RSK2 protects mice against TNF-induced bone loss.

Tumor necrosis factor (TNF)-α is a key cytokine regulator of bone and mediates inflammatory bone loss. The molecular signaling that regulates bone loss downstream of TNF-α is poorly defined. Here, we demonstrate that inactivating the pro-osteoblastogenic ERK-activated ribosomal S6 kinase RSK2 leads to a drastically accelerated and amplified systemic bone loss in mice ectopically expressing TNF-α [human TNF transgenic (hTNFtg) mice]. The phenotype is associated with a decrease in bone formation because of fewer osteoblasts as well as a drastically increased bone destruction by osteoclasts. The molecular basis of this phenotype is a cell autonomous increased sensitivity of osteoblasts and osteocytes to TNF-induced apoptosis combined with an enhancement of their osteoclast supportive activity. Thus, RSK2 exerts a strong negative regulatory loop on TNF-induced bone loss.

Blockade of TNF-α rapidly inhibits pain responses in the central nervous system.

There has been a consistent gap in understanding how TNF-α neutralization affects the disease state of arthritis patients so rapidly, considering that joint inflammation in rheumatoid arthritis is a chronic condition with structural changes. We thus hypothesized that neutralization of TNF-α acts through the CNS before directly affecting joint inflammation. Through use of functional MRI (fMRI), we demonstrate that within 24 h after neutralization of TNF-α, nociceptive CNS activity in the thalamus and somatosensoric cortex, but also the activation of the limbic system, is blocked. Brain areas showing blood-oxygen level-dependent signals, a validated method to assess neuronal activity elicited by pain, were significantly reduced as early as 24 h after an infusion of a monoclonal antibody to TNF-α. In contrast, clinical and laboratory markers of inflammation, such as joint swelling and acute phase reactants, were not affected by anti-TNF-α at these early time points. Moreover, arthritic mice overexpressing human TNF-α showed an altered pain behavior and a more intensive, widespread, and prolonged brain activity upon nociceptive stimuli compared with wild-type mice. Similar to humans, these changes, as well as the rewiring of CNS activity resulting in tight clustering in the thalamus, were rapidly reversed after neutralization of TNF-α. These results suggest that neutralization of TNF-α affects nociceptive brain activity in the context of arthritis, long before it achieves anti-inflammatory effects in the joints.

VCAM-1 serum levels are associated with arthropathy in hereditary haemochromatosis.

OBJECTIVES: The aim of this study was to assess the role of vascular adhesion molecule 1 (VCAM-1) in patients with hereditary haemochromatosis (HH) with or without arthropathy. METHODS: Sera from a large cross-sectional cohort of unselected HH patients (n=147) were obtained and compared to an age-matched and sex-matched control group. Serum levels of VCAM-1 were measured by ELISA and were correlated with clinical measures. RESULTS: VCAM-1 serum levels were elevated in HH patients as compared to matched controls (mean 913±456 vs 654±451 ng/ml, p<0.0001). Within the HH patient group, VCAM-1 levels were much higher in patients with arthropathy and joint replacement surgery. VCAM-1 levels correlated well with radiographic measures of HH arthropathy (r=0.36, p<0.0001). Multivariate regression analysis confirmed a highly significant association of VCAM-1 serum levels and the presence of HH arthropathy, independent from diabetes, body mass index and age. CONCLUSIONS: VCAM-1 serum levels emerge as a biomarker for haemochromatosis arthropathy.

Idiopathic hand osteoarthritis vs haemochromatosis arthropathy--a clinical, functional and radiographic study.

