Effect of extremely low frequency magnetic fields on cell proliferation and gene expression.

Owing to concerns regarding possible effects of extremely low frequency magnetic fields (ELF-MF) on human health, many studies have been conducted to elucidate whether ELF-MF can induce modifications in biological processes. Despite this, controversies regarding effects of ELF-MF are still rife. In this study, we investigated biological effects of ELF-MF on MCF10A, MCF7, Jurkat, and NIH3T3 cell lines. ELF-MF with a magnetic flux density of 1 mT at 60 Hz was employed to stimulate cells for 4 or 16 h, after which the effects of ELF-MF on cell proliferation, cell death, cell viability, and DNA synthesis rates were assessed. Whereas Jurkat and NIH3T3 cells showed no consistent variation in cell number, cell viability, and DNA synthesis rate, MCF10A and MCF7 cells showed consistent and significant decreases in cell number, cell viability, and DNA synthesis rates. However, there was no effect of ELF-MF on cell death in any of tested cell lines. Next, to investigate the effect of ELF-MF on gene expression, we exposed MCF7 cells to 2 mT at 60 Hz for 16 h and examined transcriptional responses by using gene expression array. We found a gene, PMAIP1, that exhibited statistically significant variation using two-fold cut-off criteria and certified its expression change by using semi-quantitative and quantitative reverse transcription polymerase chain reaction. From these results, we concluded that ELF-MF could induce the delay of cell cycle progression in MCF7 and MCF10A cells in a cell context-specific manner and could up-regulate PMAIP1 in MCF7 cells.

Effects on g2/m phase cell cycle distribution and aneuploidy formation of exposure to a 60 Hz electromagnetic field in combination with ionizing radiation or hydrogen peroxide in l132 nontumorigenic human lung epithelial cells.

The aim of the present study was to assess whether exposure to the combination of an extremely low frequency magnetic field (ELF-MF; 60 Hz, 1 mT or 2 mT) with a stress factor, such as ionizing radiation (IR) or H2O2, results in genomic instability in non-tumorigenic human lung epithelial L132 cells. To this end, the percentages of G2/M-arrested cells and aneuploid cells were examined. Exposure to 0.5 Gy IR or 0.05 mM H2O2 for 9 h resulted in the highest levels of aneuploidy; however, no cells were observed in the subG1 phase, which indicated the absence of apoptotic cell death. Exposure to an ELF-MF alone (1 mT or 2 mT) did not affect the percentages of G2/M-arrested cells, aneuploid cells, or the populations of cells in the subG1 phase. Moreover, when cells were exposed to a 1 mT or 2 mT ELF-MF in combination with IR (0.5 Gy) or H2O2 (0.05 mM), the ELF-MF did not further increase the percentages of G2/M-arrested cells or aneuploid cells. These results suggest that ELF-MFs alone do not induce either G2/M arrest or aneuploidy, even when administered in combination with different stressors.

Increased γ-H2AX by exposure to a 60-Hz magnetic fields combined with ionizing radiation, but not hydrogen peroxide, in non-tumorigenic human cell lines.

PURPOSE: Genotoxic effects have been considered the gold standard to determine if an environmental factor is a carcinogen, but the currently available data for extremely low frequency time-varying magnetic fields (ELF-MF) remain controversial. As an environmental stimulus, the effect of ELF-MF on cellular DNA may be subtle. Therefore, a more sensitive method and systematic research strategy are warranted to evaluate genotoxicity. MATERIALS AND METHODS: We investigated the effect of ELF-MF in combination with ionizing radiation (IR) or H(2)O(2) on the DNA damage response of expression of phosphorylated H2AX (γ-H2AX) and production of γ-H2AX foci in non-tumorigenic human cell systems consisting of human lung fibroblast WI-38 cells and human lung epithelial L132 cells. RESULTS: Exposure to a 60-Hz, 2 mT ELF-MF for 6 h produced increased γ-H2AX expression, as well as γ-H2AX foci production, a common DNA double-strand break (DSB) marker. However, exposure to a 1 mT ELF-MF did not have the same effect. Moreover, 2 mT ELF-MF exposure potentiated the expression of γ-H2AX and γ-H2AX foci production when combined with IR, but not when combined with H(2)O(2). CONCLUSIONS: ELF-MF could affect the DNA damage response and, in combination with different stimuli, provide different effects on γ-H2AX.

