Figure 1. Curcumin induces SIRT1 enzyme activity in vitro.

(A) FaDu and Cal27 cells were treated with curcumin (7 μmol/l) in the presence or absence of SIRT1 inhibitor nicotinamide for 6 h and harvested. Then the extracts were analysed for SIRT1 enzyme activity. Treatment of FaDu and Cal27 cells with curcumin markedly increased the deacetylating activity; conversely, pre-treatment of cells with nicotinamide significantly blocked curcumin-triggered deacetylating activity. (B–C) To further confirm curcumin activity on SIRT1, we explored SIRT1 expression by Western blotting in FaDu and Cal27 cells treated or not with curcumin. Treatment of carcinoma cells with curcumin markedly increased the SIRT1 expression. However, pre-treatment of FaDu and Cal27 cells with nicotinamide significantly blocked curcumin-triggered SIRT1 activity. (D) We determined a decrease in cell viability using MTT assay and this was due to anti-proliferative activity of curcumin. FaDu as well as Cal27 cells were treated with or without curcumin at the indicated concentrations for 24 h, followed by assessment for cell viability using MTT assays. Raw data from MTT assays were normalized to the % of viable cells in control versus curcumin-treated carcinoma cells. (E–F) FaDu and Cal27 cells were treated with curcumin and then the protein lysates were subjected to Western blot analysis with antibodies specifically against acetylated p53 and GAPDH. (G) Curcumin pretreatment of FaDu cells diluted acetylated p53 expression level at 12 h, with increasing effect at 24 h. (P < 0.01, n = 3) (H) When the effect of curcumin on acetylated p53 expression level of Cal27 cells was tested, a significant reduction was observed at 24 h. (P < 0.01, n = 3) Blots shown are representative of three independent experiments. Data were expressed as mean ± SD. **p < 0.01