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

Definition of reference ranges for β-isomerized carboxy-terminal telopeptide collagen type I for children and adolescents

BACKGROUND

Bone metabolism involves many complex pathways that are disturbed by several bone diseases. The literature shows some limitations concerning pediatric reference intervals to bone markers, mainly because of the low number of patients included in the studies, the heterogeneity of methods, beyond the fact that it is time-consuming and expensive. The aim of this study was to determine reference values for β-isomerized carboxy-terminal telopeptides collagen type I (β-CTX), a marker of bone resorption, for children and adolescents.

METHODS

Blood samples from 246 patients were collected and β-CTX was measured using an electrochemiluminescence immunoassay (ECLI).

RESULTS AND CONCLUSIONS

We propose reference ranges for β-CTX concentration from the 2.5 percentile and 97.5 percentile for each age group. The reference values obtained, concerning children and adolescents, might be useful in the evaluation of diseases such as osteosarcoma and anorexia in both childhood as adolescence.

Dental Pulp Stem Cell-Derived, Scaffold-Free Constructs for Bone Regeneration

In the present study, a scaffold-free tissue construct was developed as an approach for the regeneration of tissue defects, which produced good outcomes. We fabricated a scaffold-free tissue construct from human dental pulp stem cells (hDPSCs construct), and examined the characteristics of the construct. For its fabrication, basal sheets prepared by 4-week hDPSCs culturing were subjected to 1-week three-dimensional culture, with or without osteogenic induction, whereas hDPSC sheets (control) were fabricated by 1-week culturing of basal sheets on monolayer culture. The hDPSC constructs formed a spherical structure and calcified matrix that are absent in the control. The expression levels for bone-related genes in the hDPSC constructs were significantly upregulated compared with those in the control. Moreover, the hDPSC constructs with osteogenic induction had a higher degree of calcified matrix formation, and higher expression levels for bone-related genes, than those for the hDPSC constructs without osteogenic induction. These results suggest that the hDPSC constructs with osteogenic induction are composed of cells and extracellular and calcified matrices, and that they can be a possible scaffold-free material for bone regeneration.

Long-Term Oral Toxicity and Anti-osteoporotic Effect of Sintered Dicalcium Pyrophosphate in Rat Model of Postmenopausal Osteoporosis

Sintered dicalcium pyrophosphate (SDCP), a synthetic pyrophosphate analog, has shown potential for the management of osteoporosis. The long-term oral toxicity and anti-osteoporotic effect of SDCP in a postmenopausal osteoporosis rat model were evaluated in this study. SDCP was orally administered to bilateral ovariectomized (OVX) Wistar rats at a dose of 0.75 mg/kg daily for 24 weeks following by 2 weeks of observation. There were no abnormal findings in clinical signs of toxicity, food consumption, body weight, blood examination, necropsy, and histological inspection attributable to the ingestion of SDCP. The serum level of type I collagen fragments, a bone resorption marker, decreased in SDCP-treated rats, and the bone formation markers alkaline phosphatase, osteocalcin, and osteopontin significantly decreased. These findings indicate that the bone turnover rate decreased in SDCP-treated animals. Relative to OVX rats, the increase in serum tartrate-resistant acid phosphatase 5b level represents an increase in bony tissues in the SDCP-treated rats. Histological examinations of distal femoral metaphyses further revealed that the ingestion of SDCP improved the trabecular bone architecture and decreased bone porosity. Analysis of limb bone ashes showed a significant increase in bone mineral content. Our results show that SDCP inhibits bone resorption to restore bone mass in OVX rats without deleterious effects, and therefore that SDCP has potential in the management of osteoporosis.

Biochemical markers of aging for longitudinal studies in humans

Much progress has been made in the past decades in unraveling the mechanisms that are responsible for aging. The discovery that particular gene mutations in experimental species such as yeast, flies, and nematodes are associated with longevity has led to many important insights into pathways that regulate aging processes. However, extrapolating laboratory findings in experimental species to knowledge that is valid for the complexity of human physiology remains a major challenge. Apart from the restricted experimental possibilities, studying aging in humans is further complicated by the development of various age-related diseases. The availability of a set of biomarkers that really reflect underlying aging processes would be of much value in disentangling age-associated pathology from specific aging mechanisms. In this review, we survey the literature to identify promising biochemical markers of aging, with a particular focus on using them in longitudinal studies of aging in humans that entail repeated measurements on easily obtainable material, such as blood samples. Our search strategy was a 2-pronged approach, one focused on general mechanisms of aging and one including studies on clinical biomarkers of age-related diseases.

Bone remodeling and calcium homeostasis in patients with spinal cord injury: a review

Patients with spinal cord injury exhibit early and acute bone loss with the major functional consequence being a high incidence of pathological fractures. The bone status of these patients is generally investigated by dual-energy x-ray absorptiometry, but this technique does not reveal the pathophysiological mechanism underlying the bone loss. Bone cell activity can be indirectly evaluated by noninvasive techniques, including measurement of specific biochemical markers of bone formation (such as osteocalcin or bone-alkaline phosphatase) and resorption (such as procollagen type I N- or C-terminal propeptide). The bone loss in spinal cord injury is clearly due to an uncoupling of bone remodeling in favor of bone resorption, which starts just after the injury and peaks at about 1 to 4 months. Beyond 6 months, bone resorption activity decreases progressively but remains elevated for many years after injury. Conversely, bone formation is less affected. Antiresorptive treatment induces an early and acute reduction in bone resorption markers. Level of injury and health-related complications do not seem to be implicated in the intensity of bone resorption. During the acute phase, the hypercalcemic status is associated with the suppression of parathyroid hormone and vitamin D metabolites. The high sensitivity of these markers after treatment suggests that they can be used for monitoring treatment efficacy and patient compliance. The concomitant use of bone markers and dual-energy x-ray absorptiometry may improve the physician's ability to detect patients at risk of severe bone loss and subsequent fractures.

