Production of Physiologically Relevant Quantities of Hemostatic Proteins During Ex Situ Normothermic Machine Perfusion of Human Livers

Normothermic Machine-perfused Human Donor Livers Produce Functional Hemostatic Proteins

BACKGROUND

Normothermic machine perfusion (NMP) is used for the viability assessment of high-risk donor livers before transplantation. The production of hemostatic proteins is one of the major synthetic functions of the liver. The objective of this study was to measure the concentration and functionality of hemostatic proteins concentration in the NMP perfusate of human donor livers.

METHODS

Thirty-six livers that underwent NMP for viability assessment were included in this study. Perfusate samples taken during NMP (start, 150 min, and 300 min) were used for the measurement of antigen and activity levels of hemostatic proteins (factors II, VII, and X; fibrinogen; plasminogen; antithrombin; tissue plasminogen activator; von Willebrand factor; and proteins induced by vitamin K absence). The antigen levels were correlated with hepatocellular function according to previously proposed individual hepatocellular viability criteria: lactate clearance and perfusate pH.

RESULTS

Antigen levels of hemostatic proteins reached subphysiological levels in the NMP perfusate. Hemostatic proteins that were produced during NMP were at least partially active. All livers produced all hemostatic proteins tested within 150 min of NMP. Hemostatic protein concentrations did not significantly correlate with perfusate lactate and perfusate pH after 150 min of NMP.

CONCLUSIONS

All livers produce functional hemostatic proteins during NMP. The generation of a functional hemostatic system in NMP perfusate confirms the need for adequate anticoagulation of the perfusate to avoid generation of (micro)thrombi that may harm the graft.

Comprehensive Approach to Assessment of Liver Viability During Normothermic Machine Perfusion

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

The Emerging Role of Viability Testing During Liver Machine Perfusion

The transplant community continues to be challenged by the disparity between the need for liver transplantation and the shortage of suitable donor organs. At the same time, the number of unused donor livers continues to increase, most likely attributed to the worsening quality of these organs. To date, there is no reliable marker of liver graft viability that can predict good posttransplant outcomes. Ex situ machine perfusion offers additional data to assess the viability of donor livers before transplantation. Hence, livers initially considered unsuitable for transplantation can be assessed during machine perfusion in terms of appearance and consistency, hemodynamics, and metabolic and excretory function. In addition, postoperative complications such as primary nonfunction or posttransplant cholangiopathy may be predicted and avoided. A variety of viability criteria have been used in machine perfusion, and to date there is no widely accepted composition of criteria for clinical use. This review discusses potential viability markers for hepatobiliary function during machine perfusion, describes current limitations, and provides future recommendations for the use of viability criteria in clinical liver transplantation.

Sense and Sensibilities of Organ Perfusion as a Kidney and Liver Viability Assessment Platform

Predicting organ viability before transplantation remains one of the most challenging and ambitious objectives in transplant surgery. Waitlist mortality is high while transplantable organs are discarded. Currently, around 20% of deceased donor kidneys and livers are discarded because of “poor organ quality”, Decisions to discard are still mainly a subjective judgement since there are only limited reliable tools predictive of outcome available. Organ perfusion technology has been posed as a platform for pre-transplant organ viability assessment. Markers of graft injury and function as well as perfusion parameters have been investigated as possible viability markers during ex-situ hypothermic and normothermic perfusion. We provide an overview of the available evidence for the use of kidney and liver perfusion as a tool to predict posttransplant outcomes. Although evidence shows post-transplant outcomes can be predicted by both injury markers and perfusion parameters during hypothermic kidney perfusion, the predictive accuracy is too low to warrant clinical decision making based upon these parameters alone. In liver, further evidence on the usefulness of hypothermic perfusion as a predictive tool is needed. Normothermic perfusion, during which the organ remains fully metabolically active, seems a more promising platform for true viability assessment. Although we do not yet fully understand “on-pump” organ behaviour at normothermia, initial data in kidney and liver are promising. Besides the need for well-designed (registry) studies to advance the field, the catch-22 of selection bias in clinical studies needs addressing.

Coagulation Factors Accumulate During Normothermic Liver Machine Perfusion Regardless of Donor Type and Severity of Ischemic Injury

BACKGROUND

Coagulation factors may inform on liver function during normothermic machine perfusion (NMP). We investigated whether graft ischemic injury impairs the accumulation of anticoagulation factors during NMP of porcine and human livers.

METHODS

Dynamics of FV, FVII, FVIII, FIX, and FX during NMP and their correlation with graft injury was investigated in porcine livers with minimal (no warm ischemia, n = 5) or severe injury (60 min warm ischemia, n = 5). Next, FV, FVIII, FIX, fibrinogen, and antithrombin were measured in 35 matched human liver NMPs from the COPE trial. Correlation of these factors with outcomes was explored. Livers were categorized in to 4 groups depending on donor type and posttransplant peak aspartate aminotransferase (AST) as surrogate of minimal (peak < 500 IU/L) or moderate injury (peak > 1000 IU/L).

