Increased expression of tissue inhibitor of metalloproteinases (TIMP-I) and metallothionein in murine lungs after hyperoxic exposure

Mechanical ventilation injury and repair in extremely and very preterm lungs

Background

Extremely preterm infants often receive mechanical ventilation (MV), which can contribute to bronchopulmonary dysplasia (BPD). However, the effects of MV alone on the extremely preterm lung and the lung’s capacity for repair are poorly understood.

Aim

To characterise lung injury induced by MV alone, and mechanisms of injury and repair, in extremely preterm lungs and to compare them with very preterm lungs.

Methods

Extremely preterm lambs (0.75 of term) were transiently exposed by hysterotomy and underwent 2 h of injurious MV. Lungs were collected 24 h and at 15 d after MV. Immunohistochemistry and morphometry were used to characterise injury and repair processes. qRT-PCR was performed on extremely and very preterm (0.85 of term) lungs 24 h after MV to assess molecular injury and repair responses.

Results

24 h after MV at 0.75 of term, lung parenchyma and bronchioles were severely injured; tissue space and myofibroblast density were increased, collagen and elastin fibres were deformed and secondary crest density was reduced. Bronchioles contained debris and their epithelium was injured and thickened. 24 h after MV at 0.75 and 0.85 of term, mRNA expression of potential mediators of lung repair were significantly increased. By 15 days after MV, most lung injury had resolved without treatment.

Conclusions

Extremely immature lungs, particularly bronchioles, are severely injured by 2 h of MV. In the absence of continued ventilation these injured lungs are capable of repair. At 24 h after MV, genes associated with injurious MV are unaltered, while potential repair genes are activated in both extremely and very preterm lungs.

Metallothionein-induced zinc partitioning exacerbates hyperoxic acute lung injury

Hypozincemia, with hepatic zinc accumulation at the expense of other organs, occurs in infection, inflammation, and aseptic lung injury. Mechanisms underlying zinc partitioning or its impact on extrahepatic organs are unclear. Here we show that the major zinc-binding protein, metallothionein (MT), is critical for zinc transmigration from lung to liver during hyperoxia and preservation of intrapulmonary zinc during hyperoxia is associated with an injury-resistant phenotype in MT-null mice. Particularly, lung-to-liver zinc ratios decreased in wild-type (WT) and increased significantly in MT-null mice breathing 95% oxygen for 72 h. Compared with female adult WT mice, MT-null mice were significantly protected against hyperoxic lung injury indicated by reduced inflammation and interstitial edema, fewer necrotic changes to distal airway epithelium, and sustained lung function at 72 h hyperoxia. Lungs of MT-null mice showed decreased levels of immunoreactive LC3, an autophagy marker, compared with WT mice. Analysis of superoxide dismutase (SOD) activity in the lungs revealed similar levels of manganese-SOD activity between strains under normoxia and hyperoxia. Lung extracellular SOD activity decreased significantly in both strains at 72 h of hyperoxia, although there was no difference between strains. Copper-zinc-SOD activity was ~4× higher under normoxic conditions in MT-null compared with WT mice but was not affected in either group by hyperoxia. Collectively the data suggest that genetic deletion of MT-I/II in mice is associated with compensatory increase in copper-zinc-SOD activity, prevention of hyperoxia-induced zinc transmigration from lung to liver, and hyperoxia-resistant phenotype strongly associated with differences in zinc homeostasis during hyperoxic acute lung injury.

Nanomaterial cytotoxicity is composition, size, and cell type dependent

Background

Despite intensive research efforts, reports of cellular responses to nanomaterials are often inconsistent and even contradictory. Additionally, relationships between the responding cell type and nanomaterial properties are not well understood. Using three model cell lines representing different physiological compartments and nanomaterials of different compositions and sizes, we have systematically investigated the influence of nanomaterial properties on the degrees and pathways of cytotoxicity. In this study, we selected nanomaterials of different compositions (TiO₂ and SiO₂ nanoparticles, and multi-wall carbon nanotubes [MWCNTs]) with differing size (MWCNTs of different diameters < 8 nm, 20-30 nm, > 50 nm; but same length 0.5-2 μm) to analyze the effects of composition and size on toxicity to 3T3 fibroblasts, RAW 264.7 macrophages, and telomerase-immortalized (hT) bronchiolar epithelial cells.

Results

Following characterization of nanomaterial properties in PBS and serum containing solutions, cells were exposed to nanomaterials of differing compositions and sizes, with cytotoxicity monitored through reduction in mitochondrial activity. In addition to cytotoxicity, the cellular response to nanomaterials was characterized by quantifying generation of reactive oxygen species, lysosomal membrane destabilization and mitochondrial permeability. The effect of these responses on cellular fate - apoptosis or necrosis - was then analyzed. Nanomaterial toxicity was variable based on exposed cell type and dependent on nanomaterial composition and size. In addition, nanomaterial exposure led to cell type dependent intracellular responses resulting in unique breakdown of cellular functions for each nanomaterial: cell combination.

Conclusions

Nanomaterials induce cell specific responses resulting in variable toxicity and subsequent cell fate based on the type of exposed cell. Our results indicate that the composition and size of nanomaterials as well as the target cell type are critical determinants of intracellular responses, degree of cytotoxicity and potential mechanisms of toxicity.

