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)

Latest Advances in Structural Insights and Quantification Techniques for Type I Collagen Biomarkers: A path toward standardization?

With an aging population, the demand for sensitive and specific biomarkers to assess bone turnover has surged. Bone turnover involves 2 key processes: bone formation, during which Type I procollagen is cleaved into Type I collagen and subsequently mineralized into bone, and bone resorption, during which Type I collagen is demineralized and degraded into peptides by cathepsin K. To identify biomarkers that accurately reflect these processes, extensive efforts have been made to characterize the peptides generated during both formation and resorption. Over the years, numerous biomarkers have been discovered for various disorders. However, despite their clinical utility, many of these markers lack specificity. This is due to factors such as the degradation of trimers into monomers, the coexistence of multiple peptide species arising from the unpredictable cleavage of Type I collagen/procollagen by cathepsin K and metalloproteinases, and the lack of assay standardization. Standardization is further hindered by the incomplete characterization of many of these peptides. For accurate assay development, a gold-standard technique like LC-MS/MS is essential, requiring full peptide characterization during method development. This review aims to present recent advances in the characterization of Type I collagen-derived peptides, providing a foundation for improved biomarker standardization and application in clinical practice.

Update on the role of bone turnover markers in the diagnosis and management of osteoporosis: a consensus paper from The European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO), International Osteoporosis Foundation (IOF), and International Federation of Clinical Chemistry and Laboratory Medicine (IFCC)

PURPOSE

The International Osteoporosis Foundation (IOF) and the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) have proposed procollagen type I N propeptide (PINP) and β isomerized C-terminal telopeptide of type I collagen (β-CTX-I) as reference bone turnover markers (BTMs) for osteoporosis. This report examines the published literature since the 2011 IOF-IFCC position paper in order to determine the clinical potential of the reference BTMs and newer markers for the prediction of fracture risk and monitoring the treatment of osteoporosis.

METHODS

Evidence for the relationship between BTMs and subsequent fractures was gathered from prospective studies through literature review of the Medline database from years 2011 to May 2024. The impact of treatment on BTMs was also studied by examining publications in that period. Studies of the accuracy of BTMs in the assessment of bone turnover in the setting of advanced chronic kidney disease were also examined.

RESULTS

Increased BTM concentrations are associated with higher fracture risk in postmenopausal women. PINP and β-CTX-I measured in blood are associated with fracture risk but their interaction with other risk factors has not been sufficiently studied limiting their incorporation into fracture risk algorithms. Treatment-induced changes in PINP and β-CTX-I account for a substantial proportion of fracture risk reduction and are useful for improving adherence; they are recommended for inclusion in studies to examine adherence in individual patients. However, total PINP (tPINP) and β-CTX-I may be elevated in CKD due to renal retention. Bone alkaline phosphatase (BALP), intact PINP (iPINP), and tartrate resistant acid phosphatase 5b (TRACP5b) show the most promise in discriminating high and low turnover bone diseases in patients with advanced CKD and for predicting fracture risk, monitoring treatment response, and assessing the risk of treatment-related complications.

CONCLUSION

We re-affirm the use of serum/plasma tPINP and plasma β-CTX-I as reference BTMs with appropriate patient preparation and sample handling and measurement by standardized/harmonized assays in clinical studies to accumulate further data, and for monitoring treatment of osteoporosis in the setting of normal renal function in clinical practice. BALP and TRACP5b, measured by standardized assays, are recommended as reference BTMs for CKD-associated osteoporosis and should be included in observational and intervention studies to ascertain their utility for risk-evaluation, treatment initiation, and assessment of treatment response in CKD-associated osteoporosis.

