Zinc chloride-mediated reduction of apoptosis as an adjunct immunosuppressive modality in cardiac transplantation

Background: Zinc (Zn) blocks caspase-3 activation in cardiac allografts and therefore may synergistically decrease apoptosis along with cyclosporine (CsA), which inhibits mitochondrial release of cytochrome c. Simultaneous treatment of rat recipients of heterotopic heart transplants with zinc chloride (ZnCl₂) thus may allow lower doses of CsA for immunosuppression. Methods: PVG (RT1^c) rat hearts were transplanted heterotopically into the abdomen of ACI (RT1^a) rats. Group 1 (n = 15) rats received no treatment. Group 2 rats (n = 8) received 2 mg/kg/day CsA (sub-therapeutic dose) by oral gavage. Group 3 rats (n = 9) received 2 mg/kg/day oral CsA in addition to 1 mg/kg/day sub-cutaneous ZnCl₂ delivered by osmotic pump. All rats were imaged using Annexin V-bound ^99mTechnetium (^99mTc-Annexin V) on post-operative Day 4 and subsequently killed. Annexin V avidly binds apoptotic cells in vivo. Region of interest per whole body (WB) data were calculated using the images. The allograft survival study was conducted with n = 11, 6, and 5 in control, CsA, and CsA+Zn groups, respectively. Finally, percentages of allografts that reached tolerance were measured in both CsA-only and CsA+Zn groups (n = 8 each). Results: Zinc chloride had an additive effect with CsA on apoptotic blockade and graft survival. The regions of interest per WB uptake of ^99mTc-Annexin V were 2.43% ± 0.37%, 2.08% ± 0.52%, and 1.49% ± 0.29%*, and acute survivals were 6.4 ± 1.7, 7.2 ± 2.1, and 11.2 ± 2.5* days for control, CsA, and CsA+Zn groups, respectively (*p < 0.001 vs controls). In addition, 87.5% of allografts became tolerant and survived for 90 days in the CsA+Zn group compared with only 37.5% in the CsA-only group (p = 0.049). Conclusion: Zinc-mediated reduction of apoptosis served as an effective adjunct immunosuppressive therapy to CsA in a rat model of cardiac transplantation.