Neutrophil depletion attenuates interleukin-8 production in mild-overstretch ventilated normal rabbit lung

Characteristics of inflammatory response and repair after experimental blast lung injury in rats

BACKGROUND AND OBJECTIVES

Blast-induced lung injury is associated with inflammatory, which are characterised by disruption of the alveolar-capillary barrier, haemorrhage, pulmonary infiltrateration causing oedema formation, pro-inflammatory cytokine and chemokine release, and anti-inflammatory counter-regulation. The objective of the current study was to define sequence of such alterations in with establishing blast-induced lung injury in rats using an advanced blast generator.

METHODS

Rats underwent a standardized blast wave trauma and were euthanised at defined time points. Non-traumatised animals served as sham controls. Obtained samples from bronchoalveolar lavage fluid (BALF) at each time-point were assessed for histology, leukocyte infiltration and cytokine/chemokine profile.

RESULTS

After blast lung injury, significant haemorrhage and neutrophil infiltration were observed. Similarly, protein accumulation, lactate dehydrogenase activity (LDH), alveolar eicosanoid release, matrix metalloproteinase (MMP)-2 and -9, pro-Inflammatory cytokines, including tumour necrosis factor (TNF) and interleukin (IL) -6 raised up. While declining in the level of anti-inflammatory cytokine IL-10 occurred. Ultimately, pulmonary oedema developed that increased to its maximum level within the first 1.5 h, then recovered within 24 h.

CONCLUSION

Using a stablished model, can facilitate the study of inflammatory response to blast lung injury. Following the blast injury, alteration in cytokine/chemokine profile and activity of cells in the alveolar space occurs, which eventuates in alveolar epithelial barrier dysfunction and oedema formation. Most of these parameters exhibit time-dependent return to their basal status that is an indication to resilience of lungs to blast-induced lung injury.

Hypoxia‐inducible factor (HIF)‐1α‐induced regulation of lung injury in pulmonary aspiration is mediated through NF‐kB

Aspiration‐induced lung injury is a common grievance encountered in the intensive care unit (ICU). It is a significant risk factor for improving ventilator‐associated pneumonia (VAP) and acute respiratory distress syndrome (ARDS). Hypoxia‐inducible factor (HIF)‐1α is one of the primary transcription factors responsible for regulating the cellular response to changes in oxygen tension. Here, we sought to determine the role of HIF‐1α and specifically the role of type 2 alveolar epithelial cells in generating the acute inflammatory response following acid and particles (CASP) aspiration. Previous studies show HIF‐1 α is involved in regulating the hypoxia‐stimulated expression of MCP‐1 in mice and humans. The CASP was induced in C57BL/6, ODD‐Luc, HIF‐1α (+/+) control, and HIF‐1α conditional knockout (HIF‐1α (−/−) mice). Following an injury in ODD mice, explanted organs were subjected to IVIS imaging to measure the degree of hypoxia. HIF‐1α expression, BAL albumin, cytokines, and histology were measured following CASP. In C57BL/6 mice, the level of HIF‐1α was increased at 1 h after CASP. There were significantly increased levels of albumin and cytokines in C57BL/6 and ODD‐Luc mice lungs following CASP. HIF‐1α (+/+) mice given CASP demonstrated a synergistic increase in albumin leakage, increased pro‐inflammatory cytokines, and worse injury. MCP‐1 antibody neutralized HIF‐1α (+/+) mice showed reduced granuloma formation. The NF‐κB expression was increased substantially in the HIF‐1α (+/+) mice following CASP compared to HIF‐1α (−/−) mice. Our data collectively identify that HIF‐1α upregulation of the acute inflammatory response depends on NF‐κB following CASP.

HMGB1 and inflammatory cytokines in experimental acute lung injury induced in rabbits

ABSTRACT The aim of this work was to measure HMGB1, TNF-alpha, and IL-8 in bronchoalveolar lavage (BAL), serum and TLR2 and TLR4mRNA expression in lung tissue of rabbits with two grades of acute lung injury (ALI). The animals were randomly assigned to groups with severe (S) and mild/moderate (MM) ALI, induced with warm saline, and a control group. HMGB1, TNF-alpha, IL-8, TLR2mRNA and TLR4mRNA were measured after ALI induction. The results showed increased levels of IL-8, TNF-alpha, HMGB1 and TLR4mRNA in the ALI groups. HMGB1, IL-8 and TNF-alpha concentrations in BAL were higher in S compared MM. Increased TLR4mRNA was observed in S and MM versus control. The results suggest an early participation of HMGB1 in ALI together with IL-8 and TNF-alpha and association with severity. TLR4 has early expression and role in ALI pathophysiology but is not associated with severity.

