Pulmonary injury after combined exposures to low-dose low-LET radiation and fungal spores

Exposure to infectious microbes is a likely confounder after a nuclear terrorism event. In combination with radiation, morbidity and mortality from an infection may increase significantly. Pulmonary damage after low-dose low-LET irradiation is characterized by an initial diffuse alveolar inflammation. By contrast, inhaled fungal spores produce localized damage around pulmonary bronchioles. In the present study, we assessed lung injury in C57BL/6 mice after combined exposures to whole-body X radiation and inhaled fungal spores. Either animals were exposed to Aspergillus spores and immediately irradiated with 2 Gy, or the inoculation and irradiation were separated by 8 weeks. Pulmonary injury was assessed at 24 and 48 h and 1, 2, 4, 8, and 24 weeks later using standard H&E-stained sections and compared with sham-treated age-matched controls. Immunohistochemistry for invasive inflammatory cells (macrophages, neutrophils and B and T lymphocytes) was performed. A semi-quantitative assessment of pulmonary injury was made using three distinct parameters: local infiltration of inflammatory cells, diffuse inflammation, and thickening and distortion of alveolar architecture. Radiation-induced changes in lung architecture were most evident during the first 2 weeks postexposure. Fungal changes were seen over the first 4 weeks. Simultaneous combined exposures significantly increased the duration of acute pulmonary damage up to 24 weeks (P < 0.01). In contrast, administration of the fungus 8 weeks after irradiation did not produce enhanced levels of acute pulmonary damage. These data imply that the inhalation of fungal spores at the time of a radiation exposure alters the susceptibility of the lungs to radiation-induced injury.

Pulmonary inflammatory response to inhaled ultrafine particles is modified by age, ozone exposure, and bacterial toxin

Epidemiological studies demonstrate associations between increasing levels of ambient particles and morbidity in the elderly with cardiopulmonary disease. Such findings have been challenged partly because particles may not act alone to cause these effects. We hypothesized that carbonaceous ambient ultrafine particles and ozone can act together to induce greater oxidative stress and inflammation in the lung than when administered alone and that these effects would be amplified in the compromised, aging lung. Two models of a compromised lung were used: endotoxin priming and old-age emphysema (TSK mice). Young (10 wk) and old (22 mo) male F344 rats and male TSK mice (14-17 mo) were exposed to ultrafine carbon particles (count median diameter 25 nm, 110 micrograms/m3) and to ozone (1 ppm) alone and in combination for 6 h. Inhalation of low-dose endotoxin (70 and 7.5 units estimated alveolar deposited dose in rats and mice, respectively) was used to model respiratory-tract infection. Cellular and biochemical lavage parameters and oxidant release from lung lavage cells were assessed 24 h after exposure. Inflammatory cell influx into the alveolar space was observed for both species and age groups: The combination of inhaled ultrafine carbon and ozone after endotoxin priming resulted in the greatest increase in lavage-fluid neutrophils. In general, the unstimulated and stimulated release of reactive oxygen species (ROS) from lavage inflammatory cells correlated well with the neutrophil response. There were significant effects of carbon particles as well as a consistent interaction between carbon and ozone as determined by analysis of variance (ANOVA). However, this interaction was in the opposite direction in young rats versus old rats and old TSK mice: Carbon and ozone interacted such that ROS activity was depressed in young rats, whereas it was enhanced in old rats and old TSK mice, indicating age-dependent functional differences in elicited pulmonary inflammatory cells. These results demonstrate that ultrafine carbonaceous particles inhaled for short periods of time can induce significant pulmonary inflammation and oxidative stress that are modified by age, copollutants, and a compromised respiratory tract.

Recovery from oxidant-mediated lung injury: response of metallothionein, MIP-2, and MCP-1 to nitrogen dioxide, oxygen, and ozone exposures

Oxidant-induced lung injury is believed to be mediated by reactive oxygen species. Recovery from oxidant exposure has been associated with pulmonary inflammation. Inflammatory cell accumulation involves the synthesis of chemokines, including neutrophil chemoattractants such as macrophage inflammatory protein-2 (MIP-2) and monocyte chemoattractants such as monocyte chemoattractant protein-1 (MCP-1). Antioxidants are the first line of defense of lung cells against inhaled oxidants. Metallothionein (MT) can act as an antioxidant and free-radical scavenger. To better understand the pulmonary response associated with recovery from oxidant-mediated injury, we exposed mice to either 15 ppm nitrogen dioxide for 24 h, >99% oxygen for 72 h, or 1 ppm ozone for 24 h. Mice were examined at the end of exposure or after recovering in room air for 4 or 24 h. Neutrophils were elevated at the end of exposure and remained elevated through the postexposure period, whereas macrophage numbers were decreased at the end of exposure and remained below control levels at 4 and 24 h postexposure. MT, MIP-2, and MCP-1 mRNA levels were elevated at 4 h postexposure; however, after 24 h of recovery only MCP-1 remained elevated. These results indicate that MT, MIP-2, and MCP-1 mRNA levels responded similarly to recovery from nitrogen dioxide, oxygen, and ozone exposure. Monocyte accumulation was delayed as compared to neutrophils and was consistent with the timing of MIP-2 and MCP-1 expression. Peak expression of MT and MIP-2 preceded peak neutrophil accumulation. Consequently, the timing of MT, MIP-2, and MCP-1 expression may be important biological markers in assessing the state of injury and recovery associated with oxidant-mediated injury.

The cyclin-dependent kinase inhibitor p21 protects the lung from oxidative stress

The lung is a major target tissue for oxidative stress, including hyperoxia used to relieve tissue hypoxia. Unfortunately, severe hyperoxia damages DNA, inhibits proliferation, and kills cells, resulting in morbidity and mortality. Although hyperoxia induces the tumor suppressor p53 and its downstream target, the cyclin-dependent kinase inhibitor p21(Cip1/WAF1/Sdi1) (p21), their role in pulmonary injury remains unknown. Using p53- and p21-deficient mice we demonstrate that hyperoxia induces p21 in the absence of p53, suggesting that previous conclusions that p53 does not modify hyperoxic lung injury cannot be extrapolated to p21. In fact, mean survival of p21-deficient mice decreased by 40% and was associated with terminal deoxyribonucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labeling staining of alveolar debris, indicative of DNA fragmentation and cell death. Ultrastructural analyses revealed that alveolar endothelial and type I epithelial cells died rapidly by necrosis. Although hyperoxia decreased DNA replication in p21-wild-type lungs, it had no effect on replication in p21-deficient lungs. Our findings suggest that p21 protects the lung from oxidative stress, in part, by inhibiting DNA replication and thereby allowing additional time to repair damaged DNA. Our findings have implications for patients suffering from the toxic effects of supplemental oxygen therapies.

Pulmonary effects induced by ultrafine PTFE particles

PTFE (polytetrafluoroethylene) fumes consisting of large numbers of ultrafine (uf) particles and low concentrations of gas-phase compounds can cause severe acute lung injury. Our studies were designed to test three hypotheses: (i) uf PTFE fume particles are causally involved in the induction of acute lung injury, (ii) uf PTFE elicit greater pulmonary effects than larger sized PTFE accumulation mode particles, and (iii) preexposure to the uf PTFE fume particles will induce tolerance. We used uf Teflon (PTFE) fumes (count median particle size approximately 16 nm) generated by heating PTFE in a tube furnace to 486 degrees C to evaluate principles of ultrafine particle toxicity. Teflon fumes at ultrafine particle concentrations of 50 microg/m(3) were extremely toxic to rats when inhaled for only 15 min. We found that when generated in argon, the ultrafine Teflon particles alone are not toxic at these exposure conditions; neither were Teflon fume gas-phase constituents when generated in air. Only the combination of both phases when generated in air caused high toxicity, suggesting either the existence of radicals on the surface or a carrier mechanism of the ultrafine particles for adsorbed gas compounds. Aging of the fresh Teflon fumes for 3.5 min led to a predicted coagulation to >100 nm particles which no longer caused toxicity in exposed animals. This result is consistent with a greater toxicity of ultrafine particles compared to accumulation mode particles, although changes in particle surface chemistry during the aging process may have contributed to the diminished toxicity. Furthermore, the pulmonary toxicity of the ultrafine Teflon fumes could be prevented by adapting the animals with short 5-min exposures on 3 days prior to a 15-min exposure. Messages encoding antioxidants and chemokines were increased substantially in nonadapted animals, yet were unaltered in adapted animals. This study shows the importance of preexposure history for the susceptibility to acute ultrafine particle effects.

Ozone, but not nitrogen dioxide, exposure decreases glutathione peroxidases in epithelial lining fluid of human lung

Antioxidants, such as glutathione peroxidases (GPxs), in epithelial lining fluid (ELF) protect against health effects of oxidant pollutants, which includes O(3) or NO(2). We hypothesized that GPxs concentration in ELF is responsive to O(3) or NO(2) exposure. Subjects underwent two 4-h exposures to O(3) (0.22 ppm) and one to air. In another experiment, subjects underwent 3-h exposures to air and NO(2) (0.6 and 1.5 ppm). Bronchoalveolar lavage (BAL) was performed immediately or 18 h after O(3) exposure and 3.5 h after each NO(2) exposure. GPx activity and extracellular GPx (eGPx) protein concentrations were determined in ELF, and their relationships to markers of lung function, inflammation, and epithelial permeability were examined. Although the total amounts were not changed, basal (air) GPx activity (223.6 +/- 24.4 mU/ml), basal eGPx protein concentration (2.62 +/- 0.25 microg/ml), and basal ELF dilution factor (152.3 +/- 8.4) decreased 40% immediately after O(3) exposure and remained 30% decreased 18 h after exposure (p = 0.0001). No effect of NO(2) exposure on GPxs concentration was detected. There was an inverse correlation between baseline ELF eGPx protein concentration and the change in PMN 18 h after O(3) exposure (p = 0.04). Thus, O(3), a strong oxidant, decreases both GPx activity and eGPx protein in ELF, whereas NO(2), a weaker oxidant, does not. eGPx in ELF may protect against O(3)-induced airway inflammation.

