A new method for calculating the accretion rate of bone calcium and some observations on the suitability of strontium-85 as a tracer for bone calcium

Strontium is incorporated in different levels into bones and teeth of rats treated with strontium ranelate

The aim of this study was to evaluate the strontium incorporation into specific bones and teeth of rats treated with strontium ranelate. The relative strontium levels [Sr/(Ca + Sr) ratio] were obtained by synchrotron radiation micro X-ray fluorescence. The incisor teeth were further examined by energy dispersive X-ray spectroscopy (EDS) in a scanning electron microscope. The isolated mineral phase was investigated by EDS in a transmission electron microscope and X-ray diffraction. The strontium content was markedly increased in animals treated with strontium ranelate, with different incorporation levels found among specific bones, regions within the same bone and teeth. The highest strontium levels were observed in the iliac crest, mandible and calvaria, while the lowest were observed in the femoral diaphysis, lumbar vertebrae, rib and alveolar bone. The strontium content was higher in the femoral neck than in the diaphysis. The strontium levels also varied within the alveolar bone. High levels of strontium were found in the incisor tooth, with values similar to those in the iliac crest. Strontium was observed in both enamel and dentin. The strontium content of the molar tooth was negligible. Strontium was incorporated into the mineral substance, with up to one strontium replacing one out of 10 calcium ions within the apatite crystal lattice. The mineral from treated animals presented increased lattice parameters, which might be associated to their bone strontium contents. In conclusion, the incorporation of strontium occurred in different levels into distinct bones, regions within the same bone and teeth of rats treated with strontium ranelate.

Quantitative studies of bone with the use of 18F-fluoride and 99mTc-methylene diphosphonate

This article discusses methods for quantifying bone turnover based on tracer kinetic studies of the short-lived radiopharmaceuticals 99mTc-MDP and 18F-fluoride. Measurements of skeletal clearance obtained by using these tracers reflect the combined effects of skeletal blood flow and osteoblastic activity. The pharmacokinetics of each tracer is described, together with some of the quantitative tests of skeletal function that have been described in the literature. The physiologic interpretation of quantitative measurements of bone obtained with the use of short half-life radionuclides is discussed, and the advantages and limitations of 99mTc-MDP and 18F-fluoride are compared and contrasted. Currently, 18F-fluoride dynamic positron emission tomography (PET) is the technique of choice for physiologically precise quantitative studies of bone. However, comparable data could probably be obtained by using 99mTc-MDP if methods for single photon emission computed tomography (SPECT) quantitation were improved.

No difference in intestinal strontium absorption after an oral or an intravenous 1,25(OH)2D3 bolus in normal subjects. For the European Study Group on Vitamin D in children with renal failure

It has been suggested that 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) stimulates intestinal calcium absorption less via the intravenous (iv) than the oral route, because the first avoids direct contact of the drug with the enterocytes. However, no study has addressed the issue directly. This investigation was designed to measure the effect of a single oral or iv dose of 1,25(OH)2D3 on calcium absorption, using stable strontium (Sr) as a surrogate for calcium, and measuring the Sr fractional absorbed dose (FAD%) over 240 minutes after Sr administration. In 10 healthy volunteers, five tests were performed in a cross-over design, with a wash-out period between two consecutive tests: Sr absorption without 1,25(OH)2D3 (test A); Sr absorption immediately after either oral (test B) or iv (test C) 1,25(OH)2D3 (1.5 microg/m2 of body surface area [BSA]); Sr absorption (24 hr after either oral (test D) or iv (test E) 1, 25(OH)2D3 (1.5 microg/m2 BSA). The concurrent administration of 1, 25(OH)2D3 and Sr (tests B and C) did not significantly change the area under the Sr FAD%-time curve with respect to test A (test A: 4090 +/- 345; test B: 4510 +/- 345; test C: 4210 +/- 345), whereas Sr absorption was significantly increased (p < 0.001) when Sr was given 24 hr after either oral or iv 1,25(OH)2D3 (test D: 5710 +/- 345; test E: 5510 +/- 345). It was concluded that 1,25(OH)2D3 is likely to influence calcium absorption significantly only via its genomic effect, independent of its administration route.

Biochemical markers of bone resorption compared with estimates of bone resorption from radiotracer kinetic studies in osteoporosis

