Technique of subnormothermic ex vivo liver perfusion for the storage, assessment, and repair of marginal liver grafts

Cyclosporine A Does Not Mitigate Liver Ischemia/Reperfusion Injury in an Ex Vivo Porcine Model of Donation After Circulatory Death

BACKGROUND Ischemia/reperfusion injury (IRI) is an inherent problem in organ transplantation, owing to the obligate period of ischemia that organs must endure. Cyclosporine A (CsA), though better know as an immunosuppressant, has been shown to mitigate warm IRI in a variety of organ types, including the liver. However, there is little evidence for CsA in preventing hepatic IRI in the transplant setting. MATERIAL AND METHODS In the present study, we tested the effect of CsA on hepatic IRI in a large-animal ex vivo model of donation after circulatory death (DCD). Porcine donors were pre-treated with either normal saline control or 20 mg/kg of CsA. Animals were subject to either 45 or 60 minutes of warm ischemia before hepatectomy, followed by 2 or 4 hours of cold storage prior to reperfusion on an ex vivo circuit. Over the course of a 12-hour perfusion, perfusion parameters were recorded and perfusate samples and biopsies were taken at regular intervals. RESULTS Peak perfusate lactate dehydrogenase was significantly decreased in the lower-ischemia group treated with CsA compared to the untreated group (4220 U/L [3515-5815] vs 11 305 [10 100-11 674]; P=0.023). However, no difference was seen between controls and CsA-treated groups on other parameters in perfusate alanine or asparagine aminotransferase (P=0.912, 0.455, respectively). Correspondingly, we found no difference on midpoint histological injury score (P=0.271). CONCLUSIONS We found minimal evidence that CsA is protective against hepatic IRI in our DCD model.

Comprehensive review of the application of MP and the potential for graft modification

Introduction

Following procurement, the liver graft is exposed to an ischemic period that triggers several pathophysiologic changes in response to oxygen deprivation. Therefore, the goal during organ preservation is to attenuate such response and provide an adequate environment that prepares the graft for its metabolic reactivation following implantation. This has been widely achieved via static cold storage preservation, where the maintenance of the graft using cold preservation solutions reduce its metabolic activity and confer cytoprotection until transplantation. However, despite being the gold standard for organ preservation, static cold storage holds several disadvantages. In addition, the ongoing organ shortage has led to the use of unconventional grafts that could benefit from therapies pre-transplant. Organ preservation via machine perfusion systems appears as a promising solution to address both.

Methods

Here, we aim to present a state-of-the-art narrative review regarding liver graft modification options using machine perfusion systems in combination with adjuvant strategies including immunomodulation, gene therapy and pharmacotherapy.

Results

Available reports are scarce and mostly on experimental animal models. Most of the literature reflects the use of normothermic or subnormothermic machine perfusion devices given that these particular type of machine allows for a metabolically active organ, and therefore facilitates its modification. Although limited, promising findings in available reports suggest that organ preservation using machine perfusion system when combined with alternative therapies can be feasible and safe strategies for graft modification.

Discussion

Further research on clinical settings are needed to better elucidate the true effect of graft modification pre-transplant on short- and long-term graft and patient survival. There is a long way ahead to develop guidelines and approve these novel therapies for clinical practice. However, the path looks promising.

Perfluorocarbon-Based Oxygen Carriers and Subnormothermic Lung Machine Perfusion Decrease Production of Pro-Inflammatory Mediators

The quality of marginal donor lungs is clinically assessed with normothermic machine perfusion. Although subnormothermic temperature and perfluorocarbon-based oxygen carriers (PFCOC) have proven favourable for other organ transplants, their beneficial use for ex vivo lung perfusion (EVLP) still requires further investigation. In a rat model, we evaluated on a 4 h EVLP time the effects of PFCOC with either 28 °C or 37 °C perfusion temperatures. During EVLP at 28 °C with PFCOC, we recorded significantly lower lung pulmonary vascular resistance (PVR), higher dynamic compliance (Cdyn), significantly lower potassium and lactate levels, higher lung tissue ATP content, and significantly lower myeloperoxidase tissue activity when compared to the 37 °C EVLP with PFCOC. In the subnormothermic EVLP with or without PFCOC, the pro-inflammatory mediator TNFα, the cytokines IL-6 and IL-7, the chemokines MIP-3α, MIP-1α, MCP-1, GRO/KC as well as GM-CSF, G-CSF and the anti-inflammatory cytokines IL-4 and IL-10 were significantly lower. The 28 °C EVLP improved both Cdyn and PVR and decreased pro-inflammatory cytokines and pCO2 levels compared to the 37 °C EVLP. In addition, the 28 °C EVLP with PFCOC produced a significantly lower level of myeloperoxidase activity in lung tissue. Subnormothermic EVLP with PFCOC significantly improves lung donor physiology and ameliorates lung tissue biochemical and inflammatory parameters.

