Tartrate-resistant acid phosphatase 5b: a novel serum marker of bone resorption

Arming a replicating adenovirus with osteoprotegerin reduces the tumor burden in a murine model of osteolytic bone metastases of breast cancer

Most patients with advanced breast cancer develop osteolytic bone metastases, which have numerous complications. Because current therapies are not curative, new treatments are needed. Conditionally replicating adenoviruses (CRAds) are anticancer agents designed to infect and lyse tumor cells. However, in spite of their promise as selective cancer therapeutics, replicating adenoviruses have shown limited efficacy in the clinical setting. We hypothesized that a CRAd armed with osteoprotegerin (OPG) would eradicate bone metastases of breast cancer both directly, by oncolysis, and indirectly, by inhibiting osteoclastic bone resorption and thus reducing the tumor burden. We constructed an armed CRAd (Ad5-Δ24-sOPG-Fc-RGD) by replacing viral E3B genes with a fusion of the ligand-binding domains of OPG and the Fc portion of human IgG1. Conditional replication was conferred by a 24-base pair deletion within E1A (Δ24), which prevents the binding of E1A to the retinoblastoma tumor suppressor/cell cycle regulator protein and limits replication in normal cells. Enhanced infection of cells expressing low levels of the primary Ad5 receptor was conferred by incorporating an RGD peptide sequence into the fiber knob to mediate binding to α_v integrins. After characterization of the armed CRAd, we demonstrated that infection of breast cancer cells by Ad-Δ24-sOPG-Fc-RGD both killed the infected cells by oncolysis and inhibited the formation of osteoclasts in an in vitro co-culture model. In a murine model of osteolytic bone metastases of breast cancer, the CRAd armed with sOPG-Fc reduced tumor burden in the bone and inhibited osteoclast formation more effectively than an unarmed CRAd.

Bone metabolism markers in sports medicine

Bone mass can be viewed as the net product of two counteracting metabolic processes, bone formation and bone resorption, which allow the skeleton to carry out its principal functions: mechanical support of the body, calcium dynamic deposition and haemopoiesis. Besides radiological methods, several blood and urinary molecules have been identified as markers of bone metabolic activity for estimating the rates and direction of the biological activities governing bone turnover. The advantages for the use of bone metabolism markers are that they are potentially less dangerous than radiological determinations, are more sensitive to changes in bone metabolism than radiological methods and are easily collected and analysed. The disadvantages are that they have high biological variability. Physical exercise is a known source of bone turnover and is recommended for preventing osteoporosis and bone metabolism problems. There are numerous experiments on bone metabolism markers after acute exercise, but not after long-term training and during or after a whole competition season. Moreover, few studies on bone metabolism markers have evaluated their performance in elite and top-level athletes, who have a higher bone turnover than sedentary individuals. Despite discrepant results among studies, most have shown that short exercise is insufficient for modifying serum concentrations of bone metabolism markers. Marker variations are more evident after several hours or days after exercise, bone formation markers are more sensitive than bone resorption markers, and stimulation of osteoblast and/or osteoclast functions is exercise dependent but the response is not immediate. The response depends on the type of exercise; the markers seem to be less sensitive to resistance exercise and the intensity of exercise is not discriminate. Comparisons between trained subjects and untrained controls have demonstrated the influence of exercise on bone turnover. During training, carboxy-terminal collagen cross-links (CTx), a bone resorption marker, was shown to be less sensitive than amino-terminal cross-linking telopeptide of type I collagen (NTx) and urinary pyridinolines, which were sensitive to anaerobic exercise. Whereas, the bone formation markers, bone alkaline phosphatase (BAP) and osteocalcin (OC) changed after 1 month and 2 months of an exercise programme, respectively. After 2 months, while BAP normalized, it was found to be sensitive to aerobic exercise and OC was found to be sensitive to anaerobic exercise. After prolonged training and competition, bone formation markers are found to change in sedentary subjects enrolled in a physical activity programme. Professional athletes show changes in bone formation markers depending on programme intensity, whereas bone resorption appears to stabilize. Crucial for long-term training, are the characteristics of exercise (e.g. weight-bearing, impact).

In vitro: osteoclastic activity studies on surfaces of 3D printed calcium phosphate scaffolds

Various biomaterials have been developed for the use as bone substitutes for bone defects. To optimize their integration and functionality, they should be adapted to the individual defect. Rapid prototyping is a manufacturing method to tailor materials to the 3D geometry of the defect. Especially 3D printing allows the manufacture of implants, the shape of which can be designed to fit the bone defect using anatomical information obtained from the patient. 3D printing of calcium phosphates, which are well established as bone substitutes, involves a sintering step after gluing the granules together by a binder liquid. In this study, we analyzed if and how these 3D printed calcium phosphate surfaces can be resorbed by osteoclast-like cells. On 3D printed scaffold surfaces consisting of pure HA and β-TCP as well as a biphasic mixture of HA and TCP the osteoclastic cell differentiation was studied. In this regard, cell proliferation, differentiation, and activation were analyzed with the monocytic cell line RAW 264.7. The results show that osteoclast-like cells were able to resorb calcium phosphate surfaces consisting of granules. Furthermore, biphasic calcium phosphate ceramics exhibit, because of their osteoclastic activation ability, the most promising surface properties to serve as 3D printed bone substitute scaffolds.

Serum tartrate-resistant acid phosphatase 5b activity as a prognostic marker of survival in breast cancer with bone metastasis

Background

Serum tartrate-resistant acid phosphatase 5b (TRACP 5b) activity is a marker of osteoclast number and is elevated in breast cancer (BC) patients with extensive bone metastasis, which might in turn reflect the tumour burden. We tested the hypothesis that baseline serum TRACP 5b activity and its interval change are potential prognostic markers of survival in BC patients with bone metastasis.

Methods

We analyzed the data from previous prospective studies. A total of 100 patients with newly diagnosed bone metastasis were included. Cox proportional regression model was used to evaluate the correlation between the overall survival time (OS) and baseline serum TRACP 5b activity and its interval changes. The least significant change (LSC) of TRACP 5b was calculated from data obtained from 15 patients with early BC.

Results

Estrogen receptor status (Hazard Ratio (HR) = 0.397; p = 0.003) and visceral metastasis (HR = 0.492; p = 0.0045) were significantly correlated with OS. The OS was significantly shorter in those patients with higher baseline TRACP 5b activity based on a cut-off value to delineate the highest tertile (HR = 3.524; p < 0.0001). Further analysis demonstrated that among patients in the highest tertile, OS was significantly longer in those patients who had achieved a decrease of serum TRACP 5b activity greater than the LSC (38.59%) (p = 0.0015).

Conclusions

We found that TRACP 5b activity and its interval change after treatment bore a prognostic role in BC patients with bone metastasis and a high baseline serum TRACP 5b activity. Further prospective phase II study is necessary to confirm these results.

The assessment of fracture risk

Bone mineral density is considered to be the standard measure for the diagnosis of osteoporosis and the assessment of fracture risk. The majority of fragility fractures occur in patients with bone mineral density in the osteopenic range. The Fracture Risk Assessment Tool (FRAX) can be used as an assessment modality for the prediction of fractures on the basis of clinical risk factors, with or without the use of femoral neck bone mineral density. Treatment of osteoporosis should be considered for patients with low bone mineral density (a T-score of between -1.0 and -2.5) as well as a ten-year risk of hip fracture of > or = 3% or a ten-year risk of a major osteoporosis-related fracture of > or = 20% as assessed with the FRAX. Biochemical bone markers are useful for monitoring the efficacy of antiresorptive or anabolic therapy and may aid in identifying patients who have a high risk of fracture. An approach combining the assessment of bone mineral density, clinical risk factors for fracture with use of the FRAX, and bone turnover markers will improve the prediction of fracture risk and enhance the evaluation of patients with osteoporosis.

