Regulation of bone formation

FTIR microspectroscopic analysis of human osteonal bone

Fourier Transform Infrared Microspectroscopy (FTIRM) has been used to study the changes in mineral and matrix content and composition in replicate biopsies of nonosteoporotic human osteonal bone. Spectral maps in four orthogonal directions (in 10 microm steps) from the centers towards the peripheries of individual osteons were obtained from iliac crest biopsies of two necropsy cases. Mineral to matrix ratios, calculated from the ratio of integrated areas of the phosphate nu1,nu3 band at 900-1200 cm-1 to the amide I band at 1585-1725 cm-1, increased from the center to the periphery of the osteon. The total carbonate (based on the nu2 band at approximately 850-900 cm-1) to phosphate nu1,nu3 ratio decreased as the mineral to matrix ratio increased. Analysis of the nu2 CO32- band with a combination of second-derivative spectroscopy and curve fitting revealed a decrease in "labile" carbonate, a slight decrease in Type A and a slight increase in Type B carbonate from the center to the periphery of the osteon. Similar analysis of the components of the nu1,nu3 phosphate band with a combination of second-derivative spectroscopy and curve fitting revealed the presence of 11 major underlying moieties. These components were assigned by comparison with published frequencies for apatite and acid-phosphate containing calcium phosphates. The most consistent variations were alterations in the relative percent areas of bands at approximately 1020 and approximately 1030 cm-1, which had previously been assigned to nonstoichiometric and stoichiometric apatites, respectively. This ratio was used as an index of variation in crystal perfection throughout the osteon. This ratio decreased as the mineral to matrix ratio increased. The reproducibility of these parameters at multiple sites in multiple biopsies suggests their applicability for the analysis of mineral changes in disease.

Long-term treatment of Swiss 3T3 fibroblasts with dexamethasone attenuates MAP kinase activation induced by insulin-like growth factor-I (IGF-I)

Bone formation is reduced in hyperglucocorticoid states, e.g. Cushing's syndrome or long-term treatment with synthetic glucocorticoids during rheumatic diseases. possibly related to decreased sensitivity of the target to insulin-like growth factor-I (IGF-I). In this study, we have sought to identify postreceptor-mechanisms for glucocorticoid-induced resistance to insulin-like peptides in a model system. Treatment of Swiss 3T3 fibroblasts with 100 nM dexamethasone for 48h reduced IGF-I-induced activation of mitogen-activated protein kinase (MAP kinase). The level of insulin receptor substrate-1 (IRS-1) was reduced in dexamethasone-treated cells, as measured by Western blot; however, the pattern of tyrosine-phosphorylated protein subsequent to stimulation with IGF-I (1 min) was not altered. No inhibitory effect of dexamethasone was observed on the level of phosphotyrosine in IRS-1 in extracts from IGF-I-treated cells. The amount of IGF-I-induced association of insulin receptor substrate-1 and phosphatidylinositol 3-kinase was increased in steroid treated cells. Addition of IGF-I increased the synthesis of lipid, glycogen and protein, and the reduction of a tetrazolium dye, MTS, in untreated cells. The response to IGF-I in terms of glycogen synthesis was blunted, whereas the effect of IGF-I was unaffected for the other three parameters in cells pretreated with dexamethasone. These findings indicate that the activation of MAP kinase may be dissociated from IGF-I-induced anabolic pathways and tyrosine phosphorylation of IRS-1. The results agree with the previously proposed role for the activation of MAP kinase in the regulation of glycogen synthesis. Furthermore, they suggest that dexamethasone-induced reduction of IRS-1 expression may be important for the impaired activation of MAP kinase by insulin-like peptides in steroid-treated cells.

Bone density in young patients with congenital adrenal hyperplasia

One of the major complications of glucocorticoid treatment is bone loss. 21-Hydroxylase deficiency is the most frequent inborn error of steroidogenesis, leading to congenital adrenal hyperplasia (CAH): synthesis of cortisol is impaired and replacement therapy is therefore mandatory. We studied the bone mineral density in a group of patients with congenital adrenal hyperplasia (CAH) on long-term glucocorticoid replacement therapy. We selected 30 Caucasian patients with CAH due to 21-hydroxylase deficiency (mean +/- SD age = 17.45 +/- 2.49 years). 22 patients had the classical CAH form and the remaining 8 had the nonclassical (late-onset) form. The mean duration of therapy was 15.20 +/- 4.04 years. Bone mineral density (BMD) was evaluated with a dual-energy X-ray absorptiometer. BMD was also measured in 73 healthy white volunteers of comparable age (17.35 +/- 2.99 years). BMD values of the spine (sBMD), total body (TBBMD), legs, and arms of CAH patients, adjusted for confounding variables (age, gender, body mass index), did not differ from those of control subjects (p = 0.86; p = 0.17; p = 0.06 and p = 0.26, respectively). sBMD and TBBMD values did not show relationships with the duration of treatment and the dose of corticosteroids. Patients with the classical form of CAH had bone density values comparable with those of patients with the nonclassical form (sBMD: p = 0.33; TBBMD: p = 0.97). Our data show that, despite long-term treatment with glucocorticoids, CAH patients have bone density values comparable with controls.

Vitamin D, calcium, and sarcoidosis

Hypercalcemia occurs in about 10% of the patients with sarcoidosis; hypercalciuria is about three times more frequent. These abnormalities of calcium metabolism are due to dysregulated production of 1,25-(OH)2-D3 (calcitriol) by activated macrophages trapped in pulmonary alveoli and granulomatous inflammation. Undetected hypercalcemia and hypercalciuria can cause nephrocalcinosis, renal stones, and renal failure. Corticosteroids cause prompt reversal of the metabolic defect. Chloroquine, hydroxychloroqune, and ketoconazole are the drugs that should be used if the patient fails to respond or develops dangerous side effects to corticosteroid therapy.

