Hypothermic reconditioning in organ transplantation:

End-ischemic pharmacological cocktail treatment to mitigate rewarming/reperfusion injury

Increasing shortage of donor organs leads to the acceptance of less than optimal grafts for transplantation, up to and including organs donated after circulatory standstill of the donor. Therefore, protective strategies and pharmacological interventions destined to reduce ischemia induced tissue injury are considered a worthwhile focus of research. The present study evaluates the potential of a multidrug pharmacological approach as single flush at the end of static preservation to protect the liver from reperfusion injury. Livers were retrieved from male Wistar rats 20 min after cardiac standstill. The organs were cold stored for 18 h, flushed with 20 ml of saline, kept at room temperature for 20 min, and reperfused at 37 °C with oxygenated Williams E solution. In half of the cases, the flush solution was supplemented with a cocktail containing metformin, bucladesine and cyclosporin A. Upon reperfusion, treated livers disclosed a massive mitigation of hepatic release of alanine aminotransferase and aspartate aminotransferase, along with a significant approximately 50 % reduction of radical mediated lipid peroxidation, caspase activation and release of TNF-alpha. Even after preceding cold preservation, a pharmacological cocktail given as single flush is capable to mitigate manifestations of reperfusion injury in the present model.

Recovery from cold-induced mitochondrial fission in endothelial cells requires reconditioning temperatures of ≥ 25◦C

Mitochondrial integrity and function constitute a prerequisite for cellular function and repair processes. We have previously shown that mitochondria of different cell types exhibit pronounced fragmentation under hypothermic conditions. This fission, accompanied by a decline of cellular ATP content, showed reversibility at 37◦C. However, it is unclear whether other temperatures as currently discussed for reconditioning of organs allow this reconstitution of mitochondria. Therefore, we here study in a model of cultured porcine aortic endothelial cells how different rewarming temperatures affect mitochondrial re-fusion and function. After 48 h cold incubation of endothelial cells in Krebs-Henseleit buffer with glucose (5 mM) and deferoxamine (1 mM) at 4◦C pronounced mitochondrial fission was observed. Following 2 h rewarming in cell culture medium, marked fission was still present after rewarming at 10◦ or 15◦C. At 21◦C some re-fusion was visible, which became more marked at 25◦C. Networks of tubular mitochondria similar to control cells only re-appeared at 37◦C. ATP content decreased at 4◦C from 3.6 ± 0.4 to 1.6 ± 0.4 nmol/106 cells and decreased even further when rewarming cells to 10◦ and 15◦C. Values after rewarming at 21◦C were similar to the values before rewarming while ATP gradually increased at higher rewarming temperatures. Metabolic activity dropped to 5 ± 11% of control values during 4◦C incubation and recovered with increasing temperatures to 36 ± 10% at 25◦C and 78 ± 17% at 37◦C. Integrity of monolayers, largely disturbed at 4◦C (large gaps between endothelial cells; cell injury ≤ 1%), showed partial recovery from 15◦C upwards, complete recovery at 37◦C. Endothelial repair processes (scratch assay) at 25◦C were clearly inferior to those at 37◦C. These data suggest that reconditioning temperatures below 21◦C are not optimal with regard to reconstitution of mitochondrial integrity and function. For this goal, temperatures of at least 25◦C appear required, with 30◦C being superior and 37◦C yielding the best results.

Shifting Paradigms for Suppressing Fibrosis in Kidney Transplants: Supplementing Perfusion Solutions With Anti-fibrotic Drugs

Great efforts have been made toward addressing the demand for donor kidneys. One of the most promising approaches is to use kidneys from donation after circulatory death donors. These kidneys, however, suffer from more severe ischemia and reperfusion injury than those obtained via donation after brain death and are thus more prone to develop interstitial fibrosis and tubular atrophy. Even though machine perfusion is increasingly used to reduce ischemia and reperfusion injury, there are no effective treatments available to ameliorate interstitial fibrosis and tubular atrophy, forcing patients to resume dialysis, undergo re-transplantation, or suffer from premature death. Safe and effective anti-fibrotic therapies are therefore greatly desired. We propose a new therapeutic approach in which machine perfusion solutions are supplemented with anti-fibrotic compounds. This allows the use of higher concentrations than those used in humans whilst eliminating side effects in other organs. To the authors' knowledge, no one has reviewed whether such an approach could reduce interstitial fibrosis and tubular atrophy; we therefore set out to explore its merit. In this review, we first provide background information on ischemia and reperfusion injury as well as interstitial fibrosis and tubular atrophy, after which we describe currently available approaches for preserving donor kidneys. We then present an evaluation of selected compounds. To identify promising compounds, we analyzed publications describing the effects of anti-fibrotic molecules in precision-cut kidneys slices, which are viable explants that can be cultured ex vivo for up to a few days whilst retaining functional and structural features. LY2109761, galunisertib, imatinib, nintedanib, and butaprost were shown to exert anti-fibrotic effects in slices within a relatively short timeframe (<48 h) and are therefore considered to be excellent candidates for follow-up ex vivo machine perfusion studies.

