Early changes in biochemical markers of bone turnover and their relationship with bone mineral density changes after 24 months of treatment with teriparatide.

UNLABELLED: We report the changes in biochemical markers of bone formation during the first 6 months of teriparatide therapy in postmenopausal women with osteoporosis according to previous antiresorptive treatment. Prior therapy does not adversely affect the response to teriparatide treatment. Similar bone markers levels are reached after 6 months of treatment. INTRODUCTION: The response of biochemical markers of bone turnover with teriparatide therapy in subjects who have previously received osteoporosis drugs is not fully elucidated. We examined biochemical markers of bone formation in women with osteoporosis treated with teriparatide and determined: (1) whether the response is associated with prior osteoporosis therapy, (2) which marker shows the best performance for detecting a response to therapy, and (3) the correlations between early changes in bone markers and subsequent bone mineral density (BMD) changes after 24 months of teriparatide. METHODS: We conducted a prospective, open-label, 24-month study at 95 centers in 10 countries in 758 postmenopausal women with established osteoporosis (n = 181 treatment-naïve) who had at least one post-baseline bone marker determination. Teriparatide (20 µg/day) was administered for up to 24 months. We measured procollagen type I N-terminal propeptide (PINP), bone-specific alkaline phosphatase (b-ALP), and total alkaline phosphatase (t-ALP) at baseline, 1 and 6 months, and change in BMD at the lumbar spine, total hip and femoral neck from baseline to 24 months. RESULTS: Significant increases in formation markers occurred after 1 month of teriparatide regardless of prior osteoporosis therapy. The absolute increase at 1 month was lower in previously treated versus treatment-naïve patients, but after 6 months all groups reached similar levels. PINP showed the best signal-to-noise ratio. Baseline PINP correlated positively and significantly with BMD response at 24 months. CONCLUSIONS: This study suggests that the long-term responsiveness of bone formation markers to teriparatide is not affected in subjects previously treated with antiresorptive drugs.

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 (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.

A longitudinal study of bone gain in pubertal girls: anthropometric and biochemical correlates.

The aim of this longitudinal study was to investigate the factors associated with bone mineral acquisition in pubertal girls. Subjects were 37 healthy, Caucasian girls aged 12.1 years (SD 0.3). Measurements were made at 6-month intervals over a period of 18 months and included total body bone mineral content (TBBMC), total body bone mineral density (TBBMD), lean mass, and fat mass by dual-energy X-ray absorptiometry, anthropometry, lifestyle factors, four biochemical markers of bone turnover, hormonal status, and fractional calcium absorption. In multiple regression analysis, correlates of relative gain in TBBMC were gain in lean mass (p < 0.001) and estradiol (p = 0.008). For TBBMD, correlates were gain in lean (p < 0.001) and fat mass (p = 0.003), estradiol (p < 0.001), dietary energy intake (p = 0.003), and parathyroid hormone (p = 0.023). Statural growth and gain in bone mass were unrelated; both height velocity and bone turnover peaked approximately 20 months prior to menarche, whereas gain in bone mass peaked at menarche. Bone turnover markers correlated with height velocity (0.40 < r < 0.62), but not with bone gain. Estradiol was independently and negatively associated with all markers of bone turnover (-0.67 < r < -0.80). We conclude that estradiol is an important determinant of bone mineral gain in pubertal girls and is probably responsible for the reduction in bone turnover in late puberty; lean mass was the body composition parameter most closely associated with bone gain; height gain and bone gain are dissociated during the period of rapid growth at puberty; and bone turnover markers are modestly related to height gain, but are not predictive of bone gain.

Circadian rhythm of in vitro bone-resorbing activity in human serum.

