Cross-sectional and longitudinal associations between serum inflammatory cytokines and knee bone marrow lesions in patients with knee osteoarthritis

Inflammatory markers in early knee joint osteoarthritis differ from well-matched controls and are associated with consistent, rather than intermittent knee pain

BACKGROUND

Osteoarthritis (OA) is characterised by the failure of normal biological processes to repair following damage. Traditionally, OA was considered a "wear and tear" disorder; however, it is now a recognised inflammatory condition, preceded by molecular modifications. The aim of this study was to evaluate inflammatory markers among individuals with early knee OA (eKOA) and well-matched asymptomatic controls.

METHODS

Twenty six eKOA (females, n = 13; age = 60.2 ± 5.4 yrs, height = 1.73 ± 0.11 m, body mass = 77.8 ± 12.8 kg, body fat = 33.9 ± 8.5%) and twenty-three asymptomatic individuals (females, n = 14; age = 59.9 ± 5.5yrs, height = 1.71 ± 0.09 m, body mass = 72.6 ± 11.3 kg, body fat = 30.4 ± 8.2%) were recruited. The Timed Up and Go, and the 6 Minute Walk Tests evaluated physical function in addition to pain specific questionnaires (KOOS and ICOAP). Serum levels of IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-8(CXCL8), IL-10, hsCRP and TNF-α were quantified using a multiplex assay via V-plex®Sector Imager 2400.

RESULTS

As hypothesised, only KOOS and EQ-5D-5L metrics differed between the groups for non-blood derived measures (p < 0.04). Only IL-6 was higher in eKOA (P = 0.02; 95% CI = 0.202; by 0.197 pg/mL; 34.5%). Among eKOA, IL-6 did not relate to severity of KOOS pain (P = 0.696, r = -0.088), but had a positive relationship with ICOAP consistent (r = 0.469, P = 0.045) rather than intermittent pain. There was a moderate correlation between 6MWD and IL-8 (r = 0.471, P = 0.012).

CONCLUSION

Our results illustrate the potential for IL-6 as a biomarker for eKOA, and introduce the proposition for particular consideration in those with consistent pain. Further, for the first time the present data showed greater walking distance in eKOA with lower circulating IL-8. Future work should seek to verify these results and further investigate IL-6 and IL-8 related molecular pathways in eKOA, and their potential relationships with consistent knee pain and physical function.

The biphasic role of the infrapatellar fat pad in osteoarthritis

Osteoarthritis (OA) is a progressive degenerative disease resulting in joint deterioration. It is a whole organ disease characterized by cartilage degeneration and varying degrees of synovitis, involving pathological changes in all joint tissues, such as cartilage, subchondral bone, ligaments, meniscus, synovium, and infrapatellar fat pad (IPFP). IPFP is the largest adipose tissue structure in the knee joint and is composed of fat cells, immune cells and blood vessels. Moreover, IPFP is located close to the cartilage and bone surface so that it may reduce the impact of loading and absorb forces generated through the knee joint, and may have a protective role in joint health. IPFP has been shown to release various cytokines and adipokines that play pro-inflammatory and pro-catabolic roles in cartilage, promoting OA progression. Intra-articular injections of IPFP-derived mesenchymal stem cells and exosomes have been shown to reduce pain and prevent OA progression in patients with knee OA. Previous studies have shown that IPFP has a biphasic effect on OA progression. This article reviews the latest research progress of IPFP, discusses the role and mechanism of IPFP in OA, provide new intervention strategies for the treatment of OA. This article will also discuss the handling of IPFP during the procedure of total knee arthroplasty.

Proteomic and lipidomic landscape of the infrapatellar fat pad and its clinical significance in knee osteoarthritis

Osteoarthritis (OA) is a prevalent joint disease that can be exacerbated by lipid metabolism disorders. The intra-articular fat pad (IFP) has emerged as an active participant in the pathological changes of knee OA (KOA). However, the proteomic and lipidomic differences between IFP tissues from KOA and control individuals remain unclear. Samples of IFP were collected from individuals with and without OA (n = 6, n = 6). Subsequently, these samples underwent liquid chromatography/mass spectrometry-based label-free quantitative proteomic and lipidomic analysis to identify differentially expressed proteins (DEPs) and lipid metabolites (DELMs). The DEPs were further subjected to enrichment analysis, and hub DEPs were identified using multiple algorithms. Additionally, an OA diagnostic model was constructed based on the identified hub DEPs or DELMs. Furthermore, CIBERSORT was utilized to investigate the correlation between hub protein expression and immune-related modules in IFP of OA. Our results revealed the presence of 315 DEPs and eight DELMs in IFP of OA patients compared to the control group. Enrichment analysis of DEPs highlighted potential alterations in pathways related to coagulation, complement, fatty acid metabolism, and adipogenesis. The diagnostic model incorporating four hub DEPs (AUC = 0.861) or eight DELMs (AUC = 0.917) exhibited excellent clinical validity for diagnosing OA. Furthermore, the hub DEPs were found to be associated with immune dysfunction in IFP of OA. This study presents a distinct proteomic and lipidomic landscape of IFP between individuals with OA and those without. These findings provide valuable insights into the molecular changes associated with potential mechanisms underlying OA.