High-fat, sucrose diet impairs geometrical and mechanical properties of cortical bone in mice

Exposure to diets high in fat and sucrose can induce hyperinsulinaemia, affect Ca and Mg metabolism, and alter bone mineralisation and mechanical properties. The present study assessed morphological and mechanical changes in a murine model exposed to a high-fat/sucrose (HFS) diet, as well as corresponding molecular and endocrine markers of bone turnover. Female C57BL/6 mice (aged 9 weeks) consumed either a low-fat, complex carbohydrate diet or an HFS diet for 10 weeks. At the end of the 10 weeks, serum was collected for biochemical analysis. Tibiae from half the mice (n 15) were randomly selected to be micro-computed tomography scanned and tested to failure in cantilever bending, while the remaining half were prepared for real-time PCR analysis. Serum tartrate-resistant acid phosphatase was significantly elevated in HFS mice, while osteocalcin remained unchanged. Both body mass and percentage body fat were greater in mice fed HFS diet. After adjusting for body mass, tibial structural and morphological properties were adversely affected in the HFS cohort. Cortical thickness, cross-sectional area, and load at maximum were all significantly lower in mice fed HFS diet. Receptor activator of nuclear factor kappabeta ligand (RANKL) mRNA was significantly upregulated in HFS mice, but osteoprotegerin/RANKL mRNA ratio remained unchanged between cohorts. Moreover, cyclo-oxygenase-2 mRNA tended to be increased in HFS. Thus, ingestion of an HFS diet had a significant adverse effect on mouse bone morphology and mechanics, and these effects were likely due to elevated osteoclast activity associated with the inflammatory state of obesity, and not necessarily osteoclast recruitment/proliferation.

Biology and clinical significance of tartrate-resistant acid phosphatases: new perspectives on an old enzyme

Type 5 tartrate-resistant acid phosphatase (TRAP) has been a clinically relevant biomarker for about 50 years. It has always been a reliable and specific cytochemical marker for hairy cell leukemia and for differentiated cells of monocytic lineage. Only recently has the test for serum TRAP activity been accepted as sensitive and specific enough for clinical use as a marker of osteoclasts and bone resorption. This has come about through steady advances in knowledge about TRAP enzymology, structure, function, and molecular regulation and a consequent appreciation that TRAP isoforms 5a and 5b have very different clinical significance. As a measure of osteoclast number and bone resorption, TRAP 5b has diagnostic and prognostic applications in osteoporosis, cancers with bone metastasis, chronic renal failure, and perhaps other metabolic and pathologic bone diseases. Serum TRAP 5a, on the other hand, has no relationship to bone metabolism but seems instead to be a measure of activated macrophages and chronic inflammation. Exploration of the real clinical usefulness of serum TRAP 5a for diagnosis and disease management in a wide variety of chronic inflammatory diseases is only now beginning. This perspective traces the important basic scientific developments that have led up to the refinement of serum TRAP isoform immunoassays and their validation as biomarkers of disease. Many unanswered questions remain, providing a wealth of opportunity for continued research of this multifaceted enzyme.

Can Elevated Serum Tracp-5B Levels Predict Stress Fractures? A Cohort Study

Background and Aims:

Stress fracture is a common overuse injury in athletes and military conscripts. The reliable diagnosis of stress fractures is often difficult, however, because it is usually based solely on radiographic findings. Biochemical markers of bone resorption reflect bone degradation and may also reflect the rate of bone loss. The aim of the study was to examine whether elevated serum tartrate-resistant acid phosphatase isoform 5b (TRACP-5b) levels reflect enhanced bone remodeling and predict the occurrence of stress fractures in military conscripts.

Material and Methods:

Randomly selected military conscripts [mean age, 19.8 (range 18–28) years; n = 820] were followed for 3 months. Baseline blood samples were drawn upon arrival to the service. Four subsequent samples were obtained from subjects that developed stress fractures and one sample each was obtained from two asymptomatic control subjects for each fracture case.

Results:

Plain radiography was used to diagnose stress fractures in 20 of the 820 conscripts (2.4%). Follow-up data were available for 14 subjects with 21 stress fractures and 28 control subjects. Subjects with proportionally increasing serum TRACP-5b levels had an 8-fold greater probability of stress fracture than controls. No statistically significant difference was detected.

Conclusions:

Although assessing serum TRACP-5b levels appears to be a promising method to predict bone stress injuries, the present study failed to give a conclusive statement of its usefulness as a diagnostic tool.

Effect of impact exercise on bone metabolism

SUMMARY

Regular impact exercise in premenopausal women caused positive osteogenic effects associated to low basal serum parathormone (PTH) but had no effects on bone turnover markers PINP or TRACP5b. The low serum basal PTH levels during impact exercise may be a sign of increased incorporation of calcium to bone.

INTRODUCTION

This study aimed to determine the long-term effects of high-impact exercise on bone turnover and calciotropic hormones.

METHODS

We performed a 12-month population-based, randomized, controlled exercise trial in 120 women (age 35-40 years) randomly assigned to an exercise group (EG; n = 60) or a control group (CG; n = 60). The exercise regimen consisted of supervised high-impact exercises three times per week. Daily impact loading was assessed by using an accelerometer. Bone turnover markers and calciotropic hormones were analyzed at 0, 6, and 12 months.

RESULTS

Twelve months of impact exercise did not reveal any treatment effects in bone turnover markers PINP or TRAPC5b, whereas serum basal PTH decreased significantly more in the EG than in the CG (-11.2 vs. -2.2 pg/mL; p = 0.03). The change in PTH was dose dependent and most clearly seen in subjects with 96 to 130 daily impacts at 2.5 to 5.3 g (e.g., running or jumping).

CONCLUSIONS

Regular impact exercise does not cause persistent alterations in bone turnover emphasizing necessity of continuous training to achieve bone benefits. Impact exercise training lowers the serum basal PTH levels and possibly enables greater difference between the basal PTH and transient exercise-induced PTH peaks leading to osteogenic effects.

Complex regulation of tartrate-resistant acid phosphatase (TRAP) expression by interleukin 4 (IL-4): IL-4 indirectly suppresses receptor activator of NF-kappaB ligand (RANKL)-mediated TRAP expression but modestly induces its expression directly

Interleukin 4 (IL-4) inhibits receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast formation and functional activity in a STAT6-dependent manner. IL-4 down-regulates expression of tartrate-resistant acid phosphatase (TRAP) in mature osteoclasts. To determine whether IL-4 regulates TRAP promoter activity, RAW264.7 cells were transfected with a TRAP promoter-luciferase reporter. Treatment with IL-4 alone modestly enhanced TRAP luciferase activity. However, IL-4 suppressed the ability of RANKL to up-regulate TRAP-luciferase activity, suggesting that IL-4 has multiple effects on TRAP transcription. IL-4 also reduced the RANKL-induced association of RNA polymerase II with the TRAP gene in osteoclasts. The TRAP promoter contains a STAT6-binding motif, and STAT6 bound to the endogenous TRAP promoter after IL-4 treatment. To determine the impact of STAT6 binding, we transfected cells with STAT6VT, a constitutively active STAT6 mutant. STAT6VT alone up-regulated TRAP-luciferase activity; this effect was abrogated by mutating the STAT6 binding site in the minimal TRAP promoter. STAT6VT did not inhibit the potent up-regulation of TRAP promoter activity caused by overexpression of NFATc1, PU.1, and microphthalmia transcription factor, downstream targets of macrophage colony-stimulating factor and RANKL. IL-4 down-regulated the expression of c-Fos and NFATc1 in mature osteoclasts. Knockdown of NFATc1 by short interfering RNA caused TRAP expression to be down-regulated, and ectopic expression of NFATc1 abrogated the IL-4-induced down-regulation of TRAP. These results suggest that STAT6 plays two distinct roles in TRAP expression. The IL-4-induced activation of STAT6 mediates suppression of the RANKL-induced TRAP promoter activity indirectly by inhibiting NFATc1 expression. However, in the absence of RANKL and osteoclast differentiation, STAT6 binds the TRAP promoter after IL-4 treatment and directly enhances TRAP expression.

