Immunological characterization of circulating osteoprotegerin/osteoclastogenesis inhibitory factor: increased serum concentrations in postmenopausal women with osteoporosis

Osteoprotegerin Is Essential for the Development of Endothelial Dysfunction Induced by Angiotensin II in Mice

Opinions on the effects of osteoprotegerin (OPG) have evolved over the years from a protein protecting the vasculature from calcification to a cardiovascular risk factor contributing to inflammation within the vascular wall. Nowadays, the link between OPG and angiotensin II (Ang II) appears to be particularly important. In this study, the endothelial function was investigated in OPG-knockout mice (B6.129.S4-OPG, OPG-) and wild-type (C57BL/6J, OPG+) mice under basic conditions and after Ang II exposure by assessing the endothelium-dependent diastolic response of aortic rings to acetylcholine in vitro. A further aim of the study was to compare the effect of Ang II on the expression of cytokines in the aortic wall of both groups of mice. Our study shows that rings from OPG- mice had their normal endothelial function preserved after incubation with Ang II, whereas those from OPG+ mice showed significant endothelial dysfunction. We conclude that the absence of OPG, although associated with a pro-inflammatory cytokine profile in the vascular wall, simultaneously protects against Ang II-induced increases in pro-inflammatory cytokines in the murine vascular wall. Our study also demonstrates that the absence of OPG can result in a decrease in the concentration of pro-inflammatory cytokines in the vascular wall after Ang II exposure. The presence of OPG is therefore crucial for the development of Ang II-induced inflammation in the vascular wall and for the development of Ang II-induced endothelial dysfunction.

The association of osteoprotegerin and RANKL with osteoporosis: a systematic review with meta-analysis

OBJECTIVES

The OPG/RANKL signal pathway was important regulation mechanism of bone remodeling cycle, but the effect of osteoprotegerin (OPG) and RANKL in osteoporosis was uncertain. We did a systematic review with meta-analysis to assess the association between serum OPG/RANKL and osteoporosis.

METHODS

The systematic search, data extraction, critical appraisal, and meta-analysis were performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Randomized controlled studies were searched in PubMed, OvidMedline, Embase (1946 to present). Standard mean difference (SMD), and associated credible interval (CI) were calculated using RevMan statistical software to assess the continuous data. Heterogeneity in studies was measured by I2 values. Subgroup analysis was performed based on different bone turnover.

RESULTS

A total of 5 randomized controlled studies met the inclusion criteria. Both OPG and RANKL had no significant differences between the osteoporosis and control group, and the statistical heterogeneity was high in meta-analysis. However, RANKL had significant differences between the osteoporosis group with low bone turnover and control group (SMD =  - 1.17; 95% CI - 1.77 to 0.57; P value < 0.01) in subanalysis. Furthermore, the OPG/RANKL ratio was significant lower in the osteoporosis group than in the control group (SMD =  - 0.29; 95% CI - 0.57 to - 0.02; P value < 0.05), and the statistical heterogeneity was very low (Chi2 = 0.20, P = 0.66, I2 = 0%).

CONCLUSIONS

Our meta-analysis study supported OPG and RANKL were important modulatory factors of bone formation and resorption in bone turnover, respectively. Although the serum level of both OPG and RANKL were not associated with osteoporosis, but the OPG/RANKL ratio was associated with osteoporosis. In future, standardizing the test method and unit was good to clinical application.

Changes in alveolar bone structure during orthodontic tooth movement in adolescent and adult rats: A microcomputed tomography study

BACKGROUND

Increasing number of adults are willing to seek orthodontic treatment, but treatment duration for them is commonly longer. Although there have been studies on molecular biological changes during tooth movement, few have focused on microstructural changes in alveolar bone.

OBJECTIVE

This study aims to compare the microstructural changes in alveolar bone during orthodontic tooth movement in adolescent and adult rats.

METHODS

25 6-week-old and 25 8-month-old male Sprague-Dawley (SD) rats were used to build orthodontic tooth-movement models. On Days 0, 1, 3, 7 and 14, the rats were sacrificed. Microcomputed tomography was used to evaluate tooth movement, alveolar crest height loss and microstructural parameters of alveolar bone (bone volume fraction, trabecular thickness, trabecular separation and trabecular number).

RESULTS

Tooth movement in the adult group was slower than in the adolescent group. Alveolar bone crest height in adults was lower than it was in adolescents on Day 0. Under orthodontic force, the alveolar crest in both groups decreased and the degree of decrease are higher at early stage in adolescents. The microstructural parameters indicated that the alveolar bone was originally denser in the adult rats. With orthodontic force, it tended to be looser.

CONCLUSIONS

Under orthodontic force, changes in alveolar bone differ between adolescent and adult rats. Tooth movements in adults are slower, and the decrease in alveolar bone density are more severe.

Associations of Bone Mineral Density with RANKL and Osteoprotegerin in Arab Postmenopausal Women: A Cross-Sectional Study

Background and objective: There is limited information as to the association of several key bone markers with bone mineral density (BMD) in understudied ethnic groups. This study investigated the relationship between circulating levels of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-Β ligand (RANKL) with BMD in Arab postmenopausal women. Materials and methods: In this cross-sectional study, a total of 617 Saudi postmenopausal women from the Osteoporosis Registry of the Chair for Biomarkers of Chronic Diseases were included. Anthropometric data, BMD, and biochemical data were retrieved from the registry. Participants were stratified into three groups based on T-score; n = 169 with osteoporosis, n = 282 with osteopenia, and n = 166 normal. Analysis of bone markers including RANKL, OPG, osteocalcin, and N-terminal telopeptide (NTx) was completed using commercially available bioassays. Results: The results suggested that OPG was significantly and positively correlated with age in the osteoporosis group (r = 0.29, p < 0.05), while it was inversely correlated with BMD femoral neck left (r = −0.56, p < 0.001) and BMD femoral neck right (r = −0.37, p < 0.05) in the same group. Moreover, RANKL showed a significant inverse correlation with NTx in the osteopenia group (r = −0.37, p < 0.05). Furthermore, the RANKL/OPG ratio had a positive and significant correlation with BMI (r = 0.34, p < 0.05), BMD femoral neck left (r = 0.36, p < 0.05) and BMD femoral neck right (r = 0.35, p < 0.05) in the osteopenia group. By contrast, it showed a significant inverse correlation with waist to hip ratio in the osteoporosis group (r = −0.38, p < 0.05). Multiple regression analysis showed that OPG contributes to BMD variations in the osteopenia group (p = 0.03). Conclusions: In conclusion, changes in circulating levels of RANKL and OPG might be a protective mechanism contrary to the increased bone loss in postmenopausal women.

Rank-Rankl-Opg Axis in Multiple Sclerosis: The Contribution of Placenta

Women with multiple sclerosis (MS) can safely become pregnant and give birth, with no side effects or impediments. Pregnancy is generally accepted as a period of well-being in which relapses have a softer evolution, particularly in the third trimester. Herein, we hypothesized that the placenta, via its “secretome”, could contribute to the recognized beneficial effects of pregnancy on MS activity. We focused on a well-known receptor/ligand/decoy receptor system, such as the one composed by the receptor activator of nuclear factor-kB (RANK), its ligand (RANKL), and the decoy receptor osteoprotegerin (OPG), which have never been investigated in an integrated way in MS, pregnancy, and placenta. We reported that pregnancy at the term of gestation influences the balance between circulating RANKL and its endogenous inhibitor OPG in MS women. We demonstrated that the placenta at term is an invaluable source of homodimeric OPG. By functional studies on astrocytes, we showed that placental OPG suppresses the mRNA expression of the CCL20, a chemokine responsible for Th17 cell recruitment. We propose placental OPG as a crucial molecule for the recognized beneficial effect of late pregnancy on MS and its potential utility for the development of new and more effective therapeutic approaches.

