Protein nitration in rat lungs during hyperoxia exposure: a possible role of myeloperoxidase

Adaptive Responses to Hypoxia and/or Hyperoxia in Humans

Significance: Oxygen is indispensable for aerobic life, but its utilization exposes cells and tissues to oxidative stress; thus, tight regulation of cellular, tissue, and systemic oxygen concentrations is crucial. Here, we review the current understanding of how the human organism (mal-)adapts to low (hypoxia) and high (hyperoxia) oxygen levels and how these adaptations may be harnessed as therapeutic or performance enhancing strategies at the systemic level. Recent Advances: Hyperbaric oxygen therapy is already a cornerstone of modern medicine, and the application of mild hypoxia, that is, hypoxia conditioning (HC), to strengthen the resilience of organs or the whole body to severe hypoxic insults is an important preparation for high-altitude sojourns or to protect the cardiovascular system from hypoxic/ischemic damage. Many other applications of adaptations to hypo- and/or hyperoxia are only just emerging. HC-sometimes in combination with hyperoxic interventions-is gaining traction for the treatment of chronic diseases, including numerous neurological disorders, and for performance enhancement. Critical Issues: The dose- and intensity-dependent effects of varying oxygen concentrations render hypoxia- and/or hyperoxia-based interventions potentially highly beneficial, yet hazardous, although the risks versus benefits are as yet ill-defined. Future Directions: The field of low and high oxygen conditioning is expanding rapidly, and novel applications are increasingly recognized, for example, the modulation of aging processes, mood disorders, or metabolic diseases. To advance hypoxia/hyperoxia conditioning to clinical applications, more research on the effects of the intensity, duration, and frequency of altered oxygen concentrations, as well as on individual vulnerabilities to such interventions, is paramount. Antioxid. Redox Signal. 37, 887-912.

A Critical Role for P2X7 Receptor-Induced VCAM-1 Shedding and Neutrophil Infiltration during Acute Lung Injury

Pulmonary neutrophils are the initial inflammatory cells that are recruited during lung injury and are crucial for innate immunity. However, pathological recruitment of neutrophils results in lung injury. The objective of this study is to determine whether the novel neutrophil chemoattractant, soluble VCAM-1 (sVCAM-1), recruits pathological levels of neutrophils to injury sites and amplifies lung inflammation during acute lung injury. The mice with P2X7 receptor deficiency, or treated with a P2X7 receptor inhibitor or anti-VCAM-1 Abs, were subjected to a clinically relevant two-hit LPS and mechanical ventilation-induced acute lung injury. Neutrophil infiltration and lung inflammation were measured. Neutrophil chemotactic activities were determined by a chemotaxis assay. VCAM-1 shedding and signaling pathways were assessed in isolated lung epithelial cells. Ab neutralization of sVCAM-1 or deficiency or antagonism of P2X7R reduced neutrophil infiltration and proinflammatory cytokine levels. The ligands for sVCAM-1 were increased during acute lung injury. sVCAM-1 had neutrophil chemotactic activities and activated alveolar macrophages. VCAM-1 is released into the alveolar airspace from alveolar epithelial type I cells through P2X7 receptor-mediated activation of the metalloproteinase ADAM-17. In conclusion, sVCAM-1 is a novel chemoattractant for neutrophils and an activator for alveolar macrophages. Targeting sVCAM-1 provides a therapeutic intervention that could block pathological neutrophil recruitment, without interfering with the physiological recruitment of neutrophils, thus avoiding the impairment of host defenses.

Expression of Carcinoembryonic Cell Adhesion Molecule 6 and Alveolar Epithelial Cell Markers in Lungs of Human Infants with Chronic Lung Disease

The membrane protein carcinoembryonic antigen cell adhesion molecule (CEACAM6) is expressed in the epithelium of various tissues, participating in innate immune defense, cell proliferation and differentiation, with overexpression in gastrointestinal tract, pancreatic and lung tumors. It is developmentally and hormonally regulated in fetal human lung, with an apparent increased production in preterm infants with respiratory failure. To further examine the expression and cell localization of CEACAM6, we performed immunohistochemical and biochemical studies in lung specimens from infants with and without chronic lung disease. CEACAM6 protein and mRNA were increased ~4-fold in lungs from infants with chronic lung disease as compared with controls. By immunostaining, CEACAM6 expression was markedly increased in the lung parenchyma of infants and children with a variety of chronic lung disorders, localizing to hyperplastic epithelial cells with a ~7-fold elevated proliferative rate by PCNA staining. Some of these cells also co-expressed membrane markers of both type I and type II cells, which is not observed in normal postnatal lung, suggesting they are transitional epithelial cells. We suggest that CEACAM6 is both a marker of lung epithelial progenitor cells and a contributor to the proliferative response after injury due to its anti-apoptotic and cell adhesive properties.

