Involvement of receptor activator of NFkappaB ligand and tumor necrosis factor-alpha in bone destruction in rheumatoid arthritis

Clinical applications of RANK-ligand inhibition

An enhanced rate of bone remodelling fuelled by osteoclastogenesis mediates diseases such as osteoporosis, arthritic bone destruction, Paget's disease and malignancy-induced bone loss. Thus, the control of osteoclastogenesis is of major clinical importance. The receptor activator of nuclear factor kappa B (RANK); its ligand, RANKL and decoy receptor, osteoprotegerin, are critical determinants of osteoclastogenesis, and increased RANK signalling is involved in several bone diseases, providing the rationale for RANKL inhibition. The effects of RANKL inhibition are being witnessed in clinical trials of neutralizing fully human monoclonal antibodies that target RANKL (e.g. denosumab) and which induce profound and sustained inhibition of bone resorption. The relative efficacy, cost-effectiveness and side-effects of targeted RANKL inhibition compared with conventional antiresorptive drugs (i.e. bisphosphonates) should be resolved by clinical trials in coming years.

Parasitic helminths: new weapons against immunological disorders

The prevalence of allergic and autoimmune diseases is increasing in developed countries, possibly due to reduced exposure to microorganisms in childhood (hygiene hypothesis). Epidemiological and experimental evidence in support of this hypothesis is accumulating. In this context, parasitic helminths are now important candidates for antiallergic/anti-inflammatory agents. Here we summarize antiallergic/anti-inflammatory effects of helminths together along with our own study of the effects of Schistosoma mansoni on Th17-dependent experimental arthritis. We also discuss possible mechanisms of helminth-induced suppression according to the recent advances of immunology.

Promising bone-related therapeutic targets for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, debilitating autoimmune disease that results in inflammation and structural destruction of the joints. A hallmark of RA pathogenesis is an imbalance of the osteoblast-osteoclast axis driven by inflammatory processes, resulting in elevated bone resorption by osteoclasts. Current therapies used to treat this disease have focused on inhibition of synovitis, but such treatments do not adequately repair damaged bone. A key pathway of osteoclast formation involves the receptor activator of nuclear factor kappaB ligand (RANKL) pathway acting on myeloid progenitor cells. The Wnt pathway has been shown to be important for the differentiation of osteoblasts from mesenchymal lineage precursors, and endogenous Wnt inhibitors, such as Dickkopf1 and sclerostin, might have important roles in osteoclast dysregulation in RA. Inhibition of the RANKL pathway, or blockade of Dickkopf1 and sclerostin, might serve to restore the osteoblast-osteoclast balance and repair bone erosion in RA joints. Such treatments, in combination with anti-inflammatory therapies, could stabilize and repair damaged joints and have the potential to be valuable additions to the armory of RA treatments.

Modulation of osteoclast function in bone by the immune system

Osteoclast differentiation and function is regulated by cellular signals and cytokines that also play significant roles in the immune system. There is much scope, therefore, for immune cell influence on osteoclasts and bone metabolism. Many examples of this have been identified and T cells in particular are a source of factors affecting osteoclast formation and activity, a number which have either pro-osteolytic or anti-osteolytic actions depending on the cellular and microenvironmental context. For example, IL-12 and IL-18 participate in inflammatory processes that can lead to highly destructive osteolysis, yet these cytokines potently block osteoclast formation through mediation of T cells. IL-23 participates in chronic inflammatory processes, but lack of this cytokine results in reduced bone mass in mice, pointing to an influence on physiological regulation of bone mass. Such insights suggest that therapies that target immune responses may significantly influence osteolysis. Investigations into links between the immune system and bone metabolism are thus uncovering important information about the functioning of both systems.

Self-reported dietary intake of omega-3 fatty acids and association with bone and lower extremity function

OBJECTIVES

To assess the relationship between self-reported omega-3 fatty acid (O3FA) intake and bone mineral density (BMD) and lower extremity function in older adults.

DESIGN

Cross-sectional analysis of baseline information from three separate ongoing studies of older adults, pooled for this analysis.

SETTING

Academic health center.

PARTICIPANTS

Two hundred forty-seven men (n=118) and women (n=129) residing in the community or an assisted living facility.

MEASUREMENTS

Self-reported dietary intake (O3FA, omega-6 fatty acids (O6FA), protein, and total calorie); BMD of the hip or heel; and lower extremity function including leg strength, chair rise time, walking speed, Timed Up and Go, and frailty.

RESULTS

The mean reported intake of O3FA was 1.27 g/day. Correlation coefficients (r) between O3FA and T-scores from total femur (n=167) were 0.210 and 0.147 for combined femur and heel T scores. Similar correlations were found for leg strength (r=0.205) and chair rise time (r=-0.178), but the significance was lost when corrected for protein intake. Subjects with lower reported O3FA intake (<1.27 g/day) had lower BMD than those with higher reported O3FA intake. In a multiple regression analysis with femoral neck BMD as the dependent variable and reported intake of O3FA, O6FA, protein, and vitamin D as independent variables, reported O3FA intake was the only significant variable, accounting for 6% of the variance in BMD.

CONCLUSION

Older adults had low reported intakes of O3FA. There was an association between greater reported O3FA intake and higher BMD. There was no independent association between reported O3FA intake and lower extremity function. Results from this preliminary report are promising and suggest further investigation.

Modulation of the inflammatory response for enhanced bone tissue regeneration

Proinflammatory cytokines are infamous for their catabolic effects on tissues and joints in both inflammatory diseases and following the implantation of biomedical devices. However, recent studies indicate that many of these same molecules are critical for triggering tissue regeneration following injury. This review will discuss the role of inflammatory signals in regulating bone regeneration and the impact of both immunomodulatory and antiinflammatory pharmacologic agents on fracture healing, to demonstrate the importance of incorporating rational control of inflammation into the design of tissue engineering strategies.

The relationship between adipokines, body composition, and bone density in men with chronic obstructive pulmonary disease

Osteoporosis is common in patients with chronic obstructive pulmonary disease (COPD). Data regarding the relationship between adipokines and bone mineral density (BMD) in this population is lacking. The purpose of this pilot study was to determine associations between the adipokines tumor necrosis factor-alpha (TNF-α), leptin, adiponectin and resistin, body composition, and BMD in men with severe COPD. This was a cross-sectional study of men with severe COPD who visited the University of Colorado Hospital COPD Center. Bone density and parameters of body composition were measured by dual-energy X-ray absorptiometry. Twenty-three men were included (mean age = 66 years, mean percent predicted forced expiratory volume in one second = 32%). On bivariate analysis, there was no association between TNF-α and BMD. Parameters of body composition and serum concentrations of leptin and adiponectin were significantly associated with total hip and spine bone density. However, with partial correlation analysis, total body mass was the only independent predictor of total hip BMD, explaining approximately 50% of the variability. Overall, 18 out of 23 men enrolled (78%) had low bone density by T-score, and nine (39%) were classified as having osteoporosis. The men with osteoporosis had lower parameters of body composition, lower mean serum leptin concentrations, and a greater impairment in measures of lung function compared to the men without osteoporosis. We conclude that the effect of adipokines on BMD does not appear to be independent of body mass. However, larger studies are needed to further evaluate the relationship between adipokines, body weight, and BMD in patients with COPD.

