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Abstract Gene therapy has the potential to facilitate targeted expression of therapeutic proteins to promote cartilage regeneration in osteoarthritis (OA). The dense, avascular, aggrecan‐glycosaminoglycan (GAG) rich negatively charged cartilage, however, hinders their transport to reach chondrocytes in effective doses. While viral vector mediated gene delivery has shown promise, concerns over immunogenicity and tumorigenic side‐effects persist. To address these issues, this study develops surface‐modified cartilage‐targeting exosomes as non‐viral carriers for gene therapy. Charge‐reversed cationic exosomes are engineered for mRNA delivery by anchoring cartilage targeting optimally charged arginine‐rich cationic motifs into the anionic exosome bilayer by using buffer pH as a charge‐reversal switch. Cationic exosomes penetrated through the full‐thickness of early‐stage arthritic human cartilage owing to weak‐reversible ionic binding with GAGs and efficiently delivered the encapsulated eGFP mRNA to chondrocytes residing in tissue deep layers, while unmodified anionic exosomes do not. When intra‐articularly injected into destabilized medial meniscus mice knees with early‐stage OA, mRNA loaded charge‐reversed exosomes overcame joint clearance and rapidly penetrated into cartilage, creating an intra‐tissue depot and efficiently expressing eGFP; native exosomes remained unsuccessful. Cationic exosomes thus hold strong translational potential as a platform technology for cartilage‐targeted non‐viral delivery of any relevant mRNA targets for OA treatment. 

Exosomes show promise as next-generation therapy for osteoarthritis (OA) due to their ability to modulate inflammation and cartilage synthesis. Recent advances in the engineering of exosomes have enhanced their targeted therapeutic potential for OA. 

Cationic-motif-modified exosomes provide a platform for gene delivery by overcoming ocular barriers faced during topical delivery as they exhibit full-depth penetration in porcine retinal explants significantly higher than native exosomes. 

Surface modification of milk exosomes with hydrophilic and zwitterionic peptides improves stability in the gastrointestinal tract, permeability through intestinal mucus, and uptake into epithelial cells, thereby markedly increasing the efficiency of oral administration for gene delivery. 

Abstract Background Insulin-like growth factor-1 (IGF-1) has the potential to be used for osteoarthritis (OA) treatment but has not been evaluated in clinics yet owing to toxicity concerns. It suffers from short intra-joint residence time and a lack of cartilage targeting following its intra-articular administration. Here, we synthesize an electrically charged cationic formulation of IGF-1 by using a short-length arginine-rich, hydrophilic cationic peptide carrier (CPC) with a net charge of +14, designed for rapid and high uptake and retention in both healthy and arthritic cartilage. Methods IGF-1 was conjugated to CPC by using a site-specific sulfhydryl reaction via a bifunctional linker. Intra-cartilage depth of penetration and retention of CPC-IGF-1 was compared with the unmodified IGF-1. The therapeutic effectiveness of a single dose of CPC-IGF-1 was compared with free IGF-1 in an IL-1α-challenged cartilage explant culture post-traumatic OA model. Results CPC-IGF-1 rapidly penetrated through the full thickness of cartilage creating a drug depot owing to electrostatic interactions with negatively charged aggrecan-glycosaminoglycans (GAGs). CPC-IGF-1 remained bound within the tissue while unmodified IGF-1 cleared out. Treatment with a single dose of CPC-IGF-1 effectively suppressed IL-1α-induced GAG loss and nitrite release and rescued cell metabolism and viability throughout the 16-day culture period, while free IGF at the equivalent dose was not effective. Conclusions CPC-mediated depot delivery of IGF-1 protected cartilage by suppressing cytokine-induced catabolism with only a single dose. CPC is a versatile cationic motif that can be used for intra-cartilage delivery of other similar-sized drugs.