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Abstract

Bile acids are synthesized in the liver, stored in gallbladder, and secreted into the intestine to aid in the absorption of lipid-soluble nutrients. In addition, bile acids also actively participate in regulation of gene expression through their ability to act as ligands for the nuclear receptor farnesoid X receptor or by activating kinase signaling pathways. Under cholestatic conditions, elevated levels of bile acids in the liver induce hepatic inflammation, and because bile acid levels are also elevated in the circulation, they might also induce vascular inflammation. To test this hypothesis, primary human umbilical vein endothelial cells (HUVEC) and human aortic endothelial cells were treated with bile acids, and the expression of ICAM-1, VCAM-1, and E-selectin were monitored. The three major bile acids found in the circulation, chenodeoxycholic acid, deoxycholic acid, and lithocholic acid, all strongly induced both the mRNA and protein expression of ICAM-1 and VCAM-1. To delineate the mechanism, the experiments were conducted in the presence of various kinase inhibitors. The results demonstrate that the bile acid-mediated induction of adhesion molecule expression occurs by stimulation of NF-kappaB and p38 MAPK signaling pathways through the elevation in reactive oxygen species. The bile acid-induced cell surface expression of ICAM-1 and VCAM-1 was sufficient to result in the increased adhesion of THP-1 monocytes to the HUVEC, suggesting that elevated levels of bile acids in the circulation may cause endothelium dysfunction and contribute to the initiation of early events associated with vascular lesion formation.