Bone metabolism markers in sports medicine

Bone mass can be viewed as the net product of two counteracting metabolic processes, bone formation and bone resorption, which allow the skeleton to carry out its principal functions: mechanical support of the body, calcium dynamic deposition and haemopoiesis. Besides radiological methods, several blood and urinary molecules have been identified as markers of bone metabolic activity for estimating the rates and direction of the biological activities governing bone turnover. The advantages for the use of bone metabolism markers are that they are potentially less dangerous than radiological determinations, are more sensitive to changes in bone metabolism than radiological methods and are easily collected and analysed. The disadvantages are that they have high biological variability. Physical exercise is a known source of bone turnover and is recommended for preventing osteoporosis and bone metabolism problems. There are numerous experiments on bone metabolism markers after acute exercise, but not after long-term training and during or after a whole competition season. Moreover, few studies on bone metabolism markers have evaluated their performance in elite and top-level athletes, who have a higher bone turnover than sedentary individuals. Despite discrepant results among studies, most have shown that short exercise is insufficient for modifying serum concentrations of bone metabolism markers. Marker variations are more evident after several hours or days after exercise, bone formation markers are more sensitive than bone resorption markers, and stimulation of osteoblast and/or osteoclast functions is exercise dependent but the response is not immediate. The response depends on the type of exercise; the markers seem to be less sensitive to resistance exercise and the intensity of exercise is not discriminate. Comparisons between trained subjects and untrained controls have demonstrated the influence of exercise on bone turnover. During training, carboxy-terminal collagen cross-links (CTx), a bone resorption marker, was shown to be less sensitive than amino-terminal cross-linking telopeptide of type I collagen (NTx) and urinary pyridinolines, which were sensitive to anaerobic exercise. Whereas, the bone formation markers, bone alkaline phosphatase (BAP) and osteocalcin (OC) changed after 1 month and 2 months of an exercise programme, respectively. After 2 months, while BAP normalized, it was found to be sensitive to aerobic exercise and OC was found to be sensitive to anaerobic exercise. After prolonged training and competition, bone formation markers are found to change in sedentary subjects enrolled in a physical activity programme. Professional athletes show changes in bone formation markers depending on programme intensity, whereas bone resorption appears to stabilize. Crucial for long-term training, are the characteristics of exercise (e.g. weight-bearing, impact).

Reference intervals of biochemical bone turnover markers for Saudi Arabian women: a cross-sectional study

Biochemical bone turnover markers (BTMs) provide important information on the diagnosis, therapy and monitoring of metabolic bone diseases including osteoporosis. One goal of antiresorptive therapy in women is to decrease biochemical BTMs to the lower half of reference intervals for healthy pre-menopausal counterparts, using newly developed automated assays of such markers. The main objectives of the present study were to: (1) establish reference interval values for the following biochemical BTMs: serum osteocalcine (s-OC), bone alkaline phosphatase (s-bone ALP), procollagen type 1 N-terminal propeptide (s-PINP), crosslinked C-terminal telopeptide of Type 1 collagen (s-CTX), tartarate-resistant acid phosphatase isoform 5b (s-TRACP-5b) and urinary: CTX (u-CTX), N-telopeptides of type 1 collagen (u-NTX), pyridinoline (u-PYD) and deoxypyridinoline (u-DPD) in randomly selected Saudi healthy pre-menopausal women; (2) study the changes in biochemical BTMs in relation to age in pre- and post-menopausal women and the factors reported to influence bone turnover and (3) determine the effect of menopausal status on BTMs. A total of 2125 women were studied [including (n=1557) pre-, and (n=568) post-menopausal women, respectively, aged 20-79 years]. A total of 765 healthy pre-menopausal women (aged 35-45 years) were used to establish reference intervals for biochemical BTMs. All women studied were medically examined and had their bone mineral density (BMD) values obtained for the lumbar spine (L(1)-L(4)) and femoral neck according to detailed inclusion criteria. In all women, values of biochemical BTMs, decreased with increasing age up to the age of 45 years, increased steeply among women in their 50s and remained increased in post-menopausal women. Significant increases were evident in all biochemical BTMs in post-menopausal women with >5 years since menopause with the exception of s-OC, u-DPD, and u-PYD. Using stepwise multiple linear regression analysis, several variables were identified (depending on the BTM) as determinants of BTMs including age, BMI, parity, FSH, LH, PTH, s-Ca, s-Mg, s-PO(4) and 25(OH)D. In the reference intervals group, there are no significant correlations between any of the biochemical BTMs and age of menarche, day of menstrual cycle, physical activity, total daily dietary calcium and caffeine intakes and parity. It is recommended that the age range 35-45 years should be used when establishing biochemical BTMs reference intervals in Saudi Arabian pre-menopausal women.

