Excorporeal normothermic machine perfusion resuscitates pig DCD livers with extended warm ischemia

Intraoperative Anesthetic Strategies to Mitigate Early Allograft Dysfunction After Orthotopic Liver Transplantation: A Narrative Review

Orthotopic liver transplantation (OLT) is the most effective treatment for patients with end-stage liver disease (ESLD). Hepatic insufficiency within a week of OLT, termed early allograft dysfunction (EAD), occurs in 20% to 25% of deceased donor OLT recipients and is associated with morbidity and mortality. Primary nonfunction (PNF), the most severe form of EAD, leads to death or retransplantation within 7 days. The etiology of EAD is multifactorial, including donor, recipient, and surgery-related factors, and largely driven by ischemia-reperfusion injury (IRI). IRI is an immunologic phenomenon characterized by dysregulation of cellular oxygen homeostasis and innate immune defenses in the allograft after temporary cessation (ischemia) and later restoration (reperfusion) of oxygen-rich blood flow. The rising global demand for OLT may lead to the use of marginal allografts, which are more susceptible to IRI, and thus lead to an increased incidence of EAD. It is thus imperative the anesthesiologist is knowledgeable about EAD, namely its pathophysiology and intraoperative strategies to mitigate its impact. Intraoperative strategies can be classified by 3 phases, specifically donor allograft procurement, storage, and recipient reperfusion. During procurement, the anesthesiologist can use pharmacologic preconditioning with volatile anesthetics, consider preharvest hyperoxemia, and attenuate the use of norepinephrine as able. The anesthesiologist can advocate for normothermic regional perfusion (NRP) and machine perfusion during allograft storage at their institution. During recipient reperfusion, the anesthesiologist can optimize oxygen exposure, consider adjunct anesthetics with antioxidant-like properties, and administer supplemental magnesium. Unfortunately, there is either mixed, little, or no data to support the routine use of many free radical scavengers. Given the sparse, limited, or at times conflicting evidence supporting some of these strategies, there are ample opportunities for more research to find intraoperative anesthetic strategies to mitigate the impact of EAD and improve postoperative outcomes in OLT recipients.

Inflammatory setting, therapeutic strategies targeting some pro-inflammatory cytokines and pathways in mitigating ischemia/reperfusion-induced hepatic injury: a comprehensive review

Ischemia/reperfusion injury (IRI) is a key determining agent in the pathophysiology of clinical organ dysfunction. It is characterized by an aseptic local inflammatory reaction due to a decrease in blood supply, hence deprivation of dependent oxygen and nutrients. In instances of liver transplantation, this injury may have irreversible implications, resulting in eventual organ rejection. The deterioration associated with IRI is affected by the hepatic health status and various factors such as alterations in metabolism, oxidative stress, and pro-inflammatory cytokines. The primary cause of inflammation is the initial immune response of pro-inflammatory cytokines, while Kupffer cells (KFCs) and neutrophil-produced chemokines also play a significant role. Upon reperfusion, the activation of inflammatory responses can elicit further cellular damage and organ dysfunction. This review discusses the interplay between chemokines, pro-inflammatory cytokines, and other inflammatory mediators that contribute to the damage to hepatocytes and liver failure in rats following IR. Furthermore, it delves into the impact of anti-inflammatory therapies in safeguarding against liver failure and hepatocellular damage in rats following IR. This review investigates the correlation between cytokine factors and liver dysfunction via examining databases, such as PubMed, Google Scholar, Science Direct, Egyptian Knowledge Bank (EKB), and Research Gate.

Optimization of an in situ liver perfusion method to evaluate hepatic function of juvenile American alligators (Alligator mississippiensis)

American alligators (Alligator mississippiensis) are a sentinel species whose health is representative of environmental quality. However, their susceptibility to various natural or anthropogenic stressors is yet to be comprehensively studied. Understanding hepatic function in such assessments is essential as the liver is the central organ in the metabolic physiology of an organism, and therefore influences its adaptive capability. In this study, a novel liver perfusion system was developed to study the hepatic physiology of juvenile alligators. First, a cannulation procedure was developed for an in situ liver perfusion preparation. Second, an optimal flow rate of 0.5 ml/min/g liver was determined based on the oxygen content in the effluent perfusate. Third, the efficacy of the liver preparation was tested by perfusing the liver with normoxic or hypoxic Tyrode's buffer while various biomarkers of hepatic function were monitored in the effluent perfusate. Our results showed that in the normoxic perfusion, the aspartate transferase (AST) and lactate/pyruvate ratio in the perfusate remained stable and within an acceptable physiological range for 6 h. In contrast, hypoxia exposure significantly increased the lactate/pyruvate ratio in the perfusate after 2 h, indicating an induction of anaerobic metabolism. These results suggest that the perfused liver remained viable during the perfusion period and exhibited the expected physiological response under hypoxia exposure. The liver perfusion system developed in this study provides an experimental framework with which to study the basic hepatic physiology of alligators and elucidate the effects of environmental or anthropogenic stressors on the metabolic physiology of this sentinel species.

Quality Assessment by Bile Composition in Normothermic Machine Perfusion of Rat Livers

Background: The persistent challenge of organ scarcity in liver transplantation leads to an escalating dependence on organs obtained from extended criteria donors (ECD). Normothermic machine perfusion (NMP) is used for improved preservation. Due to the mimicked in vivo conditions during normothermic machine perfusion, the liver is metabolically active, which allows quality assessment during perfusion. Bile seems to be of rising interest in clinical studies, as it is easily collectible for analysis. As there are currently no data on biliary bile acids during NMP, the primary objective of this study was to use our experimental rodent NMP model to assess changes in bile composition through organ damage during perfusion to inform clinical evaluation of donor organs during NMP. Methods: Thirty livers from male Sprague-Dawley rats in five groups underwent 6 h of NMP using either erythrocyte-supplemented DMEM or Steen solution, with or without 30 min of warm ischemia time (WIT). We conducted regular measurements of AST, ALT, LDH, and urea levels in the perfusate at 3-hour intervals. Bile samples were analyzed for biliary pH, LDH, and gamma glutamyltransferase, as well as biliary bile acids via mass spectrometry and UHPLC. Results: Compared with regular livers, liver injury parameters were significantly higher in our donation after circulatory death (DCD) model. Bile production was significantly reduced in livers exposed to WIT, and the bile showed a significantly more alkaline pH. This correlated with the concentration of total bile acids, which was significantly higher in livers experiencing WIT. However, regular livers produced a higher total amount of biliary bile acids during perfusion. Taurocholic acid and its metabolites were most prominent. Secondary bile acids were significantly reduced during perfusion due to the missing enterohepatic circulation. Conclusions: WIT-induced liver injury affects bile composition within our small-animal NMP model. We hypothesize this phenomenon to be attributed to the energy-driven nature of bile secretion, potentially explaining why DCD livers produce less, yet more concentrated, bile. Our results may inform clinical studies, in which biliary bile acids might have a potential as a quantifiable viability marker in human NMP liver transplantation studies.

Development of a Large Animal Model of Ischemia-free Liver Transplantation in Pigs

Background

In organ transplantation, ischemia, and reperfusion injury (IRI) is considered as an inevitable event and the major contributor to graft failure. Ischemia-free liver transplantation (IFLT) is a novel transplant procedure that can prevent IRI and provide better transplant outcomes. However, a large animal model of IFLT has not been reported. Therefore, we develop a new, reproducible, and stable model of IFLT in pigs for investigating mechanisms of IFLT in IRI.

