High tidal volume upregulates intrapulmonary cytokines in an in vivo mouse model of ventilator-induced lung injury.

Mechanical ventilation has been demonstrated to exacerbate lung injury, and a sufficiently high tidal volume can induce injury in otherwise healthy lungs. However, it remains controversial whether injurious ventilation per se, without preceding lung injury, can initiate cytokine-mediated pulmonary inflammation. To address this, we developed an in vivo mouse model of acute lung injury produced by high tidal volume (Vt) ventilation. Anesthetized C57BL6 mice were ventilated at high Vt (34.5 +/- 2.9 ml/kg, mean +/- SD) for a duration of 156 +/- 17 min until mean blood pressure fell below 45 mmHg (series 1); high Vt for 120 min (series 2); or low Vt (8.8 +/- 0.5 ml/kg) for 120 or 180 min (series 3). High Vt produced progressive lung injury with a decrease in respiratory system compliance, increase in protein concentration in lung lavage fluid, and lung pathology showing hyaline membrane formation. High-Vt ventilation was associated with increased TNF-alpha in lung lavage fluid at the early stage of injury (series 2) but not the later stage (series 1). In contrast, lavage fluid macrophage inflammatory protein-2 (MIP-2) was increased in all high-Vt animals. Lavage fluid from high-Vt animals contained bioactive TNF-alpha by WEHI bioassay. Low-Vt ventilation induced minimal changes in physiology and pathology with negligible TNF-alpha and MIP-2 proteins and TNF-alpha bioactivity. These results demonstrate that high-Vt ventilation in the absence of underlying injury induces intrapulmonary TNF-alpha and MIP-2 expression in mice. The apparently transient nature of TNF-alpha upregulation may help explain previous controversy regarding the involvement of cytokines in ventilator-induced lung injury.     

Effects of melatonin in an experimental model of ventilator-induced lung injury

Melatonin is a free radical scavenger and a broad-spectrum antioxidant and has well-documented immunomodulatory effects. We studied the effects of this hormone on lung damage, oxidative stress, and inflammation in a model of ventilator-induced lung injury (VILI), using 8- to 12-wk-old Swiss mice (n = 48). Animals were randomized into three experimental groups: control (not ventilated); low-pressure ventilation [peak inspiratory pressure 15 cmH(2)O, positive end-expiratory pressure (PEEP) 2 cmH(2)O], and high-pressure ventilation (peak inspiratory pressure 25 cmH(2)O, PEEP 0 cmH(2)O). Each group was divided into two subgroups: eight animals were treated with melatonin (10 mg/kg ip, 30 min before the onset of ventilation) and the remaining eight with vehicle. After 2 h of ventilation, lung injury was evaluated by gas exchange, wet-to-dry weight ratio, and histological analysis. Levels of malondialdehyde, glutathione peroxidase, interleukins IL-1beta, IL-6, TNF-alpha, and IL-10, and matrix metalloproteinases 2 and 9 in lung tissue were measured as indicators of oxidation status, pro-/anti-inflammatory cytokines, and matrix turnover, respectively. Ventilation with high pressures induced severe lung damage and release of TNF-alpha, IL-6, and matrix metalloproteinase-9. Treatment with melatonin improved oxygenation and decreased histological lung injury but significantly increased oxidative stress quantified by malondialdehyde levels. There were no differences in TNF-alpha, IL-1beta, IL-6, or matrix metalloproteinases caused by melatonin treatment, but IL-10 levels were significantly higher in treated animals. These results suggest that melatonin decreases VILI by increasing the anti-inflammatory response despite an unexpected increase in oxidative stress.     

Anti-inflammatory effects of clarithromycin in ventilator-induced lung injury

Background

Mechanical ventilation can promote lung injury by triggering a pro-inflammatory response. Macrolides may exert some immunomodulatory effects and have shown significant benefits over other antibiotics in ventilated patients. We hypothesized that macrolides could decrease ventilator-induced lung injury.

