DHA-Derived Lipid Mediators Attenuate Osteoarthritis by Resolving Inflammation and Protecting Cartilage in Association with the SIRT1 Signaling Pathway

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by persistent low-grade inflammation and progressive cartilage destruction. Macrophage-driven inflammatory responses contribute to extracellular matrix (ECM) degradation and accelerate disease progression. Here, we investigated the therapeutic potential of a DHA-derived lipid mediator mixture (LM), generated via soybean lipoxygenase and composed of 17S-hydroxydocosahexaenoic acid, resolvin D5, and protectin DX (3:47:50), in regulating macrophage–chondrocyte crosstalk and OA progression. LM significantly reduced IL-6, IL-1β, and TNF-α production in lipopolysaccharide-induced THP-1 macrophages. Conditioned medium from LM-treated macrophages attenuated ECM degradation in primary chondrocytes by suppressing MMP13 and ADAMTS5 while restoring COL2A1 and ACAN expression, indicating that LM may indirectly protects ECM by modulating the inflammatory microenvironment. In parallel, LM directly protected chondrocytes against IL-1β-induced inflammatory and catabolic responses, and restored ECM homeostasis. Mechanistically, LM significantly increased SIRT1 expression and deacetylation activity, as demonstrated by reduced NF-κB p65 acetylation. Both pharmacological inhibition by EX527 and siRNA-mediated SIRT1 knockdown abolished the protective effects of LM on ECM preservation. In vivo, LM oral administration alleviated cartilage destruction, improved joint structure and suppressed OA progression in a monosodium iodoacetate-induced OA model. Notably, micro-CT studies have demonstrated that LM significantly improved subchondral bone architecture, as evidenced by increased bone volume fraction and improved trabecular parameters. Histological analyses confirmed that LM attenuated inflammation and maintained cartilage integrity. Consistently, immunohistochemical findings showed reduced MMP13 expression, restoration of collagen II and aggrecan, and upregulation of SIRT1 in the LM-treated group compared to OA rats. Collectively, these findings suggest that LM mitigates OA progression by reducing inflammation, preserving ECM homeostasis, and attenuating subchondral bone deterioration.