Normothermic liver preservation, current status and future directions

Liver Graft Machine Perfusion: From History Perspective to Modern Approaches in Transplant Surgery

The shortage of donor organs remains an unresolved issue in livertransplantation worldwide. Consequently, strategies for expanding the donor pool are currently being developed. Donors meeting extended criteria undergo thorough evaluation, as livers obtained from marginal donors yield poorer outcomes in recipients, including exacerbated reperfusion injury, acute kidney injury, early graft dysfunction, and primary nonfunctioning graft. However, the implementation of machine perfusion has shown excellent potential in preserving donor livers and improving their characteristics to achieve better outcomes for recipients. In this review, we analyzed the global experience of using machine perfusion in livertransplantation through the history ofthe development ofthis method to the latest trends and possibilities for increasing the number of liver transplants.

Normothermic Machine Perfusion Reduces Transfusion Requirements Even After Static Cold Storage: A 1 y Retrospective Single-center Analysis

Background

Normothermic machine perfusion (NMP) of liver grafts has been shown to reduce intraoperative catecholamine consumption and the need for allogenic blood products after reperfusion compared with organs undergoing classical static cold storage (SCS). This study aimed to investigate the effects of an NMP phase after SCS (NMP after SCS) of liver grafts in terms of postreperfusion hemodynamics and transfusion requirements.

Methods

Eighteen recipients of NMP after SCS grafts were matched according to recipient age, donor age, and model for end-stage liver disease score in a 1:2 ratio with recipients of an SCS graft. Postreperfusion hemodynamics and the need for catecholamines, blood products, and clotting factors were compared.

Results

After reperfusion of the organ, patients in the NMP after SCS group showed significantly reduced transfusion requirements for packed red blood cells and platelet concentrates compared with patients of the SCS group (P < 0.001 and P = 0.018, respectively). In addition, patients in the NMP after SCS group received less fibrinogen concentrate (NMP after SCS group 0 [0-1.5] g versus SCS group 2 [0-4] g; P = 0.0163). No differences in postreperfusion hemodynamics could be detected between groups.

Conclusions

This retrospective analysis shows that NMP reduces postreperfusion requirements of red blood cells, platelet concentrates, and fibrinogen concentrate even if installed after a phase of organ SCS, because it may be practiced on most centers where NMP is available.

Protective Effects of Bone Marrow Mesenchymal Stem Cells (BMMSCS) Combined with Normothermic Machine Perfusion on Liver Grafts Donated After Circulatory Death via Reducing the Ferroptosis of Hepatocytes

BACKGROUND To improve the quality of liver grafts from extended-criteria donors donated after circulatory death (DCD), this study explored whether bone marrow mesenchymal stem cells (BMMSCs) combined with normothermic machine perfusion (NMP) have protective effects on DCD donor livers and the effects of ferroptosis in this procedure. MATERIAL AND METHODS Twenty-four male rat DCD donor livers were randomly and averagely divided into normal, static cold storage (SCS), NMP, and NMP combined with BMMSCs groups. Liver function, bile secretion, and pathological features of DCD donor livers were detected to evaluate the protective effects of NMP and BMMSCs on DCD donor livers. Hydrogen peroxide was used to induce an oxidative stress model of hepatocyte IAR-20 cells to evaluate the protective effects of BMMSCs in vitro. RESULTS Livers treated with NMP combined with BMMSCs showed better liver function, relieved histopathological damage, reduced oxidative stress injury and ferroptosis, and the mechanism of reduction was associated with downregulation of intracellular reactive oxygen species (ROS) and free Fe²⁺ levels. BMMSCs showed significant protective effects on the ultrastructure of DCD donor livers and ROS-induced injury to IAR-20 cells under electron microscopy. BMMSCs also significantly improved the expression level of microtubule-associated protein 1 light chain 3 (LC3)-II in both DCD donor livers and ROS-induced injured IAR-20 cells, including upregulating the expression of ferritin. CONCLUSIONS BMMSCs combined with NMP could reduce the level of ROS and free Fe²⁺ in oxidative stress damaged rat DCD donor livers, potentially reduce the ferroptosis in hepatocytes, and repair both morphology and function of DCD donor livers.