Oxygen regulation of gene expression: a study in opposites

Oxygen is crucial to aerobic metabolism, but excesses of oxygen or reactive oxygen species (ROS) can injure cells. This minireview addresses two transcription factors that regulate several cellular responses to oxygen tension. Hypoxia inducible factor-1 (HIF-1) is a heterodimeric protein activated by hypoxia. Levels of HIF-1 are regulated by removal of the HIF-1alpha subunit through ubiquination and proteasomal destruction under normoxic conditions. Hypoxia inhibits the ubiquination of HIF-1alpha, preventing its destruction and allowing it to bind to hypoxia-responsive elements in gene promoter, enhancer, and intronic sequences. HIF-1 induces the expression of the hypoxia responsive genes vascular endothelial growth factor and erythropoietin. Its dysregulation has been implicated in von Hippel-Lindau disease. Nuclear factor kappaB (NFkappaB) is a family of pleotropic, dimeric transcription factors, and has a complex pattern of regulation. Under normoxic conditions, NFkappaB is bound to one of several inhibitory proteins (e.g., IkappaB) that prevent its nuclear translocation. Hyperoxia or elevations of ROS cause the ubiquination and destruction of the inhibitory proteins, freeing NFkappaB and allowing it to bind to target gene promoters. Hyperoxia in cell and animal models and acute lung injury in humans induce the expression of multiple proinflammatory cytokines through NFkappaB-dependent mechanisms. Although HIF-1 and NFkappaB respond to changes in pO(2), the precise nature of the oxygen sensing and transduction pathways is unclear in both cases. Both heme-protein and redox-sensitive mechanisms have been proposed. Improved understanding of oxygen-sensitive gene regulation may suggest targeted therapies for human disease.

Acute pulmonary effects of ultrafine particles in rats and mice

Ambient fine particles consist of ultrafine particles (< 100 nm) and accumulation-mode particles (approximately 100 to 1,000 nm). Our hypothesis that ultrafine particles can have adverse effects in humans is based on results of our earlier studies with particles of both sizes and on the finding that urban ultrafine particles can reach mass concentrations of 40 to 50 micrograms/m3, equivalent to number concentrations of 3 to 4 x 10(5) particles/cm3. The objectives of the exploratory studies reported here were to (1) evaluate pulmonary effects induced in rats and mice by ultrafine particles of known high toxicity (although not occurring in the ambient atmosphere) in order to obtain information on principles of ultrafine particle toxicology; (2) characterize the generation and coagulation behavior of ultrafine particles that are relevant for urban air; (3) study the influence of animals' age and disease status; and (4) evaluate copollutants as modifying factors. We used ultrafine Teflon (polytetrafluoroethylene [PTFE]*) fumes (count median diameter [CMD] approximately 18 nm) generated by heating Teflon in a tube furnace to 486 degrees C to evaluate principles of ultrafine particle toxicity that might be helpful in understanding potential effects of ambient ultrafine particles. Teflon fumes at ultrafine particle concentrations of approximately 50 micrograms/m3 are extremely toxic to rats when inhaled for only 15 minutes. We found that neither the ultrafine Teflon particles alone when generated in argon nor the Teflon fume gas-phase constituents when generated in air were toxic after 25 minutes of exposure. Only the combination of both phases when generated in air caused high toxicity, suggesting the existence of either radicals on the particle surface or a carrier mechanism of the ultrafine particles for adsorbed gas-phase compounds. We also found rapid translocation of the ultrafine Teflon particles across the epithelium after their deposition, which appears to be an important difference from the behavior of larger particles. Furthermore, the pulmonary toxicity of the ultrafine Teflon fumes could be prevented by adapting the animals with short 5-minute exposures on 3 days prior to a 15-minute exposure. This shows the importance of preexposure history in susceptibility to acute effects of ultrafine particles. Aging of the fresh Teflon fumes for 3.5 minutes led to a predicted coagulation resulting in particles greater than 100 nm that no longer caused toxicity in exposed animals. This result is consistent with greater toxicity of ultrafine particles compared with accumulation-mode particles. When establishing dose-response relationships for intratracheally instilled titanium dioxide (TiO2) particles of the size of the urban ultrafine particles (20 nm) and of the urban accumulation-mode particles (250 nm), we observed significantly greater pulmonary inflammatory response to ultrafine TiO2 in rats and mice. The greater toxicity of the ultrafine TiO2 particles correlated well with their greater surface area per mass. Ultrafine particles of carbon, platinum, iron, iron oxide, vanadium, and vanadium oxide were generated by electric spark discharge and characterized to obtain particles of environmental relevance for study. The CMD of the ultrafine carbon particles was approximately 26 nm, and that of the metal particles was 15 to 20 nm, with geometric standard deviations (GSDs) of 1.4 to 1.7. For ultrafine carbon particles, approximately 100 micrograms/m3 is equivalent to 12 x 10(6) particles/cm3. Homogeneous coagulation of these ultrafine particles in an animal exposure chamber occurred rapidly at 1 x 10(7) particles/cm3, so that particles quickly grew to sizes greater than 100 nm. Thus, controlled aging of ultrafine carbon particles allowed the generation of accumulation-mode carbon particles (due to coagulation growth) for use in comparative toxicity studies. We also developed a technique to generate ultrafine particles consisting of the stable isotope 13C by using 13C-graphite electrodes made in our laboratory from amorphous 13C powder. These particles are particularly useful tools for determining deposition efficiencies of ultrafine carbon particles in the respiratory tracts of laboratory animals and the translocation of particles to extrapulmonary sites. For compromised animals, we used acute and chronic pulmonary emphysema; a low-dose endotoxin inhalation aimed at priming target cells in the lung was also developed. Other modifying factors were age and copollutant (ozone) exposure. Exposure concentrations of the generated ultrafine particles for acute rodent inhalation studies were selected on the basis of lung doses predicted to occur in people inhaling approximately 50 micrograms/m3 urban ultrafine particles. Concentrations that achieved the same predicted lung burden per unit alveolar surface were used in rodents. (ABSTRACT TRUNCATED)

Pulmonary chemokine and mutagenic responses in rats after subchronic inhalation of amorphous and crystalline silica

Chronic inhalation of crystalline silica can produce lung tumors in rats whereas this has not been shown for amorphous silica. At present the mechanisms underlying this rat lung tumor response are unknown, although a significant role for chronic inflammation and cell proliferation has been postulated. To examine the processes that may contribute to the development of rat lung tumors after silica exposure, we characterized the effects of subchronic inhalation of amorphous and crystalline silica in rats. Rats were exposed for 6 h/day, on 5 days/week, for up to 13 weeks to 3 mg/m(3) crystalline or 50 mg/m(3) amorphous silica. The effects on the lung were characterized after 6.5 and 13 weeks of exposure as well as after 3 and 8 months of recovery. Exposure concentrations were selected to induce high pulmonary inflammatory-cell responses by both compounds. Endpoints characterized after silica exposure included mutation in the HPRT gene of isolated alveolar cells in an ex vivo assay, changes in bronchoalveolar lavage fluid markers of cellular and biochemical lung injury and inflammation, expression of mRNA for the chemokine MIP-2, and detection of oxidative DNA damage. Lung burdens of silica were also determined. After 13 weeks of exposure, lavage neutrophils were increased from 0.26% (controls) to 47 and 55% of total lavaged cells for crystalline and amorphous silica, with significantly greater lavage neutrophil numbers after amorphous silica (9.3 x 10(7) PMNs) compared to crystalline silica (6.5 x 10(7) PMNs). Lung burdens were 819 and 882 microg for crystalline and amorphous silica, respectively. BAL fluid levels of LDH as an indicator of cytotoxicity were twice as high for amorphous silica compared to those of crystalline silica, at the end of exposure. All parameters remained increased for crystalline silica and decreased rapidly for amorphous silica in the 8-month recovery period. Increased MIP-2 expression was observed at the end of the exposure period for both amorphous and crystalline silica. After 8 months of recovery, those markers remained elevated in crystalline silica-exposed rats, whereas amorphous silica-exposed rats were not significantly different from controls. A significant increase in HPRT mutation frequency in alveolar epithelial cells was detected immediately after 13 weeks of exposure to crystalline, but not to amorphous silica. A significant increase in TUNEL staining was detected in macrophages and terminal bronchiolar epithelial cells of amorphous silica-exposed rats at the end of the exposure period; however, crystalline silica produced far less staining. The observation that genotoxic effects in alveolar epithelial cells occurred only after crystalline but not amorphous silica exposure, despite a high degree of inflammatory-cell response after subchronic exposure to both types of silica, suggests that in addition to an inflammatory response, particle biopersistence, solubility, and direct or indirect epithelial cell cytotoxicity may be key factors for the induction of either mutagenic events or target cell death.

Mechanical strain-induced proliferation and signaling in pulmonary epithelial H441 cells

Pulmonary epithelial cells are exposed to mechanical strain during physiological breathing and mechanical ventilation. Strain regulates pulmonary growth and development and is implicated in volutrauma-induced fibrosis. The mechanisms of strain-induced effects are not well understood. It was hypothesized that mechanical strain induces proliferation of pulmonary epithelial cells and that this is mediated by signals initiated within seconds of strain. To test this hypothesis, human pulmonary adenocarcinoma H441 cells were strained in vitro. Cyclic as well as tonic strain resulted in increased cellular proliferation. Western blot analysis of strained cells demonstrated three newly phosphorylated tyrosine residues within 30 s of strain. Phosphorylation of mitogen-activated protein kinases p42/44 increased, electrophoretic mobility shift assay demonstrated activation of transcription factor activating protein-1, and immunohistochemistry demonstrated increased phosphorylation of c-jun in response to strain. The tyrosine kinase inhibitor genistein blocked the strain-induced proliferation. We conclude that strain induces proliferation in pulmonary epithelial cells and that tyrosine kinase activity is necessary to signal the proliferative response to mechanical strain.