The pyridinium cross-links of collagen pyridinoline (Pyd) and deoxypyridinoline (Dpd) are released during bone resorption and are neither metabolized nor absorbed from the diet. The aim of this study was to validate their use in osteoporosis. We studied 19 women with osteoporosis and estimated the bone resorption rate from a combined calcium balance/kinetics technique without (R) and with partial (R(H)) and "complete" (Res) correction for long-term exchange. The strongest correlation was observed between the bone-specific marker (Dpd) and with complete correction for long-term exchange (Res) (r = 0.71, p < 0.001). The intercept was not different from zero, suggesting that bone was the major source for Dpd. The crude ratio of Dpd to Res in the 19 women was 54.5; but the regression coefficient relating Dpd as the dependent variable to Res was 31.8 (95% CI 15.6-48.0), which was higher, but not significantly, than the ratio between Dpd and calcium (16.4) in 10 bone samples (cortical and trabecular bone). The weakest correlations between a biochemical marker and a kinetic index were those between hydroxyproline (a nonspecific marker of bone resorption) and R or R(H). Treatment with hormone replacement therapy (HRT) or HRT and parathyroid hormone peptide 1-38 in seven women over 1 year resulted in similar percent changes in the biochemical markers and estimates of bone resorption. We conclude that the measurement of Dpd provides a reasonably accurate assessment of bone resorption in osteoporosis, and in the context of several repeat 24-h collections of urine offers measurement precision that is similar to that obtainable with methods depending on the use of radioisotopic tracers and the assessment of metabolic calcium balance.

Calcium kinetics in glycogen storage disease type 1a

Glycogen storage disease type 1a (Von Gierke's disease) is one of the more common glycogen storage diseases (GSD). GSD 1a patients can have severe idiopathic osteopenia, often beginning at a young age. Since calcium tracer studies offer a sensitive probe of the bone microenvironment and of calcium deposition, kinetics might be disturbed in patients with GSD 1a. Plasma dilution kinetics obtained using the stable isotope 42Ca are shown in this paper to be quite different between GSD 1a patients and age-matched controls. Comparison of kinetic parameters in these two populations is made using a new binding site model for describing calcium dynamics at the plasma-bone interface. This model describes reversible binding of calcium ions to postulated short-term and long-term sites by a retention probability density function psi (t). Using this analysis, adult GSD subjects exhibited a significant decrease (P = 0.023) in the apparent half-life of a calcium ion on the longer-term site compared with controls. The general theory of calcium tracer dilution kinetics is then discussed in terms of a new model of short-term calcium homeostasis recently proposed by Bronner and Stein [5].

The use of stable tracers to study intestinal calcium absorption. The Italian Society of Osteoporosis

This paper represents the final document released by the Italian Society of Osteoporosis (S.I.OP.), on the occasion of its fifth annual meeting held in Padova, Italy (November 30-December 3, 1993). The S.I.OP. has in fact planned to periodically organize a conference on still-debated, controversial issues. After an exhaustive discussion of the various aspects of the problem by qualified experts in the field, a solution will be proposed by the members of the Society. The problems related to the use of radioactive tracers to study intestinal calcium absorption and the possible ways to over-come them were the issues discussed last year, by four panelists (R. P. Heaney, C. Gennari, G. Mioni, and S. Minisola) coordinated by G. F. Mazzuoli.

Calcium tracer kinetics show decreased irreversible flow to bone in glucocorticoid treated patients

Osteopenia resulting from pharmacologic doses of glucocorticoids is well known. Previously, there has been no satisfactory quantitative model describing the kinetics of calcium flow in subjects on chronic steroid use. A mathematical model of calcium isotope interaction with bone is described and applied to determine an estimate of kinetic parameters characterizing these changes. Calcium tracer dilution kinetics after a bolus injection of 42Ca were measured in 14 subjects with juvenile dermatomyositis, 6 on prednisone regimens and 8 on treatment regimens without prednisone. Irreversible tracer loss from plasma bone is found to be significantly reduced (P = 0.043) in the glucocorticoid-treated patients compared with patients on nonsteroid regimens. Reversible flow to bone is noted to be similar in the two groups. These results suggest a direct effect of glucocorticoids on osteoblast function.

Gastrointestinal calcium absorption and dietary calcium load: relationships with bone remodelling in vertebral osteoporosis

Patients with vertebral osteoporosis have a wide range of bone loss rates, bone remodelling rates and capacities for gastrointestinal (GI) calcium absorption. To test the hypothesis that variations in GI absorptive capacity determine rates of bone loss or remodelling, we have sought relationships between calcium absorption or vitamin D metabolite levels on the one hand and rates of cancellous and cortical bone loss (measured by serial quantitative computed tomography in the radius; n = 25) or indices of bone remodelling in tetracycline-prelabelled transiliac biopsies (n = 41) on the other, in a sequential untreated group. Calcium absorption (net and true) was measured in 18-day balances and by a two-isotope deconvolution method (fractional absorption and maximum absorption rate, MAR). There was no significant seasonal effect on any of these four measures of calcium absorption (variance ratio, F = 0.52-1.61, p > 0.1) or on 1,25-dihydroxyvitamin D levels (F = 0.13, p > 0.1; range 11-69 pg/ml), notwithstanding the expected seasonal effect on 25-hydroxyvitamin D levels (mean 18.7 ng/ml, zenith mid July, semi-amplitude 7.5 ng/ml; F = 6.82, p < 0.01). Neither this metabolite nor 1,25-dihydroxyvitamin D correlated with any index of calcium absorption (p > 0.1). No measure of calcium absorption (or intake) had a significant relationship with radial cortical or cancellous bone loss (p all > 0.1) but cancellous bone loss was associated with the rate of endogenous calcium excretion (r = 0.50, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

A non-Markovian model for calcium kinetics in the body

We present a new generalized compartmental model for calcium kinetics as measured by tracer concentration in blood plasma. The parameter measuring incorporation of calcium in bone discriminates between different levels of physical development in female teenagers and between teenagers and adults.

