In vitro digestion of microcapsule carriers for oral delivery of bioactive compounds for diabetes treatment and their inhibitory effect on the DPP-4 enzyme

Empty microcapsules, originally designed as carriers of bioactive peptides, were prepared by the combined method of a double-emulsion complex with coacervation spray drying and were subjected to an in-vitro digestion process, producing peptides from the whey protein contained in the microcapsule walls. The inhibitory effect of the enzyme dipeptidyl peptidase-4 (DPP-4) and modulation of the insulin receptor of hydrolyzed microcapsules were evaluated. The hydrolysate of the microcapsules was subjected to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) analysis, showing the presence of low-molecular-weight peptidic compounds, which apparently were responsible for the DPP-4 inhibitory effect. Fluorescence analysis showed that the effect of the hydrolyzed microcapsules on the insulin receptor was 40% that of insulin. The inhibition of DPP-4 was 54.7%. This work demonstrated that empty microcapsules initially designed as carriers of functional peptides also have the capability to inhibit DPP-4 and modulate insulin receptors by themselves.