Induction of cellular antioxidant defense by amifostine improves ventilator-induced lung injury

Amifostine ameliorates bleomycin-induced murine pulmonary fibrosis via NAD+/SIRT1/AMPK pathway-mediated effects on mitochondrial function and cellular metabolism

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a devastating chronic lung disease characterized by irreversible scarring of the lung parenchyma. Despite various interventions aimed at mitigating several different molecular aspects of the disease, only two drugs with limited clinical efficacy have so far been approved for IPF therapy.

OBJECTIVE

We investigated the therapeutic efficacy of amifostine, a detoxifying drug clinically used for radiation-caused cytotoxicity, in bleomycin-induced murine pulmonary fibrosis.

METHODS

C57BL6/J mice were intratracheally instilled with 3 U/kg of bleomycin. Three doses of amifostine (WR-2721, 200 mg/kg) were administered intraperitoneally on days 1, 3, and 5 after the bleomycin challenge. Bronchoalveolar lavage fluid (BALF) was collected on day 7 and day 21 for the assessment of lung inflammation, metabolites, and fibrotic injury. Human fibroblasts were treated in vitro with transforming growth factor beta 1 (TGF-β1), followed by amifostine (WR-1065, 1-4 µg/mL) treatment. The effects of TGF-β1 and amifostine on the mitochondrial production of reactive oxygen species (ROS) were assessed by live cell imaging of MitoSOX. Cellular metabolism was assessed by the extracellular acidification rate (ECAR), the oxygen consumption rate (OCR), and the concentrations of various energy-related metabolites as measured by mass spectrum (MS). Western blot analysis was performed to investigate the effect of amifostine on sirtuin 1 (SIRT1) and adenosine monophosphate activated kinase (AMPK).

RESULTS

Three doses of amifostine significantly attenuated lung inflammation and pulmonary fibrosis. Pretreatment and post-treatment of human fibroblast cells with amifostine blocked TGF-β1-induced mitochondrial ROS production and mitochondrial dysfunction in human fibroblast cells. Further, treatment of fibroblasts with TGF-β1 shifted energy metabolism away from mitochondrial oxidative phosphorylation (OXPHOS) and towards glycolysis, as observed by an altered metabolite profile including a decreased ratio of NAD + /NADH and increased lactate concentration. Treatment with amifostine significantly restored energy metabolism and activated SIRT1, which in turn activated AMPK. The activation of AMPK was required to mediate the effects of amifostine on mitochondrial homeostasis and pulmonary fibrosis. This study provides evidence that repurposing of the clinically used drug amifostine may have therapeutic applications for IPF treatment.

CONCLUSION

Amifostine inhibits bleomycin-induced pulmonary fibrosis by restoring mitochondrial function and cellular metabolism.

Exogenous surfactant reduces inflammation and redox imbalance in rats under prone or supine mechanical ventilation

Mechanical ventilation (MV) is a lifesaving therapy for patients with acute or chronic respiratory failure. Despite, it can also cause lung injury by inducing or worsening inflammatory responses and oxidative stress. Several clinical approaches have protective effects on the lungs, including the prone position and exogenous surfactant; however, few studies have evaluated the association between the two strategies, especially in individuals without previous lung injury. We tested the hypothesis that the effects of the homogenization in lung aeration caused by the prone position in association with the anti-inflammatory properties of exogenous surfactant pre-treatment could have a cumulative protective effect against ventilator-induced lung injury. Therefore, Wistar rats were divided into four experimental groups: Mechanical Ventilation in Supine Position (MVSP), Mechanical Ventilation in Prone position (MVPP), Mechanical Ventilation in Supine Position + surfactant (MVSPS), and Mechanical Ventilation in Prone Position + Surfactant (MVPPS). The intranasal instillation of a porcine surfactant (Curosurf®) was performed in the animals of MVSPS and MVPPS 1 h before the MV, all the rats were subjected to MV for 1 h. The prone position in association with surfactant decreased mRNA expression levels of pro-inflammatory cytokines in ventilated animals compared to the supine position; in addition, the NfκB was lower in MVPP, MVSPS and MVPPS when compared to MVSP. However, it had no effects on oxidative stress caused by MV. Pre-treatment with exogenous surfactant was more efficient in promoting lung protection than the prone position, as it also reduced oxidative damage in the lung parenchyma. Nevertheless, the surfactant did not cause additional improvements in most parameters that were also improved by the prone position. Our results indicate that the pre-treatment with exogenous surfactant, regardless of the position adopted in mechanical ventilation, preserves the original lung histoarchitecture, reduces redox imbalance, and reduces acute inflammatory responses caused by mechanical ventilation in healthy adult Wistar rats.

