Cancer promotion in a mouse-skin model by a 60-Hz magnetic field: II. Tumor development and immune response

The effects of electromagnetic fields on cultured human retinal pigment epithelial cells

A great deal of evidence has confirmed that electromagnetic fields (EMFs) can affect the central nervous system. In this study, cultured neonatal human retinal pigment epithelial (hRPE) cells were exposed to pulsed EMF of 1 mT intensity and 50 Hz frequency 8 h daily for 3 days. In addition to cell proliferation and cell death assays, immunocytochemistry for RPE65, PAX6, nestin, and cytokeratin 8/18 proteins were performed. Real-time reverse transcriptase polymerase chain reaction (RT-PCR) was performed for NES, PAX6, RPE65, and ACTA2 gene expression. Exposed hRPE cells did not demonstrate significant change in terms of cytomorphology, cell proliferation, or cell death. Protein expression of PAX6 was decreased in treated cells compared to controls and remained unchanged for RPE65, cytokeratin 8/18, and nestin. Gene expressions of NES, RPE65, and PAX6 were decreased in treated cells as compared to controls. Gene expression of ACTA2 did not significantly change. In conclusion, viability of cultivated neonatal hRPE cells did not change after short exposure to a safe dose of pulsed EMF albeit that both gene and protein expressions of retinal progenitor cell markers were reduced. Whether longer exposure durations that are being constantly produced by widely-used electronic devices may induce significant changes in these cells, needs further investigation. Bioelectromagnetics. 39:585-594, 2018. © 2018 Wiley Periodicals, Inc.

Extremely Low-Frequency Pulsed Magnetic Fields and Multiple Sclerosis: Effects on Neurotransmission Alone or Also on Immunomodulation? Building a Working Hypothesis

This paper outlines the current state of knowledge on the pathology and treatment of multiple sclerosis (MS) and critically analyses the vast clinical experience of Sandyk in the use of pulsed magnetic fields of 5 Hz at 7.5 pT to treat many symptoms of MS. A complete regression of symptoms, or at least a major improvement, is sometimes so rapid as to suggest that ELF fields exert a greater effect on axonal and synaptic neurotransmission than on the processes leading to demyelination. Pulsed magnetic fields of 50–100 Hz and a few mT (whose flux intensity is 109 times greater than that of the fields used by Sandyk) have been seen to induce profound morphological changes (the Marinozzi effect) in the plasma membrane of several cell types, including Raji human lymphoblastoid cells. These observations underlie the author's hypothesis on the possible use of such fields in the treatment of MS. Indeed, these fields should induce the functional arrest of the cells (B- and T-lymphocytes, macrophages, microglia, dendritic cells) of the MS plaque, thereby providing an ‘electromagnetic immunomodulatory boost’ to the effects of drug therapy. To test this working hypothesis, it is suggested that preliminary experimental research be carried out to ascertain: 1) the Marinozzi effect in vivo; 2) the Marinozzi effect on microglia and dendritic cells; and 3) the duration of the membrane changes and their relaxation rate. ELF magnetic fields in the picotesla and millitesla ranges are aimed at improving neurotransmission and correcting local immune pathology, respectively. Both types of field might find application in the treatment of MS patients who no longer respond to or tolerate currently used drugs.

Suppression of Natural Killer Cell Activity onCandida Stellatoideaby a 50 Hz Magnetic Field

Exposure to electromagnetic fields (EMF) is ubiquitous for almost all individuals living in industrialized countries. Epidemiological and laboratory studies suggest that exposure to Extremely Low Frequency (ELF) EMF increase cancer risk. The immune system functions as one of the body's main protective mechanisms, and Natural Killer (NK) cells are a subset of lymphocytes that can destroy several types of tumor cells. In this study, we investigated, NK cell activity after exposure to a 50 Hertz (Hz), 2 mT magnetic field generated by a Helmholtz Coil. Nineteen male, 10-12 week old guinea pigs were used, and NK cytotoxic activity of splenocytes was measured in vitro by natural anticandidial colorimetric index. The Mann-Whitney U test was applied for statistical analysis. NK cell cytotoxic activity was decreased in exposed compared to controls. Our data suggests that part of the immune system, the NK cell, can be suppressed by a 50 Hz magnetic field.

