Loss of heterozygosity in asbestos-induced mutations in a human mesothelioma cell line

Our plain-English summary of Loss of heterozygosity in asbestos-induced mutations in a human mesothelioma cell line, by K. Both, D.R. Turner, D.W. Henderson (Environmental and Molecular Mutagenesis, 1995).

The study

• Authors: K. Both, D.R. Turner, D.W. Henderson
• Journal: Environmental and Molecular Mutagenesis
• Published: 1995;26(1):67-71
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The relationship between occupational or environmental exposure to asbestos and the development of mesothelioma, typically after prolonged latency, has been accepted as one of cause and effect. Most studies have concluded that asbestos is not mutagenic to mammalian cells in vitro. We have studied the potential of crocidolite asbestos to induce mutations in a stable mesothelioma cell line, using a mutation assay that measures mutation at the autosomal HLA-A locus and permits clonal growth of mutant cells. The mesothelioma cell line chosen is more akin to the in vivo target cells of asbestos than human peripheral blood lymphocytes used in previous studies. Exposure of mesothelioma cells in culture to both 200 micrograms/ml and 50 micrograms/ml crocidolite for 72 hr did not result in a statistically significant difference in the mutation frequency (MF) in the HLA-A assay when compared to the spontaneous MF in these cells. Mutations in the mesothelioma cells were classified according to their molecular basis. Notwithstanding the lack of statistically significant change in overall MF, molecular analysis of mutants obtained following exposure of mesothelioma cells to crocidolite demonstrated a statistically significant increase in the class of mutations arising from loss of heterozygosity (LOH) events involving the selection locus (HLA-A) and more distal loci. Mutations following exposure to 200 micrograms/ml and 50 micrograms/ml crocidolite showed a greater frequency of LOH than did spontaneous mutants (P < 0.01 and P < 0.001, respectively). These results correlate with those obtained in an earlier study using lymphocytes. The mesothelioma cell-based assay may be useful in detecting the mutagenicity of other asbestiform fibers and man-made fibers.

In plain English

This was a laboratory experiment on human cells grown in culture, not a study of people. The authors screened 17 mesothelioma cell lines and used the only one meeting their criteria, called M38K. They exposed the cells to crocidolite asbestos (UICC standard) at 50 or 200 micrograms per ml for 72 hours, compared them with unexposed cells, and measured mutations at a gene called HLA-A on chromosome 6. Crocidolite did not produce a statistically significant change in overall mutation frequency. The authors then analyzed 208 mutant cell clones for loss of heterozygosity, a change in which one of a gene's two versions is lost. In the article's table, 'no-change' mutants, those without loss of heterozygosity, numbered 11 of 44 after 200 micrograms per ml, 11 of 78 after 50 micrograms per ml, and 42 of 86 in unexposed cells. Loss of heterozygosity was significantly more frequent than in untreated controls after 200 micrograms per ml (P less than 0.01) and after 50 micrograms per ml (P less than 0.001). The authors concluded that crocidolite induced a significant increase in these events in mesothelioma cells in culture, which may contribute to asbestos's role in cancer. They noted that their method could not distinguish large deletions from mitotic recombination.

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: mutation assay at the HLA-A locus in a human mesothelioma cell line exposed to crocidolite in culture, with molecular (PCR) analysis of mutant clones
• Who was studied: Human mesothelioma cell line M38K (obtained from the Institute of Occupational Health, Helsinki), the only one of 17 cell lines screened that met the selection criteria; 208 mutant clones analyzed; work done at Flinders Medical Centre, Adelaide, South Australia
• Exposure: Crocidolite asbestos (UICC standard) at 50 or 200 micrograms per ml for 72 hours. 15% of fibers were longer than 5 micrometres and 55% had a width of 0.1 to 0.3 micrometres. Control cells received no fibers.
• Main results:
  • There was no statistically significant difference in overall mutation frequency between crocidolite-treated M38K cells and untreated controls.
  • Of 208 mutants analyzed: at 200 micrograms per ml, 31 showed loss of heterozygosity at HLA-A and D6S89, 2 at HLA-A only, and 11 no change (total 44). At 50 micrograms per ml the figures were 62, 5 and 11 (total 78). In untreated cells they were 42, 2 and 42 (total 86). Column assignments are read from the scrambled table headings and the Discussion's statement that the minority of LOH events were at HLA-A only.
  • Mutations in cells treated with 50 and 200 micrograms per ml crocidolite showed a significantly higher frequency of loss of heterozygosity than untreated controls (P less than 0.001 and P less than 0.01, respectively).
  • No mutant clone showed loss of heterozygosity at 6q24, on the other arm of chromosome 6. The authors took this as indicating a lack of whole-chromosome loss. Nonselected clones showed no loss of heterozygosity at any locus tested.
• The authors' conclusion: The authors concluded that crocidolite induced a significant increase in loss of heterozygosity events in human mesothelioma cells in culture, and that this capacity may contribute to the role of asbestos in human cancer. They also suggested the assay may be useful for testing other asbestiform and man-made fibers.
• Limitations the authors state:
  • PCR analysis could not distinguish mitotic recombination from large deletions extending to the telomere.
  • The M38K cell line may have a high spontaneous mutation frequency that partly masks a heightened susceptibility to asbestos damage.
  • Because overall mutation frequency did not rise significantly, the authors noted an alternative explanation: fibers might selectively decrease no-change mutants. They argued against this explanation.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Environmental Exposure, Latency, Crocidolite, Asbestiform.

Related studies

• Asbestos and erionite fibres can induce mutations in human lymphocytes that result in loss of heterozygosity — K. Both, D.W. Henderson, et al. (1994)
• Cytotoxicity, oxidative stress and genotoxicity induced by glass fibers on human alveolar epithelial cell line A549 — V. Rapisarda, C. Loreto, et al. (2015)
• Genotoxic mechanisms of asbestos fibers: role of extranuclear targets — A. Xu, X. Huang, et al. (2007)
• Crocidolite induces cell transformation and p53 gene mutation in BALB/c-3T3 cells — F. Lin, Y. Liu, et al. (2000)
• Reduction of chrysotile asbestos-induced genotoxicity in human peripheral blood lymphocytes by garlic extract — K. Bhattacharya, S. Yadava, et al. (2004)
• Chromosomal aberrations induced by chrysotile and crocidolite in human lymphocytes in vitro — F. Valerio, M. de Ferrari, et al. (1983)

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