Figure 1.
Mean values for the direct measure of insulin sensitivity, as assessed by the glucose infusion rate during the last 20-h hyperinsulinemic-euglycemic clamp.
Silymarin (200 mg/kg body weight) was orally administered once daily to Wistar rats for 2 weeks. A glucose clamp was performed 30 min after the oral intake of silymarin (200 mg/kg) in Wistar rats fed normal or fructose-rich chow. VO-OHpic (PTEN inhibitor, 10 µg/kg) was i.p. injected 30 min before administration of silymarin. The vehicle used to dissolve the testing drugs was given at the same volume. Values (mean ± SE) were obtained from each group of 8 animals. ***P<0.001 compared with vehicle-treated normal chow-fed group. ###P<0.001 compared with the vehicle-treated fructose-rich chow-fed group.
Table 1.
Effects of silymarin on body weight, biochemical indicators and HOMA-IR) in Wistar rats receiving fed fructose-rich chow or normal chow.
Figure 2.
The effect of silymarin on the expression of PTEN.
Silymarin (200 mg/kg body weight) was orally administered once daily to Wistar rats for 2 weeks. Skeletal muscle (A) and liver (B) were isolated for identification of PTEN expression using western blotting analysis. Data are obtained from 6 individual experiments and expressed as mean ± standard error of mean. *P<0.05; **P<0.01 compared with the vehicle-treated group (first column).
Figure 3.
Silymarin disrupted insulin signaling to decrease glucose uptake in L6 myotube cells.
L6 cells were maintained in normal-glucose (5 mM) or high-glucose (25 mM) medium. Cells were treated with 1 µM silymarin, and each group was exposed or not to 0.1 µM insulin for 30 min. Equal amounts of the total lysates of each group were immunoblotted with anti-phospho-Akt (pAkt) or Akt (A). The L6 cells were then treated with 200 µM 2-NBDG for 10 min to evaluate the glucose uptake ability of each group (B). Values represent means ± standard error of mean of 3 independent experiments. *P<0.05; **P<0.01 compared with the control group.
Figure 4.
PTEN deletion in L6 cells reversed the effect of silymarin on insulin sensitivity and glucose uptake.
Cells were transfected for 48(A). Cells treated with 1 µM silymarin for 6 h with or without specific PTEN siRNA were exposed or not to 0.1 µM insulin. Equal amounts of the total lysates of each group were immunoblotted with anti-phospho-Akt (pAkt) or Akt (B). Cells were transfected for 48 h with 50 pmol PTEN siRNA or scramble siRNA were treated with 1 µM silymarin 6 h with or without specific PTEN siRNA and exposed or not to 0.1 µM insulin for 30 min. The L6 cells were then treated with 200 µM 2-NBDG for 1 h to evaluate the glucose uptake ability of each group (C). Values represent means ± standard error of mean for 3 independent.