Hyperoxia promotes polarization of the immune response in ovalbumin-induced airway inflammation, leading to a TH17 cell phenotype

Previous studies have demonstrated that hyperoxia-induced stress and oxidative damage to the lungs of mice lead to an increase in IL-6, TNF-α, and TGF-β expression. Together, IL-6 and TGF-β have been known to direct T cell differentiation toward the TH17 phenotype. In the current study, we tested the hypothesis that hyperoxia promotes the polarization of T cells to the TH17 cell phenotype in response to ovalbumin-induced acute airway inflammation. Airway inflammation was induced in female BALB/c mice by intraperitoneal sensitization and intranasal introduction of ovalbumin, followed by challenge methacholine. After the methacholine challenge, animals were exposed to hyperoxic conditions in an inhalation chamber for 24 h. The controls were subjected to normoxia or aluminum hydroxide dissolved in phosphate buffered saline. After 24 h of hyperoxia, the number of macrophages and lymphocytes decreased in animals with ovalbumin-induced airway inflammation, whereas the number of neutrophils increased after ovalbumin-induced airway inflammation. The results showed that expression of Nrf2, iNOS, T-bet and IL-17 increased after 24 of hyperoxia in both alveolar macrophages and in lung epithelial cells, compared with both animals that remained in room air, and animals with ovalbumin-induced airway inflammation. Hyperoxia alone without the induction of airway inflammation lead to increased levels of TNF-α and CCL5, whereas hyperoxia after inflammation lead to decreased CCL2 levels. Histological evidence of extravasation of inflammatory cells into the perivascular and peribronchial regions of the lungs was observed after pulmonary inflammation and hyperoxia. Hyperoxia promotes polarization of the immune response toward the TH17 phenotype, resulting in tissue damage associated with oxidative stress, and the migration of neutrophils to the lung and airways. Elucidating the effect of hyperoxia on ovalbumin-induced acute airway inflammation is relevant to preventing or treating asthmatic patients that require oxygen supplementation to reverse the hypoxemia.

Suppression of plasminogen activator inhibitor-1 by inhaled nitric oxide attenuates the adverse effects of hyperoxia in a rat model of acute lung injury

INTRODUCTION

Locally increased expression of plasminogen activator inhibitor-1 (PAI-1) in acute lung injury (ALI) is largely responsible for fibrin deposition in the alveolae and lung microvasculature. In vitro, nitric oxide (NO) effectively suppresses the ischemic induction of PAI-1. We aimed to investigate the effects of inhaled NO on PAI-1 expression in ALI in a rat model with and without hyperoxia.

MATERIALS AND METHODS

Healthy adult rats were primed with lipopolysaccharide (LPS) via an intraperitoneal challenge followed by a second dose of LPS given intratracheally to induce ALI (LPS group), whereas the control groups were given sterile saline. All groups were allocated to subgroups according to gas exposure: NO (20 parts per million, NO), 95% oxygen (O), both (ONO), or room air (A). At 4h, 24h, 48h (after 4h or 24h exposure to the various gases, 24h gas intervention and then observation until 48h), the rat lungs were processed and PAI-1 protein and mRNA expression, histopathological lung injury scores and fibrin deposition were evaluated.

RESULTS

At 4 and 24h, inhaled NO caused the PAI-1 mRNA levels in the LPS-NO and LPS-ONO subgroups to decrease compared with the untreated LPS subgroups. At 48h, higher PAI-1 mRNA levels than those of the corresponding control subgroup were only observed in the LPS-O subgroup, and these values were lower in the LPS-ONO subgroup than in the LPS-O subgroup. The trends of the PAI-1 protein levels mirrored those of PAI-1 mRNA. At 48h, PAI-1 protein levels in the LPS-NO and LPS-ONO subgroups were decreased compared with those in the untreated LPS subgroups. The histopathological lung injury scores and fibrin deposition in LPS subgroups that inhaled NO showed a decreasing trend compared with the untreated LPS subgroups.

CONCLUSIONS

Inhaled NO can suppress elevated PAI-1 expression in rats with ALI induced by endotoxin. Although exposure to high-concentration oxygen prolongs the duration of PAI-1 mRNA overexpression in ALI, inhaled NO can reduce this effect and alleviate both fibrin deposition and lung injury.

Myeloperoxidase deletion prevents high-fat diet-induced obesity and insulin resistance

Activation of myeloperoxidase (MPO), a heme protein primarily expressed in granules of neutrophils, is associated with the development of obesity. However, whether MPO mediates high-fat diet (HFD)-induced obesity and obesity-associated insulin resistance remains to be determined. Here, we found that consumption of an HFD resulted in neutrophil infiltration and enhanced MPO expression and activity in epididymal white adipose tissue, with an increase in body weight gain and impaired insulin signaling. MPO knockout (MPO(-/-)) mice were protected from HFD-enhanced body weight gain and insulin resistance. The MPO inhibitor 4-aminobenzoic acid hydrazide reduced peroxidase activity of neutrophils and prevented HFD-enhanced insulin resistance. MPO deficiency caused high body temperature via upregulation of uncoupling protein-1 and mitochondrial oxygen consumption in brown adipose tissue. Lack of MPO also attenuated HFD-induced macrophage infiltration and expression of proinflammatory cytokines. We conclude that activation of MPO in adipose tissue contributes to the development of obesity and obesity-associated insulin resistance. Inhibition of MPO may be a potential strategy for prevention and treatment of obesity and insulin resistance.

