A 700 MHz 1H-NMR study reveals apoptosis-like behavior in human K562 erythroleukemic cells exposed to a 50 Hz sinusoidal magnetic field

Purpose: To study cell damage and possible apoptosis in K562 human erythroleukemic cells exposed for 2?h to an extremely low frequency (ELF) 50 Hz sinusoidal magnetic field with a magnetic induction of either 1 or 5 mT using high resolution proton nuclear magnetic resonance (¹H-NMR) spectroscopy.

Materials and methods: One-dimensional ¹H-NMR spectra were obtained on whole K562 cells and perchloric acid extracts of these cells. In addition, two-dimensional ¹H-NMR spectra were also acquired. Cell damage was examined by lactate dehydrogenase release and changes in cell growth were monitored by growth curve analyses, bromodeoxyuridine incorporation and Ki67 antigen localization. Cell death (necrosis and apoptosis) were also studied by using the chromatin dye Hoechst 33258.

Results: The variations in numerous metabolites observed with ¹H-NMR reveal apoptosis-like behavior in response of K562 cells to ELF fields.

Conclusion: ¹H-NMR can be extremely useful in studying the effects of ELF fields on cells. In particular, the variations in metabolites which suggest apoptosis-like behavior occur when the cells are not identifiable as apoptotic by more traditional techniques.     

Extremely low frequency magnetic field (50 Hz, 0.5 mT) modifies fitness components and locomotor activity of Drosophila subobscura

Abstract

Purpose: Extremely low frequency (ELF) magnetic fields are essential ecological factors which may induce changes in many organisms. The aim of this study was to examine the effects in Drosophila subobscura exposed for 48 h to ELF magnetic field (50 Hz, 0.5 mT) at different developmental stages.

Materials and methods: Egg-first instar larvae developmental stage of D. subobscura isofemale lines was exposed to ELF magnetic field, and fitness components (developmental time, developmental dynamics, viability and sex ratio) and locomotor activity of three-day-old males and females were monitored. Also, just eclosed D. subobscura isofemale adults were exposed to ELF magnetic field and their locomotor activity was monitored just after.

Results: ELF magnetic field shortens developmental time, increases viability and does not affect sex ratio of D. subobscura. No matter which developmental stage is exposed, ELF magnetic field significantly decreases locomotor activity of adult flies, but after exposure of just eclosed adults observed change lasts longer.

Conclusions: Applied ELF magnetic field modifies fitness components and locomotor activity of D. subobscura. Observed effects can be attributed to the influence of magnetic field on different stages of development where the hormonal and nervous systems play important role in the control of examined parameters.     

Inhibition of UV‐induced G1 arrest by exposure to 50 Hz magnetic fields in repair‐proficient and ‐deficient yeast strains

Purpose: To assess the possibility that extremely low frequency (ELF) magnetic fields obstruct the damage repair process, the gene conversion frequency and cell cycle kinetics in a DNA repair‐proficient and nucleotide excision repair (NER)‐deficient strain of diploid yeast Saccharomyces cerevisiae.

Materials and methods: DNA repair‐ or NER‐deficient cells were irradiated with sublethal doses of ultraviolet light (UV) radiation followed by exposure to 50?Hz magnetic fields up to 30?mT for 48?h. After exposure, colony‐forming ability was scored as revertants in which gene conversion had restored the functional allele of the ARG4 gene conversion hotspot. Cell cycle analysis was performed using flow cytometry.

Results: Gene conversion rate was increased by the combined exposure in DNA repair‐proficient cells, whereas it remained unchanged between UV alone and the combined exposure in NER‐deficient cells. The UV‐induced G1 arrest was inhibited by exposure to 30?mT ELF magnetic fields in both repair‐proficient and ‐deficient cells.

Conclusions: The results suggest that exposure to high‐density (30?mT) ELF magnetic fields decreases the efficiency of NER by suppressing G1 arrest, which in turn led to enhancement of the UV‐induced gene conversion.     

