Differences in the kinetics of γ-H2AX fluorescence decay after exposure to low and high LET radiation

Abstract

Purpose: In order to obtain more insight into heavy ion tumour therapy, some features of the underlying molecular mechanisms controlling the cellular response to high linear energy transfer (LET) radiation are currently analysed.

Materials and methods: We analysed the decay of the integrated fluorescence intensity of γ-H2AX (phosphorylated histone H2AX) which is thought to reflect the repair kinetics of radiation-induced DNA double-strand breaks (DSB) using Laser-Scanning-Cytometry. Asynchronous human HeLa cells were irradiated with a single dose of either 1.89 Gy of 55 MeV carbon ions or 5 Gy of 70 kV X-rays.

Results: Measurements of the γ-H2AX-intensities from 15–60 min resulted in a 16 % decrease for carbon ions and in a 43 % decrease for X-rays. After 21 h, the decrease was 77 % for carbon ions and 85 % for X-rays. The corresponding time-effect relationship was fitted by a bi-exponential function showing a fast and a slow component with identical half-life values for both radiation qualities being 24 ± 4 min and 13.9 ± 0.7 h, respectively. Apparent differences in the kinetics following high and low LET irradiation could completely be attributed to quantitative differences in their contributions, with the slow component being responsible for 47 % of the repair after exposure to X-rays as compared to 80 % after carbon ion irradiation.

Conclusion: γ-H2AX loss kinetics follows a bi-exponential decline with two definite decay times independent of LET. The higher contribution of the slow component determined for carbon ion exposure is thought to reflect the increased amount of complex DSB induced by high LET radiation.

Keywords:

• H2AX
• carbon ions
• repair
• kinetics

Acknowledgements

The authors are grateful for the support of the DFG Cluster of Excellence: Munich-Centre for Advanced Photonics, the EU-project EuroDyna, the Maier Leibnitz Laboratory Munich and the German Federal Ministry of Education and Research (BMBF, PtJ-Bio, 0313909).

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