Injury to peribiliary glands and vascular plexus before liver transplantation predicts formation of non-anastomotic biliary strictures

Contribution of Resident Stem Cells to Liver and Biliary Tree Regeneration in Human Diseases

Two distinct stem/progenitor cell populations of biliary origin have been identified in the adult liver and biliary tree. Hepatic Stem/progenitor Cells (HpSCs) are bipotent progenitor cells located within the canals of Hering and can be differentiated into mature hepatocytes and cholangiocytes; Biliary Tree Stem/progenitor Cells (BTSCs) are multipotent stem cells located within the peribiliary glands of large intrahepatic and extrahepatic bile ducts and able to differentiate into hepatic and pancreatic lineages. HpSCs and BTSCs are endowed in a specialized niche constituted by supporting cells and extracellular matrix compounds. The actual contribution of these stem cell niches to liver and biliary tree homeostatic regeneration is marginal; this is due to the high replicative capabilities and plasticity of mature parenchymal cells (i.e., hepatocytes and cholangiocytes). However, the study of human liver and biliary diseases disclosed how these stem cell niches are involved in the regenerative response after extensive and/or chronic injuries, with the activation of specific signaling pathways. The present review summarizes the contribution of stem/progenitor cell niches in human liver diseases, underlining mechanisms of activation and clinical implications, including fibrogenesis and disease progression.

A cost analysis of early biliary strictures following orthotopic liver transplantation in the United States

INTRODUCTION

To date, the financial burden of biliary strictures (BS) after orthotopic liver transplantation (OLT) has remained largely unassessed. This study sought to approximate perioperative costs associated with early BS and delineate where in the hospital these costs are incurred.

METHODS

The Premier Healthcare Database was queried for patients undergoing OLT between 2010 and 2016. Patients who did and did not develop early BS were compared with respect to perioperative costs and outcome variables. Multivariable regression models were used to estimate differences between groups.

RESULTS

Patients who developed early BS had a longer length of stay (LOS) (35.3 days vs 17.8 days, P < 0.001) and were less likely to be discharged home (odds ratio = 0.45, P = 0.003). Development of early BS was associated with an incremental cost increase of $81 881 (45.8%, P < 0.001). The greatest relative cost increases were in radiology (+163.5%) and respiratory therapy (+157.1%), while the greatest absolute increase was in room and board (+$27 589).

CONCLUSIONS

Early BS after OLT result in higher costs stemming from longer LOS and increased need for various diagnostic studies and therapies. In addition to incentivizing measures that may prevent early BS, hospitals should account for these factors when developing payment schemes for OLT with payors.

Observations on the ex situ perfusion of livers for transplantation

Normothermic ex situ liver perfusion might allow viability assessment of livers before transplantation. Perfusion characteristics were studied in 47 liver perfusions, of which 22 resulted in transplants. Hepatocellular damage was reflected in the perfusate transaminase concentrations, which correlated with posttransplant peak transaminase levels. Lactate clearance occurred within 3 hours in 46 of 47 perfusions, and glucose rose initially during perfusion in 44. Three livers required higher levels of bicarbonate support to maintain physiological pH, including one developing primary nonfunction. Bile production did not correlate with viability or cholangiopathy, but bile pH, measured in 16 of the 22 transplanted livers, identified three livers that developed cholangiopathy (peak pH < 7.4) from those that did not (pH > 7.5). In the 11 research livers where it could be studied, bile pH > 7.5 discriminated between the 6 livers exhibiting >50% circumferential stromal necrosis of septal bile ducts and 4 without necrosis; one liver with 25-50% necrosis had a maximum pH 7.46. Liver viability during normothermic perfusion can be assessed using a combination of transaminase release, glucose metabolism, lactate clearance, and maintenance of acid-base balance. Evaluation of bile pH may offer a valuable insight into bile duct integrity and risk of posttransplant ischemic cholangiopathy.

Peribiliary Glands as the Cellular Origin of Biliary Tract Cancer

The identification of the cellular origin of cancer is important for our understanding of the mechanisms regulating carcinogenesis, thus the cellular origin of cholangiocarcinoma (CCA) is a current topic of interest. Although CCA has been considered to originate from biliary epithelial cells, recent studies have suggested that multiple cell types can develop into CCA. With regard to the hilar and extrahepatic bile ducts, peribiliary glands (PBGs), a potential stem cell niche of biliary epithelial cells, have attracted attention as the cellular origin of biliary tract cancer. Recent histopathological and experimental studies have suggested that some kinds of inflammation-induced CCA and intraductal papillary neoplasms of the bile duct are more likely to originate from PBGs. During inflammation-mediated cholangiocarcinogenesis, the biliary epithelial injury-induced regenerative response by PBGs is considered a key process. Thus, in this review, we discuss recent advances in our understanding of cholangiocarcinogenesis from the viewpoint of inflammation and the cellular origin of CCA, especially focusing on PBGs.

The Role of Normothermic Perfusion in Liver Transplantation (TRaNsIT Study): A Systematic Review of Preliminary Studies

INTRODUCTION

The success of liver transplantation has been limited by the unavailability of suitable donor livers. The current organ preservation technique, i.e., static cold storage (SCS), is not suitable for marginal organs. Alternatively, normothermic machine perfusion (NMP) promises to recreate the physiological environment and hence holds promise for the better organ preservation. The objective of this systematic review is to provide an overview of the safety, benefits, and insight into the other potential useful parameters of NMP in the liver preservation.

MATERIAL AND METHODS

We searched the current literature following registration in the International Prospective Register of Systematic Reviews (PROSPERO) with registration number CRD42018086034 for prospective trials comparing the role of NMP device to SCS in liver transplant by searching the PubMed, EMBASE, Cochrane, BIOSIS, Crossref, and Scopus databases and clinical trial registry.

