Kim Naylor

The effect of pregnancy on bone density and bone turnover

During pregnancy, the mother adapts to meet the calcium demands of the fetus. The effect of this adaptation on the maternal skeleton is not fully understood. Our objectives were to evaluate changes in bone mineral density (BMD) and bone turnover during pregnancy. We studied 16 women longitudinally, with baseline measurements before pregnancy; then at 16, 26, and 36 weeks of pregnancy; and postpartum. We measured total‐body BMD and biochemical markers of bone resorption (urinary pyridinium crosslinks and telopeptides of type I collagen) and bone formation (serum bone alkaline phosphatase, propeptides of type I procollagen [PINP] and osteocalcin). We also measured parathyroid hormone (PTH), insulin‐like growth factor I (IGF‐I), and human placental lactogen. Postpartum, BMD increased in the arms (2.8%, P< 0.01) and legs (1.9%, P< 0.01) but decreased in the pelvis (−3.2%, P<0.05) and spine (−4.6%, P< 0.01) compared with prepregnancy values. All biochemical markers, with the exception of osteocalcin concentration, increased during pregnancy. The change in IGF‐I at 36 weeks was related to the change in biochemical markers (e.g., PINP, r = 0.72, P= 0.002). Pregnancy is a high‐bone‐turnover state. IGF‐I levels may be an important determinant of bone turnover during pregnancy. Elevated bone turnover may explain trabecular bone loss during pregnancy.

Response of Biochemical Markers of Bone Turnover to Hormone Replacement Therapy: Impact of Biological Variability

Biochemical markers of bone turnover may be useful to monitor patients taking hormone replacement therapy (HRT). The aim of this study was to assess the utility of markers in monitoring HRT by comparing the response of a large panel of markers to HRT with their within subject variability. We measured the response of markers to transdermal estradiol in 11 postmenopausal women over 24 weeks. We measured the within subject variability of markers in 11 untreated healthy postmenopausal women over the same period. The mean decrease in markers of bone formation after 24 weeks treatment ranged from 19% for procollagen type I C‐terminal propeptide (PICP) to 40% for procollagen type I N‐terminal propeptide (PINP). The mean decrease in markers of bone resorption ranged from 10% for tartrate‐resistant acid phosphatase (TRAP) to 67% for C‐terminal cross‐linked telopeptide. The least significant change (LSC at p < 0.05), calculated from the within subject variability in the untreated group, was used to define response. LSC for osteocalcin was 21%, bone alkaline phosphatase 28%, PICP 24%, PINP 21%, type I collagen telopeptide 28%, TRAP 17%, urinary calcium 90%, hydroxyproline 75%, total deoxypyridinoline 47%, free pyridinoline 36%, free deoxypyridinoline 26%, N‐terminal cross‐linked telopeptide 70%, and C‐terminal cross‐linked telopeptide 132%. The greatest number of responders after 24 weeks of treatment were found using PINP and osteocalcin (9 each), and free deoxypyridinoline (8 each) and total deoxypyridinoline (7 each). Lumbar spine bone mineral density defined four patients as responders. The ability to detect a response differs between markers and is not dependent on the magnitude of response to therapy.

Bone turnover markers: use in osteoporosis.

Biochemical markers of bone turnover (bone turnover markers, BTMs) can be used to study changes in bone remodelling in osteoporosis. Investigators and clinicians should be aware of the appropriate sample collection and storage conditions for optimum measurements of these markers. Improvements in the variability of BTM measurements have resulted from the development of assays for automated analysers, and from international consensus regarding their use. Appropriate reference intervals should be used for the optimum interpretation of results. BTMs can provide information that is useful for the management of patients with osteoporosis, for both the initial clinical assessment and for guiding and monitoring of treatment. BTMs are clinically useful to determine possible causes of secondary osteoporosis by identifying patients with high bone turnover and rapid bone loss. In the follow-up of treatment response, BTM levels respond rapidly to both anabolic and antiresorptive treatments. BTM changes can also be used for understanding the mechanism of action of drugs in development and identifying the correct dose; they are also potentially useful as surrogate biomarkers for fracture.

Use of DXA-based finite element analysis of the proximal femur in a longitudinal study of hip fracture.