Bone marrow lesions in osteoarthritis: From basic science to clinical implications

Osteoarthritis (OA) is the most prevalent musculoskeletal disease characterized by multiple joint structure damages, including articular cartilage, subchondral bone and synovium, resulting in disability and economic burden. Bone marrow lesions (BMLs) are common and important magnetic resonance imaging (MRI) features in OA patients. Basic and clinical research on subchondral BMLs in the pathogenesis of OA has been a hotspot. New evidence shows that subchondral bone degeneration, including BML and angiogenesis, occurs not only at or after cartilage degeneration, but even earlier than cartilage degeneration. Although BMLs are recognized as important biomarkers for OA, their exact roles in the pathogenesis of OA are still unclear, and disputes about the clinical impact and treatment of BMLs remain. This review summarizes the current basic and clinical research progress of BMLs. We particularly focus on molecular pathways, cellular abnormalities and microenvironmental changes of subchondral bone that contributed to the formation of BMLs, and emphasize the crosstalk between subchondral bone and cartilage in OA development. Finally, potential therapeutic strategies targeting BMLs in OA are discussed, which provides novel strategies for OA treatment.

Longitudinal association of infrapatellar fat pad signal intensity alteration with biochemical biomarkers in knee osteoarthritis

OBJECTIVE

To explore the longitudinal association of quantitative infrapatellar fat pad (IPFP) signal intensity alteration with OA-related biomarkers.

METHODS

Eighteen OA-related biochemical biomarkers of 600 knee OA participants in the Foundation for the National Institutes of Health OA Biomarkers Consortium (FNIH) study were extracted. The quantitative IPFP signal intensity measures were acquired based on magnetic resonance imaging, including mean value [Mean (IPFP)] and standard deviation [sDev (IPFP)] of the whole IPFP signal intensity, median value [Median (H)] and upper quartile value [UQ (H)] of high signal intensity, the ratio of volume of high signal intensity to volume of whole IPFP signal intensity [Percentage (H)] and Clustering factor (H). The linear mixed-effect model was applied to determine the longitudinal associations between IPFP signal intensity alteration and biochemical biomarkers over 2 years.

RESULTS

All IPFP measures except for Clustering factor (H) were positively associated with urine collagenase-cleaved type II collagen neoepitope (uC2C), urine C-terminal cross-linked telopeptide of type II collagen (uCTX-II), urine C-terminal cross-linked telopeptide of type I collagen-α (uCTX-Iα) and urine N-terminal cross-linked telopeptide of type I collagen (uNTX-I). Mean (IPFP), Median (H) and Percentage (H) were positively associated with the nitrated form of an epitope located in the triple helix of type II collagen (Coll2-1 NO2). Mean (IPFP), Median (H) and UQ (H) were positively associated with sCTX-I and uCTX-Iβ. Positive associations between sDev (IPFP), Percentage (H) and serum hyaluronic acid (sHA) were found.

CONCLUSION

Our results suggest a role of IPFP signal intensity alteration in joint tissue remodelling on a molecular level.

Targeting inflammasome-dependent mechanisms as an emerging pharmacological approach for osteoarthritis therapy

Arthritic diseases have attracted enormous scientific interest because of increased worldwide prevalence and represent a significant socioeconomic burden. Osteoarthritis (OA) is the most prevalent form of arthritis. It is a disorder of the diarthrodial joints, characterized by degeneration and loss of articular cartilage associated with adjacent subchondral bone changes. Chronic and unresolving inflammation has been identified as a critical factor driving joint degeneration and pain in OA. Despite numerous attempts at therapeutic intervention, no effective disease-modifying agents targeting OA inflammation are available to the patients. Inflammasomes are protein complexes known to play a critical role in the inflammatory pathology of several diseases, and their roles in OA pathogenesis have become evident over the last decade. In this sense, it is relevant to evaluate the vital role of inflammasomes as potential modulators of pathogenic features in OA. This review will provide an overview and perspectives on why understanding inflammasome activation is critical for identifying effective OA therapies. We elaborate on the contribution of extracellular mediators from the circulatory system and synovial fluid as well as intracellular activators within the synovial fibroblasts and articular chondrocytes toward invoking the inflammasome in OA. We further discuss the merits of emerging inflammasome targeting therapies and speculate on the potential strategies for inflammasome blockade for OA therapy.