Absence of DNA damage after 60-Hz electromagnetic field exposure combined with ionizing radiation, hydrogen peroxide, or c-Myc overexpression.

The principal objective of this study was to assess the DNA damage in a normal cell line system after exposure to 60 Hz of extremely low frequency magnetic field (ELF-MF) and particularly in combination with various external factors, via comet assays. NIH3T3 mouse fibroblast cells, WI-38 human lung fibroblast cells, L132 human lung epithelial cells, and MCF10A human mammary gland epithelial cells were exposed for 4 or 16 h to a 60-Hz, 1 mT uniform magnetic field in the presence or absence of ionizing radiation (IR, 1 Gy), H(2)O(2) (50 µM), or c-Myc oncogenic activation. The results obtained showed no significant differences between the cells exposed to ELF-MF alone and the unexposed cells. Moreover, no synergistic or additive effects were observed after 4 or 16 h of pre-exposure to 1 mT ELF-MF or simultaneous exposure to ELF-MF combined with IR, H(2)O(2), or c-Myc activation.

Extremely low frequency magnetic fields do not elicit oxidative stress in MCF10A cells.

The aim of this study was to determine whether extremely low frequency magnetic fields (ELF-MF) could affect intracellular reactive oxygen species (ROS) levels and antioxidant enzyme activity. After MCF10A human breast epithelial cells were exposed to 1 mT of 60 Hz ELF-MF for 4 hours, intracellular ROS level, superoxide dismutase (SOD) activity, and reduced to oxidized glutathione (GSH/GSSG) ratio were measured. The cells exposed to ELF-MF did not evidence statistically significant changes in the above-mentioned biological parameters as compared to either the incubator controls or sham-exposed cells. By way of contrast, the IR-exposed cells exhibited marked changes in ROS level, SOD activity, and GSH/GSSG ratio. When we assessed morphological changes and senescence-associated beta-galactosidase (SA-ß-Gal) activity, only the IR-exposed cells were positive. According to our results, it could be concluded that ELF-MF has no effect on intracellular ROS level, SOD activity, and GSH/GSSG ratio under our exposure condition.

Combined effects of 60 Hz electromagnetic field exposure with various stress factors on cellular transformation in NIH3T3 cells.

Epidemiological studies have suggested that extremely low-frequency magnetic fields (ELF-MF) are associated with an increased incidence of cancer. Studies using in vitro systems have reported mixed results for the effects of ELF-MF alone, and the World Health Organization (WHO) Research Agenda published in 2007 suggested that high priority research should include an evaluation of the co-carcinogenic effects of ELF-MF exposure using in vitro models. Here, the carcinogenic potential of ELF-MF exposure alone and in combination with various stress factors was investigated in NIH3T3 mouse fibroblasts using an in vitro cellular transformation assay. NIH3T3 cells were exposed to a 60 Hz ELF-MF (1 mT) alone or in combination with ionizing radiation (IR), hydrogen peroxide (H2O2), or c-Myc overexpression, and the resulting number of anchorage-independent colonies was counted. A 4 h exposure of NIH3T3 cells to ELF-MF alone produced no cell transformation. Moreover, ELF exposure did not influence the transformation activity of IR, H2O2, or activated c-Myc in our in vitro assay system, suggesting that 1 mT ELF-MF did not affect any additive or synergistic transformation activities in combination with stress factors such as IR, H2O2, or activated c-Myc in NIH3T3 cells.

Effects on micronuclei formation of 60-Hz electromagnetic field exposure with ionizing radiation, hydrogen peroxide, or c-Myc overexpression.