Mechanical stimulation by intermittent hydrostatic compression promotes bone-specific gene expression in vitro

In a previous study of the cellular mechanism underlaying Wolff's law we showed that mechanical stimulation by intermittent hydrostatic compression (IHC) increases bone formation in cultured fetal mouse calvariae compared to non-stimulated cultures. To test whether mechanical stimuli may modulate bone-specific gene expression, we studied the effect of IHC on alkaline phosphatase (AP) expression and enzyme activity as well as collagen and actin mRNA levels in neonatal mouse calvariae and calvarial bone cells. Two cell populations, one resembling osteoprogenitor (OPR) cells and another resembling osteoblasts (OB) were obtained from calvariae by sequential digestion. IHC was applied by intermittently (0.3 Hz) compressing the gas- phase of a closed culture chamber (peak stress 13kPa, peak stress rate 32.5 kPas-1). In control cultures of calvariae as well as OB and OPR cells, AP activity and AP-, collagen-, and actin-mRNA levels all decreased after one or more days, with the exception of OPR cell collagen expression which increased during culture. IHC treatment upregulated AP, collagen and actin expression and AP activity in calvariae and OB cells, but decreased collagen expression in OPR cells. These results suggest that treatment with IHC promotes the osteoblastic phenotype in bone organ cultures and in osteoblasts. Osteoprogenitor cells seem to react somewhat differently to mechanical stress than osteoblasts. The loss of bone-specific gene expression under control culture conditions, in the absence of mechanical stimuli, suggests that the mechanical environment is important in maintaining the differentiated phenotype of bone cells, and that IHC treatment partially restores this environment in bone cell- and organ cultures.

Cranial sutures require tissue interactions with dura mater to resist osseous obliteration in vitro

A chemically defined serum-free medium, which supports the development of bones and fibrous tissues of rat calvaria from nonmineralized mesenchymal precursor tissues, was employed to investigate tissue interactions between the dura matter and overlying tissues. Fetal calvarial rudiments from stages prior to bone and suture morphogenesis (fetal days 19 and 20) and neonatal calvarial rudiments with formed sutures (day 1) were cultured with and without associated dura mater. Removal of calvaria for in vitro culture allowed the examination of suture morphogenesis in the absence of tensional forces exerted on the sutures via fiber tracts in the dura mater originating in the cranial base. Ossification of frontal and parietal bones proceeded in a fashion comparable to development in vivo, but the cranial (coronal) sutures--primary sites for subsequent skull growth--were obliterated by osseous tissue union in the absence of dura mater. Bony fusion did not occur when rudiments were cocultured with dura mater on the opposite sides of 0.45 microns polycarbonate transwell filters, suggesting that the influence of dura mater on sutural obliteration was mediated by soluble factors rather than cell-cell or cell-matrix interactions. These results indicate that cell signaling mechanisms rather than biomechanical tensional forces are required for morphogenesis of the calvaria.

Characterization of inhibitory effects of suspected periodontopathogens on osteogenesis in vitro

By using an in vitro bone-forming culture system, the chick periosteal osteogenesis (CPO) model, the direct effects on osteogenesis of sonicated extracts derived from oral bacteria were examined. Both extracts from bacterial species having strong associations with periodontal diseases (Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Prevotella intermedia, hereinafter referred to as suspected periodontopathogens) and extracts from species not correlated with periodontal disease (Streptococcus sanguis, Veillonella atypica, and Prevotella denticola, hereinafter referred to as nonpathogenic bacteria) were tested. All bacterial cultures were grown under standard anaerobic culture conditions. Sonicated bacterial extracts were prepared from the bacterial pellet. These were added in various proportions to the CPO cultures. Parameters of osteogenesis, including alkaline phosphatase activity, calcium and P(i) accumulation, and collagen synthesis, were measured in 6-day-old cultures. Compared with controls grown in the absence of bacterial products, osteogenesis was inhibited significantly in cultures treated with extracts derived from the suspected periodontopathogens. No osteogenic inhibition was observed in cultures treated with extracts from the nonpathogenic bacteria. These results suggest that the ability to inhibit osteogenesis in vitro may be a pathogenic property shared by a limited group of species. Further characterization of the P. gingivalis extracts revealed that both proteinaceous and nonproteinaceous products, including lipopolysaccharide, were able to inhibit osteogenesis. P. gingivalis extract-mediated inhibition of osteogenesis in CPO cultures was blocked by indomethacin, implicating prostaglandins in the regulation of the bacterial effects. The bacterial extracts had either reversible or irreversible inhibitory effects on osteogenesis when added after differentiation or before/during differentiation of bone cells, respectively.

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.

Two distinct osteoblast-specific cis-acting elements control expression of a mouse osteocalcin gene

Osteoblasts are cells of mesodermal origin that play a pivotal role during bone growth and mineralization. The mechanisms governing osteoblast-specific gene expression are still unknown. To understand these mechanisms, we analyzed the cis-acting elements of mouse osteocalcin gene 2 (mOG2), the best-characterized osteoblast-specific gene, by DNA transfection experiments in osteoblastic and nonosteoblastic cell lines and by DNA-binding assays. 5' deletion analysis of an mOG2 promoter-luciferase chimeric gene showed that a region located between -147 and -34 contained most if not all of the regulatory elements required for osteoblast-specific expression. Three different binding sites, called A, B, and C, for factors present in nuclear extracts of osteoblasts were identified in this short promoter by DNase I footprint assays. In gel retardation assays, the A element, located between bp -64 and -47, bound a factor present only in nuclear extracts of osteoblastic cell lines and nonmineralizing primary osteoblasts. The B element, located between bp -110 and -83, bound a ubiquitously expressed factor. The C element, located between bp -146 and -132, bound a factor present only in nuclear extracts of osteoblastic cell lines and nonmineralizing and mineralizing primary osteoblasts. When cloned upstream of a minimum osteocalcin promoter or a heterologous promoter, multimers of the A element strongly increased the activities of these promoters in osteoblastic cell lines at two different stages of differentiation but in no other cell line; we named this element osteocalcin-specific element 1 (OSE1). Multimers of the C element increased the activities of these promoters predominantly in a differentiated osteoblastic cell line; we named this element OSE2. This study demonstrates that two distinct cis-acting elements are responsible for osteoblast expression of mOG2 and provides for the first time a functional characterization of osteoblast-specific cis-acting elements. We speculate that these two elements may be important at several stages of osteoblast differentiation.

Gender-related effects of vitamin D metabolites on cartilage and bone

Sex steroid hormones are known to have gender-dependent effects on bone and cartilage in vivo and in vitro. To investigate whether this is a general property of steroids, or is specific to the sex steroid hormones, we examined whether the effects on bone of 1,25-(OH)2D3 and 24,25(OH)2D3, the two active metabolites of vitamin D, are also gender-dependent. One-month-old male and female rats were treated for 1 month with various doses of 1,25-(OH)2D3, 24,25-(OH)2D3, or a combination of both metabolites. The direct effects of both metabolites on the skeleton of the treated animals were similar in male and female rats. 24,25-(OH)2D3 alone or in combination with 1,25-(OH)2D3 increased bone calcium and phosphorus, while 1,25-(OH)2D3 slightly decreased bone mineral content. 24,25-(OH)2D3 also enhanced the differentiation of cartilage in the growth plate, increasing the size of the hypertrophic zone. In addition, an increased metaphyseal bone volume was observed following 24,25-(OH)2D3 treatment in rats of both sexes, but not with 1,25-(OH)2D3. Vitamin D metabolites affected the weight gain of the experimental animals in a gender-dependent manner; 1,25-(OH)2D3 increased weight gain of male rats and 24,25-(OH)2D3 decreased weight gain of female rats. In addition, 1,25-(OH)2D3 increased bone weight and ash weight in male animals. These gender-dependent effects of vitamin D metabolites may occur indirectly via effects of sex steroid hormones, the latter being a sex-related effect.

