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

Machine perfusion strategies in liver transplantation: A systematic review, pairwise, and network meta-analysis of randomized controlled trials

Machine perfusion (MP), including hypothermic oxygenated machine perfusion (HOPE), dual HOPE, normothermic machine perfusion (NMP), NMP ischemia-free liver transplantation (NMP-ILT), and controlled oxygenated rewarming (COR), is increasingly being investigated to improve liver graft quality from extended criteria donors and donors after circulatory death and expand the donor pool. This network meta-analysis investigates the comparative efficacy and safety of various liver MP strategies versus traditional static cold storage (SCS). We searched PubMed, Scopus, Web of Science, and Cochrane Controlled Register of Trials for randomized controlled trials comparing liver transplantation outcomes between SCS and MP techniques. The primary outcome was the incidence of early allograft dysfunction. Secondary endpoints included 1-year graft survival, the incidence of graft failure/loss, post-reperfusion syndrome, biliary complications, the need for renal replacement therapy, graft-related patient mortality, and the length of intensive care unit and hospital stay. R-software was used to conduct a network meta-analysis using a frequentist framework (PROSPERO ID: CRD42024549254). We included 12 randomized controlled trials involving 1628 patients undergoing liver transplantation (801 in the liver MP groups and 832 in the SCS group). Compared to SCS, HOPE/dHOPE, but not other MP strategies, was associated with a significantly lower risk of early allograft dysfunction (RR: 0.53, 95% CI [0.37, 0.74], p =0.0002), improved 1-year graft survival rate (RR: 1.07, 95% CI [1.01, 1.14], p =0.02), decreased graft failure/loss (RR: 0.38, 95% CI [0.16, 0.90], p =0.03), and reduced the risk of biliary complications (RR: 0.52, 95% CI [0.43, 0.75], p < 0.0001). Compared to SCS, NMP (RR: 0.49, 95% CI [0.24, 0.96]) and NMP-ILT (RR: 0.15, 95% CI [0.04, 0.57]), both significantly reduced the risk of postperfusion syndrome. There is no difference between SCS and MP groups in the risk of renal replacement therapy, graft-related patient mortality, and intensive care unit and hospital stay length. Our meta-analysis showed that HOPE/dual-HOPE is a promising alternative to SCS for donor liver preservation. These new techniques can help expand the donor pool with similar or even better post-liver transplantation outcomes.

Transplantation of Patients with Hepatocellular Carcinoma Through Increased Utilization of Machine Perfusion Technology

Background

With the intent to mitigate waitlist disparities, the median model for end-stage liver disease (MELD) at transplant minus 3 policy nevertheless decreased access to liver transplant for patients with hepatocellular carcinoma (HCC). However, the adoption of machine perfusion (MP) technologies has shown promise in improving deceased donor graft yield and utilization. To understand current use for patients with HCC, we examined liver transplant patterns with MP and the characteristics of patients with HCC receiving an MP liver.

Methods

Adult patients with HCC undergoing deceased donor liver transplant from September 29, 2021, to March 30, 2024, were identified using the United Network for Organ Sharing Standard Transplant Analysis and Research files. Patients were excluded if listed as status 1A or they underwent multiorgan or split liver transplant. Multivariate analysis compared patients with HCC receiving an MP liver with those receiving a static cold storage liver.

Results

Of 3774 liver recipients with HCC, 593 (15.7%) underwent transplant with an MP graft. Compared with patients donation after circulatory death graft receiving a graft with static cold storage preservation, those with MP had less advanced disease (ie, Child-Pugh class C cirrhosis 22.9% versus 29.9%, P < 0.01) and lower median match MELD (13 versus 17, P < 0.001). Tumor characteristics were similar between groups, including alpha-fetoprotein level, maximum tumor size, and locoregional treatments. Donor factors, and not tumor burden, were most predictive of receipt of an MP liver (donation after circulatory death graft: odds ratio [OR], 14.81; macrosteatosis >30%; OR, 3.85; donor age older than 60 y; OR, 2.34). A shorter waitlist time (6.5 versus 7.2 mo, P < 0.01), with similar 1-y patient survival (93.6% versus 93.2%, P = 0.82) and graft survival (92.0% versus 91.6%, P = 0.84), was also noted in patients undergoing MP transplant.

Conclusions

The strategic use of MP livers may improve graft utilization and access to liver transplants, helping offset the disadvantages of the MELD at transplant minus 3 policy for patients with HCC.

