Evaluation of the effects of power-frequency magnetic fields on the electrical activity of cardiomyocytes differentiated from human induced pluripotent stem cells

Stimulus effects of extremely low-frequency electric field exposure on calcium oscillations in a human cortical spheroid

High-intensity, low-frequency (1 Hz to 100 kHz) electric and magnetic fields (EF and MF) cause electrical excitation of the nervous system via an induced EF (iEF) in living tissue. However, the biological properties and thresholds of stimulus effects on synchronized activity in a three-dimensional (3D) neuronal network remain uncertain. In this study, we evaluated changes in neuronal network activity during extremely low-frequency EF (ELF-EF) exposure by measuring intracellular calcium ([Ca2+]i) oscillations, which reflect neuronal network activity. For ELF-EF exposure experiments, we used a human cortical spheroid (hCS), a 3D-cultured neuronal network generated from human induced pluripotent stem cell (hiPSC)-derived cortical neurons. A 50 Hz sinusoidal ELF-EF exposure modulated [Ca2+]i oscillations with dependencies on exposure intensity and duration. Based on the experimental setup and results, the iEF distribution inside the hCS was estimated using high-resolution numerical dosimetry. The numerical estimation revealed threshold values ranging between 255-510 V/m (peak) and 131-261 V/m (average). This indicates that thresholds of neuronal excitation in the hCS were equivalent to those of a thin nerve fiber.

Biological Effects of Magnetic Storms and ELF Magnetic Fields

Magnetic fields are a constant and essential part of our environment. The main components of ambient magnetic fields are the constant part of the geomagnetic field, its fluctuations caused by magnetic storms, and man-made magnetic fields. These fields refer to extremely-low-frequency (<1 kHz) magnetic fields (ELF-MFs). Since the 1980s, a huge amount of data has been accumulated on the biological effects of magnetic fields, in particular ELF-MFs. However, a unified picture of the patterns of action of magnetic fields has not been formed. Even though a unified mechanism has not yet been generally accepted, several theories have been proposed. In this review, we attempted to take a new approach to analyzing the quantitative data on the effects of ELF-MFs to identify new potential areas for research. This review provides general descriptions of the main effects of magnetic storms and anthropogenic fields on living organisms (molecular-cellular level and whole organism) and a brief description of the main mechanisms of magnetic field effects on living organisms. This review may be of interest to specialists in the fields of biology, physics, medicine, and other interdisciplinary areas.

Evaluation of the Effects of Exposure to Power-Frequency Magnetic Fields on the Differentiation of Hematopoietic Stem/Progenitor Cells Using Human-Induced Pluripotent Stem Cells

The causal association between exposure to power-frequency magnetic fields (MFs) and childhood leukemia has been under discussion. Although evidence from experimental studies is required for a conclusion to be reached, only a few studies have focused on the effects of MF exposure on the human hematopoietic system directly related to leukemogenesis. Here, we established an in vitro protocol to simulate the differentiation of human mesodermal cells to hematopoietic stem progenitor cells (HSPCs) using human-induced pluripotent stem cells. Furthermore, we introduced MF in the protocol to study the effects of exposure. After a continuous exposure to 0-300 mT of 50-Hz MFs during the differentiation process, the efficiency of differentiation of mesodermal cells into HSPCs was analyzed in a single-blinded manner. The percentage of emerged HSPCs from mesodermal cells in groups exposed to 50-Hz MFs indicated a lack of significant changes compared with those in the sham-exposed group. These results suggest that exposure to 50-Hz MFs up to 300 mT does not affect the differentiation of human mesodermal cells to HSPCs, which may be involved in the initial process of leukemogenesis. © 2022 The Authors. Bioelectromagnetics published by Wiley Periodicals LLC on behalf of Bioelectromagnetics Society.

A magnetics-based approach for fine-tuning afterload in engineered heart tissues

Afterload plays important roles during heart development and disease progression, however, studying these effects in a laboratory setting is challenging. Current techniques lack the ability to precisely and reversibly alter afterload over time. Here, we describe a magnetics-based approach for achieving this control and present results from experiments in which this device was employed to sequentially increase afterload applied to rat engineered heart tissues (rEHTs) over a 7-day period. The contractile properties of rEHTs grown on control posts marginally increased over the observation period. The average post deflection, fractional shortening, and twitch velocities measured for afterload-affected tissues initially followed this same trend, but fell below control tissue values at high magnitudes of afterload. However, the average force, force production rate, and force relaxation rate for these rEHTs were consistently up to 3-fold higher than in control tissues. Transcript levels of hypertrophic or fibrotic markers and cell size remained unaffected by afterload, suggesting that the increased force output was not accompanied by pathological remodeling. Accordingly, the increased force output was fully reversed to control levels during a stepwise decrease in afterload over 4 hours. Afterload application did not affect systolic or diastolic tissue lengths, indicating that the afterload system was likely not a source of changes in preload strain. In summary, the afterload system developed herein is capable of fine-tuning EHT afterload while simultaneously allowing optical force measurements. Using this system, we found that small daily alterations in afterload can enhance the contractile properties of rEHTs, while larger increases can have temporary undesirable effects. Overall, these findings demonstrate the significant role that afterload plays in cardiac force regulation. Future studies with this system may allow for novel insights into the mechanisms that underlie afterload-induced adaptations in cardiac force development.

Response of Cultured Neuronal Network Activity After High-Intensity Power Frequency Magnetic Field Exposure

High-intensity and low frequency (1-100 kHz) time-varying electromagnetic fields stimulate the human body through excitation of the nervous system. In power frequency range (50/60 Hz), a frequency-dependent threshold of the external electric field-induced neuronal modulation in cultured neuronal networks was used as one of the biological indicator in international guidelines; however, the threshold of the magnetic field-induced neuronal modulation has not been elucidated. In this study, we exposed rat brain-derived neuronal networks to a high-intensity power frequency magnetic field (hPF-MF), and evaluated the modulation of synchronized bursting activity using a multi-electrode array (MEA)-based extracellular recording technique. As a result of short-term hPF-MF exposure (50-400 mT root-mean-square (rms), 50 Hz, sinusoidal wave, 6 s), the synchronized bursting activity was increased in the 400 mT-exposed group. On the other hand, no change was observed in the 50-200 mT-exposed groups. In order to clarify the mechanisms of the 400 mT hPF-MF exposure-induced neuronal response, we evaluated it after blocking inhibitory synapses using bicuculline methiodide (BMI); subsequently, increase in bursting activity was observed with BMI application, and the response of 400 mT hPF-MF exposure disappeared. Therefore, it was suggested that the response of hPF-MF exposure was involved in the inhibitory input. Next, we screened the inhibitory pacemaker-like neuronal activity which showed autonomous 4-10 Hz firing with CNQX and D-AP5 application, and it was confirmed that the activity was reduced after 400 mT hPF-MF exposure. Comparison of these experimental results with estimated values of the induced electric field (E-field) in the culture medium revealed that the change in synchronized bursting activity occurred over 0.3 V/m, which was equivalent to the findings of a previous study that used the external electric fields. In addition, the results suggested that the potentiation of neuronal activity after 400 mT hPF-MF exposure was related to the depression of autonomous activity of pacemaker-like neurons. Our results indicated that the synchronized bursting activity was increased by hPF-MF exposure (E-field: >0.3 V/m), and the response was due to reduced inhibitory pacemaker-like neuronal activity.