OPG and sRANKL serum levels and incident hip fracture in postmenopausal Caucasian women in the Women's Health Initiative Observational Study

Clinical Data for Parametrization of In Silico Bone Models Incorporating Cell-Cytokine Dynamics: A Systematic Review of Literature

In silico simulations aim to provide fast, inexpensive, and ethical alternatives to years of costly experimentation on animals and humans for studying bone remodeling, its deregulation during osteoporosis and the effect of therapeutics. Within the varied spectrum of in silico modeling techniques, bone cell population dynamics and agent-based multiphysics simulations have recently emerged as useful tools to simulate the effect of specific signaling pathways. In these models, parameters for cell and cytokine behavior are set based on experimental values found in literature; however, their use is currently limited by the lack of clinical in vivo data on cell numbers and their behavior as well as cytokine concentrations, diffusion, decay and reaction rates. Further, the settings used for these parameters vary across research groups, prohibiting effective cross-comparisons. This review summarizes and evaluates the clinical trial literature that can serve as input or validation for in silico models of bone remodeling incorporating cells and cytokine dynamics in post-menopausal women in treatment, and control scenarios. The GRADE system was used to determine the level of confidence in the reported data, and areas lacking in reported measures such as binding site occupancy, reaction rates and cell proliferation, differentiation and apoptosis rates were highlighted as targets for further research. We propose a consensus for the range of values that can be used for the cell and cytokine settings related to the RANKL-RANK-OPG, TGF-β and sclerostin pathways and a Levels of Evidence-based method to estimate parameters missing from clinical trial literature.

The Imbalance of Cytokines and Lower Levels of Tregs in Elderly Male Primary Osteoporosis

INTRODUCTION

Osteoporosis (OP) is a debilitating disease that brings a heavy burden to individuals and society with reduced quality of life and lifespan. However, it's frequently overlooked and poorly studied in elderly male patients. Worse still, few anti-osteoporosis drugs are effective at the prevention and treatment of osteoporosis in men. It has been reported that the cells of bone and the immune system share common progenitors, cytokines and growth factors, and that reciprocal interactions occur during health and disease. Nevertheless, the role of immune system in OP is not fully understood, especially in male patients. Therefore, this study aimed to investigate molecular alterations in immune cells in men with OP and to identify immunomodulatory strategies with potential therapeutic value.

MATERIALS AND METHODS

A population of 121 men aged between 51 and 80 years old was recruited. Bone mineral density (BMD) was measured at the lumbar spine L1-4 and femoral neck using dual-energy X-ray absorptiometry (DXA). Twenty people were healthy, 66 people had osteopenia and 35 people had OP. Bone metabolic markers, Th1, Th2, Tregs and immune molecules were evaluated at the time of enrollment.

RESULTS

Smoking was a risk factor for OP. C-terminal crosslinking of type I collagen (β-CTX) and the ratio of receptor activator of nuclear factor-κB ligand (RANKL) to osteoprotegerin (OPG) were higher in OP group, which had lower 25-hydroxyvitamin D [25(OH)D] levels. OP had the higher levels of IL-6 and TNF-α and lower levels of IFN-γ and IL-10. CD4⁺CD25⁺CD127^-/low Tregs were significantly lower in the OP group. The imbalance of Th1/Th2 cells may play an important role in the development of OP. 25(OH)D may play essential roles in maintaining bone health. The low level of Tregs is also one of the underlying immune mechanism that leads to male primary OP.

CONCLUSION

The active function of osteoclasts and the decline in osteoblasts were characteristics of OP, and the imbalance in cytokines and lower levels of Tregs were observed in elderly male patients with primary OP.

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.

The association of OPG polymorphisms with risk of osteoporotic fractures: A systematic review and meta-analysis

BACKGROUND

Subjects with low bone mineral density and osteoporosis are more likely to suffer osteoporotic fractures during their lifetime. Polymorphisms in osteoprotegerin (OPG) gene are found to be associated with low bone mineral density and osteoporosis risk but their association with fracture risk is inconclusive. Here, we performed a meta-analysis to investigate the relationship between OPG polymorphisms with susceptibility to osteoporotic fractures.

