bluuebunny/crossref_metadata_2025_split huggingface dataset:
Post-translational control of collagen fibrillogenesis in mineralizing cultures of chick osteoblasts
Authors: Gerstenfeld Louis C. , Riva Angela , Hodgens Karen , Eyre David R. , Dr. Landis William J. 
Published: February 2010

Abstract
Cultured osteoblasts from chick embryo calvaria were used as a model system to investigate the post-translational extracellular mechanisms controlling the macroassembly of collagen fibrils. The results of these studies demonstrated that cultured osteoblasts secreted a collagenous extracellular matrix that assembled and mineralized in a defined temporal and spatial sequence. The assembly of collagen occurred in a polarized fashion, such that successive orthogonal arrays of fibrils formed between successive cell layers proceeding from the culture surface toward the media. Mineralization followed in the same manner, being observed first in the deepest and oldest fibril layers. Collagen fibrillogenesis, the kinetics of cross-link formation, and collagen stability in the extracellular matrix of the cultures were examined over a 30 day culture period. Between days 8 and 12 in culture, collagen fibril diameters increased from &lt; 30 nm to an average of 30–45 nm. Thereafter, diameters ranged in size from 20 to 200 nm. Quantitation of the collagen cross-linking residues, hydroxylysyl pyridinoline (HP) and lysyl pyridinoline (LP), showed that these mature cross-links increased from undetectable levels to concentrations found in normal chick bone. Analysis of the kinetics of their formation by pulse-chase labeling the cultures with [3H]lysine showed a doubling time of ˜ 5 days. The relationships between cross-link formation, fibrillogenesis, and collagen stability were examined in cultures treated with β-aminopropionitrile (β-APN), a potent inhibitor of lysyl oxidase and cross-link formation. In β-APN-treated cultures, total collagen synthesis was increased twofold, with no change in mRNA levels for type I collagen, whereas the amount of collagen accumulated in the cell layer was decreased by 50% and mineral deposition was reduced. The rate of collagen retention in the matrix was assessed by pulse-chase analysis of [3H]proline over a 16 day period in control and β-APN-treated cultures. In control cultures, about 20% of the labeled collagen was lost from the cell layers over a 16 day period compared with &gt; 80% in the presence of β-APN. The β-APN-treated cultures also showed a wider diversity of fibril diameters with a median in the &gt; 45–60 nm range. In summary, these data suggest that cross-linking and assembly of collagen fibrils secreted by osteoblasts in vitro occur in a fashion similar to that found in vivo. The rate of cross-link formation is relatively constant and may be correlated with increasing collagen mass. With progressive cross-linking, collagen fibrils become more stable and less susceptible to loss from the cell layer. Thus, collagen deposition is probably controlled at several post-translational stages during fibrillogenesis, including cross-link formation, lateral fibril aggregation, and increasing fibril stability.
Bone resorption activity of particulate-stimulated macrophages
Authors: Glant Tibor T. , Jacobs Joshua J. , Molnár Gyöngyi , Shanbhag Arun S. , Valyon Márta , Galante Jorge O. 
Published: February 2010

Abstract
Particulate wear debris from bone cement or prosthetic components can stimulate macrophages to cause bone resorption in a dose-dependent manner. This bone resorption activity of particulate-stimulated macrophages is associated with increased levels of both prostaglandin E2 (PGE2) and interleukin-1 (IL-1). In this study we compared the effect of particulate size, concentration, and composition on the secretion of IL-1 and PGE2 by peritoneal macrophages and on the bone-resorbing activity of conditioned medium (CM) harvested from particulate-challenged macrophages. Particulates (titanium, Ti; polymethylmethacrylate, PMMA; and polystyrene, PS) only with phagocytosable size stimulated peritoneal macrophages to secrete IL-1 and PGE2 in a dose- and time-dependent manner. Ti particles (1–3 μm) exhibited significantly enhanced bone-resorbing activity measured as 45Ca release. The maximum bone-resorbing response was observed at a concentration of 0.1% Ti (approximately 10–15 Ti particulates per cell), which also corresponded with the highest IL-1 levels measured in particulate-challenged CM. This was measured using either conditioned media from Ti-stimulated macrophages or in cocultures of calvarial bone and macrophages in the presence of Ti. Exogenous PGE2 and recombinant human IL-1 could significantly increase the 45Ca release; indomethacin (IM) significantly reduced both the spontaneous calcium efflux and active 45Ca release from in vivo labeled calvarial bones. However, IM and/or anti-Il-1 antibodies could suppress only partly the macrophage-mediated bone resorption, indicating that, in a macrophage-bone coculture system, factors other than PGE2 and IL-1 also may regulate particulate-induced bone resorption, probably involving multiple cell types.
Regulation of cytokine expression in osteoblasts by parathyroid hormone: Rapid stimulation of interleukin-6 and leukemia inhibitory factor mRNA
Authors: Greenfield Edward M. , Gornik Sandra A. , Horowitz Mark C. , Donahue Henry J. , Shaw Steven M. 
Published: February 2010

