Modulation of osteoclast differentiation and function by the new members of the tumor necrosis factor receptor and ligand families

Identification of cell cycle-arrested quiescent osteoclast precursors in vivo

How are sites suitable for osteoclastogenesis determined? We addressed this issue using in vivo and in vitro experimental systems. We first examined the formation of osteoclasts in ectopic bone induced by BMP-2. When collagen disks which contained BMP-2 (BMP-2-disks) or vehicle (control-disks) were implanted into wild-type mice, osteoclasts and osteoblasts appeared in the BMP-2-disks, but not in the control disks. RANKL-deficient (RANKL(-/-)) mice exhibited osteopetrosis, with an absence of osteoclasts. BMP-2 and control disks were implanted into RANKL(-/-) mice, which were intraperitoneally injected with RANKL. Osteoclasts formed in the BMP-2-disks, but not in the control disks. In the BMP-2-disks, osteoclasts were observed in the vicinity of osteoblasts. Cell cycle-arrested quiescent osteoclast precursors (QOP) were identified as the committed osteoclast precursors in vitro. Experiments in vivo showed that QOPs survived for several weeks, and differentiated into osteoclasts in response to M-CSF and RANKL. QOPs were identified as RANK and c-Fms double-positive cells, and detected along bone surfaces in the vicinity of osteoblasts in RANKL(-/-) mice. QOPs were also observed in the ectopic bone induced by BMP-2 implanted into RANKL(-/-) mice, suggesting that QOPs were circulating. These results imply that osteoblasts support the homing of QOPs to bone tissues. In response to bone-resorbing stimuli, QOPs promptly differentiate into osteoclasts. Therefore, the distribution of QOPs appears to determine the correct site of osteoclastic development.

Correlation of decreased survival and IL-18 in bone metastasis

OBJECTIVE

Previous studies have reported that serum IL-18 levels are increased in some cancers. We investigated whether IL-18 production is increased in sera and cancer cells of patients with non-small cell lung cancer (NSCLC).

PATIENTS OR MATERIALS

Serum levels of IFN-gamma and IL-18 and thioredoxin 1 (TRX1) were measured in 79 patients (51 males, 28 females, median age 67 years) with advanced NSCLC (57 adenocarcinoma, 22 squamous cell carcinoma; TNM stages IIIA [n=11], IIIB [n=24], and IV [n=44]) and 75 healthy age-matched controls (44 males, 31 females, median age 65 years) by enzyme-linked immunosorbent assay. We examined IL-18 production in the lungs and sites of bone metastasis of adenocarcinoma by immunohistochemistry.

RESULTS

Serum IL-18, IFN-gamma, and TRX1 levels in NSCLC patients were significantly (p<0.0001, p=0.0031, and p<0.0001, respectively) higher than in control subjects, while serum IFN-gamma levels in NSCLC were slightly increased. Serum IL-18, but not IFN-gamma or TRX1, levels were significantly (p=0.0102) and negatively associated with overall survival in NSCLC. The serum IL-18 level was identified as an independent prognostic factor for overall survival in multivariate survival analysis. Moreover, serum IL-18 levels were significantly (p=0.049) higher in NSCLC with bone metastasis than in NSCLC without bone metastasis. Based on immunohistochemistry, we observed that cancer cells in the lungs and bone metastases markedly produced IL-18.

CONCLUSION

Our results suggest that elevated serum IL-18 levels may be associated with IL-18 producing cancer cells in advanced NSCLC.

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.

Effects of soluble cobalt and cobalt incorporated into calcium phosphate layers on osteoclast differentiation and activation

Metal ions originating from mechanical debris and corrosive wear of prosthetic implant alloys accumulate in peri-implant soft tissues, bone mineral, and body fluids. Eventually, metal ions such as cobalt (II) (Co(2+)), which is a major component of cobalt-chromium-based implant alloys and a known activator of osteolysis, are incorporated into the mineral phase of bone. We hypothesize that the accumulation of Co(2+) in the mineral could directly activate osteolysis by targeting osteoclasts. To test this hypothesis, we coated tissue culture plastic with a thin layer of calcium phosphate (CaP) containing added traces of Co(2+), thereby mimicking the bone mineral accumulation of Co(2+). Murine bone marrow osteoclasts formed in the presence of M-CSF and RANKL were cultured on these surfaces to examine the effects of Co(2+) on osteoclast formation and resorptive activity. Treatment conditions with Co(2+) involved incorporation into the CaP layer, adsorption to the mineral surface, or addition to culture media. Micromolar concentrations of Co(2+) delivered to developing osteoclast precursors by all 3 routes increased both osteoclast differentiation and resorptive function. Compared to CaP layers without Co(2+), we observed a maximal 75% increase in osteoclast numbers and a 2.3- to 2.7-fold increase in mineral resorption from the tissue culture wells containing 0.1 microM Co(2+) and 0.1-10 microM Co(2+), respectively. These concentrations are well within the range found in peri-implant tissues in vivo. This direct effect of Co(2+) on osteoclasts appears to act independently of the particulate phagocytosis/inflammation-mediated pathways, thus enhancing osteolysis and aseptic implant loosening.

Osteoimmunology: cytokines and the skeletal system

It has become clear that complex interactions underlie the relationship between the skeletal and immune systems. This is particularly true for the development of immune cells in the bone marrow as well as the functions of bone cells in skeletal homeostasis and pathologies. Because these two disciplines developed independently, investigators with an interest in either often do not fully appreciate the influence of the other system on the functions of the tissue that they are studying. With these issues in mind, this review will focus on several key areas that are mediated by crosstalk between the bone and immune systems. A more complete appreciation of the interactions between immune and bone cells should lead to better therapeutic strategies for diseases that affect either or both systems.

