In vivo expression of intercellular adhesion molecule 1 in type II pneumocytes during hyperoxia

Biochemical and Ultrastructural Lung Damage Induced by Rhabdomyolysis in the Rat

Rhabdomyolysis-induced oxidative stress is associated with morphological and functional damage to the kidney and other organs, but applications of this model in the lung are still lacking. The aim of the present study was to determine the relationship between oxidative stress and the morphological changes occurring in the lungs of rats subjected to rhabdomyolysis. Rhabdomyolysis was induced by intramuscular glycerol injection (50% v/v, 10 ml/kg), and the control group was injected with saline vehicle. Arterial blood samples were drawn at 0, 2, 4, and 6 hrs for measurement of arterial gases, creatine kinase activity, and plasma free F2-isoprostane levels. Six hours later, the lungs were removed to determine the wet-to-dry weight ratio, reduced glutathione (GSH) and GSH disulfide (GSSG) levels, and activity of antioxidant enzymes (cataiase [CAT], superoxide dismutase [SOD], and GSH peroxidase [GSH-Px]). Protein carbonylation and lipid peroxidation were assessed in the lungs by measurement of carbonyl and malondialdehyde (MDA) production, respectively. Bronchoalveolar lavage, cell counts, and lung ultrastructural studies were also performed. Six hours after glycerol injection, arterial PO2 and PCO2 were 23% and 38% lower, respectively, and plasma free F2-isoprostane levels were 72% higher, compared with control values. In lungs, protein carbonyl and MDA production were 58% and 12% higher, respectively; the GSH:GSSG ratio and GSH-Px activity were 43% and 60% lower, respectively; and activities of CAT and SOD showed no significant differences compared with controls. Rhabdomyolysis-induced ultrastructural impairment of the lung showed Type II cell damage, extracytoplasmic lamellar bodies and lack of tubular myelin reorganization, endothelial cellular edema, and no disruption of the alveolar-capillary barrier. These results provide evidence that rhabdomyolysis could induce tissue injury associated with increased oxidative stress, suggesting the contribution of oxidative stress to the pathogenic mechanism of acute lung injury.

Endothelial nitric oxide synthase in dorsal root ganglia during chronic inflammatory nociception

Nitric oxide (NO) is a gaseous molecule implicated both in vascular tone and nociceptive transmission. The capillary blood supply to the dorsal root ganglia (DRG) is unique because it is highly permeable to several low and high molecular-weight compounds. This anatomical situation leads to a potential role of endothelial nitric oxide synthase (eNOS) in inflammatory nociception, which is not well established. Therefore, we examined the role of eNOS in DRG in a murine chronic inflammatory pain model induced by complete Freund's adjuvant using L-N(5)-(1-iminoethyl)ornithine (L-NIO), a potent inhibitor of eNOS activity. Pain state was examined using a behavioral test. The expression of eNOS, platelet endothelial cell adhesion molecule-1 (CD31) and vascular endothelial growth factor (VEGF) was examined by immunofluorescence. In control animals, CD31 was detected in vessels; VEGF was localized both in vessels and neurons while a weak eNOS immunopositivity was detected in both vessels and in neurons. Under inflammatory pain conditions, eNOS, CD31 and VEGF immunopositivity increased. Administration of L-NIO significantly attenuated thermal hyperalgesia by 24 h and decreased eNOS activity and CD31 immunopositivity by 7 days. VEGF was unaffected. Our results show that eNOS plays a nociceptive role in the early phases of inflammation while in the later phases it may be involved in neurotrophic support.

Effects of hyperoxia on cytoplasmic thioredoxin system in alveolar type epithelial cells of premature rats

This study investigated the effects of hyperoxia on dynamic changes of thioredoxin-1 (Trx1) and thioredoxin reductase-1 (TrxR1) in alveolar type II epithelial cells (AECII) of premature rats. Pregnant Sprague-Dawley rats were sacrificed on day 19 of gestation. AECII were isolated and purified from the lungs of premature rats. When cultured to 80% confluence, in vitro cells were randomly divided into air group and hyperoxia group. Cells in the hyperoxia group were continuously exposed to 95% O(2)/5% CO(2) and those in the air group to 95% air/5% CO(2). After 12, 24 and 48 h, cells in the two groups were harvested to detect their reactive oxygen species (ROS), apoptosis, TrxR1 activity and the expressions of Trx1 and TrxR1 by corresponding protocols, respectively. The results showed that AEC II exposed to hyperoxia generated excessive ROS and the apoptosis percentage in the hyperoxia group was increased significantly at each time points as compared with that in the air group (P<0.001). Moreover, TrxR1 activity was found to be markedly depressed in the hyperoxia group in comparison to that in the air group (P<0.001). RT-PCR showed the expressions of both Trx1 and TrxR1 mRNA were significantly increased in AECII exposed to hyperoxia for 12 and 24 h (P<0.01), respectively. At 48 h, the level of Trx1 mRNA as well as that of TrxR1 mRNA in the hyperoxia group was reduced and showed no significant difference from that in the air group (P>0.05). Western blotting showed the changes of Trx1 protein expressions in the hyperoxia group paralleled those of Trx1 mRNA expressions revealed by RT-PCR. It was concluded that hyperoxia can up-regulate the protective Trx1/TrxR1 expressed by AECII in a certain period, however, also cause dysfunction of the cytoplasmic thioredoxin system by decreasing TrxR1 activity, which may contribute to the progression of oxidative stress and cell apoptosis and finally result in lung injury.

