No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
ELF magnetic field affects proliferation of SPD8/V79 Chinese hamster cells but does not interact with intrachromosomal recombination
Abstract
Extremely low-frequency (ELF) magnetic fields have previously been shown to affect conformation of chromatin, cell proliferation, and calcium metabolism. Possible mutagenic and carcinogenic effects of ELF have also been discussed and tested. In this study, intrachromosomal recombination in the hprt gene after exposure to ELF magnetic field was investigated using the SPD8 recombination assay. SPD8 cells, derived from V79 Chinese hamster cells were exposed to ELF at a specific combination of static and ELF magnetic fields, that has been proven to have effects on chromatin conformation in several cell types. The genotoxic agent camptothecin (CPT) was used either as a positive control or simultaneously with ELF. We also analysed the effect of ELF and CPT on chromatin conformation with the anomalous viscosity time dependence (AVTD) technique, cell growth kinetics, and cell survival with clonogenic assay. DNA fragmentation was analysed by pulsed field gel electrophoresis (PFGE). ELF did not induce recombination alone, neither did ELF modify the recombinogenic effect of CPT. Although, there was no effect on cell survival in response to ELF exposure, inhibition of cell growth was observed. On the other hand, ELF exposure partly counteracted the growth inhibition seen with CPT. The data suggest that ELF exposure may stimulate or inhibit cell growth depending on the state of the cells. Although, ELF did not induce recombination, a weak but statistically significant DNA fragmentation comparable with CPT-induced fragmentation was observed with PFGE 48h after exposure to ELF.
... There is evidence that weak EMF can result in DNA damage and changes in permeability of brain– blood barrier [Lai and Singh, 1997; Persson et al., 1997]. There are a number of publications indicating that EMF can produce stress response [Lin et al., 1997; Junkersdorf et al., 2000; de Pomerai et al., 2000] and apoptosis [Simko et al., 1998; Mangiacasale et al., 2001; Olsson et al., 2001]. ''Null'' effects regarding all of the above-mentioned endpoints were also reported, however, accumulating experimental evidence suggest that EMF effects occur only in specific frequency and amplitude ''windows'' depending on several physical parameters [Adey, 1999; Binhi, 2002]. ...
... Therefore, the effects of weak ELF are usually observed only under specific combinations of frequency, amplitude, and SMF. It was shown in our previous investigations, that weak EMF affected the conformation of chromatin in cells of different types including human lymphocytes [Belyaev et al., 1999a [Belyaev et al., , 2000 Belyaev and Alipov, 2001a; Olsson et al., 2001]. In particular, temporal condensation of chromatin similar to condensation during apoptosis or stress response has been observed in human lymphocytes in response to 8 Hz magnetic field [Belyaev et al., 1999a; Belyaev and Alipov, 2001a]. ...
... It was shown in our previous investigations that weak ELF magnetic fields and microwaves affected conformation of chromatin in E. coli cells, rat thymocytes , human lymphocytes, and SPD8/V79 Chinese hamster cells under specific conditions of exposure [Belyaev et al., , 1999a [Belyaev et al., , 2000 Belyaev and Alipov, 2001a; Olsson et al., 2001]. Chromatin conformation changes are non specific cellular responses and may be induced by diverse stimuli such as temperature, DNA intercalators, inhibitors of DNA-topoisomerases, electromagnetic fields and ionizing radiation [Belyaev et al., 1999b [Belyaev et al., , 2000 [Belyaev et al., , 2001b; Belyaev and Alipov, 2001a]. ...
GSM microwaves and 50 Hz electromagnetic field induce stress response but not apoptosis in human lymphocytes from healthy and hypersensitive persons I. Belyaev 1,2, M. Harms-Ringdahl 1, L. Hillert 3, L. Malmgren 4, B. Persson 4, M. Protopopova 5, G. Selivanova 5, C. Tamm1 1Department of Genetic and Cellular Toxicology, Stockholm University, Stockholm, Sweden 2Department of Biophysics, Radiation Physics and Ecology, Moscow Engineering Physics Institute, Russia 3Department of Environmental Health, Karolinska Hospital, Stockholm County Council, Stockholm, Sweden 4Department of Radiation Physics, Lund University Hospital, Lund, Sweden 5Cancer Centrum Karolinska, Karolinska Institutet, Stockholm, Sweden Address for correspondence: Dr. Igor Y. Belyaev, Department of Genetic and Cellular Toxicology, Stockholm University S-106 91 Stockholm, Sweden, Tel: +46-8-16 41 08, FAX: +46-8-16 43 15 E-mail: Igor.Belyaev@genetics.su.se Key words: apoptosis, stress response, DNA DSB, chromatin, human lymphocytes, 53BP1 protein, hypersensitivity Glossary: anomalous viscosity time dependence (AVTD), DNA double-strand break (DSB), electromagnetic field (EMF), extremely low frequency (ELF), global system for mobile communication (GSM), integrated optical density (IOD), pulsed-field gel electrophoresis (PFGE), static magnetic fields (SMF), transverse electromagnetic cell (TEM-cell). Abstract Effects of microwaves and electromagnetic fields (EMF) of extremely low frequency (ELF) on stress response and apoptosis have been evaluated in few studies. Here, we used specific conditions of exposure to microwaves from real GSM mobile phone (915 MHz, SAR=0.4 mW/g) and ELF EMF (50 Hz, 15 T amplitude) in the transverse electromagnetic cell (TEM-cell) to investigate the response of lymphocytes from healthy subjects and from persons reporting hypersensitivity to electricity. The groups of hypersensitive and healthy donors were matched by gender and age and the data were analyzed in blind. The changes in chromatin conformation were measured with the method of anomalous viscosity time dependencies (AVTD). 53BP1 protein, which has been shown to co-localize in foci with DNA double strand breaks (DSB), was analyzed by immunostaining in situ . Exposure either to GSM microwaves or EMF/50 Hz resulted in significant condensation of chromatin, which was similar to the effect of heat shock at 410C. These effects varied between donors with a trend for prolonged condensation of chromatin in the cells from hypersensitive subjects. Cells from subjects, which were classified as pronounced hypersensitivity, responded to GSM /ELF stronger than cells from matched control subjects, but these differences in responses need to be confirmed in a larger study group. Neither GSM nor ELF exposure induced formation of 53BP1 foci. In contrary, distinct decrease in background level of 53BP1 signaling was observed upon these exposures as well as for heat shock treatments. This decrease correlated with the AVTD data and may indicate decrease in accessibility of 53BP1 to antibodies because of chromatin condensation. Apoptosis was determined by morphological changes and by apoptotic fragmentation of DNA as analyzed by pulsed-field gel electrophoresis (PFGE). No apoptosis was induced by exposure to ELF/50 Hz and GSM microwaves. In conclusion, ELF magnetic fields and GSM microwaves under the specified conditions of exposure induced stress response in lymphocytes from healthy and hypersensitive donors.
... There are a number of publications indicating that EMF can produce stress response [ Lin et al., 1997;Junkersdorf et al., 2000;de Pomerai et al., 2000] and apoptosis [Simko et al., 1998;Mangiacasale et al., 2001;Olsson et al., 2001]. ''Null'' effects regarding all of the above-mentioned endpoints were also reported, however, accumulating experimental evidence suggest that EMF effects occur only in specific frequency and amplitude ''windows'' depending on several physical parameters [Adey, 1999;Binhi, 2002]. ...
... It was shown in our previous investigations, that weak EMF affected the conformation of chromatin in cells of different types including human lymphocytes [Belyaev et al., 1999a[Belyaev et al., , 2000Belyaev and Alipov, 2001a;Olsson et al., 2001]. In particular, temporal condensation of chromatin similar to condensation during apoptosis or stress response has been observed in human lymphocytes in response to 8 Hz magnetic field [Belyaev et al., 1999a;Belyaev and Alipov, 2001a]. ...
... It was shown in our previous investigations that weak ELF magnetic fields and microwaves affected conformation of chromatin in E. coli cells, rat thymocytes, human lymphocytes, and SPD8/V79 Chinese hamster cells under specific conditions of exposure [Belyaev et al., , 1999a[Belyaev et al., , 2000Belyaev and Alipov, 2001a;Olsson et al., 2001]. ...
We used exposure to microwaves from a global system for mobile communication (GSM) mobile phone (915 MHz, specific absorption rate (SAR) 37 mW/kg) and power frequency magnetic field (50 Hz, 15 muT peak value) to investigate the response of lymphocytes from healthy subjects and from persons reporting hypersensitivity to electromagnetic field (EMF). The hypersensitive and healthy donors were matched by gender and age and the data were analyzed blind to treatment condition. The changes in chromatin conformation were measured with the method of anomalous viscosity time dependencies (AVTD). 53BP1 protein, which has been shown to colocalize in foci with DNA double strand breaks (DSBs), was analyzed by immunostaining in situ. Exposure at room temperature to either 915 MHz or 50 Hz resulted in significant condensation of chromatin, shown as AVTD changes, which was similar to the effect of heat shock at 41 degrees C. No significant differences in responses between normal and hypersensitive subjects were detected. Neither 915 MHz nor 50 Hz exposure induced 53BP1 foci. On the contrary, a distinct decrease in background level of 53BP1 signaling was observed upon these exposures as well as after heat shock treatments. This decrease correlated with the AVTD data and may indicate decrease in accessibility of 53BP1 to antibodies because of stress-induced chromatin condensation. Apoptosis was determined by morphological changes and by apoptotic fragmentation of DNA as analyzed by pulsed-field gel electrophoresis (PFGE). No apoptosis was induced by exposure to 50 Hz and 915 MHz microwaves. In conclusion, 50 Hz magnetic field and 915 MHz microwaves under specified conditions of exposure induced comparable responses in lymphocytes from healthy and hypersensitive donors that were similar but not identical to stress response induced by heat shock.
... Biochemical studies associated with ELF include effects on gene expression [Lupke et al., 2006], calcium signaling [Blackman et al., 1982;McCreary et al., 2006], enzymatic activity [Di Loreto et al., 2009;Ravera et al., 2010], growth factor receptors [Ke et al., 2008;Sun et al., 2008], melatonin synthesis [Jahandideh et al., 2010] and events involving generation of free radicals [Simko, 2007]. ELF effects on cell proliferation have been described and both inhibition and stimulation has been observed, depending on cell type and exposure conditions [Olsson et al., 2001;Strasak et al., 2002;Verheyen et al., 2003]. ELF MF have been used for medical treatments under those conditions of exposure that induce cell division [Markov, 2007;Sun et al., 2009]. ...
... The horizontal ambient magnetic field was zeroed, 0 AE 0.1 mT within exposed volume, using the vertical coils (radius 0.068 m, 100 turns, 10.6 V), supplied with DC from the current supply B5-44. As in our previous studies, the vertical static DC field was 43 AE 1 mT [Alipov and Belyaev, 1996;Olsson et al., 2001]. The magnetic flux densities of DC and AC magnetic fields were measured by means of a magnetometer (Sam3, Dowty Electronics, Cannock, England) and a one-dimensional G79 microteslameter (Mikroprovod, Nizhnij Novgorod, Russia), controlled by means of measuring the currents and subsequent calculations of the magnetic fields according to the formulae: ...
Effects of magnetic field (MF) at 50 Hz on chromatin conformation were studied by the method of anomalous viscosity time dependence (AVTD) in human lymphocytes from two healthy donors. MF within the peak amplitude range of 5-20 µT affected chromatin conformation. These MF effects differed significantly between studied donors, and depended on magnetic flux density and initial condensation of chromatin. While the initial state of chromatin was rather stable in one donor during one calendar year of measurements, the initial condensation varied significantly in cells from another donor. Both this variation and the MF effect depended on temperature during exposure. Despite these variations, the general rule was that MF condensed the relaxed chromatin and relaxed the condensed chromatin. Thus, in this study we show that individual effects of 50 Hz MF exposure at peak amplitudes within the range of 5-20 µT may be observed in human lymphocytes in dependence on the initial state of chromatin and temperature.
... Effects of weak magnetic fields (MF) of extremely low frequency (ELF, 1-300 Hz) on cell proliferation have been described, and both inhibition and stimulation has been observed, depending on cell type and exposure conditions [Olsson et al., 2001;Verheyen et al., 2003]. Recent investigations have shown that weak ELF MF under specific conditions of exposure can affect apoptosis [Simko et al., 1998;Belyaev et al., 2000Olsson et al., 2001]. ...
... Effects of weak magnetic fields (MF) of extremely low frequency (ELF, 1-300 Hz) on cell proliferation have been described, and both inhibition and stimulation has been observed, depending on cell type and exposure conditions [Olsson et al., 2001;Verheyen et al., 2003]. Recent investigations have shown that weak ELF MF under specific conditions of exposure can affect apoptosis [Simko et al., 1998;Belyaev et al., 2000Olsson et al., 2001]. Inhibitory effects of ELF on tumors have been observed [Williams et al., 2001;Tofani et al., 2002]. ...
The effects of ELF alternating magnetic fields tuned to Zn(2+) on the growth of cancer cells with different status of p53 were investigated using a cell proliferation assay. Human cancer cells HeLa (cervix cancer, p53(+/+)), Saos-2 and Saos-2-His-273 (osteosarcoma, p53(-/-) and p53 His-273 mutant, respectively), H1299tTA and H1299tTA-His175 (lung carcinoma, p53(-/-) and p53 His-175 mutant), and normal human fibroblasts VH-10 (p53(+/+)) were used. Exposure parameters were calculated for the first harmonic of Zn(2+) based either on the magnetic parametric resonance (MPR) model of Lednev or the ion parametric resonance (IPR) model of Blanchard and Blackman. ELF exposure was for 72 and 96 h. The vertical alternating field was 20 Hz at amplitudes of either 38.7 or 77.4 microT (peaks, IPR or MPR, respectively). The vertical static magnetic field was 43 microT, and the horizontal static magnetic field was zeroed. Treatments of cells with PRIMA-1 and gamma-rays were used as positive controls. Growth inhibition was observed in cells after exposure to ELF at 38.7 microT. Inhibition of HeLa, VH-10, and Saos-2-His-273 cells was statistically significant, P=0.0003, 0.02, and 0.006, respectively. No consistent ELF effects following exposure 77.4 microT were seen. PRIMA-1 inhibited the growth of all cell lines with the strongest effect in mutant p53-carrying cell line H1299tTA-His175. The effects of gamma-rays were relatively weak, suggesting that the cell proliferation assay under conditions employed in this study is not very sensitive to apoptosis. In conclusion, ELF under conditions of exposure tuned to Zn(2+) according to the IPR model inhibited the growth of cancer and normal cells. No clear relationship of the observed growth inhibition to p53 status was found. Further experiments, using complementary techniques, are required to test whether p53 reactivation by ELF is feasible.
