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

Purpose This study was designed to evaluate the effects of a calpain inhibitor on cardiac muscle apoptosis in rapid pacing canine atrial fibrillation (AF) models. Methods 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. Results 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. Conclusions 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.