No Evidence of Persisting Unrepaired Nuclear DNA Single Strand Breaks in Distinct Types of Cells in the Brain, Kidney, and Liver of Adult Mice after Continuous Eight-Week 50 Hz Magnetic Field Exposure with Flux Density of 0.1 mT or 1.0 mT

BACKGROUND: It has been hypothesized in the literature that exposure to extremely low frequency electromagnetic fields (50 or 60 Hz) may lead to human health effects such as childhood leukemia or brain tumors. In a previous study investigating multiple types of cells from brain and kidney of the mouse (Acta Neuropathologica 2004; 107: 257-264), we found increased unrepaired nuclear DNA single strand breaks (nDNA SSB) only in epithelial cells of the choroid plexus in the brain using autoradiographic methods after a continuous eight-week 50 Hz magnetic field (MF) exposure of adult mice with flux density of 1.5 mT. METHODS: In the present study we tested the hypothesis that MF exposure with lower flux densities (0.1 mT, i.e., the actual exposure limit for the population in most European countries, and 1.0 mT) shows similar results to those in the previous study. Experiments and data analysis were carried out in a similar way as in our previous study. RESULTS: Continuous eight-week 50 Hz MF exposure with 0.1 mT or 1.0 mT did not result in increased persisting unrepaired nDNA SSB in distinct types of cells in the brain, kidney, and liver of adult mice. MF exposure with 1.0 mT led to reduced unscheduled DNA synthesis (UDS) in epithelial cells in the choroid plexus of the fourth ventricle in the brain (EC-CP) and epithelial cells of the cortical collecting duct in the kidney, as well as to reduced mtDNA synthesis in neurons of the caudate nucleus in the brain and in EC-CP. CONCLUSION: No evidence was found for increased persisting unrepaired nDNA SSB in distinct types of cells in the brain, kidney, and liver of adult mice after continuous eight-week 50 Hz magnetic field exposure with flux density of 0.1 mT or 1.0 mT

Experimental set-up of the 50 Hz MF exposure of the present study.

<p>Details are provided in the main text.</p

Representative autoradiographs of Feulgen-prestained and Light Green SF Yellowish post stained paraffin sections analyzed in the present study.

<p>The photomicrographs show details of the mouse liver after an 8-week 50 Hz MF exposure with 1.0 mT with (A, B) or without (C) injection of ³H-TdR 5 min after the end of the MF exposure. Both autoradiographs were exposed in the same box for 125 days, i.e. under completely identical conditions. In A, a few (out of many) individual silver grains found over the nucleus (arrows) and cytoplasm (arrowheads) of two hepatocytes are marked; the cell bounds are indicated. In B, the arrow points to a cell that was in S phase after injection of ³H-TdR (i.e., during the last two hours of life). In C, single silver grains found over the nucleus (arrow) or cytoplasm (arrowhead) of hepatocytes are marked, representing autoradiographic background. In all panels A to C, black dots and asterisks indicate small and larger sections of liver sinusoids, respectively. The scale bar represents 25 µm.</p

Results of the autoradiographic analyses.

<p>The graphs show mean and standard error of the mean (SEM) of grain numbers representing UDS (<b>A</b>, <b>D</b>, <b>G</b>, <b>J</b>), unrepaired nDNA SSB/ISNT (<b>B</b>, <b>E</b>, <b>H</b>, <b>K</b>) and mtDNA synthesis (<b>C</b>, <b>F</b>, <b>I</b>, <b>L</b>) of neurons in the caudate nucleus in the brain (<b>A–C</b>), epithelial cells in the choroid plexus of the fourth ventricle in the brain (<b>D–F</b>), epithelial cells of the cortical collecting duct in the kidney (<b>G–I</b>), and pericentral hepatocytes in the liver (<b>J–L</b>) after sham-exposure (open bars), MF exposure with 0.1 mT for eight weeks (gray bars), or MF exposure with 1.0 mT for eight weeks (closed bars). For a detailed description of the generation of these grain numbers and grain densities see Section “Evaluation of Autoradiographs” in the main text. Statistically significant differences between groups are indicated.</p