Phosphoinositide 3-OH kinase inhibition prevents ventilation-induced lung cell activation

Investigating mechanisms of Sophora davidii (Franch.) skeels flower extract in treating LPS-induced acute pneumonia based on network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

In TCM opinion, most of pneumonia is related to "lung heat". Sophora davidii (Franch.) Skeels flower was first documented in "Guizhou Herbal Medicine", and was recorded as having functions of clearing heat, detoxifying, and cooling blood. It can be used to treat lung heat cough.

AIM OF THE STUDY

To investigate main mechanisms of Sophora davidii flower extract (SDFE) in Treating LPS-induced acute Pneumonia.

MATERIALS AND METHODS

Acute pneumonia models on BEAS-2B cells and rats were established using LPS. The rat model was used to verified the protective effects of SDFE through HE staining, lung tissue W/D ratio assay, white blood cell count analysis, and ammonia-induced coughing test. Network pharmacology was applied to predict the active compounds, core targets and main pathways of SDFE in treating acute pneumonia. Western Blot and ELISA kits were employed to validate representative proteins in selected pathway in vivo and in vitro.

RESULTS

HE staining, lung tissue W/D ratio assay, white blood cell count analysis, and ammonia-induced coughing test showed SDFE could improve pathological features (leukocyte infiltration, pulmonary edema, lung injury and cough). Network pharmacology indicated MAPK/NF-κB pathway was the most relevant pathway. SDFE could significantly inhibit the expression of Fos and Jun, and the phosphorylation levels of p38, ERK, JNK, NF-κB and IκB. It also down-regulated the expression of pro-inflammatory factors (TNF-α, IL-6 and IL-1β).

CONCLUSIONS

SDFE can exert protective effects against acute pneumonia through the MAPK/NF-κB signaling pathway.

Mollugin prevents CLP-induced sepsis in mice by inhibiting TAK1-NF-κB/MAPKs pathways and activating Keap1-Nrf2 pathway in macrophages

Sepsis is a life-threatening organ dysfunction associated with macrophage overactivation. Targeted therapy against macrophages is considered a promising strategy for sepsis treatment. Mollugin (MLG), a compound extracted from traditional Chinese medicine Rubia cordifolia L., possesses anti-tumor and anti-inflammatory activities. This study aimed to investigate the anti-inflammatory effects and mechanisms of MLG in macrophages and its therapeutic role in CLP-induced sepsis in mice. The results demonstrated that MLG downregulated the inflammatory response induced by LPS or tumor necrosis factor α (TNF-α) in macrophages. Mechanistically, MLG suppressed the phosphorylation of TAK1, the upstream modulator of IKKα/β and MAPKs, thereby inhibiting the pro-inflammatory signaling transduction of NF-κB and MAPKs. Additionally, MLG also activated the Nrf2 antioxidant pathway, reducing intracellular reactive oxygen species. CETSA and molecular docking analyses revealed that MLG could effectively bind to TAK1 and Keap1, which may be involved in the inhibition of TAK1- NF-κB/MAPKs and activation of Nrf2 mediated by MLG. Animal study demonstrated that MLG ameliorated inflammatory injury of lung and liver in CLP-induced sepsis mice probably by reducing the levels of pro-inflammatory cytokines. Therefore, our study suggests that bi-directional roles of MLG in improving sepsis via blocking the TAK1-NF-κB/MAPKs and activating Nrf2 pathways, indicating its potential as a promising candidate drug for sepsis treatment.

Modulation of the hippo-YAP pathway by cyclic stretch in rat type 2 alveolar epithelial cells-a proof-of-concept study

Background: Mechanical ventilation (MV) is a life supporting therapy but may also cause lung damage. This phenomenon is known as ventilator-induced lung injury (VILI). A potential pathomechanisms of ventilator-induced lung injury may be the stretch-induced production and release of cytokines and pro-inflammatory molecules from the alveolar epithelium. Yes-associated protein (YAP) might be regulated by mechanical forces and involved in the inflammation cascade. However, its role in stretch-induced damage of alveolar cells remains poorly understood. In this study, we explored the role of YAP in the response of alveolar epithelial type II cells (AEC II) to elevated cyclic stretch in vitro. We hypothesize that Yes-associated protein activates its downstream targets and regulates the interleukin-6 (IL-6) expression in response to 30% cyclic stretch in AEC II. Methods: The rat lung L2 cell line was exposed to 30% cyclic equibiaxial stretch for 1 or 4 h. Non-stretched conditions served as controls. The cytoskeleton remodeling and cell junction integrity were evaluated by F-actin and Pan-cadherin immunofluorescence, respectively. The gene expression and protein levels of IL-6, Yes-associated protein, Cysteine-rich angiogenic inducer 61 (Cyr61/CCN1), and connective tissue growth factor (CTGF/CCN2) were studied by real-time polymerase chain reaction (RT-qPCR) and Western blot, respectively. Verteporfin (VP) was used to inhibit Yes-associated protein activation. The effects of 30% cyclic stretch were assessed by two-way ANOVA. Statistical significance as accepted at p < 0.05. Results: Cyclic stretch of 30% induced YAP nuclear accumulation, activated the transcription of Yes-associated protein downstream targets Cyr61/CCN1 and CTGF/CCN2 and elevated IL-6 expression in AEC II after 1 hour, compared to static control. VP (2 µM) inhibited Yes-associated protein activation in response to 30% cyclic stretch and reduced IL-6 protein levels. Conclusion: In rat lung L2 AEC II, 30% cyclic stretch activated YAP, and its downstream targets Cyr61/CCN1 and CTGF/CCN2 and proinflammatory IL-6 expression. Target activation was blocked by a Yes-associated protein inhibitor. This novel YAP-dependent pathway could be involved in stretch-induced damage of alveolar cells.

The Role of Insulin Receptor Substrate Proteins in Bronchopulmonary Dysplasia and Asthma: New Potential Perspectives

Insulin receptor substrates (IRSs) are proteins that are involved in signaling through the insulin receptor (IR) and insulin-like growth factor (IGFR). They can also interact with other receptors including growth factor receptors. Thus, they represent a critical node for the transduction and regulation of multiple signaling pathways in response to extracellular stimuli. In addition, IRSs play a central role in processes such as inflammation, growth, metabolism, and proliferation. Previous studies have highlighted the role of IRS proteins in lung diseases, in particular asthma. Further, the members of the IRS family are the common proteins of the insulin growth factor signaling cascade involved in lung development and disrupted in bronchopulmonary dysplasia (BPD). However, there is no study focusing on the relationship between IRS proteins and BPD yet. Unfortunately, there is still a significant gap in knowledge in this field. Thus, in this review, we aimed to summarize the current knowledge with the major goal of exploring the possible roles of IRS in BPD and asthma to foster new perspectives for further investigations.

Attenuation of ventilator-induced lung injury through suppressing the pro-inflammatory signaling pathways: A review on preclinical studies

Mechanical ventilation (MV) is a relatively common medical intervention in ICU patients. The main side effect of MV is the so-called "ventilator-induced lung injury" (VILI). The pathogenesis of VILI is not completely understood; however, it has been reported that MV might be associated with up-regulation of various inflammatory mediators within the lung tissue and that these mediators might act as pathogenic factors in lung tissue injury. One potential mechanism for the generation of inflammatory mediators is through the release of endogenous molecules known as damage associated molecular patterns (DAMPs). These molecules are released from injured tissues and can bind to pattern recognition receptors (PRRs). PRR activation generally leads to the production and release of inflammation-related molecules including innate immune cytokines and chemokines. It has been suggested that blocking DAMP/PRR signaling pathways might diminish the progression of VILI. Herein, we review the latest findings with regard to the effects of DAMP/PRRs and their blockade, as well as the potential therapeutic targets and future research directions in VILI. Results of studies performed on human samples, animal models of disease, as well as relevant in vitro systems will be discussed.

Phosphoproteome profiling provides insight into the mechanisms of ventilator-induced lung injury

The incidence of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is a common health problem in the clinic and is projected to increase in prevalence in the future. Mechanical ventilation is commonly used to provide respiratory support and has become indispensable in emergency and critical medicine. However, ventilator use can result in lung tissue damage, collectively termed ventilator-induced lung injury (VILI). In the present study, phosphoprotein profiling of blood and tissue samples from ventilated and non-ventilated mice was performed and key changes in protein levels and cell signaling during VILI were identified. Activation of the PI3K/AKT and mitogen activated protein kinase signaling pathways, in addition to changes in expression of cancer, inflammatory and cell-death related proteins were detected in response to mechanical ventilation. Focal adhesion-related protein levels and signaling pathways were also significantly altered in an injury model compared with control. VILI can affect patient mortality in ALI and ARDS cases, and no targeted treatment options currently exist. Identifying biomarkers and understanding the signaling pathways associated with VILI is critical for the development of future therapies.

