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

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>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<jats:italic>Pig-a</jats:italic>(blood) and<jats:italic>gpt</jats:italic>(lung) mutant frequencies between MWNT-7-intratracheally treated and negative control rats. In this study, to investigate<jats:italic>in vivo</jats:italic>MWNT-7 genotoxicity on various endpoints, we attempted to develop a lung micronucleus assay through<jats:italic>ex vivo</jats:italic>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<jats:italic>in vivo</jats:italic>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.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p> 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.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>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.</jats:p></jats:sec>