Antioxidant and inflammatory response after acute nitrogen dioxide and ozone exposures in C57Bl/6 mice

Ozone (O(3)) and nitrogen dioxide (NO(2)) are highly reactive and toxic oxidant pollutants. The objective of this study is to compare chemokine, cytokine, and antioxidant changes elicited by acute exposures of O(3) and NO(2) in a genetically sensitive mouse. Eight-week-old C57Bl/6J mice were exposed to 1 or 2.5 ppm ozone or 15 or 30 ppm NO(2) for 4 or 24 h. Changes in mRNA abundance in lung were assayed by slot blot and ribonuclease protection assay (RPA). Messages encoding metallothionein (Mt), heme oxygenase I (HO-I), and inducible nitric oxide synthase (iNOS) demonstrated increased message abundance after 4 and 24 h of exposure to either O(3) or NO(2). Furthermore, increases in message abundance were of a similar magnitude for O(3) and NO(2). Messages encoding eotaxin, macrophage inflammatory protein (MIP)-1alpha, and MIP-2 were elevated after 4 and 24 h of exposure to 1 ppm ozone. Interleukin-6 was elevated after 4 h of exposure to ozone. After 4 h of 2.5 ppm ozone exposure, increased mRNAs of eotaxin, MIP-1alpha, MIP-2, Mt, HO-I, and iNOS were elevated to a higher magnitude than were detected after 1 ppm ozone. Monocyte chemoattractant protein (MCP-1) was elevated following 15 ppm NO(2) exposure. After 4 h of 30 ppm NO(2) exposure, messages encoding eotaxin, MIP-1alpha, MIP-2, and MCP-1 were elevated to levels similar to those detected after ozone exposure. Our results demonstrate a similar antioxidant and chemokine response during both O(3) and NO(2) exposure. Induction of these messages is associated with the duration and concentration of exposure. These studies suggest that these gases exert toxic action through a similar mechanism.

Newborn mice differ from adult mice in chemokine and cytokine expression to ozone, but not to endotoxin

Neonatal animals of some mammalian species are more tolerant to several pulmonary oxidative stress-inducing toxicants than adults. Our initial studies during hyperoxic injury demonstrated a rapid chemokine and cytokine response early in the development of injury in newborn mice, whereas adult mice demonstrated little alteration in cytokine abundance until lethality was imminent. Our hypothesis is that altered response between newborn and adult mice is associated with differential cell injury, rather than alterations in the regulation of the inflammatory response. To test this hypothesis we utilized two distinct models of inducing pulmonary toxicity: ozone (O(3)), which causes epithelial cell injury, and endotoxin, which causes pulmonary inflammation independent of direct epithelial cell injury. C57Bl/6J mice (36 h or 8 wk old) were exposed to O(3) at 1 or 2.5 ppm for 4, 20, or 24 h or to a 10-min inhalation of 10 ng endotoxin per mouse (estimated deposited dose) and were examined 2, 6, or 24 h postexposure. Adult mice displayed increased sensitivity to O(3), as demonstrated by increased abundance of mRNAs encoding eotaxin, macrophage inflammatory protein (MIP)-1alpha, MIP-2, interleukin (IL)-6, and metallothionein (Mt). In newborn mice, only Mt was increased after 4 h of exposure. In contrast, newborn and adult mice responded similarly at 2 h post endotoxin exposure, inducing messages encoding tumor necrosis factor (TNF)-alpha, eotaxin, MIP-1alpha, MIP-1beta, MIP-2, interferon inducible protein (IP)-10, and monocyte chemoattractant protein (MCP)-1. Furthermore, interleukin-6 (IL-6) was increased in adults but not newborns. Similar chemokine and cytokine responses of newborn and adult mice in response to an agent not causing epithelial injury (endotoxin) suggest that altered inflammatory control observed between newborn and adult mice following O(3) exposure is secondary to epithelial cell injury.

Tumor necrosis factor-alpha-induced lung cell expression of antiapoptotic genes TRAF1 and cIAP2

Tumor necrosis factor (TNF) receptor (TNFR)-associated factors 1 and 2 (TRAF1 and TRAF2) and inhibitor of apoptosis proteins cIAP1 (MIHB) and cIAP2 (MIHC) were recently identified as proteins that associate with the TNF-alpha receptors TNFRI (p55) and TNFRII (p75) and inhibit TNF-alpha-induced programmed cell death or apoptosis. In the original reports, TRAF1 expression, unlike the ubiquitous TRAF2, was restricted to specific tissues in the lung, spleen, and testis. TNF-alpha is increased in the lung in many forms of pulmonary disease. In the current study, Western analysis, immunohistochemistry, and ribonuclease protection assays were used to determine whether TNF-alpha regulates the expression of these TNFR-associated proteins in lung cells. We demonstrate for the first time TNF-alpha dose-dependent induction of TRAF1 protein and messenger RNA (mRNA) in human H441 and A549 pulmonary adenocarcinoma cell lines, as well as in lung cells of C57BL/6J mice after intratracheal administration of TNF-alpha. In contrast to the epithelial cells, TRAF1 was not induced by TNF-alpha in U937 cells, a human monocytic cell line, suggesting cell type-specific regulation. Similarly, cIAP2 mRNA was induced by TNF-alpha in both H441 and A549 pulmonary epithelial cells but not in U937 cells. TNF-alpha is a primary mediator of acute pulmonary inflammation and contributes to the pathophysiology of chronic lung diseases such as bronchopulmonary dysplasia (BPD), a fibrotic disease of prematurely born infants. Immunohistochemical staining of human neonatal lung tissue demonstrated increased TRAF1 in lungs of infants dying of pneumonia or BPD in comparison with those dying of congenital malformation. These studies support the hypothesis that the TRAF1 and cIAP2 genes are highly regulated in pulmonary cells and may play a role in human lung disease.

Silica binds serum proteins resulting in a shift of the dose-response for silica-induced chemokine expression in an alveolar type II cell line

There is a growing concern about whether the myriad of culture conditions, cell lines, and doses of nonfibrous and fibrous particles used in vitro are truly representative of the complex environment of the in vivo particle exposure situation. The use of serum as a supplement to the growth medium of cultured cells is a widely accepted practice. However, little is known about whether the various serum proteins may interact with the surfaces of particles, consequently altering their toxicity, inflammatory properties, or fibrogenicity, etc. observed in vivo. Using a murine alveolar type II cell line, MLE-15, we measured the early changes in various chemokine mRNA species following exposure of the cells to silica (cristobalite) in the presence or absence of serum. Total mRNA was isolated and assayed using an RNase protection assay after 6 h of particle exposure. We observed that the addition of serum to the culture media reduced the in vitro silica-induced chemokine response (i.e., shift in the dose-response curve) in MLE-15 cells. Further, using Western blot analysis and protein sequencing techniques, we have identified a specific serum component, apolipoprotein-A1 (apo-A1), as a protein in serum that binds selectively to silica, thus leading to the altered chemokine response. We also found that apo-A1 not only binds to silica but also binds to other nonfibrous and fibrous particles such as titanium dioxide and asbestos. These results demonstrate the importance of culture conditions for modifying the outcome of an experiment when performing in vitro particle exposure studies.

Immune-mediated inflammation directly impairs pulmonary function, contributing to the pathogenesis of Pneumocystis carinii pneumonia

The clinical severity of Pneumocystis carinii pneumonia (PCP) correlates closely with the appearance of pulmonary markers of inflammation. Therefore, a model system was developed whereby physiological studies could be performed on live mice to determine the extent to which pulmonary inflammation contributes to respiratory impairment during PCP. P. carinii-infected severe combined immunodeficient mice displayed little evidence of pulmonary inflammation and exhibited normal oxygenation and dynamic lung compliance. When comparably infected littermates were immunologically reconstituted, however, an intense immune-mediated inflammatory response was observed that resulted in significant decreases in both lung compliance and oxygenation. As the pneumonia resolved pulmonary function returned toward normal. To begin to define the cell populations contributing to inflammation-associated respiratory impairment during PCP, similar studies were performed in CD4(+) T cell-depleted mice. Mice depleted of both CD4(+) and CD8(+) cells developed infection, but they demonstrated neither abnormal lung compliance nor increased respiratory rate and displayed no markers of lung injury. In contrast, mice depleted of only CD4(+) T cells exhibited severe pulmonary inflammation and injury, decreased oxygenation and lung compliance, and increased respirations. Respiratory compromise was associated with the presence of activated CD8(+) cells and neutrophils in broncho-alveolar lavage fluid. These observations provide direct experimental evidence that the host's response to P. carinii directly impairs pulmonary function and contributes to the pathogenesis of PCP. Furthermore, CD8(+) T cells likely contribute to the respiratory compromise observed during PCP.

Antioxidant treatment attenuates cytokine and chemokine levels in murine macrophages following silica exposure

Alveolar macrophages play a key role in the development of silicosis by releasing a host of mediators, such as, cytokines and chemokines, which contribute to a complex network of interactions that result in the onset of lung injury, inflammation, and potentially fibrosis. Using a murine macrophage cell line, RAW 264.7, we exposed the cells to cristobalite-silica (35 micrograms/cm(2)) in the presence or absence of antioxidants and various modifiers of cellular antioxidant status. Treatment with dimethyl sulfoxide, extracellular glutathione, or N-acetyl-L-cysteine (NAC) decreased cristobalite-induced tumor necrosis factor (TNF)-alpha mRNA levels by 40%, 20%, and 42%, respectively. TNF-alpha protein levels were decreased by 90%, 32%, and 53%, respectively. Cristobalite-induced macrophage inflammatory protein (MIP)-2 mRNA levels were reduced by 52%, 38%, and 57%, with DMSO, GSH, and NAC treatment, respectively. Both MIP-1alpha and MIP-1beta mRNA levels were reduced at a magnitude similar to the reduction in TNF-alpha mRNA levels, whereas monocyte chemotactic protein (MCP)-1 mRNA levels were reduced at a magnitude similar to the reduction in MIP-2 mRNA levels following antioxidant treatment. These results suggests that the macrophage response to cristobalite exposure is mediated at least in part by oxidant stress.

