Absence of in vivo mutagenicity of multi-walled carbon nanotubes in single intratracheal instillation study using F344 gpt delta rats

Our plain-English summary of Absence of in vivo mutagenicity of multi-walled carbon nanotubes in single intratracheal instillation study using F344 gpt delta rats, by K. Horibata, A. Ukai, A. Ogata, et al (Genes and Environment, 2017).

The study

• Authors: K. Horibata, A. Ukai, A. Ogata, D. Nakae, H. Ando, Y. Kubo, A. Nagasawa, K. Yuzawa, M. Honma
• Journal: Genes and Environment
• Published: 2017;39:4
• Type of article: Case report
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Introduction: It is known that fibrous particles of micrometer length, such as carbon nanotubes, which have same dimensions as asbestos, are carcinogenic. Carcinogenicity of nanomaterials is strongly related to inflammatory reactions; however, the genotoxicity mechanism(s) is unclear. Indeed, inconsistent results on genotoxicity of multi-walled carbon nanotubes (MWCNTs) have been shown in several reports. Therefore, we analyzed the in vivo genotoxicity induced by an intratracheal instillation of straight MWCNTs in rats using a different test system-the Pig-a gene mutation assay-that can reflect the genotoxicity occurring in the bone marrow. Since lungs were directly exposed to MWCNTs upon intratracheal instillation, we also performed the gpt assay using the lungs.

Findings: We detected no significant differences in Pig-a mutant frequencies (MFs) between the MWCNT-treated and control rats. Additionally, we detected no significant differences in gpt MFs in the lung between the MWCNT-treated and control rats.

Conclusions: Our findings indicated that a single intratracheal instillation of MWCNTs was non-mutagenic to both the bone marrow and lung of rats.

In plain English

This short report described an animal experiment in Japan on whether multi-walled carbon nanotubes (MWCNTs) cause gene mutations. The authors describe these fibers as sharing dimensions with asbestos; asbestos itself was not tested. Male F344 gpt delta rats, six per group, received one spray of straight MWCNTs into the windpipe (0.25, 0.5 or 1 mg/kg) or the carrier liquid alone. Comparison groups received the known mutagen ENU, or ENU plus MWCNTs. Four weeks later, blood was tested with the Pig-a assay, which the authors took to reflect bone marrow mutations. Lungs were tested with the gpt assay, which for cost reasons was run only on the vehicle control, ENU and 1 mg/kg MWCNT groups. Pig-a mutant frequencies in the MWCNT-only groups did not differ significantly from controls. In the lung, the average gpt mutant frequency was 1.88 per million in MWCNT-treated rats and 1.54 in vehicle controls, which was not a significant difference. ENU-treated rats averaged 4.21, a significant increase. The authors concluded that a single instillation of MWCNTs was non-mutagenic to rat bone marrow and lung.

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: Animal experiment (short report) using two gene mutation tests, the Pig-a assay in blood and the gpt assay in lung
• Who was studied: Male F344/NSlc-Tg (gpt-delta) transgenic rats from Japan SLC, six per group, treated at eight weeks of age and killed four weeks after treatment; studied at the National Institute of Health Sciences and Tokyo Metropolitan Institute of Public Health
• Exposure: A single intratracheal spray of straight MWCNTs (about 100 nm in diameter, 27.5% at least 5 micrometers long) at 0.25, 0.5 or 1 mg/kg, suspended in 0.2% carboxymethyl cellulose. The vehicle alone was the negative control. ENU at 35.6 mg/kg by injection into the abdomen was the positive control. A further group received MWCNTs 1 mg/kg plus ENU.
• Main results:
  • Pig-a mutant frequencies in blood showed no significant differences between the MWCNT-only-treated groups and controls.
  • Pig-a mutant frequencies clearly increased in the ENU-treated and ENU plus MWCNT-treated rats compared with controls. The ENU group and the ENU plus MWCNT group did not differ significantly from each other.
  • In the lung gpt assay, the MWCNT 1 mg/kg group did not differ significantly from controls: mean mutant frequency 1.88 (SD 1.69) per million versus 1.54 (SD 2.57) per million for the vehicle group.
  • ENU-treated rats had a significantly increased lung gpt mutant frequency, with a mean of 4.21 (SD 3.34) per million (p less than 0.05 compared to control).
  • Lung gpt analysis was done only on the MWCNT 1 mg/kg, vehicle and ENU groups. Because the highest MWCNT dose was negative, analyses of the lower-dose groups were discontinued.
• The authors' conclusion: The authors concluded that a single intratracheal instillation of MWCNTs was non-mutagenic to both the bone marrow and the lung of rats. They noted that a negative Pig-a result was not unexpected because the target organ was the lung.
• Limitations the authors state:
  • Because of the high cost of the gpt assay, lung samples from the lower MWCNT doses were not analyzed once the highest dose was negative.
  • The authors stated that they cannot explain the mechanism of MWCNT genotoxicity in detail. They suspect it is complex and depends on the nature of the MWCNTs, oxidative DNA damage, inflammation and other factors.

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic, Genotoxicity.

Related studies

• A single intratracheal instillation of single-walled carbon nanotubes induced early lung fibrosis and subchronic tissue damage in mice — E.J. Park, J. Roh, et al. (2011)
• Multi-walled carbon nanotubes translocate into the pleural cavity and induce visceral mesothelial proliferation in rats — J. Xu, M. Futakuchi, et al. (2012)
• Comparative carcinogenicity study of a thick, straight-type and a thin, tangled-type multi-walled carbon nanotube administered by intra-tracheal instillation in the rat — D.M. Saleh, W.T. Alexander, et al. (2020)
• In vitro and in vivo genotoxic effects of straight versus tangled multi-walled carbon nanotubes — J. Catalán, K.M. Siivola, et al. (2016)
• Neoplastic-like transformation effect of single-walled and multi-walled carbon nanotubes compared to asbestos on human lung small airway epithelial cells — L. Wang, T.A. Stueckle, et al. (2014)
• 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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