Abstract
PTH and other hormones that stimulate resorption affect osteoclasts indirectly by modulating cytokine production by osteoblasts. However, the identity and role of the osteoblast-derived cytokines involved in this process are unclear. To examine which cytokines are regulated by PTH, we assessed cytokine mRNA levels in osteoblasts using the reverse transcription-polymerase chain reaction technique. Of the 16 cytokines we examined, unstimulated MC3T3-E1 osteoblastic cells expressed mRNA for interleukins 5, 6, and 7, macrophage and granulocyte-macrophage colony-stimulating factors, transforming growth factor β1 and leukemia inhibitory factor. PTH specifically increased expression of interleukin-6 (approximately 50-fold) and leukemia inhibitory factor (approximately 10-fold). Levels of both IL-6 and LIF mRNA peaked 30–60 minutes after addition of PTH and returned to baseline by 4–6 h. This rapid and transient mRNA response, which resembles that of immediate early genes, was also observed in primary rat osteoblasts. The transient mRNA response was accompanied by increased secretion of IL-6 protein. Lipopolysaccharide, another stimulator of resorption, increased mRNA levels of a group of cytokines that were not induced by PTH, namely interleukin-1α, tumor necrosis factor α, and granulocyte-macrophage and granulocyte colony-stimulating factors. We conclude that osteoblasts produce complex networks of cytokines that (1) are regulated by bone-resorptive agents and (2) may be involved in controlling bone resorption.
Effect of different amounts of sodium intake for 4 months on calcium metabolism in normal and oophorectomized rats
Authors: Chan Ellen Lai-Ping , Professor Swaminathan R. 
Published: February 2010

Abstract
The effects of different amounts of salt intake on urinary calcium and hydroxyproline (OHP) excretion were studied in oophorectomized (O) and sham-operated (S) rats on normal calcium diet. Groups of O and S rats were given either tap water or 2, 6, or 18 g/liter of NaCl to drink. Urinary excretion of sodium, calcium, and OHP was monitored at 0, 2, and 4 months. Urinary excretion of calcium and OHP increased with increasing salt intake (P &lt; 0.001 by ANOVA) in S and O groups. Oophorectomy did not have any additional effect on calcium or OHP excretion. We conclude that increased salt intake causes increased excretion of calcium and OHP and oophorectomy does not further aggravate the loss.
Simple measurement of femoral geometry predicts hip fracture: The study of osteoporotic fractures
Authors: Faulkner Kenneth G. , Cummings Steven R. , Black Dennis , Palermo Lisa , Glüer Claus-C. , Genant Harry K. 
Published: February 2010

Abstract
Based on engineering principles, geometric measurements of femoral size should be related to femoral strength and the risk for hip fracture. To evaluate whether a simple measurement of femoral geometry is associated with hip fracture risk, we obtained dual x-ray absorptiometry scans of the proximal femur on 8074 white women age 67 or older. During an average of 1.6 years of follow-up, 64 participants suffered hip fractures. In all fracture cases and in a random sample of 134 women who did not subsequently suffer a hip fracture, we measured hip axis length (the distance from greater trochanter to inner pelvic brim), neck width, and the neck/shaft angle on the scan printout, with the observer blinded to subsequent fracture status of the participant. Results were analyzed using multiple logistic models, and odds ratios were determined. After adjustment for age, each standard deviation decrease in femoral neck bone mineral density increased hip fracture risk 2.7-fold (95% confidence interval 1.7, 4.3), and each standard deviation increase in hip axis length nearly doubled the risk of hip fracture (odds ratio = 1.8; 95% CI 1.3, 2.5). The relationship between hip axis length and fracture risk persisted even after adjustment for age, femoral neck density, height, and weight. A longer hip axis length was associated with an increased risk of both femoral neck (OR = 1.9; 95% CI 1.3, 3.0) and trochanteric fractures (1.6; 1.0, 2.4). We found no significant association between the neck width (1.1; 0.8, 1.5) or the neck/shaft angle (1.4; 0.9, 2.2) and risk of hip fracture. In a combined analysis of the control group with an additional population of younger volunteers, no significant relationship was found between the hip axis length and age (r = 0.04, P = 0.60) or femoral neck density (r = 0.01, P = 0.84) in 225 women from 41 to 92 years of age. We conclude that hip axis length predicts hip fractures independently of age and bone mineral density in elderly women. If verified by additional studies, this simple measurement can improve the assessment of hip fracture risk compared to a measurement of femoral neck bone density alone.
Parenteral pamidronate prevents thyroid hormone-induced bone loss in rats
Authors: Rosen Harold N. , Sullivan E. Kelly , Middlebrooks V. Leah , Zeind Adib John , Gundberg Caren , Dresner-Pollak Rivka , Maitland Lauri A. , Hock Janet M. , Moses Alan C. , Greenspan Susan L. 
Published: February 2010

