Receptor activator of NF(Kappa)B ligand/osteoprotegerin (RANKL/OPG) system and osteopontin (OPN) serum levels in a population of apulian postmenopausal women

AIM: Osteoporosis is a bone disease, characterized by a reduction of bone resistance; in postmenopausal period bone metabolism is imbalanced. Several parameters have been proposed as markers of bone metabolism; the attention have been recently placed on the receptor of activator of NF(Kappa)B ligand receptor (RANKL) and osteoprotegerin (OPG), namely RANKL/OPG system. The aim of this paper is to evaluate changes in postmenopausal women in serum concentration of OPG, RANKL, and their ratio (i.e. RANKL/OPG ratio), osteopontin (OPN), bone-type alcaline phosphatase (BAP), serum-N-Telopeptide of type I collagen (serum-NTX); and their correlations with bone mineral density (BMD). METHODS: An Apulian population group of 163 native postmenopausal women were followed at the Osteoporosis Centre of Policlinico of Bari (Southenrn Italy). Patients were classified into 3 separate groups, according to T-score: osteoporotic, osteopenic and control group. Serum concentrations of OPG, RANKL, RANKL/OPG ratio, BAP and NTX have been calculated. RESULTS: No differences were found in OPG and BAP values. Significant correlations were found in the osteopenic group between OPG and RANKL (negative), and between RANKL and OPN or serum-NTX, OPN and serum-NTX or RANKL/OPG ratio, BAP and serum-NTX, serum-NTX and RANKL/OPG ratio (positive). In the other groups a significant correlation was observed between BAP and NTX. CONCLUSIONS: In postmenopausal women, important modifications of bone metabolism markers (i.e. RANKL, OPG and OPN) could be due to serious engagement of bone turnover, especially in the pre-osteoporotic phase. Low bone density in postmenopausal women should be identified as soon as possible, and urgent measures are needed to reverse the process. Parameters namely RANKL e OPG may become an important index for the evaluation of the activity of drugs against osteoporosis, old and new like AMG 162 (anti-RANKL action).     

New paradigms in the regulation of bone metabolism

Although multiple hormones and cytokines regulate various aspects of osteoclast formation, the two final effectors, osteoprotegerin (OPG) and its ligand (OPGL/RANKL) have been recently identified. Since then, there have been important advances in the understanding of the molecular mechanisms that regulate the crosstalk between osteoblasts/stromal and hematopoietic osteoclast precursor cells. In this article, we describe the new concepts from the identification of OPG, a protein with potent osteoclastogenesis inhibitory activity, to the isolation of RANKL, a transmembrane ligand expressed on osteoblasts/stromal cells that bind to RANK, a transmembrane receptor on osteoclast cells and its precursors. The interaction between RANK and RANKL triggers a series of mechanisms that result in differentiation, maturation and activation of osteoclasts. OPG inhibits osteoclastogenesis binding to RANKL and blocks its interaction with RANK. Many hormones and cytokines, like PTH and IL-11, act inhibiting production of OPG and stimulating production of RANKL. Contrary to this, estrogens inhibit production of RANKL and RANKL-stimulated osteoclastogenesis. The knowledge of the RANK/RANKL/OPG system and the understanding of osteoclast differentiation and activation has had a great impact on the field of bone metabolism, with new possible treatment strategies for diseases characterized by excessive bone resorption.     

Osteoprotegerin and its ligand: A new paradigm for regulation of osteoclastogenesis and bone resorption

In just 3 years, striking new advances have been made in understanding the molecular mechanisms that govern the crosstalk between osteoblasts/stromal cells and hemopoietic osteoclast precursor cells that leads to osteoclastogenesis. Led first by the discovery of osteoprotegerin (OPG), a naturally occurring protein with potent osteoclastogenesis inhibitory activity, rapid progress was made to the isolation of RANKL, a transmembrane ligand expressed on osteoblasts/stromal cells, that binds to RANK, a transmembrane receptor on hemopoietic osteoclast precursor cells. The interaction of RANK and RANKL initiates a signaling and gene expression cascade that results in differentiation and maturation of osteoclast precursor cells to active osteoclasts capable of resorbing bone. Osteoprotegerin acts as a decoy receptor; it binds to RANKL and blocks its interaction with RANK, thus inhibiting osteoclast development. Many of the calciotropic hormones and cytokines, including vitamin D3, parathyroid hormone, prostaglandin E2 and interleukin-11, appear to stimulate osteoclastogenesis through the dual action of inhibiting production of OPG and stimulating production of RANKL. Estrogen, on the other hand, appears to inhibit production of RANKL and RANKL-stimulated osteoclastogenesis. Recently, the results of the first clinical trial with OPG supported its potential as a therapeutic agent for osteoporosis. The new understanding provided by the RANK/RANKL/OPG paradigm for both differentiation and activation of osteoclasts has had tremendous impact on the field of bone biology and has opened new avenues for development of possible treatments of diseases characterized by excessive bone resorption.     

