Changes in receptor activator of nuclear factor-kappaB, and its ligand, osteoprotegerin, bone-type alkaline phosphatase, and tartrate-resistant acid phosphatase in ovariectomized rats

Bone Remodeling in Mandible of Wistar Rats with Diabetes Mellitus and Osteoporosis

OBJECTIVES

 This study aimed to determine some of bone molecular expressions and its possible bone remodeling pathway between diabetes mellitus (DM) and osteoporosis model in the mandibular bone of Wistar rats.

MATERIALS AND METHODS

 Twenty-seven female Wistar rats were divided randomly into control and treatment groups. Treatment groups were injected with streptozotocin intraperitoneally to induce DM (P1) and underwent bilateral ovariectomy to generate osteoporosis (P2). All groups were terminated after 12 weeks. Immunohistochemical and hematoxylin-eosin staining were performed to determine the expression of Runt-related transcription factor 2 (RUNX2), Osterix, vascular endothelial growth factor (VEGF), receptor activator of nuclear factor κB ligand (RANKL), osteoprotegerin (OPG), tartrate-resistant acid phosphatase (TRAP), and observed the osteoblast and osteoclast. Statistical analysis was performed using one-way analysis of variance.

RESULTS

 The lowest mean of RUNX2 and VEGF expression was found in the P2 group. The lowest mean of Osterix expression was found in the P1 group. Both P1 and P2 groups of osteoblast/osteoclast ratio were decreased. There were no significant differences in the expression of TRAP between all groups; however, increased expression of RANKL/OPG ratio was only found in the P2 group.

CONCLUSION

 DM and osteoporosis induce changes in the bone remodeling pathway which are represented by a decrease in osteoblast biomarkers and an increase in osteoclast biomarkers.

Novel osteoprotective nanocochleate formulation: A dual combination therapy-codelivery system against glucocorticoid induced osteoporosis

Phosphatidylserine nanocochleates (Nanocochs) are novel delivery systems that may play a prominent osteoprotective role with their cargo, vitamin D3 (Vit-D3), against osteoporosis. Therefore, this study was conducted to characterize a Nanococh containing vitamin D3 (Nanococh-D3) and investigate its potential role in improving GIO in a rat model. Roll-shaped Nanococh-D3 particles were obtained in a size range of 320 nm with a sustained release performance. Oral Nanococh-D3 significantly increased the bioavailability of Vit-D3, enhanced bone mechanical strength, and improved osteogenic biomarkers including B-ALP, osteocalcin, Ca, and OPG in GIO rats. This formulation markedly suppressed gene expression of RANK and RANKL in treated rats. Histomorphometric analysis showed significant repairs in bone tissues and TRAP staining indicated a significant decrease in osteoclasts using Nanococh-D3 in osteoporotic rats. Nanococh alone similar to Nanococh-D3 acted better than AL as a standard anti-osteoporotic drug in the improvement of bone strength. In conclusion, our results established the potential role of Nanococh-D3 against osteoporosis in rats.

Chaenomelis fructus inhibits osteoclast differentiation by suppressing NFATc1 expression and prevents ovariectomy-induced osteoporosis

Background

Osteoporosis is related to the number and activity of osteoclasts. The goal of the present study was to demonstrate the effect of Chaenomelis Fructus (CF) on osteoclastogenesis and its mechanism of bone loss prevention in an OVX-induced osteoporosis model.

Methods

Osteoclasts were induced by RANKL in RAW 264.7 cells. TRAP assay was performed to measure the inhibitory effect of CF on osteoclast differentiation. Then, Expression of nuclear factor of activated T-cells (NFATc1), c-Fos which are essential transcription factors in osteoclastogenesis were detected using western blot and RT-PCR. The osteoclast-related markers were measured by RT-PCR. Moreover, the ability of CF to inhibit bone loss was researched by ovariectomized (OVX)-induced osteoporosis.

Results

Cell experiments showed that CF inhibited osteoclast differentiation and its function. Immunoblot analyses demonstrated that CF suppressed osteoclastogenesis through the NFATc1 and c-Fos signaling pathways. RT-PCR determined that CF inhibited osteoclast-related markers, such as tartrate-resistant acid phosphatase (TRAP), cathepsin K (CTK), osteoclast-associated immunoglobulin-like receptor (OSCAR), ATPase H+ Transporting V0 Subunit D2 (ATP6v0d2) and carbonic anhydrase II (CA2). In animal experiments, CF showed an inhibitory effect on bone density reduction through OVX. Hematoxylin and eosin (H&E) staining analysis data showed that CF inhibited OVX-induced trabecular area loss. TRAP staining and immunohistochemical staining analysis data showed that CF displayed an inhibitory effect on osteoclast differentiation through NFATc1 inhibition in femoral tissue.

