Serum and plasma fragments of C-telopeptides of type I collagen (CTX) are stable during storage at low temperatures for 3 years

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.

Dose-response effects of alcohol on biochemical markers of bone turnover in non-human primates: Effects of species, sex and age of onset of drinking

Purpose

Alcohol consumption suppressed bone turnover in male non-human primates; however, it is unclear the extent to which this effect depends upon biological variables. Using archived plasma samples, we investigated whether sex, age of onset of alcohol intake, and species influence the effects of graded increases in alcohol consumption on bone turnover markers.

Methods

91 male and female macaques (rhesus and cynomolgus), ranging in age from 4 years (adolescent) to 10 years (adult) were required to increase their consumption of ethanol in 30-day increments: 0 g/kg/day, followed by 0.5 g/kg/day, 1.0 g/kg/day, and, finally, 1.5 g/kg/day. Plasma osteocalcin (formation), plasma CTX (resorption) and osteocalcin to CTX ratio (turnover balance) were measured during these intervals to assess the dose-response effects of alcohol.

Results

We detected no relationship between dose and osteocalcin when all monkeys were combined, but there was a significant effect of sex (lower levels in females) and interactions between alcohol dose and sex (osteocalcin levels increased with dose in rhesus females). In contrast, we detected a negative linear dose-response relationship for ethanol and CTX. We did not detect a relationship between dose and osteocalcin to CTX ratio overall, but there was a significant positive relationship detected in females (no change in males). Increased age predicted lower biomarker levels for both osteocalcin and CTX. Species was a significant predictor for osteocalcin and the osteocalcin to CTX ratio in these models.

Conclusion

These findings indicate that age, sex, and species influence bone turnover and support the concept that factors beyond quantity of alcohol affect skeletal response to alcohol consumption.

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Age, sex, and species influenced markers of bone turnover in non-human primates.

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Ethanol consumption resulted in a dose-dependent reduction in CTX.

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Ethanol consumption resulted in increased osteocalcin in rhesus females.

A Multicenter Study to Evaluate Harmonization of Assays for C-Terminal Telopeptides of Type I Collagen (ß-CTX): A Report from the IFCC-IOF Committee for Bone Metabolism (C-BM)

BACKGROUND

Biochemical bone turnover markers are useful tools to assess bone remodeling. C-terminal telopeptide of type I collagen (ß-CTX) has been recommended as a reference marker for bone resorption in research studies.

METHODS

We describe the results of a multicenter study for routine clinical laboratory assays for ß-CTX in serum and plasma. Four centers (Athens GR, Copenhagen DK, Liege BE and Sheffield UK) collected serum and plasma (EDTA) samples from 796 patients presenting to osteoporosis clinics. Specimens were analyzed in duplicate with each of the available routine clinical laboratory methods according to the manufacturers' instructions. Passing-Bablok regressions, Bland-Altman plots, V-shape evaluation method, and Concordance correlation coefficient for ß-CTX values between serum and plasma specimens and between methods were used to determine the agreement between results. A generalized linear model was employed to identify possible variables that affected the relationship between the methods. Two pools of serum were finally prepared and sent to the four centers to be measured in 5-plicates on 5 consecutive days with the different methods.

RESULTS

We identified significant variations between methods and between centers although comparison results were generally more consistent in plasma compared to serum. We developed univariate linear regression equations to predict Roche Elecsys®, IDS-iSYS, or IDS ELISA ß-CTX results from any other assay and a multivariable model including the site of analysis, the age, and weight of the patient. The coefficients of determination (R²) increased from approximately 0.80 in the univariate model to approximately 0.90 in the multivariable one, with the site of analysis being the major contributing factor. Results observed on the pools also suggest that long-term storage could explain the difference observed with the different methods on serum.

CONCLUSION

Our results show large within- and between-assay variation for ß-CTX measurement, particularly in serum. Stability of the analyte could be one of the explanations. More studies should be undertaken to overcome this problem. Until harmonization is achieved, we recommend measuring ß-CTX by the same assay on EDTA plasma, especially for research purposes in large pharmacological trials where samples can be stored for long periods before they are assayed.

