EGCG protects against oxidized LDL-induced endothelial dysfunction by inhibiting LOX-1-mediated signaling

Ou HC, Song TY, Yeh YC, Huang CY, Yang SF, Chiu TH, Tsai KL, Chen KL, Wu YJ, Tsai CS, Chang LY, Kuo WW, Lee SD. EGCG protects against oxidized LDL-induced endothelial dysfunction by inhibiting LOX-1- mediated signaling. J Appl Physiol 108: 1745-1756, 2010. First published March 4, 2010; doi:10.1152/japplphysiol. 00879.2009.-Lectin- like oxidized low-density lipoprotein receptor-1 (LOX-1), originally identified as the major receptor for oxidized low-density lipoprotein (oxLDL) in endothelial cells, plays a major role in the pathology of vascular diseases. Green tea consumption is associated with reduced cardiovascular mortality in some epidemiological studies. In the present study, we hypothesized that the most abundant polyphenolic compound in tea, epigallocatechin-3-gallate (EGCG), can down-regulate parameters of endothelial dysfunction by modulating LOX1-regulated cell signaling. In cultured human umbilical vein endothelial cells (HUVECs), exposure to oxLDL (130 mu g/ml), which led to an increase in LOX-1 expression at the RNA and protein levels, was abrogated by addition of EGCG or DPI, a well-known inhibitor of flavoproteins, suggesting the involveme nt of NADPH oxidase. Furthermore, oxLDL rapidly activated the membrane translocation of Rac-1 and p47(phox) and the subsequent induction of ROS generation, which was suppressed markedly by pretreatment with EGCG or anti-LOX-1 monoclonal antibody. OxLDL also increased p38 MAPK phosphorylation and decreased phosphorylation of the amino-terminal region of Akt, with maximal induction at about 30 min, and NF-kappa B phosphorylation within 1 h, resulting in redox-sensitive signaling. In addition, oxLDL diminished the expression of endothelial nitric oxide synthase (eNOS), enhanced the expression of endothelin-1 and adhesion molecules (ICAM, E-selectin, and monocyte chemoattractant protein-1), and increased the adherence of monocytic THP-1 cells to HUVECs. Pretreatment with EGCG, however, exerted significant cyto-protective effects in all events. These data suggest that EGCG inhibits the oxLDL-induced LOX-1-mediated signaling pathway, at least in part, by inhibiting NADPH oxidase and consequent ROS-enhanced LOX-1 expression, which contributes to further ROS generation and the subsequent activation of NF-kappa B via the p38 MAPK pathway. Results from this study may provide insight into a possible molecular mechanism by which EGCG suppresses oxLDL-mediated vascular endothelial dysfunction.