The OARSI histopathology initiative - recommendations for histological assessments of osteoarthritis in the rabbit

Micelle-to-Gel: Thermosensitive intra-articular hydrogels for osteoarthritis management

Osteoarthritis (OA) is a chronic and degenerative joint disease with a rising incidence worldwide. Current therapeutic approaches primarily focus on symptom relief through systemic administration, which raises safety concerns related to side effects and long-term use. In this context, the local administration of natural compounds with anti-inflammatory and anti-arthritic properties, such as β-Lapachone constitutes an interesting alternative. In this work, we prepared and characterized injectable thermosensitive hybrid hydrogels loaded with β-Lapachone. A comprehensive characterization of the hydrogel systems was performed, including micellar diameter, mechanical properties at different temperatures, the ability to control drug release and microstructure. The anti-inflammatory activity of the free drug, as well as that of the blank or loaded hydrogels was then evaluated ex vivo, using OA cartilage explants. Additionally, in vivo studies were carried out in a rabbit model of OA to assess their clinical potential. The results suggest that the hydrogel systems possess a composite microstructure integrating micelles, together with a temperature-responsive stiffness and the ability to modulate drug release. In addition, β-Lapachone-loaded hydrogels display an interesting immunomodulatory potential ex vivo, as they were able to efficiently reduce the secretion of several proinflammatory mediators, such as IL-6, MMP9, MMP13 and CXCL8. Furthermore, the drug-loaded hydrogels were found to improve in vivo cartilage and bone histomorphometric markers, such as subchondral bone thickness, as well as early signs of cartilage damage, such as the fibrillation index. Therefore, the developed β-Lapachone-loaded thermosensitive hydrogels constitute a promising alternative for OA management.

FSP1/S100A4-Expressing Stem/Progenitor Cells Are Essential for Temporomandibular Joint Growth and Homeostasis

The temporomandibular joint (TMJ) is one of the most used joints in the body. Defects and wear in the cartilage of the joint, condyle, and fibrocartilage disc lie at the heart of many common TMJ disorders. During postnatal development, the condyle acts as a growth center for the mandible, with cells moving as a conveyor belt away from the top of the condyle as they differentiate. The superficial layers of the condyle have been proposed to contain stem/progenitor populations to allow growth and maintain homeostasis. Here we have focused on the role of fibroblast-specific protein 1 (FSP1; also known as S100a4) as a key fibroblast stem/progenitor marker for the condyle. Lineage tracing with FSP1-Cre;R26RmTmG mice revealed that FSP1-expressing cells were restricted to the superficial fibroblast zone, giving rise to all layers of the condyle over time. The FSP1-expressing cells overlapped with other putative stem cell markers of the condyle, such as Gli1 and scleraxis. BrdU pulse chase experiments highlighted that a subset of FSP1 fibrocartilage was label retaining, suggesting that FSP1 labels a novel stem/progenitor cell population in the condyle. Destruction of FSP1-expressing cells by conditional diphtheria toxin activity in FSP1-Cre;R26RDTA mice resulted in severe TMJ osteoarthritis with loss of the cartilage structure. Lgr5-expressing cells in the superficial layer of the condyle have been shown to create a Wnt inhibitory niche. FSP1 expression postnatally was associated with a reduction in canonical Wnt activity in the condyle. Importantly, constitutive activation of Wnt/β catenin in FSP1-expressing cells led to a downregulation of FSP1 and progressive postnatal loss of TMJ condylar hyaline cartilage due to loss of the superficial stem/progenitor cells. These data demonstrate a novel role for FSP1-expressing cells in the superficial zone in growth and maintenance of the TMJ condylar cartilage and highlight the importance of regulating Wnt activity in this population.

LncRNA EMBP1 sponges miR-454-3p to upregulate IRF1 and activate NLRP3-mediated chondrocyte pyroptosis to drive osteoarthritis progression

BACKGROUND

Osteoarthritis (OA) is the most common degenerative joint disease worldwide. Studies have confirmed that pyroptosis is closely associated with the OA onset and progression, particularly via the classical pathway mediated by the NLRP3 inflammasome. However, the intrinsic regulatory mechanisms underlying pyroptosis in OA remain unclear.

METHODS

We conducted RNA sequencing (RNA-seq) analysis on clinical cartilage samples and identified hub genes connecting OA and pyroptosis. We validated NLRP3-mediated pyroptosis activation, evaluated the diagnostic potential of the hub gene, and explored its regulatory role using a papain-induced rabbit OA model and IL-1β-induced chondrocytes. Subsequently, we constructed a competitive endogenous RNA (ceRNA) network based on the hub gene and validated its competitive binding interactions and regulatory function in NLRP3-mediated pyroptosis. Additionally, hub gene interferon regulatory factor 1 (IRF1) serves as a recognized upstream regulator of the novel cell death paradigm PANoptosis, which integrates apoptosis, necrosis, and pyroptosis. We preliminarily explored the potential molecular mechanisms of PANoptosis in OA through clinical sample analysis and in vitro experiments.

RESULTS

RNA-seq revealed that IRF1, a hub gene linking OA and pyroptosis, is upregulated in OA cartilage and is associated with NLRP3, consistent with the in vivo and in vitro results. Dual-luciferase assays, clinical sample analysis, and in vitro experiments confirmed the competitive binding of the embigin pseudogene 1 (EMBP1)/miR-454-3p/IRF1 ceRNA network. Silencing EMBP1 increased miR-454-3p, inhibiting IRF1 and NLRP3-mediated pyroptosis in vitro; however, miR-454-3p inhibitor rescue experiments abolished the beneficial effects of si-EMBP1. Furthermore, we preliminarily characterized the occurrence of PANoptosis in OA and provided initial evidence suggesting a potential regulatory role for the EMBP1/miR-454-3p/IRF1 axis in this process.

CONCLUSIONS

In OA, EMBP1 acts as a sponge for miR-454-3p, inhibiting its negative regulatory effect on IRF1 and exacerbating NLRP3-mediated chondrocyte pyroptosis. Furthermore, EMBP1/miR-454-3p/IRF1-mediated pyroptosis may be integrated into the broader PANoptosis process, interacting with apoptosis and necrosis to influence OA progression.

Experimentally Induced Femoroacetabular Impingement Results in Hip Osteoarthritis: A Novel Platform to Study Mechanisms of Hip Disease

BACKGROUND

We previously established a small animal model of femoral head-neck cam-type hip deformity by inducing physeal injury in immature rabbits. We investigated whether this induced deformity led to hip osteoarthritis (OA) within 4 months.

METHODS

Six-week-old immature New Zealand White rabbits underwent surgery to induce physeal injury in the right femoral head, causing growth arrest and secondary head-neck deformity. Animals were divided into early-pre-OA (4 weeks) and late-OA (16 weeks) groups. Left hips served as (nonsurgical) controls. Radiographs were made to visualize deformities and OA progression. The Beck classification was used to assess macroscopic cartilage damage and OA on the acetabulum and femoral head. Micro-computed tomography (CT), histological scoring, and gene expression were used to evaluate OA progression. The Wilcoxon signed-rank test was used for group comparisons. Significance was set at p < 0.05.

RESULTS

At 16 weeks, the injured hips showed radiographic evidence of joint space narrowing and a higher OA grade than the control hips (p = 0.0002). Micro-CT confirmed degenerative OA changes and a higher femoral head bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) in the injured hips than in the control hips (BV/TV: p = 0.0001, Tb.Th: p = 0.0007). Macroscopically, the injured hips exhibited a greater prevalence and severity of chondral lesions at 4 weeks (83.3%, p = 0.015) and 16 weeks (100.0%, p = 0.002) post-injury compared with the control hips (0%), with worsening over time (4 versus 16 weeks: p = 0.016). The Osteoarthritis Research Society International (OARSI) score and synovitis score increased from 4 to 16 weeks post-injury. Compared with the control hips, the injured hips showed decreased Col2 expression and increased Col10 and MMP13 expression at 16 weeks post-injury (p = 0.062, p = 0.016, p = 0.041, respectively), confirming catabolism and OA progression.

CONCLUSIONS

To our knowledge, we have created the first small animal model of hip OA secondary to experimentally induced head-neck deformity. In this model, the deformity resulted in hip OA at 16 weeks post-injury.

CLINICAL RELEVANCE

This model can be used to test future interventional therapies and study mechanisms of femoroacetabular impingement-mediated hip OA.

An Abbreviated Rabbit Knee Model of Joint Contracture

Experimental analyses of knee joint contractures have traditionally utilized a 6-month rabbit model as the gold standard. However, this model is time-intensive and costly. The purpose of this study was to develop an abbreviated rabbit model of knee contractures and compare it to the well-established longer model. Twenty female New Zealand White rabbits were divided into two equal groups and prospectively studied to assess knee passive extension angles (PEA), contracture angles (CA), and terminal posterior capsular stiffness. Experimental knees were immobilized for either 4 weeks (n = 10) with an 8-week remobilization period in the abbreviated model (i.e., 3 months) or for 8 weeks (n = 10) with a 16-week remobilization period in the standard model (i.e., 6 months). PEAs were assessed at remobilization and several time points using differing vertical forces. At sacrifice, terminal biomechanical data were collected to assess posterior capsular stiffness. Analysis of PEAs in live animals at each torque value and time point demonstrated increased PEAs and decreased CAs in the 3-month abbreviated model as compared to the 6-month standard model. At sacrifice, biomechanical analysis demonstrated that the posterior capsules of the 3-month experimental limbs were significantly more stiff than the contralateral limb (2.4 vs. 0.05 Ncm/°, p < 0.0001), but significantly less stiff compared to the 6-month experimental limbs (2.4 vs. 4.7 Ncm/°, p < 0.0001). Our study suggests that the 6-month standard rabbit knee model of arthrofibrosis should continue to be used in the laboratory assessment of arthrofibrosis. However, the abbreviated model may be beneficial under selected experimental conditions.

Hip dysplasia induction: Establishment of a new surgical model in rabbits

Hip dysplasia (HD) is an arthropathy with an incompletely understood pathophysiology. Existing induction HD models fall short of providing feasible data to test new therapeutic strategies. This study aimed to characterize and validate a new surgical model of HD in rabbits. Seventeen 6-week-old male New Zealand white rabbits were randomly assigned to 3 groups: GI (n = 3) - control group, with six normal hips (NH); GII (n = 7) - seven left instability surgery hips (ISH) and seven right surgery sham hips (SSH); GIII (n = 7) - seven left instability surgery hips, followed by hindlimb bandage immobilization for 3 days (ISHI) and seven right hips without surgery (HWS). The instability surgery was performed by sectioning the teres ligament and the sham by accessing the capsule without its section. After 14 weeks following the induction surgery, the rabbits underwent radiographic and computed tomographic studies and histopathological characterization of the hip joint based on the severity of cartilage structure and chondrocyte pathology. In the imaging assessment, the ISHI group was the only group presenting statistically significant differences in all four parameters, consistent with HD development (P < 0.05). In the histopathologic evaluation, the ISHI group showed a higher severity of cartilage damage and chondrocyte pathology with statistically significant differences when compared with the NH group (P < 0.05). As a result, the proposed rabbit model can be recommended for HD studies aiming to test therapeutic responses to osteoarthritis in vivo, representing a valuable tool in veterinary research fields.

