Abstract
Ionizing radiations induce a variety of oxidative DNA damage including isolated and clustered DNA damage. The latter damage is a specific one with ionizing radiation, which might be involved in expression of radiation effect. On the other hand, the former one is same as common oxidative damage with other oxidative stresses. Since the yield of isolated DNA damage is tens of times corresponding clustered ones, both isolated and clustered DNA damage are thought to be similarly important in expression of molecular mechanism of radiation effect. In the present study, we estimated both damage in cultured cells irradiated with heavy particle beams. Chinese hamster ovary AA8 cells were irradiated with gamma-rays, and carbon ions (C), silicon ions (Si) and argon ions (Ar) beams. Their linear energy transfer (LET) were 0.2, 13, 55 and 90keV/µm, respectively. For isolated DNA damage, chromosomal DNA was extracted from the irradiated cells by NaI, and it was analyzed with aldehyde reactive probe quantified by the chemiluminescence. Oxidized pyrimidine and purine lesions were exposed by enzymatic treatment used with endonuclease III (Endo III) and human OGG1. The total yields of intracellular isolated DNA damage decreased with increasing LET [Gamma > C > Si > Ar]. On the other hand, yield of intracellular clustered DNA damage were analyzed by static field gel electrophoresis with similar enzymatic treatment used with Endo III and Fpg. The total yields of intracellular clustered DNA damage showed similar tendency [Gamma > C > Si > Ar]. These results conform to our previous results in test tube. The irradiated cells showed decrease of survival frequencies with increasing LET. Our present and previous results indicate that isolated and clustered DNA damage impact not only quantitatively but also qualitatively radiation effects of heavy particle beams.