... Due to the public health concerns about the power lines, mobile phones, and cancer, DNA integrity is frequently studied in pulsed MFs (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. show that DNA synthesis in cells could be increased by time-varying MFs (Liboff et al. 1984). ...
This chapter lists current evidence (from molecular level, cellular level, animal level to patient level) and some potential mechanisms for the effects of static magnetic field on cancer inhibition. The direct impacts of static magnetic fields on cancer cells are summarised, including cancer cell proliferation, division, migration and invasion, as well as cancer cell stemness. Moreover, static magnetic field s can also affect microcirculation and angiogenesis, and regulate immune system to inhibit cancer in vivo. Furthermore, the prospective applications of static magnetic field alone or in combination with chemotherapy drugs, time-varying magnetic fields as well as radiotherapy in cancer treatment are reviewed. The potential mechanisms and factors that contributed to the inconsistencies are also discussed. These evidences demonstrate that static magnetic fields have a great potential to be used as a physical tool to inhibit cancer, but further investigations are still needed to optimize the static magnetic field parameters and exposure procedures, as well as combinational therapy modalities.
... Due to the public health concerns about the power lines, mobile phones, and cancer, DNA integrity is frequently studied in pulsed MFs (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. show that DNA synthesis in cells could be increased by time-varying MFs (Liboff et al. 1984). ...
Although in most cases, people are exposed to static magnetic fields (SMFs) for just a short period of time, there are increasing situations where long-term exposure becomes inevitable, including magnets implanted in patients, magnetic therapy, and occupational exposure of magnetic resonance imaging staff. Consequently, the potential beneficial and/or harmful effects of such exposure, as well as its underlying mechanism, have triggered research endeavors. In this chapter, we have collected reported experimental data on animals and humans that were subjected to SMFs for more than 2 weeks, either continuously or intermittently. In animal models, it is found that long-term exposure to moderate SMFs can influence multiple aspects, including blood pressure and glucose regulation, the relief of pain, the promotion of bone formation, etc. Differences between continuous vs. intermittent exposure, human experimental results vs. epidemiological studies are discussed. Although most animal and human studies so far have suggested little/no risk of long-term exposure, or even beneficial effects for most moderate SMFs, there are still some exclusions that need attention. More research is still needed to comprehensively assess the exact long-term biological effects of various SMFs on different physiological and pathological conditions before we can make the best use of them.
... Due to the public health concerns about the power lines, mobile phones, and cancer, DNA integrity is frequently studied in pulsed MFs (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. show that DNA synthesis in cells could be increased by time-varying MFs (Liboff et al. 1984). ...
Although lacking mechanistic explanations, different poles of permanent magnets could generate different effects on living organisms has been claimed decades ago, especially in the field of magnetotherapy. In recent years, several studies have confirmed that different magnetic field directions could indeed induce some differential effects in biological systems, including tumor inhibition, blood glucose level regulation, etc. However, it has been a neglected factor by most researchers in the past, which has led to many inconsistent experimental results in the literature. This chapter aims to systematically compare and summarize the biological effects induced by static magnetic fields of different directions. We also discuss about the possible mechanisms, which currently is still largely a mystery. We hope researchers in this field can pay attention to the static magnetic field directions so that they can clearly describe the field direction and/or distributions information in their studies, which will help clarify some confusions and reduce inconsistencies for future investigations.
... Due to the public health concerns about the power lines, mobile phones, and cancer, DNA integrity is frequently studied in pulsed MFs (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. show that DNA synthesis in cells could be increased by time-varying MFs (Liboff et al. 1984). ...
Diabetes, a metabolic chronic disease characterized by hyperglycemia, has dire consequences for health and well-being if left uncontrolled. In recent years, there are some studies about the effects of static magnetic fields (SMFs) on diabetes and its complications, but the reported effects are highly inconsistent, especially for glycemia levels. The aim of this chapter is to compare and analyze reported effects of multiple parameter SMFs on glycemia and insulin levels, as well as diabetic complications. It is interesting that although the reported effects of SMFs on glycemia and insulin levels are variable due to the differences in SMF parameters and experimental subjects, SMFs have consistently shown beneficial effects on diabetic complications including wound healing. Mechanistic studies indicate that SMFs may play an important role in insulin secretion by affecting membrane proteins, hormone levels, and reactive oxygen species. This not only contributes to a better understanding of SMF effects on diabetes and its complications, but also lays the foundation for more systematic and in-depth studies to develop potential applications of SMFs in the clinical setting of diabetes in the future.
... Due to the public health concerns about the power lines, mobile phones, and cancer, DNA integrity is frequently studied in pulsed MFs (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. show that DNA synthesis in cells could be increased by time-varying MFs (Liboff et al. 1984). ...
Magnetic properties of materials determine their response to the externally applied magnetic field. Although most living organisms, including human bodies, are diamagnetic as a whole, they have a very complexed composition. The purpose of this chapter is to summarize the known facts about the magnetic properties of biological samples, including the magnetic susceptibility, magnetic anisotropy of biomolecules (nucleic acid, proteins and lipids, etc.), organisms, tissues, and cells. Although there are still not enough data in this aspect, especially live biological samples in physiological conditions, current evidences already show that biological samples at different states show different magnetism. For example, the oxygenated red blood cells are diamagnetic while the deoxygenated red blood cells are paramagnetic, which are mainly due to their hemoglobin at different states and have been used in magnetic resonance imaging to diagnose different types of bleeding. The chain-like ferromagnetic magnetosome in magnetotactic bacteria is also the tool for their orientation in earth magnetic field. Therefore, systematic examination of magnetic properties of biological samples is not only essential to avoid ambiguities, complexities, and limitations to the interpretations of magnetic field-induced bioeffects, but also critical for the magnetic field-based technical development.
... In particular, stress response, production of reactive oxygen species (ROS), increased sensitivity of stem cells, and inhibition of melatonin production were associated with increased cancer risks related to ELF exposure [23,24]. The ELF biological effects at intensities below the ICNIRP standards have been shown to manifest a complex dependence upon biological and physical variables similar to the NT RF effects [16,[25][26][27][28][29] and have been considered in the frames of the same physical models [15,[30][31][32][33][34][35]. ...
Cell phones expose significant parts of the human brain and head to extremely low frequency (ELF) magnetic fields (MF) classified by the IARC as a 2B carcinogen. ELF MF was measured on the front and back sides of 15 cell phones in standby, speaking, and listening modes for 2G and 3G standards in two frequency bands, LF1: 5 Hz-200 Hz and LF2: 120 Hz-10 kHz. The highest MF value was 70.03 µT (RMS) in LF1 (2G, listening mode, front side) and 12.67 µT (RMS) in LF2 (2G, speaking mode, front side). The 3G cell phones consistently emitted a lower ELF MF compared to the 2G ones. The exposure to ELF MF was also simulated at various locations (head, thorax, pelvis) using the CST Studio Suite. The simulations revealed 8.45 µT, 7.5 µT, and 6.09 µT in the middle of the head (midbrain), 3.89 µT, 3.98 µT, and 2.83 µT for the middle of the thorax (heart), and 2.03 µT, 1.96 µT, and 1.56 µT in the middle of the pelvis (scrotum) for 10 Hz, 50 Hz, and 200 Hz, respectively. These values are comparable to those reported to induce biological and health effects, including those related to carcinogenesis. The results can be used in future studies concerning the ELF exposure or the combined effects of electromagnetic fields of radiofrequency and ELF.
... Olsson et al. exposed SPD8 cells, derived from V79 Chinese hamster cells to a specific combination of static and ELF-MF, which has been proven to have effects on chromatin conformation in several cell types [77]. The genotoxic agent camptothecin (CPT) was used either as a positive control or simultaneously with the ELF-MF. ...
... These are: repetitive [16] or high frequency electromagnetic field [17], continuous and discontinuous electromagnetic field [18], sinusoidal [19], static low level MF [20] etc. In general, magnetic field is called static (SMF) if its intensity or direction over time does not change [15,21,22]. MF can be generated either electrically using direct current or mechanically using permanent magnets. ...
Current scientific evidence on the influence of magnetic field on mammalian cell lines used for industrial production of biopharmaceuticals, on human cell lines and on potential cell lines for the biopharmaceutical production is presented in this review. A novel magnetic coupling induced agitation could be the best solution to eliminate sources of contamination in stirred tank bioreactors which is especially important for mammalian cell cultures. Nevertheless, the side effect of magnetically-coupled stirring mechanism is that cells are exposed to the generated magnetic field. The influence of magnetic field on biological systems has been investigated for several decades. The research continues nowadays as well, investigating the influence of various types of magnetic field in a variety of experimental setups. In the context of bioreactors, only the lower frequencies and intensities of the magnetic field are relevant.
... Many effects of weak ELF-MFs on cell proliferation have already been reported, and both inhibition and stimulation have been observed, depending on cell type and exposure conditions [41,42]. For each biological effect described, the heterogeneity of exposure conditions makes difficult to establish the importance of intensity, frequency and waveform. ...
Background
It has been demonstrated that relatively small variations of the parameters of exposure to extremely low frequency magnetic fields (ELF-MF) can change significantly the outcome of experiments. Hence, either in trying to elucidate if these fields are carcinogenic, or in exploring their possible therapeutic use, it is desirable to screen through as many different exposures as possible. The purpose of this work is to provide a proof of concept of how a recently reported system of coils allows testing different field exposures, in a single experiment.
Methods
Using a novel exposure system, we subjected a glioblastoma cancer cell line (U251) to three different time modulations of an ELF-MF at 60 different combinations of the alternated current (AC) and direct current (DC) components of the field. One of those three time modulations was also tested on another cell line, MDA-MB-231 (breast cancer). After exposure, proliferation was assessed by colorimetric assays.
Results
For the U251 cells, a total of 180 different exposures were tested in three different experiments. Depending on exposure modulation and AC field intensity (but, remarkably, not on DC intensity), we found the three possible outcomes: increase (14.3% above control, p < 0.01), decrease (16.6% below control, p < 0.001), and also no-effect on proliferation with respect to control. Only the time modulation that inhibited proliferation of U251 was also tested on MDA-MB-231 cells which, in contrast, showed no alteration of their proliferation on any of the 60 AC/DC field combinations tested.
Conclusions
We demonstrated, for the first time, the use of a novel system of coils for magnetobiology research, which allowed us to find that differences of only a few μT resulted in statistically different results. Not only does our study demonstrate the relevance of the time modulation and the importance of finely sweeping through the AC and DC amplitudes, but also, and most importantly, provides a proof of concept of a system that sensibly reduces the time and costs of screening.
Electronic supplementary material
The online version of this article (10.1186/s12885-019-5376-z) contains supplementary material, which is available to authorized users.
... Due to the public health concerns about the power lines, mobile phones, and cancer, DNA integrity is frequently studied in pulsed MFs (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. show that DNA synthesis in cells could be increased by time-varying MFs (Liboff et al. 1984). ...
The book summarizes the emerging topic about the effects of SMF on biological samples ranging from single molecules, subcellular compartments, and cells to whole organisms, as well as the potential application of SMF in clinical treatment of cancer and other diseases. With the development and growing popularity of modern appliances, including MRI in the hospitals, the potential impact of magnetic fields on human health is invoking increasing concerns. At the same time, SMF has been used in the clinical treatment of tumors and other diseases for decades. However, there are still some reservations and uncertainties about these treatments, which are largely due to the differential biological effects reported in the literature. These experimental inconsistencies are mainly caused by variations such as different magnetic field types, intensities, treatment time as well as biological samples examined. This volume will help clarify some dilemmas in this field and encourage further investigations in order to achieve a better understanding of the biological effects of SMF, aiming for a rational application of SMF in clinical therapy in the near future. The book is useful for scientists doctors, and students who are interested in magnetic fields and life sciences.
... Due to the public health concerns about the power lines, mobile phones and cancer, DNA integrity is frequently studied in pulsed magnetic fields (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. showed that DNA synthesis in cells could be increased by time varying magnetic fields (Liboff et al. 1984). ...
This chapter summarizes the effects of static magnetic fields (SMFs) on human bodies. Some commonly seen SMFs, such as the weak earth magnetic field that we are all exposed to, moderate to ultra-high field magnetic resonance imaging (MRI) in the hospitals and research institutes, as well as SMF-based magnetic therapies, which have a long history but still lack of solid explanation or sufficient experimentation from a scientific point of view. Magnetobiology and biomagnetism are also briefly discussed.
... Due to the public health concerns about the power lines, mobile phones and cancer, DNA integrity is frequently studied in pulsed magnetic fields (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. showed that DNA synthesis in cells could be increased by time varying magnetic fields (Liboff et al. 1984). ...
Static magnetic field (SMF) exists in nature widely and plays an essential role in the biological evolution. Due to the rapid development of superconducting technology, the intensity of SMF used for medical and academic research purposes has steadily increased in recent years. This chapter presents an overview on the biological effects induced by SMF with intensity ranging from mT to several Teslas (T). The effects of SMF on microorganisms are divided into six sections, including Cellular Growth and Viability, Morphological and Biochemical Modifications, Genotoxicity, Gene and Protein Expression, Magnetosome Formation Sensing Magnetic Field, and Application of SMF on Antibiotic Resistance, Fermentation and Wastewater Treatment. The effects of SMF on plants are divided into six sections, including Germination, Growth, Gravitropism, Photosynthesis, Redox Status, and Cryptochromes Sensing Magnetic Field. The effects of SMF on animals are divided into seven sections, including Caenorhabditis elegans, Insects, Helix pomatia, Aquatic Animals, Xenopus laevis, Mice and Rats, and Magnetic Sensing Protein in Animals. This chapter will be very helpful for better understanding the biological responses to SMF in different species and their underlying mechanism(s).
