Inflammatory bone loss: pathogenesis and therapeutic intervention

The polyphenol fisetin protects bone by repressing NF-κB and MKP-1-dependent signaling pathways in osteoclasts

Osteoporosis is a bone pathology leading to increase fractures risk and challenging quality of life. Since current treatments could exhibit deleterious side effects, the use of food compounds derived from plants represents a promising innovative alternative due to their potential therapeutic and preventive activities against human diseases. In this study, we investigated the ability of the polyphenol fisetin to counter osteoporosis and analyzed the cellular and molecular mechanisms involved. In vivo, fisetin consumption significantly prevented bone loss in estrogen deficiency and inflammation mice osteoporosis models. Indeed, bone mineral density, micro-architecture parameters and bone markers were positively modulated by fisetin. Consistent with in vivo results, we showed that fisetin represses RANKL-induced osteoclast differentiation and activity as demonstrated by an inhibition of multinucleated cells formation, TRAP activity and differentiation genes expression. The signaling pathways NF-κB, p38 MAPK, JNK and the key transcription factors c-Fos and NFATc1 expressions induced by RANKL, were negatively regulated by fisetin. We further showed that fisetin inhibits the constitutive proteasomal degradation of MKP-1, the phosphatase that deactivates p38 and JNK. Consistently, using shRNA stable cell lines, we demonstrated that impairment of MKP-1 decreases fisetin potency. Taken together, these results strongly support that fisetin should be further considered as a bone protective agent.

C-reactive protein, bone strength, and nine-year fracture risk: data from the Study of Women's Health Across the Nation (SWAN)

Higher levels of C-reactive protein (CRP), an inflammatory marker, are associated with increased fracture risk, although previous studies on CRP and bone mineral density (BMD) have yielded conflicting results. We aimed to test the hypotheses that composite indices of femoral neck strength relative to load, which are inversely associated with fracture risk, would also be inversely associated with CRP, and would explain part of the association between CRP and fracture risk. We analyzed data from a multisite, multiethnic prospective cohort of 1872 community-dwelling women, premenopausal or early perimenopausal at baseline. Femoral neck composite strength indices in three failure modes were calculated using dual-energy X-ray absorptiometry (DXA)-derived femoral neck width (FNW), femoral neck axis length (FNAL), femoral neck BMD and body size at baseline, as BMD*FNW/weight for compression strength, BMD*(FNW)(2) /(FNAL*weight) for bending strength, and BMD*FNW*FNAL/(height*weight) for impact strength. Incident nondigital, noncraniofacial fractures were ascertained annually over a median follow-up of 9 years. In analyses adjusted for age, race/ethnicity, diabetes, menopause transition stage, body mass index, smoking, alcohol use, physical activity, medications, prior fracture, and study site, CRP was associated inversely with each composite strength index (0.035-0.041 SD decrement per doubling of CRP, all p < 0.001), but not associated with femoral neck or lumbar spine BMD. During the follow-up, 194 women (10.4%) had fractures. In Cox proportional hazards analyses, fracture hazard increased linearly with loge (CRP), only for CRP levels ≥ 3 mg/L. Addition of femoral neck or lumbar spine BMD to the model did not attenuate the CRP-fracture association. However, addition of any of the composite strength indices attenuated the CRP-fracture association and made it statistically nonsignificant. We conclude that fracture risk increases with increasing CRP, only above the threshold of 3 mg/L. Unlike BMD, composite strength indices are inversely related to CRP levels, and partially explain the increased fracture risk associated with inflammation.

