Hypo- and normothermic perfusion of the liver: Which way to go?

Endothelial Cells and Mitochondria: Two Key Players in Liver Transplantation

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

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.

Ultrastructural changes in porcine liver sinusoidal endothelial cells of machine perfused liver donated after cardiac death

BACKGROUND

The machine perfusion (MP) preservation including hypothermic MP (HMP) and midthermic MP (MMP) has been considered as a promising strategy to preserve the functions of liver donated after cardiac death. The importance of understanding liver sinusoidal endothelial cells (LSEC) damage in regulating liver injury during MP has been emphasized. However, the ultrastructural changes in the LSEC and sinusoids around them after MP are unclear.

AIM

To investigate the ultrastructural changes in the LSEC and sinusoids around them after MP.

METHODS

Porcine liver grafts undergo a warm ischemia time of 60 minutes perfused for 4 h with modified University of Wisconsin gluconate solution. Group A grafts were preserved with HMP at 8 °C constantly for 4 h. Group B grafts were preserved with a rewarming solution at 22 °C by MMP for 4 h. Then the ultrastructural changes in the LSEC and sinusoids in Group A and B were comparatively analyzed by using osmium-maceration scanning electron microscopy with complementary transmission electron microscopy methods.

RESULTS

An analysis of the LSEC after warm ischemia revealed that mitochondria with condensed-shaped cristae, abnormal vesicles, reduction of ribosomes and the endoplasmic reticulum (ER) surround the mitochondria appeared. The MP subsequent after warm ischemia alleviate the abnormal vesicles and reduction of ribosomes in LSEC, which indicated the reduction of the ER damage. However, MMP could restore the tubular mitochondrial cristae, while after HMP the condensed and narrow mitochondrial cristae remained. In addition, the volume of the sinusoidal space in the liver grafts after MMP were restored, which indicated a lower risk of pressure injury than HMP.

CONCLUSION

MMP alleviates the ER damage of LSEC by warm ischemia, additionally restore the metabolism of LSEC via the normalization of mitochondria and prevent the share stress damage of liver grafts.

Abrogation of graft ischemia-reperfusion injury in ischemia-free liver transplantation

Background

Ischemia‐reperfusion injury (IRI) is considered an inherent component of organ transplantation that compromises transplant outcomes and organ availability. The ischemia‐free liver transplantation (IFLT) procedure has been developed to avoid interruption of blood supply to liver grafts. It is unknown how IFLT might change the characteristics of graft IRI.

Methods

Serum and liver biopsy samples were collected from IFLT and conventional liver transplantation (CLT) recipients. Pathological, metabolomics, transcriptomics, and proteomics analyses were performed to identify the characteristic changes in graft IRI in IFLT.

Results

Peak aspartate aminotransferase (539.59 ± 661.76 U/L versus 2622.28 ± 3291.57 U/L) and alanine aminotransferase (297.64 ± 549.50 U/L versus 1184.16 ± 1502.76 U/L) levels within the first 7 days and total bilirubin levels by day 7 (3.27 ± 2.82 mg/dl versus 8.33 ± 8.76 mg/dl) were lower in the IFLT versus CLT group (all p values < 0.001). The pathological characteristics of IRI were more obvious in CLT grafts. The antioxidant pentose phosphate pathway remained active throughout the procedure in IFLT grafts and was suppressed during preservation and overactivated postrevascularization in CLT grafts. Gene transcriptional reprogramming was almost absent during IFLT but was profound during CLT. Proteomics analysis showed that “metabolism of RNA” was the major differentially expressed process between the two groups. Several proinflammatory pathways were not activated post‐IFLT as they were post‐CLT. The activities of natural killer cells, macrophages, and neutrophils were lower in IFLT grafts than in CLT grafts. The serum levels of 14 cytokines were increased in CLT versus IFLT recipients.

Conclusions

IFLT can largely avoid the biological consequences of graft IRI, thus has the potential to improve transplant outcome while increasing organ utilization.

