422.6: Effects of Argon Inhalation on Reducing Pulmonary Warm Ischemia-Reperfusion Injury in CLAWN Miniature Swine

Abstract

Background: Ischemia-reperfusion injury (IRI) remains a major cause of early death in lung transplantation. In addition, warm ischemia of the donor organ is inevitable when transplanting from DCD donor, and it is important to develop new strategies for reducing warm IRI. The cytoprotective effects of chemically inert noble gases such as argon (Ar) have been demonstrated. Ar is particularly safe and cost-effective because it is non-anesthetic and the third most abundant gas in the atmosphere, suggesting higher safety levels and lower cost advantages. The inhibitory effect of IRI has been reported in small animal models of various organs, but there are conflicting reports on the effect in large animal models. In this study, we evaluated the cytoprotective effect and safety of Ar inhalation using large animal model of pulmonary warm IRI model. Methods: Ten CLAWN miniature swine were evenly divided into two groups (Ar-treated and control group). In both groups, warm ischemia was induced for 90 minutes by clamping the left bronchus, pulmonary artery and veins. Animals were inhaled with either 70% Ar (Ar-treated) or 70% nitrogen (control) in 30% oxygen for 360 minutes throughout the procedure. Lung function and structure were serially assessed via the ratio of partial pressure of oxygen to fractional inspired oxygen (pO2/FiO2) measured by both arterial blood and pulmonary vein (PV), chest X-ray (CXR) and lung biopsy, as well as the presence of side effects. Results: Ar inhalation dramatically decreased lung injury associated with ischemia and reperfusion without apparent adverse effects. In the control group, 90 minutes of warm ischemia resulted in a significant decrease in pO2/FiO2 by arterial blood, from 568 +/-12 mmHg before ischemia to 272 +/-39 mmHg 2 hours after reperfusion (p<0.05). In sharp contrast, animals in the Ar-treated group had no significant change in pO2/FiO2 by arterial blood despite 90-min ischemia (563 +/-18 mmHg before ischemia to 431 +/-49 mmHg 2 hours after reperfusion). Moreover, pO2/FiO2 by PV showed well-maintained lung function in the Ar-treated group (331 +/-40 vs. 186 +/-17 mmHg at 2 hours, p<0.05; 519 +/-19 vs. 292 +/-33 mmHg at 2 days after reperfusion, p<0.05). In addition, histological scores of lung biopsies (calculated based on four items: cellular infiltration, intralobular edema, fibrin exudation, and hemorrhage) were significantly better in the Ar-inhalation group for both 2-hour and 2-day biopsies after reperfusion. The evaluation of serum and biopsy samples suggested that anti-oxidant and anti-apoptosis were the main mechanisms of Ar inhalation. Conclusion: In this study, we demonstrated for the first time the inhibitory effect of perioperative Ar inhalation on pulmonary warm IRI in large animals. In order to apply this new therapy to clinical practice, further detailed analysis of the mechanism and evaluation using ischemic models including cold storage are required in the future.