A randomized trial of normothermic preservation in liver transplantation

State-of-the-Art and Future Directions in Organ Regeneration with Mesenchymal Stem Cells and Derived Products during Dynamic Liver Preservation

Transplantation is currently the treatment of choice for end-stage liver diseases but is burdened by the shortage of donor organs. Livers from so-called extended-criteria donors represent a valid option to overcome organ shortage, but they are at risk for severe post-operative complications, especially when preserved with conventional static cold storage. Machine perfusion technology reduces ischemia-reperfusion injury and allows viability assessment of these organs, limiting their discard rate and improving short- and long-term outcomes after transplantation. Moreover, by keeping the graft metabolically active, the normothermic preservation technique guarantees a unique platform to administer regenerative therapies ex vivo. With their anti-inflammatory and immunomodulatory properties, mesenchymal stem cells are among the most promising sources of therapies for acute and chronic liver failure, but their routine clinical application is limited by several biosafety concerns. It is emerging that dynamic preservation and stem cell therapy may supplement each other if combined, as machine perfusion can be used to deliver stem cells to highly injured grafts, avoiding potential systemic side effects. The aim of this narrative review is to provide a comprehensive overview on liver preservation techniques and mesenchymal stem cell-based therapies, focusing on their application in liver graft reconditioning.

Comparison of Biliary Complications Rates After Brain Death, Donation After Circulatory Death, and Living-Donor Liver Transplantation: A Single-Center Cohort Study

Donation-after-circulatory-death (DCD), donation-after-brain-death (DBD), and living-donation (LD) are the three possible options for liver transplantation (LT), each with unique benefits and complication rates. We aimed to compare DCD-, DBD-, and LD-LT-specific graft survival and biliary complications (BC). We collected data on 138 DCD-, 3,027 DBD- and 318 LD-LTs adult recipients from a single center and analyzed patient/graft survival. BC (leak and anastomotic/non-anastomotic stricture (AS/NAS)) were analyzed in a subset of 414 patients. One-/five-year graft survival were 88.6%/70.0% for DCD-LT, 92.6%/79.9% for DBD-LT, and, 91.7%/82.9% for LD-LT. DCD-LTs had a 1.7-/1.3-fold adjusted risk of losing their graft compared to DBD-LT and LD-LT, respectively (p < 0.010/0.403). Bile leaks were present in 10.1% (DCD-LTs), 7.2% (DBD-LTs), and 36.2% (LD-LTs) (ORs, DBD/LD vs. DCD: 0.7/4.2, p = 0.402/<0.001). AS developed in 28.3% DCD-LTs, 18.1% DBD-LTs, and 43.5% LD-LTs (ORs, DBD/LD vs. DCD: 0.5/1.8, p = 0.018/0.006). NAS was present in 15.2% DCD-LTs, 1.4% DBDs-LT, and 4.3% LD-LTs (ORs, DBD/LD vs. DCD: 0.1/0.3, p = 0.001/0.005). LTs w/o BC had better liver graft survival compared to any other groups with BC. DCD-LT and LD-LT had excellent graft survival despite significantly higher BC rates compared to DBD-LT. DCD-LT represents a valid alternative whose importance should increase further with machine/perfusion systems.

Senolytic treatment preserves biliary regenerative capacity lost through cellular senescence during cold storage

Liver transplantation is the only curative option for patients with end-stage liver disease. Despite improvements in surgical techniques, nonanastomotic strictures (characterized by the progressive loss of biliary tract architecture) continue to occur after liver transplantation, negatively affecting liver function and frequently leading to graft loss and retransplantation. To study the biological effects of organ preservation before liver transplantation, we generated murine models that recapitulate liver procurement and static cold storage. In these models, we explored the response of cholangiocytes and hepatocytes to cold storage, focusing on responses that affect liver regeneration, including DNA damage, apoptosis, and cellular senescence. We show that biliary senescence was induced during organ retrieval and exacerbated during static cold storage, resulting in impaired biliary regeneration. We identified decoy receptor 2 (DCR2)-dependent responses in cholangiocytes and hepatocytes, which differentially affected the outcome of those populations during cold storage. Moreover, CRISPR-mediated DCR2 knockdown in vitro increased cholangiocyte proliferation and decreased cellular senescence but had the opposite effect in hepatocytes. Using the p21KO model to inhibit senescence onset, we showed that biliary tract architecture was better preserved during cold storage. Similar results were achieved by administering senolytic ABT737 to mice before procurement. Last, we perfused senolytics into discarded human donor livers and showed that biliary architecture and regenerative capacities were better preserved. Our results indicate that cholangiocytes are susceptible to senescence and identify the use of senolytics and the combination of senotherapies and machine-perfusion preservation to prevent this phenotype and reduce the incidence of biliary injury after transplantation.

Controlled oxygenated rewarming as novel end-ischemic therapy for cold stored liver grafts. A randomized controlled trial

Abrupt return to normothermia has been shown a genuine factor contributing to graft dysfunction after transplantation. This study tested the concept to mitigate reperfusion injury of liver grafts by gentle warming-up using ex vivo machine perfusion prior to reperfusion. In a single center randomized controlled study, livers were assigned to conventional static cold storage (SCS) alone or to SCS followed by 90 min of ex vivo machine perfusion including controlled oxygenated rewarming (COR) by gentle and protracted elevation of the perfusate temperature from 10°C to 20°C. Primary outcome mean peak aspartate aminotransferase (AST) was 1371 U/L (SD 2871) after SCS versus 767 U/L (SD 1157) after COR (p = 0.273). Liver function test (LiMAx) on postoperative day 1 yielded 187 μg/kg/h (SD 121) after SCS, but rose to 294 μg/kg/h (SD 106) after COR (p = 0.006). Likewise, hepatic synthesis of coagulation factor V was significantly accelerated in the COR group immediately after transplantation (103% [SD 34] vs. 66% [SD 26]; p = 0.001). Fewer severe complications (Clavien-Dindo grade ≥3b) were reported in the COR group (8) than in the SCS group (15). Rewarming/reperfusion injury of liver grafts can be safely and effectively mitigated by controlling of the rewarming kinetics prior to blood reperfusion using end-ischemic ex vivo machine perfusion after cold storage.