Experimental long-term sub-normothermic machine perfusion for non-allocable human liver grafts: first data towards feasibility

Background

Patients with end-stage liver disease can only be cured by liver transplantation. Due to the gap between demand and supply, surgeons are forced to use expanded criteria donor (ECD) organs, which are more susceptible to ischemia–reperfusion injury (IRI). Therefore, enhanced storing techniques are required. Machine perfusion (MP) has moved into the spotlight of research because of its feasibility for investigating liver function prior to implantation. However, as the perfect MP protocol has not yet been found, we aimed to investigate the potential of sub-normothermic (SN)MP in this field.

Methods

Non-allocable human livers were subjected to 24 h of SNMP at 21 °C after delivery to the study team. Perfusion was performed with Custodiol® (Dr. Franz Köhler Chemie, Bensheim, Germany) or Belzer MPS® (Bridge to Life Europe, London, UK) and perfusate liver parameters were determined. For determination of biliary conditions, pH, glucose, and HCO3- levels were measured.

Results

Liver parameters were slightly increased irrespective of perfusate or reason for liver rejection during 24 h of perfusion. Six livers failed to produce bile completely, whereas the remaining 10 livers produced between 2.4 ml and 179 ml of bile. Biliary carbonate was increased in all but one liver. The bile-glucose-to-perfusate-glucose ratio was near 1 for most of the organs and bile pH was above 7 in all but one case.

Conclusion

This study provides promising data on the feasibility of long-term SNMP as a tool to gain time during MP to optimize ECD organs to decrease the gap between organ demand and supply.

Long-term (24 h) sub-normothermic liver machine perfusion seems to be possible, although some adjustments to the protocol might be necessary to improve the general outcome. This has so far been shown for normothermic machine perfusion, bearing some drawbacks compared to the sub-normothermic variant.

Ischaemia-free liver transplantation in humans: a first-in-human trial

Background Ischaemia-reperfusion injury is considered an inevitable component of organ transplantation, compromising organ quality and outcomes. Although several treatments have been proposed, none has avoided graft ischaemia and its detrimental consequences. Methods Ischaemia-free liver transplantation (IFLT) comprises surgical techniques enabling continuous oxygenated blood supply to the liver of brain-dead donor during procurement, preservation, and implantation using normothermic machine perfusion technology. In this non-randomised study, 38 donor livers were transplanted using IFLT and compared to 130 conventional liver transplants (CLT). Findings Two recipients (5•3%) in the IFLT group experienced early allograft dysfunction, compared to 50•0% in patients receiving conventional transplants (absolute risk difference, 44•8%; 95% confidence interval, 33•6-55•9%). Recipients of IFLT had significantly reduced median (IQR) peak aspartate aminotransferase levels within the first week compared to CLT recipients (365, 238-697 vs 1445, 791-3244 U/L, p<0•001); likewise, median total bilirubin levels on day 7 were significantly lower (2•34, 1•39-4•09 mg/dL) in the IFLT group than in the CLT group (5•10, 1•90-11•65 mg/dL) (p<0•001). Moreover, IFLT recipients had a shorter median intensive care unit stay (1•48, 0•75-2•00 vs 1•81, 1•00-4•58 days, p=0•006). Both one-month recipient (97•4% vs 90•8%, p=0•302) and graft survival (97.4% vs 90•0%, p=0•195) were better for IFLT than CLT, albeit differences were not statistically significant. Subgroup analysis showed that the extended criteria donor livers transplanted using the IFLT technique yielded faster post-transplant recovery than did the standard criteria donor livers transplanted using the conventional approach. Interpretation IFLT provides a novel approach that may improve outcomes, and allow the successful utilisation of extended criteria livers. Funding This study was funded by National Natural Science Foundation of China, Guangdong Provincial Key Laboratory Construction Projection on Organ Donation and Transplant Immunology, and Guangdong Provincial international Cooperation Base of Science and Technology. Panel: Research in context.

Dual Versus Single Oxygenated Hypothermic Machine Perfusion of Porcine Livers: Impact on Hepatobiliary and Endothelial Cell Injury

Supplemental Digital Content is available in the text.

Background.

Hypothermic oxygenated machine perfusion (HOPE) reduces ischemia-reperfusion injury of donor livers and is increasingly used in clinical transplantation. However, it remains unclear whether perfusion via the portal vein alone (HOPE) or via both the portal vein and hepatic artery (dual HOPE or DHOPE) is superior.

