Immunometabolic impact of machine perfusion strategies in liver transplantation

Liver transplant numbers do not meet the existing needs, thousands of patients remain on transplant waiting lists worldwide and many die while awaiting a life-saving organ. A key contributor to organ shortage is the discarding of viable organs coming from donors considered high-risk, for fear that they might malfunction after transplantation as a result of a phenomenon called ischaemia reperfusion injury (IRI). Most of the discarded livers are those donated after circulatory death (DCD), only 27% of which are currently utilised in the UK. The quality of DCD organs can be improved by replacing the icebox (static cold storage or SCS), which remains the main approach to preserve the livers after having been retrieved, by strategies that perfuse the livers in a machine (machine perfusion or MP). There are currently 3 MP strategies employed in the clinic: normothermic regional perfusion (NRP) is used in the donors by perfusing the liver with the donor's blood at 37 degrees Celsius, and normothermic (NMP) or hypothermic (HOPE) perfusion are used in the procured livers out of the body (using warm or cold perfusion fluids, respectively). To date, no controlled objective comparisons of these different MP strategies have been undertaken and we do not have a good understanding of their mechanisms of action. Our hypothesis is that the benefits of MP will depend on whether they are capable of improving the damage to the liver cell mitochondria, which constitutes the first event that elicits IRI at the time of transplantation. To determine this, we propose to conduct a randomised clinical trial in which 36 DCD human livers will be allocated to 1 of 3 treatment arms: : i) SCS; ii) NRP; and iii) HOPE. This will be followed by a period of time in NMP in order to study the IRI response and determine if the quality of the livers is good enough to proceed to transplantation. Our proposal will include three key Objectives:

1) To investigate the role of mitochondrial damage in the IRI that takes place when DCD livers are transplanted.
2) To determine the mechanisms through which the different MP strategies influence IRI in DCD liver transplantation.
3) To develop markers to assess the quality of the livers while they are being perfused using NMP before being transplanted into patients.

Our study will allow us to decipher the mechanisms of liver IRI in humans in a much better way than what has been achieved to date. Furthermore, it will provide guidelines as to the best way of employing the MP technologies and may result in the identification of new treatments. Ultimately, our proposal will serve to improve the quality of DCD livers and increase the number of patients who can safely receive a liver transplant.

The imbalance between patients awaiting lifesaving liver transplantation and organ availability requires the development of strategies to expand organ supply. Using organs donated after circulatory death (DCD) offers the highest potential to do so. However, because of the inevitable period of warm ischaemia before procurement, DCD organs suffer increased ischaemia reperfusion injury (IRI) and worse post-transplant outcomes. This has prompted the use of machine perfusion (MP) tools to resuscitate the organs and assess their functional integrity before transplantation. The MP systems already clinically adopted are normothermic regional perfusion (NRP) in the donors, and normothermic (NMP) and hypothermic (HOPE) ex situ perfusion of the procured livers, all of which have been shown to reduce IRI-related complications post-transplant. To date, no controlled objective comparisons of the 3 MP strategies have been undertaken, and we lack rigorous mechanistic evaluations of the effects of MP on liver biochemistry and immunometabolism. Human donor livers perfused under NMP after static cold storage (SCS) develop an IRI response that closely resembles what is observed after transplantation. NMP therefore constitutes a powerful model to study IRI under controlled experimental conditions. We propose to conduct a randomised clinical trial employing this model to define the exact mechanisms of human liver IRI, and to investigate how these mechanisms are influenced by different organ preservation modalities. We hypothesize that the benefits of MP on liver IRI will depend on their capacity to ameliorate the metabolic adaptations induced by ischaemia and reduce free radical mediated mitochondrial damage. 36 DCD livers will be allocated to 1 of 3 treatment arms: i) SCS; ii) NRP; and iii) HOPE. All livers will subsequently undergo a period of NMP to allow rigorous sample collection for mechanistic studies and standardised viability assessments, before proceeding to transplantation.