Screening and identification of high bioavailable oligopeptides from rapeseed napin (Brassica napus) protein-derived hydrolysates via Caco-2/HepG2 co-culture model

Rapeseed napin (Brassica napus) protein-derived hydrolysates (RNPHs, 1-4) are mixtures of peptides, prior to reaching liver tissue and playing their antidiabetic role, at least being absorbed and metabolized by the intestinal barrier. The study aims at screening and identifying high bioavailable rapessed napin-derived oligopeptides via simulated gastrointestinal digestion and absorption. Specifically, RNPHs were obtained using a novel ultrasound-assisted digestive device. The potential capacity of treating type 2 diabetes mellitus (T2DM) was evaluated preliminarily via enhancing glucose transporter 4 (GLUT4) expression and translocation. Also, absorbable rapeseed napin-derived oligopeptides were screened and identified in a Caco-2/HepG2 co-culture model using liquid chromatography coupled with electrospray ionisation and quadrupole time of flight tandem mass spectrometry (LC-ESI-QTOF-MS). The results involved mainly two aspects. First, absorbable oligopeptides from RNPH-1 (Molecular weight, Mw ≤ 3 kDa) with the highest degree of hydrolysis (DH) were the optimal ones to enhance GLUT4 expression and translocation (P < 0.05). Secondly, oligopeptides (Thr-His-Leu-Pro-Lys (THLPK), His-Leu-Pro-Lys (HLPK), (Ile) Leu-Pro-Lys ((I)LPK), His-Leu-Lys (HLK), and Leu-His-Lys (LHK)), identified from both RNPH-1 and RNPH-2 which significantly enhanced GLUT4 expression and translocation, could be absorbed intact and reached HepG2 cells. These findings indicated that high bioavailable oligopeptides from RNPHs were the potential usefulness to treat T2DM in vitro.