Primary pulmonary responses to toxic agents

Do corticosteroids have a role in preventing or reducing acute toxic lung injury caused by inhalation of chemical agents?

OBJECTIVE

To assess the evidence that treatment with corticosteroids improves the outcome in those exposed to lung-damaging agents.

METHODS

We searched Pubmed, Toxnet, Cochrane database, Google Scholar, and Embase from 1966 to January 2010 using the search terms "steroid", "corticosteroid", "lung injury", "lung damage", and "inhalation". These searches identified 287 papers of which 118 contained information on animal studies. However, most were reviews or case reports and only a few were controlled animal experiments of which 13 were considered relevant. ROLE OF CORTICOSTEROIDS:

ANIMAL STUDIES

Corticosteroids have no beneficial effect at the alveolar level on acute lung injury, which is caused by inhalation of poorly water-soluble compounds (e.g. nitrogen dioxide, ozone, phosgene) or following severe exposure to water-soluble compounds (e.g. chlorine, ammonia). In the recovery phase, corticosteroids may even be harmful, because corticosteroids hamper the division of type II alveolar cells and hamper the differentiation from type II into type I alveolar cells. The latter is important for the re-epithelialization of the alveolus and removal of excess of water in the alveolus. Furthermore, the quality of animal studies does not always allow extrapolation to human exposures. Differences between humans and animals in anatomy, pulmonary defense systems, breathing physiology, as well as the way the animals have been exposed, and the timing and route of corticosteroids in animal studies make predictions difficult. ROLE OF CORTICOSTEROIDS:

HUMAN STUDIES

An abundance of uncontrolled case reports and a few human crossover studies have evaluated the outcome of human volunteers exposed to various lung-damaging agents. Only a few reports contained systematic information on corticosteroid treatment. Data on the efficacy of corticosteroids after human exposure to lung-damaging agents are inconclusive. Often the number of patients involved is small or the severity of exposure is unclear or not well determined. These reports are therefore limited in their ability to establish a cause-effect relationship for the treatments involved. In some studies involving mild to moderate exposure to water-soluble agents (e.g. chlorine, ammonia), corticosteroid treatment was beneficial for some physiological parameters, such as airway resistance or arterial oxygen tension. However, severe lung injury and inflammation appear not to be improved by corticosteroid treatment. The optimal duration of treatment to obtain these beneficial effects has not been assessed adequately, but it only seems to be useful in the first hours after exposure. Generally, studies evaluating exposure to water-soluble compounds have too short a follow-up, which hampers the evaluation of the efficacy of corticosteroid treatment. The results of studies with longer follow-up suggest that the initial slight improvement in some variables is lost several hours after exposure.

CONCLUSIONS

Clinical data on the efficacy of corticosteroids after human exposure to lung-damaging agents are inconclusive as the number of well-structured controlled studies is small and the indications for administration of corticosteroids are unclear. There have been no human controlled studies of high-dose exposure to lung-damaging agents. Furthermore, treatment with corticosteroids is limited by the potential side effects, such as prolonged neuromuscular weakness, deregulation of glucose metabolism, superinfection, and sepsis, which could diminish the chances for recovery.

An international registry for toxic inhalation and pulmonary edema: notes from work in progress

Acute toxic inhalation by irritant, and particularly oxidant, gases has until recently been considered to be no more complicated conceptually than a chemical burn of the epithelial surface. More recently, however, toxic inhalation has been appreciated to be a complex process involving biochemical, morphological and functional changes which are quantitatively similar, although inducible by different agents. Recent advances in pulmonary pathophysiology, inhalation toxicology, and particularly endothelial biology have clarified the events occurring at the moment of, and immediately following, exposure to oxidant gases. Studies of the pathophysiologic mechanisms associated with toxic inhalation by oxidant gases have been relatively static, however. Implications of recent findings in related fields illuminate the pathophysiology of toxic inhalation. Several principal speakers in this workshop are collaborating in an effort to develop a research facility for the study of toxic inhalation injury. This would be an international registry to serve as a teaching and research facility for documentation of cases of occupational and environmental toxic inhalation, considered as lung injury resulting from the inhalation of a toxic substance in a workplace setting or an uncontrolled release affecting residents of a community. The registry, as proposed, would encourage submissions by clinicians and institutions of a data set on each patient and on each incident; the registry would further encourage long-term follow-up of subjects and documentation of residual effects.

