Biological effects in mammalian cells irradiated with low fluences of heavy ions

There are numerous reports of bystander effects after exposure to low fluences of alpha particles. However, only a limited number of studies have examined bystander effects after exposure to low fluences of ion species heavier than helium. In this study we has been investigating bystander cellular responses in normal human fibroblasts irradiated with low-fluence beams of low energy carbon ions. Cells were exposed using 4 different protocols; (1) Cells were irradiated with all of the cells on the Mylar film; (2) Cells were irradiated with half of the cells; (3) Irradiated cells and un-irradiated control cells were pooled in a 1:1 ratio and plated as a single culture; and (4) Half of the cells were irradiated and treated with a specific inhibitor of gap-junction mediated cell-cell communication. Cell killing showed that the surviving fraction of the group (2) was almost the same as for the group (1). In addition, a similar level of survival was seen in the group (4) and in the group (3). Mutation induction showed the same trend as the cell killing. There is evidence that the bystander effect for both cell killing and mutation induction occurred in the un-irradiated half of the cells in group (2). (author)