Circulating amounts of osteoprotegerin and RANK ligand: genetic influence and relationship with BMD assessed in female twins

Correlates of Circulating Osteoprotegerin in Women with a Pathogenic or Likely Pathogenic Variant in the BRCA1 Gene

BACKGROUND

Lower levels of osteoprotegerin (OPG), the decoy receptor for receptor activator of NFκB (RANK)-ligand, have been reported among women with a BRCA1 mutation, suggesting OPG may be marker of cancer risk. Whether various reproductive, hormonal, or lifestyle factors impact OPG levels in these women is unknown.

METHODS

BRCA1 mutation carriers enrolled in a longitudinal study, no history of cancer, and a serum sample for OPG quantification, were included. Exposure information was collected through self-reported questionnaire at study enrollment and every 2 years thereafter. Serum OPG levels (pg/mL) were measured using an ELISA, and generalized linear models were used to assess the associations between reproductive, hormonal, and lifestyle exposures at the time of blood collection with serum OPG. Adjusted means were estimated using the fully adjusted model.

RESULTS

A total of 701 women with a median age at blood collection of 39.0 years (18.0-82.0) were included. Older age (Spearman r = 0.24; P < 0.001) and current versus never smoking (98.82 vs. 86.24 pg/mL; Pcat < 0.001) were associated with significantly higher OPG, whereas ever versus never coffee consumption was associated with significantly lower OPG (85.92 vs. 94.05 pg/mL; Pcat = 0.03). There were no other significant associations for other exposures (P ≥ 0.06). The evaluated factors accounted for 7.5% of the variability in OPG.

CONCLUSIONS

OPG is minimally influenced by hormonal and lifestyle factors among BRCA1 mutation carriers.

IMPACT

These findings suggest that circulating OPG levels are not impacted by non-genetic factors in high-risk women.

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.

Delineating the role of osteoprotegerin as a marker of breast cancer risk among women with a BRCA1 mutation

Women with a pathogenic germline mutation in the BRCA1 gene face a very high lifetime risk of developing breast cancer, estimated at 72% by age 80. Prophylactic bilateral mastectomy is the only effective way to lower their risk; however, most women with a mutation opt for intensive screening with annual MRI and mammography. Given that the BRCA1 gene was identified over 20 years ago, there is a need to identify a novel non-surgical approach to hereditary breast cancer prevention. Here, we provide a review of the emerging preclinical and epidemiologic evidence implicating the dysregulation of progesterone-mediated receptor activator of nuclear factor κB (RANK) signaling in the pathogenesis of BRCA1-associated breast cancer. Experimental studies have demonstrated that RANK inhibition suppresses Brca1-mammary tumorigenesis, suggesting a potential target for prevention. Data from studies conducted among women with a BRCA1 mutation further support this pathway in BRCA1-associated breast cancer development. Progesterone-containing (but not estrogen-alone) hormone replacement therapy is associated with an increased risk of breast cancer in women with a BRCA1 mutation. Furthermore, BRCA1 mutation carriers have significantly lower levels of circulating osteoprotegerin (OPG), the decoy receptor for RANK-ligand (RANKL) and thus endogenous inhibitor of RANK signaling. OPG levels may be associated with the risk of disease, suggesting a role of this protein as a potential biomarker of breast cancer risk. This may improve upon current risk prediction models, stratifying women at the highest risk of developing the disease, and further identify those who may be targets for anti-RANKL chemoprevention. Collectively, the evidence supports therapeutic inhibition of the RANK pathway for the primary prevention of BRCA1-associated breast cancer, which may generate unique prevention strategies (without prophylactic surgery) and enhance quality of life.

Regulation of TNF-Induced Osteoclast Differentiation

Increased osteoclast (OC) differentiation and activity is the critical event that results in bone loss and joint destruction in common pathological bone conditions, such as osteoporosis and rheumatoid arthritis (RA). RANKL and its decoy receptor, osteoprotegerin (OPG), control OC differentiation and activity. However, there is a specific concern of a rebound effect of denosumab discontinuation in treating osteoporosis. TNFα can induce OC differentiation that is independent of the RANKL/RANK system. In this review, we discuss the factors that negatively and positively regulate TNFα induction of OC formation, and the mechanisms involved to inform the design of new anti-resorptive agents for the treatment of bone conditions with enhanced OC formation. Similar to, and being independent of, RANKL, TNFα recruits TNF receptor-associated factors (TRAFs) to sequentially activate transcriptional factors NF-κB p50 and p52, followed by c-Fos, and then NFATc1 to induce OC differentiation. However, induction of OC formation by TNFα alone is very limited, since it also induces many inhibitory proteins, such as TRAF3, p100, IRF8, and RBP-j. TNFα induction of OC differentiation is, however, versatile, and Interleukin-1 or TGFβ1 can enhance TNFα-induced OC formation through a mechanism which is independent of RANKL, TRAF6, and/or NF-κB. However, TNFα polarized macrophages also produce anabolic factors, including insulin such as 6 peptide and Jagged1, to slow down bone loss in the pathological conditions. Thus, the development of novel approaches targeting TNFα signaling should focus on its downstream molecules that do not affect its anabolic effect.

