Effects of 60-Hz Time-Varying Electric Fields on DNA Damage and Cell Viability Support Negligible Genotoxicity of the Electric Fields

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  • ABSTRACT

    The effect of a 60 Hz time-varying electric field was studied using a facing-electrode device (FED) and a coplanar-electrode device (CED) for further investigation of the genotoxicity of 60 Hz time-varying magnetic field (MF) from preceding research. Neither a single 30-minute exposure to the CED or to the FED had any obvious biological effects such as DNA double strand break (DSB) and apoptosis in cancerous SCC25, and HeLa cells, normal primary fibroblast IMR90 cells, while exposures of 60 Hz time-varying MF led to DNA damage with induced electric fields much smaller than those used in this experiment. Nor did repetitive exposures of three days or a continuous exposure of up to 144 hours with the CED induce any DNA damage or apoptosis in either HeLa or IMR90 cells. These results imply that the solitary electric field produced by time-varying MF is not a major cause of DSBs or apoptosis in cancer or normal cells.


  • KEYWORD

    Apoptosis , DNA Double-Strand Break (DSB) , HeLa Cell , IMR90 Cell , Time-Varying Electric Field (EF)

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  • [Fig. 1.] The cellular effect of a perpendicular 60 Hz electric field (EF). (a) The device to generate the 60 Hz perpendicular EF for cell exposures, which is composed of two facing electrodes. (b) SCC25 cells experienced a single exposure to an EF for 30 minutes and were harvested or further incubated for 24 hours. The relative cell viability was determined by MTT assay for each group.
    The cellular effect of a perpendicular 60 Hz electric field (EF). (a) The device to generate the 60 Hz perpendicular EF for cell exposures, which is composed of two facing electrodes. (b) SCC25 cells experienced a single exposure to an EF for 30 minutes and were harvested or further incubated for 24 hours. The relative cell viability was determined by MTT assay for each group.
  • [Fig. 2.] The coplanar electric field (EF) device. (a) The coplanar EF generator with two parallel electrodes. (b) The device was placed in the CO2 incubator (left), and cells were exposed to the coplanar EF in humid CO2 incubator (right). (c) The voltage waveform with a frequency of 60 Hz and 25% duty ratio was applied to generate an EF intensity of 16 kV/m at the center of the culture dish (left). (d) The computer simulation results for the spatial profiles of the magnitude of the EF intensity for the given voltage waveform (bottom) and the EF intensity along with the bottom surface of the dish (top).
    The coplanar electric field (EF) device. (a) The coplanar EF generator with two parallel electrodes. (b) The device was placed in the CO2 incubator (left), and cells were exposed to the coplanar EF in humid CO2 incubator (right). (c) The voltage waveform with a frequency of 60 Hz and 25% duty ratio was applied to generate an EF intensity of 16 kV/m at the center of the culture dish (left). (d) The computer simulation results for the spatial profiles of the magnitude of the EF intensity for the given voltage waveform (bottom) and the EF intensity along with the bottom surface of the dish (top).
  • [Fig. 3.] The device generating the coplanar electric field (EF) does not increase the inside temperature of incubator. The coplanar EFgenerating device was switched on for up to 24 hours, and the temperature in the incubator was monitored at every hour for up to 24 hours.
    The device generating the coplanar electric field (EF) does not increase the inside temperature of incubator. The coplanar EFgenerating device was switched on for up to 24 hours, and the temperature in the incubator was monitored at every hour for up to 24 hours.
  • [Fig. 4.] The cellular effect of a single exposure to a 60-Hz coplanar electric field (EF) in the cancerous HeLa and the normal IMR90 cells. HeLa and IMR90 cells were exposed to a single coplanar EF for 0, 10, and 30 minutes, respectively. (a) The relative cell viability of HeLa and IMR90 cells was assessed by MTT assays. (b) Cells were harvested after the exposure to a coplanar EF as described in Materials and Methods section. The expression of p-Chk2 and γ-H2AX was detected by western blots. Actin was used as a loading control. The cells of positive control for DNA damage were produced by UV irradiation as described in Materials and Methods section.