Equal performance of HTK-based and UW-based perfusion solutions in sub-normothermic liver machine perfusion

Machine perfusion (MP) is gaining importance in liver transplantation, the only cure for many end-stage liver diseases. Varieties of different MP protocols are available. Currently, various MP protocols are available, differing not only in perfusion temperature but also in the specific perfusion solution required. We aimed to investigate the performance of an HTK-based perfusate during sub-normothermic MP (SNMP) of discarded human liver grafts compared to that of a UW-based solution. Twenty discarded livers (rejected for transplantation by all centers) were subjected to ex-vivo SNMP at 21°C with either HTK- or UW-based solution for 12 h. Perfusate and tissue samples collected before the start, after 6 h, and at the end of SNMP were analyzed for liver enzymes, along with mRNA expression of perfusate and tissue markers associated with organ damage. Hepatocellular viability was assessed by measuring bile production, monitoring pH stability, and analyzing histological changes in HE stained tissue sections. After propensity score matching 16 livers were analyzed. Overall, no differences between HTK- and UW-based solution were detected, except for an increased MLKL mRNA expression and impaired pH stability during SNMP with HTK-based perfusate. No other investigated parameters of cell injury, inflammation or hepatocellular viability supported this finding. Bile production was higher in the 6 HTK-perfused livers compared to the three UW-perfused livers that produced bile. Overall, these findings suggest that HTK performs comparably to a UW-based solution during 12 h of liver SNMP.

Detection of inflammasome activation in liver tissue during the donation process as potential biomarker for liver transplantation

Deceased donor liver transplantation (LT) is a crucial lifesaving option for patients with end-stage liver diseases. Although donation after brain death (DBD) remains the main source of donated organs, exploration of donation after circulatory death (DCD) addresses donor scarcity but introduces challenges due to warm ischemia. While technical advances have improved outcomes, challenges persist, with a 13% mortality rate within the first year. Delving into liver transplantation complexities reveals the profound impact of molecular signaling on organ fate. NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation play a pivotal role, influencing inflammatory responses. The NLRP3 inflammasome, found in hepatocytes, contributes to inflammation, fibrosis, and liver cell death. This study explores these dynamics, shedding light on potential biomarkers and therapeutic targets. Samples from 36 liver transplant patients were analyzed for ASC specks detection and inflammasome-related gene expression. Liver biopsies, obtained before and after cold ischemia storage, were processed for immunofluorescence, qRT-PCR, and Western blot. One year post-LT clinical follow-up included diagnostic procedures for complications, and global survival was assessed. Immunofluorescence detected activated inflammasome complexes in fixed liver tissues. ASC specks were identified in hepatocytes, showing a trend toward more specks in DCD livers. Likewise, inflammasome-related gene expression analysis indicated higher expression in DCD livers, decreasing after cold ischemia. Similar results were found at protein level. Patients with increased ASC specks staining exhibited lower overall survival rates, correlating with IL1B expression after cold ischemia. Although preliminary, these findings offer novel insights into utilizing direct detection of inflammasome activation in liver tissue as a biomarker. They suggest its potential impact on post-transplant outcomes, potentially paving the way for improved diagnostic approaches and personalized treatment strategies in LT.

National Trends in Utilization of Normothermic Machine Perfusion in DCD Liver Transplantation

Background

In liver transplantation, advances in ex situ normothermic machine perfusion (NMP) have improved outcomes compared with traditional static cold storage (SCS) in donation after circulatory death (DCD) organs. We aimed to characterize trends in the utilization of NMP versus SCS in DCD liver transplantation in the United States.

Methods

This retrospective cohort study used data from the United Network for Organ Sharing database to identify recipient-donor adult liver transplant pairs from DCD donors from January 2016 to June 2022. Utilization of NMP and changes in donor risk index (DRI) and components between NMP and SCS were assessed across transplant year eras (2016-2018, 2019-2020, and 2021-2022). Statistical comparisons were made using the Kruskal-Wallis test or the chi-square test.

Results

A total of 3937 SCS and 127 NMP DCD donor transplants were included. Utilization of NMP ranged from ~0.4% to 3.5% from 2016 to 2021 and rose significantly to 11.2% in early 2022. Across transplant eras, median DRI increased significantly for SCS and NMP, but the magnitude of the increase was larger for NMP. With NMP DCDs, there were significant increases in median donor age, national share proportion, and "cold ischemic time" over time. Finally, there was a shift toward including higher DRI donors and higher model for end-stage liver disease score transplant recipients with NMP in later transplant eras.