Predicting Early Allograft Function After Normothermic Machine Perfusion

BACKGROUND

Normothermic ex situ liver perfusion is increasingly used to assess donor livers, but there remains a paucity of evidence regarding criteria upon which to base a viability assessment or criteria predicting early allograft function.

METHODS

Perfusate variables from livers undergoing normothermic ex situ liver perfusion were analyzed to see which best predicted the Model for Early Allograft Function score.

RESULTS

One hundred fifty-four of 203 perfused livers were transplanted following our previously defined criteria. These comprised 84/123 donation after circulatory death livers and 70/80 donation after brain death livers. Multivariable analysis suggested that 2-h alanine transaminase, 2-h lactate, 11 to 29 mmol supplementary bicarbonate in the first 4 h, and peak bile pH were associated with early allograft function as defined by the Model for Early Allograft Function score. Nonanastomotic biliary strictures occurred in 11% of transplants, predominantly affected first- and second-order ducts, despite selection based on bile glucose and pH.

CONCLUSIONS

This work confirms the importance of perfusate alanine transaminase and lactate at 2-h, as well as the amount of supplementary bicarbonate required to keep the perfusate pH > 7.2, in the assessment of livers undergoing perfusion. It cautions against the use of lactate as a sole indicator of viability and also suggests a role for cholangiocyte function markers in predicting early allograft function.

How to improve results after DCD (donation after circulation death)

The shortage of organs for transplantation has led health professionals to look for alternative sources of donors. One of the avenues concerns donors who have died after circulatory arrest. This is a special situation because the organs from these donors are exposed to warm ischaemia-reperfusion lesions that are unavoidable during the journey of the organs from the donor to the moment of transplantation in the recipient. We will address and discuss the key issues from the perspective of team organization, legislation and its evolution, and the ethical framework. In a second part, the avenues to improve the quality of organs will be presented following the itinerary of the organs between the donor and the recipient. The important moments from the point of view of therapeutic strategy will be put into perspective. New connections between key players involved in pathophysiological mechanisms and implications for innate immunity and injury processes are among the avenues to explore. Technological developments to improve the quality of organs from these recipients will be analyzed, such as perfusion techniques with new modalities of temperatures and oxygenation. New molecules are being investigated for their potential role in protecting these organs and an analysis of potential prospects will be proposed. Finally, the important perspectives that seem to be favored will be discussed in order to reposition the use of deceased donors after circulatory arrest. The use of these organs has become a routine procedure and improving their quality and providing the means for their evaluation is absolutely inevitable.

Application of polymerized porcine hemoglobin in the ex vivo normothermic machine perfusion of rat livers

Background: In contrast to traditional static cold preservation of donor livers, normothermic machine perfusion (NMP) may reduce preservation injury, improve graft viability and potentially allows ex vivo assessment of graft viability before transplantation. The polymerized porcine hemoglobin is a kind of hemoglobin oxygen carrier prepared by crosslinking porcine hemoglobin by glutaraldehyde to form a polymer. The pPolyHb has been proved to have the ability of transporting oxygen which could repair the organ ischemia-reperfusion injury in rats. Objective: In order to evaluate the effectiveness of rat liver perfusion in vitro based on pPolyHb, we established the NMP system, optimized the perfusate basic formula and explored the optimal proportion of pPolyHb and basal perfusate. Methods: The liver was removed and perfused for 6 h at 37°C. We compared the efficacy of liver perfusion with different ratios of pPolyHb. Subsequently, compared the perfusion effect using Krebs Henseleit solution and pPolyHb perfusate of the optimal proportion, and compared with the liver preserved with UW solution. At 0 h, 1 h, 3 h and 6 h after perfusion, appropriate samples were collected for blood gas analysis and liver injury indexes detection. Some tissue samples were collected for H&E staining and TUNEL staining to observe the morphology and detect the apoptosis rate of liver cells. And we used Western Blot test to detect the expression of Bcl-2 and Bax in the tissues. Results: According to the final results, the optimal addition ratio of pPolyHb was 24%. By comparing the values of Bcl-2/Bax, the apoptosis rate of pPolyHb group was significantly reduced. Under this ratio, the results of H&E staining and TUNEL staining showed that the liver morphology was well preserved without additional signs of hepatocyte ischemia, biliary tract injury, or hepatic sinusoid injury, and hepatocyte apoptosis was relatively mild. Conclusion: Through the above-mentioned study we show that within 6 h of perfusion based on pPolyHb, liver physiological and biochemical activities may essentially be maintained in vitro. This study demonstrates that a pPolyHb-based perfusate is feasible for NMP of rat livers. This opens up a prospect for further research on NMP.

Low utilization of adult-to-adult LDLT in Western countries despite excellent outcomes: International multicenter analysis of the US, the UK, and Canada

BACKGROUND & AIMS

Adult-to-adult living donor liver transplantation (LDLT) offers an opportunity to decrease the liver transplant waitlist and reduce waitlist mortality. We sought to compare donor and recipient characteristics and post-transplant outcomes after LDLT in the US, the UK, and Canada.

METHODS

This is a retrospective multicenter cohort-study of adults (≥18-years) who underwent primary LDLT between Jan-2008 and Dec-2018 from three national liver transplantation registries: United Network for Organ Sharing (US), National Health Service Blood and Transplantation (UK), and the Canadian Organ Replacement Registry (Canada). Patients undergoing retransplantation or multi-organ transplantation were excluded. Post-transplant survival was evaluated using the Kaplan-Meier method, and multivariable adjustments were performed using Cox proportional-hazards models with mixed-effect modeling.