Green tea and bone metabolism

Osteoporosis is a major health problem in both elderly women and men. Epidemiological evidence has shown an association between tea consumption and the prevention of age-related bone loss in elderly women and men. Ingestion of green tea and green tea bioactive compounds may be beneficial in mitigating bone loss of this population and decreasing their risk of osteoporotic fractures. This review describes the effect of green tea or its bioactive components on bone health, with an emphasis on (i) the prevalence and etiology of osteoporosis; (ii) the role of oxidative stress and antioxidants in osteoporosis; (iii) green tea composition and bioavailability; (iv) the effects of green tea and its active components on osteogenesis, osteoblastogenesis, and osteoclastogenesis from human epidemiological, animal, as well as cell culture studies; (v) possible mechanisms explaining the osteoprotective effects of green tea bioactive compounds; (vi) other bioactive components in tea that benefit bone health; and (vii) a summary and future direction of green tea and bone health research and the translational aspects. In general, tea and its bioactive components might decrease the risk of fracture by improving bone mineral density and supporting osteoblastic activities while suppressing osteoclastic activities.

Breaking old paradigms: Th17 cells in autoimmune arthritis

Aberrant helper T cell activation has been implicated in the pathogenesis of an array of autoimmune diseases. In this review, we summarize evidence that suggests the involvement of a novel T cell subset, the Th17 lineage, in rheumatoid arthritis. In particular, we focus on the role of Th17 cells in inducing and perpetuating the chronic inflammation, cartilage damage, and bone erosion that are hallmark phases of joint destruction and consider current and emerging therapies that seek to disrupt the inflammatory Th17 network and shift the immune system back towards homeostasis.

Involvement of SOCS3 in regulation of CD11c+ dendritic cell-derived osteoclastogenesis and severe alveolar bone loss

To investigate the role of suppressor of cytokine signaling (SOCS) molecules in periodontal immunity and RANKL-mediated dendritic cell (DC)-associated osteoclastogenesis, we analyzed SOCS expression profiles in CD4(+) T cells and the effect of SOCS3 expression in CD11c(+) DCs during periodontal inflammation-induced osteoclastogenesis and bone loss in nonobese diabetic (NOD) versus humanized NOD/SCID mice. Our results of ex vivo and in vitro analyses showed that (i) there is significantly higher SOCS3 expression associated with RANKL(+) T-cell-mediated bone loss in correlation with increased CD11c(+) DC-mediated osteoclastogenesis; (ii) the transfection of CD11c(+) DC using an adenoviral vector carrying a dominant negative SOCS3 gene significantly abrogates TRAP and bone-resorptive activity; and (iii) inflammation-induced TRAP expression, bone resorption, and SOCS3 activity are not associated with any detectable change in the expression levels of TRAF6 and mitogen-activated protein kinase signaling adaptors (i.e., Erk, Jnk, p38, and Akt) in RANKL(+) T cells. We conclude that SOCS3 plays a critical role in modulating cytokine signaling involved in RANKL-mediated DC-derived osteoclastogenesis during immune interactions with T cells and diabetes-associated severe inflammation-induced alveolar bone loss. Therefore, the development of SOCS3 inhibitors may have therapeutic potential as the target to halt inflammation-induced bone loss under pathological conditions in vivo.

The proliferative human monocyte subpopulation contains osteoclast precursors

Introduction

Immediate precursors of bone-resorbing osteoclasts are cells of the monocyte/macrophage lineage. Particularly during clinical conditions showing bone loss, it would appear that osteoclast precursors are mobilized from bone marrow into the circulation prior to entering tissues undergoing such loss. The observed heterogeneity of peripheral blood monocytes has led to the notion that different monocyte subpopulations may have special or restricted functions, including as osteoclast precursors.

Methods

Human peripheral blood monocytes were sorted based upon their degree of proliferation and cultured in macrophage colony-stimulating factor (M-CSF or CSF-1) and receptor activator of nuclear factor-kappa-B ligand (RANKL).

Results

The monocyte subpopulation that is capable of proliferation gave rise to significantly more multinucleated, bone-resorbing osteoclasts than the bulk of the monocytes.

Conclusions

Human peripheral blood osteoclast precursors reside in the proliferative monocyte subpopulation.

High oxygen tension prolongs the survival of osteoclast precursors via macrophage colony-stimulating factor

The oxygen tension affects the function, differentiation, and transformation of various cells, including bone cells. In pathological conditions such as rheumatoid arthritis (RA), rapidly destructive arthropathy, and primary or metastatic tumors, severe bone destruction or osteolysis occurs. Abundant blood vessels are often observed around these destructive lesions. At such sites, we have confirmed the increased production of reactive oxygen species (ROS) induced by a high oxygen tension and/or oxidative stress, as well as numerous osteoclasts detectable by immunohistochemistry. These findings suggest that osteoclasts are influenced by the high oxygen tension in pathological bone lesions because the zone around blood vessels has a relatively high oxygen tension. In this study, we investigated the effects of oxygen tension on osteoclastogenesis by culturing human CD14-positive cells (osteoclast precursors) with or without osteoblast-like supporting cells (Saos-4/3 cells) under a normal oxygen tension (20% O(2)) or a high oxygen tension (40% O(2)). A high oxygen tension markedly prolonged the duration of osteoclast precursor formation in the presence of supporting cells, and also markedly and persistently increased the production of macrophage colony stimulating factor (M-CSF) by supporting cells. Furthermore, we found an increase of cells expressing M-CSF and cells positive for tartrate-resistant acid phosphatase (TRAP) in hypervascular destructive bone lesions of RA patients where ROS were also abundant.

