Circulating sclerostin in disorders of parathyroid gland function

PTH and the Regulation of Mesenchymal Cells within the Bone Marrow Niche

Parathyroid hormone (PTH) plays a pivotal role in maintaining calcium homeostasis, largely by modulating bone remodeling processes. Its effects on bone are notably dependent on the duration and frequency of exposure. Specifically, PTH can initiate both bone formation and resorption, with the outcome being influenced by the manner of PTH administration: continuous or intermittent. In continuous administration, PTH tends to promote bone resorption, possibly by regulating certain genes within bone cells. Conversely, intermittent exposure generally favors bone formation, possibly through transient gene activation. PTH's role extends to various aspects of bone cell activity. It directly influences skeletal stem cells, osteoblastic lineage cells, osteocytes, and T cells, playing a critical role in bone generation. Simultaneously, it indirectly affects osteoclast precursor cells and osteoclasts, and has a direct impact on T cells, contributing to its role in bone resorption. Despite these insights, the intricate mechanisms through which PTH acts within the bone marrow niche are not entirely understood. This article reviews the dual roles of PTH-catabolic and anabolic-on bone cells, highlighting the cellular and molecular pathways involved in these processes. The complex interplay of these factors in bone remodeling underscores the need for further investigation to fully comprehend PTH's multifaceted influence on bone health.

Reduced trabecular bone mineral density and thinner cortices in men with distal forearm fractures

Men with distal forearm fractures have reduced bone density, an increased risk of osteoporosis and of further fractures. The aim of the study was to investigate the structural determinants of these observations using quantitative CT (qCT). Ninety six men with low-trauma distal forearm fracture and 101 age-matched healthy control subjects were recruited. All subjects underwent a quantitative CT on a standard 64-slice whole body CT scanner. These were analysed on Mindways QCT PRO™ Software to generate volumetric and geometric data at the lumbar spine, femoral neck and total hip, ultra-distal and distal 33 % radius. Biochemical investigations, health questionnaires and measurements of bone turnover were made. Men with fracture had significantly lower total and trabecular vBMD at all sites. The greatest percentage reduction was at the ultra-distal radius (13.5 % total and 11.7 % trabecular vBMD). In the fracture group cortical vBMD was significantly higher in the femoral neck (p < 0.001) and maintained at the ultra-distal radius compared with control subjects. However, cortical cross-sectional area (CSA) and thickness were significantly reduced at the femoral neck (p < 0.001 and p = 0.002 respectively) and forearm sites (CSA ultradistal radius p = 0.001, cortical thickness p = 0.002, CSA distal one third radius p = 0.045 and cortical thickness p = 0.005). Cross sectional moment of inertia (CSMI) and section moduli were significantly reduced at the femoral neck (CSMI1 p = 0.002, CSMI2 p = 0.012 and section moduli Z1 p < 0.001, Z2 p = 0.004) and the ultra-distal radius (CSMI1 p = 0.008 and section moduli Z1 p = 0.018, Z2 p = 0.007). In stepwise logistic regression analysis distal forearm fracture showed the strongest association with a model comprising ultra-distal forearm trabecular vBMD (negative), procollagen type I N-terminal propeptide (PINP, positive) and sex hormone binding globulin (SHBG, negative). In conclusion, these observations explain the structural reasons for the increased fracture risk in men with distal forearm fractures.

Low Levels of Serum Sclerostin in Adult Patients With Tumor-Induced Osteomalacia Compared With X-linked Hypophosphatemia

CONTEXT

Sclerostin inhibits Wnt-β-catenin signaling, regulating bone formation. Circulating sclerostin was reported to be elevated in X-linked hypophosphatemia (XLH) patients, and sclerostin antibody (Scl-Ab) increased bone mass and normalized circulating phosphate in Hyp mice. However, circulating sclerostin levels in patients with acquired hypophosphatemia due to tumor-induced osteomalacia (TIO) are rarely reported.

OBJECTIVE

This study was designed to evaluate serum sclerostin levels in TIO patients compared with age- and sex-matched healthy controls and XLH patients to analyze correlations with bone mineral density (BMD) and laboratory parameters.

METHODS

This cross-sectional study determined serum sclerostin levels in 190 individuals, comprising 83 adult TIO patients, 83 adult healthy controls and 24 adult XLH patients.

RESULTS

TIO patients (43 male, 40 female) aged 44.3 ± 8.7 (mean ± SD) years had lower levels of circulating sclerostin than controls (94.2 ± 45.8 vs 108.4 ± 42.3 pg/mL, P = 0.01), adjusted for age, gender, BMI, and diabetes rate. Sclerostin levels were positively associated with age (r = 0.238, P = 0.030). Male patients had higher sclerostin than female patients (104.7 ± 47.3 vs 83.0 ± 41.8 pg/mL, P = 0.014). Sclerostin levels were positively associated with L1-4 BMD (r = 0.255, P = 0.028), femoral neck BMD (r = 0.242, P = 0.039), and serum calcium (r = 0.231, P = 0.043). Comparison of sclerostin levels in TIO patients (n = 24, age 35.9 ± 7.3 years) vs XLH patients vs healthy controls revealed significant differences (respectively, 68.4 ± 31.3, 132.0 ± 68.8, and 98.6 ± 41.1 pg/mL, P < 0.001).

CONCLUSION

Circulating sclerostin was decreased in TIO patients but increased in XLH patients, possibly due to histological abnormality and bone mass.

Skeletal abnormalities in Hypoparathyroidism and in Primary Hyperparathyroidism

Both hypoparathyroidism (HypoPT), as well as its pathological counterpart, primary hyperparathyroidism (PHPT), can lead to skeletal abnormalities. Chronic deficiency of PTH in patients with HypoPT is associated with a profound reduction in bone remodeling, with consequent increases in bone density, and abnormalities in microarchitecture and bone strength. It is still not clear whether there is an increase in fracture risk in HypoPT. While standard therapy with calcium supplements and active vitamin D does not restore bone homeostasis, treatment of HypoPT with PTH appears to correct some of those abnormalities. In PHPT, the continuous exposure to high levels of PTH causes an increase in bone remodeling, in which bone resorption prevails. In the symptomatic form of PHPT, patients can present with fragility fractures, and/or the classical radiological features of osteitis fibrosa cystica. However, even in mild PHPT, catabolic skeletal actions of PTH are evident through reduced BMD, deterioration of bone microarchitecture and increased risk of fragility fractures. Successful parathyroidectomy improves skeletal abnormalities. Medical treatment, such as bisphosphonates and denosumab, can also increase bone density in patients with PHPT who do not undergo surgery. This article reviews skeletal involvement in HypoPT and in PHPT, as assessed by bone remodeling, DXA, trabecular bone score, and quantitative computed tomography, as well as data on bone strength and fracture risk. The effects of PTH replacement on the skeleton in subjects with HypoPT, and the outcome of parathyroidectomy in patients with PHPT, are also reviewed here.