Menopausal Transition: Prospective Study of Estrogen Status, Circulating MicroRNAs, and Biomarkers of Bone Metabolism

OBJECTIVE

Osteoporosis is associated with an impaired balance between bone resorption and formation, which in turn leads to bone loss and fractures. Many recent studies have underlined the regulatory role of microRNAs (miRNAs) in bone remodeling processes and their potential as biomarkers of osteoporosis. The purpose of this study was to prospectively examine the association of circulating miRNAs and bone biomarkers with estrogen status in women before and after oophorectomy, as well as in oophorectomized women on estrogen therapy.

METHODS

In this prospective study, we included 11 women before oophorectomy and hysterectomy and at 201 ± 24 days after the surgery. Another 11 women were evaluated 508 ± 127 days after oophorectomy and hysterectomy and after an additional 203 ± 71 days of estradiol treatment. Serum miRNAs were profiled by sequencing. Estrogen status and biomarkers of bone metabolism were quantified. Bone mineral density was assessed in the lumbar spine.

RESULTS

Our analysis revealed 17 miRNAs associated with estrogen levels. Of those miRNAs that were upregulated with estrogen deficiency and downregulated after estrogen therapy, miR-422a correlated with serum beta-carboxy-terminal type I collagen crosslinks (β-CTX) and procollagen 1 N-terminal propeptide (P1NP); and miR-1278 correlated with serum β-CTX, P1NP, osteocalcin, sclerostin, and Dickkopf-1(Dkk1). In contrast, we found an inverse association of miR-24-1-5p with estrogen status and a negative correlation with serum β-CTX, P1NP, osteoprotegerin, and sclerostin levels.

CONCLUSION

The reported miRNAs associated with estrogen status and bone metabolism could be potential biomarkers of bone pathophysiology and would facilitate studies on the prevention of postmenopausal osteoporosis. Our findings require validation in an extended cohort.

Age-related changes and reference intervals of RANKL, OPG, and bone turnover markers in Indian women

RANKL and OPG are cytokines involved in bone remodeling that makes them potential bone biomarkers. The reference interval for these cytokines, their ratio, and bone turnover markers CTX and PINP were established in Indian women, which may serve in diagnosis and management of osteoporosis.

PURPOSE

The aim of the study was to establish reference interval for RANKL, OPG, RANKL/OPG, and bone turnover markers CTX and PINP in healthy Indian women.

METHODS

This was a cross-sectional study on 374 healthy Indian women in the age group of 20-65 years. Serum levels of total RANKL, OPG, CTX, PINP, and estradiol were determined by commercial ELISA kits. The reference intervals for these cytokines and bone turnover markers were based on the 95% centrally distributed data.

RESULTS

Median RANKL (245.6 pmol/L vs. 149 pmol/L) and RANKL/OPG (38.7 vs. 20.4) were higher, while sCTX (380 ng/L vs. 551 ng/L) and OPG levels (6.1 pmol/L vs. 7.4 pmol/L) were lower in premenopausal women than those in postmenopausal women. PINP levels were comparable in both groups. Women were classified into 5 groups according to decades of age and the reference intervals for RANKL, OPG, RANKL/OPG ratio, and CTX and PINP in each group were reported.

CONCLUSION

We reported menopausal status-based and age-related reference intervals for serum RANKL, OPG, RANKL/OPG ratio, and CTX and PINP in healthy Indian women.

Osteoprotegerin and RANKL-RANK-OPG-TRAIL signalling axis in heart failure and other cardiovascular diseases

Osteoprotegerin (OPG) is a glycoprotein involved in the regulation of bone remodelling. OPG regulates osteoclast activity by blocking the interaction between the receptor activator of nuclear factor kappa B (RANK) and its ligand (RANKL). More and more studies confirm the relationship between OPG and cardiovascular diseases. Numerous studies have confirmed that a high plasma concentration of OPG and a low concentration of tumour necrosis factor–related apoptosis inducing ligand (TRAIL) together with a high OPG/TRAIL ratio are predictors of poor prognosis in patients with myocardial infarction. A high plasma OPG concentration and a high ratio of OPG/TRAIL in the acute myocardial infarction are a prognostic indicator of adverse left ventricular remodelling and of the development of heart failure. Ever more data indicates the participation of OPG in the regulation of the function of vascular endothelial cells and the initiation of the atherosclerotic process in the arteries. Additionally, it has been shown that TRAIL has a protective effect on blood vessels and exerts an anti-atherosclerotic effect. The mechanisms of action of both OPG and TRAIL within the cells of the vascular wall are complex and remain largely unclear. However, these mechanisms of action as well as their interaction in the local vascular environment are of great interest to researchers. This article presents the current state of knowledge on the mechanisms of action of OPG and TRAIL in the circulatory system and their role in cardiovascular diseases. Understanding these mechanisms may allow their use as a therapeutic target in cardiovascular diseases in the future.

Effect of cytotoxic chemotherapy on bone health among breast cancer patients. Does it require intervention?

BACKGROUND

Breast cancer (BC) is one of the most common malignancies worldwide. Although the burden and mechanisms of endocrine therapy-related bone loss are known, the evidence is scanty regarding the impact of cytotoxic chemotherapy on bone health. We have attempted to summarize the effect of cytotoxic chemotherapy on bone health in BC patients.

METHODS

A comprehensive literature search was performed via MEDLINE and Cochrane library databases to evaluate the effect of chemotherapy on bone health among women with BC. We included articles related to skeletal-related events, bone mineral density, bone turnover markers, osteoporosis-specific quality of life, bisphosphonate, and other bone-directed therapy. We excluded articles that included patients with metastatic breast cancer and patients receiving hormonal therapy.

DISCUSSION

Bone microenvironment in cancer is directly or indirectly influenced by clinical, hormonal, nutritional, and treatment factors. Calcitonin, parathyroid hormone, calcitriol, and estrogen are the major hormonal regulators. Bone turnover markers, namely bone formation and resorption markers, have been used to predict bone loss, fracture risk, and monitoring treatment response. Chemotherapeutic drugs such as anthracyclines and taxanes synergistically affect BMD and quality of life. Calcium, vitamin D, bisphosphonates, and denosumab are supplemented to prevent excess bone resorption. Bone-targeted anti-resorptive agents have been studied as potential anticancer agents in the adjuvant treatment of breast cancer.

CONCLUSION

This review summarizes the negative effect of chemotherapy on bone health of BC patients and the importance of preventing or treating bone loss.

Association of RANKL and OPG Gene Polymorphism in Arab Women with and without Osteoporosis

Receptor activator of the nuclear factor-κB ligand (RANKL) and osteoprotegerin genes (OPG) were identified as susceptible loci for postmenopausal osteoporosis (PMO) in various ethnicities, but neither have been studied in an Arabian population. Hence, the current study aimed to fill this gap. A total of 372 postmenopausal women (174 osteoporosis (OP) and 198 control group (CTRs)) were genotyped for four SNPs: rs2277438A/G and rs9533156T/C (RANKL), and rs2073618C/G and rs3102735T/C (OPG). Anthropometrics, bone mineral density, 25(OH)D and several other bone markers were measured. The frequency distribution of the heterozygous CG genotype of rs2073618 (OPG) was lower in the OP (36.8%) than in CTRs (47%) (OR: 0.6, 95% CI: 0.3–0.97; p = 0.041). No differences in the allelic/genotypic frequencies were detected between the two groups for all other studied SNPs. However, the heterozygous TC genotype of rs3102735 (OPG) was associated significantly with lower BMD at the femoral neck in OP subjects (p = 0.04). The homozygous rare CC genotype of rs9533156 (RANKL) was associated with lower 25(OH)D levels in CTRs (p = 0.032). In contrast, heterozygous AG genotype of rs2277438 (RANKL) is associated with lower 25(OH)D in the OP group (p = 0.02). Our results suggest that RANKL SNPs may impact 25(OH)D levels and that OPG SNP rs2073618A/G is a significant genetic risk factor for PMO Saudi Arabian women.

