Oxidized low-density lipoprotein (oxLDL) is a key contributor to atherogenesis through multiple mechanisms, including the reactive oxygen species (ROS)-mediated nuclear factor-kappaB (NFκB) signaling pathway. Although shikonin, one of the main active components isolated from the Chinese herb Lithospermum erythrorhizon, has been shown to possess cardioprotective, antioxidative, and anti-inflammatory effects, the mechanisms underlying these actions are not well understood. In this study, we used EA.hy926 endothelial-like cells to examine the anti-atherogenic activity of shikonin. Shikonin (0-1 μM) concentration-dependently induced heme oxygenase-1, glutamate cysteine ligase modifier subunit, catalase, superoxide dismutase 1, glutathione peroxidase 1, and glutathione reductase protein and mRNA expression and glutathione content via activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/Nrf2 signaling pathway. In the presence of oxLDL (40 μg/ml), shikonin pretreatment reversed oxLDL-induced ROS production, antioxidant response element reporter activity, NFκB nuclear translocation, and intercellular adhesion molecule (ICAM)-1 and E-selectin expression and suppressed the increase of monocyte adhesion to endothelial cells. Nrf2 knockdown by using RNA interference attenuated the ability of shikonin to inhibit oxLDL-induced NFκB DNA binding activity, adhesion molecule expression, and monocyte adhesion. Taken together, these results suggest that shikonin protects against oxLDL-induced endothelial damage by suppressing ROS/NFκB-mediated ICAM-1 and E-selectin expression via up-regulation of PI3K/Akt/Nrf2-dependent antioxidant enzyme expression.
Keywords: Adhesion molecules; Antioxidant defense; Nuclear factor erythroid 2-related factor 2 (Nrf2); Nuclear factor-kappaB (NFκB); Oxidized LDL; Shikonin.
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