An inhibitor of NADPH oxidase and a ROS scavenger block VCAM-1 activation of endothelial cell MMP-2 and MMP-9. (A,C) MMP-9 activity. (B,D) MMP-2 activity. mHEVc cells were incubated with anti–VCAM-1 antibody-coated beads in the presence and absence of apocynin (4 mM), an NADPH oxidase inhibitor, or catalase (5000 U/mL), a H₂O₂ scavenger. Apocynin and catalase had no effect on endothelial cell viability as determined by trypan blue exclusion (data not shown). At the times indicated the cells were washed, and equal cell numbers were lysed and analyzed by zymography as described for Figure 2. Data presented are the mean ± SD from 5 experiments. Symbols without error bars indicate that the SD was smaller than the symbol. *P < .05 compared with mHEVc cells at 0 minutes. **P < .05 compared with anti–VCAM-1–bead-stimulated cells.