In vitro chromosomal aberrations induced by various shapes of multi-walled carbon nanotubes (MWCNTs)

Our plain-English summary of In vitro chromosomal aberrations induced by various shapes of multi-walled carbon nanotubes (MWCNTs), by T. Sasaki, M. Asakura, C. Ishioka, et al (Journal of Occupational Health, 2016).

The study

• Authors: T. Sasaki, M. Asakura, C. Ishioka, T. Kasai, T. Katagiri, S. Fukushima
• Journal: Journal of Occupational Health
• Published: 2016;58(6):622-631
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: IARC has classified one type of multi-walled carbon nanotubes (MWCNTs), MWNT-7, as possibly carcinogenic to humans (Group 2B); however, other types of MWCNT were categorized as not classifiable as to their carcinogenicity to humans (Group 3). In vitro chromosomal aberration assays of MWNT-7 showed polyploid formation but not structural abnormalities. This study investigated the influence of the shape and size of MWCNT on in vitro induction of chromosomal aberrations.

Methods: Microscopic analysis and viable cell counting were used to assay for chromosomal aberrations and cytotoxicity induced in a Chinese hamster lung cell line (CHL/IU) exposed to different MWCNTs.

Results: Using scanning electron microscopy, seven MWCNTs were classified into three types: straight fibrous, curved fibrous, and tangled. The straight fibrous MWCNTs were the strongest inducers of polyploidy and the most cytotoxic among the three types of MWCNTs. The curved fibrous MWCNTs induced more polyploidy than the tangled MWCNTs, and the cytotoxicity of both types seemed to be a reflection of their induction of polyploidy. None of the seven MWCNTs induced structural chromosomal aberrations.

Conclusion: The non-clastogenicity of the MWCNTs indicates that the MWCNTs may not interact directly with DNA. Since the straight fibrous MWCNTs, which exhibit a structure similar to asbestos, were the strongest inducers of polyploidy, MWCNT shape may be an important factor in induction of polyploidy. We hypothesize that CHL/IU cells endocytosed MWCNTs and formed endosomes with shapes corresponding to those of the endocytosed MWCNTs, and that the long axis diameter of the endosome is important in the capability of MWCNTs to induce polyploidy.

In plain English

This laboratory study tested seven multi-walled carbon nanotubes (MWCNTs), labelled CTa to CTg, on a Chinese hamster lung cell line (CHL/IU). The study did not test asbestos itself. The authors grouped the nanotubes by shape as straight fibrous (CTa, which is MWNT-7, and CTb), curved fibrous (CTc, CTd) and tangled (CTe, CTf, CTg). Cells were exposed for 45 hours to 0.31 to 5000 micrograms per millilitre (µg/ml). None of the seven caused structural chromosome damage. Five caused a significant increase in polyploidy, meaning cells with extra sets of chromosomes. The lowest doses that did so were 1.2 µg/ml (CTa, CTb), 21 µg/ml (CTc), 62 µg/ml (CTd) and 100 µg/ml (CTe). CTf did not up to 5000 µg/ml, nor CTg up to 2500 µg/ml; at 5000 µg/ml, CTg was so toxic that no dividing cells could be examined. At lower doses, the straight fibrous types were the most toxic to cells. The authors concluded that the nanotubes may not interact directly with DNA. They also concluded that shape may be important, since the straight fibrous types, structurally similar to asbestos, induced polyploidy most strongly.

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) cell study: chromosomal aberration assays and cell-toxicity measurements, with electron microscopy of the nanotubes and of the exposed cells
• Who was studied: A cell line (CHL/IU) derived from the lung of a newborn female Chinese hamster; no humans or live animals were studied
• Exposure: Seven multi-walled carbon nanotubes (CTa to CTg; CTa is MWNT-7) from Japanese suppliers, at 0.31 to 5000 µg/ml for 45 hours. They were classed as straight fibrous (CTa, CTb), curved fibrous (CTc, CTd) or tangled (CTe, CTf, CTg). Asbestos was not tested.
• Main results:
  • None of the seven nanotubes caused structural chromosomal aberrations in the CHL/IU cells
  • The lowest doses that significantly increased polyploidy were 1.2 µg/ml for CTa and CTb, 21 µg/ml for CTc, 62 µg/ml for CTd and 100 µg/ml for CTe
  • CTf (tangled) did not significantly increase polyploidy at any concentration up to 5000 µg/ml. CTg (tangled) did not do so up to 2500 µg/ml. At 5000 µg/ml, CTg was too toxic for any dividing (metaphase) cells to be observed, so it could not be scored at that dose.
  • The straight fibrous nanotubes (CTa, CTb) were the strongest inducers of polyploidy, and the curved fibrous ones (CTc, CTd) were intermediate
  • At lower doses (0.31 to 630 µg/ml), toxicity to cells followed nanotube shape: straight fibrous were the most toxic, then curved fibrous and CTe, then CTf and CTg
  • At their highest doses, relative cell growth was 91% for CTe, 38% for CTf and 3% for CTg
• The authors' conclusion: The authors concluded that the nanotubes may not interact directly with DNA. They also concluded that, because the straight fibrous types (which have a structure similar to asbestos) were the strongest inducers of polyploidy, nanotube shape may be an important factor in causing polyploidy.
• Limitations the authors state:
  • The authors' electron microscopy could not tell apart the membranes surrounding swallowed nanotubes inside cells, which their proposed mechanism relies on

Topics

Medical terms in this study, explained in our Lexicon: IARC, Carcinogenic, Scanning Electron Microscopy (SEM).

Related studies

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• Uptake and cytotoxic effects of multi-walled carbon nanotubes in human bronchial epithelial cells — S. Hirano, Y. Fujitani, et al. (2010)
• 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)
• 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)
• Multi-walled carbon nanotubes induce stronger migration of inflammatory cells in vitro than asbestos or granular particles but a similar pattern of inflammatory mediators — G.A. Westphal, N. Rosenkranz, et al. (2019)
• Osteopontin mRNA expression by rat mesothelial cells exposed to multi-walled carbon nanotubes as a potential biomarker of chronic neoplastic transformation in vitro — S. Sridharan, A. Taylor-Just, et al. (2021)

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