RESULTS

The literature search identified five prospective clinical trials (four being early phase single institutional and single randomized multi-institutional) comparing 187 donor livers on NMP device to 273 donor livers on SCS. The primary outcome of interest was to assess the safety and graft survival at day 30 after transplant following NMP of the donor liver. Secondary outcomes included were early allograft dysfunction (EAD) in the first seven days; serum measures of liver functions as bilirubin, aspartate aminotransferase (AST), alanine amino transferase (ALT), alkaline phosphatase (ALP), and international normalized ratio (INR) on days 1-7; major complications as defined by a Clavien-Dindo score ≥ 3; and patient and graft survival and biliary complications at six months. The peaked median AST level between days 1 and 7 in the five trials was 417-1252 U/L (range 84-15009 U/L) while on NMP and 839-1474 U/L (range 153-8786 U/L) in SCS group. The median bilirubin level on day 7 ranged within 25-79 µmol/L (range 8-344 µmol/l) and 30-47.53 µmol/l (range 9-340 µmol/l) in NMP and SCS groups, respectively. A single case of PNF was reported in NMP group in the randomized trial while none of the other preliminary studies reported any in either group. There was intertrial variability in EAD which ranged within 15-56% in NMP group while being within 23-37% in SCS group. Biliary complications observed in NMP group ranged from 0 to 20%. Single device malfunction was reported in randomized controlled trial leading to renouncement of transplant while none of the other trials reported any machine failure, although two user related device errors inadvertent were reported.

CONCLUSION

This review outlines that NMP not only demonstrated safety and efficacy but also provided the favourable environment of organ preservation, repair, and viability assessment to donor liver prior to the transplantation with low rate of posttransplantation complication as PNF, EAD, and biliary complication; however further studies are needed to broaden our horizon.

Hypothermic oxygenated machine perfusion reduces bile duct reperfusion injury after transplantation of donation after circulatory death livers

Dual hypothermic oxygenated machine perfusion (DHOPE) of the liver has been advocated as a method to reduce ischemia/reperfusion injury (IRI). This study aimed to determine whether DHOPE reduces IRI of the bile ducts in donation after circulatory death (DCD) liver transplantation. In a recently performed phase 1 trial, 10 DCD livers were preserved with DHOPE after static cold storage (SCS; www.trialregister.nl NTR4493). Bile duct biopsies were obtained at the end of SCS (before DHOPE; baseline) and after graft reperfusion in the recipient. Histological severity of biliary injury was graded according to an established semiquantitative grading system. Twenty liver transplantations using DCD livers not preserved with DHOPE served as controls. Baseline characteristics and the degree of bile duct injury at baseline (end of SCS) were similar between both groups. In controls, the degree of stroma necrosis (P = 0.002) and injury of the deep peribiliary glands (PBG; P = 0.02) increased after reperfusion compared with baseline. In contrast, in DHOPE-preserved livers, the degree of bile duct injury did not increase after reperfusion. Moreover, there was less injury of deep PBG (P = 0.04) after reperfusion in the DHOPE group compared with controls. In conclusion, this study suggests that DHOPE reduces IRI of bile ducts after DCD liver transplantation. Liver Transplantation 24 655-664 2018 AASLD.

Heparin but not tissue plasminogen activator improves outcomes in donation after circulatory death liver transplantation in a porcine model

Ischemic-type biliary lesions (ITBLs) arise most frequently after donation after circulatory death (DCD) liver transplantation and result in high morbidity and graft loss. Many DCD grafts are discarded out of fear for this complication. In theory, microvascular thrombi deposited during donor warm ischemia might be implicated in ITBL pathogenesis. Herein, we aim to evaluate the effects of the administration of either heparin or the fibrinolytic drug tissue plasminogen activator (TPA) as means to improve DCD liver graft quality and potentially avoid ITBL. Donor pigs were subjected to 1 hour of cardiac arrest (CA) and divided among 3 groups: no pre-arrest heparinization nor TPA during postmortem regional perfusion; no pre-arrest heparinization but TPA given during regional perfusion; and pre-arrest heparinization but no TPA during regional perfusion. In liver tissue sampled 1 hour after CA, fibrin deposition was not detected, even when heparin was not given prior to arrest. Although it was not useful to prevent microvascular clot formation, pre-arrest heparin did offer cytoprotective effects during CA and beyond, reflected in improved flows during regional perfusion and better biochemical, functional, and histological parameters during posttransplantation follow-up. In conclusion, this study demonstrates the lack of impact of TPA use in porcine DCD liver transplantation and adds to the controversy over whether the use of TPA in human DCD liver transplantation really offers any protective effect. On the other hand, when it is administered prior to CA, heparin does offer anti-inflammatory and other cytoprotective effects that help improve DCD liver graft quality. Liver Transplantation 24 665-676 2018 AASLD.

A literature-based cost analysis of tissue plasminogen activator for prevention of biliary stricture in donation after circulatory death liver transplantation

INTRODUCTION

This study sought to approximate the cost-effectiveness of tPA utilization for prevention of biliary strictures (PTBS) in donation after circulatory death liver transplantation (DCD-LT).

METHODS

Previously-reported PTBS rates in DCD-LT with and without tPA were used to calculate the number needed to treat (NNT) for prevention of one PTBS. The incremental cost of PTBS was then used to determine the cost effectiveness of tPA for prevention of PTBS.

RESULTS

The incidence of PTBS in the setting of tPA administration was 20%, while incidence in patients without tPA use was 43% (p < 0.001). Meta-analysis demonstrated a risk reduction of 15.7%, which translated into a NNT of 6.4. Cost associated with treating 6.4 patients was $50,353. Based on an incremental cost of $81,888 associated with PTBS management, use of tPA in DCD-LT protocols was estimated to save $31,528 per PTBS prevented.

CONCLUSION

Utilization of tPA in DCD-LT protocols represents one possible cost-effective strategy for prevention of PTBS in DCD-LT.

Hypothermic Machine Preservation of the Liver: State of the Art

PURPOSE OF REVIEW

In this review, we highlight which livers may benefit from additional treatment before implantation and describe the concept of hypothermic machine liver perfusion. Furthermore, we explain why cold oxygenated perfusion concepts could potentially lead to a breakthrough in this challenging field of transplantation. Accordingly, we summarize recent clinical applications of different hypothermic perfusion approaches.

RECENT FINDINGS

The impact of end-ischemic, hypothermic liver perfusion in liver transplantation is currently assessed by two multicenter, randomized controlled trials. Recently, new applications of hypothermic perfusion showed promising results and recipients were protected from severe intrahepatic biliary complications, despite the use of very extended criteria grafts including donation after circulatory death livers.

