Normothermic ex vivo liver perfusion using steen solution as perfusate for human liver transplantation: First North American results

Normothermic Ex Vivo Liver Perfusion Prevents Intrahepatic Platelet Sequestration After Liver Transplantation

BACKGROUND

The detrimental role of platelets in sinusoidal endothelial cell (SEC) injury during liver transplantation (LT) has been previously addressed after static cold storage (SCS), however, it is currently unknown after normothermic ex vivo liver perfusion (NEVLP).

METHODS

Pig LT was performed with livers from heart-beating donors or donation after circulatory death (DCD) donors subjected to SCS or NEVLP (n = 5/group).

RESULTS

All pigs except for 1 (DCD-SCS-group) survived 4 days. The heart-beating donor- and DCD-NEVLP-groups showed significantly lower aspartate transaminase-levels compared with the SCS-groups 3 hours post-LT (P = 0.006), on postoperative day (POD) 2 (P = 0.005), POD3 (P = 0.007), and on POD4 (P = 0.012). Post-LT total platelet count recovered faster in the NEVLP than in the SCS-groups at 12 hours (P = 0.023) and 24 hours (P = 0.0038). Intrahepatic sequestration of platelets was significantly higher in the SCS-groups 3 hours postreperfusion and correlated with severity of SEC injury. In both SCS-groups, levels of tumor growth factor-β were higher 3 hours post-LT, on POD1 and on POD3. Moreover, platelet factor 4 levels and platelet-derived extracellular vesicles were increased in the SCS-groups. Hyaluronic acid levels were significantly higher in the SCS-groups, indicating a higher grade of endothelial cell dysfunction. Platelet inhibition achieved by pretreatment with clopidogrel (n = 3) partly reversed the detrimental effects on SEC injury and therefore provided further evidence of the important role of platelets in ischemia/reperfusion injury and SEC injury.

CONCLUSIONS

Normothermic perfusion of liver grafts before transplantation effectively reduced platelet aggregation and SEC injury, which translated into an improved posttransplant organ function.

Review of Current Machine Perfusion Therapeutics for Organ Preservation

Because of the high demand of organs, the usage of marginal grafts has increased. These marginal organs have a higher risk of developing ischemia-reperfusion injury, which can lead to posttransplant complications. Ex situ machine perfusion (MP), compared with the traditional static cold storage, may better protect these organs from ischemia-reperfusion injury. In addition, MP can also act as a platform for dynamic administration of pharmacological agents or gene therapy to further improve transplant outcomes. Numerous therapeutic agents have been studied under both hypothermic (1-8°C) and normothermic settings. Here, we review all the therapeutics used during MP in different organ systems (lung, liver, kidney, heart). The major categories of therapeutic agents include vasodilators, mesenchymal stem cells, antiinflammatory agents, antiinfection agents, siRNA, and defatting agents. Numerous animal and clinical studies have examined MP therapeutic agents, some of which have even led to the successful reconditioning of discarded grafts. More clinical studies, especially randomized controlled trials, will need to be conducted in the future to solidify these promising results and to define the role of MP therapeutic agents in solid organ transplantation.

Machine Perfusions in Liver Transplantation: The Evidence-Based Position Paper of the Italian Society of Organ and Tissue Transplantation

The use of machine perfusion (MP) in liver transplantation (LT) is spreading worldwide. However, its efficacy has not been demonstrated, and its proper clinical use has far to go to be widely implemented. The Società Italiana Trapianti d'Organo (SITO) promoted the development of an evidence-based position paper. A 3-step approach has been adopted to develop this position paper. First, SITO appointed a chair and a cochair who then assembled a working group with specific experience of MP in LT. The Guideline Development Group framed the clinical questions into a patient, intervention, control, and outcome (PICO) format, extracted and analyzed the available literature, ranked the quality of the evidence, and prepared and graded the recommendations. Recommendations were then discussed by all the members of the SITO and were voted on via the Delphi method by an institutional review board. Finally, they were evaluated and scored by a panel of external reviewers. All available literature was analyzed, and its quality was ranked. A total of 18 recommendations regarding the use and the efficacy of ex situ hypothermic and normothermic machine perfusion and sequential normothermic regional perfusion and ex situ MP were prepared and graded according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) method. A critical and scientific approach is required for the safe implementation of this new technology.

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.

Donation after circulatory death liver transplantation: consensus statements from the Spanish Liver Transplantation Society

Livers from donation after circulatory death (DCD) donors are an increasingly more common source of organs for transplantation. While there are few high-level studies in the field of DCD liver transplantation, clinical practice has undergone progressive changes during the past decade, in particular due to mounting use of postmortem normothermic regional perfusion (NRP). In Spain, uncontrolled DCD has been performed since the late 1980s/early 1990s, while controlled DCD was implemented nationally in 2012. Since 2012, the rise in DCD liver transplant activity in Spain has been considerable, and the great majority of DCD livers transplanted in Spain today are recovered with NRP. A panel of the Spanish Liver Transplantation Society was convened in 2018 to evaluate current evidence and accumulated experience in DCD liver transplantation, in particular addressing issues related to DCD liver evaluation, acceptance criteria, and recovery as well as recipient selection and postoperative management. This panel has created a series of consensus statements for the standard of practice in Spain and has published these statements with the hope they might help guide other groups interested in implementing new forms of DCD liver transplantation and/or introducing NRP into their clinical practices.

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

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

Liver graft from donation after circulatory death donor: Real practice to improve graft viability

Donation after circulatory death (DCD) is an increasing source of liver grafts for transplantation, yet outcomes have been inferior compared to donation after brain death liver transplantation. These worse outcomes are mainly due to the severe graft injury resulting from mandatory warm ischemia during DCD organ recovery. New evidence, however, indicates that improved donor selection and surgical techniques can decrease the risk of graft failure and ischemic cholangiopathy (IC). Under current best practices, DCD organs are retrieved with the super-rapid technique, optimizing timing and protecting the liver graft from detrimental warm ischemia. Graft viability is influenced by both the quantity and quality of warm ischemia, which is unique to each donor and causes various degrees of pathophysiologic consequences. Evidence also shows that the choice of preservation solution and premortem heparin administration influences graft viability. Additionally, although the precise mechanism of IC remains unknown, stasis of blood during donor warm ischemia may cause the formation of microthrombi in the peribiliary vascular plexus and ischemia of the bile duct. Importantly, thrombolytic protocols show a possible preventive modality for IC. Finally, while ex vivo machine perfusion technology has gained an interest in DCD liver transplantation, further studies are necessary to evaluate the effectiveness of this evolving field to improve graft quality and transplant outcomes.

