A rabbit osteochondral defect (OCD) model for evaluation of tissue engineered implants on their biosafety and efficacy in osteochondral repair.

Osteochondral defect (OCD) is a common but challenging condition in orthopaedics that imposes huge socioeconomic burdens in our aging society. It is imperative to accelerate the R&D of regenerative scaffolds using osteochondral tissue engineering concepts. Yet, all innovative implant-based treatments require animal testing models to verify their feasibility, biosafety, and efficacy before proceeding to human trials. Rabbit models offer a more clinically relevant platform for studying OCD repair than smaller rodents, while being more cost-effective than large animal models. The core-decompression drilling technique to produce full-thickness distal medial femoral condyle defects in rabbits can mimic one of the trauma-relevant OCD models. This model is commonly used to evaluate the implant's biosafety and efficacy of osteochondral dual-lineage regeneration. In this article, we initially indicate the methodology and describe a minimally-invasive surgical protocol in a step-wise manner to generate a standard and reproducible rabbit OCD for scaffold implantation. Besides, we provide a detailed procedure for sample collection, processing, and evaluation by a series of subsequent standardized biochemical, radiological, biomechanical, and histological assessments. In conclusion, the well-established, easy-handling, reproducible, and reliable rabbit OCD model will play a pivotal role in translational research of osteochondral tissue engineering.

Combination of magnesium ions and vitamin C alleviates synovitis and osteophyte formation in osteoarthritis of mice.

INTRODUCTION: We previously demonstrated that magnesium ions (Mg2+) was a novel therapeutic alternative for osteoarthritis (OA) through promoting the hypoxia inducible factor-1α (HIF-1α)-mediated cartilage matrix synthesis. However, oxidative stress can inhibit the expression of HIF-1α, amplify the inflammation that potentially impairs the therapeutic efficacy of Mg2+ in OA. Vitamin (VC), a potent antioxidant, may enhance the efficacy of Mg2+ in OA treatment. This study aims to investigate the efficacy of combination of Mg2+ and VC on alleviating joint destruction and pain in OA. MATERIAL AND METHODS: Anterior cruciate ligament transection with partial medial meniscectomy induced mice OA model were randomly received intra-articular injection of either saline, MgCl2 (0.5 mol/L), VC (3 mg/ml) or MgCl2 (0.5 mol/L) plus VC (3 mg/ml) at week 2 post-operation, twice weekly, for 2 weeks. Joint pain and pathological changes were assessed by gait analysis, histology, western blotting and micro-CT. RESULTS: Mg2+ and VC showed additive effects to significantly alleviate the joint destruction and pain. The efficacy of this combined therapy could sustain for 3 months after the last injection. We demonstrated that VC enhanced the promotive effect of Mg2+ on HIF-1α expression in cartilage. Additionally, combination of Mg2+ and VC markedly promoted the M2 polarization of macrophages in synovium. Furthermore, combination of Mg2+ and VC inhibited osteophyte formation and expressions of pain-related neuropeptides. CONCLUSIONS: Intra-articular administration of Mg2+ and VC additively alleviates joint destruction and pain in OA. Our current formulation may be a cost-effective alternative treatment for OA.

Intra-Articular Delivery of Quercetin Using Thermosensitive Hydrogel Attenuate Cartilage Degradation in an Osteoarthritis Rat Model.

OBJECTIVE: Quercetin (Que), a bioflavonoid, is both anti-inflammatory and antioxidative. Que has been used as an oral supplement for osteoarthritis (OA) with inconsistent findings because of its low bioavailability. We encapsulated Que in a mPEG-polypeptide thermogel to prolong its bioactivity. The efficacy of this formulation was evaluated in a posttraumatic OA rat model. DESIGN: Methoxy-poly(ethylene glycol)-l-poly(alanine) (mPEG-PA) polymer was synthesized and characterized in terms of cytotoxicity and release kinetics in vitro. At 12 weeks old, Sprague-Dawley rats underwent anterior cruciate ligament transection (ACLT). At 24 weeks post-operation, rats received either an intra-articular (IA) injection of saline, hydrogel, or hydrogel with Que (50 or 500 µg). Gait analysis was performed at pre-ACLT, pre-treatment, and at 4, 8, and 12 weeks post-treatment. At 12 weeks post-treatment, knee joints were collected for histopathological evaluation. RESULTS: In vitro studies showed that chondrocytes were viable after 72 hours of incubation with mPEG-PA, and the release of Que could be sustained for >28 days. Among all OA rats, the limb idleness index (LII) were significantly increased at 24 weeks post-ACLT. Rats that received hydrogel with Que (50 µg) showed the most reduction in LII at both 4 and 8 weeks post-treatment. The Osteoarthritis Research Society International score of rats received hydrogel with Que (50 µg) was significantly lower than the control group. All rats suffered from low-grade synovitis (Krenn score: 2-4). CONCLUSION: This study suggests that a sustained delivery of Que (50 µg) could provide symptom relief and also delay the progression of OA in the knee.