Adrenomedullin inhibits MAPK pathway-dependent rheumatoid synovial fibroblast-mediated osteoclastogenesis by IL-1 and TNF-alpha

The objective of this study is to determine the effects of adrenomedullin (AM) on IL-1- and TNF-alpha-induced rheumatoid synovial fibroblasts (RASFs)-mediated osteoclastogenesis. The formation of osteoclasts in co-cultures of RASFs and peripheral blood mononuclear cells was evaluated by tartrate-resistant acid phosphatase and resorption pit formation assay. The expression of RANKL, OPG, p-ERK, p-p38, and p-JNK was examined by immunoblotting and quantitative reverse transcription-polymerase chain reaction. AM (1-52) inhibits IL-1- and TNF-alpha-induced RASFs-mediated osteoclastogenesis. AM affected IL-1-, TNF-alpha-induced RANKL and OPG expression in RASFs. AM also inhibits IL-1 and TNF-alpha-induced phosphorylation of ERK-1/2, p38 MAPK, and JNK. Inhibitor of AM (AM 22-52) inhibits the effects of AM on the osteoclastogenesis. These results suggest that AM might be involved in the inflammatory cytokines-mediated osteoclastogenesis and thus bone damage, and indicate that it can be a new therapeutic strategy against joint destruction in RA.

Cannabidiol decreases bone resorption by inhibiting RANK/RANKL expression and pro-inflammatory cytokines during experimental periodontitis in rats

Cannabidiol (CBD) is a cannabinoid component from Cannabis sativa that does not induce psychotomimetic effects and possess anti-inflammatory properties. In the present study we tested the effects of CBD in a periodontitis experimental model in rats. We also investigated possible mechanisms underlying these effects. Periodontal disease was induced by a ligature placed around the mandible first molars of each animal. Male Wistar rats were divided into 3 groups: control animals; ligature-induced animals treated with vehicle and ligature-induced animals treated with CBD (5 mg/kg, daily). Thirty days after the induction of periodontal disease the animals were sacrificed and mandibles and gingival tissues removed for further analysis. Morphometrical analysis of alveolar bone loss demonstrated that CBD-treated animals presented a decreased alveolar bone loss and a lower expression of the activator of nuclear factor-kappaB ligand RANKL/RANK. Moreover, gingival tissues from the CBD-treated group showed decreased neutrophil migration (MPO assay) associated with lower interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha production. These results indicate that CBD may be useful to control bone resorption during progression of experimental periodontitis in rats.

Mechanisms modulating inflammatory osteolysis: a review with insights into therapeutic targets

Inflammatory osteolysis is a relatively frequent and incapacitating complication of rheumatoid arthritis and multiple other inflammation-associated bone diseases. It is thought to operate through an ultimate common pathway of accelerated osteoclast recruitment and activation under the control of cytokines produced in the inflammatory environment. Over the past decade, there have been major advances in our understanding of the mechanisms of osteoclastogenesis. It is now clear that the interaction of receptor activator NF-kappaB (RANK) and its ligand, RANKL, plays a central role in osteoclast formation and activity. Therefore, understanding osteoclastogenesis offers new pathways for potential therapeutic intervention in inflammatory osteolysis. The success of anti-tumor necrosis factor-alpha and interleukin-1 therapy highlights the central role that these specific cytokines play in this disease. This review outlines our current understanding of the mechanisms mediating inflammatory osteolysis and highlights potential therapeutic strategies.

Decreased bone mineral density in adult familial Mediterranean fever patients: a pilot study

We investigated the association between familial Mediterranean fever (FMF) and osteoporosis (OP) in adult patients. Thirty-five attack-free FMF patients (28 females, 7 males; mean age 36.9 +/- 5.7 years) were individually matched to control subjects on the basis of age (within 2 years) and sex. All patients were taking regular colchicine. Subjects having any condition that can cause decreased bone mineral density (BMD) were excluded from the study. BMD was measured at the spine and femur by dual X-ray absorptiometry (DXA). Data was given as the median (IQR). T scores of the spine were -0.700 (-1.097 to -0.262) and -0.450 (-0.830 to 0.112) in FMF patients and healthy controls, respectively (p > 0.05). T scores of the femur neck were -0.900 (-1.480 to -0.570) and -0.430 (-1.472 to 0.247) in FMF patients and healthy controls, respectively (p > 0.05). Total femur T scores were significantly lower in FMF patients than healthy controls (-0.780 [-1.222 to -0.085] vs. -0.100 [-0.765 to 0.537], respectively, p = 0.021). Total femur T scores were significantly decreased in adult patients with FMF. Ongoing subclinical inflammation may be associated with decreased bone mineral content in those patients.

Reduction of urinary levels of pyridinoline and deoxypyridinoline and serum levels of soluble receptor activator of NF-kappaB ligand by etanercept in patients with rheumatoid arthritis

The effects of soluble TNF-alpha receptor, etanercept, on bone metabolism were investigated in patients with rheumatoid arthritis (RA). Thirty RA patients were administered etanercept once or twice a week for more than 6 months. We evaluated clinical and laboratory parameters and measured urinary excretion levels of pyridinoline (PYD), deoxypyridinoline (DPD), cross-linked N-telopeptides of type I collagen (NTX), and serum levels of bone alkaline phosphatase (BAP), osteoprotegerin (OPG), and soluble receptor activator of NFkappaB ligand (sRANKL) at the baseline and at 3 and 6 months after initial treatment with etanercept. Etanercept treatment resulted in an improvement of symptoms due to RA and in a reduction of urinary excretion levels of PYD and DPD as well as serum sRANKL levels, with a significant difference at 6 months, and an increase of serum BAP levels at 3 and 6 months after the initial treatment with etanercept. Urinary NTX and serum OPG levels did not show a significant change at 3 and 6 months after the initial treatment, but serum OPG levels did show a reverse correlation with serum CRP levels, suggesting that the regulation of inflammation in RA may result in an induction of OPG production. Etanercept may have the ability to reduce the levels of bone resorption markers and to increase the levels of a bone formation marker while reducing sRANKL formation in RA patients.

Targeting of the immune system in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex immune disorder in which loss of tolerance to nucleic acid antigens and other crossreactive antigens is associated with the development of pathogenic autoantibodies that damage target organs, including the skin, joints, brain and kidney. New drugs based on modulation of the immune system are currently being developed for the treatment of SLE. Many of these new therapies do not globally suppress the immune system but target specific activation pathways relevant to SLE pathogenesis. Immune modulation in SLE is complicated by differences in the immune defects between patients and at different disease stages. Since both deficiency and hyperactivity of the immune system can give rise to SLE, the ultimate goal for SLE therapy is to restore homeostasis without affecting protective immune responses to pathogens. Here we review recent immunological advances that have enhanced our understanding of SLE pathogenesis and discuss how they may lead to the development of new treatment regimens.