Preservation of Mitochondrial Coupling and Renal Function by Controlled Oxygenated Rewarming of Porcine Kidney Grafts

Background: Warm reperfusion after previous cold storage has been shown to have a negative impact on mitochondrial function of organ grafts. Here, we wanted to investigate whether a more controlled warming up of the cold graft by ex vivo machine perfusion with gradually elevated temperature from cold to normothermia (including comparison of two warming up protocols) prior to implantation would be effective in preventing mitochondrial dysfunction upon reperfusion. Methods: All experiments were conducted on porcine kidneys retrieved 15 min after cardiac arrest. After 18 h of cold storage in HTK solution (CS, n = 6), kidneys (n = 6) were subjected to 2 h of reconditioning machine perfusion starting with a hypothermic period followed by a gradual increase in perfusion temperature up to 35 °C (controlled oxygenated rewarming—COR). For a second group (n = 6), the slow warming up was begun instantly after connecting the graft onto the machine (iCOR). Functional recovery of all grafts was then observed upon normothermic reperfusion in vitro. At the conclusion of the experiments, tissue specimens were taken for immediate isolation and analysis of renal mitochondria. Results: COR resulted in a significantly and more than 3-fold increased glomerular filtration rate upon reperfusion, along with a significant higher tubular sodium reabsorption and lesser loss of glucose in comparison to the controls. Enzyme release (AST) was also massively reduced during the reperfusion period. Specific analysis at the mitochondrial level revealed significantly better coupling efficiency and spare respiratory capacity in the COR group compared to the cold storage group. Interestingly, additional experiments revealed that the omission of a hypothermic perfusion period did not deteriorate any of the results after COR, provided that the instant temperature increase from 10 to 35 °C was effectuated in the same controlled manner. Conclusion: Controlled rewarming after extended cold preservation effectively improves mitochondrial recovery upon reperfusion and early functional outcome of kidney grafts.

Beneficial effects of end-ischemic oxygenated machine perfusion preservation for split-liver transplantation in recovering graft function and reducing ischemia-reperfusion injury

This study examined the efficacy of end-ischemic hypothermic oxygenated machine perfusion preservation (HOPE) using an originally developed machine perfusion system for split-liver transplantation. Porcine split-liver grafts were created via 75% liver resection after 10 min of warm ischemia. In Group 1, grafts were preserved by simple cold storage (CS) for 8 h (CS group; n = 4). In Group 2, grafts were preserved by simple CS for 6 h and end-ischemic HOPE for 2 h (HOPE group; n = 5). All grafts were evaluated using an isolated ex vivo reperfusion model with autologous blood for 2 h. Biochemical markers (aspartate aminotransferase and lactate dehydrogenase levels) were significantly better immediately after reperfusion in the HOPE group than in the CS group. Furthermore, the HOPE group had a better histological score. The levels of inflammatory cytokines (tumor necrosis factor-α, interferon-γ, interleukin-1β, and interleukin-10) were significantly lower after reperfusion in the HOPE group. Therefore, we concluded that end-ischemic HOPE for split-liver transplantation can aid in recovering the graft function and reducing ischemia-reperfusion injury. HOPE, using our originally developed machine perfusion system, is safe and can improve graft function while attenuating liver injury due to preservation.

Advances in Kidney Preservation Techniques and Their Application in Clinical Practice

The use of cold preservation solutions to rapidly flush and cool the kidney followed by static cold storage in ice has been the standard kidney preservation technique for the last 50 y. Nonetheless, changing donor demographics that include organs from extended criteria donors and donation after circulatory death donors have led to the adoption of more diverse techniques of preservation. Comparison of hypothermic machine perfusion and static cold storage techniques for deceased donor kidneys has long been debated and is still contested by some. The recent modification of hypothermic machine perfusion techniques with the addition of oxygen or perfusion at subnormothermic or near-normothermic temperatures are promising strategies that are emerging in clinical practice. In addition, the use of normothermic regional perfusion to resuscitate abdominal organs of donation after circulatory death donors in situ before cold flushing is also increasingly being utilized. This review provides a synopsis of the different types of preservation techniques including their mechanistic effects and the outcome of their application in clinical practice for different types of donor kidney.

Persufflation—Current State of Play

With the ever-increasing disparity between the number of patients waiting for organ transplants and the number organs available, some patients are unable to receive life-saving transplantation in time. The present, widely-used form of preservation is proving to be incapable of maintaining organ quality during long periods of preservation and meeting the needs of an ever-changing legislative and transplantation landscape. This has led to the need for improved preservation techniques. One such technique that has been extensively researched is gaseous oxygen perfusion or Persufflation (PSF). This method discovered in the early 20th century has shown promise in providing both longer term preservation and organ reconditioning capabilities for multiple organs including the liver, kidneys, and pancreas. PSF utilises the organs own vascular network to provide oxygen to the organ tissue and maintain metabolism during preservation to avoid hypoxic damage. This review delves into the history of this technique, its multiple different approaches and uses, as well as in-depth discussion of work published in the past 15 years. Finally, we discuss exciting commercial developments which may help unlock the potential for this technique to be applied at scale.

Hypertonic saline solution decreases oxidative stress in liver hypothermic ischemia

BACKGROUND

Liver ischemia reperfusion injury is still an unsolved problem in liver surgery and transplantation. In this setting, hypothermia is the gold standard method for liver preservation for transplantation. Hypertonic saline solution reduces inflammatory response with better hemodynamic recovery in several situations involving ischemia reperfusion injury. Here, we investigated the effect of hypertonic saline solution in hypothermic liver submitted to ischemia reperfusion injury.

METHODS

Fifty male rats were divided into 5 groups: SHAM, WI (animals submitted to 40 minutes of partial warm liver ischemia and reperfusion), HI (animals submitted to 40 minutes hypothermic ischemia), HSPI (animals submitted to hypothermic ischemia and treated with 7.5% hypertonic saline solution preischemia), and HSPR (animals submitted to hypothermic ischemia and treated with hypertonic saline solution previously to liver reperfusion). Four hours after reperfusion, the animals were euthanized to collect liver and blood samples.

RESULTS

Aspartate aminotransferase and alanine aminotransferase, histologic score, and hepatocellular necrosis were significantly decreased in animals submitted to hypothermia compared with the warm ischemia group. Malondialdehyde was significantly decreased in hypothermic groups with a further decrease when hypertonic saline solution was administrated preischemia. Hypothermic groups also showed decreased interleukin-6, interleukin-10, and tumor necrosis factor-α concentrations and better recovery of bicarbonate, base excess, lactate, and glucose blood concentrations. Moreover, hypertonic saline solution preischemia was more effective at controlling serum potassium concentrations.