Erythropoietin-Producing Hepatoma Receptor Tyrosine Kinase A2 Modulation Associates with Protective Effect of Prone Position in Ventilator-induced Lung Injury

The erythropoietin-producing hepatoma (Eph) receptor tyrosine kinase A2 (EphA2) and its ligand, ephrinA1, play a pivotal role in inflammation and tissue injury by modulating the epithelial and endothelial barrier integrity. Therefore, EphA2 receptor may be a potential therapeutic target for modulating ventilator-induced lung injury (VILI). To support this hypothesis, here, we analyzed EphA2/ephrinA1 signaling in the process of VILI and determined the role of EphA2/ephrinA1 signaling in the protective mechanism of prone positioning in a VILI model. Wild-type mice were ventilated with high (24 ml/kg; positive end-expiratory pressure, 0 cm; 5 h) tidal volume in a supine or prone position. Anti-EphA2 receptor antibody or IgG was administered to the supine position group. Injury was assessed by analyzing the BAL fluid, lung injury scoring, and transmission electron microscopy. Lung lysates were evaluated using cytokine/chemokine ELISA and Western blotting of EphA2, ephrinA1, PI3Kγ, Akt, NF-κB, and P70S6 kinase. EphA2/ephrinA1 expression was higher in the supine high tidal volume group than in the control group, but it did not increase upon prone positioning or anti-EphA2 receptor antibody treatment. EphA2 antagonism reduced the extent of VILI and downregulated the expression of PI3Kγ, Akt, NF-κB, and P70S6 kinase. These findings demonstrate that EphA2/ephrinA1 signaling is involved in the molecular mechanism of VILI and that modulation of EphA2/ehprinA1 signaling by prone position or EphA2 antagonism may be associated with the lung-protective effect. Our data provide evidence for EphA2/ehprinA1 as a promising therapeutic target for modulating VILI.

RNA‑sequencing analysis of aberrantly expressed long non‑coding RNAs and mRNAs in a mouse model of ventilator‑induced lung injury

Long non-coding RNAs (lncRNAs) are closely associated with the regulation of various biological processes and are involved in the pathogenesis of numerous diseases. However, to the best of our knowledge, the role of lncRNAs in ventilator‑induced lung injury (VILI) has yet to be evaluated. In the present study, high‑throughput sequencing was applied to investigate differentially expressed lncRNAs and mRNAs (fold change >2; false discovery rate <0.05). Bioinformatics analysis was employed to predict the functions of differentially expressed lncRNAs. A total of 104 lncRNAs (74 upregulated and 30 downregulated) and 809 mRNAs (521 upregulated and 288 downregulated) were differentially expressed in lung tissues from the VILI group. Gene ontology analysis demonstrated that the differentially expressed lncRNAs and mRNAs were mainly associated with biological functions, including apoptosis, angiogenesis, neutrophil chemotaxis and skeletal muscle cell differentiation. The top four enriched pathways were the tumor necrosis factor (TNF) signaling pathway, P53 signaling pathway, neuroactive ligand‑receptor interaction and the forkhead box O signaling pathway. Several lncRNAs were predicted to serve a vital role in VILI. Subsequently, three lncRNAs [mitogen‑activated protein kinase kinase 3, opposite strand (Map2k3os), dynamin 3, opposite strand and abhydrolase domain containing 11, opposite strand] and three mRNAs (growth arrest and DNA damage‑inducible α, claudin 4 and thromboxane A2 receptor) were measured by reverse transcription‑quantitative polymerase chain reaction, in order to confirm the veracity of RNA‑sequencing analysis. In addition, Map2k3os small interfering RNA transfection inhibited the expression of stretch‑induced cytokines [TNF‑α, interleukin (IL)‑1β and IL‑6] in MLE12 cells. In conclusion, the results of the present study provided a profile of differentially expressed lncRNAs in VILI. Several important lncRNAs may be involved in the pathological process of VILI, which may be useful to guide further investigation into the pathogenesis for this disease.

Protective effects of ghrelin in ventilator-induced lung injury in rats

Ghrelin has exhibited potent anti-inflammatory effects on various inflammatory diseases. The aim of this study was to investigate the potential effects of ghrelin on a model of ventilator-induced lung injury (VILI) established in rats. Male Sprague-Dawley rats were randomly divided into three groups: low volume ventilation (LV, Vt=8ml/kg) group, a VILI group (Vt=30ml/kg), and a VILI group pretreated with ghrelin (GH+VILI). For the LV group, for the VILI and GH+VILI groups, the same parameters were applied except the tidal volume was increased to 40ml/kg. After 4h of MV, blood gas, lung elastance, and levels of inflammatory mediators, including tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, and (MIP)-2 and total protein in bronchoalveolar lavage fluid (BALF) were analyzed. Myeloperoxidase (MPO), (TLR)-4, and NF-κB, were detected in lung tissues. Water content (wet-to-dry ratio) and lung morphology were also evaluated. The VILI group had a higher acute lung injury (ALI) score, wet weight to dry ratio, MPO activity, and concentrations of inflammatory mediators (TNF-α, IL-6, IL-1β, and MIP-2) in BALF, as well as higher levels of TLR4 and NF-κB expression than the LV group (P<0.05). All histopathologic ALI, the inflammatory profile, and pulmonary dynamics have been improved by ghrelin pretreatment (P<0.05). Ghrelin pretreatment also decreased TLR4 expression and NF-κB activity compared with the VILI group (P<0.05). Ghrelin pretreatment attenuated VILI in rats by reducing MV-induced pulmonary inflammation and might represent a novel therapeutic candidate for protection against VILI.

The volatile anesthetic sevoflurane attenuates ventilator-induced lung injury through inhibition of ERK1/2 and Akt signal transduction

Background

Ventilator-induced lung injury (VILI) sustained during mechanical ventilator support is still a cause of a high rate of morbidity and mortality in intensive care units and in operating rooms. VILI is characterized by pulmonary inflammation that appears to be mediated by proinflammatory cytokines. This study investigates whether the volatile anesthetic sevoflurane has an anti-inflammatory effect that attenuates VILI.

Methods

Twenty one male rabbits were anesthetized and were mechanically ventilated with 50% oxygen at a peak inspiratory pressure (PIP) of 10 cmH₂O, I : E ratio of 1 : 4, and positive end expiratory pressure of 5 cmH₂O. All animals were randomly assigned to one of three groups that were ventilated for 5 h with 10 cmH₂O of PIP (Sham group, n = 7); 30 cmH₂O of PIP (Control group, n = 7); or 30 cmH₂O of PIP and 0.8 vol% sevoflurane (Sevoflurane group, n = 7). The wet/dry weight (W/D) ratio and histopathology of the lung; concentration of interleukin-8 (IL-8) in the bronchoalveolar lavage fluid; and activation of extracellular signal-regulated kinases (ERK) 1/2, p38 mitogen-activated protein kinase, and Akt were measured in the lung tissue after completing the protocol.

Results

Histopathology indicated that the sevoflurane group showed fewer inflammatory cells and architectural changes than the control group did. The W/D ratio [(5.36 ± 0.13) versus (6.61 ± 0.20)], expression of IL-8 [(144.08 ± 14.61) versus (228.56 ± 15.13) pg/ml] and phosphorylation of ERK1/2 and Akt decreased significantly in the sevoflurane group relative to the control group.

Conclusions

Sevoflurane attenuates VILI in rabbits mainly by inhibiting expression of IL-8, and Sevoflurane-induced inhibition of phosphorylated ERK1/2 and Akt might be a possible pathway for protection.

BML-111, a lipoxin receptor agonist, attenuates ventilator-induced lung injury in rats

Mechanical ventilation can cause structural and functional disturbances in the lung termed ventilator-induced lung injury (VILI). The aim of this study was to evaluate whether BML-111, a lipoxin receptor agonist, could attenuate VILI. Following induction of anesthesia and tracheostomy, Sprague-Dawley rats were ventilated with low tidal volume (6 mL/kg) or high tidal volume (20 mL/kg, HVT) for 4 h. Some rats subjected to HVT ventilation received BML-111 or vehicle (saline) by intraperitoneal injection. Some rats subjected to HVT and BML-111(1 mg/kg) received BOC-2 (a FPR2/ALX antagonist) intraperitoneally 30 min before BML-111. Sham rats were tracheotomized without ventilation. Treatment with BML-111 attenuated VILI, as evidenced by improved oxygenation and reduced histological injury compared with HVT-induced lung injury. BML-111 decreased indices of inflammation such as interleukin 1β, interleukin 6, tumor necrosis factor α, and bronchoalveolar lavage neutrophil infiltration. Administration with BML-111 suppressed the decrement of the nuclear factor κB (NF-κB) inhibitor IκB-α, diminished NF-κB activation, and reduced activation of mitogen-activated protein kinase in VILI. This study indicates that BML-111 attenuated VILI via a NF-κB and mitogen-activated protein kinase dependent mechanism. BML-111 may be a promising strategy for alleviation of VILI in patients subjected to mechanical ventilation.