Bone remodeling: Multiple cellular interactions required for coupling of bone formation and resorption

The dynamic nature of the skeleton is achieved by a process called "remodeling" which involves the co-ordinated actions of osteoclasts, osteoblasts, osteocytes within the bone matrix and osteoblast-derived lining cells that cover the surface of bone. Remodeling commences with signals that initiate osteoclast formation followed by osteoclast-mediated bone resorption, a reversal period, and then a long period of bone matrix formation mediated by osteoblasts, followed by mineralisation of the matrix. This review will discuss each of these steps with particular emphasis on the communication pathways between each cell type involved and the roles of ephrins, sclerostin, RANKL and PTHrP.

Osteotropic cancers: from primary tumor to bone

It has long been recognized that primary cancers spread to distant organs with characteristic preference. Bone metastases occur in approximately 70% of patients with advanced breast and prostate cancer, causing severe morbidity and hospitalization. In the last decade, we have gained a better understanding of the mechanisms by which certain tumor types tend to metastasize specifically to bone. It appears that the interaction between the organ microenvironment and cancer cells is fundamental for establishing metastatic growth. Accordingly, Stephen Paget's 'seed and soil' hypothesis - stating that circulating cancer cells (the 'seeds') disperse in all directions, but can accomplish metastases only in organs where the microenvironment (the 'soil') is permissive for their growth - still holds forth today. For this reason, this review uses the 'seed and soil' hypothesis as a template to discuss novel insight and developments in the bone metastasis field.

CD137L- and RANKL-mediated reverse signals inhibit osteoclastogenesis and T lymphocyte proliferation

Members of the tumor necrosis factor-related family of ligands and receptors appear to be critical regulators of osteoclastogenesis and various cellular responses in T cells. In the present study, we have investigated CD137L and RANKL (receptor activator of nuclear factor (NF)-kappaB ligand)-induced biological responses in osteoclasts and T cells, respectively. Osteoclast-like cells were generated from murine bone marrow in the presence of RANKL and monocyte-macrophage colony-stimulating factor (M-CSF). RAW264.7 cells (murine monocytic cell line) constitutively express CD137L. Ligation of CD137L with anti-CD137L mAb (TKS-1) inhibits RANKL-induced osteoclast formation in a dose-dependent manner. Bone marrow cells expressed CD137L only when induced by treatment with M-CSF. In bone marrow cells, cross-linking of CD137L with anti-CD137L mAb (TKS-1) inhibits M-CSF/RANKL-evoked formation of multi-nucleated osteoclasts. Further we examined RANKL-mediated regulation of T cell proliferation. Both mouse CD4(+) and CD8(+) T cells expressed RANKL following their activation by anti-CD3 Ab and anti-CD137 Ab. Ligation of RANKL with OPG-Fc, the decoy receptor for RANKL, inhibited both mouse CD4(+) and CD8(+) T cell proliferation. From the above results, we suggest that the cellular responses in cell-to-cell interactions between T cells and osteoclasts are regulated through reciprocal regulations of CD137/CD137L and RANK/RANKL interactions.

[OPG/RANKL: role and therapeutic target in osteoporosis]

Given the increasing risk of fractures with aging in western countries, there is a need for the development of safe and efficient anti-osteoporotic drugs for the prevention and treatment of osteoporosis. Recent studies have provided evidence for an essential role of RANKL (Receptor Activator of Nuclear Factor-kappa B Ligand) and its decoy receptor osteoprotegerin in the control of osteoclast differentiation and survival. Post-menopausal osteoporosis results from an imbalance between resorption and formation associated with decreased OPG/RANKL. Targeting the OPG/RANKL system may therefore have a beneficial impact in osteoporosis. Accordingly, the development of novel strategies targeting OPG/RANKL using anti-RANKL or therapeutic intervention proved to be efficient to reduce bone resorption and to prevent bone loss in postmenopausal osteoporosis. This opens the way for novel therapeutic strategies for correcting bone metabolism in various pathologic disorders characterized by increased bone remodelling and bone loss.

Formation of osteoclast-like cells from peripheral blood of periodontitis patients occurs without supplementation of macrophage colony-stimulating factor

AIM

To determine whether peripheral blood mononuclear cells (PBMCs) from chronic periodontitis patients differ from PBMCs from matched control patients in their capacity to form osteoclast-like cells.

MATERIAL AND METHODS

PBMCs from 10 subjects with severe chronic periodontitis and their matched controls were cultured on plastic or on bone slices without or with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-kappaB ligand (RANKL). The number of tartrate-resistant acid phosphatase-positive (TRACP(+)) multinucleated cells (MNCs) and bone resorption were assessed.

RESULTS

TRACP(+) MNCs were formed under all culture conditions, in patient and control cultures. In periodontitis patients, the formation of TRACP(+) MNC was similar for all three culture conditions; thus supplementation of the cytokines was not needed to induce MNC formation. In control cultures, however, M-CSF or M-CSF/RANKL resulted in higher numbers compared with cultures without cytokines. Upregulations of osteoclast marker mRNA cathepsin K and carbonic anhydrase II confirmed the osteoclastic character. Bone resorption was only observed when PBMCs were cultured in the presence of M-CSF and RANKL.

CONCLUSION

Our data indicate that PBMCs from periodontitis patients do not need priming by M-CSF to become osteoclast-like cells, suggesting that PBMCs from periodontitis patients are present in the circulation in a different state of activity.

