Abstract: BACKGROUND: c-Myc is a well-known oncogene overexpressed in many cancers. Alveolar macrophages are important functional cells of the lungs, not only involved in the immune defense of the lungs, swallowing bacterial particles that invade the lungs, but also secreting large amounts of biologically active substances to maintain the normal physiological functions of the lungs and the body. Superoxide dismutase has a close relationship with tumors.
OBJECTIVE: To observe the effects of superoxide dismutase on cell proliferation and c-myc expression in lung fibroblasts activated by supernatants of silicon dioxide (SiO2)-induced rat alveolar macrophages. 
METHODS: Alveolar macrophages were obtained by in situ alveolar lavage technique to prepare conditional culture supernatant: superoxide dismutase culture supernatant (superoxide dismutase+alveolar macrophages+serum-free DMEM), SiO2 supernatant (SiO2+alveolar macrophages+serum-free DMEM), SiO2+superoxide dismutase culture supernatant (SiO2+superoxide dismutase+alveolar macrophages+serum-free DMEM). The supernatant was collected at 1, 2, 4, 8, 16, and 32 hours after culture. Inducted culture of lung fibroblasts: passage 3 lung fibroblasts were taken and induced by the combination of conditional supernatant and 5% fetal bovine serum-DMEM in a 1:1 ratio. There were five groups in the experiment: negative control group (2.5% fetal bovine serum-DMEM culture), positive control group (10% fetal bovine serum-DMEM culture), superoxide dismutase supernatant group, SiO2 supernatant group, and SiO2+superoxide dismutase supernatant group. Culture time was synchronized with the above time points. MTT, immunocytochemistry and RT-PCR methods were used to detect lung fibroblast proliferation, c-myc protein and mRNA expression. The study protocol was approved by the Animal Experiment Ethics Committee of North China University of Science and Technology.
RESULTS AND CONCLUSION: Compared with the control group, cell proliferation and expression of c-myc protein and mRNA in lung fibroblasts were singificantly increased in the SiO2 supernatant group. Treatment with SiO2 and superoxide dismutase could inhibit the elevation of cell proliferation, protein and mRNA levels of c-myc (P < 0.05). To conclude, superoxide dismutase can attenuate fibroblast proliferation and high expression of c-myc in rat lung fibroblasts induced by supernatant of SiO2-treated lung macrophages.

Key words: pulmonary fibrosis, superoxid dismutase, lung fibroblast, alveolar macrophage, c-myc, immunocytochemistry, reverse transcription-polymerase chain reaction, rat