CONCLUSION

Hypertonic saline solution before hypothermic hepatic ischemia decreases hepatocellular oxidative stress, cytokine concentrations, and promotes better recovery of acid-base disorders secondary to liver ischemia reperfusion.

Potential Applications of Extracellular Vesicles in Solid Organ Transplantation

Extracellular vesicles (EVs) play an important role in cell-to-cell communication by delivering coding and non-coding RNA species and proteins to target cells. Recently, the therapeutic potential of EVs has been shown to extend to the field of solid organ transplantations. Mesenchymal stromal cell-derived EVs (MSC-EVs) in particular have been proposed as a new tool to improve graft survival, thanks to the modulation of tolerance toward the graft, and to their anti-fibrotic and pro-angiogenic effects. Moreover, MSC-EVs may reduce ischemia reperfusion injury, improving the recovery from acute damage. In addition, EVs currently considered helpful tools for preserving donor organs when administered before transplant in the context of hypothermic or normothermic perfusion machines. The addition of EVs to the perfusion solution, recently proposed for kidney, lung, and liver grafts, resulted in the amelioration of donor organ viability and functionality. EVs may therefore be of therapeutic interest in different aspects of the transplantation process for increasing the number of available organs and improving their long-term survival.

Protective Role of mTOR in Liver Ischemia/Reperfusion Injury: Involvement of Inflammation and Autophagy

Liver ischemia/reperfusion (IR) injury is a common phenomenon after liver resection and transplantation, which often results in liver graft dysfunction such as delayed graft function and primary nonfunction. The mammalian target of rapamycin (mTOR) is an evolutionarily highly conserved serine/threonine protein kinase, which coordinates cell growth and metabolism through sensing environmental inputs under physiological or pathological conditions, involved in the pathophysiological process of IR injury. In this review, we mainly present current evidence of the beneficial role of mTOR in modulating inflammation and autophagy under liver IR to provide some evidence for the potential therapies for liver IR injury.

Nonautonomous dynamics of acute cell injury

Medical conditions due to acute cell injury, such as stroke and heart attack, are of tremendous impact and have attracted huge amounts of research effort. The biomedical research that seeks cures for these conditions has been dominated by a qualitative, inductive mind-set. Although the inductive approach has not been effective in developing medical treatments, it has amassed enough information to allow construction of quantitative, deductive models of acute cell injury. In this work we develop a modeling approach by extending an autonomous nonlinear dynamic theory of acute cell injury that offered new ways to conceptualize cell injury but possessed limitations that decrease its effectiveness. Here we study the global dynamics of the cell injury theory using a nonautonomous formulation. Different from the standard scenario in nonlinear dynamics that is determined by the steady state and fixed points of the model equations, in this nonautonomous model with a trivial fixed point, the system property is dominated by the transient states and the corresponding dynamic processes. The model gives rise to four qualitative types of dynamical patterns that can be mapped to the behavior of cells after clinical acute injuries. The nonautonomous theory predicts the existence of a latent stress response capacity (LSRC) possessed by injured cells. The LSRC provides a theoretical explanation of how therapies, such as hypothermia, can prevent cell death after lethal injuries. The nonautonomous theory of acute cell injury provides an improved quantitative framework for understanding cell death and recovery and lays a foundation for developing effective therapeutics for acute injury.

Effect of the Selective NLRP3 Inflammasome Inhibitor mcc950 on Transplantation Outcome in a Pig Liver Transplantation Model With Organs From Donors After Circulatory Death Preserved by Hypothermic Machine Perfusion

BACKGROUND

We investigated whether the outcome of organs from donors after circulatory death (DCD) can be improved by the addition of mcc950 to the perfusate of the hypothermic machine perfusion (HMP) system and intravenous mcc950 injection after transplantation in a pig liver transplantation model.

METHODS

Thirty-six healthy Bama mini pigs randomized into 3 groups. All the DCD livers were preserved in an HMP system after 2 hours of simple cold storage. In HMP-Postop group, mcc950 was added to the perfusate; in the control group and Postop group, the perfusate was normal LPS. After transplantation, the pigs in the Postop group and HMP-Postop group were intravenously administered 3 mg/kg mcc950, at the time of reperfusion and on day 2 and day 3 after transplantation. During the 3-day follow-up period, general operative characteristics, and serological markers and histological features related to ischemia reperfusion injury were examined.

RESULTS

The HMP-Postop group suffer the lightest ischemia reperfusion injury (IRI), and functioned best after transplantation. Model for the Early Allograft Function Score (predictor of long-term survival), degree of injury in the hepatocytes and rate of apoptosis was lowest in the HMP-Postop group. Further, in the HMP-Postop group, the nucleotide-binding domain leucine-rich repeat containing family pyrin domain containing 3 inflammasome pathway activation was lowest, and the level of IL-1β was lowest. Postop group functioned better than control group, but not comparable with HMP-Postop group.

CONCLUSIONS

The outcome of DCD organs can be improved by the addition of mcc950 to the perfusate of the HMP system and intravenous injection of mcc950 after transplantation.

Machine Perfusion and the Pancreas: Will It Increase the Donor Pool?

PURPOSE OF REVIEW

Pancreas transplantation enables complete patient independence from exogenous insulin administration and increases both patient survival and quality of life. Despite this, there has been a decline in pancreas transplantation for the past 20 years, influenced by changing donor demographics with more high-risk extended criteria (ECD) and donation after cardiac death (DCD) donors. This review discusses whether the advent of machine perfusion (MP), if extended to the pancreas, can increase the pool of suitable donor organs.

