Honokiol: an effective inhibitor of tumor necrosis factor-α-induced up-regulation of inflammatory cytokine and chemokine production in human synovial fibroblasts

In this study, we investigated the mechanisms underlying the anti-inflammatory effects of honokiol in tumor necrosis factor (TNF)-alpha-stimulated rheumatoid arthritis synovial fibroblasts (RASFs). RASFs pre-treated with honokiol (0-20 mu M) were stimulated with TNF-alpha (20 ng/ml). The levels of prostaglandin E2 (PGE2), nitric oxide (NO), soluble intercellular adhesion molecule- 1 (sICAM-1), transforming growth factor-beta 1 (TGF-beta 1), monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1 alpha (MIP-1 alpha) in supernatants were determined by enzyme-linked immunosorbent assay (ELISA) and Griess assay. In addition, protein expression levels of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and phosphorylated Akt, nuclear factor kappa B (NF kappa B), and extracellular signal-regulated kinase (ERK) 1/2 were determined by western blot. The expression of NF kappa B-p65 was assessed by immunocytochemical analysis. TNF-alpha treatment significantly up-regulated the levels of PGE2, NO, sICAM-1, TGF-beta 1, MCP-1, and MIP-1 alpha in the supernatants of RASFs, increased the protein expression of COX-2, iNOS, and induced phosphorylation of Akt, I kappa B-alpha, NF kappa B, and ERK1/2 in RASFs. TNF-alpha-induced expression of these molecules was inhibited in a dose-dependent manner by pre-treatment with honokiol. The inhibitory effect of honokiol on NF kappa B-p65 activity was also confirmed by immunocytochemical analysis. In conclusion, honokiol is a potential inhibitor of TNF-alpha-induced expression of inflammatory factors in RASFs, which holds promise as a potential anti-inflammatory drug.