Lack of Acute Effects of 20 mT, 50 Hz Magnetic Fields on Murine Haemopoiesis

Summary

Some epidemiological studies have drawn attention to a possible association between exposure to extremely low-frequency (ELF) electromagnetic fields and the development of acute myeloid leukaemia (AML) in adults. At present there is no experimental evidence for such an association. We have investigated the acute effects of power frequency magnetic fields on haemopoiesis in CBA/H mice known to be susceptible to the induction of AML after exposure to ionizing radiation. Up to 19 days after exposure to 50 Hz fields at 20 mT for 7 days no significant effects on peripheral blood characteristics were observed. Assays of the bone marrow stem cells and myelomonocytic progenitor cells also failed to reveal significant effects. Our experiments cannot, however, rule out subtle effects on cell population dynamics, and further investigations, including longterm studies, are required to establish the extent to which ELF magnetic fields might affect the haemopoietic system.     

Different responses of Drosophila subobscura isofemale lines to extremely low frequency magnetic field (50 Hz, 0.5 mT): fitness components and locomotor activity

Purpose: Extremely low frequency (ELF) magnetic fields as essential ecological factors may induce specific responses in genetically different lines. The object of this study was to investigate the impact of the ELF magnetic field on fitness components and locomotor activity of five Drosophila subobscura isofemale (IF) lines.

Materials and methods: Each D. subobscura IF line, arbitrarily named: B16/1, B24/4, B39/1, B57/2 and B69/5, was maintained in five full-sib inbreeding generations. Their genetic structures were defined based on the mitochondrial DNA variability. Egg-first instar larvae and 1-day-old flies were exposed to an ELF magnetic field (50?Hz, 0.5?mT, 48?h) and thereafter, fitness components and locomotor activity of males and females in an open field test were observed for each selected IF line, respectively.

Results: Exposure of egg-first instar larvae to an ELF magnetic field shortened developmental time, and did not affect the viability and sex ratio of D. subobscura IF lines. Exposure of 1-day-old males and females IF lines B16/1 and B24/4 to an ELF magnetic field significantly decreased their locomotor activity and this effect lasted longer in females than males.

Conclusions: These results indicate various responses of D. subobscura IF lines to the applied ELF magnetic field depending on their genetic background.     

Modification of p21 level and cell cycle distribution by 50 Hz magnetic fields in human SH-SY5Y neuroblastoma cells

Purpose: In our previous studies, exposure to extremely low frequency (ELF) magnetic fields (MF) altered responses to DNA damage caused by menadione. The aim of this study was to evaluate possible ELF MF induced changes in proteins involved in DNA damage responses and in cell cycle distribution.

Materials and methods: Based on our previous studies, the exposure protocol included pre-exposure of human SH-SY5Y neuroblastoma cells to a 50?Hz, 100?μT MF for 24?h prior to a 3-h menadione treatment. As DNA damage responses are relatively fast processes, a 1-h menadione treatment was also included in the experiments. The menadione concentrations used were 1, 10, 15, 20, and 25?μM. Immunoblotting was used to assess the levels of DNA damage response-related proteins (γ-H2AX, Chk1, phospho-Chk1, p21, p27, and p53), while the level of DNA damage was assessed by the alkaline Comet assay. Cell cycle distribution was assayed by SYTOX Green staining followed by flow cytometry analysis.

Results: The main findings in MF-exposed cells were decreased p21 protein level after the 1-h menadione treatment, as well as increased proportion of cells in the G1 phase and decreased proportion of S phase cells after the 3-h menadione treatment. These effects were detectable also in the absence of menadione.

Conclusions: The results indicate that MF exposure can alter the G1 checkpoint response and that the p21 protein may be involved in early responses to MF exposure.     

