60 Hz magnetic field exposure induces DNA crosslinks in rat brain cells

Effects of extremely low frequency magnetic fields on animal cancer and DNA damage: A systematic review and meta-analysis

The objective of this systematic review and meta-analysis was to assess the carcinogenic effects of extremely low frequency magnetic fields (ELF-MF) by analyzing animal and comet assay studies. We have performed a global meta-analysis on all the animal studies on the relation between ELF-MF and cancer incidence and separate meta-analyses on the incidence of cancer, leukemia, lymphoma, breast cancer, brain cancer and DNA damage assessed with the comet assay. Of the 5145 references identified, 71 studies have been included in our systematic review and 22 studies in our meta-analyses. Our global meta-analysis indicated that ELF-MF exposure had no significant impact on the incidence of cancers in rodents (19 studies, OR = 1.10; 95% CI 0.91-1.32). However, our separate meta-analyses showed that ELF-MF increased the odds of developing leukemia in mice (4 studies, OR = 4.45; 95% CI 1.90-10.38) but not in rats. Our systematic review also suggests that ELF-MF can damage DNA in certain cell types like brain cells. Nevertheless, a meta-analysis on three comet assay studies indicated that ELF-MF did not increase DNA damage in neuroblastoma cells (SMD = -0.08; 95% CI -0.18-0.01). Overall, our results suggest that exposure to ELF-MF does not represent a major hazard for mammals and the carcinogenic effects of these magnetic fields could be limited to leukemia.

Genotoxic effects of electromagnetic field radiations from mobile phones

The use of wireless communication technology in mobile phones has revolutionized modern telecommunication and mobile phones have become so popular that their number exceeds the global population. Electromagnetic field radiations (EMR) are an integral part of wireless technology, which are emitted by mobile phones, mobile tower antennas, electric power stations, transmission lines, radars, microwave ovens, television sets, refrigerators, diagnostic, therapeutic, and other electronic devices. Manmade EMR sources have added to the existing burden of natural EMR human exposure arising from the Sun, cosmos, atmospheric discharges, and thunder storms. EMR including radiofrequency waves (RF) and extremely low-frequency radiation (ELF) has generated great interest as their short-term exposure causes headache, fatigue, tinnitus, concentration problems, depression, memory loss, skin irritation, sleep disorders, nausea, cardiovascular effects, chest pain, immunity, and hormonal disorders in humans, whereas long-term exposure to EMR leads to the development of cancer. The review has been written by collecting the information using various search engines including google scholar, PubMed, SciFinder, Science direct, EMF-portal, saferemr, and other websites from the internet. The main focus of this review is to delineate the mutagenic and genotoxic effects of EMR in humans and mammals. Numerous investigations revealed that exposure in the range of 0-300 GHz EMR is harmless as it did not increase micronuclei and chromosome aberrations. On the contrary, several other studies have demonstrated that exposure to EMR is genotoxic and mutagenic as it increases the frequency of micronuclei, chromosome aberrations, DNA adducts, DNA single and double strand breaks at the molecular level in vitro and in vivo. The EMR exposure induces reactive oxygen species and changes the fidelity of genes involved in signal transduction, cytoskeleton formation, and cellular metabolism.

Do 50/60 Hz magnetic fields influence oxidative or DNA damage responses in human SH-SY5Y neuroblastoma cells?

Purpose: We investigated possible effects of 50 Hz and 60 Hz magnetic fields (MFs) on reactive oxygen species (ROS) production, DNA damage, DNA damage repair rate, as well as gene expression related to oxidative stress and DNA damage signaling.Materials and methods: Human SH-SY5Y neuroblastoma cells were sham-exposed or exposed to 100 µT_RMS MFs for 24 h, then assayed or further treated with 100 µM menadione for 1 h before the assay. The levels of ROS and cytosolic superoxide anion (O₂^•-) were assayed fluorometrically. DNA damage and gene expression were assayed by comet assay and RT-qPCR, respectively. To examine whether MFs affected DNA damage repair rate, cells were allowed to repair their DNA for 1 or 2 h after menadione treatment and then assayed for DNA damage.Results: There was suggestive evidence of a general low-magnitude increase in the expression of ROS-related genes (primarily genes with antioxidant activity) when quantified immediately after MF exposure, suggesting a response to a small increase in ROS level. The possible upregulation of ROS-related genes is supported by the finding that the level of menadione-induced ROS was consistently decreased by 50 Hz MFs (not significantly by 60 Hz MFs) in several measurements 30 - 60 min after MF exposure. MF exposures did not affect cytosolic O₂^•- levels, DNA damage, or its repair rate. Changes in the expression of DNA damage-signaling genes in the MF-exposed cells did not exceed the expected rate of false positive findings. No firm evidence was found for differential effects from 50 Hz vs. 60 Hz MFs.Conclusions: While only weak effects were found on the endpoints measured, the results are consistent with MF effects on ROS signaling.

Proteomic Analysis of the Effect of Extremely Low-Frequency Electromagnetic Fields (ELF-EMF) With Different Intensities in SH-SY5Y Neuroblastoma Cell Line

Introduction: During the last 3 decades, human is exposed to extremely low frequency electromagnetic fields (ELF-EMF) emitted by power lines and electronic devices. It is now well accepted that ELF-EMF are able to produce a variety of biological effects, although the molecular mechanism is unclear and controversial. Investigation of different intensities effects of 50 Hz ELF-EMF on cell morphology and protein expression is the aim of this study. Methods: SH-SY5Y human neuroblastoma cell line was exposed to 0.5 and 1 mT 50 Hz (ELF-EMF) for 3 hours. Proteomics techniques were used to determine the effects of these fields on protein expression. Bioinformatic and statistical analysis of proteomes were performed using Progensis SameSpots software. Results: Our results showed that exposure to ELF-EMF changes cell morphology and induces a dose-dependent decrease in the proliferation rate of the cells. The proteomic studies and bioinformatic analysis indicate that exposure to 50 Hz ELF-EMF leads to alteration of cell protein expression in both dose-dependent and intensity dependent manner, but the later is more pronounced. Conclusion: Our data suggests that increased intensity of ELF-EMF may be associated with more alteration in cell protein expression, as well as effect on cell morphology and proliferation.