... Due to the public health concerns about the power lines, mobile phones and cancer, DNA integrity is frequently studied in pulsed magnetic fields (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. showed that DNA synthesis in cells could be increased by time varying magnetic fields (Liboff et al. 1984). ...
This chapter contains two parts. The first one is about parameters that influence the cellular effects of static magnetic fields (SMFs), including magnetic field intensity, cell types, cell densities as well as other cellular factors. The second part is about the various commonly seen cellular effects of SMFs, including cell orientation, proliferation, microtubule and cell division, actin, viability, attachment/adhesion, morphology, migration, membrane, cell cycle, chromosome and DNA, reactive oxygen species (ROS), adenosine triphosphate (ATP) as well as calcium. The focus of this chapter is on current evidence of SMFs on human cells and some animal cells, and especially on the potential factors that contributed to the different observations in individually reported studies.
... Due to the public health concerns about the power lines, mobile phones and cancer, DNA integrity is frequently studied in pulsed magnetic fields (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. showed that DNA synthesis in cells could be increased by time varying magnetic fields (Liboff et al. 1984). ...
This chapter summarizes different parameters of the magnetic fields, including magnetic field types, intensity, homogeneousness, field direction and exposure time. Various factors that contribute to the differential effects of magnetic fields on biological samples, which lead to the seemingly lack of consistencies in literature will be discussed.
... Due to the public health concerns about the power lines, mobile phones and cancer, DNA integrity is frequently studied in pulsed magnetic fields (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. showed that DNA synthesis in cells could be increased by time varying magnetic fields (Liboff et al. 1984). ...
This chapter lists current evidence (from molecular level, cellular level, animal level to patient level) and some potential mechanisms for the effects of static magnetic field (SMF) on cancer inhibition. The prospective applications of SMF alone or in combination with chemotherapy drugs, pulsed magnetic field (PMF) as well as radiotherapy in cancer treatment are also discussed.
... Due to the public health concerns about the power lines, mobile phones and cancer, DNA integrity is frequently studied in pulsed magnetic fields (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. showed that DNA synthesis in cells could be increased by time varying magnetic fields (Liboff et al. 1984). ...
Almost all types of life that have been investigated appropriately have shown some indication of biological response to magnetic fields. An alluring application of the information that already has been, and continues to be, collected describing how biological systems sense magnetic fields and transduce this information into physiological response is to treat human disease. Towards that goal, this chapter summarizes what has been learned about electromagnetic biosensing in a diverse set of organisms across several phyla and discusses how the underlying mechanisms apply (and in some cases, don’t apply) to humans.
... Due to the public health concerns about the power lines, mobile phones and cancer, DNA integrity is frequently studied in pulsed magnetic fields (McCann et al. 1993;Cridland et al. 1996;Olsson et al. 2001;Zhou et al. 2002;Williams et al. 2006;Ruiz-Gomez et al. 2010). As early as 1984, Liboff et al. showed that DNA synthesis in cells could be increased by time varying magnetic fields (Liboff et al. 1984). ...
This chapter provides an overview of the prospects of using electromagnetic fields (EMFs), with a specific focus on static magnetic fields (SMFs), for treatment of human disease. The information provided covers the underlying basis for widespread skepticism surrounding “magnetotherapy” – which in part is deserved based on overinflated claims by its practitioners over the past two centuries (or even longer). On the other hand, a compelling scientific foundation is in place to propel nascent efforts to use magnetotherapy from a questionable niche medical practice into the mainstream; a goal of this chapter is to provide a summary of this information using specific (but non-comprehensive) examples of human ailments that are expected (based on current information) to benefit from magnetic field treatment.
... There is evidence to suggest that static and extremely low frequency oscillatory magnetic fields (ELF) induce biologic effects even at a low MF intensity. Studies have found effects on calcium signaling (2,3), growth factor receptors (4), apoptosis (3,5), gene expression (6,7), cell proliferation (5,8), events involving generation of free radicals (9), and micronuclei induction (10). The modes of action remain unknown. ...
... Similar to our study, findings of investigators, were shown that biological effects of pulsed EMFs is more effectual than static EMFs [4,33]. In order to studies of pulsed EMFs, many records indicated that intensities of higher than 0.1 mT are more effective [33,34], whereas to generate differentiation by static MFs, stronger field intensity is require [7,35]. ...
The interaction between environment electromagnetic field (EMF) and cells can effect on various physiological processes. EMF as an external inducing factor, could effect on proliferation or differentiation of cells. The purpose of this study was to evaluate the influence of the electromagnetic field on the viability, proliferation and differentiation rate of bone marrow stem cells (BMSCs) to neuron. BMSCs were obtained from 42 adult male rats. The cells incubated and cultured in 96-wells and 6-wells plates and exposed to electromagnetic field (40 or 400μT) with a selected waveform: AC (alternative current), rectified half wave (RHW) and rectified full wave (RFW), for a week. To assess the viability and proliferation rate of treated cells, MTT assay was done, and then immunocytochemistery staining Neu N was used to evaluate cell differentiation to neuron. Results showed that EMF decreases the viability and proliferation in treated groups. But in AC group's reduction was significant. Minimum viability and proliferation rate was observed in RHW 400μT group compared with sham. Immunocytochemistry showed that EMF can induce BMSC differentiation into neuron in AC 400μT and RFW 400μT. Evidences of this research support the hypothesis that EMF can induce differentiation of BMSCs to neuron.
... 17,18 ELF biological effects at intensities below the ICNIRP standards have been shown to manifest a complex dependence upon biological and physical variables similar to MW effects. 2,15,[19][20][21][22][23][24] ELF and MW effects have been considered in the frames of the same physical models. [25][26][27][28][29][30][31] In many cases similar to mobile telephony it is difficult to discriminate the effects of exposure to ELF and MW because of additional ELF fields created by the MW sources. ...
Both potentially detrimental and beneficial responses of living cells to weak, nonthermal (NT) electromagnetic fields (EMF) have been observed. So far, focus has been on biological effects of extremely low frequency (ELF, 1–300 Hz) EMF and EMF of microwave frequency range (MW, 300 MHz to 300 GHz). There is strong evidence that biological effects of EMF are dependent on many physical, physiological, and genetic parameters, which must be controlled in replication studies. 1,2 Source of funding may also affect the data. 3 While a significant body of published data shows biological effects of NT MW, studies supported by the mobile industry are less likely to report these effects. 3,4 Failure to control important parameters in replicated studies along with reduced funding for EMF research in economically developed countries may be the main cause of the lack of accepted mechanism for biological effects of NT EMF. While funding for mechanistic EMF studies has been significantly reduced, the number of sources for ELF and MW exposure in everyday life is constantly growing. Moreover, some modern devices emit EMF in wide frequency ranges covering both ELF and MW. In particular, mobile phones not only expose the user to MW but also to ELF. 5–10 ITIS Foundation has performed detailed measurement of five mobile phones. 11 All five phones have shown the maximum B-field on the back side with extrapolated pulse heights between 35 and 75 μT. At this location, four out of the five tested phones exceeded the International Commission on Non-Ionizing Radiation Protection (ICNIRP) reference levels by several harmonics of 217 Hz. The maximum violation by a factor of two was detected at 650 Hz. The B-field on the front side of the phones tested is by a factor two to six times smaller and varies between eight and 20 μT. The maximum DC fields were detected near the phone loudspeaker and reached levels up to 20 mT (half of the corresponding ICNIRP reference level of 40 mT). Perentos et al. have recently measured and characterized the ELF magnetic field from several GSM handsets using different probes which covered frequency range from static magnetic fields (0 Hz) to 2 GHz. Peak ELF fields at the front sides of five commercial GSM phones were assessed and a maximum of 22.4 μT was reported. 12 The main ELF component at 217 Hz was about 1 μT at a distance of 3 cm from the front side of the handset. The overall pulse peak was 4.2 times greater than the 217 Hz component. The 217 Hz magnetic field decreased with distance and reached 0.3 μT at approximately 5 cm from the front handset site. The overall ELF pulse peak produced by all ELF components was 4.2 times greater than the 217 Hz component.
... Although a number of publications have indicated that EMR can produce stress response and affect apoptosis [39][40][41][42], negative results have been also reported depending on cell type and exposure characteristics [43,44]. In the present investigation, the detection of active caspase-3 along with an up-regulation of Bax and a down-regulation of Bcl-2 gives evidence that exposure to mobile phone for 60 days (SAR = 1.13 W/kg, 2 h/day) may disturb the intrinsic apoptotic machinery in rat brain tissue. ...
This study investigated the effect of exposure to mobile phone radiations on oxidative stress and apoptosis in brain of rats. Rats were allocated into six groups (three young and three adult). Groups 1 and 4 were not subjected to the radiation source and served as control groups. In groups 2 and 5, the mobile phones were only connected to the global system for mobile communication, while in groups 3 and 6, the option of calling was in use. Microwaves were generated by a mobile test phone (SAR = 1.13 W/kg) during 60 days (2 h/day). Significant increments in conjugated dienes, protein carbonyls, total oxidant status, and oxidative stress index along with a significant reduction of total antioxidant capacity levels were evident after exposure. Bax/Bcl-2 ratio, caspase-3 activity, and tumor necrosis factor-alpha level were enhanced, whereas no DNA fragmentation was detected. The relative brain weight of young rats was greatly affected, and histopathological examination reinforced the neuronal damage. The study highlights the detrimental effects of mobile phone radiations on brain during young and adult ages. The interaction of these radiations with brain is via dissipating its antioxidant status and/or triggering apoptotic cell death.
... Also, it was suggested that chronic exposure to the ELF-EMF could be involved in the development of some neurodegenerative diseases by production of reactive oxygen species [12]. Contrary, other researches identified no effects on the integrity of the DNA in the conditions of exposure to the electromagnetic fields [13][14][15][16][17]. ...
Extremely low frequency electromagnetic fields aren't considered as a real carcinogenic agent despite the fact that some studies have showed impairment of the DNA integrity in different cells lines. The aim of this study was evaluation of the late effects of a 100 Hz and 5.6 mT electromagnetic field, applied continuously or discontinuously, on the DNA integrity of Vero cells assessed by alkaline Comet assay and by cell cycle analysis. Normal Vero cells were exposed to extremely low frequency electromagnetic fields (100 Hz, 5.6 mT) for 45 minutes. The Comet assay and cell cycle analysis were performed 48 hours after the treatment.
Exposed samples presented an increase of the number of cells with high damaged DNA as compared with non-exposed cells. Quantitative evaluation of the comet assay showed a significantly (< 0.001) increase of the tail lengths, of the quantity of DNA in tail and of Olive tail moments, respectively. Cell cycle analysis showed an increase of the frequency of the cells in S phase, proving the occurrence of single strand breaks. The most probable mechanism of induction of the registered effects is the production of different types of reactive oxygen species.
The analysis of the registered comet indices and of cell cycle showed that extremely low frequency electromagnetic field of 100 Hz and 5.6 mT had a genotoxic impact on Vero cells.
... In this circumstance, the relative number of cells under risk (in terms of diseases and carcinogenesis) may be increased by exposure of 900 MHz radiation used in this study. However, there are a number of publications indicating that EMF can produce stress response and affect apoptosis (Lin et al., 1997;Junkersdorf et al., 2000;de Pomerai et al., 2000;Simko et al., 1998;Mangiacasale et al., 2001;Olsson et al., 2001;Belyaev et al., 2005). In this study, p53 status was also investigated but it was found that the radiation applied seems not to change it. ...
This study investigated the effects of cell phone exposure on the fatty acid composition in phospholipids, malondialdehyde concentration, p53 immune reactivity and histological structure of the rat brain. Sixteen Sprague-Dawley rats were divided into two groups of eight, sham and experimental (speech conditions). The rats were confined to Plexiglas cages, and cellular phone were placed 0.5 cm under the cages. For the experimental group, cellular phones were activated 20 minutes per day, 7 days a week, for 1 month. For the sham group, the cellular phones were placed beneath the cages with the phones turned off. The Whole Body Average SAR (rms) was 0.52 W/kg and 1 g averaged peak SAR (rms) 3.13 W/kg. The Mann-Whitney U-test was used for statistical comparisons of groups. Histological alteration and changes in brain phospholipid fatty acids composition were not observed in rat brains. Immunohistochemical staining of brain tissue shown that p53 immunoreactivity was not affected by cell phone exposure. Malondialdehyde concentration in exposed brains was significantly higher than sham (p < 0.05).
... Biochemical studies associated with ELF-MF include effects on gene expression [2], calcium signalling [3,4], enzymatic activity [5,6], growth-factor receptors [7,8], melatonin synthesis [9] and events involving generation of free radicals [10]. ELF-MF effects on cell proliferation have been described; both inhibition and stimulation have been observed, depending on cell type and exposure conditions [11][12][13]. While most studies were performed with humans, animals and with mammalian cell systems, plants and bacteria have also been used in the studies with ELF-MF [14][15][16][17]. ...
Extremely low-frequency magnetic fields (ELF-MF) have previously been shown to affect conformation of chromatin and cell proliferation. Possible genotoxic and carcinogenic effects of ELF-MF have also been discussed and tested. In this study, we analysed the effect of ELF-MF on chromatin conformation in E. coli GE499 cells by the anomalous viscosity time-dependence (AVTD) technique. Possible genotoxic effects of the specific combination of static and ELF-MF, which has been proven to affect chromatin conformation, were investigated by a clonogenic assay, by assessing cell-growth kinetics, and by analysis of the SOS-response by means of inducible recA-lacZ fusion-gene products and the β-galactosidase assay. The genotoxic agent nalidixic acid (NAL) was used as a positive control and in combination with ELF-MF. Nalidixic acid at 3-30μg/ml decreased the AVTD peaks and induced a cytotoxic effect. In contrast to NAL, ELF-MF fields increased AVTD, stimulated cell growth, and increased cloning efficiency. These effects depended on the frequency within the range of 7-11Hz. While NAL induced an SOS-response, exposure to ELF-MF did not induce the recA-lacZ fusion-gene product. Exposure to ELF-MF did not modify the genotoxic effects of NAL either. All together, the data show that ELF-MF, under specific conditions of exposure, acted as a non-toxic but cell-growth stimulating agent.