Conclusion

Based on the results of in vivo and in vitro experiments, CF inhibited the RANKL-induced osteoclasts differentiation and its function and effectively ameliorated OVX-induced osteoporosis rats.

Heamatococcus pluvialis ameliorates bone loss in experimentally-induced osteoporosis in rats via the regulation of OPG/RANKL pathway

BACKGROUNDS

Osteoporosis prevailing in elderly involves a marked increase in bone resorption showing an initial fall in bone mineral density leading to a significant reduction in bone formation.

AIM

The present study aimed to investigate the effect of Heamatococcus pluvialis microalgae on osteoporosis in D-galactose-treated rats. The underlying mechanism was tracked targeting the osteoprotegerin (OPG)/ nuclear factor-κβ ligand (RANKL) pathway using micro-computed tomography scanning.

METHODS

Osteoporosis was induced in rats by intraperitoneal injection of D-galactose (200 mg/kg/day) for eight consecutive weeks. Osteoporotic rats were orally treated with H. pluvialis biomass (BHP; 450 mg/kg), its polar (PHP; 30 mg/kg) and carotenoid (CHP; 30 mg/kg) fractions for the last 2 weeks of D-Gal injection. Twenty four hours after the last dose of the treatments, tibia bones of the rats were scanned using micro-computed tomography scanning for bone mineral density (BMD), bone volume fraction (BV/TV), trabecular thickness/separation/number (Tb.Th, Tb.Sp, Tb.N) evaluation, blood samples were withdrawn and sera were used for biochemical assessment. Moreover, femur bones were examined histopathologically using several stains.

RESULTS

Induction of osteoporosis was associated with a marked reduction in BMD, BV/TV, Tb.Th, Tb.Sp, Tb.N and in serum levels of phosphorus and catalase. On the other hand, a significant elevation in serum levels of calcium, bone alkaline phosphatase (BALP) and interleukin-6 was observed. Moreover, up-regulation of OPG was detected in osteoporotic rats. Oral treatment with BHP, and PHP incremented tibia BMD and serum phosphorus level along with the decrease in serum levels of calcium, BALP, interleukin-6, OPG and RANKL. However, treatment with CHP almost restored all the fore mentioned parameters to normal values. Furthermore, the histopathological evaluation emphasized the biochemical outcomes.

CONCLUSION

H. pluvialis fractions rich in astaxanthin ameliorated bone loss in experimentally-induced osteoporosis in rats probably through the down-regulation of serum OPG in concurrence with up-regulation of serum RANKL.

Effects of Amlodipine on Bone Metabolism in Orchidectomised Spontaneously Hypertensive Rats

Spontaneously hypertensive rats (SHR) represent a model of essential hypertension. We studied the effect of amlodipine (AML) on bone markers, bone mineral density (BMD), and biomechanical properties of osteopenic bone induced by orchidectomy in male SHR. Rats were allocated to 3 groups and were sacrificed after 12 weeks: sham-operated control; orchidectomised control; and orchidectomised receiving a diet supplemented with AML. Indicators of bone turnover were assessed in bone homogenate, BMD was measured by dual energy X-ray absorptiometry, and the femurs were subjected to biomechanical testing. Long-term AML administration does not have a negative impact on bone metabolism and density in male SHR.

Site-Specific Variations in Bone Mineral Density under Systemic Conditions Inducing Osteoporosis in Minipigs

Osteoporosis is a systemic bone disease with an increasing prevalence in the elderly population. There is conflicting opinion about whether osteoporosis affects the alveolar bone of the jaws and whether it poses a risk to the osseointegration of dental implants. The aim of the present study was to evaluate the effects of systemic glucocorticoid administration on the jaw bone density of minipigs. Thirty-seven adult female minipigs were randomly divided into two groups. Quantitative computed tomography (QCT) was used to assess bone mineral density BMD of the lumbar spine as well as the mandible and maxilla, and blood was drawn. One group of minipigs initially received 1.0 mg prednisolone per kg body weight daily for 2 months. The dose was tapered to 0.5 mg per kg body weight per day thereafter. The animals in the other group served as controls and received placebo. QCT and blood analysis were repeated after 6 and 9 months. BMD was compared between the two groups by measuring Hounsfield units, and serum levels of several bone metabolic markers were also assessed. A decrease in BMD was observed in the jaws from baseline to 9 months. This was more pronounced in the prednisolone group. Statistically significant differences were reached for the mandible (p < 0.001) and the maxilla (p < 0.001). The administration of glucocorticoids reduced the BMD in the jaws of minipigs. The described model shows promise in the evaluation of osseointegration of dental implants in bone that is compromised by osteoporosis.

L-Carnitine, but not coenzyme Q10, enhances the anti-osteoporotic effect of atorvastatin in ovariectomized rats

OBJECTIVE

Statins' therapy in osteoporosis can aggravate muscle damage. This study was designed to assess which agent, L-carnitine or coenzyme Q10, could enhance the anti-osteoporotic effect of atorvastatin while antagonizing myopathy in ovariectomized rats.

