RANKL protein is expressed at the pannus-bone interface at sites of articular bone erosion in rheumatoid arthritis

RANKL synthesized by articular chondrocytes contributes to juxta-articular bone loss in chronic arthritis

INTRODUCTION

The receptor activator nuclear factor-kappaB ligand (RANKL) diffuses from articular cartilage to subchondral bone. However, the role of chondrocyte-synthesized RANKL in rheumatoid arthritis-associated juxta-articular bone loss has not yet been explored. This study aimed to determine whether RANKL produced by chondrocytes induces osteoclastogenesis and juxta-articular bone loss associated with chronic arthritis.

METHODS

Chronic antigen-induced arthritis (AIA) was induced in New Zealand (NZ) rabbits. Osteoarthritis (OA) and control groups were simultaneously studied. Dual X-ray absorptiometry of subchondral knee bone was performed before sacrifice. Histological analysis and protein expression of RANKL and osteoprotegerin (OPG) were evaluated in joint tissues. Co-cultures of human OA articular chondrocytes with peripheral blood mononuclear cells (PBMCs) from healthy donors were stimulated with macrophage-colony stimulating factor (M-CSF) and prostaglandin E2 (PGE2), then further stained with tartrate-resistant acid phosphatase.

RESULTS

Subchondral bone loss was confirmed in AIA rabbits when compared with controls. The expression of RANKL, OPG and RANKL/OPG ratio in cartilage were increased in AIA compared to control animals, although this pattern was not seen in synovium. Furthermore, RANKL expression and RANKL/OPG ratio were inversely related to subchondral bone mineral density. RANKL expression was observed throughout all cartilage zones of rabbits and was specially increased in the calcified cartilage of AIA animals. Co-cultures demonstrated that PGE2-stimulated human chondrocytes, which produce RANKL, also induce osteoclasts differentiation from PBMCs.

CONCLUSIONS

Chondrocyte-synthesized RANKL may contribute to the development of juxta-articular osteoporosis associated with chronic arthritis, by enhancing osteoclastogenesis. These results point out a new mechanism of bone loss in patients with rheumatoid arthritis.

[New therapeutic targets in psoriatic arthritis]

Registries estimate that one third of patients with psoriatic arthritis (PsA) are "resistant" to of TNF-alpha blockers. Therefore, the search for new approaches to treatment of this disease may be justified. Currently the treatment options that have proven effective are associated with inhibition of the T cell costimulatory pathway (abatacept and alefacept) and blocking the P40 fraction of IL-12 and IL-23 (ustekinumab). A novel pathway inhibition, which deserves special attention is offered by apremilast. This molecule inhibits phosphodiesterase IV, responsible for hydrolyzing cyclic adenosine monophosphate to adenosine monophosphate, which causes an increase in cAMP. This metabolite is associated with decreased TNF-alpha. It has a modest efficacy (ACR 20 response of 43%), and subsequent studies have shown an improvement in visual analog scale and the SF36 compared to placebo. Currently there are five clinical trials in phase III to assess its effectiveness in parameters of inflammation and radiographic progression. The spectrum of possibilities before treatment failure with anti-TNF alpha, is augmented by the appearance of several reports that show efficacy with the individual use of CD20 inhibitors and IL-1. In patients with rheumatoid arthritis (RA) the effectiveness of molecules that inhibit signal transduction of cytokines (Anti-JAK) has been proven, so it is possible that in the future they may be used in patients with PsA.

Wnt5a-Ror2 signaling between osteoblast-lineage cells and osteoclast precursors enhances osteoclastogenesis

The signaling molecule Wnt regulates bone homeostasis through β-catenin-dependent canonical and β-catenin-independent noncanonical pathways. Impairment of canonical Wnt signaling causes bone loss in arthritis and osteoporosis; however, it is unclear how noncanonical Wnt signaling regulates bone resorption. Wnt5a activates noncanonical Wnt signaling through receptor tyrosine kinase-like orphan receptor (Ror) proteins. We showed that Wnt5a-Ror2 signaling between osteoblast-lineage cells and osteoclast precursors enhanced osteoclastogenesis. Osteoblast-lineage cells expressed Wnt5a, whereas osteoclast precursors expressed Ror2. Mice deficient in either Wnt5a or Ror2, and those with either osteoclast precursor-specific Ror2 deficiency or osteoblast-lineage cell-specific Wnt5a deficiency showed impaired osteoclastogenesis. Wnt5a-Ror2 signals enhanced receptor activator of nuclear factor-κB (RANK) expression in osteoclast precursors by activating JNK and recruiting c-Jun on the promoter of the gene encoding RANK, thereby enhancing RANK ligand (RANKL)-induced osteoclastogenesis. A soluble form of Ror2 acted as a decoy receptor of Wnt5a and abrogated bone destruction in mouse arthritis models. Our results suggest that the Wnt5a-Ror2 pathway is crucial for osteoclastogenesis in physiological and pathological environments and represents a therapeutic target for bone diseases, including arthritis.