OBJECTIVE: Haemochromatosis arthropathy is a secondary OA and the most frequent and earliest clinical presentation of hereditary haemochromatosis (HH). The aim of this study was to perform a direct clinical, functional and radiographic comparison with idiopathic hand OA (HOA) to unravel important differences between these clinical entities. METHODS: In total, 299 patients (141 with HH arthropathy of the hands and 158 patients with idiopathic HOA) were recruited. Structured clinical assessment including hand function tests, as well as hand radiographs with scoring according to Kellgren-Lawrence, were carried out in all patients. RESULTS: HH arthropathy and HOA differed significantly: patients with HH arthropathy were younger and predominantly male as compared with HOA. In males but not females, HH arthropathy led to an earlier start of symptoms than in HOA. Patients with HOA had more tender joints and worse hand function than patients with HH arthropathy, although subjective measures of joint pain and function were similar. MCP and wrist joint involvement was more frequent and severe in HH arthropathy, while HOA patients more frequently had degenerative changes in the first CMC as well as PIP and DIP joints. CONCLUSION: HH arthropathy and idiopathic HOA differ significantly in terms of epidemiology, localization, severity of symptoms and radiographic changes.

Vitamin D receptor regulates TNF-mediated arthritis.

OBJECTIVE: Reduced vitamin D intake has been linked to increased susceptibility to develop rheumatoid arthritis (RA) and vitamin D deficiency is associated with increased disease activity in RA patients. The pathophysiological role of vitamin D in joint inflammation is, however, unclear. METHODS: To determine the influence of absent vitamin D signalling in chronic arthritis, vitamin D receptor (VDR)-deficient mice were crossed with human tumour necrosis factor (TNF) transgenic mice (hTNFtg), which spontaneously develop chronic arthritis. RESULTS: Clinical signs and symptoms of chronic arthritis were aggravated in hTNFtg mice lacking functional VDR signalling. Moreover, synovial inflammation was clearly increased in VDR(-/-)hTNFtg mice as compared to hTNFtg mice and was associated with an increased macrophage influx in inflamed joints. In vitro, VDR-deficient monocytes were proinflammatory and hyper-responsive to TNF stimulation associated with prolonged mitogen-activated protein kinase activation and cytokine secretion. Also, VDR(-/-) monocytes showed enhanced potential to differentiate into bone resorbing osteoclasts in vitro. In line, VDR(-/-)hTNFtg mice had significantly increased cartilage damage and synovial bone erosions. CONCLUSIONS: VDR plays an important role in limiting the inflammatory phenotype in a mouse model of RA. Absent VDR signalling causes a proinflammatory monocyte phenotype associated with increased inflammation, cartilage damage and bone erosion.

Musculoskeletal disease burden of hereditary hemochromatosis.

OBJECTIVE: To determine the prevalence, clinical picture, and disease burden of arthritis in patients with hereditary hemochromatosis. METHODS: In this cross-sectional observational study of 199 patients with hemochromatosis and iron overload, demographic and disease-specific variables, genotype, and organ involvement were recorded. The prevalence, intensity, and localization of joint pain were assessed, and a complete rheumatologic investigation was performed. Radiographs of the hands, knees, and ankles were scored for joint space narrowing, erosions, osteophytes, and chondrocalcinosis. In addition, the number and type of joint replacement surgeries were recorded. RESULTS: Joint pain was reported by 72.4% of the patients. Their mean ± SD age at the time of the initial joint symptoms was 45.8 ± 13.2 years. If joint pain was present, it preceded the diagnosis of hemochromatosis by a mean ± SD of 9.0 ± 10.7 years. Bony enlargement was observed in 65.8% of the patients, whereas synovitis was less common (13.6%). Joint space narrowing and osteophytes as well as chondrocalcinosis of the wrist and knee joints were frequent radiographic features of hemochromatosis. Joint replacement surgery was common, with 32 patients (16.1%) undergoing total joint replacement surgery due to severe OA. The mean ± SD age of these patients was 58.3 ± 10.4 years at time of joint replacement surgery. Female sex, metacarpophalangeal joint involvement, and the presence of chondrocalcinosis were associated with a higher risk of early joint failure (i.e., the need for joint replacement surgery). CONCLUSION: Arthritis is a frequent, early, and severe symptom of hemochromatosis. Disease is not confined to involvement of the metacarpophalangeal joints and often leads to severe damage requiring the replacement of joints.

12/15-lipoxygenase counteracts inflammation and tissue damage in arthritis.