Effects of Silk-Elastin and SpheroSeev Mixture and Minced Cartilage on Cartilage Repair in Rabbit Osteochondral Defect Models

Background

Autologous chondrocyte implantation, a 2-stage, costly procedure, has limitations, prompting the development of 1-step techniques utilizing autologous minced cartilage (MC). However, novel scaffolds for cell migration and proliferation are needed to enhance their effectiveness.

Purpose

To evaluate the effectiveness of silk-elastin and SpheroSeev (SESS) scaffolds in enhancing chondrocyte activity and promoting cartilage repair in a rabbit model of osteochondral defect repair.

Study Design

Controlled laboratory study.

Methods

The effects of a SESS mixture combined with MC on cartilage repair in osteochondral defects were investigated in 42 Japanese White rabbits, with the defect (Df) group serving as the control. Bilateral osteochondral defects were created in the knees of 36 rabbits, treated with MC, SESS, and a combination of MC and SESS, with all treated sites sealed using fibrin glue. Osteochondral cartilage repair was evaluated using the modified O'Driscoll histological scoring, immunohistochemistry for collagen type II expression, and Ki67 staining for cell proliferation at 8, 12, and 24 weeks postoperatively.

Results

SESS alone and in combination with MC significantly enhanced osteochondral cartilage repair in the rabbit models by 24 weeks compared with the Df group (P < .05). Among them, histological scoring was higher in the SESS group (20.7 ± 6) than in the Df and MC groups (8.8 ± 6.7, P = .046; 7.8 ± 5.7, P = .023). This resulted in smooth surfaces and histological features similar to normal cartilage. Immunohistochemical analyses revealed improved repair quality with increased expression of type II collagen and Ki67, indicating superior repair and cellular activity relative to the controls.

Conclusion

The combined use of SESS and MC effectively promoted cartilage repair in rabbit osteochondral defects. Notably, the SESS mixture appears to enhance the structural and compositional repair of cartilage tissue, offering a promising approach for the treatment of osteochondral defects.

Clinical Relevance

The novelty of this approach lies in combining silk-elastin and recombinant spider silk fibers, both of which provide mechanical support and promote cell proliferation, making them promising candidates for enhancing cartilage repair in osteochondral defects. Utilizing the SESS mixture as a scaffold for cartilage repair in osteochondral defects offers a 1-step, cost-effective alternative to traditional autologous chondrocyte implantation, potentially enhancing cartilage repair and improving tissue structure and biochemistry.

MgO@SiO2 nanocapsules: a controlled magnesium ion release system for targeted inhibition of osteoarthritis progression

Osteoarthritis (OA) is a chronic joint disease characterized by degenerative changes in articular cartilage and chronic inflammation. Recent studies suggest that intra-articular (i.a.) injection of magnesium salts holds promise as a therapeutic approach for OA. However, the rapid diffusion of magnesium ions limits their efficacy, resulting in a short duration of action. To overcome this limitation, we developed a nanoparticle delivery system using MgO@SiO2 core/shell nanoparticles, designed as a depot for the controlled release of magnesium ions. Electron microscopy confirmed the formation of the core/shell structure with silica shells of varying thickness. Release studies demonstrated that the silica coating effectively slows nanoparticle degradation, extending magnesium release to over 72 hours. In a rabbit OA model, i.a. injection of these nanocapsules significantly mitigated the pathological progression of OA within four weeks without inducing systemic toxicity. Immunohistochemical analysis further revealed that MgO@SiO2 nanocapsules alleviate the inflammatory response in OA cartilage by inhibiting the NF-κB/p65 signaling pathway. In summary, this study confirms the potential of intra-articular magnesium supplementation as a therapeutic option for OA and introduces a novel approach to enhance the delivery and efficacy of magnesium ions in OA treatment, addressing a relatively underexplored area in the field.

Efficacy of new active viscosupplements on the behavior of an experimental model of osteoarthritis

OBJECTIVE

To evaluate with an animal model of osteoarthritis (New Zealand rabbits) the effectiveness of treatment with active viscosupplements (hyaluronic acid loaded with nanoparticles (NPs) that encapsulate anti-inflammatory compounds or drugs.

MATERIAL AND METHODS

Experimental study composed of 5 groups of rabbits in which section of the anterior cruciate ligament and resection of the internal meniscus were performed to trigger degenerative changes and use it as a model of osteoarthritis. The groups were divided into osteoarthrosis without treatment (I), treatment with commercial hyaluronic acid (HA) (II), treatment with HA with empty nanoparticles (III), treatment with HA with nanoparticles encapsulating dexamethasone (IV) and treatment with HA with nanoparticles that encapsulate curcumin (V). In groups II to V, the infiltration of the corresponding compound was carried out spaced one week apart. Macroscopic histological analysis was performed using a scale based on the Outerbridge classification for osteoarthritis.

RESULTS

We observed that this osteoarthritis model is reproducible and degenerative changes similar to those found in humans are observed. The groups that were infiltrated with hyaluronic acid with curcumin-loaded nanoparticles (V), followed by the dexamethasone group (IV) presented macroscopically less fibrillation, exposure of subchondral bone and sclerosis (better score on the scale) than the control groups (I) (osteoarthritis without treatment), group (II) treated with commercial hyaluronic acid and hyaluronic acid with nanoparticles without drug (III).

CONCLUSIONS

The use of active viscosupplements could have an additional effect to conventional hyaluronic acid treatment due to its antioxidant and anti-inflammatory effect. The most promising group was hyaluronic acid with nanoparticles that encapsulate curcumin and the second group was the one that encapsulates dexamethasone.

[Translated article] Efficacy of new active viscosupplements on the behaviour of an experimental model of osteoarthritis

OBJECTIVE

To evaluate with an animal model of osteoarthritis (New Zealand rabbits) the effectiveness of treatment with active viscosupplements (hyaluronic acid loaded with nanoparticles (NPs) that encapsulate anti-inflammatory compounds or drugs.

MATERIAL AND METHODS

Experimental study composed of 5 groups of rabbits in which section of the anterior cruciate ligament and resection of the internal meniscus were performed to trigger degenerative changes and use it as a model of osteoarthritis. The groups were divided into osteoarthrosis without treatment (I), treatment with commercial hyaluronic acid (HA) (II), treatment with HA with empty nanoparticles (III), treatment with HA with nanoparticles encapsulating dexamethasone (IV) and treatment with HA with nanoparticles that encapsulate curcumin (V). In groups II-V, the infiltration of the corresponding compound was carried out spaced one week apart. Macroscopic histological analysis was performed using a scale based on the Outerbridge classification for osteoarthritis.

RESULTS

We observed that this osteoarthritis model is reproducible and degenerative changes similar to those found in humans are observed. The groups that were infiltrated with hyaluronic acid with curcumin-loaded nanoparticles (V), followed by the dexamethasone group (IV) presented macroscopically less fibrillation, exposure of subchondral bone and sclerosis (better score on the scale) than the control groups (I) (osteoarthritis without treatment), group (II) treated with commercial hyaluronic acid and hyaluronic acid with nanoparticles without drug (III).

CONCLUSIONS

The use of active viscosupplements could have an additional effect to conventional hyaluronic acid treatment due to its antioxidant and anti-inflammatory effect. The most promising group was hyaluronic acid with nanoparticles that encapsulate curcumin and the second group was the one that encapsulates dexamethasone.

3D connective micro-fragment enriched with stromal vascular fraction in osteoarthritis: chondroprotective evidence in a preclinical in vivo model

Introduction

Adipose-derived cell therapies are one of the most common regenerative therapeutic options to alleviate the multi-component damage of osteoarthritis (OA). Adipose stromal vascular fraction (SVF) has gained scientific consensus for its ability to interact protectively with the joint microenvironment. Recently, the wide range of enzyme-free tissue processing systems has outperformed classical treatments, because of their ability to produce connective micrografts enriched with the SVF (mctSVF). This preclinical in vivo study evaluates the chondroprotective potential of a newly generated mctSVF compared with in vitro expanded adipose stromal cells (ASC) in OA.

Methods

A mild grade of OA was induced through bilateral anterior cruciate ligament transection (ACLT) surgery in 32 Specific Pathogen Free (SPF) Crl: KBL (NZW) male rabbits followed by the surgical excision of inguinal adipose tissue. After 2 months, OA joints were treated with an intra-articular (IA) injection of mctSVF or ASC. Local biodistribution analysis was used to determine migration patterns of PKH26-labelled cells in the knee joint after 1 month. Efficacy was assessed by gross analysis, histology and immunohistochemistry on the osteochondral unit, synovial membrane and meniscus.

Results

We elucidate the effectiveness of a one-step approach based on mechanical isolation of mctSVF. Through epifluorescence analysis, we found a similar pattern of cell distribution between cell treatments, mainly towards articular cartilage. Similar regenerative responses were observed in all experimental groups. These effects included: (i) osteochondral repair (promotion of typical anabolic markers and reduction of catabolic ones); (ii) reduction of synovial reactions (reduced synovial hypertrophy and inflammation, and change of macrophage phenotype to a more regenerative one); and (iii) reduction of degenerative changes in the meniscus (reduction of tears).

Discussion

Our study demonstrates the validity of a novel mechanical system for the generation of the mctSVF micrograft with chondroprotective potential in a preclinical model of moderate OA. The resulting final product can counteract inflammatory processes beyond the OA microenvironment and protect cartilage through the colonization of its structure. The intact and active microanatomy of mctSVF makes it a suitable candidate for translational medicine to treat OA without the need for cell manipulation as with ASC.

Intra-articular Injections of CXCR4-Overexpressing Human Cartilage-Derived Progenitor Cells Improve Meniscus Healing and Protect Against Posttraumatic Osteoarthritis in Immunocompetent Rabbits

BACKGROUND

Meniscal injuries that fail to heal instigate catabolic changes in the knee's microenvironment, posing a high risk for developing posttraumatic osteoarthritis (PTOA). Previous research has suggested that human cartilage-derived progenitor cells (hCPCs) can stimulate meniscal repair in a manner that depends on stromal cell-derived factor 1 (SDF-1) pathway activity.

HYPOTHESIS

Overexpressing the SDF-1 receptor CXCR4 in hCPCs will increase cell trafficking and further improve the repair efficacy of meniscal injuries.

STUDY DESIGN

Controlled laboratory study.

METHODS

hCPCs were genetically modified to overexpress CXCR4 (CXCR4-overexpressing [OE] hCPCs) using lentivirus. In vitro characterization was performed using cell viability assay, cell migration assay, and immunoblotting. These cells were then used to treat a meniscal injury in rabbits. A medial meniscal tear was surgically created in the right knees of New Zealand White rabbits, followed by 2 intra-articular injections (5.0 × 106 cells each) of either CXCR4-OE hCPCs, wild-type hCPCs, or saline alone. A histological assessment of menisci and cartilage was performed using safranin O/fast green staining. Joints were assessed for PTOA changes using the modified Osteoarthritis Research Society International scoring system. Fluorescence imaging and DNA analysis were performed to examine tissue for human cells.

