Discovery of novel dipeptidyl peptidase-IV inhibitory peptides derived from walnut protein and their bioactivities in vivo and in vitro
Xinxin Mu, Dan Li, Ran Xiao, Kaifang Guan, Ying Ma, Rongchun Wang, Tianjiao Niu
Abstract
The inhibition of dipeptidyl peptidase IV (DPP-IV) has been regarded as a major target for treating type-2 diabetes (T2D). Food-derived peptides are a great source of DPP-IV inhibitory peptides. In this study, we utilized walnut protein as the raw material and hydrolyzed it using four different proteases. The trypsin hydrolysate exhibited the highest DPP-IV inhibitory activity. A DEAE-52 anion exchange column and a Sephadex G-25 gel filtration column were used to sequentially separate and purify the enzymatic hydrolysates. Mass spectrometry identified 117 peptide sequences, of which LPFA, VPFWA, and WGLP were three highly active DPP-IV inhibitory peptides. Molecular docking results revealed that three peptides primarily bind tightly to DPP-IV through hydrogen bonds and van der Waals forces. The inhibitory activity and absorption transport of the peptides were examined using a Caco-2 cell model. LPFA, VPFWA, and WGLP could cross the Caco-2 cell monolayer intact, with in situ IC 50 s of 267.9 ± 7.2 μM, 325.0 ± 8.4 μM, and 350.9 ± 8.3 μM, respectively. Oral glucose tolerance tests (OGTT) demonstrated that the three inhibitory peptides significantly improved glucose metabolism in normal ICR mice. This study establishes a theoretical basis for the high-value utilization of walnuts and the therapeutic treatment of T2D. • Walnut protein hydrolysates were prepared using trypsin. • The DPP-IV inhibitory peptides were purified and identified from the hydrolysates. • Binding energies of three peptides to DPP-IV were estimated with molecular docking. • Three peptides could cross the Caco-2 cell monolayer intact. • The oral glucose tolerance test showed improved glucose metabolism in mice.