Reproductive and Lifestyle Factors and Circulating sRANKL and OPG Concentrations in Women: Results from the EPIC Cohort

BACKGROUND

Except for a documented increase in osteoprotegerin (OPG) concentrations with older age, data on determinants of soluble Receptor Activator of Nuclear Factor κB (sRANKL) and OPG concentrations in women are limited. We evaluated reproductive and lifestyle factors as potential sources of variation in circulating sRANKL and OPG concentrations in pre- and postmenopausal women.

METHODS

This study includes 2,016 controls [n = 1,552 (76%) postmenopausal, n = 757 (38%) using postmenopausal hormone therapy (PMH)] from a breast cancer case-control study nested in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. Serum sRANKL was measured using an ELISA and serum OPG using an electrochemiluminescent assay. Generalized linear models were used to evaluate associations between these analytes and reproductive and lifestyle factors.

RESULTS

Older age at blood collection was associated with lower sRANKL concentrations in postmenopausal women (P trend ≤ 0.03) and higher OPG concentrations in all women (P trend ≤ 0.01). Longer duration of oral contraceptive use among premenopausal women and postmenopausal PMH users was associated with higher OPG (P trend ≤ 0.04). In postmenopausal non-PMH users, sRANKL concentrations were lower with longer duration of oral contraceptive use and current (vs. never) smoking (P ≤ 0.01). sRANKL concentrations were higher among women with higher BMI (P trend ≤ 0.01). The evaluated factors accounted for 12% of the variation in sRANKL concentrations and 21% of the variation in OPG concentrations.

CONCLUSIONS

Circulating sRANKL and OPG concentrations are minimally impacted by hormone-related factors in pre- and postmenopausal women.

IMPACT

This study suggests circulating concentrations of sRANKL and OPG are unlikely to be strongly modified by hormone-related reproductive and lifestyle factors.

Serum RANKL, osteoprotegerin (OPG) and RANKL/OPG ratio in children with systemic lupus erythematosus

Background

Systemic lupus erythematosus (SLE) patients have lower bone mineral density (BMD) compared with healthy individuals because of general, genetic, disease and medication-related factors. The disturbance of the receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) ratio has been reported to be associated with low BMD in many disorders in adults and children alike.

Objectives

The objectives of this study were (i) to assess serum OPG, RANKL and RANKL/OPG ratio levels in SLE children and controls, (ii) to determine whether the cumulative glucocorticoid (CGCS) dose had any effect on the concentration of serum RANKL, OPG and RANKL/OPG ratio, and (iii) to determine the relation of these parameters to BMD.

Methods

We evaluated 50 SLE children and 50 age- and sex-matched healthy controls. RANKL and OPG were assessed in serum and compared between patients and controls. For SLE patients, a univariate followed by multivariable analysis were carried out to detect the possible predictors of the changes in RANKL, OPG and RANKL/OPG ratio levels. Lumbar BMD for all patients was assessed by dual-energy X-ray absorptiometry (DXA) scan and then correlated to different probable correlated factors.

Results

RANKL, OPG and RANKL/OPG ratio were significantly higher in SLE patients ( p ≤ 0.001). Univariate analysis showed significant correlations of RANKL with CGCS ( p ≤ 0.001) and with DXA scan z-score ( p = 0.007): OPG was significantly correlated to Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score ( p = 0.001) and anti-double-stranded DNA ( p = 0.001), whereas RANKL/OPG was significantly correlated to duration of illness and DXA z-score ( p = 0.002). The multivariable analysis showed that DXA z-score was an independent predictor of RANKL and RANKL/OPG ratio ( p = 0.019 and 0.008, respectively), whereas SLEDAI score was an independent predictor of OPG levels. BMD was negatively correlated to disease duration ( p = 0.008) and CGCS dose ( p = 0.015), but no significant correlation has been found between BMD and cumulative SLEDAI score ( p = 0.29).

Conclusions

Serum RANKL/OPG ratio is elevated in Egyptian children with SLE and is considered a risk factor for reduced bone mass in these children. Other risk factors for low BMD include high CGCS dose and disease duration, supporting that osteoporosis in SLE is multifactorial.

Premenopausal Trabecular Bone Loss is Associated with a Family History of Fragility Fracture

INTRODUCTION

Although a fragility fracture family history (FFFH+) has repeatedly been shown to be associated with lower bone mineral density (BMD), its relationship to human BMD change is unclear. Animal research, however, documented that different purebred strains within rodent species have wide ranges in rates of bone acquisition during growth as well as in change post-ovariectomy. Our objective was to compare the rate of premenopausal spinal trabecular BMD change between women with and without a general family history of fragility fracture.

PARTICIPANTS AND METHODS

Healthy premenopausal community women participated in prospective observational studies at two academic medical research centres: Vancouver, Canada (n = 66) and Munich, Germany (n = 20). The primary outcome was annual spinal BMD change, measured by quantitative computed tomography (QCT). The two studies employed similar methodologies for assessing QCT and FFFH.

