Specnuezhenide attenuates rheumatoid arthritis bone destruction via dual regulation of osteoclast-osteoblast balance through KEAP1/NRF2 signaling

Background: Rheumatoid arthritis (RA)-associated bone erosion is driven by osteoclast-osteoblast imbalance and oxidative stress. Specnuezhenide (SPN), a bioactive compound from Ligustrum lucidum, exhibits antioxidant properties, but its role in RA bone loss remains undefined.

Purpose: To explore the potential mechanisms and therapeutic targets of SPN in treating RA, with a focus on its regulation of bone remodeling and oxidative stress pathways.

Study design: Collagen-induced arthritis (CIA) mice were treated with SPN (50/100/200 mg/kg) for 28 days. Joint inflammation, bone erosion, osteoclast/osteoblast markers, and oxidative stress pathways were evaluated. In vitro, SPN's effects on osteoclastogenesis/osteoblastogenesis were assessed in inflammatory microenvironments. Molecular docking, dynamics simulations, and KEAP1 knockdown experiments were used to validate mechanisms.

Methods: In vivo, CIA was induced in DBA/1 mice, followed by SPN treatment. Paw swelling, arthritis index (AI), micro-CT for bone erosion, H&E and TRAP staining for histological analysis, Western blotting for marker proteins, and immunofluorescence for NRF2 localization were assessed. In vitro, osteoclast/osteoblast differentiation from bone marrow cells under inflammatory conditions (LPS/nigericin) was evaluated. Mechanistic investigations were performed via molecular docking, molecular dynamics simulations, cellular thermal shift assay, surface plasmon resonance, and adenovirus-mediated KEAP1 knockdown.

Results: In vivo, SPN reduced paw swelling, AI, and bone erosion in CIA mice. It downregulated osteoclast markers (TRAP, NFATC1) and upregulated osteoblast markers (RUNX2, Col1), suppressed ROS, and activated NRF2/SOD1 pathways. In vitro, SPN inhibited osteoclastogenesis and promoted osteoblast mineralization in inflammatory microenvironments, with ROS scavenging dependent on NRF2 activation. Mechanistically, SPN bound to KEAP1, promoting NRF2 nuclear translocation.

Conclusion: SPN attenuates RA bone destruction by restoring osteoclast-osteoblast balance through precise targeting of the KEAP1, thereby modulating the KEAP1/NRF2/ROS axis. This mechanism-specific phytotherapeutic strategy provides a novel approach against RA-related osteolysis distinct from broad-spectrum Antioxidants.

Bone remodeling; KEAP1/NRF2 pathway; Osteoclast-osteoblast balance; Oxidative stress; Rheumatoid arthritis; Specnuezhenide.