Novel bromomelatonin derivatives suppress osteoclastic activity and increase osteoblastic activity: implications for the treatment of bone diseases

The teleost scale is a calcified tissue that contains osteoclasts, osteoblasts, and bone matrix, all of which are similar to those found in mammalian membrane bone. Using the goldfish scale, we recently developed a new in vitro assay system and previously demonstrated that melatonin suppressed both osteoclastic and osteoblastic activities in this assay system. In mammals, 2-bromomelatonin possesses a higher affinity for the melatonin receptor than does melatonin. Using a newly developed synthetic method, we synthesized 2-bromomelatonin, 2,4,6-tribromomelatonin and novel bromomelatonin derivatives (1-allyl-2,4,6-tribromomelatonin, 1-propargyl-2,4,6-tribromomelatonin, 1-benzyl-2,4,6-tribromomelatonin, and 2,4,6,7-tetrabromomelatonin) and then examined the effects of these chemicals on osteoclasts and osteoblasts. All bromomelatonin derivatives, as well as melatonin, had an inhibitory action on osteoclasts. In particular, 1-benzyl-2,4,6-tribromomelatonin (benzyl-tribromomelatonin) possessed a stronger activity than melatonin. At an in vitro concentration of 10(-10) m, benzyl-tribromomelatonin still suppressed osteoclastic activity after 6 hr of incubation. In reference to osteoblasts, all bromomelatonin derivatives had a stimulatory action, although melatonin inhibited osteoblastic activity. In addition, estrogen receptor mRNA expression (an osteoblastic marker) was increased in benzyl-tribromomelatonin (10(-7) m)-treated scales. Taken together, the present results strongly suggest that these novel melatonin derivatives have significant potential for use as beneficial drug for bone diseases such as osteoporosis.

Cytokines in crevicular fluid and orthodontic tooth movement

This review aimed to evaluate studies on cytokines in the gingival crevicular fluid (GCF) during orthodontic treatment, summarizing the regulation patterns of the most commonly studied cytokines and exploring their clinical implications. To achieve this, a number of key databases were searched using MESH terms and free text terms. An additional search was made by reference tracking. The procedures suggested by the QUOROM statement were followed. Data from the included studies were extracted into orthodontic mechanics, GCF sampling/handling methods, and cytokine measurements. From the 85 relevant studies identified, 23 studies could be included. Common drawbacks consisted mainly of inadequacies in the study design (e.g. short duration and small number of study subjects). The most consistent result was a peak of cytokine levels at 24 h. Associations existed between prostaglandin E(2) (PGE(2)) and interleukin-1beta (IL-1beta) and pain, velocity of tooth movement, and treatment mechanics. Interleukin-1beta and PGE(2) showed different patterns of up-regulation, with IL-1beta being more responsive to mechanical stress and PGE(2) more responsive to synergistic regulation of IL-1beta and mechanical force. The results might be taken to support, at the cellular level, the use of light continuous forces for orthodontic treatment.

Microphthalmia transcription factor regulates the expression of the novel osteoclast factor GPNMB

Microphthalmia transcription factor (MITF) regulates bone homeostasis by inducing expression of critical genes associated with osteoclast function. Gpnmb is a macrophage-enriched gene that has also been shown to be expressed in osteoblasts. Here, we have shown gpnmb to be highly induced in maturing murine osteoclasts. Microarray expression profile analysis identified gpnmb as a potential target of MITF in RAW264.7 cells, subclone C4 (RAW/C4), that overexpress this transcription factor. Electrophoretic mobility shift assays identified a MITF-binding site (M-box) in the gpnmb promoter that is conserved in different mammalian species. Anti-MITF antibody supershifted the DNA-MITF complex for the promoter site while MITF binding was abolished by mutation of this site. The gpnmb promoter was transactivated by co-expression of MITF in reporter gene assays while mutation of the gpnmb M-box prevented MITF transactivation. The induction of gpnmb expression during osteoclastogenesis was shown to exhibit similar kinetics to the known MITF targets, acp5 and clcn7. GPNMB expressed in RAW/C4 cells exhibited distinct subcellular distribution at different stages of osteoclast differentiation. At days 5 and 7, GPNMB protein co-localised with the osteoclast/macrophage lysosomal/endocytic marker MAC-3/LAMP-2, suggesting that GPNMB resides in the endocytic pathway of mature macrophages and is possibly targeted to the plasma membrane of bone-resorbing osteoclasts. The inclusion of gpnmb in the MITF regulon suggests a role for GPNMB in mature osteoclast function.

Roles of specific cytokines in bone remodeling and hematopoiesis in Gaucher disease

BACKGROUND

Gaucher disease type 1 and type 3 are characterized by bone disease and hematological symptoms. It is known that monocyte/macrophage lineage is activated in Gaucher disease, and accordingly certain cytokines are elevated in blood. The aim of the present study was to explore the possible relationships between cytokines and bone remodeling and hematological abnormalities in this disease.

METHODS

The concentrations of seven cytokines and two related proteins were measured in patients with Gaucher disease type 1 and type 3 (n= 8; age range, 2-50 years) who had received enzyme replacement therapy.

RESULTS

Concentrations of interleukin-18 and transforming growth factor-beta1 were elevated in patients of all clinical types. Elevation of these cytokines in Gaucher disease has not been previously reported. Analysis of correlation among cytokines and bone-turnover markers showed that interleukin-18 concentration was correlated with each of two bone formation markers of bone-specific alkaline phosphatase activity and osteocalcin concentration, whereas macrophage colony-stimulating factor concentration correlated with the bone absorption marker of N-telopeptide to helix in urine. Concentrations of macrophage colony-stimulating factor and tumor necrosis factor-alpha were inversely correlated with hemoglobin concentration.

