Downregulation of osteoclast differentiation and activation by the soluble epoxide hydrolase inhibition

This study aimed to investigate the effects of soluble epoxide hydrolase (sEH) inhibition on osteoclast differentiation and activity in vitro and in vivo, as well as to elucidate the signaling pathways associated with osteoclastogenesis. Primary murine bone marrow monocytes were stimulated with macrophage colony-stimulating factor and receptor activator of nuclear factor kappa B ligand to induce osteoclastogenesis and treated with the sEH inhibitor 1-(1-propanoylpiperidin-4-yl)-3-[4-(trifluoromethoxy)phenyl]urea (TPPU) (0.1-10 μM). Tartrate-resistant acid phosphatase staining, gene expression analyses, and immunofluorescence were used to evaluate osteoclast formation, transcriptional regulation, and cell fusion. A murine model of ligature-induced periodontitis was used to assess in vivo effects of sEH inhibition (TPPU 10 mg/kg). Alveolar bone loss was quantified by histomorphometry, and gingival gene expression was analyzed. In vitro, sEH inhibition significantly reduced tartrate-resistant acid phosphatase-positive multinucleated osteoclast formation, downregulated the expression of key transcription factors and osteoclast activity-related genes. Immunofluorescence analysis revealed attenuation of mitogen-activated protein kinase signaling and reduced dendritic cell-specific transmembrane protein expression, indicating impaired cell fusion. In vivo, TPPU treatment preserved alveolar bone structure, reduced osteoclast-like cell numbers, and decreased the expression of osteoclastic markers in gingival tissues during experimental periodontitis. sEH acts as a crucial regulator of osteoclast differentiation and function. Pharmacological inhibition of sEH suppresses osteoclastogenesis and protects against inflammatory bone loss. Therefore, targeting sEH may represent a novel therapeutic approach to modulate osteoclast activity and prevent bone destruction in periodontitis and other bone-resorptive diseases. SIGNIFICANCE STATEMENT: This study provides direct evidence that soluble epoxide hydrolase inhibition modulates osteoclast differentiation and fusion, contributing to reduced inflammatory bone loss. By demonstrating effects on osteoclast-intrinsic pathways while also influencing the inflammatory microenvironment, our findings support soluble epoxide hydrolase as a pharmacological target for chronic inflammatory bone-resorptive diseases.