Methods

Ten pigs were subjected to IFLT or conventional liver transplantation (CLT). Donor livers in IFLT underwent 6-h continuous normothermic machine perfusion (NMP) throughout graft procurement, preservation, and implantation, whereas livers in CLT were subjected to 6-h cold storage before implantation. The early reperfusion injury was compared between the 2 groups.

Results

Continuous bile production, low lactate, and liver enzyme levels were observed during NMP in IFLT. All animals survived after liver transplantation. The posttransplant graft function was improved with IFLT when compared with CLT. Minimal histologic changes, fewer apoptotic hepatocytes, less sinusoidal endothelial cell injury, and proinflammatory cytokine (interleukin [IL]-1β, IL-6, and tumor necrosis factor-α) release after graft revascularization were documented in the IFLT group versus the CLT group.

Conclusions

We report that the concept of IFLT is achievable in pigs. This innovation provides a potential strategy to investigate the mechanisms of IRI and provide better transplant outcomes for clinical practice.

Assessing Liver Viability: Insights From Mitochondrial Bioenergetics in Ischemia-Reperfusion Injury

Orthotopic liver transplantation remains the definitive treatment for patients with end-stage liver disease. Unfortunately, the increasing demand for donor livers and the limited supply of viable organs have both led to a critical need for innovative strategies to expand the pool of transplantable organs. The mitochondrion, central to hepatic cellular function, plays a pivotal role in hepatic ischemic injury, with impaired mitochondrial function and oxidative stress leading to cell death. Mitochondrial protection strategies have shown promise in mitigating IRI and resuscitating marginal organs for transplant. Machine perfusion (MP) has been proven a valuable tool for reviving marginal organs with very promising results. Evaluation of liver viability during perfusion traditionally relies on parameters including lactate clearance, bile production, and transaminase levels. Nevertheless, the quest for more comprehensive and universally applicable viability markers persists. Normothermic regional perfusion has gained robust attention, offering extended recovery time for organs from donation after cardiac death donors. This approach has shown remarkable success in improving organ quality and reducing ischemic injury using the body's physiological conditions. The current challenge lies in the absence of a reliable assessment tool for predicting graft viability and post-transplant outcomes. To address this, exploring insights from mitochondrial function in the context of ischemia-reperfusion injury could offer a promising path toward better patient outcomes and graft longevity. Indeed, hypoxia-induced mitochondrial injury may serve as a surrogate marker of organ viability following oxygenated resuscitation techniques in the future.

Machine perfusion in liver transplantation

BACKGROUND

Liver transplantation is the only chance of cure for people with end-stage liver disease and some people with advanced liver cancers or acute liver failure. The increasing prevalence of these conditions drives demand and necessitates the increasing use of donated livers which have traditionally been considered suboptimal. Several novel machine perfusion preservation technologies have been developed, which attempt to ameliorate some of the deleterious effects of ischaemia reperfusion injury. Machine perfusion technology aims to improve organ quality, thereby improving outcomes in recipients of suboptimal livers when compared to traditional static cold storage (SCS; ice box).

OBJECTIVES

To evaluate the effects of different methods of machine perfusion (including hypothermic oxygenated machine perfusion (HOPE), normothermic machine perfusion (NMP), controlled oxygenated rewarming, and normothermic regional perfusion) versus each other or versus static cold storage (SCS) in people undergoing liver transplantation.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search date was 10 January 2023.

SELECTION CRITERIA

We included randomised clinical trials which compared different methods of machine perfusion, either with each other or with SCS. Studies comparing HOPE via both hepatic artery and portal vein, or via portal vein only, were grouped. The protocol detailed that we also planned to include quasi-randomised studies to assess treatment harms.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were 1. overall participant survival, 2. quality of life, and 3. serious adverse events. Secondary outcomes were 4. graft survival, 5. ischaemic biliary complications, 6. primary non-function of the graft, 7. early allograft function, 8. non-serious adverse events, 9. transplant utilisation, and 10. transaminase release during the first week post-transplant. We assessed bias using Cochrane's RoB 2 tool and used GRADE to assess certainty of evidence.

MAIN RESULTS

We included seven randomised trials (1024 transplant recipients from 1301 randomised/included livers). All trials were parallel two-group trials; four compared HOPE versus SCS, and three compared NMP versus SCS. No trials used normothermic regional perfusion. When compared with SCS, it was uncertain whether overall participant survival was improved with either HOPE (hazard ratio (HR) 0.91, 95% confidence interval (CI) 0.42 to 1.98; P = 0.81, I2 = 0%; 4 trials, 482 recipients; low-certainty evidence due to imprecision because of low number of events) or NMP (HR 1.08, 95% CI 0.31 to 3.80; P = 0.90; 1 trial, 222 recipients; very low-certainty evidence due to imprecision and risk of bias). No trials reported quality of life. When compared with SCS alone, HOPE was associated with improvement in the following clinically relevant outcomes: graft survival (HR 0.45, 95% CI 0.23 to 0.87; P = 0.02, I2 = 0%; 4 trials, 482 recipients; high-certainty evidence), serious adverse events in extended criteria DBD liver transplants (OR 0.45, 95% CI 0.22 to 0.91; P = 0.03, I2 = 0%; 2 trials, 156 participants; moderate-certainty evidence) and clinically significant ischaemic cholangiopathy in recipients of DCD livers (OR 0.31, 95% CI 0.11 to 0.92; P = 0.03; 1 trial, 156 recipients; high-certainty evidence). In contrast, NMP was not associated with improvement in any of these clinically relevant outcomes. NMP was associated with improved utilisation compared with SCS (one trial found a 50% lower rate of organ discard; P = 0.008), but the reasons underlying this effect are unknown. We identified 11 ongoing studies investigating machine perfusion technologies.

AUTHORS' CONCLUSIONS

In situations where the decision has been made to transplant a liver donated after circulatory death or donated following brain death, end-ischaemic HOPE will provide superior clinically relevant outcomes compared with SCS alone. Specifically, graft survival is improved (high-certainty evidence), serious adverse events are reduced (moderate-certainty evidence), and in donors after circulatory death, clinically relevant ischaemic biliary complications are reduced (high-certainty evidence). There is no good evidence that NMP has the same benefits over SCS in terms of these clinically relevant outcomes. NMP does appear to improve utilisation of grafts that would otherwise be discarded with SCS; however, the reasons for this, and whether this effect is specific to NMP, is not clear. Further studies into NMP viability criteria and utilisation, as well as head-to-head trials with other perfusion technologies are needed. In the setting of donation following circulatory death transplantation, further trials are needed to assess the effect of these ex situ machine perfusion methods against, or in combination with, normothermic regional perfusion.

Are slaughterhouse-obtained livers suitable for use in ex vivo perfusion research?

OBJECTIVES

The success of the ex vivo machine perfusion of pig livers used for preclinical research depends on organ quality and availability. In this study, we investigated whether livers obtained from slaughterhouses are suitable and equivalent to livers obtained from laboratory pigs.

METHODS

Livers were obtained from slaughterhouse pigs stunned by electrocution or CO2 inhalation and from laboratory pigs. For the latter group, 45 minutes of warm ischemia was mimicked for a subgroup, ensuring a valid comparison with slaughterhouse-derived livers.

RESULTS

Livers from CO2-stunned pigs showed lower indocyanine green clearance and bile production, higher blood lactate and potassium concentrations, and higher alanine aminotransferase activities than electrically stunned pigs. Furthermore, livers from electrically stunned pigs, and livers from laboratory pigs, subjected or not to warm ischemia, showed similar performance in terms of perfusion and metabolism.

CONCLUSION

For an ex vivo liver model generated using slaughterhouse pigs, electrical stunning is preferable to CO2 stunning. Livers from electrically stunned slaughterhouse pigs performed similarly to laboratory pig livers. These findings support the use of livers from electrically stunned slaughterhouse pigs, which may therefore provide an alternative to livers obtained from laboratory pigs, consistent with the principle of the 3Rs.