Characterization of Trivalently Crosslinked C-Terminal Telopeptide of Type I Collagen (CTX) Species in Human Plasma and Serum Using High-Resolution Mass Spectrometry

With an aging population, the increased interest in the monitoring of skeletal diseases such as osteoporosis led to significant progress in the discovery and measurement of bone turnover biomarkers since the 2000s. Multiple markers derived from type I collagen, such as CTX, NTX, PINP, and ICTP, have been developed. Extensive efforts have been devoted to characterizing these molecules; however, their complex crosslinked structures have posed significant analytical challenges, and to date, these biomarkers remain poorly characterized. Previous attempts at characterization involved gel-based separation methods and MALDI-TOF analysis on collagen peptides directly extracted from bone. However, using bone powder, which is rich in collagen, does not represent the true structure of the peptides in the biofluids as it was cleaved. In this study, our goal was to characterize plasma and serum CTX for subsequent LC-MS/MS method development. We extracted and characterized type I collagen peptides directly from human plasma and serum using a proteomics workflow that integrates preparative LC, affinity chromatography, and HR-MS. Subsequently, we successfully identified numerous CTX species, providing valuable insights into the characterization of these crucial biomarkers.

Bone turnover markers, and growth and bone parameters in infants participating in a vitamin D intervention study

Amino-terminal propeptide of type 1 procollagen (P1NP) and carboxy-terminal crosslinked telopeptide of type 1 collagen (CTX-I) are markers of bone metabolism. We examined the effect of vitamin D3 supplementation on these markers and their relationship with growth and bone parameters in 12-month-old infants. In a randomized, double-blinded, vitamin D intervention in infants (VIDI) study, 987 infants received daily vitamin D3 supplementation of 10 μg (group-10) or 30 μg (group-30) from age 2 weeks to 24 months. We conducted a secondary analysis of the original VIDI trial. At 12 months of age, P1NP (n = 812) and CTX-I (n = 786) concentrations were analyzed, and anthropometrics and total bone mineral content, volumetric bone mineral density, cross-sectional area and polar moment of inertia of tibia were measured by peripheral quantitative computed tomography. The growth rate in weight and length was calculated from birth to 12 months. The vitamin D dose did not influence mean (SD) levels of CTX-I (group-10: 0.90 (0.31); group-30: 0.89 (0.31) (P > 0.53)). The mean difference of P1NP (CI 95%) comparing group-10 with group-30 was 35 (-103, 33) ng/mL (P = 0.31) in boys and -63 (-4, 130) ng/mL (P = 0.064) in girls. In group-10, girls had higher mean (SD) value of P1NP (1509 (362) ng/mL) than boys (1407 (297) ng/mL) (P = 0.003); no sex differences were observed in group-30 (girls: 1446 (359); boys: 1442 (359), P = 0.91) or CTX-I. P1NP associated positively with the growth rate in length (B (CI 95%) 0.0003 (0.0001, 0.001), P = 0.022) in the whole cohort but not in subgroups divided by the intervention group or sex, adjusted for birth size and parental heights and corrected for multiple testing. P1NP associated positively with the growth rate in weight (0.01 (0.0003, 0.01), P < 0.001). An inverse association was observed between CTX-I and length (cm) in the whole cohort (-0.90 (-1.40, -0.40), P = 0.005) and in group-30 (-1.05 (-1.72, -0.39), P = 0.011). Furthermore, CTX-I associated negatively with weight (SDS) in the whole cohort (-0.33 (-0.55, -0.12), P = 0.015) and the growth rate in weight (-0.43 (-0.66, -0.20), P = 0.005), persisting in group-30 and in boys but not in group-10 or in girls. Neither marker was associated with bone parameters. The observed sex difference in P1NP might suggest that a higher vitamin D dose resulted in a small decrease in bone collagen matrix formation in girls but not in boys. P1NP and CTX-I associate with growth and body size but not with bone mineralization in infancy.

A single bout of jumping exercise does not modulate serum markers of bone formation or bone resorption throughout a 24 h period

INTRODUCTION

This randomized, cross-over trial assessed the effect of a single bout of high-impact exercise on serum markers of bone formation and bone resorption over a 24 h period.

METHODS

Twenty healthy males and females performed a single bout of brief jumping exercise (EXC) or no exercise (CON), 55 min following consumption of a standard breakfast. Blood markers of bone formation (P1NP) and bone resorption (CTX-I) were assessed before (t = 0 h) and over a 5 h period after breakfast, and following 24 h of post-exercise recovery (t = 24 h).

