Inhibition of Ulmus davidiana Planch (Ulmaceae) on bone resorption mediated by processing of cathepsin K in cultured mouse osteoclasts

Ulmus davidiana Planch (Ulmaceae) (UD) has long been known to be antiinflammatory in traditional Korean medicine. This experiment investigated the effects of UD on bone resorption using bone cell culture. Different concentrations of crude extract of UD were added to mouse bone cell culture. The mitochondrial activity of the bone cells after exposure of UD was determined by colorimetric 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT). It was demonstrated that UD has potential effects on bone cell culture without cytotoxicity. The most effective concentration of UD in bone cells was 100 microg/mL. Cathepsin K (Cat K) is the major cysteine protease expressed in osteoclasts and is thought to play a key role in matrix degradation during bone resorption. When mouse long bone cells including osteoclasts and osteoblasts were treated with UD, UD prevented the osteoclast-mediated intracellular processing of Cat K, suggesting that UD may disrupt the intracellular transport of pro Cat K. Since secreted proenzymes have the potential to reenter the cell via the mannose-6-phosphate (M6P) receptor, to prevent this possibility, UD was tested in the absence or presence of M6P. Inhibition of Cat K processing by UD was observed in a dose-dependent manner. Furthermore, the addition of M6P resulted in enhanced potency of UD. UD dose-dependently inhibited in vitro bone resorption with a potency similar to that observed for inhibition of Cat K processing.