A novel silicon complex is as effective as sodium metasilicate in enhancing the collagen-induced inflammatory response of silicon-deprived rats

An experiment was conducted with rats to determine whether silicon deprivation affects the inflammatory response to the injection of type II collagen, and to compare the effectiveness of the organic complex arginine silicate inositol (ASI) with inorganic silicon (NaSiO(3)) in mitigating any observed change in response. Dark Agouti rats were fed a ground corn-casein-safflower-based diet containing about 2.8 mg Si/kg. The experimental variables were supplemental 0 and 35 mg Si/kg as either ASI or NaSiO3. After five weeks on their respective treatments, each rat was injected with type II collagen and euthanized four weeks later. Urine was collected before injection during week five and week nine before euthanasia. The silicon-supplemented rats generally exhibited a more marked inflammatory response than the silicon-deprived rats. The circulating number of lymphocytes was higher (p<0.003) and number of neutrophils was lower (p<0.008) in silicon-deprived than silicon-supplemented rats. ASI and NaSiO3 were about equally effective in enhancing these changes. Post-injection of tibial release of prostaglandin E(2) (PGE(2)) (p<0.04), urinary excretion of magnesium (p<0.03) and deoxypyridinoline (p<0.009), and plasma osteopontin (p<0.009), magnesium (p<0.0007) and copper (p<0.004) were higher in silicon-supplemented than silicon-deprived rats. The increases in plasma magnesium (Si x sex, p<0.04) and copper (Si x sex, p<0.02) were more marked in male than female rats. One but not the other silicon supplement when compared to silicon deprivation significantly affected the tibial release of PGE(2), and plasma copper and iron concentrations. However, with the exception of the pre-injection urinary excretion of helical peptide, no other of the variables determined was significantly different between rats fed ASI and those fed NaSiO3. The findings suggest that, in rodents, physiological amounts of silicon promote the immune response, sex may influence the response to dietary silicon, and that both organic silicon complexes and inorganic silicon are similarly effective in preventing changes in inflammation induced by silicon deprivation.

Basic and clinical aspects of osteoporosis in inflammatory bowel disease

Low bone mineral density and the increased risk of fracture in gastrointestinal diseases have a multifactorial pathogenesis. Inflammatory bowel disease (IBD) has been associated with an increased risk of osteoporosis and osteopenia and epidemiologic studies have reported an increased prevalence of low bone mass in patients with IBD. Certainly, genetics play an important role, along with other factors such as systemic inflammation, malnutrition, hypogonadism, glucocorticoid therapy in IBD and other lifestyle factors. At a molecular level the proinflammatory cytokines that contribute to the intestinal immune response in IBD are known to enhance bone resorption. There are genes influencing osteoblast function and it is likely that LRP5 may be involved in the skeletal development. Also the identification of vitamin D receptors (VDRs) and some of its polymorphisms have led to consider the possible relationships between them and some autoimmune diseases and may be involved in the pathogenesis through the exertion of its immunomodulatory effects during inflammation. Trying to explain the physiopathology we have found that there is increasing evidence for the integration between systemic inflammation and bone loss likely mediated via receptor for activated nuclear factor kappa-B (RANK), RANK-ligand, and osteoprotegerin, proteins that can affect both osteoclastogenesis and T-cell activation. Although glucocorticoids can reduce mucosal and systemic inflammation, they have intrinsic qualities that negatively impact on bone mass. It is still controversial if all IBD patients should be screened, especially in patients with preexisting risk factors for bone disease. Available methods to measure BMD include single energy x-ray absorptiometry, DXA, quantitative computed tomography (QCT), radiographic absorptiometry, and ultrasound. DXA is the establish method to determine BMD, and routinely is measured in the hip and the lumbar spine. There are several treatments options that have proven their effectiveness, while new emergent therapies such as calcitonin and teriparatide among others remain to be assessed.

[The mechanism of bone loss in rheumatoid arthritis. Description based on a case report]

Various factors influencing bone turnover and bone loss in rheumatoid arthritis (RA) are illustrated using the example of a postmenopausal woman with a highly active RA. In particular, the relationships between disease activity, vitamin D metabolism, parathyroid hormone (PTH) levels and calcium metabolism are described. High disease activity is associated with low levels of 25-hydroxycholecalciferol, and especially of 1.25-dihydroxycholecalciferol. Despite vitamin D deficiency, PTH levels were decreased and histomorphometric investigation of the iliac crest biopsy showed severe osteoporosis but no signs of osteomalacia. Suppression of the inflammatory disease activity of RA led to a normalisation of the serum levels of 1.25-dihydroxycholecalciferol and PTH. This was associated with a reduction in the initially increased levels of bone specific alkaline phosphatase to normal values. This case report shows a close relationship between disease activity and bone turnover in RA and indicates that early investigation and therapy of disturbances of bone metabolism in RA are necessary.

ISSLS prize winner: repeated disc injury causes persistent inflammation

STUDY DESIGN

An in vivo rat model of disc degeneration with emphasis on characterizing acute and chronic cytokine production.

OBJECTIVE

To compare the morphologic and proinflammatory response between a single and triple-stab injury in attempts to establish mechanisms of chronic disc inflammation.

SUMMARY OF BACKGROUND DATA

The features that distinguish physiologic (asymptomatic) from pathologic (symptomatic) degeneration are unclear. Epidemiologic evidence suggests that cumulative damage and elevated disc cytokine levels may be linked to increased low back pain rates. Although acute injury stimulates a healing response that includes transient cytokine production, repetitive damage may be necessary to trigger the persistent inflammation suspected to underlie chronic pain.

METHODS

Tail discs were exposed surgically and stabbed with a number 11 blade. During the subsequent acute healing phase, triple-stab discs were percutaneously injured with a 23-gauge needle at day 3 and then again at day 6 after the initial blade incision. Cytokine (IL-1 beta, IL-6, IL-8, and TNF-alpha) production was quantified using enzyme linked immunosorbent assay, and, in addition to MAPK signaling pathways (phosphorylated forms of ERK, JNK, and p38), was localized by immunohistochemistry. Disc architecture was evaluated using histology.

RESULTS

Both single-stab and triple-stab discs degenerated with time, yet degeneration was more severe with repeated injury where nuclear proteoglycan was replaced by disorganized collagen. Four days after single-stab, there was a transient peak in IL-1 beta and IL-8 production that was localized to the wound track and associated granulation tissue. By contrast, triple-stab induced an activated annular fibroblast phenotype (p38 positive) that caused a prolonged, diffuse inflammatory response with elevated levels of TNF-alpha, IL-1 beta, and IL-8 up to 28 days after injury. Disc inflammation was accompanied by reactive changes in the adjacent vertebral marrow spaces that was initially lytic at day 4, becoming sclerotic by day 56.

CONCLUSION

Our results demonstrate that repeated injury during active healing leads to persistent inflammation and enhanced disc degeneration. These data support the premise that damage accumulation and its associated inflammation may distinguish pathologic from physiologic disc degeneration. In the future, this triple-stab model may be useful to evaluate the efficacy of anti-inflammatory low back pain treatments.

