A study of the effect of chrysotile fiber surface composition on genotoxicity in vitro

Our plain-English summary of A study of the effect of chrysotile fiber surface composition on genotoxicity in vitro, by M.J. Keane, J.W. Stephens, B.Z. Zhong, et al (Journal of Toxicology and Environmental Health. Part a, 1999).

The study

• Authors: M.J. Keane, J.W. Stephens, B.Z. Zhong, W.E. Miller, T.M. Ong, W.E. Wallace
• Journal: Journal of Toxicology and Environmental Health. Part a
• Published: 1999;57(8):529-41
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile fibers (NIEHS intermediate length) were treated with ultrapure HCl to alter the fiber surface chemistry without substantially changing fiber morphology or dimensions. The objective of the study was to determine whether fiber surface chemistry is an important variable in fiber genotoxicity in vitro. The modified fibers, along with native chrysotile fibers, were used to challenge Chinese hamster lung fibroblasts (V79) in vitro using the micronucleus induction genotoxicity assay. Fiber dimensions were assessed using scanning electron microscopy by measuring the distribution of fiber lengths in 3 length ranges: less than 3 microm, 3-10 microm, and greater than 10 microm. For both treated and native fiber samples, 500 fibers were examined. Results indicate that acid-treated fibers were about 20% shorter than untreated chrysotile. Surface chemistry alterations were verified by zeta-potential reversal, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM-EDS) elemental analysis. Scanning Auger spectrometry indicated the presence of Mg, O, and Si in both treated and native chrysotile samples, which confirmed the surface purity of both fiber samples. Both XPS and SEM-EDS analysis demonstrated substantial depletion of Mg from fiber surfaces. Results of the micronucleus assay showed a positive concentration-related response for both samples, with toxicity evident only at the highest concentration. No significant difference was found for the treated and untreated chrysotile samples. These results indicate that the surface chemistry is not an important variable in the in vitro genotoxicity of chrysotile asbestos in V79 cells as detected by the micronucleus assay under the conditions used in this study, and support a model of chemically nonspecific chromosomal and spindle damage effects.

In plain English

This laboratory study tested whether the surface chemistry of chrysotile asbestos fibers affects their ability to damage chromosomes in cultured cells. The authors treated intermediate-length chrysotile with hydrochloric acid for 2 hours to strip magnesium from the fiber surfaces. They compared these fibers with untreated chrysotile in Chinese hamster lung cells (V79) at 3.3 to 100 µg/ml, using a test counting cells with micronuclei, a sign of chromosome damage. The acid treatment lowered the surface magnesium-to-silicon ratio by about 21% by one method and 15% (plus or minus 5%) by another, and reversed the fibers' surface charge. The untreated fibers' median length was estimated to be about 25% longer than the treated fibers' (95% confidence interval: 10% to 40% longer). Both fiber types produced more damaged cells as the dose rose. Within each experiment the two fiber types' responses were statistically indistinguishable. Untreated fibers were somewhat more toxic to the cells. The authors concluded that surface chemistry was not an important variable in this test. They noted that cell-culture tests have limits in predicting effects in living animals.

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 (cell culture micronucleus genotoxicity assay) comparing acid-treated and untreated chrysotile fibers
• Who was studied: Chinese hamster lung fibroblast cells (V79) in culture, exposed to NIEHS intermediate-length chrysotile. The micronucleus experiment was performed twice and scored by 2 to 3 readers, giving five reader-experiment data sets.
• Exposure: Native chrysotile and chrysotile treated with 1 N HCl for 2 h to remove surface magnesium. Cells were exposed for 24 h at 0.42 to 12.7 µg/cm2, or 3.3 to 100 µg/ml.
• Main results:
  • By x-ray photoelectron spectroscopy, the acid treatment reduced the surface Mg to Si ratio by about 21%
  • By SEM-EDS, the magnesium-to-silicon count ratio decreased by 15% plus or minus 5% after acid treatment
  • Untreated fibers had a positive zeta potential (approximately +0.02 V). Treated fibers had a negative potential of similar size (approximately -0.02 V).
  • The median length of untreated fibers was about 25% longer than that of treated fibers, with a bootstrap 95% confidence interval of 10% to 40% longer
  • Both treated and untreated samples showed a positive concentration-related increase in micronucleated cells, with toxicity evident only at the highest concentration
  • Within each experiment, the genotoxic responses of treated and untreated fibers were statistically indistinguishable
  • Across four readings, the ratio of the genotoxicity estimate for untreated to treated fibers was 1.04 (0.58 to 1.51), 1.05 (0.64 to 1.47), 1.10 (0.89 to 1.32) and 1.19 (0.63 to 1.76), with a mean of 1.10. The authors interpreted this to mean the genotoxic response of untreated fibers was on average 10% greater, but probably no more than about 50% greater.
  • Untreated fibers had larger estimates of the cytotoxicity parameter, meaning greater toxicity to the cells
• The authors' conclusion: The authors concluded that surface chemistry is not an important variable in the in vitro genotoxicity of chrysotile in V79 cells, as detected by the micronucleus assay under the study conditions. They concluded that the results support a model of chemically nonspecific chromosomal and spindle damage.
• Limitations the authors state:
  • In vitro testing has limitations in predicting effects in living organisms
  • Studies in living animals would be needed to confirm that surface-altered chrysotile is equally carcinogenic
  • The genotoxicity parameter varied considerably between replications, so the data sets could not generally be combined
  • The fiber length distributions of the treated and untreated samples were not identical
  • Sample charging prevented quantitative results from Auger spectroscopy

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Genotoxicity, Fiber Morphology, Fibroblast, Fiber Dimensions, Scanning Electron Microscopy (SEM), Fiber Length, Elemental Analysis.

Related studies

• In vitro genotoxicity studies of chrysotile asbestos fibers dispersed in simulated pulmonary surfactant — J. Lu, M.J. Keane, et al. (1994)
• 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)
• Genotoxicity and cytotoxicity of multi-wall carbon nanotubes in cultured Chinese hamster lung cells in comparison with chrysotile A fibers — M. Asakura, T. Sasaki, et al. (2010)
• Reduction of chrysotile asbestos-induced genotoxicity in human peripheral blood lymphocytes by garlic extract — K. Bhattacharya, S. Yadava, et al. (2004)
• Carboxylated short single-walled carbon nanotubes but not plain and multi-walled short carbon nanotubes show in vitro genotoxicity — M. Mrakovcic, C. Meindl, et al. (2015)

Browse more research in Journal of Toxicology and Environmental Health. Part a, or return to medical research.