Bone markers in osteoporosis

Current biological markers of bone turnover have proven useful in improving fracture risk assessment and monitoring treatment efficacy in postmenopausal osteoporosis. Recent developments in the field of bone markers include 1) identification of new biochemical markers providing additional information on the complex pathways leading to bone fragility; 2) application of novel technologies such as proteomics for the discovery of novel markers; 3) automation and multiplexing for improving analytical performance and convenience; and 4) refinement of the clinical interpretation of markers. Currently, however, for the management of individual patients, their most established application is to monitor treatment efficacy and possibly to improve fracture risk assessment. The role of bone markers for improving adherence to therapy will need to be investigated in further studies. This brief review discusses these novel technological developments and the recent clinical data on the use of established and new markers in postmenopausal osteoporosis.

Effects of a low-frequency sound wave therapy programme on functional capacity, blood circulation and bone metabolism in frail old men and women

Objective: To evaluate the effects of a low-frequency sound wave therapy programme on functional capacity, blood circulation and bone metabolism of the frail elderly.

Design: Single-blind, randomized, controlled trial.

Setting: Two senior service centres.

Subjects: Forty-nine volunteers (14 males and 35 females) aged 62—93 years with up to 12 diagnosed diseases were allocated in either the intervention group (n = 30) or control group (n = 19).

Intervention: The intervention group underwent sound wave therapy, 3—5 times a week for 30 minutes per session over a period of 6 months. The control group received no intervention.

Main measurements: Blood pressure, functional capacity, mobility, bone density, biochemical markers, isometric muscle strength, balance, and skin surface temperature.

Results: Compared with the control group, the intervention group’s mobility and the amount of self-reported kilometres walked per week increased by 3 km (P<0.05), while levels of cholesterol (4.97 (0.72) to 4.52 (0.65) mmol/L, P =0.019), low-density lipoprotein (2.82 (0.72) to 2.45 (0.61) mmol/L, P =0.022), bone markers of total osteocalcin (11.0 (6.5) to 10.3 (5.9) ng/mL, P =0.048)) and tartrate-resistant acid phosphatase isoform 5b (2.50 (1.0) to 2.41 (1.1) IU/L, P =0.021)) decreased. The average skin surface temperature was significantly higher during active sessions at the end of the intervention than in the beginning (P = 0.004). No change was found during placebo sessions.

Conclusions: Low-frequency sound wave therapy may have the potential to promote well-being of frail elderly subjects via improved functional capacity, especially in subjects who are too frail to undertake exercise.

Usefulness of bone resorption markers in hemodialysis patients

Although bone biopsy is a golden standard in the diagnosis of renal osteodystrophy, it is invasive and repetitive evaluation of bone status by this method is practically impossible. Non-invasive evaluation by bone metabolic markers such as serum cross-linked N-telopeptide of type I collagen (NTX) might give us additional information which cannot be obtained only by measurements of parathyroid hormone (PTH). These days, bone resorption marker, serum tartrate-resistant acid phosphatase (TRAP5b) was reported to be correlated with histomorphometric parameters of bone resorption in a bone biopsy study enrolling hemodialysis (HD) patients. In the current study, we studied the correlation of sera NTX and TRAP5b with bone mineral density (BMD) of second metacarpal bone in 103 HD patients and serial changes of these markers just after parathyroidectomy (PTX). Sera NTX and TRAP5b showed a significant positive relationship (R=0.79 P<0.0001). Simple regression analyses showed that both markers were significantly associated with BMD Z-score, whereas 1-84 PTH showed no significant association at all. This result might be attributed to diverse difference among HD patients in skeletal sensitivity to endogenous PTH. In fact, the ratios of TRAP5b/PTH and NTX/PTH denoting PTH sensitivity were significantly higher in postmenopausal female than male patients. Female gender, hemodialysis vintage, and log(PTH) were found to be significant positive determinants of serum log(TRAP5b) by multiple linear regression analysis. Receiver operating curve analysis for young adult mean 70% revealed that sensitivity was more than 95% when the cut-off value was set at 56.5 nmol BCE/L and 340 mU/L, but the specificity was only 29.5% and 34.4% for NTX and TRAP5b, respectively. Multiple regression analysis revealed that both markers were independent determinants of Z-score in two models including respective marker. Serial changes of both markers after PTX in 2 HD patients were comparable with gradual decrease of these markers. However, the reduction was sooner and larger in serum NTX. This sooner reduction might be attributed to the difference in characteristics of these markers regarding the effect of single HD session. Whereas serum NTX decreased, TRAP5b increased significantly after single session. Taken together, both markers give us additional information that cannot be obtained just by using PTH, provided that we know the characteristics of these markers.

Bone turnover markers are correlated with quantitative ultrasound of the calcaneus: 5-year longitudinal data

SUMMARY

Associations between bone turnover markers and calcaneal ultrasound (quantitative ultrasound, QUS) were studied in a population-based sample of 810 elderly women. Baseline bone turnover markers correlated with baseline QUS as well as with 5-year prospective changes in QUS.

INTRODUCTION

Bone turnover markers are associated with areal bone mineral density, but the knowledge on the association with QUS is limited.

METHODS

Eight hundred ten women, all 75 years old, were investigated at baseline. Five hundred six completed a 5-year follow-up. Bone turnover markers and calcaneal QUS [speed of sound (SoS), broadband ultrasound attenuation (BUA), stiffness] were investigated at baseline. QUS was investigated at follow-up.

RESULTS

All bone turnover markers were correlated with baseline QUS [standardized regression (Beta(std)) values from -0.07, p < 0.05 to -0.23, p < 0.001], with the exception of bone-specific alkaline phosphatase (S-Bone ALP) which was not correlated with BUA and stiffness index. When the correlations between baseline bone turnover markers and 5-year changes in QUS were analyzed, three serum osteocalcins were correlated with changes of SoS and stiffness index (Beta(std) = -0.11, p < 0.05 to -0.17, p < 0.001). Also S-CTX-I correlated with changes of SoS and stiffness index (Beta(std) = -0.10 and -0.09, respectively, p < 0.05). S-TRACP5b, urinary deoxypyridinoline/crea, and U-MidOC/crea correlated with changes of SoS (Beta(std) = -0.10 and p < 0.05 for all). S-Bone ALP did not correlate with change of QUS. None of the bone turnover markers correlated with changes of BUA.

CONCLUSIONS

Bone turnover markers correlate with concomitantly assessed QUS as well as with longitudinal change in QUS.

Clinical significance of bone alkaline phosphatase isoforms, including the novel B1x isoform, in mild to moderate chronic kidney disease

BACKGROUND

Mineral bone disorder (MBD) is a common complication of chronic kidney disease (CKD) even during the early stages. Bone alkaline phosphatase (BALP) is a marker of bone formation and plays a pivotal role in the mineralization process. Three BALP isoforms (B/I, B1 and B2) have been identified in healthy individuals and a fourth isoform (B1x) has been discovered in serum from dialysis patients. We investigated these BALP isoforms, type I procollagen intact amino-terminal propeptide (PINP), carboxy-terminal telopeptide of type I collagen (CTX) and tartrate-resistant acid phosphatase isoform 5b (TRACP5b), as well as bone mineral density (BMD) in predialysis CKD patients.

METHODS

PINP, CTX, TRACP5b and BALP isoforms were analysed in serum from 46 patients within CKD stages 3-5. BMD was determined by dual-energy x-ray absorptiometry.

RESULTS

PINP, TRACP5b and the BALP isoforms, B/I, B1 and B2, were independent predictors of total hip BMD in all patients. Furthermore, B/I predicted osteopaenia in the hip and in the distal 1/3 of the radius in CKD stage 3. The B1x isoform was detected in nine patients (20%), who had lower GFR, higher phosphate and calcium x phosphate product.