Donation after circulatory death: Novel strategies to improve the liver transplant outcome

In many countries, donation after circulatory death (DCD) liver grafts are used to overcome organ shortages; however, DCD grafts have been associated with an increased risk of complications and even graft loss after liver transplantation. The increased risk of complications is thought to correlate with prolonged functional donor warm ischaemia time. Stringent donor selection criteria and utilisation of in situ and ex situ organ perfusion technologies have led to improved outcomes. Additionally, the increased use of novel organ perfusion strategies has led to the possibility of reconditioning marginal DCD liver grafts. Moreover, these technologies enable the assessment of liver function before implantation, thus providing valuable data that can guide more precise graft-recipient selection. In this review, we first describe the different definitions of functional warm donor ischaemia time and its role as a determinant of outcomes after DCD liver transplantation, with a focus on the thresholds proposed for graft acceptance. Next, organ perfusion strategies, namely normothermic regional perfusion, hypothermic oxygenated perfusion, and normothermic machine perfusion are discussed. For each technique, clinical studies reporting on the transplant outcome are described, together with a discussion on the possible protective mechanisms involved and the functional criteria adopted for graft selection. Finally, we review multimodal preservation protocols involving a combination of more than one perfusion technique and potential future directions in the field.

Normothermic Machine Perfusion for Declined Livers: A Strategy to Rescue Marginal Livers for Transplantation

BACKGROUND

Organ waste is a major cause of the donor liver shortage. Roughly 67% of recovered organ donors have liver utilization annually. A new technology called normothermic machine perfusion (NMP) offers a way to recover marginal and declined livers for transplant. We report interim results of the RESTORE trial (FDA investigational drug exemption trial NCT04483102) that aims to transplant NMP-treated livers that would otherwise be discarded.

STUDY DESIGN

Declined livers were screened for NMP eligibility (eg donation after circulatory death [DCD] grafts with warm ischemic time <40 minutes, donation after brain death [DBD] grafts with cold ischemic time <8 hours). Livers meeting pre-NMP eligibility criteria received NMP using the OrganOx metra device for a minimum of 4 hours. All NMP-treated livers meeting the viability criteria were transplanted to consented recipients.

RESULTS

Over 22 months, 60 declined livers from three organ procurement organizations (OPOs; 40 DCD and 20 DBD donor livers) were offered, and 22 livers (10 DCD and 12 DBD livers) met the pre-NMP eligibility. After NMP, 16 of 22 livers passed viability testing and were transplanted into needy recipients (median Model for End-Stage Liver Disease [MELD] score of 8, range 6 to 24), resulting in a 72.7% rescue rate (50% DCD, 91.7% DBD). The rate of early allograft dysfunction was 31.3%, but there were no graft-related deaths, primary nonfunction, or instances of nonanastomotic biliary strictures.

CONCLUSIONS

Interim results of the RESTORE trial suggest that a sizable number of declined livers can be reclaimed. They are safe for transplantation and can enable lower MELD patients at high risk of morbidity and mortality to receive lifesaving grafts while offering OPOs a way to allocate more livers and reduce organ waste.

Strategies for organ preservation: Current prospective and challenges

In current therapeutic approaches, transplantation of organs provides the best available treatment for a myriad of end-stage organ failures. However, shortage of organ donors, lacunae in preservation methods, and lack of a suitable match are the major constraints in advocating this life-sustaining therapy. There has been continuous progress in the strategies for organ preservation since its inception. Current strategies for organ preservation are based on the University of Wisconsin (UW) solution using the machine perfusion technique, which allows successful preservation of intra-abdominal organs (kidney and liver) but not intra-thoracic organs (lungs and heart). However, novel concepts with a wide range of adapted preservation technologies that can increase the shelf life of retrieved organs are still under investigation. The therapeutic interventions of in vitro-cultured stem cells could provide novel strategies for replacement of nonfunctional cells of damaged organs with that of functional ones. This review describes existing strategies, highlights recent advances, discusses challenges and innovative approaches for effective organ preservation, and describes application of stem cells to restore the functional activity of damaged organs for future clinical practices.

Effect of a Combined Drug Approach on the Severity of Ischemia-Reperfusion Injury During Liver Transplant: A Randomized Clinical Trial

IMPORTANCE

In a porcine model of liver transplant, a combined drug approach that targeted the donor graft and graft recipient reduced ischemia-reperfusion injury, a major hurdle to the success of liver transplant.

OBJECTIVE

To assess the effect of a clinical form of a perioperative combined drug approach delivered immediately before implantation to the procured liver and to the liver recipient on the degree of ischemia-reperfusion injury.

DESIGN, SETTING, AND PARTICIPANTS

This unicentric, investigator-driven, open-label randomized clinical trial with 2 parallel arms was conducted in Belgium from September 2013 through February 2018, with 1-year follow-up. Adults wait-listed for a first solitary full-size liver transplant were screened for eligibility. Exclusion criteria were acute liver failure, kidney failure, contraindication to treatment, participation in another trial, refusal, technical issues, and death while awaiting transplant. Included patients were enrolled and randomized at the time of liver offer. Data were analyzed from May 20, 2019, to May 27, 2020.

INTERVENTIONS

Participants were randomized to a combined drug approach with standard of care (static cold storage) or standard of care only (control group). In the combined drug approach group, following static cold preservation, donor livers were infused with epoprostenol (ex situ, portal vein); recipients were given oral α-tocopherol and melatonin prior to anesthesia and intravenous antithrombin III, infliximab, apotransferrin, recombinant erythropoietin-β, C1-inhibitor, and glutathione during the anhepatic and reperfusion phase.

MAIN OUTCOMES AND MEASURES

The primary outcome was the posttransplant peak serum aspartate aminotransferase (AST) level within the first 72 hours. Secondary end points were the frequencies of postreperfusion syndrome, ischemia-reperfusion injury score, early allograft dysfunction, surgical complications, ischemic cholangiopathy, acute kidney injury, acute cellular rejection, and graft and patient survival.

RESULTS

Of 93 randomized patients, 21 were excluded, resulting in 72 patients (36 per study arm) in the per protocol analysis (median recipient age, 60 years [IQR, 51.7-66.2 years]; 52 [72.2%] men). Peak AST serum levels were not different in the combined drug approach and control groups (geometric mean, 1262.9 U/L [95% CI, 946.3-1685.4 U/L] vs 1451.2 U/L [95% CI, 1087.4-1936.7 U/L]; geometric mean ratio, 0.87 [95% CI, 0.58-1.31]; P = .49) (to convert AST to μkat/L, multiply by 0.0167). There also were no significant differences in the secondary end points between the groups.

CONCLUSIONS AND RELEVANCE

In this randomized clinical trial, the combined drug approach targeting the post-cold storage graft and the recipient did not decrease ischemic-reperfusion injury. The findings suggest that in addition to a downstream strategy that targets the preimplantation liver graft and the graft recipient, a clinically effective combined drug approach may need to include an upstream strategy that targets the donor graft during preservation. Dynamic preservation strategies may provide an appropriate delivery platform.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02251041.

Does machine perfusion improve immediate and short-term outcomes by enhancing graft function and recipient recovery after liver transplantation? A systematic review of the literature, meta-analysis and expert panel recommendations

BACKGROUND

Recent evidence supports the use of machine perfusion technologies (MP) for marginal liver grafts. Their effect on enhanced recovery, however, remains uncertain.

OBJECTIVES

To identify areas in which MP might contribute to an ERAS program and to provide expert panel recommendations.

