The effect of a single dose of osteoprotegerin in postmenopausal women

Bone mineral density in egyptian children with juvenile idiopathic arthritis: possible correlation to serum RANKL / osteoprotegerin (OPG) ratio and OPG gene polymorphisms

BACKGROUND

Children with juvenile idiopathic arthritis (JIA) are at higher risk of decreased bone mineral density (BMD) compared with healthy children due to genetic, disease and medication-related causes. This study aims to investigate the possible effects of osteoprotegerin (OPG) gene polymorphisms and serum levels of osteoprotegerin (OPG) and receptor activator of nuclear factor κB-ligand (RANKL) and RANKL/OPG ratio on BMD in children with JIA.

METHODS

OPG gene rs2073617, rs3134069, serum RANKL, OPG and RANKL/OPG ratio were evaluated in 60 JIA children and 100 matched healthy controls. BMD was evaluated by lumbar dual energy X-ray absorptiometry (DEXA) according to which patients were classified in 2 groups (DEXA z-score above and below - 2). Composite disease activity was measured using the Juvenile Arthritis Disease Activity Score (JADAS) 27-joints. Articular damage was scored using the juvenile arthritis damage index (JADI).

RESULTS

Patients aged 12.05 ± 3.2 years, included 38 females and 31% had BMD z-score below-2. Systemic-onset JIA was the most frequent phenotype (38%). Genotypes and alleles frequencies of the 2 studied polymorphisms did not differ between patients and controls (p > 0.05 for all) while serum RANKL and RANKL/OPG ratio were significantly higher in patients compared to controls (p = < 0.001 and 0.03 respectively). Patients with BMD < -2 had significantly greater frequencies of rs2073617 TT genotype and T allele (p < 0.001), higher serum RANKL, RANKL/OPG ratio (p = 0.01, 0.002), female predominance (p = 0.02), higher articular and extra-articular damage index (p = 0.008,0.009) and more frequent steroid usage (p = 0.02) compared to patients with BMD z-score >-2. Multivariate analysis showed rs2073617 TT genotype, RANKL/OPG ratio, long disease duration (above 36 months) and use of steroid to be associated with decreased BMD (p = 0.03,0.04,0.01,0.01 respectively) in JIA children.

CONCLUSIONS

Egyptian children with JIA have decreased BMD. rs2073617 TT genotype and T allele, RANKL/OPG ratio are possible determinants of reduced BMD in JIA. Our results underline the importance of frequent monitoring of BMD in JIA children and trying to control disease activity to preserve long term bone health.

Revealing oxidative stress-related genes in osteoporosis and advanced structural biological study for novel natural material discovery regarding MAPKAPK2

OBJECTIVES

This study aimed to find novel oxidative stress (OS)-related biomarkers of osteoporosis (OP), together with targeting the macromolecule Mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK2) protein to further discover potential novel materials based on an advanced structural biology approach.

METHODS

Gene expression profiles of GSE35958 were obtained from the Gene Expression Omnibus (GEO) database, which were included for weighted gene co-expression network analysis (WGCNA) and differential analysis to identify the most correlated module, to identify OS-related hub genes in the progression of OP. Functional annotations were also analyzed on the interested module to get a comprehensive understanding of these genes. Then, a series of advanced structural biology methods, including high-throughput screening, pharmacological characteristic prediction, precise molecular docking, molecular dynamics simulation, etc., was implemented to discover novel natural inhibitor materials against the MAPKAPK2 protein.

RESULTS

The brown module containing 720 genes was identified as the interested module, and a group set of genes was determined as the hub OS-related genes, including PPP1R15A, CYB5R3, BCL2L1, ABCD1, MAPKAPK2, HSP90AB1, CSF1, RELA, P4HB, AKT1, HSP90B1, and CTNNB1. Functional analysis demonstrated that these genes were primarily enriched in response to chemical stress and several OS-related functions. Then, Novel Materials Discovery demonstrated that two compounds, ZINC000014951634 and ZINC000040976869, were found binding to MAPKAPK2 with a favorable interaction energy together with a high binding affinity, relatively low hepatoxicity and carcinogenicity, high aqueous solubility and intestinal absorption levels, etc., indicating that the two compounds were ideal potential inhibitor materials targeting MAPKAPK2.

CONCLUSION

This study found a group set of OS-related biomarkers of OP, providing further insights for OS functions in the development of OP. This study then focused on one of the macromolecules, MAPKAPK2, to further discover potential novel materials, which was of great significance in guiding the screening of MAPKAPK2 potential materials.

The pathophysiology of immunoporosis: innovative therapeutic targets

BACKGROUND

The physiological balance between bone resorption and bone formation is now known to be mediated by a cascade of events parallel to the classic osteoblast-osteoclast interaction. Thus, osteoimmunology now encompasses the role played by other cell types, such as cytokines, lymphocytes and chemokines, in immunological responses and how they help modulate bone metabolism. All these factors have an impact on the RANK/RANKL/OPG pathway, which is the major pathway for the maturation and resorption activity of osteoclast precursor cells, responsible for osteoporosis development. Recently, immunoporosis has emerged as a new research area in osteoimmunology dedicated to the immune system's role in osteoporosis.

METHODS

The first part of this review presents theoretical concepts on the factors involved in the skeletal system and osteoimmunology. Secondly, existing treatments and novel therapeutic approaches to treat osteoporosis are summarized. These were selected from to the most recent studies published on PubMed containing the term osteoporosis. All data relate to the results of in vitro and in vivo studies on the osteoimmunological system of humans, mice and rats.

FINDINGS

Treatments for osteoporosis can be classified into two categories. They either target osteoclastogenesis inhibition (denosumab, bisphosphonates), or they aim to restore the number and function of osteoblasts (romozumab, abaloparatide). Even novel therapies, such as resolvins, gene therapy, and mesenchymal stem cell transplantation, fall within this classification system.

CONCLUSION

This review presents alternative pathways in the pathophysiology of osteoporosis, along with some recent therapeutic breakthroughs to restore bone homeostasis.

RANKL regulates male reproductive function

Infertile men have few treatment options. Here, we demonstrate that the transmembrane receptor activator of NF-kB ligand (RANKL) signaling system is active in mouse and human testis. RANKL is highly expressed in Sertoli cells and signals through RANK, expressed in most germ cells, whereas the RANKL-inhibitor osteoprotegerin (OPG) is expressed in germ and peritubular cells. OPG treatment increases wild-type mouse sperm counts, and mice with global or Sertoli-specific genetic suppression of Rankl have increased male fertility and sperm counts. Moreover, RANKL levels in seminal fluid are high and distinguishes normal from infertile men with higher specificity than total sperm count. In infertile men, one dose of Denosumab decreases RANKL seminal fluid concentration and increases serum Inhibin-B and anti-Müllerian-hormone levels, but semen quality only in a subgroup. This translational study suggests that RANKL is a regulator of male reproductive function, however, predictive biomarkers for treatment-outcome requires further investigation in placebo-controlled studies.

Targeting cancer metastasis with antibody therapeutics

Cancer metastasis, the spread of disease from a primary to a distal site through the circulatory or lymphatic systems, accounts for over 90% of all cancer related deaths. Despite significant progress in the field of cancer therapy in recent years, mortality rates remain dramatically higher for patients with metastatic disease versus those with local or regional disease. Although there is clearly an urgent need to develop drugs that inhibit cancer spread, the overwhelming majority of anticancer therapies that have been developed to date are designed to inhibit tumor growth but fail to address the key stages of the metastatic process: invasion, intravasation, circulation, extravasation, and colonization. There is growing interest in engineering targeted therapeutics, such as antibody drugs, that inhibit various steps in the metastatic cascade. We present an overview of antibody therapeutic approaches, both in the pipeline and in the clinic, that disrupt the essential mechanisms that underlie cancer metastasis. These therapies include classes of antibodies that indirectly target metastasis, including anti-integrin, anticadherin, and immune checkpoint blocking antibodies, as well as monoclonal and bispecific antibodies that are specifically designed to interrupt disease dissemination. Although few antimetastatic antibodies have achieved clinical success to date, there are many promising candidates in various stages of development, and novel targets and approaches are constantly emerging. Collectively, these efforts will enrich our understanding of the molecular drivers of metastasis, and the new strategies that arise promise to have a profound impact on the future of cancer therapeutic development. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Pros and Cons of Denosumab Treatment for Osteoporosis and Implication for RANKL Aptamer Therapy

Osteoporosis is age-related deterioration in bone mass and micro-architecture. Denosumab is a novel human monoclonal antibody for osteoporosis. It is a receptor activator of nuclear factor-κB ligand (RANKL) inhibitor, which binds to and inhibits osteoblast-produced RANKL, in turn reduces the binding between RANKL and osteoclast receptor RANK, therefore decreases osteoclast-mediated bone resorption and turnover. However, adverse events have also been reported after denosumab treatment, including skin eczema, flatulence, cellulitis and osteonecrosis of the jaw (ONJ). Extensive researches on the mechanism of adverse reactions caused by denosumab have been conducted and may provide new insights into developing new RANKL inhibitors that achieve better specificity and safety. Aptamers are single-stranded oligonucleotides that can bind to target molecules with high specificity and affinity. They are screened from large single-stranded synthetic oligonucleotides and enriched by a technology named SELEX (systematic evolution of ligands by exponential enrichment). With extra advantages such as high stability, low immunogenicity and easy production over antibodies, aptamers are hypothesized to be promising candidates for therapeutic drugs targeting RANKL to counteract osteoporosis. In this review, we focus on the pros and cons of denosumab treatment in osteoporosis and the implication for novel aptamer treatment.