A paradoxical protective role for the proinflammatory peptide substance P receptor (NK1R) in acute hyperoxic lung injury

The neuropeptide substance P manifests its biological functions through ligation of a G protein-coupled receptor, the NK1R. Mice with targeted deletion of this receptor reveal a preponderance of proinflammatory properties resulting from ligand activation, demonstrating a neurogenic component to multiple forms of inflammation and injury. We hypothesized that NK1R deficiency would afford a similar protection from inflammation associated with hyperoxia. Counter to our expectations, however, NK1R-/- animals suffered significantly worse lung injury compared with wild-type mice following exposure to 90% oxygen. Median survival was shortened to 84 h for NK1R-/- mice from 120 h for wild-type animals. Infiltration of inflammatory cells into the lungs was significantly increased; NK1R-/- animals also exhibited increased pulmonary edema, hemorrhage, and bronchoalveolar lavage fluid protein levels. TdT-mediated dUTP nick end labeling (TUNEL) staining was significantly elevated in NK1R-/- animals following hyperoxia. Furthermore, induction of metallothionein and Na(+)-K(+)-ATPase was accelerated in NK1R-/- compared with wild-type mice, consistent with increased oxidative injury and edema. In cultured mouse lung epithelial cells in 95% O(2), however, addition of substance P promoted cell death, suggesting the neurogenic component of hyperoxic lung injury is mediated by additional mechanisms in vivo. Release of bioactive constituents including substance P from sensory neurons results from activation of the vanilloid receptor, TRPV1. In mice with targeted deletion of the TRPV1 gene, acute hyperoxic injury is attenuated relative to NK1R-/- animals. Our findings thus reveal a major neurogenic mechanism in acute hyperoxic lung injury and demonstrate concerted actions of sensory neurotransmitters revealing significant protection for NK1R-mediated functions.

Transcriptional profiling of murine organ genes in response to infection with Bacillus anthracis Ames spores

Bacillus anthracis is the Gram-positive, spore-forming etiological agent of anthrax, an affliction studied because of its importance as a potential bioweapon. Although in vitro transcriptional responses of macrophages to either spore or anthrax toxins have been previously reported, little is known regarding the impact of infection on gene expression in host tissues. We infected Swiss-Webster mice intranasally with 5 LD(50) of B. anthracis-virulent Ames spores and observed the global transcriptional profiles of various tissues over a 48 h time period. RNA was extracted from spleen, lung, and heart tissues of infected and control mice and examined by Affymetrix GeneChip analysis. Approximately 580 host genes were significantly over or under expressed among the lung, spleen, and heart tissues at 8 and 48 h time points. Expression of genes encoding for surfactant and major histocompatibility complex (MHC) presentation was diminished during the early phase of infection in lungs. By 48 h, a significant number of genes were modulated in the heart, including up-regulation of calcium-binding-related gene expression, and down-regulation of multiple genes related to cell adhesion, formation of the extracellular matrix, and the cell cytoskeleton. Interestingly, the spleen 8h post-infection showed striking increases in the expression of genes that encode hydrolytic enzymes, and these levels remained elevated throughout infection. Further, genes involving antigen presentation and interferon responses were down-regulated in the spleen at 8 h. In late stages of infection, splenic genes related to the inflammatory response were up-regulated. This study is the first to describe the in vivo global transcriptional response of multiple organs during inhalational anthrax. Although numerous genes related to the host immunological response and certain protection mechanisms were up-regulated in these organs, a vast list of genes important for fully developing and maintaining this response were decreased. Additionally, the lung, spleen, and heart showed differential responses to the infection, further validating the demand for a better understanding of anthrax pathogenesis in order to design therapies against novel targets.

Nitric oxide and zinc homeostasis in acute lung injury

Among putative small molecules that affect sensitivity to acute lung injury, zinc and nitric oxide are potentially unique by virtue of their interdependence and dual capacities to be cytoprotective or injurious. Nitric oxide and zinc appear to be linked via an intracellular signaling pathway involving S-nitrosation of metallothoinein--itself a small protein known to be an important inducible gene product that may modify lung injury. In the present article, we summarize recent efforts using genetic and fluorescence optical imaging techniques to: (1) demonstrate that S-nitrosation of metallothionein affects intracellular zinc homeostasis in intact pulmonary endothelial cells; and (2) reveal a protective role for this pathway in hyperoxic and LPS-induced injury.

Lung injury and mortality with hyperoxia are increased in peroxiredoxin 6 gene-targeted mice

Overexpression of peroxiredoxin 6 (Prdx6) has been shown to protect lungs of mice against hyperoxia-mediated injury. In this study, we evaluated whether genetic inactivation of Prdx6 in mice increases sensitivity to oxygen toxicity. We evaluated mouse survival, lung histopathology, total protein and nucleated cells in bronchoalveolar lavage fluid (BALF), and oxidation of lung protein and lipids by measurement of protein carbonyls and thiobarbituric reactive substances (TBARS), respectively. The duration of survival for Prdx6 -/- mice was significantly shorter than that observed in wild-type mice on exposure to 85 or 100% O(2); survival of Prdx6 +/- mice was intermediate. After 72-h exposure to 100% O(2), lungs of Prdx6-/- mice showed more severe injury than wild-type with increased wet/dry weight, epithelial cell necrosis and alveolar edema on microscopic examination, increased protein and nucleated cells in BALF, and higher content of TBARS and protein carbonyls in lung homogenate. These findings show that Prdx6 -/- mice have increased sensitivity to hyperoxia and provide in vivo evidence that Prdx6 is an important lung antioxidant enzyme.

Gene expression profiling of the early pulmonary response to hyperoxia in mice

To identify molecular events occurring during the early response to hyperoxia, we measured changes over time in total lung gene expression in C57BL/6 mice during prolonged exposure to > 95% O2. Specifically, differential gene expression of > 8,734 sequence-verified murine complementary DNAs was analyzed after 0, 8, 24, and 48 h of O2 exposure, with additional genes of interest analyzed at 24 h. Of the 385 genes differentially expressed, hyperoxia increased expression of 175 genes (2.0%) and decreased expression of 210 genes (2.3%). The majority of "classic" antioxidant enzymes, including catalase, MnSOD, and Cu-Zn SOD, showed no change in expression during hyperoxia, with a number of other antioxidant enzymes, including glutathione peroxidase, glutathione-S-Transferase (GST) Pi1, GST mu2, and heme oxygenase-1 showing relatively moderate increases. The exception was the heavy metal-binding protein metallothionein, which increased expression over 7-fold after 48 h of O2. We found no change in the expression of a number of known proinflammatory genes after 24 or 48 h of hyperoxia. A large increase in p21 expression was demonstrated, suggesting overall inhibition of cell cycle progression. Increases of the antiapoptotic gene Bcl-XL were counterbalanced by similar increases of the proapoptotic gene BAX. New findings included significant increases in expression of cysteine-rich protein 61(cyr61) at 48 h, suggesting a potential role for this factor in angiogenesis or remodeling of the extra cellular matrix during recovery from hyperoxia. In addition, downregulation of thrombomodulin expression occurred by 24 h and was further decreased at 48 h. Given the importance of thrombomodulin/thrombin interaction in regulating protein C activity, decreases in thrombomodulin may contribute to activation of the coagulation and inflammatory cascades and development of lung injury with hyperoxia.