Activities of cytochrome P450-dependent monooxygenases and antioxidant enzymes in different organs of Norway rats (Rattus norvegicus) inhabiting reference and contaminated sites

Wild Norway rats (Rattus norvegicus) were collected from a site contaminated by a range of polycyclic aromatic hydrocarbons (PAHs), mineral oils, polychlorobiphenyls (PCBs) and heavy metals. Activities of cytochrome P450 monooxygenases (ethoxy-, pentoxy- and benzoxy-resorufin O-dealkylases, and 4-nitrophenol hydroxylase) were measured in microsomal fractions from liver and lung. Antioxidant enzyme activities (superoxide dismutase, catalase, selenium-dependent and non-selenium-dependent glutathione peroxidases) were also measured in cytosolic fractions from lung and liver, and in erythrocytes. The levels of activities were compared with those found in control laboratory rats and in wild Norway rats reared in a terrarium. Results show that rats living in a polluted environment have monooxygenase activities higher than that of control animals in both liver and lung. Some modifications of antioxidant enzyme activities were also found in these animals.

Release of a mitogenic factor by adult rat lung slices in culture

In an effort to develop a suitable bioassay for testing lung growth factors that might be operative during compensatory lung growth following partial pneumonectomy, a simple and inexpensive lung organ culture system was characterized. The culture employs lung tissue slices obtained by means of a device allowing thicknesses of 500 microns to be cut reproducibly. To avoid the collapse of the organ, the alveolar spaces were filled prior to culture with Noble agar-containing Eagle's-Dulbecco's modified medium. Lung tissue sections could be maintained ultrastructurally intact for at least one week. The results showed that upon culture, a part of the type II pneumocytes undergo differentiation into type I pneumocytes, thus demonstrating that the culture system may be suited for differentiation studies. One surprising feature of this culture system was the mitogenic impulse associated with culture. Radioactively labeled thymidine incorporation was strongly stimulated in the culture, mainly affecting the epithelial cells, as could be established by "back-to-back" autoradiography. With a reconstruction experiment, it was possible to demonstrate the local release of a mitogenic factor following slicing, mincing, or dissection of the lung tissue, which could be assayed by its ability to induce serum-starved Balb/c 3T3 cells to synthesize DNA in culture.

Effects of short-term, single and combined exposure to low-level NO2 and O3 on lung tissue enzyme activities in rats

To examine the pulmonary effects of relatively low levels of NO2 and O3, and test for any possible interaction in their effects, we exposed 3-mo-old male Sprague-Dawley rats, free of specific pathogens, to either filtered room air (control) or 1.20 ppm (2256 micrograms/m3) NO2, 0.30 ppm (588 micrograms/m3) O3, or a combination of the two oxidants continuously for 3 d. We studied a series of parameters in the lung, including lung weight, and enzyme activities related to NADPH generation, sulfhydryl metabolism, and cellular detoxification. The results showed that relative to control, exposure to NO2 caused small but nonsignificant changes in all the parameters; O3 caused significant increases in all the parameters except for superoxide dismutase; and a combination of NO2 and O3 caused increases in all the parameters, and the increases were greater than those caused by NO2 or O3 alone. Statistical analysis of the data showed that the effects of combined exposure were synergistic for 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, glutathione reductase, and superoxide dismutase activities, and additive for glutathione peroxidase and disulfide reductase activities, but indifferent from those of O3 exposure for other enzyme activities.

Localization, distribution, and induction of xenobiotic-metabolizing enzymes and aryl hydrocarbon hydroxylase activity within lung

The metabolism of xenobiotics within lung often leads to toxicity, although certain pulmonary cells are more readily damaged than others. This differential susceptibility can result from cell-specific differences in xenobiotic activation and detoxication. The localization and distribution of xenobiotic-metabolizing enzymes (cytochromes P-450, NADPH-cytochrome P-450 reductase, epoxide hydrolase, glutathione S-transferases, UDP-glucuronosyltransferases, and a sulfotransferase) and of aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity determined immunohistochemically and histochemically, respectively, within lung are discussed. Findings reveal that xenobiotics can be metabolized in situ, albeit to different extents, by bronchial epithelial cells, Clara and ciliated bronchiolar epithelial cells, and type II pneumocytes and other alveolar wall cells and that enzymes and activities are not necessarily induced uniformly among these cells.

