Parthenolide inhibits LPS-induced inflammatory cytokines through the toll-like receptor 4 signal pathway in THP-1 cells

Parthenolide (PTL) shows potent anti-inflammatory and anti-cancer activities. In the present study, the molecular mechanisms of PTL's activities were explored in lipopolysaccharide (LPS)-induced human leukemia monocytic THP-1 cells and human primary monocytes. The 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium salt (MTS) assay was used to analyze the effect of PTL on THP-1 cell viability. Enzyme-linked immunosorbent assay was used to determine the effect of PTL on LPS-induced inflammatory cytokine secretion. Flow cytometry and quantitative real-time polymerase chain reaction were used to assess the effect of PTL on LPS-induced toll-like receptor 4 (TLR4) expression. Phosphorylation levels of signaling molecules were determined by western blot analysis. Results showed that PTL < 12.5 mu M did not significantly affect THP-1 cells viability. LPS treatment led to a marked up-regulation of interleukin (IL)-6, IL-1 beta, IL-8, IL-12p40, tumor necrosis factor-alpha, IL-18, and NO in THP-1 cells. However, PTL inhibited the expression of these cytokines in a dose-dependent manner, with IC50 values of 1.091-2.620 mu M. PTL blocked TLR4 expression with an IC50 value of 1.373 mu M as determined by the flow cytometry analysis, and this blocking effect was verified at both protein and mRNA levels. Up-regulation of phosphorylation levels of extracellular signal-regulated kinase 1/2, Jun N-terminal kinase, p38, nuclear factor kappa B (NF-kappa B) p65, and I kappa B alpha and up-regulation of expressions of other molecules (inducible nitric oxide synthase, TLR4, and TNF receptor-associated factor 6) induced by LPS were abolished by PTL in a dose-dependent manner. The anti-inflammatory mechanisms of PTL operate partly through the TLR4-mediated mitogen-activated protein kinase and NF-kappa B signaling pathways. Therefore, TLR4 may be a new target for anti-inflammation therapies.