Glutathione peroxidase-1 expression enhances recovery of human breast carcinoma cells from hyperoxic cell cycle arrest

We previously reported that hyperoxia (95% O(2)) induces an S-phase cell cycle arrest in glutathione peroxidase-deficient human carcinoma cells T47D-H3 (Exp. Cell Res. 256:347-357; 2000). Here, we investigated whether increasing the peroxide scavenging capacity via glutathione peroxidase-1 (GPx1) expression can prevent cell cycle alterations induced by oxidative stress. We show that GPx1-proficient T47D-GPx-2 transfectant cells, in which GPx1 concentration is most elevated in mitochondria (Biochem. Biophys. Res. Commun. 272:416-422; 2000), are partially resistant to cell cycle inhibition induced by hyperoxia or menadione exposure. Transient cell growth resistance was observed at the level of cell cycle phase distribution, Cdk2 activity, and DNA synthesis after 40 h hyperoxia. This differential resistance was associated with an inhibition of ROS production and lipid peroxidation induced by hyperoxia. After 64 h hyperoxic exposure, cell growth was completely abolished in both cell lines, despite elevated glutathione levels. However, in contrast to the GPx1-deficient cells, T47D-GPx-2 cells showed an increased capacity to recover from a cell cycle arrest mediated by a 64 h hyperoxic stress. Differential recovery was also observed at the ultrastructural level between Gpx1-proficient and -deficient cells. These data indicate that GPx1 played an important role in the cell capacity to recover from hyperoxic insults. The limited protection conferred by GPx1 during hyperoxia suggests that the deleterious effects were partially mediated by peroxide-derived free radicals, but also involved the action of nonperoxide-derived reactive species.

Neutrophil proteinases in hydrochloric acid- and endotoxin-induced acute lung injury: evaluation of interstitial protease activity by in situ zymography

We investigated the role of polymorphonuclear neutrophil (PMN) proteinases, elastase, and gelatinase B in rat models of acute lung injury. Three groups of rats were studied 6 hours after unilateral instillation of hydrochloric acid (HCl; 0.1 N), lipopolysaccharide (LPS) (4 microg), or saline. The results demonstrated that HCl-induced lung injury, as compared with LPS-induced lung injury, was associated with an increase in permeability (wet/dry weight ratio and proteins in bronchoalveolar lavage fluid). In contrast, there was similar PMN recruitment (in bronchoalveolar lavage fluid and myeloperoxidase activity in lung homogenates) and similar proteinase exocytosis (residual alveolar PMN content of elastase and gelatinase B) in both types of lung injury. In situ zymography, evaluating interstitial protease/inhibitor balance, demonstrated a decrease in gelatinolytic activity in both HCl- and LPS-injured lungs compared with normal lung. The increase in interleukin 6 concentration in lung homogenates, which is observed after both injuries compared with saline-instilled animals, could be involved in up-regulation of tissue inhibitor of matrix metalloproteinase-1, shown by immunocytochemistry to participate in antiproteinase excess. Neither inhibition of alveolar neutrophil influx using a leukocyte elastase inhibitor (EPI-hNE-4) nor inhibition of gelatinase activities by recombinant adenovirus for the human tissue inhibitor of matrix metalloproteinase 1 gene transfer decreased lung edema in HCl-induced injury. These data suggest that PMN proteinases do not contribute to HCl-induced acute lung injury in rats.

Linkage analysis of susceptibility to hyperoxia. Nrf2 is a candidate gene

A strong role for reactive oxygen species (ROS) has been proposed in the pathogenesis of a number of lung diseases. Hyperoxia (> 95% oxygen) generates ROS and extensive lung damage, and has been used as a model of oxidant injury. However, the precise mechanisms of hyperoxia-induced toxicity have not been completely clarified. This study was designed to identify hyperoxia susceptibility genes in C57BL/6J (susceptible) and C3H/HeJ (resistant) mice. The quantitative phenotypes used for this analysis were pulmonary inflammatory cell influx, epithelial cell sloughing, and hyperpermeability. Genome-wide linkage analyses of intercross (F2) and recombinant inbred cohorts identified significant and suggestive quantitative trait loci on chromosomes 2 (hyperoxia susceptibility locus 1 [Hsl1]) and 3 (Hsl2), respectively. Comparative mapping of Hsl1 identified a strong candidate gene, Nfe2l2 (nuclear factor, erythroid derived 2, like 2 or Nrf2) that encodes a transcription factor NRF2 which regulates antioxidant and phase 2 gene expression. Strain-specific variation in lung Nrf2 messenger RNA expression and a T --> C substitution in the B6 Nrf2 promoter that cosegregated with susceptibility phenotypes in F2 animals supported Nrf2 as a candidate gene. Results from this study have important implications for understanding the mechanisms through which oxidants mediate the pathogenesis of lung disease.