Genetic and pharmacologic inhibition of Tpl2 kinase is protective in a mouse model of ventilator-induced lung injury

Background

Mechanical stress induced by injurious ventilation leads to pro-inflammatory cytokine production and lung injury. The extracellular-signal-regulated-kinase, ERK1/2, participates in the signaling pathways activated upon mechanical stress in the lungs to promote the inflammatory response. Tumor progression locus 2 (Tpl2) is a MAP3kinase that activates ERK1/2 upon cytokine or TLR signaling, to induce pro-inflammatory cytokine production. The role of Tpl2 in lung inflammation, and specifically in the one caused by mechanical stress has not been investigated. The aim of the study was to examine if genetic or pharmacologic inhibition of Tpl2 could ameliorate ventilator-induced lung injury.

Methods

Adult male wild-type and Tpl2-deficient mice were ventilated with normal or high tidal volume for 4 h. Additional wild-type mice were treated with a Tpl2 inhibitor either before or 30 min after initiation of high tidal ventilation. Non-ventilated mice of both genotypes served as controls. The development of lung injury was evaluated by measuring lung mechanics, arterial blood gases, concentrations of proteins, IL-6, and MIP-2 in bronchoalveolar lavage fluid (BALF) and by lung histology. Data were compared by Kruskal-Wallis non-parametric test and significance was defined as p < 0.05.

Results

Mechanical ventilation with normal tidal volume induced a mild increase of IL-6 in BALF in both strains. High tidal volume ventilation induced lung injury in wild-type mice, characterized by decreased lung compliance, increased concentrations of proteins, IL-6 and MIP-2 in BALF, and inflammatory cell infiltration on histology. All indices of lung injury were ameliorated in Tpl2-deficient mice. Wild-type mice treated with the Tpl2 inhibitor, either prior of after the initiation of high tidal volume ventilation were protected from the development of lung injury, as indicated by preserved lung compliance and lower BALF concentrations of proteins and IL-6, than similarly ventilated, untreated wild-type mice.

Conclusions

Genetic and pharmacologic inhibition of Tpl2 is protective in a mouse model of ventilator-induced lung injury, ameliorating both high-permeability pulmonary edema and lung inflammation.

Lung injury after simulated cardiopulmonary bypass in an isolated perfused rat lung preparation: Role of mitogen-activated protein kinase/Akt signaling and the effects of theophylline

Objectives

Lung deflation and inflation during cardiac surgery with cardiopulmonary bypass contributes to pulmonary dysfunction postoperatively. Theophylline treatment for lung diseases has traditionally been thought to act by phosphodiesterase inhibition; however, increasing evidence has suggested other plausible mechanisms. We investigated the effects of deflation and reinflation on signaling pathways (p38-mitogen-activated protein kinase [MAPK], extracellular signal-regulated kinase 1 and 2 [ERK1/2], and Akt) and whether theophylline influences the deflation-induced lung injury and associated signaling.

Methods

Isolated rat lungs were perfused (15 mL/min) with deoxygenated rat blood in bicarbonate buffer and ventilated. After 20 minutes' equilibration, the lungs were deflated (60 minutes, aerobic perfusion 1.5 mL/min), followed by reinflation (60 minutes, anaerobic reperfusion 15 mL/min). Compliance, vascular resistance, and kinase phosphorylation were assessed during deflation and reinflation. The effects of SB203580 (50 μM), a p38-MAPK inhibitor, and theophylline (0.083 mM [therapeutic] or 3 mM [supratherapeutic]) on physiology and signaling were studied.

Results

Deflation reduced compliance by 44% compared with continuously ventilated lungs. p38-MAPK and Akt phosphorylation increased (three to fivefold) during deflation and reinflation, and ERK1/2 phosphorylation increased (approximately twofold) during reinflation. SB203580 had no effect on lung physiology or ERK1/2 and Akt activation. Both theophylline doses increased cyclic adenosine monophosphate, but only 3 mM theophylline improved compliance. p38-MAPK phosphorylation was not affected by theophylline; 0.083 mM theophylline inhibited reinflation-induced ERK1/2 phosphorylation (72% ± 3%); and 3 mM theophylline inhibited Akt phosphorylation during deflation (75% ± 5%) and reinflation (87% ± 4%).

Conclusions

Lung deflation and reinflation stimulates differential p38-MAPK, ERK1/2, and Akt activation, suggesting a role in lung injury during cardiopulmonary bypass. However, p38-MAPK was not involved in the compromised compliance. A supratherapeutic theophylline dose protected lungs against deflation-induced injury and was associated with inhibition of phosphoinositide 3-kinase/Akt rather than phosphodiesterase.

Ventilation-induced lung injury

Mechanical ventilation (MV) is, by definition, the application of external forces to the lungs. Depending on their magnitude, these forces can cause a continuum of pathophysiological alterations ranging from the stimulation of inflammation to the disruption of cell-cell contacts and cell membranes. These side effects of MV are particularly relevant for patients with inhomogeneously injured lungs such as in acute lung injury (ALI). These patients require supraphysiological ventilation pressures to guarantee even the most modest gas exchange. In this situation, ventilation causes additional strain by overdistension of the yet non-injured region, and additional stress that forms because of the interdependence between intact and atelectatic areas. Cells are equipped with elaborate mechanotransduction machineries that respond to strain and stress by the activation of inflammation and repair mechanisms. Inflammation is the fundamental response of the host to external assaults, be they of mechanical or of microbial origin and can, if excessive, injure the parenchymal tissue leading to ALI. Here, we will discuss the forces generated by MV and how they may injure the lungs mechanically and through inflammation. We will give an overview of the mechanotransduction and how it leads to inflammation and review studies demonstrating that ventilator-induced lung injury can be prevented by blocking pathways of mechanotransduction or inflammation.

Improvement of ventilator-induced lung injury by IPS cell-derived conditioned medium via inhibition of PI3K/Akt pathway and IP-10-dependent paracrine regulation

Mechanical ventilation in patients may increase the risk of an acute lung injury (ALI), termed ventilator-induced lung injury (VILI). Induced pluripotent stem cells (iPSCs) have previously been shown to improve tissue repair in different disease models, including ALI. However, the therapeutic efficacy of iPSCs-derived conditioned medium (iPSC-CM) on ALI or VILI remains unknown. Here, we demonstrated that both iPSCs and iPSC-CM effectively decrease high-tidal-volume-induced VILI-related inflammatory processes and HMGB1 and PAI-1 production, predominantly through suppressing PI3K/Akt signaling. Notably, iPSC-CM suppressed production of macrophage inflammatory protein-2, malondialdehyde, and increased total glutathione content. Transmission electron microscopy revealed that iPSC-CM potentially restored the bronchial microstructure. This iPSC-CM efficacy could be mimicked by PI3K inhibitor LY294002 or Akt heterozygous knockout, and either treatment showed no further improvement on VILI in iPSC-CM recipients. Furthermore, iPSC-CM increased interferon gamma-induced protein 10 (IP-10) production in injured lungs. Administration of IP-10-neutralizing antibodies increased neutrophil infiltration, impaired lung oxygenation and deteriorated the protective effects mediated by iPSC-CM. Our data provide a preclinical indication regarding the therapeutic potential of iPSC-CM in VILI and suggest that inhibiting PI3K/Akt pathway or increasing IP-10 is a prospective diagnostic and therapeutic target for VILI patients.

Mitogen-activated protein kinase phosphatase-1 modulates regional effects of injurious mechanical ventilation in rodent lungs

RATIONALE

Mechanical ventilation induces heterogeneous lung injury by mitogen-activated protein kinase (MAPK) and nuclear factor-κB. Mechanisms regulating regional injury and protective effects of prone positioning are unclear.

OBJECTIVES

To determine the key regulators of the lung regional protective effects of prone positioning in rodent lungs exposed to injurious ventilation.

METHODS

Adult rats were ventilated with high (18 ml/kg, positive end-expiratory pressure [PEEP] 0) or low Vt (6 ml/kg; PEEP 3 cm H(2)O; 3 h) in supine or prone position. Dorsal-caudal lung mRNA was analyzed by microarray and MAPK phosphatases (MKP)-1 quantitative polymerase chain reaction. MKP-1(-/-) or wild-type mice were ventilated with very high (24 ml/kg; PEEP 0) or low Vt (6-7 ml/kg; PEEP 3 cm H(2)O). The MKP-1 regulator PG490-88 (MRx-108; 0.75 mg/kg) or phosphate-buffered saline was administered preventilation. Injury was assessed by lung mechanics, bronchioalveolar lavage cell counts, protein content, and lung injury scoring. Immunoblotting for MKP-1, and IκBα and cytokine ELISAs were performed on lung lysates.

MEASUREMENTS AND MAIN RESULTS

Prone positioning was protective against injurious ventilation in rats. Expression profiling demonstrated MKP-1 20-fold higher in rats ventilated prone rather than supine and regional reduction in p38 and c-jun N-terminal kinase activation. MKP-1(-/-) mice experienced amplified injury. PG490-88 improved static lung compliance and injury scores, reduced bronchioalveolar lavage cell counts and cytokine levels, and induced MKP-1 and IκBα.