Impact of cytokines and T lymphocytes upon osteoclast differentiation and function

Historically, the osteoblast has been considered the master cell in the control of osteoclast development and, therefore, bone resorption. Now the interactions between cells of the immune system and bone cells have redefined our thinking on the regulation of bone resorption. Moreover, the crosstalk between these cell types has special significance in inflammatory conditions such as rheumatoid arthritis. This report highlights the contribution that T lymphocytes make in regulating osteoclast formation and bone resorption.

[p38 MAP Kinase inhibitor]

FR167653 is a potent inhibitor of p38 MAP Kinase and inhibits TNF-alpha and IL-1beta production in inflammatory cells. In this study we investigated the effect of FR167653 on CIA. CIA rats were subcutaneously injected with FR167653 (32 mg/kg/day) starting on the day of the booster injection and after the onset of arthritis in the prophylactic and therapeutic treatment groups, respectively. The hind paw swelling, radiolographic and histologic scores, and osteoclast number were evaluated. Serum and tissue cytokine levels were assessed by ELISA. Flow cytometric analysis of T-lymphocytes from bone marrow was also performed. The effect of FR167653 on in vitro osteoclast formation induced by sRANKL and TNF-alpha was examined. Hind paw swelling occurred in CIA rats but not in the prophylactic treatment group. Therapeutic treatment also significantly reduced the paw swelling. The mean radiographic, histologic score, and osteoclast number of the treatment group were significantly lower than those of CIA rats without treatment. FR167653 treatment reduced serum TNF-alpha and IL-1beta levels, ankle IL-1beta concentration, and CD4-CD8a+ T-cell population in bone marrow. Furthermore, FR167653 inhibited the osteoclast-like cell differentiation induced by both sRANKL and TNF-alpha in vitro. FR167653 prevented the onset of arthritis in a prophylactic treatment model and suppresses the progression of joint destruction in a therapeutic treatment model, suggesting that p38 MAP Kinase is a potential therapeutic target for rheumatoid arthritis.

Erosive arthritis

Inflammation and degradation of bone are two closely linked processes. Chronic inflammatory arthritis not only leads to inflammatory bone loss but it also involves local erosion of articular bone. This osteo-destructive feature of chronic inflammatory arthritis is a major cause of disability in patients with rheumatoid arthritis. Osteoclasts are essential for the resorption of mineralized cartilage and subchondral bone in chronic arthritis. The observed up-regulation of osteoclast differentiation factors (receptor activator of nuclear factor-κB ligand [RANKL]) in the synovial membrane of chronically inflamed joints indicates that osteoclasts are abundant in this setting, leading to rapid degradation of mineralized tissue. Blockade of osteoclast formation is thus a key strategy in preventing structural damage in arthritis. Denosumab, a humanized antibody that neutralizes RANKL, is an attractive candidate agent to inhibit inflammatory bone loss.

Soy isoflavones avert chronic inflammation-induced bone loss and vascular disease

Background

Evidence from epidemiological, clinical and animal studies suggests a link may exist between low bone density and cardiovascular disease, with inflammatory mediators implicated in the pathophysiology of both conditions. This project examined whether supplementation with soy isoflavones (IF), shown to have anti-inflammatory properties, could prevent tissue expression of TNF-α and the development of skeletal pathology in an animal model of chronic inflammation.

Methods

Eight-week old, intact, female C57BL/6J mice were used. In Phase 1, a lipopolysaccharide (LPS)-dose response study (0, 0.133, 1.33 and 13.3 μg/d) was conducted to determine the LPS dose to use in Phase 2. The results indicated the 1.33 μg LPS/d dose produced the greatest decrease in lymphocytes and increase in neutrophils. Subsequently, in Phase 2, mice were randomly assigned to one of six groups (n = 12–13 per group): 0 or 1.33 μg LPS/d (placebo or LPS) in combination with 0, 126 or 504 mg aglycone equivalents of soy IF/kg diet (Control, Low or High dose IF). Mice were fed IF beginning 2 wks prior to the 30-d LPS study period.

Results

At the end of the study, no differences were detected in final body weights or uterine weights. In terms of trabecular bone microarchitecture, μCT analyses of the distal femur metaphysis indicated that LPS significantly decreased trabecular bone volume (BV/TV) and number (TbN), and increased separation (TbSp). Trabecular bone strength (i.e. total force) and stiffness were also compromised in response to LPS. The High IF dose provided protection against these detrimental effects on microarchitecture, but not biomechanical properties. No alterations in trabecular thickness (TbTh), or cortical bone parameters were observed in response to the LPS or IF. Immunohistomchemical staining showed that tumor necrosis factor (TNF)-α was up-regulated by LPS in the endothelium of small myocardial arteries and arterioles as well as the tibial metaphysis and down-regulated by IF.

Conclusion

These results suggest IF may attenuate the negative effects of chronic inflammation on bone and cardiovascular health. Additional research is warranted to examine the anti-inflammatory properties of the soy isoflavones and the mechanisms underlying their prevention of chronic inflammation-induced bone loss.

Evaluation of pain behavior and bone destruction in two arthritic models in guinea pig and rat

The primary aim of the study was to describe and correlate pain behavior and changes in bone morphology in animal models of arthritis both in rats and guinea pigs. Either complete Freund's adjuvant (CFA) or mono-iodoacetate (MIA) solution was injected into the left knee joint to obtain a model for rheumatoid arthritis and osteoarthritis, respectively. Subsequently, animals were behaviorally tested during a period of 12 days after CFA injection and at least 19 days after MIA injection. During these observation periods increasing pain behavior was observed, characterized by decreased von Frey mechanical thresholds and weight bearing on the affected limb. In Hargreaves' paw flick test slightly increased thermal hypersensitivity was observed in some instances in guinea pigs. In rats there was also decreased limb-use during forced ambulation. To evaluate bone destruction mu-computed tomography scans of the arthritic knee were taken on the last experimental day. Different bone parameters indicative of osteolysis and decreased trabecular connectivity were significantly correlated with the observed pain behavior. Detailed description of morphological changes in arthritic joints better characterizes the different animal models and might add to the knowledge on the working mechanisms of analgesic compounds that have an influence on bone structures in arthritis.

A Triterpene Glycoside from Black Cohosh that Inhibits Osteoclastogenesis by Modulating RANKL and TNFα Signaling Pathways

Osteoporosis is a major age-related source of morbidity and mortality. Increased bone resorption mediated by osteoclasts is central to its pathogenesis. Cytokines, particularly RANKL and TNFalpha, are often increased under pathologic conditions, leading to enhanced osteoclastogenesis. Black cohosh (Actaea/Cimicifuga racemosa L), a popular herbal supplement for the treatment of menopausal symptoms, was recently shown to have the beneficial effect of preventing bone loss. Here, we demonstrate that 25-acetylcimigenol xylopyranoside (ACCX), a triterpenoid glycoside isolated from black cohosh, potently blocks in vitro osteoclastogenesis induced by either RANKL or TNFalpha. This blockage of osteoclastogenesis elicited by ACCX results from abrogation of the NF-kappaB and ERK pathways induced by either RANKL or TNFalpha, respectively. Importantly, this compound attenuates TNFalpha-induced bone loss in vivo. Therefore, ACCX represents a potential lead for the development of a new class of antiosteoporosis agents.

