TRANCE is necessary and sufficient for osteoblast-mediated activation of bone resorption in osteoclasts

T cells are able to promote lipopolysaccharide-induced bone resorption in mice in the absence of B cells

BACKGROUND AND OBJECTIVE

T cells and their cytokines are believed to be key factors in periodontal disease and bone resorption. We previously showed that T cells transferred to nude mice were related to inflammatory bone resorption in vivo. However, it has not been clarified whether T cells can induce bone resorption in the absence of B cells. In this study, we therefore investigated the ability of T cells to induce bone resorption without B cells, using both T cell- and B cell-deficient mice with severe combined immune deficiency (SCID).

MATERIAL AND METHODS

Escherichia coli lipopolysaccharide (LPS) was injected into the gingivae of SCID mice reconstituted by T cells (SCID + T mice). Wild-type C.B-17 mice and SCID mice were used as control animals. Alveolar bone resorption and production of cytokines in the gingivae were then compared histopathologically and immunohistologically.

RESULTS

The degree of bone resorption in SCID + T mice was significantly greater than that in SCID mice but less than that in wild-type mice. The same tendency was found for expression of receptor activator of nuclear factor kappaB ligand. The number of interferon-gamma-positive cells in SCID + T mice was the highest of the three groups. In contrast, interleukin-4-positive cells were detected in wild-type mice but not in SCID + T and SCID mice.

CONCLUSION

The results suggest that T cells are able to promote LPS-induced bone resorption in the absence of B cells. The expressions of cytokines in the presence of B cells are quite different.

Soy phytoestrogens: impact on postmenopausal bone loss and mechanisms of action

Due to their ability to mimic the actions of mammalian estrogens, soy phytoestrogens have been proposed as potential therapeutic agents to aid in preventing postmenopausal bone loss. In vitro, phytoestrogens promote osteoblastogenesis and inhibit osteoclastogenesis. Although a relatively large number of intervention studies have been undertaken in animals and humans, the efficacy of phytoestrogens as bone-protective agents in vivo remains unclear. Differences in the bioactivities of individual phytoestrogens, differences in phytoestrogen metabolism and bioavailability within different study populations, and imprecise reporting of the dose of phytoestrogens administered in intervention studies may have contributed to the disparity in study findings.

Denosumab treatment effects on structural damage, bone mineral density, and bone turnover in rheumatoid arthritis: a twelve-month, multicenter, randomized, double-blind, placebo-controlled, phase II clinical trial

OBJECTIVE

RANKL is essential for osteoclast development, activation, and survival. Denosumab is a fully human monoclonal IgG2 antibody that binds RANKL, inhibiting its activity. The aim of this multicenter, randomized, double-blind, placebo-controlled, phase II study was to evaluate the effects of denosumab on structural damage in patients with rheumatoid arthritis (RA) receiving methotrexate treatment.

METHODS

RA patients received subcutaneous placebo (n = 75), denosumab 60 mg (n = 71), or denosumab 180 mg (n = 72) injections every 6 months for 12 months. The primary end point was the change from baseline in the magnetic resonance imaging (MRI) erosion score at 6 months.

RESULTS

At 6 months, the increase in the MRI erosion score from baseline was lower in the 60-mg denosumab group (mean change 0.13; P = 0.118) and significantly lower in the 180-mg denosumab group (mean change 0.06; P = 0.007) than in the placebo group (mean change 1.75). A significant difference in the modified Sharp erosion score was observed as early as 6 months in the 180-mg denosumab group (P = 0.019) as compared with placebo, and at 12 months, both the 60-mg (P = 0.012) and the 180-mg (P = 0.007) denosumab groups were significantly different from the placebo group. Denosumab caused sustained suppression of markers of bone turnover. There was no evidence of an effect of denosumab on joint space narrowing or on measures of RA disease activity. Rates of adverse events were comparable between the denosumab and placebo groups.

CONCLUSION

Addition of twice-yearly injections of denosumab to ongoing methotrexate treatment inhibited structural damage in patients with RA for up to 12 months, with no increase in the rates of adverse events as compared with placebo.

Osteoimmunology: interactions of the bone and immune system

Bone and the immune system are both complex tissues that respectively regulate the skeleton and the body's response to invading pathogens. It has now become clear that these organ systems often interact in their function. This is particularly true for the development of immune cells in the bone marrow and for the function of bone cells in health and disease. Because these two disciplines developed independently, investigators in each don't always fully appreciate the significance that the other system has on the function of the tissue they are studying. This review is meant to provide a broad overview of the many ways that bone and immune cells interact so that a better understanding of the role that each plays in the development and function of the other can develop. It is hoped that an appreciation of the interactions of these two organ systems will lead to better therapeutics for diseases that affect either or both.

Phase 1 trial of denosumab safety, pharmacokinetics, and pharmacodynamics in Japanese women with breast cancer-related bone metastases

Denosumab, a fully human monoclonal antibody to receptor activator of nuclear factor-kappa B ligand (RANKL), suppresses bone resorption. This open-label, multicenter, phase 1 study evaluated the safety, pharmacodynamics, and pharmacokinetics of denosumab in Japanese women with breast cancer-related bone metastases. Patients (n = 18; median age, 57 years) received a single subcutaneous injection of denosumab 60 mg or 180 mg or three doses of denosumab 180 mg on days 1, 29, and 57 (every 4 weeks) and were followed for > or = 141 days. No major safety concerns related to denosumab were noted in any cohort. All patients experienced at least 1 adverse event (AE); most were mild (grade < or = 2). One patient reported grade 4 myositis and grade 3 anemia, malaise, and dysphagia that the investigator deemed treatment-related; other treatment-related AE were grade < or = 2. No antidenosumab antibodies or clinically significant changes in laboratory findings, vital signs, or electrocardiograms were observed. Pharmacokinetics were approximately dose-linear. Denosumab caused rapid, substantial, and sustained suppression of urinary N-telopeptide corrected for creatinine (uNTx/Cr) across all doses; at day 85, the median change from baseline uNTx/Cr ranged from -61.9% to -90.8%. No dose-limiting toxicity was observed at any dosage. Coupled with pharmacokinetic and pharmacodynamic data, these results were consistent with those observed in non-Japanese populations.

Effects of denosumab on bone mineral density and bone turnover in postmenopausal women

CONTEXT

Denosumab is an investigational fully human monoclonal antibody against receptor activator of nuclear factor-kappaB ligand, a mediator of osteoclastogenesis and osteoclast survival.

OBJECTIVE

This study evaluated the ability of denosumab to increase bone mineral density (BMD) and decrease bone turnover markers (BTMs) in early and later postmenopausal women with low BMD.

DESIGN AND SETTING

This 2-yr randomized, double-blind, placebo-controlled study was conducted in North America.

PARTICIPANTS

Subjects included 332 postmenopausal women with lumbar spine BMD T-scores between -1.0 and -2.5.

INTERVENTIONS

SUBJECTS were randomly assigned to receive denosumab sc, 60 mg every 6 months, or placebo. Randomization was stratified by time since onset of menopause (< or =5 yr or > 5 yr).

MAIN OUTCOME MEASURES

The primary end point was the percent change in lumbar spine BMD by dual-energy x-ray absorptiometry at 24 months. Additional end points were percent change in volumetric BMD of the distal radius by quantitative computed tomography; percent change in BMD by dual-energy x-ray absorptiometry for the total hip, one-third radius, and total body; hip structural analysis; percent change in BTMs; and safety.

RESULTS

Denosumab significantly increased lumbar spine BMD, compared with placebo at 24 months (6.5 vs. -0.6%; P<0.0001) with similar results for both strata. Denosumab also produced significant increases in BMD at the total hip, one-third radius, and total body (P < 0.0001 vs. placebo); increased distal radius volumetric BMD (P < 0.01); improved hip structural analysis parameters; and significantly suppressed serum C-telopeptide, tartrate-resistant acid phosphatase-5b, and intact N-terminal propeptide of type 1 procollagen. The overall incidence of adverse events was similar between both study groups.

CONCLUSIONS

Twice-yearly denosumab increased BMD and decreased BTMs in early and later postmenopausal women.

Abnormal cytokine production by bone marrow stromal cells of multiple myeloma patients in response to RPMI8226 myeloma cells

INTRODUCTION

Recent studies indicate that bone marrow stromal cells (BMSCs) derived from patients with multiple myeloma (MM) differ from those of healthy donors in their expression of extracellular matrix compounds and in cytokine production. It is not known whether these abnormalities are primary or are acquired by BMSCs on contact with MM cells.

