Curcumin diminishes human osteoclastogenesis by inhibition of the signalosome-associated IκB kinase

Curcumin is a natural polyphenolic derogate extracted from spice turmeric, exhibiting anti-inflammatory and chemopreventive activities. It was described to interact with the signalosome-associated kinases and the proteasome-ubiquitin system, which both are involved in the osteoclastogenesis. Thus, we hypothesized that curcumin could diminish osteoclast differentiation and function. For the experiments considering osteoclast differentiation and resorptional activities, preosteoclasts were cultured for 4 weeks and treated with curcumin at subapoptotic dosages. Derived mature osteoclasts were identified as large, multinucleated cells with expression of tartrate-resistant acid phosphatase activity. Formation of resorption lacunae, a hallmark of osteoclast activity, was quantified using dentine pits and light microscopy. The signaling pathways were examined by ELISA-based methods and by immunoblotting. Both 1 and 10 mu M curcumin abrogated osteoclast differentiation (by 56 and 81%) and function (by 56 and 99%) (P < 0.05) dose-dependently. The effects were accompanied by the inhibition of I kappa B phosphorylation and NF-kappa B activation. In contrast, subtoxic doses did not have any significant effects on proteasome inhibition. This manuscript is the first report that describes the effects of curcumin toward human osteoclastogenesis, and builds the framework for clinical trials of curcumin in the treatment of cancer-induced lytic bone disease.