Zinc-mediated reduction of apoptosis in cardiac allografts

Background-Apoptosis is thought to occur during immune-mediated acute rejec tion of cardiac allografts. In vitro studies have shown that zinc inhibits the activity of the proapoptotic enzyme caspase-3, We hypothesized that ZnC l2 would reduce acute cardiac rejection in vivo via the blockade of caspase -3-dependent apoptosis, Tc-99m-labeled annexin V was used to measure apopto sis in cardiac allografts through nuclear imaging. Annexin V binds to phosp hatidylserines, which are externalized to the outer membrane of apoptotic c ells. Methods and Results-Twenty-seven PVG rat hearts were transplanted heterotop ically into the abdomen of untreated ACI rats as controls (group 1). Fiftee n were scanned and euthanized on postoperative day 4, and 12 were assessed for graft survival. Group 2 and 3 rats (n=15 each) received I and 5 mg/kg Z nCl2 BID IP, respectively. Nine of each of these groups were scanned and eu thanized on postoperative day 4, and 6 were studied for allograft survival, Group 3 rats (n=3) received isografts. Region-of-interest analysis demonst rated a dose-dependent reduction in Tc-99m annexin uptake in ZnCl2-treated allografts: 2.43+/-0.37% for group I, 1.97+/-0.41% for group 3, 1.21+/-0.47 % for group 3, and 0.55+/-0.19% for group 4 (ANOVA, P=0.001). Graft surviva l times of 6.4+/-1.7, 9.3+/-3.0, and 11.5+/-3.4 days for groups I, 2, and 3 , respectively, were also observed (ANOVA, P=0.001). Caspase-3 activity in the allografts showed a 3.7-fold reduction in group 3 animals compared with group 1 animals (P=0.004). Conclusions-Apoptosis that occurs in acute cardiac allograft rejection is r educed with ZnCl2 in a dose-dependent manner via caspase-3 inhibition.