Differential responses of the endothelial and epithelial barriers of the lung in sheep to Escherichia coli endotoxin

Neutrophils and their Fc gamma receptors are essential in a mouse model of transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is the most common cause of transfusion-related mortality. To explore the pathogenesis of TRALI, we developed an in vivo mouse model based on the passive transfusion of an MHC class I (MHC I) mAb (H2Kd) to mice with the cognate antigen. Transfusion of the MHC I mAb to BALB/c mice produced acute lung injury with increased excess lung water, increased lung vascular and lung epithelial permeability to protein, and decreased alveolar fluid clearance. There was 50% mortality at a 2-hour time point after Ab administration. Pulmonary histology and immunohistochemistry revealed prominent neutrophil sequestration in the lung microvasculature that occurred concomitantly with acute peripheral blood neutropenia, all within 2 hours of administration of the mAb. Depletion of neutrophils by injection of anti-granulocyte mAb Gr-1 protected mice from lung injury following MHC I mAb challenge. FcRgamma-/- mice were resistant to MHC I mAb-induced lung injury, while adoptive transfer of wild-type neutrophils into the FcRgamma-/- animals restored lung injury following MHC I mAb challenge. In conclusion, in a clinically relevant in vivo mouse model of TRALI using an MHC I mAb, the mechanism of lung injury was dependent on neutrophils and their Fc gamma receptors.

Intravenous administration of activated protein C in Pseudomonas-induced lung injury: impact on lung fluid balance and the inflammatory response

Background

Acute lung injury (ALI) induces a coagulation/fibrinolysis imbalance and leads to fibrin deposition. The protein C pathway is an important regulator of the coagulation system and reduces the inflammatory response. The aim of the study was to examine the effects of recombinant human activated protein C (rhAPC) in the early phase of Pseudomonas aeruginosa (Pa)-induced lung injury.

Methods

The study was conducted in vivo on a rat model of Pa-induced ALI. Continuous intravenous (IV) rhAPC was administrated simultaneously with intratracheal (IT) Pa. We instilled into the airspaces a 5% bovine albumin solution with 1 μ(Ci of ¹²⁵ I-albumin and injected IV 1 μ(Ci of ¹¹¹In-albumin to measure lung liquid clearance (LLC) and endothelial injury. Cytokines levels (TNFα and IL-6) and thrombin-antithrombin (TAT) complexes were measured in blood and bronchoalveolar lavage fluid (BALF) at 4 hours. Four groups were compared: control (CTR), pneumonia (PNP) receiving IT Pa (0.5 ml/kg of 1 × 10⁹ cfu), APC: IV rhAPC (300 μg/kg/h), A-PNP: IT Pa /IV rhAPC.

Results

Alveolar-capillary permeability was increased in the PNP versus the CTR group (0.28 ± 0.08 vs. 0.03 ± 0.01, p < 0.05). IV rhAPC in Pa-induced ALI led to further injury (0.47 ± 0.17 vs. 0.28 ± 0.08, p = 0.2). The LLC was significantly decreased in the A-PNP group compared to PNP group (9.1 ± (4.3% vs. 33.4 ± 2.6%, p < 0.05). The lung wet to dry weight ratio was significantly increased in the PNP group (4.62 ± 0.31) compared to the CTR group (3.87 ± 0.22, p < 0.05). IV rhAPC administration tends to increase this parameter in Pa-induced ALI (5.80 ± 0.66, p = 0.07). These findings were associated with a loss of inflammatory response compartmentalization measured by TNFα and IL-6 systemic levels. TAT complexes in BALF were increased in the A-PNP group (23.17 ± 2.89 ng/ml) compared to the CTR group (0.92 ± 0.17 ng/ml, p < 0.05) and the PNP group (11.06 ± 2.76 ng/ml, p < 0.05).

Conclusion

rhAPC reduces LLC following Pa-induced ALI and may influence pulmonary edema formation. The early massive fibrin formation is probably beneficial in ALI limiting both the extent of injury and permeability disorders.

Effects of hypoxia and hypercapnia on surfactant protein expression proliferation and apoptosis in A549 alveolar epithelial cells

During lung injury alveolar epithelial cells are directly exposed to changes in PO(2) and PCO(2). Integrity of alveolar epithelial type II cells (AECII) is critical in lung injury but the effect of hypoxia and hypercapnia on AECII function, viability and proliferation has not been clearly investigated. Aim of the present work was to determine the direct effect of hypoxia and hypercapnia on surfactant protein expression, proliferation and apoptosis of lung epithelial cells in vitro. A549 alveolar epithelia cells were subjected to hypoxia (1%O(2)-5% CO(2)) or hypercapnia (21% O(2-) 15% CO(2)) and expression of surfactant protein C was measured and compared to normal conditions (21% O(2)- 5% CO(2)). Cell cycle progression and apoptosis were measured by flow cytometric analysis.

RESULTS

A549 alveolar epithelial cells produce surfactant proteins, including surfactant protein C, when cultured under normal conditions, which is reduced under hypoxic conditions. Specifically, pro-SpC expression is moderately decreased after 8 h of culture in hypoxia, and is completely attenuated after 48 h. Hypercapnia decreases pro-SpC expression only after 48 h of exposure. Stimulation with TNF-alpha partly reverses pSPC decrease observed under hypoxic and hypercapnic conditions. Hypoxic culture of A549 cells results in progressive arrest of cells in the G1 phase of the cell cycle and increased apoptosis first observed 4 h following exposure and peaking at 24 h. In contrast hypercapnia has no significant effect on alveolar epithelial cell proliferation or apoptosis.

CONCLUSIONS

Taken together we can conclude that hypoxia rapidly and severely affects AECII function and viability while hypercapnia has an inhibitory effect on pro-SpC production only after prolonged exposure.

RNA interference for alpha-ENaC inhibits rat lung fluid absorption in vivo

We used siRNA against the alpha-ENaC (epithelial Na channel) subunit to investigate ENaC involvement in lung fluid absorption in rats by the impermeable tracer technique during baseline and after beta-adrenoceptor stimulation by terbutaline. Terbutaline stimulation of lung fluid absorption increased fluid absorption by 165% in pSi-0-pretreated rat lungs (irrelevant siRNA-generating plasmid). Terbutaline failed to increase lung fluid absorption in rats given the specific alpha-ENaC siRNA-generating plasmid (pSi-4). pSi-4 pretreatment reduced baseline lung fluid absorption by approximately 30%. alpha-ENaC was undetectable in pSi-4-pretreated lungs, regardless of condition but was normal in pSi-0-pretreated lungs. We carried out a dose-response analysis where rats were given 0-200 microg/kg body wt pSi-4, and alpha-ENaC mRNA and protein expressions were analyzed. To reach IC(50) for alpha-ENaC mRNA expression, 32 microg/kg body wt pSi-4 was needed, and to reach IC(50) for alpha-ENaC protein expression, 59 microg/kg body wt pSi-4 was needed. We tested for lung tissue specificity and found no changes in beta-ENaC expression, at either mRNA or protein level, as well as no changes in alpha(1)-Na-K-ATPase protein expression. We isolated alveolar epithelial type II cells 24 h after in vivo pSi-4 pretreatment. In these cells, alpha-ENaC mRNA was undetectable, demonstrating that alveolar epithelial ENaC expression was attenuated after intratracheal alpha-ENaC siRNA-generating plasmid DNA instillation. We tested for organ specificity and found no changes in kidney alpha- and beta-ENaC mRNA and protein expression. Thus we provide conclusive evidence that beta-adrenoceptor stimulation of lung fluid absorption is critically ENaC dependent, whereas baseline lung fluid absorption seemed less ENaC dependent.