MATERIALS AND METHODS

Interleukin (IL)-6, IL-11, IL-10, and tumor necrosis factor (TNF)-alpha production by CD166+ mesenchymal BMSCs and the CD38+/CD138+ RPMI8226 myeloma cell line cultivated in vitro in monocultures or co-cultivated under cell-to-cell contact or non-contact conditions in the presence of a tissue culture insert were measured. Intracellular cytokines were measured by flow cytometry analysis as the percentage of cytokine-producing cells or by mean fluorescence intensity as the level of cytokine expression in cells. Additionally, ELISA was used to measure IL-6, soluble IL-6 receptor (sIL-6R), IL-11, IL-10, TNF-alpha, B-cell-activating factor of the TNF family (BAFF), hepatocyte growth factor (HGF), and osteopontin (OPN) production in the supernatants of the cultures and co-cultures.

RESULTS

A higher ability of the BMSCs of MM patients than in controls was detected to produce IL-6, IL-10, TNF-alpha, OPN, and especially HGF and BAFF in response to the RPMI8226 cells. Moreover, the BMSCs of the MM patients significantly enhanced the production of sIL-6R by the RPMI8226 cells.

DISCUSSION

Cytokines over-expressed by BMSCs of MM patients can function as growth factors for myeloma cells (IL-6, IL-10, HGF), migration stimulatory factors for tumor plasma cells (TNF-alpha, HGF), adhesion stimulatory factors (HGF, BAFF and OPN), stimulators of osteoclastogenesis (IL-6, TNF-alpha), and angiogenic factors (TNF-alpha). The results of this experiment strongly suggest that the BMSCs from MM patients differed in spontaneous and myeloma cell-induced production of cytokines, especially of HGF and BAFF, and these abnormalities were both primary and acquired by the BMSCs on contact with the MM cells. This in turn suggests the presence of an undefined, autocrine stimulation pathway resulting in a prolonged production of cytokines even in long-term cultures in vitro and in vivo. These abnormalities might provide optimal conditions for the proliferation and differentiation of residual tumor cells or their precursors in the affected bone marrow.

Skeletal deterioration induced by RANKL infusion: a model for high-turnover bone disease

RANKL was administered continuously to rats for 28 days to investigate its potential as a disease model for the skeletal system. Bone turnover rates, bone material, structural and mechanical properties were evaluated. RANKL infusion caused overall skeletal complications comparable to those in high bone-turnover conditions, such as postmenopausal osteoporosis.

INTRODUCTION

RANKL is an essential mediator for osteoclast development. No study has examined in detail the direct skeletal consequences of excess RANKL on bone turnover, mineralization, architecture, and vascular calcification. We, therefore, administrated soluble RANKL continuously into mature rats and created a bone-loss model.

METHODS

Six-month-old Sprague-Dawley (SD) rats were assigned to three groups (n = 12) receiving continuous administration of saline (VEH) or human RANKL (35 microg/kg/day, LOW or 175 microg/kg/day, HI) for 28 days. Blood was collected routinely during the study. At sacrifice, hind limbs and aorta were removed and samples were analyzed.

RESULTS

High dose RANKL markedly stimulated serum osteocalcin and TRAP-5b levels and reduced femur cortical bone volume (-7.6%) and trabecular volume fraction (BV/TV) at the proximal tibia (-64% vs. VEH). Bone quality was significantly degraded in HI, as evidenced by decreased femoral percent mineralization, trabecular connectivity, and increased endocortical bone resorption perimeters. Both cortical and trabecular bone mechanical properties were reduced by high dose RANKL. No differences were observed in the mineral content of the abdominal aorta.

CONCLUSIONS

Continuous RANKL infusion caused general detrimental effects on rat skeleton. These changes are comparable to those commonly observed in high-turnover bone diseases such as postmenopausal osteoporosis.

Clinical potential of RANKL inhibition for the management of postmenopausal osteoporosis and other metabolic bone diseases

Osteoporosis affects millions of people worldwide, causing decreases in bone strength and a marked increase in fracture risk. Current therapies increase bone mineral density and reduce the risk of fractures, but dosing requirements are often considered inconvenient, and patient compliance with therapy is poor. This review will discuss recent discoveries in bone biology, which have demonstrated that the interaction of osteoprotegerin (OPG), receptor activator of nuclear factor--kappa B (RANK), and RANK ligand (RANKL) is critical for the regulation of bone remodeling. Collectively, these preclinical studies have shown that endogenous RANKL inhibition by OPG underlies the normal mechanism for maintaining the correct balance between bone resorption and bone formation. Multiple clinical trials are in progress to investigate the therapeutic potential of RANKL inhibition by denosumab, a fully human monoclonal anti-RANKL antibody, in the treatment of postmenopausal osteoporosis and other bone loss diseases. The results of these human trials will also be discussed.

Receptor activator of nuclear factor kappaB ligand and osteoprotegerin regulation of bone remodeling in health and disease

Osteoclasts and osteoblasts dictate skeletal mass, structure, and strength via their respective roles in resorbing and forming bone. Bone remodeling is a spatially coordinated lifelong process whereby old bone is removed by osteoclasts and replaced by bone-forming osteoblasts. The refilling of resorption cavities is incomplete in many pathological states, which leads to a net loss of bone mass with each remodeling cycle. Postmenopausal osteoporosis and other conditions are associated with an increased rate of bone remodeling, which leads to accelerated bone loss and increased risk of fracture. Bone resorption is dependent on a cytokine known as RANKL (receptor activator of nuclear factor kappaB ligand), a TNF family member that is essential for osteoclast formation, activity, and survival in normal and pathological states of bone remodeling. The catabolic effects of RANKL are prevented by osteoprotegerin (OPG), a TNF receptor family member that binds RANKL and thereby prevents activation of its single cognate receptor called RANK. Osteoclast activity is likely to depend, at least in part, on the relative balance of RANKL and OPG. Studies in numerous animal models of bone disease show that RANKL inhibition leads to marked suppression of bone resorption and increases in cortical and cancellous bone volume, density, and strength. RANKL inhibitors also prevent focal bone loss that occurs in animal models of rheumatoid arthritis and bone metastasis. Clinical trials are exploring the effects of denosumab, a fully human anti-RANKL antibody, on bone loss in patients with osteoporosis, bone metastasis, myeloma, and rheumatoid arthritis.

The osteoclast: a multinucleated, hematopoietic-origin, bone-resorbing osteoimmune cell

Osteoclasts are multinucleated cells that derive from hematopoietic progenitors in the bone marrow which also give rise to monocytes in peripheral blood, and to the various types of tissue macrophages. Osteoclasts are formed by the fusion of precursor cells. They function in bone resorption and are therefore critical for normal skeletal development (growth and modeling), for the maintenance of its integrity throughout life, and for calcium metabolism (remodeling). To resorb bone, the osteoclasts attach to the bone matrix, their cytoskeleton reorganizes, and they assume polarized morphology and form ruffled borders to secrete acid and collagenolytic enzymes and a sealing zone to isolate the resorption site. Identification of the osteoclastogenesis inducer, the receptor activator of nuclear factor-kappaB ligand (RANKL), its cognate receptor RANK, and its decoy receptor osteoprotegerin (OPG), has contributed enormously to the dramatic advance in our understanding of the molecular mechanisms involved in osteoclast differentiation and activity. This explosion in osteoclast biology is reflected by the large number of reviews which appeared during the last decade. Here I will summarize the "classical" issues (origin, differentiation, and activity) in a general manner, and will discuss an untouched issue (multinucleation) and a relatively novel aspect of osteoclast biology (osteoimmunology).

Vitamin D status in gastrointestinal and liver disease

PURPOSE OF REVIEW

The purpose of this review is to report on the vitamin D status and its relationship with bone health in individuals with gastrointestinal and liver disorders. In addition, recommendations regarding replacement and maintenance of optimal vitamin D stores, as well as the state of knowledge regarding its effect on the disease through its actions on the immune system, will be reviewed.

RECENT FINDINGS

The scientific community has revised upward the serum levels of vitamin D considered optimal, and doses of vitamin D much larger than those currently recommended may be needed to maintain these levels, especially in individuals with gastrointestinal and liver disorders. The relationship between vitamin D and bone health in this population is controversial. The role of vitamin D in the regulation of the immune system continues to be elucidated.

SUMMARY

Hypovitaminosis D is prevalent among individuals with gastrointestinal and liver disease. Although replacement and supplementation guidelines have not been well defined, practitioners should aim for a serum 25-hydroxyvitamin D level of at least 32 ng/ml. The contribution of vitamin D to the bone health of these individuals and its role in altering disease course through its actions on the immune system remain to be elucidated.

