Background: Normothermic machine perfusion (NMP) is a diagnostic tool for liver assessment prior to transplantation. Recent literature on liver NMP supports the importance to analyse the composition of bile during liver NMP. Glutathione (GSH) is known to be one of the major determinants of bile flow and the osmotic driving force in acid-independent bile formation. It is known that biliary GSH efflux is impaired after ischemia. Our aim was to analyse bile GSH in NMP livers over time and hypothesize that it correlates with transplant factors.
Methods: Between 2018-2019 livers undergoing NMP were prospectively included in the study. Bile samples were retrieved at three different time points (after 1 hrs of NMP, after 6 hrs of NMP, at the end of NMP) and analysed using ELISA assays. Results were then correlated with perfusion parameters and clinical outcomes.
Results: 56 livers underwent NMP during the study period, of which 41 were successfully transplanted (73.2%). 48 (58.7%) livers were retrieved from extended criteria donors (ECD) including 14 (25%) liver grafts from donations after circulatory death (DCD). 14 (34.1%) recipients developed early allograft dysfunction and 24 (58.5%) patients developed a biliary complication within the first year of liver transplantation. The GSH content in bile of transplanted livers showed a significant increase over time (hour 1: 26.5±109.2 µmol/l vs. end: 109.2±14.02 µmol/l, p<0.001). The GSH content at 6 hours correlated significantly with the occurrence of biliary complications after one year of liver transplantation. 
Conclusions: Our data indicates that there is an active increase of GSH content in bile during liver NMP. The correlation of GSH content in bile during NMP and the occurrence of biliary complications may suggest that GSH is a potential marker for biliary viability assessment during NMP.