Pulmonary Collectins in Diagnosis and Prevention of Lung Diseases

Pulmonary surfactant is a complex mixture of lipids and proteins, and is synthesized and secreted by alveolar type II epithelial cells and bronchiolar Clara cells. It acts to keep alveoli from collapsing during the expiratory phase of the respiratory cycle. After its secretion, lung surfactant forms a lattice structure on the alveolar surface, known as tubular myelin. Surfactant proteins (SP)-A, B, C and D make up to 10% of the total surfactant. SP-B and SPC are relatively small hydrophobic proteins, and are involved in the reduction of surface-tension at the air-liquid interface. SP-A and SP-D, on the other hand, are large oligomeric, hydrophilic proteins that belong to the collagenous Ca²⁺-dependent C-type lectin family (known as “Collectins”), and play an important role in host defense and in the recycling and transport of lung surfactant (Awasthi 2010) (Fig. 43.1). In particular, there is increasing evidence that surfactant-associated proteins A and -D (SP-A and SP-D, respectively) contribute to the host defense against inhaled microorganisms (see 10.1007/978-3-7091-1065_24 and 10.1007/978-3-7091-1065_25). Based on their ability to recognize pathogens and to regulate the host defense, SP-A and SP-D have been recently categorized as “Secretory Pathogen Recognition Receptors”. While SP-A and SP-D were first identified in the lung; the expression of these proteins has also been observed at other mucosal surfaces, such as lacrimal glands, gastrointestinal mucosa, genitourinary epithelium and periodontal surfaces. SP-A is the most prominent among four proteins in the pulmonary surfactant-system. The expression of SP-A is complexly regulated on the transcriptional and the chromosomal level. SP-A is a major player in the pulmonary cytokine-network and moreover has been described to act in the pulmonary host defense. This chapter gives an overview on the understanding of role of SP-A and SP-D in for human pulmonary disorders and points out the importance for pathology-orientated research to further elucidate the role of these molecules in adult lung diseases. As an outlook, it will become an issue of pulmonary pathology which might provide promising perspectives for applications in research, diagnosis and therapy (Awasthi 2010).

Inhaled nitric oxide prevents 3-nitrotyrosine formation in the lungs of neonatal mice exposed to >95% oxygen

Inhaled nitric oxide is being evaluated as a preventative therapy for patients at risk for bronchopulmonary dysplasia (BPD). Nitric oxide (NO), in the presence of superoxide, forms peroxynitrite, which reacts with tyrosine residues on proteins to form 3-nitrotyrosine (3-NT). However, NO can also act as an antioxidant and was recently found to improve the oxidative balance in preterm infants. Thus, we tested the hypothesis that the addition of a therapeutically relevant concentration (10 ppm) of NO to a hyperoxic exposure would lead to decreased 3-NT formation in the lung. FVB mouse pups were exposed to either room air (21% O(2)) or >95% O(2) with or without 10 ppm NO within 24 h of birth. In the first set of studies, body weights and survival were monitored for 7 days, and exposure to >95% O(2) resulted in impaired weight gain and near 100% mortality by 7 days. However, the mortality occurred earlier in pups exposed to >95% O(2) + NO than in pups exposed to >95% O(2) alone. In a second set of studies, lungs were harvested at 72 h. Immunohistochemistry of the lungs at 72 h revealed that the addition of NO decreased alveolar, bronchial, and vascular 3-NT staining in pups exposed to both room air and hyperoxia. The lung nitrite levels were higher in animals exposed to >95% oxygen + NO than in animals exposed to >95% oxygen alone. The protein levels of myeloperoxidase, monocyte chemotactic protein-1, and intracellular adhesion molecule-1 were assessed after 72 h of exposure and found to be greatest in the lungs of pups exposed to >95% O(2). This hyperoxia-induced protein expression was significantly attenuated by the addition of 10 ppm NO. We propose that in the presence of >95% O(2), peroxynitrite formation results in protein nitration; however, adding excess NO to the >95% O(2) exposure prevents 3-NT formation by NO reacting with peroxynitrite to produce nitrite and NO(2). We speculate that the decreased protein nitration observed with the addition of NO may be a potential mechanism limiting hyperoxic lung injury.

Hyperoxia-induced lung injury is dose dependent in Wistar rats

Oxygen is indispensable for aerobic respiration. However, the effects of hyperoxia on the lungs are poorly defined. The aim of the present study was to determine the effects of different oxygen concentrations on rat lungs. Rats (n = 6 per group) were exposed to hyperoxia for 90 minutes at 3 different concentrations: 50% (H50%), 75% (H75%), or 100% (H100%). Bronchoalveolar lavage (BAL) was performed and the right lungs were removed for histological analyses. The BAL samples were assayed for lipid peroxidation and antioxidant status using biochemical methods. Hyperoxia induced influxes of macrophages (1.8- to 2.3-fold) and neutrophils (7.0- to 10.2-fold) into the lungs compared to the control group (exposed to normoxia; n = 6). Histological analyses of the hyperoxic groups showed hemorrhagic areas and septal edema. A significant increase (2.2-fold) in lipid peroxidation was observed in the H100% group compared to the control group (P <.05). Glutathione peroxidase and superoxide dismutase activities were reduced to approximately 20% and 40% of the control values, respectively, in all 3 hyperoxic groups, and catalase activity was reduced in both the H75% (-0.6-fold) and H100% (-0.7-fold) groups. These results indicate a harmful effect of hyperoxia on the rat lung, with evidence of oxidant/antioxidant imbalance and histological damage.

