Hypothermic Machine Perfusion in Liver Transplantation - A Randomized Trial

Can ex-situ normothermic perfusion improve graft survival compared to static cold storage among donation after circulatory death liver allografts?

Limited data suggest that ex-situ normothermic liver perfusion (ENLP) may improve the outcomes of donation after circulatory death (DCD) liver transplants compared to static cold storage (SCS). All adult DCD liver transplants performed between 2016 and 2021 were identified in the United Network of Organ Sharing database. ENLP liver transplants were compared to SCS using inverse probability of treatment weighting to balance clinical and demographic confounders. The primary analysis simulated intention-to-treat with inverse probability of treatment weighting-adjusted Cox models. Compared to SCS DCDs (N = 3,079), recipients of ENLP DCDs (N = 65) had lower Model of End Stage Liver Disease scores at transplant (16.5 v. 18.8, p = 0.033), longer wait times (468 ± 720 vs. 246 ± 467 d; p < 0.001), and received livers from donors with a greater BMI (29.2 vs. 27.5; p = 0.008). ENLP preservation was associated with a lower risk of graft failure (HR 0.31 vs. SCS, 95% CI:0.12-0.86, p = 0.023) and a lower incidence of retransplantation. A sub-analysis restricted to the 20 centers performing ENLP, encompassing 946 SCS DCDs, demonstrated similar results: (HR 0.33 vs. SCS, 95% CI: 0.13-0.94, p = 0.021). Among 111 patients who required retransplantation and where the etiology of graft failure was identified, graft failure due to ischemic cholangiopathy was noted in 1 ENLP and 46 SCS. In this retrospective analysis of the early US DCD ENLP experience, there may exist a graft survival benefit to transplants performed with ENLP compared to SCS.

Acute rejection after liver transplantation with machine perfusion versus static cold storage: A systematic review and meta-analysis

BACKGROUND AND AIMS

Acute cellular rejection (ACR) is a frequent complication after liver transplantation. By reducing ischemia and graft damage, dynamic preservation techniques may diminish ACR. We performed a systematic review to assess the effect of currently tested organ perfusion (OP) approaches versus static cold storage (SCS) on post-transplant ACR-rates.

APPROACH AND RESULTS

A systematic search of Medline, Embase, Cochrane Library, and Web of Science was conducted. Studies reporting ACR-rates between OP and SCS and comprising at least 10 liver transplants performed with either hypothermic oxygenated perfusion (HOPE), normothermic machine perfusion, or normothermic regional perfusion were included. Studies with mixed perfusion approaches were excluded. Eight studies were identified (226 patients in OP and 330 in SCS). Six studies were on HOPE, one on normothermic machine perfusion, and one on normothermic regional perfusion. At meta-analysis, OP was associated with a reduction in ACR compared with SCS [OR: 0.55 (95% CI, 0.33-0.91), p =0.02]. This effect remained significant when considering HOPE alone [OR: 0.54 (95% CI, 0.29-1), p =0.05], in a subgroup analysis of studies including only grafts from donation after cardiac death [OR: 0.43 (0.20-0.91) p =0.03], and in HOPE studies with only donation after cardiac death grafts [OR: 0.37 (0.14-1), p =0.05].

CONCLUSIONS

Dynamic OP techniques are associated with a reduction in ACR after liver transplantation compared with SCS. PROSPERO registration: CRD42022348356.

Extracellular Vesicles in Liver Transplantation: Current Evidence and Future Challenges

Extracellular vesicles (EVs) are emerging as a promising field of research in liver disease. EVs are small, membrane-bound vesicles that contain various bioactive molecules, such as proteins, lipids, and nucleic acids and are involved in intercellular communication. They have been implicated in numerous physiological and pathological processes, including immune modulation and tissue repair, which make their use appealing in liver transplantation (LT). This review summarizes the current state of knowledge regarding the role of EVs in LT, including their potential use as biomarkers and therapeutic agents and their role in graft rejection. By providing a comprehensive insight into this emerging topic, this research lays the groundwork for the potential application of EVs in LT.

A Spectrofluorometric Method for Real-Time Graft Assessment and Patient Monitoring

Biomarkers are powerful clinical diagnostics and predictors of patient outcome. However, robust measurements often require time and expensive laboratory equipment, which is insufficient to track rapid changes and limits direct use in the operating room. Here, this study presents a portable spectrophotometric device for continuous real-time measurements of fluorescent and non-fluorescent biomarkers at the point of care. This study measures the mitochondrial damage biomarker flavin mononucleotide (FMN) in 26 extended criteria human liver grafts undergoing hypothermic oxygenated perfusion to guide clinical graft assessment. Real-time data identified seven organs unsuitable for transplant that are discarded. The remaining grafts are transplanted and FMN values correlated with post-transplant indicators of liver function and patient recovery. Further, this study shows how this device can be used to monitor dialysis patients by measuring creatinine in real-time. Our approach provides a simple method to monitor biomarkers directly within biological fluids to improve organ assessment, patient care, and biomarker discovery.

A randomized-controlled trial of ischemia-free liver transplantation for end-stage liver disease

BACKGROUND & AIMS

Ischemia-reperfusion injury (IRI) has thus far been considered as an inevitable component of organ transplantation, compromising outcomes, and limiting organ availability. Ischemia-free organ transplantation is a novel approach designed to avoid IRI, with the potential to improve outcomes.

METHODS

In this randomized-controlled clinical trial, recipients of livers from donors after brain death were randomly assigned to receive either an ischemia-free or a 'conventional' transplant. The primary endpoint was the incidence of early allograft dysfunction. Secondary endpoints included complications related to graft IRI.

RESULTS

Out of 68 randomized patients, 65 underwent transplants and were included in the analysis. 32 patients received ischemia-free liver transplantation (IFLT), and 33 received conventional liver transplantation (CLT). Early allograft dysfunction occurred in two recipients (6%) randomized to IFLT and in eight (24%) randomized to CLT (difference -18%; 95% CI -35% to -1%; p = 0.044). Post-reperfusion syndrome occurred in three recipients (9%) randomized to IFLT and in 21 (64%) randomized to CLT (difference -54%; 95% CI -74% to -35%; p <0.001). Non-anastomotic biliary strictures diagnosed with protocol magnetic resonance cholangiopancreatography at 12 months were observed in two recipients (8%) randomized to IFLT and in nine (36%) randomized to CLT (difference, -28%; 95% CI -50% to -7%; p = 0.014). The comprehensive complication index at 1 year after transplantation was 30.48 (95% CI 23.25-37.71) in the IFLT group vs. 42.14 (95% CI 35.01-49.26) in the CLT group (difference -11.66; 95% CI -21.81 to -1.51; p = 0.025).

CONCLUSIONS

Among patients with end-stage liver disease, IFLT significantly reduced complications related to IRI compared to a conventional approach.

CLINICAL TRIAL REGISTRATION

chictr.org. ChiCTR1900021158.