Inflammatory monocytes and Fcγ receptor IV on osteoclasts are critical for bone destruction during inflammatory arthritis in mice

Destruction of bone tissue by osteoclasts represents a severe pathological phenotype during inflammatory arthritis and results in joint pain and bone malformations. Previous studies have established the essential role of cytokines including TNFα and receptor-ligand interactions, such as the receptor activator of nuclear factor-kappa B-receptor activator of nuclear factor-kappa B ligand interaction for osteoclast formation during joint inflammation. Moreover, autoantibodies contribute to joint inflammation in inflammatory arthritis by triggering cellular fragment crystallizable (Fc)γ receptors (FcγR), resulting in the release of proinflammatory cytokines and chemokines essential for recruitment and activation of innate immune effector cells. In contrast, little is known about the expression pattern and function of different FcγRs during osteoclast differentiation. This would allow osteoclasts to directly interact with autoantibody immune complexes, rather than being influenced indirectly via proinflammatory cytokines released upon immune complex binding to other FcγR-expressing innate immune cells. To address this question, we studied FcγR expression and function on osteoclasts during the steady state and during acute joint inflammation in a model of inflammatory arthritis. Our results suggest that osteoclastogenesis is directly influenced by IgG autoantibody binding to select activating FcγRs on immature osteoclasts, resulting in enhanced osteoclast generation and, ultimately, bone destruction.

Periodontitis in pregnant baboons: systemic inflammation and adaptive immune responses and pregnancy outcomes in a baboon model

BACKGROUND/OBJECTIVES

Chronic periodontal infections have been suggested to contribute to the risk of adverse pregnancy outcomes.

MATERIAL AND METHODS

This study describes the relationship of patterns of systemic inflammatory mediators and IgG antibody to 20 oral bacteria in pregnant female baboons (Papio anubis) coupled with clinical features of ligature-induced periodontitis, as risk indicators for adverse pregnancy outcomes. Animals showing a preterm delivery and/or low birth weight newborns, as well as those pregnancies resulting in spontaneous abortion, stillbirth, or fetal demise were tabulated as adverse pregnancy outcomes.

RESULTS

A significantly greater frequency of the periodontitis group neonates had a low birth weight (18.1%; p = 0.008) and decreased gestational age (9.8%). Spontaneous abortion/stillbirth/fetal demise were increased in the periodontitis (8.7%) versus the control group (3.8%) (p = 0.054). The baseline oral clinical presentation of the experimental animals did not relate to the adverse pregnancy outcomes. Animals with the greatest extent/severity of periodontitis progression during the initial ½ of gestation (ie. to mid-pregnancy) had the greatest risk for adverse pregnancy outcomes. Baseline biological parameters indicating historical responses of the animals to periodontal challenge demonstrated individual variation in selected mediators, some of which became more differential during ligature-induced periodontitis. The relationship of clinical parameters to systemic inflammatory responses was consistent with a temporal contribution to adverse pregnancy outcomes in a subset of the animals.

CONCLUSIONS

These results support a link between periodontitis and adverse pregnancy outcomes in the baboons and provide a prospective experimental model for delineating the biologic parameters that contribute to a causal relationship between chronic oral infections and birth events.

Structure and strength of the distal radius in female patients with rheumatoid arthritis: a case-control study

The purpose of this work was to investigate the volumetric bone mineral density (vBMD), bone microstructure, and mechanical indices of the distal radius in female patients with rheumatoid arthritis (RA). We report a cross-sectional study of 66 middle-aged female RA patients and 66 age-matched healthy females. Areal BMD (aBMD) of the hip, lumbar spine, and distal radius was measured by dual-energy X-ray absorptiometry (DXA). High-resolution peripheral quantitative computed tomography (HR-pQCT) was performed at the distal radius, yielding vBMD, bone microstructure, and mechanical indices. Cortical and trabecular vBMD were 3.5% and 10.7% lower, respectively, in RA patients than controls, despite comparable aBMD. Trabecular microstructural indices were -5.7% to -23.1% inferior, respectively, in RA patients compared to controls, with significant differences in trabecular bone volume fraction, separation, inhomogeneity, and structural model index. Cortical porosity volume and percentage were 128% and 93% higher, respectively, in RA patients, with stress being distributed more unevenly. Fourteen RA patients had exaggerated periosteal bone apposition primarily affecting the ulnovolar aspect of the distal radius. These particular patients were more likely to have chronic and severe disease and coexisting wrist deformity. The majority of the differences in density and microstructure between RA patients and controls did not depend on menstrual status. Recent exposure to glucocorticoids did not significantly affect bone density and microstructure. HR-pQCT provides new insight into inflammation-associated bone fragility in RA. It detects differences in vBMD, bone microstructure, and mechanical indices that are not captured by DXA. At the distal radius, deterioration in density and microstructure in RA patients involved both cortical and trabecular compartments. Excessive bone resorption appears to affect cortical more than trabecular bone at distal radius, particularly manifested as increased cortical porosity. Ulnovolar periosteal apposition of the distal radius is a feature of chronic, severe RA with wrist deformity.