METHODS

Forty-eight female Sprague Dawley rats were used; forty rats were ovariectomized while eight were sham-operated. Eight weeks post-ovariectomy, rats were divided into ovariectomized-untreated group and four ovariectomized-treated groups (n=8) which received by gavage (mg/(kg∙d), for 8 weeks) 17β-estradiol (0.1), atorvastatin (50), atorvastatin (50)+L-carnitine (100), or atorvastatin (50)+coenzyme Q10 (20). At the end of therapy, bone mineral density (BMD), bone mineral content (BMC), and serum levels of bone metabolic markers (BMMs) and creatine kinase (CK) were measured. Femurs were used for studying the breaking strength and histopathological changes.

RESULTS

Treatment with atorvastatin+L-carnitine restored BMD, BMC, and bone strength to near normal levels. Estrogen therapy restored BMD and BMC to near normal levels, but failed to increase bone strength. Although atorvastatin and atorvastatin+coenzyme Q10 improved BMD, BMC, and bone strength, they failed to restore levels to normal. All treatments decreased BMMs and improved histopathological changes maximally with atorvastatin+L-carnitine which restored levels to near normal. Atorvastatin aggravated the ovariectomy-induced increase in CK level while estrogen, atorvastatin+L-carnitine, and atorvastatin+coenzyme Q10 decreased its level mainly with atorvastatin+L-carnitine which restored the level to near normal.

CONCLUSIONS

Co-administration of L-carnitine, but not coenzyme Q10, enhances the anti-osteoporotic effect of atorvastatin while antagonizing myopathy in ovariectomized rats. This could be valuable in treatment of osteoporotic patients. However, further confirmatory studies are needed.

Marrow adipogenesis and bone loss that parallels estrogen deficiency is slowed by low-intensity mechanical signals

Ovariectomized mice were used to assess the ability of low-intensity vibrations to protect bone microarchitecture and marrow composition. Results indicate that low-intensity vibrations (LIV), introduced 2 weeks postsurgery, slows marrow adipogenesis in OVX mice but does not restore the bone within the period studied. However, immediate application of LIV partially protects quality.

INTRODUCTION

The aim of this study was to evaluate consequences of estrogen depletion on bone marrow (BM) phenotype and bone microarchitecture, and effects of mechanical signals delivered as LIV on modulating these changes.

METHODS

LIV (0.3 g, 90 Hz) was applied to C57BL/6 mice immediately following ovariectomy or 2 weeks postestrogen withdrawal for 2 (ST-LIV) or 6 weeks (LT-LIV), respectively. Sham-operated age-matched controls (ST-AC, LT-AC) and ovariectomized controls (ST-OVX, LT-OVX) received sham LIV treatment. Bone microstructure was evaluated through μCT and BM adipogenesis through histomorphometry, serum markers, and genes expression analysis.

RESULTS

LT-OVX increased BM adipogenesis relative to LT-AC (+136 %, p ≤ 0.05), while LT-LIV introduced for 6w suppressed this adipose encroachment (-55 %, p ≤ 0.05). In parallel with the fatty marrow, LT-OVX showed a marked loss of trabecular bone, -40 % (p ≤ 0.05) in the first 2 weeks following ovariectomy compared to LT-AC. Application of LT-LIV for 6w following this initial 2w bone loss failed to restore the lost trabeculae but did initiate an anabolic response as indicated by increased serum alkaline phosphatase (+26 %, p ≤ 0.05). In contrast, application of LIV immediately following ovariectomy was more efficacious in the protection of trabecular bone, with a +29 % (p > 0.05) greater BV/TV compared to ST-OVX at the 2w time period.

CONCLUSIONS

LIV can mitigate adipocyte accumulation in OVX marrow and protect it by favoring osteoblastogenesis over adipogenesis. These data also emphasize the rapidity of bone loss with OVX and provide perspective in the timing of treatments for postmenopausal osteoporosis where sooner is better than later.