Thioredoxin protects fetal type II epithelial cells from hyperoxia-induced injury

Oxygen toxicity is known to be one of the major contributors to bronchopulmonary dysplasia, a chronic lung disease in premature infants. Thioredoxin (Trx) is an antioxidant that prevents oxidative stress-induced cell death, suggesting a potential therapeutic role in bronchopulmonary dysplasia. The aim of this study was to determine the role of Trx in the pathogenesis of hyperoxia-induced alveolar epithelial cell injury. Alveolar type II epithelial cells from fetal rat lung were exposed to hyperoxia in vitro in the presence or absence of recombinant human Trx (rhTrx 2 µg/ml). Cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Apoptosis and levels of reactive oxygen species (ROS) were measured by flow cytometry. Activation of mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase-Akt (PI3K-Akt) pathways were detected by Western blotting. We also investigated the effects of rhTrx on the following antioxidants (superoxide dismutase, catalase, and glutathione peroxidase). Trx significantly reduced hyperoxia-induced cell death and increased cell viability. In addition, ROS generation in type II cells was inhibited by rhTrx under hyperoxic conditions. We demonstrated that rhTrx protected type II cells against hyperoxic injury via sustaining the extracellular signal regulated kinase and PI3K activation, and decreasing of c-Jun N-terminal protein kinase and p38 activation. The results also showed manganese superoxide dismutase and glutathione peroxidase activities were increased by rhTrx in type II cells exposed to hyperoxia.Taken together, these results demonstrate that rhTrx administration markedly attenuates hyperoxia-induced type II cell injury through reduction of ROS generation, elevation of antioxidant activities and regulation of both MAPK and PI3K-Akt signaling pathways.

Novel therapeutic strategies for acute lung injury induced by lung damaging agents: the potential role of growth factors as treatment options

The increasing threat from terrorism has brought attention to the possible use of toxic industrial compounds (TICs) and other lung-damaging agents as weapons against civilian populations. The way in which these agents could be used favours the development of generic countermeasures. Improved medical countermeasures would increase survivability and improve the quality of recovery of lung damaged casualties. It is evident that there is a dearth of therapeutic regimes available to treat those forms of lung damage that currently require intensive care management. It is quite possible that mass casualties from a terrorist incident or major industrial accident involving the release of large quantities of inhaled TICs would place a severe burden on already scarce intensive care facilities. The development of effective pharmacological approaches to assist the recovery of casualties suffering from acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) may improve the prognosis of such patients (which is currently poor) and would ideally be used as a means of preventing subjects from developing the pulmonary oedema characteristic of ALI/ARDS. Many promising candidate pharmacological treatments have been evaluated for the treatment of ALI/ARDS, but their clinical value is often debatable. Thus, despite improvements in ventilation strategies, pharmacological intervention for ALI/ARDS remains problematical. A new approach is clearly required for the treatment of patients with severely compromised lungs. Whilst the pathology of ALI/ARDS associated with exposure to a variety of agents is complex, numerous experimental studies suggest that generic therapeutic intervention directed at approaches that aim to upregulate repair of the damaged alveolar blood/air barrier of the lung may be of value, particularly with respect to chemical-induced injury. To this end, keratinocyte growth factor (KGF), epithelial growth factor (EGF) and basic fibroblast growth factor (bFGF) are emerging as the most important candidates. Hepatocyte growth factor (HGF) does not have epithelial specificity for lung tissue. However, the enhanced effects of combinations of growth factors, such as the synergistic effect of HGF upon vascular endothelial growth factor (VEGF)-mediated endothelial cell activity, and the combined effect of HGF and KGF in tissue repair should be investigated, particularly as the latter pair of growth factors are frequently implicated in processes associated with the repair of lung damage. Synergistic interactions also occur between trefoil factor family (TFF) peptides and growth factors such as EGF. TFF peptides are most likely to be of value as a short term therapeutic intervention strategy in stimulating epithelial spreading activities which allow damaged mucosal surfaces to be rapidly covered by epithelial cells.

Cigarette smoke, inflammation, and lung injury: a mechanistic perspective

Inflammation is a common feature in the pathogenesis of cigarette smoke-associated diseases. The recruitment of inflammatory cells into the lung following cigarette smoke exposure presents a risk of tissue damage through the release of toxic mediators, including proteolytic enzymes and reactive oxygen species. This review represents a toxicological approach to investigation of cigarette smoke-induced lung injury, with a focus on laboratory studies and an emphasis on inflammatory mechanisms. The studies discussed in this review analyze the role of inflammation and inflammatory mediators in the development of injury. In cases where information relating to cigarette smoke is limited, examples are taken from other models of lung injury applicable to cigarette smoke. The primary aim of the review is to summarize published work so as to permit (1) an evaluation of chronic lung injury and inflammatory responses in animal models, (2) a discussion of inflammatory mediators in the development of chronic injury, and (3) identification of immunological mechanisms of injury. These studies discuss the currently understood roles of cytokines, cell adhesion molecules, and oxidative stress in inflammatory reactions and lung injury. A role for lipocortin 1 (annexin 1), a naturally occurring defense factor against inflammation, is discussed because of the possibility that impaired synthesis and degradation of lipocortin 1 will influence immune responses in animals exposed to cigarette smoke either by augmenting T helper cell Th1 response or by shifting Th1 to Th2 response. While Th1 augmentation will increase the risk for development of emphysema, Th1 to Th2 shift will favor development of asthma.