Evaluation of Isoflavones as Bone Resorption Inhibitors upon Interactions with Receptor Activator of Nuclear Factor-κB Ligand (RANKL)

Receptor activator of nuclear factor-κB ligand (RANKL) is a cytokine responsible for bone resorption. It binds its receptor RANK, which activates osteoporosis. High levels of osteoprotegerin (OPG) competitively binding RANKL limit formation of ligand-receptor complexes and enable bone mass maintenance. The new approach to prevent osteoporosis is searching for therapeutics that can bind RANKL and support OPG function. The aim of the study was to verify the hypothesis that isoflavones can form complexes with RANKL limiting binding of the cytokine to its receptor. Interactions of five isoflavones with RANKL were investigated by isothermal titration calorimetry (ITC), by in silico docking simulation and on Saos-2 cells. Daidzein and biochanin A showed the highest affinity for RANKL. Among studied isoflavones coumestrol, formononetin and biochanin A showed the highest potential for Saos-2 mineralization and were able to regulate the expression of RANKL and OPG at the mRNA levels, as well as osteogenic differentiation markers: alkaline phosphatase (ALP), collagen type 1, and Runt-related transcription factor 2 (Runx2). Comparison of the osteogenic activities of isoflavones showed that the use of physicochemical techniques such as ITC or in silico docking are good tools for the initial selection of substances showing a specific bioactivity.

Impact of pharmacologic inhibition of tooth movement on periodontal and tooth root tissues during orthodontic force application

OBJECTIVE

The goal of this study was to investigate potential negative sequelae of orthodontic force application ±delivery of an osteoclast inhibitor, recombinant osteoprotegerin protein (OPG-Fc), on periodontal tissues.

SETTING AND SAMPLE POPULATION

Sprague Dawley rats from a commercial supplier were investigated in a laboratory setting.

MATERIALS AND METHODS

Rats were randomly divided into four groups (n = 7 each): one group with no orthodontic appliances and injected once prior to the experimental period with empty polymer microspheres, one group with orthodontic appliances and injected once with empty microspheres, one group with orthodontic appliances and injected once with polymer microspheres containing 1 mg/kg of OPG-Fc, and one group with orthodontic appliances and injected with non-encapsulated 5 mg/kg of OPG-Fc every 3 days during the experimental period. The animals were euthanized after 28 days of tooth movement for histomorphometric analyses.

RESULTS

Root resorption, PDL area and widths were similar in animals without appliances and animals with appliances plus high-dose OPG-Fc. PDL blood vessels were compressed and decreased in number in all animals that received orthodontic appliances, regardless of OPG-Fc. Hyalinization was significantly increased only in animals with orthodontic appliances plus multiple injections of 5 mg/kg non-encapsulated OPG-Fc when compared to animals without appliances.

CONCLUSIONS

Results of this study indicate that while pharmacological modulation of tooth movement through osteoclast inhibition is feasible when delivered in a locally controlled low-dose manner, high-dose levels that completely prevent tooth movement through bone may decrease local blood flow and increase the incidence of hyalinization.

Advances in osteoporosis from 1970 to 2018

In 1970, there were no drugs under study for osteoporosis. Estrogen was used, but little was known about the correct dose for preventing bone loss. At that time, fractures were not even recognized as a disease, but regarded as part of normal aging. From 1970 to this year (2018), there have been extensive advances in the osteoporosis field ranging from fracture epidemiology to the remarkable invention of bone density measurements. There have been major advances in therapeutic options available for patients for prevention and treatment of osteoporosis. In parallel, the advances in the laboratory helped elucidate the process of bone remodeling, not only at the macroscopic level but also at the cellular level. This led to rapid advances in translational research from cellular biology to new therapies exemplified by the development of monoclonal antibodies for osteoporosis. Further understanding of the signaling pathways in bone cells will lead to new small molecules made for osteoporosis treatment, perhaps causing less adverse events. University-based research throughout the world has been a leader in most of these advances, and Pharma support for phase 1 to 4 studies helped bring these discoveries to patients. In the osteoporosis field alone, one sees the tremendous value of grant support for university research by National funding agencies such as the National Institute of Health in this country and similar agencies in other countries. There are clinical challenges that have to be solved with long-term compliance with osteoporosis medication if we want to reduce fracture incidence in the long term.

Microsphere controlled drug delivery for local control of tooth movement

Background

Because orthodontic tooth movement is dependent upon osteoclast-mediated resorption of alveolar bone adjacent to the pressure side of tooth roots, biologic mediators that regulate osteoclasts can be utilized to control tooth movement.

Objectives

To develop a novel method to locally enhance orthodontic anchorage.

Methods

We encapsulated osteoprotegerin (OPG) in polymer microspheres and tested the effectiveness of microsphere encapsulated versus non-encapsulated OPG for enhancing orthodontic anchorage in a rodent model of tooth movement. A single injection of 1 mg/kg non-encapsulated or microsphere encapsulated OPG was delivered into the palatal mucosa mesial to the first maxillary molar 1 day prior to tooth movement. A positive control group received injections of 5 mg/kg non-encapsulated OPG every 3 days during tooth movement. After 28 days of tooth movement, hemi-maxillae and femurs were dissected. Molar mesial and incisor distal tooth movement was measured using stone casts that were scanned and magnified. Local alveolar, distant femur bone, and tooth root volumes were analyzed by micro computed tomography. Serum OPG levels were measured by ELISA. Osteoclast numbers were quantified by histomorphometry.

Results

The single injection of microsphere encapsulated OPG significantly enhanced orthodontic anchorage, while the single injection of non-encapsulated OPG did not. Injection of encapsulated OPG inhibited molar mesial movement but did not inhibit incisor tooth movement, and did not alter alveolar or femur bone volume fraction, density, or mineral content. Multiple injections of 5 mg/kg non-encapsulated OPG enhanced orthodontic anchorage, but also inhibited incisor retraction and altered alveolar and femur bone quality parameters. Increased OPG levels were found only in animals receiving multiple injections of non-encapsulated 5 mg/kg OPG. Osteoclast numbers were higher upon tooth movement in animals that did not receive OPG. Osteoclast numbers in OPG injected animals were variable within groups.

Conclusions

Microsphere encapsulation of OPG allows for controlled drug release, and enhances site-specific orthodontic anchorage without systemic side effects. With additional refinements, this drug delivery system could be applicable to a broad array of potential biologic orthodontic therapeutics.

The Molecular Mechanism of Vitamin E as a Bone-Protecting Agent: A Review on Current Evidence

Bone remodelling is a tightly-coordinated and lifelong process of replacing old damaged bone with newly-synthesized healthy bone. In the bone remodelling cycle, bone resorption is coupled with bone formation to maintain the bone volume and microarchitecture. This process is a result of communication between bone cells (osteoclasts, osteoblasts, and osteocytes) with paracrine and endocrine regulators, such as cytokines, reactive oxygen species, growth factors, and hormones. The essential signalling pathways responsible for osteoclastic bone resorption and osteoblastic bone formation include the receptor activator of nuclear factor kappa-B (RANK)/receptor activator of nuclear factor kappa-B ligand (RANKL)/osteoprotegerin (OPG), Wnt/β-catenin, and oxidative stress signalling. The imbalance between bone formation and degradation, in favour of resorption, leads to the occurrence of osteoporosis. Intriguingly, vitamin E has been extensively reported for its anti-osteoporotic properties using various male and female animal models. Thus, understanding the underlying cellular and molecular mechanisms contributing to the skeletal action of vitamin E is vital to promote its use as a potential bone-protecting agent. This review aims to summarize the current evidence elucidating the molecular actions of vitamin E in regulating the bone remodelling cycle.

