Exposure to 60-Hz magnetic fields and proliferation of human astrocytoma cells in vitro

Epidemiological studies have suggested that exposure to electric and magnet ic fields (EMF) may be associated with an increased incidence of brain tumo rs, most notably astrocytomas. However, potential cellular or molecular mec hanisms involved in these effects of EMF are not known. In this study we in vestigated whether exposure to 60-Hz sinusoidal magnetic fields (0.3-1.2 G for 3-72 h) would cause proliferation of human astrocytoma cells. Sixty-Her tz magnetic fields (MF) caused a time- and dose-dependent increase in proli feration of astrocytoma cells, measured by H-3-thymidine incorporation and by flow cytometry, and strongly potentiated the effect of two agonists (the muscarinic agonist carbachol and the phorbol ester PIMA). However, MF had no effect on DNA synthesis of rat cortical astrocytes, i.e., of similar, no ntransformed cells. To determine the amount of heating induced by MF, tempe ratures were also recorded in the medium. Both 1.2 G MF and a sham exposure caused a 0.7 degrees C temperature increase in the medium; however, H-3-th ymidine incorporation induced by sham exposure was significantly less than that caused by MF. GF 109203X, a rather specific protein kinase C (PKC) inh ibitor, and down-regulation of PKC inhibited the effect of MF on basal and on agonist-stimulated H-3-thymidine incorporation. These data indicate that MF can increase the proliferation of human astrocytoma cells and strongly potentiate the effects of two agonists. These findings may provide a biolog ical basis far the observed epidemiological associations between MF exposur e and brain tumors. (C) 2000 Academic Press.