Methods.

Twelve porcine livers donated after circulatory death were randomized for 2 h of HOPE (n = 6) or DHOPE (n = 6), followed by 4 h of warm reperfusion with whole blood, to mimic transplantation. Hepatobiliary and endothelial cell function and injury markers were determined in perfusate and bile samples. Biopsies of bile ducts, hepatic arteries, and liver parenchyma were collected to assess histological damage and the expression of endothelial protective genes (KLF-2, eNOS, ET-1, CD31, VWF, VEGF-A).

Results.

There were no differences in hepatobiliary function and injury after warm reperfusion between the groups, apart from a 2-fold lower concentration of alanine aminotransferase in the perfusate (P = 0.045) and a lower peak lactate dehydrogenase in bile (P = 0.04) of livers preserved by DHOPE. Endothelial cell function and injury, as assessed by perfusate nitric oxide and von Willebrand factor antigen levels, as well as endothelial protective gene expressions, were similar between the groups. The hepatic arteries of both groups showed no microscopic evidence of injury.

Conclusions.

This study did not reveal major differences in hepatobiliary or endothelial function and injury after preservation by single or dual HOPE of porcine livers donated after circulatory death.

Subnormothermic ex vivo lung perfusion attenuates ischemia reperfusion injury from donation after circulatory death donors

Use of normothermic ex vivo lung perfusion (EVLP) was adopted in clinical practice to assess the quality of marginal donor lungs. Subnormothermic perfusion temperatures are in use among other solid organs to improve biochemical, clinical and immunological parameters. In a rat EVLP model of donation after circulatory death (DCD) lung donors, we tested the effect of four subnormothermic EVLP temperatures that could further improve organ preservation. Warm ischemic time was of 2 hours. EVLP time was of 4 hours. Lung physiological data were recorded and metabolic parameters were assessed. Lung oxygenation at 21°C and 24°C were significantly improved whereas pulmonary vascular resistance and edema formation at 21°C EVLP were significantly worsened when compared to 37°C EVLP. The perfusate concentrations of potassium ions and lactate exiting the lungs with 28°C EVLP were significantly lower whereas sodium and chlorine ions with 32°C EVLP were significantly higher when compared to 37°C EVLP. Also compared to 37°C EVLP, the pro-inflammatory chemokines MIP2, MIP-1α, GRO-α, the cytokine IL-6 were significantly lower with 21°C, 24°C and 28°C EVLP, the IL-18 was significantly lower but only with 21°C EVLP and IL-1β was significantly lower at 21°C and 24°C EVLP. Compared to the 37°C EVLP, the lung tissue ATP content after 21°C, 24°C and 28°C EVLP were significantly higher, the carbonylated protein content after 28°C EVLP was significantly lower and we measured significantly higher myeloperoxidase activities in lung tissues with 21°C, 24°C and 32°C. The 28°C EVLP demonstrated acceptable physiological variables, significantly higher lung tissue ATP content and decreased tissue carbonylated proteins with reduced release of pro-inflammatory cytokines. In conclusion, the 28°C EVLP is a non inferior setting in comparison to the clinically approved 37°C EVLP and significantly improve biochemical, clinical and immunological parameters and may reduce I/R injuries of DCD lung donors.

Research progress on hepatic machine perfusion

Nowadays, liver transplantation is the most effective treatment for end-stage liver disease. However, the increasing imbalance between growing demand for liver transplantation and the shortage of donor pool restricts the development of liver transplantation. How to expand the donor pool is a significant problem to be solved clinically. Many doctors have devoted themselves to marginal grafting, which introduces livers with barely passable quality but a high risk of transplant failure into the donor pool. However, existing common methods of preserving marginal grafts lead to both high risk of postoperative complications and high mortality. The application of machine perfusion allows surgeons to make marginal livers meet the standard criteria for transplant, which shows promising prospect in preserving and repairing donor livers and improving ischemia reperfusion injury. This review summarizes the progress of recent researches on hepatic machine perfusion.

Hypothermic Oxygenated Liver Perfusion (HOPE) Prevents Tumor Recurrence in Liver Transplantation From Donation After Circulatory Death

OBJECTIVE

The aim of this study was to investigate tumor recurrence after liver transplantation for hepatocellular carcinoma (HCC), with and without hypothermic oxygenated liver perfusion (HOPE) before transplantation.