Soluble intercellular adhesion molecule-1 and clinical outcomes in patients with acute lung injury

OBJECTIVE

To determine if levels of soluble intercellular adhesion molecule-1 (sICAM-1), a marker of alveolar epithelial and endothelial injury, differ in patients with hydrostatic pulmonary edema and acute lung injury (ALI) and are associated with clinical outcomes in patients with ALI.

DESIGN, SETTING, AND PARTICIPANTS

Measurement of sICAM-1 levels in (1) plasma and edema fluid from 67 patients with either hydrostatic pulmonary edema or ALI enrolled in an observational, prospective single center study, and (2) in plasma from 778 patients with ALI enrolled in a large multi-center randomized controlled trial of ventilator strategy.

RESULTS

In the single-center study, levels of sICAM-1 were significantly higher in both edema fluid and plasma (median 938 and 545 ng/ml, respectively) from ALI patients compared to hydrostatic edema patients (median 384 and 177 ng/ml, P < 0.03 for both comparisons). In the multi-center study, higher plasma sICAM-1 levels were associated with poor clinical outcomes in both unadjusted and multivariable models. Subjects with ALI whose plasma sICAM-1 levels increased over the first 3 days of the study had a higher risk of death, after adjusting for other important predictors of outcome (odds ratio 1.48; 95% CI 1.03-2.12, P = 0.03).

CONCLUSIONS

Both plasma and edema fluid levels of sICAM-1 are higher in patients with ALI than in patients with hydrostatic pulmonary edema. Higher plasma sICAM-1 levels and increasing sICAM-1 levels over time are associated with poor clinical outcomes in ALI. Measurement of sICAM-1 levels may be useful for identifying patients at highest risk of poor outcomes from ALI.

Hypoxia attenuates effector-target cell interaction in the airway and pulmonary vascular compartment

Leucocyte infiltration is known to play an important role in hypoxia-induced tissue damage. However, little information is available about hypoxia and interaction of effector (neutrophils) with target cells (alveolar epithelial cells, AEC; rat pulmonary artery endothelial cells, RPAEC). The goal of this study was to elucidate hypoxia-induced changes of effector-target cell interaction. AEC and RPAEC were exposed to 5% oxygen for 2-6 h. Intercellular adhesion molecule-1 (ICAM-1) expression was determined and cell adherence as well as cytotoxicity assays were performed. Nitric oxide and heat shock protein 70 (HSP70) production was assessed in target cells. Under hypoxic conditions enhanced ICAM-1 production was found in both cell types. This resulted in an increase of adherent neutrophils to AEC and RPAEC. The death rate of hypoxia-exposed target cells decreased significantly in comparison to control cells. Nitric oxide (NO) concentration was enhanced, as was production of HSP70 in AEC. Blocking NO production in target cells resulted in increased cytotoxicity in AEC and RPAEC. This study shows for the first time that target cells are more resistant to effector cells under hypoxia, suggesting hypoxia-induced cell protection. An underlying mechanism for this phenomenon might be the protective effect of increased levels of NO in target cells.

Dissociation between alveolar transmigration of neutrophils and lung injury in hyperoxia

The objective of this study was to quantitatively assess changes in cell adhesion molecule (CAM) expression on the pulmonary endothelial surface during hyperoxia and to assess the functional significance of those changes on cellular trafficking and development of oxygen-induced lung injury. Mice were placed in >95% O2 for 0–72 h, and pulmonary injury and neutrophil (PMN) sequestration were assessed. Specific pulmonary CAM expression was quantified with a dual-radiolabeled MAb technique. To test the role of CAMs in PMN trafficking during hyperoxia, blocking MAbs to murine P-selectin, ICAM-1, or platelet-endothelial cell adhesion molecule-1 (PECAM-1) were injected in wild-type mice. Mice genetically deficient in these CAMs and PMN-depleted mice were also evaluated. PMN sequestration occurred within 8 h of hyperoxia, although alveolar emigration occurred later (between 48 and 72 h), coincident with rapid escalation of the lung injury. Hyperoxia significantly increased pulmonary uptake of radiolabeled antibodies to P-selectin, ICAM-1, and PECAM-1, reflecting an increase in their level on pulmonary endothelium and possibly sequestered blood cells. Although both anti-PECAM-1 and anti-ICAM-1 antibodies suppressed PMN alveolar influx in wild-type mice, only mice genetically deficient in PECAM-1 showed PMN influx suppression. Neither CAM blockade, nor genetic deficiency, nor PMN depletion attenuated lung injury. We conclude that early pulmonary PMN retention during hyperoxia is not temporally associated with an increase in endothelial CAMs; however, subsequent PMN emigration into the alveolar space may be supported by PECAM-1 and ICAM-1. Blocking PMN recruitment did not prevent lung injury, supporting dissociation between PMN infiltration and lung injury during hyperoxia in mice.