Dual versus single vessel normothermic ex vivo perfusion of rat liver grafts using metamizole for vasodilatation

Background

Normothermic ex vivo liver perfusion (NEVLP) is a promising strategy to increase the donor pool in liver transplantation. Small animal models are essential to further investigate questions regarding organ preservation and reconditioning by NEVLP. A dual vessel small animal NEVLP (dNEVLP) model was developed using metamizole as a vasodilator and compared to conventional portovenous single vessel NEVLP (sNEVLP).

Methods

Livers of male Wistar rats were perfused with erythrocyte-supplemented culture medium for six hours by either dNEVLP via hepatic artery and portal vein or portovenous sNEVLP. dNEVLP was performed either with or without metamizole treatment. Perfusion pressure and flow rates were constantly monitored. Transaminase levels were determined in the perfusate at the start and after three and six hours of perfusion. Bile secretion was monitored and bile LDH and GGT levels were measured hourly. Histopathological analysis was performed using liver and bile duct tissue samples after perfusion.

Results

Hepatic artery pressure was significantly lower in dNEVLP with metamizole administration. Compared to sNEVLP, dNEVLP with metamizole treatment showed higher bile production, lower levels of transaminases during and after perfusion as well as significantly lower necrosis in liver and bile duct tissue. Biochemical markers of bile duct injury showed the same trend.

Conclusion

Our miniaturized dNEVLP system enables normothermic dual vessel rat liver perfusion. The administration of metamizole effectively ameliorates arterial vasospasm allowing for six hours of dNEVLP, with superior outcome compared to sNEVLP.

A Systematic Review and Meta-Analysis of Machine Perfusion vs. Static Cold Storage of Liver Allografts on Liver Transplantation Outcomes: The Future Direction of Graft Preservation

Background: Machine perfusion (MP) and static cold storage (CS) are two prevalent methods for liver allograft preservation. However, the preferred method remains controversial.

Aim: To conduct a meta-analysis on the impact of MP preservation on liver transplant outcome.

Methods: PubMed, EMBASE, and Cochrane Library databases were systematically searched to identify relevant trials comparing the efficacy of MP vs. CS. Odds ratios (OR) and fixed-effects models were calculated to compare the pooled data.

Results: Ten prospective cohort studies and two randomized controlled trials (RCTs) were included (MP livers vs. CS livers = 315:489). Machine perfusion demonstrated superior outcomes in posttransplantation aspartate aminotransferase levels compared to CS (P < 0.05). The overall incidence of early allograft dysfunction (EAD) was significantly reduced with MP preservation than CS [OR = 0.46; 95% confidence interval (CI) = 0.31–0.67; P < 0.0001]. The incidence of total biliary complications (OR = 0.53; 95% CI = 0.34–0.83; P = 0.006) and that of ischemic cholangiopathy (OR = 0.39; 95% CI = 0.18–0.85; P = 0.02) were significantly lower in recipients with MP preservation compared with CS preservation. Hypothermic machine perfusion (HMP) but not normothermic machine perfusion (NMP) was found to significantly protect grafts from total biliary complications and ischemic cholangiopathy (P < 0.05). However, no significant differences could be detected utilizing either HMP or NMP in primary nonfunction, hepatic artery thrombosis, postreperfusion syndrome, 1-year patient survival, or 1-year graft survival (P > 0.05).

Conclusions: Machine perfusion is superior to CS on improving short-term outcomes for human liver transplantation, with a less clear effect in the longer term. Hypothermic machine perfusion but not NMP conducted significantly protective effects on EAD and biliary complications. Further RCTs are warranted to confirm MP's superiority and applications.

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.

Donation after circulatory death liver transplantation: What are the limits for an acceptable DCD graft?

The utilization of donation after circulatory death (DCD) livers has been growing over the last decade. In large-volume centers, survival outcomes have improved and are comparable to outcomes with brain death donor (DBD) liver transplantation (LT). The relatively concentrated success with DCD LT demonstrated by high-volume transplant centers has rekindled international enthusiasm. The combination of increasing expertise in DCD LT and ongoing shortage in transplantable organs has promoted expansion of the DCD donor pool with regards to donor age, body mass index and donor warm ischemia time. In this review, we focused on the practice patterns in DCD liver graft utilization in the last decade, along with the possibilities for further expansion of DCD liver graft utilization and new technologies, such as machine perfusion.

Addressing organ shortages: progress in donation after circulatory death for liver transplantation

Reducing wait list mortality among patients awaiting liver transplantation remains a substantial challenge because of organ shortage. In efforts to expand the donor pool there has been a trend toward increased use of donation after circulatory death (DCD) liver grafts. However, these marginal grafts are prone to higher complication rates, particularly biliary complications. In addition, many procured DCD livers are then deemed unsuitable for transplant. Despite these limitations, DCD grafts represent an important resource to address the current organ shortage, and as such there are research efforts directed toward improving the use of and outcomes for transplantation of these grafts. We review the current progress in DCD liver transplantation.

Ex Situ Liver Machine Perfusion: The Impact of Fresh Frozen Plasma

The primary aim of this single-center, phase 1 exploratory study was to investigate the safety, feasibility, and impact on intrahepatic hemodynamics of a fresh frozen plasma (FFP)-based perfusate in ex situ liver normothermic machine perfusion (NMP) preservation. Using an institutionally developed perfusion device, 21 livers (13 donations after brain death and 8 donations after circulatory death) were perfused for 3 hours 21 minutes to 7 hours 52 minutes and successfully transplanted. Outcomes were compared in a 1:4 ratio to historical control patients matched according to donor and recipient characteristics and preservation time. Perfused livers presented a very low resistance state with high flow during ex situ perfusion (arterial and portal flows 340 ± 150 and 890 ± 70 mL/minute/kg liver, respectively). This hemodynamic state was maintained even after reperfusion as demonstrated by higher arterial flow observed in the NMP group compared with control patients (220 ± 120 versus 160 ± 80 mL/minute/kg liver, P = 0.03). The early allograft dysfunction (EAD) rate, peak alanine aminotransferase (ALT), and peak aspartate aminotransferase (AST) levels within 7 days after transplantation were lower in the NMP group compared with the control patients (EAD 19% versus 46%, P = 0.02; peak ALT 363 ± 318 versus 1021 ± 999 U/L, P = 0.001; peak AST 1357 ± 1492 versus 2615 ± 2541 U/L, P = 0.001 of the NMP and control groups, respectively). No patient developed ischemic type biliary stricture. One patient died, and all other patients are alive and well at a follow-up of 12-35 months. No device-related adverse events were recorded. In conclusion, with this study, we showed that ex situ NMP of human livers can be performed safely and effectively using a noncommercial device and an FFP-based preservation solution. Future studies should further investigate the impact of an FFP-based perfusion solution on liver hemodynamics during ex situ normothermic machine preservation.

