Apoptosis of cultured human liver cancer cells induced by extremely low frequency magnetic field / 中国组织工程研究

ABSTRACT

BACKGROUND: Magnetic field can affect the growth and division of cancer cells both in vivo and in vitro, however, the effects on apoptosis of human liver cancer cells induced by magnetic field is still unclear.OBJECTIVE: To explore the inducing effect of extremely low fre quency (ELF) magnetic field on apoptosis of human liver cancer cell SK-HEP- 1.JESIGN An open experiment with cells as the observational subjects.SETTING: Institute of Biotechnology, Shanghai Jiaotong University.MATERIALS The experiment was carried out at the Institute of Biotechnology, Shanghai Jiaotong University from September 2004 to January 2005. The subject was human liver cancer cell line SK-HEP-1, purchased from cell bank of Chinese Academy of Science, Shanghai.METHODS: SK-HEP-1 cells were inoculated to T-flasks at the density of 2.0×107 cells L-1, and cultivated in the DMEM containing 0.1 volume fraction of heat-inactivated fetal bovine serum and 2 mmol/L L-glutamine. Exposure groups were exposed to 50 Hz, 20 mT magnetic field and the control groups were run concurrently under the same conditions with the exposed cultures but in a separate incubator which was free of magnetic field during 8-day culture process. The apoptosis of SK-HEP-1 cells were defined by DNA ladder assay, Hoechst 33258 staining and AO/EB staining respectively on day 8.MAIN OUTCOME MEASURES: ① DNA fragmentation pattern formation. ② The abnormal nucleus formation. ③ The percentage of apoptotic cells.RESULTS: ① Detection of internucleosomal DNA fragmentation by DNA ladder assay After 8-day ELF magnetic field exposure, DNA fragmentation pattern was detected by DNA ladder assay, which was not observed in control groups (free of exposure). ② Fluorescence microscopy analysis of apoptosis by Hoechst 33258 staining Hoechst 33258 staining was used to investigate the changes in the nucleus of cells, and many apoptotic bodies containing nuclear fragments were found in ELF magnetic field exposed cells, but just about none in untreated cells. At the same time, cytoplasmic shrinkage was observed in cells cultured under the exposure. And in some cells, even the cell membrane was unable to keep intact. ③ Fluorescence microscopy analysis of cell apoptosis by acridine orange/ethidium bromide (AO/EB) double staining After ELF magnetic field exposure, the percentage of viable cells in exposure groups (9.2%) was rather low compared with the control groups (91.8%), and was accompanied with a high apoptotic rate (72.3%), while only 4.2% in control group. A large number of apoptotic cells were at the early stage of apoptosis. The rate of apoptotic cells (18.5%)after treated by magnetic field was higher than that of control group (4%). With the AO/EB double staining, control cells appeared to be round,intact and bright green while some of the exposed cells exhibited irregular cell morphology and condensed nucleus.CONCLUSION: Apoptosis of human liver cancer cell SK-HEP-1 could be induced by 50 Hz, 20 mT magnetic field in vitro.