Evaluation of basement membrane degradation during TNF-alpha-induced increase in epithelial permeability

We evaluated whether tumor necrosis factor (TNF)-alpha induces an increase in permeability of an alveolar epithelial monolayer via gelatinase secretion and basement membrane degradation. Gelatinase secretion and epithelial permeability to radiolabeled albumin under unstimulated and TNF-alpha-stimulated conditions of an A549 human epithelial cell line were evaluated in vitro. TNF-alpha induced both upregulation of a 92-kDa gelatinolytic activity (pro form in cell supernatant and activated form in extracellular matrix) and an increase in the epithelial permeability coefficient compared with the unstimulated condition (control: 1.34 +/- 0.04 x 10(-6) cm/s; 1 microg/ml TNF-alpha: 1.47 +/- 0.05 x 10(-6) cm/s, P < 0.05). The permeability increase in the TNF-alpha-stimulated condition involved both paracellular permeability, with gap formation visualized by actin cytoskeleton staining, and basement membrane permeability, with an increase in the basement membrane permeability coefficient (determined after cell removal; control: 2.58 +/- 0.07 x 10(-6) cm/s; 1 microg/ml TNF-alpha: 2.82 +/- 0.02.10(-6) x cm/s, P < 0.05). Because addition of gelatinase inhibitors [tissue inhibitor of metalloproteinase (TIMP)-1 or BB-3103] to cell supernatants failed to inhibit the permeability increase, the gelatinase-inhibitor balance in the cellular microenvironment was further evaluated by cell culture on a radiolabeled collagen matrix. In the unstimulated condition, spontaneous collagenolytic activity inhibited by addition to the matrix of 1 microg/ml TIMP-1 or 10(-6) M BB-3103 was found. TNF-alpha failed to increase this collagenolytic activity because it was associated with dose-dependent upregulation of TIMP-1 secretion by alveolar epithelial cells. In conclusion, induction by TNF-alpha of upregulation of both the 92-kDa gelatinase and its inhibitor TIMP-1 results in maintenance of the gelatinase-inhibitor balance, indicating that basement membrane degradation does not mediate the TNF-alpha-induced increase in alveolar epithelial monolayer permeability.

Development of pulmonary tolerance in mice exposed to zinc oxide fumes

As a result of repeated exposures to inhaled toxicants such as zinc oxide (ZnO), numerous individuals acquire tolerance to the exposures and display reduced symptoms. To ascertain whether tolerance is developed in an animal model, NIH-Swiss mice were exposed to 1.0 mg/m(3) ZnO for 1, 3, or 5 days (1X, 3X, or 5X), and polymorphonuclear leukocyte (PMN) and protein levels in bronchoalveolar lavage (BAL) were measured. Mice acquired tolerance to neutrophil infiltration into the lungs, as total PMNs returned near baseline in 5X-exposed animals as compared to that of the 1X exposure group (1X = 2.7 +/- 0.4 x 10(4), 5X = 0.2 +/- 0.1 x 10(4), mean +/- SE, p < 0.05). Development of tolerance to changes in lavageable protein, however, was not observed (1X = 313 +/- 29 microg/ml, 5X = 684 +/- 71 microg/ml, p < 0.05). Tolerance to PMN influx did not persist following re-exposure to ZnO after 5 days of rest. In contrast to ZnO exposure, following single and repeated exposure to aerosolized endotoxin there was development of tolerance to protein in BAL (1X = 174 +/- 71 microg/ml, 5X = 166 +/- 14 microg/ml, p > 0.05), but not to PMN influx (1X = 5.5 +/- 1.7 x 10(4), 13.9 +/- 1.7 x 10(4), p < 0.05). Induction of lung metallothionein (MT) was also observed in mice exposed once or repeatedly exposed to ZnO, suggesting that MT may play a role in its molecular mechanism.

Induction, regulation, degradation, and biological significance of mammalian metallothioneins

MTs are small cysteine-rich metal-binding proteins found in many species and, although there are differences between them, it is of note that they have a great deal of sequence and structural homology. Mammalian MTs are 61 or 62 amino acid polypeptides containing 20 conserved cysteine residues that underpin the binding of metals. The existence of MT across species is indicative of its biological demand, while the conservation of cysteines indicates that these are undoubtedly central to the function of this protein. Four MT isoforms have been found so far, MT-1, MT-2, MT-3, and MT-4, but these also have subtypes with 17 MT genes identified in man, of which 10 are known to be functional. Different cells express different MT isoforms with varying levels of expression perhaps as a result of the different function of each isoform. Even different metals induce and bind to MTs to different extents. Over 40 years of research into MT have yielded much information on this protein, but have failed to assign to it a definitive biological role. The fact that multiple MT isoforms exist, and the great variety of substances and agents that act as inducers, further complicates the search for the biological role of MTs. This article reviews the current knowledge on the biochemistry, induction, regulation, and degradation of this protein in mammals, with a particular emphasis on human MTs. It also considers the possible biological roles of this protein, which include participation in cell proliferation and apoptosis, homeostasis of essential metals, cellular free radical scavenging, and metal detoxification.

Hyperoxia induces S-phase cell-cycle arrest and p21(Cip1/Waf1)-independent Cdk2 inhibition in human carcinoma T47D-H3 cells

Little is known about cell-cycle checkpoint activation by oxidative stress in mammalian cells. The effects of hyperoxia on cell-cycle progression were investigated in asynchronous human T47D-H3 cells, which contain mutated p53 and fail to arrest at G1/S in response to DNA damage. Hyperoxic exposure (95% O(2), 40-64 h) induced an S-phase arrest associated with acute inhibition of Cdk2 activity and DNA synthesis. In contrast, exit from G2/M was not inhibited in these cells. After 40 h of hyperoxia, these effects were partially reversible during recovery under normoxic conditions. The inhibition of Cdk2 activity was not due to degradation of Cdk2, cyclin E or A, nor impairment of Cdk2 complex formation with cyclin A or E and p21(Cip1). The loss of Cdk2 activity occurred in the absence of induction and recruitment of cdk inhibitor p21(Cip1) or p27(Kip1) in cyclin A/Cdk2 or cyclin E/Cdk2 complexes. In contrast, Cdk2 inhibition was associated with increased Cdk2-Tyr15 phosphorylation, increased E2F-1 recruitment, and decreased PCNA contents in Cdk2 complexes. The latter results indicate a p21(Cip1)/p27(Kip1)-independent mechanism of S-phase checkpoint activation in the hyperoxic T47D cell model investigated.

