Glabridin suppresses intercellular adhesion molecule-1 expression in tumor necrosis factor-α-stimulated human umbilical vein endothelial cells by blocking sphingosine kinase pathway:: Implications of Akt, extracellular signal-regulated kinase, and nuclear factor-κB/Rel signaling pathways

(R)-4-(3,4-Dihydro-8,8-dimethyl)-2H, 8H-benzo[1,2-b:3,4-b'] dipyran-3yl)-1,3-benzenediol (glabridin) is known to have antiinflammatory, antimicrobial, and cardiovascular protective activities. In the present study, we report the inhibitory effect of glabridin on intercellular adhesion molecule-1 (ICAM-1) expression in tumor necrosis factor-alpha (TNF-alpha)-stimulated human umbilical vein endothelial cells (HUVECs). Glabridin inhibited THP-1 cell adhesion to HUVECs stimulated by TNF-alpha and cell surface expression of ICAM-1 in TNF-alpha-stimulated HUVECs. The mRNA expression of adhesion molecules, including ICAM-1, vascular cell adhesion molecule-1, and E-selectin, was also suppressed by glabridin. Further study demonstrated the inhibitory effect of glabridin on nuclear factor (NF)-kappa B/Rel DNA binding, inhibitory factor-kappa B alpha (I kappa B alpha), and I kappa B beta degradation, I kappa B kinase activation, and p65 nuclear translocation in TNF-alpha-stimulated HUVECs. Treatment of a variety of cell lines with glabridin revealed that inhibitory effect of glabridin on NF-kappa B/Rel activation is not cell type-specific, and both inducible and constitutive NF-kappa B/Rel activation was suppressed by glabridin treatment. Moreover, TNF-alpha-induced phosphorylation of Akt and extracellular signal-regulated kinase (ERK) was blocked by glabridin treatment in HUVECs. Glabridin also suppressed sphingosine-1-phosphate (S1P)-induced cell surface expression and mRNA expression of ICAM-1. Further study demonstrated that TNF-alpha-induced sphingosine kinase activity was inhibited by glabridin, and the inhibitory effect of glabridin on TNF-alpha-induced ICAM-1 expression was reversed by addition of exogenous S1P. Together, our results indicate that the inhibitory effect of glabridin on ICAM-1 expression might be mediated, at least in part, by inhibiting sphingosine kinase pathway and subsequent inhibition of signaling pathways, including Akt, ERK, and NF-kappa B/Rel signaling pathway.