METHODS

Eligible studies investigating the association between common OPG polymorphisms (A164G, T245G, T950C, and G1181C) and risk of osteoporotic fracture were retrieved from PubMed, EMBASE, Web of Science, and the Cochrane Library. Odds ratio (OR) and the 95% confidence interval (CI) were calculated in the allelic, dominant, recessive, and homozygous model. Subgroup analyses of vertebral fractures, Caucasians, and postmenopausal women were also performed.

RESULTS

A total of 14 studies comprising 5459 fracture cases and 9860 non-fracture controls were included. A163G was associated with fracture risk in dominant (OR = 1.29, 95%CI 1.11-1.50), recessive (OR = 1.64, 95%CI 1.10-2.44), and homozygous model (OR = 1.73, 95%CI 1.16-2.59). T245G was significantly correlated with susceptibility to fractures in all genetic models. Subjects with CC genotype of T950C had a reduced risk of fracture compared to those with CT or TT genotypes (OR = 0.81, 95%CI 0.70-0.94, P = .004). Subgroup analysis showed that A163G and T245G but not T950C and G1181C were associated with vertebral fracture risk.

CONCLUSION

OPG A163G and T245G polymorphisms were risk factors of osteoporotic fractures while T950C had a protective role. These polymorphisms can be used as predictive markers of fractures.

Association of environmental cadmium exposure and bone remodeling in women over 50 years of age

Chronic cadmium (Cd) toxicity is a significant health concern, and the mechanism of long-term low-dose Cd exposure on bone has not been fully elucidated yet. This study aimed to assess the association between long-term environmental Cd exposure and bone remodeling in women who aged over 50. A total of 278 non-smoking subjects from Cd-polluted group (n = 191) and non-Cd polluted group (n = 87) were investigated. Bone mineral density (BMD), the levels of three bone turnover markers (BTMs), including total procollagen type 1 amino-terminal propeptide (P1NP), collagen type 1 cross-linked C-telopeptide (β-CTX), bone-specific alkaline phosphatase (BALP), together with serum soluble receptor activator of nuclear factor-κB ligand (sRANKL) and osteoprotegerin (OPG) were determined. Early markers of renal dysfunction were measured as well. Urinary Cd concentrations ranged from 0.41 to 87.31 μg/g creatinine, with a median of 4.91 μg/g creatinine. Age, BMD, T-score, and prevalence of osteoporosis showed no statistical differences among the quartiles of urinary Cd concentrations, while serum levels of P1NP, β-CTX, and OPG were higher in the upper quartiles. Multivariate linear regression models indicated significantly positive associations of urinary Cd concentration with serum levels of P1NP, β-CTX, BALP, sRANKL, and OPG. A ridge regression analysis with T-score and the three BTMs, sRANKL, and OPG, adjusted for age and body mass index (BMI), indicated that except for age and Cd exposure, β-CTX was a predictor of T-score. These findings demonstrated that Cd may directly accelerate bone remodeling. Serum β-CTX might be an appropriate biochemical marker for evaluating and monitoring Cd-related bone loss. Capsule: Cadmium (Cd) may directly accelerate bone remodeling and serum β-CTX is a valuable biochemical marker for evaluating Cd-related bone loss.

Impact of physical activity and exercise on bone health in patients with chronic kidney disease: a systematic review of observational and experimental studies

Background

Chronic Kidney Disease (CKD) patients frequently develop life-impairing bone mineral disorders. Despite the reported impact of exercise on bone health, systematic reviews of the evidence are lacking. This review examines the association of both physical activity (PA) and the effects of different exercise interventions with bone outcomes in CKD.

