Measurement of urinary excretion of nonisomerized and beta-isomerized forms of type I collagen breakdown products to monitor the effects of the bisphosphonate zoledronate in Paget's disease

Paget's Disease of the Bone and Lynch Syndrome: An Exceptional Finding

Our objective is to present an exceptional case of a patient diagnosed with Paget's disease of the bone (PDB) while being confirmed with Lynch syndrome (LS). A 44-year-old woman was admitted for progressive pain in the left forearm 2 years ago, and was partially relieved since admission by non-steroidal anti-inflammatory drugs. Suggestive imaging findings and increased blood bone turnover markers helped the diagnosis of PDB. She was offered zoledronate 5 mg. She had two more episodes of relapse, and a decision of new medication was taken within the following years (a second dose of zoledronate, as well as denosumab 60 mg). Her family history showed PDB (mother) and colorectal cancer (father). Whole exome sequencing was performed according to the manufacturer's standard procedure (Ion AmpliSeq™ Exome RDY S5 Kit). A heterozygous pathogenic variant in the SQSTM1 gene (c.1175C>T, p.Pro392Leu) was confirmed, consistent with the diagnosis of PDB. Additionally, a heterozygous pathogenic variant of MSH2 gene (c.2634+1G>T) was associated with LS. The patient's first-degree relatives (her brother, one of her two sisters, and her only daughter) underwent specific genetic screening and found negative results, except for her daughter, who tested positive for both pathogenic variants while being clinically asymptomatic. The phenotype influence of either mutation is still an open issue. To our current knowledge, no similar case has been published before. Both genetic defects that led to the two conditions appeared highly transmissible in the patient's family. The patient might have an increased risk of osteosarcoma and chondrosarcoma, both due to PDB and LS, and a review of the literature was introduced in this particular matter. The phenotypic expression of the daughter remains uncertain and is yet to be a lifelong follow-up as the second patient harbouring this unique combination of gene anomalies.

Bone Turnover Markers: Basic Biology to Clinical Applications

Bone turnover markers (BTMs) are used widely, in both research and clinical practice. In the last 20 years, much experience has been gained in measurement and interpretation of these markers, which include commonly used bone formation markers bone alkaline phosphatase, osteocalcin, and procollagen I N-propeptide; and commonly used resorption markers serum C-telopeptides of type I collagen, urinary N-telopeptides of type I collagen and tartrate resistant acid phosphatase type 5b. BTMs are usually measured by enzyme-linked immunosorbent assay or automated immunoassay. Sources contributing to BTM variability include uncontrollable components (e.g., age, gender, ethnicity) and controllable components, particularly relating to collection conditions (e.g., fasting/feeding state, and timing relative to circadian rhythms, menstrual cycling, and exercise). Pregnancy, season, drugs, and recent fracture(s) can also affect BTMs. BTMs correlate with other methods of assessing bone turnover, such as bone biopsies and radiotracer kinetics; and can usefully contribute to diagnosis and management of several diseases such as osteoporosis, osteomalacia, Paget's disease, fibrous dysplasia, hypophosphatasia, primary hyperparathyroidism, and chronic kidney disease-mineral bone disorder.

Clinical utility of bone markers in various diseases

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

Bisphosphonates for Paget's disease of bone in adults

BACKGROUND

Bisphosphonates are considered to be the treatment of choice for people with Paget's disease of bone. However, the effects of bisphosphonates on patient-centred outcomes have not been extensively studied. There are insufficient data to determine whether reducing and maintaining biochemical markers of bone turnover to within the normal range improves quality of life and reduces the risk of complications.

OBJECTIVES

To assess the benefits and harms of bisphosphonates for adult patients with Paget's disease of bone.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, ISI Web of Knowledge and trials registers up to March 2017. We searched regulatory agency published information for rare adverse events.

SELECTION CRITERIA

Randomised controlled trials (RCTs) of bisphosphonates as treatment for Paget's disease in adults.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened search results, extracted data and assessed studies for risk of bias. We used standard methodological procedures expected by The Cochrane Collaboration.

MAIN RESULTS

We included 20 trials (25 reports, 3168 participants). Of these, 10 trials (801 participants) compared bisphosphonates (etidronate, tiludronate, ibandronate, pamidronate, olpadronate, alendronate, risedronate, zoledronate) versus placebo, seven compared two bisphosphonates (992 participants), one trial compared a bisphosphonates with a bisphosphonate plus calcitonin (44 participants), and two studies, the largest trial (1331 participants) and its interventional extension study (502 participants), compared symptomatic treatment and intensive treatment where the goal was to normalise alkaline phosphatase.Most studies were assessed at low or unclear risk of bias. Six of 10 studies comparing bisphosphonates versus placebo were assessed at high risk of bias, mainly around incomplete outcome data and selective outcome reporting.Participant populations were reasonably homogeneous in terms of age (mean age 66 to 74 years) and sex (51% to 74% male). Most studies included participants who had elevated alkaline phosphatase levels whether or not bone pain was present. Mean follow-up was six months.Bisphosphonates versus placeboBisphosphonates tripled the proportion (31% versus 9%) of participants whose bone pain disappeared (RR 3.42, 95% confidence interval (CI) 1.31 to 8.90; 2 studies, 205 participants; NNT 5, 95% CI 1 to 31; moderate-quality evidence). This result is clinically important. Data were consistent when pain change was measured as any reduction (RR 1.97, 95% CI 1.29 to 3.01; 7 studies, 481 participants).There was uncertainty about differences in incident fractures: 1.4% fractures occurred in the bisphosphonates group and none in the placebo group (RR 0.89, 95% CI 0.18 to 4.31; 4 studies, 356 participants; very low-quality evidence).None of the studies reported data on orthopaedic surgery, quality of life or hearing thresholds.Results regarding adverse effects and treatment discontinuation were uncertain. There was a 64% risk of mild gastrointestinal adverse events in intervention group participants and 48% in the control group (RR 1.32, 95% CI 0.91 to 1.92; 6 studies, 376 participants; low-quality evidence). The likelihood of study participants discontinuing due to adverse effects was slightly higher in intervention group participants (4.4%) than the control group (4.1%) (RR 1.01, 95% CI 0.41 to 2.52; 6 studies, 517 participants; low-quality evidence). Zoledronate was associated with an increased risk of transient fever or fatigue (RR 2.57, 95% CI 1.21 to 5.44; 1 study, 176 participants; moderate-quality evidence).Bisphosphonates versus active comparatorMore participants reported pain relief with zoledronate than pamidronate (RR 1.30, 95% CI 1.10 to 1.53; 1 study, 89 participants; NNT 5, 95% CI 3 to 11) or risedronate (RR 1.36, 95% CI 1.06 to 1.74; 1 study, 347 participants; NNT 7, 95% CI 4 to 24; very low quality evidence). This result is clinically important.There was insufficient evidence to confirm or exclude differences in adverse effects of bisphosphonates (RR 1.05, 95% CI 0.95 to 1.76; 2 studies, 437 participants; low-quality evidence) and treatment discontinuation (2 studies, 437 participants) (RR 2.04, 95% CI 0.43 to 9.59; 2 studies, 437 participants; very low-quality evidence).Intensive versus symptomatic treatmentThere was no consistent evidence of difference to response in bone pain, bodily pain or quality of life in participants who received intensive versus symptomatic treatment.Inconclusive results were observed regarding fractures and orthopaedic procedures for intensive versus symptomatic treatment (intensive treatment for fracture: RR 1.84, 95% CI 0.76 to 4.44; absolute risk 8.1% versus 5.2%; orthopaedic procedures: RR 1.58, 95% CI 0.80 to 3.11; absolute risk 5.6% versus 3.0%; 1 study, 502 participants; low-quality evidence).There was insufficient evidence to confirm or exclude an important difference in adverse effects between intensive and symptomatic treatment (RR 1.05, 95% CI 0.79 to 1.41; low-quality evidence).There was insufficient evidence to confirm or exclude an important difference of risk of rare adverse events (including osteonecrosis of the jaw) from the regulatory agencies databases.