RESULTS

SDF-1 inhibited NF-κB and ERK pathways in both wild-type and CXCR4-OE hCPCs. CXCR4 overexpression increased hCPC trafficking toward sources of SDF-1, including injured meniscal fibrocartilage and an SDF-1-presoaked collagen scaffold. Intra-articular injections of CXCR4-OE hCPCs significantly improved meniscus healing, as evidenced by the complete absence of tears in 5 of 6 (83%) animals that received CXCR4-OE hCPCs compared with only 3 of 6 (50%) wild-type hCPC-treated animals and 2 of 6 (33%) animals in the saline control group. CXCR4-OE hCPC-treated animals also showed significantly less erosion in their knee cartilage compared with control animals.

CONCLUSION

Overall, CXCR4 overexpression inhibited catabolic pathway signaling in hCPCs and increased cell migration. Evidence suggests that intra-articular injections of these cells into the injured knee allow them to home in on sites of fibrocartilage injuries and ultimately result in meniscal tear healing and PTOA inhibition in immunocompetent animals.

CLINICAL RELEVANCE

This study demonstrated that cartilage progenitors with elevated CXCR4 expression have the potential to be a potent therapeutic tool for stimulating meniscal tear healing.

Development of a novel rabbit model for femoroacetabular impingement through surgically induced acetabular overcoverage

There is a lack of validated small animal models for femoroacetabular impingement (FAI) that induce intra-articular lesions and cause osteoarthritis (OA) progression. The gene expression profile of articular cartilage in patients with FAI has not been characterized in animal studies. The purpose of this study is to describe a novel rabbit model for FAI with validated induction of intra-articular lesions and OA progression and to characterize the gene expression pattern in impinged cartilage using this model. Thirty 6-month-old New Zealand White rabbits underwent unilateral endobutton implant placement at the acetabular rim to surgically create overcoverage. Radiological assessment confirmed secure placement of endobutton at the acetabular rim for all operated hips with a mean alteration in lateral center-edge angle (ΔLCEA) of 16.2 ± 6.6°. Gross inspection revealed secondary cartilage injuries in the anterosuperior region of the femoral head for the operated hips. Cartilage injuries were shown to exacerbate with increased impingement duration, as demonstrated by the modified Outerbridge scores and Mankin scores. Immunostaining and quantitative real-time polymerase chain reaction revealed elevated expression of inflammatory, anabolic and catabolic genes in impinged cartilage. RNA sequencing analysis of cartilage tissue revealed a distinct transcriptome profile and identified C-KIT, CD86, and CD68 as central markers. Our study confirmed that the novel rabbit FAI model created acetabular overcoverage and produced articular cartilage injury at the impingement zone. Cartilage from the impingement zone demonstrated a heightened metabolic state, corroborating with the gene expression pattern observed in patients with FAI.

Intra-Articular Administration of Ganglioside Sugars Protects Cartilage from Progressive Degeneration in an Instability OA Rabbit Model

OBJECTIVE

Osteoarthritis (OA) is a degenerative joint disease that has no cure, and current therapies are intended to minimize pain. There is, therefore, a need for effective pharmacologic agents that reverse or slow the progression of joint damage. We report herein on an investigation of the effects of intra-articular injections of ganglioside sugars on the progression of OA in an experimental rabbit model.

DESIGN

Knee OA was induced Japanese in White rabbits by anterior cruciate ligament transection (ACLT). Ganglioside sugars at concentrations of 0.1, 0.3, and 0.9 mg/ml were then intra-articularly injected as a possible treatment for OA. Controls received intra-articular injections of saline. Knees were assessed macroscopically, histologically, and mechanically at 13 weeks after ACLT induction.

RESULTS

Macroscopically, knees of the groups that received ganglioside sugars at concentrations of 0.3 and 0.9 mg/ml exhibited milder cartilage degradation compared to the controls. Consistent with these results, histological scores for these knees were significantly higher than the corresponding values for the control knees. Lectin histochemistry staining revealed that the treatment with ganglioside sugars at concentrations of 0.3 and 0.9 mg/ml was associated with a remarkable increase in the levels of GalNAc-positive chondrocytes in cartilage. Coefficient of friction testing also demonstrated that cartilages treated with ganglioside sugars had a lower coefficient of frictions than the values for the control group.

CONCLUSIONS

Intra-articular injections of ganglioside sugars prevented cartilage degeneration in an OA-instability model. These results highlight the promising therapeutic potential for using ganglioside sugars in the treatment of progressive OA.

In vivo impact on rabbit subchondral bone of viscosupplementation with a hyaluronic acid antioxidant conjugate

OBJECTIVE

This study aimed to assess the effects of an antioxidant-conjugated Hyaluronic Acid (HA), specifically HA-4-aminoresorcinol (HA4AR), on articular cartilage and subchondral bone in osteoarthritis (OA). We conducted a comparative analysis between HA4AR and a commercially available high molecular weight HA formulation in a rabbit model of OA.

MATERIALS AND METHODS

Eighteen rabbits underwent unilateral anterior cruciate ligament transection (ACLT) and were divided into three groups of six: Saline-group, HA-group, and HA4AR-group, based on the type of intra-articular injection received. Additionally, eight non-operated contralateral knees served as reference points (Contralateral-group). Six weeks post-surgery, iodine-enhanced micro-computed tomography imaging was used to evaluate articular cartilage volume and thickness, and to assess subchondral bone microarchitecture and mineral density.

RESULTS

Cartilage thickness in both the HA and HA4AR groups was comparable to that of the Contralateral group. Notably, there was a significant reduction in subchondral bone plate tissue mineral density in the HA-group when compared to both the HA4AR and Saline groups (p < 0.05). However, no significant differences in trabecular subchondral bone microarchitectural parameters and mineral densities were observed between the HA4AR-group and the Saline-group. When compared to the Contralateral, Saline, and HA4AR groups, the HA-group exhibited a marked decrease in subchondral bone plate tissue mineral density (p < 0.05). Additionally, a significant reduction in trabecular bone volume fraction was noted in the HA-group compared to the Contralateral-group (p < 0.05).

CONCLUSIONS

The HA-4AR hydrogel demonstrated significant preservation of subchondral bone plate tissue mineral density compared to HA alone, while other bone microarchitectural parameters remained largely unchanged. These findings indicate that HA-4AR may provide enhanced osteoprotective benefits in the treatment of osteoarthritis.

Bimetallic clusterzymes-loaded dendritic mesoporous silica particle regulate arthritis microenvironment via ROS scavenging and YAP1 stabilization

Clusterzymes are synthetic enzymes exhibiting substantial catalytic activity and selectivity, which are uniquely driven by single-atom constructs. A dramatic increase in antioxidant capacity, 158 times more than natural trolox, is noted when single-atom copper is incorporated into gold-based clusterzymes to form Au24Cu1. Considering the inflammatory and mildly acidic microenvironment characteristic of osteoarthritis (OA), pH-dependent dendritic mesoporous silica nanoparticles (DMSNs) coupled with PEG have been employed as a delivery system for the spatial-temporal release of clusterzymes within active articular regions, thereby enhancing the duration of effectiveness. Nonetheless, achieving high therapeutic efficacy remains a significant challenge. Herein, we describe the construction of a Clusterzymes-DMSNs-PEG complex (CDP) which remarkably diminishes reactive oxygen species (ROS) and stabilizes the chondroprotective protein YAP by inhibiting the Hippo pathway. In the rabbit ACLT (anterior cruciate ligament transection) model, the CDP complex demonstrated inhibition of matrix metalloproteinase activity, preservation of type II collagen and aggregation protein secretion, thus prolonging the clusterzymes' protective influence on joint cartilage structure. Our research underscores the efficacy of the CDP complex in ROS-scavenging, enabled by the release of clusterzymes in response to an inflammatory and slightly acidic environment, leading to the obstruction of the Hippo pathway and downstream NF-κB signaling pathway. This study illuminates the design, composition, and use of DMSNs and clusterzymes in biomedicine, thus charting a promising course for the development of novel therapeutic strategies in alleviating OA.

Empirical Modelling Workflow for Resolution Invariant Assessment of Osteophytes

OBJECTIVE

Traditional quantitative analysis of bone microstructure in micro-computed tomography (microCT) is dependent on animal scale and requires parametric tuning in new implementations. This study aims to develop an automated and resolution-invariant 3D image processing workflow for quantitative assessment of osteophytes.

METHODS

In this workflow, cortical bone was segmented from microCT scans, and a 3D sphere-fitting transform was performed to obtain a thickness map, for which each voxel is assigned a thickness value corresponding to the size of the largest sphere containing the voxel that fits entirely within the cortical bone. From the thickness map, a 1-voxel thick outer surface was extracted to model surface roughness. The thickness values of the outer surface were empirically estimated by a series of known statistical distributions. Resulting parameters describing best-fit distributions, along with other cortical bone metrics, were analysed to determine sensitivity to osteoarthritis and the presence of osteophytes.

RESULTS

The workflow was validated using microCT scans and histological gradings of rabbit and rat tibiofemoral joints. Visual inspection shows that samples with osteoarthritis and the presence of osteophytes have more surface voxels assigned small thickness values. The distribution of surface thickness values for each animal is best described by Gamma distributions, whose shape parameter is consistently sensitive to osteoarthritis and the presence of osteophytes.

CONCLUSION

Combining traditional image processing with empirical distribution fitting provides an automated, objective, and resolution-invariant workflow for osteophyte assessment.

SIGNIFICANCE

The proposed method is simple, yet elegant in its implementation, and can be readily used in new implementations.

Human umbilical cord mesenchymal stem cells on treating osteoarthritis in a rabbit model: Injection strategies

Human umbilical cord mesenchymal stem cells (UCMSCs) are a novel stem-cell source to treat osteoarthritis (OA). Here we investigated the therapeutic effects of UCMSCs injection strategies on knee OA in a rabbit model. Thirty OA rabbits randomly received normal saline, a single dose of 1 × 106 UCMSCs, or three injections of 1 × 106 UCMSCs at 2, 4, 6 weeks. Articular cartilages were collected after 8 weeks. Macroscopic and histological assessments indicated that intra-articular injection of UCMSCs, both single and multiple injection, significantly reduced the formation of periarticular osteophytes and articular cartilage degeneration when compared with the control. Furthermore, both UCMSCs injections increased the expression of chondrogenic markers in the articular cartilage, and reduced the levels of TNF-α and IL-6 in synovium. Micro-CT showed significant reduction of sub-chondral bone degeneration and osteophytes in the multiple-injection group compared to the control and single-injection group. Taken together, intra-articular injection of UCMSCs for OA treatment is safe and effective. Single and multiple injection of UCMSCs had comparable reparative effect on cartilage lesions, while multiple injection of UCMSCs further exerted effect on enhancing subchondral bone volume.