Methods

English-language publications in EBSCO, Web of Science and Scopus were searched up to May 2019, from which observational and experimental studies examining the relation between PA and the effect of regular exercise on bone-imaging or -outcomes in CKD stage 3–5 adults were included. All data were extracted and recorded using a spreadsheet by two review authors. The evidence quality was rated using the Cochrane risk of bias tool and a modified Newcastle-Ottawa scale.

Results

Six observational (4 cross-sectional, 2 longitudinal) and seven experimental (2 aerobic-, 5 resistance-exercise trials) studies were included, with an overall sample size of 367 and 215 patients, respectively. Judged risk of bias was low and unclear in most observational and experimental studies, respectively. PA was positively associated with bone mineral density at lumbar spine, femoral neck and total body, but not with bone biomarkers. Resistance exercise seems to improve bone mass at femoral neck and proximal femur, with improved bone formation and inhibited bone resorption observed, despite the inconsistency of results amongst different studies.

Conclusions

There is partial evidence supporting (i) a positive relation of PA and bone outcomes, and (ii) positive effects of resistance exercise on bone health in CKD. Prospective population studies and long-term RCT trials exploring different exercise modalities measuring bone-related parameters as endpoint are currently lacking.

The Women's Health Initiative: A Landmark Resource for Skeletal Research Since 1992

The Women's Health Initiative (WHI) is a large longitudinal study designed to investigate strategies for the prevention and control of common chronic diseases in postmenopausal women, including cardiovascular disease, cancer, and osteoporotic fractures. The WHI consisted of three overlapping clinical trials of hormone therapy, diet modification to reduce total dietary fat, and calcium/vitamin D supplementation. Women who were ineligible for the hormone therapy or diet modification trials or not interested were invited to participate in the observational study. Women were recruited into WHI from 1993 to 1998 at 40 US clinical centers. WHI enrolled 26,046 underrepresented minority women and 135,762 white women. Women could participate in each trial if eligible. The final enrollment included 27,347 women in the hormone trial; 48,835 women in the diet modification trial; 36,282 women in the calcium/vitamin D trial, and 93,676 in the observational study. After the main study ended in 2005, women were invited to continue follow-up for exposures and outcomes through two extensions to 2020. Proposals were recently submitted to continue follow-up through 2027. Information was collected on an extensive number of risk factors for fractures at baseline and over the follow-up, including fall and fracture history, weight patterns, comorbidities, diet, reproductive history, medications, anthropometry, and biomarkers. Bone mineral density was measured at three WHI clinical centers (n = 11,020) chosen to maximize race/ethnic diversity. WHI encourages outside investigators to make use of the publicly available WHI data and to access the biobank of specimens (www.whi.org). © 2020 American Society for Bone and Mineral Research.

An In Silico Model for the Prediction of Changes in Mineral Density in Cortical Bone Remodeling

An in silico model for the estimation of volumetric bone mineral density (vBMD) changes at a cortical bone site subjected to mechanobiological bone remodeling is proposed in this manuscript. Mechanisms of cell differentiation, receptor-ligand binding, mechanical signaling, and resorption or deposition of bone matrix were considered, therefore providing a comprehensive description of mechanobiological bone remodeling in the bone microenvironment and enabling the analysis of temporal evolution of disease or therapy scenarios. The proposed model is composed by five modules, namely, bone cells populations, mechanobiology, volume fractions and porosity, mineral density, and structural stiffness. The model is an extension of other models found in the literature because equations for the obtaining of cortical vBMD and the binding of parathyroid hormone (PTH) to parathyroid hormone 1 receptor are included. The proposed model showed a satisfactory agreement with the solutions of other in silico models found in the literature. Simulations of walking and running exercise routines were performed for the evaluation of model capability regarding the control of the numerical error and prediction of vBMD. The computational method used to solve the case study controlled the relative numerical error by less than 1 × 10-7 for approximately 1.7 × 106 time steps. The predicted values correlate with the concept of increasing BMD by vigorous physical activity; however, they contrast with the specific effect of physical activities on cortical vBMD.

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.