Chemokine gene expression during Pneumocystis carinii-driven pulmonary inflammation

Severe combined immunodeficient (SCID) mice lack functional lymphocytes and therefore develop Pneumocystis carinii pneumonia. However, when infected SCID mice are immunologically reconstituted with congenic spleen cells, a protective inflammatory cascade is initiated. Proinflammatory cytokines are produced, and lymphocytes and macrophages are recruited specifically to alveolar sites of infection. Importantly, uninfected regions of the lung remain free from inflammatory involvement, suggesting that there are specific mechanisms that limit inflammation in the infected lung. Therefore, to determine whether chemokines are involved in targeting the P. carinii-driven inflammatory response, steady-state mRNA levels of several chemokines were measured in the lungs of both reconstituted and nonreconstituted P. carinii-infected SCID mice. Despite significant organism burdens in the lungs of 8- and 10-week-old SCID mice, there was no evidence of elevated chemokine gene expression, which is consistent with the lack of an inflammatory response in these animals. However, when 8-week-old infected SCID mice were immunologically reconstituted, signs of focal pulmonary inflammation were observed, and levels of RANTES, MCP-1, lymphotactin, MIP-1alpha, MIP-1beta, and MIP-2 mRNAs were all significantly elevated. Chemokine mRNA abundance was elevated at day 10 postreconstitution (PR), was maximal at day 12 PR, and returned to baseline by day 22 PR. In situ hybridization demonstrated that during the peak of inflammation, RANTES gene expression was localized to sites of inflammatory cell infiltration and P. carinii infection. Thus, these observations indicate that chemokines play a role in the focal targeting of inflammatory cell recruitment to sites of P. carinii infection after the passive transfer of lymphocytes to the host.

Silica-induced chemokine expression in alveolar type II cells is mediated by TNF-alpha-induced oxidant stress

We have shown previously that epithelial cells may contribute to the inflammatory response in the lung after exposure to crystalline silica through the production of and response to specific chemokines and cytokines. However, the exact cellular and molecular responses of epithelial cells to silica exposure remain unclear. We hypothesize that non-oxidant-mediated silica-cell interactions lead to the upregulation of tumor necrosis factor-alpha (TNF-alpha), whereby TNF-alpha-induced generation of reactive oxygen species (ROS) leads to the activation of the monocyte chemotactic protein (MCP)-1 and macrophage inflammatory protein (MIP)-2 genes. Using a murine alveolar type II cell line, murine lung epithelial (MLE)-15, we measured the early changes in TNF-alpha, MCP-1, and MIP-2 mRNA species after exposure of the cells to 18 micrograms/cm2 silica (cristobalite) in combination with various antioxidants. Total mRNA was isolated and assayed using an RNase protection assay after 6 h of particle exposure. We found that extracellular GSH could completely attenuate the cristobalite-induced expression of MCP-1 and MIP-2 mRNAs, whereas TNF-alpha mRNA levels were unaltered. We also found using the oxidant-sensitive dye 6-carboxy-2', 7'-dichlorodihydrofluorescein diacetate di(acetoxymethyl ester) that treatment of MLE-15 cells with cristobalite and TNF-alpha (1 ng/ml) resulted in ROS production. This ROS production could be inhibited with extracellular GSH treatment, and in the case of cristobalite-induced ROS, inhibition was also achieved with an anti-TNF-alpha antibody. The results support the hypothesis that TNF-alpha mediates cristobalite-induced MCP-1 and MIP-2 expression through the generation of ROS.

Inflammatory and antioxidant gene expression in C57BL/6J mice after lethal and sublethal ozone exposures

Ozone (O3) is a highly reactive and toxic oxidant pollutant. The objective of this study is to compare cytokine, chemokine, and metallothionein (Mt) changes elicited by lethal and sublethal exposure to ozone in a genetically sensitive strain of mice. Eight-week-old C57BL/6J mice were exposed to 0.3 ppm ozone for 0, 24, or 96 hours; 1.0 ppm ozone for 0, 1, 2, or 4 hours; or 2.5 ppm ozone for 0, 2, 4, or 24 hours. After 24 hours of exposure to 0.3 ppm ozone, increases in mRNA abundance were detected for messages encoding eotaxin, macrophage inflammatory protein (MIP)-1 alpha, and MIP-2. These increases persisted through 96 hours of exposure. At this time point messages encoding lymphotactin (Ltn) and metallothionein were also increased. After 4 hours of 1.0 ppm ozone exposure, increases in mRNA abundance were detected for messages encoding eotaxin, MIP-1 alpha, MIP-2, and interleukin (IL)-6. Mt mRNA abundance was increased after 1 hour of exposure and persisted through 4 hours, although the magnitude of the alterations increased. After 2 hours of 2.5 ppm ozone exposure, increases were detected for messages encoding eotaxin, MIP-1 alpha, MIP-2, IL-6, and Mt. These increases persisted through 4 hours of exposure. Lung weights of mice exposed to 2.5 ppm ozone for 24 hours were approximately 2 times greater than air-exposed mice. At this dose lethality occurred by 36 hours. Increased mRNAs for eotaxin, MIP-1 alpha, MIP-2, and Mt were to a higher magnitude than were detected after 2 and 4 hours of exposure. Messages encoding IL-12, IL-10, interferon (IFN)-gamma, IL-1 alpha, IL-1 beta, and IL-1Ra were unaltered at all time points and doses examined. Our results demonstrate dose- and time-dependent changes in chemokine, cytokine, and Mt mRNA abundance and that early acute changes may be predictive of subacute and chronic responses to ozone.

Hyperoxia increases keratinocyte growth factor mRNA expression in neonatal rabbit lung

Acute hyperoxic lung injury remains a major factor in the development of chronic lung disease in neonates. A critical step in the repair of acute lung injury is the proliferation of type II alveolar epithelial cells. Type II cell proliferation is stimulated by keratinocyte growth factor (KGF), an epithelial cell-specific mitogen. We sought to investigate KGF mRNA expression in relation to type II cell proliferation during hyperoxic lung injury. We studied a previously described newborn (NB) rabbit model of acute and chronic hyperoxic injury [C. T. D'Angio, J. N. Finkelstein, M. B. LoMonaco, A. Paxhia, S. A. Wright, R. B. Baggs, R. H. Notter, and R. M. Ryan. Am. J. Physiol. 272 (Lung Cell. Mol. Physiol. 16): L720-L730, 1997]. NB rabbits were placed in 100% O2 for 9 days and then recovered in 60% O2. RT-PCR was used to synthesize and amplify a 267-bp fragment of rabbit KGF cDNA from whole lung RNA. KGF mRNA expression was analyzed by ribonuclease protection assay, and mRNA abundance was quantified by phosphorimaging. Proliferating cell nuclear antigen immunohistochemistry was used on lung sections to identify proliferating cells. The rabbit partial cDNA sequenced was >95% homologous to human cDNA, and all amino acids were conserved. Whole lung KGF mRNA expression was increased 12-fold after 6 days of hyperoxia compared with control lungs, and remained increased throughout the 100% O2 exposure period. Proliferating cell nuclear antigen immunohistochemistry showed an increase in type II cell proliferation after 8-12 days of hyperoxia. NB rabbits exposed to hyperoxic injury exhibit increased whole lung KGF mRNA expression preceding type II cell proliferation. KGF may be an important mitogen in the regulation of alveolar epithelial repair after hyperoxic lung injury.

Clara cell secretory protein-deficient mice differ from wild-type mice in inflammatory chemokine expression to oxygen and ozone, but not to endotoxin

The in vivo function of Clara cell secretory protein (CCSP) is unknown. Biologic and biochemical properties associated with CCSP have led to speculation that it participates in pulmonary inflammatory control. Our earlier studies have demonstrated that CCSP-deficient mice are more sensitive to either hyperoxia or ozone toxicity and show altered oxidant-induced pulmonary proinflammatory responses. In this study we test the hypothesis that altered chemokine responses seen in CCSP-/- mice following oxidant stress are a direct consequence of altered immunoregulation associated with CCSP deficiency. To test this hypothesis we utilized three distinct models of inducing pulmonary toxicity: hyperoxia and ozone (O3), which cause epithelial cell injury, and endotoxin, which causes pulmonary inflammation independent of direct epithelial cell injury. Wild-type (WT) or CCSP-/- strain 129 mice were exposed to O3 at 1.0 ppm for 24 hours, oxygen (O2) > 99% for 68 hours or inhalation of 0.0575 microgram endotoxin per mouse for 10 minutes and examined 6 hours postexposure. Mice displayed increased sensitivity to O3, as demonstrated by increased abundance of mRNAs encoding Eotaxin, macrophage inflammatory protein (MIP)-1 alpha, and MIP-2, after 4 hours of exposure, whereas WT mice were unaltered from controls. Increased sensitivity to hyperoxia was also observed, as demonstrated by increased abundance of mRNAs encoding Eotaxin, MIP-1 alpha, MIP-1 beta, MIP-2, and interferon-gamma inducible (IP)-10 after 68 hours of exposure, whereas WT mice were unaltered from controls. In contrast, WT and CCSP-/- mice responded identically 6 hours postinhalation of 0.0575 microgram lipopolysaccharide (LPS) per mouse. PMN response was 63% and 64% in WT and CCSP-/- mice, respectively. Messenger RNAs encoding Eotaxin, MIP-1 alpha, MIP-1 beta, MIP-2, IP-10, and MCP-1 were increased identically. We conclude that CCSP does not participate in regulation of the endotoxin-elicited pulmonary inflammatory response. Identical inflammatory and chemokine responses of CCSP-/- and WT mice in response to a nonepithelial toxic agent (endotoxin) suggest that altered inflammatory control observed between WT and CCSP-/- mice following O2 and O3 exposure is not the result of altered immunoregulation.

