01.18 Metabolomic Analysis of DCD Liver Allografts Reveals Distinct Alterations in Energy Metabolism

J. Seal1, H. Bohorquez1, D. Bruce1, E. Bugeaud1, I. Carmody1, A. Cohen1, G. Loss1, J. Culver2,3, C. Petucci2,3, S. Gardell2,3  1Ochsner Clinic,Multi-Organ Transplant,New Orleans, LA, USA 2Sanford Burnham Prebys Medical Discovery Institute,Orlando, FL, USA 3Southeast Center For Integrated Metabolomics,Gainesville, FL, USA

Introduction:  Donation-after-circulatory death (DCD) donors constitute an important opportunity to expand the donor pool for liver transplantation. Utilization of DCD livers is limited by the duration of donor warm ischemia (WIT) from withdrawal of support to hypothermic preservation. Most transplant centers adhere to a fixed limit of donor WIT for acceptance of DCD liver for transplant. Targeted metabolomic analysis generates a “snapshot” of the physiologic state of tissue by measuring the abundance of specific metabolites. A metabolomic approach to donor liver assessment may offer insight into key changes liver allograft physiology and offer a more precise approach to guide organ selection.

Methods:  We applied a metabolomics approach to comprehensively quantify mediators of central energy metabolism in DCD (N=10) vs standard brain dead donors (DBD, N=14). Donor liver biopsies were prospectively obtained at the end of cold storage prior to implantation, flash frozen and biobanked at -70 C storage. Metabolomic analyses were performed through the Southeast Center for Integrated Metabolomics (SECIM). Lyophylized liver tissue samples were reconstituted and analyzed using liquid chromatography (LC) and mass spectroscopy (MS) to quantify amino acids (AA), organic acids, pyridine and adenine nucleotides and acetyl-/malonyl-CoAs using isotope-labeled internal standards.

Results: The mean donor WIT in the DCD group was 20.5±7.8 minutes. There was no differences in cold ischemia time for DCD and DBD groups (4.8 vs 4.3 hrs, P=0.42) and both groups had 100% patient and graft survival at 1 year. Concentrations of ATP and ADP were significantly lower in the DCD group (P=0.021). Acetyl-CoA, a key mediator between glycolysis and Krebs cycle, was also markedly decreased in DCD livers (-37% P=0.009). With the exception of glutamine, all AA were significantly higher in DCD livers compared to DBD grafts , ranging from 44.8% increase for glycine (P=0.022) to 104.2% increase for tyrosine (P=0.001). Tyrosine is a non-essential AA that is both keto- and glucogenic. All amino acids that displayed significant increase in DCD livers can replenish TCA cycle intermediates through anaplerotic reactions (salvage pathways). We did not observe significant differences in organic acid levels between DCD and DBD donors, suggesting preservation of TCA cycle function through protein catabolism and anaplerosis. Significant increase in NMN, a precursor to NAD, in the DCD groups suggests a potential “bottleneck” in pyridine nucleotide metabolism at the NMN adenyltransferase enzyme.

Conclusion: Using a targeted metabolomics approach, we have identified distinct alterations in energy metabolism in DCD livers compared with DBD controls. Expanded applications of targeted metabolomics offers the potential to develop biomarkers to augment DCD liver allograft evaluation and selection for transplantation.