IMPACT AND IMPLICATIONS

Ischemia-reperfusion injury has thus far been considered as an inevitable event in organ transplantation, compromising outcomes and limiting organ availability. Ischemia-free liver transplantation is a novel approach of transplanting donor livers without interruption of blood supply. We showed that in patients with end-stage liver disease, ischemia-free liver transplantation, compared with a conventional approach, led to reduced complications related to ischemia-reperfusion injury in this randomized trial. This new approach is expected to change the current practice in organ transplantation, improving transplant outcomes, increasing organ utilization, while providing a clinical model to delineate the impact of organ injury on alloimmunity.

Comparative Analysis of Donor Liver Allograft Outcomes in Hepatocellular Carcinoma Patients Who Underwent Liver Transplant

OBJECTIVES

Liver transplant for patients with hepatocellular carcinoma involves 3 main types of donor allografts: donation after brain death, donation after cardiac death, and donation after brain and cardiac death. Data on this topic are limited, and controversies exist regarding liver transplant outcomes in hepatocellular carcinoma patients who have received these allografts.

MATERIALS AND METHODS

Data from 490 hepatocellular carcinoma patients who received liver transplant from 2015 to 2021 at the Shulan (Hangzhou) Hospital were retrospectively analyzed. Participants were divided into 3 cohorts according to allograft type: donation after brain death, donation after cardiac death, and donation after brain and cardiac death. Kaplan-Meier and Cox regression methods were used to evaluate patient survival, graft survival, and recurrence-free survival rates after liver transplant.

RESULTS

Kaplan-Meier analysis revealed that 3-year patient survival rates were 69.2% for donations after brain death, 69.2% for donations after cardiac death, and 46.6% for donations after brain and cardiac death (P = .42); the 3-year graft survival rates were 53.3% for donations after brain death, 56.4% for donations after cardiac death, and 46.6% for donations after brain and cardiac death (P = .44); and 3-year recurrence-free survival rates were 55% for donations after brain death, 56.6% for donations after cardiac death, and 39.5% for donations after brain and cardiac death (P = .46). Complications were also similar across the 3 cohorts (P = .36). Multivariable analysis showed that intraoperative red blood cell transfusion (hazard ratio: 1.820; P = .042) and early allograft dysfunction (hazard ratio: 3.240; P = .041) were independent risk factors for graft survival.

CONCLUSIONS

Similar outcomes can be achieved for hepatocellular carcinoma patients who undergo liver transplant with donations after brain death, donations after cardiac death, or donations after brain and cardiac death allografts, especially when strict donor selection criteria are applied.

Maximizing the Donor Potential for Patients with Acute-on-Chronic Liver Failure Listed for Liver Transplant

Owing to inherent limitations of static cold storage, marginal liver grafts from donors after circulatory death and extended criteria donors after brain death are prone to be discarded secondary to the increased risk of severe early allograft dysfunction and ischemic cholangiopathy. Marginal liver grafts resuscitated with hypothermic machine perfusion and normothermic machine perfusion demonstrate lower degree of ischemia-reperfusion injury and have decreased risk of severe early allograft dysfunction and ischemic cholangiopathy. Marginal grafts preserved by ex vivo machine perfusion technology can be used to rescue patients with acute-on-chronic liver failure who are underserved by the current deceased donor liver allocation system.

The international normalised ratio to monitor coagulation factor production during normothermic machine perfusion of human donor livers

BACKGROUND

Normothermic machine perfusion (NMP) of donor livers allows for new diagnostic and therapeutic strategies. As the liver produces most of the haemostatic proteins, coagulation assays such as the International Normalised Ratio (INR) performed in perfusate may be useful to assess hepatocellular function of donor livers undergoing NMP. However, high concentrations of heparin and low levels of fibrinogen may affect coagulation assays.

METHODS

Thirty donor livers that underwent NMP were retrospectively included in this study, of which 18 were subsequently transplanted. We measured INRs in perfusate in presence or absence of exogenously added fibrinogen and/or polybrene. Additionally, we prospectively included 14 donor livers that underwent NMP (of which 11 were transplanted) and measured INR using both a laboratory coagulation analyser and a point-of-care device.

RESULTS

In untreated perfusate samples, the INR was above the detection limit in all donor livers. Addition of both fibrinogen and polybrene was required for adequate INR assessment. INRs decreased over time and detectable perfusate INR values were found in 17/18 donor livers at the end of NMP. INR results were similar between the coagulation analyser and the point-of-care device, but did not correlate with established hepatocellular viability criteria.

CONCLUSIONS

Most of the donor livers that were transplanted showed a detectable perfusate INR at the end of NMP, but samples require processing to allow for INR measurements using laboratory coagulation analysers. Point-of-care devices bypass this need for processing. The INR does not correlate with established viability criteria and might therefore have additional predictive value.

Hypothermic oxygenated perfusion attenuates DCD liver ischemia-reperfusion injury by activating the JAK2/STAT3/HAX1 pathway to regulate endoplasmic reticulum stress

BACKGROUND

Hepatic ischemia-reperfusion injury (IRI) in donation after cardiac death (DCD) donors is a major determinant of transplantation success. Endoplasmic reticulum (ER) stress plays a key role in hepatic IRI, with potential involvement of the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway and the antiapoptotic protein hematopoietic-lineage substrate-1-associated protein X-1 (HAX1). In this study, we aimed to investigate the effects of hypothermic oxygenated perfusion (HOPE), an organ preservation modality, on ER stress and apoptosis during hepatic IRI in a DCD rat model.

METHODS

To investigate whether HOPE could improve IRI in DCD livers, levels of different related proteins were examined by western blotting and quantitative real-time polymerase chain reaction. Further expression analyses, immunohistochemical analyses, immunofluorescence staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining, and transmission electron microscopy were conducted to analyze the effects of HOPE on ER stress and apoptosis. To clarify the role of the JAK2/STAT3 pathway and HAX1 in this process, AG490 inhibitor, JAX1 plasmid transfection, co-immunoprecipitation (CO-IP), and flow cytometry analyses were conducted.

RESULTS

HOPE reduced liver injury and inflammation while alleviating ER stress and apoptosis in the DCD rat model. Mechanistically, HOPE inhibited unfolded protein responses by activating the JAK2/STAT3 pathway, thus reducing ER stress and apoptosis. Moreover, the activated JAK2/STAT3 pathway upregulated HAX1, promoting the interaction between HAX1 and SERCA2b to maintain ER calcium homeostasis. Upregulated HAX1 also modulated ER stress and apoptosis by inhibiting the inositol-requiring enzyme 1 (IRE1) pathway.

CONCLUSIONS

JAK2/STAT3-mediated upregulation of HAX1 during HOPE alleviates hepatic ER stress and apoptosis, indicating the JAK2/STAT3/HAX1 pathway as a potential target for IRI management during DCD liver transplantation.

