Reduced activation of immunomodulatory transcription factors during positive end-expiratory pressure adjustment based on volume-dependent compliance in isolated perfused rabbit lungs

Enhancing Extracellular Adenosine Levels Restores Barrier Function in Acute Lung Injury Through Expression of Focal Adhesion Proteins

Background: Acute respiratory distress syndrome (ARDS) is a clinical presentation of acute lung injury (ALI) with often fatal lung complication. Adenosine, a nucleoside generated following cellular stress provides protective effects in acute injury. The levels of extracellular adenosine can be depleted by equilibrative nucleoside transporters (ENTs). ENT inhibition by pharmaceutical agent dipyridamole promotes extracellular adenosine accumulation and is protective in ARDS. However, the therapeutic potential of dipyridamole in acute lung injury has not yet been evaluated. Methods: Adenosine acts on three adenosine receptors, the adenosine A1 (Adora1), A2a (Adora2a), the A2b (Adora2b) or the adenosine A3 (Adora 3) receptor. Accumulation of adenosine is usually required to stimulate the low-affinity Adora2b receptor. In order to investigate the effect of adenosine accumulation and the contribution of epithelial-specific ENT2 or adora2b expression in experimental ALI, dipyridamole, and epithelial specific ENT2 or Adora2b deficient mice were utilized. MLE12 cells were used to probe downstream Adora2b signaling. Adenosine receptors, transporters, and targets were determined in ARDS lungs. Results: ENT2 is mainly expressed in alveolar epithelial cells and is negatively regulated by hypoxia following tissue injury. Enhancing adenosine levels with ENT1/ENT2 inhibitor dipyridamole at a time when bleomycin-induced ALI was present, reduced further injury. Mice pretreated with the ADORA2B agonist BAY 60-6583 were protected from bleomycin-induced ALI by reducing vascular leakage (558.6 ± 50.4 vs. 379.9 ± 70.4, p < 0.05), total bronchoalveolar lavage fluid cell numbers (17.9 ± 1.8 to 13.4 ± 1.4 e4, p < 0.05), and neutrophil infiltration (6.42 ± 0.25 vs. 3.94 ± 0.29, p < 0.05). While mice lacking Adora2b in AECs were no longer protected by dipyridamole. We also identified occludin and focal adhesion kinase as downstream targets of ADORA2B, thus providing a novel mechanism for adenosine-mediated barrier protection. Similarly, we also observed similar enhanced ADORA2B (3.33 ± 0.67 to 16.12 ± 5.89, p < 0.05) and decreased occludin (81.2 ± 0.3 to 13.3 ± 0.4, p < 0.05) levels in human Acute respiratory distress syndrome lungs. Conclusion: We have highlighted a role of dipyridamole and adenosine signaling in preventing or treating ALI and identified Ent2 and Adora2b as key mediators in important for the resolution of ALI.

Resveratrol attenuates NF-κB-binding activity but not cytokine production in mechanically ventilated mice

BACKGROUND

Mechanical ventilation (MV) can result in inflammation and subsequent lung injury. Toll-like receptor (TLR)4 and NF-κB are proposed to play a crucial role in the MV-induced inflammatory response. Resveratrol (RVT) exhibits anti-inflammatory effects in vitro and in vivo supposedly by interfering with TLR4 signaling and NF-κB. In the present study, we investigated the role of RVT in MV-induced inflammation in mice.

METHODS

RVT (10 mg/kg, 20 mg/kg and 40 mg/kg) or vehicle was intraperitoneally administered 1 h before start of MV (4 h, tidal volume 8 ml/kg, positive end-expiratory pressure 1,5 cmH2 O and FiO2 0.4). Blood and lungs were harvested for cytokine analysis. DNA binding activity of transcription factor NF-κB was measured in lung homogenates.

