Sequential hypothermic and normothermic machine perfusion enables safe transplantation of high-risk donor livers

Quantifying Flavin mononucleotide: an internationally validated methodological approach for enhanced decision making in organ transplantation

BACKGROUND

Increasing donor risk, particularly in liver transplantation, where organs are often marginal, has made dynamic organ preservation techniques and viability assessment essential to safely improve organ quality and increase utilisation. However, existing viability parameters are based on routine clinical assessment in patients with acute liver failure, trauma, or liver resections. These parameters often do not correlate with clinically relevant post-transplant outcomes.

METHODS

This article presents a detailed protocol for the spectrophotometric quantification of Flavin mononucleotide (FMN), a marker of mitochondrial injury. FMN release from mitochondrial complex I was described many decades ago as the initial sign of ischaemia-reperfusion injury, i.e. when oxygen is reintroduced in ischaemic tissues during organ transplantation or machine perfusion. This study describes the detailed FMN quantification in donor plasma and various fluids obtained during machine perfusion, and discusses confounders, challenges, and the role of individual test components.

FINDINGS

FMN quantification was identified as an immediate organ assessment tool, demonstrating a strong correlation with graft survival and other relevant complications after human liver transplantation.

INTERPRETATION

The results highlight FMN quantification as a reliable and standardized method for assessing organ viability, offering significant potential for improving organ selection and better utilisation. This method could provide better a predictive value for transplant outcomes compared to existing parameters currently in use.

FUNDING

This research received no external funding but was supported by the Catalyst grant No. CCG0280 at Cleveland Clinic Ohio, U.S. dedicated to A.S.

Deceased donor liver utilisation and assessment: Consensus guidelines from the European Liver and Intestine Transplant Association

Over the past two decades, the application of machine perfusion (MP) in human liver transplantation has moved from the realm of clinical exploration to routine clinical practice. Both in situ and ex situ perfusion strategies are feasible, safe, and may offer improvements in relevant post-transplant outcomes. An important utility of these strategies is the ability to transplant grafts traditionally considered too risky to transplant using conventional cold storage alone. While dynamic assessment and ultimately transplantation of such livers is an important goal for the international liver transplant community, its clinical application is inconsistent. To this end, ELITA (the European Liver and Intestine Transplant Association) gathered a panel of experts to create consensus guidelines regarding selection, approach, and criteria for deceased donor liver assessment in the MP era. An eight-member steering committee (SC) convened a panel of 44 professionals working in 14 countries in Europe and North America. The SC identified topics related to liver utilisation and assessment for transplantation. For each topic, subtopics were created to answer specific clinical questions. A systematic literature review was performed, and the panel graded relevant evidence. The SC drafted initial statements addressing each clinical question. Statements were presented at the in-person Consensus Meeting on Liver Discard and Viability Assessment during the ELITA Summit held from April 19-20, 2024, in Madrid, Spain. Online voting was held to approve statements according to a modified Delphi method; statements reaching ≥85% agreement were approved. Statements addressing liver utilisation, the definition of high-risk livers, and strategies and criteria for dynamic liver assessment are presented.

Donor-Related Risk Factors for Normothermic Machine Perfusion in Liver Transplantation: A Meta-Analysis

BACKGROUND AND AIMS

During normothermic machine perfusion (NMP), a variety of criteria are used to gauge the suitability of an organ for transplantation. However, the relations between donor factors and these criteria are poorly understood. The aim of this meta-analysis was to investigate the association between donor-related risk factors and the decision to transplant a liver subjected to NMP.

METHODS

A comprehensive literature search was performed for articles published up to March 2025 in four databases, reporting livers subjected to NMP for viability assessment prior to transplantation. Effect size (ES) was calculated using Cohen's D and log odds ratio.

RESULTS

Out of 806 unique articles, 18 were included in this meta-analysis, encompassing 690 liver grafts that underwent NMP. Following viability assessment during NMP, utilisation rate was 82% from donors after brain death and 68% from donors after circulatory death (ES: 0.08, p = 0.88). Transplanted livers had shorter cold ischemia time (ES: -0.34, p = 0.003) and lower liver weight (ES: -0.53, p < 0.001). Donor age, BMI and donor warm ischemia time did not differentiate between transplanted and unused groups. Differences were observed in viability assessment for lactate clearance (ES: 2.0, p = 0.005), glucose metabolism (ES: 2.2, p < 0.001), bile production (ES: 1.0, p = 0.003) and pH (ES: 1.9, p < 0.001). Excellent outcomes, including 10% non-anastomotic strictures, 89% graft survival and 93% patient survival, were achieved in a large cohort of high-risk livers.

CONCLUSION

Cold ischemia time and liver weight were identified as donor-related risk factors, whereas donor type, age and donor warm ischemia time appear not to impact the decision to transplant during NMP.

Liver transplantation as a treatment for cancer: comprehensive review

BACKGROUND

Liver transplantation for cancer indications has gained momentum in recent years. This review is intended to optimize the care setting of liver transplant candidates by highlighting current indications, technical aspects and barriers with available solutions to facilitate the guidance of available strategies for healthcare professionals in specialized centres.

METHODS

A review of the most recent relevant literature was conducted for all the cancer indications of liver transplantation including colorectal cancer liver metastases, hilar cholangiocarcinoma, intrahepatic cholangiocarcinoma, neuroendocrine tumours, hepatocellular carcinoma and hepatic epitheloid haemangioendothelioma.

RESULTS

Transplant benefit from the best available evidence, including SECA I, SECA II, TRANSMET studies for colorectal liver metastases, various preoperative protocols for cholangiocarcinoma patients, standard, extended selection criteria for hepatocellular carcinoma and neuroendocrine tumours, are discussed. Innovative approaches to deal with organ shortages, including machine-perfused deceased grafts, living donor liver transplantation and RAPID procedures, are also explored.

CONCLUSION

Cancer indications for liver transplantation are here to stay, and the selection criteria among all cancer groups are likely to evolve further with improved prognostication of tumour biology using adjuncts such as radiomics, cancer genomics, and circulating DNA and RNA status. International prospective registry-based studies could overcome the limitations of smaller patient cohorts and lack of level 1 evidence.

Donation after circulatory death; cholangiopathy in the machine age

PURPOSE OF REVIEW

Published work evaluating machine perfusion of DCD (donation after circulatory death) liver grafts in situ and ex situ is rapidly evolving, with several landmark studies published in the last 6 months. The central question in DCD liver transplant remains; which strategies most effectively reduce cholangiopathy? This condition, which results in repeated hospital admissions, interventions, re-transplantation and death, is a major deterrent to DCD utilization. This review considers current evidence in the mitigation of transplant cholangiopathy by machine perfusion in DCD liver grafts.

RECENT FINDINGS

Studies which directly address DCD cholangiopathy as a primary outcome are few in number, despite their critical importance. In systematic reviews, Normothermic Regional Perfusion and Hypothermic Machine Perfusion consistently and significantly reduce transplant cholangiopathy rates. By contrast, the efficacy of Normothermic Machine Perfusion performed at donor or recipient centres is less well described and cautious interpretation is required. The most recent development, namely hypothermic followed by normothermic perfusion, has only now appeared in the literature but appears to offer advantages compared to either technology alone.

SUMMARY

To reduce DCD cholangiopathy, current data best support the use of donor centre NRP or recipient centre HMP. However, utilization is also improved when warm perfusion is involved.

Therapeutic hyperthermia promotes lipid export and HSP70/90 during machine perfusion of human livers

Liver transplantation is the only curative option for end-stage liver disease. Donor shortages necessitate the use of higher risk donor livers, including fatty livers, which are more susceptible to ischemia-reperfusion injury. Machine perfusion has improved graft utilization and is typically performed at hypothermic (8-12°C) or normothermic (35-37°C) temperatures. Here we studied the impact of mild hyperthermia (40°C) as a therapeutic intervention for fatty livers using in-depth proteomic and lipoprotein profiling of whole organ perfusion and precision-cut liver slices. We observed proteomic changes with metabolic alterations over time, evidenced by a significant increase in lipid export in whole organ perfusions. Furthermore, PCLS showed significant upregulation of metabolic processes and heat shock protein response after 24 h of hyperthermia. Machine perfusion under hyperthermic conditions may be a potential strategy to improve the utilization of fatty liver grafts, ultimately expanding the donor pool and improving transplant outcomes.

Assessment of Amniotic Fluid as a Preservation Solution in Pig Livers Undergoing Machine Perfusion

INTRODUCTION

Ischemia-reperfusion injury in organ transplantation highlights the need for advanced preservation techniques. This study evaluates the effectiveness of amniotic fluid (AF) compared to static cold storage and histidine-tryptophan-ketoglutarate (HTK) solution in preserving pig livers subjected to hypothermic oxygenated machine perfusion (HOMP) and ex vivo normothermic reperfusion.