Assessment of Clinical Utility of Assaying FGF-23, Klotho Protein, Osteocalcin, NTX, and Sclerostin in Patients with Primary Hyperparathyroidism

The purpose of this study was to assess the clinical usefulness of assaying the fibroblast growth factor (FGF-23), Klotho, osteocalcin, N-terminal telopeptide of type I collagen (NTX), and sclerostin levels in patients with primary hyperparathyroidism (PHPT) as markers of bone damage as well as for surgical treatment success. Seventeen patients with hypercalcemic PHPT and normal kidney function were studied. In all patients, PTH (parathormone), serum calcium, and creatinine were performed before and six months after parathyroidectomy (PTX). The studied group included patients whose PTH and calcium concentrations normalized post-operatively and with confirmed histopathological diagnosis. The control group consisted of nine age-matched healthy volunteers. The PHPT patients had elevated concentrations of FGF-23, osteocalcin, and NTX and reduced levels of sclerostin, as compared to the control group. After PTX, osteocalcin, NTX, and sclerostin levels normalized. The plasma values of FGF-23 decreased significantly, but remained higher than in healthy subjects. Serum Klotho protein levels did not differ significantly in the two groups. These results suggest that osteocalcin and NTX may potentially be considered as markers of PHPT progression. Additionally, serum normalization of osteocalcin, NTX, and sclerostin might be considered as indicators of PTX success. On the other hand, FGF-23 can represent a parameter reflecting the degree of calcium–phosphate imbalance in PHPT patients, but its usefulness in monitoring the effects of PTX requires further research. The clinical utility of assaying Klotho in PHPT remains to be confirmed.

Identification of Patients at High Risk for Postsurgical Hypoparathyroidism

BACKGROUND/AIM

Postsurgical hypoparathyroidism (PostHypo) is a common complication after total thyroidectomy. We studied the risk factors associated with PostHypo.

PATIENTS AND METHODS

The study included 109 women, (mean age: 50.7±10.75 years), who underwent total thyroidectomy for thyroid diseases.

RESULTS

Based on the development of biochemical hypocalcemia on the first postoperative day following total thyroidectomy, (cCa<8.4 mg/dl), 37 women developed PostHypo and 72 did not. Younger age, a lower preoperative corrected calcium and the presence of parathyroid glands in the specimens were related to the development of PostHypo. Of all patients, 51.4% had a vitamin D deficiency. A parathyroid hormone (PTH) value ≤9.4 pg/ml was 84.9% sensitive and 71.4% specific to predict PostHypo on the 1^st postoperative day. A 50% reduction of the PTH value on the 1^st postoperative day from the preoperative level could identify patients who develop PostHypo with 76% sensitivity and 75% specificity.

CONCLUSION

PTH postoperative measurement and its alteration from the preoperative level can be used to identify patients who are at increased risk to develop PostHypo.

The association of circulating sclerostin level with markers of bone metabolism in patients with thyroid dysfunction

Background

The aim of this study was to compare serum sclerostin concentrations in patients with thyroid dysfunction with euthyroid control subjects and to assess the relationship between sclerostin and markers of bone metabolism (osteocalcin and beta-cross-laps).

Methods

The study included 30 patients with thyroid dysfunction (hypothyroidism, hyperthyroidism and subclinical hyperthyroidism) and ten euthyroid controls. Free thyroxine (FT4) was measured by radioimmunoassay, while thyroid stimulating hormone (TSH) concentration was determined immunoradiometrically. We used an ELISA kit to determine the sclerostin level. The electrochemiluminescence method was applied for measuring the bone markers.

Results

Sclerostin levels were significantly lower in hypothyroid patients (p=0.009) and significantly elevated in hyperthyroid patients (p=0.008) compared to control values. Hyperthyroid patients also had higher sclerostin than patients with subclinical hyperthyroidism (p=0.013). Sclerostin concentrations were negatively correlated with TSH levels (r=-0.746, p<0.001), but positively with FT4 (r=0.696, p < 0.001). Moreover, sclerostin was positively associated with osteocalcin (r=0.605, p=0.005) and beta-cross-laps levels (r=0.573, p=0.008) in all thyroid patients.

Conclusions

Serum sclerostin is significantly affected in subjects with thyroid dysfunction. Both sclerostin and thyroid status affect bone homeostasis, which is reflected through the significant correlations with osteocalcin and beta-cross-laps.

A paternally inherited non-sense variant c.424G>T (p.G142*) in the first exon of XLαs in an adult patient with hypophosphatemia and osteopetrosis

XLαs, the extra-large isoform of alpha-subunit of the stimulatory guanine nucleotide-binding protein (Gsα), is paternally expressed. The significance of XLαs in humans remains largely unknown. Here, we report a patient who presented with increased bone mass, hypophosphatemia, and elevated parathyroid hormone (PTH) levels. His serum calcium was in the lower limit of the normal range. Whole exome sequencing of this subject found a novel non-sense variant c.424G>T (p. G142*) in the first exon of XLαs, which was inherited from his father and transmitted to his daughter. This variant was predicted to exclusively influence the expression of XLαs, while possibly having no significant effects on other gene products of this locus. Ellsworth-Howard test revealed normal renal response to PTH in proband. Human SaOS2 cells transfected with mutant XLαs failed to generate cyclic adenosine monophosphate under PTH stimulation, indicating skeletal resistance to this hormone. This subject showed higher circulating sclerostin, dickkopf1, and osteoprotegerin (OPG) levels, while lower receptor activator of nuclear factor kappa-B ligand/OPG ratio, leading to reduced bone resorption. Our findings indicate that XLαs plays a critical role in bone metabolism and GNAS locus should be considered as a candidate gene for high bone mass.

Evaluation of the association of Wnt signaling with coronary artery calcification in patients on dialysis with severe secondary hyperparathyroidism

BACKGROUND

Patients with end-stage renal disease have a higher risk of death from cardiovascular events, which can be mainly attributed to coronary artery calcification (CAC). Wnt signaling is involved in vascular development and may play a role in vascular calcification. This study aimed to evaluate CAC prevalence in patients on dialysis with severe secondary hyperparathyroidism (SHPT) and identify CAC risk factors.

METHODS

The study is a retrospective analysis of the severe hyperparathyroidism registration study that prospectively recruited patients on dialysis with severe SHPT who were candidates for parathyroidectomy, from October 2013 to May 2015. CAC and bone mineral density (BMD) were measured. Demographic and clinical data including calcium, phosphorus, alkaline phosphatase, intact parathyroid hormone, Dickkopf-related protein 1 (DKK1), and sclerostin levels were analyzed. CAC scores were reported in Agatston units (AU).