Calciotropic hormones as well as biochemical parameters of bone formation and resorption show circadian rhythms. In a previous study in the rat, we observed a circadian rhythm in serum bone-resorbing activity (SBRA). In the present study, we investigated whether there was a circadian rhythm of SBRA in human serum. For this purpose, we studied 10 healthy premenopausal women and 5 healthy men. Blood was collected every 2 h, and urine samples were collected during 4-h periods for 24 h. For the determination of SBRA, media were prepared by reconstituting serum samples with Dulbecco's Modified Eagle's Medium at a ratio of 20% serum and 80% Dulbecco's Modified Eagle's Medium. Limb bones were dissected from 19-day old fetal rats prelabelled with 45Ca and were cultured for 72 h in the presence of the sera. Bone resorption was assessed from the 45Ca released into the culture medium and from that retained in the bone and was expressed as percentage 45Ca release. Serum calcium, phosphorus, PTH, cortisol, and urinary pyridinium cross-links were also determined. SBRA in human serum followed a circadian rhythm with a peak at about 0300 h and a nadir at 0700 h. There was no significant difference between the rhythm of SBRA of women and men. At concurrent time points, SBRA and serum PTH were positively correlated (r = 0.629; P < 0.01), and SBRA and serum cortisol were negatively correlated (r = 0.797; P < 0.01). To further investigate the possible contribution of these hormones to SBRA, either neutralizing anti-PTH antibody or RU-486 (mifepristone), a glucocorticoid receptor antagonist, was added to the serum samples of 6 subjects. Neutralizing the effect of PTH did not change the pattern of SBRA rhythm. The addition of RU-486 had a significant effect on the rhythm of SBRA, reducing the peak and nadir amplitudes. Thus we conclude that cortisol plays a major role in the rhythm of SBRA present in human serum; however, the influence of other factors cannot be excluded. Cortisol may be an important determinant of the circadian rhythm of bone resorption in vivo.

The effect of calcium supplementation on the circadian rhythm of bone resorption.

Bone resorption shows a circadian rhythm in human subjects, but the physiological mechanisms underlying this rhythm are unknown. We compared the circadian rhythm of bone collagen degradation in 18 premenopausal women before and after oral calcium supplementation (1000 mg calcium for 14 days). Subjects were randomized to receive calcium at either 0800 h or 2300 h. Continuous 48-h urine collections and 1 day of 4-h urine collections were obtained before and after the 14-day supplementation period. We measured urinary deoxypyridinoline (Dpd) and the cross-linked N-telopeptide of type I collagen (NTx) as biochemical markers of bone resorption. There was a significant effect of time of day on excretion of Dpd and NTx (analysis of variance, P < 0.001) with peak excretion between 0300-0700 h and a nadir between 1500-1900 h. The mean amplitude (peak to trough) was similar for Dpd and NTx (70.3% and 63.3%, respectively). Evening calcium supplementation resulted in marked suppression of the nocturnal increase in Dpd and NTx and reversed the usual nocturnal increase in the level of parathyroid hormone. In contrast, morning calcium supplementation had no significant effect on the circadian rhythm of Dpd or NTx. Evening calcium supplementation suppressed overall daily excretion of Dpd by 20.1% (P = 0.03) and NTx by 18.1% (P = 0.03). Morning calcium supplementation had no significant effect on overall daily excretion of either Dpd or NTx. We conclude that evening calcium supplementation suppresses the circadian rhythm of bone resorption. The daily rhythm of PTH secretion or calcium intake is likely to be an important determinant of this rhythm. Experimental protocols designed to investigate the effect of calcium supplementation on bone mineral density should take the timing of supplementation into account.

Serum osteoprotegerin as a determinant of bone metabolism in a longitudinal study of human pregnancy and lactation.

Osteoprotegerin (OPG) is a soluble decoy receptor that inhibits bone resorption by binding to receptor activator of nuclear factor kappa B ligand. Murine studies suggest that OPG is elevated in pregnancy, but its role in human pregnancy is unknown. We evaluated the relationship among OPG, bone turnover, and bone density in a longitudinal study of planned human pregnancy and lactation (n = 17; age, 20-36 yr). Samples were collected before conception; at 16, 26, and 36 wk gestation; and at 2 and 12 wk postpartum. Indexes of bone resorption included serum beta C-terminal and urinary N-terminal (uNTX) telopeptides of type I collagen. OPG increased by 110 +/- 16% (mean +/- SEM) at 36 wk (P < 0.001), followed by a rapid postpartum decline in both lactating and nonlactating women. Bone resorption was elevated at 36 wk (serum beta C-terminal telopeptides by 76 +/- 17%; urinary N-terminal telopeptides by 219 +/- 41%; P < 0.001). The tissue source of OPG in pregnancy is unknown. Human breast milk contains large amounts of OPG (162 +/- 58 ng/ml in milk vs. 0.42 +/- 0.03 ng/ml in nonpregnant serum). However, the rapid postpartum decline in serum OPG and the low serum OPG in neonates suggest a placental source. There was no correlation between change in OPG and bone turnover or bone mineral density (P > 0.05), and the physiological importance of elevated OPG in human pregnancy remains uncertain.