Reciprocal inhibition of YAP/TAZ and NF-κB regulates osteoarthritic cartilage degradation.

Osteoarthritis is one of the leading causes of pain and disability in the aged population due to articular cartilage damage. This warrants investigation of signaling mechanisms that could protect cartilage from degeneration and degradation. Here we show in a murine model of experimental osteoarthritis that YAP activation by transgenic overexpression or by deletion of its upstream inhibitory kinases Mst1/2 preserves articular cartilage integrity, whereas deletion of YAP in chondrocytes promotes cartilage disruption. Our work shows that YAP is both necessary and sufficient for the maintenance of cartilage homeostasis in osteoarthritis. Mechanistically, inflammatory cytokines, such as TNFα or IL-1ß, trigger YAP/TAZ degradation through TAK1-mediated phosphorylation. Furthermore, YAP directly interacts with TAK1 and attenuates NF-κB signaling by inhibiting substrate accessibility of TAK1. Our study establishes a reciprocal antagonism between Hippo-YAP/TAZ and NF-κB signaling in regulating the induction of matrix-degrading enzyme expression and cartilage degradation during osteoarthritis pathogenesis.

Effect of SDF-1/Cxcr4 Signaling Antagonist AMD3100 on Bone Mineralization in Distraction Osteogenesis.

Distraction osteogenesis (DO) is a widely applied technique in orthopedics surgery, which involves rapid stem cell migration, homing, and differentiation. Interactions between the chemokine receptor Cxcr4 and its ligand, stromal derived factor-1 (SDF-1), regulate hematopoietic stem cell trafficking to the ischemic area and induce their subsequent differentiation. Here, we examined SDF-1 expression and further investigated the role of SDF-1/Cxcr4 signaling antagonist AMD3100 during bone regeneration in rat DO model. The results showed that expression levels of SDF-1 and osteogenic genes were higher in DO zones than in the fracture zones, and SDF-1 expression level was the highest at the termination of the distraction phase. Radiological, mechanical, and histological analyses demonstrated that the local administration of AMD3100 (400 µM) to DO rats significantly inhibited new bone formation. In the rat bone marrow mesenchymal stem cells culture, comparing to the group treated with osteogenic induction medium, AMD3100 supplement led to a considerable decrease in the expression of alkaline phosphatase and early osteogenic marker genes. However, the amount of calcium deposits in rat MSCs did not differ between the groups. Therefore, our study demonstrated that the DO process induced higher expression of SDF-1, which collated to rapid induction of callus formation. Local application of SDF-1/Cxcr4 signaling antagonist AMD3100 significantly inhibited bone mineralization and osteogenesis in DO, which may represent a potential therapeutic approach to the enhancement of bone consolidation in patients undergoing DO.

From the printer: Potential of three-dimensional printing for orthopaedic applications.

Three-dimensional (3D) printers can create complex structures based on digital models. The combination of medical diagnostic imaging with 3D printing has great potential in day-to-day clinics for patient-specific solutions and applications. In the musculoskeletal system, 3D printing is used to create custom-made implants, patient-specific instrumentation, and to regenerate tissues, in particular bone and cartilage. The major limiting factors for bioprinting include the lack of printing techniques with optimal printing resolution and materials with ideal mechanical strengths while maintaining cellular functionality. Before "tissues from the printer" can be widely applied, further research and development on improving and optimising printing techniques and biomaterials, and knowledge on the development of printed constructs into living tissues, is essential for future clinical application of this technology.