bluuebunny/crossref_metadata_2025_split huggingface dataset:
Insulinlike growth factor 1 regulates mRNA levels of osteonectin and pro-α1(I)-collagen in clonal preosteoblastic calvarial cells
Authors: Thiebaud Daniel , Ng Kong Wah , Findlay David M. , Harker Michael , Prof. Martin T. John 
Published: February 2010

Abstract
A nontransformed rat clonal cell line (UMR-201) with phenotypic characteristics of osteoblastic precursor cells was found to respond to insulinlike growth factor 1 (IGF-1) by increased osteonectin and pro-α1 (1)-collagen mRNA expression. Cells were treated for 24 h with insulin, growth hormone, or IGF-1 to study the regulation of messenger RNA for osteonectin and pro-α1(I)-collagen using Northern blot hybridization.
UMR-201 cells possess specific high-affinity receptors for growth hormone, although there were no significant effects of growth hormone (10−9-10−7 M) or insulin (10−9-10−6 M) on mRNA species for osteonectin or pro-α(I)-collagen. However, IGF-1 increased both mRNA species from a concentration of 10−9 M. The effect on osteonectin mRNA expression was likely due to increased transcription; when 5′ flanking osteonectin (ON) genomic fragments were linked to the bacterial reporter gene chloramphenicol acetyltransferase (CAT) and introduced by transfection into UMR-201 cells, the transcriptional activity of the ON-CAT construct was increased 235 and 270% by 10−8 and 10−7 M IGF-1, respectively. In contrast, growth hormone did not change the transcriptional activity of the ON-CAT construct.
In confirmation of other work, transforming growth factor β (TGF-β, 0.1-2.5 ng/ml) increased mRNA for osteonectin and pro-α1(I)-collagen in a dose-dependent manner. Transforming growth factor α (TGF-α) at 0.1-10 ng/ml had no consistent effects in repeated experiments on osteonectin and pro-α1(I)-collagen mRNA.
The positive stimulatory effect of both IGF-1 and TGF-β provides insights on the regulation of bone matrix proteins and suggests a major role of these growth factors in the remodeling process of bone.
Failure of isolated rat tibial periosteal cells to 5α reduce testosterone to 5α-dihydrotestosterone
Authors: Turner Russell T. , Bleiberg Batia , Colvard Douglas S. , Keeting Philip E. , Evans Glenda , Spelsberg Thomas C. 
Published: February 2010

Abstract
Periosteal cells were isolated from tibiae of adult male rats after collagenase treatment. Northern blot analysis of total cytoplasmic RNA extracted from the isolated periosteal cells was positive for expression of genes encoding the osteoblast marker proteins osteocalcin (BGP) and pre-pro-α2(I) chain of type 1 procollagen. The isolated periosteal cells were incubated with 1 nM [3H]testosterone ([3H]T) for up to 240 minutes and the reaction products separated by high-performance liquid chromatography. [3H]5α-dihydrotestosterone ([3H]DHT) was not detected in extracts of periosteal cell incubations. In contrast, [3H]DHT was produced in a time-dependent manner by cells from seminal vesicles. These results suggest that testosterone 5α-reductase activity is not expressed by osteoblasts in rat tibial periosteum and that the anabolic effects of androgens in this tissue are not mediated by locally produced DHT.
Regulation of 25-hydroxyvitamin D3 metabolism in cultures of osteoblastic cells
Authors: Letton Robert W. , Fanti Paolo , Malluche Hartmut H. 
Published: February 2010