Bone mineral density (BMD) measured by dual‐energy X‐ray absorptiometry (DXA) is used for clinical assessment of fracture risk; however, measurements that incorporate bone strength could improve predictive ability. The aim of this study was to determine whether bone strength derived from finite element (FE) analysis was associated with hip fracture risk in a longitudinal study. We studied 728 women (mean age 82 years), 182 with subsequent hip fracture. FE models were generated from baseline DXA scans of the hip to determine femoral bone strength and load‐to‐strength ratio (LSR). The baseline LSR was significantly higher in fracture cases (median 1.1) compared with controls (0.7, p < 0.0001). Femoral strength and BMD were also significantly lower in cases (median 1820 N, 0.557 g/cm2) compared with controls (2614 N, 0.618 g/cm2) both p < 0.0001. Fracture risk increased per standard deviation decrease in femoral strength (odds ratio [OR] = 2.2, 95% confidence interval [CI] 1.8–2.8); femoral neck (FN) BMD (OR = 2.1, 95% CI 1.7–2.6); total hip BMD (OR = 1.8, 95% CI 1.5–2.1); and per SD increase in LSR (OR = 1.8, 95% CI 1.5–2.1). After adjusting for FN BMD, the odds ratio for femoral strength (OR = 1.7, 95% CI 1.2–2.4) and LSR (OR = 1.4, 95% CI 1.1–1.7) remained significantly greater than 1. The area under the curve (AUC) for LSR combined with FN BMD (AUC 0.69, 95% CI 0.64–0.73) was significantly greater than FN BMD alone (AUC 0.66, 95% CI 0.62–0.71, p = 0.004). Strength and LSR remained significant when adjusted for prevalent fragility fracture, VFA, and FRAX score. In conclusion, the DXA‐based FE model was able to discriminate incident hip fracture cases from controls in this longitudinal study independently from FN BMD, prior fracture, VFA, and FRAX score. Such an approach may provide a useful tool for better assessment of bone strength to identify patients at high risk of hip fracture who may benefit from treatment to reduce fracture risk.

Bone Turnover in Preterm Infants

Total parenteral nutrition is associated with osteopenia in preterm infants. Insufficient calcium and phosphate are likely causes; aluminum contamination is another possible contributing factor as this adversely affects bone formation and mineralization. The study was designed to evaluate changes in biochemical markers of bone turnover in 22 preterm infants receiving total parenteral nutrition in comparison with 19 term infants. We collected urine and serum samples from 22 preterm infants, mean gestational age 29 wk, within 48 h and again at 3 wk of life. We also collected urine samples from 19 term infants, mean gestational age 39 wk, during the first day of life. Bone resorption was assessed by the measurement of urinary pyridinium cross-links by HPLC and ELISA and the N-telopeptide of type I collagen by ELISA. Bone formation was assessed in premature infants by the measurement of serum osteocalcin. The N-telopeptide of type I collagen was higher in the preterm infants compared with term at baseline (p < 0.01). There was no difference between the pyridinium cross-links in the preterm and term infants. All the biochemical markers of bone turnover increased significantly in the preterm infants during the first 3 wk of life, e.g. N-telopeptide was a 153% change from baseline (p < 0.001). Aluminum in the total parenteral nutrition solutions did not cause a decrease in bone formation at the level administered (3-6 µg, 0.1-0.2 µmol·kg-1·d-1).

Free 25-hydroxyvitamin D is low in obesity, but there are no adverse associations with bone health

BACKGROUND The mechanism and clinical significance of low circulating 25-hydroxyvitamin D [25(OH)D] in obese people are unknown. Low total 25(OH)D may be due to low vitamin D-binding proteins (DBPs) or faster metabolic clearance. However, obese people have a higher bone mineral density (BMD), which suggests that low 25(OH)D may not be associated with adverse consequences for bone. OBJECTIVE We sought to determine whether 1) vitamin D metabolism and 2) its association with bone health differ by body weight. DESIGN We conducted a cross-sectional observational study of 223 normal-weight, overweight, and obese men and women aged 25-75 y in South Yorkshire, United Kingdom, in the fall and spring. A subgroup of 106 subjects was also assessed in the winter. We used novel techniques, including an immunoassay for free 25(OH)D, a stable isotope for the 25(OH)D3 half-life, and high-resolution quantitative tomography, to make a detailed assessment of vitamin D physiology and bone health. RESULTS Serum total 25(OH)D was lower in obese and overweight subjects than in normal-weight subjects in the fall and spring (geometric means: 45.0 and 40.8 compared with 58.6 nmol/L, respectively; P < 0.001) but not in the winter. Serum 25(OH)D was inversely correlated with body mass index (BMI) in the fall and spring and in the winter. Free 25(OH)D and 1,25-dihydroxyvitamin D [1,25(OH)2D] were lower in obese subjects. DBP, the DBP genotype, and the 25(OH)D3 half-life did not differ between BMI groups. Bone turnover was lower, and bone density was higher, in obese people. CONCLUSIONS Total and free 25(OH)D and 1,25(OH)2D are lower at higher BMI, which cannot be explained by lower DBP or the shorter half-life of 25(OH)D3 We speculate that low 25(OH)D in obesity is due to a greater pool of distribution. Lower 25(OH)D may not reflect at-risk skeletal health in obese people, and BMI should be considered when interpreting serum 25(OH)D as a marker of vitamin D status.

The impact of subcutaneous oestradiol implants on biochemical markers of bone turnover and bone mineral density in postmenopausal women

Objective To evaluate the anabolic effect of oestrogen on bone by comparing the response of markers of bone formation (and resorption) and bone mineral density (BMD) to subcutaneous oestradiol implants.