DATA SOURCES

Ovid MEDLINE, Embase, Scopus, Google Scholar, and Cochrane Central.

METHODS

Systematic review and meta-analysis following PRISMA guidelines and recommendations using the GRADE approach. CRD42021237713 RESULTS: Both hypothermic (HMP) and normothermic (NMP) machine perfusion demonstrated significant benefits in preventing postreperfusion syndrome (PRS) (HMP OR .33, .15-.75 CI; NMP OR .51, .29-.90 CI) and early allograft dysfunction (EAD) (HMP OR .51, .35-.75 CI; NMP OR .66, .45-.97 CI), while shortening LOS (HMP MD -3.9; NMP MD -12.41). Only NMP showed a significant decrease in the length of ICU stay (L-ICU) (MD -7.07, -8.76; -5.38 CI), while only HMP diminishes the likelihood of major complications. Normothermic regional perfusion (NRP) reduces EAD (OR .52, .38-.70 CI) and primary nonfunction (PNF) (OR .51, .27-.98 CI) without effect on L-ICU and LOS.

CONCLUSIONS

The use of HMP decreases PRS and EAD, specifically for marginal grafts. This is supported by a shorter LOS and a lower rate of major postoperative complications (QOE; moderate | Recommendation; Strong). NMP reduces the incidence of PRS and EAD with associated shortening in L-ICU for both DBD and DCD grafts (QOE; moderate | Recommendation; High) This technology also shortens the length of hospital stay (QOE; low | Recommendation; Strong). NRP decreases the likelihood of EAD (QOE; moderate) and the risk of PNF (QOE; low) when compared to both DBD and SRR-DCD grafts preserved in SCS. (Recommendation; Strong).

Liver transplant outcomes after ex vivo machine perfusion: a meta-analysis

BACKGROUND

The pressure on liver-transplant programmes has expanded the usage of extended-criteria allografts. Machine perfusion may be better than conventional static cold storage (SCS) in alleviating ischaemia-reperfusion injury in this setting. Recipient outcomes with hypothermic or normothermic machine perfusion were assessed against SCS here.

METHODS

A search in MEDLINE, EMBASE and Scopus was conducted in February 2021. Primary studies investigating ex vivo machine perfusion were assessed for the following outcomes: morbidity, ICU and hospital stay, graft and patient survival rates and relative costs. Meta-analysis was performed to obtain pooled summary measures.

RESULTS

Thirty-four articles involving 1742 patients were included, of which 20 were used for quantitative synthesis. Odds ratios favoured hypothermic machine perfusion (over SCS) with less early allograft dysfunction, ischaemic cholangiopathy, non-anastomotic strictures and graft loss. Hypothermic machine perfusion was associated with a shorter hospital stay and normothermic machine perfusion with reduced graft injury. Two randomized clinical trials found normothermic machine perfusion reduced major complication risks.

CONCLUSION

Machine perfusion assists some outcomes with potential cost savings.

Advanced technologies for the preservation of mammalian biospecimens

The three classical core technologies for the preservation of live mammalian biospecimens-slow freezing, vitrification and hypothermic storage-limit the biomedical applications of biospecimens. In this Review, we summarize the principles and procedures of these three technologies, highlight how their limitations are being addressed via the combination of microfabrication and nanofabrication, materials science and thermal-fluid engineering and discuss the remaining challenges.

How Machine Perfusion Ameliorates Hepatic Ischaemia Reperfusion Injury

The increasing disparity between the number of patients listed for transplantation and the number of suitable organs has led to the increasing use of extended criteria donors (ECDs). ECDs are at increased risk of developing ischaemia reperfusion injury and greater risk of post-transplant complications. Ischaemia reperfusion injury is a major complication of organ transplantation defined as the inflammatory changes seen following the disruption and restoration of blood flow to an organ—it is a multifactorial process with the potential to cause both local and systemic organ failure. The utilisation of machine perfusion under normothermic (37 degrees Celsius) and hypothermic (4–10 degrees Celsius) has proven to be a significant advancement in organ preservation and restoration. One of the key benefits is its ability to optimise suboptimal organs for successful transplantation. This review is focused on examining ischaemia reperfusion injury and how machine perfusion ameliorates the graft’s response to this.

Dual versus single vessel normothermic ex vivo perfusion of rat liver grafts using metamizole for vasodilatation

Background

Normothermic ex vivo liver perfusion (NEVLP) is a promising strategy to increase the donor pool in liver transplantation. Small animal models are essential to further investigate questions regarding organ preservation and reconditioning by NEVLP. A dual vessel small animal NEVLP (dNEVLP) model was developed using metamizole as a vasodilator and compared to conventional portovenous single vessel NEVLP (sNEVLP).

Methods

Livers of male Wistar rats were perfused with erythrocyte-supplemented culture medium for six hours by either dNEVLP via hepatic artery and portal vein or portovenous sNEVLP. dNEVLP was performed either with or without metamizole treatment. Perfusion pressure and flow rates were constantly monitored. Transaminase levels were determined in the perfusate at the start and after three and six hours of perfusion. Bile secretion was monitored and bile LDH and GGT levels were measured hourly. Histopathological analysis was performed using liver and bile duct tissue samples after perfusion.

Results

Hepatic artery pressure was significantly lower in dNEVLP with metamizole administration. Compared to sNEVLP, dNEVLP with metamizole treatment showed higher bile production, lower levels of transaminases during and after perfusion as well as significantly lower necrosis in liver and bile duct tissue. Biochemical markers of bile duct injury showed the same trend.

Conclusion

Our miniaturized dNEVLP system enables normothermic dual vessel rat liver perfusion. The administration of metamizole effectively ameliorates arterial vasospasm allowing for six hours of dNEVLP, with superior outcome compared to sNEVLP.

Normothermic Machine Perfusion (NMP) of the Liver as a Platform for Therapeutic Interventions during Ex-Vivo Liver Preservation: A Review

Liver transplantation is increasingly dependent on the use of extended criteria donors (ECD) to increase the organ donor pool and address rising demand. This has necessitated the adoption of innovative technologies and strategies to protect these higher-risk grafts from the deleterious effects of traditional preservation and ischaemia reperfusion injury (IRI). The advent of normothermic machine perfusion (NMP) and rapid growth in the clinical adoption of this technology has accelerated efforts to utilise NMP as a platform for therapeutic intervention to optimise donor livers. In this review we will explore the emerging preclinical data related to ameliorating the effects of IRI, protecting the microcirculation and reducing the immunogenicity of donor organs during NMP. Exploiting the window of opportunity afforded by NMP, whereby the liver can be continuously supported and functionally assessed while therapies are directly delivered during the preservation period, has clear logistical and theoretical advantages over current preservation methods. The clinical translation of many of the therapeutic agents and strategies we will describe is becoming more feasible with widespread adaptation of NMP devices and rapid advances in molecular biology and gene therapy, which have substantially improved the performance of these agents. The delivery of novel therapeutics during NMP represents one of the new frontiers in transplantation research and offers real potential for successfully tackling fundamental challenges in transplantation such as IRI.

Present and Future Perspectives of Using Human-Induced Pluripotent Stem Cells and Organoid Against Liver Failure

Organ failure manifests severe symptoms affecting the whole body that may cause death. However, the number of organ donors is not enough for patients requiring transplantation worldwide. Illegal transplantation is also sometimes conducted. To help address this concern, primary hepatocytes are clinically transplanted in the liver. However, donor shortage and host rejection via instant blood-mediated inflammatory reactions are worrisome. Induced pluripotent stem cell-derived hepatocyte-like cells have been developed as an alternative treatment. Recently, organoid technology has been developed to investigate the pathology and mechanism of organoids in cultures. Organoids can be transplanted with vascularization and connected to host blood vessels, and functionally mature better in vivo than in vitro. Hepatic organoids improve pathology in liver disease models. In this review, we introduce induced pluripotent stem cell- and organoid-based therapies against liver diseases considering present and future perspectives.