Role of pro-inflammatory interleukins in osteoarthritis: a narrative review

PURPOSE

This manuscript will summarize the role of pro-inflammatory cytokines and tackle newly discussed ones within the scope of OA pathogenesis as mentioned in the recent literature. This will allow for a better understanding of the mechanisms behind such a complicated disease.

MATERIAL AND METHODS

Relevant articles were obtained by searching key terms including "pro-inflammatory cytokines," "inflammation," "pathophysiology," "cartilage damage," and "OA" in PubMed and Google Scholar databases. The year ranges set for the selection of the articles was between 2015 -2021. Inclusion criteria was based on the relevance and contribution to the field of the study.

RESULTS

Osteoarthritis (OA) has a complex multifactorial pathophysiology which is attributed to molecular and biomechanical changes that disrupt the normal balance of synthesis and degradation of articular cartilage and subchondral bone. Pro-inflammatory cytokines, with their wide range of action and intricate signaling pathways, are the constant subject of new discoveries revolving around this inflammatory disease. The available literature indicates that some of these cytokines such as IL-33, IL-17, IL-6, and IL-22 have a direct relation to cartilage degradation, while others like IL-15, IL-1, IL-7, and IL-34 have an indirect one.

CONCLUSIONS

Inflammation has an essential role in the manifestation of osteoarthritis clinical events. Specifically, certain cytokines exhibit pro-inflammatory properties that are markedly activated during the course of the disease and notably alter the homeostasis of the joint environment. However, clinical trials and observational studies remain insufficient to navigate the varying nature of this disease in humans.

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.

Construct validity of a clinically correlated knee osteoarthritis ultrasonographic scale: a cross-sectional observational study

OBJECTIVES

To assess the validity of a novel ultrasonographic scale for knee osteoarthritis (KOA) and its relation with the degree of pain and clinical features.

DESIGN

A cross-sectional observational study including 245 patients with knee pain who fulfilled the American College of Rheumatology criteria for KOA. All patients were subjected to clinical assessment Western Ontario and McMaster Universities Index of Osteoarthritis (WOMAC) scale, global visual analogue scale (VAS) and functional assessment through the use of Health Assessment Questionnaire-II (HAQ-II). Ultrasonographic assessment was conducted following ZAGAZIG scale comprising five domains: one for degenerative features (one-third of total score) and the other four for inflammatory features (two-thirds of score).

RESULTS

There were positive correlations between ZAGAZIG score and all WOMAC subscales (pain, stiffness and function) (r=0.71, p=0.00; r=0.62, p=0.00; r=0.70, p=0.00, respectively).Moreover, there was a strong positive correlation between ZAGAZIG scale and both VAS and HAQ-II (r=0.82, p=0.00 and r=0.67, p=0.00). At cut-off point of >5, total US score distinguishes between patients with KOA with no or mild pain and those with moderate pain (87.2 sensitivity and 87.2 specificity). At cut-off point of 7, total score of ZAGAZIG scale distinguishes between patients with KOA with moderate pain and those with severe pain (94.5 sensitivity and 42.5 specificity).

CONCLUSION

ZAGAZIG scale constitutes a validated tool for KOA assessment. ZAGAZIG scale correlated with WOMAC subscales (pain, stiffness and function), VAS and HAQ.

Prospective Association Between Inflammatory Markers and Knee Cartilage Volume Loss and Pain Trajectory

Introduction

Inflammation has been suggested to be involved in the pathogenesis of osteoarthritis and pain. We sought to explore the associations between inflammatory serum markers and magnetic resonance imaging-defined long-term structural change and pain trajectory.

Methods

A total of 169 randomly selected participants (mean age 63 years; 47% female) from a prospective cohort study were included in this study. Circulating levels of interleukin 6 (IL-6), tumour necrosis factor alpha (TNF-α) and high-sensitivity C-reactive protein (CRP) were measured at baseline. A knee MRI scan was performed to measure cartilage volume (CV) and bone marrow lesions (BMLs) at baseline and at 10.7 years. Knee pain at four visits was measured by the WOMAC pain questionnaire, and pain trajectories were identified using group-based trajectory modelling. Linear, log-binomial and multi-nominal logistic regression were used for the analyses.

Results

IL-6 was associated with lateral but not medial tibial CV loss (β = − 0.25% per annum, per standard deviation [SD] log pg/ml; P < 0.05) in the multivariate analysis. IL-6 was also associated with a ‘Moderate pain’ trajectory (relative risk ratio 1.93 per SD log pg/ml; 95% confidence interval 1.02–3.65) relative to the ‘Minimal pain’ trajectory group. There was no significant association of TNF-α and CRP with CV loss and pain trajectory groups with the exception of a beneficial relationship between CRP and medial tibial CV loss (β = 0.20% per annum, per SD log mg/l). No association between inflammatory markers and change in BML size was observed.

