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

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

Matched pair analysis of the effect of longer hypothermic machine perfusion time on kidney transplant outcomes

BACKGROUND Hypothermic machine perfusion(HMP)has demonstrated benefits in terms of early kidney transplant function compared to static cold storage.While longer preservation times have shown detrimental effects,a previous paired study indicated that longer pump times(the second kidney in a pair)might lead to improved outcomes.AIM To revisit the prior paired study's somewhat unexpected results by reviewing our program's experience.METHODS A total of 61 pairs of transplant recipients who received kidneys from the same donor(2012-2021)were analyzed.Patients were divided into two groups depending on whether they were transplanted first(K1)or second(K2).Therefore,the patients in each pair had identical donor characteristics,except for time on the pump.Statistical analyses included Kaplan-Meyer analysis and paired tests,including McNemar's test,student's paired t-test,or Wilcoxon's test,as appropriate.RESULTS The two groups of recipients had similar demographics(age,body mass index,diabetes,time on dialysis,sensit-ization and retransplants).Cold ischemic times for K1 and K2 were 8.9(95%CI:7.9,9.8)and 14.7 hours(13.7,15.8)(P<0.0001),respectively.Overall,K2 had a higher rate of freedom from biopsy-proven acute rejection at 1 year(P=0.015).Delayed graft function was less common in K2,12/61(20%)than in K1,20/61(33%)(P=0.046).Finally,K2 showed a higher graft survival than K1(P=0.023).CONCLUSION Our results agree with a previous study that suggested possible advantages to longer pump times.Both studies should encourage further research into HMP's potential anti-inflammatory effect.

Machine perfusion and the prevention of ischemic type biliary lesions following liver transplant:What is the evidence?

The widespread uptake of different machine perfusion(MP)strategies for liver transplant has been driven by an effort to minimize graft injury.Damage to the cholangiocytes during the liver donation,preservation,or early posttransplant period may result in stricturing of the biliary tree and inadequate biliary drainage.This problem continues to trouble clinicians,and may have catastrophic consequences for the graft and patient.Ischemic injury,as a result of compromised hepatic artery flow,is a well-known cause of biliary strictures,sepsis,and graft failure.However,very similar lesions can appear with a patent hepatic artery and these are known as ischemic type biliary lesions(ITBL)that are attributed to microcirculatory dysfunction rather than main hepatic arterial compromise.Both the warm and cold ischemic period duration appear to influence the onset of ITBL.All of the commonly used MP techniques deliver oxygen to the graft cells,and therefore may minimize the cholangiocyte injury and subsequently reduce the incidence of ITBL.As clinical experience and published evidence grows for these modalities,the impact they have on ITBL rates is important to consider.In this review,the evidence for the three commonly used MP strategies(abdominal normothermic regional perfusion[A-NRP],hypothermic oxygenated perfusion[HOPE],and normothermic machine perfusion[NMP])for ITBL prevention has been critically reviewed.Inconsistencies with ITBL definitions used in trials,coupled with variations in techniques of MP,make interpretation challenging.Overall,the evidence suggests that both HOPE and A-NRP prevent ITBL in donated after circulatory death grafts compared to cold storage.The evidence for ITBL prevention in donor after brain death grafts with any MP technique is weak.

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 1960 s 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.

Current and future perspectives on acute-on-chronic liver failure: Challenges of transplantation, machine perfusion, and beyond

Acute-on-chronic liver failure(ACLF)is a syndrome that occurs in patients with chronic liver disease and is characterized by acute decompensation,organ failure and high short-term mortality.Partially due to the lack of universal diagnostic criteria,the actual ACLF prevalence remains unclear;nevertheless,it is expected to be a highly prevalent condition worldwide.Earlier transplantation is an effective protective measure for selected ACLF patients.Besides liver transplantation,diagnosing and treating precipitant events and providing supportive treatment for organ failures are currently the cornerstone of ACLF therapy.Although new clinical specific therapies have been researched,more studies are necessary to assess safety and efficacy.Therefore,future ACLF management strategies must consider measures to improve access to liver transplantation because the time window for this life-saving therapy is frequently narrow.Thus,an urgent and global discussion about allocation and prioritization for transplantation in critically ill ACLF patients is needed because there is evidence suggesting that the current model may not portray their waitlist mortality.In addition,while donor organ quality is meant to be a prognostic factor in the ACLF setting,recent evidence suggests that machine perfusion of the liver may be a safe tool to improve the donor organ pool and expedite liver transplantation in this scenario.