RESULTS

A total of 2,954 living donor liver transplants were performed (US: n = 2,328; Canada: n = 529; UK: n = 97). Canada has maintained the highest proportion of LDLT utilization over time (proportion of LDLT in 2008 - US: 3.3%; Canada: 19.5%; UK: 1.7%; p <0.001 - in 2018 - US: 5.0%; Canada: 13.6%; UK: 0.4%; p <0.001). The 1-, 5-, and 10-year patient survival was 92.6%, 82.8%, and 70.0% in the US vs. 96.1%, 89.9%, and 82.2% in Canada vs. 91.4%, 85.4%, and 66.7% in the UK. After adjustment for characteristics of donors, recipients, transplant year, and treating transplant center as a random effect, all countries had a non-statistically significantly different mortality hazard post-LDLT (Ref US: Canada hazard ratio 0.53, 95% CI 0.28-1.01, p = 0.05; UK hazard ratio 1.09, 95% CI 0.59-2.02, p = 0.78).

CONCLUSIONS

The use of LDLT has remained low in the US, the UK and Canada. Despite this, long-term survival is excellent. Continued efforts to increase LDLT utilization in these countries may be warranted due to the growing waitlist and differences in allocation that may disadvantage patients currently awaiting liver transplantation.

LAY SUMMARY

This multicenter international comparative analysis of living donor liver transplantation in the United States, the United Kingdom, and Canada demonstrates that despite low use of the procedure, the long-term outcomes are excellent. In addition, the mortality risk is not statistically significantly different between the evaluated countries. However, the incidence and risk of retransplantation differs between the countries, being the highest in the United Kingdom and lowest in the United States.

Hyperspectral Imaging for Viability Assessment of Human Liver Allografts During Normothermic Machine Perfusion

Normothermic machine perfusion (NMP) is nowadays frequently utilized in liver transplantation. Despite commonly accepted viability assessment criteria, such as perfusate lactate and perfusate pH, there is a lack of predictive organ evaluation strategies to ensure graft viability. Hyperspectral imaging (HSI)-as an optical imaging modality increasingly applied in the biomedical field-might provide additional useful data regarding allograft viability and performance of liver grafts during NMP.

METHODS

Twenty-five deceased donor liver allografts were included in the study. During NMP, graft viability was assessed conventionally and by means of HSI. Images of liver parenchyma were acquired at 1, 2, and 4 h of NMP, and subsequently analyzed using a specialized HSI acquisition software to compute oxygen saturation, tissue hemoglobin index, near-infrared perfusion index, and tissue water index. To analyze the association between HSI parameters and perfusate lactate as well as perfusate pH, we performed simple linear regression analysis.

RESULTS

Perfusate lactate at 1, 2, and 4 h NMP was 1.5 [0.3-8.1], 0.9 [0.3-2.8], and 0.9 [0.1-2.2] mmol/L. Perfusate pH at 1, 2, and 4 h NMP was 7.329 [7.013-7.510], 7.318 [7.081-7.472], and 7.265 [6.967-7.462], respectively. Oxygen saturation predicted perfusate lactate at 1 and 2 h NMP (R² = 0.1577, P = 0.0493; R² = 0.1831, P = 0.0329; respectively). Tissue hemoglobin index predicted perfusate lactate at 1, 2, and 4 h NMP (R² = 0.1916, P = 0.0286; R² = 0.2900, P = 0.0055; R² = 0.2453, P = 0.0139; respectively).

CONCLUSIONS

HSI may serve as a noninvasive tool for viability assessment during NMP. Further evaluation and validation of HSI parameters are warranted in larger sample sizes.

Innate Immune Cells during Machine Perfusion of Liver Grafts-The Janus Face of Hepatic Macrophages

Machine perfusion is an emerging technology in the field of liver transplantation. While machine perfusion has now been implemented in clinical routine throughout transplant centers around the world, a debate has arisen regarding its concurrent effect on the complex hepatic immune system during perfusion. Currently, our understanding of the perfusion-elicited processes involving innate immune cells remains incomplete. Hepatic macrophages (Kupffer cells) represent a special subset of hepatic immune cells with a dual pro-inflammatory, as well as a pro-resolving and anti-inflammatory, role in the sequence of ischemia-reperfusion injury. The purpose of this review is to provide an overview of the current data regarding the immunomodulatory role of machine perfusion and to emphasize the importance of macrophages for hepatic ischemia-reperfusion injury.

Pharmacological testing of therapeutics using normothermic machine perfusion: A pilot study of 2,4-dinitrophenol delivery to steatotic human livers

INTRODUCTION

Normothermic machine perfusion (NMP) provides a platform for drug-delivery. However, pharmacological considerations for therapeutics delivered during NMP are scarcely reported. We aimed to demonstrate the ability of NMP as a platform for pharmacological testing, using a drug which increases metabolism (2,4-dinitrophenol; DNP) as an example therapeutic.

METHODS

We performed 25 h of NMP on human livers which had been declined for transplant due to steatosis (n = 7). Three livers received a DNP bolus, three were controls, and one received a DNP infusion.

RESULTS

Toxicity studies revealed DNP delivery was safe, without hepatotoxic effects. The liver surface temperature was increased in the DNP group (p = 0.046), but no livers suffered hyperthermia-the mechanism of DNP toxicity in vivo. Pharmacokinetic studies revealed DNP elimination with first-order kinetics and 7.7 h half-life (95% CI = 5.1-15.9 hrs). The clearance of DNP in bile was negligible. As expected, DNP significantly increased oxygen consumption (p = 0.023); this increase was closely correlated with perfusate DNP concentration (r2  = 0.975; p = 0.002) and the effect was lost as DNP was eliminated by the liver. A DNP infusion rate, calculated using our pharmacokinetic data, successfully maintained perfusate DNP concentration.