A simple and robust reporter gene assay for measuring the bioactivity of anti-RANKL therapeutic antibodies

The mechanism sketch of the reporter gene assay for the bioactivity determination of anti-RANKL mAbs.

Treatment of Osteoporosis, with a Focus on 2 Monoclonal Antibodies

Osteoporosis is a common skeletal disease characterized by bone loss and subsequent increased risk of fragility fractures. Recent advances in our mechanistic understanding of molecular communications among osteoblasts, osteoclasts, and osteocytes give insight into the important roles of the canonical Wnt/β-catenin pathway and the RANK/RANKL/OPG pathway in the process of bone remodeling. Due to the translation of the canonical Wnt/β-catenin pathway and the RANK/RANKL/OPG pathway in the regulation of osteoblasts and osteoclasts, new targets have been studied in recent years, such as sclerostin and receptor activator of NF-κB ligand (RANKL). In this review, we first introduce the signaling pathways involved in interactions among osteoblasts, osteoclasts, and osteocytes. Next, we describe clinical trials of denosumab and romosozumab, which are monoclonal antibodies that target RANKL and sclerostin, respectively. We analyze the efficacy of these drugs and provide a profile for the management of osteoporosis.

HDL impairs osteoclastogenesis and induces osteoclast apoptosis via upregulation of ABCG1 expression

Cholesterol is one of the major components of biological membranes and has an important function in osteoclast formation and survival. It has been reported that high-density lipoprotein (HDL) promotes cholesterol efflux from osteoclasts and induces their apoptosis, but the underlying mechanisms are unclear. In this study, we investigated how HDL promotes osteoclast cholesterol efflux and explored its effect on osteoclast formation and survival. Our results showed that the maximum diameter and fusion index of osteoclasts were decreased, while the ratios of osteoclasts with pyknotic nuclei were increased when cells were treated with HDL (600 ng/ml), as revealed by tartrate-resistant acid phosphatase-positive staining and microscopy assay. HDL enhanced cellular cholesterol efflux from osteoclasts in both concentration- and time-dependent manners. The ability of HDL3 to stimulate cholesterol efflux was stronger than preβ-HDL, HDL2, and ApoAI. Knockdown of ABCG1 expression reduced HDL-mediated cholesterol efflux and restored the HDL-induced reduction in osteoclast formation. Finally, HDL3 promoted sphingomyelin efflux from osteoclasts and reduced the expression of caveolin-1. Together, the findings demonstrate that HDL3 upregulates ABCG1 expression and promotes cholesterol efflux from osteoclast, impairs cholesterol homeostasis in osteoclasts, and consequently enhances osteoclast apoptosis.

Genetic deletion of muscle RANK or selective inhibition of RANKL is not as effective as full-length OPG-fc in mitigating muscular dystrophy

Although there is a strong association between osteoporosis and skeletal muscle atrophy/dysfunction, the functional relevance of a particular biological pathway that regulates synchronously bone and skeletal muscle physiopathology is still elusive. Receptor-activator of nuclear factor κB (RANK), its ligand RANKL and the soluble decoy receptor osteoprotegerin (OPG) are the key regulators of osteoclast differentiation and bone remodelling. We thus hypothesized that RANK/RANKL/OPG, which is a key pathway for bone regulation, is involved in Duchenne muscular dystrophy (DMD) physiopathology. Our results show that muscle-specific RANK deletion (mdx-RANK^mko) in dystrophin deficient mdx mice improves significantly specific force [54% gain in force] of EDL muscles with no protective effect against eccentric contraction-induced muscle dysfunction. In contrast, full-length OPG-Fc injections restore the force of dystrophic EDL muscles [162% gain in force], protect against eccentric contraction-induced muscle dysfunction ex vivo and significantly improve functional performance on downhill treadmill and post-exercise physical activity. Since OPG serves a soluble receptor for RANKL and as a decoy receptor for TRAIL, mdx mice were injected with anti-RANKL and anti-TRAIL antibodies to decipher the dual function of OPG. Injections of anti-RANKL and/or anti-TRAIL increase significantly the force of dystrophic EDL muscle [45% and 17% gains in force, respectively]. In agreement, truncated OPG-Fc that contains only RANKL domains produces similar gains, in terms of force production, than anti-RANKL treatments. To corroborate that full-length OPG-Fc also acts independently of RANK/RANKL pathway, dystrophin/RANK double-deficient mice were treated with full-length OPG-Fc for 10 days. Dystrophic EDL muscles exhibited a significant gain in force relative to untreated dystrophin/RANK double-deficient mice, indicating that the effect of full-length OPG-Fc is in part independent of the RANKL/RANK interaction. The sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) activity is significantly depressed in dysfunctional and dystrophic muscles and full-length OPG-Fc treatment increased SERCA activity and SERCA-2a expression. These findings demonstrate the superiority of full-length OPG-Fc treatment relative to truncated OPG-Fc, anti-RANKL, anti-TRAIL or muscle RANK deletion in improving dystrophic muscle function, integrity and protection against eccentric contractions. In conclusion, full-length OPG-Fc represents an efficient alternative in the development of new treatments for muscular dystrophy in which a single therapeutic approach may be foreseeable to maintain both bone and skeletal muscle functions.

The Role of Osteoprotegerin as a Cardioprotective Versus Reactive Inflammatory Marker: the Chicken or the Egg Paradox

Cardiovascular disease is one of the most frequent causes of mortality and morbidity worldwide. Several variables have been identified as risk factors for cardiovascular disease. Recently, the role of receptor activator of nuclear factor kappa B, receptor activator of nuclear factor kappa B ligand, and the osteoprotegerin system has been recognized as more important in the pathogenesis of cardiovascular disease. Besides their roles in the regulation of bone resorption, these molecules have been reported to be associated with the pathophysiology of cardiovascular disease. There are conflicting data regarding the impact of osteoprotegerin, a glycoprotein with a regulatory role in the cardiovascular system. The aim of this review is to discuss the current knowledge and the role of osteoprotegerin in cardiovascular disease.

Juvenile Paget disease

Juvenile Paget disease (JPD) is a rare disorder, mainly caused by mutations in the gene TNFRSF11B that encodes osteoprotegerin (OPG). Loss of OPG action causes generalized, extremely rapid bone turnover. The clinical manifestations are both skeletal - progressive skeletal deformity that develops in childhood - and extra-skeletal, including hearing loss, retinopathy, vascular calcification and internal carotid artery aneurysm formation. The severity of the phenotype seems to be related to the severity of TNFRSF11B gene deactivation. JPD is characterized biochemically by very high alkaline phosphatase activity, as well as other bone turnover markers. Bisphosphonates are commonly used to reduce the greatly accelerated bone turnover and can ameliorate the skeletal phenotype, if started early enough in childhood and continued at least until growth is complete. Limited evidence from patients treated with recombinant OPG or denosumab also provided favorable results. Recombinant OPG would represent a replacement treatment, but it is unavailable for clinical use. It seems that life-long treatment with anti-resorptives is required, since the disease is reactivated after treatment discontinuation. An international collaborating network for the continuous registration and follow-up of JPD patients could be helpful in the future.

Propofol attenuates osteoclastogenesis by lowering RANKL/OPG ratio in mouse osteoblasts

Bone remodeling plays an important role in the bone healing process; for example, following fracture. The relative ratio of the receptor activator of nuclear factor kappa B ligand (RANKL)/ osteoprotegerin (OPG) controls osteoclast differentiation, thereby playing a pivotal role in the regulation of bone remodeling. Propofol, a widely used anesthetic agent in orthopedic procedures, is considered to possess potential antioxidant properties owing to its structural similarity to α-tocopherol. Antioxidants are known to enhance bone healing. Accordingly, in the present study, we aimed to investigate osteoblastic differentiation and RANKL/OPG expression following propofol administration, in order to assess the potentially beneficial effects of this drug on the bone remodeling process, using calvarial primary osteoblasts from newborn mice. Calvarial pre-osteoblast cells were cultured in media containing clinically relevant concentrations of propofol, and cytotoxicity, effects on cell proliferation, osteogenic activity, and osteoclastogenesis were examined. The present findings indicated that propofol did not exert cytotoxic effects or alter cell proliferation in primary calvarial osteoblasts. Further, propofol did not affect osteoblast differentiation. The RANKL/OPG ratio was found to be decreased following propofol administration, and osteoclastogenesis was significantly reduced, indicating that propofol attenuated the osteoclastogenesis-supporting activity of osteoblasts. The results demonstrate that propofol, at clinically relevant concentrations, exerts beneficial effects on bone remodeling by attenuating osteoclastogenesis via suppression of the RANKL/OPG expression axis.