... Biochemical studies associated with ELF-MF include effects on gene expression [2], calcium signalling [3] [4], enzymatic activity [5] [6], growth-factor receptors [7] [8], melatonin synthesis [9] and events involving generation of free radicals [10]. ELF-MF effects on cell proliferation have been described; both inhibition and stimulation have been observed, depending on cell type and exposure conditions [11] [12] [13]. While most studies were performed with humans, animals and with mammalian cell systems, plants and bacteria have also been used in the studies with ELF-MF [14] [15] [16] [17]. ...
Extremely low frequency (ELF) magnetic fields have previously been shown to affect conformation of chromatin and cell proliferation. Possible genotoxic and carcinogenic effects of ELF have also been discussed and tested. In this study, we analyzed the effect of ELF on chromatin conformation in E. coli GE499 cells by the anomalous viscosity time dependence (AVTD) technique. Possible genotoxic ELF effects at the specific combination of static and ELF magnetic fields, that has been proven to have effects on chromatin conformation, were investigated by clonogenic assay, cell growth kinetics, and analysis of SOS-response using inducible recA-lacZ fusion and the β-galactosidase assay. Genotoxic agent nalidixic acid (NAL) was used as positive control and in combination with ELF. Nalidixic acid at 3-30μg/ml decreased the AVTD peaks and induced cytotoxic effect. In contrast to NAL, ELF increased AVTD, stimulated cell growth, and increased cloning efficiency. These effects depended on frequency within the frequency range of 7-11Hz. While NAL induced SOS response, ELF exposure did not induce the recA-lacZ fusion. Exposure to ELF did not modify the genotoxic effects of NAL either. All together, the data show that ELF, under specific conditions of exposure, acted as nontoxic but cell growth stimulating agent.
... In this circumstance, the relative number of cells under risk (in terms of diseases and carcinogenesis) may be increased by exposure of 900 MHz radiation used in this study. However, there are a number of publications indicating that EMF can produce stress response and affect apoptosis (Lin et al., 1997;Junkersdorf et al., 2000;de Pomerai et al., 2000;Simko et al., 1998;Mangiacasale et al., 2001;Olsson et al., 2001;Belyaev et al., 2005). In this study, p53 status was also investigated but it was found that the radiation applied seems not to change it. ...
The aim of this study was to investigate the effects of mobile phone exposure on glial cells in brain. The study carried out on 31 Wistar Albino adult male rats. The rat heads in a carousel exposed to 900 MHz microwave. For the study group (n:14), rats exposed to the radiation 2 h per day (7 days in a week) for 10 months. For the sham group (n:7), rats were placed into the carousel and the same procedure was applied except that the generator was turned off. For the cage control (n:10), nothing applied to rats in this group. In this study, rats were euthanized after 10 months of exposure periods and brains were removed. Brain tissues were immunohistochemically stained for the active (cleaved) caspase-3, which is a well-known apoptosis marker, and p53. The expression of the proteins was evaluated by a semi-quantitative scoring system. However, total antioxidative capacity (TAC), catalase, total oxidant status (TOS), and oxidative stress index were measured in rat brain. Final score for apoptosis in the exposed group was significantly lower than the sham (p < 0.001) and the cage control groups (p < 0.01). p53 was not significantly changed by the exposure (p > 0.05). The total antioxidant capacity and catalase in the experimental group was found higher than that in the sham group (p < 0.001, p < 0.05). In terms of the TOS and oxidative stress index, there was no statistically significant difference between exposure and sham groups (p > 0.05). In conclusion, the final score for apoptosis, total antioxidant capacity and catalase in rat brain might be altered by 900 MHz radiation produced by a generator to represent exposure of global systems for mobile communication (GSM) cellular phones.
... There is evidence to suggest that static and extremely low frequency oscillatory magnetic fields (ELF) induce biologic effects even at a low MF intensity. Studies have found effects on calcium signaling (2,3), growth factor receptors (4), apoptosis (3,5), gene expression (6,7), cell proliferation (5,8), events involving generation of free radicals (9), and micronuclei induction (10). The modes of action remain unknown. ...
Much attention is being paid to the biologic effects of magnetic fields (MFs). Although MFs enhance tumorigenesis, they are neither mutagenic nor tumorigenic. The mechanism of their tumorigenic effect has not been elucidated.
To investigate the effect of MFs on apoptosis in HL-60 cells, we exposed the cells to static MFs of 6 mT generated by a magnetic disk of known intensity. Apoptosis was triggered by the DNA topoisomerase I inhibitor, camptothecin (CPT). Activation of caspases in situ using the fluorochrome-labeled inhibitor (FLICA) method and determination of plasma membrane integrity by excluding propidium iodide (PI) were measured by both laser scanning cytometry (LSC) and flow cytometry (FC). LSC and FC identified cells at three sequential stages of their demise: early apoptosis (cells with activated caspases and PI negative); late apoptosis (cells with activated caspases but unable to exclude PI); secondary necrosis (cells with apoptotic morphology no longer stained with FLICA, not excluding PI).
MF alone did not induce any apoptogenic or necrogenic effect. CPT exposure led to the sequential appearance of apoptotic cells. In the presence of CPT and MF, the overall proportion of cells undergoing apoptosis was not significantly changed. However, we consistently observed a significant increase in the frequency of late apoptotic/necrotic cells when compared with samples treated with CPT alone (P < 0.001), as well as a decrease in the percentage of early apoptotic cells (P = 0.013). The data obtained by FC and LSC were consistent with each other, showing a similar phenomenon.
Whereas MF alone or with CPT did not affect overall cell viability, it accelerated the rate of cell transition from apoptosis to secondary necrosis after induction of apoptosis by the DNA-damaging agent, CPT. Modulation of the kinetics of the transition from apoptosis to secondary necrosis by MF in vivo may play a role in inflammation and tumorigenesis.
... Most studies support the general conclusion that ELF-MF do not disrupt the organization of genes or genomes [2][3][4] (reviewed in [5]), although mutagenic effects have been described in cultured human cell lines exposed to high intensities [6,7]. However, ELF-MF do influence control of proliferation in many normal and transformed cell lines [1,8]. ...
We have investigated the sensitivity of pre-implantation embryos obtained by natural breeding (NB) or in vitro fertilization (IVF) to extremely low-frequency magnetic fields (ELF-MF). Fertilized eggs obtained by NB were removed from mothers 12h after mating and cultured in vitro for 5 days under continuous ELF-MF exposure (constant strength of 50Hz and various intensities, i.e. 60, 120 and 220 microT). Alternatively, zygotes obtained by IVF were subjected to ELF-MF exposure (50Hz, 60 microT), starting 12h after IVF for 5 days. We found that ELF-MF exposure causes a small yet significant (P<0.05) decrease in the survival rate of NB-derived embryos at the latest stages of pre-implantation development, i.e. the eight cell-to-blastocyst transition. In embryos exposed to the highest field intensity (220 microT), the effect became apparent somewhat earlier. When IVF-derived embryos were exposed to ELF-MF, the reduction in the rate of embryo survival was more pronounced and the difference from controls was more significant (P<0.01). Moreover, the decreased survival rate in IVF embryos became apparent as early as the first cleavage and persisted throughout pre-implantation. These results suggest that IVF-derived embryos are more sensitive than NB-generated embryos to ELF-MF, and that this sensitivity occurs earlier in development.
As the basic unit of living organisms, the cell is where the macroscopic phenomenon meets the microscopic mechanisms. The focus of this chapter is on current evidence of SMFs on human cells and some animal cells, with a special focus on the factors that contributed to the seemingly inconsistent experimental results in the literature. We summarize cellular effects of static magnetic fields (SMFs), including cell orientation, proliferation, microtubule and cell division, actin, viability, attachment/adhesion, morphology, migration, membrane, cell cycle, DNA, reactive oxygen species (ROS), adenosine triphosphate (ATP) as well as calcium. Although it is obvious that for each aspect, the experimental results are highly variable, there are some effects that have clear physical explanations and confirmed phenomenon. For example, magnetic properties of the cells and their subcellular structures are determined by their compositions and structures, which will directly affect their orientation in high SMFs. However, there are still many unanswered questions. For example, the effects of SMFs on cellular ROS have been reported by numerous studies, but the effects are highly variable in different magnetic settings and sample types and there are still not clear physical explanations. Although the upscaling of the mechanisms from cells to tissues and living organisms is still a huge challenge, given the essential roles of cells in various living organisms, they are no doubt the central hub for researchers in this field to unravel the underlying mechanism and explore the future application of various SMFs.
The aim of this work was to validate the usefulness of
an Extremely Low Frequency (ELF) magnetic field exposure
system with a magnetotherapy device of common use in clinical
practice that generates Biphasic Magnetic Pulses (BMP), in order
to study the effects of the BMP on the proliferation of Human
Dermal Fibroblasts (HDF). In that regard, HDF were exposed 2h in
the morning and 2h in the afternoon for 2 days to BMP of 1.41mT
peak value at 5, 10, 25Hz continuous and 50Hz intermittent (2s on/
1.5s off). MTT assay was performed to assess proliferation. The
10Hz BMP showed a significant decrease in proliferation of 6.6%
(p = 0.001) with respect to controls, but no significant changes in
proliferation were seen with the other BMP. In order to analyze
whether these results could be related to the exposure protocol, a
50Hz power line intermittent signal (1s on/ 1s off) was generated
and tested but exposure time was increased to 48h to cover the
complete cells doubling time. A significant increase in proliferation
of 9% (p < 0.001) was found in this case.
The results validate the in vitro exposure system for its use with
the BMP. Though the MTT proliferation assay alone is not enough
to make definitive claims, the results might indicate that the
exposure time plays a key role in the outcome of the experiments.
Therefore, special attention should be paid to the exposure time on
in vitro protocols and how they relate to in vivo experiments and
current treatments.
The mechanism underlying the biological effects caused by an extremely low-frequency electromagnetic field (ELF-EMF) is still unclear. Previously, we found that L-type calcium channel and sphingosine kinase 1 (SK1) were involved in 50-Hz MF exposure-induced cell proliferation. In the present study, the role of intracellular Ca2+ and signal molecules related to SK1 in cell proliferation induced by 50-Hz MF was investigated in human amniotic epithelial (FL) cells. Results showed that the intracellular Ca2+ chelator, BAPTA, could completely inhibit 50-Hz MF-induced cell proliferation, whereas NIF, the inhibitor of L-type calcium channel, only partly blocked it. When cells were cultured in calcium-free medium, MF exposure also increased intracellular Ca2+, activated SK1 and promoted cell proliferation although all of those increasing levels were lower than those in complete medium. Moreover, MF-activated SK1 could be completely inhibited by BAPTA, and MF-induced cell proliferation was abolished by SKI II, the specific inhibitor of SK1. Additionally, a 50-Hz MF exposure did not affect the activation of ERK and PKCα under the condition of calcium-free medium, but activated the Akt, which could be precluded entirely by BAPTA, but not be inhibited by NIF. Treatment of FL cells with LY294002, the inhibitor of Akt, could delete the MF-induced SK1 activation under the condition of calcium-free medium. Based on the data from the present experiment, it is concluded that endogenous Ca2+ release was involved in 50-Hz MF-induced cell proliferation via Akt-SK1 signal cascade.
ELF-EMF, one of environmental factors, widely exists in natural world. However, the interaction between ELF-EMF and biological materials is usually neglected in the field of biological research. Very little efforts have been put forth in studying the relationship of bacteria and ELF-EMF. Here we investigated the stress reaction of Escherichia coli, Salmonella, Bacillus subtilis and OP50 cells to the stimulation of ELF-EMF. The results showed that the ELF-EMF treatment significantly decreased the colony forming efficiency of Escherichia coli, Bacillus subtilis and OP50 and this effect may be a kind of gene-dependence effect. In addition, this study also indicated that ELF-EMF could cause significant DNA damaged. Salmonella's DNA was serious damaged in 50 Hz, 3 mT for 18 and 24 h. Moreover, short time continual stimulated, for instance, 10 and 14 h continual stimulated also caused DNA chain's broken to some extent. Continual stimulated and passage's result approved that this kind of DNA damaged could be decreased by serial passage and the damaged cause by ELF-EMF exposure might be a kind of gene toxic.
The electromagnetic frequencies that induced normally in human body, comprise from the action potentials of nerves, heart tissue and skeletal muscles, were categorized in the range of extremely low frequencies. With increase in developed devices that produced or induced electromagnetic fields, human anxiety about effects of these fields on normal or abnormal body cell proliferation was increased. Experiments provided on cells and tissues indicated that electromagnetic fields at different strengths and frequencies had altered effects on cell proliferation and differentiation. Thus, this systematic review analyzed different findings and focused on extremely low frequency electromagnetic field effects on cell proliferation. The observations reinforced pulsed extremely low frequency electromagnetic fields in frequencies between 15-60 Hz had more effects on cell proliferation and less effect on cell differentiation. This effect was related to multisession irradiation or cells long term exposure. Extremely low frequency electromagnetic fields can use as a safe stimulator for cell proliferation and repair of tissue damages.
Extremely low frequency electromagnetic field (ELF-EMF) exposure is attracting increased attention as a possible disease-inducing factor. The in vivo effects of short-term and long-term ELF-EMF exposure on male Drosophila melanogaster were studied using transcriptomic analysis for preliminary screening and QRT-PCR for further verification. Transcriptomic analysis indicated that 439 genes were up-regulated and 874 genes were down-regulated following short-term exposures and that 514 genes were up-regulated and 1206 genes were down-regulated following long-term exposures (expression >2- or <0.5-fold, respectively). In addition, there're 238 up-regulated genes and 598 down-regulated genes in the intersection of short-term and long-term exposure (expression >2- or <0.5-fold). The DEGs (Differentially Expressed Genes) in D. melanogaster following short-term exposures were involved in metabolic processes, cytoskeletal organization, mitotic spindle organization, cell death, protein modification and proteolysis. Long-term exposure let to changes in expression of genes involved in metabolic processes, response to stress, mitotic spindle organization, aging, cell death and cellular respiration. In the intersection of short-term and long-term exposure, a series of DEGs were related to apoptosis, aging, immunological stress and reproduction. To check the ELF-EMF effects on reproduction, some experiments on male reproduction ability were performed. Their results indicated that short-term ELF-EMF exposure may decrease the reproductive ability of males, but long-term exposures had no effect on reproductive ability. Down-regulation of ark gene in the exposed males suggests that the decrease in reproductive capacity may be induced by the effects of ELF-EMF exposure on spermatogenesis through the caspase pathway. QRT-PCR analysis confirmed that jra, ark and decay genes were down regulated in males exposed for 1 Generation (1 G) and 72h, which suggests that apoptosis may be inhibited in vivo. ELF-EMF exposure may have accelerated cell senescence, as suggested by the down-regulation of both cat and jra genes and the up-regulation of hsp22 gene. Up-regulation of totA and hsp22 genes during exposure suggests that exposed flies might induce an in vivo immune response to counter the adverse effects encountered during ELF-EMF exposure. Down-regulation of cat genes suggests that the partial oxidative protection system might be restrained, especially during short-term exposures. This study demonstrates the bioeffects of ELF-EMF exposure and provides evidence for understanding the in vivo mechanisms of ELF-EMF exposure on male D. melanogaster.