A new monoclonal antibody to study mouse macrophage antigen during BHT-induced lung injury and repair

A rat monoclonal antibody 133-13A to a mouse lung carcinoma cell line was found to react with macrophages in mouse lung [1]. This monoclonal antibody is different from previously described antibodies to macrophages. Immunogold electron-microscopy and immunoperoxidase light microscopy have been used to show that MoAb 133-13A binds specifically to macrophages in normal and in BHT treated mouse lungs. This MoAb recognizes a protein of approximately 100 kDa (P100) on cultured lung carcinoma cells and a 87 kDa protein on macrophages from lung or the peritoneal cavity which is different from other macrophage antigens. The surface glycoprotein has been purified from cultured cells using immunoaffinity chromatography. The purified protein was radioiodinated and MoAb 133-13A was used to develop a competition radioimmunoassay to quantitate P100. Spleen, intestines, lung, skin and uterus all have high levels of P100. P100 on peritoneal macrophages has been determined to be about 94,000 molecules/cell. Analyses of lung lavage and whole lung homogenates from mice treated with BHT, BHT plus 70% O2, and 70% O2 alone show that treated animals have elevated P100 content compared to corn oil treated mice.

Changes in some histochemically demonstrable enzymes in macrophages exposed to quartz dust in vitro

Cytochemical studies were carried out on rat alveolar and peritoneal macrophage cultures following exposure to quartz and corundum dusts. Quartz increased the number of ATPase positive cells and brought about an enhancement in the peroxidase and diffusion of the acid phosphatase activity of the exposed cells. In unexposed cell cultures, acid phosphatase activity was higher in alveolar than in peritoneal macrophages and was dependent upon the duration of incubation. Corundum produced no significant effect on the enzyme activity. Quartz treatment did not alter esterase activity whereas corundum exposed cultures showed a decline. A significant increase in mitochondrial succinic dehydrogenase activity was observed in peritoneal macrophages after quartz treatment. The results demonstrate alteration in the marker enzymes of plasma membranes, mitochondria and lysosomes during phagocytosis of quartz dust as the key event of dust cell interaction in vitro.

Oxidant gas injury to the lung: a discussion on the functional implications

Acute toxic inhalation by the oxidant gases, particularly ozone (O3), nitrogen dioxide (NO2) and oxygen (O2) at high tension, has been assumed to be no more than a chemical burn of the epithelial surface. More recently, oxidant toxic inhalation has been appreciated as a complex process involving biochemical, morphological and functional changes which are qualitatively similar although inducible by different agents. Recent advances in pulmonary pathophysiology, inhalation toxicology and particularly endothelial biology now challenge the validity of a theoretical framework which seemed almost complete just 5 years ago. Considerable attention has been paid in recent years to the biochemical events occurring at the moment of and immediately following exposure to the oxidant gases. Progress in elucidating the initial events has been rapid and promises a more complete picture in the near future. Studies of the pathophysiologic mechanisms associated with toxic inhalation by the oxidant gases have been relatively static, however. In this discussion, implications of recent findings in related fields were examined in an effort to identify new hypotheses and directions for investigation.

Differences in naphthalene-induced toxicity in the mouse and rat

Following the intraperitoneal administration of naphthalene (200 mg/kg) to mice, the lung, in comparison with other organs, was selectively damaged. Histological examination of the lungs showed that it was the non-ciliated, bronchiolar epithelial cells (Clara cells) which were damaged. At higher doses (400 mg/kg and 600 mg/kg, i.p.), there was also damage to the cells in the proximal tubules of the kidney. In contrast to the effect in mice, doses of naphthalene as high as 1600 mg/kg (i.p.) caused no detectable pulmonary or renal damage in the rat. This difference in toxicity between the mouse and rat was reflected by the ability of naphthalene to more severely deplete the non-protein sulphydryls in the mouse lung and kidney than in those organs in the rat. In order to investigate the species difference in toxicity, the metabolism of naphthalene by lung and liver microsomes of the mouse and rat was studied. In all cases, naphthalene was metabolised to a covalently bound product(s) and to two major methanol-soluble products, which co-chromatographed with 1-naphthol and 1,2-dihydro-1,2-dihydroxynaphthalene. However, both the covalent binding and metabolism were approximately 10-fold greater in microsomes prepared from mouse lung compared with those from the rat. This observation may in part explain the difference in toxicity of naphthalene to the mouse and rat lung. As 1-naphthol is a major metabolite of naphthalene and previous work had suggested that most of the microsomal catalysed binding of naphthalene was due to further oxidation of 1-naphthol, the role of 1-naphthol in mediating the naphthalene-induced toxicity was investigated. In neither the mouse nor the rat did 1-naphthol cause a depletion of non-protein sulphydryl levels or tissue damage in the liver, lung or kidney. Thus the toxicity of naphthalene does not appear to be mediated via 1-naphthol.

