Metabolic preconditioning of donor organs: defatting fatty livers by normothermic perfusion ex vivo

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.

Pumping new life into old ideas: Preservation and rehabilitation of the liver using ex situ machine perfusion

Recent advances in machine perfusion technology have reinvigorated the field of liver transplantation with the possibilities of vastly improving the efficiency and safety of the life-saving procedure. With this improved preservation technology, transplant surgeons are now able to use previously untransplantable donor livers without significantly compromising patient outcomes. Early clinical studies demonstrate the ability to extend preservation times and assess a graft's potential viability using normothermic machine perfusion, in addition to restoring the energy supply in donor livers by supporting metabolism through circulation of vital nutrients and blood-based oxygen carriers. Future endeavors for surgeons and scientists should focus on improving criteria to assess viability, optimizing protocols for perfusion research, investigating mechanisms of poor graft viability, and targeting these mechanisms with novel therapies to improve graft function prior to transplantation. Long-term goals include extending preservation times on the scale of days to weeks, enabling long-distance organ sharing, and establishing regional organ perfusion centers to streamline the procurement, perfusion, and transplantation process.

The impact of postreperfusion syndrome during liver transplantation using livers with significant macrosteatosis

The impact of postreperfusion syndrome (PRS) during liver transplantation (LT) using donor livers with significant macrosteatosis is largely unknown. Clinical outcomes of all patients undergoing LT with donor livers with moderate macrosteatosis (30%-60%) (N = 96) between 2000 and 2017 were compared to propensity score matched cohorts of patients undergoing LT with donor livers with mild macrosteatosis (10%-29%) (N = 96) and no steatosis (N = 96). Cardiac arrest at the time of reperfusion was seen in eight (8.3%) of the patients in the moderate macrosteatosis group compared to one (1.0%) of the patients in the mild macrosteatosis group (P = .02) and zero (0%) of the patients in the no steatosis group (P = .004). Patients in the moderate macrosteatosis group had a higher rate of PRS (37.5% vs 18.8%; P = .004), early allograft dysfunction (EAD) (76.4% vs 25.8%; P < .001), renal dysfunction requiring continuous renal replacement therapy following transplant (18.8% vs 8.3%; P = .03) and return to the OR within 30 days (24.0% vs 7.3%; P = .002), than the no steatosis group. Both long-term patient (P = .30 and P = .08) and graft survival (P = .15 and P = .12) were not statistically when comparing the moderate macrosteatosis group to the mild macrosteatosis and no steatosis groups. Recipients of LT using livers with moderate macrosteatosis are at a significant increased risk of PRS. If patients are able to overcome the initial increased perioperative risk of using these donor livers, long-term graft survival does not appear to be different than matched recipients receiving grafts with no steatosis.

Systems engineering the organ preservation process for transplantation

Improving organ preservation and extending the preservation time would have game-changing effects on the current practice of organ transplantation. Machine perfusion has emerged as an improved preservation technology to expand the donor pool, assess graft viability and ensure adequate graft function. However, its efficacy in extending the preservation time is limited. Subzero organ preservation does hold the promise to significantly extend the preservation time and recent advances in cryobiology bring it closer to clinical translation. In this review, we aim to broaden the perspective in the field from a focus on these individual technologies to that of a systems engineering. This would enable the creation of a preservation process that integrates the benefits of machine perfusion with those of subzero preservation, with the ultimate goal to provide on demand availability of donor organs through organ banking.

Manipulation of Lipid Metabolism During Normothermic Machine Perfusion: Effect of Defatting Therapies on Donor Liver Functional Recovery

Strategies to increase the use of steatotic donor livers are required to tackle the mortality on the transplant waiting list. We aimed to test the efficacy of pharmacological enhancement of the lipid metabolism of human livers during ex situ normothermic machine perfusion to promote defatting and improve the functional recovery of the organs. Because of steatosis, 10 livers were discarded and were allocated either to a defatting group that had the perfusate supplemented with a combination of drugs to enhance lipid metabolism or to a control group that received perfusion fluid with vehicle only. Steatosis was assessed using tissue homogenate and histological analyses. Markers for lipid oxidation and solubilization, oxidative injury, inflammation, and biliary function were evaluated by enzyme-linked immunosorbent assay, immunohistochemistry, and in-gel protein detection. Treatment reduced tissue triglycerides by 38% and macrovesicular steatosis by 40% over 6 hours. This effect was driven by increased solubility of the triglycerides (P = 0.04), and mitochondrial oxidation as assessed by increased ketogenesis (P = 0.008) and adenosine triphosphate synthesis (P = 0.01) were associated with increased levels of the enzymes acyl-coenzyme A oxidase 1, carnitine palmitoyltransferase 1A, and acetyl-coenzyme A synthetase. Concomitantly, defatted livers exhibited enhanced metabolic functional parameters such as urea production (P = 0.03), lower vascular resistance, lower release of alanine aminotransferase (P = 0.049), and higher bile production (P = 0.008) with a higher bile pH (P = 0.03). The treatment down-regulated the expression of markers for oxidative injury as well as activation of immune cells (CD14; CD11b) and reduced the release of inflammatory cytokines in the perfusate (tumor necrosis factor α; interleukin 1β). In conclusion, pharmacological enhancement of intracellular lipid metabolism during normothermic machine perfusion decreased the lipid content of human livers within 6 hours. It also improved the intracellular metabolic support to the organs, leading to successful functional recovery and decreased expression of markers of reperfusion injury.