Time course of lung parenchyma remodeling in pulmonary and extrapulmonary acute lung injury

The aim of this study is to test the hypothesis that the early changes in lung mechanics and the amount of type III collagen fiber do not predict the evolution of lung parenchyma remodeling in pulmonary and extrapulmonary acute lung injury (ALI). For this purpose, we analyzed the time course of lung parenchyma remodeling in murine models of pulmonary and extrapulmonary ALI with similar degrees of mechanical compromise at the early phase of ALI. Lung histology (light and electron microscopy), the amount of elastic and collagen fibers in the alveolar septa, the expression of matrix metalloproteinase-9, and mechanical parameters (lung-resistive and viscoelastic pressures, and static elastance) were analyzed 24 h, 1, 3, and 8 wk after the induction of lung injury. In control (C) pulmonary (p) and extrapulmonary (exp) groups, saline was intratracheally (it; 0.05 ml) instilled and intraperitoneally (ip; 0.5 ml) injected, respectively. In ALIp and ALIexp groups, mice received Escherichia coli lipopolysaccharide (10 microg it and 125 microg ip, respectively). At 24 h, all mechanical and morphometrical parameters, as well as type III collagen fiber content, increased similarly in ALIp and ALIexp groups. In ALIexp, all mechanical and histological data returned to control values at 1 wk. However, in ALIp, static elastance returned to control values at 3 wk, whereas resistive and viscoelastic pressures, as well as type III collagen fibers and elastin, remained elevated until week 8. ALIp showed higher expression of matrix metalloproteinase-9 than ALIexp. In conclusion, insult in pulmonary epithelium yielded fibroelastogenesis, whereas mice with ALI induced by endothelial lesion developed only fibrosis that was repaired early in the course of lung injury. Furthermore, early functional and morphological changes did not predict lung parenchyma remodeling.

Oxytocin-induced labor augments IL-1beta-stimulated lung fluid absorption in fetal guinea pig lungs

We tested the hypothesis that oxytocin-induced labor augmented IL-1beta-induced/-stimulated lung fluid absorption in preterm guinea pig fetuses. IL-1beta was administered subcutaneously daily to timed-pregnant guinea pigs for 3 days with and without simultaneous cortisol synthesis inhibition by metyrapone. At day 3, oxytocin was administered, and fetuses were delivered by abdominal hysterotomy at 61 and by oxytocin-induced birth at 68 days gestation. Delivered fetuses were instilled with isosmolar 5% albumin into the lungs, and lung fluid movement was measured over 1 h by mass balance. Lung fluid absorption was induced in 61-day and stimulated in 68-day gestation lungs by IL-1beta. Labor induction by oxytocin augmented IL-1beta-induced/-stimulated lung fluid absorption. Metyrapone pretreatment did not affect oxytocin-induced/-stimulated lung fluid absorption, while completely blocking IL-1beta-induced/-stimulated fluid absorption. Fetal lung fluid absorption, when present, was always propranolol and amiloride sensitive, suggesting that beta-adrenoceptor stimulation and amiloride-sensitive sodium channels were critical for fluid absorption. Epithelial sodium channel and Na-K-ATPase subunit expressions were both increased by IL-1beta, but not further by oxytocin. Our results indicate that IL-1beta release into the maternal blood circulation positively affects lung maturation due to the IL-1beta-induced release of cortisol and thus prepares the lungs for the epinephrine surge associated with labor.

Physiologic, biochemical, and imaging characterization of acute lung injury in mice

RATIONALE

Most models of acute lung injury in mice have yet to be fully characterized.

OBJECTIVES

To directly compare and contrast endotoxin and oleic acid models of acute lung injury in mice in terms of their physiologic, biochemical, histopathologic, and imaging manifestations.

METHODS

Survival studies, lung weights, x-ray computed tomographic scanning, light and electron microscopy, bronchoalveolar lavage, lung uptake of ((18)F)fluorodeoxyglucose, tissue myeloperoxidase, arterial blood gases, mean arterial pressure, and lung tissue prostanoids were measured in separate groups of C57Bl/6 mice (normal animals, endotoxin only [20 microg/g], oleic acid only [0.15 microl/g], or endotoxin + oleic acid).

RESULTS

Endotoxin alone caused only mild pulmonary neutrophilic inflammation with little functional or structural damage to the alveolar architecture. In contrast, oleic acid caused severe alveolar damage with the development of alveolar edema of the increased-permeability type with associated abnormalities in gas exchange. When given together, endotoxin and oleic acid acted synergistically to increase pulmonary edema and to worsen gas exchange and hemodynamics, thereby increasing mortality. This synergism was significantly attenuated by the prior administration of the endotoxin antagonist E5564 (eritoran).

CONCLUSIONS

Under the conditions of these studies, only mice exposed to oleic acid showed both structural and functional characteristics of acute lung injury. Nevertheless, endotoxin had potent synergistic physiologic effects that increased mortality. Overall, these models, which can be translated to genetically altered mice, are amenable to study with state-of-the-art imaging techniques, and with experimental interventions that can probe the underlying mechanisms of injury.

Protective effect of IL-6 on alveolar epithelial cell death induced by hydrogen peroxide

The goal of this study was to examine whether IL-6 could directly protect lung resident cells, especially alveolar epithelial cells, from reactive oxygen species (ROS)-induced cell death. ROS induced IL-6 gene expression in organotypic lung slices of wild-type (WT) mice. ROS also induced IL-6 gene expression in mouse primary lung fibroblasts, dose dependently. The organotypic lung slices of WT were more resistant to ROS-induced DNA fragmentation than those of IL-6-deficient (IL-6−/−) mice. WT resistance against ROS was abrogated by treatment with anti-IL-6 antibody. TdT-mediated dUTP nick end labeling stain and electron microscopy revealed that DNA fragmented cells in the IL-6−/− slice included alveolar epithelial cells and endothelial cells. In vitro studies demonstrated that IL-6 reduced ROS-induced A549 alveolar epithelial cell death. Together, these data suggest that IL-6 played an antioxidant role in the lung by protecting lung resident cells, especially alveolar epithelial cells, from ROS-induced cell death.

Pulmonary and extrapulmonary acute respiratory distress syndrome: are they different?

PURPOSE OF REVIEW

Acute respiratory distress syndrome has been considered a morphologic and functional expression of lung injury caused by a variety of insults. Two distinct forms of acute respiratory distress syndrome/acute lung injury are described, because there are differences between pulmonary acute respiratory distress syndrome (direct effects on lung cells) and extrapulmonary acute respiratory distress syndrome (reflecting lung involvement in a more distant systemic inflammatory response). This article will focus on the differences in lung histology and morphology, respiratory mechanics, and response to ventilatory strategies and pharmacologic therapies in pulmonary and extrapulmonary acute respiratory distress syndrome.

RECENT FINDINGS

Many researchers recognize that experimental pulmonary and extrapulmonary acute respiratory distress syndrome are not identical. In addition, clinical studies have described the detection of differences radiographically, functionally, and by analysis of the responses to therapeutic interventions (ventilatory strategies, positive end-expiratory pressure, prone position, drugs). However, there are contradictions among the different studies addressing these issues, which could be attributed to the fact that the distinction between pulmonary and extrapulmonary acute respiratory distress syndrome is not always clear and simple. Furthermore, there may be frequent overlapping in pathogenetic mechanisms and morphologic alterations.

SUMMARY

The understanding of acute respiratory distress syndrome needs to take into account its origin. If each pathogenetic mechanism were to be considered, clinical management would be more precise, and probably the outcome could include real amelioration.

