Ultrastructural changes in the terminal bronchiole of the rat during continuous, low-level exposure to nitrogen dioxide

Combined exposure to NO2, O3 and H2SO4-aerosol and lung tumor formation in rats

The promoting effects of a combined exposure to two pollutants (NO2, O3 or H2SO4-aerosol) at near ambient levels on lung tumorigenesis induced by N-bis(2-hydroxypropyl) nitrosamine (BHPN) were investigated in male Wistar rats. The rats were given a single intraperitoneal injection of BHPN (0.5 g per kg body wt.) at 6 weeks of age. They then were exposed to clean air, 0.05 ppm O3 (mean concentration for 10 h/day; 0.1 ppm peak concentration), 0.05 ppm O3 (mean concentration for 10 h/day; 0.1 ppm peak concentration) + 0.4 ppm NO2 or 0.4 ppm NO2 + 1 mg/m3 of H2SO4-aerosol for 13 months and were then maintained in a clean room for another 11 months. Room control animals were kept after injection of BHPN in a clean room for 24 months. The incidence of primary lung tumors in rats exposed to 0.05 ppm O3, 0.05 ppm O3 + 0.4 ppm NO2 and 0.4 ppm NO2 + 1 mg/m3 of H2SO4-aerosol with BHPN treatment was 8.3% (3 out of 36 rats), 13.9% (5 out of 36 rats) and 8.3% (3 out of 36 rats), respectively. The tumors were adenomas and adenocarcinomas. The incidence of adenomas was 2.8% (1 out of 36 rats) in the O3 alone group, 11% (4 out of 36 rats) in O3 + NO2 group and 5.6% (2 out of 36 rats) in NO2 + H2SO4 group. The incidence of adenocarcinomas was 5.6% (2 out of 36 rats) in the O3 group, 2.8% (1 out of 36 rats) in O3 + NO2 group and 2.8% (1 out of 36 rats) in NO2 + H2SO4 group. No lung tumors were found in the rats exposed to clean air with BHPN treatment and in animals not given BHPN but exposed to each air pollutant. The difference in tumor incidence between the clean air group with BHPN and the O3 + NO2 group with BHPN was statistically significant. The results show that exposure to O3 alone enhances tumor development and that the combined exposure to O3 or H2SO4 with NO2 produces an additional increase in incidence of lung tumor, respectively. The incidence of slight-moderate to marked alveolar cell hyperplasia in the groups exposed to each air pollutant with BHPN treatment was higher than that in the groups exposed to clean air with BHPN. Exposure to each air pollutant had no effect on the development of bronchiolar mucosal hyperplasia in lungs of rats treated with BHPN.(ABSTRACT TRUNCATED AT 400 WORDS)