Bone lesions in multiple myeloma--the OPG/RANK-ligand system

Multiple myeloma has recently been found to induce considerable imbalance in the newly identified system of osteoprotegerin (OPG), receptor activator of nuclear factor KB ligand (RANKL) and RANK. The binding of RANKL to RANK on the surface of osteoclastic precursors in the presence of m-CSF activates the signalling pathways for differentiation and proliferation of an osteoclastic line. OPG is a decoy circulating receptor for RANKL which blocks its binding to RANK. There are at least three mechanisms by which myeloma cells affects the OPG/ RANKL/RANK system: 1: The adhesion between the myeloma / stromal cells and the osteoblastic precursors stimulates the system by increasing the production of RANKL. 2: Some myeloma lines produce independently membrane-bound or free RANKL. 3: The normal and mutated plasma cells bind, degrade and block the OPG production from the stromal cells. The OPG/RANKL/RANK system is the latest therapeutic target in the treatment of myeloma bone disease. The first results from the application of a synthetic analogue of OPG, as well as of RANKL antagonists or RANK inhibitors show decrease of the number of osteoclasts, osteolytic lesions and M-gradient.     

Serum osteoprotegerin levels are related to height loss: The Tromsø Study

Severe loss of body height is often a consequence of osteoporotic vertebral fractures. Osteoprotegerin (OPG) and receptor activator of nuclear factor-kB ligand (RANKL) are cytokines essential for the regulation of bone resorption. The aim of this study was to assess the relationship between the OPG/RANKL system and height loss. A total of 4,435 inhabitants from the municipality of Tromsø, Norway (2,169 men and 2,266 women) were followed for 6 years. Baseline measurements included height, weight, bone mineral density, OPG, RANKL, serum parathyroid hormone and information about lifestyle, prevalent diseases and use of medication. Height was measured again at follow-up, and the loss of height was categorized into 4 groups: ≤1, 1.1–2, 2.1–3, >3 cm. We found increasing height loss with increasing baseline OPG levels in both men and women (P trend = 0.02 and 0.001, respectively), after adjustments for age and other confounders. However, when the women were stratified according to menopausal status and use of hormone replacement therapy (HRT), a significant relationship was present only among postmenopausal women not using HRT (P trend = 0.02). No relations between OPG and height loss were found in post-menopausal HRT-users and premenopausal women (P trend ≥0.39). We conclude that height loss is positively associated with OPG in men and in postmenopausal women not using HRT. No relationship was found between RANKL and height loss.     

1α,25(OH)_2D_3对大鼠成骨细胞КB受体活化因子配体及骨保护素蛋白表达的影响

目的研究1α,25-二羟维生素D3(1α,25(OH)2D3)对体外培养3～4d的SD大鼠成骨细胞(OB)核因子κB受体活化因子配体(RANKL)及骨保护素(OPG)蛋白和mRNA表达的影响。方法1α,25(OH)2D3作用24、48、72h,分别采用ELISA及FQ-PCR法测定。结果10、100nmol/L1α,25(OH)2D3较对照及1nmol/L显著或极显著促进RANKL蛋白及mRNA表达;1、10nmol/L1α,25(OH)2D3较对照显著或极显著促进OPG蛋白及mRNA表达,而100nmol/L则极显著抑制OPGmRNA表达;RANKLmRNA/OPGmRNA及RANKL/OPG显示,1nmol/L组与对照组差异不显著,10、100nmol/L组RANKLmRNA/OPGmRNA及RANKL/OPG极显著高于对照组和1nmol/L组。结论低浓度1α,25(OH)2D3(1nmol/L)对骨更新作用不明显,而中、高浓度1α,25(OH)2D(310、100nmol/L)能通过上调RANKLmRNA/OPGmRNA及RANKL/OPG比例,促进OC的生成及骨吸收功能,增强骨更新。     