The differential expression of osteoprotegerin (OPG) and receptor activator of nuclear factor kappaB ligand (RANKL) in human osteoarthritic subchondral bone osteoblasts is an indicator of the metabolic state of these disease cells

OBJECTIVE

We previously reported that human OA subchondral bone osteoblasts could be discriminated into two subpopulations identified by their levels of endogenous production (low [L] or high [H]) of PGE(2). Here, we investigated the OPG and RANKL expression levels, the histologic analysis of the subchondral bone as well as the osteoclast differentiation effect of osteoblasts on normal and both OA subpopulations (L and H), and further examined on the L OA osteoblasts the modulation of bone remodelling factors on the OPG and RANKL levels, as well as on the resorption activity.

METHODS

Gene expression was determined using real-time PCR, PGE2 and OPG levels by specific ELISA, and membranous RANKL by flow cytometry. Histological observation of the subchondral bone was performed on human knee specimens. Osteoclast differentiation and formation was assayed by using the pre-osteoclastic cell line RAW 264.7. OPG and RANKL modulation on L OA osteoblasts was monitored following treatment with osteotropic factors, and the resorption activity was studied by the co-culture of differentiated PBMC/osteoblasts.

RESULTS

Human OA subchondral bone osteoblasts expressed less OPG than normal. Compared to normal, RANKL gene expression levels were increased in L OA and decreased in H OA cells. The OPG/RANKL mRNA ratio was significantly diminished in L OA compared to normal or H OA (p<0.02, p<0.03), and markedly increased in H OA compared to normal. Inhibition of endogenous PGE(2) levels by indomethacin markedly decreased the ratio of OPG/RANKL on the H OA. In contrast to H OA osteoblasts, L OA cells induced a significantly higher level of osteoclast differentiation and formation (p<0.05). Histological analysis showed a reduced subchondral bone on the L OA and an increased bone mass on the H OA compared to normal. Treatment of L OA osteoblasts with osteotropic factors revealed that the OPG/RANKL mRNA expression ratio was significantly reduced by vitamin D(3) and significantly increased by TNF-alpha, PTH and PGE(2), while IL-1Beta demonstrated no effect. OPG protein levels showed similar profiles. No true effect was noted on membranous RANKL upon treatment with IL-1Beta, PGE(2) and PTH, but a significant increase was observed with vitamin D3 and TNF-alpha. The resorption activity of the L OA cells was significantly inhibited by all treatments except IL-1Beta, with maximum effect observed with vitamin D(3) and PGE(2).

CONCLUSION

OPG and RANKL levels, and consequently the OPG/RANKL ratio, differed according to human OA subchondral bone osteoblast classification; it is decreased in L and increased in H OA. These findings, in addition to those showing that L OA osteoblasts have a reduced subchondral bone mass and induce a higher level of osteoclast differentiation, strongly suggest that the metabolic state of the L OA osteoblasts favours bone resorption.

Osteoporosis and inflammation

Osteoporosis represents a major healthcare burden, affecting approximately 10 million people aged over 50 years in the United States and with another 30 million or more at risk. One of the major contributing factors to osteoporosis is withdrawal of estrogen during menopause in women. Human and animal experiments have implicated pro-inflammatory cytokines as primary mediators of the accelerated bone loss at menopause including interleukin-1, tumor necrosis factor-alpha, and interleukin-6. Increased production of pro-inflammatory cytokines is associated with osteoclastic bone resorption in a number of disease states including rheumatoid arthritis, periodontitis, and multiple myeloma; estrogen withdrawal is associated with increased production of pro-inflammatory cytokines, and exposure of bone cultures to supernatants from activated leukocytes is associated with increased bone resorption. A major advance has been the discovery of RANKL, its receptor RANK, and the endogenous inhibitor osteoprotegerin. The binding of RANKL to RANK is essential for the differentiation and activation of osteoclasts and mediates the actions of essentially all known stimulators of osteoclastic bone resorption. RANKL expression is heightened in post- compared with pre-menopausal women, and this effect is attenuated by estrogen replacement therapy. RANKL is also a therapeutic target; a human antibody with high specificity and affinity to RANKL is currently under clinical evaluation for the treatment of osteoporosis in post-menopausal women and of metastatic bone disease in cancer patients with bone metastasis. Early data are promising.

Suppressive effects of Anoectochilus formosanus extract on osteoclast formation in vitro and bone resorption in vivo

Anoectochilus formosanus, a plant native to Taiwan, is used as a folk medicine. It was found that oral administration of A. formosanus extract (AFE) (500 mg/kg) for 4 weeks suppressed bone weight loss and trabecular bone loss in ovariectomized mice, an experimental model of osteoporosis. Although AFE at 12.5 and 25 mug/ml inhibited osteoclast formation in co-culture of osteoblasts and bone marrow cells, AFE did not inhibit the formation of osteoclast progenitor cells and preosteoclast cells in bone marrow cells and RAW264 cells. However, AFE (at 12.5 and 25 microg/ml) decreased RANKL expression. These results suggested that AFE might suppress the bone loss caused by estrogen deficiency through suppression of RANKL expression required for osteoclast formation.

Inhibition of RANKL blocks skeletal tumor progression and improves survival in a mouse model of breast cancer bone metastasis

Bone metastases cause severe skeletal morbidity including fractures and hypercalcemia. Tumor cells in bone induce activation of osteoclasts, which mediate bone resorption and release of growth factors from bone matrix, resulting in a "vicious cycle" of bone breakdown and tumor proliferation. Receptor activator of NF-kappaB ligand (RANKL) is an essential mediator of osteoclast formation, function, and survival, and is blocked by a soluble decoy receptor, osteoprotegerin (OPG). In human malignancies that metastasize to bone, dysregulation of the RANK/RANKL/OPG pathway can increase the RANKL:OPG ratio, a condition which favors excessive osteolysis. In a mouse model of bone metastasis, RANKL protein levels in MDA-MB-231 (MDA-231) tumor-bearing bones were significantly higher than tumor-free bones. The resulting tumor-induced osteoclastogenesis and osteolysis was dose-dependently inhibited by recombinant OPG-Fc treatment, supporting the essential role for RANKL in this process. Using bioluminescence imaging in a mouse model of metastasis, we monitored the anti-tumor efficacy of RANKL inhibition on MDA-231 human breast cancer cells in a temporal manner. Treatment with OPG-Fc in vivo inhibited growth of MDA-231 tumor cells in bony sites when given both as a preventative (dosed day 0) and as a therapeutic agent for established bone metastases (dosed day 7). One mechanism by which RANKL inhibition reduced tumor burden appears to be indirect through inhibition of the "vicious cycle" and involved an increase in tumor cell apoptosis, as measured by active caspase-3. Here, we demonstrate for the first time that OPG-Fc treatment of mice with established bone metastases resulted in an overall improvement in survival.

CLINICAL Review #: the role of receptor activator of nuclear factor-kappaB (RANK)/RANK ligand/osteoprotegerin: clinical implications

CONTEXT

Receptor activator of nuclear factor-kappaB ligand (RANKL), receptor activator of nuclear factor-kappaB (RANK), and osteoprotegerin (OPG) play a central role in bone remodeling and disorders of mineral metabolism.

EVIDENCE ACQUISITION

A PubMed search was conducted from January 1992 until 2007 for basic, observational, and clinical studies in subjects with disorders related to imbalances in the RANK/RANKL/OPG system.

EVIDENCE SYNTHESIS

RANK, RANKL, and OPG are members of the TNF receptor superfamily. The pathways involving them in conjunction with various cytokines and calciotropic hormones play a pivotal role in bone remodeling. Several studies involving mutations in the genes encoding RANK and OPG concluded in the discovery of a number of inherited skeletal disorders. In addition, basic and clinical studies established a consistent relationship between the RANK/RANKL/OPG pathway and skeletal lesions related to disorders of mineral metabolism. These studies were a stepping stone in further defining the role of the RANK/RANKL/OPG pathway in osteoporosis, rheumatoid arthritis, bone loss associated with malignancy-related skeletal diseases, and its relationship to vascular calcifications. Subsequently, the further understanding of this pathway led to the development of new therapeutic modalities including the human monoclonal antibody to RANKL and recombinant OPG as a target for treatment of postmenopausal osteoporosis and multiple myeloma.

CONCLUSIONS

The RANK/RANKL/OPG system mediates the effects of calciotropic hormones and, consequently, alterations in their ratio are key in the development of several clinical conditions. New agents with the potential to block effects of RANKL have emerged for treatment of postmenopausal osteoporosis and malignancy-related skeletal disease.