Human chorionic gonadotropin may not be responsible for thyroid-stimulating activity in normal pregnancy serum.

Although hCG can activate thyroid cells in culture there is considerable doubt as to whether it is responsible for the changes in thyroid function which occur during normal pregnancy. Thyroid-stimulating activity (TSA), measured using iodide uptake into FRTL-5 cells, was demonstrated in 32/51 (63%) first and 15/29 (52%) third trimester sera. Free T3 was increased (P less than 0.001) and TSH decreased (P less than 0.01) in first trimester. In the early pregnancy group there was a positive correlation between hCG and TSA (r = 0.594, P less than 0.001) and a negative correlation between hCG and TSH (r = -0.329, P less than 0.02). In third trimester hCG concentration was often below that required to produce TSA in vitro and TSA could not be neutralized by antibodies to hCG. There was no correlation between hCG and TSH or thyroid hormones in the third trimester. In 26 women TSA decreased in parallel with serum hCG concentration after termination of pregnancy (P less than 0.001). Free T3 also decreased (P less than 0.01) and TSH increased (P less than 0.05) after termination. TSA persisted in many patients even after hCG was either very low or undetectable. Purified hCG stimulated iodide uptake in a concentration-dependent manner. Stimulation of iodide uptake by TSH was inhibited by the simultaneous presence of low concentrations of hCG while activity was restored with high concentrations. hCG may contribute to the thyroid changes in early pregnancy. However the poor correlation between TSA and thyroid tests suggests that other factors may be involved. The partial agonist activity of hCG may account for some of the inconsistencies observed but TSA in serum from late pregnancy or after termination of pregnancy is almost certainly due to another hormone or growth factor.

The trace element chromium--a role in glucose homeostasis.

To better define the normal metabolism of the trace element chromium, we studied its diurnal variation and its response to an oral glucose challenge in nine healthy volunteers. Plasma and urine chromium concentrations were measured by electrothermal atomic-absorption spectroscopy and plasma insulin by radioimmunoassay. A significant inverse relationship was found between plasma chromium and plasma insulin concentrations both over a 24-h period (P less than 0.001) and after a 75-g glucose load (P less than 0.01). This interesting observation, suggesting the removal of chromium from the plasma compartment after meals (confirmed by glucose tolerance test), is not explained simply by increased urinary loss but might be explained by transient changes in uptake or binding of chromium by insulin-sensitive tissues.

Effect of feeding on bone turnover markers and its impact on biological variability of measurements.

Bone turnover markers are subject to day-to-day and within-day variability, which may influence clinical interpretation. We examined the effect of fasting vs. feeding on the concentration and between-day variability of several markers. Twenty healthy premenopausal women were studied on 10 consecutive weekdays. Subjects were studied either in the fasting (no breakfast) or fed (breakfast at 08:00 h) state on alternate days, and were randomized to begin either fasting or fed. Two hour urine collections were obtained each day between 08:00 h and 10:00 h, and blood samples were collected daily at 09:00 h. The N-telopeptide cross-link of type I collagen in urine (uNTX) and serum (sNTX), the C-telopeptide in urine (uCTX) and serum (sbetaCTX), and immunoreactive free deoxypyridinoline (uifDPD) in urine were measured as resorption markers. Procollagen type I N-terminal propeptide (PINP), osteocalcin (OC), and bone alkaline phosphatase (bone ALP) were measured as formation markers. All bone formation and resorption markers were significantly lower in the fed state with the exception of bone ALP. The magnitude of the decrease ranged from 3.8 +/- 0.9% for PINP (p < 0.0001) to 17.8 +/- 2.6% (p < 0.0001) for sbetaCTX. Measurement variability was partitioned into analytical variability based on replicate assays (CV(a)) and within-subject variability (CV(i)). The CV(i) was greater (p < 0.05) for some markers in the fasting state (uifDPD, uNTX, and sNTX) but greater in the fed state for other markers (OC and sbetaCTX). In conclusion, the clinical impact of feeding vs. fasting is small with the exception of sbetaCTX; however, in clinical practice, collection of samples in the fasting state may be necessary to minimize the unpredictable effects of feeding. The mechanism of the acute effect of feeding on bone turnover remains uncertain.