RESULTS

Factor concentrations increased significantly during NMP regardless of severity of injury. In porcine livers, factor concentrations were 2- to 6-fold lower in severely injured grafts (all P < 0.05). All factors negatively correlated with AST (coefficient range: from -0.50 to -0.93; all P < 0.05) and lactate (range: from -0.51 to -0.67; all P < 0.05). In human livers, no difference in factor accumulation rates and no correlation with other markers were observed. One graft with primary nonfunction had low rate of factor accumulation.

CONCLUSIONS

Anticoagulation factors accumulate during NMP regardless of donor type and severity of injury. In pigs, severe ischemic injury resulted in significantly lower factor concentrations. In human livers with life-sustaining function, they do not correlate with hepatic injury. Whether low concentrations predict nonfunction in high-risk livers with severe injury requires further investigation.

Long-term normothermic machine preservation of human livers: what is needed to succeed?

Although short-term machine perfusion (≤24 h) allows for resuscitation and viability assessment of high-risk donor livers, the donor organ shortage might be further remedied by long-term perfusion machines. Extended preservation of injured donor livers may allow reconditioning, repairing, and regeneration. This review summarizes the necessary requirements and challenges for long-term liver machine preservation, which requires integrating multiple core physiological functions to mimic the physiological environment inside the body. A pump simulates the heart in the perfusion system, including automatically controlled adjustment of flow and pressure settings. Oxygenation and ventilation are required to account for the absence of the lungs combined with continuous blood gas analysis. To avoid pressure necrosis and achieve heterogenic tissue perfusion during preservation, diaphragm movement should be simulated. An artificial kidney is required to remove waste products and control the perfusion solution's composition. The perfusate requires an oxygen carrier, but will also be challenged by coagulation and activation of the immune system. The role of the pancreas can be mimicked through closed-loop control of glucose concentrations by automatic injection of insulin or glucagon. Nutrients and bile salts, generally transported from the intestine to the liver, have to be supplemented when preserving livers long term. Especially for long-term perfusion, the container should allow maintenance of sterility. In summary, the main challenge to develop a long-term perfusion machine is to maintain the liver's homeostasis in a sterile, carefully controlled environment. Long-term machine preservation of human livers may allow organ regeneration and repair, thereby ultimately solving the shortage of donor livers.

Prolonged dual hypothermic oxygenated machine preservation (DHOPE-PRO) in liver transplantation: study protocol for a stage 2, prospective, dual-arm, safety and feasibility clinical trial

Introduction

End-ischaemic preservation of a donor liver by dual hypothermic oxygenated machine perfusion (DHOPE) for 2 hours prior to transplantation is sufficient to mitigate ischaemia-reperfusion damage and fully restore cellular energy levels. Clinical studies have shown beneficial outcomes after transplantation of liver grafts preserved by DHOPE compared with static cold storage. In addition to graft reconditioning, DHOPE may also be used to prolong preservation time, which could facilitate logistics for allocation and transplantation globally.

Methods and analysis

This is a prospective, pseudo-randomised, dual-arm, IDEAL-D (Idea, Development, Exploration, Assessment, Long term study-Framework for Devices) stage 2 clinical device trial designed to determine safety and feasibility of prolonged DHOPE (DHOPE-PRO). The end-time of the donor hepatectomy will determine whether the graft will be assigned to the intervention (16:00–3:59 hour) or to the control arm (4:00–15:59 hour). In total, 36 livers will be included in the study. Livers in the intervention group (n=18) will undergo DHOPE-PRO (≥4 hours) until implantation the following morning, whereas livers in the control group (n=18) will undergo regular DHOPE (2 hours) prior to implantation. The primary endpoint of this study is a composite of the occurrence of all (serious) adverse events during DHOPE and up to 30 days after liver transplantation.

Ethics and dissemination

The protocol was approved by the Medical Ethical Committee of Groningen, METc2020.126 in June 2020, and the study was registered in the Netherlands National Trial Registry (https://www.trialregister.nl/) prior to initiation.

Trial registration number

NL8740.

Synthesis of coagulation factors during long-term ex situ liver perfusion

Robust viability assessment of grafts during normothermic liver perfusion is a prerequisite for organ use. Coagulation parameters are used commonly for liver assessment in patients. However, they are not yet included in viability assessment during ex situ perfusion. In this study, we analysed coagulation parameters during one week ex situ perfusion at 34℃. Eight discarded human livers were perfused with blood-based, heparinised perfusate for one week; perfusions in a further four livers were terminated on day 4 due to massive ongoing cell death. Coagulation parameters were well below the physiologic range at perfusion start. Physiologic levels were achieved within the first two perfusion days for factor V (68.5 ± 35.5%), factor VII (83.5 ± 26.2%), fibrinogen (2.1 ± 0.4 g/L) and antithrombin (107 ± 26.5%) in the livers perfused for one week. Despite the increased production of coagulation factors, INR was detectable only at 24h of perfusion (2.1 ± 0.3) and prolonged thereafter (INR > 9). The prolongation of INR was related to the high heparin level in the perfusate (anti-FXa > 3 U/mL). Intriguingly, livers with ongoing massive cell death also disclosed synthesis of factor V and improved INR. In summary, perfused livers were able to produce coagulation factors at a physiological level ex situ. We propose that single coagulation factor analysis is more reliable for assessing the synthetic function of perfused livers as compared to INR when using a heparinised perfusate.

