Suppression of bone turnover by B-cell depletion in patients with rheumatoid arthritis

Inflammation is responsible for systemic bone loss in patients with seropositive rheumatoid arthritis treated with rituximab

BACKGROUND/AIMS

We investigated the effect of rituximab on systemic bone metabolism in patients with seropositive rheumatoid arthritis (RA).

METHODS

Twenty seropositive patients with RA were enrolled and administered one cycle of rituximab. If RA became active for > 6 months after the first rituximab cycle, a second cycle was initiated; otherwise, no additional treatment was administered. Patients were divided into two groups according to the number of rituximab treatment cycles.

RESULTS

In patients treated with a second cycle, the total hip bone mineral density (BMD) was clinically low, whereas the serum levels of receptor activator of nuclear factor kappa-B ligand (RANKL) were increased at 12 months. BMD in patients treated with one cycle did not change at 12 months, whereas serum RANKL levels decreased at all time points. DAS28 activity improved in both groups from baseline to 4 months; however, from 4 to 12 months, DAS28 activity worsened in the develgroup with the second cycle but remained stable in the group with one cycle.

CONCLUSION

Systemic inflammation, reflected by increased disease activity, may be responsible for the increase in RANKL levels, which causes systemic bone loss in rituximab-treated patients with RA. Although rituximab affects inflammation, it does not seem to alter systemic bone metabolism in RA.

The impact of long-term biologics/target therapy on bone mineral density in rheumatoid arthritis: a propensity score-matched analysis

OBJECTIVES

To investigate changes in BMD in RA patients receiving 3-year biological/targeted synthetic disease-modifying antirheumatic drugs (b/tsDMARD) or conventional synthetic DMARD (csDMARD).

METHODS

Patients with RA were recruited from September 2014 until March 2019. Clinical characteristics, BMD and evidence of fragility fractures at enrolment were documented. Participants were treated according to the National Institute for Health and Care Excellence (NICE) guidelines over a 3-year observation period. Repeated BMD was measured at the end of the study period. Participants were grouped into those receiving b/tsDMARD or csDMARD and by propensity score matching (1:2).

RESULTS

A total of 388 participants completed the 3-year follow-up. After propensity score matching, 92 and 184 participants were allocated to the b/tsDMARD (Group I) and csDMARD (Group II), respectively. After 3 years, BMD remained stable at the femoral neck (FN), hip (total) (TH) and lumbar vertebra (L1-4) (P =0.09, 0.15, 0.87) in Group I. However, BMD decreased significantly in Group II (P=0.045, <0.001, 0.004) at corresponding sites. Participants receiving combined b/tsDMARD and anti-osteoporosis therapy experienced a greater BMD preserving effect than other subgroups.

CONCLUSION

Long-term b/tsDMARDs therapy had protective effects on bone loss for patients with RA. Patients receiving concomitant anti-osteoporosis therapy and b/tsDMARDs therapy experienced the greatest BMD preserving effect.

The Role of Chronic Inflammatory Bone and Joint Disorders in the Pathogenesis and Progression of Alzheimer's Disease

Late-onset Alzheimer's Disease (LOAD) is a devastating neurodegenerative disorder that causes significant cognitive debilitation in tens of millions of patients worldwide. Throughout disease progression, abnormal secretase activity results in the aberrant cleavage and subsequent aggregation of neurotoxic Aβ plaques in the cerebral extracellular space and hyperphosphorylation and destabilization of structural tau proteins surrounding neuronal microtubules. Both pathologies ultimately incite the propagation of a disease-associated subset of microglia-the principle immune cells of the brain-characterized by preferentially pro-inflammatory cytokine secretion and inhibited AD substrate uptake capacity, which further contribute to neuronal degeneration. For decades, chronic neuroinflammation has been identified as one of the cardinal pathophysiological driving features of AD; however, despite a number of works postulating the underlying mechanisms of inflammation-mediated neurodegeneration, its pathogenesis and relation to the inception of cognitive impairment remain obscure. Moreover, the limited clinical success of treatments targeting specific pathological features in the central nervous system (CNS) illustrates the need to investigate alternative, more holistic approaches for ameliorating AD outcomes. Accumulating evidence suggests significant interplay between peripheral immune activity and blood-brain barrier permeability, microglial activation and proliferation, and AD-related cognitive decline. In this work, we review a narrow but significant subset of chronic peripheral inflammatory conditions, describe how these pathologies are associated with the preponderance of neuroinflammation, and posit that we may exploit peripheral immune processes to design interventional, preventative therapies for LOAD. We then provide a comprehensive overview of notable treatment paradigms that have demonstrated considerable merit toward treating these disorders.

