An overview of the biological effects of extremely low frequency electromagnetic fields combined with ionizing radiation

By growing the electrical power networks and electronic devices, electromagnetic fields (EMF) have become an inseparable part of the modern world. Considering the inevitable exposure to a various range of EMFs, especially at extremely low frequencies (ELF-EMF), investigating the biological effects of ELF-EMFs on biological systems became a global issue. The possible adverse consequences of these exposures were studied, along with their potential therapeutic capabilities. Also, their biological impacts in combination with other chemical and physical agents, specifically ionizing radiation (IR), as a co-carcinogen or as adjuvant therapy in combination with radiotherapy were explored. Here, we review the results of several in-vitro and in-vivo studies and discuss some proposed possible mechanisms of ELF-EMFs' actions in combination with IR. The results of these experiments could be fruitful to develop more precise safety standards for environmental ELF-EMFs exposures. Furthermore, it could evaluate the therapeutic capacities of ELF-EMFs alone or as an improver of radiotherapy.

A cohort study on adult hematological malignancies and brain tumors in relation to magnetic fields from indoor transformer stations

Extremely low frequency (ELF) magnetic fields (MF) have been classified as possibly carcinogenic. This classification was mainly based on studies indicating increased risk of leukemia in children living near power lines. Increased risks of adult hematological malignancies and brain tumors have also been reported, but the results are mixed. We assessed incidence of adult hematological malignancies and brain tumors associated with residential MF exposure. All cohort members had lived in buildings with indoor transformer stations (TS). MF exposure was assessed based on apartment location. Out of the 256,372 individuals, 9,636 (165,000 person-years of follow-up) living in apartments next to TSs were considered as exposed. Associations between MF exposure and neoplasms were examined using Cox proportional hazard models. The hazard ratio (HR) for MF exposure ≥ 1 month was below one for most hematological neoplasms (HR for any hematological neoplasm: 0.75; 95% CI: 0.54-1.03), and decreased with increasing duration of exposure (HR for exposure ≥ 10 years: 0.47; 95% CI: 0.22-0.99). However, the HR for acute lymphocytic leukemia (ALL) was 2.86 (95% CI: 1.00-8.15), based on 4 exposed cases; the risk increased with duration of exposure (HR for exposure ≥3 years: 3.61; 95% CI: 1.05-12.4) and was particularly associated with childhood exposure (2 exposed cases, HR for exposure during the first two years of life: 11.5; 95% CI: 1.92-68.9). The HR for meningioma was 0.46 (95% CI: 0.19-1.11), with no evidence of exposure-response gradient with increasing duration of exposure. The HR for glioma was 1.47 (95% CI: 0.84-2.57). The hypothesis of a positive association between ELF MFs and adult hematological malignancies was supported only for ALL. The results suggested decreased rather than increased risk of most hematological neoplasms.

Long-Term Study on the Effects of Housing C57BL/6NCrl Mice in Cages Equipped With Wireless Technology Generating Extremely Low-Intensity Electromagnetic Fields

The recent development of mouse cages equipped with monitoring wireless technology raised questions on the potential effects on animals induced by electromagnetic fields (EMFs) generated by electronic boards positioned underneath the cages. The aims of this study were to characterize the EMF produced by digitally ventilated cages (DVC) and perform a clinicopathological study on mice maintained in DVC for up to 1 year. The EMFs were measured in empty individually ventilated cages (IVC) and DVC. Male (n = 160) and female (n = 160) C57BL/6NCrl mice were randomly housed in IVC and DVC in a single rack, 4 mice per cage. Body weight and food and water consumption were recorded at 14-day intervals. At sacrifice (days 60, 120, 180, and 365), body and testes weight was measured, and necropsy, hematology, bone marrow cytology, histology, and immunohistochemistry for cleaved-caspase 3 on the testes were performed. Digitally ventilated cages produced extremely low-intensity electric fields ranging from 5 Hz to 3 GHz. No exposure-related clinical signs and mortality occurred. Occasional statistical differences in body weight, food and water consumption, hematology, bone marrow, and histopathology were recorded, but considered without biological or clinical relevance. In conclusion, long-term maintenance in DVC had no definite effects on C57BL/6NCrl mice.

Life-span exposure to sinusoidal-50 Hz magnetic field and acute low-dose γ radiation induce carcinogenic effects in Sprague-Dawley rats

Background In 2002 the International Agency for Research on Cancer classified extremely low frequency magnetic fields (ELFMF) as a possible carcinogen on the basis of epidemiological evidence. Experimental bioassays on rats and mice performed up to now on ELFMF alone or in association with known carcinogens have failed to provide conclusive confirmation. Objectives To study the carcinogenic effects of combined exposure to sinusoidal-50 Hz (S-50 Hz) magnetic fields and acute γ radiation in Sprague-Dawley rats. Methods We studied groups of male and female Sprague-Dawley rats exposed from prenatal life until natural death to 20 or 1000 μT S-50 Hz MF and also to 0.1 Gy γ radiation delivered as a single acute exposure at 6 weeks of age. Results The results of the study showed significant carcinogenic effects for the mammary gland in males and females and a significant increased incidence of malignant schwannomas of the heart as well as increased incidence of lymphomas/leukemias in males. Conclusions These results call for a re-evaluation of the safety of non-ionizing radiation.

