Medical/biological study (experimental study)

Time-varying magnetic fields of 60 Hz at 7 mT induce DNA double-strand breaks and activate DNA damage checkpoints without apoptosis med./bio.

By: Kim J, Yoon Y, Yun S, Park GS, Lee HJ, Song K

Published in: Bioelectromagnetics 2012; 33 (5): 383-393

Aim of study (acc. to author)

To study the biological effects and potential genotoxicity of exposure to 60 Hz time-varying magnetic fields of 2-14 mT on human primary cells and cancer cells.

Background/further details

The cells were investigated immediately or 24 h following exposure. Positive controls were performed with UVC radiation (for apoptosis and DNA double-strand breaks) and TBHP (tert-butyl hydroperoxide; for the induction of reactive oxygen species).
The authors also compared the position and time dependency of DNA double-strand breaks with numerical simulation of the magnetic fields. The Lorentz force and eddy currents in these experiments were numerically calculated to investigate the influence of each factor on the double-strand breaks.

Endpoint

genotoxicity/mutation: DNA damage and related signal transduction

Exposure

- 60 Hz
- 50/60 Hz
- magnetic field
- low frequency

Exposure	Parameters
Exposure 1: 60 Hz Exposure duration: continuous for 30 min	magnetic flux density: 2 mT minimum magnetic flux density: 14 mT maximum power: 400 mW maximum (5 - 400 mW)
Exposure 2: 60 Hz Exposure duration: continuous for 0 - 120 min	magnetic flux density: 7 mT (measured at 4 mm from the bottom of the cell culture dish) power: 400 mW maximum (5 - 400 mW)

Exposure 1

Main characteristics

Frequency	60 Hz
Type	magnetic field
Exposure duration	continuous for 30 min

Exposure setup

Exposure source	coil(s)
Setup	circular coils with a diameter of 0.9 cm and 3500 turns of wire wound on an acrylic cylinder; cell culture dish with a diameter of 3.5 or 6 cm placed so at the coil's base that the coil was in the center of the dish

Parameters

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	2 mT	minimum	measured	-	-
magnetic flux density	14 mT	maximum	measured	-	-
power	400 mW	maximum	-	-	5 - 400 mW

Exposure 2

Main characteristics

Frequency	60 Hz
Type	magnetic field
Exposure duration	continuous for 0 - 120 min

Exposure setup

Exposure source	same setup as exposure 1

Parameters

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	7 mT	-	measured	-	measured at 4 mm from the bottom of the cell culture dish
power	400 mW	maximum	-	-	5 - 400 mW

Exposed system:

intact cell/cell culture
HeLa cell line (human adenocarcinoma cell line) and IMR90 (human lung fibroblasts)

Methods Endpoint/measurement parameters/methodology

genotoxicity/mutation: DNA damage (double-strand breaks; formation of gamma-H2AX foci (fluorescence microscopy) and neutral comet assay); phosphorylation of gamma-H2AX (Western blot) and DNA damage checkpoint pathway (phospho-checkpoint kinase 2 expression (p-Chk2 is necessary for cell cycle arrest during DNA repair); Western blot)
molecular biosynthesis: formation of reactive oxygen species (via the fluorogenic marker carboxy-H2DCFDA; fluorescence microscopy); expression of phospho-ATM (regulates a number of proteins in the DNA damage checkpoint pathways, e.g. H2AX); Western blot)
cell viability/cell division/proliferation: apoptosis and apoptosis-related pathways (expression of caspase 3, cleaved caspase-3 and PARP; Western blot); cell proliferation/cell viability (MTT assay)

Investigated system:

isolated bio./chem. substance
intact cell/cell culture
cell lysates

Time of investigation:

after exposure

Main outcome of study (acc. to author)

Upon continuous exposure of human fibroblast and cervical cancer cells to a 60 Hz magnetic field at 7 mT for 0-120 minutes, no significant change in cell viability was observed. Cell viability of the two cell lines was also not altered by magnetic fields of 0-14 mT at an exposure time of 30 minutes.
However, DNA double-strand breaks were detected in both cell lines exposed to 7 mT or at higher intensities for 30 or 60 minutes (as shown by formation of gamma-H2AX foci and/or gamma-H2AX expression and comet assay). The DNA damage checkpoint pathway was activated in these cells (as shown by protein expression of phospho-ATM and p-Chk2) without programmed cell death (apoptosis; as shown by no change in expression of caspase-3, cleaved caspase-3 and PARP).
The exposure of the cell lines to a 60 Hz magnetic field did not induce intracellular reactive oxygen species production, suggesting that the observed DNA double-strand breaks were not directly caused by reactive oxygen species.
The DNA double-strand breaks mainly occurred at the central region of the culture plates, where the magnetic field was strongest, after a 30 minutes exposure. After 90 minutes, however, the amount of double-strand breaks increased rapidly in the outer regions, where the eddy current and Lorentz force were strong.
In conclusion, the data suggest that exposure to a 60 Hz magnetic field of 2-14 mT has a genotoxic potential in both human non-cancerous and cancerous cells even after short exposures of tens of minutes.