Pulmonary and extrapulmonary acute lung injury: inflammatory and ultrastructural analyses

To test whether pulmonary and extrapulmonary acute lung injury (ALI) of identical mechanical compromise would express diverse morphological patterns and immunological pathways. For this purpose, a model of pulmonary (p) and extrapulmonary (exp) ALI with similar functional changes was developed and pulmonary morphology (light and electron microscopy), cytokines levels, and neutrophilic infiltration in the bronchoalveolar lavage fluid (BALF), elastic and collagen fiber content in the alveolar septa, and neutrophil apoptosis in the lung parenchyma were analyzed. BALB/c mice were divided into four groups. In control groups, saline was intratracheally (it, 0.05 ml) instilled and intraperitoneally (ip, 0.5 ml) injected, respectively. In the ALIp and ALIexp groups, mice received E. coli lipopolysaccharide (10 microg it and 125 microg ip, respectively). The changes in lung resistive and viscoelastic pressures and in static elastance, alveolar collapse, and cell content in lung tissue were similar in the ALIp and ALIexp groups. The ALIp group presented a threefold increase in KC (murine function homolog to IL-8) and IL-10 levels in the BALF in relation to ALIexp, whereas IL-6 level showed a twofold increase in ALIp. Neutrophils in the BALF were more frequent in ALIp than in ALIexp. ALIp showed more extensive injury of alveolar epithelium, intact capillary endothelium, and apoptotic neutrophils, whereas the ALIexp group presented interstitial edema and intact type I and II cells and endothelial layer. In conclusion, given the same pulmonary mechanical dysfunction independently of the etiology of ALI, insult in pulmonary epithelium yielded more pronounced inflammatory responses, which induce ultrastructural morphological changes.

Bench-to-bedside review: the role of the alveolar epithelium in the resolution of pulmonary edema in acute lung injury

Clearance of pulmonary edema fluid is accomplished by active ion transport, predominantly by the alveolar epithelium. Various ion pumps and channels on the surface of the alveolar epithelial cell generate an osmotic gradient across the epithelium, which in turn drives the movement of water out of the airspaces. Here, the mechanisms of alveolar ion and fluid clearance are reviewed. In addition, many factors that regulate the rate of edema clearance, such as catecholamines, steroids, cytokines, and growth factors, are discussed. Finally, we address the changes to the alveolar epithelium and its transport processes during acute lung injury (ALI). Since relevant clinical outcomes correlate with rates of edema clearance in ALI, therapies based on our understanding of the mechanisms and regulation of fluid transport may be developed.

Oleic acid inhibits alveolar fluid reabsorption: a role in acute respiratory distress syndrome?

Levels of oleic acid (OA) are elevated in plasma and bronchoalveolar lavage fluids of patients with acute respiratory distress syndrome (ARDS). OA is also widely used to provoke edema, by unknown mechanisms, in experimental models of ARDS. We investigated the impact of intravascularly applied OA on epithelial lining fluid balance. OA (25 microM) dramatically blocked active transepithelial (22)Na(+) transport (by 92%) in an isolated, ventilated, and perfused rabbit lung model, provoking alveolar edema, assessed by increases in lung weight and epithelial lining fluid volume. OA did not alter epithelial permeability, measured by [(3)H]mannitol and fluorescently labeled albumin flux, but did increase endothelial permeability, assessed by capillary filtration coefficient. In A549 cells, OA completely blocked amiloride-sensitive sodium currents measured by patch clamp, and also largely abrogated ouabain-sensitive Na(+),K(+)-ATPase-mediated (86)Rb(+) uptake. Although OA did not alter epithelial sodium channel or Na(+),K(+)-ATPase surface expression, it covalently associated with both molecules and directly, dramatically, and dose-dependently inhibited the catalytic activity of purified Na(+),K(+)-ATPase. Therefore, OA impaired the two essential transepithelial active sodium transport mechanisms of the lung, and could thus promote alveolar edema formation and prevent edema resolution, thereby contributing to the development of ARDS.

Role of neutrophils in mucus hypersecretion in COPD and implications for therapy

Airway mucus hypersecretion is a serious and presently untreatable symptom of COPD. Over the past several years, emerging evidence has implicated epidermal growth factor receptor (EGFR) expression and activation in mucin production by airway epithelial (goblet) cells. Activated neutrophils recruited to the airways (and their secreted products) play several key roles in EGFR-dependent mucus hypersecretion: (i) activated neutrophils secrete tumor necrosis factor (TNF)-alpha, which induces EGFR expression in airway epithelial cells; (ii) activated neutrophils release reactive oxygen species, which activate EGFR; (iii) neutrophil elastase cleaves the EGFR proligand, pro-transforming growth factor (TGF)-alpha, releasing mature TGF alpha which activates EGFR in a ligand-dependent fashion; and (iv) neutrophil elastase causes potent goblet cell degranulation. The secretion of active products by neutrophils appears carefully regulated. The local release of neutrophil elastase requires close contact between the neutrophil and another cell, mediated by surface adhesion molecules, thus limiting proteolysis to the immediate pericellular environment. In the airway lumen, neutrophils undergo apoptosis and are cleared by macrophages without releasing their intracellular contents. In contrast, neutrophils that die by necrosis disgorge proteases and reactive oxygen species into the lumen. In COPD, conditions within the airway lumen promote neutrophil necrosis. It is concluded that neutrophil death via necrosis leads to the high concentrations of free neutrophil elastase and reactive oxygen species in the sputum of patients with airway neutrophilia and mucus hypersecretion. Inflammatory cells (neutrophils), molecules (neutrophil elastase and reactive oxygen species), signaling pathways (EGFR), and cellular processes (neutrophil necrosis) contribute to mucus hypersecretion in COPD, and are potential targets for therapy. Interventions that target EGFR, neutrophil elastase, and reactive oxygen species exist and can be evaluated as treatments for neutrophil-dependent mucus hypersecretion.

Effect of lung-protective ventilation on severePseudomonas aeruginosapneumonia and sepsis in rats

Pneumonia caused by Pseudomonas aeruginosa carries a high rate of morbidity and mortality. A lung-protective strategy using low tidal volume (VT) ventilation for acute lung injury improves patient outcomes. The goal of this study was to determine whether low VTventilation has similar utility in severe P. aeruginosa infection. A cytotoxic P. aeruginosa strain, PA103, was instilled into the left lung of rats anesthetized with pentobarbital. The lung-protective effect of low VT(6 ml/kg) with or without high positive end-expiratory pressure (PEEP, 10 or 3 cmH2O) was then compared with high VTwith low PEEP ventilation (VT12 ml/kg, PEEP 3 cmH2O). Severe lung injury and septic shock was induced. Although ventilatory mode had little effect on the involved lung or septic physiology, injury to noninvolved regions was attenuated by low VTventilation as indicated by the wet-to-dry weight ratio (W/D; 6.13 ± 0.78 vs. 3.78 ± 0.26, respectively) and confirmed by histopathological examinations. High PEEP did not yield a significant protective effect (W/D, 4.03 ± 0.32) but, rather, caused overdistension of noninvolved lungs. Bronchoalveolar lavage revealed higher concentrations of TNF-α in the fluid of noninvolved lung undergoing high VTventilation compared with those animals receiving low VT. We conclude that low VTventilation is protective in noninvolved regions and that the application of high PEEP attenuated the beneficial effects of low VTventilation, at least short term. Furthermore, low VTventilation cannot protect the involved lung, and high PEEP did not significantly alter lung injury over a short time course.

Elevation of KL-6, a lung epithelial cell marker, in plasma and epithelial lining fluid in acute respiratory distress syndrome

KL-6 is a pulmonary epithelial mucin more prominently expressed on the surface membrane of alveolar type II cells when these cells are proliferating, stimulated, and/or injured. We hypothesized that high levels of KL-6 in epithelial lining fluid and plasma would reflect the severity of lung injury in patients with acute lung injury (ALI). Epithelial lining fluid was obtained at onset (day 0) and day 1 of acute respiratory distress syndrome (ARDS)/ALI by bronchoscopic microsampling procedure in 35 patients. On day 0, KL-6 and albumin concentrations in epithelial lining fluid were significantly higher than in normal controls (P < 0.001), and the concentrations of KL-6 in epithelial lining fluid (P < 0.002) and in plasma (P < 0.0001) were higher in nonsurvivors than in survivors of ALI/ARDS. These observations were corroborated by the immunohistochemical localization of KL-6 protein expression in the lungs of nonsurvivors with ALI and KL-6 secretion from cultured human alveolar type II cells stimulated by proinflammatory cytokines. Because injury to distal lung epithelial cells, including alveolar type II cells, is important in the pathogenesis of ALI, the elevation of KL-6 concentrations in plasma and epithelial lining fluid could be valuable indicators for poor prognosis in clinical ALI.

