Effects of radiofrequency field exposure on proteotoxic-induced and heat-induced HSF1 response in live cells using the bioluminescence resonance energy transfer technique.

As of today, only acute effects of RF fields have been confirmed to represent a potential health hazard and they are attributed to non-specific heating (≥ 1 °C) under high-level exposure. Yet, the possibility that environmental RF impact living matter in the absence of temperature elevation needs further investigation. Since HSF1 is both a thermosensor and the master regulator of heat-shock stress response in eukaryotes, it remains to assess HSF1 activation in live cells under exposure to low-level RF signals. We thus measured basal, temperature-induced, and chemically induced HSF1 trimerization, a mandatory step on the cascade of HSF1 activation, under RF exposure to continuous wave (CW), Global System for Mobile (GSM), and Wi-Fi-modulated 1800 MHz signals, using a bioluminescence resonance energy transfer technique (BRET) probe. Our results show that, as expected, HSF1 is heat-activated by acute exposure of transiently transfected HEK293T cells to a CW RF field at a specific absorption rate of 24 W/kg for 30 min. However, we found no evidence of HSF1 activation under the same RF exposure condition when the cell culture medium temperature was fixed. We also found no experimental evidence that, at a fixed temperature, chronic RF exposure for 24 h at a SAR of 1.5 and 6 W/kg altered the potency or the maximal capability of the proteasome inhibitor MG132 to activate HSF1, whatever signal used. We only found that RF exposure to CW signals (1.5 and 6 W/kg) and GSM signals (1.5 W/kg) for 24 h marginally decreased basal HSF1 activity.

Activation of the TRPV1 Thermoreceptor Induced by Modulated or Unmodulated 1800 MHz Radiofrequency Field Exposure.

The existence of effects of radiofrequency field exposure at environmental levels on living tissues and organisms remains controversial, in particular regarding potential "nonthermal" effects produced in the absence of temperature elevation. Therefore, we investigated whether TRPV1, one of the most studied thermosensitive channels, can be activated by the heat produced by radiofrequency fields and by some specific nonthermal interaction with the fields. We have recently shown that TRPV1 activation can be assessed in real-time on live cells using the bioluminescence resonance energy transfer technique. Taking advantage of this innovative assay, we monitored TRPV1 thermal and chemical modes of activation under radiofrequency exposure at 1800 MHz using different signals (CW, GSM, UMTS, LTE, Wi-Fi and WiMAX) at specific absorption rates between 8 and 32 W/kg. We showed that, as expected, TRPV1 channels were activated by the heat produced by radiofrequency field exposure of transiently-transfected HEK293T cells, but found no evidence of TRPV1 activation in the absence of temperature elevation under radiofrequency field exposure. There was no evidence either that, at fixed temperature, radiofrequency exposure altered the maximal efficacy of the agonist Capsaicin to activate TRPV1.

Effects of 50 Hz magnetic fields on gap junctional intercellular communication in NIH3T3 cells.

The present study focused on gap junctional intercellular communication (GJIC) as a target for biological effects of extremely low-frequency (ELF) magnetic field (MF) exposure. Fluorescence recovery after photobleaching microscopy (FRAP) was used to visualize diffusion of a fluorescent dye between NIH3T3 fibroblasts through gap junctions. The direct effect of 24 h exposure to 50 Hz MF at 0.4 or 1 mT on GJIC function was assessed in one series of experiments. The potential synergism of MF with an inhibitor of GJIC, phorbol ester (TPA), was studied in another series by observing FRAP when NIH3T3 cells were incubated with TPA for 1 h following 24 h exposure to MF. In contrast to other reports of ELF-MF effects on GJIC, under our experimental conditions we observed neither direct inhibition of GJIC nor synergism with TPA-induced inhibition from 50 Hz MF exposures.

In situ expression of heat-shock proteins and 3-nitrotyrosine in brains of young rats exposed to a WiFi signal in utero and in early life.

The bioeffects of exposure to Wireless High-Fidelity (WiFi) signals on the developing nervous systems of young rodents was investigated by assessing the in vivo and in situ expression levels of three stress markers: 3-Nitrotyrosine (3-NT), an oxidative stress marker and two heat-shock proteins (Hsp25 and Hsp70). These biomarkers were measured in the brains of young rats exposed to a 2450 MHz WiFi signal by immunohistochemistry. Pregnant rats were first exposed or sham exposed to WiFi from day 6 to day 21 of gestation. In addition three newborns per litter were further exposed up to 5 weeks old. Daily 2-h exposures were performed blind in a reverberation chamber and whole-body specific absorption rate levels were 0, 0.08, 0.4 and 4 W/kg. 3-NT and stress protein expression was assayed in different areas of the hippocampus and cortex. No significant difference was observed among exposed and sham-exposed groups. These results suggest that repeated exposure to WiFi during gestation and early life has no deleterious effects on the brains of young rats.

ELF magnetic fields: animal studies, mechanisms of action.

