Anti-apoptotic effects of a calpain inhibitor on cardiomyocytes in a canine rapid atrial fibrillation model.
OBJECTIVE
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.
Li
Yue
Y
Department of Cardiology, the First Affiliated Hospital, Harbin Medical University, Harbin, 150001, People's Republic of China.
Gong
Zhi-Hua
ZH
Sheng
Li
L
Gong
Yong-Tai
YT
Tan
Xiang-Yang
XY
Li
Wei-Min
WM
Dong
De-Li
DL
Yang
Bao-Feng
BF
Fu
Song-Bin
SB
Xue
Hong-Jie
HJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis / Q000378:metabolism; D001281:Atrial Fibrillation / Q000473:pathology* / Q000503:physiopathology; D015153:Blotting, Western; D001835:Body Weight / Q000502:physiology; D002154:Calpain / Q000037:antagonists & inhibitors*; D053148:Caspase 3 / Q000378:metabolism; D004285:Dogs; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects*; D009842:Oligopeptides / Q000494:pharmacology*; D009929:Organ Size / Q000502:physiology; D011480:Protease Inhibitors / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics
D051017:Apoptosis Regulatory Proteins; D009842:Oligopeptides; D011480:Protease Inhibitors; D012333:RNA, Messenger; C069861:calpain inhibitor 2; D002154:Calpain; D053148:Caspase 3