In previous studies, the authors showed that an exposure to a gradient magnetic field with 60 Hz (6 or 7 mT) induced DNA damage and apoptosis (Kim et al., 2012; Kim et al., 2010). However, other studies showed contradictory results (e.g., Jin et al., 2014; Hong et al., 2012). Because of the inconsistency, the authors hypothesize that there is an overlooked parameter which plays a key role and paid attention to the uniformity of the magnetic field in this study.
Cell viability and reactive oxygen species level were also tested in the presence of glucose oxidase which produces low amounts of intracellular hydrogen peroxide and reduces cell viability. If the exposure to the 60 Hz-magnetic field decreased the intracellular reactive oxygen species level, the anti-proliferative effect of the glucose oxidase would be mitigated.
A positive control was used to evaluate DNA damage.
Exposure duration: 10, 30, or 60 minutes
Exposure duration: 30 minutes daily for 3 days
Exposure duration: 24, 48, 72, or 168 hours
Two exposure devices were tested: an open-type Helmholtz coil device and a closed-type Helmholtz coil device. The uniformity is better in the closed-type device, therefore it was used for all experiments and is only described here.
|Chamber||cells were exposed in a petri dish (diameter 35 mm)|
|Setup||exposure system consisted of 28 ferrite cores (85 mm x 105 mm) and had a total length of 280 mm; Helmholtz-like coils were used to generate the magnetic field; each coil was 0.4 mm in diameter and had 1,000 turns; 6 dishes were exposed simultaneously; exposure system was put into a CO2 incubator where temperature was monitored and maintained at 37°C ± 0.5°C|
|magnetic flux density||6 mT||-||measured||-||-|
The following results are always valid for both cell lines:
Neither a single exposure nor a repetitive exposure influenced cell viability or induced DNA damage. However, continuously exposed cell cultures showed a significantly increased cell viability compared to control cells dependent on the magnetic flux density: The higher the magnetic field, the stronger the increase in cell viability. This effect was reversible. When the cells were exposed for 72 hours and further incubated for 96 hours without exposure, the increase in cell viability was no longer present.
All markers indicating different cell cycle phases were increased in exposed cells compared to control cells. However, no significant changes in the distribution were observed.
The level of ROS was significantly decreased after continuous exposure to the magnetic field when compared with control cells. This finding was also supported by an increased phosphorylation of ERK 1/2 and Akt (but mainly not significant) in exposed cells compared to control cells. Additionally, the experiments with glucose oxidase indicated the involvement of ROS.
The authors suggest that continuous exposure to a 60 Hz magnetic field increased the cell viability in human lung fibroblasts and HeLa cells by reducing intracellular ROS levels.