Lack of promotion effects of 50 Hz magnetic fields on 7,12-dimethylbenz(a)anthracene-induced malignant lymphoma/lymphatic leukemia in mice

New-born CD-1 mice were initiated with a single subcutaneous injection of 60 microg 7,12-dimethylbenz(a)anthracene (DMBA) within 24 h after birth. After weaning, the mice were randomly divided into five groups of 100, 50 males and 50 females each. One group served as a cage control. The other four groups of mice were exposed to either 0 (sham-exposed), 7, 70, or 350 microT(rms) circularly polarized 50 Hz magnetic fields (MFs) for 22 h/day, 7 days/week for 30 weeks. Animals were observed daily and the development of malignant lymphoma/lymphatic leukemia was examined histopathologically. The experiment was conducted twice. There was no observed sexual difference in the cumulative proportions of mice with malignant lymphoma/lymphatic leukemia and a 3-way analysis of deviance using the Cox regression model revealed no interactions between experiment, sex, or group. The cumulative proportions of mice with malignant lymphoma/lymphatic leukemia in the MF-exposed groups were not significantly higher than those in the sham-exposed group of each sex in individual experiments and in males and females combined in each experiment, and in all the animals from the two experiments combined. These data provide no evidence to support the hypothesis that power frequency MFs is a significant risk factor for hematopoietic neoplasia.

DEXA analysis on the bones of rats exposed in utero and neonatally to static and 50 Hz electric fields

Effects of the electromagnetic fields on living bodies, bones in particular, are among the relevant issues of contemporary life. In this study, we report the influences of 50 Hz and 0 Hz (static) electric fields (EF), on intact rat bones, as evaluated by dual energy X-ray absorbtion (DEXA) measurements on bone content and density when these animals (n = 27) are continuously exposed in utero and neonatally to EFs (10 kV/m) 14 days before and 14 days after their birth, for 28 days in total. Differences between 50 Hz EF and static EF groups are found to be significant (95% confidence level) for total bone mineral content (BMC), TBMC (P = .002). Differences between 50 Hz and control groups are found to be significant for total bone mineral density (BMD), TBMD (P = .002), lumbar BMC, LBMC (P = .023), and TBMC (P = .001). Differences between static EF and control groups are found to be significant for femoral BMD, FBMD (P = .009), TBMD (P = .002), LBMC (P = .001), and TBMC (P = .001). Note that TBMC parameters are jointly significant for all differences between the three groups of test animals. These results have shown that both static and 50 Hz EFs influence the early development of rat bones. However, the influence of static EFs is more pronounced than that of the 50 Hz field.

A 60 Hz magnetic field does not affect the incidence of squamous cell carcinomas in SENCAR mice

Two groups of SENCAR mice were treated with a single dose of carcinogen and then, for 23 weeks, with a chemical tumor promoter to induce skin tumors. During this period, one group was coexposed to a 2 mT power frequency (60 Hz) magnetic field, while the other was exposed to sham conditions. Application of the tumor promoter ceased after 23 weeks, but the exposure to sham conditions or magnetic fields continued for an additional 29 weeks. No difference was found between the two groups of mice in terms of the incidence of total tumors (P =.297) or squamous cell carcinomas (SSC) (P =.501). In summary, there was no evidence to support the hypotheses that 60 Hz magnetic fields (MF) can influence the development of either papillomas or SSC under our defined experimental conditions. The overall results add to previous animal studies that find no association between exposure to 60 Hz MF and the incidence of benign or malignant tumors.

Lack of promotion of 7,12-dimethylbenz[a]anthracene-initiated mouse skin carcinogenesis by 1.5 GHz electromagnetic near fields

The effects of 1.5 GHz electromagnetic near fields of time division multiple access (TDMA) signal for the Personal Digital Cellular, Japanese cellular telephone standard (PDC) used for cellular phones, on mouse skin carcinogenesis initiated by 7,12-dimethylbenz[a]anthracene (DMBA) were examined. Ten-week-old ICR female mice were treated with a single application of DMBA on shaved dorsal skin by painting at a concentration of 100 microg/100 microl acetone per mouse. One week later, mice were divided into four groups, receiving electromagnetic near fields exposure (DMBA-EMF), sham-exposure (DMBA-Sham), 12-O-tetradecanoylphorbol-13-acetate (TPA, 4 microg /200 microl acetone/mouse), as a positive control (DMBA-TPA), and no-treatment (DMBA-Control). EMF near fields exposure conditions were as follows: skin local peak specific absorption rate (SAR) 2.0 W/kg, whole body average SAR 0.084 W/kg (ratio of peak to average SAR is 24), 90 min a day, 5 days a week, for 19 weeks. At week 20, animals were killed and skin tumors were analyzed histopathologically. The incidences of skin tumors in DMBA-EMF, DMBA-Sham, DMBA-TPA and DMBA-Control groups were 0/48 (0%), 0/48 (0%), 29/30 (96.6%) and 1/30 (3.3%), respectively. Histopathologically, papilloma and squamous cell carcinoma (SCC) were observed in the DMBA-TPA group and only papilloma observed in the DMBA-Control group. The incidences of squamous cell papillomas and squamous cell carcinomas in DMBA-TPA and DMBA-Control groups were 29/30 (96.6%) and 1/30 (3.3%), respectively, numbers of tumors per mouse (tumor multiplicity) being 18.8 +/- 13.4 and 0.1 +/- 0.5. These data clearly demonstrated that near fields exposure to 1.5 GHz EMF, used for cellular phones, does not exert any enhancing effect on skin tumorigenesis initiated by DMBA.