Human parathyroid peptide treatment of vertebral osteoporosis

Previous studies have shown that treatment with daily injections of human parathyroid peptide (hPTH) 1-34 increase axial cancellous bone mass partially at the expense of peripheral cortical bone. In the present work the same hPTH 1-34 regime given for 12 months has been combined with oestrogen or nandrolone therapy to control peripheral bone resorption. Spinal and iliac cancellous (but not cortical) bone increased by 40%-50% above initial values while no perceptible changes occurred in radial cortical or cancellous bone. The evidence of radiokinetic and histomorphometric studies performed before and in the last months of treatment suggested that bone remodeling had proceeded through a transient anabolic phase with increased activation, but that activation had become normal after 11-12 months in the cancellous bone of the ilium whereas it continued to be raised elsewhere in the skeleton. It is concluded that in combination with oestrogens, hPTH peptides given daily injections hold great promise for the treatment of patients with osteoporosis who have already lost substantial amounts of spinal cancellous bone.

Temporal variations in iliac trabecular bone formation in vertebral osteoporosis

The histologic heterogeneity of osteoporosis relative to normal controls has attracted great interest. There has been controversy as to whether patients with high turnover osteoporosis may convert to a normal or low turnover form, and vice versa. We have studied 44 patients over 12 years by dynamic histomorphometry and 85Sr kinetics+calcium balance performed within 60 days in 20 patients (Group 1) and 75-808 days apart in the remainder (Group 2). In the first group, the histologic tissue level bone formation rate (BFR/BV or BFR/BS) was predictive of the 85Sr measurements of bone formation (r = 0.66 P < 0.01). There was no statistically significant correlation in Group 2 and the regression coefficients were significantly different (P = 0.01). Periodic regression was used to determine if seasonal changes were responsible for this loss of correlation; none was found that was of statistical significance. No systematic changes with time in bone formation were found in Group 2 during the period of observation; nor were consistent secular changes detected when the data for both groups were examined according to procedure date. In conclusion, bone formation may change with time in postmenopausal osteoporosis. Evidence that these changes are systematic was not found and this has implications for the design of treatment studies.

Changes in the linear attenuation coefficient of canine appendicular bone following intravenous infusion of strontium lactate, measured using gamma-ray computed tomography

Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone "space"), were monitored continuously using gamma-ray computed tomography (gamma-CT) prior to, during, and following intravenous infusion of strontium (Sr) lactate. An infusion of 1.3-4.7 g of Sr over a period of 110-160 minutes into 20-kg dogs resulted, within 6-8 hours, in an increase of 0.019-0.045 cm-1 (P less than 0.002) in the LAC. Calibration of the gamma-CT system showed that 0.44 mg/cm3 of Sr produced a change of 0.01 cm-1 in the LAC. Using this conversion factor, the Sr concentration in the trabecular bone space resulting from infusion, as measured by flame atomic absorption spectroscopy, agreed with that predicted by the change observed in the LAC. Sr present in the serum and urine was consistent with the changes observed in the LAC over the study period. Control dogs infused with mineral-free solutions showed no change in LAC. Calcium equivalents required to give the changes observed in the LAC using Sr indicate that variations in skeletal turnover in man can be monitored in the peripheral skeleton using gamma-CT.

hPTH 1-34 treatment of osteoporosis with added hormone replacement therapy: biochemical, kinetic and histological responses

Twelve patients with vertebral fracture osteoporosis were recruited into a trial of treatment with hPTH 1-34 by daily injection for 1 year combined (from the 5th month) with an anti-resorptive agent (oestrogen, n = 9; nandrolone, n = 3). Treatment outcomes were monitored by biochemical and radiotracer measurements together with histomorphometry of transiliac biopsies before and at the end of treatment following double in vivo pre-labelling with demethylchlortetracycline. Indices of whole body bone formation, obtained from the analysis of 85Sr data, showed substantial increases (P less than 0.005) for all three indices measured) while biochemical (hydroxyproline) and kinetic measurements of bone resorption showed modest and equivocal changes only. As a result calcium balance improved. Gastrointestinal calcium absorption showed a tendency to improve, while urine calcium decreased; but these changes were statistically not significant except for radiocalcium absorption in the oestrogen treated subgroup. Histomorphometry revealed substantial increases in cancellous bone volume as reported previously with hPTH 1-34 given alone. However, iliac (as distinct from whole body) indices related to bone formation and resorption appeared to have returned towards pre-treatment values by the time of the second biopsy under the influence of the anti-resorptive agent given with the hPTH 1-34. It is confirmed that hPTH 1-34 therapy can increase iliac cancellous bone mass (as well as spinal cancellous bone mass as reported earlier) without a long-term increment in whole body bone resorption, providing the hPTH is combined with an anti-resorptive agent.

