Proving the hypothesis that the exposure to an extremely low frequency magnetic field influences the response of murine fibroblast cells to DNA-damaging agents.
Murine L929 cells were exposed to a 50 Hz magnetic field (MF, 100 and 300 µT) for 24 or 48 h, with or without ultraviolet B radiation (UVB, 160 J/m², 20 min) or the DNA-damaging agent menadione (150 µM, 1 h). 13 different combinations were tested as groups: 1) UVB + MF (100 µT) for 24 h, 2) UVB + MF (100 µT) for 48 h, 3) MF (100 µT) for 24 h + UVB + MF (100 µT) for 24 h, 4) MF (100 µT) for 24 h + UVB + incubation for 24 h, 5) MF (300 µT) for 24 h + UVB + MF (300 µT) for 24 h, 6) menadione + MF (100 µT) for 24 h, 7) menadione + MF (100 µT) for 48 h, 8) MF (100 µT) for 24 h + menadione + MF (100 µT) for 24 h, 9) MF (100 µT) for 24 h + menadione + incubation for 24 h, 10) menadione + MF (300 µT) for 24 h, 11) menadione + MF (300 µT) for 48 h, 12) MF (300 µT) for 24 h + menadione + MF (300 µT) for 24 h, 13) MF (300 µT) for 24 h + menadione + incubation for 24 h.
Each group included controls without exposure but identical incubation times, samples which were only exposed to the magnetic field and samples which were solely exposed to ultraviolet B radiation or menadione. Four to six replicated experiments were performed for each group and each replica contained two to four samples per treatment.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
for 24 or 48 h
|
|
Cells were treated in 13 groups: 1) Ultaviolet B radiation + magnetic field (100 µT) for 24 h, 2) Ultraviolet B radiation + magnetic field (100 µT) for 48 h, 3) Magnetic field (100 µT) for 24 h + ultraviolet B radiation + magnetic field (100 µT) for 24 h, 4) Magnetic field (100 µT) for 24 h + ultraviolet B radiation + incubation for 24 h, 5) Magnetic field (300 µT) for 24 h + ultraviolet B radiation + magnetic field (300 µT) for 24 h, 6) Menadione + magnetic field (100 µT) for 24 h, 7) Menadione + magnetic field (100 µT) for 48 h, 8) Magnetic field (100 µT) for 24 h + menadione + magnetic field (100 µT) for 24 h, 9) Magnetic field (100 µT) for 24 h + menadione + incubation for 24 h, 10) Menadione + Magnetic field (300 µT) for 24 h, 11) Menadione + Magnetic field (300 µT) for 48 h, 12) Magnetic field (300 µT) for 24 h + menadione + magnetic field (300 µT) for 24 h, 13) Magnetic field (300 µT) for 24 h + menadione + incubation for 24 h.
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | for 24 or 48 h |
| Exposure source | |
|---|---|
| Setup | pair of 340 mm x 460 mm Helmholtz coils, separated by 220 mm, placed inside an incubator |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 100 µT | - | measured | - | - |
| magnetic flux density | 300 µT | - | measured | - | - |
Exposure to ultraviolet B radiation plus preceding or subsequent exposure to a magnetic field did not cause any significant changes regarding the composition of cell cycle stages (groups 1-5) compared to groups which were solely exposed to ultraviolet B radiation. Only cells which were firstly exposed to a magnetic field (100 µT), then exposed to menadione and finally again exposed to a magnetic field (100 µT) (group 8) or incubated (group 9), showed a significantly lower proportion of cells at sub-G1 phase and a significantly higher proportion of cells at G2 phase and mitosis phase compared to the groups exposed to menadione solely. In experiments with the stronger magnetic field (300 µT), the results of group 12 were comparable with group 8, but additionally the proportion of cells at G1 phase was significantly reduced. Exposure of the cells to a 300 µT magnetic field for 24 h had no effect on intracellular Glutathione levels.
The authors conclude that the pre-exposure to a magnetic field can alter cellular responses to other agents. The results show that a magnetic field as low as 100 µT has a significant effect on the response of L929-cells to menadione.
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