Rituximab as a trigger factor of medication-related osteonecrosis of the jaw. A case report

Rituximab, an anti-CD20 monoclonal antibody, is an effective treatment for rheumatoid arthritis. Here we report the case of a patient with rheumatoid arthritis, having taken risedronate for 14 months to prevent corticosteroid-induced osteoporosis, more than 2 years ago, who presented osteonecrosis of jaw following herpetic gingivostomatitis two weeks after the beginning of a rituximab treatment associated with her usual anti-rheumatic drugs. Eight weeks later, no bone and/or gum healing was observed and a stage 2 medication-related osteonecrosis of the jaw (MRONJ) was diagnosed. A conservative approach was decided with antiseptic mouth washes, low-level laser treatment (LLLT) and systemic therapy with teriparatide. Complete mucosal coverage was obtained after more two years of follow-up. We suggest that rituximab as immunosuppressant might be a cause or a decompensating factor of MRONJ. Non-surgical periodontal treatment with LLLT and teriparatide are candidates for the treatment of MRONJ.

Activated B Lymphocyte Inhibited the Osteoblastogenesis of Bone Mesenchymal Stem Cells by Notch Signaling

Estrogen is very important to the differentiation of B lymphocytes; B lymphopoiesis induced by OVX was supposedly involved in osteoporosis. But the effects of B lymphocytes on the osteogenic differentiation of bone mesenchymal stem cells (BMSCs) are not clear. In this study, we detected bone quality and bone loss in a trabecular bone by electronic universal material testing machine and microcomputed tomography (micro-CT) in OVX and splenectomized-ovariectomy (SPX-OVX) rats. Additionally, changes in lymphocytes (B lymphocyte, CD4⁺ and CD8⁺ T lymphocytes, and macrophages) in the bone marrow were analyzed by flow cytometry. The osteogenesis of BMSCs cocultured with normal and LPS-pretreated B lymphocytes was detected by BCIP/NBT and Alizarin red S staining. Measurement of the Notch2, Notch4, Hey1, Hey2, Hes1, and runt-related transcription factor 2 (Runx2) expression in BMSCs cocultured with B lymphocytes was done using real-time PCR. The effects of dexamethasone and DAPT (inhibitor of Notch signaling) on osteogenesis of BMSCs were detected by BCIP/NBT, Alizarin red S staining, and real-time PCR. Osteoporosis happened in OVX rats, more serious in SPX-OVX rats, B lymphocytes increased in OVX rats, and sharply higher in SPX-OVX rats. Osteoporosis did not happen in SPX rats which is still companied with a high increase of B lymphocytes. LPS-pretreated B lymphocytes suppressed the osteogenesis of BMSCs, but the normal B lymphocytes could not. The LPS-pretreated B lymphocytes upregulated the expression of Notch4, Hes1, and Hey2 and downregulated the expression of Runx2 in BMSCs. Dexamethasone and DAPT could downregulate the high expression of Notch4, Hes1, Hey2 and upregulate the low expression of Runx2 in BMSCs which cocultured with LPS treated B lymphocytes, the inhibited ALP and Alizarin red staining in BMSCs which cocultured with LPS treated B lymphocytes also partly restored.

Osteoclasts in the Inflammatory Arthritis: Implications for Pathologic Osteolysis

The enhanced differentiation and activation of osteoclasts (OCs) in the inflammatory arthritis such as rheumatoid arthritis (RA) and gout causes not only local bone erosion, but also systemic osteoporosis, leading to functional disabilities and morbidity. The induction and amplification of NFATc1, a master regulator of OC differentiation, is mainly regulated by receptor activator of NF-κB (RANK) ligand-RANK and calcium signaling which are amplified in the inflammatory milieu, as well as by inflammatory cytokines such as TNFα, IL-1β and IL-6. Moreover, the predominance of CD4⁺ T cell subsets, which varies depending on the condition of inflammatory diseases, can determine the fate of OC differentiation. Anti-citrullinated peptide antibodies which are critical in the pathogenesis of RA can bind to the citrullinated vimentin on the surface of OC precursors, and in turn promote OC differentiation and function via IL-8. In addition to adaptive immunity, the activation of innate immune system including the nucleotide oligomerization domain leucine rich repeat with a pyrin domain 3 inflammasome and TLRs can regulate OC maturation. The emerging perspectives about the diverse and close interactions between the immune cells and OCs in inflammatory milieu can have a significant impact on the future direction of drug development.