DISCUSSION

Detailed pharmacological testing can be performed during NMP. Our therapeutic (DNP) is rapidly eliminated by the ex vivo liver, meaning the drug effect of increased metabolism is only transient. This demonstrates the importance of assessing pharmacokinetics when delivering therapeutics during NMP, especially for prolonged perfusion of organs with established roles in drug elimination. Rigorous pharmacological testing is needed to unlock the potential of NMP as a clinical drug-delivery platform.

In situ normothermic regional perfusion versus ex situ normothermic machine perfusion in liver transplantation from donation after circulatory death

In situ normothermic regional perfusion (NRP) and ex situ normothermic machine perfusion (NMP) aim to improve the outcomes of liver transplantation (LT) using controlled donation after circulatory death (cDCD). NRP and NMP have not yet been compared directly. In this international observational study, outcomes of LT performed between 2015 and 2019 for organs procured from cDCD donors subjected to NRP or NMP commenced at the donor center were compared using propensity score matching (PSM). Of the 224 cDCD donations in the NRP cohort that proceeded to asystole, 193 livers were procured, resulting in 157 transplants. In the NMP cohort, perfusion was commenced in all 40 cases and resulted in 34 transplants (use rates: 70% vs. 85% [p = 0.052], respectively). After PSM, 34 NMP liver recipients were matched with 68 NRP liver recipients. The two cohorts were similar for donor functional warm ischemia time (21 min after NRP vs. 20 min after NMP; p = 0.17), UK-Donation After Circulatory Death risk score (5 vs. 5 points; p = 0.38), and laboratory Model for End-Stage Liver Disease scores (12 vs. 12 points; p = 0.83). The incidence of nonanastomotic biliary strictures (1.5% vs. 2.9%; p > 0.99), early allograft dysfunction (20.6% vs. 8.8%; p = 0.13), and 30-day graft loss (4.4% vs. 8.8%; p = 0.40) were similar, although peak posttransplant aspartate aminotransferase levels were higher in the NRP cohort (872 vs. 344 IU/L; p < 0.001). NRP livers were more frequently allocated to recipients suffering from hepatocellular carcinoma (HCC; 60.3% vs. 20.6%; p < 0.001). HCC-censored 2-year graft and patient survival rates were 91.5% versus 88.2% (p = 0.52) and 97.9% versus 94.1% (p = 0.25) after NRP and NMP, respectively. Both perfusion techniques achieved similar outcomes and appeared to match benchmarks expected for donation after brain death livers. This study may inform the design of a definitive trial.

Transplantation of a human liver following 3 days of ex situ normothermic preservation

Current organ preservation methods provide a narrow window (usually <12 hours) to assess, transport and implant donor grafts for human transplantation. Here we report the transplantation of a human liver discarded by all centers, which could be preserved for several days using ex situ normothermic machine perfusion. The transplanted liver exhibited normal function, with minimal reperfusion injury and the need for only a minimal immunosuppressive regimen. The patient rapidly recovered a normal quality of life without any signs of liver damage, such as rejection or injury to the bile ducts, according to a 1-year follow up. This inaugural clinical success opens new horizons in clinical research and promises an extended time window of up to 10 days for assessment of viability of donor organs as well as converting an urgent and highly demanding surgery into an elective procedure.

2021 Clinical Update in Liver Transplantation

In 2021, the United States performed 9,236 liver transplantations, an increase of 3.7% from 2020. As the specialty of transplant anesthesiologist continues to grow, so does the body of evidence-based research to improve patient care. New technology in organ preservation offers the possibility of preserving marginal organs for transplant or improving the graft for transplantation. The sequalae of end-stage liver disease have wide-ranging consequences that affect neurologic outcomes of patients both during and after transplantation that anesthesiologists should monitor. Obesity presents several challenges for anesthesiologists. As an increasing number of patients with nonalcoholic steatohepatitis are listed for transplant, managing their multiple comorbidities can be challenging. Finally, the rebalanced hemostasis of end-stage liver disease can cause both bleeding and thrombus. Often, bleeding risks predominate as a concern, but anesthesiologists should be aware of risks of intracardiac thrombus and review therapeutic options for prevention and treatment.

Machine perfusion in liver transplantation

Although liver transplantation is a true success story, many patients still die awaiting an organ. The increasing need for liver grafts therefore remains an unsolved challenge to the transplant community. To address this, transplant donor criteria have been expanded and, for example, more liver grafts with significant steatosis or from donors with circulatory death are being used. These marginal grafts, however, carry an increased risk of graft-associated complications, such as primary nonfunction, delayed graft function, or late biliary injuries. Therefore, reliable assessment of graft viability before use is essential for further success. To achieve this, machine liver perfusion, a procedure developed more than 50 years ago but almost forgotten at the end of the last century, is again of great interest. We describe in this review the clinical most applied machine perfusion techniques, their mechanistic background, and a novel concept of combining immediate organ assessment during hypothermic oxygenated perfusion, followed by an extended phase of normothermic machine perfusion, with simultaneous ex situ treatment of the perfused liver. Such a new approach may allow the pool of usable livers to dramatically increase and improve outcomes for recipients.

Breaking the limits of experimental pancreas transplantation: Working toward the clinical ideal graft

Pancreas transplantation is, at present, the only curative treatment for type-1 diabetes that maintains normoglycemia thus avoiding complications arising from poor glycemic control. Despite its great benefits, the number of pancreas transplants has decreased significantly since its inception in the late 1960s, largely due to demographic changes and the consequent suboptimal quality of donors. The selection criteria for pancreas donors mainly depend on morphological variables such as fatty infiltration, fibrosis, or edema, as well as both functional (amylase and lipase) and clinical variables of the donor. However, the final criterion in the decision-making process is the somewhat subjective assessment of a trained surgeon. That being said, the recent incorporation of graft perfusion machines into clinical practice seems to be changing the work dynamics of the donor organ retrieval team, facilitating decision-making based on objective morphological and functional criteria. Normothermic perfusion using perfusate with supplemental oxygen replicates near physiological parameters thus being a promising strategy for organ preservation. Nevertheless, optimum perfusion parameters are difficult to establish in pancreas transplantation given its complex vascular anatomy combined with an intrinsically low blood flow. The objective of this work is to analyze the results published in the recent literature relating to the considerations of ex-vivo normothermic graft perfusion machines and their usefulness in the field of pancreas transplantation.