RESULTS

Volunteer community participants had a mean age of 36.0 (SD, 6.9) years, body mass index 22.5 (2.4) and baseline QCT of 150.2 (22.5) mg/cm³ trabecular bone. The rates of BMD change were similar in both cities: - 3.5 (5.1)/year Vancouver, - 2.0 (3.4)/year Munich (95 % CI of difference: - 3.9, 0.9). Over a third of the women (31 of the 86, 36 %) reported FFFH+. Those with and without a FFFH were similar in demographics, nutrition, exercise, menstrual cycle and luteal phase lengths and physiological measures (serum calcium, osteocalcin and estradiol). However, women with FFFH+ lost trabecular BMD more rapidly: FFFH+, - 4.9 (5.0), FFFH-, - 2.2 (4.4) mg/cm³/year (95 % CI diff - 0.7 to - 4.8, F_1.83 = 7.88, p = 0.006). FFFH+ explained 7.7 % of the variance in QCT volumetric trabecular spinal bone change/year in these healthy premenopausal women.

CONCLUSION

This study shows for the first time that having a history of a fragility fracture in a family member is associated with a greater rate of premenopausal spinal trabecular bone loss.

Different health behaviours and clinical factors associated with bone mineral density and bone turnover in premenopausal women with and without type 1 diabetes

BACKGROUND

Women with type 1 diabetes (T1DM) have an elevated fracture risk. We therefore compared the associations of health behaviours and clinical factors with bone mineral density (BMD) and bone remodelling between premenopausal women with and without T1DM to inform potential interventions.

METHODS

Participants included women with T1DM (n = 89) from the Wisconsin Diabetes Registry Study and age-matched and race-matched controls without diabetes (n = 76). Peripheral (heel and forearm) and central (hip and spine) BMD, markers of bone resorption and formation, bone cell signalling, glycaemic control, and kidney function were assessed. Health behaviours and medical history were self-reported.

RESULTS

In controls, but not in women with T1DM, older age was associated with lower bone resorption (p ≤ 0.006) and formation (p = 0.0007). Body mass index was positively associated with heel and forearm BMD in both controls and T1DM women (all p < 0.0001), but with hip and spine BMD only in controls (p ≤ 0.005). Worse glycaemic control during the previous 10 years, greater alcohol intake, history of smoking, and lack of physical activity were associated with poorer bone outcomes only in women with T1DM (all p ≤ 0.002), whereas use of hormonal contraceptives was related to low bone formation in both women with and without T1DM (all p ≤ 0.006). Diabetes duration, insulin dose, residual C-peptide, and kidney function were not associated with bone in T1DM.

CONCLUSIONS

Age and body mass index may not predict bone health in T1DM women. However, modifiable behaviours such as optimizing glycaemic control, limiting substance and hormonal contraceptive use, and increasing physical activity may improve bone health in T1DM women.

Family resemblance of bone turnover rate in mothers and daughters--the MODAM study

We studied bone turnover markers (BTM) and bone microarchitecture (using high-resolution peripheral quantitative computed tomography (HR-pQCT)) in 171 postmenopausal women and their 210 premenopausal daughters. BTM levels correlated positively between mothers and daughters. The mother-daughter pairs with high BTM levels had lower cortical density than those with low BTM levels.

INTRODUCTION

We assessed the correlation of serum bone turnover markers (BTM) between postmenopausal mothers and their premenopausal daughters as well as possible determinants of this association and its impact on resemblance of bone microarchitecture between mothers and their daughters.

METHODS

Cross-sectional analysis was performed in 171 untreated postmenopausal mothers (54 sustained fragility fractures) and their 210 premenopausal daughters. Intact N-terminal propeptide of type I collagen (PINP) and β-isomerized C-terminal crosslinking telopeptide of type I collagen (CTX-I) were measured in the fasting status. Bone microarchitecture was assessed using HR-pQCT.

RESULTS

After adjustment for age, weight, lifestyle factors, hormones, and mother's fracture status, BTM levels correlated positively between mothers and daughters (Intraclass Correlation Coefficient = 0.22-0.27, p <0.005). Average BTM levels were ∼ 0.6 SD higher among daughters of mothers in the highest BTM quartile vs. the ones in the lowest BTM quartile. The variability of BTM levels explained ≤ 10 and ≤ 14% of variability of bone microarchitecture in the daughters and mothers, respectively. Cortical density was lower by 2.3-2.9% (0.6 SD, p <0.05 to <0.005) in the daughters from the mother-daughter pairs with high BTM levels (defined by generation-specific quartiles) than in the daughters from the pairs with low BTM levels. Corresponding differences for the mothers were 4.5-4.8% (0.5 SD, p <0.05 to <0.01).

CONCLUSION

BTM levels correlated between postmenopausal mothers and their premenopausal daughters after adjustment for age, weight, mother's fracture status, lifestyle, and hormonal factors. Family resemblance of BTM levels may contribute to family resemblance of some bone microarchitectural parameters, especially of cortical density.

