Low-level endotoxin induces potent inflammatory activation of human blood vessels - Inhibition by statins

Background - Low-level endotoxemia (ie, greater than or equal to 50 pg/mL) in apparently healthy subjects was recently identified as a powerful, independent risk factor for atherosclerosis. Methods and Results - We treated human saphenous veins (HSVs) with low levels of endotoxin. Release of the proinflammatory chemokines interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) was measured by ELISA. Superoxide was determined by using the fluorescent probe dihydroethidium ( HE), and monocyte binding was assessed with calcein-labeled U-937 cells. Three- to 4-fold increases in MCP-1 and IL-8 release were observed at endotoxin concentrations of 100 pg/mL; these increases were inhibited by the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor atorvastatin. Studies in cultured endothelial cells suggest that the mechanism is related to inhibition of isoprenylation ( ie, geranylgeranylation) rather than cholesterol formation. Endotoxin produced dose-dependent increases in HE fluorescence that were inhibited by the superoxide dismutase mimics Tiron and MnTBAP. Endotoxin potently induced U-937 cell binding to HSV; binding was inhibited by both Tiron and atorvastatin. Toll-like receptor-4 expression was detected in cultured HSV endothelial and smooth muscle cells and in intact HSV. Conclusions - Clinically relevant levels of endotoxin, as reported in ambulatory populations, have profound inflammatory effects on intact HSV. Inhibition of endotoxin-induced vascular inflammation might contribute to the beneficial effects of statins in treating atherosclerosis.