    The cellular effect of a single exposure to a 60-Hz coplanar electric field (EF) in the cancerous HeLa and the normal IMR90 cells. HeLa and IMR90 cells were exposed to a single coplanar EF for 0, 10, and 30 minutes, respectively. (a) The relative cell viability of HeLa and IMR90 cells was assessed by MTT assays. (b) Cells were harvested after the exposure to a coplanar EF as described in Materials and Methods section. The expression of p-Chk2 and γ-H2AX was detected by western blots. Actin was used as a loading control. The cells of positive control for DNA damage were produced by UV irradiation as described in Materials and Methods section.
  • [Fig. 5.] The repetitive exposures of HeLa and IMR90 cells to a 60-Hz coplanar electric field (EF) neither induces DNA damage nor decreases cell viability. HeLa and IMR90 cells were repeatedly exposed to a 60 Hz, 25% duty ratio and to a 16 kV/m coplanar EF for 30 minutes every 24 hours for 3 days. (a) After exposure, the relative cell viability was assessed by MTT colorimetric assays. (b) The cells exposed to a coplanar EF were harvested, and the expression of p-Chk2 and γ-H2AX was detected by western blots. Actin was used as a loading control, and the cells of positive control for DNA damage were produced by UV irradiation as described in Materials and Methods section.
    The repetitive exposures of HeLa and IMR90 cells to a 60-Hz coplanar electric field (EF) neither induces DNA damage nor decreases cell viability. HeLa and IMR90 cells were repeatedly exposed to a 60 Hz, 25% duty ratio and to a 16 kV/m coplanar EF for 30 minutes every 24 hours for 3 days. (a) After exposure, the relative cell viability was assessed by MTT colorimetric assays. (b) The cells exposed to a coplanar EF were harvested, and the expression of p-Chk2 and γ-H2AX was detected by western blots. Actin was used as a loading control, and the cells of positive control for DNA damage were produced by UV irradiation as described in Materials and Methods section.
  • [Fig. 6.] The genotoxic effect of the continuous exposure of HeLa and IMR90 cells to a 60-Hz coplanar electric field (EF). (a, b) HeLa and IMR90 cells were continuously exposed to a 60 Hz, 25% duty ratio and to a 16 kV/m coplanar EF for up to 72 hours. After exposure, (a) the relative cell viability was assessed by MTT colorimetric assays, and (b) PARP and γ-H2AX were detected by western blots. (c, d) Cells previously exposed to a coplanar EF for 72 hours were detached by using 0.5% trypsin, seeded in an equal number, and were continuously exposed again to a 60 Hz, 25% duty ratio and to a 16 kV/m coplanar EF for up to another 72 hours. After exposure, (c) the relative cell viability was assessed by MTT colorimetric assays, and (d) PARP and γ-H2AX were detected by western blots. (b, d) Actin was used as a loading control, and the cells of positive control for DNA damage were produced by UV irradiation as described in Materials and Methods section.
    The genotoxic effect of the continuous exposure of HeLa and IMR90 cells to a 60-Hz coplanar electric field (EF). (a, b) HeLa and IMR90 cells were continuously exposed to a 60 Hz, 25% duty ratio and to a 16 kV/m coplanar EF for up to 72 hours. After exposure, (a) the relative cell viability was assessed by MTT colorimetric assays, and (b) PARP and γ-H2AX were detected by western blots. (c, d) Cells previously exposed to a coplanar EF for 72 hours were detached by using 0.5% trypsin, seeded in an equal number, and were continuously exposed again to a 60 Hz, 25% duty ratio and to a 16 kV/m coplanar EF for up to another 72 hours. After exposure, (c) the relative cell viability was assessed by MTT colorimetric assays, and (d) PARP and γ-H2AX were detected by western blots. (b, d) Actin was used as a loading control, and the cells of positive control for DNA damage were produced by UV irradiation as described in Materials and Methods section.
  • [Table 1.] A guideline for the reference exposure levels of timevarying electric and magnetic fields (unperturbed RMS values) for the general public from the ICNIRP [2]
    A guideline for the reference exposure levels of timevarying electric and magnetic fields (unperturbed RMS values) for the general public from the ICNIRP [2]