Experimental studies on tumor promotion by nitrogen dioxide

The effects of nitrogen dioxide (NO2) on promotion of lung tumorigenesis induced by N-bis(2-hydroxypropyl) nitrosamine (BHPN) were investigated in male Wistar rats. In a preliminary study, the highest non-effective dose of BHPN was found to be 0.5 g per kg body weight. Rats were given a single intraperitoneal injection of BHPN at a dose of 0.5 g per kg body weight or saline at 6 weeks of age, and then exposed to clean air, 0.04 ppm, 0.4 ppm or 4 ppm of NO2 for 17 months, respectively. The incidence of pulmonary tumors in rats exposed to BHPN plus 4 ppm of NO2 was 12.5%; the tumors were adenomas and adenocarcinomas. Adenomas were found in 4 out of 40 rats (10%) and adenocarcinomas were found in 1 out of 40 rats (2.5%). The tumor incidence in the lungs of rats kept in BHPN plus clean air and BHPN plus 0.04 ppm of NO2 was 2.5% (1/40). In both groups adenomas were found. There was no significant difference in tumor incidence between animals exposed to BHPN plus clean air and to BHPN plus 4 ppm of NO2. No lung tumors were found in the group of BHPN plus 0.4 ppm NO2 and in animals exposed to NO2 without BHPN treatment. A high incidence of alveolar cell hyperplasia was observed in the lungs of rats injected with BHPN, and the effect of NO2 on development of alveolar cell hyperplasia was slight. On the other hand, marked bronchiolar mucosal hyperplasia was found in 17 out of 40 rats (42.5%) in the group of BHPN plus 4 ppm of NO2, and in 1 out of 40 rats (2.5%) in each of the group exposed to clean air, 0.04 ppm or 0.4 ppm of NO2 with BHPN treatment, respectively. The hyperplasia in lungs of rats exposed to 4 ppm of NO2 without BHPN treatment was slighter than that in lung of rat exposed to 4 ppm of NO2 with BHPN treatment. On the other hand, tumor incidence in the nasal cavity of rats in each of group exposed to clean air and NO2 with BHPN treatment was 97-100%. Incidence of tumors in other organs in the groups exposed to clean air and NO2 with and without BHPN treatment was very low, and NO2 had no effect on tumor development in the nasal cavity and other organs whether animals were treated with BHPN or not.(ABSTRACT TRUNCATED AT 400 WORDS)

Light and electron microscopic observations on ciliated vacuoles and cysts in the oviductal and endocervical epithelia of the rabbit

Ciliated vacuoles and intraepithelial cysts have been observed in oviductal and endocervical epithelia of rabbits. In this study, rabbits under various hormonal conditions were studied by light and transmission electron microscopy and tissue culture in an attempt to determine their distribution and origin. Ciliated vacuoles most frequently lay in the basal cytoplasm, below or beside the nucleus, and very close to the basal lamina. A few were apically located. Their average diameter was 8.8 by 5.1 microns. Cilia and microvilli projected into the vacuolar lumen. These vacuoles were located intracellularly as evidenced first by the degeneration of both their cilia and microvilli and the moderately dense matrix that often filled the vacuolar lumen, as observed by electron microscopy. Secondly, phase microscopy of the living endocervical epithelium allowed us to observe the beating of the cilia within the vacuoles, not on the surface of such cells. Thirdly, ruthenium red stained the surface glycocalyx of ciliated and secretory cells, but not that of the cilia and microvilli within the vacuoles. The intraepithelial cysts were not observed in all tissue blocks. The largest numbers were found in ovariectomized animals treated for 3 and 5 days with estradiol. More were seen in the isthmus and cervix than in the fimbria and ampulla. The cysts were located most often within the epithelium along the sides of, and at the bases of, the mucosal folds. They were lined by flattened epithelium of various combinations of secretory and ciliated cells. An unusual cell type was associated with some of the cysts and ciliated vacuoles. Its cytoplasm contained aggregates of mitochondria and vesicles whose contents varied in density. Although the genesis of the ciliated vacuoles is not certain, our results indicate that they may arise from aberrant positioning of proliferating procentrioles or from a defect in targeting or transporting the centrioles to the apical plasma membrane to serve as basal bodies. Fusion of adjacent ciliated vacuoles with lumina lined by secretory cells having deep apical invaginations appeared to contribute to the formation of cysts.

Relationship of lipid secretion and particle size to diffuse interstitial change in pneumoconiosis: a pathogenetic perspective

Simple pneumoconiosis due to compact particles, notably in coal workers, sometimes departs from its customary focal formations and a more diffuse distribution of dust-impregnated fibrosis is superimposed. To account for this change, which may be reflected in the acquisition of radiologically irregular opacities in addition to rounded ones, attention is directed first toward type II alveolar epithelium. These cells come early into contact with inhaled particles and the lipid secretion provoked prevents their characteristic aggregation, so they remain in a more dispersed state and the consequent fibrotic reaction then tends to become diffuse. Second, submicron particles appear to act not from within the alveolus like the more usual larger ones, but after direct passage through type I epithelium into the interstitium, where lacking focal accumulation they are able to produce diffuse changes. Complexities, however, remain, among which are coalescence of focal lesions as their severity increases and interplay of agents producing interstitial fibrosis in the general population.