CONCLUSIONS

Interleukin-18 and monocyte macrophage colony-stimulating factor are cytokines mainly involved in the mechanism of bone disease, while macrophage colony-stimulating factor and tumor necrosis factor-alpha may play a role in the development of hematological abnormalities in Gaucher disease.

Genetic background influences fluoride's effects on osteoclastogenesis

Excessive fluoride (F) can lead to abnormal bone biology. Numerous studies have focused on the anabolic action of F yet little is known regarding any action on osteoclastogenesis. Little is known regarding the influence of an individual's genetic background on the responses of bone cells to F. Four-week old C57BL/6J (B6) and C3H/HeJ (C3H) female mice were treated with NaF in the drinking water (0 ppm, 50 ppm and 100 ppm F ion) for 3 weeks. Bone marrow cells were harvested for osteoclastogenesis and hematopoietic colony-forming cell assays. Sera were analyzed for biochemical and bone markers. Femurs, tibiae, and lumbar vertebrae were subjected to microCT analysis. Tibiae and femurs were subjected to histology and biomechanical testing, respectively. The results demonstrated new actions of F on osteoclastogenesis and hematopoietic cell differentiation. Strain-specific responses were observed. The anabolic action of F was favored in B6 mice exhibiting dose-dependent increases in serum ALP activity (p<0.001); in proximal tibia trabecular and vertebral BMD (tibia at 50&100 ppm, p=0.001; vertebrae at 50 and 100 ppm, p=0.023&0.019, respectively); and decrease in intact PTH and sRANKL (p=0.045 and p<0.001, respectively). F treatment in B6 mice also resulted in increased numbers of CFU-GEMM colonies (p=0.025). Strain-specific accumulations in bone [F] were observed. For C3H mice, dose-dependent increases were observed in osteoclast potential (p<0.001), in situ trabecular osteoclast number (p=0.007), hematopoietic colony forming units (CFU-GEMM: p<0.001, CFU-GM: p=0.006, CFU-M: p<0.001), and serum markers for osteoclastogenesis (intact PTH: p=0.004, RANKL: p=0.022, TRAP5b: p<0.001). A concordant decrease in serum OPG (p=0.005) was also observed. Fluoride treatment had no significant effects on bone morphology, BMD, and serum PYD cross-links in C3H suggesting a lack of significant bone resorption. Mechanical properties were also unaltered in C3H. In conclusion, short term F treatment at physiological levels has strain-specific effects in mice. The expected anabolic effects were observed in B6 and novel actions hallmarked by enhanced osteoclastogenesis shifts in hematopoietic cell differentiation in the C3H strain.

Berberine inhibits RANKL-induced osteoclast formation and survival through suppressing the NF-kappaB and Akt pathways

Berberine, an isoquinoline alkaloid isolated from several medicinal plants, has been reported to possess anti-bacterial, anti-inflammatory and antitumor properties. Although berberine also inhibits osteoclastogenesis and bone resorption, the molecular machinery for its inhibitory effects remains unknown. This study focused on the suppressive effects of berberine on receptor activator of nuclear factor kappaB (NF-kappaB) ligand (RANKL)-induced osteoclastogenesis and survival. Berberine inhibited RANKL-mediated osteoclast formation and survival while having no cytotoxic effects on bone marrow macrophages or osteoblastic cells. Berberine attenuated RANKL-induced activation of NF-kappaB through inhibiting phosphorylation at the activation loop of IkappaBalpha kinase beta, phosphorylation and degradation of IkappaBalpha, and NF-kappaB p65 nuclear translocation. RANKL-induced Akt phosphorylation was strongly inhibited by berberine; however, neither monocyte/macrophage-colony stimulating factor (M-CSF)-induced nor insulin-induced Akt activation was inhibited by the drug. Under M-CSF- and RANKL-deprived condition, berberine increased the active form of caspase-3 in osteoclasts. By contrast, berberine did not potentiate the activation of caspase-3 in M-CSF-deprived bone marrow macrophages. These findings indicate that berberine inhibits osteoclast formation and survival through suppression of NF-kappaB and Akt activation and that both pathways in the osteoclast lineage are highly sensitive to berberine treatment.

Interleukin-10 inhibits RANKL-mediated expression of NFATc1 in part via suppression of c-Fos and c-Jun in RAW264.7 cells and mouse bone marrow cells

Interleukin-10 (IL-10), an anti-inflammatory cytokine, has been shown to inhibit osteoclast formation and bone resorption in rat and mouse systems. However, the precise intracellular mechanism(s) of this action remains unclear. The aim of this study was to clarify the role of IL-10 in the regulation of critical transcription factors involved in osteoclastogenesis. A RAW264.7 macrophage cell line, which constitutively expressed IL-10 receptor, was differentiated to osteoclasts with stimulation of receptor activator of nuclear factor kappaB ligand (RANKL). IL-10 inhibited the RANKL-induced osteoclastogenesis. IL-10 potently reduced the RANKL-induced expression of NFATc1, c-Jun and c-Fos, which are known to be essential for osteoclastogenesis, in time- and dose-dependent manners. The IL-10-induced inhibition of these transcription factors was observed in the system of mouse bone marrow precursors. Besides these transcription factors, IL-10 also decreased the RANKL-induced expression of NF-kappaB p50 and phosphorylation of JNK. To determine which signaling was critical for the IL-10 effect, we examined the effect of overexpression of NFATc1, c-Fos, and c-Jun on the IL-10-induced inhibition of osteoclastogenesis. As expected, overexpression of NFATc1 abrogated the IL-10-induced inhibition of osteoclastogenesis. Interestingly, overexpression of either c-Fos or c-Jun partially rescued the reduction of RANKL-induced expression of NFATc1 and osteoclastogenesis by IL-10. These data suggest that IL-10 may down-regulate osteoclastogenesis mainly through inhibition of the expression of NFATc1, c-Fos and c-Jun. These findings provide new insight into the inhibitory action of IL-10 on RANKL-mediated osteoclastogenesis.