RESULTS

A total of 61 patients were included in this study. No CAC, mild CAC (<100 AU), moderate CAC (>100 AU), and severe CAC (>400 AU) were observed in 4.9%, 11.4%, 14.8%, and 68.9% of patients, respectively. DKK1 and sclerostin were not associated with CAC. In univariate analysis, CAC was significantly correlated with age, sex (male), total cholesterol, and intravenous pulse calcitriol (p<0.05). CAC was not inversely correlated with the BMD, T scores, or Z scores of the femoral neck (p>0.05). In multivariate analysis, the stepwise forward multiple linear regression revealed that CAC was associated with age, male sex and intravenous pulse calcitriol (p<0.05). Furthermore, serum sclerostin was positively correlated with the BMD of the femoral neck but negatively associated with intact parathyroid hormone (p<0.05). Serum sclerostin was significantly associated with severely low bone mass with Z-scores<-2.5 of the femoral neck, even when adjusted for serum intact parathyroid hormone, vitamin D status, dialysis pattern, sex, and DKK-1 (p<0.05).

CONCLUSIONS

The patients on dialysis with severe SHPT have a high prevalence of vascular calcification. Although the Wnt signaling pathway could play a role in hyperparathyroid bone disease, CAC may be mainly due to the treatment modality rather than the Wnt signaling pathway associated bone metabolism in patients on dialysis with severe SHPT.

Skeletal Manifestations of Hypoparathyroidism

Chronic PTH deficiency has a marked effect on the skeleton, leading to characteristic decreases in bone remodeling and increases in bone mass. An effect on fracture risk has not been demonstrated, although biochemical, imaging, and histomorphometric data indicate abnormalities in skeletal properties^1,21,21,21,2. Replacement with PTH leads to a new skeletal state that is maintained with long-term treatment.

Skeletal Manifestations of Hypoparathyroidism

Chronic parathyroid hormone (PTH) deficiency has a marked effect on the skeleton, leading to characteristic decreases in bone remodeling and increases in bone mass. Numerous lines of evidence using biochemical, imaging, and histomorphometric methodologies have demonstrated that the skeleton is altered when PTH is absent and that these abnormalities might be reversed with PTH treatment. More evidence is needed to determine whether fracture risk is altered in hypoparathyroidism.

The Effects of Long-term Administration of rhPTH(1-84) in Hypoparathyroidism by Bone Histomorphometry

Hypoparathyroidism is a rare disorder that is associated with abnormal bone properties. Recombinant human parathyroid hormone (1-84) [rhPTH(1-84)] in short-term studies has beneficial skeletal effects. Although rhPTH(1-84) will likely be used indefinitely, long-term effects on skeletal microstructure are unknown. We therefore studied histomorphometric changes with transiliac crest bone biopsies before and after 8.3 ± 1 years of rhPTH(1-84) in 13 hypoparathyroid subjects compared with 45 controls. Before institution of rhPTH(1-84), skeletal remodeling indices were markedly suppressed. With long-term treatment, indices of bone remodeling increased. Mineralizing surface increased by 26-fold (0.3 ± 1 to 7.9 ± 7%, p = 0.003), bone formation rate increased by 15-fold (0.003 ± 0.01 to 0.047 ± 0.05 μm² /μm/day, p = 0.007), osteoid width doubled (1.9 ± 1 to 4.3 ± 1 lamellae, p = 0.017), and osteoid surface tripled (3.3 ± 3 to 10.8 ± 6%, p = 0.011). Bone resorption as measured by eroded surface increased (4.6 ± 2 to 7.5 ± 3%, p = 0.021). Structural changes demonstrated intratrabecular tunneling, with increases in cancellous bone volume (19.6 ± 5 to 29.1 ± 11%, p = 0.017) and trabecular number (1.8 ± 1 to 2.5 ± 1 #/mm, p = 0.025). Cortical porosity tended to increase (6.3 ± 5 to 9.5 ± 3%, p = 0.07). Mineralizing surface, osteoid surface, and eroded surface surpassed control levels, as did cancellous bone volume, trabecular number, and cortical porosity. These data, the first to reflect such long exposure of any PTH for any disease, illustrate that PTH establishes and maintains a new skeletal state for at least 8 years in hypoparathyroidism. © 2018 American Society for Bone and Mineral Research.

SOST, an LNGFR target, inhibits the osteogenic differentiation of rat ectomesenchymal stem cells

OBJECTIVES

The aim of this study was to investigate whether sclerostin (SOST) regulates the osteogenic differentiation of rat ectomesenchymal stem cells (EMSCs) and whether SOST and low-affinity nerve growth factor receptor (LNGFR) regulate the osteogenic differentiation of EMSCs.

MATERIALS AND METHODS

EMSCs were isolated from embryonic facial processes from an embryonic 12.5-day (E12.5d) pregnant Sprague-Dawley rat. LNGFR⁺ EMSCs and LNGFR^- EMSCs were obtained by fluorescence-activated cell sorting and were subsequently induced to undergo osteogenic differentiation in vitro. SOST/LNGFR small-interfering RNAs and SOST/LNGFR overexpression plasmids were used to transfect EMSCs.

RESULTS

LNGFR⁺ EMSCs displayed a higher osteogenic capacity and lower SOST levels compared with LNGFR^- EMSCs. SOST silencing enhanced the osteogenic differentiation of LNGFR^- EMSCs, while SOST overexpression attenuated the osteogenic differentiation of LNGFR⁺ EMSCs. Moreover, LNGFR was present upstream of SOST and strengthened the osteogenic differentiation of EMSCs by decreasing SOST.

CONCLUSIONS

SOST alleviated the osteogenic differentiation of EMSCs, and LNGFR enhanced the osteogenic differentiation of EMSCs by decreasing SOST, suggesting that the LNGFR/SOST pathway may be a novel target for promoting dental tissue regeneration and engineering.

Effects of parathyroidectomy on bone metabolism in haemodialysis patients with secondary hyperparathyroidism

OBJECTIVE

To evaluate the outcome of bone metabolism and bone mineral density (BMD) in haemodialysis patients after parathyroidectomy (PTX).

METHODS

A total of 31 haemodialysis patients with secondary hyperparathyroidism (SHPT) were treated with PTX. BMD of lumbar spine (LS) and femoral neck (FN) was determined by dual energy X-ray absorptiometry.

RESULTS

Parathyroidectomy ledds to significant decrease of serum β-crosslaps (β-CTX), osteocalcin (OC) and procollagen type I amino-terminal propeptide (PINP) while serum sclerostin (SOST) increased after surgery. BMD was markedly improved in both LS and FN after PTX. Z-scores analysis further confirmed that PTX significantly benefited bone metabolism in haemodialysis patients, which well correlated with the improvement of serum iPTH and OC.

