Characterization of cardiopulmonary function and cardiac muscarinic and adrenergic receptor density adaptation in C57BL/6 mice with chronic Trypanosoma cruzi infection

Bone marrow cell migration to the heart in a chimeric mouse model of acute chagasic disease

BACKGROUND

Chagas disease is a public health problem caused by infection with the protozoan Trypanosoma cruzi. There is currently no effective therapy for Chagas disease. Although there is some evidence for the beneficial effect of bone marrow-derived cells in chagasic disease, the mechanisms underlying their effects in the heart are unknown. Reports have suggested that bone marrow cells are recruited to the chagasic heart; however, studies using chimeric mouse models of chagasic cardiomyopathy are rare.

OBJECTIVES

The aim of this study was to investigate the migration of bone marrow cells to the heart after T. cruzi infection in a model of chagasic disease in chimeric mice.

METHODS

To obtain chimerical mice, wild-type (WT) C57BL6 mice were exposed to full body irradiation (7 Gy), causing bone marrow ablation. Then, bone marrow cells from green fluorescent protein (GFP)-transgenic mice were infused into the mice. Graft effectiveness was confirmed by flow cytometry. Experimental mice were divided into four groups: (i) infected chimeric (iChim) mice; (ii) infected WT (iWT) mice, both of which received 3 × 104 trypomastigotes of the Brazil strain; (iii) non-infected chimeric (Chim) mice; and (iv) non-infected WT mice.

FINDINGS

At one-month post-infection, iChim and iWT mice showed first degree atrioventricular block with decreased heart rate and treadmill exercise parameters compared to those in the non-infected groups.

MAIN CONCLUSIONS

iChim mice showed an increase in parasitaemia, myocarditis, and the presence of amastigote nests in the heart tissue compared to iWT mice. Flow cytometry analysis did not detect haematopoietic progenitor cells in the hearts of infected mice. Furthermore, GFP+ cardiomyocytes were not detected in the tissues of chimeric mice.

Resveratrol Reverses Functional Chagas Heart Disease in Mice

Chronic chagasic cardiomyopathy (CCC) develops years after acute infection by Trypanosoma cruzi and does not improve after trypanocidal therapy, despite reduction of parasite burden. During disease, the heart undergoes oxidative stress, a potential causative factor for arrhythmias and contractile dysfunction. Here we tested whether antioxidants/ cardioprotective drugs could improve cardiac function in established Chagas heart disease. We chose a model that resembles B1-B2 stage of human CCC, treated mice with resveratrol and performed electrocardiography and echocardiography studies. Resveratrol reduced the prolonged PR and QTc intervals, increased heart rates and reversed sinus arrhythmia, atrial and atrioventricular conduction disorders; restored a normal left ventricular ejection fraction, improved stroke volume and cardiac output. Resveratrol activated the AMPK-pathway and reduced both ROS production and heart parasite burden, without interfering with vascularization or myocarditis intensity. Resveratrol was even capable of improving heart function of infected mice when treatment was started late after infection, while trypanocidal drug benznidazole failed. We attempted to mimic resveratrol's actions using metformin (AMPK-activator) or tempol (SOD-mimetic). Metformin and tempol mimicked the beneficial effects of resveratrol on heart function and decreased lipid peroxidation, but did not alter parasite burden. These results indicate that AMPK activation and ROS neutralization are key strategies to induce tolerance to Chagas heart disease. Despite all tissue damage observed in established Chagas heart disease, we found that a physiological dysfunction can still be reversed by treatment with resveratrol, metformin and tempol, resulting in improved heart function and representing a starting point to develop innovative therapies in CCC.

Increase in cardiac M2-muscarinic receptor expression is regulated by GATA binding protein 4 (GATA-4) in streptozotocin-induced diabetic rats

BACKGROUND

An increase in cardiac M2-muscarinic receptor (M2-mAChR) expression in diabetic rats has been observed, but the molecular mechanism of this increase remains unclear. The transcriptional activity of GATA binding protein 4 (GATA-4) has been documented to regulate the expression of M2-mAChR genes. In this study, we were interested in identifying the role of GATA-4 in the increase in M2-mAChR in diabetic rats and a primary culture of cardiomyocytes.