Regulatory Roles of Bone in Neurodegenerative Diseases

Osteoporosis and neurodegenerative diseases are two kinds of common disorders of the elderly, which often co-occur. Previous studies have shown the skeletal and central nervous systems are closely related to pathophysiology. As the main structural scaffold of the body, the bone is also a reservoir for stem cells, a primary lymphoid organ, and an important endocrine organ. It can interact with the brain through various bone-derived cells, mostly the mesenchymal and hematopoietic stem cells (HSCs). The bone marrow is also a place for generating immune cells, which could greatly influence brain functions. Finally, the proteins secreted by bones (osteokines) also play important roles in the growth and function of the brain. This article reviews the latest research studying the impact of bone-derived cells, bone-controlled immune system, and bone-secreted proteins on the brain, and evaluates how these factors are implicated in the progress of neurodegenerative diseases and their potential use in the diagnosis and treatment of these diseases.

Comprehensive assessment of tissue and serum parameters of bone metabolism in a series of orthopaedic patients

Bone diseases represent an increasing health burden worldwide, and basic research remains necessary to better understand the complexity of these pathologies and to improve and expand existing prevention and treatment approaches. In the present study, 216 bone samples from the caput femoris and collum femoris of 108 patients with degenerative or dysplastic coxarthrosis, hip fracture, or osteonecrosis were evaluated for the proportion of trabecular bone (TB) and expression of parathyroid hormone (PTH) type 1 receptor (PTH1R), osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-B ligand (RANKL). Serum levels of PTH, OPG, soluble RANKL (sRANKL), alkaline phosphatase (AP), osteocalcin, total procollagen type-1 intact N-terminal propeptide (TP1NP), tartrate-resistant acid phosphatase type 5b (TRAP5b), sclerostin, and C-telopeptide of type-1 collagen (ICTP) were also determined. Age was positively correlated with serum levels of PTH, OPG, and sclerostin but negatively associated with TB and sRANKL. Women exhibited less TB, lower sclerostin and ICTP, and higher TRAP5b. Impaired kidney function was associated with shorter bone decalcification time, less TB, lower sRANKL, and higher serum PTH, OPG, and sclerostin. Furthermore, correlations were observed between bone PTH1R and OPG expression and between serum PTH, OPG, and AP. There were also positive correlations between serum OPG and TP1NP; serum OPG and sclerostin; serum AP, osteocalcin, and TRAP5b; and serum sclerostin and ICTP. Serum OPG was negatively associated with sRANKL. In summary, clear relationships between specific bone metabolism markers were observed, and distinct influences of age, sex, and kidney function, thus underscoring their suitability as diagnostic or prognostic markers.

Correlations between the Peptide Hormone Ghrelin and Proinflammatory Cytokines in Experimental Periodontitis Models of Female Rats at Different Stages of the Life Cycle

OBJECTIVE

The aim of this study was to examine the correlations between the levels of ghrelin and inflammatory and bone metabolism markers in rats with periodontitis.

DESIGN

Thirty female Wistar rats (6 trial rats and 4 control rats in each group) were divided into pubertal, adult and postmenopausal groups. Periodontitis was induced by ligatures. On the 21 st day, blood was collected and all rats were then sacrificed. The levels of osteocalcin, osteoprotegerin, alkaline phosphatase, tumour necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), acylated ghrelin, total ghrelin and soluble receptor activator of nuclear factor-kB ligands in the blood samples were measured using enzyme-linked immunosorbent assays. The jaws were decalcified in a Tris-EDTA solution and embedded in paraffin and 4-5 μm sections were cut for IL-β, TNF -α and ghrelin staining.

RESULTS

Significantly higher serum alkaline phosphatase levels were detected in the trial rats in the pubertal group than in the control rats (p = 0.033). In the postmenopausal group, ghrelin levels positively correlated with interleukin 1 beta levels (r = 0.708, p < 0.05). Among all trial rats, the postmenopausal group exhibited significantly higher levels of acylated ghrelin than the other groups (p = 0.001). Significantly higher osteoprotegerin levels were observed in the control rats than in the trial rats in the postmenopausal group (p = 0.012). Inflammation scores were significantly higher in adult trial rats than in controls (p = 0.024); significantly higher TNF-α levels were detected in postmenopausal experimental rats than in the adult experimental group (p = 0.025).

CONCLUSIONS

We concluded that total ghrelin levels in serum only correlated with IL-β levels in postmenopausal rats.

The impact of forced swimming on expression of RANKL and OPG in a type 2 diabetes mellitus rat model

OBJECTIVE

The importance of swimming in bone metabolism during type 2 diabetes (T2DM) is not well known. Receptor activator of nuclear factor-kB ligand (RANKL)/ osteoprotegerin (OPG) system as a critical pathway in bone remodeling may play a role in pathogenesis of T2DM. Hence, we tested this pathway and the possible beneficial effects of swim training on T2DM.

MATERIALS AND METHODS

Forty male rats were assigned to groups (n = 10): control(C), diabetic (D), exercised control (E), and diabetic exercised (DE). One week after the induction of diabetes, animals were subjected to swim. At the end of training, fasting blood sugar, insulin, bone and serum OPG and RANKL levels were measured.

RESULTS

Diabetes significantly increased OPG and decreased RANKL mRNAs and proteins in bone and serum and swim training could reverse these changes to control.

CONCLUSION

Swim training could partially compensate T2DM associated changes of bone and serum OPG/RANKL in rats.

Circulating osteoprotegerin in postmenopausal osteoporotic women: marker of impaired glucose regulation or impaired bone metabolism

OBJECTIVE

Osteoprotegerin (OPG) is closely related to insulin resistance and bone remodeling. However, no studies have examined the role of OPG in postmenopausal women with coexistent impaired glucose and bone regulation. The present study investigated the relationship of OPG to glucose homeostasis and insulin resistance in postmenopausal osteoporotic women with different types of glucose tolerance.

METHODS

In all, 114 postmenopausal osteoporotic women were divided into three groups according to glucose tolerance status: 51 with normal glucose tolerance (NGT, group 1), 31 with impaired glucose tolerance (IGT, group 2), and 32 with type 2 diabetes mellitus (DM, group 3). Study participants were evaluated for metabolic parameters, OPG, Homeostasis Model Assessment of Insulin Resistance (HOMA-IR), and bone mineral density parameters.

RESULTS

The OPG levels differed significantly across groups and increased from group 1 to group 3 in a continuous fashion (analysis of variance, P < 0.0001). In post-hoc analysis, OPG was significantly lower in osteoporotic women with NGT, than participants with IGT and DM (P < 0.05 and P < 0.0001, respectively). OPG was positively associated with HOMA-IR (P < 0.0001). No association between serum OPG levels and measures of BMD was observed. In a multiple regression analysis, OPG emerged as an independent predictor of HOMA-IR even after controlling for age, body mass index, and creatinine.

CONCLUSIONS

OPG is significantly higher in postmenopausal osteoporotic women with impaired glucose regulation (IGT and DM) than women with NGT. OPG was independently associated with insulin resistance assessed by HOMA-IR. Thus, measurement of OPG may potentially be considered as a prediabetic state screening in postmenopausal osteoporotic women.

Role of Serum Osteoprotegerin as a Diagnostic Indicator of Primary Osteoporosis in Perimenopausal and Postmenopausal Women: An Indian Perspective

Introduction: Osteoporosis (OP) is a major health problem in the older population. The aim of the study was to assess the role of serum osteoprotegerin (OPG) as a diagnostic indicator of primary osteoporosis in peri- and post-menopausal women in an Indian population.

