Some infarcted myocytes undergo
caspase-dependent DNA fragmentation, but
serine protease-dependent DNA fragmentation may also be involved. There is controversy regarding whether
caspase inhibitors can reduce
infarct size, so the present study investigated whether
serine protease inhibitor can reduce the DNA fragmentation of infarcted myocytes and whether
serine protease or
caspase inhibitors attenuates
myocardial infarct size in Japanese white rabbits without collateral circulation. Rabbits were subjected to 30-min
coronary occlusion followed by 48-h reperfusion. A vehicle (
dimethylsulfoxide, control group, n=8) or
Z-Val-Ala-Asp(Ome)-CH2F (
ZVAD-fmk, a
caspase inhibitor, ZVAD group, 0.8 mg/kg iv at 20 min before
coronary occlusion and 0.8 mg/kg at 90 min after reperfusion, n=8) or
3,4-dichloroisocoumarin (DCI, a
serine protease inhibitor, 2 mg/kg iv at 20 min before
coronary occlusion, DCI group, n=8) was administered. Animals were killed at 48h after reperfusion for the detection of
myocardial infarct size and at 4h after reperfusion for the detection of dUTP nick end-labeling (TUNEL)-positive myocytes, the electrophoretic pattern of DNA fragmentation and ultrastructural analysis. The left ventricle (LV) was excised and sliced. The
myocardial infarct size as a percentage of the area at risk was assessed by
triphenyltetrazolium chloride staining. DNA fragmentation was assessed by in situ TUNEL at the light microscopic level. ZVAD and DCI significantly reduced the mean blood pressure during reperfusion without affecting heart rate. There was no significant difference in the % area at risk (AAR) of LV among the 3 groups (control: 26.3+/-3.0%; ZVAD: 25.6+/-2.6%; DCI: 25.6+/-2.0%). The %
infarct size as a percentage of the AAR in the ZVAD group (41.3+/-4.5%) and the DCI group (50.4+/-3.8%) was not significantly different from the control group (43.5+/-4.5%). However, the percent DNA fragmentation in the infarcted area in the ZVAD (3.5+/-0.8%) and DCI groups (4.2+/-0.9%) was significantly reduced compared with the control group (10.7+/-1.9%). The
DNA ladder pattern observed in the control group was attenuated in both the ZVAD and DCI groups. There was no difference in electron microscopic changes among the 3 groups.
Serine protease-dependent DNA fragmentation is present in infarcted myocytes, in addition to
caspase-dependent DNA fragmentation, but an
infarct-size reducing effect was not observed with either of these inhibitors.