Chagasic Hearts Research Articles

Canonical PI3K\u03b3 signaling in myeloid cells restricts Trypanosoma cruzi infection and dampens chagasic myocarditis

Chagas disease is caused by infection with the protozoan Trypanosoma cruzi (T. cruzi) and is an important cause of severe inflammatory heart disease. However, the mechanisms driving Chagas disease cardiomyopathy have not been completely elucidated. Here, we show that the canonical PI3Kγ pathway is upregulated in both human chagasic hearts and hearts of acutely infected mice. PI3Kγ-deficient mice and mutant mice carrying catalytically inactive PI3Kγ are more susceptible to T. cruzi infection. The canonical PI3Kγ signaling in myeloid cells is essential to restrict T. cruzi heart parasitism and ultimately to avoid myocarditis, heart damage, and death of mice. Furthermore, high PIK3CG expression correlates with low parasitism in human Chagas’ hearts. In conclusion, these results indicate an essential role of the canonical PI3Kγ signaling pathway in the control of T. cruzi infection, providing further insight into the molecular mechanisms involved in the pathophysiology of chagasic heart disease.

163 - Early Perturbations in Mitochondrial Metabolism and Bioenergetics Exerted by Trypanosoma cruzi Infection in Human Cardiomyocytes

Chagas’ disease is a zoonotic disease caused by Trypanosoma cruzi infection that is endemic in Mexico, Central and South America. Usually, the disease is transmitted by a triatomine vector and domestic and wild mammals that serve as reservoirs for this parasitic protozoan. However, due to increased immigration, individuals with the disease have been identified in developed countries like the USA, Canada and Europe, increasing the possibility of secondary transmission routes of T. cruzi via organ transplantation, blood transfusions and maternal-fetal transmission. The clinical course of the disease is divided into the acute and chronic phases. While the acute infection is mildly asymptomatic and often misdiagnosed, the chronic phase usually manifests as cardiomyopathy with a wide spectrum of manifestations, ranging from minor myocardium involvement to left ventricular (LV) systolic dysfunction, dilated cardiomyopathy, arrhythmias, thromboembolic events, and terminal cardiac failure. Interestingly, because chagasic hearts are virtually free of parasites, and the etiology of chronic Chagas disease remains under heavy discussion. The B and T cell immunity in combination with mitochondrial dysfunction, inflammatory cytokines/chemokines, and oxidative stress are the hallmark of the disease. In this work, we aimed to elucidate the early metabolic perturbations exerted by T. cruzi (Sylvio X10) infection in AC16 human cardiomyocytes. In addition, we also examined the role of innate immunity by co-treating cells with pro-inflammatory proteins and cytokines known to have a role in the infection process like IFN-γ, TNF-α and IL-6. Early changes in metabolism and mitochondrial bioenergetics were assessed in real time with a Seahorse XFe24 Extracellular Flux Analyzer. We found that T. cruzi infection alone, was not enough to induce significant changes in mitochondrial metabolism and bioenergetics and to increase ROS generation in human cardiomyocytes. However, T. cruzi infection in combination with IFN-γ, TNF-α and IL-6 exerted a drastic effect in cardiomyocyte mitochondrial bioenergetics and ROS production, suggesting that innate immunity plays a key role in Chagas-induced cardiomyopathy.