Hyaluronan reversed proteoglycan synthesis inhibited by mechanical stress: possible involvement of antioxidant effect

INTRODUCTION

Abnormal mechanical stress loaded on the cartilage leads to the osteoarthritis (OA). Although intraarticular hyaluronan (HA) injection is an effective treatment for OA, the underlying mechanism has not been made clear.

METHODS

Mechanical compression was loaded on the bovine cartilage using the Biopress system. Proteoglycan (PG) and reactive oxygen species (ROS) synthesis were measured with [(35)S] incorporation and fluorescent dye, respectively. Accumulation of peroxynitrite was determined with western blotting using nitrotyrosine antibody.

RESULTS

Mechanical compression inhibited PG synthesis and enhanced ROS. Externally added HA reversed stress-inhibited PG synthesis and attenuated ROS synthesis. HA also significantly decreased the generation of nitrotyrosine.

CONCLUSIONS

HA neutralized stress-enhanced ROS synthesis and resulted in the reversing of PG synthesis. These data suggest that HA plays an anabolic effect as an antioxidant.

MCP-1 antibody treatment enhances damage and impedes repair of the alveolar epithelium in influenza pneumonitis

Recent studies have demonstrated an essential role of alveolar macrophages during influenza virus infection. Enhanced mortalities were observed in macrophage-depleted mice and pigs after influenza virus infection, but the basis for the enhanced pathogenesis is unclear. This study revealed that blocking macrophage recruitment into the lungs in a mouse model of influenza pneumonitis resulted in enhanced alveolar epithelial damage and apoptosis, as evaluated by histopathology, immunohistochemistry, Western blot, RT-PCR, and TUNEL assays. Abrogation of macrophage recruitment was achieved by treatment with monoclonal antibody against monocyte chemoattractant protein-1 (MCP-1) after sub-lethal challenge with mouse-adapted human influenza A/Aichi/2/68 virus. Interestingly, elevated levels of hepatocyte growth factor (HGF), a mitogen for alveolar epithelium, were detected in bronchoalveolar lavage samples and in lung homogenates of control untreated and nonimmune immunoglobulin (Ig)G-treated mice after infection compared with anti-MCP-1-treated infected mice. The lungs of control animals also displayed strongly positive HGF staining in alveolar macrophages as well as alveolar epithelial cell hyperplasia. Co-culture of influenza virus-infected alveolar epithelial cells with freshly isolated alveolar macrophages induced HGF production and phagocytic activity of macrophages. Recombinant HGF added to mouse lung explants after influenza virus infection resulted in enhanced BrdU labeling of alveolar type II epithelial cells, indicating their proliferation, in contrast with anti-HGF treatment showing significantly reduced epithelial regeneration. Our data indicate that inhibition of macrophage recruitment augmented alveolar epithelial damage and apoptosis during influenza pneumonitis, and that HGF produced by macrophages in response to influenza participates in the resolution of alveolar epithelium.

UTP regulation of ion transport in alveolar epithelial cells involves distinct mechanisms

UTP is known to regulate alveolar fluid clearance. However, the relative contribution of alveolar type I cells and type II cells to this process is unknown. In this study, we investigated the effects of UTP on ion transport in type I-like cell (AEC I) and type II-like cell (AEC II) monolayers. Luminal treatment of cell monolayers with UTP increased short-circuit current (I(sc)) of AEC II but decreased I(sc) of AEC I. The Cl(-) channel blockers NPPB and DIDS inhibited the UTP-induced changes in I(sc) (DeltaIsc) in both types of cells. Amiloride, an inhibitor of epithelial Na(+) channels (ENaC), abolished the UTP-induced DeltaI(sc) in AEC I, but not in AEC II. The general blocker of K(+) channels, BaCl(2), eliminated the UTP-induced DeltaI(sc) in AEC II, but not in AEC I. The intermediate conductance (IK(Ca)) blocker, clofilium, also blocked the UTP effect in AEC II. The signal transduction pathways mediated by UTP were the same in AEC I and AEC II. Furthermore, UTP increased Cl(-) secretion in AEC II and Cl(-) absorption in AEC I. Our results suggest that UTP induces opposite changes in I(sc) in AEC I and AEC II, likely due to the reversed Cl(-) flux and different contributions of ENaC and IK(Ca). Our results further imply a new concept that type II cells contribute to UTP-induced fluid secretion and type I cells contribute to UTP-induced fluid absorption in alveoli.

[Effects of hyperoxia on Wistar rat lungs]

OBJECTIVE

To study the effects of short-term exposure to high oxygen concentrations (hyperoxia) on Wistar rat lungs.

METHODS

Animals were divided into three groups exposed to hyperoxia for 10', 30' and 90' (O10', O30', O90', respectively), together with a control group (exposed to room air). The animals were sacrificed 24 h after exposure. Bronchoalveolar lavage was performed, and the lungs were removed for histological and stereological analysis.