PATIENTS AND METHODS

We analyzed all liver recipients with HCC, transplanted between January 2012 and September 2019 with donation after circulatory death (DCD) livers after previous end-ischemic HOPE-treatment (n = 70, Center A). Tumor parameters and key confounders were compared to consecutive recipients with HCC, transplanted during the same observation period with an unperfused DBD liver (n = 70). In a next step, we analyzed unperfused DCD (n = 70) and DBD liver recipients (n = 70), transplanted for HCC at an external center (Center B).

RESULTS

Tumor parameters were not significantly different between HOPE-treated DCD and unperfused DBD liver recipients at Center A. One-third of patients were outside established tumor thresholds, for example, Milan criteria, in both groups. Despite no difference in tumor load, we found a 4-fold higher tumor recurrence rate in unperfused DBD livers (25.7%, 18/70), compared to only 5.7% (n = 4/70) recipients with tumor recurrence in the HOPE-treated DCD cohort (P = 0.002) in Center A. The tumor recurrence rate was also twice higher in unperfused DCD and DBD recipients at the external Center B, despite significant less cases outside Milan. HOPE-treatment of DCD livers resulted therefore in a 5-year tumor-free survival of 92% in HCC recipients, compared to 73%, 82.7%, and 81.2% in patients receiving unperfused DBD or DCD livers, from both centers.

CONCLUSION

We suggest that a simple machine liver perfusion approach appears advantageous to protect from HCC recurrence after liver transplantation, despite extended tumor criteria.

Ischemia-Reperfusion Injury in Marginal Liver Grafts and the Role of Hypothermic Machine Perfusion: Molecular Mechanisms and Clinical Implications

Ischemia-reperfusion injury (IRI) constitutes a significant source of morbidity and mortality after orthotopic liver transplantation (OLT). The allograft is metabolically impaired during warm and cold ischemia and is further damaged by a paradox reperfusion injury after revascularization and reoxygenation. Short-term and long-term complications including post-reperfusion syndrome, delayed graft function, and immune activation have been associated with IRI. Due to the current critical organ shortage, extended criteria grafts are increasingly considered for transplantation, however, with an elevated risk to develop significant features of IRI. In recent years, ex vivo machine perfusion (MP) of the donor liver has witnessed significant advancements. Here, we describe the concept of hypothermic (oxygenated) machine perfusion (HMP/HOPE) approaches and highlight which allografts may benefit from this technology. This review also summarizes clinical applications and the main aspects of ongoing randomized controlled trials on hypothermic perfusion. The mechanistic aspects of IRI and hypothermic MP-which include tissue energy replenishment, optimization of mitochondrial function, and the reduction of oxidative and inflammatory damage following reperfusion-will be comprehensively discussed within the context of current preclinical and clinical evidence. Finally, we highlight novel trends and future perspectives in the field of hypothermic MP in the context of recent findings of basic and translational research.

Machine perfusion strategies in liver transplantation

Machine perfusion is a hot topic in liver transplantation and several new perfusion concepts are currently developed. Prior to introduction into routine clinical practice, however, such perfusion approaches need to demonstrate their impact on liver function, post-transplant complications, utilization rates of high-risk organs, and cost benefits. Therefore, based on results of experimental and clinical studies, the community has to recognize the limitations of this technology. In this review, we summarize current perfusion concepts and differences between protective mechanisms of ex- and in-situ perfusion techniques. Next, we discuss which graft types may benefit most from perfusion techniques, and highlight the current understanding of liver viability testing. Finally, we present results from recent clinical trials involving machine liver perfusion, and analyze the value of different outcome parameters, currently used as endpoints for randomized controlled trials in the field.

The UK-DCD-Risk-Score - practical and new guidance for allocation of a specific organ to a recipient?

