Analysis of heavy-ion induced bystander effect using microbeam irradiation

Funayama, Tomoo; Wada, Seiichi*; Kakizaki, Takehiko; Hamada, Nobuyuki*; Yokota, Yuichiro; Sakashita, Tetsuya; Kobayashi, Yasuhiko

To explore a mechanism underlying bystander growth inhibition induced by heavy-ion microbeam radiation, we focused on DNA double strand breaks (DSBs), which are known as a trigger of various radiation response of direct hit cells. We irradiated by 5 count of Ar ion microbeam (11.5 MeV/u, LET=1260 keV/m), and induction of DSBs were visualized by immunostaining of phospohlylated histone H2AX (H2AX), which is known as a molecular marker of DSBs. The samples with the postincubation time longer than 30 minutes showed increased frequency of H2AX positive cells compared with medium-irradiated control sample in a range of 3-4%. This result suggested that the heavy ion irradiation induced bystander effect on the phosphorylation of histone H2AX in CHO-K1 cells. As H2AX is a molecular marker of DSBs, the result suggests that heavy-ion radiation induces DSBs not only on direct hit cells, but on bystander cells.