Weight of evidence approach using a TK gene mutation assay with human TK6 cells for follow-up of positive results in Ames tests: a collaborative study by MMS/JEMS

• Main Authors: Manabu Yasui, Takayuki Fukuda, Akiko Ukai, Jiro Maniwa, Tadashi Imamura, Tsuneo Hashizume, Haruna Yamamoto, Kaori Shibuya, Kazunori Narumi, Yohei Fujiishi, Emiko Okada, Saori Fujishima, Mika Yamamoto, Naoko Otani, Maki Nakamura, Ryoichi Nishimura, Maya Ueda, Masayuki Mishima, Kaori Matsuzaki, Akira Takeiri, Kenji Tanaka, Yuki Okada, Munehiro Nakagawa, Shuichi Hamada, Akihiko Kajikawa, Hiroshi Honda, Jun Adachi, Kentaro Misaki, Kumiko Ogawa, Masamitsu Honma
• Format: Article
• Language: English
• Published: BMC 2021-03-01
• Series: Genes and Environment
• Subjects: TK6 assay; Human lymphoblastoid TK6 cells; Ames test; Follow-up; Weight of evidence approach; Toxicoproteomics
• Online Access: https://doi.org/10.1186/s41021-021-00179-1

Abstract Background Conflicting results between bacterial mutagenicity tests (the Ames test) and mammalian carcinogenicity tests might be due to species differences in metabolism, genome structure, and DNA repair systems. Mutagenicity assays using human cells are thought to be an advantage as follow-up studies for positive results in Ames tests. In this collaborative study, a thymidine kinase gene mutation study (TK6 assay) using human lymphoblastoid TK6 cells, established in OECD TG490, was used to examine 10 chemicals that have conflicting results in mutagenicity studies (a positive Ames test and a negative result in rodent carcinogenicity studies). Results Two of 10 test substances were negative in the overall judgment (20% effective as a follow-up test). Three of these eight positive substances were negative after the short-term treatment and positive after the 24 h treatment, despite identical treatment conditions without S9. A toxicoproteomic analysis of TK6 cells treated with 4-nitroanthranilic acid was thus used to aid the interpretation of the test results. This analysis using differentially expressed proteins after the 24 h treatment indicated that in vitro specific oxidative stress is involved in false positive response in the TK6 assay. Conclusions The usefulness of the TK6 assay, by current methods that have not been combined with new technologies such as proteomics, was found to be limited as a follow-up test, although it still may help to reduce some false positive results (20%) in Ames tests. Thus, the combination analysis with toxicoproteomics may be useful for interpreting false positive results raised by 24 h specific reactions in the assay, resulting in the more reduction (> 20%) of false positives in Ames test.