Background: Oxidative stress after ischemia/reperfusion of cardiac allografts leads to cytokine production. Bcl-2, an inhibitor of apoptosis, also has strong antioxidant properties. Caspase-3 is known to cleave bcl-2. This study tests the hypothesis that bcl-2 is downregulated while tumor necrosis factor-alpha (TNF-alpha) levels increase after cardiac transplantation. Furthermore, the use of caspase-3 inhibition was investigated as a strategy for preserving myocardial bcl-2 and mitochondrial cytochrome c after transplantation.
Methods and results: PVG-to-ACI rat heterotopic cardiac transplantations were performed in 4 groups designed with 30 minutes' ischemia and 4 or 8 hours of reperfusion (n=4 per group). Treatment consisted of DEVD-CHO 500 microgram IP per animal to donor and recipient 2 hours before transplantation and 250 microgram IC into allograft. Controls were treated with saline. Grafts were analyzed by reverse transcription-polymerase chain reaction for bcl-2 mRNA, by ELISA for TNF-alpha, for myeloperoxidase activity, and by Western blot for cytochrome c. In untreated groups, bcl-2 mRNA decreased significantly over time, whereas TNF-alpha increased significantly at 4 hours (P=0.003) and returned to baseline after 8 hours' reperfusion (P=NS compared with normal hearts). Treatment with caspase-3 inhibitor showed significant upregulation of bcl-2 mRNA expression after 4 and 8 hours of reperfusion (P<0.001 versus control), with a concomitant decrease in TNF-alpha to baseline levels. Myeloperoxidase activity in all groups was no different from that of normal hearts. Mitochondrial cytochrome c release increased in both control and treatment groups.
Conclusions: Bcl-2 is actively downregulated and TNF-alpha is upregulated in this model of cardiac allograft ischemia/reperfusion. Furthermore, the caspase-3 pathway is linked to this process, and blockade of caspase-3 can ameliorate reperfusion injury by upregulating bcl-2 and inhibiting TNF-alpha without affecting cytochrome c release.