CONCLUSIONS

Parathyroidectomy leads to significant improvement of serum OC, PINP, β-CTX and SOST, which may beneficially modify calcium-phosphorus metabolism and BMD in haemodialysis patients with SHPT.

Circulating levels of sclerostin but not DKK1 associate with laboratory parameters of CKD-MBD

INTRODUCTION

Mounting evidence indicates that a disturbed Wnt-β-catenin signaling may be involved in the pathogenesis of chronic kidney disease-mineral and bone and mineral disorder (CKD-MBD). Data on the impact of CKD on circulating levels of the Wnt antagonists sclerostin and Dickkopf related protein 1 (DKK1) and the relationship with laboratory parameters of CKD-MBD are incomplete.

METHODS

We analyzed serum sclerostin and DKK1 in 308 patients across the stages of chronic kidney disease (kDOQI stage 1-2 n = 41; CKD stage 3 n = 54; CKD stage 4-5 n = 54; hemodialysis n = 100; peritoneal dialysis n = 59) as well as in 49 healthy controls. We investigated associations with demographics, renal function, parameters of mineral metabolism including 25(OH) vitamin D, 1,25(OH)2 vitamin D, biointact fibroblast growth factor 23 (FGF23), and parathyroid hormone (PTH), and bone turnover markers.

RESULTS

Serum sclerostin, but not DKK1, increases in more advanced stages of CKD and associates with PTH, phosphate, and 1,25(OH)2 vitamin D concentrations. Bone turnover markers are highest in hemodialysis patients presenting the combination of high PTH with low sclerostin level. Serum DKK1 levels are lower in CKD patients than in controls and are not associated with laboratory parameters of mineral metabolism. Interestingly, a direct association between DKK1 and platelet count was observed.

CONCLUSION

In CKD, serum levels of the Wnt inhibitors DKK1 and sclerostin are unrelated, indicating different sites of origin and/ or different regulatory mechanisms. Sclerostin, as opposed to DKK1, may qualify as a biomarker of CKD-MBD, particularly in dialysis patients. DKK1 serum levels, remarkably, correlate almost uniquely with blood platelet counts.

Hormonal and systemic regulation of sclerostin

The Wnt/β-catenin signaling pathway plays an essential role in osteoblast biology. Sclerostin is a soluble antagonist of Wnt/β-catenin signaling secreted primarily by osteocytes. Current evidence indicates that sclerostin likely functions as a local/paracrine regulator of bone metabolism rather than as an endocrine hormone. Nonetheless, circulating sclerostin levels in humans often reflect changes in the bone microenvironment, although there may be exceptions to this observation. Using existing assays, circulating sclerostin levels have been shown to be altered in response to both hormonal stimuli and across a variety of normal physiological and pathophysiological conditions. In both rodents and humans, parathyroid hormone provided either intermittently or continuously suppresses sclerostin levels. Likewise, most evidence from both human and animal studies supports a suppressive effect of estrogen on sclerostin levels. Efforts to examine non-hormonal/systemic regulation of sclerostin have in general shown less consistent findings or have provided associations rather than direct interventional information, with the exception of mechanosensory studies which have consistently demonstrated increased sclerostin levels with skeletal unloading, and conversely decreases in sclerostin with enhanced skeletal loading. Herein, we will review the existent literature on both hormonal and non-hormonal/systemic factors which have been studied for their impact on sclerostin regulation.

Sclerostin measurement in human disease: Validity and current limitations

Sclerostin a potent regulator of bone formation, is an antagonist of the Wnt-signaling pathway. The advent of assays to measure circulating sclerostin has enabled research to be performed with the aim to understand the potential role of circulating sclerostin as a pathophysiological marker in a variety of clinical settings. At this time, however, assays to measure circulating sclerostin are still relatively new and have not demonstrated consistent internal agreement in addition to which there are differences between serum and plasma levels. Nevertheless, measurement of sclerostin in the circulation has the potential to reflect the dynamics of bone formation with particular reference to situations in which osteocytes, the major source of circulating sclerostin, may be perturbed. Because of technical uncertainties regarding sclerostin assays that are currently available, circulating sclerostin measurements should be interpreted cautiously with attention to reference ranges for each assay and whether or not the measurement is made in serum or plasma.

How Accurate is Your Sclerostin Measurement? Comparison Between Three Commercially Available Sclerostin ELISA Kits

Sclerostin, bone formation antagonist is in the spotlight as a potential biomarker for diseases presenting with associated bone disorders such as chronic kidney disease (CDK-MBD). Accurate measurement of sclerostin is therefore important. Several immunoassays are available to measure sclerostin in serum and plasma. We compared the performance of three commercial ELISA kits. We measured sclerostin concentrations in serum and EDTA plasma obtained from healthy young (18-26 years) human subjects using kits from Biomedica, TECOmedical and from R&D Systems. The circulating sclerostin concentrations were systematically higher when measured with the Biomedica assay (serum: 35.5 ± 1.1 pmol/L; EDTA: 39.4 ± 2.0 pmol/L; mean ± SD) as compared with TECOmedical (serum: 21.8 ± 0.7 pmol/L; EDTA: 27.2 ± 1.3 pmol/L) and R&D Systems (serum: 7.6 ± 0.3 pmol/L; EDTA: 30.9 ± 1.5 pmol/L). We found a good correlation between the assay for EDTA plasma (r > 0.6; p < 0.001) while in serum, only measurements obtained using TECOmedical and R&D Systems assays correlated significantly (r = 0.78; p < 0.001). There was no correlation between matrices results when using the Biomedica kit (r = 0.20). The variability in values generated from Biomedica, R&D Systems and TECOmedical assays raises questions regarding the accuracy and specificity of the assays. Direct comparison of studies using different kits is not possible and great care should be given to measurement of sclerostin, with traceability of reagents. Standardization with appropriate material is required before different sclerostin assays can be introduced in clinical practice.

Low serum sclerostin levels in newborns with vitamin D deficiency

BACKGROUND

Sclerostin is a glycoprotein produced by osteocytes that is being evaluated as a potential clinical marker of bone turnover. The aim of this study was to investigate the association between neonatal vitamin D status and levels of circulating sclerostin.

METHODS

Forty newborns were recruited for the study. Vitamin D deficiency was defined as a serum 25-hydroxyvitamin D3 [25(OH)D] concentration <20 ng/mL and the newborns were divided into two groups as vitamin D deficient and vitamin D sufficient groups. Calcium, phosphate, alkaline phosphatase and sclerostin were measured at birth.