Concise review of machine perfusion in liver transplantation

With the advances and clinical growth in liver transplantation over the last four decades the focus on expanding deceased donor organs has been in need of scientific research. In the past ten years several researchers have looked at the domain of machine perfusion as it applies to deceased donor livers. The following review focuses on the clinical trials and recent advances that will likely have the earliest entrance into the clinical arena.

Therapeutics administered during ex vivo liver machine perfusion: An overview

Although the use of extended criteria donors has increased the pool of available livers for transplant, it has also introduced the need to develop improved methods of protection against ischemia-reperfusion injury (IRI), as these "marginal" organs are particularly vulnerable to IRI during the process of procurement, preservation, surgery, and post-transplantation. In this review, we explore the current basic science research investigating therapeutics administered during ex vivo liver machine perfusion aimed at mitigating the effects of IRI in the liver transplantation process. These various categories of therapeutics are utilized during the perfusion process and include invoking the RNA interference pathway, utilizing defatting cocktails, and administering classes of agents such as vasodilators, anti-inflammatory drugs, human liver stem cell-derived extracellular vesicles, and δ-opioid agonists in order to reduce the damage of IRI. Ex vivo machine perfusion is an attractive alternative to static cold storage due to its ability to continuously perfuse the organ, effectively deliver substrates and oxygen required for cellular metabolism, therapeutically administer pharmacological or cytoprotective agents, and continuously monitor organ viability during perfusion. The use of administered therapeutics during machine liver perfusion has demonstrated promising results in basic science studies. While novel therapeutic approaches to combat IRI are being developed through basic science research, their use in clinical medicine and treatment in patients for liver transplantation has yet to be explored.

Split-Liver Ex Situ Machine Perfusion: A Novel Technique for Studying Organ Preservation and Therapeutic Interventions

Ex situ machine perfusion is a promising technology to help improve organ viability prior to transplantation. However, preclinical studies using discarded human livers to evaluate therapeutic interventions and optimize perfusion conditions are limited by significant graft heterogeneity. In order to improve the efficacy and reproducibility of future studies, a split-liver perfusion model was developed to allow simultaneous perfusion of left and right lobes, allowing one lobe to serve as a control for the other. Eleven discarded livers were surgically split, and both lobes perfused simultaneously on separate perfusion devices for 3 h at subnormothermic temperatures. Lobar perfusion parameters were also compared with whole livers undergoing perfusion. Similar to whole-liver perfusions, each lobe in the split-liver model exhibited a progressive decrease in arterial resistance and lactate levels throughout perfusion, which were not significantly different between right and left lobes. Split liver lobes also demonstrated comparable energy charge ratios. Ex situ split-liver perfusion is a novel experimental model that allows each graft to act as its own control. This model is particularly well suited for preclinical studies by avoiding the need for large numbers of enrolled livers necessary due to the heterogenous nature of discarded human liver research.

The impact of short-term machine perfusion on the risk of cancer recurrence after rat liver transplantation with donors after circulatory death

Hypothermic and normothermic ex vivo liver perfusions promote organ recovery after donation after circulatory death (DCD). We tested whether these perfusions can reduce the risk of hepatocellular carcinoma (HCC) recurrence in a 1h-DCD syngeneic transplantation model, using Fischer F344 rats. DCD grafts were machine perfused for 2h with hypothermic perfusion (HOPE) or normothermic perfusion (NORMO), and transplanted. After reperfusion, we injected HCC cells into the vena porta. On day 28 after transplantation, we assessed tumour volumes by MRI. Control rats included transplantations with Fresh and non-perfused DCD livers. We observed apoptotic-necrotic hepatocyte foci in all DCD grafts, which were more visible than in the Fresh liver grafts. Normothermic perfusion allowed a faster post-transplant recovery, with lower day 1 levels of transaminases compared with the other DCD. Overall, survival was similar in all four groups and all animals developed HCCs. Total tumor volume was lower in the Fresh liver recipients compared to the DCD and DCD+HOPE recipients. Volumes in DCD+NORMO recipients were not significantly different from those in the Fresh group. This experiment confirms that ischemia/reperfusion injury promotes HCC cell engraftment/growth after DCD liver transplantation. Using the present extreme 1h ischemia model, both hypothermic and normothermic perfusions were not effective in reducing this risk.

Predictor parameters of liver viability during porcine normothermic ex situ liver perfusion in a model of liver transplantation with marginal grafts

Normothermic ex situ liver perfusion (NEsLP) offers the opportunity to assess biomarkers of graft function and injury. We investigated NEsLP parameters (biomarkers and markers) for the assessment of liver viability in a porcine transplantation model. Grafts from heart-beating donors (HBD), and from donors with 30 minutes (donation after cardiac death [DCD]30'), 70 minutes (DCD70'), and 120 minutes (DCD120') of warm ischemia were studied. The HBD, DCD30', and DCD70'-groups had 100% survival. In contrast, 70% developed primary nonfunction (PNF) and died in the DCD120'-group. Hepatocellular function during NEsLP showed low lactate (≤1.1 mmol/L) in all the groups except the DCD120'-group (>2 mmol/L) at 4 hours of perfusion (P = .04). The fold-urea increase was significantly lower in the DCD120'-group (≤0.4) compared to the other groups (≥0.65) (P = .01). As for cholangiocyte function, bile/perfusate glucose ratio was significantly lower (<0.6) in all the groups except the DCD120'-group (≥0.9) after 3 hours of perfusion (<0.01). Bile/perfusate Na+ ratio was significantly higher (≥1.2) after 3 hours of perfusion in all the groups except for the DCD120'-group (≤1) (P < .01). Three hours after transplantation, the DCD120'-group had a significantly higher international normalized ratio (>5) compared to the rest of the groups (≤1.9) (P = .02). Rocuronium levels were higher at all the time-points in the animals that developed PNF during NEsLP and after transplantation. This study demonstrates that biomarkers and markers of hepatocellular and cholangiocyte function during NEsLP correlate with the degree of ischemic injury and posttransplant function.

