Inhibition of diabetic related enzymes of Siraitia grosvenorii, Dimocarpus longan Lour., and Orthosiphon stamineus Benth. extracts combinations in vitro and in silico

Abstract

Incorporating medicinal plants in our diet to manage metabolic diseases has been one of the many goals of functional food scientists. Extracts from these plants have already been widely used in traditional foods or beverages, however, the efficacies and appropriate standardized biomarkers for these mixtures have not been fully established. This study aims to investigate the antidiabetic activity of combinations of extracts from three traditional edible plants: Siraitia grosvenorii (Swingle) C. Jeffrey, Dimocarpus longan Lour., and Orthosiphon stamineus Benth and identified the best biomarker for the mixed extract. Although the individual antidiabetic potential of these plants has been investigated, their combined effects have not been studied. The three extracts were mixed in equal proportions (1:1 or 1:1:1) at the same concentration, and HPLC quantitative analysis confirmed whether the mixing ratio of the three extracts in each combination strictly followed the equal proportion mixing. The antidiabetic potential was assessed by examining the combinations' effects on α-amylase, α-glucosidase, and DPP-4 inhibition, cytotoxicity, and glucose uptake kinetics in vitro. Phytochemical constituents were identified using UPLC-MS, followed by computer simulation analysis. Among the combinations, SGE+OSE showed the highest potential for inhibiting effects (p<0.05) on α-glucoside and α-amylase activities, with half maximal inhibitory concentrations (IC50) of 3.61±0.72 mg/ml and 7.27±0.11 mg/ml, respectively. The DLE+OSE exhibited the highest inhibition of DPP4 enzyme activity, with an IC50 of 1.199±0.073 mg/ml. In vitro glucose uptake assays revealed that 62.50 μg/ml of the combination SGE+DLE+OSE significantly enhanced (p<0.05) glucose uptake in L6 cells, achieving an uptake rate of 215±0.55%, which surpassed the effect of 100 nM insulin (127±0.54%). The glucose kinetic assays show that these combinations stimulated glucose uptake in L6 cells within 10 minutes. In silico study identified 26 and 32 compounds in the three examined extracts that exhibited notable interactions and stable binding capacities with α-amylase and DPP-4 proteins, respectively, promising their potential as effective inhibitors. Sensory evaluation revealed that the combination of SG+DL exhibited the highest score for texture, colour, aroma, taste, mouthfeel and overall acceptability. However, the presence of bitterness and herbal taste caused by O. stamineus negatively impacted the overall evaluation of other combinations. Here we concluded that combinations of S. grosvenorii extracts, D. longan extracts, and O. stamineus extracts have promising antidiabetic properties by inhibiting the activities of α-amylase, α-glucosidase, and DPP-4 and enhancing glucose uptake in muscle cells, offering a feasible therapeutic alternative for diabetes.