Extracts of bilberry (Vaccinium myrtillus L.) fruits improve liver steatosis and injury in mice by preventing lipid accumulation and cell death

Bilberry has been reported to have anti-oxidant and anti-inflammatory properties. We studied the effect of bilberry (Vaccinium myrtillus L.) fruits extracts (BEs) on the pathogenesis caused by lipid accumulation in fatty liver and non-alcoholic steatohepatitis (NASH). 5 μg/ml of BEs was enough to suppress lipid accumulation in the fatty liver model of the mouse hepatic AML12 cells. BEs increased cell viability and anti-oxidant capacity, presumably by activating (phosphorylating) Akt/STAT3 and inducing MnSOD/catalase. BEs also significantly reduced Rubicon and induced p62/SQSTM1, possibly contributing to reduce cellular lipids (lipophagy). When the mice were fed supplemented with BEs (5% or 10%, w/w), hepatic steatosis, injury, and hypercholesterolemia/hyperglycemia were significantly improved. Furthermore, histological and cytokine studies indicated that BEs possibly suppress hepatic inflammation (hepatitis) and fibrosis. Therefore, BEs improved liver steatosis and injury, and potentially suppress fibrosis by suppressing inflammatory response, which therefore may prevent the progression of fatty liver to NASH.

Normothermic liver preservation, current status and future directions

PURPOSE OF REVIEW

Normothermic machine perfusion (NMP) is an emerging technology for liver preservation. Early clinical results demonstrate beneficial effects in reconditioning high-risk grafts. This review discusses the role of normothermic perfusion as a tool to assess graft viability and as a platform for graft intervention and modification.

RECENT FINDINGS

The potential benefits of NMP extend far beyond organ reconditioning. Recent pilot studies have identified clinically relevant viability criteria, which now require validation in large randomized control trials prior to implementation. Furthermore, preclinical studies demonstrate tremendous potential for NMP as a method to extend the preservation period, thus improving transplant logistics as well as serve as a platform for graft-targeted interventions to optimize the preservation period.

SUMMARY

NMP is a multifunctional tool with potential to transform liver preservation and the field of transplantation. Large clinical trials are necessary to optimize perfusion protocols, clarify indications for NMP therapy and justify use as the standard preservation modality.

Social, economic, and policy implications of organ preservation advances

PURPOSE OF REVIEW

Despite over 60 years of progress in the field of since the first organ transplant, insufficient organ preservation capabilities still place profound constraints on transplantation. These constraints play multiple and compounding roles in the predominant limitations of the field: the severe shortages of transplant organs, short-term and long-term posttransplant outcomes and complications, the unmet global need for development of transplant infrastructures, and economic burdens that limit patient access to transplantation and contribute to increasing global healthcare costs. This review surveys ways that advancing preservation technologies can play a role in each of these areas, ultimately benefiting thousands if not millions of patients worldwide.

RECENT FINDINGS

Preservation advances can create a wide range of benefits across many facets of organ transplantation, as well as related areas of transplant research. As these technologies mature, so will the policies around their use to maximize the benefits offered by organ preservation.

SUMMARY

Organ preservation advances stand to increase local and global access to transplantation, improve transplant outcomes, and accelerate progress in related areas such as immune tolerance induction and xenotransplantation. This area holds the potential to save the healthcare system many billions of dollars and reduce costs across many aspects of transplantation. Novel preservation technologies, along with other technologies facilitated by preservation advances, could potentially save millions of lives in the coming years.