This study was undertaken to investigate whether low frequency magnetic fields can affect the characteristic of cancer cells. To achieve this, HL-60cells were exposed to 20mT, 50Hz sinusoidal magnetic field and the cell viability, cell cycle phase distribution, DNA ladder and apoptotic morphology between control and exposed cells were examined. The results demonstrated that magnetic field had pronounced inhibition effects on cell growth, and small but significant changes in cell cycle phase can be observed. Internucleosomal DNA fragmentation and morphological changes after exposure indicate that the magnetic field induces apoptosis in HL-60cells. The results also indicate that the growth-inhibitory property of MF on HL-60cell growth was mainly due to the induction of apoptosis.
In this study, we evaluated the ability of 8.8 mT static magnetic fields (SMF) to enhance the in vitro action of a chemotherapeutic agent, paclitaxel, against K562 human leukemia cells. We analyzed the cell proliferation, cell cycle distribution, DNA damage and alteration of cell surface and cell organelle ultrastructure after K562 cells were exposed to paclitaxel in the presence or absence of 8.8 mT SMF. The results showed that in the presence of SMF, the efficient concentration of paclitaxel on K562 cells was decreased from 50 to 10 ng/ml. Cell cycle analysis indicated that K562 cells treated with SMF plus paclitaxel were arrested at the G2 phase, which was mainly induced by paclitaxel. Through comet assay, we found that the cell cycle arrest effect of paclitaxel with or without SMF on K562 cells was correlated with DNA damage. The results of atomic force microscopy and transmission electron microscopy observation showed that the cell ultrastructure was altered in the group treated with the combination of SMF and paclitaxel, holes and protuberances were observed, and vacuoles in cytoplasm were augmented. Our data indicated that the potency of the combination of SMF and paclitaxel was greater than that of SMF or paclitaxel alone on K562 cells, and these effects were correlated with DNA damage induced by SMF and paclitaxel. Therefore, the alteration of cell membrane permeability may be one important mechanism underlying the effects of SMF and paclitaxel on K562 cells.
In this work the retardation of Ehrlich tumor growth implanted in mice was studied by employing 4.5 Hz magnetic field. Eighty female Balb/c mice were used, twenty as normal group; the other sixty mice were inoculated with Ehrlich tumor, then they were divided equally into three groups namely A, B and C. Group A (control group) animals were not exposed to the magnetic field. The tumors in the thigh of the animals of group B were exposed to 4.5 Hz, 2 Gauss square wave magnetic field by using a small solenoid connected to a power square wave generator. Group C animals were whole body exposed inside a large solenoid to 4.5 Hz, 2 Gauss square wave magnetic field. Both groups B and C were exposed for a period of 2 weeks at a rate 2 hours per day. Tumor volume, survival period, histological examination and dielectric relaxation of the tumor were measured to investigate the activity of the tumor of the exposed and the unexposed animals. The results indicated that exposing the tumor tissue to 4.5 Hz square wave magnetic field for 2 weeks at a rate 2 hours/day inhibited tumor growth and increased the survival period of the animals. However, group B showed more improvements than did group C. This was attributed to some distortions in the square waveform in the large solenoid (group C). By comparing data from current and previous work, it was concluded that the use of magnetic waves showed better results over previously published work using amplitude modulated electromagnetic waves with the same frequency.
Effects of magnetic fields (MFs) on cancer cells may depend on cell type and exposure conditions. Gene expression levels are different among cancer cells. However, the effect of MFs on cancer cells with different gene expressions is still unclear. In this study, the cancer cell lines BGC-823, MKN-45, MKN-28, A549, SPC-A1, and LOVO were exposed to a low-frequency MF. Specific parameters of MFs were determined. Furthermore, the potential of the MF to influence cancer cell growth with midkine (MK) expression was evaluated. Cell proliferation and cell cycle were detected using the CCK-8 assay and flow cytometry. Cell ultrastructure was observed by transmission electron microscopy. BGC-823 cells with over-expression of MK (BGC-MK cells) and stanniocalcin-1 were generated by plasmid construction and transfection. Results showed that exposure to a 0.4-T, 7.5 Hz MF inhibited the proliferation of BGC-823, MKN-28, A549, and LOVO cells, but not MKN-45 and SPC-A1 cells. Moreover, the inhibitory effect of the MF on BGC-MK cells was lower (12.3%) than that of BGC-823 cells (20.3%). Analysis of the cell cycle showed that exposure to the MF led to a significant increase in the S phase in BGC-823 cells, but not in BGC-MK cells. In addition, organelle morphology was modified in BGC-823 cells exposed to the MF. These results suggest that exposure to a 0.4-T, 7.5 Hz MF could inhibit tumor cell proliferation and disturb the cell cycle. The alteration of MK expression in cancer cells may be related to the inhibitory effect of the MF on these cells.
In recent years, there has been increasing evidence that extremely low frequency magnetic fields might be linked to tumours, particularly with childhood leukaemia. In the same period, the role of apoptosis in the tumour process has also gained increasing importance. It is the purpose of this review to describe the apoptotic process, discuss selected papers in which apoptosis is examined in cells exposed to magnetic fields and describe the possible biophysical mechanisms responsible for changes in the apoptotic process in exposed cells. Despite some differences, as a whole, the literature seems to demonstrate that magnetic fields induce changes in apoptosis in cells exposed to different experimental protocols. In addition, the important role of ions, particularly of Ca2+, in the apoptotic process is also discussed, and one possible model for magnetic field action on apoptosis that brings together experimental observations of different nature is suggested and discussed.
An increasing number of investigations has shown that weak ELF alternating (AC) magnetic fields (MF) affect biological systems (Goodman et al., 1995). The effects of AC fields have been observed within relatively narrow frequency bands at so-called resonance frequencies (Smith et al., 1987, Belyaev et al., 1994; Blackman et al., 1994; Prato et al., 1995). Relatively narrow windows were also observed in the amplitude dependencies of the AC field effects (Liboff et al., 1987; Lednev, 1991; Blackman et al., 1994; Prato et al., 1995). It has been found by Blackman et al.(1985) that the ambient static magnetic fields (DC) can significantly influence the effects of alternating magnetic fields. The importance of static MF for the ELF effects was confirmed in several papers (Lednev, 1991; Belyaev et al., 1994; Blackman et al., 1994; Fitzsimmons et al., 1994; Prato et al., 1995). Therefore, the effects of weak ELF are observed under specific combinations of DC/AC exposure. Several physical mechanisms were suggested to explain these observations (Liboff et al., 1987; Chiabrera et al., 1991; Lednev, 1991; Belyaev et al., 1994; Binhi, 1997). The dependence of ELF effects on some physiological factors such as concentration of ions during exposure of cells has been shown (Smith et al., 1987; Karabakhtsian et al., 1994).
Although extremely low frequency (ELF, <300 Hz) magnetic fields exert a variety of biological effects, the magnetic field sensing/transduction mechanism (or mechanisms) remain to be identified. Using the well-defined inhibitory effects that magnetic fields have on opioid peptide mediated antinociception or "analgesial' in the land snail Cepaea nemoralis, we show that these actions only occur for certain frequency and amplitude combinations of time-varying sinusoidal magnetic fields in a manner consistent with a direct influence of these fields. We exposed snails with augmented opioid activity to ELF magnetic fields, which were varied in both amplitude and frequency, along with a parallel static magnetic field, When the peak amplitude (0-547 mu T) of a magnetic field of 60 Hz was varied systematically, we observed a nonlinear response, i.e., a nonlinear reduction in analgesia as measured by the latency of a defined response by the snails to a thermal stimulus. When frequency (10-240 Hz) was varied, keeping the amplitude constant (141 mu T), we saw significant inhibitory effects between 30 and 35 Hz, 60 and 90 Hz and at 120 and 240 Hz. Finally, when the static field was varied but the amplitude and frequency of the time-varying field were held constant, we observed significant inhibition at almost all amplitudes. This amplitude/frequency "resonance-like" dependence of the magnetic field effects suggests that the mechanism (or mechanisms) of response to weak ELF fields likely involves a direct magnetic field detection mechanism rather than an induced current phenomenon. We examined the implications of our findings for several models proposed for the direct sensing of ELF magnetic fields.
Two independent laboratories have demonstrated that electromagnetic radiation at specific frequencies can cause a change in the efflux of calcium ions from brain tissue in vitro. In a local geomagnetic field (LGF) at a density of 38 microTesla (microT), 15- and 45-Hz electromagnetic signals (40 Vp-p/m in air) have been shown to induce a change in the efflux of calcium ions from the exposed tissues, whereas 1- and 30-Hz signals do not. We now show that the effective 15-Hz signal can be rendered ineffective when the LGF is reduced to 19 microT with Helmholtz coils. In addition, the ineffective 30-Hz signal becomes effective when the LGF is changed to +/- 25.3 microT or to +/- 76 microT. These results demonstrate that the net intensity of the LGF is an important variable. The results appear to describe a resonance-like relationship in which the frequency of the electromagnetic field that can induce a change in efflux is proportional to a product of LGF density and an index, 2n + 1, where n = 0,1. These phenomenological findings may provide a basis for evaluating the apparent lack of reproducibility of biological effects caused by low-intensity extremely-low-frequency (ELF) electromagnetic signals. In future investigations of this phenomenon, the LGF vector should be explicitly described. If the underlying mechanism involves a general property of tissue, then research conducted in the ambient electromagnetic environment (50/60 Hz) may be subjected to unnoticed and uncontrolled influences, depending on the density of the LGF.
Blastogenesis of human peripheral blood lymphocytes stimulated in vitro by non-specific mitogens (PHA, ConA, PWM) upon exposure to extremely low frequency EMF has been studied. Different frequencies of square waveforms have been used. PHA-stimulation resulted in strong inhibitions as measured by [3H]thymidine incorporation. A frequency window (3-50 Hz) within which ConA-induced blastogenesis was significantly inhibited has been individuated. The mitogenic effect of PWM was significantly affected only at 3 Hz.
Here, we present evidence that exposure of B-lineage lymphoid cells to low energy electromagnetic fields (EMF) stimulates the protein tyrosine kinases Lyn and Syk, results in tyrosine phosphorylation of multiple electrophoretically distinct substrates, and leads to downstream activation of protein kinase C (PKC). EMF exposure enhances protein tyrosine phosphorylation in Syk deficient but not in Lyn-deficient B-lineage lymphoid cells and stimulates Lyn kinase activity in wild-type as well as Syk-deficient B-lineage lymphoid cells. These results indicate that activation of Lyn kinase is sufficient and mandatory for EMF-induced tyrosine phosphorylation in B-lineage lymphoid cells. The PKC activity increases later than the Lyn activity and pretreatment with the PTK inhibitors genistein or herbimycin A abrogates the EMF-induced PKC signal. Thus, stimulation of Lyn is a proximal and mandatory step in EMF-induced activation of PKC in B-lineage lymphoid cells. Our observations prompt the hypothesis that a delicate growth regulatory balance might be altered in B-lineage lymphoid cells by EMF-induced activation of Lyn.
Although extremely low frequency (ELF, < 300 Hz) magnetic fields exert a variety of biological effects, the magnetic field sensing/transduction mechanism (or mechanisms) remain to be identified. Using the well-defined inhibitory effects that magnetic fields have on opioid peptide mediated antinociception or "analgesia" in the land snail Cepaea nemoralis, we show that these actions only occur for certain frequency and amplitude combinations of time-varying sinusoidal magnetic fields in a manner consistent with a direct influence of these fields. We exposed snails with augmented opioid activity to ELF magnetic fields, which were varied in both amplitude and frequency, along with a parallel static magnetic field. When the peak amplitude (0-547 microT) of a magnetic field of 60 Hz was varied systematically, we observed a nonlinear response, i.e., a nonlinear reduction in analgesia as measured by the latency of a defined response by the snails to a thermal stimulus. When frequency (10-240 Hz) was varied, keeping the amplitude constant (141 microT), we saw significant inhibitory effects between 30 and 35 Hz, 60 and 90 Hz and at 120 and 240 Hz. Finally, when the static field was varied but the amplitude and frequency of the time-varying field were held constant, we observed significant inhibition at almost all amplitudes. This amplitude/frequency "resonance-like" dependence of the magnetic field effects suggests that the mechanism (or mechanisms) of response to weak ELF fields likely involves a direct magnetic field detection mechanism rather than an induced current phenomenon. We examined the implications of our findings for several models proposed for the direct sensing of ELF magnetic fields.
It has been shown recently that apoptotic degradation of genomic DNA in mammalian cells starts by excision of large DNA fragments
ranging in size from 50 kilobases to more then 300 kilobases. Although it was suggested that the above fragments could represent
chromosomal DNA loops, the supposition was not supported by direct experimental evidence. In present work, we have studied
the specificity of nucleolar and euchromatic gene long-range fragmentation in mouse and human cells triggered to undergo apoptosis
either by tumor necrosis factor or by serum deprivation. Separation of the excised large DNA fragments by pulsed field gel
electrophoresis followed by Southern analysis has demonstrated that in all cases studied the above fragmentation proceeds
in a specific way. Furthermore, the patterns of DNA long-range fragmentation in the cells undergoing apoptosis were indistinguishable
from the patterns of DNA cleavage into chromosomal loops by the high salt-insoluble topoisomerase II of the nuclear matrix.