SUMMARY

Hypothermic machine liver perfusion is beneficial for high-risk livers and protects recipients from most feared complications. Importantly, such easy approach is currently implemented in several European centers and new markers obtained from perfusate may improve the prediction of liver function in the future.

Historical Perspectives and Advances in Mesenchymal Stem Cell Research for the Treatment of Liver Diseases

Liver transplantation is the only effective therapy for patients with decompensated cirrhosis and fulminant liver failure. However, due to a shortage of donor livers and complications associated with immune suppression, there is an urgent need for new therapeutic strategies for patients with end-stage liver diseases. Given their unique function in self-renewal and differentiation potential, stem cells might be used to regenerate damaged liver tissue. Recent studies have shown that stem cell-based therapies can improve liver function in a mouse model of hepatic failure. Moreover, acellular liver scaffolds seeded with hepatocytes produced functional bioengineered livers for organ transplantation in preclinical studies. The therapeutic potential of stem cells or their differentiated progenies will depend on their capacity to differentiate into mature and functional cell types after transplantation. It will also be important to devise methods to overcome their genomic instability, immune reactivity, and tumorigenic potential. We review directions and advances in the use of mesenchymal stem cells and their derived hepatocytes for liver regeneration. We also discuss the potential applications of hepatocytes derived from human pluripotent stem cells and challenges to using these cells in treating end-stage liver disease.

Repopulating the biliary tree from the peribiliary glands

The larger ducts of the biliary tree contain numerous tubulo-alveolar adnexal glands that are lined with biliary epithelial cells and connected to the bile duct lumen via small glandular canals. Although these peribiliary glands (PBG) were already described in the 19th century, their exact function and role in the pathophysiology and development of cholangiopathies have not become evident until recently. While secretion of serous and mucinous components into the bile was long considered as the main function of PBG, recent studies have identified PBG as an important source for biliary epithelial cell proliferation and renewal. Activation, dilatation, and proliferation of PBG (or the lack thereof) have been associated with various cholangiopathies. Moreover, PBG have been identified as niches of multipotent stem/progenitor cells with endodermal lineage traits. This has sparked research interest in the role of PBG in the pathogenesis of various cholangiopathies as well as bile duct malignancies. Deeper understanding of the regenerative capacity of the PBG may contribute to the development of novel regenerative therapeutics for previously untreatable hepatobiliary diseases. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Safety and Outcomes in 100 Consecutive Donation After Circulatory Death Liver Transplants Using a Protocol That Includes Thrombolytic Therapy

Donation after circulatory death (DCD) liver transplantation (LT) reportedly yields inferior survival and increased complication rates compared with donation after brain death (DBD). We compare 100 consecutive DCD LT using a protocol that includes thrombolytic therapy (late DCD group) to an historical DCD group (early DCD group n = 38) and a cohort of DBD LT recipients (DBD group n = 435). Late DCD LT recipients had better 1- and 3-year graft survival rates than early DCD LT recipients (92% vs. 76.3%, p = 0.03 and 91.4% vs. 73.7%, p = 0.01). Late DCD graft survival rates were comparable to those of the DBD group (92% vs. 93.3%, p = 0.24 and 91.4% vs. 88.2%, p = 0.62). Re-transplantation occurred in 18.4% versus 1% for the early and late DCD groups, respectively (p = 0.001). Patient survival was similar in all three groups. Ischemic-type biliary lesions (ITBL) occurred in 5%, 3%, and 0.2% for early DCD, late DCD, and DBD groups, respectively, but unlike in the early DCD group, in the late DCD group ITBL was endoscopically managed and resolved in each case. Using a protocol that includes a thrombolytic therapy, DCD LT yielded patient and graft survival rates comparable to DBD LT.

Liver Preservation by Aortic Perfusion Alone Compared With Preservation by Aortic Perfusion and Additional Arterial Ex Situ Back-Table Perfusion With Histidine-Tryptophan-Ketoglutarate Solution: A Prospective, Randomized, Controlled, Multicenter Study

Background

Arterial ex situ back-table perfusion (BP) reportedly reduces ischemic-type biliary lesion after liver transplantation. We aimed to verify these findings in a prospective investigation.

Methods

Our prospective, randomized, controlled, multicenter study involved livers retrieved from patients in 2 German regions, and compared the outcomes of standard aortic perfusion to those of aortic perfusion combined with arterial ex situ BP. The primary endpoint was the incidence of ischemic-type biliary lesions over a follow-up of 2 years after liver transplantation, whereas secondary endpoints included 2-year graft survival, initial graft damage as reflected by transaminase levels, and functional biliary parameters at 6 months after transplantation.

Results

A total of 75 livers preserved via standard aortic perfusion and 75 preserved via standard aortic perfusion plus arterial BP were treated using a standardized protocol. The incidence of clinically apparent biliary lesions after liver transplantation (n = 9 for both groups; P = 0.947), the 2-year graft survival rate (standard aortic perfusion, 74%; standard aortic perfusion plus arterial BP, 68%; P = 0.34), and incidence of initial graft injury did not differ between the 2 perfusion modes. Although 33 of the 77 patients with cholangiography workups exhibited injured bile ducts, only 10 had clinical symptoms.

Conclusions

Contrary to previous findings, the present study indicated that additional ex situ BP did not prevent ischemic-type biliary lesions or ischemia-reperfusion injury after liver transplantation. Moreover, there was considerable discrepancy between cholangiography findings regarding bile duct changes and clinically apparent cholangiopathy after transplantation, which should be considered when assessing ischemic-type biliary lesions.

Post-transplant cholangiopathy: Classification, pathogenesis, and preventive strategies

Biliary complications are the most frequent cause of morbidity, re-transplantation, and even mortality after liver transplantation. In general, biliary leakage and anastomotic and non-anastomotic biliary strictures (NAS) can be recognized. There is no consensus on the exact definition of NAS and different names and criteria have been used in literature. We propose to use the term post-transplant cholangiopathy for the spectrum of abnormalities of large donor bile ducts, that includes NAS, but also intraductal casts and intrahepatic biloma formation, in the presence of a patent hepatic artery. Combinations of these manifestations of cholangiopathy are not infrequently found in the same liver and ischemia-reperfusion injury is generally considered the common underlying mechanism. Other factors that contribute to post-transplant cholangiopathy are biliary injury due to bile salt toxicity and immune-mediated injury. This review provides an overview of the various types of post-transplant cholangiopathy, the presumed pathogenesis, clinical implications, and preventive strategies.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Long-term results after transplantation of pediatric liver grafts from donation after circulatory death donors

Background

Liver grafts from donation after circulatory death (DCD) donors are increasingly accepted as an extension of the organ pool for transplantation. There is little data on the outcome of liver transplantation with DCD grafts from a pediatric donor. The objective of this study was to assess the outcome of liver transplantation with pediatric DCD grafts and to compare this with the outcome after transplantation of livers from pediatric donation after brain death (DBD) donors.

