Optimizing DCD Liver Grafts With Prolonged Warm Ischemic Time Using Stabilized Plasmin in a Static Cold Storage Orthotopic Rat Liver Transplant Model.

Background: The clinical success of liver transplantation has led to increased demand, requiring further expansion of the donor pool. Therapeutic interventions to optimize organs from donation after circulatory death (DCD) have significant potential to mitigate the organ shortage. Dysfunction in DCD liver grafts is mediated by microvascular thrombosis during the warm ischemic period, and strategies that reduce this thrombotic burden may improve graft function. We hypothesized that the administration of the fibrinolytic enzyme plasmin to the donor organ during the cold storage period would reduce the thrombotic burden and improve DCD liver graft function. Methods: In 2 separate cohorts, 32 syngeneic orthotopic rat liver transplants were performed in Lewis rats. Livers were procured from donors with 45 min of warm ischemic injury. Liver grafts were flushed with histidine-tryptophan-ketoglutarate preservation solution mixed with either plasmin (experimental group) or albumin (control group). All investigators were blinded to treatment group. After preparing the liver for implant using a modified cuff technique, the liver was stored for 1 h by static cold storage at 4 °C. Immediately before implantation, the liver graft was flushed, and this effluent was analyzed for fibrin degradation products to determine graft clot burden. Twenty-four hours following transplantation, animals were euthanized, and samples were collected. Results: Recipient survival was significantly higher for DCD liver grafts treated with plasmin compared with control. Moreover, histology of liver graft tissue immediately before implant reflected significantly reduced congestion in plasmin-treated livers (score, mean ± SD: 0.73 ±â€…0.59 versus 1.12 ±â€…0.48; P = 0.0456). The concentration of fibrin degradation products in the final flush before implantation was significantly reduced in plasmin-treated livers (743 ±â€…136 versus 10 919 ±â€…4642 pg/mL; P = 0.0001), reflecting decreased clot burden in the graft. Conclusions: The present study demonstrates that plasmin improves survival and may reduce thrombotic burden in DCD liver grafts with prolonged warm ischemic injury, meriting further study.

Two Compartment Evaluation of Liver Grafts During Acellular Room Temperature Machine Perfusion (acRTMP) in a Rat Liver Transplant Model.

Background: Subnormothermic machine perfusion (SNMP) of liver grafts is currently less clinically developed than normothermic and hypothermic approaches, but may have logistical advantages. At intermediate temperatures, the oxygen demand of the graft is low enough to be satisfied with an acellular perfusate, obviating the need for oxygen carrying molecules. This intermediate metabolic rate, however, is sufficient to support the production of bile, which is emerging as an important indicator of graft injury and viability. In this study, we hypothesized that the biliary compartment would be more sensitive than perfusate in detecting graft injury during SNMP. Methods: To test this hypothesis in a rat model, we performed liver transplants with DCD and control liver grafts after 1 h of acellular room temperature machine perfusion (acRTMP) or static cold storage (SCS). Point of care liver function tests were measured in biliary and perfusate samples after 1 h of machine perfusion. Following transplantation, rats were sacrificed at 24 h for assessment of post-transplant graft function and histology. Results: All point-of-care liver function tests were significantly more concentrated in the biliary compartment than the perfusate compartment during acRTMP. DCD liver grafts could be distinguished from control liver grafts by significantly higher markers of hepatocyte injury (AST, ALT) in the biliary compartment, but not in the perfusate compartment. Classical markers of cholangiocyte injury, such as gammy-glut amyl transferase (GGT), amylase (AML), and alkaline phosphatase were detectable in the biliary compartment, but not in the perfusate compartment. In comparison to SCS, graft preservation by acRTMP produced a significant survival benefit in DCD liver transplantation (75 vs. 0%, p < 0.0030). Conclusion: Together, these findings demonstrate that during acRTMP, the biliary compartment may be a more sensitive indicator of graft injury than the perfusate compartment. Moreover, acRTMP provides superior graft preservation to SCS in rat DCD liver transplantation.