understanding of the requirements for induction of fully protective immunity. We established a T. cruzi strain expressing green fluorescent protein (GFP) under the control of dihydrofolate reductase degradation domain (DDD) with a hemagglutinin (HA) tag, GFP-DDDHA, which was induced by trimethoprim-lactate (TMP-lactate), which results in the death of intracellular parasites. This attenuated strain induces very strong protection against reinfection. Using this GFP-DDDHA strain, we investigated the mechanisms underlying the protective immune response in mice. Immunization with this strain led to a response that included high levels of gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α), as well as a rapid expansion of effector and memory T cells in the spleen. More CD8⁺ T cells differentiate to memory cells following GFP-DDDHA infection than after infection with a wild-type (WT) strain. The GFP-DDDHA strain also provides cross-protection against another T. cruzi isolate. IFN-γ is important in mediating the protection, as IFN-γ knockout (KO) mice failed to acquire protection when infected with the GFP-DDDHA strain. Immune cells demonstrated earlier and stronger protective responses in immunized mice after reinfection with T. cruzi than those in naive mice. Adoptive transfers with several types of immune cells or with serum revealed that several branches of the immune system mediated protection. A combination of serum and natural killer cells provided the most effective protection against infection in these transfer experiments.

Molecular mechanisms of myocarditis caused by Trypanosoma cruzi

PURPOSE OF REVIEW

American trypanosomiasis, or Chagas disease, is a lifelong and persistent infection caused by the protozoan Trypanosoma cruzi and is the most significant cause of morbidity and mortality in South and Central America. Owing to immigration and additional risks from blood transfusion and organ transplantation, the number of reported cases of Chagas disease has increased recently in Europe and the USA. The disease is caused by a moderate to intense lasting inflammatory response that triggers local expression of inflammatory mediators and activates and recruits leukocytes to various tissues to eliminate the parasites.

RECENT FINDINGS

This long-term inflammatory process triggers biochemical, physiological and morphological alterations and clinical changes in the digestive, nervous and cardiac (e.g. myocarditis, arrhythmias, congestive heart failure, autonomic dysfunctions and microcirculatory disturbances) systems. Indeed, the pathogenesis of Chagas disease is intricate and multifactorial, and the roles of the parasite and the immune response in initiating and maintaining the disease are still controversial.

SUMMARY

In this review, we discuss the current knowledge of 'strategies' employed by the parasite to persist in the host and host defence mechanisms against Trypanosoma cruzi infection, which can result in equilibrium (absence of the disease) or disease development, mainly in the cardiac systems.

P47phox-/- mice are compromised in expansion and activation of CD8+ T cells and susceptible to Trypanosoma cruzi infection

Macrophage activation of NAD(P)H oxidase (NOX2) and reactive oxygen species (ROS) is suggested to kill Trypanosoma cruzi that causes Chagas disease. However, the role of NOX2 in generation of protective immunity and whether these mechanisms are deregulated in the event of NOX2 deficiency are not known, and examined in this study. Our data showed that C57BL/6 p47(phox-/-) mice (lack NOX2 activity), as compared to wild-type (WT) mice, succumbed within 30 days post-infection (pi) to low doses of T. cruzi and exhibited inability to control tissue parasites. P47(phox-/-) bone-marrow and splenic monocytes were not compromised in maturation, phagocytosis and parasite uptake capacity. The deficiency of NOX2 mediated ROS was compensated by higher level of inducible nitric oxide synthase (iNOS) expression, and nitric oxide and inflammatory cytokine (TNF-α, IFN-γ, IL-1β) release by p47(phox-/-) macrophages as compared to that noted in WT controls infected by T. cruzi. Splenic activation of Th1 CD4(+)T cells and tissue infiltration of immune cells in T. cruzi infected p47(phox-/-) mice were comparable to that noted in infected control mice. However, generation and activation of type 1 CD8(+)T cells was severely compromised in p47(phox-/-) mice. In comparison, WT mice exhibited a robust T. cruzi-specific CD8(+)T cell response with type 1 (IFN-γ(+)TNF-α>IL-4+IL-10), cytolytic effector (CD8(+)CD107a(+)IFN-γ(+)) phenotype. We conclude that NOX2/ROS activity in macrophages signals the development of antigen-specific CD8(+)T cell response. In the event of NOX2 deficiency, a compromised CD8(+)T cell response is generated, leading to increased parasite burden, tissue pathogenesis and mortality in chagasic mice.

