Abstract

Osteoporosis is characterized by increased bone fragility and elevated fracture risk, severely compromising patients' quality of life. This study aimed to investigate the therapeutic potential of isoorientin (Iso) against osteoporosis and elucidate its underlying mechanisms. Using a combination of in vitro approaches, we demonstrated that Iso effectively inhibited RANKL-induced osteoclast differentiation in RAW 264.7 cells and downregulated the expression of key osteoclastic markers-including matrix metallopeptidase 9 (MMP9), cathepsin K (CTSK), c-fos, and nuclear factor of activated T-cells 1 (NFATc1)-at both protein and mRNA levels. Iso also exhibited potent anti-inflammatory and antioxidant activities, reducing the levels of pro-inflammatory cytokines (IL-6, TNF-α, IL-1β) and malondialdehyde (MDA) while enhancing superoxide dismutase (SOD) activity and glutathione (GSH) content. Mechanistically, Iso acts by suppressing the ROS/PPARγ/NF-κB signaling axis. In vitro, the anti-osteoclastogenic effect of Iso was attenuated by the PPARγ agonist, and either the PPARγ antagonist or the NF-κB inhibitor BAY 11-7082 alone effectively inhibited osteoclast differentiation. In an ovariectomy (OVX)-induced osteoporotic mouse model, Iso treatment significantly prevented bone loss, improved bone microarchitecture, and suppressed osteoclast activity. Notably, administration of the PPARγ antagonist GW9662 or the NF-κB inhibitor BAY 11-7082 alone also exerted clear bone-protective effects in vivo, further validating these two pathways as viable therapeutic targets for osteoporosis. In conclusion, isoorientin exerts anti-osteoporotic effects by inhibiting the ROS/PPARγ/NF-κB signaling pathway, with efficacy comparable to clinical drugs, offering a promising novel candidate for the management of osteoporosis.