Sachiko Yoshie

Evaluation of biological effects of intermediate frequency magnetic field on differentiation of embryonic stem cell

The embryotoxic effect of intermediate frequency (IF) magnetic field (MF) was evaluated using murine embryonic stem (ES) cells and fibroblast cells based on the embryonic stem cell test (EST). The cells were exposed to 21 kHz IF–MF up to magnetic flux density of 3.9 mT during the cell proliferation process (7 days) or the cell differentiation process (10 days) during which an embryonic body differentiated into myocardial cells. As a result, there was no significant difference in the cell proliferation between sham- and IF–MF-exposed cells for both ES and fibroblast cells. Similarly, the ratio of the number of ES-derived cell aggregates differentiated to myocardial cells to total number of cell aggregates was not changed by IF–MF exposure. In addition, the expressions of a cardiomyocytes-specific gene, Myl2, and an early developmental gene, Hba-x, in the exposed cell aggregate were not altered. Since the magnetic flux density adopted in this study is much higher than that generated by an inverter of the electrical railway, an induction heating (IH) cooktop, etc. in our daily lives, these results suggested that IF–MF in which the public is exposed to in general living environment would not have embryotoxic effect.

Design and implementation of multi-frequency magnetic field generator producing sinusoidal current waveform for biological researches

Recently, induction heating systems are being widely used in many applications, and wireless power transmission systems are being introduced into commercially available electrical vehicles. These applications use time varying magnetic fields (under 100 kHz) which are in close proximity of the human body. Therefore, it should be discussed an influence of the time varying magnetic fields around 100 kHz to the human body. This paper presents design and implementation of a magnetic field generator for biological research. While conventional magnetic field generators only produce one frequency component, this paper discusses a multi-frequency range magnetic field generator with frequencies of 200 Hz and 20 kHz. In addition, actual systems with the inverter circuits for the purpose of biological evaluation are presented.

Evaluation of mutagenicity and co-mutagenicity of strong static magnetic fields up to 13 Tesla in Escherichia coli deficient in superoxide dismutase.

To evaluate the biological effects of static magnetic fields (SMFs) up to 13 Tesla (T), with respect to superoxide behavior, by determining the effect on mutagenicity in superoxide dismutase (SOD)‐deficient Escherichia coli strain QC774, and its parental strain GC4468.

Estimation of mutagenic effects of intermediate frequency magnetic field using mammalian cells

Since the opportunities that people are exposed to intermediate frequency (IF) magnetic fields (MF) are increasing, the health risk assessment of IF-MF has now become important. Because there have been few studies about long-term exposure to IF-MF with high magnetic flux density, we have developed a new apparatus capable of IF-MF exposure up to 3.9 mT for in vitro study. In this study, we found out that IF-MF did not affect both cell growth and mutagenicity using the mammalian cell line CHO-K1 and its DNA repair deficient derivatives.

Effects of Static Magnetic Field on Mutagenesis in in vitro

Effects of static magnetic field up to 13 T were estimated in Escherichia coli and Saccharomyces cerevisiae. We observed that exposure to a 5 T static magnetic field resulted in a slight but significant increase in gene recombination frequency while frequency of reverse point mutation was not altered in S. cerevisiae. This mutagenic effect showed a dose response relationship as J-shape. To investigate an involvement of reactive oxygen species in possible mutagenic effect of static magnetic field, SOD deficient E. coli QC774 was used in thymine synthesis-based mutation assay. The result shows that static magnetic field up to 13 T did not indicate mutagenicity. Thus, it is suggested that frequency of point mutation does not changed under static magnetic field regardless of its susceptibility to superoxide. These results suggest that strong static magnetic field would have small but detectable mutagenic potential. Although mechanism of the mutagenic effect of static magnetic field has not been elucidated yet, the extent of this effect is estimated extremely small by comparison with other mutagens such as ultraviolet irradiation.

Evaluation of effects of intermediate frequency magnetic field on DNA methylation

To evaluate biological effects of intermediate frequency magnetic fields (IF-MFs), effect on DNA methylation was investigated. As the results, we have not observed any significant effects by exposure to 21 kHz, 3.9 mT IF-MF that is 144 times higher than reference level for public in current ICNIRP guideline. This suggests that IF-MF is unlikely to cause adverse biological effects with our previous results.

Biological effects of intermediate frequency magnetic fields — Development of exposure system and evaluate genotoxicity in vitro

To evaluate biological effects of intermediate frequency magnetic fields (IF-MFs), we developed an exposure system for in vitro study. This system is able to generate up to 3.9mT, 21kHz IF-MF under controlled culture condition. Toxicity and effect on frequency of micronucleus in CHL/IU cells by exposure to IF-MFs were investigated. As the results, we have not observed any significant effects by exposure to 21 kHz, up to 3.9 mT IF-MF in both experiment. This suggests that IF-MF is unlikely to cause adverse biological effects.

Effects of exposure to intermediate frequency magnetic fields on gene expression of estrogen-regulated gene in MCF-7 cells

To evaluate biological effects of intermediate frequency magnetic fields (IF-MF), estrogen-regulated gene expression under magnetic fields were studied. Genetically modified MCF-7 cells that transformed with ERE-luc fusion gene was used. Cells which endogenous estrogen depleted by estrogen free media are exposed to 21 kHz IF-MF for 24 hr. Then, luciferase activity was measured as estrogen-regulated gene expression. In this study, we have observed no significant difference in luciferase activity between exposed and sham-exposed cells by exposure to up to 3.9mT, 21 kHz IF-MF for 24hr. These results suggest that IF-MF is unlikely to affect directly on estrogen-regulated gene expression.

Intermediate frequency magnetic fields did not have genotoxic and promotion potentials in in vitro tests

In recent years, the use of new electrical appliances, that use or emit intermediate frequency (IF; 300 Hz to 10 MHz) electromagnetic fields (EMFs), has been increasing. We have investigated genotoxic and promotion potentials of a vertical and sinusoidal IF MF of 0.91mT (rms) at 2 kHz, 1.1mT (rms) at 20 kHz and 0.11mT (rms) at 60 kHz. We used microbial mutagenicity tests, gene conversion tests, micronucleus tests or mouse lymphoma assay for genotoxicity, and Bhas 42 promotion tests for promotion. The results indicate that the IF MFs did not have genotoxic nor promotion potentials in the experimental conditions.