Extract Containing Dieckol Suppresses RANKL-Induced Osteoclastogenesis via MAP Kinase/NF-κB Pathway Inhibition and Heme Oxygenase-1 Induction.

, an edible marine brown alga (Laminariaceae), is a rich source of bioactive compounds such as fucoidan and phlorotannins. extract (ECE) was prepared using 70% ethanol extraction and ECE contained 67% and 10.6% of total phlorotannins and dieckol, respectively. ECE treatment significantly inhibited receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation of RAW 264.7 cells and pit formation in bone resorption assay ( ＜0.05). Moreover, it suppressed RANKL-induced NF-κB and mitogen-activated protein kinase signaling in a dose dependent manner. Downregulated osteoclast-specific gene (tartrate-resistant acid phosphatase, cathepsin K, and matrix metalloproteinase-9) expression and osteoclast proliferative transcriptional factors (nuclear factor of activated T cells-1 and c-fos) confirmed ECE-mediated suppression of osteoclastogenesis. ECE treatment (100 μg/ml) increased heme oxygenase-1 expression by 2.5-fold and decreased intercellular reactive oxygen species production during osteoclastogenesis. The effective inhibition of RANKL-stimulated osteoclast differentiation and oxidative stress by ECE suggest that ECE has therapeutic potential in alleviating osteoclast-associated disorders.