Bone fragment or bone powder? ATR-FTIR spectroscopy-based comparison of chemical composition and DNA preservation of bones after 10 years in a freezer

Freezing bone samples to preserve their biomolecular properties for various analyses at a later time is a common practice. Storage temperature and freeze-thaw cycles are well-known factors affecting degradation of molecules in the bone, whereas less is known about the form in which the tissue is most stable. In general, as little intervention as possible is advised before storage. In the case of DNA analyses, homogenization of the bone shortly before DNA extraction is recommended. Because recent research on the DNA yield from frozen bone fragments and frozen bone powder indicates better DNA preservation in the latter, the aim of the study presented here was to investigate and compare the chemical composition of both types of samples (fragments versus powder) using ATR-FTIR spectroscopy. Pairs of bone fragments and bone powder originating from the same femur of 57 individuals from a Second World War mass grave, stored in a freezer at - 20 °C for 10 years, were analyzed. Prior to analysis, the stored fragments were ground into powder, whereas the stored powder was analyzed without any further preparation. Spectroscopic analysis was performed using ATR-FTIR spectroscopy. The spectra obtained were processed and analyzed to determine and compare the chemical composition of both types of samples. The results show that frozen powdered samples have significantly better-preserved organic matter and lower concentrations of B-type carbonates, but higher concentrations of A-type carbonates and stoichiometric apatite. In addition, there are more differences in the samples with a low DNA degradation index and less in the samples with a high DNA degradation index. Because the results are inconsistent with the current understanding of bone preservation, additional research into optimal preparation and long-term storage of bone samples is necessary.

Biochemically Tracked Variability of Blood Plasma Thawed-State Exposure Times in a Multisite Collection Study

The integrity of blood plasma/serum (P/S) specimens can be impacted by preanalytical handling and storage conditions that result in thawed-state exposures (> -30°C). We recently reported a simple dilute-and-shoot, intact-protein liquid chromatography/mass spectrometry (LC/MS) assay called ΔS-Cys-Albumin that quantifies cumulative exposure of P/S to thawed conditions based on the change in relative abundance of the oxidized (S-cysteinylated) proteoform of albumin (S-Cys-Albumin) in the native sample to that of an aliquot of the sample intentionally driven to its maximum oxidation state. Herein, we evaluated the effect of prestorage delay and initial storage temperature on sample integrity by applying the ΔS-Cys-Albumin assay to a set of plasma samples (n = 413) collected under a single clinical study but from 12 different collection sites. Major differences (p < 0.0001) were observed between different groups of samples with modestly inconsistent initial handling conditions (i.e., initial processing of whole blood to plasma and placement at -80°C completed in under 3 hours, 3-13 hours, and over 17 hours). ΔS-Cys-Albumin was significantly inversely correlated with delay time at 4°C before centrifugation and total delay before final storage at -80°C (p < 0.0001). Samples from two collection sites had much lower ΔS-Cys-Albumin values relative to samples from other sites, in accordance with the fact that they were stored at -20°C for an average of 7.6 months before shipment to the central repository for final storage at -80°C. Based on the rate law for S-Cys-Albumin formation in plasma ex vivo, the average time that each plasma specimen had been exposed to the equivalent of room temperature (23°C) was back calculated from the measured ΔS-Cys-Albumin values. A survey of clinical analytes in P/S whose measured concentrations are sensitive to the initial handling/storage conditions documented in this study is provided and the ramifications of the plasma integrity findings from this multisite clinical study are discussed.

Bone resorption in dogs with calcium oxalate urolithiasis and idiopathic hypercalciuria

People with calcium oxalate (CaOx) urolithiasis and idiopathic hypercalciuria (IH) often have evidence of increased bone resorption, but bone turnover has not previously been investigated in dogs with these conditions. The aim of this study was to determine whether a marker of bone resorption, β-crosslaps, differs between dogs with CaOx urolithiasis and IH compared to controls. This retrospective, cross-sectional study used a canine specific ELISA to measure β-crosslaps concentrations in stored frozen serum samples from 20 dogs with CaOx urolithiasis and IH and 20 breed-, sex-, and age-matched stone-free controls (18 Miniature Schnauzers, 14 Bichons Frise, and 8 Shih Tzus). Dogs with CaOx urolithiasis and IH had lower β-crosslaps concentrations relative to controls (P = .0043), and β-crosslaps had a moderate negative correlation with urinary calcium-to-creatinine ratios (r = -0.44, P = .0044). Miniature Schnauzers had lower β-crosslaps concentrations than the other two breeds (P = .0035). The ELISA had acceptable intra-assay precision, but concentrations decreased when samples were repeatedly assayed over time. Assay recovery rates were also below acceptance criteria. In conclusion, Miniature Schnauzers, Bichons Frise, and Shih Tzus with CaOx urolithiasis and IH have evidence of decreased bone resorption compared to stone-free controls. This suggests that other causes of IH, such as intestinal hyperabsorption of calcium, underlie risk for CaOx urolithiasis in these breeds. Results should be confirmed in larger populations and with other β-crosslaps assays and additional biomarkers of bone turnover. The stability of canine serum β-crosslaps after freeze-thaw cycles and storage at various temperatures requires investigation.

