Associations between proinflammatory cytokines in the synovial fluid and radiographic grading and pain-related scores in 47 consecutive patients with osteoarthritis of the knee

Molecular signaling pathways in osteoarthritis and biomaterials for cartilage regeneration: a review

Osteoarthritis is a prevalent degenerative joint disease characterized by cartilage degradation, synovial inflammation, and subchondral bone alterations, leading to chronic pain and joint dysfunction. Conventional treatments provide symptomatic relief but fail to halt disease progression. Recent advancements in biomaterials, molecular signaling modulation, and gene-editing technologies offer promising therapeutic strategies. This review explores key molecular pathways implicated in osteoarthritis, including fibroblast growth factor, phosphoinositide 3-kinase/Akt, and bone morphogenetic protein signaling, highlighting their roles in chondrocyte survival, extracellular matrix remodeling, and inflammation. Biomaterial-based interventions such as hydrogels, nanoparticles, and chitosan-based scaffolds have demonstrated potential in enhancing cartilage regeneration and targeted drug delivery. Furthermore, CRISPR/Cas9 gene editing holds promise in modifying osteoarthritis-related genes to restore cartilage integrity. The integration of regenerative biomaterials with precision medicine and molecular therapies represents a novel approach for mitigating osteoarthritis progression. Future research should focus on optimizing biomaterial properties, refining gene-editing efficiency, and developing personalized therapeutic strategies. The convergence of bioengineering and molecular science offers new hope for improving joint function and patient quality of life in osteoarthritis management.

Latilactobacillus sakei LB-P12 Ameliorates Osteoarthritis by Reducing Cartilage Degradation and Inflammation via Regulation of NF-κB/HIF-2α Pathway

Osteoarthritis (OA) is a degenerative joint disease characterized by cartilage degradation, inflammation, and pain. Recent studies highlight the gut-joint axis, suggesting that gut microbiota influences joint health by modulating systemic inflammation and immune responses. This study investigated the effects of Latilactobacillus sakei LB-P12 on cartilage degradation and joint inflammation in a monosodium iodoacetate induced rat model of OA. OA severity was assessed through histological analysis, weight-bearing and micro-computed tomography (Micro-CT). Serum Interleukin 6 (IL-6) and prostaglandin E2 (PGE2) levels, along with interleukin-1β (Il1b) and matrix metalloproteinase 13 (Mmp13) expression in knee tissue, were measured. Then, the effect of L. sakei LB-P12 on inflammatory responses in interleukin-1β pretreated chondrocytes has also been investigated. The L. sakei LB-P12 improved weight-bearing distribution and reduced cartilage damage based on histological scores. Micro-CT showed increased bone volume fraction and bone mineral density. Treatment reduced serum IL-6 and PGE2 levels and suppressed Il1b and Mmp13 expression in knee tissues. In vitro, L. sakei LB-P12 inhibited lipopolysaccharide induced pro-inflammatory cytokines and nitric oxide production in macrophages. It also downregulated the expression of Epas1, which encodes hypoxia-inducible factor-2α (HIF-2α), and Mmp13 in IL-1β stimulated chondrocytes. L. sakei LB-P12 shows potential as a dietary supplement for alleviating OA-related pain, cartilage degradation, and inflammation by suppressing the nuclear factor-κB (NF-κB)/ HIF-2α pathway.

Pain Assessment in Osteoarthritis: Present Practices and Future Prospects Including the Use of Biomarkers and Wearable Technologies, and AI-Driven Personalized Medicine

Osteoarthritis (OA) is a highly prevalent chronic joint disorder affecting ~600 million individuals worldwide and is characterized by complex pain mechanisms that significantly impair patient quality of life. Challenges exist in accurately assessing and measuring pain in OA due to variations in pain perception among individuals and the heterogeneous nature of the disease. Conventional pain assessment methods, such as patient-reported outcome measures and clinical evaluations, often fail to fully capture the heterogeneity of pain experiences among individuals with OA. This review will summarize and evaluate current methods of pain assessment in OA and highlight future directions for standardized pain assessment. We discuss the role of animal models in enhancing our understanding of OA pain pathophysiology and highlight the necessity of translational research to advance pain assessment strategies. Key challenges explored include identifying phenotypes of pain susceptibility, integrating biomarkers into clinical practice, and adopting personalized pain management approaches through the incorporation of multi-modal data and multilevel analysis. We underscore the imperative for continued innovation in pain assessment and management to improve outcomes for patients with OA.

Functional Attributes of Synovial Fluid from Osteoarthritic Knee Exacerbate Cellular Inflammation and Metabolic Stress, and Fosters Monocyte to Macrophage Differentiation

Background: Besides conventional norms that recognize synovial fluid (SF) as a joint lubricant, nutritional channel, and a diagnostic tool in knee osteoarthritis (kOA), based on the authors previous studies, this study aims to define functional role of SF in kOA. Methods: U937, a monocytic, human myeloid cell line, was induced with progressive grades of kOA SF, and the induction response was assessed on various pro-inflammatory parameters. This 'SF challenge test model' was further extended to determine the impact of SF on U937 differentiation using macrophage-specific markers and associated transcription factor genes. Mitochondrial membrane potential changes in SF-treated cells were evaluated with fluorescent JC-1 probe. Results: a significant increase in nitric oxide, matrix metalloproteinase (MMP) 1, 13, and vascular endothelial growth factor (VEGF)-1 was noted in the induced cells. A marked increase was seen in CD68, CD86, and the transcription factors -activator protein (AP)-1, interferon regulatory factor (IRF)-1, and signal transducer and activator of transcription (STAT)-6 in the SF-treated cells indicating active monocytes to macrophage differentiation. Reduced mitochondrial membrane potential was reflected by a reduced red-to-green ratio in JC-1 staining. Conclusions: these results underline the active role of OA SF in stimulating and maintaining inflammation in joint cells, fostering monocyte differentiation into pro-inflammatory macrophages. The decline in the membrane potential suggestive of additional inflammatory pathway in OA via the release of pro-apoptotic factors and damaged associated molecular patterns (DAMPs) within the cells. Overall, biochemical modulation of SF warrants a potential approach to intervene inflammatory cascade in OA and mitigate its progression.

Cell and transcriptomic diversity of infrapatellar fat pad during knee osteoarthritis

OBJECTIVES

In this study, we employ a multiomic approach to identify major cell types and subsets, and their transcriptomic profiles within the infrapatellar fat pad (IFP), and to determine differences in the IFP based on knee osteoarthritis (KOA), sex and obesity status.

METHODS

Single-nucleus RNA sequencing of 82 924 nuclei from 21 IFPs (n=6 healthy control and n=15 KOA donors), spatial transcriptomics and bioinformatic analyses were used to identify contributions of the IFP to KOA. We mapped cell subclusters from other white adipose tissues using publicly available literature. The diversity of fibroblasts within the IFP was investigated by bioinformatic analyses, comparing by KOA, sex and obesity status. Metabolomics was used to further explore differences in fibroblasts by obesity status.

RESULTS

We identified multiple subclusters of fibroblasts, macrophages, adipocytes and endothelial cells with unique transcriptomic profiles. Using spatial transcriptomics, we resolved distributions of cell types and their transcriptomic profiles and computationally identified putative cell-cell communication networks. Furthermore, we identified transcriptomic differences in fibroblasts from KOA versus healthy control donor IFPs, female versus male KOA-IFPs and obese versus normal body mass index (BMI) KOA-IFPs. Finally, using metabolomics, we defined differences in metabolite levels in supernatants of naïve, profibrotic stimuli-treated and proinflammatory stimuli-treated fibroblasts from obese compared to normal BMI KOA-IFPs.

CONCLUSIONS

Overall, by employing a multiomic approach, this study provides the first comprehensive map of the cellular and transcriptomic diversity of human IFP and identifies IFP fibroblasts as key cells contributing to transcriptomic and metabolic differences related to KOA disease, sex or obesity.

A Systematic Review and Meta-Analysis of Stem Cell Therapies for Pain in Diabetic Neuropathy, Osteoarthritis, and Spinal Cord Injuries

PURPOSE OF REVIEW

The use of stem cell therapy is a rapidly evolving and progressing frontier of science that has been used to treat illnesses such as malignancies, immunodeficiencies, and metabolic syndromes. This review aims to give an overview of the use of stem cell therapy in the treatment of pain caused by diabetic neuropathy, osteoarthritis, and other spinal cord pathologies.