Treatment of osteoarthritis by implantation of Mg- and WE43-cylinders - A preclinical study on bone and cartilage changes and their influence on pain sensation in rabbits

With its main features of cartilage degeneration, subchondral bone sclerosis and osteophyte formation, osteoarthritis represents a multifactorial disease with no effective treatment options. As biomechanical shift in the trabecular network may be a driver for further cartilage degeneration, bone enhancement could possibly delay OA progression. Magnesium is known to be osteoconductive and already showed positive effects in OA models. We aimed to use magnesium cylinders to enhance subchondral bone quality, condition of cartilage and pain sensation compared to sole drilling in vivo. After eight weeks of implantation in rabbits, significant increase in subchondral bone volume and trabecular thickness with constant bone mineral density was found indicating favored biomechanics. As representative for pain, a higher number of CD271+ vessels were present in control samples without magnesium. However, this result could not be confirmed by sensitive, objective lameness evaluation using a pressure sensing mat and no positive effect could be shown on either cartilage degeneration evaluated by OARSI score nor the presence of regenerative cells in CD271-stained samples. The presented results show a relevant impact of implanted magnesium on key structures in OA pain with missing clinical relevance regarding pain. Further studies with shifted focus should examine additional structures as joint capsule or osteophytes.

Sol-gel synthesis of magnesium oxide nanoparticles and their evaluation as a therapeutic agent for the treatment of osteoarthritis

Aim: We synthesized MgO NPs via sol-gel reaction and investigated them as carriers to deliver Mg2+ to the affected joint for osteoarthritis (OA).Materials & methods: The physicochemical properties of samples were characterized by transmission electron microscope (TEM), dynamic light scattering (DLS) and x-ray diffraction (XRD). The release of Mg2+ was monitored by ICP-MS. The potential cytotoxicity was evaluated using MTT assay. The efficacy and biosafety were evaluated in a rabbit OA model.Results: MgO NPs can prolong the Mg2+ release time from 0.5 h to 12 h. No significant cytotoxicity was observed when concentrations below 250 μg/ml. Intra-articular samples could effectively alleviate the degeneration and destruction of the cartilage.Conclusion: this study demonstrates the potential of MgO NPs as a safe and effective treatment of OA. Simultaneously, the size of the particles may play a significant role in influencing the therapeutic outcome.

An HFD negatively influences both joint and liver health in rabbits with and without an enzymatically-induced model of arthritis

Osteoarthritis (OA) is a common arthritis types in animals that causes persistent pain and reduces quality of life. Although a high-fat diet (HFD) is widely believed to induce obesity and have adverse effects on the body, the connection between HFD and joint health is not well understood. Therefore, in this study, 32 healthy male New Zealand rabbits were randomly divided into four groups: healthy rabbits fed a standard diet (NDG, n=8) or an HFD (HDG, n=8), rabbits fed a standard diet (OAG, n=8) and an HFD (HOG, n=8), and arthritis was induced by intra-articular enzyme injection. After 12 weeks of HFD feeding, articular cartilage, synovium, and subchondral bone were isolated and collected. Joint tissue damage was evaluated using histopathological and imaging tests. The results showed that there was no significant difference in body weight between rabbits fed a normal diet and those fed an HFD. However, the HFD led to an increase in joint injuries in both induced and non-induced arthritis rabbits. Specifically, the HFD induced lipid metabolism disorders and liver damage in vivo, significantly elevating the levels of serum inflammatory cytokines and bone metabolism markers. Moreover, HFD exacerbated articular cartilage damage in the joints and increased the accumulation of inflammatory cells in synovial tissue, resulting in a notable increase in synovial macrophages and inflammatory cytokines. Additionally, HFD accelerated the bone resorption process in subchondral bone, leading to the destruction of bone mass and subchondral bone microstructure. In summary, the results of this study indicate that an HFD can cause histological damage to the articular cartilage, synovium, and subchondral bone in rabbits, exacerbating arthritis in pre-existing joint damage. Notably, weight is not the primary factor in this effect.

High-resolution magnetic resonance imaging can predict osteoarthritic progression after medial meniscus posterior root injury: randomized in vivo experimental study in a rabbit model

IMPORTANCE

The field of meniscal root preservation has undergone significant advancement over the past decades; however, the challenge remains to fully understand whether meniscal root repair can ultimately arrest or delay osteoarthritic changes.

OBJECTIVE

To assess longitudinal changes in articular cartilage, subchondral bone, and progression to meniscal extrusion (ME) using high-resolution magnetic resonance imaging (MRI).

METHODS

Medial meniscus posterior root tear was surgically induced in 39 New Zealand white rabbits. Animals were randomly assigned into three experimental groups: partial meniscectomy after root tear (PM, n ​= ​13); root tear left in situ (CT, n ​= ​13); and transtibial root repair (RR, n ​= ​13). Contralateral limbs were used as healthy controls. High resolution 4.7 Tesla MRI of the knee joint was performed at baseline, after 2-, and 4-months of post-surgery. Cartilage thickness was calculated in medial and lateral compartments. In addition, the evaluation of ME, subchondral bone edema and healing potential after root repair were assessed too.

RESULTS

Progressive cartilage thinning, ME, and subchondral bone edema were evident in all 3 study groups after 4-months of follow-up. The mean cartilage thickness in the PM group was 0.53 ​mm (±0.050), 0.57 ​mm (±0.05) in the CT group, and 0.60 ​mm (±0.08) in the RR group. The PM group exhibited significantly higher cartilage loss when compared to the CT and RR groups (p ​< ​0.001). Moreover, progressive ME and subchondral bone edema were associated with a more severe cartilage loss at the final follow-up.

CONCLUSION

Meniscal root repair did not halt but rather reduced the progression of osteoarthritis (OA). Degenerative changes worsened at a rapid rate in the PM group compared to the RR and CT groups. Early cartilage swelling, persistent subchondral edema, and progressive ME predicted a more severe progression to knee OA in the CT and RR groups.

LEVEL OF EVIDENCE

II.

Animal Models of Osteoarthritis: Updated Models and Outcome Measures 2016-2023

Purpose

Osteoarthritis (OA) is a global musculoskeletal disorder that affects primarily the knee and hip joints without any FDA-approved disease-modifying therapies. Animal models are essential research tools in developing therapies for OA; many animal studies have provided data for the initiation of human clinical trials. Despite this, there is still a need for strategies to recapitulate the human experience using animal models to better develop treatments and understand pathogenesis. Since our last review on animal models of osteoarthritis in 2016, there have been exciting updates in OA research and models. The main purpose of this review is to update the latest animal models and key features of studies in OA research.

Method

We used our existing classification method and screened articles in PubMed and bibliographic search for animal OA models between 2016 and 2023. Relevant and high-cited articles were chosen for inclusion in this narrative review.

Results

Recent studies were analyzed and classified. We also identified ex vivo models as an area of ongoing research. Each animal model offers its own benefit in the study of OA and there are a full range of outcome measures that can be assessed. Despite the vast number of models, each has its drawbacks that have limited translating approved therapies for human use.

Conclusion

Depending on the outcome measures and objective of the study, researchers should pick the best model for their work. There have been several exciting studies since 2016 that have taken advantage of regenerative engineering techniques to develop therapies and better understand OA.

Lay Summary

Osteoarthritis (OA) is a chronic debilitating disease without any cure that affects mostly the knee and hip joints and often results in surgical joint replacement. Cartilage protects the joint from mechanical forces and degrades with age or in response to injury. The many contributing causes of OA are still being investigated, and animals are used for preclinical research and to test potential new treatments. A single consensus OA animal model for preclinical studies is non-existent. In this article, we review the many animal models for OA and provide a much-needed update on studies and model development since 2016.

Exercise following joint distraction inhibits muscle wasting and delays the progression of post-traumatic osteoarthritis in rabbits by activating PGC-1α in skeletal muscle

OBJECTIVE

Muscle wasting frequently occurs following joint trauma. Previous research has demonstrated that joint distraction in combination with treadmill exercise (TRE) can mitigate intra-articular inflammation and cartilage damage, consequently delaying the advancement of post-traumatic osteoarthritis (PTOA). However, the precise mechanism underlying this phenomenon remains unclear. Hence, the purpose of this study was to examine whether the mechanism by which TRE following joint distraction delays the progression of PTOA involves the activation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), as well as its impact on muscle wasting.

METHODS

Quadriceps samples were collected from patients with osteoarthritis (OA) and normal patients with distal femoral fractures, and the expression of PGC-1α was measured. The hinged external fixator was implanted in the rabbit PTOA model. One week after surgery, a PGC-1α agonist or inhibitor was administered for 4 weeks prior to TRE. Western blot analysis was performed to detect the expression of PGC-1α and Muscle atrophy gene 1 (Atrogin-1). We employed the enzyme-linked immunosorbent assay (ELISA) technique to examine pro-inflammatory factors. Additionally, we utilized quantitative real-time polymerase chain reaction (qRT-PCR) to analyze genes associated with cartilage regeneration. Synovial inflammation and cartilage damage were evaluated through hematoxylin-eosin staining. Furthermore, we employed Masson's trichrome staining and Alcian blue staining to analyze cartilage damage.

RESULTS

The decreased expression of PGC-1α in skeletal muscle in patients with OA is correlated with the severity of OA. In the rabbit PTOA model, TRE following joint distraction inhibited the expressions of muscle wasting genes, including Atrogin-1 and muscle ring finger 1 (MuRF1), as well as inflammatory factors such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in skeletal muscle, potentially through the activation of PGC-1α. Concurrently, the production of IL-1β, IL-6, TNF-α, nitric oxide (NO), and malondialdehyde (MDA) in the synovial fluid was down-regulated, while the expression of type II collagen (Col2a1), Aggrecan (AGN), SRY-box 9 (SOX9) in the cartilage, and superoxide dismutase (SOD) in the synovial fluid was up-regulated. Additionally, histological staining results demonstrated that TRE after joint distraction reduced cartilage degeneration, leading to a significant decrease in OARSI scores.TRE following joint distraction could activate PGC-1α, inhibit Atrogin-1 expression in skeletal muscle, and reduce C-telopeptides of type II collagen (CTX-II) in the blood compared to joint distraction alone.

CONCLUSION

Following joint distraction, TRE might promote the activation of PGC-1α in skeletal muscle during PTOA progression to exert anti-inflammatory effects in skeletal muscle and joint cavity, thereby inhibiting muscle wasting and promoting cartilage regeneration, making it a potential therapeutic intervention for treating PTOA.

Total meniscus replacement with a 3D printing of network hydrogel composite scaffold in a rabbit model

PURPOSE

The aim of this study was to evaluate the role of a novel total meniscal implant in promoting meniscal regeneration and protecting articular cartilage in a rabbit model for 3 and 6 months.

METHODS

Thirty-six New Zealand rabbits were selected and divided into poly(ɛ-caprolactone) (PG-Pg) scaffold group, meniscectomy group and sham group. In this study, it was investigated whether PG-Pg scaffold can prevent articular cartilage degeneration and promote tissue degeneration, and its mechanical properties at 3 and 6 months after surgery were also explored.

RESULT

The degree of articular cartilage degeneration was significantly lower in the PG-Pg scaffold group than in the meniscectomy group. The number of chondrocytes increased in the PG-Pg scaffold at 3 and 6 months, while a gradual increase in the mechanical properties of the PG-Pg stent was observed from 6 months.