Lung inflammatory responses to intratracheal interleukin-1alpha in ventilated preterm lambs

Interleukin-1alpha is an early response proinflammatory cytokine that has been associated with chorioamnionitis and preterm labor, brain injury, and bronchopulmonary dysplasia. However, IL-1alpha also can increase expression of surfactant proteins and induce lung maturation in the preterm fetus. We measured the effects of IL-1alpha given by intratracheal instillation (IT) and compared the responses with injection of i.v. IL-1alpha in surfactant-treated and ventilated premature lambs. IT recombinant ovine IL-1alpha at doses of 5 and 50 microg/kg caused a similar large recruitment of neutrophils into the bronchoalveolar lavage fluid. The neutrophils expressed CD11b, CD14, and CD44, but did not produce increased amounts of H(2)O(2). Cells from the bronchoalveolar lavage fluid had increased expression of proinflammatory cytokines, which also were increased in mRNA from lung tissue. The IT IL-1alpha also suppressed the expression of surfactant protein-C mRNA. Systemic effects were decreased neutrophils in blood, decreased lung function, increased heart rate, and hypotension or death in the 50 microg/kg IL-1alpha IT group and only decreased neutrophils in the blood in the 5 microg/kg IL-1alpha IT group. The i.v. IL-1alpha caused no lung inflammation or injury but did result in severe neutropenia and hypotension leading to early death. IT IL-1alpha can cause intense lung inflammation and systemic shock in ventilated preterm lungs.

TLR4 signaling is essential for survival in acute lung injury induced by virulent Pseudomonas aeruginosa secreting type III secretory toxins

Background

The relative contributions of the cytotoxic phenotype of P. aeruginosa expressing type III secretory toxins and an immunocompromised condition lacking normal Toll-like receptor 4 (TLR4) signaling in the pathogenesis of acute lung injury and sepsis were evaluated in a mouse model for Pseudomonas aeruginosa pneumonia. By using lipopolysaccharide-resistant C3H/HeJ mice missing normal TLR4 signaling due to a mutation on the tlr4 gene, we evaluated how TLR4 signaling modulates the pneumonia caused by cytotoxic P. aeruginosa expressing type III secretory toxins.

Methods

We infected C3H/HeJ or C3H/FeJ mice with three different doses of either a cytotoxic P. aeruginosa strain (wild type PA103) or its non-cytotoxic isogenic mutant missing the type III secretory toxins (PA103ΔUT). Survival of the infected mice was evaluated, and the severity of acute lung injury quantified by measuring alveolar epithelial permeability as an index of acute epithelial injury and the water to dry weight ratios of lung homogenates as an index of lung edema. Bacteriological analysis and cytokine assays were performed in the infected mice.

Results

Development of acute lung injury and sepsis was observed in all mouse strains when the cytotoxic P. aeruginosa strain but not the non-cytotoxic strain was instilled in the airspaces of the mice. Only C3H/HeJ mice had severe bacteremia and high mortality when a low dose of the cytotoxic P. aeruginosa strain was instilled in their lungs.

Conclusion

The cytotoxic phenotype of P. aeruginosa is the critical factor causing acute lung injury and sepsis in infected hosts. When the P. aeruginosa is a cytotoxic strain, the TLR4 signaling system is essential to clear the batcteria to prevent lethal lung injury and bacteremia.

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

OBJECTIVE

Acute lung injury induced by lung overstretch is associated with neutrophil influx, but the pathogenic role of neutrophils in overstretch-induced lung injury remains unclear.

DESIGN

To assess the contribution of neutrophils, we compared the effects of noninjurious large tidal volume (Vt) ventilation on lungs in normal and neutrophil-depleted animals.

SETTING

Research animal laboratory.

SUBJECTS

Twenty-six male Japanese white rabbits.

INTERVENTIONS

Animals were mechanically ventilated for 4 hrs with one of the three following protocols: large Vt (20 mL/kg), small Vt (8 mL/kg), and large Vt (20 mL/kg) with neutrophil depletion achieved by a single dose of vinblastine injection (0.75 mg/kg) intravenously 4 days before the experiment.

MEASUREMENTS AND MAIN RESULTS

Large Vt ventilation produced alveolar neutrophil influx compared with low Vt (p =.002) without evidence of edema or increased epithelial permeability. The neutrophil influx was accompanied by increases in interleukin-8 in bronchoalveolar lavage fluid (p =.04). Immunohistochemistry of large Vt lungs showed increased interleukin-8 staining in bronchial epithelial cells, alveolar epithelium, alveolar macrophages, and smooth muscles of pulmonary vessels. Neutrophil depletion attenuated the interleukin-8 increase in the lung. Large Vt did not increase plasma interleukin-8 or tumor necrosis factor-alpha in plasma and bronchoalveolar lavage fluid. No expression of p-selectin or intercellular adhesion molecule-1 was observed.

CONCLUSIONS

Cyclic overstretching of normal rabbit lungs with noninjurious large Vt produced neutrophil influx and interleukin-8 increase in bronchoalveolar lavage fluid. Production of pulmonary interleukin-8 by lung overstretch might require the interaction between resident lung cells and migrated neutrophils. This study suggests that large Vt ventilation potentiates the predisposed, subclinical lung injury, such as nosocomial pneumonia or aspiration of gastric contents.

Dynamic mechanical consequences of deep inflation in mice depend on type and degree of lung injury

In a previous study (Allen G, Lundblad LK, Parsons P, and Bates JH. J Appl Physiol 93: 1709-1715, 2002), our laboratory used deep inflations (DI) in mice to show that recruitment of closed lung units can be a very transient phenomenon in lung injury. The purpose of this study was to investigate how this transience of lung recruitment depends on the nature and degree of acute lung injury. Mice were administered 50 microl of either saline (n = 8), 0.01 M (n = 9) or 0.025 M (n = 8) hydrochloric acid, or 50 microg (n = 10) or 150 microg (n = 6) of LPS and were mechanically ventilated 24-48 h later. At various levels of positive end-expiratory pressure, two DIs were delivered, and forced oscillations were used to obtain a measure of lung stiffness (H) periodically over 7 min. After LPS exposure, pressure-volume curve hysteresis and recovery in H after DI were no different from saline-exposed controls despite 500 times more neutrophils in bronchoalveolar lavage fluid. Pressure-volume hysteresis and recovery in H were increased in acid-exposed mice (P < 0.001) and were correlated with bronchoalveolar lavage fluid protein content (R = 0.81). Positive end-expiratory pressure reduced recovery in H in all groups (P < 0.01) but reduced pressure-volume hysteresis in the acid-injured groups only (P < 0.001). We conclude that the effects of DIs in acute lung injury depend on the degree of lung injury but only to the extent that this injury reflects a disruption of the air-liquid interface.

Effects of monoclonal anti-PcrV antibody on Pseudomonas aeruginosa-induced acute lung injury in a rat model

BACKGROUND: The effects of the murine monoclonal anti-PcrV antibody Mab166 on acute lung injury induced by Pseudomonas aeruginosa were analyzed in a rat model. METHODS: Lung injury was induced by the instillation of P. aeruginosa strain PA103 directly into the left lungs of anesthetized rats. One hour after the bacterial instillation, rabbit polyclonal anti-PcrV IgG, murine monoclonal anti-PcrV IgG Mab166 or Mab166 Fab-fragments were administered intratracheally directly into the lungs. The degree of alveolar epithelial injury, amount of lung edema, decrease in oxygenation and extent of lung inflammation by histology were evaluated as independent parameters of acute lung injury. RESULTS: These parameters improved in rats that had received intratracheal instillation of either rabbit polyclonal anti-PcrV IgG, murine monoclonal anti-PcrV IgG Mab166 or Mab166 Fab-fragments in comparison with the control group. CONCLUSION: Mab166 and its Fab fragments have potential as adjuvant therapy for acute lung injury due to P. aeruginosa pneumonia.