Intravenous strontium gluconate as a kinetic marker for calcium in healthy volunteers

1. We have studied the pharmacokinetics of stable strontium in 10 healthy male volunteers. We gave each volunteer 5 mmol strontium gluconate by intravenous infusion over 1 h and measured strontium concentrations in plasma and urine samples for 20 days. The plasma strontium concentration vs time data for each volunteer were fitted by a triexponential function using NONLIN. Compartmental model-dependent and model-independent pharmacokinetic variables were then calculated. 2. The mean half-life we report (5.4 days) is longer than that previously reported (about 2 days), since we continued sampling for 20 days. However, the rates of clearance (CL 9.4 ml min-1. CLR 5.4 ml min-1, and CLNR 4.0 ml min-1) are similar to those previously reported, and the apparent volume of distribution at steady state (64 l) is similar to the values previously reported for the size of the exchangeable pool of both strontium and calcium. 3. The similarities in the pharmacokinetic behavior of strontium and calcium suggest that the in vivo disposition of strontium may be used as a marker of calcium disposition and for studying the effects of drugs such as the calcium antagonists.

Efficacy of wheat germ lectin-precipitated alkaline phosphatase in serum as an estimator of bone mineralization rate: comparison to serum total alkaline phosphatase and serum bone Gla-protein

Serum levels of total alkaline phosphatase activity (S-T-AP), wheat germ lectin-precipitated alkaline phosphatase activity (S-L-AP), and bone Gla-protein immunoreactivity (S-BGP) were measured in 26 patients (23 females and 3 males) aged 35-73 years (mean 59 years) with primary hyperparathyroidism (n = 7), hyperthyroidism (n = 9), and hypothyroidism (n = 10) in whom the bone mineralization rate (m) was determined by 47Ca-kinetics (continuously expanding calcium pool model). A weak positive correlation (r = 0.42, P less than 0.05) was found between S-T-AP and m, which in the range from 0-18 mmol Ca/day could be estimated with a standard error of 4.6 mmol/day. A closer correlation (r = 0.65, P less than 0.001) was found between S-L-AP and m which was estimated with an error of 3.9 mmol Ca/day. The AP activity in the supernatant showed no significant correlation to m (r = 0.11, P greater than 0.50). The highest correlation coefficient (r = 0.81, P less than 0.001) was found between S-BGP and m which could be predicted with an error of 3.4 mmol Ca/day. S-BGP showed a closer correlation to S-L-AP (r = 0.71, P less than 0.001) than to S-T-AP (r = 0.58, P less than 0.01). We concluded that S-L-AP predicts bone mineralization at organ level better than S-T-AP in selected metabolic bone disorders and that the supernatant activity shows no relation to bone turnover.(ABSTRACT TRUNCATED AT 250 WORDS)

Results of a stimulatory therapy of low bone metabolism in osteoporosis with (1-38)hPTH and diphosphonate EHDP. Protocol of study I, osteoporosis trial Hannover

In contrast to prevention, the therapy of manifest osteoporosis remains a clinically significant problem. So far all therapeutic attempts have yielded unsatisfying results. For this reason we have tried to achieve a positive bone balance by sequential stimulation and inhibition of the osseous metabolism. The therapy consisted of six 14-day courses with 400 units (1-38)hPTH per day and, in addition, starting with the 2nd week of PTH therapy, EHDP 5 mg per kg body weight per day for a total of 2 weeks. Already the initial therapeutic course resulted in a stimulation of decreased bone metabolism which could be documented by an increase in the calcium-47 accretion rate (six patients). An increase of the alkaline phosphatase could be noted (four patients); this, however, did not correlate with the calcium accretion. A positive calcium balance could, nonetheless, only be attained in four of eight patients within this period, while neither the alkaline phosphatase nor the kinetics would allow a prediction of this effect. Changes of the balance coincided with equal changes in the net calcium absorption. The urinary calcium excretion increased temporarily during the therapeutic phase. We were not able to detect an influence on the vitamin D metabolites. Histomorphometric studies did not demonstrate an increase in bone mass in the iliac creast after six therapeutic courses. Nevertheless, progressive deformations of vertebral bodies did not occur. We conclude that already after 2 weeks this therapeutic concept can lead to a stimulation of bone metabolism.