Conclusions

IL-6 was independently associated with compartment-specific CV loss and worse pain trajectory, but the other markers studied were not, suggesting that components of inflammation are implicated in the pathogenesis of cartilage loss and developing a worse pain course.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40122-021-00341-1.

The interactions between MRI-detected osteophytes and bone marrow lesions or effusion-synovitis on knee symptom progression: an exploratory study

OBJECTIVES

To investigate the longitudinal association between MRI-detected osteophyte scores and progression of knee symptoms, and whether the association was modified in the presence of bone marrow lesions (BMLs) or effusion-synovitis.

METHODS

Data from Vitamin D Effects on Osteoarthritis (VIDEO) study, a randomized, double-blinded and placebo-controlled clinical trial in symptomatic knee osteoarthritis (OA) patients, were analyzed as an exploratory study. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) was used to assess knee symptoms. Osteophytes, BMLs and effusion-synovitis were measured using MRI.

RESULTS

334 participants with MRI information and WOMAC score (baseline and follow-up) were included in the analyses, with 24.3% of them having knee pain increased 2 years later. Statistically significant interactions were found between MRI-detected osteophytes and BMLs or effusion-synovitis on increased knee symptoms. In participants with BMLs, higher baseline scores of MRI-detected osteophytes in most compartments were significantly associated with increased total knee pain, weight-bearing pain, stiffness, and physical dysfunction, after adjustment for age, sex, body mass index, intervention and effusion-synovitis. In participants with effusion-synovitis, higher baseline scores of MRI-detected osteophytes in almost all the compartments were significantly associated with increased total knee pain, weight-bearing pain, stiffness, and physical dysfunction, after adjustment for age, sex, body mass index, intervention and BMLs. In contrast, MRI-detected osteophyte scores were generally not associated with knee symptom progression in participants without baseline BMLs or effusion-synovitis.

CONCLUSIONS

MRI-detected OPs are associated with increased total knee pain, weight-bearing knee pain, stiffness and physical dysfunction in participants presenting BMLs or effusion-synovitis, but not in participants lacking BMLs or effusion-synovitis. This suggests they could interact with bone or synovial abnormalities to induce symptoms in knee OA.

Effects of Vitamin D Supplementation on Disabling Foot Pain in Patients With Symptomatic Knee Osteoarthritis

OBJECTIVE

The present study was undertaken to determine whether vitamin D supplementation or maintaining sufficient vitamin D level reduces foot pain over 2 years in patients with symptomatic knee osteoarthritis (OA).

METHODS

A post hoc study was conducted from a randomized, double-blind, placebo-controlled trial named the Vitamin D Effect on Osteoarthritis (VIDEO) study. Symptomatic knee OA patients with serum 25-hydroxyvitamin D levels between 12.5 nmoles/liter and 60 nmoles/liter were included and randomly allocated to either monthly vitamin D₃ or placebo treatment (1:1) for 2 years. Manchester Foot Pain and Disability Index (MFPDI) was used to evaluate foot pain and disabling foot pain was defined as at least 1 of the 10 functional limitation items (items 1-9 and 11) being documented as on "most/every day(s)" in the last month. A repeated-measures, mixed-effects model was used to analyze the change of MFPDI scores between groups adjusting for potential confounders.

RESULTS

A total of 413 patients with a mean age of 63.2 years (49.7% males) were enrolled and 340 completed the study. The mean MFPDI score was 22.8 ± 7.3, with 23.7% of participants having disabling foot pain at baseline. There were significant differences in MFPDI scores change between groups over 2 years, with more improvements in the vitamin D group than in the placebo group (-0.03 versus 1.30; P = 0.013) and more improvement in those maintaining sufficient vitamin D levels (n = 226) than those who did not (n = 114) (-0.09 versus 2.19; P = 0.001).

CONCLUSION

Vitamin D supplementation and maintenance of sufficient vitamin D levels may improve foot pain in those with knee OA.

Association of serum levels of inflammatory markers and adipokines with joint symptoms and structures in participants with knee osteoarthritis

OBJECTIVE

To investigate the longitudinal associations of serum inflammatory markers and adipokines with joint symptoms and structures in participants with knee osteoarthritis (OA).

METHODS

Two hundred participants (46.5% female, mean age 63.1 years, mean BMI 29.5 kg/m2) from Tasmania part of the VIDEO (Vitamin D Effect on OA) study were randomly selected in the current study. Serum levels of 19 biomarkers, scores of Western Ontario and McMaster Universities Index (WOMAC), and magnetic resonance imaging-assessed knee structures were evaluated at baseline and month 24. The patterns of biomarkers were derived from principal component analysis and their association with knee symptoms and structures were examined using adjusted generalized estimating equations.