SRT1720 inhibition of M1 macrophages and chronic inflammation in Chagas disease

Abstract Trypanosoma cruzi (T. cruzi) causes Chagas disease that is one of the most frequent causes of heart failure and sudden death in Latin America. We observed the therapeutic effect of SRT1720 and explored its immunological mechanisms especially its effect on macrophage phenotype and function in chronic Chagasic mouse. SRT1720, an SIRT1 agonist, was injected intraperitoneally in T. cruzi infected mice at 1 mg/mouse/dose during day 45–66 post-infection (pi, three times a week). Mice were harvested during chronic disease phase (~150 days pi). Left ventricular dysfunction was prevented in SIRT1720-treated chagasic mice. SRT1720 ameliorated the clinical severity of chronic Chagas diseases, decreased proinflammatory cytokine (IFN-γ, IL-1 β, TNF-α) gene expression and inflammatory infiltrate in chronic chagasic hearts. The expression of iNOS, a specific marker for M1, was decreased in SIRT1720-treated chagasic heart. Splenic evaluation by flow cytometry showed both M1 (CD80+ and CD64+) and M2 (CD200R+ and CD206+) macrophages were activated in chronically-infected mice, and SRT1720 inhibited T. cruzi -induced increase in M1 macrophages. These results demonstrated that SRT1720 has therapeutic potential in Chagas disease possibly through preventing the polarization of M1 macrophages and inhibiting inflammatory responses. In vitro experiments will be done to confirm these results. Spleen macrophages will be isolated from these mice and will be cultured for 24h. The release of NO and accumulation of iNOS and secretion of IFN-γ, IL-1 β, TNF-α in cultured macrophages will be examined.

Abstract 201: Enhancing Pgc-1α Activity Improves Heart Function Through Activating Mitochondrial Biogenesis in Chagas Disease

Chronic chagasic cardiomyopathy (CCM) is presented with ventricular hypertrophy and contractile dysfunction that can lead to heart failure. I have found that a substantial decline in mitochondrial biogenesis and SIRT1/PGC-1α activity ensue in chronic chagasic mice. It was evidenced by the decline in mitochondrial DNA content as well as mRNA levels of mitochondrial encoded genes and mtDNA replication machinery. Further, the activity of SIRT1 (required for PGC-1α activation) was decreased and associated with decreased nuclear levels of PGC-1-regulated NRF1 transcription factor in chagasic hearts. The mitochondrial size and number were also reduced in chagasic heart, determined by electron microscopy. Therefore, we hypothesized that enhancing the SIRT1/PGC-1α activity by SIRT1 agonist would improve heart function through activating mitochondrial biogenesis in Chagasic disease. Mice were infected with T. cruzi, and beginning at day 90 post-infection (pi), treated with resveratrol (SIRT1 agonist) or metformin (AMPK agonist, can enhance SIRT1 activity) for 21 days; and then heart function was monitored at 150 days pi. We found that treatment with resveratrol partially attenuated the heart dysfunction (stroke volume, cardiac output, ejection fraction, heart rate) and cardiac hypertrophy in chagasic mice. These benefits were associated with improved expression of the mitochondrial DNA encoded genes and mtDNA content though the expression of genes involved in mtDNA replication was not improved. Treatment with metformin was not significantly beneficial in improving the CCM outcomes. The partial beneficial effects of resveratrol could be due to inefficient activation of SIRT1 or delayed start of the treatment. We plan to treat mice with SIRT1 agonist SIRT1720 (10 fold more active than resveratrol) during the indeterminate phase of T. cruzi infection in next set of experiments. This study will improve our understanding of the molecular and immune mechanisms of chagasic heart disease and will provide a novel treatment for chronically-infected chagasic patients.

Molecular imaging, biodistribution and efficacy of mesenchymal bone marrow cell therapy in a mouse model of Chagas disease

Chagasic cardiomyopathy, resulting from infection with the parasite Trypanosoma cruzi, was discovered more than a century ago and remains an incurable disease. Due to the unique properties of mesenchymal stem cells (MSC) we hypothesized that these cells could have therapeutic potential for chagasic cardiomyopathy. Recently, our group pioneered use of nanoparticle-labeled MSC to correlate migration with its effect in an acute Chagas disease model. We expanded our investigation into a chronic model and performed more comprehensive assays. Infected mice were treated with nanoparticle-labeled MSC and their migration was correlated with alterations in heart morphology, metalloproteinase activity, and expression of several proteins. The vast majority of labeled MSC migrated to liver, lungs and spleen whereas a small number of cells migrated to chagasic hearts. Magnetic resonance imaging demonstrated that MSC therapy reduced heart dilatation. Additionally metalloproteinase activity was higher in heart and other organs of infected mice. Protein expression analyses revealed that connexin 43, laminin γ1, IL-10 and INF-γ were affected by the disease and recovered after cell therapy. Interestingly, MSC therapy led to upregulation of SDF-1 and c-kit in the hearts. The beneficial effect of MSC therapy in Chagas disease is likely due to an indirect action of the cells of the heart, rather than the incorporation of large numbers of stem cells into working myocardium.