Beyond Antibodies: B Cells and the OPG/RANK-RANKL Pathway in Health, Non-HIV Disease and HIV-Induced Bone Loss

HIV infection leads to severe B cell dysfunction, which manifests as impaired humoral immune response to infection and vaccinations and is not completely reversed by otherwise effective antiretroviral therapy (ART). Despite its inability to correct HIV-induced B cell dysfunction, ART has led to significantly increased lifespans in people living with HIV/AIDS. This has in turn led to escalating prevalence of non-AIDS complications in aging HIV-infected individuals, including malignancies, cardiovascular disease, bone disease, and other end-organ damage. These complications, typically associated with aging, are a significant cause of morbidity and mortality and occur significantly earlier in HIV-infected individuals. Understanding the pathophysiology of these comorbidities and delineating clinical management strategies and potential cures is gaining in importance. Bone loss and osteoporosis, which lead to increase in fragility fracture prevalence, have in recent years emerged as important non-AIDS comorbidities in patients with chronic HIV infection. Interestingly, ART exacerbates bone loss, particularly within the first couple of years following initiation. The mechanisms underlying HIV-induced bone loss are multifactorial and complicated by the fact that HIV infection is linked to multiple risk factors for osteoporosis and fracture, but a very interesting role for B cells in HIV-induced bone loss has recently emerged. Although best known for their important antibody-producing capabilities, B cells also produce two cytokines critical for bone metabolism: the key osteoclastogenic cytokine receptor activator of NF-κB ligand (RANKL) and its physiological inhibitor osteoprotegerin (OPG). Dysregulated B cell production of OPG and RANKL was shown to be a major contributor to increased bone loss and fracture risk in animal models and HIV-infected humans. This review will summarize our current knowledge of the role of the OPG/RANK–RANKL pathway in B cells in health and disease, and the contribution of B cells to HIV-induced bone loss. Data from mouse studies indicate that RANKL and OPG may also play a role in B cell function and the implications of these findings for human B cell biology, as well as therapeutic strategies targeting the OPG/RANK–RANKL pathway, will be discussed.

Coenzyme Q10 promotes osteoblast proliferation and differentiation and protects against ovariectomy-induced osteoporosis

Coenzyme Q10 (CoQ10) is a fat‑soluble vitamin‑like substance used for the treatment of a variety of disorders, including osteoporosis. The exact mechanism underlying CoQ10‑mediated protection against osteoporosis remains to be elucidated. The present study aimed to evaluate the effect of CoQ10 on osteoblastic cell proliferation and differentiation, and therapeutic effects on a rat model of osteoporosis. Following treatment with different concentrations of CoQ10, cell proliferation and differentiation of rat bone marrow stromal cells (BMSCs), and expression of osteoblastogenic markers, were measured. Rats with osteoporosis subjected to ovariectomy (OVX) were treated with different concentrations of CoQ10. Serum levels of estrogen and bone metabolism markers were measured. Micro computed tomography scans were used to analyze morphological changes in bones. In addition, mRNA and protein levels of phosphatidylinositol 3,4,5‑trisphosphate 3‑phosphatase and dual‑specificity protein phosphatase PTEN (PTEN)/phosphatidylinositol 4,5‑bisphosphate 3‑kinase (PI3K)/RAC‑alpha serine/threonine‑protein kinase(AKT), were determined. CoQ10 significantly increased the proliferation and osteogenic differentiation of BMSCs in a dose‑dependent manner, with an increased expression of osteogenic markers. CoQ10 significantly decreased bone resorption but exhibited no effect on serum E2 levels in vivo. CoQ10 markedly enhanced bone formation. Furthermore, the abundance of p‑PI3K and p‑AKT increased while PTEN levels decreased in a dose‑dependent manner following administration of CoQ10. CoQ10 stimulates the proliferation and differentiation of BMSCs and is effective for the treatment of OVX‑induced osteoporosis in rats. The above effects of CoQ10 may be mediated by activation of the PTEN/PI3K/AKT pathway.

Elevated serum osteoprotegerin may predict peripheral arterial disease after kidney transplantation: a single-center prospective cross-sectional study in Taiwan

Background

Osteoprotegerin (OPG) is a potential biomarker for severity and complications of cardiovascular diseases. Peripheral arterial disease (PAD) is associated with an increased risk of death in kidney transplantation (KT) patients. This prospective cross-sectional study evaluated the relationship between serum OPG and PAD in KT patients.

Methods

Seventy-four KT patients were enrolled for this PAD study. Fasting blood samples were obtained to measure serum OPG levels by using enzyme-linked immunosorbent assay kits. The ankle-brachial index (ABI) of less than 0.9 was applied for PAD diagnosis.

Results

Thirteen patients (17.6%) were diagnosed with PAD. Diabetes (P = 0.025), smoking (P = 0.010), and increased OPG levels (P = 0.001) were significantly more frequent in the PAD group. Multivariate logistic regression analysis showed that serum OPG (odds ratio [OR], 1.336; 95% CI [1.108–1.611]; P = 0.002) and diabetes (OR, 7.120; 95% CI [1.080–46.940]; P = 0.041) were independent predictors of PAD in KT patients. The area under the receiver operating characteristic (ROC) curve determined that the probability of a serum OPG level of 7.117 pg/L in predicting PAD in KT patients was 0.799 (95% CI [0.690–0.884]; P < 0.001).

Discussion

Exploration of reliable biomarkers for early identification of vascular risk is crucial for KT patients. Elevated serum OPG levels may predict PAD in KT patients with cutoff value of 7.117 pg/L.

The Effect of RANKL/OPG Balance on Reducing Implant Complications

Despite the phenomenal success of implants particularly in the realms of dentistry and orthopaedics, there are still challenges to overcome. The failure of implants resulting from infection, prosthetic loosening, and non-union continue to be the most notorious examples. The cascade of fracture healing and bone repair, especially with the presence of an implant, is complex because it involves a multifaceted immune response alongside the intricate process of bone formation and remodelling. Bone loss is a serious clinical problem that is frequently accompanied by chronic inflammation, illustrating that there is a convoluted relationship between inflammation and bone erosion. The effects of pro-inflammatory factors play a significant role in initiating and maintaining osteoclastogenesis that results in bone resorption by osteoclasts. This is because there is a disruption of the relative ratio between Receptor Activator of Nuclear Factor κB-Ligand (RANKL) and osteoprotegerin (OPG), which is central to modulating bone repair and remodelling. This review aims to provide a background to the bone remodelling process, the bone repair cascade post-implantation, and the associated complications. Furthermore, current clinical solutions that can influence bone formation via either internal or extrinsic mechanisms will be described. These efficacious treatments for osteolysis via targeting the RANKL/OPG ratio may be crucial to reducing the incidence of related implant failures in the future.

Local application of osteoprotegerin-chitosan gel in critical-sized defects in a rabbit model

BACKGROUND

Osteoprotegerin (OPG) is used for the systemic treatment of bone diseases, although it has many side effects. The aim of this study was to investigate a newly formulated OPG-chitosan gel for local application to repair bone defects. Recent studies have reported that immunodetection of osteopontin (OPN) and osteocalcin (OC) can be used to characterise osteogenesis and new bone formation.

METHODS

The osteogenic potential of the OPG-chitosan gel was evaluated in rabbits. Critical-sized defects were created in the calvarial bone, which were either left unfilled (control; group I), or filled with chitosan gel (group II) or OPG-chitosan gel (group III), with rabbits sacrificed at 6 and 12 weeks. Bone samples from the surgical area were decalcified and treated with routine histological and immunohistochemical protocols using OC, OPN, and cathepsin K (osteoclast marker) antibodies. The toxicity of the OPG-chitosan gel was evaluated by biochemical assays (liver and kidney function tests).