Molecular and functional changes of pulmonary surfactant in response to hyperoxia

Surfactant comprises phosphatidylcholine (PC) together with anionic phospholipids, neutral lipids, and surfactant proteins SP-A to-D. Its composition is highly specific, with dipalmitoyl-PC, palmitoyl-myristoyl-PC, and palmitoyl-palmitoleoyl-PC as its predominant PC species, but with low polyunsaturated phospholipids. Changes in pulmonary metabolism and function in response to injuries depend on their duration and whether adaptation can occur. We examined in rats prolonged (7 days) versus acute (2 days) exposure to non-lethal oxygen concentrations (85%) with respect to the composition and metabolism of individual lung phospholipid molecular species. Progressive inflammation, structural alteration, and involvement of type II pneumocytes were confirmed by augmented bromodeoxyuridine incorporation, broadening of alveolar septa, and increased granulocyte, macrophage, SP-A, and SP-D concentrations. Surfactant function was impaired after 2 days, but normalized with duration of hyperoxia, which was attributable to inhibition but not to alteration in SP-B/C concentrations. Phospholipid pool sizes and PC synthesis by lung tissue, as assessed by [methyl-(3)H]-choline incorporation, were unchanged after 2 days, although after 7 days they were elevated 1.7-fold. By contrast, incorporation of labeled PC into tissue pools of surfactant and lung lavage fluid decreased progressively. Moreover, concentrations of arachidonic acid containing phospholipids were augmented at the expense of saturated palmitoyl-myristoyl-PC and dipalmitoyl-PC. We conclude a persisting impairment in the intracellular trafficking and secretion of newly synthesized PC, accompanied by a progressive increase in alveolar arachidonic acid containing phospholipids in spite of recovery of acutely impaired surfactant function and adaptive increase of overall PC synthesis.

Shedding of soluble ICAM-1 into the alveolar space in murine models of acute lung injury

Intercellular adhesion molecule-1 (ICAM-1; CD54) is an adhesion molecule constitutively expressed in abundance on the cell surface of type I alveolar epithelial cells (AEC) in the normal lung and is a critical participant in pulmonary innate immunity. At many sites, ICAM-1 is shed from the cell surface as a soluble molecule (sICAM-1). Limited information is available regarding the presence, source, or significance of sICAM-1 in the alveolar lining fluid of normal or injured lungs. We found sICAM-1 in the bronchoalveolar lavage (BAL) fluid of normal mice (386 +/- 50 ng/ml). Additionally, sICAM-1 was spontaneously released by murine AEC in primary culture as type II cells spread and assumed characteristics of type I cells. Shedding of sICAM-1 increased significantly at later points in culture (5-7 days) compared with earlier time points (3-5 days). In contrast, treatment of AEC with inflammatory cytokines had limited effect on sICAM-1 shedding. BAL sICAM-1 was evaluated in in vivo models of acute lung injury. In hyperoxic lung injury, a reversible process with a major component of leak across the alveolar wall, BAL fluid sICAM-1 only increased in parallel with increased alveolar protein. However, in lung injury due to FITC, there were increased levels of sICAM-1 in BAL that were independent of changes in BAL total protein concentration. We speculate that after lung injury, changes in sICAM-1 in BAL fluid are associated with progressive injury and may be a reflection of type I cell differentiation during reepithelialization of the injured lung.

H2O2-induced proliferation of primary alveolar epithelial cells is mediated by MAP kinases

Exposure to supraphysiological oxygen concentrations during ventilatory oxygen therapy often causes tissue damage. Alveolar type II (AT II) cells are a major target for oxidant injury, and their ability to proliferate plays a critical role during the repair phase following injury. We hypothesized that reactive oxygen species (ROS), which are produced during hyperoxia, not only cause cellular damage, but may also play a role in the repair process by promoting AT II cell proliferation. We have tested the ability of ROS to induce proliferation in primary cultures of AT II cells by using a wide range of chronic and acute hydrogen peroxide (H2O2) exposures to mimic different types of oxidative stress. We found that chronic exposure to an extracellular flux of 10 microM H2O2/h can significantly increase the intracellular concentration of oxidants, DNA synthesis, and cell proliferation. H2O2-induced AT II cell proliferation was preceded by activation of the mitogen-activated protein kinase ERK (extracellular signal-regulated kinase). Inhibition of ERK and p38 activation prevented H2O2-induced proliferation. These results show that changes in intracellular oxidant concentrations can modulate downstream signaling pathways controlling AT II cell proliferation. This mechanism could be important in the repair process following hyperoxia-induced injury.

