Mass Spectrometry Based Metabolomics Comparison of Liver Grafts from Donors after Circulatory Death (DCD) and Donors after Brain Death (DBD) Used in Human Orthotopic Liver Transplantation

Abstract

Use of marginal liver grafts, especially those from donors after circulatory death (DCD), has been considered as a solution to organ shortage. Inferior outcomes have been attributed to donor warm ischaemic damage in these DCD organs. Here we sought to profile the metabolic mechanisms underpinning donor warm ischaemia. Non-targeted Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry metabolomics was applied to biopsies of liver grafts from donors after brain death (DBD; n = 27) and DCD (n = 10), both during static cold storage (T1) as well as post-reperfusion (T2). Furthermore 6 biopsies from DBD donors prior to the organ donation (T0) were also profiled. Considering DBD and DCD together, significant metabolic differences were discovered between T1 and T2 (688 peaks) that were primarily related to amino acid metabolism, meanwhile T0 biopsies grouped together with T2, denoting the distinctively different metabolic activity of the perfused state. Major metabolic differences were discovered between DCD and DBD during cold-phase (T1) primarily related to glucose, tryptophan and kynurenine metabolism, and in the post-reperfusion phase (T2) related to amino acid and glutathione metabolism. We propose tryptophan/kynurenine and S-adenosylmethionine as possible biomarkers for the previously established higher graft failure of DCD livers, and conclude that the associated pathways should be targeted in more exhaustive and quantitative investigations.

Tryptophan Metabolism via the Kynurenine Pathway: Implications for Graft Optimization during Machine Perfusion

“…One major finding of this study is the greater metabolism of tryptophan (TRP) via the kynurenine pathway (KP) in the NMP group with subsequently increased tissue concentrations of kynurenine (KYN) and kynurenate (KYNA). The difference in tryptophan metabolism during NMP compared to SNMP represents a clinically significant finding, as two studies found higher levels of KYN in transplanted livers that experienced primary nonfunction compared to livers with normal function [ 17 , 20 ]. Though KYNA levels were not reported, this highlights the therapeutic potential of this metabolic pathway.…”

“…While the higher energy charge ratios are attributed to the lower metabolic activity at subnormothermic temperatures, the depletion of glutathione is likely due to the inability to expend ATP needed to resynthesize glutathione after its breakdown. Similarly, several clinical studies have demonstrated a correlation between higher concentrations of glutathione metabolites and early allograft dysfunction [ 17 , 18 ]. Therefore, supplementation of the circulating perfusate during SNMP with exogenous glutathione could be another potential therapy to improve a DCD graft’s ability to tolerate oxidative stress during transplantation.…”

“…In addition, the NMP group included one DBD liver whereas the SNMP group was comprised of only DCD livers. Future studies should examine DCD and DBD livers separately as they have been shown to exhibit different metabolomic profiles at the end of the static cold storage period [ 17 ]. To the best of our effort, donor demographics were otherwise similar.…”

“…Many physicians envision a future where MP is used to improve the function of each donor liver to achieve maximal graft utilization and minimize discard rates [ 10 , 11 ], and one potential method to improve graft function is targeting metabolism. While numerous studies have demonstrated potential metabolic targets in the liver, renal, and intestinal IRI response [ 12 , 13 , 14 , 15 , 16 ], few studies have examined the metabolic changes that occur in the human liver during transplantation [ 12 , 17 , 18 , 19 , 20 ] and fewer still during ex situ machine perfusion [ 4 , 21 ]. This is a critical area of research since the machine perfusion platform is the only setting for liver-specific adjunct therapies prior to transplantation.…”

Deregulation of the Purine Pathway in Pre-Transplant Liver Biopsies Is Associated with Graft Function and Survival after Transplantation

“…A systematic review on the use of metabolomics to discover liver biomarkers for transplantation outcomes in liver tissue biopsies highlighted promising results [17]. These first studies identified lipid molecules [18][19][20], tryptophan, kynurenine and S-adenosylmethionine as liver biomarkers [21,22].…”