Inhibitory effect of extremely low frequency-electromagnetic field combined with static magnetic field on tumor cell proliferation and the possible mechanism / 肿瘤

ABSTRACT

Objective: To investigate the inhibitory effect of a combination of static magnetic field (SMF) and extremely low frequency-electromagnetic field (ELF-EMF) on the proliferation of tumor cells, and its causal relationship with the induction of intracellular reactive oxygen species (ROS) after exposure. Methods: The intensities of SMF and 50 Hz ELF-EMF both changed periodically and generated a magnetic field (MF) with a time-averaged intensity of 5.1 mT in the center of exposure area. The bronchial epithelium of human lung Beas-2B cells, human renal epithelial 293T cells, human nephroblastoma G401 cells, human gastric adenocarcinoma AGS cells, human pancreatic cancer BxPC cells and human neuroblastoma CHLA255 cells were exposured in MF for 2 h/d (continuous 3 days). The effects of the combined MF on the growth, proliferation, apoptosis and intracellular ROS concentration were detected by trype blue method, BrdU method, FCM method and DCFH-DA fluorescence probe method, respectively. Results: This combined MF showed no inhibitory effect on non-tumor cells including Beas-2B and 293T (both P > 0.05), while it showed inhibitory effect on tumor cells including G401, AGS, BxPC, and CHLA255 cells (all P < 0.01). G401 and CHLA255 cells were more sensitive to the MF, the inhibitory rate of G401 and CHLA255 cells at the third day of exposure was (29.41±0.81)% and (31.71±4.59)%, respectively. The apoptosis rate of G401 cells exposed to MF for 2 h/d was increased in 3 days (P < 0.05, P < 0.01 and P < 0.01). As compared with daily exposure for 2 h, the inhibition rate of daily exposure for 8 h induced another 10% increase (all P < 0.01). Furthermore, the combined MF exhibited more pronounced antitumor effect than that of SMF or ELF-EMF alone, including SMF with the same intensity of the combined field (all P < 0.01). The peak of intracellular ROS levels was reached shortly after initial exposure (1-2 h), for long before the peak of cell inhibition was reached (day 2-3 with accumulated exposure of 4-6 h). Continuous or intermittent increase of MF exposure did not result in further accumulation of intracellular ROS. However, the peak of ROS levels persisted to the next day after termination of exposure. Both SMF and ELF-EMF could induce the elevation of ROS, but without superimposition effect. Conclusion: Extending the exposure time of MF can improve its inhibitory effect on tumor cells. The antitumor effect of the combined MF is related to free radical damage, but this may be not the only mechanism.