Objectives To investigate whether curcumin (Cur) suppressed lipopolysaccharide (LPS)-induced inflammation in vascular smooth muscle cells (VSMCs) of rats, and to determine its molecular mechanisms.

Methods Primary rat VSMCs were treated with LPS (1 mg/L) and Cur (5, 10 or 30 mmol/L) for 24 h. The levels of MCP-1, TNF-α and iNOS were measured using ELISA and real-time RT-PCR. NO level was analysed with the Griess reaction. Western-blotting was used to detect the activation of TLR4, MAPKs, IκBα, NF-κB p65 and the p47phox subunit of NADPH oxidase in the cells.

Results Treatment of VSMCs with LPS dramatically increased expression of inflammatory cytokines MCP-1 and TNF-α, expression of TLR4 and iNOS, and NO production. LPS also significantly increased phosphorylation of IκBα, nuclear translocation of NF-κB (p65) and phosphorylation of MAPKs in VSMCs. Furthermore, LPS significantly increased production of intracellular ROS, and decreased expression of p47phox subunit of NADPH oxidase. Pretreatment with Cur concentration-dependently attenuated all the aberrant changes in LPS-treated VSMCs. The LPS-induced overexpression of MCP-1 and TNF-α, and NO production were attenuated by pretreatment with the ERK inhibitor PD98059, the p38 MAPK inhibitor SB203580, the NF-κB inhibitor PDTC or anti-TLR4 antibody, but not with the JNK inhibitor SP600125.

Conclusions Cur suppresses LPS-induced overexpression of inflammatory mediators in VSMCs in vitro via inhibiting the TLR4-MAPK/NF-κB pathways, partly due to block of NADPH-mediated intracellular ROS production.