RECENT FINDINGS

Pain is defined as a generalized or localized feeling of distress related to a physical or emotional stimulus and can be caused by a multitude of pathologies. The field of pain management has explored many strategies such as gene therapies, neuromodulation, platelet-rich plasma, and numerous pharmacotherapies. The approach to the delivery of these strategies has varied, with the method of stem cell therapy delivery being the focus of this present investigation. In addition, we combined several different studies to analyze the effects of stem cell therapies and improvement in pain scores quantified by the visual analog scale (VAS). The overall results showed a mean difference of -2.58, suggesting that the stem cell treatment group had a lower VAS score at 6 months compared to the control group. The use of different types of stem cells, such as pluripotent and mesenchymal stem cells, play a critical role in the care of cases suffering from pain. Effective delivery methods are evolving and can transform treatment options in the future, for which large cohort studies are warranted.

Tumor Necrosis Factor-Alpha (TNF-α) and Interleukin-6 (IL-6) Cytokines in the Injured Meniscus of Patients With Knee Subchondral Insufficiency Fractures: A Potential Association With Preoperative Pain

Background The development of subchondral insufficiency fracture (SIF) of the knee following a medial meniscal posterior root tear (MMPRT) results in pain and limitations in daily activities. Pain in patients with SIF is associated with local chronic inflammation in the knee joint, involving the production of inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and nerve growth factor (NGF). This study aimed to quantify the levels of proinflammatory cytokines (TNF-α, IL-6, NGF) in the injured medial meniscus (IMM) tissue of patients with knee SIF and examine their potential association with preoperative pain and functional scores. Methods Meniscus samples were collected from 17 patients with knee SIF (mean age: 62.8 ± 2.6 years) who underwent total knee arthroplasty. The tissue samples were categorized into two groups based on the degree of injury: the IMM and the non-injured healthy lateral meniscus (HLM) as the control group. The levels of TNF-α, IL-6, and NGF in both groups were measured using an enzyme-linked immunosorbent assay (ELISA), and differences were evaluated with the Wilcoxon signed-rank test. The association between preoperative functional and pain scores and the levels of each inflammatory mediator was analyzed using Spearman's correlation. Results TNF-α and IL-6 were detectable in the meniscus tissues, while NGF levels were negligible. The levels of TNF-α and IL-6 were significantly higher in the IMM group compared to the HLM group (p<0.05). Furthermore, TNF-α and IL-6 levels in the IMM group were correlated with the pain subscale of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Conclusions This study demonstrated a significant increase in TNF-α and IL-6 cytokine levels in the IMM compared to the non-injured healthy meniscus. These findings suggest that inflammatory mediators within the IMM may be associated with preoperative pain in patients with SIF in the medial femoral condyle resulting from MMPRT.

Clinical and omics biomarkers in osteoarthritis diagnosis and treatment

Osteoarthritis (OA) is a prevalent degenerative joint disease that significantly impacts the quality of life for hundreds of millions, and is a major cause of disability. Despite this, diagnostic and therapeutic options for OA are still limited. With advances in molecular biology, an increasing number of OA biomarkers have been identified, which not only enhances our understanding of OA pathogenesis, but also offers new approaches for OA diagnosis and treatment. This review discussed the research progress on traditional OA biomarkers, and analyzed the application of various omics, including genomics, transcriptomics, proteomics, and metabolomics, in the diagnosis and treatment of OA. Furthermore, we explored how integrating multi-omics methods can reveal interactions among different biomolecules and their roles in the development of OA. This emerging interdisciplinary approach not only provides a more comprehensive understanding of the fundamental biological characteristics of OA, but also aids in identifying new integrated biomarkers, thereby allowing for more accurate predictions of disease progression and treatment responses. The identification and development of biomarkers offer new perspectives in understanding OA, enhancing the specificity and sensitivity of biological diagnostic markers, providing a basis for the design of targeted drugs, and ultimately advancing the development of precision diagnosis and treatment strategies in clinical OA. This study provides an overview of both commonly used and emerging biomarkers of OA which is beneficial for a more accurate, timely, effective clinical diagnosis and treatment for OA.

Synovial mast cells and osteoarthritis: Current understandings and future perspectives

Osteoarthritis (OA) is a prevalent joint disease worldwide that significantly impacts the quality of life of individuals, particularly those in middle-aged and elderly populations. OA was initially considered as non-inflammatory arthritis, but recent studies have identified a substantial number of immune responses in OA, leading to the recognition of inflammation as a key factor in its pathogenesis. An increasing number of studies have found that mast cell (MC) and MC-secreted inflammatory mediators and cytokines are notably increased in the synovial fluid of OA patients, indicating a potential association between MCs and the onset and progression of synovial inflammation. The present review aims to summarize the significance and mechanism of MCs in the pathogenesis of OA. Meanwhile, we also discuss the clinical potential of using MCs as therapeutic target for OA therapy. Modulating the activities of MCs or the mediators of MCs in the synovial fluid inflammatory microenvironment will be promising new options for the treatment of OA.

Exploring the Efficacy of Joint Lavage in Knee Osteoarthritis: A Focus on Cytokines, Degrading Enzymes, and Oxidative Stress

PURPOSE/AIM

This study aimed to assess the effectiveness of joint lavage in managing knee osteoarthritis (OA) by evaluating its effect on pain relief, inflammatory markers, cartilage-degrading enzymes, and oxidative stress.

METHODS

Seventy patients with Kellgren-Lawrence grade 2 or 3 knee OA were selected for this single-center study. Joint lavage was performed, and pain and function were measured using the visual analog scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores at baseline and 24 weeks postintervention. Synovial fluid samples were collected at baseline, before lavage, and 24 weeks postintervention. Samples were stored at -80°C and analyzed in batches to minimize variability. At the time of analysis, the samples were thawed and evaluated for levels of proinflammatory cytokines, interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α), matrix metalloproteinase-3 (MMP-3), and total oxidant status (TOS), and oxidative stress index (OSI).

RESULTS

Postintervention, VAS, and WOMAC scores significantly decreased (P < 0.001), with 100% achieving the minimal clinically important difference (MCID). Patient acceptable symptom state (PASS) rates varied: VAS (80%), WOMAC pain (50%), function (81.4%), and total (84.3%). Cytokine levels (IL-1β, IL-6, TNF-α) and MMP-3 significantly decreased (P < 0.001), along with TOS and OSI. Baseline TNF-α, IL-6, and IL-1β levels were significantly correlated with improvements in VAS and WOMAC scores. Moderate correlations were observed between reductions in IL-6/TNF-α and improvements in VAS/WOMAC. No significant associations were found between confounders and outcomes.

CONCLUSIONS

Joint lavage resulted in marked pain relief and functional improvement while significantly reducing inflammatory markers, cartilage-degrading enzymes, and oxidative stress.

Immunomodulation and fibroblast dynamics driving nociceptive joint pain within inflammatory synovium: Unravelling mechanisms for therapeutic advancements in osteoarthritis

OBJECTIVE

Synovitis is a widely accepted sign of osteoarthritis (OA), characterised by tissue hyperplasia, where increased infiltration of immune cells and proliferation of resident fibroblasts adopt a pro-inflammatory phenotype, and increased the production of pro-inflammatory mediators that are capable of sensitising and activating sensory nociceptors, which innervate the joint tissues. As such, it is important to understand the cellular composition of synovium and their involvement in pain sensitisation to better inform the development of effective analgesics.

METHODS

Studies investigating pain sensitisation in OA with a focus on immune cells and fibroblasts were identified using PubMed, Web of Science and SCOPUS.

RESULTS

In this review, we comprehensively assess the evidence that cellular crosstalk between resident immune cells or synovial fibroblasts with joint nociceptors in inflamed OA synovium contributes to peripheral pain sensitisation. Moreover, we explore whether the elucidation of common mechanisms identified in similar joint conditions may inform the development of more effective analgesics specifically targeting OA joint pain.

CONCLUSION

The concept of local environment and cellular crosstalk within the inflammatory synovium as a driver of nociceptive joint pain presents a compelling opportunity for future research and therapeutic advancements.

Neuroinflammation in osteoarthritis: From pain to mood disorders

Osteoarthritis (OA) is the most common form of musculoskeletal disease, and its prevalence is increasing due to the aging of the population. Chronic pain is the most burdensome symptom of OA that significantly lowers patients' quality of life, also due to its frequent association with emotional comorbidities, such as anxiety and depression. In recent years, both chronic pain and mood alterations have been linked to the development of neuroinflammation in the peripheral nervous system, spinal cord and supraspinal brain areas. Thus, mechanisms at the basis of the development of the neuroinflammatory process may indicate promising targets for novel treatment for pain and affective comorbidities that accompany OA. In order to assess the key role of neuroinflammation in the maintenance of chronic pain and its potential involvement in development of psychiatric components, the monoiodoacetate (MIA) model of OA in rodents has been used and validated. In the present commentary article, we aim to summarize up-to-date results achieved in this experimental model of OA, focusing on glia activation and cytokine production in the sciatic nerve, dorsal root ganglia (DRGs), spinal cord and brain areas. The association of a neuroinflammatory state with the development of pain and anxiety- and depression-like behaviors are discussed. Results suggest that cells and molecules involved in neuroinflammation may represent novel targets for innovative pharmacological treatments of OA pain and mood comorbidities.