RECENT FINDINGS

Hypothermic and normothermic MP, as forms of preservation deemed superior to cold storage for high-risk kidney and liver donor organs, have opened the avenue for translation of this work into the pancreas. Recent experimental models of porcine and human ex-vivo pancreatic MP are promising. Applications of MP to the pancreas however need refinement-focusing on perfusion protocols and viability assessment tools. Emerging research shows pancreatic MP can potentially offer superior preservation capacity, the ability to both resuscitate and manipulate organs, and assess functional and metabolic organ viability. The future of MP will lie in organ assessment and resuscitation after retrieval, where ultimately organs initially considered high risk and unsuitable for transplantation will be optimised and transformed, making them then available for clinical use, thus increasing the pool of suitably viable pancreata for transplantation.

Oxygen Persufflation in Liver Transplantation Results of a Randomized Controlled Trial

Oxygen persufflation has shown experimentally to favorably influence hepatic energy dependent pathways and to improve survival after transplantation. The present trial evaluated oxygen persufflation as adjunct in clinical liver preservation. A total of n = 116 adult patients (age: 54 (23–68) years, M/F: 70/46), were enrolled in this prospective randomized study. Grafts were randomized to either oxygen persufflation for ≥2 h (O2) or mere cold storage (control). Only liver grafts from donors ≥55 years and/or marginal grafts after multiple rejections by other centers were included. Primary endpoint was peak-aspartate aminotransferase (AST) level until post-operative day 3. Standard parameters including graft- and patient survival were analyzed by uni- and multivariate analysis. Both study groups were comparable except for a longer ICU stay (4 versus 3 days) of the donors and a higher recipient age (57 versus 52 years) in the O2-group. Serum levels of TNF alpha were significantly reduced after oxygen persufflation (p < 0.05). Median peak-AST values did not differ between the groups (O2: 580 U/l, control: 699 U/l). Five year graft- and patient survival was similar. Subgroup analysis demonstrated a positive effect of oxygen persufflation concerning the development of early allograft dysfunction (EAD), in donors with a history of cardiopulmonary resuscitation and elevated ALT values, and concerning older or macrosteatotic livers. This study favors pre-implantation O2-persufflation in concrete subcategories of less than optimal liver grafts, for which oxygen persufflation can be considered a safe, cheap and easy applicable reconditioning method.

Porcine Isolated Liver Perfusion for the Study of Ischemia Reperfusion Injury: A Systematic Review

BACKGROUND

Understanding ischemia reperfusion injury (IRI) is essential to further improve outcomes after liver transplantation (LT). Porcine isolated liver perfusion (ILP) is increasingly used to reproduce LT-associated IRI in a strictly controlled environment. However, whether ILP is a reliable substitute of LT was never validated.

METHODS

We systematically reviewed the current experimental setups for ILP and parameters of interest reflecting IRI.

RESULTS

Isolated liver perfusion was never compared with transplantation in animals. Considerable variability exists between setups, and comparative data are unavailable. Experience so far suggests that centrifugal pump(s) with continuous flow are preferred to reduce the risk of embolism. Hepatic outflow can be established by cannulation of the inferior vena cava or freely drained in an open bath. Whole blood at approximately 38°C, hematocrit of 20% or greater, and the presence of leukocytes to trigger inflammation is considered the optimal perfusate. A number of parameters related to the 4 liver compartments (hepatocyte, cholangiocyte, endothelium, immune cells) are available; however, their significance and relation to clinical outcomes is not well described.

CONCLUSIONS

Porcine ILP provides a reproducible model to study early IRI events. As all models, it has its limitations. A standardization of the setup would allow comparison of data and progress in the field.

Outcomes of DCD liver transplantation using organs treated by hypothermic oxygenated perfusion before implantation

BACKGROUND & AIMS

Donation after circulatory death (DCD) liver transplantation is known for potentially worse outcomes because of higher rates of graft non-function or irreversible cholangiopathy. The impact of machine liver perfusion techniques on these complications remains elusive. We aimed to provide data on 5-year outcomes in patients receiving DCD liver transplants, after donor organs had been treated by hypothermic oxygenated perfusion (HOPE).

METHODS

Fifty HOPE-treated DCD liver transplants performed in Zurich between 2012 and 3/2017 were matched with 50 primary donation after brain death (DBD) liver transplants, and with 50 untreated DCD liver transplants in Birmingham. Match factors focussed on short cold ischaemia, comparable recipient age and low recipient laboratory model for end-stage liver disease scores. Primary endpoints were post-transplant complications, and non-tumour-related patient death or graft loss.

RESULTS

Despite extended donor warm ischaemia, HOPE-treated DCD liver transplants achieved similar overall graft survival, compared to standard DBD liver transplants. Particularly, graft loss due to any non-tumour-related causes occurred in 8% (4/50) of cases. In contrast, untreated DCD livers resulted in non-tumour-related graft failure in one-third (16/50) of cases (p = 0.005), despite significantly (p <0.001) shorter functional donor warm ischaemia. Five-year graft survival, censored for tumour death, was 94% for HOPE-treated DCD liver transplants vs. 78% in untreated DCD liver transplants (p = 0.024).

CONCLUSIONS

The 5-year outcomes of HOPE-treated DCD liver transplants were similar to those of DBD primary transplants and superior to those of untreated DCD liver transplants, despite much higher risk. These results suggest that a simple end-ischaemic perfusion approach is very effective and may open the field for safe utilisation of extended DCD liver grafts.

LAY SUMMARY

Machine perfusion techniques are currently being introduced into the clinic, with the aim of optimising injured grafts prior to implantation. While short-term effects of machine liver perfusion have been frequently reported in terms of hepatocellular enzyme release and early graft function, the long-term benefit on irreversible graft loss has been unclear. Herein, we report on 5-year graft survival in donation after cardiac death livers, treated either by conventional cold storage, or by 1-2 h of hypothermic oxygenated perfusion (HOPE) after cold storage. Graft loss was significantly less in HOPE-treated livers, despite longer donor warm ischaemia times. Therefore, HOPE after cold storage appears to be a simple and effective method to treat high-risk livers before implantation.