These results suggest the conclusion that apoptotic degradation of chromosomal DNA starts by excision of DNA loops and their
oligomers.
Evidence suggests that cell processes can be influenced by weak electromagnetic fields (EMFs). EMFs appear to represent a global interference or stress to which a cell can adapt without catastrophic consequences. There may be exceptions to this observation, however, such as the putative role of EMFs as promoters in the presence of a primary tumor initiator. The nature of the response suggests that the cell is viewing EMFs as it would another subtle environmental change. The age and state of the cell can profoundly affect the EMF bioresponse. There is no evidence that direct posttranscription effects occur as a result of EMF exposure. Although transcription alterations occur, no apparent disruption in routine physiological processes such as growth and division is immediately evident. What is usually observed is a transient perturbation followed by an adjustment by the normal homeostatic machinery of the cells. DNA does not appear to be significantly altered by EMF. If EMF exposure is associated with an increased risk of cancer, the paucity of genotoxic effects would support the suggestion that the fields act in tumor promotion rather than initiation. The site(s) and mechanisms of interaction remain to be elaborated. Although there are numerous studies and hypotheses that suggest the membrane represents the primary site of interaction, there are also several different studies showing that in vitro systems, including cell-free systems, are responsive to EMFs. The debate about potential hazards or therapeutic value of weak electromagnetic fields will continue until the mechanism of interaction has been clarified.
There is growing public concern about the possible health risks, particularly increased cancer risks of exposure to magnetic fields (MF) associated with power distribution systems. Recently, we have started a series of animal studies to investigate this issue, using the DMBA (7,12-dimethylbenz[a]anthracene) model of breast cancer in female rats. In the present study, female rats were chronically exposed to a 50-Hz, 50 microTesla (microT) MF with or without DMBA treatment. Because alterations in circulating levels of the pineal hormone melatonin and impaired immune system functions have been involved in breast cancer growth, and both melatonin and immune system are thought to be targets for MF-effects, serum melatonin and the proliferative capacity of splenic lymphocytes were determined in MF-exposed and sham-exposed rats. For this purpose, 216 female Sprague-Dawley rats were divided into four groups. Two of the groups (with 99 animals each) received oral applications of DMBA and were either sham-exposed or exposed in a 50-Hz, 50 microT MF for 24 h/day 7 days/week for a period of 91 days. The other two groups (9 animals each) were either sham-exposed or MF-exposed without DMBA treatment. The exposure chambers and all other environmental factors were identical for MF-exposed and sham-exposed animals. The DMBA-treated animals were palpated once weekly to assess the development of mammary tumors. At the end of the three-month period of MF exposure, the number and size of mammary tumors was determined by autopsy. In controls, DMBA induced tumors in approximately 55% of the animals within the 3 month period of sham-exposure. Already 8 weeks after DMBA application, the MF-exposed group exhibited significantly more tumors than sham-exposed animals. At time of autopsy, significantly more MF-exposed DMBA-treated rats exhibited macroscopically visible mammary tumors than DMBA-treated controls, thus indicating that MF exposure enhances the development and growth of cancers in this model. Comparison of the data from 50 microT with recent data from other flux densities indicated that long-term MF exposure of DMBA-treated rats increases the incidence of palpable and/or macroscopically visible mammary tumors in a highly dose-related fashion. Determination of nocturnal serum melatonin after 9 and 12 weeks of exposure at 50 microT did not yield significant differences between MF-exposed rats and sham-exposed controls, whereas a marked suppression of T cell proliferative capacity was seen in MF exposed rats. The data add further evidence to the hypothesis that hormone-dependent tissues such as breast might be particularly sensitive to MF-effects and indicate that immune system depression is involved in the increased breast cancer growth observed in MF exposed rats.
Topoisomerase I-directed agents are now in Phase I and II clinical trials and show great promise as potentially important agents for cancer chemotherapy. Because of their mechanism of action they may also be potential mutagens; however, their mutagenicity and oncogenicity still remain to be elucidated. We have previously shown that VP-16, a topoisomerase II-directed agent, induces sister chromatid exchanges and gene deletions and/or rearrangements in vitro. These observations may account for both the cytotoxic effects of topoisomerase II-directed agents as well as their recently reported leukemonogenic potential. To evaluate the potential mutagenicity of topoisomerase I-directed drugs, we measured mutant frequencies at the hypoxanthine phosphoribosyl transferase locus of the V79 Chinese hamster fibroblast cell line treated with the topoisomerase I-directed drugs camptothecin and topotecan, and compared these results with mutant frequency obtained with the topoisomerase II-directed drug VP-16 and an alkylating agent, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). All of these drugs showed a dose-dependent increase in mutant frequency at the hypoxanthine phosphoribosyl transferase locus. At a dose producing approximately 30% survival, VP-16, camptothecin, and topotecan induced mutant frequencies of 11.3 x 10(-6), 4.9 x 10(-6), and 2.7 x 10(-6), respectively, whereas the spontaneous mutant frequency at this locus was 0.3 x 10(-6). In contrast, the alkylating agent MNNG produced a mutant frequency of 562 x 10(-6) at 26% survival dose. The molar mutagenic potencies, expressed as mutant frequency/mol-h exposure, for VP-16, camptothecin, topotecan, and MNNG at approximately 30% survival dose were 0.9, 8.2, 2.3, and 56.8, respectively. On Southern blot analysis after EcoRI, PstI, or HindIII digestion, 6 of 12 independent thioguanine-resistant mutants induced by topotecan showed gene deletions or rearrangements. In contrast, five of five independent spontaneous mutants and six of six independent mutants induced by MNNG demonstrated the same restriction pattern as the parental V79 cells. These results indicate that the mutant frequency and the mutagenic potential of topoisomerase I and II active agents are quantitatively similar. The results further demonstrate that topoisomerase I and II active agents introduce mutations characterized by gene deletions and rearrangements, whereas spontaneous mutations and those induced by alkylating agents appeared to be more characteristically associated with point mutations. Thus, clinical use of the topoisomerase I and II active agents is expected to cause similar mutagenic effects that could potentially lead to secondary malignancies.
In vitro exposure to low-energy, combined magnetic fields (CMF) increased the release of insulin-like growth factor (IGF)-II from human TE-85 osteosarcoma cells. Short-term CMF exposure of only 10 min increased IGF-II levels in conditioned medium 1 h post CMF exposure. IGF-II levels were measured with a radioreceptor assay using H-35 cells that contain abundant IGF-II but not IGF-I receptors. This assay also uses a recently validated BioGel P-10 acid gel filtration method to remove IGF binding protein before quantitation of either IGF-I or IGF-II. In addition to an increase in IGF-II levels, DNA synthesis, as an index of cell proliferation, was increased during the 24-h period post CMF exposure. A monoclonal antibody against IGF-II blocked the increase in cell proliferation following CMF exposure, whereas a control monoclonal antibody against osteocalcin did not attenuate the mitogenic action of CMF exposure. The effect of CMF exposure to increase both cell proliferation and IGF-II was cell-density depend...
The method of anomalous viscosity time dependences was used to investigate the influence of extremely low frequency alternating and static magnetic field on the genome conformational state of E.coli K12 AB1157 cells. The physical model was developed on the base of obtained results to describe effects of weak static and alternating magnetic fields on the living cells. In this model the high frequency oscillations of a charged nucleoid are considered with a classical approach. The wave-like dependence of maximum effect on magnetic induction within the range from 0 to 110 μT was established.
The response of Escherichia coli cells to extremely low frequency electromagnetic fields (ELF EMFs) was investigated at a magnetic induction amplitude of 30 μT. The influence of the EMF with a frequency of 9 Hz on the previously revealed resonance of the genome conformational state (GCS) has been evaluated. The resonance effect, which was measured by the method of anomalous viscosity time dependence, depended on the concentration of exposed cells. The effect was normalized to its own sham control at each concentration. The GCS changes increased with the concentration of exposed cells and reached a plateau at a value of about 6 × 103 cell ml−1. This means that cells interact during the resonance reaction to EMF, thus enhancing the effect. Saturation of the effect at concentrations close to those in the tissues of higher eukaryotes may reflect the importance of this parameter for the regulation of living systems. The experimentally established dependence of the resonance EMF effect on the concentration of exposed cells was described well by the theoretical model. This model was obtained by assuming that the cooperative effect was produced by the electromagnetic interaction of cells in the millimeter-submillimeter range of EMF.As in the case of the resonance reaction of E. coli cells to low intensity millimeter waves, the GCS changes were shown to correlate with the changes in the spectrum of the DNA-bound proteins.
In previous research, we found an increase in DNA strand breaks in brain cells of rats acutely exposed to a 60 Hz magnetic field (for 2 h at an intensity of 0.5 mT). DNA strand breaks were measured with a microgel electrophoresis assay using the length of DNA migration as an index. In the present experiment, we found that most of the magnetic field-induced increase in DNA migration was observed only after proteinase-K treatment, suggesting that the field caused DNA-protein crosslinks. In addition, when brain cells from control rats were exposed to X-rays, an increase in DNA migration was observed, the extent of which was independent of proteinase-K treatment. However, the X-ray-induced increase in DNA migration was retarded in cells from animals exposed to magnetic fields even after proteinase-K treatment, suggesting that DNA-DNA crosslinks were also induced by the magnetic field. The effects of magnetic fields were also compared with those of a known DNA crosslink-inducing agent mitomycin C. The pattern of effects is similar between the two agents. These data suggest that both DNA-protein and DNA-DNA crosslinks are formed in brain cells of rats after acute exposure to a 60 Hz magnetic field.
Magnetic fields (MF) may affect biological systems by increasing free radical concentrations. To test this, we have investigated whether low frequency (60 Hz) low intensity (0.1 mT) MF can modulate the phorbol 12-myristate 13- acetate (PMA) induced respiratory burst in primed rat peritoneal neutrophils, followed in real time using the dye 2′,7′-dichlorofluorescin (DCFH), which reacts with free radical-derived oxidants such as H2O2 (which is formed from the dismutation of superoxide) to become 2′,7′-dichlorofluorecein (DCF), a highly fluorescent compound. In the presence of the MF, a 12.4% increase in the fluorescence signal was observed in PMA-stimulated neutrophils (n = 5, P < 0.02, 18 pairs of measurements). We believe this represents the first experimental observation of MF influencing events involving free radical species generated during signal transduction in living cells.
Recombination is a process thought to be underlying genomic instability involved in carcinogenesis. This report examines the potential of cytostatic drugs to induce intrachromosomal homologous recombination. In order to address this question, the hprt gene of a well-characterized mammalian cell line was employed as a unique endogenous marker for homologous recombination. Commonly used cytostatic drugs with different mode of action were investigated in this context, i.e. bifunctional alkylating agents, inhibitors of DNA synthesis, inhibitors of topoisomerases and a spindle poison. With the exception of the spindle poison, all these drugs were found to induce homologous recombination, with clear differences in their recombination potency, which could be related to their mechanism of action. Bifunctional alkylating agents were the least efficient, whereas inhibitors of DNA synthesis were found to be the most potent inducers of homologous recombination. This raises the question whether these later drugs should be considered for adverse effects in cancer chemotheraphy.
The possibility that extremely low frequency (ELF) magnetic fields affect the genomic integrity of the cell is the objective of this study. Human peripheral lymphocytes (HPLs) were exposed to different exposure conditions combining ac and static magnetic fields. We used the micronuclei (MN) cytogenetic technique, because MN formation is considered as a marker of chromosomal damage produced by genotoxic agents.The first set of experiments were performed at 50 Hz, 150 μT rms and 32 Hz, 75 μT and 150 μT rms magnetic fields with the static geomagnetic field components nulled. No effects were detected using the MN test on HPL as an indicator for cellular genomic damage when the static magnetic field was nulled. Moreover, such exposure to an ac magnetic field does not appear to interfere with the action of a powerful genotoxic agent mytomicin-C (MMC), i.e. there was no synergistic effect.The second set of experiments were conducted exposing cells to 32 Hz, 150 μT and 75 μT rms, parallel to a 42 μT dc magnetic field. The 75 μT rms, 32 Hz exposure condition was chosen to maximize the resonance effect on Ca2+ according to parametric resonance theory. We found a statistically significant increase of MN for both exposure conditions. This experiment provides evidence for the genotoxic effects of resonant ELF magnetic fields in human lymphocytes.
Here, the sequence in the hprt gene of the duplication mutant SPD8 originating from V79 Chinese hamster cells was determined. The duplication arose after non-homologous recombination between exon 6 and intron 7, resulting in an extra copy of the 3′ portion of exon 6, of exon 7 and of flanking intron regions. Only a duplication of exon 7 is present in the mRNA, since the duplicated exon 6 lacks its 5′ splice site and is removed during RNA processing. The findings in this study suggest that the non-homologous recombination mechanism which occurred here may have been initiated by endonucleases, rather than by a spontaneous double strand break. Subsequently, 14 spontaneous SPD8 revertants with a functional hprt gene were isolated and characterized using PCR and sequencing. The data revealed that although the SPD8 cell line arose by non-homologous recombination, it reverts spontaneously by homologous recombination. Interestingly, the downstream copy of exon 7 was restored by this process. This was indicated by the presence of a specific mutation, a T-to-G transversion, close to the breakpoint, a characteristic unique to the SPD8 clone. Our results suggest that the spontaneous reversion of this cell line by homologous recombination may involve an exchange, rather than a conversion mechanism.
To study the effect of extremely low frequency (ELF) magnetic fields on cell growth, human cells (AMA cells) and K14 skin fibroblasts cells, growing in monolayer culture, were exposed to a sinusoidal 50 Hz, 80 μT field. Exposure times varied from 15 to 90 min. Changes in cell proliferation rates were then studied during subsequent field-free incubation, for 24 h.The results showed that a 30 min exposure resulted in a much higher increase in proliferation rates in the AMA cells compared with non-exposed cells or cells exposed to electromagnetic fields for shorter or longer times. The magnitude of the increase also depended on the initial proliferation rate and confluency. The exposure to varying field densities showed that the greatest increase in proliferation occurred at 80 μT.
