Serum osteocalcin and bone mineral density at various skeletal sites: a study performed with three different assays

Update on the safety and efficacy of teriparatide in the treatment of osteoporosis

Following the completion of the Fracture Prevention Trial, teriparatide was approved by the United States Food and Drug Administration and the European Medicine Agency as the first therapeutic anabolic agent for the treatment of postmenopausal women with severe osteoporosis. It subsequently received additional approval for the treatment of osteoporosis in men, and for the treatment of osteoporosis associated with glucocorticoid therapy in men and women at risk of fracture. In this review, we summarize the most important data concerning PTH 1-34 therapy before 2016 in the treatment of osteoporosis, and report some outstanding results published in the last 2 years. New data on safety will also discussed, together with the state of art of nonclassical utilization. Finally, in view of the recent approval of biosimilars, possible future landscapes are discussed.

Puerarin enhances proliferation and osteoblastic differentiation of human bone marrow stromal cells via a nitric oxide/cyclic guanosine monophosphate signaling pathway

Puerarin, a major active isoflavone extracted from the Traditional Chinese Medicine Radix Puerariae, has been studied for its comprehensive biological effects. However, to date, its effect on bone formation and the underlying mechanism of action have not been well investigated. The present study investigated the effect of puerarin on cell proliferation and osteoblastic maturation in cultured human bone marrow stromal cells (hBMSC) in vitro. Puerarin (2.5-100 µM) increased hBMSC growth in a dose-dependent manner, as indicated by an MTT assay, and stimulated osteoblastic maturation as indicated by assessment of alkaline phosphatase (ALP) activity, as well as calcium deposition into the extracellular matrix detected by alizarin red S staining. Furthermore, polymerase chain reaction analysis showed that the expression of osteoblastic markers, including Runt-related transcription factor 2/core-binding factor alpha 1, osterix and osteocalcin, were increased in hBMSCs following incubation with puerarin. Further experiments indicated that puerarin increased the nitric oxide (NO) production and cyclic guanosine monophosphate (cGMP) content in hBMSCs. The effects of puerarin were mimicked by 17β-estrodiol (10(-8) M) and were abolished in the presence of estrogen receptor antagonist ICI182780 (10(-7) M). A NO synthase inhibitor, Nx-nitro-L-arginine methylester (6 x 10(-3) M), significantly attenuated puerarin-induced increases in NO production and cGMP content, in parallel with a reduction of cell proliferation and osteoblastic differentiation as well as the expression of osteoblastic markers. These results suggested that puerarin may prevent osteoporosis by exerting stimulatory effects on bone formation and the NO/cGMP pathway, which has an important role in puerarin-induced hBMSC proliferation and osteoblastic differentiation.

Associations between ambient air pollution and bone turnover markers in 10-year old children: results from the GINIplus and LISAplus studies

Negative associations between bone turnover markers and bone mineral density have been reported. In order to study the association between ambient air pollution and bone turnover markers, as indicators of bone loss, we investigated associations between land-use regression modeled air pollution (NO2, PM2.5 mass, PM2.5 - 10 [coarse particles], PM10 mass and PM2.5 absorbance) and bone turnover markers in 2264 children aged 10 years. Serum osteocalcin and C-terminal telopeptide of type I collagen (CTx), measured by Modular-System (Roche), were the two bone turnover markers considered in this analysis. In total population, NO2, PM2.5 - 10 and PM10 mass exposure were positively and significantly associated with both osteocalcin and CTx. A 2.5 (95% CI: 0.6, 4.4) ng/ml increase in osteocalcin and a 24.0 (95% CI: 6.7, 41.3) ng/L increase in CTx were observed per IQR (6.7μg/m(3)) increase in NO2, independent of socioeconomic status, sex, age, pubertal status, fasting status and total physical activity. The estimated coefficients were 3.0 (95% CI: 0.1, 5.8) for osteocalcin and 32.3 (95% CI: 6.1, 58.5) for CTx with PM2.5 - 10; 3.2 (95% CI: 0.0, 6.4) for osteocalcin and 30.7 (95% CI: 1.7, 59.7) for CTx with PM10. Children living close to a major road (≤ 350m) had higher levels of both osteocalcin (1.4 [-1.2, 4.0] ng/ml) and CTx (16.2 [-7.4, 39.8] ng/L). The adverse impact of ambient air pollution on bone turnover rates observed in one of the study areas showed stimulation of more such studies.

