A Comparative Study of Binding Interactions between Proteins and Flavonoids in Angelica Keiskei: Stability, α-Glucosidase Inhibition and Interaction Mechanisms

Abstract

Flavonoids are easily destroyed and their activity lost during gastrointestinal digestion. Protein-based nanocomplexes, a delivery system that promotes nutrient stability and bioactivity, have received increasing attention in recent years. This study investigated the stability, inhibitory activity against α-glucosidase and interaction mechanisms of protein-based nanocomplexes combining whey protein isolate (WPI), soybean protein isolate (SPI) and bovine serum albumin (BSA) with flavonoids (F) from A. keiskei using spectrophotometry, fluorescence spectra and molecular docking approaches. The results show that the flavonoid content of WPI-F (23.17 ± 0.86 mg/g) was higher than those of SPI-F (19.41 ± 0.56 mg/g) and BSA-F (20.15 ± 0.62 mg/g) after simulated digestion in vitro. Furthermore, the inhibition rate of WPI-F (23.63 ± 0.02%) against α-glucosidase was also better than those of SPI-F (18.56 ± 0.02%) and BSA-F (21.62 ± 0.02%). The inhibition rate of WPI-F increased to nearly double that of F alone (12.43 ± 0.02%) (p < 0.05). Molecular docking results indicated that the protein-flavonoids (P-F) binding occurs primarily through hydrophobic forces, hydrogen bonds and ionic bonds. Thermodynamic analysis (ΔH > 0, ΔS > 0) indicated that the P-F interactions are predominantly hydrophobic forces. In addition, the absolute value of ΔG for WPI-F is greater (-30.22 ± 2.69 kJ mol^-1), indicating that WPI-F releases more heat energy when synthesized and is more conducive to combination. This paper serves as a valuable reference for the stability and bioactivity of flavonoids from A. keiskei.

Keywords: A. keiskei; flavonoids; interaction mechanism; protein-based nanocomplex; stability.

Figure 1

Chemistry structures of the six flavonoids in terms of content in the A. keiskei extraction.

Figure 2

Changes of the flavonoids content after combination with different proteins. (A) the flavonoids content of the combined with different proteins; (B) the retained flavonoids content after the just the flavonoids being digested by using the simulated oral and gastrointestinal digestive solution; (C) the retained flavonoids content in the complex of proteins and flavonoids after being digested with the simulated gastric juice; (D) the retained flavonoids content in the complex of proteins and flavonoids after being digested with the simulated intestinal digestion. * p < 0.05, ** p < 0.01 and *** p < 0.001.

Figure 3

In vitro α-glucosidase inhibition rates of flavonoids with and without combied with protein before or after being digested with the simulated gastrointestinal conditions.

Figure 4

The complexe docking diagrams of the flavonoids with the different proteins. (A) the flavonoid (6)/SPI (7S), (B) the flavonoid (2)/SPI (7S), (C) the flavonoid (4)/BSA (D) the flavonoid(3)/α-La, (E) th flavonoids(5)/β-Lg.

Figure 5

Fluorescence analysis of the interaction of proteins with flavonoids. (A1–C1): The fluorescence spectra of proteins with flavonoids; (A2–C2): The plots of log[(F0 − F)/F] versus log F at different temperatures; (A3–C3): The plots of F0/F versus F at different temperatures; (A1–A3): the combined protein was SPI-F; (B1–B3): the combined protein was WPI-F, (C1–C3): the combined protein was BSA-F.4.