Mechanistic insights into the inhibition of pancreatic lipase by apigenin: Inhibitory interaction, conformational change and molecular docking studies

• Apigenin reversibly inhibited pancreatic lipase (PL) activity in a competitive manner. • The combination of apigenin and orlistat showed a synergitic inhibition on PL. • The binding of apigenin to PL induced the conformational change of the enzyme. • Apigenin bound to the active center of PL to prevent the substrate from being oxidized. The inhibition of pancreatic lipase by apigenin, a natural dietary flavonoid, was investigated by various spectroscopic techniques and computational simulation. The results showed that apigenin reversibly inhibited pancreatic lipase activity in a competitive manner with an IC 50 value of 0.45 ± 0.03 mM, and its combination with orlistat showed a synergistic effect. Formation of a complex between apigenin and pancreatic lipase driven by hydrogen bonds resulted in the fluorescence quenching of the enzyme through a static manner. The binding constant of apigenin with the enzyme was (5.47 ± 0.01) × 10 4 L mol −1 at 298 K, and the kinetic process of their interaction was characterized by the resolved concentration profiles and pure spectra of different components from the multivariate curve resolution-alternating least squares algorithm. The inhibition of pancreatic lipase by apigenin was mainly attributed to the tighter structure of the enzyme and the interaction between apigenin and the amino acid residues in the active center of the enzyme to prevent the substrate from being oxidized, as demonstrated by the analysis of circular dichroism spectra and molecular docking. Molecular dynamics simulation further characterized the binding conformation and property of apigenin-pancreatic lipase complex. This study provides novel insights into the mechanism of apigenin as pancreatic lipase inhibitor and the development of apigenin as an anti-obesity nutrient.