| Objective: The treatment of malignant tumors has been one of the main fields of medical research. As the development of science and technology, dramatic progress in the treatment of cancer has been achieved in the past decades. Now, the therapeutic method of cancer is far beyond it used to be. Except operation, radiotherapy, chemotherapy, many new methods have been used in the systemic treatment of cancer. Recent years have witnessed an increasing interest in the study of effects of the magnetic fields on the malignant tumors and its possible application in biomedical field. Many studies showed that some transient magnetic fields and static magnetic fields could inhibit the growth of the neoplasm in vivo and the tumor cells in vitro. In the contrary, there are reports suggesting certain low frequency magnetic field could accelerate tumor growth. Thus, further studies of magnetic fields with different features are needed.50Hz and 60Hz magnetic field is closely related with people's life and work. Up to now, most studies of the effects of magnetic fields on the tumors were concentrated on that of the low intensity transient and static magnetic fields. As the homogeneous ferromagnetic field is not easily available, few works on this field has been seen. To explore the effects of 50 Hz homogeneous ferromagnetic field (0.097T) exposure on the human low differentiated gastric adenocarcinoma cell line—SNU cells and to evaluate the possible usages of this magnetic field in tumor treatment, the proliferation and apoptosis of SNU cells and its possible mechanisms after exposure to 50 Hz homogeneous ferromagnetic field in vitro were studied with cell culture, flow cytometric analysis, ultrastructural observation, Western blot, confocal microscopic analysis. Methods: SNU cells were cultured in RPMI 1640 medium supplemented with 10% new-born calf serum(NBCS), streptomycin(100μg/ml), penicillin(100U/ml) at 37℃ 5%CO2. The cells were randomly divided into 5 groups: control, magnetic field exposure 5 minutes, 30 minutes, 60 minutes and 120 minutes groups, with 6 flasks in each group. The cells in magnetic field exposure groups were respectively exposed to 50Hz homogeneous ferromagnetic field (0.097T) with different time period, while control was placed at room temperature out of the magnetic field. The environmental temperature in the ferromagnetic field was kept the same as that of the control. Then, the cells were cultured at 37℃ 5% CO2 for 6 hours. Cells were harvested for flow cytometric (FCM) DNA analysis, electron microscope observation, detection of intracellular calcium-ion concentration by confocal microscope, detection of Bax, Bcl-2 and Caspase-3 antigen with flow cytometric analysis (FCM), immunocytochemical staining and Western blot.Results: 1. Effects of 50Hz homogeneous ferromagnetic field on the apoptosis and proliferation of SNU cells in vitro: (1) The effects on apoptosis of SNU cells: FCM analysis showed that apoptosis rates of SNU cells in all magnetic field exposure groups were significantly higher than that in control(P<0.05). When the magnetic field exposure time ranging from 5 min to 60 min a significant time-depended effect correlation could be found between apoptosis rate and magnetic field exposure time (n=4,r=0.965, P<0.01). Ultrastructurally, apoptotic morphological changes,such as thickening of nuclear membrane, condensation of chromatin along nuclear membrane, as well as apoptotic body further confirmed that 50Hz homogeneous ferromagnetic field exposure can induce apoptosis of SNU cells; (2)The effects on proliferation of SNU cells: FCM analysis showed that the effects of magnetic field exposure on the distribution of cell cycle and proliferation were not significant; 2. The change of intracellular calcium-ion concentration after 50Hz homogeneous ferromagnetic field exposure: The median of FI (fluorescence index, as the presents of intracellular calcium ion concentration) in control was 40.74, while the median of FI in the treatment groups was 53.97 (5min)...
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