Machine Perfusion of the Liver: A Review of Clinical Trials

Although efforts have been made by transplant centers to increase the pool of available livers by extending the criteria of liver acceptance, this practice creates risks for recipients that include primary non-function of the graft, early allograft dysfunction and post-operative complications. Donor liver machine perfusion (MP) is a promising novel strategy that not only decreases cold ischemia time, but also serves as a method of assessing the viability of the graft. In this review, we summarize the data from liver machine perfusion clinical trials and discuss the various techniques available to date as well as future applications of machine perfusion. A variety of approaches have been reported including hypothermic machine perfusion (HMP) and normothermic machine perfusion (NMP); the advantages and disadvantages of each are just now beginning to be resolved. Important in this effort is developing markers of viability with lactate being the most predictive of graft functionality. The advent of machine perfusion has also permitted completely ischemia free transplantation by utilization of in situ NMP showed promising results. Animal studies that focus on defatting steatotic livers via NMP as well as groups that work on regenerating liver tissue ex vivo via MP. The broad incorporation of machine perfusion into routine clinical practice seems incredible.

Immunological organ modification during Ex Vivo machine perfusion: The future of organ acceptance

Ex vivo machine perfusion (EVMP) has gained revitalized interest in recent years due to the increasing use of marginal organs which poorly tolerate the standard preservation method static cold storage (SCS). EVMP improves on SCS in a number of ways, most notably by the potential for reconditioning of the donor organ prior to transplantation without the ethical concerns associated with organ modulation before procurement. Immunomodulatory therapies administered during EVMP can influence innate and adaptive immune responses to reduce production of inflammatory molecules and polarize tissue-resident immune cells to a regulatory phenotype. The targeted inhibition of an inflammatory response can reduce ischemia-reperfusion injury following organ reoxygenation and therefore reduce incidence of graft dysfunction and rejection. Numerous approaches to modulate the inflammatory response have been applied in experimental models, with the ultimate goal of clinical translatability. Strategies to target the innate immune system include inhibiting inflammatory signaling pathways, upregulating anti-inflammatory mediators, and decreasing mitochondrial damage while those which target the adaptive immune system include mesenchymal stromal cells. Inhibitory RNA approaches target both the innate and adaptive immune systems with a focus on MHC knock-down. Future studies may address issues of therapeutic agent delivery through use of nanoparticles and explore novel strategies such as targeting co-inhibitory molecules to educate T-cells to a tolerogenic state. In this review, we summarize the cellular and acellular contributors to allograft dysfunction and rejection, discuss the strategies which have been employed pre-clinically during EVMP to modulate the donor organ immune environment, and suggest future directions for immunomodulatory EVMP studies.

Normothermic Machine Perfusion Combined with Bone Marrow Mesenchymal Stem Cells Improves the Oxidative Stress Response and Mitochondrial Function in Rat Donation After Circulatory Death Livers

There is a need to improve the quality of donor liver from donation after circulatory death (DCD). The purpose of this study was to investigate the effects and mechanism of normothermic machine perfusion (NMP) combined with bone marrow mesenchymal stem cells (BMMSCs) on the oxidative stress and mitochondrial function in DCD livers. DCD livers were obtained, a rat NMP system was established, and BMMSCs were extracted and identified. The DCD livers were grouped by their preservation method: Normal, static cold storage (SCS), NMP (P), and NMP combined with BMMSCs (PB), and the preservation time was up to 8 h. An IAR20 cell oxidative stress injury model was established in vitro by simulating DCD oxidative stress injury and coculturing with BMMSCs for 6 h. Compared with SCS group, after 6 h in vitro, the PB and P groups had significantly improved liver function and liver histological damage, reduced hepatocyte apoptosis and oxidative stress, improved hepatocyte mitochondrial damage, and increased mitochondrial membrane potential. These indicators were significantly better in the PB group than in the P group. BMMSCs significantly inhibited reactive oxygen species release from the IAR20 cell oxidative stress model in vitro, ameliorated mitochondrial damage, and increased mitochondrial membrane potential level. BMMSCs also downregulated the JUN N-terminal kinase-nuclear factor kappa B (JNK-NF-κB) signaling pathway significantly in the IAR20 cell oxidative stress model and promoted AMP-activated protein kinase (AMPK) activation. We verified that NMP combined with BMMSCs also played the same role in the PB group. NMP combined with BMMSCs could improve liver quality by relieving oxidative stress injury and improving mitochondrial function in rat DCD livers. The mechanism of protective role might involve inhibiting the JNK-NF-κB pathway to reduce oxidative stress and promote AMPK activation, thereby reducing mitochondrial damage and increase mitochondrial function.