Stimulation of poly(ADP-ribose) synthetase activity in the lungs of mice exposed to a low level of ozone

Toxic effects of O3 are mediated through the formation of free radicals, which can cause DNA strand breaks. Cellular DNA repair is dependent upon the formation of poly(ADP-ribose) (polyADPR) catalyzed by polyADPR synthetase. In order to evaluate whether O3 exposure inflicted DNA damage in lung tissue, we measured the activity of polyADPR synthetase (known to be activated in response to DNA damage) in mouse lungs after exposure to 0.45 ppm (882 micrograms/m3) O3 for up to 7 days. The enzyme activity was stimulated with O3 exposure relative to unexposed controls, showing a 20% (P less than 0.05) increase at Day 5 and 42% (P less than 0.001) at Day 7 of O3 exposure. In addition, the activity of superoxide dismutase (SOD), known to be stimulated in response to production of superoxide anion (.O2-), was measured as an indicator of free radical involvement. Relative to unexposed controls, the SOD activity in exposed animal lungs increased to the peak level at Day 5 (48%, P less than 0.001) and then declined at Day 7 of O3 exposure but was still higher than controls (17%, P less than 0.05). When animals, after 5 days of O3 exposure, were allowed to recover in filtered room air, the activities of both enzymes declined to their respective control values in 6 days. These results suggest a possible temporal relationship between O3 injury and the activities of polyADPR synthetase and a free radical scavenging enzyme, SOD. The stimulation of polyADPR synthetase activity with O3 exposure, reflecting a response to lung cellular DNA repair, may be a sensitive indicator for assessing DNA damage in oxidant injury.

Cellular responses to O,O,S-trimethyl phosphorothioate-induced pulmonary injury in rats

O,O,S-Trimethyl phosphorothioate (OOS-TMP), an impurity of many organophosphorus insecticides, causes a delayed toxicity in rats and mice which is associated with morphological and biochemical changes in the lung. Oral administration of doses as low as 20 mg/kg alters bronchiolar epithelial morphology and causes an increase in bronchopulmonary lavage lactate dehydrogenase levels. In the present study, the effects of OOS-TMP on alveolar and bronchiolar cells were examined by determining the patterns of cellular regeneration in rats at periods of 12 hr, 24 hr, 3 days, and 7 days after treatment. Dividing cells were labeled with tritiated thymidine and studied with autoradiographic techniques. The results showed that OOS-TMP treatment initiated proliferation of alveolar type II cells within 24 hr. The proliferative response of type II cells continued to increase in 3-day and 7-day treatment groups. Labeled alveolar type I cells began to appear after 3 days, indicating that type II cells were dividing to replace damaged type I cells. Cells of the alveoli were thickened and showed vacuolization. In the bronchioles, labeled Clara cells were increased on Day 3 and Day 7 while the number of labeled ciliated cells remained near control levels throughout all time points, indicating that in bronchiolar epithelium, OOS-TMP stimulates the proliferation of Clara cells but does not damage ciliated cells. The binding of tritiated OOS-TMP to lung tissue was also examined by autoradiography. It was found that [3H]OOS-TMP binds to all regions of lung tissue.