Pathobiology of aging mice and GEM: background strains and experimental design

The use of induced and spontaneous mutant mice and genetically engineered mice (and combinations thereof) to study cancers and other aging phenotypes to advance improved functional human life spans will involve studies of aging mice. Genetic background contributes to pathology phenotypes and to causes of death as well as to longevity. Increased recognition of expected phenotypes, experimental variables that influence phenotypes and research outcomes, and experimental design options and rationales can maximize the utility of genetically engineered mice (GEM) models to translational research on aging. This review aims to provide resources to enhance the design and practice of chronic and longevity studies involving GEM. C57BL6, 129, and FVB/N strains are emphasized because of their widespread use in the generation of knockout, transgenic, and conditional mutant GEM. Resources are included also for pathology of other inbred strain families, including A, AKR, BALB/c, C3H, C57L, C58, CBA, DBA, GR, NOD.scid, SAMP, and SJL/J, and non-inbred mice, including 4WC, AB6F1, Ames dwarf, B6, 129, B6C3F1, BALB/c,129, Het3, nude, SENCAR, and several Swiss stocks. Experimental strategies for long-term cross-sectional and longitudinal studies to assess causes of or contributors to death, disease burden, spectrum of pathology phenotypes, longevity, and functional healthy life spans (health spans) are compared and discussed.

ELF magnetic fields: animal studies, mechanisms of action

Animal studies can contribute to addressing the issue of possible greater health risk for children exposed to 50-60 Hz extremely low frequency (ELF) magnetic fields (MFs), mostly in terms of teratological effects and cancer. Teratology has been extensively studied in animals exposed to ELF MFs but experiments have not established adverse developmental effects. Childhood leukaemia has been the only cancer consistently reported in epidemiological studies as associated with exposure to ELF MFs. This association has been the basis for the classification as "possibly carcinogenic to humans" by the International Agency for Research on Cancer in 2002. Animal experiments have provided only limited support for these epidemiological findings. However, none but one study used an animal model for acute lymphoblastic leukaemia (ALL), the main form of childhood leukaemia, and exposures to ELF MFs were not carried out over the whole pregnancy period, when the first hit of ALL is assumed to occur. Moreover, there are no generally accepted biophysical mechanisms that could explain carcinogenic effects of low-level MFs. The radical pair mechanism and related cryptochromes (CRY) molecules have recently been identified in birds and other non-mammalian species, as a sensor of the geomagnetic field, involved in navigation. The hypothesis has to be tested in mammalian models. CRY, which is part of the molecular circadian clock machinery, is a ubiquitous protein likely to be involved in cancer cell growth and DNA repair. In summary, we now have some clues to test for a better characterization of the interaction between ALL and ELF MFs exposure.

The role of the Birt-Hogg-Dubé protein in mTOR activation and renal tumorigenesis

Birt-Hogg-Dubé (BHD) syndrome is a tumor-suppressor gene disorder characterized by skin tumors, cystic lung disease and renal cell carcinoma. Very little is known about the molecular pathogenesis of BHD. Clinical similarities between BHD and tuberous sclerosis complex (TSC) suggest that the BHD and TSC proteins may function within a common pathway. The TSC proteins inhibit the activity of the mammalian target of rapamycin complex 1 (TORC1), and in Schizosaccharomyces pombe, Bhd and Tsc1/Tsc2 have opposing roles in the regulation of amino-acid homeostasis. We report here that in mammalian cells, downregulation of BHD reduces the phosphorylation of ribosomal protein S6, an indicator of TORC1 activity. To determine whether folliculin, the product of the BHD gene, regulates mammalian target of rapamycin activity in vivo, we generated a mouse with targeted inactivation of the Bhd gene. The mice developed spontaneous oncocytic cysts and tumors composed of cells that resemble the renal cell carcinomas in BHD patients. The cysts and tumors had low levels of phospho-S6. Taken together, these data indicate that folliculin regulates the activity of TORC1, and suggest a new paradigm in which both inappropriately high and inappropriately low levels of TORC1 activity can be associated with renal tumorigenesis.