Green Light Exposure Reduces Primary Hyperalgesia and Proinflammatory Cytokines in a Rodent Model of Knee Osteoarthritis: Shedding Light on Sex Differences

Knee osteoarthritis (OA) often causes chronic pain that disproportionately affects females. Proinflammatory cytokines TNF-α, IL-1β, and IL-6 are key effectors of OA pathological changes. Green light shows potential as an alternative intervention for various pain conditions. However, no studies have investigated green light's analgesic effects in both sexes in chronic knee OA. We induced unilateral knee OA with intra-articular injection of monoiodoacetate (MIA) in male and female Sprague-Dawley rats. Two days post-injection, the rats were exposed to green-light-emitting diodes (GLED) or ambient room light eight hours daily for 24 days. Knee mechanical sensitivity was assessed using a small animal algometer. Blood serum concentrations of TNF-α, IL-1β, IL-6, and IL-10 were quantified at baseline and 23 days post-injection. MIA injection decreased the knee mechanical thresholds of the male and female rats. GLED exposure attenuated mechanical hypersensitivity in both sexes compared to the controls; however, GLED-induced analgesia occurred sooner and with greater magnitude in males than in females. In both sexes, the analgesic effects of green light lasted 5 days after the final GLED session. Finally, GLED exposure reversed the elevation of serum proinflammatory cytokines. These findings suggest that GLED exposure reduces primary hyperalgesia in OA, potentially by lowering proinflammatory cytokines, and indicate sex differences in GLED-induced analgesia.

Distinct patterns of cytokines, chemokines, and growth factors in synovial fluid after ACL injury in comparison to osteoarthritis

This study analyzed knee synovial fluid after anterior cruciate ligament (ACL) tear and in osteoarthritis (OA) to test the hypotheses that concentrations of cytokines, chemokines, and growth factors differ (a) by diagnosis and (b) after ACL tear by time from injury and presence/absence of concomitant meniscus tear. Synovial fluid samples were collected from two groups, ACL tears (with or without meniscus tear) (N = 13) and Kellgren-Lawrence grade 3 and 4 OA (N = 16), undergoing clinically indicated aspiration of the knee joint. Multiple cytokines, chemokines, and growth factors were assessed using a multiplexed 45-protein panel. Comparisons were made for the concentrations of all molecules between ACL tear and OA patients, isolated versus combined ACL and meniscus tears, and categorized by time from injury: acute or early subacute (<15 days, N = 8) versus late subacute or chronic (>15 days and <3 months, N = 5). ACL tear patients have higher levels of six molecules (IL-4, IL-5, IL-13, PlGF-1, bNGF, TNF-α) in knee synovial fluid compared to OA patients. Isolated ACL tears express higher levels of IL-4, IL-13 and IFN-γ and lower levels of IL-7 than ACL tears with a concomitant meniscus tear. SDF-1α, PlGF-1, IL-1RA, HGF, bNGF, and BDNF levels are elevated immediately after injury and drop off significantly in the late subacute phase (after 15 days). Synovial fluid from knees with ACL tears have elevated metabolic activity compared to knees with OA. The cytokine profiles after ACL tears are influenced by the time from injury and the presence of meniscus tears. These findings offer valuable insights into the levels of cytokines, chemokines, and growth factors in the knee after ACL injury, information which may have important implications for the diagnosis, prognosis and treatment of this common pathology.

PLOD2 gene expression in infrapatellar fat pad is correlated with fat mass in obese patients with end-stage knee osteoarthritis

Objective

To investigate associations between obesity-linked systemic factors and gene expression indicative for the inflammatory and fibrotic processes in the infrapatellar fat pad (IFP), in a population of obese patients with end-stage knee osteoarthritis (KOA).

Methods

We collected human IFPs from 48 patients with a mean body mass index (BMI) of 35.44 ​kg/m2 during total knee replacement procedures. These patients were part of a randomized controlled trial and met the criteria of having OA and a BMI of ≥30 ​kg/m2. Blood samples were collected to assess serum levels of glucose, total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, and leptin. Total body composition was measured using dual-energy X-ray absorptiometry. Gene expressions of IL6, TNFA, COL1A1, IL1B, ASMA, PLOD2 in the IFP were analyzed.

Results

Univariate analysis resulted in a positive correlation between BMI and procollagen-lysine,2-oxoglutarate 5-dioxygenase 2 (PLOD2) expression (r2 ​= ​0.13). In univariate analyses of obesity-linked systemic factors and PLOD2, significant correlations were found for lean mass (r2 ​= ​0.20), fat mass (r2 ​= ​0.20), serum cholesterol (r2 ​= ​0.17), serum triglycerides (r2 ​= ​0.19) and serum leptin (r2 ​= ​0.10). A multiple linear regression model indicated fat mass to be a strong predictor of PLOD2 production in the IFP (r2 ​= ​0.22, P ​= ​0.003).

Conclusion

Our study demonstrates the positive association between fat mass and PLOD2 expression in the IFP of obese end-stage knee OA patients. This may indicate that within this patient population the fibrotic process in the IFP is influenced by systemic adipose tissue, next to local inflammatory processes.

Fatty acid binding protein 5 inhibition attenuates pronociceptive cytokine/chemokine expression and suppresses osteoarthritis pain: A comparative human and rat study

OBJECTIVE

Osteoarthritis (OA) is often accompanied by debilitating pain that is refractory to available analgesics due in part to the complexity of signaling molecules that drive OA pain and our inability to target these in parallel. Fatty acid binding protein 5 (FABP5) is a lipid chaperone that regulates inflammatory pain; however, its contribution to OA pain has not been characterized.

DESIGN

This combined clinical and pre-clinical study utilized synovial tissues obtained from subjects with end-stage OA and rats with monoiodoacetate-induced OA. Cytokine and chemokine release from human synovia incubated with a selective FABP5 inhibitor was profiled with cytokine arrays and ELISA. Immunohistochemical analyses were conducted for FABP5 in human and rat synovium. The efficacy of FABP5 inhibitors on pain was assessed in OA rats using incapacitance as an outcome. RNA-seq was then performed to characterize the transcriptomic landscape of synovial gene expression in OA rats treated with FABP5 inhibitor or vehicle.

RESULTS

FABP5 was expressed in human synovium and FABP5 inhibition reduced the secretion of pronociceptive cytokines (interleukin-6 [IL6], IL8) and chemokines (CCL2, CXCL1). In rats, FABP5 was upregulated in the OA synovium and its inhibition alleviated incapacitance. The transcriptome of the rat OA synovium exhibited >6000 differentially expressed genes, including the upregulation of numerous pronociceptive cytokines and chemokines. FABP5 inhibition blunted the upregulation of the majority of these pronociceptive mediators.

CONCLUSIONS

FABP5 is expressed in the OA synovium and its inhibition suppresses pronociceptive signaling and pain, indicating that FABP5 inhibitors may constitute a novel class of analgesics to treat OA.

Impact of autologous platelet-rich plasma therapy vs. hyaluronic acid on synovial fluid biomarkers in knee osteoarthritis: a randomized controlled clinical trial

Objective

Observe the effects of platelet-rich plasma (PRP) therapy on inflammatory cytokines in the synovial fluid of the knee joint of patients with KOA, and explore the effects of PRP intra-articular injection on the inflammation of the knee joint environment and the possible mechanism of action.

Methods

Seventy patients were randomized to undergo three blinded weekly intra-articular injections of PRP or hyaluronic acid (HA). The concentrations of inflammatory cytokines, including interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, IL-8, IL-17A, IL-17F, IL-4, IL-5, and IL-10, in the synovial fluid were evaluated before the intervention and 1 month after the third injection. The Western Ontario and McMaster University (WOMAC) and visual analog scale (VAS) scores were used to assess pain and functional status of the knee joints in both groups before the intervention, immediately post-intervention, and 1, 3, 6, and 12 months after the intervention.

