Inability of chrysotile asbestos fibers to modulate the 2-acetylaminofluorene-induced UDS in primary cultures of rat hepatocytes

Our plain-English summary of Inability of chrysotile asbestos fibers to modulate the 2-acetylaminofluorene-induced UDS in primary cultures of rat hepatocytes, by F. Denizeau, M. Marion, G. Chevalier, et al (Mutation Research, 1985).

The study

• Authors: F. Denizeau, M. Marion, G. Chevalier, M.G. Côté
• Journal: Mutation Research
• Published: 1985;155(1-2):83-90
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

There is now growing evidence that asbestos fibers could act in association with genotoxic compounds, either as cocarcinogens or promoters, in the process of carcinogenesis. The hepatocyte/UDS assay system has been taken to advantage to investigate the capacity of fibers to modulate the effects of genotoxic compounds on the cell, as we previously demonstrated the hepatocytes can engage in phagocytosis of chrysotile fibers. Measurement of UDS was performed by a biochemical procedure involving liquid scintillation counting (LSC) of a purified DNA fraction as well as by radioautography. Both LSC and radioautography revealed that chrysotile asbestos fibers UICC B at concentrations up to 100 micrograms/ml do not elicit UDS, whereas 2-acetylaminofluorene (2-AAF) at low concentrations (0.05-0.625 micrograms/ml) significantly induces it in parallel positive controls. In an attempt to test the cocarcinogen hypothesis, cultures of hepatocytes were simultaneously exposed for 20 h to 2-AAF (0.05 and 0.25 micrograms/ml) and asbestos fibers (1 and 10 micrograms/ml) given as simple mixtures. It was found that the 2-AAF-induced UDS activity was the same whether fibers were present or not. This was observed with both UDS evaluation procedures at all concentration combinations selected. An analysis of variance applied to the data collected from several experiments confirmed that there was no significant 2-AAF-fiber interaction. Our data suggest the absence of intrinsic genotoxic properties for chrysotile fibers. They also indicate that the modulation of the cellular response to genotoxic agents by asbestos fibers is not detected under our test conditions and may require longer-term exposures to be expressed.

In plain English

This laboratory study tested whether chrysotile asbestos fibers (UICC B) damage DNA in rat liver cells, or change the DNA damage caused by a known chemical carcinogen, 2-acetylaminofluorene (2-AAF). Liver cells from male Sprague-Dawley rats were grown in dishes, and DNA repair ("unscheduled DNA synthesis", a sign of DNA damage) was measured by two methods. 2-AAF alone produced a response starting at 0.05 micrograms per ml, reaching a maximum at 0.25 to 0.625 micrograms per ml. Chrysotile fibers alone, at concentrations up to 100 micrograms per ml, produced no significant DNA repair activity and no detectable cell damage. When cells were exposed for 20 hours to mixtures of 2-AAF and fibers, the fibers did not increase or decrease the 2-AAF effect, and statistical analysis found no significant interaction. The authors concluded that their data failed to show asbestos enhancing the effects of 2-AAF. They suggested that any such effect may require longer exposures. They noted that one of their two methods gave highly variable results, which makes such effects harder to detect.

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 primary cultures of rat liver cells (hepatocytes) and the unscheduled DNA synthesis (UDS) assay, measured by liquid scintillation counting and by radioautography
• Who was studied: Liver cells isolated from male Sprague-Dawley rats weighing 150-300 g. Each experiment used cells from one animal, with several experiments per test. The study was done at universities in Montreal, Canada.
• Exposure: Chrysotile asbestos fibers UICC B alone at concentrations up to 100 micrograms per ml. 2-AAF alone at 0.05 to 0.625 micrograms per ml. Combined 20-hour exposures to 2-AAF (0.05 and 0.25 micrograms per ml) together with fibers (1 and 10 micrograms per ml) given as simple mixtures.
• Main results:
  • 2-AAF alone (the positive control) produced a DNA repair response starting at 0.05 micrograms per ml, with a maximum at 0.25 to 0.625 micrograms per ml.
  • Chrysotile fibers alone produced no significant DNA repair activity with either measurement method, and this was confirmed by statistical analysis.
  • Fibers alone caused no detectable cell damage (cytotoxicity) at any concentration tested.
  • In combined exposures, the fibers did not increase or decrease the DNA repair response caused by 2-AAF. Analysis of variance showed no significant 2-AAF-fiber interaction.
  • Radioautography gave similar results for the lower 2-AAF concentration combined with fibers.
  • Combined exposure to 2-AAF and fibers did not cause synergistic cell damage.
• The authors' conclusion: The authors concluded that their data failed to show that asbestos can enhance the genotoxic effects of 2-AAF, and that chrysotile fibers appeared to lack intrinsic genotoxic properties. They also said that any modulating effect of fibers was not detected under their test conditions and may require longer-term exposures to appear.
• Limitations the authors state:
  • Radioautography results varied widely from cell to cell (high standard deviations), so the authors expected modulating effects to be harder to detect with that method.
  • Exposure lasted only 20 hours, and fibers and 2-AAF were added as simple mixtures without the chemical first being attached to the fibers. The authors gave this as a possible reason their findings differed from another study.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Carcinogenesis, Phagocytosis, UICC.

Related studies

• Interactions of asbestos fibers with hepatocytes in vitro: an ultrastructural study — J. Fleury, M.G. Côté, et al. (1983)
• Synthesis of poly(ADP-ribose) in asbestos treated rat pleural mesothelial cells in culture — H.Y. Dong, A. Buard, et al. (1995)
• Genotoxicity of dimethylnitrosamine in the presence of chrysotile asbestos UICC B and xonotlite — F. Denizeau, M. Marion, et al. (1985)
• Phagocytosis of chrysotile fibers by pleural mesothelial cells in culture — M.C. Jaurand, H. Kaplan, et al. (1979)
• Interactions of chrysotile and benzopyrene in a human cell culture systems — R.E. Stephens, L.B. Joseph, et al. (1983)
• Reaction of mineral dusts with primary lung fibroblast cultures — R.J. Richards, J. Hunt (1983)

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