Bone metabolism markers in sports medicine

Bone mass can be viewed as the net product of two counteracting metabolic processes, bone formation and bone resorption, which allow the skeleton to carry out its principal functions: mechanical support of the body, calcium dynamic deposition and haemopoiesis. Besides radiological methods, several blood and urinary molecules have been identified as markers of bone metabolic activity for estimating the rates and direction of the biological activities governing bone turnover. The advantages for the use of bone metabolism markers are that they are potentially less dangerous than radiological determinations, are more sensitive to changes in bone metabolism than radiological methods and are easily collected and analysed. The disadvantages are that they have high biological variability. Physical exercise is a known source of bone turnover and is recommended for preventing osteoporosis and bone metabolism problems. There are numerous experiments on bone metabolism markers after acute exercise, but not after long-term training and during or after a whole competition season. Moreover, few studies on bone metabolism markers have evaluated their performance in elite and top-level athletes, who have a higher bone turnover than sedentary individuals. Despite discrepant results among studies, most have shown that short exercise is insufficient for modifying serum concentrations of bone metabolism markers. Marker variations are more evident after several hours or days after exercise, bone formation markers are more sensitive than bone resorption markers, and stimulation of osteoblast and/or osteoclast functions is exercise dependent but the response is not immediate. The response depends on the type of exercise; the markers seem to be less sensitive to resistance exercise and the intensity of exercise is not discriminate. Comparisons between trained subjects and untrained controls have demonstrated the influence of exercise on bone turnover. During training, carboxy-terminal collagen cross-links (CTx), a bone resorption marker, was shown to be less sensitive than amino-terminal cross-linking telopeptide of type I collagen (NTx) and urinary pyridinolines, which were sensitive to anaerobic exercise. Whereas, the bone formation markers, bone alkaline phosphatase (BAP) and osteocalcin (OC) changed after 1 month and 2 months of an exercise programme, respectively. After 2 months, while BAP normalized, it was found to be sensitive to aerobic exercise and OC was found to be sensitive to anaerobic exercise. After prolonged training and competition, bone formation markers are found to change in sedentary subjects enrolled in a physical activity programme. Professional athletes show changes in bone formation markers depending on programme intensity, whereas bone resorption appears to stabilize. Crucial for long-term training, are the characteristics of exercise (e.g. weight-bearing, impact).

A new approach for evaluating bone turnover in chronic kidney disease

BACKGROUND

The validity of serum parathyroid hormone (PTH) as a surrogate marker of bone turnover in chronic kidney disease (CKD) is limited by several factors such as relative resistance of bone to PTH, hyperphosphatemia, diabetes, gender, age, race and vitamin D analog action on the PTH-bone axis. Urinary collagen N-terminal telopeptide X (NTx), a bone collagen degradation product, expressed as bone collagen equivalents (BCE) per mM of creatinine (NTx/Cr ratio), is routinely used to estimate bone turnover in osteoporosis. The purpose of this study is to evaluate NTx as a marker of bone turnover in CKD.

METHODS

We studied the relationship between bone-specific alkaline phosphatase (BSAP), PTH and urine NTx/Cr in 37 CKD out-patients.

RESULTS

In a multivariate model, PTH had a positive correlation with BSAP (r=0.44, P<0.19) and U-NTx/Cr (r=0.55, P<0.30), after adjusting for age, gender, estimated glomerular filtration rate (GFR), serum phosphorus, corrected calcium, and race. However, the strongest correlation was found between the two direct markers of bone resorption and formation (U-NTx vs. BSAP; r=0.80; P<0.0001), suggesting a tight coupling of bone resorption and formation in CKD. The effect of gender on U-NTx/Cr was studied in a multivariate model after adjusting for age, race, GFR, serum calcium, phosphorus and PTH. Females had a higher U-NTx/Cr than males.

CONCLUSION

Our findings indicate that urinary NTx, a promising marker of bone resorption in CKD patients, exhibits a strong positive correlation with other markers used to assess renal osteodystrophy i.e. PTH and BSAP. Unlike PTH and BSAP, urine NTx also measures bone loss secondary to osteoporosis.

High bone turnover but normal bone mineral density in women suffering from schizophrenia

BACKGROUND

A potential association between schizophrenia and osteoporosis or osteopenia has recently been reported. Various factors affect bone mineral density (BMD) such as polydipsia, nicotine, alcohol abuse, lack of physical activity, an unbalanced diet, a lack of ultraviolet exposure and/or vitamin D. In addition, decreased BMD in women with schizophrenia has been attributed to drug-induced hyperprolactinaemia and/or secondary hypogonadism. This study was undertaken because empirical evidence from larger patient cohorts is limited and the data are still controversial.

METHOD

Seventy-two premenopausal, regularly menstruating women suffering from schizophrenia and 71 age- and sex-matched healthy controls were included in the study. Biochemical markers of bone turnover (serum osteocalcin, urinary pyridinium crosslinks), parathyroid hormone and 25-hydroxyvitamin D were measured. BMD at the femoral neck and lumbar spine was determined by dual-energy X-ray absorptiometry in a subgroup of 59 patients. In addition, 17beta-oestradiol, prolactin, testosterone, gonadotrophins and dehydroepiandrosterone sulfate were measured.

RESULTS

Compared with healthy controls, both markers of formation and resorption were increased in women with schizophrenia. However, in the subgroup of 59 patients, BMD was within the normal range. In women suffering from schizophrenia, testosterone levels were higher than in controls, and serum oestradiol levels were lower compared with the normal range.

CONCLUSION

Despite significantly increased bone turnover, we conclude that premenopausal and regularly menstruating women suffering from schizophrenia have normal spine and hip BMD. This may be due to the opposite effects of the various parameters influencing bone metabolism, especially of the gonadal hormones, and due to an intact coupling mechanism.