Definitive differences in laboratory and radiological characteristics between two subtypes of juvenile idiopathic arthritis: systemic arthritis and polyarthritis

We performed this study to investigate the differences in radiological and laboratory findings between systemic juvenile idiopathic arthritis (s-JIA) and polyarthritis (p-JIA). Twenty-two patients with s-JIA and 18 with p-JIA were enrolled. Their laboratory findings and radiographs were examined retrospectively. Plain radiographs were obtained before the induction of biological agents. All radiographs were examined for the presence of soft tissue swelling, juxta-articular osteopenia, joint space narrowing, subchondral bone cyst, erosion, epiphyseal irregularity, and growth abnormalities. Carpal length and bone mineral density of the lumbar spine, an indicator of generalized osteoporosis, were also investigated in all the patients enrolled. Laboratory examinations involved white blood cell counts, platelets, C-reactive protein (CRP), rheumatoid factor (RF), anti-cyclic citrullinated peptide (CCP) antibody, and matrix metalloproteinase (MMP)-3. Comparisons of the laboratory findings between s-JIA and p-JIA indicated that the titers of anti-CCP antibody and RF were significantly increased in p-JIA sera (P < 0.05). There was no difference in BMD between the two groups of patients. Carpal length was significantly shorter in p-JIA patients than in s-JIA patients (P < 0.05). The most frequent radiological abnormality in s-JIA was juxta-articular osteopenia (93.8%), in comparison to a frequency of 50.0% in p-JIA. Joint space narrowing was shown in 9.8% of the s-JIA patients compared to 35.7% of the p-JIA patients. Subchondral bone cyst and erosion were more frequent in p-JIA than s-JIA. In conclusion, there were differences in radiographic characteristics and laboratory data between s-JIA and p-JIA in this study. In the radiological evaluation, bone-related abnormality was prominent in s-JIA and joint-related abnormality was striking in p-JIA, and these results indicated that the pathogenic bases of arthritis appear to differ between these two subtypes of JIA.

Osteoimmunology and osteoporosis

The concept of osteoimmunology is based on growing insight into the links between the immune system and bone at the anatomical, vascular, cellular, and molecular levels. In both rheumatoid arthritis (RA) and ankylosing spondylitis (AS), bone is a target of inflammation. Activated immune cells at sites of inflammation produce a wide spectrum of cytokines in favor of increased bone resorption in RA and AS, resulting in bone erosions, osteitis, and peri-inflammatory and systemic bone loss. Peri-inflammatory bone formation is impaired in RA, resulting in non-healing of erosions, and this allows a local vicious circle of inflammation between synovitis, osteitis, and local bone loss. In contrast, peri-inflammatory bone formation is increased in AS, resulting in healing of erosions, ossifying enthesitis, and potential ankylosis of sacroiliac joints and intervertebral connections, and this changes the biomechanical competence of the spine. These changes in bone remodeling and structure contribute to the increased risk of vertebral fractures (in RA and AS) and non-vertebral fractures (in RA), and this risk is related to severity of disease and is independent of and superimposed on background fracture risk. Identifying patients who have RA and AS and are at high fracture risk and considering fracture prevention are, therefore, advocated in guidelines. Local peri-inflammatory bone loss and osteitis occur early and precede and predict erosive bone destruction in RA and AS and syndesmophytes in AS, which can occur despite clinically detectable inflammation (the so-called 'disconnection'). With the availability of new techniques to evaluate peri-inflammatory bone loss, osteitis, and erosions, peri-inflammatory bone changes are an exciting field for further research in the context of osteoimmunology.

Osteoimmunology at the nexus of arthritis, osteoporosis, cancer, and infection

Over the past decade and a half, the biomedical community has uncovered a previously unappreciated reciprocal relationship between cells of the immune and skeletal systems. Work in this field, which has been termed "osteoimmunology," has resulted in the development of clinical therapeutics for seemingly disparate diseases linked by the common themes of inflammation and bone remodeling. Here, the important concepts and discoveries in osteoimmunology are discussed in the context of the diseases bridging these two organ systems, including arthritis, osteoporosis, cancer, and infection, and the targeted treatments used by clinicians to combat them.

Estrogens in rheumatoid arthritis; the immune system and bone

Rheumatoid arthritis (RA) is an autoimmune disease that is more common in women than in men. The peak incidence in females coincides with menopause when the ovarian production of sex hormones drops markedly. RA is characterized by skeletal manifestations where production of pro-inflammatory mediators, connected to the inflammation in the joint, leads to bone loss. Animal studies have revealed distinct beneficial effects of estrogens on arthritis, and a positive effect of hormone replacement therapy has been reported in women with postmenopausal RA. This review will focus on the influence of female sex hormones in the pathogenesis and progression of RA.

Tumor necrosis factor-alpha promotes survival in methotrexate-exposed macrophages by an NF-kappaB-dependent pathway

Introduction

Methotrexate (MTX) induces macrophage apoptosis in vitro, but there is not much evidence for increased synovial macrophage apoptosis in MTX-treated patients. Macrophage apoptosis is reported, however, during clinical response to anti-tumor necrosis factor-alpha (TNF-α) treatments. This implies that TNF-α promotes macrophage survival and suggests that TNF-α may protect against MTX-induced apoptosis. We, therefore, investigated this proposal and the macrophage signaling pathways underlying it.

Methods

Caspase-3 activity, annexin-V binding/7-aminoactinomycin D (7-AAD) exclusion and cell-cycle analysis were used to measure steps in apoptosis of primary murine macrophages and cells of the RAW_264.7 macrophage cell line that had been exposed to clinically-relevant concentrations of MTX and TNF-α.