PURPOSE: Epidemiological studies have demonstrated a possible correlation between exposure to extremely low-frequency magnetic fields (ELF-MF) and cancer. However, this correlation has yet to be definitively confirmed by epidemiological studies. The principal objective of this study was to assess the effects of 60 Hz magnetic fields in a normal cell line system, and particularly in combination with various external factors, via micronucleus (MN) assays. MATERIALS AND METHODS: Mouse embryonic fibroblast NIH3T3 cells and human lung fibroblast WI-38 cells were exposed for 4 h to a 60 Hz, 1 mT uniform magnetic field with or without ionizing radiation (IR, 2 Gy), H(2)O(2) (100 µM) and cellular myelocytomatosis oncogene (c-Myc) activation. RESULTS: The results obtained showed no significant differences between the cells exposed to ELF-MF alone and the unexposed cells. Moreover, no synergistic effects were observed when ELF-MF was combined with IR, H(2)O(2), and c-Myc activation. CONCLUSIONS: Our results demonstrate that ELF-MF did not enhance MN frequency by IR, H(2)O(2) and c-Myc activation.

Intracellular Ca Mobilization and Beta-hexosaminidase Release Are Not Influenced by 60 Hz-electromagnetic Fields (EMF) in RBL 2H3 Cells.

The effects of extremely low frequency electromagnetic fields (EMF) on intracellular Ca(2+) mobilization and cellular function in RBL 2H3 cells were investigated. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not produce any cytotoxic effects in RBL 2H3 cells. Melittin, ionomycin and thapsigargin each dose-dependently increased the intracellular Ca(2+) concentration. The increase of intracellular Ca(2+) induced by these three agents was not affected by exposure to EMF (60 Hz, 1 mT) for 4 or 16 h in RBL 2H3 cells. To investigate the effect of EMF on exocytosis, we measured beta-hexosaminidase release in RBL 2H3 cells. Basal release of beta-hexosaminidase was 12.3±2.3% in RBL 2H3 cells. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not affect the basal or 1 µM melittin-induced beta-hexosaminidase release in RBL 2H3 cells. This study suggests that exposure to EMF (60 Hz, 0.1 or 1 mT), which is the limit of occupational exposure, has no influence on intracellular Ca(2+) mobilization and cellular function in RBL 2H3 cells.

Effect of Extremely Low Frequency Electromagnetic Fields (EMF) on Phospholipase Activity in the Cultured Cells.

This study was conducted to investigate the effects of extremely low frequency electromagnetic fields (EMF) on signal pathway in plasma membrane of cultured cells (RAW 264.7 cells and RBL 2H3 cells), by measuring the activity of phospholipase A(2) (PLA(2)), phospholipase C (PLC) and phospholipase D (PLD). The cells were exposed to the EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h. The basal and 0.5 µM melittin-induced arachidonic acid release was not affected by EMF in both cells. In cell-free PLA(2) assay, we failed to observe the change of cPLA(2) and sPLA(2) activity. Also both PLC and PLD activities did not show any change in the two cell lines exposed to EMF. This study suggests that the exposure condition of EMF (60 Hz, 0.1 or 1 mT) which is 2.4 fold higher than the limit of occupational exposure does not induce phospholipases-associated signal pathway in RAW 264.7 cells and RBL 2H3 cells.

Lack of a co-promotion effect of 60 Hz circularly polarized magnetic fields on spontaneous development of lymphoma in AKR mice.

The present study was conducted to investigate the possible effect of 60 Hz circularly polarized magnetic fields (MFs) as promoters of genetically initiated lymphoma in AKR mice. One hundred sixty female animals were divided into four different groups. They were exposed to four different intensities of circularly polarized MFs. Animals received exposure to 60 Hz circularly polarized MF at field strengths (rms-value) of 0 microT (sham control, T1, Group I), 5 microT(T2, Group II), 83.3 microT (T3, Group III), or 500 microT(T4, Group IV), for 21 h/day from the age of 4-6 weeks to the age of 44-46 weeks. There were no exposure-related changes in mean survival time, clinical signs, body weights, hematological values, micronucleus assay, gene expression arrays, analysis of apoptosis, and necropsy findings. At histopathological examination, lymphoma was seen in all the groups. The tumor incidence was 31/40(78%), 30/40(75%), 32/40(80%), and 31/40(78%) in sham control, 5, 83.3, and 500 microT groups, respectively. However, there were no differences in the tumor incidence between the sham control (T1) and circularly polarized MF exposure groups (T2-T4). In conclusion, there was no evidence that exposure to 60 Hz circularly polarized MF strengths up to 500 microT promoted lymphoma in AKR mice.

