DNA damage in bronchial epithelial and mesothelial cells with and without associated crocidolite asbestos fibers

Our plain-English summary of DNA damage in bronchial epithelial and mesothelial cells with and without associated crocidolite asbestos fibers, by J. Nygren, S. Suhonen, H. Norppa, et al (Environmental and Molecular Mutagenesis, 2004).

The study

• Authors: J. Nygren, S. Suhonen, H. Norppa, K. Linnainmaa
• Journal: Environmental and Molecular Mutagenesis
• Published: 2004;44(5):477-82
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Mesothelioma is induced almost exclusively by exposure to asbestos fibers. We have investigated whether the induction of DNA damage in human bronchial epithelial BEAS 2B cells and human mesothelial MeT 5A cells by crocidolite asbestos (2 microg/cm2) requires the presence of asbestos fibers in the cells. DNA damage was measured microscopically by the Comet assay, and the presence of fibers in the same cells was assessed using bright-field illumination. After treatment times of 6-72 hr, damage levels were, on the average, two times higher in cells with fibers than in cells without fibers. It was further found that DNA damage decreased with time in BEAS 2B cells both with and without fibers. No decrease in damage with time was seen in MeT 5A cells, suggesting that these mesothelial cells repair the initial damage poorly, lack induction of protective systems, or constantly produce high levels of damaging species. Our results indicate that crocidolite-treated human mesothelial MeT 5A and bronchial epithelial BEAS 2B cells show an elevated level of DNA damage if they contain a fiber. In comparison with epithelial BEAS 2B cells, mesothelial MeT 5A cells have more DNA damage after the crocidolite treatment and the damage is more persistent.

In plain English

This laboratory study asked whether DNA damage from crocidolite asbestos depends on a fiber being present in the cell. The authors exposed two transformed human cell lines, mesothelial MeT 5A and bronchial epithelial BEAS 2B, to crocidolite at 2.0 micrograms per square centimetre for 6 to 72 hours, in three experiments. They graded DNA damage with the Comet assay, then checked the same cells for fibers under ordinary light. On average, damage was about two times higher in cells with fibers than in cells without. Treated cells without fibers also had more damage than untreated controls, except BEAS 2B cells at 72 hours. Damage fell over time in BEAS 2B cells. In MeT 5A cells it did not fall significantly, except at 48 hours in cells without fibers. Heavily damaged MeT 5A cells were three times more common among cells with fibers than without. For BEAS 2B cells the figure was 1.7 times, which was not statistically significant. The authors suggested these differences may contribute to asbestos-induced mesothelioma. They noted that transformed cell lines were used and that primary cells may behave differently.

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 on cultured human cell lines; three independent experiments
• Who was studied: Two transformed human cell lines grown in culture: mesothelial MeT 5A cells and bronchial epithelial BEAS 2B cells
• Exposure: Crocidolite asbestos at 2.0 micrograms per square centimetre, for treatment times of 6 to 72 hours
• Main results:
  • In both cell lines, DNA damage levels were on average two times higher in cells with fibers than in cells without fibers
  • Crocidolite-treated cells without fibers also had higher DNA damage than untreated control cells (the Results report an exception for BEAS 2B cells at 72 hours)
  • In BEAS 2B cells, DNA damage decreased significantly with time, in cells both with and without fibers
  • In MeT 5A cells, there was no significant time-dependent reduction in DNA damage, with or without fibers, except at the 48-hour time point for cells without fibers
  • Initial DNA damage levels did not differ significantly between the two cell lines. After 72 hours, MeT 5A cells had significantly more damage than BEAS 2B cells
  • Over all time points, the fraction of highly damaged MeT 5A cells was three times greater in cells with fibers than without (statistically significant)
  • In BEAS 2B cells, DNA damage was 1.7 times higher in cells with fibers than without, but the difference was not statistically significant
  • The percentage of cells with fibers decreased with time in BEAS 2B cells but not in MeT 5A cells
  • Apoptotic cells made up 1.1% to 2.1% of MeT 5A cells and 0.4% to 1.7% of BEAS 2B cells. Necrotic cells were below 0.5% and 0.7%, respectively
• The authors' conclusion: The authors concluded that crocidolite-treated human mesothelial cells associated with fibers had more DNA damage than cells without fibers. They also concluded that mesothelial and epithelial cells differed in two ways: damage decreased over time only in BEAS 2B cells, and MeT 5A cells had more heavily damaged cells. They wrote that it is possible one or all of these factors contribute to the induction of mesotheliomas by asbestos, and that further investigation in untransformed cells is warranted.
• Limitations the authors state:
  • The experiments used transformed cell lines, and primary cells may behave differently
  • Because the asbestos was present throughout the experiment, the decrease in DNA damage in BEAS 2B cells may not be due to DNA repair

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Crocidolite, Mesothelioma, Comet Assay.

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