Alpha 1-antitrypsin for treating ventilator-associated lung injury in acute respiratory distress syndrome rats

Purpose: Mechanical ventilation (MV) is an essential life support tool for patients with acute respiratory distress syndrome (ARDS). However, MV for ARDS can result in ventilator-induced lung injury (VILI). This study aimed to assess whether alpha 1-antitrypsin (AAT) can reduce VILI in ARDS rats. Materials and Methods: Rats were randomly divided into five groups: the sham (S) group, MV (V) group, lipopolysaccharide (LPS) (L) group, MV/LPS (VL) group and MV/AAT (VA) group. Rats in the S group were anesthetized. The rats in the L group received LPS but not ventilation, the rats in the V group received only MV, and the rats in the VL and VA groups received LPS and MV. Additionally, the rats in the VA group were treated with AAT, and the other rats were injected with saline. The PaO₂/FiO₂ ratio and the wet/dry weight were assessed. The total protein and neutrophil elastase concentrations and the neutrophil and macrophage counts in bronchoalveolar lavage fluid (BALF) were evaluated. Proinflammatory factors in BALF and ICAM-1 and MIP-2 in serum were also tested. Furthermore, the oxidative stress response was detected, and histological injury and apoptosis were evaluated. Results: All the rats in the V, L and VL groups had significant lung injury, with the VL group exhibiting the most severe injury. Compared with the findings in the VL group, AAT significantly upregulated the PaO₂/FiO₂ ratio but decreased the wet/dry weight ratio and protein levels in BALF. AAT also reduced proinflammatory cytokine levels and inflammatory cell counts in BALF. Lung tissue injury and cell apoptosis were mitigated by AAT. Conclusions: AAT ameliorated VILI in ARDS rats. The protection conferred by AAT may be associated with the anti-inflammatory, antioxidative stress response and anti-apoptotic effects of AAT.

Expression profiling analysis of long noncoding RNAs in a mouse model of ventilator-induced lung injury indicating potential roles in inflammation

The key regulators of inflammation underlying ventilator-induced lung injury (VILI) remain poorly defined. Long noncoding RNAs (lncRNAs) have been implicated in the inflammatory response of many diseases; however, their roles in VILI remain unclear. We, therefore, performed transcriptome profiling of lncRNA and messenger RNA (mRNA) using RNA sequencing in lungs collected from mice model of VILI and control groups. Gene expression was analyzed through RNA sequencing and quantitative reverse transctiption polymerase chain reaction. A comprehensive bioinformatics analysis was used to characterize the expression profiles and relevant biological functions and for multiple comparisons among the controls and the injury models at different time points. Finally, lncRNA-mRNA coexpression networks were constructed and dysregulated lncRNAs were analyzed functionally. The mRNA transcript profiling, coexpression network analysis, and functional analysis of altered lncRNAs indicated enrichment in the regulation of immune system/inflammation processes, response to stress, and inflammatory pathways. We identified the lncRNA Gm43181 might be related to lung damage and neutrophil activation via chemokine receptor chemokine (C-X-C) receptor 2. In summary, our study provides an identification of aberrant lncRNA alterations involved in inflammation upon VILI, and lncRNA-mediated regulatory patterns may contribute to VILI inflammation.

