Technical and clinical validation of a new immunoradiometric assay for human osteocalcin

Osteocalcin: A bone protein with multiple endocrine functions

Bones are now recognised as endocrine organs with diverse functions. Osteocalcin, a protein primarily produced by osteoblasts, has garnered significant attention. Research into osteocalcin has revealed its impact on glucose metabolism and its unexpected endocrine role, particularly in its undercarboxylated form (ucOC). This form influences organs, affecting insulin sensitivity and even showing correlations with conditions like type 2 diabetes and cardiovascular diseases. However, analytical challenges are impeding advances in clinical research. Various immunoassays like RIA, EIA, ECLIA, IRMA, and ELISA have been developed to analyse osteocalcin. Recent innovations include techniques like OS-ELISA and OS phage Immuno-PCR, enabling fragment analysis. Advancements also encompass porous silicon for detection and ECLIA for rapid measurements. The limitations of immunoassays lead to ucOC measurement discrepancies, prompting the development of mass spectrometry-based techniques. Mass spectrometry increasingly quantifies carboxylated, undercarboxylated, and fragmented forms of osteocalcin. Mass spectrometry improves routine and clinical analysis accuracy. With heightened specificity, it identifies carboxylation status and serum fragmentations, boosting measurement reliability as a reference method. This approach augments analytical precision, advancing disease understanding, enabling personalised medicine, and ultimately benefiting clinical outcomes. In this review, the different techniques for the analysis of osteocalcin will be explored and compared, and their clinical implications will be discussed.

Plasma osteocalcin levels as a predictor of cardiovascular disease in older men and women: a population-based cohort study

OBJECTIVE

The role of osteocalcin (OC) in cardiovascular disease (CVD) is unresolved. We aimed to study the association between plasma OC concentrations and the risk of non-fatal and fatal CVDs. We also aimed to investigate whether such an association, if present, would be mediated by established metabolic risk factors.

DESIGN

A population-based longitudinal cohort study.

METHODS

In 1995/1996, OC was determined in blood samples drawn from 1319 subjects aged 65-88 years participating in the Longitudinal Aging Study Amsterdam in 1995/1996. The self-reported CVD events were collected every 3 years until 2005/2006, and CVD deaths until 1st January 2007. Cox proportional hazards regression was performed, considering potential confounders (smoking, physical activity, and BMI) and mediators (blood pressure, plasma triglycerides, total and HDL cholesterol, fructosamine, and aortic calcification).

RESULTS

During the median 4.1 years follow-up, 709 subjects (53.8%) suffered a CVD event. There was no overall association between OC and CVD: hazard ratio (HR) was 0.97 (95% CI 0.90-1.04) per nmol/l higher plasma OC, adjusted for age and sex. There was a statistical interaction between plasma OC, age, and sex on CVD (P=0.014). In those subjects aged ≥75 years, age-adjusted HRs (95% CI) were 0.86 (0.75-0.99) in men and 1.16 (1.03-1.31) in women per nmol/l higher plasma OC. Adjustment for covariates only slightly attenuated the association in older-old men, but did not affect the association in older-old women.

CONCLUSION

A higher plasma OC concentration was associated with a reduced risk of CVD in older-old men and with an increased risk of CVD in older-old women. We found no evidence that this was mediated by arterial calcification or metabolic risk factors.

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

OBJECTIVE

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

PARTICIPANTS AND METHODS

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

RESULTS

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

CONCLUSION

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

Contribution of the putative genetic factors and ANKH gene polymorphisms to variation of circulating calciotropic molecules, PTH and BGP

It is well known that regulation of calcium homeostasis in bone remodeling is one of the most crucial factors for maintaining healthy bones. Parathyroid hormone (PTH) is probably the most important hormone that participates in the bone remodeling process. Another important biochemical factor governing bone metabolism is osteocalcin (BGP). Although the physiological functions of both of these factors are well known, there is still very little known regarding their specific genetic determination and in particular, the specific genes that may regulate the circulating concentrations of these substances. In the present study, we examined whether nine single nucleotide polymorphisms (SNPs) in the human homologue of the mouse progressive ankylosis gene (ANKH)-one of the key genetic factors involved in bone mineralization-can be associated with PTH and BGP levels in apparently healthy human populations. The study sample comprised 244 nuclear families (840 individuals). After adjustment of BGP and PTH for the significant covariates (sex, age and BMI), the contribution of the putative genetic effects was statistically significant (P < 0.001) for both biochemical factors: 45.27 +/- 10.8% for PTH and 30.19 +/- 12.6% for BGP. Application of transmission disequilibrium tests (TDTs) revealed a significant association (P < 0.05) between PTH and two SNPs: rs39968 and rs875525. However, the association became particularly significant for four TDTs (P-values ranging from 0.0025 to 0.0008) when the association with the haplotypes generated from the above SNP was tested. This association remained significant even after correction for multiple testing with a false discovery rate of 0.05.