B cells inhibit bone formation in rheumatoid arthritis by suppressing osteoblast differentiation

The function of B cells in osteoblast (OB) dysfunction in rheumatoid arthritis (RA) has not been well-studied. Here we show that B cells are enriched in the subchondral and endosteal bone marrow (BM) areas adjacent to osteocalcin+ OBs in two murine RA models: collagen-induced arthritis and the TNF-transgenic mice. Subchondral BM B cells in RA mice express high levels of OB inhibitors, CCL3 and TNF, and inhibit OB differentiation by activating ERK and NF-κB signaling pathways. The inhibitory effect of RA B cells on OB differentiation is blocked by CCL3 and TNF neutralization, and deletion of CCL3 and TNF in RA B cells completely rescues OB function in vivo, while B cell depletion attenuates bone erosion and OB inhibition in RA mice. Lastly, B cells from RA patients express CCL3 and TNF and inhibit OB differentiation, with these effects ameliorated by CCL3 and TNF neutralization. Thus, B cells inhibit bone formation in RA by producing multiple OB inhibitors.

The multi-biomarker disease activity score tracks response to rituximab treatment in rheumatoid arthritis patients: a post hoc analysis of three cohort studies

BACKGROUND

A multi-biomarker disease activity (MBDA) score has been validated as an objective measure of disease activity in rheumatoid arthritis (RA) and shown to track response to treatment with several disease-modifying anti-rheumatic drugs (DMARDs). The objective of this study was to evaluate the ability of the MBDA score to track response to treatment with rituximab.

METHODS

Data were used from 57 RA patients from three cohorts treated with rituximab 1000 mg and methylprednisolone 100 mg at days 1 and 15. The MBDA score was assessed in serum samples obtained at baseline and 6 months. Spearman's rank correlation coefficients were calculated for baseline values, 6-month values, and change from baseline to 6 months (∆), between MBDA score and the following measures: disease activity score assessing 28 joints (DAS28) using erythrocyte sedimentation rate (ESR) or high-sensitivity C-reactive protein (hsCRP), ESR, (hs)CRP, swollen and tender joint counts assessing 28 joints (SJC28, TJC28), patient visual analogue scale for general health (VAS-GH), health assessment questionnaire (HAQ), and radiographic progression over 12 months using Sharp/van der Heijde score (SHS), as well as six bone turnover markers. Additionally, multivariable linear regression analyses were performed using these measures as dependent variable and the MBDA score as independent variable, with adjustment for relevant confounders. The association between ∆MBDA score and European League Against Rheumatism (EULAR) response at 6 months was assessed with adjustment for relevant confounders.

RESULTS

At baseline, the median MBDA score and DAS28-ESR were 54.0 (IQR 44.3-70.0) and 6.3 (IQR 5.4-7.1), respectively. MBDA scores correlated significantly with DAS28-ESR, DAS28-hsCRP, ESR and (hs)CRP at baseline and 6 months. ∆MBDA score correlated significantly with changes in these measures. ∆MBDA score was associated with EULAR good or moderate response (adjusted OR = 0.89, 95% CI = 0.81-0.98, p = 0.02). Neither baseline MBDA score nor ΔMBDA score correlated statistically significantly with ∆SHS (n = 11) or change in bone turnover markers (n = 23), although ∆SHS ≥ 5 was observed in 5 (56%) of nine patients with high MBDA scores.

CONCLUSIONS

We have shown, for the first time, that the MBDA score tracked disease activity in RA patients treated with rituximab and that change in MBDA score reflected the degree of treatment response.

Personalization of biologic therapy in patients with rheumatoid arthritis: less frequently accounted choice-driving variables

Objective

To propose appropriate statements that drive the choice of biologic therapies in patients with rheumatoid arthritis (RA), factoring in their impact on the following issues: anti-drug antibody (ADAb) formation, suspicion and management of infections, lupus-like syndrome (LLS), effects on bone mass and sexual sphere, and relationship between RA and periodontal disease (PD).