Curcumin alleviates glucocorticoid-induced osteoporosis through the regulation of the Wnt signaling pathway

It is known that prolonged glucocorticoid (GC) treatment results in osteoporosis. This study aimed to evaluate the protective effects of curcumin on the bones of rats with dexamethasone (DXM)-induced osteoporosis. In the present study, rats were administered DXM for 60 days to induce osteoporosis, and they were then treated with curcumin (100 mg/kg/day) for a further 60 days. H&E staining was used to observe the pathological changes in the femurs. Serum osteocalcin levels and collagen-type I fragments (CTX) were examined as bone metabolism markers. The results revealed that treatment with curcumin attenuated DXM-induced bone injury in femurs, increased the serum levels of osteocalcin and decreased the levels of CTX. In addition, in in vitro experiments, primary rat osteoblasts treated with curcumin at 0.5, 1 and 2 µM were exposed to 100 nM DXM. An MTT assay was used to determine the proliferative ability of the cells. Alkaline phosphatase activity, and the mRNA expression levels of runt-related transcription factor 2 (Runx2), osterix, osteocalcin, collagen, type 1, alpha 1 (Col1A1) and osteonectin were detected to assess transcription factor-associated osteogenic differentiation. The mRNA and protein expression levels of osteoprotegerin (OPG) and receptor activator for nuclear factor-kappa B ligand (RANKL) were detected to assess cytokine-associated osteoclastogenesis. The results demonstrated that curcumin prevented the DXM-induced inhibition of the proliferative ability of the osteoblasts in a dose-dependent manner. In addition, curcumin upregulated the mRNA expression levels of transcription factors that favor osteoblast differentiation and increased the ratio of OPG to RANKL. Moreover, the effects of curcumin on the Wnt signaling pathway were also investigated. RT-qPCR and western blot analysis demonstrated that the Wnt signaling pathway, which was inhibited by DXM, was re-activated upon treatment with curcumin. Immunofluorescence staining revealed that curcumin restored the intranuclear staining of β-catenin in the DXM-stimulated osteoblasts. Collectively, our data demonstrate that curcumin may be a potential therapeutic agent for the treatment of GC-induced osteoporosis.

Association between postmenopausal osteoporosis and experimental periodontitis

To investigate the correlation between postmenopausal osteoporosis (PMO) and the pathogenesis of periodontitis, ovariectomized rats were generated and the experimental periodontitis was induced using a silk ligature. The inflammatory factors and bone metabolic markers were measured in the serum and periodontal tissues of ovariectomized rats using an automatic chemistry analyzer, enzyme-linked immunosorbent assays, and immunohistochemistry. The bone mineral density of whole body, pelvis, and spine was analyzed using dual-energy X-ray absorptiometry and image analysis. All data were analyzed using SPSS 13.0 statistical software. It was found that ovariectomy could upregulate the expression of interleukin- (IL-)6, the receptor activator of nuclear factor-κB ligand (RANKL), and osteoprotegerin (OPG) and downregulate IL-10 expression in periodontal tissues, which resulted in progressive alveolar bone loss in experimental periodontitis. This study indicates that changes of cytokines and bone turnover markers in the periodontal tissues of ovariectomized rats contribute to the damage of periodontal tissues.

The preventive effect of biochanin a on bone loss in ovariectomized rats: involvement in regulation of growth and activity of osteoblasts and osteoclasts

Biochanin A (BCA) is a major isoflavone abundant in red clover (Trifolium pretense). The protective effect of BCA on bone loss in an ovariectomized (OVX) animal model has never been clarified. The objective of this study was to investigate the biological effects of BCA on bone loss in OVX rats in vivo and on the development of osteoblasts and osteoclasts in vitro. Ovariectomy resulted in a marked increase in body weight and a decrease in femoral bone mineral density and trabecular bone volume that was prevented by BCA or 17 β -estradiol (E2) treatment. However, an increase in uterine weight was observed in E2-treated OVX rats, but not in response to BCA treatment. Treatment with BCA increased the mRNA expression of osterix, collagen type I, alkaline phosphatase (ALP), and osteocalcin and decreased the mRNA expression of tartrate-resistant acid phosphatase (TRAP) and the receptor activator of nuclear factor- κ B ligand (RANKL)/osteoprotegerin (OPG) ratio in the femur of OVX rats. Treatment with BCA or E2 prevented the OVX-induced increase in urinary deoxypyridinoline (DPD) and serum tumor necrosis factor α (TNF- α ) and interleukin-1 β (IL-1 β ). In vitro, BCA induced preosteoblasts to differentiate into osteoblasts and increased osteoblast mineralization. BCA inhibited preosteoclasts and osteoclast proliferation and decreased osteoclast bone resorption. These findings suggest that BCA treatment can effectively prevent the OVX-induced increase in bone loss and bone turnover possibly by increasing osteoblastic activities and decreasing osteoclastic activities.

