Anti-osteoclastogenic effects of the ethyl acetate fraction and lignans from Sambucus racemosa subsp. pendula

s Excessive osteoclast activation via RANKL-RANK signaling drives pathological bone resorption in various osteolytic conditions, including inflammatory arthritis. Consequently, there is growing interest in identifying natural therapeutic agents capable of inhibiting osteoclast activation. Sambucus racemosa L. subsp. pendula (Nakai) H.I. Lim & Chin S. Chang, endemic to Ulleung Island, Korea, has traditionally been utilized in Korean folk medicine; however, its pharmacological effects on osteoclastogenesis have remained unexplored. In this study, we investigated the anti-osteoclastogenic activity of methylene chloride (MCF) and ethyl acetate (EAF) fractions obtained from the methanol extract of the plant’s stem, identifying two active compounds within the EAF. While both fractions inhibited osteoclast differentiation and the formation of mature osteoclasts in mouse bone marrow-derived macrophages (BMDMs), EAF exhibited superior efficacy with an IC 50 value of 0.42 ± 0.07 μg/mL. Mechanistic studies revealed that EAF attenuated osteoclast differentiation by inhibiting early-stage RANKL-induced signaling, including the activation of nuclear factor-κB (NF-κB), AKT, and mitogen-activated protein kinases (MAPKs). This resulted in the downregulation of the transcription factors c-Fos and nuclear factor of activated T cells cytoplasmic 1 (NFATc1). Furthermore, EAF administration protected mice against inflammation-induced bone loss in vivo . Chemical characterization of the MCF and EAF yielded 20 isolated lignans. Among these, (+)-cycloolivil (8) and sambucunol B (11) demonstrated potent anti-osteoclastogenic activity. Collectively, our findings suggest that S. racemosa subsp. pendula is a promising natural therapeutic candidate for the prevention and management of inflammatory bone loss and related osteolytic diseases.