Bystander cell-killing effect mediated by nitric oxide in normal human fibroblasts depends in part on irradiation dose but not on radiation quality

Yokota, Yuichiro; Funayama, Tomoo; Ikeda, Hiroko; Sakashita, Tetsuya; Suzuki, Michiyo; Kobayashi, Yasuhiko

Here, we investigate bystander effect. Normal human fibroblast WI-38 cells were irradiated with carbon ions or -rays. Irradiated cells and non-irradiated cells were co-cultured. The survival rates of bystander cells decreased with dose at lower than 0.5 Gy and bottomed out at around 80%. In addition, the survival rates of bystander cells were not significantly different between carbon ions and -rays at the same doses. These indicated the bystander cell-killing effect depends on irradiation dose but not on radiation quality. c-PTIO, a specific scavenger of nitric oxides (NO), suppressed the reduction of survival rates of bystander cells, showing NO has an important role to induce the bystander effect. The concentrations of nitrite, an oxide of NO, were measured. There were negative relationships between the survival rates of bystander cells and the nitrite concentrations of the medium. NO released to the medium maybe an important factor related to the bystander effect.