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

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

Subnormothermic Ex Vivo Lung Perfusion Temperature Improves Graft Preservation in Lung Transplantation

Normothermic machine perfusion is clinically used to assess the quality of marginal donor lungs. Although subnormothermic temperatures have proven beneficial for other solid organ transplants, subnormothermia-related benefits of ex vivo lung perfusion (EVLP) still need to be investigated. Material and Methods: In a rat model, we evaluated the effects of 28 °C temperature on 4-h EVLPs with subsequent left lung transplantation. The recipients were observed for 2 h postoperatively. Lung physiology data were recorded and metabolic parameters were assessed. Results: During the 4-h subnormothermic EVLP, the lung oxygenation was significantly higher (p < 0.001), pulmonary vascular resistance (PVR) lower and dynamic compliance (Cdyn) higher when compared to the 37 °C EVLP. During an end-of-EVLP stress test, we recorded significantly higher flow (p < 0.05), lower PVR (p < 0.05) and higher Cdyn (p < 0.01) in the 28 °C group when compared to the 37 °C group. After the left lung transplantation, Cdyn and oxygenation improved in the 28 °C group, which were comparable to the 37 °C group. Chemokines RANTES, MIP-3α, MIP-1α MCP-1 GRO/KC and pro-inflammatory mediators GM-CSF, G-CSF and TNFα were significantly lower after the 28 °C EVLP and remained low in the plasma of the recipient rats after transplantation. The lungs of the 28 °C group showed significantly lowered myeloperoxidase activity and lowered levels of TNFα and IL-1β. Conclusions: Compared to the normothermic perfusion, the 28 °C EVLP improved Cdyn and PVR and reduced both the release of pro-inflammatory cytokines and myeloperoxidase activity in lung tissue. These observations were also observed after the left lung transplantation in the subnormothermic group. The 28 °C EVLP significantly improved biochemical, physiological and inflammatory parameters in lung donors.

Establishing In Situ Closed Circuit Perfusion of Lower Abdominal Organs and Hind Limbs in Mice

Ex vivo perfusion is an important physiological tool to study the function of isolated organs (e.g. liver, kidneys). At the same time, due to the small size of mouse organs, ex vivo perfusion of bone, bladder, skin, prostate, and reproductive organs is challenging or not feasible. Here, we report for the first time an in situ lower body perfusion circuit in mice that includes the above tissues, but bypasses the main clearance organs (kidney, liver, and spleen). The circuit is established by cannulating the abdominal aorta and inferior vena cava above the iliac artery and vein and cauterizing peripheral blood vessels. Perfusion is performed via a peristaltic pump with perfusate flow maintained for up to 2 h. In situ staining with fluorescent lectin and Hoechst solution confirmed that the microvasculature was successfully perfused. This mouse model can be a very useful tool for studying pathological processes as well as mechanisms of drug delivery, migration/metastasis of circulating tumor cells into/from the tumor, and interactions of immune system with perfused organs and tissues.

Machine Perfusion of Extended Criteria Donor Organs: Immunological Aspects

Due to higher vulnerability and immunogenicity of extended criteria donor (ECD) organs used for organ transplantation (Tx), the discovery of new treatment strategies, involving tissue allorecognition pathways, is important. The implementation of machine perfusion (MP) led to improved estimation of the organ quality and introduced the possibility to achieve graft reconditioning prior to Tx. A significant number of experimental and clinical trials demonstrated increasing support for MP as a promising method of ECD organ preservation compared to classical static cold storage. MP reduced ischemia-reperfusion injury resulting in the protection from inadequate activation of innate immunity. However, there are no general agreements on MP protocols, and clinical application is limited. The objective of this comprehensive review is to summarize literature on immunological effects of MP of ECD organs based on experimental studies and clinical trials.

