Berberine inhibits hepatic gluconeogenesis via the LKB1-AMPK-TORC2 signaling pathway in streptozotocin-induced diabetic rats

Figure 1 Effects of berberine on plasma glucose levels in the oral glucose tolerance test and the areas under the curves for plasma glucose. ^bP < 0.01 vs the normal control group at the corresponding time point; ^dP < 0.01 vs the model group at the corresponding time point (by ANOVA). AUC: Areas under the curve.

Figure 2 Effects of berberine on fasting plasma insulin level and homeostasis model assessment of insulin resistance in diabetic rats. Each bar represents the mean ± SD (n = 8). ^bP < 0.01 vs the normal control group; ^dP < 0.01 vs the model group (by ANOVA). HOMA-IR: Homeostasis model assessment of insulin resistance.

Figure 3 Effect of berberine on hepatic LKB-1 protein expression. Western blot analyses of LKB-1 levels in liver tissues of normal control rats, model rats and diabetic rats treated with berberine, AICAR and metformin. A: Representative blots for each group are shown; B: Each bar is expressed as LKB-1/β-actin and represents the mean ± SD (n = 8). ^aP < 0.05 vs the normal control group; ^cP < 0.05 vs the model group (by ANOVA).

Figure 4 Effect of berberine on hepatic AMPK and p-AMPK protein expression. Western blot analyses of AMPK and p-AMPK protein in liver tissues of normal control rats, model rats and diabetic rats treated with berberine, AICAR or metformin. A, C: Representative blots for each group are shown; B: Each bar is expressed as AMPKD/β-actin and represents the mean ± SD (n = 8); D: Each bar is expressed as p-AMPK/β-actin and represents the mean ± SD (n = 8). ^bP < 0.01 vs the normal control group; ^dP < 0.01 vs the model group (by ANOVA).

Figure 5 Effect of berberine on hepatic p-TORC2 and total TORC2 protein expression. Western blot analyses of p-TORC2 and TORC2 proteins from liver tissues of normal rats, model rats and diabetic rats treated with Berberine, AICAR and Metformin. A: Representative blots for each group are shown; B: Each bar is expressed as p-TORC2/β-actin and represents the mean ± SD (n = 8); C: Each bar is expressed as total TORC2/β-actin and represents the mean ± SD (n = 8). ^bP < 0.01 vs the normal group; ^dP < 0.01 vs the model group (by ANOVA).There was no significant difference in the expression of total TORC2 protein across the five groups.

Figure 6 Immunohistochemical staining for TORC2 in the liver tissues. Optical microscopy image of TORC2 is shown in brown. The normal group (A) exhibited little TORC2 in the nuclei. However, more TORC2 was present in the nuclei of the model group (B). The groups treated with Berberine (C), AICAR (D) and Metformin (E) exhibited lower levels of TORC2 compared to the model group (magnification × 400).

Figure 7 Berberine inhibited expression of key gluconeogenic enzyme proteins. Western blot analyses of PEPCK and G-6-P proteins in liver tissues of normal rats, model rats and diabetic rats treated with berberine, AICAR or metformin. A: PEPCK blots for each group are shown; C: G-6-P blots for each group are shown; B: Each bar is expressed as the total PEPCK/β-actin and represents the mean ± SD (n = 8); D: Each bar is expressed as the total G-6-P/β-actin and represents the mean ± SD (n = 8). ^bP < 0.01 vs normal control group; ^dP < 0.01 vs model group; ^aP < 0.05 vs normal control group; ^cP < 0.05 vs model group (by ANOVA).