Receptor activator of nuclear factor kappa B ligand serum and synovial fluid level. A comparative study between rheumatoid arthritis and osteoarthritis

Comparative study of the synovial levels of RANKL and OPG in rheumatoid arthritis, spondyloarthritis and osteoarthritis

INTRODUCTION

In chronic arthropathies, there are several mechanisms of joint destruction. In recent years, studies have reported the implication of receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) in the process of activation and differentiation of osteoclasts, a key cell in the development of bone erosion. The RANKL/OPG ratio is increased in the serum of patients with malignant diseases and lytic bone disease, as well as rheumatoid arthritis (RA). The objective of this study was to measure and compare the concentrations of OPG and RANKL in the synovial fluid (SF) of patients with rheumatoid arthritis, spondyloarthritis (SpA) and osteoarthritis (OA).

METHODS

This was an observational and cross-sectional study with 83 patients, 33 with RA, 32 with SpA and 18 with OA, followed up regularly in the outpatient clinics of the Rheumatology Department of the Clinics Hospital of the Ribeirão Preto Medical School-USP. All patients were assessed for indications for arthrocentesis by the attending physicians at the time of SF collection and were evaluated for demographic variables and medication use. Disease activity was assessed in individuals with RA and SpA. The quantification of SF OPG and RANKL levels was performed by ELISA, and the correlations of the results with clinical, laboratory and radiological parameters were assessed.

RESULTS

We found no statistically significant difference in the RANKL and OPG levels among the groups. Patients with RA showed a positive correlation between the SF cell count and RANKL level (r = 0.59; p < 0.05) and the RANKL/OPG ratio (r = 0.55; p < 0.05). Patients with OA showed a strong correlation between C-reactive protein (CRP) and the RANKL/OPG ratio (r = 0.82; p < 0.05). There was no correlation between the OPG and RANKL levels and markers of inflammatory activity or the disease activity index in patients with RA or SpA.

CONCLUSION

Within this patient cohort, the RANKL/OPG ratio was correlated with the SF cell count in patients with RA and with serum CRP in patients with OA, which may suggest a relationship with active inflammation and more destructive joint disease.

Synovial Fluid Biomarkers in Knee Osteoarthritis: A Systematic Review and Quantitative Evaluation Using BIPEDs Criteria

OBJECTIVE

The aim of this systematic review was to analyze the evidence about the efficacy of the several synovial fluid (SF) biomarkers proposed for knee osteoarthritis (OA), categorizing them by both molecular characteristics and clinical use according to the BIPEDs criteria, to provide a comprehensive and structured overview of the current literature.

DESIGN

A systematic review was performed in May 2020 on PubMed, Cochrane Library, and Embase databases about SF biomarkers in patients with knee OA. The search was limited to articles in the last 20 years on human studies, involving patients with knee OA, reporting SF biomarkers. The evidence for each selected SF biomarker was quantified according to the 6 categories of BIPEDs classification.

RESULTS

A total of 159 articles were included in the qualitative data synthesis and 201 different SF biomarkers were identified. Among these, several were investigated multiple times in different articles, for a total of 373 analyses. The studies included 13,557 patients with knee OA. The most promising SF biomarkers were C4S, IL-6, IL-8, Leptin, MMP-1/3, TIMP-1, TNF-α, and VEGF. The "burden of disease" and "diagnostic" categories were the most represented with 132 and 106 different biomarkers, respectively.

CONCLUSIONS

The systematic review identified numerous SF biomarkers. However, despite the high number of studies on the plethora of identified molecules, the evidence about the efficacy of each biomarker is supported by limited and often conflicting findings. Further research efforts are needed to improve the understanding of SF biomarkers for a better management of patients with knee OA.

Association of fibulin-3 concentrations with the presence and severity of knee osteoarthritis: A cross-sectional study

BACKGROUND

Fibulin-3, a member of the extracellular matrix glycoproteins family, negatively regulates chondrocyte differentiation. This study aims to assess the correlation of fibulin-3 concentrations with the presence and severity of knee osteoarthritis.