Cloning and expression of guinea pig TIMP-2. Expression in normal and hyperoxic lung injury

Tissue inhibitors of metalloproteinases (TIMPs) play a key regulatory role in extracellular matrix remodeling. By screening a lung library with a human TIMP-2 cDNA probe, we have isolated the cDNA corresponding to guinea pig TIMP-2. The 3.5-kb cDNA presents an open reading frame that predicts a protein of 220 amino acids showing 97.2, 96.8, 97.2, and 77.3% overall identity with human, mouse, rat, and chicken TIMP-2, respectively. Guinea pig TIMP-2 cDNA was expressed in CHO-K1 cells, showing a protein with the expected molecular weight and activity. Northern blot analysis revealed TIMP-2 expression in brain, kidney, intestine, spleen, heart, and lung. Transforming growth factor-beta downregulated TIMP-2 mRNA in guinea pig lung fibroblasts, whereas a variety of other stimuli showed no effect. In normal and hyperoxia-exposed lungs, TIMP-2 mRNA was mainly localized in alveolar macrophages and epithelial cells. No quantitative differences were found by Northern blot. These results confirm that TIMP-2 is highly conserved in mammals and largely expressed in lungs.

Early-onset inflammatory responses in vivo to adenoviral vectors in the presence or absence of lipopolysaccharide-induced inflammation

Adenoviral vectors (Ad) have potential for use in pulmonary gene transfer for treating cystic fibrosis (CF). However, Ad may induce inflammation even in the absence of gene expression. Endotoxin from gram-negative bacteria in the airways of CF patients may also induce inflammation, and may further inhibit vector delivery and gene transfer. We used a mouse model to study the time course of Ad-induced lung inflammation and to assess additivity with lipopolysaccharide (LPS)-induced inflammatory responses. C3H/HeJ endotoxin-resistant (RES) mice hyporesponsive to inflammatory stimuli and normoresponsive C3HeB/FeJ endotoxin-sensitive (SEN) mice were studied to characterize inflammatory responses that follow intratracheal instillation of inactivated Ad, with or without simultaneous inhalation exposure to LPS. Instillation of 10(10) Ad particles dramatically increased bronchoalveolar lavage fluid (BALF) concentrations of tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 at 3 to 6 h and induced profound neutrophilia, maximal at 12 to 24 h. SEN mice had tenfold greater responses than did RES mice at 6, 12, and 24 h. Mice exposed to Ad alone, LPS alone, or Ad + LPS had significant inflammation at the 3-h time point as demonstrated by BALF neutrophils, TNF-alpha, and IL-6. With all three treatments, SEN mice had a five- to 300-fold greater response than did RES mice. Importantly, Ad + LPS yielded no greater inflammatory response than LPS without Ad. These data demonstrate that replication-deficient Ad induce early inflammation and LPS-induced inflammation is not augmented by concurrent treatment with Ad.

Defects in tracheoesophageal and lung morphogenesis in Nkx2.1(-/-) mouse embryos

NKX2.1 is a homeodomain transcriptional factor expressed in thyroid, lung, and parts of the brain. We demonstrate that septation of the anterior foregut along the dorsoventral axis, into distinct tracheal and esophageal structures, is blocked in mouse embryos carrying a homozygous targeted disruption of the Nkx2.1 locus. This is consistent with the loss of Nkx2.1 expression, which defines the dorsoventral boundary within the anterior foregut in wild-type E9 embryos. Failure in septation between the trachea and the esophagus in Nkx2.1(-/-) mice leads to the formation of a common lumen that connects the pharynx to the stomach, serving both as trachea and as esophagus, similar in phenotype to a human pathologic condition termed tracheoesophageal fistula. The main-stem bronchi bifurcate from this common structure and connect to profoundly hypoplastic lungs. The mutant lungs fail to undergo normal branching embryogenesis, consist of highly dilated sacs that are not capable of sustaining normal gas exchange functions, and lead to immediate postnatal death. In situ hybridization suggests reduced Bmp-4 expression in the mutant lung epithelium, providing a possible mechanistic clue for impaired branching. Functional deletion of Nkx2. 1 blocks pulmonary-specific epithelial cell differentiation marked by the absence of pulmonary surfactant protein gene expression. Altered expression of temporally regulated genes such as Vegf demonstrates that the lung in Nkx2.1(-/-) mutant embryos is arrested at early pseudoglandular (E11-E15) stage. These results demonstrate a critical role for Nkx2.1 in morphogenesis of the anterior foregut and the lung as well as in differentiation of pulmonary epithelial cells.

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.

Oxygen toxicity in mouse lung: pathways to cell death

Mice exposed to 100% O2 die after 3 or 4 d with diffuse alveolar damage and alveolar edema. Extensive cell death is evident by electron microscopy in the alveolar septa, affecting both endothelial and epithelial cells. The damaged cells show features of both apoptosis (condensation and margination of chromatin) and necrosis (disruption of the plasma membrane). The electrophoretic pattern of lung DNA indicates both internucleosomal fragmentation, characteristic of apoptosis, and overall degradation, characteristic of necrosis. Hyperoxia induces a marked increase in RNA or protein levels of p53, bax, bcl-x, and Fas, which are known to be expressed in certain types of apoptosis. However, we did not detect an increased activity of proteases belonging to the apoptosis "executioner" machinery, such as CPP32 (caspase 3), ICE (caspase 1), or cathepsin D. Furthermore, administration of an ICE-like protease inhibitor did not significantly enhance the resistance to oxygen. Additionally, neither p53-deficient mice nor lpr mice (Fas null) manifested an increased resistance to hyperoxia-induced lung damage. These results show that both necrosis and apoptosis contribute to cell death during hyperoxia. Multiple apoptotic pathways seem to be involved in this, and an antiapoptotic strategy does not attenuate alveolar damage.