Eicosanoids are essential mediators of the inflammatory response and contribute both to the initiation and the resolution of inflammation. Leukocyte-type 12/15-lipoxygenase (12/15-LO) represents a major enzyme involved in the generation of a subclass of eicosanoids, including the anti-inflammatory lipoxin A(4) (LXA(4)). Nevertheless, the impact of 12/15-LO on chronic inflammatory diseases such as arthritis has remained elusive. By using two experimental models of arthritis, the K/BxN serum-transfer and a TNF transgenic mouse model, we show that deletion of 12/15-LO leads to uncontrolled inflammation and tissue damage. Consistent with these findings, 12/15-LO-deficient mice showed enhanced inflammatory gene expression and decreased levels of LXA(4) within their inflamed synovia. In isolated macrophages, the addition of 12/15-LO-derived eicosanoids blocked both phosphorylation of p38MAPK and expression of a subset of proinflammatory genes. Conversely, 12/15-LO-deficient macrophages displayed significantly reduced levels of LXA(4), which correlated with increased activation of p38MAPK and an enhanced inflammatory gene expression after stimulation with TNF-alpha. Taken together, these results support an anti-inflammatory and tissue-protective role of 12/15-LO and its products during chronic inflammatory disorders such as arthritis.

Validation of a radiographic scoring system for haemochromatosis arthropathy.

BACKGROUND: Arthropathy is one of the earliest and most common manifestations of hereditary haemochromatosis with a significant impact on quality of life. Although its radiographic features are well known, there is no assessment tool for their evaluation. OBJECTIVE: To develop and validate a novel scoring system for the evaluation of radiographic features of haemochromatosis arthropathy. METHODS: A dichotomous scoring system assessing four radiographic features of haemochromatosis arthropathy and a 4-grade scale reflecting severity of radiographic change have been developed. Standard radiographs (hand, wrist, knee and ankle) of 170 subjects (116 male, 54 female) with genetically confirmed haemochromatosis and laboratory signs of iron overload were assessed by three readers and construct validity, feasibility and cross-sectional reliability (intrareader and inter-reader) were assessed. RESULTS: Intrareader and inter-reader reliability as assessed by percentage pairwise agreement and Cohen's weighed κ were good to excellent for most features and locations evaluated. Radiographic scores correlated well with clinical parameters (bony swollen joint count, hand function and physician's global health assessment; Pearson's correlation, r²=0.18-0.62, p<0.0001). A complete set of radiographs took 3.4 ± 1.2 (mean ± SD) min to be assessed. An atlas of characteristic radiographic features was compiled. CONCLUSION: A feasible and reliable radiological assessment tool for the evaluation of haemochromatosis arthropathy has been validated and an atlas of characteristic radiographic features provided.

Dual inhibition of c-abl and PDGF receptor signaling by dasatinib and nilotinib for the treatment of dermal fibrosis.

Abelson kinase (c-abl) and platelet-derived growth factor (PDGF) are key players in the pathogenesis of systemic sclerosis (SSc). The aim of the present study was to evaluate the antifibrotic potential of dasatinib and nilotinib, 2 novel inhibitors of c-abl and PDGF, which are well tolerated and have recently been approved. Dasatinib and nilotinib dose-dependently reduced the mRNA and protein levels of extracellular matrix proteins in human stimulated dermal fibroblasts from SSc patients (IC(50) of 0.5-2.0 nM for dasatinib and 0.8-2.5 nM for nilotinib). In a mouse model of bleomycin-induced dermal fibrosis, dasatinib and nilotinib potently reduced the dermal thickness, the number of myofibroblasts, and the collagen content of the skin in a dose-dependent manner at well-tolerated doses. These data indicate that dasatinib and nilotinib potently inhibit the synthesis of extracellular matrix in vitro and in vivo at biologically relevant concentrations. Thus, we provide the first evidence that dasatinib and nilotinib might be promising drugs for the treatment of patients with SSc.

High-sensitivity C-reactive protein and risk of nontraumatic fractures in the Bruneck study.