Clinical usefulness of bone markers in prostate cancer with bone metastasis

Bone metastases occur in approximately 70% of patients with advanced prostate cancer. Skeletal-related events have been correlated with reduced survival and quality of life of patients with prostate cancer. Biochemical markers of bone metabolism (e.g. bone formation, bone resorption, osteoclastogenesis) might meet an unmet need for useful, non-invasive and sensitive surrogate information for following patients' skeletal health. Recently, zoledronic acid and denosumab have been proven to have the potential for preventing skeletal-related events among prostate cancer patients with bone metastasis. An improved understanding of the mechanisms underlying bone metastasis has also led to the recognition of multiple molecular targets and advances in therapy. However, estimating the efficacy of these agents is difficult. A clinical trial for castration-resistant prostate cancer is currently underway based on the definition of The Prostate Cancer Clinical Trials Working Group, and bone turnover markers are being used as conventional end-points for the clinical trial. Bone turnover markers are useful surrogate markers reflecting the effect of new therapeutic drugs and prognosis, as well as assessment of bone metastases. In particular, N-terminal cross-linked telopeptide of type 1 collagen and bone-specific alkaline phosphatase are widely used bone metabolism markers, and offer reliable surrogate markers to detect bone metastatic spread and to predict prognosis for prostate cancer patients with bone metastases.

Association of osteocalcin and abdominal aortic calcification in older women: the study of osteoporotic fractures

Osteocalcin (OC) is produced by osteoblasts and vascular smooth muscle cells. In animal models, serum OC levels are strongly correlated with vascular calcium content, however, the association of OC with vascular calcification in humans is uncertain. The Study of Osteoporotic Fractures (SOF) enrolled community-living women, age > or =65 years. The present study included a subsample of 363 randomly selected SOF participants. Serum total OC was measured by ELISA, and abdominal aortic calcification (AAC) was evaluated on lateral lumbar radiographs. We examined the cross-sectional association between serum OC and AAC. The mean serum OC level was 24 +/- 11 ng/ml and AAC was present in 188 subjects (52%). We observed no association of OC and AAC in either unadjusted or adjusted analyses. For example, each standard deviation higher OC level was associated with an odds ratio (OR) for AAC prevalence (AAC score >0) near unity (OR = 1.06; 95% CI, 0.82-1.36) in models adjusted for CVD risk factors. Further adjustment for intact parathyroid hormone, bone-specific alkaline phosphatase, 25-hydroxyvitamin D, and hip and spine bone mineral density did not materially change the results (OR = 1.22; 95% CI, 0.86-1.75). Similarly, higher OC levels were not associated with severity of AAC (P = 0.87). In conclusion, among community-living older women, serum OC is not associated with AAC. These findings suggest that serum OC levels may more closely reflect bone formation than vascular calcification in humans.

Changes of bone formation markers osteocalcin and bone-specific alkaline phosphatase in postmenopausal women with osteoporosis

The relationship between bone formation markers osteocalcin (OC) and bone-specific alkaline phosphatase (bALP) and age in postmenopausal women was investigated. Forty-eight osteoporotic women (median age 62, range 49-76 years) were enrolled in the study. There were 17 (35%) patients aged 49-59 years (Group A), and 31 (65%) patients aged over 59 years (Group B). Parathyroid hormone, calcium, and creatinine serum levels did not differ significantly between groups. Compared with Group A, patients in Group B had higher levels of both OC (28.5 +/- 17.8 versus 46.2 +/- 19.3 ng/mL; P= 0.003) and bALP (57.3 +/- 12.4 versus 66.4 +/- 8.7 U/L; P= 0.005). A significant relationship between age and both OC (R= 0.49, P= 0.002) and bALP (R= 0.41, P= 0.009) was found only in Group B, but there was no relationship with bone mineral density. In conclusion, in postmenopausal women the increase of bone formation markers later in life may be an expression of increased bone turnover, which is partially the cause of osteoporosis.

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).