Introduction: Multiple factors contribute to the overall outcome in donation after circulatory death liver transplantation. The majority is however inconsistently reported with various acceptance criteria and thresholds, when to decline a specific graft. Recent improvement in outcome was based on an increased awareness of the cumulative risk, combining donor and recipient parameters, which encouraged the community to accept livers with an overall higher risk. Areas covered: This review pictures the large number of risk factors in this field with a special focus on parameters, which contribute to available prediction models. Next, features of the recently developed UK-DCD-Risk-Score, which led to a significantly impaired graft survival, above a suggested threshold of >10 score points, are discussed. The clinical impact of this new model on the background of other prediction tools with their subsequent limitations is highlighted in a next chapter. Finally, we provide suggestions, how to further improve outcomes in this challenging field of transplantation. Expert opinion: Despite the recent development of new prediction models, including the UK-DCD-Risk-Score, which provides a sufficient prediction of graft loss after DCD liver transplantation, the consideration of other confounders is essential to better understand the overall risk and metabolic liver status to improve the comparability of clinical studies. More uniform definitions and thresholds of individual risk factors are required.

Organ Preservation into the 2020s: The Era of Dynamic Intervention

Organ preservation has been of major importance ever since transplantation developed into a global clinical activity. The relatively simple procedures were developed on a basic comprehension of low-temperature biology as related to organs outside the body. In the past decade, there has been a significant increase in knowledge of the sequelae of effects in preserved organs, and how dynamic intervention by perfusion can be used to mitigate injury and improve the quality of the donated organs. The present review focuses on (1) new information about the cell and molecular events impacting on ischemia/reperfusion injury during organ preservation, (2) strategies which use varied compositions and additives in organ preservation solutions to deal with these, (3) clear definitions of the developing protocols for dynamic organ perfusion preservation, (4) information on how the choice of perfusion solutions can impact on desired attributes of dynamic organ perfusion, and (5) summary and future horizons.

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

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

Machine perfusion of the liver: Which is the best technique to mitigate ischaemia-reperfusion injury?

Longstanding research describes the mechanisms whereby the restoration of blood flow and reoxygenation (reperfusion) aggravates the ischaemic injury caused by a period of anoxia to a donor liver. This phenomenon, called ischaemia-reperfusion injury (IRI), leads to parenchymal cell death, microcirculatory failure, and inflammatory immune response. Clinically, IRI is the main factor responsible for the occurrence of posttransplant graft dysfunction and ischaemic-type biliary lesions. While extended criteria donor livers are more vulnerable to IRI, their utilisation is required to address the shortfall in donor organs. Thus, the mitigation of IRI should drive the setting of a new benchmark for marginal organ preservation. Herein, strategies incorporating different modalities of machine perfusion of the liver to alleviate IRI are discussed in conjunction with advantages and disadvantages of individual protocols. Techniques leading to reperfusion of the liver during machine perfusion (in situ normothermic regional perfusion and ex situ normothermic machine perfusion) may mitigate IRI by shortening the ischaemic period of the organs. This benefit potentially escalates from the minimum level, obtained following just partial alleviation of the ischaemic period, to the maximum level, which can be potentially achieved with ischaemia-free organ transplantation. Techniques that do not lead to reperfusion of the liver during machine perfusion (hypothermic, subnormothermic, and controlled-oxygenated rewarming) optimise mitochondrial oxidative function and replenish cellular energy stores, thereby lowering reactive oxygen species production as well as the activation of downstream inflammatory pathways during reperfusion. Further mechanistic insights into IRI may guide the development of donor-specific protocols of machine perfusion on the basis of the limitations of individual categories of extended criteria donor organs.

Combined Hypothermic and Normothermic Machine Perfusion Improves Functional Recovery of Extended Criteria Donor Livers