BACKGROUND: Chronic inflammatory diseases are associated with bone loss and an enhanced fracture risk. It is unknown, however, whether low-grade inflammation in healthy individuals, as estimated by the high-sensitivity C-reactive protein (hs-CRP) level, interferes with bone metabolism and affects the risk of nontraumatic fractures. METHODS: Lifetime bone fractures were carefully recorded in the cohort of the population-based Bruneck Study (n = 919) along with information on the date of occurrence and associated circumstances. The serum level of hs-CRP was measured from blood samples collected during the 1990 baseline examination and the 1995, 2000, and 2005 follow-up examinations. In addition, lifestyle and demographic characteristics, bone ultrasonographic data at the heel, and variables of bone metabolism were assessed. RESULTS: Between September 1, 1990, and August 31, 2005, 69 subjects experienced nontraumatic hip or vertebral fractures. The incidence of nontraumatic fractures was 1.3, 3.8, and 13.9 per 1000 person-years in the tertile groups for hs-CRP. In multivariate pooled logistic regression analysis, the adjusted relative risk (95% confidence interval) of nontraumatic fracture in the highest vs lowest tertile group for hs-CRP was 9.4 (3.6-24.8) (P < .001). The exclusion of subjects with cardiovascular disease, dementia, malignancies, and chronic inflammatory disease had little effect on the results obtained. The hs-CRP level was unrelated to ultrasonographic measures of bone density, but showed an inverse relation to laboratory markers of bone turnover, like beta-crosslaps and osteocalcin concentration (P < .001). CONCLUSIONS: The hs-CRP level is a significant and independent risk predictor of nontraumatic fracture. This finding is consistent with the hypothesis of a tight interplay between low-grade inflammation and bone turnover.

Induction of osteoclastogenesis and bone loss by human autoantibodies against citrullinated vimentin.

Autoimmunity is complicated by bone loss. In human rheumatoid arthritis (RA), the most severe inflammatory joint disease, autoantibodies against citrullinated proteins are among the strongest risk factors for bone destruction. We therefore hypothesized that these autoantibodies directly influence bone metabolism. Here, we found a strong and specific association between autoantibodies against citrullinated proteins and serum markers for osteoclast-mediated bone resorption in RA patients. Moreover, human osteoclasts expressed enzymes eliciting protein citrullination, and specific N-terminal citrullination of vimentin was induced during osteoclast differentiation. Affinity-purified human autoantibodies against mutated citrullinated vimentin (MCV) not only bound to osteoclast surfaces, but also led to robust induction of osteoclastogenesis and bone-resorptive activity. Adoptive transfer of purified human MCV autoantibodies into mice induced osteopenia and increased osteoclastogenesis. This effect was based on the inducible release of TNF-α from osteoclast precursors and the subsequent increase of osteoclast precursor cell numbers with enhanced expression of activation and growth factor receptors. Our data thus suggest that autoantibody formation in response to citrullinated vimentin directly induces bone loss, providing a link between the adaptive immune system and bone.

Combining functional magnetic resonance imaging with mouse genomics: new options in pain research.

This functional magnetic imaging study investigated the functional implications of genetic modification and pharmacological intervention on cerebral processing of heat-induced nociception in mice. Comparing dynorphin-overexpressing dream(-/-) with wild-type mice, smaller activated cortical and limbic brain structure sizes could be observed. Moreover, significantly reduced blood oxygenation level-dependent signal amplitudes were found in pain-related brain structures: sensory input, thalamic regions, sensory cortex, limbic system, basal ganglia, hypothalamus and periaqueductal grey. Administration of the specific kappa-opioid-receptor antagonist nor-binaltorphimine to dream(-/-) mice reversed this reduction to wild-type level in the same brain structures. These results show that blood oxygenation level-dependent functional magnetic imaging in the pain system of (transgenic) mice is feasible. Genetic modifications and pharmacological interventions modify brain responses in a structure-specific manner.

Hereditary hemochromatosis as a risk factor for joint replacement surgery.