CONCLUSION

The PG-Pg scaffold slows down the degeneration of articular cartilage, promotes tissue regeneration and improves biomechanical properties after meniscectomy. This novel meniscus scaffold holds promise for enhancing surgical strategies and delivering superior long-term results for individuals with severe meniscus tears.

LEVEL OF EVIDENCE

NA.

Recent Trends in Adipose Tissue-Derived Injectable Therapies for Osteoarthritis: A Scoping Review of Animal Models

Background and Objectives: This scoping review investigates recent trends in adipose tissue-derived injectable therapies for osteoarthritis (OA) in animal models, focusing on minimally manipulated or lightly processed adipose tissue. By evaluating and examining the specific context in which these therapies were investigated across diverse animal OA models, this review aims to provide valuable insights that will inform and guide future research and clinical applications in the ongoing pursuit of effective treatments for osteoarthritis. Materials and Methods: This research conducted a comprehensive literature review of PubMed and Embase to determine studies about minimally manipulated adipose tissue-derived injectable therapies for osteoarthritis investigated using animal models. The primary search found 530 results. After excluding articles that focused on spontaneous osteoarthritis; on transfected, preconditioned, cultured, or co-cultured adipose-derived stem cells; and articles with unavailable full text, we included 11 articles in our review. Results: The examined therapies encompassed mechanical micro-fragmented adipose tissue (MFAT) and stromal vascular fraction (SVF) obtained via collagenase digestion and centrifugation. These interventions were evaluated across various animal models, including mice, rats, rabbits, and sheep with induced OA. Notably, more studies concentrated on surgically induced OA rather than chemically induced OA. The assessment of these therapies focused on elucidating their protective immunomodulatory, anti-inflammatory, and chondroregenerative potential through comprehensive evaluations, including macroscopic assessments, histological analyses, immunohistochemical examinations, and biochemical assays. Conclusions: This review provides a comprehensive analysis of adipose tissue-derived injectable therapies for osteoarthritis across diverse animal models. While revealing potential benefits and insights, the heterogeneity of data and the limited number of studies highlight the need for further research to formulate conclusive recommendations for clinical applications.

Effect of Press-Fit Size on Insertion Mechanics and Cartilage Viability in Human and Ovine Osteochondral Grafts

OBJECTIVE

The osteochondral allograft procedure uses grafts constructed larger than the recipient site to stabilize the graft, in what is known as the press-fit technique. This research aims to characterize the relationships between press-fit size, insertion forces, and cell viability in ovine and human osteochondral tissue.

DESIGN

Human (4 donors) and ovine (5 animals) articular joints were used to harvest osteochondral grafts (4.55 mm diameter, N = 33 Human, N = 35 Ovine) and create recipient sites with grafts constructed to achieve varying degrees of press fit (0.025-0.240 mm). Donor grafts were inserted into recipient sites while insertion forces were measured followed by quantification of chondrocyte viability and histological staining to evaluate the extracellular matrix.

RESULTS

Both human and ovine tissues exhibited similar mechanical and cellular responses to changes in press-fit. Insertion forces (Human: 3-169 MPa, Ovine: 36-314 MPa) and cell viability (Human: 16%-89% live, Ovine: 2%-76% live) were correlated to press-fit size for both human (force: r = 0.539, viability: r = -0.729) and ovine (force: r = 0.655, viability: r = -0.714) tissues. In both species, a press-fit above 0.14 mm resulted in reduced cell viability below a level acceptable for transplantation, increased insertion forces, and reduced linear correlation to press-fit size compared to samples with a press-fit below 0.14 mm.

CONCLUSIONS

Increasing press-fit size required increased insertion forces and resulted in reduced cell viability. Ovine and human osteochondral tissues responded similarly to impact insertion and varying press-fit size, providing evidence for the use of the ovine model in allograft-related research.

Mechanical crosstalk between the intervertebral disc, facet joints, and vertebral endplate following acute disc injury in a rabbit model

Background

Vertebral endplate sclerosis and facet osteoarthritis have been documented in animals and humans. However, it is unclear how these adjacent pathologies engage in crosstalk with the intervertebral disc. This study sought to elucidate this crosstalk by assessing each compartment individually in response to acute disc injury.

Methods

Eleven New Zealand White rabbits underwent annular disc puncture using a 16G or 21G needle. At 4 and 10 weeks, individual compartments of the motion segment were analyzed. Discs underwent T 1 relaxation mapping with MRI contrast agent gadodiamide as well T 2 mapping. Both discs and facets underwent mechanical testing via vertebra-disc-vertebra tension-compression creep testing and indentation testing, respectively. Endplate bone density was quantified via μCT. Discs and facets were sectioned and stained for histology scoring.

Results

Intervertebral discs became more degenerative with increasing needle diameter and time post-puncture. Bone density also increased in endplates adjacent to both 21G and 16G punctured discs leading to reduced gadodiamide transport at 10 weeks. The facet joints, however, did not follow this same trend. Facets adjacent to 16G punctured discs were less degenerative than facets adjacent to 21G punctured discs at 10 weeks. 16G facets were more degenerative at 4 weeks than at 10, suggesting the cartilage had recovered. The formation of severe disc osteophytes in 16G punctured discs between 4 and 10 weeks likely offloaded the facet cartilage, leading to the recovery observed.

Conclusions

Overall, this study supports that degeneration spans the whole spinal motion segment following disc injury. Vertebral endplate thickening occurred in response to disc injury, which limited the diffusion of small molecules into the disc. This work also suggests that altered disc mechanics can induce facet degeneration, and that extreme bony remodeling adjacent to the disc may promote facet cartilage recovery through offloading of the articular cartilage.

Streamlining quantitative joint-wide medial femoro-tibial histopathological scoring of mouse post-traumatic knee osteoarthritis models

OBJECTIVES

Histological scoring remains the gold-standard for quantifying post-traumatic osteoarthritis (ptOA) in animal models, allowing concurrent evaluation of numerous joint tissues. Available systems require scoring multiple sections/joint making analysis laborious and expensive. We investigated if a single section allowed equivalent quantitation of pathology in different joint tissues and disease stages, in three ptOA models.

METHOD

Male 10-12-week-old C57BL/6 mice underwent surgical medial-meniscal-destabilization, anterior-cruciate-ligament (ACL) transection, non-invasive-ACL-rupture, or served as sham-surgical, non-invasive-ACL-strain, or naïve/non-operated controls. Mice (n = 12/group) were harvested 1-, 4-, 8-, and 16-week post-intervention. Serial sagittal toluidine-blue/fast-green stained sections of the medial-femoro-tibial joint (n = 7/joint, 84 µm apart) underwent blinded scoring of 40 histology-outcomes. We evaluated agreement between single-slide versus entire slide-set maximum or median scores (weighted-kappa), and sensitivity/specificity of single-slide versus median/maximum to detect OA pathology.

RESULTS

A single optimal mid-sagittal section showed excellent agreement with median (weighted-kappa 0.960) and maximum (weighted-kappa 0.926) scores. Agreement for individual histology-outcomes was high with only 19/240 median and 15/240 maximum scores having a weighted-kappa ≤0.4, the majority of these (16/19 and 11/15) in control groups. Statistically-significant histology-outcome differences between ptOA models and their controls detected with the entire slide-set were reliably reproduced using a single slide (sensitivity >93.15%, specificity >93.10%). The majority of false-negatives with single-slide scoring were meniscal and subchondral bone histology-outcomes (89%) and occurred in weeks 1-4 post-injury (84%).

CONCLUSION

A single mid-sagittal slide reduced the time needed to score diverse histopathological changes by 87% without compromising the sensitivity or specificity of the analysis, across a variety of ptOA models and time-points.

Heterogeneous Cells as well as Adipose-Derived Stromal Cells in Stromal Vascular Fraction Contribute to Enhance Anabolic and Inhibit Catabolic Factors in Osteoarthritis

The stromal-vascular fraction (SVF), comprising heterogeneous cell populations and adipose-derived stromal cells (ADSCs), has therapeutic potential against osteoarthritis (OA); however, the underlying mechanism remains elusive. This study aimed to investigate the therapeutic effects of heterogeneous cells in rabbit SVF on rabbit chondrocytes. Rabbit SVF and ADSCs were autografted into knees at OA onset. The SVF (1 × 105) and low-dose ADSCs (lADSC; 1 × 104) groups adjusted for their stromal cell content were compared. Animals were euthanized 8 and 12 weeks after OA onset for macroscopic and histological analyses of OA progression and synovitis. Immunohistochemical and real-time polymerase chain reaction assessments were conducted. In vitro, immune-fluorescent double staining was performed for SVF to stain macrophages with F4/80, CD86(M1), and CD163(M2). OA progression was markedly suppressed, and synovitis was reduced in the SVF groups (OARSI histological score 8 W: 6.8 ± 0.75 vs. 3.8 ± 0.75, p = 0.001; 12 W: 8.8 ± 0.4 vs. 5.4 ± 0.49, p = 0.0002). The SVF groups had higher expression of collagen II and SOX9 in cartilage and TGF-β and IL-10 in the synovium, lower expression of MMP-13, and lower macrophage M1/M2 ratio than the lADSC groups. Immunofluorescent double staining revealed a markedly higher number of M2 than that of M1 macrophages in the SVF. The therapeutic effects of SVF on chondrocytes were superior than those of lADSCs, with enhanced anabolic and inhibited catabolic factors. Heterogeneous cells, mainly M2 macrophages in the SVF, enhanced growth factor secretion and chondrocyte-protective cytokines, thus benefiting chondrocytes and knee joint homeostasis. Overall, the SVF is a safe, relatively simple, and a useful treatment option for OA.

Comparison of Four Treatment Protocols with Intra-Articular Medium Molecular Weight Hyaluronic Acid in Induced Temporomandibular Osteoarthritis: An Experimental Study

The aim was to compare the effect between a single intra-articular infiltration (1i) and two infiltrations (2i) of medium molecular weight hyaluronic acid (MMW-HA) of high viscosity (HV) and low viscosity (LV) on the histopathological characteristics of temporomandibular joint (TMJ) osteoarthritis (OA) induced in rabbits. An experimental study was conducted on Oryctolagus cuniculus rabbits, including 42 TMJs, distributed between (1) TMJ-C, control group; (2) TMJ-OA, group with OA; (3) TMJ-OA-wt, group with untreated OA; (4) group treated with HA-HV-1i; (5) group treated with HA-HV-2i; (6) group treated with HA-LV-1i; and (7) group treated with HA-LV-2i. The results were evaluated using the Osteoarthritis Research Society International (OARSI) scale and descriptive histology considering the mandibular condyle (MC), the articular disc (AD), and the mandibular fossa (MF). The Kruskal-Wallis test was used for the statistical analysis, considering p < 0.05 significant. All treated groups significantly decreased the severity of OA compared to the TMJ-OA-wt group. The HA-HV-2i group showed significant differences in the degree of OA from the TMJ-OA group. The degree of OA in the HA-HV-2i group was significantly lower than in the HA-LV-1i, HA-LV-2i, and HA-HV-1i groups. The protocol that showed better results in repairing the joint was HA-HV-2i. There are histological differences depending on the protocol of the preparation used: two infiltrations seem to be better than one, and when applying two doses, high viscosity shows better results.

