Effects of Electromagnetic Fields on Cellular Responses to Agents Causing Oxidative Stress and DNA Damage (Sähkömagneettisten kenttien soluvaikutukset yhdessä oksidatiivistä stressiä ja DNA vaurioita aiheuttavien ympäristötekijöiden kanssa)
Year: 2009
Type: dissertation
Abstract: Increased human exposure to different types of electromagnetic fields (EMFs) has raised concerns about possible adverse health effects from such exposure.Widespread human exposure occurs both to extremely low frequency (ELF) magnetic fields (MFs) from the generation, distribution and use of electricity and to radiofrequency (RF) radiation from wireless communication.The exposure limits for EMFs are based on well-known biological effects that require field intensities much higher than those commonly found in human environment, and current research on biological effects is largely focussed on possible effects from fields below the exposure limits.ELF MFs have been classified as possibly carcinogenic to humans based on findings from epidemiological studies on residential ELF MF exposure and childhood leukaemia.However, experimental studies have not provided clear support for carcinogenic effects, and there is no known mechanism for such effects.Extensive research on bioeffects of RF EMFs has not produced consistent evidence of health risks at low field intensities, but there are still some data gaps.For both ELF and RF EMFs, possible carcinogenicity and genotoxicity have been among the main concerns.There is no known biophysical mechanism for DNA damage from weak EMFs, and most experimental studies have not found any genotoxic effects from EMFs alone.However, there is increasing evidence that relatively weak ELF MFs may enhance the effects of DNA-damaging agents.For RF EMFs, less data are available about combined effects with other agents.In this study, cellular effects of weak EMFs were studied in cell cultures, with particular focus on combined effects with agents that induce DNA damage and oxidative stress.In this study, exposure to ELF MFs was found to modify responses to DNA damage both in yeast and mammalian cells.In yeast cells, simultaneous exposure to an ELF MF with a frequency of 50 Hz and magnetic flux density of 120 µT concurrent with ultraviolet (UV) radiation resulted in enhanced cell cycle arrest in the G 1phase.Consistently with the increased cell cycle arrest, MF exposure enhanced the growth delay caused by UVinduced damage.In murine L929 fibroblasts, pre-treatment with a 50 Hz MF at 100 or 300 µT inhibited apoptosis and enhanced G 2 /M-phase cell cycle arrest induced by menadione, a chemical that induces increased production of reactive oxygen species.Only pre-exposure to MFs affected responses to menadione; no MF effects were observed when MF exposure followed treatment with menadione.In fibroblasts, MF exposure did not alter responses to UV radiation in any exposure schedule.No effects of 100 or 300 µT MFs (50 Hz) on UV radiation induced oxidative processes were observed in L929 cells by measuring ultraweak chemiluminescence (photon emissions).Also, exposure to a 300 µT, 50 Hz magnetic field had no effect on intracellular reduced glutathione level (which should decrease as a result of increased production of reactive oxygen species), although similar MF exposure altered subsequent responses to menadione.Exposure to 872-900 MHz RF EMF with a pulse-modulated signal similar to that used in GSM mobile phones increased UV radiation induced apoptosis in yeast cells.In contrast, no enhancement of UV-induced apoptosis was observed in cells exposed to unmodulated RF EMF at identical exposure levels (0.4 or 3.0 W/kg).The most important contribution of the present study is the suggestion that relatively weak EMFs may have measurable impacts on cancer-relevant biological processes such as apoptosis and cell cycle arrest.Effects were found when EMFs were studied as cofactors that modify cellular responses to other agents; no effects from EMFs alone were found.The measurements of cellular oxidative processes did not support the hypothesis that the effects of ELF MFs are explained by increased levels of reactive oxygen species, but the methods used had some limitations and more studies are therefore warranted.The observation of modulation-specific effects of RF EMFs is an interesting finding that should be confirmed in further studies.Overall, studying combined effects of EMFs with other agents appears to be a fruitful avenue for further studies on biological effects of weak EMFs.
Author: Ari Markkanen
Language: Finnish
Subfield: Biophysics
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W3096616919