The Effects of a Weight-Loss Herbal Formula RCM-107 and Its Eight Individual Ingredients on Glucagon-Like Peptide-1 Secretion-An In Vitro and In Silico Study

Abstract

Obesity is a multifactorial disease that can lead to other health issues. Glucagon-like peptide-1(GLP-1), as one of the satiety signal, has been linked with appetite suppression and weight loss. Due to the limitations of GLP-1 and its analogues, alternative treatments such as herbal therapies have become popular. The herbal formula RCM-107 has demonstrated its inhibitory effects on lipid and carbohydrate absorption in our previous work. However, no published data described its effects on GLP-1 secretion. Therefore, this study aimed to determine the effects of RCM-107 and its individual ingredients on GLP-1 secretion via enzyme-linked immunosorbent assay (ELISA). Furthermore, molecular docking was performed to predict the key chemical compounds that are likely to be GLP-1 receptor agonists. Gardeniae fructus, one of the ingredients in RCM-107, demonstrated significantly greater effects on inducing GLP-1 secretion than the positive control epigallocatechin gallate (EGCG). Two Gardeniae fructus ligands, 3-epioleanolic acid and crocin were predicted to bind to the active form of GLP-1 receptor at the binding pocket with residues known for the receptor activation, suggesting that they could potentially serve as receptor agonists. Overall, this study reported the effects of researched herbs on GLP-1 secretion and proposed two compounds that may be responsible for antiobesity via GLP-1 receptor activation.

Keywords: GLP-1 secretion; appetite suppression; cell culture; herbal medicine; in silico analysis; obesity; overweight.

Figure 1

(a) Cell viability after 24 h of treatment of NCI-H716 cells with RCM-107, Camellia sinensis, Nelumbinis folium, Gardeniae fructus and epigallocatechin gallate (EGCG). Values are mean ± SD of three replicates per experiment ** p < 0.01 and **** p < 0.0001 when compared with the corresponding untreated cells.; (b) Cell viability after 24 h of treatment of NCI-H716 cells with Poria, Alismatis rhizome, Plantaginis semen, Cassiae semen and Sophorae flos. Values are mean ± SD of three replicates per experiment * p < 0.05, *** p < 0.005 and **** p < 0.0001 when compared with the corresponding untreated cells.

Figure 2

Effects of RCM107, its eight ingredients and EGCG on glucagon-like peptide-1 (GLP-1) release from the NCl-H716 cells. The maximal concentrations used for ELISA were selected from the highest concentration that maintained cell viability above 96% (0.01 mg/mL of RCM-107, Camellia sinensis, Gardeniae fructus and EGCG; 0.05 mg/mL of Nelumbinis folium; 0.1 mg/mL of Sophorae flos; 0.5 mg/mL of Plantaginis semen; 0.8 mg/mL of Poria and Cassiae semen; and 1 mg/mL Alismatis rhizome were used). Cells were incubated for 2 h with test samples and the active GLP-1 contents were normalized and expressed as ng/mL. Values are means ± SD of three replicate experiments. **** p < 0.0001 vs cells with no treatments; #### p < 0.0001 vs the positive control EGCG.

Figure 3

3D ribbon diagram showing the binding site of predicted leading compounds stigmasterol (blue), 3-epioleanolic acid (pink), crocin (orange) and the positive control EGCG (lilac), on the GLP-1 receptor (PDBID: 5NX2).

Figure 4

2D diagram of top three predicted ligands from Gardeniae fructus and the positive control with 5NX2. Hydrogen bonds (green circles with traced lines), π-Alkyl interactions (pink circles with traced lines) and π-Sigma interaction (purple circles with traced lines). (1) Stigmasterol, (2) 3-epioleanolic acid, (3) crocin and (4) EGCG. The key residues in common between EGCG and the three ligands have been circled in red and discussed in the text.

Figure 4

2D diagram of top three predicted ligands from Gardeniae fructus and the positive control with 5NX2. Hydrogen bonds (green circles with traced lines), π-Alkyl interactions (pink circles with traced lines) and π-Sigma interaction (purple circles with traced lines). (1) Stigmasterol, (2) 3-epioleanolic acid, (3) crocin and (4) EGCG. The key residues in common between EGCG and the three ligands have been circled in red and discussed in the text.