Hypothermic machine perfusion of liver grafts for transplantation: technical development in human discard and miniature swine models

Current Status of Liver Transplantation in North America

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

Ex Vivo Liver Machine Perfusion: Comprehensive Review of Common Animal Models

The most common preservation technique for liver grafts is static cold storage. Due to the organ shortage for liver transplantation (LT), extended criteria donor (ECD) allografts are increasingly used-despite the higher risk of inferior outcome after transplantation. Ex vivo liver machine perfusion (MP) has been developed to improve the outcome of transplantation, especially with ECD grafts, and is currently under evaluation in clinical trials. We performed a literature search on PubMed and ISI Web of Science to assemble an overview of rodent and porcine animal models of ex vivo liver MP for transplantation, which is essential for the present and future development of clinical liver MP. Hypothermic, subnormothermic, and normothermic MP systems have been successfully used for rat and pig LT. In comparison with hypothermic systems, normothermic perfusion often incorporates a dialysis unit. Moreover, it enables metabolic assessment of liver grafts. Allografts experiencing warm ischemic time have a superior survival rate after MP compared with cold storage alone, irrespective of the temperature used for perfusion. Furthermore, ex vivo MP improves the outcome of regular and ECD liver grafts in animal models. Small and large animal models of ex vivo liver MP are available to foster the further development of this new technology. Impact Statement Ex vivo machine perfusion is an important part of current research in the field of liver transplantation. While evidence for improve storage is constantly rising, the development of future applications such as quality assessment and therapeutic interventions necessitates robust animal models. This review is intended to provide an overview of this technology in common large and small animal models and to give an outlook on future applications. Moreover, we describe developmental steps that can be followed by others, and which can help to decrease the number of animals used for experiments based on the replace, reduce, refine concept.

Novel oxygenation technique for hypothermic machine perfusion of liver grafts: Validation in porcine Donation after Cardiac Death (DCD) liver model

BACKGROUND

Hypothermic oxygenated machine perfusion improves outcomes in Liver Transplantation, but application is limited as O₂ is supplied by a stationary circuit. A novel technique of O₂ "pre-charge" in a portable pump would broaden use and further mitigate ischemia damage from organ transport.

METHODS

Porcine DCD livers were randomized to static cold storage (SCS, n = 8) or hypothermic machine perfusion (HMP). HMP was stratified into HMP-O₂ (n = 5), non-O₂ open to air HMP-RA (n = 5), and non-O₂ with sealed lids or no air HMP-NA (n = 5). HMP-O₂ was "pre-charged" using 100% O₂ delivered at 10 L/min over 15 min. Perfusate and tissue O₂ tension (pO₂), liver biopsies, and fluid chemistries were analyzed.

RESULTS

"Pre-charge" achieves sustained tissue and perfusate pO₂ vs others. HMP-O₂ results in decreased markers of hepatocyte injury: ALT (p < 0.05) and LDH (p < 0.05), lower expression of CRP and higher expression of SOD1 vs SCS. This suggests decreased inflammation and improved ROS scavenging.

CONCLUSIONS

"Pre-charge" is an effective technique, which allows portability and transport without an O₂ source and improves graft parameters.

Machine Perfusion: Cold versus Warm, versus Neither. Update on Clinical Trials

Machine perfusion (MP) preservation is potentially one of the most significant improvements in the field of liver transplantation in the last 20 years, and it has been considered a promising strategy for improved preservation and ex situ evaluation of extended criteria donor (ECD) organs. However, MP preservation adds significant cost and logistical considerations to liver transplantation. MP protocols are mainly classified according to the perfusion temperature with hypothermic machine perfusion (HMP) and normothermic machine perfusion (NMP) being the two categories most studied so far. After extensive preclinical work, MP entered the clinical setting, and there are now several studies that demonstrated feasibility and safety. However, because of the limited quality of clinical trials, there is no compelling evidence of superiority in preservation quality, and liver MP is still considered experimental in most countries. MP preservation is moving to a more mature phase, where ongoing and future studies will bring new evidence in order to confirm their superiority in terms of clinical outcomes, organ utilization, and cost-effectiveness. Here, we present an overview of all preclinical MP studies using discarded human livers and liver MP clinical trials, and discuss their results. We describe the different perfusion protocols, pitfalls in MP study design, and provide future perspectives. Recent trials in liver MP have revealed unique challenges beyond those seen in most clinical studies. Randomized trials, correct trial design, and interpretation of data are essential to generate the data necessary to prove if MP will be the new gold standard method of liver preservation.

