Emilio García-Prieto

Resistance to Bleomycin-Induced Lung Fibrosis in MMP-8 Deficient Mice Is Mediated by Interleukin-10

Background Matrix metalloproteinases (MMPs) may have pro and antifibrotic roles within the lungs, due to its ability to modulate collagen turnover and immune mediators. MMP-8 is a collagenase that also cleaves a number of cytokines and chemokines. Methodology and Principal Findings To evaluate its relevance in lung fibrosis, wildtype and Mmp8−/− mice were treated with either intratracheal bleomycin or saline, and lungs were harvested at different time points. Fibrosis, collagen, collagenases, gelatinases, TGFβ and IL-10 were measured in lung tissue. Mmp8−/− mice developed less fibrosis than their wildtype counterparts. This was related to an increase in lung inflammatory cells, MMP-9 and IL-10 levels in these mutant animals. In vitro experiments showed that MMP-8 cleaves murine and human IL-10, and tissue from knockout animals showed decreased IL-10 processing. Additionally, lung fibroblasts from these mice were cultured in the presence of bleomycin and collagen, IL-10 and STAT3 activation (downstream signal in response to IL-10) measured by western blotting. In cell cultures, bleomycin increased collagen synthesis only in wildtype mice. Fibroblasts from knockout mice did not show increased collagen synthesis, but increased levels of unprocessed IL-10 and STAT3 phosphorylation. Blockade of IL-10 reverted this phenotype, increasing collagen in cultures. Conclusions According to these results, we conclude that the absence of MMP-8 has an antifibrotic effect by increasing IL-10 and propose that this metalloprotease could be a relevant modulator of IL-10 metabolism in vivo.

Absence or Inhibition of Matrix Metalloproteinase–8 Decreases Ventilator-Induced Lung Injury

Mechanical ventilation is a life-saving therapy that can also damage the lungs. Ventilator-induced lung injury (VILI) promotes inflammation and up-regulates matrix metalloproteinases (MMPs). Among these enzymes, MMP-8 is involved in the onset of inflammation by processing different immune mediators. To clarify the role of MMP-8 in a model of VILI and their relevance as a therapeutic target, we ventilated wild-type and MMP-8-deficient mice with low or high pressures for 2 hours. There were no significant differences after low-pressure ventilation between wild-type and knockout animals. However, lack of MMP-8 results in better gas exchange, decreased lung edema and permeability, and diminished histological injury after high-pressure ventilation. Mmp8(-/-) mice had a different immune response to injurious ventilation, with decreased neutrophilic infiltration, lower levels of IFN-γ and chemokines (LPS-induced CXC chemokine, macrophage inflammatory protein-2), and significant increases in anti-inflammatory cytokines (IL-4, IL-10) in lung tissue and bronchoalveolar lavage fluid. There were no differences in MMP-2, MMP-9, or tissue inhibitor of metalloproteinase-1 between wild-type and knockout mice. These results were confirmed by showing a similar protective effect in wild-type mice treated with a selective MMP-8 inhibitor. We conclude that MMP-8 promotes acute inflammation after ventilation with high pressures, and its short-term inhibition could be a therapeutic goal to limit VILI.

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.

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.

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.

Respuesta inflamatoria y apoptosis en la lesión pulmonar aguda

One of the principal mechanisms of pulmonary injury in acute respiratory distress is due to the effects of the precipitated inflammatory response. The damage produced to the alveolar epithelium and underlying endothelium depends on the sequestration and activation of inflammatory cells, which in turn exert their actions through mediators. On the other hand, apoptosis is a mechanism responsible for epithelial damage and regulation of inflammation. Response of the lung tissue subjected to mechanical ventilation stimulus is added to the previous mechanisms. All these processes flow into a series of common pathways of cellular activation. Knowledge of these mechanisms could serve to identify which patients would benefit from a specific treatment before applying therapies that act indiscriminately in the inflammatory response.

Impact of Initial Ventilatory Strategy in Hematological Patients With Acute Respiratory Failure: A Systematic Review and Meta-Analysis.