Therapeutically targeting essential metabolites to improve immunometabolism manipulation after liver transplantation for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most prevalent primary liver malignancy worldwide and is associated with a poor prognosis. Sophisticated molecular mechanisms and biological characteristics need to be explored to gain a better understanding of HCC. The role of metabolites in cancer immunometabolism has been widely recognized as a hallmark of cancer in the tumor microenvironment (TME). Recent studies have focused on metabolites that are derived from carbohydrate, lipid, and protein metabolism, because alterations in these may contribute to HCC progression, ischemia-reperfusion (IR) injury during liver transplantation (LT), and post-LT rejection. Immune cells play a central role in the HCC microenvironment and the duration of IR or rejection. They shape immune responses through metabolite modifications and by engaging in complex crosstalk with tumor cells. A growing number of publications suggest that immune cell functions in the TME are closely linked to metabolic changes. In this review, we summarize recent findings on the primary metabolites in the TME and post-LT metabolism and relate these studies to HCC development, IR injury, and post-LT rejection. Our understanding of aberrant metabolism and metabolite targeting based on regulatory metabolic pathways may provide a novel strategy to enhance immunometabolism manipulation by reprogramming cell metabolism.

The evolution of the liver transplant candidate

The first successful human liver transplant (LT) was done over 60 years ago; since the early pioneering days, this procedure has become a routine treatment with excellent outcomes for the great majority of recipients. Over the last six decades, indications have evolved. Use of LT for hepatic malignancy is becoming less common as factors that define a successful outcome are being increasingly defined, and alternative therapeutic options become available. Both Hepatitis B and C virus associated liver disease are becoming less common indications as medical treatments become more effective in preventing end-stage disease. Currently, the most common indications are alcohol-related liver disease and metabolic associated liver disease. The developing (and controversial) indications include acute on chronic liver failure, alcoholic hepatitis and some rarer malignancies such as non-resectable colorectal cancer liver metastases, neuroendocrine tumours and cholangiocarcinoma. Candidates are becoming older and with greater comorbidities, A relative shortage of donor organs remains the greatest cause for reducing access to LT; therefore, various countries have developed transparent approaches to allocation of this life saving and life enhancing resource. Reliance on prognostic models has gone some way to improve transparency and increase equity of access but these approaches have their limitations.

New therapeutic concepts against ischemia-reperfusion injury in organ transplantation

INTRODUCTION

Ischemia-reperfusion injury (IRI) involves a positive amplification feedback loop that stimulates innate immune-driven tissue damage associated with organ procurement from deceased donors and during transplantation surgery. As our appreciation of its basic immune mechanisms has improved in recent years, translating putative biomarkers into therapeutic interventions in clinical transplantation remains challenging.

AREAS COVERED

This review presents advances in translational/clinical studies targeting immune responses to reactive oxygen species in IRI-stressed solid organ transplants, especially livers. Here we focus on novel concepts to rejuvenate suboptimal donor organs and improve transplant function using pharmacologic and machine perfusion (MP) strategies. Cellular damage induced by cold ischemia/warm reperfusion and the latest mechanistic insights into the microenvironment's role that leads to reperfusion-induced sterile inflammation is critically discussed.

EXPERT OPINION

Efforts to improve clinical outcomes and increase the donor organ pool will depend on improving donor management and our better appreciation of the complex mechanisms encompassing organ IRI that govern the innate-adaptive immune interface triggered in the peritransplant period and subsequent allo-Ag challenge. Computational techniques and deep machine learning incorporating the vast cellular and molecular mechanisms will predict which peri-transplant signals and immune interactions are essential for improving access to the long-term function of life-saving transplants.

Liver Transplantation 2023: Status Report, Current and Future Challenges

Liver transplantation offers live-saving therapy for patients with complications of cirrhosis and stage T2 hepatocellular carcinoma. The demand for organs far outstrips the supply, and innovations aimed at increasing the number of usable deceased donors as well as alternative donor sources are a major focus. The etiologies of cirrhosis are shifting over time, with more need for transplantation among patients with alcohol-associated liver disease and nonalcoholic/metabolic fatty liver disease and less for viral hepatitis, although hepatitis B remains an important indication for transplant in countries with high endemicity. The rise in transplantation for alcohol-associated liver disease and nonalcoholic/metabolic fatty liver disease has brought attention to how patients are selected for transplantation and the strategies needed to prevent recurrent disease. In this review, we present a status report on the most pressing topics in liver transplantation and future challenges.

Endothelial Cells and Mitochondria: Two Key Players in Liver Transplantation

Building the inner layer of our blood vessels, the endothelium forms an important line communicating with deeper parenchymal cells in our organs. Previously considered passive, endothelial cells are increasingly recognized as key players in intercellular crosstalk, vascular homeostasis, and blood fluidity. Comparable to other cells, their metabolic function strongly depends on mitochondrial health, and the response to flow changes observed in endothelial cells is linked to their mitochondrial metabolism. Despite the direct impact of new dynamic preservation concepts in organ transplantation, the impact of different perfusion conditions on sinusoidal endothelial cells is not yet explored well enough. This article therefore describes the key role of liver sinusoidal endothelial cells (LSECs) together with their mitochondrial function in the context of liver transplantation. The currently available ex situ machine perfusion strategies are described with their effect on LSEC health. Specific perfusion conditions, including perfusion pressure, duration, and perfusate oxygenation are critically discussed considering the metabolic function and integrity of liver endothelial cells and their mitochondria.

How to Preserve Steatotic Liver Grafts for Transplantation

Liver allograft steatosis is a significant risk factor for postoperative graft dysfunction and has been associated with inferior patient and graft survival, particularly in the case of moderate or severe macrovesicular steatosis. In recent years, the increasing incidence of obesity and fatty liver disease in the population has led to a higher proportion of steatotic liver grafts being used for transplantation, making the optimization of their preservation an urgent necessity. This review discusses the mechanisms behind the increased susceptibility of fatty livers to ischemia-reperfusion injury and provides an overview of the available strategies to improve their utilization for transplantation, with a focus on preclinical and clinical evidence supporting donor interventions, novel preservation solutions, and machine perfusion techniques.

Current practice and novel approaches in organ preservation

Organ transplantation remains the only treatment option for patients with end-stage organ failure. The last decade has seen a flurry of activity in improving organ preservation technologies, which promise to increase utilization in a dramatic fashion. They also bring the promise of extending the preservation duration significantly, which opens the doors to sharing organs across local and international boundaries and transforms the field. In this work, we review the recent literature on machine perfusion of livers across various protocols in development and clinical use, in the context of extending the preservation duration. We then review the next generation of technologies that have the potential to further extend the limits and open the door to banking organs, including supercooling, partial freezing, and nanowarming, and outline the opportunities arising in the field for researchers in the short and long term.

End-ischemic hypothermic oxygenated perfusion for extended criteria donors in liver transplantation: a multicenter, randomized controlled trial-HOPExt

BACKGROUND

Given the scarce donor supply, an increasing number of so-called marginal or extended criteria donor (ECD) organs are used for liver transplantation. These ECD liver grafts are however known to be associated with a higher rate of early allograft dysfunction and primary non-function because of a greater vulnerability to ischemia-reperfusion injury. The end-ischemic hypothermic oxygenated machine perfusion (HOPE) technique may improve outcomes of liver transplantation with ECD grafts by decreasing reperfusion injury.