RESULTS

Five components explained 78% of the total variance. Interleukin (IL)-1β, -2, -4, -6, -8, -17A, -17F, -21, -22 and -23 loaded the highest on the first component, which was associated with increased bone marrow lesions (BMLs) and WOMAC dysfunction score. IL-10, -12 and granulocyte-macrophage colony-stimulating factor loaded on the second component, which was associated with increased cartilage volume, and decreased effusion-synovitis and WOMAC scores. Leptin, adipsin and C-reactive protein loaded on the third component, which was positively associated with WOMAC scores. Resistin loaded on the fourth component, which was associated with increased BMLs and cartilage defects. Apelin-36 and adiponectin loaded on the fifth component, which was associated with increased BMLs.

CONCLUSION

Various inflammatory and metabolic components were associated differently with joint symptoms and structural changes in knee OA, suggesting a complex inflammatory and metabolic inter-relationship in the pathogenesis of knee OA.

An Evidence-Based Systematic Review of Human Knee Post-Traumatic Osteoarthritis (PTOA): Timeline of Clinical Presentation and Disease Markers, Comparison of Knee Joint PTOA Models and Early Disease Implications

Understanding the causality of the post-traumatic osteoarthritis (PTOA) disease process of the knee joint is important for diagnosing early disease and developing new and effective preventions or treatments. The aim of this review was to provide detailed clinical data on inflammatory and other biomarkers obtained from patients after acute knee trauma in order to (i) present a timeline of events that occur in the acute, subacute, and chronic post-traumatic phases and in PTOA, and (ii) to identify key factors present in the synovial fluid, serum/plasma and urine, leading to PTOA of the knee in 23-50% of individuals who had acute knee trauma. In this context, we additionally discuss methods of simulating knee trauma and inflammation in in vivo, ex vivo articular cartilage explant and in vitro chondrocyte models, and answer whether these models are representative of the clinical inflammatory stages following knee trauma. Moreover, we compare the pro-inflammatory cytokine concentrations used in such models and demonstrate that, compared to concentrations in the synovial fluid after knee trauma, they are exceedingly high. We then used the Bradford Hill Framework to present evidence that TNF-α and IL-6 cytokines are causal factors, while IL-1β and IL-17 are credible factors in inducing knee PTOA disease progresssion. Lastly, we discuss beneficial infrastructure for future studies to dissect the role of local vs. systemic inflammation in PTOA progression with an emphasis on early disease.

Molecular Mechanisms of Sex-Related Differences in Arthritis and Associated Pain

Clinical conditions leading to chronic pain show important sex-related differences in the prevalence, severity, and degree of functional disability. Decades of epidemiological and clinical studies have demonstrated that women are more sensitive to pain than men. Arthritis, including rheumatoid arthritis (RA) and osteoarthritis (OA), is much more prevalent in females and accounts for the majority of pain arising from musculoskeletal conditions. It is therefore important to understand the mechanisms governing sex-dependent differences in chronic pain, including arthritis pain. However, research into the mechanisms underlying the sex-related differences in arthritis-induced pain is still in its infancy due to the bias in biomedical research performed largely in male subjects and animals. In this review, we discuss current advances in both clinical and preclinical research regarding sex-related differences in the development or severity of arthritis and associated pain. In addition, sex-related differences in biological and molecular mechanisms underlying the pathogenesis of arthritis pain, elucidated based on clinical and preclinical findings, are reviewed.

Infrapatellar Fat Pad and Knee Osteoarthritis

Osteoarthritis is the most prevalent arthritis typically characterized by degradation of cartilage. However, its pathogenesis is not fully understood. Currently, osteoarthritis is best considered a disease of the whole "joint organ". Infrapatellar fat pad (IFP), an adipose tissue near synovium, is now attaching importance to researchers for its inflammatory phenotype. In this narrative review, a large body of evidence has been gathered for the involvement of IFP in the development of knee osteoarthritis. Additionally, the underlying mechanisms of how IFP can be involved in this process have been proposed. However, further investigations are needed to better understand its precise role in this process and its underlying mechanism, and beyond that, to develop new strategies to slow down the degenerative process and explore an effective and timely diagnosis of the disease.

Can low-dose methotrexate reduce effusion-synovitis and symptoms in patients with mid- to late-stage knee osteoarthritis? Study protocol for a randomised, double-blind, and placebo-controlled trial

BACKGROUND

Osteoarthritis (OA) is a common chronic disease in older adults. Currently, there are no effective therapies to reduce disease severity and progression of knee OA (KOA), particularly in mid- to late-stages. This study aims to examine the effect of methotrexate (MTX) on knee effusion-synovitis and pain in symptomatic patients with mid- to late-stage KOA.