Results

MTX induces apoptosis in primary murine macrophages at concentrations as low as 100 nM in vitro. TNF-α, which has a context-dependent ability to increase or to suppress apoptosis, efficiently suppresses MTX-induced macrophage apoptosis. This depends on NF-κB signaling, initiated through TNF Receptor Type 1 ligation. Macrophage colony stimulating factor, the primary macrophage survival and differentiation factor, does not activate NF-κB or protect macrophages from MTX-induced apoptosis. A weak NF-κB activator, Receptor Activator of NF-κB Ligand (RANKL) is likewise ineffective. Blocking NF-κB in TNF-α-exposed macrophages allowed pro-apoptotic actions of TNF-α to dominate, even in the absence of MTX. MTX itself does not promote apoptosis through interference with NF-κB signaling.

Conclusions

These findings provide another mechanism by which TNF-α sustains macrophage numbers in inflamed tissue and identify a further point of clinical complementarity between MTX and anti-TNF-α treatments for rheumatoid arthritis.

Osteoporosis in inflammatory joint diseases

Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are two inflammatory joint diseases characterized by bone complications including osteoporosis. In RA, periarticular bone loss, bone erosions, and systemic osteoporosis are observed, with an increased risk of fractures. Determinants of fractures are underlying conditions (as RA has a female preponderance and an increased prevalence with age), severity of the disease, and use of glucocorticoids. However, bone loss can occur even in glucocorticoid-naive patients. Prospective data show that the optimal control of inflammation in RA is associated with decrease in structural damage and bone loss. RA illustrates the role of inflammation on bone resorption. In AS, osteoporosis is an early event and vertebral fracture risk is increased. Bone loss is related mainly to inflammation, as the disease can occur in young male adult populations, and glucocorticoids are not used in this disease. However, AS is characterized by progressive stiffness and ankylosis of the spine and illustrates also the potential role of inflammation on local bone formation.

GP130 cytokines and bone remodelling in health and disease

Cytokines that bind to and signal through the gp130 co-receptor subunit include interleukin (IL)-6, IL-11, oncostatin M (OSM), leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), and ciliary neutrophic factor (CNTF). Apart from contributing to inflammation, gp130 signalling cytokines also function in the maintenance of bone homeostasis. Expression of each of these cytokines and their ligand-specific receptors is observed in bone and joint cells, and bone-active hormones and inflammatory cytokines regulate their expression. gp130 signalling cytokines have been shown to regulate the differentiation and activity of osteoblasts, osteoclasts and chondrocytes. Furthermore, cytokine and receptor specific gene-knockout mouse models have identified distinct roles for each of these cytokines in regulating bone resorption, bone formation and bone growth. This review will discuss the current models of paracrine and endocrine actions of gp130-signalling cytokines in bone remodelling and growth, as well as their impact in pathologic bone remodelling evident in periodontal disease, rheumatoid arthritis, spondylarthropathies and osteoarthritis.

Serum levels of osteoprotegerin and receptor activator of nuclear factor -κB ligand in children with early juvenile idiopathic arthritis: a 2-year prospective controlled study

BACKGROUND

The clinical relevance of observations of serum levels of osteoprotegerin (OPG) and receptor activator of nuclear factor -κB ligand (RANKL) in juvenile idiopathic arthritis (JIA) is not clear. To elucidate the potential role of OPG and RANKL in JIA we determined serum levels of OPG and RANKL in patients with early JIA compared to healthy children, and prospectively explored changes in relation to radiographic score, bone and lean mass, severity of the disease, and treatment.

METHODS

Ninety children with early oligoarticular or polyarticular JIA (ages 6-18 years; mean disease duration 19.4 months) and 90 healthy children individually matched for age, sex, race, and county of residence, were examined at baseline and 2-year follow-up. OPG and RANKL were quantified by enzyme-immunoassay. Data were analyzed with the use of t-tests, ANOVA, and multiple regression analyses.

RESULTS

Serum OPG was significantly lower in patients than controls at baseline, and there was a trend towards higher RANKL and a lower OPG/RANKL ratio. Patients with polyarthritis had significantly higher increments in RANKL from baseline to follow-up, compared to patients with oligoarthritis. RANKL was a significant negative predictor for increments in total body lean mass. Patients who were receiving corticosteroids (CS) or disease-modifying antirheumatic drugs (DMARDs) at follow-up had higher OPG/RANKL ratio compared with patients who did not receive this medication.

CONCLUSIONS

The data supports that levels of OPG are lower in patients with JIA compared to healthy children, and higher levels of RANKL is associated with more serious disease. RANKL was a significant negative predictor of lean mass in patients with JIA. The OPG/RANKL ratio was higher in patients on DMARDs or CS treatment.

Regulatory T cells as a potent target for controlling bone loss

Metabolic bone diseases, such as rheumatoid arthritis (RA) and osteoporosis, affect hundreds and millions of people worldwide leading causes of long-term pain and disability. Effective clinical treatment for bone destruction in bone diseases is lacking because the knowledge about molecular mechanisms leading to bone destruction are incompletely understood. Recently, it has been confirmed that regulatory T cells (Tregs) play a crucial role in suppressing the immune response in the pathogenesis of various autoimmune diseases. In vitro, Tregs directly inhibit osteoclasts and differentiation and function. In mice, the injection of Tregs into the TNF transgenic results in enhanced systemic bone density. In addition, it has been shown that increase of Tregs numbers by overexpressing the FoxP3 is effective in the prevention of local and systemic bone destruction. In vivo treatment with anti-CD28 superagonist antibody leading to a stronger increase in Tregs numbers protect against TNF-a-induced bone loss in TNF-transgenic mice. In agreement, Tregs can control ovariectomy-induced bone loss in FoxP3-transgenic mice. In this paper, we will briefly discuss the biological features of Tregs and summarize recent advances on the role of Tregs in the pathogenesis and treatment of bone loss in metabolic bone diseases.