Meta-analysis of genome-wide association studies identifies two loci associated with circulating osteoprotegerin levels

Osteoprotegerin (OPG) is involved in bone homeostasis and tumor cell survival. Circulating OPG levels are also important biomarkers of various clinical traits, such as cancers and atherosclerosis. OPG levels were measured in serum or in plasma. In a meta-analysis of genome-wide association studies in up to 10 336 individuals from European and Asian origin, we discovered that variants >100 kb upstream of the TNFRSF11B gene encoding OPG and another new locus on chromosome 17q11.2 were significantly associated with OPG variation. We also identified a suggestive locus on chromosome 14q21.2 associated with the trait. Moreover, we estimated that over half of the heritability of OPG levels could be explained by all variants examined in our study. Our findings provide further insight into the genetic regulation of circulating OPG levels.

Twins and endocrinology

Twins are two independent babies delivered during the same pregnancy and are divided as monozygotic or dizygotic based on their origin. Dizygotic twins are similar to two siblings and have different genetic information. In contrary, monozygotic twins have a similar genetic identity and provide a unique opportunity to evaluate the contribution of genetic and environmental factors of the disease. The endocrine and metabolic disorders affect a large number of the population including the twins. Diabetes, obesity, and autoimmune thyroid disease are the most common endocrine disorders in general practice. It is essential to understand the genetic basis of endocrine disorders for therapy, prognostication and risk assessment for future generations. In this article, we review the endocrine disorders in relation to their occurrence in monozygotic twins to highlight the genetic and environmental contribution.

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

PURPOSE

The osteoprotogerin/receptor activator of NF-kappa β/receptor activator of NF-kappa β ligand (OPG/RANK/RANKL) pathway plays a critical role in bone remodeling. This study investigated associations between serum levels of OPG, soluble RANKL (sRANKL), and the ratio of OPG/sRANKL to risk of incident hip fracture.

METHODS

A nested case-control study was conducted among postmenopausal, Caucasian women aged 50-79 at baseline (1993-1998), followed for hip fracture through March 2005 in the Women's Health Initiative Observational Study. 400 incident hip fracture cases were selected and individually matched to 400 controls with no prior fracture or incident hip fracture. Matching factors were baseline age, enrollment date and hormone therapy (HT) exposure. Baseline serum OPG and sRANKL levels were measured using high sensitivity ELISA. Odds ratios were computed for quartiles of each biomarker adjusting for matching factors and hip fracture risk factors.

RESULTS

Serum OPG was significantly associated with older age, low physical activity and poorer physical function in control women. sRANKL was inversely associated with total calcium intake in control women, but not associated with age or other fracture risk factors. The odds ratio for hip fracture comparing the highest to lowest quartiles of OPG was 2.28 (95% confidence interval (CI), 1.45-3.61) after adjusting for the matching variables (p-value for linear trend <0.001), and 1.87 (95% CI, 1.15-3.04; p for linear trend=0.02) after adjusting for self-rated health status, physical activity and physical functioning. No significant associations between sRANKL or the ratio of OPG/sRANKL and hip fracture risk were observed.

CONCLUSION

Serum OPG levels were independently associated with a nearly twofold increased risk of hip fracture in postmenopausal women.

Relationship between serum RANKL and RANKL in bone

It is now well accepted that the molecule receptor activator of NFκB ligand (RANKL) and osteoprotegerin play key roles in regulating physiological and pathological bone turnover. There are a large number of published reports of circulating RANKL levels in both health and pathology. However, interpretation of these data has been elusive, and the relationship between circulating RANKL and RANKL levels in bone is still not clear. This review explores this subject, documenting the possible origins of circulating RANKL and suggesting additional information that is required before serum RANKL levels can provide useful diagnostic or research information.

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

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

Levels of osteoprotegerin (OPG) and receptor activator for nuclear factor kappa B ligand (RANKL) in serum: are they of any help?

The coupling of bone formation and resorption is mediated through the OPG/RANK/RANKL system. OPG and RANKL are mainly produced by osteoblasts but also a variety of other tissues. The binding of RANKL to RANK, its natural receptor which is expressed by osteoclasts, accelerates bone resorption. OPG acts as decoy receptor and prevents the interaction of RANKL with RANK and therefore leads to a decrease in activity, survival and proliferation of osteoclasts. Since assays for measurements of serum OPG and RANKL have become commercially available, intense research focused on serum OPG/RANKL levels in context with underlying disease, age, co-morbidities, bone density, and fractures has derived. This review aims to provide an overview if and to which extent serum OPG and RANKL levels may reflect bone metabolism in patients with osteoporosis and metabolic bone disease.

Bone loss in relation to serum levels of osteoprotegerin and nuclear factor-kappaB ligand: the Tromsø Study

SUMMARY

In this longitudinal study of 4,137 persons, bone mineral density was negatively associated with osteoprotegerin at baseline in both genders. In postmenopausal women not using hormone replacement therapy (HRT), bone-loss increased with increasing osteoprotegerin levels, whereas no relationship was found in men, premenopausal women, or postmenopausal women taking HRT.

INTRODUCTION

In a population-based study of 2,003 men and 2,134 women, the relationship between the osteoprotegerin (OPG)/factor-kappaB ligand (RANKL) system and bone mineral density (BMD) and changes in BMD was examined.

METHODS

Baseline measurements included height, weight, BMD of the forearm, OPG, RANKL, vitamin D, and serum parathyroid hormone (PTH) and information about lifestyle, prevalent diseases, and use of medication. BMD was remeasured at follow-up 6 years later.