Conclusions

In recent years, NMP utilization has increased and expanded to donors with higher DRI and recipients with higher model for end-stage liver disease score at transplant, suggesting increasing familiarity and risk tolerance with NMP technology. As NMP remains a relatively new technique, ongoing study of patient outcomes, organ allocation practices, and utilization patterns is critical.

A propensity score matched analysis of liver transplantation outcomes in the setting of preservation solution shortage

The recent shortage of the University of Wisconsin (UW) solution prompted increased utilization of histidine-tryptophan-ketoglutarate (HTK) solution for liver graft preservation. This contemporary study analyzed deceased donor liver transplant outcomes following preservation with HTK vs UW. Patients receiving deceased donor liver transplantations between January 1, 2019, and June 30, 2022, were retrospectively identified utilizing the Organ Procurement and Transplant Network database, stratified by preservation with HTK vs UW, and a propensity score matching analysis was performed. Outcomes assessed included rates of primary nonfunction, graft survival, and patient survival. There were 4447 patients in each cohort. Primary nonfunction occurred in 60 (1.35%) patients in the HTK group vs 25 (0.54%) in the UW group (P < .001). HTK was associated with lower 90-day graft survival (94.39% vs 96.09%; P < .001) and 90-day patient survival (95.97% vs 97.38%; P = .001). Unmatched donation after cardiac death-specific analysis of HTK vs UW demonstrated respective rates of primary nonfunction of 1.63% vs 0.82% (P = .20), 90-day graft survival of 92.50% vs 95.29% (P = .069), and 90-day patient survival of 93.90% vs 96.35% (P = .077). These results suggest that HTK may not be an equivalent preservation solution for deceased donor liver transplantation.

Current Status of Liver Transplantation in North America

Liver transplantation indications continue to evolve in North America. Several recent changes have occurred in the field with changes in the allocation system, new performance metrics, expansion of transplant oncology, and utilization of ex vivo perfusion devices and techniques. Deceased donor liver transplantation continues to be the primary modality of liver transplantation in North America, with an ongoing focus on advancing the use of living donor liver transplantation, especially in those patients who may not have favorable access to deceased donor allografts.

Donor Evaluation Protocol for Live and Deceased Donors

Donor evaluation is a critical step before proceeding with liver transplantation (LT) in both deceased donor LT (DDLT) and living donor LT (LDLT). A good, healthy graft is necessary for the success of the transplantation. Other issues in selecting a donor include the transmission of infections and malignancies from the donor. Because of the scarcity of cadaver organs, an increasing number of extended-criteria donors, or 'marginal donors', are being utilized. LDLT also has potential risks to the donor, and donor safety needs to be kept in mind before proceeding with LT. The current review highlights the factors to be considered during donor evaluation for living and deceased donors before LT.

Global liver transplantation: emerging trends and ethical challenges

PURPOSE

Liver transplant (LT) is the only definitive treatment for end-stage liver disease (ESLD). This review aims to explore current global LT practices, with an emphasis on challenges and disparities that limit access to LT in different regions of the world.

METHODS

A detailed analysis was performed of present-day liver transplant practices throughout the world, including the etiology of liver disease, patient access to transplantation, surgical costs, and ongoing ethical concerns.

RESULTS

Annually, only 10% of the patients needing a liver transplant receive an organ. Currently, the USA performs the highest volume of liver transplants worldwide, followed by China and Brazil. In both North America and Europe, nonalcoholic fatty liver disease is becoming the most common indication for LT, compared to hepatitis B and C in most Asian, South American, and African countries. While deceased donor liver transplant remains the most performed type of LT, living donor liver transplant is becoming increasingly popular in some parts of the world where it is often the only option due to a lack of well-developed infrastructure for deceased organ donation. Ethical concerns in liver transplantation fundamentally revolve around the definition of a deceased donor and the exploitation of living donor liver donation systems.

CONCLUSION

Globally, liver transplant practices and outcomes are varied, with differences driven by healthcare policies, inequities in healthcare access, and ethical concerns.