Method

All transplantations performed with a liver from a pediatric donor (≤16 years) in the Netherlands between 2002 and 2015 were included. Patient survival, graft survival, and complication rates were compared between DCD and DBD liver transplantation.

Results

In total, 74 liver transplantations with pediatric grafts were performed; twenty (27%) DCD and 54 (73%) DBD. The median donor warm ischemia time (DWIT) was 24 min (range 15–43 min). Patient survival rate at 10 years was 78% for recipients of DCD grafts and 89% for DBD grafts (p = 0.32). Graft survival rate at 10 years was 65% in recipients of DCD versus 76% in DBD grafts (p = 0.20). If donor livers in this study would have been rejected for transplantation when the DWIT ≥30 min (n = 4), the 10-year graft survival rate would have been 81% after DCD transplantation. The rate of non-anastomotic biliary strictures was 5% in DCD and 4% in DBD grafts (p = 1.00). Other complication rates were also similar between both groups.

Conclusions

Transplantation of livers from pediatric DCD donors results in good long-term outcome especially when the DWIT is kept ≤30 min. Patient and graft survival rates are not significantly different between recipients of a pediatric DCD or DBD liver. Moreover, the incidence of non-anastomotic biliary strictures after transplantation of pediatric DCD livers is remarkably low.

Biliary complications after liver transplantation; recent developments in etiology, diagnosis and endoscopic treatment

Biliary complications are considered to be the Achilles' heel of liver transplantation. The most common complications are leaks and bile duct strictures. Strictures can arise at the level of the anastomosis (anastomotic strictures; AS) or at other locations in the biliary tree (non-anastomotic strictures; NAS). Endoscopic treatment via endoscopic retrograde cholangiopancreatography (ERCP) is considered to be the preferred therapy for these complications. This review will focus on the diagnostic modalities, new insights in etiology of biliary complications and outcomes after different endoscopic therapies, in both deceased donor transplantation and living-donor liver transplantations. Advances in recent therapies, such as the use of self-expendable metal stents (SEMS) and endoscopic therapy for patients with a bilio-digestive anastomosis will be discussed.

Peribiliary Gland Dilatation in Cirrhosis: Relationship with Liver Failure and Stem Cell/Proliferation Markers

BACKGROUND AND AIMS

Dilated peribiliary glands (PBG) in patients with cirrhosis are often an incidental finding although their significance and physiopathology remain unclear. We aimed to identify clinical factors associated with dilated PBG and to perform a detailed morphometric assessment of dilated PBG in cirrhotic patients undergoing liver transplantation (LT).

METHODS

All consecutive cirrhotic patients undergoing LT at our institution between October 2006 and October 2011 were assessed for inclusion. Ten non-cirrhotic patients were included as controls. We performed morphometrical assessment of PBG, assessed baseline clinical factors associated with dilated PBG, immunohistochemistry staining with CK-19, MiB-1 and EpCAM, and radiological assessment of all available cases.

RESULTS

Seventy-one patients met the inclusion criteria, 24% had PBG dilatation of >1000 µm. On multivariable analysis, MELD (OR 1.11 per unit increase in MELD, p = 0.004) was the only significant factor associated with dilated PBG. Compared to PBG < 1000 µm, large PBG had a higher proportion of EpCAM-positive (69 vs. 28%, p < 0.001) and MiB-1-positive lining cells (2.8 vs. 0.55%, p = 0.036). Computed tomography and magnetic resonance imaging had high specificity but low sensitivity for the diagnosis of dilated PBG > 1000 µm (specificity 90-100%, sensitivity 25-29%).

CONCLUSIONS

Dilated PBGs are a common finding in explants of cirrhotic subjects undergoing LT and are associated with liver failure although diagnostic performance of cross-sectional imaging is inconstant. The high number of proliferative and EpCAM-positive cells lining the PBG may suggest a role of PBG in organ repair during liver failure.

Liver grafts procured from donors after circulatory death have no increased risk of microthrombi formation

Microthrombi formation provoked by warm ischemia and vascular stasis is thought to increase the risk of nonanastomotic strictures (NAS) in liver grafts obtained by donation after circulatory death (DCD). Therefore, potentially harmful intraoperative thrombolytic therapy has been suggested as a preventive strategy against NAS. Here, we investigated whether there is histological evidence of microthrombi formation during graft preservation or directly after reperfusion in DCD livers and the development of NAS. Liver biopsies collected at different time points during graft preservation and after reperfusion were triple-stained with hematoxylin-eosin (H & E), von Willebrand factor VIII (VWF), and Fibrin Lendrum (FL) to evaluate the presence of microthrombi. In a first series of 282 sections obtained from multiple liver segments of discarded DCD grafts, microthrombi were only present in 1%-3% of the VWF stainings, without evidence of thrombus formation in paired H & E and FL stainings. Additionally, analysis of 132 sections obtained from matched, transplanted donation after brain death and DCD grafts showed no difference in microthrombi formation (11.3% versus 3.3% respectively; P = 0.082), and no relation to the development of NAS (P = 0.73). Furthermore, no microthrombi were present in perioperative biopsies in recipients who developed early hepatic artery thrombosis. Finally, the presence of microthrombi did not differ before or after additional flushing of the graft with preservation solution. In conclusion, the results of our study derogate from the hypothesis that DCD livers have an increased tendency to form microthrombi. It weakens the explanation that microthrombi formation is a main causal factor in the development of NAS in DCD and that recipients could benefit from intraoperative thrombolytic therapy to prevent NAS following liver transplantation. Liver Transplantation 22 1676-1687 2016 AASLD.