The ultrastructural characteristics of bile canaliculus in porcine liver donated after cardiac death and machine perfusion preservation

The effects of each type of machine perfusion preservation (MP) of liver grafts donated after cardiac death on the bile canaliculi of hepatocytes remain unclear. We analyzed the intracellular three-dimensional ultrastructure of the bile canaliculi and hepatocyte endomembrane systems in porcine liver grafts after warm ischemia followed by successive MP with modified University of Wisconsin gluconate solution. Transmission and osmium-maceration scanning electron microscopy revealed that lumen volume of the bile canaliculi decreased after warm ischemia. In liver grafts preserved by hypothermic MP condition, bile canaliculi tended to recover in terms of lumen volume, while their microvilli regressed. In contrast, midthermic MP condition preserved the functional form of the microvilli of the bile canaliculi. Machine perfusion preservation potentially restored the bile canaliculus lumen and alleviated the cessation of cellular endocrine processes due to warm ischemia. In addition, midthermic MP condition prevented the retraction of the microvilli of bile canaliculi, suggesting further mitigation of the damage of the bile canaliculi.

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.

Hypothermic machine perfusion reduces the incidences of early allograft dysfunction and biliary complications and improves 1-year graft survival after human liver transplantation: A meta-analysis

BACKGROUND

The worldwide organ shortage continues to be the main limitation of liver transplantation. To bridge the gap between the demand and supply of liver grafts, it becomes necessary to use extended criteria donor livers for transplantation. Hypothermic machine perfusion (HMP) is designed to improve the quality of preserved organs before implantation. In clinical liver transplantation, HMP is still in its infancy.

METHODS

A systematic search of the PubMed, EMBASE, Springer, and Cochrane Library databases was performed to identify studies comparing the outcomes in patients with HMP versus static cold storage (SCS) of liver grafts. The parameters analyzed included the incidences of primary nonfunction (PNF), early allograft dysfunction (EAD), vascular complications, biliary complications, length of hospital stay, and 1-year graft survival.

RESULTS

A total of 6 studies qualified for the review, involving 144 and 178 liver grafts with HMP or SCS preservation, respectively. The incidences of EAD and biliary complications were significantly reduced with an odds ratio (OR) of 0.36 (95% confidence interval [CI] 0.17-0.77, P = .008) and 0.47 (95% CI 0.28-0.76, P = .003), respectively, and 1-year graft survival was significantly increased with an OR of 2.19 (95% CI 1.14-4.20, P = .02) in HMP preservation compared to SCS. However, there was no difference in the incidence of PNF (OR 0.30, 95% CI 0.06-1.47, P = .14), vascular complications (OR 0.69, 95% CI 0.29-1.66, P = .41), and the length of hospital stay (mean difference -0.30, 95% CI -4.10 to 3.50, P = .88) between HMP and SCS preservation.

CONCLUSIONS

HMP was associated with a reduced incidence of EAD and biliary complications, as well as an increased 1-year graft survival, but it was not associated with the incidence of PNF, vascular complications, and the length of hospital stay.

Organ Preservation into the 2020s: The Era of Dynamic Intervention

Organ preservation has been of major importance ever since transplantation developed into a global clinical activity. The relatively simple procedures were developed on a basic comprehension of low-temperature biology as related to organs outside the body. In the past decade, there has been a significant increase in knowledge of the sequelae of effects in preserved organs, and how dynamic intervention by perfusion can be used to mitigate injury and improve the quality of the donated organs. The present review focuses on (1) new information about the cell and molecular events impacting on ischemia/reperfusion injury during organ preservation, (2) strategies which use varied compositions and additives in organ preservation solutions to deal with these, (3) clear definitions of the developing protocols for dynamic organ perfusion preservation, (4) information on how the choice of perfusion solutions can impact on desired attributes of dynamic organ perfusion, and (5) summary and future horizons.

Evaluation Using an Isolated Reperfusion Model for Porcine Liver Donated After Cardiac Death Preserved with Oxygenated Hypothermic Machine Perfusion

BACKGROUND Machine perfusion techniques offer a solution to the serious organ shortage. However, to assess the effects of machine perfusion, many detailed studies are required. In this study, an ex vivo reperfusion model using diluted autologous blood was confirmed to evaluate the utility of machine preservation for livers donated after cardiac death (DCD). In particular, beneficial effects of the oxygenated hypothermic machine perfusion (HMP) for DCD porcine livers are evaluated. MATERIAL AND METHODS Porcine livers were procured under warm ischemia time (WIT) of 60 min. The livers were preserved by hypothermic machine perfusion (HMP) or static cold storage (CS) for 4 h. After the preservation, the livers were perfused for 2 h using the ex vivo reperfusion model with diluted blood oxygenated by a membrane oxygenator at 35-38°C. RESULTS At 2 h of ex vivo reperfusion with 60 min of warm ischemic time (WIT), the portal vein pressure for CS was higher than HMP (18.8±15.9 vs. 7.5±3.9 [mmHg] in 60 min). Furthermore, LDH in CS was higher than HMP (528.5±149.8 vs. 194.1±32.2 [IU/L/100 g liver] in 60 min. P<0.05). Lactate after CS (60) was significantly higher than HMP (60) (8.67±0.39 vs. 5.68±0.60 [mmol/L] at 60 min. p<0.01). CONCLUSIONS The ex vivo reperfusion model can be used to evaluate the utility of machine perfusion. Advantages of HMP for DCD livers are evaluated with this model.