Rank Protein Immunolabeling during Bone-Implant Interface Healing Process

The purpose of this paper was to evaluate the expression of RANK protein during bone-healing process around machined surface implants. Twenty male Wistar rats, 90 days old, after having had a 2 mm diameter and 6 mm long implant inserted in their right tibias, were evaluated at 7, 14, 21, and 42 days after healing. After obtaining the histological samples, slides were subjected to RANK immunostaining reaction. Results were quantitatively evaluated. Results. Immunolabeling analysis showed expressions of RANK in osteoclast and osteoblast lineage cells. The statistical analysis showed an increase in the expression of RANK in osteoblasts at 7 postoperative days and a gradual decrease during the chronology of the healing process demonstrated by mild cellular activity in the final stage (P < .05). Conclusion. RANK immunolabeling was observed especially in osteoclast and osteoblast cells in primary bone during the initial periods of bone-healing/implant interface.

Lymphangiogenesis, myeloid cells and inflammation

The lymphatic system is essential for the maintenance of tissue fluid balance, immune surveillance and the absorption of fatty acids in the gastrointestinal tract. The lymphatic circulation is also a key player in disease processes such as cancer metastasis, lymphedema and various inflammatory disorders. With the identification of specific growth factors for lymphatic endothelial cells and markers that distinguish blood and lymphatic vessels, as well as the development of in vivo imaging technologies that provide new tools to examine the lymphatic drainage function in real time, many advancements have been made in lymphatic vascular research during the past few years. Despite these significant achievements, our understanding of the role of lymphatics in disease processes other than cancer metastasis is still rather limited. The current review will focus on the recent progress made in studies of lymphatics in inflammatory disorders.

Immunohistochemical Analysis of Osteoblasts in Zygapophyseal Joints of Patients with Ankylosing Spondylitis Reveal Repair Mechanisms Similar to Osteoarthritis

Objective.

New bone formation of the spine is a typical feature of ankylosing spondylitis (AS). It is unknown whether new bone formation is part of a physiological repair process or a unique pathological entity of the disease.

Methods.

We analyzed zygapophyseal joints from patients with AS and osteoarthritis (OA) undergoing spinal surgery for rigid hyperkyphosis (AS) or radiculopathy caused by severe OA. In 17 patients with AS, 11 with OA, and 5 controls we performed immunohistochemical analysis of osteoprotegerin (OPG), nuclear factor-κB ligand (RANKL), and osteocalcin (OC) expression in osteoblasts and determined the trabecular thickness in AS and OA patients and controls. Osteoclasts were detected by tartrate-resistant alkaline phosphatase (TRAP) staining.

Results.

Trabecular thickness was significantly lower in patients with AS compared to OA (p = 0.01). The absolute number of CD56+ osteoblasts (p < 0.001) and OC+ (p = 0.002), OPG+ (p = 0.003), and RANKL+ osteoblasts (p = 0.03) in AS patients was also significantly lower than in OA patients. The percentages of OC+, OPG+, and RANKL+ osteoblasts did not differ between AS and OA (p > 0.05 in all cases). In controls, the percentages of OPG+ (p = 0.013) and OC+ (p = 0.034) but not RANKL+ (p > 0.05) osteoblasts were significantly lower compared to AS patients. The frequency of TRAP+ osteoclasts in AS patients was significantly lower compared to OA (p < 0.001), but higher compared to controls.

Conclusion.

Immunohistochemical analysis of zygapophyseal joints suggested that osteoblast activity is similar in AS and OA, indicating that new bone formation is possibly a physiological function of repair in both diseases.

RANKL inhibition by osteoprotegerin prevents bone loss without affecting local or systemic inflammation parameters in two rat arthritis models: comparison with anti-TNFalpha or anti-IL-1 therapies

INTRODUCTION

Rat adjuvant-induced arthritis (AIA) and collagen-induced arthritis (CIA) feature bone loss and systemic increases in TNFalpha, IL-1beta, and receptor activator of NF-kappaB ligand (RANKL). Anti-IL-1 or anti-TNFalpha therapies consistently reduce inflammation in these models, but systemic bone loss often persists. RANKL inhibition consistently prevents bone loss in both models without reducing joint inflammation. Effects of these therapies on systemic markers of bone turnover and inflammation have not been directly compared.

METHODS

Lewis rats with established AIA or CIA were treated for 10 days (from day 4 post onset) with either PBS (Veh), TNFalpha inhibitor (pegsunercept), IL-1 inhibitor (anakinra), or RANKL inhibitor (osteoprotegerin (OPG)-Fc). Local inflammation was evaluated by monitoring hind paw swelling. Bone mineral density (BMD) of paws and lumbar vertebrae was assessed by dual X-ray absorptiometry. Markers and mediators of bone resorption (RANKL, tartrate-resistant acid phosphatase 5b (TRACP 5B)) and inflammation (prostaglandin E2 (PGE2), acute-phase protein alpha-1-acid glycoprotein (alpha1AGP), multiple cytokines) were measured in serum (day 14 post onset).

