Thirty days after anterior cruciate ligament transection is sufficient to induce signs of knee osteoarthritis in rats: pain, functional impairment, and synovial inflammation

Multiscale characterization of ultrasmall fluorescent core-shell silica nanoparticles in cartilage and synovial joints reveals rapid cartilage penetration and sustained joint residence

Development of non-surgical disease-modifying interventions for knee osteoarthritis (OA) remains a persistent challenge despite decades of efforts. Therapeutic transport to cartilage in synovial joints is hindered by the dense, negatively charged cartilage matrix, and further challenged by rapid synovial fluid clearance within hours to days. In this study, we investigated ultrasmall (dh ∼ 6 nm) fluorescent core-shell silica nanoparticles (Cornell Prime Dots, or C' Dots), which have received FDA-investigational new drug approval for multiple human clinical trials in oncology, as cartilage-penetrating delivery vehicles for applications in knee OA. Across multiple length and time scales, we examined the relationship between C' Dot tissue and cellular transport kinetics and whole joint clearance. In vitro, C' Dots penetrated cartilage explants within 30 min (D ∼ 2 µm2/s). C' Dots were internalized by chondrocytes within 24 h and were retained in vesicular structures for up to 5 days. In vivo, C' Dot clearance following intra-articular knee injection was well described by two distinct time constants (τ1 ∼ 18 hours, τ2 ∼ 3 weeks), consistent with mechanisms of synovial- and tissue-mediated clearance. C' Dot clearance rates were not affected by surgically-induced cruciate ligament transection. Notably, C' Dots remained in the knee longer than 3 months after a single injection and were localized to cartilage, meniscus, ligaments, and synovium. Collectively, these results illustrate the potential of C' Dots for long-term delivery of conjugated therapeutics in the knee. STATEMENT OF SIGNIFICANCE: This research explores a cartilage-penetrating platform nanotechnology for applications in drug delivery for arthritis. The properties inherent to this particle system enabled rapid tissue penetration, chondrocyte internalization and retention, and persistence in rat knees for longer than 3 months after a single injection. The study demonstrates that ultrasmall nanoparticle delivery platforms can use tissue localization to partially avoid clearance by the synovium, while simultaneously enabling chondrocyte targeting. When paired with a therapeutic, C' Dots may be a versatile platform in early-stage OA and PTOA to protect cartilage from further degeneration. These findings inform future design and engineering of biocompatible drug delivery vehicles for other applications where access to dense tissues is needed.

Metabolic reprogramming of macrophages by a nano-sized opsonization strategy to restore M1/M2 balance for osteoarthritis therapy

Osteoarthritis is a chronic and progressive joint disease accompanied by cartilage degeneration and synovial inflammation. It is associated with an imbalance of synovial macrophage M1/M2 ratio tilting more towards the pro-inflammatory M1 than the anti-inflammatory M2. The M1-macrophages rely on aerobic glycolysis for energy whereas the M2-macrophages derive energy from oxidative phosphorylation. Therefore, inhibiting aerobic glycolysis to induce metabolic reprogramming of macrophages and consequently promote the shift from M1 type to M2 type is a therapeutic strategy for osteoarthritis. Here we developed a macrophage-targeting strategy based on opsonization, using nanoparticles self-assembled to incorporate Chrysin (an anti-inflammatory flavonoid) and V-9302 (an inhibitor of glutamine uptake), and the outer layer modified by immunoglobulin IgG by electrostatic adsorption into IgG/Fe-CV NPs. In vitro studies showed that IgG/Fe-CV NPs effectively target M1 macrophages and inhibit HIF-1α and GLUT-1 essential for aerobic glycolysis and promote polarization from M1 to M2-type macrophages. In vivo, IgG/Fe-CV NPs inhibit inflammation and protect against cartilage damage. The metabolic reprogramming strategy with IgG/Fe-CV NPs to shift macrophage polarization from inflammatory to anti-inflammatory phenotype by inhibiting aerobic glycolysis and glutamine delivery may open up new avenues to treat osteoarthritis.

