50 Hz magnetic field influences caspase-3 activity and cell cycle distribution in ionizing radiation exposed SH-SY5Y neuroblastoma cells

Abstract

Purpose

Earlier evidence suggests that extremely low frequency magnetic fields (ELF MFs) can modify the effects of carcinogenic agents. However, the studies conducted so far with ionizing radiation as the co-exposure agent are sparse and have provided inconclusive results. We investigated whether 50 Hz MFs alone, or in combination with ionizing radiation alter cell biological variables relevant to cancer and the biological effects of ionizing radiation.

Materials and methods

Human SH-SY5Y neuroblastoma cells were sham exposed or exposed to 100 or 500 µT MF for 24 h either before or after ionizing radiation exposure (0, 0.4 or 2 Gy). After the exposures, cells were assayed for viability, clonogenicity, reactive oxygen species, caspase-3 activity, and cell cycle distribution. Cell cycle distribution was assayed with propidium iodide staining followed by flow cytometry analysis and ROS levels were assayed together with cell viability by double staining with DeepRed and Sytox Blue followed by flow cytometry analysis.

Results

Increased caspase-3 activity was observed in cells exposed to 500 µT MF before or after ionizing radiation. Furthermore, exposure to the 500 µT MF after the ionizing radiation decreased the percentage of cells in S-phase. No changes in the ROS levels, clonogenicity, or viability of the cells were observed in the MF exposed groups compared to the corresponding sham exposed groups, and no MF effects were observed in cells exposed at 100 µT.

Conclusions

Only the 500 µT magnetic flux density affected SH-SY5Y cells significantly. The effects were small but may nevertheless help to understand how MFs modify the effects of ionizing radiation. The increase in caspase-3 activity may not reflect effects on apoptosis, as no changes were observed in the subG1 phase of the cell cycle. In contrast to some earlier findings, 50 Hz MF exposure after ionizing radiation was not less effective than MF treatment given prior to ionizing radiation.

Keywords:

• Non-ionizing radiation
• ionizing radiation
• caspase-3 activity
• cell cycle
• viability

Acknowledgments

The authors wish to thank senior laboratory technician Ms. Hanne Vainikainen (University of Eastern Finland, Department of Environmental and Biological Sciences) for her skillful assistance in the laboratory analyses. Figure 1. Created with Biorender.com.

Disclosure statement

The authors report no conflict of interest.

Additional information

Funding

This work was supported by the North Savo fund of Finnish Cultural Foundation, Paavo Koistinen foundation, the Paulo foundation, and the University of Eastern Finland’s Doctoral school, Environmental Physics, Health, and Biology doctoral program.

Notes on contributors

Valtteri Nieminen

Valtteri Nieminen, MSc, is a postgraduate researcher in the Radiation Research group at the Department of Environmental and Biological Sciences, University of Eastern Finland. His research focuses on the combined effects of non-ionizing and ionizing radiation or chemicals on cancer cells.

Maria-Viola Martikainen

Maria-Viola Martikainen, PhD, visiting researcher at the Department of Environmental and Biological Sciences of the University of Eastern Finland. Her research interests include investigating how different environmental exposures affect respiratory health using various in vitro techniques.

Saija Kalliomäki

Saija Kalliomäki, MSc, is a researcher at the Department of Environmental and Biological Sciences, University of Eastern Finland. Her research interests include non-ionizing and ionizing radiation-induced effects in cells using in vitro techniques.

Tuomas Virén

Tuomas Virén, PhD, medical physicist at the Radiotherapy unit of Kuopio University Hospital. His research interest includes development of radiotherapy treatment planning techniques and dosimetry as wells as quantification of tumor and normal tissue reactions induced by the radiotherapy treatments.

Jan Seppälä

Jan Seppälä, PhD, chief physicist of the Kuopio University Hospital, Center of Oncology and the Department of Radiotherapy. Has over 20 years’ experience in advanced radiotherapy techniques, SBRT of prostate and lung cancer and VMAT techniques. His main interests in scientific research include dosimetry of modulated RT, image guided RT techniques, breath-hold techniques in RT, AI assisted treatment planning, and radiobiological dose optimization.

Jukka Juutilainen

Jukka Juutilainen, PhD, is Professor Emeritus at the Department of Environmental and Biological Sciences of the University of Eastern Finland. His research interests include biological and health effects of non-ionizing and ionizing radiation using both experimental and epidemiological approaches.

Jonne Naarala

Jonne Naarala, PhD, is Professor of Radiation Biology and leader of Radiation Research Group at the Department of Environmental and Biological Sciences, University of Eastern Finland. His main research interests include cellular and molecular biology of non-ionizing and ionizing radiation-induced effects.

Jukka Luukkonen

Jukka Luukkonen, PhD, is a university lecturer in the Radiation Research Group, University of Eastern Finland, with responsibilities on research and teaching related to the radiation biology. He has over 15 years of experience conducting studies with combined exposure to radiation and other agents.