Medical/biological study (experimental study)

Increase in hypoxanthine-guanine phosphoribosyl transferase gene mutations by exposure to high-density 50-Hz magnetic fields med./bio.

By: Miyakoshi J, Yamagishi N, Ohtsu S, Mohri K, Takebe H

Published in: Mutation Research - Fundamental and Molecular Mechanism of Mutagenesis 1996; 349 (1): 109-114

Aim of study (acc. to author)

To investigate the effects of extremely low frequency magnetic field and/or gamma rays radiation on the induction of the 6-thioguanine resistent mutation in the hypoxanthine-guanine phosphoribosyl transferase gene in human melanoma 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.
Hydoxyurea and arabinofuranosylcytosine were used to inhibit DNA synthesis.
Extremely low frequency magnetic field exposure alone and in combination with X-rays (3 Gy) were performed.
The experiments were repeated twice.

Endpoint

genotoxicity/mutation: gene mutation, mutation rate

Exposure

Exposure	Parameters
Exposure 1: 50 Hz Exposure duration: continuous for 1, 2, 10 and 20 h	magnetic flux density: 400 mT unspecified electric field strength: 4.7 V/m maximum current density: 847 µA/cm² maximum

Exposure 1

Main characteristics

Frequency	50 Hz
Type	magnetic field
Waveform	sinusoidal
Exposure duration	continuous for 1, 2, 10 and 20 h

Exposure setup

Exposure source	coil(s)
Chamber	The incubator was inserted into the inner space of the core. Magnetic field was homogeneous within 1% difference for the area housing four 10 cm or ten 6 cm culture dishes.
Setup	A pair of magnetic cores (240 x 340 mm) made of silicon steel strips, 40 mm apart . Two copper coils (10 x 20 mm²) penetrate into the silicon steel core. An acrylic Incubator housing the plates was installed into the inner space of the core.
Additional info	For control experiments, a conventional incubator in a separate room was used.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	400 mT	unspecified	unspecified	-	-
electric field strength	4.7 V/m	maximum	calculated	-	-
current density	847 µA/cm²	maximum	calculated	-	-

Additional parameter details

The electric field and the current density were induced in the culture plates at the maximum radius of 7.5 cm from the center.

Reference articles

Miyakoshi J et al. (1994): A newly designed experimental system for exposure of mammalian cells to extremely low frequency magnetic fields

Exposed system:

intact cell/cell culture
MeWo cells (malignant melanoma cells)

Methods Endpoint/measurement parameters/methodology

genotoxicity/mutation: frequency of the hypoxanthine-guanine phosphoribosyl transferase gene mutations (number of 6-thioguanine resistent colonies)
cell viability/cell division/proliferation: cell growth (cloning efficiency), cell killing (survival of target cells)

Investigated system:

intact cell/cell culture

Time of investigation:

during exposure

Main outcome of study (acc. to author)

The mutant frequency of the hypoxanthine-guanine phosphoribosyl transferase gene was increased in cells exposed to extremely low frequency magnetic fields dependend on exposure time and the induced current intensities.
Mutations induced by gamma rays radiation were enhanced by post exposure to extremely low frequency magnetic fields.
The exposure to extremely low frequency magnetic fields did not affect both cell killing and cell growth.
Gamma rays radiation killing was not enhanced by extremely low frequency magnetic fields exposure.

Study character:

medical/biological study
experimental study
full/main study

Study funded by

Ministry of Education, Culture, and Science, Japan

Comments on this article

Bruce WR et al. (2001): Power-frequency electromagnetic fields and exposure geometry
David E et al. (1997): Difficulty of extrapolation of mutation results from 400 mT 50 - Hz magnetic field studies to normal human field exposures

Koyama S et al. (2007): Effects of 2.45 GHz electromagnetic fields with a wide range of SARs on bacterial and HPRT gene mutations
Ding GR et al. (2001): Increase in hypoxanthine-guanine phosphoribosyl transferase gene mutations by exposure to electric field
Gamble SC et al. (1999): Syrian hamster dermal cell immortalization is not enhanced by power line frequency electromagnetic field exposure
Walleczek J et al. (1999): Increase in radiation-induced HPRT gene mutation frequency after nonthermal exposure to nonionizing 60 Hz electromagnetic fields
Miyakoshi J et al. (1999): Long-term exposure to a magnetic field (5 mT at 60 Hz) increases X-ray-induced mutations
Miyakoshi J et al. (1998): Suppression of high-density magnetic field (400 mT at 50 Hz)-induced mutations by wild-type p53 expression in human osteosarcoma cells
Miyakoshi J et al. (1997): Mutation induction by high-density, 50-Hz magnetic fields in human MeWo cells exposed in the DNA synthesis phase
Miyakoshi J et al. (1996): Exposure to magnetic field (5 mT at 60 Hz) does not affect cell growth and c-myc gene expression
Miyakoshi J et al. (1994): A newly designed experimental system for exposure of mammalian cells to extremely low frequency magnetic fields
Murphy JC et al. (1993): International Commission for Protection Against Environmental Mutagens and Carcinogens. Power frequency electric and magnetic fields: a review of genetic toxicology
McCann J et al. (1993): A critical review of the genotoxic potential of electric and magnetic fields