The method of anomalous viscosity time dependence was used to study changes in the genome conformational state (GCS) of Escherichia coli K12 AB1157 cells after their exposure to electromagnetic fields (EMFs) with an amplitude of magnetic induction equal to 30 μ T in the frequency range 7–12 Hz. A resonance effect which had good reproducibility and disappeared 100–170 min after the exposure of the cells was demonstrated. The direction and magnitude of the effect depended on the growth stage of the bacterial culture at which the cells were exposed to the EMF. The resonance frequencies and half-widths of the resonance dependences of the effect in the early stationary and middle logarithmic phases did not differ significantly. It was shown that the EMF resonance effect on the GCS is accompanied by considerable changes in the dynamics of cell division, DNA synthesis and protein synthesis. A comparative analysis of the systematic reactions of E. coli cells to the resonance effect of extremely low frequency (ELF) EMF and electromagnetic millimeter waves was carried out.
The purpose of this study was to examine the effect of extremely low frequency (ELF) magnetic fields on the induction of genetic damage. In general, mutational studies involving ELF magnetic fields have proven negative. However, studies examining sister-chromatid exchange and chromosome aberrations have yielded conflicting results. In this study, we have examined whether 60-Hz magnetic fields are capable of inducing mutation or mitotic recombination in the yeast Saccharomyces cerevisiae. In addition we determined whether magnetic fields were capable of altering the genetic response of S. cerevisiae to UV (254 nm). We measured the frequencies of induced mutation, gene conversion and reciprocal mitotic crossing-over for exposures to magnetic fields alone (1 mT) or in combination with various UV exposures (2-50 J/m2). These experiments were performed using a repair-proficient strain (RAD+), as well as a strain of yeast (rad3) which is incapable of excising UV-induced thymine dimers. Magnetic field exposures did not induce mutation, gene conversion or reciprocal mitotic crossing-over in either of these strains, nor did the fields influence the frequencies of UV-induced genetic events.
Magnetic fields are physical, environmental agents that have been shown to produce a variety of responses in cellular and animal studies, including general changes in gene transcription. In this study, the nuclear run-off assay has been employed to assess alterations in specific gene transcription in CEM-CM3 T-lymphoblastoid cells exposed for 15-120 min to a 1 gauss sinusoidal magnetic field at 60 Hz. Time-dependent and cell density-dependent changes in the transcription of c-fos, c-jun, c-myc and protein kinase C (beta-form) have been observed and quantitated. Additionally, changes in transcript levels, assessed by slot-blot analysis, have been found to parallel the changes in gene transcription. These data suggest an important role for magnetic field exposure in altering cellular processes.
We have tested the hypothesis that extremely low frequency (ELF) time-varying magnetic fields act in combination with static magnetic fields to alter calcium signalling in the lymphocyte. Results indicate that a 60-min exposure of thymic lymphocytes at 37 +/- 0.05 degrees C to a 16 Hz, 421 mG (42.1 microT) magnetic field simultaneously with a colinear static magnetic field of 234 mG (23.4 microT) (a.c./d.c. field intensity ratio = 1.8) inhibits calcium influx triggered by the mitogen Concanavalin A. Significantly, resting lymphocytes do not respond to the fields, thus, only mitogen-activated cells undergoing calcium signalling exhibit a field response. These results indicate that signal transduction involving calcium is an important biological constraint which operates to mediate this field interaction. Additional split field exposures show that the presence of the a.c. field or the d.c. field alone does not produce an effect. This is consistent with a proposed parametric resonance theory of interaction of low intensity magnetic fields with biological systems (L.L. Lednev (1991) Bioelectromagnetics 12, 71-75), which predicts the occurrence of biological effects at specific values for the frequency and field intensity of the ELF and static magnetic fields.
To identify environmental carcinogens there is a need for inexpensive and reliable short-term tests, but certain human or animal carcinogens are persistently undetectable as mutagents with the Ames assay or with other short-term tests currently in use. Thus there is a need for short-term tests which detect carcinogens missed by the Ames assay. Because of the association of carcinogenesis with genome rearrangement, a system screening for intrachromosomal recombination resulting in genome rearrangement has been constructed in Saccharomyces cerevisiae. Evaluation of this system shows inducibility by a variety of carcinogens not detectable by the Ames assay or various other short-term tests. In the light of these results it is tempting to speculate that 'nongenotoxic carcinogens' are in fact genotoxic but, in the past, the tools to measure the genetic alterations they induce have been inappropriate.
The effect of the in vitro exposure to extremely low frequency pulsed electromagnetic fields (PEMFs) on the proliferation of human lymphocytes from 24 young and 24 old subjects was studied. The exposure to PEMFs during a 3-days culture period or during the first 24 hours was able to increase phytohaemagglutinin-induced lymphocyte proliferation in both groups. Such effect was greater in lymphocytes from old people which showed a markedly reduced proliferative capability and, after PEMF exposure, reached values of 3H-TdR incorporation similar to those of young subjects. The relevance of these data for the understanding and the reversibility of the proliferative defects in cells from aged subjects and for the assessment of risk related to the environmental exposure to PEMFs has to be considered.
Fertilized eggs of Gallus domesticus were exposed continuously during their 21-day incubation period to either 50- or 60-Hz sinusoidal electric fields at an average intensity of 10 Vrms/m. The exposure apparatus was housed in an environmental room maintained at 37 degrees C and 55-60% relative humidity (RH). Within 1.5 days after hatching, the chickens were removed from the apparatus and tested. The test consisted of examining the effect of 50- or 60-Hz electromagnetic fields at 15.9 Vrms/m and 73 nTrms (in a local geomagnetic field of 38 microT, 85 degrees N) on efflux of calcium ions from the chicken brain. For eggs exposed to 60-Hz electric fields during incubation, the chicken brains demonstrated a significant response to 50-Hz fields but not to 60-Hz fields, in agreement with the results from commercially incubated eggs [Blackman et al., 1985a]. In contrast, the brains from chicks exposed during incubation to 50-Hz fields were not affected by either 50- or 60-Hz fields. These results demonstrate that exposure of a developing organism to ambient power-line-frequency electric fields at levels typically found inside buildings can alter the response of brain tissue to field-induced calcium-ion efflux. The physiological significance of this finding has yet to be established.
The hypothesis that movement of biological ions may be predicted by cyclotron resonance theory applied to cell membranes is tested in these experiments. Diatoms (Amphora coffeaeformis) were chosen as the biosystem since they move or don't move, depending on how much calcium is transported across the membrane. The experiments demonstrate that a particular ion (calcium) is apparently moved across the cell membrane in response to the DC and AC values of magnetic flux densities (B) and the frequency derived from the cyclotron resonance theory. A clear resonance is shown and a rather sharp frequency response curve is demonstrated. The experiments also show a dose response as the AC value of the flux density is varied, and that odd harmonics of the basic cyclotron frequency are also effective.
Exposure of PC12-VG cells to an extremely low frequency magnetic field (ELFMF) enhanced the beta-galactosidase gene expression stimulated by treatment of the cells with forskolin. The enhancing effect of the ELFMF was inhibited by treatment of the cells with a specific inhibitor of PKC, calphostin C, as well as with the Ca2+ entry blockers nifedipin and dantrolen. Enhancement appeared within the first hour of a 4h forskolin treatment when the ELFMF was given at different times during culture. We speculate that exposure of PC12-VG cells to an ELFMF during the early response to forskolin treatment affects cell signal transduction, resulting in enhanced gene expression.
Oscillations of free intracellular calcium [Ca2+]i were seen in individual Jurkat cells as response to a 50 Hz, 0.15 mT magnetic field (MF). In contrast, a CD45-deficient Jurkat cell line was unable to respond to MF stimulation. The phosphatase activity of CD45 has been implicated to regulate p56lck tyrosine kinase activity by removing an inhibitory phosphate. By using Jurkat cells that expressed a chimeric molecule, comprising the cytoplasmic phosphatase domain of CD45, the MF induced calcium response was restored. This showed the necessity for an intact signal transduction pathway leading to a calcium increase as a result of stimulation of cells by MF. Thus, our data suggest that the target for the applied MF are molecules involved in early events in the signalling pathway from the T cell antigen receptor.
Incubation of human peripheral blood cultures in the presence of an electromagnetic field (EMF) of 50 Hz and 5 mT leads to stimulation of the cell cycle of dividing lymphocytes but has no influence on the frequencies of sister-chromatid exchanges. Comparative studies with two different exposure systems and with different culture temperatures indicate that the effect on the cell cycle results from the EMF and is not a thermal effect. These data support the assumption that with respect to their suspected carcinogenic effects EMFs have no initiating but probably promoting effects.
In vitro exposure to low-energy, combined magnetic fields (CMF) increased the release of insulin-like growth factor (IGF)-II from human TE-85 osteosarcoma cells. Short-term CMF exposure of only 10 min increased IGF-II levels in conditioned medium 1 h post CMF exposure. IGF-II levels were measured with a radioreceptor assay using H-35 cells that contain abundant IGF-II but not IGF-I receptors. This assay also uses a recently validated BioGel P-10 acid gel filtration method to remove IGF binding protein before quantitation of either IGF-I or IGF-II. In addition to an increase in IGF-II levels, DNA synthesis, as an index of cell proliferation, was increased during the 24-h period post CMF exposure. A monoclonal antibody against IGF-II blocked the increase in cell proliferation following CMF exposure, whereas a control monoclonal antibody against osteocalcin did not attenuate the mitogenic action of CMF exposure. The effect of CMF exposure to increase both cell proliferation and IGF-II was cell-density dependent with greater stimulation by CMF observed at lower densities. Together, these data are consistent with the hypothesis that CMF exposure stimulates release/production of IGF-II from bone cells and that increased IGF-II then promotes an increase in cell proliferation.
Genetic recombination systems are present in all living cells and viruses and generally contribute to their hosts' flexibility with respect to changing environmental conditions. Recombination systems not only help highly developed organisms to protect themselves from microbial attack via an elaborate immune system, but conversely, recombination systems also enable microorganisms to escape from such an immune system. Recombination enzymes act with a high specificity on DNA sequences that either exhibit extended stretches of homology or contain characteristic signal sequences. However, recombination enzymes may rarely act on incorrect alternative target sequences, which may result in the formation of chromosomal deletions, inversions, translocations, or amplifications of defined DNA regions. This review describes the characteristics of several recombination systems and focuses on the implication of aberrant recombination in carcinogenesis. The consequences of mitotic recombination on the inappropriate activation of protooncogenes and on the loss of tumor suppressor genes is discussed. Cases are reported where mitotic recombination clearly has been associated with carcinogenesis in rodents as well as humans. Several test systems able to detect recombinagenic activities of chemical compounds are described.
Our recent studies have shown a significant increase in the frequency of chromosomal aberrations in human amniotic cells after exposure to a sinusoidal 50 Hz, 30 microT (rms) magnetic field. To evaluate further interactions between chromosomes and electromagnetic fields, we have analyzed the effects of intermittent exposure. Amniotic cells were exposed for 72 h to a 50 Hz, 30 microT (rms) magnetic field in a 15 s on and 15 s off fashion. Eight experiments with cells from different fetuses were performed. The results show a 4% mean frequency of aberrations among exposed cells compared to 2% in sham-exposed cells. The difference is statistically significant, with P < 0.05 both excluding and including gaps. In another series of eight experiments, the cells were exposed in the same way but with the field on for 2 s and off for 20 s. Also in these experiments a similar increase in the frequency of chromosomal aberrations was seen, but only when the analysis included gaps. Continuous exposure for 72 h to 300 microT, 50 Hz, did not increase the frequency of chromosomal aberrations. The background electromagnetic fields at different locations within the two incubators used was carefully checked and was nowhere found to exceed 120 nT. Likewise, the background level of chromosomal aberrations in cells cultured at different locations in the incubators showed no significant interculture differences.
The level of c-myc transcripts is increased in cells exposed to extremely low frequency (elf) electromagnetic (EM) fields at 60 Hz. The aim of the present experiments was to determine if regulatory regions upstream of the c-myc gene modulate the response to EM fields. DNA upstream of P1 of both mouse and human c-myc genes was transfected into cells as CAT constructs. The presence of DNA 5' to the human or mouse myc genes results in increased expression of CAT following 20 min exposures of cells to 60 Hz elf EM fields. Specific portions of the human upstream DNA were deleted and introduced into cells. The region responsive to EM fields is located between -353 and -1,257 relative to the P1 promoter.
In this study we investigated whether a 60 Hz magnetic field can act at the cellular level to influence the growth of human estrogen-dependent breast cancer cells. Our experimental design assessed cell proliferation of a human breast cancer cell line, MCF-7, in the absence or the presence of melatonin which inhibits growth at a physiological concentration of 10(-9) M. In three experiments, continuous exposure to average sinusoidal 60 Hz magnetic fields of 1.90 +/- 0.01, 2.40 +/- 0.70, and 2.53 +/- 0.50 mG, or simultaneous exposure in matched incubators to average 60 Hz magnetic fields of 10.4 +/- 2.12, 11.95 +/- 2.73, and 11.95 +/- 3.28 mG, respectively, had no effect on cell proliferation in the absence of melatonin. When MCF-7 cells were cultured in the presence of 10(-9) M melatonin, an 18% inhibition of growth was observed for cells in a 2.40 +/- 0.70 mG field. This effect was blocked by a 60 Hz magnetic field of 11.95 +/- 2.75 mG. In a second experiment, a 27% inhibition of MCF-7 cell growth was observed for cells in a 2.53 +/- 0.50 mG magnetic field, and this was blocked by a 60 Hz magnetic field of 11.95 +/- 3.28 mG. These results provide the first evidence that ELF frequency magnetic fields can act at the cellular levels to enhance breast cancer cell proliferation by blocking melatonin's natural oncostatic action. In addition, there appears to be a dose threshold between 2 and 12 mG. The mechanism(s) of action is unknown and may involve modulation of signal transduction events associated with melatonin's regulation of cell growth.