Ovariectomy increases RANKL protein expression in bone marrow adipocytes of C3H/HeJ mice

Estrogen deficiency induces bone loss by increasing bone resorption, in part through upregulation of receptor activator of nuclear factor-κB ligand (RANKL). RANKL is secreted by osteoblasts and osteocytes, but more recently bone marrow (pre)adipocytes have also been shown to express RANKL. Estrogen deficiency increases bone marrow adipose tissue (BMAT). The aim of this study was to determine the effect of ovariectomy (OVX) on RANKL protein expression by bone marrow adipocytes in C3H/HeJ mice. Fourteen-week-old female C3H/HeJ mice (n = 20) were randomized to sham surgery (Sham) or OVX. After 4 wk animals were euthanized. BMAT volume fraction (BMAT volume/marrow volume) was quantified by polyoxometalate-based contrast-enhanced nano-computed tomography. The percentage of RANKL-positive bone marrow adipocytes (RANKL-positive bone marrow adipocytes/total adipocytes) and the percentage of RANKL-positive osteoblasts covering the bone surface (bone surface covered in RANKL-positive osteoblasts/total bone surface) were quantified in the distal metaphysis of immunohistochemically stained sections of the left femur. The effects of OVX were analyzed by Student's t test or Mann-Whitney U test. RANKL was detected in osteoblasts, osteocytes, and bone marrow adipocytes. OVX significantly increased mean percentage of RANKL-positive bone marrow adipocytes [mean (SD): Sham 42 (18)%; OVX 64 (12)%; P = 0.029] as well as BMAT volume/marrow volume [median (interquartile range): Sham 1.4 (4.9)%; OVX 7.2 (7.3)%; P = 0.008] compared with Sham. We show that OVX increased both the percentage of RANKL-positive bone marrow adipocytes and the total BMAT volume fraction in C3H/HeJ mice. Therefore, RANKL produced by bone marrow adipocytes could be an important contributor to OVX-induced bone loss in C3H/HeJ mice.

Clinical utility of bone markers in various diseases

Measurements of bone markers (BMs) in peripheral blood or urine are a pivotal part of bone research within modern clinical medicine. In recent years the use of BMs increased substantially as they can be useful either to diagnose bone (related) disease and to follow its natural history, but also to monitor the effects of interventions. However, the use of BMs is still complicated mainly due to (pre)analytical variability of these substances, limited accessibility of assays, variable cut-off values in different countries and laboratories and heterogeneous results with regard to clinical implications of measuring BMs in several studies. This review will provide the clinician with a practical guide, based on current evidence, in which circumstances to test which bone markers for optimal diagnostic purposes, in order to improve patient care in different areas of bone diseases including Paget's disease, primary osteoporosis, tumor induced osteomalacia, hypophosphatemic rickets, van Buchem disease, chronic kidney disease, rheumatoid arthritis, neoplasma/multiple myeloma, type 2 diabetes mellitus and primary hyperparathyroidism. The clinician should consider fasting state, recent fractures, aging, menopausal status, concomitant liver and kidney disease when ordering and interpreting BM measurements as these factors might result in misleading BM concentrations. We found that BMs are clearly useful in the current diagnosis of tumor induced osteomalacia, van Buchem disease, Paget's disease and hypophosphatemic rickets. In addition, BMs are useful to monitor disease activity in chronic kidney disease, Paget's disease and are useful to monitor treatment adherence in osteoporosis.