Bone markers in polycystic ovary syndrome: A multicentre study

OBJECTIVE

Hyperandrogenism, hyperinsulinaemia and obesity, known characteristics of polycystic ovary syndrome (PCOS), may influence bone mineral density and biochemical markers of bone turnover (BTMs) can provide a noninvasive assessment of bone turnover. To this end, the serum concentrations of BTMs and 25-hydroxyvitamin D (25OHD) were analysed in women with PCOS, and their possible associations with metabolic parameters of PCOS were determined.

SUBJECTS AND METHODS

Bone formation markers procollagen type I amino-terminal propeptide (PINP) and osteocalcin (OC), and bone resorption marker carboxy-terminal cross-linking telopeptide of type I collagen (CTX), along with 25OHD, were measured in 298 women with PCOS and 194 healthy controls.

RESULTS

Serum levels of PINP (47.0 ± 20.2 vs 58.1 ± 28.6 μg/L, P < .001) and OC (18.2 ± 7.5 vs 20.6 ± 9.8 μg/L, P < .001) were decreased in women with PCOS compared with controls, whereas no significant differences were found in CTX and 25OHD levels. Age-stratified analyses suggested that PINP (50.5 ± 21.7 vs 68.2 ± 26.6 μg/L, P < .001) and OC levels (20.4 ± 7.6 vs 25.5 ± 9.6 μg/L, P < .001) were decreased only in the younger age group (≤30 years) women with PCOS compared with controls. The formation markers and resorption marker decreased with age in both study groups.

CONCLUSIONS

Bone formation markers were decreased in younger women with PCOS when compared with healthy women, which may affect bone mass in these women.

Use of CTX-I and PINP as bone turnover markers: National Bone Health Alliance recommendations to standardize sample handling and patient preparation to reduce pre-analytical variability

The National Bone Health Alliance (NBHA) recommends standardized sample handling and patient preparation for C-terminal telopeptide of type I collagen (CTX-I) and N-terminal propeptide of type I procollagen (PINP) measurements to reduce pre-analytical variability. Controllable and uncontrollable patient-related factors are reviewed to facilitate interpretation and minimize pre-analytical variability.

INTRODUCTION

The IOF and the International Federation of Clinical Chemistry (IFCC) Bone Marker Standards Working Group have identified PINP and CTX-I in blood to be the reference markers of bone turnover for the fracture risk prediction and monitoring of osteoporosis treatment. Although used in clinical research for many years, bone turnover markers (BTM) have not been widely adopted in clinical practice primarily due to their poor within-subject and between-lab reproducibility. The NBHA Bone Turnover Marker Project team aim to reduce pre-analytical variability of CTX-I and PINP measurements through standardized sample handling and patient preparation.

METHODS

Recommendations for sample handling and patient preparations were made based on review of available publications and pragmatic considerations to reduce pre-analytical variability. Controllable and un-controllable patient-related factors were reviewed to facilitate interpretation and sample collection.

RESULTS

Samples for CTX-I must be collected consistently in the morning hours in the fasted state. EDTA plasma is preferred for CTX-I for its greater sample stability. Sample collection conditions for PINP are less critical as PINP has minimal circadian variability and is not affected by food intake. Sample stability limits should be observed. The uncontrollable aspects (age, sex, pregnancy, immobility, recent fracture, co-morbidities, anti-osteoporotic drugs, other medications) should be considered in BTM interpretation.

CONCLUSION

Adopting standardized sample handling and patient preparation procedures will significantly reduce controllable pre-analytical variability. The successful adoption of such recommendations necessitates the close collaboration of various stakeholders at the global stage, including the laboratories, the medical community, the reagent manufacturers and the regulatory agencies.