CONCLUSIONS

Injurious ventilation induces MAPK in an MKP-1-dependent fashion. Prone positioning is protective and induces MKP-1. PG490-88 induced MKP-1 and was protective against high Vt in a nuclear factor-κB-dependent manner. MKP-1 is a potential target for modulating regional effects of injurious ventilation.

IKK NBD peptide inhibits LPS induced pulmonary inflammation and alters sphingolipid metabolism in a murine model

Airway epithelial NF-κB is a key regulator of host defence in bacterial infections and has recently evolved as a target for therapeutical approaches. Evidence is accumulating that ceramide, generated by acid sphingomyelinase (aSMase), and sphingosine-1-phosphate (S1-P) are important mediators in host defence as well as in pathologic processes of acute lung injury. Little is known about the regulatory mechanisms of pulmonary sphingolipid metabolism in bacterial infections of the lung. The objective of this study was to evaluate the influence of NF-κB on sphingolipid metabolism in Pseudomonas aeruginosa LPS-induced pulmonary inflammation. In a murine acute lung injury model with intranasal Pseudomonas aeruginosa LPS we investigated TNF-α, KC (murine IL-8), IL-6, MCP-1 and neutrophilic infiltration next to aSMase activity and ceramide and S1-P lung tissue concentrations. Airway epithelial NF-κB was inhibited by topically applied IKK NBD, a cell penetrating NEMO binding peptide. This treatment resulted in significantly reduced inflammation and suppression of aSMase activity along with decreased ceramide and S1-P tissue concentrations down to levels observed in healthy animals. In conclusion our results confirm that changes in sphingolipid metabolim due to Pseudomonas aeruginosa LPS inhalation are regulated by NF-κB translocation. This confirms the critical role of airway epithelial NF-κB pathway for the inflammatory response to bacterial pathogens and underlines the impact of sphingolipids in inflammatory host defence mechanisms.

CO metabolism, sensing, and signaling

CO is a colorless and odorless gas produced by the incomplete combustion of hydrocarbons, both of natural and anthropogenic origin. Several microorganisms, including aerobic and anaerobic bacteria and anaerobic archaea, use exogenous CO as a source of carbon and energy for growth. On the other hand, eukaryotic organisms use endogenous CO, produced during heme degradation, as a neurotransmitter and as a signal molecule. CO sensors act as signal transducers by coupling a "regulatory" heme-binding domain to a "functional" signal transmitter. Although high CO concentrations inhibit generally heme-protein actions, low CO levels can influence several signaling pathways, including those regulated by soluble guanylate cyclase and/or mitogen-activated protein kinases. This review summarizes recent insights into CO metabolism, sensing, and signaling.

Effect of exogenous surfactant on phosphatidylinositol 3-kinase-Akt pathway and peroxisome proliferator activated receptor-γ during endotoxin induced acute respiratory distress syndrome

Lipopolysaccharide induced acute respiratory distress syndrome (ARDS) leads to an unacceptably high mortality. In this regard, the anti-inflammatory properties of surfactant may provide a therapeutic option. Phosphoinositide 3-kinase (PI3-K) and the downstream serine/threonine kinase Akt/protein kinase B have a central role in modulating neutrophil function, including respiratory burst, chemotaxis, and apoptosis. This study explores the mechanisms of surfactant dependent protection by regulating PPAR-γ in a rat model of ARDS. Sprague-Dawley male rats were divided into four groups: buffer controls; rats challenged with LPS (055:B5 E. coli); challenged with LPS and treated with porcine surfactant; and challenged with LPS and treated with synthetic surfactant. Expression of PI3-K, Akt, GSK3-β, and PPAR-γ were studied by western immunoblot, immunofluorescence and by immunohistochemistry. In vivo endotoxin administration to rat resulted in activation of PI3-K and Akt in the lungs. The severity of endotoxemia-induced ALI was significantly diminished in rat with surfactant administration. Similar results were also seen in PPAR-γ expression. These results show that PI3-K occupies a central position in regulating endotoxin-induced ALI involving inflammatory responses. Surfactant treatment conferred protection in rat model dependent on PPAR-γ and inhibition of PI3-K/Akt pathway.

Low-molecular-weight heparin reduces hyperoxia-augmented ventilator-induced lung injury via serine/threonine kinase-protein kinase B

Background

High-tidal-volume mechanical ventilation and hyperoxia used in patients with acute lung injury (ALI) can induce the release of cytokines, including high-mobility group box-1 (HMGB1), oxygen radicals, neutrophil infiltration, and the disruption of epithelial and endothelial barriers. Hyperoxia has been shown to increase ventilator-induced lung injury, but the mechanisms regulating interaction between high tidal volume and hyperoxia are unclear. We hypothesized that subcutaneous injections of enoxaparin would decrease the effects of hyperoxia on high-tidal-volume ventilation-induced HMGB1 production and neutrophil infiltration via the serine/threonine kinase/protein kinase B (Akt) pathway.

Methods

Male C57BL/6, either wild type or Akt^+/-, aged between 6 and 8 weeks, weighing between 20 and 25 g, were exposed to high-tidal-volume (30 ml/kg) mechanical ventilation with room air or hyperoxia for 2 to 8 hours with or without 4 mg/kg enoxaparin administration. Nonventilated mice served as a control group. Evan blue dye, lung wet-to-dry weight ratio, free radicals, myeloperoxidase, Western blot of Akt, and gene expression of HMGB1 were measured. The expression of HMGB1 was studied by immunohistochemistry.

Results

High-tidal-volume ventilation using hyperoxia induced microvascular permeability, Akt activation, HMGB1 mRNA expression, neutrophil infiltration, oxygen radicals, HMGB1 production, and positive staining of Akt in bronchial epithelium. Hyperoxia-induced augmentation of ventilator-induced lung injury was attenuated with Akt deficient mice and pharmacological inhibition of Akt activity by enoxaparin.

Conclusion

These data suggest that enoxaparin attenuates hyperoxia-augmented high-tidal-volume ventilation-induced neutrophil influx and HMGB1 production through inhibition of the Akt pathway. Understanding the protective mechanism of enoxaparin related with the reduction of HMGB1 may help further knowledge of the effects of mechanical forces in the lung and development of possible therapeutic strategies involved in acute lung injury.

Angiopoietin-1 treatment reduces inflammation but does not prevent ventilator-induced lung injury

Background

Loss of integrity of the epithelial and endothelial barriers is thought to be a prominent feature of ventilator-induced lung injury (VILI). Based on its function in vascular integrity, we hypothesize that the angiopoietin (Ang)-Tie2 system plays a role in the development of VILI. The present study was designed to examine the effects of mechanical ventilation on the Ang-Tie2 system in lung tissue. Moreover, we evaluated whether treatment with Ang-1, a Tie2 receptor agonist, protects against inflammation, vascular leakage and impaired gas exchange induced by mechanical ventilation.

Methods

Mice were anesthetized, tracheotomized and mechanically ventilated for 5 hours with either an inspiratory pressure of 10 cmH₂O (‘low’ tidal volume ∼7.5 ml/kg; LV_T) or 18 cmH₂O (‘high’ tidal volume ∼15 ml/kg; HV_T). At initiation of HV_T-ventilation, recombinant human Ang-1 was intravenously administered (1 or 4 µg per animal). Non-ventilated mice served as controls.

Results

HV_T-ventilation influenced the Ang-Tie2 system in lungs of healthy mice since Ang-1, Ang-2 and Tie2 mRNA were decreased. Treatment with Ang-1 increased Akt-phosphorylation indicating Tie2 signaling. Ang-1 treatment reduced infiltration of granulocytes and expression of keratinocyte-derived chemokine (KC), macrophage inflammatory protein (MIP)-2, monocyte chemotactic protein (MCP)-1 and interleukin (IL)-1β caused by HV_T-ventilation. Importantly, Ang-1 treatment did not prevent vascular leakage and impaired gas exchange in HV_T-ventilated mice despite inhibition of inflammation, vascular endothelial growth factor (VEGF) and Ang-2 expression.

Conclusions

Ang-1 treatment downregulates pulmonary inflammation, VEGF and Ang-2 expression but does not protect against vascular leakage and impaired gas exchange induced by HV_T-ventilation.

Effects of the TLR2 agonists MALP-2 and Pam3Cys in isolated mouse lungs

Background

Gram-positive and Gram-negative bacteria are main causes of pneumonia or acute lung injury. They are recognized by the innate immune system via toll-like receptor-2 (TLR2) or TLR4, respectively. Among all organs, the lungs have the highest expression of TLR2 receptors, but little is known about the pulmonary consequences of their activation. Here we studied the effects of the TLR2/6 agonist MALP-2, the TLR2/1 agonist Pam₃Cys and the TLR4 agonist lipopolysaccharide (LPS) on pro-inflammatory responses in isolated lungs.