Lower body negative pressure treadmill exercise as a countermeasure for bed rest-induced bone loss in female identical twins

Supine weight-bearing exercise within lower body negative pressure (LBNP) alleviates some of the skeletal deconditioning induced by simulated weightlessness in men. We examined this potential beneficial effect in women. Because dietary acid load affected the degree of bone resorption in men during bed rest, we also investigated this variable in women. Subjects were 7 pairs of female identical twins assigned at random to 2 groups, sedentary bed rest (control) or bed rest with supine treadmill exercise within LBNP. Dietary intake was controlled and monitored. Urinary calcium and markers of bone resorption were measured before bed rest and on bed rest days 5/6, 12/13, 19/20, and 26/27. Bone mineral content was assessed by dual-energy X-ray absorptiometry before and after bed rest. Data were analyzed by repeated-measures two-way analysis of variance. Pearson correlation coefficients were used to define the relationships between diet and markers of bone metabolism and to estimate heritability of markers. During bed rest, all markers of bone resorption and urinary calcium and phosphorus increased (P<0.001); parathyroid hormone (P=0.06), bone-specific alkaline phosphatase (P=0.06), and 1,25-dihydroxyvitamin D (P=0.09) tended to decrease. LBNP exercise tended to mitigate bone density loss. The ratio of dietary animal protein to potassium was positively correlated with urinary calcium excretion for all weeks of bed rest in the control group, but only during weeks 1 and 3 in the exercise group. Pre-bed rest data suggested that many markers of bone metabolism have strong genetic determinants. Treadmill exercise within LBNP had less of a protective effect on bone resorption during bed rest in women than previously published results had shown for its effect in men, but the same trends were observed for both sexes. Dietary acid load of these female subjects was significantly correlated with calcium excretion but not with other bone resorption markers.

Bone mineral density in Iranian patients with inflammatory bowel disease

Patients with inflammatory bowel disease (IBD) are at increased risk of developing osteopenia and osteoporosis. The aim of the study was to investigate the prevalence of decreased bone density and related risk factors in Iranian IBD patients. A total of 126 ulcerative colitis (UC) and 39 Crohn's disease (CD) patients were enrolled. Dual-energy x-ray absorptiometry technique was used to measure bone density, and blood samples were obtained to measure biochemical markers. To find predictive variables for bone mineral density (BMD), stepwise regression analysis was carried out. A total of 53 IBD patients (32.1%) had diminished bone mineral density at either lumbar spine (L1-L4) or femoral neck. Of these, 9 (5.4%) had osteoporosis; however, 44 (26.7%) were osteopenic. Femoral neck bone density was significantly decreased among CD patients (p<0.04). There was no significant difference in BMD between men and women. We have found significant differences in BMD T scores at lumbar L1-L4, L2-L4, and femoral neck in corticosteroid ever-users (p<0.002, p<0.001, p<0.003, respectively). There was no significant difference in biochemical markers between UC and CD patients, except that more CD patients were hypocalcemic (p<0.001). Stepwise regression analysis has revealed lumbar spine T score was predicted by age (p<0.0001), corticosteroid use (p<0.002), and body mass index (BMI) (p<0.005); however, femoral neck was predicted by age (p<0.0001), BMI (p<0.0001), smoking (p<0.009), and corticosteroid use (p<0.028). Low bone density in Iranian UC and CD patients is in accordance with Western societies. Treatment with corticosteroid has increased this possibility in both groups. Corticosteroid use, age, smoking, and BMI are predictive factors for low bone density.

Evidence-based recommendations for monitoring bone disease and the response to enzyme replacement therapy in Gaucher patients

BACKGROUND

Bone disease is a serious complication of Gaucher disease. Untreated, it can result in pain, permanent bone damage and disability. Enzyme replacement therapy reverses many of the clinical signs of Gaucher bone disease but early assessment and treatment, and regular monitoring, are essential in optimising outcomes.

SCOPE

In September 2005, a group of European experts met to review current knowledge and identify best practice and unmet needs in the monitoring of Gaucher bone disease and the response to enzyme replacement therapy.

METHODS

Medline searches of peer-reviewed literature (no date restrictions) were conducted and supplemented by additional information considered relevant by panellists to furthering discussions.

FINDINGS AND CONCLUSIONS

The group's recommendations included: currently used biochemical bone markers are not clinically practical or reliable; plain X-rays should not be the sole method of assessing bone disease; MRI is the most sensitive method for monitoring bone marrow infiltration by Gaucher cells; semi-quantitative methods for assessing bone marrow infiltration in routine clinical practice should use readily available technology, include an assessment of Gaucher cell infiltration in the lumbar spine and femur, and be validated for inter-rater reliability and in comparison to other methods; a multidisciplinary approach is required for the treatment of Gaucher patients; all Gaucher patients should receive a comprehensive initial radiologic evaluation for bone disease and ongoing radiological monitoring at least once every 2 years.

Effects of dissociated glucocorticoids on OPG and RANKL in osteoblastic cells

Glucocorticoids are effective anti-inflammatory and immunosuppressive agents, but their use is often associated with debilitating side effects such as glucocorticoid-induced osteoporosis. Newly developed glucocorticoid analogues such as the so-called dissociated glucocorticoids are potent immunosuppressants and have the potential for fewer side effects. The effects of these new analogues on osteoprotegerin (OPG) and receptor activator of NF-kappaB ligand (RANKL) in osteoblastic cells have not been studied. OPG and RANKL are osteoblast-derived proteins pivotal to the regulation of bone mass. RANKL stimulates bone resorption by increasing osteoclast differentiation, activation and survival. OPG is the decoy receptor for RANKL and thus inhibits bone resorption. Here, we show that dexamethasone, prednisolone, deflazacort and the dissociated glucocorticoids, RU24858, RU40066, RU24782, AL438-F1 and ZK216348 significantly inhibit OPG production in two human osteoblastic cell lines (MG63 and hFOB). The potency for OPG inhibition was ligand and cell-type specific. In both cell types, dexamethasone and prednisolone were the most potent ligands inhibiting OPG production with IC(50)s of approximately 0.1 nM and 10 nM respectively. In MG63 cells, deflazacort and the RU compounds were the next most potent ligands followed by AL438-F1 and ZK216348. In hFOB cells, however, the RU compounds were the least potent ligands with an IC(50) 74 times higher than in MG63 cells. In contrast, the level of maximum inhibition or effectiveness of OPG inhibition did not vary between cell types but did vary according to the ligand. Dexamethasone, prednisolone, deflazacort and the RU compounds all inhibited OPG production by a maximum of approximately 70-80%, whereas AL438-F1 and ZK 216348 inhibited OPG production by a maximum of only 40-50% at 1 microM. All of the dissociated glucocorticoids and deflazacort were poor stimulators of RANKL gene expression stimulating by only approximately 1-3-fold compared to 7-fold by prednisolone. These data demonstrate that deflazacort and the dissociated glucocorticoids are weak stimulators of the RANKL:OPG ratio compared to prednisolone. Therefore, these compounds have the potential to cause less bone loss than that seen with prednisolone, though this was not investigated here.