Bisphosphonate whole body retention test: relations to bone mineralization rate, renal function and bone mineral content in osteoporosis and metabolic bone disorders

The bisphosphonate whole body retention test (WBR) has been used to estimate bone mineralization rate (bone turnover). Bisphosphonates given i.v. are taken up by bone or excreted in urine. The aim of the present investigation was to test the efficacy of WBR in estimating bone mineralization rate (m) and to evaluate the influence of renal function (Clcr) and bone mass (forearm bone mineral content; BMC) on WBR. The 24-h retention of 3.7 MBq 99mTc-HMBP (1-hydroxymethylene-1,1-bisphosphonate) (Osteoscan) given i.v. was measured by a medium sensitive whole body counter in thirty-one patients with hyperparathyroidism (n = 14), hyperthyroidism (n = 8) or hypothyroidism (n = 9) (group 1) and in seventy-six females with postmenopausal spinal crush fracture osteoporosis (group 2). In the same individuals m was calculated from a 7-day 47Ca-kinetic study using the expanding calcium pool model. Multiple regression analysis of WBR vs. m and Clcr in group 1 disclosed that WBR correlated positively to m [rp = 0.49, P less than 0.01 (rp = partial correlation coefficient)] and inversely to Clcr (rp = -0.44, P less than 0.02). Inclusion of BMC in the analysis did not reveal any significant partial correlation between WBR and BMC (rp = -0.33, 0.05 less than P less than 0.10). In group 2 WBR correlated inversely to Clcr (rp = -0.48, P less than 0.001) but showed no significant relation to m (rp = 0.10, NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Bone turnover and balance evaluated by a combined calcium balance and 47calcium kinetic study and dynamic histomorphometry

Bone resorption and formation rates were evaluated at the organ level using calcium kinetic methods and at the trabecular bone tissue level using dynamic histomorphometry in 20 patients with various metabolic bone diseases (primary hyperparathyroidism (N = 9), hyperthyroidism (N = 6), and hypothyroidism (N = 5). Highly significant correlations were demonstrated between resorption and formation rates at organ level (r = .90, P less than .001) and at tissue level (volume referent) (r = .93, P less than .001), indicating a high degree of coupling between resorption and formation within the three disease states. Tissue level resorption rates (surface referent, as well as volume referent) both correlated significantly (P less than .01) to organ level resorption rate (r = .60 and r = .63, respectively). Fractional active resorption surface and cellular level resorption rate did not reveal significant correlations to calcium kinetic estimates. No correlation could be demonstrated between organ level mineralization rate and formative or labeled trabecular surfaces. However, all tetracycline based tissue level formation rates revealed highly significant correlations (P less than .01) to organ level mineralization rate (calcification rate, r = .71; surface referent bone formation rate, r = .59; volume referent bone formation rate, r = .68). Based on histomorphometric parameters for resorption and formation, actual and predicted tissue level trabecular bone balances were calculated. Both the actual and predicted bone balance correlated significantly to the organ level calcium balance (P less than .05). Correction for skeletal size based on BMC measurements did not improve any of the correlations significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

The assessment of bone formation and bone resorption in osteoporosis: a comparison between tetracycline-based iliac histomorphometry and whole body 85Sr kinetics

Bone formation and resorption have been measured in patients with idiopathic osteoporosis by histomorphometry of 7.5-mm trephine biopsies and in the whole body by 85Sr radiotracer methodology and calcium balances. The studies were synchronized and most were preceded by double in vivo tetracycline labeling. Correlations between histological and kinetic bone formation indices were better when better when based on the extent of double tetracycline labels than on measurements of osteoid by visible light microscopy. Correction of the kinetic data for long-term exchange, using 5 months' serial whole body counting of retained 85Sr, improved the fit of the kinetic to the histological data. A statistical analysis of the measurement uncertainties showed that the residual scatter in the best correlations (between exchange-corrected bone formation rates and double-labeled osteoid surface indices) could be attributed to measurement imprecision alone. The exchange-corrected resorption rate correlated fairly well with iliac trabecular resorption surfaces, and using a volume referent rather than a surface referent for the histological index improved the statistical fit when patients with therapeutically accelerated bone turnover were included. A much better correlation was obtained by including osteoid volume acting as an independent predictor of bone resorption in a bivariate regression with a resorption surface index. The residual errors could then be accounted for by known measurement uncertainties. Whereas osteoid taking a double label closely predicted the kinetic rate of bone formation, further analysis suggested that osteoid that took no label or a single label was more closely related to bone resorption, presumably as a secondary result of the coupling of bone formation to bone resorption. The idea that continued bone loss in some patients is associated with defective osteoblastic bone formation is supported by the low rates found in some patients by both techniques. Heuristically these studies validate both in vivo tetracycline labeling for dynamic histomorphometry and corrections for long-term exchange in kinetic studies of bone formation, providing a quantitative framework for the design and analysis of future studies of bone remodeling in the osteoporoses.