Methodology/Principal Findings

Isolated perfused mouse lungs were perfused for 60 min or 180 min with MALP-2 (25 ng/mL), Pam₃Cys (160 ng/mL) or LPS (1 µg/mL). We studied mediator release by enzyme linked immunosorbent assay (ELISA), the activation of mitogen activated protein kinase (MAPK) and AKT/protein kinase B by immunoblotting, and gene induction by quantitative polymerase chain reaction. All agonists activated the MAPK ERK1/2 and p38, but neither JNK or AKT kinase. The TLR ligands upregulated the inflammation related genes Tnf, Il1β, Il6, Il10, Il12, Ifng, Cxcl2 (MIP-2α) and Ptgs2. MALP-2 was more potent than Pam₃Cys in inducing Slpi, Cxcl10 (IP10) and Parg. Remarkable was the strong induction of Tnc by MALP2, which was not seen with Pam₃Cys or LPS. The growth factor related genes Areg and Hbegf were not affected. In addition, all three TLR agonists stimulated the release of IL-6, TNF, CXCL2 and CXCL10 protein from the lungs.

Conclusions/Significance

TLR2 and TLR4 activation leads to similar reactions in the lungs regarding MAPK activation, gene induction and mediator release. Several genes studied here have not yet been appreciated as targets of TLR2-activation in the lungs before, i.e., Slpi, tenascin C, Parg and Traf1. In addition, the MALP-2 dependent induction of Tnc may indicate the existence of TLR2/6-specific pathways.

Pulmonary-derived phosphoinositide 3-kinase gamma (PI3Kγ) contributes to ventilator-induced lung injury and edema

BACKGROUND

Ventilator-induced lung injury (VILI) occurs in part by increased vascular permeability and impaired alveolar fluid clearance. Phosphoinositide 3-kinase gamma (PI3Kγ) is activated by mechanical stress, induces nitric oxide (NO) production, and participates in cyclic adenosine monophosphate (cAMP) hydrolysis, each of which contributes to alveolar edema. We hypothesized that lungs lacking PI3Kγ or treated with PI3Kγ inhibitors would be protected from ventilation-induced alveolar edema and lung injury.

METHODS

Using an isolated and perfused lung model, wild-type (WT) and PI3Kγ-knockout (KO) mice underwent negative-pressure cycled ventilation at either -25 cmH₂O and 0 cmH₂O positive end-expiratory pressure (PEEP) (HIGH STRESS) or -10 cmH₂O and -3 cmH₂O PEEP (LOW STRESS).

RESULTS

Compared with WT, PI3Kγ-knockout mice lungs were partially protected from VILI-induced derangement of respiratory mechanics (lung elastance) and edema formation [bronchoalveolar lavage (BAL) protein concentration, wet/dry ratio, and lung histology]. In PI3Kγ-knockout mice, VILI induced significantly less phosphorylation of protein kinase B (Akt), endothelial nitric oxide synthase (eNOS), production of nitrate and nitrotyrosine, as well as hydrolysis of cAMP, compared with wild-type animals. PI3Kγ wild-type lungs treated with AS605240, an inhibitor of PI3Kγ kinase activity, in combination with enoximone, an inhibitor of phosphodiesterase-3 (PDE3)-induced cAMP hydrolysis, were protected from VILI at levels comparable to knockout lungs.

CONCLUSIONS

Phosphoinositide 3-kinase gamma in resident lung cells mediates part of the alveolar edema induced by high-stress ventilation. This injury is mediated via altered Akt, eNOS, NO, and/or cAMP signaling. Anti-PI3Kγ therapy aimed at resident lung cells represents a potential pharmacologic target to mitigate VILI.

Early growth response-1 worsens ventilator-induced lung injury by up-regulating prostanoid synthesis

RATIONALE

Ventilator-induced lung injury (VILI) is common and serious and may be mediated in part by prostanoids. We have demonstrated increased expression of the early growth response-1 (Egr1) gene by injurious ventilation, but whether-or how-such up-regulation contributes to injury is unknown.

OBJECTIVES

We sought to define the role of Egr1 in the pathogenesis of VILI.

METHODS

An in vivo murine model of VILI was used, and Egr1(+/+) (wild-type) and Egr1(-/-) mice were studied; the effects of prostaglandin E receptor subtype 1 (EP1) inhibition were assessed.

MEASUREMENTS AND MAIN RESULTS

Injurious ventilation caused lung injury in wild-type mice, but less so in Egr1(-/-) mice. The injury was associated with expression of EGR1 protein, which was localized to type II cells and macrophages and was concentrated in nuclear extracts. There was a concomitant increase in expression of phosphorylated p44/p42 mitogen-activated protein kinases. The prostaglandin E synthase (mPGES-1) gene has multiple EGR1 binding sites on its promoter, and induction of mPGES-1 mRNA (as well as the prostanoid product, PGE2) by injurious ventilation was highly dependent on the presence of the Egr1 gene. PGE2 mediates many lung effects via EP1 receptors, and EP1 blockade (with ONO-8713) lessened lung injury.

CONCLUSIONS

This is the first demonstration of a mechanism whereby expression of a novel gene (Egr1) can contribute to VILI via a prostanoid-mediated pathway.

Phosphoinositide 3-kinase gamma required for lipopolysaccharide-induced transepithelial neutrophil trafficking in the lung

Phosphoinositide 3-kinase gamma(PI3Kgamma) is a critical mediator of directional cell movement. Here, we sought to characterise the role of PI3Kgamma in mediating the different steps of polymorphonuclear leukocyte (PMN) trafficking in the lung. In a murine model of lipopolysaccharide (LPS)-induced lung injury, PMN migration into the different lung compartments was determined in PI3Kgamma gene-deficient (PI3Kgamma(-/-)) and wild-type mice. Bone marrow chimeras were created to characterise the role of PI3Kgamma on haematopoietic versus nonhaematopoietic cells. A small-molecule PI3Kgamma inhibitor was tested in vitro and in vivo. PMN adhesion to the pulmonary endothelium and transendothelial migration into the lung interstitium was enhanced in PI3Kgamma(-/-) mice. However, transepithelial migration into the alveolar space was reduced in these mice. When irradiated PI3Kgamma(-/-) mice were reconstituted with bone marrow from wild-type mice, migratory activity into the alveolar space was restored partially. A small-molecule PI3Kgamma inhibitor reduced chemokine-induced PMN migration in vitro when PMNs or epithelial cells, but not when endothelial cells, were treated. The inhibitor also reduced LPS-induced PMN migration in vivo. We conclude that PI3Kgamma is required for transepithelial but not for transendothelial migration in LPS-induced lung injury. Inhibition of PI3Kgamma activity may be effective at curbing excessive PMN infiltration in lung injury.

Cyclic stretch, reactive oxygen species, and vascular remodeling

Blood vessels respond to changes in mechanical load from circulating blood in the form of shear stress and mechanical strain as the result of heart propulsions by changes in intracellular signaling leading to changes in vascular tone, production of vasoactive molecules, and changes in vascular permeability, gene regulation, and vascular remodeling. In addition to hemodynamic forces, microvasculature in the lung is also exposed to stretch resulting from respiratory cycles during autonomous breathing or mechanical ventilation. Among various cell signaling pathways induced by mechanical forces and reported to date, a role of reactive oxygen species (ROS) produced by vascular cells receives increasing attention. ROS play an essential role in signal transduction and physiologic regulation of vascular function. However, in the settings of chronic hypertension, inflammation, or acute injury, ROS may trigger signaling events that further exacerbate smooth muscle hypercontractility and vascular remodeling associated with hypertension and endothelial barrier dysfunction associated with acute lung injury and pulmonary edema. These conditions are also characterized by altered patterns of mechanical stimulation experienced by vasculature. This review will discuss signaling pathways regulated by ROS and mechanical stretch in the pulmonary and systemic vasculature and will summarize functional interactions between cyclic stretch- and ROS-induced signaling in mechanochemical regulation of vascular structure and function.

Hospital acquired pneumonia with high-risk bacteria is associated with increased pulmonary matrix metalloproteinase activity

Background

Neutrophil products like matrix metalloproteinases (MMP), involved in bacterial defence mechanisms, possibly induce lung damage and are elevated locally during hospital- acquired pneumonia (HAP). In HAP the virulence of bacterial species is known to be different. The aim of this study was to investigate the influence of high-risk bacteria like S. aureus and pseudomonas species on pulmonary MMPconcentration in human pneumonia.

Methods

In 37 patients with HAP and 16 controls, MMP-8, MMP-9 and tissue inhibitors of MMP (TIMP) were analysed by ELISA and MMP-9 activity using zymography in bronchoalveolar lavage (BAL).

Results

MMP-9 activity in mini-BAL was increased in HAP patients versus controls (149 ± 41 vs. 34 ± 11, p < 0.0001). In subgroup analysis, the highest MMP concentrations and activity were seen in patients with high-risk bacteria: patients with high-risk bacteria MMP-9 1168 ± 266 vs. patients with low-risk bacteria 224 ± 119 ng/ml p < 0.0001, MMP-9 gelatinolytic activity 325 ± 106 vs. 67 ± 14, p < 0.0002. In addition, the MMP-8 and MMP-9 concentration was associated with the state of ventilation and systemic inflammatory marker like CRP.