Transforming growth factor-beta: a mediator of cell regulation in acute respiratory distress syndrome

OBJECTIVE

To review recent advances in the use of transforming growth factor (TGF)-beta in acute lung injury and to apply this knowledge to understanding the pathophysiology of this syndrome.

DATA SOURCES AND STUDY SELECTION

Published research and review articles in the English language related to the role of TGF-beta in acute lung injury.

DATA EXTRACTION AND SYNTHESIS

The cytokine TGF-beta plays a critical role in the resolution of tissue injury in multiple organs, including the lung. Following injury, TGF-beta has been most thoroughly evaluated during the late phases of tissue repair, where it plays a critical role in the development of pulmonary fibrosis. In contrast, recent animal studies showed that expression levels of several TGF-beta-inducible genes were dramatically increased as early as 2 days after the induction of injury. The integrin alpha(v)beta(6) activates latent TGF-beta in the lungs. Mice lacking this integrin were completely protected from pulmonary edema in a model of bleomycin-induced acute lung injury. Pharmacologic inhibition of TGF-beta also protected wild-type mice from pulmonary edema induced by bleomycin or Escherichia coli endotoxin. Similar findings also have been reported in patients in a clinical study evaluating TGF-beta in the bronchoalveolar lavage fluid during the course of acute respiratory distress syndrome (ARDS). Indeed, the bronchoalveolar lavage concentrations were dramatically increased as early as 1 day after the initiation of ARDS criteria and were correlated with decreases in the Pao(2)/Fio(2) ratio, suggesting an important role for TGF-b1 in the development of ARDS in humans.

CONCLUSIONS

These studies suggest that TGF-beta not only participates in the late phase of acute lung injury, but also might be active early in acute lung injury and potentially could contribute to the development of pulmonary edema. Integrin-mediated local activation of TGF-beta is critical to the development of pulmonary edema in ARDS, and blocking TGF-beta or its activation could be an effective treatment for this disorder.

Protein transport across the lung epithelial barrier

Alveolar lining fluid normally contains proteins of important physiological, antioxidant, and mucosal defense functions [such as albumin, immunoglobulin G (IgG), secretory IgA, transferrin, and ceruloplasmin]. Because concentrations of plasma proteins in alveolar fluid can increase in injured lungs (such as with permeability edema and inflammation), understanding how alveolar epithelium handles protein transport is needed to develop therapeutic measures to restore alveolar homeostasis. This review provides an update on recent findings on protein transport across the alveolar epithelial barrier. The use of primary cultured rat alveolar epithelial cell monolayers (that exhibit phenotypic and morphological traits of in vivo alveolar epithelial type I cells) has shown that albumin and IgG are absorbed via saturable processes at rates greater than those predicted by passive diffusional mechanisms. In contrast, secretory component, the extracellular portion of the polymeric immunoglobulin receptor, is secreted into alveolar fluid. Transcytosis involving caveolae and clathrin-coated pits is likely the main route of alveolar epithelial protein transport, although relative contributions of these internalization steps to overall protein handling of alveolar epithelium remain to be determined. The specific pathways and regulatory mechanisms responsible for translocation of proteins across lung alveolar epithelium and regulation of the cognate receptors (e.g., 60-kDa albumin binding protein and IgG binding FcRn) expressed in alveolar epithelium need to be elucidated.

Lung edema clearance: 20 years of progress: invited review: alveolar edema fluid clearance in the injured lung

Resolution of pulmonary edema involved active transepithelial sodium transport. Although several of the cellular and molecular mechanisms involved are relatively well understood, it is only recently that the regulation of these mechanisms in injured lung are being evaluated. Interestingly, in mild-to-moderate lung injury, alveolar edema fluid clearance is often preserved. This preserved or enhanced alveolar fluid clearance is mediated by catecholamine-dependent or -independent mechanisms. This stimulation of alveolar liquid clearance is related to activation or increased expression of sodium transport molecules such as the epithelial sodium channel or the Na(+)-K(+)-ATPase pump and may also involve the cystic fibrosis transmembrane conductance regulator. When severe lung injury occurs, the decrease in alveolar liquid clearance may be related to changes in alveolar permeability or to changes in activity or expression of sodium or chloride transport molecules. Multiple pharmacological tools such as beta-adrenergic agonists, vasoactive drugs, or gene therapy may prove effective in stimulating the resolution of alveolar edema in the injured lung.

Lung epithelial fluid transport and the resolution of pulmonary edema

The discovery of mechanisms that regulate salt and water transport by the alveolar and distal airway epithelium of the lung has generated new insights into the regulation of lung fluid balance under both normal and pathological conditions. There is convincing evidence that active sodium and chloride transporters are expressed in the distal lung epithelium and are responsible for the ability of the lung to remove alveolar fluid at the time of birth as well as in the mature lung when pathological conditions lead to the development of pulmonary edema. Currently, the best described molecular transporters are the epithelial sodium channel, the cystic fibrosis transmembrane conductance regulator, Na+-K+-ATPase, and several aquaporin water channels. Both catecholamine-dependent and -independent mechanisms can upregulate isosmolar fluid transport across the distal lung epithelium. Experimental and clinical studies have made it possible to examine the role of these transporters in the resolution of pulmonary edema.

Transepithelial sodium and water transport in the lung. Major player and novel therapeutic target in pulmonary edema

Active transepithelial transport of sodium from the airspaces to the lung interstitium is a primary mechanism driving alveolar fluid clearance. This mechanism depends on sodium uptake by amiloride-sensitive sodium channels on the apical membrane of alveolar type II cells followed by extrusion of sodium on the basolateral surface by the Na-K-ATPase. Injury to the alveolar epithelium can disrupt the integrity of the alveolar barrier or downregulate ion transport pathways thus reducing net alveolar fluid reabsorption, and enhancing the extent of alveolar edema. Endogenous catecholamines upregulate alveolar fluid clearance in several experimental models of acute lung injury, but this upregulation is short-term and often not sufficient to counterbalance alveolar flooding. There is new evidence, however, that pharmacological treatment with beta-adrenergic agonists and/or epithelial growth factors may induce a more sustained stimulation of alveolar fluid reabsorption and in turn facilitate recovery from experimental pulmonary edema. Similar results have been achieved experimentally by gene transfer enhancing the abundance of sodium transporters in the alveolar epithelium. Clinical studies show that impaired alveolar fluid transport mechanisms contribute to the development, severity and outcome of pulmonary edema in humans. Very recent data suggest that mechanisms that augment transepithelial sodium transport and enhance the clearance of alveolar edema may lead to more effective prevention or treatment for pulmonary edema and acute lung injury.

The pulmonary physician in critical care * 6: The pathogenesis of ALI/ARDS

An understanding of the pathogenesis of ARDS is essential for choosing management strategies and developing new treatments. The key mediators involved in the inflammatory and fibroproliferative responses are reviewed and the mechanisms which regulate these responses are highlighted.

Endotoxin induces respiratory failure and increases surfactant turnover and respiration independent of alveolocapillary injury in rats

Although endotoxin-induced acute lung injury is associated with inflammation, alveolocapillary injury, surfactant dysfunction, and altered lung mechanics, the precise sequence of these changes is polemic. We have studied the early pathogenesis of acute lung injury in spontaneously breathing anesthetized rats after intravenous infusion of Salmonella abortus equi endotoxin. The animals became hypoxic, and airway resistance, tissue resistance, lung elastance, and static compliance all deteriorated well before any change in alveolar neutrophils, macrophages, lung fluid (99mTc-labeled diethylenetriamine pentaacetic acid), or 125I-albumin flux, which were only appreciably increased at 8.5 hours. Lung elastance deteriorated before airway resistance, indicating that the compliance change was specific rather than caused by reduced lung volume. The subcellular and alveolar content of surfactant proteins A and B, cholesterol, disaturated phospholipids, and phospholipid classes remained normal in the face of a dramatic increase in the synthesis and turnover of 3H-disaturated phosphatidylcholine. Our findings indicate that the increase in surfactant disaturated phospholipid turnover reflects, at least in part, an approximately five-fold increase in "sigh frequency." We suggest that endotoxin has direct effects on tissue resistance and lung elastance independent of surfactant composition and that the initial respiratory failure results primarily from endotoxin-induced ventilation/perfusion mismatch independent of edema or alveolocapillary injury per se.