METHODS

HOPExt trial is a comparative open-label, multicenter, national, prospective, randomized, controlled study, in two parallel groups, using static cold storage, the gold standard procedure, as control. The trial will enroll adult patients on the transplant waiting list for liver failure or liver cirrhosis and/or liver malignancy requiring liver transplantation and receiving an ECD liver graft from a brain-dead donor. In the experimental group, ECD liver grafts will first undergo a classical static cold (4 °C) storage followed by a hypothermic oxygenated perfusion (HOPE) for a period of 1 to 4 h. The control group will consist of the classic static cold storage which is the gold standard procedure in liver transplantation. The primary objective of this trial is to study the efficacy of HOPE used before transplantation of ECD liver grafts from brain-dead donors in reducing postoperative early allograft dysfunction within the first 7 postoperative days compared to simple cold static storage.

DISCUSSION

We present in this protocol all study procedures in regard to the achievement of the HOPExt trial, to prevent biased analysis of trial outcomes and improve the transparency of the trial results. Enrollment of patients in the HOPExt trial has started on September 10, 2019, and is ongoing.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03929523. Registered on April 29, 2019, before the start of inclusion.

Donation after circulatory death: Novel strategies to improve the liver transplant outcome

In many countries, donation after circulatory death (DCD) liver grafts are used to overcome organ shortages; however, DCD grafts have been associated with an increased risk of complications and even graft loss after liver transplantation. The increased risk of complications is thought to correlate with prolonged functional donor warm ischaemia time. Stringent donor selection criteria and utilisation of in situ and ex situ organ perfusion technologies have led to improved outcomes. Additionally, the increased use of novel organ perfusion strategies has led to the possibility of reconditioning marginal DCD liver grafts. Moreover, these technologies enable the assessment of liver function before implantation, thus providing valuable data that can guide more precise graft-recipient selection. In this review, we first describe the different definitions of functional warm donor ischaemia time and its role as a determinant of outcomes after DCD liver transplantation, with a focus on the thresholds proposed for graft acceptance. Next, organ perfusion strategies, namely normothermic regional perfusion, hypothermic oxygenated perfusion, and normothermic machine perfusion are discussed. For each technique, clinical studies reporting on the transplant outcome are described, together with a discussion on the possible protective mechanisms involved and the functional criteria adopted for graft selection. Finally, we review multimodal preservation protocols involving a combination of more than one perfusion technique and potential future directions in the field.

Restoration of Bile Duct Injury of Donor Livers During Ex Situ Normothermic Machine Perfusion

BACKGROUND

End-ischemic ex situ normothermic machine perfusion (NMP) enables assessment of donor livers prior to transplantation. The objective of this study was to provide support for bile composition as a marker of biliary viability and to investigate whether bile ducts of high-risk human donor livers already undergo repair during NMP.

METHODS

Forty-two livers that were initially declined for transplantation were included in our NMP clinical trial. After NMP, livers were either secondary declined (n = 17) or accepted for transplantation (n = 25) based on the chemical composition of bile and perfusate samples. Bile duct biopsies were taken before and after NMP and assessed using an established histological injury severity scoring system and a comprehensive immunohistochemical assessment focusing on peribiliary glands (PBGs), vascular damage, and regeneration.

RESULTS

Bile ducts of livers that were transplanted after viability testing during NMP showed better preservation of PBGs, (micro)vasculature, and increased cholangiocyte proliferation, compared with declined livers. Biliary bicarbonate, glucose, and pH were confirmed as accurate biomarkers of bile duct vitality. In addition, we found evidence of PBG-based progenitor cell differentiation toward mature cholangiocytes during NMP.

CONCLUSIONS

Favorable bile chemistry during NMP correlates well with better-preserved biliary microvasculature and PBGs, with a preserved capacity for biliary regeneration. During NMP, biliary tree progenitor cells start to differentiate toward mature cholangiocytes, facilitating restoration of the ischemically damaged surface epithelium.

Machine perfusion of the liver and bioengineering

With the increasing number of accepted candidates on waiting lists worldwide, there is an urgent need to expand the number and the quality of donor livers. Dynamic preservation approaches have demonstrated various benefits, including improving liver function and graft survival, and reducing liver injury and post-transplant complications. Consequently, organ perfusion techniques are being used in clinical practice in many countries. Despite this success, a proportion of livers do not meet current viability tests required for transplantation, even with the use of modern perfusion techniques. Therefore, devices are needed to further optimise machine liver perfusion - one promising option is to prolong machine liver perfusion for several days, with ex situ treatment of perfused livers. For example, stem cells, senolytics, or molecules targeting mitochondria or downstream signalling can be administered during long-term liver perfusion to modulate repair mechanisms and regeneration. Besides, today's perfusion equipment is also designed to enable the use of various liver bioengineering techniques, to develop scaffolds or for their re-cellularisation. Cells or entire livers can also undergo gene modulation to modify animal livers for xenotransplantation, to directly treat injured organs or to repopulate such scaffolds with "repaired" autologous cells. This review first discusses current strategies to improve the quality of donor livers, and secondly reports on bioengineering techniques to design optimised organs during machine perfusion. Current practice, as well as the benefits and challenges associated with these different perfusion strategies are discussed.

D-dimer Release From Livers During Ex Situ Normothermic Perfusion and After In Situ Normothermic Regional Perfusion: Evidence for Occult Fibrin Burden Associated With Adverse Transplant Outcomes and Cholangiopathy

BACKGROUND

Deceased donor livers are prone to biliary complications, which may necessitate retransplantation, and we, and others, have suggested that these complications are because of peribiliary vascular fibrin microthrombi. We sought to determine the prevalence and consequence of occult fibrin within deceased donor livers undergoing normothermic ex situ perfusion (NESLiP) and evaluate a role for fibrinolysis.

METHODS

D-dimer concentrations, products of fibrin degradation, were assayed in the perfusate of 163 livers taken after 2 h of NESLiP, including 91 that were transplanted. These were related to posttransplant outcomes. Five different fibrinolytic protocols during NESLiP using alteplase were evaluated, and the transplant outcomes of these alteplase-treated livers were reviewed.

RESULTS

Perfusate D-dimer concentrations were lowest in livers recovered using in situ normothermic regional perfusion and highest in alteplase-treated livers. D-dimer release from donation after brain death livers was significantly correlated with the duration of cold ischemia. In non-alteplase-treated livers, Cox proportional hazards regression analysis showed that D-dimer levels were associated with transplant survival ( P  = 0.005). Treatment with alteplase and fresh frozen plasma during NESLiP was associated with significantly more D-dimer release into the perfusate and was not associated with excess bleeding postimplantation; 8 of the 9 treated livers were free of cholangiopathy, whereas the ninth had a proximal duct stricture.

CONCLUSIONS

Fibrin is present in many livers during cold storage and is associated with poor posttransplant outcomes. The amount of D-dimer released after fibrinolytic treatment indicates a significant occult fibrin burden and suggests that fibrinolytic therapy during NESLiP may be a promising therapeutic intervention.