Transient Cold Storage Prior to Normothermic Liver Perfusion May Facilitate Adoption of a Novel Technology

Clinical adoption of normothermic machine perfusion (NMP) may be facilitated by simplifying logistics and reducing costs. This can be achieved by cold storage of livers for transportation to recipient centers before commencing NMP. The purpose of this study was to assess the safety and feasibility of post-static cold storage normothermic machine perfusion (pSCS-NMP) in liver transplantation. In this multicenter prospective study, 31 livers were transplanted. The primary endpoint was 30-day graft survival. Secondary endpoints included the following: peak posttransplant aspartate aminotransferase (AST), early allograft dysfunction (EAD), postreperfusion syndrome (PRS), adverse events, critical care and hospital stay, biliary complications, and 12-month graft survival. The 30-day graft survival rate was 94%. Livers were preserved for a total of 14 hours 10 minutes ± 4 hours 46 minutes, which included 6 hours 1 minute ± 1 hour 19 minutes of static cold storage before 8 hours 24 minutes ± 4 hours 4 minutes of NMP. Median peak serum AST in the first 7 days postoperatively was 457 U/L (92-8669 U/L), and 4 (13%) patients developed EAD. PRS was observed in 3 (10%) livers. The median duration of initial critical care stay was 3 days (1-20 days), and median hospital stay was 13 days (7-31 days). There were 7 (23%) patients who developed complications of grade 3b severity or above, and 2 (6%) patients developed biliary complications: 1 bile leak and 1 anastomotic stricture with no cases of ischemic cholangiopathy. The 12-month overall graft survival rate (including death with a functioning graft) was 84%. In conclusion, this study demonstrates that pSCS-NMP was feasible and safe, which may facilitate clinical adoption.

The Effect of Preservation Temperature on Liver, Kidney, and Pancreas Tissue ATP in Animal and Preclinical Human Models

The recent advances in machine perfusion (MP) technology involve settings ranging between hypothermic, subnormothermic, and normothermic temperatures. Tissue level adenosine triphosphate (ATP) is a long-established marker of viability and functionality and is universal for all organs. In the midst of a growing number of complex clinical parameters for the quality assessment of graft prior to transplantation, a revisit of ATP may shed light on the underlying reconditioning mechanisms of different perfusion temperatures in the form of restoration of metabolic and energy status. This article aims to review and critically analyse animal and preclinical human studies (discarded grafts) during MP of three abdominal organs (liver, kidney, and pancreas) in which ATP was a primary endpoint. A selective review of recent novel reconditioning approaches relevant to mitigation of graft ischaemia-reperfusion injury via MP and for different perfusion temperatures was also conducted. With a current reiterated interest for oxygenation during MP, a re-introduction of tissue ATP levels may be valuable for graft viability assessment prior to transplantation. Further studies may help delineate the benefits of selective perfusion temperatures on organs viability.

Impact of Machine Perfusion on Sinusoid Microcirculation of Liver Graft Donated After Cardiac Death

BACKGROUND

The present study examined the impact of oxygenated machine perfusion on preservation of liver grafts donated after cardiac death by measuring sinusoidal endothelial injury and microcirculatory disturbances.

MATERIALS AND METHODS

Fifteen porcine livers were retrieved 60 min after warm ischemia and allocated into three groups as follows: (1) CS group: static cold storage, (2) HMP group: oxygenated hypothermic perfusion preservation, (3) SNMP group: oxygenated subnormothermic perfusion preservation. The liver grafts donated after cardiac death were preserved for 4 h in different treatment conditions mentioned previously, then subject to ex vivo reperfusion for 2 h using diluted allogeneic blood. The hemodynamic parameters, liver function tests, tissue adenosine triphosphate (ATP) levels, and immunohistochemical findings were investigated.

RESULTS

The number of sinusoidal epithelial cells and trabecular structures were maintained after 4 h of preservation in the CS, HMP, and SNMP group. Liver tissue ATP levels after 4 h of preservation in the HMP and SNMP groups were significantly higher compared with that in the CS group. The sinusoidal epithelial cells were significantly exfoliated to a more severe extent in the CS group than in the HMP and SNMP groups. Intrasinusoidal platelet aggregation occurred more frequently in the CS group than in the HMP and SNMP groups.

CONCLUSIONS

The results indicated that oxygenated machine perfusion preservation was important to prevent the depletion of tissue ATP and maintain sinusoidal homeostasis regardless of the perfusate temperature. Our findings suggest oxygenated machine perfusion preservation as an effective alternative to static cold storage.

Avoiding initial hypothermia does not improve liver graft quality in a porcine donation after circulatory death (DCD) model of normothermic perfusion

Background

Normothermic machine perfusion (NMP) of liver grafts donated after circulatory death (DCD) has shown promise in large animal and clinical trials. Following procurement, initial flush with a cold preservation solution is the standard of care. There is concern that initial cooling followed by warming may exacerbate liver injury, and the optimal initial flush temperature has yet to be identified. We hypothesize that avoidance of the initial cold flush will yield better quality liver grafts.

Methods

Twenty-four anaesthetized pigs were withdrawn from mechanical ventilation and allowed to arrest. After 60-minutes of warm ischemia to simulate a DCD procurement, livers were flushed with histidine-tryptophan-ketoglutarate (HTK) at 4°C, 25°C or 35°C (n = 4 per group). For comparison, an adenosine-lidocaine crystalloid solution (AD), shown to have benefit at warm temperatures in heart perfusions, was also used (n = 4 per group). During 12-hours of NMP, adenosine triphosphate (ATP), lactate, transaminase levels, and histological injury were determined. Bile production and hemodynamics were monitored continuously.

Results

ATP levels recovered substantially following 1-hour of NMP reaching pre-ischemic levels by the end of NMP with no difference between groups. There was no difference in peak aspartate aminotransferase (AST) or in lactate dehydrogenase (LDH). Portal vein resistance was lowest in the 4°C group reaching significance after 2 hours (0.13 CI -0.01,0.277, p = 0.025). Lactate levels recovered promptly with no difference between groups. Comparison to AD groups showed no statistical difference in the abovementioned parameters. On electron microscopy the HTK4°C group had the least edema with mean cell thickness of 2.92μm (p = 0.41) while also having the least sinusoidal dilatation with a mean diameter of 5.36μm (p = 0.04). For AD, the 25°C group had the lowest mean cell thickness at 3.14μm (p = 0.09).

Conclusions

Avoidance of the initial cold flush failed to demonstrate added benefit over standard 4°C HTK in this DCD model of liver perfusion.

Bioengineering approaches to organ preservation ex vivo

IMPACT STATEMENT

Over the past several decades, ex vivo perfusion has emerged as a promising technology for the assessment, preservation, and recovery of donor organs. Many exciting pre-clinical findings have now been translated to clinical use, and successful transplantation following ex vivo perfusion has been achieved for heart, lung, and liver. While machine perfusion provides distinct advantages over traditional cold preservation, many challenges remain, including that of long-term (multi-day) ex vivo support. Here, we provide an overview of the current status of ex vivo machine perfusion in the pre-clinical and clinical setting and share our perspective on the future direction of the field.

