Improved microcirculation by low-viscosity histidine- tryptophan-ketoglutarate graft flush and subsequent cold storage in University of Wisconsin solution: results of an orthotopic rat liver transplantation model

Ultrasound-Targeted Microbubble Cavitation During Machine Perfusion Reduces Microvascular Thrombi and Graft Injury in a Rat Liver Model of Donation After Circulatory Death

BACKGROUND

Ischemic cholangiopathy is a process of bile duct injury that might result from peribiliary vascular plexus (PBP) thrombosis and remains a dreaded complication in liver transplantation from donors after circulatory death (DCD). The aim of this study was to propose a mechanical method of clot destruction to clear microvascular thrombi in DCD livers before transplantation.

METHODS

Sonothrombolysis (STL) is a process by which inertial cavitation of circulating microbubbles entering an ultrasound field create a high-energy shockwave at a microbubble-thrombus interface, causing mechanical clot destruction. The effectiveness of STL in DCD liver treatment remains unclear. We carried out STL treatment during normothermic, oxygenated, ex vivo machine perfusion (NMP), introducing microbubbles into the perfusate with the liver enveloped in an ultrasound field.

RESULTS

The STL livers showed reduction in hepatic arterial and PBP thrombus and decreases in hepatic arterial and portal venous flow resistance, reduced parenchymal injury as measured by aspartate transaminase release and oxygen consumption, and improved cholangiocyte function. Light and electron microscopy showed reduction of hepatic arterial and PBP thrombus in STL livers compared with controls and preserved hepatocyte structure, sinusoid endothelial morphology, and biliary epithelial microvilli.

CONCLUSION

In this model, STL improved flow and functional measures in DCD livers undergoing NMP. These data suggest a novel therapeutic approach to treat PBP injury in DCD livers, which may ultimately increase the pool of grafts available to patients awaiting liver transplantation.

Danger signals in liver injury and restoration of homeostasis

Damage-associated molecular patterns are signalling molecules involved in inflammatory responses and restoration of homeostasis. Chronic release of these molecules can also promote inflammation in the context of liver disease. Herein, we provide a comprehensive summary of the role of damage-associated molecular patterns as danger signals in liver injury. We consider the role of reactive oxygen species and reactive nitrogen species as inducers of damage-associated molecular patterns, as well as how specific damage-associated molecular patterns participate in the pathogenesis of chronic liver diseases such as alcohol-related liver disease, non-alcoholic steatohepatitis, liver fibrosis and liver cancer. In addition, we discuss the role of damage-associated molecular patterns in ischaemia reperfusion injury and liver transplantation and highlight current studies in which blockade of specific damage-associated molecular patterns has proven beneficial in humans and mice.

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.

Combined Flush With Histidine-Tryptophan-Ketoglutarate and University of Wisconsin Solutions in Liver Transplantation: Preliminary Results

INTRODUCTION

Ischemia reperfusion injury (IRI) is the main cause of early allograft dysfunction (EAD) and subsequent primary allograft failure (PAF).

OBJECTIVES

The purpose of this study is to compare IRI, EAD, and PAF in liver transplantation in a cohort of patients perfused with histidine-tryptophan-ketoglutarate (HTK) solution and University of Wisconsin (UW) solution versus HTK alone.

METHODS

A randomized trial was performed to compare outcomes in liver recipients who underwent transplantation surgery in the University Regional Hospital of Malaga, Spain. Forty patients were randomized to two groups. Primary endpoints included IRI, EAD, PAF, re-intervention, acute cellular rejection, retransplantation, arterial complications, and biliary complications at postoperative day 90.

RESULTS

Postoperative glutamic oxaloacetic transaminase (1869.15 ± 1559.75 UI/L vs. 953.15 ± 777.27 UI/L; P = .004) and glutamic pyruvic transaminase (1333.60 ± 1115.49 U/L vs. 721.70 ± 725.02 U/L; P = .023) were significantly higher in patients perfused with HTK alone. A clear tendency was observed in recipients perfused with HTK alone to present moderate to severe IRI (7 patients in the HTK + UW solution group vs. 15 patients in the HTK-alone solution group; P = .06), EAD (0 patients in the HTK + UW solution group vs. 0 patients in the HTK-alone solution group; P = .76), and PAF (3 patients in the HTK + UW solution group vs. 8 patients in the HTK-alone solution group; P = .15).