Ventilator-induced lung-injury in mouse models: Is there a trap?

Ventilator-induced lung injury (VILI) is a serious acute injury to the lung tissue that can develop during mechanical ventilation of patients. Due to the mechanical strain of ventilation, damage can occur in the bronchiolar and alveolar epithelium resulting in a cascade of events that may be fatal to the patients. Patients requiring mechanical ventilation are often critically ill, which limits the possibility of obtaining patient samples, making VILI research challenging. In vitro models are very important for VILI research, but the complexity of the cellular interactions in multi-organ animals, necessitates in vivo studies where the mouse model is a common choice. However, the settings and duration of ventilation used to create VILI in mice vary greatly, causing uncertainty in interpretation and comparison of results. This review examines approaches to induce VILI in mouse models for the last 10 years, to our best knowledge, summarizing methods and key parameters presented across the studies. The results imply that a more standardized approach is warranted.

Role of HDAC6 inhibition in sepsis-induced acute respiratory distress syndrome (Review)

Acute respiratory distress syndrome (ARDS) induced by sepsis contributes remarkably to the high mortality rate observed in intensive care units, largely due to a lack of effective drug therapies. Histone deacetylase 6 (HDAC6) is a class-IIb deacetylase that modulates non-nuclear protein functions via deacetylation and ubiquitination. Importantly, HDAC6 has been shown to exert anti-cancer, anti-neurodegeneration, and immunological effects, and several HDAC6 inhibitors have now entered clinical trials. It has also been recently shown to modulate inflammation, and HDAC6 inhibition has been demonstrated to markedly suppress experimental sepsis. The present review summarizes the role of HDAC6 in sepsis-induced inflammation and endothelial barrier dysfunction in recent years. It is proposed that HDAC6 inhibition predominantly ameliorates sepsis-induced ARDS by directly attenuating inflammation, which modulates the innate and adaptive immunity, transcription of pro-inflammatory genes, and protects endothelial barrier function. HDAC6 inhibition protects against sepsis-induced ARDS, thereby making HDAC6 a promising therapeutic target. However, HDAC inhibition may be associated with adverse effects on the embryo sac and oocyte, necessitating further studies.

Amifostine ameliorates induction of experimental autoimmune encephalomyelitis: Effect on reactive oxygen species/NLRP3 pathway

Multiple sclerosis (MS) is an autoimmune disease for which conventional treatments have limited efficacy or side effects. Free radicals are primarily involved in blood-brain barrier disruption and induce neuronal and axonal damage, thus promoting the development of MS. Amifostine, a radioprotective drug used as a cytoprotective agent, attenuates oxidative stress and improves radiation damage by acting as a direct scavenger of reactive oxygen and nitrogen species. The aim of this study was to evaluate the effects of amifostine on MS in a mouse model of experimental autoimmune encephalomyelitis (EAE), which was developed by immunizing C57BL/6 mice with myelin oligodendrocyte glycoprotein and pertussis toxin. EAE mice received intraperitoneal injections of amifostine prior to onset of clinical symptoms and were monitored up to day 15 post induction. We observed abnormal clinical behavioral scores and a decrease in body weight. Histological analysis showed severe inflammatory infiltration and demyelination in the brain and spinal cord lumbar enlargements where significant upregulation of the mRNA expression of the pro-inflammatory cytokines interleukin-6 and interleukin-8, downregulation of the anti-inflammatory cytokine interleukin-10, and obvious microgliosis were also observed. Amifostine treatment potently reversed these abnormal changes. The anti-inflammatory effect of amifostine was associated with the inhibition of reactive oxygen species generation. Furthermore, the expression of proteins involved in the NLRP3 signaling pathway and pyroptosis was decreased. In conclusion, our study showed that amifostine ameliorates induction of experimental autoimmune encephalomyelitis via anti-inflammatory and anti-pyroptosis effects, providing further insights into the use of amifostine for the treatment of MS.