Secondary hypoadrenalism presenting with hypercalcaemia

We describe a young woman with lymphocytic hypophysitis presenting in the early post-partum period. She had selective corticotroph failure causing secondary adrenal insufficiency. At the time of presentation she had transient hyperthyroidism due to thyroiditis, and hypercalcaemia. This is the third case to be described of hypercalcaemia occurring in association with lymphocytic hypophysitis. Hypercalcaemia is not a recognized complication of other forms of pituitary failure. The two previously described cases also had selective corticotroph failure and hyperthyroidism due to thyroiditis. This pattern of presentation supports the concept that thyroid hormone action in the presence of glucocorticoid deficiency is responsible for the increased calcium efflux from bone into the circulation. Reduced renal excretion of calcium due to a reduction in calcium delivery to the glomerulus and increased proximal tubular reabsorption are also implicated in the aetiology of hypercalcaemia associated with adrenal failure.

Survival of split calvarial bone grafts in a dog model

To gain a better understanding of the strength and long term viability of split calvarial bone graft, nine mongrel dogs each received four trephine craniotomies (1.5 mm diameter). The harvested bone plugs were split through the diploe and a partial-thickness plug was returned to each craniotomy site. The unused partial-thickness plugs underwent strength testing. After 90-150 days the dogs were sacrificed, bone scans and X-rays of the graft recipient sites performed, and the grafted plugs harvested for strength testing and histologic examination. Bone scanning showed increased osteoblastic activity within the grafts, strength testing showed a progressive loss in strength over the 150 days, and histologic examination demonstrated a creeping substitution. These results imply a similar evolution in strength and remodeling to that seen in long-bone grafts, whose remodeling typically spans 1 year.

Osteopenia associated with non-insulin-dependent diabetes mellitus: what are the causes?

This study investigated whether alterations in bone mineral content (BMC) and/or in the phosphate-calcium metabolism exist in non-insulin-dependent diabetes mellitus (NIDDM); whether they are linked to glycaemic control and whether antidiabetic therapy--oral agents or insulin--influences BMC and mineral metabolism. A cross-section assessment compared BMC and mineral metabolism in 60 well-controlled and 50 poorly controlled diabetic patients under oral hypoglycaemic therapy with 50 healthy controls. A longitudinal assessment improved the high glucose levels of the poorly controlled diabetic group either by increasing oral treatment or by adding a bedtime NPH insulin. Glycaemic control, BMC and mineral metabolism were followed-up for 1 year. In NIDDM patients BMC is reduced. This reduction is more marked in poorly controlled diabetic patients. In well-controlled diabetes osteocalcin levels are low. In poorly controlled patients glycosuria, hypercalcuria and parathyroid hyperactivity are present. In both groups vitamins 25(OH)-D, 1,25(OH)2-D and calcitonin levels are normal. Improving metabolic control increased BMC, normalized urinary calcium excretion and parathyroid activity and reduced osteocalcin levels. The type of anti-diabetic therapy does not have any significant effect upon BMC or upon phosphate-calcium metabolism. In conclusion, in NIDDM a hard-to-define osteoblast deficit appears to exist. In poorly controlled diabetes the loss of BMC is aggravated by the negative calcium balance caused by the renal calcium leak. This is due to glucosuric-induced osmotic diuresis and is maintained by parathyroid activation.

Ultrastructural localization of endogenous hormones and receptors in bone tissue: an immunocytological approach in frozen samples

In addition to their well-known mechanical role, bones are essential for the regulation of calcium phosphate metabolism. Most of the peptide and steroid hormones acting on bone tissue exert their cellular effects directly on bone cells after binding to cell receptors. A combined method using immunocytology on ultrathin frozen sections has been applied to bone tissue and made possible the ultrastructural localization of endogenous hormones and hormone receptors. There is immunocytological evidence, at the osteoblast level, for: (1) the presence of calcitonin, parathyroid hormone, growth hormone, 1,25 dihydroxyvitamin D3, aldosterone, corticosterone and progesterone; (2) the existence of 1,25 dihydroxyvitamin D3 and progesterone receptors; (3) the absence of estradiol and receptors, testosterone and gonadoliberin. Ultimate goals of future studies are to extend the ultrastructural localization of hormones at the osteoclast level, to assess the distribution of adhesive proteins and of their receptors in bone cells and matrix, and to use well-calcified human bone samples in order to evaluate better the role of therapeutic agents.

Loss of trabecular bone mineral density in systemic lupus erythematosus

OBJECTIVE

To evaluate trabecular bone mineral density (BMD) in young ambulatory female patients with systemic lupus erythematosus (SLE).

METHODS

Bone mineral density (gm/cm2) at the lumbar vertebrae (L1-L4) and at the left femur (neck, trochanter, intertrochanter, and Ward's triangle) was measured by dual x-ray absorptiometry in 46 SLE patients (mean age 31 years, mean disease duration 76 months) and in 108 healthy female controls (mean age 32 years). Twenty-two of the SLE patients were receiving corticosteroids (CS) at the time of the study.

RESULTS

Lumbar BMD in the SLE patients was less severely reduced than was BMD at the femoral sites, but the SLE group was closer to the lumbar fracture threshold of 0.812 gm/cm2 than was the control group (P = 0.0009). There were no significant differences between the SLE patients currently being treated with corticosteroids and those who were not (P > 0.3). BMD at Ward's triangle and at the femoral neck was not significantly reduced in the SLE patients. Total femoral BMD had a sensitivity of 76% and specificity of 62% in differentiating the SLE group from the controls. The positive predictive value was 61% and the negative predictive value was 89%. The prevalence of osteopenia in the SLE patients was 25%.

CONCLUSION

SLE causes significant trabecular bone loss, which is not due to corticosteroid therapy.

Bone cell biology: new approaches and unanswered questions

In an effort to define the major unanswered questions in bone cell biology and suggest new approaches to answering these questions, I have outlined the bone remodeling cycle and briefly described the major local and systemic factors that regulate bone cell function. These factors include calcium-regulating and systemic hormones as well as locally produced prostaglandins, cytokines, and growth factors. To understand the individual roles of this large number of regulators, it will be necessary to develop new approaches to measure their production and activity in bone under physiologic and pathologic conditions. Quantitative methods in molecular and cellular biology have been developed that should make this identification possible.

