Basic methods in histopathology of joint tissues

Repeated social defeat stress differently affects arthritis-associated hypersensitivity in male and female mice

Chronic stress enhances the risk of neuropsychiatric disorders and contributes to the aggravation and chronicity of pain. The development of stress-associated diseases, including pain, is affected by individual vulnerability or resilience to stress, although the mechanisms remain elusive. We used the repeated social defeat stress model promoting susceptible and resilient phenotypes in male and female mice and induced knee mono-arthritis to investigate the impact of stress vulnerability on pain and immune system regulation. We analyzed different pain-related behaviors, measured blood cytokine and immune cell levels, and performed histological analyses at the knee joints and pain/stress-related brain areas. Stress susceptible male and female mice showed prolonged arthritis-associated hypersensitivity. Interestingly, hypersensitivity was exacerbated in male but not female mice. In males, stress promoted transiently increased neutrophils and Ly6Chigh monocytes, lasting longer in susceptible than resilient mice. While resilient male mice displayed persistently increased levels of the anti-inflammatory interleukin (IL)-10, susceptible mice showed increased levels of the pro-inflammatory IL-6 at the early- and IL-12 at the late arthritis stage. Although joint inflammation levels were comparable among groups, macrophage and neutrophil infiltration was higher in the synovium of susceptible mice. Notably, only susceptible male mice, but not females, presented microgliosis and monocyte infiltration in the prefrontal cortex at the late arthritis stage. Blood Ly6Chigh monocyte depletion during the early inflammatory phase abrogated late-stage hypersensitivity and the associated histological alterations in susceptible male mice. Thus, recruitment of blood Ly6Chigh monocytes during the early arthritis phase might be a key factor mediating the persistence of arthritis pain in susceptible male mice. Alternative neuro-immune pathways that remain to be explored might be involved in females.

The common marmoset as a translational model of age-related osteoarthritis

Age-related osteoarthritis (OA) is a degenerative joint disease characterized by pathological changes in nearly every intra- and peri-articular tissue that contributes to disability in older adults. Studying the etiology of age-related OA in humans is difficult due to an unpredictable onset and insidious nature. A barrier in developing OA modifying therapies is the lack of translational models that replicate human joint anatomy and age-related OA progression. The purpose of this study was to determine whether the common marmoset is a faithful model of human age-related knee OA. Semi-quantitative microCT scoring revealed greater radiographic OA in geriatric versus adult marmosets, and the age-related increase in OA prevalence was similar between marmosets and humans. Quantitative assessments indicate greater medial tibial cortical and trabecular bone thickness and heterogeneity in geriatric versus adult marmosets which is consistent with an age-related increase in focal subchondral bone sclerosis. Additionally, marmosets displayed an age-associated increase in synovitis and calcification of the meniscus and patella. Histological OA pathology in the medial tibial plateau was greater in geriatric versus adult marmosets driven by articular cartilage damage, proteoglycan loss, and altered chondrocyte cellularity. The age-associated increase in medial tibial cartilage OA pathology and meniscal calcification was greater in female versus male geriatric marmosets. Overall, marmosets largely replicate human OA as evident by similar 1) cartilage and skeletal morphology, 2) age-related progression in OA pathology, and 3) sex differences in OA pathology with increasing age. Collectively, these data suggest that the common marmoset is a highly translatable model of the naturally occurring, age-related OA seen in humans.

Exploratory neutron tomography of articular cartilage

OBJECTIVE

To investigate the feasibility of using neutron tomography to gain new knowledge of human articular cartilage degeneration in osteoarthritis (OA). Different sample preparation techniques were evaluated to identify maximum intra-tissue contrast.

DESIGN

Human articular cartilage samples from 14 deceased donors (18-75 years, 9 males, 5 females) and 4 patients undergoing total knee replacement due to known OA (all female, 61-75 years) were prepared using different techniques: control in saline, treated with heavy water saline, fixed and treated in heavy water saline, and fixed and dehydrated with ethanol. Neutron tomographic imaging (isotropic voxel sizes from 7.5 to 13.5 µm) was performed at two large scale facilities. The 3D images were evaluated for gradients in hydrogen attenuation as well as compared to images from absorption X-ray tomography, magnetic resonance imaging, and histology.

RESULTS

Cartilage was distinguishable from background and other tissues in neutron tomographs. Intra-tissue contrast was highest in heavy water-treated samples, which showed a clear gradient from the cartilage surface to the bone interface. Increased neutron flux or exposure time improved image quality but did not affect the ability to detect gradients. Samples from older donors showed high variation in gradient profile, especially from donors with known OA.

CONCLUSIONS

Neutron tomography is a viable technique for specialized studies of cartilage, particularly for quantifying properties relating to the hydrogen density of the tissue matrix or water movement in the tissue.

A Standardized Approach To Evaluation And Reporting of Synovial Histopathology In Two Surgically Induced Murine Models Of Osteoarthritis

OBJECTIVE

Synovial pathology has been linked to osteoarthritis (OA) pain in patients. Microscopic grading systems for synovial changes in human OA have been described, but a standardized approach for murine models of OA is needed. We sought to develop a reproducible approach and set of minimum recommendations for reporting of synovial histopathology in mouse models of OA.

METHODS

Coronal and sagittal sections from male mouse knee joints subjected to destabilization of medial meniscus (DMM) or partial meniscectomy (PMX) were collected as part of other studies. Stains included Hematoxylin and Eosin (H&E), Toluidine Blue (T-Blue) and Safranin O/Fast Green (Saf-O). Four blinded readers graded pathological features (hyperplasia, cellularity, and fibrosis) at specific anatomic locations. Inter-reader agreement of each feature score was determined.

RESULTS

There was acceptable to very good agreement when using 3-4 individual readers. After DMM and PMX, expected medial predominant changes in hyperplasia and cellularity were observed, with fibrosis noted at 12 weeks post-PMX. Synovial changes were consistent from section to section in the mid-joint area. When comparing stains, H&E and T-blue resulted in better agreement compared to Saf-O stain.

CONCLUSIONS

To account for the pathologic and anatomic variability in synovial pathology and allow for a more standardized evaluation that can be compared across studies, we recommend evaluating a minimum set of 3 pathological features at standardized anatomic areas. Further, we suggest reporting individual feature scores separately before relying on a single summed "synovitis" score. H&E or T-blue are preferred, inter-reader agreement for each feature should be considered.

Histological and immunohistochemical analyses of articular cartilage during onset and progression of pre- and early-stage osteoarthritis in a rodent model

Early diagnosis and treatment of pre- and early-stage osteoarthritis (OA) is important. However, the cellular and cartilaginous changes occurring during these stages remain unclear. We investigated the histological and immunohistochemical changes over time between pre- and early-stage OA in a rat model of traumatic injury. Thirty-six male rats were divided into two groups, control and OA groups, based on destabilization of the medial meniscus. Histological and immunohistochemical analyses of articular cartilage were performed on days 1, 3, 7, 10, and 14 postoperatively. Cell density of proteins associated with cartilage degradation increased from postoperative day one. On postoperative day three, histological changes, including chondrocyte death, reduced matrix staining, and superficial fibrillation, were observed. Simultaneously, a compensatory increase in matrix staining was observed. The Osteoarthritis Research Society International score increased from postoperative day seven, indicating thinner cartilage. On postoperative day 10, the positive cell density decreased, whereas histological changes progressed with fissuring and matrix loss. The proteoglycan 4-positive cell density increased on postoperative day seven. These findings will help establish an experimental model and clarify the mechanism of the onset and progression of pre- and early-stage traumatic OA.

Type II collagen scaffolds repair critical-sized osteochondral defects under induced conditions of osteoarthritis in rat knee joints via inhibiting TGF-β-Smad1/5/8 signaling pathway

The bidirectional relationship between osteochondral defects (OCD) and osteoarthritis (OA), with each condition exacerbating the other, makes OCD regeneration in the presence of OA challenging. Type II collagen (Col2) is important in OCD regeneration and the management of OA, but its potential applications in cartilage tissue engineering are significantly limited. This study investigated the regeneration capacity of Col2 scaffolds in critical-sized OCDs under surgically induced OA conditions and explored the underlying mechanisms that promoted OCD regeneration. Furthermore, the repair potential of Col2 scaffolds was validated in over critical-sized OCD models. After 90 days or 150 days since scaffold implantation, complete healing was observed histologically in critical-sized OCD, evidenced by the excellent integration with surrounding native tissues. The newly formed tissue biochemically resembled adjacent natural tissue and exhibited comparable biomechanical properties. The regenerated OA tissue demonstrated lower expression of genes associated with cartilage degradation than native OA tissue but comparable expression of genes related to osteochondral anabolism compared with normal tissue. Additionally, transcriptome and proteome analysis revealed the hindrance of TGF-β-Smad1/5/8 in regenerated OA tissue. In conclusion, the engrafting of Col2 scaffolds led to the successful regeneration of critical-sized OCDs under surgically induced OA conditions by inhibiting the TGF-β-Smad1/5/8 signaling pathway.

Non-invasive electroarthrography measures cartilage in live horses and correlates to direct measurements of cartilage streaming potentials in weight bearing regions of equine metacarpophalangeal joints

OBJECTIVE

To perform non-invasive Electroarthrography (EAG) on live horses and establish relationships between EAG and direct measurements of cartilage streaming potentials in weight bearing areas of the equine metacarpophalangeal joint.