RESULTS

Newborns with vitamin D deficiency had markedly lower 25(OH)D levels than vitamin D sufficient newborns (8.5±4.4 ng/mL vs. 35.3±10.6 ng/mL, p<0.001). Vitamin D deficient infants also had significantly lower serum sclerostin levels (188.4±21.9 vs. 282.3±30.4 pg/mL; p: 0.026) than vitamin D sufficient newborns at birth. However, we did not detect a significant linear association between neonatal sclerostin and maternal/neonatal 25(OH)D levels.

CONCLUSIONS

Our data also demonstrated that vitamin D deficient newborns exhibited lower sclerostin levels than vitamin D sufficient newborns. The low sclerostin level might serve as a marker of decreased osteocyte activity in newborns with vitamin D deficiency.

Normocalcaemic hypoparathyroidism: prevalence and effect on bone status in older women. The OPUS study

OBJECTIVE

There are no consistent data on the prevalence and bone status of normocalcaemic hypoparathyroidism (NHYPO) as defined by normal adjusted calcium and low PTH level. Our aim was to determine the prevalence and the metabolic bone profile of NHYPO in older women, assessing its evolution over time. The second objective was to evaluate the prevalence of other calcium metabolic disorders.

DESIGN

The Osteoporosis and Ultrasound Study (OPUS) is a 6-yr prospective study of fracture-related factors.

PARTICIPANTS

A total of 2419 older women (age 55-79 yrs) and 258 younger women (age 30-40 yrs) participated. Complete follow-up data were available in 1416 subjects.

MEASUREMENTS

After calculating the adjusted calcium according to James' formula, we identified 'abnormal' calcium and PTH using Mahalanobis distances and allocated older women into different pathological categories using reference intervals from the healthy young women.

RESULTS

We identified 57 subjects with NHYPO (2·4%). These women had lower than expected bone turnover as assessed by bone alkaline phosphatase (-14·5%, 95% CI: -26·2 to -3·0, P = 0·007), CTX (-66·3%, 95% CI: -74·0 to -56·4, P < 0·001) and osteocalcin (-36·8%, 95% CI: -45·6 to -26·6, P < 0·001). After 6 years, of the 35 NHYPO subjects with follow-up data, none developed overt hypoparathyroidism and only 15 (0·6%) subjects had persistent evidence of NHYPO. We also identified 86 subjects (3·6%) affected by hyperparathyroid hypercalcaemia.

CONCLUSION

This is the first large population-based study to investigate NHYPO in older women. NHYPO is fairly common, not always persistent and is characterized by low bone turnover.

The Wnt Inhibitor Sclerostin Is Up-regulated by Mechanical Unloading in Osteocytes in Vitro

Although bone responds to its mechanical environment, the cellular and molecular mechanisms underlying the response of the skeleton to mechanical unloading are not completely understood. Osteocytes are the most abundant but least understood cells in bones and are thought to be responsible for sensing stresses and strains in bone. Sclerostin, a product of the SOST gene, is produced postnatally primarily by osteocytes and is a negative regulator of bone formation. Recent studies show that SOST is mechanically regulated at both the mRNA and protein levels. During prolonged bed rest and immobilization, circulating sclerostin increases both in humans and in animal models, and its increase is associated with a decrease in parathyroid hormone. To investigate whether SOST/sclerostin up-regulation in mechanical unloading is a cell-autonomous response or a hormonal response to decreased parathyroid hormone levels, we subjected osteocytes to an in vitro unloading environment achieved by the NASA rotating wall vessel system. To perform these studies, we generated a novel osteocytic cell line (Ocy454) that produces high levels of SOST/sclerostin at early time points and in the absence of differentiation factors. Importantly, these osteocytes recapitulated the in vivo response to mechanical unloading with increased expression of SOST (3.4 ± 1.9-fold, p < 0.001), sclerostin (4.7 ± 0.1-fold, p < 0.001), and the receptor activator of nuclear factor κΒ ligand (RANKL)/osteoprotegerin (OPG) (2.5 ± 0.7-fold, p < 0.001) ratio. These data demonstrate for the first time a cell-autonomous increase in SOST/sclerostin and RANKL/OPG ratio in the setting of unloading. Thus, targeted osteocyte therapies could hold promise as novel osteoporosis and disuse-induced bone loss treatments by directly modulating the mechanosensing cells in bone.

Mechanisms of Normalisation of Bone Metabolism during Recovery from Hyperthyroidism: Potential Role for Sclerostin and Parathyroid Hormone

Sclerostin, a protein expressed by osteocytes, is a negative regulator of bone formation. The aim of the study was to investigate the relationship between parathyroid hormone (PTH) and markers of bone metabolism and changes of sclerostin concentrations before and after treatment of hyperthyroidism. Patients and Methods. The study involved 33 patients (26 women), age (mean ± SD) 48 ± 15 years, with hyperthyroidism. Serum sclerostin, PTH, calcium, and bone markers [osteocalcin (OC) and collagen type I cross-linked C-telopeptide I (CTX)] were measured at diagnosis of hyperthyroidism and after treatment with thiamazole. Results. After treatment of hyperthyroidism a significant decrease in free T3 (FT3) and free T4 (FT4) concentrations was accompanied by marked decrease of serum sclerostin (from 43.7 ± 29.3 to 28.1 ± 18.4 pmol/L; p < 0.001), OC (from 35.6 ± 22.0 to 27.0 ± 14.3 ng/mL; p < 0.001), and CTX (from 0.49 ± 0.35 to 0.35 ± 0.23 ng/dL; p < 0.005), accompanied by an increase of PTH (from 29.3 ± 14.9 to 39.8 ± 19.8; p < 0.001). During hyperthyroidism there was a positive correlation between sclerostin and CTX (r s = 0.41, p < 0.05) and between OC and thyroid hormones (with FT3  r s = 0.42, with FT4  r s = 0.45, p < 0.05). Conclusions. Successful treatment of hyperthyroidism results in a significant decrease in serum sclerostin and bone markers concentrations, accompanied by an increase of PTH.

Comparison of two commercially available ELISAs for circulating sclerostin

This study investigates the performance and correlation of sclerostin measurements by two commercially available sclerostin ELISAs from TECOmedical and Biomedica. We found that the correlation between the results of two sclerostin assays is strong.

INTRODUCTION

Circulating sclerostin levels may provide insight into the pathophysiology of metabolic bone diseases such as osteoporosis. However, recent studies suggest that commercially available assays give different results. We compare the analytical performance of the two most used commercially available sclerostin ELISAs from TECOmedical and Biomedica.

METHODS

Sclerostin levels were assessed in 20 paired serum, EDTA, and heparin plasma convenience samples from hospitalized patients. In addition, sclerostin was measured in serum samples from 34 patients with metabolic bone diseases and from 10 patients with chronic kidney disease (CKD). Samples from three healthy donors were used to determine stability and intra- and inter- assay precision.

