Medium-mediated bystander response of X-ray-irradiated normal human lymphocytes in vitro

Radiation-induced bystander effects occur in cells that are not directly irradiated but that communicate with irradiated cells via secreted into culture medium soluble factors or gap junction. This effect induces in irradiated and neighboring cells persistent long-term changes that result in delayed death or genomic instability leading to neoplastic transformation. Non-irradiated human normal lymphocytes were incubated in a medium transferred from irradiated another samples of lymphocytes (ICM - irradiation-conditioned medium). Immediately after replacement of the normal or conditioned medium antioxidant vitamins C or E were added. In lymphocytes incubated in a normal medium (control) or conditioned medium, with or without vitamins, the chromosomal damage and apoptosis were estimated. The results show that medium from irradiated cells (ICM) induces in normal lymphocytes micronuclei and condensation of chromatin characteristic of processes of apoptosis. Conditioned medium did not influence cell cycle division. Bystander effect-induced formation of micronuclei was inhibited by antioxidant vitamins C and E, but this had no effect on the induction of apoptosis. These observations suggest that antioxidant vitamins are able to modify radiation-induced bystander effect (by preventing the increase in micronuclei), without inhibiting elimination of damaged cells via apoptosis. This finding could have significant implication for estimating risks of radiation exposure.