AUTHORS' CONCLUSIONS

We found moderate-quality evidence that bisphosphonates improved pain in people with Paget's disease of bone when compared with placebo. We are uncertain about the results of head-to-head studies investigating bisphosphonates. We found insufficient evidence of benefit in terms of pain or quality of life from intensive treatment. Information about adverse effects was limited, but serious side effects were rare, and rate of withdrawals due to side effects was low.

The Role of Collagen Organization on the Properties of Bone

Bone is a complex tissue constituted by a collagen matrix filled in with crystal of hydroxyapatite (HAP). Bone mechanical properties are influenced by the collagen matrix which is organized into hierarchical structures from the individual type I collagen heterotrimer flanked by linear telopeptides at each end to the collagen fibrils that are interconnected by enzymatic and non-enzymatic cross-links. Although most studies focused on the role of collagen cross-links in bone strength, other organizational features may also play a role. At the molecular level it has been shown that homotrimer of type I collagen found in bone tissue of some patients with osteogenesis imperfecta (OI) is characterized by decreased mechanical competence compared to the regular heterotrimer. The state of C-telopeptide isomerization-which can be estimated by the measurement in body fluids of the native and isomerized isoforms-has also been shown to be associated with bone strength, particularly the post-yield properties independent of bone size and bone mineral density. Other higher hierarchical features of collagen organization have shown to be associated with changes in bone mechanical behavior in ex vivo models and may also be relevant to explain bone fragility in diseases characterized by collagen abnormalities e.g., OI and Paget's disease. These include the orientation of collagen fibrils in a regular longitudinal direction, the D-spacing period between collagen fibrils and the collagen-HAP interfacial bonding. Preliminary data indicate that some of these organizational features can change during treatment with bisphosphonate, raloxifene, and PTH suggesting that they may contribute to their anti-fracture efficacy. It remains however to be determined which of these parameters play a specific and independent role in bone matrix properties, what is the magnitude of mechanical strength explained by collagen organization, whether they are relevant to explain osteoporosis-induced bone fragility, and how they could be monitored non-invasively to develop efficient bone quality biomarkers.

Bone turnover markers in Paget's disease of the bone: A Systematic review and meta-analysis

The aim of this systematic review and meta-analysis is to study the utility of the commonly used bone turnover markers in evaluating disease activity in patients with Paget's disease of bone before and after treatment with bisphosphonates. We found good correlation between the bone turnover marker concentrations and disease activity assessed by bone scintigraphy.

INTRODUCTION

Paget's disease of bone is a common skeletal disorder of the elderly. Bone turnover marker concentrations are used for diagnosis and follow-up. We aimed to compare the available bone turnover markers and determine their utility in assessing disease activity when compared to quantitative bone scintigraphy.

METHODS

We conducted a systematic review and meta-analysis searching MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and Scopus. We evaluated total alkaline phosphatase (total ALP), bone-specific alkaline phosphatase (bone ALP), procollagen type 1 amino-terminal propeptide (P1NP), serum, and urine C-terminal telopeptide (uCTx and sCTx, respectively), and urine N-terminal telopeptide (uNTx). The main outcome of interest was the correlation of disease activity with concentrations of bone turnover markers in Paget's disease patients before and after treatment with bisphosphonates. Correlation coefficients were pooled across studies using the random effects model.

RESULTS

We included 17 observational studies and one trial reporting on 953 patients. Prior to treatment, all studied bone turnover markers had moderate to strong correlation with scintigraphic indices (correlation coefficients ranging from 0.58 to 0.80) with no statistically significant difference between the bone turnover markers overall (p = 0.08). P1NP, uNTx, and bone ALP tend to have higher correlation with scintigraphy. After starting treatment with bisphosphonate, there was moderate to strong correlation with disease activity with all markers except bone ALP (correlation coefficients ranging from 0.43 to 0.70).

CONCLUSION

The findings of this meta-analysis suggest the Paget's disease activity is best monitored by following P1NP levels. However, total ALP, bone ALP, and uNTx are good alternatives as markers of disease activity in untreated patients. Total ALP and uNTx can be useful in following patients with Paget's disease after treatment if P1NP is not available. Clinicians, however, should take availability, cost, and the presence of liver disease into consideration when deciding which bone turnover marker is most appropriate when evaluating patients with Paget's disease.

Modifications to nano- and microstructural quality and the effects on mechanical integrity in Paget's disease of bone

Paget's disease of bone (PDB) is the second most common bone disease mostly developing after 50 years of age at one or more localized skeletal sites; it is associated with severely high bone turnover, bone enlargement, bowing/deformity, cracking, and pain. Here, to specifically address the origins of the deteriorated mechanical integrity, we use a cohort of control and PDB human biopsies to investigate multiscale architectural and compositional modifications to the bone structure (ie, bone quality) and relate these changes to mechanical property measurements to provide further insight into the clinical manifestations (ie, deformities and bowing) and fracture risk caused by PDB. Here, at the level of the collagen and mineral (ie, nanometer-length scale), we find a 19% lower mineral content and lower carbonate-to-phosphate ratio in PDB, which accounts for the 14% lower stiffness and 19% lower hardness promoting plastic deformation in pathological bone. At the microstructural scale, trabecular regions are known to become densified, whereas cortical bone loses its characteristic parallel-aligned osteonal pattern, which is replaced with a mosaic of lamellar and woven bone. Although we find this loss of anisotropic alignment produces a straighter crack path in mechanically-loaded PDB cases, cortical fracture toughness appears to be maintained due to increased plastic deformation. Clearly, the altered quality of the bone structure in PDB affects the mechanical integrity leading to complications such as bowing, deformities, and stable cracks called fissure fractures associated with this disease. Although the lower mineralization and loss of aligned Haversian structures do produce a lower modulus tissue, which is susceptible to deformities, our results indicate that the higher levels of plasticity may compensate for the lost microstructural features and maintain the resistance to crack growth.

Correlative light and scanning X-ray scattering microscopy of healthy and pathologic human bone sections

Scanning small and wide angle X-ray scattering (scanning SWAXS) experiments were performed on healthy and pathologic human bone sections. Via crystallographic tools the data were transformed into quantitative images and as such compared with circularly polarized light (CPL) microscopy images. SWAXS and CPL images allowed extracting information of the mineral nanocrystalline phase embedded, with and without preferred orientation, in the collagen fibrils, mapping local changes at sub-osteon resolution. This favorable combination has been applied for the first time to biopsies of dwarfism syndrome and Paget's disease to shed light onto the cortical structure of natural bone in healthy and pathologic sections.

A single infusion of zoledronic acid produces sustained remissions in Paget disease: data to 6.5 years

Two trials have shown that a single 5-mg infusion of zoledronic acid achieves much higher response rates in Paget disease of bone than risedronate. The duration of this effect is unknown. We have conducted an open follow-up of responders from the two trials (152 originally treated with zoledronic acid, 115 with risedronate) out to 6.5 years without further intervention. Endpoints were times to relapse (ie, return of serum total alkaline phosphatase activity to within 20% of the pretreatment value) or loss of response (response = normalization of alkaline phosphatase or 75% or greater reduction in its excess). Bone turnover markers were lower in the zoledronic acid group throughout follow-up, with mean alkaline phosphatase (ALP) remaining within the reference range in these patients, whereas the mean in the risedronate group was above normal from 1 year. Relapse rates were substantially greater in the risedronate group (23 of 115, 20%) than in those treated with zoledronic acid (1 of 152, 0.7%, p < .001), and loss of response occurred in 19 (12.5%) zoledronic acid patients compared with 71 (62%) risedronate patients (p < .0001). Risk ratios for relapse and loss of response in zoledronic acid patients were 0.02 [95% confidence interval (CI) 0.00-0.18] and 0.12 (95% CI 0.07-0.19), respectively. Changes from baseline in quality of life, assessed using SF-36 scores, were more positive in the zoledronic acid group across the follow-up period (p = .01). Bone markers at 6 months were predictive of response duration. These data demonstrate an unprecedented duration of remission of Paget disease following treatment with zoledronic acid, accompanied by an improved quality of life.