RESULTS

Arthritis progression significantly increased paw swelling and ankle and vertebral BMD loss. Anti-TNFalpha reduced paw swelling in both models, and reduced ankle BMD loss in AIA rats. Anti-IL-1 decreased paw swelling in CIA rats, and reduced ankle BMD loss in both models. Anti-TNFalpha and anti-IL-1 failed to prevent vertebral BMD loss in either model. OPG-Fc reduced BMD loss in ankles and vertebrae in both models, but had no effect on paw swelling. Serum RANKL was elevated in AIA-Veh and CIA-Veh rats. While antiTNFalpha and anti-IL-1 partially normalized serum RANKL without any changes in serum TRACP 5B, OPG-Fc treatment reduced serum TRACP 5B by over 90% in both CIA and AIA rats. CIA-Veh and AIA-Veh rats had increased serum alpha1AGP, IL-1beta, IL-8 and chemokine (C-C motif) ligand 2 (CCL2), and AIA-Veh rats also had significantly greater serum PGE2, TNFalpha and IL-17. Anti-TNFalpha reduced systemic alpha1AGP, CCL2 and PGE2 in AIA rats, while anti-IL-1 decreased systemic alpha1AGP, IL-8 and PGE2. In contrast, RANKL inhibition by OPG-Fc did not lessen systemic cytokine levels in either model.

CONCLUSIONS

Anti-TNFalpha or anti-IL-1 therapy inhibited parameters of local and systemic inflammation, and partially reduced local but not systemic bone loss in AIA and CIA rats. RANKL inhibition prevented local and systemic bone loss without significantly inhibiting local or systemic inflammatory parameters.

A combination of methotrexate and zoledronic acid prevents bone erosions and systemic bone mass loss in collagen induced arthritis

Introduction

Osteoclasts play a key role in the pathogenesis of bone erosion and systemic bone mass loss during rheumatoid arthritis (RA). In this study, we aimed to determine the effect of methotrexate (MTX) and zoledronic acid (ZA), used alone or in combination, on osteoclast-mediated bone erosions and systemic bone mass loss in a rat model of collagen induced arthritis (CIA). We hypothesized that MTX and ZA could have an additive effect to prevent both bone erosion and systemic bone loss.

Methods

Arthritis was induced in 64 female Sprague-Dawley rats. After the clinical onset of CIA, rats were assigned to treatment with MTX (1 mg/kg/week), ZA (100 μg/kg twice weekly), both treatments at the same regimens, or vehicle. Arthritis score and paw thickness were recorded twice weekly. The rats were sacrificed on D28 and hind paws were removed for radiographic, histological and immunohistochemical analysis. The effects of treatments on osteoclastogenesis were determined by Tartrate resistant acid phosphatase (TRAP) staining. Micro-CT of the tibia was carried out for histomorphometric analysis. Bone mass density was evaluated by densitometry.

Results

MTX significantly decreased the severity of CIA, whereas ZA slightly exacerbated it. When these two drugs were used in combination, MTX prevented the pro-inflammatory effect of ZA. The combination of ZA with MTX was more effective than MTX alone for reducing structural joint damage with a dramatic decrease of osteoclasts' number in the eroded joints. However, MTX alone also significantly reduced the number of osteoclasts and the number of CD68+ mononuclear cells. ZA alone, or ZA with MTX, significantly increased the systemic bone mass density measured by densitometry and bone volume on histomorphometric analysis.

Conclusions

A combination of MTX and ZA prevented both bone erosion and systemic bone loss in a rat model of arthritis. Both treatments independently decreased the number of osteoclasts in the eroded joint. However, while MTX probably acts mainly through a decrease of inflammation, ZA has a direct effect on osteoclasts, allowing a dramatic down-regulation of these cells in inflamed joints. These two different mechanisms of action provide support for the use of a combination of these two drugs to improve the prevention of structural joint damage in RA.

Testing of the OMERACT 8 Draft Validation Criteria for a Soluble Biomarker Reflecting Structural Damage in Rheumatoid Arthritis: A Systematic Literature Search on 5 Candidate Biomarkers

Objective.

To test the OMERACT 8 draft validation criteria for soluble biomarkers by assessing the strength of literature evidence in support of 5 candidate biomarkers.

Methods.

A systematic literature search was conducted on the 5 soluble biomarkers RANKL, osteoprotegerin (OPG), matrix metalloprotease (MMP-3), urine C-telopeptide of types I and II collagen (U-CTX-I and U CTX-II), focusing on the 14 OMERACT 8 criteria. Two electronic voting exercises were conducted to address: (1) strength of evidence for each biomarker as reflecting structural damage according to each individual criterion and the importance of each individual criterion; (2) overall strength of evidence in support of each of the 5 candidate biomarkers as reflecting structural damage endpoints in rheumatoid arthritis (RA) and identification of omissions to the criteria set.

Results.

The search identified 111 articles. The strength of evidence in support of these biomarkers reflecting structural damage was low for all biomarkers and was rated highest for U-CTX-II [score of 6.5 (numerical rating scale 0–10)]. The lowest scores for retention of specific criteria in the draft set went to criteria that refer to the importance of animal studies, correlations with other biomarkers reflecting damage, and an understanding of the metabolism of the biomarker.

Conclusion.

Evidence in support of any of the 5 tested biomarkers (MMP-3, CTX-I, CTX-II, OPG, RANKL) was inadequate to allow their substitution for radiographic endpoints in RA. Three of the criteria in the draft criteria set might not be required, but few omissions were identified.

