Nasturtium officinale Extract Suppresses Osteoclastogenesis in RAW 264 Cells by Inhibiting IκB-Kinase β

Osteoclasts are large, multinucleated, bone-absorbing cells and play a crucial role in osteolytic bone diseases such as osteopetrosis and rheumatoid arthritis. Therefore, controlling osteoclast differentiation and activation has been considered a promising strategy to prevent and treat osteolytic diseases. In this study, we demonstrate, using the mouse monocyte-derived macrophage-like cell line RAW 264, that extract from Nasturtium officinale or watercress, an herb of European origin, suppresses receptor activator of nuclear factor-κB ligand-induced osteoclast differentiation in vitro . N. officinale extract decreased the emergence of tartrate-resistant acid phosphatase-positive differentiated multinuclear cells and inhibited their bone-absorbing activity. The extract decreased expression of genes associated with osteoclast differentiation and function. Induction of nuclear factor of activated T cells c1 (NFATc1), the master transcriptional regulator of osteoclastogenesis, was blunted by N. officinale extract. Activation of nuclear factor-κB and mitogen-activated protein kinases pathways, both of which are necessary for NFATc1 induction and osteoclast differentiation, was also suppressed by the extract. Among upstream kinases, activity of IκB-kinase β (IKKβ), but not that of TGFβ-activated kinase 1, was inhibited by N. officinale extract in vitro. Pharmacological inhibition of IKKβ by a specific inhibitor PS1145 in RAW 264 cells mostly recaptured the inhibitory action of N. officinale extract. These findings provide a novel pharmacological action of N. officinale and its potential usefulness for the prevention of osteoporosis.