Effect of Ex-Vivo Lung Perfusion (EVLP) on Metabolomic Profile of Human Lungs

Abstract

Purpose 1H Nuclear Magnetic Resonance Spectroscopy (NMR-spec) can identify all major metabolites in an organ, characterizing the metabolic phenotype. We used NMR-spec to determine changes in the metabolome of human lung tissue before and after normothermic EVLP with Steen solution, and in the EVLP perfusate hourly. Methods and Materials Lung biopsies were obtained before and after normothermic EVLP (6 hrs n=2; 3 hrs n=1) and extracted with 40% acetonitrile. NMR spectra were analyzed with Principal Component Analysis and Orthogonal Partial Least Squares Discriminant Analysis. EVLP fluid was analyzed directly with addition of 10% deuterated phosphate buffer. Results The primary 5 metabolites identified in the perfusate are glucose, choline glycine, lactate, & acetate. Lactate increased the most during EVLP. In the polar (water soluble) extract, there was a clear separation between pre and post EVLP biopsies, with significant increases in lactate & alanine (glucose metabolites), ATP & ADP, and acetate (indicating β-oxidation of free fatty acids). The ketone bodies, β-hydroxybutyrate, acetoacetate, and acetone, were not detected. Conclusions This pilot study shows that NMR-spec can characterize the metabolomic phenotype of lung tissue. During EVLP energy stores are replenished. Lactate is the major metabolite secreted into the perfusate during EVLP, presumably metabolized from glucose contained in Steen solution. Accumulation of acetate suggests that the TCA cycle was at capacity and AcetylCoA accumulation led to hydrolysis forming acetate. Lack of ketone bodies in the presence of large amounts of actetate suggests the lung cannot create ketone bodies, a function reserved primarily for the liver. By determining the lung metabolome, NMR-spec may identify biomarkers associated with poor or irretrievable lung function, or identify therapeutic targets that might be measured with point-of-care devices for therapy during EVLP to improve yield or quality of lungs for transplant.