Liver Transplantation Today: Where We Are Now and Where We Are Going

Liver transplantation was made a reality through the bravery, innovation, and persistence of Dr. Thomas Starzl. His death in 2017, at the age of 90, makes us pause to consider how far the field has come since its inception by this remarkable pioneer. It also is an opportunity to evaluate the continued novel innovations which contribute to the growth and potential for liver transplantation in the future. The liver transplant community in 2017 continued to be most significantly challenged by an overwhelming disparity between the need for liver transplant and the shortage of donor organs. The many ways in which this critical shortage are being addressed are examined in this article. The continued debate about equitable and efficacious organ allocation, "the liver wars," has dominated much of the recent past, while efforts to optimize current organ availability have also been aggressively pursued. Efforts to optimize the use of marginal and expanded criteria organs have escalated in recent years and have been accompanied by rigorous scientific evaluation. The ongoing opioid epidemic, combined with the approval and availability of highly effective hepatitis C treatment options, has allowed the increased use of HCV positive organs in HCV positive and negative recipients. Machine perfusion, both cold and warm, has moved solidly into the liver transplant world potentiating optimization of marginal donors and also offering potential modulation of liver grafts (ie, gene therapy, stem cell therapy, and defatting). Finally, pharmacological and mechanical interventions in DCD procurement techniques have contributed to improved outcomes in DCD transplants. All of these are explored in this article as a tribute to innovative spirit of Dr. Starzl and his continued impact on liver transplant today.

Hypothermic oxygenated machine perfusion reduces bile duct reperfusion injury after transplantation of donation after circulatory death livers

Dual hypothermic oxygenated machine perfusion (DHOPE) of the liver has been advocated as a method to reduce ischemia/reperfusion injury (IRI). This study aimed to determine whether DHOPE reduces IRI of the bile ducts in donation after circulatory death (DCD) liver transplantation. In a recently performed phase 1 trial, 10 DCD livers were preserved with DHOPE after static cold storage (SCS; www.trialregister.nl NTR4493). Bile duct biopsies were obtained at the end of SCS (before DHOPE; baseline) and after graft reperfusion in the recipient. Histological severity of biliary injury was graded according to an established semiquantitative grading system. Twenty liver transplantations using DCD livers not preserved with DHOPE served as controls. Baseline characteristics and the degree of bile duct injury at baseline (end of SCS) were similar between both groups. In controls, the degree of stroma necrosis (P = 0.002) and injury of the deep peribiliary glands (PBG; P = 0.02) increased after reperfusion compared with baseline. In contrast, in DHOPE-preserved livers, the degree of bile duct injury did not increase after reperfusion. Moreover, there was less injury of deep PBG (P = 0.04) after reperfusion in the DHOPE group compared with controls. In conclusion, this study suggests that DHOPE reduces IRI of bile ducts after DCD liver transplantation. Liver Transplantation 24 655-664 2018 AASLD.

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.

Successful transplantation of porcine liver grafts following 48-hour normothermic preservation

Current cold storage organ preservation technique fails to preserve marginal donor grafts sufficiently. Evidence from large animal experiments suggests superiority of normothermic machine preservation of liver allografts. Long-term organ preservation using normothermic perfusion might not only allow organ viability assessment before transplantation, but also provide the means for further organ modifications under physiologic conditions. Previous research has shown that porcine livers can be transplanted successfully after normothermic preservation of 20 hours. In the present study we investigate whether similar methodology is capable of further extending the safe limit to 48 hours. In this study, livers from White Landrace pigs were preserved by normothermic, oxygenated sanguineous perfusion. After a 48-hour period of preservation, livers were transplanted into recipient pigs and followed for 5 days. Outcome parameters measured included markers of synthetic and metabolic liver function as well as hepatocellular injury and blood gas analysis during perfusion and follow-up. Histological assessment of morphological liver integrity was performed. All livers showed sustained bile production and metabolic activity throughout the preservation period. Low levels of hepatocellular damage were found. Following transplantation all liver grafts revealed excellent graft function and death-censored graft survival was 100%. Porcine livers were transplanted successfully following 48 hours normothermic machine preservation.