Micronucleus induction in Syrian hamster embryo cells following exposure to 50 Hz magnetic fields, benzo(a)pyrene, and TPA in vitro

Electromagnetic fields (EMFs) have been associated with increased incidence of cancer suggested by epidemiological studies. To test the carcinogenic potency of EMF, the in vitro micronucleus assay with SHE cells has been used as a screening method for genotoxicity. A 50Hz magnetic field (MF) of 1mT field strength was applied either alone or with the tumour initiator benzo(a)pyrene (BP) or the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). All three treatments were applied in single, double or triple treatment regimes. MF or TPA (1nM) alone did not affect the number of micronuclei (MN) in initiated and non-initiated SHE cells. Changing the schedule of the typical initiation protocol, namely applying the initiator (BP) during exposure to MF, results in an 1.8-fold increased MN formation compared to BP treatment alone. Combined experiment with BP, TPA and MF did not cause further MN formation. Since initiation during MF exposure caused a significant increased MN formation, our findings suggest that MFs enhance the initiation process of BP. We think that this MF-enhanced co-carcinogenic effect is caused by an indirect "cell activation" process. The resulting genomic instability is proposed to be due to free radicals and/or to the unscheduled "switching-on" of signal transduction pathways.

Large granular lymphocytic (LGL) leukemia in rats exposed to intermittent 60 Hz magnetic fields

An animal model for large granular lymphocytic (LGL) leukemia in male Fischer 344 rats was utilized to determine whether magnetic field exposure can be shown to influence the progression of leukemia. We previously reported that exposure to continuous 60 Hz, 1 mT magnetic fields did not significantly alter the clinical progression of LGL leukemia in young male rats following injection of spleen cells from donor leukemic rats. Results presented here extend those studies with the following objectives: (a) to replicate the previous study of continuous 60 Hz magnetic field exposures, but using fewer LGL cells in the inoculum, and (b) to determine if intermittent 60 Hz magnetic fields can alter the clinical progression of leukemia. Rats were randomly assigned to four treatment groups (18/group) as follows: (1) 1 mT (10 G) continuous field, (2) 1 mT intermittent field (off/on at 3 min intervals), (3) ambient controls ( < 0.1 microT), and (4) positive control (5 Gy whole body irradiation from cobalt-60 four days prior to initiation of exposure). All rats were injected intraperitoneally with 2.2 x 10(6) fresh, viable LGL leukemic spleen cells at the beginning of the study. The fields were activated for 20 h per day, 7 days per week, and all exposure conditions were superimposed over the natural ambient magnetic field. The rats were weighed and palpated for splenomegaly weekly. Splenomegaly developed 9-11 weeks after transplantation of the leukemia cells. Hematological evaluations were performed at 6, 8, 10, 12, 14, and 16 weeks of exposure. Peripheral blood hemoglobin concentration, red blood cells, and packed cell volume declined, and total white blood cells and LGL cells increased dramatically in all treatment groups after onset of leukemia. Although the positive control group showed different body weight curves and developed signs of leukemia earlier than other groups, differences were not detected between exposure groups and ambient controls. Furthermore, there were no overall effects of magnetic fields on splenomegaly or survival in exposed animals. In addition, no significant and/or consistent differences were detected in hematological parameters between the magnetic field exposed and the ambient control groups.

Effects of 50 Hz magnetic field exposure on tumor experimental models

The aim of this study was to investigate the interaction between a 50 Hz, 2 mT magnetic field (MF) exposure and cell growth of mammary murine adenocarcinoma, injected into experimental mice. Six different experimental protocols were performed over 2 years; several different protocols of timing of exposure were tested. X-ray radiation was adopted as the positive control. Tumor incidence and the tumor development time were calculated. No effect was observed in any experiment, and there was no statistically significant difference related to time courses among the protocols used. Neither the time of tumor cell injection nor the time of exposure produced differences between unexposed, sham, and exposed mice. When X-ray radiation was applied, the cytotoxic effect of ionizing radiation was clear, but was not increased or modified by MF exposure. Finally, the study revealed how the host-tumor system has shown a distinctive variability, unmodified by MF exposure.