CONCLUSION

We found an association of BALP isoforms and other markers of bone turnover with total hip BMD, which predominantly comprises trabecular bone. The association of the new BALP isoform B1x with risk factors for vascular calcification leads us to hypothesize a possible role for B1x in this process. The significance of the BALP isoforms in CKD remains to be further explored in experimental and clinical settings in conjunction with bone histomorphometry.

Dioxins interfere with differentiation of osteoblasts and osteoclasts

We have previously shown that the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) affects bone growth, modelling and mechanical strength in vivo. In this study, we utilized differentiation of bone marrow stem cells to osteoblasts and osteoclasts as a model system to study the effects of TCDD on bones. Stem cells were isolated from bone marrow of femurs and tibias of rats and mice. Progress of osteoblastic differentiation was monitored by measuring mRNA expression levels of differentiation markers from control and TCDD-treated cells using quantitative RT-PCR. TCDD significantly and dose-dependently decreased the mRNA levels of RUNX2, alkaline phosphatase and osteocalcin. Also the activity of alkaline phosphatase was significantly inhibited in both rat and mice cells. In the case of osteoclasts, TCDD decreased the number of TRACP+ multinucleated cells, with corresponding decreases in the number of F-actin rings and the area of resorption. Studies in AHR-knockout mice indicated that TCDD has no effect on the expression of osteoblastic differentiation markers suggesting that TCDD mediates its effects by AHR. Both osteoblastic and osteoclastic effects took place at very low doses of TCDD, as in most cases 100 fM TCDD was enough to significantly affect the differentiation markers. Therefore, differentiation of osteoblasts and osteoclasts from bone marrow stem cells seems to be a very sensitive target for TCDD. Disrupting effects in osteoblastic cells, in addition to disturbed osteoclastogenesis, may thus play a role in adverse effects on bone quality in TCDD exposed animals.

Bone turnover markers are correlated with total skeletal uptake of 99mTc-methylene diphosphonate (99mTc-MDP)

Background

Skeletal uptake of ^99mTc labelled methylene diphosphonate (^99mTc-MDP) is used for producing images of pathological bone uptake due to its incorporation to the sites of active bone turnover. This study was done to validate bone turnover markers using total skeletal uptake (TSU) of ^99mTc-MDP.

Methods

22 postmenopausal women (52–80 years) volunteered to participate. Scintigraphy was performed by injecting 520 MBq of ^99mTc-MDP and taking whole body images after 3 minutes, and 5 hours. TSU was calculated from these two images by taking into account the urinary loss and soft tissue uptake. Bone turnover markers used were bone specific alkaline phosphatase (S-Bone ALP), three different assays for serum osteocalcin (OC), tartrate resistant acid phosphatase 5b (S-TRACP5b), serum C-terminal cross-linked telopeptides of type I collagen (S-CTX-I) and three assays for urinary osteocalcin (U-OC).

Results

The median TSU of ^99mTc-MDP was 23% of the administered activity. All bone turnover markers were significantly correlated with TSU with r-values from 0.52 (p = 0.013) to 0.90 (p < 0.001). The two resorption markers had numerically higher correlations (S-TRACP5b r = 0.90, S-CTX-I r = 0.80) than the formation markers (S-Total OC r = 0.72, S-Bone ALP r = 0.66), but the difference was not statistically significant. TSU did not correlate with age, weight, body mass index or bone mineral density.

Conclusion

In conclusion, bone turnover markers are strongly correlated with total skeletal uptake of ^99mTc-MDP. There were no significant differences in correlations for bone formation and resorption markers. This should be due to the coupling between formation and resorption.

Tartrate-resistant acid phosphatase (TRACP 5b): a biomarker of bone resorption rate in support of drug development: modification, validation and application of the BoneTRAP kit assay

A commercial kit assay of tartrate-resistant acid phosphatase (TRACP 5b) used for the diagnosis of bone resorption was modified with a 'Fit-For-Purpose' approach for drug development of anti-resorptive therapeutics. The modifications included changing the standard matrix from buffer to serum, using a consistent bulk reference material to prepare standards and quality controls (QC), and adding sample controls (SC) prepared from authentic sample pools. Method validation experiments were conducted for: inter- and intra-assay accuracy and precision, establishment of SC, range finding of different population groups, selectivity tests, parallelism and stability. The analytical range was 1.00-10.0 U/L and the total errors of lower limit of quantification (LLOQ) and upper limit of quantification (ULOQ) validation samples were 8% and 21%, respectively. Data of range finding experiment showed that serum samples should be collected in tubes instead of bags. Selectivity results showed accurate spike recovery among the majority of test samples from target populations. Samples were demonstrated to be stable for up to four freeze/thaw cycles and for 24 months at -70+/-10 degrees C. Our results show that the modified TRACP 5b method is reliable for the quantification of TRACP 5b in human serum samples to support clinical trials of bone resorptive effect reflected by TRACP 5b activities. The method was robust with similar assay performance characteristics shown in three bioanalytical laboratories.

Streptozotocin, type I diabetes severity and bone

As many as 50% of adults with type I (T1) diabetes exhibit bone loss and are at increased risk for fractures. Therapeutic development to prevent bone loss and/or restore lost bone in T1 diabetic patients requires knowledge of the molecular mechanisms accounting for the bone pathology. Because cell culture models alone cannot fully address the systemic/metabolic complexity of T1 diabetes, animal models are critical. A variety of models exist including spontaneous and pharmacologically induced T1 diabetic rodents. In this paper, we discuss the streptozotocin (STZ)-induced T1 diabetic mouse model and examine dose-dependent effects on disease severity and bone. Five daily injections of either 40 or 60 mg/kg STZ induce bone pathologies similar to spontaneously diabetic mouse and rat models and to human T1 diabetic bone pathology. Specifically, bone volume, mineral apposition rate, and osteocalcin serum and tibia messenger RNA levels are decreased. In contrast, bone marrow adiposity and aP2 expression are increased with either dose. However, high-dose STZ caused a more rapid elevation of blood glucose levels and a greater magnitude of change in body mass, fat pad mass, and bone gene expression (osteocalcin, aP2). An increase in cathepsin K and in the ratio of RANKL/OPG was noted in high-dose STZ mice, suggesting the possibility that severe diabetes could increase osteoclast activity, something not seen with lower doses. This may contribute to some of the disparity between existing studies regarding the role of osteoclasts in diabetic bone pathology. Examination of kidney and liver toxicity indicate that the high STZ dose causes some liver inflammation. In summary, the multiple low-dose STZ mouse model exhibits a similar bone phenotype to spontaneous models, has low toxicity, and serves as a useful tool for examining mechanisms of T1 diabetic bone loss.

Bone inflammation and altered gene expression with type I diabetes early onset

Type I diabetes is associated with bone loss and marrow adiposity. To identify early events involved in the etiology of diabetic bone loss, diabetes was induced in mice by multiple low dose streptozotocin injections. Serum markers of bone metabolism and inflammation as well as tibial gene expression were examined between 1 and 17 days post-injection (dpi). At 3 dpi, when blood glucose levels were significantly elevated, body, fat pad and muscle mass were decreased. Serum markers of bone resorption and formation significantly decreased at 5 dpi in diabetic mice and remained suppressed throughout the time course. An osteoclast gene, TRAP5 mRNA, was suppressed at early and late time points. Suppression of osteogenic genes (runx2 and osteocalcin) and induction of adipogenic genes (PPARgamma2 and aP2) were evident as early as 5 dpi. These changes were associated with an elevation of serum cytokines, but more importantly we observed an increase in the expression of cytokines in bone, supporting the idea that bone, itself, exhibits an inflammatory response during diabetes induction. This inflammation could in turn contribute to diabetic bone pathology. IFN-gamma (one of the key cytokines elevated in bone and known to be involved in bone regulation) deficiency did not prevent diabetic bone pathology. Taken together, our findings indicate that bone becomes inflamed with the onset of T1-diabetes and during this time bone phenotype markers become altered. However, inhibition of one cytokine, IFN-gamma was not sufficient to prevent the rapid bone phenotype changes.

