Appropriate in vitro test conditions for genotoxicity testing of fibers

Our plain-English summary of Appropriate in vitro test conditions for genotoxicity testing of fibers, by G. Speit (Inhalation Toxicology, 2002).

The study

• Author: G. Speit
• Journal: Inhalation Toxicology
• Published: 2002;14(1):79-90
• Type of article: Review
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

With the exception of asbestos fibers, little information is available on genotoxicity testing of fibers (i.e., respirable-sized, fiber-shaped particulates, RFP). In contrast to standard genotoxicity testing of soluble substances, fibers bring about specific problems. Test results can be influenced by fiber dimensions, surface properties, and biopersistence. The mechanisms of fiber-induced genotoxicity are not yet clear, but direct interaction with the genetic material and indirect effects via production of reactive oxygen species (ROS) have been proposed. Asbestos did not significantly induce gene mutations in bacterial and mammalian systems but led to a clear induction of structural and numerical chromosome aberrations in cultured mammalian cells. It is the purpose of this article to critically review positive in vitro genotoxicity data obtained for asbestos in the comet assay, the chromosome aberration test, and the micronucleus test and to identify the test conditions that are specifically required for the detection of asbestos-induced genotoxicity. It is concluded that appropriate cell systems are available for testing fiber-induced genotoxicity. Fiber samples have to be well characterized and phagocytosis and cytotoxic effects have to be determined for the correct interpretation of genotoxicity test results. A combination of the micronucleus test and the comet assay using continuous treatment (without exogenous metabolic activation) seems to be well suited to detect genotoxic activity of asbestos fibers with high accuracy. Further investigations are needed to shown whether this approach can be recommended for genotoxicity testing of fibers in general.

In plain English

This article was a review, not a new experiment. The author examined published cell-culture studies in which asbestos gave positive results in three tests for genetic damage: the comet assay for DNA damage, the chromosome aberration test and the micronucleus test. The aim was to identify the test conditions needed to detect such damage. In the reviewed studies, chrysotile, crocidolite, amosite and tremolite caused genetic damage in many cell types, mostly at 1 to 10 micrograms per square centimeter, though a concentration-effect relationship was rarely established. No added metabolic activation system was needed. The reviewed chromosome aberration studies had not used the short treatments with a recovery period that guidelines recommend, so whether these would also detect damage remained unclear. Most studies did not directly show that cells took up the fibers. The author concluded that, with well-characterized fibers and the conditions described, negative results in the comet assay and micronucleus test indicate that a genotoxic potential is unlikely. The author considered the approach applicable to all mineral fibers, with further study needed for synthetic fibers.

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: Narrative review of published in vitro (cell culture) genotoxicity studies of asbestos, limited to positive results in the comet assay, the chromosome aberration test and the micronucleus test
• Who was studied: Published laboratory studies using cultured cells, including Chinese hamster cell lines, Syrian hamster embryo cells, rat pleural mesothelial cells, rat lung epithelial cells, human amniotic fluid cells, human mesothelial cells, human lung epithelial cells and human lymphocytes. The comet assay section covered three papers. The article does not give a total number of studies reviewed.
• Exposure: Asbestos fibers applied directly to cultured cells: crocidolite, chrysotile, amosite and tremolite, at various concentrations, fiber lengths and treatment times
• Main results:
  • In the three comet assay studies reviewed, asbestos-induced DNA damage was detectable in mammalian cells in vitro.
  • In the chromosome aberration studies reviewed, asbestos caused chromosome breakage in various cell culture systems, not only one cell type.
  • In the micronucleus studies reviewed, the test detected both chromosome breakage and effects on chromosome number (aneuploidy) caused by asbestos.
  • In most reviewed studies, positive effects occurred at concentrations between 1 and 10 micrograms per square centimeter, regardless of fiber type or test endpoint. A concentration-effect relationship was only rarely established.
  • In the chromosome aberration studies reviewed, the short treatments (3 to 6 hours) followed by a postincubation period that international guidelines recommend had not been applied, so it remained unclear whether they would give positive results.
  • The author judged that no added metabolic activation system is needed when testing fibers.
  • In most reviewed studies, uptake of fibers by the cells (phagocytosis) was not directly demonstrated.
  • The author recommended testing at least one short (3 to 6 hour) and one long (about 24 hour) exposure in the comet assay.
• The authors' conclusion: The author concluded that, if appropriate fiber samples and the described test conditions are used, negative results in the comet assay and the micronucleus test indicate that a genotoxic potential of the fibers is unlikely. The author considered the approach appropriate for asbestos and applicable to all mineral fibers, and stated that further investigation is needed for synthetic fibers.
• Limitations the authors state:
  • Cell culture studies do not address the possible influence of biopersistence (how long fibers last in the body).
  • No systematic investigations of how exposure duration affects the chromosome aberration yield were available.
  • The sensitivity of different cell systems could not be compared in general, because most studies did not show whether the most sensitive test protocol was used.

Topics

Medical terms in this study, explained in our Lexicon: Genotoxicity, Fiber Dimensions, biopersistence, Reactive Oxygen Species (ROS), Comet Assay, Phagocytosis.

Related studies

• Mechanisms of genotoxicity of particles and fibers — R.P. Schins (2002)
• 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)
• A study of the effect of chrysotile fiber surface composition on genotoxicity in vitro — M.J. Keane, J.W. Stephens, et al. (1999)
• Chrysotile and rock wool fibers induce chromosome aberrations and DNA damage in V79 lung fibroblast cells — Y. Cui, J. Ma, et al. (2018)
• Man-made mineral fiber hazardous properties assessment using transgenic rodents: example of glass fiber testing — M.C. Bottin, J.C. Vigneron, et al. (2003)
• 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)

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