MATERIALS AND METHODS

Fifteen pig livers underwent warm ischemia for 1 h, followed by preservation under three conditions: cold storage (group 1, n = 3), HOMP with HTK (group 2, n = 3), and HOMP with AF (group 3, n = 3). Perfusion lasted 4 h, followed by 2 h of ex vivo reperfusion. Assessments included hepatic bile production, sphingomyelin levels, reactive oxygen/nitrogen species, antioxidant capacity, tissue oxygen saturation, flow dynamics, blood gas analyses, biochemical markers, and histopathological and immunohistochemical evaluations.

RESULTS

AF-HOMP showed superior blood flow, lower vascular resistance, higher oxygen saturation, and better organ protection than HTK. Blood gas measurements demonstrated stable physiological levels after reperfusion. AF-HOMP improved bile production, sphingomyelin levels, glycogen preservation, and reduced parenchymal necrosis, hepatocyte vacuolization, and sinusoidal obstruction. Immunohistochemical analysis indicated protective effects on bile duct function, apoptosis, endothelial activation, and cell proliferation.

CONCLUSIONS

AF-HOMP outperformed HTK in preserving liver tissue during warm ischemia, HOMP, and reperfusion. AF is a promising, cost-effective, and accessible alternative for liver preservation, potentially expanding donor pools and improving transplantation outcomes. Further research is warranted to explore its broader applications.

Dynamic Preservation of Donation After Circulatory Death Liver Grafts From Donors Aged 60 y and Older

BACKGROUND

Donor livers from older donation after circulatory death (DCD) donors are frequently discarded for transplantation because of the high risk of graft failure. It is unknown whether DCD livers from older donors benefit from dynamic preservation.

METHODS

In a multicenter study, we retrospectively compared graft and patient outcomes after transplantation of livers from DCD donors older than 60 y, preserved with either static cold storage (SCS), ex situ sequential dual hypothermic perfusion, controlled oxygenated rewarming, and normothermic perfusion (DHOPE-COR-NMP), or in situ abdominal normothermic regional perfusion (aNRP).

RESULTS

Fifty-six liver transplants were included in the SCS cohort, 33 in the DHOPE-COR-NMP cohort, and 27 in the aNRP cohort. Donor warm ischemia time was significantly shorter in the SCS group than in DHOPE-COR-NMP ( P  < 0.001) and aNRP ( P  < 0.001) groups. Cold ischemia times were similar. One-year incidence of nonanastomotic biliary strictures was lower after DHOPE-COR-NMP (3%, P  = 0.03) or aNRP (7%, P  = 0.13), compared with SCS alone (21%). Anastomotic strictures were less frequent in aNRP (19%) compared with DHOPE-COR-NMP (52%; P  = 0.015). One-year graft and patient survival were similar.

CONCLUSIONS

Dynamic preservation allows safe transplantation of livers from DCD donors aged 60 y or older. The risk of nonanastomotic strictures was significantly lower after DHOPE-COR-NMP than after SCS, despite longer donor warm ischemia times.

Normothermic machine perfusion in liver transplantation: a bibliometric analysis of the top 100 most cited articles

Background

Normothermic machine perfusion (NMP) has increased substantially in the recent decade, being a vital tool in further organ preservation and reducing ischemia-reperfusion injury. The purpose of this study was to objectively conduct a bibliometric analysis of the top 100 cited articles to understand the evolution of NMP in liver transplantation.

Methods

Scopus was selected as our primary database. We explored the database to extract relevant articles, which were then ranked numerically by the number of citations. A list of the top 100 articles was created in descending order, and each article was further analyzed to identify trends and characteristics. A list of the top 10 review articles was also prepared.

Results

The top 100 studies were cited a total of 6136 times from 2013 and 2023, with the most cited articles published in 2018. The total number of citations per article ranged from 7 to 787, with a median of 397 citations. The articles originated from 13 different countries, with the United Kingdom having the most articles (n = 26), followed by the Netherlands (n = 17) and the United States (n = 17). Liver Transplantation (n = 21), Transplantation (n = 10), American Journal of Transplantation (n = 10), and Annals of Surgery (n = 6) contributed to nearly half of the articles.

Conclusion

Research on NMP is rapidly growing and encompasses a variety of countries and institutions. Our analysis provides insight into the evolution of normothermic machine perfusion in liver transplantation, with the hope that this article may serve as a reference to aid healthcare professionals in efficiently assessing consensus, trends, and needs within the field.

Normothermic Liver Machine Perfusion at a Large European Center: Real-world Outcomes following 238 Applications

OBJECTIVE

To report outcomes from routine clinical practice of liver transplantation (LT) following normothermic liver machine perfusion (NLMP) and compare to LT after static cold storage (SCS).

BACKGROUND

NLMP is emerging as a clinical routine in LT and has recently received renewed attention; however, outcomes outside of clinical trials are lacking.

METHODS

All adult LT between February 2018 and January 2023 were included. A comprehensive viability assessment was applied during NLMP. Outcomes were compared between NLMP and SCS recipients, as well as benchmark and non-benchmark cases.

RESULTS

Of the 332 LT included, 174 underwent NLMP and 158 were transplanted after SCS. Sixty-seven organs were accepted and transplanted only under the premise of NLMP. One-year graft survival for SCS and NLMP recipients was 83.8% versus 81.3% and 93.4% for benchmark cases in the overall cohort. Total preservation time had no influence on graft survival in the NLMP group but was associated with inferior 1-year graft survival in the SCS group. NLMP usage increased significantly over the duration of the study period, as did the median total preservation time. With increasing NLMP use and longer preservation times, nighttime surgery decreased significantly from 41.9% to 4.2%.

CONCLUSIONS

Prolonged preservation times ease logistics and enable daytime surgery. The possibility of NLMP offers to expand LT without negatively affecting outcomes.

Perfusion Pressures and Weight Loss During Normothermic Machine Perfusion of Human Donor Livers

BACKGROUND

Normothermic machine perfusion (NMP) is increasingly used to preserve and assess donor livers prior to transplantation. Due to its success, it is expected that more centers will start using this technology. However, NMP may also cause adverse effects.

METHODS

In this retrospective, observational study, we investigated the effect of NMP pressures on donor liver weight, post-transplant outcomes, and hepatic perfusion characteristics. A total of 36 livers were transplanted after NMP. NMP perfusion pressure settings were lowered from a median (IQR) of 47 mmHg (42-54) to 34 mmHg (30-39) for the hepatic artery (HA), and from 8 mmHg (7-10) to 7 mmHg (6-8) for the portal vein (PV) to diminish potential edema formation inside the liver.

RESULTS

This change appeared to lead to a reduction of liver weight after NMP (-22 g to -143 g, p = 0.02), without affecting the PV flow velocity (35.5 to 48.0 cm/s, p = 0.54), or hepatocellular injury markers during NMP (AST 1511-1148 U/L, p = 0.44; ALT 318-849 U/L, p = 0.35), and post-transplantation outcomes. Changes in liver weight correlated significantly with the applied PV pressure during NMP (r = 0.52, p < 0.01) and the HA flow (r = 0.38, p < 0.05).

CONCLUSION

NMP can lead to a reduction in liver weight, which might be masked by edema when high perfusion pressures are used. We encourage applying the lowest perfusion pressures possible to reach adequate flows and oxygen supply during liver NMP.

Endothelial glycocalyx damage marker syndecan-1 during hypothermic oxygenated machine perfusion of donor grafts facilitates prediction of early allograft dysfunction after liver transplantation

Background

Ischemia reperfusion injury (IRI) is a major contributing factor to organ damage in liver transplantation (LT) impacting donor organ quality and patient survival. IRI-inflicted graft injury can be reduced by using hypothermic oxygenated machine perfusion (HOPE) as a preservation strategy instead of static cold storage (SCS). The endothelial glycocalyx is highly sensitive to IRI and its degradation during graft preservation and reperfusion was previously associated with inferior postoperative outcome after LT. Here, we aimed to measure glycocalyx degradation during and after HOPE in order to evaluate its potential for viability-assessment during machine perfusion and outcome prediction in patients undergoing LT.

Methods

Glycocalyx degradation was quantified via enzyme-linked immunoassay (ELISA) for its main component syndecan-1 (Sdc-1) in serum of 40 patients undergoing LT after HOPE. In addition, Sdc-1 was evaluated at multiple time points during HOPE. Patients were followed up for 3.5 years to assess postoperative complications including morbidity, the development of early allograft dysfunction (EAD) and graft survival.