Short-term modulation of interleukin-1beta signaling by hyperoxia: uncoupling of IkappaB kinase activation and NF-kappaB-dependent gene expression

We have been interested in elucidating how simultaneous stimuli modulate inflammation-related signal transduction pathways in lung parenchymal cells. We previously demonstrated that exposing respiratory epithelial cells to 95% oxygen (hyperoxia) synergistically increased tumor necrosis factor-alpha (TNF-alpha)-mediated activation of NF-kappaB and NF-kappaB-dependent gene expression by a mechanism involving increased activation of IkappaB kinase (IKK). Because the signal transduction mechanisms induced by IL-1beta are distinct to that of TNF-alpha, herein we sought to determine whether hyperoxia modulates IL-1beta-dependent signal transduction. In A549 cells, simultaneous treatment with hyperoxia and IL-1beta caused increased activation of IKK, prolonged the degradation of IkappaBalpha, and prolonged the nuclear translocation and DNA binding of NF-kappaB compared with cells treated with IL-1beta alone in room air. Hyperoxia did not affect IL-1beta-dependent degradation of the interleukin receptor-associated kinase differently from treatment with IL-beta alone. In contrast to the effects on the IKK/IkappaBalpha/NF-kappaB pathway, simultaneous treatment with hyperoxia and IL-1beta did not augment NF-kappaB-dependent gene expression compared with treatment with IL-1beta alone. Similar observations were made in a different human respiratory epithelial cell line, BEAS-2B cells. In addition, simultaneous treatment with hyperoxia and IL-1beta caused hyperphosphorlyation of the NF-kappaB p65 subunit compared with treatment with IL-1beta alone. In summary, concomitant treatment of A549 cells with hyperoxia and IL-1beta augments activation of IKK, prolongs degradation of IkappaBalpha, and prolongs nuclear translocation and DNA binding of NF-kappaB. This activation, however, is not coupled to increased expression of NF-kappaB-dependent genes, and the mechanism of this decoupling is not related to decreased phosphorylation of p65.

Aerosolized perfluorocarbon reduces adhesion molecule gene expression and neutrophil sequestration in acute respiratory distress

In acute respiratory distress syndrome, neutrophil migration into the lung plays a key role in the development of lung injury. To study the effect of different modes of ventilation with perfluorocarbon (FC77), intrapulmonary neutrophil accumulation and mRNA expression of E-selectin, P-selectin and intercellular adhesion molecule-1 (ICAM-1), mediating leukocyte sequestration, were measured in surfactant depleted piglets. After bronchoalveolar lavage, 20 animals either received aerosolized perfluorocarbon (Aerosol-PFC), partial liquid ventilation (PLV) with perfluorocarbon at functional residual capacity filling volume (FRC-PLV) or at low volume (LV-PLV) or intermittent mandatory ventilation (control). After 2 h of perfluorocarbon application, intermittent mandatory ventilation was continued for 6 h. In the Aerosol-PFC group, all measured adhesion molecules showed a significantly reduced gene expression compared to controls. FRC-PFC treatment was effective in significantly diminishing P-selectin and ICAM-1 mRNA expression. Relative lung tissue neutrophil counts were significantly reduced in the Aerosol-PFC and the FRC-PLV group. Treatment with aerosolized perfluorocarbon is at least as effective as partial liquid ventilation at FRC volume in reducing pulmonary adhesion molecule expression and neutrophil accumulation in acute respiratory distress syndrome.

Use of antenatal steroids to counteract the negative effects of tracheal occlusion in the fetal lamb model

Tracheal occlusion (TO) in fetal lambs induces pulmonary hyperplasia but has negative effects on type II cells. The purpose of this study was to determine whether antenatal steroids could reverse the adverse effects of TO on lung maturation in fetal lambs. Sixteen time-dated pregnant ewes (term, 145 d) and 24 of their fetuses were divided into six groups: 1) TO at 117 d gestation; 2) TO at 117 d with a single maternal intramuscular injection of 0.5 mg/kg betamethasone 24 h before delivery; 3) TO at 117 d and release of the occlusion 2 d before delivery; 4) TO and release of the occlusion with maternal steroids; 5) unoperated controls without antenatal steroid treatment; and 6) unoperated controls, littermates of groups 1-4, treated with antenatal steroids. All fetuses were killed at 137 d gestation. Outcome measurements consisted of lung weight-to-body weight ratio; lung morphometry determined by mean terminal bronchial density; and assessment of type II pneumocytes by in situ hybridization to the mRNA of surfactant proteins B and C. Lung weight-to-body weight ratio and mean terminal bronchial density were significantly different among groups with TO and controls, indicating increased lung growth and structural maturation. The density of type II pneumocytes was markedly decreased by TO. Release 2 d before sacrifice significantly increased the density and surfactant activity of type II pneumocytes, but to levels still far from controls. Steroids alone had an effect similar to release. An additive effect was noted with steroids and 2-d release resulting in type II cell density comparable to controls. After fetal TO, a single maternal intramuscular dose of 0.5 mg/kg of betamethasone 24 h before delivery allows partial recuperation of the type II pneumocytes, an effect that is potentiated by 2-d release.