Lgr5-expressing secretory cells form a Wnt inhibitory niche in cartilage critical for chondrocyte identity

Osteoarthritis is a degenerative joint disease that causes pain, degradation, and dysfunction. Excessive canonical Wnt signaling in osteoarthritis contributes to chondrocyte phenotypic instability and loss of cartilage homeostasis; however, the regulatory niche is unknown. Using the temporomandibular joint as a model in multiple species, we identify Lgr5-expressing secretory cells as forming a Wnt inhibitory niche that instruct Wnt-inactive chondroprogenitors to form the nascent synovial joint and regulate chondrocyte lineage and identity. Lgr5 ablation or suppression during joint development, aging, or osteoarthritis results in depletion of Wnt-inactive chondroprogenitors and a surge of Wnt-activated, phenotypically unstable chondrocytes with osteoblast-like properties. We recapitulate the cartilage niche and create StemJEL, an injectable hydrogel therapy combining hyaluronic acid and sclerostin. Local delivery of StemJEL to post-traumatic osteoarthritic jaw and knee joints in rabbit, rat, and mini-pig models restores cartilage homeostasis, chondrocyte identity, and joint function. We provide proof of principal that StemJEL preserves the chondrocyte niche and alleviates osteoarthritis.

Medial Meniscus Posterior Root Repair Reduces but Does Not Avoid Histologic Progression of Osteoarthritis: Randomized In Vivo Experimental Study in a Rabbit Model

BACKGROUND

The optimal treatment option for meniscus root tears is still challenging, and whether the meniscus root repair ultimately can arrest or delay osteoarthritic changes is still a concern.

PURPOSE/HYPOTHESIS

The purpose of this study was 2-fold: (1) to describe and compare histopathologic findings of 3 different therapeutic options for medial meniscus posterior root tear: nonoperative management, partial meniscectomy, and meniscus root repair; and (2) to test the hypothesis that meniscus root tears treated nonoperatively predispose to a lower risk of osteoarthritic progression compared with partial meniscectomy.

STUDY DESIGN

Controlled laboratory study.

METHODS

Posteromedial meniscus root tears were carried out in 39 New Zealand White rabbits. Animals were randomly assigned into 3 experimental groups: partial meniscectomy after root tear (PM; n = 13), root tears treated conservatively (CT; n = 13), and transtibial root repair (RR; n = 13). Contralateral limbs were used as healthy controls. The animals were euthanized at 16 weeks postoperatively; tissue samples of femoral and tibial articular cartilage were collected and processed for macro- and microscopic assessment to detect signs of early osteoarthritis (OA). Each sample was histopathologically assessed using the Osteoarthritis Research Society International grading and staging system.

RESULTS

Osteoarthritic changes were the hallmark in all 3 experimental groups. The RR group had the lowest scores for cartilage damage (mean, 2.5; range, 2-3), and the PM group exhibited higher and more severe signs of OA (mean, 16; range, 9-16) compared with the CT group (mean, 5; range, 4-6). The between-group comparison revealed significant differences, as the PM group showed a significantly higher rate of macro- and microscopic osteoarthritic changes compared with the RR (P < .001) and CT (P < .001) groups. The weightbearing area of the medial femoral condyle was the most severely affected, and tidemark disruption was evident in all tissue samples.

CONCLUSION

Meniscus root repair cannot completely arrest the histopathologic progression of knee OA but leads to significantly less severe degenerative changes than partial meniscectomy and nonoperative treatment. Partial meniscectomy leads to the most severe osteoarthritic progression, while stable radial tears left in situ have lower progression compared with partial meniscectomy.

CLINICAL RELEVANCE

Histologic assessment is an essential tool and metric for guiding and understanding osteoarthritic features, providing insight into the disease development and progression. This study provides histopathologic evidence on osteoarthritic progression after medial meniscus posterior root repair. This knowledge can help to set more realistic expectations and can lead to the future development of augmented techniques.

What is the Effect of Bevacizumab on Cartilage and Synovium in a Rabbit Model of Hemophilic Arthropathy?

BACKGROUND

Hemophilic arthropathy can cause recurrent hemarthroses and severe damage to the synovium and articular cartilage. Previous studies have shown that vascular endothelial growth factor (VEGF) plays an essential role in neoangiogenesis. Bevacizumab, a monoclonal VEGF inhibitor, is used clinically to prevent angiogenesis. However, its effects on hemophilic arthropathy are unknown.

QUESTIONS/PURPOSES

Using a hemophilic arthropathy rabbit model, we asked: Does an intra-articular injection of bevacizumab (1) inhibit VEGF, (2) decrease signal intensity in dynamic contrast-enhanced MRI (DCE-MRI) as an assessment of capillary permeability and neoangiogenesis, (3) reduce cartilage damage, (4) reduce synovial changes, and (5) affect macroscopic changes during the development of hemophilic arthropathy?

METHODS

Twenty-five male New Zealand rabbits were divided into four groups. Eight knees from four rabbits were used as the control group. We used an established animal model for hemophilic arthropathy in the remaining 21 rabbits. Animals were assigned randomly to three groups with seven rabbits in each group. One group was used to establish mild arthropathy, and the other two were used to establish severe arthropathy. Autologous blood from the rabbits' ears was injected into the right and left knees twice per week for 8 weeks to represent mild arthropathy and for 16 weeks to represent severe arthropathy. In the mild arthropathy group, bevacizumab was injected into the right knee once every 2 weeks. Bevacizumab was injected into the right knee of rabbits in one of the severe arthropathy groups once every 2 weeks for 16 weeks, and intra-articular bevacizumab injections were administered to the right knees of rabbits in the other severe arthropathy group once every 2 weeks after the eighth week. An equal volume of 0.9% saline was injected into the left knee of rabbits in all arthropathy groups. To explore the efficacy of bevacizumab, joint diameters were quantitatively measured, and cartilage and synovial changes were examined. Degeneration of articular cartilage was evaluated with the semiquantitative Osteoarthritis Research Society International grading system. Synovial damage was analyzed with a semiquantitative microscopic scoring system. In addition, we evaluated perfusion and angiogenesis using DCE-MRI (quantitative signal intensity changes). Immunohistochemical testing was used to measure VEGF levels (analyzed by Western blotting).

RESULTS

Intra-articular bevacizumab treatment inhibited VEGF in our rabbit model of hemophilic arthropathy. VEGF protein expression levels were lower in the mild arthropathy group that received intra-articular bevacizumab (0.89 ± 0.45) than the mild arthropathy control group (1.41 ± 0.61) (mean difference -0.52 [95% CI -0.898 to -0.143]; p = 0.02). VEGF levels were lower in the severe arthropathy group that received treatment for 16 weeks (0.94 ± 0.27) than in the control knees (1.49 ± 0.36) (mean difference -0.55 [95% CI -0.935 to -0.161]; p = 0.01). In the severe arthropathy group, the Osteoarthritis Research Society International score indicating cartilage damage was lower in the group that received intra-articular bevacizumab treatment from the beginning than in the control group (median 17 [range 13 to 18] versus 18 [range 17 to 20]; difference of medians 1; p = 0.02). Additionally, the scores indicated synovial damage was lower in the group that received intra-articular bevacizumab treatment from the beginning than the control group (median 5 [range 4 to 9] versus 9 [range 8 to 12]; difference of medians 4; p = 0.02). The mean of mean values for signal intensity changes was higher in the nontreated severe groups than in the group of healthy knees. The signal intensity changes were higher in the severe arthropathy control groups (Groups BC and CC) (median 311.6 [range 301.4 to 361.2] and 315.1 [range 269.7 to 460.4]) than in the mild arthropathy control group (Group AC) (median 234.1 [range 212.5 to 304.2]; difference of medians 77.5 and 81, respectively; p = 0.02 and p = 0.04, respectively). In the severe arthropathy group, discoloration caused by hemosiderin deposition in the cartilage and synovium was more pronounced than in the mild arthropathy group. In the severe arthropathy group treated with intra-articular bevacizumab, joint diameters were smaller than in the control group (Group BT median 12.7 mm [range 12.3 to 14.0] versus Group BC median 14.0 mm [range 13.1 to 14.5]; difference of medians 1.3 mm; p = 0.02).

CONCLUSION

Hemarthrosis damages the synovial tissues and cartilage in the knees of rabbits, regardless of whether they are treated with intra-articular bevacizumab. However, intra-articular injection of bevacizumab may reduce cartilage and synovial damage in rabbits when treatment is initiated early during the development of hemophilic arthropathy.

CLINICAL RELEVANCE

If the findings in this study are replicated in larger-animal models that consider the limitations of our work, then a trial in humans might be appropriate to ascertain whether intra-articular injection of bevacizumab could reduce cartilage damage and synovial changes in patients with hemophilia whose hemarthroses cannot otherwise be controlled.

Anti-NGF treatment worsens subchondral bone and cartilage measures while improving symptoms in floor-housed rabbits with osteoarthritis

Objective: Osteoarthritis (OA) is a common joint disorder often affecting the knee. It is characterized by alterations of various joint tissues including subchondral bone and by chronic pain. Anti-nerve growth factor (NGF) antibodies have demonstrated improvement in pain associated with OA in phase 3 clinical trials but have not been approved due to an increased risk of developing rapidly progressive OA. The aim of this study was to investigate effects of systemic anti-NGF-treatment on structure and symptoms in rabbits with surgically induced joint instability. Methods: This was elicited by anterior cruciate ligament transection and partial resection of the medial meniscus in right knee of 63 female rabbits, housed altogether in a 56 m² floor husbandry. Rabbits received either 0.1, 1 or 3 mg/kg anti-NGF antibody intra-venously at weeks 1, 5 and 14 after surgery or vehicle. During in-life phase, static incapacitance tests were performed and joint diameter was measured. Following necropsy, gross morphological scoring and micro-computed tomography analysis of subchondral bone and cartilage were performed. Results: After surgery, rabbits unloaded operated joints, which was improved with 0.3 and 3 mg/kg anti-NGF compared to vehicle injection during the first half of the study. The diameter of operated knee joints increased over contralateral measures. This increase was bigger in anti-NGF treated rabbits beginning 2 weeks after the first IV injection and became dose-dependent and more pronounced with time. In the 3 mg/kg anti-NGF group, the bone volume fraction and trabecular thickness increased in the medio-femoral region of operated joints compared to contralateral and to vehicle-treated animals, while cartilage volume and to a lesser extent thickness decreased. Enlarged bony areas were found in right medio-femoral cartilage surfaces of animals receiving 1 and 3 mg/kg anti-NGF. Alterations of all structural parameters were particularly distinct in a subgroup of three rabbits, which also exhibited more prominent symptomatic improvement. Conclusion: This study showed that anti-NGF administration exerted negative impact on structure in destabilized joints of rabbits, while pain-induced unloading of joints was improved. Our findings open up the possibility to better understand the effects of systemic anti-NGF, particularly on subchondral bone, and thus the occurrence of rapidly progressive OA in patients.