Exposure of rats to a 50-Hz, 100 muTesla magnetic field does not affect the ex vivo production of interleukins by activated T or B lymphocytes

Two separate, independent experiments were conducted to evaluate the effects of exposure of rats to a 50-Hz linearly polarized, 100 microT magnetic field (MF) on the ex vivo production of interleukins (ILs) by mitogen-stimulated splenic lymphocytes. IL-1 and IL-2 were determined by proliferation assays, using IL-dependent murine T cell lines. In the first experiment, female Sprague-Dawley rats were treated with 7,12-dimethylbenz[a]anthracene (DMBA] at a dose of 20 mg per rat (four weekly gavage doses of 5 mg), and were either MF-exposed or sham-exposed for 14 weeks. This experimental protocol has previously been shown to result in a significant increase in breast cancer growth in response to MF exposure. Furthermore, MF exposure at 50-100 microT for 3 months was recently found to induce a suppressed ex vivo proliferation of splenic T cells in response to mitogen stimulation, which could be a result of reduced IL production of spleen lymphocytes. However, the present experiments failed to demonstrate any significant difference between MF- and sham-exposed groups in production of IL-1 by mitogen-activated splenic B cells. In a second experiment, shorter MF exposure periods were studied with respect to IL production from mitogen-stimulated B and T cells. Groups of rats were MF- or sham-exposed for 1 day, 1 week, or 2 weeks, followed by preparation and activation of spleen lymphocytes. No significant difference in IL-1 or IL-2 production from stimulated B or T cells was seen. The data indicate that in vivo MF exposure of rats does not affect the ex vivo IL production of B or T lymphocytes, suggesting that the recently reported changes in T cell proliferation in response to MF exposure may not be mediated via alterations in B or T cell IL production.

Carcinogenicity test of 50 Hz sinusoidal magnetic fields in rats

Male and female F344 rats, 48 per exposure group, were sham exposed (Group A) or exposed to 0.5 (Group B) and 5 mT (Group C) magnetic fields for two years. Animals were exposed from 5-109 weeks of age in SPF conditions according to the OECD test guideline No. 451. Average exposure was 22.6 hr/day. No significant differences in body weight and food consumption were observed between the sham and exposed groups. At the end of the exposure period, survival rates of the male rats were 73, 83, and 79%, and those of the females, 77, 79, and 75% for Groups A, B, and C, respectively, with no significant differences between groups. Differential counts of leukocytes were measured at the 52nd, 78th, and 104th weeks of exposure and no significant differences were observed between the exposure groups. All survivors were euthanized on schedule, and all the organs and tissues suspected of tumoral lesions were examined histopathologically. Incidences of mononuclear cell leukemia in the male and the female rats were 5, 4, 4 and 8, 6, 7 for Groups A, B and C, respectively; incidences of malignant lymphoma in the female rats were 0, 1 and 1. Neither significant increases nor acceleration of incidence of leukemia were observed. Incidences of brain and intracranial tumors did not increase in the exposed groups. Incidences of both benign and malignant neoplasms showed no significant difference between the exposed and sham exposed groups with one exception: fibroma of the subcutis in the male rats, which was considered not to be a statistically significant when evaluated with respect to the historical control data in our laboratory.

Interaction of static and extremely low frequency electric and magnetic fields with living systems: health effects and research needs

An international seminar was held June 4-6, 1997, on the biological effects and related health hazards of ambient or environmental static and extremely low frequency (ELF) electric and magnetic fields (0-300 Hz). It was cosponsored by the World Health Organization (WHO), the International Commission on Non-Ionizing Radiation Protection (ICNIRP), the German, Japanese, and Swiss governments. Speakers provided overviews of the scientific literature that were discussed by participants of the meeting. Subsequently, expert working groups formulated this report, which evaluates possible health effects from exposure to static and ELF electric and magnetic fields and identifies gaps in knowledge requiring more research to improve health risk assessments. The working groups concluded that, although health hazards exist from exposure to ELF fields at high field strengths, the literature does not establish that health hazards are associated with exposure to low-level fields, including environmental levels. Similarly, exposure to static electric fields at levels currently found in the living and working environment or acute exposure to static magnetic fields at flux densities below 2 T, were not found to have demonstrated adverse health consequences. However, reports of biological effects from low-level ELF-field exposure and chronic exposure to static magnetic fields were identified that need replication and further study for WHO to assess any possible health consequences. Ambient static electric fields have not been reported to cause any direct adverse health effects, and so no further research in this area was deemed necessary.

Increased dexamethasone-induced apoptosis of thymocytes from mice exposed to long-term extremely low frequency magnetic fields

To address the effect of extremely low frequency electromagnetic fields on programmed cell death we assessed both the spontaneous and dexamethasone (Dex)-induced apoptosis of thymocytes and spleen cells from mice submitted to a long-term continuous exposure of a 0.4-1.0 microT 60 Hz magnetic field or an 8-20 microT direct current (DC) magnetic field. Dex-induced apoptosis but not spontaneous apoptosis was substantially increased in thymocytes from 0.4 to 1.0 microT 60 Hz field-exposed animals. Spontaneous apoptosis and Dex-induced apoptosis of spleen cells were not affected by the 0.4-1.0 microT 60 Hz field exposure. In addition, spontaneous apoptosis and Dex-induced apoptosis of thymocytes and spleen cells from mice exposed to an 8-20 microT DC field were similar to the controls. These findings represent the first demonstration that thymocytes from mice exposed to a long-term 0.4-1.0 microT 60 Hz field may show abnormal response to Dex apoptotic stimuli.

