Bystander effect studies using heavy-ion microbeam at JAEA-Takasaki

Kobayashi, Yasuhiko; Hamada, Nobuyuki*; Ni, M.*; Funayama, Tomoo; Sakashita, Tetsuya

Precise microbeams of C (18.3 MeV/u, LET = 103 keV/m) and Ne (13.0 MeV/u, 375 keV/m) ions were employed for targeting only a very small fraction of cells in confluent fibroblast cultures. Conventional broad-field irradiation was conducted in parallel to see the effects in irradiated cells. Exposure of less than 0.01%of cells led to nearly 10% reductions in the clonogenic survival and twofold rises in the apoptotic incidence regardless of ion species. Transient apoptotic response and delayed p53 phosphorylation were also observed in bystander cells. Collectively, our results indicate that heavy ions inactivate clonogenic potential of bystander cells, and that the time course of the response to heavy ions differs between irradiated and bystander cells. These induced bystander responses could be a defensive mechanism that minimizes further expansion of aberrant cells.