Results

Liver grafts which later developed EAD showed significantly higher Sdc-1 concentrations after 60 min of HOPE compared to grafts exhibiting normal postoperative function (P=0.02). Receiver operating characteristic analysis revealed a strong predictive potential with an area under the curve of 0.73. A cut-off at 808 ng/mL Sdc-1 at 60 min of HOPE allowed identification of a high-risk group with an incidence of EAD of 66.7%. Sdc-1 concentrations increased during all types of HOPE but were significantly higher in HOPE versus dual HOPE (D-HOPE) after 120 min of perfusion (P=0.02).

Conclusions

Sdc-1 evaluated at 60 min during HOPE allows prediction of EAD after LT. Accordingly, Sdc-1 should be considered a potential additional biomarker for viability assessment during HOPE.

Validation of mitochondrial FMN as a predictor for early allograft dysfunction and patient survival measured during hypothermic oxygenated perfusion

Hypothermic oxygenated machine perfusion (HOPE) preconditions liver grafts before transplantation. While beneficial effects on patient outcomes were demonstrated, biomarkers for viability assessment during HOPE are scarce and lack validation. This study aims to validate the predictive potential of perfusate flavin mononucleotide (FMN) during HOPE to enable the implementation of FMN-based assessment into clinical routine and to identify safe organ acceptance thresholds. FMN was measured in perfusate samples of 50 liver grafts at multiple time points. After transplantation, patients were followed up for development of early allograft dysfunction (EAD), transplantation, and 1-year survival. FMN concentrations were significantly higher for grafts that developed EAD at 5 and 60 minutes into HOPE ( p = 0.008, p = 0.026). The strongest predictive potential of FMN for EAD was observed at 5 minutes of HOPE with an AUC of 0.744. Similarly, 5-minute FMN was predictive for 1-year mortality ( p < 0.001), reaching a remarkable AUC of 0.890. Cutoffs for prediction of EAD (10.6 ng/mL) and early mortality (23.5 ng/mL) were determined and allowed risk stratification of grafts. Particularly, patients receiving low-risk grafts developed EAD in 9% of cases, while all patients survived the first postoperative year. In contrast, high-risk organs developed an incidence of EAD at 62%, accompanied by the necessity of retransplantation in 38% of cases. One-year mortality in the high-risk cohort was 62%. Evaluation of FMN as early as 5 minutes during HOPE allows for risk stratification of liver grafts. Low-risk grafts, according to FMN, display a negligible risk for patients. Yet, high-risk grafts are associated with increased risk for EAD, transplantation, and early mortality and should not be used for transplantation without further assessment.

Sequential Hypothermic and Normothermic Machine Perfusion of Extended Criteria Donors in Liver Transplantation: A Single-Center Preliminary Experience

INTRODUCTION

Liver transplantation (LT) is the sole curative option for liver failure and other primary liver conditions. However, the limited number of suitable donors compared with the growing number of patients requiring LT remains a leading cause of mortality among those on the waiting list. This has resulted in the expansion of criteria for donor eligibility. The sequential combination of ex situ reperfusion, dHOPE, and NMP helps reduce the occurrence of ischemia-reperfusion injury and assess organ viability prior to transplantation.

METHODS

This is a retrospective, single-arm, single-center study including all cases of liver grafts that underwent sequential perfusion between October 2021 and July 2024. Eligibility criteria for sequential perfusion were extended criteria DBD with macrosteatosis > 35%, use of high-dose vasopressors during donor ICU stay or episodes of cardiac arrest, hemodynamic instability during procurement, prolonged ischemia time for logistic reasons, as well as DCD showing prolonged fWIT, flow alteration during normothermic regional perfusion (NRP), and DCDs in Maastricht 2 class. Viability was assessed following the Groeningen group criteria.

RESULTS

Thirty-three cases were included and 16 met the viability criteria at the end of the sequential perfusion and were transplanted. One patient developed an early allograft failure (EAF) and another a primary nonfunction (PNF). All the other patients had a regular postoperative course, with no retransplantation, 56% of the cohort showing no postoperative complication and all currently in good standing, median follow-up 19 months (range 4-39).

CONCLUSIONS

Sequential dHOPE and NMP is a strategy that can help assessing both viability and functionality of liver grafts from high-risk donors, expanding the donor pool and increasing the opportunities for patients on the waiting list to get a transplant.

10 degree C static storage of porcine donation after circulatory death livers improves biliary viability and mitigates ischemia-reperfusion injury

Optimized static cold storage has the potential to improve the preservation of organs most vulnerable to ischemia-reperfusion injury. Data from lung transplantation suggest that storage at 10 °C improves mitochondrial preservation and subsequent allograft function compared with conventional storage on ice. Using a porcine model of donation after circulatory death, we compared static storage of livers at 10 °C to ice. Livers (N = 5 per group) underwent 10 hours of storage followed by 4 hours of normothermic machine perfusion (NMP) for real-time allograft assessment. Allografts were compared using established NMP viability criteria, tissue immunostaining, and tissue metabolomics. Livers stored at 10 °C demonstrated lower portal venous vascular resistance and greater hepatic artery vasoresponsiveness. Lactate clearance during NMP was similar between the groups. Livers stored at 10 °C showed favorable biochemical parameters of biliary viability, including greater bile volume, pH, and bicarbonate. Metabolomics analysis revealed increased aerobic respiration, improved electron transport chain function, and less DNA damage after reperfusion of livers stored at 10 °C. Static storage of donation after circulatory death livers with extended cold ischemic time at 10 °C demonstrates superior allograft function with evidence of improved biliary viability and mitochondrial function compared with ice. These data suggest that storage at 10 °C should be considered for translation to clinical practice.

Assessment of Ex Situ Liver Function by Indocyanine Green Clearance During Clinical Normothermic Machine Perfusion of Extended Criteria Grafts

BACKGROUND

Normothermic machine perfusion (NMP) enables pretransplantation assessment of donor liver viability to increase donor liver utilization. However, unambiguous objective criteria to determine integrated liver function during NMP to decide upon acceptance are still lacking. This study investigates whether the indocyanine green (ICG) elimination test can be applied to assess liver function during NMP.

METHODS

Donor livers underwent dual-hypothermic oxygenated machine perfusion and NMP. The ICG elimination test was improved during an optimization phase (n = 10) and tested against current functional perfusion parameters and posttransplantation outcomes in clinically perfused livers (n = 32).

RESULTS

The ICG plasma disappearance rate (PDR) during NMP was dependent on perfusion blood flow and liver weight. The corrected PDR (NMP-PDR) was correlated to the hepatic extraction rate ( R  = 0.923; P  > 0.001) and ATP content in liver biopsies at 2 h of NMP ( R  = 0.692; P  = 0.027). In the clinical phase, the length of the functional warm ischemia time in the donation process was inversely correlated to the NMP-PDR ( P  = 0.042). Both individual acceptance criteria (lactate clearance, ability of self-regulate pH, Δbicarbonate, and ΔpH) and overall hepatocellular and cholangiocellular acceptance criteria were correlated to the NMP-PDR. The NMP-PDR was higher in the cohort accepted for transplantation (n = 18; 18.1%/L·kg [14.0% to 22.7%/L·kg]) than in the nontransplanted cohort (n = 14; 11.8%/L·kg [8.8% to 12.9%/L·kg]; P  < 0.0001). Furthermore, the NMP-PDR correlated with the liver graft assessment following transplantation at 7 d score posttransplantation ( R  = -0.551; P  = 0.027).

CONCLUSIONS

We demonstrate that the NMP-PDR correlates with both liver function during NMP and short-term posttransplantation outcomes. This simple objective test has the potential to increase donor liver utilization rate, while preventing hepatocellular dysfunction posttransplantation.

Assessment of liver graft quality during hypothermic oxygenated perfusion: The first international validation study

BACKGROUND & AIMS

While it is currently assumed that liver assessment is only possible during normothermic machine perfusion, there is uncertainty regarding a reliable and quick prediction of graft injury during ex situ hypothermic oxygenated perfusion (HOPE). We therefore intended to test, in an international liver transplant cohort, recently described mitochondrial injury biomarkers measured during HOPE before liver transplantation.

METHODS

Perfusate samples of human livers from ten centers in seven countries with HOPE experience were analyzed for released mitochondrial compounds, i.e. flavin mononucleotide (FMN), NADH, purine derivatives and inflammatory markers. Livers deemed unsuitable for transplantation served as negative controls.

