The rate of X-ray-induced DNA double-strand break repair in the embryonic mouse brain is unaffected by exposure to 50 Hz magnetic fields

Abstract

Purpose: Following in utero exposure to low dose radiation (10-200 mGy), we recently observed a linear induction of DNA double-strand breaks (DSB) and activation of apoptosis in the embryonic neuronal stem/progenitor cell compartment. No significant induction of DSB or apoptosis was observed following exposure to magnetic fields (MF). In the present study, we exploited this in vivo system to examine whether exposure to MF before and after exposure to 100 mGy X-rays impacts upon DSB repair rates.

Materials and methods: 53BP1 foci were quantified following combined exposure to radiation and MF in the embryonic neuronal stem/progenitor cell compartment. Embryos were exposed in utero to 50 Hz MF at 300 μT for 3 h before and up to 9 h after exposure to 100 mGy X-rays. Controls included embryos exposed to MF or X-rays alone plus sham exposures.

Results: Exposure to MF before and after 100 mGy X-rays did not impact upon the rate of DSB repair in the embryonic neuronal stem cell compartment compared to repair rates following radiation exposure alone.

Conclusions: We conclude that in this sensitive system MF do not exert any significant level of DNA damage and do not impede the repair of X-ray induced damage.

Keywords: DNA double-strand break repair; X-rays; embryonic neuronal stem cells; extremely low frequency magnetic fields (ELF-MF); low dose radiation.

Figure 1.. Plan of treatments and controls used for analysis of 50 Hz magnetic field, 100 mGy IR or combined exposures. For sham or ELF-MF exposure alone (lines 1–2), mothers were sham exposed (light grey shading) or exposed at 300 μT (dark grey shading) in the Helmholtz coils for 9 h, and samples collected as indicated by arrows. For sham or IR exposure alone (lines 3–4), mothers were sham exposed (dotted light grey) or exposed (dark grey) in the IR facility, and samples collected at 1 and 6 h post sham, or at 1, 3, 6 and 11 h post IR. For combined exposed to ELF-MF and IR, mothers were sham-exposed to ELF-MF for 3 h, exposed to IR at 100 mGy, then sham exposed to ELF-MF post IR, with samples collected at 1 or 6 h (line 5); or exposed to ELF-MF at 300 μT for 3 h, exposed to IR at 100 mGy, then exposed to ELF-MF at 300 μT up to 9 h post IR, with samples collected at 1, 3, 6 and 11 h (line 6).

Figure 2.. Analysis of 53BP1 foci formation and disappearance after in utero exposure of embryos to ELF-MF at 300 μT, 100 mGy IR, or combined exposures. 53BP1 foci were quantified at 1, 3, 6, or 11 h post IR in the VZ/SVZ following sham exposure, exposure to 50 Hz ELF-MF at 300 μT, 100 mGy IR or both. Embryos (E13.5) were exposed in utero. Results represent the mean of 2 sections from 3 embryos from each of 4 mothers (i.e., a sample size of 24). Only two mothers were examined for IR sham (i.e., a sample size of 12). Error bars are standard deviation of repeat measurements (at least 2 animals per group).