Nanoparticles isolated from the Gubi Zhitong formula alleviate knee osteoarthritis by reprogramming macrophages

Knee osteoarthritis (KOA) is a whole-joint disease characterized by synovitis and joint cartilage destruction. The severity of KOA is highly associated with an imbalance between M1 and M2 synovial macrophages. Emerging evidence suggests that nanoparticles present in Traditional Chinese Medicine (TCM) decoctions may serve as bioactive components with therapeutic potential. Herein, we innovatively isolated nanoparticles from the Gubi Zhitong formula (NPG), a TCM formulation with long-term clinical use in OA for its anti-inflammatory effects, and aimed to investigate whether NPG attenuates KOA by reprogramming synovial macrophage polarization in KOA models. Our findings revealed that NPG, being rich in flavonoids and phenylpropanoids, could form stable nano-structures via hydrophobic interactions and hydrogen bonding, which significantly improved joint function, mitigating pathological features, including cartilage erosion and synovial hyperplasia. Comprehensive in vitro and in vivo studies confirmed that NPG effectively suppressed M1-type pro-inflammatory cytokines while promoting M2-type anti-inflammatory factors, and could reprogram M1 macrophages towards the M2 phenotype. Mechanistic studies revealed that NPG achieves dual activation of the aryl hydrocarbon receptor (AHR) through both direct and indirect mechanisms: it directly engages the receptor while also modulating the kynurenine pathway to supply endogenous ligands, thereby promoting macrophage phenotype reprogramming and ultimately ameliorating the cartilage microenvironment. Overall, our findings suggest that the intra-articular injection of TCM-based nanoparticles holds significant promise as a potential and effective therapeutic strategy for KOA treatment.