摘要:

AbstractWe observed in a controlled 2 year longitudinal trial in 248 perimenopausal women that a daily calcium supplement of either 1000 or 2000 mg Ca2+significantly reduced lumbar bone loss and bone turnover in the first year of calcium supplementation. In the second supplementation year the rate of lumbar bone loss in the treated subjects was not significantly different from that in the control group, although two of the three biochemical parameters of bone turnover remained decreased throughout the study. To quantify further the long‐term effect of calcium supplementation, we extended the study for another year in 214 women. In the women of the control group who were menstruating until the last year of the trial, the mean change in lumbar bone mineral density after 3 years was –3.2% of the initial value versus 1.6% in the calcium‐supplemented groups (p<0.01). The decrease in lumbar bone loss in these supplemented premenopausal and early perimenopausal women remained statistically significant in the second and third years of supplementation. In the women who stopped menstruating before or during the study, the long‐term reduction in lumbar bone loss was not significant (mean difference between control and treatment groups<0.6% points after 3 years). The decrease in metacarpal cortical thickness (MCT) in the treated subjects during 3 years was on average –3.0% of the initial value in the control versus–2.0% in the supplemented subjects (P<0.01). The effect of calcium supplementation on MCT was not significantly related to the menopausal status of the subjects. Serum alkaline phosphatase, osteocalcin, and urinary hydroxyproline excretion decreased after calcium supplementation in all menopausal groups. These parameters remained decreased throughout the trial, with exception of alkaline phosphatase in the 1000 mg calcium group. We conclude that calcium supplementation substantially reduces cortical and trabecular bone loss in the years immediately preceding menopause. Although it reduces postmenopausal cortical bone loss to some extent, it does not prevent the menopause‐related lum

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090702

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY

摘要:

AbstractCell‐cell interactions are important in the regulation of endocrine cell secretion. To investigate the possibility that cell communication may alter the regulation of parathyroid cell secretion, we utilized the reverse hemolytic plaque assay (RHPA) to measure parathyroid hormone (PTH) release from individual cells. Bovine parathyroid cells were dispersed and plated with protein A‐conjugated erythrocytes at cell densities ranging from 0.9 to 36 X 102cells/cm2in 0.2 mM calcium. Cell populations were greater than 98% homogeneous as determined by immunocytochemistry and in situ hybridization for PTH mRNA. Plaques were developed and data analyzed for the amount of PTH per cell released (plaque area in μm2X 104) and the determination of cell recruitment (% plaques formed). A positive correlation existed between parathyroid cell density and the amount of PTH released. As the distance between cells increased, the plaque area (amount of PTH released per cell) decreased (ranging from 1.0 X 1044μm2at 0.9 X 102cells/cm2versus 1.6 X 104μm2at 36 X 102cells/cm2). The percentage of cells releasing PTH (recruitment) also decreased (16% at 0.9 X 102cells/cm2versus 47% at 36 X 102cells/cm2). These data suggest that parathyroid cells in close proximity are stimulated to secrete more hormone than those at lesser densities. In addition, parathyroid cells are recruited to secrete PTH when plated at high density. Factor(s) released by the parathyroid cell may increase cell responsiveness and stimulate secretion in a paracrine f

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090703

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY

摘要:

AbstractDigitized morphometry of vertebral bodies on lateral spine films is used to identify and quantify vertebral deformities or fractures. One problem associated with this method is the phenomenon of “disappearing fractures,” which results from the apparent increase in vertebral body heights of previously deformed vertebrae on subsequent radiographs. These have been considered biologically implausible and therefore a result of measurement error. Measurement error is unlikely to be unidirectional, so that a proportion of fractures identified by morphometry is also the result of measurement error. Since some vertebral deformities are real events, some disappearances of deformities detected by morphometry may be real events. In this report, we examine the data from our clinical trial of sodium fluoride in spinal osteoporosis to assess critically the plausibility of two hypotheses: (1) The “rebound” phenomenon results from measurement error. If this is the case, then some fractures of the same magnitude as the rebound must also represent measurement error. (2) Some deformed vertebrae in fact rebound toward their original shape and size, displaying an elastic response to deformation. If this occurs, then some vertebral deformities are transient events, not true fractures. We conclude that the variability inherent in morphometric data obtained from serial spine x‐rays results in both disappearing fractures and a high false positive fracture rate. The use of more stringent criteria for defining significant deformities, or true fractures, will minimize these problems. We cannot exclude the second hypothesis, that some vertebral deformities may be transient events, but this needs furt