Methods

Adult mice were treated with vehicle, clarithromycin or levofloxacin, and randomized to receive mechanical ventilation with low (12 cmH₂O, PEEP 2 cmH₂O) or high (20 cmH₂O, ZEEP) inspiratory pressures for 150 minutes. Histological lung injury, neutrophil infiltration, inflammatory mediators (NFκB activation, Cxcl2, IL-10) and levels of adhesion molecules (E-selectin, ICAM) and proteases (MMP-9 and MMP-2) were analyzed.

Results

There were no differences among groups after low-pressure ventilation. Clarithromycin significantly decreased lung injury score and neutrophil count, compared to vehicle or levofloxacin, after high-pressure ventilation. Cxcl2 expression and MMP-2 and MMP-9 levels increased and IL-10 decreased after injurious ventilation, with no significant differences among treatment groups. Both clarithromycin and levofloxacin dampened the increase in NFκB activation observed in non-treated animals submitted to injurious ventilation. E-selectin levels increased after high pressure ventilation in vehicle- and levofloxacin-treated mice, but not in those receiving clarithromycin.

Conclusions

Clarithromycin ameliorates ventilator-induced lung injury and decreases neutrophil recruitment into the alveolar spaces. This could explain the advantages of macrolides in patients with acute lung injury and mechanical ventilation.     

Linking lung function and inflammatory responses in ventilator-induced lung injury

Despite decades of research, the mechanisms of ventilator-induced lung injury are poorly understood. We used strain-dependent responses to mechanical ventilation in mice to identify associations between mechanical and inflammatory responses in the lung. BALB/c, C57BL/6, and 129/Sv mice were ventilated using a protective [low tidal volume and moderate positive end-expiratory pressure (PEEP) and recruitment maneuvers] or injurious (high tidal volume and zero PEEP) ventilation strategy. Lung mechanics and lung volume were monitored using the forced oscillation technique and plethysmography, respectively. Inflammation was assessed by measuring numbers of inflammatory cells, cytokine (IL-6, IL-1β, and TNF-α) levels, and protein content of the BAL. Principal components factor analysis was used to identify independent associations between lung function and inflammation. Mechanical and inflammatory responses in the lung were dependent on ventilation strategy and mouse strain. Three factors were identified linking 1) pulmonary edema, protein leak, and macrophages, 2) atelectasis, IL-6, and TNF-α, and 3) IL-1β and neutrophils, which were independent of responses in lung mechanics. This approach has allowed us to identify specific inflammatory responses that are independently associated with overstretch of the lung parenchyma and loss of lung volume. These data provide critical insight into the mechanical responses in the lung that drive local inflammation in ventilator-induced lung injury and the basis for future mechanistic studies in this field.     

Mechanical ventilation modulates TLR4 and IRAK-3 in a non-infectious,ventilator-induced lung injury model

Background

Previous experimental studies have shown that injurious mechanical ventilation has a direct effect on pulmonary and systemic immune responses. How these responses are propagated or attenuated is a matter of speculation. The goal of this study was to determine the contribution of mechanical ventilation in the regulation of Toll-like receptor (TLR) signaling and interleukin-1 receptor associated kinase-3 (IRAK-3) during experimental ventilator-induced lung injury.

Methods

Prospective, randomized, controlled animal study using male, healthy adults Sprague-Dawley rats weighing 300-350 g. Animals were anesthetized and randomized to spontaneous breathing and to two different mechanical ventilation strategies for 4 hours: high tidal volume (V_T) (20 ml/kg) and low V_T (6 ml/kg). Histological evaluation, TLR2, TLR4, IRAK3 gene expression, IRAK-3 protein levels, inhibitory kappa B alpha (IκBα), tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL6) gene expression in the lungs and TNF-α and IL-6 protein serum concentrations were analyzed.