Interleukin-18 and High-Mobility-Group-Protein B1 are Early and Sensitive Indicators for Cell Damage During Normothermic Machine Perfusion after Prolonged Cold Ischemic Storage of Porcine Liver Grafts

In the era of organ machine perfusion, experimental models to optimize reconditioning of (marginal) liver grafts are needed. Although the relevance of cytokine signatures in liver transplantation has been analyzed previously, the significance of molecular monitoring during normothermic machine perfusion (NMP) remains elusive. Therefore, we developed a porcine model of cold ischemic liver graft injury after prolonged static cold storage (SCS) and subsequent NMP: Livers obtained from ten minipigs underwent NMP for 6 h directly after procurement (control group) or after 20 h of SCS. Grafts after prolonged SCS showed significantly elevated AST, ALT, GLDH and GGT perfusate concentrations, and reduced lactate clearance. Bile analyses revealed reduced bile production, reduced bicarbonate and elevated glucose concentrations after prolonged SCS. Cytokine analyses of graft perfusate simultaneously demonstrated an increase of pro-inflammatory cytokines such as Interleukin-1α, Interleukin-2, and particularly Interleukin-18. The latter was the only significantly elevated cytokine compared to controls, peaking as early as 2 h after reperfusion (11,012 ng/ml vs. 1,493 ng/ml; p = 0.029). Also, concentrations of High-Mobility-Group-Protein B1 were significantly elevated after 2 h of reperfusion (706.00 ng/ml vs. 148.20 ng/ml; p < 0.001) and showed positive correlations with AST (r² = 0.846) and GLDH (r² = 0.918) levels. Molecular analyses during reconditioning of liver grafts provide insights into the degree of inflammation and cell damage and could thereby facilitate future interventions during NMP reducing acute and chronic graft injury.

The liver-resident immune cell repertoire - A boon or a bane during machine perfusion?

The liver has been proposed as an important “immune organ” of the body, as it is critically involved in a variety of specific and unique immune tasks. It contains a huge resident immune cell repertoire, which determines the balance between tolerance and inflammation in the hepatic microenvironment. Liver-resident immune cells, populating the sinusoids and the space of Disse, include professional antigen-presenting cells, myeloid cells, as well as innate and adaptive lymphoid cell populations. Machine perfusion (MP) has emerged as an innovative technology to preserve organs ex vivo while testing for organ quality and function prior to transplantation. As for the liver, hypothermic and normothermic MP techniques have successfully been implemented in clinically routine, especially for the use of marginal donor livers. Although there is evidence that ischemia reperfusion injury-associated inflammation is reduced in machine-perfused livers, little is known whether MP impacts the quantity, activation state and function of the hepatic immune-cell repertoire, and how this affects the inflammatory milieu during MP. At this point, it remains even speculative if liver-resident immune cells primarily exert a pro-inflammatory and hence destructive effect on machine-perfused organs, or in part may be essential to induce liver regeneration and counteract liver damage. This review discusses the role of hepatic immune cell subtypes during inflammatory conditions and ischemia reperfusion injury in the context of liver transplantation. We further highlight the possible impact of MP on the modification of the immune cell repertoire and its potential for future applications and immune modulation of the liver.

Monobody adapter for functional antibody display on nanoparticles for adaptable targeted delivery applications

Vascular endothelial cells (ECs) play a central role in the pathophysiology of many diseases. The use of targeted nanoparticles (NPs) to deliver therapeutics to ECs could dramatically improve efficacy by providing elevated and sustained intracellular drug levels. However, achieving sufficient levels of NP targeting in human settings remains elusive. Here, we overcome this barrier by engineering a monobody adapter that presents antibodies on the NP surface in a manner that fully preserves their antigen-binding function. This system improves targeting efficacy in cultured ECs under flow by >1000-fold over conventional antibody immobilization using amine coupling and enables robust delivery of NPs to the ECs of human kidneys undergoing ex vivo perfusion, a clinical setting used for organ transplant. Our monobody adapter also enables a simple plug-and-play capacity that facilitates the evaluation of a diverse array of targeted NPs. This technology has the potential to simplify and possibly accelerate both the development and clinical translation of EC-targeted nanomedicines.

Model of Acute Liver Failure in an Isolated Perfused Porcine Liver-Challenges and Lessons Learned

Acute liver failure (ALF) is a rare but devastating disease associated with substantial morbidity and a mortality rate of almost 45%. Medical treatments, apart from supportive care, are limited and liver transplantation may be the only rescue option. Large animal models, which most closely represent human disease, can be logistically and technically cumbersome, expensive and pose ethical challenges. The development of isolated organ perfusion technologies, originally intended for preservation before transplantation, offers a new platform for experimental models of liver disease, such as ALF. In this study, female domestic swine underwent hepatectomy, followed by perfusion of the isolated liver on a normothermic machine perfusion device. Five control livers were perfused for 24 h at 37 °C, while receiving supplemental oxygen and nutrition. Six livers received toxic doses of acetaminophen given over 12 h, titrated to methemoglobin levels. Perfusate was sampled every 4 h for measurement of biochemical markers of injury (e.g., aspartate aminotransferase [AST], alanine aminotransferase [ALT]). Liver biopsies were taken at the beginning, middle, and end of perfusion for histological assessment. Acetaminophen-treated livers received a median dose of 8.93 g (8.21–9.75 g) of acetaminophen, achieving a peak acetaminophen level of 3780 µmol/L (3189–3913 µmol/L). Peak values of ALT (76 vs. 105 U/L; p = 0.429) and AST (3576 vs. 4712 U/L; p = 0.429) were not significantly different between groups. However, by the end of perfusion, histology scores were significantly worse in the acetaminophen treated group (p = 0.016). All acetaminophen treated livers developed significant methemoglobinemia, with a peak methemoglobin level of 19.3%, compared to 2.0% for control livers (p = 0.004). The development of a model of ALF in the ex vivo setting was confounded by the development of toxic methemoglobinemia. Further attempts using alternative agents or dosing strategies may be warranted to explore this setting as a model of liver disease.

