Left ventricular wall stress as a direct correlate of cardiomyocyte apoptosis in patients with severe dilated cardiomyopathy

Background: Apoptosis has been implicated as a possible mechanism in the development of heart failure (HF), but the mechanisms involved remain unclear. In patients with severe dilated cardiomyopathy, we evaluated cardiomyocyte apoptosis in relation to the transmural distribution of Bax and Bcl-2 proteins (2 molecules inhibiting or promoting apoptosis, respectively) and left ventricular wall stresses. Methods: We studied the presence and distribution of cardiomyocyte apoptosis in 90 tissue samples obtained from 8 patients who were undergoing left ventricular reduction with the Batista (ventricular remodeling) operation. Apoptosis was assessed in tissue samples taken from the entire left ventricular thickness (subdivided in subepicardial, midmyocardial, and subendocardial sections) with the terminal deoxynucleotidyl transferase mediated dUTP-biotin nick-end labeling (TUNEL) technique and DNA agarose gel electrophoresis. The expression of Bcl-2 and Bax proteins were determined with both Western analysis and immunohistochemistry. Results: TUNEL-positive cells (apoptotic index) were 2.3% ± 1.4%. Apoptotic cells were predominantly distributed in the subendocardium, where higher levels of Bax protein were detected. The ratio of Bax to Bcl-2 proteins (Bax/Bcl-2) was similar in the midmyocardium or subepicardium, but increased in the subendocardium, where it was directly related to systolic wall stress (y = 0.009x - 0.629; r2 = 0.85, P < .001). The apoptotic index was also directly related to systolic and end-diastolic stresses calculated from hemodynamic and echocardiographic data (2 = 0.77, P < .001 and r2 = 0.40, P < .01, respectively). Conclusions: In patients with dilated cardiomyopathy, in whom cardiomyocyte apoptosis is an important cause of cell loss, apoptosis is more extensively localized in the subendocardium and strictly related to ventricular wall stresses and the Bax/Bcl-2 ratio