Biochemical markers of bone formation in Thai children and adolescents

The measurement of biochemical markers of bone turnover is essential in the study of skeletal metabolism in health and diseases. Due to variations in the rate of bone growth in different age groups and possible ethnic differences, age-specific reference ranges for biochemical markers should be established in a particular pediatric population. In this study, biochemical markers of bone formation, bone-specific alkaline phosphatase (BAP), and osteocalcin (OC) in healthy Thai children and adolescents aged 9 to 18 years were evaluated in relation to their ages and pubertal development. Serum BAP levels in boys increased with age and peaked at about 12 to 13 years. In contrast, there was a progressive decline of serum BAP levels with advancing age in girls older than 9 years. Serum OC also increased with age and reached a peak at ages 12 and 13 years in girls and boys, respectively. In addition, both serum BAP and OC levels also varied with pubertal stages. The BAP levels in boys increased sharply at pubertal stage 3 and decreased at pubertal stage 5. In girls, the BAP levels showed a fairly constant high level up to stage 3, followed by a remarkable decrease thereafter. The OC levels in boys increased sharply at pubertal stage 4 and decreased thereafter. In girls, OC started to increase at pubertal stage 3 with no subsequent changes. The levels of serum BAP and OC were higher in boys than in girls at pubertal stages 3 to 5 and at stages 2, 4, and 5, respectively. Moreover, only serum BAP level showed significant positive correlation with height velocity in both genders. In multiple regression analyses, gender, age, and pubertal stage were consistently correlated with both serum BAP and OC levels. In summary, male and female adolescents have different patterns of changes in biochemical markers of bone formation.

Biochemical markers for prediction of 4-year response in bone mass during bisphosphonate treatment for prevention of postmenopausal osteoporosis

Short-term changes in biochemical markers of bone turnover (bone markers) have been suggested as predictors of long-term response in bone mass during antiresorptive treatment. In the Danish cohort (n = 306) of the Early Postmenopausal Intervention Cohort (EPIC) Study (n = 1609) of oral alendronate (ALN) for prevention of postmenopausal osteoporosis, bone markers (urine C-telopeptides of type I collagen (uCTX), urine N-telopeptide cross-links of type I collagen (uNTX), serum total osteocalcin measured by ELISA [total OC (ELISA)], and serum total osteocalcin measured by RIA [total OC (RIA)]) were measured at 6-month intervals. The correlation between 6-month change in uCTX and 4-year change in spine and hip bone mineral density (BMD) was r = -0.41 and r = -0.42, respectively (P < 0.001). The corresponding values for the other bone markers were r = -0.53 and r = -0.42 (uNTX), r = -0.46 and r = -0.47 [total OC (ELISA)], and r = -0.43 and r = -0.41 [total OC (RIA)], all P < 0.001. ROC curves were used to analyse the ability of the bone markers to predict a change in spine BMD greater than 0%. The best performance [defined as the maximum value of (sensitivity plus specificity)] was found at the cut-off values of a -29% change from baseline in uCTX, a -45% change from baseline in uNTX, a -13% change from baseline in total OC (ELISA), and a -15% change from baseline in total OC (RIA). At these values the corresponding sensitivity was 66% (uCTX), 76% (uNTX), 70% [total OC (ELISA)], and 83% [total OC (RIA)]. The specificity was 80% (uCTX), 75% (uNTX), 71% [total OC (ELISA)], and 55% [total OC (RIA)]. The positive predictive value (PPV) was 82% (uCTX), 80% (uNTX), 77% [total OC (ELISA)], and 71% [total OC (RIA)]. The negative predictive value (NPV) was 64% (uCTX), 70% (uNTX), 64% [total OC (ELISA)], and 71% [total OC (RIA)]. In conclusion, the bone markers predicted a change in spine BMD greater than 0% with a high PPV and specificity. There was a trend toward better performance in this respect for the bone resorption markers.

Short-term low-dose heparin plus bedrest impairs bone metabolism in pregnant women

OBJECTIVE

To assess the osteoporotic risk of short-term low-dose heparin plus bedrest in pregnancy.

STUDY DESIGN

In a prospective case-control study, 10 pregnant women on bedrest receiving prophylactic unfractionated heparin 10,000 IU per day for 7-46 days pre-study and 28 days per-study were compared with 6 normal pregnant controls of similar maternal and gestational age and 10 nonpregnant women of similar age. Serum ionised calcium, 1,25-dihydroxyvitamin D(3), osteocalcin, and urinary calcium/creatinine ratio were determined three times at 2-week intervals.

RESULTS

1,25-Dihydroxyvitamin D(3) was lower in the treated group than in pregnant controls throughout (P<0.03). Osteocalcin was lower at study start than end in both pregnant groups (P<0.05), and lower in the treated group than in either pregnant (n.s.) or nonpregnant controls (P<0.005). Calcium/creatinine ratio differences were non significant (n.s.).