Interspecies comparisons of lung responses to inhaled particles and gases

Two important challenges for inhalation toxicologists involve the elucidation of mechanisms of lung toxicity caused by inhalation of chemicals or particulate materials, as well as the extrapolation of animal data to humans. Because risk estimates of toxicity generally are dependent upon experimental data for which a variety of species are utilized, a fundamental knowledge of species similarities and differences in lung anatomy, physiology, biochemistry, cell biology, and corresponding disease processes is essential. In the present review, the known mechanisms of particle deposition and clearance among various species have been highlighted and related to structure/function relationships and pathogenetic responses to some selected inhaled toxicants. In the aggregate, there is remarkable homogeneity in form and function among the species. Morphologic aspects of the respiratory tract and lung defense mechanisms are qualitatively similar among species. On the other hand, quantitative differences between humans and experimental animals are known to exist with respect to deposition and mucociliary clearance of inhaled particulates, and these factors are likely to influence the dose that is delivered to specific target sites in the lung. It is interesting to consider that pathologic cellular events following asbestos, ozone, and nitrogen dioxide exposure are likely to occur at similar sites in humans, nonhuman primates, and rodents. In this respect, it has been demonstrated that the early lesions of asbestos-induced lung disease in both rats and humans are initiated at similar anatomical sites, i.e., the junctions of terminal airways and alveolar regions. PMs and complement-mediated mechanisms have been implicated in the development of asbestosis in rats; however, it remains to be determined whether complement activation plays an important role in human asbestosis, although pulmonary and interstitial macrophages clearly are associated with the fibrogenic process associated with this restrictive lung disease. The toxic pulmonary effects following ozone exposure have been well studied in rodents and nonhuman primates. It has been established that distal airway and alveolar epithelial cells are principal targets of oxidant pollutants, and this is well supported by dosimetry considerations, morphologic observations, and morphometric analyses. Chronic ozone exposure in rats and monkeys causes epithelial injury at the level of the terminal bronchiole and proximal alveolar regions of the lung.(ABSTRACT TRUNCATED AT 400 WORDS)

Protective effect of beta-naphthoflavone against NO2 toxicity in mice with genetically inducible lung cytochrome P450

The effects of the cytochrome P450 inducer beta-naphthoflavone (BNF) on NO2 toxicity were studied in two strains of mice. In one strain (C57B1/6J), cytochrome P450 could be induced by the aromatic hydrocarbon, while in the other strain (DBA/2J) cytochrome P450 was not inducible by this compound. Mice were treated with BNF before and during 4 days of exposure to 20 ppm NO2. The body growth of NO2-exposed mice improved only in BNF-treated C57B1/6J mice. In this strain, BNF reduced both pulmonary edema (as measured by wet and dry lung weights or as assessed by histological studies) and lung peroxidation (as measured by malondialdehyde). This protective effect of BNF on NO2 toxicity in C57B1/6J mice was associated with an increase in the components of the cytochrome P450 system (cytochrome P450 and cytochrome b5), whereas the activities of pulmonary antioxidant enzymes (superoxide dismutase, glutathione peroxidase, and glutathione reductase) were not significantly increased. These data suggest that the induction of the cytochrome P450 system may be important in promoting NO2 tolerance in those strains of mice in which the cytochrome P450 system is genetically inducible.