RESULTS

Serum CTX-I concentrations decreased during the 5 h postprandial period (time-effect, P < 0.001) with no differences between conditions (time x condition, P = 0.14). After a ~ 16 % decline during the first 30 min following breakfast, serum P1NP concentrations gradually returned to baseline values during the 5 h postprandial period, with no differences in the overall response between conditions (time-effect, P < 0.001; time x condition, P = 0.25). Fasted serum CTX-I concentrations decreased from 0.33 ± 0.15 and 0.35 ± 0.15 ng/mL at baseline, to 0.31 ± 0.13 and 0.31 ± 0.16 ng/mL at t = 24 h in CON and EXC, respectively, with no differences between conditions (time-effect, P < 0.01; time x condition, P = 0.70). Fasted serum P1NP concentrations did not change from baseline to t = 24 h in both CON (baseline: 76 ± 27 ng/mL, t = 24 h: 79 ± 26 ng/mL) and EXC (baseline: 80 ± 24 ng/mL, t = 24 h: 77 ± 29 ng/mL; time-effect, P = 0.89), with no differences between conditions (time x condition, P = 0.22).

CONCLUSION

High-impact exercise does not modulate the concentrations of the serum marker of bone formation P1NP and the serum marker of bone resorption CTX-I throughout a 24 h recovery period in healthy adults.

Amoli M, Fana SE, Dimai HP, Obermayer-Pietsch B, Luegger B, Rivadeneira F, Nabipour I, Larijani B, Khashayar P. Protocol for preliminary, multicenteric validation of "PoCOsteo device": A point of care tool for proteomic and genomic study of osteoporosis

One of the goals of the HORIZON 2020 project PoCOsteo was to develop a medical device, which would measure and/or quantify proteomic as well as genomic factors as present in whole blood samples collected through finger prick. After validating the tool in the clinical setting, the next step would be its clinical validation based on the existing guidelines. This article presents the protocol of a validation study to be carried out independently at two different centers (Division of Endocrinology and Diabetology at the Medical University of Graz as a clinic-based cohort, and the Endocrinology and Metabolism Research Institute at the Tehran University of Medical Sciences as a population-based cohort). It aims to assess the tool according to the Clinical & Laboratory Standards Institute guidelines, confirming if the proteomics and genomics measurements provided by the tool are accurate and reproducible compared with the existing state-of-the-art tests. This is the first time that such a detailed protocol for lab validation of a medical tool for proteomics and genomic measurement is designed based on the existing guidelines and thus could be used as a template for clinical validation of future point-of-care tools. Moreover, the multicentric cohort design will allow the study of a large number of diverse individuals, which will improve the validity and generalizability of the results for different settings.

Clinical use of bone markers: a challenge to variability

Bone markers are a group of substances released into circulation during bone formation and/or resorption. These substances can be measured in blood and urine to obtain information about metabolic bone disorders. This review provides an insight into factors influencing bone marker variability and describes different approaches to minimize variability and interpret results appropriately. Variability in bone marker concentrations results from biological and analytical variability across assays. Other influencing factors include gender, age, physical exercise, circadian rhythm, and diet. The multiplicity of influencing factors hinders the establishment of accurate reference values. Gaining a deep understanding of bone marker variability is the first step to ascertain their clinical usefulness. Bone marker variability can be minimized by controlling as many variables as it is possible and through the standardization of patient preparation and sample collection and handling.

