Background: Mechanical ventilation still causes an unacceptably high rate of morbidity and mortality because of ventilator-induced lung injury (VILI). Therefore, new therapeutic strategies are needed to treat VILI. Hydrogen sulfide can induce hypothermia and suspended animation-like states in mice. Hydrogen sulfide can also confer antiinflammatory and antiapoptotic effects. This study investigates the organ-protective effects of inhaled hydrogen sulfide during mechanical ventilation. Methods: Mice were ventilated with a tidal volume of 12 ml/kg body weight for 6 h with synthetic air in the absence or presence of hydrogen sulfide (80 parts per million) and, in a second series, at either mild hypothermia or normothermia. Staining of lung sections determined the degree of lung damage by VILI score and apoptotic cells. Bronchoalveolar lavage fluid was analyzed for the cytokines interleukin-1beta and macrophage inflammatory protein-1beta and for neutrophil accumulation. Heme oxygenase-1 and heat shock protein 70 expression were assessed in the lung tissue by Western immunoblot analysis. Results: Mechanical ventilation at both hypothermia and normothermia led to a profound development of VILI, characterized by pulmonary edema, increased apoptosis, cytokine release, neutrophil recruitment, and up-regulation of the stress proteins such as heme oxygenase-1 and heat shock protein 70. In contrast, the application of hydrogen sulfide during ventilation at either mild hypothermia or normothermia prevented edema formation, apoptosis, proinflammatory cytokine production, neutrophil accumulation, and inhibited heme oxygenase-1 expression. Conclusions: Inhalation of hydrogen sulfide during mechanical ventilation protects against VILI by the inhibition of inflammatory and apoptotic responses. Hydrogen sulfide confers lung protection independently of its ability to induce mild hypothermia during ventilation.

Rationale: Ventilator-induced lung injury (VILI) leads to an unacceptably high mortality. In this regard, the antiinflammatory properties of inhaled carbon monoxide (CO) may provide a therapeutic option. Objectives: This study explores the mechanisms of CO-dependent protection in a mouse model of VILI. Methods: Mice were ventilated (12 ml/kg, 1–8 h) with air in the absence or presence of CO (250 ppm). Airway pressures, blood pressure, and blood gases were monitored. Lung tissue was analyzed for inflammation, injury, and gene expression. Bronchoalveolar lavage fluid was analyzed for protein, cell and neutrophil counts, and cytokines. Measurements and Main Results: Mechanical ventilation caused significant lung injury reflected by increases in protein concentration, total cell and neutrophil counts in the bronchoalveolar lavage fluid, as well as the induction of heme oxygenase-1 and heat shock protein-70 in lung tissue. In contrast, CO application prevented lung injury during ventilation, inhibited stress-gene up-regulation, and decreased lung neutrophil infiltration. These effects were preceded by the inhibition of ventilation-induced cytokine and chemokine production. Furthermore, CO prevented the early ventilation-dependent up-regulation of early growth response-1 (Egr-1). Egr-1–deficient mice did not sustain lung injury after ventilation, relative to wild-type mice, suggesting that Egr-1 acts as a key proinflammatory regulator in VILI. Moreover, inhibition of peroxysome proliferator-activated receptor (PPAR)-γ, an antiinflammatory nuclear regulator, by GW9662 abolished the protective effects of CO. Conclusions: Mechanical ventilation causes profound lung injury and inflammatory responses. CO treatment conferred protection in this model dependent on PPAR-γ and inhibition of Egr-1.

Toll‐like receptors (TLR) and IL‐12 represent key elements of innate immunity. Using C57BL/10 ScCr mice it was shown that TLR4 is important for control of infection with respiratory syncytial virus (RSV). Since these mice have an additional defect in the IL‐12R, we reinvestigated immunity to RSV in several C57BL/10 and BALB/c mouse strains lacking a functional TLR4, a functional IL‐12–IL‐12R interaction or both. In the absence of a functional IL‐12 axis, early virus control was impaired in C57BL/10 mice, but not in BALB/c mice. By contrast, TLR4 had no impact on RSV elimination. Pulmonary NK cell recruitment was impaired in IL‐12 deficient BALB/c mice and NK cytotoxicity was reduced in IL‐12/IL‐12R‐deficient mice of both genetic backgrounds. Absence of TLR4 had no impact on NK cell recruitment or NK activity nor on recruitment of other pulmonary inflammatory cells. Activation of RSV‐specific T cell immunity, including T cell mediated immunopathology, was normal in all mutant strains. These findings clearly argue against a significant role for TLR4 and define a limited role for IL‐12 in primary murine RSV infection.

Transmigration and activation of neutrophils in the lung reflect key steps in the progression of acute lung injury (ALI). It is known that hydrogen sulfide (H₂S) can limit neutrophil activation, but the respective mechanisms remain elusive. Here, we aimed to examine the underlying pathways in pulmonary inflammation. In vivo, C57BL/6N mice received the H₂S slow releasing compound GYY4137 prior to lipopolysaccharide (LPS) inhalation. LPS challenge led to pulmonary injury, inflammation, and neutrophil transmigration that were inhibited in response to H₂S pretreatment. Moreover, H₂S reduced mRNA expression of macrophage inflammatory protein-2 (MIP-2) and its receptor in lung tissue, as well as the accumulation of MIP-2 and interleukin-1β in the alveolar space. In vitro, GYY4137 did not exert toxic effects on Hoxb8 neutrophils, but prevented their transmigration through an endothelial barrier in the presence and absence of MIP-2. In addition, the release of MIP-2 and reactive oxygen species from LPS-stimulated Hoxb8 neutrophils were directly inhibited by H₂S. Taken together, we provide first evidence that H₂S limits lung neutrophil sequestration upon LPS challenge. As proposed underlying mechanisms, H₂S prevents neutrophil transmigration through the inflamed endothelium and directly inhibits pro-inflammatory as well as oxidative signalling in neutrophils. Subsequently, H₂S pretreatment ameliorates LPS-induced ALI.

Ity among critically ill patients. Volatile anesthetics have been shown to exert anti-inflammatory and organ-protective effects in vivo. We investigated the effects of the volatile anesthetic isoflurane on lung injury during mechanical ventilation. METHODS: C57BL/6N mice were ventilated with a tidal volume of 12 mL/kg body weight for 6 hours in the absence or presence of isoflurane, and, in a second series, with or without the specific phosphoinositide 3-kinase/Akt inhibitor LY294002. Lung injury was determined by comparative histology, and by the isolation of bronchoalveolar lavage for differential cell counting and analysis of cytokine levels using enzyme-linked immunosorbent assays. Lung homogenates were analyzed for protein expression by Western blotting. RESULTS: Mechanical ventilation caused increases in alveolar wall thickening, cellular infiltration, and an elevated ventilator-induced lung injury score. Neutrophil influx and cytokine (i.e., interleukin-1β, and macrophage inflammatory protein-2) release were enhanced in the bronchoalveolar lavage of ventilated mice. The expression levels of the stress proteins hemeoxygenase-1 and heat shock protein-70 were elevated in lung tissue homogenates. Isoflurane ventilation significantly reduced lung damage, inflammation, and stress protein expression. In contrast, phosphorylation of Akt protein was substantially increased during mechanical ventilation with isoflurane. Inhibition of phosphoinositide 3-kinase/Akt signaling before mechanical ventilation completely reversed the lung-protective effects of isoflurane treatment in vivo. CONCLUSIONS: Inhalation of isoflurane during mechanical ventilation protects against lung injury by preventing proinflammatory responses. This protection is mediated via phosphoinositide 3-kinase/Akt signaling....