Conclusion

Pulmonary MMP concentrations and MMP activity are elevated in patients with HAP. This effect is most pronounced in patients with high-risk bacteria. Artificial ventilation may play an additional role in protease activation.

Carbon monoxide protects against ventilator-induced lung injury via PPAR-gamma and inhibition of Egr-1

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)-gamma, 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-gamma and inhibition of Egr-1.

Akt2, but not Akt1 or Akt3 mediates pressure-stimulated serum-opsonized latex bead phagocytosis through activating mTOR and p70 S6 kinase

Monocytes and macrophages play critical roles in innate host defense and are sensitive to mechanical stimuli. Tissue pressure is often altered in association with inflammation or infection. Low pressure (20 mmHg), equivalent to normal tissue pressure, increases phagocytosis by primary monocytes and PMA-differentiated THP-1 macrophages, in part by FAK and ERK inhibition and p38 activation. PI-3K is required for macrophage phagocytosis, but whether PI-3K mediates pressure-stimulated phagocytosis is not known. Furthermore, little is known about the role played by the PI-3K downstream Kinases, Akt, and p70 S6 kinase (p70S6K) in modulating macrophage phagocytosis. Thus, we studied the contribution of PI-3K, Akt, and p70S6K to pressure-increased serum-opsonized bead phagocytosis. Pressure-induced p85 PI-3K translocation from cytosolic to membrane fractions and increased Akt activation by 36.1 +/- 12.0% in THP-1 macrophages. LY294002 or Akt inhibitor IV abrogated pressure-stimulated but not basal phagocytosis. Basal Akt activation was inhibited 90% by LY294002 and 70% by Akt inhibitor IV. Each inhibitor prevented Akt activation by pressure. SiRNA targeted to Akt1, Akt2, or Akt3 reduced Akt1, Akt2, and Akt3 expression by 50%, 45%, and 40%, respectively. However, only Akt2SiRNA abrogated the pressure-stimulated phagocytosis without affecting basal. Pressure also activated mTOR and p70S6K. mTORSiRNA and p70S6K inhibition by rapamycin or p70S6KSiRNA blocked pressure-induced, but not basal, phagocytosis. Changes in tissue pressure during inflammation may regulate macrophage phagocytosis by activation of PI-3K, which activates Akt2, mTOR, and p70S6K.

Involvement of Akt and endothelial nitric oxide synthase in ventilation-induced neutrophil infiltration: a prospective, controlled animal experiment

Introduction

Positive pressure ventilation with large tidal volumes has been shown to cause release of cytokines, including macrophage inflammatory protein-2 (MIP-2), a functional equivalent of human IL-8, and neutrophil infiltration. Hyperoxia has been shown to increase ventilator-induced lung injury, but the mechanisms regulating interaction between a large tidal volume and hyperoxia are unclear. We hypothesized that large tidal volume ventilation using hyperoxia would increase MIP-2 production and neutrophil infiltration via the serine/threonine kinase/protein kinase B (Akt) pathway and the endothelial nitric oxide synthase (eNOS) pathway.

Methods

C57BL/6 mice were exposed to large tidal volume (30 ml/kg) mechanical ventilation with room air or hyperoxia for 1–5 hours.

Results

Large tidal volume ventilation using hyperoxia induced neutrophil migration into the lung, MIP-2 production, and Akt and eNOS activation in a time-dependent manner. Both the large tidal volume ventilation of Akt mutant mice and the pharmacological inhibition of Akt with LY294002 attenuated neutrophil sequestration, MIP-2 protein production, and Akt and eNOS activation.

Conclusion

We conclude that hyperoxia increased large tidal volume-induced MIP-2 production and neutrophil influx through activation of the Akt and eNOS pathways.

Redox imbalance and ventilator-induced lung injury

Mechanical ventilation (MV) is an indispensable therapy in the care of critically ill patients with acute lung injury and the acute respiratory distress syndrome; however, it is also known to further lung injury in certain conditions of mechanical stress, leading to ventilator-induced lung injury (VILI). The mechanisms by which conventional MV exacerbates lung injury and inflammation are of considerable clinical significance. Redox imbalance has been postulated, among other mechanisms, to enhance/perpetuate susceptibility to VILI. A better understanding of these pathologic mechanisms will help not only in alleviating the side effects of mechanical forces but also in the development of new therapeutic strategies. Here, we review the relevance of oxidative stress in VILI from human studies as well as cellular and mouse models of mechanical stress. Potential therapeutic avenues for the treatment of VILI with exogenous administration of antioxidants also are discussed.

Genetic and pharmacologic evidence links oxidative stress to ventilator-induced lung injury in mice

RATIONALE

Mechanical ventilation (MV) is an indispensable therapy for critically ill patients with acute lung injury and the adult respiratory distress syndrome. However, the mechanisms by which conventional MV induces lung injury remain unclear.

OBJECTIVES

We hypothesized that disruption of the gene encoding Nrf2, a transcription factor that regulates the induction of several antioxidant enzymes, enhances susceptibility to ventilator-induced lung injury (VILI) and that antioxidant supplementation attenuates this effect.

METHODS

To test our hypothesis and to examine the relevance of oxidative stress in VILI, we assessed lung injury and inflammatory responses in Nrf2-deficient (Nrf2(-/-)) mice and wild-type (Nrf2(+/+)) mice after an acute (2-h) injurious model of MV with or without administration of antioxidant.

MEASUREMENTS AND MAIN RESULTS

Nrf2(-/-) mice displayed greater levels of lung alveolar and vascular permeability and inflammatory responses to MV as compared with Nrf2(+/+) mice. Nrf2 deficiency enhances the levels of several proinflammatory cytokines implicated in the pathogenesis of VILI. We found diminished levels of critical antioxidant enzymes and redox imbalance by MV in the lungs of Nrf2(-/-) mice; however, antioxidant supplementation to Nrf2(-/-) mice remarkably attenuated VILI. When subjected to a clinically relevant prolong period of MV, Nrf2(-/-) mice displayed greater levels of VILI than Nrf2(+/+) mice. Expression profiling revealed lack of induction of several VILI genes, stress response and solute carrier proteins, and phosphatases in Nrf2(-/-) mice.

CONCLUSIONS

Our data demonstrate for the first time a critical role for Nrf2 in VILI, which confers protection against cellular responses induced by MV by modulating oxidative stress.

Phosphoinositide 3-kinase signalling in lung disease: leucocytes and beyond

The family of lipid kinases termed phosphoinositide-3-kinase (PI3K) is known to contribute at multiple levels to innate and adaptive immune responses, and is hence an attractive target for drug discovery in inflammatory and autoimmune disease, including respiratory diseases. The development of isoform-selective pharmacological inhibitors, targeted gene manipulation and short interfering RNA (siRNA) target validation have facilitated a better understanding of the role that each member of this family of kinases plays in the physiology and pathology of the respiratory system. In this review, we will evaluate the evidence for the roles of specific PI3K isoforms in the lung and airways, and discuss their potential as targets for novel drug therapies.

Differential roles of p55 and p75 tumor necrosis factor receptors on stretch-induced pulmonary edema in mice

Ventilator-induced lung injury plays a crucial role in the outcome of patients with acute lung injury. Previous studies have shown a role for the cytokine tumor necrosis factor-alpha (TNF) in stretch-induced alveolar neutrophil recruitment, but the involvement of TNF in stretch-induced pulmonary edema is unclear. We investigated the effects of TNF through its individual p55 and p75 receptors on early pulmonary edema formation during high stretch ventilation, before neutrophil infiltration. Anesthetized wild-type or TNF receptor single/double knockout mice were ventilated with high tidal volume ( approximately 38 ml/kg) for 2 h or until they developed arterial hypotension. Pulmonary edema was assessed by physiological parameters including respiratory mechanics and blood gases, and by lavage fluid protein, lung wet:dry weight ratio, and lung permeability measurements using fluorescence-labeled albumin. High stretch ventilation in wild-type and TNF receptor double knockout animals induced similar pulmonary edema, and only 25-30% of mice completed the protocol. In contrast, the p55 receptor knockout mice were strongly protected from edema formation, with all animals completing the protocol. Myeloperoxidase assay indicated that this protective effect was not associated with decreased pulmonary neutrophil sequestration. The p75 receptor knockout mice, however, displayed increased susceptibility to edema formation, and no animals survived the full 2 h. These results demonstrate a novel role for TNF signaling (independent from its effects on neutrophil recruitment) specifically through the p55 receptor, in promoting high stretch-induced pulmonary edema, whereas p75 signaling may play an opposing role.