Transplantation of Declined Liver Allografts Following Normothermic Ex-Situ Evaluation

The demand for liver transplantation (LT) exceeds supply, with rising waiting list mortality. Utilization of high-risk organs is low and a substantial number of procured livers are discarded. We report the first series of five transplants with rejected livers following viability assessment by normothermic machine perfusion of the liver (NMP-L). The evaluation protocol consisted of perfusate lactate, bile production, vascular flows, and liver appearance. All livers were exposed to a variable period of static cold storage prior to commencing NMP-L. Four organs were recovered from donors after circulatory death and rejected due to prolonged donor warm ischemic times; one liver from a brain-death donor was declined for high liver function tests (LFTs). The median (range) total graft preservation time was 798 (range 724-951) min. The transplant procedure was uneventful in every recipient, with immediate function in all grafts. The median in-hospital stay was 10 (range 6-14) days. At present, all recipients are well, with normalized LFTs at median follow-up of 7 (range 6-19) months. Viability assessment of high-risk grafts using NMP-L provides specific information on liver function and can permit their transplantation while minimizing the recipient risk of primary graft nonfunction. This novel approach may increase organ availability for LT.

Latest advances in the pathological understanding of cholangiocarcinomas

Cholangiocarcinomas (CCAs) are anatomically classified into intrahepatic, perihilar, and distal types. The gross pathological classification of intrahepatic CCAs divides them into mass-forming, periductal-infiltrating, and intraductal-growth types; and perihilar/distal CCAs into flat- and nodular-infiltrating and papillary types. Unique preinvasive lesions appear to precede individual gross types of CCA. Biliary intraepithelial neoplasia, a flat lesion, precedes periductal-, flat-, and nodular-infiltrating CCAs, whereas intraductal papillary neoplasm of the bile duct (IPNB) precedes the intraductal-growth and papillary type of CCAs. IPNBs are heterogeneous in their histological and pathological profiles along the biliary tree. Hepatobiliary cystadenomas/adenocarcinomas are reclassified as cystic IPNBs and hepatic mucinous cystic neoplasms. Peribiliary glands may participate in the development of CCAs. These latest findings present a new challenge for understanding the pathology of CCAs.

Can we prevent ischemic-type biliary lesions in donation after circulatory determination of death liver transplantation?

The pool of livers for transplantation consists of an increasingly greater proportion of marginal grafts, in particular those arising through donation after circulatory determination of death (DCD). However, a primary factor limiting the use of marginal livers, and, thereby, the applicability of liver transplantation in general, is concern over the subsequent development of ischemic-type biliary lesion (ITBL). ITBL is a devastating complication of liver transplantation; in its most severe forms, recipients suffer frequent infectious complications that require repeated invasive biliary procedures and ultimately result in either retransplantation or death. In the present review article, we discuss our current understanding of ITBL pathogenesis as it pertains to DCD, in particular. We discuss the most relevant theories regarding its development and provide a comprehensive overview of the most promising strategies we have available today to prevent the appearance of ITBL, strategies that may, furthermore, allow us to transplant a greater proportion of marginal livers in the future. Liver Transplantation 22 1025-1033 2016 AASLD.

Normothermic machine perfusion reduces bile duct injury and improves biliary epithelial function in rat donor livers

Bile duct injury may occur during liver procurement and transplantation, especially in livers from donation after circulatory death (DCD) donors. Normothermic machine perfusion (NMP) has been shown to reduce hepatic injury compared to static cold storage (SCS). However, it is unknown whether NMP provides better preservation of bile ducts. The aim of this study was to determine the impact of NMP on bile duct preservation in both DCD and non-DCD livers. DCD and non-DCD livers obtained from Lewis rats were preserved for 3 hours using either SCS or NMP, followed by 2 hours ex vivo reperfusion. Biomarkers of bile duct injury (gamma-glutamyltransferase and lactate dehydrogenase in bile) were lower in NMP-preserved livers compared to SCS-preserved livers. Biliary bicarbonate concentration, reflecting biliary epithelial function, was 2-fold higher in NMP-preserved livers (P < 0.01). In parallel with this, the pH of the bile was significantly higher in NMP-preserved livers (7.63 ± 0.02 and 7.74 ± 0.05 for non-DCD and DCD livers, respectively) compared with SCS-preserved livers (7.46 ± 0.02 and 7.49 ± 0.04 for non-DCD and DCD livers, respectively). Scanning and transmission electron microscopy of donor extrahepatic bile ducts demonstrated significantly decreased injury of the biliary epithelium of NMP-preserved donor livers (including the loss of lateral interdigitations and mitochondrial injury). Differences between NMP and SCS were most prominent in DCD livers. Compared to conventional SCS, NMP provides superior preservation of bile duct epithelial cell function and morphology, especially in DCD donor livers. By reducing biliary injury, NMP could have an important impact on the utilization of DCD livers and outcome after transplantation. Liver Transplantation 22 994-1005 2016 AASLD.

The hepatic, biliary, and pancreatic network of stem/progenitor cell niches in humans: A new reference frame for disease and regeneration

Stem/progenitors for liver, biliary tree, and pancreas exist at early stages of development in the definitive ventral endoderm forming the foregut. In humans, they persist postnatally as part of a network, with evidence supporting their contributions to hepatic and pancreatic organogenesis throughout life. Multiple stem cell niches persist in specific anatomical locations within the human biliary tree and pancreatic ducts. In liver and pancreas, replication of mature parenchymal cells ensures the physiological turnover and the restoration of parenchyma after minor injuries. Although actively debated, multiple observations indicate that stem/progenitor cells contribute to repair pervasive, chronic injuries. The most primitive of the stem/progenitor cells, biliary tree stem cells, are found in peribiliary glands within extrahepatic and large intrahepatic bile ducts. Biliary tree stem cells are comprised of multiple subpopulations with traits suggestive of maturational lineage stages and yet capable of self-replication and multipotent differentiation, being able to differentiate to mature liver cells (hepatocytes, cholangiocytes) and mature pancreatic cells (including functional islet endocrine cells). Hepatic stem cells are located within canals of Hering and bile ductules and are capable of differentiating to hepatocyte and cholangiocyte lineages. The existence, phenotype, and anatomical location of stem/progenitors in the adult pancreas are actively debated. Ongoing studies suggest that pancreatic stem cells reside within the biliary tree, primarily the hepatopancreatic common duct, and are rare in the pancreas proper. Pancreatic ducts and pancreatic duct glands harbor committed pancreatic progenitors.