Induced pluripotent stem cell-derived endothelial cells attenuate lipopolysaccharide-induced acute lung injury

The chemokine receptors CXCR1/2 and CCR2/5 play a critical role in neutrophil and monocyte recruitment to sites of injury and/or inflammation. Neutrophil-mediated inflammation and endothelial cell (EC) injury are unifying factors in the pathogenesis of the acute respiratory distress syndrome. This study tested the hypothesis that systemic administration of rat-induced pluripotent stem cell (iPS)-derived ECs (iPS-ECs) overexpressing CXCR1/2 or CCR2/5 attenuates lipopolysaccharide (LPS)-induced acute lung injury. Rat iPS-ECs were transduced with adenovirus containing cDNA of CXCR1/2 or CCR2/5. Ovariectomized Sprague-Dawley rats (10 wk old) received intraperitoneal injection of LPS and intravenous infusion of 1) saline vehicle, 2) AdNull-iPS-ECs (iPS-ECs transduced with empty adenoviral vector), 3) CXCR1/2-iPS-ECs (iPS-ECs overexpressing CXCR1/2), or 4) CCR2/5-iPS-ECs (iPS-ECs overexpressing CCR2/5) at 2 h post-LPS. Rats receiving intraperitoneal injection of saline served as sham controls. Later (4 h), proinflammatory cytokine/chemokine mRNA and protein levels were measured in total lung homogenates by real-time RT-PCR and Luminex multiplex assays, and neutrophil and macrophage infiltration in alveoli was measured by immunohistochemical staining. Pulmonary microvascular permeability was assessed by the Evans blue technique, and pulmonary edema was estimated by wet-to-dry lung weight ratios. Albumin levels and neutrophil counts were assessed in bronchoalveolar lavage fluid at 24 h post-LPS. Both CXCR1/2-iPS-ECs and CCR2/5-iPS-ECs significantly reduced LPS-induced proinflammatory mediator expression, neutrophil and macrophage infiltration, pulmonary edema, and vascular permeability compared with controls. These provocative findings provide strong evidence that targeted delivery of iPS-ECs overexpressing CXCR1/2 or CCR2/5 prevents LPS-induced acute lung injury.NEW & NOTEWORTHY We have developed a novel approach to address neutrophil-mediated inflammation and endothelial damage by targeted delivery of rat-induced pluripotent stem cell (iPS)-derived endothelial cell (ECs)overexpressing chemokine receptors CXCR1/2 and CCR2/5 in injured lung tissue in a model of acute lung injury. We have demonstrated that intravenously transfused CXCR1/2-iPS-ECs and CCR2/5-iPS-ECs are recruited to lipopolysaccharide-injured lungs and attenuate lipopolysaccharide-induced parenchymal lung injury responses, including inflammatory mediator expression, inflammatory cell infiltration, and vascular leakage compared with controls.

Staphylococcus aureus-induced endothelial permeability and inflammation are mediated by microtubule destabilization

Staphylococcus aureus is a major etiological agent of sepsis and induces endothelial cell (EC) barrier dysfunction and inflammation, two major hallmarks of acute lung injury. However, the molecular mechanisms of bacterial pathogen-induced EC barrier disruption are incompletely understood. Here, we investigated the role of microtubules (MT) in the mechanisms of EC barrier compromise caused by heat-killed S. aureus (HKSA). Using a customized monolayer permeability assay in human pulmonary EC and MT fractionation, we observed that HKSA-induced barrier disruption is accompanied by MT destabilization and increased histone deacetylase-6 (HDAC6) activity resulting from elevated reactive oxygen species (ROS) production. Molecular or pharmacological HDAC6 inhibition rescued barrier function in HKSA-challenged vascular endothelium. The HKSA-induced EC permeability was associated with impaired MT-mediated delivery of cytoplasmic linker-associated protein 2 (CLASP2) to the cell periphery, limiting its interaction with adherens junction proteins. HKSA-induced EC barrier dysfunction was also associated with increased Rho GTPase activity via activation of MT-bound Rho-specific guanine nucleotide exchange factor-H1 (GEF-H1) and was abolished by HDAC6 down-regulation. HKSA activated the NF-κB proinflammatory pathway and increased the expression of intercellular and vascular cell adhesion molecules in EC, an effect that was also HDAC6-dependent and mediated, at least in part, by a GEF-H1/Rho-dependent mechanism. Of note, HDAC6 knockout mice or HDAC6 inhibitor-treated WT mice were partially protected from vascular leakage and inflammation caused by both HKSA or methicillin-resistant S. aureus (MRSA). Our results indicate that S. aureus-induced, ROS-dependent up-regulation of HDAC6 activity destabilizes MT and thereby activates the GEF-H1/Rho pathway, increasing both EC permeability and inflammation.

