In vivo genotoxicity assessment of a multiwalled carbon nanotube in a mouse ex vivo culture

• Published in: Genes and environment 2022-10, Vol.44 (1), p.1-24, Article 24
• Main Authors: Horibata, Katsuyoshi, Takasawa, Hironao, Hojo, Motoki, Taquahashi, Yuhji, Shigano, Miyuki, Yokota, Satoshi, Kobayashi, Norihiro, Sugiyama, Kei-ichi, Honma, Masamitsu, Hamada, Shuichi
• Format: Article
• Language: English
• Subjects: Alveoli; Analysis; Asbestos; Assaying; Carbon; Carbon nanoparticle; Carcinogenicity; Carcinogens; Cell culture; Cell division; Erythrocytes; Exposure; Genotoxicity; In vivo genotoxicity; In vivo methods and tests; Inflammation; Inhalation; Lung; Lung cancer; Lungs; Multi wall carbon nanotubes; Multiwalled carbon nanotubes; Nanotechnology; Nanotubes; Respiration; Reticulocytes; Rodents; Short Report; Trachea
• ISSN: 1880-7062; 1880-7046; 1880-7062
• DOI: 10.1186/s41021-022-00253-2

Multiwalled carbon nanotubes (MWCNTs) are suspected lung carcinogens because their shape and size are similar to asbestos. Various MWCNT types are manufactured; however, only MWNT-7 is classified into Group 2B by The International Agency for Research on Cancer. MWNT-7's carcinogenicity is strongly related to inflammatory reactions. On the other hand, inconsistent results on MWNT-7 genotoxicity have been reported. We previously observed no significant differences in both Pig-a (blood) and gpt (lung) mutant frequencies between MWNT-7-intratracheally treated and negative control rats. In this study, to investigate in vivo MWNT-7 genotoxicity on various endpoints, we attempted to develop a lung micronucleus assay through ex vivo culture targeting the cellular fraction of Clara cells and alveolar Type II (AT-II) cells, known as the initiating cells of lung cancer. Using this system, we analyzed the in vivo MWNT-7 genotoxicity induced by both whole-body inhalation exposure and intratracheal instillation. We also conducted an erythrocyte micronucleus assay using the samples obtained from animals under intratracheal instillation to investigate the tissue specificity of MWNT-7 induced genotoxicities. We detected a significant increase in the incidence of micronucleated cells derived from the cellular fraction of Clara cells and AT-II cells in both MWNT-7-treated and positive control groups compared to the negative control group under both whole-body inhalation exposures and intratracheal instillation. Additionally, the erythrocyte micronucleus assay detected a significant increase in the incidence of micronucleated reticulocytes only in the positive control group. Our findings indicated that MWNT-7 was genotoxic in the lungs directly exposed by both the body inhalation and intratracheal instillation but not in the hematopoietic tissue.