Excess paternal age in apparently sporadic osteogenesis imperfecta.

The objective of this study was to examine whether parental age is associated with the occurrence of apparently sporadic osteogenesis imperfecta (OI). We compared parental age and the joint distribution of maternal and paternal age with expected distributions based on statutory birth records for each year and location of birth. The study included patients with OI based in the United Kingdom. The study was restricted to cases born in England, Wales, and Scotland between 1961 and 1998. Subgroup analysis was by clinical type [Sillence et al., 1979: J Med Genet 16:101-116] and apparent mode of inheritance based on pedigree analysis. Of 730 eligible cases, 357 were apparently sporadic. The mean age of fathers at birth of children with apparently sporadic OI was 0.87 years greater than expected (P = 0.010; 95% confidence interval = 0.21 to 1.54 years). The relative risk was 1.62 for fathers in the highest quintile of paternal age compared with fathers in the lowest quintile. The magnitude of the paternal age excess did not differ significantly between Sillence types (analysis of variance P = 0.534). In sporadic cases, paternal age was 0.51 years greater than expected, given maternal age, year, and location of birth (P = 0.033). In contrast, in familial cases, there was no significant paternal age excess, and paternal age was not significantly different from that expected given maternal age. Increased paternal age is a significant risk factor for sporadic OI. This effect is not accounted for by increasing maternal age. The magnitude of the paternal age excess is small in comparison with that in some other autosomal dominant disorders.

Asthma and Cushing's syndrome.

A female patient was treated with high-dose inhaled fluticasone propionate for her asthma. Over 2 years, she developed features of Cushing's syndrome with proximal myopathy, osteopenia, hypertension, depressive psychosis, and cushingoid appearance. She had biochemical evidence of marked adrenal suppression with a 9:00 AM serum cortisol of 20 nmol/L that returned to normal (315 mol/L) after her therapy was changed to budenoside, 0.8 mg/d. Her appearance, mental state, and myopathy also improved with no loss of asthma control. This case illustrates the potential for developing clinically relevant adverse effects of inhaled corticosteroids when given at licensed doses.

Manganese requirement and toxicity in patients on home parenteral nutrition.

Two patients who were receiving home parenteral nutrition complained of vague neurological symptoms of such severity that they underwent full clinical appraisal. The only positive finding was that plasma manganese concentrations were greater than twice the upper 95% confidence interval of normal (7-27|nmol/l). In the light of this result all nine patients receiving home parenteral nutrition underwent evaluation for possible manganese toxicity. One other patient had serum manganese concentrations exceeding twice the upper limit (127|nmol/l). The three patients with elevated serum Mn had evidence of manganese deposition in the brain on magnetic resonance imaging scanning. In contrast two patients with normal plasma results had negative scans. Patient susceptibility appears very variable. We suggest that current amounts of trace elements provided in nutrition solutions may be a potential source of nutrient activity. The fine tuning of supply and demand may be difficult on account of a limited range of commercially available trace element solutions.

The effect of dietary sodium on calcium metabolism in premenopausal and postmenopausal women.

OBJECTIVE: To investigate the effects of high and low sodium diets on urinary calcium, bone turnover and calcium absorption in pre and postmenopausal women. DESIGN: Experimental, prospective and longitudinal study. SETTING: Samples were taken at the hospital and the diets were followed at home. SUBJECTS: Volunteers were recruited from the hospital and were either hospital staff or post-graduate students. No volunteers failed to complete the study but one was omitted from analysis due to lack of compliance. INTERVENTIONS: Eleven healthy premenopausal women aged 22-47 y and 11 healthy postmenopausal women ages 45-70 y followed a high (300 mmol/d) and a low (50 mmol/d) sodium diet for one week each. On the 7th day of each diet, blood and urine samples were taken. RESULTS: On the high sodium diet 24 h urinary sodium and calcium values relative to creatinine were significantly higher for all subjects (P < 0.05). Postmenopausal women on the high sodium diet had biochemical evidence of increased bone resorption in relation to the low sodium diet. However in premenopausal women there was no such change. Calcium absorption did not change significantly in either group. CONCLUSIONS: It appears that postmenopausal, but not premenopausal, women respond to a high sodium diet by an increase in bone resorption which may lead to reduced bone density. SPONSORSHIP: Arthritis and Rheumatism Council Project Grant R44.