Gelatinases A and B are up-regulated in rat lungs by subacute hyperoxia: pathogenetic implications

Subacute hyperoxia may cause basement membrane disruption and subsequent fibrosis. To test the role of extracellular matrix degradation in hyperoxic damage, we analyzed the expression of gelatinases A and B and tissue inhibitors of metalloproteinases (TIMP)-1 and TIMP-2 in rats exposed to 85% O2. Oxygen-exposed rats were studied at 1, 3, 5, and 7 days, and compared with air-breathing rats. Lung mRNAs assayed by Northern and in situ hybridization showed an up-regulation of lung gelatinases A and B from the 3rd day on. Gelatinase A was localized in alveolar macrophages and in interstitial and alveolar epithelial cells. Gelatinase B mRNA and protein were localized in macrophages and bronchiolar and alveolar epithelial cells. Increased gelatinase A and B activities were demonstrated in bronchoalveolar lavage. TIMP-1 and TIMP-2 were constitutively expressed, and only TIMP-1 displayed a moderate increase with hyperoxia. To elucidate transcriptional mechanisms for increased gelatinase B expression after hyperoxia, nuclear transcription factor-kappabeta activation was explored. Oxidative stress significantly increased the lung expression of nuclear transcription factor-kappabeta (p65) protein, and nuclear transcription factor-kappabeta activation and increased levels of gelatinases A and B were found in isolated type II alveolar cells obtained from hyperoxic rats. Conceivably, subacute hyperoxia induces excessive gelatinase activity, which may contribute to lung damage.

Clara cell secretory protein deficiency increases oxidant stress response in conducting airways

Little is known about the molecular basis for differential pulmonary oxidant sensitivity observed between genetically disparate members of the same species. We have generated mice that are deficient in Clara cell secretory protein (CCSP -/-) and that exhibit an oxidant-sensitive phenotype. We characterized the kinetics and distribution of altered stress-response [interleukin-6 (IL-6) and metallothionein (MT)] and epithelial cell-specific [cytochrome P-450 2F2 (CYP2F2)] gene expression to further understand the cellular and molecular basis for altered oxidant sensitivity in 129 strain CCSP -/- mice. Increases in IL-6 and MT mRNA abundance were detected by 2 h of exposure to 1 part/million ozone and preceded reductions in Clara cell CYP2F2 mRNA expression. Despite being qualitatively similar, increases in IL-6 and MT mRNA expression were enhanced in CCSP -/- mice with respect to coexposed 129 strain wild-type mice. Increased MT mRNA expression, indicative of the stress response, localized to the airway epithelium, surrounding mesenchyme, and endothelium of blood vessels. These results demonstrate a protective role for Clara cells and their secretions and indicate potential genetic mechanisms that may influence susceptibility to oxidant stress.

Interleukin-1 expression during hyperoxic lung injury in the mouse

An important component of the pathophysiologic response to hyperoxia (O2) is pulmonary inflammation, although the roles of specific inflammatory mediators during pulmonary O2 toxicity are not completely known. Interleukin-1 (IL-1) is an early inflammatory mediator and is sufficient to elicit many of the responses associated with acute injury. The IL-1 family comprises two bioactive proteins, IL-1alpha and IL-1beta, and their natural antagonist IL-1ra. Here we report studies of IL-1 regulation during hyperoxic lung injury in the adult mouse. When assayed by Northern blot, increases in IL-1beta mRNA were seen after 2 days of hyperoxia. In contrast, IL-1alpha mRNA was barely detectable before 4 days of hyperoxia. To further understand the cellular origin of IL-1beta expression in lungs, in situ hybridization and immunohistochemical analyses were performed. IL-1beta mRNA or protein was not detected in the lungs of unexposed animals. At 3 days, we observed the accumulation of IL-1beta transcripts in pulmonary interstitial macrophages and in a subset of neutrophils, and immunodetectable IL-1beta protein was co-localized in adjacent sections. At 4 days of exposure, IL-1beta transcripts were widespread in lung tissue, but many areas rich in IL-1beta mRNA were devoid of immunodetectable IL-1beta. However, it is not known whether increased synthesis of IL-1beta or the uncoupling of IL-1beta protein and mRNA accumulation has a role in pathophysiology of pulmonary O2 toxicity.

Inflammatory and epithelial responses in mouse strains that differ in sensitivity to hyperoxic injury

The pulmonary response to various toxicants including bleomycin, ozone, ionizing radiation, and hyperoxia is highly variable among mouse strains. The current study tests the hypothesis that at a similar stage of injury, regardless of strain, expression of inflammatory cytokine and epithelial marker genes would be similar, indicating a common pathway of injury progression. Three strains of mice, C57B1/6J, 129/J, and C3H/HeJ, ranging from sensitive to resistant, were exposed to > 95% O2 for varying times. Ribonuclease protection was used to quantify changes in cytokine mRNA. Despite differences in the kinetics, each strain demonstrated similar hyperoxia-induced changes in the abundance of interleukin (IL)-6, IL-1 beta, IL-3, and tumor neucrosis factor (TNF)-alpha. For each strain, death was accompanied by similar increases in cytokine mRNAs above steady-state control levels. Other inflammatory cytokines, including IL-1 alpha, IL-4, and interferon (IFN)-gamma, were unaltered in all strains at all times. In situ hybridization analysis of the epithelial markers, surfactant protein B (SPB), and clara cell secretory protein (CCSP) at the time of proinflammatory induction showed a similar pattern of expression in all strains. Increased SPB was detected in bronchiolar epithelium, while the number of type II cells expressing this message declined. Both the number of cells expressing CCSP as well as abundance per cell declined. These results suggest that although differences in acute sensitivity to hyperoxia exist between mouse strains, once initiated, acute epithelial cell injury and associated inflammatory changes follow the same pattern in all strains.

The plug-unplug sequence: an important step to achieve type II pneumocyte maturation in the fetal lamb model

PURPOSE

The purpose of this study was to test the hypothesis that tracheal obstruction (plugging) in the fetal lamb model leads to a decrease in the absolute number of type II pneumocytes and that reversing the obstruction before birth (unplugging), allows the type II cells to recover while maintaining the beneficial effect on lung growth.

