Repair rates of DNA double-strand breaks under different doses of proton and γ-ray irradiation

It is known that DNA double-strand breaks (DSBs), which can be induced by a variety of treatments including ionizing radiation (IR), can cause most deleterious consequences among all kinds of DNA lesions. However, it is still under debate about whether DSBs repair is equally efficient after low and high-LET radiation, especially the basic biological responses after exposure to high-LET particles. In present study, synchronous fibroblast normal Human lung fibroblast (NHLF) cells were irradiated with graded doses of proton and γ-ray. Then γ-H2AX foci assay was used to monitor DSBs induction and repair at 0.5, 1, 2, 4, and 18 h post irradiation. The results showed that the γ-ray irradiation could produce more γ-H2AX foci than proton irradiation at the same dose. However, compared to low LET radiation with γ-ray, the results also showed a much slower DSBs repair rate after high LET radiation with protons, suggesting that the cellular ability to eliminate DSBs after low and high-LET ionizing radiation is quite different.