Improved methods for testing antiresorptive compounds in human osteoclast cultures

We cultured human bone marrow-derived stem cells on bovine bone slices in 96-well plates in the presence of M-CSF and RANKL, allowing them to differentiate into osteoclasts. Secreted TRACP 5b was a useful endpoint measurement to demonstrate effects of inhibitors of osteoclast differentiation in the culture system, reflecting accurately the number of formed osteoclasts. Inhibitors of osteoclast activity were added into the cultures after the differentiation period, and the cultures were continued to allow the formed osteoclasts to resorb bone. CTX values obtained after the resorption period were normalized with TRACP 5b values obtained after the differentiation period, before adding the inhibitors. This normalization prevents false results that could be obtained from the presence of different amounts of osteoclasts in different wells before adding the inhibitors. These results demonstrate that the use of TRACP 5b and CTX allows rapid and reliable testing of antiresorptive compounds in human osteoclast cultures.

Age-related changes of serum tartrate-resistant acid phosphatase 5b and the relationship with bone mineral density in Chinese women

AIM

Osteoclastic activity is mainly assessed by measurement of urinary markers (eg C-terminal cross-linked telopeptides of type I collagen, N-terminal crosslinked telopeptides of type I collagen, etc), the levels of which could often be affected by renal clearance. Recently, serum tartrate-resistant acid phosphatase 5b (TRACP5b) has been used as an alternative serum marker to evaluate osteoclastic activity. We investigated the age-related changes of TRACP5b level and its association with bone mineral density (BMD) in Chinese women.

METHODS

Seven-hundred and twenty-two Chinese mainland women aged 20-79 years were recruited in the study. Serum TRACP5b level was measured using immunoassay to evaluate the state of bone resorption. Bone mineral density (BMD) (g/cm2) at lumbar spine 1-4 and proximal femur were measured by duelenergy X-ray absorptiometry.

RESULTS

The serum TRACP5b level reached a bottom value in premenopausal women aged 30-39, gradually increased in women aged 40-49, rapidly rose in women aged 50-59, and culminated with a maximum value in women aged 60-69 before a slow drop in women aged 70- 79. The average level of TRACP5b was significantly higher in postmenopausal women [(3.29+/-1.07) U/L] than in premenopausal women ([1.70+/-0.59] U/L). The levels of TRACP5b were inversely correlated with BMD at all measured sites (P<0.001). Furthermore, the level of TRACP5b was obviously higher in women with osteoporosis and osteopenia than those with normal bone mass (P<0.001).

CONCLUSION

We have established the reference values of serum TRACP5b in Chinese mainland women, and found that postmenopausal women had higher TRACP5b concentration than younger women. The results showed that serum TRACP5b was a sensitive and useful parameter for the evaluation of age-related changes of bone absorption.

Overexpression of bone sialoprotein leads to an uncoupling of bone formation and bone resorption in mice

The purpose of this study was to determine the effects of bone sialoprotein (BSP) overexpression in bone metabolism in vivo by using a homozygous transgenic mouse line that constitutively overexpresses mouse BSP cDNA driven by the cytomegalovirus (CMV) promoter. CMV-BSP transgenic (TG) mice and wildtype mice were weighed, and their length, BMD, and trabecular bone volume were measured. Serum levels of RANKL, osteocalcin, osteoprotegerin (OPG), TRACP5b, and PTH were determined. Bone histomorphometry, von Kossa staining, RT-PCR analysis, Western blot, MTS assay, in vitro mineralization assay, and TRACP staining were also performed to delineate phenotypes of this transgenic mouse line. Compared with wildtype mice, adult TG mice exhibit mild dwarfism, lower values of BMD, and lower trabecular bone volume. TG mice serum contained increased calcium levels and decreased PTH levels, whereas the levels of phosphorus and magnesium were within normal limits. TG mice serum also exhibited lower levels of osteoblast differentiation markers and higher levels of markers, indicating osteoclastic activity and bone resorption. H&E staining, TRACP staining, and bone histomorphometry showed that adult TG bones were thinner and the number of giant osteoclasts in TG mice was higher, whereas there were no significant alterations in osteoblast numbers between TG mice and WT mice. Furthermore, the vertical length of the hypertrophic zone in TG mice was slightly enlarged. Moreover, ex vivo experiments indicated that overexpression of BSP decreased osteoblast population and increased osteoclastic activity. Partly because of its effects in enhancing osteoclastic activity and decreasing osteoblast population, BSP overexpression leads to an uncoupling of bone formation and resorption, which in turn results in osteopenia and mild dwarfism in mice. These findings are expected to help the development of therapies to metabolic bone diseases characterized by high serum level of BSP.

Biomarkers for osteoporosis management: utility in diagnosis, fracture risk prediction and therapy monitoring

Osteoporosis is a systemic disease characterized by low bone mass and microarchitectural deterioration of bone tissue, resulting in an increased risk of fracture. While the level of bone mass can be estimated by measuring bone mineral density (BMD) using dual X-ray absorptiometry (DXA), its measurement does not capture all the risk factors for fracture. Quantitative changes in skeletal turnover can be assessed easily and non-invasively by the measurement of serum and urinary biochemical markers; the most sensitive markers include serum osteocalcin, bone specific alkaline phosphatase, the N-terminal propeptide of type I collagen for bone formation, and the crosslinked C- (CTX) and N- (NTX) telopeptides of type I collagen for bone resorption. Advances in our knowledge of bone matrix biochemistry, most notably of post-translational modifications in type I collagen, are likely to lead to the development of new biochemical markers that reflect changes in the material property of bone, an important determinant of bone strength. Among those, the measurement of the urinary ratio of native (alpha) to isomerized (beta) CTX - an index of bone matrix maturation - has been shown to be predictive of fracture risk independently of BMD and bone turnover. In postmenopausal osteoporosis, levels of bone resorption markers above the upper limit of the premenopausal range are associated with an increased risk of hip, vertebral, and nonvertebral fracture, independent of BMD. Therefore, the combined use of BMD measurement and biochemical markers is helpful in risk assessment, especially in those women who are not identified as at risk by BMD measurement alone. Levels of bone markers decrease rapidly with antiresorptive therapies, and the levels reached after 3-6 months of therapy have been shown to be more strongly associated with fracture outcome than changes in BMD. Preliminary studies indicate that monitoring changes of bone formation markers could also be useful to monitor anabolic therapies, including intermittent parathyroid hormone administration and, possibly, to improve adherence to treatment. Thus, repeated measurements of bone markers during therapy may help improve the management of osteoporosis in patients.

Utility of serum tartrate-resistant acid phosphatase (TRACP5b) as a bone resorption marker in patients with chronic kidney disease: independence from renal dysfunction

BACKGROUND

Serum tartrate-resistant acid phosphatase (TRACP) 5b levels were assessed in predialysis patients with chronic kidney disease (CKD). The aim of the study was to establish the usefulness of a new assay for TRACP5b in assessing bone turnover in these patients.

METHODS

Serum concentrations of two bone resorption markers, TRACP5b and N-terminal cross-linking telopeptide of type I collagen (NTX); two bone formation markers, bone specific alkaline phosphatase (bone ALP) and intact osteocalcin (OC[1-49]); and PTH were measured in 98 predialysis CKD patients.

RESULTS

Log serum TRACP5b and other bone markers were significantly negatively correlated with glomerular filtration rate (GFR) and positively correlated with log serum PTH, suggesting an increase in serum bone markers with development of secondary hyperparathyroidism. Multiple regression analysis including age, gender, BMI, the presence of diabetes, GFR and log serum PTH showed an association of log serum PTH with log serum TRACP5b and other bone markers. GFR was associated with log serum NTX and log OC[1-49], but not with log serum TRACP5b or log bone ALP. These data show that renal dysfunction does not influence serum TRACP5b and bone ALP, but has an influence on NTX and OC[1-49].

CONCLUSION

Serum TRACP5b may be a good marker for serum bone resorption in predialysis CKD patients, as it is not affected by renal dysfunction.