Effects of neridronic acid on osteoclasts derived by physiological dual-cell cultures

Increased osteoclastic activity is observed in many osteopathic disorders - including postmenopausal osteoporosis, Paget's disease, primary bone tumours, lytic bone metastases, multiple myeloma and rheumatoid arthritis - that involve increased bone resorption and a loss of bone mass. Bisphosphonates are highly effective inhibitors of bone resorption that selectively affect the osteoclasts. The aim of this study was to obtain more information about the mechanism of action of bisphosphonates such as neridronic acid using a dual-cell culture model. As a model of osteoclastogenesis we used a murine monocyte/macrophage cell line RAW 264.7 type CRL 2278 co-cultured with murine osteoblasts. The monocyte-osteoblast system allows physiological experimentation of bone anti-resorption drugs, simulating bone turnover in pathologies such as osteoporosis. The direct actions of neridronic acid on cell proliferation and functionality in the co-culture model were examined using tartrate-resistant acid phosphatase (TRAP) assay, immunohistochemical localization of actin, and transmission and scanning electron microscopy (SEM). Results showed that the percentage of TRAP-positive cells, an early marker of osteoclastic differentiation, was significantly higher in control cultures than in co-cultures treated with variable concentrations of neridronic acid. Neridronic acid induced dramatic morphological changes, characterized by the loss of the ruffled border. The actin ring associated with the plasma membrane of the cells treated with neridronic acid was shown to break down. The tissue-specific targeting of neridronic acid to bone mineral suggests that it may inhibit bone resorption by direct effects on osteoclasts or other bone cells in the immediate microenvironment of the osteoclasts. From our study, we conclude that structural alterations induced by neridronic acid in our co-culture system lead to decreased osteoclast function. This may encourage the use of neridronic acid to reduce bone resorption in the therapy of demineralizing metabolic bone disorders.

Bone morphogenetic proteins in clinical applications

The role of bone morphogenetic proteins (BMPs) in bone healing has been shown in numerous animal models. To date, at least 20 BMPs have been identified, some of which have been shown in vitro to stimulate the process of stem cell differentiation into osteoblasts in human and animal models. Having realized the osteoinductive properties of BMPs and having identified their genetic sequences, recombinant gene technology has been used to produce BMPs for clinical application - most commonly, as alternatives or adjuncts in the treatment of cases in which fracture healing is compromised. BMP-2 and BMP-7 are approved for clinical use in open fractures of long bones, non-unions and spinal fusion. However, despite significant evidence of their potential benefit to bone repair and regeneration in animal and preclinical studies, there is, to date, a dearth of convincing clinical trials. The purpose of this paper is to give a brief overview of BMPs and to critically review the clinical data currently available on the use of BMP-2 and BMP-7 in fracture healing.

Effect of an estrogen-deficient state and alendronate therapy on bone loss resulting from experimental periapical lesions in rats

The aim of the research was to evaluate the impact of an estrogen-deficient state and alendronate (ALD) therapy on bone loss resulting from experimental periapical lesions in rats. Periapical lesions were induced on ovariectomized (OVX) and sham-ovariectomized (Sham) rats. After sample preparation, histologic and radiographic examination for periapical bone loss area and an enzyme histochemical test for tartrate-resistant acid phosphatase (TRAP) were performed. The results showed that OVX significantly increased bone loss resulting from periradicular lesions. After daily subcutaneous injection of ALD, the bone loss area and the number of TRAP-positive cells (osteoclasts) were reduced. These findings suggested that alendronate may protect against increased bone loss from experimental periapical lesions in estrogen-deficient rats. Given recent recognition of adverse effects of bisphosphonates, including an increased risk for osteonecrosis, the findings from this study should not be interpreted as a new indication for ALD treatment. However, they may offer insight into understanding and predicting outcomes in female postmenopausal patients already on ALD therapy for medical indications.

Receptor activator of NF-kappa B ligand inhibition suppresses bone resorption and hypercalcemia but does not affect host immune responses to influenza infection

Receptor activator of NF-kappaB (RANK) and its ligand (RANKL) are essential for osteoclast formation, function, and survival. Osteoprotegerin (OPG) inhibits RANK signaling by sequestering RANKL. This study evaluated the antiosteoclast and immunoregulatory effects of mouse rRANK-Fc, which, similar to OPG, can bind RANKL. The effect of RANKL inhibition by RANK-Fc on osteoclast function was determined by inhibition of vitamin D(3) (1,25(OH)(2)D(3))-induced hypercalcemia. Mice were injected with a single dose of 0, 10, 100, 500, or 1000 microg of RANK-Fc; 100 microg of OPG-Fc; or 5 microg of zoledronate 2 h before 1,25(OH)(2)D(3) challenge on day 0, and sacrificed on days 1, 2, 4, 6, 8, 12, 16, and 20. RANK-Fc doses of 100 or 500 microg were tested in a mouse respiratory influenza virus host-resistance model. A single dose of RANK-Fc > or =100 microg suppressed elevation of serum calcium levels and suppressed the bone turnover marker serum pyridinoline at day 4 and later time points, similar to those observed with OPG-Fc and zoledronate (p < or = 0.01 vs controls). By day 6, both immature and mature osteoclasts were depleted by high doses of RANK-Fc (500 and 1000 microg) or 100 microg of OPG-Fc. RANK-Fc doses of 100 or 500 microg had no detectable effect on immune responses to influenza infection, as measured by activation of cytotoxic T cell activity, influenza-specific IgG response, and virus clearance. RANK-Fc inhibition of RANKL has antiosteoclast activity at doses that have no detectable immunoregulatory activity, suggesting that RANKL inhibitors be further studied for their potential to treat excess bone loss.