Results

High V_T mechanical ventilation for 4 hours was associated with a significant increase of TLR4 but not TLR2, a significant decrease of IRAK3 lung gene expression and protein levels, a significant decrease of IκBα, and a higher lung expression and serum concentrations of pro-inflammatory cytokines.

Conclusions

The current study supports an interaction between TLR4 and IRAK-3 signaling pathway for the over-expression and release of pro-inflammatory cytokines during ventilator-induced lung injury. Our study also suggests that injurious mechanical ventilation may elicit an immune response that is similar to that observed during infections.     

Activation of calpains mediates early lung neutrophilic inflammation in ventilator-induced lung injury

Lung inflammatory responses in the absence of infection are considered to be one of primary mechanisms of ventilator-induced lung injury. Here, we determined the role of calpain in the pathogenesis of lung inflammation attributable to mechanical ventilation. Male C57BL/6J mice were subjected to high (28 ml/kg) tidal volume ventilation for 2 h in the absence and presence of calpain inhibitor I (10 mg/kg). To address the isoform-specific functions of calpain 1 and calpain 2 during mechanical ventilation, we utilized a liposome-based delivery system to introduce small interfering RNAs targeting each isoform in pulmonary vasculature in vivo. Mechanical ventilation with high tidal volume induced rapid (within minutes) and persistent calpain activation and lung inflammation as evidenced by neutrophil recruitment, production of TNF-α and IL-6, pulmonary vascular hyperpermeability, and lung edema formation. Pharmaceutical calpain inhibition significantly attenuated these inflammatory responses caused by lung hyperinflation. Depletion of calpain 1 or calpain 2 had a protective effect against ventilator-induced lung inflammatory responses. Inhibition of calpain activity by means of siRNA silencing or pharmacological inhibition also reduced endothelial nitric oxide (NO) synthase (NOS-3)-mediated NO production and subsequent ICAM-1 phosphorylation following high tidal volume ventilation. These results suggest that calpain activation mediates early lung inflammation during ventilator-induced lung injury via NOS-3/NO-dependent ICAM-1 phosphorylation and neutrophil recruitment. Inhibition of calpain activation may therefore provide a novel and promising strategy for the prevention and treatment of ventilator-induced lung injury.     

Lung-derived soluble mediators are pathogenic in ventilator-induced lung injury

Ventilator-induced lung injury (VILI) due to high tidal volume (V(T)) is associated with increased levels of circulating factors that may contribute to, or be markers of, injury. This study investigated if exclusively lung-derived circulating factors produced during high V(T) ventilation can cause or worsen VILI. In isolated perfused mouse lungs, recirculation of perfusate worsened injury (compliance impairment, microvascular permeability, edema) induced by high V(T). Perfusate collected from lungs ventilated with high V(T) and used to perfuse lungs ventilated with low V(T) caused similar compliance impairment and permeability and caused a dose-dependent decrease in transepithelial electrical resistance (TER) across rat distal lung epithelial monolayers. Circulating soluble factors derived from the isolated lung thus contributed to VILI and had deleterious effects on the lung epithelial barrier. These data demonstrate transferability of an injury initially caused exclusively by mechanical ventilation and provides novel evidence for the biotrauma hypothesis in VILI. Mediators of the TER decrease were heat-sensitive, transferable via Folch extraction, and (following ultrafiltration, 3 kDa) comprised both smaller and larger molecules. Although several classes of candidate mediators, including protein cytokines (e.g., tumor necrosis factor-α, interleukin-6, macrophage inflammation protein-1α) and lipids (e.g., eicosanoids, ceramides, sphingolipids), have been implicated in VILI, only prostanoids accumulated in the perfusate in a pattern consistent with a pathogenic role, yet cyclooxygenase inhibition did not protect against injury. Although no single class of factor appears solely responsible for the decrease in barrier function, the current data implicate lipid-soluble protein-bound molecules as not just markers but pathogenic mediators in VILI.     