Materials and Methods: After ethical approval, 90 cases (45 cases and 45 controls) of peri- and post-menopausal females above 40 years of age presenting to our outpatient department were included in the study. It was a case controlled study conducted between July 2014 to July 2015. Based on the clinical features, t-score and radiological evidence from the DEXA scan, they were equally divided into two groups (cases and controls). Serum osteoprotegerin (OPG) levels were measured amongst cases and controls.

Results: The total calcium (mg/dl) level was lower among the cases and the difference was significant (p-Value= <0.001). Similarly, alkaline phosphatase (u/l), osteoprotegerin (u/ml) levels were higher in the cases as compared to controls and the difference was significant (p-Value= <0.001). The mean osteoprotegerin level showed a slight increase with increase in severity of the grading of BMD of spine. The results suggested a cut-off value of ≥10.5 u/ml (86.7% sensitive and 80% specific with accuracy of 84.5%) between normal and osteoporosis.

Conclusion: From the present study, we conclude that osteoprotegerin is a valid biomarker to diagnose postmenopausal women with low bone mineral density.

Age-related changes in biochemical bone profile in thalassemic children

BACKGROUND

Osteopathy is an important cause of morbidity in β-thalassemia major (TM). Although many of the etiopathological factors implicated in thalassemic osteoporosis commence in early disease phases during childhood, limited information exists on bone turnover in children with TM. This study was conducted with the objective to compare bone turnover markers (BTMs) in thalassemic children at different ages.

METHODS

In a cross sectional case control study, 47 children (age range, 1.5-18 years) with TM were recruited. BTMs were compared to eighteen age- and sex-matched healthy controls and to 16 adults (age range, 19.67-31.08 years) with TM.

RESULTS

Thalassemic children displayed unbalanced bone turnover with an increased bone resorption (shown by high levels of tartrate-resistant acid phosphatase 5b (TRACP5), receptor activator of nuclear factor-kappa B ligand (sRANKL) and sRANKL/osteoprotegerin (OPG) ratio) and a decreased bone neoformation (shown by low levels of osteocalcin (OC)) when compared to healthy children. TRACP5b was the only BTMs studied that showed a significant correlation with age in thalassemic children. For the whole thalassemic children group, regression analyses showed an influence of sex hormones replacement therapy on TRACP5b; pretransfusion hemoglobin and splenectomy on sRANKL; pretransfusion hemoglobin on sRANKL/OPG; and pretransfusion hemoglobin and serum ferritin on OC.

CONCLUSION

The present study confirms that TM has profound effects on bone metabolism starting from early childhood. The early onset of bone turnover disturbances in TM indicates the need to investigate possible option to intervene early.

Analysis of Nkx3.1:Cre-driven Erk5 deletion reveals a profound spinal deformity which is linked to increased osteoclast activity

Extracellular signal-regulated protein kinase 5 (ERK5) has been implicated during development and carcinogenesis. Nkx3.1-mediated Cre expression is a useful strategy to genetically manipulate the mouse prostate. While grossly normal at birth, we observed an unexpected phenotype of spinal protrusion in Nkx3.1:Cre;Erk5 fl/fl (Erk5 fl/fl) mice by ~6-8 weeks of age. X-ray, histological and micro CT (µCT) analyses showed that 100% of male and female Erk5 fl/fl mice had a severely deformed curved thoracic spine, with an associated loss of trabecular bone volume. Although sex-specific differences were observed, histomorphometry measurements revealed that both bone resorption and bone formation parameters were increased in male Erk5 fl/fl mice compared to wild type (WT) littermates. Osteopenia occurs where the rate of bone resorption exceeds that of bone formation, so we investigated the role of the osteoclast compartment. We found that treatment of RANKL-stimulated primary bone marrow-derived macrophage (BMDM) cultures with small molecule ERK5 pathway inhibitors increased osteoclast numbers. Furthermore, osteoclast numbers and expression of osteoclast marker genes were increased in parallel with reduced Erk5 expression in cultures generated from Erk5 fl/fl mice compared to WT mice. Collectively, these results reveal a novel role for Erk5 during bone maturation and homeostasis in vivo.

Postmenopausal osteoporosis in rheumatoid arthritis: The estrogen deficiency-immune mechanisms link

Rheumatoid arthritis (RA) is characterized, among other factors, by systemic bone loss, reaching ~50% prevalence of osteoporosis in postmenopausal women. This is roughly a doubled prevalence in comparison with age-matched non-RA women. Postmenopausal RA women are more likely to be sero-positive for the anti-citrullinated peptide antibody (ACPA). Our extensive review of recent scientific literature enabled us to propose several mechanisms as responsible for the accelerated bone loss in ACPA(+) RA postmenopausal women. Menopause-associated estrogen deficiency plays a major role in these pathological mechanisms, as follows.

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.

Hyperbaric oxygen therapy modulates serum OPG/RANKL in femoral head necrosis patients

Hyperbaric oxygen therapy (HBOT) has beneficial effects on avascular necrosis of femoral head (ANFH), but its mechanism of action is still unclear. We investigated if HBOT upregulates serum osteoprotegerin (OPG) and/or inhibits osteoclast activation. 23 patients with unilateral ANFH at stage I, II and III consented to the study: the patients received standard HBOT. Serum OPG levels were obtained at the beginning of HBOT (T0), after 15 sessions (T1), 30 sessions (T2), after a 30-day break (T3), and after 60 sessions (T4). Magnetic resonance imaging (MRI) was obtained at T0 and about one year from the end of HBO treatments. Lesion size was compared between pre- and post-HBOT. 19 patients completed the study. HBOT reduced pain symptoms in all patients. HBOT significantly reduced lesion size in all stage I and II patients and in 2 of 11 stage III patients. HBOT increased serum OPG levels but receptor activator of nuclear factor kappa-B ligand (RANKL) levels did not change.

Substance P Promotes the Proliferation, but Inhibits Differentiation and Mineralization of Osteoblasts from Rats with Spinal Cord Injury via RANKL/OPG System

Spinal cord injury (SCI) causes a significant amount of bone loss, which results in osteoporosis (OP). The neuropeptide substance P (SP) and SP receptors may play important roles in the pathogenesis of OP after SCI. To identify the roles of SP in the bone marrow mesenchymal stem cell derived osteoblasts (BMSC-OB) in SCI rats, we investigated the expression of neurokinin-1 receptors (NK1R) in BMSC-OB and the effects of SP on bone formation by development of BMSC-OB cultures. Sixty young male Sprague-Dawley rats were randomized into two groups: SHAM and SCI. The expression of NK1R protein in BMSC-OB was observed using immunohistochemistry and Western blot analysis. The dose- and time-dependent effects of SP on the proliferation, differentiation and mineralization of BMSC-OB and the expression of osteoblastic markers by in vitro experiments. The expression of NK1R in BMSC-OB was observed on plasma membranes and in cytoplasm. One week after osteogenic differentiation, the expression of NK1R was significantly increased after SCI at mRNA and protein levels. However, this difference was gradually attenuated at 2 or 3 weeks later. SP have the function to enhance cell proliferation, inhibite cell differentiation and mineralization at a proper concentration and incubation time, and this effect would be inhibited by adding SP or NK1R antagonist. The expression of RANKL/OPG was significantly increased in tibiae after SCI. Similarly, the RANKL/OPG expression in SCI rats was significantly increased when treating with 10-8 M SP. SP plays a very important role in the pathogenesis of OP after SCI. The direct effect of SP may lead to increased bone resorption through the RANKL/OPG axis after SCI. In addition, high expression of SP also results in the suppression of osteogenesis in SCI rats. Then, the balance between bone resorption and bone formation was broken and finally osteoporosis occurred.

