Dipeptidyl peptidase IV (DPP‑IV) inhibitors are an established class of agents used in the management of type 2 diabetes mellitus. This study aimed to prepare and screen DPP‑IV inhibitory peptides derived from phycocyanin (PC), characterize their inhibitory mechanisms, evaluate hypoglycemic activity in vivo, and investigate their cellular absorption and transport.
Phycocyanin was enzymatically hydrolyzed using four different proteases to generate peptide mixtures. Among the hydrolysates tested at 10.0 mg mL‑1, the preparation produced with Neutrase demonstrated the highest DPP‑IV inhibitory activity, with an inhibitory rate of 73.65%. Based on this screening, Neutrase hydrolysates were selected for further optimization and study.
Single‑factor experiments established optimal hydrolysis conditions for producing PC hydrolysates with maximal DPP‑IV inhibitory activity. The optimal parameters reported were: Neutrase at 3.0% enzyme concentration, solid–liquid ratio of 1:30 g mL‑1, hydrolysis time of 3.0 h, hydrolysis temperature of 50.0 °C, and pH 7.0. Under these conditions the Neutrase hydrolysates had an IC50 value of 2.72 ± 0.15 mg mL‑1 for DPP‑IV inhibition.
The authors evaluated the influence of simulated gastrointestinal digestion on the hydrolysates. Gastrointestinal digestion was reported to further improve the DPP‑IV inhibitory activity of PC hydrolysates, indicating that digestive processing may enhance the generation or exposure of active peptide sequences.
Animal experiments assessed metabolic effects after oral administration of PC hydrolysates in a type II diabetic mouse model. The hydrolysates significantly reduced fasting blood glucose (FBG) and glycated serum protein levels. Treated mice demonstrated improved glucose tolerance, attenuation of insulin resistance, and alleviation of lipid disturbances. These results indicate systemic metabolic benefits in the diabetic model following oral dosing of PC hydrolysates.
From the < 3.0 kDa fraction of the PC hydrolysates, two novel peptides with DPP‑IV inhibitory activity were isolated and characterized using affinity ultrafiltration combined with molecular docking. The two identified peptides were IASY and IAGIDE. Reported IC50 values were 0.22 ± 0.01 mg mL‑1 for IASY and 0.38 ± 0.02 mg mL‑1 for IAGIDE, indicating both peptides are active DPP‑IV inhibitors at sub‑milligram per milliliter concentrations.
Kinetic characterization indicated that both IASY and IAGIDE follow a mixed inhibition pattern against DPP‑IV. Molecular docking analyses reported that the peptides bind to the active site of DPP‑IV primarily through hydrogen bonds and hydrophobic interactions, consistent with a mode of interaction involving both catalytic and non‑catalytic site contacts.
Cellular assays using Caco‑2 cells compared biocompatibility and absorption/transport between the two peptides. IASY exhibited better biocompatibility and a higher absorption transport rate than IAGIDE in this in vitro intestinal epithelial model. These findings suggest differential potential for epithelial uptake and systemic availability between the two peptides.
The study concludes that peptides derived from phycocyanin, notably IASY and IAGIDE, possess DPP‑IV inhibitory activity and demonstrated hypoglycemic and metabolic benefits in a type II diabetic mouse model. Mechanistic data indicated mixed inhibition of DPP‑IV with binding mediated by hydrogen bonds and hydrophobic interactions, and in vitro transport results favored IASY for cellular uptake.
The abstract and article summarize enzymatic screening, optimized hydrolysis parameters, in vitro inhibitory potency (IC50), simulated gastrointestinal digestion effects, in vivo metabolic outcomes in diabetic mice, isolation and identification of two active peptides, kinetic inhibition pattern, molecular docking interaction types, and Caco‑2 transport comparisons. Specific experimental protocols, dose regimens used in animal studies, full kinetic plots, statistical analyses, and comprehensive safety/toxicity data are presented in the full text; where details are not reported in the abstract, the source should be consulted for experimental parameters and complete data.
This multidimensional evaluation supports further investigation of phycocyanin‑derived peptides as candidate bioactive agents targeting DPP‑IV for glycemic control. The combination of in vitro enzymology, molecular docking, simulated digestion, cellular transport assays, and in vivo efficacy provides a preclinical framework, but additional studies will be needed to define pharmacokinetics, optimal dosing, long‑term safety, and comparative efficacy against established DPP‑IV inhibitors.