Normothermic machine perfusion of discarded liver grafts

How Can Machine Perfusion Change the Paradigm of Liver Transplantation for Patients with Perihilar Cholangiocarcinoma?

Perihilar cholangiocarcinomas (pCCA) are rare yet aggressive tumors originating from the bile ducts. While surgery remains the mainstay of treatment, only a minority of patients are amenable to curative resection, and the prognosis of unresectable patients is dismal. The introduction of liver transplantation (LT) after neoadjuvant chemoradiation for unresectable pCCA in 1993 represented a major breakthrough, and it has been associated with 5-year survival rates consistently >50%. Despite these encouraging results, pCCA has remained a niche indication for LT, which is most likely due to the need for stringent candidate selection and the challenges in preoperative and surgical management. Machine perfusion (MP) has recently been reintroduced as an alternative to static cold storage to improve liver preservation from extended criteria donors. Aside from being associated with superior graft preservation, MP technology allows for the safe extension of preservation time and the testing of liver viability prior to implantation, which are characteristics that may be especially useful in the setting of LT for pCCA. This review summarizes current surgical strategies for pCCA treatment, with a focus on unmet needs that have contributed to the limited spread of LT for pCCA and how MP could be used in this setting, with a particular emphasis on the possibility of expanding the donor pool and improving transplant logistics.

Mesenchymal Stromal Cells, a New Player in Reducing Complications From Liver Transplantation?

In response to the global burden of liver disease there has been a commensurate increase in the demand for liver transplantation. However, due to a paucity of donor organs many centers have moved toward the routine use of marginal allografts, which can be associated with a greater risk of complications and poorer clinical outcomes. Mesenchymal stromal cells (MSC) are a multi-potent progenitor cell population that have been utilized to modulate aberrant immune responses in acute and chronic inflammatory conditions. MSC exert an immunomodulatory effect on innate and adaptive immune systems through the release of both paracrine soluble factors and extracellular vesicles. Through these routes MSC can switch the regulatory function of the immune system through effects on macrophages and T regulatory cells enabling a switch of phenotype from injury to restoration. A key benefit seems to be their ability to tailor their response to the inflammatory environment without compromising the host ability to fight infection. With over 200 clinical trials registered to examine MSC therapy in liver disease and an increasing number of trials of MSC therapy in solid organ transplant recipients, there is increasing consideration for their use in liver transplantation. In this review we critically appraise the potential role of MSC therapy in the context of liver transplantation, including their ability to modulate reperfusion injury, their role in the reduction of medium term complications in the biliary tree and their potential to enhance tolerance in transplanted organs.

Transplanting Marginal Organs in the Era of Modern Machine Perfusion and Advanced Organ Monitoring

Organ transplantation is undergoing profound changes. Contraindications for donation have been revised in order to better meet the organ demand. The use of lower-quality organs and organs with greater preoperative damage, including those from donation after cardiac death (DCD), has become an established routine but increases the risk of graft malfunction. This risk is further aggravated by ischemia and reperfusion injury (IRI) in the process of transplantation. These circumstances demand a preservation technology that ameliorates IRI and allows for assessment of viability and function prior to transplantation. Oxygenated hypothermic and normothermic machine perfusion (MP) have emerged as valid novel modalities for advanced organ preservation and conditioning. Ex vivo prolonged lung preservation has resulted in successful transplantation of high-risk donor lungs. Normothermic MP of hearts and livers has displayed safe (heart) and superior (liver) preservation in randomized controlled trials (RCT). Normothermic kidney preservation for 24 h was recently established. Early clinical outcomes beyond the market entry trials indicate bioenergetics reconditioning, improved preservation of structures subject to IRI, and significant prolongation of the preservation time. The monitoring of perfusion parameters, the biochemical investigation of preservation fluids, and the assessment of tissue viability and bioenergetics function now offer a comprehensive assessment of organ quality and function ex situ. Gene and protein expression profiling, investigation of passenger leukocytes, and advanced imaging may further enhance the understanding of the condition of an organ during MP. In addition, MP offers a platform for organ reconditioning and regeneration and hence catalyzes the clinical realization of tissue engineering. Organ modification may include immunological modification and the generation of chimeric organs. While these ideas are not conceptually new, MP now offers a platform for clinical realization. Defatting of steatotic livers, modulation of inflammation during preservation in lungs, vasodilatation of livers, and hepatitis C elimination have been successfully demonstrated in experimental and clinical trials. Targeted treatment of lesions and surgical treatment or graft modification have been attempted. In this review, we address the current state of MP and advanced organ monitoring and speculate about logical future steps and how this evolution of a novel technology can result in a medial revolution.

