Inhibition Mechanism of α-Amylase/α-Glucosidase by Silibinin, Its Synergism with Acarbose, and the Effect of Milk Proteins

Abstract

As a natural flavonolignan, silibinin is reported to possess multiple biological activities, while the inhibitory potential of silibinin on carbohydrate-hydrolyzing enzymes is still unclear. Therefore, in this study, the inhibitory effect and underlying mechanism of silibinin against α-amylase/α-glucosidase were investigated. The results indicated that silibinin showed a strong inhibitory efficiency against α-amylase/α-glucosidase in noncompetitive manners and exhibited synergistic inhibition against αglucosidase with acarbose. However, interestingly, the inhibitory effect of silibinin was significantly hindered in various milk proteinrich environments, but this phenomenon disappeared after simulated gastrointestinal digestion of milk proteins in vitro. Furthermore, silibinin could combine with the inactive site of α-amylase/α-glucosidase and change the microenvironment and secondary structure of the enzymes, thereby influencing the catalytic efficiency of enzymes. This research suggested that silibinin could be used as a novel carbohydrate-hydrolyzing enzyme inhibitor, and milk beverages rich in silibinin had the potential for further application in antidiabetic dietary or medicine.

α-Glucosidase Inhibitory Activities and the Interaction Mechanism of Novel Spiro-Flavoalkaloids from YingDe Green Tea

“…Therefore, molecular docking could continuously locate and find the best matching state through spatial conformation and interaction between the binding sites and small ligands. 33 The simulation results suggested that 1 and 2, which have a galloyl group, had a stronger binding affinity with α-glucosidase than 3 and 4. The BEs between 1 and 2 and α-glucosidase were estimated to be −11.80 and −12.01 kcal/mol, respectively.…”

“…The inhibition of α-glucosidase by spiro-flavoalkaloids might result from the interaction with binding sites in certain regions of the enzyme. Therefore, molecular docking could continuously locate and find the best matching state through spatial conformation and interaction between the binding sites and small ligands . The simulation results suggested that 1 and 2 , which have a galloyl group, had a stronger binding affinity with α-glucosidase than 3 and 4 .…”

“…Compounds 1 and 2 are primarily surrounded by the same residues, namely, ASP-215, ARG-442, ASP-352, GLU-411, HIS-280, ARG-315, and ASN-415, of α-glucosidase (Figure ). Asp-352 was reported to be the catalytic residue of α-glucosidase . Compared with the positive control acarbose (Figure S48), 1 had two identical residues (ASN-415 and HIS-280) in the binding site, and 2 had four identical residues (ASN-415, HIS-280, TYR-158, and GLN-353).…”

“…UV spectroscopy is a basic method to study the interaction between enzymes and compounds. 33 The addition of compounds would form protein−compound complexes, and the absorbance of the system would change correspondingly. Thus, the changes in the enzyme structure could be determined.…”

“…28 Recently, α-glucosidase inhibitors including styracifoline, 27 pregnane glycosides, 29 and neolignans 30 have been reported. In addition, many flavonoids, such as myricetin, apigenin-7-O-glucoside, fisetin, 31 baicalein, 32 and apigenin, 33 have generally been considered to be potential inhibitors of α-glucosidase. In this article, the isolation and structural identification of novel spiro-flavoalkaloids (1−4) are introduced together with their α-glucosidase inhibition activities.…”