METHODS

Nine time-dated pregnant ewes (term, 145 days), carrying 17 fetuses, were used in this surgical trial. The fetuses were divided into three experimental groups: group A underwent plugging at 93 days gestation, followed by unplugging at 110 days; group B animals had tracheal ligation at 93 days and group C consisted of unoperated controls. All fetuses were delivered by cesarean section at 136 days' gestation. The fetal trachea was obstructed with the tracheoscopically placed detachable balloon described by our group. Unplugging was performed by needle puncture of the balloon under tracheoscopic vision. Outcome measurements consisted of lung-to-body-weight ratio (LWBR), lung morphometry (mean terminal bronchial density [MTBD] and linear intercept [Lm]), and assessment of the number of type II pneumocytes. The latter was determined by in situ hybridization to the mRNA of surfactant protein-C, which is exclusively produced by type II cells. Statistics were calculated using a two-tailed unpaired t test and P less than .05 is considered significant.

RESULTS

Seventeen animals are included in the results. All of them had lung samples analyzed for lung morphometry, whereas for type II cells analysis, three animals were studied in each group. Morphometric analyses were consistent with pulmonary hyperplasia for group B, whereas group A lungs showed more histological maturity than group C albeit not as marked as group B. In group A, there was a similar number of type II cells to that observed in group C (53.2 +/- 3.9 v 55.9 +/- 4.0, P = .66). However, for group B animals, the number of type II pneumocytes was markedly decreased compared with controls (4.7 +/- 0.1 v 55.9 +/- 4, P = .0003).

CONCLUSIONS

The authors conclude that tracheal ligation until birth, although inducing pulmonary hyperplasia, significantly decreases the number of type II pneumocytes in the alveoli. After a temporary 15-day occlusion initiated at 95 days' gestation, there is complete normalization of the density of type II cells. These results bear importance on the duration of PLUG to treat the pulmonary hypoplasia seen in congenital diaphragmatic hernia. Temporary tracheal obstruction now needs to be tested in a hypoplastic lung model.

Overexpression of metallothionein decreases sensitivity of pulmonary endothelial cells to oxidant injury

Metallothionein (MT) is a low-molecular-weight cysteine-rich protein with extensive metal binding capacity and potential nonenzymatic antioxidant activity. Despite the sensitivity of vascular endothelium to either heavy metal toxicity or oxidative stress, little is known regarding the role of MT in endothelial cells. Accordingly, we determined the sensitivity of cultured sheep pulmonary artery endothelial cells (SPAEC) that overexpressed MT to tert-butyl hydroperoxide (t-BOOH), hyperoxia, or 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN; peroxyl radical generator). Nontoxic doses of 10 microM Cd increased MT levels from 0.21 +/- 0.03 to 2.07 +/- 0.24 microg/mg and resulted in resistance to t-BOOH and hyperoxia as determined by reduction of Alamar blue or [3H]serotonin transport, respectively. SPAEC stably transfected with plasmids containing either mouse or human cDNA for MT were resistant to both t-BOOH and hyperoxia. In addition, we examined transition metal-independent, noncytotoxic AMVN-induced lipid peroxidation after metabolic incorporation of the oxidant-sensitive fluorescent fatty acid cis-parinaric acid into phospholipids and high-performance liquid chromatography separation. SPAEC that overexpressed MT after gene transfer completely inhibited peroxyl oxidation of phosphatidylserine, phosphatidylcholine, and sphingomyelin (but not phosphatidylethanolamine) noted in wild-type SPAEC. These data show for the first time that MT can 1) protect pulmonary artery endothelium against a diverse array of prooxidant stimuli and 2) directly intercept peroxyl radicals in a metal-independent fashion, thereby preventing lipid peroxidation in intact cells.

Altered pulmonary response to hyperoxia in Clara cell secretory protein deficient mice

Clara cell secretory protein (CCSP) is an abundant component of the extracellular lining fluid of airways. Even though the in vivo function of CCSP is unknown, in vitro studies support a potential role of CCSP in the control of inflammatory responses. CCSP-deficient mice (CCSP -/-) were generated to investigate the in vivo function of this protein (13). In this study, we used hyperoxia exposure as a model to investigate phenotypic consequences of CCSP deficiency following acute lung injury. The pathologic response of the mouse lung to hyperoxia, and recovery of the lung, include inflammatory cell infiltrate and edema. Continuous exposure to > 95% O2 was associated with significantly reduced survival time among CCSP -/- mice as compared with strain-, age-, and sex-matched wild-type control mice. Differences in survival were associated with early onset of lung edema in CCSP -/- mice as compared with wild-type controls. To further investigate these differences in response, mice were exposed to > 95% O2 for either 48 h or 68 h with one group receiving 68 h of hyperoxia followed by room-air recovery. Lung RNA was characterized for changes in the abundance of cytokine messenger RNA (mRNA) using a ribonuclease (RNase) protection assay. After 68 h of hyperoxia, interleukin-6 (IL-6), IL-1beta, and IL-3 mRNAs were 14-, 3-, and 2.5-fold higher, respectively, in CCSP -/- mice than in similarly exposed wild-type control mice. Increased expression of IL-1beta mRNA in hyperoxia-exposed CCSP -/- mice was localized principally within the lung parenchyma, suggesting that the effects of CCSP deficiency were not confined to the airway epithelium. We conclude that CCSP deficiency results in increased sensitivity to hyperoxia-induced lung injury as measured by increased mortality, early onset of lung edema, and induction of proinflammatory cytokine mRNAs.

The effects of tracheal occlusion and release on type II pneumocytes in fetal lambs

Fetal tracheal occlusion (TO) has been shown to lead to lung hyperplasia in various animal models, and this procedure has already been carried out in human fetuses with congenital diaphragmatic hernia (CDH). However, the authors previously showed that TO caused a decrease in type II pneumocytes.