Modulation effect of low-frequency electric and magnetic fields on CO2 production and rates of acetate and pyruvate formation in Saccharomyces cerevisiae cell culture

We studied action of one-dimensional, two-dimensional and three-dimensional low-frequency oscillating electric and magnetic fields on sugar metabolism in Saccharomyces cerevisiae cell culture. S. cerevisiae cells were grown on a minimal medium containing glucose (10%) as a carbon source and salts (0.3-0.5%) that supplied nitrogen, phosphorus and trace metals. We found that appropriate three-dimensional field patterns can either accelerate or inhibit sugar metabolism in yeast cells, as compared to control experiments. We also studied aerobic sugar metabolism, with similar results. Sugar metabolism was monitored by formation of pyruvate, acetate and CO2. We found that for the P1 parameter set the cell metabolism accelerates as evaluated by all of the monitored chemical products, and the cell density growth rate also accelerates, with opposite effects observed for the P2 parameter set. These parameter sets are introduced using D, ω, φ, B, ω', and φ' - vectors defining amplitudes, frequencies and phases of periodic electric and magnetic fields, respectively. Thus, the P1 parameter set: D = (2.6, 3.1, 2.2) V/cm; ω = (0.8, 1.6, 0.2) kHz; φ = (1.31, 0.9, 1.0) rad; B = (3.1, 7.2, 7.2) × 10(-4) T; ω' = (2.1, 1.3, 3.1) kHz; φ' = (0.4, 2.1, 2.8) rad; and the P2 parameter set: D = (4.3, 1.6, 3.8) V/cm; ω = (3.3, 1.8, 2.8) kHz; φ = (0.86, 1.1, 0.4) rad; B = (5.4, 1.3, 1.3) × 10(-4) T; ω' = (1.3, 1.7, 0.9) kHz; φ' = (2.6, 1.7, 1.7) rad. The effects obtained for the less complex field combinations that used one-dimensional or two-dimensional configurations, or omitted either the electric or the magnetic contribution, were significantly weaker than those obtained for the complete P1 and P2 parameter sets.

Can safe and long-term exposure to extremely low frequency (50 Hz) magnetic fields affect apoptosis, reproduction, and oxidative stress?

PURPOSE

To determine whether 50 Hz extremely low frequency-magnetic fields (ELF-MF) affects apoptotic processes, oxidative damage, and reproductive characteristics such as sperm count and morphology in rat testes.

MATERIALS AND METHODS

Thirty male Sprague-Dawley rats were used in the present study, which were divided into three groups (sham group, n = 10, and two experimental groups, n = 10 for each group). Rats in the experimental group were exposed to 100 and 500 μT ELF-MF (2 h/day, 7 days/week, for 10 months) corresponding to exposure levels that are considered safe for humans. The same experimental procedures were applied to the sham group, but the ELF generator was turned off. Tissues from the testes were immunohistochemically stained for active (cleaved) caspase-3 in order to measure the apoptotic index by a semi-quantitative scoring system. The levels of catalase (CAT), malondialdehyde (MDA), myeloperoxidase (MPO), total antioxidative capacity (TAC), total oxidant status (TOS), and oxidative stress index (OSI) were also measured. Additionally, epididymal sperm count and sperm morphology was evaluated.

RESULTS

There were no significant differences in the reproductive and oxidative stress parameters between the sham group and the exposed groups (p > 0.05). While no difference was observed between the final apoptosis score of the sham and the 100 μT ELF-MF group (p > 0.05), the final apoptosis score was higher in the 500 μT ELF-MF exposure group than in the sham group (p < 0.05).

CONCLUSION

Long-term exposure to 100 μT and 500 μT ELF-MF did not affect oxidative or antioxidative processes, lipid peroxidation, or reproductive components such as sperm count and morphology in testes tissue of rats. However, long-term exposure to 500 μT ELF-MF did affect active-caspase-3 activity, which is a well-known apoptotic indicator.

Magnetic nanoparticles sensitize MCF-7 breast cancer cells to doxorubicin-induced apoptosis

Background

Resistance of breast cancer cells to the available chemotherapeutics is a major obstacle to successful treatment. Recent studies have shown that magnetic nanoparticles might have significant application in different medical fields including cancer treatment. The goal of this study is to verify the ability of magnetic nanoparticles to sensitize cancer cells to the clinically available chemotherapy.

Methods

The role of iron oxide nanoparticles, static magnetic field, or a combination in the enhancement of the apoptotic potential of doxorubicin against the resistant breast cancer cells, MCF-7 was evaluated using the MTT assay and the propidium iodide method.

Results

In the present study, results revealed that pre-incubation of MCF-7 cells with iron oxide nanoparticles before the addition of doxorubicin did not enhance doxorubicin-induced growth inhibition. Pre-incubation of MCF-7 cells with iron oxide nanoparticles followed by a static magnetic field exposure significantly (P < 0.05) increased doxorubicin-induced cytotoxicity. Sensitization with pre-exposure to the magnetic field was dose-dependent where the highest cytotoxicity was seen at 1 tesla. Further experiments revealed that the anti-proliferative effect of this treatment procedure is due to induction of apoptotic cell death.

Conclusions

These results might point to the importance of combining magnetic nanoparticles with a static magnetic field in treatment of doxorubicin-refractory breast cancer 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.

Can cytogenetics explain the possible association between exposure to extreme low-frequency magnetic fields and Alzheimer's disease?