One functional variant in the 3'-untranslated region of TLR4 is associated with the elevated risk of ventilator-associated pneumonia in the patients with chronic obstructive pulmonary disease

The aim of this study was to identify the association polymorphism (rs11536889) in the 3'-untranslated region (3'-UTR) of Toll-like receptors 4 (TLR4) and the risk for ventilator-associated pneumonia (VAP). miRNA database online and luciferase assays were used to validate TLR4 as the target gene of miR-1236. Enzyme-linked immunosorbent assay analysis and western blot were used to analyze the level of TLR4 in different genotype groups. In the present study, miR-1236 was predicted to bind to the rs11536889 G allele rather than the rs11536889 C allele, which was further confirmed by the luciferase activity suppressed by a fragment of 3'-UTR containing the rs11536889 G allele induced by lipopolysaccharide (LPS) and interleukin-6 (IL-6). Bronchial epithelial cells isolated from participants genotyped as GG, GC, and CC, with no remarkable difference in TLR4 messenger RNA (mRNA) levels were observed among these genotype groups. After stimulating by LPS, a TLR4 ligand, the CC-genotyped cells expressed higher levels of IL-8, IL-6, and tumor necrosis factor alpha (TNF-α) on their surfaces than cells with the other genotypes. Finally, the western blot analysis results showed that the expression level of IL-8, IL-6, and TNF-α protein was much higher in the CC group than the GC and GG groups subsequent to stimulation by LPS, and the IL-8, IL-6, and TNF-α protein levels in the GC were grouped much lower compared with the GG group. These findings indicated the regulatory association of miR-1236 with TLR4 and the abnormal expression of TLR4 caused by the presence of rs11536889 in the 3'-UTR of mRNA, which interfere with its interaction with the miR-1236, contributing to the risk of VAP.

High-mobility group box 1 protein is involved in the protective effect of Saquinavir on ventilation-induced lung injury in mice

Saquinavir (SQV) is the first FDA approved HIV protease inhibitor. Previous studies showed that SQV can limit Toll-like receptor-4 (TLR4)-mediated inflammatory pathway and nuclear factor-κB (NF-κB) activation, thereby playing a protective role in many kinds of diseases. High-mobility group box 1 (HMGB1) has been identified as an inflammatory mediator and it might express its toxicity in a short period of time in ventilator-induced lung injury (VILI). In this study, C57BL/6 mice were randomly divided into four groups (n = 10): control group and control with SQV group (Con + SQV) were spontaneous breath. HTV group (HTV) received high tidal volume ventilation (HTV) for 4 h. HTV with SQV group (HTV + SQV) were pretreated with 5 mg/kg of SQV for 7 days before HTV. Mice were sacrificed after 4 h of HTV. Lung wet/dry weight (W/D) ratio, alveolar-capillary permeability to Evans blue albumin (EBA), cell counts, total proteins in bronchoalveolar lavage fluid (BALF), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) level in BALF and lung tissue, and lung histopathology were examined. Our results showed that HTV caused significant lung injury and NF-κB activation, which was correlated with the increase of TNF-α and IL-6 levels in BALF and plasma. SQV pretreatment significantly attenuated pulmonary inflammatory injury, as well as NF-κB activation. These findings indicate that the protective effect of SQV may be associated with the inhibition of NF-κB activation and HMGB1 expression in mice.

Cyclin-dependent kinase inhibition reduces lung damage in a mouse model of ventilator-induced lung injury

Mechanical ventilation (MV) has the potential to induce lung damage in healthy lungs or aggravate existing lung injury. Polymorphonuclear neutrophil (PMN) recruitment plays an important role in driving the inflammatory response in ventilator-induced lung injury (VILI). The cyclin-dependent kinase inhibitor r-roscovitine has been shown to induce apoptosis in PMNs. In this study, we investigated the potential of r-roscovitine treatment in reducing lung damage in a mouse model of VILI. Mice were tracheotomized and subjected to lung-protective MV with lower (∼7.5 mL/kg) or lung-injurious MV with higher (∼15 mL/kg) tidal volume (VT). R-roscovitine treatment enhanced apoptosis in PMNs in vitro. Ventilator-induced lung injury was associated with pulmonary PMN influx in low and high VT MV. During lung-injurious MV, r-roscovitine treatment reduced the number of PMNs and lowered levels of the lung damage markers RAGE (receptor for advanced glycation end products) and total immunoglobulin M in bronchoalveolar lavage fluid. R-roscovitine did not affect cytokine or chemokine levels in the bronchoalveolar space, neither during lung-protective nor lung-injurious MV. Thus, r-roscovitine treatment reduces lung damage in VILI, possibly dependent on increased apoptosis of PMNs.