Abstract
This study was designed to investigate the mechanisms involved in the regulation of the conversion of 25-hydroxyvitamin D3 (25-OHD3) to 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and 24,25-dihydroxyvitamin D3 [24,25-(OH)2D3] in primary cultures of osteoblastlike cells from neonatal mouse calvariae. These cells, when incubated with tritiated 25-OHD3 ([3H]25-OHD3), spontaneously synthesized [3H]24,25-(OH)2D3 20-50 times more efficiently than [3H]1,25-(OH)2D3 at a rate of conversion that was substrate dependent and linear from 1 to 36 h. Gas chromatography-mass spectrometry verified the identity of the dihydroxylated metabolites. The calcium ionophore A23187 (5 μM) consistently stimulated the synthesis of 1,25-(OH)2D3 while suppressing the production of 24,25-(OH)2D3. This effect was sustained for 36 h and was dose dependent for concentrations from 0.05 to 10 μM. Furthermore, A23187 stimulated cAMP production and indomethacin (50 ng/ml) blocked the A23187-induced production of cAMP and 1,25-(OH)2D3 but had no effect on the suppression of 24,25-(OH)2D3 by A23187. This led to other experiments to find out whether the stimulative effect of A23187 on 1,25-(OH)2D3 synthesis is mediated by prostaglandins or cAMP, or both. PGE2 (10−8-10−6 M) increased the production of 1,25-(OH)2D3 and of 24,25-(OH)2D3. Forskolin (0.01-10 μM) and dibutyryl cAMP (0.1-10 mM) increased the production of both metabolites but to a lesser degree than PGE2. These data suggest that osteoblastlike cells are stimulated by A23187 to increase the synthesis of 1,25-(OH)2D3 through mechanisms involving prostaglandins and cAMP. The synthesis of 24,25-(OH)2D3 is suppressed by A23187 through different mechanisms.
Subclones of a rat parathyroid cell line (PT-r): Regulation of growth and production of parathyroid hormone-related peptide (PTHRP)
Authors: Sakaguchi Kazushige , Ikeda Kyoji , Curcio Francesco , Aurbach Gerald D. , Brandi Maria Luisa 
Published: February 2010

Abstract
Four subclones from a rat parathyroid cell line (PT-r cell) have been isolated, and morphological and functional characteristics have been examined. Subclones 1 and 2 display a polygonal shape, show growth and secretory responses to calcium (half-maximal suppressions at 1.2 and 1.7 mM, respectively), and respond to secretin with cAMP production (14.5-fold and 16.9-fold over basal) and hormone secretion (41 and 58% over basal). Subclone 4 is elongated in form and does not respond to calcium or secretin. Subclone 3 shows mixed morphology, elongated and polygonal shapes, with moderate response to calcium (half-maximal suppression at 1.7 mM) and secretin (cAMP, 3.2-fold increase and hormone secretion, 50% increase over basal). The clones were tested for content of messenger RNA (mRNA) representing parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHRP). Only PTHRP mRNA was found. The peptide released is virtually all PTHRP. PTH mRNA was not detected even with a sensitive RNA probe. The amount of mRNA for PTHRP closely paralleled the amount of PTH-like bioactivity released into the medium from each clone (144.7 ± 12.1, 110.0 ± 12.9, 68.0 ± 5.6, and 39.9 ± 2.4 pgEq of rat PTH-(-34) per 107 cells per 12 h in a medium with 0.7 mM ionized calcium, from subclones 1, 2, 3, and 4, respectively). Culture conditions, low-density passage (less than 1:50 split ratio) or high-density passage (greater than 1:10 split ratio), affected morphology and function of the clones 1 and 2. They became elongated and functionally dedifferentiated like subclone 4 after 3 months of high-density culture. Upon dedifferentiation, morphological and functional properties were not reversible with high calcium, 1,25-(OH)2D3, or retinoic acid. These clones may be useful for studies of phenotypic expression, calcium regulation, and gene expression and interrelationships among these functions.
Rapid publication a chromogranin a-derived peptide differentially regulates the secretion of calcitonin gene products
Authors: Dr. Deftos Leonard J. , Hogue-Angeletti Ruth , Chalberg Cheryl , Tu Su 
Published: February 2010

Abstract
We studied the regulation of the secretion of CT and CGRP by chromogranin A (CgA)-derived peptides in a human lung tumor cell line. The amino-terminal peptide of CgA, CgA1-40, stimulated the secretion of CGRP and inhibited the secretion of CT; both effects occurred in a dose-dependent manner. These studies demonstrate a differential effect of a CgA-derived peptide on two products of the CT gene, CT itself and CGRP. CgA may be processed at its multiple dibasic sites to peptides that specifically regulate the secretion of its coresident hormones, in this case two calcitonin gene products that are present in the same secretory vesicle. This novel mechanism represents a new pathway for the control of calcium regulating hormones.
Metabolic modulation of disuse osteopenia: Endocrine-dependent site specificity of bone remodeling
Authors: Bain Steven D. , Rubin Clinton T. 
Published: February 2010