Exceeding the Limits of Static Cold Storage in Limb Transplantation Using Subnormothermic Machine Perfusion

BACKGROUND

 For 50 years, static cold storage (SCS) has been the gold standard for solid organ preservation in transplantation. Although logistically convenient, this preservation method presents important constraints in terms of duration and cold ischemia-induced lesions. We aimed to develop a machine perfusion (MP) protocol for recovery of vascularized composite allografts (VCA) after static cold preservation and determine its effects in a rat limb transplantation model.

METHODS

 Partial hindlimbs were procured from Lewis rats and subjected to SCS in Histidine-Tryptophan-Ketoglutarate solution for 0, 12, 18, 24, and 48 hours. They were then either transplanted (Txp), subjected to subnormothermic machine perfusion (SNMP) for 3 hours with a modified Steen solution, or to SNMP + Txp. Perfusion parameters were assessed for blood gas and electrolytes measurement, and flow rate and arterial pressures were monitored continuously. Histology was assessed at the end of perfusion. For select SCS durations, graft survival and clinical outcomes after transplantation were compared between groups at 21 days.

RESULTS

 Transplantation of limbs preserved for 0, 12, 18, and 24-hour SCS resulted in similar survival rates at postoperative day 21. Grafts cold-stored for 48 hours presented delayed graft failure (p = 0.0032). SNMP of limbs after 12-hour SCS recovered the vascular resistance, potassium, and lactate levels to values similar to limbs that were not subjected to SCS. However, 18-hour SCS grafts developed significant edema during SNMP recovery. Transplantation of grafts that had undergone a mixed preservation method (12-hour SCS + SNMP + Txp) resulted in better clinical outcomes based on skin clinical scores at day 21 post-transplantation when compared to the SCS + Txp group (p = 0.01613).

CONCLUSION

 To date, VCA MP is still limited to animal models and no protocols are yet developed for graft recovery. Our study suggests that ex vivo SNMP could help increase the preservation duration and limit cold ischemia-induced injury in VCA transplantation.

Trends and Obstacles to Implement Dynamic Perfusion Concepts for Clinical Liver Transplantation: Results from a Global Web-Based Survey

BACKGROUND

Organ perfusion technology is increasingly used in many countries, with a focus, however, on the Western world. This study investigates the current international trends and obstacles to the broader routine implementation of dynamic perfusion concepts in liver transplantation.

METHODS

A web-based anonymous survey was launched in 2021. Experts of all involved specializations from 70 centers in 34 countries were contacted, based on the published literature and experience in the field of abdominal organ perfusion.

RESULTS

Overall, 143 participants from 23 countries completed the survey. Most respondents were male (67.8%) and transplant surgeons (64.3%) working at university hospitals (67.9%). The majority had experience with organ perfusion (82%), applying mainly hypothermic machine perfusion (HMP; 38%) and other concepts. While most (94.4%) expect a higher utilization of marginal organs with machine perfusion, the majority considers HMP the best technique to reduce liver discard-rates. While most respondents (90%) believed machine perfusion should be fully commissioned, the lack of funding (34%) and knowledge (16%) as well as limited staff (19%) were the three main obstacles to a routine clinical implementation.

CONCLUSION

Although dynamic preservation concepts are increasingly used in clinical practice, significant challenges remain. Specific financial pathways, uniform regulations, and tight collaborations among involved experts are needed to achieve wider global clinical use.

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

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

The Current Role and Future Applications of Machine Perfusion in Liver Transplantation

The relative paucity of donor livers suitable for transplantation has sparked innovations to preserve and recondition organs to expand the pool of transplantable organs. Currently, machine perfusion techniques have led to the improvement of the quality of marginal livers and to prolonged cold ischemia time and have allowed for the prediction of graft function through the analysis of the organ during perfusion, improving the rate of organ use. In the future, the implementation of organ modulation might expand the scope of machine perfusion beyond its current usage. The aim of this review was to provide an overview of the current clinical use of machine perfusion devices in liver transplantation and to provide a perspective for future clinical use, including therapeutic interventions in perfused donor liver grafts.

Prediction, prevention, and treatment of post reperfusion syndrome in adult orthotopic liver transplant patients

IMPORTANCE

This review explores proposed predictors, preventative measures, and treatment options for post-reperfusion syndrome (PRS) in liver transplantation and provides updated data for clinicians.

OBJECTIVES

The review aims to understand the status and progress made regarding PRS during orthotopic liver transplantation. Moreover, the predictors of PRS will be analyzed to highlight risk factors. Mediators of PRS and the modes of action of the currently available preventative and management agents that target particular PRS factors will be investigated.

DATA SOURCES

Data is drawn from secondary sources from databases of peer-reviewed journals. The bibliographies of select sources were also used to obtain additional data studies using the 'snowball' method.

STUDY SELECTION

The initial data search provided 1394 studies analyzed using PRISMA Extension for Scoping Reviews (PRISMA-ScR) guidelines. After applying the eligibility criteria, 18 studies were fit for inclusion.

RESULTS

The study identified that in addition to the severity of underlying medical conditions, other significant PRS predictors included patient age, sex, duration of cold ischemia, and the surgical technique. While the use of epinephrine and norepinephrine is well-established, further preventative measures commonly involve specifically targeting known mediators of the syndrome, such as antioxidants, vasodilators, free radical scavengers, and anticoagulants. Current management strategies involve supportive therapy. Machine Perfusion may ultimately decrease the risk of PRS.

CONCLUSION

PRS still holds unknowns, including the underlying pathophysiology, controllable factors, and ideal management practices. There is a need for further study, particularly prospective trials since liver transplantation is the gold standard for treating end-stage liver disease and the incidence of PRS remains high.

Preliminary observations of an ex vivo normothermic whole blood machine perfusion in an experimental liver transplant porcine model

BACKGROUND

Even though transplantation is an essential treatment with no viable alternatives, a significant worldwide donor shortage persists. In this study, we assessed the metabolism of livers that underwent extended periods of circulatory death and subsequently conducted functional validation through transplantation to explore the feasibility of using livers from an uncontrolled donor after circulatory death (u-DCD).

METHODS

A donor model simulating u-DCD was constructed using pigs. The prolonged warm ischemia time (WIT) was set to 60, 120, and 180 minutes, and the liver function was evaluated after 24 hours of perfusion using an originally developed normothermic perfusion system. Based on the results, functional confirmation by transplantation was performed on the 2 groups with prolonged WIT of 60 and 180 minutes.

RESULTS

Based on the 24-hour perfusion of the liver alone, we evaluated the function by transplanting the WI 60-minute model and 180-minute model (N = 3 each). Warm ischemia was 73.5 ± 3.7 minutes and 188 ± 3 minutes in the 60-minute model and 180-minute model, respectively. In the model with 60 minutes of WI, one case survived until the endpoint, and 2 cases survived between 8 and 12 hours, whereas, in the model with 180 minutes of WI, they died within 6 hours.

CONCLUSION

We constructed a completely uncontrolled circulatory arrest model without anticoagulation and showed the possibility of using u-DCD livers by ex vivo machine perfusion and transplantation.