Pulmonary macrophage subpopulations in the induction and resolution of acute lung injury

Macrophages are key orchestrators of the inflammatory and repair responses in the lung, and the diversity of their function is indicated by their polarized states and distinct subpopulations and localization in the lung. Here, we characterized the pulmonary macrophage populations in the interstitial and alveolar compartments during the induction and resolution of acute lung injury induced by Pseudomonas aeruginosa infection. We identified macrophage subpopulations and polarity according to FACS analysis of cell surface protein markers, combined with cell sorting for gene expression using real-time PCR. With these techniques, we validated a novel, alternatively activated (M2) marker (transferrin receptor), and we described three interstitial and alveolar macrophage subpopulations in the lung whose distribution and functional state evolved from the induction to resolution phases of lung injury. Together, these findings indicate the presence and evolution of distinct macrophage subsets in the lung that serve specific niches in regulating the inflammatory response and its resolution. Alterations in the balance and function of these subpopulations could lead to nonresolving acute lung injury.

Reduction of neutrophil activity decreases early microvascular injury after subarachnoid haemorrhage

Background

Subarachnoid haemorrhage (SAH) elicits rapid pathological changes in the structure and function of parenchymal vessels (≤ 100 μm). The role of neutrophils in these changes has not been determined. This study investigates the role of neutrophils in early microvascular changes after SAH

Method

Rats were either untreated, treated with vinblastine or anti-polymorphonuclear (PMN) serum, which depletes neutrophils, or treated with pyrrolidine dithiocarbamate (PDTC), which limits neutrophil activity. SAH was induced by endovascular perforation. Neutrophil infiltration and the integrity of vascular endothelium and basement membrane were assessed immunohistochemically. Vascular collagenase activity was assessed by in situ zymography.

Results

Vinblastine and anti-PMN serum reduced post-SAH accumulation of neutrophils in cerebral vessels and in brain parenchyma. PDTC increased the neutrophil accumulation in cerebral vessels and decreased accumulation in brain parenchyma. In addition, each of the three agents decreased vascular collagenase activity and post-SAH loss of vascular endothelial and basement membrane immunostaining.

Conclusions

Our results implicate neutrophils in early microvascular injury after SAH and indicate that treatments which reduce neutrophil activity can be beneficial in limiting microvascular injury and increasing survival after SAH.

Toll-like receptor 4 mediates neutrophil sequestration and lung injury induced by endotoxin and hyperinflation

OBJECTIVE

To address the role of Toll-like receptor 4 signaling in mediating neutrophil recruitment and lung injury induced by lipopolysaccharide challenge coupled to lung hyperinflation, using Toll-like receptor 4 knockout (tlr4) mice. Infiltration of polymorphonuclear neutrophils into the lung is an important feature of ventilator-induced lung injury associated with pneumonia, but the mechanisms involved in neutrophil recruitment are poorly understood.

DESIGN

Experimental animal model.

SETTING

University laboratory.

SUBJECTS

tlr4 and wild-type C57BL/6 mice.

INTERVENTIONS

Wild-type or tlr4 mice were challenged by intratracheal instillation of lipopolysaccharide (0.3 mg/kg) for 2 hrs and then subjected to normal (7 mL/kg) or high (28 mL/kg) tidal volume ventilation for another 2 hrs. In other studies, neutrophils from wild-type or tlr4 mice were pretreated with lipopolysaccharide for 30 mins and then infused into the isolated lung preparation for 30 mins as the lungs were ventilated with 25 cm H2O peak inspiratory pressure.

MEASUREMENTS AND MAIN RESULTS

Lipopolysaccharide-challenged wild-type mice ventilated with a 28 mL/kg tidal volume exhibited 12-fold increase in neutrophil sequestration, 6-fold increase in bronchoalveolar lavage albumin concentration, and 1.6-fold increase in lung water content compared with unchallenged mice exposed to normal tidal volume ventilation. However, tlr4 mice showed negligible neutrophil sequestration, microvascular barrier breakdown, or edema formation. Mechanical ventilation alone or combined with lipopolysaccharide caused activation of circulating neutrophils and pulmonary endothelium in wild-type mice, whereas this was prevented in tlr4 mice.

CONCLUSIONS

High tidal volume ventilation during pneumonia/sepsis induces lung neutrophil sequestration and injury via the Toll-like receptor 4-dependent signaling pathway. The results suggest an important role of Toll-like receptor 4 in the mechanism of lung neutrophil sequestration and acute lung injury when pneumonia/sepsis is coupled to lung hyperinflation.

