Metabolic reprogramming in polyol pathway contributes to anti-inflammatory effect of glucosamine salts on synovial...

The upregulation of cyclooxygenase-2 (COX-2) and the subsequent production of prostaglandin E₂ (PGE₂) in synovial tissue are hallmarks of autoimmune arthritis, including rheumatoid arthritis (RA). While glucosamine (GlcN) derivatives modulate RA symptoms, their specific anti-inflammatory mechanisms in synovial fibroblasts (SFBs) are poorly understood. In this study, we evaluated the anti-inflammatory efficacy of various GlcN derivatives: glucosamine hydrochloride (GlcN-HCl), glucosamine sulfate (GlcN-S), glucosaminate (GlcNA), and N-acetylglucosamine (GlcNAc). GlcN-HCl and GlcN-S inhibited IL-1β-induced PGE₂ release and the expression of COX-2 at both protein and mRNA levels, whereas GlcNA and GlcNAc exhibited no such inhibitory activity. Structure-activity relationship analysis using GlcN-HCl epimers revealed that whereas the C-4 epimer, galactosamine hydrochloride (GalN-HCl), retained potent anti-inflammatory effects, the C-2 epimer, mannosamine hydrochloride (ManN-HCl), showed significantly diminished bioactivity, highlighting the critical role of the C-2 stereochemical configuration in modulating inflammatory responses. Mechanistically, we demonstrated that GlcN-HCl-mediated COX-2 suppression occurs via epigenetic silencing rather than mRNA destabilization. GlcN-HCl treatment significantly reduced the enrichment of active chromatin marks, H3K27ac and H3K4me3, at the COX-2 promoter, whereas mRNA stability remained unaffected. Given that metabolic dysregulation is intrinsically linked to inflammatory pathogenesis, we characterized the metabolic profile of GlcN-HCl-treated SFBs. We found that GlcN-HCl triggers metabolic reprogramming of the polyol pathway by modulating the expression of AKR1B1 and sorbitol dehydrogenase (SORD), resulting in elevated intracellular sorbitol levels. Pharmacological inhibition of AKR1B1 effectively abrogated the anti-inflammatory effects of GlcN-HCl, indicating that polyol pathway activation is essential for its efficacy. We confirmed the evolutionary conservation of these findings in human SFBs, demonstrating the translational relevance of the GlcN-HCl-mediated metabolic and epigenetic axis. Our findings demonstrate that GlcN-HCl induces metabolic reprogramming of the polyol pathway in synovial fibroblasts, facilitating the epigenetic silencing of inflammatory mediators. This metabolic-epigenetic axis suggests a mechanistic rationale for pharmacological metabolic intervention in RA, shifting the therapeutic paradigm toward targeted reprogramming of synovial fibroblast metabolism.