The dawn of liver perfusion machines

PURPOSE OF REVIEW

Despite high demand, a severe shortage of suitable allografts limits the use of liver transplantation for the treatment of end-stage liver disease. The transplant community is turning to the utilization of high-risk grafts to fill the void. This review summarizes the reemergence of ex-vivo machine perfusion for liver graft preservation, including results of recent clinical trials and its specific role for reconditioning DCD, steatotic and elderly grafts.

RECENT FINDINGS

Several phase-1 clinical trials demonstrate the safety and feasibility of machine perfusion for liver graft preservation. Machine perfusion has several advantages compared with static cold storage and may provide superior transplantation outcomes, particularly for marginal grafts. Ongoing multicenter trials aim to confirm the results of preclinical and pilot studies and establish the clinical utility of ex-vivo liver machine perfusion.

SUMMARY

Mounting evidence supports the benefits of machine perfusion for preservation of liver grafts. Thus, machine perfusion is a promising strategy to expand the donor pool by reconditioning and assessing viability of DCD, elderly and steatotic grafts during the preservation period. Additionally, machine perfusion will serve as a platform to facilitate graft intervention and modification to further optimize marginal grafts.

The future of organ perfusion and re-conditioning

Organ preservation and re‐conditioning using machine perfusion technologies continue to generate promising results in terms of viability assessment, organ utilization and improved initial graft function. Here, we summarize the latest findings and study the results of ex‐vivo/ex‐situ hypothermic (HMP) and normothermic machine perfusion (NMP) in the area of abdominal organ transplantation (kidney, liver, pancreas and intestine). We also consider the potential role of normothermic regional perfusion (NRP) to re‐condition donors after circulatory death organs before retrieval. The findings from clinical studies reported to date suggest that machine perfusion will offer real benefits when compared with conventional cold preservation. Several randomized trials are expected to report their findings within the next 2 years which may shed light on the relative merits of different perfusion methods and could indicate which perfusion parameters may be most useful to predict organ quality and viability. Further work is needed to identify composite endpoints that are relevant for transplanted organs that have undergone machine preservation. Multi‐centre trials to compare and analyse the combinations of NRP followed by HMP and/or NMP, either directly after organ retrieval using transportable devices or when back‐to‐base, are needed. The potential applications of machine preservation technology beyond the field of solid organ transplantation are also considered.

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.

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.

Evaluation of a micro-spectrometer for the real-time assessment of liver graft with mild-to-moderate macrosteatosis: A proof of concept study

BACKGROUND & AIMS

Liver macrosteatosis (MS) is a major predictor of graft dysfunction after transplantation. However, frozen section techniques to quantify steatosis are often unavailable in the context of procurements, and the findings of preoperative imaging techniques correlate poorly with those of permanent sections, so that the surgeon is ultimately responsible for the decision. Our aim was to assess the accuracy of a non-invasive pocket-sized micro-spectrometer (PSM) for the real-time estimation of MS.

METHODS

We prospectively evaluated a commercial PSM by scanning the liver capsule. A double pathological quantification of MS was performed on permanent sections. Initial calibration (training cohort) was performed on 35 livers (MS ≤60%) and an algorithm was created to correlate the estimated (PSM) and known (pathological) MS values. A second assessment (validation cohort) was then performed on 154 grafts.

RESULTS

Our algorithm achieved a coefficient of determination R2 = 0.81. Its validation on the second cohort demonstrated a Lin's concordance coefficient of 0.78. Accuracy reached 0.91%, with reproducibility of 86.3%. The sensitivity, specificity, positive and negative predictive values for MS ≥30% were 66.7%, 100%, 100% and 98%, respectively. The PSM could predict the absence (<30%)/presence (≥30%) of MS with a kappa coefficient of 0.79. Neither graft weight nor height, donor body mass index nor the CT-scan liver-to-spleen attenuation ratio could accurately predict MS.

CONCLUSION

We demonstrated that a PSM can reliably and reproducibly assess mild-to-moderate MS. Its low cost and the immediacy of results may offer considerable added-value decision support for surgeons. This tool could avoid the detrimental and prolonged ischaemia caused by the pathological examination of (potentially) marginal grafts. This device now needs to be assessed in the context of a large-scale multicentre study.

LAY SUMMARY

Macro-vacuolar liver steatosis is a major prognostic factor for outcomes after liver transplantation. However, it is often difficult for logistical reasons to get this estimation during procurement. Therefore, we developed an algorithm for a commercial, portable and affordable spectrometer to accurately estimate this content in a real-time fashion. This device could be of great interest for clinical decision-making to accept or discard a potential human liver graft.

