Evaluating DPP-IV Inhibitory Activity

The in vitro assessment of DPP-IV-inhibitory activity was performed following the manufacturer instructions (DPP-IV inhibitor screening assay kit–Cayman Chemical) and previously reported methods (47 (link), 48 (link)). The experiments were carried out in triplicate in a half–area 96 well solid plate (white). Each reaction (50 μL) was prepared adding the reagents in the following order in a microcentrifuge tube: 1 X assay buffer [20 mM Tris–HCl, pH 8.0, containing 100 mM NaCl, and 1 mM EDTA] (30 μL), CH and CH (F3) at final concentration range of 0.01–2.0 mg/mL (10 μL) or vehicle (10 μL of distilled H₂O) and finally the DPP-IV enzyme (10 μL). Subsequently, the samples were mixed and 50 μL of each reaction were transferred in each well of the plate. The reactions were started by adding 50 μL of substrate solution to each well and incubated at 37°C for 30 min. Fluorescence signals were measured using the Synergy H1 fluorescent plate reader from Biotek (excitation and emission wavelengths 360 and 465 nm, respectively).