In vitro genotoxicity studies of chrysotile asbestos fibers dispersed in simulated pulmonary surfactant

Our plain-English summary of In vitro genotoxicity studies of chrysotile asbestos fibers dispersed in simulated pulmonary surfactant, by J. Lu, M.J. Keane, T. Ong, et al (Mutation Research, 1994).

The study

• Authors: J. Lu, M.J. Keane, T. Ong, W.E. Wallace
• Journal: Mutation Research
• Published: 1994;320(4):253-9
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Micronucleus (MN) formation and sister-chromatid exchange (SCE) assays were performed for asbestos in cultured Chinese hamster lung (V79) cells to determine the effect of surfactant treatment on the genotoxicity of two chrysotile asbestos samples of different fiber lengths. The cells were challenged in vitro with NIEHS intermediate- and short-length chrysotile fibers in both their native state and with surfactant pretreatment. For the surfactant pretreatment, the fibers were incubated in a simulated pulmonary surfactant which was prepared by ultrasonically dispersing dipalmitoyl lecithin (DPL), a primary component of pulmonary surfactant, in minimal essential medium (MEM). Chrysotile asbestos was ultrasonically mixed into the prepared surfactant dispersion or into MEM. V79 cells were exposed to DPL-treated intermediate-length chrysotile (TICA), intermediate-length chrysotile (ICA), DPL-treated short-length chrysotile (TSCA) or short-length chrysotile (SCA) fibers for 48 h. For each treatment, 2000 mononucleated cells were scored for MN formation, and 30 M2 metaphase cells were scored for SCE induction. The results showed that all samples, TICA, ICA, TSCA and SCA, caused significant elevation in the frequency of cells with micronuclei and of cells with two or more nuclei. The increase in micronucleus frequency was greatest in cells challenged with untreated intermediate-length fibers, and was greater for untreated than for DPL-treated short-length fibers. For the short-length fiber samples, DPL surfactant treatment decreased activity for multiple nucleus formation, while DPL treatment did not result in consistent changes in that activity for intermediate-length fibers. Results of SCE assays were either negative or inconclusive. Cells were more viable following TICA and TSCA than following ICA and SCA challenge as measured by cell counts after 48 h of incubation.

In plain English

This laboratory study tested whether a lung surfactant ingredient altered chrysotile asbestos's effects on cells. The authors exposed cultured Chinese hamster lung (V79) cells for 48 hours to intermediate-length and short-length NIEHS chrysotile. Each was used untreated or pretreated with dipalmitoyl lecithin (DPL), a primary lung surfactant component. All four preparations significantly raised the share of cells with micronuclei (small extra nuclei) and with two or more nuclei, versus controls. With untreated intermediate-length fibers at the highest dose, 10.6% of scored mononucleated cells had micronuclei, versus 0.8% and 0.9% in controls. At the two highest doses, untreated short fibers produced about twice as many micronucleated cells as DPL-treated short fibers. For intermediate fibers, the authors reported no consistent significant DPL effect on micronuclei or multiple nuclei, though Table 1 marks one significant micronucleus reduction, at the lowest dose (3.9% versus 7.9%). Sister-chromatid exchange, another test of genetic damage, showed no dose-related increase. More cells survived with DPL-treated fibers. The authors concluded that surfactant treatment mainly reduced cytotoxicity. They noted the two samples may have differed in more than length.

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 in cultured cells, using micronucleus and sister-chromatid exchange tests
• Who was studied: Cultured Chinese hamster lung cells (V79 cell line); 4.0 x 10^5 cells seeded per dish; study done at West Virginia University and NIOSH, Morgantown, WV
• Exposure: NIEHS intermediate-length and short-length chrysotile asbestos, untreated or pretreated with DPL (500 mg DPL per g asbestos), added at 0.42 to 12.7 micrograms per square centimeter (3.3 to 100 micrograms per ml) for 48 hours. 98% of short-sample fibers were less than 10 micrometers; 65% of intermediate-sample fibers were greater than 10 micrometers.
• Main results:
  • All four preparations (DPL-treated and untreated, intermediate- and short-length) significantly increased the frequency of cells with micronuclei and of cells with two or more nuclei over controls (p less than 0.01). Micronuclei were scored in 2000 mononucleated cells per group. The highest micronucleated-cell frequency was 10.6% of those cells (untreated intermediate-length, 12.7 micrograms per square centimeter), compared with 0.8% (DPL control) and 0.9% (blank control).
  • For short-length fibers, untreated fibers produced about twice as many micronucleated cells as DPL-treated fibers at 4.2 and 12.7 micrograms per square centimeter (7.2% vs 3.7% and 7.8% vs 4.0%).
  • For intermediate-length fibers, the authors reported no consistent significant effect of DPL treatment on micronucleus or multiple-nucleus induction. Their Results text says micronucleated-cell frequencies were not significantly different, but Table 1 marks a significant difference (p less than 0.01 versus native chrysotile) at the lowest dose, 1.27 micrograms per square centimeter: 3.9% with DPL-treated fibers versus 7.9% with untreated fibers.
  • For cells with two or more nuclei, DPL treatment decreased activity of short-length fibers but did not produce consistent changes for intermediate-length fibers.
  • Intermediate-length fibers were more active than short fibers: untreated short fibers at 12.7 micrograms per square centimeter gave 7.8% micronucleated cells, similar to untreated intermediate fibers at 1.3 micrograms per square centimeter (7.9%).
  • Sister-chromatid exchange showed no dose-related increase with any of the four samples, and the cell replicative index was not affected.
  • At 12.7 micrograms per square centimeter, relative cell viability was 15.1% (DPL-treated intermediate) and 34.4% (DPL-treated short), compared with 3.8% (untreated intermediate) and 12.1% (untreated short).
• The authors' conclusion: The authors concluded that both fiber lengths, with or without surfactant treatment, induced micronuclei and multiple nuclei but not sister-chromatid exchange in V79 cells. They concluded that the main effect of surfactant treatment was to reduce cytotoxicity. They also concluded that it had no consistent significant effect on micronucleus or multiple-nucleus induction by intermediate-length fibers, and that it significantly reduced both for short-length fibers.
• Limitations the authors state:
  • Only two fiber samples were used, and they were not size-separated fractions of a common sample, so other structural or compositional differences could explain the length comparison.
  • The similar activity of treated and untreated intermediate-length fibers could be due to the cytotoxic effects of the untreated fibers.
  • The kinetochore staining results on whether micronuclei came from chromosome breakage or from whole lagging chromosomes were limited, and the data were not shown.

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, Fiber Length, Micronuclei.

Related studies

• A study of the effect of chrysotile fiber surface composition on genotoxicity in vitro — M.J. Keane, J.W. Stephens, et al. (1999)
• 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)
• Kerosene soot genotoxicity: enhanced effect upon co-exposure with chrysotile asbestos in Syrian hamster embryo fibroblasts — M. Lohani, E. Dopp, et al. (2000)
• Reduction of chrysotile asbestos-induced genotoxicity in human peripheral blood lymphocytes by garlic extract — K. Bhattacharya, S. Yadava, et al. (2004)
• 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-induced asbestosis: changes in the free cell population, pulmonary surfactant and whole lung tissue of rats — T.D. Tetley, P.M. Hext, et al. (1976)

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