Indomethacin and flurbiprofen speed recovery of rat bronchial epithelium after exposure to cigarette smoke

Animal models of chronic bronchitis and their relevance to studies of particle-induced disease

Chronic bronchitis is a significant cause of morbidity and mortality. Chronic irritation of the conducting airways by inhaled substances, most importantly cigarette smoke, air pollution, and occupational exposures, is thought to be a key factor in the pathogenesis of chronic bronchitis. Microbial infections have been implicated in acute exacerbations of bronchitis and in its progression. Several animal models of chronic bronchitis have been developed. This review examines similarities and dissimilarities among commonly used animal models of bronchitis and the human disease. The most commonly used animal models of chronic bronchitis are those employing SO2, tobacco smoke, lipopolysaccharide (endotoxin), proteases, and secretagogues. Bronchiolitis induced by nickel and nitric acid have also been reported. Rats, hamsters, and dogs are the species most frequently used; sheep and monkeys have been used less frequently. These models vary in the extent or location of mucous-cell hyperplasia and metaplasia, airway inflammation, chronicity, ease of induction, and reproducibility. Frequently, the deficiencies in these models are attributable to anatomic differences between human and animal airways, differences in the severity or chronicity of inflammation or fibrosis, or lack of complete characterization of the responses and their time course in the animal model. These animal models may be useful for investigating how, and under what exposure conditions, ambient pollutants might exacerbate airway inflammation, mucus hypersecretion, and airflow limitation.

Effects of indomethacin, dexamethasone, and erythromycin on endotoxin-induced intraepithelial mucus production of rat nasal epithelium

We produced hypertrophic and metaplastic changes of goblet cells in rat nasal respiratory epithelium by the intranasal instillation of endotoxin (ETN). In the present study, we examined in vivo effects of indomethacin (IND), dexamethasone (DEX), and erythromycin (EM) on intraepithelial mucus production using this animal model. Intraperitoneal injection of IND (2 to 4 mg/kg body weight x 4 days) or DEX (4 to 8 mg/kg body weight x 4 days) significantly inhibited intraepithelial mucus production induced after 3 days of ETN instillations. Intraperitoneal injection of EM (100 mg/kg body weight x 8 days), aminobenzylpenicillin (ABPC, 200 mg/kg body weight x 8 days), and cephalothin (CET, 200 mg/kg body weight x 8 days) also inhibited intraepithelial mucus production induced after 7 days of ETN instillations. When compared with ABPC and CET, EM had a greater inhibitory effect. These results indicate that ETN-induced intraepithelial mucus production can be inhibited by treatment with the anti-inflammatory drugs IND and DEX. Antibiotics such as EM, ABPC, and CET will also be effective, probably by preventing secondary bacterial infection, and EM has an additional inhibitory effect on intraepithelial mucus production.

One-month exposure to inhaled endotoxin produces a dose-dependent increase in stored mucosubstances in rat intrapulmonary airways

This study examined the production of stored mucosubtances in rats after repeated exposure to aerosolized endotoxin, a common contaminant of bioaerosols. Male Fischer 344 rats were exposed to aerosolized saline (sham control) or endotoxin (target concentrations of 0.05, 0.5, and 5.0 micrograms/m3) for 3 h/day, 5 days/week for 4 weeks. Following the final exposure, the left lung of each animal was lavaged and the right lung and nasal cavity were fixed with buffered formalin. Morphometric examination of Alcian blue/Periodic acid Schiffs-stained (AB/PAS) lung sections demonstrated dose-dependent increases in stored intraepithelial mucosubstances in the intrapulmonary airways of endotoxin-exposed rats. Threefold and eightfold increases in stored mucosubstances were observed in generation 5 airways of animals exposed to 0.5 or 5.0 microgram/m3 endotoxin, respectively (p < .05). This mucous cell metaplasia in the intrapulmonary airways was not accompanied by evidence of lung inflammation or increased AB/PAS-staining high molecular weight material in lavage fluid. Furthermore, despite significant deposition of endotoxin aerosols (mass median aerodynamic diameter of 1.9 microns) in the nasal cavity, no significant changes in stored mucosubstances were observed in the nasal septum. In animals repeatedly exposed to 5.0 micrograms/m3 endotoxin and allowed to recover for 1 month, stored mucosubstances in the intrapulmonary airway were still more than fivefold greater than control values. Thus, in rats, repeated exposure to inhaled endotoxin produced a persistent mucous cell metaplasia only in the intrapulmonary airways.

Parker B. Francis Lecture. Animal models of chronic airways injury

Airways SCM is induced by a wide variety of noxious agents that perturb but do not kill the epithelial cells. Discharge of mucus soon after first exposure to a noxious agent is frequently observed, but discharge of mucus may or may not be followed by development of SCM. Treatment with steroidal and nonsteroidal antiinflammatory agents protects against development of SCM in some models, such as tobacco smoke-induced SCM, but not in others, such as enzyme-induced SCM. In general, SCM regresses slowly or not at all spontaneously. Recovery of some models, such as tobacco smoke-induced SCM, is hastened by nonsteroidal antiinflammatory agents. Experimental protection against induction of enzyme-induced SCM by secretory leukocyte protease inhibitor, which is secreted by airways secretory cells, suggests that such protection may be the in vivo role of that antiprotease. The response of the airways to injury is heterogeneous, with patterns of response of the secretory cells varying according to agent, species, and longitudinal localization of epithelial cells in the airways. The longitudinal heterogeneity of response of secretory epithelial cells to injury is summarized in Table 1. Anatomic heterogeneity of epithelial cells may make a minor contribution to longitudinal variation in response of secretory cells to injury. Molecular heterogeneity of the cellular milieu seems the more likely explanation for this variation in cellular response.

