Valproic Acid Inhibits Ferroptosis and Improves Bone Integration in <scp>OVX</scp> Rats Through the <scp>AMPK</scp> / <scp>SIRT1</scp> Pathway

The prevalence of postmenopausal osteoporosis (PMOP) has been steadily increasing. Ferroptosis has been recognized as a critical factor influencing the bone-forming ability of bone marrow mesenchymal stem cells (BMSCs). Valproic acid (VPA), an HDAC inhibitor, has been suggested to play a role in regulating osteoporosis development; however, its underlying mechanism remains unclear. This study aims to explore the impact of VPA on ferroptosis, a process that is triggered by Erastin, and to assess its implications for postmenopausal osteoporosis (PMOP). We evaluated the effects of valproate sodium on Erastin-induced ferroptosis in BMSCs through in vitro experiments, including CCK-8 assays, Western blot analysis, mitochondrial function assessments (MDA, GSH, ROS, and MMP), and osteogenic evaluations (ALP and ARS staining). The impact of VPA on bone integration in ovariectomized (OVX) rats was assessed using micro-CT, hematoxylin-eosin (HE) staining, Masson's trichrome staining, and RT-PCR analysis. RNA sequencing was employed to investigate the underlying mechanisms of VPA action. Our findings demonstrate that VPA treatment prevents the Erastin-induced decline in the osteogenic capacity of BMSCs. In addition, VPA treatment suppresses ferroptosis, as indicated by decreased malondialdehyde levels, reduced mitochondrial ROS, and increased glutathione concentrations. Moreover, VPA treatment promotes trabecular bone growth and enhances bone integration. Mechanistic studies reveal that SIRT1-siRNA counteracts the beneficial effects of VPA in Erastin-treated BMSCs. VPA improves bone integration in OVX rats by activating the AMPK/SIRT1 pathway and inhibiting ferroptosis.