An ultrastructural study of the acute effects of 4-nitroquinoline 1-oxide on the hamster lung

The alterations, visible by light and electron microscopy, in the distal airway cells of Syrian golden hamsters were analyzed at several time intervals, from 6 hr to 4 weeks, after a single subcutaneous injection (120 mg/kg body wt) of 4-nitroquinoline 1-oxide (4NQO), a potent carcinogen. 4NQO induced injurious effects selectively on the bronchiolo-alveolar region, and morphological changes were recognizable within 12 hr after the injection. Both ciliated and nonciliated (Clara) cells of the bronchiole revealed degeneration, especially marked proliferation and dilation of smooth endoplasmic reticulum of the latter cell. Alveolar epithelial and endothelial cells were damaged, showing diffuse exudative inflammation. These regressive changes were most prominent on the third day of the experiment. After the fourth day, large cuboidal cells with scanty organelles in their abundant cytoplasm proliferated along the alveolar surfaces in the process of repairing the damaged lung tissue, and then tubular structures in the alveoli were formed. Mitotic activity appeared in the epithelium around the bronchiolo-alveolar junctional area, and immature cells with a few organelles were formed. After 2 weeks, the inflammatory changes and cell renewal in the alveoli disappeared, and bronchiolization was established as a result of atypical maturation of the respiratory cells just around the bronchiolo-alveolar junctional area.

Prolonged activation of rat lung ornithine decarboxylase in monocrotaline-induced pulmonary hypertension

Polyamines are believed to have an essential role in cellular growth and differentiation. Activation of ornithine decarboxylase, the initial rate-limiting enzyme in polyamine biosynthesis, is an early event characteristic of cell growth processes. Monocrotaline-induced pneumotoxicity is associated with cellular hypertrophy and proliferation, most notably pronounced medial thickening of pulmonary arterioles and hypertrophy of right ventricular myocardial cells. We reasoned that polyamines may be causally related to these events and, therefore, elevations in lung and right ventricular ornithine decarboxylase activities might precede development of pulmonary hypertension and right ventricular hypertrophy. To test this hypothesis adult male rats were given monocrotaline (105 mg/kg, s.c.); lung and right and left ventricular ornithine decarboxylase activities, pulmonary artery pressure, and right ventricular hypertrophy were assessed at 1, 4, 7, 10, 14, 16 and 21 days post treatment. Lung ornithine decarboxylase activity was increased approximately 8-fold on day 1 and remained elevated through day 7. Right ventricular ornithine decarboxylase activity was not elevated above control values at any time. Elevated pulmonary artery pressure and right ventricular hypertrophy were not apparent until day 16 and day 14 respectively. Thus, sustained activation of lung ornithine decarboxylase occurred at least 1 week prior to the development of pulmonary hypertension, suggesting that polyamines may play an important role in the pulmonary vascular remodeling that accompanies monocrotaline-induced pneumotoxicity.

Metabolism of bromobenzene to glutathione adducts in lung slices from mice treated with pneumotoxicants

Recent studies showing that the bronchiolar Clara cell and alveolar Type II cell are major loci of cytochrome P-450 monooxygenases in the lung suggested that measurement of xenobiotic metabolizing enzyme activity might provide a useful and sensitive index of injury to these cell types. Accordingly, an assay has been developed for quantitating the rate of formation of reactive bromobenzene metabolites in lung slices which is based upon measuring the rate of formation of bromobenzene glutathione adducts. To demonstrate that monitoring adduct formation would yield quantitatively similar data to the traditional covalent binding assay for measuring the formation of reactive bromobenzene intermediates, covalent binding and conjugate formation were assayed in incubations of phenobarbital-induced hepatic microsomes conducted in the presence of various cytochrome P-450 monooxygenase inhibitors. Incubation conditions which decreased the rate of covalent binding (incubations done in the absence of glutathione) resulted in similar decreases in conjugate formation (incubations done in the presence of glutathione). In lung slices, the metabolism of bromobenzene to glutathione conjugates was linear for 20 min and continued to increase with time over the entire 160 min of the study. The formation of bromobenzene glutathione adducts in lung slices from piperonyl butoxide-treated animals occurred at a significantly lower rate than control. Likewise, lung slices from animals treated with butylated hydroxytoluene or carbon tetrachloride, agents known to injure alveolar epithelial cells, metabolized bromobenzene to glutathione conjugates at significantly slower rates than control. In contrast, treatment with naphthalene or dichloroethylene, agents which damage the bronchiolar epithelial cells, had little or no effect on conjugate formation. Similarly, there were no significant differences in the rate of bromobenzene glutathione conjugate formation between lungs of air- and ozone-exposed (1.0 ppm X 4 hr) mice killed 2, 24, 48, 72, or 120 hr after exposure. These studies suggest that monitoring the rate of bromobenzene glutathione conjugate formation in lung slices may be a useful and sensitive biochemical index of injury to certain cells of the lung but that severe damage to the nonciliated bronchiolar epithelial cells has little effect on the rate of metabolic activation of this aromatic hydrocarbon.