Abstract
The remodeling response of bone tissue to disuse in four normal adult male turkeys and four adult males metabolically altered by castration was compared by functionally isolating the left ulna of each animal via transverse epiphyseal osteotomies. The right ulna in each animal was left intact and served as a control. After 8 weeks, the animals were euthanized, the ulnae harvested, and 100 μm undecalcified cross sections of the midshaft microradiographed. Areal properties, osteon mineral apposition rates from in vivo fluorochrome labels, and the number and ratios of bone-forming and bone-resorbing foci were quantitated. Compared to their control ulnae, the magnitude of bone resorbed from the functionally isolated ulnae of normal versus castrated males was not significantly different (-12.8 ± 3.7 versus −10.7 ± 3.5%, respectively). However, in the functionally isolated ulnae of normal birds, 94% of the total bone loss resulted from expansion of the corticoendosteal envelope, and 97% of the decrease in cross-sectional areas of the ulnae in the castrated birds was due to intracortical porosity. Furthermore, there was a significant interaction between disuse and castration, increasing the total number of intracortical remodeling events (9.4 ± 0.9) when compared to disuse alone (4.7 ± 1.4, p &lt; 0.01), or to the intact ulnae of castrated (2.1 ± 0.5) and normal adult males (2.0 ± 1.1). This work emphasizes that the manner in which the bone tissue responds to local changes in its physical environment is directly dependent on the status of the organism's metabolic milieu.
Differential modulation of growth and phenotypic expression of chondrocytes in sparse and confluent cultures by growth factors in cartilage
Authors: Hiraki Yuji , Inoue Hiroyuki , Asada Akira , Suzuki Fujio 
Published: February 2010

Abstract
The growth-promoting actions of cartilage extracts (CE) on rabbit cultured chondrocytes were studied to assess the role of locally acting growth factors in the generation and expansion of highly differentiated cells. In the present study, DNA synthesis and proteoglycan synthesis in the cultured chondrocytes were monitored by flow cytofluorometry and double-isotope autoradiography by using [3H]thymidine and [35S]sulfate. We report here that actions of the same set of growth factors extracted from cartilage evokes differential cellular responses depending upon cell density. Growth factors in the optimal dose of CE (2 μg/ml) strongly supported proliferation of the cells in sparse culture, but they had little effect on cells in confluent culture. In contrast, the optimal dose of fibroblast growth factor (FGF, 100 ng/ml) or epidermal growth factor (EGF, 40 ng/ml) did not reveal such a cell density-dependent effect on cellular proliferation. However, growth factors in CE induced proteoglycan synthesis selectively in nonproliferating and expressing cells in confluent culture.
Influence of calcium load on absorption fraction
Authors: Heaney Robert P. , Weaver Connie M. , Lee Fitzsimmons Mary 
Published: February 2010

Abstract
True calcium absorption was studied as a function of the size of the ingested load in healthy adult women, under meal conditions and at loads ranging from 15 to 500 mg calcium. Fractional absorption was highly inversely correlated with the logarithm of load (P &lt; 0.001). At the lowest loads, absorption averaged 64.0% and at the highest, 28.6%. The parameters of the best-fit relationship permit reasonably precise calculation of the impact of various calcium dosing and dietary strategies.
Bone cell responsiveness to transforming growth factor β, parathyroid hormone, and prostaglandin E2 in normal and postmenopausal osteoporotic women
Authors: Lomri Abderrahim , Marie Pierre J. 
Published: February 2010

Abstract
We have shown previously that the decreased trabecular bone formation in osteoporotic postmenopausal women results from a reduced ability of osteoblastic cells to proliferate. In this study we have tested the possibility that bone cells from osteoporotic women with low bone formation have an abnormal responsiveness to hormonal or local mitogenic factors. Primary cultures of bone cells with osteoblastic characteristics were obtained by migration from the trabecular bone surface in osteoporotic postmenopausal women with high (n = 7) or low (n = 7) bone formation as evaluated histomorphometrically by the extent of double tetracycline-labeled surface (DLS). Control bone cells were obtained under identical conditions from eight normal age-matched postmenopausal women. Parameters of osteoblastic differentiation (alkaline phosphatase activity and osteocalcin production) were found to be normal and similar in bone cells from osteoporotic women with low or high DLS. In contrast, cell replication as evaluated by [3H]thymidine into DNA was 3.4-fold lower in the low DLS group compared to the high DLS group, confirming our previous findings. Treatment of quiescent bone cells with TGF-β (0.5–1 ng/ml) for 24 h significantly stimulated DNA synthesis in osteoblastic cells from normal women and in bone cells from osteoporotic patients with low or high DLS, indicating a normal responsiveness to TGF-β in these patients. We have compared the effect of parathyroidhormone (PTH) on bone cells from normal and osteoporotic women. Basal cAMP levels and the cAMP accumulation in response to (1–34)-hPTH were similar in bone cells from patients with low or high DLS and were not different from normal values. The responsiveness of bone cells from osteoporotic women to exogenous prostaglandin E2 (PGE2) was also evaluated. PGE2 (24 h) produced a dose-related biphasic effect on DNA synthesis in bone cells from both normal and osteoporotic weomen. At low concentration (10−11 M) PGE2 increased DNA synthesis whereas at higher concentration (10−7 M) it was inhibitory. cAMP production was increased by PGE2 at doses that inhibited DNA synthesis. The responsiveness to PGE2 was not different in normal bone cells and in cells from osteoporotic women with low and high DLS. These results indicate that the reduced bone cell proliferative capacity in osteoporotic postmenopausal women with low bone formation does not result from a lower than normal responsiveness to TGF-β, PTH, and PGE2.
Presystemic 24-hydroxylation of oral 25-hydroxyvitamin D3 in rats
Authors: Dr. Vieth Reinhold 
Published: February 2010

