Electromagnetic fields in combination with elevated temperatures affect embryogenesis of Drosophila

Cellular Response to ELF-MF and Heat: Evidence for a Common Involvement of Heat Shock Proteins?

It has been shown that magnetic fields in the extremely low frequency range (ELF-MF) can act as a stressor in various in vivo or in vitro systems, at flux density levels below those inducing excitation of nerve and muscle cells, which are setting the limits used by most generally accepted exposure guidelines, such as the ones published by the International Commission on Non-Ionizing Radiation Protection. In response to a variety of physiological and environmental factors, including heat, cells activate an ancient signaling pathway leading to the transient expression of heat shock proteins (HSPs), which exhibit sophisticated protection mechanisms. A number of studies suggest that also ELF-MF exposure can activate the cellular stress response and cause increased HSPs expression, both on the mRNA and the protein levels. In this review, we provide some of the presently available data on cellular responses, especially regarding HSP expression, due to single and combined exposure to ELF-MF and heat, with the aim to compare the induced effects and to detect possible common modes of action. Some evidence suggest that MF and heat can act as costressors inducing a kind of thermotolerance in cell cultures and in organisms. The MF exposure might produce a potentiated or synergistic biological response such as an increase in HSPs expression, in combination with a well-defined stress, and in turn exert beneficial effects during certain circumstances.

The effects of microwave frequency electromagnetic fields on the development ofDrosophila melanogaster

PURPOSE

To investigate the effects of microwave frequency electromagnetic fields (EMF) on the development of Drosophila melanogaster.

MATERIALS AND METHODS

Larvae of D. melanogaster were exposed to 10 GHz EMF continuously (3 h, 4 h and 5 h) and discontinuously (3 h exposure + 30 min interval + 3 h exposure). The percentages and times of transition from larvae to pupae and from pupae to adults were determined, and the mean offspring number was examined using the offspring of the females which had been exposed as larvae.

RESULTS

No differences were found in the transition percentages from larvae to pupae and from pupae to adults (p > 0.05). However, it was found that the mean pupation time was delayed linearly with an increasing electromagnetic field (EMF) exposure period (p < 0.05). In the 3 + 3-h exposed group (E3 + 3), the mean offspring number was significantly less than that of the control (p < 0.05).

CONCLUSIONS

10 GHz EMF can cause developmental delay and decrease the number of offspring in D. melanogaster.

Electromagnetic field therapy delays cellular senescence and death by enhancement of the heat shock response

Hormesis may result when mild repetitive stress increases cellular defense against diverse injuries. This process may also extend in vitro cellular proliferative life span as well as delay and reverse some of the age-dependent changes in both replicative and non-replicative cells. This study evaluated the potential hormetic effect of non-thermal repetitive electromagnetic field shock (REMFS) and its impact on cellular aging and mortality in primary human T lymphocytes and fibroblast cell lines. Unlike previous reports employing electromagnetic radiation, this study used a long wave length, low energy, and non-thermal REMFS (50MHz/0.5W) for various therapeutic regimens. The primary outcomes examined were age-dependent morphological changes in cells over time, cellular death prevention, and stimulation of the heat shock response. REMFS achieved several biological effects that modified the aging process. REMFS extended the total number of population doublings of mouse fibroblasts and contributed to youthful morphology of cells near their replicative lifespan. REMFS also enhanced cellular defenses of human T cells as reflected in lower cell mortality when compared to non-treated T cells. To determine the mechanism of REMFS-induced effects, analysis of the cellular heat shock response revealed Hsp90 release from the heat shock transcription factor (HSF1). Furthermore, REMFS increased HSF1 phosphorylation, enhanced HSF1-DNA binding, and improved Hsp70 expression relative to non-REMFS-treated cells. These results show that non-thermal REMFS activates an anti-aging hormetic effect as well as reduces cell mortality during lethal stress. Because the REMFS configuration employed in this study can potentially be applied to whole body therapy, prospects for translating these data into clinical interventions for Alzheimer's disease and other degenerative conditions with aging are discussed.

Weak electromagnetic fields (50 Hz) elicit a stress response in human cells

The aim of this study was to demonstrate the expression of heat shock (HS) genes in human cells in response to extremely low-frequency electromagnetic fields (ELF-EMF) alone and in combination with thermal stress. After exposing human myeloid leukemia (HL-60) cells to the stressor(s) for 30 min we quantified the expression of the HS genes HSP27, HSP60, HSP70 (A, B, and C), HSC70, HSP75, HSP78, and HSP90 (alpha and beta) by RT-PCR. The results clearly show that HS genes, in particular the three HSP70 genes (A, B, and C), are induced by ELF-EMF, a reaction that is enhanced by simultaneous HS (43 degrees C for 30 min). The results show similarities and some significant differences to previous experiments in which transgenic nematodes were used to monitor the induction of the HSP70 gene under similar stress conditions. We also studied the effect of different flux densities on gene expression in the range of 10-140 microT. Even the lowest dose tested (10 microT) resulted in a significant induction of the genes HSP70A, HSP70B, and HSP70C. The reaction to ELF-EMF shows a maximum at a flux density of 60-80 microT. The unusual dose-response relation reveals an interesting difference to other stressors that elicit the HS response.

Microwave exposure induces Hsp70 and confers protection against hypoxia in chick embryos

To determine if microwave exposure could elicit a biological effect in the absence of thermal stress, studies were designed in which chick embryos were exposed to athermal microwave radiation (915 MHz) to look for induction of Hsp70, a protein produced during times of cellular stress that aids in the protection of cellular components. Levels of Hsp70 were found to increase within 2 h, with maximum expression ( approximately 30% higher than controls) typically occurring by 3 h from the start of exposure. Other embryos were exposed to microwave radiation prior to being subjected to hypoxic stress, and were found to have significantly higher survival (P < 0.05) following re-oxygenation than non-exposed controls. The results of these studies indicate that not only can athermal microwave exposures activate the stress protein response pathway; they can also enhance survivability following exposure to a subsequent, potentially lethal stress. From a public health standpoint, it is important that more studies be performed to determine if repeated exposures, a condition likely to be found in cell phone use, are still beneficial.

Interaction of Stressors and the Limits of Cellular Homeostasis

The cellular stress response which can be elicited by a variety of physical or chemical stressors challenges the homeostatic mechanisms of the cells. Two stressors may interact such that, for example, in the presence of a defined thermal stress ("costress") a second weak stressor like electromagnetic fields (50 MHz, 100 microT) produces strong biological effects. Based on the apparent interaction of these stressors a concept is suggested that explains the observed effects and defines the limits of cellular homeostasis in general terms. The homeostatic potential of a cell and hence the ability to cope with stressors can be altered by eliciting or depressing the heat shock response. This manipulation has several promising medical applications.