A novel organ preservation for small partial liver transplantations in rats: venous systemic oxygen persufflation with nitric oxide gas

Haeme Oxygenas-1-Induced Liver Regeneration Protects Graft Against Small-for-Size Syndrome in Rats

BACKGROUND

Haeme oxygenase (HO-1) affords protection against ischemia/reperfusion (I/R) injury; however, its effects on liver regeneration remain poorly explored. Our previous studies have shown that HO-1 is probably involved in liver regeneration, but its role in small-for-size syndrome (SFSS) is still unclear. Therefore, this study aims to investigate the effects of HO-1 on small-for-size graft (SFSG) and the underlying mechanism.

METHODS

Knockout of HO-1 rats by TALEN technique. Immunohistochemistry was used to detect HO-1 nuclear translocation. Haeme oxygenase activity was measured by detecting the amount of carbon monoxide (CO) generated from cell lysates. Flow cytometry was used to detect cell apoptosis and cell cycle. Western blot were performed to measure the expression level of HO-1 protein.

RESULTS

We identified that HO-1 was involved in SFSG regeneration; HO-1-knockout rats demonstrated significantly decreased liver proliferation and recovery. Interestingly, our results showed HO-1-induced SFSG regeneration was more likely to be the primary protector against SFSS than IRI. Furthermore, we verified the nuclear translocation of HO-1 and its protective effect on hypoxia/reoxygenation (H/R) damage in clone9 cells. Our results indicated that the HO-1 protein itself rather than heme breakdown metabolites might play a key role in liver regeneration.

CONCLUSIONS

The HO-1 protein itself rather than its metabolites possess a protective effect on small-for-size graft (SFSG) against SFSS via nuclear translocation.

Impact of very early introduction of everolimus on liver regeneration after partial liver transplantation in rats

BACKGROUND/PURPOSE

This experimental study in rats aimed to investigate the impact of very early introduction (within 3 h) of everolimus (EVR) + reduced-tacrolimus (TAC) after partial liver transplantation (LT) on liver regeneration, rejection, and survival.

METHODS

Based on appropriate dose of EVR + reduced-TAC in 70% hepatectomy (Experiment 1), allogeneic 30% partial LT (Experiment 2) and whole LT (Experiment 3) were performed.

RESULTS

After partial LT in EVR + reduced-TAC therapy, restoration of liver graft weight (to that of the whole liver) was delayed compared with standard dose TAC monotherapy (standard-TAC) on day 3 (59.3% vs. 72.9%; p < .001) and 14 (88.1% vs. 95.5%; p = .01). Survival was 75%, which was not as high as the value of 100% observed for standard-TAC, because neither infection nor rejection could be prevented. By contrast, survival after whole LT was 100% as neither infection nor rejection occurred.

CONCLUSIONS

The very early introduction of EVR + reduced-TAC after partial LT delayed liver regeneration, and made it difficult to manage the dose required to suppress both infection and rejection. On the other hand, EVR + reduced-TAC could be introduced safely very early after whole LT.

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.

Etiology of Liver Steatosis Influences the Severity of Ischemia/Reperfusion Injury and Survival After Liver Transplantation in Rats

Liver steatosis is a leading cause of graft disposal in liver transplantation, though the degree of steatosis is often the single factor determining acceptability of the graft. We investigated how the cause of liver steatosis affects graft function in rat orthotopic liver transplantation (OLT). OLT was performed using 2 types of steatotic liver grafts: the fasting and hyperalimentation (FHA) model and the methionine- and choline-deficient diet models. The FHA and 4-week feeding of a methionine- and choline-deficient diet (MCDD4wk) groups showed similar liver triglyceride levels without signs of steatohepatitis. Therefore, the 2 groups were compared in the following experiment. With 6-hour cold storage, the 7-day survival rate after OLT was far worse in the FHA than in the MCDD4wk group (0% versus 100%, P = 0.002). With 1-hour cold storage, the FHA group showed higher aspartate aminotransferase and alanine aminotransferase levels and histological injury scores in zones 1 and 2 at 24 hours after reperfusion than the normal liver and MCDD4wk groups. Intrahepatic microcirculation and tissue adenosine triphosphate levels were significantly lower in the FHA group after reperfusion. Hepatocyte necrosis, sinusoidal endothelial cell injury, and abnormal swelling of the mitochondria were also found in the FHA group after reperfusion. Tissue malondialdehyde levels were higher in the MCDD4wk group before and after reperfusion. However, the grafts up-regulated several antioxidant enzymes soon after reperfusion. Even though the degree of steatosis was equivalent, the 2 liver steatosis models possessed quite unique basal characteristics and showed completely different responses against ischemia/reperfusion injury and survival after transplantation. Our results demonstrate that the degree of fat accumulation is not a single determinant for the usability of steatotic liver grafts.

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.