TRPV4 initiates the acute calcium-dependent permeability increase during ventilator-induced lung injury in isolated mouse lungs

We have previously implicated calcium entry through stretch-activated cation channels in initiating the acute pulmonary vascular permeability increase in response to high peak inflation pressure (PIP) ventilation. However, the molecular identity of the channel is not known. We hypothesized that the transient receptor potential vanilloid-4 (TRPV4) channel may initiate this acute permeability increase because endothelial calcium entry through TRPV4 channels occurs in response to hypotonic mechanical stress, heat, and P-450 epoxygenase metabolites of arachidonic acid. Therefore, permeability was assessed by measuring the filtration coefficient (K(f)) in isolated perfused lungs of C57BL/6 mice after 30-min ventilation periods of 9, 25, and 35 cmH(2)O PIP at both 35 degrees C and 40 degrees C. Ventilation with 35 cmH(2)O PIP increased K(f) by 2.2-fold at 35 degrees C and 3.3-fold at 40 degrees C compared with baseline, but K(f) increased significantly with time at 40 degrees C with 9 cmH(2)O PIP. Pretreatment with inhibitors of TRPV4 (ruthenium red), arachidonic acid production (methanandamide), or P-450 epoxygenases (miconazole) prevented the increases in K(f). In TRPV4(-/-) knockout mice, the high PIP ventilation protocol did not increase K(f) at either temperature. We have also found that lung distention caused Ca(2+) entry in isolated mouse lungs, as measured by ratiometric fluorescence microscopy, which was absent in TRPV4(-/-) and ruthenium red-treated lungs. Alveolar and perivascular edema was significantly reduced in TRPV4(-/-) lungs. We conclude that rapid calcium entry through TRPV4 channels is a major determinant of the acute vascular permeability increase in lungs following high PIP ventilation.     

Inhibition of Pyk2 blocks lung inflammation and injury in a mouse model of acute lung injury

Background

Proline-rich tyrosine kinase 2 (Pyk2) is essential in neutrophil degranulation and chemotaxis in vitro. However, its effect on the process of lung inflammation and edema formation during LPS induced acute lung injury (ALI) remains unknown. The goal of the present study was to determine the effect of inhibiting Pyk2 on LPS-induced acute lung inflammation and injury in vivo.

Methods

C57BL6 mice were given either 10 mg/kg LPS or saline intratracheally. Inhibition of Pyk2 was effected by intraperitoneal administration TAT-Pyk2-CT 1 h before challenge. Bronchoalveolar lavage analysis of cell counts, lung histology and protein concentration in BAL were analyzed at 18 h after LPS treatment. KC and MIP-2 concentrations in BAL were measured by a mouse cytokine multiplex kit. The static lung compliance was determined by pressure-volume curve using a computer-controlled small animal ventilator. The extravasated Evans blue concentration in lung homogenate was determined spectrophotometrically.

Results

Intratracheal instillation of LPS induced significant neutrophil infiltration into the lung interstitium and alveolar space, which was attenuated by pre-treatment with TAT-Pyk2-CT. TAT-Pyk2-CT pretreatment also attenuated 1) myeloperoxidase content in lung tissues, 2) vascular leakage as measured by Evans blue dye extravasation in the lungs and the increase in protein concentration in bronchoalveolar lavage, and 3) the decrease in lung compliance. In each paradigm, treatment with control protein TAT-GFP had no blocking effect. By contrast, production of neutrophil chemokines MIP-2 and keratinocyte-derived chemokine in the bronchoalveolar lavage was not reduced by TAT-Pyk2-CT. Western blot analysis confirmed that tyrosine phosphorylation of Pyk2 in LPS-challenged lungs was reduced to control levels by TAT-Pyk2-CT pretreatment.

Conclusions

These results suggest that Pyk2 plays an important role in the development of acute lung injury in mice and that pharmacological inhibition of Pyk2 might provide a potential therapeutic strategy in the pretreatment for patients at imminent risk of developing acute lung injury.     

