Horibata Katsuyoshi, Takasawa Hironao, Hojo Motoki, Taquahashi Yuhji, Shigano Miyuki, Yokota Satoshi, Kobayashi Norihiro, Sugiyama Kei-Ichi, Honma Masamitsu, Hamada Shuichi
Division of Genetics and Mutagenesis, National Institute of Health Sciences, 3-25-26 Tonomachi, Kawasaki-ku, Kawasaki-shi, Kanagawa, 210-9501, Japan.
LSIM Safety Institute Corporation, 14-1 Sunayama, Kamisu-shi, Ibaraki, 314-0255, Japan.
Genes Environ. 2022 Oct 19;44(1):24. 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.
多壁碳纳米管（MWCNTs）被怀疑是肺部致癌物，因为它们的形状和大小与石棉相似。制造了各种类型的MWCNTs；然而，只有MWNT-7被国际癌症研究机构归类为2B组。MWNT-7的致癌性与炎症反应密切相关。另一方面，关于MWNT-7遗传毒性的结果并不一致。我们之前观察到，经气管内给予MWNT-7的大鼠与阴性对照组相比，在Pig-a（血液）和gpt（肺）突变频率上均无显著差异。在本研究中，为了研究MWNT-7在体内对各种终点的遗传毒性，我们试图通过针对克拉拉细胞和肺泡II型（AT-II）细胞的细胞部分进行体外培养来开发一种肺微核试验，已知这两种细胞是肺癌的起始细胞。利用该系统，我们分析了全身吸入暴露和气管内滴注诱导的MWNT-7在体内的遗传毒性。我们还使用气管内滴注动物的样本进行了红细胞微核试验，以研究MWNT-7诱导的遗传毒性的组织特异性。
我们检测到，在全身吸入暴露和气管内滴注两种情况下，与阴性对照组相比，MWNT-7处理组和阳性对照组中源自克拉拉细胞和AT-II细胞细胞部分的微核细胞发生率均显著增加。此外，红细胞微核试验仅在阳性对照组中检测到微核网织红细胞发生率显著增加。
我们的研究结果表明，MWNT-7在通过全身吸入和气管内滴注直接暴露的肺部具有遗传毒性，但在造血组织中没有。