Ontogeny of skeletal maturation in the juvenile rat

Systemic regulation of the cellular processes that produce endochondral elongation and endochondral mineralization during postnatal skeletal maturation are not completely understood. In particular, a mechanism coupling the decline of cellular activity in the bone microenvironment to the onset of sexual maturity remains elusive. The purpose of this study was to empirically integrate the dynamic progression of bone mineral accrual and endochondral elongation as a function of animal age in growing male and female Sprague-Dawley rats. We used serial dual-energy X-ray absorptiometry (DXA) and radiography to study the temporal progression of bone growth and mineral accrual from weaning to adulthood. We observed that skeletal maturation proceeds in a pattern adequately described by the Gompertz function. During this period of growth, we found that serum markers of osteoblastic bone formation declined with age, while osteoclastic bone resorption activity remained unchanged. We also report a slight lag in the age at inflection in the rate of bone mineral accrual relative to the rate of tibial elongation and that both endochondral processes eventually come to asymptotic equilibrium by approximately 20 weeks of age. In addition, we studied tibial growth plate histomorphometry at select time points through 1 year of age. We report that, despite the histologic persistence of physeal cartilage, very little proliferative or elongative activity was measured in this tissue beyond 20 weeks of age. Taken together, these data provide insight to the temporal coordination of postnatal endochondral growth processes.

p38 mitogen-activated protein kinase inhibitor LY2228820 enhances bortezomib-induced cytotoxicity and inhibits osteoclastogenesis in multiple myeloma; therapeutic implications

The interaction between multiple myeloma (MM) cells and the bone marrow (BM) microenvironment induces proliferation and survival of MM cells, as well as osteoclastogenesis. This study investigated the therapeutic potential of novel p38 mitogen-activated protein kinase (p38MAPK) inhibitor LY2228820 (LY) in MM. Although cytotoxicity against MM cell lines was modest, LY significantly enhanced the toxicity of bortezomib by down-regulating bortezomib-induced heat shock protein 27 phosphorylation. LY inhibited interleukin-6 secretion from long term cultured-BM stromal cells and BM mononuclear cells (BMMNCs) derived from MM patients in remission. LY also inhibited macrophage inflammatory protein-1alpha secretion from patient MM cells and BMMNCs as well as normal CD14 positive osteoclast precursor cells. Moreover, LY significantly inhibited in vitro osteoclastogenesis from CD14 positive cells induced by macrophage-colony stimulating factor and soluble receptor activator of nuclear factor-kappaB ligand. Finally, LY also inhibited in vivo osteoclatogenesis in a severe combined immunodeficiency mouse model of human MM. These results suggest that LY represents a promising novel targeted approach to improve MM patient outcome both by enhancing the effect of bortezomib and by reducing osteoskeletal events.

Serum levels of TRAP5b, a new bone resorption marker unaffected by renal dysfunction, as a useful marker of cortical bone loss in hemodialysis patients

Tartrate-resistant acid phosphatase (TRAP) 5b is a new marker of bone resorption that is unaffected by renal dysfunction. The significance of TRAP5b was assessed in hemodialysis (HD) patients. Serum concentrations of TRAP5b and cross-linked N-telopeptide of type I collagen (NTX) were determined as bone resorption markers, and those of bone alkaline phosphatase (BAP) and intact osteocalcin (OC) were measured as bone formation markers in 58 HD patients. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry twice in the distal third of the radius, with a 2-year interval between measurements. Serum TRAP5b correlated significantly with BAP, intact OC, intact parathyroid hormone (PTH), and especially serum NTX. TRAP5b, NTX, BAP, and intact OC all correlated significantly with BMD at the time of the second measurement; and TRAP5b, NTX, and intact OC, but not BAP and intact PTH, correlated significantly with the annual change in BMD during the 2-year period. Among the bone markers, patients in the highest tertile for serum TRAP5b and intact OC showed the fastest rate of cortical bone loss. The sensitivity and specificity for detection of rapid bone loss were 57.9% and 76.9%, respectively, for serum TRAP5b. Measurement of serum TRAP5b, as well as intact OC, may be a clinically relevant assay for estimation of bone metabolic status in HD patients, although serum intact OC accumulates in uremic serum.

Understanding the pathology and mechanisms of type I diabetic bone loss

Type I (T1) diabetes, also called insulin dependent diabetes mellitus (IDDM), is characterized by little or no insulin production and hyperglycemia. One of the less well known complications of T1-diabetes is bone loss which occurs in humans and animal models. This complication is receiving increased attention because T1-diabetics are living longer due to better therapeutics, and are faced with their existing health concerns being compounded by complications associated with aging, such as osteoporosis. Both male and female, endochondrial and intra-membranous, and axial and appendicular bones are susceptible to T1-diabetic bone loss. Exact mechanisms accounting for T1-diabetic bone loss are not known. Existing data indicate that the bone defect in T1-diabetes is anabolic rather than catabolic, suggesting that anabolic therapeutics may be more effective in preventing bone loss. Potential contributors to T1-diabetic suppression of bone formation are discussed in this review and include: increased marrow adiposity, hyperlipidemia, reduced insulin signaling, hyperglycemia, inflammation, altered adipokine and endocrine factors, increased cell death, and altered metabolism. Differences between T1-diabetic- and age-associated bone loss underlie the importance of condition specific, individualized treatments for osteoporosis. Optimizing therapies that prevent bone loss or restore bone density will allow T1-diabetic patients to live longer with strong healthy bones.

Secreted tartrate-resistant acid phosphatase 5b is a Marker of osteoclast number in human osteoclast cultures and the rat ovariectomy model

PURPOSE

To study the effects of estrogen withdrawal on osteoclast number and osteoclast activity in the rat ovariectomy (OVX) model.

METHODS

We first cultured human CD34+ osteoclast precursor cells on bovine bone slices, allowing them to differentiate into mature resorbing osteoclasts. Secreted tartrate-resistant acid phosphatase 5b (TRACP 5b) and C-terminal cross-linked telopeptides of type I collagen (CTX) were determined from the culture medium. TRACP 5b correlated strongly with osteoclast number and CTX with osteoclast activity, facilitating their subsequent use in the rat OVX model. An 8 week OVX study was then performed including sham-operated rats receiving vehicle, OVX rats receiving vehicle, and OVX rats receiving 10 microg/kg/day 17 beta-estradiol (E2). Trabecular bone parameters were determined from the tibial metaphysis using peripheral quantitative computed tomography and histomorphometry. Osteoclast number was normalized with bone perimeter (N.Oc/B.Pm) and tissue area (N.Oc/T.Ar, indicating absolute number of osteoclasts). TRACP 5b and CTX were determined from fasting serum samples.

RESULTS

Trabecular bone parameters indicated substantial bone loss after OVX that was prevented by E2. N.Oc/B.Pm increased after OVX, while N.Oc/T.Ar and TRACP 5b decreased, and TRACP 5b correlated strongly with N.Oc/T.Ar. However, CTX values increased after OVX, and the "resorption index" CTX/TRACP 5b showed more substantial changes than either CTX or TRACP 5b alone.

CONCLUSION

These results show that TRACP 5b is a reliable marker of osteoclast number, and the index CTX/TRACP 5b is a useful parameter in rat OVX model. The high elevation of CTX/TRACP 5b values by OVX demonstrates that estrogen withdrawal generates high activity of osteoclasts in the rat OVX model.

