**5. Conclusions**

FX inhibits osteoclast differentiation and bone-resorption activity through downregulating p38 and ERK, and promoting the nuclear translocation of phospho-Nrf2. The results of this study provide useful insight into the molecular mechanisms of FX action. Hence, FX could be used to treat bone diseases caused by excessive osteoclastic activity.

**Author Contributions:** Conceptualization and experiment design, Y.J.L. and Y.-J.H.; statistical analysis and data interpretation, Y.-J.H., E.H.K., G.K., and Y.-B.P.; cell experiments, Y.S.C. and Y.R.O.; writing—original-draft preparation, Y.-J.H.; writing—review and editing, Y.J.L. and G.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by gran<sup>t</sup> no. 04-2018-014 from the Seoul National Bundang Hospital Research Fund (to Lee YJ) and the National Research Foundation of Korea (NRF) gran<sup>t</sup> funded by the Korean governmen<sup>t</sup> (MSIT) (no. 2020R1C1C1010147 to Ha YJ).

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.
