Caspase inhibition in liver transplantation: from basic research to clinical studies

Liver Ischemia and Reperfusion Induce Periportal Expression of Necroptosis Executor pMLKL Which Is Associated With Early Allograft Dysfunction After Transplantation

Background

Early allograft dysfunction (EAD) following liver transplantation (LT) remains a major threat to the survival of liver grafts and recipients. In animal models, it is shown that hepatic ischemia-reperfusion injury (IRI) triggers phosphorylation of Mixed Lineage Kinase domain-like protein (pMLKL) inducing necroptotic cell death. However, the clinical implication of pMLKL-mediated cell death in human hepatic IRI remains largely unexplored. In this study, we aimed to investigate the expression of pMLKL in human liver grafts and its association with EAD after LT.

Methods

The expression of pMLKL was determined by immunohistochemistry in liver biopsies obtained from both human and rat LT. Human liver biopsies were obtained at the end of preservation (T0) and ~1 hour after reperfusion (T1). The positivity of pMLKL was quantified electronically and compared in rat and human livers and post-LT outcomes. Multiplex immunofluorescence staining was performed to characterize the pMLKL-expressing cells.

Results

In the rat LT model, significant pMLKL expression was observed in livers after IRI as compared to livers of sham-operation animals. Similarly, the pMLKL score was highest after IRI in human liver grafts (in T1 biopsies). Both in rats and humans, the pMLKL expression is mostly observed in the portal triads. In grafts who developed EAD after LT (n=24), the pMLKL score at T1 was significantly higher as compared to non-EAD grafts (n=40). ROC curve revealed a high predictive value of pMLKL score at T1 (AUC 0.70) and the ratio of pMLKL score at T1 and T0 (pMLKL-index, AUC 0.82) for EAD. Liver grafts with a high pMLKL index (>1.64) had significantly higher levels of serum ALT, AST, and LDH 24 hours after LT compared to grafts with a low pMLKL index. Multivariate logistical regression analysis identified the pMLKL-index (Odds ratio=1.3, 95% CI 1.1-1.7) as a predictor of EAD development. Immunohistochemistry on serial sections and multiplex staining identified the periportal pMLKL-positive cells as portal fibroblasts, fibrocytes, and a minority of cholangiocytes.

Conclusion

Periportal pMLKL expression increased significantly after IRI in both rat and human LT. The histological score of pMLKL is predictive of post-transplant EAD and is associated with early liver injury after LT. Periportal non-parenchymal cells (i.e. fibroblasts) appear most susceptible to pMLKL-mediated cell death during hepatic IRI.

Adenosine A2a Receptor Stimulation Attenuates Ischemia-Reperfusion Injury and Improves Survival in A Porcine Model of DCD Liver Transplantation

Orthotopic liver transplantation (OLT) using allografts from donation after circulatory death (DCD) is potentially associated with compromised clinical outcomes due to ischemia-reperfusion injury (IRI)-induced organ damage and graft-related complications. The aim of this study was to provide in vivo data on the effects of adenosine A2a receptor stimulation in a clinically relevant large animal model of DCD liver transplantation. Cardiac arrest was induced in German Landrace pigs (n = 10; 20-25 kg). After 30 min of warm ischemia, the donor liver was retrieved following a cold flush with 3 L of histidine-tryptophan-ketoglutarate-HTK solution. Animals of the treatment group (n = 5/group) received a standard dose of the selective adenosine receptor agonist CGS 21680 added to the cold flush. All grafts were stored for 4.5 h at 4 °C in HTK-solution before OLT. Hepatocellular injury, apoptosis, protein kinase A-PKA activity, graft microcirculation, liver function, and animal survival were assessed. Compared to untreated livers, adenosine A2a receptor stimulation resulted in improved tissue microcirculation (103% ± 5% vs. 38% ± 4% compared to baseline; p < 0.05), accelerated functional recovery of the graft (indocyanine green-plasma disappearance rate (ICG-PDR) of 75% ± 18% vs. 40% ± 30% after 3 h), increased PKA activity ratio (56% ± 3% vs. 32% ± 3%; p < 0.001 after 1 h), and consequently reduced tissue necrosis and apoptosis. The potent protective effects were clinically manifested in significantly improved survival in the treatment group after 72 h (100% vs. 40%; p = 0.04). The ex vivo administration of adenosine A2a receptor agonist during the back-table flush mitigates IRI-mediated tissue damage and improves functional graft recovery and survival in a large animal model of DCD liver transplantation.