Donor site morbidity is higher when comparing bone-tendon-bone vs 4-strand semitendinosus/gracilis & all-inside 4-strand semitendinosus for anterior cruciate ligament reconstruction

OBJECTIVES

To study pain and sensory alterations of 75 (three cohorts of 25 patients) patients that underwent different anterior cruciate ligament reconstruction (ACLR) techniques. The cohorts were divided in the bone-patellar tendon-bone (BTB) autograft, the quadruple strand semitendinosus/gracilis (4ST/G) autograft and the all-inside quadruple strand semitendinosus autograft cohort.

METHODS

We conducted a retrospective study to evaluate pain and sensory alterations after surgery. All these patients followed a similar rehabilitation protocol, being 2 years the minimal follow-up time. Pain was characterized by duration and anatomical location and sensory deficits were evaluated concerning duration and affected area. Patients also scored on three different subjective tests: knee walking test (KWT); Lysholm knee scoring scale (LKSS), and International Knee Documentation Committee Subjective Knee Form (IKDC-SKF) and were divided according to its Tegner activity level scale (TALS).

RESULTS

The mean anterior knee pain (AKP) duration amongst the three cohorts was 1.8 ​± ​4.5 months and was smaller in the 4ST/G cohort. The majority of patients of the BTB cohort located pain on the patellar tendon, while patients in the 4ST/G and all-inside cohorts referred that it was diffuse. At 15 days' post-surgery, hypoesthesia was reported by 56 ​% patients and was higher on the BTB cohort and lower in the all-inside cohort. At 2-year follow-up, the all-inside cohort had no patients with hypoesthesia. In the BTB cohort, the sensitive alterations were only located on the area innervated by the infra-patellar branch of the saphenous nerve (IPBSN). The 4ST/G cohort located the hypoesthesia in the area innervated by the IPBSN and in the area of the lateral sural cutaneous nerve (LSCN). The all-inside group located the sensitive alterations mostly in the LSCN. The KWT was painful in BTB and 4ST/G patients and reported 0 ​% for the all-inside cohort. No statistic significant relevance was found for the IKDC-SKF and LKSS.

CONCLUSIONS

All cohorts referred pain and sensitive alterations. Using BTB autograft for ACLR seems to condition a higher number of anterior knee pain and hypoesthesia on medium postoperative follow-up and KWT was more often reported. The 4ST/G group had the smallest duration of AKP. The all-inside cohort showed, globally, a lower number of complaints and a shorter time of symptom persistence, namely in terms of sensory deficits.

LEVEL OF EVIDENCE

III.

IL-17A exacerbates synovial inflammation in osteoarthritis via activation of endoplasmic reticulum stress

The primary clinical manifestations of osteoarthritis (OA) are joint pain and restricted movement capabilities. Synovial inflammation, serving as an initiator of OA progression, intensifies cartilage damage via the generation of various deleterious agents, including pro-inflammatory cytokines and nociceptive mediators. Despite extensive research on modulating synovial inflammation to retard OA progression, the underlying pathophysiological mechanisms of synovial inflammation in OA remain elusive. Interleukin-17A (IL-17A), a pro-inflammatory cytokine released by activated T lymphocytes, is a therapeutic target for numerous inflammatory and autoimmune pathologies. This study investigates the role and mechanism of IL-17A in OA synovial inflammation using both in vivo and in vitro models and examines the impact of the endoplasmic reticulum stress (ERS) inhibitor, 4-Phenylbutyric Acid (4-PBA). Our findings indicate that IL-17A may be implicated in synovial inflammation through ERS and suggest a potential therapeutic direction for mitigating synovial inflammation in OA.

NGF Signaling Exacerbates KOA Peripheral Hyperalgesia via the Increased TRPV1-Labeled Synovial Sensory Innervation in KOA Rats

Objectives

Knee osteoarthritis (KOA) pain is caused by nociceptors, which are actually sensory nerve fiber endings that can detect stimuli to produce and transmit pain signals, and high levels of NGF in synovial tissue led to peripheral hyperalgesia in KOA. The purpose of this study is to investigate how sensory nerve fibers respond to the NGF/TrKA signal pathway and mediate the peripheral hyperalgesia in KOA rats.

