Abstract 3367: Metformin as a Cardioprotective Agent in Heart Transplantation Decreases Ischemia-Reperfusion Injury and Chronic Rejection
Background: Ischemia-reperfusion (I-R) injury, an alloantigen-independent event, participates in the pathogenesis of chronic rejection (GCAD) in cardiac transplants. Recently, metformin has been reported to provide cardiac benefits independent of its glucose controlling properties. Here, we examine the use of metformin as a cardioprotective agent in limiting I-R injury and subsequent GCAD development.
Methods: To determine the effects of metformin on I-R injury, FVB donor hearts were transplanted into C57BL/6 recipient mice (total mismatch) and treated with either metformin or PBS (control). Donor animals received IP treatment 1 hour prior to surgery and vena cava injection 2 minutes before procurement. Cold-ischemia time approx 20 minutes. Donor hearts harvested at 24 hours (n=6 each). Caspase-3 activity (ELISA), cytoplasmic histone-associated-DNA fragments (ELISA), and TUNEL staining used as apoptosis indicators. To assess GCAD development, B6.C-H2bm12 hearts were transplanted into C57BL/6 recipients (MHC Class II mismatch) and harvested day 52 (n=6 each). Immunohistochemistry and morphometric analysis performed to assess luminal narrowing (intimal proliferation) and graft infiltrating cells. Intragraft cytokine levels determined with Luminex protein assay.
Results: Metformin-treated mice had a significant reduction in allograft cardiomyocyte apoptosis, noted by a 1.8 fold decrease in caspase-3 activity (p <0.001), a 3.1 fold decrease in cytoplasmic histone-associated-DNA fragments (p <0.01), and a 35% decrease in %TUNEL-positive cells (p=0.02) at 24 hours. In the chronic rejection model, metformin-treated animals had a significant decrease in GCAD development compared to PBS control (46.77±3.63% vs. 67.95±4.42%, p<0.001, metformin vs PBS). Metformin-treated animals also had a significant decrease in allograft inflammatory cells (CD4, CD8, macrophages) (p<0.05). While metformin-treated animals developed reduced levels of pro-inflammatory cytokines, such levels did not reach significance.
Conclusions: Preconditioning donor hearts with metformin is a novel approach to reduce GCAD development. Importantly, the beneficial effects seen with metformin therapy may be due to a reduction in I-R induced apoptosis.