Machine perfusion for liver transplantation:A concise review of clinical trials

Background: With the increased use of extended-criteria donors, static cold storage has failed to provide optimal preservation of liver grafts, resulting in early allograft dysfunction and long-term complications Machine perfusion(MP) is a beneficial alternative preservation strategy for donor livers, particularly fo those considered to be of suboptimal quality, and could expand the limited donor pool. Data sources: A comprehensive search in Pub Med, EMBASE, Ovid databases and Clinical Trials.gov website was conducted using the medical subject heading terms "machine perfusion", "machine preservation""liver transplantation", combined with free text terms such as "hypothermic", "normothermic" and "sub normothermic". The deadline for the search was September 30, 2017. Results: MP can be classified as hypothermic, subnormothermic, and normothermic with the tempera ture maintained at 0–12 °C, 25–34 °C and 35–38 °C, respectively. Twelve clinical trials of MP have been reported in recent years. MP effectively decreased AST/ALT level and the incidence of early allograft dys function. However, the graft and patient survival rate after MP were similar to static cold storage. The detailed clinical characteristics such as liver function, graft survival, patient survival and early allograf dysfunction were reviewed.Conclusions: Clinical trial results showed that MP improves delayed graft function, primary non-function and biliary strictures. However, MP still requires validation in large clinical trials and the key parameters during MP still require optimization.

Hypothermic machine perfusion with metformin-University of Wisconsin solution for ex vivo preservation of standard and marginal liver grafts in a rat model

AIM To compare the effect of University of Wisconsin(UW) solution with or without metformin, an AMP-activated protein kinase(AMPK) activator, for preserving standard and marginal liver grafts of young and aged rats ex vivo by hypothermic machine perfusion(HMP).METHODS Eighteen young(4 mo old) and 18 aged(17 mo old)healthy male SD rats were selected and randomly divided into three groups: control group, UW solution perfusion group(UWP), and UW solution with metformin perfusion group(MUWP). Aspartate aminotransferase(AST), alanine aminotransferase(ALT), lactate dehydrogenase(LDH), interleukin-18(IL-18), and tumor necrosis factor-alpha(TNF-α) in the perfused liquid were tested. The expression levels of AMPK and endothelial nitric oxide synthase(e NOS) in liver sinusoidal endothelial cells were also examined.Additionally, microscopic evaluation of the harvested perfused liver tissue samples was done. RESULTS AST, ALT, LDH, IL-18 and TNF-α levels in the young and aged liver-perfused liquid were, respectively,significantly lower in the MUWP group than in the UWP group(P < 0.05), but no significant differences were found between the young and aged MUWP groups.Metformin increased the expression of AMPK and e NOS protein levels, and promoted the extracellular release of nitric oxide through activation of the AMPK-e NOS mediated pathway. Histological examination revealed that in the MUWP group, the extent of liver cells and tissue damage was significantly reduced compared with the UWP group.CONCLUSION The addition of metformin to the UW preservative solution for ex vivo HMP can reduce rat liver injury during cold ischemia, with significant protective effects on livers, especially of aged rats.

Implementing an innovated liver ex-situ machine perfusion technology:The 2018 Joint International Congress of ILTS,ELITA and LICAGE

The 2018 Joint International Congress of ILTS,ELITA and LICAGE were held in Lisbon,Portugal on May 23–26,2018.The exciting and innovative program brought together 1144 experts in liver transplantation(LT)such as surgeons,physicians or basic scientists from 61 countries.The presentations included 110 invited speakers,181 oral presentations,and 545 posters.This editorial highlights some of the most innovative and impactful presentations in