The effects of orchidectomy on skeletal metabolism in metastatic prostate cancer

The skeletal metabolic effects of androgen withdrawal have been studied in men with metastatic prostate cancer by using a combination of sequential biochemical measurement, quantitative and subjective bone histology and selective osteoclast inhibition with the bisphosphonate Pamidronate. Results showed dissociation in the levels of biochemical markers of bone formation (alkaline phosphatase and osteocalcin) following castration, whilst markers of bone breakdown (urinary hydroxyproline creatinine (OHP) and calcium excretion (CaE)) increased in the majority of patients. The osteolytic response was inhibited by the bisphosphonate Pamidronate (Aminohydroxypropylidene Bisphosphonate (APD)), thus confirming its osteoclastic origin. Histomorphometry of tumour free bone showed an acute drop in bone volume following surgery (p < 0.05). This effect was blocked by Pamidronate suggesting that osteoclastic activity surges immediately following castration, contributing to the acute bone loss. Histology of metastatic areas showed a marked diminution in bone volume due to decreased osteoblast activity and markedly increased osteoclast mediated osteolysis. In 56% of biopsies there were residual foci of active tumour within metastatic areas after orchidectomy. These disturbed metabolic bone activity in a typically localised manner.

Rat osteoblasts and ROS 17/2.8 cells contain a similar protein tyrosine phosphatase

Tyrosine phosphorylation plays a central role in intracellular signaling by many hormones and growth factors. Termination of the signal is thought to involve dephosphorylation of target proteins by phosphotyrosine phosphatases (PTPase). Soluble protein PTPases from neonatal rat osteoblasts (ROBs) and rat osteosarcoma (ROS 17/2.8) cells were chromatographically distinguished and characterized using 32P-labelled glutamate/tyrosine co-polymer as substrate. Two activities from both cell types were chromatographically separable. The dominant PTPase activity in the presence of 60-125 mM salt (E1), was eluted from phosphocellulose by 180-280 mM NaCl, bound weakly to a strong anion exchange column (QAE-trisacryl), had an apparent Km for [32P]glutamate/tyrosine copolymer of 52 micrograms/ml, was enhanced (5-10-fold, ROS; 1.5-3-fold, ROB) by assay in 125 mM NaCl, had no significant alkaline, acid, or serine phosphatase activity and had an M(r) of 53,000. A second activity (E2) was not retained by phosphocellulose but eluted from QAE-trisacryl in a single peak at 90-130 mM NaCl. It had an apparent Km for [32P]glutamate/tyrosine copolymer of 30 micrograms/ml (ROS) and its activity was not enhanced by NaCl in the assay. Activity E1 from both cells was 50% inhibited by 0.05 microM Na3VO4, 20 microM ZnCl2, or 5-10 microM CoCl2, but not by 1 mM NaF; activity E2 had a similar inhibition profile, but was more sensitive to ZnCl2 (IC50, 5 microM). Co2+ is a relatively non-toxic metal which may be a useful tool for investigating the role of phosphotyrosine in osteoblast proliferation and function. The similarity between the E1 activity from ROS cells and ROBs suggests that ROS cells may be useful in studying PTPase regulation by hormones, but molecular approaches will be required to establish the identity of PTPases in ROBs and ROS cells.

Long-term total parenteral nutrition and osteoporosis: report of a case

A patient who had been supported with total parenteral nutrition (TPN) for over 8 years is herein presented, with emphasis on the changes observed in calcium metabolism. The patient was a 31-year-old female, who had undergone a subtotal jejunal and ileal resection for superior mesenteric artery occlusion. TPN was started soon after the surgery. She had been on TPN support for 105 months. Back pain developed at 97 months after the initiation of TPN. During her course, the serum calcium levels were judged to be within the normal ranges, while the 1 alpha, 25(OH)2Vit.D declined. Intermittent hypercalciuria was occasionally observed. Both the serum level of calcium and urinary calcium loss correlated closely to the amount of calcium infused, but they were not influenced by the amount of vitamin D (ergocalciferol) received. The serum level of parathormone and calcitonin were also within the normal ranges. The patient's vertebral bone, which was obtained at autopsy, revealed histopathological changes characteristic of osteoporosis. Based on the above, we conclude that a careful monitoring of the amount of calcium infused is called for to prevent bone disease in patients on long-term parenteral nutrition.

Parathyroid storm: immediate recognition and pathophysiological considerations

A 56-year-old white man was referred for evaluation of severe hypercalcemia following a three-week history of progressive weakness, nausea, and depression. Initial laboratory results showed serum total and ionized calcium (Ca++) values of 5.3 and 2.6 mmol/l, respectively. A short intact PTH assay was immediately performed and an extremely high value was obtained in just 30 min (1315 ng/l, normal values 6.4-70.4). The patient was therefore treated with saline solution and with salmon calcitonin (1200 IU/day, half by continuous i.v. infusion and half by i.m. route) for 10 days. There was a sudden decrease of both Ca++ and intact PTH during the first six days; then there was a trend to reach a steady-state until parathyroidectomy was performed. After withdrawal of calcitonin therapy it was possible to observe a positive uncoupling between bone formation (serum alkaline phosphatase and osteocalcin) and resorption (serum tartrate-resistant acid phosphatase) markers. On day 35 the patient underwent neck exploration, and an enlarged lower left parathyroid gland was removed that on macroscopic examination revealed the presence of a haemorrhagic cyst; microscopic appearance was suggestive of a previous glandular infarction. This is the first time the daily clinical course of a parathyroid crisis has been documented. Furthermore, changes of biomarkers of bone turnover following calcitonin therapy show that high doses of the hormone may cause a prolonged positive uncoupling of the two processes of bone remodeling.