RESULTS

We collected 473 perfusate samples of human donation after cardiac death (n = 315) and donation after brain death (n = 158) livers. Fluorometric assessment of FMN in perfusate was validated by mass spectrometry (R = 0.7011, p <0.0001). Graft loss due to primary non-function or cholangiopathy was predicted by perfusate FMN values (c-statistic mass spectrometry 0.8418, 95% CI 0.7466-0.9370, p <0.0001; c-statistic fluorometry 0.7733, 95% CI 0.7006-0.8461, p <0.0001). Perfusate FMN values were also significantly correlated with symptomatic non-anastomotic strictures and kidney failure, and superior for the prediction of graft loss than conventional scores derived from donor and recipient parameters, such as the donor risk index and the balance of risk score. Mitochondrial FMN values in liver tissues of non-utilized livers were low, and inversely correlated to high perfusate FMN values and purine metabolite release.

CONCLUSIONS

This first international study validates the predictive value of the mitochondrial cofactor FMN, released from complex I during HOPE, and may therefore contribute to a better risk stratification of injured livers before implantation.

IMPACT AND IMPLICATIONS

Analysis of 473 perfusates, collected from ten international centers during HOPE (hypothermic oxygenated perfusion), revealed that mitochondria-derived flavin mononucleotide values in perfusate are predictive of graft loss, cholangiopathy, and kidney failure after liver transplantation. This result is of high clinical relevance, as recognition of graft quality is urgently needed to improve the safe utilization of marginal livers. Ex situ machine perfusion approaches, such as HOPE, are therefore likely to increase the number of useable liver grafts.

'Back-to-base' combined hypothermic and normothermic machine perfusion of human donor livers

The shortage of suitable donor organs has resulted in the use of suboptimal, high-risk, extended-criteria donor (ECD) livers, which are at an increased risk of failure after transplantation. Compared with traditional static cold storage, dynamic preservation by ex situ machine perfusion reduces the risks associated with the transplantation of ECD organs. Ex situ machine perfusion strategies differ in timing (that is, speed of procurement and transport), perfusion duration and perfusion temperature. For 'back-to-base' protocols, the donor liver is statically cold stored during transportation to the recipient hospital (the 'base') and then perfused, instead of transporting the liver using a portable perfusion system. While dual hypothermic (8-12 °C) oxygenated machine perfusion (DHOPE) allows safe prolongation of preservation duration and reduces ischemia-reperfusion injury-related complications, including post-transplant cholangiopathy, normothermic machine perfusion (NMP) at 35-37 °C facilitates ex situ viability testing of both liver parenchyma and bile ducts. Here, we describe a clinical protocol for 'back-to-base' combined DHOPE and NMP, linked by a period of controlled oxygenated rewarming (COR), which we call the DHOPE-COR-NMP protocol. This protocol enables restoration of mitochondrial function after static ischemic preservation and minimizes both ischemia-reperfusion and temperature-shift-induced injury during the start of NMP. The NMP phase allows viability assessment before final donor liver acceptance for transplantation. Sequential DHOPE and COR-NMP may reduce the risks associated with transplantation of ECD livers and facilitate enhanced utilization, thereby helping to alleviate the organ shortage.

Viability Assessment During Normothermic Machine Liver Perfusion: A Literature Review

BACKGROUND AND OBJECTIVE

The discrepancy between donor organ availability and demand leads to a significant waiting-list dropout rate and mortality. Although quantitative tools such as the Donor Risk Index (DRI) help assess organ suitability, many potentially viable organs are still discarded due to the lack of universally accepted markers to predict post-transplant outcomes. Normothermic machine perfusion (NMP) offers a platform to assess viability before transplantation. Thus, livers considered unsuitable for transplantation based on the DRI can be evaluated and potentially transplanted. During NMP, various viability criteria have been proposed. These criteria are neither homogeneous nor consensual. In this review, we aimed to describe the viability criteria during NMP and evaluate their ability to predict hepatic graft function following transplantation. We conducted a PubMed search using the terms 'liver transplantation', 'normothermic machine perfusion' and 'assessment', including only English publications up to February 2024. Viability assessment during NMP includes multiple hepatocellular and cholangiocellular criteria. Lactate clearance and bile production are commonly used indicators, but their ability to predict post-transplant outcomes varies significantly. The predictive value of cholangiocellular criteria such as bile pH, bicarbonate and glucose levels remains under investigation. Novel markers, such as microRNAs and proteomic profiles, offer the potential to enhance graft evaluation accuracy and provide insights into the molecular mechanisms underlying liver viability. Combining perfusion parameters with biomarkers may improve the prediction of long-term graft survival. Future research should focus on standardising viability assessment protocols and exploring real-time biomarker evaluations, which could enhance transplantation outcomes and expand the donor pool.

Normothermic Machine Perfusion in Orphan Liver Graft Viability Assessment

Background: Liver transplantation constitutes a well-established treatment for patients with end-stage liver disease and selected hepatic malignancies. The introduction of normothermic machine perfusion (NMP) offers a platform for both extracorporeal organ maintenance and viability assessment, especially for organs with suspicious malfunction. These organs, discarded by the majority of transplant centers (so-called 'orphan livers'), may help to safely expand the donor pool thanks to pre-transplant appraisal; Methods: We identified all grafts undergoing normothermic ma-chine perfusions performed in the Department of General, Transplant, and Liver Surgery between December 2022 and August 2023. Their perfusion characteristics and immediate postoperative periods, as well as complications that occurred in the 90-day postoperative periods, were analyzed; Results: There were eight orphan liver grafts that underwent NMP in our Department. Postoperative complications occurring in patients receiving grafts after NMP did not seem associated with the procedure. One patient required laparotomy within the 90-day postoperative period due to biliary fistula and underwent bile duct stenting due to both fistula and nonanastomotic stricture. In one patient we observed the occurrence of anastomotic biliary stricture more than 90 days after LTx; Conclusions: NMP allows for the viability assessment of grafts with suspicious prepreservation malfunction. Some of these organs may help to expand the donor pool.

Inflammatory Monocytes Are Rapidly Recruited to the Post-Ischaemic Liver in Patients Undergoing Liver Transplantation and Cytokines Associated with Their Activation Correlate with Graft Outcomes

Liver ischaemia-reperfusion (IR) injury remains a major cause of morbidity and mortality following liver transplantation and resection. CD4+ T cells have been shown to play a key role in murine models; however, there is currently a lack of data that support their role in human patients. Methods: Data on clinical outcomes and complications were documented prospectively in 28 patients undergoing first elective liver transplant surgery. Peripheral blood samples were collected at baseline (pre-op), 2 h post graft reperfusion, immediately post-op, and 24 h post-op. A post-reperfusion biopsy was analysed in all patients, and in five patients, a donor liver biopsy was available pre-implantation. Circulating cytokines were measured, and T cells were analysed for activation markers and cytokine production. Results: Circulating levels of cytokines associated with innate immune cell recruitment and activation were significantly elevated in the peri-transplant period. High circulating IL-10 levels corresponded with the development of graft-specific complications. The proportion of CD4+ T cells in the peripheral circulation fell throughout the peri-operative period, suggesting CD4+ T cell recruitment to the graft. Although TNFα was the predominant cytokine produced by CD4+ T cells in the intrahepatic environment, the production of IFNγ was significantly upregulated by circulating CD4+ T cells. Furthermore, we demonstrated clear recruitment of inflammatory monocytes in the peri-operative period. In donor-and-recipient pairs with a mismatch at the HLA-A2 or A3 allele, we demonstrated that inflammatory monocytes in the liver are recipient-derived. Discussion: This is the first study to our knowledge that tracks early immune cell responses in humans undergoing liver transplantation. The recruitment of inflammatory monocytes from the recipient and their cytokine release is associated with liver-specific complications. Inflammatory monocytes would be an attractive target to ameliorate ischaemia-reperfusion injury.

Real-Time Biomarkers of Liver Graft Quality in Hypothermic Oxygenated Machine Perfusion

Background: Hypothermic oxygenated machine perfusion has emerged as a strategy to alleviate ischemic-reperfusion injury in liver grafts. Nevertheless, there is limited data on the effectiveness of hypothermic liver perfusion in evaluating organ quality. This study aimed to introduce a readily accessible real-time predictive biomarker measured in machine perfusate for post-transplant liver graft function. Methods: The study evaluated perfusate analytes over a 90-day postoperative period in 26 patients randomly assigned to receive a liver graft following dual hypothermic machine perfusion in a prospective randomized controlled trial. Machine perfusion was consistently conducted end-ischemically for at least 120 min, with real-time perfusate assessment at 30-min intervals. Graft functionality was assessed using established metrics, including Early Allograft Dysfunction (EAD). Results: Perfusate lactate concentration after 120 min of machine perfusion demonstrated significant predictive value for EAD (AUC ROC: 0.841, p = 0.009). Additionally, it correlated with post-transplant peak transaminase levels and extended hospital stays. Subgroup analysis revealed significantly higher lactate accumulation in livers with post-transplant EAD. Conclusions: Liver graft quality can be effectively assessed during hypothermic machine perfusion using simple perfusate lactate measurements. The reliability and accessibility of this evaluation support its potential integration into diverse transplant centers.