The ultrastructural characteristics of porcine hepatocytes donated after cardiac death and preserved with warm machine perfusion preservation

The effects of warm machine perfusion preservation of liver grafts donated after cardiac death on the intracellular three-dimensional ultrastructure of the organelles in hepatocytes remain unclear. Here we analyzed comparatively the ultrastructure of the endomembrane systems in porcine hepatocytes under warm ischemia and successive hypothermic and midthermic machine perfusion preservation, a type of the warm machine perfusion. Porcine liver grafts which had a warm ischemia time of 60 minutes were perfused for 4 hours with modified University of Wisconsin gluconate solution. Group A grafts were preserved with hypothermic machine perfusion preservation at 8°C constantly for 4 hours. Group B grafts were preserved with rewarming up to 22°C by warm machine perfusion preservation for 4 hours. An analysis of hepatocytes after 60 minutes of warm ischemia by scanning electron microscope revealed the appearance of abnormal vacuoles and invagination of mitochondria. In the hepatocytes preserved by subsequent hypothermic machine perfusion preservation, strongly swollen mitochondria were observed. In contrast, the warm machine perfusion preservation could preserve the functional appearance of mitochondria in hepatocytes. Furthermore, abundant vacuoles and membranous structures sequestrating cellular organelles like autophagic vacuoles were frequently observed in hepatocytes after warm machine perfusion preservation. In conclusion, the ultrastructure of the endomembrane systems in the hepatocytes of liver grafts changed in accordance with the temperature conditions of machine perfusion preservation. In addition, temperature condition of the machine perfusion preservation may also affect the condition of the hepatic graft attributed to autophagy systems, and consequently alleviate the damage of the hepatocytes.

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.

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

Different organ preservation methods are key factors influencing the results of liver 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.

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.

Past, Present, and Future of Dynamic Kidney and Liver Preservation and Resuscitation

The increased demand for organs has led to the increased usage of "higher risk" kidney and liver grafts. These grafts from donation after circulatory death or expanded criteria donors are more susceptible to preservation injury and have a higher risk of unfavorable outcomes. Dynamic, instead of static, preservation could allow for organ optimization, offering a platform for viability assessment, active organ repair and resuscitation. Ex situ machine perfusion and in situ regional perfusion in the donor are emerging as potential tools to preserve and resuscitate vulnerable grafts. Preclinical findings have ignited clinical organ preservation research that investigates dynamic preservation, its various modes (continuous, preimplantation) and temperatures (hypo-, sub, or normothermic). This review outlines the current status of dynamic preservation of kidney and liver grafts and describes ongoing research and emerging clinical trials.

Potential approaches to improve the outcomes of donation after cardiac death liver grafts

There is a growing discrepancy between the supply and demand of livers for transplantation resulting in high mortality rates on the waiting list. One of the options to decrease the mortality on the waiting list is to optimize organs with inferior quality that otherwise would be discarded. Livers from donation after cardiac death (DCD) donors are frequently discarded because they are exposed to additional warm ischemia time, and this might lead to primary-non-function, delayed graft function, or severe biliary complications. In order to maximize the usage of DCD livers several new preservation approaches have been proposed. Here, we will review 3 innovative organ preservation methods: (1) different ex vivo perfusion techniques; (2) persufflation with oxygen; and (3) addition of thrombolytic therapy. Improvement of the quality of DCD liver grafts could increase the pool of liver graft’s for transplantation, improve the outcomes, and decrease the mortality on the waiting list.

Liver transplantation: Current status and challenges

Great progress has been made in the field of liver transplantation over the past two decades. This progress, however, also brings up the next set of challenges: First, organ shortage remains a major limitation, and accounts for a large proportion of wait list mortality. While living donation has successfully increased the total number of liver transplants done in Asian countries, the total number of such transplants has been stagnant in the western hemisphere. As such, there has been a significant effort over the past decade to increase the existing deceased donor pool. This effort has resulted in a greater use of liver allografts following donation after cardiac death (DCD) along with marginal and extended criteria donors. Improved understanding of the pathophysiology of liver allografts procured after circulatory arrest has not only resulted in better selection and management of DCD donors, but has also helped in the development of mechanical perfusion strategies. Early outcomes demonstrating the clinical applicability of both hypothermic and normothermic perfusion and its potential to impact patient survival and allograft function have generated much interest. Second, long-term outcomes of liver transplant recipients have not improved significantly, as recipients continue to succumb to complications of long-term immunosuppression, such as infection, malignancy and renal failure. Furthermore, recent evidence suggests that chronic immune-mediated injury to the liver may also impact graft function.

Hypothermic Oxygenated Liver Perfusion: Basic Mechanisms and Clinical Application

Dynamic preservation strategies such as hypothermic machine perfusion are increasingly discussed to improve liver graft quality before transplantation. This review summarizes current knowledge of this perfusion technique for liver preservation. We discuss optimization of perfusion conditions and current strategies to assess graft quality during cold perfusion. Next, we provide an overview of possible pathways of protection from ischemia-reperfusion injury. Finally, we report on recent clinical applications of human hypothermic machine liver perfusion.

Technique of porcine liver procurement and orthotopic transplantation using an active porto-caval shunt

The success of liver transplantation has resulted in a dramatic organ shortage. Each year, a considerable number of patients on the liver transplantation waiting list die without receiving an organ transplant or are delisted due to disease progression. Even after a successful transplantation, rejection and side effects of immunosuppression remain major concerns for graft survival and patient morbidity.