Role of the pulmonary epithelium and inflammatory signals in acute lung injury

Acute lung injury (ALI) is a clinical disease marked by respiratory failure due to disruption of the epithelial and endothelial barrier, flooding of the alveolar compartment with protein-rich fluid and recruitment of neutrophils into the alveolar space. ALI affects approximately 200,000 patients annually in the USA and results in approximately 75,000 deaths. It is associated with prolonged mechanical ventilation, intensive medical care, high morbidity and mortality, and rising healthcare costs. Owing to its impact on public health, great strides have been made towards understanding the pathobiology of ALI to affect outcome. This review will focus on the role of the epithelial cell in the pathogenesis and resolution of ALI and the role of various inflammatory mediators in ALI.

Spatial and temporal heterogeneity of ventilator-associated lung injury after surfactant depletion

Volutrauma and atelectrauma have been proposed as mechanisms of ventilator-associated lung injury, but few studies have compared their relative importance in mediating lung injury. The objective of our study was to compare the injury produced by stretch (volutrauma) vs. cyclical recruitment (atelectrauma) after surfactant depletion. In saline-lavaged rabbits, we used high tidal volume, low respiratory rate, and low positive end-expiratory pressure to produce stretch injury in nondependent lung regions and cyclical recruitment in dependent lung regions. Tidal changes in shunt fraction were assessed by measuring arterial Po(2) oscillations. After ventilating for times ranging from 0 to 6 h, lungs were excised, sectioned gravitationally, and assessed for regional injury by evaluation of edema formation, chemokine expression, upregulation of inflammatory enzyme activity, and alveolar neutrophil accumulation. Edema formation, lung tissue interleukin-8 expression, and alveolar neutrophil accumulation progressed more rapidly in dependent lung regions, whereas macrophage chemotactic protein-1 expression progressed more rapidly in nondependent lung regions. Temporal and regional heterogeneity of lung injury were substantial. In this surfactant depletion model of acute lung injury, cyclical recruitment produced more injury than stretch.

Neutrophil elastase inhibitor (sivelestat) attenuates subsequent ventilator-induced lung injury in mice

Mechanical ventilation can paradoxically cause acute lung injury, which is termed ventilator-induced lung injury. Neutrophil recruitment and neutrophil elastase release play a central role in the pathogenesis of ventilator-induced lung injury including cell damage, extracellular matrix degradation and alveolar-capillary hyperpermeability. We therefore speculated that neutrophil elastase inhibition ameliorates ventilator-induced lung injury. Anesthetized C57/BL6 mice received mechanical ventilation with a high tidal volume (V(T); 20 ml/kg) for 4 h. The neutrophil elastase inhibitor (sivelestat, 100 mg/kg) or saline was given intraperitoneally (i.p.) 30 min before ventilation. Sivelestat completely inhibited both neutrophil elastase and myeloperoxidase activities that were increased by ventilation, and attenuated the histopathological degree of lung damage, neutrophil accumulation and lung water content, as well as the concentration of macrophage inflammatory protein (MIP)-2, interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha in bronchoalveolar lavage fluid and serum. Moreover, mechanical ventilation increased the phosphorylation of c-Jun NH2-terminal kinase (JNK) and the expression of early growth response gene-1 (Egr-1) mRNA, and these increases were also recovered by sivelestat. The terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) staining revealed apoptotic cells mainly in alveolar epithelial cells and their numbers corresponded to histological damage. These data suggested that sivelestat could protect against ventilator-induced lung injury by suppressing apoptotic responses through mechanical stress-induced cell signaling in addition to inhibiting neutrophil chemotaxis.

Anti-interleukin 8 autoantibody:interleukin 8 immune complexes visualized by laser confocal microscopy in injured lung

CONTEXT

Anti-interleukin 8 autoantibody:interleukin 8 (anti-IL-8 autoantibody:IL-8) complexes are present in lung fluids of patients with acute lung injury/acute respiratory distress syndrome (ALI/ARDS), and levels of these complexes correlate with progression to and the outcome of ARDS. Fc gammaRIIa, an immunoglobulin G (IgG) receptor, mediates proinflammatory activity of the complexes.