METHODS

Streptozotocin-induced diabetic rats (STZ-rats) and high-glucose (D-glucose 30 mM, 24h)-treated primary cultures of cardiomyocytes from neonatal rats were used to investigate the role of GATA-4 in the change in M2-mAChR. The protein expression was determined by Western blot analysis. Phlorizin (Na(+)-glucose co-transport inhibitor), insulin, tiron (radical scavenger), PD98059 (ERK inhibitor) and SB203580 (p38 inhibitor) were used. We also silenced GATA-4 by RNAi to investigate the changes in M2-mAChR expression.

RESULTS

The cardiac output was reduced in STZ-rats with a higher expression of M2-mAChR or phosphorylated GATA-4 in the heart. These changes were reversed after correction of the blood sugar level. In cardiomyocytes, high glucose treatment also increased M2-mAChR expression and GATA-4 phosphorylation. These changes were reversed by tiron (ROS scavenger) or PD98059 (MEK/ERK inhibitor). However, an increase in M2-mAChR expression was not observed when GATA-4 was silenced by small interfering RNA (siRNA) in cardiomyocytes.

CONCLUSIONS

We suggest that hyperglycemia can cause a higher expression of M2-mAChR in cardiomyocytes mainly through ROS to enhance MEK/ERK for phosphorylation of GATA-4.

Pathogenesis of Chagas disease: time to move on

Trypanosoma cruzi is the etiologic agent of Chagas disease. The contributions of parasite and immune system for disease pathogenesis remain unresolved and controversial. The possibility that Chagas disease was an autoimmune progression triggered by T. cruzi infection led some to question the benefit of treating chronically T. cruzi-infected persons with drugs. Furthermore, it provided the rationale for not investing in research aimed at a vaccine which might carry a risk of inducing autoimmunity or exacerbating inflammation. This viewpoint was adopted by cash-strapped health systems in the developing economies where the disease is endemic and has been repeatedly challenged by researchers and clinicians in recent years and there is now a considerable body of evidence and broad consensus that parasite persistence is requisite for pathogenesis and that antiparasitic immunity can be protective against T. cruzi pathogenesis without eliciting autoimmune pathology. Thus, treatment of chronically infected patients is likely to yield positive outcomes and efforts to understand immunity and vaccine development should be recognized as a priority area of research for Chagas disease.

Neurodegeneration and neuroregeneration in Chagas disease

Autonomic dysfunction plays a significant role in the development of chronic Chagas disease (CD). Destruction of cardiac parasympathetic ganglia can underlie arrhythmia and heart failure, while lesions of enteric neurons in the intestinal plexuses are a direct cause of aperistalsis and megasyndromes. Neuropathology is generated by acute infection when the parasite, though not directly damaging to neuronal cells, elicits immune reactions that can become cytotoxic, inducing oxidative stress and neurodegeneration. Anti-neuronal autoimmunity may further contribute to neuropathology. Much less clear is the mechanism of subsequent neuronal regeneration in patients that survive acute infection. Morphological and functional recovery of the peripheral neurons in these patients correlates with the absence of CD clinical symptoms, while persistent neuronal deficiency is observed for the symptomatic group. The discovery that Trypanosoma cruzi trans-sialidase can moonlight as a parasite-derived neurotrophic factor (PDNF) suggests that the parasite might influence the balance between neuronal degeneration and regeneration. PDNF functionally mimics mammalian neurotrophic factors in that it binds and activates neurotrophin Trk tyrosine kinase receptors, a mechanism which prevents neurodegeneration. PDNF binding to Trk receptors triggers PI3K/Akt/GSK-3β and MAPK/Erk/CREB signalling cascades which in neurons translates into resistance to oxidative and nutritional stress, and inhibition of apoptosis, whereas in the cytoplasm of infected cells, PDNF represents a substrate-activator of the host Akt kinase, enhancing host-cell survival until completion of the intracellular cycle of the parasite. Such dual activity of PDNF provides sustained activation of survival mechanisms which, while prolonging parasite persistence in host tissues, can underlie distinct outcomes of CD.

Trypanosoma cruzi-Derived Neurotrophic Factor: Role in Neural Repair and Neuroprotection

Some patients infected with the parasite Try-panosoma cruzi develop chronic Chagas' disease, while others remain asymptomatic for life. Although pathological mechanisms that govern disease progression remain unclear, the balance between degeneration and regeneration in the peripheral nervous system seems to contribute to the different clinical outcomes. This review focuses on certain new aspects of host-parasite interactions related to regeneration in the host nervous system induced by the trans-sialidase of T. cruzi, also known as a parasite-derived neurotrophic factor (PDNF). PDNF plays multiple roles in T. cruzi infection, ranging from immunosuppression to functional mimicry of mammalian neurotrophic factors and inhibition of apoptosis. PDNF affinity to neurotrophin Trk receptors provide sustained activation of cellular survival mechanisms resulting in neuroprotection and neuronal repair, resistance to cytotoxic insults and enhancement of neuritogenesis. Such unique PDNF-elicited regenerative responses likely prolong parasite persistence in infected tissues while reducing neuropathology in Chagas' disease.