Efficacy, tolerability, and safety of risedronate in Japanese patients with Paget's disease of bone

This study evaluated the clinical efficacy of treatment with oral risedronate (17.5 mg once daily) for 8 weeks in 11 Japanese patients with Paget's disease of bone (PDB). Risedronate suppressed the excessive bone turnover associated with PDB and improved several biochemical markers, including serum alkaline phosphatase (ALP), serum bone-specific ALP (BALP), urinary deoxypyridinoline (DPD), and urinary cross-linked N-telopeptide of type 1 collagen (NTX). These markers began to decrease within about 2 weeks after the initiation of treatment in most patients, and the response persisted for up to 40 weeks after the cessation of treatment. Risedronate reduced pain by week 24 in most patients. According to quantitative bone scintigraphy, the lesion with the highest radioisotope (RI) uptake showed a decrease of uptake from 12.7 +/- 6.8 to 6.0 +/- 2.3 (mean +/- SD) in week 24, although each lesion of patients with polyostotic disease had a different scintigraphic response. Overall, risedronate at a dose of 17.5 mg once daily was well tolerated by patients with PDB, even though the dosage was seven times higher than that approved for the treatment of osteoporosis in Japan (2.5 mg once daily). In conclusion, treatment with high-dose risedronate for 8 weeks resulted in clinically significant and sustained improvement of biochemical markers of bone turnover for 48 weeks in patients with PDB, and this improvement was associated with a decrease of RI uptake by Paget's bone lesions and with reduced pain.

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.

Paget's disease of bone: emphasis on treatment with zoledronic acid

The treatment of Paget's disease of bone (PDB) aims at suppression of abnormal bone turnover and bisphosphonates (BPs) are currently the drugs of choice. Zoledronic acid, a third-generation nitrogen-containing BPs, is the newest BP approved for PDB and is administered by a single intravenous infusion. In vitro zoledronic acid has higher binding affinity for hydroxyapatite and is a stronger inhibitor of farnesyl pyrophosphate synthase compared with other BPs. In vivo zoledronic acid improves symptoms, normalizes bone turnover markers and scintigraphic imaging in the majority of patients, and maintains remission of PDB longer than other BPs. This review summarizes available data on the pathogenesis, epidemiology, clinical manifestation, biochemical assessment and management of PDB, giving special attention to the treatment of PDB with zoledronic acid, based on current evidence.

Effect of three doses of conjugated estrogens/medroxyprogesterone acetate on biomarkers of bone turnover and cartilage degradation in postmenopausal women: The Pan-Asia Menopause (PAM) study

OBJECTIVE

To assess the effects of three doses of continuously combined conjugated estrogens (CE) and medroxyprogesterone acetate (MPA) on bone turnover and cartilage degradation markers in early postmenopausal Asian women (mean age 53.6 years).

METHODS

A total of 1028 women were randomly allocated to receive treatment with either 0.625/2.5, 0.45/1.5, or 0.3/1.5 mg CE/MPA for 6 months. End-points were the percent change from baseline in markers of bone resorption (alpha alpha CTX, beta beta CTX), bone formation (osteocalcin), and cartilage degradation (CTX-II).

RESULTS

The 0.45/1.5 mg and the 0.625/2.5 mg doses elicited comparable responses as measured by the biomarkers. Women with high rates of bone or cartilage turnover at baseline responded with larger changes to the effects of CE/MPA.

CONCLUSIONS

Lowering the commonly used dose of 0.625 mg CE + 2.5 mg MPA to 0.45 mg CE + 1.5 mg MPA does not significantly alter the inhibitory effect on bone and cartilage turnover in Asian women.

Bone turnover markers: understanding their value in clinical trials and clinical practice

While bone mineral density (BMD) by dual-energy X-ray absorptiometry is the primary method of determining fracture risk, assessing bone turnover may add valuable information for the management of patients with low bone mass. Bone turnover markers (BTMs) are used in clinical trials where they can provide essential information on the biological efficacy of osteoporosis treatments. In such population-based studies, BTMs can predict fracture risk independent of BMD. When combined with BMD, they improve the fracture risk estimate above and beyond BMD alone in postmenopausal osteoporotic women. Since changes in bone turnover after the initiation of therapy with bone resorption inhibitors occur much more rapidly than changes in BMD, treatment efficacy could, in theory, be determined within weeks of using BTMs. However, such predictive value is limited by the large biological variability of these biochemical markers, even though newer automated methods have reduced their analytical variability. Consequently, widespread adoption as a means of predicting treatment efficacy in fracture prevention for individual patients cannot yet be recommended. BTMs may be useful for monitoring adherence to antiresorptive therapy and may aid in identifying patients for whom antiresorptive therapy is most appropriate. Thus, although BTMs are currently confined to clinical research applications, further improvement in assay precision may extend their diagnostic value in clinical settings.

Biochemical markers of bone turnover: potential use in the investigation and management of postmenopausal osteoporosis

INTRODUCTION

The aim was to analyse data on the use of biochemical bone turnover markers (BTM) in postmenopausal osteoporosis.

METHODS

We carried out a comparative analysis of the most important papers concerning BTM in postmenopausal osteoporosis that have been published recently.

RESULTS

The BTM levels are influenced by several factors. They are moderately correlated with BMD and subsequent bone loss. Increased levels of bone resorption markers are associated with a higher risk of fracture. Changes in the BTM during the anti-osteoporotic treatment (including combination therapy) reflect the mechanisms of action of the drugs and help to establish their effective doses. Changes in the BTM during the anti-resorptive treatment are correlated with their anti-fracture efficacy.

CONCLUSION

Biological samples should be obtained in a standardised way. BTM cannot be used for prediction of the accelerated bone loss at the level of the individual. BTM help to detect postmenopausal women who are at high risk of fracture; however, adequate practical guidelines are lacking. BTM measurements taken during the anti-resorptive therapy help to identify non-compliers. They may improve adherence to the anti-resorptive therapy and the fall in the BTM levels that exceeds the predefined threshold improves patients' persistence with the treatment. There are no guidelines concerning the use of BTM in monitoring anti-osteoporotic therapy in postmenopausal women.

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.

Effects of PTH and alendronate on type I collagen isomerization in postmenopausal women with osteoporosis: the PaTH study

Fracture efficacy of PTH and alendronate (ALN) is only partly explained by changes in BMD, and bone collagen properties have been suggested to play a role. We analyzed the effects of PTH(1-84) and ALN on urinary alphaalpha/betabeta CTX ratio, a marker of type I collagen isomerization and maturation in postmenopausal women with osteoporosis. In the first year of the previously published PaTH study, postmenopausal women with osteoporosis were assigned to PTH(1-84) (100 microg/d; n = 119), ALN (10 mg/d; n = 60), or PTH and ALN together (n = 59). We analyzed patients on ALN alone (n = 60) and a similar number of patients assigned to PTH alone (n = 63). During the second year, women on PTH in the first year were reallocated to placebo (n = 31) or ALN (n = 32) and women with ALN continued on ALN. During the first year, there was no significant change in alphaalpha/betabeta CTX ratio with PTH or ALN. At 24 mo, there was a marked increase of the alphaalpha/betabeta CTX ratio in women who had received PTH during the first year, followed by a second year of placebo (median: +45.5, p < 0.001) or ALN (+55.2%, p < 0.001). Conversely, the alphaalpha/betabeta CTX ratio only slightly increased (+16%, p < 0.05) after 2 yr of continued ALN. In conclusion, treatment with PTH(1-84) for 1 yr followed by 1 yr of placebo or ALN may be associated with decreased type I collagen isomerization. The influence of these biochemical changes of type I collagen on bone fracture resistance remains to be studied.