CONCLUSIONS

Initial perfusion with HTK solution followed by UW solution in liver transplantation improves early liver function as compared to perfusion with HTK alone.

Influence of perfusate on liver viability during hypothermic machine perfusion

AIM: To optimize the perfusates used for hypothermic machine perfusion (HMP).

METHODS: Sprague-Dawley rats were assigned randomly to three groups (n = 12 per group) that received either saline, University of Wisconsin cold-storage solution (UW) or histidine-tryptophan-ketoglutarate solution (HTK) as the perfusate. Each group was divided into two subgroups: static cold storage (SCS) and HMP (n = 6 per subgroup). The liver graft was retrieved according to the method described by Kamada. For the SCS group, the graft was directly placed into cold perfusate (0-4 °C) for 6 h after liver isolation while the portal vein of the graft was connected to the perfusion machine for the HMP group. Then the perfusates were collected at different time points for analysis of aspartate aminotransferase (AST), alanine transaminase (ALT) and lactate dehydrogenase (LDH) levels. Liver tissues were obtained for evaluation of histology, dry/wet weight (D/W) ratio, and malondialdehyde (MDA) and adenosine-triphosphate (ATP) levels. The portal vein pressure and velocity were monitored in real time in all HMP subgroups.

RESULTS: Comparison of HMP and SCS: Regardless of the perfusate, HMP improved the architecture of donor graft in reducing the congestion around sinusoids and central vein and maintaining sinusoid lining in morphology; HMP improved liver function in terms of ALT, AST and LDH, especially during the 3-6 h period (SCS vs HMP using saline: ALT3, 225.00 ± 105.62 vs 49.50 ± 18.50, P = 0.047; LDH3, 1362.17 ± 563.30 vs 325.75 ± 147.43, P = 0.041; UW: LDH6, 2880.14 ± 948.46 vs 2135.00 ± 174.27, P = 0.049; HTK, AST6, 307.50 ± 52.95 vs 185.20 ± 20.46, P = 0.041); HMP decreased MDA level (saline, 2.79 ± 0.30 vs 1.09 ± 0.09, P = 0.008; UW, 3.01 ± 0.77 vs 1.23 ± 0.68, P = 0.005; HTK, 3.30 ± 0.52 vs 1.56 ± 0.22, P = 0.006). Comparison among HMP subgroups: HTK showed less portal vein resistance than UW and saline (vs saline, 3.41 ± 0.49 vs 5.00 ± 0.38, P < 0.001; vs UW, 3.41 ± 0.49 vs 4.52 ± 0.63, P = 0.007); UW reduced edema most efficiently (vs saline, 0.68 ± 0.02 vs 0.79 ± 0.05, P = 0.013), while HTK maintained ATP levels best (vs saline, 622.60 ± 29.11 vs 327.43 ± 44.66, P < 0.001; vs UW, 622.60 ± 29.11 vs 301.80 ± 37.68, P < 0.001).

CONCLUSION: HMP is superior to SCS in maintaining both architecture and function of liver grafts. Further, HTK was found to be the optimal perfusate for HMP.

Liver protection strategies in liver transplantation

BACKGROUND

Liver transplantation is the therapy of choice for patients with end-stage liver diseases. However, the gap between the low availability of organs and high demand is continuously increasing. Innovative strategies for organ protection are necessary to expand donor pool and to achieve better outcomes for liver transplantation. The present review analyzed and compared various strategies of liver protection.

DATA SOURCES

Databases such as PubMed, Embase and Ovid were searched for the literature related to donor liver protection strategies using following key words: "ischemia reperfusion injury", "graft preservation", "liver transplantation", "machine perfusion" and "conditioning". Of the 146 studies identified, only those with cutting edge strategies were analyzed.

RESULTS

A variety of therapeutic approaches were proposed to alleviate graft ischemia/reperfusion injury, which included static cold storage, machine perfusion (hypothermic, normothermic and subnormothermic), manual conditioning (pre, post and remote), and pharmacological conditioning. Evidences from animal experiments and clinical trials suggested that all these strategies could potentially protect liver graft; however, their clinical applications are limited partially due to their own disadvantages.

CONCLUSIONS

There are a plenty of methods suggested to decrease the degree of donor liver transplantation-related injury. However, none of these approaches is perfect in clinical practice. More translational researches (molecular and clinical studies) are needed to improve the techniques in liver graft protection.