The "Skinny" on Assessment and Utilization of Steatotic Liver Grafts: A Systematic Review

The frequency at which steatotic deceased donor liver grafts are encountered will likely continue to increase. Utilization of liver grafts with moderate-to-severe steatosis for liver transplantation (LT) has been previously shown to be associated with increased rates of primary nonfunction and decreased recipient survival. In order to better inform clinical decision making and guide future research, critical evaluation of the literature on donor liver steatosis and posttransplantation outcome is needed. This literature review aims to provide the "skinny" on using deceased donor steatotic livers for LT.

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.

Normothermic ex vivo liver perfusion: platform for liver graft assessment and therapeutic modification

Liver transplantation as a treatment for end stage liver failure remains limited in the United States by the number and quality of donor allografts. Static cold storage, the current standard of care for organ storage prior to transplantation, offers no method for assessment or therapeutic modification. Cold ischemia and its attendant hypoxia deplete cellular adenosine triphosphate (ATP) stores, promote cellular damage, and degrade overall organ quality. Normothermic ex vivo liver perfusion (NEVLP) offers the potential for assessment of allograft function and restoration of intracellular energy stores prior to transplantation. A completed phase III randomized trial demonstrated livers undergoing NEVLP prior to transplantation demonstrate superior early graft function and less early graft dysfunction. NEVLP offers a platform for modification of the allograft via the application of defatting or therapeutic cocktails, missense RNA technology, or gene editing modalities. The wide versatility of NEVLP appears to be a promising tool to expand the current pool of transplantable liver allografts.

Ex situ machine perfusion as a tool to recondition steatotic donor livers: Troublesome features of fatty livers and the role of defatting therapies. A systematic review

Long-standing research has shown that increased lipid content in donor livers is associated with inferior graft outcomes posttransplant. The global epidemic that is obesity has increased the prevalence of steatosis in organ donors, to the extent that it has become one of the main reasons for declining livers for transplantation. Consequently, it is one of the major culprits behind the discrepancy between the number of donor livers offered for transplantation and those that go on to be transplanted. Steatotic livers are characterized by poor microcirculation, depleted energy stores because of an impaired capacity for mitochondrial recovery, and a propensity for an exaggerated inflammatory response following reperfusion injury culminating in poorer graft function postoperatively. Ex situ machine perfusion, currently a novel method in graft preservation, is showing great promise in providing a tool for the recovery and reconditioning of marginal livers. Hence, reconditioning these steatotic livers using machine perfusion has the potential to increase the number of liver transplants performed. In this review, we consider the problematic issues associated with fatty livers in the realm of transplantation and discuss pharmacological and nonpharmacological options that are being developed to enhance recovery of these organs using machine perfusion and defatting strategies.

Normothermic ex-vivo liver perfusion: where do we stand and where to reach?

Nowadays liver transplantation is considered as the treatment of choice, however, the scarcity of suitable donor organs limits the delivery of care to the end-stage liver disease patients leading to the death while on the waiting list. The advent of ex-situ normothermic machine perfusion (NMP) has emerged as an alternative to the standard organ preservation technique, static cold storage (SCS). The newer technique promises to not only restore the normal metabolic activity but also attempt to recondition the marginal livers back to the pristine state, which are otherwise more susceptible to ischemic injury and foster the poor post-transplant outcomes. Areas covered: An extensive search of all the published literature describing the role of NMP based device in liver transplantation as an alternative to SCS was made on MEDLINE, EMBASE, Cochrane, BIOSIS, Crossref, Scopus databases and clinical trial registry on 10 May 2018. Expert commentary: The main tenet of NMP is the establishment of the physiological milieu, which permits aerobic metabolism to continue through out the period of preservation and limits the effects of ischemia-reperfusion (I/R) injury. In addition, by assessing the various metabolic and synthetic parameters the viability and suitability of donor livers for transplantation can be determined. This important technological advancement has scored satisfactorily on the safety and efficacy parameters in preliminary clinical studies. The present review suggests that NMP can offer the opportunity to assess and safely utilize the marginal donor livers if deemed appropriate for the transplantation. However, ongoing trials will determine its full potential and further adoption.