Circulating Levels of Bone and Inflammatory Markers in Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) can cause short- and long-term complications to the mother and fetus. While the precise mechanisms in preserving glucose balance in a healthy pregnancy are unknown, various growth factors and hormones have been implicated or associated with GDM risk in humans or rodents, including prolactin, tumor necrosis factor alpha (TNFα), osteoprotegerin (OPG), hepatocyte growth factor (HGF), and receptor activator of nuclear factor-kappa B ligand (RANKL). We aimed to evaluate the relationship of these and other protein markers in women with GDM. In this cross-sectional study, blood samples were collected from pregnant women with GDM and with normal glucose tolerance (NGT) at the 24- to 32-week obstetrical visit, during the 1-h oral glucose challenge test or 3-h oral glucose tolerance test. Blood plasma was analyzed for RANKL, OPG, prolactin, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), HGF, plasminogen activator inhibitor type 1 (PAI-1), and TNFα. Forty-six women with NGT and 47 women with GDM were included (mean ± standard deviation maternal age 31.6 ± 5.7, mean ± standard deviation gestational age 28.1 ± 2.2 weeks). Groups were similar in terms of age, body mass index, gestational age, and race/ethnicity. Serum levels of OPG, prolactin, TRAIL, HGF, PAI-1, and TNFα were similar in both groups. RANKL was lower in GDM subjects (p = 0.019). Contrary to previous reports in the literature, we found a lower serum RANKL level in women with GDM. Further investigation is needed to determine whether there are suitable serum markers for diagnosing GDM or determining prognosis or severity.

Leptin can promote mineralization and up-regulate RANKL mRNA expression in osteoblasts from adult female SD rats

Osteoblast-related bone formation is an indispensable part of bone remodeling. Osteoblasts can regulate osteoclast activity through the OPG/RANK/RANKL system. Therefore, studies focus on osteoblast proliferation, differentiation, mineralization, and regulation of osteoclasto genes are important. Leptin is a polypeptide encoded by the obesity gene. In the past, regulatory roles of leptin on sugar and lipid metabolism have been extensively studied. In recent years, leptin has been found to have multiple effects on bone metabolism. However, its role in osteoblasts has not been clarified. In order to investigate the effects of leptin on osteoblasts of adult female SD rats, primary cultured osteoblasts were passaged and divided into control and leptin groups. The effects of leptin on osteoblast proliferation, differentiation, mineralization, and OPG and RANKL mRNA expression were observed. Leptin significantly promoted mineralization of osteoblasts in adult female SD rats, and the mineralized area gradually increased with the increase of leptin concentration. When the concentration of leptin was 100 ng/ml, the mineralized area was the highest (P = 0.001). The expression of RANKL mRNA was also elevated by 10 ng/ml leptin. However, leptin had no significant effect on osteoblast proliferation, secretion of ALP, and expression of OPG mRNA in adult female SD rat osteoblast.

Prediction of Fractures and Major Cardiovascular Events in Men Using Serum Osteoprotegerin Levels: The Prospective STRAMBO Study

Fragility fractures and cardiovascular diseases often coincide. However, data on shared risk factors and markers are scarce. Our aim was to assess the independent associations of serum osteoprotegerin (OPG) levels with the risk of fracture and cardiovascular outcomes (acute coronary syndrome, cardiac death) in older men. A cohort of 819 home-dwelling men aged 60 to 87 years was followed prospectively for 8 years. Serum OPG was measured at baseline by ELISA. Bone mineral density (BMD) at femoral neck and Trabecular Bone Score (TBS) were assessed by DXA. Clinical risk factors and Fracture Risk Assessment Tool (FRAX) were assessed. The incident events (self-reported peripheral fractures and acute coronary syndrome, cardiac death reported by a proxy) confirmed by a health professional were retained for the statistical analysis. Incident vertebral fractures were assessed on lateral DXA scans after 4 and 8 years. Hazard risk (HR) was assessed using the Cox model. After adjustment for FRAX corrected for femoral neck BMD and TBS, diabetes mellitus, ischemic heart disease, and prior falls, the risk of fracture was twofold higher in the highest versus the lowest OPG quartile (HR 2.35; 95% CI, 1.35 to 4.10). The risk of vertebral and nonvertebral fracture was higher in the highest versus the lowest OPG quartile (OR 2.76 [95% CI, 1.08 to 7.05] and HR 2.46 [95% CI, 1.23 to 4.92]). The risk of major osteoporotic fracture was higher in the fourth versus the first OPG quartile (HR 2.43; 95% CI, 1.16 to 5.10). The risk of cardiovascular outcome (adjusted for confounders) was higher in the highest versus the lowest OPG quartile (HR 3.93; 95% CI, 1.54 to 10.04). The risk of fracture and cardiovascular outcome was higher in the highest OPG quartile versus the lower quartiles combined (HR 2.06 [95% CI, 1.35 to 3.14] and HR 2.98 [95% CI, 1.60 to 5.54], respectively). In conclusion, in older men, higher serum OPG levels represent an independent risk factor for cardiovascular and fracture risk. © 2017 American Society for Bone and Mineral Research.