Hepatocyte viability and adenosine triphosphate content decrease linearly over time during conventional cold storage of rat liver grafts

INTRODUCTION

The gold standard in organ preservation is static cold storage (SCS) using University of Wisconsin solution (UW). Although it is well-known that there is a finite limit to SCS preservation, and that there is a correlation between the adenosine triphosphate (ATP) levels and organ function post-preservation, a quantitative relationship has not been established, which is important in understanding the fundamental limitations to preservation, minimizing cold ischemic injury, and hence maximizing use of the donor organ pool.

AIM

This study determines the time limits of cellular viability and metabolic function during SCS, and characterizes the relationship between cellular viability and energetic state using clinically relevant techniques in organ preservation.

METHODS

Rat livers were procured and stored using conventional storage in UW solution at 4 °C. Viability was assessed by determining the amount of viable hepatocytes and intracellular ATP content after 0, 24, 48, 72, and 120 hours of storage.

RESULTS

Numbers of viable hepatocytes that were isolated from these livers decreased steadily during SCS. After 5 days, viable hepatocytes decreased from 25.95 × 10(6) to 0.87 × 10(6) cells/gram tissue. Intracellular ATP content decreased from 9.63 to 0.93 moles/g tissue. Statistical analysis of variance established a linear relation for both parameters as a function of time (P < .05).

CONCLUSION

The linear correlation between hepatocyte viability, ATP content, and storage time suggests a shared physiological foundation. These findings confirm ATP as direct predictor for organ quality in the context of liver preservation, which will aid quantitative assessment of donor organs for various applications.

Nicardipine reverses vasoactivity associated with University of Wisconsin solution in the rat peripheral circulation

BACKGROUND

The rapid uniform delivery of University of Wisconsin solution (UW) to the microcirculation may be compromised by its vasoactivity.

METHODS

In 2 different rodent models, we tested whether UW-mediated vasoconstriction could be reversed with nicardipine.

RESULTS

In the perfused, splanchnic circulation, intravascular control solutions (lactated Ringers [LR], Hextend [HEX], histidine-tryptophan-ketoglutarate [HTK]) or UW (± nicardipine) evoked pressure changes in 3 protocols (series 1; n = 35). In the cremaster muscle, topical control solutions or UW (± nicardipine) evoked vascular responses measured by video microscopy in 4 protocols (series 2; n = 47). In series 1A, 37°C UW increased perfusion pressure, but there was no change caused by LR, HEX, or HTK. In series 1B, 4°C UW caused a similar, albeit transient, increase. In series 1C, nicardipine reversed 37°C UW-mediated vasoconstriction in a dose-related manner. In series 2A, UW caused a 30%-59% constriction that varied with arteriolar branching order. In series 2B, the recovery from UW-induced vasoconstriction varied with duration of exposure, but nicardipine fully reversed residual vasoconstriction. In series 2C, cold and warm UW were equipotent, near maximal, vasoconstrictors. In series 2D, UW potentiated no-reflow.

CONCLUSION

UW causes a potent temperature-independent vasoconstriction by a calcium-mediated mechanism and this effect can be mitigated with nicardipine.

A novel end-to-side anastomosis technique for hepatic rearterialization in rat orthotopic liver transplantation to accommodate size mismatches between vessels

BACKGROUND/AIMS

We present our modification of a sutured arterial anastomosis in orthotopic rat liver transplantation as well as a literature survey and analysis of the existing techniques of rearterialization with regard to technical difficulties and potential limitations.

METHODS

The donor common hepatic artery (CHA) was anastomosed to the enlarged lumen of the recipient proper hepatic artery (PHA), tailored to match the size of the donor CHA, with an end-to-side interrupted suture technique. Vascular patency of hepatic rearterialization was assessed both intraoperatively and at the time the liver grafts were harvested (postoperative days 2 and 28). The effect of arterialization on hepatic morphology was confirmed by histological examination and compared to nonarterialized rat orthotopic liver transplantation.

RESULTS

The CHAs had a significantly larger diameter (up to 3-fold) compared to the PHAs, which represents a considerable size mismatch. The anastomosis procedure including the size adaptation required 15-25 min. All anastomoses were patent immediately, 5 min after rearterialization and at both harvest time points. The liver lobular architecture was intact in the rearterialized group, whereas a moderate degree of bile duct proliferation and portal/lobular lymphocytic infiltration were observed in the nonarterialized group.