RESULTS

The average serum sclerostin concentration of all patients (n = 64) was 0.713 ± 0.58 ng/mL with the Biomedica assay and 0.734 ± 0.43 ng/mL with the TECO assay (p < 0.05). The results correlated strongly (r = 0.9; p < 0.0001), with Passing-Bablok regression showing a linear relationship but with a slight systematic and proportional difference between both assays. Sclerostin levels were about 30% higher in plasma than in serum for both assays, while no significant difference was seen between EDTA and heparin plasma. Intra- and inter- precision were <10% for TECO and <20% for Biomedica. Samples were stable for up to three freeze-thaw cycles with both assays.

CONCLUSIONS

The two commercially available ELISAs for measuring circulating levels of sclerostin are comparable. However, given the small but statistically significant systematic and proportional differences between both assays, results and reference ranges will be assay-specific. Results will also be specific to serum or plasma.

Update on romosozumab : a humanized monoclonal antibody to sclerostin

INTRODUCTION

Disorders with inactivating mutations of the SOST gene result in reduced or absent expression of sclerostin and are associated with high bone mass. Sclerostin is an important regulator of bone formation due to its inhibitory actions in the osteoanabolic Wnt signaling pathway. Advances in understanding the mechanisms of action of this signaling molecule have led to the development of a pharmacological inhibitor of sclerostin with potential clinical applications as an osteoanabolic drug for the treatment of osteoporosis.

AREAS COVERED

Romosozumab is the first humanized monoclonal sclerostin antibody to be tested in clinical trials. Similar to preclinical animal studies with sclerostin antibodies, initial clinical studies show that romosozumab increases bone formation and bone mineral density.

EXPERT OPINION

Blocking sclerostin action with romosozumab is a promising new therapeutic approach to osteoanabolic therapy of osteoporosis; efficacy and safety data on large controlled studies are awaited.

Circulating sclerostin levels and markers of bone turnover in Chinese-American and white women

CONTEXT

Chinese-American women have bone microarchitectural features that confer greater bone stiffness compared to white women, but the physiology underlying these findings has not been investigated.

OBJECTIVE

The purpose of the study was to assess racial differences in serum sclerostin and bone turnover markers (BTMs), and to explore their associations with each other, volumetric bone mineral density (BMD), and bone microarchitecture in Chinese-American and white women.

DESIGN AND SETTING

We conducted a cross-sectional study at a university hospital.

PARTICIPANTS

We studied 138 women.

RESULTS

Serum osteocalcin was 19-28% lower in pre- and postmenopausal Chinese-American vs white women, respectively (both P < .01). C-Terminal telopeptide of type I collagen (CTX) level was 18-22% lower in pre- and postmenopausal Chinese-American vs white women (both P < .05). Pre- vs postmenopausal differences in osteocalcin and CTX were greater in white vs Chinese-American women. Sclerostin levels were similar in both races, but BTMs were differentially associated with sclerostin by race and menopausal status. BTMs were not correlated with sclerostin in Chinese-Americans. CTX and bone-specific alkaline phosphatase were positively associated with sclerostin (r = 0.353, r = 0.458; both P < .05) in white premenopausal women. In contrast, in postmenopausal white women, the associations of sclerostin with amino-terminal propeptide of type I procollagen, isoform 5b of tartrate-resistant acid phosphatase, and CTX were negative (all P < .05). Adjusting for covariates, sclerostin was positively associated with areal BMD in both races.

CONCLUSIONS

Lower BTMs in Chinese-American women and greater age-related differences in BTMs among white women provide a physiological framework to account for racial differences in BMD, microarchitecture, and fracture.

Osteoporosis update from the 2012 Santa Fe Bone Symposium

The core of the 2012 Santa Fe Bone Symposium consisted of plenary presentations on new developments in the fields of osteoporosis and metabolic bone disease, with a focus on current and future implications for patient care. These were complemented by oral abstracts, interactive discussions of challenging cases, a debate on benefits and risks of long-term bisphosphonate therapy, and a panel discussion of controversial issues in the management of osteoporosis. Other topics included a review of the most important scientific publications in the past year, new and emerging therapy for osteoporosis, the benefits and limitations of clinical practice guidelines in the care of individual patients, the effects of metallic elements on skeletal health, clinical applications of bone turnover markers, an engineering perspective of skeletal health and disease, and an update on the role of the International Society for Clinical Densitometry in education, certification, accreditation, and advocacy for high-quality bone density testing. The symposium was highlighted by an inaugural presentation of "2 Million 2 Many," a national campaign of the National Bone Health Alliance to increase awareness of osteoporosis.

Recovery versus persistence of disordered mineral metabolism in kidney transplant recipients

In patients with end-stage renal disease, successful renal transplantation improves the quality of life and increases survival, as compared with long-term dialysis treatment. Although it long has been believed that successful kidney transplantation to a large extent solves the problem of chronic kidney disease-mineral and bone disorders (CKD-MBD), increasing evidence indicates that it only changes the phenotype of CKD-MBD. Posttransplant CKD-MBD reflects the effects of immunosuppression, previous CKD-MBD persisting after transplantation, and de novo CKD-MBD. A major and often-underestimated problem after successful renal transplantation is persistent hyperparathyroidism. Besides contributing to posttransplant hypercalcemia and hypophosphatemia, persistent hyperparathyroidism may be involved in the pathogenesis of allograft dysfunction (nephrocalcinosis), progression of vascular calcification, and bone disease (uncoupling of bone formation and bone resorption and bone mineral density loss) in renal transplant recipients. Similar to nontransplanted patients, CKD-MBD has a detrimental impact on (cardiovascular) mortality and morbidity. Additional studies urgently are needed to get more insights into the pathophysiology of posttransplant CKD-MBD. These new insights will allow for a more targeted and causal therapeutic approach.

Clinical utility of serum sclerostin measurements

Sclerostin is an osteocyte-secreted soluble antagonist of the Wnt/β-catenin signaling pathway requisite for osteoblast development and activity. Efforts over the past several years have focused on unraveling the role of sclerostin in both normal physiological and pathological conditions. Sclerostin levels are undetectable in the serum of patients with sclerosteosis. In normal individuals, serum sclerostin levels are higher in males and increase in both sexes across the adult lifespan. Some, but not other, studies have demonstrated that higher serum sclerostin levels are associated with increased fracture risk, particularly when paired with lower bone mineral density. Levels of circulating sclerostin are highly correlated with bone marrow sclerostin levels. Sclerostin levels are inversely related to parathyroid hormone levels. Clinical conditions in which serum sclerostin levels have been measured include ankylosing spondylitis, chronic kidney disease, diabetes, fractures, hypercortisolism, multiple myeloma and spinal cord injury. Even within clearly defined clinical conditions, however, consistent changes in serum sclerostin levels have not always been seen. This may reflect differences in currently available commercial assays or sample sources (serum versus plasma), and suggests further study is needed before sclerostin measurements are introduced into routine clinical practice. Until such issues are resolved, measurement of sclerostin levels appears to be most useful for understanding the mechanisms by which osteocytes regulate bone turnover through the integration of hormonal, physical and pharmacological stimuli, rather than to guide clinical-care decisions.