RESULTS

The mean bone growth in defects filled with the OPG-chitosan gel was significantly higher than those filled with the chitosan gel or the unfilled group (p < 0.05). At 6 and 12 weeks, the highest levels of OC and OPN markers were found in the OPG-chitosan gel group, followed by the chitosan gel group. The number of osteoclasts in the OPG-chitosan gel group was lower than the other groups. The results of the liver and kidney functional tests indicated no signs of harmful systemic effects of treatment. In conclusion, the OPG-chitosan gel has many characteristics that make it suitable for bone repair and regeneration, highlighting its potential benefits for tissue engineering applications.

Sortase A-aided Escherichia coli expression system for functional osteoprotegerin cysteine-rich domain

As a natural inhibitor of the receptor activator of nuclear factor-кB ligand (RANKL), osteprotegerin (OPG) is considered a promising treatment for metabolic bone diseases. Typical approaches for preparing recombinant OPG or its derivatives employ eukaryotic expression systems. Due to the advantages of a prokaryotic expression system, which include its convenience, low cost, and abundant production, in this study, we establish a strategy for preparing functional OPG using the Escherichia coli expression system. After initial failures in preparation of OPG and its truncation, OPG cysteine-rich domain (OPG-CRD/OPGT) by using pET and pGEX vectors, we constructed a sortase A (SrtA)-aided E. coli expression system, in which the expressed protein was a self-cleaving SrtA fusion protein. Using this system, we successfully prepared the recombinant OPGT protein. The BIAcore analyses indicated that the prepared OPGT had high affinities in binding with RANKL and TRAIL. Cell experiments confirmed the inhibitory effects of the prepared OPGT on RANKL-induced osteoclast differentiation and TRAIL-induced tumor cell apoptosis. The sortase A-aided E. coli expression system for OPGT established in this study may contribute to further studies and commercial applications of OPG.

Estrogen stimulates osteoprotegerin expression via the suppression of miR-145 expression in MG-63 cells

Osteoprotegerin (OPG) is implicated in the pathogenesis of postmenopausal osteoporosis, and other metabolic bone diseases caused by estrogen deficiency. Previous studies have demonstrated that estrogen may stimulate OPG expression in osteoblast cells at the transcriptional level; however, whether estrogen can regulate OPG expression at a post-transcriptional level remains elusive. The present study aimed to investigate the role of microRNA (miRNA) in estrogen-mediated OPG production in human osteoblast-like MG-63 cells. The results from ELISA, western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) confirmed that estrogen may upregulate OPG expression. Mechanistic studies indicated that estrogen increased the activity of a luciferase reporter harboring the OPG 3′-untranslated region (3′-UTR). Bioinformatics analysis demonstrated that there is a potential targeting site in the OPG 3′-UTR for miRNA (miR)-145, which is associated with osteoblast differentiation. The results of an RT-qPCR suggested that estrogen suppressed miR-145 expression. In addition, dual-luciferase assay, RT-qPCR and western blot analysis indicated that miR-145 directly targets and negatively regulates OPG expression. Furthermore, transfection of cells with miR-145 mimics was able to partially inhibit the induction of OPG expression by estrogen, thus confirming the role of miR-145 in estrogen-mediated OPG induction. Taken together, the results of the present study demonstrated that estrogen may post-transcriptionally regulate OPG expression through suppression of miR-145 expression.

Potassium Channel-blockers as Therapeutic Agents to Interfere with Bone Resorption of Periodontal Disease

Inflammatory lesions of periodontal disease contain all the cellular components, including abundant activated/memory T- and B-cells, necessary to control immunological interactive networks and to accelerate bone resorption by RANKL-dependent and -independent mechanisms. Blockade of RANKL function has been shown to ameliorate periodontal bone resorption and other osteopenic disorders without affecting inflammation. Development of therapies aimed at decreasing the expression of RANKL and pro-inflammatory cytokines by T-cells constitutes a promising strategy to ameliorate not only bone resorption, but also inflammation. Several reports have demonstrated that the potassium channels Kv1.3 and IKCa1, through the use of selective blockers, play important roles in T-cell-mediated events, including T-cell proliferation and the production of pro-inflammatory cytokines. More recently, a potassium channel-blocker for Kv1.3 has been shown to down-regulate bone resorption by decreasing the ratio of RANKL-to-OPG expression by memory-activated T-cells. In this article, we first summarize the mechanisms by which chronically activated/memory T-cells, in concert with B-cells and macrophages, trigger inflammatory bone resorption. Then, we describe the main structural and functional characteristics of potassium channels Kv1.3 and IKCa1 in some of the cells implicated in periodontal disease progression. Finally, this review elucidates some recent advances in the use of potassium channel-blockers of Kv1.3 and IKCa1 to ameliorate the clinical signs or side-effects of several immunological disorders and to decrease inflammatory bone resorption in periodontal disease. ABBREVIATIONS: AICD, activation-induced cell death; APC, antigen-presenting cells; B(K), large conductance; CRAC, calcium release-activated calcium channels; DC, dendritic cell; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; IFN-γ, interferon-γ; IP3, inositol (1,4,5)-triphosphate; (K)ir, inward rectifier; JNK, c-Jun N-terminal kinase; I(K), intermediate conductance; LPS, lipopolysaccharide; L, ligand; MCSF, macrophage colony-stimulating factor; MHC, major histocompatibility complex; NFAT, nuclear factor of activated T-cells; RANK, receptor activator of nuclear factor-κB; TCM, central memory T-cells; TEM, effector memory T-cells; TNF, tumor necrosis factor; TRAIL, TNF-related apoptosis-inducing ligand; OPG, osteoprotegerin; Omp29, 29-kDa outer membrane protein; PKC, protein kinase C; PLC, phospholipase C; RT-PCR, reverse-transcriptase polymerase chain-reaction; S(K), small conductance; TCR, T-cell receptor; and (K)v, voltage-gated.

Fracture healing and biomarker expression in a diabetic Zucker rat model

BACKGROUND

Persons with diabetes have a higher incidence of fractures compared with persons without diabetes. However, there is little published information concerning the deleterious effect of late-stage diabetes on fracture healing. There are no studies using animal models that evaluate the effect of advanced diabetes on fracture healing. The purpose of our study was to evaluate cytokine expression, specifically macrophage inflammatory protein 1 (MIP-1) and vascular endothelial growth factor, in fracture healing in a type 2 diabetes rat model.

METHODS

We evaluated biomarker expression after femur fracture using a rat model. The two groups consisted of 24 Zucker diabetic rats (study group) and 12 Zucker lean rats (control group). An independent reviewer was used to assess delayed union. We evaluated serum samples 2, 4, 7, and 14 days after surgery for MIP-1, vascular endothelial growth factor, leptin, and other cytokine levels.

RESULTS

At 3 weeks, Kaplan-Meier estimates showed that 45.8% of femur fractures in Zucker diabetic rats had healed, whereas 81.8% of those in Zucker lean rats had healed (P = .02). A logistic regression model to predict fast healing that included the three cytokines and diabetes status showed that the only factor achieving significance was MIP-1α. Vascular endothelial growth factor was the only biomarker to show significance compared with delayed healing.

CONCLUSIONS

These results confirm significant differences in biomarker expression between diabetic and nondiabetic rats during bone healing. The key factors for bone healing may appear early in the healing process, whereas differences in diabetes versus nondiabetes are seen later in the healing process. Increased levels of MIP-1α were associated with the likelihood of delayed healing.

Advances in Controlled Drug Delivery for Treatment of Osteoporosis

Osteoporosis, which is characterized by resorption of bone exceeding formation, remains a significant human health concern, and the impact of this condition will only increase with the "graying" of the worldwide population. This review focuses on current and emerging approaches for delivering therapeutic agents to restore bone remodeling homeostasis. Well-known antiresorptive and anabolic agents, such as estrogen, estrogen analogs, bisphosphonates, calcitonin, and parathyroid hormone, along with newer modulators and antibodies, are primarily administered orally, intravenously, or subcutaneously. Although these treatments can be effective, continuing problems include patient noncompliance and adverse systemic or remote-site effects. Controlled drug delivery via polymeric, targeted, and active release systems extends drug half-life by shielding against premature degradation and improves bioavailability while also providing prolonged, sustained, or intermittent release at therapeutic doses to more effectively treat osteoporosis and associated fracture risk.