CONCLUSION

Short-term low-dose heparin plus bedrest suppresses 1,25-dihydroxyvitamin D(3) and osteocalcin levels in pregnancy.

Short-term effects of surgery in post-menopausal patients with primary hyperparathyroidism and normal bone turnover

The most common clinical presentation of primary hyperparathyroidism (PHPT) is nowadays characterized by a slight skeletal involvement. We studied 5 consecutive female patients with PHPT presenting with bone turnover marker levels within the reference range of our Center and whose bone mineral density values were above the usual fracture risk threshold. In each patient we measured, both in basal conditions and daily, for the first 5 days after surgery, the following indexes: serum total (T-ALP) and bone-specific (B-ALP) alkaline phosphatase activity, osteocalcin (BGP, by two different assays), together with the 24-hour urinary excretions of total pyridinoline (Pyr/Cr) and deoxypyridinoline (DPyr/Cr), free deoxypyridinoline (FD-Pyr/Cr), cross-linked N-telopeptide of type I collagen (NTx/Cr), and type I C-telopeptide (CTx/Cr). The markers of both bone formation and resorption significantly decreased after surgery (p<0.001 by multiple ANOVA). Individual post-surgical markers changes were all significant but T-ALP and FD-Pyr, the most pronounced percent reductions being shown by NTx and CTx. The time-course of such variations substantially differed among the various indexes. These results show that bone formation and resorption markers are up-regulated also in PHPT patients with mild skeletal involvement; acute removal of parathyroid hormone excess differently affected the markers of bone turnover in terms of both entity and time-course.

Correlations between osteocalcin content, degree of mineralization, and mechanical properties of C. carpio rib bone

Osteocalcin is one of the most abundant noncollagenous proteins in bone. It is strongly associated with the mineral phase of bone, and has long been associated as a marker of bone turnover. However, its relationship to bone composition, strength, and structure is unclear. Carp rib bone is an excellent model for the study, because osteocalcin represents almost 60% of the total extractable noncollagenous proteins found in it. Because of the abundance of osteocalcin relative to other extractable proteins, any changes in the properties of carp rib bone would be more likely influenced by the osteocalcin concentration. To test the hypotheses that the concentration of osteocalcin is reflected in other properties of bone, the correlations between the osteocalcin concentration and the mineral content, microstructural properties, and physical characteristics of the bone mineral crystals were determined utilizing radioimmunoassay (RIA), spectrophotometry, nanoindentation, and small-angle X-ray scattering (SAXS) techniques, respectively. Osteocalcin concentration was found to be correlated to the molar Ca/P ratio and inversely correlated to the elastic modulus and hardness in the longitudinal plane. This study provides evidence for a putative relationship between the concentration of osteocalcin and the microstructural mechanical properties of bone. Correlations were also found between the mechanical properties in the longitudinal plane and both the phosphate content and the molar Ca/P ratio. However, no relationships could be identified between osteocalcin concentration and several parameters of bone crystals, as determined by SAXS.

Osteocalcin metabolism in the pulmonary circulation

The aim of this study was to evaluate the role of the pulmonary vessel endothelium in the removal of circulating osteocalcin, by measuring the osteocalcin levels in serum from pulmonary and radial artery blood from 39 patients undergoing aorto-coronary bypass. Because of the discrepancies between methods of measurement, two methods were used. Significant differences were observed in group A (n = 18), tested with heterologous radioimmunoassay (2.85 +/- 0.67 microg l-1 in the pulmonary versus 2.69 +/- 0.67 microg l-1 in the radial artery serum, P<0.001) and in group B (n = 21), tested with a two-site immunoradiometric assay (5.22 +/- 1.46 versus 4.93 +/- 1.36 microg l-1, P<0.01). The percentage differences were -5.54 +/- 4.76% (P<0.001) in group A and -4.99 +/- 8.13% (P<0.01) in group B; the comparison between the percentage differences was not significant. These different osteocalcin concentrations between the two vascular compartments were considered a marker of osteocalcin degradation. Therefore, the study seems to demonstrate that, as well as kidney, liver and bone, the lung is a relevant site of osteocalcin catabolism. The proteolytic activity of pulmonary vessel endothelium seems to involve about 5% of the circulating peptide.