Lack of matrix metalloproteinase-9 worsens ventilator-induced lung injury

Matrix metalloproteinase-9 (MMP-9) is released by neutrophils at the sites of acute inflammation. This enzyme modulates matrix turnover and inflammatory response, and its activity has been found to be increased after ventilator-induced lung injury. To clarify the role of MMP-9, mice lacking this enzyme and their wild-type counterparts were ventilated for 2 h with high- or low-peak inspiratory pressures (25 and 15 cmH2O, respectively). Lung injury was evaluated by gas exchange, respiratory mechanics, wet-to-dry weight ratio, and histological analysis. The activity of MMP-9 and levels of IL-1beta, IL-4, and macrophage inflammatory protein (MIP-2) were measured in lung tissue and bronchoalveolar lavage fluid (BALF). Cell count and myeloperoxidase activity were measured in BALF. There were no differences between wild-type and Mmp9-/- animals after low-pressure ventilation. After high-pressure ventilation, wild-type mice exhibited an increase in MMP-9 in tissue and BALF. Mice lacking MMP-9 developed more severe lung injury than wild-type mice, in terms of impaired oxygenation and lung mechanics, and higher damage in the histological study. These effects correlated with an increase in both cell count and myeloperoxidase activity in the BALF, suggesting an increased neutrophilic influx in response to ventilation. An increase in IL-1beta and IL-4 in the BALF only in knockout mice could be responsible for the differences. There were no differences between genotypes in MMP-2, MMP-8, or tissue inhibitors of metalloproteinases. These results show that MMP-9 protects against ventilator-induced lung injury by decreasing alveolar neutrophilic infiltration, probably by modulation of the cytokine response in the air spaces.     

Invited review: mechanisms of ventilator-induced lung injury: a perspective.

Despite advances in critical care, the mortality rate in patients with acute lung injury remains high. Furthermore, most patients who die do so from multisystem organ failure. It has been postulated that ventilator-induced lung injury plays a key role in determining the negative clinical outcome of patients exposed to mechanical ventilation. How mechanical ventilation exerts its detrimental effect is as of yet unknown, but it appears that overdistension of lung units or shear forces generated during repetitive opening and closing of atelectatic lung units exacerbates, or even initiates, significant lung injury and inflammation. The term "biotrauma" has recently been elaborated to describe the process by which stress produced by mechanical ventilation leads to the upregulation of an inflammatory response. For mechanical ventilation to exert its deleterious effect, cells are required to sense mechanical forces and activate intracellular signaling pathways able to communicate the information to its interior. This information must then be integrated in the nucleus, and an appropriate response must be generated to implement and/or modulate its response and that of neighboring cells. In this review, we present a perspective on ventilator-induced lung injury with a focus on mechanisms and clinical implications. We highlight some of the most recent findings, which we believe contribute to the generation and propagation of ventilator-induced lung injury, placing a special emphasis on their implication for future research and clinical therapies.     

Inhibition of glycolysis alleviates lipopolysaccharide-induced acute lung injury in a mouse model

Gluconic metabolic reprogramming, immune response, and inflammation are intimately linked. Glycolysis involves in the pathologic progress in acute and chronic inflammatory diseases. However, the involvement of glycolysis in the acute lung injury (ALI) is still unclear. This study investigated the role of glycolysis in an animal model of ALI. First, we found that lactate content in serum was remarkably increased in ALI patients and a murine model induced by intratracheal administration of lipopolysaccharide (LPS). The key proteins involving in glycolysis were robustly elevated, including HK2, PKM2, and HIF-1α. Intriguingly, inhibition of glycolysis by 2-deoxyglucose (2-DG) pronouncedly attenuated the lung tissue pathological injury, accumulation of neutrophil, oxidative stress, expression of proinflammatory factors in the lung of ALI mice induced by LPS. The 2-DG treatment also strongly suppressed the activation of the NOD-like receptor (NLR) family and pyrin domain-containing protein 3 (NLRP3) inflammasome. Furthermore, we investigated the role of glycolysis in the inflammatory response of primary murine macrophages activated by LPS in vitro. We found that the 2-DG treatment remarkably reduced the expression of proinflammatory factors induced by LPS, including tumor necrosis factor-α messenger RNA (mRNA), pro-interleukin (IL)-1β mRNA, pro-IL-18 mRNA, NLRP3 mRNA, caspase-1 mRNA, and IL-1β protein. Altogether, these data provide a novel link between gluconic metabolism reprogramming and uncontrolled inflammatory response in ALI. This study suggests glycolytic inhibition as an effective anti-inflammatory strategy in treating ALI.     