METHODS

This cross-sectional study was performed in a population of 209 knee osteoarthritis subjects who received hyaluronic acid treatment and 165 healthy controls. Knee osteoarthritis diagnosis was made according to the criteria of the American College of Rheumatology. Osteoarthritis severity was scored by the Kellgren-Lawrence grading method. Synovial fluid was obtained from the knees of osteoarthritis subjects who received the treatment of hyaluronic acid injection for the first time. Serum and synovial fluid fibulin-3 concentrations were examined by enzyme-linked immunosorbent assay method.

RESULTS

Mann-Whitney U-test showed that there were higher serum fibulin-3 concentrations in the case group compared with the controls. Higher serum and synovial fluid fibulin-3 concentrations were found in knee osteoarthritis subjects compared with those with Kellgren-Lawrence grades 2 and 3. Knee osteoarthritis subjects with Kellgren-Lawrence grade 3 had higher serum and synovial fluid fibulin-3 concentrations compared with those with Kellgren-Lawrence grade 2. Serum and synovial fluid fibulin-3 concentrations were significantly correlated with Kellgren-Lawrence grading after Pearson correlation analysis (r=0.532, P<0.001 and r=0.613, P<0.001). Multinomial logistic regression analysis demonstrated a significant association between serum and synovial fluid fibulin-3 concentrations with Kellgren-Lawrence grades (P<0.001 and P<0.001).

CONCLUSION

Serum and synovial fluid fibulin-3 concentrations were correlated with the presence and severity of knee osteoarthritis.

Effects of iguratimod on the levels of circulating regulators of bone remodeling and bone remodeling markers in patients with rheumatoid arthritis

This study aims to investigate the effect of iguratimod, a novel disease-modifying antirheumatic drug, alone or combined with methotrexate (MTX), on the serum levels of regulators of bone remodeling (receptor activator of nuclear factor-κB ligand (RANKL), osteoprotegerin (OPG), and Dickkopf-1 (DKK-1)) and bone remodeling markers (C-telopeptide of type I collagen (CTX-I) and procollagen type I N-terminal propeptide (PINP)) in patients with rheumatoid arthritis (RA). Patients with RA were treated with iguratimod, MTX, or their combination for 12 months. Serum samples were collected before treatment and 6 and 12 months afterwards. RANKL, OPG, DKK-1, CTX-I, and PINP levels were measured, and radiographic progression was assessed. The serum RANKL levels decreased after treatment for 6 and 12 months with iguratimod (median: baseline 565.00 pmol/L vs. 6 months 411.00 pmol/L vs. 12 months 212.00 pmol/L), MTX (median: baseline 562.50 pmol/L vs. 6 months 399.50 pmol/L vs. 12 months 163.50 pmol/L), and their combination (median: baseline 971.00 pmol/L vs. 6 months 272.50 pmol/L vs. 12 months 241.50 pmol/L). Combination therapy showed greater effects 6 months post-treatment compared to single-drug therapy. PINP levels increased significantly 12 months post-treatment with all therapies, but only the combination therapy led to decreased CTX-I levels. OPG and DKK-1 levels showed no significant changes. The three treatments showed no significant differences in radiographic progression. Iguratimod could stimulate bone formation and regulate the RANKL/RANK/OPG system rather than DKK-1levels. Its effects are comparable to those of MTX, and combination therapy showed stronger effects.

Animal Models of Bone Loss in Inflammatory Arthritis: from Cytokines in the Bench to Novel Treatments for Bone Loss in the Bedside-a Comprehensive Review

Throughout life, bone is continuously remodelled. Bone is formed by osteoblasts, from mesenchymal origin, while osteoclasts induce bone resorption. This process is tightly regulated. During inflammation, several growth factors and cytokines are increased inducing osteoclast differentiation and activation, and chronic inflammation is a condition that initiates systemic bone loss. Rheumatoid arthritis (RA) is a chronic inflammatory auto-immune disease that is characterised by active synovitis and is associated with early peri-articular bone loss. Peri-articular bone loss precedes focal bone erosions, which may progress to bone destruction and disability. The incidence of generalised osteoporosis is associated with the severity of arthritis in RA and increased osteoporotic vertebral and hip fracture risk. In this review, we will give an overview of different animal models of inflammatory arthritis related to RA with focus on bone erosion and involvement of pro-inflammatory cytokines. In addition, a humanised endochondral ossification model will be discussed, which can be used in a translational approach to answer osteoimmunological questions.