Mitochondrial complex III defects contribute to inefficient respiration and ATP synthesis in the myocardium of Trypanosoma cruzi-infected mice

In this study, we conducted a thorough analysis of mitochondrial bioenergetic function as well as the biochemical and molecular factors that are deregulated and contribute to compromised adenosine triphosphate (ATP) production in the myocardium during Trypanosoma cruzi infection. We show that ADP-stimulated state 3 respiration and ATP synthesis supported by pyruvate/malate (provides electrons to complex I) and succinate (provides electrons to complex II) substrates were significantly decreased in left ventricular tissue and isolated cardiac mitochondria of infected mice. The decreased mitochondrial ATP synthesis in infected murine hearts was not a result of uncoupling between the electron-transport chain and oxidative phosphorylation and decreased availability of the intermediary metabolites (e.g., NADH). The observed decline in the activities of complex-I, -IV, and -V was not physiologically relevant and did not contribute to compromised respiration and ATP synthesis in infected myocardium. Instead, complex III activity was decreased above the threshold level and contributed to respiratory-chain inefficiency and the resulting decline in mitochondrial ATP synthesis in infected myocardium. The loss in complex III activity occurred as a consequence of cytochrome b depletion. Treatment of infected mice with phenyl-alpha-tert-butyl nitrone (PBN, antioxidant) was beneficial in preserving the mtDNA-encoded cytochrome b expression, and subsequently resulted in improved complex III activity, mitochondrial respiration, and ATP production in infected myocardium. Overall, we provide novel data on the mechanism(s) involved in cardiac bioenergetic inefficiency during T. cruzi infection.

Granulocyte colony-stimulating factor treatment in chronic Chagas disease: preservation and improvement of cardiac structure and function

This study investigates the effects of granulocyte colony-stimulating factor (G-CSF) therapy in experimental chronic chagasic cardiomyopathy. Chagas disease is one of the leading causes of heart failure in Latin America and remains without an effective treatment other than cardiac transplantation. C57BL/6 mice were infected with 10(3) trypomastigotes of Trypanosoma cruzi, and chronic chagasic mice were treated with G-CSF or saline (control). Evaluations following treatment were functional, immunological, and histopathological. Comparing hearts of G-CSF-treated mice showed reduced inflammation and fibrosis compared to saline-treated chagasic mice. G-CSF treatment did not alter the parasite load but caused an increase in the number of apoptotic inflammatory cells in the heart. Cardiac conductance disturbances in all infected animals improved or remained stable due to the G-CSF treatment, whereas all of the saline-treated mice deteriorated. The distance run on a treadmill and the exercise time were significantly greater in G-CSF-treated mice when compared to chagasic controls, as well as oxygen consumption (VO(2)), carbon dioxide production (VCO(2)), and respiratory exchange ration (RER) during exercise. Administration of G-CSF in experimental cardiac ischemia had beneficial effects on cardiac structure, which were well correlated with improvements in cardiac function and whole animal performance.

Involvement of the beta-adrenergic system in the cardiac chronic form of experimental Trypanosoma cruzi infection

Changes in the cardiac beta-adrenergic system in early stages of Trypanosoma cruzi infection have been described. Here, we studied an early (135 days post-infection-p.i.) and a late stage (365 days p.i.) of the cardiac chronic form of the experimental infection (Tulahuen or SGO-Z12 strains), determining plasma epinephrine and norepinephrine levels, beta-receptor density, affinity and function, cardiac cAMP concentration and phosphodiesterase activity, cardiac contractility, and the presence of beta-receptor autoantibodies. Tulahuen-infected mice presented lower epinephrine and norepinephrine levels; lower beta-receptor affinity and density; a diminished norepinephrine response and higher cAMP levels in the early stage, and a basal contractility similar to non-infected controls in the early and augmented in the late stage. The Tulahuen strain induced autoantibodies with weak beta-receptor interaction. SGO-Z12-infected mice presented lower norepinephrine levels and epinephrine levels that diminished with the evolution of the infection; lower beta-receptor affinity and an increased density; unchanged epinephrine and norepinephrine response in the early and a diminished response in the late stage; higher cAMP levels and unchanged basal contractility. The SGO-Z12 isolate induced beta-receptor autoantibodies with strong interaction with the beta-receptors. None of the antibodies, however, acted a as beta-receptor agonist. The present results demonstrate that this system is seriously compromised in the cardiac chronic stage of T. cruzi infection.