Lead and sudden infant death. Investigations on blood samples of SID babies

To investigate a potential relationship between an elevated lead burden and sudden infant death (SID), the lead concentrations (Pb-B) were determined in 41 blood samples from SID babies and compared with the Pb-B of 5 babies who died traumatically and 77 living control babies. Several factors that may influence the Pb-B were taken into consideration, especially a dependence of the Pb-B on age and social class. Moreover, a post-mortem water shift occurs in the blood. Even taking these factors into consideration the distribution of the Pb-B's of the SID group was found to differ on a highly significant level (greater than 99.9%) from the control group. Five Pb-B's of the SID group were higher than the highest lead concentration found in blood from the control babies. Negative influences of lead on the pre- and postnatal maturation of the brain are discussed in the search for a possible causal connection between an elevated lead burden and the occurrence of SID.

Nonolfactory surface epithelium of the nasal cavity of the bonnet monkey: a morphologic and morphometric study of the transitional and respiratory epithelium

The purpose of the present study was to characterize ultrastructurally the nonolfactory nasal epithelium of a nonhuman primate, the bonnet monkey. Nasal cavities from eight subadult bonnet monkeys were processed for light microscopy, and scanning and transmission electron microscopy. Nonolfactory epithelium covered the majority of the nasal cavity and consisted of squamous (SE), transitional (TE), and respiratory epithelium (RE). Stratified SE covered septal and lateral walls of the nasal vestibule, while ciliated pseudostratified RE covered most of the remaining nasal cavity. Stratified, nonciliated TE was present between SE and RE in the anterior nasal cavity. This epithelium was distinct from the other epithelial populations in abundance and types of cells present. TE was composed of lumenal nonciliated cuboidal cells, goblet cells, small mucous granule (SMG) cells, and basal cells, while RE contained ciliated cells, goblet cells, SMG cells, basal cells, and cells with intracytoplasmic lumina lined by cilia and microvilli. TE and RE contained similar numbers of total epithelial cells and basal cells per millimeter of basal lamina. TE was composed of more SMG cells but fewer goblet cells compared to RE. We conclude that nonolfactory nasal epithelium in the bonnet monkey is complex with distinct regional epithelial populations which must be recognized before pathologic changes within this tissue can be assessed adequately.

Ultrastructural changes in the respiratory tract of rats following methyl isocyanate inhalation

The static exposure of rats to 0.25 mg/l methyl isocyanate for 1 h resulted in damage to the epithelium of the proximal bronchioles and upper airways. Bronchiolar cells exhibited both nuclear and cytoplasmic damage; many epithelial cells, particularly in the bronchi and trachea, were killed and/or dislodged from the basement membrane. A "raft" of cell debris and fibrin lined most of the airways during the 1st week after exposure but repair to the underlying epithelium was well advanced within 2-3 days. The majority of airways were lined by a normal epithelium within 3 weeks of exposure, but isolated foci of hyperplasia and occluded airways probably accounted for continued respiratory impairment.

Effects of subchronic inhalation of low concentrations of nitrogen dioxide. I. The proximal alveolar region of juvenile and adult rats

Inhalation of nitrogen dioxide (NO2) produces injury to the epithelium of terminal airways and the alveoli proximal to the airways. Techniques were devised to isolate alveolar tissue from this region for morphometric studies to define the extent of alveolar septal injury caused by NO2. One-day-old and six-week-old rats were exposed to either room air or 0.5 ppm NO2 for 23 hr per day 7 days per week for 6 weeks. An additional group of 6-week-old rats were exposed to 2.0 ppm NO2 for the same duration. Two daily hour spikes to three times the background concentrations (0.5 to 1.5 ppm and 2.0 to 6.0 ppm) were applied Monday through Friday. At the end of the exposure, rat lungs were fixed by intratracheally infusing buffered 2% glutaraldehyde. Pieces of lung tissue were embedded in large plastic blocks which were softened with heat and thin (0.3 mm) sliced. Terminal bronchioles and their corresponding proximal alveolar regions were identified from the thin plastic slices, removed, and glued to cylindrical EM blocks for thin sectioning. Morphometric analysis revealed that epithelial injury occurred in all exposed animals. The juvenile rats which had been exposed to 0.5 ppm NO2 since 1 day of age exhibited changes in the characteristics of type II epithelial cells. These cells spread to cover more alveolar surface and became thinner. Adult animals exposed to 0.5 and 2.0 ppm NO2 showed changes in alveolar macrophages and in the alveolar interstitium in addition to changes in the epithelium. Animals exposed to 0.5 ppm NO2 showed spreading and hypertrophy of type II epithelial cells. Those animals exposed to the higher concentration of NO2 had similar changes in type II epithelial cells and in addition showed an increase in type I cell number. The type I epithelial cells were smaller and covered less alveolar surface area than normal type I cells, suggesting a regenerating population of type I cells. These results suggest that prolonged exposure to low concentrations of NO2 can cause injury to the alveolar epithelium indicated initially by spreading and hypertrophy of type II cells followed by differentiation into type I cells to compensate and repair the injury. Adult rats were as sensitive or more sensitive to NO2 injury than were juvenile rats.

