Sirolimus increases tissue factor expression but not activity in cultured human vascular smooth muscle cells

Abstract Background Sirolimus-eluting stents (CYPHER stents) demonstrated remarkable efficacy in reducing restenosis rates in patients with coronary artery disease. There is a concern of sub-acute and late stent thrombosis. Tissue factor (TF) is critical in thrombosis. This study investigated the effect of sirolimus on TF expression and activity in cultured human vascular smooth muscle cells (SMCs). Methods SMCs were cultured from human saphenous veins and aortas. Quiescent cells were stimulated with sirolimus (0.1 – 20 ng/ml) over 24 hours. Cellular TF expression and activity released into culture medium were measured. The effect of sirolimus on activation of m ammalian t arget o f rapamycin (mTOR) was measured by phosphorylation of the substrate p70s6k at T389, and activation of RhoA was measured by pull-down assay. Results Sirolimus increased TF protein level in cultured human SMCs in a concentration and time-dependent manner (about 2-fold, p Conclusion Although sirolimus stimulates TF protein expression in human SMC associated with inhibition of mTOR, it does not enhance TF activity released from the cells, suggesting a relatively safe profile of CYPHER stents. The inhibition of TF expression by fluvastatin favors clinical use of statins in patients undergoing coronary stenting.