Epstein-Barr virus nuclear antigen 1 does not cause lymphoma in C57BL/6J mice

To test whether transgenic Epstein-Barr virus nuclear antigen 1 (EBNA1) expression in C57BL/6 mouse lymphocytes causes lymphoma, EBNA1 expressed in three FVB lineages at two or three times the level of latent infection was crossed up to six successive times into C57BL/6J mice. After five or six crosses, 14/36, (38%) EBNA1 transgenic mice, 11/31 (36%) littermate EBNA1-negative controls, and 9/25 (36%) inbred C57BL/6J mice housed in the same facility had lymphoma. These data indicate that EBNA1 does not significantly increase lymphoma prevalence in C57BL/6J mice.

Effects of whole body exposure to extremely low frequency electromagnetic fields (ELF-EMF) on serum and liver lipid levels, in the rat

Backgound

The effects of extremely low-frequency electromagnetic fields (ELF-EMF) on the blood serum and liver lipid concentrations of male Wistar rats were assessed.

Methods

Animals were exposed to a single stimulation (2 h) of ELF-EMF (60 Hz, 2.4 mT) or sham-stimulated and thereafter sacrificed at different times (24, 48 or 96 h after beginning the exposure).

Results

Blood lipids showed, at 48 h stimulated animals, a significant increase of cholesterol associated to high density lipoproteins (HDL-C) than those observed at any other studied time. Free fatty acid serum presented at 24 h significant increases in comparison with control group. The other serum lipids, triacylglycerols and total cholesterol did not show differences between groups, at any time evaluated. No statistical differences were shown on total lipids of the liver but total cholesterol was elevated at 24 h with a significant decrease at 96 h (p = 0.026). The ELF-EMF stimulation increased the liver content of lipoperoxides at 24 h.

Conclusion

Single exposures to ELF-EMF increases the serum values of HDL-C, the liver content of lipoperoxides and decreases total cholesterol of the liver. The mechanisms for the effects of ELF-EMF on lipid metabolism are not well understand yet, but could be associated to the nitric oxide synthase EMF-stimulation.

Ultra high frequency-electromagnetic field irradiation during pregnancy leads to an increase in erythrocytes micronuclei incidence in rat offspring

Mobile telephones and their base stations are an important ultra high frequency-electromagnetic field (UHF-EMF) source and their utilization is increasing all over the world. Epidemiological studies suggested that low energy UHF-EMF emitted from a cellular telephone may cause biological effects, such as DNA damage and changes on oxidative metabolism. An in vivo mammalian cytogenetic test, the micronucleus (MN) assay, was used to investigate the occurrence of chromosomal damage in erythrocytes from rat offspring exposed to a non-thermal UHF-EMF from a cellular phone during their embryogenesis; the irradiated group showed a significant increase in MN occurrence. In order to investigate if UHF-EMF could also alter oxidative parameters in the peripheral blood and in the liver - an important hematopoietic tissue in rat embryos and newborns - we also measured the activity of antioxidant enzymes, quantified total sulfhydryl content, protein carbonyl groups, thiobarbituric acid-reactive species and total non-enzymatic antioxidant defense. No significant differences were found in any oxidative parameter of offspring blood and liver. The average number of pups in each litter has also not been significantly altered. Our results suggest that, under our experimental conditions, UHF-EMF is able to induce a genotoxic response in hematopoietic tissue during the embryogenesis through an unknown mechanism.

50 Hz Magnetic Fields of 1 mT do not Promote Lymphoma Development in AKR/J Mice

Some epidemiological studies suggest that exposure to power-frequency magnetic fields increases the risk of leukemia, especially in children with high residential exposures. In contrast, most animal studies did not find a correlation between magnetic-field exposure and hematopoietic diseases. The present study was performed to investigate whether chronic, high-level (1 mT) magnetic-field exposure had an influence on lymphoma development in a mouse strain that is genetically predisposed to thymic lymphoblastic lymphoma. Three groups of 160 unrestrained female AKR/J mice were sham-exposed or exposed to sinusoidal 50 Hz magnetic fields beginning at the age of 12 weeks for 32 weeks, 7 days per week, either for 24 h per day or only during nighttime (12 h). Exposure was carried out in a blind design. Exposure did not affect survival time, body weight, lymphoma development or hematological parameters. The resulting data do not support the hypothesis that exposure to sinusoidal 50 Hz magnetic fields is a significant risk factor for hematopoietic diseases, even at this relatively high exposure level.

Stable loss of global DNA methylation in the radiation-target tissue—A possible mechanism contributing to radiation carcinogenesis?