Impact of Hypothermic Oxygenated Machine Perfusion on Hepatocellular Carcinoma Recurrence after Liver Transplantation

BACKGROUND

Machine perfusion may be able to mitigate ischemia-reperfusion injury (IRI), which increases hepatocellular carcinoma (HCC) recurrence after liver transplantation (LT). This study aimed to investigate the impact of dual-hypothermic oxygenated machine perfusion (D-HOPE) on HCC recurrence in LT.

METHODS

A single-center retrospective study was conducted from 2016 to 2020. Pre- and postoperative data of HCC patients undergoing LT were analyzed. Recipients of a D-HOPE-treated graft were compared to those of livers preserved using static cold storage (SCS). The primary endpoint was recurrence-free survival (RFS).

RESULTS

Of 326 patients, 246 received an SCS-preserved liver and 80 received a D-HOPE-treated graft (donation after brain death (DBD), n = 66; donation after circulatory death (DCD), n = 14). Donors of D-HOPE-treated grafts were older and had higher BMI. All DCD donors were treated by normothermic regional perfusion and D-HOPE. The groups were comparable in terms of HCC features and estimated 5-year RFS according to the Metroticket 2.0 model. D-HOPE did not reduce HCC recurrence (D-HOPE 10%; SCS 8.9%; p = 0.95), which was confirmed using Bayesian model averaging and inverse probability of treatment weighting-adjusted RFS analysis. Postoperative outcomes were comparable between groups, except for lower AST and ALT peak in the D-HOPE group.

CONCLUSIONS

In this single-center study, D-HOPE did not reduce HCC recurrence but allowed utilizing livers from extended criteria donors with comparable outcomes, improving access to LT for patients suffering from HCC.

A multicenter randomized-controlled trial of hypothermic oxygenated perfusion (HOPE) for human liver grafts before transplantation

BACKGROUND & AIMS

Machine perfusion is a novel method intended to optimize livers before transplantation. However, its effect on morbidity within a 1-year period after transplantation has remained unclear.

METHODS

In this multicenter controlled trial, we randomly assigned livers donated after brain death (DBD) for liver transplantation (LT). Livers were either conventionally cold stored (control group), or cold stored and subsequently treated by 1-2 h hypothermic oxygenated perfusion (HOPE) before implantation (HOPE group). The primary endpoint was the occurrence of at least one post-transplant complication per patient, graded by the Clavien score of ≥III, within 1-year after LT. The comprehensive complication index (CCI), laboratory parameters, as well as duration of hospital and intensive care unit stay, graft survival, patient survival, and biliary complications served as secondary endpoints.

RESULTS

Between April 2015 and August 2019, we randomized 177 livers, resulting in 170 liver transplantations (85 in the HOPE group and 85 in the control group). The number of patients with at least one Clavien ≥III complication was 46/85 (54.1%) in the control group and 44/85 (51.8%) in the HOPE group (odds ratio 0.91; 95% CI 0.50-1.66; p = 0.76). Secondary endpoints were also not significantly different between groups. A post hoc analysis revealed that liver-related Clavien ≥IIIb complications occurred less frequently in the HOPE group compared to the control group (risk ratio 0.26; 95% CI 0.07-0.77; p = 0.027). Likewise, graft failure due to liver-related complications did not occur in the HOPE group, but occurred in 7% (6 of 85) of the control group (log-rank test, p = 0.004, Gray test, p = 0.015).

CONCLUSIONS

HOPE after cold storage of DBD livers resulted in similar proportions of patients with at least one Clavien ≥III complication compared to controls. Exploratory findings suggest that HOPE decreases the risk of severe liver graft-related events.

IMPACT AND IMPLICATIONS

This randomized controlled phase III trial is the first to investigate the impact of hypothermic oxygenated perfusion (HOPE) on cumulative complications within a 12-month period after liver transplantation. Compared to conventional cold storage, HOPE did not have a significant effect on the number of patients with at least one Clavien ≥III complication. However, we believe that HOPE may have a beneficial effect on the quantity of complications per patient, based on its application leading to fewer severe liver graft-related complications, and to a lower risk of liver-related graft loss. The HOPE approach can be applied easily after organ transport during recipient hepatectomy. This appears fundamental for wide acceptance since concurring perfusion technologies need either perfusion at donor sites or continuous perfusion during organ transport, which are much costlier and more laborious. We conclude therefore that the post hoc findings of this trial should be further validated in future studies.

Simultaneous thoracic and abdominal donation after circulatory death organ recovery: the abdominal surgeon's perspective

PURPOSE OF THE REVIEW

To summarize the international experience with heart-liver (joint) donation after circulatory death (DCD) procurements and to explore the technical challenges in joint abdominal and thoracic DCD procurement.

RECENT FINDINGS

Following completion of the Donors After Circulatory Death Heart Trial in the US, combined thoracic and abdominal DCD is poised to become the standard of care, expanding access to life-saving heart and lung allografts. DCD heart procurement relies on collection of donor blood for priming of the normothermic perfusion pump, which delays cooling of abdominal organs and increases risk of ischemic injury. We review the effect of donor ischemia time on abdominal organs, with several proposed technical solutions to optimize transplant outcomes for all organs.

SUMMARY

The strategies reviewed in this manuscript may inform clinical decision-making, preoperative coordination between thoracic and abdominal procurement teams, and surgical technique for joint DCD procurements. Several approaches to organ procurement organization (OPO) and national policy, as well as future areas of focus for research are proposed.

Normothermic Machine Perfusion for Declined Livers: A Strategy to Rescue Marginal Livers for Transplantation

BACKGROUND

Organ waste is a major cause of the donor liver shortage. Roughly 67% of recovered organ donors have liver utilization annually. A new technology called normothermic machine perfusion (NMP) offers a way to recover marginal and declined livers for transplant. We report interim results of the RESTORE trial (FDA investigational drug exemption trial NCT04483102) that aims to transplant NMP-treated livers that would otherwise be discarded.

STUDY DESIGN

Declined livers were screened for NMP eligibility (eg donation after circulatory death [DCD] grafts with warm ischemic time <40 minutes, donation after brain death [DBD] grafts with cold ischemic time <8 hours). Livers meeting pre-NMP eligibility criteria received NMP using the OrganOx metra device for a minimum of 4 hours. All NMP-treated livers meeting the viability criteria were transplanted to consented recipients.

RESULTS

Over 22 months, 60 declined livers from three organ procurement organizations (OPOs; 40 DCD and 20 DBD donor livers) were offered, and 22 livers (10 DCD and 12 DBD livers) met the pre-NMP eligibility. After NMP, 16 of 22 livers passed viability testing and were transplanted into needy recipients (median Model for End-Stage Liver Disease [MELD] score of 8, range 6 to 24), resulting in a 72.7% rescue rate (50% DCD, 91.7% DBD). The rate of early allograft dysfunction was 31.3%, but there were no graft-related deaths, primary nonfunction, or instances of nonanastomotic biliary strictures.

CONCLUSIONS

Interim results of the RESTORE trial suggest that a sizable number of declined livers can be reclaimed. They are safe for transplantation and can enable lower MELD patients at high risk of morbidity and mortality to receive lifesaving grafts while offering OPOs a way to allocate more livers and reduce organ waste.