Stimulation of osteoclastogenesis by enhanced levels of MIP-1alpha in BALB/c mice in vitro

OBJECTIVES

We compared osteoclast (OC) formation in bone marrow-derived macrophages (BMM) from C57BL/6 (B/6) and BALB/c (B/c) mice. After stimulation of receptor activator of nuclear factor-kappaB ligand (RANKL), enhanced OC formation and higher level of macrophage inflammatory protein-1alpha (MIP-1alpha) were observed in the BMM from B/c mice. In this study, we determined whether MIP-1alpha is responsible for stimulated OC formation in the BMM.

MATERIALS AND METHODS

OC formation was evaluated in BMM. Expression of MIP-1alpha during OC formation was analyzed at the mRNA and protein levels. Apoptosis of mature OCs was evaluated by observing the degradation of DNA. Activation of nuclear factor-kappaB (NF-kappaB) was measured by electrophoretic mobility shift assay.

RESULTS

After stimulation by RANKL expression of MIP-1alpha at the mRNA and protein levels was much higher in BMM from B/c mice than in BMM from B/6 mice. Transcripts of the MIP-1alpha receptors, CCR1 and CCR5, were present at similar levels in unstimulated BMM of the two strains. Blockade of MIP-1alpha inhibited OC formation, and exogenously added MIP-1alpha stimulated it in RANKL-stimulated BMM. MIP-1alpha affected not only the early precursors but also mature OCs. It prevented apoptosis of mature OCs by activating NF-kappaB, and the effect of RANKL on survival was dependent on its ability to induce MIP-1alpha.

CONCLUSIONS

MIP-1alpha, induced by RANKL during OC differentiation, increases OC formation by acting on OC progenitor cells, and prolongs survival of mature OC via signaling through NF-kappaB. The enhanced OC formation in BMM from B/c mice could be due to, at least in part, to their higher levels of MIP-1alpha.

Protein inhibitor of activated STAT 3 modulates osteoclastogenesis by down-regulation of NFATc1 and osteoclast-associated receptor

Protein inhibitor of activated STAT3 (PIAS3) has been shown to regulate the activity of various transcription factors. In this study, we show that the overexpression of PIAS3 in bone marrow-derived monocyte/macrophage lineage cells attenuates osteoclast formation and down-regulates the expression of NFATc1 and osteoclast-associated receptor (OSCAR), which are important modulators in osteoclastogenesis. PIAS3 has been shown to associate with histone deacetylase 1 as well as with transcription factors, including the microphthalmia transcription factor, NFATc1, and c-Fos. Moreover, overexpression of PIAS3 inhibits the transactivation of target genes such as NFATc1 and OSCAR. This inhibitory effect of PIAS3 is possibly mediated by histone deacetylase 1 recruitment to the promoter regions of NFATc1 and OSCAR. Furthermore, silencing of PIAS3 by RNA interference in osteoclast precursors enhances osteoclast formation as well as gene expression of NFATc1 and OSCAR. Taken together, our results reveal that PIAS3 acts as a modulator in osteoclastogenesis.

The selective cyclooxygenase-2 inhibitor celecoxib reduces bone resorption, but not bone formation, in ovariectomized mice in vivo

Suppression of increased bone resorption is an important issue in treatment of post-menopausal osteoporosis. Celecoxib is a highly selective inhibitor of cyclooxygenase-2 (COX-2), and inhibits osteoclastogenesis in vitro. In the present study, to test whether celecoxib can suppress elevated bone resorption caused by estrogen deficiency in vivo, celecoxib (4 mg/kg) or its vehicle was administered to sham-operated or ovariectomized (OVX) mice (model of post-menopausal osteoporosis). The treatment with celecoxib or vehicle was started immediately after the sham operation or ovariectomy, and lasted for 4 weeks. At 2 and 4 weeks after surgery, OVX mice administered vehicle had significantly higher levels of C-telopeptide, a marker of bone resorption in serum, than sham-operated mice administered vehicle (37% and 60% higher, respectively; p<0.01). At 2 and 4 weeks after surgery, celecoxib treatment significantly decreased serum C-telopeptide levels in OVX mice, but not in sham-operated mice (45% and 41%, respectively; p<0.001). In contrast, in both sham-operated and OVX mice, celecoxib did not significantly affect serum osteocalcin levels (a marker of bone formation) or bone mineral density (BMD) of the femur, which was evaluated by peripheral quantitative computed tomography (pQCT). In conclusion, treating OVX mice with celecoxib significantly suppressed the increase in serum levels of the bone resorption marker, but did not affect levels of the bone formation marker. Also, celecoxib did not prevent the decrease of femoral BMD in OVX mice. The present study suggests the possibility that celecoxib may be used to prevent bone loss caused by estrogen deficiency.