Long chain polyunsaturated fatty acids alter membrane-bound RANK-L expression and osteoprotegerin secretion by MC3T3-E1 osteoblast-like cells

Inflammation triggers an increase in osteoclast (bone resorbing cell) number and activity. Osteoclastogenesis is largely controlled by a triad of proteins consisting of a receptor (RANK), a ligand (RANK-L) and a decoy receptor (osteoprotegerin, OPG). Whilst RANK is expressed by osteoclasts, RANK-L and OPG are expressed by osteoblasts. The long chain polyunsaturated fatty acid (LCPUFA) arachidonic acid (AA, 20:4n-6) and its metabolite prostaglandin E2 (PGE2), are pro-inflammatory and PGE2 is a potent stimulator of RANKL expression. Various LCPUFAs such as eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3) and gamma-linolenic acid (GLA, 18:3n-6) have anti-inflammatory activity. We aimed to determine if AA itself can stimulate RANKL expression and whether EPA, DHA and GLA inhibit RANKL expression in osteoblasts. MC3T3-E1/4 osteoblast-like cells were cultured under standard conditions with each of the LCPUFAs (5microg/ml) for 48h. Membrane-bound RANKL expression was measured by flow cytometry and OPG secretion measured by ELISA. In a second experiment, RANKL expression in MC3T3-E1/4 cells was stimulated by PGE2 treatment and the effect of EPA, DHA and GLA on membrane-bound RANKL expression and OPG secretion determined. The percentage of RANKL-positive cells was higher (p<0.05) than controls following treatment with AA or GLA but not after co-treatment with the cyclooxygenase inhibitor, indomethacin. DHA and EPA had no effect on membrane-bound RANKL expression under standard cell culture conditions. Secretion of OPG was lower (p<0.05) in AA-treated cells but not significantly different from controls in GLA, EPA or DHA treated cells. Treatment with prostaglandin E2 (PGE2) resulted in an increase (p<0.05) in the percentage of RANK-L positive cells and a decrease (p<0.05) in mean OPG secretion. The percentage of RANKL positive cells was significantly lower following co-treatment with PGE2 and either DHA or EPA compared to treatment with PGE2 alone. Mean OPG secretion remained lower than controls in cells treated with PGE2 regardless of co-treatment with EPA or DHA. Results from this study suggest COX products of GLA and AA induce membrane-bound RANKL expression in MC3T3-E1/4 cells. EPA and DHA have no effect on membrane-bound RANKL expression in cells cultured under standard conditions however both EPA and DHA inhibit the PGE2-induced increase in RANKL expression in MC3T3-E1/4 cells.

RANK ligand as a therapeutic target for bone metastases and multiple myeloma

Osteoclastic bone resorption is a critical component of skeletal complications of malignancy including fracture, bone pain, hypercalcemia, and spinal cord compression. Three proteins, RANKL, RANK, and OPG have been recently identified as key determinants of osteoclastogenesis and the regulation of bone resorption. Both RANKL and OPG can be aberrantly regulated in the cancer setting and function as important gatekeepers of tumor-induced osteolytic bone disease. RANKL-induced osteoclastogenesis not only mediates osteolytic bone disease, but also contributes to the pathogenesis of osteoblastic bone disease resulting from tumors. In addition, an important role was recently described for bone marrow derived RANKL to mediate the bone-specific tropism of RANK-expressing tumor cells. This manuscript will review how RANKL contributes to skeletal complications of cancer and the development of targeted, mechanism-based drugs that inhibit RANKL.

Expression of receptor activator of nuclear factor kappa B ligand relates to inflammatory bone resorption, with or without occlusal trauma, in rats

BACKGROUND AND OBJECTIVE

Receptor activator of nuclear factor kappa B ligand (RANKL) is an important factor in osteoclast differentiation, activation and survival; however, its involvement in inflammatory bone resorption, with or without occlusal trauma, is unclear. The purpose of the present study was to investigate the distribution of RANKL-expressing cells in rat periodontium during lipopolysaccharide-induced inflammation with or without occlusal trauma.

MATERIAL AND METHODS

Lipopolysaccharide was injected into rat gingiva of the lower left first molar to induce inflammation. In addition, the occlusal surface of the upper left first molar of rat was raised by placing a gold inlay to induce occlusal trauma in the lower left first molars. The distribution of RANKL-expressing cells was immunohistochemically observed.

RESULTS

In the inflammatory model, many osteoclasts were observed at the apical inter-radicular septum on day 5 and they were reduced by day 10. On the other hand, in the inflammatory model with occlusal trauma, many osteoclasts were still observed on day 10. RANKL expression was similar to the changes in osteoclast number. The expression of RANKL increased in endothelial cells, inflammatory cells and periodontal ligament cells.

CONCLUSION

These findings clearly demonstrated that RANKL expression on endothelial cells, inflammatory cells and periodontal ligament cells is involved in inflammatory bone resorption and the expression is enhanced by traumatic occlusion. These results suggest that RANKL expression on these cells is closely involved in the increase of osteoclasts induced by occlusal trauma.

Pepstatin A, an aspartic proteinase inhibitor, suppresses RANKL-induced osteoclast differentiation

Pepstatin A is well known to be an inhibitor of aspartic proteinases such as pepsin, cathepsins D and E. Except for its role as a proteinase inhibitor, however, the pharmacological action of pepstatin A upon cells remain unclear. In this study, we found that pepstatin A suppressed receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast differentiation. Pepstatin A suppressed the formation of multinuclear osteoclasts dose-dependently. This inhibition of the formation only affected osteoclast cells, i.e., not osteoblast-like cells. Furthermore, pepstatin A also suppressed differentiation from pre-osteoclast cells to mononuclear osteoclast cells dose-dependently. This inhibition seems to be independent of the activities of proteinases such as cathepsin D, because the formation of osteoclasts was not suppressed with the concentration that inhibited the activity of cathepsin D. Cell signaling analysis indicated that the phosphorylation of ERK was inhibited in pepstatin A-treated cells, while the phosphorylation of IkappaB and Akt showed almost no change. Furthermore, pepstatin A decreased the expression of nuclear factor of activated T cells c1 (NFATc1). These results suggest that pepstatin A suppresses the differentiation of osteoclasts through the blockade of ERK signaling and the inhibition of NFATc1 expression.

sRANKL/osteoprotegerin complex and biochemical markers in a cohort of male and female hemodialysis patients

OBJECTIVE

The processes involved in bone remodeling are under the control of a multitude of systemic and local factors. Receptor activator of nuclear factor-kappaB ligand (RANKL)/osteoprotegerin (OPG) complex seems to be one of the major modulators of bone remodeling. In chronic renal failure, the cytokine systems involved in the regulation of bone turnover may be influenced, and are therefore likely to contribute to the pathogenesis of renal bone disease. The aim of the present study was the evaluation of RANKL/OPG complex in concert with other biochemical parameters in hemodialysis (HD) patients and the investigation of possible correlations between the serum levels of its components and several clinical parameters of these patients.

METHODS

We measured serum levels of intact PTH (iPTH), total serum RANKL (sRANKL), osteoprotegerin (OPG), alkaline phosphatase, osteocalcin (OC), and tartrate-resistant acid phosphatase (TRAP) in 104 HD patients and in 40 healthy controls.

RESULTS

The average serum OPG level was significantly higher, whereas the average serum concentration of RANKL was nonsignificantly lower in patients on HD therapy than in age-matched healthy controls. Consequently, the mean sRANKL/OPG ratio was significantly lower in patients. Among HD patients, serum level of OPG increased significantly with aging and with a longer duration of hemodialysis. RANKL levels were inversely correlated with age nonsignificantly in the whole group of patients and significantly in the female subgroup (r=-0.322, p=0.035), whereas RANKL/OPG ratio declined significantly with age in the entire cohort of patients (r=-0.259, p=0.008). In addition, iPTH, OC, TRAP were significantly higher in female, whereas RANKL/OPG ratio was significantly higher in male than female patients.

CONCLUSIONS

Lower values of sRANKL/OPG ratio in HD patients, as well as the age and duration of HD dependent increase of serum OPG and the age-dependent decrease of sRANKL concentration especially in women cannot be explained by the elimination of renal clearance only. Alterations in sRANKL/OPG ratio might reflect a compensatory mechanism to modulate bone remodeling in these patients.

Randomized active-controlled phase II study of denosumab efficacy and safety in patients with breast cancer-related bone metastases

PURPOSE

Denosumab, a fully human monoclonal antibody to receptor activator of nuclear factor-kappaB ligand, suppresses bone resorption. In this study, we evaluated the efficacy and safety of five dosing regimens of denosumab in patients with breast cancer-related bone metastases not previously treated with intravenous bisphosphonates (IV BPs).

