Tempol suppresses micronuclei formation in astrocytes of newborn rats exposed to 50-Hz, 10-mT electromagnetic fields under bleomycin administration

A number of epidemiological studies have suggested that exposure to environmental and occupational electromagnetic fields (EMFs) contribute to the induction of brain tumors. The aim of this study was to investigate the mutagenetic effects of co-exposure to 50-Hz, 10-mT EMFs and bleomycin (BLM) using an ex vivo newborn rat astrocyte micronucleus assay. We also investigated whether the mutagenetic effects of EMFs were related to active oxygen species by using 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (tempol), a superoxide radical scavenger. Three-day-old male Sprague-Dawley rats were co-exposed to 50-Hz EMFs and BLM (5 or 10 mg/kg body weight (BW)) in each group (n = 6; total 6 group), and were co-exposed to 50-Hz EMFs and 10 mg/kg BW BLM with administration of 200 μmol/kg BW tempol in each group (total 4 group). Brain cells were dissociated into single cells, cultured for 96 h, incubated with an antibody against glial fibrillary acidic protein, and stained with acridine orange. The frequency of micronucleated astrocytes was determined using a fluorescence microscope. The frequency of micronucleated astrocytes in the 10 mg/kg BW bleomycin plus EMF exposure group (Mean ± SD: 19.8 ± 5.2‰) was 1.6 times higher than that in the 10 mg/kg BW bleomycin plus sham-exposure group (Mean ± SD: 12.7 ± 3.3‰) (p < 0.05). Analysis of the frequency of micronuclei in astrocytes after co-exposure to EMF and bleomycin for 72 h and administration of tempol revealed that, in the EMF exposure group, the frequency of micronuclei in rats administered with 10 mg/kg BW bleomycin and treated with tempol (Mean ± SD: 11.2 ± 1.9‰) was 40% of that in rats administered with the same dose of bleomycin and physiological saline (Mean ± SD: 28.0 ± 15.0‰) (p < 0.01). Results of the current study suggested that the mechanism responsible for the elevated frequency of micronuclei in astrocytes of rats co-exposed to BLM and EMFs is related to active oxygen species.