Transient Cold Storage Prior to Normothermic Liver Perfusion May Facilitate Adoption of a Novel Technology

Clinical adoption of normothermic machine perfusion (NMP) may be facilitated by simplifying logistics and reducing costs. This can be achieved by cold storage of livers for transportation to recipient centers before commencing NMP. The purpose of this study was to assess the safety and feasibility of post-static cold storage normothermic machine perfusion (pSCS-NMP) in liver transplantation. In this multicenter prospective study, 31 livers were transplanted. The primary endpoint was 30-day graft survival. Secondary endpoints included the following: peak posttransplant aspartate aminotransferase (AST), early allograft dysfunction (EAD), postreperfusion syndrome (PRS), adverse events, critical care and hospital stay, biliary complications, and 12-month graft survival. The 30-day graft survival rate was 94%. Livers were preserved for a total of 14 hours 10 minutes ± 4 hours 46 minutes, which included 6 hours 1 minute ± 1 hour 19 minutes of static cold storage before 8 hours 24 minutes ± 4 hours 4 minutes of NMP. Median peak serum AST in the first 7 days postoperatively was 457 U/L (92-8669 U/L), and 4 (13%) patients developed EAD. PRS was observed in 3 (10%) livers. The median duration of initial critical care stay was 3 days (1-20 days), and median hospital stay was 13 days (7-31 days). There were 7 (23%) patients who developed complications of grade 3b severity or above, and 2 (6%) patients developed biliary complications: 1 bile leak and 1 anastomotic stricture with no cases of ischemic cholangiopathy. The 12-month overall graft survival rate (including death with a functioning graft) was 84%. In conclusion, this study demonstrates that pSCS-NMP was feasible and safe, which may facilitate clinical adoption.

Influence of 4 preservation solutions on ICU stay, graft and patient survival following liver transplantation

OBJECTIVE

The goal of this study was to evaluate the prognostic role of four preservation solutions in liver transplantation (LT).

PATIENTS AND METHODS

This is a retrospective study originating from 22 French centers performing LT, registered in the prospective databank of the Cristal Biomedicine Agency between 2008 and 2013. The preservation solutions used were Celsior (CS), Institut Georges Lopez (IGL)-1, Solution de Conservation des Organes et des Tissus (SCOT) 15 and University of Wisconsin (UW) solutions. Exclusion criteria were preservation with unknown or inhomogeneous solutions, or Histidine-tryptophan-ketoglutarate (HTK) solution (representing only 3% of LT). Patient survival was the main endpoint. Secondary endpoints were graft survival and duration of stay in intensive care.

RESULTS

Of 6347 LT performed, 4928 were included in this study, for which the distribution of preservation solution was CS (30%), IGL-1 (44%), SCOT 15 (10%) and UW (16%). Patient survival was 86%, 80% and 74% at 1, 3 and 5 years after LT, respectively, without any statistically significant difference between the four solutions (P=0.78). Graft survival was 82%, 75% and 69% at 1, 3 and 5 years after LT, respectively, without any statistically significant difference between the four solutions (P=0.80). Duration of intensive care was different according to the solution used in univariate analysis (P<0.001), but this effect disappeared in multivariate analysis when the center performing the transplantation was accounted for.

CONCLUSION

The type of preservation solution used (CS, IGL-1, SCOT 15 or UW) did not have any influence on patient or graft survival after LT.

Initial perfusate purification during subnormothermic machine perfusion for porcine liver donated after cardiac death

Improvement of machine perfusion (MP) technologies is required to enhance organ quality for donor after cardiac death (DCD) grafts. Installing a dialyzer or a filter into the perfusion circuit to maintain the perfusate condition has some advantages. However, the consequences of purification perfusate during subnormothermic machine perfusion (SNMP) remain unexplained. In this study, the effects of initial purification perfusate with simple method of replacing the first 0.5-L perfusate during SNMP were investigated to consider installation effect of the filter or the dialyzer. Porcine liver grafts, which have 60-min warm ischemia time, were procured to imitate the DCD graft condition. Purified SNMP (PSNMP) results were compared with simple cold storage and conventional SNMP. In PSNMP, initial perfusate of 0.5 L was removed to substitute for purification. After preservation process, the preserved grafts were reperfused with diluted autologous blood for 2 h under normothermic machine perfusion condition to evaluate the liver function using an isolated reperfusion model. The vascular pressures, enzyme release rates and the metabolic indexes during reperfusion were analyzed. The pressures in the hepatic artery after reperfusion 60 min were significantly lower in PSNMP group compared with cold storage (CS) and SNMP groups. In addition, lactate dehydrogenase and alkaline phosphatase were significantly lower after PSNMP than after the CS or SNMP. Also, the metabolic indexes of hyaluronic acid and lactate were significantly decreased by purifying the perfusate in MP preservation than in CS or SNMP. The effectiveness of initial purification perfusate during SNMP was investigated.

Avoiding initial hypothermia does not improve liver graft quality in a porcine donation after circulatory death (DCD) model of normothermic perfusion

Background

Normothermic machine perfusion (NMP) of liver grafts donated after circulatory death (DCD) has shown promise in large animal and clinical trials. Following procurement, initial flush with a cold preservation solution is the standard of care. There is concern that initial cooling followed by warming may exacerbate liver injury, and the optimal initial flush temperature has yet to be identified. We hypothesize that avoidance of the initial cold flush will yield better quality liver grafts.

Methods

Twenty-four anaesthetized pigs were withdrawn from mechanical ventilation and allowed to arrest. After 60-minutes of warm ischemia to simulate a DCD procurement, livers were flushed with histidine-tryptophan-ketoglutarate (HTK) at 4°C, 25°C or 35°C (n = 4 per group). For comparison, an adenosine-lidocaine crystalloid solution (AD), shown to have benefit at warm temperatures in heart perfusions, was also used (n = 4 per group). During 12-hours of NMP, adenosine triphosphate (ATP), lactate, transaminase levels, and histological injury were determined. Bile production and hemodynamics were monitored continuously.

Results

ATP levels recovered substantially following 1-hour of NMP reaching pre-ischemic levels by the end of NMP with no difference between groups. There was no difference in peak aspartate aminotransferase (AST) or in lactate dehydrogenase (LDH). Portal vein resistance was lowest in the 4°C group reaching significance after 2 hours (0.13 CI -0.01,0.277, p = 0.025). Lactate levels recovered promptly with no difference between groups. Comparison to AD groups showed no statistical difference in the abovementioned parameters. On electron microscopy the HTK4°C group had the least edema with mean cell thickness of 2.92μm (p = 0.41) while also having the least sinusoidal dilatation with a mean diameter of 5.36μm (p = 0.04). For AD, the 25°C group had the lowest mean cell thickness at 3.14μm (p = 0.09).

Conclusions

Avoidance of the initial cold flush failed to demonstrate added benefit over standard 4°C HTK in this DCD model of liver perfusion.

Machine Perfusion of Liver Grafts With Implantable Oxygen Biosensors: Proof of Concept Study in a Rodent Model

Background

Normothermic machine perfusion (NMP) is emerging as a novel preservation strategy in liver transplantation, but the optimal methods for assessing liver grafts during this period have not been determined. The aim of this study was to investigate whether implantable oxygen biosensors can be used to monitor tissue oxygen tension in liver grafts undergoing NMP.