Lack of a co-promotion effect of 60 Hz rotating magnetic fields on N-ethyl-N-nitrosourea induced neurogenic tumors in F344 rats.

The present study was conducted to investigate the possible effect of 60 Hz magnetic fields as promoters of brain tumors initiated transplacentally by ethylnitrosourea (ENU) in F344 rats. One hundred twenty mated animals were divided into six different groups and exposed in utero on day 18 of gestation to a single intravenous dose of either Saline (vehicle control, Group I), or ENU 10 mg/kg (Groups II-VI). In the present study, a total of 480 offspring was used. The offspring in group II were given no further treatment while the offspring in Groups III-VI were exposed to four different intensities of magnetic fields. Animals received exposure to 60 Hz magnetic field at field strengths of 0 Tesla (sham control, T1, Group III), 5 muT (T2, Group IV), 83.3 muT (T3, Group V), or 500 muT (T4, Group VI), for 21 h/day from the age of 4 weeks to the age of 32 or 42 weeks. At histopathological examination, tumors of the nervous system were seen in all the ENU-treated groups. The tumor incidence of the ENU group at 32nd and 42nd week necropsy was higher than that of the vehicle control group. The incidence of glial tumors at 42nd week necropsy was higher than the 32nd week necropsy. However, there were no differences in the tumor incidence between the sham control (T1) and ENU + magnetic field exposure groups (T2-T4). In conclusion, there was no evidence that exposure of offspring to 60 Hz at magnetic field strengths up to 500 muT to the age of 32 or 42 weeks promoted ENU-initiated brain tumors in rats.

Lack of adverse effects in pregnant/lactating female rats and their offspring following pre- and postnatal exposure to ELF magnetic fields.

We have recently reported that exposure of pregnant rats to 60 Hz at field strengths up to 0.5 mT during the entire period of pregnancy did not induce any biologically significant effects on both pregnant dams and embryo-fetal development. The present study was carried out to investigate the potential effects of gestational and lactational MF exposure on pregnancy, delivery, and lactation of dams and growth, behavior, and mating performance of their offspring in rats. Timed-pregnant female Sprague-Dawley (SD) rats (24/group) received continuous exposure to 60 Hz magnetic field (MF) at field strengths of 0 (sham control), 5 microT, 83.3 microT, or 0.5 mT. Dams received MF or sham exposures for 21 h/day from gestational day 6 through lactational day 21. Experimentally generated MF was monitored continuously throughout the study. No exposure-related changes in clinical signs, body weight, food consumption, pregnancy length, and necropsy findings were observed in dams. Parameters of growth, behavior, and reproductive performance of offspring showed no changes related to MF exposure. There were no adverse effects on embryo-fetal development of F2 offspring from dams exposed to MF. In conclusion, exposure of pregnant SD rats to 60 Hz at field strengths up to 0.5 mT from gestational day 6 to lactational day 21 did not produce biologically significant effects in dams, F1 offspring, or F2 fetuses.

Developmental toxicity evaluation of ELF magnetic fields in Sprague-Dawley rats.

To identify possible effects of horizontally polarized magnetic field (MF) exposure on maintenance of pregnancy and embryo-fetal development, an MF exposure system was designed and constructed and 96 time-mated female Sprague-Dawley (SD) rats (24/group) received continuous exposure to 60 Hz MF at field strengths of 0 (sham control) and 5, 83.3, or 500 microT (50, 833, or 5000 mG). Dams received MF or sham exposures for 22 h/day on gestational day 6-20. MF was monitored continuously throughout the study. There were no evidences of maternal toxicity or developmental toxicity in any MF exposed groups. Mean maternal body weight, organ weights, and hematological and serum biochemical parameters in groups exposed to MF did not differ from those in sham control. No exposure related differences in fetal deaths, fetal body weight, and placental weight were observed between MF exposed groups and sham control. External, visceral, and skeletal examination of fetuses demonstrated no significant differences in the incidence of fetal malformations between MF exposed and sham control groups. In conclusion, exposure of pregnant rats to 60 Hz at MF strengths up to 500 microT during gestation day 6-20 did not produce any biologically significant effect in either dams or fetuses.