Results

Baseline characteristics were similar in both groups with no statistical difference. The IL-6, IL-1β, TNF-α, IL-17A, and IL-10 levels in the synovial fluid of the observation group decreased significantly after, vs. before, the intervention (p < 0.05), whereas the IL-8, IL-17F, and IL-4 levels decreased (p > 0.05) and IL-5 levels increased (p > 0.05). There was no statistically significant difference between inflammatory cytokine levels in the synovial fluid of the samples from the control group before and after the intervention (p > 0.05). There were no statistically significant differences between the two groups immediately after intervention (p > 0.05). At 1, 3, 6, and 12 months after intervention, the WOMAC and VAS scores were significantly better in the observation group than in the control group (p < 0.05).

Conclusion

Platelet plasma therapy can reduce the concentrations of inflammatory cytokines IL-6, IL-1β, TNF-α, IL-17A, and IL-10 in the synovial fluid of KOA patients, reduce the expression levels of IL-8, IL-17F, and IL-4, clear the pro-inflammatory factors, improve the inflammatory environment of the affected knee joint, and alleviate pain caused by inflammation. Thus, alleviating pain and improving knee function in patients with KOA.

Better post-operative outcomes at 1-year follow-up are associated with lower levels of pre-operative synovitis and higher levels of IL-6 and VEGFA in unicompartmental knee arthroplasty patients

PURPOSE

Osteoarthritis (OA) is associated with inflammation, and residual inflammation may influence outcomes following knee arthroplasty. This may be more relevant for patients undergoing unicompartmental knee arthroplasty (UKA) due to larger remaining areas of native tissue. This study aimed to: (1) characterise inflammatory profiles for medial UKA patients and (2) investigate whether inflammation markers are associated with post-operative outcomes.

METHODS

This prospective, observational study has national ethics approval. Bloods, synovial fluid, tibial plateaus and synovium were collected from medial UKA patients in between 1 January 2021 and 31 December 2021. Cytokine and chemokine concentrations in serum and synovial fluid (SF) were measured with multiplexed assays. Disease severity of cartilage and synovium was assessed using validated histological scores. Post-operative outcomes were measured with Oxford Knee Score (OKS), Forgotten Joint Score (FJS-12) and pain scores.

RESULTS

The study included 35 patients. SF VEGFA was negatively correlated with pre-operative pain at rest (r - 0.5, p = 0.007), and FJS-12 at six-week (r 0.44, p = 0.02), six-month (r 0.61, p < 0.01) and one-year follow-up (r 0.63, p = 0.03). Serum and SF IL-6 were positively correlated with OKS at early follow-up (serum 6 weeks, r 0.39, p = 0.03; 6 months, r 0.48, p < 0.01; SF 6 weeks, r 0.35, p = 0.04). At six weeks, increased synovitis was negatively correlated with improvements in pain at rest (r - 0.41, p = 0.03) and with mobilisation (r - 0.37, p = 0.047).

CONCLUSION

Lower levels of synovitis and higher levels of IL-6 and VEGFA were associated with better post-operative outcomes after UKA, which could be helpful for identifying UKA patients in clinical practice.

LEVEL OF EVIDENCE

Level IV case series.

Two Amnion-Derived Mesenchymal Stem-Cells Injections to Osteoarthritic Elbows in Dogs-Pilot Study

The aim of the study was to investigate the potential of cell-based regenerative therapy for elbow joints affected by osteoarthritis. Interest was focused on two intra-articular applications of amnion-derived mesenchymal stem cells (A-MSCs) to a group of different breeds of dogs with elbow osteoarthritis (13 joints). Two injections were performed 14 days apart. We evaluated synovial fluid biomarkers, such as IFN-γ, IL-6, IL-15, IL-10, MCP-1, TNF-α, and GM-CSF, by multiplex fluorescent micro-bead immunoassay in the treated group of elbows (n = 13) (day 0, day 14, and day 28) and in the control group of elbows (n = 9). Kinematic gait analysis determined the joint range of motion (ROM) before and after each A-MSCs application. Kinematic gait analysis was performed on day 0, day 14, and day 28. Kinematic gait analysis pointed out improvement in the average range of motion of elbow joints from day 0 (38.45 ± 5.74°), day 14 (41.7 ± 6.04°), and day 28 (44.78 ± 4.69°) with statistical significance (p < 0.05) in nine elbows. Correlation analyses proved statistical significance (p < 0.05) in associations between ROM (day 0, day 14, and day 28) and IFN-γ, IL-6, IL-15, MCP-1, TNF-α, and GM-CSF concentrations (day 0, day 14, and day 28). IFN-γ, IL-6, IL-15, MCP-1, GM-CSF, and TNF- α showed negative correlation with ROM at day 0, day 14, and day 28, while IL-10 demonstrated positive correlation with ROM. As a consequence of A-MSC application to the elbow joint, we detected a statistically significant (p < 0.05) decrease in concentration levels between day 0 and day 28 for IFN-γ, IL-6, and TNF-α and statistically significant increase for IL-10. Statistical significance (p < 0.05) was detected in TNF-α, IFN-γ, and GM-CSF concentrations between day 14 and the control group as well as at day 28 and the control group. IL-6 concentrations showed statistical significance (p < 0.05) between day 14 and the control group.

Methylsulfonylmethane Improves Knee Quality of Life in Participants with Mild Knee Pain: A Randomized, Double-Blind, Placebo-Controlled Trial

Methylsulfonylmethane (MSM) is a food ingredient present in small amounts in many foods, and its anti-inflammatory effects have been reported. We conducted a randomized, double-blind, placebo-controlled trial of oral consumption of MSM on mild pain of the knee joint in healthy Japanese participants. A total of 88 participants were enrolled in this study and randomly assigned to MSM consumption (n = 44) and placebo control (n = 44) groups. Both groups of participants took 10 tablets, each containing 200 mg MSM or lactose, per day for 12 weeks. The primary outcome of this study was measured values of the total score of the Japanese Knee Osteoarthritis Measure (JKOM) at 12 weeks after the test sample consumption. Safety evaluation was performed through physical examination, urine analysis, peripheral blood test, and medical interview. The total scores at 12 weeks in the MSM and placebo groups as the primary outcome were significantly different (p = 0.046). The health condition of JKOM also improved after MSM consumption (p = 0.032). The questionnaire results also suggested improvement in the knee and systemic health. This study indicated that MSM oral consumption improved both knee and systemic health conditions in healthy participants who experienced mild pain in the knee joint.

Root Canal Infection and Its Impact on the Oral Cavity Microenvironment in the Context of Immune System Disorders in Selected Diseases: A Narrative Review

The oral cavity has a specific microenvironment, and structures such as teeth are constantly exposed to chemical and biological factors. Although the structure of the teeth is permanent, due to exposure of the pulp and root canal system, trauma can have severe consequences and cause the development of local inflammation caused by external and opportunistic pathogens. Long-term inflammation can affect not only the local pulp and periodontal tissues but also the functioning of the immune system, which can trigger a systemic reaction. This literature review presents the current knowledge on root canal infections and their impact on the oral microenvironment in the context of immune system disorders in selected diseases. The result of the analysis of the literature is the statement that periodontal-disease-caused inflammation in the oral cavity may affect the development and progression of autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, or Sjogren's syndrome, as well as affecting the faster progression of conditions in which inflammation occurs such as, among others, chronic kidney disease or inflammatory bowel disease.

Human synovial fluid interleukin-6, but not type II collagen breakdown, positively correlated with pain after anterior cruciate ligament injury and reconstruction

Anterior cruciate ligament (ACL) injury initiates a biochemical cascade thought to contribute to the onset and progression of posttraumatic osteoarthritis (PTOA). Interleukin-1ß (IL-1ß), IL-6, and C-telopeptide fragments of type II collagen (CTX-II) are implicated in joint inflammation and cartilage degradation following ACL injury; however, their association with pain is still being explored. The purpose of this study was to evaluate the associations between synovial fluid concentrations of IL-1ß, IL-6, and CTX-II with pain following ACL injury and reconstruction. We hypothesized that greater IL-1ß, IL-6, and CTX-II would correlate with greater Pain Visual Analogue Scale (VAS) scores. This was a secondary analysis of 23 patients (mean age = 18.4 years, BMI = 27.4, 13 females/10 males) with acute ACL tears who participated in a pilot randomized trial. Synovial fluid and VAS scores were collected on the day of initial presentation, at ACL reconstruction, and 1 and 4 weeks after surgery. Synovial fluid concentrations of IL-1ß, IL-6, and CTX-II were assessed using enzyme-linked immunoabsorbent assays, and repeated measures correlations were used to assess the relationships between pain and synovial IL-1ß, IL-6, or CTX-II after ACL injury and reconstruction. Pain was positively correlated with synovial fluid IL-6 concentrations (r = 0.52, p < 0.001); however, pain was inversely correlated with CTX-II (r = -0.39, p = 0.002). IL-1ß had no significant correlation with pain. Statement of clinical relevance: PTOA has been described as a "silent killer" and these results suggest that early PTOA may have pro-inflammatory pathways that are not primarily associated with pain but still lead to progressive cartilage loss.