RESULTS

In the O10', O30', and O90' groups, respectively and in comparison with the controls, we observed an increase in the numbers of macrophages (2169.9 +/- 118.0, 1560.5 +/- 107.0, and 1467.6 +/- 39.0 vs. 781.3 +/- 78.3) and neutrophils (396.3 +/- 35.4, 338.4 +/- 17.3, and 388.7 +/- 11.7 vs. 61.6 +/- 4.2), concomitant with an increase in oxidative damage (143.0 +/- 7.8%, 180.4 +/- 5.6%, and 235.0 +/- 13.7 vs. 100.6 +/- 1.7%). The histological and stereological analyses revealed normal alveoli and alveolar septa in the controls (83.51 +/- 1.20% and 15 +/- 1.21%), in the O10' group (81.32 +/- 0.51% and 16.64 +/- 0.70%), and in the O30' group (78.75 +/- 0.54% and 17.73 +/- 0.26%). However, in the O90' group, inflammatory cell infiltration was observed in the alveoli and alveolar septa. Red blood cells extravasated from capillaries to the alveoli (59.06 +/- 1.22%), with evidence of congestion, hemorrhage, and septal edema (35.15 +/- 0.69%).

CONCLUSION

Hyperoxia for 90' caused injury of the lung parenchyma, resulting in oxidative damage and inflammatory cell infiltration.

Ionotropic GABA receptor expression in the lung during development

Cl(-) transport is essential for lung development. Because gamma-aminobutyric acid (GABA) receptors allow the flow of negatively-charged Cl(-) ions across the cell membrane, we hypothesized that the expression of ionotropic GABA receptors are regulated in the lungs during development. We identified 17 GABA receptor subunits in the lungs by real-time PCR. These subunits were categorized into four groups: Group 1 had high mRNA expression during fetal stages and low in adults; Group 2 had steady expression to adult stages with a slight up-regulation at birth; Group 3 showed an increasing expression from fetal to adult lungs; and Group 4 displayed irregular mRNA fluctuations. The protein levels of selected subunits were also determined by Western blots and some subunits had protein levels that corresponded to mRNA levels. Further studied subunits were primarily localized in epithelial cells in the developing lung with differential mRNA expression between isolated cells and whole lung tissues. Our results add to the knowledge of GABA receptor expression in the lung during development.

Heat shock protein 90 inhibitors attenuate LPS-induced endothelial hyperpermeability

Endothelial hyperperme ability leading to vascular leak is an important consequence of sepsis and sepsis-induced lung injury. We previously reported that heat shock protein (hsp) 90 inhibitor pretreatment improved pulmonary barrier dysfunction in a murine model of sepsis-induced lung injury. We now examine the effects of hsp90 inhibitors on LPS-mediated endothelial hyperpermeability, as reflected in changes in transendothelial electrical resistance (TER) of bovine pulmonary arterial endothelial cells (BPAEC). Vehicle-pretreated cells exposed to endotoxin exhibited a concentration-dependent decrease in TER, activation of pp60(Src), phosphorylation of the focal adhesion protein paxillin, and reduced expression of the adherens junction proteins, vascular endothelial (VE)-cadherin and beta-catenin. Pretreatment with the hsp90 inhibitor, radicicol, prevented the decrease in TER, maintained VE-cadherin and beta-catenin expression, and inhibited activation of pp60(Src) and phosphorylation of paxillin. Similarly, when BPAEC hyperpermeability was induced by endotoxin-activated neutrophils, pretreatment of neutrophils and/or endothelial cells with radicicol protected against the activated neutrophil-induced decrease in TER. Increased paxillin phosphorylation and decreased expression of beta-catenin and VE-cadherin were also observed in mouse lungs 12 h after intraperitoneal endotoxin and attenuated in mice pretreated with radicicol. These results suggest that hsp90 plays an important role in sepsis-associated endothelial barrier dysfunction.

Gene expression of rat alveolar type II cells during hyperoxia exposure and early recovery

Alveolar epithelial cell (AEC) injury and repair during hyperoxia exposure and recovery have been investigated for decades, but the molecular mechanisms of these processes are not clear. To identify potentially important genes involved in lung injury and repair, we studied the gene expression profiles of isolated AEC II from control, 48-h hyperoxia-exposed (>95% O(2)), and 1-7 day recovering rats using a DNA microarray containing 10,000 genes. Fifty genes showed significant differential expression between two or more time points (P<0.05, fold change >2). These genes can be classified into 8 unique gene expression patterns. Real-time PCR verified 14 selected genes in three patterns related to hyperoxia exposure and early recovery. The change in the protein level for two of the selected genes, bmp-4 and retnla, paralleled that of the mRNA level. Many of these genes were found to be involved in cell proliferation and differentiation. In an in vitro AEC trans-differentiation culture model using AEC II isolated from control and 48-h hyperoxia-exposed rats, the expressions of the cell proliferation and differentiation genes identified above were consistent with their predicted roles in the trans-differentiation of AEC. These data indicate that a coordinated mechanism may control AEC differentiation during in vivo hyperoxia exposure and recovery as well as during in vitro AEC culture.