Interaction between the immune system and bone metabolism: an emerging field of osteoimmunology

The interaction between the immune and bone systems has long been appreciated, but recent research into arthritis as well as various bone phenotypes found in immune-related knockout mice has highlighted the importance of the interplay and the interdisciplinary field called osteoimmunology. In rheumatoid arthritis, IL-17-producing helper T cells (TH17) induces receptor activator of NF-κB ligand (RANKL), which stimulates osteoclast differentiation through nuclear factor of activated T cells (NFAT)c1. Accumulating evidence suggests that the immune and skeletal systems share cytokines, signaling molecules, transcription factors and membrane receptors. In addition, the immune cells are maintained in the bone marrow, which provides a space for mutual interaction. Thus, bone turns out to be a dynamic tissue that is constantly renewed, where the immune system participates to a hitherto unexpected extent. This emerging field of osteoimmunology will be of great importance not only to the better understanding of the two systems but also to the development of new treatment for rheumatic diseases.

RANKL Upregulation Associated With Periodontitis andPorphyromonas gingivalis

BACKGROUND

Receptor activator of nuclear factor-kappa B (NF-kappaB) ligand (RANKL) and osteoprotegerin (OPG) are critical for homeostatic control of osteoclast activity, suggesting their vital roles in the progression of bone loss in periodontitis. In this study, the expression of RANKL and OPG mRNA and the relationship between these factors and periodontopathic bacteria in periodontal tissue were studied.

METHODS

Gingival tissue and subgingival plaque samples were collected from 15 patients with chronic periodontitis and 15 periodontally healthy subjects. RNA was extracted from the tissue and subjected to reverse transcription-polymerase chain reaction (RT-PCR) using primers specific for RANKL or OPG. Beta-actin was amplified as a control to ensure equal loading. The intensity of RT-PCR products was analyzed by a densitometer in proportion to the intensity of beta-actin. The numbers of Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans were determined by quantitative real-time PCR.

RESULTS

Our results showed increased levels of RANKL mRNA in chronic periodontitis tissues. The RANKL/OPG expression ratio was significantly higher in the periodontitis group compared to the healthy control group (P = 0.001). Interestingly, the expression of RANKL (r = 0.64; P <0.001), but not OPG (r = -0.24; P = 0.20), was significantly correlated with increased numbers of P. gingivalis. A. actinomycetemcomitans was detected in only 6.7% of all sites.

CONCLUSIONS

Chronic periodontitis was associated with RANKL mRNA upregulation and increased RANKL/OPG mRNA expression ratio. In addition, our data showed for the first time to our knowledge an association between upregulated RANKL levels and the number of P. gingivalis in clinically obtained periodontal tissues.

Interleukin-4 inhibition of osteoclast differentiation is stronger than that of interleukin-13 and they are equivalent for induction of osteoprotegerin production from osteoblasts

Interleukin (IL)-4 and IL-13 are closely related cytokines known to inhibit osteoclast formation by targeting osteoblasts to produce an inhibitor, osteoprotegerin (OPG), as well as by directly targeting osteoclast precursors. However, whether their inhibitory actions are the same remains unclear. The inhibitory effect of IL-4 was stronger than that of IL-13 in an osteoclast-differentiation culture system containing mouse osteoblasts and osteoclast precursors. Both cytokines induced OPG production by osteoblasts in similar time- and dose-dependent manners. However, IL-4 was stronger in direct inhibition that targeted osteoclast precursors. Furthermore, IL-4 induced phosphorylation of signal transducer and activator of transcription-6 (STAT6) at lower concentrations than those of IL-13 in osteoclast precursors. IL-4 but not IL-13 strongly inhibited the expression of nuclear factor of activated T-cells, cytoplasmic 1 (nuclear factor-ATc1), a key factor of osteoclast differentiation, by those precursors. Thus, the activities of IL-4 and IL-13 toward osteoclast precursors were shown to be different in regards to inhibition of osteoclast differentiation, whereas those toward osteoblasts for inducing OPG expression were equivalent.

Rolipram, a phosphodiesterase 4 inhibitor, suppresses PGE2-induced osteoclast formation by lowering osteoclast progenitor cell viability

We have previously shown that phosphodiesterase (PDE) inhibitors induce osteoclast formation by suppressing the degradation of intracellular cAMP. To determine the regulatory roles of PDE inhibitors on PGE2-induced osteoclastogenesis, we investigated the effect of PDE inhibitors on osteoclast formation in the presence of PGE2. We found that IBMX, a nonselective PDE inhibitor, and rolipram, a specific PDE4 inhibitor, decreased PGE2-induced osteoclast formation in cocultures of mouse bone marrow cells and osteoblastic cells. These suppressive effects were observed only when cocultures were treated with PDE inhibitors in the presence of PGE2 at an early stage of differentiation. Northern blot analysis revealed that the PDE4 inhibitor works synergistically with PGE2 to increase the ratio of TRANCE/OPG mRNA in osteoblasts, suggesting that suppression of osteoclast formation by PGE2 and the PDE4 inhibitor is not attributable to their indirect effect on calvarial osteoblasts. We further demonstrated that the PDE4 inhibitor augments the inhibitory effect of PGE2 on osteoclast progenitor cell viability, showing that combined treatment with PGE2 and rolipram suppresses osteoclast formation by directly reducing osteoclast progenitor cell viability.

Effect of smoking on serum RANKL and OPG in sex, age and clinically matched supportive-therapy periodontitis patients

METHODS

The serum concentrations of receptor activator of nuclear factor kappaB ligand (RANKL) and osteoprotegerin (OPG) in age- and sex-matched groups of smokers and non-smokers with almost identical levels of periodontal disease were determined by an enzyme-linked immunosorbent assay (ELISA). We ensured that the 35 smokers were gender, age and clinically matched with a group of 35 non-smokers (confirmed by cotinine immunoassay) from the same population of maintained patients with susceptibility to periodontitis.