Granulocyte colony-stimulating factor partially repairs the damage provoked by Trypanosoma cruzi in murine myocardium

The hallmark of Trypanosoma cruzi infection is cardiomyopathy that leads to end-stage heart failure. We investigated whether G-CSF, known to induce heart tissue repair by bone marrow stem cell mobilization, ameliorates T. cruzi-induced myocarditis. T. cruzi-infected C3H/He mice were treated with G-CSF and monitored for parasite burden, BMSC mobilization, cytokine profile and cardiac remodeling. G-CSF increased the expression of CXCR4, CD34, and c-Kit, indicating mobilization and migration of BMSC, some of which differentiated to cardiomyocytes as evidenced by increased levels of GATA4(+)/MEF2C(+) cells and desmin expression in chagasic hearts. G-CSF enhanced a mixed cytokine response (IL-10+TGF-β>IFN-γ+TNF-α>IL-4) associated with increased heart inflammation and no beneficial effect on parasite control. Further, G-CSF controlled T. cruzi-induced extracellular-matrix alterations of collagens (Col I and Col llI), hydroxyproline, and glycosaminoglycan contents and promoted compensatory cardiac remodeling; however, these responses were not sufficient to control T. cruzi-induced cardiomyocyte atrophy. Benznidazole treatment prior to G-CSF resulted in the control of parasitism and parasite-induced inflammation, and subsequently, G-CSF was effective in executing the tissue repair, as evidenced by extracellular-matrix homeostasis and normalization of cardiomyocyte size in chagasic hearts. G-CSF treatment after T. cruzi infection enhanced migration and homing of BMSC, some of which differentiated to cardiomyocytes. Yet, G-CSF promoted a mixed (Treg>Th1>Th2) immune response that contributed to persistent inflammation and limited improvement in cardiac homeostasis. Combinatorial therapy (BZ → G-CSF) was beneficial in arresting inflammatory processes and tissue damage in chagasic hearts.

Electrophysiological and pharmacological evaluation of the nicotinic cholinergic system in chagasic rats

BackgroundTwo theories attempt to explain the changes observed in the nicotinic acetylcholine receptors (nAChRs) in chagasic cardiomyopathy. The neurogenic theory proposes that receptor changes are due to loss of intracardiac ganglia parasympathetic neurons. The immunogenic theory proposes that the nAChRs changes are the result of autoantibodies against these receptors. Both theories agreed that nAChRs functional expression could be impaired in Chagas disease.MethodsWe evaluated nAChRs functional integrity in 54 Sprague Dawley rats, divided in two groups: healthy and chronic chagasic rats. Rats were subjected to electrocardiographic studies in the whole animal under pentobarbital anesthesia, by isolation and stimulation of vagus nerves and in isolated beating hearts (Langendorff’s preparation).ResultsNicotine, 10 μM, induced a significant bradycardia in both groups. However, rats that had previously received reserpine did not respond to nicotine stimulation. β-adrenergic stimulation, followed by nicotine treatment, induced tachycardia in chagasic rats; while inducing bradycardia in healthy rats. Bilateral vagus nerve stimulation induced a significantly higher level of bradycardia in healthy rats, compared to chagasic rats; physostigmine potentiated the bradycardic response to vagal stimulation in both experimental groups. Electric stimulation (e.g., ≥ 2 Hz), in the presence of physostigmine, produced a comparable vagal response in both groups. In isolated beating-heart preparations 1 μM nicotine induced sustained bradycardia in healthy hearts while inducing tachycardia in chagasic hearts. Higher nicotine doses (e.g.,10 – 100 uM) promoted the characteristic biphasic response (i.e., bradycardia followed by tachycardia) in both groups. 10 nM DHβE antagonized the effect of 10 μM nicotine, unmasking the cholinergic bradycardic effect in healthy rats only. 1 nM α-BGT alone induced bradycardia in healthy hearts but antagonized the 10 μM nicotine-induced tachycardia in chagasic rats. In healthy but not in chagasic hearts, 10 μM nicotine shortened PQ and PR interval, an effect counteracted by MA, DHβE and αBGTConclusionOur results suggest that cholinergic function is impaired in chronic Chagas disease in rats, a phenomena that could be related to alteration on the nAChR expression.