Low body mass index is an important risk factor for low bone mass and increased bone loss in early postmenopausal women. Early Postmenopausal Intervention Cohort (EPIC) study group

Thinness (low percentage of body fat, low body mass index [BMI], or low body weight) was evaluated as a risk factor for low bone mineral density (BMD) or increased bone loss in a randomized trial of alendronate for prevention of osteoporosis in recently postmenopausal women with normal bone mass (n = 1609). The 2-year data from the placebo group were used (n = 417). Percentage of body fat, BMI, and body weight were correlated with baseline BMD (r = -0. 13 to -0.43, p < 0.01) and 2-year bone loss (r = -0.14 to -0.19, p < 0.01). Women in the lowest tertiles of percentage of body fat or BMI had up to 12% lower BMD at baseline and a more than 2-fold higher 2-year bone loss as compared with women in the highest tertiles (p </= 0.004). Women with a lower percentage of body fat or BMI had higher baseline levels of urine N-telopeptide cross-links (r = -0.24 to -0.31, p < 0.0001) and serum osteocalcin (r = -0.12 to -0.15, p < 0.01). To determine if the magnitude of treatment effect of alendronate was dependent on these risk factors, the group treated with 5 mg of alendronate was included (n = 403). There were no associations between fat mass parameters and response to alendronate treatment, which indicated that risk of low bone mass and increased bone loss caused by thinness could be compensated by alendronate treatment. In conclusion, thinness is an important risk factor for low bone mass and increased bone loss in postmenopausal women. Because the response to alendronate treatment is independent of fat mass parameters, prevention of postmenopausal osteoporosis can be equally achieved in thinner and heavier women.

Clinical Utility of Biochemical Markers of Bone Remodeling

Remodeling is essential for bone health. It begins with resorption of old bone by osteoclasts, followed by the formation of new bone by osteoblasts. Remodeling is coupled (formation is linked to resorption). After middle age or perhaps beginning earlier, bone loss occurs because resorption exceeds formation. This imbalance is accentuated by estrogen deficiency as well as by many diseases and conditions. Biochemical markers that reflect remodeling and can be measured in blood or urine include resorption markers (e.g., collagen cross-links) and formation markers (e.g., alkaline phosphatase).

Bone markers exhibit substantial short-term and long-term fluctuations related to time of day, phase of the menstrual cycle, and season of the year, as well as diet, exercise, and anything else that alters bone remodeling. These biological factors, in addition to assay imprecision, produce significant intra- and interindividual variability in markers.

Bone marker measurements are noninvasive, inexpensive, and can be repeated often. Unfortunately, most of the studies that provided insight on clinical situations did not focus on markers as a primary endpoint. Bone markers have been useful in clinical practice and have been helpful in understanding the pathogenesis of osteoporosis and the mechanism of action of therapies. In clinical trials, markers aid in selecting optimal dose and in understanding the time course of onset and resolution of treatment effect. Clinical questions that might be answered by bone markers include diagnosing osteoporosis, identifying “fast bone losers” and patients at high risk of fracture, selecting the best treatment for osteoporosis, and providing an early indication of the response to treatment. Additional information is needed to define specific situations and cut points to allow marker results to be used with confidence in making decisions about individual patients.

Circulating biochemical markers of bone remodeling in uremic patients

Chronic renal failure is often associated with bone disorders, including secondary hyperparathyroidism, aluminum-related low-turnover bone disease, osteomalacia, adynamic osteopathy, osteoporosis, and skeletal beta2-microglobulin amyloid deposits. In spite of the enormous progress made during the last few years in the search of noninvasive methods to assess bone metabolism, the distinction between high- and low-turnover bone diseases in these patients still frequently requires invasive and/or costly procedures such as bone biopsy after double tetracycline labeling, scintigraphic-scan studies, computed tomography, and densitometry. This review is focused on the diagnostic value of several new serum markers of bone metabolism, including bone-specific alkaline phosphatase (bAP), procollagen type I carboxy-terminal extension peptide (PICP), procollagen type I cross-linked carboxy-terminal telopeptide (ICTP), pyridinoline (PYD), osteocalcin, and tartrate-resistant acid phosphatase (TRAP) in patients with chronic renal failure. Most of the observations made by several groups converge to the conclusion that serum bAP is the most sensitive and specific marker to evaluate the degree of bone remodeling in uremic patients. Nonetheless, PYD and osteocalcin, in spite of their retention and accumulation in the serum of renal insufficient patients, are also excellent markers of bone turnover. The future generalized use of these markers, individually or in combination with other methods, will undoubtedly improve the diagnosis and the treatment of the complex renal osteodystrophy.