Association of rs1800795 and rs1800796 polymorphisms in interleukin-6 gene and osteoarthritis risk: evidence from a meta-analysis

Multiple studies have investigated the association of interleukin-6 (IL-6) gene polymorphisms and osteoarthritis (OA) risk, but failed to reach a consistent conclusion. Therefore, this study was designed to elucidate the association of IL-6 polymorphisms and OA by a meta-analysis approach. Literature retrieval was carried out on PubMed, EMBASE, Web of Science, CNKI, and Wanfang databases. The strength of association was appraised by odds ratios (ORs) and 95% confidence intervals (95%CIs) in five genetic models. The data were merged by using RevMan 5.3 software. Ten studies with 4944 cases and 4651 controls were analyzed. Overall, no significant association was identified between rs1800795 polymorphism and OA. Subgroup analysis by ethnicity and OA site also suggested rs1800795 polymorphism was not associated with OA. For rs1800796 polymorphism, G-allele and GG-genotype carriers appeared to have an increased risk to OA (G vs. C, OR = 1.66, 95%CI 1.30-1.96, P < 0.01; GG vs. CC, OR = 1.75, 95%CI 1.07-2.84, P = 0.03; GG vs. GC + CC, OR = 1.82, 95%CI 1.42-2.34, P < 0.01). Findings of this study indicate that the rs1800795 polymorphism is not correlated to OA susceptibility, regardless of ethnicity or OA site. However, rs1800796 polymorphism trends to be associated with susceptibility to OA.

Effects of traditional Chinese herb hot compress combined with therapeutic exercise on pain, proprioception, and functional performance among older adults with knee osteoarthritis: A randomized controlled trial

Background: Knee osteoarthritis (KOA) is one of the most common chronic progressive diseases with degenerative destruction of articular cartilage and bone, leading to knee pain, impaired proprioception, and reduced functional performance. This study was to investigate the effects of an 8-week Traditional Chinese herb hot compress (TCHHC) combined with therapeutic exercise (TE) on pain, proprioception, and functional performance among older adults with KOA. Methods: Twenty-seven older adults with KOA were recruited and randomly assigned to the TCHHC + TE or TE groups. Thirteen participants received TCHHC + TE, and fourteen received TE. At pre- (week 0) and post-intervention (week 9), their pain, joint proprioception, and functional performance were measured. Two-way ANOVA with repeated measures was adopted to analyze the data. Results: Compared with week 0, the pain score, proprioception thresholds of knee extension and ankle plantarflexion, and the times of TUG and 20-m walk tests decreased more significantly in the TCHHC + TE group than in the TE group at week 9. Conclusion: Compared with TE, the 8-week TCHHC + TE was superior in relieving pain, recovering proprioception, and improving functional performance among older adults with KOA. It is recommended that TCHHC should be adopted prior to TE to enhance the effects of KOA rehabilitation.

Osteoarthritis Pain in Old Mice Aggravates Neuroinflammation and Frailty: The Positive Effect of Morphine Treatment

Knee osteoarthritis is a common cause of pain and disability in old subjects. Pain may predispose to the development of frailty. Studies on mechanisms underlying pain in osteoarthritis models during aging are lacking. In this work, we used the monosodium iodoacetate model of osteoarthritis in adult (11-week-old) and old (20-month-old) C57BL/6J mice to compare hypersensitivity, locomotion, neuroinflammation, and the effects of morphine treatment. After osteoarthritis induction in adult and old mice, weight-bearing asymmetry, mechanical allodynia, and thermal hyperalgesia similarly developed, while locomotion and frailty were more affected in old than in adult animals. When behavioral deficits were present, the animals were treated for 7 days with morphine. This opioid counteracts the behavioral alterations and the frailty index worsening both in adult and old mice. To address the mechanisms that underlie pain, we evaluated neuroinflammatory markers and proinflammatory cytokine expression in the sciatic nerve, DRGs, and spinal cord. Overexpression of cytokines and glia markers were present in osteoarthritis adult and old mice, but the activation was qualitatively and quantitatively more evident in aged mice. Morphine was able to counteract neuroinflammation in both age groups. We demonstrate that old mice are more vulnerable to pain's detrimental effects, but prompt treatment is successful at mitigating these effects.

Correlation of Womac Index and Cytokine Values in Patients with OA Knee

Osteoarthritis (OA) of the knee (gonarthrosis) is a degenerative rheumatic disease, which is the most common rheumatic disease. Numerous factors, such as mechanical, enzymatic, and biological, are responsible for the development of this complex, multifactorial disease. The connection between inflammation and the development of knee OA is being investigated more and more. Cytokines are thought to be one of the main causes of disturbances in normal cartilage metabolism.

This study, designed as a prospective cohort study included 60 patients with knee OA. The examinees were recruited from total population of patients with knee OA, hospitalized or treated as outpatients at Department of Physical Medicine and Rehabilitation, University Clinical Centre Kragujevac. After the consent was obtained, anamnestic data were collected, blood samples were taken and functional testing was done together with anthropometric measurements. The values of the following cytokines were determined from a blood sample: IL-6, TNF-α, IL-10, IL-17. The average age of patients was 69.10±9.06 years, most of whom were females (78,3%). Both IL-6 and TNF-α correlated positively with WOMAC scores. WOMAC index subscales showed different association with cytokines. In our studies the level of cytocines in the serum of pacients with OA knee is show not correlation with radiographic image.

The present study demonstrated than the concentrations of proinflammatory cytokines (TNF-α IL-6) can be correlated with WOMAC scores of knee OA patients. The results indicate that concentrations of TNF-α and IL-6 may affect knee joint function in patients with knee OA.

A review of osteoarthritis signaling intervention using small-molecule inhibitors

Numerous small-molecule inhibitors (SMIs) have been approved as adjuvant or first-line therapies for malignancies. Based on cancer treatment using SMIs, next-generation SMIs that can be used to optimize the therapeutic index, overcome drug resistance, and establish combination therapies are in development. Osteoarthritis (OA) is the most common chronic joint disease with senescence, and there are various approaches to OA treatment; however, the gold standard treatment is controversial. Therefore, in this manuscript, we demonstrated the potential of using SMIs in OA treatment and described the general strategies for using SMIs in OA treatment.

Effect of IL-6 -174G/C and -572G/C variants on susceptibility to osteoarthritis in Turkish population

Osteoarthritis (OA) is a complex disorder characterized by degenerative articular cartilage in which inflammatory mechanisms play a major role in the pathogenesis. Interleukin-6 (IL6), a multifunctional cytokine, can trigger osteoclast differentiation and bone resorption. Our purpose in this study was to evaluate the association of IL-6 -174 G/C (rs1800795) and -572 G/C (rs1800796) variants with the susceptibility to OA. One hundred fifty OA patients and 150 healthy individuals were enrolled in the study. Polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) was used for genotyping the IL-6 gene variants. The results of analyses were evaluated for statistical significance. The pain intensity was assessed using the Visual Analogue Scale (VAS). There was a statistically significant difference in the genotype and allele frequencies of the IL-6 -174 G/C variant between patients with OA and control groups (p = 0.001, p = 0.002, respectively). IL-6 -174 G/C GG genotype and G allele were more prevalent in patients with OA. We found that the IL-6 -572 G/C variant was not different between patients and controls in either genotype distribution and allele frequency. IL-6 174 G/C and -572 G/C loci GG-GG combined genotype was significantly higher in OA patients (p = 0.00). Our study suggests that there was a strong association between the IL-6 -174 G/C variant and OA in the Turkish population. Further studies on populations of different ethnic background are necessary to prove the association of IL-6 variants with OA.

Obesity, Inflammation, and Immune System in Osteoarthritis

Obesity remains the most important risk factor for the incidence and progression of osteoarthritis (OA). The leading cause of OA was believed to be overloading the joints due to excess weight which in turn leads to the destruction of articular cartilage. However, recent studies have proved otherwise, various other factors like adipose deposition, insulin resistance, and especially the improper coordination of innate and adaptive immune responses may lead to the initiation and progression of obesity-associated OA. It is becoming increasingly evident that multiple inflammatory cells are recruited into the synovial joint that serves an important role in pathological changes in the synovial joint. Polarization of macrophages and macrophage-produced mediators are extensively studied and linked to the inflammatory and destructive responses in the OA synovium and cartilage. However, the role of other major innate immune cells such as neutrophils, eosinophils, and dendritic cells in the pathogenesis of OA has not been fully evaluated. Although cells of the adaptive immune system contribute to the pathogenesis of obesity-induced OA is still under exploration, a quantity of literature indicates OA synovium has an enriched population of T cells and B cells compared with healthy control. The interplay between a variety of immune cells and other cells that reside in the articular joints may constitute a vicious cycle, leading to pathological changes of the articular joint in obese individuals. This review addresses obesity and the role of all the immune cells that are involved in OA and summarised animal studies and human trials and knowledge gaps between the studies have been highlighted. The review also touches base on the interventions currently in clinical trials, different stages of the testing, and their shortcomings are also discussed to understand the future direction which could help in understanding the multifactorial aspects of OA where inflammation has a significant function.

