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Osteoarthritis (OA) is a common degenerative joint disease with no effective cure. Current clinical treatments still face many challenges. Recently, a research team from Guangxi Medical University published an important research result in "Advanced Materials", innovatively designing an asymmetric and highly exposed iron mononuclear nanozyme (Fe SAzymes). They modified and loaded siMMP13 onto these Fe SAzymes with a chondrocyte-targeting peptide WYRGRL to construct a si-FeSA/NGM-W nanoplatform. By inhibiting ferroptosis, this platform achieves precise targeted treatment for OA, providing a new nanomedicine strategy for the clinical intervention of OA.
Key analysis
Research background: Pain points in OA treatment and the key role of ferroptosis
OA is characterized by progressive degradation of cartilage, chronic inflammation, and remodeling of subchondral bone. It is a major cause of chronic pain and disability worldwide. Current early OA treatment mainly relies on painkillers, which can only relieve symptoms but cannot stop the disease progression. Long-term use also has side effects such as gastrointestinal and cardiovascular problems; in the late stage, only joint replacement surgery can be relied on, accompanied by risks such as prosthesis failure and postoperative complications.
It has been confirmed that the oxidative-reductive imbalance-driven ferroptosis is the core mechanism of OA progression: Active oxygen (ROS) accumulates abnormally in OA, triggering lipid peroxidation through the Fenton reaction, leading to mitochondrial dysfunction, and activating matrix metalloproteinase 13 (MMP13), down-regulating glutathione peroxidase 4 (GPX4), disrupting glutathione (GSH) metabolism, forming a "inflammation-ferroptosis-cartilage degradation" vicious cycle.
Mononuclear nanozymes (SAzymes) due to their high stability, low cost, and adjustable catalytic activity have become ideal tools for eliminating ROS and inhibiting ferroptosis. However, traditional iron-based mononuclear nanozymes have problems such as insufficient exposure of active sites, slow catalytic kinetics, and lack of targeting. Therefore, the research team optimized the structure to create a multifunctional nanozyme platform with high catalytic activity, chondrocyte targeting, and gene regulation functions.
Core design: Synthesis and structural characteristics of si-FeSA/NGM-W nanozyme
The team used a mixed salt stripping + zinc removal strategy to separate Zn-ZIF into a thin two-dimensional nitrogen-doped graphene-like nanosheet (NGM) with topological defects and hierarchical pore structures, serving as a scaffold for anchoring iron mononuclei; by constructing Fe-N₄-Cl asymmetric coordination active sites, introducing strain and defects to promote electron transfer, enhance radical adsorption, and reduce reaction energy barriers, significantly improving the catalytic activity of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)-like multi-enzyme complexes.
Based on this, the team covalently coupled the chondrocyte-targeting peptide WYRGRL and used electrostatic interactions to load the silenced siRNA of MMP13 (siMMP13), ultimately obtaining the si-FeSA/NGM-W nanozyme complex. Structural characterization confirmed:
1. FeSA/NGM is a 3-nm-thick ultrathin two-dimensional structure, with iron mononuclei uniformly dispersed, with a loading amount of 0.87 wt.% without aggregation of metal nanoparticles;
2. The asymmetric coordination of Fe-N₄-Cl achieved the intermediate oxidation state of iron, enhancing the orbital overlap with reaction intermediates, optimizing the electronic structure;
3. The modification with WYRGRL and the loading of siMMP13 changed the zeta potential from +19.47 mV to -31.63 mV, with a siMMP13 loading efficiency of >90%, and presented pH-responsive release (slow release at neutral pH, rapid release of ~55% within 4 hours at acidic pH (5.5)), achieving precise intracellular delivery.
DOI: 10.1002/adma.202520951.