Abstract
The metabolism of 25-hydroxyvitamin D3 (25-OHD3) was compared following its intracardial or gastric administration. The rats were deprived of calcium and vitamin D. A mixture of radiolabeled (0.3 μCi) and stable (2 μg) 25-OHD3 was given as a single dose. After 24 h the rats given the dose by gastric tube had significantly lower serum concentrations of 25-OHD3 and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] than those injected intracardially. In contrast, serum 24,25-dihydroxyvitamin D3 [24,25-(OH)2D3] was much higher in the rats given the 25-OHD3 dose by gastric tube (6.2 nmol/liter ±1.3 SD, n = 7) compared to the intracardial group (0.9 nmol/liter ± 0.5, p &lt; 0.001). The preceding results were based on specific radioactivity of metabolites. The same findings were obtained by reanalyzing the samples using conventional competitive binding assays for 25-OHD3, 1,25-(OH)2D3, and 24,25-(OH)2D3. The results show that orally administered 25-OHD3 is partly metabolized to 24,25-(OH)2D3 presystemically.
Desensitization of parathyroid hormone receptors on cultured bone cells
Authors: Dr. Pun Kin-Kee , Ho Patricia W. M. , Nissenson Robert A. , Arnaud Claude D. 
Published: February 2010

Abstract
Administration of excessive amounts of parathyroid hormone (PTH) in the treatment of osteoporosis can reverse the beneficial effects of a low-dose, intermittent regime. To investigate the direct actions and the possible cellular mechanisms of PTH in inducing desensitization of PTH receptors, we studied the effects of desensitization on rat osteoblastic UMR-106 cells. When the osteoblasts were preincubated with bPTH-(1–34), complete refractoriness to a subsequent challenge with the hormone developed within 1 h and at hormone concentrations as low as 5 nM. When osteoblasts thus desensitized were incubated in hormone-free medium, recovery of the cAMP responses began within 2 h and reached maximum after 16 h. Cycloheximide did not affect the process of desensitization. [NIe8, NIe18, Tyr34]bPTH-(3–34)amide significantly impaired the desensitization process by PTH-(1–34) but did not have stimulatory effect on cAMP responses. No significant heterologous desensitization was obvious after preincubation with isoprenaline (50 μM), prostaglandin E, (50 μM), or prostaglandin E2 (50 μM) for 2 h. Binding experiments with [125I]PLP-(1–36)amide after desensitization revealed that there was an approximate twofold decrease in receptor affinities as analyzed by Scatchard analysis, showing that the decrease in affinity was prominent in the process of desensitization. When the cells were treated with monensin during desensitization, PTH challenge after desensitization produced significantly lower cyclic AMP responses. Recovery after desensitization occurred over a period of 16 h. Inclusion of monensin, but not cycloheximide, impaired the recovery. The results show that homologous desensitization of rat osteoblasts to PTH is brought about by the occupancy of receptors by PTH-(1–34) but not by cAMP generation itself. It is not primarily dependent on protein synthesis or on activation of adenylate cyclase. A decrease in receptor affinity is important in the process of desensitization. Desensitization of parathyroid hormone receptors is potentiated and recovery impaired by monensin, an inhibitor of internalization and recycling, showing that both processes are important in the regulation of PTH receptors.
Identification of Ca2+-activated K+ channels in cells of embryonic chick osteoblast cultures
Authors: Ravesloot Jan H. , van Houten Ron J. , Ypey Dirk L. , Nijweide Peter J. 
Published: February 2010