Four Decades of Clinical Liver Transplantation Research: Results of a Comprehensive Bibliometric Analysis

BACKGROUND

Nearly 40 y have passed since the 1983 National Institutes of Health Consensus-Development-Conference, which has turned liver transplantation (LT) from a clinical experiment into a routine therapeutic modality. Since' clinical LT has changed substantially. We aimed to comprehensively analyze the publication trends in the most-cited top-notch literature in LT science over a 4-decade period.

METHODS

A total of 106 523 items were identified between January 1981 and May 2021 from the Web of Science Core Collection. The top 100 articles published were selected using 2 distinct citation-based strategies to minimize bias. Various bibliometric tools were used for data synthesis and visualization.

RESULTS

The citation count for the final dataset of the top 100 articles ranged from 251 to 4721. Most articles were published by US authors (n = 61). The most prolific institution was the University of Pittsburgh (n = 15). The highest number of articles was published in Annals of Surgery, Hepatology, and Transplantation ; however, Hepatology publications resulted in the highest cumulative citation of 9668. Only 10% of the articles were classified as evidence level 1. Over 90% of first/last authors were male. Our data depict the evolution of research focus over 40 y. In part, a disproportional flow of citations was observed toward already well-cited articles. This might also project a slowed canonical progress, which was described in other fields of science.

CONCLUSIONS

This study highlights key trends based on a large dataset of the most-cited articles over a 4-decade period. The present analysis not only provides an important cross-sectional and forward-looking guidance to clinicians, funding bodies, and researchers but also draws attention to important socio-academic or demographic aspects in LT.

Preserving and rejuvenating old organs for transplantation: novel treatments including the potential of senolytics

PURPOSE OF REVIEW

Older donors have the potential to close the gap between demand and supply in solid organs transplantation. Utilizing older organs, at the same time, has been associated with worse short- and long-term outcomes. Here, we introduce potential mechanisms on how treatments during machine perfusion (MP) may safely improve the utilization of older organs.

RECENT FINDINGS

Consequences of ischemia reperfusion injury (IRI), a process of acute, sterile inflammation leading to organ injury are more prominent in older organs. Of relevance, organ age and IRI seem to act synergistically, leading to an increase of damage associated molecular patterns that trigger innate and adaptive immune responses. While cold storage has traditionally been considered the standard of care in organ preservation, accumulating data support that both hypothermic and normothermic MP improve organ quality, particularly in older organs. Furthermore, MP provides the opportunity to assess the quality of organs while adding therapeutic agents. Experimental data have already demonstrated the potential of applying treatments during MP. New experimental show that the depletion of senescent cells that accumulate in old organs improves organ quality and transplant outcomes.

SUMMARY

As the importance of expanding the donor pool is increasing, MP and novel treatments bear the potential to assess and regenerate older organs, narrowing the gap between demand and supply.

Hypothermic oxygenated perfusion in extended criteria donor liver transplantation-A randomized clinical trial

Hypothermic Oxygenated Perfusion (HOPE) of the liver can reduce the incidence of early allograft dysfunction (EAD) and failure in extended criteria donors (ECD) grafts, although data from prospective studies are very limited. In this monocentric, open-label study, from December 2018 to January 2021, 110 patients undergoing transplantation of an ECD liver graft were randomized to receive a liver after HOPE or after static cold storage (SCS) alone. The primary endpoint was the incidence of EAD. The secondary endpoints included graft and patient survival, the EASE risk score, and the rate of graft or other graft-related complications. Patients in the HOPE group had a significantly lower rate of EAD (13% vs. 35%, p = .007) and were more frequently allocated to the intermediate or higher risk group according to the EASE score (2% vs. 11%, p = .05). The survival analysis confirmed that patients in the HOPE group were associated with higher graft survival one year after LT (p = .03, log-rank test). In addition, patients in the SCS group had a higher re-admission and overall complication rate at six months, in particular cardio-vascular adverse events (p = .04 and p = .03, respectively). HOPE of ECD grafts compared to the traditional SCS preservation method is associated with lower dysfunction rates and better graft survival.

Novel strategies in liver graft preservation - The French perspective

Given the increasing graft shortage, the transplant community is forced to use so called marginal liver grafts with a higher susceptibility to ischemia-reperfusion injury. This exposes the recipient to a higher risk of graft failure and post-transplant complications. While static cold storage remains the gold standard in low-risk transplant scenarios, dynamic preservation strategies may allow to improve outcomes after transplantation of marginal liver grafts. Two dynamic preservation strategies, end-ischemic hypothermic oxygenated perfusion (HOPE) and continuous normothermic machine perfusion (cNMP), have been evaluated in randomized clinical trials. The results show improved preservation of liver grafts after cNMP and reduction of post-transplant biliary complications after HOPE. In comparison to cNMP, HOPE has the advantage of requiring less logistics and expertise with the possibility to return to default static cold storage. Both strategies allow to assess graft viability prior to transplantation and may thus contribute to optimizing graft selection and reducing discard rates. The use of dynamic preservation is rapidly increasing in France and results from a national randomized trial on the use of HOPE in marginal grafts will soon be available. Future applications should focus on controlled donation after circulatory death liver grafts, split grafts and graft treatment during perfusion. The final aim of dynamic liver graft preservation is to improve post-transplant outcomes, increase the number of transplanted grafts and allow expansion of transplant indications.