DESIGN

EAG was performed bilaterally on the metacarpophalangeal joints of live horses (n = 3). Separate experiments used metacarpophalangeal joint explants (n = 11) to measure EAG obtained during simulated loading followed by direct measurements of cartilage streaming potentials on joint surfaces using the Arthro-BST probe. Joints were assigned to relatively normal (n = 5) and mildly degraded (n = 6) groups based on histological scoring of Safranin-O/Fast Green stained sections.

RESULTS

EAG, involving application of electrodes to skin surrounding the joint and repeated weight shifting, was well-tolerated in live horses. One pair of distal forelimbs were available for analogous ex vivo EAG testing and measurements were strongly correlated to in vivo EAG measurements obtained on the same joints (r = 0.804, p = 0.016, n = 8). Both indirect (EAG) and direct (Arthro-BST) measurements of cartilage streaming potentials distinguished between normal and mildly degraded cartilage with statistically significant differences at 5 of 6 and 4 of 6 electrodes during simulated standing and walking, respectively. Strong and moderate correlations for weight bearing regions on the dorsal phalanx and central metacarpus were detected during both standing and walking. At the metacarpus/sesamoid interface a moderate correlation occurred during walking.

CONCLUSION

Non-invasive EAG was used successfully in a clinical scenario and correlated to direct measurements of streaming potentials in weight bearing cartilage. These data support the potential of EAG to contribute to the diagnosis and treatment of degenerative joint diseases.

Engineering sulfated polysaccharides and silk fibroin based injectable IPN hydrogels with stiffening and growth factor presentation abilities for cartilage tissue engineering

The extracellular matrix (ECM) presents a framework for various biological cues and regulates homeostasis during both developing and mature stages of tissues. During development of cartilage, the ECM plays a critical role in endowing both biophysical and biochemical cues to the progenitor cells. Hence, designing microenvironments that recapitulate these biological cues as provided by the ECM during development may facilitate the engineering of cartilage tissue. In the present study, we fabricated an injectable interpenetrating hydrogel (IPN) system which serves as an artificial ECM and provides chondro-inductive niches for the differentiation of stem cells to chondrocytes. The hydrogel was designed to replicate the gradual stiffening (as a biophysical cue) and the presentation of growth factors (as a biochemical cue) as provided by the natural ECM of the tissue, thus exemplifying a biomimetic approach. This dynamic stiffening was achieved by incorporating silk fibroin, while the growth factor presentation was accomplished using sulfated-carboxymethyl cellulose. Silk fibroin and sulfated-carboxymethyl cellulose (s-CMC) were combined with tyraminated-carboxymethyl cellulose (t-CMC) and crosslinked using HRP/H2O2 to fabricate s-CMC/t-CMC/silk IPN hydrogels. Initially, the fabricated hydrogel imparted a soft microenvironment to promote chondrogenic differentiation, and with time it gradually stiffened to offer mechanical support to the joint. Additionally, the presence of s-CMC conferred the hydrogel with the property of sequestering cationic growth factors such as TGF-β and allowing their prolonged presentation to the cells. More importantly, TGF-β loaded in the developed hydrogel system remained active and induced chondrogenic differentiation of stem cells, resulting in the deposition of cartilage ECM components which was comparable to the hydrogels that were treated with TGF-β provided through media. Overall, the developed hydrogel system acts as a reservoir of the necessary biological cues for cartilage regeneration and simultaneously provides mechanical support for load-bearing tissues such as cartilage.

Anti-rheumatoid arthritis potential of Halodule pinifolia: development, characterization and in vivo evaluation of H. pinifolia-based oral suspension and lipid nano-emulsion

For treating chronic diseases like rheumatoid arthritis, herbal medicines are preferred due to their evident therapeutic effects and lesser side effects as compared to the long-term used conventional drugs. In this study, the anti-rheumatoid arthritis effect of an unexplored marine grass Halodule pinifolia (HP), and a combination of it with Glycyrrhiza glabra (liquorice; LQ), prepared as a conventional suspension (C1) and a lipid nano-emulsion (C1-N) was evaluated in Freund's complete adjuvant (FCA)- and collagen-induced arthritis (CIA) models. Formulations C1 and C1-N contained standardized extract HP (100 mg/kg) as major active ingredient and liquorice LQ (50 mg/kg) as both active ingredient (anti-inflammatory and anti-ulcer) and sweetening agent. Oral administration of HP and C1 to FCA-induced Sprague-Dawley rats significantly reduced the paw oedema, spleen index, controlled the haematological parameters, cytokine levels (IL-1β, IL-6, TNF-α estimated by ELISA), mRNA expression of cytokines and osteoclast markers (RANK, TRAP and cathepsin K measured by RTPCR). Histopathology and radiological scanning demonstrated lesser joint deterioration in sample-treated rats, as evident phenotypically. The downregulation of CD51 and MMP-3 (western blot) corroborated the anti-arthritic effect of HP and C1. HP showed better results among all. Further, under the CIA model, both C1 and C1-N were found to be potentially active as evidenced by their effect on rat paw oedema, spleen index, haematological parameters, rheumatoid factor, cytokines, osteoclast markers, histology and X-rays. The results proved the anti-arthritic effect of HP and the formulations, particularly the lipid nano-emulsion that showed improved stability as well as activity.

Comparison of two contrast-enhancing staining agents for use in X-ray imaging and digital volume correlation measurements across the cartilage-bone interface

OBJECTIVE

The pathogenesis of osteoarthritis (OA) is associated with subchondral bone changes, which is linked to abnormal strain distribution in the overlying articular cartilage. This highlights the importance of understanding mechanical interaction at the cartilage-bone interface. The aim of this study is to compare solutions of two contrast-enhancing staining agents (CESA) for combining high-resolution Contrast-Enhanced X-ray microfocus Computed Tomography (CECT) with Digital Volume Correlation (DVC) for full-field strain measurements at the cartilage-bone interface.

DESIGN

Bovine osteochondral plugs were stained with phosphotungstic acid (PTA) in 70% ethanol or 1:2 hafnium-substituted Wells-Dawson polyoxometalate (Hf-WD POM) in PBS. Mechanical properties were assessed using micromechanical probing and nanoindentation. Strain uncertainties (from CECT data) were evaluated following two consecutive unloaded scans. Residual strains were computed following unconfined compression (ex situ) testing.

RESULTS

PTA and Hf-WD POM enabled the visualisation of structural features in cartilage, allowing DVC computation on the CECT data. Residual strains up to ∼10,000 μɛ were detected up to the tidemark. Nanoindentation showed that PTA-staining caused an average ∼6-fold increase in articular cartilage stiffness, a ∼19-fold increase in reduced modulus and ∼7-fold increase in hardness, whereas Hf-WD POM-stained specimens had mechanical properties similar to pre-stain tissue. Micromechanical probing showed a 77% increase in cartilage surface stiffness after PTA-staining, in comparison to a 16% increase in stiffness after staining with Hf-WD POM.

CONCLUSION

Hf-WD POM is a more suitable CESA solution compared to PTA for CECT imaging combined with DVC as it allowed visualisation of structural features in the cartilage tissue whilst more closely maintaining tissue mechanical properties.

Stimulation of nuclear receptor REV-ERBs alleviates monosodium iodoacetate-induced osteoarthritis pathology of mice and the induction of inflammatory molecules expression in primary cultured chondrocytes

Because inflammation in chondrocytes contributes to the induction of osteoarthritis (OA), regulation of their activity is essential. A previous study showed that stimulation of the reverse erythroblastosis virus (REV-ERB) nuclear receptors in spinal glial cells elicits anti-inflammatory and antinociception effects in animal models of chronic pain. However, the involvement of REV-ERBs in chondrocyte functions and OA pathologies remains to be elucidated. In the current study, we found that pretreatment with the REV-ERB agonist SR9009 significantly blocked the increases in inflammatory molecules [(matrix metalloproteinase (MMP) 3, MMP9, and MMP13] and cytokines (interleukin-1β and tumor necrosis factor) in primary cultured chondrocytes following treatment with lipopolysaccharide. Furthermore, repeated intra-articular treatment with SR9009 significantly prevented monosodium iodoacetate-induced mechanical hypersensitivity and tended to partially reduce knee joint damage in mice. In conclusion, our findings suggest that REV-ERBs have a critical role in alleviating nociceptive hypersensitivity in OA pathologies by negatively regulating inflammation in chondrocytes.

Auricular and laryngeal chondritis in nursery and finishing pigs

This work aimed to characterize the clinic-pathological presentation of an outbreak of auricular and laryngeal chondritis in pigs. Visits were made to pig farms, where the clinical history was obtained, and clinical and postmortem examinations were performed. In those farms, 3% to 4% of pigs presented otohematomas, which started in the nursery and extended to the finishing phase. Moreover, some finishing pigs presented with respiratory distress, initially characterized as inspiratory dyspnea, associated by an uncommon respiratory stridor and culminating in death. Grossly, nursery piglets had enlarged ears, and on the cut surface, the cartilage was fragmented and associated with blood clots. In the finishing phase, in addition to auricular lesions, the epiglottis and arytenoid cartilages were thickened and distorted, which partially occluded the lumen. Microscopically, the laryngeal and auricular cartilages were fragmented, displayed a loss of matrix basophilia, and were surrounded by lymphohistiocytic inflammatory infiltrate, with occasional multinucleated giant cells and fibrosis. The lesions exclusively affected elastic cartilages. The disease in finishing pigs led to increased mortality and was a differential diagnosis to respiratory challenges. It was not possible to determine the factor that triggered this condition; however, a nutritional association is suspected. To the authors' knowledge, this is the first report of primary auricular and laryngeal chondritis in pigs.

