Defatting of donor transplant livers during normothermic perfusion and modulating extended-criteria donor graft tolerance to ischaemia-reperfusion injury

Thesis

The limited availability of suitable donor livers remains a critical challenge in liver transplantation, necessitating the use of extended criteria donor (ECD) livers, including those from donation after circulatory death (DCD) donors and those exhibiting moderate-to-severe hepatic steatosis (HS). These livers, however, are more susceptible to ischemia-reperfusion injury (IRI), particularly when preserved using static cold storage (SCS). This thesis investigates the clinical application of normothermic machine perfusion (NMP) as a dynamic preservation strategy to mitigate the risk profile of steatotic and DCD livers and improve transplantation outcomes. Through a large-scale analysis of donor livers from the Quality in Organ Donation (QUOD) bioresource, I have characterised pre retrieval predictors of donor HS severity and explored the use of digital image analysis (DIA) as a rapid and reproducible tool for quantifying HS, addressing limitations in macroscopic and histopathological assessments. The clinical application of these measures could facilitate early identification of steatotic livers and guide preservation strategies to improve utilisation. I further explored clinical outcomes of steatotic livers preserved using NMP compared to SCS through use of samples from a previous phase III multicentre randomised clinical trial. I demonstrated that NMP reduced IRI related complications in steatotic livers and demonstrated graft survival rates comparable to lean livers preserved with SCS. Despite these advances, metabolic challenges persisted (as assessed through biochemical perfusate measurements), highlighting the need for additional interventions beyond replacing SCS with NMP. Through proteomic analysis of this cohort, I demonstrated that while NMP enhanced mitochondrial function and lipid metabolism, it did not fully restore metabolic efficiency in steatotic livers. The potential to improve fat metabolism is therefore described in the context of an ongoing clinical trial ‘The DeFat Study’ which involves defatting of donor transplant livers during NMP. If the intervention proves effective, it could certainly expand the donor pool through utilisation of steatotic donor livers. To further optimise defatting protocols, I performed a series of pre-clinical perfusions in discarded human livers and explored the role of pharmacological modulation of hypoxiainducible factors (HIFs) during NMP. This approach facilitated a reduction in HS and improved graft function, thereby offering an opportunity to further refine current defatting protocols. Finally, I investigated the removal of damage-associated molecular patterns (DAMPs) in an ex-situ porcine DCD model of liver transplant. Through use of a specialised column, I demonstrated effective removal of DAMPs, correlating with improved graft function and reduced microclot burden during whole blood allogenic reperfusion.

Authors: Abbas, SH

• DOI: 10.5287/ora-zbzpezpyb
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: liver normothermic machine perfusion; extended-criteria donor livers; neutrophil extracellular traps; functional transplantability criteria; ischaemia-reperfusion injury; DAMPs; defatting
• Subjects: Liver Normothermic Machine Perfusion; Ischaemia-Reperfusion Injury; Neutrophil Extracellular Traps; Defatting; Extended-Criteria Donor Livers; DAMPs; Functional Transplantability Criteria