Therapeutics administered during ex vivo liver machine perfusion:An overview

Although the use of extended criteria donors has increased the pool of available livers for transplant,it has also introduced the need to develop improved methods of protection against ischemia-reperfusion injury(IRI),as these"marginal"organs are particularly vulnerable to IRI during the process of procurement,preservation,surgery,and post-transplantation.In this review,we explore the current basic science research investigating therapeutics administered during ex vivo liver machine perfusion aimed at mitigating the effects of IRI in the liver transplantation process.These various categories of therapeutics are utilized during the perfusion process and include invoking the RNA interference pathway,utilizing defatting cocktails,and administering classes of agents such as vasodilators,anti-inflammatory drugs,human liver stem cell-derived extracellular vesicles,and δ-opioid agonists in order to reduce the damage of IRI.Ex vivo machine perfusion is an attractive alternative to static cold storage due to its ability to continuously perfuse the organ,effectively deliver substrates and oxygen required for cellular metabolism,therapeutically administer pharmacological or cytoprotective agents,and continuously monitor organ viability during perfusion.The use of administered therapeutics during machine liver perfusion has demonstrated promising results in basic science studies.While novel therapeutic approaches to combat IRI are being developed through basic science research,their use in clinical medicine and treatment in patients for liver transplantation has yet to be explored.

Machine perfusion in abdominal organ transplantation: Current use in the Netherlands

Scarcity of donor organs and the increment in patients awaiting a transplant increased the use of organs from expanded criteria donors or donation after circulatory death.Due to the suboptimal outcomes of these donor organs,there is an increased interest in better preservation methods,such as ex vivo machine perfusion or abdominal regional perfusion to improve outcomes.This state-ofthe-art review aims to discuss the available types of perfusion techniques,its potential benefits and the available evidence in kidney,liver and pancreas transplantation.Additionally,translational steps from animal models towards clinical studies will be described,as well as its application to clinical practice,with the focus on the Netherlands.Despite the lack of evidence from randomized controlled trials,currently available data suggest especially beneficial effects of normothermic regional perfusion on biliary complications and ischemic cholangiopathy after liver transplantation.For ex vivo machine perfusion in kidney transplantation,hypothermic machine perfusion has proven to be beneficial over static cold storage in a randomized controlled trial,while normothermic machine perfusion is currently under investigation.For ex vivo machine perfusion in liver transplantation,normothermic machine perfusion has proven to reduce discard rates and early allograft dysfunction.In response to clinical studies,hypothermic machine perfusion for deceased donor kidneys has already been implemented as standard of care in the Netherlands.

Machine perfusion of the liver:Putting the puzzle pieces together

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

Concise review of machine perfusion in liver transplantation

With the advances and clinical growth in liver transplantation over the last four decades the focus on expanding deceased donor organs has been in need of scientific research.In the past ten years several researchers have looked at the domain of machine perfusion as it applies to deceased donor livers.The following review focuses on the clinical trials and recent advances that will likely have the earliest entrance into the clinical arena.

Standardization is needed in reporting risk and outcomes of machine perfusion in liver transplantation

We congratulate Yamamoto et al.on their study“Impact of Portable Normothermic Machine Perfusion for Liver Transplantation from Adult Deceased Donors”(1).The surge of interest in normothermic machine perfusion(NMP)in the United States(US)has generated considerable enthusiasm.The authors present generally exciting results from their single-center analysis of 541 liver transplantations.Among these,469 were from donors after brain dead(DBD);58(12.4%)received NMP and 411 static cold storage(SCS,87.6%).Seventy-two transplants were from donors after circulatory death(DCD);52(72.2%)received NMP(device-to-donor)vs.20 SCS(27.8%).