A comparison of biochemical effects of nitrogen dioxide, ozone, and their combination in mouse lung

Swiss Webster mice were exposed to either 4.8 ppm (9024 microgram/m3) nitrogen dioxide (NO2), 0.45 ppm (882 microgram/m3) ozone (O3), or their combination intermittently (8 hr daily) for 7 days, and the effects were studied in the lung by a series of physical and biochemical parameters, including lung weight, DNA and protein contents, oxygen consumption, sulfhydryl metabolism, and activities of NADPH generating enzymes. The results show that exposure to NO2 caused relatively smaller changes than O3, and that the effect of each gas alone under the conditions of exposure was not significant for most of the parameters tested. However, when the two gases were combined, the exposure caused changes that were greater and significant. Statistical analysis of the data shows that the effects of combined exposure were more than additive, i.e., they might be synergistic. The observations suggest that intermittent exposure to NO2 or O3 alone at the concentration used may not cause significant alterations in lung metabolism, but when the two gases are combined the alterations may become significant.

The action of equinatoxin, a peptide from the venom of the sea anemone, Actinia equina, on the isolated lung

On perfusion through isolated lungs from male Sprague-Dawley rats, equinatoxin caused a dose-dependent increase in the wet to dry weight ratio. Ratios were significantly elevated above control values at equinatoxin concentrations of 80-200 ng/ml. The increased ratios were accompanied by an increase in the permeability of the lung vasculature. When equinatoxin was perfused through isolated lungs at concentrations of 100 ng/ml or greater, significantly more [3H]polyethylene glycol (PEG; approximately 900 mol. wt) was retained in the extravascular space as compared to controls. Perfusion pressures of the lung were significantly elevated above controls at equinatoxin concentrations greater than 100 ng/ml. These effects of equinatoxin were not mediated by degranulation of mast cells, as preperfusion of the lung with 100 or 200 microM Na cromolyn or 1 microM lanthanum chloride did not modify the pulmonary response to equinatoxin. At concentrations of equinatoxin below 150 ng/ml the fluid movement appears to be restricted primarily to intracellular, or possibly interstitial, spaces, as no significant amounts of [3H]polyethylene glycol were recovered by tracheal lavage. At concentrations of equinatoxin equal to or greater than 150 ng/ml, significant amounts of PEG were washed from the trachea. As it is a potent inducer of pulmonary edema, equinatoxin may become an important probe to study fluid regulation in the lung.

Changes in angiotensin-converting enzyme activity in lungs damaged by the pyrrolizidine alkaloid monocrotaline

Administration of monocrotaline, a pyrrolizidine alkaloid, to male Sprague-Dawley rats for up to three weeks increased dry lung weights by 64% and reduced the specific activity of lung angiotensin-converting enzyme activity by 64%. When the total activity per lung is calculated, however, there is no significant difference between control and monocrotaline-treated animals. The decrease in specific activity is due to increase in total lung protein (52% above control) and not to an actual reduction in the total angiotensin-converting enzyme activity in th lung.

Biochemical response of rat lung to inhaled n-hexane

Biochemical response of the rat lung to inhaled n-hexane was investigated. Dose-dependent increase in protein, lipid, sialic acid, lactate dehydrogenase, angiotensin-converting enzyme, acid and alkaline phosphatase was observed in the cell-free lavage effluent of the lungs of exposed rats compared to the control animals. This was interpreted as enhanced pulmonary secretions accompanied by increased cell damage.

Age-dependent pulmonary response of rats to ozone exposure

The influence of age on O3 effects in the lung was studied in 8 groups of Sprague-Dawley rats: 7, 12, and 18 d of age (neonatal); 24, 30, and 45 d of age (infant); and 60 and 90 d of age (adult). Lung weight, total lung protein and DNA contents, and a series of marker enzyme activities in lung tissue were determined. After exposure of rats from each group to 0.8 ppm (1568 microgram/m3) O3 continuously for 3 d, a biphasic effect was noted. The biochemical parameters, expressed per lung, in O3-exposed rats relative to their corresponding controls decreased in the 7- and 12-d-old groups, increased or remained unchanged in the 18-d-old group, and increased in the 24- to 90-d-old groups. However, the increases were much greater for 60- to 90-d-old rats than for 24- to 30-d-old rats. The increase in lung biochemical parameters is thought to occur in response to lung injury and subsequent repair processes, and greater increases in the lungs of older rats suggest that they are more responsive to O3 exposure than younger rats. The decrease in lung biochemical parameters and increased mortality in 7- and 24-d-old neonatal rats suggest that they are more susceptible to O3 stress than infant and adult rats.