Class A scavenger receptor (CD204) attenuates hyperoxia-induced lung injury by reducing oxidative stress

To clarify the role of macrophage class A scavenger receptors (SR-A, CD204) in oxidative lung injury, we examined lung tissue of SR-A deficient (SR-A(-/-)) and wild-type (SR-A(+/+)) mice in response to hyperoxic treatment. Protein levels of bronchoalveolar lavage fluid (BALF) and pulmonary oedema (wet : dry weight ratios) were higher in SR-A(-/-) mice than those in SR-A(+/+) mice. Cumulative survival was significantly decreased in SR-A(-/-) mice. However, there were no differences in BALF macrophage and neutrophil count between the two groups. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) revealed that messenger RNA (mRNA) levels of the inducible nitric oxide synthase (iNOS) were increased during hyperoxic injury, and this increase was more prominent in SR-A(-/-) mice. Expression levels of iNOS in alveolar macrophages after hyperoxia in vivo and in vitro were higher in SR-A(-/-) macrophages compared with SR-A(+/+) macrophages. Immunohistochemistry using anti-nitrotyrosine antibodies revealed distinctive oxidative stress in the injured lung in both groups, but it was more remarkable in the SR-A(-/-) mice. After hyperoxic treatment, pulmonary mRNA levels of tumour necrosis factor-alpha(TNF-alpha) were elevated more rapidly in SR-A(-/-) mice than in SR-A(+/+) mice. Together these results suggest that SR-A expression attenuates hyperoxia-induced lung injury by reducing macrophage activation.

Expression profile of IGF system during lung injury and recovery in rats exposed to hyperoxia: a possible role of IGF-1 in alveolar epithelial cell proliferation and differentiation

Although several studies have shown that an induction of insulin-like growth factor (IGF) components occurs during hyperoxia-mediated lung injury, the role of these components in tissue repair is not well known. The present study aimed to elucidate the role of IGF system components in normal tissue remodeling. We used a rat model of lung injury and remodeling by exposing rats to > 95% oxygen for 48 h and allowing them to recover in room air for up to 7 days. The mRNA expression of IGF-I, IGF-II, and IGF-1 receptor (IGF-1R) increased during injury. However, the protein levels of these components remained elevated until day 3 of the recovery and were highly abundant in alveolar type II cells. Among IGF binding proteins (IGFBPs), IGFBP-5 mRNA expression increased during injury and at all the recovery time points. IGFBP-2 and -3 mRNA were also elevated during injury phase. In an in vitro model of cell differentiation, the expression of IGF-I and IGF-II increased during trans-differentiation of alveolar epithelial type II cells into type-I like cells. The addition of anti-IGF-1R and anti-IGF-I antibodies inhibited the cell proliferation and trans-differentiation to some extent, as evident by cell morphology and the expression of type I and type II cell markers. These findings demonstrate that the IGF signaling pathway plays a critical role in proliferation and differentiation of alveolar epithelium during tissue remodeling.

Alveolar type I cells protect rat lung epithelium from oxidative injury

The lung alveolar surface is covered by two morphologically and functionally distinct cells: alveolar epithelial cell types I and II (AEC I and II). The functions of AEC II, including surfactant release, cell differentiation and ion transport, have been extensively studied. However, relatively little is known regarding the physiological functions of AEC I. Global gene expression profiling of freshly isolated AEC I and II revealed that many genes were differentially expressed in AEC I. These genes have a diversity of functions, including cell defence. Nine out of 10 selected genes were verified by quantitative real-time PCR. Two genes, apolipoprotein E (Apo E) and transferrin, were further characterized and functionally studied. Immunohistochemistry indicated that both proteins were specifically localized in AEC I. Up-regulation of Apo E and transferrin was observed in hyperoxic lungs. Functionally, Apo E and transferrin play a protective role against oxidative stress in an animal model. Our studies suggest that AEC I is not just a simple barrier for gas exchange, but a functional cell that protects alveolar epithelium from injury.

Effect of cholesterol depletion on exocytosis of alveolar type II cells

Alveolar epithelial type II cells secrete lung surfactant via exocytosis. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNARE) are implicated in this process. Lipid rafts, the cholesterol- and sphingolipid-rich microdomains, may offer a platform for protein organization on the cell membrane. We tested the hypothesis that lipid rafts organize exocytotic proteins in type II cells and are essential for the fusion of lamellar bodies, the secretory granules of type II cells, with the plasma membrane. The lipid rafts, isolated from type II cells using 1% Triton X-100 and a sucrose gradient centrifugation, contained the lipid raft markers, flotillin-1 and -2, whereas they excluded the nonraft marker, Na+-K+ ATPase. SNAP-23, syntaxin 2, and VAMP-2 were enriched in lipid rafts. When type II cells were depleted of cholesterol, the association of SNAREs with the lipid rafts was disrupted and the formation of fusion pore was inhibited. Furthermore, the cholesterol-depleted plasma membrane had less ability to fuse with lamellar bodies, a process mediated by annexin A2. The secretagogue-stimulated secretion of lung surfactant from type II cells was also reduced by methyl-beta-cyclodextrin. When the raft-associated cell surface protein, CD44, was cross-linked using anti-CD44 antibodies, the CD44 clusters were observed. Syntaxin 2, SNAP-23, and annexin A2 co-localized with the CD44 clusters, which were cholesterol dependent. Our results suggested that lipid rafts may form a functional platform for surfactant secretion in alveolar type II cells, and raft integrity was essential for the fusion between lamellar bodies with the plasma membrane.