The efficacy of HBOC-201 in ex situ gradual rewarming kidney perfusion in a rat model

Gradual rewarming from hypothermic to normothermic is a novel perfusion modality with superior outcome to sudden rewarming to normothermic. However, the identification of an oxygen carrier that could function at a temperature range from 4 to 7°C or whether it is necessary to use oxygen carrier during kidney rewarming, remains unresolved. This study was designed to test the use of a hemoglobin‐based oxygen carrier (HBOC) during gradual kidney rewarming as an alternative to simple dissolved oxygen. In this study, 10 rat kidneys were randomly divided into the control and the HBOC group. In the control group, no oxygen carrier was used during rewarming perfusion and the perfusion solution was oxygenated only by applying diffused carbogen flow. The protocol mimicked a donor after circulatory death (DCD) kidney transplantation, where after 30 minutes warm ischemia and 120 minutes cold storage in University of Wisconsin solution, the DCD kidneys underwent gradual rewarming from 10 to 37°C during 90 minutes with or without HBOC. This was followed by 30 minutes of warm ischemia in room temperature to mimic the anastomosis time and 120 minutes of reperfusion at 37°C to mimic the early post‐transplant state of the graft. The HBOC group demonstrated superior kidney function which was highlighted by higher ultrafiltrate production, better glomerular filtration rate and improved sodium reabsorption. There was no significant difference between the 2 groups regarding the hemodynamics, tissue injury, and adenosine triphosphate levels. In conclusion, this study suggests better renal function recovery in DCD kidneys after rewarming with HBOC compared to rewarming without an oxygen carrier.

Opposite acute potassium and sodium shifts during transplantation of hypothermic machine perfused donor livers

Liver transplantation is frequently associated with hyperkalemia, especially after graft reperfusion. Dual hypothermic oxygenated machine perfusion (DHOPE) reduces ischemia/reperfusion injury and improves graft function, compared to conventional static cold storage (SCS). We examined the effect of DHOPE on ex situ and in vivo shifts of potassium and sodium. Potassium and sodium shifts were derived from balance measurements in a preclinical study of livers that underwent DHOPE (n = 6) or SCS alone (n = 9), followed by ex situ normothermic reperfusion. Similar measurements were performed in a clinical study of DHOPE-preserved livers (n = 10) and control livers that were transplanted after SCS only (n = 9). During DHOPE, preclinical and clinical livers released a mean of 17 ± 2 and 34 ± 6 mmol potassium and took up 25 ± 9 and 24 ± 14 mmol sodium, respectively. After subsequent normothermic reperfusion, DHOPE-preserved livers took up a mean of 19 ± 3 mmol potassium, while controls released 8 ± 5 mmol potassium. During liver transplantation, blood potassium levels decreased upon reperfusion of DHOPE-preserved livers while levels increased after reperfusion of SCS-preserved liver, delta potassium levels were -0.77 ± 0.20 vs. +0.64 ± 0.37 mmol/L, respectively (P = .002). While hyperkalemia is generally anticipated during transplantation of SCS-preserved livers, reperfusion of hypothermic machine perfused livers can lead to decreased blood potassium or even hypokalemia in the recipient.

Development of Clinical Criteria for Functional Assessment to Predict Primary Nonfunction of High-Risk Livers Using Normothermic Machine Perfusion

Increased use of high-risk allografts is critical to meet the demand for liver transplantation. We aimed to identify criteria predicting viability of organs, currently declined for clinical transplantation, using functional assessment during normothermic machine perfusion (NMP). Twelve discarded human livers were subjected to NMP following static cold storage. Livers were perfused with a packed red cell-based fluid at 37°C for 6 hours. Multilevel statistical models for repeated measures were employed to investigate the trend of perfusate blood gas profiles and vascular flow characteristics over time and the effect of lactate-clearing (LC) and non-lactate-clearing (non-LC) ability of the livers. The relationship of lactate clearance capability with bile production and histological and molecular findings were also examined. After 2 hours of perfusion, median lactate concentrations were 3.0 and 14.6 mmol/L in the LC and non-LC groups, respectively. LC livers produced more bile and maintained a stable perfusate pH and vascular flow >150 and 500 mL/minute through the hepatic artery and portal vein, respectively. Histology revealed discrepancies between subjectively discarded livers compared with objective findings. There were minimal morphological changes in the LC group, whereas non-LC livers often showed hepatocellular injury and reduced glycogen deposition. Adenosine triphosphate levels in the LC group increased compared with the non-LC livers. We propose composite viability criteria consisting of lactate clearance, pH maintenance, bile production, vascular flow patterns, and liver macroscopic appearance. These have been tested successfully in clinical transplantation. In conclusion, NMP allows an objective assessment of liver function that may reduce the risk and permit use of currently unused high-risk livers.