LncRNA AC006064.4-201 serves as a novel molecular marker in alleviating cartilage senescence and protecting against osteoarthritis by destabilizing CDKN1B mRNA via interacting with PTBP1

BACKGROUND

Osteoarthritis (OA) is the most prevalent age-related disease in the world. Chondrocytes undergo an age-dependent decline in their proliferation and synthetic capacity, which is the main cause of OA development. However, the intrinsic mechanism of chondrocyte senescence is still unclear. This study aimed to investigate the role of a novel long non-coding RNA (lncRNA), AC006064.4-201 in the regulation of chondrocyte senescence and OA progression and to elucidate the underlying molecular mechanisms.

METHODS

The function of AC006064.4-201 in chondrocytes was assessed using western blotting, quantitative real-time polymerase chain reaction (qRT-PCR), immunofluorescence (IF) and β-galactosidase staining. The interaction between AC006064.4-201 and polypyrimidine tract-binding protein 1 (PTBP1), as well as cyclin-dependent kinase inhibitor 1B (CDKN1B), was evaluated using RPD-MS, fluorescence in situ hybridization (FISH), RNA immunoprecipitation (RIP) and RNA pull-down assays. Mice models were used to investigate the role of AC006064.4-201 in post-traumatic and age-related OA in vivo.

RESULTS

Our research revealed that AC006064.4-201 was downregulated in senescent and degenerated human cartilage, which could alleviate senescence and regulate metabolism in chondrocytes. Mechanically, AC006064.4-201 directly interacts with PTBP1 and blocks the binding between PTBP1 and CDKN1B mRNA, thereby destabilizing CDKN1B mRNA and decreasing the translation of CDKN1B. The in vivo experiments were consistent with the results of the in vitro experiments.

CONCLUSIONS

The AC006064.4-201/PTBP1/CDKN1B axis plays an important role in OA development and provides new molecular markers for the early diagnosis and treatment of OA in the future. Schematic diagram of AC006064.4-201 mechanism. A schematic diagram of the mechanism underlying the effect of AC006064.4-201.

Micro-computed Tomography-Based Collagen Orientation and Anisotropy Analysis of Rabbit Articular Cartilage

The collagen network is the highly organized backbone of articular cartilage providing tissue tensile stiffness and restricting proteoglycan bleaching out of the tissue. Osteoarthritis (OA) diminishes proper collagen network adaptation. Our aim was to provide quantitative three-dimensional (3D) information of the cartilage collagen network adaptation in early osteoarthritis using high resolution micro-computed tomography (µCT)-imaging. Osteochondral samples from the femoral condyles were collected from healthy (N = 8, both legs) and experimental OA rabbit model with anterior cruciate ligament transection (N = 14, single leg). Samples were processed for cartilage µCT-imaging and histological evaluation with polarized light microscopy (PLM). Structure tensor analysis was used to analyse the collagen fibre orientation and anisotropy of the µCT-images, and PLM was used as a validation for structural changes. Depth-wise comparison of collagen fibre orientation acquired with µCT-imaging and PLM correlated well, but the values obtained with PLM were systematically greater than those measured with µCT-imaging. Structure tensor analysis allowed for 3D quantification of collagen network anisotropy. Finally, µCT-imaging revealed only minor differences between the control and experimental groups.

Adaptation of Fibril-Reinforced Poroviscoelastic Properties in Rabbit Collateral Ligaments 8 Weeks After Anterior Cruciate Ligament Transection

Ligaments of the knee provide stability and prevent excessive motions of the joint. Rupture of the anterior cruciate ligament (ACL), a common sports injury, results in an altered loading environment for other tissues in the joint, likely leading to their mechanical adaptation. In the collateral ligaments, the patterns and mechanisms of biomechanical adaptation following ACL transection (ACLT) remain unknown. We aimed to characterize the adaptation of elastic and viscoelastic properties of the lateral and medial collateral ligaments eight weeks after ACLT. Unilateral ACLT was performed in six rabbits, and collateral ligaments were harvested from transected and contralateral knee joints after eight weeks, and from an intact control group (eight knees from four animals). The cross-sectional areas were measured with micro-computed tomography. Stepwise tensile stress-relaxation testing was conducted up to 6% final strain, and the elastic and viscoelastic properties were characterized with a fibril-reinforced poroviscoelastic material model. We found that the cross-sectional area of the collateral ligaments in the ACL transected knees increased, the nonlinear elastic collagen network modulus of the LCL decreased, and the amount of fast relaxation in the MCL decreased. Our results indicate that rupture of the ACL leads to an early adaptation of the elastic and viscoelastic properties of the collagen fibrillar network in the collateral ligaments. These adaptations may be important to consider when evaluating whole knee joint mechanics after ACL rupture, and the results aid in understanding the consequences of ACL rupture on other tissues.

Micromolding-based encapsulation of mesenchymal stromal cells in alginate for intraarticular injection in osteoarthritis

Osteoarthritis (OA) is an inflammatory joint disease that affects cartilage, subchondral bone, and joint tissues. Undifferentiated Mesenchymal Stromal Cells are a promising therapeutic option for OA due to their ability to release anti-inflammatory, immuno-modulatory, and pro-regenerative factors. They can be embedded in hydrogels to prevent their tissue engraftment and subsequent differentiation. In this study, human adipose stromal cells are successfully encapsulated in alginate microgels via a micromolding method. Microencapsulated cells retain their in vitro metabolic activity and bioactivity and can sense and respond to inflammatory stimuli, including synovial fluids from OA patients. After intra-articular injection in a rabbit model of post-traumatic OA, a single dose of microencapsulated human cells exhibit properties matching those of non-encapsulated cells. At 6 and 12 weeks post-injection, we evidenced a tendency toward a decreased OA severity, an increased expression of aggrecan, and a reduced expression of aggrecanase-generated catabolic neoepitope. Thus, these findings establish the feasibility, safety, and efficacy of injecting cells encapsulated in microgels, opening the door to a long-term follow-up in canine OA patients.

Intra-osseous plasma rich in growth factors enhances cartilage and subchondral bone regeneration in rabbits with acute full thickness chondral defects: Histological assessment

Background

Intra-articular (IA) combined with intra-osseous (IO) infiltration of plasma rich in growth factors (PRGF) have been proposed as an alternative approach to treat patients with severe osteoarthritis (OA) and subchondral bone damage. The aim of the study is to evaluate the efficacy of IO injections of PRGF to treat acute full depth chondral lesion in a rabbit model by using two histological validated scales (OARSI and ICRS II).

Methodology

A total of 40 rabbits were included in the study. A full depth chondral defect was created in the medial femoral condyle and then animals were divided into 2 groups depending on the IO treatment injected on surgery day: control group (IA injection of PRGF and IO injection of saline) and treatment group (IA combined with IO injection of PRGF). Animals were euthanized 56 and 84 days after surgery and the condyles were processed for posterior histological evaluation.

Results

Better scores were obtained in treatment group in both scoring systems at 56- and 84-days follow-up than in control group. Additionally, longer-term histological benefits have been obtained in the treatment group.

Conclusions

The results suggests that IO infiltration of PRGF enhances cartilage and subchondral bone healing more than the IA-only PRGF infiltration and provides longer-lasting beneficial effects.

PPAR-γ Activation Alleviates Osteoarthritis through Both the Nrf2/NLRP3 and PGC-1α/Δψm Pathways by Inhibiting Pyroptosis

Osteoarthritis (OA) is a common degenerative joint disease with a gradually increasing morbidity in the aging and obese population. Emerging evidence has implicated pyroptosis in the etiology of OA and it may be recognized as a therapeutic target in OA. We have previously reported regarding another disease that peroxisome proliferator-activated receptor gamma (PPAR-γ) activation exerts an anti-inflammatory effect by suppressing the nucleotide-binding and oligomerization domain-like receptor containing protein (NLRP) 3 inflammasome. However, the relationship between PPAR-γ and NLRP3-mediated pyroptosis in OA cartilage and its underlying mechanisms is fully unclear. In this study, we found that the level of NLRP3-mediated pyroptosis in severe lateral femoral condyle cartilage wear in the knee of an OA patient was significantly higher than that in the mild lateral femoral condyle cartilage wear areas. Moreover, in lipopolysaccharide (LPS)/adenosine triphosphate (ATP)-induced primary chondrocytes and knee OA rat models, we demonstrated that activation of PPAR-γ by pioglitazone (Piog) attenuated LPS/ATP-induced chondrocyte pyroptosis and arthritis. These effects were partially counteracted by either blocking the nuclear factor erythroid-2-related factor (Nrf2)/NLRP3 or PGC1-α/Δψm signaling pathway. Simultaneous depression of these two signaling pathways can completely abrogate the protective effects of Piog on OA and chondrocytes. Taken together, Piog protects OA cartilage against pyroptosis-induced damage by simultaneously activating both the Nrf2/NLRP3 and PGC-1α/Δψm pathways, which enhances antioxidative and anti-inflammatory responses as well as mitochondrial biogenesis. Therefore, Piog may be a promising agent for human OA cartilage damage in future clinical treatments.

Forkhead box O3 attenuates osteoarthritis by suppressing ferroptosis through inactivation of NF-κB/MAPK signaling

Background

Ferroptosis is a nonapoptotic cell death process that is characterized by lipid peroxidation and intracellular iron accumulation. As osteoarthritis (OA) progresses, inflammation or iron overload induces ferroptosis of chondrocytes. However, the genes that play a vital role in this process are still poorly studied.

Methods

Ferroptosis was elicited in the ATDC5 chondrocyte cell line and primary chondrocytes by administration of the proinflammatory cytokines, interleukin (IL)-1β and tumor necrosis factor (TNF)-α, which play key roles in OA. The effect of FOXO3 expression on apoptosis, extracellular matrix (ECM) metabolism, and ferroptosis in ATDC5 cells and primary chondrocytes was verified by western blot, Immunohistochemistry (IMHC), immunofluorescence (IF) and measuring Malondialdehyde (MDA) and Glutathione (GSH) levels. The signal cascades that modulated FOXO3-mediated ferroptosis were identified by using chemical agonists/antagonists and lentivirus. In vivo experiments were performed following destabilization of medial meniscus surgery on 8-week-old C57BL/6 mice and included micro-computed tomography measurements.

Results

In vitro administration of IL-1β and TNF-α, to ATDC5 cells or primary chondrocytes induced ferroptosis. In addition, the ferroptosis agonist, erastin, and the ferroptosis inhibitor, ferrostatin-1, downregulated or upregulated the protein expression of forkhead box O3 (FOXO3), respectively. This, suggested, for the first time, that FOXO3 may regulate ferroptosis in articular cartilage. Our results further suggested that FOXO3 regulated ECM metabolism via the ferroptosis mechanism in ATDC5 cells and primary chondrocytes. Moreover, a role for the NF-κB/mitogen-activated protein kinase (MAPK) signaling cascade in regulating FOXO3 and ferroptosis was demonstrated. In vivo experiments confirmed the rescue effect of intra-articular injection of a FOXO3-overexpressing lentivirus against erastin-aggravated OA.

Conclusions

The results of our study show that the activation of ferroptosis promotes chondrocyte death and disrupts the ECM both in vivo and in vitro. In addition, FOXO3 can reduce OA progression by inhibiting ferroptosis through the NF-κB/MAPK signaling pathway.

