Comparative Studies of Palmatine with Metformin and Glimepiride on the Modulation of Insulin Dependent Signaling Pathway In Vitro, In Vivo & Ex Vivo

Abstract

(1) Insulin resistance, a symptom of type 2 diabetes mellitus (T2DM), is caused by the inactivation of the insulin signaling pathway, which includes IRS-PI3K-IRS-1-PKC-AKT2 and GLUT4. Metformin (biguanide) and glimepiride (sulfonylurea) are both drugs that are derivatives of urea, and they are widely used as first-line drugs for the treatment of type 2 diabetes mellitus. Palmatine has been previously reported to possess antidiabetic and antioxidant properties. (2) The current study compared palmatine to metformin and glimepiride in a type 2 diabetes model for ADME and insulin resistance via the PI3K/Akt/GLUT4 signaling pathway: in vitro, in vivo, ex vivo, and in silico molecular docking. (3) Methods: Differentiated L6 skeletal muscle cells and soleus muscle tissue were incubated in standard tissue culture media supplemented with high insulin and high glucose as a cellular model of insulin resistance, whilst streptozotocin (STZ)-induced Sprague Dawley rats were used as the diabetic model. The cells/tissue/animals were treated with palmatine, while glimepiride and metformin were used as standard drugs. The differential gene expression of PI3K, IRS-1, PKC-α, AKT2, and GLUT4 was evaluated using qPCR. (4) Results: The results revealed that the genes IRS-PI3K-IRS-1-PKC-AKT2 were significantly down-regulated, whilst PKC-α was upregulated significantly in both insulin-resistant cells and tissue animals. Interestingly, palmatine-treated cells/tissue/animals were able to reverse these effects. (5) Conclusions: Palmatine appears to have rejuvenated the impaired insulin signaling pathway through upregulation of the gene expression of IRS-1, PI3K, AKT2, and GLUT4 and downregulation of PKC-expression, according to in vitro, in vivo, and ex vivo studies.

Keywords: AKT2; GLUT4; IRS1; PI3K; T2DM; glimepiride; metformin; palmatine.

Figure 1

In the cell culture model, relative quantification of (a) IRS-1, (b) PI3K, (c) PKC-α, (d) AKT2, and (e) GLUT4 expressions in diabetic, glimepiride, metformin, and palmatine treatment groups. The gene was normalized against a geometric mean of two housekeeping genes (β-actin and γ-actin). All the data points were presented as mean SD. Palmatine group vs. other treatment groups: *** p < 0.001, **** p < 0.0001.

Figure 2

In the in vivo model, relative quantification of (a) IRS-1, (b) PI3K, (c) PKC-α, (d) AKT2, and (e) GLUT4 expressions in diabetic, glimepiride, metformin, and palmatine treatment groups. The gene was normalized against a geometric mean of two housekeeping genes (β-actin and γ-actin). All the data points were presented as mean ± SD. Palmatine group vs. other treatment groups: * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 3

In the ex vivo model, relative quantification of (a) IRS-1, (b) PI3K, (c) PKC-α (d) AKT2, and (e) GLUT4 expressions in diabetic, glimepiride, metformin, and palmatine treatment groups. The gene was normalized against a geometric mean of two housekeeping genes (β-actin and γ-actin). All the data points were presented as mean ± SD. Palmatine groups vs. other treatment groups: ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 4

Structure of (a) PI3K alpha co-crystallized (from PI3K alpha) vs. docked pose and (b) PI3K gamma co-crystallized (from PI3K gamma) vs. docked pose.

Figure 5

The structural binding interaction of (a) palmatine with PI3K alpha and (b) with PI3K gamma, (c) metformin with PI3K alpha and (d) PI3K gamma, and (e) glimepiride with PI3K alpha and (f) PI3K gamma.

Figure 6

Chemical structures of palmatine (1), metformin (2) & glimepiride (3).

Figure 7

The target classes of palmatine (1), metformin (2), and glimepiride (3).

Figure 8

Schematic diagram of the mechanisms of action of palmatine.