Injectable Hyaluronic Acid-Functionalized Nanocomposite Hydrogel for Targeted Rheumatoid Arthritis Therapy via Concurrent ROS Attenuation and Macrophage Repolarization

Background: The clinical treatment of rheumatoid arthritis (RA), a chronic systematic autoimmune disease marked by persistent synovial inflammation and irreversible joint damage, remains substantially challenging due to the limitations of current therapies including insufficient targeting, short intra-articular retention and off-target adverse effects. Therefore, developing an injectable, long-acting and targeted therapeutic hydrogel platform is urgently needed for precise and efficient RA treatment. Methods: We developed an injectable long-acting nanocomposite hydrogel platform (HA-BR nano-GEL@CLT) which integrated hyaluronic acid (HA)-polyethylene glycol (PEG) co-polymeric matrix encapsulating HA-bilirubin nanoparticles (HA-BR NPs) and celastrol (CLT). The hydrogel was characterized and its in vitro biocompatibility, antioxidant, anti-inflammatory, and macrophage polarization effects were evaluated. In vivo therapeutic efficacy and biosafety were assessed in adjuvant-induced arthritis (AIA) rats. Results: The average particle size of fabricated HA-BR NPs@CLT was 118.5 nm and the gel formulation underwent a rapid sol‑to‑gel phase transition within 200 seconds. HA-BR nano-GEL@CLT exhibited strong biomimetic lubrication, anti-inflammatory and antioxidant capacities, and could effectively modulate the polarization of macrophages in vitro, with the result that the M1/M2 ratio in HA-BR nano-GEL@CLT group was only 0.19-fold that of model group. The hydrogel also provided long-term intra-articular retention up to 21 days in AIA rats. It significantly alleviated paw swelling, inhibited bone erosion, modulated the levels of inflammatory cytokines, whereas the expressions of IL-6 and TNF-α were reduced by 27% and 43%, and the expression of IL-10 was increased by 47%, compared to HA GEL@CLT group. Besides, HA-BR nano-GEL@CLT also alleviated oxidative damage, regulated macrophage polarization and reduced systemic toxicity of CLT in vivo. Conclusion: This injectable nanocomposite hydrogel platform offers an efficient and promising approach to suppress RA progression via ROS attenuation and macrophage repolarization.