Measurement and Clinical Utility of βCTX in Serum and Plasma

Biochemical markers of bone turnover (BTM) are released during bone remodeling and can be measured in blood or urine as noninvasive surrogate markers for the bone remodeling rate. The C-terminal cross-linked telopeptide of type I collagen (βCTX) is released during bone resorption and is specific to bone tissue. Assays have been developed to measure βCTX in blood and in urine; most current use of βCTX measurement for research and in clinical practice is performed on a blood sample. Method-specific differences for serum and plasma βCTX have led to initiatives to standardize or harmonize βCTX commercial assays. βCTX demonstrates significant biological variation due to circadian rhythm and effect of food which can be minimized by standardized sample collection in the fasting state in the morning. While βCTX predicts fracture risk independent of bone mineral density, lack of data has precluded its inclusion in fracture risk calculators. The changes seen in βCTX with antiresorptive therapies have been well characterized and this has led to its widespread use for monitoring therapy in osteoporosis. However, more fracture-based data on appropriate treatment goals for monitoring need to be developed. Evidence is lacking for the use of βCTX in managing "drug holidays" of bisphosphonate treatment in osteoporosis or risk stratifying those at increased risk of developing osteonecrosis of the jaw. βCTX is useful as an adjunct to imaging techniques for the diagnosis of Paget's disease of bone and for monitoring therapy and detecting recurrence. βCTX also shows promise in the management of metastatic bone disease.

Storage of human biospecimens: selection of the optimal storage temperature

Millions of biological samples are currently kept at low tempertures in cryobanks/biorepositories for long-term storage. The quality of the biospecimen when thawed, however, is not only determined by processing of the biospecimen but the storage conditions as well. The overall objective of this article is to describe the scientific basis for selecting a storage temperature for a biospecimen based on current scientific understanding. To that end, this article reviews some physical basics of the temperature, nucleation, and ice crystal growth present in biological samples stored at low temperatures (-20°C to -196°C), and our current understanding of the role of temperature on the activity of degradative molecules present in biospecimens. The scientific literature relevant to the stability of specific biomarkers in human fluid, cell, and tissue biospecimens is also summarized for the range of temperatures between -20°C to -196°C. These studies demonstrate the importance of storage temperature on the stability of critical biomarkers for fluid, cell, and tissue biospecimens.

The clinical utility of bone marker measurements in osteoporosis

Osteoporosis is characterised by low bone mass and structural deterioration of bone tissue, resulting in increased fragility and susceptibility to fracture. Osteoporotic fractures are a significant cause of morbidity and mortality. Direct medical costs from such fractures in the UK are currently estimated at over two billion pounds per year, resulting in a substantial healthcare burden that is expected to rise exponentially due to increasing life expectancy. Currently bone mineral density is the WHO standard for diagnosis of osteoporosis, but poor sensitivity means that potential fractures will be missed if it is used alone. During the past decade considerable progress has been made in the identification and characterisation of specific biomarkers to aid the management of metabolic bone disease. Technological developments have greatly enhanced assay performance producing reliable, rapid, non-invasive cost effective assays with improved sensitivity and specificity. We now have a greater understanding of the need to regulate pre-analytical sample collection to minimise the effects of biological variation. However, bone turnover markers (BTMs) still have limited clinical utility. It is not routinely recommended to use BTMs to select those at risk of fractures, but baseline measurements of resorption markers are useful before commencement of anti-resorptive treatment and can be checked 3–6 months later to monitor response and adherence to treatment. Similarly, formation markers can be used to monitor bone forming agents. BTMs may also be useful when monitoring patients during treatment holidays and aid in the decision as to when therapy should be recommenced. Recent recommendations by the Bone Marker Standards Working Group propose to standardise research and include a specific marker of bone resorption (CTX) and bone formation (P1NP) in all future studies. It is hoped that improved research in turn will lead to optimised markers for the clinical management of osteoporosis and other bone diseases.

Age-related reference intervals for bone turnover markers from an Australian reference population

BACKGROUND

This study was performed to establish age-related serum reference intervals for procollagen type I N-propeptide (P1NP) and type I collagen C-telopeptide (CTx) in the Australian population.

METHODS

Fasting sera from 1143 males (mean age 60 years; range 20-97 years) and 1246 females (mean age 53 years; range 20-93 years) who participated in the Geelong Osteoporosis Study were analysed for CTx and P1NP using the automated Roche Modular Analytics E170 analyser.