Estrogen does not restore bone lost after ovariectomy in the rat

We recently found that 17 beta-estradiol (E2) not only suppresses bone resorption but also stimulates bone formation in the cancellous bone of female rats. This raises the possibility that E2 treatment might restore the bone lost after ovariectomy in the rat. To test this, 13-week-old rats were ovariectomized (ox). After a further 13 weeks the animals were injected with E2 (4 mg or 40 micrograms/kg daily), human calcitonin (hCT) (3 IU/kg daily), (3-amino-1-hydroxypropylidene)-1-bisphosphonate (AHPrBP) (0.3 mg/kg twice per week), or a combination of E2 with hCT or AHPrBP, for 8 weeks. The bone volume at the tibial metaphysis of ox animals was approximately 40% of that of sham-operated controls at the end of the experiment. Although the bone volume of ox rats treated with E2 and/or hCT or AHPrBP was slightly higher than that of untreated ox rats, the increase was not significant. Neither E2 alone nor a combination of E2 with hCT or AHPrBP was associated with a higher bone volume than hCT or AHPrBP alone, suggesting no effect of E2 beyond that of inhibition of bone resorption. Histodynamic indices of bone formation were increased in untreated ox rats compared to controls but suppressed in E2-treated, hCT-treated, and AHPrBP-treated animals. These results emphasize the similar responses of rat and human bone, both of which not only show bone loss with estrogen deficiency, preventable by estrogen administration, but also show an inability of estrogen to restore bone lost as a result of estrogen deficiency.

Molecular cloning of a plasma membrane calcium pump from human osteoblasts

The osteoblast plays a critical role in bone formation, bone remodelling, bone matrix formation, and matrix calcification. To better understand the process of osteoblast-controlled bone formation, we determined the structure and isoform types of the plasma membrane calcium pump from normal human osteoblasts. A complementary DNA library from normal human osteoblasts was screened for plasma membrane calcium pump clones. Sequencing and analysis of cDNA clones revealed the presence of a 3986 base pair cDNA that encoded a 1220 amino acid protein that was similar to the human plasma membrane calcium pump isoform 1. Polyadenylated RNA from human osteoblast cells contains bands of RNA approximately 5050 and 6750 bases long. Reverse transcription of polyadenylated RNA from human osteoblasts followed by amplification of the RNA-DNA duplex with calcium pump isoform-specific primers revealed the presence of isoforms 1 and 2 of the calcium pump. Isoform 4 was not detected. We conclude that normal adult human osteoblasts contain a plasma membrane calcium pump that is similar to the human plasma membrane calcium pump isoform 1. It is likely that this pump plays an important role in the cell biology of the human osteoblast.

Molecular analysis of transforming growth factor beta in giant cell tumor of bone

Giant cell tumor of bone (GCT) is a primary bone neoplasm with unique cytogenetic findings including telomeric associations. Elevated expression of message RNA for transforming growth factor beta (TGF beta), but not transforming growth factor alpha (TGF alpha), has been reported in this tumor. Further investigation of GCT was undertaken to determine whether genetic loci for TGF beta in GCT patients with and without chromosome abnormalities are altered. Due to the reported TGF beta overexpression in GCT, qualitative and quantitative Southern blot analyses with TGF beta 1 and TGF beta 2 and an internal control probe (p3-21) were performed with tumor DNA and DNA from normal tissue on ten patients with GCT and control individuals. No obvious TGF beta 1 or TGF beta 2 gene alterations were detected. Normal copy numbers were calculated when comparing tumor and normal DNA from GCT patients as well as DNA from control individuals. Abnormal chromosome findings, including telomeric associations, marker chromosome, double minutes, chromosome fragments, ring chromosomes (possibly representing intra-chromosome telomeric associations), and polyploid cells were observed in seven of the ten patients with GCT. Chromosomes 11, 16, 19, 20, and 21 were most commonly observed in telomeric associations, with the terminus of the long arm of chromosome 19 being the most frequent. We conclude that there are no TGF beta 1 or TGF beta 2 gene alterations detected in GCT with the methodologies described, and that telomeric associations are a reproducible cytogenetic characteristic of this neoplasm.

Hypercalcaemia in Addison's disease: calciotropic hormone profile and bone histology

Three cases of hypercalcaemia secondary to acute adrenocortical insufficiency are described; all the patients had moderate to severe renal impairment, one being on chronic dialysis treatment with no residual diuresis. Parathyroid hormone (PTH) and 1,25 dihydroxyvitamin D [1,25(OH)2D] were low, indicating a suppressed PTH-vitamin D axis. In the two patients with partial renal impairment, urine Ca excretion was increased, indicating increased load of the cation into the extracellular fluid (ECF), most probably from bone. Saline infusion, to correct any ECF depletion and to increase urine Ca excretion, could not fully correct the hypercalcaemia. Complete correction of plasma Ca levels was observed shortly after the institution of hormonal substitutive therapy. Despite the evidence of increased Ca mobilization from bone, bone biopsies in two patients did not show any signs of cell-mediated bone resorption; instead, bone cell activity appeared to be suppressed. Thus, glucocorticoid deficiency appears to induce Ca mobilization from bone stores by mechanism(s) unrelated to bone remodelling processes.

Glucocorticoids promote development of the osteoblast phenotype by selectively modulating expression of cell growth and differentiation associated genes

To understand the mechanisms by which glucocorticoids promote differentiation of fetal rat calvaria derived osteoblasts to produce bone-like mineralized nodules in vitro, a panel of osteoblast growth and differentiation related genes that characterize development of the osteoblast phenotype has been quantitated in glucocorticoid-treated cultures. We compared the mRNA levels of osteoblast expressed genes in control cultures of subcultivated cells where nodule formation is diminished, to cells continuously (35 days) exposed to 10(-7) M dexamethasone, a synthetic glucocorticoid, which promotes nodule formation to levels usually the extent observed in primary cultures. Tritiated thymidine labelling revealed a selective inhibition of internodule cell proliferation and promotion of proliferation and differentiation of cells forming bone nodules. Fibronectin, osteopontin, and c-fos expression were increased in the nodule forming period. Alkaline phosphatase and type I collagen expression were initially inhibited in proliferating cells, then increased after nodule formation to support further growth and mineralization of the nodule. Expression of osteocalcin was 1,000-fold elevated in glucocorticoid-differentiated cultures in relation to nodule formation. Collagenase gene expression was also greater than controls (fivefold) with the highest levels observed in mature cultures (day 35). At this time, a rise in collagen and TGF beta was also observed suggesting turnover of the matrix. Short term (48 h) effects of glucocorticoid on histone H4 (reflecting cell proliferation), alkaline phosphatase, osteopontin, and osteocalcin mRNA levels reveal both up or down regulation as a function of the developmental stage of the osteoblast phenotype. A comparison of transcriptional levels of these genes by nuclear run-on assays to mRNA levels indicates that glucocorticoids exert both transcriptional and post-transcriptional effects. Further, the presence of glucocorticoids enhances the vitamin D3 effect on gene expression. Those genes which are upregulated by 1,25(OH)2D3 are transcribed at an increased rate by dexamethasone, while those genes which are inhibited by vitamin D3 remain inhibited in the presence of dexamethasone and D3. We propose that the glucocorticoids promote changes in gene expression involved in cell-cell and cell-extracellular matrix signaling mechanisms that support the growth and differentiation of cells capable of osteoblast phenotype development and bone tissue-like organization, while inhibiting the growth of cells that cannot progress to the mature osteoblast phenotype in fetal rat calvarial cultures.

