Non-specific caspase inhibition reduces infarct size and improves post-ischaemic recovery in isolated ischaemic/reperfused rat hearts

Myocardial ischaemia and reperfusion lead to myocardial cell death due, at least in part, to apoptotic mechanisms. Although cysteinyl aspartate-specif ic proteinase (caspase) activation is a major event and the most-cited culp rit in the development of apoptosis, its potential contribution to ischaemi c myocardial cell death is largely unknown. To study the role of caspase ac tivation, isolated rat hearts (n = 6 per group) were subjected to 30 min co ronary artery occlusion followed by 120 min reperfusion. A non-selective [0 .1 or 0.5 muM acetyl-Tyr-Val-Ala-Asp chloromethylketone (YVAD-cmk)] or sele ctive caspase inhibitors [0.07 or 0.2 muM acetyl-Asp-Glu-Val-Asp-cmk (Ac-DE VD-cmk, caspase-3 inhibitor); 0.07 or 0.2 muM benzoxycarbonyl-Leu-Glu-OMe-H is-Asp(OMe)-fluoromethyl- ketone (z-LEHD-fmk, caspase-9 inhibitor)] were ad ded to the perfusate at the start of reperfusion. Non-selective caspase inh ibition with 0.1 or 0.5 muM YVAD-cmk limited in-farct size: (21 +/- 4%, P < 0.05; 17 +/- 3%, P < 0.05, respectively) compared with the ischaemic/reper fused control (32 +/- 5%). In hearts treated with 0.1 or 0.5 muM caspase II non-selective inhibitor, the fraction of terminal-deoxynucleotidyl-transfe rase deoxyuridine nick end labelling (TUNEL)-positive myocyte nuclei in the infarcted zone was reduced from the ischaemic/reperfused non-treated contr ol of 11.2 +/- 2.1% to 6.2 +/- 1.6% (P < 0.05) and 1.2 +/- 0.2% (P < 0.05), respectively. The recovery of post-ischaemic cardiac function (coronary fl ow, aortic flow and left-ventricular developed pressure) improved significa ntly with the application of the non-selective caspase inhibitor as well. I n hearts perfused with specific caspase inhibitors (caspase-3 and caspase-9 ) there was no significant reduction in the infarct size, no improvement in post-ischaemic cardiac function and no reduction of apoptotic cell death. We conclude that non-specific inhibition of caspases may be therapeutically beneficial in myocardial ischaemia/reperfusion-induced damage, while selec tive caspase inhibitors may fail to prevent such reperfusion-induced injury in our model system.