METHODS/DESIGN

This protocol describes a multicentre randomised placebo-controlled clinical trial aiming to recruit 200 participants with mid- to late-stage symptomatic KOA and with effusion-synovitis grade of ≥ 2. Participants will be randomly allocated to the MTX group (start from 5 mg per week for the first 2 weeks and increase to 10 mg per week for the second 2 weeks and 15 mg per week for the remaining period if tolerated) or the placebo group. Primary outcomes are effusion-synovitis size measured by magnetic resonance imaging (MRI) and knee pain assessed by visual analogue scale (VAS). Secondary outcomes are signal intensity alteration within infrapatellar fat pad (IPFP) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) total score and subscores, and the Outcome Measures in Rheumatology Arthritis Clinical Trials-Osteoarthritis Research Society International (OMERACT-OARSI) responders. Both intention-to-treat and per-protocol analyses will be performed.

DISCUSSION

If MTX intervention can relieve symptoms and reduce inflammation in patients with mid- to late-stage KOA, it has the potential for significant clinical and public health impact as this low-cost and commonly used intervention would delay the time to knee replacement, leading to substantial cost savings and improve quality of life.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03815448 . Registered on 21 January 2019.

Setting up distinctive outcome measures for each osteoarthritis phenotype

Osteoarthritis (OA) is an evolving chronic joint disease with a huge global impact. Given the intricate nature of the etiopathogenesis and subsequent high heterogeneity in the clinical course of OA, it is crucial to discriminate between etiopathogenic endotypes and clinical phenotypes, especially in the early stages of the disease. In this sense, we propose that an OA phenotype should be properly assessed with a set of outcome measures including those specifically related to the main underlying pathophysiological mechanisms. Thus, each OA phenotype can be related to different and clinically meaningful outcomes. OA phenotyping would lead to an adequate patient stratification in well-designed clinical trials and the discovery of precise therapeutic approaches. A significant effort will be required in this field in light of inconclusive results of clinical trials of tissue-targeting agents for the treatment of OA.

Knee Osteoarthritis: A Review of Pathogenesis and State-Of-The-Art Non-Operative Therapeutic Considerations

Being the most common musculoskeletal progressive condition, osteoarthritis is an interesting target for research. It is estimated that the prevalence of knee osteoarthritis (OA) among adults 60 years of age or older is approximately 10% in men and 13% in women, making knee OA one of the leading causes of disability in elderly population. Today, we know that osteoarthritis is not a disease characterized by loss of cartilage due to mechanical loading only, but a condition that affects all of the tissues in the joint, causing detectable changes in tissue architecture, its metabolism and function. All of these changes are mediated by a complex and not yet fully researched interplay of proinflammatory and anti-inflammatory cytokines, chemokines, growth factors and adipokines, all of which can be measured in the serum, synovium and histological samples, potentially serving as biomarkers of disease stage and progression. Another key aspect of disease progression is the epigenome that regulates all the genetic expression through DNA methylation, histone modifications, and mRNA interference. A lot of work has been put into developing non-surgical treatment options to slow down the natural course of osteoarthritis to postpone, or maybe even replace extensive surgeries such as total knee arthroplasty. At the moment, biological treatments such as platelet-rich plasma, bone marrow mesenchymal stem cells and autologous microfragmented adipose tissue containing stromal vascular fraction are ordinarily used. Furthermore, the latter two mentioned cell-based treatment options seem to be the only methods so far that increase the quality of cartilage in osteoarthritis patients. Yet, in the future, gene therapy could potentially become an option for orthopedic patients. In the following review, we summarized all of the latest and most important research in basic sciences, pathogenesis, and non-operative treatment.

Knee Osteoarthritis: A Review of Pathogenesis and State-Of-The-Art Non-Operative Therapeutic Considerations

Being the most common musculoskeletal progressive condition, osteoarthritis is an interesting target for research. It is estimated that the prevalence of knee osteoarthritis (OA) among adults 60 years of age or older is approximately 10% in men and 13% in women, making knee OA one of the leading causes of disability in elderly population. Today, we know that osteoarthritis is not a disease characterized by loss of cartilage due to mechanical loading only, but a condition that affects all of the tissues in the joint, causing detectable changes in tissue architecture, its metabolism and function. All of these changes are mediated by a complex and not yet fully researched interplay of proinflammatory and anti-inflammatory cytokines, chemokines, growth factors and adipokines, all of which can be measured in the serum, synovium and histological samples, potentially serving as biomarkers of disease stage and progression. Another key aspect of disease progression is the epigenome that regulates all the genetic expression through DNA methylation, histone modifications, and mRNA interference. A lot of work has been put into developing non-surgical treatment options to slow down the natural course of osteoarthritis to postpone, or maybe even replace extensive surgeries such as total knee arthroplasty. At the moment, biological treatments such as platelet-rich plasma, bone marrow mesenchymal stem cells and autologous microfragmented adipose tissue containing stromal vascular fraction are ordinarily used. Furthermore, the latter two mentioned cell-based treatment options seem to be the only methods so far that increase the quality of cartilage in osteoarthritis patients. Yet, in the future, gene therapy could potentially become an option for orthopedic patients. In the following review, we summarized all of the latest and most important research in basic sciences, pathogenesis, and non-operative treatment.