OBJECTIVE

To evaluate lung tissues from patients with ARDS for presence of anti-IL-8 autoantibody:IL-8 complexes and to establish whether the complexes associate with Fc gammaRIIa.

DESIGN

Lung tissue sections from 3 patients with ARDS and sections of normal lung tissues from 3 patients were stained with antibodies against IL-8 and IgG to detect immune complexes and with antibody against Fc gammaRIIa. In some experiments, sections were blocked with anti-Fc gamma RIIa antibody before staining. Samples were analyzed using confocal microscopy.

RESULTS

Interleukin 8 costained with IgG and Fc gammaRIIa in lung tissues from patients with ARDS but not in control tissues, suggesting that anti-IL-8 autoantibody:IL-8 complexes are deposited in lungs of patients with ARDS via Fc gammaRIIa. Further, colocalization between IL-8 and Fc gammaRIIa could be blocked by anti-Fc gammaRIIa.

CONCLUSIONS

Our data demonstrate that anti-IL-8 autoantibody:IL-8 complexes are present in lung tissues of patients with ARDS, and are attached to Fc gammaRIIa.

The contribution of biophysical lung injury to the development of biotrauma

Patients with severe acute respiratory distress syndrome who die usually succumb to multiorgan failure as opposed to hypoxia. Despite appropriate resuscitation, some patients' symptoms persist on a downward spiral, apparently propagated by an uncontained systemic inflammatory response. This phenomenon is not well understood. However, a novel hypothesis to explain this observation proposes that it is related to the life-saving ventilatory support used to treat the respiratory failure. According to this hypothesis, mechanical ventilation per se, by altering both the magnitude and the pattern of lung stretch, can cause changes in gene expression and/or cellular metabolism that ultimately can lead to the development of an overwhelming inflammatory response-even in the absence of overt structural damage. This mechanism of injury has been termed biotrauma. In this review we explore the biotrauma hypothesis, the causal relationship between biophysical injury and organ failure, and its implications for the future therapy and management of critically ill patients.

Contribution of high-mobility group box-1 to the development of ventilator-induced lung injury

RATIONALE

Proinflammatory cytokines play an important role in ventilator-induced lung injury (VILI). High-mobility group box-1 (HMGB1) is a macrophage-derived proinflammatory cytokine that can cause lung injury.

OBJECTIVES

This study tested the hypothesis that HMGB1 is released in intact lungs ventilated with large Vt. A second objective was to identify the source of HMGB1. A third objective was to examine the effects of blocking HMGB1 on the subsequent development of VILI.

METHODS

Bronchoalveolar lavage fluid (BALF) and lung tissues were obtained from rabbits mechanically ventilated for 4 h with a small (8 ml/kg) versus a large (30 ml/kg) Vt. BALF was also obtained from rabbits with intratracheal instillation of anti-HMGB1 antibody before the initiation of large Vt ventilation.

MEASUREMENTS AND MAIN RESULTS

The concentrations of HMGB1 in BALF were fivefold higher in the large than in the small Vt group. Immunohistochemistry and immunofluorescence studies revealed expression of HMGB1 in the cytoplasm of macrophages and neutrophils in lungs ventilated with large Vt. Blocking HMGB1 improved oxygenation, limited microvascular permeability and neutrophil influx into the alveolar lumen, and decreased concentrations of tumor necrosis factor-alpha in BALF.

CONCLUSIONS

These observations suggest that HMGB1 could be one of the deteriorating factors in the development of VILI.

Comparison of prone positioning and high-frequency oscillatory ventilation in patients with acute respiratory distress syndrome*

OBJECTIVE

Both prone position and high-frequency oscillatory ventilation (HFOV) have the potential to facilitate lung recruitment, and their combined use could thus be synergetic on gas exchange. Keeping the lung open could also potentially be lung protective. The aim of this study was to compare physiologic and proinflammatory effects of HFOV, prone positioning, or their combination in severe acute respiratory distress syndrome (ARDS).

DESIGN

: Prospective, comparative randomized study.

SETTING

A medical intensive care unit.

PATIENTS

Thirty-nine ARDS patients with a Pao2/Fio2 ratio <150 mm Hg at positive end-expiratory pressure > or =5 cm H2O.