Periodic courses of human 1-34 parathyroid peptide alternating with calcitriol paradoxically reduce bone remodelling in spinal osteoporosis

In an attempt to achieve an anabolic response in both axial and peripheral bone, we treated twelve patients with osteoporosis using human 1-34 parathyroid peptide given discontinuously. The peptide was given as seven daily subcutaneous injections followed by 21 days' treatment with 0.25 mg calcitriol orally. This regime was repeated cyclically for at least sixteen cycles, of which the first four were at a lower dose of hPTH 1-34 than used subsequently. The results of treatment were monitored by kinetic, densitometric, histomorphometric and biochemical studies performed before and during treatment. Two patients developed hPTH 1-34 binding in their plasma during treatment: this was presumed to be due to the development of antibodies. The remainder, instead of increasing their indices of bone turnover as judged by iliac bone histomorphometry, were found to have consistent reductions in trabecular resorption surfaces. The other indices of bone formation and resorption measured showed no change or comparable reductions. The small increases seen in total body calcium were consistent with 'in-filling' of deleted basic multicellular units (BMUs). Because there is no evidence that calcitriol alone causes comparable reductions in activation of bone remodelling in osteoporosis, interruption of treatment with hPTH 1-34 after 7 days may have led to a failure of the activation mechanism to proceed to the resorption stage, with a consequent overall reduction in remodelling activity. This type of treatment regime, with its calcitonin-like effect, might be effective in reducing net bone loss due to imbalance between bone formation and resorption at the BMU level, particularly in patients with increased numbers of BMUs ('high turnover' osteoporosis).(ABSTRACT TRUNCATED AT 250 WORDS)

Sr-89 therapy: strontium kinetics in disseminated carcinoma of the prostate

Strontium kinetics were investigated in a group of 14 patients receiving 89Sr palliation for metastatic bone disease secondary to prostatic carcinoma. Using 85Sr as a tracer, total body strontium retention R(t) was monitored for a 3 month period following 89Sr administration, and at 90 days was found to vary from 11% to 88% and to correlate closely with the fraction of the skeleton showing scintigraphic evidence of osteoblastic metastatic involvement. Strontium renal plasma clearance varied from 1.6 l/day to 11.6 l/day, and in nine patients was significantly reduced compared with values found in healthy adult men, probably due to increased renal tubular reabsorption associated with the disturbance of calcium homoeostasis. Renal clearance rate was the principal factor determining R(t) for t less than 6 days, and was an important secondary factor at later times. Over the interval 30 days less than t less than 90 days, R(t) was closely fitted by the power law function R(t) = R30 (t/30)-b, with R30 and b showing the close correlation expected from the effect of R(t) on strontium recycling. The correction of the data for this effect to determine the true skeletal release rate is described. Measurement of localized strontium turnover in individual metastatic deposits from whole body profiles and scintigraphic images gave retention curves that typically rose to a plateau by 10 days after therapy, and then decreased very slowly. In contrast, retention curves for adjacent normal trabecular bone showed more rapid turnover, peaking at 1 day and subsequently decreasing following a t-0.2 power law function.(ABSTRACT TRUNCATED AT 250 WORDS)

Classification of osteosarcoma by 85-Sr scintimetry

The histologic type of a classical osteosarcoma may be difficult to determine because of insufficient biopsy material and polymorphism of the tumour. Since osteoformation is directly related to the differentiation and functional capacity of the tumour cells, 85-Sr scintimetry was used to evaluate osteoid formation in 90 patients with classical osteosarcoma. Measurements over an 8-day period from isotope injection revealed a separation of the lesions into three groups, with high, medium and low activity. Compared to histologic classification into osteoblastic, chondroblastic/fibroblastic, the 41 tumours classified as osteoblastic had a high 85-Sr uptake. The anaplastic lesions belonged to the group with low 85-Sr uptake. Scintimetric determination of the functional differentiation of tumoral cells may possibly be of prognostic value in osteosarcoma.

Estimation of bone turnover evaluated by 47Ca-kinetics. Efficiency of serum bone gamma-carboxyglutamic acid-containing protein, serum alkaline phosphatase, and urinary hydroxyproline excretion

Bone gamma-carboxyglutamic acid-containing (Gla) protein (BGP, osteocalcin) is a noncollagenous protein of bone present in plasma and removed by the kidney. Plasma BGP has been shown to be elevated in patients with certain bone diseases. The present study evaluates serum BGP (S-BGP), serum alkaline phosphatase (S-AP), and urinary hydroxyproline excretion (U-OHP) in diseases with differing bone turnover rates, and compares the accuracy of these measurements for estimating bone mineralization (m) and resorption (r) rates. S-BGP, S-AP, U-OHP, and creatinine clearance (Clcr) were measured in patients with primary hyperparathyroidism (n = 13), hyperthyroidism (n = 6), and hypothyroidism (n = 6). Bone mineralization and resorption rates were calculated from a 7-d combined calcium balance and 47Ca turnover study. A highly significant correlation (r = 0.69, P less than 0.001) was found between S-BGP and m. Multiple regression analysis disclosed a partial correlation between S-BGP and m when Clcr was taken into account (r = 0.82, P less than 0.001), and between S-BGP and Clcr when m was taken into account (r = -0.62, P less than 0.005). In accordance with this, a stronger correlation (r = 0.89, P less than 0.0001) was found between S-BGP X Clcr and m than between S-BGP and m. A less significant correlation was found between S-AP and m (r = 0.45, P less than 0.05). Furthermore, U-OHP showed a highly significant positive correlation to r (r = 0.78, P less than 0.001). Thus, in the studied disorders of calcium metabolism, individual serum levels of BGP depend on both mineralization rate and renal function. Serum levels of BGP corrected for alterations in renal function are superior to uncorrected S-BGP and to S-AP levels in the estimation of bone mineralization rates.

