Ishige okamurae extract suppresses osteoclastogenesis in RANKL-induced bone marrow-derived macrophages and ovariectomized mouse model

Objective: To investigate the inhibitory effects of Ishige okamurae extract (IOE) against osteoclastogenesis in vitro and in vivo. Methods: The effects of IOE on osteoclast differentiation were examined in receptor activator of nuclear factor-KB ligand (RANKL)-stimulated bone marrow macrophages. Cell viability was examined using an MTT assay, while osteoclast formation and differentiation were determined by tartrate-resistant acid phosphatase (TRAP) staining kit. Protein expression levels of osteoclast-related factors, transcriptional factors, and signaling molecules involved in osteoclastogenesis were analyzed by Western blotting. The effect of IOE was examined in the ovariectomy (OVX) mouse model following oral administration, and osteoclast-related parameters were analyzed using 3D X-ray microscopy. Results: IOE significantly reduced RANKL-induced osteoclast formation and differentiation without causing cytotoxic effects on bone marrow macrophages. It suppressed the formation of TRAP-positive multinuclear osteoclasts and downregulated the expression of osteoclast- related factors, such as TRAP (ACP5), matrix metalloproteinase-9, calcitonin receptor, and cathepsin K. Furthermore, IOE significantly inhibited the expression of key transcriptional factors, such as nuclear factor of activated T cells, cytoplasmic 1, and c-Fos. Mechanistically, IOE attenuated the activation of upstream extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and nuclear factor-KB (NF-kB) cascades. In OVX mice, administration of IOE significantly improved bone microstructural parameters such as trabecular thickness, number, volume, and separation. Conclusions: The present findings demonstrate that IOE inhibits osteoclastogenesis via blockage of ERK, JNK, and NF-kB signaling pathways in vitro. Furthermore, IOE administration reduces bone loss in OVX mice. These results show that IOE has the potential to be a functional food for the prevention of osteoporosis.