The effect of cessation of raloxifene treatment on bone turnover in postmenopausal women

There is evidence to suggest accelerated bone loss following estrogen cessation. The effect of cessation of raloxifene therapy on bone turnover is unknown. Our aim was to determine the effect of cessation of raloxifene treatment on bone turnover and bone mineral density (BMD) in postmenopausal, osteopenic women. Women aged 50 to 80 years received raloxifene for 96 weeks and were then randomized to continue raloxifene (group 1, n=20) or placebo (group 2, n=20) for a further 96 weeks. A third group (group 3, n=14) received no treatment. Bone turnover markers and bone density (BMD) were measured throughout the study. Raloxifene treatment for 96 weeks resulted in a decrease in bone turnover (PINP by 31%) and an increase in spine BMD (by 2%) but no change in hip BMD for groups 1 and 2. Continuation of raloxifene (group 1) maintained these changes. Following cessation of raloxifene (group 2), bone markers returned to baseline levels (by 120 weeks). Hip BMD was decreased by 2% at 192 weeks compared to baseline. Bone markers in the controls (group 3) remained at the upper limit of the reference range throughout, with decreases in BMD of 2.3% (spine) and 2.8% (hip). Bone loss following cessation of raloxifene therapy at 96 weeks was greater than in the control group, suggesting accelerated bone loss. The beneficial effect on bone turnover of 96 weeks of raloxifene was lost 6 months after cessation of treatment.

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

SummaryThe National Bone Health Alliance (NBHA) recommends standardized sample handling and patient preparation for C-terminal telopeptide of type I collagen (CTX-I) and N-terminal propeptide of type I procollagen (PINP) measurements to reduce pre-analytical variability. Controllable and uncontrollable patient-related factors are reviewed to facilitate interpretation and minimize pre-analytical variability.IntroductionThe IOF and the International Federation of Clinical Chemistry (IFCC) Bone Marker Standards Working Group have identified PINP and CTX-I in blood to be the reference markers of bone turnover for the fracture risk prediction and monitoring of osteoporosis treatment. Although used in clinical research for many years, bone turnover markers (BTM) have not been widely adopted in clinical practice primarily due to their poor within-subject and between-lab reproducibility. The NBHA Bone Turnover Marker Project team aim to reduce pre-analytical variability of CTX-I and PINP measurements through standardized sample handling and patient preparation.MethodsRecommendations for sample handling and patient preparations were made based on review of available publications and pragmatic considerations to reduce pre-analytical variability. Controllable and un-controllable patient-related factors were reviewed to facilitate interpretation and sample collection.ResultsSamples for CTX-I must be collected consistently in the morning hours in the fasted state. EDTA plasma is preferred for CTX-I for its greater sample stability. Sample collection conditions for PINP are less critical as PINP has minimal circadian variability and is not affected by food intake. Sample stability limits should be observed. The uncontrollable aspects (age, sex, pregnancy, immobility, recent fracture, co-morbidities, anti-osteoporotic drugs, other medications) should be considered in BTM interpretation.ConclusionAdopting standardized sample handling and patient preparation procedures will significantly reduce controllable pre-analytical variability. The successful adoption of such recommendations necessitates the close collaboration of various stakeholders at the global stage, including the laboratories, the medical community, the reagent manufacturers and the regulatory agencies.

The effect of bisphosphonate treatment on osteoclast precursor cells in postmenopausal osteoporosis: The TRIO study.

Bisphosphonates are used to treat bone disease characterised by increased bone resorption by inhibiting the activity of mature osteoclasts, resulting in decreased bone turnover. Bisphosphonates may also reduce the population of osteoclast precursor cells. Our aims were to investigate the effect of bisphosphonates on i) osteoclast precursor cells and ii) circulating cytokine and cytokine receptor in postmenopausal women with osteoporosis compared with healthy premenopausal women. Participants were 62 postmenopausal women (mean age 66) from a 48-week parallel group trial of bisphosphonates. They received ibandronate 150mg/month (n=22), alendronate 70mg/week (n=19) or risedronate 35mg/week (n=21). Fasting blood was collected at baseline, weeks 1 and 48. At baseline, blood was also collected from 25 healthy premenopausal women (mean age 37) to constitute a control group. Peripheral blood mononuclear cells were extracted and stained for CD14, M-CSFR, CD11b and TNFRII receptors. Flow cytometry was used to identify cells expressing CD14+ and M-CSFR+ or CD11b+ or TNFRII+. RANKL and OPG were measured to evaluate potential mediation of the bisphosphonate effect. After 48weeks of treatment, there was a decrease in the percentage of cells expressing M-CSFR and CD11b receptors by 53% and 49% respectively (p<0.01). Cells expressing M-CSFR and CD11b were decreased with ibandronate and risedronate after 48weeks to the lower part of the premenopausal reference interval. These effects were not significantly different between each of the treatment groups. There was no significant effect on RANKL and OPG throughout the study period. Bisphosphonates inhibit bone resorption in the short-term by direct action on mature osteoclasts. There is also a later effect mediated in part by a reduction in the population of circulating osteoclast precursors.