Introduction: Ventilator-induced lung injury (VILI) contributes to morbidity and mortality in acute respiratory distress syndrome (ARDS). Particularly pre-injured lungs are susceptible to VILI despite protective ventilation. In a previous study, the endogenous peptide adrenomedullin (AM) protected murine lungs from VILI. We hypothesized that mechanical ventilation (MV) contributes to lung injury and sepsis in pneumonia, and that AM may reduce lung injury and multiple organ failure in ventilated mice with pneumococcal pneumonia. Methods: We analyzed in mice the impact of MV in established pneumonia on lung injury, inflammation, bacterial burden, hemodynamics and extrapulmonary organ injury, and assessed the therapeutic potential of AM by starting treatment at intubation. Results: In pneumococcal pneumonia, MV increased lung permeability, and worsened lung mechanics and oxygenation failure. MV dramatically increased lung and blood cytokines but not lung leukocyte counts in pneumonia. MV induced systemic leukocytopenia and liver, gut and kidney injury in mice with pneumonia. Lung and blood bacterial burden was not affected by MV pneumonia and MV increased lung AM expression, whereas receptor activity modifying protein (RAMP) 1–3 expression was increased in pneumonia and reduced by MV. Infusion of AM protected against MV-induced lung injury (66% reduction of pulmonary permeability p < 0.01; prevention of pulmonary restriction) and against VILI-induced liver and gut injury in pneumonia (91% reduction of AST levels p < 0.05, 96% reduction of alanine aminotransaminase (ALT) levels p < 0.05, abrogation of histopathological changes and parenchymal apoptosis in liver and gut). Conclusions: MV paved the way for the progression of pneumonia towards ARDS and sepsis by aggravating lung injury and systemic hyperinflammation leading to liver, kidney and gut injury. AM may be a promising therapeutic option to protect against development of lung injury, sepsis and extrapulmonary organ injury in mechanically ventilated individuals with severe pneumonia.

Introduction: Lung-protective ventilation reduced acute respiratory distress syndrome (ARDS) mortality. To minimize ventilator-induced lung injury (VILI), tidal volume is limited, high plateau pressures are avoided, and positive end-expiratory pressure (PEEP) is applied. However, the impact of specific ventilatory patterns on VILI is not well defined. Increasing inspiratory time and thereby the inspiratory/expiratory ratio (I:E ratio) may improve oxygenation, but may also be harmful as the absolute stress and strain over time increase. We thus hypothesized that increasing inspiratory time and I:E ratio aggravates VILI. Methods: VILI was induced in mice by high tidal-volume ventilation (HV_T 34 ml/kg). Low tidal-volume ventilation (LV_T 9 ml/kg) was used in control groups. PEEP was set to 2 cm H₂O, FiO₂ was 0.5 in all groups. HV_T and LV_T mice were ventilated with either I:E of 1:2 (LV_T 1:2, HV_T 1:2) or 1:1 (LV_T 1:1, HV_T 1:1) for 4 hours or until an alternative end point, defined as mean arterial blood pressure below 40 mm Hg. Dynamic hyperinflation due to the increased I:E ratio was excluded in a separate group of animals. Survival, lung compliance, oxygenation, pulmonary permeability, markers of pulmonary and systemic inflammation (leukocyte differentiation in lung and blood, analyses of pulmonary interleukin-6, interleukin-1β, keratinocyte-derived chemokine, monocyte chemoattractant protein-1), and histopathologic pulmonary changes were analyzed. Results: LV_T 1:2 or LV_T 1:1 did not result in VILI, and all individuals survived the ventilation period. HV_T 1:2 decreased lung compliance, increased pulmonary neutrophils and cytokine expression, and evoked marked histologic signs of lung injury. All animals survived. HV_T 1:1 caused further significant worsening of oxygenation, compliance and increased pulmonary proinflammatory cytokine expression, and pulmonary and blood neutrophils. In the HV_T 1:1 group, significant mortality during mechanical ventilation was observed. Conclusion: According to the “baby lung” concept, mechanical ventilation-associated stress and strain in overinflated regions of ARDS lungs was simulated by using high tidal-volume ventilation. Increase of inspiratory time and I:E ratio significantly aggravated VILI in mice, suggesting an impact of a “stress/strain × time product” for the pathogenesis of VILI. Thus increasing the inspiratory time and I:E ratio should be critically considered.

