Mechanisms of cytotoxicity of asbestos fibres in rat tracheal epithelial cells in culture

Our plain-English summary of Mechanisms of cytotoxicity of asbestos fibres in rat tracheal epithelial cells in culture, by T.W. Hesterberg, D.G. Ririe, J.C. Barrett, et al (Toxicology in Vitro, 1987).

The study

• Authors: T.W. Hesterberg, D.G. Ririe, J.C. Barrett, P. Nettesheim
• Journal: Toxicology in Vitro
• Published: 1987;1(2):59-65
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Little is known about the mechanism(s) of asbestos toxicity, especially in respiratory epithelium. Studies were carried out to elucidate some important aspects of the cytotoxic effects of asbestos, using a tracheal epithelial cell line in culture. Chrysotile and crocidolite asbestos with similar aspect ratios were used. Both induced in 2C5 cells a concentration-dependent inhibition of colony-forming ability, a measure of proliferative capacity. In this respect, chrysotile (LC(50), 0.95 mug/cm(2)) was about six times more toxic than crocidolite (LC(50), 5.8 mug/cm(2)). Both types of asbestos caused only minor changes in membrane permeability, measured by trypan blue exclusion and by [(75)Se]selenomethionine release, even at concentrations of asbestos that caused > 90% inhibition in colony formation. Thus membrane damage was only a minor component of the toxicity produced by the fibres. Chrysotile was phagocytized much more readily than crocidolite and produced an approximately threefold greater increase in binucleated cells and micronuclei than crocidolite, suggesting that phagocytosis was the rate-limiting step in fibre toxicity. Our studies suggest a potentially important pathway of fibre toxicity involving binding, phagocytosis, nuclear damage, disruption of mitosis, inhibition of proliferation and/or cell death. In this process, the fibre aspect ratio is not the only determinant of fibre toxicity, since chrysotile and crocidolite fibres of similar length and diameter exhibit very different degrees of toxicity. It appears that other fibre characteristics, such as fibre surface charge, are of equal importance.

Copyright © 1987. Published by Elsevier Ltd.

In plain English

This laboratory study tested asbestos on a line of rat tracheal (windpipe) epithelial cells, called 2C5, grown in culture dishes. No people or live animals were exposed. The authors used UICC chrysotile and crocidolite asbestos whose fibres had very similar average length and diameter. Both fibre types reduced the cells' ability to form colonies as the dose rose. The dose that halved colony formation (LC50) was 0.95 micrograms per square centimetre for chrysotile and 5.8 for crocidolite; the authors described chrysotile as about six times more toxic than crocidolite. Membrane-damage tests showed little effect. At 4 micrograms per square centimetre of chrysotile, more than 70% of cells passed a dye test for intact membranes, while colony formation by treated cells fell to 3% of that by untreated control cells. After 24 hours, chrysotile-treated cells held 2.7 times more fibres than crocidolite-treated cells. Chrysotile caused a threefold greater increase in two-nucleus cells. Unlike crocidolite, it also significantly increased micronuclei, which the authors used to track chromosome changes. The authors concluded that fibre characteristics other than size, possibly surface charge, help determine toxicity.

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) cell-culture experiment
• Who was studied: Cultured cell line 2C5, derived from tracheal epithelial cells of one 8-week-old male Fisher 344 rat. Experiments were run at passages 21 to 25 at the National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA.
• Exposure: UICC chrysotile and UICC crocidolite asbestos added to culture medium, at doses expressed in micrograms per square centimetre of dish. Mean fibre length was 7.8 plus or minus 0.5 µm for chrysotile and 7.2 plus or minus 1.0 µm for crocidolite. Mean diameter was 0.20 plus or minus 0.02 µm for chrysotile and 0.22 plus or minus 0.01 µm for crocidolite.
• Main results:
  • Both fibre types caused dose-related decreases in colony formation by 2C5 cells. The LC50 was 0.95 µg/cm2 for chrysotile and 5.8 µg/cm2 for crocidolite. The authors described chrysotile as about six times more toxic than crocidolite.
  • Membrane-permeability tests showed far less toxicity than the colony test. In cells given chrysotile at 4 µg/cm2, more than 70% remained viable by dye exclusion, and the isotope release assay gave values of 80% of controls. Relative survival in the colony-forming assay was only 3%. Relative survival means the colony-forming efficiency of treated cells divided by that of untreated control cells.
  • Chrysotile at 1 µg/cm2 inhibited cell division within 24 hours. Single-cell microcolonies made up 13% of control microcolonies and 52% of microcolonies in asbestos-treated cultures. Relative survival was 24% in the 7-day colony assay and 29% in the 24-hour microcolony assay.
  • Twenty-four hours after treatment at 1 µg/cm2, chrysotile-treated cells had 2.7 times more fibres than crocidolite-treated cells (25 cells examined per fibre type). The mean was 43.8 versus 16.4 cell-associated fibres per cell.
  • At 1 µg/cm2, chrysotile caused a threefold greater increase in binucleated cells than crocidolite. Binucleated cells were 9.3% with chrysotile and 3.1% with crocidolite, against 1.5% in controls; 1000 cells were examined per group.
  • Chrysotile, but not crocidolite, significantly increased micronuclei at 1 and 2 µg/cm2: 6.2% at each dose versus 1.2% in controls (P less than 0.05, Mann-Whitney test).
• The authors' conclusion: The authors concluded that membrane damage was only a minor part of fibre toxicity in these cells. In their view, toxicity runs mainly through phagocytosis (uptake of fibres by the cell), nuclear damage and interference with cell division. Chrysotile and crocidolite fibres of similar size differed greatly in toxicity. From this, the authors concluded that characteristics other than fibre size, possibly surface charge, are also crucial.
• Limitations the authors state:
  • The authors stated that the differences between chrysotile and crocidolite responsible for the difference in toxicity are not known; surface charge is offered only as a possibility.
  • The authors stated that the phagocytosis-mediated mechanism seems to apply at least where phagocytosis can occur.

Topics

Medical terms in this study, explained in our Lexicon: Epithelium, Chrysotile, Crocidolite, Aspect Ratio (Length-to-diameter ratio), Micronuclei, Phagocytosis.

Related studies

• Effect of mineral particles containing iron on primary cultures of rabbit tracheal epithelial cells: possible implication of oxidative stress — C. Guilianelli, A. Baeza-Squiban, et al. (1993)
• Cytotoxicity of refractory ceramic fibres to Chinese hamster ovary cells in culture — G.A. Hart, M.M. Newman, et al. (1992)
• Transfection of a manganese-containing superoxide dismutase gene into hamster tracheal epithelial cells ameliorates asbestos-mediated cytotoxicity — B.T. Mossman, P. Surinrut, et al. (1996)
• Effects of cigarette smoke on epithelial uptake of non-asbestos mineral particles in tracheal organ culture — B. Keeling, J. Hobson, et al. (1993)
• Asbestos cytotoxicity in a long term macrophage-like cell culture — M.J. Wade, L.E. Lipkin, et al. (1976)
• Asbestos induces nuclear factor kappa B (NF-kappa B) DNA-binding activity and NF-kappa B-dependent gene expression in tracheal epithelial cells — Y.M. Janssen, A. Barchowsky, et al. (1995)

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