Genotoxicity and cytotoxicity of multi-wall carbon nanotubes in cultured Chinese hamster lung cells in comparison with chrysotile A fibers

Our plain-English summary of Genotoxicity and cytotoxicity of multi-wall carbon nanotubes in cultured Chinese hamster lung cells in comparison with chrysotile A fibers, by M. Asakura, T. Sasaki, T. Sugiyama, et al (Journal of Occupational Health, 2010).

The study

• Authors: M. Asakura, T. Sasaki, T. Sugiyama, M. Takaya, S. Koda, K. Nagano, H. Arito, S. Fukushima
• Journal: Journal of Occupational Health
• Published: 2010;52(3):155-66
• Cited by: 81 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: The potential applications and industrial production of multi-wall carbon nanotubes (MWCNT) have raised serious concerns about their safety for human health and the environment. The present study was designed to examine the in vitro cytotoxicity and genotoxicity of MWCNT and UICC chrysotile A (chrysotile).

Methods: Cytotoxicity using both colony formation and lactate dehydrogenase (LDH) assays and genotoxicity including chromosome aberration, micronucleus induction and hgprt mutagenicity were examined by exposing cultured Chinese hamster lung (CHL/IU) cells to MWCNT or chrysotile at different concentrations.

Results: The in vitro cytotoxicity of MWCNT depended on the solvent used for suspension of MWCNT and ultrasonication duration of the MWCNT suspension. A combination of DMSO/culture medium and 3-minute ultrasonication resulted in a well-dispersed medium with dispersion and isolation of agglomerated MWCNT by ultrasonication which manifested the highest cytotoxicity. The cytotoxicity was more potent for chrysotile than MWCNT. The genotoxicity of MWCNT was characterized by the formation of polyploidy without structural chromosome aberration, and an increased number of bi- and multi-nucleated cells without micronucleus induction, as well as negative hgprt mutagenicity. Chrysotile exhibited essentially the same genotoxicity as MWCNT, except for marginal but significant induction of micronuclei. MWCNT and chrysotile were incompletely internalized in the cells and localized in the cytoplasm.

Conclusions: MWCNT and chrysotile were cytotoxic and genotoxic in Chinese hamster lung cells, but might interact indirectly with DNA. The results suggest that both test substances interfere physically with biological processes during cytokinesis.

In plain English

This laboratory study exposed cultured Chinese hamster lung cells (CHL/IU) to multi-wall carbon nanotubes (MWCNT) and UICC chrysotile A asbestos. The authors measured cell killing and several kinds of genetic damage. Nanotube toxicity depended on the suspension liquid and on how long ultrasound was used to separate clumps into single fibers. A DMSO/culture medium mix with 3 minutes of ultrasound gave the strongest effect. On an equal mass basis, chrysotile killed cells more potently than MWCNT. Neither material caused structural chromosome damage or gene mutations at the hgprt site. Both increased, dose-dependently, cells with extra chromosome sets (polyploidy) and cells with two or more nuclei. MWCNT did not significantly increase micronuclei (small extra nuclei) at any single dose compared with controls, although the trend across doses was statistically significant. Chrysotile significantly increased micronucleated cells at 0.4 µg/ml and above, and the authors considered the increases marginal. Both fibers were only partly taken into the cells. The authors concluded that the damage may arise not from direct interaction with DNA but from the fibers physically interfering with cell division's final splitting step (cytokinesis).

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 (cell culture) laboratory experiment comparing MWCNT with chrysotile asbestos
• Who was studied: CHL/IU cells, a clonal cell line derived from the lung of a newborn female Chinese hamster, supplied by the National Institute of Health Sciences, Tokyo, Japan
• Exposure: Multi-wall carbon nanotubes (MWNT-7, from Mitsui; mean fiber length 5.0 plus or minus 4.5 µm) and UICC chrysotile A asbestos, used unpurified. Concentrations varied by test (for example, 12.5 to 400 µg/ml MWCNT or 0.25 to 50 µg/ml chrysotile for 7 days in the colony formation assay).
• Main results:
  • After 3 minutes of ultrasound in DMSO/culture medium, MWCNT clumps were dispersed into single, isolated fibers
  • Of four suspension liquids tested, MWCNT in DMSO/culture medium showed the strongest cell-killing effect
  • In the colony formation assay, chrysotile was much more toxic to the cells than MWCNT
  • Neither MWCNT nor chrysotile caused structural chromosome aberrations. Both caused polyploidy in a significantly dose-dependent manner.
  • For MWCNT, polyploidy was significantly increased at 5 µg/ml and above after 24 hours, and at 1.3 and 5 µg/ml after 48 hours
  • Chrysotile induced significant polyploidy at lower doses than MWCNT, by mass
  • MWCNT did not significantly increase micronucleated cells at any dose compared with the negative control
  • MWCNT nonetheless showed a statistically significant dose-dependent trend in micronucleus induction (Cochran-Armitage test)
  • Chrysotile significantly increased micronucleated cells at 0.4 µg/ml and above
  • At 5.0 µg/ml MWCNT, bi-nucleated cells increased 14-fold and multi-nucleated cells 8.6-fold over controls
  • At 1.6 µg/ml chrysotile, bi-nucleated cells increased 17-fold and multi-nucleated cells 13-fold over controls
  • Both MWCNT and chrysotile were negative for mutagenicity at the hgprt locus
  • Both fibers were only partly taken into the cells and were located in the cytoplasm
• The authors' conclusion: The authors concluded that the genotoxicity of MWCNT and chrysotile may arise not from direct interaction with DNA but from physical interference of the fibers with biological processes during cytokinesis
• Limitations the authors state:
  • At the highest doses, micronucleated cells increased by less than 2-fold over controls for both materials, so the authors called the statistical increase marginal
  • The authors noted that a cell transformation assay might reflect early carcinogenesis better than the genotoxicity assays they used

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, UICC, Lactate Dehydrogenase (LDH), Micronuclei.

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