Animal studies can contribute to addressing the issue of possible greater health risk for children exposed to 50-60 Hz extremely low frequency (ELF) magnetic fields (MFs), mostly in terms of teratological effects and cancer. Teratology has been extensively studied in animals exposed to ELF MFs but experiments have not established adverse developmental effects. Childhood leukaemia has been the only cancer consistently reported in epidemiological studies as associated with exposure to ELF MFs. This association has been the basis for the classification as "possibly carcinogenic to humans" by the International Agency for Research on Cancer in 2002. Animal experiments have provided only limited support for these epidemiological findings. However, none but one study used an animal model for acute lymphoblastic leukaemia (ALL), the main form of childhood leukaemia, and exposures to ELF MFs were not carried out over the whole pregnancy period, when the first hit of ALL is assumed to occur. Moreover, there are no generally accepted biophysical mechanisms that could explain carcinogenic effects of low-level MFs. The radical pair mechanism and related cryptochromes (CRY) molecules have recently been identified in birds and other non-mammalian species, as a sensor of the geomagnetic field, involved in navigation. The hypothesis has to be tested in mammalian models. CRY, which is part of the molecular circadian clock machinery, is a ubiquitous protein likely to be involved in cancer cell growth and DNA repair. In summary, we now have some clues to test for a better characterization of the interaction between ALL and ELF MFs exposure.

Lack of effect of 50-Hz magnetic field exposure on the binding affinity of serotonin for the 5-HT 1B receptor subtype.

There is some concern that exposure to extremely low-frequency magnetic fields (MF) causes adverse health effects via signal transduction pathways. Two previous studies reported that exposure to 50-Hz MF decreased the binding affinity of the 1B receptor subtype of serotonin (5-HT) in rat brain membranes. The aim of this study was to investigate whether the exposure to MF affects binding to the 5-HT(1B) receptor and a physiological function associated with 5-HT(1B) receptor activation. Rat brain crude membrane fractions, including 5-HT(1B) receptor and C6-glial cells transfected with human 5-HT(1B) receptor gene, were exposed to 50-Hz MF at 1 mT using Merritt coils under temperature-regulated conditions. In the rat crude membrane, there was no significant difference in the affinity constant of [(3)H]-5-HT between exposed (K(d): 0.92±0.38 nM) and sham-exposed (K(d): 1.00±0.32 nM). The lack of affinity change after exposure was also confirmed using a chemical agonist of the 5-HT receptor, [(3)H]-5-carboxytryptamine (K(d): 0.59±0.06 nM for exposed and 0.71±0.08 nM for sham). Similar negative results in terms of affinity constant were obtained on the human 5-HT(1B) receptor in C6-glial cells. In addition, forskolin-stimulated cAMP production was inhibited by 5-HT administration in a dose-dependent manner in C6-glial cells, but exposure did not modify the inhibitory response. This study thus failed to confirm the previous results and findings suggest that exposure to MF below the current occupational limit does not affect the physiological function involved in 5-HT(1B) receptor subtypes.

Effects of head-only exposure of rats to GSM-900 on blood-brain barrier permeability and neuronal degeneration.

Salford et al. reported in 2003 that a single 2-h exposure to GSM-900 mobile telephony signals induced brain damage (increased permeability of the blood-brain barrier and presence of dark neurons) 50 days after exposure. In our study, 16 Fischer 344 rats (14 weeks old) were exposed head-only to the GSM-900 signal for 2 h at various brain-averaged SARs (0, 0.14 and 2.0 W/kg) or were used as cage or positive controls. Albumin leakage and neuron degeneration were evaluated 14 and 50 days after exposure. No apoptotic neurons were found 14 days after the last exposure using the TUNEL method. No statistically significant albumin leakage was observed. Neuronal degeneration, assessed using cresyl violet or the more specific marker Fluoro-Jade B, was not significantly different among the tested groups. No apoptotic neurons were detected. The findings of our study did not confirm the previous results of Salford et al.

Effect of GSM-900 and -1800 signals on the skin of hairless rats. III: Expression of heat shock proteins.

PURPOSE: We previously reported the inability of Global System for Mobile communication (GSM) signals at 900 (GSM-900) and 1800 (GSM-1800) MegaHertz (MHz) to induce morphological and physiological changes in epidermis of Hairless rats. The present work aimed at investigating heat shock proteins (HSP) expression--as a cellular stress marker--in the skin of Hairless rats exposed to GSM-900 and -1800 signals. MATERIALS AND METHODS: We studied the expression of the Heat-shock cognate (Hsc) 70, and the inducible forms of the Heat-shock proteins (Hsp) 25 and 70. Rat skin was locally exposed using loop antenna and restrain rockets to test several Specific Absorption Rates (SAR) and exposure durations: (i) single exposure: 2 hours at 0 and 5 W/kg; (ii) repeated exposure: 2 hours per day, 5 days per week, for 12 weeks, at 0, 2.5, and 5 W/kg. HSP expression was detected on skin slices using immunolabeling in the epidermal area. RESULTS: Our data indicated that neither single nor repeated exposures altered HSP expression in rat skin, irrespective of the GSM signal or SAR considered. CONCLUSIONS: Under our experimental conditions (local SAR < 5 W/kg), there was no evidence that GSM signals alter HSP expression in rat skin.