Lack of evidence for low-LET radiation induced bystander response in normal human fibroblasts and colon carcinoma cells

Abstract

Purpose: To investigate radiation-induced bystander responses and to determine the role of gap junction intercellular communication and the radiation environment in propagating this response.

Materials and methods: We used medium transfer and targeted irradiation to examine radiation-induced bystander effects in primary human fibroblast (AG01522) and human colon carcinoma (RKO36) cells. We examined the effect of variables such as gap junction intercellular communication, linear energy transfer (LET), and the role of the radiation environment in non-targeted responses. Endpoints included clonogenic survival, micronucleus formation and foci formation at histone 2AX over doses ranging from 10–100 cGy.

Results: The results showed no evidence of a low-LET radiation-induced bystander response for the endpoints of clonogenic survival and induction of DNA damage. Nor did we see evidence of a high-LET, Fe ion radiation (1 GeV/n) induced bystander effect. However, direct comparison for 3.2 MeV α-particle exposures showed a statistically significant medium transfer bystander effect for this high-LET radiation.

Conclusions: From our results, it is evident that there are many confounding factors influencing bystander responses as reported in the literature. Our observations reflect the inherent variability in biological systems and the difficulties in extrapolating from in vitro models to radiation risks in humans.

Keywords:

• bystander effects
• human cells
• ionising radiation
• low-LET

Acknowledgements

We thank J. Corcoran for preparation of the Figures and L. M. Markillie for performing statistical analysis of the data. This work was supported by the Biological and Environmental Research Program (BER), U.S. Department of Energy, Grant No. DE-AC06-76RLO (MBS) and DE-FG02-05ER64082 (WFM). Work performed at Brookhaven National Laboratory was supported by NASA, Grant No. NNJ06HD31G (WFM) and NNX07AT42G (JEB). Work performed at UMDNJ-New Jersey Medical School was supported by NIH-National Cancer Institute, Grant No. CA92262-01 (EIA).

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