Structural characterization, physicochemical properties and antihypertensive efficacy evaluation of four novel ACE inhibitory peptides derived from Flammulina velutipes

Four peptides with ACE inhibitory activity from the edible fungus Flammulina velutipes were prepared by proteolysis to develop high-activity functional peptides. Their secondary structures were analyzed by Fourier transform infrared (FTIR) spectroscopy and Circular dichroism (CD). The effects of pH, temperature, metal ions and gastrointestinal digestion on their ACE inhibitory activities were determined. Their antihypertensive effects were evaluated by an H₂O₂-induced oxidative stress injury, human umbilical vein endothelial cells (HUVECs) model. All four peptides had relatively stable secondary structures. The peptides with sequences FDGY and FHPGY had similar peak shapes but the FHPGY had the highest random coil content. The FAGGP peptide had a relatively flat peak shape and a high random coil content. The WADP peptide had the highest β-sheet content, the lowest random coil content, and the most stable secondary structure. The four peptides showed good resistance to pH and temperature changes, the presence of metal ions and gastrointestinal digestion. FHPGY had good ACE inhibitory activity in all tested pH and temperature ranges. Metal ions had the least effect on the ACE inhibitory activity of FHPGY. After gastrointestinal digestion, the ACE inhibitory activity of FHPGY was above 95%. At concentrations up to 3 mM, the four F. velutipes-derived ACE inhibitory peptides had no significant negative effect on HUVECs viability, while increasing intracellular NO and SOD levels and reducing ET-1 and MDA production. The four peptides all had strong antihypertensive effects. FHPGY increased the secretion of NO and reduced the ET-1 secretion of by 97.69% and 109.59%, respectively, of that of the positive control captopril, and appeared to have the potential to be developed into an effective ACE inhibitory peptide for medicinal use.