Methods

An overview of existing evidence was undertaken by an expert panel on behalf of the Italian board for the TAilored BIOlogic therapy (ITABIO). Data were extracted from controlled trials, national registries, national health care databases, post-marketing surveys, and, when required by the paucity of controlled studies, from open-label clinical series. Anti-tumor necrosis factor (anti-TNF) and non-anti-TNF-targeted biologics approved for RA were investigated.

Results

ADAb formation is chiefly associated with anti-TNFs, and it is reduced by combination therapy with methotrexate. To date, ADAb titration is not advisable for clinical practice, and, in case of anti-TNF secondary failure, a non-anti-TNF biologic is indicated. LLS is observed in anti-TNF receivers and, in most cases, resolves without anti-TNF withdrawal. A non-anti-TNF biologic is advisable in patients experiencing LLS. Non-anti-TNFs demonstrated a low or absent infection risk and are preferable in patients with comorbidities. Due to their positive effects on bone mass, anti-TNFs are indicated in women at osteoporosis risk, whereas non-anti-TNF have been poorly investigated. The emerging evidence of the relationship between RA and PD and the effects on anti-TNF efficacy should lead clinicians to consider the periodontal status in RA patients. Anti-TNFs may exert a positive effect on fertility and sexuality, and clinicians should explore these aspects in RA patients.

Conclusion

The optimization of biologic therapies by taking into proper account the above issues would improve patient outcomes.

Changes in bone density and bone turnover in patients with rheumatoid arthritis treated with rituximab, results from an exploratory, prospective study

Data describing the effect of in vivo B cell depletion on general bone loss in patients with rheumatoid arthritis (RA) are limited. Given the pathogenetic role of B cells in RA, it is tempting to speculate that B cell depletion might have a beneficial effect on bone loss. We prospectively investigated the changes in bone mineral density (BMD), bone turnover, inflammation and disease activity before and after rituximab in 45 RA patients over a 12 month period, 36 patients of whom completed the study and were included in the analysis. There was no significant change in our primary endpoint; lumbar spine BMD after 12 months. However, we found a significant decrease in neck of femur (mean -0.017 g/cm2, 95% CI -0.030, -0.004 p = 0.011) and total femur BMD (mean -0.016 g/cm2, 95% CI -0.025, -0.007 p = 0.001). Additionally, there was a significant increase in procollagen type 1 amino-terminal propeptide (P1NP) and bone specific alkaline phosphatase (BAP); biomarkers of bone formation (median change from baseline to 12 months; P1NP 11.3 μg/L, 95% CI -1.1, 24.8 p = 0.025; BAP 2.5 μg/L, 95% CI 1.2, 3.6 p = 0.002), but no significant change in bone resorption or osteocyte markers. The fall in BMD occurred despite improvement in disease control. Post-menopausal women had the lowest mean lumbar spine, femoral and forearm BMD at baseline and after 12 months, additionally they had a higher level of bone turnover throughout the study. In conclusion, BMD was maintained at the lumbar spine and forearm, but fell at the femur sites. A high prevalence of vitamin D deficiency was observed and these patients had lower BMD and evidence of higher bone turnover.

B cells and their cytokine activities implications in human diseases

B cells are the only cell type that can give rise to antibody-producing cells, and the only cell type whose selective depletion can, today, lead to an improvement of a wide range of immune-mediated inflammatory diseases, including disorders not primarily driven by autoantibodies. Here, I discuss this paradoxical observation, and propose that the capacity of B cells to act as cytokine-producing cells explains how they can control monocyte activity and subsequently disease pathogenesis. Together with current data on the effect of anti-CD20 B cell-depleting reagents in the clinic, this novel knowledge on B cell heterogeneity opens the way for novel safer and more efficient strategies to target B cells. The forthcoming identification of disease-relevant B cell subsets is awaited to permit their monitoring and specific targeting in a personalized medicine approach.

Dysregulated systemic lymphocytes affect the balance of osteogenic/adipogenic differentiation of bone mesenchymal stem cells after local irradiation

Background

While it is known that irradiation can induce local and systemic bone loss over time, how focal irradiation induces systemic bone complications remains unclear. Immune cells are thought to be crucial to bone homeostasis, and abnormal immune cells lead to serious disruption of bone homeostasis, such as in acute lymphoblastic leukaemia. This disruption primarily occurs due to inhibition of the osteogenic differentiation of bone mesenchymal stem cells (BMSCs).