Association between Hepatocellular Carcinoma Recurrence and Graft Size in Living Donor Liver Transplantation: A Systematic Review

The aim of this work was to assess the association between graft-to-recipient weight ratio (GRWR) in adult-to-adult living donor liver transplantation (LDLT) and hepatocellular carcinoma (HCC) recurrence. A search of the MEDLINE and EMBASE databases was performed until December 2022 for studies comparing different GRWRs in the prognosis of HCC recipients in LDLT. Data were pooled to evaluate 1- and 3-year survival rates. We identified three studies, including a total of 782 patients (168 GRWR < 0.8 vs. 614 GRWR ≥ 0.8%). The pooled overall survival was 85% and 77% at one year and 90% and 83% at three years for GRWR < 0.8 and GRWR ≥ 0.8, respectively. The largest series found that, in patients within Milan criteria, the GRWR was not associated with lower oncological outcomes. However, patients with HCC outside the Milan criteria with a GRWR < 0.8% had lower survival and higher tumor recurrence rates. The GRWR < 0.8% appears to be associated with lower survival rates in HCC recipients, particularly for candidates with tumors outside established HCC criteria. Although the data are scarce, the results of this study suggest that considering the individual GRWR not only as risk factor for small-for-size-syndrome but also as contributor to HCC recurrence in patients undergoing LDLT would be beneficial. Novel perfusion technologies and pharmacological interventions may contribute to improving outcomes.

Optimizing graft-recipient size matching in adolescent liver transplantation: Don't forget ex situ right posterior sectionectomy

BACKGROUND

Graft-recipient size matching is a major challenge in pediatric liver transplantation, especially for adolescent recipients. Indeed, adolescents have the lowest transplantation rate among pediatric recipients, despite prioritization policies and the use of split grafts. In case of an important graft-recipient size mismatch, ex situ graft reduction with right posterior sectionectomy (RPS) may optimize the available donor pool to benefit adolescent recipients.

METHODS

We present three cases of liver graft reduction with ex situ RPS for adolescent recipients. The surgical strategy was guided by GRWR (graft/recipient weight ratio), GW/RAP (right anteroposterior distance ratio), and CT-scan volumetric and anthropometric evaluation.

RESULTS

Recipients were 12, 13, and 14-year-old and weighed 32, 47, and 35 kg, respectively. All liver grafts were procured from brain-dead donors with a donor/recipient weight ratio >1.5. RPS was performed ex situ, removing 20% of the total liver volume leading to a decrease of the GRWR <4% and the GW/RAP <100 g/cm in each case. All three reduced grafts were successfully transplanted with a static cold storage time ranging from 390 to 510 min without the need for delayed abdominal closure. We did not observe any primary non-function, vascular complication, or delayed graft function with a median follow-up of 6 months. One biliary anastomotic stenosis occurred which required surgical treatment.

CONCLUSION

Ex situ liver graft reduction with RPS allowed for successful transplantation in case of anthropometric graft-recipient size mismatch in adolescent liver transplant candidates. Although the use of split grafts remains the gold standard, RPS should be acknowledged as a way to optimize the donor pool, especially for adolescent recipients.

Hypothermic Oxygenated Machine Perfusion Promotes Mitophagy Flux against Hypoxia-Ischemic Injury in Rat DCD Liver

Hypothermic oxygenated machine perfusion (HOPE) can enhance organ preservation and protect mitochondria from hypoxia-ischemic injury; however, an understanding of the underlying HOPE mechanism that protects mitochondria is somewhat lacking. We hypothesized that mitophagy may play an important role in HOPE mitochondria protection. Experimental rat liver grafts were exposed to 30 min of in situ warm ischemia. Then, grafts were procured, followed by cold storage for 3 or 4 h to mimic the conventional preservation and transportation time in donation after circulatory death (DCD) in clinical contexts. Next, the grafts underwent hypothermic machine perfusion (HMP) or HOPE for 1 h through portal vein only perfusion. The HOPE-treated group showed a better preservation capacity compared with cold storage and HMP, preventing hepatocyte damage, nuclear injury, and cell death. HOPE can increase mitophagy marker expression, promote mitophagy flux via the PINK1/Parkin pathway to maintain mitochondrial function, and reduce oxygen free radical generation, while the inhibition of autophagy by 3-methyladenine and chloroquine could reverse the protective effect. HOPE-treated DCD liver also demonstrated more changes in the expression of genes responsible for bile metabolism, mitochondrial dynamics, cell survival, and oxidative stress. Overall, HOPE attenuates hypoxia-ischemic injury in DCD liver by promoting mitophagy flux to maintain mitochondrial function and protect hepatocytes. Mitophagy could pave the way for a protective approach against hypoxia-ischemic injury in DCD liver.

Charged multivesicular body protein 2B ameliorates biliary injury in the liver from donation after cardiac death rats via autophagy with air-oxygenated normothermic machine perfusion

Normothermic machine perfusion (NMP) could provide a curative treatment to reduce biliary injury in donation after cardiac death (DCD) donor livers; however, the underlying mechanisms remain poorly understood. In a rat model, our study compared air-oxygenated NMP to hyperoxygenated NMP and found that air-oxygenated NMP improved DCD functional recovery. Here, we found that the charged multivesicular body protein 2B (CHMP2B) expression was substantially elevated in the intrahepatic biliary duct endothelium of the cold-preserved rat DCD liver after air-oxygenated NMP or in biliary endothelial cells under hypoxia/physoxia. CHMP2B knockout (CHMP2B^-/-) rat livers showed increased biliary injury after air-oxygenated NMP, indicated by decreased bile production and bilirubin level, elevated biliary levels of lactate dehydrogenase and gamma-glutamyl transferase. Mechanically, we demonstrated that CHMP2B was transcriptionally regulated by Kruppel-like transcription factor 6 (KLF6) and alleviated biliary injury through decreasing autophagy. Collectively, our results suggested that air-oxygenated NMP regulates CHMP2B expression through the KLF6, which reduces biliary injury by inhibiting autophagy. Targeting the KLF6-CHMP2B autophagy axis may provide a solution to reducing biliary injury in DCD livers undergoing NMP.

Ultrasound-Targeted Microbubble Cavitation During Machine Perfusion Reduces Microvascular Thrombi and Graft Injury in a Rat Liver Model of Donation After Circulatory Death

BACKGROUND

Ischemic cholangiopathy is a process of bile duct injury that might result from peribiliary vascular plexus (PBP) thrombosis and remains a dreaded complication in liver transplantation from donors after circulatory death (DCD). The aim of this study was to propose a mechanical method of clot destruction to clear microvascular thrombi in DCD livers before transplantation.

METHODS

Sonothrombolysis (STL) is a process by which inertial cavitation of circulating microbubbles entering an ultrasound field create a high-energy shockwave at a microbubble-thrombus interface, causing mechanical clot destruction. The effectiveness of STL in DCD liver treatment remains unclear. We carried out STL treatment during normothermic, oxygenated, ex vivo machine perfusion (NMP), introducing microbubbles into the perfusate with the liver enveloped in an ultrasound field.