Recently, a number of epidemiological studies have suggested that occupational as well as residential exposure to extreme low-frequency electromagnetic fields (ELF-EMFs) may be a risk factor for Alzheimer's disease. This is not proven yet and there are no known biological mechanisms to explain this alleged association. Alzheimer's disease is characterized by a number of events that have, at least partially, a genetic origin. In particular, trisomy of chromosomes 17 and 21 seems to be involved. Overall ELF-EMFs have not been identified as genotoxic agents, but there are some papers in the scientific literature that indicate that they may enhance the effects of agents that are known to induce mutations or tumors. There are also some indications that ELF-EMFs may induce aneuploïdy. This opens some perspectives for investigating the alleged association between ELF-EMFs and Alzheimer's. This paper reviews the possibility of a cytogenetic association between the electromagnetic fields and Alzheimer's disease.

Effects of acute and chronic low frequency electromagnetic field exposure on PC12 cells during neuronal differentiation

BACKGROUND/AIMS

The purpose of this study was to provide information about the in vitro neuritogenesis during cell exposure to extremely low frequency electromagnetic fields (ELF-EMFs) of different intensities and durations using pheochromocytoma-derived cell line (PC12 cells) as neuronal model.

METHODS

Proliferative rates and neuritogenesis were tested by colorimetric assay and morphological analysis, respectively; reactive oxygen species (ROS) levels and intracellular Ca(2+) variations monitored using single cell videomicroscopy.

RESULTS

The long-lasting ELF-EMF exposure (0.1-1.0 mT) did not appear to significantly affect the biological response (proliferation and neuritogenesis). However, during the acute ELF-EMF exposure (30 min), in undifferentiated PC12 cells, there were increased ROS levels and decreased catalase activity, that, conversely, resulted increased after chronic exposure (7 days) at 1.0 mT. Acute exposure (0.1-1.0 mT) affected the spontaneous intracellular Ca(2+) variations in undifferentiated cells, in which basal intracellular Ca(2+) resulted increased after chronic exposure. In addition acute exposure affected cell response to a depolarizing agent, while basal membrane potential was not changed.

CONCLUSION

Even if further studies remain necessary to identify the ROS/intracellular Ca(2+)cross-talking pathway activated by ELF-EMF exposure, we support the hypothesis that ROS and Ca(2+) could be the cellular "primum movens" of the ELF-EMF induced effects on biological systems.

A biomonitoring study of genotoxic risk to workers of transformers and distribution line stations

A cytogenetic monitoring study was carried out on a group of workers from transformer and distribution line stations in the Bursa province of Turkey, to investigate the genotoxic risk of occupational exposure to extremely low frequency electric (ELF) and magnetic fields (EMF). Cytogenetic analysis, namely chromosomal aberrations (CAs) and micronucleus (MN) tests were performed on a strictly selected group of 55 workers and compared to 17 controls. CA and MN frequencies in electrical workers appeared significantly higher than in controls (p < 0.001, 0.05, respectively). The frequency of CA in exposed groups were significantly enhanced with the years of exposure (p < 0.01). The effect of smoking on the level of CA and MN was not significant in the control and exposure groups. The results of this study demonstrated that a significant induction of cytogenetic damage in peripheral lymphocytes of workers engaged to occupational exposure to ELMF in electric transformer and distribution stations.

Assessment of genetic damage in peripheral blood of human volunteers exposed (whole-body) to a 200 muT, 60 Hz magnetic field

AIM

To investigate the extent of damage in nucleated cells in peripheral blood of healthy human volunteers exposed to a whole-body 60 Hz, 200 microT magnetic field.

MATERIALS AND METHODS

In this study, 10 male and 10 female healthy human volunteers received a 4 h whole-body exposure to a 200 microT, 60 Hz magnetic field. In addition, five males and five females were treated in a similar fashion, but were exposed to sham conditions. For each subject, a blood sample was obtained prior to the exposure period and aliquots were used as negative- (pre-exposure) and positive- [1.5 Gray (Gy) (60)Cobalt ((60)Co) gamma-irradiation] controls. At the end of the 4 h exposure period, a second blood sample was obtained. The extent of DNA damage was assessed in peripheral human blood leukocytes from all samples using the alkaline comet assay. To detect possible clastogenic effects, the incidence of micronuclei was assessed in phytohemagglutinin (PHA)-stimulated lymphocytes using the cytokinesis-block micronucleus assay.

RESULTS

There was no evidence of either increased DNA damage, as indicated by the alkaline comet assay, or increased incidence of micronuclei (MN) in the magnetic field exposed group. However, an in vitro exposure of 1.5 Gy gamma-irradiation caused a significant increase in both DNA damage and MN induction.

CONCLUSIONS

This study found no evidence that an acute, whole-body exposure to a 200 microT, 60 Hz magnetic field for 4 hours could cause DNA damage in human blood.

Extremely low frequency magnetic fields cause oxidative DNA damage in rats

PURPOSE

To detect the genotoxic effects of extremely low frequency (ELF) -magnetic fields (MF) on oxidative DNA base modifications [8-hydroxyguanine (8-OH-Gua), 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) and 4,6-diamino-5-formamidopyrimidine (FapyAde)] in rat leucocytes, measured following exposure to ELF-MF.

MATERIALS AND METHODS

After exposure to ELF-MF (50 Hz, 100 and 500 microT, for 2 hours/day during 10 months), DNA was extracted, and measurement of DNA lesions was achieved by gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS).

RESULTS

Levels of FapyAde, FapyGua and 8OHdG in DNA were increased by both 100 microT and 500 microT ELF-MF as compared to a cage-control and a sham group; however, statistical significance was observed only in the group exposed to 100 microT.

CONCLUSION

This is the first study to report that ELF-MF exposure generates oxidatively induced DNA base modifications which are mutagenic in mammalian cells, such as FapyGua, FapyAde and 8-OH-Gua, in vivo. This may explain previous studies showing DNA damage and genomic instability. These findings support the hypothesis that chronic exposure to 50-Hz MF may be potentially genotoxic. However, the intensity of ELF-MF has an important influence on the extent of DNA damage.

