Thymidine incorporation by lung fibroblasts as a sensitive assay for biological activity of asbestos

Our plain-English summary of Thymidine incorporation by lung fibroblasts as a sensitive assay for biological activity of asbestos, by I. Lemaire, D. Gingras, S. Lemaire (Environmental Research, 1982).

The study

• Authors: I. Lemaire, D. Gingras, S. Lemaire
• Journal: Environmental Research
• Published: 1982;28(2):399-409
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fibroblasts exposed to chrysotile B asbestos displayed an initial growth inhibition compared to controls during the first 24 hr of incubation. At 48 hr, however, there was resumption of cell proliferation as evidenced by elevated thymidine (TdR3H) incorporation. UICC samples of chrysotile A, chrysotile B, crocidolite, amosite, and anthophyllite all altered thymidine incorporation by lung fibroblasts in a dose-dependent manner and to different maximal levels. Amphibole asbestos was either equally or less active than chrysotile. Silica had the lowest activity. Various other particles, including latex, zymosan, titanium dioxide, magnetite, and Mt. St. Helens volcanic ash, had no effect. Chemically modified chrysotile samples which retained their fibrous structure were also tested for possible alterations of fibroblast thymidine incorporation. The DNA synthesis response of human lung fibroblasts to asbestos correlates with its in vivo fibrogenic and tumorigenic potential and may prove useful in determining the pathological effects of asbestos.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This laboratory study measured how asbestos changed the incorporation of radioactively labeled thymidine, a DNA building block, by human embryonic lung fibroblasts (WI-38 cells) in culture. The authors used this to measure DNA synthesis and cell proliferation. Cells given 10 µg/ml of UICC chrysotile B grew less than untreated cells for the first 24 hours. At 48 hours, thymidine incorporation rose and growth resumed. All five UICC samples (chrysotile A, chrysotile B, crocidolite, amosite and anthophyllite) raised thymidine incorporation in a dose-dependent way. Chrysotile B, chrysotile A and crocidolite were the most active, with half-maximal response at about 5 µg/ml. Compared with chrysotile B, amosite and anthophyllite were about 50% and 33% as active. Silica was less potent, with half-maximal response at 26 µg/ml. Latex, zymosan, titanium dioxide, magnetite and Mount St. Helens volcanic ash had no effect. Coating chrysotile with serum, heating it, or removing its magnesium reduced its activity. A sample of very short chrysotile fibers stayed active. More than half its fibers were under 1 µm and all were under 8 µm. The authors concluded that this response correlates with the in vivo fibrogenic and tumorigenic potential of asbestos.

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: in vitro (cell culture) laboratory experiment
• Who was studied: Human embryonic lung fibroblasts (WI-38 cell line) grown in culture, 5 x 10^4 cells per culture; experiments done in triplicate
• Exposure: UICC standard samples of Canadian chrysotile B, Rhodesian chrysotile A, crocidolite, amosite and anthophyllite, and a commercial Quebec grade 7D chrysotile (Paperbestos 7D). Comparison particles were silica, latex, zymosan, titanium dioxide, magnetite, atapulgite and Mt. St. Helens volcanic ash. Chrysotile was also tested after modification: water-washed, serum-coated, very short fibers, heat-treated at 325 and 500°C, and magnesium-leached. Doses ranged from 0 to 100 µg/ml.
• Main results:
  • Fibroblasts exposed to 10 µg/ml chrysotile B showed growth inhibition compared with controls during the first 24 hours. At 48 hours they showed elevated thymidine incorporation and resumed proliferation.
  • All UICC asbestos types raised thymidine incorporation in a dose-dependent manner at 48 hours. Chrysotile B, chrysotile A and crocidolite were the most active: optimal levels were reached at about 25 µg/ml and half-maximal response at about 5 µg/ml.
  • Amosite and anthophyllite were less active, about 50% and 33% as active as chrysotile B.
  • Silica was less active than chrysotile. Its half-maximal response came at 26 µg/ml, compared with 5 µg/ml for chrysotile (relative potency 19%). The text states that silica's maximal effect was identical to chrysotile's.
  • Latex, titanium dioxide, zymosan, magnetite and Mt. St. Helens volcanic ash had no effect on thymidine incorporation.
  • Washing chrysotile in water for 24 hours did not change its activity, and the water it was soaked in had no effect by itself.
  • Coating chrysotile with serum proteins lowered its maximal activity by 15% and tripled its half-maximal dose (16 µg/ml versus 5 µg/ml for untreated chrysotile).
  • A very short chrysotile fiber sample still altered thymidine incorporation, but at a higher concentration (half-maximal dose 7 µg/ml; relative potency 71%). In this sample more than 50% of fibers were under 1 µm and 100% were under 8 µm.
  • Heating chrysotile at 325°C and 500°C reduced its activity by 40% and 70%. Magnesium leaching of short chrysotile fibers reduced activity by 85%.
• The authors' conclusion: The authors concluded that the DNA synthesis response of human lung fibroblasts to asbestos correlates with its in vivo fibrogenic and tumorigenic potential. They suggested that measuring thymidine incorporation may be a sensitive, rapid way to assess the biological activity of asbestos. They added that its relevance to fibrosis and tumor formation warrants further investigation.
• Limitations the authors state:
  • The authors stated that the mechanisms behind the fibroblast DNA synthesis response are unknown.
  • The authors noted discrepancies between animal studies, which make it difficult to compare how harmful different asbestos types are in living animals.

Topics

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

Medical terms in this study, explained in our Lexicon: Fibroblast, Chrysotile, UICC, Crocidolite, Amosite, Anthophyllite, Amphibole Asbestos, Fibrogenic.

Related studies

• Incorporation of tritiated thymidine by epithelial and interstitial cells in bronchiolar-alveolar regions of asbestos-exposed rats — A.R. Brody, L.H. Overby (1989)
• 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)
• Towards predicting the lung fibrogenic activity of nanomaterials: experimental validation of an in vitro fibroblast proliferation assay — G. Vietti, S. Ibouraadaten, et al. (2013)
• Biochemical effects of asbestiform minerals on lung fibroblast cultures — P.M. Hext, R.J. Richards (1976)
• Early-passage rat lung fibroblasts do not migrate in vitro to transforming growth factor-beta — A.R. Osornio-Vargas, V.G. Kalter, et al. (1993)
• Chrysotile asbestos induces PDGF-A chain-dependent proliferation in human and rat lung fibroblasts in vitro — J.A. Lasky, J.C. Bonner, et al. (1996)

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