Betulinic Acid Self-Assembled Nanodelivery System Attenuates Osteoarthritis by Dually Modulating Macrophage Polarization and Macrophage-Chondrocyte Crosstalk via Disruption of the GSK3β/NF-κB/CCL20 Axis

Osteoarthritis (OA) is a degenerative joint disease characterized by M1 macrophage-driven synovitis, worsening progression. In this study, it is found that betulinic acid (BA), a natural compound, inhibits M1 macrophage characteristics while promoting conversion to the M2 phenotype. However, BA suffers from poor solubility and a short half-life in vivo, restricting therapeutic use. Here, a thermosensitive hydrogel is developed using hydroxypropyl chitosan, loaded with poly(betulinic acid) nanoparticles (PBA NPs) and a folic acid (FA) targeting moiety, yielding FA-modified PBA NPs-loaded hydrogel (FA-PBA NPs@Gel) with sustained release, injectability, and enhanced stability. FA-PBA NPs@Gel selectively targets M1 macrophages via FA–folate receptor 1 interaction to alleviate synovitis, while disrupting macrophage–chondrocyte crosstalk to foster cartilage regeneration. Immunofluorescence and flow cytometry demonstrate reprogramming of M1 to M2. Transcriptome sequencing, antibody microarrays, and drug affinity responsive target stability assays show that FA-PBA NPs@Gel suppressed nuclear factor-κB (NF-κB) activation by binding glycogen synthase kinase 3 beta (GSK3β), thereby downregulating chemokine ligand 20 (CCL20), disrupting macrophage–chondrocyte crosstalk and promoting cartilage regeneration. In summary, FA-PBA NPs@Gel represent a promising OA therapy with dual functions of mitigating synovitis and promoting regeneration.