Sirt6 promotes DNA damage repair in osteoarthritis chondrocytes by activating the Keap1/Nrf2/HO-1 signaling pathway

The aim of this study was to explore the effect and mechanism of Sirt6 on DNA damage repair in OA chondrocytes. Cartilage tissues were collected from OA patients with knee arthroplasty and traumatic amputation patients without OA. Besides, 7-week-old male C57BL/6 mice were randomly divided into Control and OA groups; CHON-001 cells of corresponding groups were treated with 10 ng/ml interleukin (IL)-1β, respectively. Subsequently, Sirt6 or siNrf2 was over-expressed in CHON-001 cells to observe the effect of Sirt6 on DNA damage and senescence of chondrocytes by IL-1β through the nuclear factor E2-related factor 2 (Nrf2) signaling pathway. The expression level of Sirt6 in human and mouse OA cartilage tissues was significantly decreased. However, 24 h of treatment with IL-1β significantly decreased the expression of Sirt6 in chondrocytes, induced DNA damage, and promoted cellular senescence. In addition, over-expression of Sirt6 promoted DNA damage repair and inhibited cellular senescence in IL-1β-induced chondrocytes. Moreover, the overexpression of Sirt6 activated the Keap1/Nrf2/HO-1 signaling pathway in chondrocytes, while knockdown of Nrf2 expression inhibited the DNA damage repair and anti-senescence effects of Sirt6 on IL-1β-treated chondrocytes. Sirt6 may reduce DNA damage and cellular senescence in OA chondrocytes induced by IL-1β through activating the Keap1/Nrf2/HO-1 signaling pathway.

Microtissue Culture Provides Clarity on the Relative Chondrogenic and Hypertrophic Response of Bone-Marrow-Derived Stromal Cells to TGF-β1, BMP-2, and GDF-5

Chondrogenic induction of bone-marrow-derived stromal cells (BMSCs) is typically accomplished with medium supplemented with growth factors (GF) from the transforming growth factor-beta (TGF-β)/bone morphogenetic factor (BMP) superfamily. In a previous study, we demonstrated that brief (1-3 days) stimulation with TGF-β1 was sufficient to drive chondrogenesis and hypertrophy using small-diameter microtissues generated from 5000 BMSC each. This biology is obfuscated in typical large-diameter pellet cultures, which suffer radial heterogeneity. Here, we investigated if brief stimulation (2 days) of BMSC microtissues with BMP-2 (100 ng/mL) or growth/differentiation factor (GDF-5, 100 ng/mL) was also sufficient to induce chondrogenic differentiation, in a manner comparable to TGF-β1 (10 ng/mL). Like TGF-β1, BMP-2 and GDF-5 are reported to stimulate chondrogenic differentiation of BMSCs, but the effects of transient or brief use in culture have not been explored. Hypertrophy is an unwanted outcome in BMSC chondrogenic differentiation that renders engineered tissues unsuitable for use in clinical cartilage repair. Using three BMSC donors, we observed that all GFs facilitated chondrogenesis, although the efficiency and the necessary duration of stimulation differed. Microtissues treated with 2 days or 14 days of TGF-β1 were both superior at producing extracellular matrix and expression of chondrogenic gene markers compared to BMP-2 and GDF-5 with the same exposure times. Hypertrophic markers increased proportionally with chondrogenic differentiation, suggesting that these processes are intertwined for all three GFs. The rapid action, or "temporal potency", of these GFs to induce BMSC chondrogenesis was found to be as follows: TGF-β1 > BMP-2 > GDF-5. Whether briefly or continuously supplied in culture, TGF-β1 was the most potent GF for inducing chondrogenesis in BMSCs.

Ceria-vesicle nanohybrid therapeutic for modulation of innate and adaptive immunity in a collagen-induced arthritis model

Commencing with the breakdown of immune tolerance, multiple pathogenic factors, including synovial inflammation and harmful cytokines, are conjointly involved in the progression of rheumatoid arthritis. Intervening to mitigate some of these factors can bring a short-term therapeutic effect, but other unresolved factors will continue to aggravate the disease. Here we developed a ceria nanoparticle-immobilized mesenchymal stem cell nanovesicle hybrid system to address multiple factors in rheumatoid arthritis. Each component of this nanohybrid works individually and also synergistically, resulting in comprehensive treatment. Alleviation of inflammation and modulation of the tissue environment into an immunotolerant-favourable state are combined to recover the immune system by bridging innate and adaptive immunity. The therapy is shown to successfully treat and prevent rheumatoid arthritis by relieving the main symptoms and also by restoring the immune system through the induction of regulatory T cells in a mouse model of collagen-induced arthritis.

Photo-Cross-Linkable, Injectable, and Highly Adhesive GelMA-Glycol Chitosan Hydrogels for Cartilage Repair

Hydrogels provide a promising platform for cartilage repair and regeneration. Although hydrogels have shown some efficacy, they still have shortcomings including poor mechanical properties and suboptimal integration with surrounding cartilage. Herein, hydrogels that are injectable, cytocompatible, mechanically robust, and highly adhesive to cartilage are developed. This approach uses GelMA-glycol chitosan (GelMA-GC) that is crosslinkable with visible light and photoinitiators (lithium acylphosphinate and tris (2,2'-bipyridyl) dichlororuthenium (II) hexahydrate ([RuII(bpy)3 ]2+ and sodium persulfate (Ru/SPS)). Ru/SPS-cross-linked hydrogels have higher compressive and tensile modulus, and most prominently higher adhesive strength with cartilage, which also depends on inclusion of GC. Tensile and push-out tests of the Ru/SPS-cross-linked GelMA-GC hydrogels demonstrate adhesive strength of ≈100 and 46 kPa, respectively. Hydrogel precursor solutions behave in a Newtonian manner and are injectable. After injection in focal bovine cartilage defects and in situ cross-linking, this hydrogel system remains intact and integrated with cartilage following joint manipulation ex vivo. Cells remain viable (>85%) in the hydrogel system and further show tissue regeneration potential after three weeks of in vitro culture. These preliminary results provide further motivation for future research on bioadhesive hydrogels for cartilage repair and regeneration.

Targeting multiple disease hallmarks using a synergistic disease-modifying drug combination ameliorates osteoarthritis via inhibition of senescence and inflammation

AIMS

Osteoarthritis (OA), is a debilitating disease characterized by progressive cartilage degradation, synovial inflammation, and chondrocyte senescence. Various treatment agents independently targeting these hallmarks have been investigated. However, due to the complex multifaceted nature of OA, no disease-modifying osteoarthritis drugs are clinically available. In an attempt to overcome this, we developed a combinatorial approach and demonstrated the efficacy of TsC [Tissue inhibitor of metalloproteinase-3 (TIMP3) + sulfated carboxymethylcellulose (sCMC)] and piperlongumine (PL) combination for the amelioration of OA in a goat ex vivo OA model.

MAIN METHODS

The efficacy of the drug combination was evaluated using the goat ex vivo OA explant model and results were validated in clinically relevant human OA cartilage explants. The chondroprotective effects were evaluated in terms of reduced inflammation and cartilage matrix loss, reduction in chondrosenescence, and reduced oxidative stress.

KEY FINDINGS

A combination of TsC and PL (TsC-PL) significantly reduced inflammation, cartilage matrix loss, chondrosenescence, and oxidative stress in the goat ex vivo OA model and showed chondroprotective effects. Further, similar chondroprotective effects were observed in human OA cartilage. Additionally, the coefficient of drug interaction analysis indicated that the combination of TsC and PL had a synergistic effect in reducing matrix degrading proteases and inflammation (goat ex vivo OA model) and Reactive oxygen species (ROS) production (human OA cartilage).

SIGNIFICANCE

Combinatorial treatment with TsC and PL demonstrated potential disease-modifying effects for the treatment of osteoarthritis via inhibition of inflammation and senescence and supports the usage of treatment strategies targeting multiple pathological factors of OA simultaneously.

Solution-free and simplified H&E staining using a hydrogel-based stamping technology

Hematoxylin and eosin (H&E) staining has been widely used as a fundamental and essential tool for diagnosing diseases and understanding biological phenomena by observing cellular arrangements and tissue morphological changes. However, conventional staining methods commonly involve solution-based, complex, multistep processes that are susceptible to user-handling errors. Moreover, inconsistent staining results owing to staining artifacts pose real challenges for accurate diagnosis. This study introduces a solution-free H&E staining method based on agarose hydrogel patches that is expected to represent a valuable tool to overcome the limitations of the solution-based approach. Using two agarose gel-based hydrogel patches containing hematoxylin and eosin dyes, H&E staining can be performed through serial stamping processes, minimizing color variation from handling errors. This method allows easy adjustments of the staining color by controlling the stamping time, effectively addressing variations in staining results caused by various artifacts, such as tissue processing and thickness. Moreover, the solution-free approach eliminates the need for water, making it applicable even in environmentally limited middle- and low-income countries, while still achieving a staining quality equivalent to that of the conventional method. In summary, this hydrogel-based H&E staining method can be used by researchers and medical professionals in resource-limited settings as a powerful tool to diagnose and understand biological phenomena.

Induced regeneration of articular cartilage - identification of a dormant regeneration program for a non-regenerative tissue

A mouse organoid culture model was developed to regenerate articular cartilage by sequential treatment with BMP2 and BMP9 (or GDF2) that parallels induced joint regeneration at digit amputation wounds in vivo. BMP9-induced chondrogenesis was used to identify clonal cell lines for articular chondrocyte and hypertrophic chondrocyte progenitor cells from digit fibroblasts. A protocol that includes cell aggregation enhanced by BMP2 followed by BMP9-induced chondrogenesis resulted in the differentiation of organized layers of articular chondrocytes, similar to the organization of middle and deep zones of articular cartilage in situ, and retained a differentiated phenotype following transplantation. In addition, the differentiation of a non-chondrogenic connective tissue layer containing articular chondrocyte progenitor cells demonstrated that progenitor cell sequestration is coupled with articular cartilage differentiation at a clonal level. The studies identify a dormant endogenous regenerative program for a non-regenerative tissue in which fibroblast-derived progenitor cells can be induced to initiate morphogenetic and differentiative programs that include progenitor cell sequestration. The identification of dormant regenerative programs in non-regenerative tissues such as articular cartilage represents a novel strategy that integrates regeneration biology with regenerative medicine.