Effects of resistance training and protein supplementation on bone turnover in young adult women

BACKGROUND

The strength of aging bone depends on the balance between the resorption and formation phases of the remodeling process. The purpose of this study was to examine the interaction of two factors with the potential to exert opposing influences on bone turnover, resistance exercise training and high dietary protein intake. It was hypothesized that resistance training by young, healthy, untrained women with protein intakes near recommended levels (0.8 g.kg(-1).d(-1)) would promote bone formation and/or inhibit bone resorption, and that subsequent supplementation to provide 2.4 g protein.kg(-1).d(-1) would reverse these effects.

METHODS

Bone formation was assessed with serum bone-specific alkaline phosphatase (BAP) and osteocalcin (OC), and bone resorption with urinary calcium and deoxypyridinoline (DPD). Biochemical, strength, anthropometric, dietary, and physical activity data were obtained from 24 healthy, untrained, eumenorrheic women (18-29 y) at baseline, after eight weeks of resistance training (3 d.wk(-1), approximately 1 hr.d(-1); 3 sets, 6-10 repetitions, 13 exercises, 75-85% maximum voluntary contraction), and after 12 weeks of resistance training and 10 days of protein/placebo supplementation. Subjects were randomized (double-blind) to either a high protein (HP) or training control (TC) group and, during the final 10 days, consumed either enough purified whey protein to bring daily protein intake to 2.4 g.kg(-1).d(-1), or an equivalent dose of isoenergetic, carbohydrate placebo.

RESULTS

Strength, lean tissue mass, and DPD increased significantly in both groups over time, while percent body fat and BAP decreased (repeated measures ANOVA, p < or = 0.05, Bonferroni correction). No significant changes were observed for serum OC or urinary calcium, and no significant group (TC, HP) x time (baseline, week 8, week 12) interactions emerged for any of the biochemical measures.

CONCLUSION

(1) Twelve weeks of high-intensity resistance training did not appear to enhance bone formation or inhibit bone resorption in young adult women, as assessed by biochemical markers of bone metabolism. (2) Subsequent maintenance of a high protein intake for 10 days in these regularly-training, calcium-replete women also showed no effects on bone metabolism.

Serum osteocalcin and CTX-MMP concentration in young exercising thoroughbred racehorses

Bone responds to exercise with changes in bone (re-)modelling, which might be monitored non-invasively with biochemical bone markers. The aim of this study was to evaluate the influence of exercise on serum osteocalcin and serum carboxy-terminal cross-linked telopeptide of type I collagen generated by matrix metalloproteinases (CTX-MMP) concentration in young racehorses. Seventy-one 2 to 4-year-old Thoroughbreds were included in this prospective infield study. Blood sampling was performed six times (i.e. six sampling cycles) during a 9-month period. Serum samples were analysed with commercial osteocalcin and CTX-MMP radioimmunoassays. Two-year-old racehorses had higher serum osteocalcin and CTX-MMP values than 3-year-old horses. Gender and training amplitude did not significantly influence serum osteocalcin and CTX-MMP values. Two-year-old horses showed an increase in osteocalcin values between cycles 2 and 3 and an increase in serum CTX-MMP values between cycles 1 and 2. Serum osteocalcin and CTX-MMP concentrations decreased between cycles 4 and 5, and 5 and 6. Three-year-old horses showed an increase in serum osteocalcin levels between cycles 3 and 4 and an increase in serum CTX-MMP concentrations between cycles 1 and 2, and 3 and 4. Serum osteocalcin levels decreased between cycles 5 and 6, whereas serum CTX-MMP levels decreased between cycles 4 and 5, and 5 and 6. Two- and three-year-old horses showed a decreased osteocalcin/CTX-MMP ratio between cycles 1 and 2. Moreover, 2-year-old horses showed an increase in the osteocalcin/CTX-MMP ratio between cycles 2 and 3. Sore shin formation did not significantly influence serum osteocalcin and CTX-MMP values. Serum osteocalcin and CTX-MMP are promising bone markers for monitoring exercise induced changes in equine bone metabolism.

Influence of brain injury on early posttraumatic bone metabolism

BACKGROUND

Various clinical studies and observations demonstrate enhanced osteogenesis in patients sustaining traumatic brain injury. It is presumed that the induction of this process starts early after trauma. The purpose of our study was to investigate humoral markers of bone metabolism during the early posttraumatic period, with special regard to traumatic brain injury.

METHODS

Serum concentrations of biochemical markers of bone metabolism (calcium, inorganic phosphorus, carboxyl-terminal propeptide of type 1 procollagen, pyridinoline cross-linked telopeptide domain of type 1 collagen, Ostase, osteocalcin, intact parathyroid hormone, and calcitonin) were measured in three different groups of 80 patients during the first posttraumatic week. Patients were categorized into three groups: group I, fractures only; group II, isolated traumatic brain injury; and group III, traumatic brain injury in combination with fractures.