RESULTS

BMD was negatively associated with OPG at baseline in both men and women (p trend over OPG levels = 0.01 and 0.007, respectively, after adjustments for age, and other confounders). In postmenopausal women not on hormone replacement therapy, bone loss increased with increasing OPG (p = 0.005), whereas no relationship was found in men, premenopausal women, or postmenopausal women on HRT (p >or= 0.28). BMD at baseline and BMD changes were not related to RANKL levels in any of the groups (p >or= 0.14).

CONCLUSIONS

In postmenopausal women not using HRT, bone loss associated positively with OPG. The results indicate that in women deficient in sex steroids, the OPG/RANKL system may play an important counter regulatory role in order to avoid bone loss and maintain BMD. In men and women replete in sex steroids, the OPG/RANKL system was not associated with BMD.

Serum RANKL, osteoprotegerin (OPG), and RANKL/OPG ratio in nephrotic children

Receptor activator of NF-kB ligand (RANKL) and osteoprotegerin (OPG) play key roles in the pathogenesis of glucocorticoid-induced osteoporosis (GIO). The aim of our study was to determine whether the cumulative glucocorticoid dose (CGCS) in children with idiopathic nephrotic syndrome (INS) has any effect on the concentration of serum RANKL and OPG and the RANKL/OPG ratio. The study population consisted of 90 children with INS, aged 3-20 years, who were treated with GCS. These children were divided into two groups according to the CGCS: low (L)<1 g/kg body weight (BW) and high (H)>or=1 g/kg BW, respectively. The control group (C) consisted of 70 healthy children. RANKL concentration was observed to be significantly higher and OPG significantly lower in INS children than in the reference group: 0.21 (range 0.01-1.36) versus 0.15 (0-1.42) pmol/l (p<0.05), respectively, and 3.76 (1.01-7.25) versus 3.92 (2.39-10.23) pmol/l (p<0.05), respectively. The RANKL/OPG ratio was significantly higher in INS children (p<0.01). The concentration of RANKL, similar to the RANKL/OPG ratio, was significantly higher in Group H children than in Group L children: 0.46 (0.02-1.36 ) versus 0.19 (0.01-1.25) (p<0.01) and 0.14 (0.01-0.71) versus 0.05 (0.002-0.37) (p<0.01), respectively. The concentration of OPG was similar in both groups. There was a positive correlation between CGCS and the concentration of sRANKL as well as the RANKL/OPG ratio (in both cases r=0.33, p<0.05). Based on these results, we suggest that long-term exposure to GCS results in a dose-dependent increase in serum RANKL concentration and the RANKL/OPG ratio, but not in the level of serum OPG.

Viewpoint: dried plum, an emerging functional food that may effectively improve bone health

Osteoporosis is a debilitating disorder that affects both female and male, albeit to a greater extent in women than men. As the demographic shift to a more aged population continues, a growing number of men and women will be afflicted with osteoporosis and a search for potential non-pharmacological alternative therapies for osteoporosis is of prime interest. Aside from existing drug therapies, certain lifestyle and nutritional factors are known to reduce the risk of osteoporosis. Among nutritional factors, recent observations suggest that dried plum, or prunes (Prunus domestica L.) is the most effective fruit in both preventing and reversing bone loss. Animal studies and a 3-month clinical trial conducted in our laboratories have shown that dried plum has positive effects on bone indices. The animal data indicate that dried plum not only protects against but more importantly reverses bone loss in two separate models of osteopenia. Our initial animal study indicated that dried plum prevented the ovariectomy-induced reduction in bone mineral density (BMD) of the femur and lumbar vertebra. In another study, to mimic established osteoporosis, rats were ovariectomized and allowed to lose bone before the initiation of treatment. Dried plum as low as 5% (w/w) restored BMD to the level of intact rats. More importantly, dried plum reversed the loss of trabecular architectural properties such as trabecular number and connectivity density, and trabecular separation. We have also shown the effectiveness of dried plum in reversal of bone loss due to skeletal unloading. Analysis of BMD and trabecular bone structure by microcomputed tomography (microCT) revealed that dried plum enhanced bone recovery during reambulation following skeletal unloading and had comparable effects to parathyroid hormone. In addition to the animal studies, our 3-month clinical trial indicated that the consumption of dried plum daily by postmenopausal women significantly increased serum markers of bone formation, total alkaline phosphatase, bone-specific alkaline phosphatase and insulin-like growth factor-I by 12, 6, and 17%, respectively. This review summarizes the findings of studies published to date which examine the beneficial effects of dried plum on bone in both female and male animal models of osteoporosis as well as the only published clinical study.

