Abstract
Clustered DNA damage consists of multiple DNA damage in the limited region of DNA strand scratched by the beam of ionizing radiation, as a specific form of radio-induced DNA damage. For its complex structure, clustered DNA damage is thought to strongly inhibit DNA replication and persistently resist the repair activity. However, there are little knowledge about its biological impact in radiation effect. Therefore, we analyzed the yields of clustered DNA damage in the isolated DNA molecule and the chromosomal DNA in Chinese Hamster Overy cell irradiated with various accelerated ion particle beams including carbon (13 keV/μm), silicon (55 keV/μm), iron ions (200 keV/μm), and also gamma-rays (0.2 keV/μm) as a control. The yield of clustered DNA damage were estimated by conventional and pulse-field gel electrophoresis with appropriate DNA repair enzymes for detecting base damage clusters. The results showed that the yields of clustered DNA damage decreased in both irradiated isolated DNA and chromosomal DNA in irradiated cells with an increase in LET (J. Radiat. Res., 49: 133-136, 2008). The additional experiments with binary filters indicated that the inverse correlation between the yield and LET was attributed to the LET but not to the radiation quality. Thus, the quantitative factor of clustered DNA damage seems to be not important to the effect of higher LET-radiation. We need to consider another aspect of clustered DNA damage such as implication of the quality factor for severity of higher LET radiation.
