Differential regulation of endothelial cell adhesion molecule expression by nitric oxide donors and antioxidants

Although nitric oxide (NO) and antioxidants inhibit adhesion molecule expression, their inhibitory effects on nuclear factor kappa B (NF-kappa B) activation may differ. The NO donors, but not 8-bromo-cGMP, decreased tumor necrosis factor alpha (TNF-alpha)-induced VCAM-1, ICAM-1, and E-selectin expression by 11-70%. In contrast, NAC completely abolished VCAM-1 and E-selectin expression and decreased ICAM-1 expression by 56%. Gel shift assays demonstrate that NF-kappa B activation was inhibited by both NO and antioxidants. The activation of NF-kappa B involves the phosphorylation and degradation of its cytoplasmic inhibitor I kappa B-alpha by 26S proteasomes. The 26S proteasome inhibitor MG132 prevented the degradation of phosphorylated I kappa B-alpha. NAC inhibited I kappa B kinase (IKK) activity and prevented I kappa B-alpha phosphorylation and degradation. In contrast, NO did not inhibit IKK activity, I kappa B-alpha phosphorylation, or I kappa B-alpha degradation. However, NO, but not antioxidants, induced I kappa B-alpha promoter activity. Tbe inhibitory effects of NO on adhesion molecule expression, therefore, differs from that of antioxidants in terms of the mechanism by which NF-kappa B is inactivated.