Soluble guanylyl cyclase contributes to ventilator-induced lung injury in mice

High tidal volume (HV(T)) ventilation causes pulmonary endothelial barrier dysfunction. HV(T) ventilation also increases lung nitric oxide (NO) and cGMP. NO contributes to HV(T) lung injury, but the role of cGMP is unknown. In the current study, ventilation of isolated C57BL/6 mouse lungs increased perfusate cGMP as a function of V(T). Ventilation with 20 ml/kg V(T) for 80 min increased the filtration coefficient (K(f)), an index of vascular permeability. The increased cGMP and K(f) caused by HV(T) were attenuated by nitric oxide synthase (NOS) inhibition and in lungs from endothelial NOS knockout mice. Inhibition of soluble guanylyl cyclase (sGC) in wild-type lungs (10 muM ODQ) also blocked cGMP generation and inhibited the increase in K(f), suggesting an injurious role for sGC-derived cGMP. sGC inhibition also attenuated lung Evans blue dye albumin extravasation and wet-to-dry weight ratio in an anesthetized mouse model of HV(T) injury. Additional activation of sGC (1.5 muM BAY 41-2272) in isolated lungs at 40 min increased cGMP production and K(f) in lungs ventilated with 15 ml/kg V(T). HV(T) endothelial barrier dysfunction was attenuated with a nonspecific phosphodiesterase (PDE) inhibitor (100 muM IBMX) as well as an inhibitor (10 muM BAY 60-7550) specific for the cGMP-stimulated PDE2A. Concordantly, we found a V(T)-dependent increase in lung cAMP hydrolytic activity and PDE2A protein expression with a decrease in lung cAMP concentration that was blocked by BAY 60-7550. We conclude that HV(T)-induced endothelial barrier dysfunction resulted from a simultaneous increase in NO/sGC-derived cGMP and PDE2A expression causing decreased cAMP.     

Activation of nicotinic cholinergic receptors prevents ventilator-induced lung injury in rats

Respiratory distress syndrome is responsible for 40 to 60 percent mortality. An over mortality of about 10 percent could result from additional lung injury and inflammation due to the life-support mechanical ventilation, which stretches the lung. It has been recently demonstrated, in vitro, that pharmacological activation of the alpha 7 nicotinic receptors (α7-nAChR) could down regulate intracellular mediators involved in lung cell inflammatory response to stretch. Our aim was to test in vivo the protective effect of the pharmacological activation of the α7-nAChR against ventilator-induced lung injury (VILI). Anesthetized rats were ventilated for two hours with a high stretch ventilation mode delivering a stroke volume large enough to generate 25-cmH(2)O airway pressure, and randomly assigned to four groups: pretreated with parenteral injection of saline or specific agonist of the α7-nAChR (PNU-282987), or submitted to bilateral vagus nerve electrostimulation while pre-treated or not with the α7-nAChR antagonist methyllycaconitine (MLA). Controls ventilated with a conventional stroke volume of 10 mL/kg gave reference data. Physiological indices (compliance of the respiratory system, lung weight, blood oxygenation, arterial blood pressure) and lung contents of inflammatory mediators (IL-6 measured by ELISA, substance P assessed using HPLC) were severely impaired after two hours of high stretch ventilation (sham group). Vagal stimulation was able to maintain the respiratory parameters close to those obtained in Controls and reduced lung inflammation except when associated to nicotinic receptor blockade (MLA), suggesting the involvement of α7-nAChR in vagally-mediated protection against VILI. Pharmacological pre-treatment with PNU-282987 strongly decreased lung injury and lung IL-6 and substance P contents, and nearly abolished the increase in plasmatic IL-6 levels. Pathological examination of the lungs confirmed the physiological differences observed between the groups. In conclusion, these data suggest that the stimulation of α7-nAChR is able to attenuate VILI in rats.     

