Background: While existing pharmacotherapies for osteoporosis, such as bisphosphonates, reduce fracture risk, their long-term use remains limited by adverse effects, including gastrointestinal toxicity, osteonecrosis of the jaw, and atypical femoral fractures. Hydrogen sulfide (H₂S), an endogenous gasotransmitter with anti-inflammatory properties, emerges as a potential alternative, but the role of its donor, sodium hydrosulfide (NaHS), in osteoporosis remains unexplored. Therefore, this study investigates NaHS-driven bone-protective mechanisms, emphasizing its ability to modulate the nuclear factor kappa-B (NF-κB)/ inhibitor of NF-κB alpha (IκB-α) axis—a crucial pathway in osteoclastogenesis.

Methods: Mice were divided into a sham control group (n = 6) and an ovariectomized (OVX) group (n = 6). Mice in the OVX group received varying doses of NaHS (0, 0.38, 0.75, 1.5 mg/kg/day) or vehicle for 4 weeks. Bone mineral density (BMD) was quantified using micro-computed tomography (micro-CT) analysis. Osteoclast differentiation was assessed in bone marrow-derived macrophages (BMMs) and RAW264.7 cells via tartrate-resistant acid phosphatase (TRAP) staining. Molecular mechanisms were deciphered using ubiquitination assays, nuclear/cytoplasmic fractionation, and immunofluorescence.

Results: NaHS treatment increased lumbar BMD and trabecular bone-to-tissue volume in OVX mice compared to untreated controls. In vitro, NaHS (0.15 mM) significantly suppressed receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis (p < 0.05). Mechanistically, for the first time, NaHS was found to stabilize IκB-α by inhibiting its ubiquitination, thereby blocking the nuclear translocation of NF-κB p65.

Conclusions: NaHS mitigates OVX-induced bone loss via dual inhibition of osteoclast differentiation (through IκB-α/NF-κB blockade) and bone resorption. Its capacity to circumvent the limitations of current therapies positions NaHS as a novel candidate for osteoporosis management.