Silica-induced chemokine expression in alveolar type II cells is mediated by TNF-alpha

Recent evidence has suggested that epithelial cells may contribute to the inflammatory response in the lung after exposure to crystalline silica through the production of and response to specific growth factors, chemokines, and cytokines. However, the exact cellular and molecular responses of epithelial cells to silica exposure remains unclear. Using a murine alveolar type II cell line [murine lung epithelial (MLE)-15 cell line], we measured the early changes in various cytokine and chemokine mRNA species after exposure of the cells to 4-35 microgram/cm2 of silica (cristobalite), interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and lipopolysaccharide (LPS) alone or in combination. Total mRNA was isolated and assayed with an RNase protection assay after 6 and 24 h of exposure. Cristobalite exposure alone led to an increase in monocyte chemotactic protein (MCP)-1, macrophage inflammatory protein (MIP)-2, and regulated on activation normal T cells expressed and secreted (RANTES) mRNAs. Treatment with IFN-gamma alone increased MCP-1 mRNA levels. Treatment with TNF-alpha or LPS alone led to an increase in MCP-1 and MIP-2 mRNA. The combination of cristobalite plus TNF-alpha led to an additive increase in MCP-1 and MIP-2, whereas cristobalite plus IFN-gamma or LPS had a synergistic effect. We also found with a TNF-alpha-neutralizing antibody that TNF-alpha plays a major role in mediating the type II cell chemokine response to cristobalite exposure. The results indicate that the cristobalite-induced chemokine response in the lung epithelium is mediated in part by TNF-alpha and can be enhanced by macrophage- and lymphocyte-derived inflammatory mediators in an additive and synergistic fashion.

Pulmonary cytokine and chemokine mRNA levels after inhalation of lipopolysaccharide in C57BL/6 mice

Inhaled endotoxin (lipopolysaccharide, LPS) can induce acute lung injury and at high doses may lead to respiratory distress syndrome. Using a mouse model of acute lung inflammation induced by inhalation of low doses of LPS we examined the kinetics of chemokine, proinflammatory cytokine, and metallothionein. Eight-week-old C57BL/6 mice were dosed for 10 min with LPS, resulting in an estimated alveolar dose of < 10 ng LPS/mouse, and euthanized 2,6, or 24 h postexposure. Analysis of bronchoalveolar lavage fluid demonstrated increased polymorphonuclear neutrophils (PMNs) of 6.94, 32.7, and 38.8% after 2, 6, and 24 h, respectively. Examination of proinflammatory cytokine, chemokine, and Mt mRNA in the lung revealed increases for messages encoding IL-1 alpha, IL-1 beta, IL-6, IFN-gamma, TNF alpha, Eotaxin, MIP-1 alpha, MIP-1 beta, MIP-2, Mt, and IP-10, while messages encoding IL-12, IL-10, IFN-beta, Ltn, MCP-1, TGF beta 1 + 2, and RANTES were unchanged from those of sham-exposed mice 2 h postexposure. By 6 h most messages had returned to near control levels. Comparison to 5 mg/kg body weight intraperitoneal injection and 5 micrograms/mouse intratracheal instillation 2 h postexposure demonstrated similar message responses. Our results demonstrate that low levels of LPS exposure by inhalation induce a strong PMN response and a selective cytokine response in the lung, supporting the hypothesis that PMNs may regulate inflammatory processes via cytokine and chemokine response.

Radiation-induced changes in bone perfusion and angiogenesis

PURPOSE

To determine whether blood flow of bone is altered by limb irradiation and whether bFGF, an angiogenic cytokine, might alleviate any flow or growth abnormality resulting from 30 Gy single fraction irradiation.

METHODS AND MATERIALS

C3H mice received whole right hind limb radiation at doses of 0 to 30 Gy. Additional groups received 30 Gy, and then beginning 1 or 5 weeks later received intravenous bFGF at a dose of 6 microg/mouse, twice a week for 4 weeks. Serial X-ray films were taken to measure the tibias. At 33 weeks, laser Doppler flow (LDF) measurements were made of both limbs. Cytokine measurements were made using ELISA and RNase protection.

RESULTS

Bone growth was reduced following radiation in a dose dependent manner. bFGF improved bone growth after radiation even when begun 5 weeks after radiation, however, we detected no significant improvement in LDF of the irradiated bone or periosteum. Muscle tissue surrounding bone of the irradiated leg showed no increase in isoforms of TGFbeta, TNF, or IFN. There was also no difference in the circulating plasma TGFbeta1 in irradiated mice. In contrast, LDF increased significantly as a function of radiation dose in the nonirradiated tibia. Systemic delivery of bFGF appears to further enhance the increase in flow seen in the nonirradiated limb.

CONCLUSION

Radiation induces a chronic antiangiogenic effect contributing to reduced limb growth. At 33 weeks the antiangiogenesis was not associated with local soft tissue elevations of TNF, IFN, or TGFbeta. Radiation toxicity to bone is alleviated by bFGF therapy suggesting that powerful locally-acting antiangiogenic mechanisms are involved. We postulate that the increased LDF of the contralateral tibia is due to circulating angiogenesis factors that are elevated to compensate for the radiation-induced antiangiogenesis.

Chemokine mRNA alterations in newborn and adult mouse lung during acute hyperoxia

Chemokines play a major role in the recruitment of inflammatory cells during acute lung injury. Adult and newborn C57BL/6 mice were exposed to > 95% oxygen for up to 72 hours and 7 days, respectively. Chemokine mRNA abundance was evaluated in whole lung RNA by ribonuclease protection assay and in tissue sections by in situ hybridization. Monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-2, and interferon gamma-induced protein (IP)-10 mRNAs were present in whole newborn lung by 4 days of hyperoxia and were markedly elevated by 7 days. Levels of mRNA for MCP-1, MIP-1 alpha, and MIP-2 were elevated to a lesser extent by 72 hours of hyperoxia in adults. MCP-1 mRNA abundance was moderately elevated in scattered areas of perivascular tissue, peribronchiolar tissue, and the alveolar interstitium in 4-day hyperoxic newborns and markedly upregulated diffusely throughout the peripheral airspaces in 7-day hyperoxic newborns. MCP-1 mRNA abundance was limited to scattered perivascular areas and airspaces in 72-hour hyperoxic adults. These differences in the intensity, timing, and distribution of chemokine mRNA abundance between adult and newborn mice may help to explain the marked differences in their susceptibility to oxygen injury.

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.

Alterations in the expression of chemokine mRNA levels in fibrosis-resistant and -sensitive mice after thoracic irradiation

Fibrosis, characterized by the accumulation of collagen, is a consequence of a chronic inflammatory response. The purpose of this study was to determine if the mRNA expression of the chemokines, lymphotactin (Ltn), RANTES, eotaxin, macrophage inflammatory protein (MIP)-1 alpha, -1 beta, and -2, interferon-inducible protein 10 (IP-10), and monocyte chemotactic protein-1 (MCP-1), are altered during the development of radiation-induced pneumonitis and fibrosis. Further, we wished to determine if these changes differ between two strains of mice that vary in their sensitivity to radiation fibrosis. Fibrosis-sensitive (C57BL/6) and fibrosis-resistant (C3H/HeJ) mice were irradiated with a single dose of 12.5 Gy to the thorax. Total lung RNA was prepared and hybridized utilizing RNase protection assays. Data were quantified by phosphorimaging and results normalized to a constituitively expressed mRNA L32. 8 weeks post-irradiation most chemokines measured were elevated to varying degrees. The degree of elevation of each chemokine was identical in both strains. This suggested that chemotactic activity for neutrophils, macrophages, and lymphocytes were occurring during pneumonitis. By 26 weeks post-irradiation, messages encoding Ltn, RANTES, IP-10, and MCP-1 were elevated only in fibrosis sensitive (C57BL/6) mice. In situ hybridization demonstrated that MCP-1 and RANTES transcripts were produced predominantly from macrophages and lymphocytes. These studies suggest that lymphocytic recruitment and activation are key components of radiation-induced fibrosis.

Cell-specific gene expression reveals changes in epithelial cell populations after bleomycin treatment

Epithelial repair following acute lung injury involves proliferation and differentiation of existing Clara cells and type II cells. Other mechanisms of epithelial repair may be involved in particularly severe cases. We used epithelial cell-specific markers to examine changes in the mouse lung epithelium 28 days after bleomycin treatment. The spatial distribution of surfactant proteins A, B, C (SPA, SPB, SPC), and Clara cell-specific protein (CC10) mRNA was compared by in situ hybridization in serial lung sections. CC10 mRNA-containing airway cells were replaced in many areas by SPB mRNA-expressing, ciliated cells that did not contain CC10 mRNA. In distal airway regions, we observed a subpopulation of epithelial cells that appeared to express SPA, SPB, SPC, and CC10 mRNA, and speculated that they may represent a multipotential stem cell population. These cells were found in focal clusters, which suggests that they expanded from a common cell. CC10 mRNA-containing cells were seen in alveolar-like structures thought to be the result of Clara cell migration or outpocketing. Our data suggest that there are repair mechanisms involved in epithelial repair after severe injury that have not previously been described.

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.

