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The effects of exposure of human amniotic cells to a 50 Hz magnetic field on apoptosis and mitochondrial reactive oxygen species and the role of mitochondrial permeability transition (MPT) should be investigated.
MPT is defined as an increase in the permeability of the mitochondrial membranes for small molecules via opening of so called MPT pores. In a previous study by the authors (Feng et al. 2016), it was found that exposing human amniotic cells to a 50 Hz magnetic field induced an increase in intracellular reactive oxygen species (ROS) that in turn caused MPT. The study investigated the biological implications of this result, suspecting an anti-apoptotic effect. Cells were exposed to a 0.4 mT magnetic field for up to 2 hours and were cultivated for up to 36 hours afterwards. In some approaches, cells were pretreated Bongkrekic acid, SB216763, cyclosporine A (inhibitors of MPT), acetylcysteine (ROS scavenger) or LY294002 (inhibitor of the PI3K/Akt signaling pathway) and/or treated with staurosporine (0,1 µM for 4 h) afterwards, to induce early apoptosis. Moreover, cells were exposed to a 0.2, 1 or 2 mT magnetic field for 60 min and treated with staurosporine afterwards. For each exposure, a separate sham exposure was used. Positive controls were used.
apoptosis and mitochondrial reactive oxygen species and the role of mitochondrial permeability transition
two exposure chambers in incubator with 95% air humidity and 5% CO2; the temperature was kept at 37.0 ± 0.1°C
each chamber contained a set of square Helmholtz coils (20 cm Œ 20 cm), which were double-wrapped with two lines of copper wire and encased by mu-metal to shield cells from stray fields; a fan in the wall made air and temperature uniform between chambers and incubator; cell dishes were put in the center of the coils; the magnetic field was perpendicular to the dishes
A sham exposure was conducted.
one chamber was used for sham exposure with opposite direction currents fed into the coils; exposure and the corresponding sham exposure was conducted simultaneously
there was almost no 50 Hz magnetic field at the center of the sham exposure coils; in both chambers, the total static MF was 18.5 µT with a 14.1 µT horizontal and a 12 µT vertical component; the heterogeneity of MF distribution within the 20Œ20Œ20 cm3 space in the exposure chamber was less than 1%; the sham exposure chamber isolation rate was more than 43 dB and electric fields were less than 1 V/m
Exposure to a magnetic field alone had no significant effect on cell viability or early apoptosis compared to the sham exposure conditions. However, exposure to a magnetic field of 0.4 mT or 1 mT for 1 hour significantly reduced early apoptosis induced by staurosporine compared to sham exposed cells. As other magnetic flux densities or exposure durations did not show such an effect, the authors assumed an window effect for exposure duration (1 h) and intensity (0.4 mT to 1 mT). In cells treated with the MPT inhibitor cyclosporine A and exposed to a 0.4 mT magnetic field for 1 hour, the mitochondrial reactive oxygen species level was significantly increased in comparison to cells only treated with the inhibitor, indicating that magnetic field-induced ROS are released into the cytoplasm via MPT. Treatment with MPT inhibitors Bongkrekic acid, SB216763, cyclosporine A or the ROS scavenger acetylcysteine significantly decreased the anti-apoptotic effect of the magnetic field, suggesting a relation between ROS release and the anti-apoptotic effect of the magnetic field. Finally, the protein expression of phosphorylated protein kinase B was found to be significantly increased after exposure to the 0.4 mT magnetic field for 60 minutes compared to the sham exposure, but not when combined with MPT inhibitors orROS scavengers. The authors conclude that exposure of human amniotic cells to a 50 Hz magnetic field might have an anti-apoptotic effect via mitochondrial reactive oxygen species release through mitochondrial permeability transition and subsequent activation of the PI3K/Akt pathway.