Management of patients with Paget's disease: a consensus document of the Belgian Bone Club

Paget's disease of bone (PDB) is a potentially crippling condition. Pain, fracture, spinal stenosis, nerve entrapment, vascular steal syndrome, secondary osteoarthritis, bone deformity, dental problems, deafness, excessive bleeding during orthopaedic surgery, rare sarcomatous degeneration, and hypercalcaemia constitute complications that may impair the quality of life. The therapeutic approach varies from symptomatic (analgesics, anti-inflammatory drugs) to more specific drugs such as increasingly potent bisphosphonates. Studies such as the PRISM study should in the future help to determine the superiority or not of aggressive treatment over symptomatic treatment in the prevention of complications. Various oral and/or intravenous (i.v.) bisphosphonates have been tested and are currently on the market. The most recently available nitrogen-containing bisphosphonate, i.v. zoledronic acid, is the most potent therapy available for the treatment of PDB. Its therapeutic efficacy, its long-term effect on biologic activity and its good tolerance currently supports its use as a first-line therapeutic option in patients suffering from PDB.

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.

Long-term control of bone turnover in Paget's disease with zoledronic acid and risedronate

A single 5-mg infusion of zoledronic acid restores biochemical markers of bone turnover into the reference range in the majority of patients with Paget's disease and maintains biochemical remission for at least 2 years. This effect is largely independent of pretreatment disease activity and prior bisphosphonate therapy.

INTRODUCTION

Zoledronic acid (ZOL) is a potent bisphosphonate that produces a rapid and complete control of the increased bone turnover of Paget's disease. Long-term control of disease activity is an important aim of treatment in the hope that this will reduce the risk of complications such as deformity, fracture, and degenerative joint disease.

MATERIALS AND METHODS

This study compares the ability of ZOL 5 mg given as a 15-minute intravenous infusion with risedronate (RIS) 30 mg daily by mouth for 60 days to maintain long-term control of bone turnover. No bisphosphonate was given during the extension study. All patients (n = 296) who achieved a therapeutic response, defined as normalization or a >75% reduction in the total alkaline phosphatase (total ALP) excess above the midpoint of the reference range, were eligible for inclusion.

RESULTS

ZOL maintained the mean level of total ALP at the middle of the reference range, whereas those treated with risedronate showed a linear increase in total ALP from the 6-month post-treatment time-point. Both treatments resulted in a linear relationship between the 6-month nadir and 24-month total ALP. The relationship for RIS was shifted upward, showing that for a given level of post-treatment biochemical activity, bone turnover increased with time. This was in contrast to the ZOL-treated patients where total ALP generally remained unchanged over this 18-month extension period. A similar pattern of response was seen with the other bone turnover markers.

CONCLUSIONS

ZOL maintains bone turnover within the reference range over 24 months from the initiation of treatment. A reduction in the incidence and severity of long-term complications may require persistent normalization of bone turnover over many years, and this now seems a realistic possibility with ZOL.

Biochemistry of amino acid racemization and clinical application to musculoskeletal disease

During aging, proteins are subject to numerous forms of damage. Several types of non-enzymatic post-translational modifications have been described in aging proteins, including oxidation, nitration, glycation, and racemization. Racemization of amino acids is the spontaneous conversion of L-enantiomers to the D-form, which is dependent on temperature, pH, and time. Because of the time-dependent nature of racemization, it can be used to determine the relative age and turnover rates of long-lived proteins. There are many such long-lived proteins within the body; they are found in the brain, eye, and heart, but are particularly abundant in proteins found in musculoskeletal tissues such as bone and cartilage. During disease, musculoskeletal tissues have pathologically altered turnover rates. Because turnover rates can be estimated from levels of racemization, racemized musculoskeletal protein fragments may serve as useful biomarkers of disease. This review discusses the biochemistry of amino acid racemization in proteins and its clinical application to musculoskeletal disease.

Biochemical response to bisphosphonate therapy in pagetic patients with skull involvement

The aims of this study were to compare the response to therapy in disease activity in pagetic patients with and without skull involvement and the usefulness of bone markers in the evaluation of these patients. Forty patients with Paget's disease treated with tiludronate and 26 healthy controls were included. Serum total and bone alkaline phosphatases (TAP, BAP), procollagen I N propeptide (PINP), and urinary N- and C-terminal cross-linking telopeptides of collagen I (NTX, alpha-alpha CTX, and beta-beta CTX) were measured at baseline and 6 months after therapy. The extent of the disease was evaluated using the Coutris' index. Pagetic patients were classified into three groups: patients with skull involvement (G-I, n = 12), patients without skull involvement (G-II, n = 28), and a subgroup of patients from G-II without skull involvement but with similar disease extent to G-I (G-III, n = 10). At baseline, patients from G-I showed significantly higher values in most markers compared to G-II. alpha-alpha CTX was the marker with the highest values in all groups. Moreover, monostotic patients with skull involvement showed higher serum baseline values of TAP per unit of affected area than monostotic patients without skull involvement. After therapy, the percentage of patients with markers within the normal range was lower in G-I than in G-II and G-III. In conclusion, pagetic patients with skull involvement showed a marked increase in bone turnover and a lower response to therapy.

The role of collagen in bone strength

Bone is a complex tissue of which the principal function is to resist mechanical forces and fractures. Bone strength depends not only on the quantity of bone tissue but also on the quality, which is characterized by the geometry and the shape of bones, the microarchitecture of the trabecular bones, the turnover, the mineral, and the collagen. Different determinants of bone quality are interrelated, especially the mineral and collagen, and analysis of their specific roles in bone strength is difficult. This review describes the interactions of type I collagen with the mineral and the contribution of the orientations of the collagen fibers when the bone is submitted to mechanical forces. Different processes of maturation of collagen occur in bone, which can result either from enzymatic or nonenzymatic processes. The enzymatic process involves activation of lysyl oxidase, which leads to the formation of immature and mature crosslinks that stabilize the collagen fibrils. Two type of nonenzymatic process are described in type I collagen: the formation of advanced glycation end products due to the accumulation of reducible sugars in bone tissue, and the process of racemization and isomerization in the telopeptide of the collagen. These modifications of collagen are age-related and may impair the mechanical properties of bone. To illustrate the role of the crosslinking process of collagen in bone strength, clinical disorders associated with bone collagen abnormalities and bone fragility, such as osteogenesis imperfecta and osteoporosis, are described.

Comparison of a single infusion of zoledronic acid with risedronate for Paget's disease

BACKGROUND

The advent of bisphosphonates advanced therapy for Paget's disease, but more effective and convenient agents are needed to increase adherence. Zoledronic acid, a bisphosphonate administered as a single intravenous infusion, might meet these needs.

METHODS

In two identical, randomized, double-blind, actively controlled trials of 6 months' duration, we compared one 15-minute infusion of 5 mg of zoledronic acid with 60 days of oral risedronate (30 mg per day). The primary efficacy end point was the rate of therapeutic response at six months, defined as a normalization of alkaline phosphatase levels or a reduction of at least 75 percent in the total alkaline phosphatase excess. The results of the studies were pooled.