Cold flush after dynamic liver preservation protects against ischemic changes upon reperfusion - an experimental study

Ex vivo machine perfusion of the liver after cold storage has found to be most effective if combined with controlled oxygenated rewarming up to (sub)‐normothermia. On disconnection of the warm graft from the machine, most surgeons usually perform a cold flush of the organ as protection against the second warm ischemia incurred upon implantation. Experimental evidence, however, is lacking and protective effect of deep hypothermia has been challenged for limited periods of liver ischemia in other models. A first systematic test was carried out on porcine livers, excised 30 min after cardiac arrest, subjected to 18 h of cold storage in UW and then machine perfused for 90 min with Aqix‐RSI solution. During machine perfusion, livers were gradually rewarmed up to 20 °C. One group (n = 6) was then reflushed with 4 °C cold Belzer UW solution whereas the second group (n = 6) remained without cold flush. All livers were exposed to 45 min warm ischemia at room temperature to simulate the surgical implantation period. Organ function was evaluated in an established reperfusion model using diluted autologous blood. Cold reflush after disconnection from the machine resulted in a significant increase in bile production upon blood reperfusion, along with a significant reduction in transaminases release alanine aminotransferase and of the intramitochondrial enzyme glutamate dehydrogenase. Interestingly, free radical‐mediated lipid peroxidation was also found significantly lower after cold reflush. No differences between the groups could be evidenced concerning histological injury and recovery of hepatic energy metabolism (tissue content of adenosine triphosphate). Post‐machine preservation cold reflush seems to be beneficial in this particular setting, even if the organs are warmed up only to 20 °C, without notion of adverse effects, and should therefore be implemented in the protocol.

Transplantation of Cold Stored Porcine Kidneys After Controlled Oxygenated Rewarming

The concept of "controlled oxygenated rewarming" (COR) using ex vivo machine perfusion after cold storage was evaluated as tool to improve renal graft function after transplantation. Renal function after 20 min warm ischemia and 21 h cold storage was studied in an auto-transplant model in pigs (25-30 kg, n = 6 per group). In the study group, preimplant ex vivo machine perfusion for 90 min was added after cold storage, including gentle warming up of the graft to 20°C (COR). Kidneys that were only cold stored for 21 h served as controls. In vivo follow up was one week; the remaining native kidney was removed during transplantation. COR significantly improved cortical microcirculation upon early reperfusion and reduced free radical mediated injury and cellular apoptosis. Post-transplant kidney function (peak levels in serum) was also largely and significantly improved in comparison to the control group. A weak inverse correlation was found between renal flow during COR and later peak creatinine after transplantation (r²  = 0.5), better values were seen for oxygen consumption, measured during machine perfusion at 20°C (r²  = 0.81). Gentle graft rewarming prior to transplantation by COR improves post-transplant graft outcome and may also be a valuable adjunct in pretransplant graft assessment.

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.

Hypothermic machine perfusion in liver transplantation

PURPOSE OF THE REVIEW

The purpose of the review is to report recent human application of hypothermic machine liver perfusion, and to discuss potential protective mechanisms.

RECENT FINDINGS

Human application of hypothermic machine liver perfusion is still very limited. Currently, three transplant centers apply this novel treatment in donation after cardiac death (DCD) or donation after brain death (DBD) liver grafts. In all cases, endischemic perfusion was performed after initial cold storage for organ transport. Perfusion conditions differ slightly in terms of oxygenation (pO2 15-60 kPa), perfusion route (dual vs. portal), perfusion time (2-4 h), and perfusate.

SUMMARY

The current data support the hypothesis that applying endischemic hypothermic machine liver perfusion protects extended criteria DBD and DCD livers from initial reperfusion injury, with better graft function and less biliary complications. Hypothermic machine perfusion may therefore offer revitalization of liver grafts before implantation by a simple and practical perfusion technique with a high impact on enlarging the donor pool. Multicentric phase III randomized control trials in DBD and DCD liver transplantation have been initiated to further test this strategy, which may establish machine liver perfusion in the clinical setting.

Antipsychotic inductors of brain hypothermia and torpor-like states: perspectives of application

Hypothermia and hypometabolism (hypometabothermia) normally observed during natural hibernation and torpor, allow animals to protect their body and brain against the damaging effects of adverse environment. A similar state of hypothermia can be achieved under artificial conditions through physical cooling or pharmacological effects directed at suppression of metabolism and the processes of thermoregulation. In these conditions called torpor-like states, the mammalian ability to recover from stroke, heart attack, and traumatic injuries greatly increases. Therefore, the development of therapeutic methods for different pathologies is a matter of great concern. With the discovery of the antipsychotic drug chlorpromazine in the 1950s of the last century, the first attempts to create a pharmacologically induced state of hibernation for therapeutic purposes were made. That was the beginning of numerous studies in animals and the broad use of therapeutic hypothermia in medicine. Over the last years, many new agents have been discovered which were capable of lowering the body temperature and inhibiting the metabolism. The psychotropic agents occupy a significant place among them, which, in our opinion, is not sufficiently recognized in the contemporary literature. In this review, we summarized the latest achievements related to the ability of modern antipsychotics to target specific receptors in the brain, responsible for the initiation of hypometabothermia.