Serum osteoprotegerin and RANKL levels in chronic alcoholic liver disease

OBJECTIVES: Osteoprotegerin (OPG) is a decoy receptor that binds RANK-ligand (RANKL) and prevents osteoclast activation. Oestrogens, androgens, corticosteroids, parathyroid hormone (PTH), vitamin D, and several cytokines exert their effects on bone modulating the OPG/RANKL system. Since these substances become altered in chronic alcoholic liver disease, we investigated the OPG/RANKL system in alcoholic liver disease, its relation with bone mineral density (BMD) and with several hormones and cytokines. METHODS: Serum OPG, RANKL, C-terminal cross-linking telopeptide of type 1 collagen, osteocalcin, insulin-like growth factor 1 (IGF-1), 1,25 dihydroxyvitamin D, IL-6, tumour necrosis factor (TNF)-alpha, PTH, estradiol, free testosterone and corticosterone were measured in 77 male alcoholic patients, 25 of them cirrhotics. All these patients underwent assessment of BMD at lumbar spine and left hip by a Hologic QDR-2000 (Waltham, MA) bone densitometer. Nineteen non-drinkers male sanitary workers of similar age served as controls. RESULTS: Serum OPG levels were higher in patients (12.66 +/- 6.44 pmol/l) than in controls (6.59 +/- 1.58 pml/l, P < 0.005), especially in cirrhotics (15.97 +/- 7.03 pmol/l) vs non-cirrhotics (10.96 +/- 5.45 pmol/l, P < 0.001). Patients also showed higher telopeptide levels (0.60 +/- 0.36 vs 0.20 +/- 0.10 nmol/100 ml, P < 0.001), less IGF-1 [median = 192, interquartile range (IQR) = 46.7-175.99 ng/ml vs 150, IQR = 118.8-239.4 ng/ml, P < 0.001], vitamin D (25.5, IQR = 18.25-35 pg/ml vs 77.89, IQR = 57.48-98.53 pg/ml, P < 0.001) and osteocalcin (1.8, IQR = 1-3.6 ng/ml vs 6.04, IQR = 4.63-8.20 ng/ml, P < 0.001) than controls, but no differences in PTH and RANKL. Patients also showed lower Z-scores than controls at trochanter (-0.36 +/- 1.10 vs 0.26 +/- 0.87 in controls, P = 0.026), intertrochantereal area (-0.56 +/- 1.16 vs 0.46 +/- 1.01, P = 0.001), and total hip (-0.44 +/- 1.12 vs 0.42 +/- 1, P = 0.003). TNF-alpha levels were higher in patients (7.40, IQR = 4.30-17.80 pg/ml) than in controls (5.10, IQR = 4.40-8 pg/ml, P = 0.009), especially in cirrhotics (median = 13.90, IR = 6.10-21.10 pg/ml). OPG levels showed strong correlations with TNF-alpha (rho = 0.57, P < 0.001) and IL-6 (r = 0.62, P < 0.001), but not with BMD. Estradiol levels (31.83 +/- 13.11 pg/ml) were higher and free testosterone lower (13.62 +/- 11.96 pg/ml) in patients than in controls (20.36 +/- 3.08 and 18.19 +/- 4.68 pg/ml, respectively, P < 0.001 in both cases). CONCLUSION: OPG is raised in alcoholics, especially in cirrhotics, showing no relationship with decreased BMD. Also, raised TNF and IL-6 were observed, and were strongly, directly related with OPG levels. Since TNF and IL-6 enhance bone resorption, their relation with OPG suggests a protective effect of raised OPG on bone loss.     