In vivo incorporation of 3H-choline in alveolar type-II pneumocytes in mice treated with butylated hydroxytoluene (BHT)

Butylated hydroxytoluene has been previously shown to damage alveolar type-I cells followed by proliferation of type-II pneumocytes which then redifferentiate into intermediate and newly formed type-I epithelial cells. In relation to this transformation process, in vivo incorporation of H3-choline, a precursor of the main component of lung surfactant, was studied in type-II cells of BHT-treated mice by electron microscopic radioautography. The labeling density was reduced in some type-II cells at 2, 3 and 5 days after a single injection of BHT. Cellular compartment analysis indicated that the transformation of type-II cells is accompanied by a notable loss of their lamellar body component as well as a decreased radioautographic labeling associated with this cell type, possible in relation with modified synthesis of phospholipid material of surfactant.

Biochemical changes in rat lungs after exposure to nitrogen dioxide

Sixty-day-old male, specific pathogen-free rats were exposed continuously to 5 or 15 ppm NO2 for 1-7 d. Lung tissue from exposed and control rats was then analyzed for biochemical and enzymatic parameters. The exposure resulted in increased lung enzymatic activities, including elevated protein and DNA contents and nonprotein sulfhydryl levels. Biochemical and enzymatic parameters generally increased maximally after 4 d and remained elevated for up to 7 d of continued exposure. The magnitude of these increases was higher for 15 than for 4 ppm NO2. The increases in biochemical and enzymatic parameters may have occurred in response to NO2-induced lung injury.

Biochemical studies on pulmonary response to inhalation of methylene chloride

Biochemical response to the toxic lung damage induced by inhalation of methylene chloride was studied. Significant increases in protein, hexose, sialic acid, lactate dehydrogenase, acid and alkaline phosphatase content were observed in the cell-free lavage effluents from lungs of exposed rats compared to the control animals. This was interpreted as increased cell damage accompanied by enhanced pulmonary secretions, perhaps of glycoproteins and mucins, as a result of inhalation toxicity.

Reduced yield of pulmonary surfactant: patterns of response following administration of chemicals to rats by inhalation

Repeated exposure of rats to trichloroethylene, carbon tetrachloride, gasoline vapour or to cigarette smoke is followed by significant reduction in the recovery of pulmonary surfactant, inhibition being evident as early as 5 days after commencement of treatment. The degree of reduction in surfactant recovery was dose-dependent and the kinetics of this reaction indicated the relative toxicities of the treatments. The results are discussed with reference to the use of surfactant recovery as an indicator of non-specific injury to respiratory tissue.

Adult rat lung in organ culture: maintenance of histotypic structure and ability to synthesize phospholipid

The maintenance of adult rat lung explants in organ culture was assessed both morphologically and biochemically. A comparison of several culture media indicated that Ham's F12K plus 1.0 microM dexamethasone, which maintained the explants for 14 days, was superior. The ability of the explants to synthesize dipalmitoylphosphatidylcholine increased with the length of cultivation to values greater than the noncultivated controls. The DNA content remained constant for 7 days, and a relatively normal structural relationship between type I and type II pneumocytes was maintained. Explants cultivated in Ham's F12K without dexamethasone did not maintain a histotypic morphology; the type II pneumocytes appeared to proliferate and the ability to synthesize phosphatidylcholine decreased.

An inhibitor of lipid peroxidation in rat lungs

Formation of lipid peroxides in vitro was investigated in the lung, liver, and brain homogenates of normal male rats. Unlike brain tissue, increasing the concentration of lung or liver in homogenates resulted in decreased output of lipid peroxides. Further, lung homogenates exerted an inhibition of lipid peroxide formation by brain and dilute liver homogenates. The factor responsible for such inhibition was located in the postmitochondrial supernatant, was heat stable, nondialysable, could be preserved in frozen state for 60 days, concentrated by dialysis against powdered sucrose, and precipitated by ammonium sulphate.