The effects of nitric oxide on the immune system during Trypanosoma cruzi infection

Trypanosoma cruzi infection triggers substantial production of nitric oxide (NO), which has been shown to have protective and toxic effects on the host's immune system. Sensing of trypomastigotes by phagocytes activates the inducible NO-synthase (NOS2) pathway, which produces NO and is largely responsible for macrophage-mediated killing of T. cruzi. NO is also responsible for modulating virtually all steps of innate and adaptive immunity. However, NO can also cause oxidative stress, which is especially damaging to the host due to increased tissue damage. The cytokines IFN-gamma and TNF-alpha, as well as chemokines, are strong inducers of NOS2 and are produced in large amounts during T. cruzi acute infection. Conversely, TGF-beta and IL-10 negatively regulate NO production. Here we discuss the recent evidence describing the mechanisms by which NO is able to exert its antimicrobial and immune regulatory effects, the mechanisms involved in the oxidative stress response during infection and the implications of NO for the development of therapeutic strategies against T. cruzi.

Trypanosoma cruzi induces the reactive oxygen species-PARP-1-RelA pathway for up-regulation of cytokine expression in cardiomyocytes

In this study, we demonstrate that human cardiomyocytes (AC16) produce reactive oxygen species (ROS) and inflammatory cytokines in response to Trypanosoma cruzi. ROS were primarily produced by mitochondria, some of which diffused to cytosol of infected cardiomyocytes. These ROS resulted in an increase in 8-hydroxyguanine lesions and DNA fragmentation that signaled PARP-1 activation evidenced by poly(ADP-ribose) (PAR) modification of PARP-1 and other proteins in infected cardiomyocytes. Phenyl-alpha-tert-butylnitrone blocked the mitochondrial ROS (mtROS) formation, DNA damage, and PARP-1 activation in infected cardiomyocytes. Further inhibition studies demonstrated that ROS and PARP-1 signaled TNF-alpha and IL-1beta expression in infected cardiomyocytes. ROS directly signaled the nuclear translocation of RelA (p65), NF-kappaB activation, and cytokine gene expression. PARP-1 exhibited no direct interaction with p65 and did not signal its translocation to nuclei in infected cardiomyocytes. Instead, PARP-1 contributed to PAR modification of p65-interacting nuclear proteins and assembly of the NF-kappaB transcription complex. PJ34 (PARP-1 inhibitor) also prevented mitochondrial poly(ADP-ribosyl)ation (PARylation) and ROS formation. We conclude that T. cruzi-mediated mtROS provide primary stimulus for PARP-1-NF-kappaB activation and cytokine gene expression in infected cardiomyocytes. PAR modification of mitochondrial membranes then results in a feedback cycle of mtROS formation and DNA damage/PARP-1 activation. ROS, either through direct modulation of cytosolic NF-kappaB, or via PARP-1-dependent PAR modification of p65-interacting nuclear proteins, contributes to cytokine gene expression. Our results demonstrate a link between ROS and inflammatory responses in cardiomyocytes infected by T. cruzi and provide a clue to the pathomechanism of sustained inflammation in Chagas disease.

The anti-oxidant defence response in individuals with the indeterminate form of Chagas disease (American trypanosomiasis)

In previous studies in animal models, Trypanosoma cruzi-induced oxidative stress and damage have sometimes been controlled by the host's anti-oxidant defence responses. The role of the anti-oxidant defence responses, such as the activities of the anti-oxidant enzymes glutathione peroxidase (GPx) and superoxide dismutase (SOD), in protection against inflammation and damage have now been investigated in humans infected with T. cruzi. The subjects were 32 asymptomatic but seropositive individuals with the indeterminate form of Chagas disease, 18 symptomatic and seropositive patients with the chronic disease, and 50 seronegative and apparently healthy controls. The inflammatory process was explored using serum concentrations of tumour necrosis factor (TNF) and NO. The serum concentrations of GPx in the patients in the indeterminate phase of infection were similar to those in the controls but much higher than those in the chronic cases (P=0.001). The serum concentrations of SOD in the patients in the indeterminate phase of infection were not only significantly higher than those in the cases of chronic Chagas disease (P=0.0004) but also significantly higher than those in the controls (P<0.001). The seropositive subjects had significantly higher serum concentrations of TNF and NO than the controls (P<0.01 for each) and the cases of chronic Chagas disease had significantly higher serum concentrations of TNF and NO than the subjects with the indeterminate form of the disease (P<0.01 for each). It therefore appears that the host's anti-oxidant defence responses (at least in terms of elevated concentrations of SOD) may inhibit inflammation during the indeterminate phase of Chagas disease.