Methods

Implantable phosphorescence-based oxygen sensors were tested in 3 different experimental groups: (1) in vivo during laparotomy, (2) during NMP of liver grafts with an acellular perfusate (NMP-acellular), and (3) during NMP with perfusate containing red blood cells (NMP-RBC). During in vivo experiments, intrahepatic oxygen tension was measured before and after occlusion of the portal vein (PV). In NMP experiments, intrahepatic oxygen tension was measured as a function of different PV pressure settings (3 vs 5 vs 8 mm Hg) and inflow oxygen concentration (95% O₂ vs 6% O₂).

Results

In vivo, intrahepatic oxygen tension decreased significantly within 2 minutes of clamping the PV (P < 0.05). In NMP experiments, intrahepatic oxygen tension correlated directly with PV pressure when high inflow oxygen concentration (95%) was used. Intrahepatic oxygen tension was significantly higher in the NMP-RBC group compared with the NMP-acellular group for all conditions tested (P < 0.05).

Conclusions

Implantable oxygen biosensors have potential utility as a tool for real-time monitoring of intrahepatic oxygen tension during NMP of liver grafts. Further investigation is required to determine how intrahepatic oxygen tension during NMP correlates with posttransplant graft function.

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.

A Back-to-Base Experience of Human Normothermic Ex Situ Liver Perfusion: Does the Chill Kill?

Normothermic machine perfusion (NMP) has been shown to protect livers from injury between procurement and transplantation in a randomized controlled trial, where the machine was transported to and from the donor center. The aim of this study was to determine whether an alternative, more practical back-to-base approach after initial static cold storage would compromise beneficial outcomes. Between February 2015 and June 2018, a nonrandomized pilot study was performed at a single site. Outcomes of back-to-base livers (n = 26) were compared with those of grafts procured locally that underwent immediate NMP (n = 17). The primary outcome measure (safety) was defined as 30-day patient and graft survival. A total of 46 liver grafts were perfused with NMP, of which 3 were discarded based on poor ex situ perfusion function. The 30-day patient and graft survival in the back-to-base and local NMP groups were both 100% (primary outcome: safety). Despite significantly prolonged mean cold ischemia time (6 versus 3.2 hours; P = 0.001), the back-to-base livers demonstrated no difference in graft function, incidence of complications, or graft and patient survival. In conclusion, the back-to-base approach was safe, did not compromise the overall benefit of NMP, and offers a practical alternative to portable normothermic ex situ machine transport.

Normothermic liver preservation, current status and future directions

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Organ preservation solutions: linking pharmacology to survival for the donor organ pathway

PURPOSE OF REVIEW

To provide an understanding of the scientific principles, which underpinned the development of organ preservation solutions, and to bring into context new strategies and challenges for solution development against the background of changing preservation technologies and expanded criteria donor access.

RECENT FINDINGS

Improvements in organ preservation solutions continue to be made with new pharmacological approaches. New solutions have been developed for dynamic perfusion preservation and are now in clinical application. Principles defining organ preservation solution pharmacology are being applied for cold chain logistics in tissue engineering and regenerative medicine.

SUMMARY

Organ preservation solutions support the donor organ pathway. The solution compositions allow additives and pharmacological agents to be delivered direct to the target organ to mitigate preservation injury. Changing preservation strategies provide further challenges and opportunities to improve organ preservation solutions.

The dawn of liver perfusion machines

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

The future of organ perfusion and re-conditioning

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

Bioengineering approaches to organ preservation ex vivo

IMPACT STATEMENT

Over the past several decades, ex vivo perfusion has emerged as a promising technology for the assessment, preservation, and recovery of donor organs. Many exciting pre-clinical findings have now been translated to clinical use, and successful transplantation following ex vivo perfusion has been achieved for heart, lung, and liver. While machine perfusion provides distinct advantages over traditional cold preservation, many challenges remain, including that of long-term (multi-day) ex vivo support. Here, we provide an overview of the current status of ex vivo machine perfusion in the pre-clinical and clinical setting and share our perspective on the future direction of the field.

Safety of Antithymocyte Globulin in Patients Undergoing Liver Transplantation With Livers From Donation After Circulatory Death Donors

Background: Studies suggest that rabbit-antithymocyte globulin (rATG) decreases biliary complications (BCs) after donation-after-circulatory-death-donor liver transplantation (DCD LTx), but safety data are lacking. Objective: Our aim was to assess the safety of rATG for this indication. The secondary end point was efficacy of rATG for this indication. Methods: Adult recipients of DCD LTx were divided into 2 cohorts: protocolized use of rATG in the modern era (July 1, 2013, to December 31, 2016) and a historical control without rATG (January 1, 2005, to June 30, 2013). Incidence of infection, leukopenia, and thrombocytopenia were compared for the safety assessment, incidence of BCs, ischemic cholangiopathy (IC), and transplant outcomes for the efficacy assessment. Results: A total of 83 patients met inclusion criteria: 42 in the historical cohort and 41 in the modern cohort. The modern cohort had significantly fewer bacterial infections at 3 months (historical 54.8% vs modern 23%; P = 0.004) and 1 year (historical 62.1% vs modern 34.2%, P = 0.004). The modern cohort also had fewer fungal infections at these time points (historical 33.3% and 47.9% vs modern 15% and 15%; P = 0.001). There were no significant differences in platelet or white blood cell reduction between groups. There was a nonsignificant, but numerical, trend toward reduced IC/BC in the modern cohort at 1 year (IC: historical 30.1% vs modern 13.2%, P = 0.08; BC: historical 51% vs modern 37.5%, P = 0.13). There was no difference in graft/patient survival. Conclusion and Relevance: Our data suggest no major safety issues with rATG in DCD LTx. Our study should ease clinical apprehension surrounding rATG use for this indication. Future prospective studies are needed to further evaluate the role of rATG and its impact on efficacy end points.

Clearance of transaminases during normothermic ex situ liver perfusion

Background

One of the most promising applications of liver normothermic machine perfusion (NMP) is the potential to directly assess graft viability and injury. In most NMP studies, perfusate transaminases are utilized as markers of graft injury. Our aim was to further elucidate the metabolism of transaminases by healthy porcine livers during NMP, specifically whether such livers could clear circuit perfusate transaminases.

Methods

A highly concentrated transaminase solution was prepared from homogenized liver, with an aspartate aminotransferase (AST) level of 107,427 U/L. Three livers in the treatment group were compared to three controls, during 48 hours of NMP. In the treatment group, the circuit perfusate was injected with the transaminase solution to artificially raise the AST level to a target of 7,500 U/L. Perfusate samples were taken at two-hour intervals and analyzed for biochemistry until NMP end. Graft oxygen consumption and vascular parameters were monitored.

Results

Compared to controls, treated perfusions demonstrated abrupt elevations in transaminase levels (p>0.0001) and lactate dehydrogenase (LDH) (p>0.0001), which decreased over time, but never to control baseline. Liver function, as demonstrated by lactate clearance and oxygen consumption was not different between groups. The treatment group demonstrated a higher portal vein resistance (p = 0.0003), however hepatic artery resistance was similar. Treated livers had higher bile production overall (p<0.0001).

