The effects of oxygenation on ex vivo kidneys undergoing Hypothermic Machine Perfusion

BACKGROUND: Supplemental oxygenation of the standard Hypothermic Machine Perfusion (HMP) circuit has the potential to invoke favourable changes in metabolism, optimising cadaveric organs prior to transplantation.

METHODS: Eight pairs of porcine kidneys underwent 18 hours of either oxygenated (HMP/O2) or aerated (HMP/Air) HMP in a paired DCD model of transplantation. Circulating perfusion fluid was supplemented with the metabolic tracer universally labelled glucose ([U-C] glucose).Perfusate, end-point renal cortex and medulla samples underwent metabolomic analysis using 1D and 2D NMR experiments in addition to GC-MS. Analysis of C labelled metabolic products was combined with adenosine nucleotide levels and differences in tissue architecture.

RESULTS: Metabolomic analysis revealed significantly higher concentrations of universally labelled lactate in the cortex of HMP/Air vs HMP/O2 kidneys (0.056 mM vs. 0.026 mM, p<0.05). Conversely, newly synthesised [4,5-C] glutamate concentrations were higher in the cortex of HMP/O2 kidneys inferring relative increases in tricarboxylic acid cycle activity vs HMP/Air kidneys (0.013 mmol/L vs. 0.003 mmol/L, p<0.05). This was associated with greater amounts of ATP in the cortex HMP/O2 vs HMP/Air kidneys (19.8 vs. 2.8 mmol/mg protein, p<0.05). Improved flow dynamics and favourable ultrastructural features were also observed in HMP/O2 kidneys. There were no differences in thiobarbituric acid reactive substances and reduced glutathione levels, tissue markers of oxidative stress, between groups.

CONCLUSIONS: The supplementation of perfusion fluid with high concentration oxygen (95%) results in a greater degree of aerobic metabolism vs aeration (21%) in the non-physiological environment of HMP, with reciprocal changes in ATP levels.