End products of VAP-1 enzyme activity regulate expression of endothelial selectins. Nontransfected HUVECs were treated with single doses of hydrogen peroxide, ammonium, and formaldehyde (the end products of VAP-1–mediated oxidative deamination of methylamine) at the indicated concentrations for 4 hours. When indicated, the cells were treated repeatedly with 10 μM H2O2 (8 times at 30-minute intervals) or with the combination of all 3 end products (each at 1 or 10 μM, single dose). The cells were then analyzed for (A) E-selectin and (B) P-selectin mRNA expression using quantitative PCR. Data points (○) and means (bars) from 4 to 6 samples of HUVECs from different individuals are shown. *P < .05, **P < .01