Conclusions

Addition of high levels of transaminases and LDH to a healthy porcine liver during ex situ perfusion results in progressive clearance of these enzymes, suggesting preserved liver metabolism. Such tolerance tests may provide valuable indicators of prospective graft function.

Study of Hepatic Vascular Dynamics Based on Symmetrical Pulsating Perfusion

Background

The traditionally used perfusion method is constant flow. This study proposes a novel method called Symmetric Pulsating Flow (SPF) and verified that this method is applicable.

Material/Methods

The fluid dynamic behavior of perfusate in the vessel, the shear stress, and the vascular deformation were simulated based on the bi-directional fluid-structure interaction. The differences of the fluid dynamic behaviors and the mechanical characteristics of vascular wall were studied and compared between the 2 methods during the process of hepatic perfusion. The simulations and comparisons were carried out on 3 different vascular models.

Results

Utilizing the constant flow perfusion, a double vortex clearly appeared at the rear end of the foreign matter and reflux retention can be caused by the double vortex. The reflux retention caused lower shear stress against the vascular wall and thus brought new accumulation of foreign matter. The SPF perfusion, however, prevented the double vortex, and avoided such reflux retention during the vascular perfusion. In addition, the SPF can clean the vascular wall better with a slower speed, which causes less injury to the vessel, and the pulsating effect can reduce the accumulation of new foreign matter.

Conclusions

The SPF perfusion can clean the vascular wall more thoroughly with less injury.

Pretransplant sequential hypo- and normothermic machine perfusion of suboptimal livers donated after circulatory death using a hemoglobin-based oxygen carrier perfusion solution

Ex situ dual hypothermic oxygenated machine perfusion (DHOPE) and normothermic machine perfusion (NMP) of donor livers may have a complementary effect when applied sequentially. While DHOPE resuscitates the mitochondria and increases hepatic adenosine triphosphate (ATP) content, NMP enables hepatobiliary viability assessment prior to transplantation. In contrast to DHOPE, NMP requires a perfusion solution with an oxygen carrier, for which red blood cells (RBC) have been used in most series. RBC, however, have limitations and cannot be used cold. We, therefore, established a protocol of sequential DHOPE, controlled oxygenated rewarming (COR), and NMP using a new hemoglobin-based oxygen carrier (HBOC)-based perfusion fluid (DHOPE-COR-NMP trial, NTR5972). Seven livers from donation after circulatory death (DCD) donors, which were initially declined for transplantation nationwide, underwent DHOPE-COR-NMP. Livers were considered transplantable if perfusate pH and lactate normalized, bile production was ≥10 mL and biliary pH > 7.45 within 150 minutes of NMP. Based on these criteria five livers were transplanted. The primary endpoint, 3-month graft survival, was a 100%. In conclusion, sequential DHOPE-COR-NMP using an HBOC-based perfusion fluid offers a novel method of liver machine perfusion for combined resuscitation and viability testing of suboptimal livers prior to transplantation.

Damage-Associated Molecular Patterns Induce Inflammatory Injury During Machine Preservation of the Liver: Potential Targets to Enhance a Promising Technology

Machine preservation (MP) has emerged as a promising technology in liver transplantation, but the cellular processes occurring during MP have not been characterized. Recent studies have noted the presence of inflammatory molecules generated during MP. We hypothesized that there is a metabolism-dependent accumulation of damage-associated molecular patterns (DAMPs) and inflammatory cytokines during MP and that these molecules provoke inflammation in the graft. To stratify groups by metabolic rate, MP was performed on rat livers from standard donors at 3 different temperatures: room temperature (RT), subnormothermic (30°C), and normothermic (37°C). Static cold storage at 4°C was included as a reference group. Following a 4-hour preservation period, graft reperfusion was performed ex vivo at 37°C (n = 6 for all groups). Levels of DAMPs and inflammatory cytokines were measured, and their biological activity was assessed by determining toll-like receptor (TLR) stimulation, inflammatory gene expression, and activation of cell death pathways. There was a time-dependent increase in levels of DAMPs during MP with high-mobility group box 1 and extracellular DNA levels increasing for all groups (P < 0.05, 30 versus 240 minutes). Tumor necrosis factor α levels in the perfusate also increased during MP for all groups (P < 0.05, 30 minutes versus 240 minutes). Levels of inflammatory molecules correlated with increased activation of TLRs (TLR3, P = 0.02, normothermic machine preservation [MP37] versus machine preservation at room temperature [MPRT]; TLR9, P = 0.02, MP37 versus MPRT). Priming of the NLRP3 inflammasome and activation of cell death pathways were reduced in grafts preserved by MP at room temperature. In conclusion, inflammatory molecules produced during MP have a biological impact on the graft. Therapies to attenuate DAMP-mediated inflammation during MP may further enhance this promising technology.

Liver graft preservation methods during cold ischemia phase and normothermic machine perfusion

The growing demand for donor organs requires measures to expand donor pool. Those include extended criteria donors, such as elderly people, steatotic livers, donation after cardiac death, etc. Static cold storage to reduce metabolic requirements developed by Collins in late 1960s is the mainstay and the golden standard for donated organ protection. Hypothermic machine perfusion provides dynamic organ preservation at 4°C with protracted infusion of metabolic substrates to the graft during the ex vivo period. It has been used instead of static cold storage or after it as short perfusion in transplant center. Normothermic machine perfusion (NMP) delivers oxygen, and nutrition at physiological temperature mimicking regular environment in order to support cellular function. This would minimize effects of ischemia/reperfusion injury. Potentially, NMP may help to estimate graft functionality before implantation into a recipient. Clinical studies demonstrated at least its non-inferiority or better outcomes vs static cold storage. Regular grafts donated after brain death could be safely preserved with convenient static cold storage. Except for prolonged ischemia time where hypothermic machine perfusion started in transplant center could be estimated to provide possible positive reconditioning effect. Use of hypothermic machine perfusion in regular donation instead of static cold storage or in extended criteria donors requires further investigation. Multicenter randomized clinical trial supposed to be completed in December 2021. Extended criteria donors need additional measures for graft storage and assessment until its implantation. NMP is actively evaluating promising method for this purpose. Future studies are necessary for precise estimation and confirmation to issue clinical practice recommendations.

Determination of Minimal Hemoglobin Level Necessary for Normothermic Porcine Ex Situ Liver Perfusion

BACKGROUND

In current studies of ex situ liver perfusion there exists considerable variability in perfusate composition, including the type of oxygen carrier. Herein, we aim to clarify the minimal hemoglobin level necessary during normothermic porcine ex situ liver perfusion.

