Asbestos and benzo\[a\]pyrene act synergistically to induce squamous metaplasia and incorporation of \[3H\]thymidine in hamster tracheal epithelium

Our plain-English summary of Asbestos and benzo[a]pyrene act synergistically to induce squamous metaplasia and incorporation of [3H]thymidine in hamster tracheal epithelium, by B.T. Mossman, A. Eastman, E. Bresnick (Carcinogenesis, 1984).

The study

• Authors: B.T. Mossman, A. Eastman, E. Bresnick
• Journal: Carcinogenesis
• Published: 1984;5(11):1401-4
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

When exposed to either crocidolite asbestos (single 1-h exposure to 0.4 mg/ml medium) or the polycyclic aromatic hydrocarbon, benzo[a]pyrene (BaP) (less than or equal to 2.5 micrograms/ml medium, 1x weekly for 4 weeks), the epithelium of hamster tracheal explants exhibits insignificant amounts of squamous metaplasia, an atypical lesion, in comparison to amounts observed in untreated tissues. Incorporation of [3H]thymidine, an indication of DNA synthesis by epithelial cells, likewise is unchanged. However, the extent of squamous metaplasia and numbers of labeled basal and suprabasal cells are increased substantially when BaP and asbestos are added in combination. These results suggest an important mechanism of co-carcinogenesis involving chemical and physical carcinogens and support epidemiologic observations documenting an increased risk of bronchogenic carcinoma in asbestos workers who smoke.

In plain English

This was a laboratory experiment on pieces of windpipe (tracheal explants) taken from female golden Syrian hamsters aged 6 to 8 weeks and kept alive in culture. The authors tested whether crocidolite asbestos and benzo[a]pyrene (BaP), a chemical in cigarette smoke, together cause changes that neither causes alone at low amounts. Explants received crocidolite (a single 1-hour exposure to 0.4 mg/ml), BaP alone (0.5, 1.0 or 2.5 micrograms/ml once a week), or crocidolite followed by weekly BaP at 0.5 micrograms/ml. The authors scored squamous metaplasia, an abnormal change in the lining cells. They also measured DNA synthesis by uptake of [3H]thymidine. BaP alone did not increase metaplasia at any time point. At 3 weeks, neither agent alone significantly increased metaplasia or labeling. The combination produced significantly more metaplasia (p less than 0.05), with only 2 of 15 explants remaining normal. It also produced about 4-fold more labeled cells than untreated controls. The authors concluded that the results suggest a mechanism of co-carcinogenesis and support epidemiologic observations of increased bronchogenic carcinoma risk in asbestos workers who smoke.

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 (in vitro) experiment using hamster tracheal organ cultures
• Who was studied: Tracheal explants from female golden Syrian hamsters aged 6 to 8 weeks; 15 to 16 explants per animal; groups of 14 to 22 explants at each time point; 15 explants in the combination group
• Exposure: Crocidolite asbestos (UICC reference sample) at 0.4 mg/ml medium for 1 hour, chosen as a concentration not causing metaplasia; BaP at 0.5, 1.0 or 2.5 micrograms/ml medium added once a week; and crocidolite (0.4 mg/ml for 1 hour) followed by BaP (0.5 micrograms/ml) once a week
• Main results:
  • Among untreated cultures, 15% of specimens showed moderate metaplasia
  • BaP alone at 0.5 to 2.5 micrograms/ml did not increase squamous metaplasia at any time point compared with untreated cultures
  • Some explants given BaP at 2.5 micrograms/ml showed higher labeling indices at 4 weeks, but these changes were not statistically significant because of variability
  • At 3 weeks, squamous metaplasia was not significantly increased by crocidolite alone or BaP alone
  • With crocidolite and BaP combined, severe metaplasia of more than 50% of the epithelium and significant increases (p less than 0.05) in extent of change were observed; only 2 of 15 explants remained normal
  • With crocidolite and BaP combined, the number of cells taking up [3H]thymidine was about 4-fold higher than in untreated controls; there was no increase with BaP or asbestos alone
  • In all treatment groups, labeling was most extensive in basal cells
• The authors' conclusion: The authors concluded that the results suggest a mechanism of co-carcinogenesis involving chemical and physical carcinogens. They said the results support epidemiologic observations of increased bronchogenic carcinoma risk in asbestos workers who smoke.
• Limitations the authors state:
  • Imperfections in histologic sections and autoradiographs meant that the number of cells counted was not identical across groups

Topics

Medical terms in this study, explained in our Lexicon: Epithelium, Crocidolite, Carcinogenesis, Bronchogenic Carcinoma.

Related studies

• Ascorbic acid inhibits the squamous metaplasia that results from treatment of tracheal explants with asbestos or benzo[a]pyrene-coated asbestos — G. Holtz, E. Bresnick (1988)
• Effects of crocidolite and chrysotile asbestos on cellular uptake and metabolism of benzo(a)pyrene in hamster tracheal epithelial cells — B.T. Mossman, A. Eastman, et al. (1983)
• Morphological transformation of Syrian hamster embryo cells induced by mineral fibres and the alleged enhancement of benzo[a]pyrene — S.O. Mikalsen, E. Rivedal, et al. (1988)
• 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)
• Pulmonary response of hamsters to fibrous glass: chronic effects of repeated intratracheal instillation with or without benzo[a]pyrene — V.J. Feron, P.M. Scherrenberg, et al. (1985)
• Interaction of asbestos with metaplastic squamous epithelium developing in organ cultures of hamster trachea — C.D. Woodworth, B.T. Mossman, et al. (1983)

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