Study character:

medical/biological study
experimental study
full/main study

Study funded by

Korea Research Foundation (KRF), Korea
Korea Research Institute of Chemical Technology (KRICT)
Ministry of Knowledge Economy (MKE), Korea

Sun C et al. (2018): Ataxia telangiectasia mutated deficiency does not result in genetic susceptibility to 50 Hz magnetic fields exposure in mouse embryonic fibroblasts
Song K et al. (2018): A 60 Hz uniform electromagnetic field promotes human cell proliferation by decreasing intracellular reactive oxygen species levels
Zhu K et al. (2016): Extremely low frequency magnetic fields do not induce DNA damage in human lens epithelial cells in vitro
Mun GI et al. (2015): Effects of 60-Hz magnetic fields on DNA damage responses in HT22 mouse hippocampal cell lines
Yoon YJ et al. (2015): Effects of 60-Hz Time-Varying Electric Fields on DNA Damage and Cell Viability Support Negligible Genotoxicity of the Electric Fields
Duan W et al. (2015): Comparison of the genotoxic effects induced by 50 Hz extremely low-frequency electromagnetic fields and 1800 MHz radiofrequency electromagnetic fields in GC-2 cells
Nakayama M et al. (2014): DNA Strand Breaks in Fibroblasts Exposed to a 50-Hz Magnetic Field
Giorgi G et al. (2014): An evaluation of genotoxicity in human neuronal-type cells subjected to oxidative stress under an extremely low frequency pulsed magnetic field
Luukkonen J et al. (2014): Induction of genomic instability, oxidative processes, and mitochondrial activity by 50Hz magnetic fields in human SH-SY5Y neuroblastoma cells
Bae JE et al. (2013): Electromagnetic field-induced converse cell growth during a long-term observation
Luukkonen J et al. (2011): Pre-Exposure to 50 Hz Magnetic Fields Modifies Menadione-Induced Genotoxic Effects in Human SH-SY5Y Neuroblastoma Cells
Kim J et al. (2010): Repetitive exposure to a 60-Hz time-varying magnetic field induces DNA double-strand breaks and apoptosis in human cells
Garip AI et al. (2010): Effect of ELF-EMF on number of apoptotic cells; correlation with reactive oxygen species and HSP
Focke F et al. (2010): DNA fragmentation in human fibroblasts under extremely low frequency electromagnetic field exposure
Halicka HD et al. (2009): Attenuation of constitutive ATM activation and H2AX phosphorylation in human leukemic TK6 cells by their exposure to static magnetic field
Burdak-Rothkamm S et al. (2009): DNA and chromosomal damage in response to intermittent extremely low-frequency magnetic fields
Vijayalaxmi et al. (2009): Genetic damage in mammalian somatic cells exposed to extremely low frequency electro-magnetic fields: a meta-analysis of data from 87 publications (1990-2007)
Markkanen A et al. (2008): Pre-exposure to 50 Hz magnetic fields modifies menadione-induced DNA damage response in murine L929 cells
Koh EK et al. (2008): A 60-Hz sinusoidal magnetic field induces apoptosis of prostate cancer cells through reactive oxygen species
Falone S et al. (2007): Fifty hertz extremely low-frequency electromagnetic field causes changes in redox and differentiative status in neuroblastoma cells
Palumbo R et al. (2006): Effects on apoptosis and reactive oxygen species formation by Jurkat cells exposed to 50 Hz electromagnetic fields
Wolf FI et al. (2005): 50-Hz extremely low frequency electromagnetic fields enhance cell proliferation and DNA damage: possible involvement of a redox mechanism
Nikolova T et al. (2005): Electromagnetic fields affect transcript levels of apoptosis-related genes in embryonic stem cell-derived neural progenitor cells
Panagopoulos DJ et al. (2002): Mechanism for action of electromagnetic fields on cells

Time-varying magnetic fields of 60 Hz at 7 mT induce DNA double-strand breaks and activate DNA damage checkpoints without apoptosis med./bio.

Aim of study (acc. to author)

Background/further details

Endpoint

Exposure

Exposure 1

Main characteristics

Exposure setup

Parameters

Exposure 2

Main characteristics

Exposure setup

Parameters

Methods Endpoint/measurement parameters/methodology

Main outcome of study (acc. to author)

Study funded by

Related articles