Carbon monoxide inhalation protects rat intestinal grafts from ischemia/reperfusion injury

Carbon monoxide (CO), a byproduct of heme catalysis by heme oxygenases, has been shown to exert anti-inflammatory effects. This study examines the cytoprotective efficacy of inhaled CO during intestinal cold ischemia/reperfusion injury associated with small intestinal transplantation. Orthotopic syngenic intestinal transplantation was performed in Lewis rats after 6 hours of cold preservation in University of Wisconsin solution. Three groups were examined: normal untreated controls, control intestinal transplant recipients kept in room air, and recipients exposed to CO (250 ppm) for 1 hour before and 24 hours after surgery. In air grafts, mRNA levels for interleukin-6, cyclooxygenase-2, intracellular adhesion molecule (ICAM-1), and inducible nitric oxide synthase rapidly increased after intestinal transplant. Histopathological analysis revealed severe mucosal erosion, villous congestion, and inflammatory infiltrates. CO effectively blocked an early up-regulation of these mediators, showed less severe histopathological changes, and resulted in significantly improved animal survival of 92% from 58% in air-treated controls. CO also significantly reduced mRNA for proapoptotic Bax, while it up-regulated anti-apoptotic Bcl-2. These changes in CO-treated grafts correlated with well-preserved CD31⁺ vascular endothelial cells, less frequent apoptosis/necrosis in intestinal epithelial and capillary endothelial cells, and improved graft tissue blood circulation. Protective effects of CO in this study were mediated via soluble guanylyl cyclase, because 1H-(1,2,4)oxadiazole (4,3-α) quinoxaline-1-one (soluble guanylyl cyclase inhibitor) completely reversed the beneficial effect conferred by CO. Perioperative CO inhalation at a low concentration resulted in protection against ischemia/reperfusion injury to intestinal grafts with prolonged cold preservation.