Normothermic Ex-vivo Liver Perfusion and the Clinical Implications for Liver Transplantation

Despite significant improvements in outcomes after liver transplantation, many patients continue to die on the waiting list, while awaiting an available organ for transplantation. Organ shortage is not only due to an inadequate number of available organs, but also the inability to adequately assess and evaluate these organs prior to transplantation. Over the last few decades, ex-vivo perfusion of the liver has emerged as a useful technique for both improved organ preservation and assessment of organs prior to transplantation. Large animal studies have shown the superiority of ex-vivo perfusion over cold static storage. However, these studies have not, necessarily, been translatable to human livers. Small animal studies have been essential in understanding and improving this technology. Similarly, these results have yet to be translated into clinical use. A few Phase 1 clinical trials have shown promise and confirmed the viability of this technology. However, more robust studies are needed before ex-vivo liver perfusion can be widely accepted as the new clinical standard of organ preservation. Here, we aimed to review all relevant large and small animal research, as well as human liver studies on normothermic ex-vivo perfusion, and to identify areas of deficiency and opportunities for future research endeavors.

Studying non-alcoholic fatty liver disease: the ins and outs of in vivo, ex vivo and in vitro human models

The prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing. Determining the pathogenesis and pathophysiology of human NAFLD will allow for evidence-based prevention strategies, and more targeted mechanistic investigations. Various in vivo, ex situ and in vitro models may be utilised to study NAFLD; but all come with their own specific caveats. Here, we review the human-based models and discuss their advantages and limitations in regards to studying the development and progression of NAFLD. Overall, in vivo whole-body human studies are advantageous in that they allow for investigation within the physiological setting, however, limited accessibility to the liver makes direct investigations challenging. Non-invasive imaging techniques are able to somewhat overcome this challenge, whilst the use of stable-isotope tracers enables mechanistic insight to be obtained. Recent technological advances (i.e. normothermic machine perfusion) have opened new opportunities to investigate whole-organ metabolism, thus ex situ livers can be investigated directly. Therefore, investigations that cannot be performed in vivo in humans have the potential to be undertaken. In vitro models offer the ability to perform investigations at a cellular level, aiding in elucidating the molecular mechanisms of NAFLD. However, a number of current models do not closely resemble the human condition and work is ongoing to optimise culturing parameters in order to recapitulate this. In summary, no single model currently provides insight into the development, pathophysiology and progression across the NAFLD spectrum, each experimental model has limitations, which need to be taken into consideration to ensure appropriate conclusions and extrapolation of findings are made.

An effective protocol for pharmacological defatting of primary human hepatocytes which is non-toxic to cholangiocytes or intrahepatic endothelial cells

Introduction

Pharmacological defatting of rat hepatocytes and hepatoma cell lines suggests that the same method could be used to ameliorate macrovesicular steatosis in moderate to severely fatty livers. However there is no data assessing the effects of those drugs on primary human liver cells. We aimed to determine the effectiveness of a pharmacological cocktail in reducing the in vitro lipid content of primary human hepatocytes (PHH). In addition we sought to determine the cytotoxicity of the cocktail towards non-parenchymal liver cells.

Methods

Steatosis was induced in PHH by supplementation with a combination of saturated and unsaturated free fatty acids. This was followed by addition of a defatting drug cocktail for up to 48 hours. The same experimental method was used with human intra-hepatic endothelial cells (HIEC) and human cholangiocytes. MTT assay was used to assess cell viability, triglyceride quantification and oil red O staining were used to determine intracellular lipids content whilst ketone bodies were measured in the supernatants following experimentation.

Results

Incubation of fat loaded PHH with the drugs over 48 hours reduced the intracellular lipid area by 54%, from 12.85% to 5.99% (p = 0.002) (percentage of total oil red O area), and intracellular triglyceride by 35%, from 28.24 to 18.30 nmol/million of cells (p<0.001). Total supernatant ketone bodies increased 1.4-fold over 48 hours in the defatted PHH compared with vehicle controls (p = 0.002). Moreover incubation with the drugs for 48 hours increased the viability of PHH by 11%, cholangiocytes by 25% whilst having no cytotoxic effects on HIEC.

Conclusion

These data demonstrate that pharmacological intervention can significantly decrease intracellular lipid content of PHH, increase fatty acids β-oxidation whilst being non-toxic to PHH, HIEC or cholangiocytes.