Preliminary Experience With Hypothermic Oxygenated Machine Perfusion in an Italian Liver Transplant Center

BACKGROUND

Machine perfusion is increasingly utilized in liver transplantation to face the detrimental consequences of the use of extended-criteria donors. Hypothermic oxygenated machine perfusion (HOPE) appears to be more protective relative to static cold storage. Conversely, normothermic machine perfusion (NMP) allows a better graft evaluation. We describe a pilot prospective study on machine perfusion in selected grafts.

METHODS

HOPE was executed for all the grafts procured from donors after cardiac death (DCDs) and for livers from donors after brain death (DBDs) requiring prolonged preservation time. NMP was used when a more precise evaluation was needed. Both HOPE and NMP were performed through the portal vein and hepatic artery.

RESULTS

From July 2016 to November 2017, we performed 7 HOPE procedures: 5 for DCD and 2 for DBD grafts. Two livers presented with macrovesicular steatosis >30% (1 DCD and 1 DBD). HOPE lasted 240 minutes (180-320 min) with a total ischemia time of 575 minutes (410-810 min). Six grafts were successfully transplanted. One DCD graft required additional evaluation using NMP. The graft was then discarded due to extensive hepatocellular necrosis. In the post-transplant course, acute and chronic renal failure were the main complications affecting 3 and 2 recipients, respectively. In our series, steatosis was the main risk factor for kidney injury. Patient and graft survival rate was 100% and no ischemic cholangiopathies were observed after 270 days (106-582 days).

CONCLUSIONS

Our study confirms HOPE safety and efficacy for DCD and DBD grafts. These data are particularly significant for DCD management in the Italian setting where the mandatory 20-minute hands-off interval before death declaration further prolongs warm ischemia time.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

DISCUSSION

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

Normothermic ex-situ liver preservation: the new gold standard

PURPOSE OF REVIEW

Normothermic machine perfusion of the liver (NMP-L) is a novel technology recently introduced into the practice of liver transplantation. This review recapitulates benefits of normothermic perfusion over conventional static cold storage and summarizes recent publications in this area.

RECENT FINDINGS

The first clinical trials have demonstrated both safety and feasibility of NMP-L. They have shown that machine perfusion can entirely replace cold storage or be commenced following a period of cold ischaemia. The technology currently allows transplant teams to extend the period of organ preservation for up to 24 h. Results from the first randomized control trial comparing NMP-L with static cold storage will be available soon. One major advantage of NMP-L technology over other parallel technologies is the potential to assess liver function during NMP-L. Several case series have suggested parameters usable for liver viability testing during NMP-L including bile production and clearance of lactic acidosis. NMP-L allows viability testing of high-risk livers. It has shown the potential to increase utilization of donor organs and improve transplant procedure logistics.

SUMMARY

NMP-L is likely to become an important technology that will improve organ preservation as well as have the potential to improve utilization of extended criteria donor livers.

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.

Normothermic Perfusion in the Assessment and Preservation of Declined Livers Before Transplantation: Hyperoxia and Vasoplegia-Important Lessons From the First 12 Cases

BACKGROUND

A program of normothermic ex situ liver perfusion (NESLiP) was developed to facilitate better assessment and use of marginal livers, while minimizing cold ischemia.

METHODS

Declined marginal livers and those offered for research were evaluated. Normothermic ex situ liver perfusion was performed using an erythrocyte-based perfusate. Viability was assessed with reference to biochemical changes in the perfusate.