OBJECTIVE: Hemochromatosis is an inherited disease with iron overload and joint involvement resembling osteoarthritis. To determine the rate of joint replacement surgery in patients with hemochromatosis, we performed a cross-sectional cohort study. METHODS: A total of 199 individuals with hereditary hemochromatosis were included. The prevalence of joint replacement surgery in hip, knee, and ankle joints because of secondary osteoarthritis was assessed. Data were compared with 917 healthy subjects from the population-based Bruneck study. RESULTS: A total of 32 of 199 individuals with hemochromatosis received joint replacement surgery with a total number of 52 joints replaced. Compared with expected rates in healthy individuals, patients with hemochromatosis had a significantly higher risk for joint replacement surgery (odds ratio 9.0; confidence interval, 4.6-17.4). Joint replacement occurred significantly earlier in life in patients with hemochromatosis; 21.9% of the patients with hemochromatosis and 1.7% of healthy individuals required joint replacement before the age of 50 years (P=.0027). Moreover, patients with hemochromatosis were more likely to require multiple joint replacements (8.5%) than the control group (expected rate 0.3%; P=.0001). CONCLUSION: Hemochromatosis is a risk factor for joint replacement surgery because of severe secondary osteoarthritis.

Inhibition of interleukin-6 receptor directly blocks osteoclast formation in vitro and in vivo.

OBJECTIVE: To investigate the efficacy of a murine anti-interleukin-6 receptor (anti-IL-6R) antibody in directly blocking tumor necrosis factor (TNF)- and RANKL-mediated osteoclastogenesis in vitro and in vivo. METHODS: The efficacy of a murine antibody against IL-6R in blocking osteoclast differentiation of mononuclear cells stimulated with RANKL was tested. In addition, arthritic human TNFalpha-transgenic mice were treated with anti-IL-6R antibody, and osteoclast formation and bone erosion were assessed in arthritic paws. RESULTS: Blockade of IL-6R dose dependently reduced osteoclast differentiation and bone resorption in monocyte cultures stimulated with RANKL or RANKL plus TNF. In human TNFalpha-transgenic mice, IL-6R blockade did not inhibit joint inflammation, but it strongly reduced osteoclast formation in inflamed joints as well as bone erosion in vivo. Neither the cell influx into joints nor the synovial expression of IL-6 and RANKL changed with IL-6R blockade, while the synovial expression of IL-1 was significantly reduced. In contrast, TNF-mediated systemic bone loss was not inhibited by IL-6R blockade. CONCLUSION: These data suggest that blockade of IL-6R directly affects osteoclast formation in vitro and in vivo, suggesting a direct and specific effect of anti-IL-6R therapy on osteoclasts independently of its antiinflammatory effects. This effect adds significantly to the structure-sparing potential of pharmacologic blockade of IL-6R in arthritis.

Pathogenesis of Churg-Strauss syndrome: recent insights.

Churg-Strauss syndrome (CSS) is a rare systemic necrotizing vasculitis associated with granuloma formation and severe blood and tissue eosinophilia. CSS occurs almost exclusively in patients with asthma. Its pathogenesis remains largely unknown, as triggering factors for CSS development have not been identified so far. AAb, such as anti-neutrophil cytoplasmic autoantibodies, are found in less than half of patients and possibly constitute a subtype of CSS with different clinical behaviour. On a cellular level, CSS is characterized by a strong Th2-type immune response. Th2-associated cytokines such as IL-4, IL-13 and IL-5 may precipitate the severe eosinophilia in CSS, while migration of Eos to inflammatory sites is possibly mediated by eotaxin-3. This review summarizes recent advances in the knowledge on epidemiology, clinical features, and pathogenesis of CSS.

Vascular cell adhesion molecule 1 as a predictor of severe osteoarthritis of the hip and knee joints.