A 700 MHz 1H-NMR study reveals apoptosis-like behavior in human K562 erythroleukemic cells exposed to a 50 Hz sinusoidal magnetic field

PURPOSE: To study cell damage and possible apoptosis in K562 human erythroleukemic cells exposed for 2 h to an extremely low frequency (ELF) 50 Hz sinusoidal magnetic field with a magnetic induction of either 1 or 5 mT using high resolution proton nuclear magnetic resonance (1H-NMR) spectroscopy. MATERIALS AND METHODS: One-dimensional 1H-NMR spectra were obtained on whole K562 cells and perchloric acid extracts of these cells. In addition, two-dimensional 1H-NMR spectra were also acquired. Cell damage was examined by lactate dehydrogenase release and changes in cell growth were monitored by growth curve analyses, bromodeoxyuridine incorporation and Ki67 antigen localization. Cell death (necrosis and apoptosis) were also studied by using the chromatin dye Hoechst 33258. RESULTS: The variations in numerous metabolites observed with 1H-NMR reveal apoptosis-like behavior in response of K562 cells to ELF fields. CONCLUSION: 1H-NMR can be extremely useful in studying the effects of ELF fields on cells. In particular, the variations in metabolites which suggest apoptosis-like behavior occur when the cells are not identifiable as apoptotic by more traditional techniques.     

Enhancement of biological effectiveness of carbon-ion beams by applying a longitudinal magnetic field

Abstract

Purpose: A magnetic field longitudinal to an ion beam will potentially affect the biological effectiveness of the radiation. The purpose of this study is to experimentally verify the significance of such effects.

Methods and materials: Human cancer and normal cell lines were exposed to low (12?keV/μm) and high (50?keV/μm) linear energy transfer (LET) carbon-ion beams under the longitudinal magnetic fields of B_// = 0, 0.1, 0.2, 0.3, or 0.6 T generated by a solenoid magnet. The effects of the magnetic fields on the biological effectiveness were evaluated by clonogenic cell survival. Doses that would result in a survival fraction of 10% (D₁₀s) were determined for each cell line and magnetic field.

Results: For cancer cells exposed to the low (high)-LET beams, D₁₀ decreased from 5.2 (3.1) Gy at 0 T to 4.3 (2.4) Gy at 0.1 T, while no further decrease in D₁₀ was observed for higher magnetic fields. For normal cells, decreases in D₁₀ of comparable magnitudes were observed by applying the magnetic fields.

Conclusions: Significant decreases in D₁₀, i.e. significant enhancements of the biological effectiveness, were observed in both cancer and normal cells by applying longitudinal magnetic fields of B_// ≥?0.1 T. These effects were enhanced with LET. Further studies are required to figure out the mechanism underlying the observed results.     

Clastogenicity and aneuploidy in newborn and adult mice exposed to 50 Hz magnetic fields

Purpose:?To detect possible clastogenic and aneugenic properties of a 50 Hz, 650 μT magnetic field.

Materials and methods:?The micronucleus test with CREST (Calcinosis, Raynaud's phenomenon, Esophageal dismotility, Sclerodactility, Telangectasia) antibody staining was performed on liver and peripheral blood sampled from newborn mice exposed to an ELF (Extremely Low Frequency) magnetic field during the whole intra-uterine life (21 days), and on bone marrow and peripheral blood sampled from adult mice exposed to the same magnetic field for the same period.

Results:?Data obtained in newborn mice show a significant increase in micronuclei frequencies. In absolute terms, most of the induced micronuclei were CREST-negative (i.e., formed by a chromosome fragment). However, in relative terms, ELF exposure caused a two-fold increase in CREST-negative micronuclei and a four-fold increase in CREST-positive micronuclei (i.e., formed by a whole chromosome). No significant effect was recorded on exposed adults.

Conclusions:?These findings suggest the need for investigation of aneugenic properties of ELF magnetic fields in order to establish a possible relationship to carcinogenesis.     

50-Hz magnetic field induces EGF-receptor clustering and activates RAS

Purpose: In a previous study, we found that exposure to a 50 Hz magnetic field (MF) could activate stress-activated protein kinase (SAPK) and P38 mitogen-activated protein (MAP) kinase (P38 MAPK) in Chinese hamster lung (CHL) fibroblast cells, and simultaneous exposure to a ‘noise’ MF of the same intensity inhibited these effects. In order to explore the possible target sites and upstream signal transduction molecules of SAPK and P38 MAPK, and further validate the interference effects of ‘noise’ MF on 50 Hz MF, the effects of MF exposure on clustering of epidermal growth factor (EGF) receptors and Ras protein activation were investigated.

