Most inflammatory agents activate nuclear transcription factor-kappaB (NF-kappaB) which results in expression of genes for cytokines, adhesion molecules, and enzymes involved in amplification and perpetuation of inflammation. Emodin (3-methyl-1,6,8-trihydroxyanthraquinone) is an active component from the roots of Polygonum cuspidatum that has been reported to exhibit antiinflammatory properties but the mechanism is not known. In the present study we investigated the effects of emodin on the activation of NF-kappaB in human umbelical vein endothelial cells (EC). Treatment of EC with TNF activated NF-kappaB; preincubation with emodin inhibited this activation in a dose- and time-dependent manner. Emodin did not chemically modify NF-kappaB subunits but rather inhibited degradation of IkappaB, an inhibitory subunit of NF-kappaB. Since the promoter regions of ICAM-1, VCAM-1, and ELAM-1 contain NF-kappaB binding sites and these adhesion molecules are involved in the attachment of leukocytes to EC, the effect of emodin on the adhesion of monocytes to EC and the expression of these adhesion molecules was also studied. Treatment of EC with TNF for 6 h increased the adhesion of monocytes to EC, which correlated with increases in cell surface expression of ICAM-1, VCAM-1 and ELAM-1. Pretreatment of EC for 1 h with emodin inhibited both monocyte-EC attachment and expression of ICAM-1, ELAM-1 and VCAM-1. These results indicate that emodin is a potent inhibitor of NF-kappaB activation and expression of adhesion molecules and thus could be useful in treating various inflammatory diseases.