Figure 5. Biological effects of resveratrol result mainly from its inhibition of insulin signalling pathway in liver cells.

(A) HEK-293 cells were set up in DMEM supplemented with 5% fetal bovine serum for 1 day and serum-deprived overnight prior to the treatments. Cells were then changed into DMEM supplemented with 1 μM dexamethasone and incubated with 100 μM resveratrol for 30 min before they were challenged with insulin (100 nM, 10 min), IGF-1 (50 ng/ml, 15 min), EGF (50 ng/ml, 30 min) and 5% fetal bovine serum (30 min). Total cell lysates were prepared for Western-blot analysis using antibodies against both total and phosphorylated forms of Akt and MAPK. The protein amount of phosphorylated MAPK and Akt were also quantified using ImageJ (NIH Image) program, and the results from three independent experiments were averaged and plotted relative to the basal level. The significance of resveratrol inhibition of MAPK and Akt activations elicited by these growth factors was analysed using Student's t test. *P<0.05. (B) Insulin signalling pathway is an essential pathway leading to MAPK and Akt activations in liver cells. H4IIE cells were set up as described in Figure 2(A). Cells were changed into DMEM supplemented with 1 μM dexamethasone and pre-incubated with 100 μM resveratrol for 20 min and then challenged with various growth factors, including insulin (100 nm, 10 min), IGF-1 (100 ng/ml, 30 min), EGF (50 ng/ml, 30 min) and NGF (50 ng/ml, 30 min). Whole cell lysates were prepared for Western-blot analysis under these conditions.