Insight into the synergistic inhibition of oyster pentapeptide (Phe-Pro-Val-Gly-Arg) and peonidin-3-O-glucoside against DPP-IV and their interactions

The purpose of this work was to investigate the synergistic inhibition of oyster pentapeptide (Phe-Pro-Val-Gly-Arg: FR) and the anthocyanin (Pn3G) against DPP-IV (Dipeptidyl Peptidase-IV), their interactions, digestive stability and absorption efficiency. Multiple spectroscopic methods were employed to investigate the interactions between FR and Pn3G. The synergistic inhibition of FR-Pn3G complexes against DPP-IV was explored using the Compusyn software, fluorescence spectroscopy and enzyme inhibition kinetics. UV-vis and fluorescence spectra analysis demonstrated that FR-Pn3G complexes were identified as π-π complexes. The enhanced color intensity and saturation of FR-Pn3G complexes solution, combined with the hyperchromic effect observed in UV-vis spectra and the hydrogen bonding and hydrophobic interaction between FR and Pn3G analyzed in the FT-IR spectroscopy, supported the conclusion that FR and Pn3G formed complexes through the co-pigmentation effect. Furthermore, the synergistic inhibition of FR and Pn3G against DPP-IV was confirmed: both the DPP-IV inhibitory experimental results and Compusyn simulation results demonstrated that the combination of FR and Pn3G produced a dose-reduction effect, with CI values below 0.9. Fluorescence spectrum analysis revealed that the microenvironment of DPP-IV towards a more hydrophobic environment, while enzyme inhibition kinetic studies indicated that the FR-Pn3G complexes functioned as a mixed-type inhibitor, exhibiting both competitive and non-competitive inhibition of DPP-IV. The in vitro gastrointestinal digestion and Caco-2 cell permeation studies demonstrated that FR-Pn3G complexes exhibited significantly enhanced digestive stability (96.42 % retention for DPP-IV inhibition, 1.81 times that of individual Pn3G) and improved intestinal absorption compared to individual components (3.46 times that of Pn3G alone and 1.50 times that of FR alone (P < 0.05)).