INTERVENTIONS

After 12 hrs on conventional lung-protective mechanical ventilation (tidal volume 6 mL/kg of ideal body weight, plateau pressure not exceeding the upper inflection point, and a maximum of 35 cm H2O; supine-CV), 39 patients were randomized to receive one of the following 12-hr periods: conventional lung-protective mechanical ventilation in prone position (prone-CV), HFOV in supine position (supine-HFOV), or HFOV in prone position (prone-HFOV).

MEASUREMENTS AND MAIN RESULTS

Prone-CV (from 138 +/- 58 mm Hg to 217 +/- 110 mm Hg, p < .0001) and prone-HFOV (from 126 +/- 40 mm Hg to 227 +/- 64 mm Hg, p < 0.0001) improved the Pao2/Fio2 ratio whereas supine-HFOV did not alter the Pao2/Fio2 ratio (from 134 +/- 57 mm Hg to 138 +/- 48 mm Hg). The oxygenation index ({mean airway pressure x Fio2 x 100}/Pao2) decreased in the prone-CV and prone-HFOV groups and was lower than in the supine-HFOV group. Interleukin-8 increased significantly in the bronchoalveolar lavage fluid (BALF) in supine-HFOV and prone-HFOV groups compared with prone-CV and supine-CV. Neutrophil counts were higher in the supine-HFOV group than in the prone-CV group.

CONCLUSIONS

Although HFOV in the supine position does not improve oxygenation or lung inflammation, the prone position increases oxygenation and reduces lung inflammation in ARDS patients. Prone-HFOV produced similar improvement in oxygenation like prone-CV but was associated with higher BALF indexes of inflammation. In contrast, supine-HFOV did not improve gas exchange and was associated with enhanced lung inflammation.

Sequence of endothelial signaling during lung expansion

Although high tidal volume ventilation exacerbates lung injury, the mechanisms underlying the inflammatory response are not clear. Here, we exposed isolated lungs to high or low tidal volume ventilation, while perfusing lungs with whole blood, or blood depleted of leukocytes and platelets. Then, we determined signaling responses in freshly isolated lung endothelial cells by means of immunoblotting and immunofluorescence approaches. In depleted blood perfusion, high tidal volume induced modest increases in both P-selectin expression on the endothelial surface, and in endothelial protein tyrosine phosphorylation. Both high tidal volume-induced responses were markedly enhanced in the presence of whole blood perfusion. However, a P-selectin-blocking antibody given together with whole blood perfusion inhibited the responses down to levels corresponding to those for depleted blood perfusion. These findings indicate that the full proinflammatory response occurs in two stages. First, lung distension causes modest endothelial activation. Second, subsequent endothelial-inflammatory cell interactions augment P-selectin expression and tyrosine phosphorylation. We conclude that interactions of circulating inflammatory cells with P-selectin critically determine proinflammatory endothelial activation during high tidal volume 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.

Pulmonary contusion causes impairment of macrophage and lymphocyte immune functions and increases mortality associated with a subsequent septic challenge*

OBJECTIVE AND DESIGN

Pulmonary contusion is frequently followed by acute respiratory distress syndrome, pneumonia, and sepsis. However, immunologic alterations of circulating and resident immune cell populations contributing to the posttraumatic immunosuppression are poorly understood. We therefore characterized the influence of pulmonary contusion on peripheral blood mononuclear cells, peritoneal macrophages, splenocytes, and splenic macrophages. To address the significance of the immunosuppression associated with lung contusion, we investigated how the consecutive addition of moderate or severe sepsis affected survival after blunt chest trauma.

SUBJECTS

Male C3H/HeN mice (n = 10 per group) were anesthetized and subjected to chest trauma or sham procedure.

MEASUREMENTS

The cytokine release of cultured peripheral blood mononuclear cells, peritoneal macrophages, splenocytes, and splenic macrophages and plasma levels of tumor necrosis factor-alpha and interleukin-6 from those animals were quantified. Sepsis was induced via cecal ligation and puncture 24 hrs after lung contusion.

MAIN RESULTS

Two hours after blunt chest trauma, plasma tumor necrosis factor-alpha and interleukin-6 were markedly increased, as was peripheral blood mononuclear cell cytokine production, lung myeloperoxidase activity, and lung chemokine concentrations. At 24 hrs and, in part, already at 2 hrs, cytokine release from peritoneal macrophages, splenic macrophages, and splenocytes was significantly suppressed. Furthermore, pulmonary contusion when followed by moderate sepsis significantly diminished survival rate when compared with chest trauma or moderate sepsis alone.