Potential of thermoresponsive hydrogel as an alternative therapy for rat knee osteoarthritis

Osteoarthritis is a degenerative condition that is highly prevalent and primarily affects the joints. The knee is the most commonly affected site, impacting the lives of over 300 million individuals worldwide. This study presents a potential solution to address the unmet need for a minimally invasive technique in the treatment of osteoarthritis: a biocompatible, injectable, and thermoresponsive hydrogel. In comparison to commercially available products such as lyophilized platelets, dextrose, and triamcinolone, the thermoresponsive hydrogel exhibits significantly superior performance in dynamic behaviors, including print area, stability, and step cycle, when tested on rats with knee osteoarthritis. However, it demonstrates similar treatment efficacy to these products in static behaviors, as observed through histopathological and immunohistochemical analysis. Therefore, the thermoresponsive hydrogel holds promise as an effective alternative therapy for osteoarthritis. Moreover, by blending the hydrogel with drugs, controlled and sustained release can be achieved, thereby facilitating the long-term management of osteoarthritis symptoms.

Comparative effect of platelet- and mesenchymal stromal cell-derived extracellular vesicles on human cartilage explants using an ex vivo inflammatory osteoarthritis model

Aims

Extracellular vesicles (EVs) are nanoparticles secreted by all cells, enriched in proteins, lipids, and nucleic acids related to cell-to-cell communication and vital components of cell-based therapies. Mesenchymal stromal cell (MSC)-derived EVs have been studied as an alternative for osteoarthritis (OA) treatment. However, their clinical translation is hindered by industrial and regulatory challenges. In contrast, platelet-derived EVs might reach clinics faster since platelet concentrates, such as platelet lysates (PL), are already used in therapeutics. Hence, we aimed to test the therapeutic potential of PL-derived extracellular vesicles (pEVs) as a new treatment for OA, which is a degenerative joint disease of articular cartilage and does not have any curative or regenerative treatment, by comparing its effects to those of human umbilical cord MSC-derived EVs (cEVs) on an ex vivo OA-induced model using human cartilage explants.

Methods

pEVs and cEVs were isolated by size exclusion chromatography (SEC) and physically characterized by nanoparticle tracking analysis (NTA), protein content, and purity. OA conditions were induced in human cartilage explants (10 ng/ml oncostatin M and 2 ng/ml tumour necrosis factor alpha (TNFα)) and treated with 1 × 109 particles of pEVs or cEVs for 14 days. Then, DNA, glycosaminoglycans (GAG), and collagen content were quantified, and a histological study was performed. EV uptake was monitored using PKH26 labelled EVs.

Results

Significantly higher content of DNA and collagen was observed for the pEV-treated group compared to control and cEV groups. No differences were found in GAG quantification nor in EVs uptake within any treated group.

Conclusion

In conclusion, pEVs showed better performance than cEVs in our in vitro OA model. Although further studies are needed, pEVs are shown as a potential alternative to cEVs for cell-free regenerative medicine.

Therapeutic Efficacy of Mesenchymal Stem/Stromal Cell Small Extracellular Vesicles in Alleviating Arthritic Progression by Restoring Macrophage Balance

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by joint inflammation and damage, often associated with an imbalance in M1/M2 macrophages. Elevated levels of anti-inflammatory M2 macrophages have been linked to a therapeutic response in RA. We have previously demonstrated that mesenchymal stem/stromal cell small extracellular vesicles (MSC-sEVs) promote M2 polarization and hypothesized that MSC-sEVs could alleviate RA severity with a concomitant increase in M2 polarization. Here, we treated a mouse model of collagen-induced arthritis (CIA) with MSC-sEVs. Relative to vehicle-treated CIA mice, both low (1 μg) and high (10 μg) doses of MSC-sEVs were similarly efficacious but not as efficacious as Prednisolone, the positive control. MSC-sEV treatment resulted in statistically significant reductions in disease progression rate and disease severity as measured by arthritic index (AI), anti-CII antibodies, IL-6, and C5b-9 plasma levels. There were no statistically significant differences in the treatment outcome between low (1 μg) and high (10 μg) doses of MSC-sEVs. Furthermore, immunohistochemical analysis revealed that concomitant with the therapeutic efficacy, MSC-sEV treatment increased anti-inflammatory M2 macrophages and decreased pro-inflammatory M1 macrophages in the synovium. Consistent with increased M2 macrophages, histopathological examination also revealed reduced inflammation, pannus formation, cartilage damage, bone resorption, and periosteal new bone formation in the MSC-sEV-treated group compared to the vehicle group. These findings suggest that MSC-sEVs are potential biologic disease-modifying antirheumatic drugs (DMARDs) that can help slow or halt RA joint damage and preserve joint function.

Histological and immunohistochemical guide to tendon tissue

Tendons are unique dense connective tissues with discrete zones having specific structure and function. They are juxtaposed with other tissues (e.g., bone, muscle, and fat) with different compositional, structural, and mechanical properties. Additionally, tendon properties change drastically with growth and development, disease, aging, and injury. Consequently, there are unique challenges to performing high quality histological assessment of this tissue. To address this need, histological assessment was one of the breakout session topics at the 2022 Orthopaedic Research Society (ORS) Tendon Conference hosted at the University of Pennsylvania. The purpose of the breakout session was to discuss needs from members of the ORS Tendon Section related to histological procedures, data presentation, knowledge dissemination, and guidelines for future work. Therefore, this review provides a brief overview of the outcomes of this discussion and provides a set of guidelines, based on the perspectives from our laboratories, for histological assessment to assist researchers in their quest to utilize these techniques to enhance the outcomes and interpretations of their studies.

Cell clusters in intervertebral disc degeneration: an attempted repair mechanism aborted via apoptosis

Cell clusters are a histological hallmark feature of intervertebral disc degeneration. Clusters arise from cell proliferation, are associated with replicative senescence, and remain metabolically, but their precise role in various stages of disc degeneration remain obscure. The aim of this study was therefore to investigate small, medium, and large size cell-clusters. For this purpose, human disc samples were collected from 55 subjects, aged 37-72 years, 21 patients had disc herniation, 10 had degenerated non-herniated discs, and 9 had degenerative scoliosis with spinal curvature <45°. 15 non-degenerated control discs were from cadavers. Clusters and matrix changes were investigated with histology, immunohistochemistry, and Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Data obtained were analyzed with spearman rank correlation and ANOVA. Results revealed, small and medium-sized clusters were positive for cell proliferation markers Ki-67 and proliferating cell nuclear antigen (PCNA) in control and slightly degenerated human discs, while large cell clusters were typically more abundant in severely degenerated and herniated discs. Large clusters associated with matrix fissures, proteoglycan loss, matrix metalloproteinase-1 (MMP-1), and Caspase-3. Spatial association findings were reconfirmed with SDS-PAGE that showed presence to these target markers based on its molecular weight. Controls, slightly degenerated discs showed smaller clusters, less proteoglycan loss, MMP-1, and Caspase-3. In conclusion, cell clusters in the early stages of degeneration could be indicative of repair, however sustained loading increases large cell clusters especially around microscopic fissures that accelerates inflammatory catabolism and alters cellular metabolism, thus attempted repair process initiated by cell clusters fails and is aborted at least in part via apoptosis.

Sulfated carboxymethylcellulose mediated enhancement of Timp3 efficacy synergistically attenuates osteoarthritis through inhibition of NFκB and JNK

Osteoarthritis (OA) is a prevalent degenerative joint condition with no effective disease modifying treatments. In this study, we aimed to address multiple OA hallmarks using a combination of pro-chondrogenic sulfated carboxymethylcellulose (sCMC) and anti-catabolic tissue inhibitor of metalloproteases 3 (Timp3) in relevant disease systems. Firstly, we chemically sulfated carboxymethylcellulose to impart a negative charge and improve the stability of cationic Timp3. The modified sCMC exhibited a molecular weight of 10 kDa and a degree of sulfation of ∼10 %. We further demonstrated that sulfation of CMC confers pro-chondrogenic characteristics. Subsequently, we demonstrated that the combination of sCMC and Timp3 effectively reduced key OA hallmarks, such as matrix degradation, inflammation, and protease expression, in a goat ex vivo OA model compared to individual treatments. We further demonstrated that the anti-OA effect of sCMC and Timp3 is mediated through the suppression of NFκB and JNK activation. To validate the clinical potential and mechanism of action, we conducted experiments on human OA explants. The combination treatment synergistically reduced the expression of MMP13 and NFκB in human OA explants. Overall, sCMC-mediated enhancement of Timp3 efficacy synergistically reduced OA-like traits and demonstrates the potential for OA amelioration.

A novel allogeneic acellular matrix scaffold for porcine cartilage regeneration

BACKGROUND

Cartilage defects are common sports injuries without significant treatment. Articular cartilage with inferior regenerative potential resulted in the poor formation of hyaline cartilage in defects. Acellular matrix scaffolds provide a microenvironment and biochemical properties similar to those of native tissues and are widely used for tissue regeneration. Therefore, we aimed to design a novel acellular cartilage matrix scaffold (ACS) for cartilage regeneration and hyaline-like cartilage formation.