Utilidad clínica de los biomarcadores óseos: un desafío a la variabilidad

Los biomarcadores óseos son un conjunto de sustancias que son liberadas a la circulación sanguínea durante el proceso de formación y/o resorción ósea y que podemos medir en sangre y orina para obtener información sobre los trastornos metabólicos del hueso. La revisión traza una perspectiva sobre los factores que influyen en la variabilidad de los biomarcadores óseos y describe los aspectos a considerar para reducirla al máximo e interpretar los resultados de manera adecuada. La variabilidad que podemos observar en la concentración de los biomarcadores óseos engloba diversos aspectos que abarcan desde su variabilidad biológica y la variabilidad de los ensayos empleados en su medida hasta la variabilidad derivada de la influencia de numerosos factores, entre los cuales el sexo, la edad, el ejercicio, su ritmo circadiano o la dieta. Todo ello se refleja en la dificultad de establecer valores de referencia precisos. El conocimiento de esta variabilidad es el primer desafío que debe afrontar su empleo en la práctica clínica. Es necesario minimizar la variabilidad de los biomarcadores óseos controlando el máximo de variables que sea posible, así como estandarizando la preparación del paciente antes de la toma de las muestras, así como su obtención y manejo.

Low bone mineral density and reduced bone-specific alkaline phosphatase in 5q spinal muscular atrophy type 2 and type 3: A 2-year prospective study of bone health

AIM

Individuals with spinal muscular atrophy (SMA) are at risk of developing skeletal problems. This study investigated bone mineral density (BMD), bone turnover markers and motor function in children and adolescents with SMA type 2 and type 3 over a two-year period. The effect of nusinersen was studied in a subgroup.

METHODS

Single-centre study, including 20 patients, 2-18 years, of whom ten patients received nusinersen treatment. BMD was measured by dual-energy X-ray absorptiometry.

RESULTS

All patients had low BMD levels at baseline; mean Z-score -2.3 for total body less head (TBLH) and -2.9 for total hip left (THL). Significant correlations were found both at baseline and for the follow-up change for motor function and Z-scores (TBLH and THL). For the whole study group, reduced bone formation and unchanged bone resorption, assessed by bone-specific alkaline phosphatase (BALP) (p = 0.0006, ES = -0.83) and C-terminal cross-linking telopeptide of type I collagen (CTX), respectively, were found over the study period. However, BALP decreased less in the nusinersen treatment group, which suggests a positive development on bone mass in these patients.

CONCLUSION

Bone health evaluation is important in follow-up programmes for SMA patients. Further investigations are warranted for individuals on survival motor neuron-targeted treatments.

Innovative workflow for the identification of cathepsin K cleavage sites in type I collagen

Since the late 1990s, cathepsin K cleavage sites in type I collagen have been extensively studied due to its ability to release bone resorption biomarkers such as CTX and NTX. However, gel-based methods and N-sequencing used in these studies lack sensitivity, especially for small to medium peptides. In this work, we propose a degradomics mass spectrometry-based workflow that combines protein digestion, Nano-LC-UDMSE, and several software tools to identify cathepsin K cleavage sites. This workflow not only identified previously known cleavage sites, but also discovered new ones. Multiple cleavage hotspots were found and described in type I α1 and type I α2 collagen, many of which coincided with pyridinoline crosslinks, known to stabilize the triple helix. Our results allowed us to establish a chronology of digestion and conclude that cathepsin K preferentially cleaves the extremities of type I collagen before the helical part. We also found that cathepsin K preferentially cleaves amino acid residues with long and hydrophobic lateral chains at the beginning of digestion, whereas no preferred amino acid residues were identified later in the digestion. In conclusion, our workflow successfully identified new cleavage sites and can be easily applied to other proteins or proteases.

Bone Turnover Markers in Children: From Laboratory Challenges to Clinical Interpretation

Bone turnover markers (BTMs) have been developed many years ago to study, in combination with imaging techniques, bone remodeling in adults. In children and adolescents, bone metabolism differs from adults since it implies both growth and bone remodeling, suggesting an age- and gender-dependent BTM concentration. Therefore, specific studies have evaluated BTMs in not only physiological but also pathological conditions. However, in pediatrics, the use of BTMs in clinical practice is still limited due to these many children-related specificities. This review will discuss about physiological levels of BTMs as well as their modifications under pathological conditions in children and adolescents. A focus is also given on analytical and clinical challenges that restrain BTM usefulness in pediatrics.

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.