De-epithelialization of porcine tracheal allografts as an approach for tracheal tissue engineering

Replacement of large tracheal defects remains an unmet clinical need. While recellularization of acellular tracheal grafts appeared to be a viable pathway, evidence from the clinic suggests otherwise. In hindsight, complete removal of chondrocytes and repopulation of the tracheal chondroid matrix to achieve functional tracheal cartilage may have been unrealistic. In contrast, the concept of a hybrid graft whereby the epithelium is removed and the immune-privileged cartilage is preserved is a radically different path with initial reports indicating potential clinical success. Here, we present a novel approach using a double-chamber bioreactor to de-epithelialize tracheal grafts and subsequently repopulate the grafts with exogenous cells. A 3 h treatment with sodium dodecyl sulfate perfused through the inner chamber efficiently removes the majority of the tracheal epithelium while the outer chamber, perfused with growth media, keeps most (68.6 ± 7.3%) of the chondrocyte population viable. De-epithelialized grafts support human bronchial epithelial cell (BEAS-2B) attachment, viability and growth over 7 days. While not without limitations, our approach suggests value in the ultimate use of a chimeric allograft with intact donor cartilage re-epithelialized with recipient-derived epithelium. By adopting a brief and partial decellularization approach, specifically removing the epithelium, we avoid the need for cartilage regeneration.

Initial perfusate purification during subnormothermic machine perfusion for porcine liver donated after cardiac death

Improvement of machine perfusion (MP) technologies is required to enhance organ quality for donor after cardiac death (DCD) grafts. Installing a dialyzer or a filter into the perfusion circuit to maintain the perfusate condition has some advantages. However, the consequences of purification perfusate during subnormothermic machine perfusion (SNMP) remain unexplained. In this study, the effects of initial purification perfusate with simple method of replacing the first 0.5-L perfusate during SNMP were investigated to consider installation effect of the filter or the dialyzer. Porcine liver grafts, which have 60-min warm ischemia time, were procured to imitate the DCD graft condition. Purified SNMP (PSNMP) results were compared with simple cold storage and conventional SNMP. In PSNMP, initial perfusate of 0.5 L was removed to substitute for purification. After preservation process, the preserved grafts were reperfused with diluted autologous blood for 2 h under normothermic machine perfusion condition to evaluate the liver function using an isolated reperfusion model. The vascular pressures, enzyme release rates and the metabolic indexes during reperfusion were analyzed. The pressures in the hepatic artery after reperfusion 60 min were significantly lower in PSNMP group compared with cold storage (CS) and SNMP groups. In addition, lactate dehydrogenase and alkaline phosphatase were significantly lower after PSNMP than after the CS or SNMP. Also, the metabolic indexes of hyaluronic acid and lactate were significantly decreased by purifying the perfusate in MP preservation than in CS or SNMP. The effectiveness of initial purification perfusate during SNMP was investigated.

Impact of Machine Perfusion on Biliary Complications after Liver Transplantation

We describe in this review the different types of injuries caused to the biliary tree after liver transplantation. Furthermore, we explain underlying mechanisms and why oxygenated perfusion concepts could not only protect livers, but also repair high-risk grafts to prevent severe biliary complications and graft loss. Accordingly, we summarize experimental studies and clinical applications of machine liver perfusion with a focus on biliary complications after liver transplantation. Key points: (1) Acute inflammation with subsequent chronic ongoing liver inflammation and injury are the main triggers for cholangiocyte injury and biliary tree transformation, including non-anastomotic strictures; (2) Hypothermic oxygenated perfusion (HOPE) protects livers from initial oxidative injury at normothermic reperfusion after liver transplantation. This is a unique feature of a cold oxygenation approach, which is effective also end-ischemically, e.g., after cold storage, due to mitochondrial repair mechanisms. In contrast, normothermic oxygenated perfusion concepts protect by reducing cold ischemia, and are therefore most beneficial when applied instead of cold storage; (3) Due to less downstream activation of cholangiocytes, hypothermic oxygenated perfusion also significantly reduces the development of biliary strictures after liver transplantation.

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.

Pushing the Limits: Machine Preservation of the Liver as a Tool to Recondition High-Risk Grafts

Purpose of the Review

Machine perfusion (MP) is a novel technology recently introduced in liver transplantation, redefining the current practice of organ preservation and pushing the limits of high-risk liver utilisation. This review highlights the key benefits of machine perfusion over conventional static cold storage (SCS), demonstrated in human liver research and clinical transplants.

Recent Findings

The first clinical trials have demonstrated both safety and feasibility of MP. The most recent transplant series and result from a randomised trial suggest the technology is superior to SCS. The key benefits include extended period of organ preservation, decreased incidence of early allograft dysfunction and reduction of biliary complications. Normothermic liver perfusion allows viability testing to guide transplantability of the highest-risk organs. This technology also provides opportunities for therapeutic interventions to improve liver function and quality in organs that are currently declined for clinical use.