Materials and methods: CHL cells were exposed to a 50 Hz sinusoidal MF at 0.4 mT for different durations, and clustering of EGF receptors on cellular membrane and Ras protein activation were analyzed using immunofluorescence confocal microscopy and co-precipitation technology. EGF treatment served as the positive control.

Results: The results showed that, compared with sham-exposed cells, exposure to a 50 Hz MF at 0.4 mT for 5 min slightly induced EGF receptor clustering, whereas exposure for 15 min enhanced receptor clustering significantly. Corresponding to receptor clustering, Ras protein was also activated after exposure to the 50 Hz MF. Exposure to a ‘noise’ MF (with frequency ranges from 30 – 90 Hz) at the same intensity and durations, did not significantly affect EGF receptor clustering and Ras protein. However, by superimposing the ‘noise’ MF, receptor clustering and Ras activation induced by 50 Hz MF were inhibited.

Conclusion: The results suggested that membrane receptors could be one of the most important targets where extremely low frequency (ELF) MF interacts with cells, and Ras may participate in the signal transduction process of 50 Hz MF. Furthermore, a ‘noise’ MF could inhibit these effects caused by ELF-MF.     

The influence of differently polarised microwave radiation on chromatin in human cells

Purpose: To determine the possible biological effects of differently polarised microwave radiation on the chromatin state in human cells.

Materials and methods: Isolated human buccal epithelium cells were irradiated by microwaves of frequency f = 35 GHz and surface power density E = 30 μW/cm². The state of chromatin in human cells was determined by methods of light and electron microscopy. The state of cell membranes was evaluated by the method of vital indigo carmine staining.

Results: The microwave-induced condensation of chromatin in human cells is revealed. Degree of microwave-induced condensation depends on the state of polarisation of electromagnetic wave: In some cases left circularly polarised waves induce less effect than linearly polarised radiation. The linearly polarised electromagnetic waves induce cell membrane damage revealed by increase of cell staining. The data obtained are discussed in connection with mechanisms of biological effects of electromagnetic fields.

Conclusion: The data obtained in this work demonstrate important biological effects of monochromatic microwave irradiation at 35 GHz. Low-level microwave irradiation induces chromatin condensation in human cells and damages of cell membranes.     

Extremely low frequency magnetic fields cause oxidative DNA damage in rats

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

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

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

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

Lack of acute effects of 20 mT, 50 Hz magnetic fields on murine haemopoiesis

Some epidemiological studies have drawn attention to a possible association between exposure to extremely low-frequency (ELF) electromagnetic fields and the development of acute myeloid leukaemia (AML) in adults. At present there is no experimental evidence for such an association. We have investigated the acute effects of power frequency magnetic fields on haemopoiesis in CBA/H mice known to be susceptible to the induction of AML after exposure to ionizing radiation. Up to 19 days after exposure to 50 Hz fields at 20 mT for 7 days no significant effects on peripheral blood characteristics were observed. Assays of the bone marrow stem cells and myelomonocytic progenitor cells also failed to reveal significant effects. Our experiments cannot, however, rule out subtle effects on cell population dynamics, and further investigations, including long-term studies, are required to establish the extent to which ELF magnetic fields might affect the haemopoietic system.     

Extremely low frequency (ELF) magnetic fields enhance chemically induced formation of apurinic/apyrimidinic (AP) sites in A172 cells

PURPOSE: To detect the effects of extremely low frequency (ELF) magnetic fields, the number of apurinic/apyrimidinic (AP) sites in human glioma A172 cells was measured following exposure to ELF magnetic fields. MATERIALS AND METHODS: The cells were exposed to an ELF magnetic field alone, to genotoxic agents (methyl methane sulfonate (MMS) and hydrogen peroxide (H2O2)) alone, or to an ELF magnetic field with the genotoxic agents. After exposure, DNA was extracted, and the number of AP sites was measured. RESULTS: There was no difference in the number of AP sites between cells exposed to an ELF magnetic field and sham controls. With MMS or H2O2 alone, the number of AP sites increased with longer treatment times. Exposure to an ELF magnetic field in combination with the genotoxic agents increased AP-site levels compared with the genotoxic agents alone. CONCLUSIONS: Our results suggest that the number of AP sites induced by MMS or H2O2 is enhanced by exposure to ELF magnetic fields at 5 millitesla (mT). This may occur because such exposure can enhance the activity or lengthen the lifetime of radical pairs.     