Abstract
Pamidronate (APD) is a bisphosphonate that prevents bone loss from a variety of causes. We studied the role of APD in preventing thyroid hormone-induced bone loss. A total of 32 rats were assigned to one of four treatment groups: (1) −APD/triiodothyronine (−T3), (2) −APD/+T3, (3) +APD/−T3, or (4) +APD/+T3. In the first of two studies, the rats received APD for the first week and T3 for the second week, and then their blood was analyzed for alkaline phosphatase and osteocalcin. Alkaline phosphatase and osteocalcin were significantly higher (p &lt; 0.05) in hyperthyroid rats (−APD/+T3, 3.9 ± 0.25 μcat/liter and 23 ± 1.6 nM, respectively) than in control animals (2.53 ± 0.28 μkat/liter and 18.3 ± 1.4 nM, respectively). Hyperthyroid rats pretreated with APD (+APD/+T3) had levels of alkaline phosphatase and osteocalcin no different from controls. In a second study, rats were divided into the same four groups, except they received APD/placebo and T3/placebo concomitantly for 3 weeks. At the end of the study, bone mineral density (BMD) of the femur, spine, and whole body was measured by dual-energy x-ray absorptiometry, and the calcium content of the femora was measured directly. In hyperthyroid rats (−APD/+T3) BMD was significantly lower than in controls in the spine (0.201 ± 0.004 versus 0.214 ± 0.002 g/cm2, p &lt; 0.05) and femur (0.204 ± 0.003 versus 0.218 ± 0.002, p &lt; 0.05). In hyperthyroid rats pretreated with APD (+APD/+T3) BMD of the spine, femur, and total body was significantly higher than in controls (p &lt; 0.001). Similar differences among groups were seen in femur calcium content. We conclude that hyperthyroid rats have an increased rate of bone turnover and bone loss that can be prevented by coadministration of a bisphosphonate.
Cloning and characterization of the 5′-flanking region of the mouse tartrate-resistant acid phosphatase gene
Authors: Reddy Sakamuri V. , Scarcez Thierry , Windle Jolene J. , Leach Robin J. , Hundley Jeffrey E. , Chirgwin John M. , Chou Janice Y. , Roodman G. David 
Published: February 2010

Abstract
Little information is available on the molecular mechanisms controlling osteoclastic bone resorption. We used tartrate-resistant acid phosphatase (TRAP) to begin to investigate the regulation of bone resorption at the molecular level. TRAP is expressed at high levels in osteoclasts and may play an important role in the bone resorptive process. Therefore, we isolated the murine TRAP gene from a mouse spleen genomic library and characterized its promoter. A restriction map was generated for the 17 kb TRAP insert. A 2 kb Smal fragment, containing the 5′-flanking region, was subcloned and the nucleotide sequence determined. Sequence analysis of the Smal fragment revealed the presence of numerous candidate transcription factor binding sequences, including those for API and H-APF-1. The H-APF-1 site matches the consensus sequence for the IL-6-regulated transcription factor. An intron was identified at −1 to −393 bp relative to the ATG. The presence of an intron was confirmed by PCR analysis of RNA isolated from murine osteoclasts. Primer extension analysis indicated the presence of a transcription initiation site at −552 bp from the ATG. The region from −1846 to 2 bp relative to the ATG initiation codon drove the transient expression of a luciferase reporter gene when transfected into HRE H9 rabbit endometrial cells. PMA treatment of HRE H9 cells enhanced luciferase transcription approximately threefold. These data suggest that the TRAP promoter is complex and contains multiple regulatory elements. The availability of the TRAP promoter may also permit production of transgenic mice, which can be used to develop previously unavailable osteoclast cell lines.
Importance of bone resorption in the determination of bone density in women more than 10 years past the menopause
Authors: Dr. Prince Richard , Dick Ian , Devine Amanda , Kerr Deborah , Criddle R. Arthur , Price Roger , Webb Peter Garcia 
Published: February 2010