Tartrate-resistant acid phosphatase 5b activity is a useful bone marker for monitoring bone metastases in breast cancer patients after treatment

Metabolic markers of bone metabolism may be useful for the diagnosis and monitoring of bone metastasis in breast cancer patients. Serum tartrate-resistant acid phosphatase 5b (TRACP5b) activity is a novel bone resorption marker. The treatment response of serum TRACP5b activity, bone alkaline phosphatase (BAP) activity, and concentrations of NH(2)-terminal telopeptide of type 1 collagen (NTX) in 68 breast cancer patients with bone metastasis were determined. These patients were treated and followed up as clinically indicated. Fifty-four healthy women were recruited as control. Serum TRACP5b activity, BAP activity, and NTX level of breast cancer patients with bone metastasis were significantly higher than those of normal controls. In normal subjects, serum TRACP5b activity and NTX level are significantly correlated (P < 0.0001). Neither was correlated with BAP activity. In breast cancer patients with bone metastasis, all marker pairs correlated to each other significantly (P < 0.0001). Biomarkers were examined repeatedly in 38 patients who were evaluable for treatment response. Based on clinical criteria, 20 patients were responders and 18 were nonresponders. In the 20 responders, serum TRACP5b activity and NTX level decreased significantly (P < 0.0001 and 0.0107, respectively) after treatment. In the 18 nonresponders, only NTX level showed significant increase (P = 0.0342) after treatment; TRACP5b and BAP were unchanged. By means of multiple logistic regression with stepwise selection, we determined that TRACP5b activity has a higher probability than NTX level to indicate treatment response as a function of percent change after treatment (18 times versus 12 times). Our data support the use of either TRACP5b activity or NTX level to follow up breast cancer patients with bone metastasis after treatment instead of the prevailing BAP activity.

Changes in bone density and metabolism in pregnancy

OBJECTIVE

The impact of pregnancy on maternal bone density remains unclear. As a prerequisite to investigate the pathophysiology of gestational bone metabolism, we sought to document the changes in bone metabolism biochemistry in conjunction with those in selective trabecular/cortical osteodensitometry between early and late pregnancy.

METHODS

A prospective, controlled study in a university hospital was conducted with 43 healthy women, 34 of them during uneventful pregnancy. The main outcome measures are trabecular and cortical bone density measured in the first and third trimesters using peripheral quantitative computed tomography in conjunction with a panel of bone metabolism parameters, including blood parathyroid hormone, calcitonin, osteocalcin, skeletal alkaline phosphatase, and the urinary desoxypyridinoline/creatinine ratio.

RESULTS

Cortical bone density was unaffected by pregnancy. Trabecular bone density changes showed wide interindividual variation, ranging from +1.3 to -20.7% per year, identified as fast losers (less than -3%) and slow losers (more than -3%). Serum osteocalcin levels were lower in slow versus fast bone losers in both trimesters (first: P=0.02, third: P=0.02) and were the only independent parameter to differentiate between fast and slow losers.

CONCLUSIONS

Our data suggest that wide interindividual variation and the failure to provide a separate measure of trabecular bone density account for the conflicting evidence in earlier reports. Serum osteocalcin concentration during the first trimester distinguishes between fast and slow losers of trabecular bone and should be evaluated in future studies as predictor for later bone loss (osteoporosis).

Efficacy and Safety of Ibandronate in the Treatment of Opioid-Resistant Bone Pain Associated With Metastatic Bone Disease: A Pilot Study

Purpose

Bone metastases are associated with severe and sometimes intractable pain, compromising patient quality of life (QOL). This open-label pilot study investigated the effects of short-term intensive treatment with intravenous (IV) ibandronate on opioid-resistant bone pain in patients with skeletal metastases.

Patients and Methods

Eighteen patients with advanced tumors and metastatic bone disease received nonstandard treatment with 4 mg of ibandronate administered IV (2-hour infusion) for 4 consecutive days (16-mg total dose). Baseline opioid analgesic use was equivalent to 400 mg/d of morphine. Patients were assessed for 6 weeks or until death. Changes from baseline were determined for bone pain, opioid consumption, patient functioning, QOL, performance status, and biochemical markers of calcium metabolism and bone turnover. Renal function was assessed by serum urea and creatinine measurement.