Consensus statement on blocking the effects of interleukin-6 and in particular by interleukin-6 receptor inhibition in rheumatoid arthritis and other inflammatory conditions

BACKGROUND

Since approval of tocilizumab (TCZ) for treatment of rheumatoid arthritis (RA) and juvenile idiopathic arthritis (JIA), interleukin 6 (IL-6) pathway inhibition was evaluated in trials of TCZ and other agents targeting the IL-6 receptor and ligand in various RA populations and other inflammatory diseases. This consensus document informs on interference with the IL-6 pathway based on evidence and expert opinion.

METHODS

Preparation of this document involved international experts in RA treatment and RA patients. A systematic literature search was performed that focused on TCZ and other IL6-pathway inhibitors in RA and other diseases. Subsequently, incorporating available published evidence and expert opinion, the steering committee and a broader expert committee (both including RA patients) formulated the current consensus statement.

RESULTS

The consensus statement covers use of TCZ as combination- or monotherapy in various RA populations and includes clinical, functional and structural aspects. The statement also addresses the second approved indication in Europe JIA and non-approved indications. Also early phase trials involving additional agents that target the IL-6 receptor or IL-6 were evaluated. Safety concerns, including haematological, hepatic and metabolic issues as well as infections, are addressed likewise.

CONCLUSIONS

The consensus statement identifies points to consider when using TCZ, regarding indications, contraindications, screening, dose, comedication, response evaluation and safety. The document is aimed at supporting clinicians and informing patients, administrators and payers on opportunities and limitations of IL-6 pathway inhibition.

Magnolol ameliorates ligature-induced periodontitis in rats and osteoclastogenesis: in vivo and in vitro study

Periodontal disease characterized by alveolar bone resorption and bacterial pathogen-evoked inflammatory response has been believed to have an important impact on human oral health. The aim of this study was to evaluate whether magnolol, a main constituent of Magnolia officinalis, could inhibit the pathological features in ligature-induced periodontitis in rats and osteoclastogenesis. The sterile, 3–0 (diameter; 0.2 mm) black braided silk thread, was placed around the cervix of the upper second molars bilaterally and knotted medially to induce periodontitis. The morphological changes around the ligated molars and alveolar bone were examined by micro-CT. The distances between the amelocemental junction and the alveolar crest of the upper second molars bilaterally were measured to evaluate the alveolar bone loss. Administration of magnolol (100 mg/kg, p.o.) significantly inhibited alveolar bone resorption, the number of osteoclasts on bony surface, and protein expression of receptor activator of nuclear factor-κB ligand (RANKL), a key mediator promoting osteoclast differentiation, in ligated rats. Moreover, the ligature-induced neutrophil infiltration, expression of inducible nitric oxide synthase, cyclooxygenase-2, matrix metalloproteinase (MMP)-1 and MMP-9, superoxide formation, and nuclear factor-κB activation in inflamed gingival tissues were all attenuated by magnolol. In the in vitro study, magnolol also inhibited the growth of Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans that are key pathogens initiating periodontal disease. Furthermore, magnolol dose dependently reduced RANKL-induced osteoclast differentiation from RAW264.7 macrophages, tartrate-resistant acid phosphatase (TRAP) activity of differentiated cells accompanied by a significant attenuation of resorption pit area caused by osteoclasts. Collectively, we demonstrated for the first time that magnolol significantly ameliorates the alveolar bone loss in ligature-induced experimental periodontitis by suppressing periodontopathic microorganism accumulation, NF-κB-mediated inflammatory mediator synthesis, RANKL formation, and osteoclastogenesis. These activities support that magnolol is a potential agent to treat periodontal disease.

