Anti-apoptotic Effects of a Calpain Inhibitor on Cardiomyocytes in a Canine Rapid Atrial Fibrillation Model

This study was designed to evaluate the effects of a calpain inhibitor on cardiac muscle apoptosis in rapid pacing canine atrial fibrillation (AF) models. Twenty one dogs were divided into three groups: a sham operation group, a control AF group and a calpain inhibitor group. Sustained AF was induced by rapid right atrium pacing at 600 beats per minute. N-Acetyl-Leu-Leu-Met (1.0 mg/kg/day) was administered in the calpain inhibitor group for three weeks. The activity of calpain I and cardiomyocyte apoptosis were measured by fluorometry and TUNEL assay, respectively. Protein expression of caspase-3 was detected by Western blot. The localizations of caspase-3, caspase-8, bcl-2 and ARC were assessed by immunohistochemistry. In comparison to the sham operation group, the activity of calpain I was significantly increased in the control AF group (2.3 fold, p < 0.001), and decreased in the calpain inhibitor group (1.1 fold, p < 0.005). The calpain activity correlated with the apoptosis index (r = 0.9, p < 0.05). The apoptosis index was 1.0 +/- 0.2%, 11.8 +/- 6.8% and 3.5 +/- 2.1% in the sham operation group, control AF group and calpain inhibitor group, respectively. In the sham operation group, control AF group and calpain inhibitor group, the expressions of caspase-3 (13.0 +/- 1.9%, 52.8 +/- 4.3% and 33.6 +/- 3.7%), caspase-8 (40.1 +/- 5.3%, 92.6 +/- 6.5% and 55.3 +/- 5.9%), bcl-2 (65.8 +/- 6.1%, 52.0 +/- 5.7% and 69.9 +/- 5.3%) and ARC (70.2 +/- 8.6%, 68.8 +/- 7.3% and 81.5 +/- 8.8%) were calculated as immunohistochemical indexes, respectively. The calpain inhibitor N-Acetyl-Leu-Leu-Met attenuated apoptosis through a complicated network of apoptosis-related proteins, which may result in improvement of structural remodeling in atrial fibrillation.