Immunological dysregulation of lung cells in response to vitamin E deficiency

Vitamin E supplementation exhibits anti-inflammatory properties. In the lung, the beneficial effects of vitamin E supplementation on inflammation and infections are well documented, but potential consequences of alimentary vitamin E deficiency to the immunological status of lung cells are not known. It is unclear if temporary vitamin E deficiency exhibits deleterious consequences or can be compensated for by other cellular antioxidants. To address this question, the alimentary vitamin E supply to rats was modified. We then investigated the effects on major histocompatibility molecule (MHC) class II, cell adhesion molecules, interleukin (IL)10, tumor necrosis factor (TNF)alpha in various lung cells. The constitutive expression of MHC class II, intercellular adhesion molecule (ICAM)-1, L-selectin, alpha5-integrin, and CD 166, was demonstrated by flow cytometry on type II pneumocytes, alveolar macrophages, and on co-isolated lymphocytes. Vitamin E depletion increased ICAM-1 and CD166 on type II cells and macrophages, whereas the expression of L-selectin increased only on macrophages. Furthermore, the vitamin E depletion increased the cellular content and secretion of IL10 in type II cells, but decreased the content and secretion of TNFalpha. Vitamin E depletion decreased the cellular vitamin E content, but did not change the activity of antioxidant enzymes (catalase, superoxide dismutase) and the glutathion (GSH)/oxidized glutathion (GSSG) ratio in alveolar type II cells. The shift of protein kinase C (PKC) from the cytosol to membranes indicates that a PKC-dependent signaling pathway may be involved in the change of the immunological status of type II cells. All these effects were reversed by vitamin E repletion. In summary, these results are clearly compatible with the view that a temporary vitamin E deficiency induces a reversible immunological dysregulation in alveolar type II cells and lung macrophages. This deficiency might predispose the lung to develop acute or chronic inflammation.

Mechanisms of repair and remodeling following acute lung injury

At present, we largely lack the ability to correlate the clinical course of ARDS patients with potential factors involved in the biochemical and cellular basis of lung repair. This requires very large patient databases with measurement of many biochemical parameters. Important mechanistic determinants during the repair phase can be sought by correlation with late outcomes, but a large-scale cooperative effort among multiple centers with sharing of follow-up data and patient specimens is essential. We also lack detailed human histologic material from many phases of ARDS and, particularly, know little of the long-term morphologic impact of ARDS in survivors. Establishment of a national registry that follows ARDS survivors and that would seek their cooperation in advance in obtaining autopsy specimens when they die of other causes would be very valuable. Correlating the pathology with their pulmonary function during recovery would give important insights into the reasons for the different patterns of abnormal pulmonary functions. The factors that determine the success of repair are of critical importance in testing new ARDS treatment strategies. Would accelerating the resolution of alveolar edema alter the course of subsequent fibrosis and inflammation? Does surfactant replacement therapy--a costly proposition in adults with ARDS--lead to better long-term outcomes in survivors? How much should we worry about the use of high levels of oxygen for support of arterial partial pressure of oxygen? Is it better to accept hyperoxia to avoid pressure or volume trauma induced by mechanical ventilation with higher minute ventilations? These major management issues all may affect the success of the late repair and recovery process. Intervention trials need to examine the long-term physiologic and functional outcomes.

Human SP-C gene sequences that confer lung epithelium-specific expression in transgenic mice

We used transgenic mice to identify cis-active regions of the human pulmonary surfactant protein C (SP-C) gene that impart tissue- and cell-specific expression in vivo in the lung. Approximately 3.7 kb of genomic SP-C DNA upstream of the transcription start site was sufficient to direct chloramphenicol acetyltransferase (CAT) reporter gene expression specifically in bronchiolar and alveolar epithelial cells of the lung. To further define cis-active regulatory elements that mediate cell-specific expression, we tested deletions of the parental 3.7-kb human SP-C sequence in transgenic mice. Tissue CAT assays of mice generated with truncations or overlapping internal deletions of the 3.7-kb construct functionally map alveolar cell-specific regulatory elements to within -215 bp of the SP-C promoter. Analysis of SP-C promoter deletions demonstrate that sequences between -3.7 kb and -1.9 kb contain enhancer sequences that stimulate SP-C transgene expression. In situ hybridization studies demonstrate that deletion of the -1,910- to -215-bp region abolishes the ectopic bronchiolar expression seen with the original 3.7-kb SP-C promoter construct. Comparison of sequences from -215 to +1 bp identified consensus binding sites for the homeodomain transcription factor thyroid transcription factor-1 (TTF-1). Cotransfection assays of the human 3.7-kb SP-C or -1,910- to -215-bp SP-C deletion construct with a TTF-1 expression plasmid demonstrates that TTF-1 transactivates the human SP-C gene. These results suggest that the TTF-1 cis-active sites are important in directing cell-specific expression of the SP-C gene in vivo.