A Small Animal Model of Ex Vivo Normothermic Liver Perfusion

There is a significant shortage of liver allografts available for transplantation, and in response the donor criteria have been expanded. As a result, normothermic ex vivo liver perfusion (NEVLP) has been introduced as a method to evaluate and modify organ function. NEVLP has many advantages in comparison to hypothermic and subnormothermic perfusion including reduced preservation injury, restoration of normal organ function under physiologic conditions, assessment of organ performance, and as a platform for organ repair, remodeling, and modification. Both murine and porcine NEVLP models have been described. We demonstrate a rat model of NEVLP and use this model to show one of its important applications - the use of a therapeutic molecule added to liver perfusate. Catalase is an endogenous reactive oxygen species (ROS) scavenger and has been demonstrated to decrease ischemia-reperfusion in the eye, brain, and lung. Pegylation has been shown to target catalase to the endothelium. Here, we added pegylated-catalase (PEG-CAT) to the base perfusate and demonstrated its ability to mitigate liver preservation injury. An advantage of our rodent NEVLP model is that it is inexpensive in comparison to larger animal models. A limitation of this study is that it does not currently include post-perfusion liver transplantation. Therefore, prediction of the function of the organ post-transplantation cannot be made with certainty. However, the rat liver transplant model is well established and certainly could be used in conjunction with this model. In conclusion, we have demonstrated an inexpensive, simple, easily replicable NEVLP model using rats. Applications of this model can include testing novel perfusates and perfusate additives, testing software designed for organ evaluation, and experiments designed to repair organs.

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.

The case for normothermic machine perfusion in liver transplantation

In recent years, there has been growing interest in normothermic machine perfusion (NMP) as a preservation method in liver transplantation. In most countries, because of a donor organ shortage, an unacceptable number of patients die while awaiting transplantation. In an attempt to increase the number of donor organs available, transplant teams are implanting a greater number of high-risk livers, including those from donation after circulatory death, older donors, and donors with steatosis. NMP maintains the liver ex vivo on a circuit by providing oxygen and nutrition at 37°C. This permits extended preservation times, the ability to perform liver viability assessment, and the potential for liver-directed therapeutic interventions during preservation. It is hoped that this technology may facilitate the enhanced preservation of marginal livers with improved posttransplant outcomes by reducing ischemia/reperfusion injury. Clinical trials have demonstrated its short-term superiority over cold storage in terms of early biochemical liver function, and it is anticipated that it may result in increased organ utilization, helping to reduce the number of wait-list deaths. However, further studies are required to demonstrate longer-term efficacy and the impact on biliary complications as well as further knowledge to exploit and maximize the potential of this exciting new technology. Liver Transplantation 24 269-275 2018 AASLD.

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.

Temperature and oxygenation during organ preservation: friends or foes?

PURPOSE OF REVIEW

The liberalization of donor selection criteria in organ transplantation, with the increased use of suboptimal grafts, has stimulated interest in ischemia-reperfusion injury prevention and graft reconditioning. Organ preservation technologies are changing considerably, mostly through the reintroduction of dynamic machine preservation. Here, we review the current evidence on the role of temperature and oxygenation during dynamic machine preservation.

RECENT FINDINGS

A large but complex body of evidence exists and comparative studies are few. Oxygenation seems to support an advantageous effect in hypothermic machine preservation and is mandatory in normothermic machine preservation, although in the latter, supraphysiological oxygen tensions should be avoided. High-risk grafts, such as suboptimal organs, may optimally benefit from oxygenated perfusion conditions that support metabolism and activate mechanisms of repair such as subnormothermic machine preservation, controlled oxygenated rewarming, and normothermic machine preservation. For lower risk grafts, oxygenation during hypothermic machine preservation may sufficiently reduce injuries and recharge the cellular energy to secure functional recovery after transplantation.

SUMMARY

The relationship between temperature and oxygenation in organ preservation is more complex than physiological laws would suggest. Rather than one default perfusion temperature/oxygenation standard, perfusion protocols should be tailored for specific needs of grafts of different quality.

Cold storage or normothermic perfusion for liver transplantation: probable application and indications

PURPOSE OF REVIEW

Preservation of the liver via normothermic machine perfusion (NMP) is rapidly becoming an area of great academic and clinical interest. This review focuses on the benefits and limitations of NMP and where the role for static cold storage may lie.

RECENT FINDINGS

Clinical studies have recently been published reporting the use of NMP in liver preservation for transplantation. They have described the technology to be well tolerated and feasible with potentially improved posttransplant outcomes. NMP facilitates extended preservation times as well as the potential to increase organ utilization through viability assessment and regeneration. However, this technology is considerably more costly than cold storage and carries significant logistical challenges. Cold storage remains the gold standard preservation for standard criteria livers with good long-term patient and graft survival.

SUMMARY

NMP is an exciting new technological advancement in liver preservation, which is likely to have a positive impact in liver transplantation. However, randomized controlled trials are required to justify its inclusion into standard practice and provide evidence to support its efficacy.

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.

Hypo- and normothermic perfusion of the liver: Which way to go?