RESULTS

MV resulted in elevated pulmonary concentrations of IL-1β, IL-6, keratinocyte-derived chemokine (KC) and NF-κB DNA-binding activity. RVT at 10, 20 and 40 mg/kg reduced NF-κB's DNA-binding activity following MV compared with ventilated controls. However, no differences in cytokine release were found between RVT-treated and control ventilated mice. Similarly, in plasma, MV resulted in elevated concentrations of TNF-α, KC and IL-6, but RVT did not affect cytokine levels.

CONCLUSIONS

RVT abrogates the MV-induced increase in pulmonary NF-κB activity but does not attenuate cytokine levels. This implies a less prominent role for NF-κB in MV-induced inflammation than previously assumed.

Monitoring of intratidal lung mechanics: a Graphical User Interface for a model-based decision support system for PEEP-titration in mechanical ventilation

In mechanical ventilation, a careful setting of the ventilation parameters in accordance with the current individual state of the lung is crucial to minimize ventilator induced lung injury. Positive end-expiratory pressure (PEEP) has to be set to prevent collapse of the alveoli, however at the same time overdistension should be avoided. Classic approaches of analyzing static respiratory system mechanics fail in particular if lung injury already prevails. A new approach of analyzing dynamic respiratory system mechanics to set PEEP uses the intratidal, volume-dependent compliance which is believed to stay relatively constant during one breath only if neither atelectasis nor overdistension occurs. To test the success of this dynamic approach systematically at bedside or in an animal study, automation of the computing steps is necessary. A decision support system for optimizing PEEP in form of a Graphical User Interface (GUI) was targeted. Respiratory system mechanics were analyzed using the gliding SLICE method. The resulting shapes of the intratidal compliance-volume curve were classified into one of six categories, each associated with a PEEP-suggestion. The GUI should include a graphical representation of the results as well as a quality check to judge the reliability of the suggestion. The implementation of a user-friendly GUI was successfully realized. The agreement between modelled and measured pressure data [expressed as root-mean-square (RMS)] tested during the implementation phase with real respiratory data from two patient studies was below 0.2 mbar for data taken in volume controlled mode and below 0.4 mbar for data taken in pressure controlled mode except for two cases with RMS < 0.6 mbar. Visual inspections showed, that good and medium quality data could be reliably identified. The new GUI allows visualization of intratidal compliance-volume curves on a breath-by-breath basis. The automatic categorisation of curve shape into one of six shape-categories provides the rational decision-making model for PEEP-titration.

Protective effects of dexmedetomidine-ketamine combination against ventilator-induced lung injury in endotoxemia rats

BACKGROUND

Pulmonary inflammatory response is crucial in mediating the development of ventilator-induced lung injury (VILI) in animals experiencing endotoxemia. Dexmedetomidine and ketamine are two sedative agents with potent anti-inflammatory capacity. We sought to elucidate the anti-inflammatory effects of dexmedetomidine-ketamine combination against VILI in endotoxemia rats.

MATERIALS AND METHODS

Eighty-four adult male rats were allocated to receive normal saline, VILI, VILI plus dexmedetomidine-ketamine combination (D+K), lipopolysaccharide (LPS), LPS plus D+K, LPS plus VILI, or LPS plus VILI plus D+K (designated as the NS, V, V-D+K, LPS, LPS-D+K, LPS/V, and LPS/V-D+K group, respectively; n = 12 in each group). VILI was induced by high-tidal volume ventilation (tidal volume 20 mL/kg; respiratory rate 50 breath/min; FiO(2) 21%). After being mechanically ventilated for 4 h, rats were sacrificed and the levels of pulmonary inflammatory response were evaluated.

RESULTS

Histologic findings revealed severe, moderate, and mild inflammation in lung tissues of the LPS/V, LPS, and V groups, respectively, whereas those of the LPS/V-D+K, LPS-D+K, and V-D+K groups revealed moderate, mild, and normal to minimal inflammation, respectively. Moreover, the total cell number and the concentrations of macrophage inflammatory protein-2 and interleukin-1β in bronchoalveolar lavage fluid as well as the lung water content, leukocyte infiltration, myeloperoxidase activity, and the concentrations of inducible nitric oxide synthase/nitric oxide, and cyclooxygenase 2/prostaglandin E(2) in lung tissues of the LPS/V, LPS, and V groups were significantly higher than those of the LPS/V-D+K, LPS-D+K, and V-D+K groups, respectively.

