Spica Prunella extract inhibits phosphorylation of JNK, ERK and IκBα signals during osteoclastogenesis

Since the 17 th century Spica Prunella has been used as a medicinal herb. Dried and pulverized Spica Prunella samples were extracted and used in these experiments. In this study, the effects of Spica Prunella extract (SPE) on RANKL (receptor activator of nuclear factor κB ligand)-induced osteoclastogenesis were examined. Actin ring formation, a typical marker of osteoclastogenesis, was inhibited by SPE without any toxicity. There was also a marked inhibition in the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells in bone marrow-derived monocytes (BMMs). SPE also suppressed phosphorylation of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinases (ERK) both of which are signals of the mitogen-activated protein kinases (MAPKs) signaling pathway. Additionally, SPE inhibited IκBα (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha) signaling pathway, which is an important factor in osteoclastogenesis. These results indicate that SPE might suppress osteoclast differentiation by inhibiting the phosphorylation of JNK and ERK in MAPK and NF-κB signaling pathways which act as messengers in the RANKL-induced osteoclast differentiation pathway. This means that SPE could potentially have great therapeutic usage in treating bone erosive diseases such as rheumatoid arthritis or in preventing metastasis associated with bone loss.