Effect of age on the rate of tooth movement in combination with local use of 1,25(OH)2D3 and mechanical force in the rat

The purpose of this study was to compare the amount and rate of tooth movement in young and mature rats administered 1,25(OH)2D3 simultaneous with application of mechanical force. In 30 seven-week-old and 30 28-week-old male Wistar rats, the right maxillary first molar was moved buccally with a fixed appliance. The appliances delivered forces ranging from 5 to 20 g. Twenty microL of 1,25(OH)2D3 (10(-10) and 10(-8) mol/L) was injected locally into the submucosal palatal area of the root bifurcation of the right first molar. The left side was injected with phosphate-buffered saline (PBS). In young rats receiving 10(-10) mol/L 1,25(OH)2D3 every three days, tooth movement significantly increased to 126% of that in PBS-injected control rats on day 20. In 1,25(OH)2D3-injected mature rats, tooth movement was stimulated markedly and increased with 10(-10) mol/L to 245% and with 10(-8) mol/L to 154% of the amount of tooth movement seen in the PBS-injected controls by the end of the experiment. PBS-injected rats had a plateau stage where tooth movement did not occur at all, while there was no such lag-time in the 1,25(OH)2D3-injected group which showed continuous tooth movement. The local injection of 1,25(OH)2D3 did not change serum calcium, phosphate, and alkaline phosphatase activity, and there were no apparent clinical or microscopic side-effects.

1,25-(OH)2D3 and 24,25-(OH)2D3 regulation of arachidonic acid turnover in chondrocyte cultures is cell maturation-specific and may involve direct effects on phospholipase A2

Previous studies have shown that 1,25-(OH)2D3 stimulates phospholipase A2 (PA2) activity in growth zone chondrocytes (GC), but has no effect on the resting zone chondrocyte (RC) enzyme activity. 24,25-(OH)2D3 inhibits the RC enzyme but has no effect on the GC. This study examined whether the vitamin D metabolites affect arachidonic acid turnover in their contra-target cell populations. Incorporation and release of [14C]arachidonate was measured at various times following addition of hormone. Acylation and reacylation were measured independently by incubating with p-chloromercuribenzoate. The results demonstrated that 1,25-(OH)2D3 has no effect on arachidonic acid turnover in RC, but stimulates turnover in GC. In contrast, 24,25-(OH)2D3 stimulates arachidonic acid turnover in RC, but inhibits both incorporation and release in GC. To determine whether direct interaction with PA2 is one mechanism by which 1,25-(OH)2D3 and 24,25-(OH)2D3 regulate arachidonic acid release, snake venom (Niger niger) PA2 was incubated with the vitamin D metabolites. Enzyme specific activity was inhibited by 24,25-(OH)2D3 and stimulated by 1,25-(OH)2D3 in a time- and dose-dependent manner. These results suggest that at least part of the direct effect of vitamin D3 metabolites on cell membranes may be related to changes in PA2 activity. The regulation is related to the stage of differentiation of the target cell population. Changes in fatty acid acylation and reacylation may be one mode of vitamin D3 action in cartilage.

cAMP promotion of osteoclast-like cell development from mouse bone marrow cells requires a permissive action of 1,25-(OH)2D3

Recruitment of osteoclasts from monocytic precursors is modulated by local signals. We previously showed that monoblastic differentiation in U937 cells is stimulated by 1,25-(OH)2D3 and cAMP in series. We investigate here the combined effects of these agents to stimulate differentiation of osteoclast-like cells from mouse marrow. Cells from mouse marrow were harvested and cultured in alpha-MEM with 10% fetal bovine serum. The appearance of tartrate-resistant acid phosphatase-containing multinuclear cells was measured after 8 days in culture by cytochemical staining. Continuous exposure of cultures to 10 nM 1,25-(OH)2D3 positively stimulated development of these cells after 8 days (101 +/- 3 cells per well, n = 74). No osteoclast-like cells were found when 1,25-(OH)2D3 was added for the first 4 days followed by 4 days more with no treatment. PGE2 (1 microM) as a single agent added during the last 4 days of culture was not able to recruit osteoclast-like cells. However, cultures exposed to 1,25-(OH)2D3 during the first 4 days and 1 microM PGE2 during the second 4 days developed osteoclast-like cells at 8 days [66 +/- 8% of the formation seen with 1,25-(OH)2D3 alone, p less than 0.05]. Dibutyryl cAMP (1 microM to 3 mM) was also not effective used as a single agent, but was able to stimulate formation of TRAP-positive multinuclear cells when 1,25-(OH)2D3 preceded its addition to culture medium. cAMP analogs therefore mimicked the effect of 1 microM PGE2, but these experiments do not allow us to assign the PGE2 action entirely to activation of cAMP second messenger.(ABSTRACT TRUNCATED AT 250 WORDS)

Coordinate inhibition of alkaline phosphatase and type X collagen syntheses by 1,25-dihydroxyvitamin D3 in primary cultured hypertrophic chondrocytes

The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) (2.3 x 10(-12) - 1.4 x 10(-6) [M]) on alkaline phosphatase, collagen, and cell proliferation were examined in primary cultured hypertrophic chondrocytes prepared from the distal epiphyseal growth plate of the tibias of 12-day chick embryos. 1,25(OH)2D3 showed time- and dose-dependent inhibitory effects on the alkaline phosphatase and collagen levels. The inhibition of alkaline phosphatase activity became detectable at 2 x 10(-11) [M] and reached 10% of control at 10(-7) [M]. The concentration of 1,25(OH)2D3 giving a 50% inhibition of the enzyme level was approximately 3 x 10(-10) [M]. Of the two extracellular collagen pools, a cell-associated matrix pool showed a more dramatic decrease (to 10% of control) than a culture medium pool (to 50% of control) at increased 1,25(OH)2D3 concentrations. The degree of inhibition was different for each type of chondrocyte-specific collagen (types II, IX, X, and XI). Types II and IX were inhibited in a parallel manner to only 60-80% of control. On the other hand, types X and XI were more greatly reduced up to 10% of control, and their dose-dependent inhibitory curves were similar to that of alkaline phosphatase. On cell proliferation, 1,25(OH)2D3 had a biphasic effect: stimulation at 10(-10)-10(-8) [M] and inhibition at higher levels. The results revealed the significant involvement of 1,25(OH)2D3 in the metabolism of two probable calcification-related products, alkaline phosphatase and type X collagen.