Assessing the potential carcinogenic activity of magnetic fields using animal models

We update our 1997 publication by reviewing 29 new reports of tests of magnetic fields (MFs) in six different in vivo animal models of carcinogenesis: 2-year, lifetime, or multigeneration exposure studies in rats or mice; and promotion/progression models (rat mammary carcinoma, rat liver focus, mouse skin, several models of human leukemia/lymphoma in rats and mice, and brain cancer in rats). Individual experiments are evaluated using a set of data quality criteria, and summary judgments are made across multiple experiments by applying a criterion of rough reproducibility. The potential for carcinogenicity of MFs is discussed in light of the significant body of carcinogenesis data from animal bioassays that now exists. Excluding abstracts, approximately 80% of the 41 completed studies identified in this and our previous review roughly satisfy data quality criteria. Among these studies, the criterion for independent reproducibility is not satisfied for any positive results but is satisfied for negative results in chronic bioassays in rats and mice and for negative results in both promotion and co-promotion assays using the SENCAR mouse skin model. Results of independent replication studies using the rat mammary carcinoma model were conflicting. We conclude that long-term exposure to continuous 50- or 60-Hz MFs in the range of 0.002-5 mT is unlikely to result in carcinogenesis in rats or mice. Though results of most promotion/progression assays are negative, a weak promoting effect of MFs under certain exposure conditions cannot be ruled out based on available data.

Possible cocarcinogenic effects of ELF electromagnetic fields may require repeated long-term interaction with known carcinogenic factors

Literature on cancer-related biological effects of extremely low frequency (ELF) magnetic fields (MF) is discussed in the light of the current understanding of carcinogenesis as a multistep process of accumulating mutations. Different animal models and study designs have been used to address possible cocarcinogenic effects of MFs. Based on a comparison of the results, we propose a hypothesis that MF exposure may potentiate the effects of known carcinogens only when both exposures are chronic. We also discuss possible mechanisms of MF effects on carcinogenesis and the adequacy of the classical two-step initiation/promotion animal experiments for simulating human exposure to the complex mixture of environmental carcinogens. We conclude that experiments designed according to the two-step concept may not be sufficient for studying the possible role of MF in carcinogenesis. Possible further animal studies are more likely to be productive if they include models that combine chronic exposure to MFs with long-term exposures to known carcinogens.

Lack of effect of a 60 Hz magnetic field on biomarkers of tumor promotion in the skin of SENCAR mice

It has been proposed that extremely low frequency magnetic fields may enhance tumorigenesis through a co-promotional mechanism. This hypothesis has been further tested using the two-stage model of mouse skin carcinogenesis, i.e. 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced promotion of skin carcinogenesis in mice initiated by a single subcarcinogenic dose of 7,12-dimethylbenz[a]anthracene. Experimentation utilized three different doses of TPA within its dose-response range (0.85, 1.70 or 3.40 nmol) and examined the following early biomarkers of tumor promotion after 1, 2 and 5 weeks of promotion: increases in epidermal thickness and the labeling index of epidermal cells, induction of epidermal ornithine decarboxylase activity and down-regulation of epidermal protein kinase C activity. Mice exposed to a 60 Hz magnetic field having a flux density of 2 mT for 6 h/day for 5 days/week were compared with mice exposed to an ambient magnetic field. Within the sensitivity limits of the biomarker methodology and the exposure parameters employed, no consistent, statistically significant effects indicative of promotion or co-promotion by the magnetic field were demonstrated.

Two stage model for carcinogenesis: number and size distributions of premalignant clones in longitudinal studies

The two stage clonal expansion model of carcinogenesis provides a convenient biologically based framework for the description of toxicologic and epidemiologic data on carcinogenesis. Under this model, a cancer cell is generated following the occurrence of two critical mutations in a single stem cell. Initiated cells that have sustained the first mutation undergo a stochastic birth-death process resulting in clonal expansion of the initiated cell population. In this article, we consider the analysis of longitudinal data on the number and size of premalignant clones, formed by clonal expansion of initiated cells. In particular, the joint distribution of the number of premalignant clones observed at different points in time in the same subject is derived. The application of these results in the statistical analysis of longitudinal data on the number and size of premalignant clones observed in initiation-promotion experiments is indicated.