PATIENTS AND METHODS

Eligible women (n = 255) with breast cancer-related bone metastases were stratified by type of antineoplastic therapy received and randomly assigned to one of six cohorts (five denosumab cohorts [blinded to dose and frequency]; one open-label IV BP cohort). Denosumab was administered subcutaneously every 4 weeks (30, 120, or 180 mg) or every 12 weeks (60 or 180 mg). The primary end point was percentage of change in the bone turnover marker urine N-telopeptide corrected for urine creatinine (uNTx/Cr) from baseline to study week 13. The percentage of patients achieving more than 65% uNTx/Cr reduction, time to more than 65% uNTx/Cr reduction, patients experiencing one or more on-study skeletal-related events (SRE), and safety were also evaluated.

RESULTS

At study week 13, the median percent reduction in uNTx/Cr was 71% for the pooled denosumab groups and 79% for the IV BP group. Overall, 74% of denosumab-treated patients (157 of 211) achieved a more than 65% reduction in uNTx/Cr compared with 63% of bisphosphonate-treated patients (27 of 43). On-study SREs were experienced by 9% of denosumab-treated patients (20 of 211) versus 16% of bisphosphonate-treated patients (seven of 43). No serious or fatal adverse events related to denosumab occurred.

CONCLUSION

Subcutaneous denosumab may be similar to IV BPs in suppressing bone turnover and reducing SRE risk. The safety profile was consistent with an advanced breast cancer population receiving systemic therapy.

Mitogen-activated protein kinases mediate interleukin-1?-induced receptor activator of nuclear factor-?B ligand expression in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Interleukin-1beta-stimulated receptor activator of nuclear factor-kappaB ligand (RANKL) expression in human periodontal ligament cells is partially mediated by endogenous prostaglandin E2, whereas mitogen-activated protein kinases (MAPKs) are implicated in regulating various interleukin-1-responsive genes. We investigated herein the involvement of MAPKs in interleukin-1beta-stimulated RANKL expression in human periodontal ligament cells.

MATERIAL AND METHODS

Human periodontal ligament cells were pretreated separately with specific inhibitors of MAPKs, including extracellular signal-regulated kinase, p38 MAPK and c-Jun N-terminal kinase, and subsequently treated with interleukin-1beta. Following each treatment, the phosphorylation of each MAPK, the expression of RANKL, and the production of prostaglandin E2 were determined. RANKL activity was evaluated using an assay to determine the survival of prefusion osteoclasts.

RESULTS

Interleukin-1beta induced RANKL expression at the mRNA and protein levels, as well as RANKL activity in human periodontal ligament cells. Interleukin-1beta also activated extracellular signal-regulated kinase, p38 MAPK, and c-Jun N-terminal kinase. Pretreatment with each MAPK inhibitor partially, but significantly, suppressed interleukin-1beta-induced RANKL expression and its activity, as well as prostaglandin E2 production.

CONCLUSION

In human periodontal ligament cells, three types of MAPK inhibitor may abrogate RANKL expression and activity induced by interleukin-1beta, directly or indirectly through partial suppression of prostaglandin E2 synthesis. In addition, extracellular signal-regulated kinase, p38 MAPK, and c-Jun N-terminal kinase signals may co-operatively mediate interleukin-1beta-stimulated RANKL expression and its activity in those cells.

The biology of aseptic osteolysis

Total hip arthroplasty is one of the most commonly performed and successful elective orthopaedic procedures. However, numerous failure mechanisms limit the long-term success including aseptic osteolysis, aseptic loosening, infection, and implant instability. Aseptic osteolysis and subsequent implant failure occur because of a chronic inflammatory response to implant-derived wear particles. To reduce particulate debris and their consequences, implants have had numerous design modifications including high-molecular-weight polyethylene sockets and noncemented implants that rely on bone ingrowth for fixation. Surgical techniques have improved cementation with the use of medullary plugs, cement guns, lavage of the canal, pressurization, centralization of the stem, and reduction in cement porosity. Despite these advances, aseptic osteolysis continues to limit implant longevity. Numerous proinflammatory cytokines, such as interleukin-1, interleukin-6, tumor necrosis factor-alpha, and prostaglandin E2, have proosteoclastogenic effects in response to implant-derived wear particles. However, none of these cytokines represents a final common pathway for the process of particle-induced osteoclast differentiation and maturation. Recent work has identified the fundamental role of the RANKL-RANK-NF-kappaB pathway not only in osteoclastogenesis but also in the development and function the immune system. Thus, the immune system and skeletal homeostasis may be linked in the process of osteoclastogenesis and osteolysis.

Regulation and enzymatic basis of bone resorption by human osteoclasts

Although much has been learned recently of the mechanisms that regulate osteoclastic differentiation, much less is known of the means through which their resorptive activity is controlled. This is especially so for human osteoclasts. We have recently developed an assay that allows us to measure resorptive activity while minimizing confounding effects on differentiation by optimizing osteoclastogenesis, so that measurable resorption occurs over a short period, and by relating resorption in each culture during the test period to the resorption that had occurred in the same culture in a prior control period. In the present study, we found that RANKL (receptor activator of nuclear factor kappaB ligand) strongly stimulated the release of CTX-I (C-terminal telopeptide degradation product of type I collagen) by osteoclasts over a similar range to that over which it induces osteoclastic differentiation, consistent with a distinct action on osteoclastic function. CT (calcitonin) dose-dependently inhibited bone resorption, whereas PTH (parathyroid hormone), IL (interleukin)-1, TNF-alpha (tumour necrosis factor-alpha), IL-6, IL-8, VEGF (vascular endothelial growth factor), MCP-1 (monocyte chemoattractant protein-1), MIP-1gamma (macrophage inflammatory protein-1gamma), IFN (interferon)-gamma and dibutyryl cGMP had no significant effect. Ca(2+), cyclosporin A, IFN-beta and dibutyryl cAMP all strongly suppressed resorption. Bone resorption was also strongly suppressed by alendronate, the cysteine protease inhibitor E64 and the cathepsin K inhibitor MV061194. Inhibitors of MMPs (matrix metalloproteinases) had no effect on CTX-I release. Moreover, the release of the MMP-derived collagen fragment ICTP (C-terminal cross-linked telopeptide of type I collagen) represented less that 0.01% of the quantity of CTX-I released in our cultures. This suggests that MMPs make, at most, a very small contribution to the bone-resorptive activity of osteoclasts.

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.

Physiologic root resorption in primary teeth: molecular and histological events

Root resorption is a physiologic event for the primary teeth. It is still unclear whether odontoclasts, the cells which resorb the dental hard tissue, are different from the osteoclasts, the cells that resorb bone. Root resorption seems to be initiated and regulated by the stellate reticulum and the dental follicle of the underlying permanent tooth via the secretion of stimulatory molecules, i.e. cytokines and transcription factors. The primary root resorption process is regulated in a manner similar to bone remodeling, involving the same receptor ligand system known as RANK/RANKL (receptor activator of nuclear factor-kappa B/ RANK Ligand). Primary teeth without a permanent successor eventually exfoliate as well, but our current understanding on the underlying mechanism is slim. The literature is also vague on how resorption of the pulp and periodontal ligament of the primary teeth occurs. Knowledge on the mechanisms involved in the physiologic root resorption process may enable us to delay or even inhibit exfoliation of primary teeth in those cases that the permanent successor teeth are not present and thus preservation of the primary teeth is desirable.

RANKL:osteoprotegerin ratio and bone mineral density in children with untreated juvenile dermatomyositis

OBJECTIVE

To determine bone mineral density (BMD) in patients at the time of diagnosis of juvenile dermatomyositis (DM), to compare the RANKL:osteoprotegerin (OPG) ratio in patients with juvenile DM with that in healthy control subjects, and to evaluate whether BMD is associated with the RANKL:OPG ratio and the duration of untreated disease.

METHODS

Thirty-seven children with juvenile DM were enrolled. Dual x-ray absorptiometry (DXA) was performed before treatment, and Z scores for the lumbar spine (L1-L4) were determined. The duration of untreated disease was defined as the period of time from the onset of rash or weakness to the time at which DXA was performed. Serum specimens obtained at the time of DXA were analyzed for concentrations of RANKL and OPG, using enzyme-linked immunosorbent assay. The RANKL:OPG ratio was also determined in 44 age-matched healthy control subjects.

RESULTS

At the time of diagnosis of juvenile DM, patients had a significantly increased RANKL:OPG ratio compared with that in healthy children (mean +/- SD 2.19 +/- 3.03 and 0.13 +/- 0.17, respectively; P < 0.0001). In patients with a lumbar spine BMD Z score of -1.5 or lower, the RANKL:OPG ratio was significantly higher than that in patients with a lumbar spine BMD Z score higher than -1.5 (P = 0.038). Lumbar spine BMD Z scores (mean +/- SD -0.13 +/- 1.19 [range -2.10 to 2.85]) were inversely associated with the duration of untreated disease (R = -0.50, P = 0.003).