Results

Short-term, intensive ibandronate treatment significantly reduced bone pain scores within 7 days (P < .001). Pain reductions were sustained over the study period. Ibandronate significantly improved QOL, patient functioning, and performance status (P < .05). Mean values of the urinary cross-links pyridinoline and deoxypyridinoline tended to increase after day 21, returning close to baseline values by day 42. There was no correlation between the change in crosslinks values and the change in pain scores after ibandronate treatment. Ibandronate was well tolerated, with no evidence of renal toxicity.

Conclusion

Nonstandard, intensive treatment with IV ibandronate seems to have a marked analgesic effect in patients with opioid-resistant bone pain from metastatic bone disease. Further investigation is warranted.

Hypercalcemia of malignancy

Less than 25 years ago tumor-induced hypercalcemia was often a lethal complication of cancer. Nowadays, it can be treated easily and successfully in at least 90% of cases by volume repletion in addition to the use of bisphosphonates that are potent anti-osteoclastic compounds. The standard therapy consists of the administration of 90 mg pamidronate or, more recently, 4 mg zoledronic acid, a more efficient bisphosphonate. When available, another alternative bisphosphonate is ibandronate. Recurrent hypercalcemia is nevertheless difficult to control and antibodies against parathyroid hormone-related protein could be useful for that matter in selected patients who are not in the terminal stage of their disease. Prevention of tumor-induced hypercalcemia is one of the objectives of long-term therapy with bisphosphonates in patients with tumor bone disease. The use of bisphosphonates in placebo-controlled trials has shown that the incidence of hypercalcemic episodes is reduced by more than one half.

Treatment of tumor-induced hypercalcemia: a solved problem?

Less than 25 years ago, tumor-induced hypercalcemia was often a lethal complication of cancer. Nowadays, it can be successfully and easily treated in at least 90% of the cases by rehydration and potent antiosteoclastic bisphosphonates. The standard therapy consists of the administration of 90 mg of pamidronate (Aredia Dry Powder) or more recently, 4 mg of zoledronic acid (Zometa)], which is even more efficient, at least in patients without bone metastases. Recurrent hypercalcemia is nevertheless difficult to control and antibodies against parathyroid-hormone-related protein may prove to be a useful treatment.

Influence of adjuvant tamoxifen treatment on bone mineral density and bone turnover markers in postmenopausal breast cancer patients in Japan

The effect of adjuvant tamoxifen treatment on bone mineral density (BMD) and bone turnover markers was studied in postmenopausal breast cancer patients. The relationship of tamoxifen's effect with the genetic polymorphisms of estrogen receptor (ER)-alpha and ER-beta gene was also studied. Twenty-one postmenopausal breast cancer patients were given tamoxifen (20 mg/day) as the adjuvant treatment after the surgery. BMD of the lumbar supine (dual emission X-rays absorptiometry) and bone resorption (deoxypyridinoline, aminoterminal telopeptide of type I collagen, and carboxyterminal telopeptide of type I collagen) and formation (propeptide of type I procollagen, osteocalcin, and bone-specific alkaline phosphatase) markers were examined at baseline (before the surgery), 6 and 12 months after the start of tamoxifen treatment. Genetic polymorphisms analyzed were TA dinucleotide repeats polymorphism in the promoter region and PvuII and XbaI restriction fragment length polymorphism for the ER-alpha gene and the CA dinucleotide repeats polymorphism in the intron 5 for the ER-beta gene. Tamoxifen significantly increased BMD of the lumbar spine at both 6 (P<0.01) and 12 months (P<0.01) after the start of tamoxifen as compared with that at baseline. The mean percent increase in BMD was 3.3% at 6 months and 2.7% at 12 months. All bone resorption and formation markers significantly decreased at both 6 and 12 months. Among the four genetic polymorphisms studied, only ER-beta CA repeat polymorphism was found to be significantly associated with BMD at 12 months, i.e. BMD of the 21 CA repeats allele carriers was significantly higher than that of the non-carriers (P=0.025). These results suggest that tamoxifen increases BMD of the lumbar supine by reducing the bone turnover in postmenopausal breast cancer patients, and this bone restoring effect of tamoxifen is more marked in ER-beta 21 CA repeats allele carriers than non-carriers.