Experimental animal research has been essential to the success of liver transplantation and still plays a pivotal role in the development of clinical transplantation practice. In particular, the porcine orthotopic liver transplantation model (OLTx) is optimal for clinically oriented research for its close resemblance to human size, anatomy, and physiology.

Decompression of intestinal congestion during the anhepatic phase of porcine OLTx is important to guarantee reliable animal survival. The use of an active porto-caval-jugular shunt achieves excellent intestinal decompression. The system can be used for short-term as well as long-term survival experiments. The following protocol contains all technical information for a stable and reproducible liver transplantation model in pigs including post-operative animal care.

Challenges to liver transplantation and strategies to improve outcomes

Liver transplantation (LT) is a highly successful treatment for many patients with nonmalignant and malignant liver diseases. However, there is a worldwide shortage of available organs; many patients deteriorate or die while on waiting lists. We review the important clinical challenges to LT and the best use of the scarce organs. We focus on changes in indications for LT and discuss scoring systems to best match donors with recipients and optimize outcomes, particularly for the sickest patients. We also cover controversial guidelines for the use of LT in patients with hepatocellular carcinoma and cholangiocarcinoma. Strategies to increase the number of functional donor organs involve techniques to perfuse the organs before implantation. Partial LT (living donor and split liver transplantation) techniques might help to overcome organ shortages, and we discuss small-for-size syndrome. Many new developments could increase the success of this procedure, which is already one of the major achievements in medicine during the second part of the 20th century.

The bile duct in donation after cardiac death donor liver transplant

PURPOSE OF REVIEW

This review considers the biliary complications associated with liver transplantation using donation after cardiac death (DCD) donor grafts.

RECENT FINDINGS

The increasing use of DCD liver grafts with their increased incidence of biliary complications is discussed. The ethics of this greater use is briefly analysed. Recent animal and human study evidence to support the peribiliary vascular plexus' role in ischaemic cholangiopathy is reviewed. Recent advances in in-vivo and ex-vivo perfusion are explored. In particular, the latest theories regarding perfusion's peribiliary plexus preserving effects and the mechanism by which biliary regeneration may be promoted as a consequence are discussed.

SUMMARY

This article explores the need for DCD liver graft use and the associated biliary complications. The current theories regarding the cause of DCD biliary complications are reviewed, as are the current strategies to reduce them.

Impact of machine perfusion preservation of liver grafts from donation after cardiac death

Because of the critical shortage of deceased donor grafts, using a donation after cardiac death (DCD) donor is an important resource. However, the ischemic damage of those DCD grafts jeopardizes organ viability during cold storage. Maintaining organ viability after donation until transplantation is important for optimal graft function and survival. This review describes the effective preservation in transplantation for DCD livers. Concepts and development of machine perfusion for DCD liver grafts to reduce ischemia/reperfusion injury are discussed. Despite the fact that hypothermic machine perfusion might be superior to static cold preservation, DCD livers are exposed to hypothermia-induced damage. Recently, some groups introduced the beneficial effects of normothermic or subnormothermic machine perfusion in DCD liver preservation and transplantation.

Warm vs. cold perfusion techniques to rescue rodent liver grafts

BACKGROUND & AIMS

A variety of liver perfusion techniques have been proposed to protect liver grafts prior to implantation. We compared hypothermic and normothermic oxygenated perfusion techniques in a rat liver transplant model, using higher risk grafts obtained after cardiac arrest (DCD).

METHODS

Rat livers were subjected to 30 or 60 min in situ warm ischemia, without application of heparin. Livers were excised and stored for 4 h at 4°C, mimicking DCD organ procurement, followed by conventional organ transport. In experimental groups, DCD liver grafts received a 4 h normothermic oxygenated perfusion through the portal vein and the hepatic artery instead of cold storage. The perfusate consisted of either full blood or leukocyte-depleted blood (normothermic groups). Other livers underwent hypothermic oxygenated perfusion (HOPE) for 1 h after warm ischemia and 4 h cold storage (HOPE group). Liver injury was assessed during machine perfusion and after isolated liver reperfusion, and by orthotopic liver transplantation (OLT).

RESULTS

DCD livers, subjected to normothermic perfusion, disclosed reduced injury and improved survival compared to cold storage after limited warm ischemia of 30 min (70%; 7/10), but failed to protect from lethal injury in grafts exposed to 60 min warm ischemia (0%; 0/10). This finding was consistent with Kupffer and endothelial cell activation in cold stored and normothermic perfused livers. In contrast, HOPE protected from hepatocyte and non-parenchymal cell injury and led to 90% (9/10) and 63% (5/8) animal survival after 30 and 60 min of donor warm ischemia, respectively.

