Examination of ex-vivo lung perfusion in porcine model
Lung transplantation is a lifesaving therapeutic option for a variety of endstage cardiopulmonary conditions. There is a critical mismatch between the availability of suitable lungs and the number of patients awaiting a lung transplant. Ex-vivo lung perfusion (EVLP) is an established technique that may potentially allow more donor lungs to be reconditioned and provide waiting list patients with a better opportunity for transplantation. During EVLP, lungs are connected to a circuit similar to a cardiopulmonary bypass circuit and are perfused and ventilated under normothaermic conditions. In this thesis I have validated a donor after circulatory death (DCD) large animal model, by using porcine lungs initially from local abattoirs followed by change to a more suitable lungs source. As part of the experimental validation, I have shown that there is an initial bacterial load within the perfusate prior starting EVLP, which improved or disappeared during the procedure. I have characterised the perfusate solution and have demonstrated equivalence of alternative perfusate solutions to the current best practice; I have described the inflammatory profiles of the lungs and studied the impact of novel drug and cell therapies on these lungs. In the first phase I have compared cellular and acellular solutions currently used in practice, aiding in the decision of which solution would be most appropriate for my subsequent experiments. By comparing physiological, immunological, ultrastructural parameters, I have found improved but comparable trends in the blood-based solutions. Due to the cost effectiveness and physiological effects on lungs, I have decided to use the Papworth blood-based perfusate out of the three compared solutions. Lung inflammation and rejection processes are interlinked during lung transplantation. In order to characterise the occurring inflammatory processes, I have quantified the cytokine profile in the airway and perfusate; determined the leukocytes trapped in the leukocyte filters and present in the airway. By excluding the leukocyte filters at an earlier time point than the normal use, I have measured reduced levels of lnterleukin-8 and demonstrated that a shorter period use is enough to achieve the intended benefits of these filters while avoiding the deleterious effects. EVLP offers the opportunity to recognise and recondition injured lungs. I have used this quality to develop a one lung and a lobar warm ischaemic injury model, based on the initial DCD model. Apelin is a vasoactive peptide, with previously described roles in angiogenes.is and vasodilatation through the eNOS pathway. I have investigated the modulatory effects of Apelin in the model of one lung injured by warm ischaemia. While this model produced sufficient injury, the vasodilator effects were minimal. In continuation to the reconditioning novel therapies, I have performed a transit and engraftment study of blood human derived endothelial cells. These cells were isolated and cultured in vitro previously, with potential to engraft and promote angiogenesis. I have demonstrated that injured lung lobes treated with these cells showed lower extravascular lung water and decreased warm ischaemic lung injury when compared to the injured lung without cell therapy. In conclusion, I have demonstrated that my porcine model of EVLP is a robust and promising technique that enables the assessment of lungs ex-vivo and may provide a platform for innovative therapeutic strategies.