Effect of the degree of ischaemic injury and reoxygenation time on the type of myocardial cell death in man: role of caspases.

BACKGROUND: The importance of apoptosis in the injury sustained by the human myocardium during ischaemia and reoxygenation and the underlying mechanisms remain unclear. To quantify apoptosis and necrosis induced by simulated ischaemia/reoxygenation in the human atrial myocardium, free-hand sections of right atrial appendage (n = 8/group) were subjected to 90 minutes simulated ischaemia followed by 2, 8 and 24 hours reoxygenation. RESULTS: Apoptosis, as assessed by TUNEL, was greater than necrosis after 90 minutes simulated ischaemia and 2 hours reoxygenation (35.32 +/- 3.22% vs 13.55 +/- 1.3%; p < 0.05) but necrosis was greater than apoptosis by 24 hours reoxygenation (45.20 +/- 2.75% vs 4.82 +/- 0.79%; p < 0.05). Total caspase activation was similar after 90 minutes simulated ischaemia followed by 2 hours and 24 hours reoxygenation (515270 +/- 99570 U vs 542940 +/- 95216 U; p = NS). However, caspase-3 like activation was higher at 2 hours than at 24 hours reoxygenation (135900 +/- 42200 U vs 54970 +/- 19100 U; p < 0.05). Inhibition of caspase-3 by z.DEVD.fmk (70 nM) almost completely abolished apoptosis from 23.26 +/- 2.854% to 0.73 +/- 0.28 % (p < 0.05), without affecting necrosis. CONCLUSION: Cell death by apoptosis and necrosis in the human myocardium subjected to simulated ischaemia/reoxygenation depends on the degree of the ischaemic insult and have a different time-course with apoptosis happening early during reoxygenation and necrosis becoming more important later. Importantly, the apoptosis induced by simulated ischaemia/reoxygenation is mainly mediated by activation of caspase-3 but it does not affect necrosis.