Radiofrequency electromagnetic fields (UMTS, 1,950 MHz) induce genotoxic effects in vitro in human fibroblasts but not in lymphocytes

OBJECTIVE

Universal Mobile Telecommunication System (UMTS) was recently introduced as the third generation mobile communication standard in Europe. This was done without any information on biological effects and genotoxic properties of these particular high-frequency electromagnetic fields. This is discomforting, because genotoxic effects of the second generation standard Global System for Mobile Communication have been reported after exposure of human cells in vitro.

METHODS

Human cultured fibroblasts of three different donors and three different short-term human lymphocyte cultures were exposed to 1,950 MHz UMTS below the specific absorption rate (SAR) safety limit of 2 W/kg. The alkaline comet assay and the micronucleus assay were used to ascertain dose and time-dependent genotoxic effects. Five hundred cells per slide were visually evaluated in the comet assay and comet tail factor (CTF) was calculated. In the micronucleus assay 1,000 binucleated cells were evaluated per assay. The origin of the micronuclei was determined by fluorescence labeled anticentromere antibodies. All evaluations were performed under blinded conditions.

RESULTS

UMTS exposure increased the CTF and induced centromere-negative micronuclei (MN) in human cultured fibroblasts in a dose and time-dependent way. Incubation for 24 h at a SAR of 0.05 W/kg generated a statistically significant rise in both CTF and MN (P = 0.02). At a SAR of 0.1 W/kg the CTF was significantly increased after 8 h of incubation (P = 0.02), the number of MN after 12 h (P = 0.02). No UMTS effect was obtained with lymphocytes, either unstimulated or stimulated with Phytohemagglutinin.

CONCLUSION

UMTS exposure may cause genetic alterations in some but not in all human cells in vitro.

Effects of long-term exposure of extremely low frequency magnetic field on oxidative/nitrosative stress in rat liver

Thirty-two adult Wistar-Albino female and male rats were used to investigate the long-term (45 days) effects of extremely low frequency magnetic field (ELF-MF; 50Hz, 1mT, 4h/day) exposure on oxidative/nitrosative stress in liver tissues of rats. The rats were divided randomly into four groups: female control (FC; n = 8) and MF-exposed female rats (F-MF; n = 8); male control (MC; n = 8) and MF-exposed male rats (M-MF; n = 8). Liver tissue from each animal was harvested and utilized for malondialdehyde (MDA) and 3-nitrotyrosine (3-NT) detection. MDA levels were measured by MDA-TBA method, while the 3-NT levels were determined by the HPLC-UV system. There were no significant differences between the MDA levels of the control (FC; MC) and MF-exposed (F-MF; M-MF) rats (P > 0.05). In the F-MF rats, 3-NT levels were significantly increased when compared to those of the FC rats (P < 0.05). There were no significant differences between the 3-NT levels of the MC and M-MF rats. In conclusion, our study suggests that the long-term ELF-MF exposure may enhance the oxidative/nitrosative stress in liver tissue of the female rats and could have a deteriorative effect on cellular proteins rather than lipids by enhancing 3-NT formation.

MF magnitude does not affect body condition, pro-oxidants and anti-oxidants in Eurasian kestrel (Falco tinnunculus) nestlings

Pylons of utility lines are commonly used by breeding birds as structures for supporting their nests. Nesting near power lines, however, exposes adult birds and their offspring to the electric and magnetic fields (EMFs) produced by the current. Therefore, we searched for possible relationships between the magnetic field (MF) magnitude experienced by wild kestrel (Falco tinnunculus) nestlings grown on pylons and different health-related variables: body condition, serum concentration of carotenoids, reactive oxygen metabolites (ROMs; marker of early oxidative damage), serum anti-oxidant capacity (OXY), and the ratio between ROMs and OXY (index of oxidative stress). No significant relationships were found between the MF magnitude or squared MFs and any of the variables considered. Comparisons with values recorded in nestlings from non-exposed nests seem to confirm the absence of any effect of exposure to MFs produced by power lines on the variables considered.

Formulation of ELF magnetic fields' effects on malondialdehyde level and myeloperoxidase activity in kidney using genetic programming

In vivo exposure effects of electromagnetic fields (EMFs) on various tissues of experiment animals have been investigated. In this sense, modeling and formulation of these biological effects have been of significant importance. In this study extremely low frequency (ELF) EMFs effects on malondialdehyde (MDA) level and myeloperoxidase (MPO) activity in kidney of guinea pigs exposed to 50 Hz magnetic fields of 1 mT, 2 mT and 3 mT have been presented. It has been planned to determine whether genetic programming (GP) is appropriate to analyze and formulate these biological effects. Consequently, it has been observed that GP can be effectively used to model MDA level and MPO activity. The performances of prediction of the proposed GP formulation versus actual experimental values are found to be quite satisfactory in terms of standard deviation and correlation coefficient. It is concluded that the GP application serves to form a database for the researchers in this field, without exposing tissues to EMF and without using too many guinea pigs.

Elevated sister chromatid exchange frequencies in dividing human peripheral blood lymphocytes exposed to 50 Hz magnetic fields

The in vitro cytomolecular technique, sister chromatid exchange (SCE), was applied to test the clastogenic potentiality of extremely low frequency (ELF) electromagnetic fields (EMFs) on human peripheral blood lymphocytes (HPBLs). SCE frequencies were scored in dividing peripheral blood lymphocytes (PBLs) from six healthy male blood donors in two rounds of experiments, R1 and R2, to determine reproducibility. Lymphocyte cultures in the eight experiments conducted in each round were exposed to 50 Hz sinusoidal (continuous or pulsed) or square (continuous or pulsed) MFs at field strengths of 1 microT or 1 mT for 72 h. A significant increase in the number of SCEs/cell in the grouped experimental conditions compared to the controls was observed in both rounds. The highest SCE frequency in R1 was 10.03 for a square continuous field, and 10.39 for a square continuous field was the second highest frequency in R2. DNA crosslinking at the replication fork is proposed as a model which could explain the mechanistic link between ELF EMF exposure and increased SCE frequency.