Exposure to hyperoxia induces p53 expression in mouse lung epithelium

Cells that are exposed to free radicals have increased levels of DNA strand breaks with accumulation of the tumor suppressor protein p53, which induces cell cycle arrest and/or apoptosis. Because oxidants injure pulmonary epithelial cells, it was hypothesized that exposure to hyperoxia promotes DNA strand breaks in lung epithelium, resulting in increased expression of p53 and loss of epithelial cell function. Adult male C57Bl/6J mice were exposed to > 95% oxygen for 72 h and DNA integrity was determined in their lungs by terminal transferase immunoreactivity. Both nonimmunoreactive and lightly stained nuclei were observed in cells comprising the airway and parenchyma. Exposure to hyperoxia resulted in a marked increase in the intensity of nuclear staining in distal bronchiolar epithelium and alveolar epithelial and endothelial cells. Airway epithelial cells from control lungs contained detectable levels of p53 protein, which markedly increased in both nuclei and cytoplasm of distal bronchiolar epithelial cells and to a lesser extent in alveolar epithelial cells that were morphologically consistent with type II cells. Western and Northern blot analyses revealed that hyperoxia increased total lung p53 protein expression but not levels of mRNA. Changes in terminal transferase immunoreactivity and p53 expression were not observed in large airway cells, fibroblasts underlying distal airway, or smooth muscle cells. Expression of SP-B mRNA modestly increased and Clara cell secretory protein and cytochrome P-450 2F2 mRNAs decreased, providing additional evidence that hyperoxia injured pulmonary epithelial cells. These findings support the concept that hyperoxia damages DNA of pulmonary epithelial cells, which respond by accumulating p53 and changes in epithelial cell-specific gene expression.

H441 pulmonary epithelial cell mitogenic effects and signaling pathways in response to HGF and TGF-alpha

Pulmonary epithelial cells are important in lung growth, development, and injury. H441 pulmonary adenocarcinoma cells may be a useful model for studying pulmonary epithelial cell growth factor responses in vitro. Isolated pulmonary epithelial type II cells proliferate in response to transforming growth factor (TGF)-alpha via the epidermal growth factor (EGF) receptor. Type II cells also proliferate in response to hepatocyte growth factor (HGF). In the present study, H441 cell responses to these growth factors were examined, and compared to type II cells. Both the EGF-R and the c-met proto-oncogene receptor, to which HGF binds, were immunoprecipitated from H441 cells. In H441 cells, addition of TGF-alpha resulted in phosphorylation of the EGF receptor and increased cell number and tritiated thymidine incorporation. Incubation with HGF resulted in phosphorylation of its c-met proto-oncogene receptor in type II and H441 cells, and also increased cell number and tritiated thymidine incorporation. Both HGF and TGF-alpha stimulated phosphorylation of the intracellular signaling molecules p42 and p44 mitogen activated protein kinases in H441 cells. H441 cells exhibited responses to mitogenic growth factors similar to type II cells and may be useful as a model for type II cell growth factor responses and signal transduction.

Comparison of adult and newborn pulmonary cytokine mRNA expression after hyperoxia

Neonatal animals of several species are more tolerant of hyperoxic exposure than are adults. However, the mechanisms of increased neonatal tolerance are unknown, as are the cell types that contribute to oxygen resistance. This study examined hyperoxic lung injury in neonatal and adult C57BL/6 mice. Adults and neonatal mice were exposed to > 95% oxygen for 78 h and 10 days, respectively. Lung mRNAs were assayed by RNase protection assay. After 72 h of exposure, the messages encoding tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta and 6 (IL-1 beta, IL-6) were increased 2-fold in adult lungs. However, at this time point these mice are near or at lethality. No alterations in neonatal lung mRNAs were detected until 7 days of oxygen exposure. At that time neonatal mice demonstrated increases in lung mRNAs encoding TNF-alpha, IL-1 beta, and IL-6 of 3-, 5-, and 8-fold, respectively. Acute alveolitis and slight edema were detected, but lethality wasn't observed until 10 days of exposure. In situ hybridization in neonatal mice suggests accumulation of TNF-alpha and IL-1 beta transcripts in pulmonary interstitial macrophages and in a subset of neutrophils after 7 days of exposure. Messages encoding IL-1 alpha, IL-2, IL-3, IL-4, IL-5,IL-10 interferon-gamma (IFN-gamma), and TNF-beta were not altered from controls in either adult or neonatal mice at any time point examined. In conclusion, adult mice demonstrate little change in cytokine mRNA until lethality is imminent, whereas newborn mice demonstrate an acute induction of TNF-alpha, IL-1 beta, and IL-6 early in the development of hyperoxic injury, which suggests that a rapid cytokine response early in the development of hyperoxic injury may play an important role in the adaptation of neonatal lungs to toxicity from prolonged oxygen exposure.

Analysis of cytokine mRNA profiles in the lungs of Pneumocystis carinii-infected mice

Severe combined immunodeficient (scid) mice lack functional CD4+ lymphocytes, and therefore develop life-threatening Pneumocystis carinii infection. However, when scid mice are immunologically reconstituted with spleen cells, including CD4+ cells, a protective inflammatory response is mounted against the organism. To determine whether these lymphocytes induce elevated cytokine mRNA levels in response to P. carinii infection, steady-state levels of cytokine mRNAs were measured in the lungs of both reconstituted and unaltered scid mice. Despite significant numbers of organisms and the presence of functional alveolar macrophages in the lungs of 8- and 10-wk-old scid mice, there was neither evidence of pulmonary inflammation, nor increased proinflammatory cytokine expression. However, when 8-wk-old scid mice were immunologically reconstituted, signs of intense, focal pulmonary inflammation were observed, and levels of interleukin (IL)-1alpha, IL-1beta, IL-3, IL-6, interferon-gamma (IFN-gamma), tumor necrosis factor (TNF)-alpha, and TNF-beta mRNAs were all significantly elevated. Cytokine expression was increased at day 10 post-reconstitution (PR), maximal at day 12 PR, and returned to baseline by day 22 PR. In situ hybridization demonstrated that at day 12 PR, increased IL-1beta and TNF-alpha expression was localized to sites of intense inflammation and focal P. carinii colonization. Many of the cells expressing high levels of IL-1beta and TNF-alpha in these regions were in direct contact with organisms, or contained degraded organisms within their cytoplasm. Thus, even though functional macrophages are present in scid mice, CD4+ T cells are required for proinflammatory cytokine expression, which is associated with the generation of a protective inflammatory response at sites of P. carinii infection.

Particulate-cell interactions and pulmonary cytokine expression

The type II cell plays an important role in the response of the alveolar epithelium after lung injury through its synthesis and secretion of pulmonary surfactant, and by acting as the stem cell for the replacement of damaged type I epithelial cells. The nonciliated bronchiolar epithelial (Clara) cell is thought to play a similar role during repair of the bronchiolar epithelium. Recent evidence has suggested that epithelial cells may participate in aspects of the inflammatory response and regulation of fibroblast growth during pulmonary fibrosis through the production of and response to specific growth factors and cytokines. The cellular and molecular responses of epithelial cells and how they lead to the progression of events that defines the pulmonary parenchymal response to a class of particles is unclear. We used particles differing in size, chemical composition, and fibrogenicity in vivo and in vitro to elucidate early changes in proinflammatory and profibrotic cytokine and antioxidant gene expression in lung cells. Early increases in mRNA and protein for the proinflammatory cytokines interleukin (IL)-1 beta, IL-6, and tumor necrosis factor alpha have been observed in epithelial cells following exposure. These are accompanied by changes in specific epithelial genes including surfactant protein C and Clara cell secretory protein. The data indicate that effects on the epithelium are due to direct interactions with particles, not a result of macrophage-derived mediators, and suggest a more significant role in the overall pulmonary response than previously suspected. These results suggest that type II cell growth factor production may be significant in the pathogenesis of pulmonary fibrosis.

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.

Changes in surfactant protein gene expression in a neonatal rabbit model of hyperoxia-induced fibrosis

Lung injuries, including bronchopulmonary dysplasia, alter the surfactant system. We developed a newborn rabbit model of acute, followed by chronic, hyperoxic injury to study surfactant protein (SP) gene expression. Initial litters were exposed to >95% O2 until 50% died (LD50; 7-11 days old). Subsequent litters were exposed to >95% O2 for 8 days, followed by 60% O2 until 22-36 days. Controls were exposed to room air. LD50 animals displayed acute pulmonary inflammation, edema, protein leak, and surfactant dysfunction. These changes resolved, and fibrosis developed by 22 days. Whole lung SP-A mRNA expression (measured by membrane hybridization) was twice control levels at 4 days of >95% O2, with specific elevations in terminal bronchioles and type II cells at 4 days and the LD50 by in situ hybridization. Whole lung SP-B and SP-C mRNA were unchanged from control throughout exposure. However, in situ hybridization showed elevations in SP-B and SP-C mRNA in type II cells in inflamed areas at the LD50. SP mRNA alterations resolved by 22-36 days. The surfactant system recovers from acute hyperoxic injury, despite continued 60% O2 exposure.

Bleomycin induces strain-dependent alterations in the pattern of epithelial cell-specific marker expression in mouse lung

Clinical use of the antineoplastic agent bleomycin is restricted due to pulmonary toxicity. Murine models of bleomycin-induced pulmonary fibrosis have been developed in an attempt to understand the mechanisms involved in the fibrotic process. Studies have shown that the alveolar epithelium is damaged early after bleomycin treatment. The purpose of this study was to evaluate the pattern of gene expression in airway and alveolar epithelial cells after bleomycin exposure in mice that vary in susceptibility to bleomycin-induced fibrosis. Surfactant protein C (SPC) and Clara cell-specific protein (CC10) mRNA were used as cell-specific markers of alveolar type II cells and airway Clara cells, respectively. Mice were treated with a single intratracheal dose of bleomycin and the pattern of SPC and CC10 transcripts was examined by in situ hybridization. The pattern of SPC mRNA 28 days after treatment was uniform in controls and resistant mice but exhibited a patchy appearance in sensitive mice. Bleomycin treatment also resulted in a strain-dependent loss of CC10 mRNA-expressing cells. In sensitive mice 28 days after treatment, SPC mRNA was ectopically expressed in the distal bronchiolar epithelium in a morphologically distinct cell type. Serial sections revealed that these cells either coexpressed CC10 mRNA or were located adjacent to CC10 mRNA-containing cells. This unique cell population may represent a progenitor cell type important in epithelial repair. The strain-dependent changes in CC10 and SPC gene expression after bleomycin treatment are suggestive of a role for the epithelium in pulmonary fibrosis versus repair.

