Abstract: OBJECTIVE: To study the variation of the levels of antioxidant proteins，active oxygen radicals and DNA double-strand breaks in the malignantly transformed human bronchial epithelial cell line BEP2D induced by α-particles. METHODS：Western blot was applied for the detection of the protein expressions of catalase (CAT)，glutathione peroxidase (GPXs)，Cu/Zn superoxide dismutase (Cu/Zn-SOD) and Mn superoxide dismutase (Mn-SOD) in BEP2D，RH22，and BERP35T-1 cells. SOD assay kit was employed to measure total SOD (T-SOD)，Cu/Zn-SOD and Mn-SOD enzyme activities in BEP2D，RH22 and BERP35T-1 cells. Using 2’，7’-dichlorofluorescein diacetate (DCHF-DA) and dihydroethidium (DHE)，the generation of H2O2 and superoxide anion (O2－.) in BEP2D，RH22 and BERP35T-1 cells was monitored by flow cytometry. Neutral single cell gel electrophoresis (SCGE) was used to compare the differences of the levels of DNA double-strand breaks in BEP2D，RH22 and BERP35T-1 cells. RESULTS：Compared to BEP2D cells，CAT and GPX1 were down-regulated，but GPX3，Cu/Zn-SOD and Mn-SOD were up-regulated at protein level in RH22 and BERP35T-1 cells (P＜0.05 or P＜0.01). Corresponding to their protein expression levels，RH22 and BERP35T-1 showed increased T-SOD，Cu/Zn-SOD and Mn-SOD enzyme activities (P＜0.05 or P＜0.01). Decreased basal level of O2－. and increased basal levels of H2O2 and DNA double-strand breaks were observed in RH22 and BERP35T-1 cells compared to BEP2D cells (P＜0.05). CONCLUSION： Oxidant/antioxidant imbalance promoting oxidative DNA damage which may result in genomic instability could contribute to the acceleration of cellular malignant transforming process in human bronchial epithelial cell line BEP2D induced by α-particles.

Key words: human bronchial epithelial cell line, α-particle, antioxidant proteins, active oxygen radicals, carcinogenesis