Bone turnover and its relationship with bone mineral density in pre- and postmenopausal women with or without fractures

OBJECTIVE

This work was carried out in order to investigate possible relationships between bone turnover rate, as evaluated by bone biomarkers and skeletal mass, as evaluated by bone mineral density (BMD).

METHOD

Fifty-eight normal women and 30 female patients with osteoporotic fractures were enrolled. Three groups were defined: (1) fertile subjects (n = 24), mean age 33.7 +/- 8.1 years; (2) postmenopausal women (n = 32, including 11 patients with fractures) whose BMD values, in terms of T score, were less than -2.5 S.D. below the young adult mean obtained in our laboratory (mean age 61.7 +/- 7.9 years; and years since menopause (ysm), 12.6 +/- 8.3); (3) postmenopausal women (n = 32, including 19 patients with fractures) whose BMD values in terms of T score, were below -2.5 S.D. (mean age 62.9 +/- 8.6 years; and ysm 15.9 +/- 9.0). Groups II and III characterised, by inclusion criteria, by significant different mean BMD values, were similar as far as chronological and menopausal age were considered. Metabolic tests included a short urine collection to determine calcium, hydroxyproline, cross-linked N-telopeptides of type I collagen (NTx) and creatinine (Cr); half-way through this collection, a blood sample was taken for the measurement of total alkaline phosphatase activity (ALP) and tartrate-resistant acid phosphatase activity (TRAP). BMD at lumbar spine was evaluated.

RESULTS

There were significant differences amongst the three groups in mean ALP (P < 0.001, by analysis of variance) TRAP (P < 0.006) and NTx/Cr (P < 0.001) values, but not as far as mean values of calcium/Cr or hydroxyproline/Cr ratios were concerned. Considering the group as a whole, there were significant inverse correlations between NTx/Cr, ALP, TRAP and BMD controlling for both age (r = -0.392, P < 0.001; r = -0.447, P < 0.001 and r = -0.327, P < 0.002, respectively) and ysm (r = -0.374, P < 0.001; r = -0.474, P < 0.001 and r = -0.333, P < 0.002).

CONCLUSIONS

Our results indicate, that, even after controlling for both ageing and oestrogen status, there is an inverse relationship between bone mass (that at a given time represents the balance of all previous metabolic events) and a biochemical marker (which reflects bone turnover at the time of examination). These findings are in line with the belief that increased bone turnover should be regarded as a risk factor for osteoporosis. Furthermore, our results indicate that, unless there is no increase of hepatic isozyme, total ALP still maintains a possible role as a first analysis to evaluate bone turnover before requesting markers with greater specificity, sensitivity but also more expensive and whose analysis is sometimes time-consuming.

Assessment of serum total and bone alkaline phosphatase measurement in clinical practice

The aim of the study was to measure serum levels of the bone-specific isoenzyme of alkaline phosphatase in normal subjects and patients with metabolic bone disease by using an immunoadsorption assay. We studied 140 healthy adults, 122 patients affected by metabolic bone disease and 15 patients with cholestatic liver disease. Mean values of the bone-specific isoenzyme of alkaline phosphatase in healthy men were significantly higher than those found in premenopausal women (17.8 +/- 4.2 U/l vs 15.6 +/- 4.6 U/l, p < 0.02); postmenopausal women had significantly higher levels of bone-specific isoenzyme of alkaline phosphatase (22.6 +/- 6.4 U/l) than premenopausal women (p < 0.0001). After the menopause total alkaline phosphatase increased by 46%, while the increase in bone-specific isoenzyme of alkaline phosphatase was 39%. No significant correlations were found between bone-specific isoenzyme of alkaline phosphatase and either age or years since menopause, in postmenopausal subjects. In patients with bone-specific isoenzyme of alkaline phosphatase above the upper limit of normal, the assay had a sensitivity of 100% only in patients with Paget's disease of bone. In patients with cholestatic liver disease we found no correlation between bone-specific isoenzyme of alkaline phosphatase and either total alkaline phosphatase and gamma-glutamyl transpeptidase, while a positive correlation was found between total alkaline phosphatase and gamma-glutamyl transpeptidase. Our results confirm the role of bone-specific isoenzyme of alkaline phosphatase assay in clinical research; however, its usefulness in clinical practice is unclear once liver involvement has been excluded.