Phosphoinositide 3-kinase, Src, and Akt modulate acute ventilation-induced vascular permeability increases in mouse lungs

To determine the role of phosphoinositide 3-OH kinase (PI3K) pathways in the acute vascular permeability increase associated with ventilator-induced lung injury, we ventilated isolated perfused lungs and intact C57BL/6 mice with low and high peak inflation pressures (PIP). In isolated lungs, filtration coefficients (K(f)) increased significantly after ventilation at 30 cmH(2)O (high PIP) for successive periods of 15, 30 (4.1-fold), and 50 (5.4-fold) min. Pretreatment with 50 microM of the PI3K inhibitor, LY-294002, or 20 microM PP2, a Src kinase inhibitor, significantly attenuated the increase in K(f), whereas 10 microM Akt inhibitor IV significantly augmented the increased K(f). There were no significant differences in K(f) or lung wet-to-dry weight (W/D) ratios between groups ventilated with 9 cmH(2)O PIP (low PIP), with or without inhibitor treatment. Total lung beta-catenin was unchanged in any low PIP isolated lung group, but Akt inhibition during high PIP ventilation significantly decreased total beta-catenin by 86%. Ventilation of intact mice with 55 cmH(2)O PIP for up to 60 min also increased lung vascular permeability, indicated by increases in lung lavage albumin concentration and lung W/D ratios. In these lungs, tyrosine phosphorylation of beta-catenin and serine/threonine phosphorylation of Akt, glycogen synthase kinase 3beta (GSK3beta), and ERK1/2 increased significantly with peak effects at 60 min. Thus mechanical stress activation of PI3K and Src may increase lung vascular permeability through tyrosine phosphorylation, but simultaneous activation of the PI3K-Akt-GSK3beta pathway tends to limit this permeability response, possibly by preserving cellular beta-catenin.

Role of phosphatidylinositol 3-kinase/protein kinase B signal transduction pathway in activation of neutrophils during severe acute pancreatitis

AIM: To investigate the role of phosphatidy-linositol 3-kinase/protein kinase B (PI3K/PKB) signal transduction pathway in the activation of neutrophils during severe acute pancreatitis (SAP).

METHODS: Thirty male health adult Sprague Dawley rats were averagely randomized into group A, B and C. SAP model was established in group B and C by retrograde injection of 50 g/L sodium taurocholate into the pancreatic and biliary duct. The rats in group C were treated with wortmannin 4 h before modeling, and those in group A served as the controls. All the rats were killed 6 h after modeling, and the neutrophils were isolated by density gradient centrifugation. The serum levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were analyzed by enzyme-linked immunosorbent assay (ELISA). The expression of TNF-α and IL-1β mRNA were detected by RT-PCR and the activity of phosphorylated PKB (p-PKB) was examined by Western blot.

RESULTS: The serum levels of TNF-α and IL-1β were significantly higher in group B than those in group A (150.8 ± 31.7 ng/L vs22.4 ± 5.2 ng/L, P < 0.01; 217.5 ± 38.4 ng/L vs 43.7 ± 9.6 ng/L, P < 0.01), and mRNA levels of TNF-α and IL-1β were also markedly increased (0.72 ± 0.06 vs 0.19 ± 0.03, P < 0.01; 0.84 ± 0.11 vs 0.14 ± 0.04, P < 0.01). However, the serum and mRNA levels of TNF-α and IL-1β were all significantly decreased in group C in comparison with those in group B (TNF-α: 70.9 ± 11.3 ng/L, 0.32 ± 0.04; IL-1β: 93.0 ± 11.5 ng/L, 0.22 ± 0.04; all P < 0.01). Western blot showed that the activity of p-PKB was increased in group B as compared with that in group A (0.63 ± 0.08 vs 0.34 ± 0.03, P < 0.01), but it was markedly down-regulated in group C (0.38 ± 0.06, P < 0.01).

CONCLUSION: PI3K/PKB signal transduction pathway is activated in the neutrophils during severe acute pancreatitis, which mediates the production of pro-inflammatory cytokines TNF-α and IL-1β.

Gene expression profiling of target genes in ventilator-induced lung injury

In the lungs, high-pressure mechanical ventilation induces an inflammatory response similar to that observed in acute respiratory distress syndrome. To further characterize these responses and to compare them with classical inflammatory pathways, we performed gene expression profiling analysis of 20,000 mouse genes in isolated blood-free (to exclude genes from sequestered leukocytes) perfused mouse lungs exposed to low-pressure ventilation (10 cmH2O), high-pressure ventilation (25 cmH2O, overventilation), and LPS treatment. A large number of inflammatory and apoptotic genes were increased by both overventilation and LPS. However, certain growth factor-related genes, as well as genes related to development, cellular communication, and the cytoskeleton, were only regulated by overventilation. We validated and confirmed increased mRNA expression pattern of five genes (amphiregulin, gravin, Nur77, Cyr61, interleukin-11) by real-time PCR; furthermore, we confirmed increased protein expression of amphiregulin by immunohistochemistry and immunoblotting assays. These genes represent novel candidate genes in ventilator-induced lung injury.

Regulation of phosphatidylinositol 3-kinase by polyisoprenyl phosphates in neutrophil-mediated tissue injury

Neutrophils play a central role in host defense, inflammation, and tissue injury. Recent findings indicate a novel role for polyisoprenyl phosphates (PIPPs) as natural down-regulatory signals in neutrophils. The relationship between PIPPs and neutrophil early activating signals, such as phosphoinositides, has not been previously determined. Here, we establish presqualene diphosphate (PSDP) as an endogenous PIPP regulator of phosphatidylinositol 3-kinase (PI3K). In human neutrophils, leukotriene B4 (LTB4) triggered rapid decreases in PSDP and reciprocal increases in PI3K activity. In addition, PSDP was identified by gas chromatography/mass spectrometry in p110gamma-PI3K immunoprecipitates obtained 30 s after LTB4, indicating a physical interaction between PSDP and PI3K in activated neutrophils. Moreover, PSDP (0.4-800 pmol) directly inhibited recombinant human p110gamma-PI3K activity. During an experimental model of lung injury and inflammation, a reciprocal relationship was also present in vivo for lung PSDP and PI3K activity. To investigate its therapeutic potential, we developed a new PSDP structural mimetic that blocked human neutrophil activation and mouse lung PI3K activity and inflammation. Together, our findings indicate that PSDP is an endogenous PI3K inhibitor, and suggest that in inflammatory diseases characterized by excessive neutrophil activation, PIPPs can serve as structural templates in a novel antineutrophil therapeutic strategy to limit tissue injury.

Lack of phosphoinositide 3-kinase-gamma attenuates ventilator-induced lung injury

OBJECTIVE

G protein-coupled receptors may up-regulate the inflammatory response elicited by ventilator-induced lung injury but also regulate cell survival via protein kinase B (Akt) and extracellular signal regulated kinases 1/2 (ERK1/2). The G protein-sensitive phosphoinositide-3-kinase gamma (PI3Kgamma) regulates several cellular functions including inflammation and cell survival. We explored the role of PI3Kgamma on ventilator-induced lung injury.

DESIGN

Prospective, randomized, experimental study.

SETTING

University animal research laboratory.

SUBJECTS

Wild-type (PI3Kgamma), knock-out (PI3Kgamma ), and kinase-dead (PI3Kgamma) mice.

INTERVENTIONS

Three ventilatory strategies (no stretch, low stretch, high stretch) were studied in an isolated, nonperfused model of acute lung injury (lung lavage) in PI3Kgamma, PI3Kgamma, and PI3Kgamma mice.

MEASUREMENTS AND MAIN RESULTS

Reduction in lung compliance, hyaline membrane formation, and epithelial detachment with high stretch were more pronounced in PI3Kgamma than in PI3Kgamma and PI3Kgamma (p < .01). Inflammatory cytokines and IkBalpha phosphorylation with high stretch did not differ among PI3Kgamma, PI3Kgamma, and PI3Kgamma. Apoptotic index (terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling) and caspase-3 (immunohistochemistry) with high stretch were larger (p < .01) in PI3Kgamma and PI3Kgamma than in PI3Kgamma. Electron microscopy showed that high stretch caused apoptotic changes in alveolar cells of PI3Kgamma mice whereas PI3Kgamma mice showed necrosis. Phosphorylation of Akt and ERK1/2 with high stretch was more pronounced in PI3Kgamma than in PI3Kgamma and PI3Kgamma (p < .01).

CONCLUSIONS

Silencing PI3Kgamma seems to attenuate functional and morphological consequences of ventilator-induced lung injury independently of inhibitory effects on cytokines release but through the enhancement of pulmonary apoptosis.

NF-kappaB in tracheal lavage fluid from intubated premature infants: association with inflammation, oxygen, and outcome

OBJECTIVES

To determine if tracheal lavage concentrations of the transcription factor NF-kappaB, which is activated by risk factors associated with bronchopulmonary dysplasia (BPD) and induces expression of cytokines associated with BPD, is related to BPD in premature infants.

DESIGN

Serial tracheal lavage samples from intubated premature infants were analysed for cell count and concentrations of interleukin (IL)8 and NF-kappaB, corrected for dilution by secretory component concentrations.

SETTING

Level III university hospital neonatal intensive care unit.

PATIENTS

Thirty three intubated infants (mean (SD) birth weight 903 (258) g, median gestation 27 weeks (range 24-31)) in the first 14 days of life.