Interaction of low frequency external electric fields and pancreatic β-cell: a mathematical modeling approach to identify the influence of excitation parameters

Purpose: Although the effect of electromagnetic fields on biological systems has attracted attraction in recent years, there has not been any conclusive result concerning the effects of interaction and the underlying mechanisms involved. Besides the complexity of biological systems, the parameters of the applied electromagnetic field have not been estimated in most of the experiments.

Materials and Methods: In this study, we have used computational approach in order to find the excitation parameters of an external electric field which produces sensible effects in the function of insulin secretory machinery, whose failure triggers the diabetes disease. A mathematical model of the human β-cell has been used and the effects of external electric fields with different amplitudes, frequencies and wave shapes have been studied.

Results: The results from our simulations show that the external electric field can influence the membrane electrical activity and perhaps the insulin secretion when its amplitude exceeds a threshold value. Furthermore, our simulations reveal that different waveforms have distinct effects on the β-cell membrane electrical activity and the characteristic features of the excitation like frequency would change the interaction mechanism.

Conclusion: The results could help the researchers to investigate the possible role of the environmental electromagnetic fields on the promotion of diabetes disease.     

The effect of non-targeted cellular mechanisms on lung cancer risk for chronic,low level radon exposures

Abstract

Purpose: The goal of the present study was to investigate the effect of non-targeted mechanisms on the shape of the lung cancer risk function at chronic, low level radon exposures relative to direct cellular radiation effects. This includes detrimental and protective bystander effects, radio-adaptive bystander response, genomic instability and induction of apoptosis by surrounding cells.

Methods: To quantify the dependence of these mechanisms on dose, analytical functions were derived from the experimental evidence presently available. Alpha particle intersections of bronchial target cells during a given exposure period were simulated by a Transformation Frequency-Tissue Response (TF-TR) model, formulated in terms of cellular hits within the cycle time of the cell and then integrated over the whole exposure period.

Results: In general, non-targeted effects like genomic instability and bystander effects amplify the biological effectiveness of a given radiation dose, while induction of apoptosis and adaptive response will decrease the risk values. While these observations are related to the absolute number of lung cancer cases, normalization to the epidemiologically observed risk at 0.675 Gy suggests that the effect of such mechanisms on the shape of the dose-response relationship may be different. Indeed, genomic instability and adaptive response cause a substantial reduction of the risk at low doses, while induction of apoptosis and detrimental bystander effects slightly increase the risk.

Conclusions: Predictions of lung cancer risk, including these mechanisms, exhibit a distinct sublinear dose-response relationship at low exposures, particularly for very low exposure rates. However, the relatively large error bars of the epidemiological data do not currently allow the prediction of a statistically significant deviation from the Linear – No Threshold (LNT) assumption.     

Biological characteristics of carbon-ion therapy

Purpose: Radiotherapy using charged and/or high-linear energy transfer (LET) particles has a long history, starting with proton beams up to now carbon-ions. Radiation quality of particle beams is different from conventional photons, and therefore the biological effects of high-LET irradiation have attracted scientific interests of many scientists in basic and clinical fields. A brief history of particle radiotherapy in the past half-century is followed by the reviewed biological effectiveness of high-LET charged particles.

Results: The latter includes 54 papers presenting 506 RBE (relative biological effectiveness) values for carbon ions and a total of 290 RBE values for other ions identified from 48 papers. By setting a selection window of LET up to 100 keV/μm, we fitted a linear regression line to an LET-RBE relation. The resulting slope of the regression line had a dimension of μm/keV, and showed different steepness for different cells/tissues and endpoints as well. The steepest regression was found for chromosome aberration of human malignant melanoma while the shallowest was for apoptosis of rodent cells/tissue. Both tumour and normal tissue showed relatively shallower slopes than colony formation.

