Is apoptosis a mechanism of cell death of cardiomyocytes in chronic chagasic myocarditis?

The micropathology of chronic Chagas' myocarditis reveals foci of myocardial cell loss associated with an inflammatory infiltrate composed predominantly of lymphomononuclear cells and interstitial fibrosis. The loss of myocardial cells, a devastating phenomenon in this cardiopathy, has been classically attributed to necrosis. In the present study we examined whether the loss of myocardial cells in human chronic Chagas' heart disease could result from cell death by apoptosis. A total of 11 cases of chronic chagasic myocarditis were studied: four hearts were obtained at autopsy within 8 h after death and seven endomyocardial biopsies were taken from chagasic patients with an arrhythmogenic form of the disease. The coronary arteries of all chagasic cases showed no obstructive lesions. The diagnosis of Chagas' disease was based on previously established criteria. Five cases were selected as controls: three hearts were obtained at autopsy within 8 h after death and two endomyocardial biopsies were taken from nonchagasic patients with normal myocardium morphology. As positive controls we used cardiac muscles of myocardial infarction and rat mammary glands on the fourth day after weaning. The TUNEL method was used to identify apoptotic cells in the myocardium. The expression of p53 protein, which directly or indirectly triggers apoptosis, was evaluated using immunohistochemical technique. A few apoptotic cells were stained in chronic chagasic hearts, both biopsy and autopsy cases. However, the stained nuclei were restricted to the mononuclear infiltrate accounting for about 0.5% of the mononuclear cells in the infiltrate. In contrast, the nuclei of cardiomyocytes in both regions bordering on and distant from the microfoci of myocardial cell loss were not stained by the TUNEL method. Moreover, the expression of the protein p53 in cardiomyocytes in chagasic hearts was absent. The results of the present study demonstrating negative in situ labeling of fragmented DNA associated with absence of expression of p53 provide support to the hypothesis that apoptosis is not the mechanism of cell death in chronic chagasic myocarditis. This reinforces the general opinion that the loss of cardiac muscle fibers in chagasic cardiopathy is produced by necrosis. On the other hand, the present results give support to the concept that apoptosis probably play a role in the clearing of lymphomononuclear cells in the inflammatory infiltrate in chronic chagasic myocarditis.