Viability testing during liver preservation

PURPOSE OF REVIEW

Viability assessment is one of the main indications for machine perfusion (MP) in liver transplantation. This review summarizes the rationale, evolution and limitations of proposed viability criteria and suggests a framework for future studies.

RECENT FINDINGS

Liver viability is most frequently assessed during normothermic MP by combining parameters relative to perfusate and bile composition, vascular flows and macroscopic aspect. Assessment protocols are largely heterogeneous and have significantly evolved over time, also within the same group, reflecting the ongoing evolution of the subject. Several recent preclinical studies using discarded human livers or animal models have explored other approaches to viability assessment. During hypothermic MP, perfusate flavin mononucleotide has emerged as a promising biomarker of mitochondrial injury and function. Most studies on the subject suffer from limitations, including low numbers, lack of multicenter validation, and subjective interpretation of some viability parameters.

SUMMARY

MP adds a further element of complexity in the process of assessing the quality of a liver graft. Understanding the physiology of the parameters included in the different assessment protocols is necessary for their correct interpretation. Despite the possibility of assessing liver viability during MP, the importance of donor-recipient matching and operational variables should not be disregarded.

Normothermic machine perfusion of kidneys: current strategies and future perspectives

PURPOSE OF REVIEW

This review aims to summarize the latest original preclinical and clinical articles in the setting of normothermic machine perfusion (NMP) of kidney grafts.

RECENT FINDINGS

Kidney NMP can be safely translated into the clinical routine and there is increasing evidence that NMP may be beneficial in graft preservation especially in marginal kidney grafts. Due to the near-physiological state during NMP, this technology may be used as an ex-vivo organ assessment and treatment platform. There are reports on the application of mesenchymal stromal/stem cells, multipotent adult progenitor cells and microRNA during kidney NMP, with first data indicating that these therapies indeed lead to a decrease in inflammatory response and kidney injury. Together with the demonstrated possibility of prolonged ex-vivo perfusion without significant graft damage, NMP could not only be used as a tool to perform preimplant graft assessment. Some evidence exists that it truly has the potential to be a platform to treat and repair injured kidney grafts, thereby significantly reducing the number of declined organs.

SUMMARY

Kidney NMP is feasible and can potentially increase the donor pool not only by preimplant graft assessment, but also by ex-vivo graft treatment.

Long-term and short-term preservation strategies for tissue engineering and regenerative medicine products: state of the art and emerging trends

There is an ever-growing need of human tissues and organs for transplantation. However, the availability of such tissues and organs is insufficient by a large margin, which is a huge medical and societal problem. Tissue engineering and regenerative medicine (TERM) represent potential solutions to this issue and have therefore been attracting increased interest from researchers and clinicians alike. But the successful large-scale clinical deployment of TERM products critically depends on the development of efficient preservation methodologies. The existing preservation approaches such as slow freezing, vitrification, dry state preservation, and hypothermic and normothermic storage all have issues that somehow limit the biomedical applications of TERM products. In this review, the principles and application of these approaches will be summarized, highlighting their advantages and limitations in the context of TERM products preservation.

How useful is the machine perfusion in liver transplantation? An answer from a national survey

Machine perfusion (MP) has been shown worldwide to offer many advantages in liver transplantation, but it still has some gray areas. The purpose of the study is to evaluate the donor risk factors of grafts, perfused with any MP, that might predict an ineffective MP setting and those would trigger post-transplant early allograft dysfunction (EAD). Data from donors of all MP-perfused grafts at six liver transplant centers have been analyzed, whether implanted or discarded after perfusion. The first endpoint was the negative events after perfusion (NegE), which is the number of grafts discarded plus those that were implanted but lost after the transplant. A risk factor analysis for NegE was performed and marginal grafts for MP were identified. Finally, the risk of EAD was analyzed, considering only implanted grafts. From 2015 to September 2019, 158 grafts were perfused with MP: 151 grafts were implanted and 7 were discarded after the MP phase because they did not reach viability criteria. Of 151, 15 grafts were lost after transplant, so the NegE group consisted of 22 donors. In univariate analysis, the donor risk index >1.7, the presence of hypertension in the medical history, static cold ischemia time, and the moderate or severe macrovesicular steatosis were the significant factors for NegE. Multivariate analysis confirmed that macrosteatosis >30% was an independent risk factor for NegE (odd ratio 5.643, p = 0.023, 95% confidence interval, 1.27–24.98). Of 151 transplanted patients, 34% experienced EAD and had worse 1- and 3-year-survival, compared with those who did not face EAD (NoEAD), 96% and 96% for EAD vs. 89% and 71% for NoEAD, respectively (p = 0.03). None of the donor/graft characteristics was associated with EAD even if the graft was moderately steatotic or fibrotic or from an aged donor. For the first time, this study shows that macrovesicular steatosis >30% might be a warning factor involved in the risk of graft loss or a cause of graft discard after the MP treatment. On the other hand, the MP seems to be useful in reducing the donor and graft weight in the development of EAD.

Normothermic Ex Vivo Liver Platform Using Porcine Slaughterhouse Livers for Disease Modeling

Metabolic and toxic liver disorders, such as fatty liver disease (steatosis) and drug-induced liver injury, are highly prevalent and potentially life-threatening. To allow for the study of these disorders from the early stages onward, without using experimental animals, we collected porcine livers in a slaughterhouse and perfused these livers normothermically. With our simplified protocol, the perfused slaughterhouse livers remained viable and functional over five hours of perfusion, as shown by hemodynamics, bile production, indocyanine green clearance, ammonia metabolism, gene expression and histology. As a proof-of-concept to study liver disorders, we show that an infusion of free fatty acids and acetaminophen results in early biochemical signs of liver damage, including reduced functionality. In conclusion, the present platform offers an accessible system to perform research in a functional, relevant large animal model while avoiding using experimental animals. With further improvements to the model, prolonged exposure could make this model a versatile tool for studying liver diseases and potential treatments.

