The use of pharmacological conditioning strategies to improve donor heart preservation in cardiac transplantation

Cardiac transplantation is the gold standard treatment for end-stage heart failure. Over the last 48 years, the profile of cardiac transplantation has evolved to include more higher-risk transplants, that is, longer ischaemic times, more "marginal" organs and higher-risk recipients. However this is associated with an increased risk of primary graft dysfunction (PGD), for which the main mechanisms is ischaemia-reperfusion injury (IRI). This thesis addresses strategies of minimising IRI, using myocardial preservation strategies based on the concept of pharmacological conditioning, and with a focus on improving preservation of marginal donor hearts. Initially, small animal models were developed for incorporation into myocardial preservation studies: i) A rodent model of brain death ii) A rodent abdominal heterotopic working heart transplant model and iii) Cardiac magnetic resonance (CMR) imaging of rat hearts to allow longitudinal non-invasive functional cardiac imaging. Using a Langendorff model, hearts from brain dead rats were treated with pharmacological conditioning using three pro-survival kinase agents erythropoietin, zoniporide and glyceryl trinitrate added to Celsior preservation solution used in cardioplegia and 6 hours of hypothermic storage. Compared to controls, conditioning significantly improved the recovery of aortic flow (AF) and cardiac output (CO), while reducing markers of myocardial injury such as lactate dehydrogenase (LDH). Mechanisms of cardioprotection were indicated by increased phosphorylation of pro-survival kinases Akt and ERK1/2 of the reperfusion injury salvage kinase (RISK) pathway.Older or ˜marginal" hearts (from 18-month old rats) were then assessed, and the recovery of AF and CO were again increased; myocardial oedema and LDH were reduced; and phosphorylation of Akt and ERK1/2 were increased.Sildenafil was tested for its conditioning properties. It was found to be a weak conditioning agent, with activity augmented by the addition of erythropoietin with increased recovery of AF and reduced LDH. A translational clinical study was performed to assess conditioning by erythropoietin and glyceryl trinitrate, compared to historic controls using Celsior alone or modified St. Thomas Solution (STS). The conditioned group had older donors and higher-risk recipients. Results demonstrated comparable use of post-transplant mechanical circulatory support and survival up to 12 months compared with the lower risk "standard criteria" historic controls.