Hypothermic oxygenated perfusion (HOPE) and normothermic perfusion are seen as distinct techniques of ex situ machine perfusion of the liver. We aimed to demonstrate the feasibility of combining both techniques and whether it would improve functional parameters of donor livers into transplant standards. Ten discarded human donor livers had either 6 hours of normothermic perfusion (n = 5) or 2 hours of HOPE followed by 4 hours of normothermic perfusion (n = 5). Liver function was assessed according to our viability criteria; markers of tissue injury and hepatic metabolic activity were compared between groups. Donor characteristics were comparable. During the hypothermic perfusion phase, livers down-regulated mitochondrial respiration (oxygen uptake, P = 0.04; partial pressure of carbon dioxide perfusate, P = 0.04) and increased adenosine triphosphate levels 1.8-fold. Following normothermic perfusion, those organs achieved lower tissue expression of markers of oxidative injury (4-hydroxynonenal, P = 0.008; CD14 expression, P = 0.008) and inflammation (CD11b, P = 0.02; vascular cell adhesion molecule 1, P = 0.05) compared with livers that had normothermic perfusion alone. All livers in the combined group achieved viability criteria, whereas 40% (2/5) in the normothermic group failed (P = 0.22). In conclusion, this study suggests that a combined protocol of hypothermic oxygenated and normothermic perfusions might attenuate oxidative stress, tissue inflammation, and improve metabolic recovery of the highest-risk donor livers compared with normothermic perfusion alone.

Impact of machine perfusion of the liver on post-transplant biliary complications: A systematic review

AIM

To review the clinical impact of machine perfusion (MP) of the liver on biliary complications post-transplantation, particularly ischaemic-type biliary lesions (ITBL).

METHODS

This systematic review was performed in accordance with the Preferred Reporting Systematic Reviews and Meta-Analysis (PRISMA) protocol. The following databases were searched: PubMed, MEDLINE and Scopus. The keyword “liver transplantation” was used in combination with the free term “machine perfusion”. Clinical studies reporting results of transplantation of donor human livers following ex situ or in situ MP were analysed. Details relating to donor characteristics, recipients, technique of MP performed and post-operative biliary complications (ITBL, bile leak and anastomotic strictures) were critically analysed.

RESULTS

Fifteen articles were considered to fit the criteria for this review. Ex situ normothermic MP was used in 6 studies, ex situ hypothermic MP in 5 studies and the other 4 studies investigated in situ normothermic regional perfusion (NRP) and controlled oxygenated rewarming. MP techniques which have per se the potential to alleviate ischaemia-reperfusion injury: Such as hypothermic MP and NRP, have also reported lower rates of ITBL. Other biliary complications, such as biliary leak and anastomotic biliary strictures, are reported with similar incidences with all MP techniques. There is currently less clinical evidence available to support normothermic MP as a mitigator of biliary complications following liver transplantation. On the other hand, restoration of organ to full metabolism during normothermic MP allows assessment of hepatobiliary function before transplantation, although universally accepted criteria have yet to be validated.

CONCLUSION

MP of the liver has the potential to have a positive impact on post-transplant biliary complications, specifically ITBL, and expand extended criteria donor livers utilisation.

Normothermic ex-vivo liver perfusion: where do we stand and where to reach?

Nowadays liver transplantation is considered as the treatment of choice, however, the scarcity of suitable donor organs limits the delivery of care to the end-stage liver disease patients leading to the death while on the waiting list. The advent of ex-situ normothermic machine perfusion (NMP) has emerged as an alternative to the standard organ preservation technique, static cold storage (SCS). The newer technique promises to not only restore the normal metabolic activity but also attempt to recondition the marginal livers back to the pristine state, which are otherwise more susceptible to ischemic injury and foster the poor post-transplant outcomes. Areas covered: An extensive search of all the published literature describing the role of NMP based device in liver transplantation as an alternative to SCS was made on MEDLINE, EMBASE, Cochrane, BIOSIS, Crossref, Scopus databases and clinical trial registry on 10 May 2018. Expert commentary: The main tenet of NMP is the establishment of the physiological milieu, which permits aerobic metabolism to continue through out the period of preservation and limits the effects of ischemia-reperfusion (I/R) injury. In addition, by assessing the various metabolic and synthetic parameters the viability and suitability of donor livers for transplantation can be determined. This important technological advancement has scored satisfactorily on the safety and efficacy parameters in preliminary clinical studies. The present review suggests that NMP can offer the opportunity to assess and safely utilize the marginal donor livers if deemed appropriate for the transplantation. However, ongoing trials will determine its full potential and further adoption.

Onset of Donor Warm Ischemia Time in Donation After Circulatory Death Liver Transplantation: Hypotension or Hypoxia?