Summary

Machine perfusion is likely to transform the liver preservation pathway and to improve utilisation of high-risk grafts.

Graft Reconditioning before Liver Transplantation

BACKGROUND

The high demand for livers for transplantation has led to organs of limited quality being accepted to expand the donor pool. This is associated with inferior outcomes due to more pronounced preservation injury. Accordingly, recent research has aimed to develop preservation modalities for improved preservation as well as strategies for liver viability assessment and liver reconditioning.

METHODS

The PubMed database was searched using the terms 'perfusion', 'liver', 'preservation', and 'reconditioning' in various combinations, and the according literature was reviewed.

RESULTS

Several perfusion techniques have been developed in recent years with the potential for liver reconditioning. Preclinical and first emerging clinical data suggest feasibility, safety, and superiority over the current gold standard of cold storage.

CONCLUSION

This review outlines current advances in the field of liver preservation with an emphasis on liver reconditioning methods.

Role of NK, NKT cells and macrophages in liver transplantation

Liver transplantation has become the treatment of choice for acute or chronic liver disease. Because the liver acts as an innate immunity-dominant organ, there are immunological differences between the liver and other organs. The specific features of hepatic natural killer (NK), NKT and Kupffer cells and their role in the mechanism of liver transplant rejection, tolerance and hepatic ischemia-reperfusion injury are discussed in this review.

Donor Hepatic Steatosis Induce Exacerbated Ischemia-Reperfusion Injury Through Activation of Innate Immune Response Molecular Pathways

BACKGROUND

Severe liver steatosis is a known risk factor for increased ischemia-reperfusion injury (IRI) and poor outcomes after liver transplantation (LT). This study aimed to identify steatosis-related molecular mechanisms associated with IRI exacerbation after LT.

METHODS

Paired graft biopsies (n = 60) were collected before implantation (L1) and 90 minutes after reperfusion (L2). The LT recipients (n = 30) were classified by graft macrosteatosis: without steatosis (WS) of 5% or less (n = 13) and with steatosis (S) of 25% or greater (n = 17). Plasma samples were collected at L1, L2, and 1 day after LT (postoperative [POD]1) for cytokines evaluation. Tissue RNA was isolated for gene expression microarrays. Probeset summaries were obtained using robust multiarray average algorithm. Pairwise comparisons were fit using 2-sample t test. P values 0.01 or less were significant (false discovery rate <5%). Molecular pathway analyses were conducted using Ingenuity Pathway Analysis tool.

RESULTS

Significantly differentially expressed genes were identified for WS and S grafts after reperfusion. Comprehensive comparison analysis of molecular profiles revealed significant association of S grafts molecular profile with innate immune response activation, macrophage production of nitric oxide and reactive oxygen species, IL-6, IL-8, IL-10 signaling activation, recruitment of granulocytes, and accumulation of myeloid cells. Postreperfusion histological patterns of S grafts revealed neutrophilic infiltration surrounding fat accumulation. Circulating proinflammatory cytokines after reperfusion and 24 hours after LT concurred with intragraft-deregulated molecular pathways. All tested cytokines were significantly increased in plasma of S grafts recipients after reperfusion when compared with WS group at same time.

CONCLUSIONS

Increases of graft steatosis exacerbate IRI by exacerbation of innate immune response after LT. Preemptive strategies should consider it for safety usage of steatotic livers.

Declining liver graft quality threatens the future of liver transplantation in the United States

National liver transplantation (LT) volume has declined since 2006, in part because of worsening donor organ quality. Trends that degrade organ quality are expected to continue over the next 2 decades. We used the United Network for Organ Sharing (UNOS) database to inform a 20-year discrete event simulation estimating LT volume from 2010 to 2030. Data to inform the model were obtained from deceased organ donors between 2000 and 2009. If donor liver utilization practices remain constant, utilization will fall from 78% to 44% by 2030, resulting in 2230 fewer LTs. If transplant centers increase their risk tolerance for marginal grafts, utilization would decrease to 48%. The institution of "opt-out" organ donation policies to increase the donor pool would still result in 1380 to 1866 fewer transplants. Ex vivo perfusion techniques that increase the use of marginal donor livers may stabilize LT volume. Otherwise, the number of LTs in the United States will decrease substantially over the next 15 years. In conclusion, the transplant community will need to accept inferior grafts and potentially worse posttransplant outcomes and/or develop new strategies for increasing organ donation and utilization in order to maintain the number of LTs at the current level.