A Review of Machine Perfusion Strategies in Liver Transplantation

The acceptance of liver transplantation as the standard of care for end-stage liver diseases has led to a critical shortage of donor allografts. To expand the donor organ pool, many countries have liberalized the donor criteria including extended criteria donors and donation after circulatory death. These marginal livers are at a higher risk of injury when they are preserved using the standard static cold storage (SCS) preservation techniques. In recent years, research has focused on optimizing organ preservation techniques to protect these marginal livers. Machine perfusion (MP) of the expanded donor liver has witnessed considerable advancements in the last decade. Research has showed MP strategies to confer significant advantages over the SCS techniques, such as longer preservation times, viability assessment and the potential to recondition high risk allografts prior to implantation. In this review article, we address the topic of MP in liver allograft preservation, with emphasis on current trends in clinical application. We discuss the relevant clinical trials related to the techniques of hypothermic MP, normothermic MP, hypothermic oxygenated MP, and controlled oxygenated rewarming. We also discuss the potential applications of ex vivo therapeutics which may be relevant in the future to further optimize the allograft prior to transplantation.

Danger signals released during cold ischemia storage activate NLRP3 inflammasome in myeloid cells and influence early allograft function in liver transplantation

BACKGROUND

Innate immunity plays a fundamental role in solid organ transplantation. Myeloid cells can sense danger signals or DAMPs released after tissue or cell damage, such as during ischemia processes. This study aimed to identify DAMPs released during cold ischemia storage of human liver and analyze their ability to activate the inflammasome in myeloid cells and the possible implications in terms of short-term outcomes of liver transplantation.

METHODS

79 samples of organ preservation solution (OPS) from 79 deceased donors were collected after cold static storage. We used different analytical methods to measure DAMPs in these end-ischemic OPS (eiOPS) samples. We also used eiOPS in the human macrophage THP-1 cell line and primary monocyte cultures to study inflammasome activation.

FINDINGS

Different DAMPs were identified in eiOPS, several of which induced both priming and activation of the NLRP3 inflammasome in human myeloid cells. Cold ischemia time and donation after circulatory death negatively influenced the DAMP signature. Moreover, the presence of oligomeric inflammasomes and interleukin-18 in eiOPS correlated with early allograft dysfunction in liver transplant patients.

INTERPRETATION

DAMPs released during cold ischemia storage prime and activate the NLRP3 inflammasome in liver macrophages after transplantation, inducing a pro-inflammatory environment that will complicate the outcome of the graft. The use of pharmacological blockers targeting DAMPs or the NLRP3 inflammasome in liver ischemia during static cold storage or through extracorporeal organ support could be a suitable strategy to increase the success of liver transplantation.

FUNDING

Fundación Mutua Madrileña and Instituto de Salud Carlos III, Madrid, Spain.

Emerging Role of NLRP3 Inflammasome and Pyroptosis in Liver Transplantation

The nucleotide-binding domain leucine-rich repeat-receptor, pyrin domain-containing-3 (NLRP3) inflammasome contributes to the inflammatory response by activating caspase-1, which in turn participates in the maturation of interleukin (IL)-1β and IL-18, which are mainly secreted via pyroptosis. Pyroptosis is a lytic type of cell death that is controlled by caspase-1 processing gasdermin D. The amino-terminal fragment of gasdermin D inserts into the plasma membrane, creating stable pores and enabling the release of several proinflammatory factors. The activation of NLRP3 inflammasome and pyroptosis has been involved in the progression of liver fibrosis and its end-stage cirrhosis, which is among the main etiologies for liver transplantation (LT). Moreover, the NLRP3 inflammasome is involved in ischemia-reperfusion injury and early inflammation and rejection after LT. In this review, we summarize the recent literature addressing the role of the NLRP3 inflammasome and pyroptosis in all stages involved in LT and argue the potential targeting of this pathway as a future therapeutic strategy to improve LT outcomes. Likewise, we also discuss the impact of graft quality influenced by donation after circulatory death and the expected role of machine perfusion technology to modify the injury response related to inflammasome activation.

Model of Acute Liver Failure in an Isolated Perfused Porcine Liver-Challenges and Lessons Learned