Ablation of tumor necrosis factor receptor type I (p55) alters oxygen-induced lung injury

Hyperoxic lung injury, believed to be mediated by reactive oxygen species, inflammatory cell activation, and release of cytotoxic cytokines, complicates the care of many critically ill patients. The cytokine tumor necrosis factor (TNF)-alpha is induced in lungs exposed to high concentrations of oxygen; however, its contribution to hyperoxia-induced lung injury remains unclear. Both TNF-alpha treatment and blockade with anti-TNF antibodies increased survival in mice exposed to hyperoxia. In the current study, to determine if pulmonary oxygen toxicity is dependent on either of the TNF receptors, type I (TNFR-I) or type II (TNFR-II), TNFR-I or TNFR-II gene-ablated [(-/-)] mice and wild-type control mice (WT; C57BL/6) were studied in >95% oxygen. There was no difference in average length of survival, although early survival was better for TNFR-I(-/-) mice than for either TNFR-II(-/-) or WT mice. At 48 h of hyperoxia, slightly more alveolar septal thickening and peribronchiolar and periarteriolar edema were detected in WT than in TNFR-I(-/-) lungs. By 84 h of oxygen exposure, TNFR-I(-/-) mice demonstrated greater alveolar debris, inflammation, and edema than WT mice. TNFR-I was necessary for induction of cytokine interleukin (IL)-1beta, IL-1 receptor antagonist, chemokine macrophage inflammatory protein (MIP)-1beta, MIP-2, interferon-gamma-induced protein-10 (IP-10), and monocyte chemoattractant protein (MCP)-1 mRNA in response to intratracheal administration of recombinant murine TNF-alpha. However, IL-1beta, IL-6, macrophage migration inhibitory factor, MIP-1alpha, MIP-2, and MCP-1 mRNAs were comparably induced by hyperoxia in TNFR-I(-/-) and WT lungs. In contrast, mRNA for manganese superoxide dismutase and intercellular adhesion molecule-1 were induced by hyperoxia only in WT mice. Differences in early survival and toxicity suggest that pulmonary oxygen toxicity is in part mediated by TNFR-I. However, induction of specific cytokine and chemokine mRNA and lethality in response to severe hyperoxia was independent of TNFR-I expression. The current study supports the prediction that therapeutic efforts to block TNF-alpha receptor function will not protect against pulmonary oxygen toxicity.

Hyperoxia-induced cell death in the lung--the correlation of apoptosis, necrosis, and inflammation

Prolonged exposure to hyperoxia causes tissue damage in many organs and tissues. Since the entire surface area of lung epithelium is directly exposed to O2 and other inhaled agents, hyperoxia leads to the development of both acute and chronic lung injuries. These pathologic changes in the lung can also be seen in acute lung injury (ALI) in response to other agents. Simple strategies to mitigate hyperoxia-induced ALI might not be effective by virtue of merely reducing or augmenting the extent of apoptosis of pulmonary cells. Identification of the specific cell types undergoing apoptosis and further understanding of the precise timing of the onset of apoptosis may be necessary in order to gain a greater understanding of the connection between apoptosis and tolerance to hyperoxia and ALI. Attention should also be focused on other forms of non-apoptotic programmed cell death.

Lipopolysaccharide induces functional ICAM-1 expression in rat alveolar epithelial cells in vitro

Lipopolysaccharide (LPS)-induced lung inflammation is known to increase pulmonary intercellular adhesion molecule-1 (ICAM-1) expression. In the present study, L2 cells, a cell line of alveolar epithelial cells, were stimulated with LPS, and ICAM-1 expression was studied. ICAM-1 protein on L2 cells peaked at 6 (38% increase; P < 0.01) and 10 (48% increase; P < 0.001) h after stimulation with Escherichia coli and Pseudomonas aeruginosa LPS, respectively. ICAM-1 mRNA expression was markedly increased, with a peak at 2-4 (E. coli) and 4-6 (P. aeruginosa) h. Adherence assays of neutrophils to LPS-stimulated L2 cells showed a threefold increase in adherence (P < 0.001). Pretreatment of the neutrophils with anti-lymphocyte function-associated antigen-1 and anti-Mac-1 antibodies reduced adherence by 54% (P < 0.001). Analysis of immunofluorescence staining for ICAM-1 showed an exclusive apical expression of ICAM-1. These results indicate that LPS upregulates functional active ICAM-1 on the apical part of the membrane in rat pneumocytes.

Neopterin-induced expression of intercellular adhesion molecule-1 (ICAM-1) in type II-like alveolar epithelial cells

Production and release of proinflammatory mediators such as tumour necrosis factor-alpha and neopterin are common events following the activation of the cellular immune system. Concerning inflammatory disorders of the lung, e.g. sepsis or sarcoidosis, high serum neopterin levels have been reported to correlate well with the severity of the disease. These situations are often associated with an increased expression of ICAM-1 reported to be induced in type II alveolar epithelial cells. In our study we investigated the potential effects of neopterin on ICAM-1 synthesis in the type II-like pneumocyte cell line L2. Detection of ICAM-1 gene expression by reverse transcriptase-polymerase chain reaction revealed a dose-dependent effect of neopterin, with maximum impact following 12-h incubations. Comparable results were obtained when ICAM-1 protein synthesis was measured via a cell-based ELISA. In a second set of experiments we were able to show that coincubation of L2 cells with pyrrolidine dithiocarbamate (PDTC) significantly suppressed neopterin-induced ICAM-1 synthesis. Since PDTC is known to be a potent inhibitor of NF-kappaB, the stimulating effects of neopterin on ICAM-1 gene expression and protein generation may be mediated by activation of this transcription factor. From these data we conclude that neopterin stimulates ICAM-1 production in L2 cells. In vivo, these effects may contribute to the prolongation of the inflammatory response, including cytotoxic cell host defence mechanisms that impair the functions of the airway epithelium.