Long-term outcomes after hypothermic oxygenated machine perfusion and transplantation of 1,202 donor livers in a real-world setting (HOPE-REAL study)

BACKGROUND & AIMS

Despite strong evidence for improved preservation of donor livers by machine perfusion, longer post-transplant follow-up data are urgently needed in an unselected patient population. We aimed to assess long-term outcomes after transplantation of hypothermic oxygenated machine perfusion (HOPE)-treated donor livers based on real-world data (i.e., IDEAL-D stage 4).

METHODS

In this international, multicentre, observational cohort study, we collected data from adult recipients of HOPE-treated livers transplanted between January 2012 and December 2021. Analyses were stratified by donation after brain death (DBD) and donation after circulatory death (DCD), sub-divided by their respective risk categories. The primary outcome was death-censored graft survival. Secondary outcomes included the incidence of primary non-function (PNF) and ischaemic cholangiopathy (IC).

RESULTS

We report on 1,202 liver transplantations (64% DBD) performed at 22 European centres. For DBD, a total number of 99 benchmark (8%), 176 standard (15%), and 493 extended-criteria (41%) cases were included. For DCD, 117 transplants were classified as low risk (10%), 186 as high risk (16%), and 131 as futile (11%), with significant risk profile variations among centres. Actuarial 1-, 3-, and 5-year death-censored graft survival rates for DBD and DCD livers were 95%, 92%, and 91%, vs. 92%, 87%, and 81%, respectively (log-rank p = 0.003). Within DBD and DCD strata, death-censored graft survival was similar among risk groups (log-rank p = 0.26, p = 0.99). Graft loss due to PNF or IC was 2.3% and 0.4% (DBD), and 5% and 4.1% (DCD).

CONCLUSIONS

This study shows excellent 5-year survival after transplantation of HOPE-treated DBD and DCD livers with low rates of graft loss due to PNF or IC, irrespective of their individual risk profile. HOPE treatment has now reached IDEAL-D stage 4, which further supports its implementation in routine clinical practice.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05520320.

IMPACT AND IMPLICATIONS

This study demonstrates the excellent long-term performance of hypothermic oxygenated machine perfusion (HOPE) treatment of donation after circulatory and donation after brain death liver grafts irrespective of their individual risk profile in a real-world setting, outside the evaluation of randomised-controlled trials. While previous studies have established safety, feasibility, and efficacy against the current standard, according to the IDEAL-D evaluation framework, HOPE treatment has now reached the final IDEAL-D stage 4, which further supports its implementation in routine clinical practice.

Impact of device variability and protocol differences on kidney function during normothermic machine perfusion: A comparative study using porcine and human kidneys

INTRODUCTION

A growing interest in renal normothermic machine perfusion (NMP) has resulted in more clinically available perfusion devices. While all perfusion systems have the same aim, there are significant differences in their circuits, pumps, sensors, and software. Therefore, our objective was to assess the impact of different perfusion protocols and devices on kidney function and perfusion parameters during NMP.

METHODS

Porcine kidneys were subjected to 30 min of warm ischemia, 24 h of static cold storage, and subsequently perfused for 6 h using (1) the Kidney Assist (KA) machine with a pressure of 75 mm Hg, (2) the KA device incorporating several adjustments and a pressure of 85 mm Hg (modified KA), or (3) the Perlife (PL) perfusion device (n = 4). Consecutively, discarded human kidneys were perfused using the KA or modified KA (n = 3) protocol.

RESULTS

The PL group quickly reached the device's upper flow limit and consequently received a significantly lower pressure compared to the KA groups. The arterial pO2 was significantly lower in the PL group. Yet, hemoglobin concentration increased over time, and oxygen consumption was significantly higher compared to the KA groups. Fractional sodium excretion was significantly lower in the PL group. Tissue ATP levels, urine production, and creatinine clearance rates did not differ between groups. In human kidneys, the modified KA group showed significantly lower vascular resistance, higher oxygen delivery, and lower levels of lactate in the perfusate compared to the KA group.

CONCLUSIONS

This study shows that perfusion characteristics and kidney function are significantly influenced by the perfusion protocol and the device and its settings during normothermic machine perfusion and therefore should be interpreted with caution.

Beyond the icebox: modern strategies in organ preservation for transplantation

Organ transplantation, a critical treatment for end-stage organ failure, has witnessed significant advancements due to the integration of improved surgical techniques, immunosuppressive therapies, and donor-recipient matching. This review explores the progress of organ preservation, focusing on the shift from static cold storage (SCS) to advanced machine perfusion techniques such as hypothermic (HMP) and normothermic machine perfusion (NMP). Although SCS has been the standard approach, its limitations in preserving marginal organs and preventing ischemia-reperfusion injury (IRI) have led to the adoption of HMP and NMP. HMP, which is now the gold standard for high-risk donor kidneys, reduces metabolic activity and improves posttransplant outcomes. NMP allows real-time organ viability assessment and reconditioning, especially for liver transplants. Controlled oxygenated rewarming further minimizes IRI by addressing mitochondrial dysfunction. The review also highlights the potential of cryopreservation for long-term organ storage, despite challenges with ice formation. These advances are crucial for expanding the donor pool, improving transplant success rates, and addressing organ shortages. Continued innovation is necessary to meet the growing demands of transplantation and save more lives.

EASL Clinical Practice Guidelines on liver transplantation

Liver transplantation (LT) is an established life-saving procedure. The field of LT has changed in the past 10 years from several perspectives, with the expansion of indications, transplantation of patients with acute-on-chronic liver failure, evolution of transplant oncology, the use of donations after cardiac death, new surgical techniques, and prioritisation of recipients on the waiting list. In addition, the advent of organ perfusion machines, the recognition of new forms of rejection, and the attention paid to the transition from paediatric to adult patients, have all improved the management of LT recipients. The purpose of the EASL guidelines presented here is not to cover all aspects of LT but to focus on developments since the previous EASL guidelines published in 2016.

Long-term machine perfusion of human split livers: a new model for regenerative and translational research

Recent advances in machine perfusion have revolutionised the field of transplantation by prolonging preservation, permitting evaluation of viability prior to implant and rescue of discarded organs. Long-term perfusion for days-to-weeks provides time to modify these organs prior to transplantation. By using long-term normothermic machine perfusion to facilitate liver splitting and subsequent perfusion of both partial organs, possibilities even outside the clinical arena become possible. This model remains in its infancy but in the future, could allow for detailed study of liver injury and regeneration, and ex-situ treatment strategies such as defatting, genetic modulation and stem-cell therapies. Here we provide insight into this new model for research and highlight its great potential and current limitations.

Routine end-ischemic hypothermic machine perfusion in liver transplantation from donors after brain death: results of 2-year follow-up of a randomized controlled trial

BACKGROUND

Data on routine hypothermic machine perfusion of livers procured from donors after brain death (DBD) are scarce, and the benefits of the method have only been demonstrated in extended criteria grafts. This study aimed to assess if end-ischemic dual hypothermic oxygenated machine perfusion (dHOPE) is superior to static cold storage (SCS) in preservation of livers procured from DBD donors with respect to long-term outcomes. Existing data on short-term outcomes favours dHOPE in patients receiving high-risk grafts.

METHODS

This prospective randomized controlled trial included 104 recipients of DBD livers randomly assigned to SCS arm (78 patients) and the dHOPE arm (26 patients). Endpoints of interest were the occurrence of biliary complications (biliary fistula, anastomotic, and nonanastomotic strictures) and overall patient and graft survival (GS) during the 2-year follow-up.

RESULTS

A total of 36 patients developed biliary complications (at least one event) - six events in dHOPE arm and 30 in SCS arm. There was no significant difference in biliary complications between groups (23.7 vs. 43.4%, P =0.11). No differences were found significant with respect to anastomotic (19.9 vs. 33.7%, P =0.20) and nonanastomotic strictures (0 vs. 11.1%, P =0.10) as well as biliary fistulas (11.7 vs. 12.2%, P =0.93). Survival analysis did not show significantly different results in the study population - overall survival: 92.3% in dHOPE and 83.9% in SCS ( P =0.35), and GS: 92.3 and 81.4% ( P =0.23), respectively. However, a significant difference in GS was noted in recipients of high-risk grafts - 100% in dHOPE and 73.1% in SCS, respectively ( P =0.038).