RESULTS

Osteocalcin levels were significantly lower in the presence of traumatic brain injury (p < .05). Elevated pyridinoline cross-linked telopeptide domain of type 1 collagen levels expressed enhanced bone resorption in all groups, but levels were significantly higher in the absence of traumatic brain injury (p < .05). Intact parathyroid hormone levels were significantly higher on days 0 and 1 in the combined presence of traumatic brain injury plus fractures.

CONCLUSION

These results demonstrate an imbalance of bone formation and resorption parameters in patients with traumatic brain injury during the early posttraumatic period, suggesting a central regulation in bone formation. The lower levels of osteocalcin detected in this study may play an important role in patients with brain injury and the later development of posttraumatic heterotopic ossification.

Prognostic value of urinary pyridinium crosslinks and their derivatives in multiple myeloma

Bone disease is a common feature of multiple myeloma (MM). The goal of this study was to assess the prognostic significance of urinary markers of bone metabolism in MM. Urinary levels of total pyridinoline (T-Pyd), deoxypyridinoline (T-Dpd), crosslinked N-telopeptide (Ntx), C-telopeptide (Ctx) of type I collagen and immunologic free deoxypyridinoline (f-Dpd) were assessed in 82 consecutive, previously untreated MM patients (aged 65-75 years) diagnosed between June 1995 and December 1998. A correlation between disease stage according to the Durie-Salmon classification and T-Pyd (p=0.034) and T-Dpd (p=0.007) was observed, while T-Pyd (p=0.015) and to a lesser extent f-Dpd (p=0.081) were correlated to bone involvement measured by plain X-ray. None were correlated to M-component or magnetic resonance imaging (MRI). In univariate analysis high T-Pyd (p=0.007), T-Dpd (p=0.027), f-Dpd (p<0.001), and Ctx (p=0.011) were associated with shorter overall survival, whereas only f-Dpd (p=0.0025) was associated with a shorter disease-free survival. In multivariate analysis, C-reactive protein and f-Dpd were independent prognostic factors for overall survival. This retrospective analysis defined new independent prognostic indicators of survival in patients with newly diagnosed myeloma. Indeed, urinary markers of bone resorption can easily be measured at diagnosis and have independent prognostic significance to refine the prognosis of MM patients.

Markers of bone metabolism in dog breeds of different size

Serum and urinary markers of bone turnover may be of value in animals as noninvasive tools for determining the response of the skeleton to disease and injury. Although normal values for bone markers have been reported for the Beagle, concerns remain that breed to breed differences will complicate the interpretation of bone marker data in dogs. To explore this, we examined serum bone markers in two breeds of vastly different size, Pomeranians and Irish Wolfhounds. Our hypothesis was that serum concentrations of bone markers are similar in toy and giant dog breeds and fall within the same range as those reported for Beagles. Bone alkaline phosphatase (BALP) and carboxy-terminal telopeptide of type I collagen (ICTP), respectively markers of bone formation and bone resorption, were measured in age matched Pomeranians (n=14) and Irish Wolfhounds (n=14). No statistically significant differences between the mean BALP and mean ICTP serum concentrations from Pomeranians and Irish Wolfhounds were found. All BALP and ICTP concentrations were within the reference range reported for Beagles. The results of this study suggest that serum BALP and ICTP concentrations in giant and toy breeds are the same as in Beagles and that these assays may be used for dogs of all sizes.

Evaluation of plasma carboxy-terminal cross-linking telopeptide of type I collagen concentration in horses

OBJECTIVE

To evaluate a human assay for quantification of carboxy-terminal cross-linking telopeptide of type I collagen (CTX-I), assess the influence of age on plasma CTX-I concentration, investigate the relationship between plasma CTX-I and serum osteocalcin concentrations, and determine whether concentrations of plasma CTX-I or serum osteocalcin fluctuate in circadian manner in horses. HORSES: 75 clinically normal horses.

PROCEDURE

Cross-reactivity between equine serum CTX-I and CTX-I antibodies in an automated electrochemiluminescent sandwich antibody assay (ECLIA) was evaluated via a specificity test (ie, dilution test) and recovery calculation. Serum osteocalcin concentration was measured with an equine-specific osteocalcin radioimmunoassay. To analyze diurnal variations in plasma CTX-I and serum osteocalcin concentrations, blood samples were obtained hourly during a 24-hour period.

RESULTS

Results of the dilution test indicated good correlation (r > 0.99) between expected serum CTX-I concentrations and measured serum CTX-I concentrations. The calculated CTX-I recovery was 97.6% to 109.9%. Plasma CTX-I and serum osteocalcin concentrations were correlated. Plasma CTX-I concentration was inversely correlated with age of the horse. No significant circadian variations in plasma CTX-I and serum osteocalcin concentrations were detected.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that the fully automated CTX-I ECLIA can be used for evaluation of plasma and serum samples from horses and may be a useful tool to monitor bone metabolism changes. Horses in this study did not have notable diurnal fluctuations in serum osteocalcin and plasma CTX-I concentrations.

A novel immunoassay for the determination of tartrate-resistant acid phosphatase 5b from rat serum

Osteoclasts secrete tartrate-resistant acid phosphatase 5b (TRACP 5b) into the circulation. We have developed an immunoassay for the determination of rat TRACP 5b activity. Intra-assay variation of the immunoassay was 4.5%, interassay variation was 3.8%, dilution linearity was 104.6 +/- 7.6%, and recovery of recombinant rat TRACP was 99.1 +/- 5.8%. We studied serum TRACP 5b as a marker of bone resorption using orchidectomized (ORC) rats as a model for osteoporosis and age-matched sham-operated rats as controls in a 6-month study. After the operation, trabecular bone mineral density decreased significantly more in the ORC group than in the sham group, whereas cortical bone mineral density increased similarly in both groups. Serum TRACP 5b activity was significantly elevated within the first week after ORC, returned to the control level in the third week, and was not increased above the sham level at any of the later time points. At 6 months, trabecular bone volume was 80% lower in ORC rats than in controls. Osteoclast number per trabecular bone perimeter was slightly increased, but the absolute number of osteoclasts in trabecular bone was significantly decreased. These results suggest that absolute bone resorption is increased within the first week after ORC. Later, it is decreased because there is less bone to be resorbed. However, relative bone resorption (compared with the amount of remaining bone) is still increased, leading to further bone loss. We conclude that serum TRACP 5b is a useful marker for monitoring changes in the bone resorption rate in rat ORC model.