1α,25(OH)_2D_3对大鼠成骨细胞κB受体活化因子配体及骨保护素蛋白表达的影响

目的 研究1α,25-二羟维生素D_3(1α,25(OH)_2D_3)对体外培养3～4 d的SD大鼠成骨细胞(OB)核因子κ B受体活化因子配体(RANKL)及骨保护素(OPG)蛋白和mRNA表达的影响.方法 1α,25(OH)_2D_3作用24、48、72 h,分别采用ELISA及FQ-PCR法测定.结果 10、100 nmol/L 1α,25(OH)_2D_3较对照及1 nmol/L显著或极显著促进RANKL蛋白及mRNA表达;1、10 nmol/L 1α,25(OH)_2D_3较对照显著或极显著促进OPG蛋白及mRNA表达,而100 nmol/L则极显著抑制OPG mRNA表达;RANKL mRNA/OPG mRNA及RANKL/OPG显示,1 nmol/L组与对照组差异不显著,10、100 nmol/L组RANKL mRNA/OPG mRNA及RANKL/OPG板显著高于对照组和1 nmol/L组.结论 低浓度1α,25(OH)_2D_3(1 nmol/L)对骨更新作用不明显,而中、高浓度1α,25(OH)_2D_3(10、100 nmol/L)能通过上调RANKL mRNA/OPG mRNA及RANKL/OPG比例,促进OC的生成及骨吸收功能,增强骨更新.     

Osteoprotegerin: regulator, protector and marker

Experimental and clinical trials in the field of bone biology helped to clarify the role of receptors, which belong to the tumor necrosis factor family, such as osteoprotegerin and receptor activator of nuclear factor kappaB (RANK), in the regulation of bone remodeling. The ligand of the receptor activator of nuclear factor kappaB (RANKL) is a stimulator of bone resorption, while osteoprotegerin is the soluble "decoy" receptor to RANKL, protecting thereby bone from resorption. Pathological states of bone remodeling (like osteoporosis) are associated with imbalance in the activity of osteoprotegerin and the receptor activator of nuclear factor kappaB. Recent studies, however, also indicate that the osteoprotegerin/RANKL/RANK system has important roles in the regulation of the immune and vascular system as well. In this review we summarize the function and regulation of osteoprotegerin, its role in pathological states--primarily in cardiovascular diseases--and its relevance as a marker of cardiovascular risk. Finally, we present our prospective trial performed among the chronic dialyzed patients, where we examined the association between the cardiovascular mortality, osteoprotegerin levels and the arterial stiffness.     

Pathophysiology of Vascular Calcification and Bone Loss: Linked Disorders of Ageing?

Vascular Calcification (VC), low bone mass and fragility fractures are frequently observed in ageing subjects. Although this clinical observation could be the mere coincidence of frequent age-dependent disorders, clinical and experimental data suggest that VC and bone loss could share pathophysiological mechanisms. Indeed, VC is an active process of calcium and phosphate precipitation that involves the transition of the vascular smooth muscle cells (VSMCs) into osteoblast-like cells. Among the molecules involved in this process, parathyroid hormone (PTH) plays a key role acting through several mechanisms which includes the regulation of the RANK/RANKL/OPG system and the Wnt/ß-catenin pathway, the main pathways for bone resorption and bone formation, respectively. Furthermore, some microRNAs have been implicated as common regulators of bone metabolism, VC, left ventricle hypertrophy and myocardial fibrosis. Elucidating the common mechanisms between ageing; VC and bone loss could help to better understand the potential effects of osteoporosis drugs on the CV system.     

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 cy-tokines as primary mediators of the accelerated bone loss at menopause including interleukin-1, tumor necrosis factor-α, 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 ofRANKL, 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.     

Bovine Colostrum Supplementation Improves Bone Metabolism in an Osteoporosis-Induced Animal Model

Osteoporosis is characterized by bone loss. The present study aims to investigate the effects of bovine colostrum (BC) on bone metabolism using ovariectomized (OVX) and orchidectomized (ORX) rat models. Twenty-seven-week-old Wistar Han rats were randomly assigned as: (1) placebo control, (2) BC supplementation dose 1 (BC1: 0.5 g/day/OVX, 1 g/day/ORX), (3) BC supplementation dose 2 (BC2: 1 g/day/OVX, 1.5 g/day/ORX) and (4) BC supplementation dose 3 (BC3: 1.5 g/day/OVX, 2 g/day/ORX). Bone microarchitecture, strength, gene expression of VEGFA, FGF2, RANKL, RANK and OPG, and bone resorption/formation markers were assessed after four months of BC supplementation. Compared to the placebo, OVX rats in the BC1 group exhibited significantly higher cortical bone mineral content and trabecular bone mineral content (p < 0.01), while OVX rats in the BC3 group showed significantly higher trabecular bone mineral content (p < 0.05). ORX rats receiving BC dose 2 demonstrated significantly higher levels of trabecular bone mineral content (p < 0.05). Serum osteocalcin in the ORX was pointedly higher in all BC supplementation groups than the placebo (BC1: p < 0.05; BC2, BC3: p < 0.001). Higher doses of BC induced significantly higher relative mRNA expression of OPG, VEGFA, FGF2 and RANKL (p < 0.05). BC supplementation improves bone metabolism of OVX and ORX rats, which might be associated with the activation of the VEGFA, FGF2 and RANKL/RANK/OPG pathways.     