Protein 3-nitrotyrosine formation during Trypanosoma cruzi infection in mice

Nitric oxide (.NO) is a diffusible messenger implicated in Trypanosoma cruzi resistance. Excess production of .NO and oxidants leads to the generation of nitrogen dioxide (.NO2), a strong nitrating agent. Tyrosine nitration is a post-translational modification resulting from the addition of a nitro (-NO2) group to the ortho-position of tyrosine residues. Detection of protein 3-nitrotyrosine is regarded as a marker of nitro-oxidative stress and is observed in inflammatory processes. The formation and role of nitrating species in the control and myocardiopathy of T. cruzi infection remain to be studied. We investigated the levels of .NO and protein 3-nitrotyrosine in the plasma of C3H and BALB/c mice and pharmacologically modulated their production during the acute phase of T. cruzi infection. We also looked for protein 3-nitrotyrosine in the hearts of infected animals. Our results demonstrated that C3H animals produced higher amounts of .NO than BALB/c mice, but their generation of peroxynitrite was not proportionally enhanced and they had higher parasitemias. While N G-nitro-arginine methyl ester treatment abolished .NO production and drastically augmented the parasitism, mercaptoethylguanidine and guanido-ethyl disulfide, at doses that moderately reduced the .NO and 3-nitrotyrosine levels, paradoxically diminished the parasitemia in both strains. Nitrated proteins were also demonstrated in myocardial cells of infected mice. These data suggest that the control of T. cruzi infection depends not only on the capacity to produce .NO, but also on its metabolic fate, including the generation of nitrating species that may constitute an important element in parasite resistance and collateral myocardial damage.

Macrophage-derived peroxynitrite diffusion and toxicity to Trypanosoma cruzi

We studied the capacity of macrophage-derived peroxynitrite to diffuse into and exert cytotoxicity against Trypanosoma cruzi, the causative agent of Chagas' disease. In two types of macrophage-T. cruzi co-cultures, one with a fixed separation distance between source and target cells, and another involving cell-to-cell interactions, peroxynitrite resulted in significant oxidation of intracellular dihydrorhodamine and inhibition of [(3)H]thymidine incorporation in T. cruzi, which were not observed by superoxide or nitric oxide alone. The effects were attenuated in the presence of bicarbonate, in agreement with the extracellular consumption of peroxynitrite by its fast reaction with CO(2). However, studies using different T. cruzi densities, which allow to modify average diffusion distances of exogenously added peroxynitrite to target cells, indicate that at distances <5 microm, the diffusion process outcompetes the reaction with CO(2) and that the levels of peroxynitrite formed by macrophages would be sufficient to cause toxicity to T. cruzi during cell-to-cell contact and/or inside the phagosome.

Differing phagocytic function of monocytes and neutrophils in Chagas' cardiopathy according to the presence or absence of congestive heart failure

We evaluated the in vitro phagocytic function and the production of microbicidal oxygen radicals by monocytes and neutrophils of 9 Chagas' heart disease subjects with heart failure and 9 without the syndrome in comparison with 11 healthy subjects, by assessing phagocytosis of Saccharomyces cerevisiae and NBT reduction by peripheral blood phagocytes. Phagocytic index of monocytes of chagasics without heart failure was significantly 6.7 and 10.6 times lower than those of controls and chagasics with the congestive syndrome, respectively, due to a lesser engagement in phagocytosis and to an inability of these cells to ingest particles. Neutrophils also show in chagasics without heart failure PI 11.2 and 19.8 times lower than that of controls and chagasics with heart failure, respectively. The percent of NBT reduction was normal and similar for the three groups. Balanced opposite effects of cardiovascular and immune disturbances may be acting in Chagas' disease subjects with heart failure paradoxically recovering the altered phagocytic function.