The role of normothermic machine perfusion in liver transplantation

To expand the donor pool of suitable organs for transplantation, there is an increased interest in utilizing extended criteria donor grafts (ECD). Ex-situ machine perfusion has shown to be a promising new modality in the organ preservation field to reduce injury and recover ECD liver grafts. Machine perfusion (MP) is considered a significant improvement in the field of transplantation over the past 20 years. Normothermic machine perfusion has entered the clinical arena in the last decade and has shown promising results to improve the quality of marginal organs and to increase the pool of liver grafts. It allows assessment of viability and function of grafts prior to transplantation. In addition, it has the potential to serve as a platform for pharmacologic organ treatment and graft optimization. Machine perfusion moved from the experimental phase to a more mature phase after safety was confirmed by initial clinical trials. Now, it is time to confirm its superiority and cost-effectiveness before a broader clinical use. In this paper we review the history, current status including outcomes of all clinical trials, limitations, and future trends of normothermic machine preservation.

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.

Auxiliary xenotransplantation as an in vivo bioreactor-Development of a transplantable liver graft from a tiny partial liver

BACKGROUND

We established a completely novel method of auxiliary xenogeneic partial liver transplantation and examined whether liver grafts procured from Syrian hamsters regenerated in nude rats, which were used as in vivo bioreactors.

METHODS

The hamsters and the rats were all males (n = 10). Partial liver grafts from hamsters were transplanted into nude rats in an auxiliary manner. We evaluated liver graft injury, rejection, and regeneration during 7 days after auxiliary xenogeneic partial liver transplantation.

RESULTS

All rats survived until sacrifice on post-operative day (POD) 1, 3, and 7. HE-staining showed normal at POD1, mild periportal edema, and slight bile duct and venous endothelial inflammation at POD3, and moderate acute cellular rejection at POD7 without parenchymal necrosis. The liver regeneration rates at POD3 and 7 were 1.54 ± 0.23 and 2.54 ± 0.43, respectively. The Ki-67 labeling index was also elevated at POD3 (27.5 ± 4.1%). Serum HGF and VEGF were elevated at POD1 and 3. ATP levels of liver grafts recovered at POD7.

CONCLUSIONS

These results revealed that with appropriate immunosuppressive therapy, partial liver graft regeneration occurred in a xenogeneic animal, which suggests liver grafts regenerated in xenogeneic environments, such as an in vivo bioreactor, have potential to be transplantable liver grafts for humans.

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.

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.

Optimal Timing for Venous Systemic Oxygen Persufflation Supplemented with Nitric Oxide Gas in Cold-Stored, Warm Ischemia-Damaged Experimental Liver Grafts

Background/Aim: Worldwide shortage of donor organs has increased the use of donation after cardiac death (DCD). The aim of this study was to analyze the best time point for venous systemic oxygen persufflation (VSOP) supplemented with nitric oxide (NO) gas during the 1st and 24th hour of cold storage (CS) in warm ischemia (WI)-damaged experimental liver grafts. Materials and Methods: Liver grafts (n = 5) were retrieved after 30 min of WI induced by cardiac arrest and CS in histidine-tryptophan-ketoglutarate solution at 4°C. The 1st hour group was immediately persufflated with a VSOP plus NO (VSOP+NO) mixture for 1 h followed by 23 h of static CS (DCD+NO 1st hour). The 24th hour group entailed CS for 23 h followed by 1 h of VSOP+NO persufflation (DCD+NO 24th hour). CS livers without WI but with VSOP served as controls. CS livers with WI represented the fourth group (DCD). Viability of the liver grafts was assessed by normothermic isolated reperfusion for 45 min with oxygenated Krebs-Henseleit buffer. Results: Data are presented as mean ± SEM (control vs. DCD vs. DCD+NO 1st hour vs. DCD+NO 24th hour). After 45 min of reperfusion, the DCD+NO 1st hour group showed significantly lower aspartate aminotransferase (13.4 ± 5.3, 63.2 ± 17.3, 25.6 ± 3.9, and 82.8 ± 27.3 U/l) and lactate dehydrogenase levels (289.4 ± 41.2, 2,139.4 ± 542.7, 577.2 ± 117.2, and 2,429 ± 221.6 U/l). Malondialdehyde levels were significantly abrogated (1.0 ± 0.3, 2.7 ± 1, 1.0 ± 0, and 3.9 ± 1.2 nmol/ml). Significantly higher levels of portal venous pressure were recorded in the DCD+NO 24th hour group (12.0 ± 1, 21.2 ± 3.1, 16.1 ± 1, and 23.2 ± 3.5 mm Hg). NO levels were recorded after 5 min of reperfusion (1.42 ± 0.17, 1.8 ± 0.2, 2.7 ± 0.2, and 2.6 ± 0.1 μmol/l). Bile production levels showed no statistical significance (23.2 ± 3.8, 27.3 ± 1.8, 43.5 ± 18, and 31 ± 2.5 μl/45 min). Conclusion: Our results present the beneficial effects of NO combined with VSOP during the 1st hour of CS of WI-damaged experimental liver grafts.