糖皮质激素在影响骨形成和骨吸收方面引起骨质疏松的机制研究进展

糖皮质激素（glucocorticoid．GC）在临床应用广泛,其主要的副作用之一是对骨的影响,导致糖皮质激素性骨质疏松（glucocorticoid induced osteoporosis．GIOP）的风险显著增加。目前研究认为其机制为：糖皮质激素通过调高细胞外因子DKK1、SFRPs的表达水平抑制Wnt/β-catenin信号通路,从而抑制骨细胞形成;通过增强成骨负性因子SOST、PPARγ2的活性,弱化成骨活性因子Cbfal、IGF-1的表达来抑制骨形成。同时通过调节OPG/RANKL/RANK途径促进骨吸收。本文从糖皮质激素对骨形成和骨吸收两个方面的影响对糖皮质激素性骨质疏松的发生机制进行探讨,综述了近几年国内外对糖皮质激素性骨质疏松的研究现状,以此为该疾病的治疗提供相关理论帮助。     

Improvement of bone formation biomarkers after 1-year consumption with milk fortified with eicosapentaenoic acid,docosahexaenoic acid,oleic acid,and selected vitamins

The hypothesis of this study was that the replacement of regular milk with fortified milk in hyperlipidemic adults for 1 year would improve bone biomarkers. The fortified milk contained eicosapentaenoic acid and docosahexaenoic acid from fish oils, oleic acid, vitamins A, B₆, and E, as well as folic acid. We believe that the fortified milk will improve the blood fatty acid profile and vitamin status in subjects to benefit bone health biomarkers. From the 84 patients who accepted to participate, 11 of these were excluded for the presence of metabolic diseases and 1 was excluded for noncompliance with the protocol. Seventy-two hyperlipidemic patients (35-65 years) were randomly divided between 2 study groups. The supplement group (E; n = 39) consumed 0.5 L/d of fortified milk that contained fish oil, oleic acid, and vitamins. The control group (C; n = 33) consumed 0.5 L/d of semiskimmed milk containing the same amount of total fat. Blood samples were taken at T₀, T₃, T₆, and T₁₂ months to determine plasma fatty acids, vitamins B₆, E, and 25-hydroxyvitamin D and serum folate, calcium, soluble osteoprotegerin (OPG), soluble receptor activator of NF-κB ligand (RANKL), osteocalcin, parathormone, type I collagen carboxy-terminal telopeptide, and malondialdehyde. After 1 year, the E group showed a significant increase in plasma eicosapentaenoic acid (42%), docosahexaenoic acid (60%), vitamin B6 (38%), OPG (18%), RANKL (7%), OPG/RANKL (10%), red blood cell folate (21%), serum folate (53%), calcium (4%), vitamin D (11%), and osteocalcin (22%). Dietary supplementation with the fortified milk drink improved nutritional status and bone formation markers in adult hyperlipidemic patients.     

Genistein modulates the effects of parathyroid hormone in human osteoblastic SaOS-2 cells

Genistein and parathyroid hormone (PTH) are anabolic agents that stimulate bone formation through their direct actions in osteoblastic cells. In the present study, we aimed to determine whether genistein modulates the actions of PTH in human osteoblastic SaOS-2 cells in an oestrogen-depleted condition. The present results showed that genistein (10(-8) to 10(-6) m) induced alkaline phosphatase (ALP) activity and osteoprotegrin (OPG) expression in SaOS-2 cells in a dose-dependent manner. These effects could be completely abolished by co-treatment with oestrogen antagonist ICI 182780 (7alpha-[9-[(4,4,5,5,5-pentafluoropentyl)sulfonyl]nonyl]-estra-1,3,5(10)-triene-3,17beta-diol). Genistein (at 1 microM) could stimulate the mRNA expression of receptor activator of NF-kappaB ligand (RANKL). As OPG and RANKL are known to modulate osteoclastogenesis, the ability of genistein to modulate OPG and RANKL expression in SaOS-2 cells suggested that it might modulate osteoclastogenesis through its direct actions on osteoblastic cells. PTH (at 10 nM) stimulated ALP activity, induced RANKL mRNA expression and suppressed OPG mRNA expression in SaOS-2 cells, confirming its bi-directional effects on osteoblastic cells. Pre-treatment of SaOS-2 cells with genistein and oestrogen not only enhanced PTH-induced ALP activity, but also attenuated PTH up regulation of RANKL mRNA expression and PTH down regulation of OPG mRNA expression. Taken together, the present study provides the first evidence that genistein could modulate the actions of PTH in human osteoblastic SaOS-2 cells in an oestrogen-depleted condition.     