Disruption of communication between transformed cells and normal cells is involved in tumor promotion. We have tested the hypothesis that 60 Hz electromagnetic (EM) field exposures and a chemical tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) are co-promoters that enhance focus formation of transformed cells in co-culture with normal cells. EM field exposures alone did not affect the growth curves of parental C3H/10T1/2 fibroblasts or daughter mutant cells, UV-TDTx10e. Furthermore, EM field exposures alone did not promote focus formation of mutant cells in co-culture with parental cells under the conditions tested. However, EM field exposures co-promoted with TPA by increasing focus formation in co-culture. Cell cultures were exposed to an EM field in custom-built solenoidal incubators. The field exposures were 1.0 Gauss in a schedule of 1 h epochs four times daily for 28 days. Video image analysis of three independent experiments showed that field-exposed cultures produced 1.9-fold more foci than sham-exposed cultures when treated with TPA. The total area of foci per dish increased 2.2-fold and the number of cells in stained foci increased 2.3-fold. In a TPA dose-response, focus formation began at 3 ng/ml with no difference between field-exposed and sham-exposed co-cultures. However, at the TPA concentrations of 10, 20, 40, 50 and 100 ng/ml EM field exposures enhanced focus formation by an average of 150%. This study suggests that chronic intermittent exposures to a 60 Hz EM field and a chemical tumor promoter influenced membrane-related events by co-promoting focus formation.
Exposure to extremely low frequency magnetic field (ELFMF) of 50 Hz and 400 mT induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene of human melanoma MeWo cells. The mutant frequency was enhanced both by increasing the exposure period and the induced current intensity. Mutations induced by X-rays were enhanced by ELFMF exposure. No significant increase in mutant frequency occurred when DNA replication was inhibited during ELFMF exposure. DNA replication error is suspected of causing the mutations produced by ELFMF exposure.
Sequencing of hprt cDNA revealed that three spontaneous mutants in V79 Chinese hamster cells exhibit tandem duplications of exon(s), i.e., either exons 2 and 3 or exon 7. Sequences of different sizes (4.5-8 Kb) were found to be duplicated and inserted in tandem into the hprt gene. These mutants demonstrated spontaneous reversion frequencies which were about 40-fold higher than those observed with other types of spontaneous mutants, but on the same order of magnitude as spontaneous reversions in Sp5, a mutant with a duplication insertion involving exon 2 in this gene. These data suggest that all of the duplications found have the same genetic instability, regardless of the type, size or position of the duplicated fragment. The coding sequence of the hprt cDNA and the restriction pattern of the revertants were virtually identical to the wild-type, indicating restoration of a functional hprt gene by precise deletion of the duplicated fragment.
The effect of weak extremely-low-frequency (ELF) magnetic fields (sinusoidal, 30 microT amplitude) on the genome conformational state (GCS) of E. coli mutant and wild type cells was studied by using the method of anomalous viscosity time dependency (AVTD) in the 6-37 Hz frequency range. We confirmed the existence of three resonance frequencies of 8.9, 15.5, and 29.4 Hz when mutant cells of K12 AB1157 strain were exposed. In the same frequency range, the wild type K12 EMG2 cells displayed only two effective windows, with resonance frequencies of 8.3 and 27 Hz. The resonance frequencies differed significantly (P < .001-.000001) in the strains studied, whereas other resonance parameters did not. It was concluded that mutations in the AB1157 strain resulted in a significant rearrangement in the ELF action spectrum, including the appearance of a new resonance.
Male Djungarian hamsters (Phodopus sungorus; 45 animals per group) were either sham-exposed or exposed to a sinusoidal magnetic field for 56 days (Experiment 1: 50 Hz, 450 microTesla peak; max. dB/dt = 140 mTesla s(-1); 24 hrs day(-1)). Except for day 7, no effects were observed with respect to body weights during exposure. However, testicular cell numbers were significantly increased by exposure (tetraploid (4C): p=0.022; diploid (2C): p=0.039). Rectangular magnetic fields (Experiment 2: 360 microTesla; max. dB/dt = 2.5 Tesla s(-1)) caused a significant (p<0.001) but transient suppressing effect on body weights. Significant increases were also observed in testicular cell numbers (4C: p=0.034; haploid (1C): p=0.014) and in serum melatonin (p=0.001). It is concluded that weak magnetic fields may affect reproductive and physiological functions in the mammalian species tested and that the degree of these effects depends upon the fields' gradients.
In previous research, we have found an increase in DNA single- and double-strand breaks in brain cells of rats after acute exposure (two hours) to a sinusoidal 60-Hz magnetic field. The present experiment was carried out to investigate whether treatment with melatonin and the spin-trap compound N-tert-butyl-alpha-phenylnitrone (PBN) could block the effect of magnetic fields on brain cell DNA. Rats were injected with melatonin (1 mg/kg, sc) or PBN (100 mg/kg, ip) immediately before and after two hours of exposure to a 60-Hz magnetic field at an intensity of 0.5 mT. We found that both drug treatments blocked the magnetic field-induced DNA single- and double-strand breaks in brain cells, as assayed by a microgel electrophoresis method. Since melatonin and PBN are efficient free radical scavengers, these data suggest that free radicals may play a role in magnetic field-induced DNA damage.
Tumor cell resistance to many unrelated anticancer drugs is a major obstacle during cancer chemotherapy. One mechanism of drug resistance is thought to be due to the efflux of anticancer drugs caused by P-glycoprotein. In recent years, magnetic fields have been found to enhance the potency of anticancer drugs, with favorable modulation of cancer therapy. In this study, KB-ChR-8-5-11, a multidrug resistant (MDR) human carcinoma subline, was used as a model to evaluate the ability of pulsed magnetic fields (PMF) to modulate the potency of daunorubicin (DNR) in vivo and to determine the appropriate order of exposure to drugs and PMF using an in vitro cytotoxicity assay. Solenoid coils with a ramped pulse current source were used at 250 pulses per second for both in vivo and in vitro experiments. For the in vivo study, KB-ChR-8-5-11 cells were inoculated into thymic Balbc-nu/nu female mice. Treatment was begun when the average tumor volume reached 250-450 mm3. Treatment consisted of whole body exposure to PMF for one hour, followed immediately by intravenous (i.v.) injection of 8 mg/kg DNR designated as day 0, and repeated on days 7 and 14. Among the various groups, significant differences in the tumor volume were found between PMF + saline and PMF + DNR groups (p = 0.0107) at 39 days and 42 days (p = 0.0101). No mice died in the PMF alone group, and no toxicity attributable to PMF was found during the experimental period. For the in vitro studies, the sulforhodamine blue (SRB) cytotoxicity assay was used to determine the effect of the sequence which cells are exposed to PMF and/or DNR. Cells were exposed to PMF either before (pre-PMF) or after (post-PMF) drug was added. Results showed that the IC50 was significantly different between controls and pre-PMF + DNR groups (P = 0.0096, P = 0.0088). The IC50 of the post-PMF + DNR group was not found to be significantly different from control groups. Thus, the data in this report demonstrates that PMF enhanced the potency of DNR against KB-ChR-8-5-11 xenograft in vivo, while the efficacy of DNR was potentiated in vitro by PMF exposure only when PMF exposure occurred in the presence of drug. The data in vitro suggest that the mechanism by which PMFs modulate DNR's potency may be by inhibition of the efflux pump, P-glycoprotein. Further work to determine conditions for maximum modulation of drug potency by PMFs is warranted.
Low frequency electromagnetic fields (EMF) do not produce enough energy to damage DNA, in contrast to ionizing radiations. Any relationship between increased incidence of cancer and EMF must therefore be explained by a promoting effect on cellular transformation by ionizing radiation. The aim of this study was to investigate using the cytokinesis-blocked micronucleus assay a possible amplification of the genotoxic effects of ionizing radiations in cells exposed to combined static and power-frequency electromagnetic fields. Rat tracheal epithelial cell lines were first exposed in vitro to 60Co gamma rays (0, 2 and 6 Gy) and cells were then cultured for 24 h in a homogeneous sinusoidal 50 Hz magnetic field (flux density: 100 microTrms) combined with an artificial geomagnetic-like field created by the use of horizontal and vertical pairs of Helmholtz coils. Control cells were cultured in an adjacent incubator where the background EMF was about 0.1 microTrms. Under our in vitro experimental conditions, EMF appeared to have no significant direct effect on micronucleus induction in rat tracheal cell lines. However, an increased frequency of binucleated cells with micronuclei was observed in cells exposed to 6 Gy of gamma rays and EMF, compared with gamma irradiation alone. This could enhance radiation-induced genomic alterations and increase the probability of neoplastic transformation.
In this article we review the current status of research into the mechanism of DNA fragmentation in apoptosis. There is accumulating evidence that there is no single conserved endonuclease that is responsible for DNA fragmentation in all cells. Not only are the two stages of high molecular weight fragment and DNA ladder formation likely to be catalysed by different activities, but multiple activities appear to be involved in internucleosomal DNA fragmentation in various cells. In addition to any one of a number of Ca2+/Mg2+-dependent endonucleases, acidic enzymes (i.e., endonucleases that are active at acid pH) also appear to be involved. Moreover, some enzymes currently being identified are active over a broad range of acidic and neutral pH values and have complex cation requirements that are a function of pH. DNA fragmentation in apoptosis appears to be controlled by either Ca2+ ions or a decrease in pH, depending on the cell type. DNA degradation to oligonucleosomes is not essential for apoptosis, but all cells must undergo DNA degradation to produce the large fragments. This is believed to occur in regions of DNA attached to the nuclear matrix, but the activity responsible has not yet been identified. Changes in both Ca2+ ions and pH have been recorded in a variety of cells, indicating that both mechanisms of regulation of endonuclease activation are involved in apoptosis.
We review 23 studies on the potential genotoxicity of electric and magnetic fields that have appeared in the published literature since our 1993 review of 55 published studies (McCann et al., Mutat. Res. 297 (1993) 61-95) and six additional studies published prior to 1993, which were not previously reviewed. As in our previous review, internal electric fields present in media (for in vitro experiments) and in the torso (for in vivo experiments) were estimated. Individual experiments are evaluated using basic data quality criteria. The potential for genotoxicity of electric and magnetic fields is discussed in light of the significant body of genotoxicity data that now exists. Three unsuccessful attempts to replicate previously reported positive results have appeared since our previous review. We conclude that, in spite of the 34 studies reviewed in this and our previous publication that report positive genotoxic effects, none satisfy all of three basic conditions: independent reproducibility, consistency with the scientific knowledge base, and completeness according to basic data quality criteria. As we discuss, these criteria are satisfied for several groups of negative studies in several exposure categories (ELF magnetic fields, 150 microT-5 mT, combined ELF electric and ELF magnetic fields, approx. 0.2 mT, 240 mV/m, and static magnetic fields, 1-3.7 T). The evidence reviewed here strengthens the conclusion of our previous review, that the preponderance of evidence suggests that ELF electric or magnetic fields do not have genotoxic potential. Nevertheless, a pool of positive results remains, which have not yet been tested by independent replication. Among the 12 studies reviewed here, which report statistically significant or suggestive positive results, we point particularly to results from five laboratories [J. Miyakoshi, N. Yamagishi, S. Ohtsu, K. Mohri, H. Takebe, Increase in hypoxanthine-guanine phosphoribosyl transferase gene mutations by exposure to high-density 50-Hz magnetic fields, Mutat. Res. 349 (1996) 109-114; J. Miyakoshi, K. Kitagawa, H. Takebe, Mutation induction by high-density, 50-Hz magnetic fields in human MeWo cells exposed in the DNA synthesis phase, Int. J. Radiat. Biol. 71 (1997) 75-79; H. Lai. N.P. Singh, Acute exposure to a 60-Hz magnetic field increases DNA strand breaks in rat brain cells, Bioelectromagnetics, 18 (1997) 156-165; H. Lai, N.P. Singh, Melatonin and N-tert-butyl-alpha-phenylnitrone block 60-Hz magnetic field-induced DNA single and double strand breaks in rat brain cells, J. Pineal Res. 22 (1997) 152-162; T. Koana, M. Ikehata, M. Nakagawa, Estimation of genetic effects of a static magnetic field by a somatic cell test using mutagen-sensitive mutants of Drosophila melanogaster, Bioelectrochem. Bioenergetics 36 (1995) 95-100; F.L. Tabrah, H.F. Mower, S. Batkin, P.B. Greenwood, Enhanced mutagenic effect of a 60-Hz time-varying magnetic field on numbers of azide-induced TA100 revertant colonies, Bioelectromagnetics 15 (1994) 85-93; S. Tofani, A. Ferrara, L. Anglesio, G. Gilli, Evidence for genotoxic effects of resonant ELF magnetic fields, Bioelectrochem. Bioenergetics, 36 (1995) 9-13], which satisfy most basic data quality criteria and may be of interest.
DNA topoisomerase I is essential for cellular metabolism and survival. It is also the target of a novel class of anticancer drugs active against previously refractory solid tumors, the camptothecins. The present review describes the topoisomerase I catalytic mechanisms with particular emphasis on the cleavage complex that represents the enzyme's catalytic intermediate and the site of action for camptothecins. Roles of topoisomerase I in DNA replication, transcription and recombination are also reviewed. Because of the importance of topoisomerase I as a chemotherapeutic target, we review the mechanisms of action of camptothecins and the other topoisomerase I inhibitors identified to date.
In the present study we have examined the effects of brominated flame retardants (BFR) and several other environmental contaminants in two in vitro assays for intragenic recombination at an endogenous locus in mammalian cells. A total ten compounds were investigated, i. e., two technical PCB mixtures (Aroclor 1221 and Aroclor 1254), DDT, PCP, tetrabromobisphenol A (TBBPA), 4,4'-bischlorophenyl sulfone (BCPS), hexabromocyclododecane (HBCD) and the three different polybrominated diphenylethers (PBDEs): 2-bromodiphenylether (MBDE), 3,4-dibromodiphenylether (DBDE) and 2,4,2', 4'-tetrabromodiphenylether (TBDE). In the SPD8 assay system statistically significant increases in recombination frequency were observed with Aroclor 1221, BCPS, DBDE, DDT, HBCD, MBDE and TBDE. In the Sp5 assay system, only DBDE, HBCD and MBDE caused statistically significant increases in recombination frequency. In conclusion, our findings indicate that the modern additives to plastic, i.e., HBCD and PBDEs, as well as the plastic monomer BCPS may have the same effect to human health as DDT and PCBs, in terms of inducing genetic recombination, which is known to provoke a number of diseases, including cancer.