Caspase-dependent and serine protease-dependent DNA fragmentation of myocytes in the ischemia-reperfused rabbit heart - These inhibitors do not reduce infarct size

Some infarcted myocytes undergo caspase-dependent DNA fragmentation, but se rine protease-dependent DNA fragmentation may also be involved. There is co ntroversy 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 ra bbits without collateral circulation. Rabbits were subjected to 30-min coro nary occlusion followed by 48-h reperfusion. A vehicle (dimethylsulfoxide, control group, n=8) or Z-Val-Ala-Asp(Ome)-CH2F (ZVAD-fmk, a caspase inhibit or, 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 se rine protease inhibitor, 2 mg/kg iv at 20 min before coronary occlusion, DC I group, n=8) was administered. Animals were killed at 48 h after reperfusi on for the detection of myocardial infarct size and at 4 h after reperfusio n for the detection of dUTP nick end-labeling (TUNEL)-positive myocytes, th e electrophoretic pattern of DNA fragmentation and ultrastructural analysis . The left ventricle (LV) was excised and sliced. The myocardial infarct si ze 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 sign ificant difference in the % area at risk (AAR) of LV among the 3 groups (co ntrol: 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 DC I group (50.4 +/-3.8%) was not significantly different from the control gro up (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 significant ly reduced compared with the control group (10.7 +/-1.9%). The DNA ladder p attern observed in the control group was attenuated in both the ZVAD and DC I groups. There was no difference in electron microscopic changes among the 3 groups. Serine protease-dependent DNA fragmentation is present in infarc ted myocytes, in addition to caspase-dependent DNA fragmentation, but an in farct-size reducing effect was not observed with either of these inhibitors .