Assessment of the Effect of Methotrexate Therapy on Bone Metabolism in Patients with Rheumatoid Arthritis

Proinflammatory cytokines and growth factors, which regulate mutual interactions between immune system cells and bone tissue cells, play a major role in the formation of bone changes in rheumatoid arthritis (RA). The aim of the work was to assess serum concentration of osteoprotegerin (OPG), RANKL, Dkk-1 and sclerostin in RA patients compared to a control group and to analyze changes of these concentrations during methotrexate (MTX) therapy. Patients enrolled in the study were 30 women of Caucasian origin aged 30-74 years with RA. Patients with active form of the disease were administered recommended doses of MTX for at least 6 months. The study group was divided into subgroup I-patients with improvement; and subgroup II-patients with no improvement. The control group consisted of 12 healthy women in the age of 41-73. Before MTX therapy, RA patients had higher levels of RANKL (644.97 ± 477.13 vs. 255.19 ± 130.26 pmol/l), lower values of OPG/RANKL (0.01 ± 0.0101 vs. 0.02 ± 0.0078) and higher levels of Dkk-1 protein (1821.32 ± 1060.28 vs. 548.52 ± 36.35 pg/ml) compared to the control group. In the analyzed group of patients (all patients receiving MTX regardless of responder non responder status) after 6 months of therapy, a statistically significant increase in the ratio of OPG/RANKL was found (0.0118 ± 0.0102 vs. 0.0141 ± 0.0118; p = 0.02). The index value of OPG/RANKL differed significantly depending on the resultant effect of treatment (0.01702 ± 0.01274 in the subgroup of improvement vs. 0.00675 ± 0.00289 in the subgroup without improvement). The difference in the mean concentrations of Dkk-1 before and after treatment with MTX between subgroups I and II was statistically significant (p = 0.002). In subgroup I, mean concentration of Dkk-1 decreased after 6 months of treatment with MTX (2054.72 ± 1004.74 vs. 1831.70 ± 851.70 pg/ml); while in subgroup II, the mean concentration of Dkk-1 increased (1214.48 ± 738.32 vs. 2275.01 ± 1385.23 pg/ml). There were no statistically significant changes in the mean concentrations of sclerostin before and after treatment with MTX (in whole group treatment with MTX, in subgroup I, and in subgroup II). The results confirm the presence of disorders of bone metabolism in patients with RA. Treatment with MTX affects the value of the ratio of OPG/RANKL and concentration of Dkk-1.

Non-canonical NF-κB signaling in rheumatoid arthritis: Dr Jekyll and Mr Hyde?

The nuclear factor-κB (NF-κB) family of transcription factors is essential for the expression of pro-inflammatory cytokines, but can also induce regulatory pathways. NF-κB can be activated via two distinct pathways: the classical or canonical pathway, and the alternative or non-canonical pathway. It is well established that the canonical NF-κB pathway is essential both in acute inflammatory responses and in chronic inflammatory diseases, including rheumatoid arthritis (RA). Although less extensively studied, the non-canonical NF-κB pathway is not only central in lymphoid organ development and adaptive immune responses, but is also thought to play an important role in the pathogenesis of RA. Importantly, this pathway appears to have cell type-specific functions and, since many different cell types are involved in the pathogenesis of RA, it is difficult to predict the net overall contribution of the non-canonical NF-κB pathway to synovial inflammation. In this review, we describe the current understanding of non-canonical NF-κB signaling in various important cell types in the context of RA and consider the relevance to the pathogenesis of the disease. In addition, we discuss current drugs targeting this pathway, as well as future therapeutic prospects.

