Tanshinone II-A inhibits oxidized LDL-induced LOX-1 expression in macrophages by reducing intracellular superoxide radical generation and NE-κB activation

Lectin-like oxidized LDL (oxLDL) receptor-1 (LOX-1), a novel scavenger receptor highly expressed in human and experimental atherosclerotic lesions, is responsible for the uptake of oxLDL in vascular cells. We demonstrated previously that Tanshinone II-A (Tan), a pharmacologically active compound extracted from the rhizome of the Chinese herb Salvia miltiorrhiza Bunge, inhibits atherogenesis in hypercholesterolemic rats, rabbits, and apolipoprotein-E deficient (ApoE(-/-)) mice. However, the precise mechanism by which Tan protects against atherogenesis remains to be elucidated. Therefore, we hypothesized that Tan can suppress the uptake of oxLDL by diminishing the expression of LOX-1 via suppression of NF-kappa B signaling pathway, thereby contributing to reduced macrophage foam cell formation. In cultured murine macrophages, oxLDL induced LOX-1 expression at the mRNA and protein levels, was abrogated by addition of Tan or pyrrolidinedithiocarbamic acid ammonium salt (PDTC), a widely used inhibitor of NF-kappa B, suggesting the involvement of NF-kappa B. Tan also reduced LOX-1 expression in atherosclerotic lesions of ApoE(-/-) mice fed a high cholesterol diet. Mechanistically, Tan suppressed the nuclear translocation of NF-kappa B P65 subunit and phosphorylation of I kappa B-alpha induced by oxLDL. Electrophoretic mobility shift assay (EMSA) demonstrated that Tan inhibited the nuclear protein binding to NF-kappa B consensus sequence. Functionally, we observed that Tan inhibited Dil-oxLDL uptake by macrophages in a fashion similar to that produced by LOX-1 neutralizing antibody. Our current findings reveal a novel mechanism by which Tan protects against atherogenesis and shed new light on the potential therapeutic application of Tan to the treatment and prevention of atherosclerotic cardiovascular diseases. (Translational Research 2012;160:114-124)