Acute liver failure (ALF) is a rare but devastating disease associated with substantial morbidity and a mortality rate of almost 45%. Medical treatments, apart from supportive care, are limited and liver transplantation may be the only rescue option. Large animal models, which most closely represent human disease, can be logistically and technically cumbersome, expensive and pose ethical challenges. The development of isolated organ perfusion technologies, originally intended for preservation before transplantation, offers a new platform for experimental models of liver disease, such as ALF. In this study, female domestic swine underwent hepatectomy, followed by perfusion of the isolated liver on a normothermic machine perfusion device. Five control livers were perfused for 24 h at 37 °C, while receiving supplemental oxygen and nutrition. Six livers received toxic doses of acetaminophen given over 12 h, titrated to methemoglobin levels. Perfusate was sampled every 4 h for measurement of biochemical markers of injury (e.g., aspartate aminotransferase [AST], alanine aminotransferase [ALT]). Liver biopsies were taken at the beginning, middle, and end of perfusion for histological assessment. Acetaminophen-treated livers received a median dose of 8.93 g (8.21–9.75 g) of acetaminophen, achieving a peak acetaminophen level of 3780 µmol/L (3189–3913 µmol/L). Peak values of ALT (76 vs. 105 U/L; p = 0.429) and AST (3576 vs. 4712 U/L; p = 0.429) were not significantly different between groups. However, by the end of perfusion, histology scores were significantly worse in the acetaminophen treated group (p = 0.016). All acetaminophen treated livers developed significant methemoglobinemia, with a peak methemoglobin level of 19.3%, compared to 2.0% for control livers (p = 0.004). The development of a model of ALF in the ex vivo setting was confounded by the development of toxic methemoglobinemia. Further attempts using alternative agents or dosing strategies may be warranted to explore this setting as a model of liver disease.

Hemoglobin-based oxygen carriers: Clinical application of HBOC-201 as an alternative to red blood cells for machine perfusion in liver transplantation

Background

Liver transplantation is the gold standard treatment option for end-stage liver diseases and failure. In recent years, ex vivo liver machine perfusion has been introduced to resuscitate livers before transplantation. The RBC-based solution is the main perfusate for this matter. Due to logistic and functional limitations in order to use an RBC-based solution, Hemoglobin-based oxygen carrier-201 (HBOC-201) is the new perfusion solution that is introduced to replace the RBC-based solution.

Methods

A systematic literature search of the PubMed registry was performed. A three-stage independent screening method was applied. Inclusion criteria for this review were published prospective, retrospective, clinical trials, and systematic reviews studies using acellular hemoglobin as a perfusion solution.

Results

Five studies that used HBOC-201 as the perfusate solution were identified. The overall number of livers that were resuscitated with HBOC-201 perfusate in all the studies was 50 livers. These studies have demonstrated the efficacy of HBOC-201 perfusate in terms of liver post perfusion metabolic and function assessment. Two studies compared HBOC-201 and PRBC as the perfusate solution. One study found comparable outcomes when HBOC-201 was used as the perfusate solution and in the other study, not only the results were comparable, but also, the study showed livers perfusate with HBOC-201 based solution had higher ATP levels, higher bile production, and quicker lactate reduction, and significantly lower ALT level at the end of MP.

Conclusion

Machine perfusion (MP) was introduced as an alternative preservation strategy in transplantation. The perfusion solution used in MP is a key factor in the process of organ revitalization, preventing hemolysis, and providing near-to-body physiologic hemostasis. HBOC-201 is a safe and convenient alternative to packed red blood cells in organ perfusion and recent studies showed promising results.

Role of normothermic machine perfusion in liver transplantation: Current trends and outcomes

Background

Liver transplantation is the only known curative treatment option for end-stage liver diseases and failure; however, there is an imbalance between the number of available liver organs for transplant and the number of patients as recipients due to a shortage of suitable organs. In recent years, ex vivo liver machine perfusion has been introduced to liver transplantation to expand the donor organ pool. Studies showed that using normothermic machine perfusion can increase the pool of transplantable discarded livers and is a promising strategy to improve graft resilience and performance further.

Methods

A systematic literature search of PubMed and ClinicalTrials.gov registry was performed. A three-stage independent screening method was applied. Inclusion criteria for this review were published prospective, retrospective, clinical trials, and systematic reviews studies using normothermic machine perfusion devices.

Results

Twenty-two articles on normothermic liver machine perfusion with patients and graft survival rate were identified. These studies have demonstrated the safety and efficacy of normothermic liver machine perfusion for discarded liver preservation in both standard and expanded criteria donors following patients and graft follow-ups. The overall number of livers that went under NMP was 568 in all the studies in which 503 of the livers were transplanted (88.6%). The 30,90,180 days and 1-year patients and grafts survival rates were promising.

Conclusion

Normothermic machine perfusion is a novelty method recently being used in liver transplantation and can lead to the expansion of the liver donor pool by revitalizing discarded livers. Our study was able to show the promising outcomes for both patients and grafts, which were achieved in many human clinical studies around the world using normothermic machine perfusion as a method of liver preservation and revitalization.