Insights in the application of research-grade diagnostic kits for biomarker assessments in support of clinical drug development: bioanalysis of circulating concentrations of soluble receptor activator of nuclear factor kappaB ligand

Application of research-grade diagnostic kits in clinical drug development has grown commensurate with the increased interest in utilization of biomarkers as drug development tools. Since novel biomarkers are frequently macromolecular, immunoassay methodology comprises the 'technology-of-choice' for biomarker quantification. In particular, commercial research-grade immunoassay kits are appealing for use in biomarker quantification during clinical phase drug development because of their ready availability, ease of operation and perceived convenience. However, bioanalytical validation issues arise often during the application of commercial kits, as GLP regulatory-compliant application places greater demands on kit design and performance. In this review, we have used the receptor activator of nuclear factor kappaB ligand (RANKL) as a model system to offer some insights into the challenges that can be encountered in the application of 'research-grade' diagnostic kits in support of clinical drug development. Currently only a few assays are available commercially for the determination of circulating concentrations of sRANKL. Of these, two immunoassay designs have been most often. The first design employs human osteoprotegerin to capture unbound sRANKL from serum and, thereby, provides a measure of circulating free concentrations. In contrast, the other common assay design first involves preincubation of serum samples with human osteoprotegerin to convert the free fraction of sRANKL to the osteoprotegerin-bound complex. The bound fraction is subsequently captured by an anti-osteoprotegerin antibody. In both immunoassay designs, detection is accomplished with an anti-sRANKL enzyme conjugation system. In this report we review these sRANKL immunoassay designs critically from the perspective of their potential suitability as drug development biomarker tools. In addition, analytical challenges relevant to the application of these 'research-grade' diagnostic kits for regulatory-compliant determination of sRANKL concentrations are discussed.

Vitamin K, circulating cytokines, and bone mineral density in older men and women

BACKGROUND

Vitamin K modulates cytokines involved in bone turnover, including interleukin-6 (IL-6) and osteoprotegerin in vitro.

OBJECTIVE

The objective of this study was to assess 1) associations between measures of vitamin K status [plasma phylloquinone and serum percentage of undercarboxylated osteocalcin (%ucOC)] and IL-6, osteoprotegerin, and C-reactive protein (CRP) concentrations and 2) the effect of daily 500 mug phylloquinone supplementation for 3 y on cytokine concentrations.

DESIGN

Concentrations of IL-6, osteoprotegerin, and CRP and bone mineral density (BMD) were measured at baseline and after 3 y of follow-up in 379 healthy men and women (60-81 y; 58.5% women) participating in a randomized trial that studied the effect of vitamin K supplementation on bone loss.

RESULTS

Cross-sectionally, plasma phylloquinone was inversely associated with IL-6 and CRP, whereas serum %ucOC was inversely associated with IL-6. Osteoprotegerin was associated positively with plasma phylloquinone and inversely with %ucOC. No differences were observed in the 3-y change in IL-6, osteoprotegerin, and CRP concentrations between participants who received phylloquinone supplementation and those who did not. Overall, no association was observed between the 3-y changes in circulating cytokines and BMD.

CONCLUSIONS

Poor vitamin K status was associated with high concentrations of cytokines involved in bone turnover, but vitamin K supplementation did not confer a decrease in cytokine concentrations. The healthy status of this cohort may explain a lack of effect of vitamin K supplementation on cytokine concentrations. This trial was registered with www.clinicaltrials.gov as NCT00183001.

Skeletal deterioration induced by RANKL infusion: a model for high-turnover bone disease

RANKL was administered continuously to rats for 28 days to investigate its potential as a disease model for the skeletal system. Bone turnover rates, bone material, structural and mechanical properties were evaluated. RANKL infusion caused overall skeletal complications comparable to those in high bone-turnover conditions, such as postmenopausal osteoporosis.

INTRODUCTION

RANKL is an essential mediator for osteoclast development. No study has examined in detail the direct skeletal consequences of excess RANKL on bone turnover, mineralization, architecture, and vascular calcification. We, therefore, administrated soluble RANKL continuously into mature rats and created a bone-loss model.

METHODS

Six-month-old Sprague-Dawley (SD) rats were assigned to three groups (n = 12) receiving continuous administration of saline (VEH) or human RANKL (35 microg/kg/day, LOW or 175 microg/kg/day, HI) for 28 days. Blood was collected routinely during the study. At sacrifice, hind limbs and aorta were removed and samples were analyzed.

RESULTS

High dose RANKL markedly stimulated serum osteocalcin and TRAP-5b levels and reduced femur cortical bone volume (-7.6%) and trabecular volume fraction (BV/TV) at the proximal tibia (-64% vs. VEH). Bone quality was significantly degraded in HI, as evidenced by decreased femoral percent mineralization, trabecular connectivity, and increased endocortical bone resorption perimeters. Both cortical and trabecular bone mechanical properties were reduced by high dose RANKL. No differences were observed in the mineral content of the abdominal aorta.

CONCLUSIONS

Continuous RANKL infusion caused general detrimental effects on rat skeleton. These changes are comparable to those commonly observed in high-turnover bone diseases such as postmenopausal osteoporosis.

Circulating profiles of osteoprotegerin and soluble receptor activator of nuclear factor kappaB ligand in post-menopausal women

OBJECTIVE

The aim of this study was to elucidate the detail profiles of circulating osteoprotegerin (OPG) and soluble receptor activator of nuclear factor kappaB ligand (sRANKL) in post-menopausal women.