Trypanosoma brucei and Trypanosoma cruzi Tryparedoxin Peroxidases Catalytically Detoxify Peroxynitrite via Oxidation of Fast Reacting Thiols

Macrophage activation is one of the hallmarks observed in trypanosomiasis, and the parasites must cope with the resulting oxidative burden, which includes the production of peroxynitrite, an unusual peroxo-acid that acts as a strong oxidant and trypanocidal molecule. Cytosolic tryparedoxin peroxidase (cTXNPx) has been recently identified as essential for oxidative defense in trypanosomatids. This peroxiredoxin decomposes peroxides using tryparedoxin (TXN) as electron donor, which in turn is reduced by dihydrotrypanothione. In this work, we studied the kinetics of the reaction of peroxynitrite with the different thiol-containing components of the cytosolic tryparedoxin peroxidase system in T. brucei (Tb) and T. cruzi (Tc), namely trypanothione, TXN, and cTXNPx. We found that whereas peroxynitrite reacted with dihydrotrypanothione and TbTXN at moderate rates (7200 and 3500 m(-1) s(-1), respectively, at pH 7.4 and 37 degrees C) and within the range of typical thiols, the second order rate constants for the reaction of peroxynitrite with reduced TbcTXNPx and TccTXNPx were 9 x 10(5) and 7.2 x 10(5) m(-1) s(-1) at pH 7.4 and 37 degrees C, respectively. This reactivity was dependent on a highly reactive cTXNPx thiol group identified as cysteine 52. Competition experiments showed that TbcTXNPx inhibited other fast peroxynitrite-mediated processes, such as the oxidation of Mn(3+)-porphyrins. Moreover, steady-state kinetic studies indicate that peroxynitrite-dependent TbcTXNPx and TccTXNPx oxidation is readily reverted by TXN, supporting that these peroxiredoxins would be not only a preferential target for peroxynitrite reactivity but also be able to act catalytically in peroxynitrite decomposition in vivo.

Involvement of nitric oxide (NO) and TNF-α in the oxidative stress associated with anemia in experimentalTrypanosoma cruziinfection

Trypanosoma cruzi infection in mice is associated with severe hematological changes, including anemia, which may contribute to mortality. TNF-alpha and nitric oxide (NO) play a critical role in establishing host resistance to this pathogen. We hypothesized that phagocyte-derived NO damages erythrocytes and contributes to the anemia observed during T. cruzi infection. To test this hypothesis, two strains of mice that differed in susceptibility and NO response to T. cruzi infection were used in these studies. We also blocked endogenous NO production by aminoguanidine (AG) treatment or blocked TNF-alpha with a neutralizing antibody and used mice that cannot produce phagocyte-derived NO (C57BL/6 iNOS(-/-)). Following infection with T. cruzi, resistant (C57BL/6) and susceptible (Swiss) mice displayed a parasitemia that peaked at the same time (i.e., day 9), yet parasitemia was 3-fold higher in Swiss mice (P < 0.05). All Swiss mice were dead by day 23 post-infection, while no C57BL/6 mice died during the study. At 14 days post-infection anemia in C57BL/6 mice was more severe than in Swiss mice. Treatment of both strains with the NO inhibitor, AG (50 mg/kg), and the use of iNOS(-/-) mice, revealed that the anemia in T. cruzi-infected mice is not caused by NO. However, the reticulocytosis that occurs during infection was significantly reduced after treatment with AG in both Swiss and C57BL/6 mice (P < 0.05). In addition, we showed that neutralization of TNF-alpha in vivo induced a significant increase in circulating reticulocytes in T. cruzi-infected C57BL/6 mice (P < 0.05), but did not modify other hematologic parameters in these mice. The evaluation of the oxidative stress after induction by t-butyl hydroperoxide (t-BHT) revealed that the treatment with AG completely protected against NO-mediated haemoglobin oxidation. Further, treatment with AG, but not with anti-TNF-alpha, protected against the infection-induced reduction of antioxidant capacity of erythrocytes as assessed by oxygen uptake and induction time. In summary, this is the first report showing the participation of NO and TNF-alpha in the oxidative stress to erythrocytes in acute T. cruzi infection. Further, our data suggest that NO does not play a direct role in development of the anemia. However, NO may contribute to other hematological changes noted during T. cruzi infection, such as the elevation of circulating reticulocytes and the reduction in circulating leukocytes and neutrophils.