Mesenchymal Bone Marrow Cell Therapy in a Mouse Model of Chagas Disease. Where Do the Cells Go?

BackgroundChagas disease, resulting from infection with the parasite Trypanosoma cruzi (T. cruzi), is a major cause of cardiomyopathy in Latin America. Drug therapy for acute and chronic disease is limited. Stem cell therapy with bone marrow mesenchymal cells (MSCs) has emerged as a novel therapeutic option for cell death-related heart diseases, but efficacy of MSC has not been tested in Chagas disease.Methods and ResultsWe now report the use of cell-tracking strategies with nanoparticle labeled MSC to investigate migration of transplanted MSC in a murine model of Chagas disease, and correlate MSC biodistribution with glucose metabolism and morphology of heart in chagasic mice by small animal positron emission tomography (microPET). Mice were infected intraperitoneally with trypomastigotes of the Brazil strain of T. cruzi and treated by tail vein injection with MSC one month after infection. MSCs were labeled with near infrared fluorescent nanoparticles and tracked by an in vivo imaging system (IVIS). Our IVIS results two days after transplant revealed that a small, but significant, number of cells migrated to chagasic hearts when compared with control animals, whereas the vast majority of labeled MSC migrated to liver, lungs and spleen. Additionally, the microPET technique demonstrated that therapy with MSC reduced right ventricular dilation, a phenotype of the chagasic mouse model.ConclusionsWe conclude that the beneficial effects of MSC therapy in chagasic mice arise from an indirect action of the cells in the heart rather than a direct action due to incorporation of large numbers of transplanted MSC into working myocardium.

Defects of mtDNA Replication Impaired Mitochondrial Biogenesis During Trypanosoma cruzi Infection in Human Cardiomyocytes and Chagasic Patients: The Role of Nrf1/2 and Antioxidant Response

BackgroundMitochondrial dysfunction is a key determinant in chagasic cardiomyopathy development in mice; however, its relevance in human Chagas disease is not known. We determined if defects in mitochondrial biogenesis and dysregulation of peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1 (PGC-1)–regulated transcriptional pathways constitute a mechanism or mechanisms underlying mitochondrial oxidative-phosphorylation (OXPHOS) deficiency in human Chagas disease.Methods and ResultsWe utilized human cardiomyocytes and left-ventricular tissue from chagasic and other cardiomyopathy patients and healthy donors (n>6/group). We noted no change in citrate synthase activity, yet mRNA and/or protein levels of subunits of the respiratory complexes were significantly decreased in Trypanosoma cruzi–infected cardiomyocytes (0 to 24 hours) and chagasic hearts. We observed increased mRNA and decreased nuclear localization of PGC-1-coactivated transcription factors, yet the expression of genes for PPARγ-regulated fatty acid oxidation and nuclear respiratory factor (NRF1/2)–regulated mtDNA replication and transcription machinery was enhanced in infected cardiomyocytes and chagasic hearts. The D-loop formation was normal or higher, but mtDNA replication and mtDNA content were decreased by 83% and 40% to 65%, respectively. Subsequently, we noted that reactive oxygen species (ROS), oxidative stress, and mtDNA oxidation were significantly increased, yet NRF1/2-regulated antioxidant gene expression remained compromised in infected cardiomyocytes and chagasic hearts.ConclusionsThe replication of mtDNA was severely compromised, resulting in a significant loss of mtDNA and expression of OXPHOS genes in T cruzi–infected cardiomyocytes and chagasic hearts. Our data suggest increased ROS generation and selective functional incapacity of NRF2-mediated antioxidant gene expression played a role in the defects in mtDNA replication and unfitness of mtDNA for replication and gene expression in Chagas disease.