CONCLUSIONS

This is the first evidence that HOPE is superior to normothermic oxygenated perfusion in a clinically relevant model through modulation of the innate immunity and endothelial cell activation.

Subnormothermic ex vivo liver perfusion reduces endothelial cell and bile duct injury after donation after cardiac death pig liver transplantation

An ischemic-type biliary stricture (ITBS) is a common feature after liver transplantation using donation after cardiac death (DCD) grafts. We compared sequential subnormothermic ex vivo liver perfusion (SNEVLP; 33°C) with cold storage (CS) for the prevention of ITBS in DCD liver grafts in pig liver transplantation (n = 5 for each group). Liver grafts were stored for 10 hours at 4°C (CS) or preserved with combined 7-hour CS and 3-hour SNEVLP. Parameters of hepatocyte [aspartate aminotransferase (AST), international normalized ratio (INR), factor V, and caspase 3 immunohistochemistry], endothelial cell (EC; CD31 immunohistochemistry and hyaluronic acid), and biliary injury and function [alkaline phosphatase (ALP), total bilirubin, and bile lactate dehydrogenase (LDH)] were determined. Long-term survival (7 days) after transplantation was similar between the SNEVLP and CS groups (60% versus 40%, P = 0.13). No difference was observed between SNEVLP- and CS-treated animals with respect to the peak of serum INR, factor V, or AST levels within 24 hours. CD31 staining 8 hours after transplantation demonstrated intact EC lining in SNEVLP-treated livers (7.3 × 10(-4) ± 2.6 × 10(-4) cells/μm(2)) but not in CS-treated livers (3.7 × 10(-4) ± 1.3 × 10(-4) cells/μm(2) , P = 0.03). Posttransplant SNEVLP animals had decreased serum ALP and serum bilirubin levels in comparison with CS animals. In addition, LDH in bile fluid was lower in SNEVLP pigs versus CS pigs (14 ± 10 versus 60 ± 18 μmol/L, P = 0.02). Bile duct histology revealed severe bile duct necrosis in 3 of 5 animals in the CS group but none in the SNEVLP group (P = 0.03). Sequential SNEVLP preservation of DCD grafts reduces bile duct and EC injury after liver transplantation.

"Resuscitation" of marginal liver allografts for transplantation with machine perfusion technology

As the rate of medically suitable donors remains relatively static worldwide, clinicians have looked to novel methods to meet the ever-growing demand of the liver transplant waiting lists worldwide. Accordingly, the transplant community has explored many strategies to offset this deficit. Advances in technology that target the ex vivo "preservation" period may help increase the donor pool by augmenting the utilization and improving the outcomes of marginal livers. Novel ex vivo techniques such as hypothermic, normothermic, and subnormothermic machine perfusion may be useful to "resuscitate" marginal organs by reducing ischemia/reperfusion injury. Moreover, other preservation techniques such as oxygen persufflation are explored as they may also have a role in improving function of "marginal" liver allografts. Currently, marginal livers are frequently discarded or can relegate the patient to early allograft dysfunction and primary non-function. Bench to bedside advances are rapidly emerging and hold promise for expanding liver transplantation access and improving outcomes.

Role of hypothermic machine perfusion in liver transplantation

Machine liver perfusion has significantly evolved during the last ten years to optimize extended criteria liver grafts and to address the worldwide organ shortage. This review gives an overview on available ex vivo and in vivo data on hypothermic machine liver perfusion. We discuss also possible protective pathways and show most recent clinical applications of hypothermic machine liver perfusion in human.

Impact of brain death on ischemia/reperfusion injury in liver transplantation

PURPOSE OF REVIEW

In liver transplantation, the ischemia/reperfusion injury (IRI) is influenced by factors related to graft quality, organ procurement and the transplant procedure itself. However, in brain-dead donors, the process of death itself also thoroughly affects organ damage through breakdown of the autonomous nervous system and subsequent massive cytokine release. This review highlights the actual knowledge on these proinflammatory effects of brain death on IRI in liver transplantation.

RECENT FINDINGS

Brain death affects IRI either through hemodynamical or molecular effects with proinflammatory activation. Immunological effects are mainly mediated through Kupffer cell activation, leading to TNF-α and TLR4 amplification. Proinflammatory cytokines such as interleukin (IL)-6, IL-10, TNF-β and MIP-1α are released, together with activation of the innate immune system via natural killer cells and natural killer T cells, which promote organ damage and activation of fibrosis. Preprocurement treatment regimens attempt to hamper inflammatory response by the application of methylprednisolone or thymoglobulin to the donor. Selective P-selectin antagonism resulted in improved function in marginal liver grafts. Inhaled nitric oxide was found to reduce apoptosis in liver grafts. Other medications like the immunosuppressant tacrolimus produced conflicting results regarding organ protection. Furthermore, improved organ storage after procurement - such as machine perfusion - can diminish effects of IRI in a clinical setting.

