Progressive lung cell reactions and extracellular matrix production after a brief exposure to asbestos

Our plain-English summary of Progressive lung cell reactions and extracellular matrix production after a brief exposure to asbestos, by L.Y. Chang, L.H. Overby, A.R. Brody, et al (The American Journal of Pathology, 1988).

The study

• Authors: L.Y. Chang, L.H. Overby, A.R. Brody, J.D. Crapo
• Journal: The American Journal of Pathology
• Published: 1988;131(1):156-70
• Cited by: 84 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

Inhaled chrysotile asbestos fibers have been shown to deposit initially on the first alveolar duct bifurcations. In brief accidental exposure to asbestos, this would be the most likely site of a significant cellular or fibrotic reaction. The characteristics and progression of tissue reactions occurring at first alveolar duct bifurcations after a single brief asbestos exposure was defined using morphometric techniques. Seven-week-old rats were exposed, nose only, for 1 hour to chrysotile asbestos fibers. After the exposure, the animals were kept in air for 2 days or 1 month, and then their lungs were fixed by vascular perfusion or by intratracheal instillation of 2% glutaraldehyde. The first bifurcations of seven alveolar ducts in each animal were isolated from plastic-embedded tissue and thin-sectioned for electron-microscopic analysis. Two days after exposure, the volume of epithelium and interstitium in the duct bifurcations had increased by 78% and 28%, respectively (P less than 0.05). The total number and volume of alveolar macrophages on the bifurcations increased about 10 times (P less than 0.05), whereas the number and volume of interstitial macrophages increased threefold (P less than 0.05). Statistically significant increases in the numbers of Type I (82%) and Type II (29%) epithelial cells also occurred. One month after the 1-hour exposure, the volume of epithelium and the number of Type I and Type II cells were still greater than control values, but these differences no longer achieved statistical significance. The volume of the interstitium, on the other hand, increased 67% (P less than 0.05), and this was accompanied by a persistently high number of interstitial macrophages, accumulation of myofibroblasts/smooth muscle cells, and an increased volume of interstitial matrix. These results demonstrate that a brief exposure to chrysotile asbestos causes a rapid response that involves an influx of macrophages to the first alveolar duct bifurcations and alterations in the alveolar epithelium. These acute structural changes are followed by a progressive response manifested by increased numbers of interstitial cells and localized interstitial fibrosis.

In plain English

This was an animal experiment. Seven-week-old rats breathed chrysotile asbestos from the Jeffrey Mine, Quebec, Canada, through nose-only holders for one hour, at a respirable mass of 13 mg per cubic meter. Control rats were sham-exposed to room air. After 2 days or 1 month, the authors measured the first branching points of the alveolar ducts (small air passages deep in the lung) under the electron microscope. Two days after exposure, the exposed rats had more lining tissue (epithelium) and more Type I and Type II lining cells than the controls, and these differences were statistically significant. Macrophages had gathered, and over 90% of alveolar macrophages contained fibers. At one month the lining changes were no longer statistically significant. The tissue inside the walls (interstitium) was larger, with more interstitial macrophages, more myofibroblast/smooth muscle cells, about 53% more noncellular matrix, and collagen bundles. Fibers were present in one-third of the branching points examined. The authors concluded this progressed to localized interstitial fibrosis. They stated it was not clear whether the reaction would spread or resolve.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal inhalation experiment comparing asbestos-exposed rats with sham-exposed controls, using electron-microscopic measurement (morphometry) of lung tissue at 2 days and 1 month after a single exposure
• Who was studied: Seven-week-old white CD(SD)BR rats (Charles River). The statistics section states four male rats per treatment group, with seven first alveolar duct bifurcations studied per rat. The methods state a total of 16 animals. Place and dates of the experiment are not stated.
• Exposure: A single 1-hour, nose-only exposure to aerosolized chrysotile asbestos from the Jeffrey Mine, Quebec, Canada, at a respirable mass of 13 mg/cu m. Controls were sham-exposed to room air.
• Main results:
  • At 2 days, epithelium volume (ratio to basement membrane surface area, mean plus or minus SEM) was 0.493 ± 0.017 in exposed rats versus 0.278 ± 0.006 in controls (P less than 0.001).
  • At 2 days, exposed rats had statistically significant increases in the numbers of Type I (82%) and Type II (29%) epithelial cells.
  • At 2 days, alveolar macrophages on the bifurcations increased about 10 times in exposed rats. In the table this is 945.2 ± 178.7 versus 69.4 ± 16.1 per sq mm of basement membrane, P = 0.050.
  • At 2 days, chrysotile fibers were found in over 90% of alveolar macrophages of exposed rats.
  • At 2 days, interstitial macrophage volume ratio was 0.164 ± 0.010 in exposed rats versus 0.040 ± 0.002 in controls (P less than 0.001).
  • At 2 days, capillary lumen volume ratio in the bifurcations was reduced to 0.286 ± 0.019 in exposed rats from 0.547 ± 0.022 in controls (P = 0.004).
  • At 1 month, the Type I and Type II epithelial responses had decreased and were no longer statistically different from control values.
  • At 1 month, interstitium volume ratio was 0.814 in exposed rats versus 0.441 in controls (P = 0.015).
  • At 1 month, exposed rats had a 53% increase in the volume of noncellular interstitial matrix, and both the volume and the number of myofibroblast/smooth muscle cells were significantly increased.
  • At 1 month, interstitial macrophage numbers were 782.3 ± 76.3 per sq mm of basement membrane in exposed rats versus 223.5 ± 42.6 in controls (P = 0.019).
  • At 1 month, chrysotile fibers were present in one-third of the bifurcations examined, and microcalcifications in 20% of bifurcations of exposed animals. Collagen fiber bundles were deposited.
• The authors' conclusion: The authors concluded that a brief exposure to chrysotile caused a rapid response (macrophage influx and changes in the lining epithelium). In their words, these acute changes were followed by a progressive response with increased numbers of interstitial cells and localized interstitial fibrosis.
• Limitations the authors state:
  • The authors stated it is not clear whether the fibrotic reaction will spread beyond the bifurcations or resolve.
  • Fibroblasts, myofibroblasts and smooth muscle cells were often hard to tell apart in a single section, so myofibroblasts and smooth muscle cells were combined into one category.
  • Interstitial macrophages included migratory monocytes, which could not be clearly distinguished from tissue macrophages with this method.
  • The authors stated that the biologic significance of the capillary changes was not clear.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Jeffrey mine, Asbestos, Quebec

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Asbestos Exposure, Epithelium, Alveolar Macrophage, Interstitial, Macrophage, Statistical Significance, Interstitial Fibrosis.

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