Emerging treatments for postmenopausal osteoporosis - focus on denosumab

The pathway of the receptor activator of the nuclear factor κB ligand (RANKL), RANK and osteoprotegerin (OPG) plays a central role in coupling bone formation and resorption during normal bone turnover and in a wide spectrum of diseases characterized by disturbed bone remodeling, increased bone resorption and bone destruction (osteoporosis, Paget’s disease of bone, rheumatoid arthritis [RA], metastatic bone disease). Clinical trials indicate that denosumab, a RANKL-specific recombinant humanized monoclonal antibody, is effective in suppressing bone resorption, resulting in increase in bone mineral density (BMD) in post-menopausal women with low BMD, and has the potential to prevent progression of erosions in RA and of skeletal-related events in metastatic bone disease. The effects on fracture reduction in postmenopausal osteoporosis are awaited from the recently finished FREEDOM study. In clinical trials with denosumab, overall adverse events were similar to placebo or comparators, indicating a favorable safety profile in these diseases, which until now have been available up to 4 years, but data on long-term safety will be needed.

Signaling networks that control the lineage commitment and differentiation of bone cells

Osteoblasts and osteoclasts are the two major bone cells involved in the bone remodeling process. Osteoblasts are responsible for bone formation while osteoclasts are the bone-resorbing cells. The major event that triggers osteogenesis and bone remodeling is the transition of mesenchymal stem cells into differentiating osteoblast cells and monocyte/macrophage precursors into differentiating osteoclasts. Imbalance in differentiation and function of these two cell types will result in skeletal diseases such as osteoporosis, Paget's disease, rheumatoid arthritis, osteopetrosis, periodontal disease, and bone cancer metastases. Osteoblast and osteoclast commitment and differentiation are controlled by complex activities involving signal transduction and transcriptional regulation of gene expression. Recent advances in molecular and genetic studies using gene targeting in mice enable a better understanding of the multiple factors and signaling networks that control the differentiation process at a molecular level. This review summarizes recent advances in studies of signaling transduction pathways and transcriptional regulation of osteoblast and osteoclast cell lineage commitment and differentiation. Understanding the signaling networks that control the commitment and differentiation of bone cells will not only expand our basic understanding of the molecular mechanisms of skeletal development but will also aid our ability to develop therapeutic means of intervention in skeletal diseases.

Cells of the synovium in rheumatoid arthritis. Chondrocytes

Rheumatoid arthritis (RA) is one of the inflammatory joint diseases in a heterogeneous group of disorders that share features of destruction of the extracellular matrices of articular cartilage and bone. The underlying disturbance in immune regulation that is responsible for the localized joint pathology results in the release of inflammatory mediators in the synovial fluid and synovium that directly and indirectly influence cartilage homeostasis. Analysis of the breakdown products of the matrix components of joint cartilage in body fluids and quantitative imaging techniques have been used to assess the effects of the inflammatory joint disease on the local remodeling of joint structures. The role of the chondrocyte itself in cartilage destruction in the human rheumatoid joint has been difficult to address but has been inferred from studies in vitro and in animal models. This review covers current knowledge about the specific cellular and biochemical mechanisms that account for the disruption of the integrity of the cartilage matrix in RA.

Receptor activator of nuclear factor kappaB ligand and osteoprotegerin regulation of bone remodeling in health and disease

Osteoclasts and osteoblasts dictate skeletal mass, structure, and strength via their respective roles in resorbing and forming bone. Bone remodeling is a spatially coordinated lifelong process whereby old bone is removed by osteoclasts and replaced by bone-forming osteoblasts. The refilling of resorption cavities is incomplete in many pathological states, which leads to a net loss of bone mass with each remodeling cycle. Postmenopausal osteoporosis and other conditions are associated with an increased rate of bone remodeling, which leads to accelerated bone loss and increased risk of fracture. Bone resorption is dependent on a cytokine known as RANKL (receptor activator of nuclear factor kappaB ligand), a TNF family member that is essential for osteoclast formation, activity, and survival in normal and pathological states of bone remodeling. The catabolic effects of RANKL are prevented by osteoprotegerin (OPG), a TNF receptor family member that binds RANKL and thereby prevents activation of its single cognate receptor called RANK. Osteoclast activity is likely to depend, at least in part, on the relative balance of RANKL and OPG. Studies in numerous animal models of bone disease show that RANKL inhibition leads to marked suppression of bone resorption and increases in cortical and cancellous bone volume, density, and strength. RANKL inhibitors also prevent focal bone loss that occurs in animal models of rheumatoid arthritis and bone metastasis. Clinical trials are exploring the effects of denosumab, a fully human anti-RANKL antibody, on bone loss in patients with osteoporosis, bone metastasis, myeloma, and rheumatoid arthritis.

VEGF-C, a lymphatic growth factor, is a RANKL target gene in osteoclasts that enhances osteoclastic bone resorption through an autocrine mechanism

Osteoclasts are bone-resorbing cells, but they also secrete and respond to cytokines. Here, we test the hypothesis that osteoclasts secrete the lymphatic growth factor, VEGF-C, to increase their resorptive activity. Osteoclasts and osteoclast precursors were generated by culturing splenocytes with macrophage colony-stimulating factor and RANKL from wild-type, NF-kappaBp50(-/-)/p52(-/-), and Src(-/-) mice. Expression of VEGFs was measured by real time reverse transcription-PCR, Western blotting, and immunostaining. The effect of VEGF-C signaling on osteoclast function was determined by osteoclastogenesis and pit assays. RANKL increased the expression of VEGF-C but not of other VEGFs in osteoclasts and their precursors. RANKL-induced VEGF-C expression was reduced in NF-kappaBp50(-/-)/p52(-/-) precursors or wild-type cells treated with an NF-kappaB inhibitor. VEGF-C directly stimulated RANKL-mediated bone resorption, which was reduced by the VEGF-C-specific receptor blocker, VEGFR3:Fc. Osteoclasts express VEGFR3, and VEGF-C stimulated Src phosphorylation in osteoclasts. VEGF-C-mediated bone resorption was abolished in Src(-/-) osteoclasts or cells treated with an Src inhibitor. We conclude that RANKL stimulates osteoclasts and their precursors to release VEGF-C through an NF-kappaB-dependent mechanism, indicating that VEGF-C is a new RANKL target gene in osteoclasts and functions as an autocrine factor regulating osteoclast activity.