Pirfenidone inhibits inflammatory responses and ameliorates allograft injury in a rat lung transplant model

OBJECTIVE

Tumor necrosis factor alpha is a proinflammatory cytokine that has been proved to play a crucial role in inducing posttransplantation lung injury. The present study was performed to determine whether pirfenidone, a new nonpeptide drug with potent anti-tumor necrosis factor alpha activity, promotes protection against acute allograft injury through inhibiting pulmonary inflammatory responses in a rat model of orthotopic lung transplantation.

METHODS

Three transplant groups were formed: isografts, untreated allografts, and allografts treated with pirfenidone (0.5% chow starting on day 1 after transplantation). The implants were harvested on day 21 after transplantation. Acute cellular rejection grade and degree of allograft injury were evaluated on the basis of hematoxylin-and-eosin staining. The pulmonary inflammatory response and inflammation-induced oxidative stress were assessed on the basis of neutrophil accumulation (myeloperoxidase immunoreactivity and enzymatic activity) and iron deposition (Prussian blue staining). In addition, circulating levels of tissue necrosis factor alpha in all animals were measured.

RESULTS

The degree of allograft injury was significantly reduced in pirfenidone-treated allografts relative to untreated allografts (P < .01). The beneficial effect of pirfenidone was associated with decreased lung myeloperoxidase immunoreactivity (P < .05) and enzymatic activity (P < .01). Moreover, the untreated allografts contained a high concentration of iron, which was strikingly reduced by pirfenidone. Treatment with pirfenidone resulted in a lower level of plasma tissue necrosis factor alpha, which correlated positively with lung myeloperoxidase enzymatic activity (P < .0001).

CONCLUSION

These results suggest that pirfenidone, with its anti-tissue necrosis factor alpha activity, reduced neutrophil recruitment and iron accumulation, hence limiting the acute lung allograft injury.

In vivo and in vitro oxidative regulation of rat aryl sulfotransferase IV (AST IV)

Sulfotransferase catalyzed sulfation is important in the regulation of different hormones and the metabolism of hydroxyl containing xenobiotics. In the present investigation, we examined the effects of hyperoxia on aryl sulfotransferase IV in rat lungs in vivo. The enzyme activity of aryl sulfotransferase IV increased 3- to 8-fold in >95% O2 treated rat lungs. However, hyperoxic exposure did not change the mRNA and protein levels of aryl sulfotransferase IV in lungs as revealed by Western blot and RT-PCR. This suggests that oxidative regulation occurs at the level of protein modification. The increase of nonprotein soluble thiol and reduced glutathione (GSH)/oxidized glutathione (GSSG) ratios in treated lung cytosols correlated well with the aryl sulfotransferase IV activity increase. In vitro, rat liver cytosol 2-naphthol sulfation activity was activated by GSH and inactivated by GSSG. Our results suggest that Cys residue chemical modification is responsible for the in vivo and in vitro oxidative regulation. The molecular modeling structure of aryl sulfotransferase IV supports this conclusion. Our gel filtration chromatography results demonstrated that neither GSH nor GSSG treatment changed the existing aryl sulfotransferase IV dimer status in cytosol, suggesting that oxidative regulation of aryl sulfotransferase IV is not caused by dimer-monomer status change.

NF-kappaB protects lung epithelium against hyperoxia-induced nonapoptotic cell death-oncosis

Prolonged exposure to hyperoxia induces pulmonary epithelial cell death and acute lung injury. Although both apoptotic and nonapoptotic morphologies are observed in hyperoxic animal lungs, nonapoptotic cell death had only been recorded in transformed lung epithelium cultured in hyperoxia. To test whether the nonapoptotic characteristics in hyperoxic animal lungs are direct effects of hyperoxia, the mode of cell death was determined both morphologically and biochemically in human primary lung epithelium exposed to 95% O(2). In contrast to characteristics observed in apoptotic cells, hyperoxia induced swelling of nuclei and an increase in cell size, with no evidence for any augmentation in the levels of either caspase-3 activity or annexin V incorporation. These data suggest that hyperoxia can directly induce nonapoptotic cell death in primary lung epithelium. Although hyperoxia-induced nonapoptotic cell death was associated with NF-kappaB activation, it is unknown whether NF-kappaB activation plays any causal role in nonapoptotic cell death. This study shows that inhibition of NF-kappaB activation can accelerate hyperoxia-induced epithelial cell death in both primary and transformed lung epithelium. Corresponding to the reduced cell survival in hyperoxia, the levels of MnSOD were also low in NF-kappaB-deficient cells. These results demonstrate that NF-kappaB protects lung epithelial cells from hyperoxia-induced nonapoptotic cell death.

Gene silencing in alveolar type II cells using cell-specific promoter in vitro and in vivo

RNA interference (RNAi) is a sequence-specific post-transcriptional gene silencing process. Although it is widely used in the loss-of-function studies, none of the current RNAi technologies can achieve cell-specific gene silencing. The lack of cell specificity limits its usage in vivo. Here, we report a cell-specific RNAi system using an alveolar epithelial type II cell-specific promoter--the surfactant protein C (SP-C) promoter. We show that the SP-C-driven small hairpin RNAs specifically depress the expression of the exogenous reporter (enhanced green fluorescent protein) and endogenous genes (lamin A/C and annexin A2) in alveolar type II cells, but not other lung cells, using cell and organ culture in vitro as well as in vivo. The present study provides an efficient strategy in silencing a gene in one type of cell without interfering with other cell systems, and may have a significant impact on RNAi therapy.

