Koumine inhibits osteoclastogenesis and prevents ovariectomy-induced bone loss via suppression of the MAPK signaling pathways.

Excessive osteoclast formation drives osteolytic bone diseases such as osteoporosis. Koumine (KM), an alkaloid derived from Gelsemium elegans, exhibits various bioactivities; however, its role in bone homeostasis remains unknown. This study investigated the effects of KM on RANKL-induced osteoclastogenesis in bone marrow-derived macrophages (BMMs). Cell viability, differentiation (TRAcP staining), and function (F-actin ring formation, bone resorption pit assay) were assessed. The underlying mechanisms were explored using Western blot and qPCR. The in vivo efficacy of KM was evaluated in an ovariectomized (OVX) mouse model using micro-CT and histological analyses. KM dose-dependently inhibited osteoclast formation and bone resorption without cytotoxicity. It suppressed RANKL-induced activation of the mitogen-activated protein kinase (MAPK) pathway, downregulating c-Fos, NFATc1, TRAP, and CTSK. In contrast, KM had no significant effect on RANKL-induced NF-κB activation. KM did not impair osteoblast differentiation or mineralization. In vivo, KM treatment prevented OVX-induced bone loss, improved trabecular microarchitecture, and reduced osteoclast numbers. KM suppresses osteoclastogenesis and protects against bone loss, an effect associated with inhibition of MAPK signaling, highlighting its potential as a novel therapeutic for osteolytic diseases.