Pulsed Low Intensity Electromagnetic Field (PEMF) Affects Cell Cycle of Human Osteoblast-like Cells in Vitro

High frequency electromagnetic field in the range of 4 - 33 kHz given in low frequency bursts of 7-15 Hz (PEMF) is efficient in stimulating osteoblast proliferation and differentiation in vitro. We hypothesize that osteoblast cell cycle changes following this stimulatory PEMF. In order to explore this effect we used primary explant cultures of human osteoblast-like cells. These cells were subjected to low frequency of 20-30 Hz, higher frequency of 5-15 kHz electromagnetic fields and to PEMF (5-15 kHz basic frequency in pulses of 20-30 Hz) with maximal magnetic flux of 10-12 Gauss. The maturation state of the cells was estimated by the measurement of cellular alkaline phosphatase activity and the overall cell death by the LDH activity in culture media. The cell cycle was analyzed by cytometry. The PEMF stimulation significantly increased the proportion of cells in the G1 phase (p<.001) and decreased the proportion of apoptotic and necrotic cells (p<.001), with parallel decrease in cellular alkaline phosphatase and media LDH activities. Pure 20-30 Hz or 5-15 kHz electromagnetic stimulations had no effect on these parameters. Therefore we show that PEMF with a basic frequency in the kHz range provided in pulses in the infrasonic range alters human osteoblast cell cycle by reducing cell death and cellular maturation.