Trypanosoma cruzi infection induces up-regulation of cardiac muscarinic acetylcholine receptors in vivo and in vitro

The pathogenesis of chagasic cardiomyopathy is not completely understood, but it has been correlated with parasympathetic denervation (neurogenic theory) and inflammatory activity (immunogenic theory) that could affect heart muscarinic acetylcholine receptor (mAChR) expression. In order to further understand whether neurogenic and/or immunogenic alterations are related to changes in mAChR expression, we studied two models of Trypanosoma cruzi infection: 1) in 3-week-old male Sprague Dawley rats chronically infected with T. cruzi and 2) isolated primary cardiomyocytes co-cultured with T. cruzi and peripheral blood mononuclear cells (PBMC). Using [3H]-quinuclidinylbenzilate ([3H]-QNB) binding assays, we evaluated mAChR expression in homogenates from selected cardiac regions, PBMC, and cultured cardiomyocytes. We also determined in vitro protein expression and pro-inflammatory cytokine expression in serum and cell culture medium by ELISA. Our results showed that: 1) mAChR were significantly (P < 0.05) up-regulated in right ventricular myocardium (means +/- SEM; control: 58.69 +/- 5.54, N = 29; Chagas: 72.29 +/- 5.79 fmol/mg, N = 34) and PBMC (control: 12.88 +/- 2.45, N = 18; Chagas: 20.22 +/- 1.82 fmol/mg, N = 19), as well as in cardiomyocyte transmembranes cultured with either PBMC/T. cruzi co-cultures (control: 24.33 +/- 3.83; Chagas: 43.62 +/- 5.08 fmol/mg, N = 7 for both) or their conditioned medium (control: 37.84 +/- 3.84, N = 4; Chagas: 54.38 +/- 6.28 fmol/mg, N = 20); 2) [(3)H]-leucine uptake was increased in cardiomyocytes co-cultured with PBMC/T. cruzi-conditioned medium (Chagas: 21,030 +/- 2321; control 10,940 +/- 2385 dpm, N = 7 for both; P < 0.05); 3) plasma IL-6 was increased in chagasic rats, IL-1beta, was increased in both plasma of chagasic rats and in the culture medium, and TNF-alpha level was decreased in the culture medium. In conclusion, our results suggest that cytokines are involved in the up-regulation of mAChR in chronic Chagas disease.

New perspectives of infections in cardiovascular disease

Infections have been recognized as significant causes of cardiac diseases for many decades. Various microorganisms have been implicated in the etiology of these diseases involving all classes of microbial agents. All components of the heart structure can be affected by infectious agents, i.e. pericardium, myocardium, endocardium, valves, autonomic nervous system, and some evidence of coronary arteries. A new breed of infections have evolved over the past three decades involving cardiac implants and this group of cardiac infectious complications will likely continue to increase in the future, as more mechanical devices are implanted in the growing ageing population. This article will review the progress made in the past decade on understanding the pathobiology of these infectious complications of the heart, through advances in genomics and proteomics, as well as potential novel approach for therapy.An up-to-date, state-of-the-art review and controversies will be outlined for the following conditions: (i) perimyocarditis; (ii) infective endocarditis; (iii) cardiac device infections; (iv) coronary artery disease and potential role of infections.

Cellular therapy in Chagas' disease: potential applications in patients with chronic cardiomyopathy

Nearly a century after its discovery, Chagas' disease, caused by the protozoan Trypanosoma cruzi, remains a major health problem in Latin America. Although efforts in transmission control have contributed to a decrease in the number of new cases, approximately a third of chronic Chagasic individuals have or will develop the symptomatic forms of the disease, mainly cardiomyopathy. Chagas' disease is a progressively debilitating disease, which, at the final stages, there are no currently available treatments other than heart transplantation. In this scenario, cellular therapy is being tested as an alternative for millions of patients with heart dysfunction due to Chagas' disease. In this article, we review the studies of cellular therapy in animal models and in patients with Chagasic cardiomyopathy and the possible mechanisms by which cellular therapy may act in this disease.