First report of successful transplantation of a pediatric donor liver graft after hypothermic machine perfusion

One of the main limiting factors in pediatric liver transplantation is donor availability. For adults, DCD liver grafts are increasingly used to expand the donor pool. To improve outcome after DCD liver transplantation, ex situ machine perfusion is used as an alternative organ preservation strategy, with the supplemental value of providing oxygen to the graft during preservation. We here report the first successful transplantation of a pediatric DCD liver graft after hypothermic oxygenated machine perfusion. The full-size liver graft was derived from a 13-year-old, female DCD donor and was end-ischemic pretreated with dual hypothermic oxygenated machine perfusion. Arterial and portal pressures were set at 18 and 4 mm Hg, slightly lower than protocolized settings for adult livers. During 2 hours of machine perfusion, portal and arterial flows increased from 100 to 210 mL/min and 30 to 63 mL/min, respectively. The pretreated liver graft was implanted in a 16-year-old girl with progressive familial intrahepatic cholestasis type 2. Postoperative AST, ALT, and prothrombin time normalized within a week. The recipient quickly recovered and was discharged from the hospital after 18 days. One year after transplantation, she is in excellent condition with a completely normal liver function and histology. This case is the first report of successful transplantation of a pediatric DCD liver graft after hypothermic oxygenated machine perfusion and illustrates the potential role of ex situ machine perfusion in expanding the donor pool and improving outcome after pediatric liver transplantation.

Clearance of transaminases during normothermic ex situ liver perfusion

Background

One of the most promising applications of liver normothermic machine perfusion (NMP) is the potential to directly assess graft viability and injury. In most NMP studies, perfusate transaminases are utilized as markers of graft injury. Our aim was to further elucidate the metabolism of transaminases by healthy porcine livers during NMP, specifically whether such livers could clear circuit perfusate transaminases.

Methods

A highly concentrated transaminase solution was prepared from homogenized liver, with an aspartate aminotransferase (AST) level of 107,427 U/L. Three livers in the treatment group were compared to three controls, during 48 hours of NMP. In the treatment group, the circuit perfusate was injected with the transaminase solution to artificially raise the AST level to a target of 7,500 U/L. Perfusate samples were taken at two-hour intervals and analyzed for biochemistry until NMP end. Graft oxygen consumption and vascular parameters were monitored.

Results

Compared to controls, treated perfusions demonstrated abrupt elevations in transaminase levels (p>0.0001) and lactate dehydrogenase (LDH) (p>0.0001), which decreased over time, but never to control baseline. Liver function, as demonstrated by lactate clearance and oxygen consumption was not different between groups. The treatment group demonstrated a higher portal vein resistance (p = 0.0003), however hepatic artery resistance was similar. Treated livers had higher bile production overall (p<0.0001).

Conclusions

Addition of high levels of transaminases and LDH to a healthy porcine liver during ex situ perfusion results in progressive clearance of these enzymes, suggesting preserved liver metabolism. Such tolerance tests may provide valuable indicators of prospective graft function.

Liver graft preservation methods during cold ischemia phase and normothermic machine perfusion

The growing demand for donor organs requires measures to expand donor pool. Those include extended criteria donors, such as elderly people, steatotic livers, donation after cardiac death, etc. Static cold storage to reduce metabolic requirements developed by Collins in late 1960s is the mainstay and the golden standard for donated organ protection. Hypothermic machine perfusion provides dynamic organ preservation at 4°C with protracted infusion of metabolic substrates to the graft during the ex vivo period. It has been used instead of static cold storage or after it as short perfusion in transplant center. Normothermic machine perfusion (NMP) delivers oxygen, and nutrition at physiological temperature mimicking regular environment in order to support cellular function. This would minimize effects of ischemia/reperfusion injury. Potentially, NMP may help to estimate graft functionality before implantation into a recipient. Clinical studies demonstrated at least its non-inferiority or better outcomes vs static cold storage. Regular grafts donated after brain death could be safely preserved with convenient static cold storage. Except for prolonged ischemia time where hypothermic machine perfusion started in transplant center could be estimated to provide possible positive reconditioning effect. Use of hypothermic machine perfusion in regular donation instead of static cold storage or in extended criteria donors requires further investigation. Multicenter randomized clinical trial supposed to be completed in December 2021. Extended criteria donors need additional measures for graft storage and assessment until its implantation. NMP is actively evaluating promising method for this purpose. Future studies are necessary for precise estimation and confirmation to issue clinical practice recommendations.

Determination of Minimal Hemoglobin Level Necessary for Normothermic Porcine Ex Situ Liver Perfusion

BACKGROUND

In current studies of ex situ liver perfusion there exists considerable variability in perfusate composition, including the type of oxygen carrier. Herein, we aim to clarify the minimal hemoglobin level necessary during normothermic porcine ex situ liver perfusion.

METHODS

Livers procured from 35 to 45 kg domestic pigs were connected to our experimental ex situ circuit (n = 10). In the treatment group, perfusate was sequentially diluted hourly to predetermined hemoglobin levels. At the end of each hemoglobin dilution, perfusate samples were analyzed for liver transaminases, lactate dehydrogenase (LD), total bilirubin, and lactate levels. Liver oxygen consumption was measured. In the control group, livers were perfused continually for a duration of 24 hours at target hemoglobin levels of 30 and 20 g/L.

RESULTS

Rising liver transaminases, significantly higher lactate (P < 0.001), and LD levels (P < 0.001) were noted at lower perfusate hemoglobin levels in the treatment group. Liver oxygen utilization (P < 0.001) and hepatic artery oxygen delivery (P < 0.001) were significantly lower at lower hemoglobin levels, whereas liver vessel resistance remained relatively constant. Histology demonstrated increasing parenchymal damage at lower hemoglobin levels. In control livers, higher perfusate transaminases, higher lactate, and LD levels were noted at a perfusion hemoglobin level of 20 g/L.

CONCLUSIONS

Ex situ liver function decompensated during perfusion between a mean hemoglobin level of 30 to 20 g/L, as evidenced by notably rising lactate and LD levels. This study demonstrates optimal hemoglobin concentration during normothermic ex situ liver perfusion to ensure a fully metabolically functioning graft.

Study protocol for a multicenter randomized controlled trial to compare the efficacy of end-ischemic dual hypothermic oxygenated machine perfusion with static cold storage in preventing non-anastomotic biliary strictures after transplantation of liver grafts donated after circulatory death: DHOPE-DCD trial

BACKGROUND

The major concern in liver transplantation of grafts from donation after circulatory death (DCD) donors remains the high incidence of non-anastomotic biliary strictures (NAS). Machine perfusion has been proposed as an alternative strategy for organ preservation which reduces ischemia-reperfusion injury (IRI). Experimental studies have shown that dual hypothermic oxygenated machine perfusion (DHOPE) is associated with less IRI, improved hepatocellular function, and better preserved mitochondrial and endothelial function compared to conventional static cold storage (SCS). Moreover, DHOPE was safely applied with promising results in a recently performed phase-1 study. The aim of the current study is to determine the efficacy of DHOPE in reducing the incidence of NAS after DCD liver transplantation.

METHODS

This is an international multicenter randomized controlled trial. Adult patients (≥18 yrs. old) undergoing transplantation of a DCD donor liver (Maastricht category III) will be randomized between the intervention and control group. In the intervention group, livers will be subjected to two hours of end-ischemic DHOPE after SCS and before implantation. In the control group, livers will be subjected to care as usual with conventional SCS only. Primary outcome is the incidence of symptomatic NAS diagnosed by a blinded adjudication committee. In all patients, magnetic resonance cholangiography will be obtained at six months after transplantation.

DISCUSSION

DHOPE is associated with reduced IRI of the bile ducts. Whether reduced IRI of the bile ducts leads to lower incidence of NAS after DCD liver transplantation can only be examined in a randomized controlled trial.

TRIAL REGISTRATION

The trial was registered in Clinicaltrials.gov in September 2015 with the identifier NCT02584283 .