Mechanisms of bone loss in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease in which destruction of bone in the joints causes major morbidity. Recent research has shed light on the cell and molecular mechanisms that lead to this osteolysis, all due directly or indirectly to the chronic inflammation. The aspects of this research covered in this review include the alteration of cell proliferation and survival that results in growth of the RA synovium. This process depends upon an increase in angiogenesis and local blood flow, which is also a feature of increased bone turnover. In addition, the inflammatory environment increases expression of chemokines, which are involved in the recruitment of monocytic osteoclast precursors. Chronic inflammation also promotes an overall catabolic state, with increased osteoclast differentiation and resorptive activity, driven by disregulation of receptor activator of NF-kappaB ligand (RANKL) and the synergistic activity of inflammatory cytokines such as tumor necrosis factor-alpha and interleukin-1. Osteoclast survival is increased in this environment, but osteoblast differentiation and survival are decreased, with a consequent reduction in bone formation and a net loss of bone. Recognition of these processes and the factors involved will enable more effective and targeted treatments for RA.

Osteochondral repair in synovial joints

PURPOSE OF REVIEW

One of the major challenges in rheumatology remains the induction of osteochondral repair in synovial joints. Remarkable progress has been made in controlling the inflammatory pathways of chronic synovitis and tissue damage in rheumatoid arthritis and spondyloarthropathy. Here, we provide an overview of the current knowledge on the mechanisms involved in osteochondral repair in degenerative joint diseases, as well as in immune mediated inflammatory arthritides, with special emphasis on tumor necrosis factor alpha and IL-1.

RECENT FINDINGS

Homeostasis of articular cartilage and subchondral bone are essential for maintaining the integrity of osteochondral structures within synovial joints. This is achieved by the regulation of a delicate balance between anabolic and catabolic signals. In articular cartilage one cell type, the chondrocyte, is responsible for regulation of homeostasis. In bone, however, two distinct cell types, osteoblasts and osteoclasts, are responsible for anabolic and catabolic pathways, respectively. In inflammatory joint disorders, this tight regulation is profoundly dysregulated, with tumor necrosis factor alpha acting as an important catalyst of a disturbed homeostasis, together with IL-1. Targeting these cytokines may restore the intrinsic repair capacity of osteochondral structures.

SUMMARY

To restore catabolic cytokine balances appears to be a suitable strategy to promote osteochondral repair.

Soluble receptor activator of NFkappa B-ligand and osteoprotegerin in rheumatoid arthritis - relationship with bone mineral density, disease activity and bone turnover

The aim of our study was to investigate determinants of bone mineral density (BMD) measured by dual X-ray absorptiometry at the lumbar spine (BMD-LS) and at the femoral neck (BMD-FN) in patients with rheumatoid arthritis (RA) with special respect to bone resorbing proinflammatory cytokines and their physiological antagonists. In 142 RA patients the following parameters were measured in parallel with BMD: serum levels of soluble receptor activator of nuclear factor kappa-B-ligand (sRANKL), osteoprotegerin (OPG), interleukin (IL)-6, soluble glycoprotein 130 (sgp130), 25-hydroxyvitamin D3 (25OHD(3)), 1,25-dihydroxyvitamin D3 (1,25[OH](2)D(3)), intact parathyroid hormone, osteocalcin, ionized calcium, renal excretion of pyridinolin and deoxypyridinolin, C-reactive protein, and erythrocyte sedimentation rate (ESR). No significant differences of sRANKL, OPG, IL-6, and spg130 were found between patients with osteoporosis (47.9% of patients), osteopenia (36.6%), and normal BMD (15.5%). However, total sRANKL was significantly higher in postmenopausal women with osteoporosis at FN than in those without (p < 0.05) and showed a negative correlation with BMD-LS in patients older than 60 years (p = 0.01). BMD-LS and BMD-FN (p < 0.001) and total sRANKL (p < 0.01) were negatively related with the age of the patients. Only IL-6 (positive correlation, p < 0.001) and 1,25(OH)(2)D(3) (negative correlation, p < 0.001) but not sRANKL, OPG, and sgp130 were related to disease activity. Using multiple linear regression analysis, menopause was identified as the crucial negative determinant of BMD-LS (R (2) = 0.94, p = 0.001), whereas cumulative glucocorticoid dose (beta = -0.80, p = 0.001) and ESR (beta = -0.44, p = 0.016) were the negative determinants of BMD-FN (R (2) = 0.86, p = 0.001). The results indicate that influences of age and gender must be considered in investigations on the relationship between BMD and sRANKL in RA and that high serum levels of sRANKL seems to be associated with osteoporosis only in subgroups of RA patients.

Cells of the synovium in rheumatoid arthritis. Osteoclasts

Osteoclasts are multinucleated cells of hematopoietic origin and are the primary bone resorbing cells. Numerous osteoclasts are found within the synovial tissue at sites adjacent to bone, creating resorption pits and local bone destruction. They are equipped with specific enzymes and a proton pump that enable them to degrade bone matrix and solubilize calcium, respectively. The synovial tissue of inflamed joints has a particularly high potential to accumulate osteoclasts because it harbors monocytes/macrophages, which function as osteoclast precursors, as well as cells that provide the specific molecular signals that drive osteoclast formation. Osteoclasts thus represent a link between joint inflammation and structural damage since they resorb mineralized tissue adjacent to the joint and destroy the joint architecture.

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.

Alveolar bone loss in T helper 1/T helper 2 cytokine-deficient mice

BACKGROUND AND OBJECTIVES

The role of cytokines in bone loss is important in the context of periodontitis, where inflammation-induced bone destruction is a major manifestation. Numerous cytokines have been implicated as mediators of bone resorption. The purpose of this study was to observe the impact of targeted gene deletion of T helper 1 (Th1) and T helper 2 (Th2) cytokines on naturally occurring alveolar bone loss in genetically modified mice.

MATERIAL AND METHODS

Alveolar bone loss was measured histomorphometrically in interleukin-4, interleukin-10, interleukin-12p40, interferon-gamma (IFN-gamma) and tumor necrosis factor (TNF) knockout mice at 6, 16 and 30 wk of age.

RESULTS

Both Th1 (interleukin-12p40, IFN-gamma, TNF) and Th2 (interleukin-10, interleukin-4) knockout mice exhibited significantly more alveolar bone loss than their respective wild-type control mice (p<0.001). Interleukin-10-/- and interleukin-12p40-/- mice exhibited a three-fold increase in alveolar bone loss at 30 wk of age, whereas bone loss in IFN-gamma-/-, TNF-/- and interleukin-4-/- mice was 1.5- to two-fold higher compared with wild-type control mice.