Co-formulations of adalimumab with hyaluronic acid / polyvinylpyrrolidone to combine intraarticular drug delivery and viscosupplementation

Polymer-based formulations present an attractive strategy in intraarticular drug-delivery to refrain biologicals from early leakage from the joint. In this study, co-formulations of hyaluronic acid and polyvinylpyrrolidone were investigated for their potential as viscosupplements and their influence on the transsynovial loss of adalimumab. For this purpose, polymer mixtures were evaluated for their viscosity and elasticity behavior while their influence on the permeation of adalimumab across a porcine ex-vivo synovial membrane was determined. Hyaluronic acid showed strong shear thinning behavior and exhibited high viscosity and elasticity at low motions, while combinations with polyvinylpyrrolidone provided absorption and stiffness at high mechanical stress, so that they can potentially restore the rheological properties of the synovial fluid over the range of joint motion. In addition, the formulations showed significant influence on transsynovial permeation kinetics of adalimumab and hyaluronic acid, which could be decelerated up to 5- and 3-fold, respectively. Besides viscosity effects, adalimumab was retained primarily by an electrostatic interaction with hyaluronic acid, as detected by isothermal calibration calorimetry. Furthermore, polymer-mediated stabilization of the antibody activity was detected. In summary, hyaluronic acid - polyvinylpyrrolidone combinations can be efficiently used to prolong the residence of adalimumab in the joint cavity while simultaneously supplying viscosupplementation.

Correlation between CD163 expression and resting pain in patients with hip osteoarthritis: Possible contribution of CD163+ monocytes/macrophages to pain pathogenesis

Expression of CD163, a scavenger receptor specifically expressed by monocytes and macrophages, is elevated in the synovial tissue of patients with knee osteoarthritis (OA) compared with healthy controls. However, the association between CD163 expression in the synovium and pain in OA patients is unclear. We investigated the correlation between synovial CD163 expression and resting and active pain levels in patients with hip osteoarthritis (HOA). To investigate the possible contribution of CD163+ subsets to pain pathogenesis, we compared pain-related cytokine expression and M1/M2 macrophage marker expression in CD163+ and CD163- cells. We performed flow cytometric analysis to study the CD163+ cell population. We also examined pain-related cytokine expression and M1/M2 macrophage marker expression on CD163+ CD14^high and CD163+ CD14^low cells using cell sorting. Synovial CD163 expression significantly correlated with resting pain levels (p = 0.006; R = 0.321), but not active pain levels (p = 0.155; R = 0.169). Expression of the M1 macrophage marker CD80 was significantly higher in CD163+ than CD163- cells (p = 0.010), as was the expression of M2 macrophage markers CD206 and IL10 (CD206, p = 0.014; IL10, p = 0.005), and TNFA and IL1B (TNFA, p = 0.002; IL1B, p = 0.001). TNFA expression was significantly higher in CD163+ CD14^low than CD163+ CD14^high cells, while IL1B, IL10, and CD206 expression were comparable among these subsets. Our findings suggest that CD163 expression is associated with higher resting pain scores. As TNF-α plays a role in the pain process, CD163+ CD14^low cells expressing TNFA may be a potent contributor to the pathogenesis of resting pain in HOA.

Innate Immunity at the Core of Sex Differences in Osteoarthritic Pain?

Osteoarthritis (OA) is a progressive whole-joint disease; no disease-modifying drugs are currently available to stop or slow its process. Symptoms alleviation is the only treatment option. OA is the major cause of chronic pain in adults, with pain being the main symptom driving patients to seek medical help. OA pathophysiology is closely associated with the innate immune system, which is also closely linked to pain mediators leading to joint pain. Pain research has shown sex differences in the biology of pain, including sexually dimorphic responses from key cell types in the innate immune system. Not only is OA more prevalent in women than in men, but women patients also show worse OA outcomes, partially due to experiencing more pain symptoms despite having similar levels of structural damage. The cause of sex differences in OA and OA pain is poorly understood. This review provides an overview of the involvement of innate immunity in OA pain in joints and in the dorsal root ganglion. We summarize the emerging evidence of sex differences regarding innate immunity in OA pain. Our main goal with this review was to provide a scientific foundation for future research leading to alternative pain relief therapies targeting innate immunity that consider sex differences. This will ultimately lead to a more effective treatment of pain in both women and men.

The Neuroimmune Interplay in Joint Pain: The Role of Macrophages

Chronic pain associated with joint disorders, such as rheumatoid arthritis (RA), osteoarthritis (OA) and implant aseptic loosening (AL), is a highly debilitating symptom that impacts mobility and quality of life in affected patients. The neuroimmune crosstalk has been demonstrated to play a critical role in the onset and establishment of chronic pain conditions. Immune cells release cytokines and immune mediators that can activate and sensitize nociceptors evoking pain, through interaction with receptors in the sensory nerve terminals. On the other hand, sensory and sympathetic nerve fibers release neurotransmitters that bind to their specific receptor expressed on surface of immune cells, initiating an immunomodulatory role. Macrophages have been shown to be key players in the neuroimmune crosstalk. Moreover, macrophages constitute the dominant immune cell population in RA, OA and AL. Importantly, the targeting of macrophages can result in anti-nociceptive effects in chronic pain conditions. Therefore, the aim of this review is to discuss the nature and impact of the interaction between the inflammatory response and nerve fibers in these joint disorders regarding the genesis and maintenance of pain. The role of macrophages is highlighted. The alteration in the joint innervation pattern and the inflammatory response are also described. Additionally, the immunomodulatory role of sensory and sympathetic neurotransmitters is revised.

Association between knee inflammation and knee pain in patients with knee osteoarthritis: a systematic review

OBJECTIVE

To systematically review the literature on the relationship between markers of inflammation and pain in patients with knee osteoarthritis (OA).

METHODS

We searched MEDLINE, Web of Science and EMBASE databases from inception until June 2021. Eligible articles had to report on the association between inflammation (as measured by effusion, synovitis, baker's cysts, cytokines and C-reactive protein) and pain in patients with radiographic knee OA. Two reviewers independently performed a screening on title and abstracts, data extraction and risk of bias assessment using the Newcastle-Ottawa Scale (NOS). A best evidence synthesis was conducted for each inflammatory sign included in this review.

RESULTS

37 studies were included. Articles reported on the following measures: effusion or synovitis assessed via ultrasound (n = 9) or magnetic resonance imaging (MRI) (n = 17); baker's cyst (n = 3); cytokine concentrations (n = 11); and C-reactive protein levels (n = 4). The strength of the association between inflammation and pain does not exceed the moderate level (i.e., correlation coefficient values ranging from 0.19 to 0.61). Moderate levels of evidence were found for the association between synovitis (measured with ultrasound or contrast enhanced MRI) and pain. The levels of evidence between effusion (assessed via ultrasound), effusion/synovitis (assessed via non-contrast enhanced MRI), Baker's cyst, cytokines, C-reactive protein and pain were conflicting.

CONCLUSIONS

Different inflammatory markers are associated with pain but the correlation ranges from weak to moderate, and the quality of evidence from conflicting to moderate. Further research is needed to strengthen the level of evidence and to establish mechanisms.