CONCLUSION

The hepatic, biliary, and pancreatic network of stem/progenitor cell niches should be considered as a framework for understanding liver and pancreatic regeneration after extensive or chronic injuries and for the study of human chronic diseases affecting these organs. (Hepatology 2016;64:277-286).

Liver Transplant From Unexpected Donation After Circulatory Determination of Death Donors: A Challenge in Perioperative Management

Unexpected donation after circulatory determination of death (uDCD) liver transplantation is a complex procedure, in particular when it comes to perioperative recipient management. However, very little has been published to date regarding intraoperative and immediate postoperative care in this setting. Herein, we compare perioperative events in uDCD liver recipients with those of a matched group of donation after brain death liver recipients. We demonstrate that the former group of recipients suffers significantly greater hemodynamic instability and derangements in coagulation following graft reperfusion. Based on our experience, we recommend a proactive recipient management strategy in uDCD liver transplantation that involves early use of vasopressor support; maintaining adequate intraoperative levels of red cells, platelets, and fibrinogen; and routinely administering tranexamic acid before graft reperfusion.

Functional Immune Anatomy of the Liver-As an Allograft

The liver is an immunoregulatory organ in which a tolerogenic microenvironment mitigates the relative "strength" of local immune responses. Paradoxically, necro-inflammatory diseases create the need for most liver transplants. Treatment of hepatitis B virus, hepatitis C virus, and acute T cell-mediated rejection have redirected focus on long-term allograft structural integrity. Understanding of insults should enable decades of morbidity-free survival after liver replacement because of these tolerogenic properties. Studies of long-term survivors show low-grade chronic inflammatory, fibrotic, and microvascular lesions, likely related to some combination of environment insults (i.e. abnormal physiology), donor-specific antibodies, and T cell-mediated immunity. The resultant conundrum is familiar in transplantation: adequate immunosuppression produces chronic toxicities, while lightened immunosuppression leads to sensitization, immunological injury, and structural deterioration. The "balance" is more favorable for liver than other solid organ allografts. This occurs because of unique hepatic immune physiology and provides unintended benefits for allografts by modulating various afferent and efferent limbs of allogenic immune responses. This review is intended to provide a better understanding of liver immune microanatomy and physiology and thereby (a) the potential structural consequences of low-level, including allo-antibody-mediated injury; and (b) how liver allografts modulate immune reactions. Special attention is given to the microvasculature and hepatic mononuclear phagocytic system.

Risk analysis of ischemic-type biliary lesions after liver transplant using octogenarian donors

The use of octogenarian donors to increase the donor pool in liver transplantation (LT) is controversial because advanced donor age is associated with a higher risk of ischemic-type biliary lesions (ITBL). The aim of this study was to investigate retrospectively the role of a number of different pre-LT risk factors for ITBL in a selected population of recipients of octogenarian donor grafts. Between January 2003 and December 2013, 123 patients underwent transplantation at our institution with deceased donor grafts from donors of age ≥80 years. Patients were divided into 2 groups based on the presence of ITBL in the posttransplant course. Exclusion criteria were retransplantations, presence of vascular complications, and no availability of procurement liver biopsy. A total of 88 primary LTs were included, 73 (83.0%) with no posttransplant ITBLs and 15 (17.0%) with ITBLs. The median follow-up after LT was 2.1 years (range, 0.7-5.4 years). At multivariate analysis, donor hemodynamic instability (hazard ratio [HR], 7.6; P = 0.005), donor diabetes mellitus (HR, 9.5; P = 0.009), and donor age-Model for End-Stage Liver Disease (HR, 1.0; P = 0.04) were risk factors for ITBL. Transplantation of liver grafts from donors of age ≥80 years is associated with a higher risk for ITBL. However, favorable results can be achieved with accurate donor selection. Donor hemodynamic instability, a donor history of diabetes mellitus, and allocation to higher Model for End-Stage Liver Disease score recipient all increase the risk of ITBL and are associated with worse graft survival when octogenarian donors are used. Liver Transplantation 22 588-598 2016 AASLD.

Flushing the liver with urokinase before transplantation does not prevent nonanastomotic biliary strictures

The aim of the present study was to assess whether flushing the donor liver with urokinase immediately before implantation reduces the incidence of nonanastomotic biliary strictures (NASs) after liver transplantation, without causing increased blood loss, analyzed as a historical cohort study. Between January 2005 and October 2012, all liver (re-)transplantations were included. Of the 185 liver transplant recipients included, 63 donor livers between January 2010 and October 2012 received urokinase (study group), whereas the donor liver of 122 consecutive recipients, who served as a historical control group, between January 2005 and January 2010 did not receive urokinase. Basic donor (Eurotransplant donor risk index) and recipient (age, body mass index, laboratory Model for End-Stage Liver Disease score) characteristics did not significantly differ in both groups. Thirty-three recipients developed NASs: 22 in the control group (18%) and 11 (17.5%) in the study group (P = 0.68). Analyzed separately for donation after circulatory death (P = 0.42) or donation after brain death (P = 0.89), there was no difference between the groups in incidence of NAS. Of all the recipients developing NAS, 7 (21%) needed retransplantation and all others were treated conservatively. Autologous blood transfusion requirements did not differ significantly between both groups (P = 0.91), whereas interestingly, more heterologous blood transfusions were needed in the control group (P < 0.001). This study has its limitations by its retrospective character. A multi-institutional prospective study could clarify this issue. In conclusion, arterial flushing of the liver with urokinase immediately before implantation did not lead to a lower incidence of NAS in this study, nor did it lead to increased blood loss.