Sclerostin and DKK1 in primary hyperparathyroidism

Bone formation is influenced by the Wnt pathway through effects on osteoblast functionality, and these actions are opposed by two antagonists: sclerostin and Dickkopf-1 (DKK1). Decreased levels of serum sclerostin were found after treatment with the PTH analogue teriparatide and in patients with primary hyperparathyroidism (PHPT), while treatment with teriparatide of postmenopausal osteoporosis is associated with increases in serum DKK1. We studied mineral metabolism and Wnt pathway in 21 postmenopausal women affected by PHPT and in 42 age-matched healthy women. Mean serum calcium and PTH were significantly higher and serum phosphates significantly lower in the PHPT group compared with the control group. Serum 25-OH-vitamin D (25OHD) was lower in PHPT patients and 1,25 dihydroxy-vitamin D [1,25(OH)2D] was significantly higher. Patients with PHPT had significantly higher levels of bone alkaline phosphatase (BAP) and of serum C-terminal telopeptides of type I collagene (sCTX). Serum sclerostin in PHPT was significantly lower (-26 %) and serum DKK1 significantly higher (+57 %) than in healthy control subjects. Serum PTH was positively correlated with 1,25OH2D (p < 0.001), BAP (p = 0.036), sCTX (p = 0.003), and DKK1 (p = 0.007) and negatively with 25OHD (p = 0.002) and sclerostin (p = 0.02). In PHPT patients, serum sclerostin was negatively correlated with BAP (p = 0.038) and sCTX (p = 0.07). Patients with PHPT have significantly lower sclerostin and higher DKK1 levels compared with healthy postmenopausal control subjects. Further studies are warranted in order to verify whether the balance between these two opposite effects on Wnt function might help explain the variable bone involvement among patients with PHPT.

Changes in bone sclerostin levels in mice after ovariectomy vary independently of changes in serum sclerostin levels

We examined the effects that ovariectomy had on sclerostin mRNA and protein levels in the bones of 8-week-old mice that were either sham-operated (SHAM) or ovariectomized (OVX) and then euthanized 3 or 6 weeks later. In this model, bone loss occurred between 3 and 5 weeks postsurgery. In calvaria, ovariectomy significantly decreased sclerostin mRNA levels at 6 weeks postsurgery (by 52%) but had no significant effect at 3 weeks. In contrast, sclerostin mRNA levels were significantly lower in OVX femurs at 3 weeks postsurgery (by 53%) but equal to that of SHAM at 6 weeks. The effects of ovariectomy on sclerostin were not a global response of osteocytes because they were not mimicked by changes in the mRNA levels for two other relatively osteocyte-specific genes: DMP-1 and FGF-23. Sclerostin protein decreased by 83% and 60%, at 3 and 6 weeks postsurgery in calvaria, respectively, and by 38% in lumbar vertebrae at 6 weeks. We also detected decreases in sclerostin by immunohistochemistry in cortical osteocytes of the humerus at 3 weeks postsurgery. However, there were no significant effects of ovariectomy on sclerostin protein in femurs or on serum sclerostin at 3 and 6 weeks postsurgery. These results demonstrate that ovariectomy has variable effects on sclerostin mRNA and protein in mice, which are dependent on the bones examined and the time after surgery. Given the discrepancy between the effects of ovariectomy on serum sclerostin levels and sclerostin mRNA and protein levels in various bones, these results argue that, at least in mice, serum sclerostin levels may not accurately reflect changes in the local production of sclerostin in bones. Additional studies are needed to evaluate whether this is also the case in humans.

WNT signaling in bone homeostasis and disease: from human mutations to treatments

Low bone mass and strength lead to fragility fractures, for example, in elderly individuals affected by osteoporosis or children with osteogenesis imperfecta. A decade ago, rare human mutations affecting bone negatively (osteoporosis-pseudoglioma syndrome) or positively (high-bone mass phenotype, sclerosteosis and Van Buchem disease) have been identified and found to all reside in components of the canonical WNT signaling machinery. Mouse genetics confirmed the importance of canonical Wnt signaling in the regulation of bone homeostasis, with activation of the pathway leading to increased, and inhibition leading to decreased, bone mass and strength. The importance of WNT signaling for bone has also been highlighted since then in the general population in numerous genome-wide association studies. The pathway is now the target for therapeutic intervention to restore bone strength in millions of patients at risk for fracture. This paper reviews our current understanding of the mechanisms by which WNT signalng regulates bone homeostasis.

Association of serum sclerostin with bone mineral density, bone turnover, steroid and parathyroid hormones, and fracture risk in postmenopausal women: the OFELY study

SUMMARY

Sclerostin is a key regulator of bone formation. In a population of 572 postmenopausal women (mean age, 67 years) followed prospectively for a median of 6 years, there was no significant association between baseline levels of serum sclerostin and incidence of all fractures which occurred in 64 subjects.

INTRODUCTION

Sclerostin, an osteocyte soluble factor, is a major negative regulator of osteoblastic activity. Circulating sclerostin levels were reported to increase with age and to be modestly associated with bone mineral density (BMD) and bone turnover, but there are no data on the association with fracture risk.

METHODS

We investigated 572 postmenopausal women (mean age, 67 ± 8.5 years) from the OFELY population-based cohort. The associations of serum sclerostin measured with a new two-site ELISA and spine and hip BMD by DXA, serum β-isomerized C-terminal crosslinking of type I collagen (CTX), intact N-terminal propeptide of type I collagen (PINP), intact PTH, 25-hydroxyvitamin D [25(OH)D], estradiol, testosterone, and fracture risk were analyzed. At the time of sclerostin measurements, 98 postmenopausal women had prevalent fractures. After a median of 6 years (interquartile range, 5-7 years) follow-up, 64 postmenopausal sustained an incident fracture.

RESULTS

Serum sclerostin correlated positively with spine (r = 0.35, p < 0.0001) and total hip (r = 0.25, <0.0001) BMD. Conversely, serum sclerostin was weakly negatively associated with the bone markers PINP (r = -0.10, p = 0.014) and CTX (r = -0.13, p = 0.0026) and with intact PTH (r = -0.13, p = 0.0064). There was no significant association of serum sclerostin with 25(OH)D, estradiol, free estradiol index, or testosterone. Serum sclerostin considered as a continuous variable or in quartiles was not significantly associated with the risk of prevalent or incident fracture.