Cooperativity between oxidants and tumor necrosis factor in the activation of nuclear factor (NF)-kappaB: requirement of Ras/mitogen-activated protein kinases in the activation of NF-kappaB by oxidants

The transcription factor nuclear factor (NF)-kappaB is activated by oxidative stress or cytokines and is critical to the activation of inflammatory genes. Here, we report that hydrogen peroxide or 3-morpholinosydnonimine, which simultaneously releases nitric oxide and superoxide, synergize with the cytokine tumor necrosis factor (TNF)-alpha to activate NF-kappaB in rat lung epithelial cells, suggesting that signaling pathways elicited by reactive oxygen species (ROS)/reactive nitrogen species (RNS) are different from TNF-induced signaling. These findings were substantiated by observations that levels of IkappaB-alpha did not change after exposure to ROS/RNS, whereas a rapid depletion of IkappaB-alpha was observed in cells exposed to TNF. In addition, the proteosome inhibitor MG132 did not affect activation of NF-kappaB by ROS/RNS, whereas it abolished the TNF response. Transfection of a dominant negative Ras construct prevented the activation of NF-kappaB by ROS/RNS, demonstrating the requirement for Ras in the activation of NF-kappaB by oxidants. In contrast, TNF activated NF-kappaB in a Ras-independent fashion. Evaluation of members of the mitogen-activated protein kinase (MAPK) family as downstream effectors of Ras revealed the requirement of MAPK/ extracellular-regulated kinase (ERK) kinase kinase (MEKK)1 and c-Jun N-terminal kinases in the induction of NF-kappaB by both oxidants and TNF, whereas the MEK-ERK pathway negatively regulates NF-kappaB. Our findings demonstrate that cytokines and oxidants cooperate in the activation of transcription factors through distinct pathways, and suggest that anti-inflammatory and antioxidant therapies may be required in concert to prevent the activation of NF-kappaB-regulated genes important in the development of inflammatory diseases.

Increased endothelial cell expression of platelet-endothelial cell adhesion molecule-1 during hyperoxic lung injury

Lung injury is a frequent consequence of oxygen (O2) therapy administered to newborns and adults with respiratory distress. Acute exposure to hyperoxia results in a well-described pathophysiologic response in the lungs. Because inflammation is an important component of pulmonary O2 toxicity, we have an interest in identifying the inflammatory mediators that increase during hyperoxia. Platelet-endothelial cell adhesion molecule-1 (PECAM-1), a member of the immunoglobulin superfamily that is expressed at the junctions between endothelial cells, is essential to the transendothelial migration of leukocytes. We hypothesized that increased expression of PECAM-1 occurs in pulmonary endothelial cells during hyperoxic lung injury. Adult mice were exposed to 100% O2 for up to 96 h. We analyzed PECAM-1 expression by RNA blot hybridization, in situ hybridization, and immunohistochemistry. A increase in PECAM-1 mRNA was seen as soon as 2 d of hyperoxia relative to unexposed control mice. PECAM-1 mRNA and protein were found in endothelial cells of both large and small arteries. The expression of PECAM-1 in capillary vessels was further confirmed using in situ hybridization at the electron microscope level. This increase in PECAM-1 expression coincided with the appearance of leukocytes in lung tissue. These observations suggest that PECAM-1 expression is a relatively early step in the inflammation cascade, and intervention at this phase may be critical to the prevention of further damage.

Neutrophil-dependent goblet cell degranulation: role of membrane-bound elastase and adhesion molecules

We examined the effect of the neutrophil chemoattractants interleukin (IL)-8 and N-formyl-methionyl-leucyl-phenylalanine on goblet cell (GC) degranulation in guinea pigs. Chemoattractants caused time-dependent neutrophil recruitment and GC degranulation in vivo. NPC 15669 (an inhibitor of leukocyte infiltration) prevented both responses, implicating neutrophils. ICI 200,355 (an inhibitor of neutrophil elastase and proteinase-3) or secretory leukocyte protease inhibitor (an inhibitor of elastase but not of proteinase-3) abolished IL-8-induced GC degranulation, implicating elastase. Incubating tracheal segments with IL-8 plus neutrophils caused GC degranulation in vitro, an effect due to activation of the neutrophils themselves (and not an effect present in the supernatant). Chemoattractant increased surface staining of elastase and the cleavage of elastase-specific fluorogenic substrate by neutrophils. Pretreatment with anti-intercellular adhesion molecule-1, anti-CD18, or anti-CD11b antibody inhibited the chemoattractant-induced GC degranulation in vitro, implicating adhesion molecules. These studies suggest that chemoattractants cause neutrophil-dependent GC degranulation involving adhesive interactions between cells, with elastase activity occurring at the cell interface, causing GC secretion. The findings, reproduced in human airways, suggest novel methods of therapeutic intervention.