Osteoprotegerin gene-modified BMSCs with hydroxyapatite scaffold for treating critical-sized mandibular defects in ovariectomized osteoporotic rats

Women with postmenopausal osteoporosis are at a high risk for fracture as their bone resorption rate exceeds bone formation rate, resulting in decreased bone mineral density and microarchitectural deterioration. Osteoprotegerin (OPG), a known therapeutic agent capable of inhibiting osteoclastogenesis, has been used in treatment of chronic bone resorptive diseases. On the other hand, bone mesenchymal stem cells (BMSCs) play an important role in bone formation. To inhibit excessive bone resorption and increase bone formation, we developed a novel therapeutic strategy by genetically modifying BMSCs for OPG delivery. The OPG gene-modified BMSCs were seeded on hydroxyapatite (HA) scaffolds to promote bone regeneration in critical-sized mandibular bone defects in ovariectomy (OVX) induced osteoporotic rats. Rat BMSCs were infected with human OPG adenoviruses (OPG-BMSCs). The gene-modified cells expressed higher OPG gene level than the control Ad-BMSCs (p<0.05) and maintained high expression of OPG protein for more than 2weeks. Our in vitro bone resorption experiment demonstrated that OPG-BMSCs were capable to suppress osteoclast differentiation and subsequently inhibit osteoclast-mediated bone resorption. The micro-CT and histological results showed that HA-OPG-BMSC constructs boosted bone formation and reduced osteoclastogenesis in OVX rat mandibular bone defects. In conclusion, the novel OPG-BMSC-HA constructs were demonstrated to be able to orchestrate bone-forming BMSCs and bone-resorbing osteoclasts, with the potential for osteoporotic-related bone defect reconstruction applications.

STATEMENT OF SIGNIFICANCE

Women with postmenopausal osteoporosis are at a high risk for fracture as their bone resorption rate exceeds bone formation rate. Osteoprotegerin (OPG), a known therapeutic agent capable of inhibiting osteoclast cells, has been used in treatment of chronic bone resorptive diseases. To inhibit excessive bone resorption and increase bone formation, we developed a novel therapeutic strategy by genetically modifying bone marrow stem cells (BMSCs) for OPG delivery and seeding the cells on a hydroxyapatite (HA) scaffold for in vivo bone defect repair. The novel OPG-BMSC-HA constructs were able to orchestrate bone-forming BMSCs and bone-resorbing osteoclasts, demonstrating good potential for osteoporosis-related bone defect reconstruction treatments.

In vitro evaluation of osteoprotegerin in chitosan for potential bone defect applications

Background

The receptor activator of nuclear factor kappa-B (RANK)/RANK ligand/osteoprotegerin (OPG) system plays a critical role in bone remodelling by regulating osteoclast formation and activity. OPG has been used systemically in the treatment of bone diseases. In searching for more effective and safer treatment for bone diseases, we investigated newly formulated OPG-chitosan complexes, which is prepared as a local application for its osteogenic potential to remediate bone defects.

Methods

We examined high, medium and low molecular weights of chitosan combined with OPG. The cytotoxicity of OPG in chitosan and its proliferation in vitro was evaluated using normal, human periodontal ligament (NHPL) fibroblasts in 2D and 3D cell culture. The cytotoxicity of these combinations was compared by measuring cell survival with a tetrazolium salt reduction (MTT) assay and AlamarBlue assay. The cellular morphological changes were observed under an inverted microscope. A propidium iodide and acridine orange double-staining assay was used to evaluate the morphology and quantify the viable and nonviable cells. The expression level of osteopontin and osteocalcin protein in treated normal human osteoblast cells was evaluated by using Western blot.

Results

The results demonstrated that OPG in combination with chitosan was non-toxic, and OPG combined with low molecular weight chitosan has the most significant effect on NHPL fibroblasts and stimulates proliferation of cells over the period of treatment.

RANK-RANKL signalling in cancer

Oncogenic events combined with a favourable environment are the two main factors in the oncological process. The tumour microenvironment is composed of a complex, interconnected network of protagonists, including soluble factors such as cytokines, extracellular matrix components, interacting with fibroblasts, endothelial cells, immune cells and various specific cell types depending on the location of the cancer cells (e.g. pulmonary epithelium, osteoblasts). This diversity defines specific "niches" (e.g. vascular, immune, bone niches) involved in tumour growth and the metastatic process. These actors communicate together by direct intercellular communications and/or in an autocrine/paracrine/endocrine manner involving cytokines and growth factors. Among these glycoproteins, RANKL (receptor activator nuclear factor-κB ligand) and its receptor RANK (receptor activator nuclear factor), members of the TNF and TNFR superfamilies, have stimulated the interest of the scientific community. RANK is frequently expressed by cancer cells in contrast with RANKL which is frequently detected in the tumour microenvironment and together they participate in every step in cancer development. Their activities are markedly regulated by osteoprotegerin (OPG, a soluble decoy receptor) and its ligands, and by LGR4, a membrane receptor able to bind RANKL. The aim of the present review is to provide an overview of the functional implication of the RANK/RANKL system in cancer development, and to underline the most recent clinical studies.

Locally limited inhibition of bone resorption and orthodontic relapse by recombinant osteoprotegerin protein

OBJECTIVES

To determine minimal dose levels required for local inhibition of orthodontic relapse by recombinant OPG protein (OPG-Fc), while also determining effects of injected OPG-Fc on alveolar bone and long bone.

SETTING AND SAMPLE POPULATION

The Department of Orthodontics and Pediatric Dentistry at the University of Michigan. Eighteen male Sprague Dawley rats.

MATERIALS & METHODS

Maxillary molars were moved with nickel-titanium springs and then allowed to relapse in Sprague Dawley rats. Upon appliance removal, animals were injected with a single dose of 1.0 mg/kg OPG-Fc, 0.1 mg/kg OPG-Fc, or phosphate-buffered saline (vehicle) just distal to the molar teeth. Tooth movement measurements were made from stone casts, which were scanned and digitally measured. Alveolar tissues were examined by histology. Micro-computed tomography was used to quantify changes in alveolar and femur bone.

RESULTS

Local injection of OPG-Fc inhibited molar but not incisor relapse, when compared to vehicle-injected animals. No significant differences in alveolar or femur bone were seen between the three treatment groups after 24 days of relapse.

CONCLUSIONS

Our results demonstrate that a single local injection of OPG-Fc effectively inhibits orthodontic relapse, with minimal systemic bone metabolic effects. Our results also show that a single injection of OPG-Fc will influence tooth movement only in teeth close to the injection site. These findings indicate that OPG-Fc has potential as a safe and effective pharmacological means to locally control osteoclasts, for uses such as maintaining anchorage during orthodontic tooth movement and preventing orthodontic relapse in humans.

From bones to blood pressure, developing novel biologic approaches targeting the osteoprotegein pathway for pulmonary vascular disease

Osteoprotegerin (tnfsf11b, OPG) is a soluble member of the TNF superfamily originally described as an important regulator of osteoclastogenesis almost 20 years ago. OPG is a heparin-binding secreted glycoprotein that exists as a 55–62 kDa monomer or a 110–120 kDa disulphide-linked homodimer. Acting as a soluble decoy receptor for RANKL, OPG actively regulates RANK signalling, and thereby osteoclastogenesis. OPG has subsequently been shown to also be a decoy receptor TNF related apoptosis inducing-ligand (tnfsf10, TRAIL, Apo2L). TRAIL is a type II transmembrane protein that is widely expressed in a variety of human tissues, including the spleen, lung, and prostate. Through binding to TRAIL, OPG can inhibit TRAIL-induced apoptosis of cancer cells. More recently, OPG has been demonstrated to be secreted by, and influence, vascular smooth muscle cells phenotype particularly related to vascular calcification and pulmonary vascular remodelling. In pulmonary artery smooth muscle cell (PASMC) suppression of BMP, induction of 5-HT and IL-1 signalling have been shown to stimulate the release of OPG in vitro, which causes cell migration and proliferation. Patients with idiopathic PAH (IPAH) demonstrate increased circulating and tissue levels of OPG, and circulating serum levels predict survival. In pre-clinical models, OPG levels correlate with disease severity. Since OPG is a naturally circulating protein, we are investigating the potential of novel biologic antibody therapies to rescue PAH phenotype in disease models. Further pre-clinical and mechanistic data are forthcoming, but we believe current published data identify OPG as an exciting and novel therapeutic target in PAH.

