Protective effect of 1950 MHz electromagnetic field in human neuroblastoma cells challenged with menadione

Abstract

This study aims to assess whether a 1950 MHz radiofrequency (RF) electromagnetic field could protect human neuroblastoma SH-SY5Y cells against a subsequent treatment with menadione, a chemical agent inducing DNA damage via reactive oxygen species formation. Cells were pre-exposed for 20 h to specific absorption rate of either 0.3 or 1.25 W/kg, and 3 h after the end of the exposure, they were treated with 10 µM menadione (MD) for 1 h. No differences were observed between sham- and RF-exposed samples. A statistically significant reduction in menadione-induced DNA damage was detected in cells pre-exposed to either 0.3 or 1.25 W/kg (P < 0.05). Moreover, our analyses of gene expression revealed that the pre-exposure to RF almost inhibited the dramatic loss of glutathione peroxidase-based antioxidant scavenging efficiency that was induced by MD, and in parallel strongly enhanced the gene expression of catalase-based antioxidant protection. In addition, RF abolished the MD-dependent down-regulation of oxoguanine DNA glycosylase, which is a critical DNA repairing enzyme. Overall, our findings suggested that RF pre-exposure reduced menadione-dependent DNA oxidative damage, most probably by enhancing antioxidant scavenging efficiency and restoring DNA repair capability. Our results provided some insights into the molecular mechanisms underlying the RF-induced adaptive response in human neuroblastoma cells challenged with menadione.

Figure 1

Medians with interquartile ranges of % DNA in the tail in 500 nuclei (panel A) and of viable SH-SY5Y cells (panel B) treated with different concentrations of MD for 1 h (at least six independent experiments). Same letters indicate no statistically significant differences (please, see main text for statistical details).

Figure 2

Medians with interquartile ranges of % DNA in the tail in 500 nuclei of SH-SY5Y cells: treated with 0.05 µM MD as adaptive dose (AD, given at 48 h after seeding) and 10 µM MD as challenge dose (CD, given at 71 h after seeding) (at least five independent experiments, panel A); untreated (CTRL); sham-exposed for 20 h (Sham); RF-exposed for 20 h at 0.3 W/Kg (0.3 W/Kg) or 1.25 W/Kg (1.25 W/Kg); treated with 10 µM MD for 1 h (MD); sham-exposed and treated with 10 µM MD for 1 h (Sham + MD); RF-exposed for 20 h and treated with 10 µM MD for 1 h (0.3 W/kg + MD; 1.25 W/kg + MD) (at least four independent experiments, panel B). Same letters indicate no statistically significant differences (please, see main text for statistical details).

Figure 3

Medians with interquartile ranges of RT-PCR-based gene expression data (2^−ΔΔCt method) for antioxidant and DNA repairing enzymes. Sod1 (superoxide dismutase 1, panel A), sod2 (superoxide dismutase 2, panel B), cat (catalase, panel C), gpx1 (glutathione peroxidase 1, panel D), ogg1 (8-oxoguanine DNA glycosylase 1, panel E). Cells sham-exposed for 20 h (Sham); sham-exposed and treated with 10 µM MD for 1 h (Sham + MD); RF-exposed for 20 h at 0.3 W/Kg (RF); RF-exposed for 20 h and treated with 10 µM MD for 1 h (RF + MD). Same letters indicate no statistically significant differences (please, see main text for statistical details).

Figure 4

A picture of the experimental set-up used for the exposure of cell cultures to RF. (A) Signal generation and conditioning side; (B) RF application side (WG stands for waveguide).

Figure 5

Schematic representation of the experimental procedure adopted to expose human neuroblastoma SH-SY5Y cells to 1950 MHz, UMTS signal. After 48 h of growth, treatment with radiofrequency (RF)/sham was given for 20 hours, alone or in combination with 10 µM menadione (MD) added at 71 h. 72 hours after seeding, cells were harvested and processed to evaluate viability, by trypan blue dye exclusion assay, primary DNA damage, by alkaline comet assay, or gene expression, by real time RT-PCR.