CONCLUSION

Serum sclerostin is weakly correlated with BMD, bone turnover, and PTH in postmenopausal women. It was not significantly associated with the risk of all fractures, although the number of incident fractures recorded may not allow detecting a modest association.

Bone turnover markers in primary hyperparathyroidism

Primary hyperparathyroidism is an endocrine disorder characterized by elevated or inappropriate normal levels of parathyroid hormone in a setting of hypercalcemia. The inclusion of calcium on the basic metabolic bone panel has allowed this disorder to be diagnosed even in the absence of symptoms. Nevertheless, the skeleton can be a target of excess parathyroid hormone activity even during its asymptomatic presentation. Bone turnover markers a surrogate index of the process of the remodeling process at the level of bone, and thus can be useful to monitor skeleton involvement in primary hyperparathyroidism.

Successful treatment of thyrotoxicosis is accompanied by a decrease in serum sclerostin levels

Sclerostin, a product of a SOST gene, is a protein expressed by osteocytes that inhibits osteoblastic bone formation. Several hormones, including PTH and glucocorticosteroids, have been suggested to be possible regulators of sclerostin production. The influence of thyroid hormones on sclerostin synthesis has not been investigated, so far. The aim of the study was to evaluate sclerostin concentrations in patients before and after treatment of thyrotoxicosis.

PATIENTS AND METHODS

The study involved 15 patients (4 men), mean age 51.8±15.3 years, mean BMI value - 24.7±3.5, with thyrotoxicosis due to Graves' disease or toxic multinodular goitre. Serum sclerostin was measured by immunoassay at diagnosis of thyrotoxicosis and after 6-10 weeks of treatment with thiamazole. The data were analysed by means of simple descriptive statistics of location and dispersion and Mann-Whitney U test for pairs of results, before and after thiamazole therapy. Association between variables was evaluated with use of Spearman`s correlation coefficient.

RESULTS

There was a significant decrease in free T3 (FT3) and free T4 (FT4) concentrations (from 8.74±4.79 pg/ml to 3.54±2.40 pg/ml, and from 4.48±2.21 ng/ml to 1.02±1.07 ng/ml, respectively, p<0.001). This was accompanied by a marked decrease of serum sclerostin levels from 55.46±20.90 pmol/l to 35.73±15.70 pmol/l, p<0.0015). Interestingly, enough, sclerostin levels did not correlate with serum FT3 or FT4 concentrations.

CONCLUSIONS

Restoration of a euthyroid state in patients with thyrotoxicosis results in a significant decrease in serum sclerostin concentrations. The above mentioned phenomenon may reflect lowering of bone metabolism, but a possible direct influence of thyroid hormones on SOST gene needs to be investigated.

Sclerostin levels and bone turnover markers in adolescents with anorexia nervosa and healthy adolescent girls

Sclerostin, product of the SOST gene, is an important determinant of bone formation and resorption. Adolescents with anorexia nervosa (AN) have low bone density and decreased levels of bone turnover markers. However, sclerostin has not been examined in AN as a potential mediator of impaired bone metabolism. Our study objectives were to (i) assess associations of sclerostin with surrogate bone turnover markers in girls with AN and controls and (ii) examine effects of transdermal estradiol on sclerostin in AN. 69 girls (44 with AN and 25 normal-weight controls) 13-18 years old were studied at baseline. 22 AN girls were randomized to transdermal estradiol (plus cyclic medroxyprogesterone) or placebo in a double-blind study for 12 months. Sclerostin correlated positively with P1NP and CTX in controls (r=0.67 and 0.53, p=0.0002 and 0.005, respectively) but not in AN despite comparable levels at baseline. Changes in sclerostin over twelve months did not differ in girls randomized to estradiol or placebo. The relationship between sclerostin and bone turnover markers is disrupted in adolescent girls with AN. Despite an increase in BMD with estradiol administration in AN, estrogen does not impact sclerostin levels in this group.

Serum sclerostin increases in healthy adult men during bed rest

CONTEXT

Animal models and human studies suggest that osteocytes regulate the skeleton's response to mechanical unloading in part by an increase in sclerostin. However, few studies have reported changes in serum sclerostin in humans exposed to reduced mechanical loading.

OBJECTIVE

We determined changes in serum sclerostin and bone turnover markers in healthy adult men undergoing controlled bed rest.

DESIGN, SETTING, AND PARTICIPANTS

Seven healthy adult men (31 ± 3 yr old) underwent 90 d of 6° head down tilt bed rest at the University of Texas Medical Branch Institute for Translational Sciences-Clinical Research Center.

OUTCOMES

Serum sclerostin, PTH, vitamin D, bone resorption and formation markers, urinary calcium and phosphorus excretion, and 24-h pooled urinary markers of bone resorption were evaluated before bed rest [baseline (BL)] and at bed rest d 28 (BR-28), d 60 (BR-60), and d 90 (BR-90). Bone mineral density was measured at BL, BR-60, and 5 d after the end of the study (BR+5). Data are reported as mean ± SD.

RESULTS

Consistent with prior reports, bone mineral density declined significantly (1-2% per month) at weight-bearing skeletal sites. Serum sclerostin was elevated above BL at BR-28 (+29 ± 20%; P = 0.003) and BR-60 (+42 ± 31%; P < 0.001), with a lesser increase at BR-90 (+22 ± 21%; P = 0.07). Serum PTH levels were reduced at BR-28 (-17 ± 16%; P = 0.02) and BR-60 (-24 ± 14%; P = 0.03) and remained lower than BL at BR-90 (-21 ± 21%; P = 0.14), but did not reach statistical significance. Serum bone turnover markers were unchanged; however, urinary bone resorption markers and calcium were significantly elevated at all time points after bed rest (P < 0.01).

CONCLUSIONS

In healthy men subjected to controlled bed rest for 90 d, serum sclerostin increased, with a peak at 60, whereas serum PTH declined, and urinary calcium and bone resorption markers increased.

Sclerostin: therapeutic horizons based upon its actions

Inactivating mutations of the SOST gene cause a reduction in sclerostin levels and are associated with high bone mass. The clinical phenotypes, sclerosteosis and van Buchem's disease, were described in 1950s. Much later, it was learned that both diseases are due to loss-of-function mutations in the SOST gene. As a regulator of an important osteoanabolic pathway, Wnt, inactivation of SOST leads to a stimulation of the pathway it regulates. The high bone mass in patients with either sclerosteosis or van Buchem's disease is associated with unusual skeletal strength; they do not fracture. Knowledge of this molecule and its actions led rather quickly to the development of anti-sclerostin antibodies that lead to marked increases in bone mass in both animals and human subjects. Blocking sclerostin action with anti-sclerostin antibodies is a promising new therapeutic approach to osteoanabolic therapy of osteoporosis.