Metabolomics Differences of the Donor Livers Between In Situ and Ex Situ Conditions During Ischemia-free Liver Transplantation

Normothermic Machine Perfusion of Explanted Human Metabolic Livers: A Proof of Concept for Studying Inborn Errors of Metabolism

The human liver plays a central metabolic role; however, its physiology may become imbalanced in inborn errors of metabolism (IEM), a broad category of monogenic disorders. Liver transplantation has been increasingly used to improve patient metabolic control, especially in diseases related to amino acid metabolism, such as urea cycle disorders and organic acidurias, to provide enzyme replacement. Ex vivo liver normothermic machine perfusion (NMP) techniques have recently been developed to increase the number of transplantable grafts and improve transplantation outcomes. This study used seven NMP of explanted livers from patients with IEM undergoing transplantation as models to investigate disease-related liver metabolism and function. The perfused livers demonstrated positive viability indicators and disease-specific targeted metabolomics providing the proof-of-principle that our ex vivo model expresses the biochemical disease characteristics and responds to therapeutical intervention in a unique "physiological" milieu, offering an ideal tool to study novel treatments, in a setting closely mirroring human disease.

Research on gene editing and immunosuppressants in kidney xenotransplantation

Gene-edited pig organ transplantation can solve the serious shortage of human donor organs. Currently, xenotransplantation is rapidly developing and has made significant breakthroughs. The use of GTKO (Gal knockout) pigs is an important step forward. The subsequent knockout of three genes combined with the transfer of immune-related genes effectively prolonged the survival time of non-human primate (NHP) transplantation in xenotransplantation. Due to the success of allogeneic kidney transplantation on NHP, this gene editing protocol was recently applied to clinical patients. Two patients underwent allogeneic kidney transplantation and survived for 51 days and 47 days. Exceeding the hyperacute rejection period proves that appropriate gene editing strategies and the combination of immunosuppressive agents contribute to the success of xenotransplantation. To further enhance the feasibility of pig kidney xenograft, this article mainly explores the effects of the NHP xenograft gene editing scheme and immunosuppressants on prolonging transplant survival time.

Research progress of ischemia-free liver transplantation

Ischemia-reperfusion injury (IRI) is an inherent issue in organ transplantation. Because of the allograft shortage, more and more extended criteria donor (ECD) organs are used, unfortunately these grafts are more susceptible to IRI. Although machine perfusion technology has brought hope to alleviate IRI, this technology is still unable to eradicate IRI-related organ damage. Ischemia-free liver transplantation (IFLT) can completely avoid IRI, thereby improve graft function and recipient outcome, and allow to expand organ pool. This review summarized the latest progresses in IFLT, and speculated the future development of this concept.

Assessment of Mitochondrial Respiration During Hypothermic Storage of Liver Biopsies Following Normothermic Machine Perfusion

Organ quality can be assessed prior to transplantation, during normothermic machine perfusion (NMP) of the liver. Evaluation of mitochondrial function by high-resolution respirometry (HRR) may serve as a viability assessment concept in this setting. Freshly collected tissue is considered as optimal sample for HRR, but due to technical and personnel requirements, more flexible and schedulable measurements are needed. However, the impact of cold storage following NMP before processing biopsy samples for mitochondrial analysis remains unknown. We aimed at establishing an appropriate storage protocol of liver biopsies for HRR. Wedge biopsies of 5 human livers during NMP were obtained and assessed by HRR. Analysis was performed after 0, 4, 8, and 12 h of hypothermic storage (HTS) in HTK organ preservation solution at 4°C. With HTS up to 4 h, mitochondrial performance did not decrease in HTS samples compared with 0 h (OXPHOS, 44.62 [34.75-60.15] pmol·s-1·mg wet mass-1 vs. 43.73 [40.69-57.71], median [IQR], p > 0.999). However, at HTS beyond 4 h, mitochondrial respiration decreased. We conclude that HTS can be safely applied for extending the biopsy measurement window for up to 4 h to determine organ quality, but also that human liver respiration degrades beyond 4 h HTS following NMP.

Twelve-hour normothermic liver perfusion in a rat model: characterization of the changes in the ex-situ bio-molecular phenotype and metabolism

The partial understanding of the biological events that occur during normothermic machine perfusion (NMP) and particularly during prolonged perfusion might hinder its deployment in clinical transplantation. The aim of our study was to implement a rat model of prolonged NMP to characterize the bio-molecular phenotype and metabolism of the perfused organs. Livers (n = 5/group) were procured and underwent 4 h (NMP4h) or 12 h (NMP12h) NMP, respectively, using a perfusion fluid supplemented with an acellular oxygen carrier. Organs that were not exposed to any procedure served as controls (Native). All perfused organs met clinically derived viability criteria at the end of NMP. Factors related to stress-response and survival were increased after prolonged perfusion. No signs of oxidative damage were detected in both NMP groups. Evaluation of metabolite profiles showed preserved mitochondrial function, activation of Cori cycle, induction of lipolysis, acetogenesis and ketogenesis in livers exposed to 12 h-NMP. Increased concentrations of metabolites involved in glycogen synthesis, glucuronidation, bile acid conjugation, and antioxidant response were likewise observed. In conclusion, our NMP12h model was able to sustain liver viability and function, thereby deeply changing cell homeostasis to maintain a newly developed equilibrium. Our findings provide valuable information for the implementation of optimized protocols for prolonged NMP.