The Translational potential of this article

This study highlights the important role of chondrocyte ferroptosis regulated by FOXO3 through the NF-κB/MAPK signaling in the progression of OA. The inhibition of chondrocyte ferroptosis by activating FOXO3 is expected to be a new target for the treatment of OA.

The Cartilage Protective Effect of Labrum Reconstruction Using Meniscus Allograft Compared with Labrum Resection in a Porcine Model

PURPOSE

This study aimed to verify the femoral head cartilage protective effect of labral reconstruction in a porcine model.

METHODS

Twelve pigs (24 hips) were divided into 3 groups: labrum defect group, lateral meniscus (LM) allograft group, and LM allograft wrapped with acellular peritoneum matrix (LM-APM) group before undergoing bilateral hip surgery. The pigs were sacrificed at 12 and 24 weeks postoperatively, while the femoral head cartilage was retrieved and then subjected to imaging measurement, macroscopic observations, and biomechanical and histological assessment.

RESULTS

Imaging measurement and macroscopic observations revealed that the defect area of the labrum was filled in LM and LM-APM allograft groups after 24 weeks, whereas the labrum defect remained at 24 weeks in the control group. The femoral head cartilage corresponding to the area of labral resection in the labral defect group had worse macroscopic Osteoarthritis Research Society International (OARSI) scores, uneven and discontinuous cartilage on hematoxylin and eosin (H&E) staining and Safranin O staining, decreased histopathology OARSI Osteoarthritis Cartilage Histopathology Assessment System (OOCHAS) scores, and decreased elastic modulus and hardness at 12 and 24 weeks after surgery compared with the meniscus allograft groups.

CONCLUSION

This study demonstrated that the LM allograft with or without APM for labral reconstruction had a chondroprotective effect on the femoral head in a porcine model.

Functional Loss of Terminal Complement Complex Protects Rabbits from Injury-Induced Osteoarthritis on Structural and Cellular Level

The terminal complement complex (TCC) has been described as a potential driver in the pathogenesis of posttraumatic osteoarthritis (PTOA). However, sublytic TCC deposition might also play a crucial role in bone development and regeneration. Therefore, we elucidated the effects of TCC on joint-related tissues using a rabbit PTOA model. In brief, a C6-deficient rabbit breed was characterized on genetic, protein, and functional levels. Anterior cruciate ligament transection (ACLT) was performed in C6-deficient (C6^-/-) and C6-sufficient (C6^+/-) rabbits. After eight weeks, the progression of PTOA was determined histologically. Moreover, the structure of the subchondral bone was evaluated by µCT analysis. C6 deficiency could be attributed to a homozygous 3.6 kb deletion within the C6 gene and subsequent loss of the C5b binding site. Serum from C6^-/- animals revealed no hemolytic activity. After ACLT surgery, joints of C6^-/- rabbits exhibited significantly lower OA scores, including reduced cartilage damage, hypocellularity, cluster formation, and osteophyte number, as well as lower chondrocyte apoptosis rates and synovial prostaglandin E2 levels. Moreover, ACLT surgery significantly decreased the trabecular number in the subchondral bone of C6^-/- rabbits. Overall, the absence of TCC protected from injury-induced OA progression but had minor effects on the micro-structure of the subchondral bone.

Mechanism of action of genicular artery embolization in a rabbit model of knee osteoarthritis

OBJECTIVES

To establish a rabbit osteoarthritis model for genicular artery embolization (GAE) experiments and to investigate the cellular mechanism of action of this novel procedure for interventional radiologists.

METHODS

Rabbit knee osteoarthritis was surgically modeled by anterior cruciate ligament transection and medial partial meniscectomy of the bilateral hindlimbs followed by 10 weeks of incubation. Rabbits exhibiting synovitis on magnetic resonance imaging were randomly divided into two groups: the bilateral GAE group and the control (sham procedure) group. Four weeks later, the rabbits' mobility (moving time, sec/10 min) and the histopathological features of each knee were assessed, and inter-group differences were evaluated using Student's t-test and ordinal/linear logistic models with generalized estimating equations.

RESULTS

Osteoarthritis modeling and endovascular procedures were successful in 15 of 20 rabbits (8 and 7 in the GAE and control groups, respectively). There was no significant difference in moving times between the two groups (p = .958). The degree of structural cartilage damage was similar in both groups (p = .780). However, the synovial proliferation (p = .016), synovial hypertrophy (p < .001), and villous hyperplasia of the synovial stroma (p = .002) scores were significantly lower in the GAE group than in the control group. The CD3+ cell density (p = .018) and CD3 + cell-infiltrated area (p = .019) were also significantly lower in the GAE group than in the control group.

CONCLUSION

GAE can limit inflammatory processes in the synovium of osteoarthritis-affected knees.

KEY POINTS

Surgical transection of the anterior cruciate ligament and medial partial meniscectomy of rabbit knees provides a useful animal model for research of genicular artery embolization. Osteoarthritic knees treated by genicular artery embolization showed milder synovial proliferation (p = .016), synovial hypertrophy (p < .001), and villous hyperplasia of the synovial stroma (p = .002) than the untreated knees. Osteoarthritic knees treated by genicular artery embolization presented lower CD3+ cell density (p = .018) and CD3+ cell-infiltrated area (p = .019) in the synovium than the untreated knees.

Osteoarthritis models: From animals to tissue engineering

Osteoarthritis (OA) is a chronic degenerative osteoarthropathy. Although it has been revealed that a variety of factors can cause or aggravate the symptoms of OA, the pathogenic mechanisms of OA remain unknown. Reliable OA models that accurately reflect human OA disease are crucial for studies on the pathogenic mechanism of OA and therapeutic drug evaluation. This review first demonstrated the importance of OA models by briefly introducing the OA pathological features and the current limitations in the pathogenesis and treatment of OA. Then, it mainly discusses the development of different OA models, including animal and engineered models, highlighting their advantages and disadvantages from the perspective of pathogenesis and pathology analysis. In particular, the state-of-the-art engineered models and their potential were emphasized, as they may represent the future direction in the development of OA models. Finally, the challenges in obtaining reliable OA models are also discussed, and possible future directions are outlined to shed some light on this area.

CircFOXO3 protects against osteoarthritis by targeting its parental gene FOXO3 and activating PI3K/AKT-mediated autophagy

Osteoarthritis (OA) is a degenerative joint disorder causing pain and functional disability. Emerging evidence reveals that circular RNAs (circRNAs) play essential roles in OA progression and development. This study aimed to investigate the role of a novel circRNA factor, circFOXO3, in the progression of OA and elucidate its underlying molecular mechanism. The function of circFOXO3 in OA and interaction between circFOXO3 and its downstream mRNA target, forkhead box O3 (FOXO3), were evaluated by western blot (WB), immunofluorescence (IF), RNA immunoprecipitation, reverse transcription-quantitative PCR (RT-qPCR), and fluorescence in situ hybridization (FISH). Upregulation of circFOXO3 and autophagic flux were detected both in vivo and in vitro by WB, transmission electron microscopy (TEM), IF, and immunohistochemistry (IHC). A mouse model of OA was also used to confirm the role of circFOXO3 in OA pathogenesis in vivo. Decreased expression of circFOXO3 in OA cartilage tissues was directly associated with excessive apoptosis and imbalance between anabolic and catabolic factors of the extracellular matrix (ECM). Mechanistically, circFOXO3 functioned in cartilage by targeting its parental gene FOXO3 and activating autophagy. Intra-articular injection of lentivirus-circFOXO3 alleviated OA in the mouse model. In conclusion, our results reveal the key role played by circFOXO3 in OA progression; circFOXO3 overexpression may alleviate apoptosis of chondrocytes and promote anabolism of the ECM via activation of FOXO3 and autophagy, providing a potentially effective novel therapeutic strategy for OA.

Establishment of a New Qualitative Evaluation Method for Articular Cartilage by Dynamic T2w MRI Using a Novel Contrast Medium as a Water Tracer

OBJECTIVE

In the early stages of cartilage damage, diagnostic methods focusing on the mechanism of maintaining the hydrostatic pressure of cartilage are thought to be useful. ¹⁷O-labeled water, which is a stable isotope of oxygen, has the advantage of no radiation exposure or allergic reactions and can be detected by magnetic resonance imaging (MRI). This study aimed to evaluate MRI images using ¹⁷O-labeled water in a rabbit model.

DESIGN

Contrast MRI with ¹⁷O-labeled water and macroscopic and histological evaluations were performed 4 and 8 weeks after anterior cruciate ligament transection surgery in rabbits. A total of 18 T2-weighted images were acquired, and ¹⁷O-labeled water was manually administered on the third scan. The ¹⁷O concentration in each phase was calculated from the signal intensity at the articular cartilage. Macroscopic and histological grades were evaluated and compared with the ¹⁷O concentration.

RESULTS

An increase in ¹⁷O concentration in the macroscopic and histologically injured areas was observed by MRI. Macroscopic evaluation showed that the ¹⁷O concentration significantly increased in the damaged site group. Histological evaluations also showed that ¹⁷O concentrations significantly increased at 36 minutes 30 seconds after initiating MRI scanning in the Osteoarthritis Research Society International (OARSI) grade 3 (0.493 in grade 0, 0.659 in grade 1, 0.4651 in grade 2, and 0.9964 in grade 3, P < 0.05).

CONCLUSION

¹⁷O-labeled water could visualize earlier articular cartilage damage, which is difficult to detect by conventional methods.

Psoralen downregulates osteoarthritis chondrocyte inflammation via an estrogen-like effect and attenuates osteoarthritis

Estrogen and its receptor play a positive role in the development of osteoarthritis (OA). Psoralen is a plant-derived estrogen analog. This study aimed to verify whether psoralen inhibits OA through an estrogen-like effect. First, human primary chondrocytes in the late stage of OA were extracted to complete collagen type II immunofluorescence staining and cell proliferation experiments. Subsequently, estrogen, psoralen and estrogen receptor antagonists were co-cultured with OA chondrocytes, and RT-PCR was performed to detect the gene expression. A rabbit OA model was subsequently made by anterior cruciate ligament transection (ACLT). They were set as Sham group, OA group and Psoralen group, respectively. The articular cartilage samples were taken after 5 weeks of treatment, and the effect was observed by gross observation, histological staining, micro-CT scanning of subchondral bone. The results of cellular experiments displayed that the cultured cells were positive for collagen II fluorescence staining and 12 μg/mL psoralen was selected as the optimal concentration. In addition, psoralen had effects similar to estrogen, promoting the expression of estrogen tar-get genes CTSD, PGR and TFF1 and decreasing the expression of the inflammation-related gene TNF- α, IL-1β and IL-6. The effect of psoralen was blocked after the use of an estrogen receptor antagonist. Further animal experiments indicated that the psoralen group showed less destruction of cartilage tissue and decreased OASRI scores compared with the OA group. A subchondral bone CT scan demonstrated that psoralen significantly increased subchondral bone mineral density (BMD), trabecular thickness and trabecular number and decreased trabecular separation. In summary, psoralen inhibits the inflammatory production of chondrocytes, which is related to estrogen-like effect, and can be used to attenuate the progression of OA.