Cao, Y.; Zhang, W.; Lu, M. X.; Xu, Q.; Meng, Q. Q.; Nie, J. H., and Tong, J. 900-MHz microwave radiation enhances gamma-ray adverse effects on SHG44 cells. J Toxicol Environ Health A. 2009; 72(11):727-32.

Studies on biological effects of exposure to EMF produce controversial results. Because biological effects of EMFs of low intensities can be too weak to be measured, a more potent agent, such as ionizing radiation, may be applied to strengthen and highlight EMF-induced effects so that these effects can be studied in toxicological experiments.

The study was aimed at verifying whether pre-exposure to 900 MHz microwaves (corresponding to the frequency used in mobile phones in China) enhances g-ray induced damage to SHG44 human glioma cells.

Group M2, M4 and M6 were exposed to microwave radiation with a power density of 2, 4 and 6 mW/cm2 respectively, 2 hours a day for 3 days. On day 4, cells in groups M2+I, M4+I, and M6+I were exposed to 60Co g-rays at a dose of 5 Gy with a dose rate of 1 Gy/min. Effects of the exposures on cell proliferation, cell cycle distribution and apoptosis, HSP70 expression, activity of superoxide dismutase (SOD) and levels of malondialdehyde as measures of oxidative stress were evaluated in these experiments.

900 MHz microwave exposure resulted in a significant decrease in cell proliferation in groups M4 and M6. Pre-exposure to microwaves markedly enhanced the ionizing radiation induced decrease in cell proliferation. Neither the 900 microwaves nor g-rays significantly altered cell cycle phase distribution. The rate of apoptosis was considerably increased in a dose-dependent manner after the combined exposure. Microwaves alone did not significantly affect MDA levels or SOD activity. The combined exposure resulted in a significant increase in MDA levels and a decrease in SOD activity. In the microwave exposed groups hsp70 mRNA levels were slightly higher, and in the g-ray exposed groups hsp70 mRNA and protein levels were lower compared to the unexposed control. The combination of microwave and g-ray exposure did not alter the expression of hsp70 compared to g-ray exposure alone.

Interpretation and conclusion
The results of this study indicate that, as evidenced by alterations in proliferation, inhibition, apoptosis and oxidative stress, the adverse effects of exposure to g-radiation on SHG44 glioma cell functions can be enhanced by pre-exposure to 900 MHz radiation.

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