Biological responses to electromagnetic fields

Electrification in developed countries has progressively increased the mean level of extremely low-frequency electromagnetic fields (ELF-EMFs) to which populations are exposed; these humanmade fields are substantially above the naturally occurring ambient electric and magnetic fields of approximately 10(-4) Vm(-1) and approximately 10(-13) T, respectively. Several epidemiological studies have concluded that ELF-EMFs may be linked to an increased risk of cancer, particularly childhood leukemia. These observations have been reinforced by cellular studies reporting EMF-induced effects on biological systems, most notably on the activity of components of the pathways that regulate cell proliferation. However, the limited number of attempts to directly replicate these experimental findings have been almost uniformly unsuccessful, and no EMF-induced biological response has yet been replicated in independent laboratories. Many of the most well-defined effects have come from gene expression studies; several attempts have been made recently to repeat these key findings. This review analyses these studies and summarizes other reports of major cellular responses to EMFs and the published attempts at replication. The opening sections discuss quantitative aspects of exposure to EMFs and the incidence of cancers that have been correlated with such fields. The concluding section considers the problems that confront research in this area and suggests feasible strategies.

Regulation of c-fos is affected by electromagnetic fields

The goal of the present study was to determine if regulatory regions of the c-fos gene were responsive to electromagnetic field exposure. The research design used transfected cells to increase the sensitivity of assays designed to identify changes following exposure. HeLa cells were transiently transfected with plasmids containing upstream regulating regions of c-fos up to -700 base pairs, coupled with the prokaryotic reporter gene CAT. Cells were exposed to an environmentally relevant EMF of 60 Hz at 60 mGrms. CAT expression above control levels in transfected cells (region +42 to -700 bp) was observed following 5 min exposure to the electromagnetic field, with a peak at 20 min. The expression was at basal levels following 40 min exposure. Deletion analysis of upstream DNA narrowed the responsive region to 138 base pairs from -363 to -225, which contains the SRE/AP-1 sites.

EMF and current cancer concepts

Exposure to power frequency electric and magnetic fields (EMF) is ubiquitous, and a body of epidemiologic studies has produced evidence suggestive of a possible link between EMF exposure and cancer of several types. This paper provides a perspective that holds key findings in the EMF literature against the background of important models and established principles in cancer biology. It is intended primarily for scientists whose expertise lies outside of cancer biology and animal bioassays. Current thinking holds that carcinogenesis is a multistep process that requires at least two genotoxic events in its critical path but that is facilitated by nongenotoxic proliferative effects on target cells. EMF, which itself is not believed to be genotoxic, could influence carcinogenesis if it exerted either direct or indirect effects on target cell turnover. Such effects could operate through receptor-mediated or nonreceptor-mediated pathways. However, effects relevant to carcinogenesis have not been confirmed, and a mode of action for EMF has not been determined. Chronic bioassays in rodents are in progress to examine the potential carcinogenicity of EMFs. EMF research has the opportunity to capitalize on the recent major advances in our understanding of carcinogenic processes.

Differential modulation of natural and adaptive immunity in Fischer rats exposed for 6 weeks to 60 Hz linear sinusoidal continuous-wave magnetic fields

Two separate, independent experiments were conducted to evaluate the effect of 60 Hz linearly polarized, sinusoidal, continuous-wave magnetic fields (MFs) on immune system performances in rats born and raised under these fields. Each experiment lasted for 6 weeks. A total of 96 animals, divided into groups of eight animals each, was exposed for 20 h/day to MFs of different intensities, i.e., sham (< 0.02 microT) and 2, 20, 200, and 2000 microT. Another group of animals, which was housed in a separate room, served as cage controls (CC). These animals were exposed to ambient MFs of < 0.02 microT. The following immune responses were evaluated in both experiments total T and B cells; CD4+ and CD8+ subpopulation and natural killer (NK) cell activity in splenic lymphocytes; hydrogen peroxide (H2O2), nitrous oxide (NO), and tumor necrosis factor (TNF) production by peritoneal macrophages. Our results show that a 6 week exposure to MFs induced a significant decrease in the number of CD5+, CD4+, and CD8+ populations. These changes were even more significant in rats that were exposed to fields of 2000 microT. A lower, although significant, decrease in the CD5+ population was also observed in animals that were exposed to fields of 200 microT. Linear regression analysis demonstrated a dose effect with MF intensity. B lymphocyte (Ig+ cell) populations also showed a 12% decrease (P < .05) in the groups that were exposed to fields of 20 and 200 microT. However, these results were not significant, and no relation with MF intensities could be demonstrated. In contrast, evaluation of splenic NK cell activity revealed a 50% increase (P < .05) in animals that were exposed to fields of 2000 microT. No significant results were obtained from the evaluation of TNF activity and NO secretion in peritoneal macrophages. Phorbol 12-myristate 13-acetate (PMA)-stimulated and net H2O2 productions for a minor subpopulation of peritoneal cells showed positive dose-response correlations by linear regression analysis. Taken together, our results suggest that an in vivo exposure of rats for 6 weeks to 60 Hz MFs can induce significant immunological perturbations on effector cells of both natural and adaptive immunity in a dose-dependent fashion.