Potassium citrate prevents increased osteoclastogenesis resulting from acidic conditions: Implication for the treatment of postmenopausal bone loss

The extracellular acidic milieu in bones results in activation of osteoclasts (OC) and inhibition of osteoblasts (OB) causing a net loss of calcium from the skeleton and the deterioration of bone microarchitecture. Alkalinization through supplementation with potassium citrate (K citrate) has been proposed to limit the osteopenia progression, even though its pharmacological activity in bone microenvironment is not well defined. We evaluated if K citrate was able to prevent the adverse effects that acidic milieu induces on bone cells. OC and OB were maintained in neutral (pH 7.4) versus acidic (pH 6.9) culture medium, and treated with different K citrate concentrations. We evaluated the OC differentiation at seven days, by counting of multinucleated cells expressing tartrate-resistant acid phosphatase, and the activity of mature OC at 14 days, by quantifying of collagen degradation. To evaluate the effects on OB, we analyzed proliferation, mineralization, and expression of bone-related genes. We found that the low pH increased OC differentiation and activity and decreased OB function. The osteoclastogenesis was also promoted by RANKL concentrations ineffective at pH 7.4. Non-cytotoxic K citrate concentrations were not sufficient to steadily neutralize the acidic medium, but a) inhibited the osteoclastogenesis, the collagen degradation, and the expression of genes involved in RANKL-mediated OC differentiation, b) enhanced OB proliferation and alkaline phosphatase expression, whereas it did not affect the in vitro mineralization, and c) were effective also in OC cultures resistant to alendronate, i.e. the positive control of osteoclastogenesis inhibition. In conclusion, K citrate prevents the increase in OC activity induced by the acidic microenvironment, and the effect does not depend exclusively on its alkalizing capacity. These data provide the biological basis for the use of K citrate in preventing the osteopenia progression resulting from low-grade acidosis.

Estrogens and androgens inhibit association of RANKL with the pre-osteoblast membrane through post-translational mechanisms

We have recently demonstrated that RUNX2 promoted, and 17β-Estradiol (E2) diminished, association of RANKL with the cell membrane in pre-osteoblast cultures. Here we show that, similar to E2, dihydrotestosterone (DHT) diminishes association of RANKL, and transiently transfected GFP-RANKL with the pre-osteoblast membrane without decreasing total RANKL mRNA or protein levels. Diminution of membrane-associated RANKL was accompanied with marked suppression of osteoclast differentiation from co-cultured pre-osteoclasts, even though DHT increased, not decreased, RANKL concentrations in pre-osteoblast conditioned media. A marked decrease in membrane-associated RANKL was observed after 30 min of either E2 or DHT treatment, and near-complete inhibition was observed by 1 hr, suggesting that the diminution of RANKL membrane association was mediated through non-genomic mechanisms. Further indicating dispensability of nuclear action of estrogen receptor, E2-mediated inhibition of RANKL membrane association was mimicked by an estrogen dendrimer conjugate (EDC) that cannot enter the cell nucleus. Finally, the inhibitory effect of E2 and DHT on RANKL membrane association was counteracted by the MMP inhibitor NNGH, and the effect of E2 (and not DHT) was antagonized by the Src inhibitor SU6656. Taken together, these results suggest that estrogens and androgens inhibit osteoblast-driven osteoclastogenesis through non-genomic mechanism(s) that entail, MMP-mediated RANKL dissociation from the cell membrane.