RESULTS

Optimal age-related reference intervals were based on the central 90% of the distribution. The male CTx reference interval was divided into three age groups. For men aged 25 to 40 years, the interval was 170-600 ng/L; 40 to 60 years, the interval was 130-600 ng/L; and for men aged greater 60 years the interval was 100-600 ng/L. For P1NP the male reference interval was 15-80 μg/L for men aged between 25 to 70 years. In men greater than 70 years of age values were higher possibly due to increased bone turnover. High values are frequently seen for both CTx and P1NP in males aged younger than 25 years. This is probably due to bone growth that is not completely finalised. The female CTx reference interval was divided into four age groups. For women aged less than 30 years, the interval was 150-800 ng/L; 30-39 years, the interval was 100-700 ng/L; 40-49 years, the interval was 100-600 ng/L; and for women aged 50 years or more the interval was 100-700 ng/L. The female P1NP reference interval was divided into four age groups. For women aged less than 30 years, the interval was 25-90 μg/L; 30-39 years, the interval was 15-80 μg/L; 40-49 years, the interval was 15-60 μg/L; and for women aged 50-69 years the interval was 15-75 μg/L. In women greater than 70 years of age values were higher possibly due to increased bone turnover.

CONCLUSION

Values obtained from this large study provide sound age-related reference intervals for serum P1NP and CTx values in the Australian population.

Clusters within a wide spectrum of biochemical markers for osteoarthritis: data from CHECK, a large cohort of individuals with very early symptomatic osteoarthritis

OBJECTIVE

To assess a wide spectrum of biochemical markers (biomarkers) in a large cohort of individuals with (very) early symptomatic knee and/or hip osteoarthritis (OA). Secondly, to investigate associations between biomarkers and between biomarkers and demographics to demonstrate validity of the obtained dataset and further investigate the involvement and/or role of these biomarkers in OA.

DESIGN

Fourteen biomarkers (uCTX-II, uCTX-I, uNTX-I, sCOMP, sPIIANP, sCS846, sC1,2C, sOC, sPINP, sHA, sPIIINP, pLeptin, pAdiponectin, pResistin) were assessed by ELISA or RIA in CHECK (Cohort Hip and Cohort Knee), a 10-year prospective cohort of 1,002 individuals with early symptomatic knee and/or hip OA.

RESULTS

Quality controls revealed that gathered data were technically reliable. The majority of biomarkers showed relevant associations with demographic variables, which were expectedly different between genders and/or menopausal status for some. Principal component analysis enabled identification of five clusters, consecutively designated as 'bone-CTX-II', 'inflammation', 'synovium', 'C1,2C-adipokines', and 'cartilage synthesis' cluster. Notably, uCTX-II clustered with biomarkers of bone metabolism, while sCOMP clustered with biomarkers of synovial activity.

CONCLUSIONS

The identified clusters extended knowledge on individual biomarkers from mostly smaller studies as did the observed associations between biomarker levels and demographics, from which validity of our data was deduced. uCTX-II may not only reflect articular cartilage but also bone metabolism and sCOMP may reflect synovial rather than cartilage metabolism. Major involvement of adipokines in joint metabolism was not identified.

A lifecourse study of bone resorption in men ages 49-51years: the Newcastle Thousand Families cohort study

It has been suggested that bone health in adulthood is programmed by development in utero. Most previous investigations addressing this topic have focussed on bone mineral density or content, rather than other indicators of bone health, such as biochemical markers of bone turnover. This study investigated whether potential predictors, from different stages of life, influence bone resorption in men aged 49-51years in the Newcastle Thousand Families birth cohort. The cohort originally consisted of all 1142 births in the city of Newcastle upon Tyne, UK in May and June 1947. Detailed information was collected prospectively during childhood, including birth weight and socio-economic circumstances. At 49-51years of age, 574 study members completed a detailed 'Health and Lifestyle' questionnaire, including the European Prospective Investigation of Cancer (EPIC) food frequency questionnaire and 412 study members attended for clinical examination, including 172 men in whom bone resorption was assessed by measurement of serum beta C-telopeptide of type 1 collagen (CTX). A significant trend was seen between increasingly disadvantaged socio-economic status at birth and increased bone resorption (p=0.04, r-squared 2.6%). However, birth weight, standardised for sex and gestational age, was not associated with serum CTX (p=0.77, r-squared 0.05%). Significant trends were also seen between increasing total energy intake (p=0.03, r-squared 2.9%), dietary intake of saturated fat (p=0.02, r-squared 2.6%), protein (p=0.04, r-squared 2.5%) and carbohydrates (p=0.04, r-squared 2.6%) and higher serum CTX. However, on adjustment for total energy intake, none of the other dietary variables was significant at the univariate level maintained significance. Our findings suggest that early socio-economic disadvantage and later dietary factors may be associated with increased bone resorption in middle aged men. However, as little of the variance in serum CTX was explained by the variables included within this investigation, further longitudinal studies, with sufficient statistical power, are required to assess predictors of bone resorption in adulthood and their relative importance.