MAIN OUTCOME MEASURES

Tracheal effluent NF-kappaB, IL8, and cell counts, corrected for dilution by secretory component measurement.

RESULTS

Square root transformed NF-kappaB concentrations were significantly related to signs of inflammation (cell count, p = 0.002; IL8, p = 0.019) and to simultaneous fraction of inspired oxygen in samples from the first 3 days of life (r = 0.512, p<0.003). Of the 32 subjects with samples in the first 3 days of life, the half who either died or had BPD had higher NF-kappaB concentrations than those without BPD (square root concentration 0.097 (0.043) v 0.062 (0.036) microg/microg protein/microg secretory component, p = 0.018).

CONCLUSIONS

Tracheobronchial lavage NF-kappaB concentrations are related to lung inflammation, oxygen exposure, and pulmonary outcome in intubated preterm infants. NF-kappaB activation may be an early critical step leading to BPD.

Stretch-activated signaling pathways responsible for early response gene expression in fetal lung epithelial cells

High-tidal volume ventilation has been shown to increase the expression of several inflammation-associated genes prior to overt physiologic lung injury. Herein, using an in vitro stretch system, we investigated the mechanotransduction pathways involved in ventilation-induced expression of these early response genes (i.e., early growth response gene (Egr)1, heat-shock protein (HSP)70, and the pro-inflammatory cytokines interleukin (IL)-1beta, IL-6, and MIP-2). Mechanical stretch of fetal lung epithelial cells activated various signaling pathways, resulting in transient or progressive increases in gene expression of the early response genes. The transient increase in Egr1 and IL-6 expression was mediated via p44/42 mitogen-activated protein kinase (p44/42 MAPK), while nuclear factor-kappaB (NF-kappaB) was responsible for the sustained and progressive increase in expression of HSP70 and MIP-2. Blockage of Egr-1 expression did not affect the upregulation of IL-6, HSP70, MIP-2, and itself by stretch. Inhibition of calcium mobilization abolished stretch-induced p44/42 MAPK activation and NF-kappaB nuclear translocation as well as increased expression of all early response genes. Similar results were obtained with an inhibitor of Ras. These results suggest that mechanical stretch of fetal lung epithelial cells evokes a complex network of signaling molecules, which diverge downstream to regulate the temporal expression of a unique set of early response genes, but upstream converge at calcium. Thus, calcium mobilization may be a point of hierarchical integration of mechanotransduction in lung epithelial cells.

Activation of phosphoinositide 3-kinase in response to inflammation and nitric oxide leads to the up-regulation of cyclooxygenase-2 expression and subsequent cell proliferation in mesangial cells

In this study, we showed that nitric oxide (NO) donors induced the mesangial cell proliferation and cyclooxygenase-2 (COX-2) protein expression in murine mesangial cells. An inflammatory condition [lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma)] could also induce cell proliferation and significantly enhance inducible nitric oxide synthase (iNOS) and COX-2 expression. Phosphoinositide 3-kinase (PI3K) inhibitor, LY294002, inhibited these responses. LPS/IFN-gamma-induced COX-2 expression in mesangial cells could be inhibited by iNOS inhibitor, aminoguanidine. Selective COX-2 inhibitor, NS398, was capable of inhibiting NO donor- or LPS/IFN-gamma-induced mesangial cell proliferation. Both NO donor and LPS/IFN-gamma markedly activated the PI3K activity and the phosphorylation of Akt and nuclear factor (NF)-kappaB DNA binding activity in mesangial cells, which could be inhibited by LY294002 and transfection of dominant-negative vectors of PI3K/p85 and Akt. These results indicate that a PI3K/Akt-dependent pathway involved in the NO-regulated COX-2 expression and cell proliferation in mesangial cells under inflammatory condition.

Mechanical Stretch Alters Alveolar Type II Cell Mediator Release toward a Proinflammatory Pattern

Increased mechanical stretch of alveolar type II (ATII) cells occurs during mechanical ventilation. The effects of three patterns of stretching rat ATII cells (frequency [min-1]-Deltasurface area [%]: S40-13, S60-13, S40-30) were compared with those in static cultures at 12, 18, and 24 h. Cell viability and expression of cyclooxygenase-2,5-lipoxygenase, inducible nitric oxide synthase (iNOS), and endothelial nitric oxide synthase (eNOS) were characterized. Supernatants were analyzed for eicosanoids, nitrite, cytokines, and stimulatory effects on rat lymphocytes. S40-13 simulates normal breathing; the other patterns increased amplitude and frequency. There were no significant differences between S40-13 and static cultures. S60-13 only significantly increased the supernatant nitrite (11.2+/-1.6 versus 3.9+/-0.4 microM at 24 h). S40-30 significantly reduced the number of trypan blue-excluding cells, increased the supernatant concentration of TXB2 (4.1+/-0.61 versus 2.2+/-0.36 pg/ml), 6-keto-PGF1alpha (8.7+/-1.0 versus 6.7+/-0.52 pg/ml), cysteinyl-LT (12.2+/-2.0 versus 6.1+/-0.75 pg/ml) and nitrite (7.2+/-1.7 versus 3.9+/-0.4 microM). S40-30 did not alter the release of tumor necrosis factor-alpha and monocyte chemotactic protein-1, but significantly reduced the concentration of the anti-inflammatory interleukin-10 (20.8+/-13.3 versus 130+/-21.5 pg/ml). Expression of cyclooxygenase-2/5-lipoxygenase was increased/decreased; expression of iNOS/eNOS was unchanged by high-amplitude stretch. Supernatants from S40-30 experiments caused lymphocyte activation measured by CD71 and CD54 surface expression. Continuing mechanical distension of ATII cells contributes to an inflammatory response by a shift in the balance of pro- and anti-inflammatory mediators.

5-Lipoxygenase deficiency prevents respiratory failure during ventilator-induced lung injury

RATIONALE

Mechanical ventilation with high VT (HVT) progressively leads to lung injury and decreased efficiency of gas exchange. Hypoxic pulmonary vasoconstriction (HPV) directs blood flow to well-ventilated lung regions, preserving systemic oxygenation during pulmonary injury. Recent experimental studies have revealed an important role for leukotriene (LT) biosynthesis by 5-lipoxygenase (5LO) in the impairment of HPV by endotoxin.

OBJECTIVES

To investigate whether or not impairment of HPV contributes to the hypoxemia associated with HVT and to evaluate the role of LTs in ventilator-induced lung injury.

METHODS

We studied wild-type and 5LO-deficient mice ventilated for up to 10 hours with low VT (LVT) or HVT.

RESULTS

In wild-type mice, HVT, but not LVT, increased pulmonary vascular permeability and edema formation, impaired systemic oxygenation, and reduced survival. HPV, as reflected by the increase in left pulmonary vascular resistance induced by left mainstem bronchus occlusion, was markedly impaired in animals ventilated with HVT. HVT ventilation increased bronchoalveolar lavage levels of LTs and neutrophils. In 5LO-deficient mice, the HVT-induced increase of pulmonary vascular permeability and worsening of respiratory mechanics were markedly attenuated, systemic oxygenation was preserved, and survival increased. Moreover, in 5LO-deficient mice, HVT ventilation did not impair the ability of left mainstem bronchus occlusion to increase left pulmonary vascular resistance. Administration of MK886, a 5LO-activity inhibitor, or MK571, a selective cysteinyl-LT(1) receptor antagonist, largely prevented ventilator-induced lung injury.

CONCLUSIONS

These results indicate that LTs play a central role in the lung injury and impaired oxygenation induced by HVT ventilation.

How to ventilate patients with acute lung injury and acute respiratory distress syndrome

PURPOSE OF REVIEW

The purpose of this paper is to review the mechanisms of ventilator-induced lung injury as a basis for providing the less damaging mechanical ventilation in patients with acute respiratory failure.

RECENT FINDINGS

In normal lungs, high tidal volume causes an immediate gene upregulation and downregulation. Although the importance of alveolar inflammatory reaction is well known, recent findings suggest the potential role of airway distension in causing ventilator-induced lung injury. The initial activation has been shown to occur in the airways, accounting for the damages induced by high peak flow. The healthier lung regions are more exposed to the injury, since they may be subjected to strain. Challenge with endotoxin enhances in a synergistic manner the pulmonary inflammation induced by mechanical ventilation. However, mechanical strain and endotoxin seem to trigger lung inflammation through two different pathways. Despite convincing experimental and clinical evidences of lung injury, the clinical implementation of low tidal volume ventilation is still limited and has not yet become part of standard clinical practice. Setting positive end-expiratory pressure remains an open problem because the ALVEOLI study did not provide any exhaustive answers, likely because of methodologic problems and, unphysiologic design.

SUMMARY

Gentle lung ventilation must be standard practice. Because stress and strain are the triggers of ventilator-induced lung injury, their clinical equivalents should be measured (transpulmonary pressure and the ratio between tidal volume and end-expiratory lung volume). For a rational application of positive end-expiratory pressure, the potential for recruitment in any single patient should be estimated.