Stem/Progenitor Cell Niches Involved in Hepatic and Biliary Regeneration

Niches containing stem/progenitor cells are present in different anatomical locations along the human biliary tree and within liver acini. The most primitive stem/progenitors, biliary tree stem/progenitor cells (BTSCs), reside within peribiliary glands located throughout large extrahepatic and intrahepatic bile ducts. BTSCs are multipotent and can differentiate towards hepatic and pancreatic cell fates. These niches' matrix chemistry and other characteristics are undefined. Canals of Hering (bile ductules) are found periportally and contain hepatic stem/progenitor cells (HpSCs), participating in the renewal of small intrahepatic bile ducts and being precursors to hepatocytes and cholangiocytes. The niches also contain precursors to hepatic stellate cells and endothelia, macrophages, and have a matrix chemistry rich in hyaluronans, minimally sulfated proteoglycans, fetal collagens, and laminin. The microenvironment furnishes key signals driving HpSC activation and differentiation. Newly discovered third niches are pericentral within hepatic acini, contain Axin2+ unipotent hepatocytic progenitors linked on their lateral borders to endothelia forming the central vein, and contribute to normal turnover of mature hepatocytes. Their relationship to the other stem/progenitors is undefined. Stem/progenitor niches have important implications in regenerative medicine for the liver and biliary tree and in pathogenic processes leading to diseases of these tissues.

Activation of biliary tree stem cells within peribiliary glands in primary sclerosing cholangitis

BACKGROUND & AIMS

Primary sclerosing cholangitis (PSC) is characterised by fibro-stenosing strictures involving extrahepatic and/or large intrahepatic bile ducts. Mechanisms leading to bile duct injury are poorly understood. We aimed to study the biliary tree stem cell compartment located in peribiliary glands of extrahepatic and large intrahepatic bile ducts and its role in the pathogenesis of biliary fibrosis in PSC.

METHODS

Specimens containing extrahepatic or large intrahepatic bile ducts were obtained from normal liver (n=6), liver explants from patients with PSC (n=11), and primary biliary cirrhosis (n=6). Specimens were processed for histology, immunohistochemistry and immunofluorescence.

RESULTS

In PSC samples, progressive hyperplasia and mucinous metaplasia of peribiliary glands were observed in large ducts with fibrosis, but not in inflamed ducts without fibrosis. Peribiliary gland hyperplasia was associated with progressive biliary fibrosis and the occurrence of dysplastic lesions. Hyperplasia of peribiliary glands was determined by the expansion of biliary tree stem cells, which sprouted towards the surface epithelium. In PSC, peribiliary glands and myofibroblasts displayed enhanced expression of Hedgehog pathway components. Peribiliary glands in ducts with onion skin-like fibrosis expressed epithelial-to-mesenchymal transition traits associated with components of Hedgehog pathway, markers of senescence and autophagy.

CONCLUSIONS

The biliary tree stem cell compartment is activated in PSC, its activation contributes to biliary fibrosis, and is sustained by the Hedgehog pathway. Our findings suggest a key role for peribiliary glands in the progression of bile duct lesions in PSC and could explain the associated high risk of cholangiocarcinoma.

End-ischemic machine perfusion reduces bile duct injury in donation after circulatory death rat donor livers independent of the machine perfusion temperature

A short period of oxygenated machine perfusion (MP) after static cold storage (SCS) may reduce biliary injury in donation after cardiac death (DCD) donor livers. However, the ideal perfusion temperature for protection of the bile ducts is unknown. In this study, the optimal perfusion temperature for protection of the bile ducts was assessed. DCD rat livers were preserved by SCS for 6 hours. Thereafter, 1 hour of oxygenated MP was performed using either hypothermic machine perfusion, subnormothermic machine perfusion, or with controlled oxygenated rewarming (COR) conditions. Subsequently, graft and bile duct viability were assessed during 2 hours of normothermic ex situ reperfusion. In the MP study groups, lower levels of transaminases, lactate dehydrogenase (LDH), and thiobarbituric acid reactive substances were measured compared to SCS. In parallel, mitochondrial oxygen consumption and adenosine triphosphate (ATP) production were significantly higher in the MP groups. Biomarkers of biliary function, including bile production, biliary bicarbonate concentration, and pH, were significantly higher in the MP groups, whereas biomarkers of biliary epithelial injury (biliary gamma-glutamyltransferase [GGT] and LDH), were significantly lower in MP preserved livers. Histological analysis revealed less injury of large bile duct epithelium in the MP groups compared to SCS. In conclusion, compared to SCS, end-ischemic oxygenated MP of DCD livers provides better preservation of biliary epithelial function and morphology, independent of the temperature at which MP is performed. End-ischemic oxygenated MP could reduce biliary injury after DCD liver transplantation.

Hepatic artery bridging lessens temporary ischemic injury to bile canaliculi

AIM: To study whether transfer of blood between the right gastroepiploic artery and gastroduodenal artery could lessens the damage to bile canaliculi.

METHODS: Forty male Bama miniature pigs were divided into four groups as follows: a control group, two hepatic artery ischemia groups (1 h and 2 h), and a hepatic artery bridging group. The hemodynamics of the hepatic artery in the hepatic artery bridging group was measured using color Doppler ultrasound. Morphological changes in the bile canaliculus were observed by transmission electron microscopy. Cofilin, heat shock protein 27 and F-actin expression was detected by immunohistochemistry, Western blot, and real-time polymerase chain reaction. Terminal deoxynucleotidyl transferase-mediated nick end-labeling method was used to evaluate liver injury.

RESULTS: The hemodynamics was not changed in the hepatic artery bridging group. The microvilli in the bile canaliculus were impaired in the two hepatic artery ischemia groups. The down-regulation of cofilin and F-actin and up-regulation of heat shock protein 27 were observed in the two hepatic artery ischemia groups, while there were no significant differences between the control group and hepatic artery bridging group.

CONCLUSION: Hepatic artery ischemia aggravates damage to bile canaliculi, and this damage can be diminished by a hepatic artery bridging duct.

Machine perfusion in liver transplantation as a tool to prevent non-anastomotic biliary strictures: Rationale, current evidence and future directions

The high incidence of non-anastomotic biliary strictures (NAS) after transplantation of livers from extended criteria donors is currently a major barrier to widespread use of these organs. This review provides an update on the most recent advances in the understanding of the etiology of NAS. These new insights give reason to believe that machine perfusion can reduce the incidence of NAS after transplantation by providing more protective effects on the biliary tree during preservation of the donor liver. An overview is presented regarding the different endpoints that have been used for assessment of biliary injury and function before and after transplantation, emphasizing on methods used during machine perfusion. The wide spectrum of different approaches to machine perfusion is discussed, including the many different combinations of techniques, temperatures and perfusates at varying time points. In addition, the current understanding of the effect of machine perfusion in relation to biliary injury is reviewed. Finally, we explore directions for future research such as the application of (pharmacological) strategies during machine perfusion to further improve preservation. We stress the great potential of machine perfusion to possibly expand the donor pool by reducing the incidence of NAS in extended criteria organs.

