α-Amylase inhibition, anti-glycation property and characterization of the binding interaction of citric acid with α-amylase using multiple spectroscopic, kinetics and molecular docking approaches

The quest to suppress complications associated with diabetes mellitus is ever increasing, while food additives and preservatives are currently being considered to play additional roles besides their uses in food enhancement and preservation. In the present study, the protective prowess of a common food preservative (citric acid, CA) against advanced glycation end-products (AGEs) formation and its binding interaction mechanism with α-amylase (AMY), an enzyme linked with hyperglycemia management, were examined. Enzyme inhibition kinetics, intrinsic fluorescence, synchronous and 3D fluorescence spectroscopies, ultraviolet–visible (UV–Vis) absorption spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy, thermodynamics, and molecular docking analyses were employed. Results obtained showed that citric acid decreased α-amylase activity via mixed inhibition (IC50 = 5.01 ± 0.87 mM, Kic = 2.42 mM, Kiu = 160.34 mM) and suppressed AGEs formation (IC50 = 0.795 ± 0.001 mM). The intrinsic fluorescence of free α-amylase was quenched via static mechanism with high bimolecular quenching constant (Kq) and binding constant (Ka) values. Analysis of thermodynamic properties revealed that AMY-CA complex was spontaneously formed (ΔG < 0), entropy driven (TΔS > ΔH), with involvement of electrostatic forces. UV–Vis, FT-IR and 3D fluorescence spectroscopies affirmed alterations in α-amylase native conformation due to CA binding interaction. CA interacted with His-101, Asp-197, His-299, and Glu-233 within AMY active site. Our findings indicated that CA could impair formation of AGEs and interact with α-amylase to slow down starch hydrolysis; vital properties in management of type 2 diabetes complications.