METHODS

Eighty Japanese post-menopausal women were enrolled in this cross-sectional study. Circulating OPG and free fraction of sRANKL (free sRANKL), PTH, calcium and phosphorus, age, years since menopause, body mass index, bone mineral density of the vertebral bodies (LBMD) and bone turnover markers were determined in each subject.

RESULTS

In rank order correlation analysis, serum OPG concentrations had a significant positive correlation with age (r=0.291, p=0.024) and a marginal significant negative correlation with LBMD (r=-0.247, p=0.062). However they did not have correlations with LBMD or other parameters after adjustment for age. Serum free sRANKL concentrations had a significant positive correlation with age (r=0.332, p=0.010) and a significant negative correlation with LBMD (r=-0.608, p<0.001). This correlation with LBMD persisted after adjustment for age. In a multiple regression analysis with a stepwise model, the main determinants of LBMD were age and serum free sRANKL (p=0.015 and p=0.006, respectively).

CONCLUSIONS

We found the increase in circulating OPG and sRANKL with age and a robust negative correlation between circulating free sRANKL and LBMD after adjustment for age. The increase in circulating free sRANKL may reflect directly or indirectly the conditions coexistent with bone loss in post-menopausal women.

The sex-specific association of serum osteoprotegerin and receptor activator of nuclear factor kappaB legend with bone mineral density in older adults: the Rancho Bernardo study

OBJECTIVE

The role of osteoprotegerin (OPG) and its receptor activator of nuclear factor kappaB legend (RANKL) in the regulation of bone in humans remain unclear. We examined the sex-specific associations of serum OPG, RANKL, and their ratio with bone mineral density (BMD) in older adults.

DESIGN

Participants were 681 community-dwelling adults, ages 45-90 years, who had serum OPG and RANKL measured and bone density scans in 1988-1991, with follow-up scans 5 and/or 10 years later.

METHODS

Analyses were sex-specific; women using and not using estrogen were evaluated separately. Cross-sectional analyses used multivariable regression models; longitudinal analyses used repeated measures mixed effects models.

RESULTS

In cross-sectional analyses, age- and weight-adjusted serum OPG levels were significantly positively associated with BMD at the lumbar spine in men, and at the femoral neck, total hip, and lumbar spine in women using estrogen, but not in non-users of estrogen. RANKL concentrations were significantly and inversely associated with BMD in men only, and at the total hip. Neither OPG nor RANKL was significantly associated with bone loss. Results for the RANKL/OPG ratio were the same as those for RANKL alone.

CONCLUSIONS

These results suggest a modulatory effect of both endogenous and exogenous sex hormones on the biologic interaction of OPG, RANKL, and bone.

Osteoprotegerin and RANKL serum levels and their relationship with serum ghrelin in children with chronic renal failure and on dialysis

BACKGROUND

Osteoprotegerin (OPG) and receptor activator of the nuclear factor kappaB ligand (RANKL) constitute a complex system of mediators involved in the regulation of bone resorption process. Ghrelin, a growth hormone secretagogue, has been shown to modulate proliferation and differentiation of osteoblasts. The present study was carried out to evaluate the serum concentrations of OPG and sRANKL in children with chronic renal impairment (CRI) and on dialysis, and to establish a possible relationship between their serum levels and that of ghrelin.

METHODS

33 patients including 10 patients with CRI, 12 peritoneal dialysis (PD) and 11 hemodialysis (HD) patients and 22 healthy controls were enrolled into the study. OPG, sRANKL and ghrelin levels were studied with radioimmunoassay.

RESULTS

Serum OPG levels in CRI, PD and HD groups were significantly higher than the healthy controls (p = 0.002, p < 0.001, p < 0.001, respectively) whereas sRANKL levels were significantly lower than the healthy controls (p = 0.03, p = 0.01, p = 0.001, respectively). Ghrelin levels were significantly higher in CRI, PD and HD groups compared to healthy controls (p = 0.001, p < 0.001, p < 0.001, respectively). We observed a negative correlation between the sRANKL and OPG levels (r = -0.27, p = 0.04) as well as between sRANKL and ghrelin levels (r = -0.31, p = 0.02). OPG levels showed a positive correlation with ghrelin levels (r = 0.63, p < 0.001).

CONCLUSION

We found a lower RANKL bioactivity index in children with CRI and on dialysis. The mechanism and the role of elevated OPG and low sRANKL in uremia are unclear, but they might partly represent a compensatory mechanism to the negative balance of bone remodeling in renal bone disease in children. Additionally, we demonstrated for the first time that ghrelin and the RANKL/OPG system have a close relationship in CRF. Therefore, ghrelin may be of importance in mediating the effects of the RANKL/OPG system in renal bone disease.