CONCLUSIONS

The long-term outcome data suggest that the routine use of dHOPE may be beneficial for recipients of high-risk grafts from DBD donors. The present study does not provide any evidence for the benefits of dHOPE in low-risk grafts.

Multinational Analysis of Marginal Liver Grafts Based on the Eurotransplant Extended Donor Criteria

OBJECTIVE

To evaluate the outcome of marginal liver grafts based on the Eurotransplant extended criteria donor (ECD) criteria.

BACKGROUND

Eurotransplant uses a broad definition of ECD criteria (age >65 years, steatosis >40%, body mass index >30 kg/m 2 , intensive care unit stay >7 days, donation after circulatory death, and certain laboratory parameters) for allocating organs to recipients who have consented to marginal grafts. Historically, marginal liver grafts were associated with increased rates of dysfunction.

METHODS

Retrospective cohort analysis using the German Transplant Registry and the U.S. Scientific Registry of Transplant Recipients (SRTR) from 2006 to 2016. Results were validated with recent SRTR data (2017-2022). Donors were classified according to the Eurotransplant ECD criteria, donation after circulatory death was excluded. Data were analyzed with cutoff prediction, binomial logistic regression, and multivariate Cox regression.

RESULTS

The study analyzed 92,330 deceased brain-dead donors (87% SRTR) and 70,374 transplants (87% SRTR) in adult recipients. Predominant ECD factors were donor age in Germany (30%) and body mass index in the United States (28%). Except for donor age, grafts meeting ECD criteria were not associated with impaired 1 or 3-year survival. Cutoffs had little to no predictive value for 30-day graft survival (area under the receiver operating curve: 0.49-0.52) and were nominally higher for age (72 vs 65 years) in Germany as compared with those defined by current Eurotransplant criteria.

CONCLUSIONS

The outcome of transplanted grafts from higher risk donors was nearly equal to standard donors with Eurotransplant criteria failing to predict survival of marginal grafts. Modifying ECD criteria could improve graft allocation and potentially expand the donor pool.

Production of physiological amounts of hemostatic proteins by human donor livers during ex situ long-term normothermic machine perfusion for up to 7 days

BACKGROUND

Normothermic machine perfusion (NMP) is used for preservation and assessment of human donor livers prior to transplantation. During NMP, the liver is metabolically active, which allows detailed studies on the physiology of human livers.

OBJECTIVES

To study the production of hemostatic proteins in human donor livers during NMP for up to 7 days.

METHODS

In this observational study, 9 livers underwent NMP for up to 7 days with a heparinized perfusate based on red blood cells and colloids using a modified Liver Assist device (XVIVO). Perfusate samples were collected before NMP and daily thereafter for measurement of antigen and activity levels of a comprehensive panel of hemostatic proteins after heparin neutralization.

RESULTS

Within 1 day, perfusate samples displayed the potential for coagulation activation as evidenced by international normalized ratio and activated partial thromboplastin assays. This was accompanied by detection of substantial quantities of functionally active coagulation proteins and inhibitors, although the specific activity of many proteins was decreased, compared with that in normal plasma. Perfusate levels of hemostatic proteins increased in the first days, reaching a stable level after 3 to 4 days of perfusion.

CONCLUSION

During long-term NMP of human livers, functionally active hemostatic proteins are released into the perfusate in substantial quantities, but some proteins appear to have decreased functional properties compared with proteins in normal human plasma. We propose that NMP may be used as a platform to test efficacy of drugs that stimulate or inhibit the production of coagulation factors or to test liver-mediated clearance of prohemostatic protein therapeutics.

Comparative Analysis of Digestion Methods for Bile Proteomics: The Key to Unlocking Biliary Biomarker Potential

BACKGROUND

Bile's potential to reflect the health of the biliary system has led to increased attention, with proteomic analysis offering deeper understanding of biliary diseases and potential biomarkers. With the emergence of normothermic machine perfusion (NMP), bile can be easily collected and analyzed. However, the composition of bile can make the application of proteomics challenging. This study systematically evaluated various trypsin digestion methods to optimize proteomics of bile from human NMP livers.

METHODS

Bile was collected from 12 human donor livers that were accepted for transplantation after the NMP viability assessment. We performed tryptic digestion using six different methods: in-gel, in-solution, S-Trap, SMART, EasyPep, and filter-aided sample purification, with or without additional precipitation before digestion. Proteins were analyzed using untargeted proteomics. Methods were assessed for total protein IDs, variation, and protein characteristics to determine the most optimal method.

RESULTS

Methods involving precipitation surpassed crude methods in protein identifications (4500 vs 3815) except for in-gel digestion. Filtered data (40%) resulted in 3192 versus 2469 for precipitated and crude methods, respectively. We found minimal differences in mass, cellular components, or hydrophobicity of proteins between methods. Intermethod variability was notably diverse, with in-gel, in-solution, and EasyPep outperforming others. Age-related biological comparisons revealed upregulation of metabolic-related processes in younger donors and immune response and cell cycle-related processes in older donors.

CONCLUSIONS

Variability between methods emphasizes the importance of cross-validation across multiple analytical approaches to ensure robust analysis. We recommend the in-gel crude method for its simplicity and efficiency, avoiding additional precipitation steps. Sample processing speed, cost, cleanliness, and reproducibility should be considered when a digestion method is selected for bile proteomics.

Graft repair during machine perfusion: a current overview of strategies

PURPOSE OF REVIEW

With changing donor characteristics (advanced age, obesity), an increase in the use of extended criteria donor (ECD) livers in liver transplantation is seen. Machine perfusion allows graft viability assessment, but still many donor livers are considered nontransplantable. Besides being used as graft viability assessment tool, ex situ machine perfusion offers a platform for therapeutic strategies to ameliorate grafts prior to transplantation. This review describes the current landscape of graft repair during machine perfusion.

RECENT FINDINGS

Explored anti-inflammatory therapies, including inflammasome inhibitors, hemoabsorption, and cellular therapies mitigate the inflammatory response and improve hepatic function. Cholangiocyte organoids show promise in repairing the damaged biliary tree. Defatting during normothermic machine perfusion shows a reduction of steatosis and improved hepatobiliary function compared to nontreated livers. Uptake of RNA interference therapies during machine perfusion paves the way for an additional treatment modality.

SUMMARY

The possibility to repair injured donor livers during ex situ machine perfusion might increase the utilization of ECD-livers. Application of defatting agents is currently explored in clinical trials, whereas other therapeutics require further research or optimization before entering clinical research.

Viability assessment of the liver during ex-situ machine perfusion prior to transplantation

PURPOSE OF REVIEW

In an attempt to reduce waiting list mortality in liver transplantation, less-than-ideal quality donor livers from extended criteria donors are increasingly accepted. Predicting the outcome of these organs remains a challenge. Machine perfusion provides the unique possibility to assess donor liver viability pretransplantation and predict postreperfusion organ function.

RECENT FINDINGS

Assessing liver viability during hypothermic machine perfusion remains challenging, as the liver is not metabolically active. Nevertheless, the levels of flavin mononucleotide, transaminases, lactate dehydrogenase, glucose and pH in the perfusate have proven to be predictors of liver viability. During normothermic machine perfusion, the liver is metabolically active and in addition to the perfusate levels of pH, transaminases, glucose and lactate, the production of bile is a crucial criterion for hepatocyte viability. Cholangiocyte viability can be determined by analyzing bile composition. The differences between perfusate and bile levels of pH, bicarbonate and glucose are good predictors of freedom from ischemic cholangiopathy.

SUMMARY

Although consensus is lacking regarding precise cut-off values during machine perfusion, there is general consensus on the importance of evaluating both hepatocyte and cholangiocyte compartments. The challenge is to reach consensus for increased organ utilization, while at the same time pushing the boundaries by expanding the possibilities for viability testing.

Preclinical validation of a customized circuit for ex situ uninterrupted cold-to-warm prolonged perfusion of the liver

CONTEXT

Clinical adoption of ex situ liver perfusion is growing. While hypothermic perfusion protects against ischemia-reperfusion injury in marginal grafts, normothermic perfusion enables organ viability assessment and therefore selection of borderline grafts. The combination of hypothermic and normothermic perfusion, known as "cold-to-warm," may be the optimal sequence for organ preservation, but is difficult to achieve with most commercial perfusion systems. We developed an adaptable customized circuit allowing uninterrupted "cold-to-warm" perfusion and conducted preclinical studies on healthy porcine livers and discarded human livers to demonstrate the circuit's efficacy.