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090704

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY

摘要:

AbstractWith the knowledge that estrogen replacement therapy can circumvent postmenopausal osteoporosis and with the discovery of estrogen receptors (ER) in cultures of normal osteoblast‐like cells, extensive investigations have been directed toward understanding the role of the ER in normal bone homeostasis. ROS 17/2.8 and UMR‐106‐01, two established osteoblast‐like cell lines derived from rat osteosarcomas, have been shown to have estrogen‐regulated biologic responses. Only the ROS 17/2.8 cell line has been reported to contain ER. In this study, high‐affinity, saturable binding sites characteristic of the ER were detected in UMR‐106‐01 cells by binding assays with the high‐affinity ligand, [125I]17β‐estradiol. An initial immunoconcentrtion step before western blot analysis also allowed detection of the full‐length ER protein. In addition, northern blot analysis indicated that the entire ER transcript was expressed and that the half‐life of the ER message was increased following cycloheximide treatment. Message levels were also regulated by removal of serum and treatment with estradiol. An estrogen‐regulated reporter vector, ERET81CAT, was transfected into the UMR‐106‐01 cells to determine whether the detected level of ER was transcriptionally functional. Using this assay, estrogen responsiveness was evident; however, the response was inconsistent. Multiple factors, such as serum, estradiol, and cell density, influence the ER levels in these cells and probably cause fluctuations in the abundance of receptors available to induce the CAT response. When the cells are responsive, the ICI 164,384 antagonist could block the estrogen‐induced activation of CAT.The ROS 17/2.8 cells were also analyzed in parallel with the UMR‐106‐01 cells to allow comparisons between these two osteoblast‐like cell lines because they exhibit phenotypes for two unique stages of differentiation. ROS 17/2.8 cells were found to contain more receptor sites/cell by the125I‐E2(estradiol) binding assays, as well as higher levels of ER‐specific transcripts, than UMR‐106‐01 cells (two‐ to threefold). This level of ER was consistently able to modulate estrogen‐induced stimulation of the reporter CAT vector. Therefore, functional ER is expressed in both cell types, but the higher level of receptors found in the ROS 17/2.8 cell line improves the estrogen responsiveness of these osteoblast‐like cells. These data also indicate that levels of ER that are low or undetectable by conventional methods are able to mediate biologic responses through direct interacti

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090705

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY

摘要:

AbstractUrinary excretion of type I collagen cross‐linked N‐telopeptides was studied in 52 children and adolescents with osteogenesis imperfecta (OI) and found to be above the 75th percentile of controls in 44 of the patients. OI patients suffering from fractures during the preceding 6 months had significantly higher values (p<0.05). In contrast, patients with better motor performance tended to have lower values (p= 0.059). The concentration of urinary type I collagen cross‐linked N‐telopeptides was positively correlated with urinary calcium excretion (p<0.05), which was found to be elevated in 20 of the patients. Our results show that during childhood and adolescence in OI not only the synthesis but also the turnover of mature cross‐linked type I collagen is disturbed and provide evidence that bone resorption rates are

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090706

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY

摘要:

AbstractSecond‐messenger systems have been implicated to transmit mechanical stimulation into cellular signals; however, there is no information on how mechanical stimulation is affected by such systemic factors as parathyroid hormone (PTH). Regulation of adenylyl cyclase and phosphatidylinositol pathways in rat dentoalveolar bone cells by mechanical strain and PTH was investigated. Two different cell populations were isolated after sequential enzyme digestions from dentoalveolar bone (group I and group II) to study potential differences in response. Mechanical strain was applied with 20 kPa of vacuum intermittently at 0.05 Hz for periods of 0.5, 1, 5, 10, and 30 minutes and 1, 3, and 7 days using the Flexercell system. Levels of cAMP, measured by RIA, and levels of inositol 1,4,5‐triphosphate (IP3) and protein kinase C activity (PKC), measured by assay systems, increased with mechanical strain. When PTH was added to the cells, there was a significant increase in levels of all the intracellular signals, which appeared to potentiate the response to mechanical strain. IP3levels (0.5 minute) peaked before those of PKC activity (5 minutes), which in turn peaked before those of cAMP (10 minutes). Group II cells showed higher levels of cAMP and IP3than the group I cells. This suggests that the former may ultimately play the predominant roles in skeletal remodeling in response to strain. Immunolocalization of the cytoskeleton proteins vimentin and α‐actinin, focal contact protein vinculin, and PKC showed a marked difference between strained and nonstrained cells. However, the addition of PTH did not cause any significant effect in cytoskeleton reorganization. Staining of PKC and vimentin, α‐actinin, and vinculin suggests that PKC participates actively in the transduction of mechanical signals to the cell through focal adhesions and the cytoskeleton, although only PKC seemed to change with short time periods of strain. In conclusion, dentoalveolar osteoblasts responded to mechanical strain initially through increases in levels of IP3, PKC activity, and later cAMP, and this response was potentiated when PTH was applied together with mechanic

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090707

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY

摘要:

AbstractCells harvested from 12 human giant cell tumors of bone and kept in culture for several passages were characterized for bone‐resorbing capability, total and tartrate‐resistant acid phosphatase activity, response to the calciotropic hormone calcitonin, cell proliferation, multinucleation after passages, and presence of calcium sensing. Cells obtained from three tumors presented a complete panel of osteoclast characteristics and maintained their multinuclearity after several passages. Cells from four other tumors increased their cAMP levels after treatment with calcitonin, and the other five apparently consisted of cells of stromal origin. These human cell populations with osteoclast characteristics may provide valid in vitro models for the investigation of osteoclastic differentiation and activ

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090708

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY

摘要:

AbstractWe investigated possible inhibitory effects of five synthetic Arg‐Gly‐Asp (RGD)‐containing peptides on osteoclastic resorption in three distinct in vitro resorption assays (17‐day‐old fetal mouse bone organ cultures) that differ in stages of osteoclast differentiation. RGD peptides, which can bind the adhesion receptors called integrins, inhibited osteoclastic resorption (45Ca release) in fetal mouse bone explants in which osteoclast precursors have yet to adhere to the mineralized matrix and develop into mature osteoclasts (metacarpals and coculture system). Treatment of metacarpals with RGD peptides inhibited the formation of multinucleated TRAP+osteoclasts in the mineralized matrix because their mononuclear TRAP+osteoclast precursors remained localized in the periosteum. In particular, echistatin, a viper venom protein with known affinity for αvβ3integrin, and GdRGDSP inhibited osteoclastic resorption dose dependently in these systems (ED5010−9and 10−4M, respectively) but did not alter the activity of mature resorbing osteoclasts in radii. In addition,45Ca release was significantly inhibited by the cyclic peptide GPenGRGDSPCA, which has a relatively higher affinity for the vitronectin than fibronectin receptor(s). In contrast, GRDGdSP, which has a much higher affinity for the fibronectin receptor (than the vitronectin receptors), had no effect on resorption at similar concentrations in any resorption system used. In summary, the data presented in this paper show that peptides with RGD motifs are capable of inhibiting osteoclastic resorption in bone organ cultures. Our studies not only support the hypothesis concerning the importance of αvβ3in osteoclastic resorption but also suggest an important role of integrin(s) in events preceding the actual resorption of calcified matr

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090709

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY

摘要:

AbstractBisphosphonates are inhibitors of bone resorption and are used increasingly as therapeutic agents for treating clinical disorders of skeletal metabolism. Their mode of action is still not fully understood. The demonstration that methylenebisphosphonate, a simple methylene analog of pyrophosphate, inhibits the axenic growth of amoebae of the slime moldDictyostelium discoideumand is incorporated into adenine nucleotides suggested that this organism might be useful in elucidating the cellular effects of bisphosphonates. We examined 24 bisphosphonates, including all those of clinical interest as inhibitors of osteoclast‐mediated bone resorption in vivo, for their effects onD. discoideum.All the geminal bisphosphonates inhibited growth ofDictyostelium, although the effectiveness of individual compounds varied widely. When the bisphosphonates were ranked there was a remarkable similarity between the order of potency as inhibitors of growth ofDictyosteliumand the order of potency as inhibitors of bone resorption. Thus, bisphosphonates with more complex side‐chain structures, especially those containing a nitrogen group, were more potent than simple substituted bisphosphonates, some inhibitingDictyosteliumgrowth even at concentrations below 10 μM. It therefore appears that the mechanism by which bisphosphonates preventDictyosteliumgrowth could be similar to the mechanism by which these compounds affect the activity of osteoclasts. Because the mechanisms of action of bisphosphonates on osteoclasts remains unclear,Dictyosteliummay provide an additional model for studying the biochemical mode of action of bisphosphonates. Furthermore, these studies suggest thatDictyosteliummay also be a convenient organism for rapid evaluation of potentially active bisphosphon

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090710

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY

摘要:

AbstractThe biologic activities of human parathyroid hormone‐related protein [hPTHrP(1–34] and bovine PTH [bPTH(1‐34)]are remarkably similar despite marked sequence divergence in their primary binding domain, residues 25–34. Chicken PTHrP (cPTHrP) is identical to hPTHrP through residue 21. However, in the 25–34 region, cPTHrP displays three fewer basic residues than hPTHrP and contains five residues not present in any other member of the PTH/PTHrP family. To assess the biologic consequences of these structural differences, we compared the activities of synthetic [36Tyr]cPTHrP(1–36)NH2and hPTHrP(1–34)NH2with those of bPTH(1–34) in avian systems (chicken renal plasma membranes and 19 day chick embryonic bone cells) and mammalian systems [canine renal plasma membranes and rat osteosarcoma cells (UMR‐106‐H5)]. In both avian and mammalian systems the binding affinity of [36Tyr]cPTHrP(1–36)NH2(0.8–3.4 nM) was approximately one‐half that of hPTHrP(1–34)NH2(0.4–1.1 nM). The potencies of [36Tyr]cPTHrP(1–36)NH2and hPTHrP(1–34)NH2for activation of adenylate cyclase were similar in canine renal membranes (5.2 and 6.7 nM) and chick bone cells (1.0 nM). In UMR‐106 cells and chicken renal membranes the potency of [36Tyr[cPTHrP(1–36)NH2for activation of adenylate cyclase was about one‐half that of [36Tyr]hPTHrP(1–36)NH2. Binding of125I‐[36Tyr]cPTHrP(1–36)NH2to chick bone cells and chicken renal membranes was completely displaced by bPTH(1–34) and hPTHrP(1–34)NH2: thus there was no evidence for a distinct chicken PTHrP receptor. In general, [36Tyr]cPTHrP(1–36)NH2and hPTHrP(1–34)NH2activated adenylate cyclase similarly despite their sequence differences in the 25–32 region. This suggests that basic residues in the 25–32 region are not required for the peptide to assume a biologically active conformation at the receptor. In cross‐linking studies, both125I‐hPTHrP(1–34)NH2and125I‐[36Tyr]cPTHrP(1–36)NH2labeled a major 85 kD PTH/PTHrP receptor component in canine renal plasma membranes.125I‐hPTHrP(1–34)NH2also labeled a ≤14 kD receptor fragment, whereas125I‐[36Tyr]cPTHrP(1–36)NH2did not. The present results suggest that retained sequence features in the 25–32 region may be critical determinants of receptor binding and that sequence differences in this regi

ISSN:0884-0431    

DOI:10.1002/jbmr.5650090711

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1994

数据来源: WILEY