Interaction of asbestos with metaplastic squamous epithelium developing in organ cultures of hamster trachea

Our plain-English summary of Interaction of asbestos with metaplastic squamous epithelium developing in organ cultures of hamster trachea, by C.D. Woodworth, B.T. Mossman, J.E. Craighead (Environmental Health Perspectives, 1983).

The study

• Authors: C.D. Woodworth, B.T. Mossman, J.E. Craighead
• Journal: Environmental Health Perspectives
• Published: 1983;51:27-33
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The normal mucociliary epithelium of the respiratory tract in chronic cigarette smokers often is replaced focally by a metaplastic squamous epithelium. Because asbestos workers who smoke have a substantially greater risk of bronchogenic carcinoma than nonsmokers, we hypothesized that interaction of asbestos with squamous epithelium might be a contributing factor. To address this question, an in vitro model was developed to study the interaction of asbestos with both mucociliary and squamous epithelium. Explants of tracheas from hamsters were cultured in either a chemically defined minimal essential medium, which maintains a differentiated epithelium, or a nutritionally complex medium, which encourages the development of squamous metaplasia. Scanning electron microscopy (SEM) was used to measure quantitatively the development of a squamous epithelial surface on the explants. The interaction of chrysotile and crocidolite asbestos with cells of the mucociliary and squamous epithelium was studied using both SEM and transmission electron microscopy (TEM). Long fibers of asbestos were cleared, whereas shorter fibers were phagocytized by cells of the mucociliary epithelium. In contrast, asbestos was phagocytized by superficial squamous cells regardless of fiber length, and fibers penetrated between intercellular junctions in the metaplastic epithelium. The relevance of these interactions to the induction of bronchogenic carcinoma is discussed.

In plain English

This was a laboratory study using small pieces of windpipe (trachea) from young male Syrian hamsters, kept alive in culture. The authors studied how asbestos fibers interact with squamous metaplasia, a change, common in smokers, in which the normal lining with mucus and cilia is replaced by flat squamous cells. Here the squamous change was produced by a rich culture medium (W-87/3), not by smoke. Pieces kept in a simpler medium (MEM) kept their normal lining for as long as 4 weeks. Pieces exposed to UICC crocidolite or Canadian chrysotile were examined by electron microscopy. On normal lining, fibers longer than 5 micrometers were caught in the cilia and appeared to be carried to the edge. Some short fibers were taken up by cells. High doses made ciliated and goblet cells slough off. On squamous lining, fibers did not appear to be cleared. Surface cells took up both short and long fibers within 8 hours, and fibers were seen between cells. The authors suggested this as a possible way inhaled asbestos and cigarette smoke could act together in bronchogenic carcinoma.

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: Laboratory experiment on organ cultures of hamster trachea, examined by scanning and transmission electron microscopy
• Who was studied: Tracheas from 6- to 8-week-old male Syrian hamsters, each cut into 14-16 explants of about 2 x 3 mm. The number of animals is not stated. Explants were kept either in MEM, which preserves the normal lining, or in W-87/3, which induces squamous metaplasia.
• Exposure: Crocidolite and Canadian chrysotile (UICC reference samples), suspended at 0.3, 1.0, 3.0 and 10.0 mg/mL. Explants were submerged for 1 hour and examined immediately and after 3, 8 and 24 hours, and 3 and 7 days.
• Main results:
  • Explants cultured in MEM kept normal mucociliary differentiation for as long as 4 weeks. Explants in W-87/3 developed squamous metaplasia, most pronounced after 2-3 weeks, with little progression after that.
  • On mucociliary (normal) lining, longer fibers (more than 5 micrometers) became trapped in the cilia and appeared to be transported to the edge of the explant.
  • On mucociliary lining, an undetermined number of short crocidolite or chrysotile fibers settled on nonciliated cells. In some instances these were taken up (phagocytized) into lysosomes.
  • High concentrations of crocidolite (10.0 mg/mL) or chrysotile (3.0 mg/mL) caused sloughing of ciliated and goblet cells from the mucociliary lining.
  • On squamous (metaplastic) lining, fibers of various lengths settled on the surface and did not appear to be cleared.
  • Surface squamous cells took up both short and long crocidolite and chrysotile fibers within 8 hours, with or without serum. Six explants per time point were examined by scanning microscopy.
  • By transmission microscopy (6-12 explants at 0, 1 and 3 days), asbestos was seen occasionally inside surface squamous cells. Crocidolite and chrysotile fibers were seen between squamous cells 24 hours after treatment.
• The authors' conclusion: The authors concluded that their observations suggest a possible mechanism by which inhaled asbestos and components of cigarette smoke could act together in inducing bronchogenic carcinoma. Squamous areas might interrupt normal clearance, and fibers might reach the underlying basal cells, which the authors describe as presumably the progenitors of this cancer.

Topics

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

Medical terms in this study, explained in our Lexicon: Epithelium, Mucociliary Clearance, Bronchogenic Carcinoma, Scanning Electron Microscopy (SEM), Chrysotile, Crocidolite, Transmission Electron Microscopy (TEM), Squamous Cell.

Related studies

• Use of hamster tracheal organ cultures for assessing the cocarcinogenic effects of inorganic particulates on the respiratory epithelium — B.T. Mossman, J.E. Craighead (1979)
• Asbestos and benzo[a]pyrene act synergistically to induce squamous metaplasia and incorporation of [3H]thymidine in hamster tracheal epithelium — B.T. Mossman, A. Eastman, et al. (1984)
• Effects of cigarette smoke on epithelial uptake of non-asbestos mineral particles in tracheal organ culture — B. Keeling, J. Hobson, et al. (1993)
• Ozone enhances the uptake of mineral particles by tracheobronchial epithelial cells in organ culture — A. Churg, M. Brauer, et al. (1996)
• Crocidolite asbestos and SV40 are cocarcinogens in human mesothelial cells and in causing mesothelioma in hamsters — B. Kroczynska, R. Cutrone, et al. (2006)
• Assessment of the pathogenic potential of asbestiform vs. nonasbestiform particulates (cleavage fragments) in in vitro (cell or organ culture) models and bioassays — B.T. Mossman (2008)

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