Delivery of antigenic candidates by a DNA/MVA heterologous approach elicits effector CD8+T cell mediated immunity against Trypanosoma cruzi

In this study, we have characterized the immune mechanisms elicited by antigenic candidates, TcG2 and TcG4, delivered by a DNA-prime/MVA-boost approach, and evaluated the host responses to Trypanosoma cruzi infection in C57BL/6 mice. Immunization of mice with antigenic candidates elicited antigen-specific, high-avidity, trypanolytic antibody response (IgG2b>IgG1) and CD8+T cells that exhibited type-1 cytolytic effector (CD8+CD107a+IFN-γ+Perforin+) phenotype. The extent of TcG2-dependent type 1 B and T cell immunity was higher than that noted in TcG4-immunized mice, and expanded accordingly in response to challenge infection with T. cruzi. The progression of chronic phase in immunized mice was associated with persistence of IgGs, 55–90% reduction in the frequency of proinflammatory (IFN-γ+ or TNF-α+) CD8+T cells, and an increase or emergence of immunoregulatory (IL-10+) CD4/CD8 T cells. The tissue parasitism, infiltration of inflammatory infiltrate, parasite persistence, and fibrosis were decreased by 82–92% in heart and skeletal muscle of immunized/chronically infected mice. Control mice exhibited a significantly low antibody response, consistent activation of effector CD8+T cells dominated by pro-inflammatory phenotype and mixed cytokine profile (IFN-γ+TNF-α>IL-4+IL-10), parasite persistence and pathologic damage in chagasic hearts. We conclude that delivery of TcG2 or TcG4 by DNA-rMVA approach elicits effective antibody and CD8+T cell mediated immunity against T. cruzi and Chagas disease. The emergence of type 2 cytokine and T cell response in chronic phase was indicative of prevention of clinical disease.

Reversion of gene expression alterations in hearts of mice with chronic chagasic cardiomyopathy after transplantation of bone marrow cells

Chronic chagasic cardiomyopathy is a leading cause of heart failure in Latin American countries, being associated with intense inflammatory response and fibrosis. We have previously shown that bone marrow mononuclear cell (BMC) transplantation improves inflammation, fibrosis, and ventricular diameter in hearts of mice with chronic Chagas disease. Here we investigated the transcriptomic recovery induced by BMC therapy by comparing the heart transcriptomes of control, chagasic, and BMC transplanted mice. Out of the 9390 unique genes quantified in all samples, 1702 had their expression altered in chronic chagasic hearts compared to those of normal mice. Major categories of significantly upregulated genes were related to inflammation, fibrosis and immune responses, while genes involved in mitochondrion function were downregulated. When BMC-treated chagasic hearts were compared to infected mice, 96% of the alterations detected in infected hearts were restored to normal levels, although an additional 109 genes were altered by treatment. Transcriptomic recovery, a new measure that considers both resotrative and side effects of treatment, was remarkably high (84%). Immunofluorescence and morphometric analyses confirmed the effects of BMC therapy in the pattern of inflammatory-immune response and expression of adhesion molecules. In conclusion, by using large-scale gene profiling for unbiased assessment of therapeutic efficacy we demonstrate immunomodulatory effects of BMC therapy in chronic chagasic cardiomyopathy and identify potentially relevant factors involved in the pathogenesis of the disease that may provide new therapeutic targets.

