Human recombinant Sirt1 were incubated with CPE (0.5, 2.5, and 5 μg/mL) or resveratrol (5 μM), a Sirt1 activator, as well as substrate peptide, NAD, and developer, and Sirt1 activity was measured (A). C2C12 cells were incubated with CPE (100 μg/mL) with or without treatment with EX527 (40 μM), and 2NBDG uptake (B), Akt phosphorylation at Ser473, and tyrosine phosphorylation of IRS (C) were measured. Sirt1 expression was determined after treatment with Sirt1 siRNA (D). Cells were incubated with CPE (100 μg/mL) with or without Sirt1 knockdown, and 2NBDG uptake (E) and Akt phosphorylation level at Ser473 (F) were determined. The effects of CPE on the phosphorylation level of AMPK (G). Values are expressed as the mean ± SEM (n = 3–4). *p < 0.05, **p < 0.01 vs. the vehicle-treated control.