Pulsed electromagnetic field stimulation of MG63 osteoblast-like cells affects differentiation and local factor production

Pulsed electromagnetic field stimulation has been used to promote the heali ng of chronic nonunions and fractures with delayed healing, but relatively little is known about its effects on osteogenic cells or the mechanisms inv olved. The purpose of this study was to examine the response of osteoblast- like cells to a pulsed electromagnetic field signal used clinically and to determine if the signal modulates the production of autocrine factors assoc iated with differentiation. Confluent cultures of MG63 human osteoblast-lik e cells were placed between Helmholtz coils and exposed to a pulsed electro magnetic signal consisting of a burst of 20 pulses repeating at 15 Hz for 8 hours per day for 1, 2, or 4 days. Controls were cultured under identical conditions, but no signal was applied. Treated and control cultures were al ternated between two comparable incubators and, therefore, between active c oils; measurement of the temperature of the incubators and the culture medi um indicated that application of the signal did not generate heat above the level found in the control incubator or culture medium. The pulsed electro magnetic signal caused a reduction in cell proliferation on the basis of ee l number and [H-3] thymidine incorporation. Cellular alkaline phosphatase-s pecific activity increased in the cultures exposed to the signal, with maxi mum effects at day 1. In contrast, enzyme activity in the eel-layer lysates , which included alkaline phosphatase-enriched extracellular matrix vesicle s, continued to increase with the time of exposure to the signal. After 1 a nd 2 days of exposure, collagen synthesis and osteocalcin production were g reater than in the control cultures. Prostaglandin E-2 in the treated cultu res was significantly reduced at 1 and 2 days, whereas transforming growth factor-beta 1 was increased; at 4 days of treatment, however, the levels of both local factors were similar to those in the controls. The results indi cate enhanced differentiation as the net effect of pulsed electromagnetic f ields on osteoblasts, as evidenced by decreased proliferation and increased alkaline phosphatase-specific activity, osteocalcin synthesis, and collage n production. Pulsed electromagnetic field stimulation appears to promote t he production of matrix vesicles on the basis of higher levels of alkaline phosphatase at 4 days in the cell layers than in the isolated cells, commen surate with osteogenic differentiation in response to transforming growth f actor-beta 1. The results indicate that osteoblasts are sensitive to pulsed electromagnetic field stimulation, which alters cell activity through chan ges in local factor production.