Radiation-induced lymphomagenesis and leukemogenesis are complex processes involving both genetic and epigenetic changes. Although genetic alterations during radiation-induced lymphoma- and leukemogenesis are fairly well studied, the role of epigenetic changes has been largely overlooked. Rodent models are valuable tools for identifying molecular mechanisms of lymphoma and leukemogenesis. A widely used mouse model of radiation-induced thymic lymphoma is characterized by a lengthy "pre-lymphoma" period. Delineating molecular changes occurring during the pre-lymphoma period is crucial for understanding the mechanisms of radiation-induced leukemia/lymphoma development. In the present study, we investigated the role of radiation-induced DNA methylation changes in the radiation carcinogenesis target organ--thymus, and non-target organ--muscle. This study is the first report on the radiation-induced epigenetic changes in radiation-target murine thymus during the pre-lymphoma period. We have demonstrated that acute and fractionated whole-body irradiation significantly altered DNA methylation pattern in murine thymus leading to a massive loss of global DNA methylation. We have also observed that irradiation led to increased levels of DNA strand breaks 6 h following the initial exposure. The majority of radiation-induced DNA strand breaks were repaired 1 month after exposure. DNA methylation changes, though, were persistent and significant radiation-induced DNA hypomethylation was observed in thymus 1 month after exposure. In sharp contrast to thymus, no significant persistent changes were noted in the non-target muscle tissue. The presence of stable DNA hypomethylation in the radiation-target tissue, even though DNA damage resulting from initial genotoxic radiation insult was repaired, suggests of the importance of epigenetic mechanisms in the development of radiation-related pathologies. The possible role of radiation-induced DNA hypomethylation in radiation-induced genome instability and aberrant gene expression in molecular etiology of thymic lymphomas is discussed.

Epstein-Barr virus nuclear antigen 1 does not induce lymphoma in transgenic FVB mice

The lymphoma-inducing potential of Ig heavy-chain enhancer- and promoter-regulated Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) was evaluated in three transgenic FVB mouse lineages. EBNA1 was expressed at a higher level in transgenic B220(+) splenocytes than in EBV-infected lymphoblastoid cell lines. EBNA1 was also expressed in B220(-) transgenic splenocytes and thymocytes. Before killing and assessments at 18-26 months, EBNA1-transgenic mice did not differ from control mice in mortality. At 18-26 months EBNA1-transgenic mice did not differ from littermate control in ultimate body weight, in spleen size or weight, in lymph node, kidney, liver, or spleen histology, in splenocyte fractions positive for cluster of differentiation (CD)3epsilon, CD4, CD8, CD62L, B220, CD5, IgM, IgD, MHC class II, CD11b, or CD25, or in serum IgM, IgG, or total Ig levels. Lymphomas were not found in spleens or other organs of 18- to 26-month-old EBNA1-transgenic (n=86) or control (n=45) FVB mice. EBNA1-transgenic lineages had a higher pulmonary adenoma prevalence than did littermate controls (39% versus 7%). However, the adenoma prevalence was not higher in EBNA1-transgenic mice than has been described for FVB mice, and EBNA1 was not expressed in normal pulmonary epithelia or adenomas.

The risk of lymphoma in AKR/J mice does not rise with chronic exposure to 50 Hz magnetic fields (1 microT and 100 microT)

Some epidemiological studies suggest that exposure to 50 or 60 Hz magnetic fields might increase the risk of leukemia, especially in children with a comparable high residential exposure. To investigate this possibility experimentally, the influence of 50 Hz magnetic-field exposure on lymphoma induction was determined in a mouse strain that is genetically predisposed to this disease. The AKR/J mouse genome carries the AK virus, which leads within 1 year to spontaneous development of thymic lymphoblastic lymphoma. Beginning at an age of 4-5 weeks, groups of 160 female mice were sham-exposed or exposed to 50 Hz magnetic fields at 1 or 100 microT for 24 h per day, 7 days per week, for 38 weeks. Animals were checked visually daily and were weighed and palpated weekly. There was no effect of magnetic-field exposure on body weight gain or survival rate, and lymphoma incidence did not differ between exposed and sham-exposed animals. Therefore, these data do not support the hypothesis that chronic exposure to 50 Hz magnetic fields is a significant risk factor for developing hematopoietic malignancy.

Electric fields induced in humans and rodents by 60 Hz magnetic fields

Numerical computations are used to evaluate electric field dosimetry for high-resolution anatomically based inhomogeneous models of a human male child, and male and female rats and mice, under exposure to 60 Hz uniform magnetic field sources of three perpendicular orientations. The goal is to compare the child data to previously computed adult dosimetry and to evaluate the accuracy of linear scaling of organ dosimetry between species. It is expected that this work will aid in the design and interpretation of experiments involving rodents. It is found that child-to-adult and mouse-to-rat organ dosimetry shows the expected linear dependence on the geometric scale factor between models. The comparison between mice and the human child shows that postural and individual organ differences do have significant effects, and that care is required in scaling-based extrapolation of rodent experiment results to humans. However, for unrestrained animals, linear scaling appears to be a reasonable and conservative approach. Most of the rodent organ fields, for at least one field orientation, are greater than those expected from linear scaling.