Experimental study on sensibility to γ ray irradiation of two glioma cell lines

AIM: To study the dose and time dependence in the killing effect of γ ray irradiation for two glioma cell lines, investigate the underlying mechanism and compare the radiosensitivity of the two lines. METHODS: Both C6 and SHG 44 cells were divided into 6 groups: 4 Gy, 8 Gy, 16 Gy, 32 Gy, 64 Gy and negative control. A single irradiation was given to achieve each absorbed dose. After irradiation, changes in cell morphology were studied by an invert microscope. To distinguish the possible cell apoptosis, Hoechst 33258 was used to stain the cells nuclei. A flow cytometry was conducted to analyze the composition of the cells by determining the fractions of apoptosis, necrosis and normal in several different time phases after 16 Gy irradiation and also 48 h after the irradiation of each doses. RESULTS: 24 h after 64 Gy or 32 Gy irradiation, many cells of both two lines showed apparent changes in morphology. The classical appearance of cells with apoptosis could be found in the irradiated cells stained by Hoechst 33258. 6 h after irradiation, the apoptosis rates of both cell lines were significantly higher than those of control and they increased greatly with time till 48 h after irradiation. As the absorbed doses raised, the apoptosis rates of both cell lines increased significantly( P 0.01 vs control) but the necrosis rates remained stable( P 0.05 vs control). In 4 Gy, 32 Gy and 64 Gy group, the SHG 44 cells had higher apoptosis rates than C6 cells( P 0.01). CONCLUSION: γ ray irradiation (≤64 Gy) can kill the two glioma cell lines mainly by inducing cell apoptosis. The apoptosis peak appears about 48 h after irradiation. There is a dose dependence in the killing effects of γ ray irradiation. SHG 44 cells are more sensitive to γ ray radiation than C6 cells.