Hepatic ischemia-reperfusion injury in liver transplant setting: mechanisms and protective strategies

Hepatic ischemia-reperfusion injury is a major cause of liver transplant failure, and is of increasing significance due to increased use of expanded criteria livers for transplantation. This review summarizes the mechanisms and protective strategies for hepatic ischemia-reperfusion injury in the context of liver transplantation. Pharmacological therapies, the use of pre-and post-conditioning and machine perfusion are discussed as protective strategies. The use of machine perfusion offers significant potential in the reconditioning of liver grafts and the prevention of hepatic ischemia-reperfusion injury, and is an exciting and active area of research, which needs more study clinically.

Prediction of rat liver transplantation outcomes using energy metabolites measured by microdialysis

BACKGROUND

Warm ischemia jeopardizes graft quality and recipient survival in donation after cardiac death (DCD) transplantation. Currently, there is no system to objectively evaluate the liver quality from DCD. The present study tried to use energy metabolites to evaluate the donor liver quality.

METHODS

We divided 195 Sprague-Dawley rats into five groups: the control (n = 39), warm ischemic time (WIT) 15 min (n = 39), WIT 30 min (n = 39), WIT 45 min (n = 39), and WIT 60 min (n = 39) groups. Three rats from each group were randomly selected for pretransplant histologic evaluation of warm ischemia-related damage. The remaining 36 rats were randomly divided into donors and recipients of 18 liver transplantations, and were subjected to postoperative liver function and survival analyses. Between cardiac arrest and cold storage, liver energy metabolites including glucose, lactate, pyruvate, and glycerol were measured by microdialysis. The lactate to pyruvate ratio (LPR) was calculated.

RESULTS

The changes in preoperative pathology with warm ischemia were inconspicuous, but the trends in postoperative pathology and aminotransferase levels were consistent with preoperative energy metabolite measurements. The 30-day survival rates of the control and WIT 15, 30, 45, and 60 min groups were 100%, 81.82%, 76.92%, 58.33%, and 25.00%, respectively. The areas under the receiver operating characteristic curves of glucose, lactate, glycerol, and LPR were 0.87, 0.88, 0.88, and 0.92, respectively.

CONCLUSION

Glucose, lactate, glycerol, and LPR are predictors of graft quality and survival outcomes in DCD transplantation.

Perfusion settings and additives in liver normothermic machine perfusion with red blood cells as oxygen carrier. A systematic review of human and porcine perfusion protocols

Liver machine perfusion (MP) at normothermic temperature (NMP) is a promising way to preserve and evaluate extended criteria donor livers. Currently, no consensus exists in methodology and perfusion protocols. Here, the authors performed a systematic literature search to identify human and porcine studies reporting on liver NMP with red blood cells. A qualitative synthesis was performed concerning technical aspects of MP, fluid composition, gas supply, and liver positioning. Thirty-seven publications including 11 human and 26 porcine studies were considered for qualitative synthesis. Control mode, pressure, flow, perfusate additives, and targeted blood gas parameters varied across human as well as porcine studies. For future analyses, it is advisable to report flow adjusted to liver weight and exact pressure parameters including mean, systolic, and diastolic pressure. Parenteral nutrition and insulin addition was common. Parenteral nutrition included amino acids and/or glucose without lipids. Taurocholic acid derivatives were used as bile flow promoters. However, short-term human NMP without taurocholic acid derivatives seems to be possible. This finding is relevant due to the lack of clinical grade bile salts. Near physiological oxygen tension in the perfusate is doable by adjusting gas flows, while blood gas parameters regulation needs more detailed description.

The Role of Normothermic Perfusion in Liver Transplantation (TRaNsIT Study): A Systematic Review of Preliminary Studies

INTRODUCTION

The success of liver transplantation has been limited by the unavailability of suitable donor livers. The current organ preservation technique, i.e., static cold storage (SCS), is not suitable for marginal organs. Alternatively, normothermic machine perfusion (NMP) promises to recreate the physiological environment and hence holds promise for the better organ preservation. The objective of this systematic review is to provide an overview of the safety, benefits, and insight into the other potential useful parameters of NMP in the liver preservation.

MATERIAL AND METHODS

We searched the current literature following registration in the International Prospective Register of Systematic Reviews (PROSPERO) with registration number CRD42018086034 for prospective trials comparing the role of NMP device to SCS in liver transplant by searching the PubMed, EMBASE, Cochrane, BIOSIS, Crossref, and Scopus databases and clinical trial registry.

RESULTS

The literature search identified five prospective clinical trials (four being early phase single institutional and single randomized multi-institutional) comparing 187 donor livers on NMP device to 273 donor livers on SCS. The primary outcome of interest was to assess the safety and graft survival at day 30 after transplant following NMP of the donor liver. Secondary outcomes included were early allograft dysfunction (EAD) in the first seven days; serum measures of liver functions as bilirubin, aspartate aminotransferase (AST), alanine amino transferase (ALT), alkaline phosphatase (ALP), and international normalized ratio (INR) on days 1-7; major complications as defined by a Clavien-Dindo score ≥ 3; and patient and graft survival and biliary complications at six months. The peaked median AST level between days 1 and 7 in the five trials was 417-1252 U/L (range 84-15009 U/L) while on NMP and 839-1474 U/L (range 153-8786 U/L) in SCS group. The median bilirubin level on day 7 ranged within 25-79 µmol/L (range 8-344 µmol/l) and 30-47.53 µmol/l (range 9-340 µmol/l) in NMP and SCS groups, respectively. A single case of PNF was reported in NMP group in the randomized trial while none of the other preliminary studies reported any in either group. There was intertrial variability in EAD which ranged within 15-56% in NMP group while being within 23-37% in SCS group. Biliary complications observed in NMP group ranged from 0 to 20%. Single device malfunction was reported in randomized controlled trial leading to renouncement of transplant while none of the other trials reported any machine failure, although two user related device errors inadvertent were reported.

CONCLUSION

This review outlines that NMP not only demonstrated safety and efficacy but also provided the favourable environment of organ preservation, repair, and viability assessment to donor liver prior to the transplantation with low rate of posttransplantation complication as PNF, EAD, and biliary complication; however further studies are needed to broaden our horizon.

Ex situ liver perfusion: Organ preservation into the future

In recent years, remarkable progress has occurred in the development of technologies to support ex situ liver perfusion. Building upon extensive preclinical studies in large animal models, pilot and randomized clinical trials have been initiated, and preliminary outcomes suggest more optimal protection of both standard and extended criteria liver grafts. There currently exists an incredible opportunity and need to further refine this technology, determine appropriate viability measures to predict usable liver grafts, and to explore potent protective additive strategies to further optimize the quality of extended criteria organs. These findings will have major bearing in expanding the limited liver donor pool, and may save lives where up to a quarter of listed patients die on wait-lists. Herein we offer a brief overview of the history and current status of ex situ liver perfusion, and discuss future directions that will likely have major impact on the practice of clinical liver transplantation.

Normothermic Machine Preservation of the Liver: State of the Art

Purpose of Review

This review aims to introduce the concept of normothermic machine perfusion (NMP) and its role in liver transplantation. By discussing results from recent clinical studies and highlighting the potential opportunities provided by this technology, we aim to provide a greater insight into NMP and the role it can play to enhance liver transplantation.

Recent Findings

NMP has recently been shown to be both safe and feasible in liver transplantation and has also demonstrated its superiority to traditional cold storage in terms of early biochemical liver function. Through the ability to perform a viability assessment during preservation and extend preservation times, it is likely that an increase in organ utilisation will follow. NMP may facilitate the enhanced preservation with improved outcomes from donors after cardiac death and steatotic livers. Furthermore, it provides the exciting potential for liver-directed therapeutic interventions.