Temporal changes in expression of TGF-beta isoforms in mouse lung exposed to oxygen

Oxygen-induced pulmonary injury is associated with cell death and a significant inflammatory response. Because transforming growth factor (TGF)-beta is a potent modulator of the immune response, changes in expression of the three TGF-beta (beta 1, beta 2, beta 3) isoforms was determined in lungs of adult mice exposed to > 95% oxygen. TGF-beta 1 immunostaining within cuboidal nonciliated bronchiolar epithelial cells was increased within 3 h of oxygen exposure and continued to increase for 48 h before decreasing to control levels by 72 h. A similar but less marked change that was morphologically consistent with alveolar type II cells was observed in granulated cells. Immunostaining for TGF-beta 2 and TGF-beta 3 revealed a similar change in bronchiolar epithelium with little change observed in the alveolar epithelium. Immunohistochemical changes in TGF-beta expression were not observed in any other pulmonary cells. Northern blot analysis of total lung RNA revealed that expression of the TGF-beta mRNA was not markedly altered over the 72-h exposure period. Exposure to > 95% oxygen resulted in cell type-specific posttranscriptional changes in TGF-beta isoforms in the lung.

Characterization of the early pulmonary inflammatory response associated with PTFE fume exposure

Heating of polytetrafluoroethylene (PTFE) has been described to release fumes containing ultrafine particles (approximately 18 nm diam). These fumes can be highly toxic in the respiratory tract inducing extensive pulmonary edema with hemorrhagic inflammation. Fischer-344 rats were exposed to PTFE fumes generated by temperatures ranging from 450 to 460 degrees C for 15 min at an exposure concentration of 5 x 10(5) particles/cm3, equivalent to approximately 50 micrograms/m3. Responses were examined 4 hr post-treatment when these rats demonstrated 60-85% neutrophils (PMNs) in their lung lavage. Increases in abundance for messages encoding the antioxidants manganese superoxide dismutase and metallothionein (MT) increased 15- and 40-fold, respectively. For messages encoding the pro- and anti-inflammatory cytokines: inducible nitric oxide synthase, interleukin 1 alpha, 1 beta, and 6 (IL-1 alpha, IL-1 beta, and IL-6), macrophage inflammatory protein-2, and tumor necrosis factor-alpha (TNF alpha) increases of 5-, 5-, 10-, 40-, 40-, and 15-fold were present. Vascular endothelial growth factor, which may play a role in the integrity of the endothelial barrier, was decreased to 20% of controls. In situ sections were hybridized with 33P cRNA probes encoding IL-6, MT, surfactant protein C, and TNF alpha. Increased mRNA abundance for MT and IL-6 was expressed around all airways and interstitial regions with MT and IL-6 demonstrating similar spatial distribution. Large numbers of activated PMNs expressed IL-6, MT, and TNF alpha. Additionally, pulmonary macrophages and epithelial cells were actively involved. These observations support the notion that PTFE fumes containing ultrafine particles initiate a severe inflammatory response at low inhaled particle mass concentrations, which is suggestive of an oxidative injury. Furthermore, PMNs may actively regulate the inflammatory process through cytokine and antioxidant expression.

Early and persistent alterations in the expression of interleukin-1 alpha, interleukin-1 beta and tumor necrosis factor alpha mRNA levels in fibrosis-resistant and sensitive mice after thoracic irradiation

Fibrosis, characterized by the accumulation of collagen, is a consequence of a chronic inflammatory response. The purpose of this study was to determine if tumor necrosis factor alpha (TNF-alpha), interleukin-1 alpha (IL-1 alpha) and IL-1 beta mRNA expression are altered acutely after irradiation, during the so-called "latent" phase of pulmonary injury, and to examine if these alterations persist through the development of pneumonitis and fibrosis. Further, we wished to determine if these changes differ between two strains of mice which vary in their sensitivity to radiation. Fibrosis-sensitive (C57BL/6) and fibrosis-resistant (C3H/HeJ) mice were irradiated with a single dose of 5 or 12.5 Gy to the thorax. Total lung RNA was prepared and immobilized by slot blotting and hybridized with radiolabeled cDNA probes encoding for TNF-alpha, IL-1 alpha and IL-1 beta. Autoradiographic data were quantified by video densitometry and results normalized to a control probe encoding for glyceraldehyde-3-phosphate dehydrogenase. It was found that TNF-alpha mRNA levels were increased in C57BL/6 mice at days 1 and 7 postirradiation after 5 Gy and day 14 postirradiation after both 5 and 12.5 Gy, and IL-1 alpha mRNA levels were increased in C57BL/6 mice at days 56, 112 and 182 postirradiation after both 5 and 12.5 Gy, and IL-1 beta mRNA levels in the C3H/HeJ mice were increased at days 56 and 182 postirradiation after 12.5 Gy. In summary, these studies demonstrated early and persistent alterations in TNF-alpha, IL-1 alpha and IL-1 beta mRNA levels even at the lower dose (5 Gy). The temporal relationship between the elevation of these cytokines and the strain-dependent variation in fibrosis response suggests that IL-1 alpha and TNF-alpha contribute to the radiation-induced component of pulmonary fibrosis, whereas IL-1 beta may have a protective function.

Extracellular glutathione peroxidase in human lung epithelial lining fluid and in lung cells

The epithelial cells of the lower respiratory tract are exposed to high levels of inhaled oxygen and other oxidants. We hypothesized that lung cells would secrete the antioxidant enzyme, extracellular glutathione peroxidase (eGPx), into epithelial lining fluid (ELF). To investigate this hypothesis, we used specific immunoprecipitations of GPx enzymes from ELF, specific immunoprecipitations of 75Se metabolically labeled proteins from lung cells in culture, and in situ hybridization, Northern blot, and reverse transcription-polymerase chain reaction (RT-PCR) analyses. Fifty-seven percent of ELF GPx activity was due to eGPx and 40% was due to cellular GPx (cGPx). Primary bronchial epithelial cells (BEC), primary alveolar macrophages (AM), and two human bronchial epithelial cell lines, BEP2D and A549, synthesized both eGPx and cGPx and secreted eGPx into the medium. Freshly isolated human AM and BEC expressed eGPx mRNA, while freshly isolated rabbit type 2 pneumocytes did not. In lung tissue, eGPx mRNA was found mainly in interstitial cells of tissue surrounding airways. It is concluded that more than half of GPx activity in BAL is due to eGPx, and that BEC, AM, and interstitial cells are potential sources of pulmonary eGPx.

Relationship of lead-induced proteins to stress response proteins in astroglial cells

Astroglial cells are resistant to cell death and morphologic damage following lead (Pb) exposure at concentrations which elicit detrimental effects in neurons. A possible explanation may be that astroglial cells respond to Pb by increasing the expression of specific proteins, such as heat-shock proteins (HSPs), which confer resistance to low levels of Pb. However, there has been relatively limited information regarding the ability of Pb to evoke the synthesis of HSPs. In the current study, pulse-labeling of cultured astroglial proteins with [3H]-leucine was used to evaluate the nature of Pb-induced changes in protein expression. The effect of Pb on newly synthesized proteins was compared to the response elicited by heat-shock and oxidative injury. Immunoblot analysis was utilized to examine alterations in levels of various stress proteins including HSP27, HSP70, HSP90, and heme oxygenase-1 (HO-1). Even though Pb induced the synthesis of proteins with estimated molecular weights of 23 kDa, 32 kDa, 70 kDa, and 90 kDa, the accumulation of HSPs other than HO-1 was not observed. Hyperthermia and treatment with Na arsenite both resulted in enhanced expression of HSP70 and HO-1. In addition, exposure to hydrogen peroxide (H2O2), cadmium (Cd), and lipopolysaccharide (LPS) stimulated a rise in HO-1 levels. Although cellular insult failed to elicit an increase in either HSP27 or HSP90, cultured astroglia expressed readily detectable levels of both these proteins. Furthermore, Pb exposure resulted in the development of crosstolerance to subsequent injury by treatment with either Cd or H2O2. The results of this study indicate that Pb triggers a less conventional stress response in astroglial cells, which may provide enhanced resistance to the toxic effects of Pb.

Vascular endothelial growth factor mRNA increases in alveolar epithelial cells during recovery from oxygen injury

Destruction of pulmonary endothelial cells is characteristic of hyperoxic lung injury. During recovery from hyperoxia, pulmonary endothelial cells proliferate to regenerate the vascular endothelium. Vascular endothelial growth factor (VEGF) is a peptide growth factor that is mitogenic specifically for endothelial cells. We hypothesized that VEGF messenger RNA (mRNA) increases during recovery from acute hyperoxic lung injury. Adult rabbits were exposed to 100% oxygen for 64 h and allowed to recover in air for 0, 1, 3, and 5 days. In situ hybridization showed increased VEGF expression in alveolar epithelial cells beginning at 1 day recovery. By 3 days recovery the message was in alveolar epithelial cells throughout the lung. Compared with alveolar epithelial cells, little or no expression was noted in large vessel endothelial cells, airway cells, or smooth muscle cells. Combined in situ hybridization for VEGF and immunostaining for macrophages and other mesenchymal cells found no VEGF message in those cell types. Isolated alveolar macrophages had no detectable VEGF message. Cells expressing VEGF mRNA were enriched in alveolar type II cell preparations from recovering lung. Double in situ hybridization for VEGF and surfactant protein-C (SP-C) showed co-expression in a population of type II cells, but with an inverse relationship: cells with abundant VEGF mRNA did not have abundant SP-C mRNA. Type II cells in vitro expressed VEGF message, but only when the SP-C message abundance was relatively low. We conclude that alveolar type II cells express increased VEGF mRNA during recovery from acute hyperoxia. These findings are consistent with a role for VEGF in regulating microvascular endothelial repair after oxidant injury.