CONCLUSIONS

Dexmedetomidine-ketamine combination could mitigate pulmonary inflammatory response induced by VILI in endotoxemia rats.

Noninjurious mechanical ventilation activates a proinflammatory transcriptional program in the lung

Mechanical ventilation is a life-saving intervention in patients with respiratory failure. However, human and animal studies have demonstrated that mechanical ventilation using large tidal volumes (>or=12 ml/kg) induces a potent inflammatory response and can cause acute lung injury. We hypothesized that mechanical ventilation with a "noninjurious" tidal volume of 10 ml/kg would still activate a transcriptional program that places the lung at risk for severe injury. To identify key regulators of this transcriptional response, we integrated gene expression data obtained from whole lungs of spontaneously breathing mice and mechanically ventilated mice with computational network analysis. Topological analysis of the gene product interaction network identified Jun and Fos families of proteins as potential regulatory hubs. Electrophoretic mobility gel shift assay confirmed protein binding to activator protein-1 (AP-1) consensus sequences, and supershift experiments identified JunD and FosB as components of ventilation-induced AP-1 binding. Specific recruitment of JunD to the regulatory region of the F3 gene by mechanical ventilation was confirmed by chromatin immunoprecipitation assay. In conclusion, we demonstrate a novel computational framework to systematically dissect transcriptional programs activated by mechanical ventilation in the lung, and show that noninjurious mechanical ventilation initiates a response that can prime the lung for injury from a subsequent insult.

Cell wounding and repair in ventilator injured lungs

Acute lung injury (ALI) is a common, frequently hospital-acquired condition with a high morbidity and mortality. The stress associated with invasive mechanical ventilation represents a potentially harmful exposure, and attempts to minimize deforming stress through low tidal ventilation have proven efficacious. Lung cells are both sensors and transducers of deforming stress, and are frequently wounded in the setting of mechanical ventilation. Cell wounding may be one of the drivers of the innate immunologic and systemic inflammatory response associated with mechanical ventilation. These downstream effects of mechanotransduction have been referred to collectively as "Biotrauma". Our review will focus on cellular stress failure, that is cell wounding, and the mechanisms mediating subsequent plasma membrane repair, we hold that a better mechanistic understanding of cell plasticity, deformation associated remodeling and repair will reveal candidate approaches for lung protective interventions in mechanically ventilated patients. We will detail one such intervention, lung conditioning with hypertonic solutions as an example of ongoing research in this arena.

NF-kappaB in the lungs of premature rabbits during mechanical ventilation--comparison between conventional mechanical ventilation (CMV) and high-frequency oscillation (HFO)

The purpose of this study is to compare pulmonary nuclear factor-kappaB (NF-kappaB) activity of conventional mechanical ventilation (CMV) with that of high-frequency oscillation (HFO) in premature rabbit lungs. For surfactant-depleted model, we used premature rabbits in order to exclude the effect of lung lavage on the activation of NF-kappaB. The premature rabbits were delivered at a gestational age of 27 days by hysterotomy. Both modes of the ventilator were set at the same MAP and FiO(2). We used animals that had PCO(2) levels of approximately 50-mmHg. Animals were sacrificed after 1-hr ventilation with CMV or HFO. Then activity of pulmonary NF-kappaB was assessed. We observed that NF-kappaB activity was higher in the lungs of CMV compared with those of HFO, as measured by Western blot analysis. The activity level of NF-kappaB in the lungs measured by ELISA was significantly higher in CMV group than in HFO group. We conclude that a higher level of NF-kappaB activation was associated with CMV when compared to HFO.

