Effects of AGEs on DPP-4 production released from HUVECs. HUVECs were treated with or without 100 μg/ml AGE-BSA, 100 μg/ml non-glycated BSA or the indicated concentrations of H2O2 in the presence or absence of 1 mM NAC, 5 μg/ml RAGE-Ab or 10 nM linagliptin for 24 hr. Conditioned medium were collected and concentrated 20-fold using an Amicon ultrafiltration system. Then 20 μg proteins were separated by SDS-PAGE and transferred to polyvinylidene difluoride membranes. Soluble DPP-4 expression released from the cells was measured. Each upper panel shows the representative bands. Lower panel shows the quantitative data. (A) N = 3 per group. (B) N = 9 per group.