Effect of dietary legumes on bone-specific gene expression in ovariectomized rats

In previous studies, we found that the consumption of legumes decreased bone turnover in ovariectomized rats. The purpose of the present study is to determine whether the protective effects on bone mineral density (BMD) and the microarchitecture of a diet containing legumes are comparable. In addition, we aim to determine their protective actions in bones by studying bone specific gene expression. Forty-two Sprague-Dawley rats are being divided into six groups during the 12 week study: 1) rats that underwent sham operations (Sham), 2) ovariectomized rats fed an AIN-93M diet (OVX), 3) ovariectomized rats fed an AIN-93M diet with soybeans (OVX-S), 4) ovariectomized rats fed an AIN-93M diet with mung beans (OVX-M), 5) ovariectomized rats fed an AIN-93M diet with cowpeas (OVX-C), and 6) ovariectomized rats fed an AIN-93M diet with azuki beans (OVX-A). Consumption of legumes significantly increased BMD of the spine and femur and bone volume of the femur compared to the OVX. Serum calcium and phosphate ratio, osteocalcin, expression of osteoprotegerin (OPG), and the receptor activator of nuclear factor κB ligand (RANKL) ratio increased significantly, while urinary excretion of calcium and deoxypyridinoline and expression of TNF-α and IL-6 were significantly reduced in OVX rats fed legumes, compared to OVX rats that were not fed legumes. This study demonstrates that consumption of legumes has a beneficial effect on bone through modulation of OPG and RANKL expression in ovariectomized rats and that legume consumption can help compensate for an estrogen-deficiency by preventing bone loss induced by ovarian hormone deficiency.     

Integrin antagonists as inhibitors of bone resorption: implications for treatment.

Currently 'accepted' treatments for bone disease utilise drugs that inhibit osteoclastic bone resorption; these lead to a reduction in subsequent bone loss and thence, indirectly, to an increase in bone mass and fewer fractures. Three classes of compounds currently form the mainstay of therapy for osteoporosis: oestrogens (hormone-replacement therapy), 'selective oestrogen receptor modulators' and the bisphosphonates. Problems of patient compliance, real or theoretical long-term toxicological risks and the lack of bone anabolic agents of clinical utility suggest that there is a need for the development of further novel osteoclast resorption inhibitors. Recent biological and genetic findings in the area of bone cell function have led to the identification of new drug targets. These drugs include agents that (directly or indirectly): inhibit osteoclast adhesion to bone matrix; modify osteoclast differentiation; act on the proton pump and hence affect extracellullar acidification; antagonise extracellular enzymes that are involved in bone matrix protein degradation. Particular emphasis is placed in the present review on the evaluation of antagonists of alphavbeta3 integrin-mediated cell adhesion for use in bone disease. The wealth of new agents being developed suggests that resorption inhibition will be the best treatment for osteoporosis in the short to medium term, with the long-term aim still being toward developing anabolic drugs or cell therapeutics.     

Inhibition of osteoporosis in autoimmune disease prone MRL/Mpj-Fas(lpr) mice by N-3 fatty acids

