Global and gene-specific DNA methylation effects of different asbestos fibres on human bronchial epithelial cells

Our plain-English summary of Global and gene-specific DNA methylation effects of different asbestos fibres on human bronchial epithelial cells, by D. Öner, M. Ghosh, M. Moisse, et al (Environment International, 2018).

The study

• Authors: D. Öner, M. Ghosh, M. Moisse, R.C. Duca, R. Coorens, J.A.J. Vanoirbeek, D. Lambrechts, L. Godderis, P.H.M. Hoet
• Journal: Environment International
• Published: 2018;115:301-311
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Inhalation exposure to asbestos is associated with lung and pleural diseases in humans and remains a major public health issue worldwide. Human bronchial epithelial cells (16HBE) were exposed to UICC amosite, crocidolite and chrysotile. Cytotoxicity, genotoxicity, global DNA methylation on cytosine residues (using LC-MS/MS) were investigated at different doses (2.5-100 μg/ml). Gene-specific DNA methylation alterations at the whole genome were investigated using a microarray that interrogates >450 thousand CpG sites. Subsequently, gene functional analyses (KEGG pathway, Gene Ontology and functional classification) were performed on genes with differentially methylated gene promoters. At non-cytotoxic doses, global DNA methylation was altered after 24 h exposure to amosite and crocidolite (>2.5 μg/ml). Exposure to amosite and crocidolite (amphibole type asbestos) induced both hypomethylation and hypermethylation at single CpG site and gene promoter levels whereas exposure to chrysotile (serpentine type asbestos) induced hypomethylation at the gene promoter level. Gene functional classification analyses revealed that all types of asbestos fibres induce alterations on GO-clusters i.e. on regulation of Rho-protein signal transduction, nucleus, (e.g. homeobox genes), ATP-binding function and extracellular region (e.g. WNT-group of genes). These differentially methylated genes might contribute to asbestos-related diseases in bronchial cells.

Copyright © 2018 Elsevier Ltd. All rights reserved.

In plain English

This was a laboratory study on cultured cells, not on people. A human bronchial epithelial cell line (16HBE) was exposed for 24 hours to UICC reference samples of amosite, crocidolite and chrysotile at 2.5, 5, 25 and 100 μg/ml. The authors measured cell viability, DNA damage, overall (global) DNA methylation (chemical tags on DNA), and methylation at more than 450,000 sites across the genome. A statistically significant drop in cell viability was seen only at 200 μg/ml of crocidolite and chrysotile. All three fibre types increased DNA damage, and chrysotile produced the most. Above 2.5 μg/ml, amosite raised global methylation and crocidolite lowered it. Chrysotile did not change it. At 2.5 μg/ml, amosite altered methylation on 9107 genes and crocidolite on 7576. Chrysotile altered 849, all with reduced methylation at the gene promoter. All three fibres affected 545 genes. Of five genes tested for activity, only MRAS changed significantly, falling after crocidolite. The authors concluded that asbestos altered DNA methylation and that the size of the changes depended on the type 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 laboratory experiment on a human cell line
• Who was studied: 16HBE14o- human bronchial epithelial cells grown in culture at KU Leuven, Belgium; six replicates for the DNA methylation experiments
• Exposure: UICC standard reference fibres (Amosite South African, Crocidolite South African, Chrysotile 'A' Rhodesian) at 2.5, 5, 25 and 100 μg/ml for 24 hours. Gene-specific methylation was studied at 2.5 μg/ml.
• Main results:
  • Significant cytotoxicity, measured with the WST-1 cell-viability assay, occurred only at 200 μg/ml of crocidolite and chrysotile
  • At non-cytotoxic doses, all asbestos types increased DNA damage
  • Chrysotile-exposed cells had much more DNA damage than amosite- and crocidolite-exposed cells
  • Above 2.5 μg/ml, amosite caused global hypermethylation and crocidolite caused global hypomethylation
  • Chrysotile did not affect global DNA methylation at the tested concentrations
  • Amosite caused differential methylation on 9107 genes, 17 of them hypermethylated
  • Crocidolite altered methylation on 7576 genes, 4 of them hypermethylated
  • 6824 genes were shared between amosite- and crocidolite-exposed cells, and all of them were hypomethylated
  • Chrysotile caused differential methylation on 849 genes, all hypomethylated at their promoters
  • 545 genes were differentially methylated by all three fibre types
  • The genes shared by all fibre types fell into five functional clusters, including HOX genes, Rho protein signal transduction, ATP-binding function, WNT genes and ankyrin repeat domains
  • In gene expression tests at 2.5 μg/ml, MRAS was significantly reduced after crocidolite
  • Reductions in TCF7, HOXB3, PIK3R5 and WNT7A were not statistically significant
• The authors' conclusion: The authors concluded that asbestos exposure altered global and gene-specific DNA methylation, that the size of the changes depended on the type of asbestos, and that the different types affected similar sets of genes.
• Limitations the authors state:
  • Microarrays may produce many false positives, so selected genes were checked by RT-PCR
  • Longer exposure or higher doses might be needed to see changes in gene expression
  • The global hypermethylation seen with amosite was not reflected in the genome-wide site-specific analysis
  • The authors suggested that longer incubation or higher chrysotile concentrations might produce loss of DNA methylation not seen under the tested conditions

Topics

Medical terms in this study, explained in our Lexicon: UICC, Amosite, Crocidolite, Chrysotile, Genotoxicity, Amphibole Group, Serpentine Group.

Related studies

• Induction and recovery of CpG site specific methylation changes in human bronchial cells after long-term exposure to carbon nanotubes and asbestos — D. Öner, M. Ghosh, et al. (2020)
• Distinct autophagy-apoptosis related pathways activated by Multi-walled (NM 400) and Single-walled carbon nanotubes (NIST-SRM2483) in human bronchial epithelial (16HBE14o-) cells — M. Ghosh, S. Murugadoss, et al. (2020)
• Aberrant methylation of the CDKN2a/p16INK4a gene promoter region in preinvasive bronchial lesions: a prospective study in high-risk patients without invasive cancer — A. Lamy, R. Sesboüé, et al. (2002)
• Progressive aberrant methylation of the RASSF1A gene in simian virus 40 infected human mesothelial cells — S. Toyooka, M. Carbone, et al. (2002)
• Role of mesothelin in carbon nanotube-induced carcinogenic transformation of human bronchial epithelial cells — X. He, E. Despeaux, et al. (2016)
• N-acetylcysteine prevents cytotoxic effects induced by man-made mineral fibers in a human bronchial epithelial cell line — M. Zhang, H. Xia, et al. (2018)

Browse more research in Environment International, or return to medical research.