A perpetual cascade of cytokines postirradiation leads to pulmonary fibrosis

PURPOSE

Radiation-induced pulmonary reactions have classically been viewed as distinct phases--acute pneumonitis and, later, fibrosis--occurring at different times after irradiation and attributed to different target cell populations. We prefer to view these events as a continuum, with no clear distinction between the temporal sequence of the different pulmonary reactions; the progression is the result of an early activation of an inflammatory reaction, leading to the expression and maintenance of a cytokine cascade. In the current study, we have examined the temporal and spatial expression of cytokine and extracellular matrix messenger ribonucleic acid (mRNA) abundance in fibrosis-sensitive mice after thoracic irradiation.

METHODS AND MATERIALS

Radiation fibrosis-prone (C57BL/6) mice received thoracic irradiation of 5 and 12.5 Gy. At Day 1, and 1, 2, 8, 16, and 24 weeks after treatment, animals were killed and lung tissue processed for light microscopy and isolation of RNA. Expression of cytokine and extracellular matrix mRNA abundance was evaluated by slot-blot analysis and cellular localization by in situ hybridization and immunochemistry.

RESULTS

One of the cytokines responsible for the inflammatory phase (IL-1 alpha) is elevated at 2 weeks, returns to normal baseline values, then increases at 8 weeks, remaining elevated until 26 weeks when lung fibrosis appears. Transforming growth factor-beta (TGF beta), a proliferative cytokine, is elevated at 2 weeks, persists until 8 weeks, and then returns to baseline values. In parallel with the cytokine cascade, the fibrogenic markers for CI/CIII/IV (collagen genes) correlate by showing a similar early and then later elevation of activity. For instance, the collagen gene expression of CI/CIII is a biphasic response with an initial increase at 1-2 weeks that remits at 8 weeks, remains inactive from 8 to 16 weeks, and then becomes elevated at 6 months when collagen deposition is recognized histopathologically.

CONCLUSION

These studies clearly demonstrate the early and persistent elevation of cytokine production following pulmonary irradiation. The temporal relationship between the elevation of specific cytokines and the histological and biochemical evidence of fibrosis serves to illustrate the continuum of response, which, we believe, underlies pulmonary radiation reactions and supports the concept of a perpetual cascade of cytokines produced immediately after irradiation, prompting collagen genes to turn on, and persisting until the expression of late effects becomes apparent pathologically and clinically.

Secretion of transforming growth factor-alpha (TGF alpha) by postnatal rabbit alveolar macrophages

Transforming growth factor-alpha (TGF alpha) is a cytokine secreted by stimulated alveolar macrophages (AM) in vitro and after in vivo particulate or hyperoxia exposure and has been implicated in the processes of postnatal lung development. It is unknown if AM TGF alpha secretion changes during normal postnatal lung development. After sacrifice of New Zealand white rabbits on postnatal d 0-2, 5-7, 9-10, 14, 21, and 28 and > 4 mo (adult), AM were isolated by discontinuous density centrifugation and placed in culture in the presence or absence of concanavalin A (ConA) for 24 h. Media were collected, and the concentration and isoforms of TGF alpha in AM media samples were determined by an epidermal growth factor/TGF alpha radioreceptor assay and Western immunodetection, respectively. TGF alpha was present in media of AM from the 1.06 and 1.08 g/dL Percoll densities, but not in the 1.10 g/dL density. Statistically significant differences in TGF alpha secretion by unstimulated and ConA-stimulated AM at the various ages were not detected until d 14 (p < 0.02). Western blot analysis of unstimulated AM media samples from d 0-7 rabbits demonstrated the presence of TGF alpha isoforms at 46, 30, and 14.3 kD. At later postnatal ages (> or = d 9), a single 14.3-kD isoform was present. In contrast, analysis of ConA-stimulated AM media samples showed TGF alpha isoforms at 46, 30, and 14.3 kD for all ages; however, the 6-kD mature isoform was present only in juvenile (d 28) and adult media.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in correlation of mRNA gene expression in mice sensitive and resistant to radiation-induced pulmonary fibrosis

Fibrosis, characterized by the accumulation of collagen, is a late result of thoracic irradiation. The purpose of this study was to determine if extracellular matrix protein and transforming growth factor beta mRNA expression are altered late in the course of pulmonary fibrosis after irradiation, and then to determine if these changes differ between two strains of mice which vary in their sensitivity to radiation. Radiation-sensitive (C57BL/6) and radiation-resistant (C3H/HeJ) mice were irradiated with a single dose of 5 or 12.5 Gy to the thorax. Total lung RNA was prepared and immobilized by Northern and slot blotting and hybridized with radiolabeled cDNA probes for collagens I, III and IV, fibronectin, and transforming growth factor beta 1 and beta 3. Autoradiographic data were quantified by video densitometry and results normalized to a control probe encoding for glyceraldehyde-3-phosphate dehydrogenase. Alterations in mRNA abundance were observed in the sensitive mice at all times, while levels in the resistant mice were unaffected until 26 weeks after irradiation. The relationship between extracellular matrix protein per se and increased mRNA abundance suggests that late matrix protein accumulation may be a function of gene expression. Differences in levels of transforming growth factor beta mRNA may lead to strain-dependent variation in fibrotic response and may also contribute to the radiation-induced component of pulmonary fibrosis.

Interleukin-8 and monocyte chemoattractant protein-1 mRNAs in oxygen-injured rabbit lung

The chemokines interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) are neutrophil and monocyte attractants, respectively. We hypothesized that IL-8 and MCP-1 mRNA expression in alveolar macrophages (AM) lavaged from rabbit lung would be increased by oxygen exposure, which is known to induce inflammation. Adult rabbits were exposed to > 95% oxygen for up to 64 h and allowed to recover in room air for up to 72 h before killing and pulmonary lavage. Numbers of lavageable polymorphonuclear cells (PMN) and AM rose during the exposure protocol. Quantitative in situ hybridization with 3H-labeled cRNA probes showed both IL-8 and MCP-1 mRNA expression in AM during oxygen exposure, with peak levels of IL-8 mRNA at 56-h oxygen exposure and of MCP-1 mRNA at 64-h oxygen exposure with 24-h room air recovery. IL-8 mRNA was present in PMN between 48-h oxygen exposure and 64-h oxygen exposure with 24-h room air recovery. MCP-1 mRNA was not expressed in PMN. This pattern of chemokine mRNA expression emphasizes the importance of inflammatory cells as effectors in the pulmonary response to oxygen exposure.

Induction of newly synthesized proteins in astroglial cells exposed to lead

Although astroglial cells accumulate lead (Pb), they appear to be less sensitive to its overt deleterious effects than are neurons. One possible mechanism in which as rocytes adapt to Pb may be by upregulating the expression of particular genes. This study evaluated the effect of exogenous Pb on proteins synthesized in primary rat astroglial cultures. Following incubations with 0-50 microM Pb acetate cells were radiolabeled with leucine for various time intervals. Proteins were subsequently analyzed using SDS-PAGE followed by fluorography. Changes observed within the first 24 hr resembled a classical stress response and included increased synthesis of proteins with apparent molecular weights of 90, 70, 32-35, and 23 kDa. The most notable change was the enhanced synthesis and abundance of the 23-kDa protein (p23) which persisted throughout a 14-day treatment period, whereas the synthesis of the other proteins declined. This protein did not appear to be induced in rat lung fibroblasts treated with similar concentrations of Pb. Subcellular fractionation indicated that p23 was localized to the cytosol. Treatment with actinomycin D or cycloheximide prior to the addition of Pb precluded induction of p23. Pulse labeling of cells following a 24-hr Pb exposure revealed that p23 continued to be synthesized for 12 but not 24 hr following removal of Pb. Pulse-chase experiments indicated that the protein was stable for at least 18 hr following the removal of Pb. Two-dimensional gel electrophoresis revealed that the 23-kDa Pb-induced protein consisted of multiple-charged species with pl values ranging from 4.3 to 7.8.

Cell-specific expression of fibronectin in adult and developing rabbit lung

Fibronectin (FN), a glycoprotein component of the extracellular matrix, plays a role in tissue morphogenesis and tissue-specific differentiation through its effects on cell adhesion, cell shape, and cytoskeletal organization. Immunohistochemistry has been used to show that during lung development FN deposition changes, yet the cell-specific sites of pulmonary FN synthesis have not been determined. Because cellular FN synthesis is reflected by FN mRNA abundance, we performed in situ hybridizations to identify pulmonary tissue with the capacity to synthesize FN. Both in situ mRNA hybridization and immunohistochemical staining were performed on tissue sections from lungs of adults and late gestation fetal and neonatal rabbits. In adults, FN transcripts and immunostaining were clearly seen in endothelial cells, smooth muscle cells, and chondrocytes. During lung development, FN transcripts were virtually ubiquitous except in airway epithelium. There was a gradual decrease in FN mRNA abundance with advancing fetal age, but low levels of FN mRNA persisted in neonatal and adult lungs. In contrast, parenchymal immunostaining increased throughout fetal development and remained elevated in the newborn. FN immunostaining was lower in adult lung. In all tissues examined, airway epithelial cells contained no FN transcripts above background. However, immunostaining was detected in airway basement membrane zones and on luminal surfaces of some epithelial cells. The lack of FN transcripts in airway epithelial cells suggests that FN synthesis does not normally occur in this cell type and that its associated FN immunostaining is from another source. The colocalization of FN mRNA and protein in pulmonary endothelial cells, smooth muscle cells, and chondrocytes in adults strongly suggests that these cells are sites of FN synthesis.