Correlation of changes in nitric oxide synthase, superoxide dismutase and nitrotyrosine with endothelial regeneration and neointimal hyperplasia in the balloon-injured rabbit subclavian artery

OBJECTIVES

Alterations in nitric oxide (NO) and superoxide production within the wall of injured vessels may modulate the development and eventual extent of neointima after balloon injury.

METHODS

In this study we have characterized a rabbit model of subclavian artery injury and have used immunocytochemistry to detect NO synthase (NOS) isoforms, Cu-Zn superoxide dismutase (SOD) and nitrotyrosine in the injured vessel from 2 h to 28 days after injury.

RESULTS

At 48 h after injury, when cellular proliferation that will ultimately form the neointima is commencing, there was upregulation of inducible NOS, Cu-Zn SOD and nitrotyrosine. Recovery of endothelial NOS occurred at 28 days after injury, when the neointima is stabilizing and cellular proliferation has slowed down. There was no increase in neuronal NOS at any time point studied.

CONCLUSIONS

NO may serve to limit the development of neointima while superoxide may attenuate the effect of NO by formation of peroxynitrite, detected as increased nitrotyrosine staining. Upregulation of Cu-Zn SOD would limit superoxide both at sites of inflammation in the vessel wall from 48 h and in the adventitia up to 28 days after injury. Very early intervention to protect NO may reduce neointimal size.

Oxygen tension and inhaled nitric oxide modulate pulmonary levels of S-nitrosocysteine and 3-nitrotyrosine in rats

The oxidative environment within the lung generated upon administration of oxygen may be a critical regulator for the efficacy of inhaled nitric oxide therapy, possibly as a consequence of changes in nitrosative and nitrative chemistry. Changes in S-nitrosocysteine and 3-nitrotyrosine adducts were therefore evaluated after exposure of rats to 80% or >95% oxygen for 24 or 48 h with and without 20 ppm inhaled nitric oxide. Exposure to 80% oxygen led to increased formation of S-nitrosocysteine and 3-nitrotyrosine adducts in lung tissue that were also associated with increased expression of iNOS. The addition of inhaled nitric oxide in 80% oxygen exposure did not alter any of these adducts in the lung or in the bronchoalveolar lavage (BAL). Exposure to >95% oxygen led to a significant decrease in S-nitrosocysteine and an increase in 3-nitrotyrosine adducts in the lung. Co-administration of inhaled nitric oxide with >95% oxygen prevented the decrease in S-nitrosocysteine levels. The levels of S-nitrosocysteine and 3-nitrotyrosine returned to baseline in a time-dependent fashion after termination of exposure to >95% oxygen and inhaled nitric oxide. These data suggest the formation of S-nitrosating and tyrosine-nitrating species is regulated by oxygen tensions and co-administration of inhaled nitric oxide restores the nitrosative chemistry without a significant impact upon the nitrative pathway.

Identification of two novel markers for alveolar epithelial type I and II cells

Alveolar epithelial type I and type II cells (AEC I and II) are closely aligned in alveolar surface. There is much interest in the precise identification of AEC I and II in order to separate and evaluate functional and other properties of these two cells. This study aims to identify specific AEC I and AEC II cell markers by DNA microarray using the in vitro trans-differentiation of AEC II into AEC I-like cells as a model. Quantitative real-time PCR confirmed five AEC I genes: fibroblast growth factor receptor-activating protein 1, aquaporin 5, purinergic receptor P2X 7 (P2X7), interferon-induced protein, and Bcl2-associated protein, and one AEC II gene: gamma-aminobutyric acid receptor pi subunit (GABRP). Immunostaining on cultured cells and rat lung tissue indicated that GABRP and P2X7 proteins were specifically expressed in AEC II and AEC I, respectively. In situ hybridization of rat lung tissue confirmed the localization of GABRP mRNA in type II cells. P2X7 and GABRP identified in this study could be used as potential AEC I and AEC II markers for studying lung epithelial cell biology and monitoring lung injury.

Isolation of highly pure alveolar epithelial type I and type II cells from rat lungs

There are no ideal cell lines available for alveolar epithelial type I and II cells (AEC I and II) at the present time. The current methods for isolating AEC I and II give limited purities. Here, we reported improved and reproducible methods for the isolation of highly pure AEC I and II from rat lungs. AEC I and II were released from lung tissues using different concentrations of elastase digestion. Macrophages and leukocytes were removed by rat IgG 'panning' and anti-rat leukocyte common antigen antibodies. For AEC II isolation, polyclonal rabbit anti-T1alpha (an AEC I apical membrane protein) antibodies were used to remove AEC I contamination. For AEC I isolation, positive immunomagnetic selection by polyclonal anti-T1alpha antibodies was used. The purities of AEC I and II were 91 +/- 4 and 97 +/- 1%, respectively. The yield per rat was approximately 2 x 10(6) for AEC I and approximately 33 x 10(6) for AEC II. The viabilities of these cell preparations were more than 96%. The protocol for AEC II isolation is also suitable to obtain pure AEC II (93-95%) from hyperoxia-injured and recovering lungs. The purified AEC I and II can be used for gene expression profiling and functional studies. It also offers an important tool to the field of lung biology.