Translational medical research and liver transplantation: systematic review

Translational medicine has become a priority, but there is still a big difference between the arrival of new treatments and investment. Basic science should not be neglected because the translation from basic research is not sustained in the absence of basic research. The purpose of this literature review was to analyze the translational medicine in the liver transplant field: liver ischemia-reperfusion injury (IRI), immunosuppression, clinical and surgical complications, small-for-size syndrome (SFSS), rejection, and ongoing innovations (liver machine, liver preservation, artificial livers, and regenerative medicine). We performed a systematic literature review that were updated in October 2016. The searches were performed in the Cochrane Central Register of Controlled Trials and Review, PubMed/Medline, Embase, and LILACS databases. All the selected studies on the management of translational medical research in liver transplantation (LT) were analyzed. Initially the search found 773 articles. Methodological viewing and analysis of the articles, followed by the application of scientific models, including translational medicine in the liver transplant field. In conclusions, this review demonstrates the application of scientific research with translation medical benefits regarding the LT. The literature has a great tendency, improvements and investments in the study of translational medicine in LT. Innovative studies and technologies from basic science help to clarify clinical doubts. Moreover, evidence increases the importance of scientific research in quality of clinical practice care.

MiR-27a-5p regulates apoptosis of liver ischemia-reperfusion injury in mice by targeting Bach1

Ischemia-reperfusion (I/R) injury causes cellular dysfunction and a series of immune or apoptotic reactions. Bach1 is a mammalian transcription factor that represses Hmox1, which encodes heme oxygenase-1 (HO-1) that can degrade heme into free iron, carbon monoxide, and biliverdin, to play an important role in antioxidant, anti-inflammatory, and antiapoptotic activities. MicroRNAs (miRNAs) can be found in a variety of eukaryotic cells and viruses, a class of noncoding small RNAs that are encoded by endogenous genes. The aims of this study were to determine whether miR-27a-5p targets Bach1 and regulates cellular death; the dual-luciferase reporter assay was used to detect this and the results showed that miR-27a-5p significantly decreased the luciferase activity of the Bach1 3'-untranslated region. MiR-27a-5p was increased in mice during hepatic I/R and Bach1 was decreased. By transfecting the AML12 cells with the mimic, inhibitor miR-27a-5p in hypoxia/reoxygenation (H/R) models showed that overexpression of miR-27a-5p decreased Bach1 messenger RNA, upregulated HO-1 expression, and promoted antiapoptotic Bcl-2 and downregulated proapoptotic caspase-3 gene expression. In contrast, the miR-27a-5p inhibitor yielded the opposite results. Meanwhile, transfection with Bach1 small interference RNA obviously upregulated the protein levels of HO-1 and resulted in an increase in Bcl-2 and a decrease in caspase-3 protein levels. Thus, we can conclude that miR-27a-5p is relevant to liver I/R injury and overexpression of miR-27a-5p may alleviate apoptosis in H/R injury by targeting Bach1 in vitro.

Changing paradigms in organ preservation and resuscitation

PURPOSE OF REVIEW

Shortage of donor organs has increased consideration for use of historically excluded grafts. Ex-vivo machine perfusion is an emerging technology that holds the potential for organ resuscitation and reconditioning, potentially increasing the quality and number of organs available for transplantation. This article aims to review the recent advances in machine perfusion and organ preservation solutions.