Dynamic versus static respiratory mechanics in acute lung injury and acute respiratory distress syndrome

OBJECTIVES

It is not clear whether the mechanical properties of the respiratory system assessed under the dynamic condition of mechanical ventilation are equivalent to those assessed under static conditions. We hypothesized that the analyses of dynamic and static respiratory mechanics provide different information in acute respiratory failure.

DESIGN

Prospective multiple-center study.

SETTING

Intensive care units of eight German university hospitals.

PATIENTS

A total of 28 patients with acute lung injury and acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS

Dynamic respiratory mechanics were determined during ongoing mechanical ventilation with an incremental positive end-expiratory pressure (PEEP) protocol with PEEP steps of 2 cm H2O every ten breaths. Static respiratory mechanics were determined using a low-flow inflation.

MAIN RESULTS

The dynamic compliance was lower than the static compliance. The difference between dynamic and static compliance was dependent on alveolar pressure. At an alveolar pressure of 25 cm H2O, dynamic compliance was 29.8 (17.1) mL/cm H2O and static compliance was 59.6 (39.8) mL/cm H2O (median [interquartile range], p < .05). End-inspiratory volumes during the incremental PEEP trial coincided with the static pressure-volume curve, whereas end-expiratory volumes significantly exceeded the static pressure-volume curve. The differences could be attributed to PEEP-related recruitment, accounting for 40.8% (10.3%) of the total volume gain of 1964 (1449) mL during the incremental PEEP trial. Recruited volume per PEEP step increased from 6.4 (46) mL at zero end-expiratory pressure to 145 (91) mL at a PEEP of 20 cm H2O (p < .001). Dynamic compliance decreased at low alveolar pressure while recruitment simultaneously increased. Static mechanics did not allow this differentiation. The decrease in static compliance occurred at higher alveolar pressures compared with the dynamic analysis.

CONCLUSIONS

Exploiting dynamic respiratory mechanics during incremental PEEP, both compliance and recruitment can be assessed simultaneously. Based on these findings, application of dynamic respiratory mechanics as a diagnostic tool in ventilated patients should be more appropriate than using static pressure-volume curves.

Computational identification of key biological modules and transcription factors in acute lung injury

RATIONALE

Mechanical ventilation augments the acute lung injury (ALI) caused by bacterial products. The molecular pathogenesis of this synergistic interaction remains incompletely understood.

OBJECTIVE

We sought to develop a computational framework to systematically identify gene regulatory networks activated in ALI.

METHODS

We have developed a mouse model in which the combination of mechanical ventilation and intratracheal LPS produces significantly more injury to the lung than either insult alone. We used global gene ontology analysis to determine overrepresented biological modules and computational transcription factor analysis to identify putative regulatory factors involved in this model of ALI.

RESULTS

By integrating expression profiling with gene ontology and promoter analysis, we constructed a large-scale regulatory modular map of the important processes activated in ALI. This map assigned differentially expressed genes to highly overrepresented biological modules, including "defense response," "immune response," and "oxidoreductase activity." These modules were then systematically incorporated into a gene regulatory network that consisted of putative transcription factors, such as IFN-stimulated response element, IRF7, and Sp1, that may regulate critical processes involved in the pathogenesis of ALI.

CONCLUSIONS

We present a novel, unbiased, and powerful computational approach to investigate the synergistic effects of mechanical ventilation and LPS in promoting ALI. Our methodology is applicable to any expression profiling experiment involving eukaryotic organisms.

Alveolar recruitment in acute lung injury

Alveolar recruitment is one of the primary goals of respiratory care for acute lung injury. It is aimed at improving pulmonary gas exchange and, even more important, at protecting the lungs from ventilator-induced trauma. This review addresses the concept of alveolar recruitment for lung protection in acute lung injury. It provides reasons for why atelectasis and atelectrauma should be avoided; it analyses current and future approaches on how to achieve and preserve alveolar recruitment; and it discusses the possibilities of detecting alveolar recruitment and derecruitment. The latter is of particular clinical relevance because interventions aimed at lung recruitment are often undertaken without simultaneous verification of their effectiveness.