ETHNOPHARMACOLOGICAL RELEVANCE: Magnolia officinalis as a traditional Chinese herb has long been used for the treatment of anxiety, cough, headache and allergic diseases, and also have been used in traditional Chinese medicine to treat a variety of mental disorders including depression. AIM OF THE STUDY: Magnolol, a hydroxylated biphenyl compound isolated from Magnolia officinalis, has been reported to have anti-inflammatory properties. However, the underlying molecular mechanisms are not well understood. The aim of this study was to investigate the molecular mechanism of magnolol in modifying lipopolysaccharide (LPS)-induced signal pathways in RAW264.7 cells. MATERIAL AND METHODS: The purity of magnolol was determined by high performance liquid chromatography. RAW264.7 cells were stimulated with LPS in the presence or absence of magnolol. The expression of proinflammatory cytokines were determined by ELISA and reverse transcription-PCR. Nuclear factor-kappaB (NF-kappaB), inhibitory kappa B (IkappaBalpha) protein, p38, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and Toll-like receptor 4 (TLR4) were determined by Western blot. Further analyses were performed on mTLR4 and mMD2 co-transfected HEK293 cells. RESULTS: The result showed that the purity of magnolol used in this study was 100%. Magnolol inhibited the expression of TNF-alpha, IL-6 and IL-1beta in LPS-stimulated RAW264.7 cells in a dose-dependent manner. Western blot analysis showed that magnolol suppressed LPS-induced NF-kappaB activation, IkappaBalpha degradation, phosphorylation of ERK, JNK and P38. Magnolol could significantly down-regulated the expression of TLR4 stimulating by LPS. Furthermore, magnolol suppressed LPS-induced IL-8 production in HEK293-mTLR4/MD-2 cells. CONCLUSIONS: Our results suggest that magnolol exerts an anti-inflammatory property by down-regulated the expression of TLR4 up-regulated by LPS, thereby attenuating TLR4 mediated the activation of NF-kappaB and MAPK signaling and the release of pro-inflammatory cytokines. These findings suggest that magnolol may be a therapeutic agent against inflammatory diseases. CI - Copyright (c) 2012 Elsevier Ireland Ltd. All rights reserved.