Sodium alginate microencapsulation of human mesenchymal stromal cells modulates paracrine signaling response and enhances efficacy for treatment of established osteoarthritis

Mesenchymal stromal cells (MSCs) have shown promise as osteoarthritis (OA) treatments; however, effective translation has been limited by high variability and heterogeneity of MSCs, suboptimal delivery strategies, and poor understanding of critical quality and potency attributes. Furthermore, most pre-clinical studies of MSC therapeutics for OA have focused on delaying OA development and not on treating established OA, which brings added clinical relevance. Thus, the objective of the current study was to assess the effects of sodium alginate microencapsulation on human MSC (hMSC) secretion of immunomodulatory cytokines in an OA microenvironment and therapeutic efficacy in treating established OA. A Medial Meniscal Transection (MMT) pre-clinical model of OA was implemented. Three weeks post-surgery, after OA was established, intra-articular injections of encapsulated hMSCs or nonencapsulated hMSCs were administered. Six weeks post-surgery, microstructural changes in the knee joint were quantified using microCT. Encapsulated hMSCs reduced articular cartilage degeneration and subchondral bone remodeling. A multiplexed immunoassay panel was used to profile the in vitro secretome of hMSCs in response to IL-1β. Nonencapsulated hMSCs showed an indiscriminate increase in all cytokines in response to IL-1β while encapsulated hMSCs showed a targeted secretory response with increased expression of pro-inflammatory (IL-1β, IL-6, IL-7, IL-8), anti-inflammatory (IL-1RA), and chemotactic (G-CSF, MDC, IP10) cytokines. These data show that sodium alginate microencapsulation can modulate hMSC paracrine signaling and enhance the therapeutic efficacy of the hMSCs in treating established OA. This cytokine profile provides a foundation for the identification of key factors affecting the overall potency of hMSC therapeutics for OA. STATEMENT OF SIGNIFICANCE: While there has been considerable interest in material based MSC encapsulation for treatment of OA, there are critical gaps in our translational understanding of these biomaterial-based technologies for OA. More specifically, previous studies have several important limitations: (1) they have been largely focused on preventing OA development, which limits their translational utility and (2) little prior work has been done to delineate potential routes/mechanisms by which material encapsulation alters MSC therapeutic action. In our manuscript, we aimed to fill these gaps in knowledge by testing the hypotheses that: (1) hMSC encapsulation can attenuate established disease progression, which is a more clinically relevant scenario and (2) hMSC encapsulation significantly changes the secreted paracrine factors from hMSCs.

Effect of Inflammatory Signaling on Human Articular Chondrocyte Hypertrophy: Potential Involvement of Tissue Repair Macrophages

OBJECTIVE

In osteoarthritis, chondrocytes tend to acquire a hypertrophic phenotype, which contributes to the modification of the extracellular matrix, resulting in permanent cartilage changes. In mouse chondrocytes, pro-inflammatory macrophages and pro-inflammatory cytokines have been shown to stimulate hypertrophy via the activation of the nuclear factor kappa B (NF-κB) pathway. Whether or not this also occurs in human chondrocytes remains unclear. We therefore aimed to investigate whether hypertrophy-like responses in human cartilage are driven mainly by intrinsic inflammatory signaling or shaped by specific macrophage populations.

DESIGN

Human articular chondrocytes were cultured with pro-inflammatory cytokines or medium conditioned by defined macrophage subsets. Furthermore, the effect of inhibition of NF-κB-dependent gene expression was evaluated using the NF-κB inhibitor SC-514. Hypertrophy was assessed by measuring the transcription level of alkaline phosphatase (ALPL), type X collagen (COL10A1), Indian hedgehog (IHH), and runt-related transcription factor 2 (RUNX2).

RESULTS

The expression of hypertrophic genes was not promoted in human chondrocytes by pro-inflammatory cytokines neither pro-inflammatory M(IFNγ + TNFα) macrophages. Inhibition of the NF-κB-dependent gene expression did not affect human articular chondrocyte hypertrophy. However, tissue repair M(IL4) macrophages induced hypertrophy by promoting the expression of COL10A1, RUNX2, and IHH.

CONCLUSION

Intrinsic inflammatory signaling activation is not involved in the hypertrophic shift observed in human articular chondrocytes cultured in vitro. However, tissue repair macrophages may contribute to the onset of this detrimental phenotype in human osteoarthritic cartilage, given the effect observed in our experimental models.

Synovial Adiponectin Was More Associated with Clinical Severity than Synovial Leptin in Women with Knee Osteoarthritis

OBJECTIVE

Different adipokines have been reported to play a role in the development, progression, and severity of knee osteoarthritis, but this association may be mediated by obesity. The aim of this study was to evaluate separately the associations of leptin and adiponectin with clinical severity and inflammatory markers in nonobese and obese women with knee osteoarthritis.

DESIGN

Cross-sectional study with systematic inclusion of 115 women with symptomatic primary knee osteoarthritis. Age, physical exercise, symptoms duration, and body mass index were collected. Radiographic severity was evaluated according to Kellgren-Lawrence scale. Pain and disability were assessed by WOMAC-total, -pain, -function subscales. Two adipokines (leptin and adiponectin) and 3 inflammatory markers (TNF-α, hsCRP, and IL-6) were measured by ELISA in synovial fluid and serum.

RESULTS

Synovial fluid adiponectin was associated with WOMAC pain, function, and total and with synovial fluid IL-6 in nonobese female knee osteoarthritis after controlling by confounders (partial correlation coefficient [PCC] = 0.395, 0.387, 0.427, and 0.649, respectively). Synovial fluid and serum leptin were significantly associated with IL-6 (PCC = 0.354) after controlling by confounders but associations with clinical severity and the rest of inflammatory markers were mitigated after control.

CONCLUSIONS

Adiponectin in synovial fluid was associated with clinical severity and local inflammatory markers in knee osteoarthritis women, while leptin relation was attenuated when controlled by confounders.

Fat Chance for Hidden Lesions: Pictorial Review of Hoffa's Fat Pad Lesions

Hoffa's fat pad (HFP) is the most commonly afflicted among all the knee fat pads. Anterior knee pain is common in various pathologies of HFP, as it is richly innervated. A potpourri of the intrinsic and extrinsic pathologies and the tumors and tumor-like conditions affect HFP, and MRI remains the fundamental modality to assess them and provide a specific diagnosis.

Pharmacological characterization of the chronic phase of the monoiodoacetate-induced rat model of osteoarthritis pain in the knee joint

For patients with osteoarthritis (OA) of the knee, pain is the most debilitating symptom. Although it has been proposed that the chronic phase of the monoiodoacetate (MIA)-induced rodent model of knee joint pain may be superior to other chronic or acute OA models for assessing the analgesic efficacy of novel molecules, relatively few pharmacological studies have been conducted in the chronic phase of this model. Hence, this study was designed to use pharmacological methods to characterize the chronic phase of the MIA-induced rat model of knee joint OA pain. Rats received a single intraarticular injection of MIA at 2.5 mg or vehicle (saline) into the left (ipsilateral) knee joint. Pain behaviour was assessed by measuring paw withdrawal thresholds (PWTs) in the hindpaws pre-MIA injection and twice-weekly until study completion on day 42. Mechanical allodynia was fully developed in the ipsilateral hindpaws (PWTs ≤6 g) from day 7 and it persisted until day 42. MIA-injected rats with PWTs ≤6 g in the ipsilateral hindpaws received single doses of one of four clinically available drugs that represent four distinct pharmacological classes, viz gabapentin, amitriptyline, meloxicam and morphine, according to a 'washout' protocol with at least 48 hours between successive doses. Gabapentin evoked dose-dependent anti-allodynia as did morphine whereas amitriptyline and meloxicam were inactive. Our findings are aligned with clinical data showing that gabapentin and morphine alleviated OA pain in the knee. The lack of efficacy of amitriptyline is consistent with the loss of descending diffuse noxious inhibitory controls reported by others in this model.

Synovial tissue from sites of joint pain in knee osteoarthritis patients exhibits a differential phenotype with distinct fibroblast subsets

BACKGROUND

Synovial inflammation is associated with pain severity in patients with knee osteoarthritis (OA). The aim here was to determine in a population with knee OA, whether synovial tissue from areas associated with pain exhibited different synovial fibroblast subsets, compared to synovial tissue from sites not associated with pain. A further aim was to compare differences between early and end-stage disease synovial fibroblast subsets.

METHODS

Patients with early knee OA (n = 29) and end-stage knee OA (n = 22) were recruited. Patient reported pain was recorded by questionnaire and using an anatomical knee pain map. Proton density fat suppressed MRI axial and sagittal sequences were analysed and scored for synovitis. Synovial tissue was obtained from the medial and lateral parapatellar and suprapatellar sites. Fibroblast single cell RNA sequencing was performed using Chromium 10X and analysed using Seurat. Transcriptomes were functionally characterised using Ingenuity Pathway Analysis and the effect of fibroblast secretome on neuronal growth assessed using rat DRGN.

FINDINGS

Parapatellar synovitis was significantly associated with the pattern of patient-reported pain in knee OA patients. Synovial tissue from sites of patient-reported pain exhibited a differential transcriptomic phenotype, with distinct synovial fibroblast subsets in early OA and end-stage OA. Functional pathway analysis revealed that synovial tissue and fibroblast subsets from painful sites promoted fibrosis, inflammation and the growth and activity of neurons. The secretome of fibroblasts from early OA painful sites induced greater survival and neurite outgrowth in dissociated adult rodent dorsal root ganglion neurons.