Clinical Acute Lung Injury and Acute Respiratory Distress Syndrome

This article provides a description of the clinical disorders associated with the development of acute noncardiogenic pulmonary edema, better known as clinical acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS). Much has been learned about the mechanisms by which the lung is injured in patients with sepsis, pneumonia, aspiration of gastric contents, and following major trauma. In the last 5 years, major progress has been made in the treatment of patients with ALI/ARDS. A lung protective ventilatory strategy with a low tidal volume (6 mL/kg/predicted body weight) in conjunction with a plateau pressure limit of 30 cm H(2)0 attenuated the severity of clinical lung injury and reduced mortality by 22%. Ironically, after years of searching for anti-inflammatory treatments for ALI/ARDS, it turns out that a lung protective ventilatory strategy has proven to be the most efficacious anti-inflammatory treatment ever discovered for ALI/ARDS. However, it is still possible that pharmacologic treatments also may enhance survival. For example, a recent report that activated protein C reduces mortality in patients with sepsis raises hope that the incidence and severity of sepsis-induced ALI/ARDS may be reduced by treatment with this agent that has both anti-inflammatory and anticoagulant properties. Also, therapy directed at hastening the resolution of lung injury by increasing the functional recovery of the alveolar epithelium may be of value, both in diminishing the fibroproliferative phase of ALI/ARDS as well as accelerating the resolution of alveolar edema.

Intratracheal endotoxin causes systemic inflammation in ventilated preterm lambs

Intratracheal endotoxin causes acute inflammation in the adult lung, and injurious styles of mechanical ventilation can result in systemic inflammation derived from the lungs. We asked how ventilated premature and near-term lungs responded to intratracheal endotoxin and if systemic inflammation occurred. Lambs delivered at 130 d gestational age (GA) were treated with surfactant or surfactant plus endotoxin (0.1 mg/kg or 10 mg/kg) (Escherichia coli, serotype O55:B5) and were ventilated for 6 h. Both endotoxin doses resulted in impaired gas exchange and systemic inflammation in the preterm lambs. Lambs at 141 d GA (term 146 d) were given either 10 mg/kg intratracheal endotoxin, 10 mg/kg endotoxin plus high tidal volume ventilation for the first 30 min of life, or 5 microg/kg endotoxin given intravenously. Endotoxin alone (10 mg/kg) caused lung inflammation but no systemic effects after 6 h of ventilation. Lambs given 10 mg/kg endotoxin plus high tidal volume ventilation or 5 microg/kg endotoxin intravenously had decreased gas exchange and systemic inflammation. Endotoxin was detected in the plasma of lambs at 130 d GA but not at 141 d GA. Inflammation in the lungs was more severe in preterm animals. Mechanical ventilation of the endotoxin-exposed preterm lung resulted in systemic effects at a low endotoxin dose and without high tidal volume ventilation.

Therapeutic administration of anti-PcrV F(ab')(2) in sepsis associated with Pseudomonas aeruginosa

The effects of rabbit-derived polyclonal Ab against PcrV, a protein involved in the translocation of type III secreted toxins of Pseudomonas aeruginosa, was investigated in two animal models of P. aeruginosa sepsis. In a mouse survival study, the i.v. administration of anti-PcrV IgG after the airspace instillation of a lethal dose of P. aeruginosa resulted in the complete survival of the animals. In a rabbit model of septic shock associated with Pseudomonas-induced lung injury, animals treated with anti-PcrV IgG intratracheally or i.v. had significant decreases in lung injury, bacteremia, and plasma TNF-alpha and significant improvement in the hemodynamic parameters associated with shock compared with animals treated in a similar manner with nonspecific control IgG. The administration of anti-PcrV F(ab')(2) showed protective effects comparable to those of whole anti-PcrV IgG. These results document that the therapeutic administration of anti-PcrV IgG blocks the type III secretion system-mediated virulence of P. aeruginosa and prevents septic shock and death, and that these protective effects are largely Fc independent. We conclude that Ab therapy neutralizing the type III secretion system has significant potential against lethal P. aeruginosa infections.

Endotoxemia increases relative perfusion to dorsal-caudal lung regions

Changes in the spatial distribution of perfusion during acute lung injury and their impact on gas exchange are poorly understood. We tested whether endotoxemia caused topographical differences in perfusion and whether these differences caused meaningful changes in regional ventilation-to-perfusion ratios and gas exchange. Regional ventilation and perfusion were measured in anesthetized, mechanically ventilated pigs in the prone position before and during endotoxemia with the use of aerosolized and intravenous fluorescent microspheres. On average, relative perfusion halved in ventral and cranial lung regions, doubled in caudal lung regions, and increased 1.5-fold in dorsal lung regions during endotoxemia. In contrast, there were no topographical differences in perfusion before endotoxemia and no topographical differences in ventilation at any time point. Consequently, endotoxemia increased regional ventilation-to-perfusion ratios in the caudal-to-cranial and dorsal-to-ventral directions, resulting in end-capillary PO2 values that were significantly lower in dorsal-caudal than ventral-cranial regions. We conclude that there are topographical differences in the pulmonary vascular response to endotoxin that may have important consequences for gas exchange in acute lung injury.

Fas/FasL-dependent apoptosis of alveolar cells after lipopolysaccharide-induced lung injury in mice

To determine the possible contribution of apoptosis in the pathogenesis of acute lung injury (ALI), we investigated Fas antigen (Fas), Fas ligand (FasL), perforin, granzyme A, and granzyme B expressions in a murine model of ALI after intratracheal instillation of Escherichia coli lipopolysaccharide (LPS: 0.3-30 microg) into the left lung. Lung injury, examined by water-to-dry weight ratio and albumin leakage, demonstrated maximal epithelial injury 1 d after 30 microg LPS instillation. Expressions of the proapoptosis molecules' mRNA were dose-dependently up-regulated, with maximal expression in the early phase in the instilled lung and most apparent 1 d after LPS instillation. Negligible mRNA expression of proapoptosis molecules was observed in noninstilled lungs. The terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labeling (TUNEL) demonstrated positive signals in neutrophils and macrophages as well as in alveolar wall cells of the instilled lung 1 d after LPS instillation. Immunohistochemistry demonstrated that Fas was up-regulated in alveolar and inflammatory cells and FasL-positive inflammatory cells migrated into the air spaces in the LPS-instilled lung. Intratracheal administration of P2 antibody, which is an anti-Fas blocking antibody, attenuated the lung injury after 30 microg LPS instillation without attenuating mRNA expressions of proapoptosis molecules and neutrophil accumulation in the lung. In contrast, concanamycin A, which inhibits the function of perforin, did not alter the outcome after LPS instillation. These results indicate that the Fas/FasL system could be important in the pathogenesis of LPS-induced ALI, and proper regulation of the FasL/Fas system might be important for potential treatment of ARDS.

Protective effects of low tidal volume ventilation in a rabbit model of Pseudomonas aeruginosa-induced acute lung injury

OBJECTIVE

To determine whether low "stretch" mechanical ventilation protects animals from clinical sepsis after direct acute lung injury with Pseudomonas aeruginosa as compared with high "stretch" ventilation.

DESIGN

Prospective study.

SETTING

Experimental animal laboratory.

SUBJECTS

Twenty-seven anesthetized and paralyzed rabbits.