Protein kinase C activity is altered in HL60 cells exposed to 60 Hz AC electric fields

We examined the effects of electric fields (EFs) on the activity and subcellular distribution of protein kinase C (PKC) of living HL60 cells. Sixty Hertz AC sinusoidal EFs (1.5-1,000 mV/cm p-p) were applied for 1 h to cells (10(7)/ml) in Teflon chambers at 37 degrees C in the presence or absence of 2 microM phorbol 12-myristate 13-acetate (PMA). PMA stimulation alone evoked intracellular translocation of PKC from the cytosolic to particulate fractions. In cells that were exposed to EFs (100-1,000 mV/cm) without PMA, a loss of PKC activity from the cytosol, but no concomitant rise in particulate PKC activity, was observed. In the presence of PMA, EFs (33-330 mV/cm) also accentuated the expected loss of PKC activity from the cytosol and augmented the rise in PKC activity in the particulate fraction. These data show that EFs alone or combined with PMA promote down-regulation of cytosolic PKC activity similar to that evoked by mitogens and tumor promoters but that it does not elicit the concomitant rise in particulate activity seen with those agents.

Human natural killer cytotoxic activity is not affected by in vitro exposure to 50-Hz sinusoidal magnetic fields

Epidemiological studies have suggested, but not demonstrated, a role of exposure to 50/60-Hz magnetic fields in increasing cancer risk in man (workers and the general population). A possible target of magnetic fields is the immune system. In particular, it is known that an important defence against cancer is represented by natural killer (NK) cells capable of killing cancer cell targets. To test this hypothesis, human NK cells, stimulated or not with phytohaemagglutinin or interleukin 2, were exposed to 50-Hz sinusoidal magnetic fields before or during the cytotoxicity test, and then mixed with a variety of target cancer cell lines (Daudi, Raji, U937, H14, IGROV, SW626, K562, HL60). The experiments were performed in two laboratories (Rome and Modena) by means of two different exposure systems. The results of both laboratories suggest that 50-Hz sinusoidal magnetic fields with flux densities up to 10 mT do not affect the cytotoxic activity of human NK cells.

A 60-Hz magnetic field increases the incidence of squamous cell carcinomas in mice previously exposed to chemical carcinogens

The exposure of tumor-bearing SENCAR mice to a magnetic field of 2 mT at a frequency of 60 Hz for 52 weeks, was found to increase the rate of malignant conversion in chemically-induced dorsal skin papillomas. Detailed histopathology revealed the presence of squamous cell papillomas and squamous cell carcinomas in both sham and magnetic field exposed mice at week 52. However, of the nine mice assessed as having squamous cell carcinomas, eight came from the group exposed to magnetic fields, a difference which is statistically significant at P = 0.03.

Animal studies on the role of 50/60-Hertz magnetic fields in carcinogenesis

A number of epidemiological studies have suggested that exposure to 50/60-Hz magnetic fields (MF) from power lines and electrical equipment may be associated with a modestly increased incidence of various types of cancer. Laboratory studies have indicated that nonionizing radiation has no mutagenic effect, i.e. does not initiate cancer. Thus, if 50/60-Hz MF are truly associated with an increased risk of cancer, then these fields must act as a promoter or co-promoter of cancer in cells that have already been initiated. This paper reviews the evidence produced by animal studies. As shown in this review, the available animal data on 50/60-Hz MF exposures seem to indicate that intermediate MF exposure exerts co-promoting effects in different tumor models, particularly cocarcinogenesis models of breast cancer, while chronic (up to life-time) exposure may exert promoting effects on "spontaneous" development of certain tumors. The tumor promoting or co-promoting effects of 50/60-Hz MF exposure found in several animal studies could relate to actions of MF on gene expression, immune surveillance, and Ca2+ homeostasis as demonstrated by in vitro experiments in cell cultures. However, the most plausible evidence for an in vivo effect of MF exposure which could be related to tumor promotion is reduction of circulating levels of melatonin, i.e. a hormone which is inhibitory to the growth of a wide range of cancers, particularly breast cancer. Animal studies have shown that 50-Hz MF exposure at flux densities as low as 0.3-1 mu Tesla significantly reduces nocturnal melatonin levels in plasma. While decrease of melatonin levels alone could explain tumor promoting or co-promoting effects of MF exposure, recent data indicate that MF exposure also impairs the effects of melatonin at the cellular level. Thus, the oncostatic effect of melatonin on cell proliferation of a human breast cancer cell line was antagonized by 60-Hz MF exposure at a flux density of about 1 mu Tesla. All these data indicate that interactions between 50/60-HZ MF exposure and melatonin may be the key mechanism of any carcinogenic effects. Although the existing experimental evidence is still insufficient for discerning a cause-effect relationship for MF exposure and human disease or injury, it does suggest the need for further laboratory research under well-defined laboratory exposure conditions to allow for a realistic assessment of the possible health risks and their magnitude.

