Sesquiterpene lactone parthenolide blocks lipopolysaccharide-induced osteolysis through the suppression of NF-κB activity

Abstract

Effective treatment for bacteria-induced bone lytic diseases is not yet available. In this study, we showed that PAR, an NF-κB inhibitor found in medicinal herbs, can block LPS-induced osteolysis. PAR does this by inhibiting osteoclastogenesis and bone resorption and promoting apoptosis of osteoclasts through the suppression of NF-κB activity. Introduction: Osteolysis induced by chronic gram-negative bacterial infection underlies many bone diseases such as osteomyelitis, septic arthritis, and periodontitis. Drugs that inhibit lipopolysaccharide (LPS)-induced osteolysis are critically needed for the prevention of bone destruction in infective bone diseases. In this study, we investigated the effect of parthenolide (PAR) on LPS-induced osteolysis in vivo and studied its role in osteoclastogenesis, bone resorption, apoptosis, and NF-κB activity. Materials and Methods: The LPS-induced osteolysis in the mouse calvarium model was used to examine the effect of PAR in vivo. RANKL-induced osteoclast differentiation from RAW264.7 cells and bone resorption assays were used to assess the effect of PAR in vitro. Assays for NF-κB activation, p65 translocation, and IκB-α degradation were used to determine the mechanism of action of PAR in osteoclasts and their precursors. Flow cytometry and confocal microscopic analysis were used to examine cell apoptosis. Semiquantitative RT-PCR was performed to examine the effect of PAR on gene expression of RANK and TRAF6. Results: We found that PAR (0.5 and 1 mg/kg), injected simultaneously with LPS (25 mg/kg) or 3 days later, blocked the LPS-induced osteolysis in the mouse calvarium model. In vitro studies showed that low concentrations of PAR (<1 μM) inhibited in vitro osteoclastogenesis and osteoclastic bone resorption, whereas higher concentrations (>5 μM) triggered apoptotic cell death of osteoclasts and their precursor cells in a dose-dependent manner. Furthermore, PAR inhibited LPS-induced NF-κB activation, p65 translocation, and IκB-α degradation both in mature osteoclasts and their precursors in a time- and dose-dependent manner. In addition, PAR inhibited NF-κB activation induced by osteoclastogenic factors RANKL, interleukin (IL)-1β, or TNF-α to varying degrees and reduced the gene expression of RANK and TRAF6. Conclusion: The NF-κB pathway is known to mediate both osteoclast differentiation and survival. These findings indicate that PAR blocks LPS-induced osteolysis through the suppression of NF-κB activity and suggest that it might have therapeutic value in bacteria-induced bone destruction. © 2004 American Society for Bone and Mineral Research.