METHODS

Four types of cartilage injury models, including full-thickness cartilage defects (6.5 and 8.5 mm in diameter and 2.5 mm in depth) and osteochondral defects (6.5 and 8.5 mm in diameter and 5 mm in depth), were constructed in the trochlear groove of the right femurs of pigs (n = 32, female, 25-40 kg). The pigs were divided into 8 groups (4 in each group) based on post-surgery treatment differences. was assessed by macroscopic appearance, magnetic resonance imaging (MRI), micro-computed tomography (micro-CT), and histologic and immunohistochemistry tests.

RESULTS

At 6 months, the ACS-implanted group exhibited better defect filling and a greater number of chondrocyte-like cells in the defect area than the blank groups. MRI and micro-CT imaging evaluations revealed that ACS implantation was an effective treatment for cartilage regeneration. The immunohistochemistry results suggested that more hyaline-like cartilage was generated in the defects of the ACS-implanted group.

CONCLUSIONS

ACS implantation promoted cartilage repair in full-thickness cartilage defects and osteochondral defects with increased hyaline-like cartilage formation at the 6-month follow-up.

Epidemiology of Modic changes in dogs: Prevalence, possible risk factors, and association with spinal phenotypes

Background

Chronic low back pain, a leading contributor to disease burden worldwide, is often caused by intervertebral disc (IVD) degeneration. Modic changes (MCs) are MRI signal intensity changes due to lesions in vertebral bone marrow adjacent to degenerated IVDs. Only a few studies described the histopathological changes associated with MC to date. MC type 1 is suggested to be associated with bone marrow infiltration of fibrovascular tissue, type 2 with fatty infiltration, and type 3 with bone sclerosis in humans.

Methods

This study investigated whether the dog can be a valuable animal model to research MCs, by examining the prevalence, imaging, and histological characteristics of lumbar MCs in dogs (340 dogs, 2496 spinal segments).

Results

Logistic regression analysis indicated that the presence of lumbosacral MCs was associated with age and disc herniation (annulus fibrosis protrusion and/or nucleus pulposus extrusion). According to MRI analysis, MCs were mostly detected at the lumbosacral junction in dogs. Most signal intensity changes represented MC type 3, while previous spinal surgery seemed to predispose for the development of MC type 1 and 2. Histological analysis (16 dogs, 39 spinal segments) indicated that IVDs with MCs showed more histopathological abnormalities in the endplate and vertebral bone marrow than IVDs without MCs. Mostly chondroid proliferation in the bone marrow was encountered, while the histologic anomalies described in humans associated with MCs, such as fibrovascular or fatty infiltration, were scarcely detected.

Conclusions

Dogs spontaneously develop MCs, but may exhibit other pathological processes or more chronic bone marrow pathologies than humans with MCs. Therefore, more research is needed to determine the translatability of the MCs encountered in dog low-back-pain patients.

The continuous structure of the joint capsule and meniscus in the pig knee

The knee joint capsules composed of a fibrous layer and a synovial layer. The knee meniscus consists of the superficial network, lamellar layer, tie fibre and circumferential bundles. However, the continuous structure of the knee joint capsule and meniscus has not been reported. Fetal and adult pigs were used to investigate the structural relationship between the stifle joint capsule and meniscus based on the gross anatomy and histological findings. In the gross anatomical examination, the joint capsule appeared to have separated attachments to the meniscus, except for the lower aspect of the popliteal hiatus. Histologically, the lower half of the popliteal hiatus was found to have separated attachments, with vessels running between the attachments of the joint capsules. The synovial layer of the joint capsule continued to the superficial network, and the fibrous layer of the joint capsule continued to the lamellar layer and tie fibres. There were two routes of arterial entry into the meniscus: intracapsular and intercapsular. It appeared that the presence of separated attachments of the joint capsule was necessary to allow the intercapsular route. This study clarified for the first time the routes of feeding vessels entering the meniscus and proposed to call this entry point the meniscus hilum. We consider that this detailed anatomical information is important for understanding the continuation between the joint capsule and the meniscus.

Early Degenerative Changes in a Spontaneous Osteoarthritis Model Assessed by Nanoindentation

Understanding early mechanical changes in articular cartilage (AC) and subchondral bone (SB) is crucial for improved treatment of osteoarthritis (OA). The aim of this study was to develop a method for nanoindentation of fresh, unfixed osteochondral tissue to assess the early changes in the mechanical properties of AC and SB. Nanoindentation was performed throughout the depth of AC and SB in the proximal tibia of Dunkin Hartley guinea pigs at 2 months, 3 months, and 2 years of age. The contralateral tibias were either histologically graded for OA or analyzed using immunohistochemistry. The results showed an increase in the reduced modulus (Er) in the deep zone of AC during early-stage OA (6.0 ± 1.75 MPa) compared to values at 2 months (4.04 ± 1.25 MPa) (*** p < 0.001). In severe OA (2-year) specimens, there was a significant reduction in Er throughout the superficial and middle AC zones, which correlated to increased ADAMTS 4 and 5 staining, and proteoglycan loss in these regions. In the subchondral bone, a 35.0% reduction in stiffness was observed between 2-month and 3-month specimens (*** p < 0.001). The severe OA age group had significantly increased SB stiffness of 36.2% and 109.6% compared to 2-month and 3-month-old specimens respectively (*** p < 0.001). In conclusion, this study provides useful information about the changes in the mechanical properties of both AC and SB during both early- and late-stage OA and indicates that an initial reduction in stiffness of the SB and an increase in stiffness in the deep zone of AC may precede early-stage cartilage degeneration.

Development of a method to investigate strain distribution across the cartilage-bone interface in guinea pig model of spontaneous osteoarthritis using lab-based contrast enhanced X-ray-computed tomography and digital volume correlation

OBJECTIVE

Strain changes at the cartilage-bone interface play a crucial role in osteoarthritis (OA) development. Contrast-Enhanced X-ray Computed Tomography (CECT) and Digital Volume Correlation (DVC) can measure 3D strain changes at the osteochondral interface. Using lab-based CT systems it is often difficult to visualise soft tissues such as articular cartilage without staining to enhance contrast. Contrast-Enhancing Staining Agents (CESAs), such as Phosphotungstic Acid (PTA) in 70% ethanol, can cause tissue shrinkage and alter tissue mechanics. The aims of this study were, firstly, to assess changes to the mechanical properties of osteochondral tissue after staining with a PTA/PBS solution, and secondly, to visualise articular cartilage during loading and with CECT imaging in order to compare strain across the interface in both healthy and OA joints using DVC.

DESIGN

Nanoindentation was used to assess changes to mechanical properties in articular cartilage and subchondral bone before and after staining. Hindlimbs from Dunkin-Hartley guinea pigs were stained with 1% PTA/PBS at room temperature for 6 days. Two consecutive CECT datasets were acquired for DVC error analysis. In-situ compression with a load corresponding to 2x body weight was applied, the specimen was re-imaged, and DVC was performed between the pre- and post-load tomograms.

RESULTS

Nanoindentation before and after PTA/PBS staining showed similar cartilage stiffness (p < 0.05), however, staining significantly decreased the stiffness of subchondral bone (∼9-fold; p = 0.0012). In severe OA specimens, third principal/compressive (εp3) strain was 141.7% higher and shear strain (γ) was 98.2% higher in tibial articular cartilage compared to non-OA (2 - month) specimens. A 23.1% increase in third principal stain strain and a 54.5% significant increase in the shear (γ) strain (p = 0.0027) was transferred into the mineralised regions of calcified cartilage and subchondral bone in severe OA specimens.

CONCLUSIONS

These results indicate the suitability of PTA in PBS as a contrast agent for the visualisation of cartilage during CECT imaging and allowed DVC computation of strain across the cartilage-bone interface. However, further research is needed to address the reduction in stiffness of subchondral bone after incubation in PBS.

No Evidence for Cognitive Impairment in an Experimental Rat Model of Knee Osteoarthritis and Associated Chronic Pain

Although chronic pain states have been associated with impaired cognitive functions, including memory and cognitive flexibility, the cognitive effects of osteoarthritis (OA) pain remain to be clarified. The aim of this study was to measure cognitive function in the mono-iodoacetate (MIA) rat model of chronic OA-like knee pain. We used young adult male Lister hooded rats, which are well-suited for cognitive testing. Rats received either a unilateral knee injection of MIA (3 mg/50 µL) or saline as control. Joint pain at rest was assessed for up to 12 weeks, using weight-bearing asymmetry, and referred pain at a distal site, using determination of hindpaw withdrawal thresholds. The watermaze delayed-matching-to-place test of rapid place learning, novel object recognition memory assay, and an operant response-shift and -reversal task were used to measure memory and behavioral flexibility. Open-field locomotor activity, startle response, and prepulse inhibition were also measured for comparison. MIA-injected rats showed markedly reduced weight-bearing on the injured limb, as well as pronounced cartilage damage and synovitis, but interestingly no changes in paw withdrawal threshold. Rearing was reduced, but otherwise, locomotor activity was normal and no changes in startle and prepulse inhibition were detected. MIA-injected rats had intact watermaze delayed-matching-to-place performance, suggesting no substantial change in hippocampal function, and there were no changes in novel object recognition memory or performance on the operant task of behavioral flexibility. Our finding that OA-like pain does not alter hippocampal function, unlike other chronic pain conditions, is consistent with human neuroimaging findings. PERSPECTIVE: Young adult rats with OA-like knee pain showed no impairments in hippocampal memory function and behavioral flexibility, suggesting that OA pain impacts cognitive functions less than other chronic pain conditions. In patients, OA pain may interact with other factors (e.g., age, socio-economic factors, and medication) to impair cognition.

