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; Kobayashi, Yasuhiko

To get the whole picture of bystander effects is necessary to better understand the effect of low-dose irradiation. Normal human fibroblasts were irradiated with carbon ions or rays. After irradiation, irradiated and non-irradiated cells were co-cultured in the upper and lower parts of porous membrane, respectively. The survival rates of bystander cells decreased with dose and bottomed out at around 80%. In addition, the survival rates of bystander cells were not different between carbon ions and rays at the same doses. These indicate that the bystander effect depends in part on irradiation dose but not on radiation quality. Treatment of a specific scavenger of nitric oxides suppressed the reduction of survival rates of bystander cells. There were also negative relationships between the survival rates of bystander cells and the nitrite concentrations of the medium, suggesting that the amounts of nitric oxide released are an important factor related to the bystander effect.