Multiple myeloma: changes in serum C-terminal telopeptide of collagen type I and bone-specific alkaline phosphatase can be used in daily practice to detect imminent osteolysis

Objective: Monitoring of bone disease in multiple myeloma is becoming increasingly important because bone-protecting treatment with bisphosphonate is becoming restricted after the awareness of osteonecrosis of the jaw. Despite the potential of biochemical markers of bone remodeling to monitor dynamic bone turnover, they are not used in everyday practice. Here, we investigate their usefulness to detect imminent progressive osteolysis in relapsing patients with multiple myeloma. Methods: In an unselected cohort of 93 patients, we measured the bone resorption markers C-terminal telopeptide of collagen type I (CTX-I), C-terminal cross-linked telopeptide of type-I collagen generated by MMPs (ICTP), N-terminal cross-linked telopeptide of type-I collagen (NTX-I), and the bone formation marker bone-specific alkaline phosphatase (bALP) monthly for 2 yr. Retrospectively, we identified 40 cases where patients had progressive disease. We investigated how the bone markers developed prior to disease progression. Results: We observed that CTX-I and bALP changed significantly before progressive disease were recognized. More interestingly, these changes differed depending on whether concurrent progressive osteolysis was present. In patients with progressive osteolysis, there was a large increase in bone resorption which was not compensated by increased bone formation. In contrasts, patients with stable bone disease had only a slight increase in bone resorption which was compensated by concurrent increased bone formation. By calculating a patient-specific CTX-I/bALP ratio, we quantified the risk a patient experiences if the ratio increases. Conclusion: By analyzing patient-specific changes in the ratio of CTX-I/bALP, we might tailor treatment with bone-protecting agents in the individual patient.

Diabetes and skeletal health

Osteoporosis and diabetes affect a large proportion of the elderly population. The prevalence of diabetes and osteoporosis is increasing. Compared with individuals without diabetes, both men and women with diabetes have a higher risk of fractures, particularly at the hip, with consequent significant morbidity and mortality. Type 1 diabetes is associated with decreased bone mass and although bone mass data for Type 2 diabetes may or may not be decreased, there is evidence of altered bone quality in diabetes. The mechanisms involved include effects of insulin, insulin-like growth factor 1, cytokines, advanced glycation end products, and altered calcium homeostasis. In addition, a drug-induced increase in the incidence of fractures has been noted with the use of thiazolidinediones (TZDs). TZDs improve insulin sensitivity and have multitude other beneficial effects. Osteoblasts and adipocytes are derived from a common multipotential mesenchymal stem cell progenitor, with activation of peroxisome proliferator-activated receptor γ2 by both currently available TZDs (i.e. rosiglitazone and pioglitazone) stimulating adipogenesis and inhibiting osteoblastogenesis. The use of both rosiglitazone and pioglitazone is associated with an increased fracture risk, with changes in bone turnover markers and decreased bone mineral density.

Bone markers and current laboratory assays

Metastasis of cancer to bone leads to significant alterations in normal bone remodelling that are reflected in changes in bone turnover markers. These markers are classically defined as markers of bone resorption or formation; markers of bone resorption are measures of osteoclastic activity, whereas markers of bone formation are measures of osteoblastic activity. Recently, there has been growing interest in the use of these markers in metastatic bone disease (MBD), and an increasing number of studies have investigated the potential use of these markers in diagnosis, monitoring of disease progression and treatment, and prediction of outcome. In this review, we briefly discuss the biology of bone metastases as well as describe the bone turnover markers and their possible role in aiding clinicians in the treatment of patients with MBD.

Lack of hepatic metabolism of C-telopeptides of type I collagen

BACKGROUND

Bone biochemical markers have been used in dynamic studies of bone metabolism, and, for accurate interpretation of measured marker levels, it is essential to have information of extra-skeletal metabolism. Therefore, the objective of the present study was to investigate if the circulating C-telopeptides of type I collagen (CTX) was subject to hepatic extraction.

METHODS

Splanchnic plasma flow, total plasma volume and the plasma concentration of CTX was determined in an artery and the liver vein of eight healthy female volunteers. For comparison, the concentration of N-terminal propeptide of type I collagen, PINP, was measured.

RESULTS

No change in plasma level of CTX could be detected over the liver. In contrast, PINP decreased from an average of 52.9 ng/ml in the artery to 42.4 ng/ml in the vein, corresponding to a 19.8% reduction.

CONCLUSIONS

The C-telopeptides of type I collagen (CTX) are not subject to hepatic metabolism.