Improved metabolism and redox state with a novel preservation solution: implications for donor lungs after cardiac death (DCD)

Abstract

Lungs donated after cardiac death (DCD) are an underutilized resource for a dwindling donor lung transplant pool. Our study investigates the potential of a novel preservation solution, Somah, to better preserve statically stored DCD lungs, for an extended time period, when compared to low-potassium dextran solution (LPD). We hypothesize that Somah is a metabolically superior organ preservation solution for hypothermic statically stored porcine DCD lungs, possibly improving lung transplant outcomes. Porcine DCD lungs (n = 3 per group) were flushed with and submerged in cold preservation solution. The lungs were stored up to 12 h, and samples were taken from lung tissue and the preservation medium throughout. Metabolomic and redox potential were analyzed using high performance liquid chromatography, mass spectrometry, and RedoxSYS®, comparing substrate and pathway utilization in both preservation solutions. Glutathione reduction was seen in Somah but not in LPD during preservation. Carnitine, carnosine, and n-acetylcarnosine levels were elevated in the Somah medium compared with LPD throughout. Biopsies of Somah exposed lungs demonstrated similar trends after 2 h, up to 12 h. Adenosine gradually decreased in Somah medium over 12 h, but not in LPD. An inversely proportional increase in inosine was found in Somah. Higher oxidative stress levels were measured in LPD. Our study suggests suboptimal metabolic preservation in lungs stored in LPD. LPD had poor antioxidant potential, cytoprotection, and an insufficient redox potential. These findings may have immediate clinical implications for human organs; however, further investigation is needed to evaluate DCD lung preservation in Somah as a viable option for transplant.

Keywords: metabolomics; organ longevity; transplant.

Fig. 1.

Schematic overview of experimental set-up. Pigs were shocked and rapidly exsanguinated without anesthetics before organ harvest. The lungs were randomly assigned to either LPD or Somah and individually rinsed with 1 L of preservation solution by anterograde flushing through the pulmonary trunk. Subsequently the lungs were surgically separated and submerged in their respective preservation solution. Medium samples and lung biopsies were taken from the before introducing the preservation solution to the lungs (t = 0) and at t = 2 h, t = 6 h, and at t = 12 h. Tissue biopsies and solution samples were immediately snap frozen in liquid nitrogen and stored at −80℃.

Fig. 2.

(a) Reduced glutathione (GSH) in Somah and LPD medium over time. (b) Oxidized glutathione (GSH) in Somah and LPD medium over time. n = 3 for each group, plotted values are mean ± SEM, *P < 0.05.

Fig. 3.

(a) Carnitine in Somah and LPD medium over time. (b) Carnosine in Somah and LPD medium over time. (c) Carnitine in Somah and LPD lung biopsies over time. (d) Acetylcarnitine in Somah and LPD lung biopsies over time. (e) n-acetylcarnosine in Somah and LPD lung biopsies over time. (f) n-acetylcarnosine in Somah and LPD medium over time. n = 3 for each group, plotted values are mean ± SEM, *P < 0.05.

Fig. 4.

(a) Adenosine in Somah and LPD medium over time. (b) Adenosine in Somah and LPD lung biopsies over time. (c) Inosine in Somah and LPD medium over time. (d) Inosine in Somah and LPD lung biopsies over time. n = 3 for each group, plotted values are mean ± SEM, *P < 0.05.

Fig. 5.

(a) Glucose in Somah and LPD medium over time. (b) Fructose in Somah and LPD medium over time. (c) Malate in Somah and LPD medium over time. (d) Fumarate in Somah and LPD medium over time. (e) Malate in Somah and LPD lung biopsies over time. (f) Mannitol/sorbitol in Somah and LPD lung biopsies over time. n = 3 for each group, plotted values are mean ± SEM, *P < 0.05.

Fig. 6.

(a) Static oxidation reduction (sORP) in millivolts (mV) of Somah and LPD medium over time. (b) Capacity oxidation reduction potential (cORP) in microcoulombs (µC) of Somah and LPD medium over time. n = 3 for each group, plotted values are mean ± SEM, *P < 0.05.