The beneficial effects of hydrogen gas inhalation during ex vivo lung perfusion on donor lungs obtained after cardiac death in pig lung transplantation model

Abstract

INTRODUCTION

Lung transplantation (LTx) is the optimal treatment for end-stage lung diseases. However, a shortage of donor lungs is the major obstacle to LTx. To overcome this problem, the donation after cardiac death (DCD) lungs are used. The use of DCD lungs brings several disadvantages including longer warm ischemic times compared to brain death donor lung, and absence of objective methods such as arterial blood gas analysis (ABGA) and pulmonary artery pressure to evaluate DCD lung function. Ex Vivo Lung Perfusion (EVLP) is a system that circulates normothermic perfusate into procured lungs, allowing for improved lung function and lung assessment. In this study, we investigated whether ventilation with hydrogen gas during EVLP improves DCD lung function, and whether this effect persists after actual transplantation.

MATERIALS and METHODS

10 pigs were randomly divided into control group (n = 5) and hydrogen group (n = 5). After fibrillation by electric shock, no further treatment was administered in order to induce warm ischemic injury for 1 hour. Next, the lung was procured and EVLP was applied for 4 hours. During EVLP, the control group was given room air for respiration while the hydrogen group was given 2% hydrogen gas. After EVLP, the left lung graft was orthotopically transplanted into the recipient pig and reperfused for 3 hours. During EVLP and reperfusion, the functional parameters and ABGA were measured every hour. Superoxide dismutase (SOD), heme oxygenase (HO)-1, interleukin (IL)-6, IL-10, tumor necrosis factor-alpha (TNF-α) and NOD-like receptor protein 3 (NLRP3) were evaluated in lung tissue after reperfusion. Pathological evaluations were performed using lung injury severity (LIS) scores and the degree of apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Wet/dry ratio was also measured.

RESULTS

During EVLP, pulmonary vascular resistance (PVR), and peak airway pressure (PAP) were lower in the hydrogen group, but lung compliance (LC) was lower in the control group. After LTx, oxygen capacity (p = 0.033), LC (p = 0.002), and PAP (p = 0.020) were significantly better in the hydrogen group. The expressions of SOD (p = 0.022) and HO-1 (p = 0.047) were significantly higher in the hydrogen group. The expressions of IL-6 (p = 0.024) and NLRP3 (p = 0.042) were higher in the control group, but IL-10 (p = 0.037) was higher in the hydrogen group. LIS score and the number of apoptotic cells were higher, and the degree of pulmonary edema was more severe in the control group than in the hydrogen group (LIS score: 2.2 ± 0.2 vs 0.7 ± 0.2; number of apoptotic cells: 3.4 ± 1.6 vs 2.1 ± 0.4; Wet/dry ration: 2.833 ± 0.354 vs 1.766 ± 0.078, respectively).

CONCLUSION

Hydrogen gas inhalation during EVLP improved DCD lung function via reduction of inflammation and apoptosis, and this effect persisted after LTx. Hydrogen gas inhalation during EVLP may increase the utilization of DCD lungs.