Sulforaphane attenuates acute lung injury by inhibiting oxidative stress via Nrf2/HO-1 pathway in a rat sepsis model

Sulforaphane (SFN), an antioxidant derived from cruciferous vegetables, exerts antioxidant capacity and protects organ against oxidative damage. However, the effects of SFN on sepsis-induced acute lung injury (ALI) have not been determined. The aim of this study was to investigate the effect of SFN in sepsis-induced ALI and the role of Nrf2/HO-1 in this process. Rats were subjected to either sham-operated or cecal ligation and puncture-induced sepsis without or with SFN. Pulmonary oxidative stress was significantly increased (reduced SOD activity, enhanced 8-OHdG concentration, elevated 15-F2t-isoprostane level, and enhanced 4-HNE expression) in sepsis that were associated with elevated lung injuries (Increased lung injury index, elevated lung water content, and reduced endothelial barrier integrity). Supplementation of SFN significantly enhanced Nrf2 and HO-1 protein expression in the lungs in sepsis. Further, SFN dose-dependently reduced pulmonary oxidative stress and attenuated lung injuries in sepsis. However, these beneficial effects of SFN were reduced by HO-1 inhibition. Therefore, we concluded that SFN attenuated ALI in sepsis by reducing oxidative stress through activating Nrf2/HO-1.

Cyclic mechanical stretch-induced oxidative stress occurs via a NOX-dependent mechanism in type II alveolar epithelial cells

Cyclic mechanical stretching (CMS) of the alveolar epithelium is thought to contribute to alveolar epithelial injury through an increase in oxidative stress. The aim of this study was to investigate the mechanisms of CMS-induced oxidative stress in alveolar epithelial cells (AECs). A549 cells were subjected to CMS, and the levels of 8-isoprostane and 3-nytrotyrosine were measured. Twenty-four hours of CMS induced a significant increase in the levels of 8-isoprostane and 3-nytrotyrosine. Although CMS did not increase the xanthine oxidase activity or the mitochondrial production of reactive oxygen species, it upregulated the expression of nicotine adenine dinucleotide phosphate oxidase (NOX) 2, 4, 5 and DUOX2. The NOX inhibitors DPI and GKT137831 significantly attenuated CMS-induced oxidative stress. Furthermore, the measurement of annexin V/propidium iodide by flow cytometry showed that CMS induced late-phase apoptosis/necrosis, which was also attenuated by both DPI and GKT137831. These data suggest that CMS mainly induces oxidative stress, which may lead to cell injury by activating NOX in AECs.

Extracellular superoxide dismutase is necessary to maintain renal blood flow during sepsis development

Background

Extracellular superoxide dismutase (ECSOD) protects nitric oxide (NO) bioavailability by decreasing superoxide levels and preventing peroxynitrite generation, which is important in maintaining renal blood flow and in preventing acute kidney injury. However, the profile of ECSOD expression after sepsis is not fully understood. Therefore, we intended to evaluate the content and gene expression of superoxide dismutase (SOD) isoforms in the renal artery and their relation to renal blood flow.

Methods

Sepsis was induced in Wistar rats by caecal ligation and perforation. Several times after sepsis induction, renal blood flow (12, 24 and 48 h); the renal arterial content of SOD isoforms, nitrotyrosine, endothelial and inducible nitric oxide synthase (e-NOS and i-NOS), and phosphorylated vasodilator-stimulated phosphoprotein (pVASP); and SOD activity (3, 6 and 12 h) were measured. The influence of a SOD inhibitor was also evaluated.

Results

An increase in ECSOD content was associated with decreased 3-nitrotyrosine levels. These events were associated with an increase in pVASP content and maintenance of renal blood flow. Moreover, previous treatment with a SOD inhibitor increased nitrotyrosine content and reduced renal blood flow.

Conclusions

ECSOD appears to have a major role in decreasing peroxynitrite formation in the renal artery during the early stages of sepsis development, and its application can be important in renal blood flow control and maintenance during septic insult.

VEGF Production by Ly6C+high Monocytes Contributes to Ventilator-Induced Lung Injury

Background

Mechanical ventilation is a life-saving procedure for patients with acute respiratory failure, although it may cause pulmonary vascular inflammation and leakage, leading to ventilator-induced lung injury (VILI). Ly6C^+high monocytes are involved in the pathogenesis of VILI. In this study, we investigated whether pulmonary infiltrated Ly6C^+high monocytes produce vascular endothelial growth factor (VEGF) and contribute to VILI.