On the relevant model for the human electrocardiogram: the so called "imaginary cardiac vector hypothesis" - fact or illusion?

This paper evaluates the plausibility of the recently proposed "Imaginary cardiac vector" hypothesis, viz. that the cardiac vector is an imaginary scalar quantity, and thus not a true vector. The arguments presented in favour of this "Imaginary cardiac vector" hypothesis, do not in fact contradict vector theory, and are thus not crucial arguments. The actual values obtained by Einthoven, are examined vectorially, in order to demonstrate that his original analysis was fundamentally vectorial. Theoretical limitations imposed by the simplistic use of the equivalent dipole concept, are discussed.

Age related changes in biochemical markers of bone metabolism in horses.

Biochemical markers of bone metabolism were analysed in serum samples obtained from 60 horses with no history of orthopaedic disease (age 3 months-20 years). Serum levels of the carboxyterminal propeptide of type I procollagen (PICP), a marker of bone formation and the pyridinoline cross linked telopeptide domain of type I collagen (ICTP), a putative marker of bone resorption, were measured by radioimmunoassay (RIA). Serum levels of the bone specific isoenzyme of alkaline phosphatase (BALP), another marker of bone formation, were measured by a wheatgerm agglutinin affinity (WGA) method. Total alkaline phosphatase levels were also determined. Serum levels of PICP were significantly correlated with bone ALP (r = 0.78, P < 0.0001) and ICTP (r = 0.87, P < 0.0001). ICTP levels also correlated significantly with bone ALP (r = 0.81, P < 0.0001). However, total alkaline phosphatase did not correlate significantly with PICP, ICTP and BALP in horses over 1 year of age. There was an inverse correlation between serum levels of all biochemical markers and age of animals, with the most significant changes seen over the first 2 years. In animals less than 1 year of age, the reference ranges (mean +/- s.d. 1.96) were as follows: PICP 1216-2666 micrograms/l, ICTP 13.8-26.7 micrograms/l, bone ALP 134-288 u/l and total ALP 223-498 u/l. In 2-year-olds, the equivalent reference ranges were: PICP 550-1472 micrograms/l, ICTP 7.96-22.8 micrograms/l, bone ALP 32.7-125 u/l and total ALP 134-238 u/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian variation in biochemical markers of bone cell activity and insulin-like growth factor-I in two-year-old horses.

Studies in humans have found circadian changes to be one of the most important sources of controllable preanalytical variability when evaluating bone cell activity using biochemical markers. It remains unclear whether similar circadian changes influence bone marker concentrations in the horse. The aim of this study was to characterize changes in serum concentrations of three biochemical markers of bone cell activity over a 24-h period in six 2-yr-old Thoroughbred mares, and to determine circadian variability in IGF-I, which regulates bone turnover. Three bone markers were measured in serum: osteocalcin, a marker of bone formation, the carboxy-terminal propeptide of type-I collagen (a marker of bone formation), and the carboxy-terminal telopeptide of type-I collagen (a marker of bone resorption). Data were analyzed using the cosinor technique, which fits a 24-h cycle to each dataset. A significant circadian rhythm was observed for osteocalcin (P = 0.028), with an estimated amplitude of 7.6% of the mean (95% confidence interval 1.3% to 16.3%), and an estimated peak time of 0900. However, the observed rhythm for the carboxy-terminal telopeptide of type-I collagen (amplitude = 7.4%) was not significant (P = 0.067), and there were no significant changes in concentrations of the carboxy-terminal propeptide of type-I collagen over the 24-h study period (P = 0.44). There was a small but significant circadian rhythm for IGF-I (P = 0.04), with an estimated amplitude of 3.4% (95% confidence interval 0.2 to 7.1%) and peak at 1730. Further studies are now required to determine the potential association between circadian changes in IGF-I and osteocalcin in the horse. Although no significant circadian variation was found in concentrations of the car-boxy-terminal propeptide of type-I collagen and the carboxy-terminal telopeptide of type-I collagen, this may in part be a result of the age of the animals that were still skeletally immature. Future studies should aim to determine whether these markers develop a circadian rhythm at a later age when growth is complete. In the meantime, consistency in time of sampling should continue to be considered best practice when measuring biochemical markers of bone turnover in the horse.