Abstract
Primary cultures of embryonic chick osteoblasts consist of a heterogeneous cell population. Patch clamp measurements were done on 1- to 5-day-old osteoblasts, osteocytes, fibroblastlike cells, and cells that could not be classified on morphologic criteria. The measurements showed the omnipresence of depolarization-activated high-conductance channels in cell-attached patches. The whole-cell experiments showed an outward rectifying conductance activating at positive membrane potentials. Channels underlying the latter conductance were found to be K+ conducting in outside-out membrane patches. The activation potential of the outward rectifying K+ conductance shifted to negative membrane potentials upon increasing the intracellular Ca2+ concentration within the range of 10−8–10−3.2 M. The same happened with the activation potential of the K+ channels found in outside-out patches. Finally, inside-out patch experiments directly demonstrated the dependency of the activation potential of K+ channels on Ca2+ ions. Thus the identity and main characteristics of Ca2+-activated K+ channels expressed by the various cell types present in chick osteoblast cultures have now been established. Decreased input resistances were found in cells of cultures more than 2 days old. This is consistent with the establishment of electrical coupling between the cells. Functions in which Ca2+-activated K+ channels could play a role are discussed.
Proportion of human vertebral body bone that is cancellous
Authors: Eastell Richard , Mosekilde Li , Hodgson Stephen F. , Dr. Riggs B. Lawrence 
Published: February 2010

Abstract
The concept that vertebral fractures are caused by excessive loss of cancellous bone has been challenged by a recent study (J Bone Min Res 2:221, 1987) suggesting that vertebral bodies are composed mainly of cortical bone rather than cancellous bone. To resolve disagreement we used two independent methods to quantify the proportions of cortical and cancellous bone in 400 μm thick sections of the bodies of the second lumbar vertebrae from six men (aged 21–58 years) and seven women (aged 25–58 years). Based on the ash weight of the manually dissected components, 80% of the total bone in men and 72% in women was cancellous bone. Based on computer-assisted scanning of sections with a microdensitometer, 81% of the total bone in men and 71% in women was cancellous bone. We conclude that the traditional concept is correct: the vertebral body is composed mainly of cancellous bone.
The effects of extracellular pH on bone resorption by avian osteoclasts in vitro
Authors: Walsh C.A. , Dawson W.E. , Birch M.A. , Gallagher J.A. 
Published: February 2010

Abstract
It has previously been reported that low extracellular pH stimulates the excavation of resorption lacunae by rodent osteoclasts in vitro. Using avian bone cells in a similar in vitro assay we have demonstrated that osteoclast activity is optimal at pH 7.20–7.40 and is inhibited at extremes of pH (&lt;7.10 and &gt;7.60). Over the first 24 h of incubation at low pH there may be an increase in osteoclastic resorption but to a lesser extent than that reported for rodent cells. However, after 24–30 h in culture there is little or no further increase in bone resorption, presumably due to a cytotoxic effect of low pH acting either on the osteoclast directly or via nonosteoclastic bone cells. In contrast to a previous report, in which preincubation of wafers for 24 h had no effect on bone resorption, we found that preincubation of bone substrates at pH 6.50 for longer periods enhances subsequent resorption at pH 7.20.
Effects of testosterone and venesection on spinal and peripheral bone mineral in six hypogonadal men with hemochromatosis
Authors: Dr. Diamond Terrence , Stiel Daniel , Posen Solomon 
Published: February 2010

Abstract
To measure the effect of testosterone replacement and venesection on spinal and peripheral bone mineral we prospectively studied six hypogonadal men and six eugonadal men with idiopathic hemochromatosis for 24 months. Venesections were performed every week on all patients, and intramuscular injections of testosterone were administered every 3 weeks to the hypogonadal men only. Bone mineral was measured by quantitative computed tomography in the spine and by single-photon absorptiometry in the forearm.
During the 24 month period of observation serum testosterone concentrations and serum ferritin levels became normal. In the hypogonadal men mean lumbar spine bone mineral increased by 13.1 ± 4.9% (95% CI, 0.5–25.6) and mean forearm bone mineral increased by 4.7 ± 3.8% (95% CI, −5.1 to 14.6). In contrast in the eugonadal men treated over the same period, mean lumbar spine bone mineral decreased by 3.5 ± 2.8% (95% CI, −10.9 to 3.8, P &lt; 0.01) and mean forearm bone mineral remained virtually unchanged (0.07 ± 0.9%; 95% CI, −1.7 to 3.1, P &lt; 0.05).
These data suggest that bone mineral increases in the lumbar spine and in the forearm in hypogonadal men with hemochromatosis treated by testosterone replacement and venesection.