Objective: To study the protective effect of nuclear factor erythroid 2-related factor 2 (Nrf2) activation by curcumin against lead-induced toxicity and apoptosis in SH-SY5Y human neuroblastoma cells and its impact on expression of apoptosis-related proteins.
Methods: After the cells were treated with 0, 0.5, 1, 5, or 10 μmol/L curcumin for 24 hours, nucleoprotein was extracted and electrophoretic mobility shift assay was used to measure Nrf2-antioxidant responsive element (ARE) binding capacity. The optimal concentration of curcumin was figured out for treating cells. After pretreatment with 5 μmol/L curcumin for 24 hours, cells were exposed to lead acetate at different concentrations (0, 5, 25, and 125 μmol/L for control, low-dose, medium-dose, and high-dose groups). The 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyl tetrazolium bromide (MTT) assay, flow cytometry, and Western blot were used to evaluate cell viability, apoptosis, and expression of apoptosis-related proteins, respectively.
Results: Curcumin of 5 μmol/L caused significantly increased cell viability in low-, medium-, and high-dose groups exposed to lead acetate for 12 hours (98.42%±1.12% vs 92.92%±0.14%, P<0.05; 95.30%±1.17% vs 91.15%±0.67%, P<0.05; 94.50%±1.45% vs 85.98%±0.45%, P<0.05). Curcumin of 5 μmol/L also caused significantly increased cell viability in medium-and high-dose groups exposed to lead acetate for 24 hours (93.10%±1.63% vs 88.40%±4.13%, P<0.05; 90.13%±2.03% vs 83.63%±3.42%, P<0.05). The high-dose group had a significantly higher apoptotic rate than the control group 6.17%±1.31% vs 3.30%±0.53%, P<0.05). Curcumin of 5.0 μmol/L significantly reduced the apoptotic rate in the high-dose group (2.97%±0.15% vs 6.17%±1.31%, P<0.05). Exposure to lead acetate elevated the expression of Bax, cytochrome C, and caspase-3 and reduced Bcl-2 expression. Curcumin of 5.0 μmol/L significantly reduced the expression of Bax, cytochrome C, and caspase-3 in the high-dose group (P<0.05).
Conclusion: Nrf2 activation by curcumin has a protective effect against lead-induced toxicity and apoptosis in SH-SY5Y cells. The protective effect of Nrf2 against apoptosis may be associated with the regulation of apoptosis-related proteins.