Liver graft preconditioning, preservation and reconditioning

Liver transplantation is the successful treatment of end-stage liver disease; however, the ischaemia-reperfusion injury still jeopardizes early and long-term post-transplant outcomes. In fact, ischaemia-reperfusion is associated with increased morbidity and graft dysfunction, especially when suboptimal donors are utilized. Strategies to reduce the severity of ischaemia-reperfusion can be applied at different steps of the transplantation process: organ procurement, preservation phase or before revascularization. During the donor procedure, preconditioning consists of pre-treating the graft prior to a sustained ischaemia either by a transient period of ischaemia-reperfusion or administration of anti-ischaemic medication, although a multi-pharmacological approach seems more promising. Different preservation solutions were developed to maintain graft viability during static cold storage, achieving substantial results in terms of liver function and survival in good quality organs but not in suboptimal ones. Indeed, preservation solutions do not prevent dysfunction of poor quality organs and are burdened with inadequate preservation of the biliary epithelium. Advantages derived from either hypo- or normothermic machine perfusion are currently investigated in experimental and clinical settings, suggesting a reconditioning effect possibly improving hepatocyte and biliary preservation and resuscitating graft function prior to transplantation. In this review, we highlight acquired knowledge and recent advances in liver graft preconditioning, preservation and reconditioning.

Challenges for Production of Human Transplantable Organ Grafts

The described research methods explain how you could generate a three-dimensional kidney, based on recent research results. The first method is to fabricate human organs in a pig body. The second is to transplant the so-called "organ bud" into a patient's body for further development. The third method is to regenerate organs by filling cells into the cytoskeleton as a scaffold. Research for the in vitro fabrication of organ buds has been elaborately accelerated. The organ bud transplantation has been confronted with issues of continuity with the original organs, so the development of technology for achieving continuity between a transplanted organ bud and the existing organs is progressing well. The "organ fabrication" methodology, whereby cells are placed into completely decellularized organs, is supported by recent research results using pig organs taking the size of humans into consideration.

An ex vivo comparison of adenosine and lidocaine solution and University of Wisconsin solution for hypothermic machine perfusion of porcine kidneys: potential for development

BACKGROUND

The optimal hypothermic machine perfusion (HMP) solution has not yet been developed. An adenosine and lidocaine (AL) solution has been shown to be protective in cardiac preservation. The aim of the present study was to examine a modified AL solution with low Ca²⁺, 16 mM Mg²⁺, and 4% albumin on kidney preservation compared with University Wisconsin solution (UW).

METHODS

Twenty donation of organs after cardiac death porcine kidneys underwent HMP for 10 h (AL, n = 10; UW, n = 10) and then 2 h of normothermic reperfusion. Perfusion dynamics, functional parameters, histology, and real-time microdialysis were used to assess kidney responses and viability.

RESULTS

During HMP, modified AL-perfused kidneys maintained higher flow rates (21.5 versus 17.9 mL/min/100 g, P = 0.01), with perfusion flow index during the first 3 h 25% greater than with UW (AL = 0.50 ± 0.2, UW = 0.40 ± 0.17 mL/min/100 g/mmHg; P = 0.03), followed by an increase in UW kidneys which was not significantly different to AL over the remaining 7 h (0.54 versus 0.55 mL/min/100 g/mmHg, respectively). During warm reperfusion, there were no significant differences between the two HMP groups in creatinine clearance, oxygen, and glucose consumption between groups. Modified AL kidneys had significantly lower perfusate lactates (3.1 versus 4.1 mmol/L, P = 0.04) during reperfusion and lower cortical lactate levels (AL = 0.66 ± 0.31, UW = 0.89 ± 0.53 mM, P = 0.33). Histology showed similar degrees of reperfusion injury.

CONCLUSIONS

We conclude that HMP with modified AL solution showed improved perfusion compared with UW and lower perfusate lactate levels during warm reperfusion. Further modification of the AL composition is warranted and may lead to more rapid kidney stabilization and improved graft viability assessment, potentially expanding donor pools.

Beneficial Effect of Short Pretransplant Period of Hypothermic Pulsatile Perfusion of the Warm-Ischemic Kidney after Cold Storage: Experimental Study

Warm ischemia (WI) produces a significant deleterious effect in potential kidney grafts. Hypothermic machine perfusion (HMP) seems to improve immediate graft function after transplant. Our aim was to analyze the effect of short pretransplant periods of pulsatile HMP on histology and renal injury in warm-ischemic kidneys. Twelve minipigs were used. WI was achieved in the right kidney by applying a vascular clamp for 45 min. After nephrectomy, autotransplant was performed following one of two strategies: cold storage of the kidneys or cold storage combined with perfusion in pulsatile HMP. The graft was removed early to study renal morphology, inflammation (fibrosis), and apoptosis. Proinflammatory activity and fibrosis were less pronounced after cold storage of the kidneys with HMP than after cold storage only. The use of HMP also decreased apoptosis compared with cold storage only. The detrimental effects on cells of an initial and prolonged period of WI seem to improve with a preservation protocol that includes a short period of pulsatile HMP after cold storage and immediately before the transplant, in comparison with cold storage only.

Using pediatric liver grafts (≤ 6 yr) for adult recipients: A considerable option?

In LT, the common policy is to allocate pediatric liver grafts to pediatric recipients. Pediatric organs are also offered to adults if there is no pediatric recipient. However, they are rarely accepted for adult recipients. So far, there is no information available reporting outcome of LT in adult recipients using pediatric livers from donors ≤ 6 yr. In this study, we included nine adult recipients (seven females and two males) who received grafts from children ≤ 6 yr from January 2008 to December 2013. We evaluated the graft quality, the GBWR and analyzed the recipients' perioperative course. Laboratory samples and graft perfusion were analyzed. Nine adults with a median age of 49 yr (range: 25-65) and a median weight of 60 kg (range: 48-64) underwent LT with a pediatric donor graft. Median donor age was five yr (range: 3-6). Median GBWR was 1.02 (range: 0.86-1.45). After a median follow-up of 3.9 yr (range: 11 months-6.6 yr), patient survival was 100%; graft survival was 89%. One patient needed re-transplantation on the second postoperative day due to PNF. Eight recipients were discharged from the ICU after 2-9 days with a regular graft function. Doppler scans revealed regular flow patterns at any time. Only if denied for pediatric recipients, the use of pediatric livers from donors ≤ 6 yr for adult recipients is a considerable option.