Methods

In this study, we detected local and systemic bone loss in trabecular bone by micro-computed tomography (micro-CT) and measurement of peroxisome proliferator-activated receptor gamma (PPARγ) and runt-related transcription factor 2 (RUNX2) expression in BMSCs using real-time polymerase chain reaction and western blotting. Additionally, changes in lymphocytes (B cells and CD4⁺ and CD8⁺ T cells) in the peripheral blood and bone marrow were analysed by flow cytometry. BMSC-derived osteoblasts and adipocytes, cultured in osteogenic or adipogenic media or co-cultured with lymphocytes, were detected by BCIP/NBT, Alizarin Red S and Oil Red O staining.

Results

Focal irradiation induced local and systemic bone loss in trabecular bone. Increased PPARγ expression and decreased RUNX2 expression were observed, accompanied by upregulated adipogenesis and downregulated osteogenesis of BMSCs. B cells and CD8⁺ T lymphocytes were increased in the blood and bone marrow after irradiation, while CD4⁺ T lymphocytes were decreased in the blood. Inhibition of RUNX2 expression and reduction of alkaline phosphatase activity and mineralization deposits were observed in lymphocyte-co-cultured BMSCs, accompanied by an increase in PPARγ expression and in the number of lipid droplets.

Conclusions

Focal irradiation induced local and systemic bone loss in trabecular bone. Increased B cells and CD8⁺ T lymphocytes led to systemic bone loss by decreasing BMSC osteogenesis.

Physiological and pathophysiological bone turnover - role of the immune system

Osteoporosis develops when the rate of osteoclastic bone breakdown (resorption) exceeds that of osteoblastic bone formation, which leads to loss of BMD and deterioration of bone structure and strength. Osteoporosis increases the risk of fragility fractures, a cause of substantial morbidity and mortality, especially in elderly patients. This imbalance between bone formation and bone resorption is brought about by natural ageing processes, but is frequently exacerbated by a number of pathological conditions. Of importance to the aetiology of osteoporosis are findings over the past two decades attesting to a deep integration of the skeletal system with the immune system (the immuno-skeletal interface (ISI)). Although protective of the skeleton under physiological conditions, the ISI might contribute to bone destruction in a growing number of pathophysiological states. Although numerous research groups have investigated how the immune system affects basal and pathological osteoclastic bone resorption, recent findings suggest that the reach of the adaptive immune response extends to the regulation of osteoblastic bone formation. This Review examines the evolution of the field of osteoimmunology and how advances in our understanding of the ISI might lead to novel approaches to prevent and treat bone loss, and avert fractures.

Production of RANKL by Memory B Cells: A Link Between B Cells and Bone Erosion in Rheumatoid Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a systemic autoimmune disease that often leads to joint damage. The mechanisms of bone damage in RA are complex, involving activation of bone-resorbing osteoclasts (OCs) by synoviocytes and Th17 cells. This study was undertaken to investigate whether B cells play a direct role in osteoclastogenesis through the production of RANKL, the essential cytokine for OC development.

METHODS

RANKL production by total B cells or sorted B cell subpopulations in the peripheral blood and synovial tissue from healthy donors or anti-cyclic citrullinated peptide-positive patients with RA was examined by flow cytometry, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistochemical analysis. To define direct effects on osteoclastogenesis, B cells were cocultured with CD14+ monocytes, and OCs were enumerated by tartrate-resistant acid phosphatase staining.

RESULTS

Healthy donor peripheral blood B cells were capable of expressing RANKL upon stimulation, with switched memory B cells (CD27+IgD-) having the highest propensity for RANKL production. Notably, switched memory B cells in the peripheral blood from RA patients expressed significantly more RANKL compared to healthy controls. In RA synovial fluid and tissue, memory B cells were enriched and spontaneously expressed RANKL, with some of these cells visualized adjacent to RANK+ OC precursors. Critically, B cells supported OC differentiation in vitro in a RANKL-dependent manner, and the number of OCs was higher in cultures with RA B cells than in those derived from healthy controls.

CONCLUSION

These findings reveal the critical importance of B cells in bone homeostasis and their likely contribution to joint destruction in RA.

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.

Osteoimmunology: from mice to humans

The immune system has been recognized as one of the most important regulators of bone turnover and its deregulation is implicated in several bone diseases such as postmenopausal osteoporosis and inflammatory bone loss; recently it has been suggested that the gut microbiota may influence bone turnover by modulation of the immune system. The study of the relationship between the immune system and bone metabolism is generally indicated under the term 'osteoimmunology'. The vast majority of these studies have been performed in animal models; however, several data have been confirmed in humans as well: this review summarizes recent data on the relationship between the immune system and bone with particular regard to the data confirmed in humans.

