Extremely low frequency magnetic fields and the promotion of H₂O₂‐induced cell death in HL‐60 cells

Abstract

Purpose: To test whether exposure to an extremely low frequency magnetic field (60 Hz, 5 mT) affects hydrogen peroxide (H₂O₂)‐induced cell death in human leukaemia HL‐60 cells.

Materials and methods: Cells were treated with H₂O₂ with or without exposure to an extremely low frequency magnetic fields. Viable cells, apoptotic and necrotic cells were determined by annexin V flow cytometry assay. The levels of apoptosis‐related proteins (caspase‐3, caspase‐7, Bcl‐2 and Bax) and poly(ADP‐ribose) polymerase were detected using Western blotting.

Results: Simultaneous treatment with exposure to the magnetic field and H₂O₂ (85 or 100 µM) for 24 h increased the number of apoptotic and necrotic cells significantly, and significantly decreased the number of viable cells compared with cells treated with H₂O₂ alone. The protein levels of Bax and Bcl‐2 showed no differences between H₂O₂‐treated cells and those treated with both H₂O₂ and an extremely low frequency magnetic field. Exposure to the magnetic field also had no effect on H₂O₂‐induced caspase‐3 activation. However, the protein levels of active caspase‐7 in cells simultaneously exposed to an extremely low frequency magnetic field and H₂O₂ for 2 and 8 h was higher than that of H₂O₂ treatment alone. In addition, simultaneous exposure to an extremely low frequency magnetic field and H₂O₂ caused poly(ADP‐ribose) polymerase cleavage and induced early inactivation at 2 h, while H₂O₂ treatment alone did not produce this effect until 4 h.

Conclusions: The data suggest that although the magnetic field itself cannot induce apoptosis and necrosis, it exerts a promoting effect on H₂O₂‐induced cell death, and it demonstrates that caspase‐7 as well as poly(ADP‐ribose) polymerase might be involved in this process.