Influence of Factors of Cryopreservation and Hypothermic Storage on Survival and Functional Parameters of Multipotent Stromal Cells of Placental Origin

Human placenta is a highly perspective source of multipotent stromal cells (MSCs) both for the purposes of patient specific auto-banking and allogeneic application in regenerative medicine. Implementation of new GMP standards into clinical practice enforces the search for relevant methods of cryopreservation and short-term hypothermic storage of placental MSCs. In this paper we analyze the effect of different temperature regimes and individual components of cryoprotective media on viability, metabolic and culture properties of placental MSCs. We demonstrate (I) the possibility of short-term hypothermic storage of these cells; (II) determine DMSO and propanediol as the most appropriate cryoprotective agents; (III) show the possibility of application of volume expanders (plasma substituting solutions based on dextran or polyvinylpyrrolidone); (IV) reveal the priority of ionic composition over the serum content in cryopreservation media; (V) determine a cooling rate of 1°C/min down to -40°C followed by immersion into liquid nitrogen as the optimal cryopreservation regime for this type of cells. This study demonstrates perspectives for creation of new defined cryopreservation methods towards GMP standards.

Challenges to liver transplantation and strategies to improve outcomes

Liver transplantation (LT) is a highly successful treatment for many patients with nonmalignant and malignant liver diseases. However, there is a worldwide shortage of available organs; many patients deteriorate or die while on waiting lists. We review the important clinical challenges to LT and the best use of the scarce organs. We focus on changes in indications for LT and discuss scoring systems to best match donors with recipients and optimize outcomes, particularly for the sickest patients. We also cover controversial guidelines for the use of LT in patients with hepatocellular carcinoma and cholangiocarcinoma. Strategies to increase the number of functional donor organs involve techniques to perfuse the organs before implantation. Partial LT (living donor and split liver transplantation) techniques might help to overcome organ shortages, and we discuss small-for-size syndrome. Many new developments could increase the success of this procedure, which is already one of the major achievements in medicine during the second part of the 20th century.

New strategies and concepts in organ preservation

Organ transplantation is still affected by a notable degree of preservation-associated ischemia and reperfusion injury, which can seriously hamper early graft function. The increasing extension of the criteria for donor organ acceptance, especially for organs that have suffered from periods of warm ischemic injury prior to graft retrieval, results in even higher demands on preserving these ischemia-sensitive grafts. Growing attention is thus directed towards more dynamic preservation methods instead of simple static storage. Particularly in grafts that are retrieved after cardiac standstill of the donor, provision of oxygen to enable some kind of regenerative metabolism appears to be desirable, although the optimal temperature for oxygenated preservation/revitalization is still under debate. Hybrid solutions, comprising conventional cold storage for ease of graft procurement and transportation together with more sophisticated 'in-house' reconditioning protocols after arrival at the implantation clinic, might help to minimize graft injury during the critical transition from preservation to reperfusion.

One or 4 h of "in-house" reconditioning by machine perfusion after cold storage improve reperfusion parameters in porcine kidneys

In-house machine perfusion after cold storage (hypothermic reconditioning) has been proposed as convenient tool to improve kidney graft function. This study investigated the role of machine perfusion duration for early reperfusion parameters in porcine kidneys. Kidney function after cold preservation (4 °C, 18 h) and subsequent reconditioning by one or 4 h of pulsatile, nonoxygenated hypothermic machine perfusion (HMP) was studied in an isolated kidney perfusion model in pigs (n = 6, respectively) and compared with simply cold-stored grafts (CS). Compared with CS alone, one or 4 h of subsequent HMP similarly and significantly improved renal flow and kidney function (clearance and sodium reabsorption) upon warm reperfusion, along with reduced perfusate concentrations of endothelin-1 and increased vascular release of nitric oxide. Molecular effects of HMP comprised a significant (vs CS) mRNA increase in the endothelial transcription factor KLF2 and lower expression of endothelin that were observed already at the end of one-hour HMP after CS. Reconditioning of cold-stored kidneys is possible, even if clinical logistics only permit one hour of therapy, while limited extension of the overall storage time by in-house machine perfusion might also allow for postponing of transplantation from night to early day work.

The effects of profound hypothermia on pancreas ischemic injury: a new experimental model

OBJECTIVE

Pancreatic ischemia-reperfusion (IR) has a key role in pancreas surgery and transplantation. Most experimental models evaluate the normothermic phase of the IR. We proposed a hypothermic model of pancreas IR to evaluate the benefic effects of the cold ischemic phase.

METHODS

We performed a reproducible model of hypothermic pancreatic IR. The ischemia was induced in the pancreatic tail portion (1-hour ischemia, 4-hour reperfusion) in 36 Wistar rats. They are divided in 3 groups as follows: group 1 (control), sham; group 2, normothermic IR; and group 3, hypothermic IR. In group 3, the temperature was maintained as close to 4.5°C. After reperfusion, serum amylase and lipase levels, inflammatory mediators (tumor necrosis factor α, interleukin 6), and pancreas histology were evaluated.

RESULTS

In pancreatic IR groups, amylase, cytokines, and histological damage were significantly increased when compared with group 1. In the group 3, we observed a significant decrease in tumor necrosis factor α (P = 0.004) and interleukin 6 (P = 0.001) when compared with group 2. We did not observe significant difference in amylase (P = 0.867), lipase (P = 0.993), and histology (P = 0.201).

CONCLUSIONS

In our experimental model, we reproduced the cold phase of pancreas IR, and the pancreas hypothermia reduced the inflammatory mediators after reperfusion.

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.

Supercooling enables long-term transplantation survival following 4 days of liver preservation

The realization of long–term human organ preservation will have groundbreaking effects on the current practice of transplantation. Herein we present a novel technique based on sub–zero non–freezing tissue preservation and extracorporeal machine perfusion that allows transplantation of rat livers preserved for up to 4 days, thereby tripling the viable preservation duration.