CONCLUSION

Children with juvenile DM have an elevated RANKL:OPG ratio at the time of diagnosis, resulting in expansion of the number of osteoclasts and activation of the bone resorptive function. This may lead to a lack of normal bone mineral accretion and a subsequent reduction in the lumbar spine BMD Z score. Patients with a longer duration of untreated juvenile DM have reduced lumbar spine BMD Z scores. These data suggest that early diagnosis could reduce the likelihood of reduced lumbar spine BMD in these patients by prompting intervention strategies at an early stage.

Macrophage lineage phenotypes and osteoclastogenesis--complexity in the control by GM-CSF and TGF-beta

Bone-resorbing osteoclasts (OCs) derive from macrophage lineage precursors under the potential control of many factors. Addition of macrophage-colony stimulating factor (M-CSF or CSF-1) to murine bone marrow cells gives rise to so-called bone marrow-derived macrophages (BMM); this adherent population can then be quantitatively converted into OC lineage cells when receptor activator of NFkappaB ligand (RANKL) is included. The effect of another CSF, granulocyte macrophage-CSF (GM-CSF), on OC differentiation in vitro is quite complex with both enhancing and suppressive actions being described. We report here that GM-CSF can generate a population of adherent macrophage lineage cells from murine bone marrow precursors (GM-BMM) which is also capable of giving rise to OC lineage cells in the presence of M-CSF and RANKL as effectively as BMM. The degree of this differentiation was surprising considering that GM-BMM are often referred to as immature dendritic cells and that, for both BMM and the GM-BMM, GM-CSF suppressed subsequent OC differentiation governed by M-CSF and RANKL. Unlike for BMM, this GM-CSF-mediated suppression for GM-BMM appeared to be independent of c-fos expression. The effects on bone of another cytokine, transforming growth factor-beta (TGF-beta), are also quite complex although usually found to be stimulatory for OC differentiation. Unexpectedly, we observed that TGF-beta1 also potently suppressed M-CSF+RANKL-driven OC differentiation from both BMM and GM-BMM. Using cells from gene-deficient mice, this inhibition of OC differentiation by both GM-CSF and TGF-beta1 appeared to be independent of endogenous interferon alpha/beta production. It appears therefore that the influence of GM-CSF and TGF-beta on osteoclastogenesis depends on the presence or otherwise of other stimuli such as RANKL and possibly upon the maturation state of the OC precursors. It is proposed that the findings have particular relevance for the control of bone resorption in pathology, for example, in inflammatory lesions.

Cell-based assay strategy for identification of motif-specific RANK signaling pathway inhibitors

Osteoclasts, the principal bone-resorbing cells, not only play a pivotal role in skeletal development and maintenance but are also implicated in the pathogenesis of various bone disorders such as postmenopausal osteoporosis, bone erosion in inflammatory conditions, and tumor-induced osteolysis. As a result, several antiresorptive drugs (agents capable of inhibiting osteoclast formation and/or function) have been developed and are widely used to prevent and treat these bone diseases. However, current antiresorptive agents either lack satisfactory efficacy or cause serious side effects in clinical management of these bone disorders. Almost a decade ago, the receptor activator of nuclear factor-kappaB (RANK) ligand (RANKL) was identified as an essential factor required for osteoclast formation. RANKL exerts the effect by binding to its receptor RANK on osteoclast precursors. RANKL also has a decoy receptor, osteoprotegerin (OPG), which inhibits RANKL function by competing with RANK for RANKL. The unraveling of the critical role for the RANKL/RANK/OPG system in osteoclast biology provides an unprecedented opportunity to develop more effective antiresorptive drugs. Unfortunately, the agents currently under development, such as OPG, RANK-Fc, and anti-RANKL antibodies, all inherit a serious drawback--lack of specificity, due to the involvement of the RANKL/RANK/OPG system in other biological processes such as immune response and mammary gland development. Thus, future efforts may need to shift to explore RANK signaling pathways as more effective therapeutic targets. Here, we review our current understanding of RANK signaling in osteoclasts and then discuss the potential of RANK signaling pathways as therapeutic pathways. Moreover, we further describe a strategy for constructing novel cell-based systems for identifying compounds inhibiting signaling from two recently identified RANK motifs through high throughput screening. We hope that this review will not only provide readers with an update on progress in this area of research but, more importantly, will also serve as a starting point for further discussion and eventual development of new strategies for harnessing the ultimate potential of the RANKL/RANK/OPG system as antiresorptive therapeutic targets.

RANKL inhibition: from mice to men (and women)

RANKL, the primary mediator of osteoclast formation, function and survival, is implicated in bone loss across a broad range of conditions. RANK and RANKL are expressed by cells involved in bone remodeling, by cells of the immune system, and by cells in other tissues. Preclinical and clinical data support the following conclusions: (1) The immune and skeletal phenotypes associated with RANKL inhibition differ in important ways from those associated with the complete absence or ablation of RANK or RANKL. (2) Immune challenge performed in animals in the presence of RANKL inhibition demonstrates normal immune function, consistent with the interpretation that RANKL inhibition does not impair the ability of animals to mount an effective immune response. (3) In animal models of inflammatory disease, inhibition of RANKL prevents bone loss but does not show a detectable effect on immune mediators or inflammation. (4) A phase 2 study in postmenopausal women with low BMD using the RANKL inhibitor denosumab showed an increase in BMD with an incidence of adverse events that was similar to placebo and to open-label alendronate. In addition, in a subset of patients tested for immunological markers, there were no clinically meaningful differences in T, B, or NK cell numbers or in immunoglobulin levels across dose or treatment groups.

The effect of methotrexate on bone metabolism markers in patients with rheumatoid arthritis

The aim of the present study was to evaluate the influence on urinary excretion levels of N-telopeptide of type I collagen (NTX) and deoxypyridinoline (DPD) as a useful marker for bone resorption, and on serum-bone alkaline phosphate (BAP) levels as a useful marker for bone formation and an early marker of osteoblast differentiation in patients with rheumatoid arthritis (RA) treated with methotrexate (MTX). Thirty patients with RA, diagnosed according to the criteria of the American College of Rheumatology, were involved in this study between March 2003 and January 2005. None of the patients had a history of hormone (estrogen) replacement therapy. All patients were treated with MTX. Methotrexate was administered perorally at a dosage of 4-10 mg/week. All patients underwent general and physical examinations and routine blood and urinary analysis at the baseline, 3 months and 6 months after the initial treatment. Then the levels of NTX and DPD in urine and BAP in serum were measured in all patients. For comparison with the effect of other DMARDs on bone metabolism markers in RA patients, we measured the levels of NTX and DPD in urine and BAP in serum of RA patients, 13 patients treated with salazosulfapyridine (SASP), and 14 patients treated with actarit (ACT). In patients treated with MTX, NTX levels decreased significantly at 3 months after the initial treatment and remained low at 6 months after the initial treatment, and DPD levels significantly decreased at 6 months after the initial treatment. The mean serum BAP levels changed without significant differences from the baseline at 3 months and 6 months. In patients treated with SASP and ACT, all bone metabolism markers had not changed significantly at the three time points. On disease activity erythrocyte sedimentation rate, C-reactive protein, the number of swollen joints and tender joints, and mHAQ score decreased significantly at 3 months after the initial treatment, and remained at low levels at 6 months after the initial treatment with MTX. Methotrexate therapy looks promising in inhibiting generalized bone loss in patients with RA. In addition, NTX is a more sensitive marker than DPD.

Wnt antagonism in multiple myeloma: a potential cause of uncoupled bone remodeling

Bone disease in patients with multiple myeloma (MM) is characterized by uncoupled bone remodeling, evident as enhanced osteolytic resorption and decreased rather than increased bone formation. MM-triggered osteolysis follows deregulation of the receptor activator of nuclear factor kappaB ligand (RANKL)/osteoprotegerin cytokine axis. Inhibition of bone formation may result from the ability of MM to inhibit the function of Wnts, secreted glycoproteins critical to osteoblast development. Recent studies show how these processes may be linked.

Cytokines regulating osteoclast formation and function

PURPOSE OF REVIEW

The osteoclast is the principal bone-resorbing cell. Because of its unique ability to efficiently remove both the mineral and the organic matrix of bone, the osteoclast is an important element of the homeostatic mechanisms that maintain skeletal integrity and serum calcium levels. Over the past 30 years, a number of immune cell modulators have been shown to have effects on osteoclast formation and function. This review will briefly summarize the roles that cytokines have in osteoclast regulation.

RECENT FINDINGS

A large number of cytokines have been shown to regulate osteoclast formation and function. In addition, a number of additional cytokines are now known to have a major influence on the ability of osteoclasts to resorb bone. Interactions of the immune system with bone, which has been recently labeled 'osteoimmunology', appear to be mediated mainly by cytokine signals. Cytokines are known to regulate many of the responses of bone to inflammatory conditions; however, they also may regulate physiologic responses of bone.