RESULTS

Cigarette smoker patients tended to have lower serum concentrations of RANKL and OPG than non-smoker patients. While no statistically significant difference was observed for RANKL, there were significant differences in the median serum concentration of OPG (smokers 23.76 pM, non-smokers 59.28 pM) and the ratio of serum concentrations of RANKL and OPG. Concentrations of OPG in the smoker patients also had a statistically significant negative correlation with tobacco consumption.

CONCLUSION

Bone loss in smoker-related periodontitis patients may be partially explained by suppression of OPG production.

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.

Temporal and spatial expression of osteoprotegerin and receptor activator of nuclear factor -kappaB ligand during mandibular distraction in rats

PURPOSE

The expression profiles of osteoprotegerin and receptor activator of nuclear factor-kappaB ligand (RANKL) were investigated in the distraction region to reveal bone remodelling characters during mandibular distraction osteogenesis.

MATERIAL AND METHODS

Osteotomies were performed and external distractors were used on the mandibles of 42 adult male SD rats. After a 5-day latency period, the distractors were activated at a rate of 0.4mm/day for 6 days, followed by a 4-week consolidation period. Radiographs were taken, and specimens were harvested at the end of the latency period, when distraction was completed, and at the end of 1, 2, 3 and 4 weeks of the consolidation period. Tartrate-resistant acid phosphatase staining was used to detect activated osteoclasts. Temporospatial expression of osteoprotegerin and RANKL was investigated by using immunohistochemistry, in situ hybridization and reverse transcription polymerase chain reaction. Semi-quantitative analysis was used to characterize osteoprotegerin (OPG). RANKL and RANKL/OPG ratio.

RESULTS

In all time points, osteoprotegerin and RANKL were co-localized in bone marrow lining cells, osteoblasts and newly embedded osteocytes. Osteoprotegerin mRNA expression increased to a peak when distraction was completed and maintained this level until the end of week 2 of the consolidation period. RANKL mRNA expression increased steadily until the end of week 1 of the consolidation period and maintained a peak level until the end of week 3, with a slight decrease at the end of week 2. The RANKL/OPG ratio increased continuously and reached its highest level at the end of weeks 3 and 4 of the consolidation period. Tartrate-resistant acid phosphatase staining positive osteoclasts were mainly detected at weeks 2, 3 and 4 of the consolidation period in bone marrow cavities and bone surfaces.

CONCLUSIONS

The temporospatial expression patterns of osteoprotegerin and RANKL suggest that the osteoblast lineage cell network orchestrates bone remodelling during distraction osteogenesis and most activated bone resorption takes place during weeks 3 and 4 of the consolidation phase.

Bone remodeling

The skeleton is a metabolically active organ that undergoes continuous remodeling throughout life. Bone remodeling involves the removal of mineralized bone by osteoclasts followed by the formation of bone matrix through the osteoblasts that subsequently become mineralized. The remodeling cycle consists of three consecutive phases: resorption, during which osteoclasts digest old bone; reversal, when mononuclear cells appear on the bone surface; and formation, when osteoblasts lay down new bone until the resorbed bone is completely replaced. Bone remodeling serves to adjust bone architecture to meet changing mechanical needs and it helps to repair microdamages in bone matrix preventing the accumulation of old bone. It also plays an important role in maintaining plasma calcium homeostasis. The regulation of bone remodeling is both systemic and local. The major systemic regulators include parathyroid hormone (PTH), calcitriol, and other hormones such as growth hormone, glucocorticoids, thyroid hormones, and sex hormones. Factors such as insulin-like growth factors (IGFs), prostaglandins, tumor growth factor-beta (TGF-beta), bone morphogenetic proteins (BMP), and cytokines are involved as well. As far as local regulation of bone remodeling is concerned, a large number of cytokines and growth factors that affect bone cell functions have been recently identified. Furthermore, through the RANK/receptor activator of NF-kappa B ligand (RANKL)/osteoprotegerin (OPG) system the processes of bone resorption and formation are tightly coupled allowing a wave of bone formation to follow each cycle of bone resorption, thus maintaining skeletal integrity.

FR177995, a novel vacuolar ATPase inhibitor, exerts not only an inhibitory effect on bone destruction but also anti-immunoinflammatory effects in adjuvant-induced arthritic rats

There is considerable evidence that osteoclasts are involved in the pathogenesis of juxta-articular bone destruction in rheumatoid arthritis. Vacuolar ATPases (V-ATPases), which are highly expressed in the ruffled border membrane of osteoclasts, play a central role in the process of bone resorption, and V-ATPase inhibitors are effective in preventing bone destruction in several animal models of lytic bone diseases. Here, we evaluated for the first time the effects of V-ATPase inhibition in rats with adjuvant-induced arthritis (AIA) using FR177995, a novel V-ATPase inhibitor. FR177995 completely inhibited H(+) transport driven by V-ATPase, but exerted no effect on the H(+) transport activities of F- and P-ATPase, indicating that FR177995 is a specific inhibitor of V-ATPase. FR177995 acted directly on osteoclastic bone resorption and equally inhibited in vitro bone resorption stimulated by IL-1, IL-6 or PTH. In addition, FR177995 dose-dependently reduced retinoic acid-induced hypercalcemia in thyroparathyroidectomized-ovariectomized rats. When FR177995 was administered to AIA rats once a day, the loss of femoral bone mineral density was significantly improved. Moreover, indicators of cartilage damage (arthritis score and glycosaminoglycan content in the femoral condyles) and inflammation parameters (paw swelling volume, erythrocyte sedimentation rate and plasma sialic acid level) were found to be unexpectedly ameliorated. These results strongly suggest that V-ATPase may be an interesting drug target in the treatment of rheumatoid arthritis.