Preparation, structural characterization, and hypoglycemic activity of DPP-IV inhibitory peptides derived from β-casein

The hydrolysate of β-casein generated by bromelain exhibits potent DPP-IV inhibitory activity. • β-Casein hydrolysate significantly increased glucose consumption in insulin-resistant HepG2 cells. • MPIQAF, a β-casein-derived Xaa-Pro motif peptide, inhibits DPP-IV and alleviates glucose metabolism disorders. Bioactive peptides have shown therapeutic potential for type 2 diabetes by inhibiting dipeptidyl peptidase-IV (DPP-IV). In this study, β-casein (β-CN) hydrolysates were prepared using enzymatic hydrolysis and characterized spectroscopically, followed by activity analysis. The results showed that the particle size and surface hydrophobicity of β-CN were significantly reduced after enzymatic hydrolysis ( p  < 0.05). Fluorescence spectroscopy revealed a red shift in the maximum emission wavelength, and secondary structure analysis indicated a conformational transition toward random coils and β-turns. Bromelain hydrolysate inhibited DPP-Ⅳ activity and significantly increased glucose consumption and glycogen synthesis in IR-HepG2 cells ( p  < 0.05). A total of 439 peptide sequences were identified from the bromelain hydrolysate, among which 34.40% had a bioactivity score above 0.5, and most showed potential DPP-IV inhibitory ability. Through in silico analysis, the Xaa-Pro-type peptide MPIQAF was screened and showed strong binding affinity with DPP-IV, suggesting its hypoglycemic potential. MPIQAF was further synthesized and experimentally validated, and its direct DPP-IV inhibitory IC 50 was determined to be 2.832 mM. The peptide could ameliorate insulin resistance-induced glucose metabolism disorders in a dose-dependent manner and significantly reduce DPP-IV levels (p < 0.05). In summary, the bromelain hydrolysate, as a multi-peptide mixture, exhibited stronger overall DPP-IV inhibitory activity and holds promise for direct application as a functional food ingredient. The purified peptide MPIQAF, although a weak direct inhibitor, provides a valuable lead compound for mechanistic studies and future structural optimization toward glucose regulation. Download: Download high-res image (345KB) Download: Download full-size image