SUMMARY

Brain death plays a fundamental role in the regulation of molecular markers triggering inflammation and IRI-related tissue damage in liver transplants. Although several treatment options have reached clinical application, to date, the effects of brain death during donor conditioning and organ procurement remain relevant for organ function and survival.

Preservation solutions for static cold storage of abdominal allografts: which is best?

PURPOSE OF REVIEW

To update the reader on the recent literature in liver, kidney, pancreas, and intestine static cold preservation, and to identify which solutions are most advantageous for each organ.

RECENT FINDINGS

The comparison of randomized trials of histidine-tryptophan-ketoglutarate (HTK), Celsior, and University of Wisconsin solutions has shown equivalent risk of delayed graft function after kidney transplantation. Similar outcomes have been observed after pancreas preservation with University of Wisconsin, HTK, and Celsior solution. In live-donor liver transplantation, University of Wisconsin and HTK solution have shown equivalent results, whereas in the recent trials of deceased-donor liver transplantation, University of Wisconsin, HTK, and Celsior solutions have shown equivalence. Contrary to the most clinical trials, national registry data in kidney, pancreas, and liver transplantation demonstrate more detrimental effects and earlier graft loss after preservation with HTK versus University of Wisconsin solution. Early outcomes after intestinal transplantation with University of Wisconsin or HTK solution have shown no significant difference and animal studies indicate intraluminal preservation may be beneficial.

SUMMARY

The University of Wisconsin solution is the standard criterion static cold preservation for the procurement of liver, kidney, pancreas, and intestine. University of Wisconsin, HTK, and Celsior solutions all provide similar allograft outcomes in most clinical trials, but subtle differences have become more apparent in the recent studies and registry reports.

Challenges in machine perfusion preservation for liver grafts from donation after circulatory death

Donation after circulatory death (DCD) is a promising solution to the critical shortage of donor graft tissue. Maintaining organ viability after donation until transplantation is essential for optimal graft function and survival. To date, static cold storage is the most widely used form of preservation in clinical practice. However, ischemic damage present in DCD grafts jeopardizes organ viability during cold storage, and whether static cold storage is the most effective method to prevent deterioration of organ quality in the increasing numbers of organs from DCD is unknown. Here we describe the historical background of DCD liver grafts and a new preservation method for experimental and clinical transplantation. To prevent ischemia-reperfusion injury in DCD liver grafts, a hypothermic machine perfusion (HMP) technique has recently been developed and may be superior to static cold preservation. We present evidence supporting the need for improving liver perfusion performance and discuss how doing so will benefit liver transplantation recipients.

Rewarming Machine Perfusion System for Liver Transplantation

The liver is one of the most essential organs, and transplantation is an established treatment for patients with end-stage disease who have lost their liver function. However, organ shortage is a critical problem in transplantation; thus, the development of an innovative preservation system to adopt critical grafts obtained from extended criteria donors or donation after cardiac death donors as viable organs for transplantation is necessary. We recently developed a novel rewarming machine perfusion preservation system for liver transplantation, and herein discuss this system, which allows the perfusion temperature to be controlled during the transition from hypothermic to subnormothermic conditions. This system has two functions: (1) the preservation and recovery of organ function and (2) screening the organ for viability. To achieve these functions, this system has three features: (1) temperature control of the preservation perfusate and liver graft, (2) dual-controlled perfusion of the portal vein and hepatic artery, and (3) real-time monitoring of the perfusion conditions, including the flow rate, perfusion pressure and temperature. This system was useful for liver preservation and for evaluating the graft viability and recovery of functions during machine perfusion before transplantation. This novel rewarming machine preservation system was tested in an experimental model using porcine liver grafts. We report that this system has certain advantages in liver preservation, and believe that this system will positively contribute to the expansion of the organ donor pool.

Innovations in organ donation

The growing disparity between organ availability for transplantation and the number of patients in need has challenged the donation and transplantation community of practice to develop innovative processes, ideas, and techniques to bridge the gaps. Advances in the sharing of best practices in the donation community have contributed greatly over the last 8 years. Broader sharing of updated guidelines for declaration of brain death in conjunction with improvements in deceased donor management have increased opportunities for organ donation. New techniques for organ preservation and organ resuscitation have allowed for better utilization of the potential donor pool. This review will highlight processes, ideas, and techniques in organ donation.

Preservation methods for kidney and liver

With the successful testing of the immunosuppressive effects of cyclosporine in transplant patients in 1978, the field of organ transplants began an exponential growth. With that, the field of organ preservation became increasingly important as the need to increase preservation time and improve graft function became paramount. However, for every patient that receives a transplanted organ, there are four more on the waiting list. In addition, a patient dies from the lack of a transplant almost every 1(1/2) hour. To alleviate this donor crisis, there is a need to expand the donor pool to marginal donor organs. The main reason these organs are underutilized is because the current method of static preservation, simple cold storage, is ineffective. This article will provide a general review of the methods of preservation including simple cold storage, hypothermic machine perfusion, normothermic machine perfusion, and oxygen persufflation. In addition, the article will provide a review of how these dynamic preservation methods have improved the recovery and preservation of marginal donor organs including Donation after Cardiac Death and Fatty livers.