Pathogenesis of calciphylaxis: Hans Selye to nuclear factor kappa-B

The clinical syndrome of calciphylaxis is characterized by arteriolar medial calcification, thrombotic cutaneous ischemia, necrotic skin ulceration, and a high mortality rate. This review integrates calciphylaxis risk factors with the molecular processes governing osseous and extraosseous mineralization. As the pathogenesis of calciphylaxis is better understood, targeted therapies aimed at disease prevention and reversal will follow.

The natural history of Charcot's neuroarthropathy

The goal of this article is to outline the progression of Charcot's neuroarthropathy. A historical background is detailed, with an emphasis on the current trends in the literature. Acute Charcot's neuroarthropathy requires a prompt diagnosis with the proper practical offloading methods of the affected limb. This, coupled with directed medical and surgical approaches designed to prevent or mitigate deformities, may subsequently reduce the risk of amputation in this high-risk population.

Developments in the synovial biology field 2006

Synovial pathophysiology is a complex and synergistic interplay of different cell populations with tissue components, mediated by a variety of signaling mechanisms. All of these mechanisms drive the affected joint into inflammation and drive the subsequent destruction of cartilage and bone. Each cell type contributes significantly to the initiation and perpetuation of this deleterious concert, especially in rheumatoid arthritis. Rheumatoid arthritis synovial fibroblasts and macrophages, both cell types with pivotal roles in inflammation and destruction, but also T cells and B cells are crucial for complex network in the inflamed synovium. An even more complex cellular crosstalk between these key players maintains a process of chronic inflammation. As outlined in the present review, in the past year substantial progress has been made to elucidate further details of the rich pathophysiology of rheumatoid arthritis, which may also facilitate the identification of novel targets for future therapeutic strategies.

Differential expression of RANK, RANK-L, and osteoprotegerin by synovial fluid neutrophils from patients with rheumatoid arthritis and by healthy human blood neutrophils

Functional links between bone remodeling and the immune system in chronic inflammatory arthritis are mediated, in part, by the ligand of receptor activator of nuclear factor-kappa-B (RANK-L). Because neutrophils play a crucial role in chronic inflammation, the goal of this study was to determine whether proteins of the RANK/RANK-L pathway are expressed by synovial fluid (SF) neutrophils from patients with rheumatoid arthritis (RA) and to characterize this pathway in normal human blood neutrophils. The expression of RANK-L, osteoprotegerin (OPG), RANK, and tumor necrosis factor receptor-associated factor 6 (TRAF6) was determined by polymerase chain reaction, enzyme-linked immunosorbent assay, Western blotting, and cytofluorometry. RANK signaling was analyzed by the degradation of inhibitor of kappaB-alpha (I-κB-α). SF neutrophils from patients with RA express and release OPG and express the membrane-associated forms of RANK-L and RANK. In contrast, normal blood neutrophils express only the membrane-associated form of RANK-L. They do not express the mRNAs encoding OPG and RANK. SF neutrophils from RA patients and normal blood neutrophils release no soluble RANK-L. They express the mRNA for TRAF6. The expression of OPG and RANK by normal human blood neutrophils, however, can be induced by interleukin-4 + tumor necrosis factor-alpha and by SFs from patients with RA. In contrast, SFs from patients with osteoarthritis do not induce the expression of OPG and RANK. Moreover, the addition of RANK-L to normal blood neutrophils pretreated by SF from patients with RA decreased I-κB-α, indicating that RANK signaling by neutrophils stimulated with SF is associated with nuclear factor-kappa-B activation. In summary, RANK-L is expressed by inflammatory and normal neutrophils, unlike OPG and RANK, which are expressed only by neutrophils exposed to an inflammatory environment. Taken together, these results suggest that neutrophils may contribute to bone remodeling at inflammatory sites where they are present in significantly large numbers.

Tumor necrosis factor antagonist mechanisms of action: a comprehensive review

During the past 30 years, elucidation of the pathogenesis of rheumatoid arthritis, Crohn's disease, psoriasis, psoriatic arthritis and ankylosing spondylitis at the cellular and molecular levels has revealed that these diseases share common mechanisms and are more closely related than was previously recognized. Research on the complex biology of tumor necrosis factor (TNF) has uncovered many mechanisms and pathways by which TNF may be involved in the pathogenesis of these diseases. There are 3 TNF antagonists currently available: adalimumab, a fully human monoclonal antibody; etanercept, a soluble receptor construct; and infliximab, a chimeric monoclonal antibody. Two other TNF antagonists, certolizumab and golimumab, are in clinical development. The remarkable efficacy of TNF antagonists in these diseases places TNF in the center of our understanding of the pathogenesis of many immune-mediated inflammatory diseases. The purpose of this review is to discuss the biology of TNF and related family members in the context of the potential mechanisms of action of TNF antagonists in a variety of immune-mediated inflammatory diseases. Possible mechanistic differences between TNF antagonists are addressed with regard to their efficacy and safety profiles.