SUMMARY

In the future it is hoped that therapies that target cytokine actions may be used to reduce the effects of inflammatory diseases on bone, as well as to regulate normal bone physiology.

RANKL expression in rat periodontal ligament subjected to a continuous orthodontic force

OBJECTIVES

This study investigated longitudinal changes in receptor activator NF kappa B ligand (RANKL) expression in periodontal ligament (PDL) cells subjected to a continuous orthodontic force.

DESIGN

Fifty-five-day-old male Wistar rats were divided into experimental and control groups. The experimental group had the first molars laterally expanded by a continuous orthodontic force. In each group, the horizontal section specimens were embedded in OTC compound and frozen at 0, 1, 3 and 7 days after the expansion. Sections were observed by immunostaining with anti-RANKL and the tartrate-resistant acid phosphatase (TRAP) staining.

RESULT

Immunoreaction of RANKL and TRAP-positive cells were observed in the distal region of the controls and on the compressed side of the expansion group in the 3 and 7 days. Immunoreaction of RANKL was also observed after 1 day on the compression side of the expansion group, but here TRAP-positive cells were few.

CONCLUSIONS

The experiments have showed that PDL cells are continuously producing RANKL on the PDL pressure side of rats subjected to mechanical stress with a continuous orthodontic force, there was no noticeable the excessive appearance of osteoclasts however. Considering this, it is expected that not only RANKL production but also other cytokines play an important role in the balancing adjustment in the alveolar bone remodeling.

Treatment for Myeloma Bone Disease: Table 1

Multiple myeloma (MM) is a B cell malignancy characterized by enhanced bone loss commonly associated with diffuse osteopenia, focal lytic lesions, pathologic fractures, hypercalcemia, and bony pain. Bone destruction in MM results from asynchronous bone turnover wherein increased osteoclastic bone resorption is not accompanied by a comparable increase in bone formation. Consequently, patients with MM frequently require radiation therapy, surgery, and analgesic medications. The recent development of minimally invasive surgical procedures such as kyphoplasty allows patients with myeloma with vertebral compression fractures to have immediate improvement in their quality of life with shorter hospital stays. Bisphosphonates are specific inhibitors of osteoclastic activity, and these agents have been evaluated in patients with MM with bone disease during the past 15 years. Monthly i.v. infusions of either pamidronate or zoledronic acid have reduced the skeletal complications among patients with MM and are now a mainstay of myeloma therapy. Orally administered bisphosphonates, in contrast, have shown little ability to slow the development of skeletal complications in these patients. Although preclinical studies suggest that nitrogen-containing bisphosphonates have potent antitumor effects, clinical trials will be necessary, probably at higher doses given more slowly, to establish their possible antitumor effects clinically. Moreover, recent advances in the use of bone-seeking radiopharmaceuticals make these attractive therapeutic candidates to combine with bisphosphonates or radiosensitizing drugs (e.g., bortezomib) to achieve a synergistic effect. As our understanding of the pathophysiology of myeloma bone disease continues to grow, new target therapies will continue to emerge, offering new and more advanced options for the management of myeloma bone disease.

Association of TNFSF11 gene promoter polymorphisms with bone mineral density in postmenopausal women

OBJECTIVES

The receptor activator of nuclear factor-kappaB ligand (RANKL) is recognized as one of the important regulators of osteoclastogenesis. The expression of the tumour necrosis factor superfamily, member 11 (TNFSF11) gene, which encodes for RANKL protein, is increased relative to the expression of osteoprotegrin in cases of senile osteoporosis with hip bone fracture. Our aim was to find polymorphisms in the TNFSF11 gene promoter and to investigate their possible association with bone mineral density (BMD).

METHODS

The TNFSF11 gene promoter region was screened for the presence of new sequence variations by direct sequencing. DNA sequencing revealed the presence of four sequence variations: -290C>T, -643C>T, -693G>C and -1594G>A. Association of the discovered polymorphisms with BMD was investigated in 115 Slovenian postmenopausal women, using restriction fragment length polymorphism analysis. After a year, bone loss in the association with the identified sequence variations was evaluated in 43 postmenopausal women.

RESULTS

Three of the discovered sequence variations (-290C>T, -643C>T, -693G>C) proved to be polymorphic, whereas variation -1594G>A was only found in one patient. The frequencies of genotypes were as follows: CC (27.8%), CT (43.5%), TT (28.7%) for -290C>T polymorphism; CC (23.5%), CT (47.8%), TT (28.7%) for -643C>T polymorphism; and GG (22.6%), GC (51.3%), CC (26.1%) for -693G>C polymorphism. A statistically significant association of genotype with BMD at the femoral neck was observed only in the -290C>T polymorphism. Genotype CC was associated with lower BMD than the TT genotype (P = 0.022). In polymorphism -693G>C, a significant difference in bone loss rate was observed in total hip (P = 0.011) and femoral neck BMD (P = 0.037).

CONCLUSIONS

Four sequence variations were identified in the studied region of TNFSF11 gene promoter. Our results of preliminary clinical evaluation suggest that the -290C>T polymorphism in the TNFSF11 gene promoter could contribute to the genetic regulation of BMD.

Identification of the osteoprotegerin/receptor activator of nuclear factor-kappa B ligand system in gingival crevicular fluid and tissue of patients with chronic periodontitis

BACKGROUND AND OBJECTIVE

Recent findings have suggested that osteoclastogenesis is directly regulated by receptor activator of nuclear factor-kappa B ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG). However, no studies have described interactions of OPG/RANKL and the gp130 cytokine family in periodontal disease. This study aimed to identify and quantify OPG/RANKL in the gingival crevicular fluid (GCF) and connective tissue of patients with periodontitis, and to clarify possible correlations with disease severity and interleukin-6 (IL-6) cytokines.

MATERIAL AND METHODS

Ninety-five sites in 20 patients with generalized chronic periodontitis were divided into four groups by site based on probing depth (PD) and bleeding on probing (BOP). In periodontitis patients, GCF was obtained using sterile paper strips from clinically healthy sites (PD <or= 3 mm without BOP, n = 12 in periodontitis subjects), mildly diseased sites (PD <or= 3 mm with BOP, n = 23), moderately diseased sites (PD <or= 4-6 mm with BOP, n = 33) and severely diseased sites (PD > 6 mm with BOP, n = 27). Fourteen clinically healthy sites from four periodontally healthy individuals were used as the control group. The levels of OPG, RANKL and two gp130 cytokines - IL-6 and oncostatin M (OSM) - in the GCF were determined by an enzyme-linked immunosorbent assay (ELISA) and are expressed as total amounts (pg/site). Immunohistochemical localization of OPG- and RANKL-positive cells was also performed on gingival connective tissues harvested from patients with periodontitis (inflammatory group, n = 8 biopsies) and from non-diseased individuals (healthy group, n = 8 biopsies).

RESULTS

GCF RANKL, but not OPG, was elevated in diseased sites of patients with periodontitis. However, the expressions of OPG and RANKL showed no correlation with disease severity (r = 0.174 and 0.056, respectively), but the content of RANKL in the GCF was significantly positively correlated with those of IL-6 (r = 0.207) and OSM (r = 0.231) (p < 0.01). Immunohistochemical staining showed that RANKL-positive cells were significantly distributed in the inflammatory connective tissue zone of diseased gingiva, compared with those of samples from non-diseased persons (p < 0.01). However, few OPG-positive cells were found in connective tissue zones of either the diseased gingiva or healthy biopsies.

CONCLUSION

These findings imply that in this cross-sectional study of GCF, RANKL, IL-6 and OSM were all prominent in periodontitis sites, whereas OPG was inconsistently found in a few samples of diseased sites but was undetectable in any of the control sites. The results also imply that the expression of RANKL was positively correlated with IL-6 and OSM in the GCF.

Serum markers of bone turnover in dialyzed patients separated according to age

BACKGROUND

Bone metabolism changes with aging in healthy population. Our aim was to determine serum markers of bone turnover in dialysis patients separated according to age.

METHODS

Peritoneal dialysis (PD) or hemodialysis (HD) patients were divided into two groups. Group I (n = 30) consisted of patients older than 65 years. Patients at the age less or equal 65 years were included in group II (n = 37). In all patients we determined serum concentration of intact parathyroid hormone (iPTH), cyclase activating parathyroid hormone (CAP), osteoprotegrin (OPG) and osteoprotegrin ligand (OPGL). Cyclase inactive parathyroid hormone (CIP) was calculated. Healthy volunteers (n = 13) at the age of 42.1 years (range 23.5-70.9 years) served as controls.

