Physiological functions of human body are regulated by electric currents. Therefore, is not surprising that placing human body within electromagnetic field, of sufficient strength, may affect physiological processes. The possibility of induction of biological and health effects by low energy radiation emitted by mobile phones (radiofrequency-modulated electromagnetic fields: RF-EMF) remains a controversial issue. In spite of years of research, there is still ongoing discussion whether RF-EMF could induce any physiologically relevant effects [1]. The vast majority of the so far conducted research has focused on cancer. However, RF-EMF is also suspected as potential cause of such ailments as sleep disorders, headaches or allergy-like symptoms [2].

We have proposed that proteomics screening may be used to reveal molecular targets of RF-EMF and help to understand the possible biochemical mechanism of the RF-EMF-induced effects [3]. Our earlier proteomics studies have shown that changes in protein expression and activity (phosphorylation) were induced in human endothelial cell line EA.hy926 that was exposed to RF-EMF [4–7]. These in vitro observed effects, however, do not automatically mean that similar changes would happen in the cells of mobile phone users. Therefore, the present pilot study was undertaken to determine whether a local exposure of human skin to RF-EMF will induce any changes in protein expression and whether it will be possible to find common protein(s) that respond to RF-EMF in all volunteers.

Ethical permit to perform this study was obtained from the Ethics Committee of Department of Surgery of Hospital District of Helsinki and Uusimaa, Finland. A small skin area of a forearm of 10 of same sex (female) volunteers (age 27 – 65 years; mean 51 years) were irradiated for 1 hour with 900 MHz GSM signal at specific absorption rate (SAR) of 1.3 W/kg, using specially designed exposure setup [8]. The mobile phone safety limit SAR is 2.0 W/kg, as recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).

Immediately after the exposure, a punch biopsy of the exposed area of skin (experimental sample) was taken by a physician. Another punch biopsy was taken from the other, non-exposed, forearm (sham sample). In this experimental set-up each volunteer acted as its own sham control. Both exposed and non-exposed skin samples of all volunteers were immediately snap-frozen in liquid nitrogen and stored before extraction of proteins.

Proteins from all samples were extracted using TRIzol Reagent (Invitrogen) and separated using 2-dimensional gel electrophoresis (2-DE) with pH gradient range of 4–7 in the first dimension and 9% SDS-PAGE gel in the second dimension (GE Healthcare). Proteins were detected by silver staining and spot distribution pattern was analyzed using PDQuest 7.2 software (Bio-Rad).

We have analyzed a fragment of proteome: proteins with the isoelectric point (pI) 4–7 and the molecular weight <40 kDa, because the protein spot separation in 2-DE in this area was clearly distinguishable (Figure 1). Firstly, using PDQuest software, for each volunteer was generated an artificial gel, by combining protein expression profiles from sham and exposed samples. Thereafter, all 10 artificial gels were combined into single artificial master gel and the differentially expressed protein spots, which were detected in at least 4 volunteers, were statistically analyzed.

Proteomics approach to study effects of mobile phone radiation on cells has been used so far only by two research groups, ours in Helsinki and group the Zhejiang University, Hangzhou, China. Our studies, using human endothelial cell lines have shown that mobile phone radiation induces statistically significant changes in the expression of several tens of proteins [6] and that the response of cell might be proteome-dependent [7]. In one study, the group in China has not found statistically significant differences in protein expression in MCF-7 cells [9]. The reason for it might be too low number of experiments in MCF-7 study [9]. In our studies statistical analysis was based on 10 different experiments whereas Zeng et al. [9] based their analysis on only three replicates. Another reason for the difference might be different sensitivity of MCF-7 cells as compared with ours endothelial cell lines EA.hy926 and EA.hy926v1. In the other study from Zhejiang University [10] were found 4 differentially expressed proteins in lens epithelial cells, among them the stress response protein Hsp70.

The obtained results, suggesting effect of mobile phone radiation on protein expression in human cell lines, do not automatically mean that this exposure will have any effect on protein expression in humans. The so far conducted human volunteer studies have focused on cognitive responses to RF-EMF [2] and there is no information available about the proteome, as well as transcriptome, response to mobile phone radiation in humans. This study is, to our knowledge, the first one where human response to RF-EMF was examined on molecular level. Our results suggest that human skin might respond to RF-EMF and change protein expression profile. Interestingly, when adjusting results of our previous cellular study [6] using the size of proteome analyzed in the present study (pI 4–7; <40 kDa) the number of the statistically significantly affected proteins appears to be similar in this and in earlier [6] study, 8 spots and 9 spots, respectively. The number of differentially expressed protein spots in both studies is below the number of expected false positives. However, as we have demonstrated experimentally [6] and discussed previously [11] it is likely that some of the proteins will be indeed, real positives. However, without further testing, it is not possible to predict whether these changes will have impact on skin physiology.

Finally, our study confirms that the proposed by us proteomics approach [3] can identify protein targets of RF-EMF. This approach to EMF research has been subsequently accepted by the EMF scientists [12, 13] and has been included into the 2006 World Health Organization Research Agenda [14]. However, new and larger study is urgently needed to strengthen our pilot observations and to determine what impact mobile phone exposure might have on human tissues.

é Mobile phone radiation might alter protein expression in human skin.

é Physiological significance of this change is not known and requires further study.

é Larger human volunteer study will be needed to confirm results of this pilot study.

é Proteomics screening is valid method for search for molecular targets of mobile phone radiation. Without this approach the identification of the proteins responding to mobile phone radiation would not be reasonably possible.