The role of morphogens in endochondral ossification

The formation of bone occurs normally by one of two developmental processes: intramembranous or endochondral ossification. Endochondral ossification occurs in the morphogenesis of the limb buds and growth plates, and in the regeneration of bone following injury (fracture callus). Two classes of diffusible morphogen-like molecules (MLMs) involved in limb development are the bone morphogenetic proteins (BMPs) and retinoic acid (RA). These MLMs are associated, respectively, with the apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA) of the primitive limb bud. They function as potent regulators of pattern formation and are involved in tissue proliferation and differentiation. The presence of endochondral ossification in fracture callus suggests a role for MLMs in that process as well. To date, virtually nothing is known about the role of morphogens in the regeneration of bone (fracture healing). In this article, we review the current knowledge of MLMs in bone formation and propose a theory on their role in fracture healing. We hypothesize that MLMs involved in fracture healing may also express spatial and temporal information. A more complete understanding of the role of morphogens in both limb development and fracture healing is of major importance to practicing orthopedists and their patients.

Determinants of disease and disability in the elderly: the Rotterdam Elderly Study

In this paper the Rotterdam Elderly Study is presented. The aim of the study is to investigate determinants of disease occurrence and progression in the elderly. In addition to contributing to our understanding of the etiology of geriatric illnesses, the study is expected to lead to specific recommendations for intervention. The study focuses on causally related determinants of major diseases in the elderly. Fields of interest for the Rotterdam Elderly Study are conditions which interfere the most with the quality of life for the elderly. The aims of the Rotterdam Elderly Study are: (1) To investigate, by means of epidemiologic, clinical and basic research, the determinants of diseases in order to assess their etiologic significance. (2) To investigate potentially modifiable determinants in order to be able to develop preventive strategies by providing specific recommendations for intervention studies. The Rotterdam Elderly Study focuses on four primary areas of research: neurogeriatric diseases, cardiovascular diseases, locomotor diseases and ophthalmologic diseases. It is a prospective follow-up study, in which determinants of disease and determinants of progression of disease will be investigated in the total population of 55 years or over of the district of Ommoord in Rotterdam. It is anticipated that about 10,000 people will participate in the study and they will be examined in the period of 1991 to 1995.

Effects of medroxyprogesterone acetate on some parameters of calcium metabolism in patients with glucocorticoid-induced osteoporosis

Long-acting medroxyprogesterone acetate (MPA) effect on some important parameters of calcium metabolism in patients with glucocorticoid-induced osteoporosis (GCO) was evaluated. Twelve steroid-dependent asthmatic male patients with GCO were administered 200 mg of MPA (Depo-Provera) intramuscularly, and had fasting serum samples obtained at baseline and at weekly intervals for 5 consecutive weeks. Baseline serum samples were also obtained from 12 control healthy male subjects matched for age. The following measurements were made from each serum sample: osteocalcin (OC), skeletal (SAP) and total alkaline phosphatase (TAP), calcitonin (C), insulin-like growth factor I (IGF1), 1,25-dihydroxyvitamin D and 25-hydroxyvitamin D. Significantly lower baseline serum levels of OC and C were found in the patients with GCO than in controls (P less than 0.001). Following MPA administration in GCO patients statistically significant and sustained increases in OC, SAP and C were noticed during the next 5 weeks. No significant differences in baseline levels for TAP, IGF1, 1,25(OH)2D and 25(OH)D between GCO patients and controls were found, and no significant changes following MPA administration in GCO patients were obtained for these parameters. In conclusion, when administered to patients with GCO, MPA seems to stimulate the osteoblastic activity as suggested by sustained increases in OC and SAP serum levels, and also enhances the C production by the C-cells of the thyroid.

The influence of ibuprofen on fracture repair: biomechanical, biochemical, histologic, and histomorphometric parameters in rats

Ibuprofen is a widely used cyclo-oxygenase inhibitor in clinical practice. It has been demonstrated by others to have an inhibitory effect on fracture repair in animals. In the present study, we were unable to demonstrate any significant alterations in fracture biomechanics as measured by torsion testing and fracture stage in mature Sprague-Dawley rats treated with 30 mg/kg/day oral dose of ibuprofen, starting 3 days following fracture, over a 12-week time interval. Fracture histology and serum osteocalcin levels were no different in treated animals than control animals. Furthermore, histomorphometric parameters of bone remodeling, including bone volume and bone formation rate in the intact tail vertebrae of these animals with unilateral femur fractures, were no different between treated and control animals.

Multiple miliary osteoma cutis

We describe the clinical, radiographic, histologic, and metabolic features of an unusual case of multiple miliary osteoma cutis in an otherwise healthy 57-year-old woman. Although the pathogenesis of this rarely reported entity is not fully understood, the novel application of a dynamic bone study revealed a high rate of internal bone remodeling within the lesion. This finding prompted a brief therapeutic trial of a diphosphonate, not previously reported in the treatment of this condition.

Blood levels of vitamin D metabolites in gonarthrosis

The blood levels of the active metabolites of vitamin D3 25-hydroxycholecalciferol [25(OH)D3]. 1,25-dihydroxycholecalciferol [1,25(OH)2D3], and 24,25-dihydroxycholecalciferol [24,25(OH)2D3] were determined in 27 patients suffering from arthrosis of the knee, including 4 patients with non-insulin-dependent diabetes mellitus. The blood level of 24,25-dihydroxycholecalciferol was found to be significantly lower in patients with gonarthrosis than in patients with coxarthrosis. With the exclusion of the diabetic patients, the mean value for this metabolite was lower than in the coxarthrosis group, but the difference was not significant statistically.

Regulation of alkaline phosphatase by 1,25-dihydroxyvitamin D3 and ascorbic acid in bone-derived cells

The bone, liver, and kidney isozyme of alkaline phosphatase (ALP) has been measured in MG-63 human osteosarcoma cells after treatment with ascorbic acid (AA) and/or 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Both compounds were required to achieve maximum ALP activity. When grown in the absence of 1,25-(OH)2D3 cells had low basal ALP activity regardless of whether media contained AA. In AA-free medium, 1,25-(OH)2D3 (10 nM) increased ALP activity fourfold. Addition of AA further increased levels of ALP activity induced by 1,25-(OH)2D3 to 10-15 times those found in -AA controls. The earliest effects of 1,25-(OH)2D3 were seen after 24-48 h, and ALP activity continued to increase for 6-8 days. AA and 1,25-(OH)2D3 had similar effects on ALP activity in ROS 17/2.8 rat osteosarcoma cells. In MG-63 cells the effects of AA and 1,25-(OH)2D3 could not be simply explained by the ability of these compounds to inhibit cell growth because another mitotic inhibitor, hydroxyurea, had a minimal effect on ALP activity. 1,25-(OH)2D3-specific induction of ALP +/- AA was totally blocked by inhibitors of protein and RNA synthesis. Maximal ALP induction was obtained when cells were plated at low density. Consistent with our previous report (Franceschi et al. 1988 J Biol Chem 263:18938-18945), 1,25-(OH)2D3 rapidly stimulated type I collagen synthesis and acid-precipitable hydroxyproline production in MG-63 cells and this stimulation was further increased by AA. These results suggest that induction of the osteoblast marker, ALP, is directly or indirectly coupled to collagen matrix synthesis and/or accumulation.

