Soy phosphatidylcholine inhibited TLR4-mediated MCP-1 expression in vascular cells

Inflammatory signaling via Toll-like receptor 4 (TLR4) has been shown to facilitate atherogenesis. Recent lines of evidence show that saturated fatty acids (SFAs) induce the inflammatory response via the TLR4 pathway in macrophages and adipocytes. The aims of this study are to confirm the role of SFAs in TLR4-mediated inflammatory signaling in vascular cells and to propose soy phosphatidylcholine (SPC) as an effective inhibitor against TLR4-mediated agonists. SFAs such as palmitate and stearate increased the expression and secretion of MCP-1 in human umbilical vein endothelial cells (HUVECs) and rat vascular smooth muscle cells (VSMCs). SFAs up-regulated the activity of MCP-1 promoter through the activation of NF-kappaB. Knockdown of TLR4 using siRNA diminished the SFA-induced MCP-1 expression in HUVECs and rat VSMCs, while PKC or ceramide signal inhibitor did not inhibit the expression. Furthermore, we found that SPC effectively inhibited the MCP-1 expression induced by palmitate or LPS in a dose-dependent manner. However, SPC did not inhibit the mRNA expression of MCP-1 induced by cytokines such as TNF-alpha and IL-1beta, or by agonists binding to TLRs other than TLR4. In addition, SPC did not affect the activity of LPS assessed by clotting activity of the Limulus amoebocyte lysate. These results clearly show that SPC specifically inhibits the inflammatory responses induced by the TLR4-dependent signal. In conclusion, we have demonstrated a role of SFAs for inflammatory response via TLR4-NF-kappaB signaling in vascular cells. Moreover, we propose that SPC can be useful as a selective inhibitor to suppress the TLR4-mediated inflammatory signaling.