Erythropoietin treatment in murine multiple myeloma: immune gain and bone loss

Multiple myeloma (MM) is a plasma cell malignancy, characterized by osteolytic lesions and monoclonal immunoglobulins. The anemia, accompanying the disease is often treated with recombinant human EPO. Diverse non-erythropoietic effects of EPO have led us to question its combined action on the immune system and bone in the 5T33MM mouse model. EPO administration to MM mice attenuated disease progression as demonstrated by a decrease in serum MM IgG2b, splenic CD138 expressing cells, IL-6 and RORγτ transcripts in bone marrow (BM). IFN-γ transcript levels and macrophages (F4/80⁺CD11b⁺) in the BM both increased ~1.5 fold in the EPO-treated MM mice. In-vitro, EPO stimulated phagocytosis of 5T33MM cells (+30%) by BM-derived macrophages. In contrast, high-resolution microCT analysis of distal femurs revealed EPO-associated bone loss in both healthy and 5T33MM mice. EPO significantly increased expression of the osteoclastogenic nuclear factor-kappa B ligand (RANKL) in healthy mice, but not in MM mice, likely due to antagonizing effects on MM progression. Thus, in MM, EPO may act as a double-edged-sword stimulating immune response, while accelerating bone resorption, possibly via direct action on BM macrophages. This study supports a prudent approach of treating anemia in MM patients, aiming to maintain EPO-associated anti-MM effects, while considering bone damage.

Diagnostic and Prognostic Properties of Osteoprotegerin in Patients with Acute Dyspnoea: Observations from the Akershus Cardiac Examination (ACE) 2 Study

BACKGROUND

Circulating osteoprotegerin (OPG) levels are increased in patients with chronic heart failure (HF). The diagnostic and prognostic merit of OPG measurement in patients admitted with acute dyspnoea is unknown.

OBJECTIVES

To evaluate the diagnostic and prognostic value of measuring OPG in patients admitted to hospital with acute dyspnoea.

METHODS

OPG was analysed by ELISA in 308 patients admitted due to acute dyspnoea. Investigators blinded to OPG results adjudicated the diagnosis for the index hospitalization. Clinical outcomes were obtained from hospital records.

RESULTS

In total, 139 patients (45%) were hospitalized with acute HF. OPG levels on hospital admission were higher in patients with acute HF vs. no acute HF, 7.8 (5.5-10.4) vs. 5.4 (3.8-7.2) pmol/L, p<0.001. The area under the receiver operator characteristic curve (ROC AUC) of OPG to discriminate between HF vs. non-HF was 0.695 [95% CI 0.636-0.754]. OPG did not provide incremental information to the ED physician's prediction or N-terminal pro-B-type natriuretic peptide regarding the diagnosis of acute HF. OPG levels (log transformed) were associated with mortality in crude analysis (HR (95% CI) 1.87 (1.34 to 2.61), p<0.001), but this association was attenuated and no longer significant after including established cardiac biomarkers into the model.

CONCLUSION

In patients admitted to hospital with acute dyspnoea, OPG levels are higher in patients with acute HF than in those with dyspnoea from other causes. However, OPG does not provide incremental information beyond ED physician assessment for the diagnosis of acute HF or beyond clinical risk variables and established cardiac biomarkers concerning prognosis.

Values of osteoprotegerin in aortic valve tissue in patients with significant aortic stenosis depend on the existence of concomitant coronary artery disease

INTRODUCTION

Calcific aortic valve stenosis (CAVS) is a serious clinical problem. The strongest predictor of CAVS progression is the amount of calcium in the aortic valve. The pathogenesis of CAVS is largely consistent with the pathogenesis of atherosclerosis; however, about 50% of patients with CAVS do not exhibit significant atherosclerosis. Cardiovascular calcification is currently considered an actively regulated process, in which the important role is attributed to the RANKL/RANK/OPG (receptor activator of nuclear factor κB ligand/RANK/osteoprotegerin) axis. We measured OPG levels in the tissue of calcified, stenotic aortic valves in relation to the presence or absence of coronary artery disease (CAD).

MATERIALS AND METHODS

Aortic valve samples were collected from 105 patients with calcified, mainly severe aortic stenosis, who were divided into two groups according to the presence of CAD. In Group A (n=44), there were normal coronary artery findings, while in Group B (n=61), there was angiographically demonstrated >50% stenosis of at least one coronary artery. The control Group C (n=21) consisted of patients without aortic stenosis and with normal angiographic findings on coronary arteries.

RESULTS

The highest tissue concentrations of OPG [median (pmol/L), 25th-75th percentile] were found in Group A [6.95, 3.96-18.37], which was significantly different compared to the other two groups (P=.026 and .001, respectively). The levels of OPG in Group B [4.15, 2.47-9.16] and in Group C [2.25, 1.01-5.08] did not differ significantly (P=.078); however, the lowest concentrations of OPG were found in Group C. Neither age nor gender in our study had effect on tissue levels of OPG (P=.994 for gender; P=.848 for age).

CONCLUSION

Calcified and narrowed aortic valves, compared to the normal valves, were accompanied by a change in tissue concentrations of OPG, which is, in addition, dependent on the presence or absence of CAD. The highest tissue concentrations of OPG in our work were found in patients with significant aortic stenosis without concomitant CAD.

Bone remodelling markers in hypertensive patients with and without diabetes mellitus: link between bone and glucose metabolism

OBJECTIVE

Growing evidence suggests the presence of a complex interplay between hypertension as well as type 2 diabetes mellitus (DM) and osteoporosis. The present study was designed to investigate a possible effect of type 2 DM on bone remodelling markers such as osteoprotegerin and N-terminal propeptide of type 1 collagen (P1NP) in hypertensive patients.

DESIGN AND METHODS

The 100 study participants were divided into three groups according to the presence of DM and hypertension: group one included diabetic hypertensive subjects, group 2 included hypertensive subjects without diabetes and group 3 included subjects without hypertension and without DM (controls). Blood sampling for metabolic parameters, including osteoprotegerin, P1NP, adiponectin, fasting glucose, HbA1c , CRP, homeostasis model assessment-insulin resistance, homeostasis model assessment-beta function was performed.

RESULTS

Circulating P1NP increased from group 1 to group 3 in a continuous fashion. P1NP was significantly lower in hypertensive subjects with DM (group 1), than in groups 2 and 3 (p < 0.0001). P1NP, was marginally lower in diabetic hypertensive subjects as compared with nondiabetic subjects with hypertension (p = 0.079). Circulating osteoprotegerin did not differ significantly between groups (p = 0.593).

CONCLUSIONS

In the present study, bone formation marker, P1NP, was significantly lower in diabetic hypertensive subjects as compared with nondiabetic subjects with and without hypertension. P1NP was inversely associated with parameters of glucose homeostasis such as fasting glucose, HbA1c and positively with homeostasis model assessment-beta cell function. Type 2 DM was associated with an adverse effect on bone formation independently of age, sex and exposure to anti-diabetic drugs.

Effect of metformin treatment on circulating osteoprotegerin in patients with nonalcoholic fatty liver disease

PURPOSE/INTRODUCTION

Growing evidence suggests complex interplay between nonalcoholic fatty liver disease (NAFLD) and bone health. The present study's aim was to examine the impact of metformin treatment on circulating osteoprotegerin (OPG) in patients with NAFLD, a population in which this relationship has not yet been studied.

METHODS

In a randomized, placebo-controlled study, 63 patients with NAFLD were assigned to one of two groups: Group 1 received daily metformin; Group 2 received a placebo. Metabolic parameters, insulin resistance markers and OPG levels were examined at baseline and at the end of the study.

RESULTS

In the placebo group, liver function and OPG levels did not change during the study. Among metformin-treated patients, significant declines in OPG and alkaline phosphatase were observed. CRP and ALT decreased marginally during the 4-month treatment period. While at baseline circulating OPG levels did not differ significantly between the groups, by the end of the study OPG was significantly lower in patients treated with metformin than in the placebo group (p < 0.0001). Delta OPG was significantly greater in the metformin group than the placebo group (p = 0.001). In the general linear model, metformin treatment was the only significant independent predictor of endpoint and delta OPG.