RECENT FINDINGS

Flow and pressure-based machine perfusion has shown improved kidney graft function and survival, especially among expanded criteria donors. Pressure-based machine perfusion is demonstrating promising results in preservation and resuscitation of liver, pancreas, heart, and also lung grafts. August 2014 marked Food and Drug Administration approval of XPS XVIVO Perfusion System (XVIVO Perfusion Inc., Englewood, Colorado, USA), a device for preserving and resuscitating lung allografts initially considered unsuitable for transplantation. Although there is no consensus among physicians about the optimal preservation solution, adding antiapoptotic and cell protective agents to preservation solutions is an interesting research area that offers potential to improve preservation.

SUMMARY

Ex-vivo machine perfusion of solid organs is a promising method that provides the opportunity for resuscitation and reconditioning of suboptimal grafts, expanding the number and quality of donor organs.

Autophagy and liver ischemia-reperfusion injury

Liver ischemia-reperfusion (I-R) injury occurs during liver resection, liver transplantation, and hemorrhagic shock. The main mode of liver cell death after warm and/or cold liver I-R is necrosis, but other modes of cell death, as apoptosis and autophagy, are also involved. Autophagy is an intracellular self-digesting pathway responsible for removal of long-lived proteins, damaged organelles, and malformed proteins during biosynthesis by lysosomes. Autophagy is found in normal and diseased liver. Although depending on the type of ischemia, warm and/or cold, the dynamic process of liver I-R results mainly in adenosine triphosphate depletion and in production of reactive oxygen species (ROS), leads to both, a local ischemic insult and an acute inflammatory-mediated reperfusion injury, and results finally in cell death. This process can induce liver dysfunction and can increase patient morbidity and mortality after liver surgery and hemorrhagic shock. Whether autophagy protects from or promotes liver injury following warm and/or cold I-R remains to be elucidated. The present review aims to summarize the current knowledge in liver I-R injury focusing on both the beneficial and the detrimental effects of liver autophagy following warm and/or cold liver I-R.

Nuclear antigens and auto/alloantibody responses: friend or foe in transplant immunology

In addition to cellular immune responses, humoral immune responses, mediated by natural antibodies, autoantibodies, and alloantibodies, have increasingly been recognized as causes of organ transplant rejection. In our previous studies, we have demonstrated the induction of antinuclear antibodies against histone H1 and high-mobility group box 1 (HMGB1), in both experimental and clinical liver transplant tolerance. The active induction of antinuclear antibodies is usually an undesirable phenomenon, but it is often observed after liver transplantation. However, the release of nuclear antigens and its suppression by neutralizing antibodies are proposed to be important in the initiation and regulation of immune responses. In this review article, we summarize the current understanding of nuclear antigens and corresponding antinuclear regulatory antibodies (Abregs) on infection, injury, inflammation, transplant rejection, and tolerance induction and discuss the significance of nuclear antigens as diagnostic and therapeutic targets.

Ischemia-Reperfusion Injury and Ischemic-Type Biliary Lesions following Liver Transplantation

Ischemia-reperfusion (I-R) injury after liver transplantation (LT) induces intra- and/or extrahepatic nonanastomotic ischemic-type biliary lesions (ITBLs). Subsequent bile duct stricture is a significant cause of morbidity and even mortality in patients who underwent LT. Although the pathogenesis of ITBLs is multifactorial, there are three main interconnected mechanisms responsible for their formation: cold and warm I-R injury, injury induced by cytotoxic bile salts, and immunological-mediated injury. Cold and warm ischemic insult can induce direct injury to the cholangiocytes and/or damage to the arterioles of the peribiliary vascular plexus, which in turn leads to apoptosis and necrosis of the cholangiocytes. Liver grafts from suboptimal or extended-criteria donors are more susceptible to cold and warm I-R injury and develop more easily ITBLs than normal livers. This paper, focusing on liver I-R injury, reviews the risk factors and mechanisms leading to ITBLs following LT.