Effects of co-exposure to extremely low frequency (50 Hz) magnetic fields and xenobiotics determined in vitro by the alkaline comet assay

In the present study, we used human peripheral blood leukocytes from 4 different donors, to investigate in vitro the possible genotoxic and/or co-genotoxic activity of extremely low frequency magnetic fields (ELF-MF) at 3 mT intensity. Two model mutagens were used to study the possible interaction between ELF-MF and xenobiotics: N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and 4-nitroquinoline N-oxide (4NQO). Primary DNA damage was evaluated by the alkaline single-cell microgel-electrophoresis ("comet") assay. Control cells (leukocytes not exposed to ELF-MF, nor treated with genotoxins) from the different blood donors showed a comparable level of basal DNA damage, whereas the contribution of individual susceptibility toward ELF-MF and the tested genotoxic compounds led to differences in the extent of DNA damage observed following exposure to the genotoxins, both in the presence and in the absence of an applied ELF-MF. A 3 mT ELF-MF alone was unable to cause direct primary DNA damage. In leukocytes exposed to ELF-MF and genotoxins, the extent of MNNG-induced DNA damage increased with exposure duration compared to sham-exposed cells. The opposite was observed in cells treated with 4NQO. In this case the extent of 4NQO-induced DNA damage was somewhat reduced in leukocytes exposed to ELF-MF compared to sham-exposed cells. Moreover, in cells exposed to ELF-MF an increased concentration of GSH was always observed, compared to sham-exposed cells. Since following GSH conjugation the genotoxic pattern of MNNG and 4NQO is quite different, an influence of ELF-MF on the activity of the enzyme involved in the synthesis of GSH leading to different activation/deactivation of the model mutagens used was hypothesized to explain the different trends observed in MNNG and 4NQO genotoxic activity in the presence of an applied ELF-MF. The possibility that ELF-MF might interfere with the genotoxic activity of xenobiotics has important implications, since human populations are likely to be exposed to a variety of genotoxic agents concomitantly with exposure to this type of physical agent.

Evaluating DNA Damage in Rodent Brain after Acute 60 Hz Magnetic-Field Exposure

In recent years, numerous studies have reported a weak association between 60 Hz magnetic-field exposure and the incidence of certain cancers. To date, no mechanism to explain these findings has been identified. The objective of the current study was to investigate whether acute magnetic-field exposure could elicit DNA damage within brain cells from both whole brain and cerebellar homogenates from adult rats, adult mice and immature mice. Rodents were exposed to a 60 Hz magnetic field (0, 0.1, 1 or 2 mT) for 2 h. Then, at 0, 2 and 4 h after exposure, animals were killed humanely, their brains were rapidly removed and homogenized, and cells were cast into agarose gels for processing by the alkaline comet assay. Four parameters (tail ratio, tail moment, comet length and tail length) were used to assess DNA damage for each comet. For each species, a significant increase in DNA damage was detected by each of the four parameters in the positive control (2 Gy X rays) relative to the concurrent nonirradiated negative and sham controls. However, none of the four parameters detected a significant increase in DNA damage in brain cell homogenates from any magnetic-field exposure (0- 2 mT) at any time after exposure. The dose-response and time-course data from the multiple animal groups tested in this study provide no evidence of magnetic-field-induced DNA damage.

Controversial cytogenetic observations in mammalian somatic cells exposed to extremely low frequency electromagnetic radiation: a review and future research recommendations

During the years 1990-2003, a large number of investigations were conducted using animals, cultured rodent and human cells as well as freshly collected human blood lymphocytes to determine the genotoxic potential of exposure to nonionizing radiation emitted from extremely low frequency electromagnetic fields (EMF). Among the 63 peer reviewed scientific reports, the conclusions from 29 studies (46%) did not indicate increased damage to the genetic material, as assessed from DNA strand breaks, incidence of chromosomal aberrations (CA), micronuclei (MN), and sister chromatid exchanges (SCE), in EMF exposed cells as compared with sham exposed and/or unexposed cells, while those from 14 investigations (22%) have suggested an increase in such damage in EMF exposed cells. The observations from 20 other studies (32%) were inconclusive. This study reviews the investigations published in peer reviewed scientific journals during 1990-2003 and attempts to identify probable reason(s) for the conflicting results. Recommendations are made for future research to address some of the controversial observations.

DNA Interduplex Crosslinks Induced by AlKαX Rays under Vacuum

Dry pGEM-3Zf(-) plasmid DNA was exposed to Al(kalpha) X rays (1.5 keV) for various times in an ultra-high vacuum chamber with mean absorbed dose rates ranging from 1.8 to 41.7 Gy s(-1). The different forms of plasmid DNA were separated by neutral agarose gel electrophoresis and quantified by staining and laser scanning. In addition to the bands for supercoiled, nicked circular, linear and concatameric forms of plasmid DNA, two additional bands were observed in X-irradiated samples; these migrated at rates similar to those for 8-kb and >10-kb linear double-stranded DNA. Digestion of irradiated DNA with the restriction enzymes EcoR1 and PvuI suggested that the two slowly migrating bands were interduplex crosslinked DNA. Alkaline agarose gel electrophoresis of irradiated DNA digested with EcoR1 confirmed that the interduplex crosslink was covalent. Exposure-response curves were determined for the formation of nicked circular, linear and interduplex crosslinked DNA as well as for the loss of supercoiled and concatameric DNA. Formation and loss of these species were independent of absorbed dose rate over a 20-fold range. The G values for DNA single-strand breaks, double-strand breaks and crosslinks were determined to be 62 +/- 6, 5.6 +/- 0.6 and 16 +/- 4 nmol J(-1), respectively. The formation of DNA interduplex crosslinks appears to be due to single event. The mechanism responsible for the formation of DNA interduplex crosslinks is discussed with emphasis on its implications in vivo.