Inverse Association Between Serum Osteoprotegerin and Bone Mineral Density in Renal Transplant Recipients

BACKGROUND

Osteoprotegerin (OPG) has pleiotropic effects on bone metabolism as well as endocrine function. Our aim was to evaluate the relationship between bone mineral density (BMD) and serum OPG concentration in renal transplant recipients.

METHODS

Fasting blood samples were obtained from 69 renal transplant recipients. BMD was measured in lumbar vertebrae (L2-L4) by dual-energy X-ray absorptiometry. Eight patients (11.6%) had BMD values indicative of osteoporosis, 28 patients (40.6%) had BMD values indicative of osteopenia, and 33 patients had normal BMD values. Increased serum OPG levels (P < .001), decreased body mass index (BMI) (P = .033), and decreased body weight (P = .010) were significantly correlated with low lumbar T-score cut-off points between groups (normal, osteopenia, and osteoporosis).

RESULTS

Women had significantly lower lumbar BMD values than men (P = .013). Menopause (P = .005), use of tacrolimus (P = .020), and use of cyclosporine (P = .046) were associated with lower lumbar BMD in renal transplant recipients. Univariate linear regression analysis revealed that lumbar BMD was positively correlated with height (P = .016), body weight (P = .001), and BMI (P = .015) and negatively correlated with age (P = .039) and log-OPG (P = .001). Multivariate linear regression analysis revealed that log-OPG (β: -0.275, R(2) change = 0.154, P = .014), body weight (β: 0.334, R(2) change = 0.073, P = .004), and age (β: -0.285, R(2) change = 0.079, P = .008) were independent predictors of lumbar BMD values in renal transplant recipients.

CONCLUSIONS

Serum OPG concentration correlated negatively with lumbar BMD values in renal transplant recipients.

Bone remodeling and regulating biomarkers in women at the time of breast cancer diagnosis

PURPOSE

The majority of breast cancer patients receive endocrine therapy, including aromatase inhibitors known to cause increased bone resorption. Bone-related biomarkers at the time of breast cancer diagnosis may predict future risk of osteoporosis and fracture after endocrine therapy.

METHODS

In a large population of 2,401 female breast cancer patients who later underwent endocrine therapy, we measured two bone remodeling biomarkers, TRAP5b and BAP, and two bone regulating biomarkers, RANKL and OPG, in serum samples collected at the time of breast cancer diagnosis. We analyzed these biomarkers and their ratios with patients' demographic, lifestyle, clinical tumor characteristics, as well as bone health history.

RESULTS

The presence of bone metastases, prior bisphosphonate (BP) treatment, and blood collection after chemotherapy had a significant impact on biomarker levels. After excluding these cases and controlling for blood collection time, several factors, including age, race/ethnicity, body mass index, physical activity, alcohol consumption, smoking, and hormonal replacement therapy, were significantly associated with bone biomarkers, while vitamin D or calcium supplements and tumor characteristics were not. When prior BP users were included in, recent history of osteoporosis and fracture was also associated.

CONCLUSIONS

Our findings support further investigation of these biomarkers with bone health outcomes after endocrine therapy initiation in women with breast cancer.

Bioavailable 25(OH)D but Not Total 25(OH)D Is an Independent Determinant for Bone Mineral Density in Chinese Postmenopausal Women