RESULTS

At six months, 96.0 percent of patients receiving zoledronic acid had a therapeutic response (169 of 176), as compared with 74.3 percent of patients receiving risedronate (127 of 171, P<0.001). Alkaline phosphatase levels normalized in 88.6 percent of patients in the zoledronic acid group and 57.9 percent of patients in the risedronate group (P<0.001). Zoledronic acid was associated with a shorter median time to a first therapeutic response (64 vs. 89 days, P<0.001). Higher response rates in the zoledronic acid group were consistent across all demographic, disease-severity, and treatment-history subgroups and with changes in other bone-turnover markers. The physical-component summary score of the Medical Outcomes Study 36-item Short-Form General Health Survey, a measure of the quality of life, increased significantly from baseline at both three and six months in the zoledronic acid group and differed significantly from those in the risedronate group at three months. Pain scores improved in both groups. During post-trial follow-up (median, 190 days), 21 of 82 patients in the risedronate group had a loss of therapeutic response, as compared with 1 of 113 patients in the zoledronic acid group (P<0.001).

CONCLUSIONS

A single infusion of zoledronic acid produces more rapid, more complete, and more sustained responses in Paget's disease than does daily treatment with risedronate.

New therapeutic agents for the treatment of bone diseases

Bisphosphonates have demonstrated important clinical benefits for patients with malignant bone disease, metabolic bone diseases, such as Paget's disease, and postmenopausal osteoporosis. The introduction of nitrogen-containing bisphosphonates with high affinity for hydroxyapatite in bone represents an important advancement. These agents are now a standard of care for osteoporosis, Paget's disease, osteogenesis imperfecta, primary bone lesions from multiple myeloma and bone metastases from breast cancer. Moreover, the recent clinical development of zoledronic acid (4 mg by 15-minute intravenous infusion) has expanded the benefits of bisphosphonate therapy to patients with bone metastases from any solid tumour. Bisphosphonates are also being investigated at present for the prevention of bone loss resulting from cancer therapy. In addition, a variety of novel biologic agents, receptor activator of nuclear factor-kappaB (RANK) ligand antibodies, osteoprotegerin and cathepsin K inhibitors are being investigated at present for the treatment of malignant bone disease. The management of bone health is an important area of active research, and the armamentarium and role of bone-specific therapies continue to expand.

Maladie de Paget, exploration et surveillance

Paget's disease is a progressive bone disease, characterized by bone hypertrophy and increased bone resorption. The pain and deformity that characterize its clinical course are not simple to assess, but it has a characteristic radiographic appearance. In most cases, treatment can be monitored through biological markers of bone turnover. Total alkaline phosphatase is the best marker and measurement of collagen breakdown products is useful in difficult cases. The goal of treatment is the normalization of these biological markers, to prevent complications of the disease.

Urinary type II collagen helical peptide (HELIX-II) as a new biochemical marker of cartilage degradation in patients with osteoarthritis and rheumatoid arthritis

OBJECTIVE

Type II collagen, which consists of a large helical domain and telopeptides at each end, is the most abundant protein of cartilage matrix. The aim of this study was to develop a biochemical marker reflecting the degradation of the helical region of type II collagen and to evaluate its clinical performance in patients with osteoarthritis (OA) and rheumatoid arthritis (RA).

METHODS

We developed a competitive polyclonal antibody-based enzyme-linked immunosorbent assay (ELISA) using the 622-632 peptide derived from the sequence of the alpha1 chain of human type II collagen (HELIX-II) as immunogen and standard. We measured urinary levels of HELIX-II peptide and C-terminal crosslinking telopeptide of type II collagen (CTX-II) in 90 patients with knee OA (73% women; mean +/- SD age 63.0 +/- 8.0 years, mean +/- SD disease duration 6.1 +/- 6.8 years), 89 patients with early RA (disease duration </=3 years) (79% women; mean +/- SD age 48.7 +/- 11.6 years), 25 patients with Paget's disease of bone (HELIX-II only), and 162 healthy controls. In RA patients, we investigated the relationships between baseline urinary HELIX-II and CTX-II levels and the progression of joint destruction as measured by the changes in the total Sharp score (average from 2 independent readers) over 1 year.

RESULTS

The intraassay and interassay variations of the HELIX-II ELISA were lower than 13% and 15%, respectively. The HELIX-II ELISA showed no significant cross-reactivity with human intact or denatured type II collagen, with the homologous peptides from human type I or type III collagens, or with HELIX-II peptides elongated (by 1 amino acid) or shortened (by 1 or 2 amino acids) at the C-terminal end, indicating that the HELIX-II ELISA recognized a neoepitope from the alpha1 chain of type II collagen. Median urinary HELIX-II levels were increased in patients with knee OA (by 56%; P < 0.0001) or early RA (by 123%; P < 0.0001) compared with those in age- and sex-matched healthy controls. Baseline urinary HELIX-II levels in the highest tertile were associated with an increased risk of radiographic progression in RA (increase in the total Sharp score >/=0.5 units/year), with an odds ratio (OR) of 5.9 (95% confidence interval [95% CI] 2.0-17.2) after adjustment for serum C-reactive protein (CRP) levels and baseline joint damage. Patients with increased levels of both urinary HELIX-II and CTX-II had the highest risk of progression (OR 17.5 [95% CI 3.1-99]).

CONCLUSION

The HELIX-II ELISA is specific for type II collagen degradation, has adequate technical performance, and can distinguish patients with knee OA or RA from healthy controls. Elevated HELIX-II levels are associated with increased risk of radiographic progression in RA independently of CRP levels, baseline joint damage, and urinary CTX-II levels. The HELIX-II ELISA should be useful for the clinical investigation of patients with arthritis and for identifying RA patients at higher risk of progression.

Medical management of skeletal metastasis

This article discusses general principles of medical management of bone metastases, including diagnosis and follow-up; management of specific symptoms; options for systemic treatment, including bisphosphonates; specific details about each cancer type; and future directions in therapy.

Comparative responses of bone turnover markers to bisphosphonate therapy in Paget's disease of bone

The measurement of biochemical markers of bone turnover is integral to the diagnosis and management of Paget's disease. Recently, there has been a proliferation of new markers and a move to carry out existing assays on automated platforms. We have assessed the performance of seven currently available markers in 20 patients with Paget's disease undergoing ibandronate therapy (6 or 12 mg) and in nine placebo-treated controls. Samples were collected at baseline and 6 months following intervention. The mean reductions in serum markers following treatment with either dose of ibandronate were: total alkaline phosphatase (AP; Roche Modular) 70%, bone AP (Beckman Access, Ostase) 80%, osteocalcin (Roche Elecsys 2010) 33%, beta-C-terminal telopeptide of type I collagen (betaCTX; Roche Elecsys 2010) 50%, and procollagen-N-terminal peptide (P1NP; Roche Elecsys 2010) 80%. For urine markers the reductions were: free deoxypyridinoline/creatinine (fDPD/creat) (DPC Immulite 2000) 36%, and N-telopeptide/creatinine (NTX/creat) (Osteomark) 81%. Total AP, bone AP, P1NP, and NTX all showed >95% of subjects to have abnormal values at baseline, reducing to 15-30% following treatment, and these treatment effects were highly significant (P < or = 0.0005), except for NTX (P = 0.02). The poorer precision of NTX reduced its utility. Baseline sensitivity was lower for the other markers (osteocalcin 68% of subjects abnormal, fDPD 22%, betaCTX 50%). Total AP, bone AP, and P1NP are suitable osteoblast markers for monitoring bisphosphonate therapy in Paget's disease, with performance approaching that of bone scintigraphy. NTX is less sensitive in detecting the effects of therapy, but is the best performing bone resorption marker. There is no clear evidence from this study that any of these newer markers are superior to total AP in assessing patients with this severity of Paget's disease.