Biocompatibility and inflammation profile of B2A-coated granules used in arthrodesis

The biocompatibility/inflammation profile of B2A-coated ceramic granules was evaluated using a panel of standard biocompatibility protocols (International Organization for Standardization-10993) including skin irritation and delayed-type hypersensitivity (Kligman maximization test), as well as acute, subacute, and chronic toxicity. Additionally, the potential of B2A-coated granules to elicit inflammatory reactions was also assessed using in vivo air pouch models, and B2A was evaluated using in vitro models of leukocyte recruitment and endothelial cell activation. Overall, the findings demonstrate that B2A-coated ceramic granules exhibit good biocompatibility profiles in the murine air pouch model and in standard subcutaneous implant models, and B2A did not demonstrate evidence of leukocyte recruitment or endothelial cell activation. These findings suggest that B2A and B2A-coated granules have little, if any, propensity to initiate inflammation reactions based on leukocyte recruitment. Thus, traditional biocompatibility and specially designed inflammation models indicate a high degree of biocompatibility and a low possibility of toxicity, inflammation, or edema following the implant of B2A-coated granules.

Effects of anti-tumor necrosis factor α agents on bone

PURPOSE OF REVIEW

Tumor necrosis factor (TNF) inhibitors are effective for achieving disease control in several inflammatory diseases. Although anti-TNF agents can inhibit bone loss in vitro, their role in the prevention of clinically relevant outcomes such as osteoporosis and fractures has not been clearly established.

RECENT FINDINGS

There are many studies of the effects of TNF inhibitors on markers of bone turnover; however, few have measured bone mineral density (BMD) or fractures. Most of these studies have small sample sizes and a minority had a placebo control group. Overall these studies suggest that the antiresorptive effects of anti-TNF therapy are related to control of disease activity.

SUMMARY

The antiresorptive effects of TNF inhibitors are likely related to their anti-inflammatory properties. Studies to date have not demonstrated any advantages of TNF inhibitors over traditional nonbiologic therapies in the prevention of bone loss and fractures.

Resolvin E1 and chemokine-like receptor 1 mediate bone preservation

The polyunsaturated ω-3 fatty acid eicosapentaenoic acid-derived resolvin E1 (RvE1) enhances resolution of inflammation, prevents bone loss, and induces bone regeneration. Although the inflammation-resolving actions of RvE1 are characterized, the molecular mechanism of its bone-protective actions are of interest. To test the hypothesis that receptor-mediated events impact bone changes, we prepared transgenic mice overexpressing the RvE1 receptor chemokine-like receptor 1 (chemR23) on leukocytes. In zymosan-initiated peritonitis, neutrophil polymorphonuclear leukocyte infiltration in response to RvE1 was limited requiring log order lower doses in chemR23tg mice. Ligature-induced alveolar bone loss was diminished in chemR23tg mice. Local RvE1 treatment of uniform craniotomy in the parietal bone significantly accelerated regeneration of the bone defect. In in vitro bone cultures, RvE1 significantly enhanced expression of osteoprotegerin (OPG) without inducing change in receptor activator of NF-κB ligand levels, whereas the osteogenic markers alkaline phosphatase, bone sialoprotein, and Runt-related transcription factor 2 remained unchanged. These results indicate that RvE1 modulates osteoclast differentiation and bone remodeling by direct actions on bone, rescuing OPG production and restoring a favorable receptor activator of NF-κB ligand/OPG ratio, in addition to known anti-inflammatory and proresolving actions.

Bone turnover markers in patients with type 1 Gaucher disease

Bone complications occur frequently in Gaucher disease (GD) and reduce the quality of life of these patients. Skeletal involvement is an important indication for treatment to ameliorate symptoms and reduce the risk of irreversible and debilitating disease. Bone biomarkers have been used to assess disease status and the response to therapy in a number of bone disorders. Here, we examine the literature for evidence of abnormalities in bone turnover markers in patients with type 1 GD to assess whether they might be useful for the assessment of bone involvement in GD. We have found that bone biomarkers in GD show highly variable results which do not currently support their routine use for clinical assessment of bone status, as an indication for therapy initiation, or for monitoring the response to therapy. A greater understanding of bone markers and their relation to the bone manifestations of GD is required.