Osteoporosis and vertebral fractures in ankylosing spondylitis

PURPOSE OF REVIEW

To review recent data, in the context of what is already known, about an increased risk of vertebral fractures in ankylosing spondylitis patients.

RECENT FINDINGS

Osteoporosis and fractures of the vertebral body and its dorsal arch are now well recognized features in patients with ankylosing spondylitis, but their diagnosis is still often a challenge. The risk factors and clinical consequences for fractures in ankylosing spondylitis are increasingly understood in the context of osteoimmunology and of spinal biomechanical changes in material and structural components in the spine that result in bone failure.

SUMMARY

Diagnosing fractures of the vertebral body and its dorsal arch remains a challenge in studies and in clinical practice. Prospective studies are needed to evaluate to what degree such fractures can be prevented in ankylosing spondylitis.

Polyethylene particle-induced bone resorption in alpha-calcitonin gene-related peptide-deficient mice

This study investigates the impact of alpha-CGRP on bone metabolism after implantation of polyethylene particles. alpha-CGRP knockout mice showed less osteolysis compared with wildtype mice. The local neurogenic microenvironment might be a crucial factor in particle-induced osteolysis.

INTRODUCTION

Periprosthetic osteolysis is the major reason for aseptic loosening in joint arthroplasty. This study aimed to investigate the potential impact of alpha-calcitonin gene-related peptide (alpha-CGRP) deficiency on bone metabolism under conditions of polyethylene particle-induced osteolysis.

MATERIALS AND METHODS

We used the murine calvarial osteolysis model based on polyethylene particles in 14 C57BL 6 mice and 14 alpha-CGRP-deficient mice divided into four groups of 7 mice each. Groups 1 (C57BL/J 6) and 3 (alpha-CGRP knockout) received sham surgery, and groups 2 (C57BL/J 6) and 4 (alpha-CGRP knockout) were treated with polyethylene particles. Qualitative and quantitative 3D analyses were performed using microCT. In addition, bone resorption was measured within the midline suture by histological examination. The number of osteoclasts was determined by counting the TRACP(+) cells. Calvarial bone was tested for RANKL expression by RT-PCR and immunocytochemistry.

RESULTS

Bone resorption was significantly reduced in alpha-CGRP-deficient mice compared with their corresponding wildtype C57BL 6 mice as confirmed by histomorphometric data (p < 0.001) and microCT (p < 0.01). Osteoclast numbers were significantly reduced in group 3 and the particle subgroup compared with group 1 (p < 0.001). We observed a >3-fold increase of basal RANKL mRNA levels within group 1 compared with group 3. Additional low RANKL immunochemistry staining was noted in groups 3 and 4.

CONCLUSIONS

In conclusion, alpha-CGRP knockout mice did not show the expected extended osteolysis compared with wildtype mice expressing alpha-CGRP. One of the most reasonable explanations for the observed decrease in osteolysis could be linked to the osteoprotegerin (OPG)/RANK/RANKL system in alpha-CGRP-deficient animals. As a consequence, the fine tuning of osteoclasts mediating resorption in alpha-CGRP-null mice may be deregulated.

Inflammation-induced bone loss: can it be prevented?

Inflammatory synovitis induces profound bone loss and OCLs are the instrument of this destruction. TNF blockers have an established role in the prevention of inflammatory bone loss in RA; however, not all patients respond to anti-TNF therapy and side effects may prevent long-term treatment in others. The B-cell--depleting antibody rituximab and the T-cell costimulation blocker abatacept are emerging as major treatment options for patients who are resistant to anti-TNF [96,97]. Proof-of-concept studies demonstrate that targeting RANK-mediated osteoclastogenesis prevents inflammatory bone loss and clinical application has only just begun. The efficacy of RANKL inhibition has been witnessed in trials of Denosumab, and RANKL-neutralizing antibodies are likely to become the treatment of choice for blocking RANKL in RA [77,78]. A major limitation of RANKL antagonism is that it does not treat synovitis. Therefore, anti-RANKL therapy most likely will be used in the context of MTX therapy. There is uncertainty about the possible extraskeletal adverse effects of long-term effects of long-term RANKL blockade. In particular, anti-RANKL therapy could jeopardize dendritic cell function or survival. The demonstrable role of OCLs in inflammation-induced bone loss also invites a reconsideration of the new BPs for bone protection [98]. Studies of ZA in preclinical models indicate that bone protection is comparable to that afforded by OPG. One possible caveat is that intravenous BPs are linked to jaw osteonecrosis [99], although the incidence is confined mainly to intensive treatment in the oncology setting. Although pulsed PTH stimulated bone formation in arthritic models, it has yet to be proven clinically in the context of powerful OCL inhibition with TNF or RANKL antagonists. With strategies that normalize OCL numbers, clinicians are poised to accomplish effective prevention of inflammation-induced bone loss.

Novel therapies for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, systemic inflammatory disease that causes significant morbidity and mortality. The pathogenesis outlined to date in RA consists of a cascade of pro-inflammatory cytokines and chemokines leading to the recruitment of inflammatory cells and the self perpetuation of inflammation, ultimately leading to cartilage and bone destruction. The dramatic progress in understanding the molecular immunology in RA has led to a transition from conventional treatment with aggressive immune suppression to targeted biological-based therapies that control the inflammatory pathways associated with RA. This article reviews the current biological and small-molecule therapies approved for the treatment of RA and those in development, including antibodies, tolerising agents and vaccines.