The surgical destabilization of the abductor muscle leads to development of instability-associated hip osteoarthritis in mice

Osteoarthritis (OA) of the hip is a common and debilitating painful joint disease. However, there is paucity of surgically induced hip OA models in small animals that allow scientists to study the onset and progression of the disease. A growing body of evidence indicates a positive association between periarticular myotendinous pathology and the development of hip OA. Thus, in the current study, we aimed to establish a novel mouse instability-associated hip OA model via selective injury of the abductor complex around the hip joint. C57BL6/J mice were randomized to sham surgery or abductor injury, in which the myotendinous insertion at the third trochanter and greater trochanter were surgically detached. Mice were allowed free active movement until they were sacrificed at either 3 weeks or 20 weeks post-injury. Histologic analyses and immunohistochemical staining of the femoral head articular cartilage were performed, along with microCT (µCT) analysis to assess subchondral bone remodeling. We observed that mice receiving abductor injury exhibited significantly increased instability-associated OA severity with loss of proteoglycan and type II collagen staining compared to sham control mice at 20 weeks post-surgery, while comparable matrix metalloproteinase 13 expression was observed between injury and sham groups. No significant differences in subchondral bone remodeling were found after 3 or 20 weeks following injury. Our study further supports the link between abductor dysfunction and the development of instability-associated hip OA. Importantly, this novel surgically induced hip OA mouse model may provide a valuable tool for future investigations into the pathogenesis and treatment of hip OA.

Regeneration of Rabbit Auricular Cartilage After the Intravenous Stem Cell Injection

Background

The restoration of auricular cartilage is a major problem of otolaryngology. The low regenerative capacity of cartilage requires alternative approaches such as cell and tissue engineering. Stem cells are one of the ways to repair auricular cartilage damages. The aim of the investigation was the regeneration of an artificial defect of the auricular cartilage of rabbits after the intravenous injection of stem cells.

Materials and Methods

The study was carried out on rabbits. A narrow strip of auricular cartilage was surgically removed. A previously prepared suspension of homologous mesenchymal stem cells (5 million) in 0.5 ml physiological solution was injected into the vein of the opposite ear. Tissue samples from the site of the injury were collected after 1, 2, and 3 months. Histological examinations of the tissues were carried out after staining with fuchsin-eosin, azure II-eosin, and according to Weigert. In addition, the amount of interleukin-6 (IL-6) and the transforming growth factor β1 (TGF-β1) in the blood serum were determined.

Results

The main method of healing is the formation of a connective tissue scar. Yret, an increase of the number of fibroblasts and single islands of the newly formed auricular cartilage was found, which indicates the migration of the injected stem cells to the site of the damage and settling there. The intravenous injection of stem cells did not affect the secretion of pro-inflammatory IL-6, but significantly increased the amount of TGF-β1.

Conclusions

We assume that regenerative processes were stimulated. Nevertheless, they were aimed at quickly restoring the tissue integrity through the typical stages of scar formation. The restoration of cartilage integrity requires additional regulatory factors which will determine the chondrogenic differentiation of stem cells.

Protective and Therapeutic Effects of Lactic Acid Bacteria against Aflatoxin B1 Toxicity to Rat Organs

BACKGROUND

Aflatoxin (AF), a metabolite of Aspergillus flavus, is injurious to vital body organs. The bacterial defense against such mycotoxins has attracted significant attention. Lactic acid bacteria (LAB) are known to ameliorate AF toxicity.

METHODS

Thirty adult male rats were divided into six groups (five each) to perform the experiments. The control (Co) group was fed a basal diet and water. Each of the following periods lasted 21 days: the milk (MK) group orally received milk (500 µL); LAB suspension (500 µL) containing 10⁷ cfu/mL was orally provided to the LAB group; AF (0.5 mg/kg) was orally given to the AF group; and a combination of AF and LAB was administered to the AF + LAB group. The AF/LAB group was initially given AF for 21 days, followed by LAB for the same period. Finally, the rats were dissected to retrieve blood and tissue samples for hematological, biochemical, and histological studies.

RESULTS

The results revealed a significant decrease in RBCs, lymphocytes, total proteins, eosinophil count, albumin, and uric acid, whereas the levels of WBCs, monocytes, neutrophils, creatinine, urea, aspartate aminotransferase, alkaline phosphatase, alanine aminotransferase, lactate dehydrogenase, and creatinine kinase significantly increased in the AF group in comparison to the control group. The histological examination of the AF group revealed necrosis and apoptosis of the kidney's glomeruli and renal tubules, nuclei vacuolization and apoptosis of hepatocytes, congestion of the liver's dilated portal vein, lymphoid depletion in the white pulp, localized hemorrhages, hemosiderin pigment deposition in the spleen, and vacuolization of seminiferous tubules with a complete loss of testis spermatogenic cells. Meanwhile, protective and therapeutic LAB administration in AF-treated rats improved the hematological, biochemical, and histological changes.

CONCLUSIONS

The study revealed LAB-based amelioration to AFB1-induced disruptions of the kidney, liver, spleen, and testis by inhibiting tissue damage. The therapeutic effects of LAB were comparatively more pronounced than the protective effects.

Physical Properties of E143 Food Dye as a New Organic Semiconductor Nanomaterial

Organic semiconductors (OSCs) have attracted considerable attention for many promising applications, such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic photovoltaics (OPVs). The present work introduced E143 food dye as a new nanostructured organic semiconductor that has several advantages, such as low cost, easy fabrication, biocompatibility, and unique physical properties. The material was characterized using a transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and optical absorption spectroscopy. The study of X-ray diffraction (XRD) showed that E143 dye has a monoclinic polycrystalline structure. Electrical and dielectric properties were performed by impedance spectroscopy at frequencies (20 Hz-1 MHz) in the temperature range (303-473 K). The values of interband transitions and activation energy recommended the application of E143 dye as a new organic semiconductor material with promising stability, especially in the range of hot climates such as KSA.

Automated Prediction of Osteoarthritis Level in Human Osteochondral Tissue Using Histopathological Images

Osteoarthritis (OA) is the most common arthritis and the leading cause of lower extremity disability in older adults. Understanding OA progression is important in the development of patient-specific therapeutic techniques at the early stage of OA rather than at the end stage. Histopathology scoring systems are usually used to evaluate OA progress and the mechanisms involved in the development of OA. This study aims to classify the histopathological images of cartilage specimens automatically, using artificial intelligence algorithms. Hematoxylin and eosin (HE)- and safranin O and fast green (SafO)-stained images of human cartilage specimens were divided into early, mild, moderate, and severe OA. Five pre-trained convolutional networks (DarkNet-19, MobileNet, ResNet-101, NasNet) were utilized to extract the twenty features from the last fully connected layers for both scenarios of SafO and HE. Principal component analysis (PCA) and ant lion optimization (ALO) were utilized to obtain the best-weighted features. The support vector machine classifier was trained and tested based on the selected descriptors to achieve the highest accuracies of 98.04% and 97.03% in HE and SafO, respectively. Using the ALO algorithm, the F1 scores were 0.97, 0.991, 1, and 1 for the HE images and 1, 0.991, 0.97, and 1 for the SafO images for the early, mild, moderate, and severe classes, respectively. This algorithm may be a useful tool for researchers to evaluate the histopathological images of OA without the need for experts in histopathology scoring systems or the need to train new experts. Incorporating automated deep features could help to improve the characterization and understanding of OA progression and development.

Elastomeric Porous Poly(glycerol sebacate) Methacrylate (PGSm) Microspheres as 3D Scaffolds for Chondrocyte Culture and Cartilage Tissue Engineering

Cartilage defects can be difficult to treat; therefore, tissue engineering of cartilage is emerging as a promising potential therapy. One interesting area of research explores the delivery of cells to the cartilage defect via scaffold-based cell delivery vehicles and microsurgery. This study explores the use of novel poly(glycerol sebacate) methacrylate (PGSm)-polymerised high internal phase emulsion (polyHIPE) microspheres as scaffolds with embedded cells for cartilage tissue engineering. Porous microsphere scaffolds (100 µm-1 mm diameter) were produced from emulsions consisting of water and a methacrylate-based photocurable resin of poly(glycerol sebacate). These resins were used in conjunction with a T-junction fluidic device and an ultraviolet (UV) curing lamp to produce porous microspheres with a tuneable size. This technique produced biodegradable PGSm microspheres with similar mechanical properties to cartilage. We further explore these microspheres as scaffolds for three-dimensional culture of chondrocytes. The microspheres proved to be very efficient scaffolds for primary chondrocyte culture and were covered by a dense extracellular matrix (ECM) network during the culture period, creating a tissue disk. The presence of glycosaminoglycans (GAGs) and collagen-II was confirmed, highlighting the utility of the PGSm microspheres as a delivery vehicle for chondrocytes. A number of imaging techniques were utilised to analyse the tissue disk and develop methodologies to characterise the resultant tissue. This study highlights the utility of porous PGSm microspheres for cartilage tissue engineering.