PURPOSE

The aim of this study is to examine the effects of TO and release on type II pneumocytes.

METHOD

To was carried out with a Swan Ganz or Fogarty catheter in fetal sheep at 116 to 118 days of gestation. TO was maintained for 2 weeks followed by deflation of the balloon for 1 week before delivery, in group 1; in group 2, TO was maintained for 19 days and released 2 days before delivery. Group 3 consisted of previously reported animals who had TO maintained until birth. Unoperated twins served as controls. All specimens were analyzed using the surfactant protein C (SP-C) mRNA as a specific marker for type II pneumocytes. We used Northern Blot and in situ hybridization techniques to quantify total SP-C and the density of type II cells. Electron microscopy (EM) was also used to evaluate and quantitate type II cells.

RESULTS

TO resulted in significant lung growth in all groups. In situ hybridization and Northern Blot analysis showed that there was a complete recovery of type II cells in group 1 versus controls. Quantitative EM analysis confirmed these findings. In group 2 the number of type II cells was decreased but there was an increase in SP-C content per type II cell versus group 3.

CONCLUSION

Lung growth after TO appears to occur at the expense of type II cell differentiation. This effect is reversible with the release of TO before birth in this animal model.

Deleterious effect of tracheal obstruction on type II pneumocytes in fetal sheep

It was previously shown that tracheal obstruction accelerated fetal lung growth and eventually reversed the pulmonary hypoplasia in experimental diaphragmatic hernia. We have successfully developed a reversible tracheal obstruction technique in fetal sheep using balloon occlusion and showed that 3 wk of obstruction induced significant lung growth of the same magnitude as the tracheal ligation. The purpose of this study was to examine the effects of 1 and 3 wk of tracheal occlusion on the alveolar cell population with specific attention to the type II pneumocytes. We first showed that 1 wk of occlusion induced a significant increase in lung weight and in alveolar surface area. We then used the surfactant protein C (SP-C) mRNA as a specific marker of differentiated type II pneumocytes. Total RNA was isolated from fetal sheep lung with or without tracheal occlusion, and Northern blots were hybridized with a cDNA probe specific for the sheep SP-C. The results show a dramatic decrease in SP-C mRNA expression (8.8-fold, p < 0.01). In situ hybridization showed a marked decrease in the density of cells expressing SP-C, as well as the amount of SP-C mRNA expressed by the cells. The effect was present as early as 1 wk of occlusion. The sparseness of type II pneumocytes was further confirmed by electron microscopy. We thus conclude that tracheal obstruction causes a profound decrease in the number of type II pneumocytes in the lungs. Given the crucial role of type II pneumocytes in surfactant production, we could speculate that, if tracheal occlusion is able to accelerate lung growth, the final product is probably surfactant-deficient.

Cellular oxygen toxicity. Oxidant injury without apoptosis

All forms of aerobic life are faced with the threat of oxidation from molecular oxygen (O2) and have evolved antioxidant defenses to cope with this potential problem. However, cellular antioxidants can become overwhelmed by oxidative insults, including supraphysiologic concentrations of O2 (hyperoxia). Oxidative cell injury involves the modification of cellular macromolecules by reactive oxygen intermediates (ROI), often leading to cell death. O2 therapy, which is a widely used component of life-saving intensive care, can cause lung injury. It is generally thought that hyperoxia injures cells by virtue of the accumulation of toxic levels of ROI, including H2O2 and the superoxide anion (O2-), which are not adequately scavenged by endogenous antioxidant defenses. These oxidants are cytotoxic and have been shown to kill cells via apoptosis, or programmed cell death. If hyperoxia-induced cell death is a result of increased ROI, then O2 toxicity should kill cells via apoptosis. We studied cultured epithelial cells in 95% O2 and assayed apoptosis using a DNA-binding fluorescent dye, in situ end-labeling of DNA, and electron microscopy. Using all approaches we found that hyperoxia kills cells via necrosis, not apoptosis. In contrast, lethal concentrations of either H2O2 or O2- cause apoptosis. Paradoxically, apoptosis is a prominent event in the lungs of animals injured by breathing 100% O2. These data indicate that O2 toxicity is somewhat distinct from other forms of oxidative injury and suggest that apoptosis in vivo is not a direct effect of O2.

P-selectin is upregulated early in the course of hyperoxic lung injury in mice

While treatment with supplemental oxygen is often essential in patients with lung disease, prolonged therapy may cause lung injury by itself. Although the mechanisms responsible for initiating hyperoxic lung damage almost certainly involve primary oxidative transformations, the possible contributions of inflammation to the tissue injury have been attracting increasing research activity. Increases in intercellular adhesion molecule-1 (ICAM-1) coincide with the inflammation, but in other models of inflammation transient adhesion mediated by members of the Selectin gene family was found to be essential before ICAM-1/beta 2 interactions could occur. We, therefore, wondered whether a similar sequence of initial transient adhesion followed by subsequent responses would be observed in hyperoxic lung inflammation. We, therefore, determined the effects of hyperoxia exposure on lung mRNA for P- and E-Selectin in mouse lungs. We found that there was no detectable mRNA for E-Selectin through 72 h of hyperoxia exposure by Northern blotting, but that mRNA for P-Selectin was detectable as early as 48 h after initiation of hyperoxia. To determine the location of P-Selectin upregulation we examined hyperoxia-exposed mouse lungs by in situ hybridization and found that the upregulation of P-Selectin at 48 h was localized to large muscularized vessels, at 72 h expression was detected in some medium size muscularized vessels, and at 96 h abundant expression was observed also on nonmuscularized small vessels. In conclusion, increases in mRNA for P-Selectin early in the course of hyperoxia exposure suggest that P-Selectin expression in hyperoxic lungs increases in parallel with upregulation of ICAM-1, leading to the accumulation of neutrophils in hyperoxic lungs, and that interventions targeting these two adhesion molecules may lead to a diminution in hyperoxic lung inflammation and lung injury.