Study on the preservation effects of the amputated forelimb by machine perfusion at physiological temperature

Purpose:Ischemia and hypoxia are the main factors limiting limb replantation and transplantation.Static cold storage(SCS),a common preservation method for tissues and organs,can only prolong limb ischemia time to 4-6 h.The normothermic machine perfusion(NMP)is a promising method for the preservation of tissues and organs,which can extend the preservation time in vitro by providing continuous oxygen and nutrients.This study aimed to evaluate the difference in the efficacy of the 2 limb preservation methods.Methods:The 6 forelimbs from beagle dogs were divided into 2 groups.In the SCS group(n=3),the limbs were preserved in a sterile refrigerator at 4°C for 24 h,and in the NMP group(n=3),the perfusate prepared with autologous blood was used for the oxygenated machine perfusion at physiological temperature for 24 h,and the solution was changed every 6 h.The effects of limb storage were evaluated by weight gain,perfusate biochemical analysis,enzyme-linked immunosorbent assay,and histological analysis.All statistical analyses and graphs were performed using GraphPad Prism 9.0 one-way or two-way analysis of variance.The p value of less than 0.05 was considered to indicate statistical significance.Results:In the NMP group,the weight gained percentage was 11.72%±4.06%;the hypoxia-inducible factor-1αcontents showed no significant changes;the shape of muscle fibers was normal;the gap between muscle fibers slightly increased,showing the intercellular distance of(30.19±2.83)μm;and the vascularα-smooth muscle actin(α-SMA)contents were lower than those in the normal blood vessels.The creatine kinase level in the perfusate of the NMP group increased from the beginning of perfusion,decreased after each perfusate change,and remained stable at the end of perfusion showing a peak level of 4097.6 U/L.The lactate dehydrogenase level of the NMP group increased near the end of perfusion and reached the peak level of 374.4 U/L.In the SCS group,the percentage of weight gain was 0.18%±0.10%,and the contents of hypoxia-inducible factor-1αincreased gradually and reached the maximum level of(164.85±20.75)pg/mL at the end of the experiment.The muscle fibers lost their normal shape and the gap between muscle fibers increased,showing an intercellular distance of(41.66±5.38)μm.The contents of vascularα-SMA were much lower in the SCS group as compared to normal blood vessels.Conclusions:NMP caused lesser muscle damage and contained more vascularα-SMA as compared to SCS.This study demonstrated that NMP of the amputated limb with perfusate solution based on autologous blood could maintain the physiological activities of the limb for at least 24 h.

Long-term normothermic machine perfusion of fatty livers:towards transplanting untransplantable livers?

Since the very early days of clinical liver transplantation(LT),transplant surgeons and professionals have been confronted with the increased risk of failure associated with the use of fatty liver grafts(1).Notwithstanding the wide variability in steatosis assessment across different centers and pathologists(2),utilization of livers with moderate(≥30%)or severe(≥60%)macrovesicular steatosis has been consistently associated with an increased risk of primary non-function,early allograft dysfunction,acute kidney injury,as well as inferior graft and patient survival(3).The mechanisms behind the increased susceptibility of steatotic livers to ischemia-reperfusion injury(IRI)are multiple,including disturbances to microcirculation due to sinusoidal narrowing,increased oxidative stress upon reperfusion and enhanced lipid peroxidation,leading to an increased release of inflammatory mediators like IL6,IL1βand so-called damage associated molecular patterns(DAMP),like cell-free DNA and mitochondrial DNA.Histologically,this is reflected by hepatocyte death by necrosis rather than apoptosis,pseudopeliotic steatosis(i.e.,the expulsion of lipid droplets into the extracellular space)and lately,by tissue remodelling and fibrosis(4,5).

Does ischemia-free machine perfusion lead to early allograft dysfunction (EAD) free liver transplantation?

Normothermic machine perfusion(NMP)is an innovative technique used in solid organ transplantation that involves perfusing the organ with specialized solution or leukocyte depleted red blood cells at near-normal body temperature aiming at mimicking physiological conditions,and providing optimal conditions for organ preservation which leads to reduced risk of ischemia reperfusion injury(IRI)when compared to the standard static cold storage(SCS)(1).One of the key advantages of NMP is its ability to assess the quality of the organ in real-time and assessment of the organ performance prior to transplantation.By continuously monitoring parameters such as blood flow,oxygen consumption,and lactate production,clinicians can evaluate the viability of the organ and make more informed decisions about its suitability for transplantation.This real-time assessment can help reduce the risk of transplanting organs that may not function optimally or have a higher likelihood of complications post-transplant.Additionally,NMP may expand the pool of donor organs by allowing for the use of organs that may have been deemed marginal or unsuitable for transplantation using traditional methods(1,2).