Conclusions: In general, there is a large variation of slope values, but the majority (25 out of 29 values) of data was smaller than 0.05 μm/keV.     

Reaction of the endocrine system to continuous and intermittent electromagnetic fields

This paper reviews Soviet and foreign data about the effects of low frequency electromagnetic fields of continuous and intermittent generation on the endocrine system of animals and humans. It has been shown that the pituitary-adrenal, pituitary-thyroid and reproductive systems are sensitive to these effects. It is postulated that the endocrine responses to electromagnetic effects are similar to the general adaptive reactions to various pathophysiological exposures.     

Long-term exposure of cockroach Blaptica dubia (Insecta: Blaberidae) nymphs to magnetic fields of different characteristics: effects on antioxidant biomarkers and nymphal gut mass

Abstract

Purpose: The main goal of this study was to analyze the long-term effects of static (SMF) and extremely low-frequency magnetic field (ELF MF) on nymphal gut mass and antioxidant biomarkers in this tissue of cockroach Blaptica dubia.

Materials and methods: One-month-old nymphs were exposed to magnetic field (MF) for 5 months in three experimental groups: control, exposure to SMF (110?mT) and exposure to ELF MF (50?Hz, 10?mT).

Results: The gut masses of the MF groups were significantly lower when compared to control. Superoxide dismutase (SOD) and catalase (CAT) activities were markedly higher than for the control and the differences between the MF groups were statistically significant only for SOD. The applied MF had no effect on total glutathione (GSH) content. Glutathione reductase (GR) and glutathione S-transferase (GST) activities were significantly lower in both MF groups in comparison to the control. There was a significant difference between MF groups for GR activity. Principal Component Analysis (PCA) showed that CAT and GST were the main factors contributing to the differentiation of the control group from the treated experimental groups along PCA 1, and SOD and GR along PCA 2. PCA revealed clear separation between experimental groups depends on antioxidant biomarker response.

Conclusion: The applied magnetic fields could be considered a potential stressor influencing gut mass, as well as examined antioxidative biomarkers.     

Effect of Static Magnetic Fields on the Amplitude of Action Potential in the Lateral giant Neuron of Crayfish

Purpose: To investigate whether exposure to static magnetic field (SMF) affects the passive properties of neurons that mediate tail‐flip escape behavior in crayfish.

Materials and methods: A permanent magnet was placed under the isolated nerve cord of crayfish to experience SMF at 4.74 to 43.45?mT intensity for various period of time (20 seconds to 3 hours). An intracellular electrode was impaled on the axon of the lateral giant neuron (LG) of the last abdominal ganglion of crayfish to record the evoked action potential (AP) and excitatory postsynaptic potential (EPSP). The amplitudes of evoked AP and EPSPs before and after SMF exposure were measured to study the effect of SMF exposure.

Results: The exposure to SMF increased the amplitude of AP in the LG depending upon both the intensity of field and duration of field exposure. The changes in AP by field exposure are likely to be mediated by the increasing level of intracellular Ca²⁺ in the LG because the chelating of intracellular Ca²⁺ would block the effects by SMF exposure, while the injection of Ca²⁺ into the LG could mimic the effects of SMF exposure. SMF exposure also increases the input resistance of the LG membrane. Therefore, the magnitude of the EPSP in LG evoked by electrical shock on the sensory nerves was found to be enhanced after SMF exposure.

Conclusion: SMF is usually considered to be safe for the biological issues since no electrical current is induced via the Faraday effect. Our results showed that some passive membrane properties of neurons are affected by SMF exposure. The increase in magnitude of evoked AP and EPSP suggests an increase in the sensitivity of the LG neuron. These changes by SMF exposure may not necessarily to be harmful to animals; however, further study is needed to address the biological effects from SMF exposure, especially in nervous systems.