Osteoarthritis year 2013 in review: biomarkers; reflecting before moving forward, one step at a time

In 2010, in Osteoarthritis and Cartilage, we published a comprehensive systematic review applying the consensus BIPED criteria (Burden of Disease, Investigative, Prognostic, Efficacy of Intervention and Diagnostic) criteria on serum and urinary biochemical markers for knee and hip osteoarthritis (OA) using publications that were available at that time. It appeared that none of the biochemical markers at that time were sufficiently discriminating to allow diagnosis and prognosis of OA in individual or limited numbers of patients, nor performed so consistently that they could function as primary outcome parameters in clinical trials. Also at present, almost 3 years later, this ultimate goal has not been reached (yet). Frankly, it might be questioned whether we are making the most adequate steps ahead and maybe we have to take a step back to reconsider our approaches. Some reflections are made and discussed: A critical review of molecular metabolism in OA and validation of currently investigated marker molecules in this may be vital and may lead to new and better markers. Creating cohorts in which synovial fluid (SF) is obtained in a systematic way, together with serum and urine, may also bring the field a further step ahead. Thirdly, better understanding of different phenotypes (subtypes) of OA may facilitate identification and validation of biochemical markers. Finally, the systems biology approach as discussed in the last years OA in review on biomarkers, although very complex, might provide steps forward. Looking ahead, we are optimistic but realistic in our expectations, we believe that the field can be brought forward by critically and cautiously reconsidering our approaches, and making changes forward, one step at a time.

Chronic low dose tumor necrosis factor-α (TNF) suppresses early bone accrual in young mice by inhibiting osteoblasts without affecting osteoclasts

The inflammatory cytokine tumor necrosis factor-α (TNF-α) is known to cause bone resorption and inhibit bone formation in arthritis and aging but less is known about TNF effects in the young growing skeleton. While investigating the mechanism of bone loss in TNF transgenic mice, we identified an early TNF-sensitive period marked by suppression of osteoblasts and bone accrual as the sole mechanism of TNF action, without an effect on osteoclasts or bone resorption. TgTNF mice express low concentrations of hTNFα (≤5 pg/ml). Osteoblasts cultured from TgTNF mice express reduced levels of RUNX2, Osx, alkaline phosphatase, bone sialoprotein, and osteocalcin and have delayed formation of mineralized nodules. Early accrual of bone in TgTNF mice is suppressed until 6 weeks of age, after which the rate of bone accrual normalizes without catch up. Histomorphometry revealed that TgTNF mice fail to generate a transient surge in osteoblast number that is seen in wild type (WT) mice at 4 weeks. Osteoclasts, TRAP staining, erosive surfaces, serum CTx, and OPG/RANKL expression did not differ between young TgTNF and WT mice. Canonical Wnts and signaling through β-catenin were reduced in TgTNF mice at 4 weeks and partially recovered by 12 weeks, associated with reduced cytoplasm to nuclear transfer of β-catenin and Wnt regulated genes. TgTNF mice were crossed with BatGal Wnt reporter mice. Active Wnt signaling in tibial trabecular lining cells was reduced in TgTNF mice at 4 weeks compared to control littermates. Our results demonstrate that a low dose inflammatory stimulus is sufficient to inhibit the early surge in osteoblasts and optimal bone formation of young mice independent of changes in osteoclasts. TNF inhibition of the Wnt pathway contributes to the suppression of osteoblasts.

Pathways for bone loss in inflammatory disease

Chronic inflammation including autoimmune disease is an important risk factor for the development of osteoporosis. Receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) play a central role in osteoclast differentiation and function, and the molecular pathways by which M-CSF and RANKL induce osteoclast differentiation have been analyzed in detail. Proinflammatory cytokines directly or indirectly regulate osteoclastogenesis and bone resorption providing a link between inflammation and osteoporosis. Tumor necrosis factor-α, interleukin (IL)-1, IL-6, and IL-17 are the most important proinflammatory cytokines triggering inflammatory bone loss. Inhibition of these cytokines has provided potent therapeutic effects in the treatment of diseases such as rheumatoid arthritis. Further investigation is needed to understand the pathophysiology and to develop new strategies to treat inflammatory bone loss. This review summarizes new data on inflammatory bone loss obtained in 2011.