Long-term Outcomes After Controlled Oxygenated Rewarming of Human Livers Before Transplantation.Transplant Direct. 2020;6:e542. [PMID: 32309628 DOI: 10.1097/TXD.0000000000000987]

Real-time monitoring of mitochondrial oxygenation during machine perfusion using resonance Raman spectroscopy predicts organ function

Organ transplantation is a life-saving procedure affecting over 100,000 people on the transplant waitlist. Ischemia reperfusion injury (IRI) is a major challenge in the field as it can cause post-transplantation complications and limit the use of organs from extended criteria donors. Machine perfusion technology has the potential to mitigate IRI; however, it currently fails to achieve its full potential due to a lack of highly sensitive and specific assays to assess organ quality during perfusion. We developed a real-time and non-invasive method of assessing organs during perfusion based on mitochondrial function and injury using resonance Raman spectroscopy. It uses a 441 nm laser and a high-resolution spectrometer to quantify the oxidation state of mitochondrial cytochromes during perfusion. This index of mitochondrial oxidation, or 3RMR, was used to understand differences in mitochondrial recovery of cold ischemic rodent livers during machine perfusion at normothermic temperatures with an acellular versus cellular perfusate. Measurement of the mitochondrial oxidation revealed that there was no difference in 3RMR of fresh livers as a function of normothermic perfusion when comparing acellular versus cellular-based perfusates. However, following 24 h of static cold storage, 3RMR returned to baseline faster with a cellular-based perfusate, yet 3RMR progressively increased during perfusion, indicating injury may develop over time. Thus, this study emphasizes the need for further refinement of a reoxygenation strategy during normothermic machine perfusion that considers cold ischemia durations, gradual recovery/rewarming, and risk of hemolysis.

Current practice and novel approaches in organ preservation

Organ transplantation remains the only treatment option for patients with end-stage organ failure. The last decade has seen a flurry of activity in improving organ preservation technologies, which promise to increase utilization in a dramatic fashion. They also bring the promise of extending the preservation duration significantly, which opens the doors to sharing organs across local and international boundaries and transforms the field. In this work, we review the recent literature on machine perfusion of livers across various protocols in development and clinical use, in the context of extending the preservation duration. We then review the next generation of technologies that have the potential to further extend the limits and open the door to banking organs, including supercooling, partial freezing, and nanowarming, and outline the opportunities arising in the field for researchers in the short and long term.

Machine perfusion of the liver: Putting the puzzle pieces together

The realm of extended criteria liver transplantation created the 'adjacent possible' for dynamic organ preservation. Machine perfusion of the liver greatly expanded donor organ preservation possibilities, reaching before unattainable goals, including the mitigation of ischemia-reperfusion injury, viability assessment, and organ reconditioning prior to transplantation. However, current scientific evidence lacks uniformity between studies, perfusion protocols, and acceptance criteria. Construction of collaborative research networks for sharing knowledge should, therefore, enable the development of high-level evidence and guidelines for machine perfusion utilization, including donor acceptance criteria. Finally, this approach shall guarantee conditions for further progress to occur.

Normothermic Machine Perfusion (NMP) of the Liver - Current Status and Future Perspectives

A shortage of available organs for liver transplantation has led transplant surgeons and researchers to seek for innovative approaches in hepatoprotection and improvement of marginal allografts. The most exciting development in the past decade has been continuous mechanical perfusion of livers with blood or preservation solution to mitigate ischemia-reperfusion injury in contrast to the current standard of static cold storage. Two variations of machine perfusion have emerged in clinical practice. During hypothermic oxygenated perfusion the liver is perfused using a red blood cell-free perfusate at 2-10°C. In contrast, normothermic machine perfusion mimics physiologic liver perfusion using a red blood cell-based solution at 35.5-037.5°C, offering a multitude of potential advantages. Putative effects of normothermic perfusion include abrogation of hyperfibrinolysis after reperfusion and inflammation, glycogen repletion, and regeneration of adenosine triphosphate. Research in normothermic machine perfusion focuses on development of biomarkers predicting allograft quality and susceptibility to ischemia-reperfusion injury. Moreover, normothermic perfusion of marginal allografts allows for application of a variety of therapeutic interventions potentially enhancing organ quality. Both methods need to be subjected to translational investigation and evaluation in clinical trials. A clear advantage is transformation of an emergency procedure at night into a planned daytime surgery. Current clinical trials suggest that normothermic perfusion not only increases the use of hepatic allografts but is also associated with milder ischemia-reperfusion injury, resulting in a reduced risk of early allograft dysfunction and less biliary complications, including ischemic cholangiopathy, compared to static cold storage. The aim of this review is to give a concise overview of normothermic machine perfusion and its current applications, benefits, and possible advances in the future.

