Mechanism of cell death during warm hepatic ischemia-reperfusion in rats: Apoptosis or necrosis?

Reperfusion injury can cause liver dysfunction after cold storage and warm ischemia. Recently it has been suggested that more than 50% of hepatocytes and sinusoidal endothelial cells (SEC) are undergoing apoptosis during the first 24 hours of reperfusion. The aim of our study was to quantify apoptotic and necrotic hepatocytes and apoptotic SEC after 60 or 120 minutes of warm, partial no-flow ischemia and 0 to 24 hours reperfusion in male SD rats. Apoptotic cells were identified by TUNEL assay in combination with morphological criteria. After 60 minutes of ischemia and 1 hour of reperfusion there was a significant increase of apoptotic hepatocytes (0.7 +/- 0.1% vs. 0.3 +/- 0.1% in controls) and SEC (1.5 +/- 0.6% vs. 0.3 +/- 0.1% in controls). The number of apoptotic SEC and hepatocytes was not different from controls at 6 hours or 24 hours of reperfusion. In contrast, the number of necrotic hepatocytes was quantified as 12 +/- 2% at 1 hour, 34 +/- 6% at 6 hours, and 57 +/- 11% at 24 hours. These results correlated with the increase in plasma ALT levels at these time points. Longer (120 min) ischemia times did not affect the number of apoptotic cells but increased hepatocellular necrosis to 58 +/- 4% at 6 hours reperfusion. No significant increase in caspase-3 activity and processing was detectable in any of these livers. Moreover, the caspase inhibitor Z-Asp-cmk (2 mg/kg IV) had no significant effect on reperfusion injury. Our results suggest that only a small minority of SEC and hepatocytes undergo apoptosis after 60 to 120 minutes of warm ischemia followed by 0 to 24 hours of reperfusion. Oncotic necrosis appears to be the principal mechanism of cell death for both cell types.