Abstract: BACKGROUND AND AIM: Coculture of 60Co-γ irradiated and nonirradiated osteogenic sarcoma U2OS cells was examined for the bystander effects and the interfering effects of Trolox. MATERIALS AND METHODS:groups with 5 samples each:control group,irradiated group,effect group and intervention group,the Trolox control group. In the irradiated group, U2OS cells were treated with 60Co -γ at the dose of 3 Gy and then cultured. In the effect group, after the medium of the irradiated cells was changed, and kept for 1 h, cells with digested with trypsin and collected. After that, the irradiated and nonirradiated cells were co-cultured in the ratio of 1∶1. The intervention group was treated the same as the effect group except the addition of Trolox (10 μg/ml final concentration) . At different time points, cells from the five groups were collected. The cell activity was determined by MTT; the colony formation efficiency and micronucleus frequency were assessed by counting method; the survival rates were estimated by Trypan Blue Staining; and the MDA content in the culture medium was determined by chemical fluorometric method. RESULTS: Compared with the control group, cells in the irradiated group exhibited decreased survival rate (P<0.05), suppressed cell activity (P<0.05), decrease in colony formation efficiency (P<0.05), increase in micronucleus frequency (P<0.05) and increase in MDA content in the culture medium(P<0.05). With the intervention of Trolox, exhibitions of the above indexes were greatly improved. CONCLUSION: Trolox could suppress the bystander and other effects as an antioxidant.

Key words: bystander effect, Trolox, colony formation efficiency (CFE), micronucleus frequency (MF), antioxidant