Oxidative DNA damage in rats exposed to extremely low frequency electro magnetic fields

Extremely low frequency (ELF) electromagnetic field (EMF) is thought to prolong the life of free radicals and can act as a promoter or co-promoter of cancer. 8-hydroxy-2'-deoxyguanosine (8OHdG) is one of the predominant forms of radical-induced lesions to DNA and is a potential tool to asses the cancer risk. We examined the effects of extremely low frequency electro magnetic field (ELF-EMF) (50 Hz, 0.97 mT) on 8OHdG levels in DNA and thiobarbituric acid reactive substances (TBARS) in plasma. To examine the possible time-dependent changes resulting from magnetic field, 8OHdG and TBARS were quantitated at 50 and 100 days. Our results showed that the exposure to ELF-EMF induced oxidative DNA damage and lipid peroxidation (LPO). The 8OHdG levels of exposed group (4.39+/-0.88 and 5.29+/-1.16 8OHdG/dG.10(5), respectively) were significantly higher than sham group at 50 and 100 days (3.02+/-0.63 and 3.46+/-0.38 8OHdG/dG.10(5)) (p<0.001, p<0.001). The higher TBARS levels were also detected in the exposure group both on 50 and 100 days (p<0.001, p<0.001). In addition, the extent of DNA damage and LPO would depend on the exposure time (p<0.05 and p<0.05). Our data may have important implications for the long-term exposure to ELF-EMF which may cause oxidative DNA damage.

Non-thermal DNA breakage by mobile-phone radiation (1800MHz) in human fibroblasts and in transformed GFSH-R17 rat granulosa cells in vitro

Cultured human diploid fibroblasts and cultured rat granulosa cells were exposed to intermittent and continuous radiofrequency electromagnetic fields (RF-EMF) used in mobile phones, with different specific absorption rates (SAR) and different mobile-phone modulations. DNA strand breaks were determined by means of the alkaline and neutral comet assay. RF-EMF exposure (1800 MHz; SAR 1.2 or 2 W/kg; different modulations; during 4, 16 and 24h; intermittent 5 min on/10 min off or continuous wave) induced DNA single- and double-strand breaks. Effects occurred after 16 h exposure in both cell types and after different mobile-phone modulations. The intermittent exposure showed a stronger effect in the comet assay than continuous exposure. Therefore we conclude that the induced DNA damage cannot be based on thermal effects.

Cell type-specific genotoxic effects of intermittent extremely low-frequency electromagnetic fields

The issue of adverse health effects of extremely low-frequency electromagnetic fields (ELF-EMFs) is highly controversial. Contradictory results regarding the genotoxic potential of ELF-EMF have been reported in the literature. To test whether this controversy might reflect differences between the cellular targets examined we exposed cultured cells derived from different tissues to an intermittent ELF-EMF (50 Hz sinusoidal, 1 mT) for 1-24h. The alkaline and neutral comet assays were used to assess ELF-EMF-induced DNA strand breaks. We could identify three responder (human fibroblasts, human melanocytes, rat granulosa cells) and three non-responder cell types (human lymphocytes, human monocytes, human skeletal muscle cells), which points to the significance of the cell system used when investigating genotoxic effects of ELF-EMF.

The effect of weak 50 Hz magnetic fields on the number of free oxygen radicals in rat lymphocytes in vitro

The aim of the work was verification of the hypothesis that weak power frequency (50 Hz) magnetic fields (MF) affected the number of free oxygen radicals in living biological cells and that these changes could be qualitatively explained by the radical pair mechanism. The experiments were performed on rat lymphocytes. One-hour exposure to 50 Hz MF at 20, 40, or 200 microT flux densities was performed inside a pair of Helmholtz coils with axis along or crosswise to the Earth's static MF. Iron ions (FeCl2) were used as a stimulator of the oxidation processes. Oxygen radicals were measured by fluorimetry using a DCF-DA fluorescent probe. Only in the lymphocytes exposed at 40 microT MF directed along the Earth's static MF there was a decrease of fluorescence in relation to non-exposed samples. Our observation seems to confirm the hypothesis that low level power frequency MF affects oxidative processes which occur in living biological cells and that this effect can be explained by the radical pair mechanism.

Effects of in vitro exposure to power frequency magnetic fields on UV-induced DNA damage of rat lymphocytes

The mechanisms of biological effects of 50/60 Hz (power frequency) magnetic fields (MF) are still poorly understood. There are a number of studies indicating that MF affect biochemical processes in which free radicals are involved, such as the biological objects' response to ultraviolet radiation (UVA). Therefore, the present study was aimed to assess the effect of 50 Hz MFs on the oxidative deterioration of DNA in rat lymphocytes irradiated in vitro by UVA. UVA radiation (150 J/m2) was applied for 5 min for all groups and 50 Hz MF (40 microT rms) exposure was applied for some of the groups for 5 or 60 min. The level of DNA damage was assessed using the alkaline comet assay, the fluorescence microscope, and image analysis. It has been found that the 1 h exposure to MF caused an evident increase in all parameters consistent with damaged DNA. This suggest that MF affects the radical pairs generated during the oxidative or enzymatic processes of DNA repair.

Evaluation of genotoxic effect of low level 50 Hz magnetic fields on human blood cells using different cytogenetic assays

The question whether extremely low frequency magnetic fields (ELFMFs) may contribute to mutagenesis or carcinogenesis is of current interest. In order to evaluate the possible genotoxic effects of ELFMFs, human blood cells from four donors were exposed in vitro for 48 h to 50 Hz, 1 mT uniform magnetic field generated by a Helmholtz coil system. Comet assay (SCGE), sister chromatid exchanges (SCE), chromosome aberrations (CAs), and micronucleus (MN) test were used to assess the DNA damage. ELF pretreated cells were also irradiated with 1 Gy of X-ray to investigate the possible combined effect of ELFMFs and ionizing radiation. Furthermore, nuclear division index (NDI) and proliferation index (PRI) were evaluated. Results do not evidence any DNA damage induced by ELFMF exposure or any effect on cell proliferation. Data obtained from the combined exposure to ELFMFs and ionizing radiation do not suggest any synergistic or antagonistic effect.