The demand of donor livers for transplantation exceeds the supply. In an attempt to maximize the number of potentially usable donor livers, several centers are exploring the role of machine perfusion. This review provides an update on machine perfusion strategies and basic concepts, based on current clinical issues, and discuss challenges, including currently used biomarkers for assessing the quality and viability of perfused organs. The potential benefits of machine perfusion on immunogenicity and the consequences on post-operative immunosuppression management are discussed.

NAFLD and liver transplantation: Current burden and expected challenges

Because of global epidemics of obesity and type 2 diabetes, the prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing both in Europe and the United States, becoming one of the most frequent causes of chronic liver disease and predictably, one of the leading causes of liver transplantation both for end-stage liver disease and hepatocellular carcinoma. For most transplant teams around the world this will raise many challenges in terms of pre- and post-transplant management. Here we review the multifaceted impact of NAFLD on liver transplantation and will discuss: (1) NAFLD as a frequent cause of cryptogenic cirrhosis, end-stage chronic liver disease, and hepatocellular carcinoma; (2) prevalence of NAFLD as an indication for liver transplantation both in Europe and the United States; (3) the impact of NAFLD on the donor pool; (4) the access of NAFLD patients to liver transplantation and their management on the waiting list in regard to metabolic, renal and vascular comorbidities; (5) the prevalence and consequences of post-transplant metabolic syndrome, recurrent and de novo NAFLD; (6) the alternative management and therapeutic options to improve the long-term outcomes with particular emphasis on the correction and control of metabolic comorbidities.

Liver graft preconditioning, preservation and reconditioning

Liver transplantation is the successful treatment of end-stage liver disease; however, the ischaemia-reperfusion injury still jeopardizes early and long-term post-transplant outcomes. In fact, ischaemia-reperfusion is associated with increased morbidity and graft dysfunction, especially when suboptimal donors are utilized. Strategies to reduce the severity of ischaemia-reperfusion can be applied at different steps of the transplantation process: organ procurement, preservation phase or before revascularization. During the donor procedure, preconditioning consists of pre-treating the graft prior to a sustained ischaemia either by a transient period of ischaemia-reperfusion or administration of anti-ischaemic medication, although a multi-pharmacological approach seems more promising. Different preservation solutions were developed to maintain graft viability during static cold storage, achieving substantial results in terms of liver function and survival in good quality organs but not in suboptimal ones. Indeed, preservation solutions do not prevent dysfunction of poor quality organs and are burdened with inadequate preservation of the biliary epithelium. Advantages derived from either hypo- or normothermic machine perfusion are currently investigated in experimental and clinical settings, suggesting a reconditioning effect possibly improving hepatocyte and biliary preservation and resuscitating graft function prior to transplantation. In this review, we highlight acquired knowledge and recent advances in liver graft preconditioning, preservation and reconditioning.

Machine Perfusion of Donor Livers for Transplantation: A Proposal for Standardized Nomenclature and Reporting Guidelines

With increasing demand for donor organs for transplantation, machine perfusion (MP) promises to be a beneficial alternative preservation method for donor livers, particularly those considered to be of suboptimal quality, also known as extended criteria donor livers. Over the last decade, numerous studies researching MP of donor livers have been published and incredible advances have been made in both experimental and clinical research in this area. With numerous research groups working on MP, various techniques are being explored, often applying different nomenclature. The objective of this review is to catalog the differences observed in the nomenclature used in the current literature to denote various MP techniques and the manner in which methodology is reported. From this analysis, we propose a standardization of nomenclature on liver MP to maximize consistency and to enable reliable comparison and meta-analyses of studies. In addition, we propose a standardized set of guidelines for reporting the methodology of future studies on liver MP that will facilitate comparison as well as clinical implementation of liver MP procedures.

Glial cell line-derived neurotrophic factor-induced mice liver defatting: A novel strategy to enable transplantation of steatotic livers