METHODS

Livers procured from 35 to 45 kg domestic pigs were connected to our experimental ex situ circuit (n = 10). In the treatment group, perfusate was sequentially diluted hourly to predetermined hemoglobin levels. At the end of each hemoglobin dilution, perfusate samples were analyzed for liver transaminases, lactate dehydrogenase (LD), total bilirubin, and lactate levels. Liver oxygen consumption was measured. In the control group, livers were perfused continually for a duration of 24 hours at target hemoglobin levels of 30 and 20 g/L.

RESULTS

Rising liver transaminases, significantly higher lactate (P < 0.001), and LD levels (P < 0.001) were noted at lower perfusate hemoglobin levels in the treatment group. Liver oxygen utilization (P < 0.001) and hepatic artery oxygen delivery (P < 0.001) were significantly lower at lower hemoglobin levels, whereas liver vessel resistance remained relatively constant. Histology demonstrated increasing parenchymal damage at lower hemoglobin levels. In control livers, higher perfusate transaminases, higher lactate, and LD levels were noted at a perfusion hemoglobin level of 20 g/L.

CONCLUSIONS

Ex situ liver function decompensated during perfusion between a mean hemoglobin level of 30 to 20 g/L, as evidenced by notably rising lactate and LD levels. This study demonstrates optimal hemoglobin concentration during normothermic ex situ liver perfusion to ensure a fully metabolically functioning graft.

Normothermic Ex Vivo Kidney Perfusion Reduces Warm Ischemic Injury of Porcine Kidney Grafts Retrieved After Circulatory Death

BACKGROUND

Cold storage is poorly tolerated by kidney grafts retrieved after donation after circulatory death. It has been determined that normothermic ex vivo kidney perfusion (NEVKP) preservation decreases injury by minimizing cold ischemic storage. The impact of NEVKP on warm ischemic injury is unknown.

METHODS

We compared pig kidneys retrieved after 30 minutes warm ischemia and immediate transplantation (no-preservation) with grafts that were exposed to 30 minutes of warm ischemia plus 8-hour NEVKP or plus 8-hour static cold storage (SCS).

RESULTS

After transplantation, the NEVKP group demonstrated lower daily serum creatinine levels indicating better early graft function compared with no-preservation (P = 0.02) or SCS group (P < 0.001). In addition, NEVKP preserved grafts had a significantly lower grade of tubular injury and interstitial inflammation 30 minutes after reperfusion compared to grafts without any storage (injury score, NEVKP 1-2 vs no-preservation, 2-2, P = 0.029; inflammation score, NEVKP, 0-0.5 vs no-preservation, 1-2; P = 0.002), although it did not reach significance level when compared to the SCS group (injury score, 1-2, P = 0.071; inflammation score, 1-1; P = 0.071). Regeneration was assessed 30 minutes after reperfusion by Ki-67 staining. The NEVKP group demonstrated significantly higher number of Ki-67-positive cells: 9.2 ± 3.7 when compared with SCS group (3.9 ± 1.0, P = 0.015) and no-preservation group (4.2 ± 0.7, P = 0.04).

CONCLUSIONS

In this porcine model of donation after circulatory death kidney transplantation NEVKP reduced kidney injury and improved graft function when compared with no-preservation. The results suggest that NEVKP does not cause additional damage to grafts during the preservation period, but may reverse the negative effects of warm ischemic insult itself and promotes regeneration.

Impact of Different Clinical Perfusates During Normothermic Ex Situ Liver Perfusion on Pig Liver Transplant Outcomes in a DCD Model

Supplemental digital content is available in the text.

Background

Human albumin/dextran (HA-D), bovine-gelatin (BG), and packed red blood cells plus plasma have been used in European and North-American clinical trials of normothermic ex situ liver perfusion (NEsLP). We compared the effects of these perfusates in a porcine model during NEsLP and after transplantation.

Methods

Porcine livers were retrieved 30 minutes after circulatory death. After 5 hours of NEsLP, grafts were transplanted. Three groups (n = 6) were assessed (HA-D vs BG vs whole blood [WB]). One group of static cold storage (SCS) was evaluated for comparison with the perfusion groups. Hemodynamic variables, liver and endothelial injury, and function were assessed during NEsLP and posttransplantation.

Results

Hepatic artery flow was higher since the beginning of NEsLP in the HA-D group (HA-D, 238 ± 90 mL/min vs BG, 97 ± 33 mL/min vs WB, 148 ± 49 mL/min; P = 0.01). Hyaluronic acid was lower in the HA-D at the end of perfusion (HA-D, 16.28 ± 7.59 ng/μL vs BG, 76.05 ± 15.30 ng/μL vs WB, 114 ± 46 ng/μL; P < 0.001). After transplant, aspartate aminotransferase was decreased in the HA-D group when compared with the rest of the groups (HA-D, 444 ± 226 IU/L vs BG, 1033 ± 694 IU/L vs WB, 616 ± 444 IU/L vs SCS, 2235 ± 1878 IU/L). At 5 hours after transplant, lactate was lower in the HA-D group (HA-D, 3.88 ± 1.49 mmol/L vs BG, 7.79 ± 2.68 mmol/L vs WB, 8.16 ± 3.86 mmol/L vs SCS, 9.06 ± 3.54 mmol/L; P = 0.04). International Normalized Ratio was improved in HA-D group compared to the rest of the groups (HA-D, 1.23 ± 0.30 vs BG, 1.63 ± 0.20 vs WB, 1.50 ± 0.31 vs SCS, 1.97 ± 1.55; P = 0.03) after transplantation. In contrast, BG displayed lower aspartate aminotransferase levels during NEsLP (HA-D, 183 ± 53 IU/L vs BG, 142 ± 52 IU/L vs WB, 285 ± 74 IU/L; P = 0.01) and less cleaved-caspase-3 staining (HA-D, 2.05 ± 0.73% vs BG, 0.95 ± 1.14% vs WB, 1.74 ± 0.54% vs SCS, 7.95 ± 2.38%) compared with the other groups. On the other hand, the bile from the WB showed higher pH (HA-D, 7.54 ± 0.11 vs BG, 7.34 ± 0.37 vs WB, 7.59 ± 0.18) and lower glucose levels (HA-D, 0.38 ± 0.75 mmol/L vs BG, 1.42 ± 1.75 mmol/L vs WB, 0 ± 0 mmol/L) by the end of perfusion.

Conclusions

Overall HA-D displayed more physiologic conditions during NEsLP that were reflected in less graft injury and improved liver function and survival after transplantation. Optimization of the perfusates based on the beneficial effects found with these different solutions would potentially improve further the outcomes through the use of NEsLP in marginal grafts.