Prophylactic Efficacy of TcVac2 against Trypanosoma cruzi in Mice

BackgroundChagas disease is a major health problem in Latin America, and an emerging infectious disease in the US. Previously, we have screened the Trypanosoma cruzi sequence database by a computational/bioinformatics approach, and identified antigens that exhibited the characteristics of vaccine candidates.MethodologyWe investigated the protective efficacy of a multi-component DNA-prime/protein-boost vaccine (TcVac2) constituted of the selected candidates and cytokine (IL-12 and GM-CSF) expression plasmids in a murine model. C57BL/6 mice were immunized with antigen-encoding plasmids plus cytokine adjuvants, followed by recombinant proteins; and two-weeks later, challenged with T. cruzi trypomastigotes. ELISA and flow cytometry were employed to measure humoral (antibody isotypes) and cellular (lymphocyte proliferation, CD4+ and CD8+ T cell phenotype and cytokines) responses. Myocardial pathology was evaluated by H&E and Masson's trichrome staining.Principal FindingsTcVac2 induced a strong antigen-specific antibody response (IgG2b>IgG1) and a moderate level of lymphocyte proliferation in mice. Upon challenge infection, TcVac2-vaccinated mice expanded the IgG2b/IgG1 antibodies and elicited a substantial CD8+ T cell response associated with type 1 cytokines (IFN-γ and TNF-α) that resulted in control of acute parasite burden. During chronic phase, antibody response persisted, splenic activation of CD8+ T cells and IFN-γ/TNF-α cytokines subsided, and IL-4/IL-10 cytokines became dominant in vaccinated mice. The tissue parasitism, inflammation, and fibrosis in heart and skeletal muscle of TcVac2-vaccinated chronic mice were undetectable by histological techniques. In comparison, mice injected with vector or cytokines only responded to T. cruzi by elicitation of a mixed (type 1/type 2) antibody, T cell and cytokine response, and exhibited persistent parasite burden and immunopathology in the myocardium.ConclusionTcVac2-induced activation of type 1 antibody and lymphocyte responses provided resistance to acute T. cruzi infection, and consequently, prevented the evolution of chronic immunopathology associated with parasite persistence in chagasic hearts.

Adenosine Induces Ventricular Arrhythmias in Hearts With Chronic Chagas Cardiomyopathy

Adenosine released during ischemia and hypoxia can induce ventricular arrhythmias. This phenomenon is also observed in Chagas disease. This study involved pharmacologic analysis of the arrhythmogenic properties of adenosine in healthy Sprague-Dawley rats (n=14) and in rats with chronic Chagas cardiomyopathy (n=14). Electrocardiographic and pharmacologic studies were performed on isolated hearts prepared using the Langendorff method. Adenosine increased ventricular arrhythmias in both groups of animals in a dose-dependent manner: 50% of chagasic rats developed ventricular fibrillation compared with 7.14% of healthy rats (P< .05). Fibrillation was prevented by A1 (i.e., DPCPX) and A2a (i.e., 8-CSC) receptor antagonists. Arrhythmia was associated with a prolonged QT interval, early depolarization, and the R-on-T and torsade de pointes phenomena. In conclusion, adenosine is a proarrythmic drug that is able to induce ventricular fibrillation in chagasic rat hearts.

Not Available

There is growing evidence to suggest that chagasic myocardia are exposed to sustained oxidative stress induced injuries that may contribute to disease progression. Trypanosoma cruzi invasion- and replication-mediated cellular injuries and immune-mediated cytotoxic reactions are the common source of reactive oxygen species (ROS) during acute infection. Mitochondria are proposed to be the major source of ROS in chronic chagasic hearts. However, it has not been established yet, whether mitochondrial dysfunction is a causative factor in chagasic cardiomyopathy or a consequence of other pathological events. A better understanding of oxidative stress in relation to cardiac tissue damage would be useful in the evaluation of its true role in the pathogenesis of Chagas disease and other heart diseases. In this review, we discuss the evidence for increased oxidative stress in chagasic disease, with emphasis on mitochondrial abnormalities, and its role in sustaining oxidative stress in myocardium.

Phenyl-α- tert-Butyl Nitrone Reverses Mitochondrial Decay in Acute Chagas' Disease

In this study, we investigated the mechanism(s) of mitochondrial functional decline in acute Chagas' disease. Our data show a substantial decline in respiratory complex activities (39 to 58%) and ATP (38%) content in Trypanosoma cruzi-infected murine hearts compared with normal controls. These metabolic alterations were associated with an approximately fivefold increase in mitochondrial reactive oxygen species production rate, substantial oxidative insult of mitochondrial membranes and respiratory complex subunits, and >60% inhibition of mtDNA-encoded transcripts for respiratory complex subunits in infected myocardium. The antioxidant phenyl-alpha-tert-butyl nitrone (PBN) arrested the oxidative damage-mediated loss in mitochondrial membrane integrity, preserved redox potential-coupled mitochondrial gene expression, and improved respiratory complex activities (47 to 95% increase) and cardiac ATP level (>or=40% increase) in infected myocardium. Importantly, PBN resulted twofold decline in mitochondrial reactive oxygen species production rate in infected myocardium. Taken together, our data demonstrate the pathological significance of oxidative stress in metabolic decay and energy homeostasis in acute chagasic myocarditis and further suggest that oxidative injuries affecting mitochondrial integrity-dependent expression and activity of the respiratory complexes initiate a feedback cycle of electron transport chain inefficiency, increased reactive oxygen species production, and energy homeostasis in acute chagasic hearts. PBN and other mitochondria-targeted antioxidants may be useful in altering mitochondrial decay and oxidative pathology in Chagas' disease.