Klebsiella pneumoniae is a leading cause of severe hospital-acquired respiratory tract infections and death but little is known regarding the modulation of respiratory dendritic cell (DC) subsets. Plasmacytoid DC (pDC) are specialized type 1 interferon producing cells and considered to be classical mediators of antiviral immunity.

Rationale: Mechanical ventilation is life-saving but may evoke ventilator-induced lung injury. Objectives: To explore how the circadian clock modulates severity of murine ventilator-induced lung injury via the core clock component BMAL1 in myeloid cells. Methods: Myeloid cell BMAL1-deficient (LysM^Bmal1-/-) or wild type control (LysM^Bmal1+/+) mice were subjected to 4 hours mechanical ventilation (34 mL/kg bodyweight) to induce lung injury. Ventilation was initiated at dawn or dusk, or in complete darkness (circadian time 0 or 12) to determine diurnal and circadian effects. Lung injury was quantified by lung function, pulmonary permeability, blood gas analysis, neutrophil recruitment, inflammatory markers and histology. Neutrophil activation and oxidative burst were analyzed ex vivo. Measurements and Main Results: In diurnal experiments, mice ventilated at dawn exhibited higher permeability and neutrophil recruitment compared to dusk. Experiments at circadian time showed deterioration of pulmonary function, worsening of oxygenation and increased mortality at circadian time 0 compared to circadian time 12. Wild type neutrophils isolated at dawn showed higher activation and ROS production compared to dusk, while these day-night differences were dampened in LysM^Bmal1-/-neutrophils. In LysM^Bmal1-/-mice, circadian variations in VILI severity were dampened and VILI-induced mortality at circadian time 0 was reduced compared with LysM^Bmal1+/+mice. Conclusion: Inflammatory response and lung barrier dysfunction upon mechanical ventilation exhibit diurnal variations, regulated by the circadian clock. LysM^Bmal1-/-mice are less susceptible to ventilation-induced pathology and lack circadian variation of severity compared with LysM^Bmal1+/+mice. Our data suggest that the internal clock in myeloid cells is an important modulator of ventilator-induced lung injury.

Respiratory infections caused by multidrug-resistant Acinetobacter baumannii are difficult to treat and associated with high mortality among critically ill hospitalized patients. Bacteriophages (phages) eliminate pathogens with high host specificity and efficacy. However, the lack of appropriate preclinical experimental models hampers the progress of clinical development of phages as therapeutic agents. Therefore, we tested the efficacy of a purified lytic phage, vB_AbaM_Acibel004, against multidrug-resistant A. baumannii clinical isolate RUH 2037 infection in immunocompetent mice and a human lung tissue model. Sham- and A. baumannii-infected mice received a single-dose of phage or buffer via intratracheal aerosolization. Group-specific differences in bacterial burden, immune and clinical responses were compared. Phage-treated mice not only recovered faster from infection-associated hypothermia but also had lower pulmonary bacterial burden, lower lung permeability, and cytokine release. Histopathological examination revealed less inflammation with unaffected inflammatory cellular recruitment. No phage-specific adverse events were noted. Additionally, the bactericidal effect of the purified phage on A. baumannii was confirmed after single-dose treatment in an ex vivo human lung infection model. Taken together, our data suggest that the investigated phage has significant potential to treat multidrug-resistant A. baumannii infections and further support the development of appropriate methods for preclinical evaluation of antibacterial efficacy of phages.