Transcriptomic profiles of human livers undergoing rewarming machine perfusion before transplantation-first insights

Machine perfusion by controlled oxygenated rewarming (COR) is feasible and safe in clinical application and result in a promising outcome. This study utilizes next-generation sequencing (NGS) to investigate the transcriptome of human liver tissue undergoing COR before liver transplantation. Cold-stored livers were subjected to machine-assisted slow COR for ~120 min before transplantation. Biopsies were taken before (preCOR) and after COR (postCOR) and 1 h after reperfusion (postRep). The samples were sequenced, using RNA-seq to analyze differential transcriptional changes between the different stages and treatments of the grafts. Comparison of differential gene expression preCOR and postCOR demonstrated 10 upregulated genes. postRep 97 and 178 genes were upregulated and 7 and 13 downregulated compared to preCOR and postCOR, respectively. A shift of gene expressions by machine perfusion to the TGF-beta pathway was observed. The present study demonstrates distinct transcriptome profiles associated with machine perfusion by COR and transplantation of human livers. Such data provide a deeper understanding of the molecular mechanisms of machine perfusion technology in human liver transplantation.

[Machine Perfusion for Liver Transplantation - What is Possible and Where Do We Stand in Germany? Review of the Literature and Results of a National Survey]

Machine perfusion of donor livers is currently regarded as the most important innovation in transplant surgery to address the continuing shortage of organs in liver transplantation. Hypothermic machine perfusion (HMP) is safe to use and appears to reduce the risk of biliary complications and improve the long-term survival of transplanted organs following preservation by cold static storage - even in donors after cardiac death. A potential functional test of donor organs during HMP uses flavin mononucleotide and is still under clinical investigation. Normothermic machine perfusion (NMP) has a greater risk of technical problems, but functional testing using conventional laboratory parameters during NMP allows significant expansion of the donor pool, even though no prospective randomised study has been able to demonstrate a survival advantage for transplanted organs after NMP. In addition, the preservation time of the donor organs can be significantly extended with the help of NMP, which is particularly advantageous for complex recipient operations and/or logistics. Both methods could be applied for various scenarios in transplantation medicine - theoretically also in combination. The majority of German transplant centres regard machine perfusion as an important innovation and already actively perform perfusions or are in preparation for doing so. However, the overall practical experience in Germany is still relatively low, with only 2 centres having performed more than 20 perfusions. In the coming years, multi-centre efforts to conduct clinical trials and to develop national guidelines on machine perfusion will therefore be indispensable in order to define the potential of these technological developments objectively and to exploit it optimally for the field of transplantation medicine.

Ex vivo machine perfusion: current applications and future directions in liver transplantation

BACKGROUND

Liver transplantation is the only curative treatment option for end-stage liver disease; however, its use remains limited due to a shortage of suitable organs. In recent years, ex vivo liver machine perfusion has been introduced to liver transplantation, as a means to expand the donor organ pool.

PURPOSE

To present a systematic review of prospective clinical studies on ex vivo liver machine perfusion, in order to assess current applications and highlight future directions.

METHODS

A systematic literature search of both PubMed and ISI web of science databases as well as the ClinicalTrials.gov registry was performed.

RESULTS

Twenty-one articles on prospective clinical trials on ex vivo liver machine perfusion were identified. Out of these, eight reported on hypothermic, eleven on normothermic, and two on sequential perfusion. These trials have demonstrated the safety and feasibility of ex vivo liver machine perfusion in both standard and expanded criteria donors. Currently, there are twelve studies enrolled in the clinicaltrials.gov  registry, and these focus on use of ex vivo perfusion in extended criteria donors and declined organs.

CONCLUSION

Ex vivo liver machine perfusion seems to be a suitable strategy to expand the donor pool for liver transplantation and holds promise as a platform for reconditioning diseased organs.

Research progress on hepatic machine perfusion

Nowadays, liver transplantation is the most effective treatment for end-stage liver disease. However, the increasing imbalance between growing demand for liver transplantation and the shortage of donor pool restricts the development of liver transplantation. How to expand the donor pool is a significant problem to be solved clinically. Many doctors have devoted themselves to marginal grafting, which introduces livers with barely passable quality but a high risk of transplant failure into the donor pool. However, existing common methods of preserving marginal grafts lead to both high risk of postoperative complications and high mortality. The application of machine perfusion allows surgeons to make marginal livers meet the standard criteria for transplant, which shows promising prospect in preserving and repairing donor livers and improving ischemia reperfusion injury. This review summarizes the progress of recent researches on hepatic machine perfusion.