Machine Perfusion for Extended Criteria Donor Livers: What Challenges Remain?

Based on the renaissance of dynamic preservation techniques, extended criteria donor (ECD) livers reclaimed a valuable eligibility in the transplantable organ pool. Being more vulnerable to ischemia, ECD livers carry an increased risk of early allograft dysfunction, primary non-function and biliary complications and, hence, unveiled the limitations of static cold storage (SCS). There is growing evidence that dynamic preservation techniques—dissimilar to SCS—mitigate reperfusion injury by reconditioning organs prior transplantation and therefore represent a useful platform to assess viability. Yet, a debate is ongoing about the advantages and disadvantages of different perfusion strategies and their best possible applications for specific categories of marginal livers, including organs from donors after circulatory death (DCD) and brain death (DBD) with extended criteria, split livers and steatotic grafts. This review critically discusses the current clinical spectrum of livers from ECD donors together with the various challenges and posttransplant outcomes in the context of standard cold storage preservation. Based on this, the potential role of machine perfusion techniques is highlighted next. Finally, future perspectives focusing on how to achieve higher utilization rates of the available donor pool are highlighted.

Normothermic liver machine perfusion as a dynamic platform for regenerative purposes: What does the future have in store for us?

Liver transplantation has become an immense success; nevertheless, far more recipients are registered on waiting lists than there are available donor livers for transplantation. High-risk, extended criteria donor livers are increasingly used to reduce the discrepancy between organ demand and supply. Especially for high-risk livers, dynamic preservation using machine perfusion can decrease post-transplantation complications and may increase donor liver utilisation by improving graft quality and enabling viability testing before transplantation. To further increase the availability of donor livers suitable for transplantation, new strategies are required that make it possible to use organs that are initially too damaged to be transplanted. With the current progress in experimental liver transplantation research, (long-term) normothermic machine perfusion may be used in the future as a dynamic platform for regenerative medicine approaches, enabling repair and regeneration of injured donor livers. Currently explored therapeutics such as defatting cocktails, RNA interference, senolytics, and stem cell therapy may assist in the repair and/or regeneration of injured livers before transplantation. This review will provide a forecast of the future utility of normothermic machine perfusion in decreasing the imbalance between donor liver demand and supply by enabling the repair and regeneration of damaged donor livers.

Radiomic analysis of liver grafts from brain-dead donors can predict early allograft dysfunction following transplantation: a proof-of-concept study

BACKGROUND

Selection of liver grafts suitable for transplantation (LT) mainly depends on a surgeon's subjective assessment. This study aimed to investigate the role of radiomic analysis of donor-liver CTs after brain death (DBD) to predict the occurrence of early posttransplant allograft dysfunction (EAD).

METHODS

We retrospectively extracted and analyzed the left lobe radiomic features from CT scans of DBD livers in training and validation cohorts. Multivariate analysis was performed to identify predictors of EAD.

RESULTS

From 126 LTs included in the study in the training cohort, 27 (21.4%) had an EAD. For each patient, 279 radiomic features were extracted of which 5 were associated with EAD (AUC = 0.81) (95% CI 0.72-0.89). Among donor and recipient clinical characteristics, cardiac arrest, steatosis on donor's CT, cold ischemic time and age of recipient were also identified as independent risk factors for EAD. Combined radiomic signature and clinical risk factors showed a strong predictive performance for EAD with a C-index of 0.90 (95% CI 0.84-0.96). A validation cohort of 23 patients confirmed these results.

CONCLUSION

Radiomic signatures extracted from donor CT scan, independently or combined with clinical risk factors is an objective and accurate biomarker for prediction of EAD after LT.

The use of normothermic liver preservation in combined liver and lung transplantation: A single-center experience

Combined liver and lung transplantation (CLLT) is indicated in patients with both end-stage liver and lung disease. Ex-situ normothermic machine perfusion (NMP) has been previously used for extended normothermic lung preservation in CLLT. We aim to describe our single-center experience using ex-situ NMP for extended normothermic liver preservation in CLLT. Four CLLTs were performed from 2019 to 2020 with the lung transplanted first for all patients. Median ex-situ pump time for the liver was 413 min (IQR 400-424). Over a median follow-up of 15 months (IQR 14-19), all patients were alive and doing well. Normothermic extended liver preservation is a safe method to allow prolonged cold ischemia using normothermic perfusion of the liver during CLLT.

Liver Machine Perfusion—When Physiopathology Matters

Liver transplantation (LT) has become a victim of its own success [...]

Mitochondria and Cancer Recurrence after Liver Transplantation—What Is the Benefit of Machine Perfusion?

Tumor recurrence after liver transplantation has been linked to multiple factors, including the recipient’s tumor burden, donor factors, and ischemia-reperfusion injury (IRI). The increasing number of livers accepted from extended criteria donors has forced the transplant community to push the development of dynamic perfusion strategies. The reason behind this progress is the urgent need to reduce the clinical consequences of IRI. Two concepts appear most beneficial and include either the avoidance of ischemia, e.g., the replacement of cold storage by machine perfusion, or secondly, an endischemic organ improvement through perfusion in the recipient center prior to implantation. While several concepts, including normothermic perfusion, were found to reduce recipient transaminase levels and early allograft dysfunction, hypothermic oxygenated perfusion also reduced IRI-associated post-transplant complications and costs. With the impact on mitochondrial injury and subsequent less IRI-inflammation, this endischemic perfusion was also found to reduce the recurrence of hepatocellular carcinoma after liver transplantation. Firstly, this article highlights the contributing factors to tumor recurrence, including the surgical and medical tissue trauma and underlying mechanisms of IRI-associated inflammation. Secondly, it focuses on the role of mitochondria and associated interventions to reduce cancer recurrence. Finally, the role of machine perfusion technology as a delivery tool and as an individual treatment is discussed together with the currently available clinical studies.