Altered protein levels in bone marrow lesions of hip osteoarthritis: Analysis by proteomics and multiplex immunoassays

AIM

To assess tissue level changes of proteome and cytokine profiles of subchondral bone in hip osteoarthritis (OA) affected by bone marrow lesions (BMLs). We compared significant protein level differences in osteoarthritic bone with BMLs to control bone without bone marrow lesions.

METHODS

Subchondral bone biopsies were taken from femoral heads of end-stage osteoarthritis patients with (BML, n = 21) and without (CON, n = 9) BMLs. Proteins were extracted through a standardized Trizol protocol and used in the subsequent analyses. Angiogenesis and bone markers were assessed using multiplex immunoassays (Luminex). Liquid chromatography tandem mass spectrometry (LC-MS/MS) was performed to detect significant differences in proteome and peptide profiles between BML and CON.

RESULTS

Multiplex immunoassays revealed increased tissue contents of vascular endothelial growth factors (VEGF-A/C/D), endothelin-1, angiopoietin-2 and interleukin-6 (IL-6) in bone with BMLs compared to control bone, whereas osteoprotegerin levels were reduced. Mass spectrometry demonstrated pronounced increase in the levels of hemoglobin (73-fold), serum albumin (30-fold), alpha-1-antitrypsin (9-fold), apolipoprotein A1 (4.7-fold), pre-laminin-A/C (3.7-fold) and collagen-alpha1-XII (3-fold) in BMLs, while aggrecan core protein (ACAN) and hyaluronan and proteoglycan link protein 1 (HAPL1) decreased 37- and 29-fold respectively.

CONCLUSION

Reduced osteoprotegerin, ACAN and HAPL1 are consistent with osteoclastic activation and high remodeling activity in BMLs. The pronounced increase in angiogenesis markers, hemoglobin and serum albumin support the presence of increased vascularity in subchondral bone affected by BMLs in OA. VEGFs and IL-6 are known nociceptive modulators, and increased levels are in keeping with pain being a clinical feature frequently associated with BMLs.

Association of IL-17A-197G/A and IL-17F-7488T/C polymorphisms and osteoarthritis susceptibility: A meta-analysis

AIM

This meta-analysis was conducted with the aim of collecting and synthesizing the existing evidence on the association of interleukin-17A (IL-17A)-197G/A and IL-17F-7488T/C gene polymorphisms and osteoarthritis (OA) susceptibility.

METHODS

Six electronic databases including PubMed, EMBASE, Web of Science, Cochrane Library, CNKI, and Wanfang were systematically searched for potentially relevant studies previous to June 2019. The strengths of association were estimated by summary odds ratios (ORs) and 95% confidence intervals (95%CIs) in a model-free approach. Heterogeneity test and sensitivity analysis were also conducted to guarantee the reliability of this study.

RESULTS

Six eligible case-control studies comprising 1989 OA patients and 2116 healthy controls were obtained for the meta-analysis. Dominant model was confirmed to be the optimal genetic model (MM + Mm vs mm). The pooled estimate supported that IL-17A-197G/A and IL-17F-7488T/C polymorphisms were significantly associated with OA susceptibility in the overall population (IL-17A-197G/A: GG + GA vs AA, OR = 0.69, 95%CI 0.57-0.80; P < .001; IL-17F-7488T/C, TT + TC vs CC, OR = 0.46, 95%CI 0.29-0.71, P < .001). However, subgroup analyses suggested the association only existed in Asians and knee OA.

CONCLUSION

The findings of the present study indicate that IL-17A-197G/A and IL-17F-7488T/C polymorphisms are positively associated to reduced risk of knee OA, especially in Asian populations.

Mitochondrial DNA haplogroups associated with MRI-detected structural damage in early knee osteoarthritis

OBJECTIVE

Magnetic resonance imaging (MRI)-detected structural features are associated with increased risk of radiographic osteoarthritis (ROA). Specific mitochondrial DNA (mtDNA) haplogroups have been associated with incident ROA. Our objective was to compare the presence of MRI-detected structural features across mtDNA haplogroups among knees that developed incident ROA.

DESIGN

Knees from the Osteoarthritis Initiative (OAI) that developed incident ROA during 48 months follow-up were identified from Caucasian participants. mtDNA haplogroups were assigned based on a single base extension assay. MRIs were obtained annually between baseline and 4-year follow-up and scored using the MRI Osteoarthritis Knee Score (MOAKS). The association between mtDNA haplogroups and MRI-detected structural features was estimated using log-binomial regression. Participants who carried haplogroup H served as the reference group.