The aim of this study was to investigate the impact of hypoxia and hypotension during the agonal phase of donor warm ischemia time (DWIT) on hepatic ischemia/reperfusion injury (IRI) and complications in donation after circulatory death (DCD) liver transplantation. A retrospective single-center study of 93 DCD liver transplants (Maastricht type III) was performed. DWIT was divided into 2 periods: the agonal phase (from withdrawal of treatment [WoT] until circulatory arrest) and the asystolic phase (circulatory arrest until cold perfusion). A drop to <80% in peripheral oxygenation (SpO₂ ) was considered as hypoxia in the agonal phase (SpO₂ -agonal) and a drop to <50 mm Hg as hypotension in the agonal phase (SBP-agonal). Peak postoperative aspartate transaminase level >3000 U/L was considered as severe hepatic IRI. SpO₂ dropped within 2 minutes after WoT <80%, whereas the systolic blood pressure dropped to <50 mm Hg after 9 minutes, resulting in a longer SpO₂ -agonal (13 minutes) than SBP-agonal (6 minutes). In multiple logistic regression analysis, only duration of SpO₂ -agonal was associated with severe hepatic IRI (P = 0.006) and not SBP-agonal (P = 0.32). Also, recipients with long SpO₂ -agonal (>13 minutes) had more complications with a higher Comprehensive Complication Index during hospital admission (43.0 versus 32.0; P = 0.002) and 90-day graft loss (26% versus 6%; P = 0.01), compared with recipients with a short SpO₂ -agonal (≤13 minutes). Furthermore, Cox proportional hazard modeling identified a long SpO₂ -agonal as a risk factor for longterm graft loss (hazard ratio, 3.30; 95% confidence interval, 1.15-9.48; P = 0.03). In conclusion, the onset of hypoxia during the agonal phase is related to the severity of hepatic IRI and postoperative complications. Therefore, SpO₂ <80% should be considered as the start of functional DWIT in DCD liver transplantation.

Role of perfusion machines in the setting of clinical liver transplantation: A qualitative systematic review

Growing enthusiasm around machine perfusion (MP) in clinical liver transplantation (LT) may be the preamble for standardized practice to expand the donors' pool. The present systematic review investigated all the liver transplantations performed using grafts treated with MP. A systematic review of 309 papers was performed. Eventually, 27 articles were enrolled for the study. A total number of 173 cases were reported. Only 12 cohort studies were identified: the remaining ones were case reports or case series. Hypothermic machine perfusion was performed in 102 (59.0%), normothermic machine perfusion in 65 (37.6%), and controlled oxygenated rewarming in the remaining 6 (3.4%) cases. Donor characteristics, evaluation of graft quality, and endpoints were not homogeneous among the studies. Overall, post-LT results were excellent, with 1.2 and 4.0% of patients experienced primary non-function and ischemic-type biliary lesions, respectively.

CONCLUSION

Until now, no study exists that addresses the role of MP in selecting liver grafts available for LT. All the published studies mainly focused on the feasibility and safety of this new technology. Further research investigating the selection process of marginal donors is required.

Organ preservation: from the past to the future

Organ transplantation is the most effective therapy for patients with end-stage disease. Preservation solutions and techniques are crucial for donor organ quality, which is directly related to morbidity and survival after transplantation. Currently, static cold storage (SCS) is the standard method for organ preservation. However, preservation time with SCS is limited as prolonged cold storage increases the risk of early graft dysfunction that contributes to chronic complications. Furthermore, the growing demand for the use of marginal donor organs requires methods for organ assessment and repair. Machine perfusion has resurfaced and dominates current research on organ preservation. It is credited to its dynamic nature and physiological-like environment. The development of more sophisticated machine perfusion techniques and better perfusates may lead to organ repair/reconditioning. This review describes the history of organ preservation, summarizes the progresses that has been made to date, and discusses future directions for organ preservation.

Does Ischemia Free Liver Procurement Under Normothermic Perfusion Benefit the Outcome of Liver Transplantation?

Background

In contrast to conventional static cold preservation, normothermic machine perfusion (NMP) provides a beneficial alternative preservation of donor livers. However, the liver still suffered cold ischemic injury before attaching to the perfusion device.