Enhanced mutagenic effect of a 60 Hz time-varying magnetic field on numbers of azide-induced TA100 revertant colonies

Forty-eight hours exposure to a two Gauss (0.2 mT) rms 60 Hz time varying sinusoidal electromagnetic field increased the number of azide induced TA100 revertant colonies of Salmonella typhimurium 14% as compared with controls in the ambient < 2 milli-Gauss 60 Hz field. In the absence of the electromagnetic field, the numbers of mutant colonies grown within and outside the non-energized coil were nearly identical. Without azide, the number of "spontaneous" mutant colonies forming in the experimental field was not statistically significant from numbers of colonies not exposed to field effects. Experimental temperature variation of 2 degrees C had little effect on colony formation, and the enhanced production of revertant colonies in the presence of the magnetic field was maintained during continued culture for 5 additional days.

Effects of time-varying uniform magnetic fields on natural killer cell activity and antibody response in mice

Natural Killer cell activity and antibody response were studied in Balb/c mice which were exposed in vivo to uniform pulsed magnetic fields (square-wave, 0.8 Hz, 120 mT maximum field strength, 0.1 s rise-time) for 5 days, 10 h/day. No effects were found in antibody response to sheep red blood cell (SRBC) immunization as assayed by counting the plaque-forming cells (PFC) in the spleens of animals on the sixth day. Following 5-day exposures, the activity of Natural Killer (NK) cells was measured in vitro by challenge with YAC-1 cells, in experiments in which mice were not immunized. An increase of NK cytotoxic activity due to exposure was found which depended on the age of the mice (effect observed above 12 weeks) and on the strength of the applied field (effect observed above 30 mT).

Effects of magnetic fields on mammary tumor development induced by 7,12-dimethylbenz(a)anthracene in rats

A series of epidemiological studies have indicated associations between exposure to magnetic fields (MFs) and a variety of cancers, including breast cancer. In order to test the possibility that MF acts as a cancer promoter or copromoter, four separate experiments have been conducted in rats in which the effects of chronic exposure to MFs on the development of mammary tumors induced by 7,12-dimethylbenz(a)anthracene (DMBA) were determined. Female rats were exposed in magnetic coils for 91 days (24 h/day) to either alternating current (AC; 50 Hz)-MF or direct current (DC)-MF. Magnetic flux density of the DC-MF was 15 mT. Two AC-MF exposures used a homogeneous field with a flux density of 30 mT (rms); one used a gradient field with flux density ranging from 0.3-1 microT. DMBA (5 mg) was administered orally at the onset of MF exposure and was repeated thrice at intervals of 1 week. In each experiment, 18-36 animals were exposed in 6 magnetic coils. The same number of rats were used as sham-exposed control. These control animals were treated with DMBA and were placed in dummy coils in the same room as the MF-exposed rats. Furthermore, groups of age-matched rats (reference controls) were treated with DMBA but housed in another room to exclude any MF exposure due to the magnetic stray field from the MF produced by coils. At the end of the exposure or sham-exposure period, tumor number and weight or size of tumors were determined at necropsy. Results were as follows: In sham-exposed animals or reference controls, the tumor incidence varied between 50 and 78% in the 4 experiments. The average number of mammary tumors per tumor-bearing animal varied between 1.6 and 2.9. In none of the experiments did MFs significantly alter tumor incidence, but in one of the experiments with AC-MF exposure at 30 mT, the number of tumors per tumor-bearing animal was significantly increased. Furthermore, exposure to a DC-MF at 15 mT significantly enhanced the tumor weight. Exposure to a gradient AC-MF at 0.3-1 microT exerted no significant effects. These experiments seem to indicate that MFs at high flux densities may act as a promoter or copromoter of breast cancer. However, this interpretation must be considered only a tentative conclusion because of the limitations of this study, particularly the small sample size used for MF exposure and the lack of repetition of data.

Mechanisms of electromagnetic interaction with cellular systems

The question of how electromagnetic fields--static or low to high frequency--interact with biological systems is of great interest. The current discussion among biologists, chemists, and physicists emphasizes aspects of experimental verification and of defining microscopic and macroscopic mechanisms. Both aspects are reviewed here. We emphasize that in certain situations nonthermal interactions of electromagnetic fields occur with cellular systems.