Abstract
There is general agreement that bone density falls with age and is higher in heavy people than light people. We have studied a variety of potential correlates of vertebral, ankle, and hip bone density to evaluate other potential influences on the skeleton. We recruited 196 healthy women who were more than 10 years past the menopause and collected a diet and activity record, a 24 h urine, and a fasting blood and urine specimen. These blood and urine samples were analyzed for factors related to calcium homeostasis. We then measured bone density at lumbar vertebrae 1–4 and the hip and the ankle bone density of the nondominant leg. Correlations between vertebral, hip, and ankle bone density and other measured variables were explored using the statistical package SPSS PC. At the vertebral site, in addition to correlations with age and body mass index (BMI), a negative correlation with a measure of bone resorption, the hydroxyproline creatinine ratio (OHPCR), was noted. At the ankle site, in addition to correlation with age, BMI, and OHPCR, a positive correlation with activity and a negative correlation with serum calcitriol were noted. At the hip site, as well as age, BMI, and OHPCR, significant correlations with GFR and dietary calcium intake were noted. These data suggest that even in women 10 years past the menopause bone resorption has a significant effect on bone density, that renal function may account for some of the variance in bone density at the hip, and that activity effects are more marked at sites of greater loading, namely the ankle.
Streaming potentials in healing, remodeling, and intact cortical bone
Authors: MacGinitie Laura A. , Wu D.D. , Cochran G.V.B. 
Published: February 2010

Abstract
Electrical fields have been implicated in accelerated bone healing and as a transduction mechanism for mechanically driven bone remodeling. Applied mechanical or electrical stimulation of bone remodeling suggests that this depends on the magnitude, frequency, and duration of the stimulus. The magnitude of endogenous electrical fields, manifest by streaming potentials (SPs) across canine cortical bone, were measured as a function of bending frequency in vivo and then in vitro at healing drill holes and at remodeling (ipsilateral) and normal, intact (contralateral) control sites in canine tibia. SP magnitudes normalized to periosteal strain were smaller for drill holes at 2 and 4 weeks postsurgery relative to either remodeling (P &lt; 0.05 at 10 Hz) or normal intact (P &lt; 0.001 at 10 Hz) controls both in vivo and in vitro. SPs of 12 week drill holes were similar to SPs of remodeling controls and tended to be smaller than SPs of normal intact controls. Mean SP normalized to bone impedance was approximately the same for all sites, suggesting that the smaller SPs during healing and remodeling relate to smaller bone impedance and/or larger porosity. SP as a function of bending frequency for normal sites was similar to that observed previously. SP versus frequency for drill holes and remodeling controls was more variable, probably because of variations in bone microstructure, and displayed a higher frequency content. The observed differences in SP magnitude and frequency response to loading associated with stages of healing indicate that endogenous electrical fields do indeed respond to the structural changes in healing and remodeling and are therefore capable of providing structural feedback information for the repair and remodeling process.
A 5-year longitudinal study of forearm bone mass in 307 postmenopausal women
Authors: Prof. Nordin B.E. Christopher , Cleghorn David B. , Chatterton Barry E. , Morris Howard A. , Need Allan G. 
Published: February 2010

