Measurement of the plasma DPP‐4 activity, serum glucose and serum lipid parameters

Blood samples were collected for measurement of the plasma DPP‐4 activity, serum glucose and serum lipid levels. Plasma DPP‐4 activity was measured using the fluorescent substrate, Gly‐Pro‐MCA (Peptide Institute, Osaka, Japan), as reported previously²¹. Serum glucose and serum total cholesterol and HDL‐C levels were measured using commercially available assay reagents (Wako Pure Chemical, Osaka, Japan), according to the manufacturers’ instructions. Non‐HDL‐C was calculated as the serum total cholesterol minus HDL‐C. The lipid profile was examined by a high‐performance liquid chromatography method, as previously described²².