Bone turnover in early rheumatoid arthritis. 1. Biochemical and kinetic indexes

Biochemical, hormonal, and kinetic indexes of bone turnover were measured in 17 ambulant female patients with rheumatoid arthritis (RA) of recent onset (mean disease duration 14.2 months) and 19 controls. Mean serum osteocalcin concentration and 85Sr accretion rates were reduced and mean urinary hydroxyproline-creatinine ratios were increased in RA, but these differences were not significant compared with control values. Mean total body potassium (TBK), an index of skeletal muscle mass, was significantly reduced in RA, and the ratio of observed to predicted TBK correlated with indexes of bone formation. No abnormality of skeletal metabolism could be shown in early RA, but reduced rates of bone formation associated with diminished muscle mass may influence the development of osteopenia later in the disease.

Calcium metabolism evaluated by 47Ca kinetics. Methodologic aspects with optimization of a whole-body counter

Optimization of a four-crystal stretcher geometry whole-body (WB) counter was performed. The measured geometric characteristic did not differ significantly from the theoretically calculated characteristic (p greater than 0.05). The linearity of the WB counter was high in the range 3.7 kBq to 3.7 MBq. Longtime variability of local background was CV = 3.7 per cent. In vivo sensitivity was calculated to 18 cpm/kBq and the detection limit to about 5 kBq. The reproducibility was estimated to 0.7 per cent. The WB counter was used in 47Ca turnover and calcium balance studies of 15 normal individuals. The data were analysed according to a modification of the expanding calcium pool model using an improved Bauer-Carlsson-Lindquist formulation. Variability and method errors of main parameters for calcium metabolism were evaluated.

Calcium metabolism evaluated by 47calcium-kinetics: a physiological model with correction for faecal lag time and estimation of dermal calcium loss

Sixty-two calcium balance and 47Ca-turnover studies were performed in 51 individuals to evaluate the accuracy and the sensitivity of the methods. The data were analysed according to a modification of the expanding calcium pool model using an improved Bauer-Carlsson-Lindquist (BCL) formulation and an iterative computer procedure. A 7-day whole body retention curve (R1) combined with a retention curve constructed from excretion data alone (R2) was used to estimate dermal calcium loss (d) and to demonstrate the significance of individual corrections for delay in faecal excretion (faecal lag time = delta t). The mean d was 1.58 mmol Ca/day. The introduction of delta t improved the goodness of fit of the data to the model. delta t based on 47Ca-kinetics was superior to a fixed delta t of zero (P less than 0.01) or 2 days (P less than 0.05). The model derived renal calcium excretion rate was highly correlated (r = 0.98, P less than 0.001) to the chemical measured excretion rate. A similar highly significant correlation [RS = 0.78 (Spearman), P less than 0.001] was found between the model derived delta t and the carmine red delta t. These results indicate a high accuracy of the model. The directly measured parameters showed an excellent reproducibility with a coefficient of variation (CV) less than 4%. The reproducibility of the derived parameters was acceptable (CV = 10-20%) except for the balance (CV = 72%).

Regional measurement of bone calcium accretion rate and exchangeable pool with a whole-body counter: method and studies in subjects without bone disease

A whole-body counter was used to measure the retention and distribution of radioactivity along the longitudinal axis of the body during 10 days after the intravenous injection of 50 microCi of 47Ca. These data and the simultaneous measurements of the serum specific activity allowed us to calculate, by the Bauer-Carlsson-Lindquist (BCL) formulas generalized by Marshall, the calcium accretion rate and exchangeable pool in 7 areas: skull, thorax, pelvis, thighs, knees, legs, and ankles and feet. For the whole body, the accretion rate was 336 +/- 115 mg/24 h, and the exchangeable pool 5668 +/- 1221 mg, in 26 subjects without bone disease. Both parameters were significantly correlated with body height; the exchangeable pool was significantly higher in men than in women. The accretion rate and exchangeable pool expressed on a basis of bone content varied widely from one area to another, reflecting the ratio of spongy to compact bone: the thorax, pelvis, and arms, which contain 49% of the skeletal mass, accounted for 57% of the total accretion rate and 53% of the exchangeable pool; the skull, 18% of the skeletal mass, accounted for 14% of the accretion and 11% of the pool.