CONCLUSION

The new technique is a time-consuming and microsurgically challenging but universally applicable and robust procedure accommodating even a substantial mismatch in vessel diameter.

Pharmacological strategies against cold ischemia reperfusion injury

IMPORTANCE OF THE FIELD

Good organ preservation is a determinant of graft outcome after revascularization. The necessity of increasing the quality of organ preservation, as well as of extending cold storage time, has made it necessary to consider the use of pharmacological additives.

AREAS COVERED IN THIS REVIEW

The complex physiopathology of cold-ischemia-reperfusion (I/R) injury--and in particular cell death, mitochondrial injury and endoplasmic reticulum stress--are reviewed. Basic principles of the formulation of the different preservation solutions are discussed.

WHAT THE READER WILL GAIN

Current strategies and new trends in static organ preservation using additives such as trimetazidine, polyethylene glycols, melatonin, trophic factors and endothelin antagonists in solution are presented and discussed. The benefits and mechanisms responsible for enhancing organ protection against I/R injury are also discussed. Graft preservation was substantially improved when additives were added to the preservation solutions.

TAKE HOME MESSAGE

Enrichment of preservation solutions by additives is clinically useful only for short periods. For longer periods of cold ischemia, the use of such additives becomes insufficient because graft function deteriorates as a result of ischemia. In such conditions, the preservation strategy should be changed by the use of machine perfusion in normothermic conditions.

Uncoupling protein-2 deficient mice are not protected against warm ischemia/reperfusion injury of the liver

BACKGROUND

Uncoupling protein-2 (UCP2) might play an important role in mediating ischemia/reperfusion (I/R) injury due to its function in uncoupling of oxidative phosphorylation and in the proton leak-associated increase of reactive oxygen species (ROS) production. The aim of this study was to elucidate the role of UCP2 in hepatic I/R injury.

MATERIALS AND METHODS

UCP2 wild type and UCP2 deficient mice were subjected to I/R of the left liver lobe. Sham-operated animals without I/R served as controls. Intravital fluorescence microscopy was used for assessing postischemic microcirculatory dysfunction. Indicators of hepatic inflammatory response, oxidative stress, and bioenergetic status as well as histomorphology were investigated.

RESULTS

Under sham conditions UCP2-/-mice presented slightly but not significantly higher levels of hepatic ATP and energy charge than wild type mice. In addition, they exhibited higher systemic IL-6 levels and intrahepatic leukocyte adherence. After exposure to I/R, the extent of reperfusion injury did not differ between UCP2+/+ and UCP2-/-mice, as indicated by a comparable loss of sinusoidal perfusion, hepatic ATP, and energy charge levels, as well as rise of transaminases and disintegration of liver structures. Intrahepatic leukocyte adherence and plasma IL-6 levels of postischemic UCP2-/-mice still exceeded those of UCP2+/+mice.

CONCLUSIONS

UCP2 appears to be of minor relevance for the manifestation and extent of postischemic reperfusion injury in nondiseased livers with the increased ATP availability being counteracted by the higher pro-inflammatory IL-6 levels in UCP2 deficient mice.

Machine perfusion or cold storage in organ transplantation: indication, mechanisms, and future perspectives

Most organs are currently preserved by cold storage (CS) prior to transplantation. However, as more so called marginal donor organs are utilized, machine perfusion has regained clinical interest. Recent studies have demonstrated advantages of pulsatile perfusion over CS preservation for kidney transplantation. However, it remains unclear whether there is a significant benefit of one preservation method over the other in general, or, whether the utilization of particular preservation approaches needs to be linked to organ characteristics. Proposed protective mechanisms of pulsatile perfusion remain largely obscure. It can be speculated that pulsatile perfusion may not only provide nutrition and facilitate the elimination of toxins but also trigger protective mechanisms leading to the amelioration of innate immune responses. Those aspects may be of particular relevance when utilizing grafts with suboptimal quality which may have an increased vulnerability to ischemia/reperfusion injury and compromised repair mechanisms. This review aims to enunciate the principles of organ perfusion and preservation as they relate to indication, aspects of organ protection and to highlight future developments.