INTERVENTIONS

P. aeruginosa (109 colony forming units) was instilled into the right lungs of rabbits that were then ventilated at a tidal volume of either 15 mL/kg (n = 11) or 6 mL/kg (n = 7) for 8 hrs. Control animals were ventilated at a tidal volume of either 15 mL/kg (n = 4) or 6 mL/kg (n = 5) for 8 hrs, but an instillate without bacteria was used. A positive end-expiratory pressure of 3-5 cm H2O was used for all experiments. Radiolabeled albumin was used as a marker of alveolar epithelial permeability.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics, arterial blood gas determination, alveolar permeability, wet-to-dry ratios on lungs, and time course of bacteremia were determined. When final values were compared with the values at the beginning of the experiment, there were significant decreases in mean arterial pressure (from 104 +/- 15 to 57 +/- 20 mm Hg), pH (from 7.46 +/- 0.04 to 7.24 +/- 15), Pao2 (from 528 +/- 35 to 129 +/- 104 torr [70.4 +/- 4.7 to 17.2 +/- 13.9 kPa]), and temperature (from 38.2 +/- 1 to 36.2 +/- 1.2 degrees C) in the high tidal volume group, whereas no significant differences were found in the low tidal volume group. Decreased alveolar permeability was shown in the low tidal volume group, as was decreased extravascular lung water in the uninstilled lung in the low tidal volume group (12.7 +/- 2.5 vs. 4.3 +/- 0.45 g H2O/g dry lung). No noteworthy difference was noted in the time course of bacteremia, although there was a trend toward earlier bacteremia in the high tidal volume group.

CONCLUSIONS

In our animal model of P. aeruginosa-induced acute lung injury, low tidal volume ventilation was correlated with improved oxygenation, hemodynamic status, and acid-base status as well as decreased alveolar permeability and contralateral extravascular lung water.

Fas (CD95) induces alveolar epithelial cell apoptosis in vivo: implications for acute pulmonary inflammation

Activation of the Fas/FasL system induces apoptosis of susceptible cells, but may also lead to nuclear factor kappaB activation. Our goal was to determine whether local Fas activation produces acute lung injury by inducing alveolar epithelial cell apoptosis and by generating local inflammatory responses. Normal mice (C57BL/6) and mice deficient in Fas (lpr) were treated by intranasal instillation of the Fas-activating monoclonal antibody (mAb) Jo2 or an irrelevant control mAb, and studied 6 or 24 hours later using bronchoalveolar lavage (BAL), histopathology, DNA nick-end-labeling assays, and electron microscopy. Normal mice treated with mAb Jo2 had significant increases in BAL protein at 6 hours, and BAL neutrophils at 24 hours, as compared to lpr mice and to mice treated with the irrelevant mAb. Neutrophil recruitment was preceded by increased mRNA expression for tumor necrosis factor-alpha, macrophage inflammatory protein-1alpha, macrophage inflammatory protein-2, macrophage chemotactic protein-1, and interleukin-6, but not interferon-gamma, transforming growth factor-ss, RANTES, eotaxin, or IP-10. Lung sections from Jo2-treated normal mice showed neutrophilic infiltrates, alveolar septal thickening, hemorrhage, and terminal dUTP nick-end-labeling-positive cells in the alveolar septae and airspaces. Type II pneumocyte apoptosis was confirmed by electron microscopy. Fas activation in vivo results in acute alveolar epithelial injury and lung inflammation, and may be important in the pathogenesis of acute lung injury.

Alveolar epithelial barrier. Role in lung fluid balance in clinical lung injury

Several studies have established that transport of sodium from the air spaces to the lung interstitium is a primary mechanism driving alveolar fluid clearance, although further work is needed to determine the role of chloride in vectorial fluid transport across the alveolar epithelium. Although there are significant differences among species in the basal rates of sodium and fluid transport, the basic mechanism seems to depend on sodium uptake by channels on the apical membrane of alveolar type II cells, followed by extrusion of sodium on the basolateral surface by Na,K-ATPase. This process can be upregulated by several catecholamine-dependent and independent mechanisms. The identification of water channels expressed in lung, together with the high water permeabilities, suggest a potential role for channel-mediated water movement between the air space and capillary compartments, although definitive evidence will depend on the results of transgenic mouse knock-out studies. The application of this new knowledge regarding salt and water transport in alveolar epithelium in relation to pathologic conditions has been successful in clinically relevant experimental studies, as well as in a few clinical studies. The studies of exogenous and endogenous catecholamine regulation of alveolar fluid clearance are a good example of how new insights into the basic mechanisms of alveolar sodium and fluid transport can be translated to clinically relevant experimental studies. Exogenous catecholamines can increase the rate of alveolar fluid clearance in several species, including the human lung, and it is also apparent that release of endogenous catecholamines can upregulate alveolar fluid clearance in animals with septic or hypovolemic shock. It is possible that therapy with beta-adrenergic agonists might be useful to accelerate the resolution of alveolar edema in some patients. In some patients, the extent of injury to the alveolar epithelial barrier may be too severe for beta-adrenergic agonists to enhance the resolution of alveolar edema, although some experimental studies indicate that alveolar fluid clearance can be augmented in the presence of moderately severe lung injury. A longer-term upregulation of alveolar epithelial fluid transport might be achieved by strategies that accelerate the proliferation of alveolar type II cells repopulating the injured epithelium in clinical lung injury. More clinical research is needed to evaluate the strategies that can upregulate alveolar epithelial fluid transport with both short-term therapy (i.e., beta-agonists) and more sustained, longer-term effects of epithelial mitogens such as keratinocyte growth factor. These approaches may be useful in reducing mortality in the acute respiratory distress syndrome.

Pretreatment with cationic lipid-mediated transfer of the Na+K+-ATPase pump in a mouse model in vivo augments resolution of high permeability pulmonary oedema

Resolution of pulmonary oedema is mediated by active absorption of liquid across the alveolar epithelium. A key component of this process is the sodium-potassium ATPase (Na+K+-ATPase) enzyme located on the basolateral surface of epithelial cells and up-regulated during oedema resolution. We hypothesised that lung liquid clearance could be further up-regulated by lipid-mediated transfer and expression of exogenous Na+K+-ATPase cDNA. We demonstrate proof of this principle in a model of high permeability pulmonary oedema induced by intraperitoneal injection of thiourea (2.5 mg/kg) in C57/BL6 mice. Pretreatment of mice (24 h before thiourea) by nasal sniffing of cationic liposome (lipid #67)-DNA complexes encoding the alpha and beta subunits of Na+K+-ATPase (160 microg per mouse), significantly (P<0.01) decreased the wet:dry weight ratios measured 2 h after thiourea injection compared with control animals, pretreated with an equivalent dose of an irrelevant gene. Whole lung Na+K+-ATPase activity was significantly (P<0.05) increased in mice pretreated with Na+K+-ATPase cDNA compared both with untreated control animals as well as animals pretreated with the irrelevant gene. Nested RT-PCR on whole lung homogenates confirmed gene transfer by detection of vector-specific mRNA in three of four mice studied 24 h after gene transfer. This demonstration of a significant reduction in pulmonary oedema following in vivo gene transfer raises the possibility of gene therapy as a novel, localised approach for pulmonary oedema in clinical settings such as ARDS and lung transplantation.