OBJECTIVE: Osteoarthritis (OA) is a leading cause of pain and physical disability in middle-aged and older individuals. We undertook this study to determine predictors of the development of severe OA, apart from age and overweight. METHODS: Joint replacement surgery due to severe hip or knee OA was recorded over a 15-year period in the prospective Bruneck cohort study. Demographic characteristics and lifestyle and biochemical variables, including the level of soluble vascular cell adhesion molecule 1 (VCAM-1), were assessed at the 1990 baseline visit and tested as predictors of joint replacement surgery. RESULTS: Between 1990 and 2005, hip or knee joint replacement due to OA was performed in 60 subjects. VCAM-1 level emerged as a highly significant predictor of the risk of joint replacement surgery. Intervention rates were 1.9, 4.2, and 10.1 per 1,000 person-years in the first, second, and third tertiles, of the VCAM-1 level, respectively. In multivariable logistic regression analysis, the adjusted relative risk of joint replacement surgery in the highest versus the lowest tertile group of VCAM-1 level was 3.9 (95% confidence interval 1.7-8.7) (P<0.001). Findings were robust in various sensitivity analyses and were consistent in subgroups. Addition of the VCAM-1 level to a risk model already including age, sex, and body mass index resulted in significant gains in model discrimination (C statistic) and calibration and in more accurate risk classification of individual participants. CONCLUSION: The level of soluble VCAM-1 emerged as a strong and independent predictor of the risk of hip and knee joint replacement due to severe OA. If our findings can be reproduced in other epidemiologic cohorts, they will assist in routine risk classification and will contribute to a better understanding of the etiology of OA.

Treg cells suppress osteoclast formation: a new link between the immune system and bone.

OBJECTIVE: To investigate whether Treg cells can suppress osteoclast differentiation, and to define a new potential link between the immune system and the skeleton. METHODS: Regulatory CD4+,CD25+,Foxp3+ T cells were isolated and purified from the spleen and cocultured with CD11b+ osteoclast precursor cells isolated from bone marrow. Osteoclastogenesis and bone erosion were assessed by tartrate-resistant acid phosphatase staining and pit resorption assay, respectively. In addition, Transwell experiments and cytokine-blocking experiments were performed to define the mechanisms of interaction between Treg cells and osteoclasts. RESULTS: CD4+,CD25+,Foxp3+ T cells, but not CD4+,CD25- T cells, dose dependently inhibited macrophage colony-stimulating factor- and RANKL-dependent osteoclast formation. Pit formation was inhibited by up to 80% when Treg cells were added. The blockade of osteoclast formation was not based on the alteration of RANKL/osteoprotegerin balance but was essentially dependent on direct cell-cell contact via CTLA-4. Treg cell-mediated expression of transforming growth factor beta, interleukin-4 (IL-4), and IL-10 contributed but was not essential to the inhibitory effect on osteoclastogenesis. CONCLUSION: These data show that CD4+,CD25+,Foxp3+ Treg cells suppress osteoclast formation, provide a new link between the immune system and bone, and extend our knowledge on regulation of bone homeostasis by the immune system.

Bone erosions and bone marrow edema as defined by magnetic resonance imaging reflect true bone marrow inflammation in rheumatoid arthritis.

OBJECTIVE: To investigate the pathologic nature of features termed "bone erosion" and "bone marrow edema" (also called "osteitis) on magnetic resonance imaging (MRI) scans of joints affected by rheumatoid arthritis (RA). METHODS: RA patients scheduled for joint replacement surgery (metacarpophalangeal or proximal interphalangeal joints) underwent MRI on the day before surgery. The presence and localization of bone erosions and bone marrow edema as evidenced by MRI (MRI bone erosions and MRI bone marrow edema) were documented in each joint (n=12 joints). After surgery, sequential sections from throughout the whole joint were analyzed histologically for bone marrow changes, and these results were correlated with the MRI findings. RESULTS: MRI bone erosion was recorded based on bone marrow inflammation adjacent to a site of cortical bone penetration. Inflammation was recorded based on either invading synovial tissue (pannus), formation of lymphocytic aggregates, or increased vascularity. Fat-rich bone marrow was replaced by inflammatory tissue, increasing water content, which appears as bright signal enhancement on STIR MRI sequences. MRI bone marrow edema was recorded based on the finding of inflammatory infiltrates, which were less dense than those of MRI bone erosions and localized more centrally in the joint. These lesions were either isolated or found in contact with MRI bone erosions. CONCLUSION: MRI bone erosions and MRI bone marrow edema are due to the formation of inflammatory infiltrates in the bone marrow of patients with RA. This emphasizes the value of MRI in sensitively detecting inflammatory tissue in the bone marrow and demonstrates that the inflammatory process extends to the bone marrow cavity, which is an additional target structure for antiinflammatory therapy.