Anticoagulant Management and Synthesis of Hemostatic Proteins during Machine Preservation of Livers for Transplantation

Liver transplantation remains the only curative treatment for patients with end-stage liver disease. Despite a steadily increasing demand for suitable donor livers, the current pool of donor organs fails to meet this demand. To resolve this discrepancy, livers traditionally considered to be of suboptimal quality and function are increasingly utilized. These marginal livers, however, are less tolerant to the current standard cold preservation of donor organs. Therefore, alternative preservation methods have been sought and are progressively applied into clinical practice. Ex situ machine perfusion is a promising alternative preservation modality particularly for suboptimal donor livers as it provides the ability to resuscitate, recondition, and test the viability of an organ prior to transplantation. This review addresses the modalities of machine perfusion currently being applied, and particularly focuses on the hemostatic management employed during machine perfusion. We discuss the anticoagulant agents used, the variation in dosage, and administration, as well as the implications of perfusion for extended periods of time in terms of coagulation activation associated with production of coagulation factors during perfusion. Furthermore, in regard to viability testing of an organ prior to transplantation, we discuss the possibilities and limitations of utilizing the synthesis of liver-derived coagulation factors as potential viability markers.

Normothermic Machine Perfusion Enhances Intraoperative Hepatocellular Synthetic Capacity: A Propensity Score-matched Analysis

BACKGROUND

Normothermic machine perfusion (NMP) of liver grafts is increasingly being incorporated in clinical practice. Current evidence has shown NMP plays a role in reconditioning the synthetic and energy capabilities of grafts. Intraoperative coagulation profile is a surrogate of graft quality and preservation status; however, to date this aspect has not been documented.

METHODS

The liver transplantation recipients who received NMP liver grafts in the QEHB between 2013 and 2016 were compared in terms of intraoperative thromboelastography characteristics (R time, K time, α-angle, maximum amplitude, G value, and LY30) to a propensity score-matched control group, where the grafts were preserved by traditional static cold storage (SCS).

RESULTS

After propensity matching, none of the thromboelastography characteristics were found to differ significantly between the 72 pairs of SCS and NMP organs when measured preimplantation. However, postimplantation, NMP organs had significantly shorter K time (median: 2.8 vs 3.6 min, P = 0.010) and R + K time (11.4 vs 13.7 min, P = 0.016), as well as significantly larger α-angle (55.9° vs 44.8°, P = 0.002), maximum amplitude (53.5 vs 49.6 mm, P = 0.044), and G values (5.8 vs 4.9k dynes/cm, P = 0.043) than SCS organs. Hyperfibrinolysis after implantation was also mitigated by NMP, with fewer patients requiring aggressive factor correction during surgery (LY30 = 0, NMP vs SCS: 83% vs 60%, P = 0.004). Consequently, NMP organs required significantly fewer platelet units to be transfused during the transplant procedure (median: 0 vs 5, P = 0.001).

CONCLUSIONS

In this study, we have shown that NMP liver grafts return better coagulation profiles intraoperatively, which could be attributed to the preservation of liver grafts under physiological conditions.

An integrated perfusion machine preserves injured human livers for 1 week

The ability to preserve metabolically active livers ex vivo for 1 week or more could allow repair of poor-quality livers that would otherwise be declined for transplantation. Current approaches for normothermic perfusion can preserve human livers for only 24 h. Here we report a liver perfusion machine that integrates multiple core physiological functions, including automated management of glucose levels and oxygenation, waste-product removal and hematocrit control. We developed the machine in a stepwise fashion using pig livers. Study of multiple ex vivo parameters and early phase reperfusion in vivo demonstrated the viability of pig livers perfused for 1 week without the need for additional blood products or perfusate exchange. We tested the approach on ten injured human livers that had been declined for transplantation by all European centers. After a 7-d perfusion, six of the human livers showed preserved function as indicated by bile production, synthesis of coagulation factors, maintained cellular energy (ATP) and intact liver structure.

Livers are stored long term in a sophisticated perfusion system.

Normothermic perfusion and outcomes after liver transplantation

Ischemia has been a persistent and largely unavoidable element in solid organ transplantation, contributing to graft deterioration and adverse post-transplant outcomes. In liver transplantation, where available organs arise with greater frequency from marginal donors (i.e., ones that are older, obese, and/or declared dead following cardiac arrest through the donation after circulatory death process), there is increasing interest using dynamic perfusion strategies to limit, assess, and even reverse the adverse effects of ischemia in these grafts. Normothermic perfusion, in particular, is used to restore the flow of oxygen and other metabolic substrates at physiological temperatures. It may be used in liver transplantation both in situ following cardiac arrest in donation after circulatory death donors or during part or all of the ex situ preservation phase. This review article addresses issues relevant to use of normothermic perfusion strategies in liver transplantation, including technical and logistical aspects associated with establishing and maintaining normothermic perfusion in its different forms and clinical outcomes that have been reported to date.