DCD pigs' kidneys analyzed by MRI to assess ex vivo their viability

BACKGROUND

Magnetic resonance imaging (MRI) gadolinium-perfusion was applied in simulated Donation after Cardiac Death (DCD) in porcine kidneys to measure intrarenal perfusion. Adenosine triphosphate (ATP) resynthesis during oxygenated hypothermic perfusion was compared to evaluate the "ex vivo organ viability". Adenine nucleotide (AN) was measured by P nuclear magnetic resonance (NMR) spectroscopy. Whereas this latter technique requires sophisticated hardware, gadolinium-perfusion can be realized using any standard proton-MRI scanner. The aim of this work was to establish a correlation between the two methods.

METHODS

Twenty-two porcine kidneys presenting up to 90 min warm ischemia were perfused with oxygenation at 4 °C using our magnetic resonance-compatible machine. During the perfusion, P NMR spectroscopy and gadolinium-perfusion sequences were performed. Measures obtained from the gadolinium-perfusion were the speed of elimination of the cortical gadolinium and the presence or absence of a corticomedullar shunt. For ATP resynthesis analysis, P chemical shift imaging was acquired and analyzed. All the kidneys have been submitted to histologic examination.

RESULTS

ATP resynthesis was observed in all organs presenting a cortical gadolinium elimination slope of (-) 23° or greater. In organs with lower gadolinium elimination, no AN or only precursors were detected. This study reveals a link between the two methods and demonstrates ex vivo viability in 93% of the analyzed kidneys. Benefits and side effects of both methods are discussed.

CONCLUSION

Oxygenated hypothermic perfusion enables the evaluation of kidneys in DCD simulated situation; gadolinium-perfusion can be introduced into any center equipped with a proton-MRI scanner allowing results superposable with ATP measurement.

Machine perfusion in solid organ transplantation: where is the benefit?

BACKGROUND

Machine perfusion (MP) in solid organ transplantation has been a topic of variable importance for decades. At the dawn of organ transplantation, MP was one of the standard techniques for preservation; today's gold standard for organ preservation for transplantation is cold storage (CS). The outcome after transplantation of solid organs has tremendously improved over the last five decades. MP has been continuously under investigation and may be an option for organ preservation in selected cases; however, there is only little evidence from clinical trials that can be used to advocate for MP as a routine organ preservation method.

METHODS

This article reviews the current knowledge on MP in the field of solid organ transplantation with special focus on findings from clinical trials.

CONCLUSION

Especially in heart and lung transplantation, MP seems to be a promising tool to improve postoperative outcome, but a general evidence-based recommendation for or against an application of MP cannot be given due to the lack of the highest level of clinical evidence. Gold standards such as CS should not be left behind without good reason. Randomized clinical trials are desperately needed to further improve outcome and for better understanding of the underlying pathophysiological mechanisms.

Regulation of molecular pathways in ischemia-reperfusion injury after liver transplantation

BACKGROUND

Ischemia-reperfusion (I/R) injury is a multifactorial phenomenon that occurs during the transplant event and frequently compromises early graft function after liver transplantation (LT). Current comprehension of molecular mechanisms and regulation processes of I/R injury lacks clarity. MicroRNA (miRNA) regulation results critical in several biological processes.

METHODS

This study evaluated gene expression and miRNA expression profiles using microarrays in 34 graft biopsies collected at preimplantation (L1) and at 90 min postreperfusion (L2) from consecutives deceased-donor LT recipients. miRNA profiles were first analyzed. Data integration analysis (gene expression/miRNA expression) aimed to identify potential target genes for each identified miRNA from the L1/L2 differential gene expression profile.

RESULTS

Pairwise comparison analyses identified 40 miRNAs and 3168 significantly differentially expressed genes at postreperfusion time compared with preimplantation time. Pathway analysis of miRNAs associated these profiles with antiapoptosis, inhibition of cellular proliferation, and proinflammatory processes. Target analysis identified an miRNA-associated molecular profile of 2172 genes involved in cellular growth and proliferation modulation by cell cycle regulation, cell death and survival, and proinflammatory and anti-inflammatory processes. miRNA-independent genes involved proinflammatory molecules.

CONCLUSION

We identified a miRNA profile involved in posttranscriptional regulatory mechanisms in I/R injury post-LT. A better understanding of these molecular processes involved in I/R may contribute to develop new strategies to minimize graft injury.

Adding pulsatile vascular stimulation to venous systemic oxygen persufflation of liver grafts

The effect of adding pulsatility to gaseous oxygen persufflation during liver preservation was studied in an isolated rat liver model. Livers from male Wistar rats were retrieved 30 min after cardiac arrest of the donor and subjected to 18 h of cold storage. Some grafts were subjected to nonpulsatile or pulsatile gaseous oxygen persufflation. Graft viability was assessed thereafter upon warm reperfusion in vitro (n = 5 per group). Pulsatile persufflation significantly improved parenchymal integrity (enzyme release, bile flow) upon reperfusion, with respect to nonpulsatile persufflation or cold storage (CS) (e.g., max. release of alanine aminotransferase: 44 ± 10 vs. 178 ± 29 vs. 345 ± 100 U/L; pulsatile vs. nonpulsatile persufflation vs. CS).The effect was associated with the prevention of the ischemic decline in gene and protein expression of the vasoprotective Krüppel-like factor 2, increased perfusate levels of the endogenous vasodilator nitric oxide, and reduced portal vascular resistance upon reperfusion, while nonpulsatile persufflation was less effective (e.g., vascular resistance: 1235 ± 108 vs. 1607 ± 155 vs. 2215 ± 208 Pa s/mL; pulsatile vs. nonpulsatile persufflation vs. CS). In conclusion, pulsatile mechanostimulation of the hepatovasculature seems a genuine protective mechanism, affecting early graft recovery upon reperfusion.