In vitro genotoxicity of asbestos substitutes induced by coupled stimulation of dissolved high-valence ions and oxide radicals

Our plain-English summary of In vitro genotoxicity of asbestos substitutes induced by coupled stimulation of dissolved high-valence ions and oxide radicals, by T. Huo, F. Dong, J. Deng, et al (Environmental Science and Pollution Research International, 2018).

The study

• Authors: T. Huo, F. Dong, J. Deng, Q. Zhang, W. Ye, W. Zhang, P. Wang, D. Sun
• Journal: Environmental Science and Pollution Research International
• Published: 2018;25(23):22356-22367
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The wide use of asbestos and its substitutes has given rise to studies on their possible harmful effects on human health and environment. However, their toxic effects remain unclear. The present study was aimed to disclose the coupled effects of dissolved high-valence ions and oxide radicals using the in vitro cytotoxicity and genotoxicity of chrysotile (CA), nano-SiO2 (NS), ceramic fiber (CF), glass fiber (GF), and rock wool (RW) on Chinese hamster lung cells V79. All samples induced cell mortality correlated well with the chemical SiO2 content of asbestos substitutes and the amount of dissolved Si. Alkali or alkaline earth metal elements relieved mortality of V79 cells; Al2O3 reinforced toxicity of materials. Asbestos substitutes generated lasting, increasing amount of acellular ·OH which formed at the fiber surface at sites with loose/unsaturated bonds, as well as by catalytic reaction through dissolved iron. Accumulated mechanical and radical stimulation induced the intracellular reactive oxygen species (ROS) elevation, morphology change, and deviating trans-membrane ion flux. The cellular ROS appeared as NS > GF > CF ≈ CA > RW, consistent with cell mortality rather than with acellular ·OH generation. Chromosomal and DNA lesions in V79 cells were not directly associated with the cellular ROS, while influenced by dissolved high-valence irons in the co-culture medium. In conclusion, ions from short-time dissolution of dust samples and the generation of extracellular ·OH presented combined effects in the elevation of intracellular ROS, which further synergistically induced cytotoxicity and genotoxicity.

In plain English

In this laboratory study, Chinese hamster lung cells (V79) were exposed in culture dishes to ground dusts of chrysotile asbestos, glass fiber, ceramic fiber and rock wool, with non-fibrous nano-silica as a comparison particle. After 24 hours, cell survival fell as dose rose. The concentrations that killed half the cells were 77.40 μg/mL for nano-silica, 133.85 for glass fiber, 151.81 for ceramic fiber, 182.75 for chrysotile and 220.43 for rock wool. Cell death rose with the materials' silica content. All dusts produced hydroxyl radicals in a cell-free solution, ceramic fiber the most. Chrysotile, nano-silica and glass fiber significantly raised reactive oxygen inside cells. Every dust increased DNA comet tail length compared with untreated cells, and the authors reported that all dusts caused DNA fragmentation. At 50 μg/mL, DNA and chromosome damage did not rise in step with reactive oxygen inside cells. The authors concluded that chrysotile was not the most toxic material tested and that replacing asbestos with artificial fibers does not necessarily lower health risk. They did not consider fiber aspect ratio (length to width) or diameter.

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 cultured cells: cell survival (MTT assay), dissolved ions, cell-free hydroxyl radical generation, intracellular reactive oxygen species, cell appearance, micronucleus test and comet assay
• Who was studied: Chinese hamster lung cells (V79 cell line) obtained from the Chinese Academy of Sciences cell collection, Shanghai, China; no people or animals were studied
• Exposure: Ball-milled, sieved dusts of chrysotile asbestos (collected in Mangnai, Qinghai province, China), glass fiber, ceramic fiber and rock wool (bought at a building materials market in Mianyang, Sichuan), plus nano-SiO2 as a non-fibrous particle control. The authors group chrysotile with the substitutes. Cells were exposed for 24 hours at 0 to 800 μg/mL for survival tests, 50 μg/mL for intracellular ROS, and 50, 100 and 200 μg/mL for micronucleus and comet tests.
• Main results:
  • Toxicity to cells was ordered nano-SiO2 > glass fiber > ceramic fiber > chrysotile > rock wool. Concentrations killing 50% of cells (LC50) were 77.40, 133.85, 151.81, 182.75 and 220.43 μg/mL respectively.
  • At 100 μg/mL, cell survival was lowest with nano-SiO2 (35.36 ± 4.17%) and highest with rock wool (74.39 ± 9.1%).
  • Cell death correlated positively with the silica (SiO2) content of the materials.
  • In a cell-free solution, after 2 hours, the total hydroxyl radical trapped was ordered ceramic fiber > rock wool > nano-SiO2 > chrysotile > glass fiber.
  • Inside cells, chrysotile, nano-SiO2 and glass fiber significantly increased reactive oxygen species compared with untreated cells (p less than 0.05).
  • Intracellular reactive oxygen species in cells treated with rock wool and ceramic fiber was lower than with chrysotile.
  • Micronucleus test at 50 μg/mL: nano-SiO2 significantly increased micronucleated cells; rock wool showed no effect on chromosome splitting.
  • Comet assay: comet tail length was higher than in the control group for all treated groups (p less than 0.05). The authors stated that all tested dusts induced DNA fragmentation in V79 cells.
  • Among the fibrous materials, chrysotile caused the highest toxicity at 50 μg/mL, but higher doses reversed this.
  • When correlations were analyzed at 50 μg/mL, chromosomal and DNA damage measures did not increase in a straight line with intracellular reactive oxygen species.
• The authors' conclusion: The authors concluded that chrysotile and the manufactured substitutes showed potential cytotoxicity and genotoxicity. They found chrysotile was not the most toxic material tested, and they concluded that substituting artificial fibers for asbestos does not necessarily lower the health risk. They also concluded that ions from short-time dissolution of the dusts and extracellular hydroxyl radicals together raised intracellular ROS.
• Limitations the authors state:
  • The comparison did not take fiber aspect ratio or diameter into account.
  • High death of cells treated with glass fiber and ceramic fiber may have lowered their chromosomal and DNA damage scores, because the most damaged cells had died and were not counted. The authors call this an artifact of the measures.
  • The authors found no clear evidence linking short-term toxicity to how long the dusts persist (biopersistence), possibly because of interfering ions.

Topics

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

Medical terms in this study, explained in our Lexicon: Genotoxicity, Chrysotile, Reactive Oxygen Species (ROS), DNA lesions.

Related studies

• The utility of the in vitro micronucleus test for evaluating the genotoxicity of natural and manmade nano-scale fibres — P. Fowler, A. Homan, et al. (2016)
• Chrysotile and rock wool fibers induce chromosome aberrations and DNA damage in V79 lung fibroblast cells — Y. Cui, J. Ma, et al. (2018)
• Cytotoxicity, oxidative stress and genotoxicity induced by glass fibers on human alveolar epithelial cell line A549 — V. Rapisarda, C. Loreto, et al. (2015)
• Biological effects of naturally occurring and man-made fibres: in vitro cytotoxicity and mutagenesis in mammalian cells — R. Okayasu, L. Wu, et al. (1999)
• A study of the effect of chrysotile fiber surface composition on genotoxicity in vitro — M.J. Keane, J.W. Stephens, et al. (1999)
• Silica, asbestos, man-made mineral fibers, and cancer — K. Steenland, L. Stayner (1997)

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