Postmortem Studies of the Intertruncal Plexus and Cardiac Conduction System From Patients With Chagas Disease Who Died Suddenly

Throughout the cardiac conduction system of each heart there were numerous destructive lesions including focal inflammatory infiltration with lymphocytes and in neighboring regions extensive focal fibrotic degeneration. These lesions involved myocytes, nerves and blood vessels. They were adequate explanation for the familiar disturbances in cardiac rhythm and conduction typical of Chagasic cardiomyopathy. In one heart there was a left ventricular apical aneurysm, which is often considered typical of Chagasic cardiomyopathy. To our surprise, virtually every myocyte in the region of the aneurysm was undergoing extensive dehiscence, thus severing all intercellular junctions of the involved myocytes. Therefore, we suggest that the left ventricular apical aneurysms represent a form of disuse atrophy produced by the sympathetic denervation caused by neuropathology in the intertruncal plexus of each heart. Sympathetic innervation of virtually the entire left ventricle is derived from nerves supplied through ganglia in the intertruncal plexus. The random nature of the neuropathology in the intertruncal plexus is the probable explanation of why some Chagasic hearts exhibit generalized Chagasic cardiomyopathy, while others have a more restricted denervation ending in left ventricular apical aneurysms. Perhaps the most intriguing finding in our study was the abundance of flagellated trypanosoma cruzi within the intertruncal plexus of each heart. The trypanosomes were often in clusters, sometimes encysted by a thin fibrous membrane, but more often in loose aggregates without a surrounding membrane. Some trypanosomes were seen boring into intertruncal nerves while others formed dense clusters of trypanosomes attached to the outer surface of an intertruncal vein. We believe that these observations have seldom, if ever, been described before, and they represent interesting opportunities in future diagnosis and treatment of cardiac disease caused by trypanosoma cruzi.

Oxidative modification of mitochondrial respiratory complexes in response to the stress of Trypanosoma cruzi infection

Previously, we have shown deficiencies in the activities of the mitochondrial respiratory complexes and reduced mitochondrial ATP generation capacity in chagasic hearts infected by Trypanosoma cruzi. In this study, we determined whether the oxidative stress that occurs in response to T. cruzi infection contributes to the catalytic impairment of respiratory complexes and to subsequent mitochondrial dysfunction in murine myocardium. Our data show that oxidative injuries, as determined by the levels of lipid peroxides and protein carbonyls, are incurred in cardiac mitochondria as early as 3 days postinfection and persist throughout the infection and disease. The individual components of the respiratory complexes were separated by two-dimensional, blue-native gel electrophoresis, and carbonyl adducts were detected by Western blotting. We observed substantial carbonylation of the specific subunits of mitochondrial respiratory complexes in infected murine hearts. Of note is the oxidative modification of NDUFS1, NDUFS2, and NDUFV1, which form the catalytic core of the CI complex; UQCRC1, UQCRC2, and UQCRQ, the subunits of the core subcomplex, and UQCRH and CYC1, which form the cyt c 1 subcomplex of CIII; and a γ chain that is essential for ATP synthesis by CV complex. The extent of oxidative modifications of the subunits correlated with the catalytic defects of the respiratory complexes in the infected myocardium. Taken together, our data demonstrate that respiratory complexes are oxidatively damaged in response to the stress of T. cruzi infection. These data also suggest involvement of the specific susceptibility of the protein subunits, and not generalized mitochondrial oxidative damage in respiratory chain impairment of chagasic hearts.

