報告書番号

V07005

タイトル（和文）

中間周波磁界の生物影響評価 -マウスリンフォーマ試験による遺伝毒性評価-

タイトル（英文）

Evaluation of Genotoxicity of Intermediate Frequency Magnetic Fields by Mouse Lymphoma Assay

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究では、マウスリンフォーマ試験により中間周波磁界の遺伝毒性の有無について評価した。2kHzで0.91mTrms（国際ガイドラインの146倍）、20kHzで1.1mTrms（同176倍）、60Hzで0.11mTrms（同18倍）の磁界を、マウスリンパ腫由来の細胞株にそれぞれ24時間曝露し、点突然変異などの小さな遺伝子突然変異、遺伝子欠失や構造異常などの大きな遺伝子突然変異度および総遺伝子突然変異への影響を検討した。試験(n=3)は5回以上繰り返し行い、t検定によりその差を統計学的に評価した。その結果、いずれの周波数帯の磁界曝露に対しても、磁界曝露群と対照群との間で上記の遺伝子突然変異の頻度に再現性のある統計学的に有意な差は見られなかった。また、変異原であるメチルメタンスルフォネートを磁界と同時曝露し、同様に遺伝子突然変異頻度に対する影響を評価したところ、両群間の遺伝子突然変異頻度に再現性のある統計学的に有意な差は見られなかった。これらのことから、本研究で検討した高い磁束密度の中間周波磁界は、哺乳類細胞において点突然変異や遺伝子欠失、構造異常などの大きな遺伝子突然変異を引き起こさず、また、既知変異原の遺伝子突然変異の作用機作に影響しないことがわかった。

概要 （英文）

In contrast to extremely low frequency and radio frequency electromagnetic fields (EMF), the biological effects of intermediate frequency (IF; 300Hz to 10MHz) EMF have not been studied very well. In our previous studies, we have reported the novel exposure system which can generate strong IF magnetic fields (MFs) of 0.91mTrms (146 times greater than ICNIRP guidelines for public) at 2kHz, 1.1mTrms (176 times) at 20kHz and 0.11mTrms (18 times) at 60kHz of IF MFs for in vitro research. We have also reported that the exposure of the IF MFs did not have mutagenic, co-mutagenic and/or gene conversion potentials in microbial genotoxicity tests, or micronucleus formation test with a mammalian cell line. In this study, we have investigated the effects of the IF MFs on genotoxicity in mammalian cells by mouse lymphoma assay. The assay can detect both point mutation (as large colony) and chromosomal aberration such as deletion (as small colony). A mouse lymphoma cell line, L5178Y tk+/- -3.7.2c, was used to evaluate the effects of the MF exposure on direct genotoxixity and DNA damage repair caused by methylmethane sulfonate (MMS). The cells were exposed to MFs of 0.91mTrms at 2kHz, 1.1mTrms at 20kHz or 0.11mTrms at 60kHz, for 24h at 37 C in 5% carbon dioxide. The ratio of mutation frequency of point mutation, chromosomal aberration or total mutation between MF exposed and unexposed control groups were mostly in the range from 0.8 to 1.2. In statistical analysis, neither significant nor reproducible difference in the mutation frequencies was found between exposure and control groups under the all MF exposure conditions. To examine the effects on DNA damage, the cells were exposed to each MF with MMS that potentiates mutation. In statistical analysis, neither significant nor reproducible difference in the mutation frequencies was found between exposure and control groups under the all MF exposure conditions. These results indicated that the strong IF MFs used in this study did not induce point mutation and chromosomal aberration, and did not affect DNA damage by MMS or DNA damage repair system in mammalian cells.

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