Autores

Chavdoula ED, Panagopoulos DJ, Margaritis LH. Comparison of biological effects between continuous and intermittent exposure to GSM-900-MHz mobile phone radiation: detection of apoptotic cell-death features. Mutat. Res.  Ahead of print. Apr 28, 2010.

Background
A number of studies have reported DNA or cell damage, such as DNA breaks, cell malformations, cell death, changes in chromatin conformation and micronucleus formation in different cell types or organisms in response to electromagnetic fields (EMF). In other studies, no genotoxic effects of exposure to EMF were observed.

Objective
The objective of this study was to compare the influence of different types of intermittent exposure with different intervals with the effects of continuous exposure of the same total duration of GSM radiation on the reproductive capacity of Drosophila melanogaster.

Methods
A digital mobile phone handset connected to a GSM-900-MHz network was used in order to analyze the effects of real exposure conditions. Flies were exposed for 6 minutes daily to mobile phone radiation modulated by human voice. The continuous (C) type of exposure was one 6 minute continuous exposure. The intermittent exposure types employed 6 exposures of 1 minute each (I1), 3 exposures of 2 minute each (I2), and 2 exposures of 3 minute each (I3), respectively. The interval duration between the different exposure sessions was 10 minutes. The final exposure type (I4) comprised 2 exposures of 3 minutes each with a 6-hour interval. Flies were subsequently mated, F1 pupae hatched and some maternal flies were anesthetised and their egg chambers were dissected. A terminal transferase- mediated dUTP nick-end labelling (TUNEL) assay was then conducted to detect DNA fragmentation.

Results
Each exposure protocol significantly decreased the number of F1 pupae of the exposed insects compared with that of the sham-exposed groups. The C and I1, I2, I3 types of exposure produced very similar decreases in the mean number of F1 pupae (41.6%, 43.2%, 43.4%, 42.3%, respectively), whereas the I4 procedure produced the smallest decrease in reproductive capacity (31.6%). All types of exposure were found to induce cell death at all stages of early and mid oogenesis but mainly at germarium and stages 7–8. In the C, I1, I2, I3, and I4 exposure protocols the overall ratios of the number of egg chambers with DNA fragmentation vs the total number of egg chambers ±S.D. were 0.51±0.05, 0.52±0.04, 0.53±0.05, 0.52±0.05 and 0.41±0.05, respectively, whereas in the sham group’s the corresponding percentage was 0.06±0.02.

Interpretation and Limitations
The results of this study correlate with the authors’ previous findings that acute exposure to GSM signals brings about DNA fragmentation in the ovarian cells and consequently a large reduction in the reproductive capacity of the insects. The effects of exposure were not as significant in the I4 group where the decrease in reproductive capacity was smaller than the corresponding effect of the induced cell death which may be a result of compensatory mechanisms that replace defective egg chambers with new ones. However, one limitation of this study is the difference in the time when the I4 egg chambers were dissected compared to the other exposure groups (3 minutes earlier). During this time, damaged egg chambers may have been phagocytosed by neighbouring follicle cells and new non-defective egg chambers produced. Experimentation should be repeated to take into account this time discrepancy. Also, in order to confirm the interference of exposure to EMF with apoptosis, more aspects of apoptotic cell death in ovarian cells, such as caspase activation and chromatin condensation, need to be studied.

Conclusion
This study suggests that intermittent EMF exposures are almost equally as effective as continuous exposure of the same total duration. Longer intervals between exposures allow D. melanogaster the time required to recover and partly overcome effects of GSM exposure.



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