Effects of a new compound (Zy 15850A) on cigarette smoke-induced bronchitis in the rat

The effect of 4H-4 phenylthieno-(3,2-C)-(1)-benzopyran-2-carboxylate (Zy 15850A) on mucous cell hyperplasia was examined in vivo using a well established rat model of cigarette smoke-induced bronchitis. Zy 15850A was given by gavage (25 mg/kg body weight) to male rats before and after sub-acute exposure (i.e. daily for 14 days) to an atmosphere of cigarette smoke (CS). CS significantly increased the thickness of the epithelium at three of the four sites studied in the trachea and in both of the intrapulmonary levels examined. CS increased the number of epithelial mucous cells in all intrapulmonary airways and also increased the mass of submucosal gland present in the larynx and upper trachea. Zy 15850A completely inhibited CS-induced increases in epithelial thickness in the upper trachea and the two intrapulmonary airway levels studied, and tended to inhibit CS-induced epithelial mucous cell hyperplasia in all the six intrapulmonary airway levels examined, with statistically significant inhibition in two. Zy 15850A had no inhibitory effect of the CS-induced enlargement of laryngo-tracheal submucosal glands. We conclude that, in the rat, the predominant inhibitory effect of Zy 15850A is on CS-induced epithelial thickening with weaker inhibitory effects on mucous cell hyperplasia and enlargement of submucosal glands. Zy 15850A is less effective than other mucoregulatory drugs or antiinflammatory agents we have tested in the same bronchitic model.

Effect of cumulative ozone exposure on ozone-induced nasal epithelial hyperplasia and secretory metaplasia in rats

Repeated exposure of rats to O3 induces proliferative and secretory metaplastic changes within nasal airway epithelia that may protect against subsequent exposures. Our study assessed the effect of different cumulative exposure times on O3-induced nasal epithelial hyperplasia and secretory metaplasia. Rats were exposed 6 h/day to air or to 0.8 ppm O3 and were sacrificed 18 h after the end of their last exposure. The rats were exposed to either air or 0.8 ppm O3 for 3 or 7 days, or to 0.8 ppm O3 for 3 days followed by a 4-day exposure to air. The effects of the exposures were determined by quantitating the hyperplastic (epithelial nuclei/mm basal lamina) and secretory metaplastic changes (volume densities of acidic and neutral mucosubstances) within the nasal nonciliated cuboidal epithelium (NNCE). There were no significant changes in NNCE cell numeric density, or in the volume density of intraepithelial mucus, compared to air-exposed control rats, in rats exposed to O3 for 3 days and sacrificed 18 h later. Compared to control rats, there was significant epithelial hyperplasia and secretory metaplasia within the NNCE of rats exposed to O3 either for 7 days or for 3 days followed by 4 days of exposure to air. There were no significant differences in NNCE cell hyperplasia or secretory metaplasia between these two experimental groups. Three 6 h/day exposures to 0.8 ppm O3 triggered hyperplastic and metaplastic changes within rat NNCE that were indistinguishable from those produced by seven 6 h/day exposures to the same concentration of O3. The data suggest that O3 is capable of rapidly inducing hyperplastic and metaplastic responses within rat NNCE, and that once initiated, development of the phenotypic changes within the epithelium does not require further O3 exposure.

Regional difference in airway epithelial response to neutrophil elastase: tracheal secretory cells discharge and recover in hamsters that develop bronchial secretory-cell metaplasia

Human neutrophil elastase (HNE) causes secretory granule discharge and conversion of many Clara cells to mucous cells in hamster bronchi. We investigated whether the trachea responds to HNE in a similar manner because of its abundance of Clara cells. By light microscopy, the tracheal epithelium of animals exposed to a single intratracheal injection of HNE was normal at 21 days, although bronchial secretory-cell metaplasia (SCM) was present. An ultrastructural differential cell count showed no increase in the proportion of granulated secretory cells in HNE-treated animals at 8 and 21 days postinjection compared to saline or untreated controls. At 2 h, the percentage of granulated secretory cells was lower and that of granulated secretory cells was higher in HNE-treated animals than in controls. The HNE-treated animals had fewer secretory granules per cell profile and more surface undulation than controls. By 1 day, the differential cell count and number of granules per cell profile were normal. Saline did not affect the differential cell count or granule number at any time. Ultrastructural study of untreated trachea disclosed the same three types of Clara cell that are found in the bronchus, but their frequencies, with one exception, are significantly different in the two regions. We conclude that HNE acts as a secretagogue in both trachea and bronchus but that an amount of enzyme sufficient to cause bronchial SCM does not induce a similar lesion in trachea. Heterogeneity of Clara cell types in hamster airways may explain the regional variation in secretory-cell modulation by HNE.

Oral N-acetylcysteine speeds reversal of cigarette smoke-induced mucous cell hyperplasia in the rat

We set out to determine whether or not the "mucolytic" drug N-acetylcysteine would speed the reversal of cigarette smoke-induced secretory-cell hyperplasia to normal, similar to that found previously for two nonsteroidal antiinflammatory drugs. Cigarette smoke alone significantly (p less than 0.01) increased the number of secretory cells in seven out of eight airway levels studied and maintained a significant increase in five of the levels at least 3 weeks after cessation of exposure. Treatment of rats with N-acetylcysteine, as 1% of their drinking water during the recovery period, reduced the time taken for secretory cell number to return to normal to between 4 days and 3 weeks, depending on airway level.