Study type: Medical/biological study (experimental study)

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

Published in: J Radiat Res 2007; 48 (1): 69-75

Aim of study (acc. to author)

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.

Background/further details

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.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 2.45 GHz
Exposure duration: continuous for 30 min
  • SAR: 200 W/kg (5, 50, 100, 200 W/kg)
Exposure 2: 2.45 GHz
Exposure duration: continuous for 2 h
CHO-K1 cells
  • SAR: 200 W/kg (5, 10, 20, 50, 100, 200 W/kg)

Exposure 1

Main characteristics
Frequency 2.45 GHz
Type
Exposure duration continuous for 30 min
Additional info bacterial cells
Additional info 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.
Exposure setup
Exposure source
Chamber 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".
Setup 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 info 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.
Parameters
Measurand Value Type Method Mass Remarks
SAR 200 W/kg - measured - 5, 50, 100, 200 W/kg

Exposure 2

Main characteristics
Frequency 2.45 GHz
Type
Exposure duration continuous for 2 h
Additional info CHO-K1 cells
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Additional info 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.
Parameters
Measurand Value Type Method Mass Remarks
SAR 200 W/kg - measured - 5, 10, 20, 50, 100, 200 W/kg

Reference articles

  • Koyama S et al. (2004): Effects of 2.45-GHz electromagnetic fields with a wide range of SARs on micronucleus formation in CHO-K1 cells.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

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.

Study character:

Study funded by

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