Short-term effects of synthetic human parathyroid hormone-(1--34) administration on bone mineral metabolism in osteoporotic patients

Since studies in animals and humans have shown that parathyroid hormone can stimulate bone formation and increase trabecular bone, and patients with primary and secondary hyperparathyroidism may exhibit osteosclerosis, we evaluated the effect of short-term administration of human parathyroid hormone, hPTH-(1--34), in patients with osteoporosis. Six patients with osteoporosis underwent detailed studies including blood and urinary measurements of calcium, phosphate, and magnesium; 47Ca kinetic studies; and 18-d balance studies before and during the short-term administration (3--4 wk) of a daily subcutaneous injection of hPTH fragment 1--34 given as 450 or 750 U/dose. The mean fasting plasma calcium values rose slightly after hPTH-(1--34) administration, primarily in the high-dose group. There was no difference in the mean fasting plasma inorganic phosphate levels. The mean daily urinary excretion of calcium and phosphate was significantly increased in patients given the higher dose. In patients given 750 U, net intestinal calcium absorption increased, phosphate absorption increased, calcium balance improved, and phosphate balance improved. In patients given 450 U, calcium balance and phosphate balance worsened. 47Ca kinetic studies showed a minimal increase in bone accretion rate, a decrease in the mean transit time of calcium in the exchangeable pools, and a decrease in the exchangeable-pool size. In all six patients there was an increased renal clearance of 47Ca as a result of hPTH-(1--34) administration. These studies indicate that low doses of parathyroid hormone may promote bone formation, whereas higher doses clearly have an adverse effect on the skeleton.

Comparison of bone graft materials. Part I. New bone formation with autografts and allografts determined by Strontium-85

The purpose of this study was to obtain a direct comparison of the bone forming abilities of autogenous osseous coagulum, autogenous bone blend, freeze-dried bone allograft, and decalcified freeze-dried bone allograft. Defects were created in the calvaria of 35 guinea pigs. The graft materials were placed in porous nylon chambers and implanted into the defects. Empty nylon chambers served as the controls. Three days prior to sacrifice, each animal received an injection of 85Sr. The animals were killed in groups of five at 3, 7, 14, 21 28, 35, and 42 days. At sacrifice, a small section of ilium was removed from each animal. The samples were recovered, weighed, and the uptake of 85Sr into new bone determined. An osteogenic index was obtained by dividing cpm/mg for each sample by cpm/mg of ilium. It was concluded that in this model system decalcified freeze-dried bone allograft is a graft material of high osteogenic potential while autogenous bone blend and osseous coagulum were of less potential, and freeze-dried bone allograft even less.

Anabolic effect of human parathyroid hormone fragment on trabecular bone in involutional osteoporosis: a multicentre trial

After baseline studies, 21 patients with osteoporosis were treated with human parathyroid hormone fragment (PTH 1-34) given as once-daily subcutaneous injections for 6-24 months. The dose used did not cause hypercalcaemia even in the first few hours after injection. Calcium and phosphate balances improved in some patients, but there was no significant improvement in the group values. There were, however, substantial increases in iliac trabecular bone volume: the mean increase, confirmed by repeat blind measurements, was 70% above mean baseline volume. The new bone was histologically normal. Those patients who had the largest increases in 47Ca-kinetic and histomorphometric indices of new bone formation showed the greatest increases in trabecular bone volume, suggesting that treatment with human parathyroid hormone fragment caused a dissociation between formation and resorption rates that was confined to trabecular bone. Since vertebrae are four-fifths composed of trabecular bone, this hormone fragment may prove useful in treating patients with the crush fracture syndrome.

The turnover time of calcium in the exchangeable pools of bone in man and the long-term effect of a parathyroid hormone fragment

(1) A non-compartmental method is described for analysing the kinetics of the exchange of calcium between the bloodstream and the exchangeable bone pools. (2) This method has been applied to studies on osteoporotic patients treated with low doses of an active fragment of human parathyroid hormone. The data of Phang et al. (1969), who studied the effects of dietary calcium peturbation on normal volunteers, were also analysed. (3) It was found that in response to chronic PTH treatment the transit time of calcium in the exchangeable pools decreased. This could not be explained by the observed changes in the calcium accretion rate to the fixed bone pools, and it was necessary to postulate an alteration in the ratio of the rate constants governing the interchange of calcium between bloodstream and exchangeable pools. (4) The changes in the behaviour of the exchangeable pools in response to dietary perturbation could not be explained by the postulated increase in endogenous PTH secretion rate in response to dietary calcium restriction.

A model-independent comparison of the rates of uptake and short term retention of 47Ca and 85Sr by the skeleton

1. A method has been devised for comparing the impulse response functions of the skeleton for two or more boneseeking tracers, and for estimating the contribution made by measurement errors to the differences between any pair of impulse response functions. 2. Comparisons were made between the calculated impulse response functions for 47Ca and 85Sr obtained in simultaneous double tracer studies in sixteen subjects. Collectively the differences between the 47Ca and 85Sr functions could be accounted for entirely by measurement errors. 3. Because the calculation of an impulse response function requires fewer a priori assumptions than other forms of mathematical analysis, and automatically corrects for differences induced by recycling of tracer and non-identical rates of excretory plasma clearance of tracer, it is concluded that differences shown in previous in vivo studies between the fluxes of Ca and Sr into bone can be fully accounted for by undetermined oversimplifications in the various mathematical models used to analyse the results of those studies. 85Sr is therefore an adequate tracer for bone calcium in most in vivo studies.