Oxidative damage during chagasic cardiomyopathy development: role of mitochondrial oxidant release and inefficient antioxidant defense

In this study, we evaluated the oxidant status and antioxidant defense capabilities of the heart during the course of Trypanosoma cruzi infection and disease development in a murine model system. Our data show that the extent of protein carbonylation and lipid peroxidation is increased in the heart, but not the skeletal muscle, of infected mice. The level of oxidative injury biomarkers in the myocardium consistently increased with chronic disease severity. The antioxidant defense constituted by catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GSR), and reduced glutathione was increased in murine heart and skeletal tissue in response to the stress of T. cruzi infection. After the initial burst, CAT, GPx, and GSR remained unresponsive to the severity of chronic tissue damage in chagasic hearts. The cardiac level of Mn 2+ superoxide dismutase (MnSOD) was diminished in chagasic mice. Our data suggest that the host responds to acute injuries by activating antioxidant defenses that are of sufficient magnitude to scavenge the reactive oxidants in skeletal tissue. The myocardia of infected mice, however, sustain increased oxidative injuries with disease progression. We surmise that MnSOD deficiencies, resulting in the increased release of mitochondrial free radicals, lead to sustained oxidative stress that exceeds the cardiac antioxidant defense capacity and contribute to persistent oxidative damage in chagasic myocardium.

Gene expression analysis in mitochondria from chagasic mice: alterations in specific metabolic pathways.

Cardiac hypertrophy and remodelling in chagasic disease might be associated with mitochondrial dysfunction. In the present study, we characterized the cardiac metabolic responses to Trypanosoma cruzi infection and progressive disease severity using a custom-designed mitoarray (mitochondrial function-related gene array). Mitoarrays consisting of known, well-characterized mitochondrial function-related cDNAs were hybridized with 32P-labelled cDNA probes generated from the myocardium of mice during immediate early, acute and chronic phases of infection and disease development. The mitoarray successfully identified novel aspects of the T. cruzi-induced alterations in the expression of the genes related to mitochondrial function and biogenesis that were further confirmed by real-time reverse transcriptase-PCRs. Of note is the up-regulation of transcripts essential for fatty acid metabolism associated with repression of the mRNAs for pyruvate dehydrogenase complex in infected hearts. We observed no statistically significant changes in mRNAs for the enzymes of tricarboxylic acid cycle. These results suggest that fatty acid metabolism compensates the pyruvate dehydrogenase complex deficiencies for the supply of acetyl-CoA for a tricarboxylic acid cycle, and chagasic hearts may not be limited in reduced energy (NADH and FADH2). The observation of a decrease in mRNA level for several subunits of the respiratory chain complexes by mitoarray as well as global genome analysis suggests a limitation in mitochondrial oxidative phosphorylation-mediated ATP-generation capacity as the probable basis for cardiac homoeostasis in chagasic disease.

Impaired mitochondrial respiratory chain and bioenergetics during chagasic cardiomyopathy development.

In this study, we evaluated the activities of respiratory chain complexes and oxidative phosphorylation (OXPHOS) capacity of the heart to gain insights into the pathological significance of mitochondrial dysfunction in chagasic cardiomyopathy (CCM). In a murine model of Trypanosoma cruzi infection, biochemical and histochemical analysis of the cardiac mitochondria revealed deficiency of the respiratory chain complexes (CI-CV) in infected mice; the inhibition of CI activity was more pronounced in the acute infection phase, CIII was constitutively repressed throughout the infection and disease phase, and the CV defects appeared in chronic phase only. A substantial decline in cardiac mtDNA content (54-60%) and mitochondria-encoded transcripts (50-65%) with disease development indicated that the alterations in mtDNA contribute to the quantitative deficiencies in respiratory chain activity in chagasic hearts. The observations of a selective inhibition of redox-sensitive CI and CIII complexes that are also the site of free radical generation in mitochondria, and the decline in cardiac mtDNA content in infected mice, all support the free radical hypothesis of mitochondria dysfunction in CCM. Consequently, OXPHOS-mediated ATP synthesis capacity of the cardiac mitochondria in infected mice was substantially reduced (37-50%), suggesting an energy homeostasis in the affected tissue.