Triptolide inhibits proliferation, differentiation and induces apoptosis of osteoblastic MC3T3-E1 cells

Ankylosing spondylitis (AS) is characterized by the formation of bony spurs. Treatment of the resulting ankylosis, excessive bone formation and associated functional impairment, remain the primary therapeutic aims in research regarding this condition. Triptolide is the primary active component of the perennial vine Tripterygium wilfordii Hook. f., and has previously been demonstrated to exert anti-tumor activities including inhibition of cell growth and the induction of apoptosis, however, the effect of triptolide on osteoblasts remains to be elucidated. In the present study, the MC3T3-E1 mouse osteoblast cell line was treated with differing concentrations of triptolide for various intervals. Cell proliferation was detected using the bromodeoxyuridine assay, cell cycle and apoptosis were measured by flow cytometry, nuclear apoptosis was observed by Hoechst staining and associated proteins were determined via western blot analysis. The cells were then further incubated with osteogenic induction medium supplemented with triptolide for 7 or 12 days and the differentiation to osteoblasts was examined by picrosirius staining, observation of alkaline phosphatase activity and a calcium deposition assay. It was demonstrated that treatment with triptolide significantly inhibited osteoblast proliferation and induced cell cycle arrest and apoptosis of the osteoblasts. Furthermore, treatment with triptolide reduced collagen formation, alkaline phosphatase activity and calcium deposition. The present study demonstrated an inhibitory effect of triptolide on osteoblast proliferation and differentiation, and therefore suggests a potential therapeutic agent for the treatment of AS in the future.