METHODS

In collaboration with bioengineers, we developed a customized circuit that adapts to extracorporeal circulation consoles used in cardiovascular surgery and includes a proprietary reservoir enabling easy perfusate change without interrupting perfusion. This preclinical study was conducted on porcine and human livers. Perfusion parameters (pressures, flows, oxygenation) and organ viability were monitored.

RESULTS

The customized circuit was adapted to a LivaNova S5® console, and the perfusions were flow-driven with real-time pressure monitoring. Ten porcine liver and 12 discarded human liver perfusions were performed during 14 to 18 h and 7 to 25 h, respectively. No hyperpressure was observed (porcine and human portal pressure 2-6 and 2-8 mm Hg; arterial pressure 10-65 and 20-65 mm Hg, respectively). No severe histological tissue injury was observed (Suzuki score ≤ 3 at the end of perfusion). Seven (70%) porcine livers and five (42%) human livers met the UK viability criteria.

CONCLUSION

The customized circuit and system design enables smooth uninterrupted "cold-to-warm" perfusion not present in current commercial perfusion systems.

Machine perfusion in liver transplantation: recent advances and coming challenges

PURPOSE OF REVIEW

Machine perfusion has been adopted into clinical practice in Europe since the mid-2010s and, more recently, in the United States (US) following approval of normothermic machine perfusion (NMP). We aim to review recent advances, provide discussion of potential future directions, and summarize challenges currently facing the field.

RECENT FINDINGS

Both NMP and hypothermic-oxygenated perfusion (HOPE) improve overall outcomes after liver transplantation versus traditional static cold storage (SCS) and offer improved logistical flexibility. HOPE offers additional protection to the biliary system stemming from its' protection of mitochondria and lessening of ischemia-reperfusion injury. Normothermic regional perfusion (NRP) is touted to offer similar protective effects on the biliary system, though this has not been studied prospectively.The most critical question remaining is the optimal use cases for each of the three techniques (NMP, HOPE, and NRP), particularly as HOPE and NRP become more available in the US. There are additional questions regarding the most effective criteria for viability assessment and the true economic impact of these techniques. Finally, with each technique purported to allow well tolerated use of riskier grafts, there is an urgent need to define terminology for graft risk, as baseline population differences make comparison of current data challenging.

SUMMARY

Machine perfusion is now widely available in all western countries and has become an essential tool in liver transplantation. Identification of the ideal technique for each graft, optimization of viability assessment, cost-effectiveness analyses, and proper definition of graft risk are the next steps to maximizing the utility of these powerful tools.

Gradual rewarming with a hemoglobin-based oxygen carrier improves viability of donation after circulatory death in rat livers

Background

Donation after circulatory death (DCD) grafts are vital for increasing available donor organs. Gradual rewarming during machine perfusion has proven effective in mitigating reperfusion injury and enhancing graft quality. Limited data exist on artificial oxygen carriers as an effective solution to meet the increasing metabolic demand with temperature changes. The aim of the present study was to assess the efficacy and safety of utilizing a hemoglobin-based oxygen carrier (HBOC) during the gradual rewarming of DCD rat livers.

Methods

Liver grafts were procured after 30 min of warm ischemia. The effect of 90 min of oxygenated rewarming perfusion from ice cold temperatures (4 °C) to 37 °C with HBOC after cold storage was evaluated and the results were compared with cold storage alone. Reperfusion at 37 °C was performed to assess the post-preservation recovery.

Results

Gradual rewarming with HBOC significantly enhanced recovery, demonstrated by markedly lower lactate levels and reduced vascular resistance compared to cold-stored liver grafts. Increased bile production in the HBOC group was noted, indicating improved liver function and bile synthesis capacity. Histological examination showed reduced cellular damage and better tissue preservation in the HBOC-treated livers compared to those subjected to cold storage alone.

Conclusion

This study suggests the safety of using HBOC during rewarming perfusion of rat livers as no harmful effect was detected. Furthermore, the viability assessment indicated improvement in graft function.

The Risk of Microbial Transmission in Recipients of Donor Livers That Underwent Hypothermic or Normothermic Machine Perfusion

Background

Ex situ machine perfusion is increasingly used to preserve and assess donor livers before transplantation. Compared with traditional static cold storage (SCS), machine perfusion exposes livers to an additional risk of microbial contamination. However, information on the risk of microbial transmission during machine perfusion is lacking.

Methods

All livers that underwent either hypothermic oxygenated machine perfusion (HOPE) or normothermic machine perfusion (NMP) in our center between September 2021 and September 2023, and during which samples were taken from SCS fluid and/or machine perfusion solution for microbiological examination, were included in this retrospective, observational clinical study. Microbial transmission was examined from SCS fluid to machine perfusion solution fluid and, subsequently, to recipients of these livers.

Results

A total of 90 cases of liver machine perfusion were included: 59 HOPE and 31 NMP. SCS preservation fluid cultures before HOPE or NMP were positive for at least 1 microorganism in 52% of the cases. After HOPE, there were no cases of positive machine perfusion fluid or evidence of microbial transmission to the recipients. After NMP, in 1 (3%) patient Escherichia coli was grown from abdominal drain fluid, the same bacterial strain that was also grown from the SCS preservation fluid before NMP. This E coli was resistant to the antibiotics that are routinely added to the NMP perfusion fluid.

Conclusions

The risk of microbial transmission after machine perfusion is very low but not absent. We recommend routine sampling of machine perfusion fluid at the end of the procedure for microbiological analysis.

Normothermic machine perfusion for liver transplantation: current state and future directions

PURPOSE OF REVIEW

The number of patients on the liver transplant waitlist continues to grow and far exceeds the number of livers available for transplantation. Normothermic machine perfusion (NMP) allows for ex-vivo perfusion under physiologic conditions with the potential to significantly increase organ yield and expand the donor pool.

RECENT FINDINGS

Several studies have found increased utilization of donation after cardiac death and extended criteria brain-dead donor livers with implementation of NMP, largely due to the ability to perform viability testing during machine perfusion. Recently, proposed viability criteria include lactate clearance, maintenance of perfusate pH more than 7.2, ALT less than 6000 u/l, evidence of glucose metabolism and bile production. Optimization of liver grafts during NMP is an active area of research and includes interventions for defatting steatotic livers, preventing ischemic cholangiopathy and rejection, and minimizing ischemia reperfusion injury.

SUMMARY

NMP has resulted in increased organ utilization from marginal donors with acceptable outcomes. The added flexibility of prolonged organ storage times has the potential to improve time constraints and transplant logistics. Further research to determine ideal viability criteria and investigate ways to optimize marginal and otherwise nontransplantable liver grafts during NMP is warranted.

Challenges With the Implementation of Machine Perfusion in Clinical Liver Transplantation

Dynamic organ preservation is a relatively old technique which has regained significant interest in the last decade. Machine perfusion (MP) techniques are applied in various fields of solid organ transplantation today. The first clinical series of ex situ MP in liver transplantation was presented in 2010. Since then, the number of research and clinical applications has substantially increased. Despite the notable beneficial effect on organ quality and recipient outcome, MP is still not routinely used in liver transplantation. Based on the enormous need to better preserve organs and the subsequent demand to continuously innovate and develop perfusion equipment further, this technology is also beneficial to test and deliver future therapeutic strategies to livers before implantation. This article summarizes the various challenges observed during the current shift from static to dynamic liver preservation in the clinical setting. The different organ perfusion strategies are discussed first, together with ongoing clinical trials and future study design. The current status of research and the impact of costs and regulations is highlighted next. Factors contributing to costs and other required resources for a worldwide successful implementation and reimbursement are presented third. The impact of research on cost-utility and effectivity to guide the tailored decision-making regarding the optimal perfusion strategy is discussed next. Finally, this article provides potential solutions to the challenging field of innovation in healthcare considering the various social and economic factors and the role of clinical, regulatory, and financial stakeholders worldwide.

Bile Chemistry During Ex Situ Normothermic Liver Perfusion Does Not Always Predict Cholangiopathy

BACKGROUND

Bile chemistry during normothermic ex situ liver perfusion (NESLiP) has been suggested to be an indicator of cholangiopathy. The normal range of biochemical variables in bile of livers undergoing NESLiP has not been defined, nor have published biliary viability criteria been assessed against instances of posttransplant nonanastomotic bile strictures (NASs).

METHODS

The bile and perfusate chemistry of 200 livers undergoing NESLiP between February 1, 2018, and October 30, 2023, was compared. In addition, 11 livers that underwent NESLiP and later developed NAS were selected and their bile chemistry was also examined.

