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.