Methods

A clinically relevant two-hit mouse model of VILI, with intravenous lipopolysaccharide (LPS, 20 ng/mouse) immediately before high tidal volume (HTV, 20 mL/kg) ventilation (LPS+HTV), was established. Blood gas and respiratory mechanics were measured to ensure the development of VILI. Flow cytometry and histopathological analyses revealed pulmonary infiltration of leukocytes subsets. Clodronate liposomes were intravenously injected to deplete pulmonary monocytes. In vitro endothelial cell permeability assay with sorted Ly6C^+high monocytes condition media assessed the role of Ly6C^+high monocytes in vascular permeability.

Results

LPS+HTV significantly increased total proteins, TNF-α, IL-6, vascular endothelial growth factor (VEGF) and mononuclear cells in the bronchoalveolar lavage fluid (BALF). Pulmonary Ly6C^+high monocytes (SSC^lowCD11b⁺F4/80⁺Ly6C^+high), but not Ly6C^+low monocytes (SSC^lowCD11b⁺F4/80⁺Ly6C^+low), were significantly elevated starting at 4 hr. Clodronate liposomes were able to significantly reduce pulmonary Ly6C^+high monocytes, and VEGF and total protein in BALF, and restore PaO₂/FiO₂. There was a strong correlation between pulmonary Ly6C^+high monocytes and BALF VEGF (R² = 0.8791, p<0.001). Moreover, sorted Ly6C^+high monocytes were able to produce VEGF, resulting in an increased permeability of endothelial cell monolayer in an in vitro endothelial cell permeability assay.

Conclusion

VEGF produced by pulmonary infiltrated Ly6C^+high monocytes regulates vasculature permeability in a two-hit model of HTV-induced lung injury. Ly6C^+high monocytes play an important role in the pathogenesis of VILI.

Effects of mechanical ventilation with different tidal volume on oxidative stress and antioxidant in lung

Purpose

The aim of this study was to investigate the changes in oxidative stress and antioxidants in lung tissue under different tidal volume ventilation conditions.

Methods

Forty-eight male Wistar rats were randomized into four groups, namely, group C, the control group, which was not ventilated, and groups C1, C2 and C3, the treatment groups, which were ventilated for 2 h with tidal volumes of 8, 30 and 42 ml/kg, respectively. The right middle lobe was assayed for malondialdehyde (MDA), the right posterior lobe was assayed using Western blotting for Nrf2, GCLm and SrX1 and the left lobe was assayed for Nrf2, GCLm and SrX1 mRNA.

Results

The MDA levels were increased in the three treatment groups, with MDA levels highest in group C3 and lowest in group C1 (C3 > C2 > C1) (all P < 0.05). The mRNA expression of Nrf2, GCLm and SrX1 was highest in group C3 and lowest in group 1 (C3 > C2 > C1) (all P < 0.05). No significant difference was observed between group C1 and group C (P > 0.05). A Western blot analysis showed that Nrf2, GCLm and SrX1 expression was highest in group C3 and lowest in group C1 (C3 > C2 > C1) (all P < 0.05). No significant difference was observed between group C1 and group C (P > 0.05).

Conclusions

Oxidative stress and antioxidant enzyme levels in the lungs of rats were positively associated with the tidal volumes of mechanical ventilation, suggesting that higher tidal volumes cause more severe oxidative stress and increased antioxidant responses.

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.

Lysophosphatidic acid receptor-2 deficiency confers protection against bleomycin-induced lung injury and fibrosis in mice