Abstract
We measured forearm bone mineral content at the beginning and end of a 5 year period in 307 untreated postmenopausal volunteers. We also measured height, weight, and a number of biochemical variables in plasma and urine after an overnight fast. The initial mean age of the subjects was 59.0 years (range 39–72), and the mean years since menopause was 10.0 (range 1–37). The mean forearm BMC fell from 1034 ± 9.6 (SEM) to 982 ± 9.3 mg/cm (P &lt; 0.001). The coefficient of correlation between the first and second measurements was 0.96. The mean rate of change was −1.0% per annum (with a 99% range of −4 to 1% per annum), which agreed well with previous estimates from cross-sectional data. There was a significant negative correlation between rate of change in bone mass and initial value (r = −0.23; P &lt; 0.001), which was eliminated by expressing change as a percentage of initial bone mass. Of the other variables measured, the one that was most significantly related to the percentage change in bone mass was the urinary hydroxyproline/creatinine ratio (r = −0.35; P &lt; 0.001), which we regard as a marker only. By stepwise regression, the only significant determinants of the rate of change in bone mass were body weight (positive, P &lt; 0.001), years since menopause (positive, P &lt; 0.005), urine calcium (negative, P &lt; 0.01), and serum estrone (positive, P &lt; 0.05). The rate of change in BMC was not significantly related to dietary calcium, plasma alkaline phosphatase, serum DHEAS, or any other variable measured at the outset or to serum PTH or serum osteocalcin measured at the conclusion.
Changes in markers of bone formation and resorption in a bed rest model of weightlessness
Authors: Lueken Sandra A. , Arnaud Sara B. , Dr. Taylor Arch K. , Baylink David J. 
Published: February 2010

Abstract
To study the mechanism of bone loss in physical unloading, we examined indices of bone formation and bone resorption in the serum and urine of eight healthy men during a 7 day −6° head-down tilt bed rest. Prompt increases in markers of resorption — pyridinoline (PD), deoxypyridinoline (DPD), and hydroxyproline (Hyp)/g creatinine—during the first few days of inactivity were paralleled by tartrate-resistant acid phosphatase (TRAP) with significant increases in all these markers by day 4 of bed rest. An index of formation, skeletal alkaline phosphatase (SALP), did not change during bed rest and showed a moderate 15% increase 1 week after reambulation. In contrast to SALP, serum osteocalcin (OC) began increasing the day preceding the increase in Hyp, remained elevated for the duration of the bed rest, and returned to pre-bed rest values within 5 days of reambulation. Similarly, DPD increased significantly at the onset of bed rest, remained elevated for the duration of bed rest, and returned to pre-bed rest levels upon reambulation. On the other hand, the other three indices of resorption, Hyp, PD, and TRAP, remained elevated for 2 weeks after reambulation. The most sensitive indices of the levels of physical activity proved to be the noncollagenous protein, OC, and the collagen crosslinker, DPD. The bed rest values of both these markers were significantly elevated compared to both the pre-bed rest values and the post-bed rest values. The sequence of changes in the circulating markers of bone metabolism indicated that increases in serum OC are the earliest responses of bone to head-down tilt bed rest.
Effects of high calcium concentration on the functions and interactions of osteoblastic cells and monocytes and on the formation of osteoclast-like cells
Authors: Sugimoto Toshitsugu , Kanatani Masanori , Kano Junichi , Kaji Hiroshi , Tsukamoto Tatsuo , Yamaguchi Toru , Fukase Masaaki , Chihara Kazuo 
Published: February 2010

Abstract
The present study was performed to clarify the role of high calcium concentration and the appearance of mononuclear cells at the resorptive site in bone remodeling. Our recent study revealed that the high concentration of extracellular calcium ([Ca2+]e) stimulated DNA synthesis in osteoblastic MC3T3-E1 cells not only directly but also indirectly via monocytes. Human monocyte-conditioned medium (CM) significantly stimulated DNA synthesis and inhibited alkaline phosphatase (ALP) activity. In contrast, when monocytes were cultured at high [Ca2+]e concentrations (more than 3 mM), CM from these monocytes significantly stimulated ALP activity in MC3T3-E1 cells. Such stimulatory effect of CM was not observed at a high magnesium concentration (Mg2+, 5 mM). Treatment of monocytes with the calcium ionophore A23187 did not affect the CM-induced effect on DNA synthesis and ALP activity in these cells. To determine the migration potency of MC3T3-E1 cells and monocytes toward the high [Ca2+]e, chemotaxis assay was performed. The increasing [Ca2+]e (more than 3 mM) induced a chemotactic response of MC3T3-E1 cells as well as monocytes, but the high concentration of Mg2+ (5 mM) did not induce it. On the other hand, treatment with high [Ca2+]e (more than 3 mM) or CM significantly inhibited the 1,25-(OH)2D3-induced formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNC) from their precursors derived from mouse spleen cells. The present study indicated that an increase in [Ca2+]e stimulated DNA synthesis and ALP activity of osteoblasts via monocytes, induced chemotaxis of osteoblasts as well as monocytes, and inhibited the formation of TRAP-positive MNC, suggesting the importance of the high Ca2+ concentration and mononuclear cells at the resorptive site in bone remodeling.