Comprehensive Approach to Assessment of Liver Viability During Normothermic Machine Perfusion

Liver transplantation is the most effective treatment of advanced liver disease,and the use of extended criteria donor organs has broadened the source of available livers.Although normothermic machine perfusion(NMP)has become a useful tool in liver transplantation,there are no consistent criteria that can be used to evaluate the viability of livers during NMP.This review summarizes the criteria,indicators,and methods used to evaluate liver viability during NMP.The shape,appearance,and hemodynamics of the liver can be analyzed at a macroscopic level,while markers of liver injury,indicators of liver and bile duct function,and other relevant indicators can be evaluated by biochemical analysis.The liver can also be assessed by tissue biopsy at the microscopic level.Novel methods for assessment of liver viability are introduced.The limitations of evaluating liver viability during NMP are discussed and suggestions for future clinical practice are provided.

The conclusion of reducing acute rejection after liver transplantation by machine perfusion should be extrapolated with caution

There is a theory that the unavoidable graft damage caused by ischemia-reperfusion injury(IRI)during liver transplantation(LT)can lead to severe IRI-related inflammation and trigger an early activation of the innate immune response mediated by T-cells,which potentially worsening the acute cellular rejection(ACR)cascade.As a result,machine perfusion(MP)has been placed great expectations for the potential to diminish post-LT ACR and other related immune responses by alleviating IRI through removing harmful substances and restoring cellular metabolism homeostasis(1,2).However,there has been much debate about MP’s benefits on ACR as relative data is limited.

Predictive value of hypothermic machine perfusion parameters combined perfusate biomarkers in deceased donor kidney transplantation

Background:Delayed graft function(DGF)is the main cause of renal function failure after kidney transplantation.This study aims at investigating the value of hypothermic machine perfusion(HMP)parameters combined with perfusate biomarkers on predicting DGF and the time of renal function recovery after deceased donor(DD)kidney transplantation.Methods:HMP parameters,perfusate biomarkers and baseline characteristics of 113 DD kidney transplantations from January 1,2019 to August 31,2019 in the First Affiliated Hospital of Xi’an Jiaotong University were retrospectively analyzed using univariate and multivariate logistic regression analysis.Results:In this study,the DGF incidence was 17.7%(20/113);The multivariate logistic regression results showed that terminal resistance(OR:1.879,95%CI 1.145-3.56)and glutathione S-transferase(GST)(OR=1.62,95%CI 1.23-2.46)were risk factors for DGF;The Cox model analysis indicated that terminal resistance was an independent hazard factor for renal function recovery time(HR=0.823,95%CI 0.735-0.981).The model combining terminal resistance and GST(AUC=0.888,95%CI:0.842-0.933)significantly improved the DGF predictability compared with the use of terminal resistance(AUC=0.756,95%CI 0.693-0.818)or GST alone(AUC=0.729,95%CI 0.591-0.806).Conclusion:According to the factors analyzed in this study,the combination of HMP parameters and perfusate biomarkers displays a potent DGF predictive value.

Machine perfusion versus cold storage of livers： a meta-analysis

Abstract Different organ preservation methods are key factors influencing the results of fiver transplantation. In this study, the outcomes of experimental models receiving donation after cardiac death （DCD） livers preserved through machine perfusion （MP） or static cold storage （CS） were compared by conducting a meta-analysis. Standardized mean difference （SMD） and 95% confidence interval （CI） were calculated to compare pooled data from two animal species. Twenty-four studies involving MP preservation were included in the meta-analysis. Compared with CS preservation, MP can reduce the levels of aspartate aminotransferase （AST）, alanine aminotransferase （ALT）, lactate dehydrogenase （LDH）, and hyaluronic acid （HA） and the changes in liver weight. By contrast, MP can enhance bile production and portal vein flow （PVF）. Alkaline phosphatase （ALP） levels and histological changes significantly differed between the two preservation methods. In conclusion, MP of DCD livers is superior to CS in experimental animals.