Presentation Transmission and repair of DNA damage signal to bystander cells from the population of proton microbeam irradiated human cells

N. Pandey, Bandri  ,  Desai, Sejal  ,  Kobayashi, Alisa  ,  Konishi, Teruaki

Microbeam provides important tool to study radiation induced bystander effect with precise localization of target cells in a population delivering defined radiation dose/number of particles. Microbeam technique has been employed to investigate radiation effects to bystander cells using various biological end points. However, studies are limited in literature revealing transmission and repair of DNA damage signal from microbeam irradiated cells to bystander cells. In present study, we have studied direct and bystander damage in proton microbeam irradiated human lung cancer (A549) and normal lung fibroblasts (WI38) cells using SPICE microbeam facility (3.4 MeV; ~2 M beam diameter; LET 11.7 KeV/M) at NIRS, Japan. A549 or WI38 cells were irradiated with increasing number of protons (10-200 protons/cell) followed by measurement of -H2AX foci. -H2AX foci were observed in A549 cells irradiated with ≥50 protons/cell, which were observed at ≥200 protons/cell in WI38 cells. These results suggest requirement of higher number of protons to detect proton microbeam induced DSBs by -H2AX foci in WI38 than in A549 cells. Repair kinetics of DSBs induced by proton microbeam was faster in WI38 than A549 cells. To evaluate the bystander effect in proton irradiated A549 cells, -H2AX foci were analyzed in irradiated area of cells as well as three adjacent side-by-side areas of non-irradiated (bystander) cells on the irradiation dish. When images were analyzed for -H2AX intensity, a pattern was observed, which showed maximum DNA damage in directly irradiated cells after 30 min of irradiation. Measurement at subsequent incubation periods showed transmission of damaging signal in adjacent areas and distance travelled of damaging signal was dependent on incubation period. Our results provide novel understanding of transmission and repair signal from proton microbeam irradiated cells to bystander cells.
The 12th International Workshop on Microbeam Probes of Cellular Radiation Response

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