A basic consideration for porcine liver preservation using a novel continuous machine perfusion device

INTRODUCTION

The aims of this study were to compare extracellular and intracellular-type University of Wisconsin (UW) solutions for liver grafts and to assess oxygenation in this perfusion system.

MATERIALS AND METHODS

The organ preservation system consisted of 3 circulating systems for the portal vein, hepatic artery, and maintenance of the perfusion solution. The portal vein or hepatic artery system had a roller pump, a flow meter, and a pressure sensor. In this study, we perfused livers with UW or extracellular type UW-gluconate at 4°C-6°C for 4 hours. The flow rates at the entrance were 0.5 mL/min/g liver in the portal vein and 0.2 mL/min/liver in the hepatic artery. Orthotopic liver transplantation was performed in pigs: group 1-a, grafts procured after acute hemorrhagic shock were preserved by a solution without O(2); group 1-b, grafts were preserved with O(2); group 2-a, grafts were perfused using intracellular type solution (UW); and group 2-b, grafts were perfused using extracellular-type solution (UW-gluconate).

RESULTS

Effluent aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels in group 1-b were lower than those in group 1-a. Survival rates in group 2-a and group 2-b were 1/4 and 3/3, respectively. Effluent AST and LDH levels in the perfusate of group 2-b were lower than group 2-a. Histological study revealed necrosis of hepatocytes and sinusoidal congestion in group 2-a.

CONCLUSION

A beneficial effect of extracellular-type solution with oxygenation in a novel continuous machine preservation system yielded well-preserved liver graft function.

Flow Competition between Hepatic Arterial and Portal Venous flow during Hypothermic Machine Perfusion Preservation of Porcine Livers

Hypothermic machine perfusion (HMP) is regarded as a better preservation method for donor livers than cold storage. During HMP, livers are perfused through the inlet blood vessels, namely the hepatic artery (HA) and the portal vein (PV). In previous HMP feasibility studies of porcine and human livers, we observed that the PV flow decreased while the HA flow increased. This flow competition restored either spontaneously or by lowering the HA pressure (PHA). Since this phenomenon had never been observed before and because it affects the HMP stability, it is essential to gain more insight into the determinants of flow competition. To this end, we investigated the influence of the HMP boundary conditions on liver flows during controlled experiments. This paper presents the flow effects induced by increasing PHA and by obstructing the outlet blood vessel, which is the vena cava inferior (VCI).

Flow competition was evoked by increasing PHA to 55–70 mmHg, as well as by obstructing the VCI. Remarkably, a severe obstruction resulted in a repetitive and alternating tradeoff between the HA and PV flows. These phenomena could be related to intra-sinusoidal pressure alterations. Consequently, a higher PHA is most likely transmitted to the sinusoidal level. This increased sinusoidal pressure reduces the pressure drop between the PV and the sinusoids, leading to a decreased PV perfusion. Flow competition has not been encountered or evoked under physiological conditions and should be taken into account for the design of liver HMP protocols. Nevertheless, more research is necessary to determine the optimal parameters for stable HMP.

Protective effects of hypothermic ex vivo perfusion on ischemia/reperfusion injury and transplant outcomes

Hypothermic machine preservation (HMP) has been used in renal transplantation since the late 1960s with recent robust prospective, multicenter data showing lower rates of delayed graft function and improved graft survival. Although now clearly beneficial for renal transplantation, extrarenal machine perfusion has remained predominantly in preclinical investigations. Pancreatic HMP has drawn little clinical interest because HMP has been suggested to cause graft edema and congestion, which is associated with early venous thrombosis and graft failure. Early investigation showed no benefit of HMP in whole-organ pancreas transplant. One report did show that HMP increases islet cell yield after isolation. Preclinical work in liver HMP has been promising. Short- and long-term HMP has been shown to improve graft viability and reduce preservation injury, even in animal models of steatotic and donation after cardiac death. The first clinical study of liver HMP using a centrifugal dual perfusion technique showed excellent results with lower hepatocellular injury markers and no adverse perfusion-related outcomes. In addition, a dramatic attenuation of proinflammatory cytokine expression was observed. Further studies of liver HMP are planned with focus on developing a reproducible and standard protocol that will allow the widespread availability of this technology. Future research and clinical trials of novel organ preservation techniques, solutions, and interventions are likely to bring about developments that will allow further reduction of preservation-related ischemia/reperfusion injury and improved outcomes and allow safer utilization of the precious and limited resource of donor organs.