RESTORATION OF THE CAMP 2ND MESSENGER PATHWAY ENHANCES CARDIAC PRESERVATION FOR TRANSPLANTATION IN A HETEROTOPIC RAT MODEL

Current organ preservation strategies subject graft vasculature to severe hypoxia (PO2 approximately 20 Torr), potentially compromising vascular function and limiting successful transplantation. Previous work has shown that cAMP modulates endothelial cell (EC) antithrombogenicity, barrier function, and leukocyte/EC interactions, and that hypoxia suppresses EC cAMP levels. To explore the possible benefits of cAMP analogs/agonists in organ preservation, we used a rat heterotopic cardiac transplant model; dibutyryl cAMP added to preservation solutions was associated with a time- and dose-dependent increase in the duration of cold storage associated with successful graft function. Preservation was also enhanced by 8-bromo-cAMP, the S(p) isomer of adenosine 3',5'monophosphorothioate, and types III (indolidan) and IV (rolipram) phosphodiesterase inhibitors. Neither butyrate alone nor 8-bromoadenosine were effective, and the cAMP-dependent protein kinase antagonist R(p) isomer of adenosine 3',5'monophosphorothioate prevented preservation enhancement induced by 8-bromo-cAMP. Grafts stored with dibutyryl cAMP demonstrated a 5.5-fold increase in blood flow and a 3.2-fold decreased neutrophil infiltration after transplantation. To explore the role of cAMP in another cell type critical for vascular homeostasis, vascular smooth muscle cells were subjected to hypoxia, causing a time-dependent decline in cAMP levels. Although adenylate cyclase activity was unchanged, diminished oxygen tensions were associated with enhanced phosphodiesterase activity (59 and 30% increase in soluble types III and IV activity, respectively). These data suggest that hypoxia or graft ischemia disrupt vascular homeostasis, at least in part, by perturbing the cAMP second messenger pathway. Supplementation of this pathway provides a new approach for enhancing cardiac preservation, promoting myocardial function, and maintaining vascular homeostatic properties.