Protective effect of carbon monoxide inhalation on lung injury after hemorrhagic shock/resuscitation in rats

Background: Hemorrhagic shock and resuscitation (HSR) induces pulmonary inflammation that leads to acute lung injury. Carbon monoxide (CO), a by-product of heme catalysis, was shown to have potent cytoprotective and anti-inflammatory effects. The aim of this study was to examine the effects of CO inhalation at low concentration on lung injury induced by HSR in rats. Methods: Rats were subjected to HSR by bleeding to achieve mean arterial pressure of 30 mm Hg for 60 minutes followed by resuscitation with shed blood and saline as needed to restore blood pressure. HSR animals were either maintained in room air or were exposed to CO at 250 ppm for 1 hour before and 3 hours after HSR. Results: HSR caused an increase in the DNA binding activity of nuclear factor-κB and activator protein-1 in the lung followed by the up-regulation of pulmonary gene expression of tumor necrosis factor-α, inducible nitric oxide synthase, and interleukin (IL)-10. HSR also resulted in an increase in myeloperoxidase activity and wet weight to dry weight ratio in the lung, and more prominent histopathologic changes including congestion, edema, cellular infiltration, and hemorrhage. In contrast, CO inhalation significantly ameliorated these inflammatory events as judged by fewer histologic changes, less up-regulation of inflammatory mediators, and less activation of nuclear factor-κB and activator protein-1. Interestingly, the protective effects against lung injury afforded by CO were associated with further increases in mRNA expression of IL-10 in the lung. Conclusions: These findings suggest that inhaled CO at a low concentration ameliorated HSR-induced lung injury and attenuated inflammatory cascades by up-regulation of anti-inflammatory IL-10.