Effects of hypothermic oxygenated machine perfusion on bile composition after liver transplantation - Findings from a randomized controlled trial.

Background & Aims: In liver transplantation, bile acid (BA) toxicity contributes to injury of both hepatocytes and cholangiocytes. While hypothermic oxygenated machine perfusion (HOPE) reduces ischemia-reperfusion injury (IRI) and improves clinical outcomes, its impact on bile composition remains unclear because of the lack of bile samples available after LT. Methods: Bile, blood, and liver tissue were collected within a multicentric randomized controlled trial (NCT03124641), from 26 patients receiving extended criteria donation (ECD) allografts from donors after brain death (DBD). Fourteen donor livers were static cold stored (SCS group), while 12 livers underwent end-ischemic HOPE. Grafts were randomly assigned. BA levels and metabolic parameters were analyzed across samples with mass spectrometry. Expression of bile transporters and enzymes was assessed in liver biopsies before and after transplantation. Results: Serum and biliary levels of hydrophobic BAs were positively correlated with IRI severity, such as serum aspartate aminotransferase and alanine aminotransferase, and decreased across postoperative days (POD) for all allografts (bile: POD-1 vs. POD-2/-3, p <0.001; blood: admission vs. POD-1-3, p <0.001). Expression of the hepatocyte bile transporters ABCB4 and ABCG8 decreased post-reperfusion (p = 0.045; p <0.001). In the SCS group, intrahepatic BA levels increased post-reperfusion (8.71 to 10.77 pmol/mg, p = 0.023), while biliary BA levels decreased postoperatively (POD-1 vs. POD-3, p = 0.06). The HOPE group showed higher biliary BA and phosphatidylcholine (PC) levels on POD-3 compared with the SCS group (total BAs: 2.30 × 109 vs. 2.03 × 109 peak area, p = 0.047; PC: 6.49 × 108 vs. 4.48 × 108 peak area, p = 0.031), and a decline in biliary BA/PC ratio. Conclusions: This is the first randomized study demonstrating effects of HOPE treatment on bile composition following ECD-DBD liver transplantation. Protection from BA toxicity may represent a novel mechanism underlying the effects of HOPE. Clinical trials registration: This trial is registered at ClinicalTrials.gov (NCT03124641). Impact and implications: Worldwide liver allograft scarcity has led to the implementation of hypothermic oxygenated machine perfusion (HOPE) to enhance the safety of liver transplantation (LT) using extended criteria donors. However, its protective mechanisms remain incompletely understood, largely because of limited human data. In this study, we provide evidence that HOPE improves biliary lipid secretion after LT, limits intrahepatic bile acid accumulation upon allograft reperfusion, reduces the biliary bile acid to phosphatidylcholine ratio and promotes normalization of serum bile acids levels post-LT. Our findings suggest that protection from bile acid toxicity may constitute a novel mechanism underlying the effects of HOPE.