Paget's disease of bone

Paget's disease of bone is characterized by an anarchic bone remodelling, associated with morphological and functional abnormalities of osteoclasts. Its prevalence and incidence rates decreased gradually over the past two decades; the reason for this remains unclear. The aetiology of the disease is still obscure, the paramyxoviral theory being very controversial. Recent advances in understanding of the disease come from genetic studies, with the identification of specific mutations in the p62-sequestosome gene, which could be involved in pathogenetic mechanisms leading to increased osteoclast activity. The disease affects one or several bone pieces, leading to bone pain, deformities, characteristic imaging features, and increased markers of bone remodelling. The long-lasting disease activity leads to complications, including arthropathies, neurological compressions, fissures or fractures and, rarely, osteosarcomatous transformation of a pagetic lesion. Potent bisphosphonates have proven their efficacy in reducing symptoms and disease activity. They are currently used as the first-line treatment with the goal of normalizing bone remodelling and, hopefully, preventing late complications.

Zoledronic acid: A new parenteral bisphosphonate

BACKGROUND

Inhibition of bone resorption using bisphosphonates is an important step in palliation of complications of advanced cancer, such as hypercalcemia and metastatic bone disease.

OBJECTIVE

The goal of this article was to describe the pharmacologic properties of zoledronic acid (zoledronate) and discuss findings from preclinical and clinical studies of its use in skeletal disorders.

METHODS

Relevant English-language literature was identified using the terms zoledronic acid, zoledronate, Zometa, and 118072-93-8 through searches of MEDLINE (1966-June 2003) and International Pharmaceutical Abstracts (1970-June 2003), and abstract proceedings from the American Society of Clinical Oncology (1997-2002).

RESULTS

Zoledronic acid is a nitrogen-containing bisphosphonate that inhibits bone resorption. It is indicated for the treatment of hypercalcemia of malignancy and for the treatment of patients with multiple myeloma or documented metastasis from solid tumors, in conjunction with standard antineoplastic therapy. The recommended dosage is 4 mg via IV over >or= 15 minutes every 3 or 4 weeks. Compared with pamidronate 90 mg, zoledronic acid 4 and 8 mg provided a higher complete response rate for hypercalcemia of malignancy by day 10 (88.4% and 86.7% vs 69.7%; P = 0.002 and P = 0.015) and longer duration of action (median time to relapse, 30 and 40 days vs 17 days; P = 0.001 and P = 0.007). In patients with breast cancer or multiple myeloma, zoledronic acid was as effective as pamidronate in delaying time to a first skeletal-related event (373 days vs 363 days). In patients with hormone-refractory prostate cancer and bone metastases, zoledronic acid 4 mg reduced the proportion of patients who experienced a skeletal-related event (33% vs 44% with placebo; P = 0.021) or a skeletal fracture (13% vs 22% with placebo; P = 0.015). In patients with bone metastases from solid tumors, zoledronic acid delayed the median time to a first skeletal-related event (230 days vs 163 days with placebo; P = 0.023). Common adverse events include fever, nausea, constipation, fatigue, and bone pain.

CONCLUSION

Zoledronic acid is an effective and generally well-tolerated treatment for hypercalcemia of malignancy and skeletal complications of metastatic bone disease.

Modern Therapy for Paget??s Disease of Bone

There has been a dramatic change in the therapeutic approach to patients with Paget's disease of bone over the last 40 years. In the 1960s, only symptomatic therapy could be given, with control of pain the main objective. Analgesics and nonsteroidal anti-inflammatory drugs were the most commonly used agents. From 1968 onwards, antiosteoclastic agents became available, including calcitonin, plicamycin (mithramycin) and etidronate (etidronic acid), a first-generation bisphosphonate. Limitations with these agents, including potentially deleterious effects on bone mineralization with etidronate (etidronic acid), has cleared the way for increasingly potent second- and third-generation bisphosphonates, including clodronate (clodronic acid), pamidronate (pamidronic acid), alendronate (alendronic acid) and risedronate (risedronic acid). Even more potent bisphosphonates will become available in the near future. With the newer bisphosphonates, there is some hope for long-term remission (if not definitive healing) of pagetic lesions, as well as prevention of long-term complications in both symptomatic and asymptomatic patients. Thus, indications for therapy have been extended to include younger patients to prevent bone deformity of the limbs and skull, leading to secondary osteoarthritis, facial deformities and potentially to sarcoma transformation; as well as to elderly patients to prevent bone fragility, leading to fracture, and pagetic vascular steal syndromes. The increased potency and longer duration of action of newer bisphosphonates more than compensates for their marginally increased cost compared with older bisphosphonates.

Usefulness of biochemical markers of bone turnover in assessing response to the treatment of Paget's disease

The aim of this study was to investigate the usefulness of biochemical markers of bone turnover for monitoring treatment efficacy of Paget's disease of bone, and also to evaluate the utility of biological variation data in choosing the best markers for assessment of biochemical response to therapy. Thirty-eight patients with Paget's disease were included in a prospective study. All received 400 mg/day of oral tiludronate for 3 months. In 31 patients that completed treatment, biochemical markers were measured at baseline and at 1 and 6 months after treatment ended. In serum we determined the levels of total alkaline phosphatase (tAP), bone alkaline phosphatase (bAP), procollagen type I N-terminal propeptide (PINP), and C-terminal telopeptide of type I collagen (sCTx). Urine samples were analyzed for hydroxyproline (Hyp) and for C- and N-terminal telopeptides of type I collagen (CTx and NTx, respectively). Quantitative bone scintigraphy was performed at baseline and at 6 months after discontinuation of therapy. A ratio for monitoring response to treatment was obtained for each marker. This ratio reflected the size of treatment response of the marker in relation to the value of its critical difference. Thus, ratio values of >1 indicated a significant decrease of the marker after therapy. In addition, response to therapy was evaluated according to disease activity. Mean values of all markers of bone turnover decreased significantly after therapy. Serum bAP and PINP and urinary NTx showed the highest percentage reduction (between 58% and 68%). Furthermore, serum bAP and PINP showed the highest ratios for monitoring changes induced by treatment, followed by serum tAP and urinary NTx. sCTx and urinary CTx as well as Hyp showed mean ratios for monitoring changes of <1, indicating a low sensitivity for monitoring treatment. Patients with polyostotic disease showed a continuous decrease in mean values for all markers at 6 months from the end of therapy, whereas, in monostotic patients, there was a trend toward increased levels at this timepoint. In conclusion, serum bAP and PINP were the most sensitive markers for monitoring treatment efficacy in Paget's disease, although serum tAP and urinary NTx were also sensitive markers for monitoring changes. Data on biological variation are useful for assessing actual changes induced by treatment.

Biochemical markers of bone turnover

BACKGROUND

Osteoporosis in many countries has reached epidemic proportions. This has stimulated the development of biochemical markers to assist in the assessment of osteoporotic risk and in monitoring the efficacy of treatment. Biochemical markers of bone turnover are products released from osteoblasts and osteoclasts or collagen breakdown products.

MARKERS

Markers of bone formation include bone-specific alkaline phosphatase (BAP), osteocalcin (OC) and procollagen peptides. All of these can be measured easily by immunoassay techniques. Of these markers, OC has been extensively studied. However, OC undergoes in vitro degradation, thus, assay results are variable. BAP, on the other hand, is much more stable and shows less within-person biological variation. Bone resorption markers include tartrate-resistant acid phosphatase (TRAP) and collagen breakdown products, such as pyridinium cross-links, galactosyl hydroxylysine and cross-linked telopeptides, such as CTx and NTx. Of these, deoxypyridinium (DPD) has been extensively studied. DPD shows diurnal variation and the within-individual biological variation is large. Of the newer assays, NTx appear to show large differences at menopause.