Reference intervals of serum tartrate-resistant acid phosphatase type 5b activity measured with a novel assay in Japanese subjects

Among the isotypes of serum tartrate-resistant acid phosphatase (TRACP), only type 5b (TRACP-5b) is derived from osteoclasts, and it is necessary to develop an assay specific for this TRACP-5b for evaluation of osteoclastic activity. Recently, a novel assay system for TRACP-5b called the fragments absorbed immunocapture enzymatic assay (FAICEA) has been developed. With two unique monoclonal antibodies, one that is highly specific for TRACP-5b and another which absorbs inactive TRACP-5b fragments that interfere with measuring active TRACP-5b, this assay provides correct measurement of TRACP-5b activity in the serum without interference by the inactive fragments of TRACP-5b and other isotypes of TRACP, especially TRACP-5a. To study the reference data of Japanese subjects, we measured TRACP-5b activity in the serum of 320 men (age, 20-82 years) and 466 women [315 premenopausal (age, 18-55 years) and 151 postmenopausal (age, 45-77 years)] with this novel assay. In men, serum TRACP-5b activity did not vary significantly with age. The postmenopausal women had significantly higher serum TRACP-5b activity than the premenopausal women. The reference intervals (logarithmic mean +/-1.96 SD) for men, premenopausal women, and postmenopausal women were 1.7-5.9 U/l, 1.2-4.4 U/l, and 2.5-7.6 U/l, respectively.

Associations between HLA-DRB1, RANK, RANKL, OPG, and IL-17 genotypes and disease severity phenotypes in Japanese patients with early rheumatoid arthritis

We examined associations between human leukocyte antigen DRB1 (HLA-DRB1) shared epitope (SE), receptor activator of nuclear factor-kappaB (RANK), RANK ligand (RANKL), osteoprotegerin (OPG), and interleukin 17 (IL-17) genotypes with age of disease onset and radiographic progression in Japanese patients with early rheumatoid arthritis (RA). HLA-DRB1 genotypes were evaluated in 123 patients with early RA (98 female, 25 male) within 1 year of symptom onset. In 72 patients, radiographic progression over a 2-year period was evaluated using Larsen's methods, and genotypes of three polymorphic sites in RANK, five sites in RANKL, two sites in OPG, and three sites in IL-17 were determined by direct polymerase chain reaction sequencing. Possession of an SE allele was significantly associated with earlier disease onset in females (median 46.9 vs 51.9 years in SE- patients; P = 0.04). Single nucleotide polymorphisms (SNPs) in RANKL (rs2277438, P = 0.028) and IL-17 (rs3804513, P = 0.049) were significantly associated with radiographic progression at 2 years. RANKL-G-, SE- patients (n = 12) had significantly less joint damage than did RANKL-G+, SE- patients (n = 11; P = 0.0038), RANKL-G-, SE+ patients (n = 21; P = 0.0018) and RANKL-G+, SE+ patients (n = 28; P = 0.0024). In Japanese RA patients, HLA-DRB1 SE alleles are associated with disease onset at an earlier age, as has been observed in Caucasian RA patients. In addition, SNPs in RANKL and IL-17 may be associated with radiographic progression in Japanese patients with early RA.

Local delivery of osteoprotegerin inhibits mechanically mediated bone modeling in orthodontic tooth movement

INTRODUCTION

The RANKL-OPG axis is a key regulator of osteoclastogenesis and bone turnover activity. Its contribution to bone resorption under altered mechanical states, however, has not been fully elucidated. Here we examined the role of OPG in regulating mechanically induced bone modeling in a rat model of orthodontic tooth movement.

METHODS

The maxillary first molars of male Sprague-Dawley rats were moved mesially using a calibrated nickel-titanium spring attached to the maxillary incisor teeth. Two different doses (0.5 mg/kg, 5.0 mg/kg) of a recombinant fusion protein (OPG-Fc), were injected twice weekly mesial to the first molars. Tooth movement was measured using stone casts that were scanned and magnified. Changes in bone quantity were measured using micro-computed tomography and histomorphometric analysis was used to quantify osteoclasts and volumetric parameters. Finally, circulating levels of TRAP-5b (a bone resorption marker) was measured using enzyme-linked immunosorbent assay.

RESULTS

The 5.0 mg/kg OPG-Fc dose showed a potent reduction in mesial molar movement and osteoclast numbers compared to controls (p<0.01). The molar movement was inhibited by 45.7%, 70.6%, and 78.7% compared to controls at days 7, 14, and 21 respectively, with the high dose of OPG. The 0.5 mg dose also significantly (p<0.05) inhibited molar movement at days 7 (43.8%) and 14 (31.8%). While incisor retraction was also decreased by OPG-Fc, the ratio of incisor to molar tooth movement was markedly better in the high-dose OPG group (5.2:1, p<0.001) compared to the control group (2.3:1) and the low-dose OPG group (2.0:1).

CONCLUSIONS

Local delivery of OPG-Fc inhibits osteoclastogenesis and tooth movement at targeted dental sites.

Prediction of bone loss using biochemical markers of bone turnover

The association between baseline levels of eleven bone turnover markers and 5-year rate of bone density change was prospectively studied in a population-based sample of 601 75-year-old women. Several bone formation and resorption markers as well as urinary osteocalcin were modestly correlated to rate of bone density change.

INTRODUCTION

Prediction of bone loss by bone turnover markers (BTMs) has been investigated with conflicting results. There is limited information in the elderly.

METHODS

Eleven bone turnover markers were analyzed in 75-year old women in the OPRA study (n = 601) and compared to the 5-year change of areal bone mineral density (aBMD) in seven skeletal regions.

RESULTS

Annual aBMD change varied between +0.4% (spine) and -2.0% (femoral neck). Significant associations (p < 0.01) were found for four different serum osteocalcins (S-OCs) (standardized regression coefficient -0.20 to -0.22), urinary deoxypyridinoline (-0.19), serum TRACP5b (-0.19), serum CTX-I (-0.21), two of the three urinary osteocalcins (U-OCs) (-0.16) and aBMD change of the leg region (derived from the total body measurement). After adjustment for baseline aBMD, associations were found for all S-OCs (-0.11 to -0.16), two of the three U-OCs (-0.14 to -0.16) and aBMD change at the total hip, and for three of the four S-OCs (-0.14 to -0.15), S-TRACP5b (-0.11), two of the three U-OCs (-0.14 to -0.15) and aBMD change at the femoral neck. There were no significant results concerning aBMD change at the spine.

CONCLUSION

This study indicates that BTMs are correlated with aBMD loss in some skeletal regions in elderly women.

The semiquantitative bone scintigraphy index correlates with serum tartrate-resistant acid phosphatase activity in breast cancer patients with bone metastasis

OBJECTIVE

To determine if a correlation exists between the semiquantitative bone scintigraphy index (SQBSI) and serum tartrateresistant acid phosphatase 5b (TRACP5b) activity, a novel osteoclast marker that has been shown to be useful for monitoring bone metastasis in breast cancer (BC) patients.

PARTICIPANTS AND METHODS

Among patients enrolled in 2 prospective studies conducted at Tri-Service General Hospital, Taipei, Taiwan, between December 2000 and July 2002, we identified post hoc 52 patients with both BC and bone metastasis who had detailed records of clinical condition, bone scintigraphy, and concordant serum TRACP5b levels. Between January 1, 2003, and December 31, 2005, we performed bone scintigraphy and serum TRACP5b activity assays to monitor these patients, while they were treated according to clinical need. To assess clinical condition, we obtained information from patient records, such as performance status and visual analogue pain score, as well as from selected laboratory tests for tumor markers and serum TRACP5b activity. Those patients with BC and bone metastasis who had undergone whole-body bone scintigraphy and serum TRACP5b activity determination before any therapeutic intervention were designated the pretreated group (n=30). We developed our own formula for calculating SQBSI on the basis of bone scintigraphy findings.

RESULTS

A significant correlation was observed between SQBSI and serum TRACP5b activity in pretreated BC patients with bone metastasis, but the strength of the correlation lessened after treatment. No significant correlation was noted between the change in serum TRACP5b activity and the change in SQBSI in treated patients. Compared with the change in SQBSI, the change in TRACP5b activity had higher sensitivity, specificity, and positive predictive value as well as a greater likelihood ratio for reflecting the clinical scenarios of bone morbidity over time.

