Medical/biological study (experimental study)

Suppression of high-density magnetic field (400 mT at 50 Hz)-induced mutations by wild-type p53 expression in human osteosarcoma cells med./bio.

By: Miyakoshi J, Mori Y, Yamagishi N, Yagi K, Takebe H

Published in: Biochem Biophys Res Commun 1998; 243 (2): 579-584

Aim of study (acc. to author)

To assess the roles of the wild type p53 protein in DNA repair and in maintaining DNA stability after extremely low frequency magnetic field exposure.

Background/further details

Human osteosarcoma cells (transfected with inducible wild type p53) were compared in the mutant frequency of hypoxanthine-guanine phosphoribosyl transferase gene (induction of the 6-thioguanine resistent mutation in the hyphxanthine-guanine phosphoribosyl transferease gene) and the mutant spectrum (e.g. transition, deletion, insertion).
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.
The experiments were repeated three times.

Endpoint

genotoxicity/mutation: gene mutation

Exposure

- 50/60 Hz
- magnetic field

Exposure	Parameters
Exposure 1: 50 Hz Exposure duration: continuous for 4 h	magnetic flux density: 400 mT unspecified current density: 766 A/m² mean

Exposure 1

Main characteristics

Frequency	50 Hz
Type	magnetic field
Waveform	sinusoidal
Exposure duration	continuous for 4 h
Additional info	The magnetic field was oriented vertically.

Exposure setup

Exposure source	magnetic cores and copper coils
Chamber	An acrylic CO2 incubator was installed in the inner space between cores which housed the annular plates.
Setup	magnetic cores (silicon steel plates) 240 x 340 mm, 40 mm apart; 2 copper coils penetrating through them
Sham exposure	A sham exposure was conducted.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	400 mT	unspecified	unspecified	-	-
current density	766 A/m²	mean	unspecified	-	-

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
Saos-LP-12 (cell line derived from human osteosarcoma)

Methods Endpoint/measurement parameters/methodology

genotoxicity/mutation: number of hypoxanthine-guanine phosphoribosyl transferase gene mutations (number of 6-thioguanine resistent colonies, sequence analysis, RT-PCR); wild type p53 expression (Northern blot)

Investigated system:

DNA/RNA
intact cell/cell culture

Time of investigation:

after exposure

Main outcome of study (acc. to author)

The exposure of human osteosarcoma cells to high-density extremely low frequency magnetic fields induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene.
The mutation in the cells was suppressed by expression of the introduced wild type p53 gene during 400 mT extremely low frequency magnetic fields exposure.
No marked difference in the mutation spectrum was observed among the exposed p53 induced, exposed p53 not-induced and sham exposed cells.
Our findings suggest that wild type p53 has a function in suppression of DNA replication errors and/or in maintenance of genomic stability after high-density extremely low frequency magnetic field exposure.

Study character:

medical/biological study
experimental study
full/main study

Study funded by

Life Science Foundation, Japan
Ministry of Education, Culture, Sports, Science and Technology, Japan

Koyama S et al. (2007): Effects of 2.45 GHz electromagnetic fields with a wide range of SARs on bacterial and HPRT gene mutations
Akdag Z et al. (2006): Effect of ELF magnetic fields on lipid peroxidation, sperm count, p53, and trace elements
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