Background: Carbon monoxide (CO), a byproduct of heme catalysis by heme oxygenases, has been shown to provide protection against ischemia/reperfusion (I/R) injury. We examined the cytoprotective effect of CO at a low concentration on cold I/R injury of transplanted lung grafts. Methods: Orthotopic left lung transplantation was performed in syngenic Lewis to Lewis rat combination. Grafts were preserved in University of Wisconsin solution at 4°C for 6 hours. Donors and/or recipients were exposed to CO (250 ppm) in air for 1 hour before surgery and then continuously post-transplantation. Results: Blood oxygen partial pressure of graft pulmonary veins in the CO-treated group versus the air-treated group was significantly higher. The increase of messenger RNA of inflammatory mediators such as interleukin-6, tumor necrosis factor-α, inducible nitric oxide synthase, and cycloooxygenase-2 was markedly inhibited in the CO-treated group. The expression of phosphorylated-extracellular signal-regulated protein kinase 1/2 was significantly reduced in the CO-treated group. CO treatment reduced the number of infiltrating macrophages into the lung grafts. Vascular endothelial cells detected by CD31 stain were well preserved in CO-treated grafts, while those in air-treated grafts were faint and interrupted. Conclusions: These results demonstrate that exogenous low-dose CO treatment of donors and recipients can prevent lung I/R injury and significantly improve function of lung grafts after extended cold preservation and transplantation.
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