Trypanosoma cruzi infection in tumor necrosis factor receptor p55-deficient mice

Tumor necrosis factor receptor p55 (TNFRp55) mediates host resistance to several pathogens by allowing microbicidal activities of phagocytes. In the studies reported here, TNFRp55-/- mice infected with the intracellular parasite Trypanosoma cruzi showed clearly higher parasitemia and cumulative mortality than wild-type (WT) controls did. However, gamma interferon (IFN-gamma)-activated macrophages from TNFRp55-/- mice produced control levels of nitric oxide and killed the parasite efficiently in vitro. Trypanocidal mechanisms of nonphagocytic cells (myocardial fibroblasts) from both TNFRp55-/- and WT mice were also activated by IFN-gamma in a dose-dependent way. However, IFN-gamma-activated TNFRp55-/- nonphagocytes showed less effective killing of T. cruzi than WT control nonphagocytes, even when interleukin 1beta (IL-1beta) was added as a costimulator. In vivo, T. cruzi-infected TNFRp55-/- mice and WT mice released similar levels of NO and showed similar levels of IFN-gamma mRNA and inducible nitric oxide synthase mRNA in their tissues. Instead, increased susceptibility to T. cruzi of TNFRp55-/- mice was associated with reduced levels of parasite-specific immunoglobulin G (IgG) (but not IgM) antibodies during infection, which is probably linked to abnormal B-cell differentiation in secondary lymphoid tissues of the mutant mice. Surprisingly, T. cruzi-infected TNFRp55-/- mice showed increased inflammatory and necrotic lesions in several tissues, especially in skeletal muscles, indicating that TNFRp55 plays an important role in controlling the inflammatory process. Accordingly, levels of Mn2+ superoxide dismutase mRNA, a TNF-induced enzyme which protects the cell from the toxic effects of superoxide, were lower in mutant than in WT infected mice.

In vivo macrophage function in experimental infection with Trypanosoma cruzi subpopulations

The macrophage function was investigated in mice infected with Trypanosoma cruzi. Two subpopulations of the parasite were utilized, RA and K98. Strain RA is efficiently internalized by macrophages and is lethal for mice, and clone K98 is poorly phagocytosed by macrophages and is not lethal. Treatment with silica enhanced parasitemia and mortality in mice infected with both parasite subpopulations. Parasitemia kinetics, however, were affected only in mice infected with RA, which suggests that macrophage effector mechanisms may play a more relevant role in this experimental group than in mice infected with K98. Resistance to Salmonella typhimurium infection and bactericidal activity of macrophages depended upon the T. cruzi subpopulation utilized and the infection period. Infection with K98 induced only a trend towards enhanced resistance to bacterial challenge during both the acute and chronic phases, whereas a significantly enhanced bactericidal activity of spleen and liver phagocytes was observed. Mice acutely infected with RA showed significantly enhanced susceptibility to S. typhimurium infection and lower bactericidal activity. Mice surviving infection with this aggressive strain, however, showed significantly enhanced resistance and bactericidal activities. Mice acutely infected with the RA strain displayed a dissociation between macrophage capacities to control S. typhimurium and T. cruzi. A similar phenomenon was also observed in other parasitoses (schistosomiasis, African trypanosomiasis). This fact may be due to differences in the lethal mechanisms through which macrophages control these parasites and S. typhimurium.

Trypanosoma cruzi: enhanced alpha-macroglobulin levels correlate with the resistance of BALB/cj mice to acute infection

Trypanosoma cruzi proteinases are very likely involved in host-cell invasion. Physiological plasma-proteinase inhibitors from the macroglobulin (MG) family, among them alpha-2-macroglobulin (A2M), are found in tissues and in the plasma of mammals. By complexing to all classes of proteinases, MGs inhibit their action on high-molecular-weight substrates. In vitro studies have shown that A2M impairs T. cruzi proteases and, consequently, the parasite's ability to invade host cells and enhances the phagocytic and microbicidal actions of resident macrophages against T. cruzi. To test the hypothesis of a putative "protective" effect for MG, we quantified it in BALB/cj mice during the course of an experimental T. cruzi infection, comparing a posteriori the levels in mice that died with those in animals that survived, which were considered as being susceptible and resistant to the infection, respectively. The results showed that surviving mice showed an increase in plasma concentrations of MG during the first few weeks after the infection, whereas the levels in mice that died during the acute phase did not differ significantly from those in non-infected mice. These findings and the previous in vitro data indicate a role for physiological proteinase inhibitors, particularly alpha-macroglobulins, in resistance to T. cruzi infection, whereby a balance between parasite proteases and host protease inhibitors may be crucial. MG may thus participate in the complex network of reactions involved in the early acute phase of the disease and contribute by conferring to the host an ability to survive the infection.