Skeletal aspects of Gaucher disease: a review

In Gaucher disease, a genetic deficiency in the activity of the lysosomal enzyme beta-glucocerebrosidase (acid beta-glucosidase) causes monocytes and macrophages to store excessive amounts of glucocerebroside in lysosomes. The resulting distended cells are called Gaucher cells, and the pathology associated with this condition stems from the accumulation of Gaucher cells in organ systems. The skeletal manifestations are probably the most disabling aspect of the disease. Patients commonly experience bone pain, some suffer bone crises, and up to 20% have impaired mobility. Radiological findings include Erlenmeyer flask deformity, osteopenia, osteosclerosis, osteonecrosis, fractures and bone marrow infiltration. Findings from the Gaucher Registry show that nearly all patients with Gaucher disease have radiological evidence of skeletal involvement, and the majority have a history of serious skeletal complications. Skeletal involvement follows three basic processes: focal disease (irreversible lesions such as osteonecrosis and osteosclerosis), local disease (reversible abnormalities adjacent to heavily involved marrow such as cortical thinning and long bone deformity) and generalized osteopenia. Infarctions are involved in some of the skeletal manifestations, but the mechanisms causing high rates of bone turnover and failure of remodelling are not known. The availability of a beta-glucocerebrosidase-deficient mouse model of Gaucher disease with long-term survival should help elucidate the skeletal pathology in Gaucher disease and may ultimately lead to improved management of skeletal complications.

Plasma amino acid concentrations in healthy and cognitively impaired oldest-old individuals: associations with anthropometric parameters of body composition and functional disability

Only a few reports exist of plasma amino acid profiles in the oldest-old, and none exist of the oldest-old with cognitive problems. Therefore, we measured fasting plasma amino acid concentrations in twenty-three healthy community-dwellers aged 90-103 years (group A); eighteen community-dwellers with mild cognitive impairment without dementia aged 91-104 years (group B); thirty-three patients with dementia aged 96-100 years (group C); and sixty healthy young controls aged 20-50 years. Biochemical and anthropometric parameters, and the basic activities of daily living (ADL) were also measured. Independent of cognitive status, in all oldest-old groups, essential:non essential amino acids (EAA:NEAA) was lower than in young controls and positively associated with body muscle mass. Patients with dementia were further characterized by a negative association between EAA:NEAA and the number of dependent ADL. All oldest-old groups had higher values of tyrosine:other large neutral amino acids (LNAA) than young controls. Groups B and C also had a higher phenylalanine:other LNAA. These data show that abnormalities in plasma amino acid profile are common in oldest-old individuals independent of their cognitive status, but that, in oldest-old patients with dementia, they are associated with functional disability. The abnormalities in phenylalanine and tyrosine plasma availability could contribute to the cause or aggravation of concurrent cognitive problems because these amino acids are neurotransmitter precursors and compete with other LNAA for transport into the brain.

Measurement of serum beta-crosslaps is influenced by proteolytic conditions

Serum beta-crosslaps are an established laboratory test to investigate bone metabolism. However, lytic conditions may affect the measurement of serum beta-crosslaps. Therefore, we investigated the effect of cathepsin C and human leukocyte lysate on serum beta-crosslaps in relation to temperature and time. We divided eight serum samples with elevated beta-crosslaps levels into three aliquots and stored them at 4, 21 and 37 degrees C. Another five serum samples were divided into three aliquots and adjusted to contain different cathepsin C concentrations (50, 250, 500 IU/l). These aliquots were divided again and stored at 4, 21 and 37 degrees C. Finally, three aliquots from three additional serum samples were treated with human leukocyte lysate (100, 300, 500 microl), divided again and stored at 4, 21 and 37 degrees C. Measurements of serum beta-crosslaps were then carried out before and immediately after manipulation, and after 2 and 5 days of storage. When stored at 21 degrees C, serum beta-crosslaps diminished significantly (25% after 5 days), but no significant change was detectable when they were stored at 4 degrees C. Cathepsin C induced up to a 14% increase in beta-crosslaps while human leukocyte lysate caused up to a 17% decrease. This study demonstrates that the influence of proteolytic conditions on the serum concentration of beta-crosslaps is not uniform. Leukocyte lysate decreased serum beta-crosslaps while the addition of cathepsin C increased their concentration. Therefore, serum should be separated from the whole blood immediately after coagulation and stored until analysis in a deep freezer.

Can biochemical markers be used to screen patients with inflammatory bowel disease for osteoporosis?

Reduced bone mineral density has been reported in patients with inflammatory bowel disease and recent studies indicate that there is also an increase in the relative risk of fracture. Absolute risk of fracture is, however, generally low and thus measurement of bone mineral density as a screening procedure for all patients with inflammatory bowel disease may be inappropriate. In one study, urinary excretion of N-telopeptides, which reflects whole body bone resorption, was shown to be negatively related to bone mineral density, raising the possibility that this measurement could be used to select those in whom bone densitometry is required. However, the value of this approach in predicting fracture risk remains unproven and the relative contributions of clinical risk factors, biochemical markers of bone turnover and bone mineral density measurements to fracture risk in patients with inflammatory bowel disease require further study.