A novel signaling mechanism between gas and blood compartments of the lung

Propagation of inflammatory signals from the airspace to the vascular space is pivotal in lung inflammation, but mechanisms of intercompartmental signaling are not understood. To define signaling mechanisms, we microinfused single alveoli of blood-perfused rat lung with TNF-alpha, and determined in situ cytosolic Ca(2+) concentration ([Ca(2+)](i)) by the fura-2 ratio method, cytosolic phospholipase A(2) (cPLA(2)) activation and P-selectin expression by indirect immunofluorescence. Alveolar TNF-alpha increased [Ca(2+)](i) and activated cPLA(2) in alveolar epithelial cells, and increased both endothelial [Ca(2+)](i) and P-selectin expression in adjoining perialveolar capillaries. All responses were blocked by pretreating alveoli with a mAb against TNF receptor 1 (TNFR1). Crosslinking alveolar TNFR1 also increased endothelial [Ca(2+)](i). However, the endothelial responses to alveolar TNF-alpha were blocked by alveolar preinjection of the intracellular Ca(2+) chelator BAPTA-AM, or the cPLA(2) blockers AACOCF(3) and MAFP. The gap-junction uncoupler heptanol had no effect. We conclude that TNF-alpha induces signaling between the alveolar and vascular compartments of the lung. The signaling is attributable to ligation of alveolar TNFR1 followed by receptor-mediated [Ca(2+)](i) increases and cPLA(2) activation in alveolar epithelium. These novel mechanisms may be relevant in the alveolar recruitment of leukocytes.

A novel alveolar type I cell-specific biochemical marker of human acute lung injury

Currently there is no recognized biochemical or molecular marker for human parenchymal lung injury analogous to markers for acute myocardial injury. Injury to the alveolar epithelial barrier is of central importance in the pathogenesis of and recovery from acute lung injury. In animal models, an alveolar type I cell-specific protein, RTI(40), has been shown to be an accurate marker of alveolar epithelial damage. We now report that HTI(56), a novel apical plasma membrane protein specific to the human type I cell, is a biochemical marker for lung injury. Using a sensitive, quantitative, light-based ELISA, we measured HTI(56) in pulmonary edema fluid from 15 patients with a clinical diagnosis of acute lung injury and 12 control patients with hydrostatic (cardiogenic) pulmonary edema. HTI(56) was also measured in plasma from these two groups and from 11 normal volunteers. The amount of HTI(56) was 4. 3-fold higher (p < 0.0001) in alveolar edema fluid and 1.4-fold higher (p < 0.05) in plasma from the patients with acute lung injury, compared with patients with hydrostatic pulmonary edema. To our knowledge, this study is the first to utilize a specific marker of alveolar epithelial damage in human disease and demonstrates the feasibility of using a blood test to detect lung parenchymal damage.

TNF-alpha stimulates alveolar liquid clearance during intestinal ischemia-reperfusion in rats

Intestinal ischemia-reperfusion commonly occurs in critically ill patients and may lead to the development of remote organ injury, frequently involving the lungs. In the present study, alveolar liquid clearance was studied in ventilated, anesthetized rats subjected to 45 min of intestinal ischemia followed by 3 h of reperfusion. An isosmolar 5% albumin solution was instilled into the lungs, and alveolar liquid clearance was measured from the increase in alveolar protein concentration as water was reabsorbed over 45 min. Intestinal ischemia-reperfusion resulted in a 76% increase in alveolar liquid clearance compared with the control value (P < 0.05). The stimulated alveolar liquid clearance seen after intestinal ischemia-reperfusion was not inhibited by propranolol, indicating stimulation through a noncatecholamine-dependent pathway. Intestinal ischemia-reperfusion did not result in increased intracellular cAMP levels. Amiloride inhibited similar fractions in animals subjected to ischemia-reperfusion and control animals. Administration of a neutralizing polyclonal anti-tumor necrosis factor-alpha antibody before induction of intestinal ischemia completely inhibited the increased alveolar liquid clearance observed after intestinal ischemia-reperfusion. In conclusion, our results suggest that intestinal ischemia-reperfusion in rats leads to stimulation of alveolar liquid clearance and that this stimulation is mediated, at least in part, by a tumor necrosis factor-alpha-dependent mechanism.

Acid-induced lung injury. Protective effect of anti-interleukin-8 pretreatment on alveolar epithelial barrier function in rabbits

Although prior experimental work has demonstrated that anti-interleukin-8 (anti-IL-8) therapy reduces lung endothelial injury after acid instillation, there is no information regarding the effect of anti-IL-8 on the function of the alveolar epithelial barrier after acid-induced lung injury. Therefore, the primary objective of this study was to determine the effect of acid-induced lung injury on the function of the alveolar epithelium, and secondly to determine whether pretreatment with anti-IL-8 attenuates acid-induced injury to the lung epithelial barrier. Hydrochloric acid (pH = 1.5 in 1/3 normal saline) was instilled into the lungs of anesthetized, ventilated rabbits. Anti-IL-8 monoclonal antibody (2 mg/kg) or saline was given intravenously 5 min before acid instillation. Acid instillation into the distal airspaces caused an increase in the alveolar epithelial permeability to protein and an approximately 50% reduction in net alveolar fluid clearance. Because a decrease in net alveolar fluid clearance could be due to lung endothelial injury and increased fluid flux from the blood into the airspaces, additional experiments were carried out in which pulmonary blood flow was eliminated. In the absence of pulmonary blood flow, acid instillation led to a 50% decrease in net alveolar fluid clearance. Pretreatment with anti-IL-8 antibody significantly reduced the acid-mediated increase in bi-directional transport of protein across the alveolar epithelium and restored alveolar fluid clearance to normal. The results indicate that acid instillation causes injury to the alveolar epithelial barrier that can be distinguished from the injury to the lung endothelium. Furthermore, pretreatment with anti-IL-8 therapy prevents acid-induced alveolar epithelial injury, a finding of potential clinical importance.

Effects of antibiotic therapy on Pseudomonas aeruginosa-induced lung injury in a rat model

The effect of antibiotics on the acute lung injury induced by virulent Pseudomonas aeruginosa PA103 was quantitatively analyzed in a rat model. Lung injury was induced by the instillation of PA103 directly into the right lower lobes of the lungs of anesthetized rats. The alveolar epithelial injury, extravascular lung water, and total plasma equivalents were measured as separate, independent parameters of acute lung injury. Four hours after the instillation of PA103, all the parameters were increased linearly depending on the dose of P. aeruginosa. Next, we examined the effects of intravenously administered antibiotics on the parameters of acute lung injury in D-galactosamine-sensitized rats. One hour after the rats received 10(7) CFU of PA103, an intravenous bolus injection of aztreonam (60 mg/kg) or imipenem-cilastatin (30 mg/kg) was administered. Despite an MIC indicating resistance, imipenem-cilastatin improved all the measurements of lung injury; in contrast, aztreonam, which had an MIC indicating sensitivity, did not improve any of the lung injury parameters. The antibiotics did not generate different quantities of plasma endotoxin; therefore, endotoxin did not appear to explain the differences in lung injury. This in vivo model is useful to quantitatively compare the efficacies of parenteral antibiotic administration on Pseudomonas airspace infections.

Pathogenesis of septic shock in Pseudomonas aeruginosa pneumonia

The pathogenesis of septic shock occurring after Pseudomonas aeruginosa pneumonia was studied in a rabbit model. The airspace instillation of the cytotoxic P. aeruginosa strain PA103 into the rabbit caused a consistent alveolar epithelial injury, progressive bacteremia, and septic shock. The lung instillation of a noncytotoxic, isogenic mutant strain (PA103DeltaUT), which is defective for production of type III secreted toxins, did not cause either systemic inflammatory response or septic shock, despite a potent inflammatory response in the lung. The intravenous injection of PA103 did not cause shock or an increase in TNF-alpha, despite the fact that the animals were bacteremic. The systemic administration of either anti-TNF-alpha serum or recombinant human IL-10 improved both septic shock and bacteremia in the animals that were instilled with PA103. Radiolabeled TNF-alpha instilled in the lung significantly leaked into the circulation only in the presence of alveolar epithelial injury. We conclude that injury to the alveolar epithelium allows the release of proinflammatory mediators into the circulation that are primarily responsible for septic shock. Our results demonstrate the importance of compartmentalization of inflammatory mediators in the lung, and the crucial role of bacterial cytotoxins in causing alveolar epithelial damage in the pathogenesis of acute septic shock in P. aeruginosa pneumonia.