INTERPRETATION

Sites of patient-reported pain in knee OA exhibit a different synovial tissue phenotype and distinct synovial fibroblast subsets. Further interrogation of these fibroblast pathotypes will increase our understanding of the role of synovitis in OA joint pain and provide a rationale for the therapeutic targeting of fibroblast subsets to alleviate pain in patients.

FUNDING

This study was funded by Versus Arthritis, UK (21530; 21812).

Plasma and Joint Fluid Glypican-3 Are Inversely Correlated with the Severity of Knee Osteoarthritis

OBJECTIVE

Glypican-3 possesses a possible action in regulation of bone growth and development implicated in osteoarthritis (OA) pathology. Therefore, this study aimed to investigate glypican-3 in plasma and synovial fluid of knee OA patients and to determine the possible association between glypican-3 levels and radiographic severity.

DESIGN

A total of 80 knee OA patients and 80 healthy controls were recruited. Glypican-3 levels in plasma and synovial fluid were measured using enzyme-linked immunosorbent assay. The severity of knee OA was assessed by radiographic grading according to the Kellgren-Lawrence classification. Relative mRNA expression of glypican-3 in 10 inflamed synovial tissues from OA patients and 10 noninflamed synovial controls was quantified using real-time polymerase chain reaction.

RESULTS

Plasma glypican-3 levels were significantly lower in OA patients than in healthy controls (P = 0.03), whereas synovial fluid glypican-3 levels were remarkably greater than in paired plasma samples of OA patients (P < 0.001). Subsequent analysis demonstrated that plasma and synovial fluid glypican-3 levels were inversely associated with the radiographic severity of knee OA (r = -0.691, P < 0.001; r = -0.646, P < 0.001, respectively). Furthermore, there was a positive relationship between plasma and synovial fluid glypican-3 levels in knee OA patients (r = 0.515, P < 0.001). Additionally, overexpression of glypican-3 mRNA was observed in inflamed synovium of OA patients (P = 0.021).

CONCLUSIONS

The present study revealed that plasma and synovial glypican-3 levels were negatively associated with radiographic severity of knee OA. Glypican-3 could emerge as a potential biomarker for reflecting the severity of knee OA and might play a plausible role in the pathophysiology of degenerative joint disease.

Targeting Soluble Epoxide Hydrolase and Cyclooxygenases Enhance Joint Pain Control, Stimulate Collagen Synthesis, and Protect Chondrocytes From Cytokine-Induced Apoptosis

Objective: To determine the symptomatic and disease-modifying capabilities of sEH and COX inhibitors during joint inflammation. Methods: Using a blinded, randomized, crossover experimental design, 6 adult healthy horses were injected with lipopolysaccharide (LPS; 3 μg) from E. coli in a radiocarpal joint and concurrently received the non-selective cyclooxygenase (COX) inhibitor phenylbutazone (2 mg/kg), the sEH inhibitor t-TUCB (1 mg/kg) or both (2 mg/kg phenylbutazone and 0.1, 0.3, and 1 mg/kg t-TUCB) intravenously. There were at least 30 days washout between treatments. Joint pain (assessed via inertial sensors and peak vertical forces), synovial fluid concentrations of prostanoids (PGE₂, TxB₂), cytokines (IL-1β, IL-6, TNF-α) and biomarkers of collagen synthesis (CPII) and degradation (C2C) were measured at pre-determined intervals over a 48-h period. The anti-apoptotic effect of COX and sEH inhibitors was determined via ELISA technique in primary equine chondrocytes incubated with TNF-α (10 ng/ml) for 24 h. Apoptosis was also determined in chondrocytes incubated with sEH-generated metabolites. Results: Combined COX and sEH inhibition produced significantly better control of joint pain, prostanoid responses, and collagen synthesis-degradation balance compared to each compound separately. When administered separately, pain control was superior with COX vs. sEH inhibition. Cytokine responses were not different during COX and/or sEH inhibition. In cultured chondrocytes, sEH inhibition alone or combined with COX inhibition, but not COX inhibition alone had significant anti-apoptotic effects. However, sEH-generated metabolites caused concentration-dependent apoptosis. Conclusions: Combined COX and sEH inhibition optimize pain control, attenuate loss of articular cartilage matrix during joint inflammation and cytokine-induced chondrocyte apoptosis.

Correlation between serum pro inflammatory cytokines and clinical scores of knee osteoarthritic patients using resveratrol as a supplementary therapy with meloxicam

OBJECTIVE:

The objective of this study was to analyze the associations between the pro-inflammatory markers with the clinical outcomes of knee osteoarthritis (OA) in patients using resveratrol as an add-on treatment with meloxicam.

MATERIALS AND METHODS:

This was a double-blind controlled clinical investigation, with 110 eligible patients with OA assigned randomly to receive 15 mg a day meloxicam with either resveratrol 500 mg a day or placebo for 90 days. The standard tools for assessment of pain severity and physical functions were utilized. The tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 in the blood were evaluated. Spearman's correlation coefficient test was used to determine the significance of correlations.

RESULTS:

The regression analysis to determine the correlation between reductions of the inflammatory biomarkers with the amelioration of the clinical scores showed a nonsignificant weak correlation between these variables. Total clinical scores of each assessment tool that was used “Knee Injury and OA Outcome Score (KOOS) and WOMAC” displayed a weak and nonsignificant correlation with TNF-α, IL-1β blood level. The Spearman's correlation shows a relatively nonsignificant association between IL-6 levels and KOOS, WOMAC, and Visual Analog Scale scores after incorporating resveratrol as an adjuvant with meloxicam for 90 days.

CONCLUSION:

A weak and nonsignificant correlation between serum biomarkers and the clinical outcomes has been suggested in patients with painful knee OA treated with meloxicam and resveratrol.

Aggrecan, IL-1β, IL-6, and TNF-α profiles in the Articular Cartilage of Miniature Horses with Chondrodysplastic Dwarfism

Dwarfism is a skeletal disorder that causes abnormal growth. In Miniature horses, dwarfism can occur as chondrodysplastic dwarfism, an autosomal recessive disorder associated with five mutations (D1, D2, D3*, D4 and c.6465A > T variant) in the aggrecan (ACAN) gene. The aim of this study was to evaluate the expression of aggrecan (at the gene and protein level) and specific cytokines (IL-1β, IL-6, and TNF-α) in the articular cartilage of Miniature horses with chondrodysplastic dwarfism (D4/c.6465A > T genotype). Metatarsal bone samples from eight dwarf Miniature horses were collected for histopathological analysis, and articular cartilage was collected to detect and quantify aggrecan levels through Western blotting and determine the relative expression levels of ACAN, IL-1β, IL-6, and TNF-α through qPCR. All affected animals presented chondrodysplasia-like lesions with disorganization of the chondrocyte layers and reduced the amount of an extracellular matrix. No significant difference in aggrecan expression levels in uncleaved samples from the dwarf and control groups (composed of phenotypically normal animals of similar age and breed (P = .7143)) was found using Western blotting. qPCR revealed that ACAN gene expression was higher in the affected animals than in normal animals (P = .0119). No significant difference in cytokine levels was detected between the groups. Mutant aggrecan may interfere with normal cellular function, leading to chondrodysplasia and the observed phenotypic findings.

New Trends in Pharmacological Treatments for Osteoarthritis

Osteoarthritis (OA) is the leading cause of function loss and disability among the elderly, with significant burden on the individual and society. It is a severe disease for its high disability rates, morbidity, costs, and increased mortality. Multifactorial etiologies contribute to the occurrence and development of OA. The heterogeneous condition poses a challenge for the development of effective treatment for OA; however, emerging treatments are promising to bring benefits for OA management in the future. This narrative review will discuss recent developments of agents for the treatment of OA, including potential disease-modifying osteoarthritis drugs (DMOADs) and novel therapeutics for pain relief. This review will focus more on drugs that have been in clinical trials, as well as attractive drugs with potential applications in preclinical research. In the past few years, it has been realized that a complex interaction of multifactorial mechanisms is involved in the pathophysiology of OA. The authors believe there is no miracle therapeutic strategy fitting for all patients. OA phenotyping would be helpful for therapy selection. A variety of potential therapeutics targeting inflammation mechanisms, cellular senescence, cartilage metabolism, subchondral bone remodeling, and the peripheral nociceptive pathways are expected to reshape the landscape of OA treatment over the next few years. Precise randomized controlled trials (RCTs) are expected to identify the safety and efficacy of novel therapies targeting specific mechanisms in OA patients with specific phenotypes.