Decreased Bone Mineral Density Is an Independent Predictor for the Development of Atherosclerosis: A Systematic Review and Meta-Analysis

Background

There is conflicting evidence regarding the association between decreased bone mineral density (BMD) and atherosclerosis. To this end, we performed a systematic review and meta-analysis to clarify the association.

Methods

To identify relevant studies, PubMed, Embase, and the Cochrane Library were systematically searched up to November 2015. All observational and comparative studies directly investigating the relationship between decreased BMD and clinical consequences of atherosclerotic vascular abnormalities, including carotid artery calcification (CAC), cardiovascular disease (CAD), and coronary artery disease (CAD) were obtained, without limitation of language or publication year.

Results

A total of 25 studies involving 10,299 patients were included. The incidence of atherosclerotic vascular abnormalities was significantly increased in low BMD patients, compared to patients with normal BMD (OR, 1.81, 95% CI [1.01, 2.19], p<0.00001)). Similar results were also observed for postmenopausal women (OR, 2.23, 95% CI [1.72, 2.89], p<0.00001). Subgroup analyses of osteopenia, osteoporosis, and normal BMD also revealed that the combined ORs for the incidence of atherosclerotic vascular abnormalities increased as BMD decreased. Of note, after adjusting for age, sex, body mass index (BMI) and other vascular risk factors, decreased BMD remained significantly associated with the incidence of atherosclerotic vascular abnormalities (OR, 2.96, 95% CI [2.25, 3.88], p < 0.00001).

Conclusions

Based on the results of this study, decreased BMD is an independent predictor for the development of atherosclerosis in elderly individuals. Moreover, the risk of atherosclerotic vascular abnormalities increased as BMD decreased. Future studies focusing on individuals with different severities of atherosclerosis and comorbidities are of interest.

Osteoprotegerin Regulates Pancreatic β-Cell Homeostasis upon Microbial Invasion

Osteoprotegerin (OPG), a decoy receptor for receptor activator of NF-κB ligand (RANKL), antagonizes RANKL’s osteoclastogenic function in bone. We previously demonstrated that systemic administration of lipopolysaccharide (LPS) to mice elevates OPG levels and reduces RANKL levels in peripheral blood. Here, we show that mice infected with Salmonella, Staphylococcus, Mycobacteria or influenza virus also show elevated serum OPG levels. We then asked whether OPG upregulation following microbial invasion had an effect outside of bone. To do so, we treated mice with LPS and observed OPG production in pancreas, especially in β-cells of pancreatic islets. Insulin release following LPS administration was enhanced in mice lacking OPG, suggesting that OPG inhibits insulin secretion under acute inflammatory conditions. Consistently, treatment of MIN6 pancreatic β-cells with OPG decreased their insulin secretion following glucose stimulation in the presence of LPS. Finally, our findings suggest that LPS-induced OPG upregulation is mediated in part by activator protein (AP)-1 family transcription factors, particularly Fos proteins. Overall, we report that acute microbial infection elevates serum OPG, which maintains β-cell homeostasis by restricting glucose-stimulated insulin secretion, possibly preventing microbe-induced exhaustion of β-cell secretory capacity.

Osteoprotegerin disrupts peripheral adhesive structures of osteoclasts by modulating Pyk2 and Src activities

Osteoprotegerin has previously been shown to modulate bone mass by blocking osteoclast maturation and function. The detailed mechanisms of osteoprotegerin-induced disassembly of podosomes, disruption of adhesive structures and modulation of adhesion-related proteins in osteoclasts, however, are not well characterized. In this study, tartrate-resistant acidic phosphatase staining demonstrated that osteoprotegerin inhibited differentiation of osteoclasts. The use of scanning electron microscopy, real-time cell monitoring and confocal microscopy indicated that osteoclasts responded in a time and dose-dependent manner to osteoprotegerin treatments with retraction of peripheral adhesive structures and detachment from the extracellular substrate. Combined imaging and Western blot studies showed that osteoprotegerin induced dephosphorylation of Tyr 402 in Pyk2 and decreased its labeling in peripheral adhesion regions. osteoprotegerin induced increased intracellular labeling of Tyr 402 in Pyk2, Tyr 416 in Src, increased dephosphorylation of Tyr 527 in Src, and increased Pyk2/Src association in the central region of osteoclasts. This evidence suggests that Src may function as an adaptor protein that competes for Pyk2 and relocates it from the peripheral adhesive zone to the central region of osteoclasts in response to osteoprotegerin treatment. Osteoprotegerin may induce podosome reassembly and peripheral adhesive structure detachment by modulating phosphorylation of Pyk2 and Src and their intracellular distribution in osteoclasts.

A comprehensive review of denosumab for bone metastasis in patients with solid tumors

BACKGROUND

Denosumab is fully human monoclonal antibody that specifically binds and inactivates receptor activator of NF-kB ligand (RANKL), an important ligand that regulates bone remodeling. In this review, we aimed to show the clinical data about denosumab treatment and discuss its advantages for the management of patients with solid tumors and bone metastasis.

SCOPE

Denosumab showed positive results in clinical studies of solid tumors with bone metastasis. PubMed database and ASCO Symposium Meeting abstracts were searched until August 2015 by using the terms 'denosumab', 'RANKL inhibitor' and 'bone metastasis'. The last search was on 21 August 2015. All resulting studies were retrieved and were also checked for related publications. Clinical trials in this review fulfilled the following criterion: inclusion of sufficient data to allow estimation of the efficacy and safety of denosumab.

FINDINGS

The effects of denosumab on skeletal-related events (SREs) were investigated in three large randomized trials: one in patients with breast cancer, one in patients with prostate cancer, and one in patients with multiple myeloma or solid tumors other than breast or prostate cancer. In the breast cancer and prostate cancer studies denosumab was non-inferior and also superior to zoledronic acid in terms of the primary outcome time to first on-study SRE. In the third study denosumab was non-inferior to zoledronic acid but was not superior to zoledronic acid in solid tumors excluding breast and prostate cancer with bone metastases. In the three studies median overall survival and disease progression rates were similar between zoledronic acid and denosumab. Denosumab has also been studied in bone loss associated with hormonal therapy in both breast and prostate cancer. Adjuvant denosumab significantly reduced the risk of clinical fracture risk by 50% in breast cancer patients and by 62% in non-metastatic prostate cancer patients treated with adjuvant aromatase inhibitors or androgen deprivation therapy. In addition, biochemical markers of bone turnover and fractures were significantly reduced in patients under denosumab treatment.

CONCLUSION

The promising outcomes in the initial trials with denosumab have shown clinical activity and a favorable safety profile in patients with solid tumors and bone metastasis. Denosumab significantly reduced treatment-related osteoporosis associated with breast and prostate cancer and was superior to zoledronic acid in prevention or delaying of SRE.

Hypocalcaemia in patients with metastatic bone disease treated with denosumab

BACKGROUND

This analysis was performed to further characterise treatment-emergent hypocalcaemia in patients with bone metastases receiving denosumab.

METHODS

Laboratory abnormalities and adverse events of hypocalcaemia in patients with metastatic bone disease were analysed using data from three identically designed phase 3 trials of subcutaneous denosumab 120 mg (n = 2841) versus intravenous zoledronic acid 4 mg (n = 2836).

RESULTS

The overall incidence of laboratory events of hypocalcaemia grade ⩾ 2 was higher with denosumab (12.4%) than with zoledronic acid (5.3%). Hypocalcaemia events were primarily grade 2 in severity and usually occurred within the first 6 months of treatment. Patients who reported taking calcium and/or vitamin D supplements had a lower incidence of hypocalcaemia. Prostate cancer or small-cell lung cancer, reduced creatinine clearance and higher baseline bone turnover markers of urinary N-telopeptide of type I collagen (uNTx; > 50 versus ⩽ 50 nmol/mmol) and bone-specific alkaline phosphatase (BSAP; > 20.77 μg/L [median] versus ⩽ 20.77 μg/L) values were important risk factors for developing hypocalcaemia. The risk associated with increased baseline BSAP levels was greater among patients who had > 2 bone metastases at baseline versus those with ⩽ 2 bone metastases at baseline.

CONCLUSION

Hypocalcaemia was more frequent with denosumab versus zoledronic acid, consistent with denosumab's greater antiresorptive effect. Low serum calcium levels and potential vitamin D deficiency should be corrected before initiating treatment with a potent osteoclast inhibitor, and corrected serum calcium levels should be monitored during treatment. Adequate calcium and vitamin D intake appears to substantially reduce the risk of hypocalcaemia.