Skeletal and extraskeletal actions of denosumab

Osteoclasts and osteoblasts define skeletal mass, structure and strength through their respective actions in resorbing and forming bone. This remodeling process is orchestrated by the actions of hormones and growth factors, which regulate a cytokine system comprising the receptor activator of nuclear factor κB ligand (RANKL), its receptor RANK and the soluble decoy receptor osteoprotegerin (OPG). Bone resorption depends on RANKL, which determines osteoclast formation, activity and survival. Importantly, cells of the osteoblastic lineage mainly provide RANKL and therefore, are central in the regulation of osteoclast functions. Catabolic effects of RANKL are inhibited by OPG, a TNF receptor family member that binds RANKL, thereby preventing the activation of its receptor RANK, which is expressed by osteoclast precursors. Because this cytokine network is pivotal for the regulation of bone mass in health and diseases, including osteoporosis, rheumatoid arthritis and malignant bone conditions, it has been successfully used for the generation of a targeted therapy to block osteoclast actions. The clinical approval of denosumab, a fully monoclonal antibody against RANKL, provides a novel option to treat bone diseases with a potent, targeted and reversible inhibitor of bone resorption. Although RANKL is also expressed by endothelial cells, T lymphocytes, synovial fibroblasts and various tumor cells, no meaningful clinical extraskeletal effects have been reported after administration of denosumab. This article summarizes the molecular and cellular basis of the RANKL/RANK/OPG system and presents preclinical and clinical studies on the skeletal actions of denosumab.

Protective effect of amlodipine on rat bone tissue after orchidectomy

AIM

Our study aimed to investigate the effect of amlodipine on bone metabolism in orchidectomized rats.

METHODS

Eight-week-old rats were divided into three groups. The sham-operated control group (SHAM) and the control group after orchidectomy (ORX) received the standard laboratory diet (SLD). The experimental group after orchidectomy (ORX+AML) received SLD enriched with amlodipine for 12 weeks. Bone marker concentrations in serum of PINP, OPG and IGF-1, and the levels of CTX-I, BAP and BMP-2 in a bone homogenate were measured using enzyme-linked immunosorbent assay. Bone mineral density (BMD) was measured by dual energy X-ray absorptiometry. The femurs were used for biomechanical testing.

RESULTS

Bone markers (CTX-I, BAP, BMP-2) in ORX were higher versus SHAM. In ORX+AML there was a decrease in PINP, CTX-I, BAP, BMP-2 and OPG versus ORX. IGF-1 was decreased in ORX versus SHAM. In ORX+AML it was increased versus ORX. In ORX, a decrease was demonstrated versus SHAM in BMD of the whole body, in the lumbar vertebrae and in both femurs. In ORX+AML there was an increase in BMD of the whole body versus ORX. Three-point bending test revealed a decrease in maximal load values in ORX versus SHAM. After amlodipine administration there was an increase in the left femur versus ORX.

CONCLUSIONS

Amlodipine is capable of mitigating the negative effects of orchidectomy and could be a good prevention of osteoporosis.

Raloxifene therapy inhibits osteoclastogenesis during the alveolar healing process in rats

OBJECTIVE

To investigate the expression of OPG, RANKL and TRAP during alveolar healing process (7, 14, 21, 28 and 42 postoperative days) in ovariectomized rats treated with raloxifene or with oestrogen replacement therapy, using immunohistochemistry reaction approach.

MATERIALS AND METHODS

Wistar female rats (10 weeks age) were submitted to ovariectomy surgery (OVX) or sham surgery. The female rats were divided in four groups: (1) sham; (2) OVX/O (ovariectomy and oil); (3) OVX/E2 (ovariectomy and oestrogen replacement); (4) OVX/RLX (ovariectomy and raloxifene therapy).

RESULTS

It was observed high amount of OPG immunolabelling with predominance at 14 and 21 postoperative days on sham and OVX/RLX groups, respectively. At 7 postoperative days, there was no difference between the groups for TRAP protein. Otherwise, to the other periods, it was observed greater expression of TRAP and RANKL protein on OVX/O group compared to sham, OVX/E2 and OVX/RLX groups. It was also observed a discrete TRAP immunolabelling at 28 and 42 postoperative days on OVX/RLX group.

CONCLUSIONS

Oestrogen deficiency induces osteoclastogenesis in the alveolar healing process. Quantitative changes in the osteoclastic activity could be prevented through the raloxifene therapy.

RANKL inhibition for the management of patients with benign metabolic bone disorders

The receptor activator of NF-kappaB ligand (RANKL) is a member of the TNF receptor superfamily, essential for osteoclastogenesis. It binds to its receptor activator of NF-kappaB on the surface of osteoclast precursors and enhances their differentiation, survival and fusion, while it activates mature osteoclasts and inhibits their apoptosis. The effects of RANKL are counteracted by osteoprotegerin (OPG), a neutralizing decoy receptor. Derangement of the balance in RANKL/OPG action is implicated in the pathophysiology of metabolic bone diseases, including osteoporosis. Current therapies used to prevent or treat metabolic bone diseases are thought to act, at least in part, through modification of the RANKL/OPG dipole. The idea of using a molecule that could specifically bind and neutralize RANKL to decrease bone resorption and subsequent bone loss is appealing. Recombinant OPG was initially tested. Denosumab, a fully human monoclonal antibody against RANKL, is a promising antiresorptive agent under investigation. It rapidly decreases bone turnover markers resulting in a significant increase in bone mineral density and reduction in fracture risk. However, because receptor activator of NF-kappaB activation by RANKL is also essential for T-cell growth and dendritic-cell function, inhibition of its action could simultaneously affect the immune system, leading to susceptibility in infections or malignancies.