Methods

Forty SD male rats were randomly divided into 4 groups: normal, KOA, KOA + NGF, and KOA + siRNA TrKA. KOA model rats were induced by anterior cruciate ligament transection (ACLT). Mechanical and cold withdrawal thresholds (MWT and CWT) were measured 4 times in each group. The synovial tissues were harvested on day 28, and the expressions of NGF, TrKA, TRPV1, IL-1β, and PGP9.5 were determined using western blot, qPCR, and immunofluorescence staining. The primary rat fibroblast-like synoviocytes (FLSs) and DRG cells were divided into 4 groups as in vivo. The expressions of NGF, TrKA, TRPV1, and CGRP in vitro were determined using western blot and qPCR.

Results

KOA and intra-articular injection with NGF protein increased both mRNA and protein levels, not only TRPV1, PGP 9.5, and IL-1β in the synovial tissue, but also TRPV1, PGP 9.5, and S100 in the DRG tissue, while above changes were partly reversed after siRNA TrKA intervention. Besides, siRNA TrKA could improve peripheral hyperalgesia and decreased the TRPV1 positive nerve fiber innervation in synovial tissue. The results in vitro were consistent with those in vivo.

Conclusion

This study showed the activation of the NGF/TrKA signaling pathway in KOA promoted the release of pain mediators, increased the innervation of sensory nerve fibers in the synovium, and worsened peripheral hyperalgesia. It also showed increased TRPV1 positive sensory innervation in KOA was mediated by NGF/TrKA signaling and exacerbated peripheral hyperalgesia.

Daily low-intensity pulsed ultrasound stimulation mitigates joint degradation and pain in a post-traumatic osteoarthritis rat model

Objectives

The aim of this study was to investigate the effects of low-intensity pulsed ultrasound (LIPUS) in a post-traumatic osteoarthritis (OA) rat model and in vitro.

Methods

Thirty-eight male, four-month-old Sprague Dawley rats were randomly assigned to Sham, Sham ​+ ​US, OA, and OA ​+ ​US. Sham surgery was performed to serve as a negative control, and anterior cruciate ligament transection was used to induce OA. Three days after the surgical procedures, Sham ​+ ​US and OA ​+ ​US animals received daily LIPUS treatment, while the rest of the groups received sham ultrasound (US) signals. Behavioral pain tests were performed at baseline and every week thereafter. After 31 days, the tissues were collected, and histological analyses were performed on knees and innervated dorsal root ganglia (DRG) neurons traced by retrograde labeling. Furthermore, to assess the activation of osteoclasts by LIPUS treatment, RAW264.7 ​cells were differentiated into osteoclasts and treated with LIPUS.

Results

Joint degradation in cartilage and bone microarchitecture were mitigated in OA ​+ ​US compared to OA. OA ​+ ​US showed improvements in behavioral pain tests. A significant increase of large soma-sized DRG neurons was located in OA compared to Sham. In addition, a greater percentage of large soma-sized innervated neurons were calcitonin gene-related peptide-positive. Daily LIPUS treatment suppressed osteoclastogenesis in vitro, which was confirmed via histological analyses and mRNA expression. Finally, lower expression of netrin-1, a sensory innervation-related protein, was found in the LIPUS treated cells.

Conclusion

Our findings demonstrate that early intervention using LIPUS treatment has protective effects from the progression of knee OA, including reduced tissue degradation, mitigated pain characteristics, improved subchondral bone microarchitecture, and less sensory innervation. Furthermore, daily LIPUS treatment has a suppressive effect on osteoclastogenesis, which may be linked to the suppression of sensory innervation in OA.

The translational potential of this article

This study presents a new potential for early intervention in treating OA symptoms through the use of LIPUS, which involves the suppression of osteoclastogenesis and the alteration of DRG profiles. This intervention aims to delay joint degradation and reduce pain.