Changes in the Subchondral Bone, Visfatin, and Cartilage Biomarkers after Pharmacological Treatment of Experimental Osteoarthritis with Metformin and Alendronate

Subchondral bone that has intense communication with the articular cartilage might be a potential target for pharmacological treatment in the early stages of osteoarthritis (OA). Considering the emerging data about the role of adipokines in the pathogenesis of OA, the administration of drugs that influence their level is also intriguing. Metformin and alendronate were administered in mice with collagenase-induced OA (CIOA) as a monotherapy and in combination. Safranin O staining was used for the assessment of changes in subchondral bone and articular cartilage. Before and after treatment, serum levels of visfatin and biomarkers of cartilage turnover (CTX-II, MMP-13, and COMP) were assessed. In the current study, the combined administration of alendronate and metformin in mice with CIOA led to the protection against cartilage and subchondral bone damage. In mice with CIOA, metformin led to a decrease in visfatin level. In addition, treatment with metformin, alendronate, or their combination lowered the level of cartilage biomarkers (CTX-II and COMP), while the level of MMP-13 was not influenced. In conclusion, personalized combination treatment in OA according to clinical phenotype, especially in the early stages of the disease, might lead to the identification of a successful disease-modifying therapeutic protocol in OA.

Insights into S. aureus-Induced Bone Deformation in a Mouse Model of Chronic Osteomyelitis Using Fluorescence and Raman Imaging

Osteomyelitis is an infection of the bone that is often difficult to treat and causes a significant healthcare burden. Staphylococcus aureus is the most common pathogen causing osteomyelitis. Osteomyelitis mouse models have been established to gain further insights into the pathogenesis and host response. Here, we use an established S. aureus hematogenous osteomyelitis mouse model to investigate morphological tissue changes and bacterial localization in chronic osteomyelitis with a focus on the pelvis. X-ray imaging was performed to follow the disease progression. Six weeks post infection, when osteomyelitis had manifested itself with a macroscopically visible bone deformation in the pelvis, we used two orthogonal methods, namely fluorescence imaging and label-free Raman spectroscopy, to characterise tissue changes on a microscopic scale and to localise bacteria in different tissue regions. Hematoxylin and eosin as well as Gram staining were performed as a reference method. We could detect all signs of a chronically florid tissue infection with osseous and soft tissue changes as well as with different inflammatory infiltrate patterns. Large lesions dominated in the investigated tissue samples. Bacteria were found to form abscesses and were distributed in high numbers in the lesion, where they could occasionally also be detected intracellularly. In addition, bacteria were found in lower numbers in surrounding muscle tissue and even in lower numbers in trabecular bone tissue. The Raman spectroscopic imaging revealed a metabolic state of the bacteria with reduced activity in agreement with small cell variants found in other studies. In conclusion, we present novel optical methods to characterise bone infections, including inflammatory host tissue reactions and bacterial adaptation.

Mild treadmill exercise inhibits cartilage degeneration via macrophages in an osteoarthritis mouse model

Objective

We previously reported how treadmill exercise can suppress cartilage degeneration. Here, we examined the changes in macrophage dynamics in knee osteoarthritis (OA) during treadmill exercise and the effect of macrophage depletion.

Design

OA mouse model, generated via anterior cruciate ligament transection (ACLT), was subjected to treadmill exercise of different intensities to investigate the effects on cartilage and synovium. In addition, clodronate liposomes, which deplete macrophages, were injected intra-articularly into the joint to examine the role of macrophages during treadmill exercise.

Results

Cartilage degeneration was delayed by mild exercise, and concomitantly, an increase in anti-inflammatory factors in the synovium was observed, with a decrease in the M1 and increase in M2 macrophage ratio. On the contrary, high-intensity exercise led to the progress of cartilage degeneration and was associated with an increase in the M1 and a decrease in the M2 macrophage ratio. The clodronate liposome-induced reduction of synovial macrophages delayed cartilage degeneration. This phenotype was reversed by simultaneous treadmill exercise.

Conclusions

Treadmill exercise, especially at high intensity, was detrimental to articular cartilage, whereas mild exercise reduced cartilage degeneration. Moreover, M2 macrophage response appeared necessary for the chondroprotective effect of treadmill exercise. This study indicates the importance of a more comprehensive analysis of the effects of treadmill exercise, not limited to the mechanical stress added directly to cartilage. Hence, our findings might help determine the type and intensity of prescribed exercise therapy for patients with knee OA.

The whole genomic analysis of the Orf virus strains ORFV-SC and ORFV-SC1 from the Sichuan province and their weak pathological response in rabbits

The Orf virus (ORFV) is a member of the Parapoxvirus genus of the Poxviridae family and can cause contagious diseases in sheep, goats, and wild ungulates. In the present study, two ORFV isolates (ORFV-SC isolated from Sichuan province and ORFV-SC1 produced by 60 passages of ORFV-SC in cells) were sequenced and compared to multiple ORFVs. The two ORFV sequences had entire genome sizes of 14,0707 bp and 141,154 bp, respectively, containing 130 and 131 genes, with a G + C content of 63% for the ORFV-SC sequence and 63.9% for the ORFV-SC1 sequence. Alignment of ORFV-SC and ORFV-SC1 with five other ORFV isolates revealed that ORFV-SC, ORFV-SC1, and NA1/11 shared > 95% nucleotide identity with 109 genes. Five genes (ORF007, ORF20, ORF080, ORF112, ORF116) have low amino acids identity between ORFV-SC and ORFV-SC1. Mutations in amino acids result in changes in the secondary and tertiary structure of ORF007, ORF020, and ORF112 proteins. The phylogenetic tree based on the complete genome sequence and 37 single genes revealed that the two ORFV isolates originated from sheep. Finally, animal experiments demonstrated that ORFV-SC1 is less harmful to rabbits than ORFV-SC. The exploration of two full-length viral genome sequences provides valuable information in ORFV biology and epidemiology research. Furthermore, ORFV-SC1 demonstrated an acceptable safety profile following animal vaccination, indicating its potential as a live ORFV vaccine.

Stem cell-based modeling and single-cell multiomics reveal gene-regulatory mechanisms underlying human skeletal development

Although the skeleton is essential for locomotion, endocrine functions, and hematopoiesis, the molecular mechanisms of human skeletal development remain to be elucidated. Here, we introduce an integrative method to model human skeletal development by combining in vitro sclerotome induction from human pluripotent stem cells and in vivo endochondral bone formation by implanting the sclerotome beneath the renal capsules of immunodeficient mice. Histological and scRNA-seq analyses reveal that the induced bones recapitulate endochondral ossification and are composed of human skeletal cells and mouse circulatory cells. The skeletal cell types and their trajectories are similar to those of human embryos. Single-cell multiome analysis reveals dynamic changes in chromatin accessibility associated with multiple transcription factors constituting cell-type-specific gene-regulatory networks (GRNs). We further identify ZEB2, which may regulate the GRNs in human osteogenesis. Collectively, these results identify components of GRNs in human skeletal development and provide a valuable model for its investigation.

Prussian blue nanozymes coated with Pluronic attenuate inflammatory osteoarthritis by blocking c-Jun N-terminal kinase phosphorylation

Osteoarthritis (OA) is a degenerative joint disorder associated with inflammation, functional disability, and high socioeconomic costs. The development of effective therapies against inflammatory OA has been limited owing to its complex and multifactorial nature. The efficacy of Prussian blue nanozymes coated with Pluronic (PPBzymes), US Food and Drug Administration-approved components, and their mechanisms of action have been described in this study, and PPBzymes have been characterized as a new OA therapeutic. Spherical PPBzymes were developed via nucleation and stabilization of Prussian blue inside Pluronic micelles. A uniformly distributed diameter of approximately 204 nm was obtained, which was maintained after storage in an aqueous solution and biological buffer. This indicates that PPBzymes are stable and could have biomedical applications. In vitro data revealed that PPBzymes promote cartilage generation and reduce cartilage degradation. Moreover, intra-articular injections with PPBzymes into mouse joints revealed their long-term stability and effective uptake into the cartilage matrix. Furthermore, intra-articular PPBzymes injections attenuated cartilage degradation without exhibiting cytotoxicity toward the synovial membrane, lungs, and liver. Notably, based on proteome microarray data, PPBzymes specifically block the JNK phosphorylation, which modulates inflammatory OA pathogenesis. These findings indicate that PPBzymes might represent a biocompatible and effective nanotherapeutic for obstructing JNK phosphorylation.

Inhibition of TRADD ameliorates chondrocyte necroptosis and osteoarthritis by blocking RIPK1-TAK1 pathway and restoring autophagy

Osteoarthritis (OA) is an age-related disease characterized by cartilage degeneration. TNFR1-associated death domain protein (TRADD) is a key upstream molecule of TNF-α signals but its role in OA pathogenesis is unknown. This study aimed to verify that whether inhibition of TRADD could protect against chondrocyte necroptosis and OA, and further elucidate the underlying mechanism. We demonstrated that TNF-α-related OA-like phenotypes including inflammation response, extracellular matrix degradation, apoptosis, and necroptosis in chondrocytes were inhibited by TRADD deficiency. Furthermore, TRADD interacted with TRAF2 and knockdown of TRADD suppressed the activation of RIPK1-TAK1-NF-κB signals and restored impaired autophagy. ICCB-19, the selective inhibitor of TRADD, also attenuated necroptosis in chondrocytes. Mechanismly, ICCB-19 blocked the phosphorylation of TAK1-NF-κB signals and restored impaired autophagy, whereas inhibiting autophagic process with 3-Methyladenine compromised these effects of ICCB-19. The in vivo study showed that the intra-articular injection of ICCB-19 rescued the expression of collagen alpha-1(II) chain and LC3, and mitigated the cartilage degeneration of OA mice. This study demonstrates that TRADD mediates TNF-α-induced necroptosis and OA-like phenotypes of chondrocytes and suggests that ICCB-19 suppresses chondrocyte damage and cartilage degeneration by inhibiting TNF-α-TRADD-mediated signals and dysregulation of autophagy in chondrocytes. ICCB-19 may serve as an important option for OA therapy.