CONCLUSIONS

These results indicate that pulmonary contusion causes severe immunodysfunction of splenocytes, macrophages, and monocytes in different local compartments and systemically. Moreover, this immunosuppression is associated with an increased susceptibility to infectious complications, which results in a decreased survival rate if blunt chest trauma is followed by a septic insult.

Overview of ventilator-induced lung injury mechanisms

PURPOSE OF REVIEW

Mechanical ventilation is the main supportive therapy for patients with acute respiratory distress syndrome. As with any therapy, mechanical ventilation has side effects and may induce lung injury. This review will focus on stretch-dependent activation of alveolar epithelial and endothelial cells and polymorphonuclear leukocytes, and apoptosis/necrosis balance.

RECENT FINDINGS

The past year has seen important research in the area of mechanotransduction and lung native immunity, suggesting further mechanisms of lung inflammation and injury in ventilator-induced lung injury. Research in the past year has also stressed the importance of inflammatory response by alveolar cells and role of polymorphonuclear leukocytes in stretch-induced lung injury and has suggested a role for apoptosis in the maintenance of the alveolar epithelium.

SUMMARY

The proportion of patients receiving protective ventilatory strategies remains modest. If efforts to minimize the iatrogenic consequences of mechanical ventilation are to succeed, there must be a greater understanding of the signal transduction mechanisms and the development of potential pharmacologic targets to modulate the molecular and cellular effects of lung stretch.

Bench-to-bedside review: Biotrauma and modulation of the innate immune response

The innate immune network is responsible for coordinating the initial defense against potentially noxious stimuli. This complex system includes anatomical, physical and chemical barriers, effector cells and circulating molecules that direct component and system interactions. Besides the direct effects of breaching pulmonary protective barriers, cyclic stretch generated during mechanical ventilation (MV) has been implicated in the modulation of the innate immunity. Evidence from recent human trials suggests that controlling MV-forces may significantly impact outcome in acute respiratory distress syndrome. In this paper, we explore the pertinent evidence implicating biotrauma caused by cyclic MV and its effect on innate immune responses.

Ventilation strategy affects cytokine release after mesenteric ischemia-reperfusion in rats

OBJECTIVE

To evaluate the impact of different ventilation modalities on lung and plasma concentrations of cytokines in a model of secondary lung inflammation, mesenteric ischemia-reperfusion, in rats.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Research laboratory of a university.

SUBJECTS

Sixty-four male adult Wistar rats weighing 320-380 g.

INTERVENTIONS

Eight groups were studied. Two groups underwent no surgical procedure: They were either not ventilated or ventilated with an injurious modality consisting of 30 mL/kg tidal volume (Vt) without positive-end expiratory pressure (PEEP). Animals of the other groups underwent laparotomy with or without 2-hr mesenteric ischemia followed by 4 hrs of reperfusion during which the rats were mechanically ventilated. Ventilation modalities were conventional (tidal volume 10 mL/kg, PEEP 3 cm H2O), protective (6 mL/kg, 6 cm H(2)O), or injurious (tidal volume 30 mL/kg and no PEEP). Rats were killed by exsanguination, and their lungs were excised and homogenized in buffer. Supernatants of lung homogenates and plasmas were stored at -80 degrees C for subsequent measurements.

MEASUREMENTS AND MAIN RESULTS

Tumor necrosis factor-alpha, interleukin-1 beta, interleukin-6, macrophage inhibitory protein 2, and interleukin-10 were determined in lung supernatants and plasmas with a rat-specific enzyme-linked immunosorbent assay. Lung and plasma cytokine concentrations were not significantly different between rats ventilated with the injurious modality only and nonventilated rats. Lung and plasma cytokine concentrations were higher in rats that had undergone mesenteric ischemia-reperfusion than in rats with laparotomy only, whatever ventilation modality. Lung and plasma cytokine concentrations were higher in these rats after the injurious ventilation modality than after the other modalities.

CONCLUSION

This study shows that an injurious ventilation does not produce significant in vivo release of cytokines in intact animals but promotes the release of pro- and anti-inflammatory cytokines in an inflammatory context.