CONCLUSIONS

Metformin treatment was associated with a significant decrease in OPG levels in patients with NAFLD. The effect on OPG was associated with exposure to metformin per se.

CLINICAL TRIAL REGISTRATION NUMBER

NCT01084486.

Association of osteoprotegerin and bone loss after adjuvant chemotherapy in early-stage breast cancer

PURPOSE

Chemotherapy induced ovarian failure (CIOF) results in rapid bone loss. Receptor Activator of Nuclear Factor Kappa-B (RANK)-RANK ligand (RANK-L) signaling balances bone resorption and formation. Osteoprotegerin (OPG) acts as a decoy receptor for RANK, interrupting osteoclast activation and bone resorption. This study examined the relationship between OPG and bone loss in women with CIOF.

METHODS

Premenopausal women with stage I/II breast cancers receiving adjuvant chemotherapy were evaluated at chemotherapy initiation, 6 and 12 months. Bone mineral density (BMD) at the lumbar spine (LS) and femoral neck (FN), follicle stimulating hormone (FSH), ionized calcium, osteocalcin, and OPG were serially measured. CIOF was defined as a negative pregnancy test, FSH levels >30 MIU/mL, and ≥3 months of amenorrhea.

RESULTS

Forty women were enrolled; 31 (77.5%) met CIOF criteria. BMD significantly decreased (p < 0.001) in the CIOF group at both time points: LS BMD decreased from a median of 0.993 g/cm(2) to 0.976 g/cm(2) and 0.937 g/cm(2) at 6 and 12 months, respectively. OPG was significantly elevated at 6 months (median increase 0.30 pmol/L, p = 0.015) and then decreased at 12 months to levels still above baseline (median difference 0.2 pmol/L, p = 0.70).

CONCLUSIONS

In what was likely a compensatory response to rapid bone loss, CIOF patients' OPG levels increased at 6 months and then decreased at 12 months to values greater than baseline assessments. This phenomenon is described in other diseases, but never before in CIOF.

A predator-prey based mathematical model of the bone remodelling cycle: exploring the relationship between the model parameters and biochemical factors

Bone remodelling is a vital process which enables bone to repair, renew and optimize itself. Disorders in the bone remodelling process are inevitably manifested in bone-related diseases, such as hypothyroidism, primary hyperparathyroidism and osteoporosis. In our previous work, a predator-prey based mathematical model was developed to simulate bone remodelling cycles under normal and two pathological conditions, hypothyroidism and primary hyperparathyroidism, for trabecular bone at a fixed point. However, the biochemical meanings of the model parameters were not fully explored. This article first extends the previous work by proposing relationships between the model parameters and biochemical factors involved in the bone remodelling process and by examining whether those relationships do predict the behaviours observed in vivo. The model is then applied to the simulation and investigation of bone remodelling of postmenopausal osteoporosis. The proposed connections are supported by good agreement between the model simulations and published experimental observations for the normal condition and all three pathological variations in bone remodelling.

No relationship between osteoprotegerin concentrations and endothelial dysfunction in non-obese women with and without polycystic ovary syndrome

PURPOSE

To investigate the relationships of osteoprotegerin (OPG) concentrations to brachial artery flow-mediated vasodilation (FMD) and the carotid artery intima media thickness (CIMT) in polycystic ovary syndrome (PCOS).

METHODS

Thirty-seven women with PCOS and 41 controls matched for body mass index (BMI) and age were included in study. The serum OPG concentrations, hormonal and metabolic profiles were measured in women with PCOS and in control group. The CIMT and brachial artery FMD were evaluated in both groups.

RESULTS

The mean serum concentrations of all hormones were comparable, except LH, which was higher in women with PCOS. Lipid parameters were similar between groups. There were no differences between groups with respect to fasting glucose, 2-h glucose, fasting insulin, HbA1c and HOMA-IR. The mean osteoprotogerin concentrations were higher in PCOS group (11.39 ± 2.29 vs. 10.22 ± 2.25 pmol/L, P = 0.026). The mean CIMT was higher in PCOS group than control group (0.52 ± 0.058 vs. 0.45 ± 0.059 mm, P < 0.01). The mean brachial artery FMD was lower in PCOS group (0.068 ± 0.022 vs. 0.055 ± 0.029, P = 0.017).

CONCLUSIONS

We found high osteoprotogerin concentrations, increased CIMT and decreased FMD, in women with PCOS. However, there was no correlation between osteoprotegerin and cardiovascular risk markers.

Bone biomarkers in patients with chronic traumatic spinal cord injury

BACKGROUND CONTEXT

Bone loss after spinal cord injury (SCI) occurs because of pathologic changes in osteoblastic and osteoclastic activities due to mechanical unloading. Some biochemical changes in bone metabolism after SCI are described before that were related to bone mineral loss.

PURPOSE

Our purpose was to determine bone markers' changes and related effective factors in patients with chronic traumatic SCI.

STUDY DESIGN

This investigation was designed as an observational cross-sectional study.

PATIENT SAMPLE

All patients with chronic SCI who were referred to Brain and Spinal Injury Research Center and did not meet our exclusion criteria entered the study.

OUTCOME MEASURES

Self-reporting measures including patient's demographic features and date of accident were obtained using a questionnaire and physiologic measures including spinal magnetic resonance imaging to determine the level of injury accompanied with physical examination along with dual-energy X-ray absorptiometry were performed. Blood samples were analyzed in the laboratory.

METHODS

Dual-energy X-ray was used to determine bone mineral density in femoral and spinal vertebrae bone sites. Serum level of C-telopeptide cross-linked Type 1 collagen (CTX), parathyroid hormone, calcitonin, osteocalcin, and bone alkaline phosphatase (BALP) were measured.

RESULTS

We detected a negative association between CTX level and bone mineral density in femoral and spinal bone sites that confirms that CTX is a bone resorption marker. C-telopeptide cross-linked Type 1 collagen and BALP levels did not show any significant correlation with postduration injury. Patients with spinal injury at lumbar level had the highest calcitonin level (p<.04). C-telopeptide cross-linked Type 1 collagen was positively related with osteocalcin and BALP (p<.0001, r=0.51), and osteocalcin was positively related with BALP (p<.0001, r=0.44). Osteocalcin was related negatively only to femoral intertrochanteric zone bone mineral density.

CONCLUSIONS

Some bone biomarkers undergo noticeable changes after SCI. C-telopeptide cross-linked Type 1 collagen was positively correlated with BALP and osteocalcin that shows the coincidental occurrence of osteoblastic and osteoclastic activities. Our data also support this fact that although bone reduction after 2 years is slower than acute phase after SCI, bone resorption rate is higher than bone formation. These bone markers also revealed different site of action as osteocalcin level only affected femoral intertrochanteric bone mineral density. Generally, it seems that the coincidental consideration of these factors that influence bone mineral density can lead to a better understanding of bone changes after SCI.

Biomarkers of Bone Metabolism in Ankylosing Spondylitis in Relation to Osteoproliferation and Osteoporosis

Objective.

To identify biomarkers for bone metabolism in patients with ankylosing spondylitis (AS) and to determine the relationship between these biomarkers and disease activity, back mobility, osteoproliferation, and bone mineral density (BMD).

Methods.

Serum levels of Wingless protein (Wnt-3a), Dickkopf-1 (DKK-1), sclerostin, soluble receptor activator of nuclear factor-κB ligand (sRANKL), and osteoprotegerin were assessed using ELISA. Ankylosing Spondylitis Disease Activity Score-C reactive protein, Bath Ankylosing Spondylitis Disease Activity Index, Bath Ankylosing Spondylitis patient global score, and C-reactive protein (CRP) were used as disease activity measures, and Bath Ankylosing Spondylitis Metrology Index (BASMI) as a measure of spinal mobility. Lateral spine radiographs were scored for chronic AS-related changes (mSASSS). BMD was measured with dual-energy x-ray absorptiometry.

Results.