RESULTS

The STL livers showed reduction in hepatic arterial and PBP thrombus and decreases in hepatic arterial and portal venous flow resistance, reduced parenchymal injury as measured by aspartate transaminase release and oxygen consumption, and improved cholangiocyte function. Light and electron microscopy showed reduction of hepatic arterial and PBP thrombus in STL livers compared with controls and preserved hepatocyte structure, sinusoid endothelial morphology, and biliary epithelial microvilli.

CONCLUSION

In this model, STL improved flow and functional measures in DCD livers undergoing NMP. These data suggest a novel therapeutic approach to treat PBP injury in DCD livers, which may ultimately increase the pool of grafts available to patients awaiting liver transplantation.

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.

Sequential hypothermic and normothermic perfusion preservation and transplantation of expanded criteria donor livers

BACKGROUND

The purpose of this study was to assess the safety and feasibility of sequential hypothermic oxygenated perfusion and normothermic machine perfusion and the potential benefits of graft viability preservation and assessment before liver transplantation.

METHODS

With the Food and Drug Administration and institutional review board approval, 17 expanded criteria donor livers underwent sequential hypothermic oxygenated perfusion and normothermic machine perfusion using our institutionally developed perfusion device.

RESULTS

Expanded criteria donor livers were from older donors, donors after cardiac death, with steatosis, hypertransaminasemia, or calcified arteries. Perfusion duration ranged between 1 and 2 hours for the hypothermic oxygenated perfusion phase and between 4 and 9 hours for the normothermic machine perfusion phase. Three livers were judged to be untransplantable during normothermic machine perfusion based on perfusate lactate, bile production, and macro-appearance. One liver was not transplanted because of recipient issue after anesthesia induction and failed reallocation. Thirteen livers were transplanted, including 9 donors after cardiac death livers (donor warm ischemia time 16-25 minutes) and 4 from donors after brain death. All livers had the standardized lactate clearance >60% (perfusate lactate cleared to <4.0 mmol/L) within 3 hours of normothermic machine perfusion. Bile production rate was 0.2 to 10.7 mL/h for donors after brain death livers and 0.3 to 6.1 mL/h for donors after cardiac death livers. After transplantation, 5 cases had early allograft dysfunction (3 donors after cardiac death and 2 donors after brain death livers). No graft failure or patient death has occurred during follow-up time of 6 to 13 months. Two livers developed ischemic cholangiopathy. Compared with our previous normothermic machine perfusion study, the bile duct had fewer inflammatory cells in histology, but the post-transplant outcomes had no difference.

CONCLUSION

Sequential hypothermic oxygenated perfusion and normothermic machine perfusion preservation is safe and feasible and has the potential benefits of preserving and evaluating expanded criteria donor livers.

Cryopreservation of Whole Rat Livers by Vitrification and Nanowarming

Liver cryopreservation has the potential to enable indefinite organ banking. This study investigated vitrification-the ice-free cryopreservation of livers in a glass-like state-as a promising alternative to conventional cryopreservation, which uniformly fails due to damage from ice formation or cracking. Our unique "nanowarming" technology, which involves perfusing biospecimens with cryoprotective agents (CPAs) and silica-coated iron oxide nanoparticles (sIONPs) and then, after vitrification, exciting the nanoparticles via radiofrequency waves, enables rewarming of vitrified specimens fast enough to avoid ice formation and uniformly enough to prevent cracking from thermal stresses, thereby addressing the two main failures of conventional cryopreservation. This study demonstrates the ability to load rat livers with both CPA and sIONPs by vascular perfusion, cool them rapidly to an ice-free vitrified state, and rapidly and homogenously rewarm them. While there was some elevation of liver enzymes (Alanine Aminotransferase) and impaired indocyanine green (ICG) excretion, the nanowarmed livers were viable, maintained normal tissue architecture, had preserved vascular endothelium, and demonstrated hepatocyte and organ-level function, including production of bile and hepatocyte uptake of ICG during normothermic reperfusion. These findings suggest that cryopreservation of whole livers via vitrification and nanowarming has the potential to achieve organ banking for transplant and other biomedical applications.

Management of Intraoperative Cardiac Arrest

Perioperative arrests are both uncommon and heterogeneous and have not been described or studied to the same extent as cardiac arrest in the community. These crises are usually witnessed, frequently anticipated, and involve a rescuer physician with knowledge of the patient's comorbidities and coexisting anesthetic or surgically related pathophysiology ultimately leading to better outcomes. This article reviews the most probable causes of intraoperative arrest and their management.

A Review of Machine Perfusion Strategies in Liver Transplantation

The acceptance of liver transplantation as the standard of care for end-stage liver diseases has led to a critical shortage of donor allografts. To expand the donor organ pool, many countries have liberalized the donor criteria including extended criteria donors and donation after circulatory death. These marginal livers are at a higher risk of injury when they are preserved using the standard static cold storage (SCS) preservation techniques. In recent years, research has focused on optimizing organ preservation techniques to protect these marginal livers. Machine perfusion (MP) of the expanded donor liver has witnessed considerable advancements in the last decade. Research has showed MP strategies to confer significant advantages over the SCS techniques, such as longer preservation times, viability assessment and the potential to recondition high risk allografts prior to implantation. In this review article, we address the topic of MP in liver allograft preservation, with emphasis on current trends in clinical application. We discuss the relevant clinical trials related to the techniques of hypothermic MP, normothermic MP, hypothermic oxygenated MP, and controlled oxygenated rewarming. We also discuss the potential applications of ex vivo therapeutics which may be relevant in the future to further optimize the allograft prior to transplantation.

Metabolomics Differences of the Donor Livers Between In Situ and Ex Situ Conditions During Ischemia-free Liver Transplantation

BACKGROUND

Ischemia-free liver transplantation (IFLT) has been innovated to avoid graft ischemia during organ procurement, preservation, and implantation. However, the metabolism activity of the donor livers between in the in situ and ex situ normothermic machine perfusion (NMP) conditions, and between standard criteria donor and extend criteria donor remains unknown.

METHODS

During IFLT, plasma samples were collected both at the portal vein and hepatic vein of the donor livers in situ during procurement and ex situ during NMP. An ultra-high performance liquid chromatography-mass spectrometry was conducted to investigate the common and distinct intraliver metabolite exchange.

RESULTS

Profound cysteine and methionine metabolism, and aminoacyl-tRNA biosynthesis were found in both in situ and ex situ conditions. However, obvious D-arginine and D-ornithine metabolism, arginine and proline metabolism were only found in the in situ condition. The suppressed activities of the urea cycle pathway during ex situ condition were confirmed in an RNA expression level. In addition, compared with extend criteria donor group, standard criteria donor group had more active intraliver metabolite exchange in metabonomics level. Furthermore, we found that the relative concentration of p-cresol, allocystathionine, L-prolyl-L-proline in the ex situ group was strongly correlated with peak alanine aminotransferase and aspartate aminotransferase at postoperative days 1-7.

CONCLUSIONS

In the current study, we show the common and distinct metabolism activities during IFLT. These findings might provide insights on how to modify the design of NMP device, improve the perfusate components, and redefine the criteria of graft viability.