Hypercalcaemia of melanoma: incidence, pathogenesis and therapy with bisphosphonates

Tumour-induced hypercalcaemia (TIH) is a frequent complication of advanced cancer but has been rarely reported in patients with malignant melanoma, and its pathogenesis remains unexplored. We studied eight patients with TIH and melanoma. We determined the incidence and pathogenesis of this complication and the effects of bisphosphonate therapy. The incidence of TIH in 751 patients with melanoma was 1.1%. All patients had liver and bone metastases at the time of hypercalcaemia. All patients had osteolytic lesions, most often multiple. The median survival was 30 days (range 4-136 days). After rehydration, the mean (+/- SEM) corrected calcium was 3.42 +/- 0.17 mmol/l. Parathyroid hormone levels were adequately suppressed and vitamin D concentrations were normal. Serum osteocalcin, a marker of bone formation, was low, except in the two patients with renal insufficiency, whereas fasting urinary calcium and hydroxyproline were increased, indicating inhibition of bone formation and stimulation of bone resorption. Increased parathyroid hormone-related protein secretion was noted in only one patient. Three of four patients became normocalcaemic after bisphosphonate therapy for a median duration of 2 weeks. In conclusion, hypercalcaemia is a rare complication of melanoma. It occurs in the context of far advanced disease and is essentially due to aggressive lytic bone metastases with an uncoupling in bone turnover. Bisphosphonates can offer short-term palliation.

Current and future directions in medical therapy: hypercalcemia

BACKGROUND

Tumor-induced hypercalcemia (TIH) is essentially due to a marked stimulation of osteoclast-mediated bone resorption. An inhibition of bone formation and an enhanced tubular reabsorption of calcium play an important contributory role. These factors explain why serum calcium often rises rapidly in cancer patients and why high doses of bisphosphonates are needed to normalize bone resorption and to overcome the contributory role of the kidney.

METHODS

The author provides a short review of clinical trials in hypercalcemic cancer patients, with an emphasis on the most recent trials.

RESULTS

Rehydration and bisphosphonates now constitute the standard treatment of TIH. A single-day 1500-mg infusion of clodronate achieves normocalcemia in approximately 80% of the cases. Clodronate also can be given by subcutaneous infusion that can be particularly useful in the palliative setting. A dose of 90 mg of pamidronate achieves normocalcemia in more than 90% of the patients and has a longer-lasting effect than clodronate. Newer more potent bisphosphonates, such as ibandronate and zoledronate, may improve these results, and they certainly will simplify the therapeutic schemes. Ibandronate at the dose of 6 mg normalizes serum calcium in more than 75% of the patients with moderate or severe hypercalcemia. Of note, the same doses of pamidronate and ibandronate, repeated monthly for 1-2 years, have been shown to substantially reduce the skeletal morbidity rate in normocalcemic patients with tumor bone disease. Even lower doses of zoledronate, the most potent bisphosphonate tested so far, are able to correct TIH when administered as a 30-minute infusion.

CONCLUSIONS

Bisphosphonates have become the standard treatment for cancer hypercalcemia. Success is achieved in more than 90% of the cases. Other classes of compounds are being tested for their antiosteoclastic activity, and animal studies suggest that osteoprotegerin could be as efficient and act faster than bisphosphonates.

Development and Evaluation of Three Immunofluorometric Assays That Measure Different Forms of Osteocalcin in Serum

Background: Circulating human osteocalcin (hOC) has been used as a marker of bone formation. Our aim was to validate three immunofluorometric assays (IFMAs), measuring different forms of hOC.

Methods: The two-site IFMAs were based on previously characterized monoclonal antibodies. Assay 2 recognized intact hOC, assays 4 and 9 measured the NH2-terminal mid-fragment and the intact hOC. In addition, assay 9 required hOC to be γ-carboxylated.

Results: A 76–79% increase of serum immunoreactive hOC was found in the postmenopausal group compared with the premenopausal group with all IFMAs. With EDTA-plasma samples, the observed increases were lower (49–65%). The hOC concentration in the postmenopausal group receiving hormone replacement therapy was 42–44% lower than that in the postmenopausal control group in both serum and EDTA-plasma samples. The depressed carboxylation in warfarin-treated patients was accompanied by lower results in assay 9. The ratio of assay 9 to assay 4 totally discriminated the warfarin-treated patients from the controls. Assay 9 showed the smallest decreases in measured hOC after storage of serum or plasma for 4 weeks at 4 °C, followed by assay 4 and assay 2. Results from the last assay were &lt;17% of their initial values after 4 weeks of storage. No diurnal variation was observed with assay 9 as opposed to the two other IFMAs.

Conclusion: The three assays with their distinct specificity profiles (intact vs fragmented and carboxylated vs decarboxylated hOC) may provide valuable tools for investigating the significance of different hOC forms in various bone-related diseases.

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.