Correlation of biochemical and morphological changes induced by chemical injury to the lung

Comparison has been made of injury to the rat pulmonary alveolar parenchyma evoked by intravenous injection of N-nitrosomethylurethane, intratracheal instillation of 3-methylcholanthrene or repeated inhalation for up to 15 days of carbon tetrachloride, trichloroethylene or gasoline vapour. Biochemical analyses, including assessment of rates of RNA and DNA synthesis and secretion of pulmonary surfactant, were correlated with morphological changes determined by electron microscopy. Single doses of N-nitrosomethylurethane or 3-methylcholanthrene inhibited incorporation of [14C] orotate into lung RNA 1--3 days after treatment. Daily exposure for 30 min to carbon tetrachloride or trichloroethylene vapour caused less marked reduction in orotate incorporation. Ultrastructural examination revealed that 3-methylcholanthrene toxicity was characterised by cytoplasmic change including disruption of surfactant lamellaie of Type 2 pneumocytes and variable degenerative changes Type 1 pneumocytes. Eight to ten days after treatment, the morphological evidence of hypertrophy/hyperplasia and transformation of Type 2 pneumocytes correlated well with biochemical evidence of stimulated incorporation of [3H]thymidine. Inhalation of carbon tetrachloride or trichloroethylene vapour produced milder responses including occasional degenerative changes in Type 1 pneumocytes, reduced numbers of surfactant lamellae in Type 2 pneumocytes and no change in [3H]thymidine incorporation. In contrast to the gradation of injury produced by the various chemicals, all procedures caused a marked and reproducible reduction in secretion of pulmonary surfactant as determined by endobronchial lavage. Following solvent inhalation, reduced recovery of surfactant was detected within 5 days of repeated exposure and thereafter no further change in this depressed level resulted from continued exposure for a further 10 days. The data are discussed in terms of a generalised pattern of response by pulmonary alveolar tissue to chemical injury and the apparent sensitivity of surfactant secretion as an indicator of damage to the lung.

Pulmonary responses to atmospheric pollutants. II. Effect of petrol vapour inhalation on secretion of pulmonary surfactant

Inhalation of air contaminated with petrol vapour has been shown to produce reduced surfactant levels in the lungs of rats. Pulmonary surfactant was obtained by endobronchial lavage followed by salt extraction and freeze drying to obtain the dry, hydrophobic product. During 45 days of continuous exposure, the lowest yield of surfactant was obtained after 15 days of treatment. During the following 30 days of treatment, the surfactant yield reached a relatively constant level, approximately half the mean value for control animals. Chromatographic analysis indicated no qualitative alteration in the phospholipid components of surfactant with increasing times of exposure to the irritant. It has been possible to correlate biochemical evidence of toxic lung injury with signs of cellular damage obtained from ultrastructural studies.

Pulmonary responses to atmospheric pollutants. I: an ultrastructural study of fibrosing alveolitis evoked by petrol vapour

Rats exposed to an atmosphere contaminated with petrol vapour at a concentration of 100 parts per million for up to 12 weeks exhibit a high incidence of electron microscopic changes in the lung parenchyma characterized by interstitial fibrosis with associated alveolar collapse. Initial changes appearing after 6 weeks include degeneration of endothelium and interstitial fibroblasts followed by hypertrophy of Type 2 pneumocytes. Subsequent degeneration of surfactant organelles of the hypertrophied Type 2 pneumocytes correlates with the appearance of focal alveolar collapse and associated interstitial fibrosis. Because of the rapidity with which lesions are induced in the rat lung, this experimental technique provides an economical and reproducible model for an integrated study of the sequential morphological and biochemical events preceding pulmonary fibrosis which might well lead to a better understanding of the enigmatic human syndrome of fibrosing alveolitis.

Human granulocyte specific nuclear antigen(s). I: Production of antisera and determination of specificity

Non-histone protein-DNA complexes isolated from human lung tissue were used to immunize New Zealand rabbits. Quantitative microcomplement fixation and immunocytochemistry revealed a specific chromatin antigen(s) in the human granulocyte nucleus. The study demonstrates the feasibility of employing antisera against chromosomal non-histone protein-DNA complexes for the immunochemical identification of cell types.