Can hydrogen peroxide induce DSBs through a long-term cellular response?

Abstract

Reactive oxygen species (ROS) are generated within cells by ionizing radiation via primary ionizing events as well as through secondary amplification systems including metabolic synthesis. Mediating oxidation of cell components, ROS not only cause dysfunction of the target molecules but also perturb intra- and inter-cellular signal transduction pathways. Our ultimate aim is to elucidate the contribution of ROS in cellular events, especially DNA damages, elicited by ionizing radiation. In the current study, we compared cellular responses to hydrogen peroxide (H₂O₂) and X-rays in DNA repair-deficient cells. XRCC4-deficient mutant cells exhibited lower survival rates than XRCC4-proficient parental cells after exposure to either H₂O₂ or X-irradiation. The LD37 values of the XRCC4^-/- and parental cells after a 1-hr treatment with H₂O₂ were 8.5 and 11.1 µM and those for X-irradiation were 0.5 and 1.7 Gy, respectively. XRCC4 is a component of the non-homologous end-joining, a predominant repair pathway for DNA double-strand breaks (DSBs). To date, no other functions of XRCC4 have not been reported yet. Thus, marked increases in death of the XRCC4^-/- cells exposed to H₂O₂ or X-irradiation must be attributed to DSBs. Consistently, γH2AX staining revealed a dose-dependent formation of DSBs in the X-irradiated cells (~50 DSBs/cell/Gy). However, the formation of DSBs was not so significant just after a 1-hr exposure to 0-50 µM H₂O₂ in both the mutant and parental cells. DSBs might be formed at later stages in the H₂O₂-treated cells through some long-term cellular response.