RESULTS

The sample included 255 participants contributing 277 knees that developed ROA. Haplogroups included H (116, 45%), J (17, 7%), T (26, 10%), Uk (61, 24%), and the remaining less common haplogroups ("others") (35, 14%). Knees of participants with haplogroup J had significantly lower risk of medium/large bone marrow lesions (BMLs) in the medial compartment [3.2%, relative risks (RR) = 0.17; 95%CI: 0.05, 0.64; P = 0.009] compared to knees of participants who carried haplogroup H [16.3%], as did knees from participants within the "others" group [2.8%, RR = 0.20; 95%CI: 0.08, 0.55; P = 0.002], over the 4 year follow-up period.

CONCLUSIONS

mtDNA haplogroup J was associated with lower risk of BMLs in the medial compartment among knees that developed ROA. Our results offer a potential hypothesis to explain the mechanism underlying the previously reported protective association between haplogroup J and ROA.

Imaging of osteoarthritis-recent research developments and future perspective

In osteoarthritis research, imaging plays an important role in clinical trials and epidemiological observational studies. In this narrative review article, we will describe recent developments in imaging of osteoarthritis in the research arena, mainly focusing on literature evidence published within the past 3 years (2014-2017). We will primarily focus on MRI including advanced imaging techniques that are not currently commonly used in routine clinical practice, although radiography, ultrasound and nuclear medicine (radiotracer) imaging will also be discussed. Research efforts to uncover the disease process of OA as well as to discover a disease modifying OA drug continue. MRI continues to play a large role in these endeavors, while compositional MRI techniques will increasingly become important due to their ability to assess "premorphologic" biochemical changes of articular cartilage and other tissues in and around joints. Radiography remain the primary imaging modality for defining inclusion/exclusion criteria as well as an outcome measure in OA clinical trials, despite known limitations for visualization of OA features. Compositional MRI techniques show promise for predicting structural and clinical outcomes in OA research. Ultrasound can be a useful adjunct to radiography and MRI particularly for evaluation of hand OA. Newer imaging techniques such as hybrid PET/MRI may have a potential but require further research and validation.

A Comprehensive Review of Stem Cells for Cartilage Regeneration in Osteoarthritis

Osteoarthritis (OA) is an age related joint disease associated with degeneration and loss of articular cartilage. Consequently, OA patients suffer from chronic joint pain and disability. Weight bearing joints and joints that undergo repetitive stress and excessive 'wear and tear' are particularly prone to developing OA. Cartilage has a poor regenerative capacity and current pharmacological agents only provide symptomatic pain relief. OA patients that respond poorly to conventional therapies are ultimately treated with surgical procedures to promote cartilage repair by implantation of artificial joint structures (arthroplasty) or total joint replacement (TJR). In the last two decades, stem cells derived from various tissues with varying differentiation and tissue regeneration potential have been used for the treatment of OA either alone or in combination with natural or synthetic scaffolds to aid cartilage repair. Although stem cells can be differentiated into chondrocytes in vitro or aid cartilage regeneration in vivo, their potential for OA management remains limited as cartilage regenerated by stem cells fails to fully recapitulate the structural and biomechanical properties of the native tissue. Efficient tissue regeneration remains elusive despite the simple design of cartilage, which unlike most other tissues is avascular and aneural, consisting of a single cell type. In this article, we have comprehensively reviewed the types of stem cells that have been proposed or tested for the management of OA, their potential efficacy as well as their limitations. We also touch on the role of biomaterials in cartilage tissue engineering and examine the prospects for their use in cell-based therapies.

Do immune cells lead the way in subchondral bone disturbance in osteoarthritis?

Osteoarthritis (OA) is a whole-joint disorder, and non-cartilage articular pathologies, e.g. subchondral bone disturbance, contribute substantially to the onset and progression of the disease. In the early stage of OA, abnormal mechanical loading leads to micro-cracks or micro-fractures that trigger a reparative process with angiogenesis and inflammatory response. With the progression of disease, cystic lesion, sclerosis and osteophytosis occur at tissue level, and osteoblast dysfunction at cellular level. Osteoblasts derived from OA sclerotic bone produce increased amount of type I collagen with aberrant Col1A1/A2 ratio and poor mineralization capability. The coupling mechanism of bone resorption with formation is also impaired with elevated osteoclastic activities. All these suggest a view that OA subchondral bone presents a defective fracture repair process in a chronic course. It has been found that T and B cells, the major effectors in the adaptive immunity, take part in the hard callus formation at fracture site in addition to the initial phase of haematoma and inflammation. Infiltration of lymphocytes could interplay with osteoclasts and osteoblasts via a direct physical cell-to-cell contact. Several lines of evidence have consistently shown the involvement of T and B cells in osteoclastogenesis and bone erosion in arthritic joints. Yet the biological link between immune cells and osteoblastic function remains ambiguous. This review will discuss the current knowledge regarding the role of immune cells in bone remodelling, and address its implications in emerging basic and clinical investigations into the pathogenesis and management of subchondral bone pathologies in OA.