Total 25(OH)D levels were determined to assess bone health in elderly populations; however, the bioavailability of 25(OH)D is regulated by the albumin and vitamin D binding protein (DBP) levels and DBP variations. Whether bioavailable 25(OH)D level is a superior biomarker for vitamin D than total 25(OH)D level regarding the BMD and the bone metabolism were not yet fully understood. With a community based cross-sectional study of 967 postmenopausal women, we found that the variant rs7041, but not rs4588, of DBP was significantly associated with the blood DBP level, which was positively correlated with the total 25(OH)D level but negatively associated with bioavailable 25(OH)D levels. Both total and bioavailable 25(OH)D levels were significantly correlated with the BMD value in postmenopausal women; however, only the bioavailable 25(OH)D level was an independent determinant of the BMD values when adjusted for age, body mass index and bone turnover biomarkers (OST and β-CTX). The bioavailable and total 25(OH)D were negatively correlated with bone formation biomarkers (OST, PINP and ALP) and PTH levels, while they were positively correlated with osteoprotegerin (OPG) level; however, the bone resorption biomarker (β-CTX) was not correlated with the 25(OH)D levels. An increment of PTH level, along with reduced bioavailable 25(OH)D levels, was evident when the bioavailable 25(OH)D level was < 5 ng/mL, which may be the optimal cutpoint for sufficient vitamin D in Chinese elderly women. The blood calcium, magnesium, ALP, TSH, FGF23, and phosphorus levels were not correlated with the total or the bioavailable 25(OH)D levels. These results suggested that high bioavailable 25(OH)D levels were correlated with reduced bone turnover processes and were a biomarker superior to total 25(OH)D for vitamin D in assessing the risks of bone-related diseases. The results indicate that the bioavailable 25(OH)D level should be determined in assessing the bone health.

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DBP levels and variants on DBP were associated with the total and bioavailable 25(OH)D levels in the elderly populations.

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Both the total and bioavailable 25(OH)D levels were correlated with the BMD in postmenopausal women.

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Multivariate analyses suggested that the bioavailable but not total 25(OH)D was an independent determinant for the BMD.

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Higher bioavailable 25(OH)D levels were correlated with reduced bone turnover and lower PTH in postmenopausal women.

With a cross-sectional community study, we found that the variant rs7041, but not rs4588, of DBP was significantly associated with the blood DBP level, which was positively correlated with the total 25(OH)D levels but negatively associated with the bioavailable 25(OH)D levels. The bioavailable 25(OH)D level was an independent determinant for BMD but not total 25(OH)D. Higher vitamin D levels were correlated with the reduced bone turnover process and lower PTH levels, which might lead to the higher BMD value in postmenopausal women. These results suggested that bioavailable 25(OH)D was a superior biomarker than total 25(OH)D regarding the bone metabolism, and that vitamin D intervention may improve the bone health in elderly populations.

Effect of nicotine on RANKL and OPG and bone mineral density

AIM

The signaling pathway OPG/RANK/RANKL is a key in maintaining the balance between the activity of osteoblasts and osteoclasts in order to prevent bone loss. In this study, our aim was to assess the effects of long-term nicotine exposure on plasma RANKL and OPG levels, tissue RANKL and OPG immunoreactivities, and bone mineral density (BMD) scores in rats.

MATERIALS AND METHODS

Thirty-six Swiss Albino rats weighing 70 ± 10 g were divided into three groups. While the controls (n = 12) were only given normal drinking water, for low-dose nicotine (LDN) group (n = 12) 0.4 mg/kg/day; for high-dose nicotine (HDN) group (n = 12), 6.0 mg/kg/day nicotine was added to drinking water for a year. At the end of 12th month, BMD scores were measured using an X-ray absorptiometry and bone turnover was assessed by measuring plasma RANKL and OPG levels and RANKL and OPG immunoreactivities in tail vertebrae of the rats.

RESULTS

There was no statistically significant difference in BMD scores of lumbar spine and femoral regions of the nicotine groups in comparison to controls. Plasma OPG levels were found to be significantly higher in HDN group, in comparison to the controls and LDN groups (p = .001) unlike plasma RANKL levels. Tissue RANKL and OPG immunoreactivities decreased significantly in the LDN and HDN groups (p < .001, p < .01, respectively).

CONCLUSIONS

The results of this study show that nicotine is not primarily responsible for the decrease in BMD frequently seen in smokers. Measuring plasma RANKL and OPG levels did not reflect tissue immunoreactivities.