CONCLUSION

As monitors of the response of bone metastasis in BC to treatment, serial determinations of serum TRACP5b activity and SQBSI were both shown to be useful by our preliminary findings. However, serum TRACP5b activity proved the better monitoring tool. If follow-up studies were conducted within 6 months, the combined use of SQBSI and TRACP5b would allow distinction of genuine disease progression from the "flare" phenomenon, in which bone metastasis can appear to progress in bone scintigraphic images although clinical symptoms improve. Larger prospective studies are needed to confirm these findings.

Sequence and TLR9 independent increase of TRACP expression by antisense DNA and siRNA molecules

Reactive oxygen species generating activity of tartrate-resistant acid phosphatase (TRACP) has been suggested to have several functions in TRACP expressing bone resorbing osteoclasts, macrophages, and dendritic cells. This work aimed to study the TRACP knock down phenotype in osteoclasts by using antisense DNA and RNA interference methods. Unexpectedly, both TRACP specific DNA oligonucleotides and siRNA molecules extensively increased the TRACP expression in human osteoclasts and monocytes. Toll-like receptor 9 (TLR9) is an immunity sensor for CpG motifs in DNA. We cultured bone marrow-derived osteoclast precursor cells from wild-type and TLR9-/- mice with CpG and non-CpG DNA oligonucleotides, and observed that the increased TRACP expression was sequence and TLR9 independent. In contrast, cells with increased TRACP activity showed decreased activity of tartrate-sensitive acid phosphatases.

CONCLUSION

DNA oligonucleotides and RNA molecules extensively increase TRACP expression in monocyte-macrophage lineage. These results suggest a potential role of TRACP in pathogen recognition and in innate immunity.

Markers of bone metabolism in hemodialyses and hemodiafiltration

Renal osteodystrophy is a common complication of chronic renal failure and renal replacement therapy. The purpose of the study was to assess whether hemodialysis (HD) or hemodiafiltration (HDF) affects bone turnover. In all, 45 HD and 17 HDF patients were evaluated with respect to bone metabolism markers. We assessed PTH; markers of bone formation-alkaline phosphatase and its bone isoform, osteocalcin; markers of bone resorption- PICP, ICTP; Ctx; beta2-microglobulin; and urinary DPD. BMD were determined for femoral neck and lumbar spine (L2-L4) using DEXA. Hemodialyzed patients had lower calcidiol, calcitriol, and BMD in the femur neck, and higher phosphate, Kt/V, residual renal function, venous pH, osteocalcin, ALP, bALP, DPD, beta2-microglobulin, ICTP, Ctx, osteoprotegerin, and RANKL than patients on HDF. HDF seems to ameliorate bone metabolism in comparison with HD. Bone turnover in end-stage renal failure might be affected to some extent by the choice of renal replacement therapy.

Biochemical markers in preclinical models of osteoporosis

Although several treatments for osteoporosis exist, further understanding of the mode of action of current treatments, as well as development of novel treatments, are of interest. Thus, preclinical models of osteoporosis are very useful, as they provide the possibility for gaining knowledge about the cellular mechanisms underlying the disease and for studying pharmaceutical prevention or intervention of the disease in simple and strictly controlled systems. In this review, we present a comprehensive collection of studies using biochemical markers of bone turnover for investigation of preclinical models of osteoporosis. These range from pure and simple in vitro systems, such as osteoclast cultures, to ex vivo models, such as cultures of embryonic murine tibiae and, finally, to in vivo models, such as ovariectomy and orchidectomy of rats. We discuss the relevance of the markers in the individual models, and compare their responses to those observed using 'golden standard' methods.

Assessment of osteoclast number and function: application in the development of new and improved treatment modalities for bone diseases

Numerous experimental and clinical observations suggest that overall changes in bone resorption during menopause or treatment with hormone replacement therapy (HRT) are combined effects of changes in osteoclast number and function. Moreover, due to a coupling between osteoclastic bone resorption and osteoblastic bone formation, pronounced alteration of osteoclast number will eventually lead to alteration of osteoblastic bone formation. Fragments of type I collagen, such as the C- and N-terminal telopeptides of collagen type I (CTX and NTX, respectively), are generated during bone resorption and hence can be used as surrogate markers of osteoclast function. Circulating levels of different enzymes in the serum, such as TRAP 5b and cathepsin K are proportional to the number of osteoclasts, and hence can be used as surrogate markers of osteoclast number. Since antiresorptive effects can be obtained in different ways, we felt it was timely to discuss the different scenarios, highlight differences specific to different pharmacological interventions with different mechanisms of action, and discuss how these bone markers can assist us in a deeper analysis of the pharmacodynamics and safety profile of existing and upcoming drug candidates.

The incidence of osteopenia and osteoporosis in women with hip osteoarthritis scheduled for cementless total joint replacement

INTRODUCTION

The co-existence of osteoporosis (OP) and osteoarthritis (OA) remains obscure. No systematic studies have been carried out to exclude the possibility that especially female osteoarthritic patients selected for cementless total hip arthroplasty (THA) suffer from primary or secondary OP.

METHODS

A subgroup of fifty-three female patients (average age, 64.7 years) with advanced primary hip OA scheduled for cementless THA were recruited for DXA and laboratory screening. Before surgery, bone mineral density (BMD) of the lumbar spine, the proximal femurs and the distal forearm were measured. The serum concentrations of calcium, 25-hydroxyvitamin D, parathyroid hormone and biochemical markers of bone resorption and formation were determined to exclude secondary OP.

RESULTS

The prevalence of OP (T score <-2.5) and osteopenia (-1.0 >T score >-2.5) were 28% and 45%, respectively. Statistically, OP was related to patient's age, low BMI, postmenopausal status and not having estrogen replacement therapy. Five patients (9%) had laboratory findings of secondary OP. Two of them were found to have a parathyroid adenoma. The prevalence of vitamin D insufficiency [S-25(OH)D levels <or=50 nmol/l] was 36% (n=19). As a sign of high bone turnover, the patients with reduced BMD values showed significantly increased serum levels of osteocalcin (p=0.049), intact procollagen type I N propeptide (p=0.040) and N-terminal crosslinking telopeptide of type I collagen (p=0.046). The BMC of the femoral necks of the osteoarthritic hips were significantly higher (p<0.001) and the BMC of the trochanter regions significantly lower (p=0.005) compared to the contralateral hips.

CONCLUSION

Against a general belief, OA does not seem to protect a patient from generalized primary OP. The majority (74%) of the female hip OA patients were osteopenic or osteoporotic with signs of increased bone turnover. The observed prevalence of reduced BMD corresponds with the published data of age-matched population. An unexpectedly high number of patients required preoperative consultation with an endocrinologist. The altered distribution of BMD observed in the proximal femurs may explain the lower prevalence of fractures reported in the femoral necks of osteoarthritic hips.

Tartrate-resistant acid phosphatase 5b (TRAP 5b) as a marker of osteoclast activity in the early phase after cementless total hip replacement

BACKGROUND

After total hip replacement, increased bone metabolism is seen. A local periprosthetic osteopenia can be measured by dual-energy X-ray absorptiometry (DXA), but it is still unkown whether biochemical markers can be used to monitor the local remodeling at an earlier stage.

PATIENTS AND METHODS

In this prospective study we compared the biochemical markers tartrate-resistant acid phosphatase 5b (TRAP 5b), bone ALP, osteocalcin and CrossLaps with periprosthetic DXA in 17 consecutive patients after uncemented total hip replacement.

RESULTS

We found a highly significant early increase in TRAP 5b after 2 weeks and 6 weeks, which was followed by a densitometrically detectable decrease in bone mineral density after 26 weeks, especially in periprosthetic section Gruen zone 7. Bone ALP and osteocalcin levels as markers of osteoblast activity, and also Cross-Laps as a further marker of osteoclast activity, did not appear to allow any significant prediction of local bone remodeling.

DISCUSSION

Our findings show that TRAP 5b is a sensitive parameter for monitoring of osteoclast activity after cementless total hip replacement, and may predict local osteopenia.