Osteoprotegerin and ligand of receptor activator of nuclear factor kappaB expression in ovariectomized rats during tooth movement

OBJECTIVE

To test the null hypothesis that increased tooth displacement in ovariectomized rats is not related to differential expressions of OPG and RANKL in the periodontium.

MATERIALS AND METHODS

Eighty-four 12-week female rats were used; half were ovariectomized and half were not. Three months later, the maxillary first molar was moved mesially. Groups of rats were sacrificed at days 0, 1, 3, 5, 7, 10, and 14 after activation. Tooth movement was measured at each time point. OPG and RANKL expressions were examined through immunohistochemistry.

RESULTS

Ovariectomized and nonovariectomized rats showed three-phase tooth movement. In both groups, OPG expression increased at the tension area and RANKL increased at the pressure area. The OPG/RANKL ratio coincided with tooth movement, especially in the linear phase from 7 to 14 days.

CONCLUSIONS

The null hypothesis is rejected. The increased rate of tooth movement in ovariectomized rats was related to differential expressions of OPG and RANKL.

Role of RANKL in bone diseases

Bone remodeling is a tightly regulated process of osteoclast-mediated bone resorption, balanced by osteoblast-mediated bone formation. Disruption of this balance can lead to increased bone turnover, resulting in excessive bone loss or extra bone formation and consequent skeletal disease. The receptor activator of nuclear factor kappaB ligand (RANKL) (along with its receptor), the receptor activator of nuclear factor kappaB and its natural decoy receptor, osteoprotegerin, are the final effector proteins of osteoclastic bone resorption. Here, I provide an overview of recent studies that highlight the key role of RANKL in the pathophysiology of several bone diseases and discuss the novel therapeutic approaches afforded by the modulation of RANKL.

RANKL inhibition with osteoprotegerin increases bone strength by improving cortical and trabecular bone architecture in ovariectomized rats

INTRODUCTION

Ovariectomy (OVX) results in bone loss caused by increased bone resorption. RANKL is an essential mediator of bone resorption. We examined whether the RANKL inhibitor osteoprotegerin (OPG) would preserve bone volume, density, and strength in OVX rats.

MATERIALS AND METHODS

Rats were OVX or sham-operated at 3 mo of age. Sham controls were treated for 6 wk with vehicle (Veh, PBS). OVX rats were treated with Veh or human OPG-Fc (10 mg/kg, 2/wk). Serum RANKL and TRACP5b was measured by ELISA. BMD of lumbar vertebrae (L(1)-L(5)) and distal femur was measured by DXA. Right distal femurs were processed for bone histomorphometry. Left femurs and the fifth lumbar vertebra (L(5)) were analyzed by muCT and biomechanical testing, and L(6) was analyzed for ash weight.

RESULTS

OVX was associated with significantly greater serum RANKL and osteoclast surface and with reduced areal and volumetric BMD. OPG markedly reduced osteoclast surface and serum TRACP5b while completely preventing OVX-associated bone loss in the lumbar vertebrae, distal femur, and femur neck. Vertebrae from OPG-treated rats had increased dry and ash weight, with no significant differences in tissue mineralization versus OVX controls. muCT showed that trabecular compartments in OVX-OPG rats had significantly greater bone volume fraction, vBMD, bone area, trabecular thickness, and number, whereas their cortical compartments had significantly greater bone area (p < 0.05 versus OVX-Veh). OPG improved cortical area in L(5) and the femur neck to levels that were significantly greater than OVX or sham controls (p < 0.05). Biomechanical testing of L(5) and femur necks showed significantly greater maximum load values in the OVX-OPG group (p < 0.05 versus OVX-Veh). Bone strength at both sites was linearly correlated with total bone area (r(2) = 0.54-0.74, p < 0.0001), which was also significantly increased by OPG (p < 0.05 versus OVX).

CONCLUSIONS

OPG treatment prevented bone loss, preserved trabecular architecture, and increased cortical area and bone strength in OVX rats.

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.

Comparison of dried plum supplementation and intermittent PTH in restoring bone in osteopenic orchidectomized rats

Bone loss was confirmed after 90 days in 50 6-month-old male Sprague Dawley rats that were sham-operated or orchidectomized (ORX). In this study, we have shown that dried plum (DP) has potent effects on bone in terms of bone mass, microarchitecture, and strength in osteopenic male rats. Although these changes may be mediated through the suppression of bone resorption, the fact that the restoration in some of the bone structural and biomechanical parameter shares some similarities with parathyroid hormone (PTH) should not be overlooked. Further investigation is needed on a mechanistic level to clarify the influence of DP on bone metabolism.

