Kurarinone suppresses RANKL-induced osteoclastogenesis via calcineurin downregulation and NFATc1-GSK3β modulation

Background and purpose: Osteoclasts play a critical role in bone resorption, and their excessive activity contributes to osteoporosis and other bone-related diseases. This study aimed to isolate and identify chromane and chromanone derivatives from Sophora flavescens extracts that inhibit osteoclastogenesis. Experimental approach: Five compounds were isolated from S. flavescens using TLC-guided fractionation and HPLC analysis: trifolirhizin (C1), kushenol I (C2), maackiain (C3), kurarinone (C4), and sophoraflavanone G (C5). We evaluated the effects of these compounds on RANKL-induced osteoclast differentiation. We assessed osteoclast formation, F-actin ring organization, bone resorption activity, and the expression of osteoclast-specific genes, including NFATc1, CTSK, ACP5, and DC-STAMP . The underlying mechanism was further investigated by analyzing calcineurin A expression. Findings/Results: Among the five compounds, kurarinone (C4) exhibited a significant inhibitory effect on RANKL-induced osteoclast differentiation. Kurarinone reduced the formation of multinucleated osteoclasts, suppressed F-actin ring formation, and decreased bone resorption activity. It downregulated the expression of osteoclast-specific genes by affecting the early phase of differentiation. Mechanistically, kurarinone dose-dependently decreased the expression of calcineurin A, suggesting suppression of NFATc1 activation via inhibition of its dephosphorylation. Conclusion and implications: Kurarinone is a promising natural compound that regulates osteoclast activity through downregulation of calcineurin A expression. These findings support its potential as a therapeutic agent for osteoporosis and other bone-related disorders.