Preservation of Nitric Oxide Synthase Activity Required for Beneficial Effects of Hypothermic Oxygenated Perfusion in Cardiac Grafts Obtained with DCD

Abstract

<h3>Purpose</h3> Cardiac donation after circulatory death (DCD) is a promising option to increase graft availability. We recently reported that cardiac graft preservation with hypothermic oxygenated perfusion (HOPE) between graft procurement and normothermic reperfusion improves graft recovery as compared to preservation with cold static storage (CSS), the current clinical standard. As the precise mechanisms remain incompletely characterized, we investigated the role of preserved nitric oxide synthase (NOS) activity during HOPE on its beneficial effects. <h3>Methods</h3> Using an adult rat model of DCD, hearts underwent in-situ ischemia (21 minutes), were explanted for a cold storage period (30 minutes), and then reperfused under normothermic conditions (60 minutes) with left ventricular loading. Three cold storage conditions were compared: CSS, HOPE, and HOPE with L-NAME (NOS inhibitor). To evaluate potential confounding effects of high coronary flow during early reperfusion in HOPE hearts, bradykinin (BK) was administered to normalize coronary perfusion to HOPE levels in two additional groups (CSS and HOPE with L-NAME). <h3>Results</h3> Cardiac recovery was significantly improved in HOPE vs. CSS hearts, as determined by cardiac output, left ventricular work (heart rate-developed pressure product), contraction and relaxation rates, as well as coronary flow and oxygen efficiency (oxygen consumption per work performed; p<0.05). Strikingly, the addition of L-NAME during HOPE largely abolished its beneficial effects, even when early reperfusion coronary flow was normalized to HOPE levels with BK. Furthermore, preliminary experiments demonstrate a tendency for reduced release of cell death markers in hearts treated with HOPE compared to all other groups. <h3>Conclusion</h3> HOPE provides superior preservation of ventricular and vascular function, as well as improved metabolic recovery, compared to the current clinical standard (CSS). Importantly, preservation of NOS activity during the cold storage period is required for the protective effects of HOPE. The application of HOPE prior to normothermic reperfusion is a promising approach to help optimize cardiac graft recovery following warm ischemia in DCD cardiac grafts.