MAGL inhibition relieves synovial inflammation and pain via regulating NOX4-Nrf2 redox balance in osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by cartilage injury, hyperplasia of bone and inflammatory lesions of synovium. Monoacylglycerol lipase (MAGL), a member of the α/β hydrolase superfamily, is involved in regulation of injury protection and immune-inflammation response. Autoinflammatory response of the synovium and the release of inflammatory mediators play critical roles in occurrence of early-stage OA. Fibroblast-like synoviocytes (FLSs) are resident mesenchymal cells of the synovial tissue. Considering that MAGL inhibition regulates the inflammatory signaling cascade, it is crucial to ascertain the biological effects and specific mechanisms of MAGL in alleviating inflammatory infiltration of OA FLSs. The aim of this study was to investigate the effect of MAGL on biological function in OA FLSs. Results from in vitro experiments showed that MAGL blockade not only effectively inhibited proliferation, invasion and migration of FLSs, but also downregulated expression of inflammatory-associated proteins. Sequencing results indicated that MAGL inhibition significantly suppressed NOX4-mediated oxidative stress, thus promoting Nrf2 nuclear accumulation and inhibiting generation of intracellular reactive oxygen species (ROS). Attenuation of NOX4 further alleviated redox dysplasia and ultimately improved tumor-like phenotypes, such as abnormal proliferation, migration and migration of FLSs. In vivo results corroborated this finding, with MAGL inhibition found to modulate pain and disease progression in an OA rat model. Collectively, these results indicate that MAGL administration is an ideal therapy treating OA.

Influence of Staphylococcus epidermidis on Collagen Crimp Patterns of Soft Tissue Allograft

BACKGROUND

Postoperative infections, commonly from Staphylococcus epidermidis, may result in anterior cruciate ligament graft failure and necessitate revision surgery. In biomechanical studies, S. epidermidis has been shown to establish biofilms on tendons and reduce graft strength.

PURPOSE/HYPOTHESIS

The goal of this study was to determine the effect of bacterial bioburden on the collagen structure of tendon. It was hypothesized that an increase in S. epidermidis biofilm would compromise tendon crimp, a pattern necessary for mechanical integrity, of soft tissue allografts.

STUDY DESIGN

Controlled laboratory study.

METHODS

Cultures of S. epidermidis were used to inoculate tibialis anterior cadaveric tendons. Conditions assessed included 5 × 105 colony-forming units or concentrated spent media from culture (no living bacteria). Incubation times of 30 minutes, 3 hours, 6 hours, and 24 hours were utilized. Second-harmonic generation imaging allowed for visualization of collagen autofluorescence. Crimp lengths were determined using ImageJ and compared based on incubation time.

RESULTS

Incubation time positively correlated with increasing S. epidermidis bioburden. Both fine and coarse crimp patterns lengthened with increasing incubation time. Significant coarse crimp changes were observed after only 30-minute incubations (P < .029), whereas significant fine crimp lengthening occurred after 6 hours (P < .0001). No changes in crimp length were identified after incubation in media lacking living bacteria.

CONCLUSION

The results of this study demonstrate that exposure to S. epidermidis negatively affects collagen crimp structure. Structural alterations at the collagen fiber level occur within 30 minutes of exposure to media containing S. epidermidis.

CLINICAL RELEVANCE

Our study highlights the need for antimicrobial precautions to prevent graft colonization and maximize graft mechanical strength.

