Medical/biological study (experimental study)

Increase in radiation-induced HPRT gene mutation frequency after nonthermal exposure to nonionizing 60 Hz electromagnetic fields med./bio.

By: Walleczek J, Shiu EC, Hahn GM

Published in: Radiat Res 1999; 151 (4): 489-497

Aim of study (acc. to author)

To explore the question whether a non-thermal 60 Hz magnetic field can enhance the 2 Gy gamma radiation induced hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene mutation frequency.

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.

Endpoint

genotoxicity/mutation: mutation frequency, gene mutation

Exposure

Exposure	Parameters
Exposure 1: 60 Hz Exposure duration: 12 h	magnetic flux density: 0.7 mT effective value magnetic flux density: 0.47 mT effective value magnetic flux density: 0.23 mT effective value electric field strength: 3 µV/cm maximum (in the center of the cells) current density: 0.05 µA/cm² maximum (in the center of the cells)

General information

Prior to the MF exposure samples were treated with 2 Gy at 1.76 Gy/min gamma radiation.

Exposure 1

Main characteristics

Frequency	60 Hz
Type	magnetic field
Waveform	sinusoidal
Exposure duration	12 h

Exposure setup

Exposure source	solenoid
Setup	two electrically coupled solenoid coils (length 0.25 m, diameter 0.13 m) were wound in 348 turns of magnetic wire on a cylindrical support
Sham exposure	A sham exposure was conducted.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	0.7 mT	effective value	measured	-	-
magnetic flux density	0.47 mT	effective value	measured	-	-
magnetic flux density	0.23 mT	effective value	measured	-	-
electric field strength	3 µV/cm	maximum	calculated	-	in the center of the cells
current density	0.05 µA/cm²	maximum	calculated	-	in the center of the cells

Exposed system:

intact cell/cell culture
CHO (Chinese hamster ovary) cells

Methods Endpoint/measurement parameters/methodology

genotoxicity/mutation: hypoxanthine-guanine phosphoribosyl transferase gene mutations (number of 6-thioguanine resistent colonies)
cell viability/cell division/proliferation: cell growth (cloning efficiency), cytotoxicity (percentage: survival of irradiated cells/survival of non-irradiated cells)

Investigated system:

intact cell/cell culture

Time of investigation:

after exposure

Main outcome of study (acc. to author)

An increase in the hypoxanthine-guanine phosphoribosyl transferase gene mutation frequency induced by gamma rays was observed in magnetic field exposed cells. The increase was dependent on the applied magnetic flux density and enhanced with higher magnetic flux densities.
The magnetic field exposure did not enhance the gamma radiation-induced cytotoxicity.
These data indicate that moderate-strength, oscillating magnetic fields may act as an enhancer of mutagenesis in mammalian cells.

Study character:

medical/biological study
experimental study
full/main study
blind study

Study funded by

Department of Energy, USA
Fetzer Institute, USA

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