No associations between OPG gene polymorphisms or serum levels and measures of osteoporosis in elderly Australian women

Bone mass is the single most important risk factor for osteoporotic fractures in the elderly and is mainly influenced by genetic factors accounting for 40-75% of the inter-individual variation. Critical for the bone remodeling process is the balance between the newly discovered members of the tumor necrosis factor ligand and receptor superfamilies, osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB ligand, which mediate the effects of many upstream regulators of bone metabolism. In the present study, we evaluated the impact of sequence variations in the OPG gene on bone mass, bone-related biochemistry including serum OPG and fracture frequency in elderly Australian women. A total of 1101 women were genotyped for 3 different single nucleotide polymorphisms (SNP) within the OPG gene (G1181C, T950C and A163G). The effects of these SNPs and serum OPG on calcaneal quantitative ultrasound measurements, osteodensitometry of the hip and bone-related biochemistry were examined. We found no significant relationship between sequence variations in the OPG gene or serum OPG and bone mass, bone-related biochemistry or fracture frequency. Our findings confirm some recent publications investigating the same SNPs but diverge from others, indicating that generalization of the relationships found in this type of study must be done with caution and signify the importance of determining associations between polymorphisms and osteoporosis in different ethnic groups.

OPG, RANK-L, bone metabolism, and BMD in patients on peritoneal dialysis and hemodialysis

OBJECTIVES

Bone turnover is regulated locally by osteoprotegerin (OPG) and receptor activator of NFkappaB ligand (RANK-L); it is not known how the circulating concentrations of these cytokines reflect renal osteodystrophy.

METHODS

We measured serum OPG, RANK-L, parathyroid hormone (iPTH), collagen C-terminal cross-linked telopeptide (betaCrossLaps), and bone densitometry (BMD) in 79 patients with end-stage renal disease (ESRF) undergoing dialysis. A hand X-ray of these patients was also analyzed. Controls were 65 healthy subjects.

RESULTS

ESRF patients had high OPG and RANK-L levels; RANK-L was higher in hemodialysis than in peritoneal dialysis. OPG and RANK-L did not depend on iPTH. The bone markers were significantly increased and correlated with serum iPTH, but not with OPG or RANK-L; neither OPG nor RANK-L correlated significantly with BMD. OPG was significantly higher in patients with acro-osteolysis.

CONCLUSIONS

OPG and RANK-L serum concentrations do not strongly reflect bone status in ESRF. However, OPG was significantly higher in patients with acro-osteolysis.

Age of donor alters the effect of cyclic hydrostatic pressure on production by human macrophages and osteoblasts of sRANKL, OPG and RANK

Background

Cyclic hydrostatic pressure within bone has been proposed both as a stimulus of aseptic implant loosening and associated bone resorption and of bone formation. We showed previously that cyclical hydrostatic pressure influenced macrophage synthesis of several factors linked to osteoclastogenesis. The osteoprotegerin/soluble receptor activator of NF-kappa β ligand /receptor activator of NF-kappa β (OPG/ RANKL/ RANK) triumvirate has been implicated in control of bone resorption under various circumstances. We studied whether cyclical pressure might affect bone turnover via effects on OPG/ sRANKL/ RANK.

Methods

In this study, cultures of human osteoblasts or macrophages (supplemented with osteoclastogenic factors) or co-cultures of macrophages and osteoblasts (from the same donor), were subjected to cyclic hydrostatic pressure. Secretion of OPG and sRANKL was assayed in the culture media and the cells were stained for RANK and osteoclast markers. Data were analysed by nonparametric statistics.

Results

In co-cultures of macrophages and osteoblasts, pressure modulated secretion of sRANKL or OPG in a variable manner. Examination of the OPG:sRANKL ratio in co cultures without pressurisation showed that the ratio was greater in donors <70 years at the time of operation (p < 0.05 Mann Whitney U) than it was in patients >70 years. However, with pressure the difference in the OPG:sRANKL ratios between young and old donors was not significant. It was striking that in some patients the OPG:sRANKL ratio increased with pressure whereas in some it decreased. The tendency was for the ratio to decrease with pressure in patients younger than 70 years, and increase in patients ≥ 70 years (Fishers exact p < 0.01).

Cultures of osteoblasts alone showed a significant increase in both sRANKL and OPG with pressure, and again there was a decrease in the ratio of OPG:RANKL. Secretion of sRANKL by cultures of macrophages alone was not modulated by pressure. Only sRANKL was assayed in this study, but transmembrane RANKL may also be important in this system. Macrophages subjected to pressure (both alone and in co-culture) stained more strongly for RANK on immunohistochemstry than non-pressurized controls and 1,25-dihydroxyvitamin D₃ (1,25 D₃) further increased this. Immunocytochemical staining also demonstrated that more cells in pressurized co-cultures exhibited osteoclast markers (tartrate-resistant acid phosphatase, vitronectin receptor and multinuclearity) than did unpressurized controls.

Conclusion

These data show that in co-cultures of osteoblasts and macrophages the ratio of OPG : sRANKL was decreased by pressure in younger patients but increased in older patients. As falls in this ratio promote bone resorption, this finding may be important in explaining the relatively high incidence of osteolysis around orthopaedic implants in young patients. The finding that secretion of OPG and sRANKL by osteoblasts in monoculture was sensitive to hydrostatic pressure, and that hydrostatic pressure stimulated the differentiation of macrophages into cells exhibiting osteoclast markers indicates that both osteoblasts and preosteoclasts are sensitive to cyclic pressure. However, the effects of pressure on cocultures were not simply additive and coculture appears useful to examine the interaction of these cell types.

These findings have implications for future therapies for aseptic loosening and for the development of tests to predict the development of this condition.