抄録
It is becoming clear that ionizing radiation causes cell death and chromosome aberration not only in directly irradiated cells but in non-irradiated cells surrounding the exposed cells, whose phenomena are called bystander effects. Some factors secreted into the culture medium have been thought to be involved in the induction of bystander effects, but the mechanism is not clear. We aimed to identify bystander factors in normal human diploid cells exposed to X-rays. The experiments are performed with preparing two 60X24 mm cover slips, on which 2X104 cells are attached. The cells on one cover slip are irradiated with X-rays as donor cells, while the other cells are co-cultured with donor cells as recipient cells. We analyzed cell growth and micronuclei induction in the recipient cells. Twenty-four hours after irradiation, the number of recipient cells was similar to that of the control ((1.17±0.11)X105). In contrast, the frequency of micronuclei observed in recipient cells were (7.0±1.5)X10-3, and control were (3.2±0.3)X10-3. It was two-fold higher than that of the control. Furthermore, we found the frequency of micronuclei was independent of the donor cell's number, or doses. Because ROS and NOS are suggested to be involved in the induction of bystander effects, we examined the effect of DMSO on the induction of micronuclei in the recipient cells. However, there was no suppression, indicating that not short-lived ROS, but long-lived ROS or NOS may be involved in bystander effects.