Lipid metabolism disorders and bone dysfunction--interrelated and mutually regulated (review)

The association between lipid and bone metabolism has become an increasing focus of interest in recent years, and accumulating evidence has shown that atherosclerosis (AS) and osteoporosis (OP), a disorder of bone metabolism, frequently co-exist. Fat and bone are known to share a common progenitor cell: Multipotent mesenchymal stem cells (MSC) in the bone marrow (BM), which are able to differentiate into various cell phenotypes, including osteoblasts, adipocytes and chondrocytes. Laboratory-based and clinical trials have shown that increasing adipocytes are accompanied by a decrease in bone mineral density (BMD) and bone mass. Statins, lipid-lowering drugs used to treat hyperlipidemia, also provide benefit in the treatment of OP. There is thus evidence that the metabolism of lipids is correlated with that of bone, and that the two are mutually regulated. The present review primarily focuses on the potential association between lipid metabolism disturbance and OP, based on biological metabolism, pathophysiological processes, results from clinical and experimental animal studies, processes involved in the differentiation of adipocytes and osteoblasts, as well as pharmacological treatments of these diseases.

Anti-RANKL treatment improves screw fixation in cancellous bone in rats

Bisphosphonates improve implant fixation in randomised clinical trials of knee prostheses, hip prostheses and dental implants. However, a limited amount of bone resorption is required for bisphosphonates to exert an effect. Anti-RANKL treatment does not have this limitation, and we therefore tested whether if they might be more effective for improvement of implant fixation. This is of interest, as anti-RANKL treatment with denosumab is now in common clinical use. Male SD rats received a stain-less steel screw in the right proximal tibia and a drill hole in the left (n = 42). They were randomised to subcutaneous injections of either alendronate (20 μg/kg/day), alendronate (200 μg/kg/day), osteoprotegerin with an Fc tag (OPG-Fc; 8 mg/kg, twice weekly), or saline control. After 4 weeks, the fixation of the steel screw was measured by pull-out test. The tibia with the drill hole was evaluated with μCT. OPG-Fc increased the pull-out force compared to saline controls by 153% (p < 0.001). There was no significant difference between OPG-Fc and the alendronate groups. OPG-Fc increased the bone density (BV/TV) in the previous drill hole compared to controls 7-fold (p < 0.001). This increase was higher than with any alendronate dose (p < 0.001). OPG-Fc increased the bone density of the L5 vertebral body, but there was no significant difference between OPG-Fc and alendronate. Our results suggest that screw fixation in cancellous bone can be dramatically improved by an anti-RANKL agent. The effect was comparable to very high bisphosphonate doses. Screw insertion in cancellous bone elicits a metaphyseal fracture healing response, and our findings might be relevant not only for implant fixation, but also for fracture healing in cancellous bone.

Chronic kidney disease and the skeleton

Fractures across the stages of chronic kidney disease (CKD) could be due to osteoporosis, some form of renal osteodystrophy defined by specific quantitative histomorphometry or chronic kidney disease-mineral and bone disorder (CKD-MBD). CKD-MBD is a systemic disease that links disorders of mineral and bone metabolism due to CKD to either one or all of the following: abnormalities of calcium, phosphorus, parathyroid hormone or vitamin D metabolism; abnormalities in bone turnover, mineralization, volume, linear growth or strength; or vascular or other soft-tissue calcification. Osteoporosis, as defined by the National Institutes of Health, may coexist with renal osteodystrophy or CKD-MBD. Differentiation among these disorders is required to manage correctly the correct disorder to reduce the risk of fractures. While the World Health Organization (WHO) bone mineral density (BMD) criteria for osteoporosis can be used in patients with stages 1-3 CKD, the disorders of bone turnover become so aberrant by stages 4 and 5 CKD that neither the WHO criteria nor the occurrence of a fragility fracture can be used for the diagnosis of osteoporosis. The diagnosis of osteoporosis in stages 4 and 5 CKD is one of the exclusion-excluding either renal osteodystrophy or CKD-MBD as the cause of low BMD or fragility fractures. Differentiations among the disorders of renal osteodystrophy, CKD-MBD or osteoporosis are dependent on the measurement of specific biochemical markers, including serum parathyroid hormone (PTH) and/or quantitative bone histomorphometry. Management of fractures in stages 1-3 CKD does not differ in persons with or without CKD with osteoporosis assuming that there is no evidence for CKD-MBD, clinically suspected by elevated PTH, hyperphosphatemia or fibroblast growth factor 23 due to CKD. Treatment of fractures in persons with osteoporosis and stages 4 and 5 CKD is not evidence-based, with the exception of post-hoc analysis suggesting efficacy and safety of specific osteoporosis therapies (alendronate, risedronate and denosumab) in stage 4 CKD. This review also discusses how to diagnose and manage fragility fractures across the five stages of CKD.

Are OPG and RANKL involved in human fracture healing?

Human fracture healing is a complex interaction of several cytokines that regulate osteoblast and osteoclast activity. By monitoring OPG (osteoprotegerin) and sRANKL we aimed to possibly predict normal or impaired fracture healing. In 64 patients with a fracture of a long bone serum level of sRANKL and OPG were evaluated with respect to bony union (n=57) or pseudarthrosis (n=7). Measurements were carried out at admission and at 1, 2, 4, 6, 8, 12, 24, and 48 weeks after the injury. Patients' serum levels were compared to 33 healthy controls. Fracture hematoma contained significantly higher sRANKL and OPG concentrations compared to patients serum (p=0.005, p=0.028). OPG level in fracture hematoma was higher compared to the unions serum level (p=0.028). sRANKL was decreased in unions during the observation period. In non-unions sRANKL and OPG levels showed a variable course, with no statistical significance. This is the first study to document the course of OPG and sRANKL in normal and delayed human fracture healing emphasizing its local and systemic involvement. We provide evidence of strongly enhanced OPG levels in patients with a long bone fracture compared to healthy controls. Further, levels of free sRANKL were decreased during regular fracture repair.

OPG and PgR show similar cohort specific effects as prognostic factors in ER positive breast cancer

The RANK/RANKL/OPG pathway is well known for bone destruction in skeletal metastases but has also been implicated in osteoclast-independent roles in tumorigenesis and de novo metastasis. Experimental data suggest contribution of progesterone to tumorigenesis may be mediated by RANKL. Importantly, modulation of this pathway became possible through the availability of denosumab, an artificial counterpart of OPG, but significant gaps remain in the translation of preclinical findings on the pathway. We analyzed gene expression of RANK, RANKL and OPG from 40 Affymetrix datasets encompassing 4467 primary breast cancers and focused on ER positive disease. We did not observe a significant prognostic value of RANK and RANKL mRNA expression. In contrast, OPG was associated with a better prognosis among 1941 ER positive cancers (HR 0.64, 95% CI 0.53-0.77; P < 0.0001) using a cutoff from its highly bimodal expression. We detected considerable heterogeneity regarding the prognostic value of OPG between different datasets. This heterogeneity could neither be attributed to technical reasons nor to differences in standard clinical parameters or treatments of the cohorts. Interestingly, the prognostic value of the progesterone receptor and of OPG showed similar cohort specific effects. Still both factors were no surrogates for each other but contributed independent prognostic value in multivariate analyses. Thus, both OPG and PgR are independently associated with good prognosis in ER positive breast cancer. However both markers share common cohort specific differences in contrast to proliferation markers as Ki67 which may be based on the underlying biology.

Molecular and cellular basis of bone resorption

Osteoclast research has an exciting history and a challenging future. More than 3 decades ago, it became evident that bone-resorbing osteoclasts are of hematopoietic origin and are ultimately linked to the "basic multicellular unit," where they team up with the other cell types, including bone-forming osteoblasts. Since 2 decades, we have learned about the signaling pathways controlling genes relevant for osteoclastogenesis and bone resorption. It took another decade until the hypothesized "osteoclast differentiation" factor was discovered and was translated into an approved pharmacologic strategy. Here, the focus is on another molecular target, cathepsin K, a cysteine protease being released by the osteoclast into the resorption compartment. Genetic deletion and pharmacological blocking of cathepsin K reduces bone resorption but with ongoing bone formation. This observation not only holds great promise to become a new pharmacologic strategy, but it also provides new insights into the coordinated work of cells in the "basic multicellular unit" and thus, bridges the history and future of osteoclast research. This article is a short primer on osteoclast biology for readers of the special issue on odanacatib, a cathepsin K inhibitor.