Medical/biological study (experimental study)

Effect of low frequency magnetic field on efficiency of chromosome break repair med./bio.

By: Burgos-Molina AM, Mercado-Sáenz S, Sendra-Portero F, Ruiz-Gómez MJ

Published in: Electromagn Biol Med 2020; 39 (1): 30-37

Aim of study (acc. to author)

The effects of exposure of Saccharomyces cerevisiae to a 50 Hz magnetic field on DNA repair should be investigated.

Background/further details

Two different strains of Saccharomyces cerevisiae were used: Pho91 and Rmd5. Both strains were genetically modified to express an endonuclease upon growth on galactose-containing culture media, which inserts double-strand breaks at two defined sites of the genome. These two sites flank the TRP1 gene, which allows cells to synthesize tryptophan (an amino acid). Thus, successful insertion of the two double-strand breaks removes this gene and makes the cells tryptophan-auxotrophic. The two strains differ in the location of the double-strand breaks on the chromosome.
The following groups were used: 1) exposure of the Pho91 strain to the 50 Hz magnetic field, 2) exposure of the Rmd5 strain to the 50 Hz magnetic field, 3) control group of the Pho91 strain, 4) control group of the Rmd5 strain.

Endpoint

cell viability/cell division/proliferation: cell growth
cell function: DNA repair

Exposure

- 50/60 Hz
- magnetic field

Exposure	Parameters
Exposure 1: 50 Hz Exposure duration: 21 days	magnetic flux density: 2.45 mT electric field strength: 1.44317 µV/m (induced field in a single cell) SAR: 1.88842 fW/g (in a single cell)

Exposure 1

Main characteristics

Frequency	50 Hz
Type	magnetic field
Waveform	sinusoidal
Exposure duration	21 days

Exposure setup

Exposure source	Helmholtz coils
Setup	Helmholtz coils were 40 cm in diameter and consisted of 154 turns of 1.4 mm copper wire, coil centers 20 cm apart, mounted on a wooden frame, connected in series and axial directed, so that the magnetic currents flow perpendicular to the surface of the culture plates; plates were located in the region within the coils where the fields’ homogeneity was high (±3%); the temperature was measured periodically and a difference of 0.5°C between control and exposed samples was observed, with 29°C as the mean temperature of plates; the control cultures were located in a thermostatic plastic box, 5 m apart from the coils at the same temperature; the background magnetic field in the room at control location was 0.68 μT, the geomagnetic field was 42.95 µT

Exposure source

Helmholtz coils

Setup

Helmholtz coils were 40 cm in diameter and consisted of 154 turns of 1.4 mm copper wire, coil centers 20 cm apart, mounted on a wooden frame, connected in series and axial directed, so that the magnetic currents flow perpendicular to the surface of the culture plates; plates were located in the region within the coils where the fields’ homogeneity was high (±3%); the temperature was measured periodically and a difference of 0.5°C between control and exposed samples was observed, with 29°C as the mean temperature of plates; the control cultures were located in a thermostatic plastic box, 5 m apart from the coils at the same temperature; the background magnetic field in the room at control location was 0.68 μT, the geomagnetic field was 42.95 µT

Parameters

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	2.45 mT	-	measured	-	-
electric field strength	1.44317 µV/m	-	calculated	-	induced field in a single cell
SAR	1.88842 fW/g	-	calculated	-	in a single cell

Methods Endpoint/measurement parameters/methodology

cell viability/cell division/proliferation: cell growth (number of cell colonies) after 5, 9, 11, 15, 17 and 21 days of exposure and plating on galactose-containing culture medium
cell function: DNA repair of double-strand breaks (percentage of tryptophan-auxotrophic colonies) after 5, 9, 11, 15, 17 and 21 days of exposure and plating on galactose-containing culture medium

Investigated system:

yeast

Time of investigation:

during exposure
after exposure

Main outcome of study (acc. to author)

Exposure to the magnetic field led to a significant increase in the number of cell colonies in the Pho91 strain (group 1; 1.29-fold increase) and Rmd5 strain (group 2; 1.5-fold increase) after 21 days compared to the control groups. DNA repair was significantly higher on day 15 for the Rmd5 strain (55.56-fold) and for the Pho91 strain (1.18-fold) compared to the control groups.
The authors conclude that exposure of Saccharomyces cerevisiae to a 50 Hz magnetic field might increase DNA repair. Differences in repair kinetics between different strains might be related to the position of the DNA damage and the distance to the centromere.

Study character:

medical/biological study
experimental study
full/main study

Study funded by

Plan Andaluz de Investigacion, Desarrollo e Innovacion, Junta de Andalucia, Spain

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