Molecular pathways in protecting the liver from ischaemia/reperfusion injury: a 2015 update

Ischaemia/reperfusion injury is an important cause of liver damage during surgical procedures such as hepatic resection and liver transplantation, and represents the main cause of graft dysfunction post-transplantation. Molecular processes occurring during hepatic ischaemia/reperfusion are diverse, and continuously include new and complex mechanisms. The present review aims to summarize the newest concepts and hypotheses regarding the pathophysiology of liver ischaemia/reperfusion, making clear distinction between situations of cold and warm ischaemia. Moreover, the most updated therapeutic strategies including pharmacological, genetic and surgical interventions, as well as some of the scientific controversies in the field are described.

Improving Research Practice in Rat Orthotopic and Partial Orthotopic Liver Transplantation: A Review, Recommendation, and Publication Guide

Background: Due to a worldwide shortage of donor organs for liver transplantation, alternative approaches, such as split and living donor liver transplantations, were introduced to increase the donor pool and reduce mortality on liver transplant waiting lists. Numerous details concerning the mechanisms and pathophysiology of liver regeneration, small-for-size syndrome, rejection, and tolerance in partial liver transplantation facilitated the development of various animal models. The high number of preclinical animal studies contributed enormously to our understanding of many clinical aspects of living donor and partial liver transplantations. Summary: Microsurgical rat models of partial orthotopic liver transplantation are well established and widely used. Nevertheless, several issues regarding this procedure are controversial, not clarified, or not yet properly standardized (graft rearterialization, size reduction techniques, etc.). The major aim of this literature review is to give the reader a current overview of rat orthotopic liver transplantation models with a special focus on partial liver transplantation. The aspects of model evolution, microsurgical training, and different technical problems are analyzed and discussed in detail. Our further aim in this paper is to elaborate a detailed publication guide in order to improve the quality of reporting in the field of rat liver transplantation according to the ARRIVE guidelines and the 3R principle. Key Messages: Partial orthotopic liver transplantation in rats is an indispensable, reliable, and cost-efficient model for transplantation research. A certain consensus on different technical issues and a significant improvement in scientific reporting are essential to improve transparency and comparability in this field as well as to foster refinement.

"Resuscitation" of marginal liver allografts for transplantation with machine perfusion technology

As the rate of medically suitable donors remains relatively static worldwide, clinicians have looked to novel methods to meet the ever-growing demand of the liver transplant waiting lists worldwide. Accordingly, the transplant community has explored many strategies to offset this deficit. Advances in technology that target the ex vivo "preservation" period may help increase the donor pool by augmenting the utilization and improving the outcomes of marginal livers. Novel ex vivo techniques such as hypothermic, normothermic, and subnormothermic machine perfusion may be useful to "resuscitate" marginal organs by reducing ischemia/reperfusion injury. Moreover, other preservation techniques such as oxygen persufflation are explored as they may also have a role in improving function of "marginal" liver allografts. Currently, marginal livers are frequently discarded or can relegate the patient to early allograft dysfunction and primary non-function. Bench to bedside advances are rapidly emerging and hold promise for expanding liver transplantation access and improving outcomes.

Graft reconditioning with nitric oxide gas in rat liver transplantation from cardiac death donors. Transplantation. 2014;97:618-625. [PMID: 24521773 DOI: 10.1097/tp.0000000000000025]

BACKGROUND

Liver transplant outcomes using grafts donated after cardiac death (DCD) remain poor.

METHODS

We investigated the effects of ex vivo reconditioning of DCD grafts with venous systemic oxygen persufflation using nitric oxide gas (VSOP-NO) in rat liver transplants. Orthotopic liver transplants were performed in Lewis rats, using DCD grafts prepared using static cold storage alone (group-control) or reconditioning using VSOP-NO during cold storage (group-VSOP-NO). Experiment I: In a 30-min warm ischemia model, graft damage and hepatic expression of inflammatory cytokines, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and endothelin-1 (ET-1) were examined, and histologic analysis was performed 2, 6, 24, and 72 hr after transplantation. Experiment II: In a 60-min warm ischemia model, grafts were evaluated 2 hr after transplantation (6 rats/group), and survival was assessed (7 rats/group).

RESULTS

Experiment I: Group-VSOP-NO had lower alanine aminotransferase (ALT) (P<0.001), hyaluronic acid (P<0.05), and malondialdehyde (MDA) (P<0.001), hepatic interleukin-6 expression (IL-6) (P<0.05), and hepatic tumor necrosis factor-alpha (TNF-α) expression (P<0.001). Hepatic eNOS expression (P<0.001) was upregulated, whereas hepatic iNOS (P<0.01) and ET-1 (P<0.001) expressions were downregulated. The damage of hepatocyte and sinusoidal endothelial cells (SECs) were lower in group-VSOP-NO.Experiment II: VSOP-NO decreased ET-1 and 8-hydroxy-2'deoxyguanosine (8-OHdG) expression and improved survival after transplantation by 71.4% (P<0.01).

CONCLUSION

These results suggest that VSOP-NO effectively reconditions warm ischemia-damaged grafts, presumably by decreasing ET-1 upregulation and oxidative damage.

Machine perfusion in solid organ transplantation: where is the benefit? Langenbecks Arch Surg. 2014;399:421-427. [PMID: 24429900 DOI: 10.1007/s00423-014-1161-2]

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.