Ion-species dependence of chromatin breaks in normal human fibroblasts induced by different ion-species with similar LET value.

Recent studies have shown that the biological endpoints, such as cell killing, mutation induction, transformation and chromosome aberration, were dependent on LET and ion-species. We also indicated that the peak of RBE values for cell killing were different even if ion-species were different. We also investigated LET and ion-species dependence of the induction of chromatin breaks measured immediately after irradiation and 24hr of post-irradiation. The chromatin breaks for 24hr of post-irradiation were dependent on LET and ion-species. Although the initially measured chromatin breaks increased with increasing LET values up to 100 keV/µm as well as no-rejoined breaks, no LET and ion-species. These results implied that the biological effects occurred after repair process was dependent on LET and ion-species. We investigated whether repair kinetics of chromatin breaks induced by different heavy ions with a similar LET values were different or not. Normal human fibroblasts were irradiated with around 100 keV/µm of carbon, neon and silicon ions. Chromatin breaks were counted as excess fragments of prematurely condensed chromosomes using a technique of prematurely chromosome condensation (PCC). The ratios of residual chromatin breaks after 24h of post-irradiation incubation and the repair half times of slow repair in carbon and neon ions were different in these of silicon ions. However, the repair half times of fast repair in three ions were the same. From these results, it is likely that difference in the ratios of residual chromatin breaks after 24h of post-irradiation reflected the results of slow repair process, and these suggested that repair process of chromatin breaks are dependent on ion-species.9th international symposium on chromosome aberration