Micronucleus induction in cells co-exposed in vitro to 50 Hz magnetic field and benzene, 1,4-benzenediol (hydroquinone) or 1,2,4-benzenetriol☆

The generation, transmission (e.g. power lines, transformers, service wires, and electrical panels), and use (e.g. home appliances, such as electric blankets, shavers, and televisions) of electrical energy is associated with the production of weak electric and magnetic fields (EMF) which oscillate 50 (Europe) or 60 (USA) times per second (power-line frequency), falling in the extremely-low frequency (ELF) region of the electromagnetic spectrum. Epidemiological reports suggest a possible association between exposure to ELF-EMF and an increased risk of cancer (e.g. childhood acute leukaemia). Benzene is an established human leukomogen. This xenobiotic, which is unlikely to be the ultimate carcinogen, is metabolized in the liver to its primary metabolite phenol, which is hydroxylated to hydroquinone (1,4-benzenediol) and 1,2,4-benzenetriol. In this in vitro approach, to test the genotoxic and / or co-genotoxic potency of ELF-EMF, the cytokinesis block micronucleus (MN) method with Jurkat cells has been used. A 50 Hz magnetic field (MF) of 5 mT field strength was applied for different length of time (from 1 to 24 h), either alone or with benzene, 1,4-benzenediol, or 1,2,4-benzenetriol. Our preliminary results show that, after 24 h exposure, the frequency of micronucleated cells in MF-exposed cultures is 1.9 fold higher than in sham-exposed (control) cultures. Benzene exposure does not show any cytogenetic activity, whereas 1,4-benzenediol or 1,2,4-benzenetriol alone significantly affect the number of MN in Jurkat cells, as compared to untreated cultures. Moreover, co-exposure to ELF-MF does not seem to affect the frequency of micronuclei induced by benzene, 1,4-benzenediol, or 1,2,4-benzenetriol.

DNA-protein cross-linking via guanine oxidation: dependence upon protein and photosensitizer

DNA-protein cross-links form when guanine undergoes a 1-electron oxidation in a flash-quench experiment, and the importance of reactive oxygen species, protein, and photosensitizer is examined here. In these experiments, a strong oxidant produced by oxidative quenching of a DNA-bound photosensitizer generates an oxidized guanine base that reacts with protein to form the covalent adduct. These cross-links are cleaved by hot piperidine and are not the result of reactive oxygen species, since neither a hydroxyl radical scavenger (mannitol) nor oxygen affects the yield of DNA-histone cross-linking, as determined via a chloroform extraction assay. The cross-linking yield depends on protein, decreasing as histone > cytochrome c > bovine serum albumin. The yield does not depend on the cytochrome oxidation state, suggesting that reduction of the guanine radical by ferrocytochrome c does not compete effectively with cross-linking. The photosensitizer strongly influences the cross-linking yield, which decreases in the order Ru(phen)(2)dppz(2+) [phen = 1,10-phenanthroline; dppz = dipyridophenazine] > Ru(bpy)(3)(2+) [bpy = 2,2'-bipyridine] > acridine orange > ethidium, in accordance with measured oxidation potentials. A long-lived transient absorption signal for ethidium dication in poly(dG-dC) confirms that guanine oxidation is inefficient for this photosensitizer. From a polyacrylamide sequencing gel of a (32)P-labeled 40-mer, all of these photosensitizers are shown to damage guanines preferentially at the 5' G of 5'-GG-3' steps, consistent with a 1-electron oxidation. Additional examination of ethidium shows that it can generate cross-links between histone and plasmid DNA (pUC19) and that the yield depends on the quencher. Altogether, these results illustrate the versatility of the flash-quench technique as a way to generate physiologically relevant DNA-protein adducts via the oxidation of guanine and expand the scope of such cross-linking reactions to include proteins that may associate only transiently with DNA.

Absence of genotoxicity in human blood cells exposed to 50 Hz magnetic fields as assessed by comet assay, chromosome aberration, micronucleus, and sister chromatid exchange analyses

In the past, epidemiological studies indicated a possible correlation between the exposure to ELF fields and cancer. Public concern over possible hazards associated with exposure to extremely low frequency magnetic fields (ELFMFs) stimulated an increased scientific research effort. More recent research and laboratory studies, however, have not been able to definitively confirm the correlation suggested by epidemiological studies. The aim of this study was to evaluate the effects of 50 Hz magnetic fields in human blood cells exposed in vitro, using several methodological approaches for the detection of genotoxicity. Whole blood samples obtained from five donors were exposed for 2 h to 50 Hz, 1 mT uniform magnetic field generated by a Helmholtz coil system. Comet assay, sister chromatid exchanges (SCE), chromosome aberrations (CA), and micronucleus (MN) tests were used to assess DNA damage, one hallmark of malignant cell transformation. The effects of a combined exposure with X-rays were also evaluated. Results obtained do not show any significant difference between ELFMFs exposed and unexposed samples. Moreover, no synergistic effect with ionizing radiation has been observed. A slight but significant decrease of cell proliferation was evident in ELFMFs treated samples and samples subjected to the combined exposure.