Pulmonary changes in a mouse model of combined burn and smoke inhalation-induced injury.

The morbidity and mortality of burn victims increase when burn injury is combined with smoke inhalation. The goal of the present study was to develop a murine model of burn and smoke inhalation injury to more precisely reveal the mechanistic aspects of these pathological changes. The burn injury mouse group received a 40% total body surface area third-degree burn alone, the smoke inhalation injury mouse group received two 30-s exposures of cotton smoke alone, and the combined burn and smoke inhalation injury mouse group received both the burn and the smoke inhalation injury. Animal survival was monitored for 120 h. Survival rates in the burn injury group, the smoke inhalation injury group, and the combined injury group were 70%, 60%, and 30%, respectively. Mice that received combined burn and smoke injury developed greater lung damage as evidenced by histological changes (septal thickening and interstitial edema) and higher lung water content. These mice also displayed more severely impaired pulmonary gas exchange [arterial PO2 (PaO2)/inspired O2 fraction (FiO2)<200]. Lung myeloperoxidase activity was significantly higher in burn and smoke-injured animals compared with the other three experimental groups. Plasma NO2-/NO3-, lung inducible nitric oxide synthase (iNOS) activity, and iNOS mRNA increased with injury; however, the burn and smoke injury group exhibited a higher response. Severity of burn and smoke inhalation injury was associated with more pronounced production of nitric oxide and accumulation of activated leukocytes in lung tissue. The murine model of burn and smoke inhalation injury allows us to better understand pathophysiological mechanisms underlying cardiopulmonary morbidity secondary to burn and smoke inhalation injury.     

Inflammation and matrix remodeling during repair of ventilator-induced lung injury

High-pressure ventilation triggers different inflammatory and matrix remodeling responses within the lung. Although some of them may cause injury, the involvement of these mediators in repair is largely unknown. To identify mechanisms of repair after ventilator-induced lung injury (VILI), mice were randomly assigned to baseline conditions (no ventilation), injury [90 min of high-pressure ventilation without positive end-expiratory pressure (PEEP)], repair (injury followed by 4 h of low-pressure ventilation with PEEP), and ventilated controls (low-pressure ventilation with PEEP for 90 and 330 min). Histological injury and lung permeability increased during injury, but were partially reverted in the repair group. This was accompanied by a proinflammatory response, together with increases in TNF-α and IFN-γ, which returned to baseline during repair, and a decrease in IL-10. However, macrophage inflammatory protein-2 (MIP-2) and matrix metalloproteinases (MMP)-2 and -9 increased after injury and persisted in being elevated during repair. Mortality in the repair phase was 50%. Survivors showed increased cell proliferation, lower levels of collagen, and higher levels of MIP-2 and MMP-2. Pan-MMP or specific MMP-2 inhibition (but not MIP-2, TNF-α, or IL-4 inhibition) delayed epithelial repair in an in vitro wound model using murine or human alveolar cells cultured in the presence of bronchoalveolar lavage fluid from mice during the repair phase or from patients with acute respiratory distress syndrome, respectively. Similarly, MMP inhibition with doxycycline impaired lung repair after VILI in vivo. In conclusion, VILI can be reverted by normalizing ventilation pressures. An adequate inflammatory response and extracellular matrix remodeling are essential for recovery. MMP-2 could play a key role in epithelial repair after VILI and acute respiratory distress syndrome.