Dexmedetomidine alleviates osteoarthritis inflammation and pain through the CB2 pathway in rats

As a common joint disease, osteoarthritis (OA) is often associated with chronic pain. Synovial inflammation is correlated with OA progression and pain. Synovial inflammation can produce a series of destructive substances, such as inflammatory factors and pain mediators, which aggravate cartilage injury and further accelerate the progression of OA. Although many studies investigated the effects of synovial inflammation on the onset and progression of OA, there are limited reports regarding slowing the progression of OA and relieving pain by modulating synovial inflammation. Therefore, there is an urgent need to search for safe and effective drugs to alleviate synovial inflammation. Dexmedetomidine, a selective α₂ agonist, has been shown to have anti-inflammatory and analgesic effects. However, its role and mechanism in OA remain unclear. Here, the effects and mechanisms of dexmedetomidine in OA synovial inflammation were investigated both in vivo and in vitro. We observed that dexmedetomidine stunted LPS-induced migration and invasion of FLSs and the expression of inflammatory factors by upregulating cannabinoid receptor type 2 (CB₂) expression. Surprisingly, the application of AM630 (CB₂ antagonist) reversed this therapeutic effect. The results of the animal experiments showed that dexmedetomidine reduced synovial inflammation and increased the pain threshold in an OA rat model. These preliminary results imply that dexmedetomidine may be an effective compound for OA treatment.

Assessment of osteoarthritis functional outcomes and intra-articular injection volume in the rat anterior cruciate ligament transection model

The rat surgical anterior cruciate ligament transection (ACLT) model is commonly used to investigate intra-articular osteoarthritis (OA) therapies, and histological assessment is often the primary outcome measure. However, histological changes do not always correlate well with clinical outcomes. Therefore, this study evaluated functional outcomes in the rat surgical ACLT model and compared intra-articular injection volumes ranging from 20 to 50 μl. Unilateral ACLT was surgically induced and static weight-bearing, mechanical allodynia, motor function, and gait were assessed in four groups of male, Sprague-Dawley rats (n = 6 per group). Intra-articular injections of 20 µl Dulbecco's phosphate-buffered saline (DPBS), 50 µl DPBS, or 50 µl of synthetic biomimetic boundary lubricant were administered once weekly for 3 weeks postoperatively. Structural changes were evaluated histologically at 20 weeks. Rat cadaver knees were injected with 20, 30, 40, or 50 µl of gadolinium solutions and were imaged using magnetic resonance imaging (MRI). Static weight-bearing, mechanical allodynia, and gait parameters in ACLT groups revealed differences from baseline and naïve controls for 4 weeks post-ACLT; however, these differences did not persist beyond 6 weeks. Different intra-articular DPBS injection volumes did not result in functional or histological changes; however, peri-articular leakage was documented via MRI following 50, 40, and 30 µl but not 20 µl gadolinium injections. Statement of clinical significance: Differences in functional parameters were predominantly restricted to early, postoperative changes in the rat surgical ACLT model despite evidence of moderate histologic OA at 20 weeks. Injection volumes of 20-30 µl are more appropriate for investigating intra-articular therapies in the rat knee.

Effect of bone marrow mesenchymal stem cell transplantation combined with lugua polypeptide injection on osteoarthritis in rabbit knee joint

PURPOSE

This study aimed to elucidate the effect of bone marrow mesenchymal stem cell (BMSC) transplantation combined with the administration of Lugua polypeptide injection into the knee joint cavity to treat knee osteoarthritis (KOA) in rabbits.

MATERIAL AND METHODS

Sixty white New Zealand rabbits were randomly divided into the blank, model, Lugua polypeptide, BMSC, and combined (Lugua polypeptide plus BMSC) groups, with 12 rabbits in each group. The mRNA and protein expression levels of cyclin D1, bcl-2, TIMP-1, p21, caspase-3, Bax, MMP-1, MMP-13, TLR-4, and NF-κB p65 in chondrocytes, and levels of IL-1, NO, TNF-α, and IL-6 in the synovial fluid were compared.

RESULTS

The severity of cartilage damage in the combined group was significantly less (P <0.01). Compared to the MG, the mRNA and protein expression levels of cyclin D1, bcl-2 and TIMP-1 in chondrocytes of the three other groups were significantly increased, while those of p21, caspase-3, Bax, MMP-1, MMP-13, TLR-4, and NF-κB p65 in the chondrocytes and levels of IL-1, NO, TNF-α, and IL-6 in the synovial fluid of the three other groups were significantly reduced (P <0.05). The aforementioned indicators in the combined group were significantly better than those of the Lugua polypeptide and BMSCs groups (P <0.05).