INTRODUCTION

This study was designed to investigate the extent to which DP reverses bone loss in osteopenic ORX rats and to compare its effects to PTH.

MATERIALS AND METHODS

Fifty, 6-month-old male Sprague Dawley rats were sham-operated or ORX, and bone loss was confirmed after 90 days. The ORX groups were assigned to control (AIN-93M) diet, 25% DP diet, or PTH (80 microg/kg) for 90 days.

RESULTS

DP induced an 11% increase in vertebral and femoral BMD compared to ORX-controls. BMD in the PTH-treated group was increased by 20.7% (vertebra) and 17.9% (femur). Vertebral trabecular bone volume (BV/TV) and number were increased by DP and trabecular separation was decreased compared to controls, which were similar to PTH. Alterations in trabecular bone of the femur were similar to those in the vertebra, but DP did not restore BV/TV to the same extent. Cortical thickness was improved by DP and further enhanced by PTH. DP tended to decrease urinary deoxypyridinoline and calcium, but did not alter alkaline phosphatase or osteocalcin.

CONCLUSION

We conclude that though the degree of improvement was not equivalent to PTH with regard to all parameters, DP reverses bone loss due to ORX and the mechanisms should be further investigated.

Effects of the administration of corticosterone, parathyroid hormone, or both, and of their withdrawal, on rat bone and cartilage histomorphometric parameters, and on osteoprotegerin and RANKL mRNA expression and proteins

We have studied the effects of the treatment with corticosterone (CORT), parathyroid hormone (PTH), or both (CORT + PTH), and of their withdrawal (CORT-rec and CORT + PTH-rec), on the osteoprotegerin (OPG) and receptor activator of nuclear factor-kB ligand (RANKL) localization and expression and on histomorphometric parameters in primary and secondary spongiosa of rat femur and tibia metaphyses. In the secondary spongiosa of the CORT group, the bone remodeling and the OPG/RANKL mRNA ratio decreased. In the PTH group, the bone turnover and the structural and connectivity indices increased, and the OPG/RANKL mRNA ratio fell; this ratio rose, however, in the primary spongiosa. In the CORT + PTH group, remodeling values intermediate between those of the CORT and PTH groups, were detected in the secondary spongiosa, where OPG and RANKL mRNA rose. Return towards control values was found in the recovery groups. The Cartilage Growth Plate Width was reduced in the CORT and CORT + PTH groups and returned to normal values in the recovery groups, while it was not affected by PTH. Independently of treatments, both OPG and RANKL mRNA and proteins were co-localized in the same cartilage and bone cells and in several bone marrow cells. In conclusion, the catabolic effects induced by CORT treatment occur together with an OPG fall and a RANKL rise. In the PTH group in which the bone turnover increase, the OPG and RANKL mRNA expressions differ in the primary and secondary spongiosa, confirming that the bone tissue in these sites can have different metabolic trends.

Estrogen receptor agonists and immune system in ovariectomized mice

Several data implicate the immune system in bone lost after estrogen deficiency, however, some of the effects on the immune system of estrogen deficiency or of estrogen receptor (ER) modulation are not well established. In this study, the effect of ER agonists on the immune system in ovariectomized mice is analyzed. Mice were ovariectomized and were administered 17beta-estradiol (E2), raloxifene (RAL) or genistein (GEN). The effect of a 4-week treatment on bone turnover and on several parameters that reflect the status of the immune system was studied. Results show that ovariectomy provoked both uterine atrophy and thymic hypertrophy. Although RAL corrected thymic hypertrophy, only E2 corrected both. Ovariectomized mice showed increased levels of serum calcium and cathepsin K gene expression and decreased levels of serum alkaline phosphatase (ALP) activity, which suggests that there is a persistent alteration in bone metabolism. Moreover, ovariectomy increased B-cells and CD25+ cells, and decreased the percentages of T-cells and Cbfa1 gene expression in bone marrow (BM). All ER agonists corrected, although to different degrees, changes induced by the ovariectomy. Furthermore, results showed that it is essential to adjust ER agonist doses to avoid immunosuppression, since all ER agonists decreased BM T-cell levels.

