Effect of caspase inhibitors on myocardial infarct size and myocyte DNA fragmentation in the ischemia-reperfused rat heart

Objective: Caspase family proteases are recognized as key mediators of apop tosis. However, the role of caspases in the ischemia-reperfused heart remai ns uncertain. We evaluated the effect of caspase inhibitors on myocardial i nfarct size and the myocyte DNA fragmentation in the ischemia-reperfused ra t hearts. Methods: Three groups of Sprague-Dawley rats (n=7, each) were sub jected to 30 min of ischemia followed by 6 h of reperfusion. One of the fol lowing drugs: (1) YVAD-aldehyde, a caspase-1-like protease inhibitor (3.5 m g/kg; YVAD), (2) DEVD-aldehyde, a caspase-3-like protease inhibitor (3.5 mg /kg, DEVD), (3) vehicle (140 mu l/kg) was administered intravenously 5 min prior to the ischemia in each group. Myocardial infarct size was defined by triphenyltetrazolium chloride (TTC) staining. Immunohistochemical staining by in situ nick end labeling (TUNEL) of cardiomyocytes and DNA electrophor esis were used for detecting DNA fragmentation. Ultrastructural analysis wa s done by electron microscopy. The caspase activity was measured in the myo cardium of both groups. Results: The percentage of TUNEL-positive myocyte n uclei (%AP) was quantified by microscopy. A ladder pattern was detected by electrophoresis of DNA from the risk area and TUNEL-positive myocytes were seen in the risk area. The %AP was significantly reduced from 20+/-1% to 12 +/-3% by YVAD and to 10+/-3% by DEVD (both P<0.01). However, caspase inhibi tors did not significantly change the infarct size. Electronmicrograph show ed similar salcolemmal and mitochondrial damage in both group. The caspase activity was blocked by DEVD at 4 h after reperfusion. Conclusion: Myocyte DNA fragmentation and caspase activation was inhibited by caspase inhibitor s without reduction of the infarct size in ischemia-reperfused rat hearts. (C) 2000 Elsevier Science BN. All rights reserved.