RESULTS

When results of dialysis patients were adjusted to gender, dialysis modality and duration, group I revealed significantly lower iPTH (113.0, 10.3-606.3 pg/ml), CAP (70.0, 6.5-442.6 pg/ml) and CIP (53.3, 3.3-214.4 pg/ml) than group II (310.6, 13.7-1266.9 pg/ml for iPTH; 205.0, 9.3-887.9 pg/ml for CAP; 76.0, 2.4-399.0 pg/ml for CIP), but this group showed significantly higher serum OPG (7.39, 1.52-15.84 pg/ml) than group II (5.45, 0.95-16.47 pg/ml) and controls (2.17, 1.05-3.95 pg/ml). Only patients of group II showed significantly higher iPTH, CAP and CIP than controls (34.9, 18.9-76.9 pg/ml; 24.3, 11.2-42.6 pg/ml, 12.0, 1.0-34.2 pg/ml, respectively for iPTH, CAP and CIP).

CONCLUSION

Our results suggest that age over 65 years is a risk factor for low bone turnover in dialyzed patients. An increase in serum OPG probably reflects a paracrine mechanism of bone cells to compensate for age dependent bone loss.

Myeloma bone disease and treatment options

Multiple myeloma (MM) is a B-cell malignancy characterized by enhanced bone loss commonly associated with a diffuse osteopenia, focal lytic lesions, pathologic fractures, hypercalcemia, and bony pain. Bone destruction in MM results from asynchronous bone turnover wherein increased osteoclastic bone resorption is not accompanied by a comparable increase in bone formation. Recent characterization of osteoclast-activating factors (OAFs), receptor activator of nuclear factor-kappaB (RANK) ligand (RANKL)-osteoprotegerin-RANK system, and inhibitors of Wnt signaling have provided a better understanding of myeloma bone disease in molecular level. The development of minimally invasive surgical procedures such as kyphoplasty and vertebroplasty allows myeloma patients with vertebral compression fractures to have immediate improvement in quality of life and shorter hospital stays. Monthly intravenous infusion of either pamidronate or zoledronic acid have reduced the skeletal complications among MM patients and are now a mainstay of myeloma therapy. Orally administered bisphosphonates, in contrast, have shown little ability to slow the development of skeletal complications in these patients. Although pre-clinical studies suggest nitrogen-containing bisphosphonates have potent anti-tumor effects, clinical trials will be necessary, probably at higher doses given more slowly, to establish their possible anti-tumor effects clinically. As our understanding of the pathophysiology of myeloma bone disease continues to increase, new target therapies will continue to emerge offering new and more advanced options for the management of myeloma bone disease.

Anti-RANKL therapy for inflammatory bone disorders: Mechanisms and potential clinical applications

Focal bone loss around inflamed joints in patients with autoimmune disease, such as rheumatoid arthritis, remains a serious clinical problem. The recent elucidation of the RANK/RANK-ligand/OPG pathway and its role as the final effector of osteoclastogenesis and bone resorption has brought a tremendous understanding of the pathophysiology of inflammatory bone loss, and has heightened expectation of a novel intervention. Here, we review the etiology of inflammatory bone loss, the RANK/RANK-ligand/OPG pathway, and the clinical development of anti-RANK-ligand therapy.

Imatinib as a potential antiresorptive therapy for bone disease

Osteoclasts (OCs) are large multinucleated cells derived from progenitor cells of the monocyte-macrophage lineage. Signal transduction via the macrophage–colony-stimulating factor (M-CSF) receptor, c-fms, is essential for OC formation. Since we have previously demonstrated inhibition of c-fms by imatinib, we examined the effect of imatinib on OC formation and activity. OC formation was not affected by concentrations of 1.0 μM imatinib and lower, but was reduced by 75% at 3.0 μM imatinib. In contrast, both the area of resorption and the number of resorption lacunae were reduced by 80% at 0.3 μM imatinib, and no resorption was observed at concentrations above 3.0 μM. A dose-dependent decrease in receptor activator of nuclear factor κB (RANK) expression was observed in OCs when cultured in the presence of imatinib, providing a mechanism for the decrease in OC function. In vivo analysis of the effect of imatinib on OC activity in adult mice following 8 weeks of imatinib treatment also demonstrated a decrease in OC activity. These results suggest that imatinib may have therapeutic value as an antiosteolytic agent in diseases such as osteoporosis, metastatic bone disease, and multiple myeloma.

The effects of thyrotropin-suppressive therapy on bone metabolism in patients with well-differentiated thyroid carcinoma

Patients with differentiated thyroid carcinoma (DTC) are commonly treated long-term with thyrotropin (TSH)- suppressive thyroxine replacement therapy resolving in a state of subclinical hyperthyroidism. The relationship between subclinical hyperthyroidism and osteoporosis is not clear. In this review, we systematically selected and analyzed 21 studies addressing this issue. Although multiple methodological differences between studies prevented a structured meta-analysis, our data suggest that postmenopausal women with subclinical hyperthyroidism are most at risk, whereas no increased risk was observed in men and premenopausal women. Based on these findings we believe that measurement of bone mineral density is recommended in postmenopausal women with DTC starting TSH suppressive therapy. This should be subsequently regularly measured to enable timely intervention with bone protective agents.

Carbonate Substituted Hydroxyapatite; Development and Function of Osteoclasts

Human osteoclasts derived from CD14+ precursors were cultured on discs of stoichiometric hydroxyapatite (HA) and carbonate substituted hydroxyapatite (CHA) of varying carbonate contents. Resorption of the ceramic increased with increasing carbonate content up to 2.35 wt. %. Development of osteoclasts is qualitatively different on ceramics compared to dentine, occurring in discrete, confluent subpopulations, which suggests local cell signalling may be important in the process. Resorption appears to drive further development of osteoclasts. Controlling carbonate content may be one way of controlling the rate of resorption of synthetic HA ceramics.

OSTEOIMMUNOLOGY: Interplay Between the Immune System and Bone Metabolism

Studies of bone and the immune system have converged in recent years under the banner of osteoimmunology. The immune system is spawned in the bone marrow reservoir, and investigators now recognize that important niches also exist there for memory lymphocytes. At the same time, various factors produced during immune responses are capable of profoundly affecting regulation of bone. Mechanisms have evolved to prevent excessive interference by the immune system with bone homeostasis, yet pathologic bone loss is a common sequela associated with autoimmunity and cancer. There are also developmental links, or parallels, between bone and the immune system. Cells that regulate bone turnover share a common precursor with inflammatory immune cells and may restrict themselves anatomically, in part by utilizing a signaling network analogous to lymphocyte costimulation. Efforts are currently under way to further characterize how these two organ systems overlap and to develop therapeutic strategies that benefit from this understanding.

Maturation-state dependent response of human periodontal ligament cells to an intermittent parathyroid hormone exposure in vitro

BACKGROUND AND OBJECTIVES

Parathyroid hormone (parathyroid hormone) has been shown to be capable of exerting anabolic effects on bone when administered intermittently. We hypothesized that parathyroid hormone will modulate the response of periodontal ligament cells in terms of anabolic effects with respect to proliferation, differentiation and the production of key regulatory factors of bone remodeling such as osteoprotegerin and receptor activator of nuclear factor kappaB ligand (RANKL) in a maturation-state dependent manner.

METHODS

Periodontal ligament cells were cultured from human bicuspids obtained from six patients. Following characterization, confluent and preconfluent periodontal ligament cells were challenged with parathyroid hormone (1-34) for 0, 1, 3, 6 or 24 h within three incubation cycles of 48 h each. At harvest, the cell number, alkaline phosphatase specific activity and osteocalcin, osteoprotegerin and RANKL production were determined by means of semiquantitative polymerase chain reaction (PCR) and immunoassays. Dermal fibroblasts and MG63 osteoblast-like cells served as a reference.

RESULTS

Intermittent parathyroid hormone treatment of confluent periodontal ligament cells caused a significant increase in proliferation (+32% maximum) whereas alkaline phosphatase activity, osteocalcin and osteoprotegerin decreased at the transcriptional and translational level (-59.7% maximum). In preconfluent periodontal ligament cells, parathyroid hormone induced a decrease in proliferation (-66.3% maximum) but an increase in differentiation and osteoprotegerin production (+49.2% maximum). RANKL was hardly detectable and unaffected by parathyroid hormone treatment. Similar results were obtained in MG63 cells, whereas parathyroid hormone stimulation did not alter any of the parameters examined in dermal fibroblasts.

CONCLUSION

These results indicate that human periodontal ligament cells respond to an intermittent parathyroid hormone exposure with changes in proliferation, differentiation and osteoprotegerin production in a maturation-state dependent manner and therefore might be regulatorily involved in periodontal regeneration.