Prevention and Treatment of Glucocorticoid-Induced Osteoporosis in Adults: Consensus Recommendations From the Belgian Bone Club

Glucocorticoids are effective immunomodulatory drugs used for many inflammatory disorders as well as in transplant recipients. However, both iatrogenic and endogenous glucocorticoid excess are also associated with several side effects including an increased risk of osteoporosis and fractures. Glucocorticoid-induced osteoporosis (GIOP) is a common secondary cause of osteoporosis in adults. Despite availability of clear evidence and international guidelines for the prevention of GIOP, a large treatment gap remains. In this narrative review, the Belgian Bone Club (BBC) updates its 2006 consensus recommendations for the prevention and treatment of GIOP in adults. The pathophysiology of GIOP is multifactorial. The BBC strongly advises non-pharmacological measures including physical exercise, smoking cessation and avoidance of alcohol abuse in all adults at risk for osteoporosis. Glucocorticoids are associated with impaired intestinal calcium absorption; the BBC therefore strongly recommend sufficient calcium intake and avoidance of vitamin D deficiency. We recommend assessment of fracture risk, taking age, sex, menopausal status, prior fractures, glucocorticoid dose, other clinical risk factors and bone mineral density into account. Placebo-controlled randomized controlled trials have demonstrated the efficacy of alendronate, risedronate, zoledronate, denosumab and teriparatide in GIOP. We suggest monitoring by dual-energy X-ray absorptiometry (DXA) and vertebral fracture identification one year after glucocorticoid initiation. The trabecular bone score might be considered during DXA monitoring. Extended femur scans might be considered at the time of DXA imaging in glucocorticoid users on long-term (≥ 3 years) antiresorptive therapy. Bone turnover markers may be considered for monitoring treatment with anti-resorptive or osteoanabolic drugs in GIOP. Although the pathophysiology of solid organ and hematopoietic stem cell transplantation-induced osteoporosis extends beyond GIOP alone, the BBC recommends similar evaluation, prevention, treatment and follow-up principles in these patients. Efforts to close the treatment gap in GIOP and implement available effective fracture prevention strategies into clinical practice in primary, secondary and tertiary care are urgently needed.

Analytical evaluation of the Nittobo Medical tartrate resistant acid phosphatase isoform 5b (TRACP-5b) EIA and comparison with IDS iSYS in different clinically defined populations

OBJECTIVES

Tartrate-resistant acid phosphatase, isoform 5b (TRACP-5b) is a bone resorption marker not influenced by renal function or food intake. TRACP-5b can be measured with Nittobo Medical enzymatic-immunoassay and IDS-iSYS automated immunoassay. We evaluated the Nittobo assay and established reference ranges for a Western-European population. We compared Nittobo and IDS results in different well-defined clinical populations.

METHODS

We established the limits of detection and quantification (LOD-LOQ), linearity, imprecision and the reference ranges in 119 males, 50 women (<45 years) and 120 women (>60 years) for TRACP-5b with the Nittobo assay. We compared both assays in 30 hemodialyzed (HD), and 40 stage 3-5 patients suffering from chronic kidney disease (CKD), 40 patients suffering from rheumatoid arthritis and osteoporosis and 80 post-menopausal women. We measured TRACP-5b, β-crosslaps (β-CTX), bone alkaline phosphatase (B-ALP) and PTH in 20 hemodialyzed (HD) and 40 CKD patients.

RESULTS

LOD and LOQ were 0.02 and 0.35 U/L. CV ranged from 8.3 to 4.3% (2/5 samples presenting CV > desirable CV). Method was linear up to of 11.3 U/L. Upper and lower limits of normality were 0.8-7.6 U/L in men, 0.9-4.7 U/L in women <45 and 0.9-7.1 U/L in women >60. The regression equation between the 2 methods was Nittobo = 1.13 (95% CI: 1.09-1.16) × iSYS - 0.4 (95% CI: -0.5; -0.3). TRACP-5b and b-ALP were in their respective reference ranges for most of CKD and HD patients. That was not the case for β-CTX, which increased with decreasing eGFR.

CONCLUSIONS

Nittobo TRACP-5b presents interesting analytical features and a good concordance with IDS iSYS. These methods could thus potentially be harmonized.