CONCLUSION

The results of the present study indicate that both Th1 and Th2 cytokines play an important role in maintaining alveolar bone homeostasis. The kinetics of alveolar bone loss seen in cytokine gene knockout mice indicates that bone loss is age dependent and late in onset.

Bradykinin potentiates cytokine-induced prostaglandin biosynthesis in osteoblasts by enhanced expression of cyclooxygenase 2, resulting in increased RANKL expression

OBJECTIVE

Bradykinin (BK) stimulates bone resorption in vitro and synergistically potentiates interleukin-1 (IL-1)-induced bone resorption and prostaglandin (PG) formation, suggesting that kinins are important in inflammation-induced bone loss. The present study was undertaken to study 1) the role of the kinin B1 and B2 receptors in the synergistic interaction with IL-1 and tumor necrosis factor alpha (TNFalpha), 2) the molecular mechanisms involved in synergistic enhancement of PG formation, and 3) the effects of kinins on cytokine-induced expression of RANKL, RANK, and osteoprotegerin (OPG) (the latter being crucial molecules in osteoclast differentiation).

METHODS

Formation of PGs, expression of enzymes involved in arachidonic acid metabolism, and expression of RANKL, RANK, and OPG were assessed in the human osteoblastic cell line MG-63 and in mouse calvarial bones. The role of NF-kappaB and MAP kinases was studied using pharmacologic inhibitors.

RESULTS

PGE(2) formation and cyclooxygenase 2 (COX-2) protein expression were induced by IL-1beta and potentiated by kinins with affinity for the B1 or B2 receptors, resulting in PGE(2)-dependent enhancement of RANKL. The enhancements of PGE(2) formation and COX-2 were markedly decreased by inhibition of p38 and JNK MAP kinases, whereas inhibition of NF-kappaB resulted in abolishment of the PGE(2) response with only slight inhibition of COX-2.

CONCLUSION

Kinin B1 and B2 receptors synergistically potentiate IL-1- and TNFalpha-induced PG biosynthesis in osteoblasts by a mechanism involving increased levels of COX-2, resulting in increased RANKL. The synergistic stimulation is dependent on NF-kappaB and MAP kinases. These mechanisms might help to explain the enhanced bone resorption associated with inflammatory disorders, including that in rheumatoid arthritis.

Regulation of matrix metalloproteinase gene expression by a retinoid X receptor-specific ligand

OBJECTIVE

To evaluate the effects of LG100268 (LG268), a synthetic ligand for the nuclear hormone receptor retinoid X receptor, on the expression of matrix metalloproteinase 1 (MMP-1) and MMP-13 induced by proinflammatory cytokines in a chondrocyte model.

METHODS

SW-1353 human chondrosarcoma cells were used to study the effects of LG268 on interleukin-1beta (IL-1beta)-stimulated MMP production and collagen degradation. Gene expression was determined by quantitative real-time reverse transcription-polymerase chain reaction, and protein levels were determined by Western blot analysis. Collagen degradation was determined by an in vitro matrix destruction assay. The effects of LG268 on nuclear protein binding and histone acetylation were determined by electrophoretic mobility shift assay and chromatin immunoprecipitation assay, respectively.

RESULTS

LG268 treatment specifically antagonized the IL-1beta-mediated induction of MMP-1 and MMP-13 heterogeneous nuclear RNA, messenger RNA, and protein. The inhibitory effect of LG268 was found to be due to a decrease in the rate of MMP-1 and MMP-13 transcription. LG268 treatment also prevented the in vitro degradation of a type I collagen matrix by IL-1beta-treated SW-1353 cells. The inhibitory effect of LG268 on MMP-1 and MMP-13 transcription appears to be mediated, at least in part, through modulation of histone modification in regions of the MMP-1 and MMP-13 promoters that contain binding sites for activator protein 1 transcription factors.

CONCLUSION

These data indicate that LG268 treatment selectively inhibits inflammatory cytokine-induced production of MMP-1 and MMP-13 at the level of gene transcription and blocks collagen destruction by proinflammatory cytokine-stimulated chondrocytic cells. This study is among the first to describe how rexinoids affect gene expression, and the findings suggest that the rexinoid class of compounds may have a future role in preventing the irreversible collagen destruction seen in the arthritides.

Murine dendritic cell transdifferentiation into osteoclasts is differentially regulated by innate and adaptive cytokines

Dendritic cells (DC) are the mononuclear cells that initiate adaptive immune responses. Osteoclasts (OC) are the multinucleated giant cells that resorb bone. As previously described for human conventional DC (cDC), we demonstrate that murine cDC, either in vitro generated from Fms-like tyrosine kinase 3 (Flt3)+ bone marrow progenitors or ex vivo purified from spleen, are able to develop into OC in response to M-CSF and receptor activator of NF-kappaB ligand (RANKL) in vitro. This transdifferentiation is driven by the immune environment that controls cDC maturation, cell fusion, tartrate-resistant acid phosphatase (TRAP) and bone resorption activities. Only immature cDC have the capacity to become OC since mature cDC or plasmacytoid DC do not. Additions of the pro-inflammatory cytokines, such as IL-1beta and TNF-alpha, or human rheumatoid synovial fluid, increase murine cDC transdifferentiation into OC, whereas IFN-alpha inhibits it. The adaptive cytokine, IFN-gamma, inhibits cDC fusion while IL-4 increases it. IL-2, IFN-gamma and IL-4 inhibit TRAP and bone resorption activities contrary to IL-10, which enhances both activities. A putative new "immune multinucleated giant cell" unable to resorb bone, which is formed owing to IL-4, is underlined. The future analysis of cDC transdifferentiation into OC in murine models of inflammatory arthritis will give us the quantitative importance of this phenomenon in vivo.

Inhibitory effect of ribbon-type NF-kappaB decoy oligodeoxynucleotides on osteoclast induction and activity in vitro and in vivo

In this study we examined the effect of ribbon-type (circular-type) NF-κB decoy oligodeoxynucleotides (RNODN) on osteoclast induction and activity. We extracted bone marrow cells from the femurs of rats and incubated non-adherent cells with receptor activator of nuclear factor κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). First, transfer efficiency into osteoclasts and their precursors, resistance to exonuclease, and binding activity of decoy to NF-κB were examined. Next, to examine the effect of RNODN on osteoclast induction and activity, osteoclast differentiation and pit formation assays were performed. RNODN were injected into the ankle joints of rats with collagen-induced arthritis. Joint destruction and osteoclast activity were examined by histological study. The resistance of RNODN to exonuclease and their binding activity on NF-κB were both greater than those of phosphorothionated NF-κB decoy oligodeoxynucleotides. The absolute number of multinucleate cells scoring positive for tartrate-resistant acid phosphatase was significantly decreased in the RNODN-treated group. The average calcified matrix resorbed area was significantly decreased in the RNODN-treated group. Histological study showed marked suppression of joint destruction and osteoclast activity by intra-articular injection of RNODN. These results suggest the inhibitory effect of RNODN on the induction and activity of osteoclasts. Direct intra-articular injection of RNODN into the joints may be an effective strategy for the treatment of arthritis.