Effect of 7 mT static magnetic field and iron ions on rat lymphocytes: apoptosis, necrosis and free radical processes

Simultaneous exposure of rat lymphocytes to 7 mT static magnetic field (SMF) and iron ions caused an increase in the number of cells with DNA damage. The mechanism by which MF induces DNA damage and the possible cytotoxic consequences are not known. However, we suppose that free radicals are involved. Potentially, the deterioration of DNA molecules by simultaneous exposure to 7 mT SMF and iron ions may lead to cell death: apoptosis or necrosis. The possible prooxidative properties of these two agents may result in an induction of the lipid peroxidation process as a marker of free radical mechanism in the cells. Experiments were performed on rat blood lymphocytes incubated for 3 h in Helmholtz coils at SMF of flux density 7 mT. During SMF exposure, some samples were treated with ferrous chloride (10 microg/ml), the rest serving as controls. We used the dye exclusion method with the DNA-fluorochromes: ethidium bromide and acridine orange. No significant differences were observed between unexposed lymphocytes incubated with medium alone and lymphocytes exposed to 7 mT SMF. Three-hour incubation with FeCl(2) (10 microg/ml) did not affect cell viability. However, when lymphocytes were exposed to 7 mT SMF and simultaneously treated with FeCl(2), there was a significant increase in the percentage of apoptotic and necrotic cells accompanied by significant alterations in cell viability. As compared to lipid peroxidation, there is a significant increase in the amount of lipid peroxidation end products MDA+4 HNE in rat lymphocytes after simultaneous exposure to 7 mT SMF and FeCl(2) (vs. to the control samples and those exposed to SMF alone). This suggests that 7 mT static magnetic field in the presence of Fe(2+) ions can increase the concentration of oxygen free radicals and thus may lead to cell death.

Induction of DNA strand breaks by intermittent exposure to extremely-low-frequency electromagnetic fields in human diploid fibroblasts

Results of epidemiological research show low association of electromagnetic field (EMF) with increased risk of cancerous diseases and missing dose-effect relations. An important component in assessing potential cancer risk is knowledge concerning any genotoxic effects of extremely-low-frequency-EMF (ELF-EMF). Human diploid fibroblasts were exposed to continuous or intermittent ELF-EMF (50Hz, sinusoidal, 24h, 1000microT). For evaluation of genotoxic effects in form of DNA single- (SSB) and double-strand breaks (DSB), the alkaline and the neutral comet assay were used. In contrast to continuous ELF-EMF exposure, the application of intermittent fields reproducibly resulted in a significant increase of DNA strand break levels, mainly DSBs, as compared to non-exposed controls. The conditions of intermittence showed an impact on the induction of DNA strand breaks, producing the highest levels at 5min field-on/10min field-off. We also found individual differences in response to ELF-EMF as well as an evident exposure-response relationship between magnetic flux density and DNA migration in the comet assay. Our data strongly indicate a genotoxic potential of intermittent EMF. This points to the need of further studies in vivo and consideration about environmental threshold values for ELF exposure.

Study on the effect of electromagnetic impulse on neurotransmitter metabolism in nerve cells by high-performance liquid chromatography-electrochemical detection coupled with microdialysis

In this paper, a reverse-phase high-performance liquid chromatographic method using a chemically modified electrode coupled with microdialysis was developed to study the effect of electromagnetic impulse (EMI) on monoamine neurotransmitter metabolism in nerve cells. To detect the monoamines and their metabolites, a poly (para-aminobenzoic acid) (P-pABA)-modified electrode was prepared. The modified electrode exhibited efficiently electrocatalytic oxidation for monoamines and their metabolites with relatively high sensitivity, stability, and long life. Nerve cells were primarily cultured. EMI was radiated to three experimental model nerve cells: (i) on mature nerve cells, (ii) on the culture medium, and (iii) on juvenile nerve cells for various periods of time. Then the levels of monoamines in the culture medium were detected by high-performance liquid chromatography-electrochemical detection. The data indicated that electromagnetic fields could influence neurotransmitter metabolism by direct effect on nerve cells or effect on the nutrient medium and that the effect was not only relevant with the length of radiation time, but also with the growing state of the nerve cells.

DNA damage and apoptosis in the immature mouse cerebellum after acute exposure to a 1 mT, 60 Hz magnetic field

Several recent studies have reported that whole-body exposure of rodents to power frequency magnetic fields (MFs) can result in DNA single- and double-strand breaks in the brains of these animals. The current study was undertaken to investigate whether an acute 2h exposure of a 1 mT, 60 Hz MF could elicit DNA damage, and subsequently apoptosis, in the brains of immature (10-day-old) mice. DNA damage was quantitated at 0, 2, 4, and 24h after exposure using the alkaline comet assay. Apoptosis was quantitated in the external granule cell layer (EGCL) of the immature mouse cerebellum at 0 and 24h after exposure to MF by the TdT-mediated dUTP nick-end labeling (TUNEL) assay. Four parameters (tail ratio, tail moment, comet length and tail length) were used to assess DNA damage for each comet. While increased DNA damage was detected by tail ratio at 2h after MF exposure, no supporting evidence of increased DNA damage was detected by the other parameters. In addition, no similar differences were observed using these parameters at any of the other post-exposure times. No increase in apoptosis was observed in the EGCL of MF-exposed mice, when compared to sham mice. Taken together, these results do not support the hypothesis that acute MF exposure causes DNA damage in the cerebellums of immature mice.

Lack of mutagenic and co-mutagenic effects of magnetic fields during magnetic resonance imaging

Mutagenic and co-mutagenic effects of static, pulsed bipolar gradient, and high-frequency magnetic fields, as well as combinations of them, were examined using the Ames test. The Ames test using Salmonella typhimurium bacteria, wild-type strain RTA, preincubation assay, without metabolic activation, was performed. All combinations of magnetic fields were tested with and without co-exposure to N-methyl-N'-nitro-N-nitrosoguanidine and benzo[a]pyrene-4,5-oxide, ethylene oxide, carboplatin, or cisplatin. As expected, chemical mutagens caused a clear-cut increase of the revertants in the Ames test. However, neither the static fields nor a combination of a static magnetic field with the time-varying bipolar gradient field or a pulsed high-frequency magnetic field caused an alteration in the number of revertants in the Ames test. No co-mutagenic effect of any magnetic field combination was observed. In conclusion, magnetic fields used during clinical magnetic resonance imaging (MRI) were neither mutagenic nor co-mutagenic.