Moderate macrovesicular steatosis (>30%), which is present in almost 50% of livers considered for transplantation, increases the risk of primary graft dysfunction. Our previously published data showed that glial cell line-derived neurotrophic factor (GDNF) is protective against high-fat diet (HFD)-induced hepatic steatosis in mice. Hence, we hypothesized that perfusion of steatotic livers with GDNF may reduce liver fat content before transplantation. Livers from 8 weeks of regular diet (RD) and of HFD-fed mice were perfused ex vivo for 4 hours with either vehicle, GDNF, or a previously described defatting cocktail. The liver's residual fat was quantified colorimetrically using a triglyceride (TG) assay kit and by Oil Red O (ORO) and Nile red/Hoechst staining. Liver tissue injury was assessed by using a lactate dehydrogenase (LDH) activity assay. In vitro induction of lipolysis in HepG2 cells was assessed by measuring glycerol and free fatty acid release. ORO staining showed significantly more steatosis in livers from HFD-fed mice compared with RD-fed mice (P < 0.001). HFD livers perfused with GDNF had significantly less steatosis than those not perfused (P = 0.001) or perfused with vehicle (P < 0.05). GDNF is equally effective in steatotic liver defatting compared to the defatting cocktail; however, GDNF induces less liver damage than the defatting cocktail. These observations were consistent with data obtained from assessment of liver TG content. Assessment of liver injury revealed significant hepatocyte injury in livers perfused with the control defatting cocktail but no evidence of injury in livers perfused with either GDNF or vehicle. In vitro, GDNF reduced TG accumulation in HepG2 cells and stimulated increased TG lipolysis. In conclusion, GDNF can decrease mice liver fat content to an acceptable range and could be a potential defatting agent before liver transplantation.

Metabolic Flux Distribution during Defatting of Steatotic Human Hepatoma (HepG2) Cells

Methods that rapidly decrease fat in steatotic hepatocytes may be helpful to recover severely fatty livers for transplantation. Defatting kinetics are highly dependent upon the extracellular medium composition; however, the pathways involved are poorly understood. Steatosis was induced in human hepatoma cells (HepG2) by exposure to high levels of free fatty acids, followed by defatting using plain medium containing no fatty acids, or medium supplemented with a cocktail of defatting agents previously described before. We measured the levels of 28 extracellular metabolites and intracellular triglyceride, and fed the data into a steady-state mass balance model to estimate strictly intracellular fluxes. We found that during defatting, triglyceride content decreased, while beta-oxidation, the tricarboxylic acid cycle, and the urea cycle increased. These fluxes were augmented by defatting agents, and even more so by hyperoxic conditions. In all defatting conditions, the rate of extracellular glucose uptake/release was very small compared to the internal supply from glycogenolysis, and glycolysis remained highly active. Thus, in steatotic HepG2 cells, glycolysis and fatty acid oxidation may co-exist. Together, these pathways generate reducing equivalents that are supplied to mitochondrial oxidative phosphorylation.

Normothermic liver preservation: a new paradigm?

Despite increasing donor numbers, waiting lists and pre-transplant mortality continue to grow in many countries. The number of donor organs suitable for liver transplantation is restricted by cold preservation and ischemia-reperfusion injury (IRI). Transplantation of marginal donor organs has led to renewed interest in new techniques which have the potential to improve the quality of preservation, assess the quality of the organ and allow repair of the donor organ prior to transplantation. If successful, such techniques would not only improve the outcome of currently transplanted marginal livers, but also increase the donor pool. Experimental evidence suggests that preservation under near physiological conditions of temperature and oxygenation abrogates IRI. Normothermic perfusion maintains the organ in a physiological state, avoiding the depletion of cellular energy and the accumulation of waste products, which occurs with static cold storage. It enables viability assessment prior to transplantation thereby reducing the risk of transplanting inherently marginal organs. Here we review the use of normothermic machine perfusion as a means of organ preservation.

Liver preservation with machine perfusion and a newly developed cell-free oxygen carrier solution under subnormothermic conditions

We describe a new preservation modality combining machine perfusion (MP) at subnormothermic conditions(21 °C) with a new hemoglobin-based oxygen carrier (HBOC) solution. MP (n=6) was compared to cold static preservation (CSP; n=6) in porcine orthotopic liver transplants after 9 h of cold ischemia and 5-day follow-up. Recipients' peripheral blood, serial liver biopsies, preservation solutions and bile specimens were collected before, during and after liver preservation. Clinical laboratorial and histological analyses were performed in addition to mitochondrial functional assays, transcriptomic, metabolomic and inflammatory inflammatory mediator analyses. Compared with CSP, MP animals had: (1) significantly higher survival (100%vs. 33%; p<0.05); (2) superior graft function (p<0.05);(3) eight times higher hepatic O2 delivery than O2 consumption (0.78 mL O2/g/h vs. 0.096 mL O2/g/h) during MP; and (4) significantly greater bile production (MP=378.5 ± 179.7; CS=151.6 ± 116.85). MP downregulated interferon (IFN)-α and IFN-γ in liver tissue. MP allografts cleared lactate, produced urea, sustained gluconeogenesis and produced hydrophilic bile after reperfusion. Enhanced oxygenation under subnormothermic conditions triggers regenerative and cell protective responses resulting in improved allograft function. MP at 21 °C with the HBOC solution significantly improves liver preservation compared to CSP.