Two hundred four patients with AS (NY criteria; 57% men), with a mean age of 50 ± 13 years and disease duration 15 ± 11 years, and 80 age and sex-matched controls were included. The patients with AS had significantly higher serum levels of Wnt-3a (p < 0.001) and lower levels of sclerostin (p = 0.014) and sRANKL (p = 0.047) compared with the controls. High CRP was associated with low sclerostin (rS = −0.21, p = 0.003) and DKK-1 (rS = −0.14, p = 0.045). In multiple linear regression analyses, increasing BASMI and mSASSS were independently associated with older age, male sex, high CRP, and elevated serum levels of Wnt-3a. In addition, mSASSS remained associated with a high number of smoking pack-years after adjusting for age. Low BMD of femoral neck was associated with high mSASSS after adjusting for age.

Conclusion.

Serum levels of Wnt-3a are elevated in AS and associated with increased BASMI and mSASSS, independent of age, indicating that Wnt-3a could be a biomarker for the osteoproliferative process.

Age and gender predict OPG level and OPG/sRANKL ratio in maintenance hemodialysis patients

PURPOSE

Cardiovascular disease (CVD) is a major cause of death among chronic hemodialysis (HD) patients. Gender and age belong to its classical risk factors. OPG/RANK/sRANKL (Osteoprotegerin/ Receptor Activator of Nuclear Factor κB/ soluble Receptor Activator of Nuclear Factor κB Ligand) axis constitute a system connecting bone and vascular remodeling.

METHODS

We aimed to evaluate the plasma levels of OPG, sRANKL and OPG/sRANKL ratio in 21 HD patients and 16 healthy volunteers in relation to gender, age and the other clinical parameters.

RESULTS

OPG and OPG/sRANKL ratio were significantly higher in HD patients than in controls whereas sRANKL was similar in both groups. Adjusted for gender, in controls OPG were higher in women whereas sRANKL did not differ between men and women. In HD group OPG and sRANKL were higher in women whereas OPG/sRANKL ratio was similar in both genders. Female patients compared to healthy women revealed 56% higher OPG concentration and 54% higher OPG/ sRANKL ratio. Comparison of male patients and controls revealed 61% higher level of OPG and 75% higher OPG/sRANKL ratio in HD group. Interestingly, OPG and OPG/sRANKL ratio positively correlated with age only in male patients. Contrary, the association between OPG/sRANKL ratio and age was negative in HD women.

CONCLUSION

Higher OPG levels in HD women comparing to age matched HD men indicate the necessity of more careful screening towards the presence of CVD and bone-mineral disorders. The negative association between age and OPG/ sRANKL ratio in HD women warrant in-depth study for thorough understanding of this complex interrelationship.

Osteoprotegerin contributes to the metastatic potential of cells with a dysfunctional TSC2 tumor-suppressor gene

In addition to its effects on bone metabolism, osteoprotegerin (OPG), a soluble member of the tumor necrosis factor family of receptors, promotes smooth muscle cell proliferation and migration and may act as a survival factor for tumor cells. We hypothesized that these cellular mechanisms of OPG may be involved in the growth and proliferation of lymphangioleiomyomatosis (LAM) cells, abnormal smooth muscle-like cells with mutations in one of the tuberous sclerosis complex tumor-suppressor genes (TSC1/TSC2) that cause LAM, a multisystem disease characterized by cystic lung destruction, lymphatic infiltration, and abdominal tumors. Herein, we show that OPG stimulated proliferation of cells cultured from explanted LAM lungs, and selectively induced migration of LAM cells identified by the loss of heterozygosity for TSC2. Consistent with these observations, cells with TSC2 loss of heterozygosity expressed the OPG receptors, receptor activator of NF-κB ligand, syndecan-1, and syndecan-2. LAM lung nodules showed reactivities to antibodies to tumor necrosis factor-related apoptosis-inducing ligand, receptor activator of NF-κB ligand, syndecan-1, and syndecan-2. LAM lung nodules also produced OPG, as shown by expression of OPG mRNA and colocalization of reactivities to anti-OPG and anti-gp100 (HMB45) antibodies in LAM lung nodules. Serum OPG was significantly higher in LAM patients than in normal volunteers. Based on these data, it appears that OPG may have tumor-promoting roles in the pathogenesis of lymphangioleiomyomatosis, perhaps acting as both autocrine and paracrine factors.

Influence of hormone replacement therapy on osteoprotegerin and receptor activator of nuclear factor kappa-B ligand concentrations in menopausal women

The study was designed to compare the levels of the receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) in the serum and saliva of menopausal women and verify whether there is a correlation between concentrations of these cytokines and bone mineral density (BMD) of the femur and mandible. Blood and saliva samples were collected from a group of 60 women during menopause--30 untreated (control group) and 30 treated with hormone replacement therapy (HRT) (research group). Densitometry was conducted on the femoral bone and mandible. BMD in the research group was significantly higher than in the control group. The OPG concentration was slightly higher in the research group. The concentration of RANKL was slightly higher in the control group. Differences in RANKL/OPG between groups were not high enough to be statistically significant. Analysis of the RANKL in saliva revealed a significantly higher concentration of this factor in the control group. Observed beneficial effects of HRT on bone tissue may be exerted through the RANKL/OPG ratio, but further research is required to clearly confirm this thesis.

The role of osteoprotegerin in cardiovascular disease

Osteoprotegerin (OPG) is a 401 amino acid N-glycosylated protein, which is highly expressed in a large number of tissues. OPG mainly binds to two ligands, i.e. RANKL (receptor activator of nuclear factor κB ligand) and TRAIL (tumor necrosis factor- related apoptosis-inducing ligand). Upon binding to the former ligand, OPG inhibits the activation of osteoclasts and promotes apoptosis of osteoclasts, whereas the binding of OPG with TRAIL prevents apoptosis of tumor cells. There is now emerging evidence that OPG participates in the pathogenesis of atherosclerosis and cardiovascular diseases by amplifying the adverse effects of inflammation and several traditional risk factors such as hyperlipidemia, endothelial dysfunction, diabetes mellitus, and hypertension. Some epidemiological studies also showed a positive association between OPG levels and cardiovascular morbidity and mortality. The aim of this article is to provide an overview of the main biochemical, physiological, and pathological aspects of OPG biology in cardiovascular disease.

Efficacy and safety of echinacoside in a rat osteopenia model

This study aimed to investigate the efficacy and safety of echinacoside (ECH) using an osteopenia rat model. Forty-eight 6-month-old female Sprague-Dawley rats were randomly divided into one sham-operated group (SHAM) and five OVX (ovariectomized) subgroups: SHAM with vehicle 0.5% carboxymethylcellulose sodium (0.5% CMC-Na) and OVX with vehicle (OVX), OVX with 17 β -estradiol (E2), and OVX with ECH of graded doses (ECH-L, ECH-M, and ECH-H). The effects of ECH and E2 on serum biochemical parameters, bone mineral density (BMD), bone biomechanical properties, bone microarchitecture, and immunohistochemistry were examined, and safety assessments were also evaluated. The results showed that ECH treatments improved total femur BMD, bone microarchitecture, and biomechanical properties and decreased serum marker levels in comparison to OVX group. Moreover, ECH administration significantly increased osteoprotegerin (OPG) level, and decreased receptor activator of nuclear factor- κ B ligand (RANKL) level in serum, as well as in proximal femur. Importantly, ECH treatment ameliorated the lipid parameters without the overall incidences of adverse events of uterus and mammary gland compared to OVX and SHAM groups. This study demonstrated that administration of ECH for 12 weeks can effectively and safely prevent OVX-induced osteoporosis in rats via increasing the OPG/RANKL ratio.

