研究のタイプ: 医学／生物学の研究 (experimental study)

[パクテリアおよびHPRT遺伝子の突然変異に対する広範囲SARの2.45 GHz電磁界の影響] med./bio.

Effects of 2.45 GHz electromagnetic fields with a wide range of SARs on bacterial and HPRT gene mutations

著者: Koyama S, Takashima Y, Sakurai T, Suzuki Y, Taki M, Miyakoshi J
掲載誌: J Radiat Res 2007; 48 (1): 69-75
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現代において携帯電話は世界中至る所で使用されている。このことは、携帯電話からの高周波電磁界(HFEMF)被曝による人の健康に対する懸念を生じる。このため、バクテリアの突然変異およびヒポキサンチン・グアニン・ホスホリボシル・トランスフェラーゼ(HPRT)遺伝子の突然変異に対する2.45GHz高周波電磁界の影響を研究した。エームズ検査を用い、バクテリアは、比吸収率5～200W/kgで30分間のHFEMFばく露を受けた。すべてのバクテリア種において、擬似ばく露とHFEMFばく露グループとの間で、復帰突然変異株コロニーの頻度に重要な差異はなかった。HPRT遺伝子の突然変異の検査において、チャイニーズハムスター卵巣(CHO)-K1細胞は、5～200W/kgのSARで2時間のHFEMFばく露を受けた。我々は、各SARにおいて、HFEMFとブレオマイシンの同時ばく露の組合せ効果を見出した。200W/kgのSARでHFEMFばく露された細胞で、統計的に有意な差異が観察された。SARが50～200W/kgのHFEMFとブレオマイシンの組合せで処置された細胞は、HPRT突然変異上昇を示した。HFEMFばく露はは温度上昇を引き起こしたので、これらの突然変異頻度の増加は、熱によるブレオマイシンの活性化の結果かもしれない。我々は、突然変異頻度の増加は熱による効果が原因だと見なしている。

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研究目的（著者による）

This in vitro study was performed to investigate the effects of radiofrequency electromagnetic field on bacterial mutations and hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene mutation in mammalian cells.

詳細情報

The hypoxanthine-guanine phosphoribosyl transferase (HPRT) is an enzyme in the purine (for example guanine) synthesis pathway. HPRT-negative cells are not able to use guanine for GTP synthesis und thus, they have to synthesize the base de novo. Using the guanine analog 6-thioguanine HPRT-positive cells use 6-thioguanine for nucleotide synthesis. However, integration of 6-thioguanine leads to DNA and RNA damage and it is lethal for these cells. In contrast, HPRT-negative cells are not able to utilize 6-thioguanine and survive.
The HPRT gene mutation assay is a well-established mutagenicity assay based on the selection of clones resistant to the purine analog 6-thioguanine. I.e. for determination of the induction of 6-thioguanine resistant mutation in the HPRT gene exposed cells are plated in a medium containing 6-thioguanine.
Experiments were performed with different specific absorption rates.
The frequency of HPRT gene mutations were compared between: 1.) sham exposed, 2.) radiofrequency electromagnetic field exposed, 3.) co-exposed (radiofrequency electromagnetic field exposure plus bleomycin treatment) and 4.) heat (39°, 41°, 44° with or without bleomycin) treated cells.

影響評価項目

ばく露

ばく露 パラメータ
ばく露1: 2.45 GHz
ばく露時間: continuous for 30 min
bacterial cells
  • SAR: 200 W/kg (5, 50, 100, 200 W/kg)
ばく露2: 2.45 GHz
ばく露時間: continuous for 2 h
CHO-K1 cells
  • SAR: 200 W/kg (5, 10, 20, 50, 100, 200 W/kg)

ばく露1

主たる特性
周波数 2.45 GHz
タイプ
  • electromagnetic field
ばく露時間 continuous for 30 min
Additional information bacterial cells
Additional information Ames, B. N., McCann, J., and Yamazaki, E. (1975) Methods for detecting carcinogens and mutagens with the Salmonella/mammalian-microsome mutagenicity test. Mutat. Res. 31: 347-363.
ばく露装置
ばく露の発生源／構造
チャンバの詳細 Details of the exposure system have been described previously [Koyama et al., 2004]. To generate standing waves, one end of the waveguide was terminated with a short-circuiting plate. Exposure was performed in an acrylic incubator with an atmosphere of humidified 95% air and 5% CO2 that was "installed into inner space of the core".
ばく露装置の詳細 Aliquots of 20.1 ml of the cell suspensions were seeded into a specially designed culture dish that was placed on two slits bored on the waveguide through which cells were exposed.
Sham exposure A sham exposure was conducted.
Additional information Bacterial cells were exposed according to the protocol of the pre-incubation method of the Ames test [Ames et al., 1975]. Three chemical mutagens were used as positive control.
パラメータ
測定量 値 種別 Method Mass 備考
SAR 200 W/kg - 測定値 - 5, 50, 100, 200 W/kg
測定および計算の詳細

SAR distribution of the exposure setup was measured.

ばく露2

主たる特性
周波数 2.45 GHz
タイプ
  • electromagnetic field
ばく露時間 continuous for 2 h
Additional information CHO-K1 cells
ばく露装置
ばく露の発生源／構造
  • E1と同じ装置
Sham exposure A sham exposure was conducted.
Additional information As a positive control or co-mutagenic treatment, CHO-K1 cells were exposed to bleomycin for 1 h before EMF exposure. During heat treatment, cells were incubated for 2 h at 39, 41, and 44°C corresponding to the heat induction of about 50, 100, and 200 W/kg. Co-mutagenic treatment with bleomycin was also performed.
パラメータ
測定量 値 種別 Method Mass 備考
SAR 200 W/kg - 測定値 - 5, 10, 20, 50, 100, 200 W/kg

Reference articles

  • Koyama S et al. (2004): [CHO-K1細胞での小核形成に対する広範囲のSARをもたらす2.45GHz電磁界の影響]

ばく露を受けた生物:

方法 影響評価項目／測定パラメータ／方法

研究対象とした生物試料:
調査の時期:
  • ばく露後

研究の主なアウトカム（著者による）

There was no significant difference in the number of revertant colonies between sham exposed and radiofrequency electromagnetic field exposed bacterial strains.
A significant difference in the HPRT gene mutation frequency between sham exposed and electromagnetic field exposed cells was only observed at the highest specific absorption rate (200 W/kg), but not at lower ones.
The mutation frequency of co-exposed cells at 5, 10 and 20 W/kg were the same as bleomycin alone treated controls. However, co-exposure at 50, 100 and 200 W/kg resulted in a dose-dependent increase of mutation frequency.
Heat treatment revealed a significant increase in HPRT gene mutation at 44° (corresponding to the 200 W/Kg radiofrequency electromagnetic field). Combined treatment of heat (41° and 44°) and bleomycin induced significant difference in gene mutation compared to bleomycin alone treated cells. Therefore the increase of mutation frequency might be a result of a thermal effect.

研究の種別:

研究助成

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