RESULTS

Twelve livers (9 donation after circulatory death [DCD] and 3 from brain-dead donors), median Donor Risk Index 2.15, were subjected to NESLiP for a median 284 minutes (range, 122-530 minutes) after an initial cold storage period of 427 minutes (range, 222-877 minutes). The first 6 livers were perfused at high perfusate oxygen tensions, and the subsequent 6 at near-physiologic oxygen tensions. After transplantation, 5 of the first 6 recipients developed postreperfusion syndrome and 4 had sustained vasoplegia; 1 recipient experienced primary nonfunction in conjunction with a difficult explant. The subsequent 6 liver transplants, with livers perfused at lower oxygen tensions, reperfused uneventfully. Three DCD liver recipients developed cholangiopathy, and this was associated with an inability to produce an alkali bile during NESLiP.

CONCLUSIONS

Normothermic ex situ liver perfusion enabled assessment and transplantation of 12 livers that may otherwise not have been used. Avoidance of hyperoxia during perfusion may prevent postreperfusion syndrome and vasoplegia, and monitoring biliary pH, rather than absolute bile production, may be important in determining the likelihood of posttransplant cholangiopathy. Normothermic ex situ liver perfusion has the potential to increase liver utilization, but more work is required to define factors predicting good outcomes.

Current challenges and future directions for liver transplantation

Liver transplantation is an effective and widely used therapy for several patients with acute and chronic liver diseases. The discrepancy between the number of patients on the waiting list and available donors remains the key issue and is responsible for the high rate of waiting list mortality. The recent news is that the majority of patients with hepatitis C virus related liver disease will be cured by new antivirals therefore we should expect soon a reduction in the need of liver transplantation for these recipients. This review aims to highlight, in two different sections, the main open issues of liver transplantation concerning the current and future strategies to the best use of limited number of organs. The first section cover the strategies to increase the donor pool, discussing the use of older donors, split grafts, living donation and donation after cardiac death and mechanical perfusion systems to improve the preservation of organs before liver transplantation. Challenges in immunosuppressive therapy and operational tolerance induction will be evaluated as potential tools to increase the survival in liver transplant recipients and to reducing the need of re-transplantation. The second section is devoted to the evaluation of possible new indications to liver transplantation, where the availability of organs by implementing the strategies mentioned in the first section and the reduction in the number of waiting transplants for HCV disease is realized. Among these new potential indications for transplantation, the expansion of the Milan criteria for hepatocellular cancer is certainly the most open to question.

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.

Subnormothermic ex vivo liver perfusion is a safe alternative to cold static storage for preserving standard criteria grafts

We developed a novel technique of subnormothermic ex vivo liver perfusion (SNEVLP) for the storage of liver grafts before transplantation. To test the safety of SNEVLP for the nonextended criteria grafts (standard grafts), we compared it to a control group with minimal cold static storage (CS) time. Heart-beating pig liver retrieval was performed. Grafts were either stored in cold unmodified University of Wisconsin solution (CS-1), in cold University of Wisconsin solution with ex vivo perfusion additives (CS-2), or preserved with a sequence of 3 hours CS and 3 hours SNEVLP (33°C), followed by orthotopic liver transplantation. Liver function tests and histology were investigated. Aspartate aminotransferase (AST) levels during SNEVLP remained stable (54.3 ± 12.6 U/L at 1 hour to 47.0 ± 31.9 U/L at 3 hours). Posttransplantation, SNEVLP versus CS-1 livers had decreased AST levels (peak at day 1, 1081.9 ± 788.5 versus 1546.7 ± 509.3 U/L; P = 0.14; at day 2, 316.7 ± 188.1 versus 948.2 ± 740.9 U/L; P = 0.04) and alkaline phosphatase levels (peak at day 1, 150.4 ± 19.3 versus 203.7 ± 33.6 U/L; P = 0.003). Bilirubin levels were constantly within the physiological range in the SNEVLP group, whereas the CS-1 group presented a large standard deviation, including pathologically increased values. Hyaluronic acid as a marker of endothelial cell (EC) function was markedly improved by SNEVLP during the early posttransplant phase (5 hours posttransplant, 1172.75 ± 598.5 versus 5540.5 ± 2755.4 ng/mL). Peak international normalized ratio was similar between SNEVLP and CS-1 groups after transplantation. Immunohistochemistry for cleaved caspase 3 demonstrated more apoptotic sinusoidal cells in the CS-1 group when compared to SNEVLP grafts 2 hours after reperfusion (19.4 ± 19.5 versus 133.2 ± 48.8 cells/high-power field; P = 0.002). Adding normothermic CS-2 had no impact on liver injury or function after transplantation when compared to CS-1. In conclusion, SNEVLP is safe to use for standard donor grafts and is associated with improved EC and bile duct injury even in grafts with minimal CS time.

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.

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.