Goblet and Clara cells of human distal airways: evidence for smoking induced changes in their numbers

The goblet cell and Clara cell populations of human distal airway epithelium were examined. The bronchioles, terminal bronchioles, and respiratory bronchioles of 16 smokers and four non-smokers were studied by both light and electron microscopy in surgically resected specimens. A very significantly (p less than 0.001) greater number of goblet cells were found in the bronchioles of smokers compared than in those of non-smokers but no such difference was evident in terminal/respiratory bronchioles. Clara cell numbers in contrast were lower in the bronchioles (p less than 0.01) and terminal and respiratory bronchioles of smokers (p less than 0.01). Both of these alterations in cell frequency may adversely affect small airway function in smokers.

Surface architecture of the mucosal epithelium of the cat trachea: I. Cartilaginous portion

The mucosal covering of the cartilaginous portion of the cat trachea was studied by correlated light, transmission-electron, and scanning-electron microscopy. While in some areas the ciliated pseudostratified epithelial lining is fairly smooth in contour, in other areas it contains longitudinally oriented, cilia-lined clefts. Ducts from submucosal glands sometimes open into the base of these clefts, or into funnel-shaped stomata that are lined by either ciliated or microvillus-rich cells. Specialized epithelial cells are occasionally associated with the clefts or with other regions of surface epithelium. In single sections, these cells appear to contain a cilium-lined vacuole, but serial sectioning has demonstrated that these apparent vacuoles actually are long intracellular invaginations in enormously elongated cells that extend longitudinally in the plane of the epithelium. The function of these cells is undetermined. Basal cells are attached to the lamina densa by means of hemidesmosomes that consistently lack peripheral densities; in contrast, the tall columnar cells have no hemidesmosomes.

Tubular myelin figures in the lung with Wilson-mikity syndrome

An electron microscopic examination of the lung from a patient with Wilson-Mikity syndrome revealed abundant tubular myelin in the atelectatic areas. The tubular myelin was seen free and adjacent to secreted lamellar bodies in the alveolar spaces as well as within macrophages, but never in type II cells. The transverse dimension of the tubular units ranged from 24 to 30 nm, and the distance between two tubules was 5-6 nm. Occasionally the center of a tubule contained a single electron dense particle. The structure of the tubular myelin presented here differs to some degree from that in rat lungs. To our knowledge, the presence of tubular myelin figures has not been reported in cases of Wilson-Mikity syndrome. Their relation to the etiology of the disease is totally unknown; however, our findings that they were present only in the area of atelectasis but not in emphysematous areas may be significant. An accumulation of similar cases with ultrastructural study and combined biochemical and physiological studies is awaited to permit some interpretation.

