Digested Adzuki Bean (Vigna angularis) β-vignin Protein Exhibits Potential Antidiabetic Activity via Stimulating the Glucose Uptake Pathway

Objectives: To assess and characterize the antidiabetic potential of digested adzuki bean β-vignin functional peptides in modulating hepatic glucose metabolism. Methods: Human liver cells (HepG2) were treated with either digested adzuki bean β-vignin (AB7S) obtained from simulated gastrointestinal digestion (10 μg/mL, 100 μg/mL, and 1000 μg/mL) or dipeptidyl peptidase IV (DPP IV) inhibitors (gliptins). Cell viability (CV), glucose uptake (GU), and DPP IV activity in the cells were measured by MTS-CV, GU, and luminescence-based DPP IV inhibitory assays, respectively. The protein expression of glucose transporter 2 (GLUT 2), and protein kinase B (AKT)/p-AKT pathway were measured by ELISA and western blot. LC-QTOF-MS/MS was used to identify peptides in the digested AB7S and data was analyzed using the MassLynx V4.2 software. In addition, computational molecular docking was used to assess the peptide functionality to inhibit the DPP IV enzyme, modulating the hepatic glucose metabolism. ANOVA and post-hoc tests were conducted, p < 0.05 was considered statistically significant. Results: Purified AB7S (146 kDa) had a purity of > 90%. Peptide Pro-Val (PV) (214 Da; PI: 5.69; hydrophobicity: 7.58 kcal/mol) was identified by peptide sequencing from the purified AB7S colonic digests. PV showed the highest interaction with the DPP IV active site (-6.1 kcal/mol), like linagliptin, a Food and Drug Administration-approved diabetic medication. Three conventional hydrogen bonds were formed at Arg 358, Arg 669, and Glu 206. Digested AB7S (10-1000 μg/mL) did not affect CV. GU in the cells was ≥ 40% higher than the untreated control, suggesting that the digest was effective in increasing hepatic GU. CV of cells treated with 10 μg/mL (∼25 μM) AB7S digest was the same as that of cells treated with 80 μM DPP IV inhibitor (p > 0.05). Hepatic GU was 40% higher than the untreated control after 10 μg/mL AB7S digest treatment, comparable to that of 40 μM DPP IV inhibitor (p > 0.05). Conclusions: Digested AB7S was not harmful to hepatic cells at the concentrations tested and was effective in enhancing the hepatic GU pathways. These results suggested the effectiveness of digested AB7S in modulating markers of type 2 diabetes, similar to a DPP IV inhibitor. Funding Sources: USDA Pulse Crop Health Initiative's (grant number 58-3060-9-045).