CONCLUSIONS

BMSC transplantation combined with Lugua polypeptide injection may improve KOA-related cartilage tissue damage in rabbits.

Clinical-like cryotherapy in acute knee arthritis of the knee improves inflammation signs, pain, joint swelling, and motor performance in mice

To assess the effects of clinical-like cryotherapy on inflammatory signs (in vivo neutrophil migration, cytokines, and joint inflammation), pain, joint swelling, balance, and motor coordination in mice with knee arthritis. Young C57BL/6 mice were randomly divided into three groups (8 to 10 mice per group): Control group: mice with no intervention; antigen-induced arthritis (AIA) group: mice sensitized and immunized with intra-articular (i.a.) injection of methylated bovine serum albumin (mBSA); and AIA + cryotherapy group: mice sensitized, immunized with i.a. injection of mBSA, and submitted to a clinical-like cryotherapy protocol. After 21 days of sensitization, AIA and AIA + cryotherapy groups received i.a. injection of mBSA (100 μg/joint) to induce joint inflammation, and a clinical-like cryotherapy protocol was applied to AIA + cryotherapy group (crushed ice bag, two cryotherapy sessions of 20 min every two hours). Experimental analysis was conducted in the initial (immediately after i.a. injection of mBSA) and final periods (two hours after the second cryotherapy session). The number of synovial fluid neutrophils, cytokine levels, joint histology, pain, joint swelling, and motor performance were also analyzed. Our results showed that clinical-like cryotherapy in mice with acute knee arthritis reduced inflammatory signs, pain, and joint swelling, and improved balance and motor coordination.

Characteristics of sensory innervation in synovium of rats within different knee osteoarthritis models and the correlation between synovial fibrosis and hyperalgesia

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Synovial fibrosis was positively correlated with pain sensitivity in KOA rats.

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Synovial fibrosis was most prominent in DMM group 14 days after modeling.

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ACLT replaced DMM to be the most typical at 28 days after modeling.

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Increased synovial sensory innervation followed the same trend as fibrosis.

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ACLT is more applicable for KOA pain research.

Introduction

Knee osteoarthritis (KOA) showed synovial fibrosis and hyperalgesia, although the correlation between the two is unclear. Besides, the specific changes of sensory innervation in animal models are still controversial, which makes it difficult to choose the modeling methods for KOA pain research.

Objectives

Study the characteristics of sensory innervation within three commonly used KOA rat models and the correlation between synovial fibrosis and hyperalgesia.

Methods

KOA models were induced by destabilization of medial meniscus (DMM), anterior cruciate ligament transection (ACLT), and monoiodoacetate (MIA), respectively. Mechanical, cold and thermal withdrawal threshold (MWT, CWT and TWT) were measured. The harvested tissues were used for pathological sections, immunofluorescence and quantitative analysis.

Results

KOA synovium showed more type I collagen deposition, increased expression of CD31, VEGF and TGF-β. These changes were most pronounced in surgical models, with DMM presenting the most prominent at Day 14 and ACLT at Day 28. Day 14, changes in mechanical hyperalgesia and cold hyperalgesia were most typical in DMM model and statistically different from MIA. There was a negative correlation between the percentage of type I collagen and MWT value (r = −0.88), as well as CWT value (r = −0.95). DMM synovium showed more axonal staining, upregulated CGRP, TRPV1, NGF and Netrin1 compared with MIA. Above changes were also observed at Day 28, but ACLT replaced DMM as the most typical. In DRG, only the levels of CGRP and NGF were different among KOA models at Day 14, and the highest in DMM, which was statistically different compared with MIA.

Conclusions

This study described the details of sensory innervation in different KOA model of rats, and the degree of synovial fibrosis was positively correlated with the pain sensitivity of KOA model rats. Additionally, surgical modeling especially ACLT method is more recommended for KOA pain research.