Crocus sativus Extract as a Biological Agent for Disease-Modifying Therapy of Collagenase-Induced Mouse Model of Osteoarthritis

Objectives: Osteoarthritis (OA) is an age-related joint disease that involves the degeneration of cartilage and is the most prevalent form of arthritis, affecting a large part of the population. OA is a multifactorial disorder, and no single etiological mechanism has been found to be common to all forms of the disease. Currently used therapies for control of the disease are mainly nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroid medications. The aim of this study was to investigate the extract from Crocus sativus as a biological disease-suppressing therapy agent. Methods: Balb/c mice were injected intra-articularly with Clostridium histolyticum type IA for induction of osteoarthritis. The mice were randomized to five groups: control group, I group (CIOA untreated), II group (CIOA + 100 mg/kg/daily saffron), III group (CIOA + 50 mg/kg/daily saffron), IV group (CIOA + 25 mg/kg/daily saffron). Flow-cytometry analysis was used to study the splenocytes’ phenotype isolated from the treated animals. The serum levels of inflammatory and anti-inflammatory cytokines were analyzed with ELISA. The histological assessment was used to analyze the saffron extract effect on histopathological alterations. Results: Saffron treatment significantly decreased osteoarthritis-associated joint histological manifestations and decreased serum TNFα levels. The flow-cytometry analysis showed a decrease in pro-inflammatory immune cell subtypes in the spleen. Conclusions: The results obtained suggest that saffron affected the disease progression and could be a potential therapeutic approach in osteoarthritic patients’ therapy.

Redox Homeostasis Strategy for Inflammatory Macrophage Reprogramming in Rheumatoid Arthritis Based on Ceria Oxide Nanozyme-Complexed Biopolymeric Micelles

The synovial tissues under rheumatoid arthritis conditions are usually infiltrated by inflammatory cells, particularly M1 macrophages with aberrant redox homeostasis, which causes rapid deterioration of articular structure and function. Herein, we created an ROS-responsive micelle (HA@RH-CeO_X) through the in situ host-guest complexation between ceria oxide nanozymes and hyaluronic acid biopolymers, which precisely delivered nanozyme and clinically approved rheumatoid arthritis drug Rhein (RH) to proinflammatory M1 macrophage populations in inflamed synovial tissues. The abundant cellular ROS could cleave the thioketal linker to trigger the release of RH and Ce. Specifically, the Ce³⁺/Ce⁴⁺ redox pair could present SOD-like enzymatic activity to rapidly decompose ROS and alleviate the oxidative stress in M1 macrophages, while RH could inhibit the TLR4 signaling in M1 macrophages, both of which could act in a concerted manner to induce their repolarization into anti-inflammatory M2 phenotype to ameliorate local inflammation and promote cartilage repair. Notably, rats bearing rheumatoid arthritis showed a drastic increase in the M1-to-M2 macrophage ratio from 1:0.48 to 1:1.91 in the inflamed tissue and significantly reduced inflammatory cytokine levels including TNF-α and IL-6 following the intra-articular injection of HA@RH-CeO_X, accompanied by efficient cartilage regeneration and restored articular function. Overall, this study revealed an approach to in situ modulate the redox homeostasis in inflammatory macrophages and reprogram their polarization states through micelle-complexed biomimetic enzymes, which offers alternative opportunities for the treatment of rheumatoid arthritis.

A triphasic biomimetic BMSC-loaded scaffold for osteochondral integrated regeneration in rabbits and pigs

Osteochondral tissue involves cartilage, calcified cartilage and subchondral bone. These tissues differ significantly in chemical compositions, structures, mechanical properties and cellular compositions. Therefore, the repairing materials face different osteochondral tissue regeneration needs and rates. In this study, we fabricated an osteochondral tissue-inspired triphasic material, which was composed of a poly(lactide-co-glycolide) (PLGA) scaffold loaded with fibrin hydrogel, bone marrow stromal cells (BMSCs) and transforming growth factor-β1 (TGF-β1) for cartilage tissue, a bilayer poly(L-lactide-co-caprolactone) (PLCL)-fibrous membrane loaded with chondroitin sulfate and bioactive glass, respectively, for calcified cartilage, and a 3D-printed calcium silicate ceramic scaffold for subchondral bone. The triphasic scaffold was press-fitted into the osteochondral defects in rabbit (cylindrical defects with a diameter of 4 mm and a depth of 4 mm) and minipig knee joints (cylindrical defects with a diameter of 10 mm and a depth of 6 mm). The μ-CT and histological analysis showed that the triphasic scaffold was partly degraded, and significantly promoted the regeneration of hyaline cartilage after they were implanted in vivo. The superficial cartilage showed good recovery and uniformity. The calcified cartilage layer (CCL) fibrous membrane was in favor of a better cartilage regeneration morphology, a continuous cartilage structure and less fibrocartilage tissue formation. The bone tissue grew into the material, while the CCL membrane limited bone overgrowth. The newly generated osteochondral tissues were well integrated with the surrounding tissues too.

A guide to preclinical evaluation of hydrogel-based devices for treatment of cartilage lesions

The drive to develop cartilage implants for the treatment of major defects in the musculoskeletal system has resulted in a major research thrust towards developing biomaterial devices for cartilage repair. Investigational devices for the restoration of articular cartilage are considered as significant risk materials by regulatory bodies and therefore proof of efficacy and safety prior to clinical testing represents a critical phase of the multidisciplinary effort to bridge the gap between bench and bedside. To date, review articles have thoroughly covered different scientific facets of cartilage engineering paradigm, but surprisingly, little attention has been given to the preclinical considerations revolving around the validation of a biomaterial implant. Considering hydrogel-based cartilage products as an example, the present review endeavors to provide a summary of the critical prerequisites that such devices should meet for cartilage repair, for successful implantation and subsequent preclinical validation prior to clinical trials. Considerations pertaining to the choice of appropriate animal model, characterization techniques for the quantitative and qualitative outcome measures, as well as concerns with respect to GLP practices are also extensively discussed. This article is not meant to provide a systematic review, but rather to introduce a device validation-based roadmap to the academic investigator, in anticipation of future healthcare commercialization. STATEMENT OF SIGNIFICANCE: There are significant challenges around translation of in vitro cartilage repair strategies to approved therapies. New biomaterial-based devices must undergo exhaustive investigations to ensure their safety and efficacy prior to clinical trials. These considerations are required to be applied from early developmental stages. Although there are numerous research works on cartilage devices and their in vivo evaluations, little attention has been given into the preclinical pathway and the corresponding approval processes. With a focus on hydrogel devices to concretely illustrate the preclinical path, this review paper intends to highlight the various considerations regarding the preclinical validation of hydrogel devices for cartilage repair, from regulatory considerations, to implantation strategies, device performance aspects and characterizations.

Alleviation of arthritis through prevention of neutrophil extracellular traps by an orally available inhibitor of protein arginine deiminase 4

Protein arginine deiminases (PAD) 4 is an enzyme that catalyzes citrullination of protein and its role in autoimmune diseases has been established through clinical genetics and gene knock out studies in mice. Further, studies with PAD4 - deficient mice have shown that PAD4 deficiency does not lead to increased infection or immune suppression, which makes PAD4 an attractive therapeutic target for auto-immune and inflammatory diseases. PAD4 has critical enzymatic role of promoting chromatin decondensation and neutrophil extracellular traps (NETs) formation that is associated with a number of immune-mediated pathological conditions. Here, we present a non-covalent PAD4 inhibitor JBI-589 with high PAD4 isoform selectivity and delineated its binding mode at 2.88 Å resolution by X-ray crystallography. We confirmed its effectiveness in inhibiting NET formation in vitro. Additionally, by using two mouse arthritis models for human rheumatoid arthritis (RA), the well-known disease associated with PAD4 clinically, we established its efficacy in vivo. These results suggest that JBI-589 would be beneficial for both PAD4 and NET-associated pathological conditions.

Bone Marrow-Derived Mesenchymal Stem Cell Implants for the Treatment of Focal Chondral Defects of the Knee in Animal Models: A Systematic Review and Meta-Analysis

Osteoarthritis remains an unfortunate long-term consequence of focal cartilage defects of the knee. Associated with functional loss and pain, it has necessitated the exploration of new therapies to regenerate cartilage before significant deterioration and subsequent joint replacement take place. Recent studies have investigated a multitude of mesenchymal stem cell (MSC) sources and polymer scaffold compositions. It is uncertain how different combinations affect the extent of integration of native and implant cartilage and the quality of new cartilage formed. Implants seeded with bone marrow-derived MSCs (BMSCs) have demonstrated promising results in restoring these defects, largely through in vitro and animal studies. A PRISMA systematic review and meta-analysis was conducted using five databases (PubMed, MEDLINE, EMBASE, Web of Science, and CINAHL) to identify studies using BMSC-seeded implants in animal models of focal cartilage defects of the knee. Quantitative results from the histological assessment of integration quality were extracted. Repair cartilage morphology and staining characteristics were also recorded. Meta-analysis demonstrated that high-quality integration was achieved, exceeding that of cell-free comparators and control groups. This was associated with repair tissue morphology and staining properties which resembled those of native cartilage. Subgroup analysis showed better integration outcomes for studies using poly-glycolic acid-based scaffolds. In conclusion, BMSC-seeded implants represent promising strategies for the advancement of focal cartilage defect repair. While a greater number of studies treating human patients is necessary to realize the full clinical potential of BMSC therapy, high-quality integration scores suggest that these implants could generate repair cartilage of substantial longevity.