Date Published: October 27, 2016
Publisher: Public Library of Science
Author(s): Glaucia Vilar-Pereira, Vitor C. Carneiro, Hilton Mata-Santos, Amanda R. R. Vicentino, Isalira P. Ramos, Naira L. L. Giarola, Daniel F. Feijó, José R. Meyer-Fernandes, Heitor A. Paula-Neto, Emiliano Medei, Marcelo T. Bozza, Joseli Lannes-Vieira, Claudia N. Paiva, Leda Q Vieira.
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.
Protection against functional damage (i.e., disease tolerance) represents a strategy that allows hosts to survive infection at minimum cost . This strategy is successful against diseases caused by pathogens the immune system cannot eliminate and explains why individuals with similar pathogen burdens can present varying disease gravities . The mechanisms underlying disease tolerance include activation of molecular pathways that are involved in tissue repair, fuel-sensing/energy production, and antioxidant defenses .
The several attempts to treat CCC with trypanocidal drugs have produced inconsistent results, despite reductions in parasite load. Infected mice have been studied pre- and post-treatment with benznidazole : treatment eliminated the parasite and prevented to a small extent the prolongation of the PR interval over time, but by the end of the study, benznidazole-treated mice offered no improvements over controls. A study of infected rats treated with benznidazole found no improvement of heart function analyzed by catheterism . In human CCC, an attempt to reduce parasite load with benznidazole cured heart disease in some cases , but not in another study . The recent results of the BENEFIT trial of benznidazole at the chronic phase show that despite greatly reducing parasite burden, it does not affect cardiac deterioration . These results reinforce the notion that heart pathology and parasite burden have a loose association at the chronic stage and discourage the trypanocidal strategy against disease. Here, we show that resveratrol improves heart function (a diagrammatic illustration of its heart function effects in CCC is shown in Fig 5) and reduces heart parasite burden. Nevertheless, we believe that instead of acting primarily by reducing parasite burden to improve heart function, resveratrol acted as an antioxidant. Different from resveratrol, trypanocidal drug benznidazole failed to restore heart pumping function. Moreover, both metformin (AMPK activator) and tempol (SOD-mimetic) improved heart function and decreased lipid peroxidation, but did not change parasite burden. These findings support raising disease tolerance as an effective strategy against CCC, as long as the parasite burden is kept low in order to avoid a rebound.
The complete procedures for electrocardiography, histopathological studies, SIRT1 deacetylase activity, ATP dosage, lipid peroxidation, quantitative Polymerase Chain Reaction (qPCR) for parasite detection, western blot, ex-vivo heart confocal microscopy for ROS and vessels, and second-harmonic generation for collagen detection are described on an online appendix.