Dried plum prevents bone loss in a male osteoporosis model via IGF-I and the RANK pathway

Previously, dietary supplementation with dried plums, a rich source of polyphenolic compounds with antioxidant and anti-inflammatory properties, has been shown to improve bone density, microstructure and biomechanics in female animal models of osteopenia. We designed this study to determine the extent to which dried plum prevents skeletal deterioration in gonadal hormone deficient male animals and to begin to understand its mechanism of action. Sixty 6-month-old male Sprague-Dawley rats were either sham-operated (Sham = 1 group) or orchidectomized (ORX = 4 groups) and randomly assigned to dietary treatments: standard semi-purified diet (Control) with either LD = 5%, MD = 15%, or HD = 25% (w/w) dried plum for 90 days. At the end of the treatment period, both the MD and HD dried plum completely prevented the ORX-induced decrease in whole body, femur, and lumbar vertebra bone mineral density (BMD). Biomechanical testing indicated that the MD and HD of dried plum prevented the ORX-induced decrease in ultimate load of the cortical bone as well as the compressive force and stiffness of trabecular bone within the vertebrae. Analyses of trabecular microarchitecture of the distal femur metaphysis and vertebral body revealed that HD dried plum protected against the decrease in trabecular bone volume (BV/TV) induced by ORX. In the distal femur, all doses of dried plum improved trabecular number (TbN) and separation (TbSp) compared to the ORX-control group, while MD and HD dried plum prevented the ORX-induced changes in vertebral TbN and TbSp. At the end of the 90-day treatment, no remarkable changes in serum osteocalcin or alkaline phosphatase in any of the treatment groups were observed, while serum insulin-like growth factor (IGF)-I was increased by dried plum. The ORX-induced increase in urinary deoxypyridinoline (DPD) excretion was completely prevented by all doses of dried plum coinciding with down-regulation of gene expression for receptor activator of NFkappa-B ligand (RANKL) and osteoprotegerin (OPG) in the bone. We conclude that dried plum prevents osteopenia in androgen deficient male rats, and these beneficial effects may be attributed in part to a decrease in osteoclastogenesis via down-regulation of RANKL and stimulation of bone formation mediated by IGF-I.

Alterations in the phenotype and function of immune cells in ovariectomy-induced osteopenic mice

BACKGROUND

Within the last few years, much evidence has been presented on the involvement of the immune system in certain types of bone loss, such as activated T cells in rheumatoid arthritis and in periodontitis. Estrogen deficiency induces bone loss; however, how this deficiency affects the immune system has not been sufficiently studied.

METHODS

To evaluate the effects of estrogen withdrawal on the status and functionality of the immune system, mice were ovariectomized or sham-operated, and 5 weeks after surgery, when osteopenia had developed, several parameters were analysed in spleen and in bone marrow. We analysed bone turnover, cell phenotype by flow cytometry, cell function by cell proliferation assays, and the expression of several genes related to the process.

RESULTS

Five weeks after ovariectomy, augmented osteoclastogenesis persisted in the bone marrow. In addition, the ovariectomized mice had more B-cells and CD3+ T-cells expressing the receptor activator of NF-kappaB ligand (CD3+/RANKL+). The ovariectomized mice had lower serum alkaline phosphatase activity, a normal amount of T cells, lower percentages of CD11b+ and CD51+ cells in the bone marrow, and a lower serum interferon-gamma level compared with sham-operated controls.

CONCLUSIONS

The data suggest that, 5 weeks after ovariectomy, bone turnover remains imbalanced, with increased osteoclastogenesis and a decreased rate of bone formation. Moreover, there is an increase in B-cell formation, with normal and decreased percentages of T cells and myelomonocytic cells (CD11b+), respectively, in the bone marrow. Decreased serum interferon-gamma levels could be involved in the increased osteoclastogenesis found in the present work.

Receptor activator of NF-kappaB ligand protein expression in UMR-106 cells is differentially regulated by parathyroid hormone and calcitriol

Expression of the cytokine, receptor activator of NF-kappaB ligand (RANKL), is stimulated by both parathyroid hormone (PTH) and calcitriol in osteoblasts. Most studies have examined the effects on RANKL mRNA, and less information is available on the protein products. We have determined the effects of PTH, the adenylate cyclase stimulator forskolin, and calcitriol, alone and in combination, on endogenous RANKL protein expression in UMR-106 rat osteoblastic osteosarcoma cells by Western blotting and enzyme immunoassay (EIA). PTH and forskolin dose dependently increased a approximately 52 kDa band in whole cell lysates that was detected by both C- and N-terminal directed RANKL antibodies. Calcitriol treatment produced little or no expression of this approximately 52 kDa band, but markedly increased the expression of a approximately 32 kDa band that was only detected with an antibody directed to the N-terminus of RANKL. An EIA based on RANKL binding to OPG detected a large increase in RANKL expression following calcitriol treatment, and much smaller increases with PTH or forskolin. The combination of PTH and calcitriol or forskolin and calcitriol elicited effects similar to those of PTH and forskolin alone, as detected by both Western blotting and EIA. In contrast to the effects on protein, all agents increased RANKL mRNA expression, with the greatest effects seen with the co-treatments. The results indicate that PTH, likely through effects on cyclic AMP, has a different effect on RANKL processing than calcitriol. The approximately 52 and approximately 32 kDa RANKL products appear to interact differently with OPG, which could affect responses to the agents in target cells.