Exposure to low level chronic radiation leads to adaptation to a subsequent acute X-ray dose and communication of modified acute X-ray induced bystander signals in medaka (Japanese rice fish, Oryzias latipes)

Abstract

Purpose: To determine the effect of acute high dose X-rays on the direct and bystander response of chronically exposed medaka in vivo using the fish communication model.

Methods: Medaka were obtained from the Low Dose Rate Irradiation Facility (LoDIF) located at the Savannah River Ecology Laboratory (SREL), University of Georgia, Aiken, South Carolina, USA where they had been exposed over 264 days to cumulative total doses of 0, 0.03, 0.66 and 5.88 Gy. They were exposed to the acute dose at McMaster University and then allowed to swim with unexposed medaka. All groups were sacrificed and fins were cultured as explants and assayed using an established technique and reporter assay.

Results: Directly irradiated medaka with no chronic exposure showed a classic in vivo bystander response. Chronic pre-exposure resulted in a chronic dose-dependent increase in reporter cell survival in directly exposed fish. A ‘pro-survival’ response was also seen in the bystander fish. The proteins bcl-2 (b cell lymphoma 2) and c-Myc (myelocytomatosis oncogene cellular) in tissue explants were good predictors of pro-life or pro-death signals.

Conclusions: Environmentally relevant chronic exposure to medaka in vivo results in adaptive responses in fish subsequently irradiated with high acute doses and in communication of protective signals to fish swimming with exposed fish. The data have implications for interpretation of radiation effects in biota.

Keywords::

• Environmental radiobiology
• medaka
• chronic radiation dose
• biomarkers
• bystander effects

Acknowledgements

We acknowledge financial support from the National Science and Engineering Research Council (NSERC) Industrial research Chairs Programme, The Canada Research Chairs Programme and the NSERC Discovery Grants Programme. We also acknowledge our participation in the European Union Integrated Project ‘Non-Targeted Effects of Radiation’ (NOTE). The assistance of D. Coughlin and Yi Yi at the LoDIF facility, and H. Mitani for supplying fish is much appreciated.

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