Acid phosphatases

Acid phosphatases (APs) are a family of enzymes that are widespread in nature, and can be found in many animal and plant species. Mystery surrounds the precise functional role of these molecular facilitators, despite much research. Yet, paradoxically, human APs have had considerable impact as tools of clinical investigation and intervention. One particular example is tartrate resistant acid phosphatase, which is detected in the serum in raised amounts accompanying pathological bone resorption. This article seeks to explore the identity and diversity of APs, and to demonstrate the relation between APs, human disease, and clinical diagnosis.

Clinical, radiographic and biochemical assessment of IL-1/TNF-alpha antagonist inhibition of bone loss in experimental periodontitis

OBJECTIVES

To assess clinical, radiographic, and biochemical markers as diagnostic indicators of disease activity by comparing ligature-induced bone loss in the presence or absence of IL-1/TNF-alpha antagonist inhibition of bone loss in a primate model.

MATERIAL AND METHODS

6 animals with a naturally-occurring gingivitis were evaluated over a 6-week time period following the placement of silk ligatures and initiation of a soft diet. Three animals received intrapapillary injections of soluble receptors (blockers), capable of blocking the biologic activity for both IL-1 and TNF-alpha, and 3 animals received vehicle (control) injections. Injections were given 3X per week over the course of the study. Clinical assessments included a gingival index and quantification of gingival crevicular fluid (GCF) levels. Collected GCF samples were then used in the biochemical assessment of pyridinoline (PYD) and bone alkaline phosphatase (BAP). Radiographic assessment was made using computer-assisted subtraction radiography to measure both bone density (CADIA) values and linear changes in crestal bone height.

RESULTS

Significant (p<0.01) changes using both radiographic measures occurred between 2 and 4 weeks following initiation of disease in this model. The use of the blockers significantly (p<0.01) reduced the levels of radiographic bone loss by approximately 50% over that found in the control sites. Both biochemical markers showed the greatest increase during the first two weeks of the study with PYD levels increased 35-fold over baseline levels after 1 week. This difference in response was significantly (p<0.05) greater than the levels found in the non-ligated teeth or in the ligated teeth receiving blockers injections. BAP levels showed significant increases in ligated teeth compared to non-ligated teeth, but failed to show any significant differences between animals treated with vehicle and those treated with IL-1/TNF antagonists. In contrast to these radiographic and biochemical effects, there were no significant differences detected between animals treated with antagonists and the control group for any of the clinical measures.

CONCLUSIONS

The results of this study demonstrate that both subtraction radiography and PYD crevicular fluid levels can detect relative differences in periodontal disease progression, while BAP crevicular fluid levels cannot.

The relation between lifestyle factors and biochemical markers of bone turnover among early postmenopausal women

We examined the associations of two biochemical markers of bone turnover with lifestyle factors in 340 postmenopausal women in Hawaii, ages 45-59 years, from the Early Postmenopausal Intervention Cohort. Physical activity, calcium supplement use, smoking and alcohol use in the prior 2 weeks were measured and examined as independent variables in multiple regression analyses with bone turnover markers as dependent variables, adjusted for weight, height, whole body bone mass, serum estradiol, years since menopause, and ethnicity. Calcium supplement and alcohol use were significantly associated with reduced levels of urinary type I collagen cross-linked N-telopeptides (NTX). The mean NTX level was 12% lower among women using > or = 250 mg of calcium supplements per day as compared with other women, and 20% lower among alcohol users compared with nonusers. Both calcium supplement use and alcohol intake were associated with lower mean serum osteocalcin (a marker of bone formation) and NTX z-scores. By contrast, smoking was associated with lower osteocalcin levels, without any effect on NTX. The osteocalcin level was 12% lower among smokers compared with nonsmokers. In addition, the z-score difference between NTX and osteocalcin was significantly associated with smoking, with a shift towards more NTX than osteocalcin. Physical activity was not significantly associated with either of the markers. These findings suggest that biochemical markers may help to identify lifestyle factors that affect bone, and provide estimates of the relative magnitude of these effects on bone formation and resorption, independent of each other.

Biochemical Markers of Bone Formation in Patients with Plasma Cell Dyscrasias and Benign Osteoporosis

Background: Myeloma-induced bone loss is related to an uncoupling of bone formation and bone resorption. The aim of the present study was to assess the potential clinical value of biochemical markers of bone formation in the work up of patients with plasma cell dyscrasias.

Methods: Serum total alkaline phosphatase, bone-specific alkaline phosphatase (BAP), and osteocalcin (OC) were measured in 43 patients with newly diagnosed multiple myeloma (MM), in 40 patients with monoclonal gammopathy of undetermined significance (MGUS), in 40 patients with untreated benign vertebral osteoporosis (OPO), and in 48 healthy adults.

Results: In MM and MGUS patients, serum BAP, but not serum OC, was lower than in healthy controls (P &lt;0.05). Serum OC was higher in patients with OPO than in healthy controls (P &lt;0.05). The strongest associations between markers were found in OPO patients and in healthy adults. MM patients with early-stage disease or without detectable osteolysis had decreased serum BAP values (P &lt;0.05). Serum OC was higher in MM patients with stage III disease (P &lt;0.05) than in healthy controls. MM patients with OPO-like bone involvement had lower BAP values than sex- and age-matched MGUS patients with OPO-like bone involvement and patients with benign OPO (P &lt;0.05).

Conclusions: In patients with plasma cell dyscrasias, serum BAP, rather than serum OC, appears to reflect a suppressed bone formation rate and may be helpful in the differentiation between benign and myeloma-induced OPO. However, the overall clinical use of biochemical markers of bone formation in patients with plasma cell dyscrasia appears limited.