Objective: Acute respiratory failure in hematological patients is related to a high mortality. Noninvasive mechanical ventilation may benefit a subset of these patients, but the overall effect on mortality and the risks derived from its failure are unclear. Our objective was to review the impact of initial ventilatory strategy on mortality and the risks related to noninvasive mechanical ventilation failure in this group of patients. Data Sources: Data sources, including PubMed and conference proceedings, were searched from the year 2000 to January 2015. Study Selection: We selected studies reporting mortality and the need for mechanical ventilation in hematological patients with acute respiratory failure. Data Extraction: Two trained reviewers independently conducted study selection, abstracted data, and assessed the risk of bias. Discrepancies between reviewers were resolved through discussion and consensus. The outcomes explored were all-cause mortality after mechanical ventilation and incidence of noninvasive mechanical ventilation failure. Data Synthesis: A random-effects model was used in all the analysis. Thirteen studies, involving 2,380 patients, were included. Use of noninvasive mechanical ventilation was related to a better outcome than initial intubation (risk ratio, 0.74; 95% CI, 0.65–0.84). Failure of noninvasive mechanical ventilation did not increase the overall risk of death (risk ratio, 1.02; 95% CI, 0.93–1.13). There were signs of publication bias and substantial heterogeneity among the studies. Compensation of this bias by using the trim-and-fill method showed a significant risk of death after noninvasive mechanical ventilation failure (risk ratio, 1.07; 95% CI, 1.00–1.14). Meta-regression analysis showed that the predicted risk of death for the noninvasive mechanical ventilation group acted as a significant moderator, with a higher risk of death after noninvasive mechanical ventilation failure in those studies reporting lower predicted mortality. Conclusions: Noninvasive mechanical ventilation is associated with a lower risk of death in hematological patients with respiratory failure. Noninvasive mechanical ventilation failure may worsen the prognosis, mainly in less severe patients.

Therapeutic Implications of Immunoparalysis in Critically Ill Patients

In opposite to the classic view of the systemic inflammatory response, there is increasing evidence that, during critical illness, there is a systemic antiinflammatory state intended to avoid the spread of the local proinflammatory response. The resulting immunosuppression increases the risk of nosocomial infections, and has been related to an increase in morbidity and mortality in critically ill patients. Monocytes play a key role in orchestrating the inflammatory response, and a functional impairment of this population is the responsible for these phenomena. The decreased surface expression of class II molecules of the Main Histocompatibility Complex is both a marker of this state and a pathogenetic mechanism, as it decreases the antigen presentation capabilities of the mononuclear phagocytes. There are some therapeutic strategies to overcome this situation. Cytokines like IFNgamma or GM-CSF have been tested in animal models and patients, but there are no conclusive data. Other drugs like Flt3, AS101 or antibodies against IL-10 have been tested only in experimental models. The development of a new framework on the inflammatory response, the need for a consensus in immune monitoring and the development of experimental and clinical trials are required to improve the outcome of severe patients with systemic injuries.

Impact of Recruitment on Static and Dynamic Lung Strain in Acute Respiratory Distress Syndrome.

Background:Lung strain, defined as the ratio between end-inspiratory volume and functional residual capacity, is a marker of the mechanical load during ventilation. However, changes in lung volumes in response to pressures may occur in injured lungs and modify strain values. The objective of this study was to clarify the role of recruitment in strain measurements. Methods:Six oleic acid–injured pigs were ventilated at positive end-expiratory pressure (PEEP) 0 and 10 cm H2O before and after a recruitment maneuver (PEEP = 20 cm H2O). Lung volumes were measured by helium dilution and inductance plethysmography. In addition, six patients with moderate-to-severe acute respiratory distress syndrome were ventilated with three strategies (peak inspiratory pressure/PEEP: 20/8, 32/8, and 32/20 cm H2O). Lung volumes were measured in computed tomography slices acquired at end-expiration and end-inspiration. From both series, recruited volume and lung strain (total, dynamic, and static) were computed. Results:In the animal model, recruitment caused a significant decrease in dynamic strain (from [mean ± SD] 0.4 ± 0.12 to 0.25 ± 0.07, P < 0.01), while increasing the static component. In patients, total strain remained constant for the three ventilatory settings (0.35 ± 0.1, 0.37 ± 0.11, and 0.32 ± 0.1, respectively). Increases in tidal volume had no significant effects. Increasing PEEP constantly decreased dynamic strain (0.35 ± 0.1, 0.32 ± 0.1, and 0.04+0.03, P < 0.05) and increased static strain (0, 0.06 ± 0.06, and 0.28 ± 0.11, P < 0.05). The changes in dynamic and total strain among patients were correlated to the amount of recruited volume. An analysis restricted to the changes in normally aerated lung yielded similar results. Conclusion:Recruitment causes a shift from dynamic to static strain in early acute respiratory distress syndrome.

Mechanical ventilation in acute respiratory distress syndrome: The open lung revisited

Acute respiratory distress syndrome (ARDS) is still related to high mortality and morbidity rates. Most patients with ARDS will require ventilatory support. This treatment has a direct impact upon patient outcome and is associated to major side effects. In this regard, ventilator-associated lung injury (VALI) is the main concern when this technique is used. The ultimate mechanisms of VALI and its management are under constant evolution. The present review describes the classical mechanisms of VALI and how they have evolved with recent findings from physiopathological and clinical studies, with the aim of analyzing the clinical implications derived from them. Lastly, a series of knowledge-based recommendations are proposed that can be helpful for the ventilator assisted management of ARDS at the patient bedside.