Glucocorticoids: bad or safe for the bones?

Until recently, patients with rheumatoid arthritis (RA) were treated with monotherapy using conventional drugs such as sulfasalazine, antimalarials, intramuscular gold and methotrexate, which often leads to persistent arthritis, loss of functional capacity and decreased quality of life. The use of high-dose glucocorticoids (GCs) and active RA are both associated with generalised bone loss and fractures, while GCs have a strong immunosuppressive effect. With the introduction of very effective tumour-necrosis factor-blockers and other biologics, clinical remission is a realistic target in around half of the early patients with RA; the same appears true for the use of methotrexate with chronic low dose or initially high-dose GCs. With the use of a treat-to-target strategy focusing on clinical remission or low disease activity in early patients with RA, the negative effects of systemic inflammation on bone can be inhibited and local bone loss (in the joints), and generalised bone loss at the spine and hips, can be limited or prevented. Whether this also leads to a reduction in vertebral and non-vertebral fractures remains to be demonstrated. Another issue is, in other systemic rheumatic diseases in which treatment options are smaller and less effective than in RA, local and systemic bone loss may still occur.

Bone-immune cell crosstalk: bone diseases

Bone diseases are associated with great morbidity; thus, the understanding of the mechanisms leading to their development represents a great challenge to improve bone health. Recent reports suggest that a large number of molecules produced by immune cells affect bone cell activity. However, the mechanisms are incompletely understood. This review aims to shed new lights into the mechanisms of bone diseases involving immune cells. In particular, we focused our attention on the major pathogenic mechanism underlying periodontal disease, psoriatic arthritis, postmenopausal osteoporosis, glucocorticoid-induced osteoporosis, metastatic solid tumors, and multiple myeloma.

Management of osteoporosis in rheumatoid arthritis patients

INTRODUCTION

In rheumatoid arthritis (RA) patients, the risk of both vertebral and non-vertebral fractures is roughly doubled, which is for an important part caused by inflammation-mediated amplification of bone loss and by immobilization. New treatments have become available in the last two decades to treat both RA and osteoporosis.

AREAS COVERED

Epidemiology and assessment of osteoporosis and fracture risk (including the influence of RA disease activity and bone-influencing medications such as glucocorticoids), the importance of vertebral fracture assessment in addition to bone density measurement in patients with RA, the use of disease-modifying antirheumatic drugs and their effects on generalized bone loss, and current and possible future anti-osteoporotic pharmacotherapeutic options are discussed with special focus on RA.

EXPERT OPINION

Assessment of osteoporosis in RA patients should include evaluation of the effects of disease activity and bone-influencing medications such as (the dose of) glucocorticoids, above standard risk factors for fractures or osteoporosis as defined by the FRAX instrument. Disease-modifying antirheumatic drugs are now well able to control disease activity using treat to target strategies. This lowering of disease activity by antirheumatic medications such as anti-TNF-α results in hampering of generalized bone loss; however, no fracture data are currently available. When treating osteoporosis in RA patients, additional focus should be on calcium supplementation, particularly in glucocorticoid users, and also on sufficient vitamin D use. Several anti-osteoporotic medications are now on the market; oral bisphosphonates are most commonly used, but in recent years, more agents have entered the market such as the parenteral antiresorptives denosumab (twice yearly) and zoledronic acid (once yearly), and the anabolic agent parathyroid hormone analogues. New agents, such as odanacatib and monoclonal antibodies against sclerostin, are now being tested and will most likely enlarge the possibilities of osteoporosis treatment in RA patients.