Essential updates 2018/2019: Liver transplantation

Among the recent topics in the field of liver transplantation (LT), one of the significant therapeutic breakthroughs is the introduction of direct-acting antiviral agents (DAAs) against hepatitis C virus (HCV) infection. With cure rates close to 100%, a better proportion of LT candidates and recipients can be cured of HCV infection by DAA therapies that are simple and well-tolerated. Other critical topics include the issue of indication of LT for patients with hepatocellular carcinoma, which has been continuously studied. Several expanded criteria beyond the Milan criteria with acceptable results have been recently reported. The role of donor-specific antibodies (DSAs) in intractable rejection is also an important matter that has been studied. Although long recognized as an important factor in antibody-mediated rejection and even graft survival in renal transplantation, the impact of DSAs on graft and patient survival in LT remains to be elucidated. Including the issues described above, this article focuses on recent advances in LT, management to avoid recurrence of primary diseases, optimization of immunosuppressive treatment, and extended donor criteria.

Bone marrow mesenchymal stem cells combine with normothermic machine perfusion to improve rat donor liver quality-the important role of hepatic microcirculation in donation after circulatory death

Donation after circulatory death (DCD) can expand the donor pool effectively. A gap remains in outcome between DCD livers and living donor livers, warranting improved DCD liver quality and urgent resolution. Bone marrow mesenchymal stem cells (BMMSCs) can regulate immunity, participate in the anti-inflammatory response, and secrete cytokines. We investigated the effect of BMMSCs combined with normothermic machine perfusion (NMP) on DCD liver quality, and the role of microcirculation therein. Rat thoracic aortas were clipped to obtain DCD livers, and a rat NMP system was established. The DCD livers were grouped by preservation method: normal, static cold storage (SCS), NMP (P), and BMMSCs plus NMP (BP); storage time was up to 8 h. Liver function in outflow perfusate was detected by biochemical methods; liver tissue histopathology was observed by hematoxylin–eosin staining; hepatocyte ultrastructure was observed by transmission electron microscopy; hepatocyte apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labeling; liver microcirculation–related indicators were detected by immunofluorescence, immunohistochemistry, Western blotting, and enzyme-linked immunosorbent assay. Compared with SCS, P and BP significantly improved liver function and liver histological damage, reduced hepatocyte apoptosis, and repaired hepatocyte mitochondrial damage after 6 h in vitro. BP also significantly inhibited intrahepatic macrophage activation and intercellular adhesion, improved endothelial damage, and significantly improved endothelin 1–nitric oxide balance and microcirculation perfusion. In conclusion, BP can improve DCD liver microcirculation and quality. The mechanism may be the improvement of improve hepatic sinusoidal endothelial injury and microcirculation perfusion by inhibiting macrophage activation and intercellular adhesion.

Effects of immediate versus delayed ex-vivo lung perfusion in a porcine cardiac arrest donation model

OBJECTIVE

Ex-vivo lung perfusion is a promising tool to evaluate and recondition marginal donor lungs usually after a cold static preservation. The concept of continuous organ perfusion is supposed to reduce ischemic damage; however, the optimal perfusion protocol has not been established yet. The aim of this study was to compare immediate ex-vivo lung perfusion (I-EVLP) to delayed ex-vivo lung perfusion (D-EVLP) after a certain cold static preservation period on lung function in a large animal model.

METHODS

In a porcine model, lungs were procured after circulatory death and 60 min of no-touch warm ischemia. Lungs were preserved with single-flush cold low potassium dextran solution and prepared either for I-EVLP (n = 8) or stored cold for 9 h with subsequent D-EVLP (n = 8). Functional outcomes and morphology were compared during 4 h of ex-vivo lung perfusion, using STEEN Solution^TM as perfusion solution.

RESULTS

Pulmonary functional data, perfusate activities of lactate dehydrogenase, alkaline phosphatase, and products of lipid peroxidation did not differ significantly. There was a trend toward lower wet-dry ratio (I-EVLP: 13.4 ± 2.9; D-EVLP: 9.1 ± 2.5) and higher ΔpO₂ in D-EVLP group (I-EVLP: 209 ± 51.6 mmHg; D-EVLP: 236.3 ± 47.3 mmHg).

CONCLUSION

In this donation-after-circulatory-death model, 9 h of cold static preservation followed by ex-vivo lung perfusion results in comparable pulmonary function to I-EVLP as indicated by oxygenation capacities and wet-dry ratio. Our findings indicate that prolonged cold static preservation prior to ex-vivo lung perfusion is as safe and effective as I-EVLP in the procurement of donor lungs.