Structural determinants of the capacity of heparin to inhibit collagen synthesis in 21-day fetal rat calvariae

Earlier work from our laboratory demonstrated that heparin inhibits type I collagen and DNA synthesis in fetal rat calvariae in vitro. In this paper we have analyzed the structural features of heparin that determine its inhibitory effect on collagen synthesis. These experiments were performed using unmodified heparins and low-molecular-weight heparins from different manufacturers, nonheparin glycosaminoglycans, desulfated heparins, anticoagulant and nonanticoagulant heparin, and chemically defined heparin oligosaccharides. Low-molecular-weight heparin (Mr 3700-5100) inhibited collagen synthesis, but oligosaccharides (disaccharides to decasaccharide, Mr 665-3000) did not. The glycosaminoglycans chondroitin sulfate B, heparan sulfate, and hyaluronic acid did not alter collagen synthesis but dextran sulfate was as inhibitory as unmodified heparin. Nonanticoagulant as well as anticoagulant low-molecular-weight heparin fractions inhibited collagen synthesis. Modification of heparin by total desulfation, O-desulfation, or N-desulfation and re-N-acetylation resulted in the loss of inhibitory property, suggesting that the degree of sulfation contributed to heparin's inhibitory effect. Low-molecular-weight heparins from different manufacturers were just as inhibitory as native heparin on collagen synthesis. We therefore conclude that low-molecular-weight heparin compounds offer no protection against heparin-induced osteoporosis. Our findings also suggest that the size and sulfation of a heparin-derived oligosaccharide contribute to its ability to inhibit collagen synthesis in bone.

Sex steroids and osteoporosis: effects of deficiencies and substitutive treatments

Adult mammalian bone is continuously renewed by the process of remodelling. In young healthy adults the amount of bone that is resorbed by osteoclasts is replaced by osteoblasts so that no net loss of bone occurs. In a situation of reduced sex hormone levels, such as in females after menopause or ovariectomy, in males after orchidectomy, or in patients of either sex with gonadal dysfunction, there is an imbalance between bone resorption and bone formation resulting in bone loss. The various hypotheses to explain the aetiology of this imbalance are reviewed. Substitution therapy of females with oestrogen results in the prevention of oestrogen deficiency-induced bone loss. It is generally agreed that the effect is due to inhibition of bone resorption. Recent in vitro data, however, indicate that oestrogens also have the capacity to stimulate the proliferation and functioning of bone-forming cells. Prevention of oestrogen deficiency-induced bone loss can also be achieved by treatment with high doses of progestagens. Available data suggest that this too is caused by resorption inhibition. The aim of treatment of females, who have lost so much bone that there is an increased risk of fractures after minimal trauma, is to increase bone mass rather than to prevent further bone loss. This can be accomplished by treatment with anabolic steroids. Both biochemical and histological data indicate that anabolics stimulate the activity of functioning osteoblasts. The increase in bone mass during continuous treatment is temporary because anabolics most probably also inhibit bone resorption. Substitution therapy with anabolics or androgens in males is equally effective and increases trabecular bone mass in the spine.

The relationship of 1,25-dihydroxyvitamin D and radial bone mass

We assessed the association between radial bone mass and vitamin D considering age, estrogen sufficiency and thiazide use in 373 women, aged 20-80 years in a geographically defined area. We measured cortical bone mass of the radius, using photon absorptiometry, and serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, using preliminary chromatography and protein-binding assay. We found that 1,25-dihydroxyvitamin D levels were higher in premenopausal women and postmenopausal women using estrogen replacement as compared to postmenopausal women (P less than 0.02). Users of thiazide-based antihypertensive medications had significantly lower 1,25-dihydroxyvitamin D than their age-matched peers (P less than 0.02). Dietary calcium intake was negatively associated with 1,25-dihydroxyvitamin D levels. Estimates of vitamin D intake from diet or sunlight were not associated with 1,25-dihydroxyvitamin D levels; nor were levels of 1,25-dihydroxyvitamin D related to 25-hydroxyvitamin D levels. 1,25-Dihydroxyvitamin D was negatively and significantly associated with radial bone mass, contributing approximately 6% of the explained variability of bone mass measurements. Together age, body size, thiazide use and 1,25-dihydroxyvitamin D accounted for about 47% of the explained variability in radial bone mass measurement. 1,25-Dihydroxyvitamin D was not associated with bone mass in women currently using a thiazide medication.

Multiple forms of mechanosensitive ion channels in osteoblast-like cells

Patch-clamp recording techniques were used to examine the direct effects of mechanical stimulation on ion channel activity in human osteoblast-like osteosarcoma cells. Three classes of mechanosensitive ion channels were present and could be distinguished on the basis of conductance, ionic selectivity, and sensitivity to membrane tension. The largest conductance channel (160 pS) was K(+)-selective and showed both a decrease in long closed interval duration and an increase in burst length with increasing membrane tension. For low applied pressures, there was an e-fold increase in the probability of this channel being open (Popen) for every 3.4 cm2 Hg change in pressure. Two additional pressure-dependent channels had smaller conductances, i.e., 60 pS and 20 pS; the 60 pS channel appeared to be non-selective for cations. We propose that one or more of these mechanosensitive channels is involved in the response of bone to mechanical loading.

Case report 631: Neo-osseous porosis (metaphyseal osteopenia) in polyglandular autoimmune (Schmidt) syndrome

In summary, a case is reported of a patient with the radiographic findings of diffuse, symmetrical metaphyseal osteopenia of long bones. A constellation termed neo-osseous porosis, associated with polyendocrine failure (Schmidt syndrome) involving the thyroid gland, adrenal glands, and gonads has been described in this case. Neo-osseous porosis has been observed previously in idiopathic juvenile osteoporosis. This case represents the first instance in which this distinctive radiographic picture has been observed in the setting of specific (multiple) endocrine dysfunction disorders.