CONCLUSIONS

Thus, serum BAP and DPD or NTx are the current choice of bone markers.

Markers of bone turnover in prostate cancer

Prostate cancer is the most common malignancy in elderly men and is often associated with bone metastases. Although bone metastases are osteosclerotic, histological and biochemical studies clearly indicate an increase of both bone formation and bone resorption, providing the rational for using bisphosphonate as a palliative treatment in these patients. The recent development of specific and sensitive biochemical markers, reflecting the overall rate of bone formation and bone resorption, has improved the non-invasive assessment of bone turnover abnormalities in patients with prostate cancer. The immunoassays for bone-specific alkaline phosphatase and type I collagen propeptides are currently the most sensitive markers to assess bone, formation. The best indices of bone resorption are the immunoassay for the pyridinoline cross-links and the related peptides that can be measured in urine and more recently in serum. A better knowledge of the biochemistry, especially of the age-related post-translational modifications of type I collagen in the abnormal bone matrix, associated with bone metastases from prostate cancer may lead to markers of increased sensitivity. A recent example is the demonstration that the isomerization and racemization of the aspartic acid residue in C-telopeptides of type I collagen is impaired in patients with prostate cancer and bone metastases, a pattern than can be detected with specific conformational antibodies. The most sensitive markers of bone formation and bone resorption are markedly increased in patients with bone metastases compared with patients with cancer but without metastases, the levels correlating with the extent of the bone involvement. However, their sensitivity remains limited, suggesting that the currently available biochemical markers cannot be used as a surrogate for bone scintigraphy in the diagnosis of bone involvement. A few studies have suggested that the measurement of bone markers may be useful in the assessment of response to anti-endocrine therapy, although available data indicate a lower sensitivity than with prostates specific antigen. Additional longitudinal studies are required to assess the potential use of bone markers, especially to identify patients who relapse during the course of the treatment and, more specifically 3 those that result from the progression in bone metastases.Clearly, the established use of bone markers is for monitoring effects of bisphosphonate treatment. Several studies have shown a rapid decrease of bone resorption markers in patients with prostate cancer and bone metastases, the magnitude of the decrease correlating with the efficacy of the treatment in reducing bone pain. Thus, bone markers are likely to become a useful and objective tool to monitor bisphosphonate treatment and individual the therapy scheme.

The bisphosphonate zoledronate decreases type II collagen breakdown in patients with Paget's disease of bone

Bisphosphonates have been suggested to be partially chondroprotective in animal models of arthritis. The aim of this study was to assess the short-term effect of the bisphosphonate zoledronate on type II collagen degradation in patients with Paget's disease of bone. Twenty-six patients with active Paget's disease who were a part of a double-blind, placebo-controlled, randomized study comparing the effects of several doses of a single injection of zoledronate, a potent bisphosphonate, were studied. Type II collagen destruction was assessed by urinary levels of type II collagen C-telopeptide (CTX-II) using a new immunoassay. Bone resorption was assessed by measuring the urinary excretion of nonisomerized type I collagen C-telopeptide (alpha CTX-I). Biochemical markers were measured at baseline and 5, 10, 30, and 60 days after injection. At baseline, no significant increase of CTX-II was observed in patients with Paget's disease compared with a group of 27 gender-and age-matched controls, in contrast to the ninefold (p < 0.0001) increase of urinary alpha CTX-I. After a single intravenous injection of zoledronate (200 or 400 microg), urinary CTX-II transiently decreased by a median of 25% 5 days after the injection of zoledronate (p = 0.0023 vs. placebo), then increased to pretreatment levels after 10 days. In contrast, urinary alpha CTX-I decreased within 5 days with a maximal decrease of 51% at day 10 (p < 0.001 vs. baseline and placebo), and levels remained suppressed during the 2 months of the study. Zoledronate not only reduces bone turnover but also directly decreases type II collagen degradation in patients with Paget's disease, suggesting that bisphosphonates may have chondroprotective effects in humans. Measurement of type II collagen breakdown by a new urinary biochemical marker may be useful for in vivo assessment of the effects of drugs that potentially inhibit cartilage destruction.

Excretion of Sweat and Urine Pyridinoline Crosslinks in Healthy Controls and Subjects with Established Metabolic Bone Disease

Convenient techniques for measuring rates of bone turnover have been developed in recent years with the advent of biochemical markers of bone metabolism. One recent of these techniques is a collection method and quantitative enzyme immunoassay for free pyridinoline crosslinks in human sweat. The concentrations of pyridinoline crosslinks in 5-day sweat collections and first morning void and 24-hour urine collections from healthy subjects and subjects with established metabolic bone disorders were determined. T-scores were higher in the sweat system than in the urine system by up to 10-fold in postmenopausal subjects, women with hyperparathyroidism, and subjects with postmenopausal osteoporosis. For subjects with postmenopausal osteoporosis, receiver-operating characteristic curve analysis yielded areas under the curve of 0.699, 0.629, and 0.520 for sweat pyridinoline, first morning void urine pyridinoline, and 24 hour urine pyridinoline respectively. The areas under the curve of the sweat and first morning void urine measurements were significantly greater (p<0.05) than the 24-hour pyridinoline measurements. Healthy postmenopausal subjects and subjects with postmenopausal osteoporosis were monitored before and during estrogen replacement therapy or alendronate therapy. Sweat pyridinoline values declined by 49.0 +/- 12.4% and 19.4 +/- 19.9% for estrogen and alendronate subjects respectively. We conclude that this non-invasive technique is a sensitive and specific measure of bone resorption and is appropriate as an adjunct to techniques such as bone density and may also be useful in monitoring of response to anti-resorptive therapies.

Biochemical markers of bone turnover, endogenous hormones and the risk of fractures in postmenopausal women: the OFELY study

The mechanisms leading to increased bone loss and skeletal fragility in women with postmenopausal osteoporosis are still poorly understood. Increased bone resorption, low serum estradiol and high serum sex-hormone-binding globulin (SHBG) recently have been reported as predictors of vertebral and hip fractures in elderly women. In a cohort of healthy untreated younger postmenopausal women aged 50-89 years (mean, 64 years), we compared baseline levels of bone markers and endogenous hormones in 55 women who subsequently had a fracture (20 vertebral and 35 peripheral fractures) with levels in the 380 women who did not fracture during a mean 5 years of follow-up. Women with levels in the highest quartile of four bone resorption markers including urinary-free deoxypyridinoline (D-Pyr), urinary type I collagen N-telopeptides (NTX), and urinary and serum type I collagen C-telopeptides (CTX) had about a 2-fold increased risk of fractures compared with women with levels in the three lowest quartiles with relative risk (RR) and 95% CI of 1.8 (1.0-3.4) for free D-Pyr, 1.7 (0.9-3.2) for urinary NTX, 2.3 (1.3-4.1) for urinary CTX, and 2.1 (1.2-3.8) for serum CTX. Serum levels of bone alkaline phosphatase (BAP) in the highest quartile were associated with an RR of fracture of 2.4 (1.3-4.2). Women with serum levels of estradiol and dehydroepiandrosterone (DHEA) sulfate in the lowest quartile had an RR of fracture of 2.2 (1.2-4.0) and 2.1 (1.2-3.8), respectively. Increased levels of SHBG and intact parathyroid hormone (PTH) were moderately associated with an increased risk of fracture. Similar results were obtained when the analysis was restricted to symptomatic vertebral and nonvertebral fractures. Adjustment of biochemical markers by hormone levels did not significantly alter the results. Women with both high bone resorption markers and low estradiol (or low DHEA sulfate) had a higher risk of fracture with RRs of 3.0-3.3 (p < 0.001). After adjustment for bone mineral density (BMD) of the hip, spine, radius, or total body, bone markers and hormones were still predictive of fracture risk with similar RRs. We conclude that high levels of some biochemical markers of bone turnover, low serum estradiol, low DHEA sulfate, high SHBG, and high PTH are associated with increased risk of osteoporotic fracture in postmenopausal women, independently of each other and of BMD. The mechanism by which some postmenopausal women have an increased rate of bone turnover leading to an increased risk of fracture remains to be elucidated.