Material/Methods

To prevent cold ischemic injury during procurement, we describe a novel procedure called ischemia-free liver procurement (IFLP) under NMP. Two liver grafts were procured from brain death donor under NMP and underwent 2-hour ex vivo NMP followed by 3 and 6 hours of static cold preservation. From procurement to post-transplantation course, evidence was collected to prove that IFLP is safe and benefits recipients.

Results

The post-transplantation course was uneventful, and the liver function tests and histological study revealed minimal hepatocyte and biliary epithelium injury during the preservation.

Conclusions

This preliminary experience demonstrates the clinical feasibility and safety of IFLP under NMP which offering opportunities to increase the number of donor livers and to improve the organ function.

Preconditioning-Like Properties of Short-Term Hypothermia in Isolated Perfused Rat Liver (IPRL) System

Hypothermia may attenuate the progression of ischemia-induced damage in liver. Here, we determined the effects of a brief cycle of hypothermic preconditioning applied before an ischemic/reperfusion (I/R) episode in isolated perfused rat liver (IPRL) on tissue damage and oxidative stress. Rats (male, 200–250 g) were anaesthetised with sodium pentobarbital (60 mg·kg⁻¹ i.p) and underwent laparatomy. The liver was removed and perfused in a temperature-regulated non-recirculating system. Livers were randomly divided into two groups (n = 6 each group). In the hypothermia-preconditioned group, livers were perfused with hypothermic buffer (cycle of 10 min at 22 °C plus 10 min at 37 °C) and the other group was perfused at 37 °C. Both groups were then submitted to 40 min of warm ischemia and 20 min of warm reperfusion. The level of tissue-damage indicators (alanine amino transferase, ALT; lactate dehydrogenase, LDH; and proteins), oxidative stress markers (thiobarbituric acid-reactive substances, TBARS; advanced oxidation protein products, AOPP; and glutathione, GSH) were measured in aliquots of perfusate sampled at different time intervals. Histological determinations and oxidative stress biomarkers in homogenized liver (AOPP; TBARS; nitric oxide derivatives, NO_x; GSH and glutathione disulphide, GSSG) were also made in the tissue at the end. Results showed that both damage and oxidant indicators significantly decreased while antioxidant increased in hypothermic preconditioned livers. In addition, homogenized liver determinations and histological observations at the end of the protocol corroborate the results in the perfusate, confirming the utility of the perfusate as a non-invasive method. In conclusion, hypothermic preconditioning attenuates oxidative damage and appears to be a promising strategy to protect the liver against IR injury.

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.

Hepatocellular cancer and recurrence after liver transplantation: what about the impact of immunosuppression?

Liver transplantation (LT) has originally been designed to treat hepatobiliary malignancies. The initial results of LT for hepatocellular cancer (HCC) were, however, dismal this mainly due to the poor patient selection procedure. Better surgical and perioperative care and, especially, the refinement of selection criteria led to a major improvement of results, making HCC nowadays (again!) one of the leading indications for LT. This evolution is clearly shown by the innumerable reports aiming to further extend inclusion criteria for LT in HCC patients. Nonetheless, the vast majority of papers only deals with morphologic (tumour diameter and number) and (only recently) biologic (tumour markers and response to locoregional treatment) parameters to do so. Curiously enough, the role of both the immune competent state of the recipient as well as the impact of both immunosuppression (IS) type and load has been very poorly addressed in this context, even if it has been shown for a long time, based on both basic and clinical research, that they all play a key role in the outcome of any oncologic treatment and in the development of de novo as well as recurrent tumours. This chapter aims to give, after a short introductive note about the currently used inclusion criteria of HCC patients for LT and about the role of IS in carcinogenesis, a comprehensive overview of the actual literature related to the impact of different immunosuppressive drugs and schemes on outcome of LT in HCC recipients. Unfortunately, up to now solid conclusions cannot be drawn due to the lack of high-level evidence studies caused by the heterogeneity of the studied patient cohorts and the lack of prospectively designed and randomized studies. Based on long-term personal experience with immunosuppressive handling in LT some proposals for further clinical research and practice are put forward. The strategy of curtailing and minimising IS should be explored in the growing field of transplant oncology taking thereby into account the immunological privilege of the liver allograft. These strategies will become more and more compelling when further extending the indications in which adjuvant chemotherapy will probably become an inherent part of the therapeutic scheme of HCC liver recipients.