Elderly donor liver grafts are not associated with a higher incidence of biliary complications after liver transplantation: results of a national multicenter study

BACKGROUND

Liver transplantation with livers grafts from elderly donors has been associated with a higher risk of biliary complications. The aim of this study was to examine whether our national protocol could contribute to a lower incidence of biliary complications.

METHODS

All adult recipients in the Netherlands transplanted with a liver from an elderly donor (≥ 65 yrs; n = 68) in the period January 2000-July 2011 were matched with recipients of a liver from a donor <65 yr (n = 136). Outcome parameters were 90-d, one-yr, and three-yr patient/graft survival rates, biliary complications (non-anastomotic stricture, anastomotic stricture, biliary leakage, and post-transplant cholangitis), and postoperative hepatic ischemic injury serum markers (AST/ALT).

RESULTS

The median cold ischemia time (CIT) was 7:25 (h:min) in the group recipients of an elderly donor liver graft. Ninety-day, one-yr, and three-yr patient/graft survival rates were similar between the group with an elderly donor liver and their younger controls. Moreover, no differences were found in the incidence of biliary complications and postoperative levels of AST/ALT between the two groups.

CONCLUSION

Transplantation of livers from elderly donors (≥ 65 yr) is not associated with a higher incidence of biliary complications, in a national policy wherein the CIT is kept short.

First experience of liver transplantation with type 2 donation after cardiac death in France

Organ donation after unexpected cardiac death [type 2 donation after cardiac death (DCD)] is currently authorized in France and has been since 2006. Following the Spanish experience, a national protocol was established to perform liver transplantation (LT) with type 2 DCD donors. After the declaration of death, abdominal normothermic oxygenated recirculation was used to perfuse and oxygenate the abdominal organs until harvesting and cold storage. Such grafts were proposed to consenting patients < 65 years old with liver cancer and without any hepatic insufficiency. Between 2010 and 2013, 13 LTs were performed in 3 French centers. Six patients had a rapid and uneventful postoperative recovery. However, primary nonfunction occurred in 3 patients, with each requiring urgent retransplantation, and 4 early allograft dysfunctions were observed. One patient developed a nonanastomotic biliary stricture after 3 months, whereas 8 patients showed no sign of ischemic cholangiopathy at their 1-year follow-up. In comparison with a control group of patients receiving grafts from brain-dead donors (n = 41), donor age and cold ischemia time were significantly lower in the type 2 DCD group. Time spent on the national organ wait list tended to be shorter in the type 2 DCD group: 7.5 months [interquartile range (IQR), 4.0-11.0 months] versus 12.0 months (IQR, 6.8-16.7 months; P = 0.08. The 1-year patient survival rates were similar (85% in the type 2 DCD group versus 93% in the control group), but the 1-year graft survival rate was significantly lower in the type 2 DCD group (69% versus 93%; P = 0.03). In conclusion, to treat borderline hepatocellular carcinoma, LT with type 2 DCD donors is possible as long as strict donor selection is observed.

High peak alanine aminotransferase determines extra risk for nonanastomotic biliary strictures after liver transplantation with donation after circulatory death

Orthotopic liver transplantation (OLT) with donation after circulatory death (DCD) often leads to a higher first week peak alanine aminotransferase (ALT) and a higher rate of biliary nonanastomotic strictures (NAS) as compared to donation after brain death (DBD). This retrospective study was to evaluate whether an association exists between peak ALT and the development of NAS in OLT with livers from DBD (n = 399) or DCD (n = 97) from two transplantation centers. Optimal cutoff value of peak ALT for risk of development of NAS post-DCD-OLT was 1300 IU/l. The 4-year cumulative incidence of NAS after DCD-OLT was 49.5% in patients with a high ALT peak post-OLT, compared with 11.3% in patients with a low ALT peak. (P < 0.001). No relation between peak ALT and NAS was observed after DBD-OLT. Multivariate analysis revealed peak ALT ≥1300 IU/l [adjusted hazard ratio (aHR) = 3.71, confidence interval (CI) (1.26-10.91)] and donor age [aHR = 1.04, CI 1.00-1.07] to be independently associated with development of NAS post-DCD-OLT. A peak ALT of <1300 IU/l carries a risk for NAS similar to DBD-OLT. Thus, in DCD-OLT, but not in DBD-OLT, peak ALT discriminates patients at high or low risk for NAS.

Biomarkers to assess graft quality during conventional and machine preservation in liver transplantation

A global rising organ shortage necessitates the use of extended criteria donors (ECD) for liver transplantation (LT). However, poor preservation and extensive ischemic injury of ECD grafts have been recognized as important factors associated with primary non-function, early allograft dysfunction, and biliary complications after LT. In order to prevent for these ischemia-related complications, machine perfusion (MP) has gained interest as a technique to optimize preservation of grafts and to provide the opportunity to assess graft quality by screening for extensive ischemic injury. For this purpose, however, objective surrogate biomarkers are required which can be easily determined at time of graft preservation and the various techniques of MP. This review provides an overview and evaluation of biomarkers that have been investigated for the assessment of graft quality and viability testing during different types of MP. Moreover, studies regarding conventional graft preservation by static cold storage (SCS) were screened to identify biomarkers that correlated with either allograft dysfunction or biliary complications after LT and which could potentially be applied as predictive markers during MP. The pros and cons of the different biomaterials that are available for biomarker research during graft preservation are discussed, accompanied with suggestions for future research. Though many studies are currently still in the experimental setting or of low evidence level due to small cohort sizes, the biomarkers presented in this review provide a useful handle to monitor recovery of ECD grafts during clinical MP in the near future.

Role of hypothermic machine perfusion in liver transplantation

Machine liver perfusion has significantly evolved during the last ten years to optimize extended criteria liver grafts and to address the worldwide organ shortage. This review gives an overview on available ex vivo and in vivo data on hypothermic machine liver perfusion. We discuss also possible protective pathways and show most recent clinical applications of hypothermic machine liver perfusion in human.