Inhibitory effect of a weight-loss Chinese herbal formula RCM-107 on pancreatic α-amylase activity: Enzymatic and in silico approaches

Abstract

Reducing carbohydrates digestion by having a low glycaemic index (GI) foods has been linked to weight loss. Inhibiting related enzymes is an alternative way to decrease carbohydrate digestion. RCM-107 (Slimming Plus), an eight-herb formula that is modified from RCM-104, indicated significant weight-loss action in clinical trials. However, no published research has studied its mechanism of action on reducing carbohydrate absorption via suppressing the activities of porcine pancreatic alpha-amylase (PPA). In this paper, we used fluorescence PPA inhibition assay to investigate the inhibitory effects of RCM-107 and the individual herbs present in this herbal mixture on amylase activity. Subsequently, molecular docking predicted the key active compounds that may be responsible for the enzyme inhibition. According to our results, both the RCM-107 formula and several individual herbs displayed α-amylase inhibitory effects. Also, marginal synergistic effects of RCM-107 were detected. In addition, alisol B, (-)-epigallocatechin-3-gallate (EGCG) and plantagoside have been predicted as the key active compounds that may be responsible for the α-amylase inhibition effect of RCM-107 according to inter-residue contact analysis. Finally, Glu233, Gln63, His305, Asp300 and Tyr151 are predicted to be markers of important areas with which potential amylase inhibitors would interact. Therefore, our data has provided new knowledge on the mechanisms of action of the RCM-107 formula and its individual herbal ingredients for weight loss, in terms of decreasing carbohydrate digestion via the inhibition of pancreatic alpha-amylase.

Fig 1. Suppressive effects of the RCM-107 formula, eight single herbal granules and acarbose (inhibitor) at 300 μg mL^-1 on porcine pancreatic α-amylase activity.

The enzyme activity with an absence of the samples or inhibitor was presented as 100%. Data are expressed as means ± standard error of the mean (SEM) from three independent experiments, including three replicates each time. **** indicates P < 0.0001 as compared to the control.

Fig 2. Dose-dependent inhibitory effects of the RCM-107 formula (1–800μg mL^-1) on porcine α-amylase.

Data represent mean ± SEM from three independent experiments with three replicates per condition.

Fig 3. 2D diagram of interactions between corn starch and 1OSE.

Fig 4. a-b. Chemical structures of selected compounds.

Fig 5

a. 2D diagram of top 3 predicted ligands from each herb with 1OSE. Hydrogen bonds (green circles with traced lines), van der Waals forces of attraction (light green circles), Pi-Alkyl interactions (pink circles with traced lines), Pi-Sigma interaction (purple circles with traced lines). 1) Acarbose (3 binding poses); 2). Stigmasterol. b. 3) Campesterol; 4) Cassiaside; 5) Theaflavin; 6) Thearubigin. c. 7) EGCG; 8) Cycloartenol; 9) Quercetin; 10) Isorhamnetin. d. 11) Beta-sitosterol; 12) N-[6-(acridin-9-ylamino) hexyl] benzamide; 13) Sophoradiol; 14) Sudan III. e. 15) Alisol B; 16) Alisol A. 17) Alisol C; 18) Stellasterol. f. 19) Eburicoic acid; 20) Dehydroeburicoic acid; 21) plantagoside; 22) Daucostero_qt.

Fig 6. 3D interactions between predicted leading compounds EGCG (pink), plantagoside (yellow), the known inhibitor acarbose (red) and 1OSE.