OBJECTIVE: Rheumatoid arthritis (RA) is a systemic autoimmune inflammatory disease involving the breakdown of cartilage and juxta-articular bone, which is often accompanied by decreased bone mineral density (BMD) and increased risk of fracture. Anti-inflammatory omega-3 fatty acids may prevent arthritis and bone loss in MRL/lpr mice model of arthritis and in humans. METHODS: In this study, the effect of long term feeding of 10% dietary n-3 (fish oil (FO)) and n-6 (corn oil (CO)) fatty acids begun at 6 weeks of age on bone mineral density (BMD) in different bone regions in an MRL/lpr female mouse model of RA was measured at 6, 9, and 12 months of age by dual energy x-ray absorptiometry (DEXA). After sacrificing the mice at 12 months of age, antioxidant enzyme activities were measured in spleen, mRNA for receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG) was measured by RT-PCR in lymph nodes, and synovitis was measured in leg joints. RESULTS: At 6, 9 and 12 months of age, BMD was significantly higher (p < 0.05) in distal femur, proximal tibia, and lumbar spine of FO fed mice than those of CO fed mice. Spleen catalase (CAT) and superoxide dismutase (SOD) activities were also significantly higher (p < 0.01) in FO fed mice than in CO fed mice. Histology of knee joints revealed mild synovitis in CO fed mice, which was not present in FO fed mice. RT-PCR analysis of lymph nodes revealed decreased RANKL mRNA (p < 0.001) expression and enhanced OPG mRNA expression (p < 0.01) in FO fed mice compared to CO fed mice. CONCLUSIONS: These results suggest beneficial effects of long-term FO feeding in maintaining higher BMD and lower synovitis in this mouse model. These beneficial effects may be due, in part, to increased activity of antioxidant enzymes, decreased expression of RANKL, and increased expression of OPG in FO fed mice thereby altering the RANKL/OPG ratio. These significant beneficial effects on BMD suggest that FO may serve as an effective dietary supplement to prevent BMD loss in patients with RA.     

Hijikia fusiforme protects against ovariectomy-induced bone loss in rats

The prophylactic effects of Hijikia fusiforme on bone metabolism were examined using in vitro indices of bone formation and resorption. As the indices of bone formation, osteoblast proliferation and differentiation were measured through mitochondrial enzyme activity [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay] and bone marker alkaline phosphatase (ALP) activity. The aqueous extract of H. fusiforme stimulated the proliferation of the human osteoblast-like cell line MG63 and the ALP activity of the mouse osteoblast-like cell line MC3T3-E1. Moreover, extracellular matrix mineralization was accelerated by the addition of H. fusiforme. As the indices of bone resorption, differentiation of the murine macrophage/osteoclast precursor cell line RAW 264.7 by receptor activator of nuclear factor-κB ligand (RANKL) was measured as tartrate-resistant acid phosphatase-positive multinucleated cells, which were suppressed by H. fusiforme. Additionally, H. fusiforme lowered the secreted amount of RANKL that is required for the osteoclastic differentiation and activation, but the amount of osteoprotegerin as a decoy receptor for RANKL was not affected. The bone-protective effects of H. fusiforme in estrogen-deficient ovariectomized rats were also investigated. Osteoporosis was induced in female Sprague-Dawley rats by ovariectomy for 15 weeks, and then H. fusiforme was orally administered at a dose of 100 mg/kg of body weight every day for 6 weeks. Bone mineral density in the group orally administered H. fusiforme was increased, compared with ovariectomized rats, but not significantly (P>.05). Oral administration of H. fusiforme improved microarchitecture of bone in terms of bone volume (bone volume/total volume ratio) and trabecular separation (P<.05). The amounts of osteocalcin and C-telopeptide type I collagen in serum were measured as the biomarkers for bone formation and resorption. The level of osteocalcin in serum was increased, but not significantly. However, the level of C-telopeptide type I collagen in serum was significantly decreased (P<.05). When the results are taken together, the present study indicates that H. fusiforme might be useful in the treatment of osteoporosis.     

Irradiation effect on osteoclastogenesis stimulated by breast cancer cells

To examine the effects of carbon ion and gamma ray irradiation on cancer-induced osteoclastogenesis, mouse calvaria MC3T3-E1 cells were cultured with conditioned medium from irradiated and non-irradiated MCF7 human breast cancer cells. The authors examined RANKL and OPG mRNA expression in osteoblastic MC3T3-E1 cells following treatment with conditioned MCF7 medium. Co-cultured MC3T3-E1 and bone marrow cells treated with conditioned medium from irradiated MCF7 cells showed decreased numbers of osteoclasts, assessed using TRAP staining. Conditioned medium from control MCF7 cells elevated the RANKL/OPG mRNA ratio in MC3T3-E1 cells; this effect was suppressed by carbon ion irradiation of the MCF7 cells. These data demonstrate that indirect interactions between breast cancer cells and MC3T3-E1 cells induce osteoclastogenesis in vitro through modulation of RANKL expression and that this process is suppressed by carbon ion irradiation.