Summary

Evidence to date suggests that NMP facilitates the enhanced preservation of liver grafts with improved early post-transplant outcomes. The key role for this technology is to increase the number and quality of liver grafts available for transplantation and to reduce waiting list deaths.

Lipid metabolism and functional assessment of discarded human livers with steatosis undergoing 24 hours of normothermic machine perfusion

Normothermic machine perfusion (NMP) is an emerging technology to preserve liver allografts more effectively than cold storage (CS). However, little is known about the effect of NMP on steatosis and the markers indicative of hepatic quality during NMP. To address these points, we perfused 10 discarded human livers with oxygenated NMP for 24 hours after 4-6 hours of CS. All livers had a variable degree of steatosis at baseline. The perfusate consisted of packed red blood cells and fresh frozen plasma. Perfusate analysis showed an increase in triglyceride levels from the 1st hour (median, 127 mg/dL; interquartile range [IQR], 95-149 mg/dL) to 24th hour of perfusion (median, 203 mg/dL; IQR, 171-304 mg/dL; P = 0.004), but tissue steatosis did not decrease. Five livers produced a significant amount of bile (≥5 mL/hour) consistently throughout 24 hours of NMP. Lactate in the perfusate cleared to <3 mmol/L in most livers within 4-8 hours of NMP, which was independent of bile production rate. This is the first study to characterize the lipid profile and functional assessment of discarded human livers at 24 hours of NMP. Liver Transplantation 24 233-245 2018 AASLD.

Combined liver-kidney perfusion enhances protective effects of normothermic perfusion on liver grafts from donation after cardiac death

It has been shown that combined liver-kidney normothermic machine perfusion (NMP) is able to better maintain the circuit's biochemical milieu. Nevertheless, whether the combined perfusion is superior to liver perfusion alone in protecting livers from donation after circulatory death (DCD) is unclear. We aimed to test the hypothesis and explored the mechanisms. Livers from 15 DCD pig donors were subjected to either static cold storage (group A), liver-alone NMP (group B), or combined liver-kidney NMP (group C). Livers were preserved for 6 hours and reperfused ex vivo for 2 hours to simulate transplantation or were transplanted in situ. During perfusion, group C showed an improved acid-base and biochemical environment in the circuit over group B. After reperfusion, the architecture of the liver grafts was best preserved in group C, followed by group B, then group A, as shown by the histology and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining of both hepatocytes and biliary epithelium. Ki-67 staining showed substantial hepatocyte proliferation and biliary epithelial regeneration after perfusion in group B and group C. Group C produced more bile in the reperfusion phase than those in group A and group B, with more physiological bile composition and less severe biliary epithelium injury. Von Willebrand factor-positive endothelial cells and E-selectin expression decreased in both group B and group C. Combined liver-kidney NMP not only produced more adenosine triphosphate, protected the nitric oxide signaling pathway, but also diminished oxidative stress (high mobility group box-1 protein and 8-hydroxy-2-deoxy guanosine levels) and inflammatory cytokine (IL6 and IL8) release when compared with liver-alone NMP and CS. In addition, the 7-day survival rate of liver transplant recipients was higher in group C than that in groups A and B. In conclusion, combined liver-kidney NMP can better protect DCD livers from warm ischemia and reperfusion injury probably by maintaining the stability of the internal environment and by abolishing oxidative stress injury. Liver Transplantation 24 67-79 2018 AASLD.

Mechanisms of autophagy activation in endothelial cell and their targeting during normothermic machine liver perfusion

Ischaemia-reperfusion injury (IRI) is the leading cause of injury seen in the liver following transplantation. IRI also causes injury following liver surgery and haemodynamic shock. The first cells within the liver to be injured by IRI are the liver sinusoidal endothelial cells (LSEC). Recent evidence suggests that LSEC co-ordinate and regulates the livers response to a variety of injuries. It is becoming increasingly apparent that the cyto-protective cellular process of autophagy is a key regulator of IRI. In particular LSEC autophagy may be an essential gatekeeper to the development of IRI. The recent availability of liver perfusion devices has allowed for the therapeutic targeting of autophagy to reduce IRI. In particular normothermic machine liver perfusion (NMP-L) allow the delivery of pharmacological agents to donor livers whilst maintaining physiological temperature and hepatic flow rates. In this review we summarise the current understanding of endothelial autophagy and how this may be manipulated during NMP-L to reduce liver IRI.

The Implications of the Shift Toward Donation After Circulatory Death in Australia

BACKGROUND

In recent years, an increasing number of donor livers are being declined for transplantation in Australia. The aim of this study was to evaluate the impact of donation after cardiac death and other factors associated with organ quality on liver utilization rates in Australia.

METHODS

Data on organ donors who donated at least 1 organ between 2005 and 2014 were obtained from the Australia and New Zealand organ donation registry. Temporal changes in donor characteristics were assessed and a logistical regression analysis was performed to evaluate their association with liver nonuse.

RESULTS

The number of organ donors increased from 175 in 2005 to 344 in 2014, with overall 19% being donation after cardiac death donors (P < 0.001). The percentage of livers deemed unsuitable for transplantation increased from 24% in 2005 to 41% in 2014 (P < 0.001). Donation after cardiac death was identified as the most important risk factor for nonuse with an odds ratio of 25.88 (95% confidence interval, 18.84-35.56), P < 0.001) followed by donor age, obesity, and diabetes.

DISCUSSION

This study shows that livers donated after circulatory death are an underused resource in Australia. Better use of these currently available organs would be a highly cost-effective way of reducing waiting list mortality in liver transplantation.

Perfusion machines and hepatocellular carcinoma: a good match between a marginal organ and an advanced disease?

Hepatocellular carcinoma (HCC) accounts for 90% of primary liver cancers, is the second leading cause of cancer-related deaths and the leading cause of death in patients with cirrhosis. Liver transplantation (LT) represents the ideal treatment for selected patients as it removes both the tumor and the underlying cirrhotic liver with 5-year survival rates higher than 70%. Unfortunately, due to tumor characteristics, patient co-morbidities or shortage of organs available for transplant, only 20% of patients can undergo curative treatment. Ex situ machine perfusion (MP) is a technology recently introduced that might potentially improve organ preservation, allow graft assessment and increase the pool of available organs. The purpose of this review is to provide an update on the current role of ex situ liver MP in liver transplantation for HCC patients.

Liver ex situ machine perfusion preservation: A review of the methodology and results of large animal studies and clinical trials

Ex vivo machine perfusion (MP) is a promising way to better preserve livers prior to transplantation. Currently, no methodology has a verified benefit over simple cold storage. Before becoming clinically feasible, MP requires validation in models that reliably predict human performance. Such a model has been found in porcine liver, whose physiological, anatomical, and immunological characteristics closely resemble the human liver. Since the 1930s, researchers have explored MP as preservation, but only recently have clinical trials been performed. Making this technology clinically available holds the promise of expanding the donor pool through more effective preservation of extended criteria donor (ECD) livers. MP promises to decrease delayed graft function, primary nonfunction, and biliary strictures, which are all common failure modes of transplanted ECD livers. Although hypothermic machine perfusion (HMP) has become the standard for kidney ex vivo preservation, the precise settings and clinical role for liver MP have not yet been established. In research, there are 2 schools of thought: normothermic machine perfusion, closely mimicking physiologic conditions, and HMP, to maximize preservation. Here, we review the literature for porcine ex vivo MP, with an aim to summarize perfusion settings and outcomes pertinent to the clinical establishment of MP. Liver Transplantation 23 679-695 2017 AASLD.