Melatonin protects human cells from clustered DNA damages, killing and acquisition of soft agar growth induced by X-rays or 970 MeV/n Fe ions

Abstract

Purpose: We tested the ability of melatonin (N-acetyl-5 methoxytryptamine), a highly effective radical scavenger and human hormone, to protect DNA in solution and in human cells against induction of complex DNA clusters and biological damage induced by low or high linear energy transfer radiation (100 kVp X-rays, 970 MeV/nucleon Fe ions).

Materials and methods: Plasmid DNA in solution was treated with increasing concentrations of melatonin (0.0–3.5 mM) and were irradiated with X-rays. Human cells (28SC monocytes) were also irradiated with X-rays and Fe ions with and without 2 mM melatonin. Agarose plugs containing genomic DNA were subjected to Contour Clamped Homogeneous Electrophoretic Field (CHEF) followed by imaging and clustered DNA damages were measured by using Number Average length analysis. Transformation experiments on human primary fibroblast cells using soft agar colony assay were carried out which were irradiated with Fe ions with or without 2 mM melatonin.

Results: In plasmid DNA in solution, melatonin reduced the induction of single- and double-strand breaks. Pretreatment of human 28SC cells for 24 h before irradiation with 2 mM melatonin reduced the level of X-ray induced double-strand breaks by ∼50%, of abasic clustered damages about 40%, and of Fe ion-induced double-strand breaks (41% reduction) and abasic clusters (34% reduction). It decreased transformation to soft agar growth of human primary cells by a factor of 10, but reduced killing by Fe ions only by 20–40%.

Conclusion: Melatonin's effective reduction of radiation-induced critical DNA damages, cell killing, and striking decrease of transformation suggest that it is an excellent candidate as a countermeasure against radiation exposure, including radiation exposure to astronaut crews in space travel.

Keywords:

• human cells
• clustered DNA damage
• double-strand breaks
• abasic clusters
• melatonin
• cell transformation
• cell survival

Acknowledgements

This paper is dedicated to our beloved Dr Betsy Sutherland, the guide, supervisor and mentor of this work. We thank Drs Adam Rusek, Michael Sivertz and I Hung Chiang of the NSRL Physics Dosimetry group for providing the ion beams and for dosimetry. We also thank Medical Division for providing X-ray irradiation facility. Supported by grants from the National Space Biomedical Institute to A. Gewirtz and BMS, the Human Research Program of the Exploration Systems Mission Directorate of the National Aeronautics and Space Administration, the Low Radiation Dose Program of the Office of Biological and Environmental Research of the US Department of Energy, and the National Institutes of Health (R01 CA86897) to BMS.

Declaration of interest:

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.