Machine perfusion for liver transplantation in the era of marginal organs-New kids on the block

In the face of a critical organ shortage in the Western world, various strategies are employed to expand the donor pool for orthotopic liver transplantation (OLT). Among them is the transplantation of organs from extended criteria donors, a valuable source of liver allografts, however, characterized by potential risks for post-OLT complications and inferior outcomes. In recent years, machine perfusion (MP) of the explanted donor liver as well as regional perfusion techniques has witnessed significant advancements. Here, we aim to discuss different modes of dynamic organ preservation in OLT. These include hypothermic and normothermic MP, hypothermic oxygenated machine perfusion (HOPE), controlled oxygenated rewarming as well as regional perfusion protocols. Over recent years, multiple feasibility trials have demonstrated the clinical prospects of MP. In the context of OLT using organs from extended criteria donors, MP has numerous advantages compared to conventional cold storage, some of which include the preservation and reconditioning of borderline transplantable organs and the viability assessment of high-risk donor allografts. This review aims to address the topic of liver allograft MP, highlighting particularly the current trends in clinical applications and future perspectives. Furthermore, different approaches of liver storage and reconditioning are reviewed in the context of ongoing research.

Gene Silencing With siRNA (RNA Interference): A New Therapeutic Option During Ex Vivo Machine Liver Perfusion Preservation

RNA interference (RNAi) is a natural process of posttranscriptional gene regulation that has raised a lot of attention culminating with the Nobel Prize in Medicine in 2006. RNAi-based therapeutics have been tested in experimental transplantation to reduce ischemia/reperfusion injury (IRI) with success. Modulation of genes of the innate immune system, as well as apoptotic genes, and those involved in the nuclear factor kappa B pathways can reduce liver injury in rodent liver pedicle clamping and transplantation models of IRI. However, in vivo use of RNAi faces limitations regarding the method of administration, uptake, selectivity, and stability. Machine perfusion preservation, a more recent alternative approach for liver preservation showing superior results to static cold preservation, could be used as a platform for gene interference therapeutics. Our group was the first to demonstrate uptake of small interfering RNA (siRNA) during liver machine preservation under both normothermic and hypothermic perfusion. Administering siRNA in the perfusion solution during ex vivo machine preservation has several advantages, including more efficient delivery, lower doses and cost-saving, and none/fewer side effects to other organs. Recently, the first RNAi drug was approved by the US Food and Drug Administration for clinical use, opening a new avenue for new drugs with different clinical applications. RNAi has the potential to have transformational therapeutic applications in several areas of medicine including transplantation. We believe that machine preservation offers great potential to be the ideal delivery method of siRNA to the liver graft, and future studies should be initiated to improve the clinical applicability of RNAi in solid organ transplantation.

Comparison of BQ123, Epoprostenol, and Verapamil as Vasodilators During Normothermic Ex Vivo Liver Machine Perfusion

BACKGROUND

The optimal vasodilator to avoid hepatic artery vasospasm during normothermic ex vivo liver perfusion (NEVLP) is yet to be determined. We compared safety and efficacy of BQ123 (endothelin1 antagonist), epoprostenol (prostacyclin analogue), and verapamil (calcium channel antagonist).

METHODS

Livers from porcine heart beating donors were perfused for 3 hours and transplanted into recipient pigs. Four groups were compared: group 1, livers perfused with a dose of 1.25 mg of BQ123 at baseline and at 2 hours of perfusion; group 2, epoprostenol at a continuous infusion of 4 mg/h; group 3, verapamil 2.5 mg at baseline and at 2 hours of perfusion; group 4, no vasodilator used during ex vivo perfusion. Liver injury and function were assessed during perfusion, and daily posttransplantation until postoperative day (POD) 3. All groups were compared with a cold storage group for postoperative graft function.

RESULTS

Hepatic artery flow during NEVLP was significantly higher in BQ123 compared with verapamil, epoprostenol, and no vasodilator-treated livers. Aspartate aminotransferase levels were significantly lower with BQ123 and verapamil compared with epoprostenol and control group during perfusion. Peak aspartate aminotransferase levels were lower in pigs receiving BQ123 and verapamil perfused grafts compared with epoprostenol and control group. International Normalized Ratio, alkaline phosphatase, and total bilirubin levels were lower in the BQ123 and verapamil groups compared to epoprostenol group. Cold storage group had increased markers of ischemia reperfusion injury and slower graft function recovery compared to machine perfused grafts.

CONCLUSION

The use of BQ123, epoprostenol, and verapamil during NEVLP is safe. Livers perfused with BQ123 and verapamil have higher hepatic artery flow and reduced hepatocyte injury during perfusion compared with epoprostenol. Hepatic artery flow is significantly reduced in the absence of vasodilators during NEVLP.

Hydrogen Flush After Cold Storage as a New End-Ischemic Ex Vivo Treatment for Liver Grafts Against Ischemia/Reperfusion Injury

Cold storage (CS) remains the gold standard for organ preservation worldwide, although it is inevitably associated with ischemia/reperfusion injury (IRI). Molecular hydrogen (H₂ ) is well known to have antioxidative properties. However, its unfavorable features, ie, inflammability, low solubility, and high tissue/substance permeability, have hampered its clinical application. To overcome such obstacles, we developed a novel reconditioning method for donor organs named hydrogen flush after cold storage (HyFACS), which is just an end-ischemic H₂ flush directly to donor organs ex vivo, and, herein, we report its therapeutic impact against hepatic IRI. Whole liver grafts were retrieved from Wistar rats. After 24-hour CS in UW solution, livers were cold-flushed with H₂ solution (1.0 ppm) via the portal vein (PV), the hepatic artery (HA), or both (PV + HA). Functional integrity and morphological damages were then evaluated by 2-hour oxygenated reperfusion at 37°C. HyFACS significantly lowered portal venous pressure, transaminase, and high mobility group box protein 1 release compared with vehicle-treated controls (P < 0.01). Hyaluronic acid clearance was significantly higher in the HyFACS-PV and -PV + HA groups when compared with the others (P < 0.01), demonstrating the efficacy of the PV route to maintain the sinusoidal endothelia. In contrast, bile production and lactate dehydrogenase leakage therein were both significantly improved in HyFACS-HA and -PV + HA (P < 0.01), representing the superiority of the arterial route to attenuate biliary damage. Electron microscopy consistently revealed that sinusoidal ultrastructures were well maintained by portal HyFACS, while microvilli in bile canaliculi were well preserved by arterial flush. As an underlying mechanism, HyFACS significantly lowered oxidative damages, thus improving the glutathione/glutathione disulfide ratio in liver tissue. In conclusion, HyFACS significantly protected liver grafts from IRI by ameliorating oxidative damage upon reperfusion in the characteristic manner with its route of administration. Given its safety, simplicity, and cost-effectiveness, end-ischemic HyFACS may be a novel pretransplant conditioning for cold-stored donor organs.