Idiopathic pulmonary fibrosis is a devastating disease characterized by alveolar epithelial cell injury, the accumulation of fibroblasts/myofibroblasts, and the deposition of extracellular matrix proteins. Lysophosphatidic acid (LPA) signaling through its G protein-coupled receptors is critical for its various biological functions. Recently, LPA and LPA receptor 1 were implicated in lung fibrogenesis. However, the role of other LPA receptors in fibrosis remains unclear. Here, we use a bleomycin-induced pulmonary fibrosis model to investigate the roles of LPA2 in pulmonary fibrogenesis. In the present study, we found that LPA2 knockout (Lpar2(-/-)) mice were protected against bleomycin-induced lung injury, fibrosis, and mortality, compared with wild-type control mice. Furthermore, LPA2 deficiency attenuated the bleomycin-induced expression of fibronectin (FN), α-smooth muscle actin (α-SMA), and collagen in lung tissue, as well as levels of IL-6, transforming growth factor-β (TGF-β), and total protein in bronchoalveolar lavage fluid. In human lung fibroblasts, the knockdown of LPA2 attenuated the LPA-induced expression of TGF-β1 and the differentiation of lung fibroblasts to myofibroblasts, resulting in the decreased expression of FN, α-SMA, and collagen, as well as decreased activation of extracellular regulated kinase 1/2, Akt, Smad3, and p38 mitogen-activated protein kinase. Moreover, the knockdown of LPA2 with small interfering RNA also mitigated the TGF-β1-induced differentiation of lung fibroblasts. In addition, LPA2 deficiency significantly attenuated the bleomycin-induced apoptosis of alveolar and bronchial epithelial cells in the mouse lung. Together, our data indicate that the knockdown of LPA2 attenuated bleomycin-induced lung injury and pulmonary fibrosis, and this may be related to an inhibition of the LPA-induced expression of TGF-β and the activation and differentiation of fibroblasts.

Cyclic stretch-induced oxidative stress increases pulmonary alveolar epithelial permeability

Mechanical ventilation with high tidal volumes has been associated with pulmonary alveolar flooding. Understanding the mechanisms underlying cyclic stretch-induced increases in alveolar epithelial permeability may be important in designing preventive measures for acute lung injury. In this work, we assessed whether cyclic stretch leads to the generation of reactive oxygen species in type I-like alveolar epithelial cells, which increase monolayer permeability via activation of NF-κB and extracellular signal-regulated kinase (ERK). We cyclically stretched type I-like rat primary alveolar epithelial cells at magnitudes of 12, 25, and 37% change in surface area (ΔSA) for 10 to 120 minutes. High levels of reactive oxygen species and of superoxide and NO specifically were detected in cells stretched at 37% ΔSA for 10 to 120 minutes. Exogenous superoxide and NO stimulation increased epithelial permeability in unstretched cells, which was preventable by the NF-κB inhibitor MG132. The cyclic stretch-induced increase in permeability was decreased by the superoxide scavenger tiron and by MG132. Furthermore, tiron had a dramatic protective effect on in vivo lung permeability under mechanical ventilation conditions. Cyclic stretch increased the activation of the NF-κB signaling pathway, which was significantly decreased with the ERK inhibitor U0126. Altogether, our in vitro and in vivo data demonstrate the sensitivity of permeability to stretch- and ventilation-induced superoxide production, suggesting that using antioxidants may be helpful in the prevention and treatment of ventilator-induced lung injury.

Ventilation with "clinically relevant" high tidal volumes does not promote stretch-induced injury in the lungs of healthy mice

OBJECTIVE

Ventilator-induced lung injury is a crucial determinant of the outcome of mechanically ventilated patients. Increasing numbers of mouse studies have identified numerous pathways and mediators that are modulated by ventilation, but it is conceptually difficult to reconcile these into a single paradigm. There is substantial variability in tidal volumes used in these studies and no certainty about the pathophysiology that such varied models actually represent. This study was designed to investigate whether ventilation strategies ranging from "very high" to more "clinically relevant" tidal volumes induce similar pathophysiologies in healthy mice or represent distinct entities.

DESIGN

In vivo study.

SETTING

University research laboratory.

SUBJECTS

C57/Bl6 mice.

INTERVENTIONS

Anesthetized mice were ventilated with various tidal volumes up to 40 mL/kg.

MEASUREMENTS AND MAIN RESULTS

Respiratory system compliance and arterial blood gases were used to evaluate physiological variables of injury. Lung wet:dry weight ratio, lavage fluid protein, and cytokines were used to assess pulmonary edema and inflammation. All ventilation strategies induced changes in respiratory system compliance, although the pattern of change was unique for each strategy. Ventilation with 10 mL/kg and 40 mL/kg also induced decreases in arterial PO2 and blood pressure. Any physiological changes induced during the 10, 20, and 30 mL/kg strategies were largely reversed by recruitment maneuvers at the end of the protocol. Markers of pulmonary edema and inflammation indicated that only 40 mL/kg induced substantial increases in both, consistent with development of lung injury.

CONCLUSIONS

Tidal volumes up to 20 mL/kg are unlikely to induce substantial lung overstretch in models using healthy, young mice. Signs of injury/inflammation using such models are likely to result from other factors, particularly alveolar derecruitment and atelectasis. The results of such studies may need to be reevaluated before clinical relevance can be accurately determined.