THR0921, a novel peroxisome proliferator-activated receptor gamma agonist, reduces the severity of collagen-induced arthritis

THR0921 is a novel peroxisome proliferator-activated receptor gamma (PPARγ) agonist with potent anti-diabetic properties. Because of the proposed role of PPARγ in inflammation, we investigated the potential of orally active THR0921 to inhibit the pathogenesis of collagen-induced arthritis (CIA). CIA was induced in DBA/1J mice by the injection of bovine type II collagen in complete Freund's adjuvant on days 0 and 21. Mice were treated with THR0921 (50 mg/kg/day) starting on the day of the booster injection and throughout the remaining study period. Both clinical disease activity scores as well as histological scores of joint destruction were significantly reduced in mice treated with THR0921 compared to untreated mice. Proliferation of isolated spleen cells, as well as circulating levels of IgG antibody to type II collagen, was decreased by THR0921. Moreover, spleen cell production of IFN-γ, tumor necrosis factor (TNF)-α and IL-1β in response to exposure to lipopolysaccharide or type II collagen was reduced by in vivo treatment with THR0921. Steady state mRNA levels of TNF-α, IL-1β, monocyte chemotactic protein-1 and receptor activator of nuclear factor κB ligand (RANKL) in isolated joints were all decreased in mice treated with THR0921. Finally, THR0921 inhibited osteoclast differentiation of bone marrow-derived cells stimulated with macrophage colony-stimulating factor and RANKL. In conclusion, THR0921 attenuates collagen-induced arthritis in part by reducing the immune response. As such, PPARγ may be an important therapeutic target for rheumatoid arthritis.

Phenethyl isothiocyanate suppresses receptor activator of NF-kappaB ligand (RANKL)-induced osteoclastogenesis by blocking activation of ERK1/2 and p38 MAPK in RAW264.7 macrophages

Osteoclastogenesis is induced by differentiation of hemopoietic cells of monocyte-macrophage lineage into bone-resorbing osteoclasts. The process is initiated by receptor activator of NF-kappaB ligand (RANKL) and resultant activation of mitogen-activated protein kinases (MAPK), including extracellular signal-regulated kinase (ERK)1/2, as well as the NFkappaB pathway. Phenethyl isothiocyanate (PEITC), a phytochemical present in various cruciferous plants, has been shown to disrupt those signaling pathways in several cell types. In this study, we examined the efficacy of PEITC for suppressing RANKL-induced osteoclastogenesis in RAW264.7 murine macrophages and addressed the underlying molecular mechanisms. PEITC (2-10 microM) suppressed osteoclastogenesis in a concentration dependent manner, as detected by tartarate-resistant acid phosphatase (TRAP) activity and microscopic observations. RANKL-up-regulated extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) activities were attenuated by PEITC, whereas c-Jun N-terminal kinase (JNK1/2) activation was increased. PEITC also abrogated the RANKL-induced degradation of IkappaB-alpha, a suppressive partner of nuclear factor kappaB (NFkappaB), thereby inhibiting transcription activity, as detected by a reporter assay. In addition, PEITC reduced the level of NFkappaB-dependent mRNA expression of nuclear factor of activated T cell (NFAT)c1, a master regulator of osteoclastogenesis. Our results indicate that PEITC is a promising agent for treatment of osteoclastogenesis with a reasonable action mechanism.

p38 MAPK as a potential therapeutic target for inflammatory osteolysis

Inflammatory osteolysis is a relatively frequent and incapacitating complication of rheumatoid arthritis and other inflammatory diseases, and is induced by accelerated osteoclast recruitment and activation in bone under the aegis of cytokines produced in the inflammatory environment. The success of antitumor necrosis factor-alpha and interleukin-1 therapy in correcting this condition highlights the central role of these cytokines in this process. Recent years have witnessed a revolution in understanding the molecular mechanism and pathogenesis of this family of diseases. It is now clear that p38 mitogen-activated protein kinase plays an essential role in the production of proinflammatory cytokines and cytokine-induced osteoclastogenesis, thus providing a potential therapeutic target for prevention of pathologic bone loss.

Citrus nobiletin suppresses bone loss in ovariectomized ddY mice and collagen-induced arthritis in DBA/1J mice: possible involvement of receptor activator of NF-kappaB ligand (RANKL)-induced osteoclastogenesis regulation

Bone resorption is known to accelerate during the onset of several disorders, including osteoporosis (OP) and rheumatoid arthritis (RA). Some epidemiological surveys have suggested that a high intake of vegetables and fruits has an inverse relation to such disease incidence, though the number of active constituents elucidated thus far is limited. In the present study, we examined the efficacy of various food phytochemicals using two animal models. First, female ddY mice were ovariectomized (OVX) or sham-operated (sham), after which five different compounds (phenethyl isothiocyanate, zerumbone, auraptene, 1'-acetoxychavicol acetate, and nobiletin) were administered separately to OVX mice with a mini-osmotic pump at doses of 0.25 or 0.5 mg/day for 4 weeks, with 17beta-estradiol (E_{2}, 0.03 microg/day) used as a positive control. Nobiletin, in contrast to the other tested phytochemicals, significantly (P<0.05) suppressed the reduction of whole bone mineral density by 61%, which was comparable to or higher than the efficacy of E_{2}. Next, nobiletin given as an i.p. administration at 20 mg/kg of body weight, but not 2 mg/kg, to male DBA/1J mice every 2 days for 12 days led to a marked decrease in type II collagen-induced arthritis by 45% (P < 0.05). Furthermore, the flavonoid (4-50 microM) attenuated receptor activator of nuclear factor kappaB ligand (RANKL)-induced osteoclastogenesis of RAW264.7 cells, as detected by tartarate-resistant acid phosphatase activity and microscopic observations. Of note, nobiletin also suppressed RANKL-activated extracellular signal-regulated kinase1/2, c-Jun N-terminal kinase1/2, and p38 mitogen-activated protein kinase activities, and thereby regulated the promoter activation of nuclear factor kappaB (NFkappaB) and activator protein-1, key transcription factors for differentiation. Together, our results suggest that nobiletin is a promising phytochemical for the prevention or treatment of osteoclastogenesis-related disorders, including OP and RA, with reasonable action mechanisms.