RANK, RANKL and OPG Expression in Breast Cancer - Influence on Osseous Metastasis

In women, malignant breast tumours are among the most common malignant diseases in Europe. In advanced breast cancer, the risk of bone metastasis increases to 65-75 %. The discovery of the physiological bone metabolism parameters RANK (receptor activator of nuclear factor-κB), RANKL (receptor activator of nuclear factor-κB ligand) and OPG (osteoprotegerin) as well as their pathophysiological involvement in bone-related diseases is the subject of new therapeutic strategies. The formation of osteolytic bone metastasis requires increased osteoclast activity. Activation of osteoclasts by excessive direct RANKL or reduced OPG expression of osseous metastatic tumour cells remains to be elucidated. More than 50 % of primary breast cancer cells express OPG and RANK, while RANKL could be detected only in 14-60 %. Increased OPG concentrations in the serum of patients with bone metastases have been shown in several studies, whereas the RANKL results are described in an opposite manner. The use of OPG as a biomarker for the detection of osteolytic bone metastases is not consistent and needs to be proved in further studies. Increased RANKL activity was found in diseases characterised by excessive bone loss and formed the basis of new therapeutic options. In several studies, a human monoclonal antibody to RANKL (denosumab) was investigated for the treatment of bone diseases. Denosumab is a promising therapeutic option due to its bone-protective effects.

Osteoprotegerin is associated with hip fracture incidence: the Tromso Study

BACKGROUND

Osteoprotegerin (OPG) is a cytokine essential for the regulation of bone resorption, but large longitudinal studies on its relationship to fracture risk in humans are lacking. In this population-based study of 2740 men and 2857 post-menopausal women, it was examined whether serum OPG was associated with hip fracture incidence. The participants were followed for 15 years.

METHODS

Baseline measurements included height, weight and serum OPG, and information about lifestyle, prevalent diseases and use of medication.

RESULTS

Men with OPG in the highest quartile were 2.79-fold [95% confidence interval (CI) 1.34-5.82] more likely to have a hip fracture during follow-up, compared with those with OPG in the lowest quartile (P-trend over OPG quartiles ≤ 0.001, after adjustments for age and other confounders). In women not using post-menopausal hormone therapy (HT), the risk of hip fracture was 1.64-fold higher (95% CI 0.94-2.86) in the highest quartile compared with the lowest OPG quartile (P-trend over OPG quartiles = 0.05). No relationship was found in post-menopausal women using HT (P-trend over OPG quartiles = 0.23).

CONCLUSIONS

In men, OPG was positively associated with the incidence of hip fracture. In post-menopausal women not using HT a similar, but weaker, relationship was found.

The association of serum osteoprotegerin and osteoporosis in postmenopausal hemodialysis patients: a pilot study

AIM

Osteoprotegerin (OPG) is a potent inhibitor of osteoclasts and plays an important role in bone metabolism. Relatively high serum levels of OPG have been observed in postmenopausal women with osteoporosis compared with age-matched controls. No data, however, are available on the relationship between low bone density and serum OPG levels in postmenopausal hemodialysis (HD) patients.

METHODS

The enrolled subjects included 28 postmenopausal HD patients and 28 age-matched postmenopausal women with normal renal function as controls. Bone mineral density (BMD) was measured by dual energy x-ray absorptiometry (DEXA) in both hips. Low BMD was defined as femoral neck T-score <-2.5. Serum OPG levels were measured using a commercial enzyme-linked immunosorbent assay (ELISA) kit.

RESULTS

Eight of the age-matched postmenopausal controls (28.6%) and 12 of the postmenopausal HD patients (42.9%) had low BMD. There was no statistically significant difference in low BMD between postmenopausal HD patients and age-matched postmenopausal patients (p = 0.263). The serum OPG level was significantly higher in the postmenopausal HD group (p < 0.001). Increased serum OPG (p = 0.017) and decreased serum albumin (p = 0.021) were significantly correlated with low BMD in postmenopausal HD patients. Univariate linear regression analysis showed that serum albumin (r = -0.455, p = 0.015) was negatively correlated, whereas age (r = 0.423, p = 0.025) and the length of time since menopause (r = 0.397, p = 0.036) were positively correlated with the serum OPG level in postmenopausal HD patients. Multivariate forward stepwise linear regression analysis showed that serum OPG (adjusted R(2) = 0.262, p = 0.003) was an independent predictor of low BMD in postmenopausal HD patients and explained 26.2% of the variance.

CONCLUSIONS

Serum OPG is associated with low BMD in postmenopausal HD patients.

Omentin-1 exerts bone-sparing effect in ovariectomized mice

Omentin-1 inhibited osteoblast differentiation in vitro. In co-culture systems of osteoblasts and osteoclast precursors, omentin-1 reduced osteoclast formation by stimulating osteoprotegerin (OPG) and inhibiting receptor activator for nuclear factor κB ligand (RANKL) production in osteoblasts. In vivo, adenovirus-mediated overexpression of omentin-1 suppressed bone turnover and restored bone mineral density (BMD) and bone strength in ovariectomized mice.

INTRODUCTION

Omentin-1 (also intelectin-1) is a recently identified visceral adipose tissue-derived cytokine that is highly abundant in plasma. This study was undertaken to investigate the effects of omentin-1 on bone metabolism.

METHODS

Osteoblast differentiation was assessed by measuring alkaline phosphatase activity, osteocalcin production and matrix mineralization. OPG and RANKL protein expression and secretion in osteoblasts were detected by Western blot and ELISA, respectively. The effect of recombinant omentin-1 on osteoclast formation was examined in co-culture systems of osteoblasts and osteoclast precursors. The effects of intravenous administration of adenoviral-delivered omentin-1 on bone mass, bone strength, and bone turnover were also examined in ovariectomized mice.

RESULTS

In vitro, omentin-1 inhibited osteoblast differentiation, while it had no direct effect on osteoclast differentiation; it also reduced osteoclast formation in the co-culture systems through stimulating OPG and inhibiting RANKL production in osteoblasts. In vivo, adenovirus-mediated overexpression of omentin-1 partially restored BMD and bone strength in ovariectomized mice, accompanied by decreased levels of plasma osteocalcin and tartrate-resistant acid phosphatase-5b and lower serum RANKL/OPG ratios.

CONCLUSION

The present study suggests that omentin-1 ameliorates bone loss induced by estrogen deficiency via downregulating the RANKL/OPG ratio.

Association between increased serum osteoprotegerin levels and improvement in bone mineral density after parathyroidectomy in hemodialysis patients

Secondary hyperparathyroidism (SHPT) is a common complication in chronic renal disease. Osteoprotegerin (OPG), an extracellular cytokine receptor secreted by osteoblasts, can promote bone formation by inhibiting the function of osteoclasts. Hemodialysis (HD) patients have elevated serum OPG levels. OPG secretion can be suppressed with high parathyroid hormone (PTH) levels. HD patients with refractory SHPT can benefit from parathyroidectomy (PTX) treatment, but the changes of serum OPG, bone turnover markers and bone mineral density (BMD) following PTX in HD patients remain unclear. In this study, patients on maintenance HD who received PTX for refractory SHPT (n = 28) were prospectively followed for 1 year. Serum intact PTH (iPTH), alkaline phosphatase (Alk-P), and OPG were measured serially; BMD was measured pre-PTX and at 1 year after PTX. After PTX, serum iPTH levels reduced profoundly. Serum Alk-P levels increased rapidly, peaking at 2 weeks post-PTX, while serum OPG levels gradually increased at 2 weeks after PTX and peaked at 2 months. BMD improved in both femoral neck (FN; cancellous and cortical bone) and lumbar spine (LS; cancellous bone). Higher baseline iPTH levels were associated with greater FN and LS BMD improvements at one year after PTX. The increment of serum OPG was correlated with the increase in LS BMD, implying that inhibition of osteoclastic bone resorption may improve BMD within the first year after PTX. These findings suggest that PTX removes the suppressive effects of high PTH on OPG secretion, resulting in the increased serum OPG levels that may contribute to BMD improvement.