Components of biological variation of biochemical markers of bone turnover in Paget's bone disease

The aims of this study were to evaluate the components of biological variation of the new markers of bone turnover in patients with Paget's bone disease and to compare the results with data obtained in healthy subjects. Fifteen patients with Paget's disease in a stable period of the disease and 12 healthy premenopausal women were included for a 1 year follow-up study. Within- and between-subject biological variation, indices of individuality, and critical differences were evaluated for the following biochemical markers: in serum, total (tAP), and bone (bAP) alkaline phosphatases, procollagen type I N-terminal propeptide (PINP) and beta-carboxyterminal telopeptide of type I collagen (sCTx); in urine, hydroxyproline (Hyp), and amino (NTx) and beta-carboxyterminal (CTx) telopeptides of collagen type I. Serum markers of bone turnover showed lower biological variability than urinary markers. Within-subject biological variation was higher in pagetic patients than in healthy subjects for all serum markers. In both groups, bAP presented the lowest within-subject biological variation. In pagetic patients, all markers presented indices of individuality of <0.6, indicating their usefulness for patient monitoring. Critical differences were lower for serum markers than for urinary markers. Among pagetic patients, serum bAP and PINP showed the lowest critical differences with values close to 30%, whereas urinary CTx presented the highest critical differences (near 70%). Conversely, in healthy subjects, tAP was the marker with the lowest critical differences, being two-fold higher in pagetic patients. This study confirms the lower sensitivity of urinary markers to detect significant changes and indicates that data obtained on biological variations from healthy populations cannot always be extrapolated to pathological conditions. In addition, serum bAP and PINP seem to be the markers that best reflect a significant change in activity of Paget's disease.

Markers of bone turnover for the management of patients with bone metastases from prostate cancer

Although increased bone formation is a prominent feature of patients with osteosclerotic metastases from prostate cancer, there is also some evidence for increased bone resorption. The aim of this study was to compare the clinical utility of new bone resorption markers to that of bone formation in patients with bone metastases from prostate cancer before and after bisphosphonate treatment. Thirty-nine patients with prostate cancer and bone metastasis, nine patients with prostate cancer without bone metastases, nine patients with benign prostatic hyperplasia and 355 healthy age-matched men were included. Urinary non-isomerized (alpha CTX) and beta isomerized (beta CTX) type I collagen C-telopeptides (CTX) and a new assay for serum CTX were used to assess bone resorption. Bone formation was determined by serum osteocalcin, serum total (T-ALP) and bone (BAP) alkaline phosphatase and serum type I collagen C-terminal propeptide (PICP). Fourteen patients with bone metastases were also evaluated 15 days after a single injection of the bisphosphonate pamidronate (120 mg). Levels of all bone formation and bone resorption markers were significantly (P < 0.006-0.0001) higher in patients with prostate cancer and bone metastasis than in patients with benign prostatic hyperplasia, patients with prostate cancer without bone metastases and healthy controls. In patients with bone metastases the median was increased by 67% for serum osteocalcin, 128% for T-ALP, 138% for BAP, 79% for PICP, 220% for urinary alpha CTX, 149% for urinary beta CTX and 214% for serum CTX. After bisphosphonate treatment all three resorption markers significantly decreased by an average of 65% (P = 0.001), 71% (P = 0.0010) and 61% (P = 0.0015) for urinary alpha CTX, urinary beta CTX and serum CTX, respectively, whereas no significant change was observed for any bone formation markers. Patients with prostate cancer and bone metastases exhibit a marked increase in bone resorption, which decreases within a few days of treatment with pamidronate. These findings suggest that these new resorption markers may be useful for the management of these patients.

Biochemical markers of bone turnover in Paget's disease of bone

Although the measurement of total alkaline phosphatase activity in serum is a valid index to assess the activity of Paget's disease of bone and to monitor treatment efficacy, this marker may lack sensitivity in some cases. Among the various markers of bone formation and resorption that have been developed, serum bone specific alkaline phosphatase and procollagen I N-terminal peptide (PINP) for formation, urinary N-telopeptide (NTX) and alpha-C-telopeptide (CTX) for bone resorption have emerged as the most sensitive ones, and may be useful in the management of pagetic patients. We have recently shown that the beta-isomerization of type I collagen CTX is impaired in pagetic bone matrix characterized by the existence of woven bone, as compared to normal lamellar bone matrix. This abnormality results in a preferential urinary excretion of nonisomerized (alpha-CTX) over beta-isomerized (beta-CTX) that can be measured with specific immunoassays. Patients with active Paget's disease of bone are characterized by an abnormally high alpha/beta-CTX ratio which goes down to the normal range after bisphosphonate therapy, probably reflecting the lamellar structure of newly formed bone matrix in pagetic skeletal sites after treatment.

Basic principles and clinical applications of biochemical markers of bone metabolism: biochemical and technical aspects

The interest in and the need for effective measures to be used in the screening, diagnosis, and follow-up of disorders of connective tissue, bone, and mineral metabolism has markedly grown. Next to clinical and imaging techniques, indices of bone turnover have come to play an important role in the assessment of metabolic bone disease. In osteoporosis, recent research has shown that bone markers may also be used to predict future bone loss and hip fractures (in larger cohorts of older patients), identify individuals at risk for osteoporosis, select therapy, and predict and monitor the therapeutic response in individual patients. The development of new markers of bone metabolism has greatly enriched the spectrum of serum and urine analytes used in the assessment of skeletal pathologies. Besides total alkaline phosphatase, other markers such as bone-specific alkaline phosphatase, osteocalcin, or the collagen propeptides are being used to measure bone formation. Bone resorption, previously assessed only by the measurement of urinary calcium and hydroxyproline, may now be detected more precisely by a number of new serum and urine markers. Among these, the pyridinium crosslinks and the telopeptides of collagen type I are presently considered the most specific markers of bone resorption. More recently, bone sialoprotein has also been suggested as a marker of bone resorption in serum. Tartrate-resistant acid phosphatase is now measurable by immunoassay. This article surveys the biochemistry and relevant technical aspects of the currently available markers of bone metabolism.

Biochemical markers of bone turnover. Applications for osteoporosis

The recent discovery of specific and sensitive biochemical markers reflecting the overall rate of bone formation and bone resorption has markedly improved the noninvasive assessment of bone turnover in various metabolic bone diseases, especially in osteoporosis. The immunoassay of human osteocalcin, recognizing the intact molecule and its major proteolytic fragment, and assays for bone alkaline phosphatase and the intact form of the N-terminal extension propeptide of type I collagen are currently the most sensitive markers for assessing bone formation. The best indices of bone resorption are the new immunoassays for pyridinoline cross-links and type I collagen-related peptides in urine and, recently, in serum. Several studies indicate that screening for these bone markers may be useful for improving the prognostic assessment of postmenopausal women in combination with bone mass measurement, that is, their risk for osteoporosis and, ultimately, for fractures and to monitor rapidly the efficacy of antiresorptive drugs.