RESULTS

In livers that did not develop cholangiopathy, concentrations of sodium, potassium, and chloride were slightly higher in bile than in perfusate, whereas the concentration of calcium was slightly lower. Bile was alkali and had a lower glucose concentration than perfusate. Cholangiocyte glucose reabsorption was shown to saturate at high perfusate concentrations and was more impaired in livers donated after circulatory death than in livers donated after brain death. Published criteria failed to identify all livers that went on to develop NASs.

CONCLUSIONS

A significant false-negative rate exists with current biliary viability criteria, probably reflecting the patchy and incomplete nature of the development of NASs in the biliary tree. The data presented here provide a benchmark for future assessment of bile duct chemistry during NESLiP.

From Patients to Providers: Assessing Impact of Normothermic Machine Perfusion on Liver Transplant Practices in the US

BACKGROUND

Normothermic machine perfusion (NMP) of livers allows for the expansion of the donor pool and minimization of posttransplant complications. Results to date have focused on both donor and recipient outcomes, but there remains potential for NMP to also impact transplant providers.

STUDY DESIGN

Using United Network for Organ Sharing Standard Transplant Analysis file data, adult deceased donors who underwent transplantation between January 1, 2016, and December 31, 2022, were identified. Transplanted livers were divided by preservation methods (static cold storage [SCS] and NMP) and case time (day-reperfusion 8 am to 6 pm ). Patient factors, transplant characteristics, and short-term outcomes were analyzed between Mahalanobis-metric-matched groups.

RESULTS

NMP livers represented 742 (1.4%) of 52,132 transplants. NMP donors were more marginal with higher Donor Risk Index scores (1.78 ± 0.50 NMP vs 1.49 ± 0.38 SCS, p < 0.001) and donation after cardiac death frequency (36.9% vs 8.4%, p < 0.001). NMP recipients more often had model for end-stage liver disease (MELD) exception status (29.9% vs 23.4%, p < 0.001), lower laboratory MELD scores (20.7 ± 9.7 vs 24.3 ± 10.9, p < 0.001), and had been waitlisted longer (111.5 [21.0 to 307.0] vs 60.0 [9.0 to 245.0] days, p < 0.001). One-year graft survival (90.2% vs 91.6%, p = 0.505) was similar between groups, whereas length of stay was lower for NMP recipients (8.0 [6.0 to 14.0] vs 10.0 [6.0 to 16.0], p = 0.017) after adjusting for confounders. Notably, peak case volume occurred at 11 am with NMP livers (vs 9 pm with SCS). Overall, a higher proportion of transplants was performed during daytime hours with NMP (51.5% vs 43.0%, p < 0.001).

CONCLUSIONS

NMP results in increased use of marginal allografts, which facilitated transplantation in lower laboratory MELD recipients who have been waitlisted longer and often have exception points. Importantly, NMP also appeared to shift peak caseloads from nighttime to daytime, which may have significant effects on the quality of life for the entire liver transplant team.

Routine utilization of machine perfusion in liver transplantation: Ready for prime time?

The last decade has been notable for increasing high-quality research and dramatic improvement in outcomes with dynamic liver preservation. Robust evidence from numerous randomized controlled trials has been pooled by meta-analyses, providing the highest available evidence on the protective effect of machine perfusion (MP) over static cold storage in liver transplantation (LT). Based on a protective effect with less complications and improved graft survival, the field has seen a paradigm shift in organ preservation. This editorial focuses on the role of MP in LT and how it could become the new "gold standard". Strong collaborative efforts are needed to explore its effects on long-term outcomes.

Obstacles to implement machine perfusion technology in routine clinical practice of transplantation: Why are we not there yet?

Machine perfusion of solid human organs is an old technique, and the basic principles were presented as early as 1855 by Claude Barnard. More than 50 years ago, the first perfusion system was used in clinical kidney transplantation. Despite the well-known benefits of dynamic organ preservation and significant medical and technical development in the last decades, perfusion devices are still not in routine use. This article describes the various challenges to implement this technology in practice, critically analyzing the role of all involved stakeholders, including clinicians, hospitals, regulatory, and industry, on the background of regional differences worldwide. The clinical need for this technology is discussed first, followed by the current status of research and the impact of costs and regulations. Considering the need for strong collaborations between clinical users, regulatory bodies, and industry, integrated road maps and pathways required to achieve a wider implementation are presented. The role of research development, clear regulatory pathways, and the need for more flexible reimbursement schemes is discussed together with potential solutions to address the most relevant hurdles. This article paints an overall picture of the current liver perfusion landscape and highlights the role of clinical, regulatory, and financial stakeholders worldwide.

Evolution of Liver Transplantation Indications: Expanding Horizons

Liver transplantation (LT) has significantly transformed the prognosis of patients with end-stage liver disease and hepatocellular carcinoma (HCC). The traditional epidemiology of liver diseases has undergone a remarkable shift in indications for LT, marked by a decline in viral hepatitis and an increase in metabolic dysfunction-associated steatotic liver disease (MASLD), along with expanded indications for HCC. Recent advancements in surgical techniques, organ preservation and post-transplant patients' management have opened new possibilities for LT. Conditions that were historically considered absolute contraindications have emerged as potential new indications, demonstrating promising results in terms of patient survival. While these expanding indications provide newfound hope, the ethical dilemma of organ scarcity persists. Addressing this requires careful consideration and international collaboration to ensure equitable access to LT. Multidisciplinary approaches and ongoing research efforts are crucial to navigate the evolving landscape of LT. This review aims to offer a current overview of the primary emerging indications for LT, focusing on acute-on-chronic liver failure (ACLF), acute alcoholic hepatitis (AH), intrahepatic and perihilar cholangiocarcinoma (i- and p-CCA), colorectal liver metastasis (CRLM), and neuroendocrine tumor (NET) liver metastases.

Transplant oncology - Current indications and strategies to advance the field

Liver transplantation (LT) was originally described by Starzl as a promising strategy to treat primary malignancies of the liver. Confronted with high recurrence rates, indications drifted towards non-oncologic liver diseases with LT finally evolving from a high-risk surgery to an almost routine surgical procedure. Continuously improving outcomes following LT and evolving oncological treatment strategies have driven renewed interest in transplant oncology. This is not only reflected by constant refinements to the criteria for LT in patients with HCC, but especially by efforts to expand indications to other primary and secondary liver malignancies. With new patient-centred oncological treatments on the rise and new technologies to expand the donor pool, the field has the chance to come full circle. In this review, we focus on the concept of transplant oncology, current indications, as well as technical and ethical aspects in the context of donor organs as precious resources.

Continuous Renal Replacement Therapy During Long-term Normothermic Machine Perfusion of Human Donor Livers for up to 7 D

Background

Normothermic machine perfusion (NMP) is used to preserve and test donor livers before transplantation. During NMP, the liver is metabolically active and produces waste products, which are released into the perfusate. In this study, we describe our simplified and inexpensive setup that integrates continuous renal replacement therapy (CRRT) with NMP for up to 7 d. We also investigated if the ultrafiltrate could be used for monitoring perfusate concentrations of small molecules such as glucose and lactate.

Methods

Perfusate composition (urea, osmolarity, sodium, potassium, chloride, calcium, magnesium, phosphate, glucose, and lactate) was analyzed from 56 human NMP procedures without CRRT. Next, in 6 discarded human donor livers, CRRT was performed during NMP by integrating a small dialysis filter (0.2 m2) into the circuit to achieve continuous ultrafiltration combined with continuous fluid substitution for up to 7 d.

Results

Within a few hours of NMP without CRRT, a linear increase in osmolarity and concentrations of urea and phosphate to supraphysiological levels was observed. After integration of CRRT into the NMP circuit, the composition of the perfusate was corrected to physiological values within 12 h, and this homeostasis was maintained during NMP for up to 7 d. Glucose and lactate levels, as measured in the CRRT ultrafiltrate, were strongly correlated with perfusate levels (r = 0.997, P < 0.001 and r = 0.999, P < 0.001, respectively).

Conclusions

The integration of CRRT into the NMP system corrected the composition of the perfusate to near-physiological values, which could be maintained for up to 7 d. The ultrafiltrate can serve as an alternative to the perfusate to monitor concentrations of small molecules without potentially compromising sterility.

Role of Machine Perfusion in Liver Transplantation

Given the current severe shortage of available livers for transplantation, there is an urgent need to maximize the utilization of donor organs. One of the strategies to increase the number of available livers for transplantation is to improve organ utilization through the use of elderly, overweight, or organs donated after circulatory death. However, the utilization of these "marginal" organs was associated with an increased risk of early allograft dysfunction, primary nonfunction, ischemic biliary complications, or even re-transplantation. Ischemia-reperfusion injury is a key mechanism in the pathogenesis of these complications.