Histological examination of the rat after long-term exposure to subtoxic automotive exhaust gas

Regarding the potential impact of traffic-born air pollutants on public health, in recent years attention has increasingly been focused on the possible effects on the cardiovascular system. In order to investigate this problem further, the influence of long-term exhaust gas exposure on rats has been studied. One hundred Wistar rats of either sex were exposed 5 X 8 h/week up to 28 months to an atmosphere polluted by the emissions of an idling Otto engine, CO concentrations held constant at 90 ppm. A second group (50 rats) was exposed to 250 ppm for 6 months. Blood parameters and body weight were controlled. Specimens of CNS, heart, vessels, kidney etc. were investigated light microscopically. Focal necroses of the myocardium with inflammatory reactions as well as interstitial fibrosis were found in the heart muscle of the 90 ppm group. In the 250 ppm group endothelial proliferations, edema of the intima and deposits of proteoglycanes in the media were observed. We conclude that subtoxic concentrations of CO which only lead to slight morphologic changes may aggravate preexisting lesions caused by high risk conditions, e.g., hypertension or hypercholesteremia.

Biochemical changes in humans upon exposure to nitrogen dioxide while at rest

The biological response to controlled exposures of nitrogen dioxide (NO2) was studied in 19 human subjects exposed to 0.2 ppm NO2 for 2 hr and compared to 15 control subjects exposed to filtered air for 2 hr. Seven biochemical blood parameters, including glutathione, red blood cell glutathione reductase, 2,3-diphosphoglycerate, methemoglobin, vitamin E, complement C2, and IgA were measured prior to exposure, immediately after exposure, and 22 hr following exposure. The only variable that showed significant change due to NO2 exposure was glutathione. Glutathione is known to protect the erythrocyte from oxidative stress. The increase in glutathione observed upon exposure to NO2 may be a protective reaction of the erythrocyte to meet the oxidative stress.

Effects of nitrogen dioxide on elastin and collagen contents of lung

Male Syrian hamsters were exposed to 30 +/- 5 ppm nitrogen dioxide for 22 hr daily for 3 wk. Nitrogen dioxide-exposed hamsters sacrificed at various times during the 3 wk exposure showed a general loss of body weight and an increased dry lung weight when compared with the controls, which were housed in a similar, but nitrogen dioxide-free environment. Analysis of total lung collagen and total lung elastin revealed a net decrease in the moieties within 4 and 10 days, respectively, following commencement of nitrogen dioxide exposure. Total lung collagen returned toward pre-exposure levels by the 14th day of nitrogen dioxide exposure. Total lung elastin did not return toward normal until termination of nitrogen dioxide exposure. Recovery in room air for 3 wk following 21 days of nitrogen dioxide exposure restored the total pulmonary collagen and elastin to valutin and collagen degradation and synthesis differ during and after nitrogen dioxide exposure. Lung collagen loss was observed earlier and was restored to normal values during the continuation of nitrogen dioxide exposure. Lung elastin loss occurred later and persisted during the entire period of exposure but returned to normal after exposure was terminated.

Ultrastructural changes of the rabbit lung after a 5 ppm nitric oxide exposure

Four male rabbits were continuously exposed to 5 ppm nitric oxide for 14 days. Four rabbits served as controls. Specimens from pulmonary arterioles and alveolar tissue were examined by light and transmission electron microscopy. The most conspicuous findings were fluid-containing vacuoles inside the arteriolar endothelial cells and/or in the intercellular junctions. Thickening of the alveolo-capillary membrane due to accumulation of edema fluid in the interstitial space was also observed.

Histological changes of terminal bronchioles in rats during the exposure to nitrogen dioxide

At long-term exposure to 5 ppm NO2 (w/w), courses of histological changes in the epithelium of the terminal bronchioles of rats were observed. In the course of the experiment the first alterative changes were expressed by the loss of cilia and cell differentiation. The changes were followed by epithelial hyperplasia, leading to conspicuous narrowing of the lumen of bronchioles. After the phase of hyperplasia a phase of reparation followed, leading to the development of nonciliated epithelium without determinable Clara cells, with areas of uniform multi-layered epithelium. At the same time, in the longest interval of 11 weeks new alterative changes analogous to those found at the beginning of the experiment were observed.