Gene expression profile induced by ovariectomy in bone marrow of mice: a functional approach to identify new candidate genes associated to osteoporosis risk in women

Osteoporosis is a multifactorial skeletal pathology with a main genetic component. To date, however, the majority of genes associated with this pathology remain unknown since genes cataloged to date only explain a part of the heritability of bone phenotypes. In the present study, we have used a genome-wide gene expression approach by means of microarrays to identify new candidate genes involved in the physiopathology of osteoporosis, using as a model the ovariectomized (OVX) mice by comparing global bone marrow gene expression of the OVX mice with those of SHAM operated mice. One hundred and eighty transcripts were found to be differentially expressed between groups. The analysis showed 23 significant regulatory networks, of which the top five canonical pathways included B-cell development, primary immunodeficiency signaling, PI3K signaling in B-cells, phospholipase C signaling, and FcgRIIB signaling in B-cells. Twelve differentially expressed genes were validated by MALDI-TOF mass spectrometry with good reproducibility. Finally, the association to bone phenotypes of SNPs in genes whose expression was increased (IL7R and CD79A) or decreased (GPX3 and IRAK3) by OVX in mice was analyzed in a cohort of 706 postmenopausal women. We detected an association of a SNP in a gene involved in the detoxification of free radicals like glutathione peroxidase 3 (GPX3) with femoral neck BMD (rs8177447, P=0.043) and two SNPs in the Ig-alpha protein of the B-cell antigen component gene (CD79A) with lumbar spine BMD (rs3810153 and rs1428922, P=0.016 and P=0.001, respectively). These results reinforce the role of antioxidant pathways and of B-cells in bone metabolism. Furthermore, it shows that a genome-wide gene expression approach in animal models is a useful method for detecting genes associated to BMD and osteoporosis risk in humans.

Can bone loss in rheumatoid arthritis be prevented?

Rheumatoid arthritis (RA) is a systemic inflammatory disease that can lead to local joint deformations (bone erosions and joint space narrowing) and to extra-articular phenomena, including generalized osteoporosis. In addition, in patients with RA, the risk of vertebral and nonvertebral fractures is doubled. High disease activity (inflammation), immobility, and glucocorticoid use are common factors that substantially increase fracture risk in these patients, on top of the background fracture risk based on classical risk factors such as high age, low body mass, and female gender. New insights on the links between the immune system and the bone system, the field of osteoimmunology, have shown that local and generalized bone loss share common pathways. The receptor activator of nuclear factor κB ligand/osteoprotegerin pathway (RANKl/OPG) is one of the most important pathways, as it is (strongly) upregulated by inflammation. In modern treatment of RA with biologics, for example, TNFα-blocking agents and combination therapy of conventional disease-modifying antirheumatic drugs (DMARDs), clinical remission is a realistic treatment goal. As a consequence, in recent studies, it has been documented that both local and generalized bone loss is absent or minimal in those patients who are in clinical remission.

The clinical utility of bone marker measurements in osteoporosis

Osteoporosis is characterised by low bone mass and structural deterioration of bone tissue, resulting in increased fragility and susceptibility to fracture. Osteoporotic fractures are a significant cause of morbidity and mortality. Direct medical costs from such fractures in the UK are currently estimated at over two billion pounds per year, resulting in a substantial healthcare burden that is expected to rise exponentially due to increasing life expectancy. Currently bone mineral density is the WHO standard for diagnosis of osteoporosis, but poor sensitivity means that potential fractures will be missed if it is used alone. During the past decade considerable progress has been made in the identification and characterisation of specific biomarkers to aid the management of metabolic bone disease. Technological developments have greatly enhanced assay performance producing reliable, rapid, non-invasive cost effective assays with improved sensitivity and specificity. We now have a greater understanding of the need to regulate pre-analytical sample collection to minimise the effects of biological variation. However, bone turnover markers (BTMs) still have limited clinical utility. It is not routinely recommended to use BTMs to select those at risk of fractures, but baseline measurements of resorption markers are useful before commencement of anti-resorptive treatment and can be checked 3–6 months later to monitor response and adherence to treatment. Similarly, formation markers can be used to monitor bone forming agents. BTMs may also be useful when monitoring patients during treatment holidays and aid in the decision as to when therapy should be recommenced. Recent recommendations by the Bone Marker Standards Working Group propose to standardise research and include a specific marker of bone resorption (CTX) and bone formation (P1NP) in all future studies. It is hoped that improved research in turn will lead to optimised markers for the clinical management of osteoporosis and other bone diseases.

Biologicals and bone loss

Inflammatory joint diseases are associated with extra-articular side effects including bone involvement.There is an increased risk of osteoporotic fractures. The pathogeneses of local and generalized bone loss share a common pathway. Early and active rheumatoid arthritis is associated with longitudinal observed bone loss and fracture rate is of vertebral and nonvertebral fractures is doubled compared with matched healthy controls. Lowering disease activity with TNF inhibitors or is associated with stabilisation of bone mineral density by counteracting elevated bone resorption.